Las trayectorias de las variables termodinámicas en la sucesión paragenética del skarn de Carracedo (Palencia, España)

Laburpena

The skam considered appears in the contact aureole of a granitic stock that intrudes carboniferous formations of the Palentian Region. The pirometasomatic action related to the granitic stock has caused replacements in the carbonated phases of the wall-rock, as well as a precipitation of metallic ores. Three types of skam have been distinguished: Type A, mainly formed by widely mineralized siliceous rocks; type B, which is constituted by carbonates, chlorite and ore minerals; and type C, pyroxenic homfels without a significant metasomatic influence. The following zonation has been observed: marble, clinopyroxene, clinopyroxene + garnet, garnet, actinolite and calcite + quartz. The reaction buffering the chemical potentials in the system is: ad + tr = 5di + 2/3mt + Q + H20 + 1/6 0 2 (pH20 /p 0 2 = -1/6). The replacement of the pyroxene skam by the tremolite-actinolite skam takes place under increasing conditions of p 0 2/|i.H20 and ratios |i.H20 / p.02 > 0,60. The apparition of final association with actinolitic amphibole allows to state that from temperatures higher than 500°C and pressure P > 1 Kb, p.02/T complex paths can be suggested starting with a descent of temperature under high conditions of oxygen fugacity, between 10'10 and 10-20, followed by a later and stronger descending of the oxygen fugacity in relation with the temperature.