Early Cretaceous Metasomatized Lithospheric Mantle beneath the Central Jiangnan Orogen in South China:Geochemical and Sr-Nd Isotope Evidence from the Tuanshanbei Dolerite

It is well established that Cretaceous magmatism in the South China Block(SCB)is related to the Paleo-Pacific subduction.However,the starting time and the associated deep crust-mantle processes are still debatable.Mafic dike swarms carry important information on the deep earth(including mantle)geodynamics and geochemical evolution.In the Jiangnan Orogen(South China).there is no information on whether the Mesozoic magmatic activities in this region are also directly related to the Pacific subduction or not.In this study,we present detailed zircon U-Pb geochronological,wholerock element and Sr-Nd isotope data for Early Cretaceous Tuanshanbei dolerite dikes,and provide new constraints on the condition of the lithospheric mantle and mantle dynamics of the SCB during that time.LA-ICP-MS zircon U-Pb dating suggests that this dolerite erupted in the Early Cretaceous(~145 Ma).All samples have alkaline geochemical affinities with K_(2)O+Na_(2)O=3.11-4.04 wt%,K_(2)O/Na_(2)O=0.50-0.72,and Mg^(#)=62.24-65.13.They are enriched in LILE but depleted in HFSE with higher initial^(87)Sr/^(86)Sr ratio(0.706896-0.714743)and lower ε_(Nd)(t)(-2.61 to-1.67).They have high Nb/U,Nb/La,La/Sm and Rb/Sr,and low La/Nb,La/Ta,Ce/Pb,Ba/Rb,Tb/Yb and Gd/Yb ratios.Such geochemical signatures suggest that the fractional crystallization is obvious but crustal contamination play a negligible role during magmatic evolution.Tuanshanbei dolerite were most likely derived from low-degree(2%-5%)partial melting of a phlogopite-bearing mantle material consisted of~85% spinel peridotite and~15% garnet peridotite previously metasomatized by asthenospherederived fluids/melts with minor subduction-derived fluids/melts.Slab-rollback generally lead to the upwelling of the hot asthenosphere.The upwelling of asthenosphere consuming the lithospheric mantle by thermo-mechanical-chemical erosion.The lithospheric mantle may have partially melted due to the heating by the upwelling asthenosphere and lithospheric extension.It is inferred that the Tuanshanbei dolerite might be associated with the initial slab rollback and corresponding lithospheric extension occurred potentially at ca.145 Ma.

Detrital Zircon Records of the Banxi Group in the Western Jiangnan Orogen:Implications for Crustal Evolution of the South China Craton

The Neoproterozoic evolution of the Jiangnan Orogen is important for understanding the tectonic history of South China.As a volcanic-sedimentary sequence developed in the Nanhua rift,the Banxi Group preserves the records of important magmatic and tectonic events linked to the assembly and breakup of the Rodinia supercontinent.In this study,we report the results from whole-rock major-and trace-element concentrations,with zircon LA-(MC)-ICP-MS U-Pb ages,trace elements and Lu-Hf isotopic compositions of sandstones from the Banxi Group.The rocks are characterized by high SiO_(2)(65.88%–82.76%,with an average of 75.50%)contents,moderate(Fe_(2)O_(3)^(T)+MgO)(1.81%–7.78%,mean:3.79%)and TiO_(2)(0.39%–0.54%,mean:0.48%),low K_(2)O/Na_(2)O(0.03–0.40,mean:0.10)ratios and low Al_2O_(3)/SiO_(2)(0.11–0.24,mean:0.15)ratios.The sandstones have highΣREE contents(mean:179.1 ppm),with chondrite-normalized REE patterns similar to the upper crust and PAAS,showing enriched LREE((La/Yb)_N mean:14.85),sub-horizontal HREE curves and mild Eu(Eu/Eu^(*):0.75–0.89,mean:0.81)negative anomalies.Their geochemical characteristics resemble those of passive continental margin sandstones.Most of the zircons are magmatic in origin and yield a U-Pb age distribution with three peaks:a major age peak at 805 Ma and two subordinate age peaks at 1990 Ma and 2470 Ma,implying three major magmatic sources.The Neoproterozoic zircons haveε_(Hf)(t)values ranging from-47.4 to 12.4(mostly-20 to 0),suggesting a mixture of some juvenile arc-derived material and middle Paleoproterozoic heterogeneous crustal sources.The Hf model ages of middle Paleoproterozoic zircons(~1990 Ma)with negativeε_(Hf)(t)values(-12.65 to-6.21,Ave.=-9.8)concentrated around the Meso-Paleoarchean(mean T_(DM)^(C)=3.3–3.1 Ga).For late Neoarchean detrital zircons(~2470 Ma),ε_(Hf)(t)values are divided into two groups,one with negative values(-9.16 to-0.6)with model ages of 3.5–2.9 Ga,the other featuring positive values(1.0 to 3.9)with model ages of 2.9–2.7 Ga,recording a crustal growth event at~2.5 Ga.Neoproterozoic zircons show volcanic arc affinities with partly intraplate magmatic features.We propose that the Banxi Group formed in a rift basin within a passive continental margin setting,which derived detritus from felsic to intermediate rocks from the Yangtze Block and a small amount of arc volcanic rocks.The middle Paleoproterozoic detrital zircon data suggest Columbia-aged basement lies beneath the western Jiangnan orogen.

Intra-continental Orogeny:Insights from Magnetotelluric Data into the Mesozoic Uplift History of the Eastern Jiangnan Orogen in South China

Despite extensive efforts to understand the tectonic evolution of the Jiangnan Orogen in South China,the orogenic process and its mechanism remain a matter of dispute.Previous geodynamic studies have mostly focused on collisional orogeny,which is commonly invoked to explain the Jiangnan Orogen.However,it is difficult for such hypotheses to reconcile all the geological and geophysical data,especially the absence of ultrahigh-pressure metamorphic rocks.Based on the magnetotelluric data,we present a group of resistivity models produced through the combination of two-dimensional and three-dimensional inversions,revealing the geo-electrical structures of Jiangnan and a typical collisional orogen.In our models,the resistive crust is separated into three parts by a prominent conductive layer with opposite dipping directions on both sides.A special thrust-nappe system,which is different from that developed in a typical collisional process,is revealed in the Jiangnan Orogen.This structure suggests a process different from the simple collisional orogeny.To interpret our observations,an'intra-continental orogeny'is proposed to address the development of the Jiangnan Orogen in the Mesozoic.Furthermore,this'reworked'process may contain at least two stages caused by the decoupling of the lithosphere,which is revealed by an extra conductive layer beneath Jiangnan.

Fe-bearing minerals and implications for gold mineralization for the Wangu deposit in Central Jiangnan Orogen

Hydrothermal alteration with bleaching of host rocks is the most important prospecting indicator for gold deposits in the Jiangnan Orogen Belt.The alteration has been identified as pre-ore carbonate(siderite)-sericitization and the Fe of siderite in the alteration zone is derived from the host rocks rather than fluids.In addition,such alteration decreases in intensity and width with depth and gold mineralization also occur in the non-bleached rocks,casting doubt on the reliability of the prospecting indicator.Detailed petrographic work and SEM analysis on the Wangu deposit indicate that there are two types of siderites,i.e.,Sd1 and Sd2.Among them,Sd1 grains are relatively small and distributed along the planes of unaltered host rocks,while Sd2 grains,only occurring in the altered slates,are commonly larger.Both types of siderites were altered by auriferous fluids,producing porous cores and minerals such as pyrite,quartz,and ankerite.Compared with unaltered parts,the altered parts have lower Fe,but higher U,Pb,and REE.In addition,Sd1 and Sd2 are similar in Mn,Na,V,and Sr concentrations but different in Fe and Mg.The occurrence and geochemical compositions of both siderites indicate that Sd1 could be transformed into Sd2 by pre-mineralization alteration through dissolution-reprecipitation.Chlorite is another important Fe-bearing mineral in the host rocks,and EPMA analysis suggests that it is ripidolite with relatively high Fe contents.Consequently,chlorite can also provide Fe to form the pre-ore carbonate(siderite)-sericitization.Geochemical modeling demonstrates that both ripidolite and siderite can result in sulfidation and therefore gold precipitation.As a result,this study demonstrates that pre-ore alteration with characterized bleaching is not a prerequisite for gold mineralization despite of its prominent features.Due to the presence of Fe-bearing Sd1 and chlorite,gold mineralization could still occur through sulfidation in the unaltered rocks.

Neoproterozoic–Early Paleozoic Tectonic Evolution of the South China Craton： New Insights from the Polyphase Deformation in the Southwestern Jiangnan Orogen

A 〉1500–km–long northeast–southwest trending Neoproterozoic metamorphic belt in the South China Craton（SCC） consists of subduction mélange and extensional basin deposits. This belt is present under an unconformity of Devonian–Carboniferous sediments. Tectonic evolution of the Neoproterozoic rocks is crucial to determining the geology of the SCC and further influences the reconstruction of the Rodinia supercontinent. A subduction mélange unit enclosed ca.1000–850–Ma mafic blocks, which defined a Neoproterozoic ocean that existed within the SCC, is exposed at the bottom of the Jiangnan Orogen（JO） and experienced at least two phases deformation. Combined with new（detrital） zircon U–Pb ages from metasandstones, as well as igneous rocks within the metamorphic belt, we restrict the strongly deformed subduction mélange as younger than the minimum detrital age ca. 835 Ma and older than the ca. 815 Ma intruded granite. Unconformably overlying the subduction mélange and the intruded granite, an intra–continental rift basin developed 〈800 Ma that involved abundant mantle inputs, such as mafic dikes. This stratum only experienced one main phase deformation. According to our white mica ^40Ar/^（30）Ar data and previously documented thermochronology, both the Neoproterozoic mélange and younger strata were exhumed by a 490–400–Ma crustal–scale positive flower structure. This orogenic event probably induced the thick–skinned structures and was accompanied by crustal thickening, metamorphism and magmatism and led to the closure of the pre–existing rift basin. Integrating previously published data and our new results, we agree that the SCC was located on the periphery of the Rodinia supercontinent from the Neoproterozic until the Ordovician. Furthermore, we prefer that the convergence and dispersal of the SCC were primarily controlled by oceanic subduction forces that occurred within or periphery of the SCC.

Geochronology, Geochemistry, Whole Rock Sr-Nd and Zircon Hf-O Isotopes of the Early Neoproterozoic Volcanic Rocks in Jiangshan, Eastern Part of the Jiangnan Orogen: Constraints on Petrogenesis and Tectonic Implications

This paper presents the results of combined studies of geochronology, geochemistry, whole rock Sr-Nd and zircon Hf-O isotopes carried out upon the rhyodacite and ignimbrite of Shangshu village, Shangyu town and Shanghupeng village of Jiangshan City in Zhejiang Province, along the northwestern side of the Jiangshan–Shaoxing suture. SHRIMP zircon U-Pb dating of samples in the three areas yielded weighted mean 206 Pb/238 U ages of 842.8 ± 6.9 Ma and 850.0 ± 7.3 Ma, 839 ± 9 Ma and 832.2 ± 8.1 Ma, 828.3 ± 8.5 Ma and 836.9 ± 9.9 Ma, respectively. These ages are older than the volcanic rocks of the Shangshu Formation dated at around 780 Ma distributed in Fuyang City, Hangzhou City, Kaihua County, etc. The volcanic rocks generally have high SiO2(54.08–76.80 wt%) and Al2 O3(12.40–21.31 wt%), low Fe2 O3(0.68–8.92 wt%), MgO(0.29–2.49 wt%), CaO(0.12–2.86 wt%), TiO2(0.10–1.59 wt%) and P2 O5(0.01–0.39 wt%), with variable total alkalis(K2 O + Na2 O =5.42–8.29 wt%). There exists a clear negative correlation between SiO2 and P2 O5. The volcanic rocks have A/CNK ratios of 1.03–2.77 and thus are peraluminous. They are characterized by enrichment in LREE, Rb, Ba, Zr, Hf, K, Th, La, U and depletion in Nb, Sr, P, Ti, with distinct LREE and HREE fractionation of(La/Yb)N values of 5.68–11.67, and with a moderate negative Eu anomaly(&Eu=0.58–0.89). Whole-rock geochemical data shows that the Jiangshan volcanic rocks are possibly I-type granitic rocks, even though they have some characteristics of A&S-type granites due to the magma fractional crystallization and water-rock interaction. Zircon δ18 O values are 3.97‰–5.49‰(average 4.50‰), 2.90‰–5.21‰(average 4.32‰) for ignimbrite from Shangshu village section, and Shanghupeng village section, respectively. They are slightly lower than the average δ18 O values of igneous zircons in equilibrium with mantle magmas(5.3 ± 0.6‰(2σ)), the lower δ18 O value also demonstrating the presence of high temperature water-rock interactions. The ignimbrite rocks have positive εNd(t)(4.02, 3.37, 3.91, 4.74, 2.85, 4.39, totals from the three areas) and εNd(t)(in-situ zircon)(4.3–14.6, a weighted mean of 8.4;6.6–12.7, a weighted mean of 9.0;8.1–12.0, a weighted mean of 9.5, respectively, from the three areas). In conjunction with the trace element studies, they indicate that the source region of the Jiangshan volcanic rocks was mainly composed of juvenile lower crustal material, mixed with some mantle-sourced magma. Detailed elemental and isotopic data suggest that the Jiangshan volcanic rocks were formed in a continental arc setting. There is a series of ca. 860–830 Ma volcanic rocks formed in a back-arc extensional setting in the southern margin of the eastern Jiangnan Orogen, along the northwest side of the Jiangshan–Shaoxing suture. The first stage rift-related anorogenic magmatism may have occurred as early as ca. 860 Ma in the eastern Jiangnan Orogen.

Rare Earths of Magmatic Rocks in Yanshanian Stage in Adjacent Region of Anhui and Jiangxi Provinces, Jiangnan Uplift

The geochemical characteristics of rare earth elements of magmatic rocks of Yanshanian stage were studied in the south of Anhui Province and northeast of Jiangxi Province, Jiangnan Uplift. The result shows that the magmatic rocks of Yanshanian stage in the south of Anhui Province are the typical crust source type and those in the northeast of Jiangxi Province have the characteristics of mantle source type. So the polymetal deposits having relation to the magmatic rocks of Yanshanian stage in the northeast of Jiangxi Province were developed better than those in the south of Anhui Province. The research results of the rare earth elements are confirmed by the studies of geophysics,tectonic setting and stable isotope at the same time. It also indicates that the rare earth elements are the effective approach to tracing the material sources of magmatic rocks.

Neoproterozoic Trench-arc System in the Western Segment of Jiangnan Orogenic Belt, South China

The Jiangnan orogenic belt is a key to understanding of the Neoproterozoic tectonic evolution of the South China Block. We investigate the mafic-ultramafic suites of lherzolite, pyroxenite, gabbro, pillow basalt and gabbroic diorite as well as red jasper interbedded with marine marbles that are mainly exposed as fault-trapped blocks in the Yuanbaoshan and Longsheng domains of the western Jiangnan belt. The postcollisional granite plutons that intruded the ultramafic-mafic rocks are developed well. Zircons in the gabbro yield crystallization ages of 867±10 Ma, 863±8 Ma, 869±9 Ma and 855±5 Ma whereas those from the granites show ages of 823±5 Ma, 831±5 Ma, 824±5 Ma and 833±6 Ma. The Neoproterozoic serpentinited ultramafic samples display minor REE enriched pattern with depletion of Rb, Ba, Nb, Ta and Ti, similar to those of SSZ type ophiolite. The coeval gabbro shows tholeiitic features and is characterized by negative Ba, Nb, Ta, Zr, Hf and Sr anomalies and LREE enriched patterns, with a minor negative Eu anomaly. Some zircon grains from the Longshen gabbro yield Neoarchean-Paleoproterozoic ages(2859–2262 Ma), suggesting its continental arc setting. Geochemical signature of the maficultramafic rocks is consistent with subduction related setting. The pyroxene-bearing diorite exhibits a distinctive arc affinity. The zircons from the gabbro show positive εHf(t) values ranging from 3.9 to 13.8. The granitoids are typical S–type granites with high ACNK values(1.15–1.40) and negative εHf(t) values(–15.1 to –3.2), and are classified as collision–related granites. Combined with the occurrences of mafic-ultramafic rocks, siliceous marble and red jasper mixed with basalt, our new results suggest the presence of a Tonian(863–869 Ma) SSZ ophiolite system and continental arc-type magmatism in the western Jiangnan orogen.

Ore-forming Fluid Systems and Mineralization in the Eastern Jiangnan Uplift in the Border Area of Anhui and Jiangxi Provinces, China

Obvious differences in mineralization characteristics exist between the southern and northern parts of the eastern part of the Jiangnan Uplift in northern Jiangxi Province and southern Anhui Province. The regional metallogeny is discussed, and the ore-forming fluid systems are classified in this article. It is proposed that the fluid ore-forming activities in the Jiangnan Uplift both in northern Jiangxi and southern Anhui have close relationships with the crust-mantle interaction and magmatic-tectonic activities. The types and scales of the mineralization on the both sides of the eastern Jiangnan Uplift were determined by fluid ore-forming systems and geological backgrounds.

Sedimentary Facies, Provenance and Geochronology of the Heshangzhen Group: Implications for the Tectonic Evolution of the Eastern Jiangnan Orogen, South China

The Neoproterozoic Jiangnan orogen plays an important role in the study of the Precambrian tectonic evolution of South China. The tectonic nature of the Neoproterozoic sedimentary basins is still controversial, due to poor understanding of the sedimentary sequences and the lack of geochronological data. Here, we present sedimentological, provenance and geochronological data from the Heshangzhen Group in the eastern Jiangnan orogen. Sedimentological analysis shows that the Luojiamen Formation was deposited in a submarine fan, and the overlying Hongchicun Formation was deposited in front of a fan delta. The youngest detrital zircons constrain the lower Luojiamen and Hongchicun formations with ages of 827.3 ± 8.4 Ma and 825 ± 12 Ma, respectively. The sandstones of the Luojiamen Formation are characterized by a large number of intermediate to felsic volcanic grains, suggesting a volcanic arc source. In contrast, quartz and sedimentary lithic grains increase in the Hongchicun Formation, showing a new input from a collisional orogenic source. Detrital zircon from six sandstone samples in the Luojiamen and Hongchicun formations yield similar age spectra of 930–820 Ma with a peak at ca. 845–860 Ma, with one main cluster at 930–820 Ma. Detrital zircons of 930–845 Ma show a positive value of εHf(t)(+2.4 to +11, mean +7.6), which is similar to the volcanic arc of the nearby Shuangxiwu Group. There are a minor group of zircons with U-Pb ages ranging from 820 Ma to 845 Ma from the middle part of the Luojiamen Formation and Hongchicun Formation, with εHf(t) values between-20 to +2.4, which are consistent with the characteristics of the Shuangqiaoshan Group. within light of the bidirectional paleocurrents in the Luojiamen Formation, it is speculated that the zircons of 820–845 Ma were recycled from the Shuangqiaoshan Group, which is derived from a continental arc to the northwest. Our data suggests that the Luojiamen Formation was formed in an inter-arc basin, while the Hongchicun Formation was formed in an accretionary wedge-top basin. When juxtaposed with the conglomeratic characteristics at the bottom of the Luojiamen Formation, it is believed that the unconformity represented by the ‘Shen Gong Movement' reflects the rapid erosion and accumulation process of island arc volcanic material. The disconformity between the Luojiamen and Hongchicun formations is the imprint of transition from inter-arc basin to accretionary wedge-top basin,which represents the collision between the Shuangxiwu arc and the Yangtze Plate.

Electrical Structure of Wulingshan and Middle Jiangnan Orogen by Three-Dimensional Magnetotelluric Data Inversion

Funded by The National Key Research and Development Program of China,China Deep Exploration(Sinoprobe)and The China Geological Suvery Project on 2009–2019,a large scale magnetotelluric sounding(MT)survey grid(Fig.1)has covered whole south China.

Renovation of Traditional Water Villages in Jiangnan:A Case Study of Renovation Planning of Wenchang Village

The rapid urbanization and new rural construction have being exerted serious impact on the renovation and protection of traditional water villages in Jiangnan area(the southern regions of the Yangtze River). More and more distinctive villages are losing their historical background and regional architectural culture in modern society. Taking the renovation planning of Wenchang village as a case study, its function structure and land use are determined by the theory of "three layers of HSR(high-speed rail) station" after deep mining its history and culture. Then, the design method of rebuilding characteristic space in traditional villagesaiming at finding a proper way to handle the relationship between development and protection of traditional villagesis investigated from the perspective of natural landscape, spatial form and architectural features.

Study on the Art of Stone Piling in Jiangnan Gardens under the Influence of Taoist Aesthetic Thought in Ming and Qing Dynasties

This paper explored the signifi cant impact of Taoist views on stone-piled rockeries in Jiangnangardens (Jiangnan refers to southern region of the Yangtze River) in Ming and Qing dynasties from theperspectives of morphology (Xing ), meaning (Yi ), pneuma (Qi ), including the view for life “modeling afterthe nature and valuing authenticity” in Taoist aesthetics , view of space “only Tao gathering nothingness”,and ecological ethical view of “everything as the same”. Moreover, it disclosed the process of gardenrockery design’s simulation of nature and aesthetic renovation, reviewed aesthetic value of garden rockeries,and contributed to the further understanding of garden design.

China Jiangnan Space Industry Group

The China Jiangnan Space Industry Group (CJSIG) is subordinate to the China Space Industry Corporation. On the approval of the State Planning Commission, the State Commission for Restructuring the Economy, and the Economic and Trade Office of the State Council, it was established in 1992, an enterprise group with the China Jiangnan Space Industry Group Corporation as a core enterprise, be-

Jiangnan Shipyard:Extending from the Yangtze River to the Ocean

The Jiangnan Shipyard has expanded its presence from the Yangtze River region to the ocean,making outstanding contributions to the advancement of the shipbuilding and shipping industries.WITH its predecessor dating back to 1865,Jiangnan Shipyard(Group)Co.,Ltd.has been acclaimed as the birthplace of China’s national industry,the cradle of Chinese industrial workers,and a forerunner of the country’s opening-up drive.Over the vicissitudes of the last one and a half centuries,Jiangnan Shipyard has expanded its presence from the Yangtze River region to the blue oceans.

Timing of Metamorphism and Provenance of the Metamorphic Basement of the Xiangshan Uranium Orefield, Jiangxi Province, China

The origin, age and evolution of the Precambrian metamorphic basement of southern China provide useful insights into early crustal development. Here, we present new laser ablation-inductively coupled plasma-mass spectrometry （LA-ICP-MS） U-Pb age data for detrital zircons from five samples of the Precambrian metamorphic basement of the Xiangshan uranium orefield. Two of these samples, from the northern Xiangshan volcanic basin, yielded a total of 140 U-Pb ages that cluster within the Neoproterozoic （773-963 Ma; 79.3% of data points）, with the rest being scattered through the Paleoproterozoic and Mesoproterozoic, along with a single Archean age. These ages indicate that this basement material is associated with the Cathaysia Block. In comparison, the 172 concordant ages from the other three samples from the southern part of the Xiangshan volcanic basin cluster within the Neoproterozoic （767-944 Ma; 59.8%） as well as the Proterozoic （37.8%） and the Archean （2502-2712 Ma; 14.5%）. These samples are also free of zircons with Grenvillian ages, indicating that these units are associated with the southeastern Yangtze Block. Combining these data with the geochemistry of these units, which suggests that the metamorphosed sedimentary rocks within the northern and southern parts of the Xiangshan basin have a common component from a magmatic island arc that formed during the early Neoproterozoic, we infer that the basin was located along the boundary between the Cathaysian and Yangtze blocks. In addition, the zircons within the samples from the southern and northern parts of the Xiangshan basin show different pre-Neoproterozoic （963 Ma） age populations but similar post- Neoproterozoic zircon populations, indicating that the amalgamation of the Cathaysian and Yangtze blocks occurred after the Neoproterozoic （960 Ma）, with magmatism peaking at 830 Ma and rifting starting at -770 Ma, leading to the subsequent deposition （from bottom to top） of the Shenshan, Kuli, and Shangshi formations.

Multistage Deformation in the Northeastern Segment of the Jiangshao Fault (Suture) Belt: Constraints for the Relationship between the Yangtze Plate and the Cathaysia Old Land

Multistage deformation events have occurred in the northeastern Jiangshao Fault （Suture） Belt. The earliest two are ductile deformation events. The first is the ca. 820 Ma top-to-the-northwest ductile thrusting, which directly resulted from the collision between the Cathaysia Old Land and the Chencai Arc （？） during the Late Neoproterozoic, and the Jiangnan Orogenic Belt that formed as the ocean closed between the Yangtze Plate and the jointed Cathaysia Old Land and the Chencai Arc due to continuous compression. The second is the ductile left-lateral strike-slipping that occurred in the latest Early Paleozoic. Since the Jinning period, all deformation events represent the reactivation or inversion of intraplate structures due to the collisions between the North China and Yangtze plates during the Triassic and between the Philippine Sea and Eurasian plates during the Cenozoic. In the Triassic, brittle right-lateral strike-slipping and subsequent top-to-the south thrusting occurred along the whole northeastern Jiangshao Fault Zone because of the collision between the North China and Yangtze plates. In the Late Mesozoic, regional extension took place across southeastern China. In the Cenozoic, the collision between the Philippine Sea and Eurasian plates resulted in brittle thrusts along the whole Jiangnan Old land in the Miocene. The Jiangshao Fault Belt is a weak zone in the crust with long history, and its reactivation is one of important characteristics of the deformation in South China; however, late-stage deformation events did not occur beyond the Jiangnan Old Land and most of them are parallel to the strike of the Old Land, which is similar to the Cenozoic deformation in Central Asia. In addition, the Jiangnan old Land is not a collisional boundary between the Yangtze Plate and Cathaysia Old Land in the Triassic.

Geochronology and Tectonic Evolution of the West Section of the Jiangnan Orogenic Belt

As an important part of South China Old Land, the Jiangnan Orogenic Belt plays a significant role in explaining the assembly and the evolution of the Upper Yangtze Block and Cathaysia, as well as the structure and growth mechanism of continental lithosphere in South China.The Lengjiaxi and the Banxi groups are the base strata of the west section of the Jiangnan Orogenic Belt.Thus, the research of geochronology and tectonic evolution of the Lengjiaxi and the Banxi groups is significant.The maximum sedimentary age of the Lengjiaxi Group is ca.862 Ma, and the minimum is ca.822 Ma.The Zhangjiawan Formation, which is situated in the upper part of the Banxi Group is ca.802 Ma.The Lengjiaxi Group and equivalent strata should thus belong to the Neoproterozoic in age.The Jiangnan Orogenic Belt consisting of the Lengjiaxi and the Banxi groups as important constituents is not a Greenville Orogen Belt（1.3 Ga–1.0 Ga）.The Jiangnan Orogenic Belt is a recyclic orogenic belt, and the prototype basin is a foreland basin with materials derived from the southwest and the sediments belong to the active continental sedimentation.By combining large amounts of dating data of the Lengjiaxi and the Banxi groups as well as equivalent strata, the evolutionary model of the western section of the Jiangnan Orogenic Belt is established as follows： Before 862 Ma, the South China Ocean was subducted beneath the Upper Yangtze Block, while a continental island arc was formed on the side near the Upper Yangtze Block.The South China Ocean was not closed in this period.From 862 Ma to 822 Ma, the Upper Yangtze Block was collided with Cathaysia; and sediments began to be deposited in the foreland basin between the two blocks.The Lengjiaxi Group and equivalent strata were thus formed and the materials might be derived from the recyclic orogenic belt.From 822 Ma to 802 Ma, Cathaysia continued pushing to the Upper Yangtze Block, experienced the Jinning-Sibao Movement（Wuling Movement）; as result, the folded basement of the Jiangnan Orogenic Belt was formed.After 802 Ma, Cathaysia and the Upper Yangtze Block were separated from each other, the Nanhua rift basin was formed and began to receive the sediments of the Banxi Group and equivalent strata.These large amounts of dating data and research results also indicate that before the collision of the Upper Yangtze Block with Cathaysia, materials of the continental crust became less and less from the southwest to the east in the Jiangnan Orogeneic Belt; only island arc and neomagmatic arc were developed in the eastern section.Ocean-continent subduction or continent-continent subduction took place in the western and southern sections, while intra-oceanic subduction occurred in the eastern section.Comprehensive analyses on U-Pb ages and Hf model ages of zircons, the main provenance of the Lengjiaxi Group is Cathaysia.

Hydrothermal alteration processes in the giant Dahutang tungsten deposit, South China: Implications from litho-geochemistry and mass balance calculation

The giant Dahutang tungsten(W)deposit has a total reserve of more than 1.31 Mt WO3.Veinlet-disseminated scheelite and vein type wolframite mineralization are developed in this deposit,which are related to Late Mesozoic biotite granite.Four major types of alterations,which include albitization,potassic-alteration,and greisenization,and overprinted silicification developed in contact zone.The mass balance calculate of the four alteration types were used to further understanding of the mineralization process.The fresh porphyritic biotite granite has high Nb,Ta,and W,but low Ca and Sr while the Jiuling granodiorite has high Ca and Sr,but low Nb,Ta,and W concentrations.The altered porphyritic biotite granite indicated that the Nb,Ta,and W were leached out from the fresh porphyritic biotite granite,especially by sodic alteration.The low Ca and Sr contents of the altered Neoproterozoic Jiuling granodiorite indicate that Ca and Sr had been leached out from the fresh granodiorite by the fluid from Mesozoic porphyritic biotite granites.The metal W of the Dahutang deposit was mainly derived from the fluid exsolution from the melt and alteration of W-bearing granites.This study of alteration presents a new hydrothermal circulation model to understand tungsten mineralization in the Dahutang deposit.