The Triassic rift system in the northern Calabrian-Peloritani Orogen: evidence from basaltic dyke magmatism in the San Donato Unit

摘要

Green to gray-green metabasite dykes occur within the metasedimentary sequence of the San Donato Unit, the lowest tectonic Unit cropping out in the Mt. Pollino area (northern Calabria). These metabasites are intruded in the Anisian-Ladinian metasediments of the San Donato sequence, but not in the overlying Carnic levels, suggesting a Middle Triassic emplacement age. The original porphyritic texture is locally preserved in weakly foliated samples affected by very low- to low-grade metamorphism during the Alpine Orogeny. The metamorphic assemblages are indicative of a polyphase evolution: an early synkinematic albite + actinolite + chlorite + epidote + quarz + Fe-Ti oxides association developed at the subgreenschist-greenschist facies transition, and a later albite + calcite + chlorite + quartz +Fe-Ti oxides mineral association, in microdomains and patches, suggests localised increase of X-CO2 in the fluid phase. The protolith of the metabasites has been identified in alkaline to transitional basalts with geochemical features consistent with generation by partial melting of an enriched mantle source in a within plate setting. In particular, their geochemical composition is consistent with a low degree partial melting of a enriched mantle source. Based on geological constrains and on petrological considerations, these Middle Triassic metabasites may document the initial break-up stage of the Pangea, evolving to continent rifling and subsequent oceanization processes.