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
thesis
posted on 2015-07-09, 08:57 authored by Nina Johanna JordanThis 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.
History
Supervisor(s)
Branney, Michael; Norry, MikeDate of award
2015-03-01Author affiliation
Department of GeologyAwarding institution
University of LeicesterQualification level
- Doctoral
Qualification name
- PhD