Postobductional extension along and within the Frontal Range of the Eastern Oman Mountains

Mattern, Frank; Scharf, Andreas

doi:10.1016/j.jseaes.2017.12.031

Cited by 45 publications

(41 citation statements)

References 18 publications

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“…This exhumation scenario is corroborated by 40 Ar/ 39 Ar ages of white micas associated with the top‐to‐NNE lineations yielding 82–79 Ma (Miller et al, ). Exhumation was also interpreted to be related to low‐ and high‐angle normal faulting (Miller et al, ) or gravitational collapse after obduction (Hanna, ; Mattern & Scharf, ). Orogen‐scale normal faults, also identified in the overlying ophiolite, tectonically thin it from more than 15 to roughly 5 km thickness (Gray & Gregory, ; Gray et al, ).…”

Section: Introductionmentioning

confidence: 99%

Multiphase Structural Evolution of a Continental Margin During Obduction Orogeny: Insights From the Jebel Akhdar Dome, Oman Mountains

et al. 2018

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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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Section: Introductionmentioning

confidence: 99%

Multiphase Structural Evolution of a Continental Margin During Obduction Orogeny: Insights From the Jebel Akhdar Dome, Oman Mountains

et al. 2018

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“…100 Ma. Additional temperature data refer to zircon fission track ages from (*)Saddiqi et al (2006), apatite fission track ages from ( )Poupeau et al (1998) and (+)Mount et al (1998), and AHe, AFT, and ZFT ages from ( • , gray)Hansman et al (2017). Moreover, the locations of samples used for fluid-inclusion measurements are shown.…”

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confidence: 99%

Tectono-thermal evolution of Oman's Mesozoic passive continental margin under the obducting Semail Ophiolite: a case study of Jebel Akhdar, Oman

et al. 2019

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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.

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“…The final doming of the JAD occurred from Eocene to Miocene (Hansman et al, 2017(Hansman et al, , 2018Grobe et al, 2018Grobe et al, , 2019. This process was accompanied by extensional shearing at the northern and eastern margin of the dome (Mattern and Scharf, 2018;Scharf et al, 2019), and tilting of the Arabian rocks along a WNW-ENE trending rotation axis at the northern and southern margin of the dome by ∼30° and ∼20°, respectively (compare Beurrier et al, 1986;Rabu et al, 1986).…”

Section: Shd's Neoproterozoic Formations Differ From Jad's Includingmentioning

confidence: 98%

“…Obduction was followed by extension (e.g., Fournier et al, 2006;Searle, 2007;Mattern and Scharf, 2018;Grobe et al, 2018Grobe et al, , 2019 as indicated by extensional faults, which displaced the ophiolite Searle, 2007). It is worth mentioning that both SHD and JAD display large-scale listric normal faults bounding their flanks (Searle, 2007).…”

Section: Shd's Neoproterozoic Formations Differ From Jad's Includingmentioning

confidence: 99%

Gondwana accretion tectonics and implications for the geodynamic evolution of eastern Arabia: first structural evidence of the existence of the Cadomian Orogen in Oman (Jabal Akhdar Dome, Central Oman Mountains)

Callegari¹

2019

Preprint

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The present work describes two early Cambrian folding events within Cryogenian to earliest Cambrian rocks of the western Jabal Akhdar Dome (Central Oman Mountains). This sequence is truncated at an angular unconformity and topped by Permo-Mesozoic sedimentary shelf strata. The Permo-Mesozoic is brittlely deformed and largely unfolded. This differs in style and intensity of deformation with the refolded underlying Neoproterozoic-Cambrian rocks. Evidences for an older Paleozoic deformation (D1) have been identified within limestone of the Hajir Formation. Tight to close inclined folds (F1) reflect the ductile deformation affecting Neoproterozoic-Cambrian rocks. The folds yield 5-50m amplitudes, with a short-overturned limb, sub-horizontal to gently plunging fold axes and moderately to sub-horizontally inclined axial surfaces. A younger event (D2) has refolded the F1 folds. F2 folds are open to close with amplitudes and wavelengths from several hundred meters to 3 and 5km respectively. The F2 folds display sub-vertical to steep axial planes dipping towards NNW, and fold axes plunging either ENE-wards with ∼50°, or SW-wards with ∼30°, at the northern and southern side of the Jabal Akhdar Dome, respectively. F2 folds have been mentioned by previous authors as possibly Hercynian in age, while the occurrence of F1 folds is here firstly presented, revealing a uniform NW-vergence of F1 folds after restoration at pre D2 geodynamic conditions.We present in this work the first structural evidence related to the D1 Cadomian event which occurred in eastern Arabia between ∼542 and 525 ±5Ma, due to the convergence between Arabia and microcontinents and/or oceanic subduction of the Proto-Tethys Ocean. The two deformation events, D1 (Cadomian Orogeny) and D2 (Angudan Orogeny), are related to NE-SW and ∼NW-SE main compressional directions, respectively. The evidence arising from the present research study directly challenges former accounts of a “Hercynian Orogeny” in eastern Arabia.

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Postobductional extension along and within the Frontal Range of the Eastern Oman Mountains

Cited by 45 publications

References 18 publications

Multiphase Structural Evolution of a Continental Margin During Obduction Orogeny: Insights From the Jebel Akhdar Dome, Oman Mountains

Multiphase Structural Evolution of a Continental Margin During Obduction Orogeny: Insights From the Jebel Akhdar Dome, Oman Mountains

Tectono-thermal evolution of Oman's Mesozoic passive continental margin under the obducting Semail Ophiolite: a case study of Jebel Akhdar, Oman

Gondwana accretion tectonics and implications for the geodynamic evolution of eastern Arabia: first structural evidence of the existence of the Cadomian Orogen in Oman (Jabal Akhdar Dome, Central Oman Mountains)

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