Resumo

CASTRO DE MACHUCA, B. et al. Neopaleozoic magmatism in the Sierra de La Huerta, Western Sierras Pampeanas, province of San Juan: the Marayes Viejo and El Arriero porphyries. Rev. Asoc. Geol. Argent. [online]. 2007, vol.62, n.3, pp.447-459. ISSN 0004-4822.

Two subvolcanic porphyritic bodies assigned to the gondwanic magmatic cycle intrude the crystalline basement at El Arriero creek (El Arriero Dacite) and Marayes Viejo area (Marayes Viejo Andesite) in the Sierra de La Huerta, Western Sierras Pampeanas. They are medium to high-K calc-alkaline andesites to dacites. A 299.9 ± 3.6 Ma biotite Ar/Ar age was determined in the El Arriero Dacite meanwhile a 259 ± 13 Ma whole-rock K/Ar age was obtained for the Marayes Viejo Andesite. The age from the El Arriero Dacite represents the earliest manifestation of Neopaleozoic magmatism in the Western Sierras Pampeanas, San Juan province, and demonstrates that volcanic activity in the study area was continuous during the Upper Carboniferous to Late Triassic. The evidences presented here indicate that the Marayes Viejo Andesite and the El Arriero Dacite constitute co-sanguineous rocks, having typical volcanicarc geochemical signatures and rare earth elements patterns consistent with a subduction-related zone active during the Neopaleozoic. According to the petrology, age dating and whole-rock chemistry, these rocks can be correlated with similar outcrops from Punta del Agua Formation described in the Precordillera of La Rioja.

Palavras-chave : Gondwanic cycle; Active margin; Andesites; Petrology; Geochronology.

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