新疆坡北杂岩体西端镁铁--超镁铁质岩体成因的稀有气体同位素制约  

The noble gas isotopic constrains on the petrogenesis of mafic-ultramafic intrusions in the western end of the Pobei complex,Xinjiang,northwestern China

作　　者：冯鹏宇 张铭杰 李立武[2] 胡飞 孙凡婷 王亚磊[3] 曹春辉[2] FENG PengYu;ZHANG MingJie;LI LiWu;HU Fei;SUN FanTing;Wang YaLei;CAO ChunHui(Gansu Key Laboratory of Mineral Resources in Western China,School of Earth Sciences,Lanzhou University,Lanzhou 730000,China;Gansu Key Laboratory of Petroleum Resource Research,Institute of Geology and Geophysics,CAS,Lanzhou 730000,China;MLR Key Lab of Genesis and Exploriation of Magrnatic Ore Deposits,Xi＇an Center of Geological Survey,CGS,Xi＇an 710054,China)

机构地区：[1]兰州大学地质科学与矿产资源学院,甘肃省西部矿产资源重点实验室,兰州730000 [2]中国科学院地质与地球物理研究所兰州油气资源研究中心,甘肃省油气资源研究重点实验室,兰州730000 [3]中国地质调查局西安地质调查中心,国土资源部岩浆作用成矿与找矿重点实验室,西安710054

出　　处：《岩石学报》2018年第11期3445-3454,共10页Acta Petrologica Sinica

基　　金：国土资源部公益性行业科研专项(201511020); 国家自然科学基金项目(41372095、41472070)联合资助

摘　　要：新疆坡北镁铁-超镁铁质杂岩体由一个辉长岩体以及二十多个超镁铁质侵入体组成,其中坡一超镁铁质岩体稀有气体同位素组成揭示存在地幔柱的贡献。坡北杂岩体西端的坡一、坡四、坡十和坡十四等几个超镁铁质岩体的稀有气体同位素对比分析结果表明,岩浆矿物的~3He/~4He值(0.26~2.79Ra)分布于地壳与地幔值之间,较高的^(20)Ne/^(22)Ne和较低的^(21)Ne/^(22)Ne值分布于Ne质量分馏线(MFL)和L-K线之间,^(40)Ar/^(36)Ar=295~598。~3He/~4He与^(40)Ar/^(36)Ar比值揭示坡北杂岩体西端不同超镁铁质岩体形成过程中地幔(柱)、地壳和大气组分的贡献不同,岩体成因也可能不同。其中,坡一岩体具有地幔柱作用的贡献,其他三个岩体的岩石圈地幔及地壳流体组分的贡献较大。岩浆地幔源区由深部地幔柱物质叠加俯冲流体交代的岩石圈地幔物质所组成,大气与地壳物质组分可能由俯冲再循环洋壳带入到岩浆地幔源区以及围岩物质的混入。The large Pobei Permian layered mafic-ultramafic complex in the northeastern margin of the Tarim craton,western China is composed of a gabbro intrusion and more than 20 ultramafic intrusions.The isotopic compositions of noble gases in the Poyi（No.1）ultramafic intrusion revealed information of mantle plume.In present study the abundance and isotopic compositions of noble gases were analyzed for fresh minerals in mafic-ultramafic rock samples from No.1,4,10 and 14 ultramafic intrusions in the western end of Pobei complex.The results showed that olivine（Ol）,pyroxene（Px）and plagioclase（Pl）magmatic minerals in the Pobei~#1,4,10 and 14ultramafic intrusions were in low values of^3He/~4He ratios（0.26~2.79Ra）.The^（21）Ne/^（22）Ne and^（20）Ne/^（22）Ne were plotted and distributed between the Ne mass fraction line（MFL）and L-K line,the^（40）Ar/^（36）Ar ratios ranged from 295 to 598.These isotopic compositions of noble gases indicated a mixture of different portion of mantle（plume）,crust and air during the Pobei magmatic processes with different petrogenesis.The mantle plume was identified in the Poyi ultramafic intrusion,and more crustal fluid was added into lithospheric mantle in other three ultramafic intrusions.The magmatic source area of Pobei ultramafic intrusion was superimposed by deep mantle plume on lithospheric mantle that was reformed by subducted fluids.

关 键 词：地幔柱 稀有气体同位素 成因 坡北杂岩体西端镁铁-超镁铁质岩体 

分 类 号：P588.124[天文地球—岩石学] P588.125[天文地球—地质学]