A granodiorite body was sampled in an exploratory well in the Northern Adriatic Sea, close to the Venice Lagoon. It stands 4711 m below the sea floor, directly overlain by Triassic dolostones. The drilled core represents a unique evidence of the Southalpine crystalline basement underneath the Po plain. A Llandeilian emplacement age (461–463 Ma) is inferred by U/Pb single grain conventional dating, which supports the occurrence of an Ordovician plutonic event far southwards from the sites where it is well known in the Eastern Alps. The granodiorite is undeformed, and does not display metamorphic overprints: it therefore limits the extent of the Variscan metamorphic belt to the south. Major and trace element geochemistry, together with oxygen isotopic composition, mineralogy and occurrence of abundant metasedimentary xenoliths, point to an anatectic origin of the granodiorite.