摘要
青藏高原南部的冈底斯岩浆弧广泛发育新生代的花岗岩,然而这些花岗岩的成因仍存在争议。本文对冈底斯东段米林地区的晚渐新世二云母花岗岩进行了年代学和地球化学研究。全岩化学分析结果显示,这些花岗岩为中钾—高钾钙碱性系列,偏铝质,富集轻稀土元素和Rb、Th、U等大离子亲石元素,亏损重稀土元素和Nb、Ta、Ti等高场强元素,高Sr、低Y,具有较高的Sr/Y比值(37~85),显示出埃达克质岩石的地球化学特征。锆石U-Pb定年结果显示,所研究的二云母花岗岩结晶年龄为~26.6 Ma。这些花岗岩中的锆石具有较低的正εHf(t)值(+0.4~+7.3)。综合现有的研究结果,我们认为冈底斯弧东段的晚渐新世花岗岩起源于加厚下地壳始新世弧岩浆岩的部分熔融,但具有古老地壳物质的贡献。印度与亚洲大陆的持续汇聚导致冈底斯弧地壳加厚,加厚下地壳发生高级变质和部分熔融形成了晚渐新世的埃达克质花岗岩。
Cenozoic granites are widely exposed in the Gangdese magmatic arc of the southern Tibetan Plateau.However,the origin of these granites remains controversial.We report geochronology and geochemistry study about the late Oligocene two-mica granites from the Milin area in the eastern Gangdese arc.Wholerock chemical analyses show that these granites belong to medium-high potassium calc-alkaline series,weakly peraluminous.The samples are enriched in light rare earth elements and large ion lithophile elements such as Rb,Th and U,and depleted in heavy rare earth elements and high field strength elements such as Nb,Ta and Ti.All samples exhibit high Sr and low Y,with high Sr/Y ratio(37~85),and chemical affinity to adakites.The two-mica granites have the crystallization age of~26.6 Ma.Zircon Hf isotopes show that these granites have low and positiveεHf(t)values(+0.4 to+7.3).Taking previous data into account,we conclude that the late Oligocene granites from the Milin area were derived from partial melting of the Eocene arc-type magmatic rocks in the thickened lower crust,but with contribution of ancient crustal materials.The continental collision-induced crustal shortening and thickening resulted in the partial melting of the thickened lower crust,and formation of the widespread late Oligocene adakitic granites.
作者
王迪
张泽明
李文坛
WANG Di;ZHANG Zeming;LI Wentan(School of Earth Science and Resources,China University of Geosciences(Beijing),Beijing 100083,China;Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China)
出处
《地质学报》
EI
CAS
CSCD
北大核心
2024年第2期447-466,共20页
Acta Geologica Sinica
基金
国家自然科学基金项目(编号U2244203,91855210)
中国地质调查项目(编号DD20221630)联合资助的成果。
关键词
冈底斯弧
晚渐新世
埃达克质花岗岩
地壳加厚
Gangdese magmatic arc
late Oligocene
adakitic granites
crust thickening
