New Insights Into the Early Development of a Volcanic Passive Margin – 3-D Imaging of Seaward Dipping Reflectors and a South Atlantic Transfer Zone

Abstract

The margins around the South Atlantic - particularly offshore Uruguay, Argentina and Brazil - are commonly described as typical volcanic passive margins. However, limited data has meant that the true complexity of these margins has never been fully resolved, largely due to a lack of high quality seismic data. Previous datasets were restricted to widely spaced 2D seismic data which allowed only a glimpse of the major structural trends and features in the subsurface, due to limited spatial distribution and primarily the lack of deep penetration related to the limited record lengths of the seismic data. A newly acquired regional 3D seismic dataset covering over 13000km² offshore Uruguay is used in conjunction with long-offset 2D data to provide a new 3D insight into the Uruguayan margin. The data images both the crustal structure and early rift architecture and allows the full complexity of early rifting to be mapped and interpreted. We describe an oblique Atlantic transfer zone and the interaction of faulting and magmatic processes, indicative of margin formation during early South Atlantic rifting. The data also allows a window into the regional margin geometry which includes imaging of the Moho, seaward dipping reflectors (SDRs), a crustal-scale transfer fault and an incipient spreading centre. Contrary to many of the large transfer faults of Argentina and Brazil, we find transverse extension has resulted in the development of a previously unmapped rift system. We also observe the interaction between SDRs and this intricate fault network which has resulted in a variety of reflection geometries representing extrusive and possibly intrusive magmatism. We suggest a number of interpretations and models to explain the observed geometries. This work will expand on the current understanding of volcanic passive margins, an increasingly popular petroleum exploration environment.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016