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Australia: The Land Where Time Began |
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Gondwana Breakup
Implications – K-Ar Dating of Fault Gouge in the Northern Sydney Basin,
NSW, Australia It is common for synkinematic and authigenic clays
to be present in fault gauges. The dating of fault gouges has not often
been attempted. In this paper Zwingmann et
al. present the first data
for the growth of synkinematic illite-smectite for 2 fault zones in the
northern Sydney Basin, New South Wales, at Burwood Beach that are hosted
by siltstones, tuffs and coals of Early Permian age in the Lambton
Formation, Newcastle Coal Measures. The faults are 1.5 m apart, showing
normal displacement and trend N-S with steep easterly dips. Along both
fault surfaces are developed foliated gouge zones, comminutional and
dilational breccias. Samples from the gouge and tuffs in the damage
zones have given K-Ar ages of 172 (6-10 μm) to 119 Ma (<0.4 μm),
respectively. Older ages of 272–281 Ma for the coarse fractions (>2 μm),
237–245 Ma for the <2 μm fraction, 218 Ma for the <0.4 μm fraction and
196 Ma for the <0.1 μm fraction were obtained from siltstones within and
outside the damage zone. Zwingmann et
al. suggest the younger ages
of 237-196 Ma indicate the time of formation of the illite-smectite and
the 150-122 Ma from the <2 μm fraction represent the maximum age for the
formation of the gouge. The younger ages are believed to reflect the
last slip event which occurred on the faults, which is related to the
rifting and dispersal of the Australian continent’s eastern margin.
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Author: M.H.Monroe Email: admin@austhrutime.com Sources & Further reading |