A possible transition from island arc to continental arc magmatism in the eastern Jiangnan Orogen, South China: Insights from a Neoproterozoic (870-860 Ma) gabbroic-dioritic complex near the Fuchuan ophiolite
A possible transition from island arc to continental arc magmatism in the eastern Jiangnan Orogen, South China: Insights from a Neoproterozoic (870-860 Ma) gabbroic-dioritic complex near the Fuchuan ophiolite
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华南江南造山带东部可能从岛弧向大陆弧岩浆作用的转变：来自富川蛇绿岩附近新元古代（870-860Ma）辉长岩-闪长岩杂岩的见解
DOI：
10.1016/j.gr.2017.02.012
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发表时间：
2017
影响因子：
6.1
通讯作者：
Wu Xinhui
中科院分区：
文献类型：
--
作者：
Cui Xiang;Zhu Wenbin;Fitzsimons I. C. W.;Wang Xi;Lu Yuanzhi;Wu Xinhui
江南造山带东部的富川蛇绿岩带对扬子-华夏板块新元古代缝合带的构造背景和演化具有重要的制约作用。歙县杂岩体位于富川蛇绿岩主体西南10 km处，其辉长岩和闪长岩样品中锆石的U单键Pb单键Hf同位素和稀土元素分析表明，该杂岩体的结晶时间约为10000 ~ 10000年。870-860 Ma，锆石εHf（t）值变化较大，从− 4.80到+ 13.30。全岩地球化学研究表明，岩浆主要经历了橄榄石、单斜辉石和斜长石的分异作用，部分受地壳混染的影响，Th/Nb、Th/La和La/Sm比值升高，εHf（t）值分散。最镁铁质和污染最少的样品显示MORB的亲和力，可能是由部分熔融的亏损俯冲交代地幔楔。其他样品表现出弧形签名，可能是修改了熔融和流体相关的俯冲交代作用。歙县杂岩的侵位时间对应于俯冲作用从一个约400 km-1的俯冲带转换到另一个约400 km-1的俯冲带。沿着扬子地块东南缘由1000-880 Ma的洋内岛弧演化为870-830 Ma的陆内岛弧。与这一大陆弧有关的火成岩序列类似于弧前特提斯蛇绿岩中保存的火成岩，岩浆从约100万年前演化而来。870-860 Ma MORB到CA。860-850 Ma弧拉斑玄武岩和约830 Ma玻安岩。弧岩浆作用结束于830-800 Ma扬子地块和华夏地块的最后组合。
The Fuchuan ophiolite belt in the eastern Jiangnan Orogen of South China provides important constraints on the tectonic setting and evolution of the Neoproterozoic suture zone between the Yangtze and Cathaysia blocks. Combined Usingle bondPbsingle bondHf isotopic and REE analysis of zircon from gabbroic and dioritic samples of the Shexian complex, located 10 km southwest of the main Fuchuan ophiolite body, indicate that the complex crystallized at ca. 870–860 Ma with a large variation of zirconεHf(t) values from − 4.80 to + 13.30. Whole-rock geochemistry reveals that the magma mainly experienced fractionation of olivine, clinopyroxene and plagioclase and was partly affected by crustal contamination, which resulted in elevated Th/Nb, Th/La and La/Sm ratios, as well as the scatteredεHf(t) values. The most mafic and least contaminated sample shows MORB affinity and was probably formed by partial melting of a depleted subduction-metasomatized mantle wedge. Other samples exhibit arc-like signatures and were probably modified by both melt- and fluid-related subduction metasomatism. The emplacement of the Shexian complex corresponds to the time that subduction switched from a ca. 1000–880 Ma intra-oceanic island arc to a 870–830 Ma continental arc along the southeastern Yangtze Block. The sequence of igneous rocks associated with this continental arc resemble those preserved in forearc Tethyan ophiolites, with magma evolving from ca. 870–860 Ma MORB to ca. 860–850 Ma arc tholeiite and ca. 830 Ma boninite. Arc magmatism concluded with the final assembly of the Yangtze and Cathaysia blocks at 830–800 Ma.