Metasomatismo modal y críptico en xenolitos de manto del norte de Santa Cruz, Argentina

ALIANI, P; BJERG, E A; NTAFLOS, TH

Rio Cuarto

Congreso; VII Congreso de Mineralogia y Metalogenia; 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;} --> Ultramafic xenoliths from Estancia Poklepovic, Santa Cruz province, Argentina, comprise Iherzolites, harzburgites and wehrlites, hosted by alkaline lavas and cinder cones. Most of the samples carry glass veins andlor melt pockets and most of them also bear amphibol, mica or both. Criptic mestasomatism is demonstrated by enrichment of light rare earth elements in bulk rock analyses of samples devoid of hydrous phases, melt pockets and glass veins. Modal metasomatism is evident in samples carrying hydrous phases, melt pockets and glass veins, which led to high contents of incompatible elements in bulk rock analyses. Textural evidences suggest that two metasomatic events affected this part of the mantle. One event allowed the crystallization of amphibol and mica, and the second is responsible for the melt pockets. The presence of glass veins (± carbonate) in samples devoid of melt pockets is a strong evidence in favour of a third metasomatic episode. Textural evidences demonstrate that at least part of the carbonate was precipitated from meteoric water rich in carbonates.