Resumo

TIBALDI, Alina M et al. Petrología, termobarometría y geoquímica de las rocas anatécticas del sector norte de la sierra de Valle Fértil, San Juan: implicancias en la determinación de variaciones laterales en la construcción del arco magmático. Rev. Asoc. Geol. Argent. [online]. 2016, vol.73, n.2, pp.195-210. ISSN 0004-4822.

In the northern portion of the sierra de Valle Fértil a group of anatectic rocks formed by partial melting processes under granulite facies conditions crops out. The analysis of major and trace elements, its comparison with plausible protoliths and with experimental results, suggests that the variation in lithology is strongly controlled by the advance of partial melting associated with the efficacy of melt extraction in middle to deep levels of the Famatinian magmatic arc. Although both metatexites and diatexites contain variable proportions of melt, the volumetrically dominant metatexites have similar wholerock compositions to those of their assumed precursors suggesting that to a large extent the generated anatectic melts fail to leave behind the metasedimentary sources. The composition of leucosomes in metatexites varies from pure to differentiated melts. Diagnostic geochemical features indicate that the observed range of leucosome compositions can be derived by peritectic crystallization of feldspar during melting and/or subsequent accumulation of feldspar. Modeling of major and trace elements strongly partitioned between melt and residuum suggests that metatexites reach partial melting proportion ranging at least from 29 to 49 wt %. Comparison of these sequences with those studied in the central portion of the range reflects that although the physicochemical conditions of formation are similar, they have different geochemical characteristics, suggesting the existence of lateral variation within this range. Thus, it follows that the northern segment of the mountain preserves evidence of partial melting frozen at an earlier stage than that observed in the central portion.

Palavras-chave : Migmatites; Chemical differentiation; P-T estimations; Valle Fértil.

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