51. FORMATION AND DESTRUCTION OF THE ERATOSTHENES SEAMOUNT, EASTERN MEDITERRANEAN SEA, AND IMPLICATIONS FOR COLLISIONAL PROCESSES1Alastair H.F. Robertson2 |
ABSTRACTThe first of two tectonic-oriented objectives during Leg 160 in the Eastern Mediterranean Sea (April–May, 1995) was concerned with study of processes of genesis and incipient collision of the Eratosthenes Seamount, a substantial crustal feature, with the active margin of the Eurasian plate to the north, represented by southern Cyprus. The upper part of the Eratosthenes Seamount (upper several hundred meters) was found to include both shallow- and deep-water carbonates dating back to pre-Aptian time (Early Cretaceous). Shallow-water platform carbonate deposition, similar to that of the onshore Levant continental margin to the east (part of the North African plate), was followed by submergence to bathyal depths in the Late Cretaceous to middle Eocene, punctuated by depositional and tectonic hiatuses. Tectonic uplift (~1 km) was followed by shallow-water carbonate deposition in the Miocene. The platform was subaerially exposed during the Messinian desiccation crisis. During the early Pliocene, the platform subsided to bathyal depths associated with localized accumulation of limestone debris flows. Subsidence accelerated in the late Pliocene–early Pleistocene. Interpretation of site-survey seismic data suggests that the base of the northern slope of the Eratosthenes Seamount is in the processes of detachment to form an allochthonous thrust slice, with implications for the formation of on-land melange terrains. Comparisons can be made with the collapse, high-angle faulting, and partial subduction of the mainly igneous Daisha Seamount in the Japan trench, and counterparts in the Mariana and Izu-Bonin fore-arcs, and elsewhere. The break-up of the Eratosthenes Seamount was achieved by loading-related flexural subsidence, accompanied by high-angle normal faulting, which may have exploited pre-existing structural weaknesses. Subsidence of the Eratosthenes Seamount was synchronous with rapid surface uplift of the over-riding plate, represented by the late Pliocene–mid-Pleistocene uplift of the Troodos ophiolite and its sedimentary cover. The flexural and isostatic effects of sediment loading and flooding of the Mediterranean Sea after the Messinian also influenced subsidence of the Eratosthenes Seamount, to some extent. The ultimate fate of the Eratosthenes Seamount is likely to be preservation as allochthonous slices, mainly limestone, within a subduction-accretion complex, forming part of a collisional suture zone. Accretionary units similar to the Eratosthenes Seamount are indeed found within the Tethyan orogenic belt to the north, in areas including Turkey and Greece. |
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