Sarantis Dimitriadis

Dextral rotations and tectonomagmatic evolution of the southern Rhodope and adjacent regions (Greece)

Abstract Palaeomagnetic measurements deduced from Eocene, Oligocene, Miocene and Pliocene formations, exposed in the Greek Rhodope and surrounding areas, reveal significant clockwise rotations, displaying an apparent systematic increase in magnitude from Thrace westwards and a decrease northwards. The Pelagonian zone in the west has suffered no rotation, at least since the Late Miocene. A transition from rotated to unrotated regions seems to exist close to the western boundary of the Vardar zone. No rotations are apparent earlier than the mid-Oligocene. Parts of the Rhodope may have been rotated clockwise by ∼12° during the Late Oligocene. Additional clockwise rotations occurred after the Early Miocene. It is proposed that at least the post-Early Miocene rotations were the result of plate tectonic motions in the north Aegean area, initiated by Middle Miocene times and continuing to the present day. Southward stretching and bending of the ductile part of the lithosphere was accomplished at brittle upper-crustal levels by the detachment, translation and rotation of the upper plate of the Rhodope core complex (the Serbomacedonian element), possibly followed by further fragmentation and rotation of individual blocks.

Age and significance of radiolarian sediments within basic extrusives of the marginal basin Gevgueli Ophiolite (northern Greece)

Well-preserved Radiolaria have been discovered in calcareous silt turbidites and mudstones intercalated with basic extrusives of the Guevgueli Ophiolite, northern Greece. The mudstones contain terrigenous silt, probably derived from adjacent continental basement of the Serbo-Macedonian and/or Paikon units. Volcanic quartz and rare volcanic glass were probably derived from an active continental margin arc (Paikon volcanic arc) to the west. The radiolarian sediments were deposited within fault-controlled hollows in the ophiolitic extrusives, and then covered by massive and pillowed extrusives. The radiolarian assemblage is indicative of an early Late Jurassic (Oxfordian) age, which therefore dates the genesis of the Guevgueli Ophiolite. Our data are consistent with the age of the intrusive Late Jurassic Fanos Granite, believed to be contemporaneous with the Guevgueli Ophiolite. In general, the Guevgueli and related ophiolites of northern Greece are thought to have formed within a transtensional intra-continental marginal basin, generated in response to oblique eastward subduction of older Tethyan oceanic crust (Almopias ocean).

A preliminary AMS study in some tertiary granitoids from Northern Greece: integration of tectonic and paleomagnetic data

The present study focuses on some of the Tertiary granitoids of the Rhodope Massif, Northern Greece, namely the Early Miocene plutons of Symvolon, W. Vrondou and the Oligocene Xanthi pluton. Their low-field anisotropy of magnetic susceptibility (AMS) was studied in a number of stations and was combined with existing paleomagnetic and tectonic data in order to check their mutual consistency and to assess to what extent they can help clarifying the tectonic regime prevailing during emplacement of these granitoids. The bulk susceptibility magnitude is generally high, as well as the mean anisotropy degree which reaches 1.23, pointing to a dominant ferromagnetic control of the magnetic properties. Microscopic observation, isothermal remanent magnetization (IRM), and thermomagnetic analysis reveal that the magnetic mineralogy is controlled mainly by magnetite. The magnetic fabrics are well-defined in the plutons, with the Kmax axes (magnetic lineations) varying from gently to moderate plunges. Paleomagnetic results obtained from the same bodies display clear clockwise rotations for all the plutons, with minor or no tilt during their emplacement. Despite of the age differences, the tectonic and magnetic fabrics have mostly similar directions. The prevailing NE–SW-trending linear fabrics, visible mainly in the Early Miocene plutons are also clearly imprinted magnetically in the Early Oligocene pluton, in which no macroscopic fabric is visible. Finally, a preliminary attempt to correct the paleomagnetic results from the magnetic anisotropy effect showed that only qualitative conclusions can be reached from the AMS data, and that complementary AIRM measurements are required.