Precambrian metamorphic evolution of the Arabian-Nubian Shield in the Roded area, southern Israel

Structural and metamorphic field data combined with detailed petrological and geothermobarometric studies were used to define the Precambrian pressure-temperature (P-T) evolution of the northern Arabian-Nubian Shield exposed in the eastern Roded area, southern Israel. Rock units in the Roded area include amphibolite facies schists, quartzofeldspathic gneisses, and amphibolites intruded by several generations of (now) schistose dikes, and a late kinematic quartz-dioritic pluton. Our petrological investigation reveals that the peak P-T metamorphic assemblage composed of biotite+garnet+cordierite crystallized at P < 5 kbar and 653 ± 42°C. The highest grade metamorphic conditions were accompanied by limited partial melting and migmatization of metapelites, and by the formation of a N-S-striking subvertical cleavage. The metamorphic analysis of concordant schistose dikes yields maximum temperatures of ca. 510°C, indicating that they were intruded and metamorphosed during cooling of the host basement complex. Aluminum-in-hornblende barometry and amphibole-plagioclase thermometry on the late-kinematic quartz-dioritic pluton indicate pressures of 2.8 ± 0.5 kbar and sub-solidus cooling through 700°C. A second generation of schistose dikes cuts both the basement and the pluton and locally shows a sigmoidal schistosity with a normal sense of motion. The age of the deformation and high-temperature metamorphism in the Roded area is not known. Our preliminary K-Ar ages on biotite and amphibole mineral separates from the metamorphic basement yield ca. 725 Ma, whereas an age of 634 ± 2 Ma was determined on the quartz-dioritic pluton using the U-Pb zircon method. Our results in the Roded area suggest a cycle of high-temperature metamorphism, deformation, and magmatism, possibly within an island arc setting. Neverthless, we note that the nearest oceanic suture occurs more than 500 km south of the Roded in Saudia Arabia, and that the quartz-dioritic pluton was formed well after Arabo-Nubian subduction ceased.