| Popis: |
In the western Carpathians of Romania, clinopyroxene with a very high content of the Ca-Tschermak (up to 24 wt.% Al2O3) and esseneite components occurs as veinlets and inclusions, in places associated with kalsilite, in calcite and in wollastonite very close to the marble contacts of two shallow monzodioritic intrusive complexes, Magureaua Vatei, in the Apuseni Mountains, and Oravita-Ciclova, in Banat, both of Upper Cretaceous age. These relics originate from magmatic veinlets, emplaced at an early stage of the magmatic process and later recrystallized at high temperature (> 800 degrees C) by a CO2-dominated fluid (stage 1). Such fluid probably resulted from the reaction of calcite with the main intrusive body at the time of its emplacement, a reaction also witnessed by the development of a symplectitic association of anorthite and aluminous pyroxene at the intrusive margins, and by the (exceptional) occurrence of Na-rich melilite. Part of the intrusive boundaries were later invaded by pegmatite-forming liquids or fluids that, upon reaction with calcite, first produced idiomorphic crystals of (Fe,Mg)-rich wollastonite (stage 2), occasionally hosting minerals of stage 1, followed by the development of a fibrous wollastonite-grossular association (stage W) accompanied by an (Al-poor) diopside that progressively became Al-rich (stage P) through further modification of the fluid by reaction with calcite. The later appearance of vesuvianite initiated the large-scale postmagmatic hydrothermal process. |
