Structural evolution of the sedimentary accretionary wedge of the alpine system in Eastern Sicily: thermal and thermochronological constraints

Temperature-dependent clay-mineral assemblages, vitrinite reflectance, and apatite fission-track data have been used to investigate levels of diagenesis and time of exhumation of the double-verging Sicilide-Antisicilide accretionary wedge in Eastern Sicily. The integration of organic and inorganic thermal indicators allowed us to distinguish parts of the accretionary wedge with different thermal signature and evolution. We recognize a warmer core made up of the Mount Soro and Troina units and two colder rims (Antisicilide and far-traveled Sicilide units). The Antisicilide unit was thrust back toward the hinterland, and the far-traveled Sicilide units were gravity-driven toward the Hyblean Plateau. In detail, the highest percentages of vitrinite reflectance (VRo) values (0.60%–0.96%) and percentages of illite layers in illite-smectite (I-S; 60%–85%) are found in the Mount Soro and Troina units. Apatite fission-track data, together with the paleotemperature estimates from vitrinite-reflectance data and clay-mineral–based geothermometers, indicate that fission tracks were partially to totally annealed during wedge accretion and that the subsequent exhumation occurred mainly in Burdigalian times. Low VRo values (0.35%–0.50%) and percentages of illite layers in I-S (30%–60%) occur in early thrust-top deposits (Reitano Flysch) that unconformably overlie the Sicilide Complex, as well as the far-traveled Sicilide and Antisicilide units. Apatite fission-track data for the Antisicilide unit confirm low paleotemperature values. Thus the far-traveled Sicilide and Antisicilide units were probably at higher structural levels in the original accretionary prism and were remobilized since late Aquitanian–Burdigalian times.