A palaeomagnetic study of Upper Pliocene volcanic rocks in the area of the Levant Fault near Homs, western Syria

Abstract

Thermal demagnetisation of samples from 75 sites in basaltic rocks, mostly within 5 km of the Levant Fault, identifies consistent directions of remanence in most sites. Normal, Reversed and Intermediate polarities are identified, with Reversed polarities dominating. The Normal and Reversed sites are similarly magnetised, 5.6±5.3 A/m, while those of sites of Intermediate or undefined direction are somewhat more strongly magnetised, 11.9±9.5 A/m. The low field susceptibilities are consistent, 30.9±15.2 mSI, implying the geomagnetic field may have been somewhat stronger than during Normal or Reversed polarity. When the mean directions of the Normal sites are reversed, all sites have similar mean inclination values, 48.2° (δInc. = 2.7°), but the site mean declinations show a regional pattern. Sites from the 3 regions west of the Levant Fault zone (Marmarita, Qalat El-Hossen, Tel Kalakh) have similar declinations, 186° (δDec. = 5.4°). These are consistent with those from the Sufer and E. Ain Kut regions, 197° (δDec. = 3.9°), furthest east of the Levant Fault zone. All these localities have directions that are consistent with those expected for this part of Arabia for this time. However, all sites east and close to the Levant Fault zone (Bahur, W. Ain-Kut, Mzeineh and Buqeia) have more eastern declinations, averaging 154.0±12.0°. The declination difference, 37.3°, indicates the presence of rotated blocks adjacent to the eastern side of the Levant Fault. Such a rotation is consistent with the 25 km displace-ment predicted for this location and appears consistent with the subsequent volcanological and tectonic evolution of the Levant Fault, suggesting significant rotation and seismic activity during the last 5 Ma.