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Saint Petersburg, Russia

Skolotnev S.G.,Russian Academy of Sciences | Bel'tenev V.E.,Polar Marine Geosurvey Expedition | Lepekhina E.N.,Russian Academy of Sciences | Ipat'eva I.S.,Russian Academy of Sciences
Geotectonics | Year: 2010

Local U-Pb dating of zircons separated from various rocks in the crest zone of the Mid-Atlantic Ridge (MAR) and Carter Seamount (Sierra Leone Rise) is performed. Younger zircons formed in situ in combination with older xenogenic zircons are revealed in enriched basalts, alkaline volcanic rocks, gabbroic rocks, and plagiogranites. Only older zircons are found in depleted basalts and peridotites. Older zircons are ubiquitous in the young oceanic lithosphere of the Central Atlantic. The age of the younger zircons from the crest zone of the MAR ranges from 0.38 to 11.26 Ma and progressively increases receding from the axial zone of the ridge. This fact provides additional evidence for spreading of the oceanic floor. The rate of half-spreading calculated from the age of the studied zircons is close to the rate of half-spreading estimated from magnetic anomalies. The age of the younger zircons from Carter Seamount (58 Ma) corresponds to the age of the volcanic edifice. Older zircons make up an age series from 53 to 3200 Ma. Clusters of zircons differing in age reveal quasiperiodicity of about 200 Ma, which approximately corresponds to the global tectonic epochs in the geological evolution of the Earth. Several age groups of older zircons combine grains close in morphology and geochemistry: (1) Neoproterozoic and Phanerozoic (53-700 Ma) prismatic grains with slightly resorbed faces, well-preserved or translucent oscillatory zoning, and geochemical features inherent to magmatic zircons; (2) prismatic grains dated at 1811 Ma with resorbed faces and edges, fragmentary or translucent zoning, and geochemical features inherent to magmatic zircons; (3) ovoid and highly resorbed prismatic grains with chaotic internal structure and metamorphic geochemical parameters; the peak of their ages is 1880 Ma. The performed study indicates that older xenogenic zircons from young rocks in the crest zone of the MAR were captured by melt or incorporated into refractory restite probably in the sublithospheric mantle at the level of magma generation in the asthenosphere. It is suggested that zircons could have crystallized from the melts repeatedly migrating through the asthenosphere during geological history or were entrapped by the asthenosphere together with blocks of disintegrated and delaminated continental lithosphere in the process of breakup of the continents older than Gondwana. The variability in the age of older zircons even within individual samples may be regarded as evidence for active stirring of matter as a result of periodically arising and destroyed within-asthenospheric convective flows varying in orientation and scale. © 2010 Pleiades Publishing, Ltd. Source

Richter A.,TU Dresden | Popov S.V.,Polar Marine Geosurvey Expedition | Schroder L.,TU Dresden | Schwabe J.,TU Dresden | And 4 more authors.
Geophysical Research Letters | Year: 2014

The question whether Antarctica's largest lake, subglacial Lake Vostok, exchanges water is of interdisciplinary relevance but has been undecided so far. We present the potential pathway, outlet location, and threshold height of subglacial water discharge from this lake based on a quantitative evaluation of the fluid potential. If water left Lake Vostok, it would flow toward Ross Ice Shelf. Discharge would occur first to the east of the southern tip of the lake. At this location the bedrock threshold is 91 ± 23 m higher than the hydrostatic equipotential level of Lake Vostok. It is concluded that Lake Vostok is not likely to reach this level within climatic timescales and that no discharge of liquid water is to be expected. We show that in absence of the ice sheet the Lake Vostok depression would harbor a lake significantly deeper and larger than the present aquifer. Key Points Lake Vostok is not expected to discharge liquid water in climatic timescalesDischarge would lead from east of the lake's southern tip to Ross Ice ShelfLake Vostok would be significantly deeper and larger without ice sheet ©2014. American Geophysical Union. All Rights Reserved. Source

Richter A.,TU Dresden | Fedorov D.V.,FGUP Aerogeodeziya | Fritsche M.,TU Dresden | Popov S.V.,Polar Marine Geosurvey Expedition | And 7 more authors.
Journal of Glaciology | Year: 2013

Repeated Global Navigation Satellite Systems (GNSS) observations were carried out at 50 surface markers in the Vostok Subglacial Lake (East Antarctica) region between 2001 and 2011. The horizontal ice flow velocity vectors were derived with accuracies of 1 cma-1 and 0.5°, representing the first reliable information on ice flow kinematics in the northern part of the lake. Within the lake area, ice flow velocities do not exceed 2ma-1. The ice flow azimuth is southeast in the southern part of the lake and turns gradually to east-northeast in the northern part. In the northern part, as the ice flow enters the lake at the western shore, the velocity decreases towards the central lake axis, then increases slightly past the central axis. In the southern part, a continued acceleration is observed from the central lake axis across the downstream grounding line. Based on the observed flow velocity vectors and ice thickness data, mean surface accumulation rates are inferred for four surface segments between Ridge B and Vostok Subglacial Lake and show a steady increase towards the north. Source

Siegert M.J.,University of Edinburgh | Popov S.,Polar Marine Geosurvey Expedition | Studinger M.,Lamont Doherty Earth Observatory | Studinger M.,NASA
Geophysical Monograph Series | Year: 2011

Vostok Subglacial Lake is the largest and best known sub-ice lake in Antarctica. The establishment of its water depth (>500 m) led to an appreciation that such environments may be habitats for life and could contain ancient records of ice sheet change, which catalyzed plans for exploration and research. Here we discuss geophysical data used to identify the lake and the likely physical, chemical, and biological processes that occur in it. The lake is more than 250 km long and around 80 km wide in one place. It lies beneath 4.2 to 3.7 km of ice and exists because background levels of geothermal heating are sufficient to warm the ice base to the pressure melting value. Seismic and gravity measurements show the lake has two distinct basins. The Vostok ice core extracted >200 m of ice accreted from the lake to the ice sheet base. Analysis of this ice has given valuable insights into the lake's biological and chemical setting. The inclination of the ice-water interface leads to differential basal melting in the north versus freezing in the south, which excites circulation and potential mixing of the water. The exact nature of circulation depends on hydrochemical properties, which are not known at this stage. The age of the subglacial lake is likely to be as old as the ice sheet (~14 Ma). The age of the water within the lake will be related to the age of the ice melting into it and the level of mixing. Rough estimates put that combined age as ~1 Ma. Copyright © 2010 by the American Geophysical Union. Source

Ewert H.,TU Dresden | Popov S.V.,Polar Marine Geosurvey Expedition | Richter A.,TU Dresden | Schwabe J.,TU Dresden | And 2 more authors.
Geophysical Journal International | Year: 2012

Based on the Ice, Cloud and Land Elevation Satellite (ICESat) laser altimetry data, the hydrostatic equilibrium (HE) condition for the subglacial Lake Vostok, East Antarctica, is evaluated. A digital elevation model (DEM) of the ice surface is derived by a regional crossover adjustment. The analysis of the DEM and its comparison with GPS derived ice-surface elevations and an ice-surface DEM based on radar altimetry data reveal an overall accuracy of better than ± 0.7 m for the lake area. The DEM is combined with an ice-thickness model and a regional geoid model to determine the deviation of the local ice-surface height from HE. For large parts of the lake, the ice sheet fulfils the HE. Our results reveal a strong positive deviation of about 10 m along the lake shoreline. In addition, positive deviations are found in the northern part of the lake which coincide with ice rumples detected by radio-echo sounding. In the southern part of the lake, we find a linear negative deviation (-4.0 m) which coincides with the convoy route from Vostok station to Mirny base. In addition to the DEM, relative biases for the ICESat laser operational periods are determined in the regional crossover adjustment. © 2012 The Authors Geophysical Journal International © 2012 RAS. Source

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