Coronitic metagabbros from the Sobrado Unit (Órdenes Complex, NW Iberian Massif) IGeological setting and mineral assemblages

Resumo

HP-HT unit exposed in the core of the Sobrado tectonic window (Órdenes Complex, NW Iberian Massif) contains a lithological ensemble of arc affinity, affected by Lower Ordovician metamorphism and which reached highest conditions in the high-P granulite facies and in the eclogite facies. Alternating with metasediments, map-scale bands of metabasites include a large number of metagabbro bodies ranging from several meters to 2 km in length. The metagabbros were variably affected by the regional metamorphism. Well-preserved gabbros with almost intact igneous textures and mineralogy can be found, as well as metagabbros showing a diversity of reactional coronitic textures, and highly recrystallized types with no preserved igneous features and wholly transformed into granoblastic rocks. This contribution deals with the coronitic types, where the variety of textures and assemblages in the coronas is interpreted as reflecting the prograde reaction history of the metagabbros. Three groups of coronas have been distinguished: l)Amp+Opx; II) (Amp)+(Cpx)+Opx+Crt; III) (Amp)+Cpx+Opx+Crt (subordinate phases in brackets)