Permo-Triassic and Jurassic palaeomagnetic components in the Greek Pelagonian and sub-Pelagonian zones: Implications for successive counterclockwise and clockwise rotations

During the last three decades, comprehensive palaeomagnetic investigations have beenconducted in North and North – Western Greece. A variety of formations ranging in age from Cenozoic to Paleozoic/Mesozoic were analyzed. These reveal the existence of an “ancient” component directed WNW, acquired probably in Late-Jurassic/Cretaceous times. A younger ENE direction of Tertiary age has previously been reported from Western /South Western and Northern Greece. In order to further extend this dataset, we have sampled systematically along the Greek Pelagonian and Sub/ Pelagonian zone. Emphasis was placed on the Vourinos and Orthrys ophiolites and nonophiolitic accompanying sediments and lavas.
   The Vourinos Ophiolite is one of the best documented ophiolitic complexes on global scale. It comprises a continuous ~12km thick Jurassic lithospheric section relatively unbroken by late intraformational tectonism. The entire pseudostratigraphic section, in today’s geologic setting, is oriented (from east to west) steep westward dipping – vertical – overturned to eastdipping. Much of the rotation of this lithospheric section occurred previous to the upper Cretaceous, and an internal “bowing” in the ophiolitic section could represent inhomogeneous strain recorded during transport from spreading center to initiation of obduction. The sampling localities in Vourinos represent two depths within the oceanic lithosphere and a later, post-emplacement, formation.
   The Jurassic-aged Orthris ophiolite is a thrust disrupted lithospheric section. A continuous section is lacking, though some nappes include over-lapping pseudo-stratigraphic elements. None of the composite nappes are overturned, and a reverse lithosphericstratigraphic order is observed. The entire nappe sequence is emplaced above older lavasediment sections and in the east, the Pelagonian margin. Western Othris, like the Pindos ophiolite, is in its entirety re-thrust above the Pindos flysch (late Cretaceous – Eocene). This latter backthrust occurred approximately 100 My later than the original ophiolite obduction.
   In many areas, the standard palaeomagnetic and rock magnetic procedures revealed the presence of westward directions grouping around D=3300. Secondary overprints correspond to the Tertiary clockwise rotation and often masked the older component. Inclinations are very low for the Permo-Triassic, implying an almost equatorial position for the area, in contrast to the ones corresponding to Jurassic / Cretaceous which are not far from the present position.
   These results, together with previous research, are analyzed within the geotectonic framework of the broader area, providing an opportunity to compare palaeomagnetic directions during different stages of ophiolite emplacement.