El basalto olivínico del cerro El Pedrero, Chubut

Abstract

This paper deals with geologic and petrologic history of a Quaternary olivine basaltic lava flow in Western Patagonia, Tie flow lies in a tabular area between the Cordillera and a region of folded Cretaceons (Chubutense) terrestrial formatión,
around Cerro San Bernardo in Central Patagonia. The tabular area is underlain by Tertiary (Santacrucense) tulfaceons beds and Pleistocene gravels. Two terrace levels are there present. The Co. Pedrero volcanic center and the main parte of the flow are on the higher level, but the flow margin reached the lower level. This eruptive center is considered a lateral and late manifestation
of the basic eruptivity characteristic of Sierras de San Bernardo, Buen Pasto and Nevada, from which alkaline and subalkaline basic derivatives are known. The petrography of the different structural units of the flow is described, and petrological consideration are made. The structure ol the lava fMlows is related to the phisical properties of the magma and to the evolution of its crystallization. Chemical analyses of the lavas are presented.