Mark McLean '3D inversion modelling of Full Spectrum FALCON® airborne gravity data over Otway Basin'
Dr Mark McLean (Geological Survey of Victoria and University of Melbourne) presents '3D inversion modelling of newly acquired Full Spectrum FALCON® airborne gravity data over the Otway Basin, Victoria' for the August GSA Victoria Division Meeting.
Abstract:
A new airborne Full Spectrum Gravity and magnetic survey was undertaken over the Otway Basin as part of the Geological Survey of Victoria’s (GSV) Victorian Gas Program (VGP) using the FALCON® airborne data acquisition system. A total of 31042 line km of gravity, gravity gradiometry (Full Spectrum), magnetic and laser scanner data were acquired along 500 m spaced lines in a NW-SE orientation. This survey is the first publicly available Full Spectrum Falcon survey and is intended to capture the full spectrum of wavelengths by conforming the short wavelengths from the gravity gradiometry with the longer wavelengths obtained from concurrently acquired conventional gravity.
Forward and inversion modelling results in the Otway Basin model suggest that significant gravity anomalies are caused not only by the thickness of basin fill, but also by structures and geological diversity contained within the Proterozoic-Early Palaeozoic basement crust that hosts the basin, and by the shape of the Moho at the base of the crust. The Moho depth shallows from the continental interior into the Otway Basin region and beyond the southern coastline, and this change has a very significant influence on the gravity response. Previous models of Victoria’s crustal and Moho architecture constrained by surface geological mapping, seismic reflection data, aeromagnetic data, ground gravity, and petrophysical properties measured for a variety of local basement rocks were used as a starting point to build structures and attributed rock volumes within the basement under the Otway Basin, and test and refine these models iteratively. This study showcases a workflow that allowed for full-crust-scale variations to be taken into account in the modelling of a sedimentary basin. This is particularly important on continental margins where the crust changes dramatically in thickness across the width of a single basin. The study has improved the understanding of the basement structures below the Otway Basin and, with the geological complexity of the basement accounted for, also allowed for refinement of the geometry of the top of basement interface. Specifically, inversion results allowed the shape of the Otway Basin rift to be mapped in greater detail, revealing new potential exploration opportunities such as indications that the Portland Trough in the southwestern region of the onshore Otway Basin is significantly deeper than previously thought.
Biography:
Mark completed Arts/Science and Master of Science degrees at Monash University and then completed a PhD at The University of Melbourne in 2008 which involved acquisition, interpretation and modelling of an airborne geophysical survey over the Lambert Rift region in East Antarctica. Since then, Mark has worked at the Geological Survey of Victoria building regional 3D framework and rock property models using geological and geophysical datasets. Mark's time is now split between the GSV, and The University of Melbourne where he lectures in Applied Geophysics.
Virtual background credit: Rory MacLeod
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