青藏高原东缘四姑娘山花岗岩地球化学特征和锆石U-Pb年代学证据  

Geochemistry and U-Pb Dating of Zircons from the Four-Girl Mountain Plutons in the Eastern Margin of Tibetan Plateau

作　　者：戴宗明[1,2] 孙传敏[1] 张宽忠[2] 李振江[2] 

机构地区：[1]成都理工大学地球科学院,成都610059 [2]四川省地质矿产局区域地质调查队,成都610213

出　　处：《地质科技情报》2011年第4期1-14,共14页Geological Science and Technology Information

基　　金：中国地质调查局项目"1:25万马尔康县幅区域地质调查"(1212010510304)

摘　　要：松潘-甘孜地体中的花岗岩主要形成于印支晚期至燕山初期,其主体是扬子地块沿龙门山构造带向松潘-甘孜地体内楔入导致松潘-甘孜地体中下地壳低速层发生部分熔融的结果。虽然在松潘-甘孜地体中多数岩体长轴走向和矿物定向均呈北西向,但过去区调中划分的北西向的金川-理县构造岩浆带不能代表这种楔入作用的产物,而应重新划分为北东向的道孚-金川-小金-黑水构造岩浆带,四姑娘山岩体是这个北东向构造岩浆带中的典型岩体。四姑娘山花岗岩属高Ba-Sr的钙碱性岩石,具有碰撞花岗岩的特征和岛弧花岗岩的某些特征,而非A型花岗岩;其岩浆成分以中下地壳为主并有幔源物质的加入,其锆石普遍具有岩浆锆石的特征。通过对四姑娘山花岗岩体的黑云母花岗闪长岩中的23粒锆石激光探针U-Pb定年,确定其岩浆结晶年龄为燕山早期(191±1)Ma。此年龄对解决龙门山断裂带形成的初始时间具有重要意义。The granitoid intrusions occurred in the eastern part of the Songpan-Garze terrane from the Late Indo-Chinese epoch to Early Yenshan epoch. It is the product of partial melting in the low velocity layer of the middle-lower crust of the Songpan-Garze terrane caused by the intrusion of the Yangtze massif along the Longmenshan structural belt. Although the major axis and mineral direction of most of the single granitic masses trend NW in the parallel arrangement in the Songpan-Garze terrane, the NW-trending Jingchuan-Lixian tectono-magmatic belt identified in the previous regional geological survey cannot represent products of the collision between the Yangtze massif and the Songpan-Garze terrane. It is necessary to recategorize the NE trending Daofu-Jinchuan-Xiaojin-Heishui tectono-magmatic belt. The Four-Girl Mountain granitic（FGMG） pluton is one representative granitic mass for this purpose. The FGMG pluton exhibits a strong affinity to ealc-alkaline series of high Ba-Sr（Ba 1 200-1 850 μg/g,Sr 321-1 540μg/g）,showing characteristics of collision-granite and some characteristics of arc-granite, and non A-type granite. The geochemical characteristics indicate that the middle-low crust and some mantle provide heat and part of source material for FGMG, and these zircons has characteristics of magma zircons. According to the LA- ICP-MS zircon U-Pb dating of the 23 crystal zircons from biotite granodiorite which yielded a weighted 206 pb/238U mean age of （191±1）Ma, interpreted as FGMG＇s magma crystallizaton age（Early Yenshan）. This age has great significance to understanding the initial formation time of the Longmenshan fault belt .

关 键 词：青藏高原 松潘-甘孜地体 四姑娘山 花岗岩 锆石 U-PB定年 地球化学 

分 类 号：P588.12[天文地球—岩石学]