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Magmatic characteristics and geochronology of Ordovician igneous rocks from the Cadia - Neville region, New South Wales: implications for tectonic evolution

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Squire, RJ and Crawford, AJ (2007) Magmatic characteristics and geochronology of Ordovician igneous rocks from the Cadia - Neville region, New South Wales: implications for tectonic evolution. Australian Journal of Earth Sciences, 54 (2-3). pp. 293-314. ISSN 0812-0099

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Abstract

TheOrdovician 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 preprocessing
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.

Item Type: Article
Keywords: Forest Reefs Volcanics, geochronology, Lachlan Orogen, Ordovician, shoshonite, tectonics.
Journal or Publication Title: Australian Journal of Earth Sciences
Page Range: pp. 293-314
ISSN: 0812-0099
Identification Number - DOI: 10.1080/08120090601147001
Additional Information:

The definitive published version is available online at: http://www.tandf.co.uk/journals

Date Deposited: 25 Jun 2008 03:58
Last Modified: 18 Nov 2014 03:43
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