Mantle Transition Zone Topography in New Zealand From Teleseismic P‐Wave Receiver Functions

Abstract The geology of New Zealand has been shaped by tectonic plate interactions driven by mantle convection over the past 60 million years, but the effects of these interactions on the transition to the lower mantle are not yet well understood. We analyze 10 years of teleseismic ‐wave receiver functions using common conversion point stacking to investigate mantle transition zone discontinuities. The resulting topography of the 410‐km and 660‐km discontinuities, smoothed using kriging interpolation, reveals localized thermal anomalies. We observe more than 10 km of thinning in the mantle transition zone beneath central North Island coincident with the Hikurangi slab, accompanied by a significantly thickened and hydrous melt‐rich layer above the 410‐km discontinuity. In northern South Island, the 410‐km discontinuity is uplifted by approximately 15 km, likely reflecting subducted materials from the oblique Hikurangi slab material reaching mantle transition zone depths. These observations are consistent with patterns of seismicity and seismic velocity anomalies from tomographic models. Additionally, we identify significant thinning of the mantle transition zone beneath both the Northland region (10 km) and the Great South Basin (15 km), indicating the influence of potential local thermal upwellings. The different slab polarities and transpressional boundary may drive lateral mantle flow, shaping the complex transition zone topography beneath New Zealand.