Evaluation of the contributions of possible sources to the leucosome of the diatexite of Socorro-Guaxupé Nappe, in the Alfenas Region, MG, Brazil

Abstract

The Socorro-Guaxupé Nappe crops out in southern Minas Gerais and it has an intermediate unit called Metaxite Unit, dominated by diatexites at its base, with large volumes of leucosome and schollen of stromatic garnet-biotite metatexite. Leucosome within the schollen crystallized via fractional crystallization and is dominated by plagioclase and quartz, although K-feldspar might be present. However, the larger volume of the coarse-grained leucosome, that dominates the unit, has granite, sometimes close to minimum granite composition. So, its formation, after partial melting, involved, segregation, fractional crystallization and accumulation. Proportions of leucosome / residue and leucosome / residue / peritectic phases indicate that the leucosome crystallized from more melt than a pelite source could produce, and probably diatexite worked as a pre-magmatic chamber and stocked melt produced from the granulites sitting at its bottom. Large proportion of biotite crystallized in the residue was formed due to equalization of water chemical potential between residue and leucosome.The Brasilia Orogen has been interpreted as the result of the neoproterozoic collision between the passive margin of the São Francisco and the active margin of the Paranapanema Evaluation of the contributions of possible sources to the leucosome of the diatexite of Socorro-Guaxupé Nappe, in the Alfenas Region, MG, Brazil Figure 10. Proportions of the migmatite parts recognized in field and normalized to 100%; peritectic garnet (Grt), leucosome (Leu) and schollen -residue (Rsd).

Relation between partial melting, granulite metamorphism, crystallization, deformation of leucosome and the influence of these processes in the rheology of the lower continental crust

“…It means that these high temperatures favoring the concentration of existing fluids in the migmatites, making the composition more fertile and consequently, generate more liquid and causing different stages of crystallization in the residue and leucossome. Studies in metatexite unit byTasco and Moraes (2019) indicate that its protolith may have been a mixture between pelites and wackes, or that partial melting must have had an external contribution of H2O, since the melt volume is larger than the proportional volume inferred from the amount of present peritectic phases, in addition, crystallization of leucosome occurred by combining more than one stage of segregation/fractional and crystallization/segregation. Microstructures, quartz c-axis fabrics temperatures and CL images indicate that:  The quartz studied in both parts of the rocks, residue and leucosome, presents SGR and GBM microstructures, related to high and medium temperatures; The quartz c-axis fabrics exhibit temperatures in the basal granulite unit between 796-966 °C for the residue and 727-855 °C for the leucosome.…”