香格里拉九龙二叠系峨眉山玄武岩的岩石成因研究  

Petrogenesis of Permian Emeishan Basalts in Jiulong,Shangri-la

作　　者：王涛[1,2] 邓江红[1] 肖渊甫[1] 吕劲松[1] 王明国 

机构地区：[1]成都理工大学地球科学学院,成都610059 [2]中国科学院地球化学研究所矿床地球化学国家重点实验室,贵阳550002 [3]河南省有色金属地质勘查总院,郑州450052

出　　处：《矿物岩石地球化学通报》2013年第2期269-278,共10页Bulletin of Mineralogy, Petrology and Geochemistry

基　　金：中国地质调查局项目(1212011120587);四川省重点学科基金资助项目(SZD0407);矿床地球化学国家重点实验室开放基金资助项目(201105);国家自然科学基金资助项目(41103017)

摘　　要：本文从矿物学和主微量元素地球化学方面对香格里拉九龙峨眉山玄武岩进行研究,以期对其成因作合理的解释。该玄武岩的SiO2含量为41.84%～50.14%,富MgO(2.59%～16.13%)、Na2O+K2O为0.76%～9.91%,且Na2O>K2O,属于碱性玄武岩系列;相对富集轻稀土而亏损重稀土(LREE/HREE=4.71～9.58),轻重稀土发生了一定程度的分异,没有明显的Eu异常(δEu=0.97～1.12),富集高场强元素(Ta、Nb、Zr、Hf、Ti)、LREEs、P、Th和U等元素,而亏损K和Y等元素,Ba和Sr元素有明显的波动,Ti/Y比值反映该玄武岩为高钛型。研究表明,该玄武岩为下地幔石榴石地幔橄榄岩部分熔融的产物,形成于大陆板内拉张的构造环境,其形成与地幔柱活动有关,系地幔柱上涌发生减压部分熔融引发岩浆喷发形成的玄武岩,在成岩的过程中不存在明显的地壳混染,并且发生了橄榄石、单斜辉石、磷灰石、磁铁矿和金红石的分离结晶作用。This paper studied petrological and geochemical characteristics of Emeishan basalts from Jiulong of Shan- gri-la and discussed the petrogenesis of these rocks. These rocks belong to alkaline basalt series, SiO2, MgO and Na2O＋ K2 O contents vary from 41.84 to 50.14 %, 2.59 % ~ 16.13%, and 0.76 % ~ 9.91%, respectively, where Na2O contents are higher than K2O contents. The basalts exhibit flat chondrite-normalized patterns with moderate HREEdepletion （LREE/HREE=4. 71--9. 58, （La/Yb）N=5. 47~13. 66）, no Eu anomalies （3Eu=0. 97~ 1.12）. The primitive mantle-normalized spidergrams show that the basalts enrich, relatively, HSFEs （Ta, Nb, Zr, Hf and Ti）, LREEs, P, Th and U, deplete K and Y, and vary in the contents of Ba and Sr. The ratio of Ti/Y （530~726） indicates that the Emeishan basalts are high-Ti basalts. Based on above geochemical features, we pro- pose that these basalts were derived from partial melting of the lower mantle of the garnet mantle peridotites in the continental intra-plate extensional tectonic setting. Meanwhile, the parental magma underwent intense mineral fractional crystallization, including olivine, clinopyroxene, apatite, magnetite and rutile, whereas there had little crustal contamination during magma ascent. It was considered that the Emeishan basalts represent a major magmat- ic event triggered by the mantle plume, that is, decompressional melting of the upwelling mantle plume produced basaltic melts.

关 键 词：地球化学特征 岩石成因 峨眉山玄武岩 二叠系 香格里拉 

分 类 号：P588.145[天文地球—岩石学] P581[天文地球—地质学]