藏南亚东地区超高温叠加的榴辉岩中文象浅色体成因及其对软流圈上涌的制约  

Genesis of graphic leucosomes in the UHT-overprinted eclogites from Yadong area,southern Tibet and its constraints on the asthenospheric upwelling

作　　者：吴晨光 张立飞[1] 张贵宾[1] 王杨 WU ChenGuang;ZHANG LiFei;ZHANG GuiBin;WANG Yang(MOE Key Laboratory of Orogenic Belts and Crustal Evolution,School of Earth and Space Sciences,Peking University,Beijing 100871,China;Key Laboratory of Computational Geodynamics,College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing)

机构地区：[1]北京大学地球与空间科学学院,造山带与地壳演化教育部重点实验室,北京100871 [2]中国科学院大学地球与行星科学学院,计算地球动力学重点实验室,北京100049

出　　处：《岩石学报》2023年第8期2238-2256,共19页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(91755206、8200904178)资助。

摘　　要：在藏南亚东地区榴辉岩中新识别出的超高温变质作用拓展了对喜马拉雅这一正在进行中的陆陆碰撞造山带的认识,但是对于该超高温变质作用的时代及热源目前仍缺乏限定。本文在藏南亚东地区超高温叠加的榴辉岩中发现了一种文象结构的浅色体。该浅色体由大量文象结构的斜长石、石英以及中条纹长石组成,是变质熔体冷却结晶的产物。通过详细的矿物学、地球化学、地质温度计和锆石年代学研究发现:该熔体最初是由片麻岩部分熔融产生,在榴辉岩相条件下侵入榴辉岩,体系的温度在~16Ma时至少为900℃;随后发生近等温降压折返,在~15Ma时温度仍保持在~950℃,并开始冷却结晶。由于被侵入的榴辉岩在~17Ma时温度仅为750℃,说明该地区的岩石在大约2Myr的时间内温度升高了200℃,要求有异常热源提供热量。结合区域上在具有时空一致性的南北向裂谷和可能的俯冲印度岩石圈的撕裂,由此导致的软流圈上涌可以作为喜马拉雅中部的榴辉岩在早中新世快速升温达到超高温变质作用叠加的热源,对喜马拉雅造山带的演化具有重要意义。The ultrahigh-temperature(UHT)metamorphisms in the central Himalayan orogen expand our understanding about this ongoing continent-continent collisional belt.However,the era and heat source of these UHT metamorphisms are not well constrained.In this paper,graphic leucosomes in the UHT-overprinted eclogites are reported in the Yadong region,central Himalaya.These leucosomes are mainly composed of graphic plagioclase and quartz and abundant mesoperthite,which are the crystallization product of metamorphic melt.Based on detailed mineralogy,geochemistry,geothermometer and zircon geochronology,the origin and evolution of this melt are as follows:this melt generated from the partially melted pelitic gneisses,and then invaded into the eclogite under eclogite-facies condition;At~16Ma,the melt temperature was at least 900℃;subsequently,the melt-eclogite system experienced an isothermal decompression,and the temperature maintained 950℃and started to cool at~15Ma.Based on the documents of eclogites on the same outcrop,the temperature at~17Ma was only 750℃.Therefore,these results show that the temperature increased by 200℃or more within a timescale less than 2Myr.Considering the spatio-temporal consistencies between the UHT metamorphisms,the north-trending rifts and the possible slab tears of subducted Indian lithosphere,the upwelling asthenosphere could be a reliable heat source for such rapid temperature increase in early Miocene and play a significant role in Himalayan orogenic evolution.

关 键 词：喜马拉雅 亚东地区 超高温变质作用 快速加热 软流圈上涌 

分 类 号：P541[天文地球—构造地质学] P588.345[天文地球—地质学] P597.3