The Paparoa Tectonic Zone

The Paparoa Tectonic Zone (new name) extends for 120 miles from the Alpine Fault at the Hokitika River to Kongahu Point, west Nelson, thus obliquely crossing the Paparoa Range. In the Late Tertiary and Quaternary, the zone was folded and fractured in a scissors movement, pivoting north‐east of Greymouth, and up‐faulting eastern blocks in the north and western ores in the south. A previous scissors movement along the same zone but in the opposite sense had occurred in late Cretaceous and early Tertiary times. The areas of down‐faulting and thickest sedimentary fill are indicated by their coincidence with the highest ranks of the Brunner coals; and coarse breccias and conglomerates, extending outwards from the zone at several localities, were produced by vigorous faulting about uppermost Eocene times. Some Miocene faulting also occurred, perhaps accounting for the absence of lower Tertiary beds in the Kawhaka bore. Orogenic movements during the Miocene‐Quaternary were accompanied by reverse faulting and overfolding, and the Paparoa and Papahaua Ranges probably were produced by high‐angle overthrusting. In contrast the late Cretaceous ‐ early Tertiary movements were accompanied by normal faulting. Changes in the direction of Principal Horizontal Stress in the zone and their implications on the history of the Alpine Fault are discussed.