A geophysically constrained multi-scale litho-structural analysis of the Trans-Tanami Fault, Granites-Tanami Orogen, Western Australia

Abstract

The Trans-Tanami Fault in the poorly exposed Paleoproterozoic Granites-Tanami Orogen of Western Australia is an ∼100 km long curvilinear structure with ∼6 km right lateral displacement. Multi-scale integration and analysis of aeromagnetic, gravimetric, reflection seismic and remote sensing data have constrained the relative timing and architectural relationship of this structure. Interpretation of regional scale long-wavelength potential field (gravity and magnetic) anomalies, which are commonly used to define first-order structures, show that the fault is not a terrane boundary. Structural interpretation of short-wavelength potential field data illustrates that the structural domains on either side of the fault represent the products of a non-homogeneous stress regime developed between rigid granitic plutons. Additionally, 2D joint forward modelling of gravity and magnetic data and interpretation of reflection seismic data confirms the vertical displacement across this fault to be negligible indicating a predominant lateral displacement. The lateral displacement along a portion of this structure has exploited a pre-existing plane of a north-dipping thrust fault. Where this early thrust fault terminates, the Trans-Tanami Fault displaces previously unfaulted rock as a wrench fault step-over. These observations differ from previous findings in the area by constraining the absolute displacement of this structure and through the recognition of a wrench fault system that includes lateral step-overs between re-activated early thrust fault planes.