Using the Tilt-Depth method to map depth of cover in areas of relatively shallow basement in Australia from high resolution aeromagnetic data
Abstract
The Tilt-Depth method is investigated as a means to rapidly derive estimates of depth to basement from magnetic data. This method involves calculating the tilt angle from reduced-to-pole magnetic data. Magnetic sources are assumed to have simple contact geometry. The depth to these sources can be estimated from the distance between contours of the mapped tilt angle. Previous studies have demonstrated that this method yields useful results for continent and basin-scale analysis. Here we test the potential of this method to be used for detailed analysis of high-resolution continent-wide data. The Australian continent comprises a collage of ancient cratonic blocks and orogenic belts. These ancient basement rocks are at or near the surface over large areas of the continent, while in other areas the basement is buried beneath up to 10 km of sediments in Neoproterozoic and younger basins. Mapping the thickness of these sediments across the continent is important for a number of reasons - important amongst these is the need to define the depth to basement in areas of relatively thin cover adjacent to exposed cratonic rocks. Exposed expressions of the basement rocks are often richly mineralised. Efficient targeting of deposits located under cover at up to 1 km depth requires mapping of depth to basement around the margins of exposed basement areas across the whole of Australia. Geophysical data provide a means to achieve this, in particular the continent-wide compilation of high resolution aeromagnetic surveys. Our case study focuses on two areas in South Australia where the Archean to Proterozoic Gawler Craton dips beneath younger cover sediments. Area 1, on the northern edge of the craton, contains approximately 20% of basement outcrop, the remaining basement is obscured by cover up to ~400 m. Area 2, on the north-eastern edge of the craton, extends from the edge of the basement outcrop to a depth of ~1100 m of cover. Both areas are covered by aeromagnetic data with a line spacing ranging from 300 to 500 m with flight heights between 70 and 100 m. The flight line data for both areas were gridded using 80 m cell size. The areas were selected due to the availability of large numbers of drill holes that have intersected basement which were used to validate the Tilt-Depth results. The results of the of Tilt-Depth analysis show a good level of agreement with the drill-hole data.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMGP34A..06W
- Keywords:
-
- 0905 EXPLORATION GEOPHYSICS / Continental structures;
- 0925 EXPLORATION GEOPHYSICS / Magnetic and electrical methods;
- 1517 GEOMAGNETISM AND PALEOMAGNETISM / Magnetic anomalies: modeling and interpretation