A PALEOMAGNETIC STUDY OF SOME BASALTIC ROCKS IN BAHARIYA- BENI SUEF SECTOR, EGYPT.

Abstract

A paleomagnetic investigation has been carried out on 58 independently oriented hand blocks (comprising 483 specimens) collected from seven reasonably spaced basaltic volcanic exposures, distributed within and around the Baltariya depression. After AF and I or thermal demagnetization, all specimens showed stable components of magnetization probably of TRM origin residing mainly in magnetite (with some contribution of ilmenite) grains. A tentative correlation of these lava extrusions, on the basis of polarity of magnetization, has been suggested. Three distinct populations of paleomagnetic pole positions of the encountered occurrences are computed from their stable remanence orientations. These paleopoles represent three ages of magnetization and therefore, three different volcanic episodes.

Basalt Hill and El-Bahr exposures (olivine basalt) represent the first group of paleopoles which are 78.16°S I 34.32°E and 78.91°S I 21.65°E respectively with an age of 20 Ma (Lowermost Miocene). El-hefhuf, Mandisha/El-Aguz, Maesera and west Tebniya (olivine dolerite) represent the second group of paleopoles which are 56.20°S I 10.80°E, 50.56°S I 14.77°E, 58.87°S I 19.36°E and 63.69°S I 349.47°E respectively with an age of 18 Ma (end of Lower Miocene). This may indicate that the Bahariya Oasis region was subjected to two main alternative episodes of volcanicity. This activity is considered intimately related with the Late Tertimy (pre-Miocene to Lower Miocene) epirogenic movements.

On the other hand, the corresponding paleopole (the third group) for Zaruq basalt (olivine basalt), 4.96°S I 275.82°E, is found completely deviated from the other two groups of paleopeles (or from the other African poles of Tertiary age). This is because it is a single cooling unit which can not has averaged the geomagnetic secular variation.