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

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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.; Gumsley, A. P.

In: Australian Journal of Earth Sciences, Vol. 64, No. 2, 01.03.2017, p. 225-237.

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TY - JOUR

T1 - Paleomagnetism and U–Pb geochronology of the Black Range dykes, Pilbara Craton, Western Australia

T2 - a Neoarchean crossing of the polar circle

AU - Evans, D. A. D.

AU - Smirnov, Aleksey V.

AU - Gumsley, A. P.

PY - 2017/3/1

Y1 - 2017/3/1

N2 - 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.

AB - 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.

KW - Black Range Dolerite Suite

KW - Neoarchean

KW - paleomagnetism

KW - Pilbara craton

KW - U–Pb geochronology

KW - Western Australia

UR - http://www.scopus.com/inward/record.url?scp=85014500337&partnerID=8YFLogxK

U2 - 10.1080/08120099.2017.1289981

DO - 10.1080/08120099.2017.1289981

M3 - Article

VL - 64

SP - 225

EP - 237

JO - Australian Journal of Earth Sciences

JF - Australian Journal of Earth Sciences

SN - 1320-1271

IS - 2

ER -