History

Crust in the Mediterranean Sea Found to be 340 Million Years Old

oceanic crust

When magma at a mid ocean rim axis cools, the newly forming rocks align with the direction of Earth’s magnetic field due to magnetization of the minerals in the rock. Any change in the orientation of Earth’s magnetic fields over time is recorded in the ocean floors in this way. This effect creates a unique barcode that can be used as a time stamp for crust formation.

In the eastern Mediterranean, the crust is covered by an extremely thick sedimentary layer (10 to 15 km). This coupled to the fact that there is insufficient accurate magnetic anomaly data for the area, means that the fundamental tectonic characteristics of the eastern Mediterranean have remained unresolved.

Researchers at Ben-Gurion University of the Negev (BGU), led by Dr. Granot, recently towed magnetic sensing equipment to collect 4,300 miles (7,000 km) of marine magnetic profiles in the area. The study focused on the Levant and Herodotus basins in the eastern Mediterranean and the purpose was to study the age and nature of the underlying igneous crust.

The magnetic data was used to analyze the nature of the crust in the Herodotus Basin. The rocks were characterized by magnetic stripes, which is the hallmark of oceanic crust formed at a mid-ocean ridge. The study has uncovered the tectonic architecture and evolution of the region and has significant implications on a number of geodynamic processes.

tethys ocean
Reconstruction of Earth plate maps at 360m, 340m and 320 million years ago, just at the time a new ocean formed in what is currently eastern Mediterranean Sea. Image credit: Roi Granot

Based on the skewed patterns in the magnetic stripes, Dr. Granot believes that the oceanic crust in the Herodotus Basin could be older than 340 million years. Due to its high density, oceanic crust at subduction zones is normally recycled back into the Earth’s mantle fast. The result is that most oceanic crust is a mere 200 million years old.

Due to the thick sedimentary coverage, it has been unclear until now exactly how old the crust is and even whether it is oceanic or not. The new geophysical data has resulted in a big step forward in the geological understanding of the area.

Dr. Granot suggests that the crust might be a leftover of the ancient Tethys Ocean, which existed long before the Indian and Atlantic Oceans. If this is correct, it implies that the ocean formed much sooner than previously thought (around 100 million years earlier).

The study was published in the Nature Geoscience and was conducted by Dr. Roi Granot, a senior lecturer in the BGU Department of Geology and Environmental Sciences.

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