Late Precambrian metamorphism and cooling in the Arabian–Nubian Shield: Petrology and 40Ar/ 39Ar geochronology of metamorphic rocks of the Elat area (southern Israel)

Abstract

Representative samples of metamorphic rocks and one sample of undeformed granite from the Elat area of southern Israel have been analyzed by microprobe and conventional 40Ar/ 39Ar geochronological methods. The highest-grade metamorphic assemblages, formed during the collision of greater east and west Gondwanaland, give equilibrium P–T conditions of 7±1 kbar and 650–700°C. The timing of regional metamorphism in Elat has been estimated at 620±10 Ma on the basis of published single zircon evaporation ages, correlations with geochronological data from rocks that adjoined the Elat area prior to later faulting and 40Ar/ 39Ar age spectra from amphibole and phlogopite of the Shahmon metabasite complex. Samples of muscovite and biotite from the Elat schists, Taba gneiss, Elat granitic gneiss and Elat granite yield remarkably uniform ages ∼600 Ma, interpreted to record the potentially rapid cooling and unroofing of the metamorphic basement. Unroofing of the Elat metamorphic basement was synchronous with widespread igneous activity in the Sinai Peninsula and elsewhere in the Arabian–Nubian Shield, reflecting its transition from orogenic to post-orogenic tectonics. The P–T and 40Ar/ 39Ar data agree well with field, geochemical, geochronological and structural data consistent with a single metamorphic event at 620±10 Ma followed by large-scale extension and tectonic escape in the northern Arabian–Nubian Shield during the late stages of the Pan-African orogenic cycle. The lack of any evidence of a Devonian thermal event in the Elat area, previously inferred from complex 40Ar/ 39Ar age spectra from altered dikes, indicates that any such event was very localized.