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Paleomagnetism and chronology of B-1 marginal sills of the Bushveld Complex from the eastern Kaapvaal Craton, South Africa

Wabo, H.; de Kock, M. O.; Klausen, M. B.; Söderlund, U. LU and Beukes, N. J. (2016) In GFF 138(1). p.133-151
Abstract

The Rustenburg Layered Suite (RLS) of the Bushveld Complex in South Africa is the largest mafic–ultramafic-layered complex on Earth. The RLS is associated with marginal sills that penetrate into the ~2.2 billion-year-old sedimentary strata of the Pretoria Group. These sills are in contact and share some geochemical similarities with different zones of RLS and are classified in terms of chemical composition, which suggests their derivation from distinct parental magma compositions (so-called B-1, B-2 and B-3 parental magmas). Existing paleomagnetic constraints for the Bushveld Complex originate from the upper Critical to Upper zones of the RLS, which are associated with B-2 and B-3 marginal sills. Geochemically, verified B-1 marginal... (More)

The Rustenburg Layered Suite (RLS) of the Bushveld Complex in South Africa is the largest mafic–ultramafic-layered complex on Earth. The RLS is associated with marginal sills that penetrate into the ~2.2 billion-year-old sedimentary strata of the Pretoria Group. These sills are in contact and share some geochemical similarities with different zones of RLS and are classified in terms of chemical composition, which suggests their derivation from distinct parental magma compositions (so-called B-1, B-2 and B-3 parental magmas). Existing paleomagnetic constraints for the Bushveld Complex originate from the upper Critical to Upper zones of the RLS, which are associated with B-2 and B-3 marginal sills. Geochemically, verified B-1 marginal intrusions are here used as a proxy for constraining the paleomagnetism and chronology of the Lower and lower Critical zones of the RLS. We identified a dual-polarity magnetic component with a paleopole (Latitude = 13.1°N, Longitude = 44.0°E, A95 = 14.3, N = 7) that is very similar to the established Bushveld Complex poles. We further report 2058.4 ± 1.3 Ma and 2058.1 ± 6 Ma U–Pb baddeleyite ages from B-1 sills that record opposite magnetic polarities. The ca. 2058 Ma ages are older than the 2054.89 ± 0.37 Ma age recently reported from throughout the RLS, but near identical to a previously reported ages of the Marginal Zone and from the upper Critical Zone. The ages could be interpreted as distinct pulses of magma emplacement separated in time by up to 4 million years (i.e., B-1 type magma pulse around ca. 2058 Ma and the B-2 and B-3 types magma pulses following closely on each other around ca. 2054 Ma), but is unlikely when petrological models are considered.

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organization
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Contribution to journal
publication status
published
subject
keywords
critical–main zone contact, geochemistry, geochronology, Kaapvaal Craton, paleomagnetism, Rustenburg Layered Suite
in
GFF
volume
138
issue
1
pages
19 pages
publisher
Geological Society of Sweden
external identifiers
  • scopus:84959103843
  • wos:000371812700010
ISSN
1103-5897
DOI
10.1080/11035897.2015.1099566
language
English
LU publication?
yes
id
df199456-0ddc-4a9e-b532-eb48142fbead
date added to LUP
2016-09-20 09:47:28
date last changed
2017-05-21 04:53:43
@article{df199456-0ddc-4a9e-b532-eb48142fbead,
  abstract     = {<p>The Rustenburg Layered Suite (RLS) of the Bushveld Complex in South Africa is the largest mafic–ultramafic-layered complex on Earth. The RLS is associated with marginal sills that penetrate into the ~2.2 billion-year-old sedimentary strata of the Pretoria Group. These sills are in contact and share some geochemical similarities with different zones of RLS and are classified in terms of chemical composition, which suggests their derivation from distinct parental magma compositions (so-called B-1, B-2 and B-3 parental magmas). Existing paleomagnetic constraints for the Bushveld Complex originate from the upper Critical to Upper zones of the RLS, which are associated with B-2 and B-3 marginal sills. Geochemically, verified B-1 marginal intrusions are here used as a proxy for constraining the paleomagnetism and chronology of the Lower and lower Critical zones of the RLS. We identified a dual-polarity magnetic component with a paleopole (Latitude = 13.1°N, Longitude = 44.0°E, A<sub>95</sub> = 14.3, N = 7) that is very similar to the established Bushveld Complex poles. We further report 2058.4 ± 1.3 Ma and 2058.1 ± 6 Ma U–Pb baddeleyite ages from B-1 sills that record opposite magnetic polarities. The ca. 2058 Ma ages are older than the 2054.89 ± 0.37 Ma age recently reported from throughout the RLS, but near identical to a previously reported ages of the Marginal Zone and from the upper Critical Zone. The ages could be interpreted as distinct pulses of magma emplacement separated in time by up to 4 million years (i.e., B-1 type magma pulse around ca. 2058 Ma and the B-2 and B-3 types magma pulses following closely on each other around ca. 2054 Ma), but is unlikely when petrological models are considered.</p>},
  author       = {Wabo, H. and de Kock, M. O. and Klausen, M. B. and Söderlund, U. and Beukes, N. J.},
  issn         = {1103-5897},
  keyword      = {critical–main zone contact,geochemistry,geochronology,Kaapvaal Craton,paleomagnetism,Rustenburg Layered Suite},
  language     = {eng},
  month        = {01},
  number       = {1},
  pages        = {133--151},
  publisher    = {Geological Society of Sweden},
  series       = {GFF},
  title        = {Paleomagnetism and chronology of B-1 marginal sills of the Bushveld Complex from the eastern Kaapvaal Craton, South Africa},
  url          = {http://dx.doi.org/10.1080/11035897.2015.1099566},
  volume       = {138},
  year         = {2016},
}