Depleted lithosphere from the mantle wedge beneath Tres Lagos, southern Patagonia, Argentina.

NTAFLOS, TH; BJERG, E A; LABUDIA, C; KURAT, G

LITHOS

Elsevier

Año: 2007 vol. 94 p. 46 - 65

0024-4937

Anhydrous spinel lherzolite and harzburgite xenoliths from Tres Lagos, situated inboard of the Volcanic Arc Gap (VAG) in southernmost Patagonia, are samples of a depleted lithospheric mantle and can be divided into two major groups: metasomatized and non-metasomatized. Metasomatized samples, which are the minority, are partly mylonitized and their metasomatism is related to this tectonic process. A group of non-metasomatized samples have enriched whole rock LREE-abundances that are not consistent with the depleted LREE-abundances in their clinopyroxenes. Intergranular host basalt infiltration could be responsible for the whole rock LREE enrichments. Their Sr- and Nd-isotopic ratios have also been affected by host basalt infiltration, whereas their high Sr-isotopic ratios point to subsequent contamination by ground-water and/or Ca-rich surface solutions. Similar contamination is thought to cause the decoupling of Sr- and Nd-isotopes (high Sr- and Nd-isotopic ratios) observed in the nonmetasomatized samples with depleted whole rock LREE. A two-stage partial melting process could be responsible for the origin of the Tres Lagos xenoliths. Model calculations have shown that in the first stage, 2% of batch melting took place in the garnet peridotite field and subsequently the residue experienced 2–8% batch melting in the spinel peridotite field. The Tres Lagos peridotites have not been affected by subduction-related metasomatic processes and they could represent an old lithospheric mantle. © 2006 Elsevier B.V. All rights reserved. peridotites have not been affected by subduction-related metasomatic processes and they could represent an old lithospheric mantle. © 2006 Elsevier B.V. All rights reserved. –8% batch melting in the spinel peridotite field. The Tres Lagos peridotites have not been affected by subduction-related metasomatic processes and they could represent an old lithospheric mantle. © 2006 Elsevier B.V. All rights reserved.