东北地区中—新生代盆地群形成演化的动力学背景

Dynamic evolution of the Mesozoic-Cenozoic basins in the northeastern China

东北地区的中—新生代盆地之下并非都是变质结晶基底,松辽和二连等盆地大部分叠加在未变质的晚古生代残余沉积盆地之上。嫩江—开鲁断裂和嘉荫—牡丹江断裂是两条深达岩石圈尺度的断裂构造,将东北地区分为额尔古纳—兴安、松嫩和佳木斯三大基底构造单元和与之相对应的西部、中部和东部三大中—新生代盆地群。3个盆地群不但基底和深部岩石圈结构明显不同,而且盆地结构及充填特征也存在明显的差异。东北地区与中生代盆地演化相关的火山活动主要发生在中—晚侏罗世（167~147 Ma）,早白垩世早期（136~126 Ma）和早白垩世晚期（122~109 Ma）。侏罗纪火山岩主要发育在大兴安岭及其以西地区;早白垩世火山岩全区均有分布,且具有由西向东时代渐新变新的演化趋势。从深部构造和区域动力学背景角度,东北地区的侏罗纪和白垩纪—新生代构造演化分别属于两大动力学体系。前者的形成演化与西伯利亚板块和华北板块对东北地区西部产生的南北向挤压作用及后继的伸展作用有关,北北东向展布的中—晚侏罗世火山岩大面积叠加在近东西向展布的漠河前陆盆地和突泉等含煤盆地之上;后者的形成演化明显与西北太平洋构造域大洋板块对东北亚大陆边缘的作用有关。根据同位素年龄和生物地层学证据重新厘定的中—新生代盆地地层对比结果显示,即使是同时代形成的早白垩世盆地由于与大陆边缘的距离不同,其盆地的沉积充填特征和后期构造改造特点也不尽相同。西部以海拉尔盆地为代表的早白垩世盆地主要发育以火山岩为主的断陷沉积,之后长期处于隆升环境;中部以松辽盆地为代表的白垩纪盆地不但发育早白垩世早期的断陷沉积,而且之上基本连续叠加了早白垩世晚期和晚白垩世坳陷沉积;东部盆地群由三江、勃利、鸡西和虎林等众多中、小型盆地构成,它们在早白垩世早期曾是一个统一的近海大陆边缘盆地（大三江盆地）,以发育海陆交互相沉积为特点。由于该区紧邻西北太平洋大陆边缘,受大陆边缘构造转换的影响,统一的大三江盆地在早白垩世末期被强烈的逆冲构造和左行走滑构造所破坏和改造。该区目前分散孤立存在的多个中、小型早白垩世盆地均为早白垩世末期构造改造后的残余盆地。

All Mesozoic-Cenozoic basins in the northeastern China were not formed on the crystalline basement, and for the most part were superimposed on the unmetamorphosed Late Paleozoic sedimentary strata. The Nenjiang-Kailu fault in the west and the Jiayin-Mudanjiang fault in the east are the most important deep faults, which separate the northeastern China into three basement units, i. e. , the Ergun- Higgan, Songnen and J iamusi massif s, and three corresponding Mesozoic-Cenozoic basin groups from west to east. The west basin group is situated to the west of the Nenjiang-Kailu fault and represented by the Mohe and Hailaer basins; the central one distributed between the Nenjiang-Kailu and Jiayin-Mudanjiang faults and represented by the Songliao Basin. The east basin group located to the east of the Jiayin-Mudanjiang fault comprises many small-sized basins represented by the Sanjiang, Boll, Jixi and Hulin basins and so on. The three basin groups are distinct not only in the basement and lithosphere structures, but also in basin structures and fillings. The Mesozoic basin-related volcanism is divided into three stages, i. e. , the Middle-Late Jurassic （167-147 Ma）, the early Early Cretaceous（136-126 Ma） and the late Early Cretaceous（122-109 Ma）. The Middle-Late Jurassic volcanic rocks were mainly developed in the Dahinggan Mountains to the west of the Nenjiang-Kailu fault. The Early Cretaceous volcanic rocks are distributed in the whole northeastern China, and show an evolutional trend from west to east becoming younger and younger. The Jurassic and Cretaceous volcanism can be classified into two systems of geodynamic settings. The former is related to the extension after the compressional process of the North China Plate and Siberia Plate to the area. The Middle- Late Jurassic volcanic rocks in a NNW trending were superimposed on the Early-Middle Jurassic Mohe foreland basin and simultaneous coal bearing basins trending in an EW direction. The latter was related to the actions of the oceanic plates in the northwest Pacific to the area, including the basins formed since the Cretaceous. The revised chronostratigraphic chart of the Mesozoic- Cenozoic basins in Northeast China indicates that the structures and fillings of the Early Cretaceous basins are different depending on their tectonic places how far from the continental margin, even if they formed nearly simultaneously. The Early Cretaceous basins in the west mainly developed the early Early Cretaceous fault basins filled by predominant volcanic rocks. The Songliao Basin in the central is characterized by late Early Cretaceous-Late Cretaceous successive depression sediments on the basis of the early fault basins. The many small-sized basins in the east part once were a unified Early Cretaceous continental marginal basin （Pan-Sanjiang Basin） and marked by marine-land transitional facies sedimentation. The unified basin was transformed and destroyed by thrust and sinistral slip faults in the last Early Cretaceous as the region close to the continental margin. Therefore, the present separate Early Cretaceous basins in the east part are relict basins.