内蒙古林西早中生代O型高镁埃达克质安山岩的发现及其意义  

Early Mesozoic O-type High-Mg Adakitic Andesites from Linxi Area,Inner Mongolia and Its Implication

作　　者：王冬兵[1,2] 刘勇胜[1,3,4,5] 宗克清[1] 高长贵[1] 徐娟[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 [2]成都地质矿产研究所,成都610081 [3]中国地质大学地球科学学院,武汉430074 [4]西北大学大陆动力学国家重点实验室 [5]西北大学地质学系,西安710069

出　　处：《地质科技情报》2009年第6期31-38,共8页Geological Science and Technology Information

基　　金：国家自然科学基金委创新研究群体科学基金项目"大陆岩石圈深部再循环与华北克拉通及其邻区中新生代演化"(40521001)

摘　　要：对内蒙古林西地区火山岩样品的地球化学研究表明,其具有大洋型(O型)高镁埃达克质安山岩的地球化学特征[w(SiO2)=57.89%～63.97%、w(Al2O3)=15.39%～16.17%、w(Na2O)/w(K2O)=1.5～2.2(除一个为0.9)、A/CNK=0.83～0.97、Mg#=49～64、w(Cr)=91～209μg/g、w(Ni)=52.2～111.4μg/g、w(Sr)=551～1018μg/g、w(Yb)=1.18～1.71μg/g、w(Y)=12.6～17.7μg/g、δ(Eu)=0.86～0.94]。利用LA-ICP-MS对其锆石进行了U-Pb定年,得到206Pb/238U加权平均年龄为(244±2)Ma(MSWD=0.36)。此时,区域内古亚洲洋已闭合,综合地球化学特征和区域地质环境说明,林西高镁埃达克质安山岩是由残余洋壳部分熔融并随后与地幔橄榄岩相互作用形成的。内蒙古林西早中生代高镁埃达克质安山岩的产出表明,洋壳来源的埃达克岩(O型埃达克岩)不仅可以随俯冲同时产生,而且也可以在非俯冲环境下由保存在古俯冲带地幔中的残余洋壳部分熔融产生。This paper studies geochemical compositions of volcanic samples from Linxi area, Inner Mongolia. The results show that these samples have similar geochemical characteristics of ocean-type（O-type） high-Mg adakitic andesites[SiO2 =57.89% -63.97% ,Al2O3 = 15.39% - 16.17% ,Na2O/K2O= 1.5-2.2 （except one of 0.9）, A/CNK=0. 83-0.97, Mg^#=49-64,Cr=91-209 μg/g, Ni=52.2-111.4 μg/g, Sr=551-1 018 μg/g, Yb=1. 18-1. 71μg/g, Y=12.6-17.7 μg/g, andδ（Eu）=0.86-0.94]. LA-ICP MS zircon U-Pb dating results for the Linxi high-Mg adakitic andesites yield a weighted mean ^206pb/^233U age of （244±b2）Ma （MSWD=0. 36）, when the Paleo-Asian ocean was closed. The combination of geological setting and geochemical characteristics of the Linxi high-Mg adakitic andesites suggests that the Linxi high-Mg adakitic rocks were most probably derived from partial melting of the remnant of Paleo-Asian oceanic crust and subsequently hybridized by mantle peridotite. Generation of the Linxi early Mesozoic high- Mg adakitic andesites indicates that O-type high-Mg adakitic rocks could occur in a variety of tectonic setting, where oceanic lithosphere subduetion had occurred and subsequent p-T conditions permit melting of the remnants of the oceanic crust.

关 键 词：内蒙古 早中生代 高镁埃达克质岩 残余洋壳 

分 类 号：P588.14[天文地球—岩石学]