The Aegean Laboratory: Tracking Fluids from Subduction to Volcanoes and Ores

16th to the 28th of September

Dre Charline Lormand, UNIGE Dr Thorsten Markmann, UNIBE Dre Ariadni Georgatou, University of Athens

Dre Charline Lormand, UNIGE Dr Thorsten Markmann, UNIBE Dre Ariadni Georgatou, University of Athens Pre Nomikou Paraskevi, University of Athens M. Stamatis Xydous, Hellenic Survey of Geology and Mineral Exploration Pr Pierre Lanari, UNIL

Subduction is a fundamental geodynamic feature on Earth responsible for the global geochemical cycle. Volcanism, metamorphism and metallurgy are all direct results that have shaped our planet, and which are governed by fluids circulating from the mantle to the surface. Understanding the generation and the relationships between these processes, which occur at different spatial and temporal scales is an ongoing challenge for geoscientists. The Aegean back-arc basin is a unique geodynamic domain that facilitates a wide variety of geological processes linked to subduction zones processes in a relatively small area. The geology of the Aegean islands, stretching from northwest to southeast, highlights the exhumation of high-pressure low-temperature metamorphic rocks towards the ongoing volcanic activity and mineralization. It provides a unique opportunity to explore the intricate process of subduction zone fluids, from seafloor alteration and dehydration reactions during metamorphism, to the formation of arc magmas and related ore deposits. The island of Syros offers one of the most prominent samples for studying high-pressure metamorphism, showcasing dehydration reactions, fluid–rock interactions, and mass transfer processes at depth. Its exceptionally well-preserved blueschists and eclogites occur within a mélange zone that represents a fossilized subduction channel, where metamorphosed volcanic textures and mineral relicts are frequently preserved. In two full day trips the outcrops of the Kampos unit in the north will display some of the best examples of these high-pressure rocks, including volcanic features as well as zones that highlight fluid–rock interactions and mass transfer. In the south, Fabrikas provides key exposures of tectonic structures that document both subduction-related deformation and subsequent exhumation, while intermediate localities such as Finikas, Kini, and Ormos Lakkoi reveal magmatic textures and further evidence of subduction-zone metamorphism. Together, these field sites capture the processes that not only shape seismicity within subduction zones but also contribute to mantle wedge melting through the release of fluids. The island of Milos, located in the southern Aegean volcanic arc, records a prolonged history of volcanic activity beginning at ~2.66 Ma, with subaerial emergence established by ~1.44 Ma. The volcanic succession, locally exceeding 700 m in thickness, comprises a complex association of submarine and subaerial volcanic, sedimentary, and intrusive formations, which collectively define 11 distinct volcanic facies associations. The volcanic products are calc-alkaline in composition, ranging from basaltic andesite through andesite and dacite to rhyolite. Limited exposures of the pre-volcanic metamorphic basement are preserved along the southeastern coast. Mafic enclaves are also present, occurring in dacites, rhyolites and in highly mingled andesite-dacite domes and exhibiting considerable diversity, ranging from quenched recharged magma to gabbroic xenoliths. The island hosts a vigorous hydrothermal system, expressed through hot springs, fumaroles, hot soils, and submarine gas emissions, reflecting elevated heat flow and sustained magmatic input. These conditions have facilitated the development of low- to intermediate-sulfidation epithermal systems, accompanied by extensive hydrothermal alteration and mineralization. Obsidian, exploited since the Neolithic, represents one of the earliest mined resources of Milos. Subsequent mining targeted sulfur, kaolin, manganese, baryte, gypsum, and alum, whereas modern exploitation focuses on industrial minerals such as bentonite and perlite, for which Milos represents one of the most significant production centres in Europe. A speciliast in Milos' geology (SX) will secure access to the mines offering the participants a chance to learn about present mining activity, methodology and related industrial needs. The island therefore is an excellent study area for this fieldtrip as it provides a natural laboratory investigating magmatic evolution, the transition from magmatic to hydrothermal processes, and the genesis of mineralised systems within a long-lived volcanic field. The island Santorini is a geologic laboratory which is shaped by large caldera-forming eruptions associated with multiple collapse events and tsunamis. Santorini sits within an active rift zone, marked by grabens (Anhydros and Anaphi) and a horst (the Santorini-Amorgos Ridge), which reflect ongoing tectonic extension. It also presents a broad diversity of volcanic deposits witnessing different eruptions styles and magma compositions. Initially, Santorini volcanism produced small-scale eruptions such as the rhyodacitic lavas of Akrotiri representing the oldest activity (~645 ka) so far known. In the same period, both phreatomagmatism and Strombolian activity produced tuff deposits and cinder cones. At 200 ka, the island experienced an increase in activity and entered a first cycle of large Plinian eruptions intercalated by smaller inter-Plinian eruptions, often effusive. Ending with a caldera collapse at 100 ka, the first cycle was followed by a second cycle with increasing activity producing more frequent eruptions and three caldera collapses, including the famous and latest collapse after the Minoan eruption during the Late Bronze age. The most recent activity formed two islands at the center of the caldera, Nea Kameni and Palea Kameni, during effusive activity emitted between 40 AD and 1950. Due to ground deformation and seismic activity in 2011, these highlands are highly monitored. Steep caldera cliffs up to 300 meters high reveal succession of volcanic deposits, sometimes hindered by caldera collapses and rebuilds, while nearby submarine activity, particularly at Kolumbo volcano, shows that the region remains volcanically and seismically active today. The purpose of this fieldtrip is to show the large diversity of geodynamic processes and geological formations linked to subduction zone systems hosted in the Aegean Sea craton and to study volcanic and metamorphic processes that occurred during the evolution of the Aegean domain. We will also explore the anthropological aspects associated with the geology and the geological processes of the region by visiting archaeological

Modern style subduction is a fundamental geodynamic feature on planet Earth responsible
for the global geochemical cycle. Volcanism, metamorphism, metallurgy but also
earthquakes are direct results shaping the planet and understanding the linkage between
these processes is an ongoing challenge for geosciences. The Aegean back-arc basin is a
unique geodynamic domain that facilitates the huge variety of geological processes linked
to subduction zones processes in a relatively small space. Crossing from northwest to
southeast the geology of the islands highlights the exhumation of metamorphic cores
towards the ongoing volcanic activity and when present, mineralisation.
This course covers kick-off presentations at the Museum of Petrology and Mineralogy NKUA
in Athens and continues with a field trip to Syros, Milos and Santorini.

- Weather: at this time of the year, the sun is strong, and we will be exposed to sun for
long hours with little shelter. Temperatures can reach up to 30 °C in September in
Greece. Applying high SPF sunscreen and wearing sun protective clothing is strongly
suggested. Each participant must carry and manage their own water supply.
- Equipment:
o Shoes: hiking shoes are mandatory as we walk on challenging terrain. The
organizers have the right to refuse the participation on the field to participants
who do not have the required equipment.
o Mosquito spray
o Backpack: refrain from bringing a large suitcase for yourself. Rucksacks or
duffle bags (~40-50 L capacity) are preferred and can be accommodated in the
rental cars.
o Don't forget your swimming suits :)
- Accommodation: Mix between dorms and double room single beds. We will do our
best to find accommodations with single beds in 2-person shared rooms but sharing
with more than one person is not unlikely (dorm style). If you prefer female-only room,
let us know in the additional information field. We will do our best to accommodate
your needs, but we cannot guarantee.
- Travelling: travelling requires long transport distance by boat (ferry rides between 2-6
h) and car rides on bumpy roads. People sensitive should evaluate carefully the
participation or let us know in the additional information field.
- Arrival/Departure: each participant is responsible to organize and pay their travel
expenses to and from Greece to join the fieldtrip. We provide suggestions for plane and
ferry. The start of the CUSO fieldtrip is in Athens on the 16th of September 2026 and the
official end is in Santorini on the 28th of September 2026. Arriving on time for the course
is mandatory. Each participant should do the necessary regarding visa requirements (if
visa needed, please check for yourself).
- Additional activities during the time of the fieldtrip that are not planned must be paid by
the participant.
- Medication: if you are currently taking medications or have any allergy, please take all
the medication you need for the entire duration of the fieldtrip and bring your
prescription along (for over-the-counter medicine).

Syros, Milos, and Santorini, Cyclades, Greece

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