Inessa V. Golovanova

Composition of the Uralide crust from seismic velocity (Vp, Vs), heat flow, gravity, and magnetic data

Abstract P-wave velocity (Vp), S-wave velocity (Vs), Poisson’s ratio (σ), heat flow, potential field, and surface geological data are integrated to constrain a model for the composition of the Uralide crust along the URSEIS transect. The model is constructed using published laboratory measurements of Vp, Vs, σ and density for a variety of crustal rock types. These laboratory data have been corrected for depth (pressure) and the Uralides temperature–depth function. The model shows clear differences between the composition of the old continental crustal nucleus of the East European Craton and the newly added crust of the accreted arc terranes to the east. The crust of the East European Craton is more felsic than that of the Magnitogorsk and East Uralian zones, and the latter two have a lowermost crust whose characteristics indicate a high garnet content (mafic garnet granulite) and/or the presence of hornblendite. The overall composition of the arc terranes is basaltic. Physical properties suggest that eclogite is not present in the arc terranes, or if present it exists in small amounts that are below the resolution of the data set. The lack of eclogite in the lower crust favours an intracrustal differentiation model for the evolution of the bulk composition of the continental crust. Nevertheless, the absence of surface uplift, the lack of metamorphism and late orogenic mantle melts, and the current crustal thickness indicate that crustal thinning did not affect the bulk composition of the Uralide crust.

Evidence of climatic warming in the southern Urals region derived from borehole temperatures and meteorological data

Abstract Thirty borehole temperature–depth profiles in the central and southern Urals, Russia were scrutinized for evidence of ground surface temperature histories. We explored two inversion schemes: a simple ramp inversion in which solutions are parameterized in terms of an onset time and magnitude of change and a more sophisticated functional space inverse algorithm in which the functional form of the solution is left unspecified. To enhance and potentially identify latitudinal differences in the ground surface temperature signal, we subdivided the data into three groups based on geographic proximity and simultaneously inverted the borehole temperature–depth logs. The simultaneous inversions highlighted 13 temperature–depth logs that could not both fit a common ground surface temperature history and a priori models within reasonable bounds. Our results confirm that this is an effective way to reduce site-specific noise from an ensemble of boreholes. Each inversion scheme gives comparable results indicating locally variable warming on the order of 1°C starting between 1800 and 1900 AD. Similarly surface air temperature records from 12 nearby meteorological stations exhibit locally variable warming also on the order of 1°C of warming during the 20th century. To explore the degree to which borehole temperatures and surface air temperature (SAT) time series are responding to the same signal, we average the SAT data into the same three groups and used these averages as a forcing function at the Earths surface to generate synthetic transient temperature profiles. Root mean square (RMS) misfits between these synthetic temperature profiles and averaged temperature–depth profiles are low, suggesting that first-order curvature in borehole temperatures and variations in SAT records are correlated.

Climate change record in the Earth—Example of borehole data analysis in the Urals Region, Russia

Abstract Primary evidence of global warming, provided by surface air temperature data (SAT), is generally constrained to the last century. However, since the Earth continuously records ground surface temperature (GST) variations, information on earlier climate change is potentially contained in borehole temperatures and can be recovered with the use of appropriate inversion algorithms. Synthetic data were used to evaluate two inversion strategies: loose (robust, less sensitive to noise but less successful in identifying the climate signal) and tight inversion (able to recover the whole climate perturbation but sensitive to noise). The inversion was applied at 31 temperature logs from the Urals region, which forms a N-S oriented band 1000 km long. The regional GST history is characterised by a cold period of 0.5 – 1.0 K below the long term mean (LTM) which culminated in 1700–1750. GST then warmed to about 1 K above LTM by 1980 consistent with warming indicated by 160 year long SAT records.

Climate Change in the Urals, Russia, Inferred from Borehole Temperature Data

Borehole temperatures in the central and south Urals were analysed for the past ground surface temperature (GST) signal. 31 highquality temperature logs were selected for this purpose and inverted with algorithms based on the generalised least squares theory. The signal to noise ratio was improved by averaging the results of individual borehole inversions. No distinct regional trends were found in the studied region except for some indications of more pronounced warming in the south. The mean GST history (GSTH) was characterised by cooling down to −0.6 °C in the 18th century and subsequent warming to 0.5 °C above the longterm mean at the beginning of this century, and to 1 – 1.5 °C by 1980. The stability of the mean GSTH was tested in dependence on the number of holes used for the averaging. It showed that any subset of 15 holes yielded a GSTH similar to that obtained from the whole set. A surface air temperature (SAT) time series comprising the period 1832 – 1989 was combined from 17 meteorological records. Its least squares warming rate of 1.1 °C per 100 years is somewhat higher than that of the GST (0.7 – 0.8°C/100 years) in the same period.

Paleomagnetism of sedimentary strata and the origin of the structures in the western slope of South Urals

Paleomagnetic data may contribute to studying the formation history of orogens; in particular, these data can promote identifying the pattern and scales of deformations at the final stages of orogeny. We have conducted paleomagnetic studies of the Paleozoic and Neoproterozoic sediments in the western part of the Western Ural Megazone in South Urals. The detailed thermal demagnetization revealed the intermediate temperature magnetization component in most samples. This magnetization has a reversed polarity and has been acquired before folding or at the early stages of the deformations. The directions of this component are narrowly grouped in rocks of a different age in all the segments of the studied part of South Urals, and the regional average direction closely agrees with the reference paleomagnetic direction of 270 Ma for the East European Platform. The results of our study suggest the following conclusions: (1) the main magnetization component in the studied sedimentary rocks has a secondary origin; (2) this component has an age of ~270 Ma and has been formed during the Kungur deformations (279–272 Ma ago) of the western part of South Urals; (3) neither a general rotation of the studied part of the Urals relative to the East European Platform nor local rotations of the individual tectonic blocks relative to each other are revealed; (4) the changes in the strike of the structures from NE within the Karatau uplift to the submeridional in the remaining part of the Urals is not an oroclinal bend.

Late Paleozoic Remagnetization: Evaluation of the Sequence of Folding in the South Urals

Analysis of secondary magnetization components (Late Paleozoic remagnetization) makes it possible to trace the formation of the South Ural folded system. This paper presents new data on Late Paleozoic remagnetization in the rocks of the eastern Bashkir Meganticlinorium. Combined analysis of the newly obtained results and previously published data on Late Paleozoic remagnetization along the western slope of the South Urals shows that in the western segment the intermediate-temperature magnetization component (ITC) was acquired prior to or at the initial stages of deformation. In contrast, the ITC observed in the eastern segment postdates folding. Collision processes which occurred in the South Urals from the Late Devonian until the Late Permian time had undoubtedly left their trace in the western structures (in present-day coordinates). Within the passive margin of Baltica the collision resulted in the formation of a lateral series of fold-and-thrust structures. They started from the Main Uralian Fault westward, with possible gradual termination of this process towards the Pre-Uralian Foredeep. Paleomagnetic results of this research work support these assumptions.

Paleomagnetic study of the Lower Carboniferous volcanites in the Magnitogorsk-Bogdanovka graben

New paleomagnetic data on the Lower Carboniferous volcanites of the Central-Magnitogorsk zone (Southern Urals) are represented in the paper. An independent assessment of the geological concepts of the history of the Magnitogorsk Island Arc development was the main aim of our study. Nine sections of effusive basic rocks which are attributed to the Grekhovskaya and Berezovskaya Formations, located in the meridional current of the Ural River between Kizilskoe and Ershovka villages were chosen for our study. Paleomagnetic investigations were conducted in accordance with the generally accepted up-to-date methodology including thermal magnetic cleaning and component analysis of identified directions of magnetization. The average direction of the high-temperature component of remanence obtained from the 21 sites and the paleolatitude calculated from it practically coincide with the world-known data for the eastern margin of the paleocontinent Baltica. Consequently, based on the paleomagnetic data, it can be concluded that during the early Carboniferous period the Central Magnitogorsk Zone was part of Baltica continent. An analysis of the middle-temperature components of magnetization allows to conclude that the bulk of the deformations in the territory of the Central part of the Magnitogorsk Zone (MagnitogorskBogdanovka graben) occurred later than in the West-Magnitogorsk Zone studied by the authors.