Gravity profiles across the Samail Ophiolite, Oman

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Abstract
Four hundred and sixty gravity stations have been established over the Samail ophiolite and adjacent units exposed in the Oman Mountains. The Bouguer anomaly pattern follows more or less parallel to ophiolite exposures. Along the coastal areas the Bouguer anomaly values range from +20 to +140 mGal and increase northward. Four gravity profiles across the ophiolite are correlated with known geology and structure. The main gravity profile extending 325 km northward from Ibra to Muscat and into the Gulf of Oman shows two positive Bouguer anomalies (+85 over the southern folded ophiolite nappe and +110 mGal near the shoreline at Muscat) that are associated with two nappes of tabular form. The nappes are nearly continuous, and there is no evidence that they are rooted in the mantle. The gravity high across the southern nappe is centered over the axis of the synform (maximum nappe thickness); its position over the gabbro‐peridotite contact rather than over the peridotite suggests extensive serpentinization of the peridotite. At the southern end of the profile, in the Ibra Dome area, the negative Bouguer anomaly (−10 to −15 mGal) is interpreted as an Infracambrian salt piercement similar to those in the Zagros fold belt. Geologic modeling of the main gravity profile provides a good correlation in terms of known thicknesses of the mappable ophiolite units. The nature of the gravity anomaly across the continental margin indicates a transition from ∼42‐km‐thick continental crust to a thinner (16–18 km) oceanic crust. The two gravity profiles in the north Oman region show a doublet of positive residual Bouguer anomalies (+50 to +90 mGal). The anomalies correlate well with imbricated ophiolite exposures, a result of low‐angle thrusting caused by strong compressive forces. In the absence of imbricate thrusting, the gravity profile in the central region has only one large positive residual Bouguer anomaly (+130 mGal). The anomalies of all the four profiles are further analyzed to elucidate the nappe‐transport distances.