ISSN 1009-6248CN 61-1149/P 双月刊

主管单位:中国地质调查局

主办单位:中国地质调查局西安地质调查中心
中国地质学会

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    中亚造山带中段早—中三叠世埃达克岩和A型花岗岩成因及构造意义

    Early-Middle Triassic Adakitic and A-type Granite in Middle Segment of Central Asian Orogenic Belt: Petrogenesis and Tectonic Implications

    • 摘要: 中亚造山带增生过程中发育的典型岩浆作用是研究其演化过程的关键。中亚造山带中段南缘达伦乌苏二长花岗岩、花岗斑岩系统的岩石学、地球化学和年代学研究表明,达伦乌苏二长花岗岩具有明显高Sr、低Y、Yb含量,高Sr/Y值(88.55~140.34),无明显Eu异常(δEu值为0.68~0.98),具埃达克岩地球化学特征。花岗斑岩富SiO2,贫CaO和MgO,具高的FeOT/(FeOT+MgO)和10000×Ga/Al值,高Zr、Nb、Ta 含量,富集Pb、Hf、 Rb、K和Th,相对亏损Ba、Sr、P和Ti,属于典型的A型花岗岩。二者的锆石U-Pb年龄分别为(249.0±2.3)Ma和(241.0±2.8)Ma。结合区域地质资料,埃达克岩指示了古亚洲洋闭合后陆壳碰撞加厚的背景,而A型花岗岩指示了碰撞后伸展构造背景。两种典型的岩浆作用记录了早—中三叠世中亚造山带中段南缘由增生造山到造山后期伸展的转换过程。

       

      Abstract: Typical igneous rocks during the accretionary orogeny process in the Central Asian Orogenic Belt (CAOB) play a key role in understanding its tectonic evolution. We present new LA-ICP-MS in-situ zircon U-Pb and bulk geochemical data for the Dalunwusu monzogranite and granite porphyry suites which are located in Southernmost CAOB. The Dalunwusu monzogranites, have a crystallization age of (249.0±2.3) Ma, exhibit adakite-like geochemical characteristics, such as high Sr content and low Yb and Y contents, coupled with high Sr/Y values (88.55~140.34) and show a weakly negative Eu anomalies (δEu=0.68~0.98). Geochemical compositions indicate the Dalunwusu monzogranites derived from partial melting of mafic granulite in the lower thickened crust. The Dalunwusu granite porphyrys, have a crystallization age of (241.0±2.8) Ma, show typical geochemical features of A-type granites, which are characterized by having high SiO2, low CaO and MgO content, high FeOT/(FeOT+MgO) and 10000×Ga/Al values. Moreover, the granite porphyrys show trace element features of A-type granites including rich in Zr, Nb, Ta abundances, and high values for Pb, Hf, Rb, K and Th, and low values for Ba, Sr, P, and Ti. Taking into account available data of the regional geological background, we may suggest that the adakites were products through partial melting of the thickened lower crust after the closure of the Paleo-Asian Ocean, and the A-type granite porphyry were likely produced at the tectonic setting of post-collisional phase with crustal extension and thinning. These two typical igneous rocks reflect the shift of geodynamic setting, from an earlier accretionary orogen environment to a later extensional setting during early- middle Triassic.

       

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