藏南哈热地区淡色花岗岩年代学、地球化学特征及地质意义

Geochronology,Geochemistry and Geological Significance of Leucogranite in the Hare Region,South Tibetan

哈热地区淡色花岗岩分布在北喜马拉雅淡色花岗岩带,大地构造位于特提斯喜马拉雅造山带中东部的喜马拉雅地块。主要岩性为白云母二长花岗岩,少量为含白云母二长花岗岩、含电气石白云母二长花岗岩与二长花岗岩。具有高SiO_(2)、富Al_(2)O_(3)与K_(2)O,贫CaO、MgO、TiO_(2)的特征,属于高钾钙碱性系列过铝质岩石,岩浆的结晶分异程度较高。稀土元素总量含量较低,总体上明显低于世界上酸性岩的平均丰度,具轻稀土富集特征。微量元素中大离子亲石元素Rb、K及高场强元素Th相对较为富集,大离子亲石元素Sr及高场强元素Ti呈现低谷负异常。同时大部分样品高场强元素Hf无负异常,稀土及微量元素均反映源区可能有斜长石的残留。锆石U-Pb年龄为22±1Ma,反映成岩时代为中新世。与STDS活动时代相吻合,形成于STDS启动之后的伸展构造减薄背景下,为印度板块和欧亚大陆碰撞过程中地壳中泥岩部分熔融的产物。

Leucogranite in the Hare region,south Tibet consists of tourmaline-bearing monzonite and muscovite monzonite which are characterized by enrichment in SiO_(2),Al_(2)O_(3) and K_(2)O and depletion in CaO,MgO and TiO_(2),belonging to peraluminous rocks of high potassium calc-alkaline series.Geochemically,it is characterized by lowΣREE,relative enrichment in LIL such as Rb,K and HFSE Th and lower negative Sr and Ti anomalies which indicate that it was product of partial melting of argillaceous rock during the collision of the Indian plate with Eurasia plate and formed under condition of extensional thinning after the start of STDS.The zircon U-Pb age values are 22±1 Ma.