--> Analysis of the South Atlantic Margins From Regional Seismic Data: Implications for Break-Up Tectonics and Thermal History

AAPG Annual Convention and Exhibition

Datapages, Inc.Print this page

Analysis of the South Atlantic Margins From Regional Seismic Data: Implications for Break-Up Tectonics and Thermal History

Abstract

The conjugate margins of the South Atlantic Ocean have been used as the natural laboratory to assess continental extension and break-up for over fifty years. More recently the discoveries of significant hydrocarbon accumulations on both African and South American margins have ensured continued focus and a proliferation of data. Yet still significant questions remain due in no small part to imaging challenges from the thick evaporite deposits and igneous material, both plutonic and volcanic. Interpretation of recent, high quality, deep seismic reflection data from both margins leads us to propose and attempt to constrain models for the development of these margins and to compare them to analogues from other locations. We observe a spectrum of magma volumes and distributions in different locations, implying that the common end-member models, while useful constructs, do not explain every situation. Variability can be abrupt or gradual in both the dip and strike direction inferring a complex interaction between magma generation and tectonic activity. The relative timing of structure generation and magmatism are investigated and compared with other margins. From this interpretation it is possible to infer that magmatism has a modifying, rather than a primary role in the rift process. The distribution of Seaward Dipping Reflectors over continental syn-rift architecture and further outboard and its link to interpreted high velocity lower crustal bodies is investigated. We consider the imaging challenges in these areas and review different possible interpretations and their feasibility and propose a model of basinward magmatic evacuation to explain observed geometries such as steeply dipping volcanic strata. Quantification of the models has been undertaken using a range of evaluation techniques including subsidence modelling, gravity modelling and thermal basin modelling. These techniques are used to constrain interpretations of the seismic data and to highlight inconsistencies and areas where existing models should be challenged.