【摘要】 腾冲火山岩区是我国全新世以来记载火山喷发的少数地区之一,该地区岩浆作用的性质与成因是揭示青藏高原东缘的现今侧向生长过程与深部作用的重要依据。本文对腾冲火山岩区的马鞍山、黑空山、打鹰山全新世火山岩开展了矿物化学和岩石地球化学研究,以期揭示岩石成因和深部动力学过程。腾冲全新世火山岩主体岩性为高钾钙碱性系列的玄武粗安岩和粗安岩。岩石的CaO、Fe₂O₃^T、TiO₂与SiO₂负相关,而K₂O与SiO₂正相关,表明岩浆演化过程中可能存在橄榄石、辉石和斜长石的分离结晶作用。岩石中存在酸性斜长石（更长石,An=28）大颗粒捕掳晶,其边部发育了基性斜长石（拉长石,An=65）增生边;在大颗粒石英捕掳晶的边部发育了辉石的反应边,这些结构表明在岩浆上升到地壳浅部时,曾受到了花岗岩围岩的混染,但岩石的Th/Nb值均小于1.16,表明地壳混染总体不显著。腾冲全新世火山岩大离子亲石元素富集、高场强元素相对亏损,高Th/U、低Ba/La,富集Sr-Nd同位素,其岩浆源区应为经历过洋壳沉积物交代后的富集地幔。腾冲火山岩属于大陆板内环境,是印度与亚洲大陆碰撞后岩浆作用的产物。火山岩是沿着腾冲盆地南北向展布,且熔岩分布面积有限。由于高原侧向生长过程中的区域性走滑断裂会引起局部的伸展,腾冲火山岩产出可能与富集岩石圈地幔的减压熔融有关。更多还原

【Abstract】 Tengchong volcanic field is one of the areas with the records of Holocene volcanos in China.The magmatism nature and petrogenesis of this Tengchong Holocene Volcanics（THV）are essential evidences in revealing the present southeastward growth and deep processes of the Tibetan Plateau.This paper carried out mineral chemistry and whole rock geochemistry study on three volcanos（Maanshan,Heikongshan,and Dayingshan）of the THV,and discuss the origin and dynamics of the magmatism.The majority of the THV are high potassium calc-alkaline rocks,including basaltic trachyandesite and trachyandesite.We found negative correlations between SiO₂and CaO,Fe₂O₃^T,TiO₂,MgO,and positive correlation between SiO₂and K₂O,which indicate the fractional crystallization of olivine,pyroxene,and plagioclase.The xenocrysts of plagioclase with acidic composition（An=28）has overgrowth basic plagioclase rim（An=65）,and xenocrysts of quartz with narrow pyroxene reaction rim,were found in the trachyandesite samples,which possibly suggest the crustal contamination by granitoid country rock during the magma upwelling processes in shallow level of the crust.On the contrary,the whole rock Th/Nb ratio is small（<1.16）,which reflects a minor overall contamination.The THV show enrichment in large ion lithophile element（LILE）,and depletion in high field strength element（HFSE）,high Th/U and low Ba/La ratios,and enrichment of Sr-Nd isotopes,which as a whole implies that the magma should have come from an enriched upper mantle that have experienced metasomatism by subduction of pelagic sediments of the Neo-Tethys.The THV are formed in intraplate tectonic setting of post-collision regime after the collision between India and Asia.The volcanos are distributing in north-south trending along the Tengchong basin and erupted in limited volume.Considering the highly localized extension along regional strike-slip faults during the lateral spreading in the eastern Tibetan plateau,the trigger of the Tengchong Holocene volcanic rocks may be interpreted as resulting of the decompression melting of the enriched metasomatized mantle lithosphere.更多还原