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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

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.