Tectonic rotation about the termination of a major strike‐slip fault, Marlborough Fault System, New Zealand

Abstract

The Marlborough fault system comprises a series of major right‐lateral strike‐slip faults that link the Alpine fault to the Hikurangi subduction zone in the Pacific/Australia plate boundary zone in New Zealand. All of the major active faults of the Marlborough fault system have continuous traces except for the Clarence fault which terminates abruptly near the Ward syncline. Paleomagnetic data from upper Miocene and lower Pliocene sedimentary rocks between the Marlborough faults indicate a consistent post‐early Pliocene regional clockwise rotation of about 20°. An additional rotation of about 10° is evident at many localities near the termination of the Clarence fault. It is proposed that the additional rotation, relative to the rest of the region, is caused by a velocity gradient that likely exists between the active Awatere fault and the termination of the Clarence fault. The existence of such a velocity gradient is consistent with inferences from geodetic strain data which suggest that one‐third of the displacement in the Marlborough fault system occurs between the Awatere and Clarence faults. The kinematics of rotation can be modelled by treating the area as a rigid block that pivots about the termination of the Clarence fault. The block rotation model satisfies field constraints on the styles of deformation observed at the boundaries of the block and is consistent with available paleomagnetic and geodetic data.