拉萨地块东部米拉山地区中新世地层的特征及构造意义

中新世是拉萨地块增厚隆升的重要时期.本次报道了拉萨地块东部首次厘定的中新世地层，岩石类型包括流纹岩、英安岩、火山碎屑岩、黑曜岩和岩屑砂岩等，由3组喷发旋回构成.锆石U-Pb定年显示，该套地层形成于17.2~18.2 Ma.全岩地球化学和锆石Hf同位素分析显示，地层中的流纹岩具有钾质火山岩的地球化学特征，同时兼具A型花岗岩的亲缘性，为古老中下地壳部分熔融的产物.英安岩具有埃达克质岩的地球化学特征，为增厚新生下地壳部分熔融的产物.米拉山钾质流纹岩和埃达克质英安岩野外共生，丰富了拉萨地块中新世岩浆岩的研究内容，为青藏高原中新世岩石圈减薄/拆沉模型提供了新的证据. 

Characteristics and Tectonic Significance of the Miocene Strata in the Milashan Area,Eastern Lhasa Terrane

Miocene is an important period for the thickening and uplifting of the Lhasa terrane. A set of Miocene strata were recently identified in the eastern Lhasa terrane. It can be divided into three eruption cycles, and consists of rhyolite, dacite, pyroclastic rock, obsidian and lithic sandstone. Zircon U-Pb dating shows that the strata formed during 17.2-18.2 Ma. Whole-rock major and trace element analysis and zircon Hf isotope analysis show that the rhyolite has the geochemical characteristics of potassic volcanic rocks, and is derived from the partial melting of a middle-lower crust. The dacite has the geochemical characteristics of adakite related with A-type granite, and is derived from the partial melting of a new thickened lower crust. The coexistence of the potassic and adakitic rocks enriches the research of the Miocene volcanic rocks, and provides new evidence for the Miocene lithospheric detachment model in the Tibetan Plateau.