NinaJordan_PhD_2014.pdf (96.65 MB)
Pre‐Green Tuff explosive eruptive history, petrogenesis and proximal‐distal tephra correlations of a peralkaline caldera volcano: Pantelleria, Italy
thesisposted on 2015-07-09, 08:57 authored by Nina Johanna Jordan
This study reconstructs the explosive volcanic history of Pantelleria, a peralkaline caldera volcano situated in a rift zone in the central Mediterranean Sea, from the earliest exposed eruption products (~324 ka) to the 46 ka Green Tuff Formation which forms a marker horizon blanketing the entire island. The pre‐Green Tuff stratigraphy has been revised by tracing and logging eruption‐units around the island, making extensive use of coastal cliff sections not reported before. Eight widespread ignimbrite formations have been defined and for the first time have been given type localities. Most ignimbrites are welded and contain lithic breccias. Caldera collapse is thought to have occurred during five of the eight major eruptions and is thought to have re‐used the same scarps multiple times. In interignimbrite repose periods, which last between ~3 and ~52 ka, nearly twenty localised cone or shield‐shaped eruptions have occurred producing mostly pumice falls and lavas of dominantly rhyolitic composition. In contrast, ignimbrites are commonly trachytic but some are strongly zoned and include rhyolitic end‐members. The chemical zonation is more pronounced after longer repose periods. Petrogenetically, the volcano has followed the same liquid line of descent, dominated by fractional crystallisation, throughout its >300 ka history and no recurring chemical cycles have been detected. Calculation of accurate volumes is hindered by the island’s small size, with most eruption products deposited under water. To help constrain eruption volumes, distal ash layers found across the Mediterranean Sea (at up to 1300 km distance: Lesvos, Greece) have been chemically correlated with the proximal eruptions and their volumes calculated to 0.1‐18 km3. Distal ash volumes are up to 45 times larger than onshore volumes for the same formation (0.1‐0.8 km3) and are a powerful tool to complement the proximal record, thereby significantly improving previous volume estimates.
Supervisor(s)Branney, Michael; Norry, Mike
Date of award2015-03-01
Author affiliationDepartment of Geology
Awarding institutionUniversity of Leicester