Reconstructing the plumbing system of the Vavilov Seamount (southern Tyrrhenian Sea): insights into the transition from fissural to central-type volcanism back-arcs

Stretching of the crust, seafloor spreading, and volcanism commonly affect the overriding plate above retreating slabs in subduction settings. The Vavilov Basin (Tyrrhenian Sea) is a Pliocene–Quaternary back-arc basin formed in response to the eastward rollback of the Apennine–Tyrrhenian subduction system. The basin has a roughly triangular shape and it is bounded by major escarpments (e.g. the Selli Line) separating it from the continental margins (Cornaglia Terrace, De Marchi Seamount and Flavio Gioia Seamount). Its western sector is characterized by N–S–oriented ridges interpreted as the surface expression of basaltic magma injections during, or shortly after, mantle exhumation (e.g. the Gortani and the D’Ancona Ridges).

Near the centre of the basin, the Vavilov Volcano (VAV), a large volcanic edifice ~60 km long and ~32 km wide, rises from ~3600 m below sea level (b.s.l.) to a minimum depth of ~795 m b.s.l. The VAV consists of three main volcanic units: (i) west-tilted pillow lava flows below ~1500 m b.s.l., (ii) radial lava flows between ~1500 and 1000 m b.s.l., and (iii) scoriaceous lava flows from ~1000 m b.s.l. to the summit. K–Ar dating of pillow lavas sampled along the eastern flank at ~1000 m depth yields Pleistocene ages of 0.37 and 0.09 Ma, consistent with the observed magnetic pattern. Magnetic data show a positive anomaly over the shallow part of the volcano related to the Brunhes geomagnetic chron, and contrasting with negative anomalies on the outer flanks and surrounding basin.

Here we present an integrated magnetic and morphologic analysis of VAV aimed at constraining its internal plumbing system and the relationship with surface volcanic and tectonic structures. We develop an inverse magnetic model that images subsurface structural elements related to both an early spreading ridge and a later central volcanic system. Our results indicate that intervening intrusive ridges in small back-arc basins may evolve following a polyphasic evolution with a transition from fissural to central-type volcanism and developing a multi-level plumbing system. The VAV morphological asymmetry reflects an eastward migration of volcanic activity through time, possibly associated with asymmetric basin opening. The shallow plumbing system comprises: (a) an early NNE–SSW–elongated dike sheet feeding fissural volcanism along the summit ridge, and (b) a younger central magma reservoir beneath the summit feeding central vents. A NW–SE–oriented apophysis extending southeastward from the central reservoir likely supplied volcanic cones on the eastern flank.