Post-Caldera Volcanic, Magmatic, and Structural Evolution of Ischia Volcano, Italy

Overview

Large, long-lived volcanic systems are dynamic in time and space over a range of scales and are subject to competing, yet linked, volcanic, magmatic and tectonic forces (e.g., Hutchison et al. 2016). Unravelling the complex geological past of such systems is critical for defining their present and future states and geohazards. The island of Ischia, in the Bay of Naples, Italy, is the top of a large, long-lived volcanic system with an extremely varied and enigmatic history. Volcanic activity started >150 ka BP, and continued periodically until the most recent eruption (1302 AD). The magmas vary in composition from shoshonite to trachyte. Temporal variations in isotopic composition of the products emplaced since 55 ka indicate a complex magmatic system, characterized by phases of magma evolution under closed system conditions and by arrival of new, isotopically distinct magmas. As the island is permanent home to 60 000 people and is a popular tourist destination there is a pressing need to better understand its volcanic history.
This project will illuminate the volcanic, magmatic, and structural history of the island from around 55-20 ka BP. This period followed a major, M6, caldera-forming eruption (Brown et al., 2008) that catastrophically changed the morphology of the island, and submerged its centre under the sea. This period also spans the onset of caldera resurgence, when a block of crust was uplifted >900 m by repeated magma intrusion in only a few tens of thousands of years. Synchronous with uplift were numerous eruptions from vents along the caldera margin and (later) concentrated in the eastern sector of the island.
The objectives are:
(1) Locate, document and interpret the deposits of eruptions on the island between 60-20 ka BP to understand the nature of post-caldera volcanism and its relationships with tectonic and volcano-tectonic features
(2) Use major and trace element geochemistry and Sr and Nd isotopic data to track changes in magma supply over time and investigate long-term magma evolution and recharge (open and closed system processes, and crustal contamination) following the destruction of the magma reservoir by caldera collapse.
(3) Use (1) and (2) to reconstruct the geological evolution of the island between caldera formation and caldera resurgence.
(4) Use the new data to correlate the onshore tephra deposits with distal terrestrial and offshore marine tephra layers using published geochemical data.
This project will provide insights into magma recharge processes in frequently active caldera systems, and impacts that these processes have on volcanism and tectono-volcanic processes, and will provide critical missing data on one of Europe’s most hazardous volcanoes.
The project would suit a numerate Earth Science graduate student with a broad interest in volcanology and geochemistry, a strong demonstrable fieldwork record, and a sense of adventure. A willingness and capacity to learn Italian would be advantageous and encouraged.

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Image Captions

Figure 1. Ischia looking north from Mont Sant’Angelo. Coastal exposures of tuff ring deposits are overlain by mass movement deposits shed from the resurgent block (background).

Methodology

This project will involve extended fieldwork (2 x multi-week seasons) on Ischia to document, log, map, and sample the products from eruptions in the period of interest under the supervision of Brown, de Vita, and Hutchison. Land-based fieldwork will be supplemented by UAV reconnaissance (in collaboration with INGV UAV scientists, Marotta and Avvisati) to capture photographic and video footage of deposits exposed in steep sea cliffs. Boats may be used to access headlands and bays. Structural data will be measured, and samples will be taken of intervening sedimentary deposits to assess their provenance and emplacement processes, and to seek evidence for the onset and rate of caldera resurgence.
A comprehensive suite of samples will be collected for petrographic study, and for major and trace element analyses. Sr and Nd isotopic investigations will be performed on both whole rock samples and on the most abundant mineral phases (feldspar and pyroxene). The student will model the nature of open and closed system magmatic processes under Ischia using petrological tools (e.g., MELTs code, Ghiorso and Sack, 1995). Isotopic analyses will be run by the student at laboratories in the Vesuvius Volcano Observatory, Naples, under the supervision of Ilenia Arienzo.

Project Timeline

Year 1

Training and literature review followed by field season 1 (4-6 weeks) to use land-, air- and sea-based methods to document the deposits of the eruptions in the period of interest and collect samples. Initial laboratory and petrographic analysis of samples. Analysis and interpretation of field data.

Year 2

Training in use of petrological tools and geochemical analysis. Field season 2 (4 weeks) to complete fieldwork and sampling programme. Sample preparation and thin-section analysis, followed by geochemical isotopic analysis of the samples at INGV, Naples in collaboration with Dr Arienzo (4-6 week placement at INGV).

Year 3

Analysis and interpretation of field and laboratory data. Modelling of geochemical data (e.g., using MELTs code). Preparation of papers on (1) Volcanic history and eruption styles on Ischia for the period of interest, (2) Evolution of the magmatic system, (3) Synthesis of the geological evolution of Ischia incorporating new volcanological, geochemical, and structural data and insights. The new data will be integrated with published data from distal, terrestrial and marine core tephra layers to improve tephro-chronology across the eastern Mediterranean.

Year 3.5

Continuation of preparation of papers and thesis.

Training
& Skills

The student will receive a broad training in volcanology, petrology and structural geology. Specifically, the student will be trained in the field-based documentation of pyroclastic rocks and lavas, in structural geology in modern volcano-tectonic environments, and in the geochemical characterization of the volcanic rocks (samples dissolution, isotopic ratio determination by Thermal Ionization Mass Spectrometry analyses, major and minor element content determination by Electron Microprobe Analyses) and modelling of geochemical data. Training will occur both in the lab and in the field. The student will also be trained to use UAVs for mapping and 3D outcrop reconstruction. The student will receive training in how to best present work in a variety of formats (scientific papers, posters, and oral presentations).
The student will join a dynamic collaborative research environment with 8 staff and 20 postdocs and postgraduate students. Co-supervision will extend this group to St. Andrews and to INGV. It would be expected that the student will take advantage of free university language courses.

References & further reading

Brown, R.J., et al., 2008. New insights into Late Pleistocene explosive volcanic activity and caldera formation on Ischia (southern Italy). Bulletin of Volcanology, 70(5), pp.583-603.

Casalini M., et al. 2017. Geochemical and radiogenic isotope probes of Ischia volcano, Southern Italy: Constraints on magma chamber dynamics and residence time. American Mineralogist, 102 (2), 264-274.

de Vita S., et al., , 2010. Volcanological and structural evolution of the Ischia resurgent caldera (Italy) over the past 10 ka. In: Groppelli G. and Viereck L. (Eds.) “Stratigraphy and geology in volcanic areas”, GSA Book series, Special paper n. 464: 193-239.

Ghiorso MS, Sack RO (1995) Chemical mass-transfer in magmatic processes. A revised and internally consistent thermodynamic model for the interpolation of liquid-solid equilibria in magmatic systems at elevated temperatures and pressures. Contrib Miner Petrol 119:197-212

Marotta E., de Vita S., 2014. The role of pre-existing tectonic structures and magma chamber shape on the geometry of resurgent blocks: analogue models. J. Volcanol. Geotherm. Res., 272, 23-38.

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