St. Catherine area, some 900 km in size, is dominated by basement rocks Encompassing old continental gneisses, metasediments, greenstone belt, calc-alkaline granites (G-II-granites), rift-related volcanics (RV), and anorogenic within plate granites (G-III-granites). The greenstone belt is composed of subduction-related volcanics (SV) intercalated with metasediments. These volcanics split into older group (moderately metamorphosed) and younger group (slightly metamorphosed). The calc-alkaline granites were formed during collision and partial melting of the lower crust. Probably mantle materials were incorporated in the melt.
The rift-related volcanics (RV), and the anorogenic granites form, in the central part of St. Catherine, an incomplete ring massif intruded by a granitic belt of younger age. The igneous activity and the structural development are related in space and time. The first event was the formation of the southern part of the ring fault along which alkalibasalts were erupted (rift-related old volcanics). This phase was followed by the eruption of alkalirhyolites and ignimbrites (rift-related young volcanics). Wide assimilation processes occurred where the alkalibasalts are converted into a black syenitoid rock. This later volcanic phase was the surface expression of an alkaline syenite-granite magmatism. The earlier member of these alkaline plutonites was alkalie-red syenite emplaced along the progressively formed northern part, of the ring fault. Crustal melting then increased and acidic members of red-granite, leuco-granite, and granophyric granite were successively emplaced, crossing the ring massif. These alkaline granitoids are anorogenic plutonites formed during hot spot and incipient rifting mechanism.تغطي صخور القاعدة منطقة سانت كاترين (900 كم 2) ، وتشمل هذه الصخور الرسوبيات القارية المتحولة في نطاق الحزام الجزري والرسوبيات المتحولة القديمة والصخور البركانية ( أ س في ) ، الجرانيت الكالس قلوي (جـ 2 ) ، الصخور البركانية ( ارفي ) والجرانيت (جـ 3) . وتكون الصخور البركانية (ارفي ) والجرانيت (جـ 3) معقد حلقي بيضاوي الشكل غير كامل . ولقد تكونت الصخور البركانية (ا س في ) ، الجرانيت (ب 2) في بيئات جزر قوسية بينما تكون الجرانيت (جـ 3) والصخور البركانية (ارفي ) خلال الألواح .
ولقد تكون معقد سانت كاترين الحلقي لطفح البازلت القلوي خلال صدع دائري ثم تلا ذلك طفح الرايوليت القلوي حيث تمت عملية تمثيل بينهما كونت صخور مماثلة للسيانيت في الجزء الجنوبي اما الجزء الشمالي فيتكون من السيانيت الأحمر الذي قطع بالجوانيت (جـ3) فيما بعد
