The nature of the basement to the Kimberley Block, Northwestern Australia

Abstract

Magnetic effects of the extensive hot-spot related Hart Dolerite, Carson Volcanics, and related feeders that occur within the sedimentary section complicate interpretations of aeromagnetic data in defining the nature of the basement beneath the sediments of the Kimberley Basin, of Northwestern Australia. The magnetic effects of these sources can however be suppressed by upward continuation and stabilised downward continuation to reveal what appears to be a largely granitic basement to the area. Computer modelling has defined the geometry, density, and magnetic characteristics of what may be a remnant of an ophiolite slice emplaced under the southeastern margin of the Kimberley Block during subduction related to the convergence of a Kimberley "microcontinent" with the main Australian continent. Linear gravity lows over the Kimberley Block may define granites formed as a result of the subduction process. Five northeast trending zones of differing lithologies can be identified in the basement on the basis of differing characteristic in their associated magnetic and gravity fields. A conjugate dyke-filled fracture system, apparently related to Devonian-Carboniferous rifting processes, has been superimposed on the block. Suites of these fractures are located over areas interpreted as junctions between zones of different lithological character in the basement.