漠河盆地绣峰组形成时代及物源分析:对蒙古?鄂霍茨克洋东段演化的启示

漠河盆地位于蒙古?鄂霍茨克缝合带（MOSB）东段南缘，是研究蒙古?鄂霍茨克洋东段演化的绝佳窗口.本文对漠河盆地东缘出露的绣峰组砂岩进行详细的岩相学、U-Pb锆石定年和主微量元素地球化学分析，综合前人研究成果，限定了蒙古?鄂霍茨克洋乃至中亚造山带东段演化历史.结果表明，绣峰组砂岩碎屑物磨圆度较低、分选差，表现出近源剥蚀的特点；U-Pb锆石定年共获得217个谐和年龄，可划分为3个年龄组，其峰值均与盆地南缘额尔古纳地块的岩浆事件相吻合，其中最年轻的碎屑锆石206Pb/238U年龄加权平均值为158±2 Ma（N=5）；样品相对富集大离子亲石元素（LILEs）和轻稀土元素（LREEs），亏损高场强元素（HFSEs）和重稀土元素（HREEs），具有明显的Eu负异常.样品源岩为上地壳长英质岩石，形成于大陆岛弧的构造环境，源区可能为漠河盆地南侧的大陆岛弧、额尔古纳地块以及盆地的古老基底.综上所述，绣峰组的最大沉积年龄为晚侏罗世，物源区构造背景为活动大陆边缘的大陆岛弧环境，形成于晚侏罗世蒙古?鄂霍茨克洋向南俯冲、闭合造山的构造背景下，指示在绣峰组沉积时期（约158 Ma），蒙古?鄂霍茨克洋仍处于俯冲阶段，尚未完全闭合.综合前人研究成果，推断蒙古?鄂霍茨克洋最终闭合的时间可能在晚侏罗世至早白垩世之间. 

Geochronology and Provenance Analysis of the Xiufeng Formation in Mohe Basin: Implications for the Evolution of the Eastern Mongol-Okhotsk Ocean

The Mohe basin is located in the southern margin of the eastern Mongol-Okhotsk suture zone (MOSB), which is an excellent window for studying the evolution of the eastern Mongol-Okhotsk Ocean. In this paper, four sandstone samples from the Xiufeng Formation in the eastern margin of the Mohe basin were analyzed by petrography, chronology and geochemistry. The results show that the sandstone debris of the Xiufeng Formation has poor roundness and sorting, and shows the characteristics of near-source denudation. A total of 217 concordant ages were obtained from U-Pb zircon dating, divided into three age groups, and the peak ages of all concordant ages correspond identically to the regional magmatic activities on the Erguna Block. LA‐ICP‐MS U-Pb zircon dating yields the youngest concordant ages of 158±2 Ma (N=5) for the Xiufeng Formation. Based on the previous research results, we try to limit the evolution of the Mongol-Okhotsk Ocean and even the eastern part of the Central Asian Orogenic Belt. All samples are enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREEs), depleted in high field strength elements (HFSEs) and heavy rare earth elements (HREEs), and have obvious negative Eu anomalies. The lithology of the source rocks is mainly felsic from the upper crust and is situated in active continental margins. The continental island arc provides the sediments in the Xiufeng Formation in the south of the Mohe basin, the Erguna block and the old basement of the basin. The provenance is located in the tectonic environment of the continental island arc, which is related to the southward subduction, collision and closure of the Mongol-Okhotsk Ocean in the Late Jurassic. Based on all the evidence above, we can infer that the Mongol-Okhotsk Ocean was still in the subduction stage and did not close during the sedimentation of the Xiufeng Formation (ca. 158 Ma). Combined with previous data, it is inferred that the final closure of the Mongol-Okhotsk Ocean may be limited between the Late Jurassic and Early Cretaceous.