云南马关地区新生代碧玄岩中地幔包体研究  

A Study on the mantle xenoliths in the Cenozoic volcanic rocks from Maguan Area,Yunnan Province.

作　　者：喻学惠[1] 莫宣学[1] 曾普胜[2] 朱德勤[1] 肖小牛[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,岩石圈构造,深部过程及探测技术教育部重点实验室,中国地质大学(北京),北京100083 [2]云南财贸学院,昆明650221

出　　处：《岩石学报》2006年第3期621-630,共10页Acta Petrologica Sinica

基　　金：国家重点基础研究发展规划项目(2002CB412603);国家自然科学基金(40172025);国土资源部青藏高原专项(批准号:200101020404)的联合资助。

摘　　要：自晚新生代以来,由于受印度-亚洲板块碰撞和青藏高原整体快速抬升的影响,在云南省东南的马关地区发育了大量新生代碱性火山岩。其中有的火山岩中含有丰富的地幔包体。本文提供了马关八寨碧玄岩和钾玄岩的2个全岩化学分析资料,以及石榴二辉橄榄岩、尖晶二辉橄榄岩、石榴辉石岩和石榴二辉岩包体的全岩化学和电子探针分析结果,采用矿物温压计获得各种地幔包体的平衡温压条件,建立了本区地幔地温线,并与世界典型大地构造单元的地温线进行了对比。研究表明,石榴石二辉橄榄岩的平衡温压为1209℃～1230℃和2．13～2．93GPa,石榴石二辉岩为1034℃～1095℃和1．69～2．35GPa,尖晶石二辉橄榄岩的平衡温压为944℃～1072℃和1．46～2．74GPa,其对应的深度分别为69～93km、55～75km和48～87km。因此尖晶石二辉橄榄岩与石榴二辉橄榄岩和石榴二辉岩共存,其间没有截然的界限,而是一种过渡关系。由包体平衡温压建立的上地幔地温线与华北地区地温线一样,位于澳大利亚克拉通东缘地温线与碱性玄武岩省地温线之间,但本区地温线显著高于华北地温线,与本区具有高于华北地区的大地热流值相吻合。这证明各种辉石岩和橄榄岩包体来自地幔。根据平衡压力反演的包体起源深度推测,含石榴石的二辉橄榄岩可能来源于岩石圈底部或软流圈。基于上述研究,结合高原及滇西地区新生代钾质岩浆活动时空结构的研究成果,提出马关地区新生代碱性岩浆活动和地幔包体的成因,与印度-欧亚大陆俯冲碰撞诱发的软流圈横向地幔流的活动有关。There is a large numbers of Cenozoic volcanic rocks in Maguan area, Eastern Yunnan province due to Indo-Asian collision and uplift of whole Tibet Plateau quickly since late-Cenozoic Era. Abundant xenoliths derived from mantle contained in the some volcanic rocks. This paper provide the analytic data of the whole rock chemistry of the Cenozoic volcanic rocks and EMB data of the garnet-lherzolite, spinel-lherzolite, garnet-pyroxenite and garnet-websterite xenoliths in the volcanic rocks from Bazhai, Maguan area; and obtained equilibrium temperatures and pressures of the xenoliths using the mineralogical thermobarometer; and to contributed local mantle geotherm and made a compare with the geotherm of typic geotectonic units from worldwide. The studies showed that, the equilibrium T and P of the garnet-lherzolite and websterite are 1209℃ - 1230℃ and 2.13 -2.93GPa, 1034℃ - 1095℃ and 1.69 - 2.35GPa respectively, but the equilibrium T and P of spinel lherzolite are 944℃ - 1072℃ and 1.46 - 2.74GPa, the depth origined the xenoliths is corresponding to 69 -93km, 55 -75km and 48 -87kin respectively. Therefore, the xenoliths of spinel-lherzolite, garnetlherzolite and garnet- websterite are coexistence and transition each other, but not boundary sharply among of them. The geotherm contributed by equilibrium T and P of the xenoliths located at between the geotherm of the eastern margin of the Australian Craton and alkanic volcanic province, similar to the geotherm of Huabei area but higher than the Huabei geotherm clearly, which consistent with the value of heat flow in Maguan area and eastern China, and demonstrate the pyroxenit and lherzolite xenoliths come from mantle. The depth inversed by equilibrium T and P of the xenoliths demonstrate the garnet lherzolite may be come from the base of lithosphere or asthenospher. This paper advanced that, according to the studies mentioned above, link the achievements about the time-space structure of the Cenozoic potassic magmatism in Tibetan Plateau and western Yunnan, the

关 键 词：云南 马关 新生代火山岩 地幔包体 地幔地温线 

分 类 号：P588.145[天文地球—岩石学]