Marine Heat Flow Measurements of the Northern and Southern Hikurangi Margin, New Zealand

Abstract:

The 120 Ma Hikurangi Plateau, a large igneous province on the Pacific plate, is subducting below the Australian plate at the Hikurangi margin. Large along-strike variations in apparent interseismic coupling and in the depth range over which slow slip occurs provide the opportunity to better understand which factors affect the slip behavior along the megathrust. Prior to our heat flow survey the thermal regime of the incoming Hikurangi Plateau was largely unknown. In May and June, 2015, we collected 196 seafloor heat flow values in a series of transects consisting of closely-spaced measurements with a 3.5 m “violin-bow” type probe. Heat flow measurements are located around the northern and southern Hikurangi margin and are collocated with seismic reflection lines. The background heat flow on the incoming plate is 49 ± 7, and 52 ± 9, mW/m² for the northern and southern areas, respectively. These values are consistent with cooling plate models for this age of oceanic crust and suggest no difference in the basal heat flux between these two areas. However, heat flow transects in the northern Hikurangi trough show clear evidence for crustal fluid flow associated with the basement relief, while heat flow transects along the southern Hikurangi trough do not show evidence for crustal fluid flow, which may be due to a lack of basement relief. We are developing a 2D thermal model for each region to understand the thermal and hydrologic regimes and their influence on clay diagenesis and modes of deformation.