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Opening of the Tethys in southwest China and its significance to the breakup of East Gondwanalang in late PaleozoicEvidence from SHRIMP U-Pb zircon analyses for the Garze ophiolite block [查看] YANQuanren、WANGZongqi、LIUShuwen、LIQiugen、ZHANGHongyuan、WANGTao、LIUDunyi、SHIYuruo、JIANPing、WANGJianguo、ZHANGDehui、ZHAOJian

Abstract SHRIMP U-Pb zircon analyses for a gabbro sample from the Garzê ophiolite block yielded a mean 206Pb/238U age of 292±4 Ma, which indicated that the spreading time of the Garzê-Litang Tethys was most likely at the earliest Permian. Combined with previous studies, we suggest that the opening of the Tethys in southwest China was derived from breakup of the East Gondwanaland in the late Paleozoic.

Zircon SHRIMP geochronology and geochemistry of TTG rocks in Sushui Complex from Zhongtiao Mountains with its geological implications [查看] TIANWei、LIUShuwen、LIUChaohui、YUShengqiang、LIQiugen、WANGYueran

The tonalite-trondhjemite-granodiorite(TTG)rocks in Sushui Complex of Zhongtiao Block can be divided into two series according to their zircon U-Pb ages and geochemical characteristics:one is subduction-related(SR)and the other collision-related(CR).The SR TTG rocks,together with other late Archean island arc magmatism,were developed as a result of oceanic subduction betwween the Eastern and Western blocks in Late Archean;while the CR TTG rocks formed in a thickened crustal envionment,which was responding to the collision between the Eastern and Western blocks in Paleproterozoic.All these features support a model that the Zhongtiao Block is a part of the Trans-North China Orogen in the middle of the North China Craton

What Happened in the Trans-North China Orogen in the Period 2560-1850 Ma [查看] GuochunZHAO、LIUShuwen、MinSUN、LISanzhong、SimonWILDE

Abstract: The Trans-North China Orogen (TNCO) was a Paleoproterozic continent-continentcollisional belt along which the Eastern and Western Blocks amalgamated to form a coherent North China Craton (NCC). Recent geological, structural, geochemical and isotopic data show that the orogen was a continental margin or Japan-type arc along the western margin of the Eastern Block, which was separated from the Western Block by an old ocean, with eastward-directed subduction of the oceanic lithosphere beneath the western margin of the Eastern Block. At 2550-2520 Ma, the deep subduction caused partial melting of the medium-lower crust, producing copious granitoid magma that was intruded into the upper levels of the crust to form granitoid plutons in the low- to medium-grade granite-greenstone terranes. At 2530-2520 Ma, subduction of the oceanic lithosphere caused partial melting of the mantle wedge, which led to underplating of mafic magma in the lower crust and widespread mafic and minor felsic volcanism in the arc, forming part of the greenstone assemblages. Extension driven by widespread mafic to felsic volcanism led to the development of back-arc and/or intm-arc basins in the orogen. At 2520-2475 Ma, the subduction caused further partial melting of the lower crust to form large amounts of tonalitic-trondhjedtic-granodioritic (TTG) magmatism. At this time following further extension of back-arc basins, episodic granitoid magmatism occurred, resulting in the emplacement of 2360 Ma, -2250 Ma 2110-21760 Ma and -2050 Ma granites in the orogen.Contemporary volcano-sedimentary rocks developed in the back-arc or intra-arc basins. At 2150-1920Ma, the orogen underwent several extensional events, possibly due to subduction of an oceanic ridge,leading to emplacement of mafic dykes that were subsequently metamorphosed to amphibolites and medium- to high-pressure mafic granulites. At 1880-1820 Ma, the ocean between the Eastern and Western Blocks was completely consumed by subduction, and the closing of the ocean led to the continent-arc-continent collision, which caused large-scale thrusting and isoclinal folds and transported some of the rocks into the lower crustal levels or upper mantle to form granulites or eclogites. Peak metamorphism was followed by exhumatioduplift, resulting in widespread development of asymmetric folds and symplectic textures in the rocks.

SHRIMP Zircon U-Pb Chronology and Geochemistry of the Henglingguan and Beiyu Granitoids in the Zhongtiao Mountains [查看] YUShengqiang、LIUShuwen、TIANWei、LIQiugen、FENGYonggang

Abstract：Henglingguan and Beiyu metamorphic granitoids，distributed in the northwest of the Zhongtiaoshan Precambrian complex，comprise trondhjemites and calc-alkaline monzogranites，displaying intrusive contacts with the Archean Zhaizi TTG gneisses．And the Beiyu metamorphic granitoids consist mainlY of trondhjemites，distributed at the core of the Hujiayu anticline fold．New SHRIMP zircon U-Pb dating data show that the weighted mean207Pb/206Pb ages are 2435.9 Ma and 2477 Ma for the Henglingguan metamorphic calc-alkaline monzogranites and Beiyu meta morphic trondhjemites．respectively，and reveal ～2600 Ma inherited core in magmatic zircons．Whole-rock geochemical data indicate that all the Henglingguan and Beiyu metamorphic trondhjemites and calcalkaline monzogranites belong to the metaluminous medium-and high-pota ssium calc-alkaline series．These rocks are characterized by relatively high total alkali contents (Na20+K20，up to 9.08％)，depleted Nb，Ta，P and Ti，and right-declined REE patterns with m oderate to high LREEs/HREEs fractionation (the mean ratio of(La/Yb)n= 25)．The Henglingguan and Beiyu metamorphic trondhjemites display negative Rb．Th and K anomalies in the multi-element spider diagrams normalized by primi tive mantle．Sm-Nd isotopic data reveal that these granitoids have initial Nd(f)=-12 to +24 and Nd depleted mantle model ages of TMD= 2622 Ma-2939 Ma．A11 these geoc hemical features indicate that these granitoids were form ed in an continent-marginal arc and the trondhjemites mainly originated from partial melting of juvenile basaltic materials and，howbeit，the Henglingguan metamorp hic calc-alkaline monzogranites derived from recycling of materials in the ancient crust under a continent-marginal arc．The granitic magma underwent contami nation and fractional crystallization during their formation.

Paleoproterozoic Potassic Granitoids in the Sushui Complex from the Zhongtiao Mountains,Northern China Geochronology,Geochemistry and Petrogenesis [查看] TIANWei1、LIUShuwen、ZHANGHuafeng

Abstract: Paleoproterozoic potassic granitoids in the southern Sushui Complex from the Zhongtiao Mountains yielded SHRIMP zircon U-Pb ages of 1968–1944 Ma. Lithologically, the potassic granitoid series consists chiefly of monzodiorite, quartz monzonite and syenogranite. Their trace elements and Sm-Nd isotope characteristics indicate that they were derived from partial melting of Archean TTG rocks in an overthickened continental crust. Petrogenesis of this potassic granitoid series implies a collisional environment within the Trans-North China Orogen in the Paleoproterozoic, which supports a tectonic model of Eastern and Western Continental Blocks being amalgamated in the Paleoproterozoic.

U-Pb Zircon Dating of the Granitic Conglomerates of the Hutuo GroupAffinities to the Wutai Granitoids and Significance to the Tectonic Evolution of the Trans-North China Orogen [查看] JimZHANG、GuochunZHAO、LISanzhong、MinSUN、LIUShuwen、XiaopingXIA、YanhongHE

The Wutai Complex associated with the adjacent Fuping and Hengshan Complexes represents the best and classical cross-section in the middle segment of the Trans-North China Orogen, generally divided into Eastern and Western Blocks. Unconformably overlying the Wutai and Fuping Complexes is the Hutuo Group considered as the youngest lithostratigraphic unit in the region and important both for interpreting Precambrian history as well as the overall evolution of the Trans-North China Orogen. Lack of knowledge about provenance of the sedimentary rocks in this group has hindered understanding of the depositional environments and tectonic significance. LA-ICP-MS was applied to obtain U-Pb zircon ages for the granitic pebbles, the lowest lithostratigraphic rock of the Hutuo Group, which, combined with previous lithostratigraphic, geochronological, structural and metamorphic data, provides new constraints on the sedimentary provenance and tectonic evolution of the region. The sequence of the Hutuo Group ranges upward from lower basal conglomerates and volcaniclastic rocks (Doucun Subgroup), through clastic sediments, slates, dolomites and marbles (Dongye Subgroup), to sandstones and conglomerates at the top (Guojiazhai Subgroup). Zircons from granitic pebbles preserved in the Doucun Subgroup basal conglomerates give weighted mean 207Pb/206Pb ages between 2517 Ma and 2566 Ma, which are the same as those for the late Archean Wutai Cranitoids, indicating that the pebbles were derived from the Wutai granitic intrusions (2566-2515Ma). Based on the new data and previous studies, combined with an igneous zircon crystallization age of 2087±9 Ma obtained for volcanics in the Hutuo Group, the Hutuo Group was deposited in a subduction-related retro-arc foreland basin environment that developed behind the Wutai arc during the eastward-directed subduction of the Western Block beneath the western margin of the Eastern Block. This basin underwent long-lived sedimentation and finally closed during the -1850 Ma collisional event that resulted in the final amalgamation of the North China Craton.