Tectonism, metasomatism and p-t conditions of the sublithospheric mantle beneath Patagonia, Argentina.

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

Denver

Congreso; Geological Society of America, Denver Annual Meeting; 2004

The hills of La Huerta and Valle Fertil, wich belong to the Western Pampean Ranges in the Province of San Juan, NW Argentina, mainly consist of metagabboic to metadioritic rocks that intruded the Proterozoic basement in the Early Middle Ordovician (Famat <!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";} @page Section1 {size:21.0cm 842.0pt; margin:70.9pt 3.0cm 70.9pt 3.0cm; mso-header-margin:35.45pt; mso-footer-margin:35.45pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> Patagonian alkali lavas (with OIB signature) and cinder cones carrying mantle xenoliths occupy a back arc tectonic environment. A suite of spinel harzburgites, garnet harzburgites, garnet spinel harzburgites, spinel lherzolites, spinel websterites and minor amounts of wehrlites, dunites and pyroxenites, were collected in the region between 40° to 52° S and 67° to 71° W. Their dominant texture is porphyroclastic followed by equigranular, both tabular and mosaic; protogranular and the transitional types are also present. The different types are randomly distributed in Patagonia and indicate that the sub-lithospheric mantle is mildly to strongly tectonized and recrystallized on both local and regional scale. In northern Patagonia (between 41° and 44° S), xenoliths depleted in basaltic component dominate. In the south, rather primitive and depleted xenoliths occur together, however, with the majority being depleted ones. The most fertile xenoliths fairly closely approach a primitive UM chemical composition. Bulk rock and mineral analyses indicate complex elemental depletion and variably intensive metasomatic enrichments relative to primitive UM abundances, both modal and cryptic.