Mapping Structures of Ancient Exposed Hyperextended Margins in the Alps: A Key to Understand the Evolution of Ultra-Deep Water Passive Continental Margins?
Gianreto Manatschal1, Geoffroy Mohn1, Emmanuel Masini1, Gwenn Peron-Pinvidic1, Patrick Unternehr2, and Garry D. Karner3
1Geology, EOST-ULP, Strasbourg, France
2Total, Paris, France
3ExxonMobil, Houston, TX
Research into the formation of passive rifted margins is incontestably undergoing a paradigm shift. The discovery of exhumed continental mantle and hyperextended crust devoid of significant normal faulting directly overlain by shallow marine sediments is proving fundamental in defining the controls and processes that thin continental lithosphere. However, the development of these new concepts critically depends on the access to pertinent geological and geophysical data sets, which remains a key problem. At present, little is known about the depositional environments, sedimentary facies, the kinematics and age of structures, or the subsidence and thermal history of pre-to syn-rift sediments of many distal margins.
Mapping of rift structures and depositional systems in the Alps has helped to identify lithologies and structures similar to those drilled along the Iberia-Newfoundland margins or those supposedly comprising the pre-salt sag basins of the South Atlantic. The most prominent structure observed in the Alps are top-basement detachment faults. These structures can be traced from relatively unextended continental crust across the ocean-continent transition towards embryonic oceanic crust and are overlain by extensional allochthons, tectono-sedimentary breccias overlain by syn- and post-rift sediments and further oceanwards, MOR-basalts. Crucial observations include: 1) detachment faults formed either late in the extension process or after the crust was already thinned to less than 10 km; 2) shallow depositional environments despite major crustal thinning; and 3) even though there is a lack of volcanic activity, magmatic infiltration has occurred in the underlying mantle while the crust was thinning. These crucial observations have major implications for the thermal evolution and thus survivability of syn-to post-rift petroleum systems in hyperextended margins.
AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery