Abstract:Recently shot 3D seismic data allowed for a detailed interpretation, aimed at the tectonic evolution of the central part of the Mid-Hungarian Shear Zone (MHZ). The MHZ acted as a NW vergent fold and thrust belt in the Late Oligocene. The intensity of shortening increased westwards, causing clockwise rotation of the western regions, relatively to the mildly deformed eastern areas. Blind thrusting and related folding in the MHZ continued in the Early Miocene. Thrusting and gentle folding in the MHZ partly continued in the earliest Pannonian, and was followed by sinistral movements in the whole MHZ, with maximal displacement along the Tóalmás zone. Late Pannonian inversion activated thrusts and generated transpressional movements along the Tóalmás zone.

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Several main tectonic lineaments originating in the Alps and Dinarides merge in Central Hungary to form the Mid-Hungarian Shear Zone. As these structures are hidden beneath sub-basins of the Neogene Pannonian Basin, it has long been debated whether the tectonic style of the shear zone is mainly contractional or strike-slip. New 3D seismic data allowed a detailed analysis of one of these sub-basins, the Adony Basin, located south of Budapest. Its evolution is linked to the tectonics between the southern Tisza unit of European passive margin affinity, the northern ALCAPA block with Alpine affinity, and sheared remnants of Dinaric units in between. During the Oligocene and Early to Middle Miocene, a flexural basin related to the convergent thrusting of Dinaric-and ALCAPA-derived units was developed. On the southern side, N-NW verging thrust sheets were observed. On the opposite front, Triassic carbonates of ALCAPA were thrust several kilometres above Palaeogene formations to the SW. Dextral transpression is assumed for the Middle Miocene. Local deposition of Middle Miocene salt in the basin formed a detachment surface. Late Miocene sinistral strike-slip faulting resulted in a pull-apart basin above that part of the earlier flexural basin that has not been overthrust. The margins of the basin coincided with the fronts of earlier thrusts. Faults on the basin margins partly detached on the salt, decoupling the supra-salt basin fill from the underlying formations. Within the pull-apart basin, gravity sliding on the steep margins resulted in salt welds, detachment and roll-over folds.

This paper presents field observations and measurements from the Hawasina Window, Oman Mountains. An updated geological map is based partly on previous publications and four NEtrending cross-sections. Along each cross-section key structural features are described, illustrated and interpreted. Based on these (and other) observations several differences between our interpretation and the former published geological maps and cross sections were noted as follows.(1) Late Cretaceous original (Hamrat Duru; Haybi) nappes that formed during intra-oceanic obduction underwent out-of-sequence thrusting beneath the Semail thrust. The repetitions of the nappe complexes are out-of-sequence because: (a) repetition of original nappe packages; (b) the presence of Haybi-derived lenses along boundaries between two Hamrat Duru nappes; (c) the presence of sheared serpentinite in the same nappe boundaries. The Hamrat Duru and Haybi nappes are repeated three times.(2) The tectonic boundaries of the Hawasina Window are steep, normal- or strike-slip faults, unconformable to, and cutting the original nappe boundaries. A main strike-slip corridor at the southern edge of the Hawasina structure was mapped. The northern edge is a top-north thrust.(3) Ductile-brittle extension created mega-boudins of preserved nappe units and areas where complete nappe units are missing. Extension is present in Sumeini and Hamrat Duru units; therefore it is post-out-of-sequence thrusting.(4) Two main antiforms were recognised inside the Hawasina Window (Jabal Rais and its northward and southward continuations in Hamrat Duru units, and Jabals Mawq - Matid). Several folding phases were recognised and the two antiforms are the result of interference. A main, sub-horizontal axial plane, syn-regional cleavage folding is present in the whole Window. This folding gives top NE or N regional shear.(5) Structural dips of regional cleavage suggest a major NW-striking dome beneath the Hawasina Window. This dome would correspond to the upwarp of the Autochthon, similar to Al Jabal al-Akhdar. In the southern zone of this dome we observed several occurrences of small gypsum diapirs. The best outcrops of these features are in the Wadi ad Dil-Wadi Hawasina area, where the evaporite bodies rise from beneath the Hawasina nappes. We suggest that they originate from the underlying Arabian Platform, or they form the basal detachment of the Sumeini units. Our observations are fit into a proposed deformation scenario resulting from plate-tectonic events occurring at the Arabian Plate margin during Cretaceous – Tertiary time.

<p>The basement of the south-eastern part of the Miocene Pannonian back-arc basin is represented by the Tisza Unit. The deep structure of the Tisza unit is poorly studied, despite its significant geothermal and CH potential.  This work is a first step in our structural mapping project, which investigates the structures within the basement of the Pannonian Basin. <br /><br />The Tisza unit is composed of Proterozoic to Early Paleozoic poly-metamorphic basement rocks, and Late Paleozoic to Mesozoic sedimentary cover. The Tisza Unit is built up by three main nappes, the Mecsek, the Villány-Bihar and the Codru subunits. The Tisza Unit is exposed in inselbergs (Mecsek, Villány, Apuseni Mts.), however, most of it is covered by several km thick Miocene succession. The pore space containing energy source materials is located in the Miocene Pannonian Basin cover sediments, and in the fractured basement rocks near its surface and in their deeper part, especially in the Cretaceous sedimentary formation. Our research targets the better understanding of the Alpine shortening tectonics and structure of the Tisza Unit, with special attention to the structures of these tectonically buried sedimentary basement patches.<br /><br />In this study we use modern 3D seismic data sets and well data to investigate the central part of the Tisza Unit. Based on that, the Tisza Unit is a Late Cretaceous fold and thrust belt, which can be characterized by major thick-skinned nappes, and second-ordered thin-skinned structures. Such second-ordered structures are the active and passive roof-duplexes below the Villány nappe (Derecske), and out-of-the-syncline thrusts in the front of the Codru nappe (Vésztő). The basal thrust of the Villány nappe cuts across pre-existing normal faults and associated half-grabens, demonstrating the presence of the early Alpine rift-related structures. Major nappes are unconformably overlain by Santonian to Maastrichtian beds, nevertheless, the presence of growth-synclines in this succession indicates ongoing shortening after major nappe emplacement during the latest Cretaceous. The Cretaceous fold and thrust belt of the Tisza Unit is strongly overprinted by Miocene extensional and transtensional structures, which are related to the rifting of the Pannonian back-arc basin.</p>