Pressure-temperature path of Arquia Group rocks : a petrographic analysis from mineral assemblages

Based on the type locality mineral associations of the Arquia Group metamorphic rocks in Colombia, the pressure-temperature conditions of metamorphism were obtained and the associated P-T path was built. The analysis of the mineral assemblages indicates a prograde regional metamorphism, which varies from low to medium grade and is represented by greenschist, epidote-amphibolite and amphibolite facies. The results that are based on the prograde mineralogy [actinolite + chlorite + albite + quartz + muscovite + epidote minerals for greenschist facies and hornblende + epidote minerals + garnet + albite ± quartz for epidote-amphibolite and amphibolite facies] indicate a constant increase of metamorphic conditions from 433°C/11.8 kbar to 696°C/14.4 khar in the metamorphic peak. Retrograde mineral assemblages [muscovite + chlorite + epidote minerals + albite + actinolite] indicate new metamorphic conditions between 417-357°C and 8.1-6.5 kbar. In addition, four deformation events and evidence of shear zone and intracrystalline deformation were found in these rocks. Key words: Arquia Complex, Arquia Group, mineral assemblages, metamorphism, P-T path. Con base en las asociaciones minerales existentes en las rocas metamorficas del Grupo Arquia en su seccion tipo en Colombia, se determinaron las condiciones de presion-temperatura del metamorfismo y se construyo la trayectoria P-T que siguieron estas rocas. El analisis de las asociaciones minerales es consistente con un metamorfismo regional progrado de bajo a medio grado, representado por facies de esquistos verdes, facies epidota-anfibolita y facies anfibolita. Las asociaciones minerales progradas [actinolita + clorita + albita + cuarzo + moscovita + epidota en facies de esquistos verdes y hornblenda + epidota + granate + albita ± cuarzo en facies epidota-anfibolita and anfibolita] indican un aumento constante en las condiciones del metamorfismo, desde 433°C/11.8 kbar hasta 696°C/14.4 kbar en el pico metamorfico. Las asociaciones minerales retrogradas [moscovita + clorita + epidota + albita + actinolita] senalan nuevas condiciones metamorficas entre 417-357°C y 8.1-6.5 kbar. Adicionalmente, estas rocas evidencian cuatro eventos de deformacion, presencia de zonas de cizalla y deformacion cristalina. Palabras clave: Complejo Arquia, Grupo Arquia, asociaciones minerales, metamorfismo, trayectoria P-T.