CAJ | 학술논문

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(SiO_2)=57.89%～63.97%、w(Al_2O_3)=15.39%～16.17%、w(Na_2O)/w(K_2O)=1.5～2.2(除一个为0.9)、A/CNK=0.83～0.97、Mg~#=49～64、w(Cr)=91～209 μg/g、w(Ni)=52.2～111.4 μg/g、w(Sr)=551～1 018 μg/g、w(Yb)=1.18～1.71 μg/g、w(Y)=12.6～17.7 μg/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~(206)Pb/~(238)U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.
대내몽고림서지구화산암양품적지구화학연구표명,기구유대양형(O형)고미애체극질안산암적지구화학특정[w(SiO_2)=57.89%～63.97%、w(Al_2O_3)=15.39%～16.17%、w(Na_2O)/w(K_2O)=1.5～2.2(제일개위0.9)、A/CNK=0.83～0.97、Mg~#=49～64、w(Cr)=91～209 μg/g、w(Ni)=52.2～111.4 μg/g、w(Sr)=551～1 018 μg/g、w(Yb)=1.18～1.71 μg/g、w(Y)=12.6～17.7 μg/g、δ(Eu)=0.86～0.94]. 이용LA-ICP-MS대기고석진행료U-Pb정년,득도~(206)Pb/~(238)U가권평균년령위(244±2)Ma(MSWD=0.36).차시,구역내고아주양이폐합,종합지구화학특정화구역지질배경설명,림서고미애체극질안산암시유잔여양각부분용융병수후여지만감람암상호작용형성적.내몽고림서조중생대고미애체극질안산암적산출표명,양각래원적애체극암(O형애체극암)불부가이수부충동시산생,이차야가이재비부충배경하유보존재고부충대지만중적잔여양각부분용융산생.
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[SiO~2 = 57.89%～63.97%,A1_2O_3= 15.39%～16.17%,Na_2O/K_2O=l.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=l.18～1.71 μg/g, Y=12.6～17.7 μg/g, and δ(Eu)=0.86～0.94]. LA-ICP-MS zircon U-Pb dating results for the Linxi high-Mg adakitic andesites yield a weighted mean ~(206)Pb/~(238)U age of (244±2)Ma (MSWD=0.36), when the Paleo-Asian ocean was closed. The combination of geolog-ical 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 oce-anic crust and subsequently hybridized by mantle peridotite. Generation of the Linxi early Mesozoic high-Mg adakitic andesites indicates that Otype high-Mg adakitic rocks could occur in a variety of tectonic set-ting, where oceanic lithosphere subduction had occurred and subsequent p-T conditions permit melting of the remnants of the oceanic crust.