Tectonic Evolution of the Southern Apennines Thrust-Belt (Italy) as Reflected in Modal Compositions of Cenozoic Sandstone

Abstract

The composition of sandstones derived from erosion of the southern Apennines orogen provides constraints for Cenozoic tectonic evolution. Clastic wedges were derived mainly from the strongly deformed Calabrian arc allochthon. This key tectonic element is interpreted as a thrust sheet of European crust, moved about 300-400 km eastward during the Paleogene to Neogene toward the Adria foreland. During the Paleogene to Early Miocene, the Liguride Complex oceanic terrane was deposited in a remnant ocean basin, east of the Calabrian arc, related to northwestward subduction of Ligurian oceanic lithosphere beneath the European margin. Upper Paleogene quartzofeldspathic and volcanolithic Liguride sandstones testify to provenance from the subduction complex to the magmatic arc, respectively. Upper Oligocene to lower Miocene quartzolithic sandstone suggests a recycled-orogen provenance (i.e., metasedimentary rocks in the growing accretionary Calabrian arc). Final closure of the Liguride remnant ocean basin and onset of continental collision in southern Italy culminated in overthrusting of the Calabrian and Liguride thrust-sheets onto the Adriatic passive continental margin. Continental collision is dated as Early Miocene and was followed by formation of foreland, foredeep, and thrust-top basins. The unroofing history of the Calabrian arc is documented in the detrital modes of Langhian to Tortonian foreland quartzolithic, volcanolithic, and quartzofeldspathic sandstones. A drastic shift in composition toward "ideal arkose" occurred during late Tortonian-Messinian in both foreland and syn-rift sandstone strata, reflecting a crustal-block provenance. An oceanic backarc rift in the southern Tyrrhenian area (i.e., Vavilov basin) contributed to increased uplift of the deeper Calabrian arc crystalline terranes. The Cenozoic geodynamic history of the Peri-Tyrrhenian area, which included an arc-trench system/continental margin collisional suture zone and, since late Tortonian, back-arc oceanic-crust spreading (i.e., Vavilov basin), is reflected in sandstone modal composition. The type of sedimentary provenance analysis presented here, providing an example of the wchanging nature of a collisional-belt source area through time, may have general application to other major orogens.