Formation of chromitites and ferrogabbros in ultramafic and mafic members of the Variscan Sleza ophiolite (SW Poland)

摘要

Ultramafic and mafic rocks of the Variscan gleia ophiolite (Bohemian Massif, Sudetes, SW Poland) contain abundant Cr and Fe-Ti mineralizations. The occurrence of chromitites is related with serpentinites of refractory harzburgitic protoliths. Chromite I from chromitites has variable Cr and Mg numbers (Cr# = 0.41-0.58, Mg#= 0.62-0.83) and low TiO2 contents (< 0.20 wt%). Chromite 11 surrounds chromite I or fills fissures in it and is enriched in Cr and depleted in Al relative to chromite I (Cr# = 0.54-0.68). Chromite I grains contain spherical grains of diopside, phlogopite, pargasite, pyrite and chalcopyrite, occurring as mono-or polyphase solid inclusions. Metagabbros with isotropic fabric contain locally up to 14.6 vol% of magnetite and ilmenite. Magnetite has variable TiO2, Al2O3 and V2O3 contents (0.19-9.82 wt%, 0.13-1.67 wt% and 1.08-1.61 wt%, respectively). It forms xenomorphic grains with trellis or sandwich exsolutions of ilmenite, as well as aggregates with individual ilmenite grains.