basement-rocks, capped by Mesozoic sedimentary sequences related to an ancient passive continental margin. In the Peloritani Mountains, the basement nappes form an Africa-verging thrust belt, now located at the trailing edge of the Late Oligocene to Early Miocene Maghrebian accretionary wedge of Sicily. The innermost basement nappes of the Peloritani Mountains, including their Mesozoic sedimentary covers, show a locally preserved mylonitic overprint of alpine age, suggesting their exhumation from deep-seated crustal levels, during the mountain building. Field investigations integrated by petrographic structural analyses, evidenced that the Paleogene edifice, overthrusting as a whole the Late Cretaceous-Eocene accretionary wedge terranes of the Mt. Soro Unit along the Taormina Line, actually consists of three superimposed tectonic nappes. They are represented from the top, by the high grade Aspromonte Unit (AU), the low to medium grade Upper Metapelitic Unit (UMU) and the very low- to low grade Lower Metapelitic Unit (LMU). These three tectonic units are separated by two main shear zones, the Aspromonte Shear Zone (ASZ) and the Upper Metapelitic Shear Zone (UMSZ) respectively, involving highly sheared remnants of distinct Mesozoic to Tertiary passive margin successions. Upper Eocene to Upper Oligocene clastic sequences, unconformably covering the Mt. Soro Unit and the LMU, are involved in the footwall of the Taormina Line and of the UMSZ. Upper Chattian to Lower Miocene deposits conceal the Taormina Line, the UMSZ and the ASZ. The structural and petrographic analyses evidenced that the two upper tectonic units are affected by an alpine metamorphic overprint. It consists of an earlier sub-greenschist to greenschist mineral assemblages developed during isoclinal folding, which also affected the Mesozoic sedimentary sequences along the AUSZ. This event was followed by ductile shearing that produced a mylonitic band along the AUSZ. Lithons of Mesozoic terranes deformed in ductilebrittle conditions are involved along the UMSZ which shows evidences of brittle shearing. The more external LMU and the Mt. Soro Unit are unaffected by any alpine metamorphic overprint, as well as the intervening Taormina Line which developed in a brittle condition. The collected data well constrain a Paleogene alpine metamorphic event which was associated to the emplacement of the inner nappes of the Peloritani Mountain Belt (AU and UMU), which represented an alpine deep-crustal root that overthrust portions of the Variscan basement unaffected by the alpine metamorphism. The overall alpine evolution of the Peloritani Mountains implies a collision event that pre-dates the propagation of the Sicilide accretionary wedge terrains and the Middle Miocene collision onto the African margin. This evidence suggest the occurrence of a continental crustal domains, different from the african domains, now involved in the outer portion of the arc, at the footwall of the Paleogene collision zone.
|Titolo:||Paleogene collision tectonics in the Peloritani Mountains: geological and petrographical constraints|
|Data di pubblicazione:||2015|
|Appare nelle tipologie:||1.5 Abstract in rivista|