Volcano-tectonic deformation in the Monti Sabatini Volcanic District at the gates of Rome (central Italy): evidence from new geochronologic constraints on the Tiber River MIS 5 terraces

Abstract

The accumulation of magma within the Monti Sabatini Volcanic District (MSVD), Italy, coupled with the extensional tectonics of the region, pose both volcanic and tectonic hazards to the city of Rome, located 20 km to the southeast. We combine 40 Ar/ 39 Ar geochronology of volcanic deposits and a geomorphologic/stratigraphic/paleomagnetic study of fluvial terraces to determine the recurrence interval and the time elapsed since the last eruption of the MSVD. Moreover, we provide a date for the youngest known eruption of the MSVD and assess the timing of the most recent volcanic phase. Results of this study show: (i) The most recent eruptive phase occurred between 100 ka and 70 ka; (ii) the anomalously high elevation of the MIS 5 terrace indicates that it was concurrent with 50 m of uplift in the volcanic area; (iii) the time since the last eruption (70 ka) exceeds the average recurrence interval (39 ky) in the last 300 ky, as well as the longest previous dormancy (50 ky) in that time span. (iv) the current duration of dormancy is similar to the timespan separating the major explosive phase that occurred 590–450 ka.

Monti Sabatini and Colli Albani: the dormant twin volcanoes at the gates of Rome

“…Concerning the widespread phreatomagmatic activity, the Valle Santa Maria pyroclastic surge, dated in the present work, as well as two other phreatomagmatic products (Acquarello surge and Baccano main unit) dated in 1 , revealed a wide range in dates, which is likely due to the presence of antecrysts and/or xenocrysts. In these cases, the eruption ages are assessed based on the youngest populations of crystals (either sanidine or leucite; Table 2) extracted from both scoria clasts and the enclosing matrix of bulk samples.…”

“…Ten samples were selected for 40 Ar/ 39 Ar dating. Results for three of these samples have been already published 1 , while the remaining seven are unpublished. We combine new data with a review of previous literature data, allowing for a comprehensive overview of the phases of eruptive activity in the last 350 kyr.…”

“…The complete MS stratigraphic succession on top of the SC unit, spanning 614 ± 4-70 ± 3 ka, has been reconstructed based on a large number of investigated exposures 1,[21][22][23][24][29][30][31] . Therefore, the average eruption recurrence times and dormancies (periods of quiescence) during this interval can be assessed more confidently.…”

“…A-InSAR processing for the descending and the ascending orbits were repeated for two different areas, resulting in a total of four processing: i) a larger area, extending from the Tyrrhenian coast to the Tiber valley and comprising the sector affected by differential uplift since 125 ka identified in a previous study 1 ; a smaller area corresponding to the MS. The retrieved results were uploaded into a dedicated GIS, in order to perform an accurate analysis and comparison among the various outcomes.…”

“…Geologic map drawn by F.M. showing the Roman volcanic province of northern-central Latium and the area affected by local uplift since 125 ka 1 . The deep geologic structure from gravimetry and borehole data by 7 is re-drawn by F.M.…”