AAPG Middle East Region Geoscience Technology Workshop, Rift Basin Evolution and Exploration

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Applying Hyperextended Models to Rifted Margins: Lessons Learned, Implications and Limitations

Abstract

Advances in the development of long offset, high-resolution seismic imaging methods, combined with drill-hole data and direct field observations have resulted in a paradigm shift in our understanding of the tectono-magmatic evolution of rifted margins. Notably, the pronounced structural and magmatic variability observed along hyperextended rifted margins requires a closer investigation of the parameters that may control these differences. In order to do so, new approaches have been developed that enable to identify, describe and map inheritance, first-order architectural features and their along strike variations. Some of these methods combine geological observations and geophysical techniques and have been calibrated along the southern North Atlantic margins. The application of these approaches to other margins, characterized by different inheritance and variable magmatic budgets remains, however, challenging. In the presentation I will focus on three aspects: 1) definition of inheritance and its role in controlling the evolution of rifted margins, 2) presentation of multi-disciplinary methodological approaches that can be adapted to successfully describe and map rift domains, and 3) highlight and discuss the pitfalls in applying the new models to rifted margins that are yet undrilled and uncalibrated. In a first part the importance of lithological, structural and thermal inheritance and their possible control of the extensional and magmatic processes will be evaluated. It is critical to emphasize the consequences of integrating inheritance in models and to compare the results with simple, homogeneous layer cake models. In the presentation particular focus will be on mantle characteristics inherited from the previous orogenic cycle in controlling strain distribution and magmatic budget during rifting. A second part will address key architectural features identified on seismic reflection data across Atlantic-type margins that can be used to subdivide and map rift domains along passive margins. The identification and mapping of rift domains help to define and characterize the along strike segmentation, degree of asymmetry and structural, magmatic and stratigraphic variability. These observations are fundamental and necessary to determine and model the isostatic, thermal and kinematic evolution of rifted margins. In a third part the example of the North Atlantic will be presented with the aim to illustrate the relationship between crustal/lithospheric thinning, the evolution of magmatic systems (i.e. where and when first magma is formed) and how it interacts with the extensional systems. Particular attention will be paid on the role of pronounced along strike changes of structural, compositional and thermal inheritance observed along the rifted margins and the related changes of the margin architecture and magmatic budget. The presentation of concrete examples enables also to highlight and discuss potential pitfalls in applying conceptual models to real rifted margins that are yet undrilled and uncalibrated Existing observations suggest a complex link between magmatic/asthenospheric and structural/lithospheric processes that cannot be easily predicted from oversimplified, McKenzie type models. The along strike spatial and temporal changes observed in the evolution of rift systems reflect the interplay between their inheritance (innate/"genetic code") and the physical processes at play (acquired/external factors) nicely documented in the example of the North Atlantic.