Plastic deformation and magmatic impregnation in serpentinized ultramafic rocks from the Garrett transform fault (East Pacific Rise)

Details Plastic deformation and magmatic impregnation in serpentinized ultramafic rocks from the Garrett transform fault (East Pacific Rise) Plastic deformation and magmatic impregnation in serpentinized ultramafic rocks from the Garrett transform fault (East Pacific Rise)

Dec 1990

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990e%26psl.101..216c&link_type=abstract

Earth and Planetary Science Letters, Volume 101, Issue 2-4, p. 216-232.

Mathematics

Logic

30

Scientific paper

The microstructural study of a set of serpentinized ultramafic samples dredged in the Garrett transform fault, shows that these rocks have been deformed plastically at temperatures probably in excess of 1000°C, and under moderate deviatoric stresses (below 1 kbar). Such temperature and stress conditions probably prevail in the asthenosphere, or in the deepest and hottest part of the lithosphere below the ridge. The deformed paragenesis of the studied samples belong to two groups: harzburgites with petrological characteristics typical of residual mantle; and plagioclase-dunites. A melt circulated in these two groups of deformed ultramafic rocks at the end of their deep-seated plastic deformation. This melt crystallized plagioclase, clinopyroxene, and also possibly orthopyroxene in one sample, in dykelets, and in interstices between the minerals of the deformed host rock. The deformation and magmatic impregnation history of the studied ultramafic samples recall the results of on-land studies of the crust-mantle transition zone of ophiolitic massifs. This suggests that our set of samples may represent fragments of the East Pacific Rise crust-mantle transition zone. The deformed ultramafic paragenesis of these samples was chemically modified by interactions with the impregnating melt: the deformed spinel was enriched in TiO2 and Cr2O3, the deformed clinopyroxene and orthopyroxene of the harzburgitic samples were also enriched in TiO2, and the orthopyroxene was significantly depleted in Al2O3. The high mobility of titanium during the impregnation process suggests that the Ti content of a melt, often used as an indicator of its degree of evolution, or of the degree of partial melting undergone by its source rock, may also be modified by melt/rock interactions during the circulation of the magma through the crust and upper mantle.

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