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SUMMARY:Seismological evidence for secular mantle cooling beneath cratons 
 - Federico Munch -- ETH Zürich
DTSTART:20231101T160000Z
DTEND:20231101T170000Z
UID:TALK205372@talks.cam.ac.uk
CONTACT:Lisanne Jagt
DESCRIPTION:Cratons are thought to be underlain by a thick ‘root’ of m
 antle that has experienced very high degrees of partial melting\, resultin
 g in a cold\, strong\, and buoyant mantle compared to its oceanic counterp
 art. However\, the degree to which such cratonic regions are stabilized du
 e to differences in composition as opposed to their thermal structures rem
 ains debated. \n\nAnalyses of xenoliths provide insights on the thermal st
 ructure and composition of the continental mantle. However\, xenoliths onl
 y record a temporal snapshot of an often geographically limited region of 
 the mantle lithosphere. In order to provide a more spatially extensive vie
 w of the nature of the sub-continental lithospheric mantle\, geophysical t
 echniques are invaluable. Current inversions of seismic data\, for example
 \, consider the mantle to be a binary mixture of basalt and harzburgite\, 
 which is then used to compute the stable mineral assemblage at the desired
  pressure and temperature (Munch et al.\, 2020\; Bissig et al.\, 2021). Ho
 wever\, a simple binary mixture cannot account for the high Mg# (Mg/[Mg+Fe
 ]) and low Mg/Si ratios recorded in xenoliths from cratonic regions induce
 d by metasomatic processes (Boyd\, 1989\; Canil\, 2004\; Pearson et al. 20
 22) . \n\nIn this study\, we extend the chemically-differentiated oceanic-
 lithosphere (basalt-harzburgite) model to better capture the compositional
  diversity observed in cratonic mantle peridotites (Canil\, 2004) in the s
 tochastic inversion of seismic data for mantle temperature and composition
 . This new framework is applied to the inversion of receiver function wave
 forms and fundamental-mode Rayleigh wave dispersion data recorded at 40 se
 ismic stations located in different tectonic settings around the world. \n
 \nThe retrieved mantle compositions are in overall agreement with the comp
 ositions and thermal profiles obtained from analyses of mantle xenoliths. 
 Our results suggest that the geotherms recorded by xenoliths are compatibl
 e with steady-state conductive conditions in and around the lithosphere/as
 thenosphere. We find a decrease in mantle potential temperature under crat
 ons as a function of their age\, reflecting the secular cooling of the lit
 hospheric mantle.\n
LOCATION:Wolfson Lecture Theatre
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