Seismic tomographic constraints on the Antarctic-Eastern Australian margin of Gondwanaland and the southwest Pacific oceans
Han-Fang Liu1, Jonny Wu2, John Suppe3, Prof. Renqi Lu, PhD1,4 and Ravi V S Kanda1,5, (1)Department of Geoscience, National Taiwan University, Taipei, Taiwan, (2)University of Houston, Department of Earth and Atmospheric Sciences, Houston, TX, United States, (3)Department of Earth and Atmospheric Sciences, University of Houston, Houston, United States, (4)Institute of Geology, China Earthquake Administration, Beijing, China, (5)Utah State University, Geosciences, Logan, UT, United States
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.
