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Lithostratigraphy and Lithochemistry of Ordovician volcano-plutonic rocks in the Blayney area, central Molong Belt, NSW

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Duerden, PB (1999) Lithostratigraphy and Lithochemistry of Ordovician volcano-plutonic rocks in the Blayney area, central Molong Belt, NSW. Honours thesis, University of Tasmania.

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Abstract

The Late Ordovician Cabonne Group lies in the southern portion of the Molong Volcanic
Belt in central western NSW. It broadly comprises an extensive lava-dominated package
of high-K calc alkaline mafic volcanics (Blayney Volcanics) overlain by a package of
shoshonitic lavas and intrusives (Forest Reefs Volcanics).
Regional aeromagnetic and structural data suggest that thrust style faulting may have
caused the extensive lithological repetition observed within the Cabonne Group.
Volcanic facies mapping, combined with geochemical sampling, has provided a basis for
re-interpretation of areas within the Cabonne Group. Facies mapping has demonstrated a
number of possible stratigraphic correlations, including a possible link between limestones
present at and surrounding Browns Creek with limestones within the Weemalla Formation
at the base of the Forest Reefs Volcanics.
Geochemical and petrological data define a temporal change in magmatic affinities within
the Ordovician volcanics of the Molong Volcanic Belt. This change in magmatism from
high Kin the Blayney Volcanics to shoshonitic in the Forest Reefs Volcanics is broadly
coincident with the late Middle Ordovician limestone interval at the base of the Forest
Reefs Volcanics.
This broad lithochemical stratigraphy provides a framework for comparisons with the
Ordovician Junee-Narromine volcanic belt located 100 km to the west, where a similar
temporal transition exists from high-Kin the Nelungaloo Volcanics to shoshonitic in the
overlying Goonumbla Volcanics.
The Ordovician volcanics from the Molong belt are also similar to the early to midMiocene
calc-alkaline to shoshonitic suites from Fiji. On the basis of these similarities, the
transition from high-K to shoshonitic volcanism is likely to be the result of fragmentation
of a mature oceanic island arc as a result of a major tectonic disturbance as marked by the
late Middle Ordovician limestones.

Item Type: Thesis (Honours)
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Date Deposited: 19 Aug 2011 02:11
Last Modified: 11 Mar 2016 05:54
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