Recurrence of volcanic activity along the Roman Comagmatic Province (Tyrrhenian margin of Italy) and its tectonic significance

The Roman Comagmatic Province (RCP) developed along the NW-SE striking extensional Tyrrhenian margin of Italy since middle Pleistocene and includes ultrapotassic small eruptive centers and large volcanic districts. By means of a review and statistical analysis of a large data set of radiometric ages we demonstrate that in the RCP, major eruptive cycles occurred at different volcanic districts almost simultaneously and with an almost constant recurrence time. Our analysis started with the Alban Hills Volcanic District, where a detailed 40Ar/ 39Ar chronology of the eruptive cycles has been recently achieved, and then extended to include a database of 264 radiometric ages of the RCP volcanics published since 1980. Statistical treatment of the data set shows a marked non-Poissonian behavior of volcanic activity through the whole magmatic province, with climax of each major eruptive cycle occurring simultaneously at the different districts approximately every 48 kyr. The concomitant eruption of many volcanic districts spreading over a 250-km-long chain implies a control mechanism acting at a regional scale. After discussing the possible relationship between tectonics, sea level changes, and volcanic activity we hypothesize that constant rates of slab retreat during middle Pleistocene could have been a key factor controlling the rate of magma upwelling and the major cycles of recharge of the magma chambers. As a working hypothesis, we propose that the duration of the cycles may be related to (1) progressive weakening of the crust due to magma underplating or (2) cyclic injection of convective plumes into the mantle wedge. Copyright 2004 by the American Geophysical Union.