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Comparison between the Permian mafic dykes in Tarim and the western part of Central Asian Orogenic Belt (CAOB), NW China: Implications for two mantle domains of the Permian Tarim Large Igneous Province
Abstract
Ages and chemical and isotopic compositions of the Permian mafic dyke swarms from Kelamayi, eastern Tianshan and western Tianshan in western part of the Central Asian Orogenic Belt (CAOB), NW China, are reported here in order to gain more insights into the Permian Tarim Large Igneous Province (Tarim LIP). These CAOB mafic (-andesitic) dyke swarms from Kelamayi, eastern Tianshan and western Tianshan were emplaced at 267 ± 3 Ma, 278 ± 2 Ma and 260–290 Ma, respectively, and are coeval with the radiating mafic dyke swarm in the Tarim Block. The dykes in CAOB exhibit subalkalic character in major element compositions, and are enriched in LILE and LREE and depleted in HFSE and HREE, with the exception of a few LREE-depleted samples from western Tianshan. Isotopically, dykes from Kelamayi and western Tianshan are characterized by significant positive εNd(t) values (3.1 to 7.9 for Kelamayi; 7.2 to 7.3 for western Tianshan), while dykes form eastern Tianshan exhibit variable negative εNd(t) values (− 0.7 to − 3.3). Their geochemical features suggest that the mafic (-andesitic) dykes in CAOB were derived from a recently metasomatized lithospheric mantle source (sub-continental lithosphere mantle) with subsequent variable extents of assimilation of the crustal materials in a non-orogenic setting. In contrast, the mafic dykes in Tarim exhibit systematic chemical signatures similar to those of OIB, indicating that they were derived from a depleted sub-lithospheric mantle source. We thus propose that the Permian Tarim LIP has two different mantle domains for the coeval mafic rocks, i.e., the Tarim domain and the CAOB domain.
... The latter is supported by the extensive silica and carbonate alteration (Section 4.2); observed in most samples. The mafic igneous rocks from this study share similar geochemical features to mafic magmas that comprise LIPs, including incompatible-element enriched trace element patterns ( Figure 9) and Nb, Ti, P and Ta anomalies relative to MORB (Augland et al., 2019;Ernst et al., 2005;Glass & Phillips, 2006;Li et al., 2014;Neumann et al., 2011;Wingate et al., 2004;Xu et al., 2014;Zhang & Zou, 2013). The alkali and incompatible-element enriched feature is attributed to low degree mantle melting and/or melting of enriched mantle sources, while negative Nb, Ta and Ti anomalies have been interpreted to be indicative of crustal contamination by the LIP magmas (Augland et al., 2019;Ernst et al., 2005;Glass & Phillips, 2006;Neumann et al., 2011;Xu et al., 2014;Zhang & Zou, 2013). ...
... The mafic igneous rocks from this study share similar geochemical features to mafic magmas that comprise LIPs, including incompatible-element enriched trace element patterns ( Figure 9) and Nb, Ti, P and Ta anomalies relative to MORB (Augland et al., 2019;Ernst et al., 2005;Glass & Phillips, 2006;Li et al., 2014;Neumann et al., 2011;Wingate et al., 2004;Xu et al., 2014;Zhang & Zou, 2013). The alkali and incompatible-element enriched feature is attributed to low degree mantle melting and/or melting of enriched mantle sources, while negative Nb, Ta and Ti anomalies have been interpreted to be indicative of crustal contamination by the LIP magmas (Augland et al., 2019;Ernst et al., 2005;Glass & Phillips, 2006;Neumann et al., 2011;Xu et al., 2014;Zhang & Zou, 2013). ...
... A major punctuated CO 2 release may have contributed to rapid global climate change such as the end Permian mass extinction (Augland et al., 2019;Burgess et al., 2017;Ernst et al., 2005;Glass & Phillips, 2006;Kravchinsky, 2012;Wingate et al., 2004). Additionally, the Tarim LIP (Li et al., 2014;Xu et al., 2014) may be related to the Northwest Shelf MMP as the Tarim Block rifted from the Northwest Shelf in the Permian (Yang et al., 2013;Zhang & Zou, 2013). ...
The formation of mafic magmatic provinces are significant geological events that can drive mass extinctions and continental rifting and can influence basin evolution, petroleum prospectivity and mineralization. Buried magmatic provinces, however, are rarely identified and difficult to define. The Northwest Shelf of Australia contains large volumes of potentially interconnected mafic igneous material across several sedimentary basins. However, limited study and a lack of surface exposure have prevented detailed description and classification of these rocks. In this study, the distribution and composition of these mafic igneous rocks are described using an integrated geophysical and geochemical approach, which included over 10,000 km line length of 2D seismic data, well log data and chemical analysis of samples from 14 wells across the Browse, Roebuck, Canning and North Carnarvon basins. Using this combined data set, we demonstrate interconnectivity of buried mafic igneous rocks across the Northwest Shelf and calculate a total surface area exceeding 280,000 km² and a cumulative minimum volume of ∼140,000 km³. Petrology and geochemistry of samples indicate they are basaltic and doleritic with alkaline and sub‐alkaline compositions and formed in a continental rift setting. Collectively, the igneous rocks meet the criteria for classification as a mafic magmatic province (MMP) and closely match the criteria required for classification as a large igneous province (LIP). Emplacement of the newly defined Northwest Shelf MMP may represent hotspot magmatism that could have initiated rifting of the Cimmerian Block from NW Australia during the Permian and could have potential for future, large scale CO2 sequestration and storage.
... The Tarim Basin is the largest petroliferous basin in northwestern China (Fig. 1a;Jia, 1997;Nishidai and Berry, 1990;Wu et al., 2018;Zhang and Huang, 2005 (Chang et al., , 2017He et al., 2019;Li et al., 2014;Long et al., 2010, Wu et al., 2012Xu et al., 2013;Yang et al., 2007Zhang and Zou, 2013), which were important for oil and gas generation, migration, and accumulation Yang et al., 2007;Zhu et al., 2015). As such, the Tarim Basin hosts a complex oil-gas system consisting of several sets of source, reservoir, and cap rocks that have experienced multi-phase tectonic, thermal, and sedimentary events (Fig. 1b-c;Jia, 1997;Pang et al., 2018;Shen et al., 2018;Xiao et al., 2000;Zhang and Huang, 2005;Zhao et al., 2005). ...
... Journal of Asian Earth Sciences 194 (2020) 104267 et al., 2016a. It underwent the Kalpin, Caledonian, and Hercynian orogenies during the Paleozoic, and was modified by the Indosinian, Yanshanian, and Himalayan orogenies in the Mesozoic-Cenozoic ( Fig. 1c; Carroll et al., 2001;Ngia et al., 2019;Pang et al., 2018;Qiu et al., 2011;Wu et al., 2018;Zhang et al., 2013), possibly principally influenced by the opening and closure of the Paleo-Tethys during the Paleozoic-Mesozoic and India-Asia collision during the Cenozoic (Jia, 1997;Li et al., 2010;Lin et al., 2012aLin et al., , 2012bWu et al., 2016a, and references therein). Specifically, it was an intracratonic basin/aulacogen during the Sinian-Ordovician, a foreland basin during the Silurian-Devonian, and cratonic marginal depression or intra-cratonic rift during the Carboniferous-Permian (Jia, 1997;Jia and Wei, 2002;Turner, 2010;Wu et al., 2012Wu et al., , 2016aWu et al., , 2018). ...
... The Tarim Basin experienced multiple phases of subsidence, uplift, and tectonism due to collisions between the Qiangtang, Lhasa, and Kohistan blocks, and deformation events in the Tianshan and Altyn belts (Carroll et al., 2001;He et al., 2019;Jia, 1997;Liu et al., 2005;Wu et al., 2012Wu et al., , 2016aWu et al., , 2018Zhang et al., 2013). The Caledonian, Hercynian, Indosinian, Yanshanian, and Himalayan orogenies all played an important role in the evolution of the Tarim Basin (He et al., 2019;Ngia et al., 2019;Pang et al., 2018;Shen et al., 2018). ...
The tectono-thermal evolution is an important control on petroliferous basin development; however, this evolution is difficult to reconstruct in sedimentary basins subjected to multiple tectono-thermal events. The Tarim Basin is the largest petroliferous basin in northwestern China and hosts a complex oil–gas system comprising several sets of source, reservoir, and cap rocks that have experienced multiple tectonic, thermal, and sedimentary events. Large oil and gas reserves have been discovered in the central and northern Tarim Basin during the last 30 years, but none in the eastern part of the basin. This is generally attributed to the high thermal maturity reached by source rocks during the Late Ordovician, and subsequent hydrocarbon loss. Therefore, reconstructing the Cambrian–Ordovician tectono-thermal evolution is critical in facilitating successful oil and gas exploration in this region. We compiled equivalent vitrinite reflectance data (n = 178) of source rocks from seven wells in the Tarim Basin, which for Cambrian–Ordovician source rocks are >1.3%, beyond the hydrocarbon generation threshold and in the main gas and dry gas generation stages. The Cambrian–Ordovician source rocks experienced rapid burial and heating during the Caledonian period, entered the hydrocarbon generation stage during the Middle–Late Ordovician, and reached peak hydrocarbon generation at the end-Caledonian period. They might have experienced secondary hydrocarbon generation after the Jurassic. Homogenization temperatures of fluid inclusions (n = 616) from wells GC4, LX1, MD1, and YD2 as well as the modeled thermal evolution reveal a main hydrocarbon generation event during the Caledonian period and a secondary event in the Yanshanian and Himalayan period in other wells (LX1, MD1, and YD2). Hercynian and Indosinian uplift and exhumation in the eastern Tarim Basin controlled the main structures, and faulting created favorable conditions for secondary hydrocarbon generation and migration at this time. Since the Yanshanian and Himalayan, the Tarim Basin has experienced further sedimentation and heating, and the tectono-thermal evolution might have been related to the formation of the Tibetan Plateau. In summary, our reconstruction of the tectono-thermal evolution of Cambrian–Ordovician strata and the hydrocarbon generation history of the Tarim Basin suggests that the eastern Tarim Basin may also have hydrocarbon generation potential and can guide future oil and gas exploration.
... To date, some crucial issues related to accretion and collision evolution histories in different parts of the CAOB, such as the timing of the closure of the PAO, are still hotly debated (Li et al. 2002b;Shu et al. 2004;Gao et al. 2006;Xiao et al. 2006b;Zhang et al. 2007a). Meanwhile, the existence of Permian large igneous provinces (LIPs) or giant mantle plumes in the Tarim and Eastern Tianshan in Xinjiang (Northwest China) also needs comprehensive discussion (Xia et al. 2004(Xia et al. , 2006(Xia et al. , 2008Zhang and Zou 2013). Previous studies have mostly focused on accretionary complexes, granitic rocks, and volcanic and sedimentary rocks. ...
... Zhang et al. 2007bZhang et al. , 2008aYin et al. 2009;Luo et al. 2012;Tang et al. 2012;Wang et al. 2015;Yang et al. 2015). For instance, the dykes in Western Junggar have been dated via different methods Xu et al. 2008;Zhou et al. 2008;Feng et al. 2012a, b;Yin et al. 2012;Zhang and Zou 2013), and the occurrence of diorite dyke swarms have been explained as the result of ridge subduction (Ma et al. 2012) or vertical magmatic intrusion and regional extension during post-collision evolution (Li et al. 2005a). Some curved dykes in Beishan ) and truncated dykes in Eastern Tianshan (Feng et al. 2012c) indicate the shearing sense along local large faults. ...
... Dykes in these areas mostly emplaced during the Late Carboniferous to Early Permian, based on previous chronological studies of dykes in Western Junggar Xu et al. 2008;Zhou et al. 2008;Feng et al. 2012a, b;Yin et al. 2012;Zhang and Zou 2013), constrained by the cutting relationship between the dykes and the host rocks (plutons and volcanic-sedimentary formations) in Eastern Junggar (Feng et al. 2015) and Chingis-Taerbahatai. ...
Mafic dykes in continents are a special type of intrusive rock formed by different tectonic events including earlier fracturing deformation in host rocks and successive magma intrusions originating at depth. Dyke swarms indicate regional crustal deformation related to continental formation and evolution, and play the role of messenger regarding magma activities from the deeper crust or even mantle. The large number of mafic dykes in Central Asia hold the keys to resolve some debated tectonic problems such as subduction-accretion-collision processes during the formation of Central Asia (the western part of the Central Asian Orogenic Belt). However, spatial-temporal distribution patterns of mafic dykes in this vast area have not been comprehensively described and discussed to date. This study carried out a fundamental work on the spatial-temporal distribution patterns of dykes in Central Asia, and is intended to provide basic preparation for more in-depth studies in the future. In Enhanced Thematic Mapper Plus (bands 7, 4, and 2) images, major mafic dykes (greater than 5 m wide) displayed as dark-colored linear objects against their host rocks, and can be distinguished and plotted one-by-one and further analyzed using Geographic Information System software. The results indicate that more than 99% of the mafic dykes were emplaced in the Eastern Tianshan and Beishan, Western Mongolian-Altai, Eastern Junggar, North and West bank of Balkhash, Western Junggar, and Chingis-Taerbahatai. Most dykes formed during the Late Paleozoic, and the occurrence of these dykes is a result of various regional fracturing processes along different tectonic boundaries as well as immense magmatic intrusions (related to subduction, post-collisional processes, or large igneous provinces/giant mantle plumes). Other much older dykes were emplaced in the marginal areas of cratons, such as the Neoproterozoic dykes that intruded into the metamorphosed basement of the Tarim Craton (Aksu blueschist complex) and dykes emplaced in the Kuruktag area, which record the break-off history of the cratons. This study provides a general framework of mafic dykes in Central Asia on a large scale, and more intensive studies of mafic dykes at medium to small scales in different areas need a combined application of different observation methods, which will provide a better understanding of the continental evolution of Central Asia.
... Some researchers proposed that the oceanic subduction in West Junggar likely terminated at 320 Ma and followed by intensive post-collisional magmatism since the early period of Late Carboniferous (e.g. Chen et al. 2010;Xu et al. 2012;Han and Zhao 2018), and the generation of Early Permian magmatic rocks in the region were interpreted as having been influenced by a mantle plume existed beneath the Junggar basin (Zhang and Zou 2013;Gao et al. 2014;Miao et al. 2019). Whereas some authors suggest that West Junggar was still in a subduction-related environment until the Early Permian time (e.g. ...
... It is pertinent to mention that these obtained ages are well consistent with Early Permian Keping basalts within the Tarim Large Igneous Province (ca. 288-287 Ma; Wei et al. 2014; see the location in Figure 1b), which led some authors to believe that there may exist an Early Permian mantle plume beneath the Junggar basin, and mafic igneous rocks formed during this period in the region were possibly linked to the Tarim mantle plume (Zhang and Zou 2013;Gao et al. 2014;Miao et al. 2019). However, there is absence of contemporaneous mantle plumederived flood basalts or high-temperature magmatic associations in the Hala'alate Mountain or adjacent regions in the SWJ, indicating that an Early Permian mantle plume was not conspicuous beneath the West Junggar. ...
The late Early Permian basaltic rocks in the West Junggar of northwest China provide a critical geological record for revealing the termination of the Late Palaeozoic final-stage subduction history of the southwestern Palaeo-Asian Ocean. With the aim of providing constraints on the late stage of the Late Palaeozoic geodynamic evolution of the southwestern Altaids, an integrated study of detailed field observation, geochronology and geochemistry has been carried out on the Early Permian basaltic rocks from the Hala'alate Mountain of the southern West Junggar. Zircon LA-ICP-MS U-Pb dating of four basaltic andesites suggests that they were erupted during the late Early Permian with ages of ca. 286-283 Ma, coeval with the neighbouring mafic diabase stock and gabbroic dyke swarms. The basaltic rocks have low SiO 2 and moderate MgO contents, with low (87 Sr/ 86 Sr) i ratios (0.70397-0.70447) and high positive εNd(t) values (+5.94-+7.19), and also show remarkable enrichment in large ion lithophile elements (Ba, U, K, Pb, Sr) and prominent depletion in high field strength elements (Nb, Ta, Zr, Hf, Ti), indicating that they were originated from the partial melting of a garnet-dominant with minor spinel lherzolitic depleted mantle source previously metasomatized by slab-derived fluids and subducted sediments. These basaltic rocks were most likely formed in a fore-arc extensional setting in response to the slab retreat of the Junggar oceanic slab during the mid-late stage of Early Permian. Combined with previously published regional achievements, our new results support that the down-going of the remnant oceanic slab and the resultant arc magmatic activity of the southern West Junggar probably continued until the ca. 283 Ma, and the closure of the West Junggar branch of the Palaeo-Asian Ocean should be later than the late Early Permian.
... In addition, petroleum drill holes and seismic exploration data revealed that basalt and rhyolite layers up to 2500 m thick are buried by sedimentary rocks in the Tarim Basin (e.g., Tian et al., 2010;Yu et al., 2011;Liu et al., 2014). Although Permian igneous rocks in the adjacent Tian Shan orogenic belt and other areas of the Central Asian Orogenic Belt (Zhou et al., 2004;Zhang et al., 2010;Zhang and Zou, 2013b;Zhang and Zou, 2013a;Ma et al., 2016;Loury et al., 2018) have been named as 'Bachu large igneous province' or 'Permian Tarim large igneous province' together with the Tarim igneous rocks by some researchers (Zhang et al., 2010;Zhang and Zou, 2013b), these rocks show different geochemical characteristics (e.g., Zhang et al., 2010;Zhang and Zou, 2013a) and were interpreted to be caused by post-orogenic processes of the Central Asian Orogenic Belt (Zhou et al., 2004;Ma et al., 2016). Therefore, we do not group these into the Tarim LIP. ...
... In addition, petroleum drill holes and seismic exploration data revealed that basalt and rhyolite layers up to 2500 m thick are buried by sedimentary rocks in the Tarim Basin (e.g., Tian et al., 2010;Yu et al., 2011;Liu et al., 2014). Although Permian igneous rocks in the adjacent Tian Shan orogenic belt and other areas of the Central Asian Orogenic Belt (Zhou et al., 2004;Zhang et al., 2010;Zhang and Zou, 2013b;Zhang and Zou, 2013a;Ma et al., 2016;Loury et al., 2018) have been named as 'Bachu large igneous province' or 'Permian Tarim large igneous province' together with the Tarim igneous rocks by some researchers (Zhang et al., 2010;Zhang and Zou, 2013b), these rocks show different geochemical characteristics (e.g., Zhang et al., 2010;Zhang and Zou, 2013a) and were interpreted to be caused by post-orogenic processes of the Central Asian Orogenic Belt (Zhou et al., 2004;Ma et al., 2016). Therefore, we do not group these into the Tarim LIP. ...
... Some of these intrusions host economically valuable magmatic Ni-Cu sulfide ore deposits, such as Huangshanxi (Mao et al. 2014), Huangshandong (Mao et al. 2015), and Tulaergen (San et al. 2010). The formation of these deposits has been linked to the Tarim mantle plume (Pirajno et al. 2008;Qin et al. 2011;Zhang and Zou 2013), to subduction-related magmatism (Xiao et al. 2004), or to magmatism associated with lithospheric delamination coupled with asthenosphere upwelling in a post-subduction environment (Song et al. 2013(Song et al. , 2021Li et al. 2019). Central to the debate of these different models are the different views on the timing of the final Communicated by Editorial handling: W. D. Maier. ...
... The classification of the Tulaergen mafic-ultramafic complex as an arc igneous complex implies that other contemporaneous mafic-ultramafic intrusions in the region are also subduction-related. Previously, other researchers suggested that all of the Permian mafic-ultramafic intrusions in the region are linked to the Tarim mantle plume (e.g., Pirajno et al. 2008;Qin et al. 2011;Su et al., 2014;Zhang and Zou 2013), or lithospheric delamination coupled by asthenosphere upwelling in a post-subduction environment (e.g., Song et al. 2013Song et al. , 2021Han and Zhao 2018;Li et al. 2019). These two competing models are all based on the same assumption that the Tarim Craton and the micro-continents and associated arc terranes to the north were amalgamated by the end of the Carboniferous, which in turn is based on the geology of Western Tianshan, not that of the East Tianshan-Beishan region where these intrusions are located (see Fig. 1a and b for locations). ...
The Tulaergen magmatic Ni-Cu sulfide ore deposit is located along the southern margin of the Central Asian Orogenic Belt in northwestern China. This deposit is hosted by a small mafic–ultramafic complex composed of a Late Carboniferous (~ 301 Ma) gabbroic member at the margin and a younger ultramafic dyke in the center. Net-textured and semi-massive sulfides are mainly concentrated in the steeply dipping, widened parts of the dyke. Zircons from the ultramafic member yield a U–Pb age of 281 ± 2 Ma, ~ 20 myr younger than the gabbroic member. The average εHf(t) value of the zircons is ~ 16. The Tulaergen mafic–ultramafic rocks are characterized by light REE enrichments, pronounced negative Nb–Ta anomalies, (87Sr/86Sr)i ratios from 0.7034 to 0.7036, and εNd(t) values from 5.1 to 6.9. The isotope data indicate negligible bulk contamination with the crust. The δ34S values of sulfide ores are from − 0.3 to 1.5‰, similar to the values of the country rocks. The γOs values of the sulfide ores are from + 605 to + 954, much higher than typical mantle values. The Os-S isotope data together support the view that the addition of Os-bearing organic matter from the country rocks may have played a critical role in triggering sulfide saturation. In the sub-vertical segment of the deposit, the upper zone has lower PGE tenors coupled with lower and rather constant olivine Fo contents compared to the lower zone. Based on the geometry of the dyke and sulfide distribution, we conclude that the Tulaergen deposit formed in a dynamic magma conduit.
... Gao et al., 2009;Han et al., 2011;Xiao et al., 2013;Xiao & Santosh, 2014) and whether the Tarim mantle plume played a role in the widespread Permian magmatism in the area (e.g. Qin et al., 2011;Zhang & Zou, 2013a, b;Zhang et al., 2014;He et al., 2016;Xue et al., 2016;Zheng et al., 2016;Han et al., 2019). The presence of Permian bimodal volcanic rocks and A-type granitoids in the Tianshan Orogen is likely consistent with a post-orogenic setting (Long et al., 2011;Gou et al., 2012;Zhang & Zou, 2013a, b;Li et al., 2015a;Xia et al, 2016). ...
... Qin et al., 2011;Zhang & Zou, 2013a, b;Zhang et al., 2014;He et al., 2016;Xue et al., 2016;Zheng et al., 2016;Han et al., 2019). The presence of Permian bimodal volcanic rocks and A-type granitoids in the Tianshan Orogen is likely consistent with a post-orogenic setting (Long et al., 2011;Gou et al., 2012;Zhang & Zou, 2013a, b;Li et al., 2015a;Xia et al, 2016). However, the detailed mechanism for these magmatisms is poorly constrained. ...
Whole-rock geochemistry, usually changed by magmatic processes, might provide misleading information on the petrogenesis of adakites. The Heishantou porphyritic diorites in Nileke, Western Tianshan orogenic belt record complex magma chamber processes, such as magma replenishment, fractional crystallization and crustal contamination, and thus, provide ideal samples for tracing the magmatic processes that generate the typical high Sr and La contents and Sr/Y and La/Yb ratios of adakites. In situ clinopyroxene and amphibole compositions of Heishantou porphyritic diorites (271 ± 2 Ma) are characterized by low Yb and Y content with high Sr/Y and La/Yb ratios, from which calculated early magmas resemble typical adakites derived from partial melting of a subducted slab. But whole-rock composition shows low MgO, Ni and Cr, thus, the Heishantou diorites were previously regarded as the result of partial melting of thickened lower crust. Plagioclase phenocrysts exhibit complex compositional zoning due to magma replenishment, and the rims have higher 87Sr/86Sr ratio and Sr content than the cores, indicating crustal assimilation. The cores of zoned clinopyroxene phenocrysts have high Mg#, Cr and Ni but low Yb and Y with high Sr/Y and La/Yb ratios, which are consistent with the high Mg# of primary adakitic magmas. Magmatic processes have significantly changed the primary adakitic features of Yb, Y and Sr content, Sr/Y and La/Yb ratios, in addition to Mg# values. The Heishantou primitive high-Mg# adakite was derived from partial melting of a delaminated lower crust followed by storage, recharge, and assimilation in a crustal magma chamber. The Western Tianshan orogenic belt experienced a succession of lower crust delamination events in the Early Permian that involved melting of thickened lower crust, subsequent lithospheric detachment and asthenospheric upwelling.
... Some authors suggest that the continental growth in CAOB was dominated by the lateral accretion of arc complexes related to oceanic subduction (e.g., Sengör et al., 1993), whereas others propose that the post-collisional vertical underplating of mantle-derived materials played a more important role (e.g., Han et al., 1997;Jahn et al., 2000;Chen and Arakawa, 2005;Zhang et al., 2008). Alternatively, some point out that ridge-subduction (e.g., Geng et al., 2009;Tang et al., 2012;Yin et al., 2015), remnant ocean transition (Xu et al., 2013), mantle plume activity (e.g., Zhang and Zou, 2013;Gao et al., 2014) or reworking of Precambrian materials (Kröner et al., 2014) in the crustal generation of CAOB may be significant as well. These uncertainties hamper our understanding of the nature of Phanerozoic crustal growth which played an important role in the formation of the CAOB. ...
... Bimodal volcanic suites commonly occur in extensional tectonic settings related to post-collision, intraplate or back-arc rifting (e.g., Zhang et al., 2008;Chen et al., 2013;Zhang et al., 2017;Chen et al., 2018;Su et al., 2018). Some authors have suggested the presence of a Carboniferous to Permian mantle plume beneath the Junggar and Tianshan areas, possibly linked to the Tarim Large Igneous Province (LIP) (e.g., Zhang and Zou, 2013;Gao et al., 2014). However, rocks derived from mantle plumes generally show geochemical compositions similar to those of OIB (e.g., Hofmann, 1997), inconsistent with the features of the studied bimodal-type volcanic rocks (Figs. 8 and 9). ...
The Central Asian Orogenic Belt (CAOB) is one of the world's largest and longest-lived accretionary orogens that has been regarded as an important area of crustal growth during the Phanerozoic, yet the growth mechanism is still under debate. A combined study of petrology, geochronology and geochemistry for drilling-sampled early Carboniferous volcanic rocks from the Junggar Basin (NW China), southwestern CAOB, aims to constrain their petrogenesis and implications for Phanerozoic crustal growth. The volcanics show a bimodal-type suite, dominated by basalts, basaltic andesites and subordinate rhyolites, and have consistent zircon Usingle bondPb ages of 334–336 Ma. The mafic rocks exhibit arc-like trace-element distribution patterns characterized by enrichment of LILEs (e.g., Pb) and LREEs but depletion of HFSEs (e.g., Nb, Ta and Ti). They have juvenile isotopic signatures of zircon ɛHf(t) (+11.4 to +15.4) and whole-rock ɛNd(t) (+7.8 to +8.5), with initial (87Sr/86Sr)i of 0.7040–0.7054 and (206Pb/204Pb)i of 17.681–17.817. These geochemical features, together with their variable Ba/La (4.28–44.2) but low (Tb/Yb)N (1.24–1.85) and Sm/Yb (1.65–3.44) ratios, suggest that the mafic volcanics could be derived from a main spinel-bearing mantle source metasomatized by subduction-related fluids. In contrast, the felsic samples are geochemically equivalent to A2-type granite, with high contents of SiO2, Zr, Ga, and show strong depletions in Eu, Sr and Ti. They have zircon Hf (ɛHf(t) = +12.0 to +15.3) and whole-rock Sr-Nd-Pb isotopic compositions ((87Sr/86Sr)i = 0.7032–0.7038; ɛNd(t) = +7.8 to +8.1; (206Pb/204Pb)i = 17.973–18.004) similar to the coeval mafic rocks. These observations, along with the model calculations using MELTS, favor a derivation of felsic rocks from the mafic magma by fractional crystallization. We suggest that the early Carboniferous bimodal-type volcanism formed in a localized back-arc extension within an overall convergent setting, presumably triggered by slab roll-back of the subducting Paleo-Junggar Ocean plate. This bimodal-type magmatism recorded a significant vertical crustal growth event in the Junggar Basin during the Phanerozoic. We propose that oceanic subduction (flare-ups) not only leads to the lateral accretion of arcs, but also results in the vertical growth of mantle-derived materials and subsequent magma differentiation during slab roll-back (flare-lulls); this may considerably change our view of the models of crustal growth in CAOB.
... Mantle xenolith suites seem suggesting that the Tarim lithospheric mantle is formed by, at least partly, juvenile mantle material related to the Early Permian mantle plume event, which caused flood basalt magmatism covering nearly all the Permian strata in the Tarim Basin . Recently, Zhang and Zou (2013), by analysing chemical compositions of mafic dikes, argue for two distinct mantle domains in the Tarim Large Igneous Province: a long-term enriched continental lithospheric mantle of the Tarim domain in the south, and a more depleted lithospheric mantle of the Central Asian Orogenic Belt (CAOB) (i.e: Tian Shan, Junggar and Altai Range) region in the north, due to slab-derived fluids or subducted sediments. ...
... Tian Shan, Junggar, and Altai Range) (Mantle 2, Table 5.3); and iii) an undepleted mantle in the deepest portion of Tarim lithosphere, with a composition equivalent (at least in major oxides) to the primitive mantle of the underlying asthenosphere (Mantle 3-PUM, Table 5.3). The thermal anomaly located at 300-400 km depth beneath the Tarim Basin is probably the responsible of the enrichment in incompatible elements (CaO and Al 2 O 3 ), calling for metasomatization of the lithospheric mantle by means of ascending asthenospheric fluids, according to the plume-lithosphere interaction hypothesis proposed by different studies , Zhang and Zou, 2013, Xu et al., 2014. ...
The Central Asia region is dominated by one of the largest areas of distributed
deformation on Earth, which spans eastern Turkey, northern Middle East, central and south-
eastern Asia, covering the central and eastern sectors of the Alpine-Himalayan mountain belt.
The lithosphere structure plays an important role in controlling the surface deformation
and its propagation to the continental interiors. The compositional and strength
heterogeneities within the lithosphere directly affect to the tectonic behaviour of the region
and, hence, to the evolution of the orogenic systems. This thesis focalizes on the
characterization of the present-day lithospheric structure of the Zagros and the Himalayan-
Tibetan orogens and the role of the lithospheric structure and rheology in the accommodation of the deformation related to the Arabia and India convergence against Eurasia.
... These Early Palaeozoic rocks generally intrude the Precambrian basement rocks and are therefore believed to have been initially emplaced in the northern edge of Palaeozoic Tarim. In addition, some Early Permian, large igneous province (LIP)-related magmatic suites represented by kimberlitic intrusions, OIB-like mafic intrusions and basalts, bimodal dykes and A1-type syenites/granites have also been recently identified in the western and central parts of the NTC (see Zhang & Zou, 2013a, 2013b, and references therein). ...
... On the other hand, the more juvenile Hf-in-zircon signatures of Early to Middle Permian igneous zircons from the northern margin of Tarim Craton, compared with that of coeval or slightly older zircons from the STT, likely requires higher-degree of regional-scale input of juvenile materials. Recently, a Permian mantle plume beneath the Tarim Craton has been proposed by many authors (e.g., Zhang & Zou, 2013a, 2013b, and references therein). If this is the case, the comparatively juvenile sources for Permian felsic rocks in northern Tarim was likely associated with plume-triggered magmatism. ...
The South Tianshan Terrane (STT) is located in the boundary between the south‐western Central Asian Orogenic Belt (CAOB) and the Tarim Craton and is a key area for understanding the geologic and tectonic history of the craton and the orogenic belt. In this paper, we report detrital zircon ages from the Late Palaeozoic and Mesozoic clastic sedimentary rocks from the southern part of STT. In combination with the U–Pb ages for felsic igneous and meta‐igneous rocks exposed in the STT and adjacent tectonic units, we identify several distinct age populations. Provenance analysis suggests that the detrital zircon grains were predominately derived from the felsic magmatic rocks in the Tarim Craton and South Tianshan Terrane. The pre‐Neoproterozoic age populations may be associated with the early history of the Tarim Craton. Several pulses of Neoproterozoic magmatism are revealed by our dataset, presumably related to the assembly and break‐up of the supercontinent Rodinia. The 995 to 901 Ma detrital zircon grains were likely sourced from magmatic rocks associated with the assembly of Neoproterozoic Tarim to Australia. Among the age population of 886 to 752 Ma, the older group might be related to the subduction‐related magmatism after the assembly of Rodinia, and the younger one records a protracted magmatic event in a continental rift‐related setting associated with the break‐up of Rodinia. Two younger Neoproterozoic age populations (736 to 694 Ma and 665 to 610 Ma), showing narrow spreads with weak peaks, represent the waning stages of igneous activities related to the break‐up of Rodinia. Regarding the Palaeozoic evolution, together with other evidence, our data indicate a two‐stage subduction model for the SW Palaeo‐Asian Ocean. The 490 to 384 Ma age population corroborates the existence of Early Palaeozoic continental arc magmatism at the northern margin of Palaeozoic Tarim generated by the bidirectional subduction of the South Tianshan Ocean. After a ~30 My period of tectonomagmatic quiescence, the second stage is marked by the northward subduction of the South Tianshan Terrane during Late Devonian to Early Carboniferous. The final collision of Tarim and the south‐western CAOB likely occurred during the Late Carboniferous, followed by syn‐ and post‐collisional magmatism, as represented by the 320 to 265 Ma age population. Based on the detrital zircon ages in conjunction with the Hf isotopic features of zircons from Palaeozoic igneous rocks, our study does not support the model of large‐scale Phanerozoic net continental growth in the South Tianshan Terrane.
... This [Bagdassarov et al., 2011], in the western Tarim Basin [Chen et al., 2014], and in Qaidam Basin [Song et al., 2007]. Black rhomboids represent mafic dikes localities from Zhang and Zou [2013]. INDEPTH [Nelson et al., 1996;Zhao et al., 2011]; SF4-SF6, Sino-French passive seismic experiments in 1998 and 1993 Vergne et al., 2002;Jiang et al., 2006]; Hi-CLIMB [Nabelek et al., 2009;Wittlinger et al., 2009]; TIPAGE [Mechie et al., 2012]; TIBET-31 N [Y. ...
... In the Tarim Basin, mantle xenolith suites [Chen et al., 2014] suggest that the lithospheric mantle is formed by, at least partly, juvenile mantle material related to the Early Permian mantle plume event, which caused flood basalt magmatism covering nearly all the Permian strata in the Tarim Basin. Zhang and Zou [2013], by analyzing chemical compositions of two magmatic dikes localities, argue for two distinct mantle domains in the Tarim Large Igneous Province: a long-term enriched continental lithospheric mantle of the Tarim domain in the south and a more depleted lithospheric mantle of the Central Asian Orogenic Belt (CAOB) region in the north (i.e., Tian Shan, Junggar and Altai), due to slab-derived fluids or subducted sediments. The existence of different lithospheric domains suggests different mantle compositions. ...
We present a new crust and upper mantle cross-section of the western India-Eurasia collision zone by combining geological, geophysical and petrological information within a self-consistent thermodynamic framework. We characterize the upper mantle structure down to 410 km depth from the thermal, compositional and seismological viewpoints along a profile crossing western Himalayan orogen and Tibetan Plateau, Tarim Basin, Tian Shan and Junggar Basin, ending in the Chinese Altai Range. Our results show that the Moho deepens from the Himalayan foreland basin (~40 km depth) to the Kunlun Shan (~90 km depth), and it shallows to less than 50 km beneath the Tarim Basin. Crustal thickness between the Tian Shan and Altai mountains varies from ~66 km and ~62 km. The depth of the lithosphere-asthenosphere boundary (LAB) increases from 230 km below the Himalayan foreland basin to 295 km below the Kunlun Shan. To NE the LAB shallows to ~230 km below the Tarim Basin and increases again to ~260 km below Tian Shan and Junggar region, and to ~280 km below the Altai Range. Lateral variations of the seismic anomalies are compatible with variations in the lithospheric mantle composition retrieved from global petrological data. We also model a preexisting profile in the eastern India-Eurasia collision zone, and discuss the along-strike variations of the lithospheric structure. We confirm the presence of a noticeable lithospheric mantle thinning below the Eastern Tibetan Plateau, with the LAB located at 140 km depth, and of mantle compositional differences between the Tibetan Plateau and the northern domains of Qilian Shan, Qaidam Basin and North China.
... Therefore, a possible Permian large igneous province with a mantle plume origin in the Tarim Basin has been proposed by previous workers (Zhang et al. 2008Zhang and Zou 2013). The igneous rocks including basalt, diabase and basaltic andesite in the Tarim Basin may be resulted from plume-lithosphere interactions (Yang et al. 1997;Zhang et al. 2008Zhang et al. , 2010aZhang et al. , b, 2012Zhang and Zou 2012, samples from outcrops along the margins of the basin and from cores from several wells, and these studies have predominantly focused on certain rock types, such as flood basalts, acid lava and intrusive rocks (Yang et al. 2007;Zhang et al. 2008;Zhang andZou 2012, 2013). Studies of the internal parts of the basin are rare. ...
... The rocks are dominated by basalt, andesitic basalt, diabase and ultramafic units. Felsic series are also present and include syenite, rhyolite, dacite, granodiorite and pyroclastic rocks Zhang and Zou 2012). ...
A 1445-km2 high-resolution 3D seismic reflection dataset is used to analyze the Permian large igneous province in the subsurface of the Tazhong area in the central Tarim Basin in northwestern China. Constrained by the synthetic seismograms of four wells, the top and base of the igneous rocks were identified in the seismic data. Seven large volcanic craters, each >10 km2 in area, have been discovered via the application of coherency and amplitude attributes. The thickness and volume of the igneous rocks were obtained by time–depth transformation. In the study area, all of the igneous rocks, with thicknesses from 120 to 1133 m, were formed by eruptions in the Early Permian. These events produced huge erupted volumes (178 km3) and multiple closely spaced volcanic edifices (<13 km). These features suggest that the study area may be the part of the eruptive center of the Permian igneous rocks in the Tarim Basin.
... As researches continuing, more attention has been paid to silicic volcanic rocks in the LIP, but the origin of the silicic magmas is still debatable. Two origins have been proposed, including 1) fractional crystallization of coeval mantle-derived basaltic magmas, if any, combined with assimilation of crustal materials (Tian et al., 2010;Huang et al., 2012;Zhang and Zou, 2013;Liu et al., 2014;Wei et al., 2014bWei et al., , 2019, and 2) anatexis of crust material induced by mantle upwelling (Liu et al., , 2019. ...
... first episode occurred during the Early Ordovician but only localized in the central-western part of the basin (H. L. Chen et al., 1997). The second thermal episode, occurred during the Early Permian and the most intense one, was widely regarded as related to mantle plume-originated magmatism (Huang et al., 2012;C. L. Zhang, Li, Li, Ye, & Li, 2008;C. L. Zhang & Zou, 2013). This event resulted in formation of a large igneous province, the exposure of which is mainly distributed in the northwestern margin of the Tarim Basin, that is, the Aksu-Kalpin areas (H. L. Chen et al., 1997;Jin et al., 2006;C. L. Zhang et al., 2010). The last one activity took place during the Cretaceous but was only restricted aroun ...
The Shunnan area is a newly discovered hydrocarbon field in Shuntuoguole lower uplift, in which the host rocks are Lower–Middle Ordovician carbonates. The carbonate reservoirs are well affected by hydrothermal silicification with well‐preserved intercrystalline pore of replacement quartz and megaquartz cements. Based on the petrography, pore types, and diagenetic processes, this research evaluated the reservoir quality and re‐constructed the porosity evolution in different diagenetic stages. Samples are collected from 7‐cored wells distributed along NNE‐ or ENE‐trending sinistral strike‐slip faults. Nine types of lithofacies were identified in the study area, including mudstone, bioclast wackestone, peloidal bioclast packstone, boundstone, peloidal grainstone, ooid grainstone, slightly silicified limestone (silica less than 25%), strongly silicified limestone (silica around 50%), and chert. Chert has better porosity (average 21.3%) and permeability (average 44.7 mD) than other lithofacies. The main reservoir pores are mainly developed in forms of fractures, intercrystalline replacement quartz and dissolved vugs. The porosity evolution shows that the primary porosity was limited due to cementation and compaction, and the earlier secondary porosity was occlusive as a result of coarse calcite cementation. Therefore, the precursor limestones may be tight, and the reservoir quality of the Lower–Middle Ordovician carbonates was controlled by hydrothermal silicification. During the hydrothermal silicification event, the burial depth of the Lower–Middle Ordovician carbonates was more than 3,000 m and their stratum temperature was higher than 120°C, representing a deep burial condition. The statistical data of porosity‐depth/temperature trends for carbonates suggest that the early secondary pores would be significantly reduced when the burial temperature reaches 100°C (or depth of strata reaches 3,000 m). Therefore, the dissolved vugs in strongly silicified limestone or hydrothermal chert are caused by hydrothermal silicification and not inherited from precursor carbonate rocks. The precursor limestones were tight, and the hydrothermal silicification significantly enhanced the reservoir properties of the deep carbonates and not inherited from precursor carbonates.
... Because Permian mafic-ultramafic igneous rocks are widely distributed on the Tarim craton, these rocks were considered as a large igneous province related to a mantle plume (e.g., Xu et al., 2014). Given that the Permian magmatic rocks in the Tianshan possess scattered zircon e Hf (t) and d 18 O values and occur coevally with the Tarim igneous activity, some researchers suggested that the Permian magmatism in the Tianshan area was likely triggered by the same mantle plume (Pirajno et al., 2008;Qin et al., 2011;Su et al., 2011a;Su et al., 2011b;Zhang and Zou, 2013). On the contrary, some other researchers argued that the Permian magmatic rocks in the Tianshan were formed in a supra-subduction environment, based on their arc-like geochemical characterizes, such as enrichment of LILEs and depletions of HFSEs (Chen et al., 2019;Mao et al., 2014a;Mao et al., 2019). ...
Multiple arc systems were developed in response to Neoproterozoic to Mesozoic consumption of the Paleo-Asian Ocean and their magmatic evolution is crucial for understanding the arc-arc amalgamation in the Central Asian Orogenic Belt. Here, we report whole-rock geochemical data as well as simultaneous in situ zircon U-Pb and Lu-Hf isotope results for the late Paleozoic magmatic rocks associated with the shear zones in the Gangou section of the Eastern Tianshan to constrain their petrogenesis and arc-arc amalgamation processes. We obtained ∼307 Ma and ∼270 Ma zircon U-Pb ages for the Late Carboniferous diorites and Middle Permian andesites, respectively. These rocks have high Mg# (∼65 and ∼47, respectively) values, and are enriched in large ion lithophile elements (LILEs) and depleted in high field strength elements (HFSEs), with depleted zircon εHf(t) values (+12.1 to +18.1), suggesting an origin from partial melting of the depleted mantle with various degree of differentiation. Furthermore, our results also provided ∼276 Ma zircon U-Pb ages for the Middle Permian granitic porphyries and ∼256 Ma zircon U-Pb ages for the Late Permian diabase rocks. The granitic porphyries are geochemically similar to A2-type granites, i.e., high K2O+Na2O, FeOT/MgO, Ga/Al and low CaO, Sr and Ba. They have high zircon εHf(t) (+9.0 to +13.7) values, indicating a possible derivation from juvenile lower crust. The diabase rocks show depletion of light rare earth elements (LREEs), resembling normal mid-ocean ridge basalt. These rocks have depleted zircon Hf isotopic compositions (εHf(t) = +8.9 to +15.8), demonstrating a possible derivation from partial melting of the depleted mantle. The available geochemical data from the Eastern Tianshan show that the Permian mafic rocks along the shear zones possess higher Nb/La and lower Ba/La ratios than their counterparts in the Carboniferous. These contrasting features imply that the Carboniferous mafic rocks originated from a metasomatic mantle wedge, while the Permian mafic rocks were likely derived from the depleted mantle with addition of enriched asthenosphere components. The high zircon saturation temperatures (mostly > 800 ℃) of the Permian A-type granitoids and diverse magma sources of coeval mafic rocks also imply possible asthenosphere upwelling. Therefore, we propose that the Late Carboniferous magmatic rocks were likely resulted from subduction of the North Tianshan oceanic plate, while the spatial and temporal evolution of the Permian magmatic rocks were probably attributed to large-scale dextral transcurrent tectonics associated with arc-arc amalgamation.
... The Tarim Basin shows a strong negative radial anisotropy in the upper mantle, which indicates that the vertical movement of material plays a dominant role. Therefore, we suggest that the low SH-wave velocity anomaly and negative radial anisotropy of the Tarim Basin are related to the Tarim mantle plume (Long et al. 2011;Zhang and Zou 2013). ...
The Tien Shan is one of the most active intracontinental orogenic belts worldwide and shows intensive seismicity and tectonic activity that reflects laterally heterogeneous structures. Here, we employ multimode surface wave tomography to construct an anisotropic 3-D shear-wave velocity model, which achieves a resolution of 2.0°. The new tomographic model reveals pronounced velocity contrasts between the central Tien Shan, which shows low velocity, and the eastern Tien Shan, which shows high velocity in the depth range of 50–300 km. We interpret that this velocity contrast as potentially resulting from the difference in the uplift mechanism of the Tien Shan. A comprehensive analysis suggested that the uplift of the central Tien Shan might be related to northward subduction of the Tarim lithosphere while the low-velocity anomaly beneath the central Tien Shan might be related to subsequent mantle upwelling. In contrast, the Tarim block in the south collided with the Junggar Basin in the north, which may have led to the uplift of the eastern Tien Shan. The Tarim Basin is mainly characterized by high-velocity anomalies of SV waves but low-velocity anomalies of SH waves beneath the western Tarim Basin, which may be related to the Tarim mantle plume.
... A number of models have been proposed for the tectonic environment in which the intrusions were formed, including a subduction-related environment in the Early Permian (Ao, 2010;Xiao et al., 2010); a post-subduction setting ; or a Beishan rift-related environment (Su et al., 2011b). It has also been suggested that they are a part of the Permian Tarim Large Igneous Province and are hence produced by the mantle plume (Jiang et al., 2006;Pirajno et al., 2008;Zhang and Zou, 2013). A considerable amount of research has been done on the Permian magmatic Ni-Cu sulfide occurrences/deposits in the western Beishan (Su et al., 2013;Xia et al., 2013;Xue et al., 2016). ...
The Permian Luotuoshan mafic-ultramafic intrusion is one of the ∼280 Ma mafic-ultramafic complexes located in the Beishan Orogenic Belt at the southern margin of the Central Asian Orogenic Belt, NW China. The intrusion is predominantly composed of wehrlite, olivine clinopyroxenite, troctolite, olivine gabbro, and gabbro. Disseminated sulfides occur in wehrlite and olivine clinopyroxenite at the center of the intrusion. SHRIMP zircon U–Pb dating of a gabbro sample yielded a concordia age of 282.6 ± 2.6 Ma. The Luotuoshan mafic-ultramafic rocks are characterized by elevated εNd (282.6Ma) values from +0.42 to +6.10 and εHf (282.6Ma) values from +7.9 to +14.1, relatively low initial ⁸⁷Sr/⁸⁶Sr (0.703919–0.705272) and Pb isotope composition, and low ratios of TiO2/Yb, Nb/Yb, etc., suggesting the Luotuoshan magma was derived from a depleted asthenosphere mantle source. Some arc-like geochemical characteristics such as enrichment of light rare earth elements and large ion lithophile elements (Ba, Sr, Rb, etc.), pronounced negative Nb–Ta–Zr–Hf anomalies, and La/Nb, Ce/Pb, and Th/Yb ratios indicate that the mantle source was previously modified by subduction-related metasomatism. Petrographic features and mixing calculations of Sr–Nd–Hf isotopes suggest that the parental magma of the Luotuoshan intrusion underwent a moderate degree of crustal contamination (5–15%) followed by fractional crystallization process. Petrological modeling reveals that both fractional crystallization and crustal contamination may have played the important role in triggering the sulfide saturation in the Luotuoshan magma. The comparable formation age, petrographic and mineralogical characteristics, geochemistry of the parental magma and evolution process compared with intrusions in the Pobei area, indicate that the Luotuoshan intrusion may also have similar mineralization potential. This also suggests that the mineralization prospection of Permian mafic-ultramafic intrusions in the Gansu Beishan area should not be neglected, and it is worth considering that whether further exploration is worthy of being implemented in this region.
... The studied and analyzed paleogeographic [9,10] and pa leotectonic maps and diagrams [8,11] depict the SarysuTeniz depression as a single basin before the Permian. At the end of the Lower Permian, one of the powerful tectonic movements of the Paleozoic occurs in the studied area, due to the collision of the Kazakhstan continent with Tarim and EastEuropean continent. ...
Purpose. To study the features of the paleotectonic development of the area and to construct paleotectonic reconstruction of the deposit formation to establish the nature of impurity elements accumulation in the coals and enclosing rocks of the Shubarkol deposit, as well as to increase the mineral resource potential of coals. Methodology. 25 samples of coal and mudstone from the Shubarkol deposit were analyzed. The samples were studied by instrumental neutron- activation analysis (INAA) at the Nuclear Geochemical Laboratory of National Research Tomsk Polytechnic University. Findings. An analysis of geological-structural and paleotectonic formation conditions of the Jurassic coal deposit was carried. The factors of formation of coal and carbon-containing rocks enriched with impurity elements and the conditions needed for its leaching and transportation to the coal seam were analyzed. It was found that the coals in individual samples have average concentrations of Ce, Ba, Sr, Sc, Zn that are higher than the clarke, and Sm, Ce, U, Cr, Yb, Ba, Sr, Nd, As, Sc, Zn, Eu, La in the composition of mudstone have average values that are higher than in coals, and higher than the clarke. It was established that one of the sources of rare-metal mineralization of coals (peat) in the Mesozoic and Cenozoic times were the rock massifs of the Kokchetau uplift in the north and northwest, the Kaptyadyr, Arganatinsk and Ulutau mountains in the west. They form the chain of the Kokchetau-North Tien Shan ancient folded structure and the Central Kazakhstan (Devonian) volcanic-plutonic belt in the east. They surround the sedimentation basin and serve as suppliers of clastic material during the coal-bearing strata formation due to tectonic processes of the Mesozoic-Cenozoic time. Originality. The paleotectonic development of the Shubarkol deposit area during the coal-bearing formation has been reconstructed. It has been established that the Sarysu-Teniz uplift in the Permian-Triassic is separated into an independent block, to which the studied deposit is spatially and genetically related. It has been established that the distribution of elements in the coals of the Shubarkol deposit is determined by the peculiarities of metallogeny, geochemistry of the framing area and the mechanisms of the elements entering the coal seams. Practical value. A purposeful analysis of materials for the peculiarities of high concentrations of impurity elements accumulation in coal in connection with deep fault zones at the Shubarkol deposit serves as an objective justification of the possibility of their integrated use, ensuring the development of the countrys coal industry.
... Some authors have proposed the presence of a Carboniferous to Permian mantle plume beneath the Junggar and Tianshan regions, possibly related to the Tarim large igneous province (e.g., Zhang and Zou, 2013;Gao et al., 2014;Xia and Li, 2020). However, rocks that originated from mantle plumes usually have elemental compositions similar to those of OIB (Hofmann, 1997), inconsistent with the studied Carboniferous igneous rocks, which show subduction-related geochemical features (Fig. 9). ...
Knowledge of the subduction to postcollision tectonic transition in response to oceanic closure is crucial for tracking the final stage of orogenic evolution. Here, we report new geochronology, geochemistry, and isotopic data for Carboniferous magmatism in East Junggar (NW China), southwestern Central Asian orogenic belt, which may record such processes following the closure of the Kalamaili Ocean (a branch of the Paleo-Asian Ocean). The early Carboniferous calc-alkaline volcanic rocks (dominated by basalt and basaltic andesite) yielded zircon U-Pb ages of ca.
340–330 Ma and are characterized by arc-like trace-element patterns showing enrichment of light rare earth elements (LREEs) and large ion lithophile elements (LILEs; e.g., Pb) but depletion of high field strength elements (HFSEs; e.g., Nb, Ta, and Ti). Combined with their variable Ba/Nb (9.80–454) and low
Nb/La (0.21–0.54) and Sm/Yb (1.77–3.08) ratios as well as depleted mantle–like Sr-Nd-Pb-Hf (whole-rock 87Sr/86Sri = 0.7037–0.7040; εNd[t] = +3.5 to +5.9; 206Pb/204Pbi = 17.728–17.996; zircon εHf[t] = +11.8 to +18.8) isotopic values, we suggest that they were produced by melting of a lithospheric mantle wedge fluxed by slab-derived fluids under spinel-facies conditions. With whole-rock 40Ar/39Ar dating of ca. 320 Ma, the late Carboniferous mafic dikes have geochemical features and Sr-Nd-Pb (87Sr/86Sri = 0.7039–0.7041; εNd[t] = +6.6 to +6.8; 206Pb/204Pbi = 17.905–17.933) isotopic compositions similar to those of the early Carboniferous volcanics, but they show less pronounced Pb anomalies and negative Nb and Ta anomalies. They are interpreted to have formed by partial melting of a spinel-bearing lithospheric mantle metasomatized by limited influx of subduction-related fluids. The late Carboniferous felsic volcanic rocks (dacite and rhyolite) yielded zircon U-Pb ages of ca. 305 Ma and are geochemically equivalent to those of A2-type granites in East Junggar. They have juvenile isotopic compositions (εNd[t] = +4.5 to +6.8; εHf[t] = +13.3 to +18.7) and relatively young Nd and Hf model ages that roughly coincide with the ages of the ophiolites in the area, suggesting that they could have originated from melting of a juvenile basaltic lower crust. Whole-rock geochemistry, assimilation–fractional crystallization (AFC), and isotopic mixing modeling argue for insignificant crustal contamination for the Carboniferous magmatism. We suggest that the early Carboniferous lavas erupted in an island-arc setting related to the northward subduction of the Kalamaili oceanic crust, whereas the late Carboniferous magmatism formed in a postcollisional extensional regime in response to slab breakoff or lithospheric delamination. Combined with regional geological information, we propose that a rapid tectonic transition from oceanic subduction to postcollisional extension may have occurred in East Junggar during the Carboniferous, marking the final closure of the Kalamaili Ocean, which most likely took place ca. 330–320 Ma. This study provides overall geochronological and petrogeochemical evidence to better constrain the amalgamation of the southwestern Central Asian orogenic belt and may be of great importance for understanding the final stage of orogenic evolution elsewhere.
... In the CAOB, there are numerous large-scale magmatic Ni-Cu sulfide deposits. The magmatic source for these deposits was depleted mantle that interacted with subduction-related material and fluids (Song and Li 2009;Su et al. 2011;Li et al. 2012;Tang et al. 2013;Zhang and Zou 2013). Therefore, the Ni-Cu sulfide deposits in the CAOB are ideal natural laboratories in which to study the effects of H 2 O in the mantle source and in the mineralized magma. ...
Magmatic Ni-Cu sulfide deposits in orogenic belts have distinct petrological and geochemical features compared with world-class intraplate magmatic deposits. One such feature is the presence of abundant primary hydrous minerals such as phlogopite and amphibole, indicating a H2O-rich parental magma. However, the origin and nature of the fluids have not been established. In the southern Central Asian Orogenic Belt, the Permian Baishiquan and Tianyu mafic–ultramafic intrusions host magmatic Ni-Cu sulfide deposits. Both intrusions are composed of lherzolite, olivine websterite, gabbronorite, gabbro, and diorite. The main ore-host rocks are lherzolite and websterite, with disseminated, net-textured, and massive ores comprising the dominant primary ore types. Low zircon εHf (− 6.9 to 7.9 ‰) and varying δ¹⁸O values (5.2 to 6.6 ‰), as well as both arc-type and MOR-type zircon Nb/Yb (0.0013–0.011) and U/Yb (0.33–10.22), identify an altered lower oceanic crust component in the mantle source. A combination of altered lower oceanic crust and upper crust can account for the zircon Hf–O isotopic characteristics. A mixing model further reveals that the Baishiquan and Tianyu magmatic sulfide deposits originated from a depleted mantle source that experienced two stages of subduction metasomatism with a 30% addition of altered oceanic crust in the first stage and 20% in the second. In the second stage, > 10% oceanic sediment with high δ¹⁸O must also have been added to result in olivine δ¹⁸O values higher than those in mantle. This staged evolution is reflected in both the olivine and zircon signatures with olivine from disseminated and net-textured ores at the Tianyu deposit having high δ¹⁸O (4.6 to 6.3 ‰) with a similar range to zircon and high δ⁷Li isotopic compositions (12.03 to 19.46 ‰). Contamination in the source by oceanic sediment with high δ¹⁸O values can account for the olivine δ¹⁸O values (4.8 to 5.7 ‰ at Baishiquan) being higher than those in the mantle, while the addition of brine (5% at the Baishiquan deposit) can explain the olivine δ⁷Li values (20.96 to 31.01 ‰). The results suggest that H2O content, Li content, and δ⁷Li and δ¹⁸O isotopic signatures in olivine and zircon are good indicators of mantle metasomatism and olivine fluid processes in magmatic Ni-Cu sulfide deposits.
... (1)~300 Ma aillikite, which had been regarded as kimberlite rocks in Zhang et al. (2013, 2)~290 Ma flood basalts and rhyolites (Tian et al., 2010;Zhou et al., 2009); and (3)~280 Ma A-type granites and maficultramafic intrusions as well as various alkaline mafic dykes Yu et al., 2011;Zhang et al., 2008;Zhang and Zou, 2013). ...
The Tarim large igneous province (TLIP) located in northwestern China is characterized by a relatively long duration of magmatism and complex lithology as compared to other global LIPs. Previous studies correlated these features to the interaction between mantle plume and subducted slab. However, no direct subduction-related magmatic records were so far recognized to support this interpretation. Here we report the petrological, mineralogical, and geochemical characteristics of a suite of ultramafic xenoliths occurring within aillikites from the northwestern margin of the TLIP. The xenoliths include dunite, wehrlite, olivine clinopyroxenite, clinopyroxenite, amphibole clinopyroxenite, clinopyroxene hornblendite, and hornblendite. These rocks show broadly similar mineralogy and are mainly composed of olivine, clinopyroxene and amphibole with rare phlogopite, chromite, and magnetite, in the absence of orthopyroxene and plagioclase. We evaluate the petrogenesis of these rocks based on whole-rock major and trace element compositions and mineral chemistry. The rocks exhibit enrichment of large ion lithophile elements (LILEs) relative to high field strength elements (HFSE) with negative Nb, Ta, and Ti anomalies, similar to the features of arc-like lavas. Their (⁸⁷Sr/⁸⁶Sr)t (0.7035–0.7041) and εNd(t) (1.17–5.67) values are consistent with depleted mantle source. The Mg# [molar Mg/(Mg + Fe²⁺)] and Fe³⁺# [molar Fe³⁺/(Fe³⁺+Al + Cr)] values of spinel in the ultramafic xenoliths are consistent with those of the Alaskan-type mafic-ultramafic intrusions. The Al2O3 contents in clinopyroxene increase with decreasing Mg#, which is comparable with the Al2O3 variation trend of clinopyroxene in Alaskan-type and arc-related magma, in contrast to those of the LIPs. Our data establish that the ultramafic xenoliths in the aillikites are comparable to Alaskan-type ultramafic complexes, and correspond to magmatism associated with the southward subduction of oceanic plate beneath the Tarim craton during Neoproterozoic or Early Paleozoic. Our study provides direct evidence for the interaction between mantle plume and subducted slab in generating the TLIP.
... In deviation to the previous models, our study shows that the TLIP has a strong continental rift affinity, where "triple junction" rift structure is expected to develop. Within this framework, the plume-derived material and heat will migrate and conduct along the rift structures and induce magmatism only at the intersection point with the CAOB, as exemplified by the Haladala gabbroic intrusions in the western part and Eastern Tianshan Ni-Cu-(PGE) sulfide deposits at the eastern part Yao et al., 2018;Zhang & Zou, 2013), instead of having a full impact on the CAOB. ...
... • Tarim LIP formation is attributed to decompression melting, plume excess temperature, high water contents, and slow plate motion velocities • The uplifted range of pre-eruption topography is only controlled by the plume radius and enables us to constrain the ancient mantle plume size well • We infer that the ancient Tarim plume had a very large radius of 200 km, a high excess temperature of~250 K, and a high water content of~5 wt.% is 160-200 km (Kumar et al., 2005;Priestley et al., 2006;Lei & Zhao, 2007;Bao et al., 2015). Many early Permian basalts, rhyolites, and mafic-ultramafic dikes crop out in the interior of the Tarim craton and around its margins, with an area and average thickness of approximately 250,000-300,000 km 2 and 600 m, respectively (Tian et al., 2010;Li et al., 2012;Zhang & Zou, 2013;Wei et al., 2014;Liu et al., 2014;Xu et al., 2014). Three episodes of volcanic activity occurred in the Tarim basin from the late Carboniferous to the early Permian ( Figure 1). ...
Large igneous provinces (LIPs) can form by interactions between a hot mantle plume and the lithosphere. The Tarim LIP between ~300 and 280 Ma, located in Northwest China, has been investigated by geochemistry and sedimentology studies. However, the factors controlling Tarim LIP formation and the ancient Tarim plume characteristics remain unclear. Here, a series of 3‐D geodynamic models are combined with geological observations to constrain the Tarim LIP evolution and the features of the related Tarim plume. Our results show that (1) an ancient plume produced abundant melts attributed to decompression melting, excess temperature, high water contents, and slow plate motion velocities to form the banded Tarim LIP. (2) The simulated pre‐eruption topography coincides with the stratigraphic records from the late Carboniferous to early Permian. Specifically, the swell area of pre‐eruption topography is sensitive only to the plume radius and enables us to constrain the ancient mantle plume size well. (3) Based on the volcanic activity and pre‐eruption topography, we infer that the ancient Tarim plume had a very large radius of ~200 km, a high excess temperature of ~250 K, and a high water content of ~5 wt.%. (4) Our parameter tests and global plate reconstruction results show that high water contents and slow plate motion velocities facilitate continental flood basalts to form with thick lithosphere. Our geodynamic modeling not only provides new constraints for the Tarim LIP evolution but also first quantificationally demonstrates that water in the mantle plays a key role in continental flood basalt formation.
... In deviation to the previous models, our study shows that the TLIP has a strong continental rift affinity, where "triple junction" rift structure is expected to develop. Within this framework, the plume-derived material and heat will migrate and conduct along the rift structures and induce magmatism only at the intersection point with the CAOB, as exemplified by the Haladala gabbroic intrusions in the western part and Eastern Tianshan Ni-Cu-(PGE) sulfide deposits at the eastern part Yao et al., 2018;Zhang & Zou, 2013), instead of having a full impact on the CAOB. ...
The Tarim large igneous province (TLIP) corresponds to a transitional large igneous province based on the high proportion of felsic rocks, classifying between mafic and silicic large igneous provinces. Here we investigate a bimodal suite including trachydacite, rhyolite, and basanite from the Northern Tarim Uplift using petrological, geochemical, stable, and radiogenic isotopic techniques with a view to understand the formation of the TLIP. Our study reveals a multistage origin involving multiple components, although the various rock suites are genetically linked and formed under a rift incubation setting related to mantle plume. The low δ²⁶ Mg values (−0.48‰ to −0.71‰), Fe/Mn > 60, FC3MS (FeOT/CaO‐3*MgO/SiO2) > 0.65, and high TiO2 contents (4.45–4.93 wt.%) of basanite from this suite suggest formation through partial melting of carbonated eclogite formed by recycled oceanic crust. The thick lithosphere beneath the Tarim Craton promoted extensive interaction between the underplated basaltic magmas and crust‐derived magmas leading to the formation of multistage magma chambers. Geochemical and mineralogical studies suggest that the trachydacite experienced a mixing, assimilation, storage, and hybridization process, whereas the rhyolite was produced by fractional crystallization from the associated mantle‐derived magma with significant crustal contamination. The abundance of amphibole in the trachydacite suggests a hydrous parental magma with H2O content in the range of 2.75 to 4.05 wt.%. Our results suggest that hydrous crustal components contributed significantly in the formation of voluminous felsic rocks of the TLIP.
... However, the geodynamic processes controlling the basaltic magmatism are still highly debated. The different views mainly are (a) the origin of the intrusions was considered to have evolved from basaltic magma, which generated from lithospheric mantle via a mantle plume Su et al., 2011;Xia, Jiang, & Xia, 2015;Zhang & Zou, 2013), or (b) induced by lithospheric delamination and asthenosphere upwelling in a convergent tectonic setting , or (c) in a post-orogenic extension setting (Ruan, 2017;Zhang, 2008), or (d) in an intracontinental rifting setting (Ma et al., 2016). In addition, the genesis of parental magma for the Bijiashan intrusion belt remains essentially unstudied. ...
The Bijiashan intrusion belt, one of the basic–ultrabasic intrusion belts in the Beishan Terrane, northeastern Tarim Craton, is composed of the Hongshishan, Hongshishanxi, Xuanwoling, Bijiashandong, and Bijiashan intrusions. These intrusions are mainly composed of dunite, troctolite, olivine gabbro, and gabbro. Magma evolution of the intrusions was strongly controlled by fractional crystallization, and the crystallization sequence was mainly olivine → plagioclase → pyroxene. This is evidenced by whole‐rock MgO contents that are positively correlated with TFe2O3 and negatively correlated with Al2O3, CaO, and Na2O and an increase in total rare‐earth element and trace elements contents from ultrabasic to basic rocks. Most of the basic–ultrabasic rocks are enriched in large ion lithophile elements (Cs, Rb, Sr, and U) and depleted of high field strength elements (Zr, Hf, Nb, Ta, and Ti). The variable and relatively low Ce/Pb (0.17–7.3) and Nb/U (0.13–10.1) ratios, variable Th/Yb (0.02–4.1) ratio, initial ⁸⁷Sr/⁸⁶Sr ratios (0.7033 to 0.7094) and εNd (t) (7.54 to −4.25), suggest less than 6% crustal contamination. Based on the maximum Fo value of olivine (Fo90), whole‐rock average composition and olivine–liquid compositional relationships, the parental magma is of high‐Mg basaltic magma containing 13.4 wt.% MgO. According to rare‐earth element contents and Sr–Nd isotopic compositions, the parental magma was originated from partial melting of depleted sub‐continental lithospheric mantle.
... North Tianshan, East Junggar, Altai and East Tianshan-Baishan) (Jahn, Wu & Chen, 2000a,b;Chen & Jahn, 2004;Wang et al. 2007;Geng et al. 2009;. Furthermore, Carboniferous-Permian intermediate-mafic dyke swarms (Yin et al. 2010;Feng et al. 2012;Zhang & Zou, 2013) are widespread in the Junggar and East Tianshan-Baishan areas, which supports the role of a mantle plume or superplume event (Stein & Hofmann, 1994;Condie, 1998;Pirajno et al. 2008Pirajno et al. , 2009. In the (Dy/Yb) N versus (Ce/Yb) N source discrimination diagram (Fig. 10), the linear relationship of our samples is consistent with a 'plume source'. ...
In this paper, zircon U–Pb geochronology, major and trace elements, and Sr–Nd isotope geochemistry of the Baiyanghe dolerites in northern West Junggar of NW China are presented. The U–Pb dating of zircons from the dolerites yielded ages of 272.2±4 Ma and 276.7±6.2 Ma, which indicate the emplacement times. The dolerites are characterized by minor variations in SiO 2 (46.89 to 49.07 wt%), high contents of Al 2 O 3 (13.60 to 13.92 wt%) and total Fe 2 O 3 (11.14 to 11.70 wt%), and low contents of MgO (2.67 to 3.64 wt%) and total alkalis (Na 2 O+K 2 O, 5.1 to 5.97 wt%, K 2 O/Na 2 O = 0.37–0.94), which indicate affinities to metaluminous tholeiite basalt. The REE pattern ((La/Sm) N = 2.25–2.34, (La/Yb) N = 7.42–8.36), V–Ti/1000 and 50*Zr–Ti/50–Sm discrimination diagrams show that these rocks are OIB-type. The high contents of Zr and Ti indicate a within-plate tectonic setting, and samples plot in the ‘plume source’ field shown on the Dy/Yb (N) versus Ce/Yb (N) diagram. The positive εNd(t) values (+7.09 to +7.48), high initial ⁸⁷ Sr/ ⁸⁶ Sr ratios (0.70442 to 0.70682) and depletions of Nb and Ta elements in the samples can be explained by the involvement of subducted sediments. In summary, it is possible that the Baiyanghe dolerites were derived from an OIB-like mantle source and associated with a mantle plume tectonic setting. Therefore, our samples provide the youngest evidence for the existence of a mantle plume, which may provide new insights into the Late Palaeozoic tectonic setting of West Junggar.
... They show genetic affiliation with the Tarim LIP in the western part of the Tarim craton ( Fig. 1) (Qin et al., 2011;Su et al., 2012a;Zhang et al., 2015). The Tarim LIP comprises coeval~250,000 km 2 of Permian volcanic rocks, mafic dykes and mafic-ultramafic intrusions, including Bachu, Wajilitag and Piqiang intrusions (e.g., Zhang et al., 2008a, 2010a,b, 2012, Zhang and Zou, 2013Li et al., 2011Li et al., , 2012aLi et al., ,b, 2014aXu et al., 2014;Cao et al., 2014). ...
The large Pobei Permian layered mafic–ultramafic complex in the northeastern margin of Tarim craton, western China is related temporally and spatially to adjacent Tarim Large Igneous Province (LIP), and hosts Ni–Cu sulfide mineralization. The chemical composition, carbon and noble gas isotopic compositions of volatiles in olivine, pyroxene and plagioclase minerals of the Pobei complex have been measured to reveal the composition and origin of magmatic volatiles, mantle information and dynamic settings. The magmatic volatiles in the Pobei complex are composed of dominant H2O (av. 3284.3 mm³·STP/g, STP = standard temperature and pressure), H2 (449.1) and CO2 (449.4), indicated a H2O-rich reduced magmatic condition. The δ¹³C values of CH4, C2H6, C3H8 and C4H10 show normal or (partial) reversal distribution pattern with carbon number. The δ¹³C values of CO2 and CH4 range among mantle, crust (methane oxidation) and thermogenic origins. The ³He/⁴He (1.13 to 6.15 Ra) and ⁴⁰Ar/³⁶Ar (326.4 to 1004.3) ratios are plotted on a trend of the mantle plume to atmosphere. The high ²⁰Ne/²²Ne and low ²¹Ne/²²Ne ratios fall along the mass fractionation line. The volatile compositions indicated that the Pobei mafic-ultramafic complex could be originated from the staged partial melting of heterogeneous H2O-rich mantle sources triggered by a mantle plume, the air and crust components from subducted altered oceanic crust have been added into the Pobei magma.
... A-type granites are anhydrous, alkaline, anorogenic, and high temperature magmas that generally reflect an extensional environment (Clemens et al. 1986;Eby 1990Eby , 1992Bonin 2007). The extensional environment in the Central Asian Orogenic Belt (CAOB) was proposed to be either post-collision extension settings (Han et al. 1997(Han et al. , 2010; slab break-off ; mantle plume (Zhang and Zou 2013); slab roll-back (Yin et al. 2015(Yin et al. , 2016; or ridge subduction (Geng et al. 2009;Shen et al. 2011;Tang et al. 2012a;Yang et al. 2014). Consequently, A-type granites provide significant information on magma sources and geodynamic mechanisms. ...
Zircon U–Pb ages, and geochemical, Sr–Nd and zircon Hf isotopic compositions are reported for the A-type granites and dikes in the Alataw Mountains of the northwestern Tianshan Orogenic Belt (NTOB), with the aim of investigating the sources and genesis of A-type granites and dikes. The laser ablation inductively coupled plasma mass spectrometry zircon U–Pb dating of A-type granites yielded a concordant weighted mean ²⁰⁶Pb/²³⁸U age of 297.4 ± 1.5 and 300.6 ± 0.9 Ma, respectively, defining a late Carboniferous–early Permian magmatic event. Geochemically, the granitic intrusions and dikes are characterized by high SiO2 and total alkalies (K2O + Na2O), high Zr, Nb, Ta content, and Ga/Al ratio with prominent negative Ba, Sr, P, Eu, and Ti anomalies. These features indicate that the granitic intrusions and dikes in the eastern Alataw Mountains are of an A-type affinity. The depleted Nd isotope compositions of the granitic intrusions and dikes are consistent with those of the Carboniferous volcanic rocks in the Alataw Mountains, especially Carboniferous adakites (εNd(t) = +3.6 to +6.6), suggesting that they were likely generated by partial melting of less evolved crustal materials, such as oceanic crust stored in the middle and/or lower crust or Carboniferous volcanic arc crust. The widespread late Carboniferous–early Permian magmatism in the NTOB may have been related to a ridge subduction accompanied by slab roll-back of the subducting plate of the North Tianshan Ocean.
... Previous studies documented that the magmatic rocks in the Chinese Southern Tianshan mountain range are dominantly of the late Carboniferous to early Permian age (Pirajno et al., 2008; 2015 and references therein), which roughly overlaps with the age span of the aforementioned magmatism in the TLIP. This closely temporal and spatial association has compelled some researchers to propose a single geodynamic process (e.g., lithospheric extension in a post-collisional tectonic setting or mantle plume model in anorogenic intraplate setting) to explain the roughly coeval magmatism in the northern Tarim Craton and Chinese Southern Tianshan mountain range (e.g., Yang et al., 2007;Zhang and Zou, 2013). However, the early Permian magmatic rocks in the northern Tarim Craton consist primarily of basaltic rocks with minor felsic rocks, whereas most of igneous rocks in the Chinese Southern Tianshan mountain range are granitoids over the course of late Paleozoic. ...
The Wajilitag and Puchang igneous complexes host two known economic Fe–Ti oxide deposits in the recently recognized Tarim large igneous province (TLIP). The Wajilitag complex comprises clinopyroxenite and melagabbro, whereas the Puchang complex is generally gabbroic and anorthositic in lithology apart from minor plagioclase–bearing clinopyroxenites in the marginal contact zone. The Fe–Ti oxide ores are disseminated throughout the Wajilitag complex and principally restricted to the ultramafic unit, whereas the Puchang complex contains massive to disseminated Fe–Ti oxide ores mainly hosted within the gabbroic rocks. Both secondary ion mass spectroscopy and laser ablation–inductively coupled plasma–mass spectrometry U–Pb dating of zircon grains from the Wajilitag and Puchang complexes yield U–Pb zircon ages of ca. 283 Ma and ca. 275 Ma, respectively, clearly indicating that there were two independent episodes of the magmatic events related to Fe–Ti oxide mineralization in the TLIP. The new zircon U–Pb ages of intrusive rocks studied here, coupled with available geochronological data from elsewhere in the TLIP, show a long duration of magmatism (up to 30 Myr), although the precise age of the TLIP remains to be determined. The two complexes are late–stage events that notably postdate most, if not all, the basaltic lava flows. Furthermore, the occurrence of the earliest manifestation (e.g., ca. 300 Ma kimberlitic rocks) of a proposed mantle plume in the Bachu area and the potential temporal migration of the late–stage magmatism from the Bachu and Keping areas to the edges of the Tarim Craton, indicate a possible plume centre near the Bachu–Keping district. The εHf(t) values of zircons from each complex show a range of several εHf(t) units (Wajilitag: + 2.7 to + 9.2, Puchang: − 5.2 to + 2.6), probably suggesting late-stage crustal contamination in magma chambers at the time of zircon saturation. Unlike the Lu–Hf isotopic system, the zircons may preserve the original O isotope signature of their mantle sources. The increase of O isotopic composition from the Wajilitag complex (δ18O = 5.2–5.9‰) to the Puchang complex (δ18O = 5.6–7.1‰‰), indicate a relatively high proportion of recycled subduction–related materials (e.g., eclogite and garnet pyroxenite) incorporated into the subcontinental lithospheric mantle source for the Puchang intrusive rocks. Partial melting of the refertilized subcontinental lithospheric mantle with the involvement of garnet–bearing mafic components can be of great importance for the formation of parental Fe–rich magmas and ultimately Fe–Ti oxide deposits. This observation is consistent with the occurrence of some mineralized LIPs (e.g., Emeishan) in formerly active convergent plate margins of ancient cratonic blocks, contributing to a global understanding valuable to exploration efforts.
... However, we noticed that the gabbros in the Longyou Group have elevated Nb/La ratios (0.25-0.7) and Nb/Th ratios (5-15) compared with that of the Nb-enriched gabbros. Thus, we suggest that these gabbros were most possibly derived from previous metasomatized mantle source with variable involvement of magma derived from sub-lithospheric mantle source (e.g., Neal et al., 2002;Pearce, 2008;Zhang and Zou, 2013). ...
For better understanding the Caledonian tectonic event of Cathaysia block, this paper documents a set of new zircon U-Pb geochronological and Hf isotopic analytical results for the Caledonian massive and gneissic granites from Wuyishan-Jinggangshan area. Crystallization ages of gneissic granites range from 415 Ma to 440 Ma, crystallization ages of massive granites range from 430 Ma to 449 Ma. The ϵ Hf(t) values of zircons range from -20 to 0(n=247), most data below -10. The two stage Hf model ages (tdmc) range from 1.5 Ga to 2.8 Ga. Combined with previous data, the authors revealed that the formation age, zircon Hf isotopic form and two stage Hf model ages (tdmc) of the two kinds of granite are similar. Granites were derived from crustal source of different times, which recycled during Caledonian. In addition, the addition of juvenile mantle-derived magma was insignificant. The Caledonian tectothermal event of Cathaysia block took place within an intracontinental orogenic environment. Caledonian orogen may have transformed its tectonic regime at about 43OMa, and gneissic structure resulted from synorogenic or late-orogenic deformation.
... There are many examples of dyke swarms hosted by a magmatic arc with a close spatial, temporal and genetic relationship with it (Llambías and Sato, 1990;Chen and Moore, 1979;Coleman et al., 1994;Carracedo et al., 1997;Teixeira et al., 2002;El-Sayed, 2006;Zhang and Zou, 2012). In general, these swarms show transitional geochemical features between subduction-related magmatic arc and collisional or continental within-plate settings. ...
... Some researchers (Zhou et al., 2004) suggested that they are the products of a Permian mantle plume beneath East Tianshan. Other researchers proposed that they belong to the Tarim mantle plume (Pirajno et al., 2008;Qin et al., 2011;Su et al., 2011;Zhang and Zou, 2013). The Tarim mantle plume is inferred from the Permian alkaline basalts that are present in the western part of the Tarim basin and characterized by OIB-like trace element compositions (Tian et al., 2010;Zhou et al., 2009). ...
The convenient mantle plume model for the Permian protracted mafic–ultramafic intrusions and mafic dykes (266–286 Ma) in the Beishan–Tianshan region, northern Xinjiang, western China can be rejected, because their temporal–spatial distribution does not show a hotspot track predicted by such model. New zircon U–Pb ages reveal that two small mafic dyke clusters (Podong, 280.5 ± 2 Ma; Luodong, 266.2 ± 3.2 Ma) that are separated by only ~ 20 km in the Pobei area, the southernmost part of the Beishan–Tianshan region, have a large age difference of ~ 18 Ma. The older mafic dykes are characterized by nearly flat mantle-normalized rare-earth-element patterns, pronounced negative Nb–Ta anomalies and positive εNd(t) values from 5.5 to 7.5, similar to the majority of the Permian mafic–ultramafic intrusions in the region. The younger mafic dykes are characterized by significant light rare-earth-element enrichments as well as pronounced negative Nb–Ta anomalies, plus lower εNd(t) (− 1.2 to 2.6) values and higher initial 87Sr/86Sr ratios than the older mafic dykes. The observed compositional variations can be explained by source mantle heterogeneity plus different degrees of crustal contamination. Overall, the Permian mafic–ultramafic rocks in the Beishan–Tianshan region are geochemically consistent with the products of basaltic magmatism induced by lithospheric delamination and asthenosphere upwelling in a convergent tectonic zone.
Numerous Late Carboniferous – Early Permian dykes are found in West Junggar and represent an important part of the Central Asian Orogenic Belt. In this contribution, we use these dykes to assess the tectonic regime and stress state in the Late Carboniferous – Early Permian. The West Junggar dykes are mainly diorite/dioritic porphyrite with minor diabase and were formed in 324–310 Ma. They have been divided into two groups based on their orientation, petrology and geochronology. Group 1 dykes mostly comprise WNW-striking dioritic porphyrite and NE-striking diorite with minor diabase and resemble the Karamay-Baogutu sanukitoid. They were probably formed from depleted mantle at a relatively high temperature and pressure with the addition of 1–2% sediment/sedimental partial melt and 0–5% trapped oceanic crust-derived melts. Group 2 dykes are ENE-striking and are similar to sanukite in the Setouchi Volcanic Belt. These dykes were also derived from depleted mantle at a shallow depth but high temperature with the addition of 2–3.5% sediment/sedimental partial melt. Magma banding and injection folds in dykes and host granitoids indicate magma flow. Paleostress analysis reveals that both groups of dykes were formed in a tensile stress field. Their emplacement is favoured by presence of pre-existing joints or fractures in the host granitoids and strata. We conclude that large-scale asthenosphere mantle upwelling induced by trapped oceanic slab-off can explain the magmatism and significant continental crustal growth of West Junggar during Late Carboniferous to Early Permian.
Tungsten (W) deposits are commonly related to the exsolution of magmatic‐hydrothermal fluids from high‐Si granites (SiO 2 > 70%). However, whether the W‐related high‐Si granitic magma is produced via partial melting of metasedimentary source rocks or by high degree of fractional crystallization remains controversial. Here we present new geochronological and geochemical data on the intrusions associated with the Lyangar W‐Mo skarn deposit in the Southern Tianshan Orogenic Belt, Uzbekistan. Our new U–Pb zircon age data show that the major intrusion exposed in the region are ca. 280 Ma biotite gabbroic diorite and biotite granite and about 260 Ma porphyritic granite and muscovite porphyritic granite. The molybdenite grains in the skarn rocks and orebodies show weighted Re‐Os ages of 261.4 ± 7.8 Ma and 261.1 ± 3.8 Ma, respectively. In combination with the field contact, we confirm that the muscovite porphyritic granite is genetically related to the W mineralization. The gradual transition from the porphyritic granite to muscovite porphyritic granite, similar mineral assemblages and geochemical variations indicate that they are co‐magmatic, and that the porphyritic granite represents less evolved member. Rhyolite‐MELTS modeling further reinforces that the muscovite porphyritic granites can be produced by high degree of fractional crystallization (~33%, including ~1.2% biotite, ~27% plagioclase, ~2% alkali‐feldspar, ~0.21% Fe‐Ti oxides, and ~2.7% amphibole) of the porphyritic granite magma. On the basis of the positive Ɛ Hf (t) values (+3.03 to +6.02), high‐SiO 2 contents and CIPW characters, the porphyritic granite is considered to have formed from dehydration melting at low pH 2 O of juvenile basaltic source rocks around 16 kbar and 850–1000°C. Our study demonstrates that extreme fractional crystallization of granitic magma plays a significant role in W enrichment in the granitic melt.
The Permian mafic dykes of Santanghu Basin offer an opportunity to study the nature of mantle source and tectonic setting of the basin, as well as to provide the theoretical basis for structural transformation of East Junggar region. In this study, zircon U–Pb geochronology, mineral composition analysis, whole-rock elemental, and Sr-Nd isotopic geochemistry were conducted to explore the origin and evolution of the primitive magma. LA-ICPMS zircon U–Pb dating yields ages at 269 Ma. The elemental geochemistry results suggest enrichments in Ba, Pb, and Sr but depletions in Nb, Ta, Zr, and Hf, which indicate that the magma source was influenced by fluid metasomatism. All samples show moderate initial Sr-Nd isotope results ((⁸⁷Sr/⁸⁶Sr)I = 0.704299 to 0.704490 and εNd(t) = +6.16 to +6.83) and have high Sm/Yb ratios, which suggest that the diabases were derived from partial melting of 5%–7% spinel-garnet Iherzolite lithospheric mantle. Combined with petrological, geochronological data, and the regional tectonic background, it is interpreted that the diabases from Santanghu Basin originated from lithospheric mantle metasomatized by subduction fluids under the background of intracontinental extension.
The igneous units of Permian Tarim Large Igneous Province (TLIP) is typically characterized by alkaline affinity. Here we report for the first time the petrological, geochemical and isotopic characteristics of phonotephrite and phonolite dykes from the Wajilitag complex in the northwestern margin of TLIP. Our data, especially Sr-Nd-Mg isotopes, suggest that the dykes have different mantle sources. Phonotephrite with mantle-like Mg values (δ²⁶Mg =-0.295--0.330‰), relatively enriched Sr isotopes ((⁸⁷Sr/⁸⁶Sr)t=0.70487-0.70574) and slightly lower εNd(t) values (εNd(t)=-0.23-+2.06), were possibly derived from a lithospheric mantle source that was metasomatized by calcitic carbonate melt. The phonotephrites are highly evolved rocks formed through fractional crystallization from a parental magma which is similar to that of the mafic-ultramafic intrusions. Phonolites show relatively depleted Sr isotopes ((⁸⁷Sr/⁸⁶Sr)t=0.70362-0.70409), higher εNd(t) values (εNd(t)=+1.27-+3.45), markedly lighter Mg isotopes (δ²⁶Mg =-0.851--0.906‰) than the normal mantle indicating a mantle plume source with the involvement of carbonated eclogite. The parental magma of phonolites may be related to the liquid immiscibility with calciocarbonatites present in the Wajilitag complex due to their similar extremely light Mg isotopic compositions. The distinct geochemical features between two series of dykes in the Wajilitag complex reflect the diversity of mantle source of the TLIP, and their Sr-Nd-Mg isotopic characteristics indicate the role of subducted recycled sedimentary carbonates at different depths in the mantle.
The studied area (Galali- Varmaqan) located at the northern part of the Sanandaj- Sirjan zone, south of the Qorveh city. The granitic rocks are dominated by quartz, alkali- feldspar and plagioclase. Amphibole and biotite are the most important mafic minerals, apatite, sphene, zircon and Fe- oxides are the accessories. The Galai- Varmaqan granitoids show geochemical characteristics of metaluminous A-type granites with mainly shoshonitic and high- K calc- alkaline affinity. Based on geotectonic diagrams, these rocks are mostly clusterred at the volcanic arc granites (VAG) and within plate granites (WPG) fields which points to their formation in a post- orogenic magmatic system. LILEs and HFSEs enrichment indicates the existence of a crustal source for the studied granites and formation of the parent magma at the stability field of plagioclase in the lack of garnet. In this study, we suggest that the A-type granites have been formed by partial melting of lower crust charnokitic rocks. The A-type granites are related to extensional magmatism of the Neo- Tethys oceanic crust beneath the Central Iranian microcontinent, due to roll- back of subducting slab. Thus, change of tectonic regime from compressional to tensional in the late- Jurassic to early- Cretaceous time (probably in a pull-apart basin tectonic setting), is suggested for the formation of A-type granites in this region of the Sanandaj- Sirjan zone.
Geological study of the Khan Tengri and Pobedi massifs highlights two phases of compressional fault displacements. A Late Permian/Triassic displacement phase is highlighted (1) by biotite ⁴⁰Ar/³⁹Ar ages of 265–256 Ma, suggestive of cooling of Pobedi mid-crustal granulites during >8 km of top-to-the-north motion of the Pobedi Thrust; (2) by ⁴⁰Ar/³⁹Ar dating of syn-kinematic phengite at 249–248 Ma, which suggests a crystallization age during top-to-the-south motion of the Khan Tengri Thrust shear zone; (3) by Apatite Helium (AHe) ages of 280-240 Ma on the crystalline basement below the Mesozoic peneplain, which gives insight into the final exhumation stage. Cenozoic reactivation of the Pobedi Thrust is indicated by AHe thermochronology with a mean age of 8.3 ± 2.5 Ma, in agreement with ∼3 km exhumation and ∼4.2 km of top-to-the-north motion in the Late Miocene. Along a north-south transect of the west Tian Shan range from Issyk-Kul Lake to Tarim Basin, compiled thermochronological data outline out-of-sequence deformation beginning with the activation of north-directed crustal-scale faults at 22-15 Ma along the northern margin of the north Tian Shan, followed by 20-10 Ma motion at the boundary between the Middle and the South Tian Shan, and ending with the <10 Ma reactivation of the Pobedi Thrust in the South Tian Shan. This latter coincided with south-directed motion on the South Tian Shan Front (the Maidan Fault) and fold and thrust belt propagation towards the Tarim Basin.
We identify an early Neoproterozoic Large Igneous Province (LIP) fragment in the South Tarim Terrane (STT) of the NW China (herein term as the Sailajiazitage LIP fragment). The thickness of the volcanic sequence, mainly composed of basalts (ca. 4600 m) and minor rhyolites (ca. 800 m), is up to ca.5300 m. Four zircon samples from the three units of rhyolite at the top, middle and lower parts of the lava sequence yield consistent and concordant SHRIMP/LA-ICPMS U-Pb ages of 895.8 ± 3.7 /892.0 ± 4.1 Ma, 891.8 ± 3.5/894.5 ± 5.8 Ma, 899.0 ± 4.6/893.0 ± 5.9 Ma and 884.5 ± 4.9/894.2 ± 4.8 Ma, respectively, indicating the short duration of the thick volcanic sequence. Systematic geochemical data revealed that the basalts were derived from partial melting of a depleted asthenenospheric mantle source coupled with variable degrees of AFC effect. The rhyolites show typical A-type (or A1-type) granite geochemical features as demonstrated by their high HFSE contents (e.g., Zr = 400–900 ppm, Nb = 70–140 ppm). Both elemental and Nd-Hf-O isotope compositions argue that the silicic magma was the daughter product of the intensive fractionation of the coeval basalts and their zirconium saturation temperature was up to 900 °C, significantly higher than those of A-type granites emplaced in a post-orogenic setting but consistent with those A-type granites genetically related to a mantle plume. Its huge thickness (>5300 m), short duration at ca. 890 Ma and typical continental flood basalt (CFB) geochemical features argue for this being a fragment of an early Neoproterozoic LIP and likely proximal to its plume centre.
The c. 890 Ma age suggests a link with the previously proposed reconstruction of North China, São Francisco and Congo cratons, based on their shared 920–890 Ma LIP fragments. This study supplies further evidence for a ca. 920–890 Ma plume or superplume inducing the initial breakup of the supercontinent Rodinia.
The Permian Tarim large igneous province (TLIP) is located in the Tarim basin, NW China. Although the flood basalt of the TLIP has been intensively studied, other igneous components within TLIP have not yet been sufficiently investigated. The Wajilitag igneous complex is outcropped with a rather limited exposure by regional tectonic uplift. However, various igneous rocks, both mafic–ultramafic and syenitic, can be observed as either intrusions or extrusions in this area. It is an ideal location for studying the magmatic evolution of different components within the TLIP. We systematically examine the geological, geochronological, and geochemical characteristics of the Wajilitag complex, to further constrain the petrogenesis of each component and their interrelationships, as well as the implications to the petrogenetic model of TLIP. The igneous rocks in Wajilitag complex can be classified into two series based on their geochemical features: Series A and Series B. Series A are more alkalic, more trace element enriched and more isotopically depleted than Series B. Series A includes nephelinite, aegirine–nepheline syenite (ANS), and syenite porphyry (SP), whereas the Series B consists of clinopyroxenite, gabbro, diorite, hornblende-bearing syenite (HS), and quartz syenite (QSN). Dolerites can either belong to Series A or Series B depend on its geochemistry. Kimberlitic rocks are independent of the Wajilitag complex geologically, geochemically, and geochronogically. The temporal sequences of Wajilitag complex would be clinopyroxenite→gabbro→ diorite/syenite→nephelinite. The dolerite can be emplaced later than the syenite but can extend to an earlier period. In contrast to the Tarim basalts, the Wajilitag complex belongs to the second stage of magmatism in the TLIP. The mantle source for the Tarim basalts, the Series B and Series A gradually changed from SCLM-dominated to plume-dominated component.
The Chinese Tianshan is located in the south of the Central Asian Orogenic Belt and formed during final consumption of the Paleo-Asian Ocean in the late Palaeozoic. In order to further elucidate the tectonic evolution of the Chinese Tianshan, we have established the temperature-time history of granitic rocks from the Chinese Tianshan through a multi-chronological approach that includes U/Pb (zircon), ⁴⁰Ar/³⁹Ar (biotite and K-feldspar), and (U-Th)/He (zircon and apatite) dating. Our data show that the central Tianshan experienced accelerated cooling during the late Carboniferous- to early Permian. Multiple sequences of complex multiple accretionary, subduction and collisional events could have induced the cooling in the Tianshan Orogenic Belt. The new ⁴⁰Ar/³⁹Ar and (U-Th)/He data, in combination with thermal history modeling results, reveal that several tectonic reactivation and exhumation episodes affected the Chinese central Tianshan during middle Triassic (245–210 Ma), early Cretaceous (140–100 Ma), late Oligocene-early Miocene (35–20 Ma) and late Miocene (12–9 Ma). The middle Triassic cooling dates was only found in the central Tianshan. Strong uplift and deformation in the Chinese Tianshan has been limited and localized. It have been concentrated in around major fault zone and the foreland thrust belt since the early Cretaceous. The middle Triassic and early Cretaceous exhumation is interpreted as distal effects of the Cimmerian collisions (i.e. the Qiangtang and Kunlun-Qaidam collision and Lhasa-Qiangtang collision) at the southern Eurasian margin. The Cenozoic reactivation and exhumation is interpreted as a far field response to the India-Eurasia collision and represents the beginning of modern mountain building and denudation in the Chinese Tianshan.
Three Fe–Ti oxide-bearing layered intrusions (Mazaertag, Wajilitag, and Piqiang) in the Tarim large igneous province (NW China) have been investigated for understanding the relationship of sulfide saturation, Platinum-group element (PGE) enrichment, and Fe–Ti oxide accumulation in layered intrusions. These mafic-ultramafic layered intrusions have low PGE concentrations (<0.4 ppb Os, <0.7 ppb Ir, <1 ppb Ru, <0.2 ppb Rh, <5 ppb Pt, and <8 ppb Pd) and elevated Cu/Pd (2.2 × 104 to 3.3 × 106). The low PGE concentrations of the rocks are mainly attributed to PGE-depleted, parental magma that was produced by low degrees of partial melting of the mantle. The least contaminated rocks of the Mazaertag and Wajilitag intrusions have slightly enriched Os isotopic compositions with γOs(t = 280 Ma) values ranging from +13 to +23, indicating that the primitive magma may have been generated from a convecting mantle, without appreciable input of lithospheric mantle. The Mazaertag and Wajilitag intrusions have near-chondritic γOs(t) values (+13 to +60) against restricted ε
Nd(t) values (−0.4 to +2.8), indicating insignificant crustal contamination. Rocks of the Piqiang intrusion have relatively low ε
Nd(t) values of −3.1 to +1.0, consistent with ∼15 to 25 % assimilation of the upper crust. The rocks of the Mazaertag and Wajilitag intrusions have positive correlation of PGE and S, pointing to the control of PGE by sulfide. Poor correlation of PGE and S for the Piqiang intrusion is attributed to the involvement of multiple sulfide-stage liquids with different PGE compositions or sulfide-oxide reequilibration on cooling. These three layered intrusions have little potential of reef-type PGE mineralization. Four criteria are summarized in this study to help discriminate between PGE-mineralized and PGE-unmineralized mafic-ultramafic intrusions.
The Balkhash metallogenic belt (BMB) in Kazakhstan is a famous porphyry Cu–Mo metallogenic belt in the Central Asian Orogenic Belt (CAOB). The late Palaeozoic granitoids in the BMB are mainly high-K calc-alkaline and I-type granites, with shoshonite that formed during a late stage. Geochemical analyses and tectonic discrimination reveal a change in the tectonic environment from syn-collision and volcanic arcs during the Carboniferous to post-collision during the Permian. The late Palaeozoic granitoids from the Borly porphyry Cu deposit formed in a classical island-arc environment, and those from the Kounrad and Aktogai porphyry Cu deposits and the Sayak skarn Cu deposit are adakitic. The εNd(t) values for the late Palaeozoic granitoids are between −5.87 and +5.94, and the εSr(t) values range from −17.16 to +51.10. The continental crustal growth histories are different on either side of the Central Balkhash fault. On the eastern side, the εNd(t) values of the granitoids from the Aktogai and Sayak deposits are very high, which are characteristic of depleted mantle and suggest that crustal growth occurred during the late Palaeozoic. On the western side, the εNd(t) values of the granitoids from the Borly and Kounrad deposits are slightly low, which suggests the presence of a Neoproterozoic basement and the mixing of crust and mantle during magmatism. The granitoids have initial 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values of 18.335–20.993, 15.521–15.732, and 38.287–40.021, respectively, which demonstrate an affinity between the late Palaeozoic magmatism in the BMB and that in the Tianshan, Altai, and Junggar orogens.
The Solonker ophiolite is exposed along the border between Mongolia and China within the Solonker zone, the southeastern Central Asian Orogenic Belt (CAOB), and it is composed dominantly of serpentinized peridotite with subordinate gabbro, basaltic lava, radiolarian-bearing siliceous rocks, and minor plagiogranite. Meanwhile, layered mafic-ultramafic cumulates are not ubiquitous. In this study, zircon grains from two gabbros and a plagiogranite yield 206Pb/238U ages of 259 ± 6 Ma, 257 ± 3 Ma and 263 ± 1 Ma. These data were interpreted to represent the formation age of the Solonker ophiolite. The studied gabbros and basalts have a tholeiitic composition, showing a MORB affinity. They are also characterized by enrichment of Pb and depletion of Nb relative to La and Th. Furthermore, the studied gabbros contain inherited zircon grains and display a large range of zircon Hf isotopes (εHf(t) = - 5.27 to + 10.19). These features imply that crustal contamination played an important role in the generation of these mafic rocks. Major elements derived from the radiolarian-bearing siliceous rocks suggest a continental margin setting. This is confirmed by rock association. Terrigenous rocks (sandstones and siltstones) interstratified with siliceous rocks. U-Pb dating of detrital zircon grains in sandstones from both the northern and southern sides of the Solonker ophiolite belt, along with published data, reveals that the Late Carboniferous-Early Permian strata in fault contact with the Solonker ophiolite was deposited above Early Paleozoic orogens. The lines of petrological, geochemical, geochronological, and isotopic evidence led us to propose that the Solonker ophiolite is a Late Permian continental margin-type body formed during the early stages of opening of an ocean basin, following rifting and break-up of the Early Paleozoic orogens. Accordingly, the Permian Solonker zone is characterized by an intra-continental extensional setting.
Huge Permian basalts and igneous rocks related (260-292 Ma), occurred in the Tarim Basin, Xinjiang are mainly composed of basalts, diabases, basaltic andesites, ultramafic rocks and syenites. This study is the first report of the quartz syenitic porphyritic dyke occurred in Shuigongtuan of Bachu County, Tarim Basin. The quartz syenitic porphyry in this dyke is metaluminous (A/CNK < 1), and has SiO2 of 66-67%, enriched in K2O + Na2O(10-11%) and K2O/Na2O(0.8-0.9), and low Mg/(Mg + Fe) ratios. The rocks are enriched in LILE (Ba,Rb) and HSFE (Zr,Nb,Y), Ga/Al ratios and total rare earth elements (631-734 × 10-6), high LREE/HREE ratios, and having negative Eu anomalies. The chemical characteristics and tectonic discriminative diagrams show that the rocks have geochemical affinity with A - type granites. Low Y/Nb (0.4) < 1.2, and enriched in LILE and Nb evenness - enrichment in the spider diagram indicates typical within - plate environment and a source from mantle, which may be derived from hot basic magma by fractional crystallization. Compared with the Xiaohaizi syenites, the quartz syenitic porphyry has almost the same geochemical characteristics, and they may be derived from the same source. The concordia age of 277Ma 4 Ma was obtained from the Xiaohaizi syenitic body by the SHRIMP U - Pb zircon age dating in this study, indicating that the intrusive age of the Xiaohaizi syenitic body is approximately 277Ma. Based on the present study, the Shuigongtuan quartz syenitic porphyritic dyke and Xiaohaizi syenitic body probably formed during Early Permian (277Ma), and represented the products of within - plate environments, indicating the end of the last large magmatic thermal event happened in the Tarim Basin.
Twenty six samples representing the wide range of lithologies drilled during Leg 125 at Sites 782 and 786 on the Izu-Bonin outer-arc high have been analyzed for Sr, Md and Pb isotopes. In all isotopic projections, the samples form consistent groupings: the tholeiites from Site 782 and Hole 786A plot closest to PMM, the boninites and related rocks from Sites 786B plot closest to PVS, and the boninite lavas from Hole 786A and late boninitic dikes from Hole 786B occupy an intermediate position. Isotope-trace element covariations indicate that these isotopic variations can be explained by a three-component mixing model. -from Authors
After comparing study on Permian basalts from Stantanghu basin eastern of Xinjiang and Liuyuan area of Beishan western of Gansu, on the basis of geochemical characteristics, it is concluded that nearly synchronogenic basalts from Permian fault basins of eastern Xinjiang-Beishan area have different geochemical characteristics and magma sources. A united dynamic model is presented, which is that eastern Xinjiang-Beishan area was under the rift-extensional tectonic setting in early Permian which might be a result from both upwelling of partial melting asthenospheric mantle induced by delamination of thickened subcontinental mantle root, and upwelling of small mantle plume from the boundary between upper mantle and lower mantle. This kind of small mantle plume is not from boundary between core and mantle, but may be from boundary between upper mantle and lower mantle where partial melting of pyrolites brought about after subducted oceanic crust fell down. In Permian, upwelling of partial melting asthenospheric mantle induced by delamination of thickened subcontinental mantle root and upwelling of small mantle plume from the boundary between upper mantle and lower mantle was likely the most magnificent crust-mantle interaction that made Central Asian Orogenic Belt (CAOB) distinguished from other orogenic belts, with intense basalt eruption, formation of fault basins, prominent metallogenesis, and emplacement of voluminous granitic and mafic-ultramafic rocks with positive εND (t).
Southern Tianshan is one of the regions with most complex structural evolution history in the Tianshan Orogenic belt. Compared with other regions in the northern Xinjiang, studies on problems of continental dynamics of the post-collision procedure and the magma genesis are relatively weak. Baleigong pluton, which is located in the southwestern section of the Southern Tianshan, is carefully studied in this study. Based on geochemistry and geochronology, the petrogenesis, characteristics of the magma source, as well as the geodynamic are discussed, in order to provide some constraints for the further studies on the evolutionary patterns of the ocean-crust system in the region such as closure of the oceanic crust and timing of the collisional orogeny. The Baleigong pluton located in the Southwestern Kokshal area, the western segment of the Southwestern Tianshan; and emplaced into the south of the Baleigong ophiolitic m lange. Lithologically, the pluton consists mainly of biotite moyites. Geochemically, the rocks are high-K calc-alkaline to shoshonitic series, and rich in alkali (K2O + Na2O 8.25% - 8.72%) and K (K2O/Na2O 1.34 - 1.56), with the A/CNK values between 0.94 and 1.05, which fall into the range of metaluminous to slightly peraluminous rocks. The rocks are also characterized by enrichment of LREE and LILE (Cs, Rb, Th and Ba) and depletion of Sr, P, Nb and Ti, with moderate negative Eu anomaly (δEu 0.49 - 0.59), showing the transitional features between high-K catc-alkaline and A-type granites. The elemental ratios of the Baleigong pluton, such as Nd/Th (1.64 - 3.19), Th/U (5.95 - 7.11), Nb/Ta (7.26 - 9.17, combined with the high K2O/Na2O and low Sr/Ba ratios, indicate the partial melting of middle to lower crust with intermediate magmatic rocks as protoliths, with plagioclase amphibolite as the restite. In situ zircon U-Pb LA-ICP-MS dating on the magmatic genetic zircons yielded an age of the 273 ± 2Ma, representing the emplacement age of the pluton. Combined with the previous studies, it is concluded that the Late Paleozoic post-collisional granitic magmatism in the South Tianshan took place in the period between 282 and 259Ma and obviously later than that of other areas in the Northern Xinjiang. Together, these studies also indicate that the post-collisional granitic magmas evolved from high-K calc-alkaline series (282 - 266Ma) to alkaline series (266 - 259Ma) successively, which suggest the process of orogenic collapse and continuously extensional tinning of the continental crust during the post-collisional stage. The Baleigong high-K granite was probably formed during the first stage of the collapse after the collisional orogeny or during the transitional stage between collision and post-collision, by partial melting of the middle to lower crust materials. The post-collisional magmatism in the South Tianshan indicates that before the Middle Permian, the Paleozoic South Tianshan Ocean has been closed and the South Tianshan was in a post-collisional setting, which probably represents the last closure of southern part of the Paleo-Asia oceanic crust, as well as the ending of the accretionary orogeny in the southern section of the Central Asia. These conclusions provide some new constraints to the further study on the timing and petrogenesis of the post-collisional magmatism in the Central Asia.
SUMMARY: Trace-element data for mid-ocean ridge basalts (MORBs) and ocean island basalts (OIB) are used to formulate chemical systematics for oceanic basalts. The data suggest that the order of trace-element incompatibility in oceanic basalts is Cs ≈ Rb ≈ (≈Tl) ≈ Ba(≈ W) > Th > U ≈ Nb = Ta ≈ K > La > Ce ≈ Pb > Pr (≈ Mo) ≈ Sr > P ≈ Nd (> F) > Zr = Hf ≈ Sm > Eu ≈ Sn (≈ Sb) ≈ Ti > Dy ≈ (Li) > Ho = Y > Yb. This rule works in general and suggests that the overall fractionation processes operating during magma generation and evolution are relatively simple, involving no significant change in the environment of formation for MORBs and OIBs.
In detail, minor differences in element ratios correlate with the isotopic characteristics of different types of OIB components (HIMU, EM, MORB). These systematics are interpreted in terms of partial-melting conditions, variations in residual mineralogy, involvement of subducted sediment, recycling of oceanic lithosphere and processes within the low velocity zone. Niobium data indicate that the mantle sources of MORB and OIB are not exact complementary reservoirs to the continental crust. Subduction of oceanic crust or separation of refractory eclogite material from the former oceanic crust into the lower mantle appears to be required. The negative europium anomalies observed in some EM-type OIBs and the systematics of their key element ratios suggest the addition of a small amount (≤1% or less) of subducted sediment to their mantle sources. However, a general lack of a crustal signature in OIBs indicates that sediment recycling has not been an important process in the convecting mantle, at least not in more recent times (≤2 Ga). Upward migration of silica-undersaturated melts from the low velocity zone can generate an enriched reservoir in the continental and oceanic lithospheric mantle. We propose that the HIMU type (eg St Helena) OIB component can be generated in this way. This enriched mantle can be re-introduced into the convective mantle by thermal erosion of the continental lithosphere and by
Huge Permian basalts and igneous rocks related (260-292 Ma), occurred in the Tarim Basin, Xinjiang are mainly composed of basalts, diabases, basaltic andesites, ultramafic rocks and syenites. This study is the first report of the quartz syenitic porphyritic dyke occurred in Shuigongtuan of Bachu County, Tarim Basin. The quartz syenitic porphyry in this dyke is metaluminous (A/CNK < 1), and has SiO2 of 66-67%, enriched in K2O + Na2O(10-11%) and K2O/Na2O(0.8-0.9), and low Mg/(Mg + Fe) ratios. The rocks are enriched in LILE (Ba,Rb) and HSFE (Zr,Nb,Y), Ga/Al ratios and total rare earth elements (631-734 × 10-6), high LREE/HREE ratios, and having negative Eu anomalies. The chemical characteristics and tectonic discriminative diagrams show that the rocks have geochemical affinity with A - type granites. Low Y/Nb (0.4) < 1.2, and enriched in LILE and Nb evenness - enrichment in the spider diagram indicates typical within - plate environment and a source from mantle, which may be derived from hot basic magma by fractional crystallization. Compared with the Xiaohaizi syenites, the quartz syenitic porphyry has almost the same geochemical characteristics, and they may be derived from the same source. The concordia age of 277Ma 4 Ma was obtained from the Xiaohaizi syenitic body by the SHRIMP U - Pb zircon age dating in this study, indicating that the intrusive age of the Xiaohaizi syenitic body is approximately 277Ma. Based on the present study, the Shuigongtuan quartz syenitic porphyritic dyke and Xiaohaizi syenitic body probably formed during Early Permian (277Ma), and represented the products of within - plate environments, indicating the end of the last large magmatic thermal event happened in the Tarim Basin.
This article summarizes the geological setting, spatial-temporal distribution, and major-element, trace-element, and Nd-Sr-Pb isotopic compositional variation of rocks representative of Tibetan postcollisional magmatic activity. The implications of petrogenesis and spatial-temporal distribution are discussed in relation to lithospheric mantle heterogeneity and a possible role for collision-induced asthenospheric mantle flow. Rocks indicative of postcollisional volcanism are widely distributed across the terranes making up the Tibetan plateau. Three stages of activity are recognized (ca. 45-25, 25-5, and 5-0 Ma), mostly conforming to potassic to ultrapotassic shoshonitic and high-potassium calc-alkaline types. These show strong relative enrichments in large-ion lithophile elements (LILE), U, Th, and light rare earth elements (LREE); depletions in high field strength elements (HFSE) and heavy rare earth elements (HREE)-with (La/Yb)(N) ratios ranging from 4.3 to 699, mainly 40-50; and Sigma REE abundances of 50-2560 ppm, mainly 300-500 ppm-in most cases lacking significant negative Eu anomalies. However, the element distributions for kamafugite and carbonatite show ocean island basalt-like nondepleted or even slightly enriched HFSE patterns. The plots of epsilon Nd versus (87)Sr/(86)Sr define a mixing array between Neo-Tethyan mid-ocean ridge basalts (MORB) and High Himalayan crustal compositions, with epsilon Nd(t) varying from +5.95 to -17.42 and (87)Sr/(86)Sr (i) 0.702059 to 0.746320. The range of Nd and Sr isotopic compositions in the northern parts of the plateau, Sanjiang, and west Qinling is relatively small compared to that from Gangdese to the south, where (87)Sr/(86)Sr ratios range from 0.703785 to 0.746320 and (143)Nd/(144)Nd from 0.511737 to 512710. The variation of Pb isotopic ratios is somewhat less, with (206)Pb/(204)Pb ranging from 18.149 to 19.345, (207)Pb/(204)Pb from 15.476 to 15.803, and (208)Pb/(204)Pb from 37.613 to 40.168. In general, magmatic isotopic compositions indicate the regional-scale presence of DUPAL-like mantle, reflecting additions of the "enriched mantle" components (EM1, EM2) to an ambient MORB-HIMU (high mu, i.e., high U/Pb mantle) asthenospheric hybrid. The observed geochemical, isotopic, and mineral phase compositional variations of primitive magmatic products and their entrained mantle xenoliths clearly suggest LILE-enriched and HFSE-depleted phlogopite/amphibole-bearing mantle wedge sources contaminated by (presumably subduction-related) hydrous fluids or small-fraction H(2)O-CO(2)-rich melts. Tibetan lithospheric mantle appears to reflect the presence of and interaction between at least three compositional end-members. The overall spatial-temporal pattern of Tibetan collisional and postcollisional activity is consistent with the hypothesis that the Neo-Tethyan asthenospheric mantle was laterally displaced along discrete northeast- and southwestward flow channels in response to the India-Asia collision.
As an important part of the Paleozoic orogonic belt in northern Xinjiang, the Junggar is characterized by intense and extensive development of Late Paleozoic granitoid plutons together with minor mafic plutons, and it is one of the representative regions for the Phanerozoic continental crustal growth in the Central Asian Orogenic Belt. On the basis of new SHRIMP zircon U-Pb dating on the plutons in the East and West Junggar, in association with the zircon U-Pb ages from the literature, an attempt is made in this study to establish the timing of the late Paleozoic post-collisional plutonism in the region. It is concluded that the late Paleozoic post-collisional plutonism occurred from middle-late Visean of Carboniferous to the end of Early Permian in accordance to the Geological Time Scale (Gradstein et al., 2004). Temporally, the plutons in the East and West Junggar formed in a period of 65Ma, from 330 to 265Ma and from 340 to 275Ma, respectively. However, the plutonism in the East Junggar showed two peaks of 330 to 310Ma and 305 to 280Ma, whereas most plutons in the West Junggar were emplaced from 310 to 295Ma. Spatially, the plutonism occurred in all tectonic units separated by ophiolite belts and even some granitoid plutons intruded in ophiolites. Furthermore, the post-collisional plutons can be found not only in the Junggar, but also in the Altai orogenic belt to the north and in the Tianshan orogenic belt to the south.
The Altai Mountains are a key area for understanding the development of the Altai Tectonic Collage and accretionary orogen. However, the orogenic processes, particularly their early stage, have not been well understood. In this work, we undertake zircon U-Pb dating of six Paleozoic synorogenic plutons in order to better define the early magmatic and tectonic evolution of the Chinese Altai Mountains. The results revealed three Paleozoic granitic plutonic events at ca. 460, 408, and 375 Ma. These ages, along with the structural patterns of the plutons, suggest two periods of regional deformation, 460–410 Ma and 410–370 Ma. The granitoids mainly follow the tholeiitic and calc-alkaline trends and are mostly I type. Sr-Nd isotopic analyses indicate that the sources of the granitoids contain both old continental and younger (juvenile) mantle-derived components. Chemical, isotopic, and structural features suggest that the plutons were formed mainly in continental arc settings and that the subduction and accretion processes began at ca. 460 Ma and culminated at ca. 408 Ma. Thus, the Altai orogen was mainly built up during early-middle Paleozoic time, rather than during late Paleozoic time. Furthermore, the southern Altai terrane comprises not only Silurian to Devonian island arcs but also old continental fragments. With these new constraints, we present a new model to account for the tectonic evolution of the Altai orogen. This model proposes that early-middle Paleozoic Altai orogenic processes could have experienced formation of an active continental margin, the splitting of this margin to form a back-arc oceanic basin, and the final closing of the back-arc basin. Consequently, the opening and closure of back-arc basins along active margins is probably a common process in the central Asian accretionary orogen.
Twenty-six samples representing the wide range of lithologies (low- and intermediate-Ca boninites and bronzite andesites, high-Ca boninites, basaltic andesites-rhyolites) drilled during Leg 125 at Sites 782 and 786 on the Izu-Bonin outer-arc high havenbeen analyzed for Sr, Nd, and Pb isotopes. Nd-Sr isotope covariations show that most samples follow a trend parallel to a line from Pacific MORB mantle (PMM) to Pacific Volcanogenic sediment (PVS) but displaced slightly toward more radiogenic Sr. Pb isotope covariations show that all the Eocene-Oligocene samples plot along the Northern Hemisphere Reference Line, indicating little or no Pb derived from subducted pelagic sediment in their source. Two young basaltic andesite coasts within sediment do have a pelagic sediment signature but this may have been gained by alteration rather than subduction. In all isotopic projections, the samples form consistent groupings: the tholeiites from Site 782 and Hole 786A plot closest to PMM, the boninites and related rocks from Sites 786B plot closest to PVS, and the boninite lavas from Hole 786A and late boninitic dikes from Hole 786B occupy an intermediate position. Isotope-trace element covariations indicate that these isotopic variations can be explained by a three-component mixing model. One component (A) has the isotopic signature of PMM but is depleted in the more incompatible elements. It is interpreted as representing suboceanic mantle lithosphere. A second component (B) is relatively radiogenic (εNd = ca 4-6; 206Pb/204Pb = ca 19.0-19.3; εSr = ca -10 to -6)). Its trace element pattern has, among other characteristics, a high Zr/Sm ratio, which distinguishes it from the "normal" fluid components associated with subduction and hotspot activity. There are insufficient data at present to tie down its origin: probably it was either derived from sub ducted lithosphere or volcanogenic sediment fused in amphibolite facies; or it represents an asthenospheric melt component that has been fractionated by interaction with amphibole-bearing mantle. The third component (C) is characterized by high contents of Sr and high εSr values and is interpreted as a subducted fluid component. The mixing line on a diagram of Zr/Sr against ε Sr suggests that component C may have enriched the lithosphere (component A) before component B. These components may also be present on a regional basis but, if so, may not have had uniform compositions. Only the boninitic series from nearby Chichijima would require an additional, pelagic sediment component. In general, these results are consistent with models of subduction of ridges and young lithosphere during the change from a ridge-transform to subduction geometry at the initiation of subduction in the Western Pacific.
The identification of large igneous provinces (LIPs) and associated
mantle plumes has been confined for the most part to the Mesozoic and
Cenozoic record. With few exceptions, pre-Mesozoic LIPs have been
partially or totally destroyed by tectonic and erosional processes.
Here, we describe a method of identifying the remnants of pre-Mesozoic
LIPs and the location of paleoplumes from the convergent points of giant
radiating dyke swarms. It is based on the observations from seven case
histories that giant radiating dyke swarms converge towards known mantle
plume centers beneath the volcanic accumulations of Mesozoic and
Cenozoic LIPs. We describe three additional Mesozoic and 14 pre-Mesozoic
swarms which likely focus on paleoplumes. Several other candidates are
also considered.
We report field characteristics, petrography, geochemistry and isotopic ages of the Neoarchaean intrusive complex and the Paleoproterozoic metamorphic belt around Quruqtagh in the northern margin of the Tarim Block, NW China in an attempt to evaluate the evolution of the Precambrian basement of the Tarim Block. Zircon U–Pb ages indicate that the tonalite–trondhjemite complex with gabbroic enclaves and the slightly younger potassic granites crystallized at ca. 2.60Ga and ca. 2.53Ga respectively, and were metamorphosed at ca.1.85–1.80Ga. Zircon U–Pb ages indicate that the amphibolite to granulite facies assemblages in the strongly deformed Paleoproterozoic gneiss-schist belt were generated during a major thermal event at 1.85–1.80Ga, and were again overprinted by late Mesoproterozoic to early Neoproterozoic metamorphism (1.1–0.95Ga). Geochemically, the gabbros occurring within the tonalite–trondhjemite suite exhibit arc tholeiite signature and their chemical and Nd isotopic compositions suggest that they were derived from partial melting of a metasomatised and depleted mantle. The tonalites and trondhjemites have varied geochemical compositions but both preserve distinct Archaean TTG (tonalite–trondhjemite–granodiorite) signatures. However, the ca. 2.53Ga potassic granites have very different geochemical compositions as compared to the tonalite–trondjemite suite and show extreme enrichment of LREE and LILE, as well as a marked depletion of HREE and HFSE. Based on the geochemical and geochronological data presented in this contribution, we suggest that: (1) the gabbro–tonalite–trondhjemite suite and the late potassic granites represent an evolution from an arc system through the final collision and late or post-orogenic extension when the potassic granite was emplaced, thus building the cratonic architecture of the proto-crust of the Tarim Block; (2) the ca.1.9–1.8Ga metamorphism marks an important orogenic event in the crystalline basement of the Tarim Block which was stabilized during the early Precambrian; (3) the 1.9–1.8Ga and 1.1–0.9Ga metamorphic ages form part of the global-scale orogeny identified to be related to the Paleoproterozoic Columbia and Neoproterozoic Rodinia supercontinent assemblies.
Zircon has long been recognized as the best geochronometer and the most
important timekeeper in geosciences. Modern microbeam techniques such as
SIMS and LA-ICPMS have been successfully applied to in situ U-Pb zircon
age determinations, at spatial resolutions of 20-30 μm or less.
Matrix-matched calibration by external standardization of
well-characterized natural zircon references is a principal requirement
for precise microbeam U-Pb zircon age determination due to fractionation
effects between Pb and U, which usually result in an external age error
exceeding 1%. Alternatively, zircons with a closed U-Pb system can be
directly dated by measurement of 207Pb/206Pb
isotopic ratio without external standardization, which has been a common
practice for zircons older than 1.0 Ga, but not for relatively young
(<1.0 Ga and particularly Phanerozoic) ones because of limitations of
analytical precision. We describe in this paper a method of
207Pb/206Pb measurement on Phanerozoic zircons
using a new generation of large radius magnetic sector multicollector
Cameca IMS-1280 SIMS. In combination with multicollector mode, a Nuclear
Magnetic Resonance (NMR) magnet controller and oxygen flooding
techniques, we achieve precisions of 207Pb/206Pb
ratio of <0.1% and 0.1 ˜ 0.2%, propagating to Pb/Pb age errors
<0.4% and 1-3% (excluding U decay constant uncertainties), for
zircons of latest Neoproterozoic and late Paleozoic to Mesozoic age,
respectively. Therefore, the multicollector SIMS is capable of direct
determination of zircon Pb/Pb ages as young as Mesozoic age with
uncertainties of geological significance. This technique is useful for
direct dating of zircons in thin sections. Moreover, it has significance
for dating of some other U-rich minerals (i.e., baddeleyite and
zirconolite) that are not suitable for SIMS U-Pb dating by external
standardization.
Zircon laser ablation inductively coupled plasma mass spectrometry U-Pb age and geochemical and Sr-Nd-Hf isotopic data are reported for the Bachu layered intrusive complex (BLIC) in the western Tarim Block and are used to assess the possible presence of a Permian large igneous province (LIP) in the region. The BLIC intrudes the Silurian-Devonian sedimentary rocks, and our U-Pb zircon dating gives a crystallization age of Ma. Rock types of the BLIC 274 2 include pyroxenite, diorite, syenite, and quartz syenite, with a wide range of SiO 2 contents (38.6%–68.7%) and variably high alkalinity (,). They are enriched in Rb, Ba, Th, Nb, Ta, Zr, Na O K O p 1.5%–12.0% K O/Na O p 0.23–0.9 2 2 2 2 Hf, and light rare earth elements. Isotopically, they are characterized by positive whole-rock Nd(t) values (0.25–2.8, mostly above 2.0) and zircon Hf(t) values (5.8–8.9) and low initial 87 Sr/ 86 Sr ratios (0.7035–0.7045). These features suggest that the BLIC was likely formed by crystal cumulation and fractionation (with negligible crustal contami-nation) of alkali basalts derived from an ocean island basalt–like mantle source (i.e., the asthenospheric mantle) in an extensional regime. We suggest that these mid-Permian igneous rocks, in combination with the voluminous coeval basalts and intrusive rocks covering an total area of ca. 250,000 km 2 in the Tarim Block and surrounding regions, constitute an LIP (the "Bachu LIP") and that the BLIC could be the residue of a feeder for this LIP.
The Central Asian Orogenic Belt (CAOB), also known as the Altaid Tectonic Collage, is characterised by a vast distribution of Paleozoic and Mesozoic granitic intrusions. The granitoids have a wide range of compositions and roughly show a temporal evolution from calc-alkaline to alkaline to peralkaline series. The emplacement times for most granitic plutons fall between 500 Ma and 100 Ma, but only a small proportion of plutons have been precisely dated. The Nd-Sr isotopic compositions of these granitoids suggest their juvenile characteristics, hence implying a massive addition of new continental crust in the Phanerozoic. In this paper we document the available isotopic data to support this conclusion. Most Phanerozoic granitoids of Central Asia are characterised by low initial Sr isotopic ratios, positive (epsilon)(Nd)(T) values and young Sm-Nd model ages (T-DM) of 300-1200 Ma. This is in strong contrast with the coeval granitoids emplaced in the European Caledonides and Hercynides. The isotope data indicate their 'juvenile' character and suggest their derivation from source rocks or magmas separated shortly before from the upper mantle. Granitoids with negative (epsilon)(Nd)(T) values also exist, but they occur in the environs of Precambrian microcontinental blocks and their isotope compositions may reflect contamination by the older crust in the magma generation processes. The evolution of the CAOB is probably related to accretion of young are complexes and old terranes (microcontinents). However, the emplacement of large volumes of post-tectonic granites requires another mechanism, probably through a series of processes including underplating of massive basaltic magma, intercalation of basaltic magma with lower crustal granulites, partial melting of the mixed lithologic assemblages leading to generation of granitic liquids, followed by extensive fractional crystallisation. The proportions of the juvenile or mantle component for most granitoids of Central Asia are estimated to vary from 70% to 100%.
Using the in situ zircon U-Pb dating method of LA-ICPMS, we analyzed the 31 Ma old SHRIMP U-Pb age of the Yongsheng nepheline syenite from southern Jilin Province under different spot sizes. The obtained ages are comparable with that of SHRIMP in both accuracy and precision. The age is also identical to that of the Yinmawanshan gabbro from the Liaodong Peninsula within error. Both the Yongsheng nepheline syenite and the Yinmawanshan gabbro represent the youngest known exposed intrusions in northeastern and even eastern China. The results indicate the Eocene mantle-derived magmatic underplating, and the rapid crustal uplifting of this region since 30 Ma. The analyses also document extremely high LREE concentrations and relatively flat REE patterns for the zircons from the Yongsheng nepheline syenite, which represent a new type of zircon REE pattern.
The Permian dike rock is great development at Kuruktag Region, their rock association is diabase-tjosite-plagiophyrite-granite-porphyry, among them, diabse is the most main rock type. Granite-porphyry belongs to high-K calcium-alkali series, which has the geochemical characteristics of the rare earth element and trace element for A-type granite. The geochemical feature of playlophyrite is similar to granite-porphyry, and they both deplete U, Nb, Ta. The chemical compositions of tjosite belong to peralkali series, and they are rich in LREE and LILE. The chemical composition of diabase is mainly calcium-alkali series, and abundances of Cs, Rb, Ba, Th and ∑REE are greatly various, but U, Nb, Ta are generally depleted. The study shows that the geochemical characters of the diabase veins should be ascribed to contamination, the varying LILE abundance has also something to do with hydrothermal alteration. The diabases have riched type Nd, Sr isotopic composition and have great varying range, which is the result of action together both magma source and contamination. Their Pb isotopic composition belongs to normal Pb of the low U(Th)/Pb, mainly be controlled by contaminated materials, and don't represent the feature of source. The Nd, Sr, Pb isotopes of lithospheric mantle in Kuruktag region are richer than those in the western margin of the Tarim plate, and show wider varying range, which indicates the evolution history of lithospheric mantle has obvious difference in these two regions.
This chapter reviews the present-day composition of the continental crust, the methods employed to derive these estimates, and the implications of the continental crust composition for the formation of the continents, Earth differentiation, and its geochemical inventories. We review the composition of the upper, middle, and lower continental crust. We then examine the bulk crust composition and the implications of this composition for crust generation and modification processes. Finally, we compare the Earth's crust with those of the other terrestrial planets in our solar system and speculate about what unique processes on Earth have given rise to this unusual crustal distribution.
Late Paleozoic shoshonitic series volcanic rocks and adakite are wide spread in north Xinjiang. They are rich in alkali together with the widely distributed alkali-rich granites to constitute alkali-rich igneous rock province of north Xinjiang. Different isotopic dating methods gave the age of 250-280 Ma for the shoshonitic series volcanic rocks and adakite. High 143Nd/144Nd ratios, positive εNd (t) (> 0), lower Nd model ages(t2DM<1.0Ga) and lower with wide variation of (87Sr/86Sr)i (0.7040-0.710) have shown their source rocks are mantle-derived and/or contaminated by crust. Thickened crust, complex Moho, high geothermal heat flow and widely distributed basic dike swarms and alkali-rich granites have systematicly proved evidences for the underplating during late Paleozoic (later Carboniferous - Permian) in north Xinjiang.
A group of Permain vein rocks, which intrude into the stratum of Sliurian system, Devonian system, Carboniferous system and lower Permain series, occur in Mazhartag region, located in the west margin of the Tarimu plate, eastern Bachu county. Their main rock types have diabases, diabase-prophyrites, chromocratic olivine gabbros and lamprophyres. The chromocratic olivine gabbros, with Fe2O3+FeO=14.40%-16.88%, MgO=17.21%-18.59%, Mg#=67-68, FeOt/MgO<1 and Ni=469×10-6-635×10-6, belong to the Fe-riched-type high-Mg magma and are more or less representative of the primary magma, while Mg#, FeOt/MgO and Ni abundance of the diabases and diabase-prophyrites show these rocks belong to the moderately evolved magma. It is proved by the petrography and petrochemistry that the fractional crystallization of the olivines and clinopyzoxenes is the main mechanism of the magmatic evolution. All varial vein rocks have the characteristics of the rare earth element and trace element geochemical characteristics of basalts formed under the extension settings of the intra-plate. All rocks, with 143Nd/144Nd = 0.512508-0.512786, 87Sr/86Sr = 0.704246-0.706444, 206Pb/204Pb = 18.17-19.24, 207Pb/204Pb = 15.47-15.71 and 208Pb/204Pb = 38.63-39.32, have the identical Nd, Sr and Pb isotopic compositions. Therefor, it can be proved that these vein rocks have Nd, Sr and Pb isotopic compositions of the primitive mantle and their magmatic source maybe lay in the lower mantle.
Specific complex of different types of mineralization (early Cu-Ni-Pt and Ni-Co-As and late Hg, Au-Hg, and porphyry-Cu-Mo) has been revealed in the areas of influence of the Siberian and Tarim mantle plumes. In some regions, Mo-W, Sn-W, Ag-Sb, hydrothermal Fe-skarn, Fe-Ti (apatite), REE-Ta-Nb-carbonatite, and other types of mineralization have been found. The central parts of the areas bear large Cu-Ni-Pt deposits, whereas the peripheries are made up of Ni-Co-As, Hg, Au-Hg, and Cu-Mo ores. In some ore districts, the largest commercial deposits are confined to rift structures or deep-fault zones. Formation of large ore deposits was determined by the spatial co-occurrence of plume magmatism and within-plate rifting and the active mantle-crust interaction.
Zhongposhanbei rock body lies in the middle belt of Beishan rift zone in Xinjiang and covers an area of 180km2 in shape of interconnected lopolith. It consists of hornblende gabbros, olivine pyroxenites, olivine gabbros, noritegabbros and anorthosites, these lithofacies belts extend in concentric ring form, and each other gradual transition. Zircon U-Pb age is 274 ± 4Ma. Evidences for greatly developmental fractional crystallization comes from the petrography, petrochemistry, crystal chemistry of petrogenetic minerals and REEs geochemistry. Olivine pyroxenites and olivine gabbros are mainly formed by assembly of early crystallized phases; olivine is original liquidus phase, and clinopyrixene is mainly fractional crystallized phase in quantity. Formation of anorthosites are originate from crystallization of residual magma. Primary magma formed these rocks should be high-Mg tholeiitic magma. Nd, Sr, Pb isotopic compositions and lithogeochemical characteristics fully imply the exchange of material between magma and wallrock. Contamination have changed evidently the isotopic compositions and LILE abundances of the intrusive rocks. All kinds of rocks have very low TiO2, Na2O, K2O contents and LILE, REEs abundances except anorthosites. A olivine gabbro sample has εNd(t) = + 6.8, it is inflenced less by contamination. These characteristics indicate that their magmatic source belong to the depleted mantle. FeO* and SiO2 content also prove that main rock of magmatic source is Iherzolite when melting just begin, then the source rock has changed into harzburgite when the function maintain to the certain degree. REEs geochemical Characteristics suggest that melting occur in the spinel stable field. It is proved by various pertinent data that Zhongposhanbei rock body is the product of partial melting of the fourth type mantle source region in Permian epoch in Tarim plate.
The Tianshan Carboniferous-Early Permian rift-related volcanism in northwestern China represents a newly-recognized large igneous province extending over at least 1. 7 × 106 km2. The volcanic successions comprise thick piles of basaltic lavas and subordinate intermediate and silicic lavas and pyroclastics, and are interpreted to result from a mantle plume with component of εNd (t) ≁ + 5, (87Sr/88Sr (t) ≁0. 704 and La/Nb ≁ 0. 9. On the basis of petrogeochemical data, the Carboniferous-Early Permian basic lavas can be classified into high-Ti/Y (HT, TI/Y>500) and low-Ti/Y (LT, Ti/Y < 500) magma types. The LT lavas can be further divided into four subtypes: LT1, LT2, LT3 and LT4. The chemical evolution of the LT1, LT2 (.in central Tianshan and Baishan of Gansu), LT4 (in western Tianshan, Jungar and Baishan of Xinjiang) and LT3, HT (Tarim) lavas is controlled by an olivine (ol) + clinopyroxene (cpx) fractionation, but gabbroic fractionation accounts for the chemical variation of the LT4 lavas from eastern Tianshan. Elemental and isotopic data suggest that the chemical variation of the Carboniferous-Early Permian rift-related basic lavas in the Tianshan and their neighboring areas can not be explained by crystallization from a common parental magma. The Sr-Nd isotopic variation of the crustally contaminated LT3 and LT4 lavas is related to the nature of lithosphere through which the plume-derived melts have erupted. The involvement of an older (Precambrian) lithosphere led the Carboniferous LT4 lavas in western Tianshan and the Early Permian LT3 lavas in Keping rift to have lower to negative εNd (t) (-2-91 to+6.1) and middle to high 87Sr/ 86Sr (t) (0. 7036∼0.7081), whereas the Carboniferous LT4 lavas from eastern Tianshan and Jungar are characterized by high εNd (t) (+ 4. 2 to + 9. 7) and low 87Sr /86 Sr (t) (0. 7035∼0. 7044), that are related to the contamination of upper crust containing early Paleozoic and Devonian arc-basin volcanic rocks and/or to a pre-Carboniferous subduction enrichment of the lithospheric mantle source region. The observed geochemical variations in the Carboniferous-Early Permian rift-related basic lavas from the Tianshan and its neighboring areas are consistent with an AFC process. The Carboniferous-Early Permian rift-related volcanic rocks in the Tianshan and its neighboring areas display a temporal and spatial petrogeochemical variation. During Caboniferous predominantly uncontaminated LT1 and less-contaminated LT2 lavas erupted in central Tianshan rift and predominantly the strongly contaminated LT4 lavas erupted in the circurcumjacent regions of the central Tianshan rift. The Carboniferous LT1 and LT2 lavas were generated by a higher degree (10%∼30%) of partial melting in the garnet stability field of the mantle plume compared to the Carboniferous LT4 lavas. The lower degree (<10%) of partial melting in the spinel-garnet transition zone of the mantle plume, as is characteristic of the Carboniferous LT4 lavas, may be the result of a relatively lower geotherm. During Early Permian the uncontaminated HT, LT1 and less-contaminated LT3 lavas erupted in Tarim and Baishan rifts and the strongly contaminated LT4 lavas erupted in the northern Bogda-Harlike rift.
We report new K-Ar ages, Sr, Nd, and Pb isotope ratios and
concentrations of 34 trace elements in volcanic rocks from the Society
Islands. Maximum ages of volcanism at Mehetia, Tahiti, and Maupiti
indicate that volcanism in the Society Islands progresses southeastward
at a rate of 11 cm/yr, which is consistent with current estimates of
Pacific Plate motion. Tahaa has the largest range in ages, 2.3 million
years. This large range reflects the eruption of highly undersaturated
lavas during a posterosional phase that followed a volcanic hiatus of
1.2 million years. The entire range of isotope ratios observed in the
Society Islands is nearly encompassed by the range observed on Tahaa:
the two post-erosional lavas have among the most depleted isotopic
signatures while the shield series lavas have the most enriched isotopic
signatures. The isotopic and chemical evolution of Tahaa thus follows
the Hawaiian pattern. There is a strong correlation between Sr and Nd
isotope ratios and weaker correlations involving Pb isotope ratios.
Compared to other oceanic islands, Sr and Nd ratios range to extremely
high and low values respectively, but Pb isotope ratios are
intermediate. The isotope correlations indicate the Society plume can be
approximately modeled as consisting of two slightly heterogeneous end
members. All magmas are moderately to strongly enriched in light rare
earth elements as well as other incompatible elements. After exclusion
of weathered (as indicated by anomalous Ba/Rb ratios) and differentiated
lavas, there are strong correlations between Hf/Sm, Pb/Ce, Zr/Nb, Nb/U,
and Rb/Sr and 87Sr/86Sr (and
ɛNd and 207Pb/204Pb) and weaker
correlations between Nb/La and La/Sm and 87Sr/86Sr
(and ɛNd and 207Pb/204Pb). This
indicates the variation in Hf/Sm, Pb/Ce, Zr/Nb, Nb/U, and Rb/Sr is
largely due to variations in the composition of the source. This
inference is confirmed by factor analysis. On the other hand, variance
in the La/Sm ratio appears dominated by varying degrees of partial
melting, perhaps because differences between the two end members in
La/Sm are small. The high 87Sr/86Sr component in
the plume has high 207Pb/204Pb and Pb/Ce and low
Nb/U. These characteristics are consistent with this component
consisting partly of sediment that has been subducted into the deep
mantle. The low 87Sr/86Sr component in the Society
plume appears to be also richer in incompatible elements than depleted
mantle and is isotopically similar to the common component of plumes
postulated by others. This component is most prevalent in late and very
early stage Society magmas and thus probably constitutes the sheath of
the Society plume. This sheath was most likely viscously entrained in
the deep mantle during ascent of the plume.
The Tarim Block is characterized by a double layer structure consisting of a Precambrian basement and Neoproterozoic to Cambrian cover series. It experienced different stages of tectonic evolution since its generation, with similarities and dissimilarities to the North and South China Blocks in many aspects. This has brought about complexities in understanding the tectonic processes of crustal growth and reworking in the Tarim Block. In this contribution, we provide a comprehensive synthesis on the regional geology and analytical data. Based on the study herein, we constructed its tectonic framework and main evolution stages and its sedimentary-magmatic-metamorphic concurrence to the main tectonic events. In the Archean, the 2.80–2.57 Ga Archaean TTG was intruded by the ca.2.53 Ga high Ba-Sr granite, leading to the formation of the Archean proto crust of the Tarim. During the Proterozoic, two periods of tectono-metamorphic events occurred in the Orosirian–Statherian period (2.0–1.8 Ga) and the late Mesoproterozoic to early Neoproterozoic (1.0–0.9 Ga), respectively. They were concurrent with the global assembly of Columbia and Rodinia supercontinents, respectively. Since 760 Ma, Tarim and other landmasses started to split from Rodinia in response to the Rodinian breakup. In the middle to late Neoproterozoic, the Rodinia breakup resulted in the diverse and voluminous intriguing igneous activities along the northern margin of the Tarim. In the Early Cambrian, the Tarim Block drifted away from the other parts of Rodinian landmass in response to the Pan-African tectonic event. During the late Neoproterozoic to the Carboniferous, the early Paleozoic Northern Kunlun orogen was produced by collision of the Qaidam with the southern margin of Tarim, whereas in the late Paleozoic the southern Tianshan orogen was brought about due to collision between the Yili terrane and the northern margin of Tarim. In the Permian, a large igneous province occurred in Tarim, which is the last igneous activity in this block.
Late Paleozoic magmatic rocks (including basic dykes, basaltic andesite, rhyolite, keratophyre and syenite-porphyry with minor tuff) are widespread in the western margin of the East Junggar terrane. In-situ zircon U–Pb dating and Hf isotope analyses were carried out for these magmatic rocks from the Baijiangou and Zhangpenggou localities of East Junggar, integrating with geochemical data, to investigate their tectonic evolution as well as crustal accretionary process of this region in the Late Paleozoic. Inherited zircons from basic dykes range in age from 435Ma to 300Ma. The Zhangpenggou rhyolite and keratophyre have typical arc-like geochemical signatures and were formed in the Early Carboniferous (332Ma and 336Ma, respectively), suggesting they are products of subduction-related magmatism. The Baijiangou rhyolites were formed in the Late Carboniferous (315Ma and 323Ma) and their formation ages are similar to those of the syenite-porphyries (307Ma and 312Ma). The Hf model ages and the formation ages of zircons from these magmatic rocks are alike, with positive εHf(t) values vary from +0.7 to +16.6, implying that voluminous growth of juvenile crust happened in the East Junggar terrane during the Late Paleozoic. The absence of Precambrian inherited zircons in basic dykes indicates the lack of Precambrian basement beneath the East Junggar terrane. Taking geochronological studies on regional ophiolites into account, the East Junggar terrane is considered as a Devonian–Carboniferous oceanic island arc which has been continuously accreted to the southern active margin of the Siberian Craton since the Early Carboniferous.
A regional-scale tectonic event of closure of ocean and collision-orogeny took place in the interval from Late Devonian to Late Carboniferous in the Xinjiang area. At the late stage of collision, some tectonic changes occurred in the piedmont area. The preliminary framework of mountains-basins of northern Xinijiang was composed of both Late Carboniferous-Early Permian orogenic belt and piedmont basins. In the direction toward continent, post-collision intracontinental rifting and olistostrome developed well. The bedded diabase and bimodal volcanic rocks were distributed in the Early Permian strata in the piedmont area. The most typical area is located on the southern slope of Bogda Mountains, namely the Qijiaojing-Cheguluquan segment of Harm city and the Baiyanggou section of Urumgi. This paper studied the geometrical, petrological and geochemical features of intracontinent bimodal volcanic rocks and olistostrome. Of them, post-collision olistostrome is the first time discovery by us. In the Qijiaojing-Cheguluquan segment, basalt and rhyolite are ranged alternately that overlie the Early Permian red molasses. This post-collision bimodal volcanic series with a big thickness is distributed in parallel with the sub-E-W mountain extension. In the Baiyanggou section, post-collision underwater olistostrome co-exists with underwater eruption and is composed of olistostrome zone, pillow lava and pore basalt zone, and siliceous shale and siltstone zone; the bottom plane is contacted with Late Carboniferous limestone and sandstone series by a NEE-trending detachment fault.
We propose a flat-slab subduction model for Mesozoic South China based on both new sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon data and a synthesis of existing structural, geochronological, and sedimentary facies results. This model not only explains the development of a broad (˜1300-km-wide) intracontinental orogen that migrated from the coastal region into the continental interior between ca. 250 Ma and 190 Ma, but can also account for the puzzling chain of events that followed: the formation of a shallow-marine basin in the wake of the migrating foreland fold-and-thrust belt, and the development of one of the world's largest Basin and Range style magmatic provinces after the orogeny. The South China record may serve as an example of the multiple effects of flat-slab subduction, including migrating orogenesis and foreland flexure, synorogenic sagging behind the active orogen, postdelamination lithospheric rebound, and the development of a Basin and Range style broad magmatic province.
This study reports for the first time the occurrence of bimodal dyke in the Shuigongtuan area of Bachu County, Tarim Basin, NW China. Here, quartz syenite porphyry and diabase dykes occur in direct contact showing bimodal feature. The quartz syenitic porphyry is metaluminous, enriched in K2O+Na2O (10–11 wt.%) and total rare earth elements (REE), with low Mg/(Mg+Fe) ratios, high LREE/HREE, and negative Eu anomalies. The chemical characteristics and tectonic discriminative diagrams show that the rocks have geochemical affinity with A-type granites. The diabase dyke shows 45–52 wt.% SiO2 and Mg/(Mg+Fe) ratio in the range of, with high total REE, high LREE/HREE ratios and lack of Eu anomalies, broadly corresponding to tholeiitic composition. Based on low Y/Nb (as low as 0.4, and less than 1.2), enrichment in LILE and HFSE, and uniform Nb-enrichment patterns in spider diagram for the quartz syenitic porphyry, together with the geochemical patterns of the diabases, this biomodal association is interpreted to be derived from a mantle source and formed under typical within-plate environment. The quartz syenitic porphyry and diabase have Daly gap of 46 wt.%–67 wt.% in SiO2, which is explained through formation under bimodal rifting. The quartz syenitic dyke probably formed during Early Permian (277 Ma) and has geochemical affinity with the Xiaohaizi syenitic body. We propose that magmas sourced from the mantle intruded into middle–upper crust and were emplaced as dykes, which indicate large-scale extension during the Permian in Tarim Basin. The bimodal dyke has genetic affinity with the huge volume of Permian basalts and igneous rocks (248–292 Ma) that occur in the Tarim Basin. The magmatism manifests the culmination of the major thermal event in the Tarim Basin.
Zircon U–Pb ages and geochemical data are reported for the Piqiang oxide-bearing ultramfic–mafic complex, the Bachu mafic dyke swarm, the Yingan and Kaipaizileike basalts and the Halajun A-type granites in the Tarim Block, Northwest China. The Piqiang complex and the Halajun A-type granites were emplaced at ca. 276Ma and ca. 278Ma, respectively. Together with previously reported geochronological data, the diverse intrusive and extrusive rocks in Tarim show a peak age at ca. 275Ma. Elemental and Nd isotope geochemistry suggests that the spatially and temporally related Piqiang complex (including some dolerite dykes or stocks) and the Halajun A-type granites were formed via crystal fractionation/accumulation of a common plume-derived parental mafic magma (melting degree >10%), coupled with variable extents of crustal contamination. Crystal fractionation/accumulation in one or several magma chambers resulted in the diversity of rocks types. The Bachu mafic dyke swarm shares a similar mantle source with the intrusive rocks in the Piqiang–Halajun area but with a relatively lower degree of partial melting (~5%). In contrast, the basalts were derived from a time-integrated, enriched lithospheric mantle source as suggested by their high-Ti, LREE- and LILE-enriched trace element signature and negative εNd(t) values (−2.0 ~ −2.6). The synchronous yet diverse range of Permian igneous rocks in Tarim can best be accounted for by a Permian mantle plume, which is about 15Ma earlier than the Emeishan plume in southwestern China.