Re-Os isotope constraints on subcontinental lithospheric mantle evolution of southern South America

• Autores: Schilling, Manuel Enrique; Carlson, Richard Walter; Vieira Conceição, Rommulo; Dantas, Celine; Bertotto, Gustavo Walter; Koester, Edinei
• Año de publicación: 2008
• Idioma: inglés
• Tipo de recurso: artículo
• Materia: Mantle Xenoliths; Os Isotopes; South America; Subcontinental Lithospheric Mantle
• Institución: Consejo Nacional de Investigaciones Científicas y Técnicas

We present Re-Os isotopic data for widely dispersed mantle xenoliths carried to the surface of southern South America (36°-52° S) by Eocene to recent alkaline magmatism. Our hypothesis is that the lithospheric mantle sections formed as the roots of southern South America reflect the history of crust formation and amalgamation at different periods of time and so present a complimentary picture of continent growth in South America by sampling deeper sections of continental lithosphere than provided by crustal rocks from the area. The Re-Os isotopic system gives unique chronological information about the time of mantle depletion that is associated with lithosphere formation. Our data show coherent model ages for the lithospheric mantle that can be correlated with some hypotheses for crustal evolution of this region. Most samples show Os isotopic values similar to the present suboceanic mantle, suggesting a relatively recent lithospheric mantle formation from the convecting mantle. Xenoliths from Agua Poca and Prahuaniyeu represent fragments of an ancient depleted lithosphere, probably corresponding to the roots of the Cuyania terrane inferred to be a fragment derived from Laurentia and formed during the Mesoproterozoic. Alternatively, all or parts of the recognized ancient lithosphere are relicts of other known ancient continental blocks, such as the Pampia terrane or the Río de la Plata craton. Samples erupted in the southwest corner of the Deseado Massif give Proterozoic depletion ages (1.34 to 2.11 Ga) that are considerably older than previous radiogenic formation ages obtained for the very few basements rocks of this continental block. We propose that Deseado Massif is Proterozoic in age, probably related to the Malvinas/Falkland Islands and plateau and so should be considered for the reconstruction of the supercontinent of Rodinia.
Fil: Schilling, Manuel Enrique. Universidad de Chile; Chile
Fil: Carlson, Richard Walter. Carnegie Institution of Washington; Estados Unidos
Fil: Vieira Conceição, Rommulo. Universidade Federal do Rio Grande do Sul; Brasil
Fil: Dantas, Celine. Centre National de la Recherche Scientifique; Francia
Fil: Bertotto, Gustavo Walter. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Ciencias de la Tierra y Ambientales de La Pampa. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales. Instituto de Ciencias de la Tierra y Ambientales de La Pampa; Argentina
Fil: Koester, Edinei. Universidade Federal de Pelotas; Brasil