3.2. Gabbroic rocks
The gabbroic rocks of the Rio Boba sequence form a stack of kilometer-thick sills with the underlaying Quita Espuela gabbronorites been compositionally different from the overlaying oxide-rich Matel gabbronorites (Fig. 2). The Quita Espuela gabbronorite is a 0.8-1.6 km-thick unit, mainly composed of medium- to coarse-grained layered spinel-bearing gabbronorite and olivine gabbronorite, with subordinate troctolite and olivine gabbro. In the field, the contact between the different gabbroic rocks is gradacional. The compositional layering is defined by variations of the mafic mineral/plagioclase ratio at the millimeter to meter scale (Fig. 3f), or by grain-size graded layers. The layering is generally oriented WNW-ESE to NW-SE and dip a low angle (<30ยบ) to the NE and SW. It is often sheared, boudinaged and locally isoclinally folded, suggesting deformation and foliation development at high-temperature (Fig. 3c).
The least deformed Quita Espuela gabbronorites exhibit in thin section an orthocumulate to partly equilibrated granoblastic texture with interpenetrated grain boundaries (2-10 mm) (Fig. 5f). They have an anhydrous association of clinopyroxene (15-35 vol.%, hereinafter %), brownish orthopyroxene (5-25 %), plagioclase (30-65 %), olivine (0-15 %) and green spinel (<8 %). Relict igneous cumulate textures indicate ortho- to adcumulus growth. Clinopyroxene contains exsolution lamellae of orthopyroxene, and vice versa. Zoning has not been detected in any of the phases. Green spinel (hercynite) or Fe-Ti oxides (magnetite-ilmenite) occurs interstitially. Some undeformed gabbronorites are characterized by coronitic shells of orthopyroxene and Fe-Ti oxide around olivine at the contact with plagioclase (Fig. 5d). Deformed gabbronorite exhibits a penetrative grain-shape defined by polycrystalline ellipsoidal clusters of pyroxene alternating with bands of elongate plagioclase grains (Fig. 5e). The grain boundaries range from straight to lobate. Lobate grain boundaries are indicative of dynamic recrystallization at relatively high-temperatures (Passchier and Trouw, 1996). In these deformed rocks, green-brown calcic amphibole (0-15 %) poikilitically enclose both orthopyroxene and clinopyroxene.