CD-CAT 101: Non-Technical Description

Overview of the geology of Turkey: modern tectonic setting

 

The continents of Europe and Asia meet in Turkey -- specifically, in Istanbul at the Bosphorus Strait -- and the Asian part of Turkey is called Anatolia. Anatolia is also a tectonic plate. Plates are made of crust and the underlying upper mantle (together these are also known as the lithosphere) and they move in response to forces acting at the boundaries of the plate.

Satellite image of Turkey, showing the land boundaries of the country (red line), the major plate-bounding faults (white), and some other important faults (yellow). The pink arrows show the approximate direction of motion of the Arabian plate relative to Eurasia (at 15 millimeters per year), and the motion of Anatolia to the west at 21 millimeters per year.

 

In the case of the Anatolian plate, the crust is mostly continental crust, but it contains pieces of old oceanic crust, representing the ancient Tethyan Ocean that was consumed tens of millions of years ago as continents and fragments of continents (microcontinents) collided and created the modern Anatolian plate.

 

Today, the Anatolian plate is experiencing extension (pulling apart) on its western margin, where it meets the Aegean Sea, and it is experiencing convergence (compression) on its southeastern margin, where the Arabian plate is colliding with Anatolia (see arrows on the map above). The Anatolian plate is moving to the west, mostly as a large, rigid block.

 

The boundaries of the plate to the north and south(east) are major strike-slip faults that experience many earthquakes: the North Anatolian and East Anatolian Faults. (map) The North Anatolian fault has been compared to the San Andreas Fault in California: both are large strike-slip faults within continental crust and both are major seismic hazards for the people living near them because they both generate earthquakes of large magnitude.

 

This type of lateral motion of a plate is called tectonic escape. Anatolia is escaping to the west, perhaps in response to the collision of Arabia in the east.

 

Compared to most other tectonic plates, the Anatolian plate is very small. In fact, some (simplified) maps showing the tectonic plates of the world don't even distinguish it from the Eurasian plate, even though Anatolia is one of the most geologically active places in the world. For our research on the Anatolian plate, the small size and high level of activity are advantages because these allow us to study the plate margins and interior in one research project, and to observe many different types of recent and ongoing geological activity.

 

In the CD-CAT (Continental Dynamics : Central Anatolian Tectonics) project, we are studying how the Anatolian plate has moved and changed -- laterally and vertically, from the mantle below the Anatolian plate to the Earth's surface -- over the past ~65 million years, a period of time in Earth history known as the Cenozoic Era.

 

Goals of CD-CAT and why we are working in Turkey

 

The Anatolian plate has had an interesting history. The mountains of Turkey are part of a very long tectonic zone that extends from the Pyrenees to the Himalayas. There are some similarities between Anatolia and other parts of this belt, but there are some important and intriguing differences as well.

Relief map of south-central Europe and Asia, showing the belt of mountains that reaches from France and Spain to SE Asia. The zoomed-in map of Turkey and neighboring regions has arrows on it that show the motion of the Anatolian plate, from the collision zone with the Arabian plate in SE Turkey to the zone of extension in the Aegean Sea. This motion has been determined by GPS measurements of recent motion of the Anatolian plate. (Figure with arrows modified from Reilinger et al., 2006).

 

At first glance, Anatolia has some similarities with the Himalaya and Tibet, although at a smaller scale. Both have big plateau areas behind collision zones and both have tectonic escape systems, but the Tibetan Plateau is underlain by very thick crust, whereas the Turkish-Iranian Plateau, at least in Turkey, is underlain by thin crust.

 

In addition, Anatolia has the hottest continental lithosphere on the planet. Why are the rocks of the continental crust here so hot?

 

This question may have been partly answered by previous geophysical imaging of the region. These results show that the plate that subducted below Anatolia and Eurasia (leading to eventual collision) may have broken off, allowing hot mantle to flow up close to the bottom of the crust, which has crumpled without much thickening.

 

How has this possible break-off or tear of the subducting Arabian plate affected the overlying Anatolian plate, including the development of escape tectonics?

 

We are working in central and east-central Anatolia, where there are major strike-slip faults and other deformation features that pre-date the plate-bounding North and East Anatolian faults, a major volcanic area (Cappadocia), and evidence for reorganization of major landscape features. All of these are in the plate interior, and need to explained in the context of the continental dynamics of Anatolia.

 

Current models cannot explain some of these features. As an example, the high Taurus Mountains (up to nearly 12,000') have young marine sediments at high elevation, indicating that the mountains were uplifted in the past 8 million years. What happened in the past 10 million years to create these high mountains?

 

Specific research questions that we will try to answer are:

 

1. What are the mantle (deep) to surface (shallow) dynamics during the development of escape tectonics in Anatolia?

 

2. How and when did the Anatolian plate evolve from a system of widepread deformation within the plate to one of very localized deformation along the major bounding strike-slip faults?

 

3. Why is there a large volcanic (magmatic) area in Central Anatolia? (what melted and why?)

 

4. How has the landscape responded to tectonic and climatic processes through time, including before and after the development of escape tectonics?

 

Most importantly, we are integrating results from a wide variety of methods and considering these questions together, not as separate items, as illustrated in this conceptual sketch showing a cross-section through the Anatolian lithosphere: