U-Pb Isotopic evidence for the accretion of a continental microplate in the Zalm region of the Saudi Arabian Shield

摘要: The area covered by this work includes three of the main tectonic units Arabian Shield: Afif continental terrain, Nabitah suture with its associated mobile belt, and Asir ensimatic arc terrain. geology Zalm is well understood, geochronologic isotopic study confirms that southern terrain was a microplate in late Proterozoic. also provides time frame for crustal evolution part Shield. Kabid formation oldest region comprises pelitic, arkosic felsic high-grade paragneisses. U-Pb zircon data from pelitic garnet-sillimanite gneiss show basement may be as old 1770 Ma. Isotopic nalyses indicate lead resided upper crust long period before Ma, consequently Archaean source rocks present within Pb Rb-Sr reveal change nature underlying crust, northeast, to less radiogenic marginal southwest. This coincident both aeromagnetic data, facies pre-collision basin. Miogeosynclinal shelf Siham group lie unconformably over formation, are signatures. Eugeosynclinal deep water sediments volcanics, association ultramafic rocks, occur age determinations 9Andean9 margin developed about 720 emplacement calc-alkaline plutonic continued until 690 During 685-640 collided orogeny. At approximately 640 Ma ago, Najd strike-slip faulting commenced dextral phase controlled granitic plutons development series large pull-apart grabens. Some these grabens were floored new oceanic filled volcanosedimentary Bani Ghayy group. Subsequently, fault system changed sinistral motion at 620 ago.