A tale of two domes: Neogene to recent volcanism and dynamic uplift of northeast Brazil and southwest Africa

Klöcking, Marthe S. and Hoggard, M. J. and Rodríguez Tribaldos, Verónica and Richards, F. D. and Guimarães, A. R. and Maclennan, John and White, Nicky (2020) A tale of two domes: Neogene to recent volcanism and dynamic uplift of northeast Brazil and southwest Africa. Earth and Planetary Science Letters, 547. ISSN 0012 821X DOI do:10.1016/j.epsl.2020.116464

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Abstract

Topographic domes that are located far from active plate boundaries are often characterised by rapid, youthful uplift, contemporaneous mafic volcanism, radial drainage patterns, and positive long-wavelength gravity anomalies. There is increasing evidence that they are underlain by anomalously low sub-plate seismic velocities. Despite their well-known geomorphological expression, the origin of these epeirogenic features remains enigmatic and is much debated. Here, we investigate potential mechanisms of uplift by combining disparate observations from the Borborema and Angolan plateaux that straddle the Brazilian and southwest African margins, respectively. Oceanic residual depth measurements, drainage analysis, stratigraphic architecture, emergent marine terraces and basement denudation are used to constrain their regional uplift histories. In both cases, the bulk of topographic growth occurred within the last 30 Ma in the absence of significant tectonic deformation. We derive present-day mantle temperature and lithospheric thickness from Neogene to recent volcanic trace element compositions and upper mantle shear wave velocities. Volcanic geochemistry in northeast Brazil is compatible with decompression melting of warm asthenosphere and potentially a minor contribution from metasomatised lithospheric mantle. In Angola, melting of metasomatised lithosphere is most likely triggered by injection of small-degree asthenospheric-derived melts. We find no evidence for an asthenospheric thermal anomaly > 50 ◦ C above ambient beneath either region. Present-day lithospheric thickness is ∼ 100 km beneath Angola and could be as thin as 60 km in the Borborema Province. For Angola, thermobarometry on mantle xenocrysts from Cretaceous kimberlites is used to estimate palaeogeothermal gradients. Results indicate a pre- existing gradient in lithospheric thickness between the edge of the Congo craton and the centre of the Angolan dome at ∼ 120 Ma. This gradient likely steepened as a result of additional Neogene thinning by ∼ 30 ± 10 km beneath the centre of the dome. We conclude that the mechanism for Neogene epeirogenic uplift of the Borborema and Angolan domes is introduction of a small positive temperature anomaly into the asthenosphere that causes thermomechanical thinning of the overlying lithospheric mantle.

Item Type: Article
Uncontrolled Keywords: 2020AREP; IA76
Subjects: 02 - Geodynamics, Geophysics and Tectonics
Divisions: 02 - Geodynamics, Geophysics and Tectonics
08 - Green Open Access
12 - PhD
Journal or Publication Title: Earth and Planetary Science Letters
Volume: 547
Identification Number: do:10.1016/j.epsl.2020.116464
Depositing User: Sarah Humbert
Date Deposited: 09 Jul 2020 17:19
Last Modified: 21 Jan 2021 21:50
URI: http://eprints.esc.cam.ac.uk/id/eprint/4779

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