Phase 9: Closure of the Eastern Oceanic Connection

The last phase that characterized the tectonic history of the Mediterranean region during the Mesozoic comprises, as the previous one, two stages: from 74.3 Ma (C33n, Upper Campanian) to 72.5 Ma (C32n.2n, Upper Campanian), and from 72.5 Ma to 67.7 Ma (C31n, Upper Maastrichtian). In the eastern regions, this time period marks the completion of the process of subduction of the Vardar Ocean (Northeast Neo-Tethys) under Eurasia and the first direct contact between Kirsehir and the Tauride Platform, with the subsequent closure of the former oceanic connection with the Indian Ocean (Fig. 21). This event also triggered compression in the southern branch of Neotethys, between the Tauride Platform and Arabia [e.g., Robertson, 1998]. At the end of the second stage, in the Upper Maastrichtian, only a remnant of the oceanic crust that formed during the Jurassic and Early Cretaceous survived in the eastern region: the Inner Tauride Ocean, which was still subducting under the Western Pontides, Sakarya and Kirsehir.

Figure 21. Reconstruction at 67.7 Ma (Upper Maastrichtian)

Reconstruction at 67.7 Ma (Upper Maastrichtian)

Vectors represent direction and magnitude of the relative velocity fields in the Mediterranean region. Blue lines represent the modeled 172.0 Ma, 170.0 Ma, M25, M21, M16 and M10 isochrons. The 130.0 Ma, M4, M0 and 74.3 Ma isochrons are indicated in green.

Regarding the Western region, the velocity field shown in Figure 21 indicates the onset of weak compressive tectonics in the Liguride Ocean, associated to the eastward motion of Iberia with respect to Africa since 72.5 Ma (C32n.2n, Upper Campanian), tough an earlier phase of compression is likely to have occurred in conjunction with relative motion between Northwest Africa and Northeast Africa. Evidence of compression in this region during the Late Cretaceous is well documented by both geological and geophysical data. A recent paper of Faccenna et al. [2001] shows that initiation of slow subduction under the eastern margin of Iberia (Corsica-Sardinia-Balearics) occurred between 80 Ma and 70 Ma. These authors estimate an average velocity of convergence of 8 mm/yr from the Late Cretaceous to the Oligocene, which agrees well with the value predicted by our model for this initial stage: 6 mm/yr offshore Corsica. However, radiometric ages of the blueschist metamorphic facies of Alpine Corsica indicate an earlier initiation of compressive motions in the Liguride Ocean, about 105 Ma for the emplacement of the Schistes Lustrés nappes [Cohen et al., 1981]. We assume that this event, which predates the onset of subduction of oceanic crust in this region, is associated to large-scale tectonic motions that deformed the African continent between anomalies M0 and C34, when Northwest Africa and Iberia were subject to a small clockwise rotation with respect to Northeast Africa.