地质通报Issue(1)：55-70,16.
西藏拉萨地体西北部革吉地区两期早白垩世岩浆作用--锆石U-Pb年龄、Hf同位素和地球化学特征
摘要
Abstract
A series of sub-parallel, NS-trending dikes of rhyolitic composition intruded the Bangba granitic complex in Geji area, western central Lhasa Block. Field investigation and LA-MC-ICP-MS zircon U-Pb dating indicate that two episodes of Early Cre⁃taceous magamatism occurred at 131~132Ma and 127Ma respectively in this area. Earlier episode magmatism is represented by the for⁃mation of the dioritic enclaves and their hosts of granodiorite and granite. The magmatic rocks of this episode are characterized by ①enrichment of LILEs (K, Cs) and depletion of HFSEs (Nb, Ti, Zr); ②negative Eu anomalies (Eu/Eu∗=0.49~0.61) and negative Ce anomalies;③negative zirconεHf(t) (-3.2~-0.3) and ancient two stage model ages (1.210~1.399Ga);and (4)unradioenic to radiogen⁃ ic initial 87Sr/86Sr (0.70424~0.71472), and negative Nd(t) (-5.70~-5.54). The rhyolitic dikes, generated by the second episode of mag⁃matism, are characterized by①enrichment of LILEs (K, Cs) and depletion of HFSEs (Nb,Ti,Zr);②weak negative Eu anomalies (Eu/Eu∗=0.74~0.87);and③highly variable negative zirconεHf(t) (-6.1~-0.7) and more ancient two stage model ages (1.226~1.576Ga). Both the zircon saturation thermometer (777~796℃) and monazite saturation thermometer (794~812℃) yielded slightly higher mag⁃ma temperature for the rhyolitic dike than the temperatures (661~762℃and 750~769℃) either for granodiotite or for the mafic en⁃clave. Both episodes of magmatism are considered to have been the consequence of mixing of mantle-derived magma with the mag⁃ma derived from melting of ancient continental crust, which might have resulted from roll-back of southward subduction of the Ban⁃gong-Nujiang oceanic lithosphere.关键词
革吉地区/邦巴岩体/两期岩浆作用/锆饱和温度/轻稀土元素不饱和温度/LA-MC-ICP-MS锆石U-Pb年龄Key words
Geji area/Bangba complex/two episodes of magmatism/zircon saturation thermometer/monazite saturation thermome-ter/LA-MC-ICP-MS zircon U-Pb ages分类
天文与地球科学引用本文复制引用
高家昊,曾令森,高利娥,侯可军,郭春丽..西藏拉萨地体西北部革吉地区两期早白垩世岩浆作用--锆石U-Pb年龄、Hf同位素和地球化学特征[J].地质通报,2016,(1):55-70,16.基金项目
国家自然科学基金项目(批准号41425010、41273034)和中国地质调查局项目 （批准号41425010、41273034）
