Garnet-bearing ultramafic rocks forming a decametric outcrop occur associated to the eclogites of the
upper catazonal unit of the Cabo Ortegal Complex. These ultramafites are included within variably
mylonitized amphibole-pyroxene gneisses located between the eclogite band on top and the so-called
‘banded gneisses’ formation below. They are harzburgites with orthopyroxene, olivine and amphibole as
main phases and spinel, garnet and ilmenite as minor phases. Serpentine and chlorite are the main
secondary minerals. The absence of pervasive deformational features, lack of anisotropy and poikilitic
texture of pyroxene and amphibole are noteworthy and point to a possible magmatic/mantle origin of
these rocks. However, a detailed petrographic study has shown the existence of discrete domains made of
aggregates of minute pyrope-rich garnet, orthopyroxene and olivine with subgrain recrystallization. The
mineralogical and textural features thus reveal a metamorphic origin for, at least part, of the present
mineral association. Calculated P-T conditions for the orthopyroxene-garnet assemblages are ca. 760 °C
and 19 kbar. The rocks studied bear important textural and, to some extent, mineralogical similarities to
ultramafic rocks elsewhere within the complex along major tectonic contacts (e.g. Carreiro Zone of Tectonic
Movement), although, in view of the relatively Mg-poor olivine and orthopyroxene compositions, an origin
through recrystallization of serpentinite protoliths appears unlikely. Instead, an origin through partial
recrystallization of mantle fragments related to the subduction and tectonic stacking processes that gave
rise to the Complex is proposed
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