He-Ar and Nd-Sr isotopic compositions of ultramafic xenoliths and host alkali basalts from the Korean peninsula
He-Ar and Nd-Sr isotopic compositions of ultramafic xenoliths and host alkali basalts from the Korean peninsula
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DOI：
10.2343/geochemj.39.341
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发表时间：
2005
影响因子：
0.8
通讯作者：
Kyu Han Kim;K. Nagao;Tsuyoshi Tanaka;H. Sumino;Toshio Nakamura;M. Okuno;J. B. Lock;Jeung-Su Youn;Jeehye Song
中科院分区：
文献类型：
--
作者：
Kyu Han Kim;K. Nagao;Tsuyoshi Tanaka;H. Sumino;Toshio Nakamura;M. Okuno;J. B. Lock;Jeung-Su Youn;Jeehye Song
本文测定了朝鲜半岛的白头山、白翎岛、山国里、济州岛和中国东北靠近白头山的龙泉超镁铁岩捕虏体及其寄主新生代碱性玄武岩的稀有气体、Nd和Sr同位素比值、主量和微量元素组成。欧亚大陆东南部活动大陆边缘岩石圈地幔特征和碱性玄武岩浆源区板捕虏体样本的3 He/4 He比变化显着，范围从<0.2到16.8 RA，大多数样本（3.5-7.9 RA）低于MORB值（~8 RA）。其中，通过熔融样品获得的高3 He/4 He比值被认为反映了宇宙成因的贡献。40 Ar/36 Ar比值远低于MORB值。富集Nd-Sr同位素组成的捕虏体和寄主玄武岩从Baegdusan和Baegryongdo地区建议同化的EMII岩石圈和/或大陆地壳。广泛的微量元素浓度的包体和高度饱和的不相容元素的主机碱性玄武岩中观察。K-Ar年龄数据表明，朝鲜半岛新生代碱性火山作用呈间歇性，年龄范围为21 Ma ~ 11.5- 5.0Ma ~ 0.1Ma，并向半岛南部逐渐变年轻。我们的地球化学和同位素数据表明，在欧亚板块东南端的大陆边缘的一个古老的俯冲带内产生的非均匀交代富集岩石圈地幔的存在。根据捕虏体橄榄石中的3 He/4 He比值，讨论了交代作用的富集程度。
Noble gas, Nd and Sr isotopic ratios and major and trace element compositions were determined for ultramafic xenoliths and their host Cenozoic alkali basalts from Baegdusan, Baegryongdo, Jogokri, Jejudo in the Korean peninsula, and Long Quan, close to the Baegdusan in northeastern China, to characterize the lithospheric mantle and the source of alkali basaltic magmatism beneath the active continental margin of the southeastern part of the Eurasian plate. The xenolith samples yield significantly variable 3He/4He ratios ranging from <0.2 to 16.8 RA, with most samples (3.5-7.9 RA) lower than the MORB value (~8 RA). Among them, high 3He/4He ratios obtained by melting the samples are considered to reflect cosmogenic contribution. The 40Ar/36Ar ratios are much lower than the MORB values. Enriched Nd-Sr isotopic compositions in xenoliths and host basalts from the Baegdusan and Baegryongdo areas suggest assimilation of EMII lithosphere and/or continental crust. Widely ranging trace element concentrations in the xenoliths and highly saturated incompatible elements in the host alkali basalts are observed. K-Ar age data show that Cenozoic alkali volcanism in the Korean peninsula occurred intermittently, ranging in age from 21 Ma through 11.5-5.0 Ma to 0.1 Ma, and becoming gradually younger toward the south of the peninsula. Our geochemical and isotopic data suggest the presence of heterogeneously metasomatized enriched lithospheric mantle generated at an ancient subduction zone within the continental margin of the southeastern end of the Eurasian plate. Degree of enrichments by the metasomatism is discussed based on the observed 3He/4He ratios in the xenolithic olivines.