Mantle sources and magma evolution of the Rooiberg lavas, Bushveld Large Igneous Province, South Africa

Journal article
(Original article)


Publication Details

Author(s): Günther T, Haase K, Klemd R, Teschner C
Journal: Contributions To Mineralogy and Petrology
Publisher: SPRINGER
Publication year: 2018
Volume: 173
Journal issue: 6
ISSN: 0010-7999
Language: English


Abstract

We report a new whole-rock dataset of major and trace element abundances and Sr-87/Sr-86-Nd-143/Nd-144 isotope ratios for basaltic to rhyolitic lavas from the Rooiberg continental large igneous province (LIP). The formation of the Paleoproterozoic Rooiberg Group is contemporaneous with and spatially related to the layered intrusion of the Bushveld Complex, which stratigraphically separates the volcanic succession. Our new data confirm the presence of low- and high-Ti mafic and intermediate lavas (basaltic-andesitic compositions) with > 4 wt% MgO, as well as evolved rocks (andesitic-rhyolitic compositions), characterized by MgO contents of < 4 wt%. The high- and low-Ti basaltic lavas have different incompatible trace element ratios (e.g. (La/Sm)(N), Nb/Y and Ti/Y), indicating a different petrogenesis. MELTS modelling shows that the evolved lavas are formed by fractional crystallization from the mafic low-Ti lavas at low-to-moderate pressures ( 4 kbar). Primitive mantle-normalized trace element patterns of the Rooiberg rocks show an enrichment of large ion lithophile elements (LILE), rare-earth elements (REE) and pronounced negative anomalies of Nb, Ta, P, Ti and a positive Pb anomaly. Unaltered Rooiberg lavas have negative epsilon Nd-i (- 5.2 to - 9.4) and radiogenic epsilon Sr-i (6.6 to 105) ratios (at 2061 Ma). These data overlap with isotope and trace element compositions of purported parental melts to the Bushveld Complex, especially for the lower zone. We suggest that the Rooiberg suite originated from a source similar to the composition of the B1-magma suggested as parental to the Bushveld Lower Zone, or that the lavas represent eruptive successions of fractional crystallization products related to the ultramafic cumulates that were forming at depth. The Rooiberg magmas may have formed by 10-20% crustal assimilation by the fractionation of a very primitive mantle-derived melt within the upper crust of the Kaapvaal Craton. Alternatively, the magmas represent mixtures of melts from a primitive, sub-lithospheric mantle plume and an enriched sub-continental lithospheric mantle (SCLM) component with harzburgitic composition. Regardless of which of the two scenarios is invoked, the lavas of the Rooiberg Group show geochemical similarities to the Jurassic Karoo flood basalts, implying that the Archean lithosphere strongly affected both of these large-scale melting events.


FAU Authors / FAU Editors

Günther, Thomas
Lehrstuhl für Endogene Geodynamik
Haase, Karsten Prof. Dr.
Lehrstuhl für Endogene Geodynamik
Klemd, Reiner Prof. Dr.
Professur für Geochemie und Lagerstättenkunde


External institutions
Ludwig-Maximilians-Universität München


How to cite

APA:
Günther, T., Haase, K., Klemd, R., & Teschner, C. (2018). Mantle sources and magma evolution of the Rooiberg lavas, Bushveld Large Igneous Province, South Africa. Contributions To Mineralogy and Petrology, 173(6). https://dx.doi.org/10.1007/s00410-018-1477-y

MLA:
Günther, Thomas, et al. "Mantle sources and magma evolution of the Rooiberg lavas, Bushveld Large Igneous Province, South Africa." Contributions To Mineralogy and Petrology 173.6 (2018).

BibTeX: 

Last updated on 2019-08-02 at 07:38