CHEMICAL REMANENT MAGNETISM RELATED TO THE DEAD-SEA RIFT - EVIDENCE FROM PRECAMBRIAN IGNEOUS ROCKS OF MOUNT TIMNA, SOUTHERN ISRAEL

A paleomagnetic and mineralogical study of shallow intrusive basement rocks on Mount Timna (Arabo Nubian Massif in Sinai) shows that althoug h all the igneous rocks are of late Precambrian age, a remanent magnet ic direction similar to the subrecent field (Miocene to present) is id entified in samples of quartz-monzodiorite, monzodiorite, dikes of var ious composition, and altered gabbro. The average direction of then ro ck units is (D/I) 359-degrees/41-degrees, alpha95=4-degrees, and the p ole is at 83.6-degrees-N,223.2-degrees-E. The ''subrecent'' direction appears both as an overprint direction and as the sole stable vector i n dolerite, rhyolite, and andesite dikes. The magnetic mineral assembl age of these rocks includes secondary minerals, such as hematite and g oethite, which formed by oxidation and hydration of the original magne tite and Ti-magnetite. The subrecent direction is interpreted to have been acquired as a chemical remanent magnetization (CRM) by hydrotherm al activity and circulation of thermal brines through fractures relate d to the adjacent Dead Sea transform. The hydrothermal activity occurr ed before uplift and erosion exposed the basement rocks, i.e., in the middle Miocene, during the early stages of activity of the Dead Sea ri ft. The north trending declinations indicate that Mount Timna has not rotated about a vertical axis after acquisition of the CRM, a conclusi on that confirms a previous structural analysis. An absence of reversa ls implies that the duration of CRM acquisition was probably less than approximately 1 m.y., the maximum length of normal polarities since t he Oligocene. Other field directions were found in an alkali granite ( one site, 343-degrees/14-degrees, alpha95=22-degrees), in a dolerite d ike (one site, 318-degrees/0-degrees, alpha95=2-degrees) and in a gabb ro (seven sites, 303-degrees/56-degrees, alpha95=6-degrees). The field direction in the granite is similar to that for Early Cretaceous, a t ime of magmatic activity in Timna. Northwest trending declinations and shallow inclinations found in several samples of the dikes am carried by unaltered parts of the rocks. These directions are interpreted as late Precambrian-Early Cambrian in age, indicating a near-equational l ocation of the region at that time.