Deflection, gravity anomalies and tectonics of doubly subducted continental lithosphere: Adriatic and Ionian seas

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Abstract
Three profiles across the southern Adriatic and northern Ionian seas span an intermediate foreland area that is or has recently been subducted both westward under the Apennine‐Calabrian thrust belt and eastward under the Hellenide belt Gravity and deflection data (from the base of the Pliocene) along the three profiles are qualitatively similar to those predicted for a thin elastic sheet subject to end loads at both plate ends. More detailed analysis of the profiles shows very good agreement between observations and predictions if the intermediate foreland lithosphere is treated as a thin elastic sheet with an effective elastic thickness between about 15 and 20 km (equivalent to a flexural rigidity between 2×1022 and 6×1022 Nm). These results, coupled with seismicity data, suggest that active convergence within the Hellenides extends as far north as southwestern Yugoslavia. Analysis of the northernmost profile, across the southern Adriatic Sea, shows a well‐constrained elastic plate thickness of 14 km and an initial water depth, prior to loading, of about 1 km. The distance between the two subduction systems on this profile is estimated at about 275 km. Analysis of the two more southerly profiles yields a minimum effective elastic plate thickness of about 15 km, but no maximum value could be determined. The initial water depths for these two profiles are well constrained at 1.3 and 1.6 km prior to loading, and the distance between the two subduction systems is estimated at about 175 km on both profiles. Along the northwest trend of the two opposing subduction systems the change in distance between the two systems occurs abruptly, and the Hellenic subduction system appears to be segmented into a series of northwest trending, roughly linear subduction segments. The calculated deflection profiles also show pronounced asymmetry on the northernmost profile and an opposite sense of asymmety on the southernmost profile.