The Balkan Peninsula is a geologically complex region, and new research is shedding light on the unusual ways the African tectonic plate is interacting with the European plate beneath it. Specifically, scientists are investigating how pieces of ancient African crust are not only being subducted – sinking beneath Europe – but also, surprisingly, resurfacing in a process called vertical extrusion.
Around the Balkan Peninsula, the African plate is descending under the European plate, a process driven by plate tectonics. According to the USGS, most plate movement occurs along narrow zones where these forces are most evident. There are four main types of plate boundaries: divergent (moving apart), convergent (colliding), transform (sliding past), and plate boundary zones (complex interactions). The situation in the Balkans falls primarily under convergent boundaries, but with a unique twist.
Researchers at TU Bergakademie Freiberg, led by Dr. Iskander Muldashev and Prof. Thorsten Nagel, have been studying this phenomenon, focusing on the Rhodope mountain range in southern Bulgaria. Their recent work, published in the journal Geology, suggests that a portion of deeply submerged African crust resurfaced approximately , far from the primary subduction zone. This isn’t a simple uplift; it’s a vertical ascent of material from significant depths.
The process, termed “vertical extrusion,” has been a matter of scientific debate. The team’s computer models demonstrate how the Rhodope mountains were formed by the ascent of rocks originating from the African plate, rather than through the more conventional processes previously assumed. Their modeling indicates the range is younger than earlier estimates, forming around .
“Our computer models…explain the tectonic process of this so-called vertical extrusion,” explains Dr. Muldashev. “The modelling shows how the Rhodope mountain range was only formed by the ascent of rocks from the African plate, instead of around as previously assumed.”
The research builds on decades of work by Prof. Nagel, who has been studying the tectonic history of the Rhodopes for . Mineralogical investigations reveal that large portions of the Rhodope mountains were submerged to depths of up to . This deep burial, followed by a relatively rapid ascent, is what makes the vertical extrusion so remarkable.
The mechanics of this process involve the African crust plunging deep into the Earth and then rising vertically, even against the compressive forces exerted by the overlying European plate. The researchers used a color-coded system in their models to “track” the maximum depth of the sinking crust before its ascent. The visualization helps illustrate how the material detaches from the sinking plate and pushes upwards, deforming the overlying plate.
The Balkans, as defined geographically, encompass southeastern Europe, taking its name from the Balkan Mountains in Bulgaria. The region’s complex geological history is intertwined with its geopolitical past, having been a crossroads of empires and cultures. The peninsula is bordered by the Adriatic, Ionian, Aegean, Black, and Turkish straits, and its boundaries are not always clearly defined.
While the specifics of vertical extrusion in the Rhodope mountains are still being investigated, the research provides valuable insights into the dynamic interactions between tectonic plates. The broader implications of this work could help scientists better understand mountain formation processes in other regions where similar subduction and extrusion events may be occurring. The USGS notes that understanding plate motions is crucial for understanding earthquake activity, and this research adds another layer of complexity to that understanding.
The discovery challenges previous assumptions about the age and formation of the Rhodope range and highlights the potential for unexpected geological processes to occur at plate boundaries. Further research will be needed to determine the extent to which vertical extrusion contributes to mountain building in other parts of the Balkans and beyond.
