INTRACONTINENTAL SEAS RESULTING FROM BACK-ARC SPREADING DURING COLLISION OF CONTINENTAL PLATES

Abstract

As is well known, intracontinental seas with oceanic-type crust, such as the Caspian, Black, and Mediterranean seas located within the Alpine-Himalayan fold belt, are among the most enigmatic of geological formations. A characteristic feature of the deep-water basins in a number of these seas, formed primarily during the Late Cenozoic within continental sections of the lithosphere, is their truncation by border structures of the Alpine belt. Detailed investigations show that intensive basaltic submarine volcanism and spreading are taking place on the floors of the Tyrrhenian, Balearic, and Alboran seas in the back-arc portion of the structure. As is well known, such processes widely occur within back-arc seas in regions of active transition from ocean to continent, where they are described under the collective term 'back-arc spreading. There are interesting differences between the processes of back-arc spreading in the Western Mediterranean, where submarine basaltic volcanism is widespread, and in the Caucasus section, where such volcanism has not been found. This is apparently due to the different geological histories of the regions and corresponding differences in material composing the upper mantle: in the Western Mediterranean, this material is slightly depleted 1herzolite; whereas, depleted dunite and harzburgite, joined with a basaltic component during the preceding geological epoch, predominate in the east.