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Australia: The Land Where Time Began |
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Sydney Basin –
Constraining Timing of Brittle Deformation and Fault Gouge In this paper Och, Offler & Zwingmann1
report the results of structural and K-Ar studies of gouges in faults
that trend N-S, NNE and E-W at 4 locations in the Sydney-Hunter region.
The fault zones are manifest as joint swarms and zones that are highly
brecciated and contain gouge with authigenic illite that results from
the infiltration of fluid. Minor dip slip, accompanied strike-slip
movement, on the NNE faults normal movement occurred, and on the N-S and
E-W trending faults dip slip occurred. In this study Och, Offler &
Zwingmann1 analysed gouge from a NE-trending, steep,
SE-dipping fault that exhibited dip-slip movement at Cut 10 on the
Hunter Expressway, and from a E-W trending, steep south-dipping, normal
fault at the West Side open Cut, Lake Macquarie. Ages that vary from
166-119 Ma for the <2 μm and finer fractions, and a mean age of about
120 Ma for the <0.4 μm fraction were found by K-Ar dating of illite and
illite-smectite in fractions extracted from fault gouges in areas that
were unaffected by thermal overprint. The ages obtained from fractions
of similar size both for the gouge and for the host rocks are younger
(134-76 Ma; av. <0.4 μm = 111 Ma), in the Sydney area and the Westside
Open Cut coal mine, Lake Macquarie. Influence of a thermal overprint
associated with subsurface magmas that were emplaced in the early stages
of rifting of eastern Gondwana during the Early Cretaceous is indicated
by the data.
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Author: M.H.Monroe Email: admin@austhrutime.com Sources & Further reading |