QM11 Wairarapa
The Wairarapa 1:250,000 geological map covers a land area of c.7000 km2, the southeastern part of the North Island, New Zealand, and nearly 11 000 km2 of the adjacent offshore area.Onshore, the Tararua and Ruahine ranges, the axial ranges of the North Island, separate the Horowhenua lowlands from the Pahiatua basin. Major valleys formed by the Manawatu, Mangatainoka, Mangahao, Ruamahanga and Waingawa rivers occupy a broad depression between the Tararua/Ruahine ranges and the eastern uplands. The eastern uplands comprise the undulating and dissected hill country between the Pahiatua and Masterton basins and the sea. The Puketoi and Waewaepa ranges in the north of the area, part of the eastern uplands, reach the highest elevation. Uplifted marine terraces border much of the eastern coastline.
Offshore, the gently sloping continental shelf extends for 5-20 km to a depth of 150-200 m. Canyons and depressions incise the outer edge of the shelf, and the continental slope beyond it comprises a series of ridges and basins. The northeast-trending highs and ridges mark the location of anticlines underlain by west-dipping active thrust faults. The deformation front of the Hikurangi Trough is 65-125 km southeast of the Wairarapa coast and represents the boundary between the Pacific and Australian plates.
The complex geology of the Wairarapa area results partly from its proximity to the active plate boundary during the last c.25 million years.