Advanced

Constraining the chronology of the mashishing dykes from the eastern kaapvaal craton in South Africa

Wabo, H.; Humbert, F.; de Kock, M. O.; Belyanin, G.; Söderlund, U. LU ; Maré, L. P. and Beukes, N. J. (2019) In Springer Geology p.215-261
Abstract

The present study focuses on NNE-trending dykes (sites LDA to LDJ) that occur near Mashishing in the eastern Kaapvaal craton. The Mashishing dykes were previously considered to be coeval and regarded as the extension of the 1.875–1.835 Ga Black Hills dyke swarm into the sedimentary rocks of the Pretoria Group. Thin sections exhibit well-preserved igneous textures, with primary minerals (e.g., hornblende, clinopyroxene, plagioclase) extensively altered to secondary minerals in most cases. Our dykes can be petrographically grouped as pyroxenite (LDB and LDC), dolerite (LDH) and diorite (remainder of samples). REE and multi-element profiles of pyroxenites and two of the diorites (LDI and LDJ) suggest a common origin of the four dykes, but... (More)

The present study focuses on NNE-trending dykes (sites LDA to LDJ) that occur near Mashishing in the eastern Kaapvaal craton. The Mashishing dykes were previously considered to be coeval and regarded as the extension of the 1.875–1.835 Ga Black Hills dyke swarm into the sedimentary rocks of the Pretoria Group. Thin sections exhibit well-preserved igneous textures, with primary minerals (e.g., hornblende, clinopyroxene, plagioclase) extensively altered to secondary minerals in most cases. Our dykes can be petrographically grouped as pyroxenite (LDB and LDC), dolerite (LDH) and diorite (remainder of samples). REE and multi-element profiles of pyroxenites and two of the diorites (LDI and LDJ) suggest a common origin of the four dykes, but show no similarity with known mafic units of the Kaapvaal craton. An age estimate between 2208 and 2276 Ma for dyke LDB, obtained from two overlapping amphibole 40Ar/39Ar plateau results, indicates that these four dykes predates the ~2.05 Ga Bushveld event. The six remaining dykes have similar chemistry to either the ~2.06 Ga Dullstroom Lavas (LDG), the 1.875–1.835 Ga Black Hills dyke swarm (LDH) or the ~1.11 Ga Umkondo dolerites (LDA, LDD, LDE and LDF). An U–Pb baddeleyite date of 1867 ± 10 Ma for dyke LDH confirms it as a member of the Black Hills dyke swarm. Demagnetization of eighty-three specimens reveals five stable magnetizations carried by titanomagnetite. Two of these are regarded as magnetic overprints while three magnetizations are likely representative of primary remanences. The corresponding virtual geomagnetic poles (Lat.−26.84°N, Long. 31.66°E; Lat. 26.07°N, Long. 11.01°E, and Lat. 55.84°N, Long. 65.02°E) resemble those from the ~2.23 Ga Hekpoort Formation, the ~1.88–1.83 Ga post-Waterberg intrusions, and the ~1.11 Ga Umkondo dolerites respectively. The above results suggest that the Mashishing dykes, despite similar trends, constitute swarms of different generations.

(Less)
Please use this url to cite or link to this publication:
author
organization
publishing date
type
Chapter in Book/Report/Conference proceeding
publication status
published
subject
keywords
Geochemistry, Geochronology, Kaapvaal craton, NNE-dyke, Paleomagnetism
host publication
Springer Geology
series title
Springer Geology
pages
47 pages
publisher
Springer
external identifiers
  • scopus:85067957805
ISSN
2197-9553
2197-9545
DOI
10.1007/978-981-13-1666-1_6
language
English
LU publication?
yes
id
a8880fa1-fb83-435a-b86b-6043037227c6
date added to LUP
2019-07-09 14:46:35
date last changed
2019-07-30 05:06:49
@inbook{a8880fa1-fb83-435a-b86b-6043037227c6,
  abstract     = {<p>The present study focuses on NNE-trending dykes (sites LDA to LDJ) that occur near Mashishing in the eastern Kaapvaal craton. The Mashishing dykes were previously considered to be coeval and regarded as the extension of the 1.875–1.835 Ga Black Hills dyke swarm into the sedimentary rocks of the Pretoria Group. Thin sections exhibit well-preserved igneous textures, with primary minerals (e.g., hornblende, clinopyroxene, plagioclase) extensively altered to secondary minerals in most cases. Our dykes can be petrographically grouped as pyroxenite (LDB and LDC), dolerite (LDH) and diorite (remainder of samples). REE and multi-element profiles of pyroxenites and two of the diorites (LDI and LDJ) suggest a common origin of the four dykes, but show no similarity with known mafic units of the Kaapvaal craton. An age estimate between 2208 and 2276 Ma for dyke LDB, obtained from two overlapping amphibole <sup>40</sup>Ar/<sup>39</sup>Ar plateau results, indicates that these four dykes predates the ~2.05 Ga Bushveld event. The six remaining dykes have similar chemistry to either the ~2.06 Ga Dullstroom Lavas (LDG), the 1.875–1.835 Ga Black Hills dyke swarm (LDH) or the ~1.11 Ga Umkondo dolerites (LDA, LDD, LDE and LDF). An U–Pb baddeleyite date of 1867 ± 10 Ma for dyke LDH confirms it as a member of the Black Hills dyke swarm. Demagnetization of eighty-three specimens reveals five stable magnetizations carried by titanomagnetite. Two of these are regarded as magnetic overprints while three magnetizations are likely representative of primary remanences. The corresponding virtual geomagnetic poles (Lat.−26.84°N, Long. 31.66°E; Lat. 26.07°N, Long. 11.01°E, and Lat. 55.84°N, Long. 65.02°E) resemble those from the ~2.23 Ga Hekpoort Formation, the ~1.88–1.83 Ga post-Waterberg intrusions, and the ~1.11 Ga Umkondo dolerites respectively. The above results suggest that the Mashishing dykes, despite similar trends, constitute swarms of different generations.</p>},
  author       = {Wabo, H. and Humbert, F. and de Kock, M. O. and Belyanin, G. and Söderlund, U. and Maré, L. P. and Beukes, N. J.},
  issn         = {2197-9553},
  keyword      = {Geochemistry,Geochronology,Kaapvaal craton,NNE-dyke,Paleomagnetism},
  language     = {eng},
  pages        = {215--261},
  publisher    = {Springer},
  series       = {Springer Geology},
  title        = {Constraining the chronology of the mashishing dykes from the eastern kaapvaal craton in South Africa},
  url          = {http://dx.doi.org/10.1007/978-981-13-1666-1_6},
  year         = {2019},
}