冈底斯古近纪花岗斑岩地球化学特征及地质意义——以西藏措勤地区为例

Lithogeochemistry and Its Geological Significances of Paleogene Granite Porphyry in West Gangdisê

冈底斯西段古近纪花岗斑岩为过铝质岩石,岩石类型为I型,属高钾钙碱性系列。该岩石具绢云母化、高岭土化发育,交代结构非常显著。岩石稀土元素配分模式为右倾型,轻稀土富集型,Ce负异常,中等负铕异常,整体上表现为富Rb,Th,K,Ce,Hf,Sm,而亏损Ba,U,Ta,Nb,Sr,P,Ti等元素。岩浆源区可能存在俯冲板片流体或熔体的交代作用,在岩浆演化过程中斜长石、碱性长石及磷灰石有可能发生了结晶分离作用。花岗斑岩岩浆形成于火山弧环境,角闪石为主要源区残留相,是燕山晚期-喜山早期岩浆活动的产物。

Paleogene granite porphyry in West Gangdisê is I-type peraluminous rock of K-rich calc-alkaline series.Sericitization and kaolinization as well as metasomatic texture are developed in the rock.The REE patterns for the rock are characterized by LREE enrichment with negative Ce anomaly and moderate negative Eu anomaly.The rock is rich in Rb,Th,K,Ce,Hf,Sm and depleted in Ba,U,Ta,Nb,Sr,P and Ti.The magma was originated from Yanshanian-Himalayan volcanic arc.