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Paleomagnetic testing of the Lachlan Orocline hypothesis: overprinting of remanence in Paleozoic rocks of the Lachlan Orogen in southeast Australia
journal contribution
posted on 2023-05-21, 00:58 authored by Habib, U, Musgrave, R, Sebastien MeffreSebastien MeffrePaleomagnetic 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 (420–410 Ma) or early Tabberabberan (405–380 Ma) orogenies.
Funding
Australian Research Council
Alkane Exploration NL
AngloGold Ashanti Australia Limited
CMOC Mining Services Pty Ltd T/A Northparkes Mines
Department of Economic Development, Jobs, Transport and Resources
Department of State Growth (Tas)
Emmerson Resources Limited
Evolution Mining
Geological Survey of New South Wales - Department of Industry
Geoscience Australia
Heron Resources Limited
New South Resources Limited
Rio Tinto Limited
Sandfire Resoures NL
History
Publication title
Australian Journal of Earth SciencesPagination
1-22ISSN
0812-0099Department/School
School of Natural SciencesPublisher
Blackwell Publishing AsiaPlace of publication
54 University St, P O Box 378, Carlton, Australia, Victoria, 3053Rights statement
Copyright 2021 Geological Society of AustraliaRepository Status
- Restricted