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| Titel |
Flexure and rheology of Pacific oceanic lithosphere |
| VerfasserIn |
Johnny Hunter, Tony Watts |
| 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 |
250130169
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| Publikation (Nr.) |
 EGU/EGU2016-10384.pdf |
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| Zusammenfassung |
| The idea of a rigid lithosphere that supports loads through flexural isostasy was first
postulated in the late 19th century. Since then, there has been much effort to investigate the
spatial and temporal variation of the lithosphere’s flexural rigidity, and to understand how
these variations are linked to its rheology. We have used flexural modelling to first re-assess
the variation in the rigidity of oceanic lithosphere with its age at the time of loading, and then
to constrain mantle rheology by testing the predictions of laboratory-derived flow
laws.
A broken elastic plate model was used to model trench-normal, ensemble-averaged
profiles of satellite-derived gravity at the trench-outer rise system of circum-Pacific
subduction zones, where an inverse procedure was used to find the best-fit Te and loading
conditions. The results show a first-order increase in Te with plate age, which is best fit by
the depth to the 400 ± 35∘C plate-cooling isotherm. Fits to the observed gravity are
significantly improved by an elastic plate that weakens landward of the outer rise, which
suggests that bending-induced plate weakening is a ubiquitous feature of circum-Pacific
subduction zones.
Two methods were used to constrain mantle rheology. In the first, the Te derived by
modelling flexural observations was compared to the Te predicted by laboratory-derived
yield strength envelopes. In the second, flexural observations were modelled using
elastic-plastic plates with laboratory-derived, depth-dependent yield strength. The results
show that flow laws for low-temperature plasticity of dry olivine provide a good fit to the
observations at circum-Pacific subduction zones, but are much too strong to fit observations
of flexure in the Hawaiian Islands region. We suggest that this discrepancy can be explained
by differences in the timescale of loading combined with moderate thermal rejuvenation of
the Hawaiian lithosphere. |
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