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... The collision was accompanied by extrusion of lithospheric sub-blocks. Calculated by the length of the Qinling Tectonic Belt, the indentation distance is 850 km (Zhang, 2002;Zhang & Xing, 2003). Geophysical data show that after the NCB-GSCB collision, the NCB along the Sulu Orogen indented into the GSCB, causing the bending of the SDO. ...
The lithospheric “de‐rooting” of the Sulu‐Dabie Orogen (SDO) is an important tectonic mechanism for post‐orogenic tectono‐magmatism, which influenced the sedimentation, evolution, and development of oil–gas accumulation in the Hefei Basin (HB). Combined with seismic, geological, and sedimentary data of the HB and the SDO, this paper studies the coupling of the HB and the SDO since the Late Mesozoic. While the North China Block (NCB) indented south‐eastwards under the Greater South China Block (GSCB) since the Mesozoic, the SDO underwent three intense tectonic stages, i.e., subduction, exhumation, and uplift. The upwelling of deep mantle material causes the exhumation of the ultrahigh‐pressure metamorphic (UHPM) rocks to the upper crust or surface, forming the UHPM. Influenced by the indentation of the NCB, the “de‐rooting” of the SDO lithosphere, caused the delamination and thinning of the lithosphere, accompanied by the continuous flexural subsidence in the HB. The basin underwent at least four stages of tectonic evolution, involving sequentially: the flexural basin, the foreland basin, the strike‐slip‐related basin, and the faulted graben development periods. The tectonic evolution of the HB was closely coupled with the SDO orogeny. The “de‐rooting” of the SDO lithosphere resulted in a strong uplift and erosion of the orogen, providing abundant source of material for the HB and causing the successively northwards migration of basin depocenters at its early stage. Finally, influenced by the subduction retreat of the (Palaeo‐) Pacific Plate and the strike‐slip movement of the Tanlu Fault, the depocenters migrated to the east.
... The zircon U-Pb metamorphic ages reported for Shiwandashan, Yunkai, Nanling, and Zhejiang are mostly concentrated between 233 and 253 Ma (Peng et al. 2004;Xiang et al. 2008;Zhao et al. 2010;Wang et al. 2012), indicating a compressional environment during the Early to Middle Triassic. The compressional environment was also confirmed by (Shu et al. 1994;Zhang and Zhu 2003;. The U-Pb ages of the Late Triassic (late Indosinian) A-type granites in the SCB are from 232 to 202 Ma, and most concentrated in 225 and 230 Ma. ...
The Triassic (Indosinian) granites in the South China Block (SCB) have important tectonic significance for understanding the evolution of Eastern Asia. The Dengfuxian biotite granite in eastern Hunan Province, China, reported in this article, was recognized as Late Triassic (late Indosinian) weakly peraluminous A-type granite with a zircon laser ablation inductively coupled plasma mass spectrometry U–Pb age of 225.7 ± 1.6 Ma. It is enriched in F, Cs, Rb, Th, high field strength elements, and rare earth elements (REEs) and depleted in Ba, Sr, P, Ti, Nb, and Ta, with high Ga/Al ratios and zircon saturation temperatures. The Dengfuxian biotite granite shows high initial Sr isotope values (0.715932 to 0.716499) and negative ɛ Nd(t) (−10.46 to −9.67) and ɛ Hf(t) (−9.92 to −6.29) values, corresponding to the Nd model ages of 1.79 to 1.85 Ga and the Hf model ages of 1.65 to 1.88 Ga. It is proposed that the Dengfuxian biotite granite was derived from high-temperature partial melting of the Palaeoproterozoic lower crust undergoing granulitization. Some Late Triassic A-type granites were recently identified in the SCB with the ages between 202 and 232 Ma. These A-type granites have the same geochemical characteristics and petrogenesis as Dengfuxian A-type granite, and show A2-subtype granite affinity. The Late Triassic A-type granite formed a NE-trending granite belt, which is consistent with the main NE-trending faults in the SCB. The formation of these A-type granites was in response to the subduction of the palaeo-Pacific plate underneath the SCB, and indicates an extensional tectonic environment in the SCB. Combined with previous studies on tectonic evolution, we suggest that there may be a tectonic transition inside the SCB from compression to extension at least from 225 to 230 Ma.
... Subsequently, the SCB moved toward northern and collided with the North China Block along the Dabie-Sulu ultrahigh-pressure metamorphic belt, and the peak age of the collision is dated at 240-225 Ma (Li et al., 1993;Zheng, 2008). During this period, strong folding, thrust faulting and nappe structure were developed in the SCB (Liang et al., 2005;Shu et al., 1994;Zhang and Zhu, 2003;Zhang et al., 2009). Most Indosinian folds were EW-trending and were superimposed by Jurassic NE-trending folds . ...
... Thus, the SCB was clamped between these two collision belts, resulting in a significant compressional stress. In this period, strong folding, thrust faulting and nappe structure were developed in the SCB (Liang et al., 2005;Shu et al., 1994;Zhang and Zhu, 2003). Zhang et al. (2009) identified early Mesozoic west-east trending folds in the SCB. ...
A detailed study utilizing zircon U-Pb dating, major and trace
element geochemistry, and Sr-Nd-Hf isotope geochemistry has
been carried out for the Caijiang granite in Jiangxi Province and the
Gaoxi granite in Fujian Province, South China. The new data indicate
that the Caijiang and Gaoxi granites are Triassic (228-230 Ma) and
have the petrographic and geochemical characteristics of A-type
granites. In both granites, biotite occurs along the boundary of
euhedral plagioclase and quartz, which implies that the primary magma
could have been anhydrous. The two granites show high contents of total
alkalis (Na2O + K2O = 7.81-12.15%), high
field strength elements (e.g. Zr = 240-458 ppm, Y =
16.8-38.0 ppm, Nb = 13.5-33.8 ppm and Zr + Nb + Ce + Y =
382-604 ppm) and rare earth elements (total REE = 211-373
ppm) as well as high Ga/Al ratios (10000 × Ga/Al =
2.41-3.53). The lowest magmatic temperatures estimated from zircon
saturation thermometer were 800-840 °C for the Caijiang
granite and 820-850 °C for the Gaoxi granite, respectively.
The Caijiang granite has relatively high
(87Sr/86Sr)i ratios of 0.71288 to
0.72009, low ɛNd(t) values of - 9.9 to -
9.3, and low zircon ɛHf(t) values (peak value of
- 7.5). Whole-rock Nd isotopic model ages and zircon Hf isotopic
model ages mostly vary from 1.65 Ga to 1.80 Ga. The Gaoxi granite has
also high (87Sr/86Sr)i ratios of
0.71252 to 0.71356, low ɛNd(t) value of - 13.8
and low zircon ɛHf(t) values (peak value of -
12.0). Whole-rock Nd isotopic model ages and zircon Hf isotopic model
ages mostly vary from 1.95 Ga to 2.10 Ga. According to these data, we
suggest that the two granites might have been derived from partial
melting of Precambrian crustal rocks that had been granulitized during
an earlier thermal event. Our study of the Caijiang and Gaoxi granites,
together with previous studies on two Triassic alkaline syenites
(Tieshan and Yangfang) in Fujian Province and one A-type granite
(Wengshan) in Zhejiang Province in South China, indicate a wide
transtensional tectonic environment in the Cathaysia Block that lasted
at least from 254 Ma to 225 Ma. Combined with extant data for the
Indosinian granites and tectonic evolution in South China, we suggest
that the formation of A-type granites was related to the local
NE-trending extensional faults probably caused by collision between the
South China Block and the Indochina Block or the North China Block.
... Thus, the South China Block was clamped between these two collision belts, resulting in a significant W-E trend compressional stress in the Indosinian era. In this period, strong folding, thrust faulting and nappe structure were developed in the South China Block (Shu et al., 1994;Zhang and Zhu, 2003;Liang et al., 2005;Zhang et al., 2011). The Indosinian granites in South China are dated at the cluster of 243-235 Ma and 218-210 Ma respectively, which were suggested to form as syn-and late-collisional granites Wang et al., 2007;Chen et al., 2011). ...
The Shi-Hang zone is an important NE trending Mesozoic magmatic belt composed of granites with relative high εNd(t) values and young TDM model ages in South China. However, the petrogenesis and the tectonic environment for the Shi-Hang zone magmatic rocks remain controversial. We report here mineral chemistry, geochemical and Sr–Nd–Hf isotopic data for the Cailing and Furong granites and mafic microgranular enclaves (MMEs) from the Qitianling granite batholith in southern Hunan province, South China. The Qitianling granite batholith is a multi-staged composite pluton with three phases (Cailing, Furong, and Huangtangling) according to their ages and petrography. The Cailing (163–160Ma) and Furong (157–153Ma) phases are mainly composed of porphyritic amphibole–biotite monzogranite, and they share similar geochemical and isotopic characteristics. Both of them show similar SiO2 contents from 66.50 to 70.28%, and metaluminous A/CNK values of 0.80 to 0.98. The granites are characterized by high contents of large ion lithosphile elements (LILE) such as Rb, Th, U, Pb; high field strength elements (HFSE) such as Nb, Ta, Zr, Hf; and Zr+Nb+Ce+Y contents >350ppm, and high 10,000∗Ga/Al ratios >2.6. Chondrite-normalized REE patterns show relative enrichment of light rare earth elements (LREEs) and significant negative Eu anomalies. Mineralogical and geochemical features suggest that the Cailing and Furong granites are A-type, which can be further classified as A2 subtype. They have relatively lower (87Sr/86Sr)i ratios (0.7091–0.7132), higher εNd(t) values (−5.5 to −7.6) and younger Nd isotopic model ages (1.48–1.56Ga) than those common S-type granites in South China. Zircon εHf(t) values vary from −8.1 to −3.7. The MMEs in the Cailing phase show similar trace element and Sr–Nd isotopic characteristics with the host granites. But zircons from the MMEs show different εHf(t) values (−6.4–+2.6) with those from the host granites (−8.1 to −3.7). This indicates that the MMEs and host granites were crystallized from different sources of magmas, providing direct evidence for mafic–felsic magma mixing processes. The isotope data indicate that the Cailing and Furong granites from the Qitianling batholith were derived from a hybrid magma consisting of about 80% felsic magma derived from old crust and about 20% mantle-derived mafic magma. The strong magma mixing at about 160–155Ma caused by intra-arc rifting or back arc extension related to subduction of the Paleo-Pacific plate, is favored to explain the petrogenesis of the Cailing and Furong granites, as well as the Shi-Hang zone.
... Thus, the SCB was clamped between these two collision belts, resulting in a significant compressional stress. In this period, strong folding, thrust faulting and nappe structures were developed in the SCB (Shu et al., 1994; Zhu et al., 1999; Zhang and Zhu, 2003; Liang et al., 2005). The absence of synchronous bimodal volcanic rocks or A-type granitoids also supports a collisonal rather than extensional setting. ...
The F-rich Hongshan pluton in the eastern Nanling Range, southern China, is a topaz-bearing albite leucogranite. It is distinctive from other topaz-bearing felsic rocks in South China with respect to age, size, geochemical evolution and topaz mode and morphology. The Hongshan granites are highly peraluminous and characterized by high K2O/Na2O, Si, Rb, Cs, Nb, Ta and F, and low Ca, Ba, Sr, Zr, Hf, P, K/Rb, Zr/Hf and Eu/Eu*. The granites show significant trace-element variations with magma evolution, with increasing Rb, Cs, Nb, Ta, Sn, W and decreasing Sr, Ba, Zr, Hf, Y, REE, Pb, Th, K/Rb, Zr/Hf, Th/U and Eu/Eu*. These changes dominantly reflect fractional crystallization of plagioclase, biotite and accessory minerals such as zircon and monazite. The granites also exhibit a decrease in ɛNd(t = 225 Ma) from −7.9 to −11.7 with magma evolution. Modeling shows that the Nd isotopic variation could result from assimilation of the Taoxi Group wall rocks during fractional crystallization. The Hongshan pluton also shows spatial geochemical variations; the most evolved parts are located in the southeastern part of the pluton, which would be the most likely target area for rare-metal mineralization commonly associated with other topaz-bearing granites.
Two types of Late Triassic granite are found in the Guandimiao Complex of the South China Block (SCB). Here, we present new LA–ICP–MS zircon U–Pb ages as well as geochemical and Sr–Nd–Pb–Hf isotopic data in order to elucidate the genesis of these granites. The Guandimiao Complex, located in southern Hunan Province, consists dominantly of the Shizhuqiao two-mica alkali feldspar granite and the Jingtou hornblende-bearing biotite monzogranite. The latter contains abundant microgranular enclaves. Zircon U–Pb isotopic analyses show that the microgranular enclaves and the two types of granite were all emplaced during the Late Triassic (226–220 Ma). The Shizhuqiao peraluminous granite has high (⁸⁷Sr/⁸⁶Sr)i ratios (0.72173–0.72485), enriched εNd(t) and εHf(t) values (–9.6 to –9.4 and –10.5 to –5.5, respectively), and Pb isotopic compositions similar to those of the metamorphic basement of the Cathaysia Block (part of the SCB), implying derivation from the crust. The granite’s low molar CaO/(MgO + FeOT) ratios and high molar Al2O3/(MgO + FeOT) ratios indicate a metasedimentary source. The Jingtou metaluminous granite exhibits εHf(t) values (–10.0 to –5.6) that are similar to those of the Shizhuqiao granite, but it has lower (⁸⁷Sr/⁸⁶Sr)i ratios (0.71326–0.71454) and higher εNd(t) values (–7.2 to –6.6). Its high ratios of molar CaO/(MgO + FeOT) and low ratios of molar Al2O3/(MgO + FeOT) suggest an amphibolitic source. The microgranular enclaves contain acicular apatite and are more mafic than their hosts. The combined textural, geochemical, and isotopic data indicate that the enclaves in the Jingtou granite originated from a more mafic crust-derived melt that was injected into the host felsic melt. The geochemical signatures indicate that the microgranular enclaves and the two types of coeval granite that constitute the Guandimiao Complex were derived from different source rocks. The Late Triassic granites in the SCB were emplaced in an extensional post-orogenic setting and related to underplating of mantle-derived magma.
The Miao'ershan uranium ore district is one of the most important granite-hosted uranium producers in South China. There are several Triassic granite plutons in the Miao'ershan batholith, but uranium ore deposits mainly occur within the Douzhashan granitic body. Precise zircon U–Pb dating indicated that these Triassic granite plutons were emplaced during 204 to 215 Ma. The Douzhashan U-bearing granite lies in the central part of the Miao'ershan batholith, and has higher U contents (8.0 to 26.1 ppm, average 17.0 ppm) than the nearby Xiangcaoping granite (5.0 to 9.3 ppm, average 7.0 ppm) and the Yangqiaoling granite (6.4 to 18.3 ppm, average 11.5 ppm) in the south part of the batholith. The Douzhashan granite is composed of medium-grained two-mica granite, whereas the Xiangcaoping and Yangqiaoling granites are composed of porphyritic biotite granite. Both the Xiangcaoping and Douzhashan granites have high A/CNK ratios (> 1.10), high (87Sr/86Sr)i ratios (> 0.720) and low εNd(t) values (− 11.3 to − 10.4), suggesting that they belong to strongly peraluminous S-type granites. The Douzhashan granite has low CaO/Na2O ratios, high Rb/Sr and Rb/Ba ratios, indicating a partial melting origin of clay-rich pelitic rocks. In contrast, the Xiangcaoping granite formed from clay-poor psammite-derived melt. The Yangqiaoling granite shows different geochemical characteristics with the Douzhashan and Xiangcaoping granites, indicating a different magma source. The Yangqiaoling granite has higher εNd(t) of − 9.4 to − 8.3 and variable A/CNK values from 0.98 to 1.19, suggesting a mixture source of meta-sedimentary rocks and meta-igneous rocks. Crystallization fractionation is not the main mechanism for U enrichment in the Douzhashan granite. We suggest that U-rich pelitic rock sources may be the key factor to generate peraluminous U-bearing granites in South China. Searching for those granites which are reduced, strongly peraluminous and were derived from U-rich pelitic rocks, is the most effective way for exploring granite-hosted U deposits.
The Fucheng granitic complex is located in the southeastern Jiangxi province, which is combined with the Hongshan granite in the southwestern Fujian province to be the Fucheng-Hongshan Complex. The Fucheng Complex may be divided to three units, the Fucheng megacrystic porphyrotic biotite monzogranite, the Cushiba middle-grained two-mica granite and the Zhuchangdong andalusite-bearing fine-grained granite. The Fucheng biotite granites have relatively low SiO2, Rb and Nb concentrations and high Al2O3, Ba, Sr, Zr, REE concentrations. Their ACNK are > 1.10 and K2O/Na2,O > 1.60. The Cushiba granites are characterized by high SiO2, K2O and Al2O3 (ACNK = 1.13∼1.20), and low CaO and P2,O5. The rocks are rich in Rb and Nb, and poor in Ba, Sr, Zr and REE. They all have relatively low K/Rb and Eu/Eu ° ratios. The Zhuchangdong andalusite-bearing granites are similar to the Fucheng granites in geochemistry, except for higher ACNK (1.22∼1.36), Cs, Rb, Nb, Ta and Sn concentrations and lower Sr, Ba, Zr, Hf and REE contents. The Fucheng granites have initial 87Sr/86Sr ratios of 0.7135∼0.7196 and εNd (t) of -9.4∼10.2 with the Nd model ages ranging from 1.84Ga to 1.78Ga. The zircons in the Fucheng granite have Hf model ages of 1.70 ∼ 1.89Ga, consistent with bulk Nd model ages. The Cushiba granites have bulk Nd isotope and zircon Hf isotope similar to the Fucheng granites, The Zhuchangdong granite has higher initial 87Sr/86Sr ratio (0.7214) and lower εNd (t) value (-16.9) with older Nd model age (2.37Ga). These geochemical data indicate that the protoliths of granites in the Fucheng Complex are sedimentary rocks consisting of ancient crustal materials. The original magma of the Fucheng and Cushiba granites probably originated from late Paleoproterozoic basement, and the source of the Zhuchangdong granites is early Paleoproterozoic basement. A variety of granites from the three units in the complex do not exhibit coherent geochemical change, suggesting they are not the results evolved from an original magma, which also is supported by field observation and geochronological studies. The difference in geochemistry among granites from three units is likely caused by the source compositions. LA ICPMS zircon U-Pb dating indicates that the Fucheng granite formed at ca. 239Ma, and the Cushiba and Zhuchangdong granites formed at 231 ∼ 229 Ma, which are in accordance with peak time of early Indosinian tectonic-magmatic activity in south China. Coupled with the geochemical characteristics and assemblage of Indosinian rocks, it is suggested that the Fucheng-Hongshan granitic complex was probably formed in the syn-orogenic tectonic setting.
