Geochemical and Re-Os isotope constraints on the origin and age of the Songshugou peridotite massif in the Qinling orogen, central China
Geochemical and Re-Os isotope constraints on the origin and age of the Songshugou peridotite massif in the Qinling orogen, central China
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地球化学和铼锇同位素对秦岭造山带松树沟橄榄岩地块成因和年龄的限制
DOI：
10.1016/j.lithos.2017.09.009
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发表时间：
2017-11
期刊：
影响因子：
3.5
通讯作者：
Yuanbao Wu
中科院分区：
文献类型：
--
作者：
Hu Nie;Jianzhou Yang;Guangyan Zhou;Chuanzhou Liu;Jianping Zheng;Wen-Xiang Zhang;Yu-Jie Zhao;Hao Wang;Yuanbao Wu
秦岭造山带松树沟橄榄岩块是中国中部最大的造山尖晶石橄榄岩岩体之一，但其成因仍存在争议，年龄限制较差。本文对松树沟橄榄岩地块中的1个方辉橄榄岩和12个英安岩进行了主量元素和微量元素组成、矿物化学、铂族元素(PGE)和Re-Os同位素体系的综合研究。这些样品含有较高的镁橄榄石(90.0-91.3)和铬尖晶石(83.4-96.0)。方辉橄榄岩和英安岩的全岩Al_2O_3(0.32-0.60 wt.%)、CaO(0.26-1.57 wt.%)和Na2O(0.07-0.12 wt.%)含量较低。所研究的样品中重稀土元素含量很低，相对于钯族铂族元素，Ir族铂族元素(IPGE)表现出明显的富集性。松树沟橄榄岩表现出不同程度的轻稀土元素、大离子亲石元素、Re、Zr和Hf的丰度，这些元素是与对流地幔分离后与熔体反应的结果。结合前人的研究结果，我们的资料表明松树沟橄榄岩是来自弧前地幔楔体的高难熔地幔残留物。所研究样品的OS-187/Os-188值在0.12073~0.12390之间，Re-187/Os-188比值在0.005~0.081之间。松树沟橄榄岩的平均Re-Os模式年龄(T-MA)和最大亏损模式年龄(T-Rd)约为1.2~1.1Ga，表明该橄榄岩与南中国地块具有构造亲和力，是在Rodinia超大陆组装过程中形成的。松树沟橄榄岩来源于俯冲带上方的地幔楔体，经折返作用并入下伏大陆岩石圈。
The Songshugou peridotite massif in the Qinling orogenic belt is one of the largest orogenic spinel peridotite bodies in central China, but its origin remains controversial and its age is poorly constrained. We have carried out an integrated study of major and trace element composition, mineral chemistry, platinum group elements (PGE), as well as Re-Os isotope systematics of 1 harzburgite and 12 dunites from the Songshugou peridotite massif. These samples contain high Mg# olivine (90.0-91.3) and Cr# spinel (83.4-96.0). The harzburgite and dunites are characterized by relatively low whole-rock Al2O3 (0.32-0.60 wt.%), CaO (0.26-1.57 wt.%), and Na2O (0.07-0.12 wt.%) concentrations. The studied samples have very low concentrations of middle and heavy rare earth elements and exhibit enrichments in iridium-group platinum-group elements (IPGE) relative to palladium-group PGE. The Songshugou peridotites exhibit variable enrichments of light rare earth elements, large ion lithophile elements, Re, Zr, and Hf, which resulted from reactions with melt after their isolation from the convecting mantle. Combined with previous results, our data suggest that the Songshugou peridotites are highly refractory mantle residues derived from a forearc mantle wedge. Os-187/Os-188 values of the studied samples vary from 0.12073 to 0.12390, and Re-187/Os-188 ratios are 0.005-0.081. The average Re-Os model ages (T-MA) and maximum Re depletion model age (T-RD) of the Songshugou peridotites are ca. 1.2-1.1 Ga, suggesting a tectonic affinity to the South China Block and that the peridotites formed during the assembly of the Rodinia supercontinent. The Songshugou peridotites were sourced from a mantle wedge above a subduction zone, and finally incorporated into the underlying continental lithosphere by exhumation.
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