胶北西留古元古代～2.1Ga变辉长岩岩石学与年代学初步研究  

Petrological and geochronological preliminary study of the Xiliu ～ 2.1Ga meta-gabbro from the Jiaobei terrane,the southern segment of the Jiao-Liao-Ji Belt in the North China Craton

作　　者：刘平华[1] 刘福来[1] 王舫[1] 刘建辉[1] 蔡佳[1] 

机构地区：[1]中国地质科学院地质研究所,北京100037

出　　处：《岩石学报》2013年第7期2371-2390,共20页Acta Petrologica Sinica

基　　金：科技部973项目(2012CB416603);国家杰出青年科学基金项目(40725007);中国地质调查局地质大调查项目(1212010811065;1212011120150);中国地质科学院地质研究所基本科研业务经费(J1212)联合资助

摘　　要：胶北西留古元古代变辉长岩主要由二辉麻粒岩与辉石斜长角闪岩所组成,且以不规则透镜体的形式赋存于新太古代花岗质片麻岩与英云闪长质片麻岩之中。岩相学观察、矿物相转变分析、矿物化学研究、传统地质温压计计算与锆石LA-ICP-MS定年结果表明,胶北西留变辉长岩记录了十分复杂的演化历史,其中早期残留的原岩标志性岩浆结构以辉长辉绿结构为特征,早期残留的单斜辉石为高温低钙的普通辉石(M0),此阶段形成的岩浆锆石记录了其原岩形成时代为2102±3Ma。峰期麻粒岩相变质阶段(M1)的矿物组合以斜方辉石+单斜辉石+斜长石+石英为特征,记录的温压条件为T=800～850℃,P<0.65～0.75GPa;晚期角闪石的生长表明岩石又经历了降温冷却的过程(M2),其稳定的矿物组合为角闪石+斜长石+石英+单斜辉石,记录的温压条件为T=675～700℃,P=0.40～0.55GPa,变质阶段形成的变质锆石记录了其变质时代为1907±16Ma。胶北西留变辉长岩记录了含有近等压降温变质过程的顺时针P-T轨迹。结合本区其它研究资料,本文认为西留古元古代变辉长岩是胶北地区古元古代地层沉积之前一次地壳伸展作用的产物,并于古元古代晚期(1.95～1.80Ga)卷入了胶北碰撞造山作用过程。The Xiliu meta-gabbros are composed predominantly of orthopyroxene-clinopyroxene granulites and clinopyroxene amphibolites,and are found as irregular lenses within the Neoachean granitic and tonalitic gneisses in the Jiaobei terrane.On the basis of petrography,mineral transformation,mineral composition,temperature-pressure estimation and in situ U-Pb dating of zircons,three distinct mineral assemblages of the meta-gabbros have been identified by the characteristics of mineral reactions and evolutions.The relict ophitic and gabbro textures represent the early index igneous textures.High-augite core in clinopyroxene is regarded as one of the early igneous assemblage （M 0）.The magmaitic zircons record a weighted mean 207 Pb /206 Pb age of 2102 ± 3Ma,which represents the magmatic crystallization timing of the meta-gabbros.The granulite-facies metamorphism （M 1） is defined by the mineral assemblage of orthopyroxene ＋ clinopyroxene ＋ plagioclase ＋ quartz,which formed at 800 ～ 850℃ and less than 0.65 ～ 0.75GPa.The mineral assemblage of amphibole ＋ plagioclase ＋ quartz formed at a cooling retrograde stage （M 2） with P-T conditions of 675 ～700℃ and 0.40 ～ 0.55GPa.The metamorphic zircon records a younger 207 Pb /206 Pb age of 1907 ± 16Ma,which represent the timing of the granuliteamphibolite facies metamorphism of the meta-gabbros.These data indicate that the meta-gabbros record a clockwise P-T path involving near-isobaric cooling （IBC） process.Combined with other investigations of the Jiaobei terrane,it was suggested that the Xiliu metagabbros were formed by crustal extension before the deposition of Paleoproterozoic strata,and were involved in the Late Paleoproterozoic （1.95 ～1.80Ga） collisional orogenic process in the Jiaobei terrane.

关 键 词：胶北 古元古代 变辉长岩 岩石学 年代学 

分 类 号：P588.124[天文地球—岩石学]