Three-dimensional structure of relict stratovolcanoes in Taranaki, New Zealand: evidence from gravity data

Abstract

The andesite stratovolcanoes of Taranaki occur in a spatially distinct age progression, being eroded to different levels and situated within a large well-known sedimentary basin, thus providing particularly favourable circumstances for geophysical investigation. New gravity data presented here show that the Kaitake and Pouakai volcanoes, two of the older relict centres, are associated with large positive residual gravity anomalies (240 g.u. and 160 g.u., respectively). Detailed three-dimensional gravity models define confined high-density dyke/stock complexes below the volcanoes which constrain the likely locus of eruptive activity and extend to at least basement depths (about 5 km). The older Kaitake edifice is modelled as solid andesite whereas the younger Pouakai edifice comprises a solid andesite core mantled by lower-density volcaniclastics. These andesite bodies are interpreted as regions of extensive dyke injection, a process clearly important in cone development and possibly also in cone stability.