Making Cyprus: create the Troodos ophiolite and lift it up

In my first post about Cyprus, I introduced some basics about its geologic and human history (https://landscapes-revealed.net/cyprus-a-pop-up-island-between-converging-plates/). In my third post about Cyprus, I described the features found in the Troodos Geopark (https://landscapes-revealed.net/troodos-unesco-global-geopark-in-cyprus/). In this post, I’ll explain the geology of the Geopark—how the ophiolite sequence that makes up the park was created and how it got lifted up to its current elevation. Unless otherwise stated, the diagrams are all from a Geopark publication that can be downloaded from the Cyprus Geological Survey’s web site: https://www.moa.gov.cy/moa/gsd/gsd.nsf/6C44F59ED2870601C22584870039315E/$file/EN%20Geopark%20brochure_www.pdf. As always, unless otherwise stated, the photos are my own.

Where the Troodos Ophiolite was created

The name ophiolite is derived from the Greek words ophio (=snake) and lithos (=rock). It was initially applied to outcrops of serpentine rock that have a dark green shiny color, and a scaly texture. Serpentine rocks are just one of the rock types found in ophiolite complexes, but the ophiolite term is now applied to all of the rock types.

Ophiolites are sections of oceanic crust and underlying upper mantle. Partial melting of the upper mantle supplies magma (liquid rock) that migrates upward to form the ocean crust. Typically, ocean crust forms in the middle of oceans at spreading ridges, where newly created seafloor diverges and provides space for new ocean crust to form. In one of my Plate Tectonics 101 posts, I explained the basics of divergent plate boundaries where ocean crust is created: https://landscapes-revealed.net/plate-tectonics-101-what-happens-when-plates-move-away-from-each-other/.

The Troodos Ophiolite formed 92–82 Ma (millions of years ago) in a rather unusual position: above a subduction zone, where previously created oceanic crust attached to the African plate was subducting northward beneath the Eurasian plate (see diagram below). As explained in my first post, the Mediterranean Sea is a remnant of the Tethys Ocean, whose closure has been complex. It is thought that a new subduction zone was just starting in the Tethys Ocean and that this induced a new “supra-subduction” spreading center to begin creating new oceanic crust.

The rock sequence that makes up ocean crust is pretty much the same, regardless of where it was created. But the supra-subduction-zone position is important for the uplift history of the Troodos Ophiolite, and the preservation of the entire crust as a coherent sequence. It is probably why the Troodos is the most complete ophiolite sequence on our planet. In California, and now Oregon, where I’ve been living for decades, there are many bits and pieces of ocean crust—for example, in the Francisco Complex in San Francisco (https://landscapes-revealed.net/why-are-there-so-many-hills-in-san-francisco/) and in the Klamath Mountains in northwest California and southwest Oregon (https://landscapes-revealed.net/marble-mountain-wilderness-in-northern-california/). But I had to go to Cyprus to see a complete, coherent ophiolite!

Components of the Troodos Ophiolite

First, we need to consider the process of hydrothermal circulation (diagram below). This process affects all components of ophiolite sequences.

The processes that create each part of the sequence are complicated and not fully understood—they happen far beneath Earth’s surface, after all. It’s important not to think of the sequence as older (bottom of diagram) to younger (top of diagram). These units do not form sequentially, as do sedimentary layers. Rather, these units are forming all together, at the same time.

Ultramafic upper-mantle rocks—mainly peridotite (lowest green color in sequence above)

Keep in mind that the ocean is low and the land is high. This is because the minerals that make up ocean crust are much denser than the minerals that make up continental crust. Continental rocks (called felsic) consist mainly of minerals made of light elements such as silica, oxygen and aluminum, whereas oceanic rocks (called mafic) consist mainly of minerals made of heavier elements such as iron and magnesium. Felsic rocks contain >65% silica; mafic rocks contain <55% silica.

Ultramafic refers to even denser (<45% silica) rocks with even more heavy elements. This is the material of the upper mantle. When it partially melts, it provides the magma that rises up to form the overlying layers of the ocean crust.

Layered and massive gabbro (two green units below the purple units in sequence above)

Gabbro is a mafic rock that is plutonic like granite, its felsic complement. Gabbro has large crystals because it cools and crystallizes slowly below Earth’s surface. Although it is not a sharp boundary, we have now transitioned into the ocean crust.

Sheeted dikes (light-pink-colored unit with black vertical lines in the sequence above)

Again, the transition between units is gradual, not abrupt. Dikes are the conduits that enable magma from the magma chamber to rise upward to the seafloor, where they form pillow lava.

Lower and upper pillow lavas (upper dark pink and purple units in sequence above)

Once magma in the dikes reaches the seafloor, it erupts and flows as lava. The composition is basalt, the volcanic equivalent of the plutonic rock gabbro. Some of the gabbroic magma cooled deeper in the crust and some of the magma flowed upward in dikes to erupt on the seafloor. When lava erupts into water, the exterior cools quickly while the interior can keep flowing. This process causes pillow shapes to form. It even occurs in Hawaii, where lava flows into the ocean.

Umber (top red unit in sequence above)

At the top of the ophiolite sequence, we finally find sediments! Umbers are chemical sediments of iron and manganese oxides deposited on pillow lavas following extrusion of hot mineral solutions at hydrothermal vents.

Marine sediments deposited on top of the ophiolite

The ocean crust continued to form for 10 million years, from 92–82 Ma, followed by a period of tectonic quiescence when a variety of marine sediments were deposited on top of the ophiolite. In some places, thin layers of radiolarian chert overlie the umber. Radiolaria are single-celled organisms that make their shells of silica. They live near the ocean surface but when they die, their shells fall to the seafloor to form a type of biogenous sediments. Most of the marine sediments above the ophiolite are limestones that consist of remains of organisms with hard parts made of calcium carbonate. More details are in the figure captions.

Lifting up the Troodos Ophiolite

The only way to explain the geologic history of Cyprus, including its uplift, is with images. The words on the figure below are difficult to read, but I provide a brief summary below the caption.

A. Upper Cretaceous (92–70 Ma). The Troodos ophiolite was formed as new ocean crust in a divergent basin above a subduction zone from 92–82 Ma. This extension occurred while Eurasia and Africa were continuing to collide. Although not an exact analogue, you could think of Japan, which has a convergent subduction zone on the east side and an extensional basin on the west side (Japan Sea). After the ocean crust formed, deep-marine sediments of mostly biological origin were deposited on top of the ophiolite.

B. Upper Cretaceous–Lower Miocene (70 Ma–23 Ma). The Mamonia Complex (piece of crust formed elsewhere) collided with the south side of Cyprus around 70 Ma (brown color). Deep-water sediments (mostly limestone) continued to be deposited on top of the ophiolite from 67–23 Ma. Compressional forces associated with the subduction zone may have produced some initial uplift during this time.

C. Lower Miocene (23–20 Ma). Marine sediments were deposited in shallower water as the island continued to be uplifted by compressive forces.

D. Upper Miocene (10 Ma). The Kyrenia terrane (piece of crust formed elsewhere) collided with the north side of Cyprus (yellow color). Shallow marine sediments continued to be deposited. Notice how the green-colored interior of the ophiolite is shown rising up, almost like magma. This is the ultramafic mantle rocks that were hydrothermally altered to serpentine. Because the mineralogical change includes water, the serpentine rock is less dense than its peridotite parent. Since the rock is less dense, while it was still at sufficient depth to be pliable it could “burble upward” to some extent.

E. Pliocene–Quaternary (3 Ma–present). The Eratosthenes Seamount, a piece of carbonate platform on the African plate, began to be subducted beneath Cyprus. This piece of continental crust is too buoyant to be easily subjected and this causes strong compressive forces that have uplifted Cyprus above the sea to its current elevation. It continues to be uplifted today. My first post has more information about the Eratosthenes Seamount: https://landscapes-revealed.net/cyprus-a-pop-up-island-between-converging-plates/.

I mentioned above that the supra-subduction-zone position contributed to the island’s uplift and preservation. The history described above demonstrates how this happened. The uplift was, and continues to be, mostly a result of compressive forces associated with the subduction zone. Diapiric uplift of the buoyant serpentine rocks was a lesser factor. As the geologic units have been folded and uplifted, erosion has removed all of the younger units at the top of the dome, thus exposing rocks formed in the depths of the mantle at the top of the Troodos Mountains.

End note

If you made it to the end of this post, you deserve an A+ and a ⭐️! You swallowed a big piece of crust! I tried to simplify this story, but even the simplification remains complex. The next post will be more digestible—I’ll describe the gorgeous gorges we traversed in SW Crete.