Mantle plumes, continental magmatism and asymmetry in the South Atlantic

Details Mantle plumes, continental magmatism and asymmetry in the South Atlantic Mantle plumes, continental magmatism and asymmetry in the South Atlantic

May 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994e%26psl.123..105g&link_type=abstract

Earth and Planetary Science Letters, Volume 123, Issue 1-3, p. 105-117.

Mathematics

Logic

11

Scientific paper

Melt production rates are estimated along the ocean tracks (Rio Grande Rise, Walvis Ridge) and the onshore Paraná/Etendeka Flood Basalt Province for the mantle plume currently associated with Tristan da Cunha in the South Atlantic. Assuming that the volcanic edifice is locally compensated with a thickened crust, the maximum oceanic rate (~ 0.3 km3 a -1) is similar to the value for the continental flood basalt, calculated using the surface volume of lava and a duration of 5 m.y. However, this latter estimate is conservative, and the appropriate rate is probably at least a factor of 5 higher.
The maximum mantle potential temperature for the ocean plume tracks is estimated to have been 1450-1540°C, assuming a dry peridotite source. Using a similar model, temperatures in excess of 1600°C are required to explain the observed magma volumes onshore. This is because there is no significant extension in the region where the oldest lavas occur. It is argued that the observed volumes of melt can be generated with small amounts of extension and with plume temperatures of < 1500°C if melting in the lithosphere is strongly influenced by the relative enrichment of volatiles. Moreover, the model predicts the inferred change to an asthenosphere-dominated source when significant extension occurs.
Recent geochonological data have shown that the continental volcanics are ~ 138 Ma in the northwest of the Paraná province and become progressively younger to the southeast. Oceanic melt production rates decrease by a factor of 3-5 towards the mid-ocean ridge/Tristan da Cunha. Intriguingly, melt production rates on the Rio Grande Rise vary to more than twice that of the Walvis Ridge for oceanic crust of similar age. This asymmetry is also seen in the continental regions, most obviously in the preserved volume of lava in the Paraná and Etendeka, but also in the topography of the underplated continental margin and the orientation of dykes and oblique extension structures. These observations reflect the combined roles of the plume temperature, lithospheric thickness, crustal tectonics and magma source region composition during the evolution of the South Atlantic over the last 150 Ma.

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