Seismic tomographic constraints on the Antarctic-Eastern Australian margin of Gondwanaland and the southwest Pacific oceans

Abstract:

We have mapped a distinct swath of flat slabs at depths of 1900 to 2500 km below present-day West Antarctica and the southernmost Pacific. The slab anomalies occupy a minimum area of 8000 x 5000 km and are distinguishable on multiple global tomography datasets including TX2011 (Grand and Simmons, 2011) and MIT-P08 (Li et al., 2008). When reconstructed within a lower mantle reference, the restored slab positions show a compelling fit opposite the pre-breakup (~185 Ma) southern margin of Gondwanaland from published plate reconstructions (Seton et al., 2012).

Here we present a new plate reconstruction with the subducted slab constraints. At ~185 Ma the southern mapped slabs began to subduct under a SSE-moving Eastern Gondwanaland margin formed by Antarctica-Eastern Australia. The northern slabs were subducted during the formation of the new oceans at the Ellice Basin, Osbourn Trough and the present-day Tonga-Kermadec slabs. The mapped flat slabs were completely subducted by ~85 Ma, at which time subduction ceased at the Eastern Australian-Antarctica margin.

We mapped subducted slabs by manually picking the midpoints of fast seismic tomographic anomalies and constructing meshed mid-slab surfaces. Slabs were restored to their pre-subduction geometries by structurally unfolding to a spherical Earth model surface. Unfolded slabs were used as plate reconstruction constraints using Gplates software.