北祁连扎柯山寒武纪高镁安山岩地球化学及构造动力学特征
Northwestern Geology(2018)
Abstract
北祁连扎柯山高镁安山岩铷锶同位素年龄为早 中寒武世[(516±7)Ma(1σ)],高镁安山岩类(SiO2=51.45%~59.62%,平均为56.33%),具有比典型岛弧安山岩更高的MgO(4.85%~9.64%,平均为6.2%,Mg# =66.68~74.15,平均为71.44),高Cr(21.6×10-6~476×10-6,平均为196.26×10-6)、高Ni(14×10-6~102×10-6,平均为56.14×10-6),低Al贫Ca(Al2O3=13.22%~17.37%,均值为15.69%,CaO=2.01%~10.33%,均值为5.64%),富Na、贫K(Na2O=1.57%~5.2%,K2O=1.04%~2.79%,Na2O/K2O=0.59~5.0,均值为2.36),弱负Eu异常以及富集Rb、Th、K大离子不相容元素(LILE),亏损Sr、Ti、P、Nb、Ta等高场强元素(HFSE),富集LREE,强烈亏损HREE,LREE/HREE=7.19~13.58,Yb=1.47×10-6~3.26×10-6,Y=11.6×10-6~22.5×10-6,含有较低的Sr(119×10-6~278×10-6,平均为193×10-6).综合区域地质背景等资料研究表明,扎柯山寒武纪高镁安山岩可能是蚀变洋壳和俯冲的沉积物熔融进入地幔楔诱发橄榄岩部分熔融的产物,形成于岛弧环境.
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Key words
high-Mg andesite,Cambrian,geoehemistry,geodynamics,Zakeshan area,North Qilian
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