ИНДИКАТОРЫ ИНТЕНСИВНОСТИ ГЕОДИНАМИЧЕСКИХ ПРОЦЕССОВ ВДОЛЬ АТЛАНТИКО-АРКТИЧЕСКОЙ РИФТОВОЙ СИСТЕМЫ

Seismicity, heat flow, seismic tomography data, prerift and synrift magmatism are considered as intensity indicators of geodynamic processes along the Atlantic-Arctic rift system (AARS). In this rift system, several large (over 100 km ) sub-latitudinal displacements of the rift axis are due to left-lateral strike-slip faulting. The AARS segments are distinguished by the age of splitting of continental plates from each other. A dependence is revealed between the current thermal state of the mantle under the AARS and the age of spreading start. This dependence is established from both seismic tomography and heat flow data. In section δ(Vp/Vs), the locations of the main segmenting faults and ‘cold’ anomalies in the upper mantle are coincident. Distributions of total seismic moments are practically synchronous in the depth intervals of 0–13, 13–35, and >35 km. The maximum values above the plumes are represented by higher seismic moments in the surface layer. The main demarcation zones differ in maximum energy release values in the AARS with shearing features. Comparison of these values against the age of the start of spreading processes shows trends of heat flow and medium field tomography in the AARS segments. The trends confirm the thermal interpretation of the seismic tomography data and suggest mantle cooling with age and a decrease in the mean temperatures of the mantle. The main factor causing the sublatitudinal asymmetry of heat flow in the AARS is the impact of Coriolis forces on the magma in the asthenospheric source. Most of the synrift igneous formations seem to be related to the influence of long-lived anomalies in the mantle, which had lower rates of magma generation than those typical of the formation of magmatic provinces. In conditions for spreading and the formation of the oceanic crust, the process followed the principle of energy cost minimization, and the prerift magmatic provinces with the pre-processed crust contributed to the choice and positioning of the AARS trajectory. The plume branches are imposed in the tomographic section and thus ‘concealing’ the relationship between the age and the thermal state. However, that does not change the trend to cooling of the mantle beneath the AARS, proportionally to the time since the start of spreading.Рассмотрены сейсмичность, тепловой поток, сейсмотомографический разрез, дорифтовый и синрифтовый магматизм как индикаторы интенсивности геодинамических процессов вдоль Атлантико-Арктической рифтовой системы (ААРС), имеющей несколько крупных (более 100 км) субширотных смещений оси рифта с левосдвиговой морфологией. Данные характеристики в сегментах ААРС, разграниченных по возрасту раскола континентальных плит, показывают, что существует зависимость современного термального состояния мантии под ААРС от возраста старта спрединговых процессов, выделяемая как по данным сейсмотомографии, так и по тепловому потоку. В разрезе δ(Vp/Vs) основные сегментирующие разломы и «холодные» аномалии верхней мантии совпадают в пространстве. Распределение суммарного момента в интервалах глубин 0–13, 13–35 и >35 км практически синхронное. Максимумы над выходами плюмов представлены бóльшим моментом в поверхностном слое. Главные демаркационные зоны отличаются максимальным энерговыделением в ААРС с событиями сдвигового механизма. Полученные сопоставлением с возрастом старта спрединговых процессов тренды теплового потока и среднего уровня поля томографии по сегментам ААРС подтверждают правильность термальной интерпретации данных сейсмотомографии и показывают остывание с возрастом среднего показателя температуры мантии по обоим параметрам. Показано, что главным фактором, обусловливающим субширотную асимметрию теплового потока в ААРС, является действие силы Кориолиса на магматические массы в астеносферном очаге. Большинство синрифтовых магматических образований можно связать с действием долгоживущих аномалий в мантии, имеющих меньшие скорости магмогенерации, чем при формировании магматических провинций. При реализации условий для спрединга с образованием океанической коры процесс следует принципу минимизации энергетических затрат и дорифтовые магматические провинции с предварительно переработанной корой способствуют выбору и оформлению траектории ААРС. Наложение ветвей плюма в томографическом разрезе маскирует связь между возрастом и термальным состоянием, однако не отменяет тенденции к остыванию мантии под ААРС пропорционально времени с начала спрединга

The possible impact of gas-bearing fluids on sediment in the arch Fedynskogo (Barents sea)

A comparative analysis of facies and composition of precipitation on the bottom areas where the discharge of methane fluid occurs rapidly or not registered. Effect of gaseous fluids on postsedimentary transformation of clay minerals not found. Possible local manifestation of the fluid can be lithogenesis authigenic carbonate formation

INTENSITY INDICATORS OF GEODYNAMIC PROCESSES ALONG THE ATLANTIC-ARCTIC RIFT SYSTEM

Seismicity, heat flow, seismic tomography data, prerift and synrift magmatism are considered as intensity indicators of geodynamic processes along the Atlantic-Arctic rift system (AARS). In this rift system, several large (over 100 km ) sub-latitudinal displacements of the rift axis are due to left-lateral strike-slip faulting. The AARS segments are distinguished by the age of splitting of continental plates from each other. A dependence is revealed between the current thermal state of the mantle under the AARS and the age of spreading start. This dependence is established from both seismic tomography and heat flow data. In section δ(Vp/Vs), the locations of the main segmenting faults and ‘cold’ anomalies in the upper mantle are coincident. Distributions of total seismic moments are practically synchronous in the depth intervals of 0–13, 13–35, and >35 km. The maximum values above the plumes are represented by higher seismic moments in the surface layer. The main demarcation zones differ in maximum energy release values in the AARS with shearing features. Comparison of these values against the age of the start of spreading processes shows trends of heat flow and medium field tomography in the AARS segments. The trends confirm the thermal interpretation of the seismic tomography data and suggest mantle cooling with age and a decrease in the mean temperatures of the mantle. The main factor causing the sublatitudinal asymmetry of heat flow in the AARS is the impact of Coriolis forces on the magma in the asthenospheric source. Most of the synrift igneous formations seem to be related to the influence of long-lived anomalies in the mantle, which had lower rates of magma generation than those typical of the formation of magmatic provinces. In conditions for spreading and the formation of the oceanic crust, the process followed the principle of energy cost minimization, and the prerift magmatic provinces with the pre-processed crust contributed to the choice and positioning of the AARS trajectory. The plume branches are imposed in the tomographic section and thus ‘concealing’ the relationship between the age and the thermal state. However, that does not change the trend to cooling of the mantle beneath the AARS, proportionally to the time since the start of spreading

COMPOSITION AND ORIGIN OF POSTGLACIAL BOTTOM SEDIMENTS FROM CENTRAL AND NORTHEASTERN PARTS OF THE BARENTS SEA (RUSSIAN SECTOR)

The lighology of postglacial bottom sediments are studied in cores from central and north-eastern part of the Barents Sea (25 and 28 cruises of R/V “Academic Nikolai Strakhov” in 2007 and 2011 respectively). Petrographic and chemical composition of modern and late Quaternary sediments from the Fedynskii swell area and the southern rim of the Franz Josef Land were examined. The study revealed sources of clastic material and permitted to estimate their influence on the various stages of post glacial sedimentation. At the end of Late Pleistocene (the initial phase of the ice cover degradation) granitoid rocks of the Kola peninsula are considered to be the main source of clastics in the Fedynskii swell area, while volcanic-sedimentary strata that compose FJL governed sedimentation in the North- East. Sedimentation was accompanied by intense ice-rafting that resulted in mixing of clastics from both sources. Ate the Late Pleistocene to Holocene boundary and later in Holocene the main source of clastic material remained unchanged in the central part of the sea. In the North-East sedimentation was controlled by recycling of previously accumulated deposits. Ice-rafting had no significant values such as at early deglaciation phase. In the case of poor faunal characterization and/or the absence of radiocarbon data petrographic and geochemical study can be used for stratification of the Barents sea bottom sediments

New Data on the Structure of the Megatransform System of the Doldrums (Central Atlantic)

none13Abstract: The geological and geophysical data acquired during cruise 45 of R/V Akademik Nikolaj Strakhov regarding the structure of the Doldrums megatransform system in the Central Atlantic are presented. Taking into account the data of the previous expeditions, the structure of this region is examined in detail. The bathymetric data confirm the complex morphology, consisting of five dextral transform faults, separated by four active intra-transform rift segments and indicates the variability of tectonic conditions in this region. The dredged rocks are represented by the entire spectrum from the mantle to the upper crustal varieties and, together with the detailed topographic data, make it possible to identify the origin of the key structures in the Doldrums megatransform system.noneSkolotnev S.G.; Sanfilippo A.; Peyve A.A.; Muccini F.; Sokolov S.Y.; Sani C.; Dobroliubova K.O.; Ferrando C.; Chamov N.P.; Pertsev A.N.; Gryaznova A.S.; Sholukhov K.N.; Bich A.S.Skolotnev, S. G.; Sanfilippo, A.; Peyve, A. A.; Muccini, F.; Sokolov, S. Y.; Sani, C.; Dobroliubova, K. O.; Ferrando, C.; Chamov, N. P.; Pertsev, A. N.; Gryaznova, A. S.; Sholukhov, K. N.; Bich, A. S

Large-scale structure of the doldrums multi-fault transform system (7-8ºn equatorial atlantic): Preliminary results from the 45th expedition of the R/V A.N. strakhov

The Equatorial portion of the Mid Atlantic Ridge is displaced by a series of large offset oceanic transforms, also called “megatransforms”. These transform domains are characterized by a wide zone of deformation that may include different conjugated fault systems and intra-transform spreading centers (ITRs). Among these megatransforms, the Doldrums system (7-8ºN) is arguably the less studied, although it may be considered the most magmatically active. New geophysical data and rock samples were recently collected during the 45th expedition of the R/V Akademik Nikolaj Strakhov. Preliminary cruise results allow to reconstruct the large-scale structure and the tectonic evolution of this poorly-known feature of the Equatorial Atlantic. Swath bathymetry data, coupled with extensive dredging, were collected along the entire megatransform domain, covering an area of approximately 29,000 km2. The new data clearly indicate that the Doldrums is an extremely complex transform system that includes 4 active ITRs bounded by 5 fracture zones. Although the axial depth decreases toward the central part of the system, recent volcanism is significantly more abundant in the central ITRs when compared to that of the peripheral ITRs. Our preliminary interpretation is that a region of intense mantle melting is located in the central part of the Doldrums system as consequence of either a general transtensive regime or the occurrence of a more fertile mantle domain. Large regions of basement exposure characterize the transform valleys and the ridge-transform intersections. We speculate that different mechanisms may be responsible for the exposure of basement rocks. These include the uplift of slivers of oceanic lithosphere by tectonic tilting (median and transverse ridges formation), the denudation of deformed gabbro and peridotite by detachment faulting at inner corner highs, and the exposure of deep-seated rocks at the footwall of high-angle normal faults at the intersection of mid-ocean ridges with transform valleys

Investigation of the Andrew Bain transform fault zone (African-Antartctic Region)

The Andrew Bain FZ is among the longest oceanicfaults with the active part extending over about 750 km.Since this mid-oceanic ridge (MOR) region is characterizedby very low spreading rates (16 mm/yr), itsactive part is one of the oldest in the whole MOR system. The study of the fault is of great importance forunderstanding the geodynamics and evolution of Circum-Antarctic regions of the World Ocean. Theresults of previous bathymetric and magnetic investigationsand the spatial distribution of earthquakes showedthat the Andrew Bain FZ includes numerous differentsecond-order structures. This feature is typical of continentalstrike-slip fault zones. Such megatransform fault zones can emerge in slowspreading ridges at a relative displacement of the lithosphere, which is thicker and colder than in most transformfaults. The aim of the present work was to substantiatethis suggestion with factual material