Early Indosinian Weiya Gabbro in Eastern Tianshan, China: Elemental and Sr‐Nd‐O Isotopic Geochemistry, and Its Tectonic Implications
Early Indosinian Weiya Gabbro in Eastern Tianshan, China: Elemental and Sr‐Nd‐O Isotopic Geochemistry, and Its Tectonic Implications
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DOI：
10.1111/j.1755-6724.2007.tb00965.x
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发表时间：
2007-06
期刊：
影响因子：
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通讯作者：
Zhang Zunzhong;Gu Lianxing;Wu Changzhi;Zhai Jianping;Li Weiqiang;Tang Junhua
中科院分区：
文献类型：
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作者：
Zhang Zunzhong;Gu Lianxing;Wu Changzhi;Zhai Jianping;Li Weiqiang;Tang Junhua
文摘：东天山尾崖辉长岩形成于印支早期。该岩石的Ce/Pb比值较低（5.74 - 10.16），其显著特征是富集大离子亲石元素（LILE），如Rb、K、Ba和Pb，以及高场强元素（HSFE），如U和Th，但亏损Nb和Ta。尾崖辉长岩的球粒陨石标准化模式相似，轻稀土元素中等富集（72.58-135.61ppm），重稀土元素中等亏损（15.26 - 25.31ppm），轻、重稀土元素分馏较轻（L/H=4.09 - 5.98）。岩石的平均初始Sr值为0.7069，岩石的δ18 O值范围为5.67%-8.04%。在Nd同位素比值方面，尾崖辉长岩具有正Nd（t）值（0.52 - 0.76）的特征。这些特征表明，尾崖辉长岩源区是由俯冲的年轻陆壳释放的流体交代的，岩浆上升侵位过程中地壳混染有限。大陆（A型）俯冲是由古特提斯洋板块在二叠纪末至三叠纪期间向北俯冲引起的。从这个角度来看，从古亚洲到古特提斯的构造转换发生在二叠纪末或三叠纪初。
Abstract: The Weiya gabbro in eastern Tianshan was formed during the early Indosinian. This rock, with low ratios of Ce/Pb (5.74‐10.16), is notably characterized by enrichment in large ion lithophile elements (LILE), such as Rb, K, Ba and Pb, and in high field strength elements (HSFE), such as U and Th, but depletion in Nb and Ta. All samples of the Weiya gabbro display similar chondrite‐normalized patterns with moderate enrichment in LREE (72.58–135.61ppm), moderate depletion in HREE (15.26‐25.31 ppm) and mild fractionation between LREE and HREE (L/H=4.09‐5.98). The average initial Sr value of the rock is 0.7069, and δ18 O values of the rock range from 5.67%‐8.04%. In terms of Nd isotope ratios, the Weiya gabbro is characterized by positive Nd(t) values (0.52‐0.76). All these characteristics indicate that the source region of the Weiya gabbro was metasomatized by fluids released from subducted young continental crust, with limited crustal contamination during magma ascent and emplacement. Continental (A‐type) subduction was induced by northward subduction of the Paleo‐Tethyan oceanic plate during the latest Permian to Triassic. From this point of view, it is supposed that tectonic conversion from the Paleo‐Asian to the Paleo‐Tethys regime occurred during the latest Permian or earliest Triassic.