Ordovician S-type granite and related pegmatite, Sierra de San Luis, Argentina: a fluid inclusions study

SOSA, G.; VAN DEN KERKHOF, A.; LÓPEZ DE LUCHI, M. G.; ORTÍZ SUAREZ, A.

Berna, Suiza

Congreso; European Current Research on Fluid Inclusions (ECROFI-XIX); 2007

University of Bern, Switzerland

Ordovician syn-orogenic garnet-biotite-muscovite-granodiorite, granite, and minor biotite-tonalite from the Sierra de San Luis, are closely associated with barren internal and external pegmatites. These granitoids form meter- to km-scale bodies within meta-sedimentary schists. The largest pluton (La Tapera) outcrops in an area of ca. 20 square km in the Conlara Metamorphic Complex whereas the smaller ca.1.7 km Paso del Rey pluton crops out in the Pringles Metamorphic Complex Pegmatites make out variable volume fractions of the plutonic bodies (internal pegmatite) and also form swarms of external pegmatites around the plutons. Fluid inclusion and cathodoluminescence studies were performed in order to correlate the fluid evolution of the granitoids and pegmatites. Furthermore, the results were compared with Sn-Nb-Ta-Li-bearing pegmatites, which occur in a larger area of the Sierra de San Luis. The fluid inclusions in quartz, plagioclase and apatite from the granitoids and internal pegmatites contain only aqueous low-salinity solutes of ca. 3-4 wt.% NaCl-eq. The fluid inclusions form clusters and intragranular trails. Primary inclusions are found in all the minerals, but best preserved in apatite. Decrepitated fluid inclusions decorated with halos of tiny fluid inclusions indicate implosion-decrepitation and testify isobaric cooling. Melt (glass + vapor) inclusions are sometimes preserved in quartz, garnet, zircon, apatite and rutile