松辽盆地构造演化与中国东部构造体制转换

Tectonic Evolution of Songliao Basin and the Prominent Tectonic Regime Transition in Eastern China

本文综合应用盆地构造解析、平衡地质剖面恢复、构造物理模拟等方法,探讨了松辽盆地构造演化及其地球动力学背景。松辽盆地基底是前侏罗纪古亚洲洋构造域众多微板块、地体拼贴形成的复合陆块。中—晚侏罗世,盆地基底受到郯(城)—庐(江)断裂系北段大规模左旋走滑活动的强烈改造,派生NNE、NNW和近NS向次级断裂,控制了基底构造格局、断陷盆地分布及其构造。断陷期可划分为早、晚两个脉冲式伸展阶段,早期阶段受多方向平面式正断层控制发育堑—垒构造,具有双向纯剪伸展的特点,但NNE向拉伸更显著,可能是深部岩石圈拆沉引起热穹窿与基底断裂持续左旋走滑拉分的叠加;晚期阶段受低角度犁式正断层控制发育西断东超的复合半地堑,受控于近EW向单剪伸展机制,是区域性地壳伸展拆离与岩石圈减薄的结果。拗陷期大规模热沉降是对古太平洋构造域向东迁移的响应。白垩纪末期盆地受到NWW向脉冲式挤压而发生反转,可能与伊泽纳奇板块消亡、太平洋板块开始俯冲这一转换过程中的地体拼贴有关。

Structural analyses,balanced cross-section restoration and tectonophysical modeling were jointly used in this study to investigate the tectonic evolution and geodynamics of the Songliao basin. The basement of the Songliao basin was formed prior to Jurassic by coalescing multiple microplates and tectonic terranes in the Paleo-Asian Ocean. During the Middle and Late Jurassic the basement was altered by the large scale sinistral strike-slip faulting of the northern segment of the Tancheng—Lujiang fault system,producing series of secondary NNE-,NNW-and near NS-trending faults,which exerted primary controls on the tectonic configuration of the basement and the distribution of fault depressions. Two episodes of extension are recognized during rifting. The early episode is marked by the occurrence of graben-host structures bounded by multi-directional planar faults. These structures are typical of biaxial doming extension in the pure-shear mode. Together with the slightly NNE-dominated orientation,these structures suggest that the early episode of extension was probably a result of lithosphere delamination and continued sinistral strike-slip faulting in the basement. The late episode is characterized by the development of westerly tilted half-grabens separated by low-angle listric normal faults. This episode of extension was attributed to the near EW stretching in a simple-shear mode due to the regional crustal detachment and lithosphere thinning. The large scale thermal subsidence of the basin was the result of the subsequent eastward migration of Paleo-Pacific domain. The basin was inverted during the latest Cretaceous due to episodic,NWW compression,which was possibly associated with terrane accretions as the Izanagi Plate demised and the subduction of Pacific Plate began.