THE TECTONIC HISTORY OF THE TASMAN SEA - A PUZZLE WITH 13 PIECES

We present a new model for the tectonic evolution of the Tasman Sea ba sed on dense satellite altimetry data and a new shipboard data set. We utilized a combined set of revised magnetic anomaly and fracture zone interpretations to calculate relative motions and their uncertainties between the Australian and the Lord Howe Rise plates from 73.6 Ma to 52 Ma when spreading ceased. From chron 31 (67.7 Ma) to chron 29 (64.0 Ma) the model implies transpression between the Chesterfield and the Marion plateaus, followed by strike-slip motion. This transpression ma y have been responsible for the formation of the Capricorn Basin south of the Marion Plateau. Another major tectonic event took place at chr on 27 (61.2 Ma), when a counterclockwise change in spreading direction occurred, contemporaneous with a similar event in the southwest Pacif ic Ocean. The early opening of the Tasman Sea cannot be modeled by a s imple two-plate system because (1) rifting in this basin propagated fr om south to north in several stages and (2) several rifts failed. We i dentified 13 continental blocks which acted as microplates between 90 Ma and 64 Ma. Our model is constrained by tectonic lineaments visible in the gravity anomaly grid and interpreted as strike-slip faults, by magnetic anomaly, bathymetry and seismic data, and in case of the Sout h Tasman Rise, by the age and affinity of dredged rocks. By combining all this information we derived finite rotations that describe the dis persal of these tectonic elements during the early opening of the Tasm an Sea.