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SUMMARY:Mapping Seismic Tomography into Earth Structure: Implications for 
 Dynamic Topography\, Lithospheric Stability and Sea-Level Reconstructions 
 - Fred Richards - Imperial College London
DTSTART:20200205T160000Z
DTEND:20200205T170000Z
UID:TALK137407@talks.cam.ac.uk
CONTACT:Jenny Jenkins
DESCRIPTION:Advances in seismic tomography over the past four decades have
  dramatically improved our knowledge of Earth’s internal structure. Over
  the same period\, observational constraints on mantle dynamics have stead
 ily improved thanks to the growing accuracy and geographic coverage of gra
 vity\, heat flow and residual topography measurements.However\, although m
 antle flow simulations that incorporate tomographically inferred buoyancy 
  structure  are  able  to  fit  the  longest  wavelength  components  of  
 the  gravityfield\, the dynamic topography they predict tends to diverge s
 ignificantly from observed patterns.  Similarly\, the inferred temperature
  structure of the mantle is often in poor agreement with constraints from 
 mid-ocean ridge basalts and suites of mantle xenoliths. A significant sour
 ce of discrepancy in these calculations can be linked to the simplistic me
 thodology used to convert upper mantle seismic velocity variations into bu
 oyancy anomalies.   In  this  talk\,  I  will  show  that  much  of  the  
 disagreement  between  modelsand observations of dynamic topography can be
  resolved by using experimentally de-rived anelasticity parameterisations 
 to infer the temperature and density structure ofthe lithosphere and asthe
 nosphere (e.g. Priestley and McKenzie\, 2013\; Yamauchi andTakei\, 2016). 
  This updated Earth structure is then used to investigate time-dependent c
 hanges  in  dynamic  topography  and  lithospheric  thickness.   First\,  
 by  simulating  the history  of  mantle  flow  beneath  Australia\,  I  de
 monstrate  that  the  associated  spatio-temporal evolution of dynamic top
 ography can explain the∼±250 m relative sea-level changes observed acro
 ss the continent since the Mid-Pliocene Warm Period (MPWP\;∼3 Ma).  Remo
 val of the dynamic topography signal from this dataset places import-ant c
 onstraint on eustatic sea-level and ice volume during the MPWP\, the last 
 time in Earth history that atmospheric CO2concentrations were similar to t
 he present.  Second\,by comparing xenolith-derived palaeogeotherms with pr
 esent-day temperature profiles inferred from seismic tomography models\, I
  will present evidence for post-Cretaceous lithospheric thinning beneath C
 entral Angola.  However\, this dynamism appears to be relatively  rare.   
 Similar  comparisons  in  other  regions  and  the  distribution  of  anci
 ent sediment-hosted  mineral  deposits  along  present-day  cratonic  edge
 s\,  suggest  that\,  in general\, continental lithosphere is remarkably s
 table.
LOCATION:Marine/Wolfson Building lecture hall\, Bullard Labs.
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