The northeastern portion of the Clarence Fault: tectonic implications for the late Neogene evolution of Marlborough, New Zealand

The Clarence Fault does not extend northeastward to the Marlborough coast as traditionally mapped. Instead, it joins with a northerly trending shear zone within the Torlesse Supergroup near Peggioh Station, 10 km west of Ward. In this region the Clarence Fault is a blind, west-dipping moderate-angle reverse or thrust fault, east of which, on the downthrown side, the Late Cretaceous and Tertiary sedimentary and volcanic succession has been overturned. The Clarence Fault and a number of associated splay faults represent a positive flower structure that formed in association with drape folding. These structures probably began forming in the early Miocene. If the present-day rate of dextral strike-slip on the Clarence Fault of 4-8 mm/yr were extrapolated into the past, the total inferred lateral offset of 15 km along the fault could be accomplished in 3 million years. Consequently, it is suggested that the Clarence Fault has acted as a dextral strike-slip structure only comparatively recently, in the order of the last few million years, and that before this it was a southward-directed thrust fault.