Petrogenesis and T-fO2 estimates of Mt. Monzoni complex (central Dolomites, southern Alps): a Triassic shoshonitic intrusion in a transcurrent geodynamic setting

Petrography, bulk rock and mineral chemistry, as well as mass balance calculations, in agreement with field volume estimates, indicate that shallow level fractional crystallization in a nearly closed system played a dominant role in the petrogenesis of the complex. Removal from a parental gabbroic magma of 8.2% solid fraction gave rise to clinopyroxenite mesocumulates. The subsequent evolution from differentiated gabbros to monzogabbros can be accounted for by the removal of about 51.8% of gabbroic assemblages, whereas monzonites, corresponding to a liquid fraction of 39%, were in turn generated from monzogabbros. Crystallization temperatures and oxygen fugacities have been calculated using a modified version of the Burkhard (1991) model for biotite - K-feldspar - magnetite equilibrium. The restricted range of Sr-Nd isotopic ratios for the main lithologies of the complex confirms that fractional crystallization from a common gabbroic parent magma was the dominant petrogenetic process. -from Authors