LOWER AND MIDDLE JURASSIC PALEOMAGNETIC RESULTS FROM THE SOUTH LESSERCAUCASUS AND THE EVOLUTION OF THE MESOZOIC TETHYS OCEAN

We studied Lower Jurassic (Pliensbachian-Toarcian) basalts and tuffs a nd Middle Jurassic (Bajocian) limestones and marls from 9 sites in the southern part of the Lesser Caucasus (ca. 39.3 degrees N, 45.4 degree s E). A component showing rectilinear decay to the origin was reliably isolated from most volcanics. This characteristic component reveals n early antipodal directions for both polarities and passes the fold tes t; the conglomerate test performed on lava boulders from the Aalenian basal conglomerates is also positive. We think that a primary remanenc e (D = 20 degrees, I = 38 degrees a95 = 5 degrees) was isolated from t he volcanics. In contrast, Middle Jurassic sediments yielded controver sial results, and the only reliably isolated intermediate-temperature component (ITC) does not pass the fold test. The ITC directions show a considerable improvement in data grouping during incremental unfoldin g, with a maximum at 40% unfolding. We argue, however, that the thus o btained mean direction does not correspond to any paleofield and is mo st probably an artefact. When compared to reference data for the Euras ian and African plates, the Lower Jurassic mean inclination of 21 degr ees N +/- 4 degrees agrees well with the latter, thus implying that, i n the Early Jurassic, the area studied belonged to Gondwana and was se parated by the Tethys ocean from Eurasia, in agreement with paleontolo gical data. We tried to locate the position of the boundary between th e Eurasian and Gondwanian realms in the Caucasus region in the Early-M iddle Jurassic; unfortunately, the available Jurassic paleomagnetic da ta from other tectonic units of the region did not reveal any clear pa ttern.