Displays

The Masirah nappes are represented by allochthonous Late Jurassic to Cretaceous volcanic rocks and ophiolites well as Permian to Maastrichtian marine sediments, obducted onto the Oman continental margin at the cretaceous/Tertiary boundary (Schreurs and Immenhauser, 1999). The Masirah ophiolite forms a straight NNE-SSW trending strip 40 km wide, extending 450 km from Ras Madrakah to the Batain coast. The ophiolite is truncated by the ophiolitic mélange (known as Masirah Mélange) which makes a high angle with the sheeted dike trend and has been interpreted as a transform fault zone (Moseley and Abbotts 1979). The Masirah Mélange shows all the features characteristic of a tectonic mélange, in particular indefinite, non-stratigraphic, contacts and scanty matrix, indicating that it is not a diapiric mélange (Shackletonet and Ries.1990). The blocks within the mélange range in size from several kilometers to a few meters and are composed of blocks of all the rock types of the ophiolite beside metamorphic rocks. Metamorphic rocks from RasMedraka Mélange are mainly composed amphibolite, two mica gneiss, and schist. The amphibolite consists of hornblende, plagioclase, clinopyroxene, sphene, chlorite, epidote, calcite, quartz, biotite, prehnite, magnetite, and ilmenite. Geochemical data shows amphibolites have similar MORBgeochemical characteristics. The Masirah ophiolite and mélange preserve a very long (80 Ma) history of igneous and sedimentary activity prior to emplacement onto the Arabian continental crust. However, dating of the mélange is so far proving difficult. It clearly post-dates the main ophiolite and pre-dates the early Tertiary (Shackletonet al. 1990).

This study is focused on providing age constraints for the amphibolite and greenschist facies metamorphic rocks of the Masirah Mélange in Ras Madraka by 40Ar ⁄ 39Ar dating. All 40Ar ⁄ 39Ar results were obtained in the ALF Argonlab, Freiberg University, Germany.  Most of the samples show large degrees of Ar-loss or, in some cases, the presence of an excess Ar component, reflected by disturbed age spectra. In general, however, the large number of temperature steps measured in one hornblende sample allows the determination of well-constrained inverse isochron ages that generally provide a more robust error estimate than plateau ages. Laser stepwise heating of these hornblende samples yielded flat age spectra with plateau ages of 83.8+0.96 Ma.

The Indian Ocean was characterized by stepwise breakup of east and west Gondwana at 157 Ma, breakup of east Gondwana at 130 Ma, Madagascar and India/Seychelles at 95–84 Ma, India and Seychelles at 65 Ma, and, finally at40 Ma, rifting between Africa and Arabia Peters, 2000; Nasir 2016). The range from 160 Ma to 80 Ma suggests that magmatic activity in the Masirah ophiolite was more or less continuous over a period of ~80 Ma, and correlates with large-scale tectonic events recorded in the early Indian Ocean at 80-160 Ma. The 40Ar ⁄ 39Ar ages indicate that hornblende formed before 84 Ma and this age can be interpreted as cooling ages dating approximately the formation of the plastic deformation and abduction. We attribute the Masirah Mélange to the Madagascar and India/Seychelles breaking event at 95–84.

How to cite: Nasir, S.: Petrogenesis of the Masirah ophiolite Me'lange at Ras Madraka, Oman, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1393, https://doi.org/10.5194/egusphere-egu2020-1393, 2020.

Zagros foreland basin is the most important oil-gas foreland basin in the world. At least 60 oil and gas fields have been found. Therefore, research in this area will enrich the petroleum geological information of the foreland basin as an important basis for oil and gas exploration. First, we conduct 2D restoration of Lorestan salient in North Zagros Mountain Belt with 2DMove to test the rationality of the equilibrium profile and understand the structural evolution of the Lorestan salient. Base on the 2D restoration, faults evolved in the ways of in-sequence and out-of-sequence, many faults have breached the cover layer from basement then produced anticline, in the earlier stage of deformation. Anaran anticline and Kabir Kuh anticline caused by the thrusts that displacement along the thrust are 5769 m and 11496 m, respectively. The Vardalan, Dareh Baneh and Naft Anticline also produced by the basement thrust later, this result suggest that surface topography and anticline are highly associated with basement thrust. Second, using the Move2017-Surface to establish the 3D structural model to observe the lateral variation of the strata, some strata have lateral variation, the Mishan formation is absent in the NW but gradually appear to the SE and the Triassic carbonates thickness decreases from almost 1000 m in the southwest to 200 m in the northeast. This reduction in thickness may associated with late Triassic normal faulting and erosion. Third, we project the earthquake on the cross section to understanding the relation between earthquake distribution and tectonic patterns. Based on the analysis of seismicity and geological profiles, earthquake focal mechanisms are mostly reverse faulting with NW–SE strikes and the distribution is over whole horizontal Zagros belt but concentrated in depth of 5~16 km. In addition, larger magnitude earthquakes mainly distribute in southwest Lorestan, it implies that it is the main regime of active tectonics.

How to cite: Pang, J. W. and Hu, J.-C.: Structural Evolution of Lorestan salient in North Zagros Mountain Belt, Iran, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7803, https://doi.org/10.5194/egusphere-egu2020-7803, 2020.

The Barzaman Formation is 150-200 m thick and subdivided into five lithostratigraphic/facies intervals recording syndepositional thrusting and changes from shallow marine to terrestrial environments and from arid/semiarid to more humid conditions.

(1) The basal lower conglomerate and sandstone unit is >36 m thick, marked by beige and gray/greenish colors, thick-bedded pebbly, calciclastic litharenites which may display parallel lamination and thick-bedded matrix-supported pebble to cobble conglomerates with subrounded clasts of chert, basalt, gabbro, quartzite and carbonates. Pores may be lined by isopachous, microcrystalline calcite cement. The depositional environment is shallow marine with one coarse-grained fill of a high-energy tidal inlet.

(2) The light-colored carbonate facies unit is 1-15 m thick, consisting of thick-bedded coral limestone, a very thick limestone coral and algae debrite and some minor beds of conglomerate and sandstone. The corals may be partly silicified by brown-stained silica. This unit was deposited in a warm, shallow marine, nearshore environment with clear water which may indicate an arid climate.

(3) The varicolored thick sandstone and conglomerate facies unit is 14-28.5 m thick. These clastic deposits are similar to those of unit 1, but more colorful, slightly coarser grained (presence of boulders) and include also thin and medium beds. The sandstones may exhibit cross-bedding. The depositional environment is shallow marine as indicated by coral debris.

(4) The claystone and conglomerate facies unit is 19 m thick. The clastic sediments are similar to those of unit 1, but pebbly sandstones are comparatively rare, and claystone beds are present, including a 20-cm-thick cellular claystone (palygorskite, vermiculite with some calcite) as well as light gray, medium-bedded claystone beds, consisting mainly of palygorskite with some saponite and/or clinochlore, associated with minute, euhedral dolomite or ankerite crystals. All claystone beds are evaporitic, lacustrine deposits of ephemeral ponds and pools on wadi floors whereas the coarser beds represent wadi conglomerates. Some beds are imbricated slide units. The paleoclimate was hot, semiarid or arid.

(5) The dolomitic conglomerate facies unit may measure >61 m in thickness. The respective pebble conglomerates consist of clasts that seem to “float” in cement. The cements of the basal >10 m are brown-stained silica and some white dolomite. The silica content gradually decreases upward. The upper part is dominated by white dolomite and some calcite. The dolomite cement may have formed under phreatic conditions (groundwater) during the Late Miocene to Pliocene when the arid/semiarid Miocene climate became more humid.    

Close to the base of unit 4, the upper part of an east-dipping syndepositional thrust is exposed (Mattern et al., 2018). Faulting approximately coincides with the change from marine to terrestrial conditions. In addition, the syndepostional tectonic activity may explain aspects of slope instability: debrite in unit 2, slide units in unit 4.

References

Mattern, F., Scharf, A., Al-Amri, S.H.K., 2018. East-west directed Cenozoic compression in the Muscat area (NE Oman): timing and causes. Gulf Seismic Forum, 19-22 March 2018, Muscat, Oman, Book of Abstracts, p. 4-7.

How to cite: Mattern, F., Al-Amri, S., and Scharf, A.: Lithostratigraphy, facies, mineralogy and diagenesis of the retrograding, syntectonic Neogene Barzaman Formation (Al-Khod, Sultanate of Oman), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9679, https://doi.org/10.5194/egusphere-egu2020-9679, 2020.

Neoproterozoic rocks exposed in the Jebel Akhdar massif of northern Oman preserve glaciogenic deposits associated with multiple Cryogenian glaciations. Although the depositional history of these rocks is well understood, the significance of post-depositional deformation is poorly constrained. In this study, we examine low-grade metasedimentary rocks exposed in the Ghubrah Bowl, an erosional window in the Jebel Akhdar massif, in order to quantify the 3D finite strain, understand deformation kinematics, and determine the timing of deformation/metamorphism.

In the Jebel Akhdar massif, the older Ghubrah (Sturtian glaciation) and younger Fiq (Marinoan glaciation) formations comprise a >1 km thick sequence of diamictite interbedded with sandstone, siltstone, conglomerate, volcanic rock, and minor carbonate. Diamictites contain abundant clasts of siltstone and sandstone, with lesser amounts of granite and metavolcanic rock in a fine-grained quartz + sericite ± chlorite matrix. Clasts range from granules to boulders. Harder clasts tend to be subangular and poorly aligned with low aspect ratios, whereas fine-grained rock clasts are well-aligned with large aspect ratios. Bedding generally dips to the NW, but is gently folded in accord with the overall structure of the Jebel Akhdar massif. A penetrative foliation strikes E-W and dips to the S. At some locations, a prominent elongation lineation/pencil structure occurs and plunges gently to moderately to the S.

R_f/phi strain analysis in the diamictites reveals a range of 3D strain geometries (apparent flattening to apparent constriction) with strain ratios up to 2.8 in XZ sections. Strain is strongly partitioned, as clasts of igneous rock have low aspect ratios and are only weakly aligned. Penetrative strain in clast-supported sandstones is negligible (XZ ratios of <1.2). Outsized clasts of granite and sandstone are mantled by distinctive symmetric pressure shadows (double-duckbill structures) that include more recrystallized minerals than elsewhere in the diamictite. ⁴⁰Ar/³⁹Ar geochronology of sericite in pressure shadows yields ages as young as 90 Ma, which are interpreted as mixed ages containing an older detrital component and a younger fraction formed during growth. Deformation is associated with southward emplacement and loading by the Oman ophiolite & Hawasina Group sediments over the autochthonous sequence in the late Cretaceous.

How to cite: Bailey, C. and Rae, C.: Deformation timing and strain in Neoproterozoic strata, Jebel Akhdar, northern Oman, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12361, https://doi.org/10.5194/egusphere-egu2020-12361, 2020.

The main Meso-Cenozoic tectonic event that affected northern Oman was the obduction of allochthonous Hawasina Basin-derived sedimentary and volcanic rocks as well as the Semail Ophiolite during the Late Cretaceous. The allochthonous units were thrust onto the passive Arabian margin and platform. Obduction was followed by immediate uplift (doming) of the Saih Hatat Dome in the Southeastern Oman Mountains. The present work relates to the postobductional tectonic development of the Semail Ophiolite in the Ibra region southwest of the Saih Hatat Dome. The main aim of this work is to develop a regional brittle deformation model using structural field data comparing with borehole wireline log structural data from the Oman Drilling Project (ODP) wells sites, drilled in the same area for the investigation of active serpentinization in the peridotite aquifers.

The study area of ~100 km² contains a brittle fault zone of ~3 km kilometers in width and ~30 km in length herein called the “Issmaiya Fault Zone (IFZ)”. Along the IFZ, a structural field analysis and eleven structural survey stations using the 1-D scanline method for the kinematics elements were realized. In particular, the structural stations were chosen close to the ODP wells sites location, in order to compare the field survey with the borehole logging data.

The IFZ is characterized by sub-vertical faults within the mantle part of the Semail Ophiolite which also partially affected latest Cretaceous to Paleocene/early Eocene sedimentary rocks. The latter are also mapped within a structural basin, 25 km NE of Ibra (the so called “Ibra Basin”). Our field work and satellite imagery interpretations demonstrate that most faults are within the Semail Ophiolite and few affecting the postobductional sedimentary rocks. This indicates that the ILS was mostly active immediately after the Late Cretaceous emplacement of the Semail Ophiolite.

The IFZ strikes NW and forms an acute angle of ~30° with the southwestern margin of the Saih Hatat Dome which strikes WNW-ESE. The LFZ is a transtensional fault zone as indicated by the coexistence of sub-vertical fault planes, with mainly sinistral strike-slip kinematic indicators, and from medium to high angle fault planes with dip-slip movement. The IFZ seems to end towards the NW at the tectonic contact with the Mesozoic sedimentary rocks of the Arabian Plate (Hajar Supergroup). The southwestern margin of the Saih Hatat Dome is marked by a major sinistral transtensional fault (Wadi Mansah Fault Zone; Scharf et al., 2019). This shear zone was active during the Eocene to Miocene and postdates the IFZ.

This work provides key insights on the effect of the fault zone to the hydrogeology of the ODP multi-borehole site, in terms of anomalies in the hydrogeochemical log and intervals of high transmissivity.

How to cite: Callegari, I., Braathen, A., Scharf, A., Mattern, F., Holzbecher, E., Al Kharosi, A., and Al Hajri, A.: Evidence of postobductional, brittle and transtensional deformation: the lineamentary Issmaiya Fault Zone – insights from kinematic analyses and remote sensing data interpretation (Semail Ophiolite near Ibra, Oman Mts., Sultanante of Oman), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12472, https://doi.org/10.5194/egusphere-egu2020-12472, 2020.

Listwaenite (fully serpentinized and carbonatized/silicified ultramafic rock) is common within the Oman Mountains near Fanja. The Oman Mountains formed during the late Cretaceous obduction of the Semail Ophiolite. Eventually, major exhumation and associated extensional shearing formed the Saih Hatat Dome during the latest Cretaceous to Paleocene. This dome displays rocks of the Arabian platform, framed by the Hawasina Allochthonous and the Semail Ophiolite. Postobductional rapid exhumation/cooling of the Saih Hatat Dome is reflected by a major extensional shear zone at the northern margin of the dome (Frontal Range Fault, FRF; Mattern and Scharf, 2018). Shearing along the FRF with a throw of few to several kilometers, occurred within two intervals. The major first event occurred during the latest Cretaceous to Paleocene while the minor second event lasted probably from the late Eocene to Oligocene (Mattern et al., 2019). Along and within the FRF, major tabular listwaenite bodies occur displaying a lateral extend from few meters to hundreds of meters and a thickness of up to a few to tens of meters. According to Scharf et al. (2020), the listwaenite dates as latest Cretaceous to Paleocene.

Most of the numerous SiO₂-rich listwaenite bodies near Fanja preserve a brittle deformation pattern, indicating that the temperature during and after formation was less than 250°C. As an exception, we found one unusually well-developed, intensely foliated and wide strike-slip ductile-brittle shear zone at the surface, exhibiting a width of 5m and a length of a few tens of meters within a large listwaenite body near the community of Sunub. The foliation of the shear zone dips to the SW with about 50-80°. The shear zone intersects at a high angle with the FRF (strike SW-NE) and the listwaenite unit it contains. The shear movement is unrelated to that of the FRF. Approximately 6km WNW of the sheared listwaenite, a mafic dike of Lutetian age (42.7±0.5Ma; Mattern et al., 2019) intruded Cenozoic limestone. Intrusion is associated with the second shearing interval of the FRF. Because listwaenite bodies usually display brittle deformation, we tentatively conclude that the ductile-brittle shear zone formed during the late Eocene because of mafic intrusions. We assume that another mafic body is located near the shear zone and provided the heat for the ductile-brittle deformation conditions.

References:

Mattern, F., Scharf, A., 2018. Postobductional extension along and within the Frontal Range of the Eastern Oman Mountains. Journal of Asian Earth Sciences 154, 369-385, doi: 10.1016/j.jseaes.2017.12.031.

Mattern, F., Sudo, M., Callegari, I., Pracejus, B., Bauer, W., Scharf, A., 2019. Late Lutetian ⁴⁰Ar/³⁹Ar Age Dating of a Mafic Intrusion into the Jafnayn Formation and its Tectonic Implications (Muscat, Oman). AAPG Event, 2^nd Edition, Structural styles of the Middle East, 9^th-11^th December 2019, Muscat, Oman.

Scharf, A., Mattern, F., Bolhar, R., Bailey, C.M., Ring, U., 2020. U-Pb dating of postobductional carbonate veins in listwaenite of the Oman Mountains near Fanja. International Conference on Ophiolites and the Oceanic Lithosphere: Results of the Oman Drilling Project and Related Research, 12-14^th January, 2020, Sultan Qaboos University, Muscat, Sultanate of Oman.

How to cite: Scharf, A., Mattern, F., and Mattern, P.: Ductile-brittle shear zone in a listwaenite body, within the Frontal Range Fault of the Oman Mountains (Sultanate of Oman), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12672, https://doi.org/10.5194/egusphere-egu2020-12672, 2020.

Exploration work has indicated reservoir potential and targets within the Pre-Cambrian Basement and associated sedimentary succession in the Saudi Arabia  and surrounding areas in the Arabian Plate. Understanding of fracture, characteristics, and distribution in petroleum basins are essential to improve exploration and production. Fractures are usually the main source for porosity and permeability within basement rocks and it controls the fluid flow. Usage of field outcrop analog studies, are very valuable for estimating the fractures distribution in the subsurface. We conducted an integrated outcrop-based study of the fracture pattern at Midyan Region, NW Saudi Arabia for the aim of identifying the fracture types, pattern and distribution on the Pre-Cambrian Basement rocks and associated Cenozoic sedimentary rocks in the region. The approach and methods used included integrated Landsat analysis and interpretation supported by outcrop based high-resolution observation, mapping and measurements of the fracture within the Basements and the Red Sea Cenozoic sedimentary succession. The Midyan Region has evolved through complex tectonic, structural history where four rifting phases have been reported that associated with several distinctive silici-clastic and carbonate facies and paleoenvironments. The Landsat and outcrop data measurements and analysis of fractures revealed characteristic pattern that generally show NW, NE, NS and EW trends. Some of these trends show similarity to fracture patterns associated with the Najid fault system and the also those associated with the Red Sea tectonic in Midyan region. Moreover, the fracture types within the Cenozoic outcropping rocks tend to correlate with those within the Pre-Cambrian Basement rocks. Fracture distribution was observed also cutting through reservoirs/ seals outcrop equivalents to the subsurface in Midyan region. Integration of outcropping results obtained in this study with subsurface geological and geophysical data and faults and fracture pattern data might provide guide for comparison and enhances prediction for identifying fractured reservoir potential targets, hydrocarbon migration pathways, trapping mechanisms, fracture distribution and modeling.

How to cite: Abdullatif, O. and Osman, M.: Characteristics and Fracture Pattern within the Basement and Cenozoic Rocks and Implication to Reservoir Potential, Red Sea, Midyan Region, NW Saudi Arabia., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13641, https://doi.org/10.5194/egusphere-egu2020-13641, 2020.

The Oman ophiolite is one of the best preserved and studied ophiolites, where oceanic lithosphere was obducted on top of a continent. It covers an area of about 700 x 140 km² but its 3D geometry, as well as the properties of the underlying continental lithosphere are largely unknown. We operated a temporary broadband seismic network with 40 instruments for continuous, passive seismic registration for 27 months, complemented by 18 permanent stations in the study region. Ambient noise cross-correlation functions are calculated for vertical and transverse components for all station pairs. We derive azimuthally anisotropic phase velocity maps for Rayleigh- and Love waves in the period range 2 – 40s which show velocity anomalies that are very consistent with geological features at the shortest periods (<10s). At longer periods (>15s) the velocity pattern subdivides the study region into a faster eastern and slower northwestern part below the Oman Mountains. 

We then invert local dispersion curves to shear wave velocity profiles using a novel implementation of a radially anisotropic, probabilistic inversion. Combination of the obtained 1D models to a 3D model provides the first three-dimensional view of shear wave velocity variations along the Eastern Arabian Plate margin. The model highlights at shallow levels strong lateral velocity contrasts between unconsolidated young sediments south of the Oman Mountains (slow) and areas covered by ophiolite and where autochtonous shelf sediments are exposed (fast).

At middle to lower crustal levels, we image linearly northeast trending velocity contrasts that we attribute to assembly of the Arabian plate in late Proterozoic. These features are overprinted by obduction-related convergence in late Cretaceous with thickening of the middle to lower crust below the Oman mountains. Moho depth is around 40-45km northwest of Semail Gap but shallows significantly east of it to 20km at the eastern coast. This is largely in consistency with independent estimates from Receiver Functions calculated with the same data.

How to cite: Weidle, C., Wiesenberg, L., El-Sharkawy, A., Meier, T., Krüger, F., Agard, P., and Scharf, A.: A 3-D crustal model of the eastern Arabian plate margin below the Oman Ophiolite, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17800, https://doi.org/10.5194/egusphere-egu2020-17800, 2020.

Plate tectonics can lead to construction of mountain belts, whereas surface processes destruct the orogenic masses and redistribute the surface load. These processes can be modulated by climate through variation in air temperature and the magnitude-frequency distribution of precipitation. In the northwestern Zagros orogenic belt the driving force for hinterland uplift has been baffling. The key concern is whether uplift is due to upper crustal shortening and related crustal thickening (local uplift) or to deep lithospheric processes (regional dynamic uplift) such as slab breakoff and/or to lithospheric mantle delamination. The stratigraphic record is sensitive to geodynamic processes, yet distinguishing the tectonic signatures from the climate-induced signatures is necessary. The goal of this research is to test these competing mechanisms of orogenesis through field-based evaluations of shifts in foreland basin stratigraphy, provenance, detrital geochemistry, and climate change through time as well as flexural modeling for the northwestern Zagros orogenic belt. In the Kurdistan region of Iraq, the northwestern Zagros orogenic belt is characterized by a well preserved ~4 km thick stratigraphic column of the Neogene synorogenic predominantly clastic continental deposits that coarsen and thicken upwards: The Fatha (middle Miocene), Injana (late Miocene), Mukdadiya (latest Miocene), and the Bai-Hasan (Pleistocene) Formations. These units, in addition to sandstone beds, include thick poorly consolidated mudstone packages that in some places reach ~100 m. Preliminary results show that the frequency and thickness of sandstone-filled channels increases upsection, leading to an amalgamation of sandstone packages towards the top. This thickening-upward trend was additionally associated with an increase in the grain size. These patterns of stratigraphy dynamics hint to a progradation of the depositional systems, driven either by an increase in the sediment flux relative to the subsidence rate, or by a propagation of the orogen front towards the foreland basin. Sm-Nd analysis on the fine material packages revealed a crustal origin (εNd-) comparable to the Arabian shield, with an older crustal age upsection. Weathering proxy data such as chemical index alteration (CIA) and K₂O/Al₂O₃ ratio yield evidence for a weathering intensity that increases upsection. X-Ray diffraction data from the clay-size materials (<2-μm) show contents of smectite, illite, kaolinite and Fe-rich chlorite, with an increasing abundance of smectite minerals upsection. These mineral assemblages demonstrate a semi- arid/humid climate likely with an increasing seasonality through time, which could possibly have resulted in an increasing sediment flux. Furthermore, basic flexural modeling for the northwestern Zagors orogenic belt indicates that the present-day Zagros topography, and thus topographic load alone, cannot explain the observed basin depth. Overall, these evidences suggest that exhumation of the source terranes was enhanced by increased weathering, yet a geodynamic process could have been the main driver for controlling the formation of accommodation space and uplift of the mountain belt.

How to cite: Koshnaw, R., Kley, J., Schlunegger, F., Wemmer, K., Eynatten, H., and Willbold, M.: Linking deep-Earth processes, basin stratigraphy, and topographic build-up during the Neogene Zagors orogeny in the Kurdistan region of Iraq, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18275, https://doi.org/10.5194/egusphere-egu2020-18275, 2020.