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Structure and mineralisation of western Tasmania. CODES/AMIRA Project P.291A Report No. 5, May 1996


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Berry, RF, Selley, D, White, M, Corbett, KD, Kitto, PA and Roach, M 1996 , Structure and mineralisation of western Tasmania. CODES/AMIRA Project P.291A Report No. 5, May 1996.

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Executive Summary - Ron Berry

The project is now getting into the latter stages. The
original proposal included nine tests of the structural
model proposed in project P291. Three sections have
been completed in previous years. The report here
gives progress on five other sections. The only section
not begun is the investigation of sedimentological
evidence for Middle Cambrian movement on the Firewood Siding Fault/Linda Zone.

Additional whole rock chemistry of sedimentary rocks from western Tasmania were obtained to confirm the trends identified in the previous report. The Tyndall Group has a distinctive source composition which has contributed to the magnetic susceptibility of this unit. This composition is best reflected in the Lynchford Member and reflects an
andesitic character with a tholeiitic incompatible element pattern. The closest match to this pattern in western Tasmania is the Henty dykes and the basalts of the Henty Fault wedge. The White Spur Formation is not easily distinguished from the CVC on volcanic chemistry. Further work on the Sticht Range Formation confirmed its similarity to the Stitt Quartzite.

Chromite in Dundas Group sandstones is largely from a MUC (ophiolite) source. The MUC are very rich in chromite and even a small contribution from this source leads to a dominance of low-Ti02 chromite in the heavy mineral assemblage. Chromite composition is the clearest indicator of a MUC contribution to the provenance of sandstones in
western Tasmania. The whole rock chemistry usually
reflects more enriched sources such as the Crimson Creek Formation. The Animal Creek Greywacke has a contribution from the MUC. The metamorphic basement signature associated with the Stitt Quartzite and Sticht Range Formation was not recognised in the whole rock chemistry of Animal Creek Greywacke despite the clear component of basement source in the heavy mineral assemblage. This probably reflects the effect of mixing in a significant additional component from the MUC source.

A new geological cross-section was drawn along the northing 5350000mN, from west of the Professor Range to the Tyndall Range. This section matches the style of sections to the south (Queenstown and Mt. Jukes), with only moderate total shortening of 14 km. No dominant transport direction was recognised. A possible position for a major low angle Devonian thrust is west of the section under Permian cover. The level of erosion is such that a very good separation of this shortening between Cambrian and Devonian deformation is possible. The section emphasized the importance of late Cambrian folding in the structure of the Mt. Read Volcanics. The section drawn at
Rosebery continues to be anomalous compared to other sections drawn in this project.

The Mt. Cripps Fault was identified as a major Cambrian transfer largely based on differences between structure and stratigraphy north and south of this fault. We proposed a major Cambrian normal fault roughly in the position of the Henty Fault was offset along this structure and this offset was not entirely a result of Late Cambrian and Devonian compressional tectonics. New cross-sections were drawn north (5396OOOnM) and south (5392000mN) of the Mt. Cripps Fault. Detailed investigations along the Mt. Cripps Fault have provided supporting evidence that the fault was present during the
deposition of the Southwell Subgroup. No additional
evidence has been found for the existence of this structure during the earlier part of the Mt. Read
depositional cycle.

Item Type: Report (Technical Report)
Authors/Creators:Berry, RF and Selley, D and White, M and Corbett, KD and Kitto, PA and Roach, M
Publisher: CODES/AMIRA
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