Dyke-induced fault and pit crater measurements and predicted dyke properties offshore NW Australia

There are two components to this dataset: (1) fault analyses used to estimate underlying dyke properties, imaged in 3D seismic reflection data; and (2) dimension measurements and calculations of pit craters associated with the dykes and faults. This dataset specifically supplements https://webapps.bgs.ac.uk/services/ngdc/accessions/index.html#item170389. The seismic reflection data are located offshore NW Australia and image a series of Late Jurassic dykes and overlying dyke-induced normal faults; these structures occur within a sedimentary basin and are now buried beneath several kilometres of rock. The specific seismic reflection dataset used for this study so far is the Chandon 3D survey, which is available through https://www.ga.gov.au/nopims and is also deposited within the NGDC.

Dyke-induced faults: Analyses of these faults uses an array of point pairs, defined by X, Y, and Z co-ordinates, that mark where certain sedimentary beds are intersected by the fault in its footwall and hanging wall. Mapping of these points for 11-14 sedimentary horizons was conducted using Petrel seismic interpretation software. From the footwall and hanging wall point pairs, the throw, heave, displacement, and dip of each fault was calculated. By measuring distances between corresponding point pairs on opposing faults, graben width properties and estimated down-dip fault continuations were calculated. The expression of dyke-induced faults observed at the surface in active volcanic areas is often used to estimate dyke location, thickness (expected to roughly equal the heave on overlying faults), and upper tip depth (expected to occur where overlying, oppositely dipping faults meet; i.e. the point of the 'V'). This study represents the first time natural dyke-induced faults and underlying dykes have been imaged in 3D and quantitatively studied. The dataset presented here allows hypotheses concerning relationships between dyke-induced fault geometries and dyke properties to finally be tested, and provides insight into normal fault kinematics; this will be useful to structural geologists and volcanologists.

Pit craters: These features are enigmatic, quasi-circular depressions that commonly occur at the surface above inferred dykes and faults. The long axis and short axis lengths, as well as the area and depression depth, of the pit crater plan-view morphologies were measured. 3D seismic reflection data reveal the pit craters are underlain by pipes, for which the height, diameter, and volumes are calculated. These pipes often connect to dykes and faults, providing the first conclusive evidence that dyking and faulting mechanisms can drive pit crater formation. However, although studies of pit craters on other planets has used their surface shape to predict subsurface processes and geology, the data presented here suggest pit crater surface expressions are not diagnostic of formation mechanisms or geology.