Reaktionen im alpinotypen Peridotitmassiv von Ronda (Spanien) und seinen partiellen Schmelzprodukten

The alpine type peridotite of Ronda (Spain) essentially is spinel lherzolite plus minor (< 5 vol.-%) amounts of basic layers. Basic layers are thin bands of several cm in thickness with different extent, arranged parallel to the lineation a of the lherzolite. 5 new rock analyses are presented, showing that the basic layers are olivine tholeiitic in composition, supporting their genetic interpretation as partial fusion products from an upper mantle peridotite of nearly pyrolitic chemism. Basic parts are not removed from the lherzolite host but consolidated as garnet pyroxenites, spinel pyroxenites, and olivine gabbros. Microprobe analyses of 6 olivines, 6 orthopyroxenes, 5 clinopyroxenes, 1 garnet, 2 spinels are given, most of them from coexisting minerals of pyroxenites and olivine gabbros.In garnet pyroxenite and in spinel pyroxenite the two pyroxenes are Al-rich pyroxenes, changing continuously by subsolidus reactions to Al-poor pyroxenes+anorthite ± spinel in the gabbro. Subsolidus transformations are marked by exsolution reactions and recrystallizations, favoured by weak deformation. Detailed study of mineral textures combined with chemical data show that spinel pyroxenite was isochemically transformed to spinel bearing olivine gabbro. This transformation mainly was caused by change in the P-T-conditions, related to the further steady uplift of the entire massif. P-T-estimations according to several methods indicate consolidation of garnet pyroxenite bands at 1100 ° C/20 kb. Subsolidus reactions changing spinel pyroxenite (1000-900 ° C/15 kb) to olivine gabbro layers show final re-equilibration in the range of 900–800 ° C at 15–10 kb.

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Gekürzter, spezieller Teil einer vom Naturwiss. FB III der Universität Würzburg 1975 angenommenen Habilitationsschrift

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Die Mikrosondenuntersuchungen wurden an einer CAMECA MS 46 (Leihgabe der Deutschen Forschungsgemeinschaft im Mineralogischen Institut Würzburg) durchgeführt. Für die Bewilligung beantragter Sachmittel und Reisekostenzuschüsse bin ich der DFG zu Dank verpflichtet. Dank schulde ich den Herren Prof. Dr. A. San Miguel, Mineralogisches Institut der Universität Barcelona, sowie Prof. Dr. S. Matthes, Dr. E. Knauer, Dr. P. Richter, Mineralogisches Institut Würzburg für Hilfe und Kritik. Der Comisión Nacional de Geologia, Madrid, danke ich für die offizielle Erlaubnis zu den Geländearbeiten.