Palaeomagnetic and magnetic fabric investigations of tertiary rocks from the Alexandroupolis area, N.E. Greece

Spais, Christos (1987) Palaeomagnetic and magnetic fabric investigations of tertiary rocks from the Alexandroupolis area, N.E. Greece. University of Southampton, Doctoral Thesis.

Abstract

The palaeomagnetism and anisotropy of magnetic susceptibility of rocks of Tertiary age from an area to the north of Alexandroupolis were studied. The area mainly comprises the Kirki-Essimi volcano-sedimentary basin, which occurs on the southern margin of the crystalline basement of the Rhodope massif. The occurrence of mixed sulphide base metal mineralization within the Kirki-Essimi basin has recently been the focus for an interdisciplinary investigation, of which this present study formed an ancillary part. Various major rock types (sedimentary, extrusive and plutonic/intrusive), were sampled at 39 different locations for the purposes of this study.Weak magnetizations were exhibited by the vast majority of the sediments. An effect associated with the remanence measurement procedure, using a cryogenic magnetometer, was identified and this limited significantly the reliability of some of the acquired data. A method has been established to assess the extent of this effect by utilization of a lower limit for the Koenigsberger ratio. Application of this criterion of acceptability necessitated rejection of a considerable number of specimens. This posed a major obstacle in attempts to construct a magnetostratigtraphy for part of the basin sequence, based mainly on detailed sampling of two sites. However, primary magnetization directions were defined for a majority of the basin sites and subsequently for the basin sequence, as well as for sites from the adjacent Drymou-Melias Series. According to these results, the basin sedimentary sequence appearss to be unrotated since its formation, whilst a relative rotation of the order of 50^o -60^o clockwise has affected the Drymou-Melias Series.Well-defined mean magnetization directions were obtained for a group of igneous rocks outcropping within the basin (Essimi volcanics) and a major granodioritic intrusion (Leptokarya intrusion), situated adjacent to the northern margin of the basin, both considered to be Oligocene in age. Interpretation of the magnetization directions suggests that no major tectonic rotation has affected the area, whilst a small-scale clockwise rotation, probably associated with thrusting can be inferred for the Leptokarya body.The magnetization directions and palaeopole positions deduced for all geological units investigated were compared to other published data and possible geological implications are discussed relating to the local geotectonic framework of the N.E. Aegena region. Analysis of magnetic fabric data from 16 sedimentary sites from the Kirki-Essimi basin and the Drymou-Melias Series is another major component of this study. Measurements were carried out using a low field torque magnetometer (LFTM). The primary style depositional magnetic fabric exhibited by the majority of the sites allows estimation of palaeocurrent directions within the basin. Sedimentological and geological implications of the two main emerging palaeocurrent trends (approximately N-S and E-W) are summarized in terms of basin infilling. (D80442)

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