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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 Meffre
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 (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 Sciences

Pagination

1-22

ISSN

0812-0099

Department/School

School of Natural Sciences

Publisher

Blackwell Publishing Asia

Place of publication

54 University St, P O Box 378, Carlton, Australia, Victoria, 3053

Rights statement

Copyright 2021 Geological Society of Australia

Repository Status

  • Restricted

Socio-economic Objectives

Expanding knowledge in the earth sciences

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    University Of Tasmania

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