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Magmatic characteristics and geochronology of the Ordovician volcanic and intrusive rocks of the Cadia-Neville region, Eastern Lachlan Orogen, New South Wales: implications for tectonic evolution

journal contribution
posted on 2023-05-16, 21:36 authored by Squire, RJ, Anthony CrawfordAnthony Crawford
The Ordovician volcanic and intrusive rocks of the Cadia-Neville region, in the southern Molong Volcanic Belt section of the Macquarie Arc in central-western New South Wales, display a temporal progression from shoshonitic basaltic volcanism (e.g. Mt Pleasant Basalt Member) in the late Darriwilian to Gisbornian (ca 460-453 Ma) to small-volume dacitic medium-K calc-alkaline magmatism (e.g. Copper Hill-type dacite) in the late Eastonian to early Bolindian (ca 450-445 Ma) to large-volume, high-K calc-alkaline to shoshonitic, mafic to highly evolved magmatism (e.g. Nullawonga Latite Member and Cadia Intrusive Complex) at about 445-440 Ma. The two episodes of shoshonitic magmatism are separated by at least 15 (but up to ∼20) million years, during which time limestones, associated with regional uplift, were deposited broadly coincident with emplacement of the medium-K calc-alkaline dacitic intrusions. Despite this, the lavas and intrusions associated with both episodes of shoshonitic magmatism have strikingly similar geochemistry, indicating that a similar mantle source and partial melting processes were involved over this time interval. The arc-type geochemistry of the volcanic and intrusive rocks in the Cadia-Neville region is very similar to the lavas and intrusions forming the Pliocene Tavua Caldera in Viti Levu, Fiji. The Pliocene shoshonitic rocks at Tavua Caldera were emplaced following cessation of arc magmatism when the arc moved into an extensional phase. By analogy with the Pliocene tectonic setting in Fiji, the arc-like signature of the Ordovician magmas of the Macquarie Arc may be due to pre-processing of the mantle above a subduction zone prior to extension and fragmentation of arc lithosphere that led to generation of the subduction-modified shoshonite-dominated magmas.

History

Publication title

Australian Journal of Earth Sciences

Volume

54

Issue

2/3

Pagination

293-314

ISSN

0812-0099

Department/School

School of Natural Sciences

Publisher

Taylor & Francis

Place of publication

UK

Repository Status

  • Restricted

Socio-economic Objectives

Other mineral resources (excl. energy resources) not elsewhere classified

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