2.0GPa,850～1070℃条件下多硅白云母榴辉岩脱水熔融研究--对大别早白垩富K埃达克岩成因的约束  

Dehydration Melting of a Phengite-bearing Eclogite at 2.0 GPa and 850～1070℃-Constraints on the Petrogenesis of the Early Cretaceous,K-rich Adakite in Dabie Orogenic Belt

作　　者：闻卫军[1,2,3] 周文戈[1] 范大伟[1] 李朋[1,2] 胡贤旭[1,2] 

机构地区：[1]中国科学院地球化学研究所,地球内部物质高温高压实验室,贵阳550002 [2]中国科学院大学,北京100049 [3]安徽省化工地质勘查总院,安徽马鞍山243000

出　　处：《矿物岩石地球化学通报》2012年第6期622-634,共13页Bulletin of Mineralogy, Petrology and Geochemistry

基　　金：国家自然科学基金资助项目(90914008;40873052);贵州省科学技术基金资助项目(黔科合J字[2010]2231号)

摘　　要：以产出于大别新店高压变质杂岩带的含角闪石多硅白云母榴辉岩(XD963)为实验源岩,使用YJ-3000t紧装式六面顶压机装置,在2.0GPa,850～1070℃条件下,进行了脱水部分熔融实验研究。结果显示,在850～950℃下,多硅白云母通过不一致脱水熔融反应产生了≤12%的过铝质(铝饱和指数ASI>1.2)的高K钙碱性(K2O/Na2O=1.2～1.4)花岗质熔体,与其共存的残留相为石榴子石+绿辉石+石英+多硅白云母+角闪石+Fe-Ti氧化物+蓝晶石±金红石。1000～1070℃时,熔体比例陡然增大(>35%),成分变为准铝质的钙碱性花岗闪长质,残留相组合以石榴子石+绿辉石+普通辉石为主。实验熔体与早白垩世富K埃达克岩的主微量元素对比结果表明:除ASI以及Eu/Eu*值特征外,低温熔体(900～950℃)与富K埃达克岩具有很好的相似性。此外,本次实验源岩在相对低温(900和950℃)条件下形成的熔体具备富K埃达克岩的两个主要特征—高K钙碱性和花岗质。因此可认为形成高K钙碱性的花岗质岩浆不需要过高的压力以及高度富K的源岩。Dehydration melting experiments were conducted on an amphibole-phengite-bearing eclogite sample（XD963）,collected from the Xingdian high pressure metamorphic complex,northern Dabie orogenic belt,using the multianvil apparatus（YJ-3000t） under conditions of 2.0 GPa and 850~1070℃.Phengite-dehydration melting produced ≦12% melt with peraluminous（ASI1.2）,high-potassium,calc-alkaline（K2O/Na2O =1.2~1.4） and granitic features,coexisting with omphacite,garnet,quartz,phengite,amphibole,Fe-Ti oxides and rutile restites up to 950℃ via incongruent melting reactions.at temperatures of 1000~1070℃,the melt fraction abruptly elevated to 35% and became metaluminous,calc-alkaline and granodioritic coexisting with omphacite,augite and garnet-rich restites.The major and trace element compositions of the experimentally produced melts were compared with those of the Early Cretaceous K-rich adakite in Dabie orogenic belt,the results showed that the melts of phengite-bearing eclogite produced by the dehydration melting at relatively low temperatures of 900-950℃ are very similar to the K-rich adakite except significant peraluminous and marginally negative Eu anomalie.Furthermore,the melts produced under temperatures of 900-950℃ are characterized by high-potassium,calc-alkaline and granitic,two critical features of K-rich adakitic rocks.Based on these evidences,it is suggested that high pressure and high K protoliths are not the indispensable requirements for the generation of the high-potassium,calc-alkaline and granitic magma.

关 键 词：富K埃达克岩 多硅白云母 榴辉岩 脱水熔融 

分 类 号：P589[天文地球—岩石学]