揭示地质现象的本质与核心

青藏高原的形成与演化是举世瞩目的现代地学前缘 ,岩石圈结构及其演变对于探讨高原隆升及其资源环境效应具有重要意义。多年来 ,对于青藏高原岩石圈结构的认识主要基于地球物理探测结果和地质研究 ,尚未发现深达地幔的物质。我们在西昆仑地区康西瓦新生代火山岩中首次发现了以含金云母方辉橄榄岩为主的深源包体 ,其主要组成矿物为橄榄石和斜方辉石 ,含有少量单斜辉石、尖晶石和金云母。橄榄岩具有平衡粒状变晶结构 ,部分橄榄石颗粒仍保留有扭折带。电子探针分析结果表明 ,尖晶石的x(Cr) /x(Cr +Al)变化为 2 5%～ 8% ,属于尖晶石铬铁矿系列。根据CarrollWebb和Wood(1986 )提出的温压图解 ,橄榄岩形成压力大致为16 0 0MPa ,约相当于深度 56km。据此 ,认为康西瓦新生代玄武岩中产出的橄榄岩包体系岩浆活动过程中从岩石圈地幔携带上来的幔源物质 ,对于探讨青藏高原北部的岩石圈结构及其演化具有重要意义。

CHARACTERISTIC AND GEOLOGICAL SIGNIFICANCE OF THE DEEP-SEATED XENOLITHS IN CENOZOIC BASALT IN KANGXIWA, WESTERN KUNLUN MOUNTAINS, CHINA

The study on formation and evolution of Qinghai—Tibet plateau is a well known frontier in modern geology Studying the characteristics and evolution of the lithosphere is very important for us to understand the plateau uplift and its effect on mineral resources and environment For many years, we have known a lot about the lithosphere structure of Qinghai—Tibet plateau through geophysical detecting and geology, but deep|delived mantle xenoliths have not been found Last year, we found deep seated mantle xenoliths bearing phlogopite harzbergite from Cenozoic basalt in Kanxiwa area, western Kunlun mountains The harzbergite xenoliths mainly have equilibrium granoblastic texture They consist mainly of olivine, orthopyroxene and minor clinopyroxene, spinel and phlogopite Some olivines still remain kink band According to electric proble analysis results, The spinel belongs to spinel chromitite series with the ratio of x (Cr)/ x (Cr+Al)=8%～25% According to the thermobarometer of Carroll Webb and Wood, the pressure of peridotite formed is 1 6GPa So we think peridotite xenoliths in Cenozoic basalt are mantle materials from lithosphere Mantle And the discovery is very important for us to realize the structure and evolution of lithosphere in north part of Qinghai—Tibet plateau