Late-stage tectonic evolution of the Al-Hajar Mountains, Oman: New constraints from Palaeogene sedimentary units and low-temperature thermochronometry

Mountain building in the Al-Hajar Mountains (NE Oman) occurred during two major shortening stages, related to the convergence between Africa-Arabia and Eurasia, separated by nearly 30 Ma of tectonic quiescence. Most of the shortening was accommodated during the Late Cretaceous, when northward subduction of the Neo-Tethys Ocean was followed by the ophiolites obduction on top of the former Mesozoic margin. This shortening event lasted until the latest Santonian - early Campanian. Maastrichtian to Eocene carbonates unconformably overlie the eroded nappes and seal the Cretaceous foredeep. These neo-autochthonous post-nappe sedimentary rocks were deformed, along with the underlying Cretaceous tectonic pile, during the second shortening event, itself including two main exhumation stages. In this study we combine remotely sensed structural data, seismic interpretation, field-based structural investigations and apatite (U-Th)/He (AHe) cooling ages to obtain new insights into the Cenozoic deformation stage. Seismic interpretation indicates the occurrence of a late Eocene flexural basin, later deformed by an Oligocene thrusting event, during which the post-nappe succession and the underlying Cretaceous nappes of the internal foredeep were uplifted. This stage was followed by folding of the post-nappe succession during the Miocene. AHe data from detrital siliciclastic deposits in the frontal area of the mountain chain provide cooling ages spanning from 17.3 to 42 Ma, consistent with available data for the structural culminations of Oman. Our work points out how renewal of flexural subsidence in the foredeep and uplift of the mountain belt were coeval processes, followed by layer-parallel shortening preceding final fold amplification

Tectono-stratigraphic evolution of salt-controlled minibasins in a fold and thrust belt, the Oligo-Miocene central Sivas Basin

ACLInternational audienceThe Central Sivas Basin (Turkey) provides an outcrop example of a minibasin province developed above a salt canopy within a foreland-fold and thrust belt. Several minibasins are examined to assess the influence of regional Oligo-Miocene shortening during the development of a minibasin province. The results are based on extensive field work, including regional and detailed outcrop mapping of at least 15 minibasin margins and analysis of the structural elements at all scales. This reveals a progressive increase in shortening and a decrease in salt tectonics during evolution of the province. The initiation of minibasins is driven mostly by the salt-induced accommodation forming a polygonal network of salt structures with mainly local halokinetic sequences (i.e. hooks and wedges). The initiation of shortening is marked by an abrupt increase in sedimentation rate within the flexural foreland basin causing burial of the preexisting salt structures. Subsequently, orogenic compression encourages the rejuvenation of linear salt structures oriented at right angle to the regional shortening direction. The influence of orogenic shortening during the last steps of the minibasin province evolution is clearly shown by: (i) the squeezing of salt structures to form welds which are developed both at right angle and oblique to the regional shortening direction, (ii) the emergence of thrust faults, (iii) the tilting and rotation of minibasins about vertical axis associated with the formation of strike-slip fault zones, and (iv) the extrusion of salt sheets. The pre-shortening geometry of the salt structures pattern, polygonal network of walls and diapirs versus linear and sub-parallel walls, influence the resultant structural style of the minibasin province subjected to shortening. Preexisting linear depocenter limited by sub-parallel walls accommodate preferentially the shortening compare to the preexisting sub-circular depocenter limited by polygonal network of salt walls and diapirs. © 2017 Elsevier Lt

Alternating thin versus thick-skinned decollements, example in a fast tectonic setting: The Misool–Onin–Kumawa Ridge (West Papua)

International audienc

Mechanisms of basin contraction and reactivation in the basement involved Malargue fold-and thrust-belt, Central Andes (34°S-36°S)

ACLInternational audienc

Detection and discrimination of complex thrust and salt tectonics structures using field data and RASAT images around the Emirhan region (Sivas, Turkey) [Emirhan (Sivas) Civarinda Karmasik Bindirme ve Tuz Tektonigi Yapilarinin Arazi Verileri ve RASAT Görüntüleriyle Ortaya Çikarilmasi ve Ayrimi]

ACTInternational audienceRASAT L2 visible and panchromatic images were used to detect both thrust and salt tectonics structures as a reliable geologic mapping tool in this research. As a geographical transition plateau between Inner and Eastern Anatolian region, Sivas Basin doesn't show hampering vegetation on geologic outcroppings for remote sensing analyses. This feature also allow healthy interpretation possibilities. Salt structures in Sivas Basin can be counted in worldwide well-known examples (e.g. La Popa Mexico, Great Kavir Iran and Axel Heiberg Canada) conveniently. In this research, a detailed geological map was prepared in the field. The results show that both of visual interpretations and digital image processing methods spectrally could provide healthy discrimination power between different rock lithologies. Image fusion method was contributed to reveal these subtle tectonic and geomorphologic evidences that developed in and between salt and clastic lithologies. In addition, specifically chosen Landsat ETM+ bands such as 5 and 7 images together with RASAT visible bands were also used to create RGB combinations for geological studies. © 2016 IEEE

Exploration in a thick to thin-skinned transition: Faja Plegada triangle zone. Neuquén, Argentina

Pure kinematic models are classically used to validate and balance geological cross sections in fold-and-thrust belts, impacting the interpretation of the structural style, the kinematics, and finally their exploration potential. During the 1960s and 1970s, surface geological data were largely used to interpret the structural style of the “Faja Plegada,” along the outer sector of Chos Malal Triangle Zone (Argentina), with the aim to steer the hydrocarbon exploration. Some of the original proposed concepts are still considered valid nowadays. The discoveries of El Portón and Filo Morado fields encouraged the acquisition of seismic data in the area, to better image these structures, both for field development and further Hydrocarbon exploration. The use of a thin-skinned structural model, with multiple detachments (Choiyoi Group, Vaca Muerta and Huitrín Formations), and a “Rocky Mountain structural style” have been used since the sixties to describe the anticline geometries and propose subthrust structures, enhancing hydrocarbon prospectivity in Chos Malal. Nevertheless, a thick-skinned structural model is considered more appropriate, even though the style of the area is still debated, and several alternative models have been illustrated in the scientific literature. Despite the effort put into seismic acquisition, design, and processing, the subthrust images are still unclear and alternative interpretations can be proposed with a strong impact on the exploration potential. This paper illustrates the impact that the improvement of the seismic reprocessing had in better understanding the kinematics and structural style of the area, and the consequent evolution of the exploration concepts, in terms of geometry and structural uncertainties. In addition, we discuss the role played by multiple detachments in controlling the localization and growth of the anticlines and also in the migration of the deformation from thick to thin-skinned along the outer front of the Chos Malal thrust belt.Peer reviewe

Mechanisms of basin contraction and reactivation in the basement-involved Malargüe fold-and-thrust belt, Central Andes (34-36°S)

ACLInternational audienceWe have conducted a structural study of both the basement-involved Malargüe fold-andthrust belt (MFTB) and the active San Rafael Block (SRB), which are located in the Central Andes at latitude 34-36° S. Based on several field examples located both in the inner and frontal part of belt and from the distal foreland zone, we focus on the relationships between basement and cover deformation with respect to the known palaeogeography and structural inheritance. In several zones, we point out similarities in the structural and sedimentary responses to Andean shortening. The recent morphologic response has also been investigated through the analysis of active deformation along the eastern border of the SRB. We show that these structural and sedimentary processes are continuous in time and space since they can be applied in the various parts of the fold belt and also at different stages of fold-and-thrust-belt building as well. Finally, we propose the illustration of those mechanisms by complete cross-section along the Rio Grande valley and a possible kinematic scenario of deformation propagation. © 2016 Cambridge University Press

Deformation zone ‘jumps’ in a young convergent setting; the Lengguru fold-and-thrust belt, New Guinea Island

International audienc

Minibasins and salt canopy in foreland fold-and-thrust belts: The central Sivas Basin, Turkey

ACLInternational audienceThe Sivas Basin in the Central Anatolian Plateau (Turkey), which formed in the context of a foreland fold-and-thrust belt (FTB), exhibits a typical wall and basin (WAB) province characterized by symmetric minibasins separated by continuous steep-flanked walls and diapirs. Extensive fieldwork including regional and detailed local mapping of the contacts and margins of minibasins, and interpretation of a set of 2-D regional seismic lines, provide evidence for the development of a shallow evaporite level separating two generations of minibasins within the WAB province. Here beds of symmetric exposed minibasins along diapir flank are younger than minibasins observed over autochthonous evaporites. Laterally away from the WAB province, increase in wavelength of the tectonic structures suggests a deepening of the decollement level. We interpret that a shallower evaporite level developed in the form of an evaporite canopy, triggered by significant lateral shortening. The Upper Eocene-Lower Oligocene autochthonous Tuzhisar evaporite level was remobilized by the northward migrating sedimentary load and the tilting of the southern basin margin during propagation of the foreland fold-and-thrust belt. Asymmetric and symmetric primary minibasins were overrun by an allochthonous sheet forming a canopy. A second generation of salt withdrawal minibasins subsided into the allochthonous salt sheet. The polygonal pattern of the WAB province influences the growing fold-and-thrust belt system during the late stage of the secondary minibasins development. The Sivas FTB basin is the result of the interaction between fold-and-thrust belt propagation, evaporite remobilization, and interaction between evaporite flow and sedimentation in the minibasins. ©2016. American Geophysical Union. All Rights Reserved

Microtectonic record of the strain pat- tern in the Malargüe fold and thrust belt using fractures analysis and ASM data

ACTInternational audienc