藏北羌塘中部存在志留纪洋盆——来自桃形湖蛇绿岩中斜长花岗岩的锆石U-Pb年龄证据  

The Silurian Tethyan Ocean in central Qiangtang, northern Tibet: Constraints from zircon U-Pb ages of plagiogranites within the Taoxinghu ophiolite

作　　者：胡培远[1] 李才[2] 吴彦旺[3] 解超明[2] 王明[2] 张红雨[4] 李娇[5] 

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]吉林大学地球科学学院,吉林长春130061 [3]中国国土资源航空物探遥感中心,北京100083 [4]中国地质大学(北京),北京100083 [5]中国科学院地质与地球物理研究所,北京100029

出　　处：《地质通报》2014年第11期1651-1661,共11页Geological Bulletin of China

基　　金：国家自然科学基金项目(批准号:41072166;41272240)

摘　　要：报道了羌塘西部桃形湖蛇绿岩中斜长花岗岩的锆石U-Pb定年结果和岩石地球化学资料及锆石Hf同位素成分。斜长花岗岩中的锆石具有典型的岩浆生长环带,结合其Th/U值(0.16~0.44),表明为典型的岩浆成因。锆石LA-ICP-MS和Cameca U-Pb定年结果分别为441Ma±2Ma和442Ma±3Ma,相当于早志留世,略年轻于伴生的堆晶辉长岩。锆石的εHf(t)值为+8.13^+11.23,平均值为+9.50,具有明显的幔源成因特征。全岩地球化学分析结果表明,斜长花岗岩是洋壳运移过程辉长岩部分熔融形成的。斜长花岗岩的年龄数据表明,羌塘中部地区存在志留纪洋盆。New zircon U-Pb age, Hf isotope, and whole-rock major and trace element data of the Silurian plagiogranites from Taoxinghu ophiolite in central Qiangtang of northern Tibet are reported in this paper. The zircons from plagiogranites have clear oscillatory zones and high Th/U ratios（0.16~0.44）, suggesting a magmatic origin. Zircon LA-ICP-MS and Cameca dating of plagiogranites yielded two weighted mean ages of 441Ma±2Ma and 442Ma±3Ma, which are younger than the ages of cumulate gabbros of Taoxinghu ophiolite. The zircons from plagiogranites have positive εHf（t） values（＋8.13~＋11.23）, implying that the plagiogranites were derived from the depleted mantle. Geochemical analysis indicates that the plagiogranites were probably generated by partial melting of cumulate gabbros and their ages were coeval with or slightly younger than oceanic crust generation. The determination of Silurianplagiogranites in Taoxinghu ophiolite reveals the presence of a Silurian Tethyan ocean in central Qiangtang.

关 键 词：青藏高原 羌塘中部 特提斯 蛇绿岩 斜长花岗岩 LA-ICP-MS锆石U-Pb年龄 

分 类 号：P534.43[天文地球—古生物学与地层学] P588.121[天文地球—地质学]