Boletin de Geología
Print version ISSN 0120-0283
GARCIA R., Carlos Alberto; KAREN, Correa; MANTILLA F., Luis C. and BERNAL., Luis. PETROGRAPHIC AND GEOCHEMISTRY ASPECTS OF METAMORPHIC ROCKS IN BARRANCO DE LOBA AREA (SERRANIA DE SAN LUCAS). bol.geol. [online]. 2009, vol.31, n.1, pp. 45-60. ISSN 0120-0283.
The metamorphic rocks that outcrop in the San Lucas foothills (in the area covered by the map indentifed as number 64), are grouped in two stratigraphic units: The so-called San Lucas Gneiss Formation and the Pinillos Metamorphic Unit (informal stratigraphic denomination). This latter unit is composed by The Armenia Schists and Tapoa Phyllites. The San Lucas Gneiss Formation, comprise quartz-feldspar gneisses (quartz-feldspar gneisses with biotite, quartz-feldspar gneisses with hornblende) and metamafc rocks (hornblende gneiss, granulites and metagabbros). The Armenia Schists is composed by pelite schists; such as micaceous schists; micáceous schists with andalusite; and calco-silicate schists, quartz rich and with variable amounts of minerals from epidote, hornblende and actinolite groups. The Tapoa Phyllite Rocks are composed by quartz and sericite with altered opaque minerals. The San Lucas Gneiss Formation Metamorphism is regional and reaches the high anfbolite and pyroxene granulites facies. The 1.124Ma ± 22 zircon U-Pb age, indicates a Mesoproterozoic tectonothermal event, related to the Grenville Orogeny, that took place during the Rodinia supercontinent consolidation. The Pinillos Metamorphic Rocks Unit, is Early Paleozoic in age, according to the feld relations.
Keywords : Metamorphism; San Lucas Gneiss Formation; Armenia Schist; Geochronology.