ABSTRACT

Modern river and beach sands carried to and deposited along the coasts of the Tyrrhenian Sea are derived from multiple magmatic-arc and orogenic sources, including ophiolitic sequences and turbidites issued from the Ligurian Ocean, carbonate-platform to pelagic sedimentary and metasedimentary successions originally deposited onto the Adria continental margin, and overlying foredeep clastic wedges.

"Undissected arc" feldspatholithic signatures characterize limited areas (Capraia Island, Tarquinia and Napoli gulfs). Contrasting features, with respect to Circum-Pacific suites (low to very low P/F ratio), include sanidine as the most abundant detrital feldspar and common leucite and leucite-bearing lithic fragments, reflecting the potassic to ultrapotassic character of Neogene-Quaternary magmatism. Green augite, associated with oxyhornblende and either abundant hypersthene (Tuscan magmatic province) or minor olivine and spinel (Roman magmatic province) is the dominant dense mineral. "Dissected arc" arkosic signatures reflect unroofing of Miocene monzogranitic stocks in the Tuscan archipelago.

Sands from ophiolitic sequences and remnant-ocean sediments ("subduction-complex provenance") are characterized by common cellular serpentinite with few chert grains, basaltic to diabase and gabbroic grains, and by abundant shale to slate lithic grains, respectively. Dense mineral suites are dominated by either diallage or chrome spinel.

Sedimentaclastic sands ranging in composition from lithic to quartzofelspathic are widespread ("thrust-belt provenance"). Richest in lithic grains is detritus from Mesozoic platform (dominant carbonates with abundant dolostone) to pelagic (dominant limestone with abundant chert) sedimentary successions. Metamorphiclastic sands with polycrystalline quartz, phyllite, and quartz-mica or marble lithic grains from denuded core complexes are found locally (Apuane Alps). Relatively quartzose sands with abundant feldspars and garnet-rich dense-mineral assemblages are recycled from foredeep turbidites derived, directly or indirectly, chiefly from the Alps.