It’s not all Greek to me

Hand lens and compass clinometer in hand, I was ready for my first geology trip. Little did I know that I would return just two weeks later with a greater understanding and appreciation for the subject I’m studying.

The trips aim was to develop our geological mapping skills and our ability to read the rock record. But the trip taught me a lot more than this! And here’s why…

The fascinating geology of Greece is a result of the coming together of the African and Eurasian plates during the Cenozoic. The closure of the Tethys Ocean and the development of the Alpine orogenic belt accommodated this convergence. However, the collision was also accompanied by the opening up of continental and oceanic basins in the upper plate above the retreating subduction zone systems. The term ‘slab roll back’ describes the rapid extension generated in the overriding plate. This phenomenon is responsible for much of the complexity of late Cenozoic Mediterranean tectonics. The Hellenides form a curved orogen above the subducting Hellenic slab. Present day tectonic movement involves the interaction between the African, Eurasian, Arabian and Anatolian plates. This movement is accommodated by strike-slip displacement. During our trip we saw that volcanism in the Aegean also was rampant due to the back arc extension caused by the retreat of the Hellenic slab. Pliocene to recent volcanism seen during the trip was related to the subduction of the African plate beneath the Eurasian.

Simplified tectonic map of the Aegean showing the main tectonic domains above the Hellenic subduction zone (after Ring et al., 2010).
Simplified tectonic map of the Aegean showing the main tectonic domains above the Hellenic subduction zone (after Ring et al., 2010).

Corinth canalThe trip started at the Gulf of Corinth on the mainland of Greece. This region forms a narrow land bridge between this large bay and the Saronic Gulf. Here we spent four days, examined the shallow marine carbonates and slivers of oceanic crust caught up as ophiolite fragments during the closing of the Tethys. It was our first day in the field and I felt overwhelmed by the enormous amount of information confronted with at each outcrop. But this soon passed as we progressed and a routine developed. This day was followed by examining a crustal extension opening as series of rift basins filled by Plio-Pleistocene to Holocene sediments. Faulting in Corinth is still very active today – the city has been destroyed by earthquakes several times. We measured the movement of the Pisia fault, followed by my favourite exercise: mapping beach terraces at Perachora Peninsula. It was only at Kerinitis Gorge that I really realised the sheer size of geological features when we had to sketch out the Plio-Pleistocene Gilbert-type fan deltas. The foresets alone were over 300m in height!

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Students sketching a large delta in Kerinitis Gorge.

Destination number two was the island of Naxos whose complex metamorphic dome sent me into total bewilderment.  Here we mapped a complex metamorphic sequence across the island and produced a cross-section. By the end of Naxos I was so pleased by what we had achieved. We had managed to map, draw and interpret these awe inspiring rocks. The structural section through the middle and lower units are marked by a Barrovian metamorphic gradient that I have only ever studied occurring over much greater distances than the mere 8km transect we mapped. How does such a small area present such a distinct metamorphic sequence?

Finally, the trip ended on the Island of Santorini, which hides a complex and interesting volcanic history beneath the beautiful tourist destination. Santorini being one of the most spectacular stratovolcanoes in the world it was an opportunity of a lifetime to uncover its eruptive past. Starting with the most recent catastrophic caldera forming eruption, the Minoan, which not only had environmental impacts as well as social ones discovered during the excavation of a Minoan port town at Akrotiri. Seeing the excavated ruins showed the massive and extended volumes of debris that are ejected during a highly explosive eruption and producing a typical pyroclastic sequence we could log. The days following this we examined further explosive cycles around the island that included a lot of walking up and down the caldera sides that was not met with great enthusiasm by a very “tired” group. However the trip ended on a high when on our final day we compiled all the information we had collected in a detailed write up of the eruptive history starting at the first caldera collapse about 180 000 years ago and ending at the new effusive eruptions forming the central island.

Group in Santorini

Throughout the trip I realised that reality contrasts with the idealized examples of our textbooks. The conceptual examples are not necessarily observed in the geology seen in the field and one must keep and interpretative mind open at all times!

By Tess Oude Essink, undergraduate student, Trinity College Dublin.

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