Birth of a volcanic margin off Argentina, South Atlantic

Abstract

[1] Based on a dense grid of multichannel reflection seismic lines we study the evolution of a volcanic rifted margin segment off Argentina. The segment under study is located between 44°S and 41°S. We describe in detail the facies of the extrusive basaltic complexes across the margin. These include single and multiple Inner Seaward Dipping Reflectors (SDRs) with varying architecture along the margin, Outer Highs, and Outer SDR wedges. A detailed interpretation of a transitional zone between the Inner and Outer SDR wedges is presented. Multiple Inner SDRs are concentrated at the southern part of the margin segment, while in the north only one steeply dipping wedge is present. The dip of the Inner SDR wedges changes along the margin, and we propose subsidence by loading as main cause. The transitional zone between the Inner and Outer SDR wedges becomes narrower toward the north. By correlating with magnetic data we conclude that the emplacement of the 30-100 km wide multiple Inner SDRs occurred episodically. We propose an injection center which migrated in a seaward direction with proceeding extension as the origin for the multiple Inner SDRs. A scissor-like opening of the margin segment resulted in different amounts of stretching along-strike of the margin segment and is likely the cause for the varying distribution of the extrusive basaltic complexes. The varying extension rates within the margin segment contribute to decreasing volumes of melts generated in a northward direction within this rift segment.Components: 9834 words, 12 figures, 1 table.

Crustal breakup and continent-ocean transition at South Atlantic conjugate margins

“…Finally, along the conjugate Argentine-South Africa margin, seismic reflection profiles acquired by BGR (Argentine margin) were at our disposal. Line drawings from Hinz et al [1999] and Franke et al [2007Franke et al [ , 2010 together with two sets of wide-angle seismic refraction data [Franke et al, 2006;Schnabel et al, 2008] on the Argentine margin and published seismic reflection/refraction profiles on the conjugate South Africa margin [Emery et al, 1979;Brown et al, 1995;Séranne and Anka, 2005;Paton et al, 2008;de Vera et al, 2010;Hirsch et al, 2009] have also been incorporated into our interpretations for this margin.…”

“…Structures located in onshore Namibia are after Gladczenko et al [1998]. Seawarddipping reflections (SDRs) and related volcanics are from Moulin et al [2005] and Franke et al [2007Franke et al [ , 2010 for South America and Bauer et al [2000] for Africa. "G magnetic anomaly" after Rabinowitz and LaBrecque [1979]; Lin, lineament; WA, West Africa Craton; CC, Congo Craton, DB, Damara Belt; GB, Gariep Belt; KC, Kalahari Craton; CFB, Cape Fold Belt; AMZ, Amazonia Craton; SF, São Francisco Craton; DFOB, Dom Feliciano Orogenic Belt; RDPC, Río de La Plata Craton; VFB, Ventana Fold Belt; GFS, Gastre Fault System; TZ, transfer zone; FZ, fracture zone.…”

“…These observations suggest that the Paleozoic prerift basin may be filled with basalt flows and can also be interpreted as inner SDRs (Figure 13b). Along the Argentine margin farther south, there are clear evidences of inner SDRs (Figure 13a) [e.g., Franke et al, 2010] that are also associated with a prominent positive magnetic anomaly, including the LMA and "G magnetic anomaly." Along the conjugate margin off South Africa, inner SDRs and inner basalt flows have also been proposed [e.g., Bauer et al, 2000;Blaich et al, 2009;Hirsch et al, 2009] and appear to be associated with the landward part of the very wide LMA (Figure 13b).…”

Asymmetry of high-velocity lower crust on the South Atlantic rifted margins and implications for the interplay of magmatism and tectonics in continental breakup

“…The presence of HVLC bodies along the South Atlantic rifted margins is well established from seismic and gravity studies (e.g., Bauer et al, 2000;Blaich et al, 2011;Franke, 2013;Franke et al, 2010;Maystrenko et al, 2013;Schnabel et al, 2008), but they have not yet been studied for areal extent and rifting process determination. That is the purpose of the study reported here.…”

Architecture of rifted continental margins and break-up evolution: insights from the South Atlantic, North Atlantic and Red Sea–Gulf of Aden conjugate margins

“…These reflectors are interpreted to mark the continentocean transition towards an oceanic crust that was developed probably by Aptian time (about 112 Ma). Dating the magnetic anomalies associated with these volcanic wedges provides important insights, suggesting that rifting started in the southernmost basins (Argentina) and advanced northwards by oceanic propagators (Hinz et al 1999;Mohriak 2001;Franke et al 2010).…”