Mediterranean Basins Relative to Lithosphere Structure: Oblique Element in the Eur-Africa Convergence

Robert C. Bostrom

We have correlated structural data in the Mediterranean portion of the Alpide tectonic belt with the high-degree geoid and SeaSat-derived gravity. The geoid provides a uniform synoptic view of the region; by suppressing the effect of surficial tectonic features, we can identify the major lithosphere structural units.

The region is dominated by a geoidal high centered on Macedonia, elongated in the direction of the Dinarides, and fronted by a low associated with the sub-Aegean subduction. Allochthons and nappes radiate outward from geoidal highs in the direction of the geoidal gradient. The process seems to represent tectonic transport as a form of surficial flow outward from regions underlain by excess resulting from subduction, heating, and expansion of Tertiary lithosphere. SeaSat gravity outlines basinal features such as the northern and southern Adriatic basins and the ridge separating them more clearly than the regional Bouguer anomaly, evidently because the latter artificially removes the expression of surface masses associated with the tectonics.

The Insubric Line is seen as the western end of an extended zone of dextral shearing. Eastward, the zone south-borders the region of dextral rotational folding. Elsewhere in the Mediterranean Alpide region, large-scale right-lateral displacement is manifest in such features as the post-Miocene strain field of the Aegean and in the North Anatolia fault and its southwestern continuation. Dextral displacement greatly outweighs conjugate sinistral displacement, signifying the Eur-Africa convergence is composed of "head-on" motion as well as dextral shear. It seems impossible to resolve basinal architecture in a region such as the Pannonian basin without accounting for the shear element. The combination of convergence and dextral shear in the Mediterranean region is akin to the motion described by Pavoni in 1976 with respect to the Asia Minor portion of the Alpide belt, adjacent to the east.

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.