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Abstract

Consideration of the latest geophysical datasets and new mapping and stratigraphic data
shows the Koonenberry Belt of far western NSW, to be an Early to Mid Palaeozoic foldand-thrust
belt.
This study presents the results of geologically-controlled qualitative interpretation and twodimensional
modelling of gravity and magnetic data which permit a new tectonic
interpretation, relying upon the different petrophysical, structural and metamorphic
attributes of three distinct tectonostratigraphic packages.
The oldest known sequence in the belt comprises shales, sands, dolomites and strongly
magnetic transitional alkaline basalts, which are believed to exist in large volumes at
depth, producing a major magnetic anomaly. These rocks are disconformably overlain by
a regionally extensive ?Lower to ?Middle Cambrian turbidite sequence. The two packages
represent Late Neoproterozoic continental rifting, dated at 587 Ma, and Early Cambrian
volcanic passive margin formation. Dense, rifted blocks of Neoproterozoic sedimentary
sequences are believed to underlie this remnant margin at depth, on the basis of high
gravity signatures.
A second widespread rifting or crustal attenuation event is represented by marine shelf
sequences interbedded with minor volumes of calc-alkaline volcanic rocks. This event has
been dated around 525 Ma. Comparison of turbidite sequences in the belt and South Australia indicates fewer
similarities than previously thought; equivalent passive margin sequences to those in
western NSW may lie in westernmost Victoria.
Equivalents to the Cambrian shelf sequences exist within the Warburton Basin of northern
South Australia, and indicate that the second episode of rifting dated at 525 Ma was
widespread. The late Middle Cambrian-Late Cambrian thrusting event and subsequent post-collisional
volcanism in the belt is also believed to be represented in western Victoria and western
Tasmania. In these locations, it is represented by allochthonous slices of intra-oceanic arc
mafic-ultramafic complexes and overlying 'in situ' post-collisional volcanics. The structural
and metamorphic character of these sequences, and their common timing, contrast
strongly with the exposed sequences of the Adelaide Fold Belt and other portions of the
Ross-Delamerian Orogen in Antarctica, and strongly suggest that the orogen is divided
into internal and external zones. Analysis of differences in timing and character of
deformation between the two zones suggests that the Delamerian Orogeny was a long
lived, mantle-driven process with overprinting effects from short-lived plate-geometries.
This model contrasts with earlier suggestions of a rigid arc-continent style collision.
Subsequent development of the Koonenberry and related fold-belts in an in-board position
is related to long-lived accretion at the free plate margin to the east. Effects include major
fold and thrust deformation in the Ordovician-Silurian, and widespread high crustal-level
strike-slip deformation in the Devonian and Carboniferous. A second major mantle-driven
thermal event in the Devonian found elsewhere in the Lachlan Orogen is absent within the
Belt.
The tectonostratigraphic sequences and deformation style of the belt suggest significant
prospectivity for a wide variety of base and precious metals, and diamonds. Correlations
with equivalent sequences elsewhere support this conjecture. Petroleum prospectivity is
also high, with known mature sources and reservoir facies; however, the structural
complexity of the belt suggest all plays will have a high element of risk.

Item Type:	Thesis - PhD
Authors/Creators:	Direen, NG
Keywords:	Geology, Geophysics, Stratigraphic, Gondwana (Geology)
Copyright Holders:	The Author
Copyright Information:	Copyright 1999 the Author
Additional Information:	5 col. folded maps in pocket at back of vol. 2. Thesis (Ph.D.)--University of Tasmania, 1999. Includes bibliographical references
Related URLs:	Publisher
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