辽宁瓦房店金伯利岩中铬尖晶石成分的两种分带趋势及其成因探讨  

TWO KINDS 0F CHEMICAL COMPOSITION ZONING TRENDS AND THEIR GENESIS IN Cr─SPINELS FROM KIMBERLITES,WAFANGDIAN AREA

作　　者：鲍学昭[1] 关雅先[1] 王公庆[1] 黄顺福 

机构地区：[1]地矿部天津地质矿产研究所,长春地质学院,辽宁省地质六队

出　　处：《长春地质学院学报》1995年第4期381-386,共6页

摘　　要：首次报道金伯利岩中铬尖晶石的两种成分分带趋势，其中斑晶铬尖晶石以核部富Ｃｒ、边缘逐渐富Ａｌ和Ｆｅ￣（＋３）为特征，该铬尖晶石为金伯利岩岩浆上升过程中形成的；基质铬尖晶石则同上述变化趋势相反，它们是岩浆在温、压增大或母岩在熔融程度增加过程中形成的。根据Ｃｒ＿２Ｏ＿３含量，基质铬尖晶石可分为两类：一是岩浆演化晚期，岩管爆发前槽压过程中结晶的低铬铁尖晶石（Ｃｒ＿２Ｏ＿３＜５４％）；二是来自深源捕虏体的高铬铁尖晶石（Ｃｒ＿２Ｏ＿３＞６０％），本文探讨了它们的形成机制。Two kinds of chemical composition zoning trends are discovered in Cr-spinels from kimberlites,Wafangdian area. The core of phenocryst Cr-spinel is rich inFe￣(2+)and Cr and become rich in Fe￣(3+) and Al gradually outwards to tim. They areconsidered undertaking crystallization during the upward movement of kimberlitemagma,a process of pressure decreasing. But in the fine-grained matrix Cr-spinels,thecore of their crystals is rich in Al￣(3+)and Fe￣(3+),and become rich in Cr and Fe￣(2+)graduallyoutward to rim. The authors consider that there is an increasing process of temperatureand pressure,which produces this kind of composition zoning trend. Two kinds of genesisabout it are proposed:1.The high chromium Cr-spinel (Cr_2O_3 > 60%)is shed intokimberlite from the Cr-rich peridotite xenoliths. The Cr/A1 ratio increasing from core torim in the crystals shows that they crystallized during the enhancement of partial meltingof mantle rocks,a process of rising of temperature and pressure, which is due todowngoing of oceanic plate,2.The lowerchromium Cr-spinel(Cr_2O_3<54%)crystallizesbefore the eruption of magma,a stage of increasing pressure.

关 键 词：金伯利岩 铬尖晶石 成分 分带 成因 辽宁 

分 类 号：P588.125[天文地球—岩石学]