| 1. |
- Ayarza, P, et al.
(författare)
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Integrated geological and geophysical studies in the SG4 borehole area, Tagil Volcanic Arc, Middle Urals: Location of seismic reflectors and source of the reflectivity
- 2000
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Ingår i: Journal of Geophysical Research. - : AMER GEOPHYSICAL UNION. - 0148-0227 .- 2156-2202. ; 105:B9, s. 21333-21352
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Tidskriftsartikel (refereegranskat)abstract
- Near-vertical incidence reflection seismic data acquired in the Tagil Volcanic Arc (Middle Urals) show the upper crust to be highly reflective. Two intersecting seismic lines located near the ongoing ∼5400 m deep SG4 borehole show that the main reflectivity strikes approximately N-S and dips ∼35°–55° to the east. Prominent reflections intercept the borehole at ∼1000, ∼1500, 2800–2900, ∼3400, and between ∼4000 and 5400 m, which correspond to intervals of low velocity/low density/low resistivity. The surface projections of these reflections lie parallel to the strike of magnetic anomaly trends. Multioffset vertical seismic profile (VSP) data acquired in the SG4 borehole show a seismic response dominated by P to S reflected converted waves from the moderately east dipping reflectivity and from a set of very steep east dipping reflectors not imaged by the surface data. Modeling of the VSP data constrains the depth at which reflectors intercept the borehole and suggests that the P to S conversions are best explained by low-velocity porous intervals rather than higher-velocity mafic material. The most prominent east dipping reflection on the surface seismic data is only imaged on VSP shots that sample the crust closer to the E-W seismic line. This discrepancy between the VSP and the surface seismic data is attributed to rapid lateral changes in the physical properties of the reflector. Surface and borehole data suggest that the low-velocity/low-density/low-resistivity intervals are the most important source of reflectivity in the SG4 borehole area, although lithological contrasts may also play a role. Drill cores from the these zones contain hydrothermal alteration minerals indicating interaction with fluids. Tectonic criteria suggest that they might represent imbricated fracture zones often bounding different lithologies and/or intrusions. Some of them might also represent high-porosity lava flows or pyroclastic units, common in island arc environments.
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| 2. |
- Brown D., Juhlin C., Tryggvason A., Steer D., Ayarza P., Beckholmen M., Rybalka A. and Bliznetsov M.
(författare)
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The Crustal Architecture of the Southern and Middle Urals from the URSEIS, ESRU, and Alapaev Reflection Seismic Profiles, in Orogenic Processes in the Paleozoic Uralides
- 2002
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Ingår i: Geophysical Monograph Series, AGU. ; , s. 33-48
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Tidskriftsartikel (refereegranskat)
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| 3. |
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| 4. |
- Juhlin, Christopher, et al.
(författare)
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Seismic imaging of reflectors in the SG4 borehole, Middle Urals, Russia
- 1997
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Ingår i: Tectonophysics. - : Elsevier. - 0040-1951 .- 1879-3266. ; 276:1-4, s. 1-18
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The upper crust in the Middle Urals is known to be highly reflective. However, it is not clear whether the observed reflections originate from lithological boundaries or from fault zones. The SG4 borehole located in the Tagil Synform of the Middle Urals, drilled to 5354 m as of August 1995, presents one opportunity to study the source of this reflectivity. The hole has penetrated several different lithologies as well as numerous tectonic or fracture zones. The upper 5070 m consist of island arc rocks which have presumably been thrust on top of basalts. To allow correlations between available surface seismic studies and the borehole observations vertical and offset seismic profile data were acquired in the borehole over the interval 520 m to 3940 m. Two shot points were used, a near offset one at 135 m from the wellhead and a far offset one at 1845 m from the wellhead. After processing, the borehole seismic data show numerous reflecting horizons. Many reflections correlate with major fracture zones, while others have no clear correlation with fracture zones nor lithological contrasts. The interval between approximately 4450 m and 5100 m, which is imaged below the bottom of the survey, shows a layered reflective pattern that correlates with the lower part of a flysch unit which ends at 5070 m. The basalts below appear to be relatively transparent. A prominent east-dipping reflector on a W-E CDP line about 700 m north of the wellhead is not clearly imaged on the borehole seismic. However, in a pilot hole which deviates a few hundred metres in the northerly direction from the main hole, a marked low-velocity zone is observed at the corresponding depth for this reflector, indicating its source to be from a fault zone. That the fault zone is not clearly observed on the borehole seismic data is attributed to 3D effects.
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| 5. |
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| 6. |
- Friberg, M, et al.
(författare)
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Europrobe seismic reflection profiling across the eastern Middle Urals and West Siberian Basin
- 2001
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Ingår i: Terra Nova. - : Blackwell Publishing. - 0954-4879 .- 1365-3121. ; 12:6, s. 252-257
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Tidskriftsartikel (refereegranskat)abstract
- New deep seismic reflection data provide images of the crust and uppermost mantle underlying the eastern Middle Urals and adjacent West Siberian Basin. Distinct truncations of reflections delineate the late-orogenic strike-slip Sisert Fault extending vertically to ∼28 km depth, and two gently E-dipping reflection zones, traceable to 15–18 km depth, probably represent normal faults associated with the opening of the West Siberian Basin. A possible remnant Palaeozoic subduction zone in the lower crust under the West Siberian Basin is visible as a gently SW-dipping zone of pronounced reflectivity truncated by the Moho. Continuity of shallow to intermediate-depth reflections suggest that Palaeozoic accreted island-arc terranes and overlying molasse sequences exposed in the hinterland of the Urals form the basement for Triassic and younger deposits in the West Siberian Basin. A highly reflective lower crust overlies a transparent mantle at about 43 km depth along the entire 100 km long seismic reflection section, suggesting that the lower crust and Moho below the eastern Middle Urals and West Siberian Basin have the same origin.
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| 7. |
- Juhlin, Christopher, et al.
(författare)
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Crustal structure of the Middle Urals: Results from the (ESRU) Europrobe seismic reflection profiling in the Urals experiments
- 1998
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Ingår i: Tectonics. - : American Geophysical Union (AGU). - 0278-7407 .- 1944-9194. ; 17:5, s. 710-725
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- As a contribution to Europrobe's seismic reflection profiling in the Urals (ESRU)project, three overlapping seismic reflection data sets were acquired in the Middle Urals. A 56 km long profile was registered over the Europe-Asia suture, two 25 km long intersecting profiles were collected over the Urals superdeep borehole (SG4), and an 80 km long profile was recorded eastward extending east toward the West Siberian Basin. Reflections on the seismic sections delineate several major middle to late Paleozoic thrust zones in the upper crust. These thrust zones have a bivergent geometry with westerly vergence west of the Uralian orogenic axis and easterly vergence to the east. The principal terrane boundaries are the Main Uralian Thrust Fault in the west and the Trans- Uralian Thrust Zone in the east. Normal faults are spatially associated with former thrust faults, or they crosscut them. The thrust and normal faults can be confidently correlated with surface geological features. Near-vertical and wide-angle seismic reflection profiling reveals thickening of the crust from about 45 km to approximately 53 km below the central axis of the Urals. East and west of the root zone, the lower crust is reflective, particularly toward the West Siberian Basin. We interpret the reflectivity of the crust below the East European Craton as pre-Uralian, whereas that toward the West Siberian Basin is interpreted as late orogenic. Although the principal tectonic features imaged by the seismic sections are probably of Paleozoic age, a post-Paleozoic origin for the lower crustal reflectivity in the east cannot be ruled out.
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| 8. |
- Juhlin, Christopher, et al.
(författare)
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Moho imbrication in the Middle Urals
- 2007
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Ingår i: Terra Nova. - : Wiley. - 0954-4879 .- 1365-3121. ; 19:3, s. 189-194
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Tidskriftsartikel (refereegranskat)abstract
- New processing of part of the Europrobe's Seismic Reflection Profiling in the Urals (ESRU) reflection seismic data in the Middle Urals shows a southwest-dipping Moho imbrication and crustal underthrusting that was not previously imaged. The area of thickening associated with it roughly coincides with a deepening of the Moho imaged by the GRANIT refraction data. This feature does not fit with the currently known Palaeozoic crustal architecture of the Uralides or with its geodynamic history. Geological data suggest that it is not related to a relict southwest-dipping subduction zone. Based on its lower crustal and Moho reflection seismic character it is presently interpreted to be a post-Uralide feature, possibly related to Mesozoic intraplate shortening in the area. Its coincidence with a locus of mild earthquake activity further suggests that it might be active today.
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| 9. |
- Kashubin, Artem S., et al.
(författare)
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The Krasnouralsky profile in the Middle Urals, Russia : a tomographic approach to vintage DSS data
- 2009
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Ingår i: Tectonophysics. - : Elsevier BV. - 0040-1951 .- 1879-3266. ; 472:1-4, s. 249-263
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Tidskriftsartikel (refereegranskat)abstract
- The Middle Urals region has been widely studied with geophysical methods over the past decades. An integrated program is in progress to summarize this knowledge, including modern reprocessing of controlled-source seismic data. This work is devoted to the Krasnouralsky DSS profile. We applied modern tomography inversion algorithms in 2D and 2.5D on first break traveltime picks from an archive catalogue. A number of initial models and various smoothing constraints were used to investigate the influence of starting models on the final model. Robustness and uncertainty of the recovered models were estimated with hypothesis testing and checkerboard tests. The recovered velocity structure shows a thicker crust below the contact of the West Uralian Zone and the Central Uralian Zone and below the Tagil–Magnitogorsk Zone. Deep high velocity anomalies on both sides of this zone are interpreted as crustal thinning or alteration of the crust by intrusions of mantle material. Our results suggest that it is worthwhile reinterpreting DSS traveltime data with modern inversion techniques.
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| 10. |
- Kashubin, S., et al.
(författare)
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Crustal structure of the Middle Urals based on seismic reflection data
- 2006
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Ingår i: European Lithosphere Dynamics. - London : Geological Society. - 1862392129 ; , s. 427-442
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- EUROPROBE-related seismic reflection surveys in the Middle Urals, Russia (latitude 56-62°) since 1993 have led to an increased understanding of the crustal structure and tectonic evolution of this region. A 400 km long profile now extends from the foreland basin in the west well into the West Siberian Basin in the east. Bivergent structures characterize the upper crust of the Uralide orogen, whereas the middle and lower crust generally contain gently west-dipping reflections. A crustal root is imaged down to almost 60 km beneath the exposed Urals. Below the foreland and the West Siberian Basin the lower crustal reflectivity is pronounced and the Moho lies at a depth of 40-45 km. Below the foreland on the recently acquired Serebrianka-Beriozovka profile, two sets of late arriving (20-25 s) reflections are present. One set reflects from a zone in the mantle at about 60-70 km depth that strikes ENE and dips about 45° to the SSE. The other set may represent imbricated lower crust. Major events during the Palaeozoic tectonic evolution of the Middle Urals were: continental and oceanic rifting (Late Cambrian to Early Ordovician); development of a passive continental margin (Mid-Ordovician to Mid-Carboniferous); intra-oceanic subduction below the Tagil arc (Silurian to Devonian); east-dipping subduction of the Baltica plate (Silurian to Early Devonian); possible subduction reversal with formation of the Alapaevsk island arc and the Krasnoturjinsk-Petrokamensk active continental margin (Devonian to Early Carboniferous); active building of a mountain belt and intrusion of collision-related granitic plutons (Carboniferous to Permian).
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