北喜马拉雅淡色花岗岩带岩体地球化学分析及构造意义

Geochemical analysis and structural significance of the rock mass in the leucogranite belt of the northern Himalayas

北喜马拉雅穹窿(NHGD)中分布有一条近东西向展布的淡色花岗岩带,其完整的地质记录和良好的野外露头为研究喜马拉雅碰撞造山过程提供了良好的岩石探针。在理清北喜马拉雅淡色花岗岩带不同岩体展布特征的基础上,详细对比研究各岩体年代学和地球化学特征,深入探讨其成因差异及大地构造背景,综合分析认为:(1)北喜马拉雅淡色花岗岩大致可分为始新世(48~30Ma)、渐-中新世(28~12Ma)和中-上新世(12~4Ma)三个期次,其中始新世淡色花岗岩以角闪石部分熔融作用为主,变沉积岩部分熔融为辅;渐-中新世淡色花岗岩以变沉积岩白云母脱水部分熔融为主,水致白云母部分熔融为辅;中-上新世淡色花岗岩则以变泥岩白云母脱水熔融为主。(2)印度-亚欧板块碰撞到始新世,北喜马拉雅受南北向挤压构造体制控制,地壳始终处于增厚阶段;约从26Ma开始,加厚的岩石圈由于拆沉作用,由逆冲增厚向伸展垮塌转换,导致藏南拆离系的形成;13Ma以来,北喜马拉雅发生东西向伸展作用,导致大量呈南北向展布的断层发育。

A leucogranite belt distributed near east-west distribution in the northern Himalaya gneiss dome(NHGD).its complete geological records and good field outcrops provide a good rock probe for the study of the Himalayan collision orogenic process.On the basis of confirming the distribution characteristics of different rock masses in the leucogranite belt in the northern Himalayas.the age and geochemical characteristics of each rock mass were studied in detail,and the genetic differences and geotectonic background were discussed in depth.The comprehensive analysis shows that:(1)the northern Himalaya leucogranite can be divided into three phases:Eocene(48~30Ma),Oligocene-Miocene(28~12Ma)and Miocene-Pliocene(12~4Ma),The leucogranites of the Eocene are dominated by partial melting of hornblende supplemented by partial melting of metamorphic sedimentary rocks,the leucogranite of the Oligocene-Miocene are dominated by the dehydration and partial melting of the Muscovite,and was supplemented by partial melting of Muscovite caused by water,and the Middle-Eocene leucogranites are dominated by the dehydration and melting of Muscovite of metamorphic mudstone.(2)In Eocene,because of the Indian-Asia-Europe plate collision,and the crust of the North Himalayas was always in the thickening stage under the control of the north-south compression tectonic system.From 26Ma,because of delamination,the thickened lithosphere changed from thrust thickening to extension collapse,which resulted in the formation of detachment system in southern Tibet.From 13Ma,the east-west extension of the North Himalayas occurred,resulting in a large number of faults spreading north-south.