Carboniferous-Permian extensive magmatism in the West Junggar, Xinjiang, northwestern China: its geochemistry, geochronology, and petrogenesis
Carboniferous-Permian extensive magmatism in the West Junggar, Xinjiang, northwestern China: its geochemistry, geochronology, and petrogenesis
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DOI：
10.1016/j.lithos.2014.05.028
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发表时间：
2014-09
期刊：
影响因子：
3.5
通讯作者：
R. Gao;Long Xiao;F. Pirajno;Guocan Wang;Xin He;Gang Yang;Shenghao Yan
中科院分区：
文献类型：
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作者：
R. Gao;Long Xiao;F. Pirajno;Guocan Wang;Xin He;Gang Yang;Shenghao Yan
西准噶尔位于塔里木、哈萨克斯坦和西伯利亚板块之间，是古生代中亚造山带的重要组成部分，晚古生代火成岩分布广泛。本文报道了西准噶尔花岗岩类的岩石学、年代学和地球化学资料。根据年代学，I型花岗岩和A型花岗岩主要形成于347.9- 319.0Ma和321.4-290 Ma。早期I型花岗岩以低SiO_2、Na_2O、K_2O含量为特征，Na_2O/K_2O> 1，具准铝质-弱过铝质特征。（87 Sr/86 Sr）i值为0.7028-0.7044，εNd（t）值为+ 5.74 ~+ 7.76，富大离子亲石元素（LILE）和Sr，贫高场强元素（HFSE）。晚期I型花岗岩以低Si_2O、K_2O和相对高的FeO、MgO、Na_2O（Na_2O/K_2O> 1）为特征，具准铝质-弱过铝质特征。富LILE，亏损HFSE，Eu异常，（87 Sr/86 Sr）i值为0.703-0.704，εNd（t）值为+ 5.20 ~+ 8.00。A型花岗岩具有高SiO2含量、高K钙碱性钾玄岩亲合性、正εNd（t）值（5.76-7.77）和低87 Sr/86 Sr初始值（0.7017-0.7045）。沿着，结合已有的Sr-Nd同位素资料和区域地质证据，认为早石炭世I型花岗岩是由底侵地幔楔源玄武质岩浆触发的圈闭洋壳部分熔融的产物，晚石炭世-早二叠世I型花岗岩是圈闭洋壳部分熔融的衍生物;而A型花岗岩是在伸展体制下被捕获的幼年洋壳部分熔融的产物。具有高εNd（t）值和高Zr饱和温度的A型花岗岩可能与CAOB地幔柱或区域地幔上涌有关。
Located between the Tarim, Kazakhstan, and Siberian plates, the West Junggar terrane is a key component of the Paleozoic Central Asian Orogenic Belt (CAOB) with widespread late Paleozoic igneous rocks. In this paper, we report petrological, geochronological, and geochemical data for selected granitoids from the West Junggar. Based on geochronology, the I-type and A-type granites were formed predominantly at 347.9–319.0 Ma and at 321.4–290 Ma respectively. The early-stage I-type granites are characterized by low SiO2, Na2O, and K2O contents with Na2O/K2O ratios > 1 and are metaluminous to weakly-peraluminous. They are enriched in large ion lithophile elements (LILE) and in Sr but depleted in high field strength elements (HFSE), with (87Sr/86Sr)iratios of 0.7028–0.7044 and εNd(t)values varying from + 5.74 to + 7.76. The late-stage I-type granites are characterized by low contents of Si2O and K2O and relatively high contents of FeO, MgO, and Na2O with Na2O/K2O ratios > 1, and are metaluminous to weakly-peraluminous. They are also enriched in LILE and depleted in HFSE with Eu anomalies, (87Sr/86Sr)iratios of 0.703–0.704, and εNd(t)values varying from + 5.20 to + 8.00. The A-type granites have high SiO2contents, high K calc-alkaline-shoshonitic affinities, positive εNd(t) values (5.76–7.77), and low initial87Sr/86Sr ratios (0.7017–0.7045). Along with reported Sr-Nd isotopic data and regional geologic evidence the Early Carboniferous I-type granites are interpreted as products of partial melting of trapped oceanic crust triggered by underplated mantle wedge-derived basaltic magma; the Late Carboniferous–Early Permian I-type granites as derivatives of partially melted trapped oceanic crust; and the A-type granites as resulting from partial melting of trapped juvenile oceanic crust in an extensional regime. The A-type granitoids with high positive εNd(t) values and high Zr-saturation temperatures could be genetically related to a mantle plume or a regional-scale mantle upwelling in the CAOB.