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SUMMARY:Structure and evolution of the upper mantle of the Australian Plat
 e from waveform tomography with massive datasets - Janneke de Laat  -- Uni
 versity of Cambridge
DTSTART:20231004T150000Z
DTEND:20231004T160000Z
UID:TALK205363@talks.cam.ac.uk
CONTACT:Yihe Xu
DESCRIPTION:In this talk I present a new S-wave velocity tomographic model
  of the upper mantle beneath the Australian Plate and its boundaries\, Aus
 22\, and the insights obtained from it. Aus22  includes azimuthal anisotro
 py and is constrained by waveforms from 0.9 million vertical-component sei
 smograms\, with the densest data sampling in the hemisphere centred on the
  Australian continent\, using all available data covering this hemisphere.
  Waveform inversion extracted structural information from surface waves\, 
 S- and multiple S-waves and constrained S- and P-wave speeds and S-wave az
 imuthal anisotropy of the crust and upper mantle\, down to the 660- km dis
 continuity. The model was validated by resolution tests and\, for particul
 ar locations in Australia with notable differences from previous models\, 
 by independent inter-station measurements of surface-wave phase velocities
 . As the model is generated with data extending beyond the boundaries of t
 he Australian Plate\, it images the both the Australian Plate as well as i
 ts boundaries in detail.\n\nAus22 offers new insights into the structure a
 nd evolution of the upper mantle of the Australian Plate and its boundarie
 s. Thick\, high-velocity (and\, by inference\, cold) cratonic lithosphere 
 occupies nearly all of western and central Australia but shows substantial
  lateral heterogeneity. It extends up to the northern edge of the plate\, 
 where it collides with island arcs\, without subducting. Diamondiferous ki
 mberlites and lamproite deposits are underlain by cratonic lithosphere\, e
 xcept for the most recent diamondiferous lamproites in the King Leopold Or
 ogen. The rugged eastern boundary of the cratonic lithosphere resolved by 
 the model provides a lithospheric definition of the Tasman Line. The easte
 rn part of Australia is underlain by thin\, warm lithosphere\, evidenced b
 y low seismic velocities. All the sites of Cenozoic intraplate volcanism i
 n eastern Australia are located on thin lithosphere. A low-velocity anomal
 y is present in the mantle transition zone beneath the Lord Howe and Tasma
 nid hotspots\, indicative of anomalously high temperature and consistent w
 ith a deep mantle upwelling feeding these hotspots and\, possibly\, also t
 he East Australia hotspot. High seismic velocities are observed in the tra
 nsition zone below northeast Australia and indicate the presence of subduc
 ted lithospheric fragments trapped in the transition zone\, possibly parts
  of the former northern continental margin of Australia.\n\n
LOCATION:Bullard Labs tearoom\, Department of Earth Sciences\, Madingley R
 ise
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