How can rocks in the Alps, the Apennines, and the Balkans share a common origin when they sit on opposite sides of seas and political borders? The answer lies deep beneath the continent’s roads and cityscapes, in a region of the crust that no longer constitutes a continuous whole on the surface of the Earth. Geologists have reconstructed the history of the Greater Adria, a Greenland-sized chunk of continent that rifted away from Gondwana some 240 million years ago and subsequently collided with the southern margin of Eurasia. A lot of it didn’t fold neatly into a single mountain range, says one geologist. It was torn apart, dissected, overturned, and finally forced beneath the surface.
Unpacking and reconstructing this story required more than the recognition of familiar ranges of limestone. The tectonic environment of the Mediterranean has been described by the lead author of this study as “a geological mess” where “Everything is curved, broken, and stacked.” The study required a reconstruction over the last decade in more than 30 countries, combining the age of the rocks, structural data, and the orientation of magnetically aligned minerals to reconstruct the relative motion of the fragments against each other as the ancient plate moved north and rotated counterclockwise. Advances in computer software for reconstruction of the last 15 years or so also aided in combining locally incompatible maps into a regional kinematic framework.
A model of this process was outlined by Douwe van Hinsbergen: “Suppose you have a sweater on,” he told Business Insider. ‘As an “arm” of the sweater moves under a table, the sleeve can pile up and rise while the arm continues its motion. “The piled-up sleeve corresponds to the upper few kilometers of Adria’s crust, and your arm is the plate that is now sinking into the mantle, hundreds or thousands of kilometers beneath our feet.” The mountain ranges of Europe are the areas where the sleeve sediments and upper crust, buoyant and pushed ahead and piled up while the heavier parts sank further has been stripped off.
Seismic imaging has finally filled in the missing dimension: depth. The slabs that have been associated with this long convergence are still identifiable in mantle tomography, a kind of CT scan that is generated by seismic waves. Van Hinsbergen has pointed out that traces have been found to extend to 1,500 kilometers below Greece, in accordance with “underworld” maps of cold, dense material that have been stranded well below the Aegean region. Technical literature on the Aegean slab demonstrates how subduction episodes can stack and separate in the geological record an important truth about the series of encounters with changing plate boundaries that marked the disappearance of Greater Adria.
Why is this significant beyond the naming of a “lost continent”? Because subduction is also a materials pipeline. When crust is subducted, it carries volatiles and chemical elements that can change the mantle and fuel subsequent magmatism. Studies of ultrahigh-pressure rocks in central Europe describe melt inclusions trapped in garnet at depths of 130 to 150 km, averaging 3.89 wt% H2O and total CO2 of 20,180 ± 4,440 ppm after adjustments to direct measurements that illuminate the potential of buried continental material to metasomatize the mantle and influence post-collisional magmas.
The useful thread at the surface is mineral systems. Modern critical metal exploration emphasizes the need to recognize that ore-forming systems are not proportionally represented in time and tectonic type, and that new discoveries are increasingly made beneath younger sedimentary cover or at deeper levels. The logic of the need for greater Adria mapping was succinctly summarized by Van Hinsbergen: “Metals, ceramics, building materials, everything came out of a rock,” and “You don’t find the next gold or copper mine, or the 25 materials you’ve never even heard of that make your iPhone work, by taking a stroll in the woods.” The greater Adria mapping project does not locate the next deposit, but it improves the tectonic framework that exploration models employ to determine where to search and where Europe’s familiar landscapes still hide buried, recycled roots.
