西藏达布矿区含矿岩体的时代、岩石地球化学特征及岩石成因

Geochronology,Petrogeochemistry and Petrogenesis of Ore-Bearing Rock Massif in Dabu Mining Area,Tibet

达布矿区位于冈底斯成矿带中段南侧,具较大的铜(钼)成矿潜力.通过对达布矿区含矿花岗闪长岩体开展岩石学、LAICP-MS锆石U-Pb定年和岩石地球化学等方面的分析研究,结果显示达布矿区花岗闪长岩体是主要的含矿岩体之一,其LAICP-MS锆石U-Pb年龄为16.5±0.3 Ma^16.0±0.4 Ma,属中新世(N1).岩体具高Al(Al_2O_3=15.6%~16.5%)、高Na(Na_2O=4.51%~4.82%)、钙碱性系列、弱过铝质;稀土元素具弱正铕异常(Eu/Eu*=1.02~1.27)和正铈异常(Ce/Ce*=0.99~1.53);富集Rb、Ba、Sr和亏损Nb、Ta、Ti、Y.达布矿区花岗闪长岩体属I型花岗岩,类似于典型的C型埃达克岩,明显有别于冈底斯带中新世高K埃达克岩;为印度-亚洲大陆碰撞后局部伸展背景下,由加厚下地壳物质(石榴石角闪岩)较高程度部分熔融的岩浆产物.

Dabu mining area is located in the southern part of the middle Gangdese metallogenic belt,which has great metallogenic potential of Cu（Mo）deposit.In this paper,petrology,LA-ICP-MS zircon U-Pb dating,rock geochemistry of the Dabu ore-bearing granodiorite body are systematically studied.The results suggest that the Dabu granodiorite pluton is one of the major ore-bearing rock body,and its LA-ICP-MS zircon U-Pb age is 16.5±0.3 Ma-16.0±0.4 Ma,with the corresponding age of Miocene（N1）.The rock mass has high Al（Al2O3 =15.6%-16.5%）,high Na（Na2O=4.51%-4.82%）,and it is calc-alkaline and weakly peraluminous.REE elements have weak positive Eu anomalies（Eu/Eu＊=1.02-1.27）and positive Ce anomalies（Ce/Ce＊=0.99-1.53）.Trace elements ratio spider diagram displays apparent enrichments of Rb,Ba,Sr and marked depletions of Nb,Ta,Ti,Y.The Dabu granodiorite pluton belongs to I-type granite,which is similar to the typical C-type adakite,but is obviously different from the Miocene high-K adakite in the Gangdese belt.It is concluded that Dabu granodiorite pluton is a relatively high degree of partial melting of the thickened lower crust material（garnet amphibolite）formed in the background of partial extension of the India Asian continent post-collision.