东秦岭北部富碱侵入岩带岩石地球化学特征及构造意义  

THE GEOCHEMISTRY OF THE ALKALI-RICH INTRUSIVE ROCKS IN THE EAST QINLING,CENTRAL CHINA

作　　者：张正伟[1] 朱炳泉[1] 常向阳[1] 

机构地区：[1]中国科学院地球化学研究所

出　　处：《地学前缘》2003年第4期507-519,共13页Earth Science Frontiers

基　　金：国家自然科学基金(40072033);中国科学院知识创新工程重要方向项目(KZCX3-SW-125)

摘　　要：在东秦岭北部,富碱侵入岩的侵位与空间分布受同一个区域构造带(华北陆块南缘)控制,构成一个区域性的富碱岩浆岩带。根据岩石学和岩石化学研究,岩石类型主要分为碱性正长岩、碱性花岗岩和石英正长岩三大类。富碱岩浆岩带自北而南可以划分为3个亚带:北部碱性正长岩亚带,中部碱性花岗岩亚带,南部石英正长岩亚带。3个亚带富碱岩浆在化学成分方面虽有差异,但都具有富碱高钾特征,ALK=9～15,ω(K_2O)为5％～15％,ω(K_2O)/ω(Na_2O)=1.26～8.30。岩石中的暗色矿物辉石类主要为霓辉石和霓石,角闪石类主要为钙质浅闪石、阳起石质闪石、镁质角闪石、钠钙质绿闪石,黑云母类主要为铁云母和金云母。岩石中的长石类主要为K-Na系列富K端员的微斜长石和最大微斜长石,少量钠长石,极少Na-Ca系列的斜长石。霞石类主要为钾霞石和钙霞石。根据岩石地球化学研究,有以下显示:(1)REE总量200～1100μg/g,LREE/HREE比值4～15,δEu表现为无Eu异常或轻微正负Eu异常,(La/Yb)_n值多为10～30;(2)部分岩石类型富集大离子亲石元素,不相容元素分布模式曲线总斜率为负,Ba,Nb,Zr具明显负异常,表明他们具有大陆裂谷碱性花岗岩的特征;(3)岩石Nd、Sr和Pb同位素的研究表明,富碱侵入体的源区应是以下地壳为主,带入少量地幔和上地壳物质。The alkali-enriched intrusive rocks are mainly located in the north of East Qinling, central China, and their occurrences are controlled by a regional tectonic zone. Based upon systematic petro-graphic and geochemical studies, the intrusive rocks are divided into three types: (1) The alkaline rock type, that is syenitoid containing foid or alkaline dark minerals; (2) The alkaline granitoid including arfvedsonite granite and assemblage moyite; (3) Quartz syenite including quartz syenite, nordmarkite and granosyenite (porphyry) , which took alkaline feldspars as the dominate factors. Based upon systematic petrographic and dark minerals chemistry studies, we divided the dark minerals into three types, i. e. , alkaline augite including aegirine and aegirin-augite, alkali amphibole including calc-edenite, actinol-ite-amphibole, magnesio-hornblende, and sodium-calcium taramite, and biotite including phlogopite and annite. It is demonstrated that the light-colored minerals K-feldspars mainly include microcline, bar-bierite and maximum microcline, nephelines including K-nepheline and cancrinite. All these rocks constitute an alkali-rich magmatic rock belt in space( about length 400 km), which can be divided into three subzones according to the features of petrochemistry from north to south: the northern subzone of alkaline syenite, middle subzone of alkaline granitoid and southern subzone of quartz syenite (porphyry). The three subzones of alkali-rich intrusive rocks belong to the same category of the high-K, ALK=10-15,w(K2O) = 5%-15%,w(K2O)/w(Na2O) = 1. 26-8. 30. The REE and trace element show: (1) All rocks have the same REE characters: The REE distribution pattern is a LREE-rich type without obvious Eu anomaly, the ratios of (wn(La)/wn(Yb) ranging between 10 and 30; (2)The rocks are enriched in LILE (Large Ion Lithosphile Element) with significant negative anomalies of Ba, Nb, Zr, indicating a character of continental rift related magmatic rocks; (3)The different alkali-rich intrusive rocks in the eastern Qinling were

关 键 词：富碱侵入岩 地球化学 碱性花岗岩 东秦岭地区 

分 类 号：P588.1[天文地球—岩石学]