Integrated Tectonic Basin Modelling as from Aid to Understanding Deepwater Rifted Continental Margin Structure and Location

Roberts, Alan¹
 Kusznir, Nick²
 Corfield, Richard³
 Thompson, Mark³

An integrated workflow has been devised for the investigation of deepwater rifted continental margins. This allows us to predict crustal structure, distribution of lithosphere thinning and location of the OCT with a new degree of confidence. The workflow is as follows:

2D/3D gravity inversion. Key to gravity inversion is incorporation of both a lithosphere thermal gravity correction and a prediction of new volcanic crustal addition at high stretching factors. This allows us to predict (i) depth to Moho, (ii) thickness of residual continental crust, (iii) location of the OCT.

2D/3D post-breakup backstripping. Backstripping and knowledge of the margin stratigraphy is used to quantify the post-breakup subsidence history of continental margin lithosphere. This allows us to predict the spatially-varying magnitude of the lithosphere thermal anomaly and stretching factor resulting from the breakup process.

2D/3D syn-kinematic backstripping. At many margins the location of the base post-breakup sequence is unclear, particularly where mobile salt is involved. The base of the syn-breakup sequence may, however, be more easily identified. Backstripping to reveal syn-plus-post-breakup subsidence allows us to derive estimates of lithosphere stretching, allowing for the isostatic consequences of volcanic addition (underplating), a process which in turn leads to the formation of new ocean crust. From this we can map crustal thicknesses and the OCT in a comparable way to the gravity inversion.

Quantifying upper-crustal fault extension. We believe that the process of depth-dependent stretching during breakup means that upper-crustal extension need not necessarily balance whole crust and/or lithosphere stretching and thinning. It is therefore important to quantify fault-controlled upper-crustal extension either by forward modelling or section restoration. This provides information about the partitioning of extension through the crust.

Forward modelling the kinematics of breakup. Finally we bring together the complete breakup process within a single forward model. The forward model of full (conjugate) margin structure is calibrated against present-day bathymetry and gravity measurements and is used not just to predict the crustal structure and evolution of the margin, but also the time-dependent heat-flow history, controlled by the breakup process.

Examples are illustrated with reference to the Brazilian, Indian, NW Australian and Norwegian continental margins.