Feldespatos de pegmatitas de clase II y IV en el área de Colmenar Viejo - Manzanares (Madrid)

Abstract

Los Rancajales-Colmenar Viejo Il-class pegmatite is associated with Los Remedios regional aureole S-type peraluminic granitoids. Alkali feldspars (OR, IM-LM and LA) display mainly subsolidus stage crystallization as shown by their textural characteristics (regular and irregular vein-type perthites), as well as the Si-Al distribution and solid solution compositions. Pegmatites El Jaralon IV-class are associated with La Pedriza alkaline biotitic leucogranite. The feldspars observed in the pegmatites and pockets show characteristics of hydrothermal stage as indicated by patch perthite textures, Al-Si distribution and low degree of solid solution. Both types of body pegmatites are fundamentally differenciated by the vapour-fluid hydrothermal stage in the IV-class pegmatites. Alkali feldspars chemical-structural characteristics are homogeneized by the vapour-fluid phase: veil ordered and pure feldspars with patch perthite textures are formed; the biotites are transformed into chlorites; Ca and Fe are dissolved into a fluid phase. On the other hand, pockets mineralogy (quartz, stilbite, hematite, opal and fluorite) are deposited from C 0 2, H20 y F rich solutions below °C 500.