Carboniferous Post‐collisional Rift Volcanism of the Tianshan Mountains, Northwestern China
Carboniferous Post‐collisional Rift Volcanism of the Tianshan Mountains, Northwestern China
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DOI：
10.1111/j.1755-6724.2003.tb00751.x
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发表时间：
2003-09
期刊：
影响因子：
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通讯作者：
Xia Linqi;Xu Xueyi;Zuchun Xia;Xiangmin Li;Zhongping Ma;Wang Lishe
中科院分区：
文献类型：
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作者：
Xia Linqi;Xu Xueyi;Zuchun Xia;Xiangmin Li;Zhongping Ma;Wang Lishe
摘要天山石炭纪后碰撞裂谷火山岩是中国西北部的一个大火成岩省。根据岩石地球化学资料，天山石炭纪碰撞后裂谷基性熔岩可分为两大类：（1）低Ti/Y型，位于天山中东部，表现为低Ti/Y（500）、Ce/Yb（>11）和SiO2（49-55%），相对低Fe 2 O3 T（5.8-7.8%）。元素数据表明，低Ti/Y和高Ti/Y熔岩的化学变化不能用来自共同母岩浆的分离结晶来解释。天山石炭纪基性熔岩可能来源于类似OIB的软流圈地幔源区（87 Sr/86 Sr（t）<$0.703 -0.705，εNd（t）<$+4 ~+7）。地壳混染和大陆岩石圈地幔对天山石炭纪碰撞后裂谷基性熔岩的形成也有重要贡献。火山熔岩可能是地壳部分熔融的产物。研究结果表明，天山石炭纪后碰撞裂谷火山岩区存在岩石地球化学空间变异。以拉斑玄武岩为主的最厚火山岩的出现可能意味着当时地幔熔融异常（地幔柱）的中心在东天山地区。东天山地区的基性火山岩浆是尖晶石-石榴石过渡带附近地幔源区相对高度部分熔融的产物，而西天山地区的碱性玄武质岩浆是稳定石榴石区地幔源区相对低度部分熔融的产物，因此，西天山地区基性熔岩可能是岩石圈较厚、地温梯度较低的结果。
Abstract The Tianshan Carboniferous post‐collisional rift volcanic rocks occur in northwestern China as a large igneous province. Based on petrogeochemical data, the Tianshan Carboniferous post‐collisional rift basic lavas can be classified into two major magma types: (1) the low‐Ti/Y type situated in the eastern‐central Tianshan area, which exhibits low Ti/Y (500), Ce/Yb (>11) and SiO2 (49–55%), and relatively low Fe2O3T (5.8–7.8%). Elemental data suggest that chemical variations of the low‐Ti/Y and high‐Ti/Y lavas cannot be explained by fractional crystallization from a common parental magma. The Tianshan Carboniferous basic lavas originated most likely from an OIB‐like asthenospheric mantle source (87Sr/86Sr(t) ∼ 0.703–0.705, εNd(t) ∼ +4 to +7). The crustal contamination and continental lithospheric mantle have also contributed significantly to the formation of the basic lavas of the Tianshan Carboniferous post‐collisional rift. The silicic lavas were probably generated by partial melting of the crust. The data of this study show that spatial petrogeochemical variations exist in the Carboniferous post‐collisional rift volcanics province in the Tianshan region. Occurrence of the thickest volcanics dominated by tholeiitic lavas may imply that the center of the mantle‐melting anomaly (mantle plume) was in the eastern Tianshan area at that time. The basic volcanic magmas in the eastern Tianshan area were generated by a relatively high degree of partial melting of the mantle source around the spinel‐garnet transition zone, whereas the alkaline basaltic lavas are of the dominant magma type in the western Tianshan area, which were generated by a low degree of partial melting of the mantle source within the stable garnet region, thus the basic lavas of the western Tianshan area might have resulted from relatively thick lithosphere and low geothermal gradient.