The precambrian magmatic rocks of timna valley,southern israel

In the Timna Valley in southern Israel a small ‘layered’ serpentinized-chloritized gabbroic rock occupies the core of Har Timna and an alkali-potassium syenite to granite composes most of the area. Intermediary rock types between the basic and acid rocks are common. This magmatic sequence is in agreement with the latest model suggested for the last phase of Precambrian activity in the Arabo-Nubian massif.Mantle-derived basaltic magma intruded the crust from a shallow, layered magmatic chamber. This magma was the heat source that caused a partial melting of the crust and the formation of A-type, alkali, potassium rich, granitic magma. This acid magma was the source of the alkali rhyolitic dykes and the Biqat Hayareah volcanic rock types. This whole process took place in a cyclic manner under a tensional tectonic regime. Creation or reactivation of deepseated faults caused a new pulse of intrusion of basic magma and a remelting of the crust.Serpentinization was the last phase - hydrothermal activity at temperatures of less than 400°C. This hydrothermal activity could have been caused by radioactive heating of the alkali granite after its final stage of crystallization or by recent Dead Sea Rift hydrothermal waters.