Mangatete: Evolution of a paleo-hydrothermal system, Taupo Volcanic Zone (TVZ)

Abstract

Hydrothermal activity in the TVZ occurs along two NE-SW trending alignments, located on either side of the Taupo Fault Belt (TFB). Lack of present-day hydrothermal activity within the TFB can be explained if the belt behaves as a major recharge zone to the large-scale convection system. However, siliceous hot-spring deposits (sinters) within the fault belt attest to a rich history of past hydrothermal activity: i.e. the current disposition of the convection system is not necessarily ‘steady-state’. The Mangatete paleo-hydrothermal system is located on the Whirinaki fault, where inferred cross-faults presumably provide enhanced permeability. Displacement on the Whirinaki Fault has exposed deposits of hydrothermal eruption breccias, zeolitised lake sediments and sinter. In situ sinter is patchy, distributed over a 1.5 km2 area, and surrounded by extensive debris flow deposits (maximum ~2 ka BP) containing ex situ sinter clasts. Sinter fabrics preserve paleoenvironmental signatures and assist in reconstructing the geographical extent of the paleohydrothermal field. 14C dating establishes geothermal activity from possibly as long ago as 32 kyrs (ex situ sinter), and definitely over a period of 18.5 ka to 8.5 ka (in situ sinter) in the immediate Mangatete N & S quarry area, with sinters in surrounding areas dated from ~17.9 ka to