HR: 17:30h
AN: V44B-06    [Abstracts]
TI: Should Rome Worry? The Sabatini Volcanic District, Central Italy
AU: * Karner, D B
EM: karner@sonoma.edu
AF: Department of Geology, Sonoma State University, 1801 East Cotati Avenue, Rohnert Park, CA 94985 United States
AU: Marra, F
EM: Marra@ingv.it
AF: Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, Rome, 00143 Italy
AU: Palladino, D M
EM: danilo.palladino@uniroma1.it
AF: Dipartimento di Scienze della Terra, Universita' La Sapienza, P.le A. Moro 5, Rome, 00185 Italy
AU: Renne, P R
EM: prenne@bgc.org
AF: Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, CA 94709 United States
AU: Renne, P R
EM: prenne@bgc.org
AF: Department of Earth and Planetary Sciences, 301 McCone Hall, University of California, Berkeley, CA 94720 United States
AU: Sottili, G
EM: empedokles71@hotmail.com
AF: Dipartimento di Scienze della Terra, Universita' La Sapienza, P.le A. Moro 5, Rome, 00185 Italy
AB: The Sabatini Volcanic District (SVD) extends over a 1800 km² area north of Rome and belongs to the potassic Quaternary Roman Comagmatic Region. The Early eruptive activity (0.6-0.4 Ma) from the SVD is characterised by dominant explosive activity (VEI up to 4-5, column height up to 29 km and magma volume up to tens of km³ for individual events) from the Morlupo and Southern Sabatini centers with time repose up to 10⁴ years. Volcanic products were mostly deposited to the E and SE due to prevailing winds, and as such these volcanic deposits comprise much of the shallow geology of Rome and the Quaternary successions of the central Apennines. Here we report new field observations, ⁴⁰Ar/³⁹Ar ages and major element analyses in order to put physical and chronologic constraints on the late SVD eruptive activity. Moreover, SEM image analyses (ash particle morphologies and vesicle patterns) and componentry (upsection changes in crystal, lithic and vitric fragment proportions) provide insights into fragmentation mechanisms and eruptive styles (i.e. magmatic vs. hydromagmatic), as well as emplacement and post-depositional processes. In particular, ⁴⁰Ar/³⁹Ar ages of 12 volcanic units allow us to define better the geochronology of the most recent phase of activity of the SVD and to give new insights into its evolution. The ages we have obtained show that the major explosive phase of activity of the SVD reached a climax around 300 ka with the eruption of at least two large caldera-forming pyroclastic-flow deposits (Tufo di Bracciano and Tufo Giallo di Sacrofano). This was followed by a strombolian-effusive phase of activity from several scoria cones located along the caldera-ring and by the hydromagmatic activity from small tuff rings located mainly in the northeastern sector of the SVD; this activity lasted until 285 ka. A significant reduction of the volcanic activity characterized the interval 285-90 ka, when hydromagmatic activity occurred probably at the Sacrofano Caldera around 200 ka, and in the northern area of Bracciano around 165 ka. Finally, a network of monogenetic tuff rings (e.g. Martignano, Baccano, Stracciacappe, etc.) developed 90 ka in the eastern sector of Bracciano. The ages we obtained on the products of the morphologically and stratigraphically youngest volcanic centers, combined to previous geochronology data, suggest that this tuff ring activity was nearly contemporaneous and that no younger eruption occurred at the SVD after 90 ka. However, the time elapsed since this last verified eruptive activity is on the same order of the previous dormancy that occurred after the activity of the hydromagmatic centers in the northern area around 165 ka, suggesting that the SVD is to be considered a dormant volcanic district. Therefore, these data provide information that is important for evaluating the long-term volcanic hazard potential that the SVD may place on Rome.
UR: http://www.webalta.de/
DE: 0468 Natural hazards
DE: 1105 Quaternary geochronology
DE: 8404 Volcanoclastic deposits
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005