Margin segmentation and volcano-tectonic architecture along the volcanic margin off Argentina/Uruguay, South Atlantic

Some 25,000 kilometers of regional multichannel seismic data, acquired by BGR along the continental margins off Argentina and Uruguay document that the Early Cretaceous South Atlantic continental break-up and initial sea-floor spreading were accompanied by large-scale, transient volcanism emplacing voluminous extrusives, manifested in the seismic data by huge wedges of seaward dipping reflectors (SDRs). The emplacement of the deeply buried, 60-120 km wide SDRs was probably episodic as documented by at least three superimposed SDRs units. Distinct along-margin variations in architecture, volume, and width of the SDRs wedges are probably related to margin segmentation. It is suggested that the margin can be divided, at least, in four compartments bounded by the Falkland Fracture Zone/Falkland transfer, the Colorado transfer, the Ventana transfer and the Salado transfer. The individual margin segments reflect in the distribution and thickness of the post-rift sediments. The individual transfer zones may have acted as rift propagation barriers, selectively directing rift segments in left stepping patterns along the western South Atlantic margin. Although we found extensive variations in the architecture, style, and extent of the seaward dipping reflector sequences, a general trend is that the largest volumes are emplaced close to the proposed transfer zones and the width of the SDRs wedges decreases northward within the individual margin segments. We suggest that mainly adiabatic decompression and melt generation from shallow sources can explain distinct along-margin variations in the volcano-tectonic architecture and volumes of extruded magmas. (c) 2007 Elsevier B.V. All rights reserved.