Pre-caldera (N22 ka) lateral activity at Somma-Vesuvius is related to scoria- and spatter-cone forming events of monogenetic or polygenetic nature. A new stratigraphic, sedimentological, textural and lithofacies investigation was performed on five parasitic cones (Pollena cones, Traianello cone, S. Maria a Castello cone and the recently found Terzigno cone) occurring below the Pomici di Base (22 ka) Plinian products emplaced during the first caldera collapse at Somma-Vesuvius. A newAr/Ar age of 23.6±0.3 ka obtained for the Traianello cone aswell as the absence of a paleosol or reworked material between the S. Maria a Castello cone and the Pomici di Base deposits suggest that such cone-forming eruptions occurred near the upper limit of the pre-caldera period (22–39 ky). The stratigraphy of three of these eccentric cones (Pollena cones and Traianello cone) exhibits erosion surfaces, exotic tephras, volcaniclastic layers, paleosols, unconformity and paraconformity between superimposed eruptive units revealing their multi-phase, polygenetic evolution related to activation of separate vents and periods of quiescence. Such eccentric cones have been described as composed of scoria deposits and pure effusive lavas by previous authors. Lavas are here re-interpreted as welded horizons (lava-like) composed of coalesced spatter fragments whose pyroclastic nature is locally revealed by relicts of original fragments and remnants of clast outlines. These welded horizons show, locally, rheomorphic structures allowing to define them as emplaced as clastogenic lava flows. The lava-like facies is transitional, upward and downward, to lesswelded facies composed of agglutinated to unwelded spatter horizons in which clasts outlines are increasingly discernible. Such textural characteristics and facies variation are consistentwith a continuous fall deposition ofHawaiian fire-fountains episodes alternatedwith Strombolian phases emplacing loose scoria deposits. High enrichment factor values,measured in the scoria deposits, imply the ejection of large proportion of ash even during Strombolian events.

New insights on lithofacies architecture, sedimentological characteristics and volcanological evolution of pre-caldera (> 22 ka), multi-phase, scoria- and spatter-cones at Somma-Vesuvius / Sparice, Domenico; Scarpati, Claudio; Perrotta, Annamaria; Mazzeo, Fabio Carmine; Calvert, Andrew T.; Lanphere, Marvin A.. - In: JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH. - ISSN 0377-0273. - 347:(2017), pp. 165-184. [10.1016/j.jvolgeores.2017.09.010]

New insights on lithofacies architecture, sedimentological characteristics and volcanological evolution of pre-caldera (> 22 ka), multi-phase, scoria- and spatter-cones at Somma-Vesuvius

Sparice, Domenico
Investigation
;
Scarpati, Claudio
Supervision
;
Perrotta, Annamaria;Mazzeo, Fabio Carmine;
2017

Abstract

Pre-caldera (N22 ka) lateral activity at Somma-Vesuvius is related to scoria- and spatter-cone forming events of monogenetic or polygenetic nature. A new stratigraphic, sedimentological, textural and lithofacies investigation was performed on five parasitic cones (Pollena cones, Traianello cone, S. Maria a Castello cone and the recently found Terzigno cone) occurring below the Pomici di Base (22 ka) Plinian products emplaced during the first caldera collapse at Somma-Vesuvius. A newAr/Ar age of 23.6±0.3 ka obtained for the Traianello cone aswell as the absence of a paleosol or reworked material between the S. Maria a Castello cone and the Pomici di Base deposits suggest that such cone-forming eruptions occurred near the upper limit of the pre-caldera period (22–39 ky). The stratigraphy of three of these eccentric cones (Pollena cones and Traianello cone) exhibits erosion surfaces, exotic tephras, volcaniclastic layers, paleosols, unconformity and paraconformity between superimposed eruptive units revealing their multi-phase, polygenetic evolution related to activation of separate vents and periods of quiescence. Such eccentric cones have been described as composed of scoria deposits and pure effusive lavas by previous authors. Lavas are here re-interpreted as welded horizons (lava-like) composed of coalesced spatter fragments whose pyroclastic nature is locally revealed by relicts of original fragments and remnants of clast outlines. These welded horizons show, locally, rheomorphic structures allowing to define them as emplaced as clastogenic lava flows. The lava-like facies is transitional, upward and downward, to lesswelded facies composed of agglutinated to unwelded spatter horizons in which clasts outlines are increasingly discernible. Such textural characteristics and facies variation are consistentwith a continuous fall deposition ofHawaiian fire-fountains episodes alternatedwith Strombolian phases emplacing loose scoria deposits. High enrichment factor values,measured in the scoria deposits, imply the ejection of large proportion of ash even during Strombolian events.
2017
New insights on lithofacies architecture, sedimentological characteristics and volcanological evolution of pre-caldera (> 22 ka), multi-phase, scoria- and spatter-cones at Somma-Vesuvius / Sparice, Domenico; Scarpati, Claudio; Perrotta, Annamaria; Mazzeo, Fabio Carmine; Calvert, Andrew T.; Lanphere, Marvin A.. - In: JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH. - ISSN 0377-0273. - 347:(2017), pp. 165-184. [10.1016/j.jvolgeores.2017.09.010]
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11588/695427
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