Structural analysis of the central and southwestern parts of the Neoproterozoic Salalah Crystalline Basement, Sultanate of Oman

摘要

The Salalah Crystalline Basement (SCB) is the largest Precambrian exposure in Oman located on the southern margin of the Arabian Plate at the Arabian Sea shore. It is thought to represent one of the eastern-most exposures of the Arabian-Nubian Shield. We used detailed structural analysis 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) which is made-up of two-mica gneisses, amphibolites and ultramafic lenses, and the Sadh complex (816 +/- 12 Ma) which is composed of 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 emplacement of the Sadh complex atop the Juffa complex. This event resulted in the formation of possibly N-verging nappe structure. Associated with this event was the development of mesoscopic asymmetrical tight folds and thrusts with various orientations because of folding during subsequent event. However, the dip of these structures fluctuates between SE and SW suggestive of an initial N-verging nappe structure; (2) Regional folding event around SE- and SW-plunging axes that deformed the regional fabric developed during the N-verging nappe structure. 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 NW-trending dextral strike-slip shear zones dissected the northeastern part of the Juffa-Sadh semi-dome whereas the NE-trending sinistral strikeslip shear zones dissected the southwestern part of the semi-dome. Strong mylonitic fabric, stretching lineation and associated kinematic indicators were developed during this event; and (4) Localized SE-directed extension manifested by top-to-the-southeast 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 SE-plunging antiform.