By analyzing the rocks of Sulcis, the researchers reconstructed the tectonic processes responsible for the origin of Sardinia and its current position in the Mediterranean Sea
Thanks to the palaeomagnetic analysis carried out on rock samples taken in various places in Sardinia (particularly in the Sulcis), a team of researchers from theNational Institute of Geophysics and Volcanology (INGV) and Department of Sciences of the Roma Tre University highlighted how the island would appear to be the product of the union of two independent tectonic microplates that occurred between 30 and 21 million years ago. This is the result of the study “Paleomagnetic Evidence for Pre-21 Ma Independent Drift of South Sardinia From North Sardinia-Corsica: “Greater Iberia” Versus Europe”, recently published in the scientific journal tectonics of the AGU. “It is known, thanks to paleomagnetic data obtained in Sardinia and Corsica since the 70s, that the Sardinian-Corso tectonic block detached 21 million years ago from the Provençal-Catalan European margin, reaching its current position with an anti-clockwise rotation of 50°-60°”he explains Fabio Speranza, Director of the Roma2 Section of INGV and co-author of the study. “However, with this work we have taken an important step forward: we have in fact discovered that south-western Sardinia - specifically the territory of Sulcis - has undergone a greater rotation, of about 90°, after 30 million years. Not only that: in the light of the new evidence we have re-evaluated data already present in the literature relating to much older rocks, dating back to the interval 300-150 million years ago, and we have discovered that the rotation of the southern portion of the island is even wider , equal to about 120°”. Sardinia, Therefore, would have formed from two independent microplates which in geologically recent times, between 30 and 21 million years ago, they bonded with each other and, together, they detached themselves from the European margin to locate themselves in the central Mediterranean. “While the northern part of Sardinia was part of a single block with Corsica and Provence, the southern plate of the island belonged to the so-called Iberian plate, which decoupled from Europe between 120 and 150 million years ago, during the opening of the Bay of Biscay, with a first counterclockwise rotation of 30°”, goes on Gaia Siravo, researcher at INGV and co-author of the study. “With a second counterclockwise rotation of 30° which occurred between 30 and 21 million years ago, southern Sardinia was welded to the rest of the Sardinian-Corso block along the so-called Nuoro fault. After that, between 21 and 15 million years ago, the entire 'new' Sardinian-Corsa plate definitively detached from the European margin with an anti-clockwise rotation of 60° and reached its current position". The results obtained from this work therefore suggest that before 30 million years ago the Iberian plate was actually much larger than it is today (in fact, we speak of Greater Iberia) since it was united not only with southern Sardinia, but also with the Balearic Islands, the Calabro-Peloritan block, the Kabili blocks (northern Algeria) and the Alboran block (which includes Morocco and Andalusia). After that, starting 30 million years ago, Greater Iberia was fragmented and the microplates produced by this fragmentation dispersed until they reached their current location. “The paleomagnetic analyzes underlying our study were carried out on sandstone and clay samples from 31 localities in Sulcis, in south-western Sardinia. The samples, analyzed in the Paleomagnetism Laboratory of the INGV Rome branch, allowed us to re-evaluate all the previous paleomagnetic data in the literature and then propose our evolutionary model", he adds Fabio Speranza. “This work reminds us that even in a country like ours, where many geophysical and paleomagnetic studies have been carried out in the last 50 years, there are still many aspects to understand on the process of fragmentation and drift of microplates which has led to the current Italian tectonic structure”he concludes Gaia Siravo. “Our next objectives certainly include trying to determine with greater precision the age of the oldest counterclockwise rotation of 30° in southern Sardinia, currently included in a very long time interval, between 250 and 40 million years ago: being able to better date this event would allow us to further deepen our knowledge of the tectonics of our country".