OPPOSITE P-PATHS, T-PATHS, T-PATHS OF HERCYNIAN METAMORPHISM BETWEEN THE UPPER UNITS OF THE CABO ORTEGAL COMPLEX AND THEIR SUBSTRATUM (NORTHWEST OF THE IBERIAN MASSIF)

In the Cabo Ortegal region two metamorphic groups can be distinguished, which have followed opposite P-T paths in their Hercynian metamorphism. The upper group comprises the three uppermost units of the allochthonous complex, with mafic and related lithologies, of Cabo Ortegal. The lower metamorphic group includes the two basal units of the complex and the lithological sequence outcropping in the Ollo de Sapo Anticlinorium. The lithologies of the upper group were affected by high-P and medium-high-T eo-Hercynian metamorphism, during a subduction episode related to the onset of the Hercynian Orogenic Cycle. As a result of such metamorphism, the basic rocks were transformed into B-type eclogites and also into high-P mafic granulites. The advance of the Hercynian collision produced the progressive uplift of the subducted lithologies and, finally, their emplacement as large thrust sheets over the lower metamorphic group. This final evolution is clearly reflected in the P, T, t paths of the high-P lithologies, which show pronounced decompressions with only minor cooling. The evolution of the Lower Metamorphic Group does not reflect high-P events. The characteristic regime is a Barrovian-type medium-P metamorphism, showing P, T, t paths with a progressive compression during heating. At least partially, the burial of the rock association was due to the overthrusting of a thick allochthonous pile; this is represented by the Upper Metamorphic Group.