9.11.2019 10:50 PM


Scientists Recreate What Happened to an Ancient Continent Shoved Beneath Europe

Meet Greater Adria.

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Around 180 million years ago, Earth fundamentally changed when Gondwana began to dismember. Today, present-day places, including South America and Australia, are visible chunks of this former ancient supercontinent, as well as not-so visible slices of land, like the submerged Zealandia — debatably Earth’s eighth continent.

However, scattered from Spain towards Iran, are signs of another lost continent — a once-Greenland sized relic called Greater Adria. Last week, in the journal Gondwana Research, geologists published the most detailed look at Greater Adria’s demise yet, in turn explaining how it went from being part of a supercontinent to being buried beneath Europe.

A team led by Professor Douwe van Hinsberg from Utrecht University spent the past decade collecting and examining geological data from parts of southern Europe, Africa, and western Asia, looking for evidence of Greater Adria. They took specific note of the orientation of minuscule magnetic minerals, which were formed by primeval bacteria.

Hinsberg explained to Live Science that bacteria make the magnetic particles in order to orient themselves to Earth’s magnetic field. When mineral-filled sediment turns into rocks, that orientation is frozen in time. In turn, this team’s examination revealed that the rocks had undergone extremely large rotations — evidenced by fault lines that look “like pieces of a broken plate.”

Greater Adria was a Greenland-size landmass.Gondwana Research 

With this knowledge — and GPlates, software that enabled the team to create how Earth’s tectonic plates have moved over time — the team extrapolated that Greater Adria broke away from Gondwana around 240 million years ago. From there, it began to drift northward, collecting mineral-filled sediments. Between 100 million and 120 million years ago, it collided with what’s now Europe.

In that destruction, it’s likely that a fraction of the ancient formation was scraped off — and today those scraps exist as rocks found in places like Turin, Italy, and Croatia’s Istria region. It’s also likely that this collision served as the foundation for the formation of a handful of southern Europe’s mountains. At speeds of no more than 3 to 4 centimeters per year, the ancient continent drove into Europe, shattering its crust, and driving the majority of it within Earth’s mantle.

Understanding Greater Adria is a puzzle that’s been ten years in the making, and things aren’t completely settled yet. Even what to name the ancient landmass has been debated. But its known existence is a sign that undiscovered history can still be found in unexpected places, and a reminder that while our own continents may seem settled, our own landmasses are still moving today.

The basins and orogens of the Mediterranean region ultimately result from the opening of oceans during the early break-up of Pangea since the Triassic, and their subsequent destruction by subduction accommodating convergence between the African and Eurasian Plates since the Jurassic. The region has been the cradle for the development of geodynamic concepts that link crustal evolution to continental break-up, oceanic and continental subduction, and mantle dynamics in general. The development of such concepts requires a first-order understanding of the kinematic evolution of the region for which a multitude of reconstructions have previously been proposed. In this paper, we use advances made in kinematic restoration software in the last decade with a systematic reconstruction protocol for developing a more quantitative restoration of the Mediterranean region for the last 240 million years. This restoration is constructed for the first time with the GPlates plate reconstruction software and uses a systematic reconstruction protocol that limits input data to marine magnetic anomaly reconstructions of ocean basins, structural geological constraints quantifying timing, direction, and magnitude of tectonic motion, and tests and iterations against paleomagnetic data. This approach leads to a reconstruction that is reproducible, and updatable with future constraints. We first review constraints on the opening history of the Atlantic (and Red Sea) oceans and the Bay of Biscay. We then provide a comprehensive overview of the architecture of the Mediterranean orogens, from the Pyrenees and Betic-Rif orogen in the west to the Caucasus in the east and identify structural geological constraints on tectonic motions. We subsequently analyze a newly constructed database of some 2300 published paleomagnetic sites from the Mediterranean region and test the reconstruction against these constraints. We provide the reconstruction in the form of 12 maps being snapshots from 240 to 0 Ma, outline the main features in each time-slice, and identify differences from previous reconstructions, which are discussed in the final section.
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