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Titel |
An integration to optimally constrain the thermal structure of oceanic lithosphere |
VerfasserIn |
Bruno Goutorbe, John K. Hillier |
Konferenz |
EGU General Assembly 2013
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 15 (2013) |
Datensatznummer |
250077003
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Zusammenfassung |
The evolution through time of the oceanic lithosphere is a substantial, incompletely resolved
geodynamical problem. Consensus remains elusive regarding its thermal structure, physical
properties, and the best model through which to unify observational constraints.
We robustly re-evaluate all three of these by i) simultaneously fitting heat flow,
bathymetry, and temperatures derived from a shear velocity model of the upper mantle,
ii) using the three main thermal models (half-space, plate and Chablis) and iii)
analysing five depth–age curves, wherein contrasting techniques were used to exclude
anomalous features from seafloor depths. The thermal models are updated to all include a
temperature-dependent heat capacity, a temperature- and pressure-dependent thermal
conductivity and an initial condition of adiabatic decompression including melting. The
half-space model, which lets the lithosphere thicken indefinitely, cannot accurately fit the
subsidence curves and requires mantle potential temperatures, Tm, that are too high.
On the other hand, the models including a mechanism of basal heat supply are
able to simultaneously explain all observations within two standard errors, with
best-fitting parameters robust to the choice of the filtered bathymetry curve. For the plate
model, which imposes a constant temperature at a fixed depth, Tm varies within
1380–1390°C, the equilibrium plate thickness a within 106–110 km, and the bulk thermal
expansivity α¯ within 2.95–3.20 -
10-5Â K-1. For the Chablis model, which prescribes a
fixed heat flow at the base of a thickening lithosphere, the best-fitting values are
Tm = 1320–1380°C, a = 176–268 km, ¯α = 3.05–3.60 -
10-5Â K-1. Driven by
more accurate ocean depths, the plate model provides better joint-fittings to the
observations; however, it requires values of ¯α lower than experimentally measured,
which can be explained by a reduction of the apparent expansivity due to elastic
rigidity of the upper lithosphere. The Chablis model better fits the data when ¯α is set
close to or above the experimental values. Whilst statistically consistent within two
standard errors, a tendency toward incompatibility between observed depth–age curves
and seismically-derived temperatures is revealed with new clarity, as the latter do
not exhibit a clear steady state whereas the former flatten: further work is needed
to identify the origin of this apparent discrepancy. This work opens the way to
investigations fully independent from particular solutions of the heat equation. |
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