NEOPROTEROZOIC GRANITIC MAGMATISM AND TECTONIC EVOLUTION OF THE NORTHERN ARABIAN SHIELD - EVIDENCE FROM SOUTHWEST JORDAN

The crystalline basement outcrop exposed in southwest Jordan, is subdi vided into two broad lithos- tratigraphic divisions, the older Aqaba c omplex and the Araba complex separated by a regional unconformity. The Aqaba complex principally comprises cdc-alkaline plutonic rocks of pr obable age range 630-580 Ma cut by extensive regional dyke swarms whil e the Araba complex is characterized by alkaline rhyolitic, volcanics and minor coeval granites with an approximate age of 550-540 Ma. The p lutonic rocks of the Aqaba complex are interpreted to be the products of subduction at, or dose to, a continental margin, while the Araba co mplex rocks were most probably formed in an extensional setting. The A qaba complex granitoids are isotopically primitive and were derived fr om a depleted source region like the mantle. The Arabian Shield of sou thwest Jordan provides an example of rapid crustal growth during the N eoproterozoic and the new data gives no support to models invoking the presence or involvement of significantly older basement in its develo pment.