Geochemistry and tectonic significance of the Mesoproterozoic Kgwebe metavolcanic rocks in northwest Botswana; implications for the evolution of the Kibaran Namaqua-Natal Belt

Saved in:
Online Access: Get full text
doi: 10.1017/S001675689800123X
Authors:Kampunzu, A. B.; Akanyang, P.; Mapeo, R. B. M.; Modie, B. N.; Wendorff, M.
Author Affiliations:Primary:
University of Botswana, Gaborone, Botswana
Geological Survey of Botswana, Botswana
Volume Title:Geological Magazine
Source:Geological Magazine, 135(5), p.669-683. Publisher: Cambridge University Press, London, United Kingdom. ISSN: 0016-7568
Publication Date:1998
Note:In English. 85 refs.; illus., incl. strat. col., 2 tables, geol. sketch map
Summary:The late Kibaran (∼ 1100 m.y.) Kgwebe metavolcanic rocks exposed in the NW of Botswana, represent a bimodal suite of within-plate, low-Ti-P continental tholeiites, and post-orogenic within-plate high-K rhyolites. The Kgwebe mafic rocks are characterized by low Ce/Pb (< 10) and high La/Nb values (average ∼ 2, maximum 4), whilst MORB-normalized spidergrams show enrichment in mobile elements (Sr, K, Rb and Ba) and negative Nb anomalies, implying origination from a mantle enriched during a previous subduction event. The Kgwebe metarhyolites have Y > 60 ppm, Sr/Y < 1, Rb/Th > 20 and high K contents, and therefore cannot be produced by either melting of sediments or of a subducting slab, but rather represent felsic magmas produced by melting of Mesoproterozoic (Kibaran) calc-alkaline rocks underplated in the middle and/or lower crust. The Kgwebe bimodal metavolcanic rocks pre-date the Neoproterozoic Ghanzi group rocks which are correlated with the lower Damara sequence. Chemical composition and field relations suggest that these metavolcanic rocks were produced during extensional collapse of the thickened crust, produced during the Kibaran collision in the Namaqua-Natal belt of SW Africa. [J.F.]
Subsections:Igneous petrology
Subjects:Acidic composition; Basalts; Emplacement; Extension; Igneous rocks; Kibaran Orogeny; Mafic composition; Major elements; Metamorphic rocks; Metavolcanic rocks; Mid-ocean ridge basalts; Plate collision; Precambrian; Proterozoic; Rhyolites; Subduction; Tholeiite; Trace elements; Upper Precambrian; Volcanic rocks; Africa; Botswana; Kaapvaal Craton; Southern Africa; Ghanzi-Chobe Belt; Kgwebe Botswana; Namaqua-Natal Belt
Abstract Numbers:99M/3157
Record ID:1999006832
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
Tags: Add Tag
No Tags, Be the first to tag this record!
Be the first to leave a comment!
You must be logged in first