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The Neoproterozoic mafic rocks in western Hunan, South China, form a NNE-striking mafic rock belt for which outcrops are found predominantly in Guzhang, Qianyang and Tongdao. Samples from Qianyang and Tongdao yielded ion microprobe U–Pb zircon ages of 747±18 Ma and 772±11 Ma, respectively. The mafic rocks are geochemically divided into two subtypes...
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... mafic rocks from Qianyang and Guzhang have Mg no. ranging from 65 to 25, suggesting that fractional crystallization is an important factor in the evolution of the mafic magmas in the area. Moreover, the Zr/Nb-Zr plot (Fig. 4) implies that the slight chemical differences between samples would reflect variations in the degree of fractional crystallization rather than partial melting. The effects of fractional crystallization for the mafic rocks from western Hunan are indicated by the compositional variations of both major and trace elements with respect to Mg no. as fractionation index (Fig. 7). CaO, CaO/Al 2 O 3 and CaO/TiO 2 increase with the increased Mg no. (Fig. 7), which indicates the crystallization of clinopyroxene (Class et al. 1994). It should be pointed out that two types of correlations with Mg no. have been shown by some elements and element ratios (Fig. 7). Under Mg no. ≥ 45 (predominantly including the ultramafic and mafic rocks), negative correlations are revealed by TiO 2 , Al 2 O 3 , Na 2 O+K 2 O and V versus Mg no., whereas positive correlations exist between Al 2 O 3 /TiO 2 and Mg no., implying the fractional crystallizations of olivine and clinopyroxene. Under Mg no. < 45, however, there are positive correlations of TiO 2 and V versus Mg no., relatively constant Na 2 O + K 2 O and Al 2 O 3 versus Mg no., and negative correlation of Al 2 O 3 /TiO 2 versus Mg no., probably indicating the fractionation of Fe-Ti oxides. Incompatible trace elements (e.g. Zr, Nb and Y) show negative correlations with Mg no., while the compatible trace elements (e.g. Ni and Cr) have positive correlations with Mg no., supporting the fractionation of olivine and pyroxene. Furthermore, a Eu anomaly is lacking in most mafic samples (Fig. 5), indicating that plagioclase fractionation was not important in the mafic magma ...
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... mafic rocks from Qianyang and Guzhang have Mg no. ranging from 65 to 25, suggesting that fractional crystallization is an important factor in the evolution of the mafic magmas in the area. Moreover, the Zr/Nb-Zr plot (Fig. 4) implies that the slight chemical differences between samples would reflect variations in the degree of fractional crystallization rather than partial melting. The effects of fractional crystallization for the mafic rocks from western Hunan are indicated by the compositional variations of both major and trace elements with respect to Mg no. as fractionation index (Fig. 7). CaO, CaO/Al 2 O 3 and CaO/TiO 2 increase with the increased Mg no. (Fig. 7), which indicates the crystallization of clinopyroxene (Class et al. 1994). It should be pointed out that two types of correlations with Mg no. have been shown by some elements and element ratios (Fig. 7). Under Mg no. ≥ 45 (predominantly including the ultramafic and mafic rocks), negative correlations are revealed by TiO 2 , Al 2 O 3 , Na 2 O+K 2 O and V versus Mg no., whereas positive correlations exist between Al 2 O 3 /TiO 2 and Mg no., implying the fractional crystallizations of olivine and clinopyroxene. Under Mg no. < 45, however, there are positive correlations of TiO 2 and V versus Mg no., relatively constant Na 2 O + K 2 O and Al 2 O 3 versus Mg no., and negative correlation of Al 2 O 3 /TiO 2 versus Mg no., probably indicating the fractionation of Fe-Ti oxides. Incompatible trace elements (e.g. Zr, Nb and Y) show negative correlations with Mg no., while the compatible trace elements (e.g. Ni and Cr) have positive correlations with Mg no., supporting the fractionation of olivine and pyroxene. Furthermore, a Eu anomaly is lacking in most mafic samples (Fig. 5), indicating that plagioclase fractionation was not important in the mafic magma ...
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... mafic rocks from Qianyang and Guzhang have Mg no. ranging from 65 to 25, suggesting that fractional crystallization is an important factor in the evolution of the mafic magmas in the area. Moreover, the Zr/Nb-Zr plot (Fig. 4) implies that the slight chemical differences between samples would reflect variations in the degree of fractional crystallization rather than partial melting. The effects of fractional crystallization for the mafic rocks from western Hunan are indicated by the compositional variations of both major and trace elements with respect to Mg no. as fractionation index (Fig. 7). CaO, CaO/Al 2 O 3 and CaO/TiO 2 increase with the increased Mg no. (Fig. 7), which indicates the crystallization of clinopyroxene (Class et al. 1994). It should be pointed out that two types of correlations with Mg no. have been shown by some elements and element ratios (Fig. 7). Under Mg no. ≥ 45 (predominantly including the ultramafic and mafic rocks), negative correlations are revealed by TiO 2 , Al 2 O 3 , Na 2 O+K 2 O and V versus Mg no., whereas positive correlations exist between Al 2 O 3 /TiO 2 and Mg no., implying the fractional crystallizations of olivine and clinopyroxene. Under Mg no. < 45, however, there are positive correlations of TiO 2 and V versus Mg no., relatively constant Na 2 O + K 2 O and Al 2 O 3 versus Mg no., and negative correlation of Al 2 O 3 /TiO 2 versus Mg no., probably indicating the fractionation of Fe-Ti oxides. Incompatible trace elements (e.g. Zr, Nb and Y) show negative correlations with Mg no., while the compatible trace elements (e.g. Ni and Cr) have positive correlations with Mg no., supporting the fractionation of olivine and pyroxene. Furthermore, a Eu anomaly is lacking in most mafic samples (Fig. 5), indicating that plagioclase fractionation was not important in the mafic magma ...
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Citations
... Data for primitive mantle, N-MORB, OIB and E-MORB are from Sun and McDonough (1989). Kay (1978); Hart (1984Hart ( , 1988; Zindler and Hart (1986); Burton-Johnson et al. (2020) and Wang et al. (2008Wang et al. ( , 2018Wang et al. ( , 2020aWang et al. ( ,b, 2021a at $185-145 Ma, $136-112 Ma and $95-85 Ma, respectively. The presence of xenocrystic grains among these rocks potentially indicates crustal contamination en route. ...
... Multi-stage folds and faults were formed during the Wuling, Caledonian, Hercynian and Indosinian-Yanshanian orogenic episodes and are broadly distributed in the WHEGMB (Fig. 1c;Li et al., 2014). Regional magmatism occurred in the Neoproterozoic era, but it was minor (840-503 Ma; Zhang et al., 2014;Wang et al., 2008) and unrelated to Zn-Pb mineralization (Yang and Lao, 2007). ...
... There have been many studies on these rocks in the Jiangnan Orogen (eg. Chen et al., 2018;Ge et al., 2001;Li et al., 1999;Wang et al., 2007;Yao et al., 2019;Zhao et al., 2018). The results indicate that these rocks consist of two groups with distinct ages and tectonomagmatic affinities, separated by an unconformity that marks the ca. ...
The Neoproterozoic tectonic setting of the West Cathaysia terrane and its relationship with the Yangtze Block are critical to understanding the formation and tectonic evolution of South China. A detailed study of late Tonian mafic-ultramafic cumulate slivers embedded in the Shenshan tectonic mélange along the northwest margin of West Cathaysia is presented here with the aim of elucidating its Neoproterozoic tectonic history. These partly-altered mafic-ultramafic rocks include olivine-bearing cumulates (olivine pyroxene hornblendite or olivine hornblende pyroxenite), pyroxene hornblendite, and gabbroic cumulates. The early crystallization of clinopyroxene and the abundance of hornblende indicate that they formed from hydrous magmas. The rocks have similar geochemical distribution patterns and show variable initial 87Sr/86Sr ratios of 0.702679 to 0.709742 and positive εNd(t) values of +2.10 to +4.52. The mineral compositions of the clinopyroxene and hornblende and their whole-rock extended normalized trace element patterns show features (e.g., negative Nb anomalies, LILE enrichment) typical of rocks with an arc affinity. The high calculated Mg# values (58–77, average 71) of the equilibrium magmas are close to those of primary mantle-derived basalts. We conclude that these mafic and ultramafic cumulates were derived from a subduction-related, hydrous, magnesian basalt in a subduction setting. The estimated crystallization temperature and pressure, based on the composition of the amphiboles, suggest that the minerals accumulated in magma chambers at middle to lower crustal depths. LA-ICP-MS U-Pb dating of zircon from the gabbroic cumulate indicates crystallization at ca. 785 Ma. A previous interpretation for West Cathaysia at this time involved a continental rift basin (the Nanhua basin) that straddled the southeastern margin of the Yangtze Block and the northwestern margin of West Cathaysia. In contrast, our results suggest that West Cathaysia was an arc at ca. 785 Ma, which supports the interpretation that the amalgamation between Yangtze and West Cathaysia did not occur in the Tonian, but more likely in the early Paleozoic.
... The South China Block (SCB) comprises the Yangtze Block to the north-west and the Cathaysia Block to the south-east (Figure 1a), and the final amalgamation of the two blocks formed the Jiangnan Orogen Li et al., 2013aLi et al., , 2016Shu et al., 2015Shu et al., , 2021Wang et al., 2004Wang et al., , 2006Wang et al., , 2008Wang, Shu, et al., 2012;Yao et al., 2017;Zhao, 2015;Zheng et al., 2007Zheng et al., , 2008, followed by post-collision collapse or orogenic extension along the orogenic belt (Li et al., 1995;Wang, Shu, et al., 2012). Although this orogen is now widely accepted to have formed during the early middle Neoproterozoic (Han et al., 2020;Li et al., 2016;Wang et al., 2007;Wang et al., 2013;Wei & Zhao, 2020;Zhang et al., 2013Zhang et al., , 2020Zhao & Cawood, 2012;Zheng et al., 2007Zheng et al., , 2008), the precise time of assembly and the evolution history of the Jiangnan Orogen still remain controversial (Sun et al., 2018). ...
The Neoproterozoic magmatism along the Jiangnan Orogen preserves significant information for understanding the tectonic evolution of the South China Block (SCB). We conducted a systematic zircon U–Pb geochronological and whole‐rock geochemical study on the basalts from the Yingchuan Formation in the eastern Jiangnan Orogen, SCB. The basalts yielded a weighted mean 206Pb/238U age of 817 ± 13 Ma, enriched in Rb, Th, U, LREE and HFSE (e.g., Zr and Ti). The basalts have positive εNd(t) (+1.9 to +2.1) and high (87Sr/86Sr)i (0.69853–0.70737), indicating a slightly depleted mantle source. The high La/Nb (2.14–2.35) and La/Ta (28.6–33.3) ratios indicate a lithospheric mantle source for the basalts. Their high Ba/Yb (7.85–44.3) and Th/Yb (0.59–0.74) ratios and high absolute Nb contents (7.64–11.6 ug/g) indicate that the lithospheric mantle source has been metasomatized by melts and fluids derived from a subducted slab. The basalts are characterized by (La/Yb) N ratios (3.0–3.5) and Sm/Nd ratios (0.24–0.26), comparable to intra‐continental back arc basin basalts (BABBs). Their Ta/Yb (0.14–0.16) and Th/Yb (0.59–0.74) ratios are similar to those of Okinawa Trough basalts and contemporary mafic rocks formed in the back‐arc basin in the Jiangnan Orogen. Combined with their source features, we propose that the basalts were formed in a back‐arc basin setting. The identification of BABBs from the Yingchuan Formation shows that there were Neoproterozoic back‐arc basins in the south‐eastern Yangtze Block, indicating that the final assembly between the Yangtze and Cathaysia blocks did not occur before ca. 817 Ma.
... Numerous ca. 770 Ma mafic dykes and sills in the SCC have been reported over the last two decades (Ge et al., 2001;Kou et al., 2018;Liu et al., 2020Liu et al., , 2021Wang et al., 2008Wang et al., , 2009Zhou et al., 2007). They are widely distributed in the Yangtze block, intruding the Banxi Group and its equivalents (Figure 1; HNBGMR , 1988). ...
Plain Language Summary
Multiple lines of geological evidence may suggest a close paleogeographic relationship between the south China craton (SCC) and India. Their specific connection, including the alignment of tectonic features, if had ever existed in any way, can be tested and determined through the use of coeval high‐quality paleomagnetic data from the two cratons. In this paper, we report a new paleomagnetic pole obtained from seven ca. 770 Ma mafic sills in the SCC, which is coeval to the pole obtained from the Malani igneous suite in India. The data quality of both poles is assured by robust paleomagnetic field tests. Our reconstruction based on the updated paleomagnetic database and geological data demonstrates that the SCC was connected with India at ca. 770 Ma via linkages with other smaller Asian blocks. Furthermore, the SCC‐India landmass was located at high‐to‐mid latitudes and far from the core of Rodinia, for example, Laurentia and Australia, which were located at low latitudes at ca. 770 Ma.
... Asthenospheric or deep or plume and lithospheric or shallow or non-plume derived mafic melts or basalts can be differentiated or evaluated by geochemical ratios like Lanthanum (La) /Tantalum (Ta) and La/Nb. Thompson and Morrison [55] suggested that values of La/Ta =10-12 and La/Ta >30 indicates that basaltic rocks may have been derived from asthenospheric mantle and lithospheric [56] used La/Nb ratio to discriminate asthenospheric mantle and lithospheric mantle sources. They suggested La/Nb <1.5 for asthenospheric mantle derived mafic rocks and La/Nb >1.5 for lithospheric mantle derived mafic rocks. ...
Precambrian mafic magmatism and its role in the evolution of Earth’s crust has been paid serious attention by researchers for the last four decades. The emplacement of mafic dyke swarms acts as an important time marker in geological terrains. Number of shield terrains throughout the world has been intruded by the Precambrian dyke swarms, hence the presence of these dykes are useful to understand the Proterozoic tectonics, magmatism, crustal growth and continental reconstruction. Likewise, the Protocontinents of Indian Shield e.g. Aravalli-Bundelkhand, Dharwar, Bastar, and Singhbhum Protocontinent had experienced the dyke swarm intrusions having different characteristics and orientations. In Singhbhum craton, an impressive set of mafic dyke swarm, called as Newer dolerite dyke swarm, had intruded the Precambrian Singhbhum granitoid complex through a wide geological period from 2800 to 1100 Ma. Present chapter focuses on the published results or conclusions of these dykes in terms of their mantle source characteristics, metasomatism of the mantle source, degree of crustal contamination and partial melting processes. Geochemical characteristics of these dykes particularly Ti/Y, Zr/Y, Th/Nb, Ba/Nb, La/Nb, (La/Sm)PM are similar to either MORB or subduction zone basalts that occur along the plate margin. The enriched LREE-LILE and depletion of HFSE especially Nb, P and Ti probably indicate generation of these dykes in a subduction zone setting.
... Zhao 2015). After the collision, the detachment and sinking of oceanic crust, coupled with asthenospheric upwelling, led to post-orogenic extension at c. 815-750 Ma, responsible for the formation of c. 760 Ma OIB-like mafic rocks in western Hunan Province (Wang et al. 2008). Therefore, it is reasonable to conclude that the metasomatites formed during the post-orogenic stage (c. ...
South China Block (SCB) underwent a tectonic switch from compression to extension between Late Jurassic and Early Cretaceous, but the extension process has not been well understood. Here we report the Meiziwo lamprophyres in northern Guangdong formed at Early Cretaceous (ca. 136 Ma; 40Ar/39Ar dating) are characterized by oceanic island basalt (OIB)-like geochemical signatures and Pb enrichment, together with moderately high (87Sr/86Sr)i
(0.70642-0.70766), positive εNd(t) (+4.6 to +5.1), intermediate (206Pb/204Pb)i (18.579-18.602), (207Pb/204Pb)i (15.727-15.733), (208Pb/204Pb)i (38.871-38.909). The lamprophyres were derived from an asthenosphere-dominated source, with recycled oceanic crust and terrigenous sediments contribution. In contrast, the previously reported ca. 154 Ma mafic dyke in eastern Guangdong, and the ca. 165-155 Ma A-type granite belt in southern Hunan and nearby regions, show arc-like signatures and unradiogenic Nd but moderately radiogenic Pb isotopes, suggesting magma derivation from a lithospheric mantle. Hence, the change from lithospheric to asthenospheric sources may be caused by progressive lithospheric extension and thinning
associated with the rollback and tearing of the paleo-Pacific plate. The 136 Ma Meiziwo lamprophyres, together with the 140 Ma asthenosphere-derived OIB-like mafic rocks nearby, signify the petrologic response to regional extension in the South China Block from ca. 140 Ma onward.
... Metamorphism is a material accumulation and texture alteration phenomenon that happens as a result of physiological symptoms in hard rock caused by events such as crust movement, magma activity, or changes in the earth's thermal fluid. An acute anticline physically separates the Neoproterozoic metamorphosed strata of the Jiangnan Orogenic Belt into two low-grade mutated phases (BGMRHN 1988;BGMRJX 1984;BGMRGX 1985;BGMRZJ 1989;Guo et al. 1980;Zhou and Zhu 1993;Charvet et al. 1996;Wang et al. 2007Wang et al. , 2008aWang et al. , 2008bZhao 2015). A metamorphic facies series is a series of metamorphic zones, and the Barrovian is the most common. ...
... Volcaniclastics are sedimentary rocks that occur when lava erupts into the air. Despite being previously assumed to be Recent zircon U-Pb age analyses in the Mesoproterozoic have demonstrated that these groups arose during the early Neoproterozoic (850-820 Ma) (Yang et al. 1994;Wang et al. 2007Wang et al. , 2008aWang et al. , 2008bGao et al., 2008Gao et al., , 2010aGao et al., , 2011aZhou et al. 2009;Wang et al. 2010Wang et al. , 2012b. They have similar deformation and structural properties, with high-angle tight linear and isoclinal overturned folds being the most prevalent. ...
... They have similar deformation and structural properties, with high-angle tight linear and isoclinal overturned folds being the most prevalent. ((BGMRZJ 1989;BGMRJX 1984;BGMRHN 1988;BGMRGX 1985;Zhou et al. 2004;Wang et al. 2007Wang et al. , 2008aWang et al. , 2008bZhao and Cawood 2012). However, The Danzhou Group in north Guangxi Province, the Xiajiang Group in northeast Guizhou Province, the Banxi Group in Hunan Province, the Dengshan Group in Jiangxi Province, and the Likou Group/Jingtan Formation in south Anhui Province and the Heshangzhen Goup in northwest Zhejiang Province are among the metamorphic sequences above the unconformity and are only deformed into relatively simple, nearby vertical and open folds (BGMRJX 1984;BGMRHN 1988;BGMRGX 1985;Zhou et al. 2004;Wang et al. 2007Wang et al. , 2008aWang et al. , 2008bZhao and Cawood 2012) (Fig. 1). ...
The Jiangnan Orogenic Belt in South China formed as a result of the amalgamation between the Yangtze Block and the Cathaysian Block and records the geological information of collision. However, the timing of the amalgamation of two blocks remains controversial. Here, structural deformation and zircon U-Pb geochronological results from Precambrian metamorphosed sedimentary-volcanic rock units at the eastern domain of the Jiangnan orogenic belt in southern Anhui Province are presented. The pre-Nanhua rocks in the study area were widely involved in the metamorphism and deformation to with NW or SE-dipping foliation, tight folds and local development of strike-slip ductile shear zones, which is induced by collision of Yangtze Block and the Cathaysia Block. In this study, a mylonitic granodiorite sample intruding in the Xikou Group, a mylonitic dacite sample from Jingtan Formation and two deformed quartz veins samples in the Shexian region were dated by LA-ICP-MS zircon U-Pb dating method. Zircons from the mylonitic granodiorite and dacite yield the weighted mean ages of 811.2 ± 7.5 Ma (MSWD = 0.51, n = 30) and 779 ± 7.4 Ma (MSWD = 0.42, n = 29), respectively, interpreted as the crystallization ages of the original rocks, whereas the zircons from deformed quartz veins yield the weighted mean ages of 779 ± 14 Ma (MSWD = 2.6, n = 22) and 769 ± 16 Ma (MSWD = 2.4, n = 16), respectively, representing the crystallization age of the quartz veins. Combined with previous data, our results show that the metamorphosis and deformation of Pre-Nanhua rocks took place during the period of 820–770 Ma. Therefore, we consider that the Yangtze Block and the Cathaysian Block the eastern Jiangnan Orogenic Belt don’t amalgamate until 770 Ma.
... In addition, abundant basic and bimodal volcanic rocks of late Yanshanian ages (ca. 136-83 Ma) also occur in this area (Jia et al., 2003;Wang et al., 2008). These S-type granitoids and mafic rocks have been interpreted to be formed in an extensional tectonic setting (Jia et al., 2003;Li et al., 2009;Li and Li, 2007;Wang et al., 2008Wang et al., , 2014Xu et al., 2009). ...
... 136-83 Ma) also occur in this area (Jia et al., 2003;Wang et al., 2008). These S-type granitoids and mafic rocks have been interpreted to be formed in an extensional tectonic setting (Jia et al., 2003;Li et al., 2009;Li and Li, 2007;Wang et al., 2008Wang et al., , 2014Xu et al., 2009). ...
Hydrothermal alteration commonly occurs in lode gold deposits, and contributes to metal precipitation through water–rock interactions. In the Wangu gold deposit in northeastern Hunan, South China, bleaching of slates enclosing auriferous quartz veins widespreadly occur, with the colour transformed from dark-grey into pale yellow-grey. The bleaching has been used to guide gold exploration, but its nature and genesis, as well as the relationship with gold mineralization, remains unclear. Field and petrographic work, combined with Tescan Integrated Mineral Analyzer (TIMA), demonstrates that the bleaching is mainly caused by the combination of sericitization and carbonatization. Combined with fluid inclusion studies, it is inferred that bleaching is caused by the pre-ore hydrothermal event characterized with CO2-bearing fluids. Large amounts of siderite are distributed within the bleaching zones, and they are locally crosscut by sulfides, suggesting that the bleaching happened before gold mineralization. Mass balance calculation and μ-XRF analysis indicate that despite the abundance of siderite, Fe is not gained during alteration. Geochemical path modeling further suggests that siderite is efficient in precipitating Au by decreasing S contents in fluids and destroying Au-bearing complexes. In addition, the siderite contents in altered slates and Au contents in sulfides suggest that the chemical interaction between siderite and ore fluids can produce ores with economic significance. The siderite developed during the pre-mineralization alteration, provided ideal chemical traps and prepared the ground for gold mineralization. When the gold-bearing fluids overprinted the altered rocks, sulfides formed through reaction with siderite. It is concluded that the sulfidation, which resulted in the destruction of Au-S complexes, is the major mechanism for gold mineralization within the bleached slates.
... The Neoproterozoic igneous rocks have been studied for decades and received great attention in recent years due to the absence of diagnostic features of regional deformation and metamorphism in the orogenic belt Li et al., 2016b;Wang et al., 2012b;Wang et al., 2013a;Zheng et al., 2008b;Zhao and Cawood, 2012;Zhang et al., 2013a). One hotly debated issue is the exact time of the collision between the Yangtze and Cathaysia blocks, with one group suggesting that the collision occurred at some time between 900 Ma and 860 Ma Wang and Li, 2003;Wang et al., 2011a;Wang et al., 2011b), accompanied with extensive and intensive arc-related magmatism (Kou et al., 2018;Zheng et al., 2008a), while some authors considered that it might have happened during the interval between 870 Ma and 830 Ma Zhao and Cawood, 1999;Wang et al., 2008;Zhao et al., 2011). Recent geochemical and geochronological studies on the volcanic-sedimentary sequences in this orogenic belt conducted by argue against the two hypothesis and proposed a time of the collision should not be earlier than 830 Ma, accounting for the metamorphism and deformation of older successions, as well as the generation of ~835-815 Ma granitic rocks in the Jiangnan orogen. ...
... The overlying early Neoproterozoic sedimentary sequences in the western Jiangnan orogen are dominated by sandstone, siltstone, slate and phyllite, represented by the Sibao Group (local stratigraphic equivalents include the Fanjingshan Group in northeast Guizhou Province, the Lengjiaxi Group in central Hunan Province, the Shuangqiaoshan Group in northwest Jiangxi Province), corresponding to the Shangxi Group in south Anhui Province and the Shuangxiwu Group in west Zhejiang Province in the eastern Jiangnan orogen (for province locations see Fig. 3) (Zhao and Cawood, 2012). These early Neoproterozoic sedimentary rocks are commonly deformed into high-angle tight linear and isoclinal overturned folds (Hunan BGMR, 1988;Wang et al., 2007a;Wang et al., 2008;Wang et al., 2017a). The Sibao Group and its equivalents were traditionally considered as Mesoproterozoic in age, but new sedimentological and geochronological evidence indicates that they are Neoproterozoic with an upper age limit of ~820 Ma (Wang et al., 2017a). ...
... The north and south tectonic boundaries of the eastern Jiangnan orogen were previously thought to be along the Shitai-Jiujiang fault and Shaoxing-Jiangshan-Pingxiang fault (also called the Jiang-Shao fault), respectively ( Fig. 1) (Guo and Gao, 2018). Note that the Jiang-Shao fault is considered as the suture zone between the Cathaysia and Yangtze blocks in the Neoproterozoic (860-820 Ma) (Fig. 1, Cawood et al., 2013;Wang et al., 2008;Yao et al., 2014;Yao et al., 2017;Zhao and Cawood, 2012), but the southwestern extension of the boundary is unknown due to poor exposure and thermo-tectonic modification (Li et al., 2010c;Ren, 1991). ...
The Neoproterozoic NE-striking Jiangnan orogen in the South China Block (SCB) separates the Cathaysia microcontinent on the southeast from the Yangtze craton in the northwest. The origin and evolution of the Jiangnan orogen is unresolved, with individual models explaining part of the history, such as various magmatic, deformational, metamorphic, and sedimentary events including extensional, contractional, and transpressional modes. Here, we present detailed geochronological and Nd-Hf isotopic data for Neoproterozoic mafic and felsic intrusions in the Jiangnan orogen and identify three episodes of Neoproterozoic magmatism. The first stage ranging from ~1013–942 Ma is preserved predominantly in the eastern segment of the orogen, including a series of mafic rocks with ages of ~1010–952 Ma, contrasting with weak magmatic activity in the western segment with a peak at ~997 Ma. The second stage ranges from ~906 Ma to ~820 Ma, with intensive and extensive bimodal magmatism occurring in the eastern and western parts. The last stage mainly occurred in the western Jiangnan orogen in the period from ~800 to 780 Ma, associated with drastic mafic magmatism and weakly bimodal volcanic activities. The bimodal volcanism in the eastern segment exhibits a striking weak trend after ~823 Ma, distinctly different from the western segment where the magmatism lasted until ~785 Ma, indicating its syn- to post-collisional in nature. The pre-800 Ma magmatic rocks in western Jiangnan orogen have a dominant negative Nd isotopic signature but exhibit a significant positive trend after 800 Ma, different from those in east, which have a decreasing trend. Both parts display a roughly decoupled Nd-Hf isotopic character presented by a dominant positive pattern in Hf isotopes of the Neoproterozoic intrusive rocks, indicating a significant addition of previous slab-derived components or accretionary wedges in the pre-800 Ma magma evolution, and more depleted materials involved in the source in the later stages. Oceanic subduction under the northwestern Cathaysia Block occurred around ~1.0 Ga, slightly earlier than the subduction to the southeastern Yangtze. A gradual tectonic transition from post-orogenic extension to intracontinental rifting dominated the tectonics in Jiangnan orogen in the middle-late Neoproterozoic, followed by slab failure after ~790 Ma. Arc magmatism was the dominant source of crustal growth before 820 Ma in the SCB, but was exceeded in volume by later slab failure magmatism after ~790 Ma.
