Crustal structure of the Newer Volcanics Province, SE Australia, from ambient noise tomography

Abstract

Intraplate volcanism is a widespread phenomenon, and is generally regarded to be independent of plate tectonics. The Newer Volcanics Province (NVP) of SE Australia represents the most recent (and arguably still active) intraplate volcanism on the Australian continent, and has been postulated to originate from the combined effect of localized shear flow and edge-driven convection. In this study, we adopt ambient noise tomography and Monte-Carlo inversion methods to construct the first local-scale 3D crustal Vs model of the NVP region with a resolution of ~35km. The model displays distinct crustal velocity features near the eastern and western margins of the NVP, which may point to the existence of a lithosphere-scale plumbing system for the migration of melt associated with the boundary between the Delamerian Orogen and the Lachlan Orogen, which underlies the NVP. In particular, exceptionally high velocities are observed in the middle crust of the Delamerian Orogen, and are best explained by buried magmatic arcs. This interpretation is consistent with a subduction-accretion origin for the Delamerian Orogen. Trans-lithospheric faults might have developed during the accretion processes, providing possible pathways for the migration of NVP magmas to the crust and surface. Our 3D model also images small localized velocity reductions in the lower crust at the region where the two distinct lithospheric units meet. The low velocity zone is spatially correlated with the top of a prominent lithosphere-scale low-resistivity zone (10–30Ωm), which we interpret to represent intruded magmatic sills with small proportions of melt remaining.