Mantle temperature anomaly in southern Kermadec speculated by three-dimensional numerical subduction modeling

Along-strike geochemical variations of the Quaternary volcanic rocks in southern Kermadec are classified into two types, “arc-type” (e.g., Rumble V Ridge) and “rift-type” basalts (e.g., Ngatoro Rift), that indicate partial melting and no melting of the subducted sediment, respectively. A recent geochemical study attributed the arc-type basalts to the increased slab surface temperatures resulting from a hot finger-like temperature anomaly in the mantle wedge. To test the existence of the temperature anomaly, we conducted three-dimensional numerical subduction models varying the size of a hot temperature anomaly in the mantle wedge under the Rumble V Ridge. A temperature anomaly with a diameter of 60 km and magnitude of ~ 150 °C increased the slab surface temperature by up to 60 °C and resulted in the localized partial melting of the subducted sediment under the Rumble V Ridge, which is reflected in the arc-type basalts. In addition, the temperature anomaly in the mantle wedge explains the spacing (~ 80 km) between the Rumble V Ridge and Ngatoro Rift. Thus, hot finger-like temperature anomalies in the mantle wedge plausibly explain both the along-strike geochemical variations of the Quaternary volcanic rocks and the spacing between the Rumble V Ridge and Ngatoro Rift in southern Kermadec. High-resolution seismic tomography of the mantle wedge and back-arc mantle could confirm the existence of the temperature anomalies.