Slab-Plume Interactions Beneath Australia and New Zealand: New Insight From Whole-Mantle Tomography

Abstract

Australia, New Zealand, and the surrounding regions have experienced complex plate interactions with significant seismic and volcanic activities. The Taupo volcano on the North Island of New Zealand has experienced multiple catastrophic eruptions. Although Australia is known as a stable landmass with low seismic and volcanic activity, intraplate volcanoes along its eastern coast are considered to be caused by hot mantle plumes. To better understand the seismic and volcanic activities in the region, it is necessary to study the detailed 3-D structure of the crust and mantle. Here we apply a well-established global tomography method to reveal the 3-D P-wave velocity ($V_P$) structure of the whole mantle beneath this region. We used ∼7 million P, pP, PP, PcP, and Pdiff wave arrival times of 23,666 earthquakes recorded at 14,181 seismograph stations worldwide. The resulting $V_P$ tomography clearly shows high-$V_P$ subducted slabs, and low-$V_P$ anomalies above and below the slabs, which may reflect corner flow in the mantle wedge and subslab hot mantle upwelling (SHMU), respectively. A slab window is revealed beneath the North Island of New Zealand. Given the development of SHMU beneath this region, the catastrophic eruptions of the Taupo volcano might be powered by a mixture of island arc magma and SHMU through the slab window. Beneath the intraplate volcanoes along the eastern coast of Australia and the Tasman Sea, a thin low-$V_P$ zone exists and extends down to the core-mantle boundary, suggesting that the intraplate volcanoes might be, at least partially, fed by a plume rising from the lower mantle.