PETROLOGY AND THERMOBAROMETRIC ESTIMATES FOR METASEDIMENTS, ORTHOGNEISSES, AND ECLOGITES FROM THE NEVADO-FILABRIDE COMPLEX IN THE WESTERN SIERRA NEVADA (BETIC CORDILLERA, SPAIN)

摘要

Using PERPLEX and garnet isopleth thermobarometry we tested whether Permian metasediments, orthogneisses, and amphibolitized eclogites from the Nevado-Filabride Complex in the western Sierra Nevada (Betics, Spain) underwent the same high-pressure metamorphism, or whether the different lithologies were tectonically emplaced after metamorphism as is commonly assumed. Our results highlight the role of some accessory minerals, especially small inclusions of Ti-bearing phases (mainly titanite and rutile) in garnet, in the thermobarometric estimates and indicate the presence of several populations of garnets in the orthogneisses recording different stages of the prograde and retrogressive Alpine metamorphic path in addition to pre-Alpine garnets. The schists also contain two populations of garnet: rare detrital grains and metamorphic crystals. Despite the scarcity of key phases proving that the orthogneisses and metasediments experienced high-pressure conditions, this study yields a number of lines of evidence suggesting that both rock types followed a clockwise pressure-temperature path similar to the eclogites, reaching peak pressures of 2.0-2.2 GPa for temperatures of 550-600 degrees C, and that the lithologies were all in contact prior to the high-pressure Alpine event.