Modelling of Gravity Data from Tongariro National Park

Abstract

Data, both from previous gravity and recent measurements made across the Tama Lakes Saddle, have been used to calculate a Bouguer anomalymap for National Removal of a regional field represented by a third degree polynomial produces a anomalymap which covers an area of 40 x Two-dimensional modelling across Tama Lakes Saddle shows thatthe data can be modelled predominantly by pyroclastic material of density 1. overlying a high density basement. A thincover of higher density andesites to the west of Tama Lakes. A model Ruapehu shows layers (andesites, pyroclastics and basement) and a low density volcanic chimney. Three-dimensionalmodelling of the area around Ruapehu elucidates this structure and reveals considerable topography in the high density basement. The is that the high density basement beneath Ruapehu itself may actually represent an andesite sill overlying greywacke. The gravity data alone is not able to distinguish whether this is the case but it is hoped that electrical data across the Tama Lakes Saddle, where a similar structure may exist, will be able to detect the presence of any magmatic component.