Thrust tectonics in the Wetterstein and Mieming mountains, and a new tectonic subdivision of the Northern Calcareous Alps of Western Austria and Southern Germany

We investigate the tectonic evolution of the Wetterstein and Mieming mountains in the western Northern Calcareous Alps (NCA) of the European Eastern Alps. In-sequence NW-directed stacking of thrust sheets in this thin-skinned foreland thrust belt lasted from the Hauterivian to the Cenomanian. In the more internal NCA major E-striking intracontinental transform faults dissected the thrust belt at the Albian–Cenomanian boundary that facilitated ascent of mantle melts feeding basanitic dykes and sills. Afterwards, the NCA basement was subducted, and the NCA were transported piggy-back across the tectonically deeper Penninic units. This process was accompanied by renewed Late Cretaceous NW-directed thrusting, and folding of thrusts. During Paleogene collision, N(NE)-directed out-of-sequence thrusts developed that offset the in-sequence thrust. We use this latter observation to revise the existing tectonic subdivision of the western NCA, in which these out-of-sequence thrusts had been used to delimit nappes, locally with young-on-old contacts at the base. We define new units that represent thrust sheets having exclusively old-on-young contacts at their base. Two large thrust sheets build the western NCA: (1) the tectonically deeper Tannheim thrust sheet and (2) the tectonically higher Karwendel thrust sheet. West of the Wetterstein and Mieming mountains, the Imst part of the Karwendel thrust sheet is stacked by an out-of-sequence thrust onto the main body of the Karwendel thrust sheet, which is, in its southeastern part, in lateral contact with the latter across a tear fault.

On the relationships between the Al2SiO5 polymorphs during formation of blastomylonites (North Yenisei Ridge)

Relevance. When mapping the vast areas of the Precambrian polymetamorphic complexes in the North Yenisei Ridge, there is a problem of metamorphism interpretation and phasing of geological development of a particular area along with thrust tectonics. The solution of these issues is also of great importance for the purposes of areas delineation of metamorphic rocks that are favorable for the detection of high-alumina (andalusite, kyanite, sillimanite) schists. Purpose of the work: to substantiate and itemize some geological prospecting, mineralogical and petrological indicator criteria for the development of high-alumina garnet-kyanite-staurolite blastomylonites of dislocation metamorphism formed by andalusite-bearing rocks of regional metamorphism. Research methodology: detailed mapping of structural-metamorphic zoning of dislocation (collisional) metamorphism in the Mayakon key area with sampling of polymetamorphic rocks for petrographic studies of mineral parageneses. Investigation of polished thin sections of polymetamorphic rocks by microprobe analysis with elucidation of minerals zoning, their chemical composition, calculation of the Р–Т paths of metamorphism and determination of the absolute age of blastomylonite formation based on the 40Ar/39Ar dating of biotite. Analysis and generalization of the results obtained for the Mayakon area and their comparison with other key areas of the North Yenisei Ridge. Results. At the Mayakon potential area, a progressive metamorphic zoning of kyanite-bearing blastomylonites has been identified, and the transitional I, outer II, middle III, and inner zones are determined as the dislocation metamorphism intensifies towards the Panimba thrust fault. Based on the compositions of garnets, biotite, and plagioclase, the P–T paths of the early regional metamorphism of andalusite-sillimanite type and late local kyanitesillimanite type were calculated. A list of geological prospecting, petrological and isotope-geochronological criteria for recognizing blastomylonites among rocks of regional metamorphism in thrust zones has been substantiated and itemized. Conclusions. Method of polymetamorphism reconstruction in the North Yenisei Ridge shows that tectonic inversion conditions took place in the Neoproterozoic, in the late Tonian era (~850 Ma ago In terms of occurrences, they are related to the final stage of the Grenville orogeny (1.1–0.85 Ga). The formation of blastomylonites of dislocation (collisional) metamorphism by metapelites of regional metamorphism in thrust zones is accompanied by an increase in the number of mineral phases and leads to a reduction in usable space of high-alumina andalusite schists.

The petrological and geochemical study of granitoid rocks from Mashhad area, Iran: Evidence for the Late Triassic Collisional Belt Northeast of Iran

<p>Mashhad granitoid complex is part of the northern slope of the Binalood Structural Zone (BSZ), Northeast of Iran, which is composed of granitoids and metamorphic rocks. This research presents new petrological and geochemical whole-rock major and trace elements analyses in order to determine the origin of granitoid rocks from Mashhad area. Field and petrographic observations indicate that these granitoid rocks have a wide range of lithological compositions and they are categorized into intermediate to felsic intrusive rocks (SiO<sub>2</sub>: 57.62-74.39 Wt.%). Qartzdiorite, tonalite, granodiorite and monzogranite are common granitoids with intrusive pegmatite and aplitic dikes and veins intruding them. Based on geochemical analyses, the granitoid rocks are calc-alkaline in nature and they are mostly peraluminous. On geochemical variation diagrams (major and minor oxides versus silica) Na<sub>2</sub>O and K<sub>2</sub>O show a positive correlation with silica while Al<sub>2</sub>O<sub>3</sub>, TiO<sub>2</sub>, CaO, Fe<sub>2</sub>O<sub>3</sub>, and MgO show a negative trend. Therefore fractional crystallization played a considerable role in the evolution of Mashhad granitoids. Based on the spider diagrams, there are enrichments in LILE and depletion in HFSE. Low degrees of melting or crustal contamination may be responsible for LILE enrichment. Elements such as Pb, Sm, Dy and Rb are enriched, while Ba, Sr, Nd, Zr, P, Ti and Yb (in monzogranites) are all depleted. LREE enrichment and HREE depletion are observed in all samples on the Chondrite-normalized REE diagram. Similar trends may be evidence for the granitoids to have the same origin. Besides, LREE enrichment relative to HREE in some samples can indicate the presence of garnet in their source rock. Negative anomalies of Eu and Yb are observed in monzogranites. Our results show that Mashhad granitoid rocks are orogenic related and tectonic discrimination diagrams mostly indicate its syn-to-post collisional tectonic setting. No negative Nb anomaly compared with MORB seems to be an indication of non-subduction zone related magma formation. According to the theory of thrust tectonics of the Binalood region, the oceanic lithosphere of the Palo-Tethys has subducted under the Turan microplate. Since the Mashhad granitoid outcrops are settled on the Iranian plate, this is far from common belief that these granitoid rocks are related to the subduction zones and the continental arcs. The western Mashhad granitoids show more mafic characteristics and are possibly crystallized from a magma with sedimentary and igneous origin. Thus, Western granitoid outcrops in Mashhad are probably hybrid type and other granitoid rocks, S and SE Mashhad are S-type. Evidences suggest that these continental collision granitoid rocks are associated with the late stages of the collision between the Iranian and the Turan microplates during the Paleo-Tethys Ocean closure which occurred in the Late Triassic.</p>

TYPE DESIGNS OF THE PALEOZOIC COMPLEX SECTIONS OF THE EAST EDGE OF THE PERI-CASPIAN DEPRESSION

The present article highlights the features of the geological structure, sedimentation conditions and the influence tectonic evolution factors on the petroleum potential within the eastern edge of the Precaspian basin. According to the features of the geological structure and lithological characteristics of the sedimentary formations of the eastern edge of the Precaspian basin, different facies zones can be distinguished, corresponding to the distinguished structural-formational zones with several types of Paleozoic sections. НЕФТЬ И ГАЗ 2021 1 (121) 7 ГЕОЛОГИЯ Based on the comparison of the Paleozoic sections for the eastern edge of the Precaspian basin it is concluded that collision tectonics was the major factor for sedimentation. Vertical facies succession influenced by tectonics and sea level fluctuations. Carbonate platforms played an important role in the distribution of sedimentary material and controlled the depth of the sea, which influenced on the composition and texture of the rocks. The presence of carbonate platforms was also reflected in the reduced thickness of the Lower Permian sediments, which are less presented within the carbonate platforms stratigraphic section comparing to the adjacent relatively deep-water areas located to the west outside the carbonate platforms. The structure of carbonate platforms was to the largest extent defined by the thrust tectonics and that controlled the distribution of oil and gas fields and potential traps.

Late Miocene thrust tectonics of the Latin Valley: insights from seismic lines (Central Apennines, Italy)

<p>In west-directed subduction zones, as the compression moves towards the foreland, the accretionary prism progressively expands to follow the hinge migration towards the east. Although late Miocene foreland propagation implies the shift of the thrust front, in the central Apennines, the effects of the Messinian compression can be observed on a much broader area, implying out-of-sequence thrusting in the rear.</p><p>In order to understand the Messinian involvement of the previously formed Tortonian belt-foredeep system, a regional reinterpretation is here provided. The analysis of publicly available 2D seismic reflection lines across the upper and middle Latin Valley and 10 wells enables the identification of two main seismostratigraphic units: i) the Meso-Cenozoic neritic carbonates and ii) the upper Tortonian siliciclastic pelitic and arenaceous turbiditic associations of the Frosinone Formation.</p><p>The most evident reflectors are the upper Cretaceous and upper Serravallian top paraconformities, which, due to tectonic repetition can be followed at different depths. We find that minor reflectors can be attributed to the several thrusts affecting folded Meso-Cenozoic neritic carbonates. This observation allows us, together with field and well evidences, to trace several thrust sheets characterized by a general top-to-the NE sense of shear. In a few sections from the Latin Valley (e.g. Line FR-309-80), we recognized the Meso-Cenozoic neritic carbonates being thrusted together with the Tortonian Frosinone Formation, on top of a laterally variably thick siliciclastic succession. This further syn-orogenic unit could be related to the early Messinian sandstones of the Torrice Formation, implying that out-of-sequence thrusting took place in the Latin Valley during the wedge-top sedimentation. The thin-skinned fold-and-thrust fabric is defined by en-échelon distributed thrusts, NNE- and ENE striking tear faults and minor pop-up structures often determining ideal traps for hydrocarbon and geothermal fluids. Finally, conjugated NW-striking high-angle normal faults crosscut the orogenic heritage and sets a horst and graben structure associated with continental deposition and the Volsci Volcanic Field.</p><p>The limited oil exploitation over the past century has targeted only the shallower siliciclastic traps and some evidences in the shallower neritic carbornate thrust sheets. At the light of our new interpretation, the deeper carbonate units could be a new focus for hydrocarbon accumulation and may furnish targets for geothermal and/or hydrocarbon research in the area. Future work aims at quantify the Tortonian and Messinian amount of shortening by taking into consideration the adjoining Volsci Range. Finally, our findings bear implications on geodynamic reconstructions and may represent an example of the geometry and kinematic evolution of platform derived thrust sheets and similar belts worldwide associated with W-directed subduction zones.</p>

Weakening mechanisms and the role of easy slip horizons in thrust belt development: a microstructural approach

<p>The Late Silurian Moine Thrust Zone (MTZ) of the NW Highlands of Scotland has long been fundamental to the understanding of the nature and processes that occur during thrust tectonics in the upper continental crust. This complex imbrication zone formed during final Scandian stages of the Caledonian orogeny when collision of Baltica and Laurentia led to WNW-ESE tectonic foreshortening of >100km. The MTZ juxtaposed greenschist to amphibolite facies Neoproterozoic metamorphic rocks of the Moine Supergroup over sequences of little metamorphosed Cambro-Ordovician and Neoproterozoic sedimentary rocks and their Neoarchean to Paleoproterozoic gneissic basement in a zone ranging from <1km to >20km wide.</p><p>The mechanical problems represented by thrust wedges being transported over such great distances without losing their internal cohesion has highlighted the role played by detachment structures and the need for mechanisms that create significant weakening along basal detachments that allow overthrusts to accommodate major horizontal displacements in the shallow crust. Field studies and use of section balancing techniques have highlighted that a substantial proportion of the displacement seems to be accommodated along detachments that follow specific stratigraphic levels.</p><p>Other than the Moine Thrust Mylonites and the mylonitised parts of the Cambrian Quartzites, relatively little is known about the grain scale deformation and potential weakening processes that have occurred in other parts of the MTZ. New lithological descriptions of the fault rocks and sedimentary protoliths observed in the Assynt, Durness and Eriboll areas are presented here and provide detailed microstructural evidence for the long-term weakening mechanisms that were operating at the time. These mechanisms are consistently related to the onset of grain size reduction, triggered by both chemical enhanced and geometric processes. These include feldspar alteration to fine phyllosilicates associated with cataclasis and dynamic recrystallization of quartz.</p><p>Pressure solution, evidenced by changes in the shape of minerals along cleavage surfaces and the presence of dissolution seams and caps, is widespread throughout the studied rock sequences. The profuse occurrence of this grain-scale mechanism makes it very likely that syn-deformational fluid-influx lead to the destruction of load bearing microstructural frameworks and the development of interconnected weak layers due to alteration, explaining the occurrence of detachments within impure layers of the predominantly quartzose Pipe Rock and Salterella Grit members. The progressive development of these interconnecting fine-grained weak layers resulting from incongruent diffusive mass transfer is enhanced in the more mineralogically heterogeneous units of the Cambro-Ordovician sedimentary sequence (in particular, Fucoid Beds dolomitic siltstones and Durness limestones) explaining the consistently observed slip localization in these horizons.</p>

Combination of satellite SAR and GNSS data of co-seismic deformation after the November 26, 2019 Albania earthquake: first results

<p>The November 26, 2019 a Mw 6.2 earthquake struck the city of Durres as well as several towns in the Northwestern of Albania. The event killed 51 people, injured more than 900 and destroyed several buildings in the epicentral area. This area is dominated by active thrust tectonics due to the collision between Adriatic and Eurasian plates. This study shows the first results about the co-seismic displacements field estimated by the analysis of satellite SAR and GNSS data. In particular, GNSS observations were acquired by a network of 18 continuous GNSS stations located in the Albanian area. Using the GAMIT/GLOBK, GNSS data were processed within a time period ranging from January 1, 2016 to December 31, 2019 and time series produced. Moreover, a number of ascending and descending radar images acquired by the Sentinel-1 satellite in the period of the seismic event were processed using the ESA SNAP software. Pre-seismic, co-seismic and post-seismic interferograms provided the LOS displacement maps of the event and characterized the main deformation phenomena produced by such an event. The first preliminary results about the co-seismic displacements will be presented and compared with some theoretical co-seismic displacement fields provided thanks to the knowledge of the fault system affecting the area.</p>