Post-depositional intrusion and extrusion through a scoria and spatter cone of fountain-fed nephelinite lavas (Las Herrerías volcano, Calatrava, Spain)

Abstract

The effusion of lava flows from the base of volcanic cones is a common process in continental monogenetic basaltic fields. However, there are no descriptions in the literature of the structures that channel the lava output through the cone. The Pliocene-Quaternary Las Herrerias volcano (Calatrava, Spain) was constructed from the superposition of a nephelinite spatter and scoria cone and related lavas over a maar. Different eruptive styles contributed to the construction of the current volcanic cone: phreatomagmatic, Hawaiian, Strombolian and violent Strombolian. Quarrying has exposed a lava pond inside the volcanic cone, the intrusion of lava through cone-forming pyroclastic deposits and the ponding of associated lava flows within the maar crater. Low fire-fountaining activity formed a lava pond that stagnated within the crater protected by the cone’s highly welded spatter deposits at its base and overlying scoria deposits. Once the pressure exerted by ponding lava and overlying pyroclastic deposits exceeded the yield strength of the damming rock walls, the melt oozed out through fractures to form an intricate network of dikes and sills and extruded through the lower part of the volcanic cone, forming lava flows. We propose that lava intrusions similar to those here described may represent the final stage of feeding systems for lava flows associated with scoria and spatter cones.