Rapid creation and destruction of sedimentary basins on mature strike-slipfaults: an example from the offshore Alpine Fault, New Zealand

Seismic reflection profiles and multibeam bathymetric data are integrated t o analyse the structure of the 25 km-long strike-slip Dagg Basin associated with the marine section of the Alpine Fault, Fiordland, New Zealand. The b asin is developing in almost 3000 in water depth at a releasing bend, whils t contemporaneous transpression results in inversion of its southern end. F iord-derived glacio-marine sediments flooded the basin during the last glac iation, and provide a stratigraphic framework for structural analysis. Geom etrical analysis enables an estimation of 450-1650 in of dextral displaceme nt on the Alpine Fault at the releasing bend since the development of an un conformity estimated to have formed at between 30 and 110 ka. This implies a dextral slip rate ranging from a possible minimum of 4 mm/yr to the maxim um of 35 mm/yr constrained by the Pacific-Australian plate motion rate. Des pite total dextral displacement of 480 km on the Alpine Fault zone and a gr owth history spanning 15-20 Myr, this geomorphically well expressed and str ucturally complex strike-slip basin developed and evolved rapidly during th e late Pleistocene, and thus represents only the latest phase in the evolut ion of the Alpine Fault. Upward splaying structures within the fault zone e xhibit a rapid spatial evolution in Pleistocene strata, which may reflect t he interactions between high fault slip rate, voluminous sedimentation supp ly, inherited structural complexities in the basement rocks and deeper cove r sequence, and interactions between adjacent faults. The present through-g oing releasing bend at the northern end of the basin may have evolved from a more complex pull-apart basin that developed between separate segments of the Alpine Fault. The results from Dagg Basin illustrate the rates at whic h structural complexities and sedimentary basins can develop within highly active, very mature, through-going continental wrench faults. Strike slip b asins on the scale of 40-80 km(2) on such faults may be ephemeral features that can be developed and destroyed on a time scale of 10(5)-10(6) years. ( C) 2001 Elsevier Science Ltd. All rights reserved.