二连盆地吉尔嘎朗图凹陷南部基底花岗岩形成演化及其大地构造背景研究

Emplacement and episodic denudation of basement granites from the southern Jiergalangtu Sag,Erlian Basin and its tectonic implications

二连盆地是中国北方重要的油气基地、煤炭基地和铀矿床富集区。基底花岗岩是盆地重要的含铀岩系沉积物源和铀源,以及重要的油气储层。然而,至今对二连盆地基底花岗岩的形成年代、成岩后剥蚀抬升历史及其与盆地构造演化关系的认识仍然比较薄弱。本文以吉尔嘎朗图凹陷南部地区钻井揭露的基底花岗岩为研究对象,通过锆石U-Pb年龄分析、锆石和磷灰石裂变径迹年龄分析,结合盆地地层和构造演化历史,对吉尔嘎朗图凹陷南部基底花岗岩的形成和演化进行了系统研究。研究结果表明,凹陷南部地区基底花岗岩成岩时代为早侏罗世(约175 Ma),成岩后经历了晚侏罗世((154±7) Ma、(146±7) Ma)和早白垩世中晚期((114±8) Ma)两期冷却事件。本文认为早侏罗世花岗岩的形成与蒙古—鄂霍茨克洋板块南向俯冲有关,成岩后的两期冷却事件记录了二连盆地经历的两期挤压构造作用,其中晚侏罗世冷却事件可能与蒙古—鄂霍茨克洋的关闭有关,早白垩世中晚期的冷却事件可能与亚洲大陆东缘发生的陆-陆碰撞事件有关。

The Erlian Basin is one of the most important oil, gas, coal, and uranium-bearing basins in northern China, and basement granites of the Erlian Basin are gaining importance as uranium source and petroleum reservoir. However, the emplacement time and denudation history of the basement granites are poorly studied. Here, based on newly obtained zircon U-Pb geochronological data and zircon/apatite fission track evidence, the diagenetic age and uplift history of basement granites of the southern Jiergalangtu Sag, Erlian Basin are analyzed. The diagenetic age is constrained to the Early Jurassic(ca. 175 Ma), and two cooling events are recognized. The two cooling events are refined to the Late Jurassic(ca. 154 Ma and ca. 146 Ma) and late Early Cretaceous(ca. 114 Ma), respectively, and considered to be related to the contractional deformation in the Erlian Basin. The present study tentatively attributes the formation of basement granites to the southward subduction of the Mongol-Okhotsk Ocean Block, Late Jurassic cooling to the closure of the eastern Mongol-Okhotsk Ocean, and late Early Cretaceous cooling to the collision of micro-block with East Asia.