川西北塔公石英闪长岩地球化学特征和岩石成因.doc

川西北塔公石英闪长岩地球化学特征和岩石成因.doc川西北塔公石英闪长岩地球化学特征和岩石成因摘要:川西北塔公地区位于青藏高原东部,属于松潘―甘孜造山带的东南部边缘。塔公石英闪长岩侵位于晚三叠世地层中, 岩体的 KAr 同位素年龄为 134 ~ 136 Ma, 形成于早白垩世。岩石 SiO2 质量分数为 % ~ % ,铝饱和指数为 ~ ,全碱质量分数为 % ~ % ,里特曼指数为 ~ ,样品属于亚碱性准铝质高钾钙碱系列石英闪长岩。岩石 Mg# 值较高,总体具有高 Sr 含量、低 Nd 含量的同位素地球化学特征。 N( 87Sr ) /N( 86Sr )值为 589 ~ 009 ,初始 N( 87Sr ) /N( 86Sr ) 值为 503 ~ 878 ,N( 143Nd ) /N( 144Nd ) 值为 135 ~ 196 ,ε Nd(t) 值均为负( -86 ~ - ), Nd 模式年龄为 ~ Ga, Hf 模式年龄为 ~ Ga 。该岩体是早白垩世期间,川西北地区陆缘陆内造山环境下由松潘―甘孜造山带古老的下地壳镁铁质物质局部熔融形成的晚碰撞碰撞后非分异Ⅰ型花岗岩类。关键词:石英闪长岩;早白垩世;地球化学;岩石成因;花岗岩;下地壳局部熔融;松潘―甘孜造山带;川西北中图分类号: 文献标志码: A Geochemistry and Petrogenesis of Quartz Diorite in Tagong Area of Northwest Sichuan LAI Shaocong1 ,2, ZHAO Shaowei1 ,2 ( 1. State Key Laboratory of Continental Dynamics , Northwest University , Xian 710069 , Shaanxi , China ; 2. Department of Geology , Northwest University , Xian 710069 , Shaanxi , China ) Abstract : Tagong area of Northwest Sichuan is located in the east of QinghaiTibet Plateau , and belongs to the southeast margin of SongpanGanzi orogenic belt. The quartz diorites in Tagong area form in Early Cretaceous with KAr isotopic ages of 134136 Ma, and emplace into Late Triassic strata. Mass fractions of SiO2 are %% , K values are , mass fractions of total alkali are %% , Rittmann indexes are , so that the samples belong to subalkaline metaperaluminous highK calcalkaline series quartz diorites. The rocks have relative high Mg# values with the isotopic geochemical characteristics of high contents of Sr and low contents of Nd. N( 87Sr ) /N( 86Sr ) is 009 with the initial N( 87Sr ) /N( 86Sr ) of 878 ,N( 143Nd ) /N( 144Nd ) is 196 with negative ε Nd(t) of -- ; Nd and Hf model ages are Ga and Ga, respectively. The quartz diorites belong to undifferentiation Ⅰ type granitoids with late to postcollision caused by partial melting of ancie