Age determinations in the Precambrian basement of the Wadi Araba area, southwest Jordan

Abstract

The Precambrian basement of Jordan belongs to the northern margin of the Arabian-Nubian Shield. Age determinations by U-Pb isotopic analyses on sized and magnetic zircon fractions, a monazite and an apatite sample and by Rb-Sr isotopic studies on whole-rocks and minerals of metasedimentary rocks, granodiorites, granites and dykes have elucidated the following events: (1)A major regional high-grade metamorphism accompanied by migmatization and synkinematic plutonism occurred at about 800 Ma according to U-Pb zircon ages of metasediments and granites. (2)During a postkinematic plutonic event between 615 and 600 Ma extensive masses of granodioritic to granitic composition and dykes were emplaced. The U-Pb data of zircons of the rocks yielded upper intercept ages with the concordia consistent with Rb-Sr biotite ages. The Rb-Sr mineral ages of the older metasedimentary rocks document the resetting of the Rb-Sr system due to the thermal pulse at this time. (3)A younger plutonic event produced diorites and dykes at about 570 Ma. The plutonic events are related to the Pan-African orogenic phase. The low initial 87Sr/ 86Sr ratios of the plutonic rocks (0.7032–0.7046) correspond to values reported from equivalent rocks throughout the Arabian-Nubian Shield and suggest that no significant portions of ancient sialic crustal material contributed to the generation of the granitic to granodioritic magmas.