Driving forces of Mediterranean orogeny

Abstract

A critical review of newer data on the Tyrrhenian area (marine geology, land geology, paleomagnetism and seismicity) leads to a formulation of some general aspects of its evolution in Cenozoic time. A solution is suggested for the geodynamic puzzle of Corsica and Sardinia, based on a relativistic structural analysis of the apparent rotations and translations of these islands with respect to a deforming continental frame. During the Cenozoic the central Tyrrhenian area was subjected to pulses of doming and intervening periods of subsidence. The youngest uplift occurred in Mid-Pliocene time and thereafter it collapsed to bathyal depths at a rate of 1 mm/yr. This diastrophic evolution was accompanied by a geochemical transformation of the original continental type of crust (formed during the Hercynian orogeny) into an intermediary type of sialic crust (about 11 to 12 km thick). Meanwhile an orogenic crustal wave migrated radially outward from the Tyrrhenian centre of diastrophism, accompanied by radially outward directed overthrusts, imbrications, and other compressive tectonic features. The driving forces of this orogeny are evidently acting from the concave side of the orogenic arc. The expectations of three geodynamic models of interpretation, advanced for the Tyrrhenian test-case, are compared with the observed aspects of its evolution. These models are (I) plate tectonics, (II) radiogenic heating by the continental crust, and (III) active mantle diapirism. It appears that only the third model provides an explanation which is consistent with the available geonomic evidence.