Gravitational, Extension-Compression Linked Tectonic Systems in Passive Continental Margin

The gravitational, extension-compression linked tectonic system developed on lots of passive margins provide an excellent sample for the reseach of interaction between up-slope extension and down-slop compression.Many cases had been carried out in geometric description and kinematic restoration, however, a comprehensive understanding of the structural characteristics, main control factors, geometric features of sedimentary wedge, as well as dynamic mechanism and scientific classification is still weak relatively.

More than 82 typical sections of 21 passive margin basins have been collected and analyzed in dimensions of geometry and material. According to detachment layer, the gravitational linked tectonic systems could be divided into three categories, the salt detached, the shale detached, and the shale and salt composite detached. Structural analysis shows that the salt detached tectonic systems are usually accompanied with salt rollovers and extensive salt diapers in extension domain and densely developed salt diapirs and mini-basins in transition domain. Besides, salt core fold and thrust structures are developed in compressional domain. Contrastively, shale diapirs are rare for shale detached tectonic systems which have simpler structural deformation style.The deformation of these gravitational tectonic systems is mainly controlled by the physical properties and thickness of detachment, the geometry of the detachment surface, and the thickness of overlying sediments.

Taper angles of sedimentary wedges have been measured. And the result shows value of taper angle is extraordinarily small, within a range of -2.5°~4.5°, most of them are less than 3°. In some cases the taper angle is lower than 1° (-1°~1°). According to the value of α+β, wedges could be divided into two categories: Type I, α+β>0; Type II, α+β<0, where α>0, β<0, and α<|β|. Secondly, Type I could be divided into three sub-types: Sub-type I₁, α>0, β>0; Sub-type I₂, α>0, β≈0; Sub-type I₃, β<0, and α>|β|.

Theory of Dynamic Critical Wedge is applied to explain the development of the tectonic system.It is similar to the classic principle of critical taper angle wedge, but for passive margin, the detachment strength, F, and wedge strength, W (Suppe.J.2007), are variables, which vary over time owing to syn-tectonic deposition.