Geoid roughness and long-wavelength segmentation of the South Atlantic spreading ridge

Nature ◽  
1988 ◽  
Vol 333 (6170) ◽  
pp. 255-258 ◽  
Author(s):  
Dominique Gibert ◽  
Vincent Courtillot
2019 ◽  
Vol 7 (4) ◽  
pp. SH71-SH97 ◽  
Author(s):  
Kyle Reuber ◽  
Paul Mann ◽  
Jim Pindell

We have interpreted 27,550 km of deep-penetrating, 2D-seismic reflection profiles across the South Atlantic conjugate margins of Uruguay/Southern Brazil and Namibia. These reflection profiles reveal in unprecedented detail the lateral and cross-sectional, asymmetrical distribution of voluminous, postrift volcanic material erupted during the Barremian-Aptian (129–125 Ma) period of early seafloor spreading in the southernmost South Atlantic. Using this seismic grid, we mapped the 10–200 km wide, continental margin-parallel limits of seaward-dipping reflector (SDR) complexes — that are coincident with interpretations from previous workers using seismic refraction data from the South American and West African conjugate margins. Subaerially emplaced and tabular SDRs have rotated downward 20° in the direction of the mid-Atlantic spreading ridge and are up to 22 km thick near the limit of continental crust. The SDR package is wedge shaped and thins abruptly basinward toward the limit of oceanic crust where it transitions to normal, 6–8 km thick oceanic crust. We have developed a model for the conjugate rifted margins that combine diverging tectonic plates and northwesterly plate motion relative to a fixed mantle position of the mantle plume. Our model explains an approximately 30% higher volume of SDRs/igneous crust on the trailing Namibian margin than on the leading Brazilian margin during the syn- and postrift phases. Our model for volcanic margin asymmetry in the South Atlantic does not require a simple shear mechanism to produce the asymmetrical volcanic material distribution observed from our data and from previously published seismic refraction studies. Determining the basinward extent of the extended continental basement is crucial for understanding basin evolution and for hydrocarbon exploration. Although these conjugate margins have evolved asymmetrically, their proximity during the early postrift stage suggests a near-equivalent, early basin evolution and similar hydrocarbon potential. Understanding the tectonic and magnetic processes that produce these observed asymmetries is critical for understanding volcanic passive margin evolution.


2021 ◽  
Author(s):  
Anastasiia Tolstova ◽  
Eugene Dubinin ◽  
Andrey Groholsky

<p>The evolution of the Agulhas oceanic basin was influenced by the formation of the southern part of the Mid-Atlantic Ridge (MAR) as a result of the jump of the spreading axis. This sector of the South Atlantic began to open up as a result of the breakup of Gondwana about 135-140 million years ago. The process of opening was accompanied by kinematic rearrangements in the movement of the lithospheric plates. According to some evolutionary models, the jumps of the spreading axis in the area of the Agulhas basin occurred under the influence of hot spots. The hot spots of Shona, Bouvet, and Discovery played an important role in the evolutionary process of plate boundaries. </p><p>The previously active Agulhas spreading ridge is located in the central part of basin. From the east, the basin is framed by the Agulhas plateau, from the west is the Meteor rise. On the north the basin is bounded by the Agulhas transform fault, and on the south by the Southwest Indian Ridge.</p><p>Using the method of physical modeling, the formation of volcanic provinces that influenced the formation of the Agulhas basin was modeled.</p><p>The first series of experiments is devoted to the jump of the spreading axis of the Agulhas Ridge and the formation of the MAR and the Meteor rise. The purpose of the experiments was to determine the conditions for the formation of Meteor rise, located on the western edge of the Agulhas basin. Experiments have shown that the formation of this block may be due to the action of a hot spot, and the block itself may have a complex structure and contain inclusions of continental crust, which could have separated during the break of the Falkland Plateau and the jump of the spreading axis.</p><p>The second series of experiments was devoted to modeling the Agulhas ridge, located on the northern rim of the Agulhas basin. The ridge has a linear structure extending along the Agulhas-Falkland transform fault. The purpose of the experiments was to test the hypothesis of the magmatic origin of this ridge in the conditions of a transform fault with transtension under the thermal influence of the Shona and Discovery hot spot. Experiments have shown that a linear magmatic ridge similar to the Agulhas ridge is formed in the transtension condition. It is also possible that the formation of the ridge may be associated with a change in the speed and direction of spreading.</p><p>The Antarctic sector of the South Atlantic, and in particular the Agulhas Basin, has a complex history of evolution. This is due to the displacement of the three major Gondwanan continents, and the activity of hot spots in this region and kinematic rearrangements, and the spatiotemporal migration of the Bouve triple junction with a complex stress field, the existence of the continental Falkland Plateau, and other factors.</p><p>The geological environment of the Agulhas basin is characterized by objects and structures that allow us to approach the history of the evolution of this complex area.</p>


2016 ◽  
Vol 31 (2) ◽  
pp. 19-36
Author(s):  
Paulo Fagundes Visentini ◽  
Analúcia Danilevicz Pereira

The creation of the Zone of Peace and Cooperation of the South Atlantic (ZPCSA) in 1986 and the Gulf of Guinea Commission (GGC) in 2001 was about changes in the distribution of world power. This article argues that though they emerged at different times, their strategic orientation converges in a number of areas related to the significant interests in the South Atlantic as an area of stability in the region to be marked by strong political, economic and military ties. They also converge on the ideal for development, security and greater projection of power and influence in international affairs. The South Atlantic being a route of passage and trade, as a means of access and flow of energy products, the region became a site for new calculations of regional strategic powers about world affairs. The article also argues that ZPCSA and GGC are therefore crucial for the regional order and the development of higher capacities for cooperation on strategic issues. The actual point of convergence extends to ensuring the sovereignty through dialogue between the states in the region that are involved.


2019 ◽  
Author(s):  
Hamed D. Ibrahim

North and South Atlantic lateral volume exchange is a key component of the Atlantic Meridional Overturning Circulation (AMOC) embedded in Earth’s climate. Northward AMOC heat transport within this exchange mitigates the large heat loss to the atmosphere in the northern North Atlantic. Because of inadequate climate data, observational basin-scale studies of net interbasin exchange between the North and South Atlantic have been limited. Here ten independent climate datasets, five satellite-derived and five analyses, are synthesized to show that North and South Atlantic climatological net lateral volume exchange is partitioned into two seasonal regimes. From late-May to late-November, net lateral volume flux is from the North to the South Atlantic; whereas from late-November to late-May, net lateral volume flux is from the South to the North Atlantic. This climatological characterization offers a framework for assessing seasonal variations in these basins and provides a constraint for climate models that simulate AMOC dynamics.


2014 ◽  
Vol 31 (2) ◽  
Author(s):  
Mariela Gabioux ◽  
Vladimir Santos da Costa ◽  
Joao Marcos Azevedo Correia de Souza ◽  
Bruna Faria de Oliveira ◽  
Afonso De Moraes Paiva

Results of the basic model configuration of the REMO project, a Brazilian approach towards operational oceanography, are discussed. This configuration consists basically of a high-resolution eddy-resolving, 1/12 degree model for the Metarea V, nested in a medium-resolution eddy-permitting, 1/4 degree model of the Atlantic Ocean. These simulations performed with HYCOM model, aim for: a) creating a basic set-up for implementation of assimilation techniques leading to ocean prediction; b) the development of hydrodynamics bases for environmental studies; c) providing boundary conditions for regional domains with increased resolution. The 1/4 degree simulation was able to simulate realistic equatorial and south Atlantic large scale circulation, both the wind-driven and the thermohaline components. The high resolution simulation was able to generate mesoscale and represent well the variability pattern within the Metarea V domain. The BC mean transport values were well represented in the southwestern region (between Vitória-Trinidade sea mount and 29S), in contrast to higher latitudes (higher than 30S) where it was slightly underestimated. Important issues for the simulation of the South Atlantic with high resolution are discussed, like the ideal place for boundaries, improvements in the bathymetric representation and the control of bias SST, by the introducing of a small surface relaxation. In order to make a preliminary assessment of the model behavior when submitted to data assimilation, the Cooper & Haines (1996) method was used to extrapolate SSH anomalies fields to deeper layers every 7 days, with encouraging results.


2020 ◽  
Author(s):  
Shannon J. Haynes ◽  
◽  
Kenneth G. MacLeod ◽  
Jean-Baptiste Ladant ◽  
Christopher J. Poulsen ◽  
...  

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