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Indosinian collisional orogeny: Evidence from structural and sedimentary geology in Shiwandashan basin, South China
... In fact, two episodes of Mesozoic deformation are recognized in Jiulingshan and Wugongshan massifs of South China (Lin et al., 2001;Shu et al., 1998;Faure et al., 1996;Guo et al., 2001). For the Shiwandashan Basin and its adjacent region (such as Yunkaidashan) within South China, a Late Permian-middle Triassic NW-SE compressional phase characterized by southeast verging thrusts, upright folds and vertical cleavage was followed by a Late Triassic-Cretaceous extensional phase characterized by high-angle normal-fault, layer parallel slip, collapse folds and allochthons of Devonian sandstones or siliceous rocks on top of Carboniferous-Early Permian carbonates and Late Permian-Middle Triassic molasse (Ma et al., 1983;Qiu, 1993;Guo, 1994;Yun et al., 1998;Zhu et al., 1999;Xu et al., 2001a;Liang et al., 2005). Indeed, strata up to Upper Jurassic are strongly folded and involved in thrusting, also documented by drilling (Han and Yang, 1980), and give evidence for an important Early Mesozoic Indosinian and Late Mesozoic Yanshanian tectonism (Chen and Zheng, 1993;Xu et al., 2001b;Wang, 1986;Guo, 1994). ...
... The top unconformity is recognized as a stratigraphic break throughout the foreland basin system (GXBGMR, 1985). This indicates that pre-Upper Triassic rocks were exposed subaerially and that the Shiwandashan region went into a stage of regional post-orogenic extension in the Late Triassic (Liang et al., 2005;Zhu et al., 1999;Yun et al., 1998;Shu et al., 1998;Faure et al., 1996). ...
... During continuous slow thrust of early Late Permian, source uplift and plate flexure are recorded by the thick coarsening-upward sedimentation and the increase of sedimentation rates of Lower Upper Permian. Locally, in the center of the basin, this tectonic event caused a second inversion event of the Late Paleozoic inherited structures GXBGMR, 1985), in a left lateral convergent regime (Liang et al., 2005). This deformation gave rise to local progressive unconformities producing a local second-order stratigraphical response to the uplift event. ...
The Shiwandashan Basin is an elongate region of the Late Permian–Middle Triassic potential sediment accommodation that formed on continental crust between the Yunkai Orogen and the adjacent Yangtze Craton Block, South China. Several terms such as remanent marine trough, structural window, rift and pull-apart basin have been proposed. Studies of the Late Permian–Middle Triassic sedimentary sequences and the tectonics lithofacies and paleogeography of the Shiwandashan Basin indicate that the Late Permian–Middle Triassic succession is composed of thick, coarse molasse deposits and fine clastics, organized into coarsening-upward and fining-upward stratigraphic sequences. The Shiwandashan Basin went through the process of growth and disappearance from molasse to turbidite deposition and finally to volcanic eruption during Late Permian–Middle Triassic. To some extent, the facies evolution reflects the tectonic controls on the sedimentation of the foreland basin. The coarsening-upward sequences (hundreds to thousands of metres scale), occurring immediately adjacent to the thrust front, demonstrate that important episodic thrusting-orogenesis and piedmont flexuring-subsidence with low velocity took place in the northwestern part of the Yunkai Orogen, whereas fining-upward sequences are the indicator of continued deformation with high thrust velocity. The following four facts have been demonstrated: (1) a foreland basin existed in Late Permian–Middle Triassic. (2) The development of the foreland basin was controlled by the evolution the Yunkai Orogen. (3) The basin and mountains continuously changed and migrated. (4) The Shiwandashan Basin was a key demarcation between an active region in southeastern South China (Cathaysian Block) and a relatively stable region in northwestern (Yangtze Block). It was a convergent boundary in Late Permian–Middle Triassic and its tectonic nature changed in the wake of the tectonic evolution of the surrounding area.
... The six samples of dolerite collected in this study intruded into the fine interbedded sandstone within deep gray, gray-black thin to medium-bedded mudstone and siltstone (Figure 1c). [38], (b) adopted from [39], (c) adopted from the geological map from the Jiangxi Provincial Geological Information Center. ...
... Another dike to the southwest has a width of about 70 m and extends for approximately 500 m, but its orientation is unclear. The two mafic dikes are controlled by northeast−southwest and east- [38], (b) adopted from [39], (c) adopted from the geological map from the Jiangxi Provincial Geological Information Center. ...
Mafic dikes are developed in the Shangsu region of Jiangxi, including Nanyuan Mountain and Mianhuaao. These dikes intrude into the Upper Triassic Anyuan Formation and are primarily composed of pyroxene, plagioclase, and opaque minerals, exhibiting a dolerite texture. The mafic dikes were found to have an SiO2 content ranging from 48.38% to 50.53% and the (K2O + Na2O) content ranging from 2.88% to 4.16%. The Na2O/K2O ratio was found to be between 2.56 and 3.99. The Eu anomaly was absent (δEu = 0.91–0.95), suggesting no influence of plagioclase fractionation during the rock formation process. The Ce anomaly was found to be absent (δCe = 1.04–1.08). The Mg# was found to range from approximately 40.06 to 45.06, indicating minimal crystal fractionation within the magma. The mafic dikes are enriched in light rare earth elements and large ion lithophile elements (LILE) and Th, while they showed significant depletion of high field strength elements (Nb, Ta, Ti). The Ti depletion may be related to the separation and crystallization of Ti-bearing minerals such as amphibole and ilmenite. Zr and Hf anomalies were evident, likely due to the contamination of zircon minerals in the samples. The mafic dikes were most likely products of the Middle–Late Yanshanian magmatic intrusion, formed in an extensional setting within the intracontinental rift environment caused by the collision of the Pacific Plate and the Eurasian Plate. The lithospheric mantle source was influenced by subduction zone fluid, and the magma source region exhibited mixed crustal materials.
... Wu et al. (2012) also discovered a group of magmatic zircons of 243 Ma in the late Indosinian granite when they studied Miaoershan-Yuechengling complex granite and inferred that the early Indosinian granite was emplaced in the deep position. The studies in recent years show that the South China block was in the collisional, compressional, and orogenic environment in the early Indosinian (Liang et al., 2005;Charvet et al., 1996;Wang Y J et al., 2012Wang Y J et al., , 2013. Wang Y J et al. (2013) proposed that the collision between the blocks around South China block triggered Indosinian intracontinental orogenesis. ...
... The studies on the Shiwandashan Basin show that the southeast Guangxi had entered into the transformational extensional setting from the Late Triassic (Liang et al., 2005;Charvet et al., 1996;Wang Y J et al., 2012). The discovery of the late Indosinian A-type hypersthene granite in the south of the Darongshan-Shiwandashan granite belt also suggests this area turned into the extensional environment after the early Indosinian collisional orogenesis (Peng et al., 2004). ...
The samples from the hidden Daqiling muscovite monzonite granite, which has recently been recognized within the Limu Sn-polymetallic ore field, have been analyzed for zircon U-Pb ages and whole rock geochemical and Nd-Hf isotopic compositions to discuss its genesis, source, and tectonic setting. LA-ICP-MS zircon U-Pb dating indicates that the granite crystallized in the late Indosinian (224.8±1.6 Ma). The granite is enriched in SiO2 and K2O and low in CaO and Na2O. It is strongly peraluminous with the A/CNK values of 1.09–1.20 and 1.4 vol%–2.7 vol% normal corundum. Chondrite-normalized REE patterns show slightly right-dipping shape with strongly negative Eu anomalies (δEu =0.08–0.17). All samples show enrichment of LILEs (Cs, Rb and K) and HFSEs (U, Pb, Ce and Hf), but have relatively low contents of Ba, Sr and Ti. The zircon saturation temperatures (T
zr) are from 711 to 740°C, which are slightly lower than the average value of typical S-type granite (764°C). The granite has negative ɛ
Nd(t) and ɛ
Hf(t) values, which change from −9.1 to −10.1 with the peak values of −9.2 to −9.0 and from −3.7 to −12.6 with the peak values of −6 to −5, respectively. The T
DMC (Nd) and T
DMC (Hf) values are 1.74–1.82 Ga with the peak values of 1.73–1.75 Ga and 1.49–2.04 Ga with the peak values of 1.5–1.6 Ga, respectively. These characteristics reveal that the source region of the granite is dominantly late Paleoproterozoic to early Mesoproterozoic crustal materials. Seven inherited magmatic zircons are dated at the age of 248.6±4.3 Ma, which suggests the existence of the early Indosinian granite in Limu area. These zircons have the ɛ
Hf(t) values of −6.7–−2.3, similar to those of the Daqiling granite, implying the involvement of the early Indosinian granite during the formation of the Daqiling granite. Inherited zircon of 945±11 Ma has the ɛ
Hf(t) and T
DM(Hf) values of 8.7 and 1.14 Ga, respectively, compatible with those of the Neoproterozoic arc magmatic rocks in the eastern Jiangnan orogenic belt. Therefore we inferred that Neoproterozoic arc magma might have been involved in the formation of the Daqiling granite, and that the Neoproterozoic arc magma belt and continent-arc collision belt between the Yangtze and Cathaysia Blocks might have extended westsouthward to Limu region. It is proposed that the underplating of mantle materials triggered by crustal extension and thinning resulted in partial melting of crustal materials to form the Daqiling granite in the late Indosinian under post-collisional tectonic setting.
... 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.
... One of such shear zones is exposed in the Hetai gold district (Fig. 6c) that has been long recognized as having a mean N70 • E strike (Zhou, 1990;Duan et al., 1992a,b). A same striking of mylonitic foliation steeply dipping to NW or SE dominates, bearing a lineation plunging shallowly to N45-60 • E (Liang et al., 2005). Kinematic criteria, such asand ␦-type porphyroclasts (Fig. 5a), S/C fabrics, and curved mica flakes on the sections perpendicular to foliation and parallel to lineation, suggest a dextral sense of shear. ...
... The same tectonic regime has also been proposed for the development of the ductile shear zones near Song Wang in the southernmost part of the fault belt ( Fig. 2) (Qin, 2002). An early Jurassic age has been grossly assigned to these dextral shears based on the overprinting relationships with SE-verging thrusts supposedly with a broad Triassic age (Zhang et al., 1995b;Liang et al., 2005). However, precise radiometric constraints on the dextral shear faulting are still lacking. ...
Ductile shear structure of the Guanging-Bobai fault belt in the SW part of the Qin-Hang belt, South China, has been investigated and interpreted in terms of radiometric dating data. A series of ductile shear zones occurs within the fault belt with deformation and metamorphic features indicative of formation under medium temperature and pressure conditions. The foliation such formed is steeply dipping and bears a gently plunging lineation, which along with the dextral kinematic indicators determines a broad NE-SW-trending dextral strike-slip regime responsible for the development of these shear zones. Field overprinting relationships indicate that this dextral shear is pre-dated by the Indosinian (P2-T) NNE-verging thrusting and post-dated by the Yanshanian (J2-K2) SE-verging thrusting, and thus occurred during a transitional period between the two orogenies. 40Ar–39Ar radiometric dating on muscovite from mylonites further constrains timing of the dextral shear to the Early Jurassic (187–193 Ma). Based on the coeval tectonic framework of eastern Asia, we propose here that the dextral strike-slip system was initiated by the far-field oblique stress field from the incipient subduction of the Izanagi oceanic plate. An offset continental margin of the South China plate may have been created in response to this transcurrent movement along the fault belt, dissecting and displacing not only a relict Caledonian foreland basin, but also an Indosinian magmatic belt.
... Based on these, it can be inferred that the tectonic setting of the SCB was transformed into post-collisional extension in the late Triassic. According to the detailed structural and sedimentological analyses of the Shiwandashan Basin, Liang, Li, Qiu, and Yang (2005) ...
The mafic igneous activities in the late Triassic play an important role in the tectonic evolution of the Hornblende South China Block (SCB). In this paper, relevant data of the bojites in Yajiangqiao area, eastern Hunan Province, South China were provided, including zircon U–Pb ages, whole‐rock geochemical data, Sr–Nd–Pb isotopic data, and zircon Hf isotope data. These data indicate that the bojites were crystallized at ~ 215.7 Ma, and thus are coeval with biotite monzonitic granites of Yajiangqiao pluton. The bojite samples feature a low SiO2 content of 48.84–49.94 wt%, a low ALK (K2O + Na2O) content of 5.13–6.13 wt%, a relatively high Al2O3 content of 17.64–21.22 wt%, a moderate MgO content of 4.32–7.07 wt%, and a moderate FeOT content of 5.66–7.33 wt%. In addition, the samples have a total rare earth element (REE) content of 108–163 ppm. They display right‐declined REE patterns, enriched in light rare earth elements and large‐ion lithophile elements (such as Rb, K, Th, and U) and depleted in high field strength elements (such as Nb, Ta, P, and Ti). All the samples have homogeneous Sr–Nd–Pb and zircon Hf isotopic compositions, with the (87Sr/86Sr)i ratio varying from 0.708 202 to 0.709 515, (143Nd/144Nd)i ratio from 0.512 156 to 0.512 229, (206Pb/204Pb)t ratio from 18.185 to 18.264, (207Pb/204Pb)t ratio from 15.667 to 15.672, (208Pb/204Pb)t ratio from 38.510 to 38.587, and initial 176Hf/177Hf ratio ranging from 0.282 428 to 0.282 530. Meanwhile, the calculated εNd(t) and εHf(t) values range from −4.0 to −2.6 and from −7.9 to −4.1, respectively, with two‐stage Nd model ages of 1.20–1.32 Ga and two‐stage Hf model ages of 1.35–1.56 Ga, respectively. As indicated by geochemical data, the primitive magmas of the bojites in Yajiangqiao area were derived from lithospheric mantle in post‐collisional extensional environment, which underwent low‐degree partial melting (1–5 %) of spinel‐garnet lherzolites (spinel > garnet) and was subjected to metasomatism of slab‐derived fluids. Furthermore, it can be concluded from these data and previous data that the SCB was transformed from syn‐collisional compression to post‐collisional extension in the late Triassic (~ 234 Ma) and the post‐collisional extension lasted until 215 Ma.
... Considering palaeocurrents and the presence of volcanic lithic fragments, detrital zircons from this age span were considered to be the first-cycled input from the Tethyan subduction-collisional belt to the southwest (Yang et al. 2012). Subsequently an unconformity developed between the Middle and Upper Triassic in the SCB (Guo 1994;Liang et al. 2005), Ailaoshan suture, and Indochina Block, representing the final amalgamation between the Indochina Block and SCB (Figure 2(a)). Several layers of volcanic rocks from Late Devonian (Wu 1991), early Carboniferous, Late Permian, and Middle-Late Triassic have been reported near the contemporaneous Mn ore deposits (BGMRY 1990;Liu et al. 1993). ...
The evolution of the Palaeo-Tethys Ocean played an important role in the Palaeozoic tectonometallogenesis in Southeast Asia, in which diverse blocks amalgamated due to its closure. Previous researches focused mostly on endogenic metallogenesis related to the evolution of the Palaeo-Tethys Ocean. However, the tectonic control on the numerous Mn ore deposits in the southwestern South China Block (SCB) developed during Palaeo-Tethys evolution is largely unknown. In this article, we review Palaeo-Tethys evolution and define its four evolutionary stages from initial opening, maturity, incipient subduction, to post-closure. This study further investigated the geology and palaeogeography of Mn ore deposits in Upper Devonian, lower Carboniferous, middle Permian, and Lower-Middle Triassic formations in the southwestern SCB. We show that each of the four Mn metallogenic episodes was a response to each of the four evolutionary stages of the Palaeo-Tethys Ocean. Wall rocks of orebodies transitioned from chert-mudstone-carbonate in the Devonian, Carboniferous, and Permian to siltstone-mudstone in Lower-Middle Triassic. The ores of the four episodes of Mn mineralization are composed primarily of rhodochrosite, manganocalcite, and rhodonite. The carbonate C–O isotope and ore trace element composition data suggest that ore-forming fluids were dominated by seafloor water with involvement of magmatic hydrothermal fluids and organic matter as well. Palaeogeography reconstructions indicate the Mn-ore deposits formed along the margins or in the centre of the abyssal basins. Despite the diverse tectonic settings of the four Mn mineralization episodes, it is proposed that the crustal sagging, restricted seafloor environment, and hydrothermal activities that occurred in the southwestern margin of SCB contributed to Mn mineralization.
... Qinling-Dabie Suture Zone occurred at ca. 238-218 Ma (Li et al., 1993Ayers et al., 2002;Li, 2004;Weislogel et al., 2006;Zheng, 2008). As a result, strong compressional deformation occurred in the South China Block that is located between the Song Ma and Qinling-Dabie Suture Zones, and resulted in crustal thickening associated with folding and thrusting, as well as compressional deformation within the contemporaneous basins (Wang et al., 2002;Sun et al., 2003;Liang et al., 2005;Yan et al., 2006;Qiu et al., 2016). Subsequent release of compressional stresses resulted in a shift from compressional to extensional deformation, during which upwelling of mantle-derived magmas occurred about 10-20 Ma after the change of tectonic settings (cf. ...
The Xitian pluton in southeast Hunan province is one of the early Mesozoic (Indosinian) granitic plutons in the South China Block. It is composed of biotite adamellite with K-feldspar megacrysts, biotite adamellite, and biotite granite that have U-Pb zircon ages of 229.9 +/- 1.4 Ma, 223.6 +/- 1.3 Ma, and 224.0 +/- 1.4 Ma, respectively. The Indosinian granitoids in the Xitian pluton belong to S-type granites, with highly radio genic initial Sr-87/Sr-86 ratios (0.71397-0.71910), negative epsilon(Nd)(t) values ranging from -10.1 to -9.4, and old Nd model ages (1858-1764 Ma). They are enriched in radiogenic Pb isotopes, with (Pb-206/Pb-204)(t) ranging from 18.130 to 18.903, (Pb-207/Pb-204)(t) from 15.652 to 15.722, and (Pb-208/Pb-204)(t) from 38.436 to 39.037, respectively. These features indicate that the granitoidswithin the Xitian pluton were formed from magmas generated by remelting of metapelite and metapsammite of the Paleoproterozoic metamorphic basement at temperatures of ca. 800 degrees C, with low oxygen fugacity. The Sr-Nd isotopic compositions of the rocks from Xitian pluton indicate that the granitic magmas were mixed with less than 10% mantle-derived magmas. We suggest that the Xitian pluton was emplaced in an extensional tectonic setting related to release of compressional stresses within the thickened crust during the early Mesozoic.
... Structural and sedimentological studies of the Shiwandashan Basin by Liang et al. [84,85] show that the Yangtze and Cathaysia blocks collided in the early Indosinian, beginning in Late Permian and continuing until Middle-Late Triassic. At the end of the collisional phase in the Middle-Late Triassic, the region shifted from compression to extension. ...
Zircon LA-ICP-MS U-Pb dating of the Jingju syenogranites in the southwestern part of Zhejiang Province shows that these rocks were crystallized in the Late Triassic at 215±2 Ma, rather than in the Cretaceous as previously proposed. The Jingju syenogranites are characterized by relatively high K2O and FeO*, and low MgO. They have high concentrations of large ion lithophile elements (LIL) and LREE, such as K, Th, La, and Ce, but are depleted in high field strength elements (HFSE) such as Nb, Ta, and Ti. Their 104Ga/Al ratios and (Zr+Nb+Ce+Y) contents are also high. These characteristics are similar to those of A-type granites. The syenogranites have high I
Sr (0.7179–0.7203), low ɛ
Nd(t) (from −14.2 to −13.2), and relatively old T
2DM ages, similar to those of the ancient metamorphic basement in the Cathaysia Block. It is suggested that the Jingju syenogranites were formed by partial melting of the Cathaysia basement rocks during tectonic extension. This identification of Indosinian A-type granite in Jingju has significant implications for understanding the early Mesozoic tectonic evolution of South China.
... 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.
... During Indosinian, The tectonic stress of SC was dominated by compressing during early-to middle-Triassic but extension began from late-Triassic based on studies of Shiwandashan basin [96] . Moreover, previous studies indicated that the crust of SC would be thickened to ca. ...
Zircon LA-ICP-MS U-Pb dating reveals that the Baimashan Pluton is composed mainly of late Indosinian (204.5±2.8 Ma-209.2±3.8 Ma) biotite granodiorites/monzonitic granites (LIGs) and early Yanshanian (176.7±1.7 Ma) two-micas monzonitic granites (EYGs), and the coeval (203.2±4.5 Ma-205.1±3.9 Ma) mafic microgranular enclaves (MMEs) are generally found in the former. In addition, the ages of cores within zircons from LIGs and MMEs ranging from 221.4±4.0 Ma to 226.5±4.1Ma provide evidence of multistage magma intrusion during Indosinian in the study area. Measured 3010±20.6 Ma of inherited zircon age suggests that there may be recycling Archaean curstal material in existence in this area. LIGs and EYGs share some similar geochemical features: subalkaline and peraluminous granites, enrichment of Th, U, K, Ta, Zr, Hf and LREE but depletion of Ba, Nb, P, Ti and Eu, low ɛ
Nd(t) values but high (87Sr/86Sr)i ratios, and old T
2DM (ca. 1.9–2.0 Ga). The behaviors of incompatible elements and REE are mainly dominated by fractional crystallization of plagioclase, K-feldspar, ilmenite and apatite, but that of Sr isotope mainly controlled by EC-AFC. They are crust-sourced and derived from partial melting of paleo-Proterozoic metagreywackes and related to biotite dehydration melting. LIGs are formed in post-collisional tectonic setting as crustal local extension and thinning during late Indosinian. But EYGs may be evolved products of congeneric granitic magma with LIGs formed in late Indoinian, which were emplaced again when crust underwent extensive thinning and extension in post-orogenic tectonic setting during Yanshanian in SC after undergoing EC-AFC. MMEs should be cognate enclaves and derived from liquid immiscibility of host magma.
Indosinian W-Sn metallogeny associated with granites in South China has been reported in recent years by many researchers. However, the refined genetic relations between these deposits and the related granites remain unclear in most areas, and the tectonic setting of Indosinian magmatism and W-Sn mineralization are still widely controversial. The Banjiaoyuan tin deposit is located in the east vicinity of Yangmingshan pluton in the middle Nanling Range, South China. The granitic stocks in this deposit comprise two intrusive episodes, i.e., the first episode of medium-coarse-grained porphyritic tourmaline-biotite monzogranite (G1), and the second episode of micron-fine-grained tourmaline-muscovite monzogranite (G2). LA-ICP-MS zircon U-Pb dating gives weighted ages of 226.9 ± 1.6 Ma to 223.8 ± 1.9 Ma for G1, and 224.3 ± 2.0 Ma for G2, respectively. LA-MC-ICP-MS cassiterite U-Pb dating yields Tera-Wasserburg concordia age of 216.7 ± 2.4 Ma for tin mineralization. These ages indicate that both the granitic magmatism and related mineralization were initiated in the late Indosinian period. All the granites have high SiO2, Al2O3, P2O5 contents, and low TFeO, CaO, MgO, TiO2 contents, indicating that the granites are highly differentiated S-type granites, and furthermore, the high DI and Rb, K, U, Hf, Sm, low SI and Ba, Sr, Ti, TREE further show that the granites have undergone high extent of differentiation and evolution. High Rb/Nb and K/Nb ratios, low Nb/Ta and Zr/Hf ratios, widely varying CaO/Na2O ratios, low and uniform εNd(t) values, and dominantly negative and relatively dispersed εHf(t) values jointly indicate that the granites were derived from a heterogeneous mixture of calcium-poor mudstone and calcium-rich psammite (or metamorphic igneous rocks) in the crust. The known Indosinian W-Sn deposits in South China are more closely related to S-type granites than to I-type granites, suggesting that their ore-forming materials are mainly derived from the crust. In addition, individual positive εHf(t) values indicate that a small amount of newborn crustal components were involved in the formation of granitic magma. Compared with G1, G2 differs distinctly in petrological, chemical and isotopic characteristics, especially it is more richer in F content and contains magmatic cassiterite and wolframite crystals, suggesting that G2 have undergone higher extent of differentiation and evolution, and are much more closely related to the Sn-W mineralization than G1. The late Indosinian granites in this deposit were formed in post-collisional extensional tectonic environment, while the early Indosinian granites intruded in the Yangmingshan area were formed in syn-collision compression environment. Based on the statistics, the metallogenic ages of Indosinian W-Sn deposits in South China are between 212-230 Ma, and the petrogenetic ages of related granites are between 211-230 Ma, both age groups belong to the late Indosinian period, representing a regional large-scale granitic magma intrusion and mineralization event that initiated in post-collisional extensional tectonic environment.
We conducted field mapping coupled with radiometric dating across the Shiwandashan and Youjiang structural belts (SWSB and YJSB), to investigate how southwest South China evolved and to better understand its links to plate boundary dynamics during the Late Permian to Middle Triassic. Our results reveal an episodic tectono-magmatic evolutionary history of the SWSB and YJSB. The SWSB underwent significant NW-SE shortening punctuated by ∼250-240 Ma S-type pluton emplacement during the Late Permian to Middle Triassic; the shortening was expressed by thin-skinned NW-verging thrusts and folds, and conjugate sets of ∼N-trending sinistral and ∼E-trending dextral faults. The NW-SE shortening overlapped with, and was succeeded by Triassic NE-SW shortening in the YJSB. The NE-SW shortening was expressed by NE-verging thrusts and folds, which documented a northeastward propagation of foreland deformation. The NE-verging folds overprinted older NW-verging folds, forming superimposed folds at the juncture of the YJSB and SWSB in the Long'an area. Our results, combined with regional considerations, support a model of the NW-SE shortening as an Andean-type orogeny that developed in response to westward subduction of the Paleo-Pacific Plate, and the NE-SW shortening as a product of the Indochina-South China collision. The subduction of the Paleo-Pacific plate assisted in westward motion of the South China oceanic lithosphere, which may have facilitated the closure of the Paleo-Tethys ocean and subsequent collisions of South China with North China and Indochina.
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.
East Asia suffered an important transformation from the Tethys to the Pacific tectonic domain during the early Mesozoic. Moreover, the South China Block (SCB) in East Asia has an obvious change from an Indosinian syn-orogenic compression to a post-orogenic extensional tectonic setting. The dynamic evolution of the SCB that caused this change is still unclear. Here, we combine the petrology and whole-rock geochemistry of the Daoxian mafic granulite xenoliths in basalts from South Hunan Province and the structural features of the Xuefengshan tectonic belt, to propose a late Triassic tectonic model in the central SCB. The Daoxian region is located in the eastern part of the Xuefengshan basement uplift belt. The Daoxian mafic granulite xenoliths, forming in the late Triassic, have high Mg# value, high MgO and low SiO2 contents. They have flat REE patterns with a positive Eu anomaly, enriched in Rb, Ba, and depleted in Th, U, Nb, Zr and Hf. These xenoliths are the product of pyroxene and plagioclase accumulation of the mafic melts. The mafic melts originated from the asthenosphere and then underplated to the bottom of the lower crust. In the Xuefengshan belt, it is observed that the unconformities during the Late Triassic changed from high-angle unconformity, through low-angle unconformity and para-unconformity, to conformity, from the central to western parts of the SCB. The detachment layer beneath the Xuefengshan belt displaying NW-trending thrusts cross-cuts the late Palaeozoic strata. We suggest that orogenic collapse happened beneath the central SCB during the Late Triassic, which was accompanied by lithospheric extension and asthenospheric upwelling. These dynamic processes induced different effects on the SCB. Beneath the central SCB, the mantle-derived melt underplated the lower crust, and subsequently influenced the deep crust. From central to western SCB, the regular westward change of the stratal unconformities is related to the weakening of the lithospheric extension. In the central and eastern SCB, the orogenic collapse and the subsequent asthenosphere upwelling could have contributed to the mantle disturbance to enhance the roll-back of the Palaeo-Pacific slab. Copyright
The petrogenesis and tectonic setting of the Indosinian granites within the South China Block (SCB) are controversial, and there is no sound geochronological proof on occurrence of Indosinian magmatism in northwestern Jiangxi Province. Mengshan granitoids in this region were thought to be a Yanshanian intrusion. However, our new geochronological results show that Mengshan granites consist of three Indosinian magmatisms, with ages of 236±3 Ma, 220±3 Ma and 217±1 Ma respectively. Researches on geochemistry and Hf isotope of zircons are carried out. The Mengshan granites are metaluminous peraluminous, having high SiO2 and K2O, with K2O+Na2O 7.53%-8.86%. The granites have ∑REE of 213.09-380.75 ug/g and REE patterns of LREE enrichment with moderate negative Eu anomalies (Eu/Eu* = 0.07-0.40). There is strong enrichment in LILE, but showing pronounced negative anomalies in HFSE (Nb, Ta and TiO2) relative to neighbouring elements. Calculated εNd (t) values for most of samples are -9.9 to -6.1 and corresponding two stage Nd model ages (tDM2) are 1.5-1.8 Ga. Most of the zircons from the grayish white coarse biotite granites which were formed firstly have εHf(t) of 1.10 to 2.65, their single stage Hf model ages tDM1 range from 782 to 866 Ma and two stage Hf model ages tDM2 are 1 096-1 186 Ma. The zircons from the fined grained granites which were formed thirdly in Mengshan complex have εHf (t) values of 1.71- 4.98, and Hf tDM1 of 671-832 Ma and Hf tDM2 mostly are 932-1 139 Ma. The compositions of zircon Hf isotope suggest an addition of newly mantle derived magma during the diagenesis of Mengshan granites, which provide a direct proof for the relationship between basalts underplating and the genesises of some Indonisian granites in South China. Decoupling between Nd and Hf isotopes has been found in Mengshan granites, and it probably resulted from the involvement of Neoproterozoic island arccrust. The regularity of genentic types and the temporal spatial distribution of the Indosinian magmatism in SCB are summarized. On this basis, the Indosinian tectonic setting and the petrogenesis of the Indosinian granites in SCB are discussed. The northwestward subduction of Pacific was probably responsible to the Indosinian magmatisms in SCB.
The eastern South China continental block can be subdivided into the Yangtze block and the Cathaycian block. The Xuefengshan intracontinental tectonic system is one important part of the Yangtze block. The distribution of the unconformities between Triassic and Jurassic in the Xuefengshan tectonic system reveals four kinds of contact interfaces, including high-angle unconformity, low-angle unconformity, disconformity and conformity and becoming younger and younger to the west. Then the characteristics of Indosinian folds are also subdivided into two directions of fold axial traces in the South China, i. e. northeast-and northwest-striking folds, which were superimposed by the N-S-trending thrusts. The authors proposed that the longitudinal arcuate and northeastward structures in the Xuefengshan intracontiental tectonic system result from a control of different block borders under the same stress field as the previous one. The first-generation NEE-striking folds are rotated from the earlier NNE-striking folds due to late block rotating. The second-generation NNE-striking folds superimpose the NEE-striking folds. The intracontinental shortening between the Yangtze and Cathaysian blocks was earlier than the collision of the South China block with the Qinling - Dabie micro-continent. The Yangtze block and the Qinling - Dabie micro-continent had rotated in Early Indosinian orogeny. these resulted in a difference between those earlier structural lines formed in Early Triassic, the perpendicular relation to these structural lines was at last remained although they underwent small rotation between the Yangtze and Cathaysian blocks.
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.
Kimura's disease (KD) is a rare and benign chronic inflammatory soft tissue disorder of unknown origin, which predominantly inflicts young male adults in Asia. IgG4-related disease is a new disease concept, established this century and characterized by fibrosis and sclerosis of the involved organs, with infiltration of IgG4-positive plasma cells. These two kinds of diseases share similar characteristics, which may complicate their diagnosis.
A 47-year-old Chinese man presented to our Department of Ophthalmology with a 26-month history of painless swelling and redness left upper eyelid. Surgical excisions of the left lacrimal gland were performed. A histopathology examination showed follicular hyperplasia with reactive germinal centres and eosinophilic infiltration involving the interfollicular areas as well as proliferation of post capillary venules, all signs of Kimura disease. Immunohistochemical analysis of the cells demonstrated positive staining for CK, Vimentin, CD3, CD4, CD20, CD21, CD117, CD5, CD8, CD23, IgG and IgG4 (30 per high-power field) and negative staining for CD10 and CD34. Some ophthalmologists in our department questioned whether the histological and immunohistochemical findings were also compatible with features of IgG4-related diseases. There was no sign of recurrence during the twelve months of regular follow-up.
Kimura's disease may present with high serum IgG4 levels, which may be an epiphenomenon related to chronic antigen exposure. As clinical doctors, especially ophthalmologists, we should recognize the possibility of the occurrence of increased serum levels of IgG4 in Kimura's disease to ensure correct diagnosis.
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.
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