STRUCTURAL ANALYSIS AND SYNTHESIS OF THE PRECAMBRIAN SALALAH CRYSTALLINE BASEMENT, OMAN

The Salalah Crystalline Basement (SCB) is the largest Precambrian exposure in the Sultanate of Oman located on the southern margin of the Arabian plate at the Arab Sea shore. It is thought to represent one of the eastern-most exposures of the Arabian-Nubian Shield. We used remote sensing and detailed structural mapping to establish the deformational history of the SCB by focusing on its central and southwestern parts. This part of the SCB is dominated by the Juffa complex (820+/-10 Ma) made-up of two-mica gneisses, amphibolites and ultramafic lenses, and the Sadh complex (816+/-12 Ma) which constitutes biotite and amphibolite gneisses. Our work found that the SCB evolved through four deformational events that shaped its final architecture: (1) Folding and thrusting event that resulted in the juxtaposition of the older Juffa complex adjacent to the younger Sadh complex. This event resulted in the formation of NW-verging nappe structure. Associated with this event is the development of NW-verging mesoscopic tight folds and thrusts as well as top-to-the-northwest kinematic indicators. (2) Regional folding event around SE- and SW-plunging axes that affected the regional fabric developed during the NW-verging fold and thrust event. This event produced map-scale SE- and SW-plunging antiforms resulting in shaping the Juffa and Sadh complexes into a semi-dome structure. (3) Strike-slip shearing event that produced a conjugate set of NE-trending sinistral and NW-trending dextral strike-slip shear zones. The dextral NW-trending dextral strike-slip shear zones dissected the northeastern part of the Juffa-Sadh semi-dome whereas the NE-trending sinistral strike-slip shear zones deformed its southwestern part. Strong mylonitic fabric and associated kinematic indicators were developed during this event. (4) Localized SW-directed gravitational collapse that produced top-to-the-southwest kinematic indicators and the development of stretching lineation in the form of stretched amphibole crystals overprinted on older planar fabric. This is particular apparent in the hinge of the map-scale SW-plunging antiform. An Andean-type collision is proposed as the tectonic model responsible for the generation of these four deformational events, possibly the collision of the Arabian-Nubian Shield with East Gondwana.