AEGEAN PALEOMAGNETIC INCLINATION ANOMALIES - IS THERE A TECTONIC EXPLANATION

More than a decade of paleomagnetic research in the Aegean area, mainly by French investigators (C. Laj, C. Kissel and their colleagues), has provided a valuable data base for the evaluation of Cenozoic Aegean tectonics. Systematic rotations are documented and have been interpreted by the original investigators in the light of the evolution of the Hellenic arc. However, less attention has been paid to the significance of the paleomagnetic inclinations, which also are anomalous. Twenty one out of 22 paleomagnetic studies performed to date within the general Aegean region have yielded paleolatitudes that are too shallow when compared with reference curves for either Africa or Eurasia, suggesting northward relative transport with respect to both continents. Sedimentary, volcanic and plutonic units are involved; ages range from Oligocene to Pliocene. Some of these apparent paleolatitude anomalies may merely be the result of inclination flattening in certain kinds of clastic sedimentary rocks. However, shallow inclinations in igneous rocks cannot be so easily dismissed. The explanation for these anomalously shallow inclinations does not appear to lie with the reference curves, because several other reference curves calculated in several different ways yield essentially the same result. We suggest that the paleomagnetic pattern may reflect real northward displacement of crustal blocks within the Aegean region, measured with respect to both Europe and Africa. The amount of displacement appears to increase systematically to the west. The pattern of local block rotations noticed by earlier investigators argues that the displacement did not involve a single coherent Aegean block, but rather a collection of smaller blocks moving quasi-independently. Geological consequences of northward relative displacement of the Aegean block ought to include mid-Tertiary and/or later compressional structures in the north (e.g., Rhodope) and ''tensional structures in the leading edge of the African plate.