Quaternary faulting in the offshore Flaxbourne and Wairarapa Basins, southern Cook Strait, New Zealand

Marine seismic reflection profiles, bathymetric data, and seabed samples re veal the stratigraphy and Quaternary structure of the southern Wairarapa an d Flaxbourne Basins in southeastern Cook Strait and eastern Marlborough. Th ese SW-NE-trending basins began forming before the late Miocene (>10 Ma), b ut their development has been mainly during and since that time and continu es today within the Pacific-Australia plate boundary zone. Recently active structures deforming and bounding the basins are recognised by growth strat a and deformation of Quaternary sediments. Observed structural geometries r eflect Pliocene-Recent changes in the kinematics of faulting in central New Zealand. The 12-22 km wide southern Wairarapa Basin contains up to c. 2.9 km of strata and is deforming between offshore segments of the dextral stri ke-slip Wairarapa Fault and associated Wharekauhau Thrust on the western ma rgin, and offshore extensions of the Aorangi Mountains range-front reverse faults on the eastern margin. To the southwest, in the eastern Marlborough Fault System, the 15-20 km wide, 80 km long Flaxbourne Basin contains >4.5 km of strata and is deforming by strike-slip and oblique-slip faults includ ing offshore sections of the Hope and Kekerengu Faults. A new set of strike -slip faults, probably younger than 1 Ma, strike parallel (c. 080 +/- 10 de grees) to the current Pacific-Australian plate motion vector and obliquely to inherited structural trends. Three of these faults are possibly separati ng the Flaxbourne and Wairarapa Basins in central, southern Cook Strait. Cu rved traces of the Needles and Wairarapa Faults on the western margins of t he basins are aligned, and may cut across disrupted Miocene structures to l ink part of the eastern Marlborough Fault System with the North Island Dext ral Fault Belt.