Modelling the Complexity of Continental Breakup and Basin Formation Including the Role of Magmatism

Abstract

Continental breakup controls the origin as well as the geometric and thermal evolution of sedimentary basins, and consequently is of major importance for petroleum exploration. The architecture of basins is controlled by extensional faults formed at the onset of rifting, and the geometry of such faults governs the overall sedimentary thickness, depositional environment, fluid pathways and thermal conditions. Numerical models have to date struggled to capture the complex expression of continental extension in nature, which features a variety of structures. In addition, some extension systems have been accompanied, and possibly triggered, by voluminous magmatism; whereas others involved relatively little magma activity. Some extensional systems have been stretched for more than 100 Myr prior to breakup, whereas others ruptured to produce a passive margin after only 5–10 Myr. In an attempt to better understand the variety of continental deformation modes, we have incorporated the explicit role of magmatism and metamorphic fluids in addition to the classical brittle localization mechanism during extension of the lithosphere (Liu et al. 2014). These three different weakening mechanisms may act as triggers for localization of deformation. They represent physically distinct processes that can all occur simultaneously, i.e. with some overlap in time and space. Our new model also treats melting through the incorporation of parameterized free-energy curves generated from the MELTS model for phase equilibria. The application of the numerical models to real case studies led to identification of a new style of tectonics, where instead of breaking plates apart through fast brittle faults that propagate into the ductile realm, the opposite mechanism is observed. The propagation of melt-rich ductile shear zones upwards into the brittle domain requires longer time scales but is extremely efficient and can potentially break cratons. We present an application to plate breakup in the Arabian Peninsula that provides new insights into extensional processes and the timing between initiation of extension and of magmatism. These models help understanding and improving thermal and depositional models of basins, and may provide an enriched geodynamic exploration toolkit for search of (un)conventional oil and gas reserves in previously unexplored domains. References: Liu, J., et al. (2014). Combined mechanical and melting damage model for geomaterials. GJI, 198, 1319–1328

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015