High pressure breakdown of antigorite to spinifex-textured olivine and orthopyroxene, SE Spain |
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Authors: | V Trommsdorff V López Sánchez-Vizcaíno M T Gómez-Pugnaire O Müntener |
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Institution: | (1) Institut für Mineralogie und Petrographie, ETH Zentrum, CH-8092 Zürich, Switzerland, CH;(2) Depto. Geologia, Escuala Universitaria Politécnica, Universidad de Jaen, E-23700 Linares, Spain, ES;(3) Depto. Mineralogia y Petrologia, Facultad de Ciencias, Universitad de Granada, E-18002 Granada, Spain, ES |
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Abstract: | The prograde, high pressure, transition from antigorite serpentinite to enstatite-olivine rock occurs along a tectonically
undisturbed profile at Cerro del Almirez, SE Spain. The reactant assemblage is antigorite + olivine with tremolite rimming
precursor diopside. The product assemblage of tremolite + chlorite + enstatite + olivine has a spinifex-like texture with
arborescent or radiating olivine elongated parallel to 001] and with radially grown enstatite. Product enstatite is very
poor in Al2O3. Due to numerous oriented submicroscopic inclusions of chromian magnetite, product olivine has a brownish pleochroism and
a bulk chromium content similar to precursor antigorite. Titanian clinohumite with a fluorine content of 0.45–0.50 wt% persisted
beyond the breakdown of antigorite. The partitioning of iron and magnesium amongst the silicate phases is almost identical
to that at lower pressures. Average Kd values Mn/Mg and Ni/Mg are 0.17 and 0.70 for antigorite-olivine pairs and 1.83 and 0.22 for orthopyroxene-olivine pairs,
respectively. These data are useful in discriminating generations of olivine grown on each other. From the field data a phase
diagram topology for a portion of the system CaO-MgO-SiO2-H2O is derived. This topology forms the basis for extrapolations into inaccessible P-T regions.
Received: 6 February 1998 / Accepted: 24 March 1998 |
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