碧口地块王坝楚花岗岩成因及其地质意义  

Petrogenesis and geological significance of Wangbachu granite from Bikou area,Northwest margin of Yangtze Block

作　　者：骆金诚[1] 赖绍聪[1] 秦江锋[1] 李学军[1] 臧文娟[1] 李海波[1] 

机构地区：[1]西北大学大陆动力学国家重点实验室/地质学系,陕西西安710069

出　　处：《西北大学学报（自然科学版）》2010年第6期1055-1063,共9页Journal of Northwest University（Natural Science Edition）

基　　金：国家自然科学基金资助项目(40872060);教育部博士点基金资助项目(20096101110001);西北大学地质学系国家基础科学人才培养基地创新基金资助项目(XDCX08-08)

摘　　要：目的探讨扬子板块西北缘碧口地区王坝楚岩体的岩石成因、成岩物质来源及其构造环境。方法对该岩体进行详细的野外地质、岩相学及全岩地球化学分析。结果该岩石具有高的SiO2（71.55%~72.04%）、Al2O3（14.96%~15.19%）含量,高场强元素（Ta,Nb,Ti,P等）明显负异常,大离子亲石元素（Rb,Ba,Sr等）正异常,有弱的Eu负异常;具有高的Sr/Y比值（20.75~42.49）、低Y（Y=8.28~9.13μg/g,平均8.89μg/g）和低的HREE（eg.Yb=0.49~0.61μg/g）的特征,并具有强分异的稀土元素组成模式（La/Yb）N=20.18~29.41。结论该岩体的时空位置及地球化学特征显示,其形成于典型的后碰撞构造环境,可能是在印支期华北和扬子板块碰撞导致地壳加厚的环境下,以砂屑岩为主和角闪岩为辅组成的源区部分熔融,产生的熔体进行不同程度的混合而成。在增厚地壳的条件下,下地壳角闪岩的部分熔融可能是导致碧口地区缩短增厚—伸张垮塌转换、发生拆沉作用的重要因素之一。Aim To explore the granite petrogenesis of Wangbachu pluton,ore-forming material source and structural setting,in the Bikou Area of the northwest margin of Yangtze Block.Methods Field obvervation,petrographical description and geochemical analysis on the whole rocks were used.Results The plutonis was characteristized by high SiO2（71.55%~72.04%）,Al2O3（14.96%～15.19%）,high field strength elements such as Ta,Nb,P and Ti show distinct nagetive anomly while lithophile elements such as Rb,Ba and Sr exhibit obvious positive anomalies and obvious negative Eu abnormity;and high Sr/Y（20.75～42.49）,and low Y（8.28～9.13 μg/g,average 8.89 μg/g） and low HREE（eg.Yb=0.49～0.61 μg/g）,strongly fractionated REE patterns with（La/Yb）N=20.18～29.41.Conclusion According to those properties,combined with the themoral-spatial location of occurrence of the intrusion and geochemistry characters,it was thought that the Wangbachu granite pluton intrusion was formed in a typical post-collsional tectonic environment.It was possible that it was deprived from partial melt of source region dominatied by greywacke with subordinate amphibolite and mixing in different degrees,in such a geologic condition of crustal thickening resulted from collision between the North China and Yangtze plates during the Indosinian Time.This evevt might be a major factor that led to be the transition from compressional to extensional deformation in the overthickened Bikou area.

关 键 词：王坝楚花岗岩 地球化学 地壳深熔作用 岩石成因 碧口地区 

分 类 号：P588.121[天文地球—岩石学]