Structure of the Hawke’s Bay Forearc Basin and North Island Shear Belt, eastern North Island, New Zealand

Abstract

This report describes the broad structure of the forearc basin in Central Hawke’s Bay, provides descriptive details about many of the faults and folds and interprets the timing of formation of these structures. The structures are illustrated on 1: 50 000 geological maps (Bland and Kamp 2014) and four regional cross-sections (Enclosure 1). The North Island Shear Belt (NISB) encompasses a series of sub-parallel reverse and oblique-slip faults lying along the western margin of the basin. We infer no more than 10 km dextral offset on Ruahine Fault and a few hundred metres on Mohaka Fault, and their formation during the Late Pliocene (3.0 – 2.6 Ma). This was preceded by regional tilting along the western basin margin from c. 4.7 Ma. The southeastern margin of the basin has been offset by dip-slip reverse faults and uplifted through growth of the inboard margin of the accretionary wedge formed within the Hikurangi margin.