Petrología y geoquímica de sedimentitas silicoclásticas triásicas de la Sierra Pintada, Provincia de Mendoza

SPALLETTI, L.A.; MERODIO, J.C.; MATHEOS, S.D.; IÑIGUEZ RODRÍGUEZ, A.M.

Revista de la Asociación Geológica Argentina

Asociación Geológica Argentina

Lugar: Buenos Aires; Año: 1996 vol. 51 p. 51 - 60

0004-4822

Petrographical characteristics and compositional trends of siliciclastic rocks from the Puesto Viejo Formation have been studied. Primary tuffs and welded tuffs, and epiclastic rocks are rich in acidic glass associated with minor amounts of quartz and potassium feldspar. These rocks provide evidence of an important phase of acidic volcanism, synchronous with basin infilling. Sandstone grains, derived from volcanic source areas, are characterised by poor degree of compositional and textural maturity as a result of short transport distance and brief exposure to sedimentary processes. Smectite, illite and mixed-layer illite/smectite make up the clay mineral association of pelitic rocks, which are geochemically classified as quartz-feldespathic mudstones. An active tectonic setting with a significant component of basin subsidencde is inferred from chemical composition of the fine-grained rocks. The weathering of the source rocks as well as the formation of authigenic smectite and/or illite, influenced the resulting values of the chemical index of alteration.