吉南地区温春镇中生代花岗岩年代学、地球化学及构造背景

    Geochronology, geochemistry and tectonic setting of the Mesozoic granites in Wenchun Town, southern Jilin Province

    • 摘要: 吉林省南部位于欧亚板块东部边缘,经历了华北克拉通、中亚造山带演化过程,中生代受古太平洋西向俯冲作用影响,形成了强烈的构造岩浆活动和成矿作用. 吉林南部温春镇地区发育的白垩纪二长花岗岩和正长花岗岩对于研究东亚陆缘演化具有重要指示意义. 本文采用岩石地球化学和年代学方法对该区构造背景进行研究. 岩石地球化学研究显示,花岗岩SiO2含量为68.46%~74.52%, Al2O3为13.55%~16.24%,全碱Na2O+K2O为7.69%~10.45%, K2O/Na2O为0.92~1.3,具有高硅、富钾、富铝的特征,铝饱和指数A/CNK介于0.98~1.17之间,平均1.04 (<1.1),为准铝质-弱过铝质,整体显示I型花岗岩的特征. 花岗岩锆石U-Pb年龄分别为122.2±1.2 Ma、123.1±1.8 Ma、126.02±0.95 Ma,形成时代为早白垩世晚期. 构造环境判别显示陆缘弧环境. 综合分析认为,花岗岩形成于古太平洋板块西向俯冲过程的伸展环境.

       

      Abstract: Southern Jilin Province, located in the eastern margin of the Eurasian Plate, has undergone the tectonic evolution of the North China Craton and the Central Asian Orogenic Belt. During the Mesozoic, the region was affected by the westward subduction of the Paleo-Pacific Ocean, resulting in intense tectonomagmatic activity and associated mineralization. The Cretaceous monzogranites and syenogranites exposed in the Wenchun area of southern Jilin Province are therefore of great significance for understanding the evolution of the East Asian continental margin. This study integrates petrogeochemical and geochronological analyses to investigate the tectonic setting of the area. Petrogeochemical results indicate that the granites have SiO2 contents of 68.46%-74.52%, Al2O3 of 13.55%-16.24%, total alkali (Na2O+K2O) of 7.69%-10.45%, and K2O/Na2O ratios of 0.92-1.30. The rocks are characterized by high Si, K, and Al, with aluminum saturation index(A/CNK) ranging from 0.98 to 1.17(averagely 1.04, <1.1), defining a metaluminous to weakly peraluminous composition, and exhibiting overall I-type granite affinities. Zircon U-Pb dating yields ages of 122.2±1.2 Ma, 123.1±1.8 Ma, and 126.02±0.95 Ma, indicating a late Early Cretaceous formation. Tectonic discrimination diagrams suggest a continental arc setting. Integrated analysis suggests that these granites were formed in an extensional environment related to the westward subduction of Paleo-Pacific slab.

       

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