Abstract

SOLA, Alfonso  and  BECCHIO, Raúl. Trace element distribution and degree of partial melting in migmatites of Sierra de Molinos, Salta. Rev. Asoc. Geol. Argent. [online]. 2012, vol.69, n.2, pp.240-251. ISSN 0004-4822.

The amphibolite facies (high temperature/ low pressure; HT/LP) migmatites from Sierra de Molinos, Eastern Cordillera, offer an excellent opportunity to evaluate the trace element distribution and the degree of partial melting throughout anatexis, because they preserve much of the structures indicative of an almost perfect separation between melt and solid residuum. The key samples were taken from leucosomes and melanosomes from metatexites (Sil-Kfs zone) with a rock core drill machine. Leucosomes were sampled from dilatant sites within a stromatic metatexite, whereas the melanosomes were taken from the boudinaged matrix. This enables getting the maximum separation between the materials that represents pure melt (leucosomes) and the residuum left after melt extraction (melanosomes). Major and trace element concentrations were acquired from a metapelite from the Puncoviscana Formation, assumed as the protolith, the leucosome-melanosome pairs, metatexites and diatexites migmatites. The degree of partial melting was calculated by simple mass balance, using the major and trace element composition of leucosome-melanosome pairs, obtaining a result of 17 to 23 wt%. The assessment of trace element distribution allowed to understand the complexity of processes implicated in the evolution and diversification of anatectic magmas which occurred close to the source. Because of this, these processes must be taken into account when modelling partial melting processes using composition of granitic rocks emplaced in crustal levels far from the source.

Keywords : Trace elements; Mass balance; Migmatites; Northwestern Argentina.

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