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Paleomagnetic testing of the Lachlan Orocline hypothesis: overprinting of remanence in Paleozoic rocks of the Lachlan Orogen in southeast Australia


Habib, U and Musgrave, R and Meffre, S, Paleomagnetic testing of the Lachlan Orocline hypothesis: overprinting of remanence in Paleozoic rocks of the Lachlan Orogen in southeast Australia, Australian Journal of Earth Sciences pp. 1-22. ISSN 0812-0099 (2021) [Refereed Article]

Copyright Statement

Copyright 2021 Geological Society of Australia

DOI: doi:10.1080/08120099.2021.1918246


Paleomagnetic studies in the Lachlan Orogen have indicated rotation of elements within it, but the evidence for rotation is limited and has significant statistical uncertainty. This study presents a detailed paleomagnetic investigation, assisted by X-ray analysis of magnetic mineralogy of middle Cambrian to lower Silurian sedimentary and igneous rocks in Victoria and New South Wales. Four demagnetisation behaviours (types A, B, C and D) have been recognised. Type A is characterised by a single component, resulting in an approximately linear path over the magnetite unblocking temperature range. Type B specimens exhibit slow progressive demagnetisation over a wide temperature range, with clustering of demagnetised directions above the magnetite Curie temperature, indicating hematite. Behaviour C is also characterised by clustering of directions, but this extends over a wider temperature range. Samples with behaviour D show noisy and non-informative demagnetisation, indicating very low magnetic stability. Hysteresis data confirm that samples with behaviour B and C have high coercivities and remain unsaturated above 300 mT. Mineral liberation analysis of selected samples indicates presence of iron oxides, magnetite, titanomagnetite, botryoidal hematite and iron hydroxides. Only three sites yielded specimens with type A primary magnetisation, with a poorly defined pole from the Dookie Volcanics on the central limb of the orocline, which does match a previous result from the same district. Two paleopoles, of type B and C specimens from the rocks in Tabberabbera Zone and the Rockley Volcanics, plot within the confidence limit of poles defining the late Silurian to Early Devonian Australian apparent polar wander path. These poles match other poles representing Devonian overprints around the margins of the Lachlan Orogen that have been interpreted to be the result of alteration mineralisation produced by fluids driven by tectonic compression during events in the Bindian (420410 Ma) or early Tabberabberan (405380 Ma) orogenies.

Item Details

Item Type:Refereed Article
Keywords:Lachlan Orogen, paleomagnetism, Devonian, overprint, tectonic, reconstruction, Paleozoic era, southeast Australia
Research Division:Earth Sciences
Research Group:Geophysics
Research Field:Magnetism and palaeomagnetism
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the earth sciences
UTAS Author:Habib, U (Mr Umer Habib)
UTAS Author:Meffre, S (Dr Sebastien Meffre)
ID Code:145448
Year Published:2021
Funding Support:Australian Research Council (LP160100483)
Deposited By:CODES ARC
Deposited On:2021-07-21
Last Modified:2021-08-25

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