The origin of Patagonia revealed by Re-Os systematics of mantle xenoliths

We present mineral chemistry and whole rock major, trace, and platinum group element (PGE) concentrations, and Re-Os isotope data for eighteen mantle xenoliths carried to the surface of southern Patagonia (45°–52°S) by Paleocene to Pleistocene alkaline basalts in seven localities scattered widely across southern South America. The new data along with those previously published show that peridotites derived from the lithospheric mantle of the Deseado Massif (DM), southern Patagonia, have compositions indicative of higher degrees of partial melt extraction compared to those from surrounding regions. Re-depletion model ages (TRD) of mantle xenoliths from the DM (n = 20) range from 0.5 to 2.1 Ga, with an average of 1.5 Ga. In contrast, samples from the surrounding areas (n = 39) have a wider range of Re-depletion ages from 0.0 to 2.5 Ga, with an average of 1.0 Ga. Similar geochemical characteristics are recognized between the lithospheric mantle section of the DM and that beneath East Griqualand (∼1.1 Ga), south-eastern Africa, which is related to the Proterozoic Namaqua-Natal Province. The Re-Os systematics of the mantle xenoliths are indicative of Meso to Paleoproterozoic ages for partial melting and stabilization processes of the lithospheric mantle of southern Patagonia, which are considerably older than the crystallization ages obtained for the scarce basement rocks of Patagonia (