Search Results (6)

Detrital zircon U–Pb dating from the Muti Formation sheds light on sediment sources and foreland basin development along the northeastern Arabian margin during the Late Cretaceous. The siliciclastic-rich Muti Formation was deposited in a syn-obduction foreland basin that formed as the Semail Ophiolite advanced. Zircon age spectra from eastern (Nakhal and Sayga) and western (Murri) sections are dominated by Neoproterozoic–Cambrian ages (450–900 Ma), linked to the Pan-African orogeny and the Arabian–Nubian Shield, indicating these as the main sediment sources. The Murri section also contains older Mesoproterozoic to Archean zircons, likely recycled from the Nafun Group (part of the Huqf Supergroup), suggesting reworking of ancient Gondwanan cover sequences rather than direct input from the Indian craton. Additional Permian zircons reflect input from Arabian Plate magmatic rocks, while Jurassic–Cretaceous grains indicate material derived from the Semail Ophiolite and related arc terranes. Overall, the Muti Formation records a mixed sediment supply from the Arabian Shield, reworked Gondwanan sandstones, and ophiolitic detritus, marking the transition from a passive margin to a flexural foreland basin. The dominance of Pan-African zircon ages highlights continued recycling of Gondwanan sequences and refines models of Late Cretaceous basin evolution in northern Oman, underscoring the complex, multi-cycle nature of sedimentation in this tectonically active setting. Full article

The metamorphic sole, tectonically welded to the base of the Samail ophiolite in a supra-subduction system, is assumed to play the main role in strain accumulation during later thrusting onto the Arabian Plate (i.e., during obduction). The present study deals with five quartzite samples representative of the upper amphibolite and lower greenschist facies parts of the sole. Whole-rock textures obtained by neutron time-of-flight technique were coupled with microstructural observation using electron backscatter diffraction analyses. The quartz microstructural fabrics and textures in the upper and lower parts of the sole represent grain boundary migration and [c]-in-Y textures and subgrain rotation recrystallization and {r}-in-Z textures, respectively. The shear sense in these samples points to top-to-the-SW to SSW shear. One sample of the upper part, yielding a higher calcite amount, is later overprinted by bulging and displays top-to-the-NNE shear. We postulate to differentiate two main deformation steps. The first is the overall present subgrain rotation and grain boundary migration recrystallization combined to top ~SW shear is related to the sole accretion to the ophiolite and the eventually following thrusting onto the Arabian Plate. The second is correlated to a post-obduction extensional top-to-the-NNE shearing, which is associated with tectonic thinning of the ophiolite and mainly documented in the underlying autochthonous units. Full article

For the first time, Quaternary thrusts are documented within the Central Oman Mountains to the northwest of the Jabal Akhdar Dome. Thrusts with a throw of up to 1.1 m displace Quaternary alluvial fan conglomerates. These conglomerates have an Optical Stimulate Luminescence (OSL) age of 159 ± 7.9 ka BP and were deposited during MIS 6 (Marine Isotope Stage). The thrusts occur in two sets. Sets 1 and 2 formed during NE/SW and NW/SE shortening, respectively. Set-1-thusts correlate with the present-day stress field of NE/SW shortening which is related to subduction in the Makran Subduction Zone, and they strike parallel to the main continuous fold axis of the Jabal Akhdar and Hawasina windows. Set-2-thrusts correspond to NW/SE shortening and Plio-Pleistocene contractional structures in the southwestern Jabal Akhdar Dome. Set-2-thrusts are probably related to local variations of the present-day stress field originating from the Musandam area which is a part of the Zagros Collision Zone. Both thrust sets mimic the main thrust directions (NW/SE and NE/SW) within the Permo-Mesozoic allochthonous units (Semail Ophiolite, Hawasina napps) of the larger study area. The investigated thrusts imply some reactivation of the Hawasina and Semail thrusts due to far-field stress either from the Makran Subduction Zone and/or the Zagros Collision Zone. The ongoing tectonic activity of this part of the Oman Mountains, which has been considered of moderate activity, is for first time identified by structural data as contractional. Full article

The role of water-rich solutions in the formation of chromitites has been the matter of controversy. We found small chromite concentrations (chromitites) in diopsidites, precipitated from high-temperature hydrothermal fluids, in the mantle to the crust of the Oman ophiolite. Here, we present petrologic characteristics of the hydrothermal chromitites to understand their genesis. In the chromitites, the chromite is associated with uvarovite in the crust and diopside + grossular in the mantle. They are discriminated from the magmatic podiform chromitite by dominance of the Ca-Al silicates in the matrix. The fluids responsible for chromite precipitation are possibly saline, being derived from the seawater circulated into the mantle through the crust. The saline fluids precipitate chromite to form chromite upon decompression and cooling, and transport platinum-group elements (especially Pt and Pd). The fluids obtain Ca and Al from the crustal rocks and Cr from the mantle rocks during circulation. Saline fluids are also supplied from the slab to the mantle wedge, and can metasomatically precipitate chromite and pyroxenes within peridotites. They re-distribute Cr and chromite in peridotites along with circulation of saline fluids in the mantle wedge. Full article

Holes BA1B and BA3A were drilled into the Wadi Tayin Massif, southern ophiolite complex of Oman, a fragment of the Tethyan oceanic lithosphere obducted onto the Arabian continent. Within the sequence, we have studied a portion of the shallow mantle, composed mainly of strongly serpentinised harzburgite that embeds dunitic levels, the biggest being over 150 m thick. The formation of thick dunitic channels, already approached via published structural and mathematical models, is here investigated with a mineral chemistry approach. We focused on Cr-spinel, the only widespread phase preserved during serpentinization, whose TiO₂ content displays a wide variability from low in harzburgite, (TiO₂ < 0.25 wt. %), typical of non-metasomatised ophiolite mantle, to moderately high in dunite (TiO₂ < 1.10 wt. %) characterizing a rock/melt interactions. The high variability of TiO₂, accompanied by similar patterns of Cr# and Mg# is observed, in a fractal pattern, at all scales of investigation, from the whole channel scale to the single thin section, where it affects even single grain zonings. Our results suggest that the over 150 m thick dunite channel here investigated was formed by coalescence of different scale melt channels and reaction zones with different sizes, confirming the published structural model. Full article

This study aims at modeling groundwater flow using MODFLOW in a transboundary hardrock–alluvium aquifer, located in northwestern Oman. A three-dimensional stratigraphic model of the study area representing the vertical and spatial extent of four principal hydro-geologic units (specifically, the Hawasina, ophiolite, Tertiary and alluvium) was generated using data collected from hundreds drilled borehole logs. Layer elevations and materials for four layers grid cells were taken from the generated stratigraphic model in which the materials and elevations were inherited from the stratigraphic model that encompasses the cell. This process led to accurate grid so that the developed groundwater conceptual model was mapped to simulate the groundwater flow and to estimate groundwater balance components and sustainable groundwater extraction for the October 1996 to September 2013 period. Results show that the long-term lateral groundwater flux ranging from 4.23 to 11.69 Mm³/year, with an average of 5.67 Mm³/year, drains from the fractured eastern ophiolite mountains into the alluvial zone. Moreover, the long-term regional groundwater sustainable groundwater extraction is 18.09 Mm³/year for 17 years, while it is, respectively, estimated as 14.51, 16.31, and 36.00 Mm³/year for dry, normal, and wet climate periods based on standardized precipitation index (SPI) climate condition. Considering a total difference in groundwater levels between eastern and western points of the study area on the order of 228 m and a 12-year monthly calibration period (October 1996 to September 2008), a root mean squared error (RMSE) in predicted groundwater elevation of 2.71 m is considered reasonable for the study area characterized by remarkable geological and hydrogeological diversity. A quantitative assessment of the groundwater balance components and particularly sustainable groundwater extraction for the different hydrological period would help decision makers to better understand the water resources in the Al-Buraimi region. In addition, it would assist decision makers to improve existing strategies to enhance the decision making for future developments. Full article