不整合结构构造与构造古地理环境 ——以加里东中期青藏高原北缘及塔里木盆地为例

不整合结构与不整合面结构具有不同的属性及特征.本文在分析不整合三层结构的基础上,进一步剖析了平行不整合、角度不整合、异岩不整合等3大类不整合的结构构造,划分出10个具有不同结构特征的不整合亚类.重点针对不整合面下的构造变形特征、不整合结构类型的平面分布、不整合面上的初始沉积物、物源及其层序结构等展开了精细研究,对不同结构类型的不整合形成运动学及动力学进行了初步探讨.并以塔里木盆地志留系与奥陶系不整合为例,在盆地尺度,解析不同区域不整合结构类型的特征、性质及差异.现今保留的志留系与奥陶系不整合在盆地中南部广大地区呈角度不整合,在阿瓦提-满加尔坳陷南部、巴楚隆起中西部、塔中隆起北部为低角度、北倾的单斜角度不整合；在塘古兹巴斯凹陷表现为中-低角度的断褶不整合,呈北东向展布,在巴楚隆起东部及塔中隆起的南部局部也存在北东向展布的断褶不整合.在盆地北部塔北隆起西部局部存在褶皱不整合,东部存在低角度、南倾、单斜不整合.而盆地中部在阿瓦提-满加尔凹陷中北部、塔东凹陷东北则以平行不整合为特征.结合沉积地层发育及构造演化分析,恢复了志留系沉积前构造古地理,塔里木盆地大部分为混积陆棚沉积、中部碳酸盐岩台地被逐渐淹没,满加尔及英吉苏凹陷为盆地相沉积.伴随着盆地南缘西昆仑-库地洋、南阿尔金洋的闭合及碰撞造山,在盆地南部主体为南北向的缩短,塘古兹巴斯凹陷为南东-北西向缩短,且变形强度明显大于南北向的缩短.因此,盆地南部的南东-北西向挤压作用是该期最活跃的构造作用,和田古隆起北部、塘古兹巴斯凹陷北东向加里东期褶皱带西北部,应是塔里木盆地第一期油气大规模运移聚集的有利区,值得进一步探索.本文通过对不同时期不整合结构的解剖,尝试区别分析不同期次构造事件的作用及效应,识别单一构造事件(或构造运动)在构造古地理重建及成藏、成矿中的作用.

Unconformity structural architecture and tectonic paleo-geographic environment: A case of the Middle Caledonian on the northern margin of Tibet Plateau and Tarim basin

The property and characteristic of structural architecture are differences between unconformity and unconformity surface. In this study, the 3-layer configurations of parallel unconformity, angular unconformity and heterolithic unconformity are analyzed, especially the structural deformation underlying unconformity surface, the distribution of the style of unconformity configuration in basin-wide, and the sequence architecture and initial sediments overlying unconformity surface. The unconformity configurations are divided into 10 subdivision unconformities. The process of kinematic and dynamics during these unconformities formed are discussed. The distribution of unconformity configuration presents obviously differences between Silurian to Upper Ordovician (S/O₃) in different units of Tarim basin. The medium-low angle monocline and faulted-fold unconformity occurred on the upthrown blocks of a series of thrust faults with NEE-SWW trending at Tangguzibasi depression in the southern of Tarim basin. The low angle dipping-north monocline unconformity occurred widely from south and across the central uplift of basin to the southern of Awati-Manjiaer depression, the parallel unconformity in the northwestern and the northeastern of Awati-Manjiaer depression, and locally low angle monocline and fold unconformity at the western and the eastern of the Tabei uplift in the northern of the basin. The analysis of balanced cross sections presents that there were the strongest shortening with SEE-NWW in southeastern of basin, and there existed the shortening with S-N orientation in the southern of basin before Silurian depositing yet. The unconformity configuration and fault system development responded to tecto-orogenic processes of the South Altun and the West Kunlun. Analyzing the sedimentary development and structure evolution, the tectonic paleo-geographic setting is reconstructed before Silurian depositing. The northern of Hetian paleo-uplift and the northwestern of NE-trending folds zone on Caledonian in Tangguzibasi depression should be favorable to the potential exploration area for the first large-scale period of hydrocarbon migration and accumulation.