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| Titel |
Exploring the Morphology of oceanic ridges with experiments using colloidal dispersions |
| VerfasserIn |
Anne Davaille, Aurore Sibrant, Eric Mittelstaedt, Alban Aubertin, Lionel Auffray, Raphael Pidoux |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250143968
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| Publikation (Nr.) |
 EGU/EGU2017-7741.pdf |
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| Zusammenfassung |
| Mid-ocean ridges exhibit significant changes in their structural, morphological, and volcanic
characteristics with changes in lithospheric thickness and/or spreading velocity. However, to
separate the respective roles of those two partly correlated effects is difficult with only field
data. We therefore designed a series of laboratory experiments using colloidal silica
dispersions as an Earth analogue. Saline water solutions placed in contact with these
fluids, cause formation of a skin through salt diffusion, whose rheology evolves
from purely viscous to elastic and brittle with increasing salinity. Applying a fixed
spreading rate to this pre- formed, brittle plate results in cracks, faults and axial ridge
structures. Lithospheric (skin) thickness at a given extension rate can be varied by
changing the surface water layer salinity. Moreover, the mechanical properties of
the skin can also be independently controlled by changing the type of colloid. We
focus here on cases where the spreading direction is perpendicular to the ridge
axis.
For a given dispersion and salinity, we observe four regimes as the spreading rate
increases: (1) at the slowest spreading rates, the spreading axis is composed of several
segments separated by non-transform offsets and has a fault-bounded, deep, U-shaped axial
valley. The axis has a large sinuosity, rough topography, and jumps repeatedly. (2) At
intermediate spreading rates, the spreading axis shows low sinuosity, overlapping spreading
centers (OSC) , a smooth axial morphology, and very few to no jumps. The axial valley is
shallow and shows a V-shape morphology. The OSCs have a ratio of length to width of 3 to 1.
(3) At faster spreading rates, the axis is continuous and presents an axial high topography. (4)
At the fastest spreading rates tested, the spreading axis is again segmented. Each segment is
offset by well developed transform faults and the axis has a sinuosity comparable to those of
regimes 2 and 3. Rotating and growing microplates are also observed in regimes 3 and
4.
These four regimes, as well as the decrease in sinuosity with increasing spreading rate
(regime 1) down to a critical value (regimes 2 to 4), present strong similarities with natural
cases. This is predicted by a new dimensionless number ΠF comparing the maximum
fracture length attainable without plasticity to the axial thickness. Slow spreading,
fault-dominated ridges and fast spreading, dike-dominated ridges on Earth and in the
laboratory are separated by the same critical ΠF value. Moreover, our results suggests that
the fraction M of spreading rate accomodated by magmatic dyke opening is closely related to
ΠF. |
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