3.3. Retrograde metamorphic mineral assemblages
Metamorphic overprint is variably developed and depends on the intensity of the retrograde deformation. In less deformed rocks, it is defined by formation of coronitic shells of orthopyroxene ± Fe-oxide around olivine and clinopyroxene + spinel and calcic amphibole + spinel symplectites between olivine and plagioclase. These replacement microstructures record subsolidus cooling in granulite and amphibolite-facies metamorphic conditions. However, retrograde metamorphism and hydrous assemblages becomes more pervasive structurally downward the Rio Boba plutonic sequence, i.e. toward the Jobito basal detachment zone. In these 250 m-thick lower structural levels, retrograde metamorphism is related to development of a network of amphibolite to upper greenschist-facies mylonitic shear zones and veins, where pyroxene is extensively replaced by green-brown and green calcic amphibole and plagioclase by epidote/clinozoisite, albite and chlorite. In the shear zones, the gabbronorites have been completely recrystallized and transformed into amphibolites, characterized by a well-developed penetrative plane-linear fabric. This metamorphic fabric is sub-parallel to the foliation in the Jobito amphibolites (91-85 Ma), the magmatic foliation in the La Manaclá suite of hornblende gabbro-diorite-tonalite (89-83 Ma), the Jobito basal detachment zone (75-71 Ma), and the elongation of the lenticular bodies of sheared and pervasive serpentinized peridotites, suggesting that it is a late feature (Fig. 1c; Escuder-Viruete et al., 2013a; Escuder-Viruete & Castillo-Carrión, 2016).