Resumen de Volcanismo Cámbrico en el sector Zafra-Nogales (Antiforma de Monesterio, Zona de Ossa-Morena): evidencias de su carácter explosivo en condiciones subaéreas y/o subacuáticas muy someras

Maider Etxebarria Akaiturri, Arturo Apraiz Atutxa

• The Cambrian of the Ossa-Morena Zone is divided in three main successions that were deposited in a platform environment. For this reason, Cambrian volcanism of the Zafra-Nogales area has traditionally been considered as shallow submarine. Nevertheless, the very detailed study of volcanoclastic products has shown that most of the acid volcanoclastic products were deposited in a subaereous environment. The occurrence of welded tuffs, horizontally laminated and cross-bedded ashes (interpreted as fallout ashes and pyroclastic surges), plastic deformation of pyroclasts, as well as glass-shards, devitrification of ashes, concentric joints in pyroclastic deposits, accretionary lapillis and boiled surfaces, indicate high temperatures of deposition, that support a subaereous deposition environment or, in any case, a very shallow subaqueous one. On the other hand, the occurrence in some areas of products with evidences of submarine deposition, such as spilitic alteration, abundance of secondary chlorite and carbonates, textures indicative of quenching or very fast chilling (sieve, dendritic and squeletic textures), indicate that submarine conditions prevailed in those areas. All data indicate that the Zafra-Nogales area was situated near the coastline, with submerged and emerged areas. The region would then be strongly influenced by the sea-level fluctuations that were mainly controlled by volcanic and tectonic activity.