Irene Zananiri

Tectonic evolution of fault-bounded continental blocks : Comparison of paleomagnetic and GPS data in the Corinth and Megara basins (Greece)

[1] We report on new paleomagnetic and anisotropy of magnetic susceptibility (AMS) data from Plio-Pleistocene sedimentary units from Corinth and Megara basins (Peloponnesus, Greece). Paleomagnetic results show that Megara basin has undergone vertical axis CW rotation since the Pliocene, while Corinth has rotated CCW during the same period of time. These results indicate that the overall deformation in central Greece has been achieved by complex interactions of mostly rigid, rotating, fault bounded crustal blocks. The comparison of paleomagnetic results and existing GPS data shows that the boundaries of the rigid blocks in central Greece have changed over time, with faulting migrating into the hanging walls, sometimes changing in orientation. The Megara basin belonged to the Beotia-Locris block in the past but has now been incorporated into the Peloponnesus block, possibly because the faulting in the Gulf of Corinth has propagated both north and east. Paleomagnetic and GPS data from Megara and Corinth basins have significant implications for the deformation style of the continental lithosphere. In areas of distributed deformation the continental lithosphere behaves instantaneously like a small number of rigid blocks with well-defined boundaries. This means that these boundaries could be detected with only few years of observations with GPS. However, on a larger time interval the block boundaries change with time as the active fault moves. Paleomagnetic studies distinguishing differential rotational domains provide a useful tool to map how block boundaries change with time. INDEX TERMS: 1208 Geodesy and Gravity: Crustal movements—intraplate (8110); 1518 Geomagnetism and Paleomagnetism: Magnetic fabrics and anisotropy; 1525 Geomagnetism and Paleomagnetism: Paleomagnetism applied to tectonics (regional, global); 8107 Tectonophysics: Continental neotectonics; 9335 Information Related to Geographic Region: Europe;

Rock magnetic property and paleointensity determination on historical Santorini lava flows

Eight historical dacitic lava flows from Santorini with ages between 46 A.D. and 1950 A.D. (four of them within the past century) have been subjected to detailed rock magnetic analyses and various experiments of absolute paleointensity. Thermomagnetic measurements and acquisition of isothermal magnetization have revealed the presence of two physically distinct magnetic phases with Curie temperatures of 280°C and 500°C. In most of the samples, the second phase does not play a prominent role for the characteristic remanent magnetization, which is dominated by titanomagnetite. Magnetostatic interaction is very limited and does not considerably change upon heating. Back-field curve spectra indicate a good thermochemical stability of these dacitic lava samples, which is also supported by the absence of noticeable changes in the remanent coercive force prior heating to 450°C. Hysteresis measurements show typical pseudo-single-domain behavior without noticeable superparamagnetism. Such characteristics were favorable to conduct and to test the most widely used experimental approaches for absolute paleointensity determination. Despite a success rate of 38%, the microwave technique has provided rather scattered within-flow determinations. The results obtained from approaches involving alternating field demagnetization were biased by considerable differences between the NRM and the TRM coercive force spectra. We have also noticed that most determinations obtained by microwave heating differ from the historical field value at the site for the most recent flows. Last, techniques involving double-heating protocols were successful due to a dominant low Curie temperature phase with a narrow grain size distribution. The results were characterized by low dispersion and were found in good agreement with the historical field.

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.