DEVELOPMENT OF THE IDEAS ON THE OPHIOLITES OF THE ALPINE-APENNINE AND THE DINARIDE-HELLENIDE OROGENIC SYSTEMS

The term “ophiolites” was first defined in 1813 by Brogniart studying serpentinites, gabbros and diabases from the Alpine-Apennine orogenic system. Subsequently, these ophiolites, as well as those of the Dinaride-Hellenide belt, were studied by Steinmann, Brunn and Aubouin, who recognized their allocthonous nature and Jurassic age. After acceptance of the concept that ophiolites are fragments of oceanic lithosphere, studies on the ophiolites from Northern Apennines, Western Alps and Corsica considerably increased in order to assess their tectono-magmatic significance. The peculiar MOR-type ophiolitic stratigraphy of these sequences was defined early in the 1970s by several Italian and French researchers. In accordance with Modern oceanic analogues, some authors suggested that the Alpine-Apennine ophiolites were generated in a true oceanic environment. By contrast, other authors postulated a denudation of sub-continental lherzolitic mantle during a passive, asymmetric oceanic opening. In this model no genetic relationships between mantle and magmatic rocks are postulated. Ophiolites from the Dinaride-Albanide-Hellenide belt have been studied since the beginning of the XX century, mostly by French, Austrian and American researchers. However, the idea that two types of ophiolitic sequences, showing different lithostratigraphical, petrological, geochemical, and metallogenic features occur in this orogenic systems only took place from the end of the ‘70s. These ophiolitic types generally identify two sub-parallel NNW-SSE trending belts delimited by a high-angle thrust, and are usually defined as the Eastern (EOB) and Western (WOB) ophiolitic belts. The EOB shows low- and very low-Ti geochemical character and has been interpreted as originating in a supra-subduction zone (SSZ) setting. The WOB mainly shows high-Ti geochemical affinity, and has been interpreted as originating in a mid-ocean ridge setting probably characterized by low spreading rate. Recent geological and petrological studies indicate that the EOB and WOB probably originated in a single oceanic basin, and that some ophiolitic sequences from the WOB also record an interaction between magmatic processes related to both MOR and SSZ settings, suggesting a more complex tectono-magmatic scenario than that previously depicted.