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 intrusivebasement rocks on Mount Timna (Arabo Nubian Massif in Sinai) shows thatalthough all the igneous rocks are of late Precambrian age, a remanent magneticdirection similar to the subrecent field (Miocene to present) is identified insamples of quartz-monzodiorite, monzodiorite, dikes of various composition, andaltered gabbro. The average direction of these rock units is (D/I)359°/41°, α₉₅=4°, and the pole is at 83.6°N,223.2°E. The “subrecent”direction appears both as an overprint direction and as the sole stable vectorin dolerite, rhyolite, and andesite dikes. The magnetic mineral assemblage ofthese rocks includes secondary minerals, such as hematite and goethite, whichformed by oxidation and hydration of the original magnetite and Ti-magnetite.The subrecent direction is interpreted to have been acquired as a chemicalremanent magnetization (CRM) by hydrothermal activity and circulation ofthermal brines through fractures related to the adjacent Dead Sea transform.The hydrothermal activity occurred before uplift and erosion exposed thebasement rocks, i.e., in the middle Miocene, during the early stages ofactivity of the Dead Sea rift. The north trending declinations indicate thatMount Timna has not rotated about a vertical axis after acquisition of the CRM,a conclusion that confirms a previous structural analysis. An absence ofreversals implies that the duration of CRM acquisition was probably less than ∼1m.y., the maximum length of normal polarities since the Oligocene. Other fielddirections were found in an alkali granite (one site, 343°/14°, α₉₅=22°),in a dolerite dike (one site, 318°/0°, α₉₅=2°) and in a gabbro(seven sites, 303°/56°, α₉₅=6°). The field direction in the graniteis similar to that for Early Cretaceous, a time of magmatic activity in Timna.Northwest trending declinations and shallow inclinations found in severalsamples of the dikes are carried by unaltered parts of the rocks. Thesedirections are interpreted as late Precambrian-Early Cambrian in age,indicating a near-equatorial location of the region at that time.