Spatial and directional analysis of potential field gradients ? new methods to help solve and display three-dimensional crustal architecture

Abstract

Edge detection and automatic trend analysis using potential field gradients are methods for producing unbiased estimates of sharp lateral changes in physical properties of rock packages. Where the points lying on the maximum horizontal gradients of potential field data show a lateral continuity, they can be mapped as ``strings'. These strings may be generated for many different levels of upward continuation. When analysed in three dimensions, the strings provide information about the strength of the gradients, the locality of source-body edges, and possibly their dip directions and depth. For automatic analysis, sets of string-points may be converted into poly-lines, or curves, for each level of continuation. The best-fitting straight lines for curves with high linearity can be plotted as circular histograms (rose diagrams), or balloon diagrams, to provide a statistical representation of their orientations. Discrete areas can be windowed separately to show how dominant trend directions change in different geological settings. Balloon diagrams calculated for many levels of upward continuation may show how interpreted fracture sets evolve vertically. Examples of analyses are shown for two areas of Australia, using gravity data. The first is from the Olympic Cu-Au province of the eastern Gawler Craton, mapping NW- and NE-trending structures, and the second maps the broad domains of an area of northern Australia.