Geological and geophysical interpretation of the Rio Grande Rise, south-eastern Brazilian margin: extensional tectonics and rifting of continental and oceanic crusts

Mohriak, Webster Ueipass; Nóbrega, Monisa Martins; Odegard, Mark E.; Gomes, Benedito Souza; Dickson, William

doi:10.1144/1354-079309-910

Cited by 114 publications

(88 citation statements)

References 32 publications

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“…Remnants of abandoned ridges in this location have been interpreted from gravity anomalies at the 'Abimael Ridge' (Fig. 1, Mohriak et al, 2010;Sandwell et al, 2014) and from bathymetric and gravity features at the Rio Grande Rise (Pérez-Díaz and Eagles, 2014). Successive jumps transferred the spreading centre to locations nearer to the African coast, eventually detaching the SPP from the African plate (Fig.…”

Section: Geodynamic Frameworkmentioning

confidence: 87%

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Interaction between a hotspot and a fracture zone: The crustal structure of Walvis Ridge at 6° E

2017

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A B S T R A C TThe Walvis Ridge is one of the major hotspot trails in the South Atlantic and a classical example for volcanic island chains. Two models compete about the origin of the ridge: It is either the result of a deep mantle plume or active fracture zones above mantle inhomogeneities. Among other things crustal information is needed to constrain the models. Here, we provide such constraint with a 480 km long P-wave velocity model of the deep crustal structure of the eastern Walvis Ridge at 6• E. According to our data the Walvis Ridge stretches across the Florianopolis Fracture Zone into the Angola Basin. Here, we observe a basement high and thick basaltic layers covering the oceanic crust and the fracture zone. We found two crustal roots along the profile: one is located beneath the ridge crest, the other one beneath the northern basement high in the Angola Basin. The crustal thickness reaches 18 km and 12 km and the lower crustal velocities are 7.2 km/s and 7.4 km/s, respectively. The bathymetric expression of the ridge along the profile is less pronounced than closer to shore, which is mainly attributable to the absence of a thick layer of volcanic debris, rather than to reduced crustal thickness below the basement surface. Therefore, this part of the ridge was never or only briefly subaerially exposed. The crustal structure suggests that the ridge and the fracture zone formed independently of each other. The oceanic crust north of the fracture zone, which is buried underneath the basalt layer, is younger than the reconstructed age of hotspot volcanism of the Walvis Ridge. We interpret these structures north of the fracture zone to be at least partly a product of late stage volcanism.

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Section: Geodynamic Frameworkmentioning

confidence: 87%

“…During initial opening, the Sao Paolo Plateau (SPP) was still attached to South Africa and seafloor spreading north of Walvis Ridge was focussed at a mid-ocean ridge lying west of it (Mohriak et al, 2010). Remnants of abandoned ridges in this location have been interpreted from gravity anomalies at the 'Abimael Ridge' (Fig.…”

Section: Geodynamic Frameworkmentioning

confidence: 99%

Interaction between a hotspot and a fracture zone: The crustal structure of Walvis Ridge at 6° E

2017

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“…The load is applied atop very thin crust (Mohriak et al, 2010;Assumpção et al, 2011;Zalán et al, 2011;Mohriak & Leroy, 2012). A diffuse belt of seismicity occurs near or beyond the Cretaceous hinge line (Fig.…”

Section: The Model Abroadmentioning

confidence: 99%

Some remarks on the earthquakes of Fennoscandia: A conceptual seismological model drawn from the perspective of hyperextension

Redfield¹,

Osmundsen²

2015

NJG

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To a first order, patterns of Fennoscandia's seismicity reflect the benchmark domain boundaries of its Mesozoic rifted margin. Three distinct belts of earthquakes strike sub-parallel to the generalized line of breakup. The outermost seismic belt (SB1) marks the Taper Break (TB), or the zone of flexural coupling/decoupling between the distal (seaward) and proximal/necking (landward) domains. A coastal belt (SB2) follows the Innermost Limit of Extension, defined as the onset of 39 km-thick crystalline continental crust. An interior belt (SB3) follows the Hinterland Break in Slope, or the landward limit of the Scandinavian rifted margin. Between each belt, large portions of the necking, proximal, and hinterland domains are seismically quiescent. Evaluation of the 'Cumulative Seismic Moment' (CSM w ) per unit area indicates that the release of seismic energy is asymmetric. Although some of Fennoscandia's largest seismic events occur in the dominantly Proterozoic to Archean lithosphere of the eastern craton, 80% of Fennoscandian CSM w maps to the domain boundaries of the western rifted margin. CSM w energy tends to be highest at the TB and decreases system atically towards the continental interior.As proposed by many previous studies, a first-order spatial correlation between Scandinavia's offshore earthquake belt and voluminous, geo logically rapid, sedimentary loading during the Neogene period is evident. However, the presence of thinned, faulted crystalline basement is also a very important factor behind Scandinavia's offshore seismicity. Where the Neogene deposits are at their thickest the underlying crust is dominantly oceanic; CSM w is lower per unit area there than where lesser Plio-Pleistocene loading impacts continental crust that was fully prepared by Mesozoic necking and hyperextension. CSM w data suggest that the 'strength' of the TB and the continental margin's distal domain is significantly less than that of relatively young (ca. 54 Ma) oceanic lithosphere. Our data imply that ridge push does not contribute significantly to Fennoscandia's seismicity. Rather, we find that thin-plate bending stresses stemming from offshore depositional loading conspire with unbuttressed Gravitational Potential Energy (GPE), onshore erosion, and post-glacial isostatic rebound to generate Fennoscandia's earthquakes.We present a conceptual seismological model for Fennoscadia that is consistent with modern hypotheses of extended margin evolution, including post-breakup reactivation by footwall uplift in regions adjacent to sharp crustal taper. Illustrated by simple concepts of elastic thin-plate theory, the model honors our conclusion that Fennoscandian seismicity is principally the product of locally derived stress fields and that far field stress from the oceanic domain is unlikely to penetrate deeply into a hyperextended continental margin. It predicts the locations of the observed seismic belts and seismic gaps with the mathematics of thin-plate bending. It describes how the outer seismic belt will remain localized in the...

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“…5a and 6. Analyzing the basement structure, it is possible to see a set of volcanic chains, related to the Rio Grande Rise (RGR), Florianopolis Fracture Zone (FFZ) (Mohriak et al 2002) and Cruzeiro do Sul lineament (CSL) (Mohriak et al 2010). A valley at approximately 40 ı longitude, between latitude 29 ı and 31 ı , trending northwards, can be associated to the Vema channel (VC) (Mohriak et al 2002).…”

Section: Resultsmentioning

confidence: 99%

Basement Structure of the Santos Basin from Gravity Data

Constantino

Molina

2014

Gravity, Geoid and Height Systems

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The ocean basement represents the tectonic situation of a specific area and its knowledge is crucial in studies aimed at exploring the seabed. Due to the high sedimentation rate, especially in ocean basins, the topography of the basement is masked and its structures can be buried, inaccessible to direct observation. This paper aims to estimate the depth of the basement in the region of the Santos Basin in Brazil from a combined analysis of gravity data obtained from satellite altimetry and marine gravimetry, bathymetric data and sediment thickness. In the first step of the work the gravity effect of sediments in Santos Basin was calculated and the Crustal Mantle Interface (CMI) was modeled from constrained gravity inversion. Next, the reliability of the models so obtained was tested by flexural analysis. The flexural and gravity CMI proved to be in agreement. The gravity effect of the CMI and the gravity effect of the sediments were then calculated and subtracted from the original Bouguer anomaly. The residual field thus obtained, which is assumed to represent the topographical features of the basement, was inverted in the last step of the work, providing information that shows a basement with features of up to 700 m that appear to be in agreement with tectonic features previously discussed, such as the Avedis volcanic chain. The depth of the basement estimated during this study showed values ranging from 1,500 to 10,500 m, and the deepest region is consistent with the Cabo Frio Fault.

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Geological and geophysical interpretation of the Rio Grande Rise, south-eastern Brazilian margin: extensional tectonics and rifting of continental and oceanic crusts

Cited by 114 publications

References 32 publications

Interaction between a hotspot and a fracture zone: The crustal structure of Walvis Ridge at 6° E

Interaction between a hotspot and a fracture zone: The crustal structure of Walvis Ridge at 6° E

Some remarks on the earthquakes of Fennoscandia: A conceptual seismological model drawn from the perspective of hyperextension

Basement Structure of the Santos Basin from Gravity Data

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