Chemical and minero-petrographical changes on granulite rocks affected by weathering processes

摘要

The purpose of this work is to study the weathering processes of the granulite rocks of the Serre Massif (southern Calabria, Italy) using a multidisciplinary approach based on field studies, geochemical modeling, and minero-petrographical analyses. The granulite rocks are plagioclase-rich with minor amphibole, clinopyroxene, orthopyroxene, biotite, and garnet and their texture are coarse-grained. The reaction path modeling was performed to simulate the evolution of groundwaters upon interaction with local granulite by means of the software package EQ3/6, version 8.0a. Simulations were performed in kinetic (time) mode under a closed system at a constant temperature of 11.5 degrees C, (which reproduces the average temperature of local area) and fixing the fugacity of CO2 at 10(-2.34) bar (mean value). During the most advanced stage of weathering the main mineralogical changes are: partial destruction and transformation of biotite and plagioclase associated with neoformation of ferruginous products and secondary clay minerals producing a change in the origin rock fabric. The secondary solid phases observed during the geochemical modeling (kaolinite, vermiculite and ferrihydrite) are similar to those found in this natural system. Thus, the soil-like material mainly characterized by mostly sand to gravel grain-size fractions is the final result of the weathering processes.