Abstract

LOPEZ DE AZAREVICH, Vanina L.  and  AZAREVICH, Miguel B. Alkaline Volcanism Involved In The Rifting Process Of The Pensilvanian Basin, Mendoza Province. Ser. correl. geol. [online]. 2013, vol.29, n.2, pp.33-42. ISSN 1666-9479.

The inter-Carboniferous volcanic rocks of firontal Cordillera, Mendoza, are represented by the Meso-Variscic Volcanic Association composed by dikes (5 m-thick) and vessiculated lava-fows of black color. They are stratigraphically pre-Pennsylvanian. Develop an intergranular to intersertal texture, composed of 2 mm plagioclase (57%), and in-between clinopyroxene (13%), opaques (12%), 1 cm amphibole (10%), olivine, and occasionally quartz, K-feldspar and epidote; with apatite up to 1 mm as the common accessory. Chemically they are basalts, K-traquibasalts, mugearites and hawaites, with an alkaline trend and Basanite-Phonolite Suite affinities. It registers a firactioned crystallization of olivine-plagioclase in the initial stage and of clinopyroxene-plagioclase in later stages. They were generated in an intraplate tectonic environment firom partial melting of mantle of lhertzolite to harzburgite composition, of MORB signature, modifed by crustal contamination. K vs K/Th* relation and presence of hydrous mineral fases mineral fases sugest a subduction process and metasomatism by fuids asociated to subduction that brings these rocks a continental magmatic arc signature. The geochemical signature is equivalent to basalts firom the Afirican Rift, with some similar variations registered in the diverse arms of the mega-structure. Although, a complex arrangement of geochemical elements make the necessity of isotope studies to confirm the interpretations presented. This magmatic episode occurred during an extensional regime (rifting) marks the initiation of the marine Carboniferous basin of the Alto Tunuyán Formation, and is equivalent to that register in other localities along the Cordillera axis and implies and generalized extensional event in the western margin of Gondwana, limited stratigraphically by the Chanica Diastrofic Fase (Upper Devonian) and the Permo-Triassic volcanic arc (Choiyoi Group).

Keywords : Alkaline basalts; Intraplate rifting; Pre-Pennsylvanian; firontal Cordillera; Mendoza-Argentina.

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