Advanced

Paleomagnetism and U–Pb geochronology of the Black Range dykes, Pilbara Craton, Western Australia : a Neoarchean crossing of the polar circle

Evans, D. A. D.; Smirnov, Aleksey V. and Gumsley, A. P. LU (2017) In Australian Journal of Earth Sciences 64(2). p.225-237
Abstract

We report a new paleomagnetic pole for the Black Range Dolerite Suite of dykes, Pilbara craton, Western Australia. We replicate previous paleomagnetic results from the Black Range Dyke itself, but find that its magnetic remanence direction lies at the margin of a distribution of nine dyke mean directions. We also report two new minimum ID-TIMS 207Pb/206Pb baddeleyite ages from the swarm, one from the Black Range Dyke itself (>2769 ± 1 Ma) and another from a parallel dyke whose remanence direction lies near the centre of the dataset (>2764 ± 3 Ma). Both ages are slightly younger than a previous combined SHRIMP 207Pb/206Pb baddeleyite weighted mean date from the same swarm, with slight... (More)

We report a new paleomagnetic pole for the Black Range Dolerite Suite of dykes, Pilbara craton, Western Australia. We replicate previous paleomagnetic results from the Black Range Dyke itself, but find that its magnetic remanence direction lies at the margin of a distribution of nine dyke mean directions. We also report two new minimum ID-TIMS 207Pb/206Pb baddeleyite ages from the swarm, one from the Black Range Dyke itself (>2769 ± 1 Ma) and another from a parallel dyke whose remanence direction lies near the centre of the dataset (>2764 ± 3 Ma). Both ages are slightly younger than a previous combined SHRIMP 207Pb/206Pb baddeleyite weighted mean date from the same swarm, with slight discordance interpreted as being caused by thin metamorphic zircon overgrowths. The updated Black Range suite mean remanence direction (D = 031.5°, I = 78.7°, k = 40, α95 = 8.3°) corresponds to a paleomagnetic pole calculated from the mean of nine virtual geomagnetic poles at 03.8°S, 130.4°E, K = 13 and A95 = 15.0°. The pole's reliability is bolstered by a positive inverse baked-contact test on a younger Round Hummock dyke, a tentatively positive phreatomagmatic conglomerate test, and dissimilarity to all younger paleomagnetic poles from the Pilbara region and contiguous portions of Australia. The Black Range pole is distinct from that of the Mt Roe Basalt (or so-called ‘Package 1’ of the Fortescue Group), which had previously been correlated with the Black Range dykes based on regional stratigraphy and imprecise SHRIMP U–Pb ages. We suggest that the Mt Roe Basalt is penecontemporaneous to the Black Range dykes, but with a slight age difference resolvable by paleomagnetic directions through a time of rapid drift of the Pilbara craton across the Neoarchean polar circle.

(Less)
Please use this url to cite or link to this publication:
author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Black Range Dolerite Suite, Neoarchean, paleomagnetism, Pilbara craton, U–Pb geochronology, Western Australia
in
Australian Journal of Earth Sciences
volume
64
issue
2
pages
13 pages
publisher
Taylor & Francis
external identifiers
  • scopus:85014500337
  • wos:000398079400002
ISSN
0812-0099
DOI
10.1080/08120099.2017.1289981
language
English
LU publication?
yes
id
04e22280-086b-45b4-87e4-3aac2acddd12
date added to LUP
2017-03-15 09:38:15
date last changed
2018-05-06 04:31:50
@article{04e22280-086b-45b4-87e4-3aac2acddd12,
  abstract     = {<p>We report a new paleomagnetic pole for the Black Range Dolerite Suite of dykes, Pilbara craton, Western Australia. We replicate previous paleomagnetic results from the Black Range Dyke itself, but find that its magnetic remanence direction lies at the margin of a distribution of nine dyke mean directions. We also report two new minimum ID-TIMS <sup>207</sup>Pb/<sup>206</sup>Pb baddeleyite ages from the swarm, one from the Black Range Dyke itself (&gt;2769 ± 1 Ma) and another from a parallel dyke whose remanence direction lies near the centre of the dataset (&gt;2764 ± 3 Ma). Both ages are slightly younger than a previous combined SHRIMP <sup>207</sup>Pb/<sup>206</sup>Pb baddeleyite weighted mean date from the same swarm, with slight discordance interpreted as being caused by thin metamorphic zircon overgrowths. The updated Black Range suite mean remanence direction (D = 031.5°, I = 78.7°, k = 40, α<sub>95</sub> = 8.3°) corresponds to a paleomagnetic pole calculated from the mean of nine virtual geomagnetic poles at 03.8°S, 130.4°E, K = 13 and A<sub>95</sub> = 15.0°. The pole's reliability is bolstered by a positive inverse baked-contact test on a younger Round Hummock dyke, a tentatively positive phreatomagmatic conglomerate test, and dissimilarity to all younger paleomagnetic poles from the Pilbara region and contiguous portions of Australia. The Black Range pole is distinct from that of the Mt Roe Basalt (or so-called ‘Package 1’ of the Fortescue Group), which had previously been correlated with the Black Range dykes based on regional stratigraphy and imprecise SHRIMP U–Pb ages. We suggest that the Mt Roe Basalt is penecontemporaneous to the Black Range dykes, but with a slight age difference resolvable by paleomagnetic directions through a time of rapid drift of the Pilbara craton across the Neoarchean polar circle.</p>},
  author       = {Evans, D. A. D. and Smirnov, Aleksey V. and Gumsley, A. P.},
  issn         = {0812-0099},
  keyword      = {Black Range Dolerite Suite,Neoarchean,paleomagnetism,Pilbara craton,U–Pb geochronology,Western Australia},
  language     = {eng},
  month        = {03},
  number       = {2},
  pages        = {225--237},
  publisher    = {Taylor & Francis},
  series       = {Australian Journal of Earth Sciences},
  title        = {Paleomagnetism and U–Pb geochronology of the Black Range dykes, Pilbara Craton, Western Australia : a Neoarchean crossing of the polar circle},
  url          = {http://dx.doi.org/10.1080/08120099.2017.1289981},
  volume       = {64},
  year         = {2017},
}