The Opening of the Tasman Sea: A Gravity Anomaly Animation

Abstract

The first plate tectonic gravity anomaly grid animation using data from the Tasman Sea is presented. In this animation the tectonic elements are represented by their respective gravity fields, based on recent marine-satellite-derived gravity anomalies and a new onshore gravity compilation for eastern Australia. Rifting in the Tasman Sea propagated from south to north in several stages and included a number of failed rifting events. Thus, the tectonic evolution cannot be modeled as a simple two-plate system. Based on tectonic lineaments visible in the gravity data, interpreted as strike–slip faults, and based on magnetic anomaly, bathymetry, and seismic data, as well as on the age and affinity of dredged rocks, 13 tectonic units have been identified as microplates that were active between 90 and 64 Ma. These blocks gradually separated from the Australian continent, either by extensional or strike–slip movement. In order to show the motion through time of the different tectonic blocks, the authors created an animation of 39 sequential gravity field reconstructions. This animation allows visualization of all major tectonic events in the history of the basin, including the evolution of several oceanic fracture zones. It also illustrates how a large part of the eastern Australian margin (from central New South Wales to the Marion Plateau) was subjected to strike–slip motion from 84 to 64 Ma after a counterclockwise change in spreading direction. The animation shows how the opening of the Capricorn Basin is linked to a period of transpression between the Chesterfield and Marion Plateaus from chron 31 (67.7 Ma) to chron 27 (61.2 Ma).