No abstract

No abstract

An interpretation of geological and geophysical data is presented to suggest that the Precambrian rocks of Tasmania comprise a series of Palaeozoic thrust slices embedded in the western part of the Lachlan Fold Belt and the eastern part of the Kanmantoo Fold Belt. This interpretation contrasts with previous interpretations which regarded the Precambrian rocks as the basement on which the Palaeozoic rocks formed.In western Tasmania, east-or west-facing thrusts and involving detached Precambrian blocks occur in discrete zones. Westfacing thrusts only occur northwest of an axis from Elliott Bay in southwest Tasmania to Penguin in northern Tasmania. This thrust system overlaps an older east-facing system which becomes more intense eastward but which may be recognised across the entire island.

The substantial gravity data base in Tasmania has been used to formulate a regional crustal model. This was derived by array modelling techniques for geological sources of crustal scale. A simultaneous solution for mantle, basement and granite forms was created by this means within a framework of realistic and internally consistent assumptions. The regional field derived from this geological model (including the ocean basins) is not dependent on any filtering or smoothing procedure and thus the magnitude and sign of any residuals is absolute. The residual map was produced by removing the effect of the crustal model at individual data points. The resultant map enables detailed and reliable modelling of upper crustal features as well as revealing crustal character hitherto concealed beneath post Carboniferous cover. An important example of the value of the residual separation is shown by the structural relationships exposed in NE Tasmania which involve gold mineralisation.

No abstract