Subsurface structural mapping using gravity data of Al-Ain region, Abu Dhabi Emirate, United Arab Emirates

A gravity survey of the Al-Ain region within the United Arab Emirates (UAE) was designated to compare a regional gravity map with surface structural and geophysical studies of the area. The study area is located in the eastern part of the UAE near the Oman border. Gravity data were collected at 452 stations using a Scintrex CG-6 gravimeter. The gravity measurements define the subsurface density distributions in the study area. The Bouguer anomaly map shows values ranging from -21.5 to 10.8 mGal. High Bouguer anomalies were observed in the eastern and western parts of the study area, in good agreement with the location of known thrust faults. Gravity gradient derivative methods (horizontal gradient, analytic signal and tilt angle) were applied to the corrected gravity data to enhance visibility of subsurface geological features. The gradient derivative methods applied to the gravity data outline subsurface structures trending NNE-SSW, NE-SW and E-W. These trends can be correlated with regional tectonic phases and are in agreement with known surface structural trends. The power spectrum of the gravity data shows two distinct geological layers'a deeper layer from 2 to 6 km depth representing Cretaceous formations, and a shallower layer from 0.5 to 2 km depth representing Tertiary formations. The 3-D gravity inversion results show subsurface density distribution characterized by high density contrast of geological bodies located in eastern and western parts of the study area, representing the Semail Ophiolites and Barzaman Formation, respectively. The Hafit Mountain is characterized by a low density contrast body at near surface (-500 kg m^-3) beneath which density increases with depth to +50 kg m^-3 at 7 km (b.s.l.). This study is the first of its kind to image the regional subsurface and geological features of Al-Ain region with density distribution from ground surface to 15 km (b.s.l.).