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Du Q.,Chengdu Institute of Geology and Mineral Resources | Du Q.,Key Laboratory for Sedimentary Basin and Oil and Gas Resources | Wang Z.,Chengdu Institute of Geology and Mineral Resources | Wang Z.,Key Laboratory for Sedimentary Basin and Oil and Gas Resources | And 7 more authors.
Precambrian Research | Year: 2013

The Yangtze Block is an important component in reconstructing the Proterozoic tectonic evolution of South China within the Rodinia supercontinent. The geochronology and paleoenvironment of the Liantuo Formation in the Yangtze Block are still highly controversial. An integrated approach of facies analysis, paleogeography and geochronology provides new insights into understanding the sedimentology and paleogeography of the formation. Here, results are presented from a detailed U-Pb zircon examination of geochronology and paleoenvironment of the Liantuo Formation in the Yangtze Block. The formation was deposited in the period of ca. 790-730. Ma, which coeval with the development of the Wuqiangxi Formation in the middle-upper part of the Banxi Group. The top of the Liantuo Formation gives a U-Pb age of 736. ±. 5.8. Ma, which signifies an onset time of the Sturtian glaciation as ca. ≤730. Ma. The zircon U-Pb ages reveal magmatic events that were correlated with Neoproterozoic continental growth indicating that the Rodinia initiated rifting occurred at ca. 824. Ma and extensive rift-related magmatism took place at ca. 780. Ma in the northern Yangtze Block. Moreover, these results provide geochronological and petrologic evidence that confirms the stratigraphic framework of the Nanhuan System, thereby promoting a better understanding of the Neoproterozoic tectonic development of South China. © 2013 Elsevier B.V.

Jian P.,Chinese Academy of Geological Sciences | Kroner A.,Chinese Academy of Geological Sciences | Kroner A.,University Mainz | Zhou G.,Hubei Geological Survey
Chemical Geology | Year: 2012

We present SHRIMP U-Pb ages and REE data for zircon of two granulites, a garnet pyroxenite and a clinopyroxene amphibolite from the North Dabie complex. The North Dabie complex is a major fault-bounded petrotectonic unit in the Dabie continental collisional orogen between the South and North China Blocks. Zircon REE data are applied to link ages to specific petrological processes. In addition to SHRIMP zircon U-Pb dating, measurements were made on monazites from a HP-UHT metapsammitic granulite. Metamorphic zircon grains and coeval overgrowths on detrital cores from one granulite yielded a weighted mean 207Pb/ 206Pb age of 2042±7Ma, corresponding to peak HP/UHT metamorphism. The zircon cores have well-preserved oscillatory, magmatic growth zoning and generated a range of 207Pb/ 206Pb ages from 2766±8Ma to 3089±3Ma, representing the detrital source. Concordant analyses of monazites from the same granulite sample yielded a weighted mean 207Pb/ 206Pb age of 2001±6Ma, which we interpret as the time of exhumation to the middle crustal level. A magnetite-orthopyroxene-garnet quartzite associated with a banded iron formation has a metamorphic zircon age of 2293±7Ma (granulite-facies) with a detrital core age of 2435±28Ma. These results are interpreted to indicate a composite affinity to the South China and North China Blocks for the ancient Archean-Paleoproterozoic crust in the North Dabie metamorphic rocks. The garnet pyroxenite, known as a typical HP-UHP granulite, contains a multiple, latest Permian to Triassic metamorphic zircon population with 206Pb/ 238U ages of ca. 254-253, ca. 242-226, ca. 210, and ca. 203Ma. Along with published zircon and titanite U-Pb age data and mineralogical evidence, we suggest that the HP-UHP granulite evolved broadly synchronously with UHP eclogites during continental collision in the latest Permian to Triassic. In the garnet pyroxenite, there is also zircon inheritance of variable ages (ca. 291-2477Ma), indicative of a probable sedimentary origin of the protolith; there also occur young, mid-Jurassic to Cretaceous zircons ranging in age between 165 and 112Ma, signifying considerable crustal reworking in mid-Jurassic and Cretaceous times. Zircons from the clinopyroxene amphibolite have a weighted mean 206Pb/ 238U age of 780±6Ma representing the minimum time of protolith emplacement, and 133±2Ma for an anatectic event in the post-collisional stage. The age data of this amphibolite are similar to those of granitic gneisses/migmatites in the North Dabie complex. The new U-Pb zircon ages for the North Dabie rocks provide constraints on the affinity of collided crustal blocks, the metamorphic history of HP-UHP granulites, and post-collisional crustal reworking. © 2012 Elsevier B.V.

Hu F.,Wuhan University | Chen J.,Wuhan University | Sun S.,Hubei Geological Survey
Energy Education Science and Technology Part A: Energy Science and Research | Year: 2014

Soil geochemical analysis is a common prospecting method in mining areas. The chemical prospecting data of mining areas is not in line with a normal distribution law and thus a good effect is difficult to obtain if it is processed using a conventional geochemical processing method. In this paper, the geochemical data of the soil in mining areas was studied and analyzed using the multi-fractal “C-A” model to make the element fractal dimensions comparatively fractal, indicating the fractal dimension of the ore-forming elements was less than 2 and the multi-fractal dimensions of the associated elements were similar. Based on the fractal dimension, the directional minerals as well as the related ore-forming elements were quickly determined and also the local anomalies area was smaller compared with the traditional method, so that the principle of the maximum ore-bearing rate within the minimum area was more effectively embodied. This will be of guiding significance for the future work in mining areas. © Sila Science. All rights reserved.

Liu B.,Yangtze University | Ma C.-Q.,Wuhan University | Guo P.,Hubei Geological Survey | Sun Y.,Yangtze University | And 2 more authors.
Lithos | Year: 2016

An integrated study of the geochronology, mineralogy, geochemistry and Sr–Nd isotope compositions of the upper Permian Yushu mafic rocks in the central Tibetan Plateau (CTP) was conducted to evaluate the interaction between the Emeishan mantle plume and the Paleo-Tethyan subduction system. These mafic rocks can be geochemically subdivided into three groups. Group 1 rocks yielded a weighted mean 206Pb/238U age of 258 ± 2 Ma. They have relatively high TiO2, FeOt, Nb/Y and high εNd(t) values and display oceanic island basalts (OIB)-like rare earth and trace element patterns, with obvious enrichment of Nb and Ta. Group 2 and 3 rocks yield weighted mean 206Pb/238U ages of 258 ± 1 Ma and 257 ± 1 Ma, respectively. Both have relatively low TiO2, FeOt, Nb/Y and εNd(t) values and island arc tholeiites (IAT)-like rare earth and trace element patterns with obvious depletion of Nb and Ta. However, the Group 2 rocks have relatively low FeOt/MgO ratios, but high MgO, Mg#, Cr and Ni contents, resembling primitive magmas. They have lower light rare earth element (LREE), Nb, Ti and Zr contents and higher εNd(t) values than the Group 1 rocks. The geochemical and isotopic variations suggest that the Group 1 rocks might be derived from a plume-related mantle source, whereas Group 2 and Group 3 rocks originated from subduction-modified asthenospheric mantle and lithospheric mantle. Moderate degrees of olivine and clinopyroxene fractionation under low oxygen fugacities (fO2) appear to be responsible for the Fe-Ti enrichment in the Group 1 rocks. We propose a model involving plume-subduction interaction to explain the geodynamics and generation of the late Permian mafic magmatism in the CTP. The study region was rifted by the Emeishan mantle plume activity in association with rollback of Longmuco-Shuanghu oceanic lithosphere in late Permian times. Deep melting of the plume source led to the generation of the Group 1 plume-related magmas, whereas shallower melting of the subduction-metasomatized asthenospheric and lithospheric mantle resulted in the generation of the Group 2 and Group 3 subduction-related magmas. © 2016 Elsevier B.V.

Liu B.,Yangtze University | Ma C.-Q.,Wuhan University | Guo Y.-H.,Wuhan University | Xiong F.-H.,Chengdu University of Technology | And 2 more authors.
Lithos | Year: 2016

Although numerous Paleo-Tethyan ophiolites with mid-oceanic ridge basalts (MORB) and/or oceanic-island basalt (OIB) affinities have been reported in the central Tibetan Plateau (CTP), the origin and tectonic nature of these ophiolites are not well understood. The petrogenesis, mantle sources and geodynamic setting of the mafic rocks from these ophiolites are unclear, which is the main reason for this uncertainty. In this paper, we present new geochronological, mineralogical and Sr-Nd isotopic data for the Chayong and Xiewu mafic complexes in the western Garzê-Litang suture zone (GLS), a typical Paleo-Tethyan suture crossing the CTP. Zircon LA-ICP-MS U–Pb ages of 234 ± 3 Ma and 236 ± 2 Ma can be interpreted as formation times of the Chayong and Xiewu mafic complexes, respectively. The basalts and gabbros of the Chayong complex exhibit enriched MORB (E-MORB) compositional affinities except for a weak depletion of Nb, Ta and Ti relative to the primitive mantle, whereas the basalts and gabbros of the Xiewu complex display distinct E-MORB and OIB affinities. The geochemical features suggest a probable fractionation of olivine ± clinopyroxene ± plagioclase as well as insignificant crustal contamination. The geochemical and Sr-Nd isotopic data reveal that the Chayong mafic rocks may have been derived from depleted MORB-type mantle metasomatized by crustal components and Xiewu mafic rocks from enriched lithospheric mantle metasomatized by OIB-like components. The ratios of Zn/Fet, La/Yb and Sm/Yb indicate that these mafic melts were produced by the partial melting of garnet + minor spinel-bearing peridotite or spinel ± minor garnet-bearing peridotite. We propose that back-arc basin spreading associated with OIB/seamount recycling had occurred in the western GLS at least since the Middle Triassic times, and the decompression melting of the depleted MORB-type asthenosphere mantle and partial melting of sub-continental lithosphere were metasomatized by plume-related melts, such as OIB s, which led to the generation of the Chayong and Xiewu mafic melts. © 2016

Liu R.,Wuhan University | Li J.-W.,Wuhan University | Bi S.-J.,Wuhan University | Hu H.,Wuhan University | Chen M.,Hubei Geological Survey
International Journal of Earth Sciences | Year: 2013

In this paper, we present zircon U-Pb age and Hf isotope data to document the significance of magma mixing in the formation of Late Jurassic granitoid intrusions in the eastern Qinling Orogen, China. The Muhuguan granitoid pluton from this orogen consists of monzogranite and lesser biotite granite and granodiorite, all containing abundant hornblende-rich cumulates, dioritic xenoliths, and mafic magmatic enclaves (MMEs). The monzogranite and granodiorite are intruded by a number of lamprophyre dykes. Both a cumulate and a dioritic xenolith samples have concordant zircon U-Pb ages of ca. 161 ± 1 Ma, but possess contrasting Hf isotopic compositions. The cumulate has more radiogenic zircon Hf isotopes with negative ε Hf(t) values (-7.9 to -2.5) and T DM1 ages of 0.9-1.1 Ga, indicating its derivation likely from basaltic rocks of the Neoproterozoic to early Paleozoic Kuanping Group in the area. The dioritic xenolith has much lower zircon ε Hf(t) values of -19.5 to -8.8 and T DM2 ages of 2.4-1.7 Ga, consistent with a juvenile Paleoproterozoic crust source presumably represented by the metabasic rocks of the Qinling Group in the area. Individual samples of the monzogranite, MME, and a lamprophyre dyke have U-Pb ages of 150 ± 1, 152 ± 1, and 152 ± 1 Ma, respectively, demonstrating coeval mafic and felsic magmatism in the Late Jurassic. The lamprophyre dyke has homogeneous, highly negative zircon ε Hf(t) values (-29.8 to -24.8) and Archean T DM2 ages (3.0-2.7 Ga), and its genesis is interpreted as partial melting of an ancient enriched subcontinental mantle source. Zircons from the fine-grained MME show a large range of ε Hf(t) between -29.1 and -9.8, overlapping values of the monzogranite and lamprophyre dyke samples. Zircon U-Pb age and Hf isotopes of the MMEs are consistent with their formation by mixing of crustal- and enriched mantle-derived magmas. The main group of zircons from the monzogranite has ε Hf(t) values (-17.9 to -9.3) and T DM2 ages (2.3-1.8 Ga) that are compatible with the dioritic xenoliths, indicating that the former was produced by partial melting of Paleoproterozoic crustal source with involvement of mantle-derived magmas. Mafic magmatism revealed from the Muhuguan pluton indicates that the eastern Qinling Orogen was dominated by lithospheric extension during the Late Jurassic. Compilation of existing geological and geochronological data suggests that this extensional event started in Late Jurassic (ca. 160 Ma) and persisted into the Early Cretaceous until ca. 110 Ma. The Jura-Cretaceous extension may have resulted from the late Mesozoic westward subduction of the Pacific plate beneath the East Asian continental margin. © 2013 Springer-Verlag Berlin Heidelberg.

Tang R.,Wuhan University | Lu X.,Wuhan University | Cao X.,Wuhan University | Mei W.,Wuhan University | And 3 more authors.
Diqiu Kexue - Zhongguo Dizhi Daxue Xuebao/Earth Science - Journal of China University of Geosciences | Year: 2014

Weilasituo and Bairendaba are two large-scale silver polymetallic deposits, discovered in the western slope of the south and central sections of Great Hinggan Mountains in recent years. This study focuses on identifying and analyzing the mineral associations and occurrence of silver minerals using scanning electron microscopy-energy dispersive spectrometry and electron microprobe. The analyses suggest that mineral associations change from tungstate and oxide, to diatomic sulphide, to simple sulphide, to antimony sulfosalt mineral, to antimonide with decreasing temperature based on the microscopy observations. The silvers contained in the ore occur in several forms, including mainly visible silver minerals, followed by the lattice silver (isomorphous substitution) and sub-micron inclusion silver. The mineral sequence of visible silver's formation is Ag-bearing tetrahedrite-argentian tetrahedrite-freibergite-diaphorite- freieslebenite-pyrargyrite-dyscrasite. Ag occurs in lattice of chalcopyrite, bornite, chalcocite, pyrite and galena in isomorphism in small amount, and also as the microscopic wrappage in galena. The results, combined with the characteristics of mineral association and fluid inclusions in different mineralizing stages, indicate that W and Sn are transported as wolframic acid and tungstate at the early high-temperature meta-acid oxidizing environment, while Zn2+, Pb2+, Cu+ and other metalions are transported as chloride complexes. After wolframite's precipitation and the changes of metallogenetic fluid physical and chemical condition, the metallogenetic environment becomes slightly alkaline and reductive, and Zn2+, Cu+ and other metalions form HS- complexes. The continuous drop of temperature and water-rock interaction lead to the separation of Zn2+, Cu+ with HS- to form pyrrhotite, sphalerite etc.. In late phases, Ag+ can combine Sb3+, Cu+, Pb2+, Sb3-, S2- etc., which results in multiple silver antimony sulfide minerals, boulangerite etc..

Mei W.,Wuhan University | Lu X.,Wuhan University | Liu Z.,Wuhan University | Tang R.,Wuhan University | And 3 more authors.
Geosciences Journal | Year: 2015

Huanggang skarn Fe-Sn deposit is located in the main ridge Sn-polymetallic metallogenic sub-belt of the Southern Great Xing’an Range. A combination of zircon U-Pb age, geochemistry and Hf isotopic composition are reported for the orerelated granite (K-feldspar granite) of the Huanggang deposit to constrain its petrogenesis and tectonic setting. LA-ICP-MS U-Pb Zircon dating results indicate that the K-feldspar granite was intruded at 145.3 ± 1.6Ma. The K-feldspar granites belong to high-K calc-alkaline and shoshonite series, mainly peraluminous. These rocks have a negative slope from La to Lu with strongly negative Eu anomalies, they demonstrate negative Ba, Sr P, Ti and Nb spikes and positive Th, U, Nd spikes on the normalized incompatible element diagrams. The regional geological setting together with the geochemistry of the K-feldspar granite indicates that it is formed in a post-orogenic setting. The zircon Hf isotopic compositions (ɛHf(t): +5.2 to +6.6, 176Hf/177Hf: 0.282837–0.282876) indicate both juvenile crust sources that originated from depleted mantle and some ancient continental crust sources contributed to its origin, and there is a significant addition of juvenile crust under the Southern Great Xing’an Range during the time from Paleo-Neoproterozoic to Phanerozoic. © 2015, The Association of Korean Geoscience Societies and Springer-Verlag Berlin Heidelberg.

Deng Q.,Chinese Academy of Geological Sciences | Deng Q.,Chengdu Center | Wang J.,Chengdu Center | Wang Z.-J.,Chengdu Center | And 6 more authors.
International Geology Review | Year: 2013

It is generally accepted that Neoproterozoic extension and dispersal of the supercontinent Rodinia was associated with mantle plume or superplume activities. However, plume-generated contemporaneous continental flood basalts (CFBs) have rarely been identified. In this study, we present geochronological and geochemical evidence for the basalts from the Liufangzui Formation of the Huashan Group in the Dahongshan region of east-central China. A representative sample yields a SHRIMP U-Pb zircon age of 824 ± 9 Ma, interpreted as the crystallization age of the rocks. Geochemically, these basalts belong to the subalkaline tholeiite series and display slight enrichments in light rare earth elements (LREE) and varying degrees of deficiency of high field strength elements (HFSE) such as Nb, Ta, and Ti. This pattern is very similar to that of CFBs from the Bikou Group and Tiechuanshan Formation in the northwestern Yangtze block in China and Siberia in Russia. The basaltic magmas underwent partially-fractional crystallization during ascent, but were not intensely influenced by crustal contamination. The characteristic element ratios and negative Hf isotopic analyses (εHf(t) =-6.6-2.6) in zircons indicate that the parental magmas of the basalts might have been derived from an enriched lithospheric mantle rather than from the depleted mantle such as normal mid-ocean ridge basalts (N-MORBs). The geochemical signatures and regional geological characteristics show that these basalts were formed along intraplate continental rifts rather than in island arcs or ocean basins. Considering the coeval basic volcanic rocks in South China, we propose that these Huashan Group basalts represent the remnants of plume-generated CFBs and have close spatiotemporal ties with a coeval basic igneous province in Australia. Our results support the Neoproterozoic location of the South China block adjacent to southeastern Australia in the reconstruction model of the supercontinent Rodinia. © 2013 Taylor and Francis.

Wang J.,Chengdu Center | Deng Q.,Chengdu Center | Wang Z.-J.,Chengdu Center | Qiu Y.-S.,Hubei Geological Survey | And 3 more authors.
Precambrian Research | Year: 2013

Recent field geological investigations and sedimentary facies analysis have disclosed that the "Macaoyuan conglomerates" should be assigned to the dolomitized intraclastic lime grainstones rather than the basal conglomerates as previously reported. The conglomerates display depositionally-erosional conformable contacts with their underlying stratigraphic succession. There is no so-called "angular unconformity" or associated "Shennong movement" between the Macaoyuan Group and Shennongjia Group. The Macaoyuan Group consists primarily of carbonate platform facies association and mixed clastic and carbonate shelf facies association, while the "Macaoyuan conglomerates" are mainly made up of carbonate platform slope-channel gravity flow deposits. The sedimentary structures such as basal scouring structures, slump-convolute structures, imbricate structures, inverse grading bedding and lenticular filling deposits are well developed in the slope-channel gravity flow sedimentary succession, whereas cross bedding, wavy bedding, parallel bedding, ripple bedding, and normal grading bedding are common in the mixed inner shelf and platform-margin shoal sedimentary succession. The SHRIMP and LA-ICP-MS zircon age dating techniques are employed for the synsedimentary tuff sample collected from the upper part and sedimentary detrital zircons from the topmost part of the Baliya Formation in the lower part of the Macaoyuan Group. The synsedimentary tuff sample gives a SHRIMP zircon U-Pb age of 1157. ±. 19. Ma, which agrees well with the maximum depositional age of 1180 Ma for the sedimentary detrital zircons. It follows that the age of deposition of the Macaoyuan Group should be traced back to the Mesoproterozoic rather than the Neoproterozoic. The ages of the detrital zircons are mainly concentrated in two time intervals: 1.16-1.26. Ga and 2.60-2.95. Ga. The ca. 2.60. Ga as a marked peak age may represent an important period for the crustal accretion and evolution of the Yangtze block. © 2013 Elsevier B.V.

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