An island born from the sea (history of the tectonics of Cyprus) ⋆ KiprGuru

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749 0 19.01.2023

One of the most interesting topics that can be studied and, moreover, developed for your own benefit, is the ancient history of our planet. You can do this from any corner of it, for example in Cyprus.

However, it will not be easy to imagine what our planet looked like tens and hundreds of millions of years ago. However, if you have good illustrations at hand, as well as a coherent theory, then it will become much easier to discover the ancient secrets of the Earth.

One winter evening, succumbing to the right mood, I found a file of my article on this topic (a few years ago I started writing it with the support of my good friends, professional geologists), took a few more articles from magazines for compilation and tried to write a popular story. What eventually turned out to be the real article:

How did the island of Cyprus come into being?

Almost every second tourist asks me the question “How did the island of Cyprus come into being?”. There is something mystical in the metaphor that the island of Aphrodite, like the goddess Aphrodite herself, appeared from the depths of the sea. And this metaphor is very successful, and we will continue to develop it. And so that the picture of the birth of the island does not confuse you with its complexity, first we will analyze some important definitions:

1. The Tethys Ocean

The first continents of the Earth appeared about 3 billion years ago. years ago. If we recall school textbooks on natural sciences (the surrounding world), then an illustration of the globe in the section will pop up in our memory: there is a hot solid core in the center of the globe, it is surrounded by a mantle (also hot, but already plastic), and the earth’s crust will remain on top. This crust consists of blocks – lithospheric plates, and the plates, in turn, are in constant motion (due to the convection movement of the mantle masses). This model gives us an understanding that the Earth’s surface is constantly moving, and continents, seas and oceans are constantly changing their size, shape and location. If you had seen a map of the Earth a hundred million years ago, you would not have recognized our modern planet on it.

Gondwana breakup and the Western Tethys (regional view)Gondwana breakup and the Western Tethys (regional view)

So, the Tethys Ocean (one of the variants of the name of the Greek goddess of the sea, Tethys, Thetis) existed from about 850 to 5 million years ago. And from 200 to 5 million years ago, Tethys divided two ancient continents that existed at that time: Laurasia and Gondwana. Cyprus began to form in the Mesozoic about 90 million years ago. Thus, when the island of Cyprus was already in full existence, there was still no Mediterranean Sea (Cyprus is an oceanic island).

2. Convergent boundaries

These are the boundaries along which lithospheric plates collide. Lithospheric plates come in two types: continental (lighter, thicker) and oceanic (cooler, and therefore heavier and rather thin). Oceanic plates are much more ancient than continental ones.

As you can see, Cyprus lies on a convergent border along which the African plate and the Eurasian plate collide. In fact, this is a zone of constant subduction. This term also needs to be sorted out.

3. Subduction

Subduction is the process of subducting an oceanic plate under a continental or other oceanic plate. Most convergent boundaries are subductive in nature. The subduction boundaries correspond to deep-sea troughs and island arcs. The typical structure of subduction zones looks like a deep–sea trough, followed by an island arc, and behind it is a back-arc basin. A deep-water trough is formed at the site of the subducting plate. Behind the island arc, a part of the plate is stretched, resulting in the formation of an arc basin. In the zone of the back-arc basin, plate stretching can become significant, and this in turn can lead to cracking of the plate crust and spreading.

The immersion of a part of the subducting plate into the asthenosphere is accompanied by earthquakes (they occur extremely often in Cyprus), the foci of which occur at the points of contact of the plates, as well as in the subducting plate itself. The zones of these foci are called seismofocal zones (Benioff boundaries). In the subduction zones, the process of forming a new continental crust begins, and at the same time, part of the oceanic plate is absorbed by the asthenosphere. Simultaneously with these processes, the oceanic plate is growing in the spreading zone.

Мантийная конвекция и геодинамические процессыMantle convection and geodynamic processes

4. Obduction

A rather rare tectonic process is obduction. Obduction is called the pushing of layers of the upper part of the oceanic plate onto the edge of the continental plate.

This can happen if there are several specific factors:

a) There are dense areas of heterogeneity in the subducting oceanic plate: the so-called microcontinents or island arcs, as if embedded in the plate. Thus, when the plates converge, a collision of continental blocks will occur, and this, by the way, is the mechanism of formation of mountain ranges. Further movement of a part of the plate stops, and a new subduction zone is formed from the outside of the island arc.

b) The immersion of the subducting plate is hindered by the local high viscosity of the asthenosphere. In this case, the process of sinking of the plate, its bending and the formation of a fold when moving on the continental plate is inhibited. As the movement of the oceanic platform as a whole continues, a new subduction zone, a new fold, etc. is subsequently formed behind the fold until the next bend of the plate falls into the low viscosity zone of the asthenosphere. As a result of obduction, ophiolite complexes are formed.

Also, due to the deformation of the oceanic plate, cracks form in it with foci of magmatism, evidence of which we can now see in the form of unusual formations in the mountains of Cyprus. I mean dykes. These are unusual and beautiful natural monuments. They are worthy of a separate article, I will write it later.

5. Ophiolites

Ophiolites (from Greek. όφις — snake and λίθος — stone, literally translated – serpentine rocks or serpentinites), which are combined with the remains of a layer of rocks of the ancient oceanic plate. Ophiolites are the remains of ancient oceanic plates that came to the surface of the Earth. The composition of ophiolites is quite complex: they consist of dunites, peridotites, gabro, diabase, etc.

The bottom line is that it is extremely difficult to study the structure of ancient oceanic plates, drilling operations are specific and extremely expensive. But these studies are very important because they can reveal to us the ancient secrets of our planet. But in places where ophiolites come to the surface of the earth, scientists have a unique opportunity to study the ancient history of the Earth without serious difficulties and costs. There are few such places on Earth, and Troodos is the most accessible, visual and therefore the most studied ophiolite complex by scientists. In the truest sense of the word, a unique place on the scale of the whole Earth.

In addition, ophiolite layers often carry a lot of minerals. For example, mining was highly developed in Cyprus at one time. Nickel, cobalt, chromium, asbestos, and pyrite ores containing copper, zinc, gold, and silver were mined in Troodos).

The emergence of the island of Cyprus. The main faults.

(Based on the materials of K.A.Krylov, 2000)

According to modern concepts, the formation of igneous rocks of Trodos is associated with magmatism over the subduction zone that occurred in the Late Mesozoic in the Tethys Ocean [Pearce et al., 1984].

The main faults of various nature are indicated on the graphical model of the island of Cyprus. The southwestern and central part of the island is occupied by the Troodos mountain range. This ophiolite massif is a fragment of an oceanic plate of the Cretaceous period. Its age is estimated at about 90 million years [Mukasa, Ludden, 1987]. The Troodos ophiolites were divided into fragments by transform faults formed at different times.

The Arakapas fault is the oldest of the four shown in the illustration. Geochemical features of igneous rocks indicate that they formed above the Middle Cretaceous seismofocal zone. According to the most common reconstructions, this seismofocal zone began to form about 100-93 million years ago in the southern part of the Mesozoic Tethys Ocean. 70-65 million years ago, during the obduction, the Troodos massif experienced a counterclockwise rotation of 90 degrees.

The Yarasa fault is younger, and the ophiolite complex borders on Cenozoic carbonate deposits along it. The Moni terrigenous chaotic complex (thrust sedimentary melange in the area of the convergence line) runs along the Yaras fault.

The Petra tou Romio lineament fault is young, which is confirmed by modern seismic activity, has a shear component due to the modern oblique thrust of the African lithospheric plate under the Cyprus Island arc.

The Ovgos fault is also young, it was laid down approximately in the Middle Miocene (15-12 million years ago), representing at that time the outskirts of the marine platform. Compression from north to south began in the early Pliocene (about 4 million years ago) and caused the accumulation of internal stresses in the lithosphere and, as a result, compression tectonism – rock thrust in the forming Kyrenia ridge [Geosciences and Environmental Change Science Center, 2004].


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