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| Titel |
Seismic constraints on thermo-chemical nature of the lower mantle and on S − to − P heterogeneity ratio |
| VerfasserIn |
Fabio Cammarano, Andrea Tesoniero, Lapo Boschi, Mattia Guerri |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250134098
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| Publikation (Nr.) |
 EGU/EGU2016-14786.pdf |
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| Zusammenfassung |
| We analyse our joint V P-V S model SPani and the data that went into it to assess the
thermochemical nature of the lower mantle. Robust structural variations between V P and
V S and an increase of decorrellation with depth between δlnV S and δlnV P in
the two Large Low Shear Velocity Provinces (LLSVPs) indicate the presence of
compositional heterogeneity inside the LLSVPs and compositional layering. The
morphology of subducting slabs confirms the complexities recently imaged by V P models
(e.g. Fukao and Obayashi 2013) and the comparison between V P and V S suggests
the presence of chemical variations also in the transition zone and mid-mantle. A
quantitative interpretation of chemical heterogeneity is hampered by the difficulty to
provide precise estimates of the heterogeneity ratio δlnV S∕δlnV P (RS∕P). For
instance, the global median value of RS∕P (< RS∕P >) drops from ∼2.8 to ∼1.9, at
2500km depth when the V P component of SPani is replaced by a V P model resulting
from a differently regularized inversion. Boosting the V P anomalies of 20% also
drastically reduces < RS∕P > without significantly degrading the data fit. In spite of
robust decorrelations between V P and V S structure, we found that high values of
RS∕P associated with both positive and negative velocity anomalies in the lower
mantle, including the two LLSVPs, are affected by noise in the model parameters
and can be overestimated. Additional uncertainties in compositional effects on
RS∕P from mineral physics and in the conversion of δlnV S or δlnV P into density
contributes to further complicate a quantitative thermo-chemical interpretation. |
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