The contribution of paleomagnetism and 40Ar/39Ar datings to understand the evolution of Quaternary and active volcanoes

In this work, paleomagnetism investigations and 40Ar/39Ar datings have been applied to lavas and pyroclastic deposits to understand the evolution of Quaternary and active volcanoes. Paleomagnetic method was used in order to get (i) dating of Holocene lava successions, (ii) correlations of various Quaternary pyroclastic welded units and (iii) the emplacement temperatures of pyroclastic density currents (PDCs). Conversely, 40Ar/39Ar datings have been carried out on selected minerals of pyroclastic products in order to date them and constrain, through a multidisciplinary approach, the volcanological and stratigraphic results. The paleomagnetic dating of recent volcanic successions was carried out on lava flows emplaced in the Valle del Bove depression (Etna volcano, Italy), to understand their geochronological evolution and reconstruct the phases following the flank collapse. Stratigraphic and petrographic analyses, radiocarbon (14C) and paleomagnetic datings have been used to constrain the age of (a) the Milo debris avalanche related to the landslide of the volcano flank and (b) the overlying lava flow succession exposed at three quarries recently carved at the end of the valley. Paleomagnetism and alternating field (AF) demagnetization method, coupled with new 40Ar/39Ar data and stratigraphic evidence, was applied to the tuff matrix of sillar-type ignimbrites to resolve the correlation among some different outcrops of pyroclastic deposits at the Latera Volcanic Complex (Vulsini Volcanic District, Italy) during the last caldera-forming eruptions. The new 40Ar/39Ar dating and paleomagnetic correlation have allowed to merge the eruptions of Grotte di Castro and Onano into a single event, renamed “Grotte di Castro-Onano”, dated at 213±0.4 ka. In addition, the paleomagnetic method on lithic clasts, addressed to estimate ignimbrite emplacement temperatures, was applied to the pyroclastic products of the Grotte di Castro-Onano eruption. The results allowed to reconstruct the first eruptive phases of Etna volcano occurred after the flank collapse of the Valle del Bove and gave significant constraints on the ongoing scientific debate on the eruptive history of the Latera Volcanic Complex. They also testify that the use of multiple techniques is highly desirable when approaching stratigraphy of volcanic deposits and emplacement mechanisms of pyroclastic products. The application of paleomagnetism to establish the age of Holocene eruptions (i.e., those of Etna volcano) allowed to obtain narrower time intervals of the eruptions than those provided by methods based on radiometric dating only. Nevertheless, when the use of radiometric methods, such as 40Ar/39Ar dating, is possible, it provides fundamental constraints on the stratigraphy of the erupted products that can be further corroborated by palaeomagnetic correlation. Furthermore, the application of paleomagnetism to pyroclastic flows can provide not only an estimate of the emplacement temperature of the pyroclastic density currents, but also fundamental data to understand their emplacement mechanisms. This Ph.D. thesis is a relevant issue in the framework of the “Research Methods in Science and Technology” course of the University of Urbino Carlo Bo, mainly showing how the use of complementary methods (paleomagnetism, 40Ar/39Ar dating) is of paramount importance to understand the stratigraphy and eruptive history of active, dormant, or extinct volcanoes.