Геодинамическая интерпретация геолого-геофизической неоднородности литосферы Днепровско-Донецкой впадины

Впервые на основе результатов 3D гравитационного и магнитного моделирования с использованием данных ГСЗ, сейсмотомографии, геологического строения докембрийского фундамента и осадочного чехла рассмотрены геолого-геофизические неоднородности литосферы как показатели разных этапов формирования рифта – начального пассивного и последующего активного. Показана роль сдвиговых деформаций и вращательных движений при заложении и развитии рифта.Вперше за результатами 3D гравітаційного і магнітного моделювання з використанням даних ГСЗ, сейсмотомографії, геологічної будови докембрійського фундаменту та осадового чохла розглянуто геолого-геофізичні неоднорідності літосфери як показники різних етапів формування рифту — початкового пасивного і подальшого активного. Показано роль зсувів і обертальних рухів під час закладання і розвитку рифту.For the first time on the base of 3D gravity and magnetic modeling results with the use of the data of DSS, seis mic tomography, geological structure of the Precambrian basement, and sedimentary cover, the geologo- geophysical heterogeneities of the lithosphere are considered as indicators of different stages of the rift formation — the initial passive and subsequent active ones. The roles of shear deformations and rotational movements in the formation and development of the rift are shown

Sedimentary geology of the Middle Carboniferous of the Donbas region (Dniepr-Donets basin, Ukraine)

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Lithospheric structure along wide-angle seismic profile GEORIFT 2013 in Pripyat–Dnieper–Donets Basin (Belarus and Ukraine)

The GEORIFT 2013 (GR'13) WARR (wide-angle reflection and refraction) experiment was carried out in 2013 in the territory of Belarus and Ukraine with broad international co-operation. The aim of the work is to study basin architecture and deep structure of the Pripyat-Dnieper-Donets Basin (PDDB), which is the deepest and best studied Palaeozoic rift basin in Europe. The PDDB is located in the southern part of the East European Craton (EEC) and crosses Sarmatia-one of the three segments of the EEC. The PDDB was formed by Late Devonian rifting associated with domal basement uplift and magmatism. The GR'13 extends in NW SE direction along the PDDB strike and crosses the Pripyat Trough (PT) and Dnieper Graben (DG) separated by the Bragin Uplift (BU) of the basement. The field acquisition along the GR'13 (of 670 km total length) involved 14 shots and recorders deployed every similar to 2.2 km for several shot points. The good quality of the data, with first arrivals visible up to 670 km for several shot points, allowed for construction of a velocity model extending to 80 km depth using ray-tracing modelling. The thickness of the sediments (Vp <6.0 km s(-1)) varies from 1-4 km in the PT, to 5 km in the NW part of the DG, to 10-13 km in the SE part of the profile. Below the DG, at similar to 330-530 km distance, we observed an upwarping of the lower crust (with Vp of similar to 7.1 km s(-1)) to 25 km depth that represents a rift pillow or mantle underplate. The Moho shallows southeastwards from similar to 47 km in the PT to 40-38 km in the DG with mantle velocities of 8.35 and similar to 8.25 km s(-1) in the PT and DG, respectively. A near-horizontal mantle discontinuity was found beneath BU (a transition zone from the PT to the DG) at the depth of 50-47 km. It dips to the depth of similar to 60 km at distances of 360-405 km, similar to the intersecting EUROBRIDGE'97 profile. The crust and upper mantle structure on the GR'13 may reflect varying intensity of rifting in the PDDB from a passive stage in the PT to active rifting in the DG. The absence of Moho uplift and relatively thick crystalline crust under the PT is explained by its tectonic position as a closing unit of the PDDB, with a gradual attenuation of rifting from the southeast to the northwest. The most active stage of rifting is evidenced in the DG by a shallower Moho and by a presence of a rift pillow caused by mafic and ultramafic intrusions during the active phase. The junction of the PT and the DG (the BU) locates just at its intersection with the NS regional tectonic zone Odessa-Gomel. Most likely, the 'blocking' effect of this zone did not allow for further propagation of active rifting to the NW.Peer reviewe

Comparison of hydrocarbon gases (C1–C5) production from Carboniferous Donets (Ukraine) and Cretaceous Sabinas (Mexico) coals

The main purpose of this contribution is to compare the ability of Carboniferous coals from the Donets Basin of the Ukraine and Cretaceous coal from the Sabinas Basin of the Mexico to generate hydrocarbon gases (C1–C5). Two bituminous coals from the Donets Basin (2c10YD and 1l1Dim; 0.55 and 0.65%Rr respectively) and one bituminous coal from the Sabinas Basin (Olmos, 0.92%Rr) were studied using heating experiments in a confined-pyrolysis system. The highest rank reached during the heating experiments corresponds to the anthracite stage (2.78 and 2.57%Rr) for the 2c10YD and 1l1Dim coals and (2.65%Rr) for the Olmos coal. The composition of the generated (C1–C5) gases was evaluated using a thermodesorption-multidimensional gas chromatography. The results show that the Carboniferous Donets coals produced more wet gas and methane during pyrolysis than the Cretaceous Olmos coal. This is probably due to their higher liptinite (6–20%) and collodetrinite content and to the loss of a major part of the petroleum potential of the Olmos coal during natural coalification. C2–C5 compounds are mainly derived from the cracking of liquid hydrocarbons. Ethane is the most stable compound and formed from the cracking of higher hydrocarbon component. Large amounts of methane (up to 81 mg/g coal for the Donets coals and 50 mg/g coal for the Sabinas coal) were formed at high temperatures by cracking of previously formed heavier hydrocarbons and by dealkylation of the coal matrix. A linear relationship was observed between methane generation and the maturity level of both coal types

Devonian-Mississippian magmatism related to extensional collapse in Svalbard: implications for radiating dyke swarms.

BackgroundDespite extensive studies of the Mesozoic-Cenozoic magmatic history of Svalbard, little has been done on the Paleozoic magmatism due to fewer available outcrops.Methods2D seismic reflection data were used to study magmatic intrusions in the subsurface of eastern Svalbard.ResultsThis work presents seismic evidence for west-dipping, Middle Devonian-Mississippian sills in eastern Spitsbergen, Svalbard. The sills crosscut a late Neoproterozoic Timanian thrust system, which was reworked during Caledonian contraction. The sills are unconformably overlain by relatively undeformed Pennsylvanian-Mesozoic sedimentary rocks and crosscut by Cretaceous dykes of the High Arctic Large Igneous Province. The sills probably intruded along extensional fractures during post-Caledonian reactivation-overprinting of the late Neoproterozoic thrust system. Kimberlitic accessory minerals in exposed contemporaneous intrusions and the chemical composition of chromium spinel grains in Upper Triassic sedimentary rocks in Svalbard suggest that the Middle Devonian-Mississippian intrusions in eastern Spitsbergen show affinities with diamond-rich kimberlites in northwestern Russia. Overall, the sills were emplaced during a regional episode of extension-related Devonian-Carboniferous magmatism in the Northern Hemisphere including the Kola-Dnieper and Yakutsk-Vilyui large igneous provinces.ConclusionsThis work presents the first evidence for extensive Middle Devonian-Mississippian magmatism in Svalbard. These intrusions may be part of the Kola-Dnieper Large Igneous Province and intruded parallel to preexisting, Proterozoic-early Paleozoic orogenic structures. Their strike is inconsistent with a source from a potential mantle plume center in the eastern Barents Sea. Thus, the radiating emplacement pattern of the magmatic intrusions of the Kola-Dnieper Large Igneous Province are not the product of plume-related uplift but of structural inheritance. A similar line of reasoning is successfully applied to intrusions of the Yakutsk-Vilyui and High Arctic large igneous provinces

A volcanic scenario for the Frasnian–Famennian major biotic crisis and other Late Devonian global changes: More answers than questions?

Although the prime causation of the Late Devonian Frasnian–Famennian (F–F) mass extinction remains conjectural, such destructive factors as the spread of anoxia and rapid upheavals in the runaway greenhouse climate are generally accepted in the Earth-bound multicausal scenario. In terms of prime triggers of these global changes, volcanism paroxysm coupled with the Eovariscan tectonism has been suspected for many years. However, the recent discovery of multiple anomalous mercury enrichments at the worldwide scale provides a reliable factual basis for proposing a volcanic–tectonic scenario for the stepwise F–F ecological catastrophe, specifically the Kellwasser (KW) Crisis. A focus is usually on the cataclysmic emplacement of the Viluy large igneous province (LIP) in eastern Siberia. However, the long-lasted effusive outpouring was likely episodically paired with amplified arc magmatism and hydrothermal activity, and the rapid climate oscillations and glacioustatic responses could in fact have been promoted by diverse feedbacks driven by volcanism and tectonics. The anti-greenhouse effect of expanding intertidal–estuarine and riparian woodlands during transient CO2-greenhouse spikes was another key feedback on Late Devonian land. An updated volcanic presspulse model is proposed with reference to the recent timing of LIPs and arc magmatism and the revised date of 371.9 Ma for the F–F boundary. The global changes were initiated by the pre-KW effusive activity of LIPs, which caused extreme stress in the global carbonate ecosystem. Nevertheless, at least two decisive pulses of sill-type intrusions and/or kimberlite/carbonatite eruptions, in addition to flood basalt extrusions on the East European Platform, are thought to have eventually led to the end-Frasnian ecological catastrophe. These stimuli have been enhanced by effective orbital modulation. An attractive option is to apply the scenario to other Late Devonian global events, as evidences in particular by the Hg spikes that coincide with the end- Famennian Hangenberg Crisis

Palaeozoic high-grade metamorphism within the Centralian Superbasin, Harts Range region, central Australia

Dating of remnant detrital zircon from high-grade metasediments of the Harts Range Group (HRG) in central Australia shows that the sedimentary protoliths were deposited during the Neoproterozoic to Cambrian, demonstrably younger than Palaeoproterozoic metamorphic rocks of the surrounding Arunta Inlier. The inferred depositional age of the HRG indicates that it was deposited at the same time as sedimentary rocks of the former Centralian Superbasin, now represented by the Amadeus and Georgina structural basins adjacent to the Harts Range. Detrital zircon data from the sedimentary rocks in these basins show that both the unmetamorphosed and high-grade metamorphic sequences shared common source regions and display similar provenance changes with time. These similarities imply that the HRG is the high-grade metamorphic equivalent of the Centralian Superbasin, meaning that the well-studied patterns of sedimentation in the basin can be used to constrain tectonism that occurred at mid- to lower-crustallevels in the Harts Range. The detrital zircon data indicate that the HRG extends at least 100 km east of the Harts Range, possibly grading eastwards beneath cover into unmetamorphosed sedimentary rocks of the Warburton Basin. Granitoids from the lower part of the HRG have Early Cambrian crystallisation ages of - 520 Ma, around 45 million years older than metamorphism recorded by metamorphic zircon, which has ages between -475-460 Ma (the Larapinta Event). The granites appear to have been derived from partial melting of their Early Cambrian host rocks and were coeval with mafic magmas, forming a bimodal igneous complex. During the Early Cambrian, deposition in the Centralian Superbasin adjacent to the Harts Range was clastic-poor and was accompanied by a marine transgression in the southern part of the Georgina Basin, implying that the Harts Range region was actively subsiding. Deeperwater pelitic sedimentation in the Harts Range area at this time and the presence of bimodal magmatism are consistent with an extensional setting for Early Cambrian partial melting and magmatism, here termed the Stanovos Event. Continued extension and subsidence resulted in the formation of a shallow marine seaway across central Australia in the Early Ordovician, below which granulite-facies metamorphism of the HRG took place at -10-12 kbar (-30-35 km). This metamorphism was accompanied by the formation of a pervasive layer-parallel foliation and the intrusion of syn-tectonic mafic dykes. Rare metamorphic and igneous zircon ages at -475 Ma possibly date peak metamorphism of the Larapinta Event, while widespread metamorphic zircon overgrowths at -460 Ma are probably related to retrograde metamorphism. Burial of the HRG to lower crustal levels is interpreted to have taken place in a rift or transtensional setting, implying that burial took place primarily by sediment loading within an actively subsiding basin (the Irindina sub-basin). The -30-35 km depth of metamorphism indicated by thermobarometric data imply that the Irindina sub-basin was deeper than any other known basin in Earth history. Potential field modelling of magnetic and gravity data was unable to distinguish whether a prominent linear gravity high in the Harts Range region is due to a preserved thick remnant of the Irindina Sub-basin or a large mafic body in the lower crust. However, the intensity of the anomaly indicates that a large accumulation of mafie material is present at depth, consistent with the interpreted rift setting for both the Stanovos and Larapinta Events. U-Pb zircon dating of the Entia Gneiss Complex and adjacent Strangways Metamorphic Complex shows that Larapinta Event had little effect on the Palaeoproterozoic basement adjacent to the Irindina sub-basin, with evidence limited to rare Early Ordovician isotopic disturbance. This is consistent with the interpretation that the Larapinta Event took place within the lower part of a deep sub-basin rather than as a result of a contractional event that would have affected both the basement and cover sequences. Basin inversion and uplift closely followed the retrograde phase of the Larapinta Event, culminating in the Alice Springs Orogeny at --400-300 Ma. The HRG was exhumed at this time and thrust over Palaeoproterozoic basement of the Entia Gneiss Complex along a major crustal detachment. Metamorphic zircon overgrowths between -~360-330 Main both the basement and cover sequences, and granitoid intrusions in the HRG at -360 Ma confirm that the Alice Springs Orogeny was a major tectonothermal event in the Harts Range region. U-Pb dating of monazite indicates that the Entia Gneiss Complex was pervasively reworked by a flat-lying kyanite-grade foliation at - 336 Ma, which was subsequently deformed into a complex domal culmination, the Entia Dome. The flat-lying foliation and doming possibly reflecting extensional collapse towards the end of the Alice Springs Orogeny, following a prolonged period of N-S to NNE-SSW directed contraction