内蒙古乌拉特中旗新忽热地区二叠纪典型侵入岩地球化学特征及成因探讨

发布时间：2018-07-18 13:21

【摘要】：研究区位于华北克拉通北缘中段,距其北部的索伦缝合带约100km左右,区内中-晚古生代岩浆活动强烈,这些岩浆活动不仅能为区域构造的演化提供时间制约,而且是研究汇聚大陆边缘壳-幔相互作用和大陆地壳演化的重要载体,因此本次研究选取了区内二叠纪的典型岩体作为研究对象,通过对这些典型岩体开展详细的岩石学、地球化学、同位素地质学和年代学等方面的研究,厘定了研究区内典型岩体的侵位时代、探讨了各个岩体的地球化学特征、揭示了岩浆成因及构造背景,取得的主要认识如下:(1)获得乌毫来岩体的边缘相辉长闪长岩的LA-ICP-MS锆石U-Pb年龄为265.9±2.4Ma,结合前人资料认为,该区二叠纪岩体的侵位顺序依次为大乌淀岩体(~290Ma)、赵根陶拉岩体(~275Ma)、乌毫来岩体(265.9Ma)、哈尼河岩体(265.9Ma)。(2)大乌淀岩体和赵根陶拉岩体具有准铝质-弱过铝质的特征,均为高钾钙碱性I型花岗岩,在微量、稀土元素组成上,轻重稀土元素分异较明显,明显富集K、Rb、Ba等大离子亲石元素,亏损Nb、Ta、Ti、P等高场强元素的特征,具有弧岩浆岩的性质。乌毫来岩体具有较高的Mg#值(0.50~0.72),稀土元素含量较低,富集V、Cr、Ni等相容元素,富集K、Sr、Ba等大离子亲石元素(LILE),亏损Nb、Ta等高场强元素(HFSE),与被俯冲流体交代的富集岩石圈地幔的部分熔融密切相关。哈尼河岩体具有高硅、高钾、过铝质的特征,具有S型花岗岩的特征,轻重稀土元素分异较强,同样强烈富集大离子亲石元素,亏损高场强元素,富集Th、U,具有壳源岩浆岩的性质。(3)大乌淀岩体、赵根陶拉岩体和乌毫来岩体具有比较相似的Sr-Nd同位素组成,在(~(87)Sr/~(86)Sr)_i-ε_(Nd)(t)图解中均投点于地幔演化序列的左下方和下地壳演化线的上方,具有壳幔岩浆混合的特征,通过壳幔岩浆二元混合模型计算表明,大乌淀岩体是俯冲板片熔体与下地壳熔体混合成因,赵根陶拉岩体和乌毫来岩体则是俯冲流体交代的富集岩石圈地幔部分熔融熔体与下地壳熔体发生混合的产物。而哈尼河岩体具有非常高的(~(87)Sr/~(86)Sr)i比值(0.732355~0.740484)和很低的εNd(t)值(-34.59~-36.60),与中-下地壳同位素组成相似,暗示岩浆可能起源于中-下地壳。(4)根据岩体的地球化学特征,结合前人研究成果,认为大乌淀岩体形成于活动大陆边缘环境,是古亚洲洋向华北克拉通北缘俯冲作用的产物;赵根陶拉岩体和乌毫来岩体形成于同碰撞向后碰撞转变的过渡环境,两个岩体可能均是由板片断离作用导致软流圈物质上涌诱发上部富集岩石圈地幔发生部分熔融,然后与下地壳熔体发生不同程度的混染之后,先后上升侵位形成;哈尼河岩体形成于后碰撞环境,是地壳加厚导致中-下地壳物质部分熔融的产物。(5)研究区的岩浆岩记录了由古亚洲洋向华北克拉通北缘俯冲到最终碰撞造山的全过程,在早二叠世(~290Ma)古亚洲洋板片向华北克拉通北缘的俯冲作用依然在进行中,形成区内具有典型活动大陆边缘弧特征的大乌淀岩体;在晚二叠世早期(275~265Ma),南蒙古微板块与华北克拉通北缘已经发生了碰撞拼贴作用,形成具有同碰撞性质的赵根陶拉岩体和乌毫来岩体;随后两个板块之间发生了强烈的碰撞造山作用,地壳明显加厚,使得中-下地壳物质部分熔融形成哈尼河岩体。
[Abstract]:The study area is located in the middle part of the northern margin of the North China Craton, which is about 100km from the northern Solon suture zone. The Mesozoic and late Palaeozoic magma activity is strong. These magma activities not only provide time constraints for the evolution of regional tectonic evolution, but also an important carrier to study the crust mantle interaction on the continental margin and the continental crust evolution. In the study, the typical rock mass of the Permian in the region was selected as the research object. Through the detailed petrology, geochemistry, isotopic geology and chronology, the emplacement times of typical rock bodies in the study area were determined, and the geochemical characteristics of various rock bodies were discussed, and the genesis of the magma and the formation of the magma were revealed. The main understanding of the tectonic setting is as follows: (1) the LA-ICP-MS zircon U-Pb age of the marginal facies of the pluton rock is 265.9 + 2.4Ma. According to the previous data, the Permian intrusive order of the Permian rocks in this area is in order of the great Wu Dian rock mass (~290Ma), the Zhao Gen pluton (~275Ma), the urumi rock mass (265.9Ma), and the Hani river rock mass (2) (65.9Ma) (2) the (2) the characteristics of the Da Wu Dian rock mass and the Zhao Gentao rock body have the characteristics of quasi aluminum and weak peraluminous, all of which are high potassium calc alkaline I type granites. In the trace and rare earth elements, the fractionation of heavy and heavy rare earth elements is obvious, and the major ionic stone elements such as K, Rb and Ba are obviously enriched, and the characteristics of the high field strong elements, such as Nb, Ta, Ti, P and other high field elements, are characterized by the characteristics of the arc magmatic rocks. Pluton has high Mg# value (0.50~0.72), low rare-earth element content, enriched V, Cr, Ni and other compatible elements, enriched K, Sr, Ba and other large ion lithospheric elements (LILE), loss Nb, Ta and other high field elements (HFSE), which are closely related to the partial melting of the rich lithospheric mantle which is subducted by the subduction fluid. The Hani river rock has high silicon and high potassium. The characteristics of peraluminous, characterized by S type granite, heavy and heavy rare earth elements, and strong enrichment of large ion stone elements, loss of high field and strong elements, enrichment of Th, U, and the properties of crust source magma. (3) the great Wu lake rock mass, the Zhao Gentao and urumi rocks have similar Sr-Nd isotopic composition, in (~ (87) Sr/~ (86) Sr The _i- epsilon (Nd) (T) diagram is above the lower left and lower crust evolution lines of the mantle evolution sequence, and has the characteristics of the mixture of crust and mantle magma. Through the two element mixing model of crust mantle magma, it is shown that the didiin rock is a mixture of subducted sheet melts and lower crust melts, while the Zhao Gentao La and urumu rock are subduction flow. The partial melting melt of the enriched lithosphere mantle is mixed with the lower crust melts, and the Hani rock mass has a very high (~ (87) Sr/~ (86) Sr) I ratio (0.732355~0.740484) and a very low Nd (T) value (-34.59~-36.60), similar to the middle and lower crust composition, suggesting that the magma may originate in the middle and lower crust. (4) base rock The geochemical characteristics of the body, combined with the previous research results, suggest that the Da Wu Dian rock formed on the active continental margin environment, which is the product of the subduction of the ancient Asian Ocean to the north margin of the North China Craton, and the Zhao Gentao and urumi rock bodies formed in the transition environment with the collision of the same collision, and the two rocks may be separated from the plate fragments. Resulting in partial melting of the upper enriched lithosphere mantle resulting from the upwelling of the asthenosphere material, and then after mixed dyeing with the lower crust melts, the emplacement formed successively, and the Hani river rock formed in the post collision environment, which is the product of the partial melting of the middle and lower crust material in the crust thickening. (5) the magmatic rocks in the study area have been recorded. The subduction of the ancient Asian Ocean to the northern margin of the North China Craton to the final collision orogenic process, the subduction of the early Permian (~290Ma) palaeo Asian Ocean plates to the northern margin of the North China Craton remains in progress, forming a large Urumqi rock with typical continental margin arcs in the region, and in the early Late Permian (275~265Ma) and southern Mongolia microplates. The collision collage has occurred on the northern margin of the North China Craton to form the Zhao Gentao La pluton with the property of the same collision and the urieli rock mass; then the two plates have a strong collision orogeny between them, and the crust is obviously thickened, so that the middle and lower crust material is partially fused into the Hani river rock mass.
【学位授予单位】：长安大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P59;P588.12

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