准噶尔盆地南缘晚古生代双峰式火山岩成因机制及其地球动力学背景

发布时间：2018-10-17 22:04

【摘要】：准噶尔盆地南缘晚古生代双峰式火山岩组合以玄武岩和英安斑岩的伴生出现为特征。锆石LA-ICP-MS U-Pb定年结果显示,英安斑岩和玄武岩的结晶年龄分别为298±2 Ma和297~304 Ma。在地球化学组成上,英安斑岩样品富SiO_2、Al_2O_3和Na_2O,相对于原始地幔富集Th和LREE,明显亏损Nb、Ta和Ti等高场强元素;而玄武岩样品相对于原始地幔明显富集Th、LREE、Zr和Hf等,明显亏损Nb、Ta和Ti。全岩Sr-Nd同位素研究结果显示,英安斑岩样品(~(87)Sr/~(86)Sr)t值为0.705,εNd(t)值分布在+6.5~+11之间,而玄武岩样品的(~(87)Sr/~(86)Sr)t值为0.704,εNd(t)值分布在+7.5~+8.4之间。这些特征指示玄武岩和英安斑岩应分别起源于相对亏损的地幔源区和新生地壳组分的部分熔融。综合野外地质、岩石学、地球化学和同位素地质学等多方面的资料,可以确定准南地区玄武岩和英安斑岩并非同源岩浆作用的产物。其中,玄武岩应起源于亏损地幔的部分熔融,并且岩浆在上升侵位过程中经历了一定程度的陆壳混染。英安斑岩的形成与玄武质岩浆的底侵导致新生地壳组分的部分熔融有关。结合区域上已有的研究成果,认为至少从早二叠世(~298 Ma)开始,天山地区已经进入后碰撞阶段,区域构造体制开始由挤压转向伸展。
[Abstract]:The late Paleozoic bimodal volcanic assemblage in the southern margin of Junggar Basin is characterized by the associated occurrence of basalt and Yingan porphyry. The results of zircon LA-ICP-MS U-Pb dating show that the crystallization ages of porphyry and basalt are 298 卤2 Ma and 297 ~ 304 Ma., respectively. In terms of geochemical composition, SiO_2,Al_2O_3 and Na_2O, enriched by SiO_2,Al_2O_3 and Na_2O, are obviously depleted of high field strength elements such as Nb,Ta and Ti compared with primitive mantle, while basalt samples are obviously enriched with Th,LREE,Zr and Hf, and Nb,Ta and Ti. are depleted with respect to primitive mantle. The results of Sr-Nd isotopic study of the whole rock show that (87) Sr/~ (86) Sr) t = 0.705, 蔚 Nd (t) = 6.5 ~ 11) and basalt samples (~ (87) Sr/~ (86) Sr) t = 0.704, 蔚 Nd (t) = 7.5 ~ 8.4) are found in the whole rock. These characteristics indicate that basalt and porphyry are derived from partial melting of relatively depleted mantle source and new crustal components, respectively. Based on the field geology, petrology, geochemistry and isotopic geology, it can be concluded that basalt and porphyry are not the product of homologous magmatism. Among them, basalt originated from partial melting of depleted mantle, and magma experienced a certain degree of continental crust mixing in the process of rising emplacement. The formation of Yingan porphyry is related to the partial melting of nascent crustal components caused by the underthrust of Black Tortoise magma. In combination with the existing research results in the region, it is considered that since at least the early Permian (~ 298 Ma), the Tianshan area has entered the post-collision stage, and the regional tectonic system has begun to shift from compression to extension.
【作者单位】：中国石化胜利油田分公司勘探开发研究院西部分院;
【基金】：国家科技重大专项(2016ZX05002-002)~~
【分类号】：P588.14

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