A comparison of melt depletion, thermal structure and metasomatism of proterozoic mantle lithosphere in the Namaqua-Natal and Rehoboth Provinces of Southern Africa
type: CreativeWork
description: Major and trace element mineral data are presented for garnet and spinel bearing peridotite xenolith suites from four Late Cretaceous kimberlites to the west of the Kaapvaal craton in two Proterozoic terranes: Hoedkop and Pofadder in the north-western Namaqua-Natal Province and Rietfontein and Louwrensia (Gibeon) in the Rehoboth Province. These are used to constrain and compare the thermal structure, the extents of melt extraction and metasomatism of the two mantle terranes with each other and with the Archaean Kaapvaal craton. Xenoliths from the Rietfontein and Pofadder localities have never previously been studied in detail. The information from this study is crucial for understanding the thermal and chemical evolution of Southern Africa's off-craton lithospheric mantle and the various processes (e.g., kimberlite and other magmatism, continental breakup) that have affected it. Mineral thermobarometry from a variety of independent thermobarometers indicates that, at pressures less than about 4 GPa, xenoliths from the Rehoboth Province (Louwrensia and Rietfontein) lie on or very near the Kaapvaal geotherm and between the 40mWm⁻² and 45mWm⁻² conductive geotherms, demonstrating that the lithospheric mantle in the Rehoboth Province was thermally similar to that of the Kaapvaal craton during the Late Cretaceous. In contrast, peridotites from the Namaqua-Natal Province (Hoedkop and Pofadder) in this pressure range fall at temperatures approximately 100°C - 200°C warmer than the Kaapvaal geotherm at any given depth and lie between the 45mWm⁻² and 50 mWm⁻² conduction geotherms, suggesting a Phanerozoic thermal disturbance in these regions. At higher pressures, samples from both terranes (represented only by Louwrensia and Hoedkop) fall above the Kaapvaal geotherm. However, these deeper, higher temperature peridotites are mostly sheared and indicate localised melt-rock interaction, therefore are not likely representative of the general thermal state of the lithosphere. Peri…
abstract: Major and trace element mineral data are presented for garnet and spinel bearing peridotite xenolith suites from four Late Cretaceous kimberlites to the west of the Kaapvaal craton in two Proterozoic terranes: Hoedkop and Pofadder in the north-western Namaqua-Natal Province and Rietfontein and Louwrensia (Gibeon) in the Rehoboth Province. These are used to constrain and compare the thermal structure, the extents of melt extraction and metasomatism of the two mantle terranes with each other and with the Archaean Kaapvaal craton. Xenoliths from the Rietfontein and Pofadder localities have never previously been studied in detail. The information from this study is crucial for understanding the thermal and chemical evolution of Southern Africa's off-craton lithospheric mantle and the various processes (e.g., kimberlite and other magmatism, continental breakup) that have affected it. Mineral thermobarometry from a variety of independent thermobarometers indicates that, at pressures less than about 4 GPa, xenoliths from the Rehoboth Province (Louwrensia and Rietfontein) lie on or very near the Kaapvaal geotherm and between the 40mWm⁻² and 45mWm⁻² conductive geotherms, demonstrating that the lithospheric mantle in the Rehoboth Province was thermally similar to that of the Kaapvaal craton during the Late Cretaceous. In contrast, peridotites from the Namaqua-Natal Province (Hoedkop and Pofadder) in this pressure range fall at temperatures approximately 100°C - 200°C warmer than the Kaapvaal geotherm at any given depth and lie between the 45mWm⁻² and 50 mWm⁻² conduction geotherms, suggesting a Phanerozoic thermal disturbance in these regions. At higher pressures, samples from both terranes (represented only by Louwrensia and Hoedkop) fall above the Kaapvaal geotherm. However, these deeper, higher temperature peridotites are mostly sheared and indicate localised melt-rock interaction, therefore are not likely representative of the general thermal state of the lithosphere. Peri…
author: Shiimi, Ellwin Taleni
language: eng
date published: 2017
date modified: 2026-07-22T22:22:44Z
provider: University of Cape Town
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Department of Geological Sciences

PropertyValue
property ID: Handle
value: http://hdl.handle.net/11427/25528