caa a22 4500 477062261 CHVBK 20180405111404.0 cr unu---uuuuu 170330e19960401xx s 000 0 eng 10.1007/BF00304440 doi (NATIONALLICENCE)springer-10.1007/BF00304440 Stoppa F. Departimento Scienze della Terra, Piazza Università, I-06123, Perugia, Italy aut The San Venanzo maar and tuff ring, Umbria, Italy: eruptive behaviour of a carbonatite-melilitite volcano [Elektronische Daten] [F. Stoppa] The late Pleistocene San Venanzo maar and nearby Pian di Celle tuff ring in the San Venanzo area of Umbria, central Italy, appear to represent different aspects of an eruptive cycle accompanied by diatreme formation. Approximately 6x106 m3 of mostly lapillisized, juvenile ejecta with lesser amounts of lithics and 1x106 m3 of lava were erupted. The stratigraphy indicates intense explosive activity followed by lava flows and subvolcanic intrusions. The pyroclastic material includes lithic breccia derived from vent and diatreme wall erosion, roughly stratified lapilli tuff deposited by concentrated pyroclastic surge, chaotic scoriaceous pyroclastic flow and inverse graded grain-flow deposits. The key feature of the pyroclastics is the presence of concentric-shelled lapilli generated by accretion around the lithics during magma ascent in the diatreme conduits. The rock types range from kalsilite leucite olivine melilitite lavas and subvolcanic intrusions to carbonatite, phonolite and calcitic melilitite pyroclasts. Juvenile ejecta contain essential calcite whose composition and texture indicate a magmatic origin. Pyroclastic carbonatite activity is also indicated by the presence of carbonatite ash beds. The San Venanzo maar-forming event is believed to have been trigered by fluid-rich carbonatite-phonolite magma. The eruptive centre the moved to the Pian di Celle tuff ring, where the eruption of degassed olivine melilititic magma and late intrusions ended magmatic activity in the area. In both volcanoes the absence of phreatomagmatic features together with the presence of large amounts of primary calcite suggests carbonatite segregation and violent exsolution of CO2 which, flowing through the diatremes, produced the peculiar intrusive pyroclastic facies and triggered explosions. Springer-Verlag, 1996 Explosive volcanism nationallicence Maar Diatreme nationallicence Carbonatite nationallicence Concentric lapilli nationallicence Italy nationallicence Bulletin of Volcanology Springer-Verlag 57/7(1996-04-01), 563-577 0258-8900 57:7<563 1996 57 445 https://doi.org/10.1007/BF00304440 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/BF00304440 text/html Onlinezugriff via DOI NATIONALLICENCE 100 1- Stoppa F. Departimento Scienze della Terra, Piazza Università, I-06123, Perugia, Italy aut NATIONALLICENCE 773 0- Bulletin of Volcanology Springer-Verlag 57/7(1996-04-01), 563-577 0258-8900 57:7<563 1996 57 445 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer