Is the Late Cenozoic Intra-Plate Magmatism from Northern Patagonia driven by Mantle "Hot Fingers"?

HALLER MJ; MASSAFERRO GI

Potsdam

Congreso; 19th Colloquium on Latin American Geosciences; 2005

The Somuncura plateau is the largest basaltic plateau of the Patagonian Basaltic Province, of Late Oligocene - early Miocene age and located in Northern Patagonia. The presence of the Somuncura Plateau of OIB-like chemistry has been explained in terms of a transient thermal anomaly or "baby hot-spot". A relatively small Quaternary basaltic field is located at the southwestern rim of Somuncura. This Quaternary intra-plate basaltic volcanism is spatially linked to the development of a major intracontinental lithospheric heterogeneity. Quaternary effusive centers are aligned following tensional directions determined by the regional stress field. Basalts from the Northern Patagonia Quaternary volcanic province have relatively low contents of MgO (6-9%) and relatively high contents of Cr (136-289 ppm) and Ni (25-198 ppm) and classify as trachybasalts, basanites and alkaline basalts. Small dunite and lherzolite xenoliths are carried in the lavas. Measured Sr isotope relations range between 0.70478 and 0.70425. Petrographic and geochemical characteristics suggest that the source of this magma is compatible with a granatiferous lherzolite. If the assumption for a thermal anomaly for Somuncura plateau origin is correct, and considering the similar incompatible elements distribution and comparable geological setting, an akin origin by mantle diapirs can be postulated for the Quaternary basalts, but in a lesser extent and duration, comparable with the Hot Fingers proposed for the European Central Massif, Eifel and Pannonian Basin Neogene-Quaternary volcanism. The present data are indicative but by no means conclusive. Further seismic and geochemical studies would help to confirm the presence of these thermal anomalies.