Paleogene seafloor spreading in the southeast Tasman Sea

Abstract

Magnetic anomalies 11–18 have been identified in the southeast Tasman Sea, the area of ocean crust southwest of Fiordland, New Zealand, west of the Puysegur Trench (the present plate boundary) and southeast of the older (80–58 Ma) ocean crust of the Tasman Sea basin. Structures associated with two changes in spreading direction are preserved in the area. Spreading between the Australian and Pacific plates began in the Eocene, about 40 Ma in this area, orthogonal to Cretaceous‐Paleocene spreading between them in the Tasman Sea. The boundary between the two ages of ocean crust is abrupt and associated with what we have interpreted as marginal uplift blocks and rift basins of the Resolution Ridge system. Rifting appears to have propagated northeast along a fracture zone. The northern blocks of the Resolution Ridge system may be isolated fragments of continental crust of the Campbell Plateau. Between anomalies 18 and 11 (40–30 Ma) the spreading rate was about 1.5 cm/yr. Swath mapping and satellite altimetry data show that a second change in relative plate motion direction began shortly after anomaly 11, about 30 Ma, and led to a change from tension to transcurrent motion along the plate boundary. The timing of the changes in spreading direction agrees with tectonic events interpreted from onshore data.