Supervisors: Dr. Mike Branney, Dr. Mike Norry

What this PhD is about

I am investigating the explosive history of Pantelleria caldera volcano. Several caldera-collapse eruptions occurred in the last 300 ka; each emplaced a widespread rheomorphic ignimbrite, and distal tephra. Most recent work on the island  has been on units younger than the last caldera-collapse eruption (the well-known 45 ka ‘Green ignimbrite’). Instead, my study focuses on the older history of  the volcano. Previous workers described the main extensive welded pyroclastic units as welded fall deposits, but our research indicates that many of them are topography-draping low aspect-ratio rheomorphic ignimbrites. This is inferred from the following field evidence:

•       lateral changes over topography in thickness and facies;
•       imbricated clasts;
•       very poor sorting and matrix support;
•       low-angle diffuse cross-bedding and splay-and-fade bedding (features of ignimbrites);
•       erosional scours; and
•       lateral chemical zonation.

Aerial photograph of Pantelleria, Mediterranean Sea (courtesy of University of Tübingen, Germany). Pantelleria town lies in the NNW of the island. The green areas are vegetated; these are areas of higher altitude (up to ca. 830 m) and extensive lavas. In the E two caldera scarps are visible (dark lines).

Work-in-progress

We are dividing the volcanic stratigraphy into ‘eruption-units’, each bounded by palaeosols that represent periods of repose.

Each eruption-unit contains a rheomorphic ignimbrite with a widespread lithic breccia. The breccias contain cognate and accidental blocks, and may record caldera-collapse-events.

Each eruption-unit will be dated, and the petrology and chemistry characterised.
 

Preliminary results and research plans

The recognition that several of the widespread welded units are sectorally-zoned, topography-draping ignimbrites, is leading to a substantial revision of the island’s stratigraphy.

The caldera is complex, with a multiple subsidence history, rather than simple two-fold history as previously inferred.

I plan to date the eruption units using ⁴⁰Ar/³⁹Ar, and will investigate eruption periodicity and magma chamber evolution using glass and crystal chemistry.

Several Mediterranean peralkaline tephras should correlate with the newly defined eruption-units: I will start correlating the distal tephras and investigate whether they record Plinian, phreatomagmatic or co-ignimbrite plumes, to improve our understanding of the volcano's explosive behaviour.

 

If you have any questions or comments about this project, feel free to contact me at njj5@le.ac.uk.

Please also visit the website of my colleague Rebecca Williams, who works on the famous 'Green Tuff' of Pantelleria: http://www2.le.ac.uk/departments/geology/extranet/staff/postgraduate-students/postgrad-pages/RW89/PhD_research

See also the website of the Crustal Processes group at Leicester: http://www2.le.ac.uk/departments/geology/extranet/research/CrustalProc/crustal-process-group

Mike Branney´s site: http://www2.le.ac.uk/departments/geology/extranet/staff/academic-and-research-staff/mjb

Mike Norry´s site: http://www2.le.ac.uk/departments/geology/extranet/staff/academic-and-research-staff/nah