3. The Rio Boba mafic-ultramafic plutonic sequence: field
relations and petrography
The Rio Boba mafic-ultramafic plutonic sequence is a lenticular massif,
whose approximate dimensions are 30 km long and 15 km wide, composed of
gabbroic rocks and subordinate lenses of pyroxenite (Fig. 2 and Appendix
A). Cross-sections show that the southern Rio San Juan complex is folded
by late WNW–ESE trending, subvertical antiforms and synforms of
kilometer wavelength, which fold on a regional scale the main foliation
in the different units, the tectonic contact between Jobito and
Guaconejo assemblages, and the magmatic and solid-state deformation
fabrics in the overlying Rio Boba plutonic sequence (Escuder-Viruete et
al., 2013a). The plutonic sequence is overprinted by late thrust,
reverse and strike-slip faults related to Neogene transpressive
tectonics.