Chemical remanent magnetism related to the Dead Sea Rift: Evidence from Precambrian igneous rocks of Mount Timna, southern Israel

Abstract

A paleomagnetic and mineralogical study of shallow intrusive basement rocks on Mount Timna (Arabo Nubian Massif in Sinai) shows that although all the igneous rocks are of late Precambrian age, a remanent magnetic direction similar to the subrecent field (Miocene to present) is identified in samples of quartzmonzodiorite, monzodiorite, dikes of various composition, and altered gabbro. The average direction of these rock units is (D/I) 359ø/41 ø, •x95=4 ø, and the pole is at 83.6øN,223.2øE. The "subrecent" direction appears both as an overprint direction and as the sole stable vector in dolerite, rhyolite, and andesitc dikes. The magnetic mineral assemblage of these rocks includes secondary minerals, such as hematite and goethite, which formed by oxidation and hydration of the original magnetite and Ti-magnetite. The subrecent direction is interpreted to have been acquired as a chemical remanent magnetization (CRM) by hydrothermal activity and circulation of thermal brines through fractures related to the adjacent Dead Sea transform. The hydrothermal activity occurred before uplift and erosion exposed the basement rocks, i.e., in the middle Miocene, during the early stages of activity of the Dead Sea rift. The north trending declinations indicate that Mount Timna has not rotated about a vertical axis after acquisition of the CRM, a conclusion that confirms a previous structural analysis. An absence of reversals implies that the duration of CRM acquisition was probably less than --1 m.y., the maximum length of normal polarities since the Oligocene. Other field directions were found in an alkali granite (one site, 343ø/14 ø, 0•95=22ø), in a dolerite dike (one site, 318ø/0% 0•95=2 ø) and in a gabbro (seven sites, 303ø/56% 0•95=6ø). The field direction in the granite is similar to that for Early Cretaceous, a time of magmatic activity in Timna. Northwest trending declinations and shallow inclinations found in several samples of the dikes are carried by unaltered parts of the rocks. These directions are interpreted as late Precambrian-Early Cambrian in age, indicating a near-equatorial location of the region at that time. Nubian Massif has been attached to Africa since the beginning

Low‐temperature thermochronology of francolite: Insights into timing of Dead Sea Transform motion

“…Beyth, ; Segev et al., ). Furthermore, altered Neoproterozoic gabbros in the Mt Timna Igneous Complex (Figure ) acquired a chemical remanent magnetisation in the middle Miocene, which Marco, Ron, Matthews, Beyth, and Navon () attributed to early DST‐induced hydrothermal activity. The normal polarity suggests that alteration took place within a short time interval (<~1 Ma), while the basement still resided under a sedimentary cover.…”

Post-depositional processes on a buried Cambrian sequence in southern Israel, north Arabian Massif: evidence from new K–Ar dating of Mn-nodules

“…Palaeomagnetic measurements of the nodules studied and other types of mineralization hosted in Cambrian and Precambrian rocks (Marco et al 1993;Marco & Segev, unpub. data) indicate that the intensive Miocene-Recent karstification and mineralization processes (Segev & Sass, 1989a) overprinted the previous mineralizations in Timna Valley.…”

The origin, cooling and alteration of A-type granites in southern Israel (northernmost Arabian–Nubian shield): a multi-mineral oxygen isotope study

“…The Timna igneous complex was thus interpreted as a 610 Ma quasistratified alkaline magmatic cell, which formed within a 625 Ma calc-alkaline porphyry granite crust. Stable isotope and palaeomagnetic studies suggested that the alteration of the Timna igneous complex was not related to its emplacement and Early Cambrian exhumation, but was related to Neogene fluid-rock interaction initiated by the Dead Sea Transform tectonics (Marco et al 1993;Beyth et al 1997;Matthews et al 1999). Beyth et al 1994).…”

“…The hydrothermal activity presumably responsible for the 18 O/ 16 O-enrichments in the Timna igneous complex was attributed to circulation of brines through fractures related to the Dead Sea transform (Beyth et al 1997;Matthews et al 1999). The timing of the hydrothermal event was considered as Miocene, based on 'subrecent' remanent magnetic direction measured in the igneous rocks of Timna (Marco et al 1993). None the less, a thermochronological study based on fission tracks in apatite demonstrated that the temperature in the Timna igneous rocks did not exceed 95 • C after the Cretaceous and 65 • C after Eocene times (Feinstein et al 2003).…”

“…Had fluids circulated through the Timna rocks at 250 • C during the Miocene, a fast and complete obliteration of apatite fission tracks should have occurred. Thus the secondary minerals, hematite and goethite, thought to induce the chemical remanent magnetization in the rocks of Timna (Marco et al 1993), must have formed at T ≤ 65 • C during the Miocene. Thermochronology shows, however, that a major thermal event occurred in southern Israel and Sinai in Early Carboniferous times (Kohn, Eyal & Feinstein, 1992).…”