Uralides Research Articles

Zircons from Eclogite-Associated Rocks of the Marun–Keu Complex, the Polar Urals: Trace Elements and U–Pb Dating

The Marun–Keu complex plays a significant role in our understanding of the geological evolution of the Ural orogen; however, it remains poorly understood. This study aims to provide insights into the complex’s age, protolith composition, rock formation conditions, and its position in the geological history. The zircons from the host granitic gneiss are characterized by magmatic cores with an age of 473 Ma and metamorphic rims with an age of approximately 370 Ma. We suggest that the metamorphic rims were formed during eclogite metamorphism and that the metagranitoids hosting the eclogites experienced eclogite metamorphism simultaneously with the basic and ultrabasic rocks that are common in this area. Heterogeneous zircons were also isolated from the selvage of a pegmatite vein, in which four domains are distinguished, two to three of which can be identified within single grains, as follows: (1) igneous cores with an age of approximately 470 Ma and the geochemical characteristics of zircon crystallized in basic rocks; (2) zircons recrystallized during eclogite metamorphism with geochemical characteristics intermediate between those of the magmatic cores and true eclogitic zircon; (3) pegmatitic zircon, exhibiting the most sharply differentiated REE spectra of all four domains, characterized by a prominent positive Ce anomaly and a weakly expressed negative Eu anomaly; and (4) eclogitic zircon, observed in the form of veins and rims, superimposed in relation to the other three domains. The age of the latter three domains is within the error range and is estimated to be approximately 370 Ma. This indicates that the processes of eclogite metamorphism and the formation of pegmatites occurred at approximately the same time in the studied area.

The Late Devonian contraction along the Precaspian Basin north margin: Transpressional range building in the intracratonic domain

The evolution of intraplate sedimentary basins located in the vicinity of an active convergent plate boundary is often controlled by the collisional dynamics of the adjacent orogen. The transfer of compression from the orogen to the platform's interior results in the formation of complex structural geometry and kinematics that often reactivate older crustal faults, focus far-field stresses and control the evolution of associated sedimentary basins. One place where this localisation can be optimally understood is the Precaspian Basin, situated at the SE periphery of the East European Craton and bordered to the east by the Uralian orogen. The Precaspian Basin and its northern margin experienced long-term extension and subsidence interrupted by several short-lived shortening episodes. To understand the impact and role of pre-existing basement structures on the geometry and kinematics of the subsequent deformation, we analysed subsurface data from the northern margin of the Precaspian Basin by the means of 3D seismic interpretation correlated with wells and structural modelling. The analysis results provide new insights into the kinematic effects of the Late Devonian contraction event. The superposition of stratigraphic units above and below the angular unconformity suggests an intra-Famennian age of the deformation event. Steeply dipping bi-verging reverse fault zones associated with variable amounts of sinistral strike-slip movement component display an arcuate geometry, trending from WSW-ENE to NW-SE. The distribution of deformation indicates that this complex kinematic pattern was driven by a NE-SW oriented contraction and transpression, where faults show the characteristics of a restraining bend area. This area is interpreted as part of a regional transcurrent fault system developed on the northern periphery of the Precaspian Basin. Furthermore, the study results suggest that intralithospheric stress localisation transmitted by the Paleouralian subduction zone resulted in the reactivation of pre-existing basement structures, propagation of faults, and localized short-term exhumation of the Precaspian Basin north margin. Generated by the collision of Magnitogorsk volcanic arc with East European Craton, far-field stress transfer produced a zone of oblique deformation. These data and interpretation demonstrate that the northern margin of the Precaspian Basin is an excellent natural setting to investigate and better understand mechanisms of far-field strain localisation and reactivation of deformational structures in stable platform areas resulting in the intracratonic mountain building process.

Neotectonics and seismicity of the Urals

Introduction. The Ural submeridional mountain belt is an epipaleozoic orogen rejuvenated in the contemporary period (in the Neogene-Quaternary period in the last 20–30 million years). In the pre-Paleozoic era, the Urals developed as a submeridional upland, presumably as a result of the interaction (clash) between the East European and West Siberian plates. In the Mesozoic and Cenozoic eras, the Urals developed as a submeridional upland. As a result, the Ural Paleozoic orogen was largely (almost completely) destroyed by weathering, but in the second half of the Cenozoic time it was rejuvenated and experienced some growth again. The reason for the rejuvenation of the Urals could be the subhorizontal compression of the Urals crust between the East European (EEP) and West Siberian (WSP) plates, which occurred in the contemporary period (in the last 20–30 million years). The epicenters of contemporary Ural sensible earthquakes are localized in the East European Craton bordering the Urals along the boundaries of the Ufa obduction of the EEP. The intensity of Ural earthquakes ranges from 3–4 to 5–6 according to MSK-64 scale, and their magnitude is estimated in the range from 2.0 to 6.0–6.5. Research objective is to assess the seismicity and seismic activity of the Urals in the contemporary period and the relationship between Ural sensible earthquake epicenters and its rejuvenated tectonic structures. Methods of research. The spacing of sensible earthquake epicenters in the Urals relative to tectonic structures of different age was estimated by comparing the corresponding geological and tectonic schemes of the Urals. Results. The analysis showed that the epicenters of sensible earthquakes are located mainly along the periphery of the Ufa obduction of the EEP, which interacts with the Ural orogen. Most of the epicenters are located in the northeastern boundary of the Ufa obduction of the EEP. Earthquake epicenters are located both within the Ural orogen (in the zone of geodynamic influence of the Serov-Mauk regional submeridional fault), and within the eastern edge of the East European Craton, in the trough of the western piedmont of the Ural Mountains and adjacent areas.

Finnmark Platform Composite Tectono-Sedimentary Element, Barents Sea

Abstract The Finnmark Platform Composite Tectono-Sedimentary Element (CTSE), located in the southern Barents Sea, is a northward-dipping monoclinal structural unit. It covers most of the southern Norwegian Barents Sea where it borders the Norwegian mainland. Except for the different age of basement, the CTSE extends eastwards into the Kola Monocline on the Russian part of the Barents Sea. The general water depth varies between 200 and 350 m, and the sea bottom is influenced by Plio-Pleistocene glaciations. A high frequency of scour marks and deposition of moraine materials exists on the platform areas. Successively older strata sub-crop below the Upper Regional Unconformity (URU), which was formed by several glacial periods. Basement rocks of Neoproterozoic age were heavily affected by the Caledonian Orogeny, and previously by the Timanide tectonic compression in the easternmost part of the Finnmark Platform CTSE. Depth to crystalline basement varies considerably and is estimated to be from 4–5 to 10 km. Following the Caledonian orogenesis, the Finnmark Platform was affected by Lower–Middle Carboniferous rifting, sediment input from the Uralian Orogen in the east, the Upper Jurassic–Lower Cretaceous rift phase and the Late Plio-Pleistocene isostatic uplift. A total of eight exploration wells drilled different targets on the platform. Two minor discoveries have been made proving the presence of both oil and gas, and potential sandstone reservoirs of good quality identified in the Visean, Induan, Anisian and Carnian intervals. In addition, thick sequences of Permo-Carboniferous carbonates and spiculitic chert are proven in the eastern Platform area. The deep reservoirs are believed to be charged from Paleozoic sources. A western extension of the Domanik source rocks well documented in the Timan–Pechora Basin may exist towards the eastern part of the Finnmark Platform. In the westernmost part, charge from juxtaposed downfaulted basins may be possible.

Chromite Paleoplacer in the Permian Sediments at the East Edge of the East European Platform: Composition and Potential Sources

A chromite occurrence called the Sabantuy paleoplacer was discovered in the Southern Pre-Ural region, at the east edge of the East-European Platform in the transitional zone to the Ural Foredeep. A ca. 1 m-thick chromite-bearing horizon is traced at a depth of 0.7–1.5 m from the earth’s surface for the area of ca. 15,000 m2. The chromspinel content in sandstones reaches 30–35%, maximum values of Cr2O3 are 16–17 wt.%. The grain size of detrital chromspinel ranges from 0.15 to 0.25 mm. Subangular octahedral crystals dominate; rounded grains and debris are rare. The composition of detrital chromspinel varies widely and is constrained by the substitution of Al3+ and Cr3+, Fe2+ and Mg2+ cations. Chemically, low-Al (Al2O3 = 12 wt.%) and high-Cr (Cr2O3 = 52–56 wt.%) chromspinel prevail. The compositional analysis using discrimination diagrams showed that most chromites correspond to mantle peridotites of subduction settings. Volcanic rocks could be an additional source for detrital chromites. It is confirmed by compositions of monomineralic, polymineralic and melt inclusions in chromspinels. The presented data indicates that ophiolite peridotites and related chromite ore associated with oceanic and island-arc volcanic rocks, widespread in the Ural orogen, could be the main sources of the detrital chromspinel of the Sabantuy paleoplacer.

Features of earthquake epicenters and mineral deposits spatial relationship in the Urals

Introduction. Recent Ural mountain belt is an N-S Paleozoic orogen rejuvenated in the NeogeneQuaternary period. It separates the East European plate located to the west of it and the West Siberian plate located to the east of it. The Uralian orogeny presumably occurred at the Paleozoic time as a result 36 "Izvestiya vysshikh uchebnykh zavedenii. Gornyi zhurnal". No. 4. 2021 ISSN 0536-1028 of these plates interaction, which affected the geologic structure of the region. In the modern era, low tectonic activity in the bowels of the Urals continues supported by rare tangible earthquakes with a magnitude from 2.0–3.0 to 5.0–5.5, 3.0 – 3.5 on the average, and the intensity in the epicenter from 3.0–4.0 to 5.0–6.0 on MSK-64 scale. Research aim is to analyze the spatial relationship of sensible earthquakes epicenters and mineral deposits in the Urals. Research methodology included estimating the position of Ural earthquakes epicenters and mineral deposits relative to the geologic and tectonic structures of Paleozoic time, recent epoch, and the modern era. Research results. Most earthquake epicenters in the Urals are concentrated within the western part of the Uralian Orogeny to the west of the Main Uralian Fault (MUF), while most mineral deposits, especially ore deposits, are concentrated within the eastern part of the Uralian orogeny to the east of MUF. In the axial zone of MUF, earthquake epicenters are close and sometimes coincide. Consequently, the processes of ore deposits and earthquake foci formation are of a similar nature

Korotaikha Composite Tectono-Sedimentary Element, Northwestern Russia

Abstract The Korotaikha Composite Tectono-Sedimentary Element constitutes the northeastern part of the Timan–Pechora petroleum province. It has evolved through rifting, continental margin development, and a two-stage collisional phase related to the Uralian Orogeny in the Late Artinskian–Late Permian and the Pay-Khoy Orogeny in the Late Triassic. In the course of the later phase, the sedimentary cover was delaminated along the Upper Ordovician evaporites, which produced general uplift. The complex tectonostratigraphic history resulted in the deposition of an up to 15 km-thick sedimentary section that has all the essential ingredients for a prolific petroleum system, including the world-class Domanik source rock and a wide variety of structural and stratigraphic traps. Nevertheless, up to now, no commercial discoveries have yet been made. A review of the geological setting and petroleum habitat suggests that the petroleum systems development was more complex than was assumed previously. The amount of uplift and erosion related to the updip displacement on the salt detachment was underestimated. Reinterpretation of the available data shows the presence of large untested exploration opportunities including duplex thrust sheets and subsalt structures related to squeezed diapirs.

Structural Reconstruction of the Middle Uralian Part of the Uralian Orogen at the Initial Stage of Its Formation: Evidence from Clay Geochemistry

The Uralian foredeep is a classical marginal structure located on the foreland of the Late Paleozoic Uralian Orogen. It is subdivided into several depressions/sedimentation basins. This paper presents the analysis of the REE and Th distribution in the Middle Carboniferous and Lower Permian clay rocks of the Yuryuzan–Sylva Depression. This structure, like other depressions of the foredeep, is made up of diverse associations of the first sedimentation cycle clastic and clay rocks, which were formed during the orogen erosion. In the (La/Yb)N–Eu/Eu* and (La/Yb)N–Th diagrams, individual and average data points are confined to the field of bottom sediments of mouths of modern rivers draining volcanic provinces. This likely suggests a homogeneous composition of orogen provenance in the Carboniferous and Early Permian.

Regional correlation and seismic stratigraphy of Triassic Strata in the Greater Barents Sea: Implications for sediment transport in Arctic basins

AbstractThe Greater Barents Sea Basin (GBSB) in Arctic Russia and Norway is an intracratonic basin that accommodated an enormous amount of sediment during the Triassic. These deposits are up to 4.5 km thick over an area 2,500,000 km2, and consist of marine mudstones and mudstone‐rich fluvio‐deltaic topsets with sandstone‐dominated fluvial channels. The basin is well‐studied and data‐rich, but regional correlation between different parts is lacking. Provenance data from adjacent Arctic basins have been interpreted to imply sediment transport from the Ural orogen across the GBSB, but these are disputed because of great transport distances, poorly constrained sediment‐transport directions and unknown timing of bypass. We integrated data from 3,238 seismic lines, 257 wells and palynostratigraphy, as well as published outcrop data, to create the first unified stratigraphic framework for the Triassic deposits across the entire GBSB. Results show that (1) sediment was transported northwest by one linked sedimentary system stretching across the entire basin; (2) sediment was derived from a source in the east comprising the Urals and West Siberia; (3) the main stratigraphic boundaries are major flooding surfaces which can be traced throughout the basin; and (4) significant amounts of sediment overspilled from the Barents Sea into adjacent sedimentary basins, starting with the Lomonosov Ridge from the Early Triassic, and into basins to the northwest (e.g. Sverdrup, Chukotka) during the late Carnian. These results provide a better understanding of geodynamics and provenance data in the Arctic, to improve the prediction of reservoirs in the area, and indicate a protracted uplift‐history of the northernmost Urals that started in the Carnian ~237 Ma. Furthermore, it shows how large intracratonic basins interact with uplands and subside over tens of millions of years.

Sapphire-bearing magmatic rocks trace the boundary between paleo-continents: A case study of Ilmenogorsky alkaline complex, Uralian collision zone of Russia

Metamorphic gem corundum (mainly ruby) deposits are robust indicators of continent-continent collision processes. However, a systematic link of primary magmatic blue sapphire occurrences to orogenic belts is less understood. An example is the Ilmenogorsky alkaline complex, within the Ilmen Mountains region and part of the Uralian orogenic belt. The mobile belt is a product of the collision among Kazakhstania, Laurussia, and Siberia continents prior to the closure of the Paleo-Uralian ocean and formation of the Laurasia supercontinent (330–250 Ma). It is believed that the alkaline complex became inсluded into the separate Sysertsk-Ilmenogorsk microcontinent with unconstrained borders, when sandwiched between Kazakhstania and Laurussia during that collision. Paleo-reconstructions illustrate that magmatic and metasomatic sapphire deposits linked to alkaline magmatism trace the natural boundary of the “lost” microcontinent with a high precision. The syenite pegmatites of alkaline complex carried unusually large corundum-blue sapphire megacrysts that have recorded the multi-stage development of the Ilmenogorsky complex. The deposits were formed at about 275–295 Ma ago as reconstructed by in situ LA-ICP-MS U–Pb zircon dating. This formation stage corresponds to a broader continental collision process followed by the formation of Uralian orogeny in the area of the Ilmenogorsky complex. One pegmatite deposit, the “298” mine, is characterized by the occurrence of unusually large corundum megacrysts. The analyses of Rb–Sr isotopic system in the rocks from this deposit revealed two isochrons at 249 ± 2 Ma and 254 ± 22 Ma implying a late stage modification of original pegmatites. The timing of this stage corresponds to the limited post-collision stretching time. Hence, corundum-blue sapphire studied from magmatic (syenites) and metasomatic rocks linked to alkaline rocks in Uralian orogen suggests as a promising indicator for constraining the timing of continent-to-continent collision processes.

Constraining stratal architecture and pressure barriers in the subsalt Karachaganak Carboniferous carbonate platforms using forward stratigraphic modelling

Predicting reservoir quality and pressure barriers is a challenging task in carbonate systems. In this paper, we present new model results from the Lower Carboniferous Serpukhovian carbonates in the Karachaganak Field (Northern Kazakhstan), which is characterized by complex facies architectures and reservoir compartmentalization. The Serpukhovian sequence at Karachaganak is poorly imaged by seismic due to the presence of thick Permian salt canopies. The carbonate sequence comprises two carbonate build-ups: a larger Main build-up (MBU) in the eastern portion of the field, and a smaller isolated Western build-up (WBU). We used diffusion-based DionisosFlow forward stratigraphic modeling (FSM) coupled with a CougarFlow sensitivity analysis workflow to (1) review sub-salt seismic horizon picks based on process-modeling constraints, (2) understand the regional controls on the stratigraphic stacking patterns, (3) understand the distribution of reservoir facies, including potential lateral pressure barriers, and (4) constrain the impact and uncertainties of our choice of boundary conditions in the model. Results point out the need for revisions of existing reservoir-scale static models as FSM simulations indicate that the current seismic reflector pick for the base of the Serpukhovian Stage below the WBU is incompatible with the seismic geometries and facies distribution for this system. To reconcile modelling results with existing seismic geometries, the base of the Serpukhovian stage is expected to be about 180 m higher in the stratigraphy. This suggested revision is also supported by the drilling of a recent well that penetrated the top of the Permian 200 m higher in the stratigraphy on the WBU than anticipated. Modeling results also show that fast regional subsidence rates were the primary control for the Early Serpukhovian aggradational stacking pattern, but that slowing subsidence rate during the Late Serpukhovian due to the Uralian orogeny resulted in a switch to progradational sequence patterns. The forward stratigraphic model additionally demonstrates the major role of wind direction and short-term eustatic changes on the presence and distribution of reefs and breccia reservoir facies. Models show that the clinoforms’ angle of repose varies between the leeward and windward sides of the build-up, which leads to the deposition of mud draping on the leeward side that acted as fluid barriers. The presence and distribution of the reservoir and mud facies in the model can explain the observed reservoir compartmentalization at Karachaganak. Finally, our forward stratigraphic modeling workflow coupled with uncertainty analysis provides new quantitative constraints to understand the impact of diffusion coefficients and sediment production rates on the vertical and lateral reservoir heterogeneities and associated lateral pressure-barriers.

Carboniferous Magmatism in the Polar Urals

Dikes and sills of dolerites, essexite–dolerites, diorites, monzodiorites, and lamprophyres belonging to the Musyur (Malyi Khanmey) hypabyssal complex (Polar Urals) cut all Ordovician–Middle Devonian oceanic and island arc formations. Based on the geological data and previous isotope dating, the age of this complex is estimated from the end of the Late Devonian to the Early Triassic. The 40Ar/39Ar dating of hypabyssal magmatic bodies (various intrusive phases) of the Musyur complex was performed for the first time for the northern part of the Urals. The following 40Ar/39Ar ages were obtained: 349 ± 3, 347 ± 9, 339 ± 4, 334 ± 3, and 313 ± 10 Ma. They recorded the collision of the Polar Ural island-arc system with the continent of Arct–Laurussia (Arctida + Baltica + Laurentia), which led to the formation of the Carboniferous Early Ural Orogen. The prevailing northwestern (transversely to the supposed orogen) strike of most dikes in the Toupugol–Khanmeyshor area, predominantly the subduction zone geochemical features of the rocks (low and moderate TiO2 contents (0.7–2.1 wt %), P2O5 (0.1–0.8 wt %), enrichment in large-ion lithophile elements (Cs, Rb, Ba, Pb, Sr) compared to high-field-strength trace elements, the Ta–Nb minimum, and Pb and Th–U maxima), and the Early Carboniferous age estimates (349–334 Ma) lead to the conclusion that they probably formed in a syncollisional setting. The orthogonal northeastern (along the orogen axis) strike of some dikes (essexite–dolerites in more southerly regions), significantly higher concentrations of TiO2 (3.1–3.6 wt %), P2O5 (0.6–1.3 wt %), high-field-strength (Ta, Nb) and most rare earth elements (Eu, Gd, Tb, Dy, Y, Ho, Er, Tm, Yb, Lu), which are more typical for rift-related and intraplate igneous rocks, and their Late Carboniferous age (313 Ma) may testify to their emplacement in a post-collision setting.

The importance of trace element analyses in detrital Cr‐spinel provenance studies: An example from the Upper Triassic of the Barents Shelf

AbstractInvestigations of sandstone provenance often involve U–Pb dating and chemical/mineralogical investigations of detrital minerals that are stable in sediments. As most stable detrital minerals are from felsic–intermediate rocks, investigations of the only mafic–ultramafic mineral considered stable in sediments, chromian spinel (Cr‐spinel), can reveal contributions from mafic–ultramafic sources. Cr‐spinel chemical compositions are tied to petrogenesis, making it possible to identify the nature of, and differentiate between, potential sources. Earlier detrital Cr‐spinel studies have focused on major and minor element compositions, however, the advent of laser‐ablation analytical techniques now allow routine mineral trace element analyses. Here, we integrate major, minor and trace element compositions of detrital Cr‐spinel from sandstones with a well‐characterised provenance from the Triassic (Anisian to Early Norian) Snadd and De Geerdalen formations of the Barents Shelf. The analysed Cr‐spinel compositions are depleted in the major element cations Fe3+, Al and Mg and enriched in Cr and Fe2+. Relative to MORB chromite, the minor and trace element data show high concentrations of Zn, Co and Mn, low concentrations of Ni and Ga and variable concentrations of Ti, V and Sc. The major element compositions of the detrital Cr‐spinel are similar to ophiolite‐associated Cr‐spinel, while the trace element compositions indicate a more complex petrogenesis influenced by metamorphic alteration. The compositional variations between sample locations are small, suggesting similar source rocks for the detrital Cr‐spinel throughout the study area. The most likely sources of the Cr‐spinel grains are metamorphosed ophiolite complexes in the Uralian Orogen, in accordance with earlier provenance studies. The novel addition of trace element compositions to detrital Cr‐spinel studies adds significant source‐sensitive information.

Prospects for the titanium carrying Triassic formations of the Bolshaya Synya depression of the Pre-Uralian marginal flexure

It was established potentially industrial titanium-containing terrigenous rocks from the Lower and Middle Triassic formations of the southern part of the Bolshaya Synya depression, Pre-Uralian marginal flexure. Sandstones contain the bulk of productive mineralization and makeup about 80% of the Triassic section. Sandstones are represented by weakly lithified, finely grained lithoclast greywackes scattered in the hands with weakly rounded unsorted fragments, with pore, film, and contact type of cement form by hydrogetite and illite and chlorite. The proportion of relatively strong sandstones with calcite-siderite cement does not exceed 10% of the studied section. The deposits are formed in alluvial and pluvial, lacustrine depositional environments within the wide alluvial plain. The rocks belong to the upper part of the thick Permo-Triassic continental molasses formed in compensated depressions as a result of the destruction of the Paleo Uralian Orogeny. The main minerals of the heavy fraction are epidote, ilmenite, titanomagnetite, and amphibole; the minor minerals are chlorite, goethite, martite, pyroxene, chrome spinel and a group of garnets. The share of zircon does not exceed the first percent. The main mineral concentrator of titanium is ilmenite, the minor minerals are manganilmenite, titanomagnetite, titanite, leucoxene aggregates, rutile, and pyrophanite. The hypothetical primary source of ilmenite was epidote and amphibole contains shale or epidote containing amphibolite formed from a mafic substrate. The thickness of titanium contains layers is 1–4 m with an ilmenite content of more than 30 kg/m3. At the local level, ilmenite and titanomagnetite mineralization is concentrated in the form of small jets, lenses, puffs, and interlayer bodies. The average contents of ilmenite are comparable with those of the well-known titanium and zirconium placer deposits in Russia. The data presented in the article make it possible to predict the existence of new titanium contains region in the Triassic deposits of the south part of the Bolshaya Synya depression. The productivity of the region should be associated with continental ilmenite placers.

Shallow reworking of magmatic zircon grains of latest Neoproterozoic (Timanian) age in serpentinite of the Voykar Massif, Polar Urals: new constraints from U-Pb isotopic data, and first trace elements and Lu-Hf isotopic data

ABSTRACTThe Voykar Massif of the Polar Urals in Russia consists of an ultramafic complex (mantle section) in the northwest, followed by a late Cambrian to Silurian mafic complex (intra-oceanic primitive island arc) and early Devonian intrusive rocks of an evolved island arc to the southeast. These complexes represent tectonic nappes thrust over the East European continental margin during the late Palaeozoic Uralian Orogeny. LA-ICP-MS U-Pb dating of zircon grains (n = 42) from an antigorite-serpentinite lens within the mafic complex yielded a Concordia age of 542 ± 2 Ma with an age range of 549–527 Ma. Additionally, few grains contain inherited domains with ages between ~990 and 3277 Ma. Hafnium isotopic data of the main age group show 176Hf/177Hft from 0.28242 to 028249 and εHft ranging from +1.9 to −6.5. The evolved Hf isotope data and the trace-element composition of the zircon grains point to an involvement of a continental crustal component in the parental magma. The zircon grains originate from igneous rocks formed during the Timanian Orogeny that affected the East European margin in the latest Neoproterozoic. During the Timanian or Uralian Orogeny, the magmatic zircons were eroded and shallowly recycled into the serpentinised mantle above the subduction zone. Finally, Uralian thrusting led to juxtaposition and imbrication of the zircon-bearing serpentinite and intra-oceanic volcanic rocks of the mafic complex.

U-Pb and oxygen isotope characteristics of Timanian- and Caledonian-age detrital zircons from the Brooks Range, Arctic Alaska, USA

AbstractThe Devonian connection between the Brooks Range of Alaska, USA, with the continental margin of Arctic Canada and its subsequent Jurassic–Cretaceous counterclockwise rotation to form the Amerasian Basin, is a highly debated topic in Arctic tectonics. This resource-rich region was assembled from terranes that formed part of Laurentia or Baltica, or were juvenile oceanic arcs in the early Paleozoic that were brought together during Caledonian Orogenesis and the subsequent collision that formed Pangea (Uralide Orogeny). Elements of these orogens, as well as older ones, are predicted to occur in the Brooks Range of Arctic Alaska. This study presents the first combined zircon U-Pb and oxygen data from six Brooks Range metasedimentary units with assumed Neoproterozoic to Devonian ages. Three distinct detrital zircon patterns are identified in these units: (1) those with Neoproterozoic maximum depositional ages characteristic of the Timanide Orogen of northern Baltica and adjacent parts of Siberia, (2) an almost unimodal Siluro–Ordovician (443.5 ± 2.3 Ma) detrital zircon population consistent with the oceanic Apoon arc believed to have existed off shore of northern Laurentia and to have accreted to the North Slope subterrane during the Caledonian event, and (3) those with Middle Devonian maximum depositional ages consistent with post-accretion extension during the final (Scandian) phase of Caledonian Orogenesis. Oxygen isotopes from the same zircons reveal minor to significant crustal contamination with approximately two thirds (n = 255/405) having δ18O values >5.9‰ (above the mantle field of 5.3 ± 0.6‰). Pattern 1 units exhibit a progressive increase in δ18O values throughout the Proterozoic (5.99 to 9.29‰) indicative of increasing crustal growth and Timanide age zircons yield average δ18O values of 7.18 ± 0.64‰ (n = 26) suggestive of more crustal influence than Caledonian age zircons, possibly reflecting northern Baltica signatures. The unimodal population in Pattern 2 yields average δ18O values of 5.49 ± 0.66‰ (n = 17) and 6.02 ± 0.27‰ (n = 23) prior to and during, respectively, the main Caledonian event and suggest derivation from Devonian juvenile arc sources possibly representing the initiation of the collision between Laurentia and Baltica. Similar to Pattern 1, the δ18O values associated with Pattern 3 show a progressive increase in δ18O values throughout the Proterozoic (5.00 to 9.39‰). However, Pattern 3 also exhibits a distinct juvenile fingerprint (6.13 ± 0.24‰, n = 51) during the main Caledonian event and a slight increase to 7.12 ± 1‰ (n = 7) in post-Caledonian zircons possibly suggest correlating with a post-accretion phase in which proximally sourced zircon-bearing detritus was deposited in extension-related basins marking the joining of Laurentia and Baltica.

Сравнительная характеристика песчаных пород уфимского яруса в Соликамской впадине

The results of study of sands rocks of the Ufimian Stage in the wells cross-sections of the Solikamsk depression allowed determining evolution of their composition expressed in the change from predominantly oligomictic quartz partially with fragments of rock to polymictic greywacke presented mostly by the fragments of volcanic rock. This change may be resulted from successive erosion from external to internal zone of the Uralian orogen or shifting the base level of erosion eastward. Facial analysis of rock allowed identifying that the sedimentation initially occurred in the lagoon conditions following the shallow-water and deltaic (Solikamsk time), and continental lake and river (Sheshminskiy time) conditions. The obtained results allowed restoring paleogeographic and tectonic conditions of sedimentation. In the latitudinal section of the Solikamskaya depression, a regular variation of sand material from the east (Uralian orogenic belt) to the sea basin (westward) was revealed, and the deposits were associated with channel and fan deltaic facies. Overlying continental lacustrine, alluvial, and proluvial sediments, are widely developed only at the southwestern part of the basin.

Architecture, deformation style and petrophysical properties of growth fault systems: the Late Triassic deltaic succession of southern Edgeøya (East Svalbard)

AbstractThe Late Triassic outcrops on southern Edgeøya, East Svalbard, allow a multiscale study of syn‐sedimentary listric growth faults located in the prodelta region of a regional prograding system. At least three hierarchical orders of growth faults have been recognized, each showing different deformation mechanisms, styles and stratigraphic locations of the associated detachment interval. The faults, characterized by mutually influencing deformation envelopes over space‐time, generally show SW‐ to SE‐dipping directions, indicating a counter‐regional trend with respect to the inferred W‐NW directed progradation of the associated delta system. The down‐dip movement is accommodated by polyphase deformation, with the different fault architectural elements recording a time‐dependent transition from fluidal‐hydroplastic to ductile‐brittle deformation, which is also conceptually scale‐dependent, from the smaller‐ (3rd order) to the larger‐scale (1st order) end‐member faults respectively. A shift from distributed strain to strain localization towards the fault cores is observed at the meso to microscale (<1 mm), and in the variation in petrophysical parameters of the litho‐structural facies across and along the fault envelope, with bulk porosity, density, pore size and microcrack intensity varying accordingly to deformation and reworking intensity of inherited structural fabrics. The second‐ and third‐order listric fault nucleation points appear to be located above blind fault tip‐related monoclines involving cemented organic shales. Close to planar, through‐going, first‐order faults cut across this boundary, eventually connecting with other favourable lower‐hierarchy fault to create seismic‐scale fault zones similar to those imaged in the nearby offshore areas. The inferred large‐scale driving mechanisms for the first‐order faults are related to the combined effect of tectonic reactivation of deeper Palaeozoic structures in a far field stress regime due to the Uralide orogeny, and differential compaction associated with increased sand sedimentary input in a fine‐grained, water‐saturated, low‐accommodation, prodeltaic depositional environment. In synergy to this large‐scale picture, small‐scale causative factors favouring second‐ and third‐order faulting seem to be related to mechanical‐rheological instabilities related to localized shallow diagenesis and liquidization fronts.

U–Pb and Hf isotope analysis of detrital zircons from Devonian–Permian strata of Kotel’ny Island (New Siberian Islands, Russian Eastern Arctic): Insights into the Middle–Late Paleozoic evolution of the Arctic

U–Pb and Lu–Hf isotope analyses of detrital zircons collected from the Devonian–Permian strata of Kotel’ny Island (New Siberian Islands, Eastern Russian Arctic) provide vital information about provenance areas and history of the poorly studied Paleozoic basement of the Laptev and East Siberian shelves. Based on detrital zircon signatures, our study reveals that the studied succession can be divided into two distinct groups: Devonian–Lower Carboniferous and uppermost Carboniferous–Permian. U–Pb and Lu–Hf isotope signatures of detrital zircons from the Devonian–Lower Carboniferous deposits correspond to well-known Precambrian–Early Paleozoic magmatic and metamorphic events within the northern part of Baltica, indicative of a peri-Baltican affinity of the New Siberian Islands during this time. A lack of zircon ages close to the depositional age of the formation, along with a mature composition of the sandstones, suggest that the Devonian–Lower Carboniferous succession formed as a result of extensive sediment reworking from a distal provenance. By contrast, uppermost Carboniferous–Permian sandstones have an immature composition, with numerous young detrital zircons close to the age of sedimentation and Hf signatures typical of a continental arc environment. We therefore suggest that the provenance for these younger deposits was located within a coeval orogeny and based on previous studies, we conclude that these deposits were sourced from the north-western part of the Uralian Orogen.

Late Paleozoic – Mesozoic tectonic evolution of the Eastern Taimyr-Severnaya Zemlya Fold and Thrust Belt and adjoining Yenisey-Khatanga Depression

Combined structural, thermochronological and geochronological studies were carried out to unravel the complex late Paleozoic – Mesozoic tectonic evolution of the eastern Taimyr – Severnaya Zemlya Fold and Thrust Belt, along with the adjoining Yenisey-Khatanga Depression and Olenek Fold Zone. New detailed field mapping, a fault and fold geometry and kinematic study, and paleostress reconstruction were undertaken for key areas within the Central and Southern Taimyr domains and the Olenek Fold Zone. Thirty seven samples were used for apatite fission track (AFT) analysis along with two samples for U-Pb zircon granite dating, and three samples for Ar-Ar metamorphic muscovite dating.The late Paleozoic (Early Carboniferous – Permian) tectonic event is recognized only in a relatively narrow zone including the Northern Taimyr Domain and part of the Central Taimyr Domain. It started in the Early Carboniferous (Visean) and is synchronous with the earliest stages of collision in the Uralian Orogen. Our results reveal a widespread distribution of latest Triassic – earliest Jurassic and Cretaceous deformations. The latest Triassic – earliest Jurassic tectonic event significantly overprinted the Northern and Central Taimyr domains and original unaltered late Paleozoic AFT ages are identified only locally. New completely reset AFT cooling ages group at 195-180 Ma, in reasonable agreement with structural data. Older Neoproterozoic and late Paleozoic Ar-Ar ages of metamorphic muscovite are retained, demonstrating that the dated rocks were not heated above 300 °C. An Early Cretaceous tectonic event is inferred from both the structural study and ca. 115–125 Ma AFT cooling ages, and is most widespread in the Southern Taimyr Domain, Olenek Fold Zone and adjoining parts of the Yenisey-Khatanga Depression, modifying older geological structures. A younger Late Cretaceous tectonic event at ca. 100-60 Ma is also inferred from AFT cooling ages, but its distribution is poorly constrained.Our study reveals that the distribution of late Mesozoic tectonic events has been significantly underestimated in previous structural studies of the region. The latest Triassic – earliest Jurassic and Cretaceous tectonic events are easily correlated with those in the Pai-Khoi – Novaya Zemlya and northern Verkhoyansk fold and thrust belts.