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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.

SRHIMP U-Pb Zircon Dating of the Tula Granite Pluton on the South Side of the Altun Fault and Its Geological Implications [查看] WUSuoping、WUCailai、WANGMeiying、CHENQilong、JosephL.WOODEN

The Tula A2-sutbtype granite pluton is located between the Altun fault and its branching fault.According to the geological,geochemical,REE and trace elements characteristics,it belongs to the A2(PA)subtype granite.The SHRIMP U-Pb zircon dating gives a result of 385.2±8.1Ma，which is located between the Middle and Late Devonian in the international stratigraphic chart,and can be regarded as the crystallization age of the Tula granite.The study indicates that the Tula area was in a local extensional environment in the end of the Middle Devonian,and that environment was probably related to the synchronized strike-slip activity of the Altun fault.

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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