Abstract:
The contiguous Taranaki, Aotea and Northland Basins are host to a range of volcanic fields and
intrusions ranging from the Late Cretaceous to the early Pliocene. Seismic reflection data was used to
investigate the West Ngatatura Volcanic field, a Pliocene aged monogenetic volcanic field located on
the boundary of the Northland and Taranaki Basins. The volcanic seismic facies of the extrusive
components were divided into the Pre-Eruptive Surface (PrErS) and Post-Eruptive Surface (PoErS). The
PoErS was interpreted from onlaps, downlaps, and anomalous high amplitude reflections against low
amplitude, stratified horizons corresponding to sedimentary units and the PrErS was interpreted as
negative polarity reflections beneath high amplitude discontinuous reflections. Saucer-shaped sills
were interpreted from high amplitude, horizontal-subhorizontal reflections with inclined or
discontinuous flanks. 3D surfaces were then interpolated from the interpreted data and used to
further interpret the macro-morphologies of the volcanic field. ~40 different volcanic edifices across
three different clusters present themselves in two linear trends that align with interpreted NNE-SSW
trending basement faults. Seismic attenuation and automatic gain control prevented the direct linking
magma conduits to specific faults. All of the edifices were volcanic cones and little evidence of maars
or craters was found. The cones range in diameter from <1 km – 4.5 km and in height from <700 m to
>1200 m. A spatiotemporal analysis was then conducted to determine a relative sequence of events
based on spatial patterns within the volcanic edifices and found that the sill emplacement occurred
before the extrusive volcanism. The possibility of a northward trending direction of volcanism is
presented and discussed with the large assumptions of sedimentation rates during the Pliocene.
