Paper No. 20
Presentation Time: 1:30 PM-5:30 PM
PRELIMINARY DIFFERENCES IN THE COMPOSITION AND GEOCHEMISTRY, BETWWEEN THE NORTH AND SOUTH ZONES OF THE LA ESCALERILLA PLUTON, SIERRA DE SAN LUIS, ARGENTINA
In the southwestern of the Sierras de San Luis, lies a basement of Late Proterozoic-Early Paleozoic, where are recognized several plutons corresponding to Famatinian magmatic arc (450 Ma), they are intruded in metamorphic rocks of greenschist-anfibolites facies. Are distingue, dioritic-tonalitic-granodioritic plutons (DTG), and the La Escalerilla granitoid pluton (LEG). In this paper are shows some geochemistry and compositional preliminary differences between the north and south zones of this last. LEG is a longed body of 50 kilometers in N-S sense, extensive from San Luis city at the south to La Carolina locality at the north. In the north part, is a leucomonzogranite varying to granodiorite, with scarce biotite, majority of metamorphic origin (Qz+Fk+Pl±Mv±Bt), with some longed quart-dioritic enclaves. Geochemistry shows calc-alkaline affinity of high-K, peraluminous to powerlessly peraluminous, of collisional intraplate ambient, this would have evolutional independently of the DTG suite and not provide of the extreme differentiation of that metaluminuos suite; the LEG probably provide of melting of grauvaquic protholit (upper crust), and would be a S-type granite of hybrid sources (Brogioni et al, 2005 and references therein). W-deposits are related too to LEG at the north zone. However, the south part is composed of granites (Qz+Fk+Pl+Bt), and tonalites to granodiorites (less K-feldespar); these last lies principally in the border facies and inside sometimes. Although LEG in the south part present calc-alkaline affinity of high-K, equivalent of north part, this is minor evolutional and is lies near to tholehiitic boundary into the AFM diagram, similar to the DTG suite, and to the enclaves of LEG at the north part, indicated a moderate metaluminous. The increasing of biotite to 26% present of LEG at the south is equivalent an increase of Fe2O3 (6%), MgO (2%), MnO (0.05%), TiO2 (1%), CaO (1.5%) and Al2O3 (2%) and a decreasing of SiO2 (15%), Na2O (2.2%) and K2O (2.5%), with respect to the LEG north part (% oxides in total rock analyses). Up to date and with the data presents is not possible to define a petrology boundary and not to discriminate the magmatic source to the LEG at south part. Is necessary more analyses, would be motive of ours future studies and is suggested for moment, named La Escalerilla granitoid (LEG).