Global Geodynamic Processes Research Articles

LA-ICPMS U-Pb dating reveals cassiterite inheritance in the Yazov granite, Eastern Siberia: Implications for tin mineralization

U-Pb dating of cassiterite and zircon from the Yazov granite (Transbaikalia region, Eastern Siberia, Russia) and cassiterite from spatially associated tin mineralization in the Tuyukan ore district in the Tonod uplift was conducted using in situ laser ablation inductively coupled plasma mass spectrometry. These analyses allow comparison of isotopic systematics for both minerals, especially related to transport in granitic magma. These data are also useful for understanding possible genetic links between the granite and the tin mineralization. Most of the U-Pb zircon analyses define a 206Pb/238U age of 719 ± 15 Ma for the granite; in addition, several zircon cores define an inheritance age of 1839 ± 21 Ma. U-Pb data for 10 nearly concordant analyses of disseminated cassiterite from the same samples yield a 206Pb/238U age of 1838 ± 34 Ma. This is the first documented evidence of cassiterite inheritance in granitic magma. These data indicate the robust character of U-Pb isotope systematics in cassiterite, comparable to that in zircon. The presence of numerous inclusions of cassiterite in zircon from the Yazov granite (revealed by nanotomography) supports the interpretation of inherited cassiterite included during Neoproterozoic zircon crystallization. The data indicate that high tin concentrations in the Yazov granite are due to the incorporation of older cassiterite crystals from country rock, not coeval cassiterite crystallization. Cassiterite samples from two ore occurrences spatially associated with the Yazov granite yield Pb-Pb isochron ages of 1.86–1.82 Ga, indicating that tin mineralization occurred in the Paleoproterozoic, nearly 1 Ga before emplacement of the Yazov granite. Tin mineralization of the ore region is probably related to ~ 1.85 Ga Chuya-Kodar tin-bearing granitic rocks that host tin deposits. These results have broad implications for understanding how critical elements, such as tin, may become enriched in rare-metal granites and how they are related to regional to global geodynamic processes.

Seismotectonic Deformation of Active Segments of the Junction Zone of the Kolyma–Omolon Superterrane and South Anui Suture (Southeastern Russia)

Our seismotectonic studies focus on active segments of the junction zone of the Kolyma–Omolon superterrane and the South Anui suture. The aim of our research is to identify features that show activation of suture zones and to determine the parameters of the stress–strain state of the crust in the study area. The analysis was based on the average seismotectonic deformation tensors, which were estimated for the main epicentral fields of Russia’s northeastern regions. New data are now available on the focal characteristics of moderate earthquakes, which can improve determination of the kinematic types of junctions of suture zones of the tectonic taxa located along the Arctic and Pacific continental margins. Seismotectonic crustal destruction regimes are determined for the active segments of the junction zone of the Kolyma–Omolon superterrane and the South Anui suture. These regimes are influenced by global geodynamic processes taking place at lithospheric plate margins, as well as by the dominant deformation fields of adjacent tectonic taxa. The seismotectonic analysis results suggest activation of the suture zones of the northwestern flank of the Kolyma–Omolon superterrane under stable north-eastward compression. The suture zones may extend into the Laptev Sea area, where they are conjugate with the structural elements of the South Anui suture (Novosibirsk–Svyatoi Nos segment). In the Anui–Chukotka segment of the suture, seismotectonic crustal destruction changes from compression to extension. This is due to the effect of deformation fields of active megazones of conjugated tectonic taxa of the Novosibirsk–Chukotka fold-and-thrust and Okhotsk–Chukotka active margin zones. For the tectonic taxa of the Arctic sector of Russia’s northeastern regions, a database has been consolidated, including the of seismotectonic crustal deformation parameters, which may be useful for various geodynamic reconstructions.

Техногенные риски освоения шельфа Каспийского моря

The article presents a detailed analysis of the technogenic risks in building and operating oil and gas complexes in the offshore area of the Caspian Sea and actualizes the problem of the Caspian environmental crisis, the possible measures for preventing and minimizing the negative consequences from the extensive offshore oil and gas production for the ecosystem being considered. The geothermal regime of the ground of the Caspian Sea has been analyzed in respect of the deep-earth processes. The bottom of the Caspian Sea is rather varied, hence, the risks for constructing facilities in the area under development are possible. The surface, underwater and island mud volcanoes formed by the large longitudinal and transverse tectonic disturbances pose a threat to oil production and transportation facilities. The tectonic processes of the bottom of the Caspian Sea are studied in detail. It has been stated that the global geodynamic processes are taking place in the earth's crust of the region affecting the natural environment of the Caspian Sea, which will inevitably affect the industrial objects on the shelf. The Caspian Sea ground is divided into two parts in terms of seismic activity: the seismically inactive northern part (the Scythian-Turanian platform and the East European platform) and the southern part (alpine orogenic-folded belt) that is currently seismically active. The diagrams of possible earthquakes and seismic activity in the bottom area of the Caspian Sea are presented. Since the mechanism of the developing seismic activity caused by volcanoes is not fully examined, there has been substantiated the need to prognose precisely the location of hazardous zones and joints in connection with the development of the oil and gas industry. The tectonic and geological frame of the Caspian region has been illustrated; the regional fractures that influence the formation of biosphere zones and the largest tectonic joints that affect natural and man-made processes are noted. Particular attention is paid to the risks of the hydrogen sulfide pollution of the Caspian Sea. Conclusions are drawn about the prospects for the development of the Caspian, which is rich in oil and gas reserves; on the need to ensure safety and reduce losses in the ecological system of the Caspian Sea.

Common features in the manifestation of natural and induced geodynamic events in the eastern regions of Russia and China

The study of geodynamic processes observed in the Earth’s crust at densely populated and commercially developed areas in the east of Russia and China is of great importance for their sustainable development. The research results available show that not only natural, but also man-made geodynamic events associated with mining operations reflect the global geodynamic processes. Geodynamic events that occurred while mining in impact-hazardous areas allowed to identify some common features in the manifestation of natural and man-made geodynamic events in the eastern regions of Russia and China. Thus, both natural and disastrous technogenic geodynamic events (tectonic rock bursts, induced earthquakes, cracking on the earth’s surface) have positional connection with the linear zones of earth’s crust modern destruction (block boundaries and faults). Existing tectonic faults get re-activated during major geodynamic events, i.e. they get displaced in response to the mining operations. Areas hazardous for manifestation of geodynamic phenomena can be defined by geodynamic zoning method which can be used to draft the development programs for the eastern regions of Russia and China

Widespread seismic anisotropy in Earth’s lowermost mantle beneath the Atlantic and Siberia

Deep inside the Earth, just above the core-mantle boundary at around 2,700 km depth, large-scale mantle structures are assumed to play a key role for global geodynamic processes. While unusual hot regions are attributed to feed rising mantle plumes and volcanic hotspots, the accumulation of subducted lithospheric plates is associated with colder than average features. In both environments the appearance of dynamic-driven processes such as deformation and mantle flow can directly be inferred by the presence of seismic anisotropy. However, the geometries as well as the interactions of these massive anomalous structures with the surrounding mantle material are still under debate. Based on new seismic data from a dense and large-aperture recording network in Scandinavia we characterize the anisotropic signatures of two so far unexplored regions in the lowermost mantle by using observations of clearly discrepant SKS-SKKS shear wave splitting measurements. Thereby we can demonstrate that anisotropy is located along the northern edges of the Large Low Shear Velocity Province beneath Africa. Furthermore, we recover an anisotropic structure in a region of fast seismic velocity underneath Siberia which provides additional evidence for widespread deformation caused by a deeply subducted slab.

Seismotectonic Activation of Modern Structures of the Siberian Craton

Our research of the modern structures of Siberian Craton aims to reveal regional regularities in the seismotectonic destruction of the Earth’s crust and to clarify the dynamics of the formation of the focal zones of strong earthquakes. Analysis of activated structures and marginal suture zones located in the study area was based on structural and geophysical data, the modern structural plan, and the quantitative characteristics of modern and recent tectonic movements, active faults, and tectonic stress fields identified by tectonophysical analysis of deformation and seismological parameters. Unambiguous correlation between the seismic activity level of modern structures and the rates of modern and recent tectonic movements were not determined in our study. The most active structures of the Siberian Craton located in zones of the dynamic influence of marginal sutures are contrasted against the gradient field of modern vertical tectonic movements and characterized by the mosaic field of the mean and low rates of modern movements. The kinematics of seismotectonic deformation and levels of seismic activation of suture zones of the Siberian Craton are governed by global geodynamic processes taking place at the boundaries between the Eurasian, North American and Amur lithospheric plates. The activated structures in the northern regions of Siberian platform, which are characterized by the highest rates of modern movements, are heterogeneous. Both fluid processes and glacioisostatic movements may have influenced the dynamics of the formation of these high-gradient deformation zones. In seismotectonic studies aimed at determining levels of the potential seismic hazard of modern structures, we find it important to take into account errors in geodetic data and ensure more correct reference to the rates of tectonic movements at the neotectonic stage. In order to correctly assess the degree of geodynamic activity of modern structures, special consideration should be given to the fluid-geodynamic factor that controls most geodynamic processes, including tectonic stress accumulation, the formation of earthquake focal zones, and the intensity of seismic events.

The key role of global solid‐Earth processes in preconditioning Greenland's glaciation since the Pliocene

AbstractAfter >500 Ma of absence, major Northern Hemisphere glaciations appeared during the Plio‐Pleistocene, with Greenland leading other northern areas. Here, we propose that three major solid‐Earth processes underpinned build‐up of the Greenland ice‐sheet. First, a mantle‐plume pulse, responsible for the North Atlantic Igneous Province at ~60 Ma, regionally thinned the lithosphere. Younger plume pulses led to uplift, which accelerated at ~5 Ma, lifting the parts of the East Greenland margin closest to Iceland to elevations of more than 3 km above sea level. Second, plate‐tectonic reconstruction shows a ~6° northward component of Greenland motion relative to the mantle since ~60 Ma. Third, a concurrent northward rotation of the entire mantle and crust towards the pole, dubbed True Polar Wander (TPW), contributed an additional ~12° change in latitude. These global geodynamic processes preconditioned Greenland to sustain long‐term glaciation, emphasizing the role of solid‐Earth processes in driving long‐term global climatic transitions.

Geodetic observations at geomagnetic observatories

Geodetic observations at geomagnetic observatories are used to orient reference directions in relation to a common coordinate grid. This problem is solved with the use of the measuring tools of global navigation satellite systems (GNSS). The results of experimental GNSS determinations at the St. Petersburg Geomagnetic Observatory, Russia, are presented. Combination of magnetic and GNSS observations is proposed in order to reveal the cause-effect relationships between magnetic field variations and global geodynamic processes.

Drilling the solid earth: global geodynamic cycles and earth evolution

The physical and chemical evolution of the Earth is driven by geodynamic cycles that are global in scale, operating over 4.57 Ga of Earth’s history. Some processes are truly cyclic, e.g., the Wilson Cycle, while others are irreversible (e.g., core formation). Heat and mass transfer between the lowermost mantle (e.g., core-mantle boundary) and the surface drives these global geodynamic processes. Subduction of lithospheric plates transfers cool fractionated material into the lower mantle and leads indirectly to the formation of new oceanic lithosphere, while the rise of thermochemical plumes recycles the remnants of these plates back to the surface, driven by heat transfer across the core–mantle boundary. These global geodynamic cycles are responsible for hotspot volcanism, the formation of continental crust, collisional orogenies, continental rifting, subduction zone processes (arcs, accretionary prisms), and ore deposits. Each of these presents opportunities for investigation by continental scientific drilling. In addition, these cycles affect other processes that are targets of continental scientific drilling: the origin and evolution of life and an oxygenated atmosphere, the impact of large volcanic eruptions on climate, and geological hazards such as earthquakes and volcanic eruptions. In this paper, we present the scientific rationale for continental scientific drilling to study global geodynamic processes, review past successes in this realm that were sponsored in part by ICDP, and suggest potential new targets for drilling campaigns that focus on solid earth evolution. This paper builds on discussions at the 2013 ICDP Science Meeting on the future of continental scientific drilling, held in Potsdam in November 2013.

Regional geodynamic monitoring system for ensuring safety in geological and exploratory production of oil and gas

Global geodynamic processes have a significant influence on the tempo of human society development and can cause the complete devastation of large areas of the Earth and mass mortality in a number of catastrophic cases. Technogenous factors can sometimes trigger geodynamic events. The potential consequences of natural and technogenous disasters became apparent during the catastrophe on the Deepwater Horizon platform on April 20, 2010. This paper takes a brief look at some aspects of this disaster. The possibilities of preventing the similar events in the future are discussed here. For this purpose, the development of a geodynamics information system (IS-Geodynamics) based on a network of global (subglobal) monitoring of the Earth’s hydrogeodeformation (HGD) field, is suggested.

New fluid dynamic model for formation of giant hydrocarbon deposits

Geomechanical models of fluid dynamics with both one-phase and two-phase fluids in overthrusts and faults, more than 7km deep, are proposed in this work. Based on the models, we studied accumulation conditions and mechanisms of formations of giant gas and gas condensate deposits in structures like the Astrakhan Arch carbonate massif. The Astrakhan carbonate massif is characterized by an increase in reservoir capacity of carbonate rocks owing to generation of joint during faulting. Moreover, the entire Caspian depression serves as a giant oil-generating basin, which is able to supply any trap with hydrocarbons within this region. Shifts of fault boundaries cause self-oscillation processes in these faults. The oscillations squeeze fluids out from faults intooverthrusted rocks from where they migrate along weakness zones. Migration of a two-phase fluid in the porous medium takes place between two reverse self-oscillations. That results in gas accumulations in fractured cavities (pockets. Any fluid migration is initially induced by lateral stresses in the crust and lithosphere, which in turn result from globalgeodynamic processes related to the mantle convection. The global processes are further transformed into regional movements along weakness zones.

Analysis of long-term variations in the geomagnetic poloidal field intensity and evaluation of their relationship with global geodynamics

SUMMARY The 1167 published cooling unit (CU) palaeointensity estimates contained in the 400‐10 Ma portion of the PINT global database were rigorously filtered according to accurate age determinations, palaeodirectional reliability, recognition of polarity and the method of palaeointensity acquisition. The remaining 865 estimates (group 1) were further filtered to ensure self-consistency, reducing the data set to 425 estimates (group 2). Group 1 and 2 data were clustered into temporally and/or spatially distinct rock suites (RS) enabling each part of the record to be assessed for potential biasing by overrepresentation of palaeosecular variation (PSV). The record was segmented according to the distribution of the data, rather than using arbitrary time windows, to ensure quasi-consistent behaviour within each segment. Differences between these segments clearly indicate that a significant long-timescale (10 7 and 10 8 yr) variation of the mean geomagnetic poloidal field intensity (GPFI) occurred during the 400‐10 Ma period and hence that changing lowermost mantle conditions affect the capacity of the geodynamo to generate a poloidal field. Both the mean dipole moment and its standard deviation appear to be a function of the range of values each CU may adopt at one particular time. This range is itself controlled by the variation of the maximum limit of dipole moment, while the value of the minimum limit remains relatively constant. Tentative support is provided for the recent suggestion that PSV may have been reduced during the Cretaceous normal superchron (CNS), though more data are needed in the range 120‐60 Ma to confirm this. No conclusive evidence was found to support the suggestion that the GPFI record may be biased towards low or high values by palaeointensity determinations obtained using methods that do not adopt pTRM checks. Indeed, offsets caused by unreliable data in well-represented parts of the record are likely to be random and cancel one another out. When GPFI variation is analysed at a sufficiently high resolution to allow comparisons with the geomagnetic polarity reversal frequency (RF), it is not possible to confirm whether the two parameters are anticorrelated, decoupled or related in some more complex way. However, it is clear that GPFI and RF are definitely not positively correlated as has been previously suggested. The present database documents sharp increases in GPFI around the onset times of the two recognized superchrons, itself implying an anticorrelation. The implications, for geodynamo and mantle modelling, of both an anticorrelation and a decoupling of the geomagnetic parameters are discussed briefly. A generic geodynamic model is proposed to explain the relationship between observed longterm changes in GPFI and global geodynamic processes. The model predicts that changes in GPFI result from a chain of geodynamic processes extending from crust to core, beginning with plate reorganizations at the surface and culminating in increases in the vigour of outer core convection. Supercontinents are transient surface expressions of such geodynamic processes and provide the potential to test the generic model. Four time stages are proposed to describe the major long-term changes in GPFI since the Early Devonian: 400‐350, 350‐250, 250‐175

The geologic history of Venus: A stratigraphic view

On the basis of regional and global stratigraphic analyses, we outline the major events in the geologic history of Venus determined by photogeological study of surface features. Because the morphological signatures of terrain emplaced prior to the time of tessera formation are not preserved, the stratigraphic record presented comprises only the last 10–20% of the total history of Venus. The estimated range of the mean crater retention age of the surface (from ∼200 to 1600 million years) leads us to describe the timing and duration of different events in terms of fractions of the mean surface age T. The beginning of the observed history of Venus was characterized by intensive tectonic deformation of global or semi‐global scale which formed the tessera terrain. Termination of the compressional stage is estimated to have occurred at about 1.4T while the tensional stage lasted for another 0.1–0.2T. After tessera formation, several stages of extensive volcanism occurred, burying vast areas of tessera and forming what are now observed as regional plains. The combined duration of the emplacement of these plains is estimated to be about 0.2–0.3T, with an implied average global rate of volcanism of a few cubic kilometers per year. Regional plains‐forming materials can be subdivided and are separated from each other, and from underlying and overlying units, by unconformities. These unconformities are formed, from oldest to youngest, by tessera‐forming deformation, dense fracturing, broad ridging, and, finally, wrinkle ridging. These tectonic episodes are interpreted to be generally globally synchronous and to represent successive episodes characterized by the dominance of compression, then tension, then again compression, and, finally, tension. The last global‐scale tectonic episode, extensive wrinkle ridging, happened at about time T, which was very close in time to the emplacement of the most areally abundant plains unit. This marked the transition to the present stage of the history of Venus, which is characterized by a predominance of regional rifting and related volcanism. This stage appears to have lasted from about time T to the present, making it the longest time duration among the stratigraphic units considered, although the resulting tectonic and volcanic features and deposits cover only 10–20% of the surface of Venus. These observations mean that the general intensity of tectonics and the flux of volcanism (a few tenths of a cubic kilometer per year) in this latest period were much lower than those in earlier times. In summary, the morphologically observable part of the history of Venus was characterized by two key characteristics that stand in contrast to the comparable period of Earth history (approximately the Phanerozoic) when global geodynamic processes were dominated by plate tectonics: (1) Venus shows no signature of plate tectonics; instead, its global tectonic environment passed from an initial dominance of compression, through tension, then again compression, and finally tension, with the density of deformational structures and the strain rate declining with time. (2) In the beginning of this period of time on Venus, plains‐forming volcanism occurred at a rate comparable to volcanism at mid‐ocean ridges but was emplaced in an entirely different style. The predominant component of volcanism on Earth during this time was the extrusive volcanism at mid‐oceanic ridges. For the last few hundred million years, Venus has been dominated primarily by rift‐associated volcanism emplaced at a production rate comparable to or even lower than present intraplate volcanism production rates on Earth.