Coupled Paleomagnetism and 40Ar/39Ar Dating of Latera Ignimbrites (Vulsini Volcanic District, Italy) Unravel Processes Associated to Piston-Collapse Calderas

Abstract

Correlation of ignimbrite units at polygenic calderas is mandatory for the reconstruction of caldera-forming events and proper identification of their eruption dynamics. However, ignimbrites erupted at different times from the same caldera can display similarities in composition and lithology that can hamper proper correlation of outcrops across the caldera structure. Here, high-resolution paleomagnetic and ⁴⁰Ar/³⁹Ar data are used along with stratigraphic evidence to address and resolve the relationships between two ignimbrites associated with the Latera caldera (Grotte di Castro and Onano Formations, Vulsini Volcanic District, Central Italy). These were characterized at 32 paleomagnetic sites and eleven ⁴⁰Ar/³⁹Ar sampling sites encompassing proximal and distal facies. Overall, the paleomagnetic directions of the two ignimbrites are statistically indistinguishable whereas single-grain ⁴⁰Ar/³⁹Ar ages of sanidine and leucite crystals show systematic preservation of pre-eruptive ages with sectorial variations closely controlled by eruption dynamics, yet with a neatly defined common juvenile (syn-eruptive) age at 205 ka. The data show that the two ignimbrites are the product of a single event, here renamed the “Grotte di Castro-Onano” eruption, representing the largest and latest caldera-forming stage of the Latera system. The sectorial preservation of pre-eruptive ⁴⁰Ar/³⁹Ar ages across the depositional sequence is interpreted to reflect the extraction processes with selective (re)mobilization of magma batches associated to piston collapse dynamics. Coupling paleomagnetism with ⁴⁰Ar/³⁹Ar dating is shown to be a key step in such cases for successful resolution of individual caldera-forming events at the millennial scale.