Evidenze di vulcanismo sinsedimentario nella successione Pleistocenica del graben del Mesima (Calabria centro-occidentale)

Abstract

The Mesima graben is a Miocene-Pleistocene extensional sedimentary basin developed in the central western sector of Calabria, between the risen blocks of the Serre Massif to the east and the Monte Poro (Capo Vaticano) to the west During the Pleistocene the entire area underwent a strong tectonic uplift and local fault movements. At present time, the sedimentary succession outcrops mostly between 300-600 m of altitude. Field investigation allowed for the division of the pleistocenic unit in two main lithofacies. The lithofacies A consists of intensely bioturbated calcarenite containing interlayers and pockets of centimetric pumiceous fragments in its upper part. The lithofacies B is characterized by the occurrence of volcaniclastic deposits which locally forms a 6 m thick volcaniclastic sequence of pumiceous lapilli and ashes. Both lateral and vertical lithofacies associations suggest that the deposition occurred in a low-energy beach environment. The presence of volcaniclastic sedimentation in the shore facies suggests the occurrence of coeval explosive eruptions which liberate large volumes of erodible pyrociastic debris. Textural characteristics of fragments indicate that the volcanic component derives from subaereal eruptive centers; it was deposited near the shoreline and was subsequently reworked by sea waves. The petrography and chemistry of the fragments indicate a dacltic composition similar to that of the more evolved which erupted during the last 100 ka by the neighbouring Aeolian volcanoes. Taking into account the general stratigraphy of the area, .the depositional features of the volcanoclastic deposits and their textural and composition characteristics, two contrasting hypothesis may be made. The first hypothesis suggests that more ancient volcanoes should be active in the southern Tyrrhenian Sea during the Pleistocene time. The second one expects the volcanic source in the Aeolian islands and an uplift rate similar to that evaluted from the Aspromonte massif in southern Calabria, which are much higher than that of 0,3/1,3 m/ka calculated for the Mesima Basin.