El Paleozoico de les Guilleries

Abstract

The Guilleries form a large massif of metasedimentary and igneous Paleozoic rocks, in the northern part of the Catalonian Coastal Ranges. The oldest rocks croping out have been considered as Cambrian-Early Ordovician. They consist of two lithostratigraphical units separated by a laminar body of orthogneises, several hundred meters thick. The lower unit (Osor Formation) is essentially metapelitic, with a horizon of orthoamphibolites up to 50 m thick. The upper unit (Susqueda Formation) is also essentially metapelitic, but it shows a thick marble horizon near its base, a few meters above the top of the gneisses. The existence of this marble horizon has been traditionally taken as an argument to support the Cambrian age. Stratigraphically higher, there is a volcano-clastic sequence, containing acid volcanic horizons, in which Caradoc brachiopods have been collected. Silurian and Devonian rocks also crop out in the area although very incomplete due to faulting. The whole sequence was folded and metamorphosed during the Hercynian orogeny. The deformation is polyphasic, the deeper zones show a gently diping schistosity which shows to be the result of the crenulation of an older foliation. In the shallower crustal levels the dominant foliation is a slaty cleavage. All rocks exposed in the area have been affected by the Hercynian metamorphism. The deep seated levels show an amphibolite facies metamorphism, with cordierite and K-feldspar in pelites. In the shallower zones green-schist facies rocks with chlorite prevail in pelites. Several intrusive events, with the emplacement of different types of granitoids can be evidenced. The oldest, are represented by deformed diorite and quartzdiorite dykes. Later on two-mica leucogranites were emplaced. coinciding with the higher-grade zones. These granites are also deformed, at least in some localities. Finally, late tectonic granitoids were emplaced inducing a contact metamorphism, particularly clear where they reach high structural levels.