大兴安岭中生代火山岩地层时空分布与蒙古—鄂霍茨克洋、古太平洋板块俯冲作用响应

为了提高大兴安岭中生代火山岩地层的区域可对比性、深入研究大兴安岭中生代火山岩与古太平洋和蒙古—鄂霍茨克洋的构造关系,本文在大兴安岭地区1: 1 000 000地质图编图的基础上,依据岩石组合、古生物、接触关系、区域对比以及最新的年代学(锆石U-Pb、⁴⁰Ar/³⁹Ar测年)资料,对大兴安岭中生代火山岩地层重新进行了厘定。进一步界定了塔木兰沟组(172~161 Ma)、满克头鄂博组(162~148 Ma)、玛尼吐组(158~145 Ma)、白音高老组(145~129 Ma)、梅勒图组(143~128 Ma)、龙江组(128~120 Ma)、光华组(128~118 Ma)、甘河组(120~113 Ma)和孤山镇组(118~110 Ma)的形成时代。结合古太平洋、蒙古—鄂霍茨克洋板块对东亚大陆边缘的俯冲作用,解析了中生代火山岩形成的构造背景,认为中—晚侏罗世NE向展布的火山岩主要形成于蒙古—鄂霍茨克洋板块向南东俯冲的伸展背景,早白垩世NNE向展布的火山岩主要形成于伊泽奈岐板块向东亚大陆俯冲的伸展背景。晚侏罗世与早白垩世火山岩地层之间发育的开库康组、木瑞组等类磨拉石建造,是两个构造体系转换阶段的主要沉积记录。

Spatio-temporal distribution of Mesozoic volcanic strata in the Great Xing'an Range:Response to the subduction of the Mongol-Okhotsk Ocean and Paleo-Pacific Ocean

To improve the regional comparability of Mesozoic volcanic rock strata in the Great Xing’an Range region, we examined in-depth the tectonic relationship between the volcanic rock strata and the Paleo-Pacific/Mongol-Okhotsk Plates. By mapping (1: 1 million) the Great Xing’an Range region, combined with data on rock association, paleontology, contact relationship and regional comparison, as well as the latest zircon chronology (through U-Pb,⁴⁰Ar/³⁹Ar zircon dating), we redefined the Mesozoic volcanic strata of the Great Xing’an Range region, and subsequently further defined the formation periods of the Tamulangou (172-161 Ma), Manketouebo (162-148 Ma), Manitu (158-145 Ma), Baiyingaolao (145-129 Ma), Meiletu (143-128 Ma), Longjiang (128-121 Ma), Guanghua (128-118 Ma), Ganhe (120-113 Ma) and Gushanzhen (118-110 Ma) Formations. Together with the spatial distribution analysis of volcanic strata, taking into account the subduction of the Paleo-Pacific and Mongol-Okhotsk Plates at the continental margin of East Asia, the tectonic setting of the Mesozoic volcanic rock strata was analyzed. We found that the NE-trending volcanic rock strata of the Middle-Late Jurassic mainly formed in the extensional tectonic setting associated with the southward subduction of the Mongol-Okhotsk Plate, while the NNE-trending volcanic rock strata of the Early Cretaceous mainly formed in the extensional tectonic setting associated with the subduction of the Izenaki Plate beneath the East Asian continent. The molasse-like deposits in the Kaikukang and Murui Formations, developed between the Late Jurassic-Early Cretaceous volcanic strata, are the main sedimentary record of the transition stage between the two tectonic domains.