Petrology and Geochemistry of Basaltic Rocks from Rio Grande Rise, South Atlantic: Deep Sea Drilling Project Leg 72, Hole 516F

Thompson, Geoffrey; Humphris, Susan E.; Schilling, Jean-Guy

doi:10.2973/dsdp.proc.72.115.1983

Cited by 13 publications

(8 citation statements)

References 16 publications

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“…1). Rocks drilled along this site and over the main platform, consist of tholeiitic basalts, presenting a trace-element chemistry characteristic of transitional mid-ocean ridge basalts (Thompson et al, 1983). Nevertheless, the guyots and seamounts are composed of Eocene age alkaline basaltic rocks typical of oceanic islands (Fodor et al, 1977).…”

Section: Basement Characteristics Of the Rgrmentioning

confidence: 95%

Basement structures over Rio Grande Rise from gravity inversion

Constantino

Hackspacher

Souza

et al. 2017

Journal of South American Earth Sciences

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The basement depth in the Rio Grande Rise (RGR), South Atlantic, is estimated from combining gravity data obtained from satellite altimetry, marine surveys, bathymetry, sediment thickness and crustal thickness information. We formulate a crustal model of the region by inverse gravity modeling. The effect of the sediment layer is evaluated using the global sediment thickness model of National Oceanic and Atmospheric Administration (NOAA) and fitting the sediment compaction model to observed density values from Deep Sea Drilling Project (DSDP) reports. The Global Relief Model ETOPO1 and constraining data from seismic interpretation on crustal thickness are integrated in the inversion process. The modeled Moho depth values vary between 6 and 27 km over the area, being thicker under the RGR and also in the direction of São Paulo Plateau. The inversion for the gravity-equivalent basement topography is applied to gravity residual data, which is free from the gravity effect of sediments and from the gravity effect of the estimated Moho interface. We find several short-wavelengths structures not present in the bathymetry data. Our model shows a rift crossing the entire Rio Grande Rise deeper than previously presented in literature, with depths up to 5 km in the East Rio Grande Rise (ERGR) and deeper in the West Rio Grande Rise (WRGR), reaching 6.4 km. An interesting NS structure that goes from 34 S and extends through de São Paulo Ridge may be related to the South Atlantic Opening and could reveal an extinct spreading center.

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Section: Basement Characteristics Of the Rgrmentioning

confidence: 95%

Basement structures over Rio Grande Rise from gravity inversion

Constantino

Hackspacher

Souza

et al. 2017

Journal of South American Earth Sciences

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“…From anomaly 34 time, spreading anomalies, which were forming at the time of each particular reconstruction, were rotated, along with the Walvis Ridge bathymetry (and African continent), to their respective predrift positions. An appropriate rotation parameter was calculated for each reconstruction from the Africa/hot spots finite poles given in Table 3 Thompson, 1982Thompson, , 1983Richardson et al, 1982Richardson et al, , 1984Thompson and Humphris, 1984;Thompson et al, 1983;Humphris et al, 1985].…”

Section: Spatial Rei•at!()nship Be'i'wi:t-n I'!ie Spreading Axis and mentioning

confidence: 99%

“…The elements Zr and Nb (and also Y and the REE elements) are of particular use in the investigation of magma source regions, as these elements are highly incompatible and their ratio will be influenced only slightly by variations in partial melting and crystal fractionation [Erlank and Kable, 1976;Sun et al, 1979;Pearce and Norry, 1979]. They are also among the trace elements which are most highly resistant to mobilization by seawater alteration [Thompson, 1973] Thompson, 1982Thompson, , 1983, DSDP 530 and CH18 and 19 [Humphris and Thompson, 1983] Thompson, 1983]. This points to 527 and 528 basalts having formed at a hot spot-fed spreading ridge, as was the case for 530 basalts, which had formed at an earlier time [Humphris and Thompson, 1983].…”

Section: Spatial Rei•at!()nship Be'i'wi:t-n I'!ie Spreading Axis and mentioning

confidence: 99%

“…They are also among the trace elements which are most highly resistant to mobilization by seawater alteration [Thompson, 1973] Thompson, 1982Thompson, , 1983, DSDP 530 and CH18 and 19 [Humphris and Thompson, 1983] Thompson, 1983]. This points to 527 and 528 basalts having formed at a hot spot-fed spreading ridge, as was the case for 530 basalts, which had formed at an earlier time [Humphris and Thompson, 1983]. A similar pattern of binary mixing between "enriched" (Tristan) and "depleted" Those features which formed in an intraplate setting (i.e., old, thick seafloor) are supported by the elastic stresses produced by the bending of the plate; as the plate distributes the compensating masses over a wide area, the gravity signature measured directly over the load will be large.…”

Section: Spatial Rei•at!()nship Be'i'wi:t-n I'!ie Spreading Axis and mentioning

confidence: 99%

See 1 more Smart Citation

Evolution of the Walvis Ridge‐Rio Grande Rise Hot Spot System: Implications for African and South American Plate motions over plumes

O’Connor¹,

Duncan²

1990

J. Geophys. Res.

376

212

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Crystallization ages of volcanic rocks, dredged or drilled from the Walvis Ridge (ten sites) and the Rio Grande Rise (one site), have been determined by the 40Ar/39Ar incremental heating technique. The fundamentally age‐progressive distribution of these basement ages suggests a common hot spot source for volcanism on the island of Tristan da Cunha, along the Walvis Ridge and Rio Grande Rise, and for the formation of the continental flood basalts located in Namibia (Africa) and Brazil (South America). The Walvis Ridge‐Rio Grande Rise volcanic system evolved along a section of the South Atlantic spreading‐axis, as the African and South American plates migrated apart, astride, or in close proximity to, an upwelling plume. Reconstructions of the spatial relationship between the spreading‐axis, the Tristan hot spot, and the evolving Walvis Ridge‐Rio Grande Rise volcanic feature show that, at about 70 Ma, the spreading‐axis began to migrate westward, away from the hot spot. The resulting transition to intraplate hot spot volcanism along the Walvis Ridge (and associated termination of Rio Grande Rise formation) also involved a northward migration of previously formed African seafloor over the hot spot. Rotation parameters for African motion over fixed hot spots (i.e., absolute motion) have been recalculated such that the predicted trail of the Tristan hot spot agrees with the distribution of radiometric and fossil basement ages along the Walvis Ridge. African absolute motion has been extended to the South and North American plates, by the addition of relative motion reconstruction poles.

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“…Fig. 3 show the demarca tion which is evident between CFB and MORB (Sun et al, 1979); however, alkalic basaltic compositions from Hawaii (Chen and Frey, 1983;Frey and Clague, 1983), the Rio Grande Rise (Thompson et al, 1983) suggest chemical overlaps of tholeiitic CFB with alkalic oceanic basalts of aseismic ridges, especially at higher total REE contents. At lower REE abundances SG and other CFB lavas maintain a more de finitive segregation from the basalts of aseismic (Anders and Ebihara, 1982).…”

Section: Resultsmentioning

confidence: 97%

Trace element and Sr-Nd isotopic constraints on the compositions of lithospheric primary sources of Serra Geral continental flood basalts, southern Brazil.

et al. 1986

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Multi-element abundances in twenty-four samples from the Serra Geral continental flood basalt system (Parana Basin) were determined by INAA to assess the trace element signature of primary magmatric sources. Isotopic Sr and Nd data were obtained on a 24-sample composite and three individual samples of the suite to constrain the influences of older enriched material. Twenty basaltic samples have enriched LILE commensurate with most continental tholeiites and , display fractionated REE patterns similar to those in the Columbia River Group and other flood basalt provinces. The mafic units exhibit low-moderate Ti, variable V, Cr and Ni and relatively uniform Co and Sc . abundances. Four intermediate to silicic units exhibit higher overall incompatible element abundances, strongly fractionated patterns and depletions of compatible elements consistent with derivation by fractionation of basaltic parents. Isotopic data for two basalts and the composite analysis indicate 87Sr/86Sr = 0.7090 to 0.7105 and eNd = -6.6 to -6.9 requiring magma genesis in an evolved LILE-enriched upper mantle or lower crust. A silicic sample has 87Sr/86Sr = 0.7219 and eNd = -9.2 reflecting a stronger crustal influence.Chemical comparisons within the basaltic members allow the delineation of ten least-evolved composi tions having a regionally characteristic trace element pattern and two additional samples (of one flow) re presenting a second, less fractionated pattern. Trace element models for both types predict magma segrega tion from lower lithospheric sources having relatively uniform enrichments of incompatible elements via regional metasomatism. The most viable scenarios for basalt magma production require either enriched mantle partial-melt liquids, some of which comingle with crustal components, or partial melting of ultra mafic, LILE-enriched lower crust. Either process requires a zone of primary magma extraction in a region where initially uniform source enrichments act independently of subsequent contamination, probably in the crust/mantle transition zone.

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Petrology and Geochemistry of Basaltic Rocks from Rio Grande Rise, South Atlantic: Deep Sea Drilling Project Leg 72, Hole 516F

Cited by 13 publications

References 16 publications

Basement structures over Rio Grande Rise from gravity inversion

Basement structures over Rio Grande Rise from gravity inversion

Evolution of the Walvis Ridge‐Rio Grande Rise Hot Spot System: Implications for African and South American Plate motions over plumes

Trace element and Sr-Nd isotopic constraints on the compositions of lithospheric primary sources of Serra Geral continental flood basalts, southern Brazil.

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