The structural evolution of the carbonate platform in the footwall of the Semail ophiolite emplaced onto the passive continental margin of Arabia helps to better understand the early stages of obduction‐related orogens. These early stages are rarely observable in other orogens as they are mostly overprinted by later mountain building phases. We present an extensive structural analysis of the Jebel Akhdar anticline, the largest tectonic window of the Oman Mountains, and integrate it on different scales. Outcrop observations can be linked to plate motion data, providing an absolute timeframe for structural generations consistent with radiometric dating of veins. Top‐to‐S overthrusting of the Semail ophiolite and Hawasina nappes onto the carbonate platform during high plate convergence rates between Arabia and Eurasia caused rapid burial and overpressure, generation and migration of hydrocarbons, and bedding‐confined veins, but no major deformation in the carbonate platform. At reduced convergence rates, subsequent tectonic thinning of the ophiolite took place above a top‐to‐NNE, crustal‐scale ductile shear zone, deforming existing veins and forming a cleavage in clay‐rich layers in early Campanian times. Ongoing extension occurred along normal‐ to oblique‐slip faults, forming horst‐graben structures and a precursor of the Jebel Akhdar dome (Campanian to Maastrichtian). This was followed by NE‐SW oriented ductile shortening and the formation of the Jebel Akhdar dome, deforming the earlier structures. Thereafter, exhumation was associated with low‐angle normal faults on the northern flank of the anticline. We correlate the top‐to‐NNE crustal‐scale shear zone with a similar structure in the Saih Hatat window to develop a unified model of the tectonic evolution of the Oman Mountains.

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Abstract. We present a study of pressure and temperature evolution in the passive continental margin under the Oman Ophiolite using numerical basin models calibrated with thermal maturity data, fluid-inclusion thermometry, and low-temperature thermochronometry and building on the results of recent work on the tectonic evolution. Because the Oman mountains experienced only weak post-obduction overprint, they offer a unique natural laboratory for this study. Thermal maturity data from the Adam Foothills constrain burial in the basin in front of the advancing nappes to at least 4 km. Peak temperature evolution in the carbonate platform under the ophiolite depends on the burial depth and only weakly on the temperature of the overriding nappes, which have cooled during transport from the oceanic subduction zone to emplacement. Fluid-inclusion thermometry yields pressure-corrected homogenization temperatures of 225 to 266 ∘C for veins formed during progressive burial, 296–364 ∘C for veins related to peak burial, and 184 to 213 ∘C for veins associated with late-stage strike-slip faulting. In contrast, the overlying Hawasina nappes have not been heated above 130–170 ∘C, as witnessed by only partial resetting of the zircon (U-Th)/He thermochronometer. In combination with independently determined temperatures from solid bitumen reflectance, we infer that the fluid inclusions of peak-burial-related veins formed at minimum pressures of 225–285 MPa. This implies that the rocks of the future Jebel Akhdar Dome were buried under 8–10 km of ophiolite on top of 2 km of sedimentary nappes, in agreement with thermal maturity data from solid bitumen reflectance and Raman spectroscopy. Rapid burial of the passive margin under the ophiolite results in sub-lithostatic pore pressures, as indicated by veins formed in dilatant fractures in the carbonates. We infer that overpressure is induced by rapid burial under the ophiolite. Tilting of the carbonate platform in combination with overpressure in the passive margin caused fluid migration towards the south in front of the advancing nappes. Exhumation of the Jebel Akhdar, as indicated by our zircon (U-Th)/He data and in agreement with existing work on the tectonic evolution, started as early as the Late Cretaceous to early Cenozoic, linked with extension above a major listric shear zone with top-to-NNE shear sense. In a second exhumation phase the carbonate platform and obducted nappes of the Jebel Akhdar Dome cooled together below ca. 170 ∘C between 50 and 40 Ma before the final stage of anticline formation.

Abstract. The Mesozoic sequences of the Oman Mountains experienced only weak post-obduction overprint and 15deformation, thus they offer a unique natural laboratory to study obduction. We present a study of the pressure and 16 temperature evolution in the passive continental margin under the Oman Ophiolite, using numerical basin models 17 calibrated with thermal maturity data, fluid inclusion thermometry and low-temperature thermochronology. Solid Earth Discuss., https://doi

Organic-rich silty marls and limestones (Pliensbachian to earliest Toarcian) exposed at Aït Moussa in Boulemane Province are the only known example of an effective petroleum source rock in the Middle Atlas of Morocco. In this study, petrological and organic-geochemical analyses (vitrinite reflectance measurements, Rock-Eval pyrolysis, GC-MS) were carried out in order to evaluate the maturity, quality and quantity of the organic matter (OM) and to investigate the depositional environment of these source rocks. Results indicate the presence of Type I/II kerogen which was deposited under marine conditions with an input of predominantly algal-derived organic matter. The presence of woody particles indicates minor input of terrestrial material. Organic-geochemical and biomarker analyses are consistent with deposition of carbonate-rich sediments under oxygendepleted but not anoxic conditions. In terms of thermal maturity, the sediments have reached the oil window (0.5-0.6 %VR r ) but not peak oil generation, although petroleum generation and migration are indicated by organic geochemical and microscopic evidence.Kinetic parameters derived from an investigation of petroleum generation characteristics show that the kerogen decomposes within a narrow temperature interval due to the fairly homogenous structure of the algal-derived organic matter. The kinetic parameters together with vitrinite reflectance data were used to construct a 1D model of the burial, thermal and maturation history of the Aït Moussa locality. The model suggested that deepest burial (approx. 3200 m) for the Pliensbachian succession took place in the Eocene (approx. 40 Ma). Two phases of hydrocarbon generation occurred, the first in the Late Jurassic/Early Cretaceous (approx. 150 Ma), and the second at the time of deepest burial (Eocene).

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Thermal maturity analyses provide a valid basis to reconstruct the burial and temperature history of sedimentary rocks. In combination with computer based modeling it is possible to quantify former overburden and erosional thickness. This study was carried out to analyze thermal maturity and elaborate the burial history of PermoMesozoic sediments of the Western Dolomites, Northern Italy. Based on their location in the non-metamorphosed Southern Alps of the Alpine realm, the Dolomites are well suited to study thermal maturation in a complex orogenic setting. Determination of maturity was carried out by vitrinite reflectance and solid bitumen reflectance measurements on a large number of samples as well as by RockEval pyrolysis. Vitrinite reflectance commonly ranges between 0.5 % VR r for Triassic and 0.76 % VR r for Permian sediments allowing an analysis of the lateral and vertical maturation patterns. Several 1D basin models were developed and calibrated by maturity measurements. Results show that deepest burial probably occurred at the end of Cretaceous times, followed by erosion of about 1800 ± 200 m. The estimated heat flows were moderate with 75 mW/m 2 for Jurassic rifting, 46 mW/m 2 for times of deepest burial and 41 mW/m 2 for present day.

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