The structural controls on Karst Development, Oparure Block, North Island, New Zealand

Abstract

Te Kuiti Group limestones and Mahoenui Group mudstones crop out extensively on the Oparure Block, souther Waikato District, New Zealand. Reactivation of major north-south oriented normal faults, including the Waipa Fault, to an oblique-slip motion has resulted in a consisten set of Riedel fractures in the Te Kiti Group limestones. Large discontinuous fracture breccias form along first-order Riedel faults. The Mangawhitikau Stream drains the Oparure Block from west to east, down the regional dip on the Te Kuiti Group of a few degrees to the east. As groundwater interacted with the Te Kuiti Group limestones, karst development began. Along with the epikarst zone a shaft and conduit zone was formed primarily along first- and second-order Riedel fractures. By the time the Mangawhitkau Stream eroded down to the Te Kuiti Group many open conduits were present in the limestone and captured the stream flow, resulting in the formation of caves.