Amphibole-derived evidence of medium P/T metamorphic ratio in Alpujárride and Federico “HP” units (Western Betic-Northern Rif, Spain and Morocco): possible interpretations

Abstract

The significance of zoned Ca-amphibole found in metapelites, quartzites, and synfolial veins of the Internal Zone of the Betic-Rif range (Federico units from Northern Rif and Alpujarride units from Western Betic) in the Alpine tectono-metamorphic evolution of these units is discussed for first time. Typical Al-rich metapelites from both areas show assemblages consisting of white mica and chlorite, with sporadic kyanite and chloritoid. Nevertheless, in the Rif zone, phyllites and synfolial veins of Permo-Triassic units show the assemblage pumpellyite + epidote + actinolite. In the Jubrique area (Betic zone), Ca-rich phyllites, fine-grained quartzites, and quartz veins show assemblages consisting of Ca-amphibole, plagioclase, epidote, titanite, chlorite, and quartz. The Al-in-amphibole thermobarometer defines clockwise pressure–temperature paths with a range of prograde temperatures and pressures between 272°C-1.2 kbar and 484°C-3.2 kbar for the Federico unit and between 274°C-1.1 kbar and 620°C-6.1 kbar in the Jubrique unit. Amphiboles from both areas define prograde pressure–temperature paths typical of Barrovian-type metamorphism. This finding contrasts with previous estimates, which deduced high-pressure conditions in both areas. The described amphiboles indicate metamorphic conditions similar to those found in the tectonically deepest complex (Veleta complex) of the Betic Internal Zone and suggest formation during a medium P/T Alpine event, which has not been previously identified in the Alpujarride complex.