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| Titel |
Numerical model of crustal accretion and cooling rates of fast-spreading mid-ocean ridges |
| VerfasserIn |
P. Machetel, C. J. Garrido |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1991-959X
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| Digitales Dokument |
URL |
| Erschienen |
In: Geoscientific Model Development ; 6, no. 5 ; Nr. 6, no. 5 (2013-10-14), S.1659-1672 |
| Datensatznummer |
250084999
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| Publikation (Nr.) |
 copernicus.org/gmd-6-1659-2013.pdf |
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| Zusammenfassung |
| We designed a thermo-mechanical numerical model for fast-spreading mid-ocean
ridge with variable viscosity, hydrothermal cooling, latent heat release,
sheeted dyke layer, and variable melt intrusion possibilities. The model
allows for modulating several accretion possibilities such as the "gabbro glacier"
(G), the "sheeted sills" (S) or the "mixed shallow and MTZ lenses" (M).
These three crustal accretion modes have been explored assuming viscosity
contrasts of 2 to 3 orders of magnitude between strong and weak phases and
various hydrothermal cooling conditions depending on the cracking
temperatures value. Mass conservation (stream-function), momentum
(vorticity) and temperature equations are solved in 2-D cartesian geometry
using 2-D, alternate direction, implicit and semi-implicit finite-difference
scheme. In a first step, an Eulerian approach is used solving iteratively
the motion and temperature equations until reaching steady states. With this
procedure, the temperature patterns and motions that are obtained for the
various crustal intrusion modes and hydrothermal cooling hypotheses display
significant differences near the mid-ocean ridge axis. In a second step, a
Lagrangian approach is used, recording the thermal histories and cooling
rates of tracers travelling from the ridge axis to their final emplacements
in the crust far from the mid-ocean ridge axis. The results show that the
tracer's thermal histories are depending on the temperature patterns and the
crustal accretion modes near the mid-ocean ridge axis. The instantaneous
cooling rates obtained from these thermal histories betray these
discrepancies and might therefore be used to characterize the crustal
accretion mode at the ridge axis. These deciphering effects are even more
pronounced if we consider the average cooling rates occurring over a
prescribed temperature range. Two situations were tested at
1275–1125 °C and 1050–850 °C. The first temperature
range covers mainly the crystallization range that is characteristic of the
high temperature areas in the model (i.e. the near-mid-oceanic-ridge axis).
The second temperature range corresponds to areas in the model where the
motion is mainly laminar and the vertical temperature profiles are closer to
conductive. Thus, this situation results in less discriminating efficiency
among the crustal accretion modes since the thermal and dynamic properties
that are described are common to all the crustal accretion modes far from
the ridge axis. The results show that numerical modeling of
thermo-mechanical properties of the lower crusts may bring useful
information to characterize the ridge accretion structure, hydrothermal
cooling and thermal state at the fast-spreading ridges and may open
discussions with petrological cooling rate results. |
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