4D Anatomy of Continental Rifts Transitioning into Sea Floor Spreading: Insights from Afar, Ethiopia for Oil and Gas Exploration of Global Rift Systems and Passive Continental Margins
PIs: Mohamed Abdelsalam, Stephen Gao, Kelly Liu, and Kevin Mickus
4/1/08-3/31/11
About 61% of all worldwide oil and gas discoveries came form extensional tectonic regimes (rift basins and passive continental margins). About 30% of these discoveries came from rift systems alone. Future hydrocarbon exploration of these widely-spread structural features is promising, since many of the World’s unexplored rift systems and passive continental margins will be available in the near future because of improved accessibility. Future hydrocarbon exploration activities in these tectonic settings will hugely benefit from advancement in our understanding of their evolution both in space and time. Hence, it is crucially important to develop detailed four-dimensional (4D) models of rift basins and passive continental margins addressing their spatial and temporal evolution. This can be readily achieved through the integration of geological and geophysical data that can be subsequently used for conceptual and numerical modeling. The Afar Depression in Ethiopia lends itself as an unmatched site that can be used as an analogue for the evolution of continental rifts, transitioning from continental rifting to sea floor spreading, and the onset of passive continental margins. Not only that it is the only place of Earth where these features are exposed onto land, but it is also where time snap-shots of various evolutionally stages of an extensional regime are preserved in a relatively small area.
We request three-year funding from StatoilHydro ASA to acquire and analyze geological and geophysical data to produce detailed 4D crustal and upper mantle structural models of various stages on an extensional regime using the Afar Depression in Ethiopia as a focus site. Specifically: (1) We will use field studies aided by remote sensing analysis for detailed structural mapping. These results will be integrated with results from geodetic surveying (previous and in progress by other researchers), fault plane solution and displacement tensors from seismic data to create a precise surface picture of rift kinematics. (2) Use dense gravity surveying (0.5 to 1 km interval) to examine the nature of the lithosphere, determine variations in crustal thickness, image locations of solidified magma bodies, and delineate areas of higher heat flow or magma sources. (3) Use detailed (~10 km spacing) broadband passive seismic surveying to develop 3D velocity, anisotropy, and attenuation models with an unprecedented resolution for the crust and upper mantle. These data will be integrated to address three fundamental issues that have been identified by the hydrocarbon exploration community as challenges that need to be addressed for successful exploration efforts in the future: (1) The role of crustal and mantle heterogeneity in rift localization, asymmetry and geometry; (2) The transition for mechanical seismic extension (along border faults) to magma-maintained aseismic extension (within rift floor) and the relative roles of these mechanisms during continental lithospheric rupturing and the emergence of a plate boundary leading to the formation of a passive continental margin; (3) The source of extension obliquity and its influence on surface strain partitioning.
We plan to deliver our results to StatoilHydro ASA in the form of two annual and one final report (both in digital and hardcopy format) that will provide comprehensive documentation of our findings in terms of rifts and passive continental margins surface, crustal and upper mantle structure. In addition, all geological, remote sensing, and geophysical data will be delivered in digital format. Year 1 report will contain data and results from the first phase of field and gravity studies; Year 2 report will present data and results from the second phase of field and gravity studies; whereas the final report will include results from the broadband passive seismic study as well as comprehensive synthesis of the integrated geological and geophysical results. We also plan to publish our results in the peer-reviewed literature following the rules and regulation of StatoilHydro ASA.
