兴蒙造山区及邻区早白垩世盆地岩石地层格架与沉积古地理演化

Stratigraphy and depositional palaeogeography of the Early Cretaceous basins in Da Hinggan Mountains-Mongolia orogenic belt and its neighboring areas

在重点梳理兴蒙造山区及其相邻地区早白垩世地层分布与沉积古地理特征的基础上,从地层沉积学角度探讨了研究区早白垩世沉积盆地特征。兴蒙造山区中东部在晚侏罗世巨厚粗碎屑沉积建造之上发育了巨厚的酸性-中性火山岩-火山碎屑岩与河流-湖泊相沉积岩系,构成中国东北部巨型NE向火山岩-沉积岩带。兴蒙造山区中东部早白垩世早中期以断陷(裂谷)盆地为主,古地貌以高地、河流和湖泊共存为特征,气候温湿且炎热,热河生物群萌生;早白垩世中晚期,北东向地壳强烈伸展并进一步向外围地区扩展,沉积盆地及充填建造和热河生物群也相应地向更广泛区域辐射发展。兴安岭-燕山沉积-火山岩带与古太平洋板块俯冲无关,板内软流圈上涌导致的区域性伸展是其主要的成因动力机制,也是中国东部早白垩世中晚期更大规模区域性伸展作用的序幕。兴蒙东部早白垩世晚期沉积盆地发育和古地理格局受Izanagi板块向亚洲大陆东部俯冲弧后伸展构造机制约束。

Based on a review of the Early Cretaceous stratigraphy and depositional palaeogeography in the Da Hinggan Mountains- Mongolian orogenic belt（DMOB）（i.e., the southern margin of the Central Asian Orogenic Belt） in combination of previous results and regional geological survey, this paper attempts to discuss the Early Cretaceous sedimentary basins in term of stratigraphy and sedimen- tology. Overlying the early coarse grained deposits of the late Jurassic-early Cretaceous period, there exists a huge NE-trending vol-canic and sedimentary rock belt consisting of thick acidic-intermediate lavas, volcaniclastic rocks and fluvial-lacustrine sedimentary rocks, which is well correlatable with the Zhang^iakou Formation and the younger strata（Dabeigou,Formation, Yixian Formation etc.）. Studies show that rifting basins were unique in the east of the DMOB in the Early Cretaceous period, and high terrain, fluvial and la- custrine environments were co-existent as well, which provided a favorable paleoecology and an ideal setting for emerging of the Je- hol Biota at that time. Moreover, as a result of intense NE-trending crust extension in the Early Cretaceous period, the basins extend- ed farther. At the same time, sedimentary basins and the Jehol Biota correspondently extended fu^her, reaching such regions as north- ern Hebei, western Liaoning, southern Inner Mongolia, Far East and East Asia. Studies show that the Da Hinggan volcanic rocks belt was likely generated by partial melting of newly underplated basaltic lower crust as a result of asthenosphere upwelling, but with no well-grounded evidence showing the relation with the subduction of the Izanagi plate, which preluded more large-scale regional crust stretch of eastern China in the mid-late Early Cretaceous. In addition, eastern China in the late Early Cretaceous was totally in a back-arc tectonic setting of the subduction of the Izanagi plate towards the Eurasia.