Mantle plume and rift-related volcanism during the evolution of the Rio Grande Rise

Patrick A Hoyer,Wolfram H Geissler,Stephan Homrighausen,John M O’Connor,Wilfried Jokat,Marcel Regelous,Karsten M Haase

doi:10.1038/s43247-022-00349-1

Abstract

The Rio Grande Rise in the western South Atlantic Ocean has been interpreted as either an oceanic plateau related to the Tristan-Gough mantle plume, or a fragment of detached continental crust. Here we present new major and trace element data for volcanic rocks from the western and eastern Rio Grande Rise and the adjacent Jean Charcot Seamount Chain. The eastern Rio Grande Rise and older parts of the western Rio Grande Rise are comprised of tholeiitic basalt with moderately enriched trace element compositions and likely formed above the Tristan-Gough mantle plume close to the southern Mid-Atlantic Ridge. Younger alkalic lavas from the western Rio Grande Rise and the Jean Charcot Seamount Chain were formed by lower degrees of melting beneath thicker lithosphere in an intraplate setting possibly during rifting of the plateau. There is no clear geochemical evidence that remnants of continental crust are present beneath the Rio Grande Rise.

Highlights

The Rio Grande Rise in the western South Atlantic Ocean has been interpreted as either an oceanic plateau related to the Tristan-Gough mantle plume, or a fragment of detached continental crust
We present major and trace element compositions for volcanic rocks drilled from Deep Sea Drilling Project (DSDP) Site 516 which serve as a reference for the local geochemical signature
The Eastern Rio Grande Rise (ERGR) samples were dredged from the northern shoulder of the Cruzeiro do Sul Rift (CdSR) from depths between 915 and 5266 m below sea level (Fig. 1b)

Summary

Results

Porphyritic basalts with phenocrysts of plagioclase and/or clinopyroxene embedded in a fine-grained matrix occur. Both aphanitic and porphyritic rocks contain numerous vesicles of variable size and shape, which are filled with calcite and/or brownish alteration material. In contrast to the lavas from the ERGR, those from the WRGR are more heterogeneous ranging from mafic to intermediate compositions Both aphanitic and porphyritic textures are common, whereby phenocrysts of plagioclase and/or clinopyroxene are the dominant mineral phases within the latter. The samples from the JCSC were dredged from steep slopes of distinct submarine volcanoes from depths between 1780 and 3335 m below sea level (Fig. 1b) The rocks display both aphanitic and porphyritic textures with phenocrysts of plagioclase, clinopyroxene and/or altered olivine. DSDP Site 516 ERGR JCSC 0.2 alkali rhyolite phonolite trachyte rhyolite + dacite trachyGough andesite tephriphonolite andesite + 0.02 basaltic andesite

Th Ta Ce Pr Sm Zr Gd Dy Y Tm Lu Nb La Pb Nd Hf Eu Tb Ho Er Yb

Discussion

Methods

Code availability