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    Permian flood basalts from the Tarim Basin, Northwest China SHRIMP zircon U-Pb dating and geochemical characteristics [查看] XingYu、Shu-FengYang、Han-LinChen、Zhong-QiangChen、Zi-LongLi、GeoffreyE.Batt、Yin-QiLi
    This study documents the Permian basalts from the Tarim large igneous province, northwest China. Detailed field work has led to recognition of eight basalt units (BU) in the Permian sequences exposed in the Keping area, northern Tarim Basin. These basalt units are interbedded with terrestrial clastics, and thus represent eight discrete eruptive episodes. The basalt sequence is divided into two major eruption cycles, with an earlier cycle comprising two BUs within the uppermost Kupukuziman Formation, separated by ~1000 m of clastic sediments from an upper eruptive cycle represented by a further six BUs in the upper part of the Kaipaizileike Formation. SHRIMP U–Pb zircon ages of 289.5±2.0 Ma (MSWD=2.2) for the lowermost BU1 and 288±2.0 Ma (MSWD=3.1) for the uppermost BU8 are statistically indistinguishable, and limit the duration of the entire eruptive phase to no more than 5.5 Ma. The Keping basalts exhibit OIB-like trace element patterns,enrichment of LILE and HFSE, high (87Sr/86Sr)i ratios and negative εNd(t) values — all of which are consistent with the mantle plume derivation. The parental magmas for these basalts were extracted from spinel to garnet lherzolite by low-degree (less than 8%) partial melting. The magmas underwent pre-eruption fractional crystallization, but did not experience significant crustal contamination.
    Paleozoic sedimentary record of the Xing-Meng Orogenic Belt, Inner Mongolia Implications for the provenances and tectonic evolution of the Central Asian Orogenic Belt [查看] LIDaPeng、CHENYueLong、WANGZhong、LINYu、ZHOUJian
    The Xing-Meng Orogenic Belt is the eastern extension of the Central Asian Orogenic Belt, which marks the boundary between the North China and Siberian blocks. Key information on the collision between these two blocks and the evolution of this orogenic belt at the end of the Paleozoic are preserved in the widely distributed Paleozoic sedimentary sequences. Petrographic studies of the clastic sedimentary rocks from the Ordovician to the Permian in this region have shown that the rocks are mainly greywackes and arkosic sandstones characterized by low maturity, poor sorting and a large number of lithic fragments. Provenances of Paleozoic sandstones are mainly newly accreted crustal materials. Nd model ages range from the Neoproterozoic to the Late Mesoproterozoic.These ages are very different from those of the North China Block, but the change of εNd(t) (from the initialεNd value) is similar to that of igneous rocks in the Xing-Meng Orogen. This result indicates that provenances of these Paleozoic sedimentary rocks mainly arise from the Xing-Meng Orogen itself. These clastic sedimentary rocks mainly consist of inputs of juvenile accreted crustal materials and limited recycled old crusts. Their provenance is controlled by the following three end members: a felsic basement, a partially melted mafic, and a mafic end member. From the point view of lithology, these three end members must have mixed in a ratio of 53:41:5 to form the average composition of the clastic sedimentary rocks. The depositional environment began to change from an arc to an orogen during the Permian, and therefore the collision was complete before the Triassic. This interpretation is consistent with the argument that the final collision time was at the end of the Permian or beginning of the Triassic.
    Palaeoproterozoic tectonothermal evolution and deep crustal processes in the Jiao-Liao-Ji Belt,North China Cratona review [查看] S.Z.LI、G.C.ZHAO、SANTOSH、X.LIU、L.M.DAI
    The Palaeoproterozoic Jiao-Liao-Ji Belt is located in the eastern margin of the Eastern Block of the North China Craton. In this paper, we synthesize the tectonothermal evolution and deep crustal processes in the Jiao-Liao-Ji Belt based on recent information. A mantle plumerelated underplating from 2.53 to 2.36 Ga is envisaged which led to the emplacement of the 2.47–2.33 Ga alkali granite plutons and mafic dyke swarms, followed by the development of the Jiao-Liao-Ji Rift and bi-modal volcanism. The underplating resulted not only in different sedimentary environments in the upper crust, but also in a differentiation of the initial thermal structure in the rift. This controlled the metamorphism and style of P-T-t paths in the different parts of the rift. Subsequent underplating resulted in the emplacement of the A-type Liaoji granites of ca. 2.17 Ga in the lower crust, and the formation of associated pegmatites of 2.2 and 2.0 Ga, together with the development of a bedding-parallel extension. However, the main orogeny occurred between 1.93 and 1.88 Ga with closing of the rift, compressional deformation and high-pressure granulite metamorphism in the southern part of the orogen. Subsequently, lithospheric blocks were possibly delaminated at 1.85 Ga; anorogenic magmatic rocks such as rapakivi granite, alkaline granites and syenite were intruded, and pegmatite veins and mafic dyke swarms were emplaced cross-cutting all the earlier structural traces. We identify that the underplating styles, collision processes and delamination types in the deep lithosphere controlled the tectonothermal evolution of the crust in the Jiao-Liao-Ji region.
    Origin of postcollisional magmatic rocks in the Dabie orogen Implications for crust-mantle interaction and crustal architecture [查看] Zi-FuZhao、Yong-FeiZheng、Chun-ShengWei、Fu-YuanWu
    Zircon Hf and whole-rock Sr–Nd isotopic compositions were determined for postcollisional mafic–ultramafic and felsic intrusive rocks in the Dabie orogen. The results provide not only insights into the character of their source rocks and the nature of crust–mantle interaction, but also constraints on the crustal architecture of continental collision orogen. SHRIMP zircon U–Pb dating gave concordant ages of 121±6 to 131±2 Ma for the bimodal intrusives. Zircon Hf isotope analyses gave negative εHf(t) values of−26.3±0.6 to−7.0±0.5 for the mafic–ultramafic rocks, with two-stage Hf model ages of 1.62 to 2.83 Ga. Zircons from felsic granitoids also gave negative εHf(t) values of −31.6±0.5 to −16.9±0.9 with two-stage Hf model ages of 2.25 to 3.16 Ga.Both the mafic–ultramafic and felsic rocks have high initial 87Sr/86Sr raios of 0.7065 to 0.7084 and very low εNd(t) values of −21.7 to −11.7 for whole-rock. The crust-like geochemical signatures in the mafic– ultramafic rocks suggest their derivation from partialmelting of an orogenic lithospheric mantle source that is enriched in radiogenic isotopes as well as incompatible trace elements such as LILE and LREE. It would be generated by reaction of the overlying subcontinental lithospheric mantle (SCLM) wedge peridotite with the felsic melt derived from the subducted continental crust during the continental collision. Therefore, these postcollisional mafic–ultramafic rocks record recycling of the subducted continental crust and consequent crust–mantle interaction in the continental subduction zone. The granitoids have Hf model ages as old as Paleoarchean, which cannot be derived from partial melting of surrounding orthogneisses alone, but requires involvement of more ancient Archean crust in their source region. Thus, their source represents a mixture of crustal rocks from Paleoproterozoic and Paleoarchean basement. In combination of the present and previous studies, the Dabie orogen is suggested to have a three-layer crustal structure prior to the postcollisional magmatism: Central Dabie in the upper with dominantly young Hf model ages of late Mesoproterozoic to Neoproterozoic, North Dabie in the middle with dominantly middle Paleoproterozoic Hf model ages, and the source region of the postcollisional granitoids in the lower with Paleoproterozoic to Paleoarchean Hf model ages.
    Oligo-Miocene shearing along the Ailao Shan-Red River shear zone Constraints from structural analysis and zircon UPb geochronology of magmatic rocks in the Diancang Shan massif,SE Tibet,China [查看] ShuyunCao、JunlaiLiu、BerndLeiss、FranzNeubauer、JohannGenser、ChunqiangZhao
    The left-lateral strike-slip shearing along the Ailao Shan–Red River (ASRR) shear zone in the Southeastern Tibet, China, has been widely advocated to be a result of the Indian–Eurasian plate collision and postcollisional processes. The Diancang Shan (DCS) massif, which occurs at the northwestern extension of the Ailao Shan massif, is a typical high-grade metamorphic complex aligned along the ASRR tectonic belt. Structural and microstructural analysis of the plutonic intrusions in the DCS revealed different types of granitic intrusions spatially confined to the shear zone and temporally related to the left-lateral shearing along the ASRR shear zone in the DCS massif. The combined structural and geochronological results of SHRIMP-II and LA-ICP-MS zircon U/Pb isotopic dating have revealed successive magmatic intrusions and crystallization related to the Oligo-Miocene shearing in the DCS massif. The pre-, early- and syn-kinematic emplacements are linked to regional high-temperature deformation (lower amphibolite facies) at relatively deep crustal levels. The zircon U/Pb geochronological results suggest that the left-lateral ductile shearing along the ASRR shear zone was initiated at ca. 31 Ma, culminated between ca. 27 and 21 Ma resulting in hightemperature metamorphic conditions and slowed down at ca. 20 Ma at relatively low-temperatures.
    Neoproterozoic (~900 Ma) Sariwon sills in North Korea Geochronology,geochemistry and implications for the evolution of the south-eastern margin of the North China Craton [查看] PengPeng、Ming-GuoZhai、QiuliLi、FuyuanWu、QuanlinHou、ZhongLi、TieshengLi、YanbinZhang
    The Sariwon sills are distributed in the Pyongnam basin at the center of the Korean peninsula, eastern part of the North China Craton. These sills are up to 150 m in thickness and up to more than 10 km in length. Baddeleyite grains separated from a ~50 m thick sill give a SIMS 206Pb–207Pb age of 899±7 Ma(MSWD=0.34, n=14), which is interpreted to be the crystallization age of this sill. Zircon grains from the same sill gives a lower intercept U–Pb age of ~400 Ma, which is likely a close estimation of the greenschistfacies metamorphism of this sill. The Sariwon sills are dolerites and have tholeiitic compositions. They show enrichment of light rare earth element concentrations (La/YbN=1.4–2.8) and are slightly depleted in high field strength elements (e.g. Nb, Zr, and Ti), in comparison to neighboring elements on the primitive-mantle normalized spidergram. The whole rock εNdt (t=900 Ma) values are around −2, whereas in-situ εHft(t=900 Ma) values from zircon grains vary from−25 to+8. They are similar to the coeval sills in other parts of the North China Craton, e.g., the Chulan sills (Xu-Huai basin, Shandong peninsula) and the Dalian sills (Lv–Da basin, Liaodong peninsula). These sills possibly originated from a depleted mantle source (e.g., asthenosphere), rather than from the ancient lithospheric mantle of the North China Craton, and have experienced significant assimilation of lithospheric materials. The strata and sills in the Xu-Huai, Lv–Da and Pyongnam basins are comparable; moreover the three basins are geographically correlatable based on Neoproterozoic geographical reconstruction. We therefore propose that there is a Xu-Huai–Lv–Da–Pyongnam rift system along the south-eastern edge of the North China Craton during Neoproterozoic (~900 Ma), with the closure of the rift at ~400 Ma as a result of a continent-margin process. It is possible that this southeastern margin of the NCC did not face the inland in the configuration of the supercontinent Rodinia.
    Multistage metamorphic events in granulitized eclogites from the North Dabie complex zone, central China Evidence from zircon U–Pb age, trace element and mineral inclusion [查看] Yi-CanLiu、Xiao-FengGu、Shu-GuangLi、Zhen-HuiHou、BiaoSong
    The studied ultrahigh-pressure (UHP) eclogites, located in the southwestern part of the North Dabie complex zone (NDZ) in central China, represent deeply subducted mafic lower continental crust of the South China Block and display a multiple metamorphic evolution. However, the exact timing of the UHP metamorphism in the NDZ is poorly constrained, and thus impedes our understanding of the tectonic evolution of this area. In order to constrain the ages of peak UHP metamorphism and subsequent retrogression during continental subduction and exhumation, zircon from the eclogites in the NDZ has been investigated by a combined petrological, trace element and U–Pb isotopic study. In combination with petrological data, the present zircon SHRIMP and LA-ICPMS U–Pb dating provides precise constraints on the timing of multistage metamorphic events on the eclogites in the region. The U–Pb isotope in zircon from the eclogites records the times of multiple discrete events in the history of the rock such as Neoproterozoic, 238±2 Ma, 222±4–227±2 Ma,210±4–215±2 Ma, 199±2 Ma and 176±2–188±2 Ma. Neoproterozoic ages defined by relic igneous cores represent their protolith time and the other age-groups reflect their metamorphic records by CL images, low Th/U ratios and mineral inclusions. By U–Pb age, trace element and mineral inclusion of zircon, at least two episodes of eclogite-facies metamorphism have been identified from the eclogites, best estimated at 226±3 and 214±3 Ma, respectively. The younger ages of 199±2 and 176–188 Ma most likely record the granulitefacies overprinting and amphibolite-facies retrogression occurring during exhumation whereas the age of 238±2 Ma probably reflects the prograde metamorphic timing prior to the UHP metamorphism. Thus,Neoproterozoic mafic lower continental crust was subducted to depths greater than 120 km (corresponding to the lowest pressure for diamond formation) and suffered from UHP metamorphism at 226±3 Ma. Then these UHP metamorphic rocks were exhumed to about 60 km depth at 214±3 Ma and experienced highpressure quartz eclogite-facies retrograde metamorphism, and subsequently to lower- and upper-crustal levels and overprinted by granulite- and amphibolite-facies metamorphism, respectively.
    Mtamorphic patterns and SHRIMP zircon ages of medium-to-high grade rocks from the Tongbai orogen,central China,implications for ultiple accretion,col,lision processes pe=rior to terminal continental collision [查看] X.C.LIU、B.-M.JAHN、J.HU、S.Z.LI、X.LIU、B.SONG
    The Qinling-Tongbai-Dabie-Sulu orogenic belt comprises a Palaeozoic accretion-dominated system in the north and a Mesozoic collision-dominated system in the south. A combined petrological and geochronological study of the medium-to-high grade metamorphic rocks from the diverse Palaeozoic tectonic units in the Tongbai orogen was undertaken to help elucidate the origins of Triassic ultrahighpressure metamorphism and collision dynamics between the Sino-Korean and Yangtze cratons. Peak metamorphic conditions are 570–610 C and 9.3–11.2 kbar for the lower unit of the Kuanping Group,630–650 C and 6.6–8.9 kbar for the upper unit of the Kuanping Group, 550–600 C and 6.3–7.7 kbar for the Erlangping Group, 770–830 C and 6.9–8.5 kbar for the Qinling Group and 660–720 C and 9.1–11.5 kbar for the Guishan complex. Reaction textures and garnet compositions indicate clockwise P–T paths for the amphibolite facies rocks of the Kuanping Group and Guishan complex, and an anticlockwise P–T path for the granulite facies rocks of the Qinling Group. Sensitive high-resolution ion microprobe U–Pb zircon dating on metamorphic rocks and deformed granite ⁄ pegmatites revealed two major Palaeozoic tectonometamorphic events. (i) During the Silurian-Devonian (c. 440–400 Ma), the Qinling continental arc and Erlangping intra-oceanic arc collided with the Sino-Korean craton.The emplacement of the Huanggang diorite complex resulted in an inverted thermal gradient in the underlying Kuanping Group and subsequent thermal relaxation during the exhumation. Meanwhile, the oceanic subduction beneath the Qinling continental arc produced magmatic underplating and intrusion,leading to granulite facies metamorphism followed by a near-isobaric cooling path. (ii) During the Carboniferous (c. 340–310 Ma), the northward subduction of the Palaeo-Tethyan ocean generated a medium P ⁄ T Guishan complex in the hangingwall and a high P ⁄ T Xiongdian eclogite belt in the footwall. The Guishan complex and Xiongdian eclogite belt are therefore considered to be paired metamorphic belts. Subsequent separation of the paired belts is inferred to be related to the juxtaposition of the Carboniferous eclogites with the Triassic HP metamorphic complex during continental subduction and exhumation.
    Magmatic-hydrothermal evolution of the Cretaceous Duolong gold-rich porphyry copper deposit in the Banggongco metallogenic belt,tibet,evidence from U-Pb and 40Ar-39Ar geochronology [查看] JinxiangLi、KezhangQin、GuangmingLi、BoXiao、JunxingZhao、LeiChen
    The Duolong gold-rich porphyry copper deposit was recently discovered and represents a giant prospect(inferred resources of 4–5 Mt fine-Cu with a grade of 0.72% Cu; 30–50 t fine-gold with a grade of 0.23 g/t Au) in the Bangongco metallogenic belt, Tibet. Zircon SHRIMP and LA-ICP-MS U–Pb geochronology shows that the multiple porphyritic intrusions were emplaced during two episodes, the first at about 121 Ma (Bolong mineralized granodiorite porphyry (BMGP) and barren granodiorite porphyry (BGP)) and the second about 116 Ma (Duobuza mineralized granodiorite porphyry (DMGP)). Moreover, the basaltic andesites also have two episodes at about 118 Ma and 106 Ma, respectively. One andesite yields an U–Pb zircon age of 111.9 ± 1.9 Ma, indicating it formed after the multiple granodiorite porphyries. By contrast,the 40Ar/39Ar age of 115.2 ± 1.1 Ma (hydrothermal K-feldspar vein hosted in DMGP) reveals the close temporal relationship of ore-bearing potassic alteration to the emplacement of the DMGP. The sericite from quartz-sericite vein (hosted in DMGP) yields a 40Ar/39Ar age of 115.2 ± 1.2 Ma. Therefore, the ore-forming magmatic-hydrothermal evolution probably persisted for 6 m.y. Additionally, the zircon U–Pb ages (106–121 Ma) of the volcanic rocks and the porphyries suggest that the Neo-Tethys Ocean was still subducting northward during the Early Cretaceous.
    Mafic dykes derived from Early Cretaceous depleted mantle beneath the Dabie orogenic belt_ implications for changing lithosphere mantle beneath eastern China [查看] LINGCHEN、CHANGQ.MA、JINY.ZHANG、ROGERMASON、CHAOZHANG
    SHRIMP zircon U–Pb geochronological, elemental and Sr–Nd isotopic data from Early Cretaceous mafic dykes in North Dabie orogenic belt elucidate a change of Mesozoic lithospheric mantle in eastern China. The dykes are predominantly dolerite with the major mineral assemblage clinopyroxeneþhornblendeþplagioclase and yield a SHRIMP zircon U–Pb age of 111.65.3 Ma. They have a narrow range of SiO2 from 46.16% to 49.78%, and relative low concentrations of K2O (1.072.62%), Na2O (2.453.54%), Al2O3 (13.0414.07%), and P2O5 (0.420.55%) but relatively high concentration of MgO (5.94–6.61%) with Mg# 52–54. All the samples are characterized by enrichment of large ion lithophile elements (LILE, e.g., Ba, Th) and high field strength elements (HFSE, e.g., Nb, Ti). (87Sr/86Sr)i ratios from 0.704 to 0.705, eNd values from 3.36 to 4.33 and mantle-depletion Nd model ages (T2DM) in the range 0.56–0.64 Ga indicate that the magma of the Baiyashan mafic dykes was derived from a young depleted mantle source. This finding is different from previous research on mafic dykes in the age range 120–138 Ma that revealed enrichment of LILE and depletion of HFSE, high initial Sr isotopic ratios and negative eNd, value which represents an old enriched mantle source. Ours is the first report of the existence of Early Cretaceous depleted mantle in eastern China and it implies that changing of enriched mantle to depleted mantle occurred at ca. 112 Ma, associated with back-arc extension which resulted from the subduction of the Palaeo-Pacific Plate towards the Asian Continent.
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