Compositional variations in tourmalines from peraluminous rocks of the Dipilto Granitic Batholith, Eastern Chortis Terrane, Nicaragua: tracers of magmatic to hydrothermal evolution

Abstract

The granitoids of the Dipilto Batholith in northern Nicaragua range in composition from amphibole–biotite tonalite to cordierite–biotite and biotite granite. The petrographic and geochemical features indicate hybrid origin for the metaluminous granodiorite and tonalite (El Paraiso Suite). Dominant peraluminous granites (leucogranite dykes, Yumpali and La Piedra suites) represent a typical product of fractional crystallization of crust-derived melts. Tourmaline occurs as rare mineral in peraluminous granites of the Yumpali Suite (randomly distributed grains and quartz– tourmaline nodules), but is common in the younger leucogranite, pegmatite dykes and hydrothermal veins. Chemical variations (mainly X Fe and F) in tourmaline as well as in biotite are consistent with magmatic differentiation processes in granites and pegmatites. The presence of quartz–tourmaline hydrothermal veins indicates involvement of B-rich post-magmatic hydrothermal fluids at the final stage of the Dipilto Batholith evolution. Tourmaline chemistry evolved from Mg-rich schorl in peraluminous granites, to F-rich schorl–foitite in the hydrothermal veins. This evolutionary trend is typical of F-poor granite–pegmatite systems.