汉诺坝辉石岩包体中单斜辉石的微区微量元素组成特征及其地球动力学意义  

In situ trace elemental compositions and geodynamic significance of clinopyroxene in pyroxenite xenoliths from Hannuoba.

作　　者：宗克清[1] 刘勇胜[1] 高山[1] 袁洪林[2] 柳小明[2] 王选策[1] 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,武汉430074 [2]西北大学地质系 大陆动力学教育部重点开放实验室,西安710069

出　　处：《岩石学报》2005年第3期909-920,共12页Acta Petrologica Sinica

基　　金：本研究受国家自然科学基金项目(Nos.40473013;40133020)教育部长江学者和创新团队发展计划中国地质大学地质学理科基地资金共同资助

摘　　要：本文对来自汉诺坝玄武岩中的三类辉石岩包体的单斜辉石(Cpx)利用LA-ICP-MS进行了原位微区微量元素分析研究。金云母单斜辉石岩中的单斜辉石具有低Cr、Co和Ni,高CaO、Zr、Hf、Ta和LREE特征,并且具有较低的Mg#,反映金云母单斜辉石岩可能是经受了后期交代作用的地幔岩浆堆晶产物。尖晶石二辉橄榄岩中的石榴辉石岩脉体中的Cpx具有高 Na,O低CaO特征,其Ti、Zr、Hf、Y含量明显高于其它石榴辉石岩Cpx中的含量,反映了石榴辉石岩脉体可能是富Na硅酸盐熔体与地幔尖晶石二辉橄榄岩反应的成因。部分石榴辉石岩包体的Cpx具有特征的La富集或微量元素(如Zr、Hf、Ta、Li、P、 REE等)环状对称分布特征,暗示华北克拉通北缘可能存在多期次地幔交代富集作用。通过对同一Cpx颗粒中的流体包裹体密集区和干净区域的对比研究,发现Cpx中的流体包裹体不仅富集LILE和LREE,而且HFSE中的Nb、Ta、Zr和P也具有明显的富集特征,LREE和HFSE未发生明显分异,这可能暗示地幔交代流体中含有少量的络阴离子(如F-和Cl-等)。Clinopyroxenes of pyroxenite xenoliths from the Hannuoba basah were in situ analyzed by LA-ICP-MS. Clinopyroxenes of spinel phlogopite clinopyroxenites have considerably low Cr,Co and Ni contents and Mg^# and high CaO ,Zr,Hf,Ta and LREE eontents,which suggests that the spinel phlogopite clinopyroxenites could be cumulates modified by subsequent metason,atism. Clinopyroxenes of olivine garnet pyroxenite vein hosted in spinel lherzolite have relatively high Na2O and low CaO contents, and are characterized by higher Ti,Zr,Hf and Y contents compared with the other garnet-bearing pyroxenites. These features indicate a possible Na-rich meltmantle peridotite interaction responsible for the formation of these garnet pyroxenite veins. La-enrichment and/or trace elemental zonation demonstrated by clinopyroxene of some garnet-bearing pyroxenites indicate multi-episode partial mehing and mantle metasomatism in the north of North China craton. On the other hand, the in situ analyses for fluid inclusion-bearing area of clinopyroxene suggest that fluid inclusion is not only enriched in light rare earth elements and large ion lithophile elements, but also enriched in some high field strength elements （ e. g. , Nb,Ta,Zr and P）. These observations imply that the fluid involved in mantle metasomatism could contain certain amount of anion （ e. g. , F^- and Cl^ - ） , and does not fractionate I.REE from HFSE.

关 键 词：汉诺坝 辉石岩包体 单斜辉石 LA—ICP—MS 微量元素 原位微区分析 

分 类 号：P588.125[天文地球—岩石学] P588.145[天文地球—地质学]