The lithosphere and upper mantle of Adria microplate from integrated geophysical-geochemical and geodynamic modeling

The Central Mediterranean region is characterized by a wide diversity of geodynamic processes in the context of the long-term plate convergence between Africa and Eurasia during the entire Alpine Cycle. The Adria microplate, deformed amid the two major converging plates of Africa and Eurasia, results in a key piece for the reconstruction of this complex tectonic region. Adria is surrounded by highly deformed converging margins involving three plate subductions with different polarity and with Adria acting as both upper plate in the Alps and lower plate in the Apennines and Dinarides. One of the striking aspects of these subducted/delaminated slabs is their conspicuous segmentation at depth, as observed in tomographic studies, separated by lithospheric gaps that have been commonly interpreted as occurring during the subduction processes. Moreover, the NW-dipping Ionian subduction under the Calabrian Arc seems to be connected with the SE termination of the slab beneath the Apennines. Unveiling the lithospheric structure of the Calabrian subduction zone, one of the narrowest arcs on Earth, is crucial for understanding the geodynamic evolution of the Mediterranean and adjacent marginal seas.

In this presentation, we will show our findings of a geophysical-geochemical model of the lithosphere and uppermost sublithospheric mantle of the Adria microplate and its surroundings. We will present the lithospheric structure of the Adria microplate and the two opposing mantle slabs along its NE and SW margins. The modeling shows the presence of two asthenospheric mantle wedges aligning with the Apennine and Dinaride continental mantle slab rollback, along with cold sublithospheric anomalies beneath the NE and SW margins of Adria. The structure of the northern Adria region, is consistent with the northeastward rollback of the SW Adriatic slab (beneath Northern Apennines), leading to subsequent delamination of the continental mantle. In the southern Adria region (southern Apennines), the complex deep structure results from the variably oriented lithospheric slabs, and nearly 90-degree shift of the tectonic grain between the southern Apennines and the Calabrian Arc. At the SW Adria margin, beneath the northern Apennines, we interpret the subducting slab attached to the shallower lithosphere, while a slab gap is modeled in the southern Apennines. Our studies suggest that they may represent inherited segments of the Mesozoic Adria plate margins. Underneath the Ionian Sea, our results show a thick crust and a relatively deep Lithosphere-Asthenosphere Boundary (LAB), contrasting with the thinner magmatic crust and lithospheric mantle of the Tyrrhenian Basin. The sharp change in lithosphere thickness, from the Calabrian accretionary wedge to the Tyrrhenian back-arc basin, contrasts with the greater lithosphere thickening below the subduction zone. Our results confirm the presence of an attached Ionian slab beneath the Calabrian Arc. The slab is colder and denser than the surrounding mantle and has a more fertile composition than the lithospheric mantle of the Southern Tyrrhenian.

This research is funded by the GEOADRIA (PID2022-139943NB-I00) project from the Spanish Government