Break-up Processes at Magma-Rich Rifted Margins: Imaged Through the Lens of a Mega-Regional, Long-Offset, Trans-Crustal Reflection Seismic Dataset

Abstract

Abstract

Magma-rich (volcanic) rifted margins are a common end member rifted continental margin variant, the other end member being a magma-poor margin. Magma-rich margins are typically constructed from a number of structural and volcanostratigraphic elements; stretched continental crust, inner & outer seaward dipping reflector packages (SDRs), an outer (volcanic) high, landward flows, and a high velocity lower crust. The Namibian Margin, a classic example of a magma-rich margin, is the focus of a newly acquired mega-regional seismic dataset that allows for a re-evaluation of the principle processes and mechanisms involved in highly magmatic continental break-up. We present a model integrating crustal structure, depositional architecture, and the structural development of the Namibian Margin, and comment on how it affects margin prospectivity.

Detailed observations taken from within the continent-ocean transition (COT) reveal that four crustal domains may be delineated (continental, magmatic, oceanic, and oceanic plateau crust). Each crustal domain has a characteristic deformation style apparently dependent on the volume of magma present during extension. A new tectonic model of the Namibian Margin is presented here together with seismic data that demonstrates the change in deformation style both across and along the Namibian Margin. Through the identification of four distinct crustal types (in particular the magmatic crust), we suggest an updated nomenclature for crustal boundaries at magma-rich margins to supersede the COT: the limit of continental crust (LoCC); and limit of oceanic crust (LoOC). This updated model for magma-rich margin formation – including the effect of variable melt volume during continental stretching and break-up, and formation of SDR trains – demonstrates where syn-rift sediments are likely to be encountered (and the possible facies present), and describes strongly diachronous post-rift and drift phase subsidence.

The observations and processes described here underpin the development of a regional petroleum system, allowing prediction of regional heatflow through time as well the likely location of source, and reservoir lithologies along the entire margin, and may serve to reduce uncertainty in exploration of commercial hydrocarbons.

AAPG Datapages/Search and Discovery Article #90260 © 2016 AAPG/SEG International Conference & Exhibition, Cancun, Mexico, September 6-9, 2016