HISTORY OF DEVELOPMENT OF THE IDEAS ON THE ORIGIN OF THE ALBANIAN OPHIOLITES AND ITS CONTRIBUTION TO THE OPHIOLITE CONCEPT

The Albanian ophiolites are part of the Dinaride-Hellenide segment of the Alpine-Himalayan orogenic system and occur in two subparallel belts between the Pelagonian and Apulian platforms. The western belt consists of lherzolite, gabbro, and extrusive rocks in a <5 km-thick sequence, whereas the eastern belt includes harzburgite-dunite, gabbro, diorite, plagiogranite, sheeted dikes, and extrusive rocks in a ~10-km-thick sequence. Nowack (1929) expressed the idea that peridotites in Albania might represent an exhumed ‘sima’ at the surface. Russian geologists (1951-1961) considered all plutonic rocks and peridotites as Jurassic intrusions within Triassic volcanic rocks. Aubouin & Ndojaj (1964) used the term ‘ophiolite’ and interpreted this assemblage as a differentiation product of basaltic magma. Dede et al. (1966) based on petrological and metallogenic data and Tashko (1974) based on geochemical data distinguished the western and eastern belts of ultrabasic rocks, respectively. Shallo et al. (1980) and Shallo (1980) suggested a seafloor-spreading origin of the ophiolites in a marginal basin west of the Pelagonian platform and recognized in the eastern belt the existence of a sheeted dike complex. Turku (1981) separated in the Mirdita region a calci-basalto-dacitic series of an island arc affinity and a diabasic series of tholeiitic affinity within the volcanic sequence. In 1985, 1987, Shallo et al. distinguished the eastern vs. western ophiolites as characterized by their disparate pseudostratigraphy, showing different petrological, geochemical, and metallogenic features; their alternative tectonic model suggested a seafloor spreading origin of the western belt followed by an intra-oceanic subduction to produce the eastern belt. Subsequent studies (i.e., Beccaluva et al., 1994; Bebien et al., 1995, 1998; Bortolotti et al., 1996; Dilek et al., 2001) confirmed the existence of two geochemically different ophiolite types. Interpretations derived from the studies of the Albanian ophiolites have closely followed the evolving concepts in ophiolite research over the years and may yet provide significant clues for the formation and tectonic emplacement of "oceanic crust" in subduction-accretion cycles in Tethyan-type orogenic belts.