Pliocene-Quaternary deformation and mechanisms of near-surface strain close to the eastern tip of the Clarence Fault, northeast Marlborough, New Zealand

In coastal northeast Marlborough, New Zealand, the termination of the dextr al strike-slip Clarence Fault requires a mechanism for the accommodation of strain about its tip. The Awatere Block, to the northeast of the tip, is i nferred to be undergoing a clockwise vertical-axis rotation as mid-lower cr ustal simple shear is transmitted upward into an upper crustal rigid-body r otation. Clockwise vertical-axis rotation of the Awatere Block of up to 44 degrees has previously been constrained by paleomagnetic data in Pliocene r ocks, and the deflection of near-vertical bedding in Torlesse Terrane basem ent rocks suggests a rotation of up to c. 55 degrees. The attitude and slip direction of mesoscopic faults in coastal exposures of late Miocene-Plioce ne rocks allow directions of faulting-related maximum instantaneous strain to be deduced. These directions swing from east-west in the north of the Aw atere Block to southeast-northwest in the south of the block as the style o f faulting changes from oblique-normal to strike-slip to thrust. This chang ing pattern of strain is inferred to be due to a clockwise rotation of the Awatere Block. The London Hill Fault forms an eastern boundary to the rotating Awatere Blo ck. Gouge-zone foliation and stratigraphic data reveal that the London Hill Fault is currently a reverse fault that reactivates an Eocene(?) normal fa ult. Post-Pliocene dip-slip on the London Hill Fault is in the order of 2 k m. New radiocarbon dating of a marine terrace to the southwest of Cape Camp bell requires a rate of uplift of 1.7-2.5 mm/yr over the last 5500 yr, much faster than other rates nearby. This difference in rate is inferred to be due to active folding of the adjacent Cape Campbell Syncline. Regional Holo cene northeast tilting of the Awatere Block is inferred from stream piracy patterns and tilted fluvial and coastal marine terraces. Local tilting patt erns are more complex and indicate surface deformation near currently activ e fault and fold structures.