(AGENPARL) - Roma, 26 Maggio 2023 - (AGENPARL) – ven 26 maggio 2023 SARDEGNA | L'isola formata dall'unione di due microplacche tettoniche
Analizzando le rocce del Sulcis i ricercatori hanno ricostruito i processi
tettonici responsabili dell’origine della Sardegna e del suo posizionamento
attuale nel Mar Mediterraneo
[Roma, 26 maggio 2023]
Grazie all’analisi paleomagnetica effettuata su campioni di roccia
prelevati in diverse località della Sardegna (in particolare nel Sulcis),
un team di ricercatori dell’Istituto Nazionale di Geofisica e Vulcanologia
(INGV) e del Dipartimento di Scienze dell’Università Roma Tre ha
evidenziato come l’isola sembrerebbe essere il prodotto dell’unione di due
microplacche tettoniche indipendenti avvenuta tra 30 e 21 milioni di anni
È questo il risultato dello studio “Paleomagnetic Evidence for Pre-21 Ma
Independent Drift of South Sardinia From North Sardinia-Corsica: “Greater
Iberia” Versus Europe
<https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2022TC007705>”,
recentemente pubblicato sulla rivista scientifica Tectonics dell’AGU.
“È noto, grazie a dati paleomagnetici ottenuti in Sardegna e in Corsica sin
dagli anni ‘70 del secolo scorso, che il blocco tettonico Sardo-Corso si è
staccato 21 milioni di anni fa dal margine europeo Provenzale-Catalano,
raggiungendo la sua posizione attuale con una rotazione antioraria di
50°-60°”, spiega Fabio Speranza, Direttore della Sezione Roma2 dell’INGV e
coautore dello studio. “Con questo lavoro abbiamo però fatto un importante
passo in avanti: abbiamo infatti scoperto che la Sardegna sud-occidentale –
nello specifico il territorio del Sulcis – ha subito una rotazione
maggiore, di circa 90°, dopo 30 milioni di anni. Non solo: alla luce delle
nuove evidenze abbiamo rivalutato dati già presenti in letteratura relativi
a rocce molto più antiche, risalenti all’intervallo 300-150 milioni di anni
fa, e abbiamo scoperto che la rotazione della porzione meridionale
dell’isola risulta ancora più ampia, pari a circa 120°”.
La Sardegna, dunque, si sarebbe formata a partire da due microplacche
indipendenti che in epoca geologicamente recente, tra 30 e 21 milioni di
anni fa, si sono saldate tra loro e, insieme, si sono staccate dal margine
europeo per collocarsi nel Mediterraneo centrale.
“Mentre la parte settentrionale della Sardegna faceva parte di un unico
blocco con la Corsica e la Provenza, la placca meridionale dell’isola
apparteneva alla cosiddetta placca Iberica, disaccoppiatasi dall’Europa tra
120 e 150 milioni di anni fa, durante l’apertura del Golfo di Biscaglia,
con una prima rotazione antioraria di 30°”, prosegue Gaia Siravo,
ricercatrice dell’INGV e coautrice dello studio. “Con una seconda rotazione
antioraria di 30° avvenuta tra 30 e 21 milioni di anni fa, la Sardegna
meridionale si è saldata al resto del blocco Sardo-Corso lungo la
cosiddetta faglia di Nuoro. Dopodiché, tra 21 e 15 milioni di anni fa,
l’intera ‘nuova’ placca Sardo-Corsa si è staccata definitivamente dal
margine europeo con una rotazione antioraria di 60° e ha raggiunto la sua
posizione attuale”.
I risultati ottenuti da questo lavoro suggeriscono, dunque, che prima di 30
milioni di anni fa la placca Iberica fosse in realtà molto più grande di
come è oggi (si parla, infatti, di “Greater Iberia”) poiché era unita non
soltanto alla Sardegna meridionale, ma anche alle Isole Baleari, al blocco
Calabro-Peloritano, ai blocchi Kabili (Algeria settentrionale) e al blocco
Alboran (che comprende Marocco e Andalusia). Dopodiché, a partire da 30
milioni di anni fa, Greater Iberia è stata frammentata e le microplacche
prodotte da questa frammentazione si sono disperse fino a raggiungere la
loro posizione attuale.
“Le analisi paleomagnetiche alla base del nostro studio sono state
effettuate su campioni di arenarie e argille provenienti da 31 località nel
Sulcis, nella Sardegna sud-occidentale. I campioni, analizzati nel
Laboratorio di Paleomagnetismo della Sede di Roma dell’INGV, ci hanno
permesso di rivalutare tutti i precedenti dati paleomagnetici di
letteratura per poi proporre il nostro modello evolutivo”, aggiunge Fabio
Speranza.
“Questo lavoro ci ricorda che anche in un Paese come il nostro, in cui
negli ultimi 50 anni sono stati effettuati moltissimi studi geofisici e
paleomagnetici, ancora ci sono molti aspetti da comprendere sul processo di
frammentazione e deriva delle microplacche che ha portato all’attuale
assetto tettonico italiano”, conclude Gaia Siravo. “Tra i nostri prossimi
obiettivi c’è sicuramente quello di provare a determinare con maggiore
precisione l’età della più antica rotazione antioraria di 30° della
Sardegna meridionale, ad oggi compresa in un intervallo di tempo
lunghissimo, tra 250 e 40 milioni di anni fa: riuscire a datare meglio
questo evento ci consentirebbe di approfondire ulteriormente le conoscenze
sulla tettonica del nostro Paese”.
Citazione dello studio:
Siravo, G., Speranza, F., & Mattei, M. (2023). Paleomagnetic evidence for
pre-21 Ma independent drift of South Sardinia from North Sardinia-Corsica:
“Greater Iberia” versus Europe. Tectonics, 42, e2022TC007705.
Link: Paleomagnetic Evidence for Pre-21 Ma Independent Drift of South
Sardinia From North Sardinia-Corsica: “Greater Iberia” Versus Europe
<https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2022TC007705>
#ingv #tectonics #agu #sardegna #paleomagnetismo #placchetettoniche
[image: image.png]
Fig. 1: Mappa del Mediterraneo centro-occidentale e principali elementi
tettonici
[image: image.png]
Fig. 2: Modello Evolutivo del margine Africa-Europa tra 130 e 20 milioni di
anni
Abstract
It is unanimously acknowledged that the Corsica-Sardinia microplate rotated
counterclockwise (CCW) by 40–50° between 21 and 15 Ma, synchronous with
Liguro-Provençal Basin oceanic spreading. Conversely, 60–120° CCW rotations
with respect to Europe from Sardinia (Permian dykes, volcanics and
sediments, Mesozoic carbonates, and lower Eocene limestones) have been
interpreted to be related to (a) late Permian intra-Pangea shear events,
(b) Aptian Iberia rotation, and (c) Eocene Valais Ocean closure. We report
paleomagnetic data from 31 red-bed sites from the mid-late Eocene (45–32
Ma) Cixerri Fm. exposed in SW Sardinia. Characteristic paleomagnetic
directions from 25 dual polarity sites (240 samples) define an 86 ± 7° CCW
rotation. We suggest that a S Sardinia block located NE of Balearic Islands
rotated 30° CCW during the 30–21 Ma Liguro-Provençal rifting, and was
decoupled from N Sardinia along the left-lateral Nuoro fault. After 21 Ma,
Corsica-Sardinia underwent a drift-related 60° CCW rotation as a whole. A
re-analysis of available paleomagnetic results shows that Permian data from
N Sardinia-Corsica align with European directions considering a 60° CCW
rotation, whereas Permian and mid Jurassic data from S Sardinia match
European directions only after considering a ?35° CCW Iberia rotation
besides the 90° post-Eocene event. We suggest that S Sardinia was part of
Iberia, and rotated CCW during both Aptian Iberia drift and Oligo-Miocene
Liguro-Provençal opening. Our data, along with recent paleomagnetic results
from Calabria, suggest that S Sardinia, Balearic Islands, Calabria,
Peloritan, Kabylies, and Alboran were fragments of “Greater Iberia,” joined
to Iberia before 30 Ma Liguro-Provençal rifting.
SARDINIA | The island formed by the coalescence of two tectonic microplates
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
[Rome, 26th may 2023]
Thanks to the paleomagnetic analyses carried out on rock samples taken in
various places in Sardinia (particularly in the Sulcis area), a team of
researchers from the Istituto Nazionale di Geofisica e Vulcanologia (INGV)
and from the Department of Sciences of the Università Roma Tre has
highlighted that the island is the product of the coalescence 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
<https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2022TC007705>”,
recently published in the AGU’s scientific journal Tectonics.
“It is known, thanks to paleomagnetic data obtained in Sardinia and Corsica
since the 1970s, that the Corsica-Sardinia tectonic block detached 21
million years ago from the Provençal-Catalan European margin, reaching its
current position with a counterclockwise rotation of 50°-60°”, explains Fabio
Speranza, Director of the Roma2 Section of INGV and co-author of the
study. “With
this work we made an important improvement: in fact, we’ve discovered that
South-Western Sardinia – specifically the territory of Sulcis – has
undergone a greater rotation, of about 90°, after 30 million years. Not
just that: with this new evidence we have re-evaluated data already present
in literature relating to much older rocks, dating back to the interval
300-150 million years ago, and we’ve 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, welded
together and, together, detached from the European margin to be located 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 an initial
30° counterclockwise rotation”, continues Gaia Siravo, INGV researcher 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 Corsica-Sardinia block along the so-called Nuoro
fault. After that, between 21 and 15 million years ago, the entire 'new'
Corsica-Sardinia plate definitively detached from the European margin with
a counterclockwise rotation of 60° and reached its current position”.
The results obtained from this work suggest, therefore, that before 30
million years ago the Iberian plate was actually much larger than it is
today (we speak, in fact, of "Greater Iberia") since it was joined not only
to South Sardinia, but also to the Balearic Islands, Calabria, Peloritan,
Kabylies (Northern Algeria) and Alboran (which includes Morocco and
Andalusia) blocks. 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 analyses underlying our study were carried out on
sandstone and clay samples from 31 places in Sulcis, in South-Western
Sardinia. The samples, analyzed in the Paleomagnetism Laboratory of the
INGV in Rome, allowed us to re-evaluate all the previous paleomagnetic data
in literature and then to propose our model”, adds Fabio Speranza.
“This work reminds us that even in a Country like Italy, where many
geophysical and paleomagnetic studies have been carried out in the last 50
years, there are still many aspects to understand about the process of
fragmentation and drift of microplates which has led to the current Italian
tectonic structure”, concludes Gaia Siravo. “Our next goals 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".
How to cite:
Siravo, G., Speranza, F., & Mattei, M. (2023). Paleomagnetic evidence for
pre-21 Ma independent drift of South Sardinia from North Sardinia-Corsica:
“Greater Iberia” versus Europe. Tectonics, 42, e2022TC007705.
Link: Paleomagnetic Evidence for Pre-21 Ma Independent Drift of South
Sardinia From North Sardinia-Corsica: “Greater Iberia” Versus Europe
<https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2022TC007705>
#ingv #tectonics #agu #sardinia #paleomagnetism #tectonicsplates
[image: image.png]
Fig. 1: Map of the central-western Mediterranean and main tectonic elements
[image: image.png]
Fig. 2: Evolutionary model of the Africa-Europe margin between 130 and 20
million years
Abstract
It is unanimously acknowledged that the Corsica-Sardinia microplate rotated
counterclockwise (CCW) by 40–50° between 21 and 15 Ma, synchronous with
Liguro-Provençal Basin oceanic spreading. Conversely, 60–120° CCW rotations
with respect to Europe from Sardinia (Permian dykes, volcanics and
sediments, Mesozoic carbonates, and lower Eocene limestones) have been
interpreted to be related to (a) late Permian intra-Pangea shear events,
(b) Aptian Iberia rotation, and (c) Eocene Valais Ocean closure. We report
paleomagnetic data from 31 red-bed sites from the mid-late Eocene (45–32
Ma) Cixerri Fm. exposed in SW Sardinia. Characteristic paleomagnetic
directions from 25 dual polarity sites (240 samples) define an 86 ± 7° CCW
rotation. We suggest that a S Sardinia block located NE of Balearic Islands
rotated 30° CCW during the 30–21 Ma Liguro-Provençal rifting, and was
decoupled from N Sardinia along the left-lateral Nuoro fault. After 21 Ma,
Corsica-Sardinia underwent a drift-related 60° CCW rotation as a whole. A
re-analysis of available paleomagnetic results shows that Permian data from
N Sardinia-Corsica align with European directions considering a 60° CCW
rotation, whereas Permian and mid Jurassic data from S Sardinia match
European directions only after considering a ?35° CCW Iberia rotation
besides the 90° post-Eocene event. We suggest that S Sardinia was part of
Iberia, and rotated CCW during both Aptian Iberia drift and Oligo-Miocene
Liguro-Provençal opening. Our data, along with recent paleomagnetic results
from Calabria, suggest that S Sardinia, Balearic Islands, Calabria,
Peloritan, Kabylies, and Alboran were fragments of “Greater Iberia,” joined
to Iberia before 30 Ma Liguro-Provençal rifting.