11 - The Neapolitan Yellow Tuff eruption as the source of the Campi Flegrei caldera

Abstract

Campi Flegrei is large caldera, 12×16km across that lies immediately west of Naples in Southern Italy. Conventional interpretations consider the caldera to be the result of two ignimbrite eruptions—the Campanian Ignimbrite, 39,000 years ago, and the Neapolitan Yellow Tuff (NYT), 15,000 years ago. We present new geological and volcanological constraints to argue that the caldera was instead produced only during the eruption of the NYT. Caldera collapse occurred by a combination of downsag and trap door mechanisms. The NYT consists of two prominent facies: an original loose, gray Pozzolana and a yellow tuff lithified by secondary mineralization. The sea filled the caldera, until it was displaced by the products of younger intracaldera eruptions and resurgence of a block, about 5km across and offset slightly ENE from the caldera's center. The block was raised at mean rates of about 30m per 1000 years until about 5200 years ago. Most intracaldera eruptions occurred outside the block before a hiatus in activity that lasted between 8200 and 5800 years BP. Following the hiatus, about 50% of the active intracaldera centers were formed across the resurgent block. The change in vent distribution reflects fracturing of the block, which allowed a new magmatic plumbing system to develop through the central area of the caldera.