Crustal-scale architecture and segmentation of the Argentine margin and its conjugate off South Africa

Abstract

S U M M A R YIntegration of regional seismic reflection and refraction profiles and potential field data across the Argentine margin and its conjugate off South Africa, complemented by crustal-scale gravity modelling, is used to reveal and illustrate the whole-crust architecture, onshore-offshore crustal structure correlations, the character of the continent-ocean boundary/transition and the relationship of crustal structure to regional variation of potential field anomalies. The study reveals, within these two provinces, distinct along-margin structural and magmatic changes that are spatially related to a number of conjugate transfer systems governing the margin segmentation and evolution, clearly implying structural inheritance. In particular, the Colorado transfer system on the Argentina margin, marks a distinct along-margin boundary in the distribution and volume of breakup-related magmatism. Similarly, the Hope transfer system on the conjugate South Africa margin also marks a distinct along-margin transition from a zone of relative magnetic quiescence to a zone of prominent magnetic anomalies. Furthermore, the study indicates that the 'G-magnetic anomaly' along the South Africa margin probably defines the eastern limit of the continent-ocean transition (COT) rather than a discrete continentocean boundary (COB). Potential field plate reconstructions of the South Atlantic suggest conjugate margin asymmetry, characterized by a rather broad Argentine margin conjugate to a narrow South Africa margin. In detail, the Argentine margin is characterized by a sharp and relatively constant COT, whereas the COT along the conjugate South Africa margin is considerably wider. An along-strike tectonomagmatic asymmetry variation is also observed and is expressed by the northward increase in width of the COT on the South African margin. The study clearly shows that integration of regional seismic reflection and refraction profiles, potential field data and gravity modelling provide a powerful resource for testing and validating alternative seismic profile structural interpretations and plate tectonic reconstructions, as well as geodynamic models for lithospheric breakup and early drift.

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

“…The regional transects are based on the interpreted seismic reflection profiles, extracted bathymetry and gravity anomaly data, and on initial estimates of the Moho relief using both isostatic balancing and inverse gravity modeling; the latter method is described in detail by Blaich et al [2008Blaich et al [ , 2009. The conjugate crustal transects presented in this study comprise both new transects along the southeastern Brazil-Angola and southeastern Brazil-Namibia conjugate margins, and updated ones presented earlier (along northeastern Brazil-Gabon [Blaich et al, 2010] and along Argentine-South Africa [Blaich et al, 2009]). In this setting, two sets of representative crustal transects were compiled for each conjugate province along the central and south segments.…”

“…Alternative explanations for the "G magnetic anomaly" have been offered as the cause of this anomaly is controversial. For example, magnetic modeling across the Argentine [Hinz et al, 1999], Namibia [Bauer et al, 2000] and South Africa margins [Blaich et al, 2009] has indicated thick layers of extrusive basalts, identified as SDRs, as the causal source of the "G magnetic anomaly." Thus, the "G magnetic anomaly" coincides roughly with the landward edge of the SDRs [Hinz et al, 1999;Blaich et al, 2009].…”

“…The first oceanic crust in this segment was formed in Hauterivian time, between 134 and 132 Ma in the south and 132-130 Ma toward the north [Austin and Uchupi, 1982;Moulin et al, 2010]. Furthermore, this segment is characterized by SDRs and high-velocity/ high-density lower crust, which are associated with voluminous igneous activity during continental breakup, implying "magma-dominated" conjugate margins [Gladczenko et al, 1998;Hinz et al, 1999;Talwani and Abreu, 2000;Franke et al, 2007;Schnabel et al, 2008;Blaich et al, 2009;Hirsch et al, 2009].…”

Variability of geothermal gradient across two differently aged continental volcanic passive margins: The Southwest African and the Norwegian margins

“…About 130 Ma ago the continental lithosphere broke apart and generated the South Atlantic Ocean (Brown et al, 1995;Rabinowitz and LaBrecque, 1979;Nürnberg and 10 Müller, 1991;O'Connor and Duncan, 1990;Unternehr et al, 1988;Larson and Ladd, 1973;Talwani and Abreu, 2000;Blaich et al, 2009). These processes were followed by rifting and post-breakup cooling, resulting in several sedimentary basins formed along the margins of the South Atlantic (Séranne and Anka, 2005;Macdonald et al, 2003;Stewart et al, 2000).…”

Speculative petroleum systems of the Punta del Este Basin (offshore Uruguay)

“…Based on Moulin et al (2005), Franke et al (2007) and Soto et al (2011). Seafloor topography based on Becker et al (2009 Moulin et al 2005, Blaich et al 2009). …”