西藏阿里西部地区超镁铁岩的岩石化学及其上地幔化学模式的探讨

本文探讨了该区超镁铁岩化学成分的分带性;本区方辉橄榄岩与其它地区的化学成分的对比;以及与其密切共生的岩浆岩化学成分的互补关系;及本区上地幔可能的化学分带模式。得出结论:(1)从地质和岩石化学证据表明本区的方辉橄榄岩是地幔物质呈固态侵位的。(2)方辉橄榄岩与共生的岩浆岩有成因联系。(3)本区可能存在上地幔双层化学模式。

THE STUDY OF PETROCHEMISTRY OF ULTRAMAFIC ROCKS AND CHEMICAL MODEL OF THE UPPER MANTLE IN ALI REGION, XIZANG (TIBET)

The southern Qinghai-xizang (Tibet) Plateau is situated in eastern part of Tethys belt. The ultramafic rocks are widely exposed. In this region, from north to south, it may be divided into Ritu belt, Lameila-Gagi belt, sigong-Geer belt, Laozishan-Bage belt and Daba-pulan belt. The main rock type is harzburgite mostly serpentinized. Based on the data of 27 bulk rock analyses and some REE analyses, this paper has discussed; ( 1 ) The division of petrochemical belts of the ultramafic rocks in Ali region, ( 2 ) A comparion of composition of the ultramafic rocks in Ali region to those in other areas, ( 3 ) Compositional complementarity between the harzburgites and associated basic rocks in Ali region, ( 4 ) The chemical model of the upper mantle in Ali region. We have come to the conclusions. ( 1 ) The geological and petrochemical evidences indicate that the ultramafic massifs in Ali are mantle material emplaced in solid state, ( 2 ) the compositional complementarity between the harzburgites and associated pyroxenites, diabases, basic volcanic rocks and gabbros provides a rigorous evidence of their genetical relationship, ( 3 ) petrochemical data imply that two layer mantle model may exist in Ali region.