先存构造对裂谷发育的控制作用研究—以澳大利亚西北陆架Dampier盆地为例

Dampier Basin is a typical continental rift basin, situated at the North West Shelf of Australia and controlled by complex basement structures. It underwent a series of continental rifting events associated with the rapture of the northern Gondwana and the subsequent formation of the Tethys Oceans. This research attempts to reveal (1) how basement structures of distinct properties, such as heterogenous suture belt and transcurrent fault, could exert their influence on rift basin evolution during multiphase extensions? (2) what is the rift timing, structural styles, and rift process of the Gondwana dispersions, which led to collages of microplate drifted away from it since the Late Palaeozoic? This project aims to interpret and analyse the distribution and magnitude of pre-existing basement grains and to constrain fault timing, fault geometry, and fault array arrangement through integrated study of the gravity and magnetic data, seismic and well data, and other geological and geophysical data. To constrain the basin deformation and subsidence history, we are also motivated to quantitatively or semi-quantitatively calculate the amount of deformation by section balancing and back-stripping. In addition, we are going to conduct physical modelling to elucidate the influence of pre-existing structures on the lithospheric deformation during continental rifting, based on analysis results of the palaeostress direction and the configuration of basement weaknesses. The present continental rifting model only considers the situation that lithospheric stretching occurs in a homogeneous material, although the fact that heterogenous continental lithosphere is very obvious. Therefore, the control of pre-existing basement grains or weakness on the development of continental rifting is the earth science research frontier, and thus our research is theoretically important in the respective area. Apart from that, the research area is located at the conjugate margin, where its counterpart has been rifted away along with Gondwana dispersion and has been significantly altered, if not destructed, in the later stage of accretion.

Dampier盆地是发育在澳大利亚西北大陆架内侧复杂基底构造带之上的典型裂谷盆地，经历了自晚古生代以来冈瓦纳大陆裂解等多期次的区域构造事件。本研究拟解决（1）不同性质基底构造在多次伸展过程中究竟是怎样控制盆地发育的；（2）冈瓦纳大陆自古生代以来伴随微陆块裂解的大陆裂谷发生的确切时间、构造样式、裂解过程。本项目拟通过重-磁数据、井-震数据和其他地质地球物理资料的解释、分析，厘定基底断裂的性质及其分布规律，详细确定多期伸展形成断裂的几何特征及其组合样式；定量-半定量计算构造变形量和盆地沉降史，重建盆地发育演化过程；分析区域构造的动力边界条件，开展物理模拟，阐明基底薄弱带对裂谷发育过程的控制机制。目前，裂谷研究领域的理论模式主要基于均一基底条件下岩石圈伸展变形的研究，而基底先存构造对裂谷发育的控制作用研究正在成为令人关注的前沿，同时本研究的开展将可能为冈瓦纳大陆裂解过程提供重要线索。

利用高精度地震数据、钻井数据和重-磁数据，开展详细的构造变形和沉积特征分析，确立了澳大利亚西北被动陆缘自晚古生代以来的两次主要裂谷事件，分别为晚石炭-晚二叠（305-250 Ma）和晚三叠-晚侏罗（209-162 Ma）。第一次裂谷事件在Mermaid Nose发育低角度正断层系统和变质核杂岩，在厚层沉积盆地底部发现大面积分布的低角度正断层。第二次裂谷事件在Enderby Terrace主要以早期断裂体系活化为变形特征，断裂带活化形成复杂的断裂网络。本项目通过上述工作，明确了澳大利亚西北陆缘两期裂谷事件的变形时间和变形样式，为冈瓦纳大陆裂解和特提斯洋形成提供了详细的变形依据。此外，断裂带活化形成复杂的三维空间结构，但最终趋向于形成平直构造带，便于应力和应变的传递，而形成更大的断层。