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    Zircon U-Pb SHRIMP dating of the Yematan batholith in Dulan,North Qaidam,NW China [查看] WUCailai、YANGJingsui、JosephL.Wooden、SHIRendeng、CHENSongyong、AndersMeibom、ChrisMattinson
    Abstract The Yematan batholith crops out over 120 km2 in the North Qaidam ultrahigh pressure (UHP) metamorphic belt. It consists of granodiorite, monzogranite and biotite granite and forms an irregular intrusion into Neoproterozoic gneiss that has undergone Caledonian UHP metamorphism. Zircons from the Yematan granodiorite yield a SHRIMP U-Pb age of 397±3 Ma. These granitic rocks have geochemical characteristics intermediate between I- and S-type granites，and are post-collisional. We suggest that the Yematan granitic rocks were formed during the last exhumation event of the North Qaidam UHP belt.
    SHRIMP U-Pb zircon dating for Qiashikansayi granodiorite,the Northern Altyn Tagh Mountains and its geological implications [查看] QIXuexiang、LIHaibing、WUCailai、YANGJingsui、ZHANGJianxin、MENGFancong、SHIRendeng、CHENSongyong
    Abstract The Qiashikansayi granodiorite is foliated resulting in a granodioritic gneiss. Its geochemical features,such as alumina saturation index(A/CNK) of 0.81—0.99,Na2O/K2O values>1, TiO2 contents <1.0%, LREE enrichment with high fractionation factors, weakly negative or no Eu anomalies, and significant Ba and Ti negative anomalies,suggest that it is similar to a typical island arc pluton. The trace elements of the Qiashikansayi granodiorite are plotted in the island arc field in the tectonic setting discrimination diagrams as well. Cathodoluminescence images demonstrated that the zircons have clear rhythmic crystallized zoning, without any remnant core and new crystallized rim,suggesting the zircons be magmatic ones. Their U and Th contents vary in the range of 574—870 μg/g, and 279—556 μg/g respectively, with the Th/U ratio in the range of 0.52—0.68. SHRIMP zircon U-Pb dating yielded the 481.5±5.3 Ma age for the intrusion of the granodiorite, which is coeval with the island arc volcanic rocks in the northern Qilian Mountain, and confirms that there is an early Paleozoic island arc in the Hongliugou- Lapeiquan area.
    Mineral inclusions in zircon domains and geological significance of SHRIMP U-Pb dating for coesite-bearing zircons of paragniess in Sulu terrane,eastern China [查看] LIUFulai、YANGJingsui、XUZhiqin
    Abstract Laser Raman spectroscopy and cathodoluminescence (CL) image reveal that zircons separated from paragneisses in the southwestern Sulu terrane (eastern China) preserve multi-stage mineral assemblages in different zircon domains. In the same paragneiss zircon sample, some zircon grains retain inherited (detrital) cores with abundant low-pressure mineral inclusions of Qtz + Phe + Ap + impurities and Qtz + Phe impurities. The ultrahigh-pressure (UHP) metamorphic overgrowths mantles of these zircons preserve Coe, Coe + Phe and other UHP mineral inclusions, indicating that these inherited (detrital) zircons from protoliths experi-enced metamorphic recrystallization during the Sulu UHP metamorphic event. However, other zircon grains preserve UHP mineral inclusions of Coe, Coe + Ap and Coe + Phe in the cores and mantles, whereas the outmost rims contain quartz (Qtz) and other low-pressure mineral inclusions. These phenomena prove that the second group zircons were crystallized at UHP metamorphic stage and overprinted by the late retrogressive metamorphism related to the Sulu terrane exhumation. SHRIMP U-Pb dating reveals that zircons separated from the paragneisses recorded complicated geochronological traces. Some zircons retain inherited cores with the 206Pb/238U ages of 284 754 Ma, indicating the complexity of the detrital zircons in protoliths.Coesite-bearing zircon domains recorded 238 266 Ma (with the average age of 245r14 Ma) for the UHP metamorphic event. The retrogressive rims of zircons recorded 213 223 Ma (with the average age of 217r15 Ma) for the late-stage amphibolite facies metamorphic event, indicating that the rapid exhumation time for the Sulu UHP terrane is about 220 Ma.
    Bashikaogong-Shimierbulake granitic complex, north Altun, NW China Geochemistry and zircon SHRIMP ages [查看] WUCailai、YAOSunzhi、ZENGLingsen、YANGJingsui、JosephL.Wooden、CHENSongyong1&FrankK.Mazdab
    The Bashikaogong-Shimierbulake granitoid complex is about 30 km long and 2 ―6 km wide, with an area of 140 km2, located at the north margin of the Bashikaogong Basin in the north Altun terrain. It intruded into schist, metapelite and metatuff of Precambrian ages. This granitoid complex consists of darkish quartz diorite, grey granite, pink granite and pegmatite. Geochemically, the quartz diorite has I-type granite affinity and belongs to Calc-alkaline sereies, and the other gran-ites have S-type affinity and to high-K calc-alkaline series. Zircon SHRIMP U-Pb dating shows that the quartz diorite has a bigger age than those of other granites, which is 4 81.6±5.6 Ma for quartz diorite, 437.0±3.0 Ma―433.1±3.4 Ma for grey granite and 443±11 Ma―434.6±1.6 Ma for pink granite, re-spectively. Combined with regional geology, we think that the quartz diorite formed in tectonic envi-ronment related to oceanic crust subduc tion and the granites in post-collision.
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