Serie correlación geológica
On-line version ISSN 1666-9479
MARTINEZ, Amancay N et al. Preliminary petrography and geochemistry of the Cretacic basalts of the Sierra de Las Quijadas and Cerrillada de Las Cabras, San Luis province, Argentina. Ser. correl. geol. [online]. 2012, vol.28, n.1, pp. 9-22. ISSN 1666-9479.
We present preliminary results of the petrology and geochemistry of Cretaceous basalts exposed in the anticlines of the sierra of Las Quijadas and cerrillada of Las Cabras. In the mountainous western of San Luis crop out at least two depositional sequences which together exceed the 1500 m thick and consists mainly of clastic sedimentary sequences typical continental red beds belonging to the Giant Group and Lagarcito Formation. Within this group, recognizes two types of basalt events, represented by lava flows and dykes. The lava flows were described in the northeastern sector of the anticline, in a landscape of gentle hills. The dykes were found on the western flank of the anticline, northern sector of that mountain. Basalt lava flows have porphyritic texture with phenocrystals show idiomorphic olivine with clinopyroxene, amphibole and plagioclase, while the basaltic dykes show olivine in porphyritic texture embedded in a plagioclase paste without orientation, amphibole and apatite needles. The basalts of the cerrillada de Las Cabras presented as a volcanic breccia associated with basaltic bombs. They have phenocrystals of olivine and clinopyroxene in paste with plagioclase oriented. The basalts are classified as alkali basalts and related to intraplate basalts. When analyzing rare earth elements chondrite normalized according to Nakamura's design are observed with a steep negative slope for the heavy rare earth elements, a design that is similar to that found in alkaline basalts from the Sierra Chica de Córdoba.
Keywords : Cretaceous magmatism; Basaltic deposits; Petrochemistry; Gondwana rupture.