Lithostratigraphy and geochronology of the Neoproterozoic crystalline basement of Salalah, Dhofar, Sultanate of Oman

The crystalline basement of the Salalah area (Dhofar, Sultanate of Oman) is the largest portion of Proterozoic basement of the Arabian-Nubian Shield outcropping in Oman. This paper presents new geochronological data and proposes a new lithostratigraphical subdivision of this basement. Four major units have been defined: I. The Juffa Group consisting of metasedimentary mica-gneisses, amphibolites and few meta-ultramafic lenses. II. The Sadh Group with two sub-units, the highly deformed and metamorphosed Banded Gneiss Complex intruded by the slightly deformed diorite and tonalite of the Mahall Complex. III. The Tonalite Group including three large calc-alkaline plutons, the gabbroic Hasik Complex, the dioritic-tonalitic Fusht Complex and the tonalitic Hadbin Complex. IV. The Granite Group comprising different type of dykes and small bodies, i.e. the Pegmatite Complex, the Marbat Granodiorite, the Leger Granite and the basaltic to rhyolitic Shaat Dyke Swarm. The source rocks of the clastic sedimentary protolith of the Juffa Group gneisses represent the oldest stage (>1300 Ma) recorded in the geological evolution of the Salalah basement. Crustal accretion processes culminate around 800 Ma. Extensive cyclic calc-alkaline magmatism during ca. 50 Ma (830-780 Ma), intercalated by intense deformation and recrystallisation at amphibolite facies (>815-790 Ma), built up the major lithostratigraphical units (Juffa-, Sadh-and Main Intrusive Group). The intrusion of a large amount of aplites and pegmatites forming the Pegmatite Complex took place between 770 and 750 Ma. The younger (750-700 Ma?) emplacement of the Marbat Granodiorite, Shaat Dyke Swarm and Leger Granite mark the end of the magmatic and metamorphic activity in this area. Subsequently these units were exhumed to the surface and overlain by clastic sediments of the Marbat Formation of probable Ediacaran age (630-542 Ma) and by the Phanerozoic sedimentary sequences.