Workshop and field work on Syros Island

Authored by Jesús Muñoz. 

One of the most exciting things about being a geologist is the never-ending feeling of always discovering new things, no matter if you have seen the same area or similar places dozens of times; it’s like being a kid again and playing treasure hunt, with the big difference that this time you find it!

This time I am writing about a great adventure we experienced as a team on the Island of Syros, Greece. Broadly speaking, it can be said that this expedition had 2 stages that converge towards the same goal: to understand and provide a new light on thevarious rheological factors that could be associated with slow earthquakes. During the first 5 days, we met with a number of renowned scientists in the area of seismology, geodesy and geology to exchange perspectives on these phenomena. This seems trivial, however, there is still a big gap between what we geologists document in the field and what geophysicists observe through instrumental results. The second stage of this expedition (last 5 days) consisted of using the new insights gained and using them in my postdoctoral project field, which I will talk about last.

Top: Whitney Behr explaining the local geology of Syros. Bottom: Several members of the Syros crew standing just above a major shear zone.

Our adventure started with a considerable delay that made us to arrive at midnight and exhausted to our final destination in Syros. Immediately we noted the low temperatures inside our respective lodgings; it sounds odd since the beaches of Greece are paradisiacal, but to our misfortune, the first night we almost froze! In the following days, each participant presented on some topic related to slow earthquakes or deformation in subduction zones, but the best part is yet to come. All together we visited different locations in Syros; we were delighted by the beauty of the rocks: the green-red of the eclogites and the electric blue of the blueschists make this island a world-class paradise for metamorphic geology. In the field, we discussed about how the geological structures we observed could be related to the geophysical signals that our colleagues study – now I believe that our geophysicist fellows no longer think that geologists are only good for hammering rocks. We were able to observe a variety of ductile shear zones in conjunction with brittle structures, such as localized shear bands, fractured boudins, and metamorphic veins. These findings led us to discuss the effects of rheology and the role of metamorphic fluids in the occurrence of slow earthquakes. Another point to highlight is the intense metasomatism that affected these rocks at depths. In this context, the reaction of the rocks with hydrothermal fluids would have generated radical mineralogical changes, thus transforming the original rock into a monomineralic aggregate. This point is particularly interesting as it could represent a mechanism capable of modifying the rheological properties of the subduction zone. This part of the trip ended with an excellent afternoon of “aperitifs” on the beach and a fine dining dinner. Science aside, the best part of the trip was getting to know and laugh with my team with whom I will share the next few years of my life (this expedition took place only three weeks after I started my postdoc), as well as meeting great people like Amanda, Jimmy, Jonathan, Marisa, Roland (including his family) and all the guys from the University of Oregon.

Top left: Extensional vein containing fibrous minerals in a blueschist matrix. Top center: Huge garnet crystals in a metasediment. Right top: Astonishing lawsonite pseudomorphs persevering their lozenge habit in a blueschist. Bottom: Strain partitioning caused by a rheological contrast between an omphacite-rich pod (eclogitic lithology) and the surrounding weaker blueschist matrix.
Top left: Jesús enjoying a blueschist boulder. Top Right: Markus standing just on the contact between blueschist and serpentinite lithologies. Center: Derek serving as a scale for the outcrop published in Kotowski and Behr (2019 Geosphere). Bottom: Lonnie and Markus enjoying free time.

Over the next few days, Whitney and I moved to the Megas Gialos locality where we stayed until the end of the expedition – it was time to apply everything we had learned during the previous days. This project can be divided into two parts. In the first instance, the idea is to characterize the vein systems outcropping in Megas Gialos. The fundamental hypothesis is that these veins would represent fluids that percolated through the subduction interface and to the forearc and the different fracturing events would be associated to the periodic injection of fluids during tectonic tremor events. Thus, characterizing the petrophysical properties of this locality would help to understand the in-situ properties of deep subduction zones. The second part of the project is to characterize the architecture of the Kampos belt. The objective is to illuminate, through a detailed petrological and field study, the anatomy of a subduction interface and to understand the different metasomatism and fluid circulation events. We had the opportunity to use the pack-rafts to get a better perspective of the outcrops and discover incredible rocks such as the cliffs of the Kampos belt. During one of the drone surveys, we had the bad fortune to hit a rock and lose connection with it (in the picture below you can see what would be the “last ride of the drone”). Fortunately, the drone did not fall into the sea, so it was possible to rescue it without major damage other than a couple of damaged propellers. Personally, this was my first time using a pack-raft as a working tool, and I must admit that it is an incredible alternative as it allows us to observe outcrops from another perspective. We ended this expedition with more questions than answers and realized that although Syros has been extensively studied for over 40 years, there are still many things left to discover, especially if you look at them from a different perspective, we have discovered a treasure and we will come back for more!

The last ride of the drone. View of a thrust contact between blueschists and metasediments in the Kampos belt. 

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