Resolving the nature and geometry of major fault systems from geophysical and structural analysis: The Palmerville Fault in NE Queensland, Australia

Abstract

The Palmerville Fault in northeastern Queensland, Australia, forms a major terrane-bounding structure that probably had a major influence on the evolution of the adjacent Palaeozoic Hodgkinson Province, the northernmost part of the Tasman Fold Belt System in eastern Australia. The nature and subsurface expression of the Palmerville Fault remain poorly constrained and models for contrasting geometries exist. In addition to structural field and microscopic observations, we have combined results from multi-scale wavelet edge analysis (‘worming’), forward modelling of regional magnetic and gravity data, and geochemical data sets to develop an improved understanding of the nature and subsurface geometry and depth extent of the Palmerville Fault. Results from ‘worming’ suggest a steeply dipping geometry for the Palmerville Fault. Based on constraints from field observations and ‘worming’, we have generated a number of sections across the Palmerville Fault and forward modelled their magnetic and gravity response to compare with the observed magnetic and gravity response. Our results show that the Palmerville Fault represents a steeply eastward-dipping structure that may become listric at depth (suggesting the presence of Proterozoic basement underneath the Hodgkinson Province). Our findings suggest that the Palmerville Fault was a first-order normal fault that controlled Early-Middle Palaeozoic basin development in the Hodgkinson Province. Subsequently, the fault acted as a (mid-crustal) décollement zone accommodating basin inversion in the Hodgkinson Province during the Late Palaeozoic. These results provide important constraints on the tectonic evolution of the Hodgkinson Province in northeastern Australia, and, importantly, demonstrate the strength of combining geological observations with geophysical analysis, in particular multi-scale wavelet edge analysis, in resolving the surface geometry and evolution of major fault systems, especially in areas of low-data density.