An Upper Pliocene coarse pumice breccia generated by a shallow submarine explosive eruption, Milos, Greece

Abstract

The Filakopi Pumice Breccia (FPB) is a very well exposed, Pliocene volcaniclastic unit on Milos, Greece, and has a minimum bulk volume of 1 km3. It consists of three main units: (A) basal lithic breccia (4–8 m) mainly composed of angular to subangular, andesitic and dacitic clasts up to 2.6 m in diameter; (B) very thickly bedded, poorly sorted pumice breccia (16–17 m); and (C) very thick, reversely graded, grain-supported, coarse pumice breccia (6.5–20 m), at the top. The depositional setting is well constrained as shallow marine (up to a few hundred metres) by overlying fossiliferous and bioturbated mudstone. This large volume of fine pumice clasts is interpreted to be the product of an explosive eruption from a submarine vent because: (1) pumice clasts are the dominant component; (2) the coarse pumice clasts (>64 mm) have complete quenched margins; (3) very large (>1 m) pumice clasts are common; (4) overall, the formation shows good hydraulic sorting; and (5) a significant volume of ash was deposited together with the coarsest pyroclasts.