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1

Journal of Geodynamics  

NSDL National Science Digital Library

The Journal of Geodynamics, from Elsevier Science, focuses on "solid earth research in geodetic, geophysical, geological and geochemical geodynamics, with special emphasis on the large scale processes involved."

2

1, 591624, 2004 Hadean geodynamic  

E-print Network

BGD 1, 591­624, 2004 Hadean geodynamic and metabolic cycles M. J. Russell and N. T. Arndt Title and metabolic cycles in the Hadean M. J. Russell and N. T. Arndt LGCA, Universit´e de Grenoble 1, 1381, rue de­624, 2004 Hadean geodynamic and metabolic cycles M. J. Russell and N. T. Arndt Title Page Abstract

Boyer, Edmond

3

NASA: Geodynamics Branch  

NSDL National Science Digital Library

The Geodynamics Branch at NASA's Goddard Space Flight Center conducts "research into the structure, dynamics, and evolution of the solid Earth and planets using space-techniques and remote sensing data." The website features the Branch's latest scientific findings, internship opportunities, and annual reports. Users can find fantastic images and text detailing many of its research projects such as the monitoring of oceanic islands with satellite remote sensing and the development of an interactive analysis tool to study the Mars Orbiter Laser Altimeter (MOLA) gridded data. Educators and students can find links to numerous, graphically enhanced tutorials and activities.

4

Geodynamics Branch research report, 1982  

NASA Technical Reports Server (NTRS)

The research program of the Geodynamics Branch is summarized. The research activities cover a broad spectrum of geoscience disciplines including space geodesy, geopotential field modeling, tectonophysics, and dynamic oceanography. The NASA programs which are supported by the work described include the Geodynamics and Ocean Programs, the Crustal Dynamics Project, the proposed Ocean Topography Experiment (TOPEX) and Geopotential Research Mission. The individual papers are grouped into chapters on Crustal Movements, Global Earth Dynamics, Gravity Field Model Development, Sea Surface Topography, and Advanced Studies.

Kahn, W. D. (editor); Cohen, S. C. (editor)

1983-01-01

5

Seismological Constraints on Geodynamics  

NASA Astrophysics Data System (ADS)

Earth is an open thermodynamic system radiating heat energy into space. A transition from geostatic earth models such as PREM to geodynamical models is needed. We discuss possible thermodynamic constraints on the variables that govern the distribution of forces and flows in the deep Earth. In this paper we assume that the temperature distribution is time-invariant, so that all flows vanish at steady state except for the heat flow Jq per unit area (Kuiken, 1994). Superscript 0 will refer to the steady state while x denotes the excited state of the system. We may write ? 0=(J{q}0?X{q}0)/T where Xq is the conjugate force corresponding to Jq, and ? is the rate of entropy production per unit volume. Consider now what happens after the occurrence of an earthquake at time t=0 and location (0,0,0). The earthquake introduces a stress drop ? P(x,y,z) at all points of the system. Response flows are directed along the gradients toward the epicentral area, and the entropy production will increase with time as (Prigogine, 1947) ? x(t)=? 0+? {1}/(t+? )+? {2}/(t+? )2+etc A seismological constraint on the parameters may be obtained from Omori's empirical relation N(t)=p/(t+q) where N(t) is the number of aftershocks at time t following the main shock. It may be assumed that p/q\\sim\\alpha_{1}/\\beta times a constant. Another useful constraint is the Mexican-hat geometry of the seismic transient as obtained e.g. from InSAR radar interferometry. For strike-slip events such as Landers the distribution of \\DeltaP is quadrantal, and an oval-shaped seismicity gap develops about the epicenter. A weak outer triggering maxi?m is found at a distance of about 17 fault lengths. Such patterns may be extracted from earthquake catalogs by statistical analysis (Lomnitz, 1996). Finally, the energy of the perturbation must be at least equal to the recovery energy. The total energy expended in an aftershock sequence can be found approximately by integrating the local contribution over volume V: \\int${V}? {k}? {k}2(grad? P)2dV where the Lik are Onsager coefficients and ? k} is the stoichiometric coefficient of phase k. This enables us to calibrate the process. Note that there are contributions to the excited state that include material flows Jkx (flows of water and electrons into the epicentral area), in addition to the excited heat flow values Jqx. A geodynamic model of the earthquake process would be essential for earthquake prediction. Kuiken, G.D.C., Thermodynamics of Irreversible Processes (John Wiley & Sons, New York, 1994). Lomnitz, C., On thermodynamics of planets, Geophys. J. Roy. Astr. Soc., 5, 157-161, 1961. Lomnitz, C., Search of a worldwide catalog for earthquakes triggered at intermediate distances, Bull. Seismol. Soc. Am., 86, 293-298, 1996.

Lomnitz, C.

2004-12-01

6

From Geodynamics to Simplicity  

NASA Astrophysics Data System (ADS)

Mantle convection and plate tectonics are often thought as synonymous. Convection is sometimes treated as the driver or plate tectonics is viewed as simply a manifestation of mantle convection. Mantle plumes are regarded as supplying some of the elements missing in the plate tectonic and mantle convection paradigms, such as island chains, swells and large igneous provinces. An alternate view is motivated by Prigogine's concept of far-from-equilibrium self-organization ( SOFFE), not to be confused with Bak's self-organized criticality ( SOC) . In a SOFFE system the components interact, and the system is small compared to the outside world to which it is open. There must be multiple possible states and dissipation is important. Such a system is sensitive to small changes. Rayleigh-Benard convection in a container with isothermal walls is such a self-organizing system ; the driving bouyancy and the dissipation ( viscosity ) are in the fluid. In Marangoni convection the driving forces ( surface tension ) and dissipation are in the surface film and this organizes the surface and the underlying fluid. The mantle provides energy and matter to the interacting plate system but forces in the plates drive and dissipate the energy. Thus, plate tectonics may be a SOFFEE system that drives convection,as are systems cooled from above, in general. If so, plates will reorganize as boundary conditions change ; incipient plate boundaries will emerge as volcanic chains at tensile regions. Plates are defined as regions of lateral compression ( force chains ), rather than strength, and they are ephemeral. The plate system, rather than mantle viscosity, will modulate mantle cooling. The supercontinent cycle, with episodes of reorganization and massive magmatism, may be a manifestation of this far-from-equilibrium, driven from above, system. Geodynamics may be simpler than we think. Plate tectonics is certainly a more powerful concept once the concepts of rididity, elasticity, homogeneity, steady-state, equilibrium and uniformity are dropped or modified, as qualifiers of the system,as recommended in Occam's philosophy.

Anderson, D. L.

2002-12-01

7

Grand Challenges in Geodynamics Outstanding geodynamics problems and emerging research  

E-print Network

opportunities for the Earth Sciences March 1, 2010 #12;2 Grand ChallenGes in GeodynamiCs Preface This report future. Nevertheless, they all have out- standing merit, and in the end, our committee found it relatively easy to come to a consensus. Cover Illustration: Earth's Interior. Courtesy: Calvin J. Hamilton

Olson, Peter L.

8

Global disasters: Geodynamics and society  

NASA Astrophysics Data System (ADS)

The problem of reducing the damage caused by geodynamic and social disasters is an important and urgent task facing humanity. By the middle of this century, damage from these disasters will exceed the combined gross national product (GNP) of all countries in the world. The authors have developed the first database to include the largest geodynamic and social phenomena that occurred on Earth before 2005. All disasters are classified by size using a single-logarithmic scale suggested by Rodkin and Shebalin in 1993. The base consists of 47 dates and 104 disasters. The following phenomenological model is proposed: the scale of disasters does not decrease in time and a minimum of disasters was recorded in the 15th century; the number of disasters is characterized by cycles that last as long as the first thousand years. Natural and social disasters taken together are uniformly distributed in time, but their separate distribution is not uniform. One fundamentally new feature of this paper is that the assumption about the statistical significance of the impact of the biosphere and society on the geodynamic processes is justified. The results allow us to formulate a new understanding of global disasters as an event, the damage from which will not be possible to eliminate by the joint resource potential. The consequences of a global disaster may cause the irreversible destruction of civilization.

Vikulin, A. V.; Semenets, N. V.; Vikulina, M. A.

2013-12-01

9

Basic research for the geodynamics program  

NASA Technical Reports Server (NTRS)

Work performed and data obtained in geodynamic research is reported. The purpose was to obtain utilization of: (1) laser and very long baseline interferometry (VLBI); (2) range difference observation in geodynamics; (3) development of models for ice sheet and crustal deformations. The effects of adopting new precession, nutation and equinox corrections on the terrestrial reference frame are investigated.

Mueller, I. I.

1982-01-01

10

Basic research for the geodynamics program  

NASA Technical Reports Server (NTRS)

Some objectives of this geodynamic program are: (1) optimal utilization of laser and VLBI observations as reference frames for geodynamics, (2) utilization of range difference observations in geodynamics, and (3) estimation techniques in crustal deformation analysis. The determination of Earth rotation parameters from different space geodetic systems is studied. Also reported on is the utilization of simultaneous laser range differences for the determination of baseline variation. An algorithm for the analysis of regional or local crustal deformation measurements is proposed along with other techniques and testing procedures. Some results of the reference from comparisons in terms of the pole coordinates from different techniques are presented.

1984-01-01

11

International GPS Service for Geodynamics  

NASA Technical Reports Server (NTRS)

This 1995 annual report of the IGS International GPS (Global Positioning System) Service for Geodynamics - describes the second operational year of the service. It provides the many IGS contributing agencies and the rapidly growing user community with essential information on current organizational and technical matters promoting the IGS standards and products (including organizational framework, data processing strategies, and statistics showing the remarkable expansion of the GPS monitoring network, the improvement of IGS performance, and product quality). It also introduces important practical concepts for network densification by integration of regional stations and the combination of station coordinate solutions. There are groups of articles describing general aspects of the IGS, the Associate Analysis Centers (AACs), Data Centers, and IGS stations.

Zumberge, J. F. (Editor); Urban, M. P. (Editor); Liu, R. (Editor); Neilan, R. E. (Editor)

1996-01-01

12

The NASA Geodynamics Program report, 1981  

NASA Technical Reports Server (NTRS)

The activities of the NASA Geodynamics Program in 1981 both in achieving improved measurement precision and in establishing the foundation for the acquisition and analysis of scientific data are discussed.

1982-01-01

13

Research program of the Geodynamics Branch  

NASA Technical Reports Server (NTRS)

This report is the Fourth Annual Summary of the Research Program of the Geodynamics Branch. The branch is located within the Laboratory for Terrestrial Physics of the Space and Earth Sciences Directorate of the Goddard Space Flight Center. The research activities of the branch staff cover a broad spectrum of geoscience disciplines including: tectonophysics, space geodesy, geopotential field modeling, and dynamic oceanography. The NASA programs which are supported by the work described in this document include the Geodynamics and Ocean Programs, the Crustal Dynamics Project and the proposed Ocean Topography Experiment (TOPEX). The reports highlight the investigations conducted by the Geodynamics Branch staff during calendar year 1985. The individual papers are grouped into chapters on Crustal Movements and Solid Earth Dynamics, Gravity Field Modeling and Sensing Techniques, and Sea Surface Topography. Further information on the activities of the branch or the particular research efforts described herein can be obtained through the branch office or from individual staff members.

Kahn, W. D. (editor); Cohen, S. C. (editor); Boccucci, B. S. (editor)

1986-01-01

14

COURSE SYLLABUS GEO 6600/7600 Geodynamics  

E-print Network

in fundamental physics and highly interdisciplinary. The important elements of geodynamics are the same line modeling exercises using standard codes (which we will learn together as a group). Another third of ductile flow, fault slip, earthquakes and volcanism. Elements of my research also have implications

Lowry, Anthony R.

15

Numerical Geodynamics An introduction to computational methods  

E-print Network

Thorsten W. Becker Department of Earth Sciences University of Southern California Los Angeles CA, USA Boris J. P. Kaus Department of Earth Sciences ETH Z¨urich, Switzerland Editing and additions by Francois . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 3 Introduction to Numerical Geodynamics 34 3.1 Numerical methods in the Earth Sciences

Becker, Thorsten W.

16

Research activities of the Geodynamics Branch  

NASA Technical Reports Server (NTRS)

A broad spectrum of geoscience disciplines including space geodesy, geopotential field modeling, tectonophysics, and dynamic oceanography are discussed. The NASA programs, include the Geodynamics and Ocean Programs, the Crustal Dynamics Project, the proposed Ocean Topography Experiment (TOPEX), and the Geopotential Research Mission (GRM). The papers are grouped into chapters on Crustal Movements, Global Earth Dynamics, Gravity Field Model Development, Sea Surface Topography, and Advanced Studies.

Kahn, W. D. (editor); Cohen, S. C. (editor)

1984-01-01

17

The evolution of Hadean-Eoarchaean geodynamics  

NASA Astrophysics Data System (ADS)

Geodynamic modelling of Hadean/Eoarchaean tectonics typically requires higher rates of internal heat production, and higher mantle temperatures, in models that possess temperature-dependent viscosity and a yield criterion. In such models under Hadean conditions, for a wide range of geodynamic configurations and modelling approaches, subduction has a propensity to fail. This has led to the suggestion that the predominant tectonic regime in the Hadean was stagnant-lid convection, with intermittent recycling events. Various lines of evidence support this suggestion, from i) the long mixing time of mantle isotopic anomalies or compositional heterogeneities, such as 142Nd, 182W, and platinum group elements, to ii) the long residence time of the Hadean protolith to the Jack Hills zircons, and iii) thermal evolution models, which typically require lower heat flux in the past to avoid the "Archaean thermal catastrophe". The framework provided by stagnant lid, or episodic overturn, convection, iv) provides an explanation for the formation of early Archaean TTGs and greenstones, and v) explains the interleaving arc-plume sequence observed in many Archaean terranes, suggesting subduction initiation events may have been common, increasing their preservation potential. Implications include a low magnetic field strength in the Hadean, which is consistent with emerging paleointensity data from these times.

O'Neill, C.; Debaille, V.

2014-11-01

18

Geodynamic Movements of The Sudeten Area  

NASA Astrophysics Data System (ADS)

GPS data of five annual campaigns monitored during the period 1997-2001 on re- gional geodynamic network SUDETEN, that consists of the SILESIA and the GEO- SUD networks, were processed by the Bernese 4.2 software (by its modules ADDNEQ and ADDNEQ2) to find movements vectors of individual selected sites of the net- work. From methodological and mainly from interpretation viewpoints data were linked always independently to one of the following EUREF GPS stations: (a) GOPE and/or WETR, (b) BOR1 and (c) PENC. This approach allowed movement relations of the Sudeten area with respect to main European geological units (parts of the European Platform, the Pannonian basin, etc.) to be evaluated. The movement pat- tern of the Sudeten area was correlated with existing geodynamic regional evidences such as earthquake occurrences, recent rejuvenating tectonics, and other geophysi- cal and geodetic fields, e.g. the stress field, vertical crustal movements. The inten- sive joint activity of the Polish and the Czech researchers could not be realized with- out considerable financial supports of many national institutions, mainly by the grant agencies of both countries (GACR 205/97/0679 and 205/01/0480, 9T12E02918, and 9T12E00518), and of research programmes pursued in Poland and in the Czech Re- public (e.g. MEYS LN00A005) in this field.

Schenk, V.; Kontny, B.; Borkowski, A.; Bosy, J.; Kottnauer, P.; Schenkov, Z.

19

Geodynamic Signals Detected by Geodetic Methods in Iceland  

Microsoft Academic Search

The geodynamics laboratory provided by Iceland's position on an active mid-ocean ridge has been recognized for several decades. Geodetic experiments have been designed and carried out in Iceland since 1938 to verify various global geodynamic theories, such as Wegener's theory of continental drift, the sea floor spreading hypothesis, plate tectonics, mantle plumes etc. State-of-the-art techniques have been used to obtain

Pll Einarsson; Freysteinn Sigmundsson; Erik Sturkell; ra rnadttir; Rikke Pedersen; Carolina Pagli; Halldr Geirsson

20

Adaptive Finite Element Methods in Geodynamics  

NASA Astrophysics Data System (ADS)

Adaptive finite element methods are presented for improving the quality of solutions to two-dimensional (2D) and three-dimensional (3D) convection dominated problems in geodynamics. The methods demonstrate the application of existing technology in the engineering community to problems within the `solid' Earth sciences. Two-Dimensional `Adaptive Remeshing': The `remeshing' strategy introduced in 2D adapts the mesh automatically around regions of high solution gradient, yielding enhanced resolution of the associated flow features. The approach requires the coupling of an automatic mesh generator, a finite element flow solver and an error estimator. In this study, the procedure is implemented in conjunction with the well-known geodynamical finite element code `ConMan'. An unstructured quadrilateral mesh generator is utilised, with mesh adaptation accomplished through regeneration. This regeneration employs information provided by an interpolation based local error estimator, obtained from the computed solution on an existing mesh. The technique is validated by solving thermal and thermo-chemical problems with known benchmark solutions. In a purely thermal context, results illustrate that the method is highly successful, improving solution accuracy whilst increasing computational efficiency. For thermo-chemical simulations the same conclusions can be drawn. However, results also demonstrate that the grid based methods employed for simulating the compositional field are not competitive with the other methods (tracer particle and marker chain) currently employed in this field, even at the higher spatial resolutions allowed by the adaptive grid strategies. Three-Dimensional Adaptive Multigrid: We extend the ideas from our 2D work into the 3D realm in the context of a pre-existing 3D-spherical mantle dynamics code, `TERRA'. In its original format, `TERRA' is computationally highly efficient since it employs a multigrid solver that depends upon a grid utilizing a clever repeated subdivision of nested icosahedrons. Unfortunately, the standard finite element method of obtaining higher resolution in local grids (such as the adaptive unstructured methods presented above) would throw away the regular grid and all the benefits of the current method. The use of an `adaptive multigrid' however, allows the incorporation of local high resolution grids nested within these efficient global models. Although in the early stages of development, this method appears promising, with initial tests suggesting it has the capability to maintain computational efficiency whilst improving solution accuracy and resolution where required.

Davies, R.; Davies, H.; Hassan, O.; Morgan, K.; Nithiarasu, P.

2006-12-01

21

Geodynamic contributions to global climatic change  

NASA Technical Reports Server (NTRS)

Orbital and rotational variations perturb the latitudinal and seasonal pattern of incident solar radiation, producing major climatic change on time scales of 10(exp 4)-10(exp 6) years. The orbital variations are oblivious to internal structure and processes, but the rotational variations are not. A program of investigation whose objective would be to explore and quantify three aspects of orbital, rotational, and climatic interactions is described. An important premise of this investigation is the synergism between geodynamics and paleoclimate. Better geophysical models of precessional dynamics are needed in order to accurately reconstruct the radiative input to climate models. Some of the paleoclimate proxy records contain information relevant to solid Earth processes, on time scales which are difficult to constrain otherwise. Specific mechanisms which will be addressed include: (1) climatic consequences of deglacial polar motion; and (2) precessional and climatic consequences of glacially induced perturbations in the gravitational oblateness and partial decoupling of the mantle and core. The approach entails constructing theoretical models of the rotational, deformational, radiative, and climatic response of the Earth to known orbital perturbations, and comparing these with extensive records of paleoclimate proxy data. Several of the mechanisms of interest may participate in previously unrecognized feed-back loops in the climate dynamics system. A new algorithm for estimating climatically diagnostic locations and seasons from the paleoclimate time series is proposed.

Bills, Bruce G.

1992-01-01

22

Basic research for the geodynamics program  

NASA Technical Reports Server (NTRS)

The mathematical models of space very long base interferometry (VLBI) observables suitable for least squares covariance analysis were derived and estimatability problems inherent in the space VLBI system were explored, including a detailed rank defect analysis and sensitivity analysis. An important aim is to carry out a comparative analysis of the mathematical models of the ground-based VLBI and space VLBI observables in order to describe the background in detail. Computer programs were developed in order to check the relations, assess errors, and analyze sensitivity. In order to investigate the estimatability of different geodetic and geodynamic parameters from the space VLBI observables, the mathematical models for time delay and time delay rate observables of space VLBI were analytically derived along with the partial derivatives with respect to the parameters. Rank defect analysis was carried out both by analytical and numerical testing of linear dependencies between the columns of the normal matrix thus formed. Definite conclusions were formed about the rank defects in the system.

1991-01-01

23

Unified Gravimetric Reference Frame for Polish IGS\\/EPN Stations and Geodynamic Test Fields  

Microsoft Academic Search

Absolute gravity values are useful to regional geodynamic purposes as a complement of position monitoring at IGS\\/EPN permanent stations. Absolute gravity stations in region of geodynamic test field are also necessary as precise reference level for relative gravimetric measurements and long-period gravity monitoring. Absolute gravimetric network to unify gravimetric reference level for GNSS permanent stations and geodynamic test fields had

Janusz Walo; Tomasz Olszak; Andrzej Pachuta; Dominik Prchniewicz; Ryszard Szpunar

2010-01-01

24

Archean Geodynamics and Environments Geophysical Monograph Series 164  

E-print Network

Archean Geodynamics and Environments Geophysical Monograph Series 164 Copyright 2006 by the American Geophysical Union 10.1029/164GM06 Archean Thermal Regime And Stabilization of The Cratons Jean at Montréal, Canada Claude Jaupart Institut de Physique du Globe de Paris, France Archean provinces

Long, Bernard

25

Archean Geodynamics and Envionments Geophysical Monograph Series 164  

E-print Network

Archean Geodynamics and Envionments Geophysical Monograph Series 164 Copyright 2006 by the American Geophysical Union Thermal and Mechanical Controls on the Evolution of Archean Crustal Deformation: Examples of Melbourne, Victoria, Australia Dome-and-keel formation in Archean granite­greenstone terrains was uniquely

Sandiford, Mike

26

Metamorphic chemical geodynamics of subduction zones Gray E. Bebout  

E-print Network

, and the chemical changes in subducting rocks potentially contributing to the geochemical heterogeneityFrontiers Metamorphic chemical geodynamics of subduction zones Gray E. Bebout Lehigh University, and experimental evidence for the physical and chemical properties of fluids at the pressures and temperatures

Bebout, Gray E.

27

Planetary cores: a geodynamic perspective (Invited)  

NASA Astrophysics Data System (ADS)

How can measurements of planetary core materials improve our understanding of their geodynamical behaviour? Here I will focus on three aspects of this questions: 1) core formation; 2) the growth and rheology of solid cores; 3) dynamo activity. Core formation occurs either due to the heat generated by short-lived nuclides (for small bodies) or due to gravitational energy released during impacts (for large bodies) [1]. Core formation results in elemental fractionation; such fractionation depends on P,T and oxygen fugacity [2], and for Earth-mass bodies occurs as a succession of discrete events. Experimental measurements of siderophile element partition coefficients are necessary to infer conditions during accretion, though these inferences are non-unique [3]. Core formation may also lead to isotopic fractionation of elements such as Si [4] and Fe [5], although the latter in particular is currently uncertain and merits further experimental investigation. Core solidification depends on the slopes of the adiabat and melting curve, and on the concentration and nature of the light element(s) present [6,7]. Solidification may proceed from outside in (for small bodies) or from inside out (for larger bodies); the solid may be either lighter or heavier than the fluid, depending on the core composition. Thus, core solidification is complex and poorly understood; for instance, Ganymede and Mercurys cores may be in a completely different solidification regime to that of the Earth [8,9]. Solidification can also vary spatially, giving rise to inner core seismological structure [10,11]. The viscosity of a solid inner core is an important and poorly constrained parameter [12] which controls core deformation, core-mantle coupling and tidal heating. Super-Earths probably lack solid inner cores [13], though further high-P experimental data are needed. Core dynamos are usually thought to be driven by compositional or thermal buoyancy [14] , with the former effect dominant for small bodies. However, forcing driven by tidal or precessional effects may also be important [e.g. 15]. As noted above, the complexities of core solidification can lead to a rich range of potential dynamo styles [e.g. 16]. The long-term evolution of dynamos is governed primarily by the mantle's ability to extract heat from the core. For the Earth, a factor of 2 uncertainty in the thermal conductivity of liquid iron is a current impediment to a better understanding of the dynamo's evolution [14]. [1] Rubie et al. Treat. Geophys. 2007 [2] Righter 2003 [3] Rudge et al. 2010 [4] Ziegler et al. 2010 [5] Polyakov 2009 [6] Chen et al. 2008 [7] Morard et al. 2007 [8] Nimmo & Alfe 2007 [9] Hauck et al. 2006 [10] Monnereau et al. 2010 [11] Alboussiere et al. 2010 [12] Mound & Buffett 2006 [13] Gaidos et al. 2010 [14] Nimmo Treat. Geophys. 2007 [15] Tilgner 2005 [16] Vilim et al. in press

Nimmo, F.

2010-12-01

28

Study of a close-grid geodynamic measurement system  

NASA Technical Reports Server (NTRS)

The Clogeos (Close-Grid Geodynamic Measurement System) concept, a complete range or range-rate measurement terminal installed in a satellite in a near-polar orbit with a network of relatively simple transponders or retro-reflectors on the ground at intervals of 0.1 to 10 km was reviewed. The distortion of the grid was measured in three dimensions to accuracies of + or - 1 cm with important applications to geodynamics, glaciology, and geodesy. User requirements are considered, and a typical grid, designed for earthquake prediction, was laid out along the San Andreas, Hayward, and Calaceras faults in southern California. The sensitivity of both range and range-rate measurements to small grid motions was determined by a simplified model. Variables in the model are satellite altitude and elevation angle plus grid displacements in latitude, and height.

1977-01-01

29

Geodynamics of the Yellowstone Hotspot: Plume or Not?  

Microsoft Academic Search

A collaborative research project has focused study on the Yellowstone hotspot to understand its geodynamic processes and to assess whether it has a deep mantle source. The study includes seismic and GPS investigations over a large portion of northwestern U.S., focusing on the possible plume-plate interaction that is hypothesized for the Yellowstone-Snake River Plain (YSRP) volcanic field. Regional deformation reveals

R. B. Smith; E. Humphreys; P. J. Tackley; C. M. Meertens; K. G. Dueker; G. Waite; J. Crosswhite; D. Schutt; C. Puskas; J. W. Hernlund

2002-01-01

30

Monitoring of global geodynamic processes using satellite observations  

NASA Astrophysics Data System (ADS)

To study mechanisms of destructive geodynamic phenomena including determination of places of possible severe earthquakes, volcano eruptions and some other natural hazards, it is important to have means to evolve areas where maximum changes of the displacement velocities and the terrestrial crust vertical movements are possible. The previous experience has shown that the satellite geodesy techniques including global navigation systems and satellite laser ranging are the most effective for research activities in this field. Permanent control of secular movement of GPS-stations of the international geodynamic network, located in Russia, has allowed improving the reference coordinate frame for North Eurasia since Russian network stations provide representative covering of the largest stable areas (the Siberian and the East European) of the Eurasian plate. Along its southern border, there is a zone consisting of a great number of microplates surrounding the South-Eurasian stable plate. Interaction of these small plates and blocks influences distribution of seismic stresses in internal parts of the continent that is confirmed by the highest seismic activity of the triangle bordered by thrusts of the Himalayas and faults of the Pamirs, the Tien-Shan, the Baikal and the North-Eastern China. One of the active tectonic zones of Egypt located in Aswan, is characterized by regional basement rock uplift and regional faulting. In 1997, the African Regional Geodynamic Network was developed around the northern part of Lake Nasser, consists of 11 points, on both sides of the Lake. Its main goal is to study the geodynamical behavior around the northern part of the lake. The collected data were processed using the Bernese software version 5.0. From the velocity results, including also the African plate motion, it can be noticed that all stations of this network are moved to the northeast direction and it is typically the direction of the African plate motion.

Tatevian, S. K.; Attia, G. F.; Abou-Aly, N.; Ghoneim, R.; Hegazy, M.

2014-06-01

31

Applications of Geodesy to Geodynamics, an International Symposium  

NASA Technical Reports Server (NTRS)

Geodetic techniques in detecting and monitoring geodynamic phenomena are reviewed. Specific areas covered include: rotation of the earth and polar motion; tectonic plate movements and crustal deformations (space techniques); horizontal crustal movements (terrestrial techniques); vertical crustal movements (terrestrial techniques); gravity field, geoid, and ocean surface by space techniques; surface gravity and new techniques for the geophysical interpretation of gravity and geoid undulation; and earth tides and geodesy.

Mueller, I. I. (editor)

1978-01-01

32

Fluidity: A New Adaptive, Unstructured Mesh Geodynamics Model  

NASA Astrophysics Data System (ADS)

Fluidity is a sophisticated fluid dynamics package, which has been developed by the Applied Modelling and Computation Group (AMCG) at Imperial College London. It has many environmental applications, from nuclear reactor safety to simulations of ocean circulation. Fluidity has state-of-the-art features that place it at the forefront of computational fluid dynamics. The code: Dynamically optimizes the mesh, providing increased resolution in areas of dynamic importance, thus allowing for accurate simulations across a range of length scales, within a single model. Uses an unstructured mesh, which enables the representation of complex geometries. It also enhances mesh optimization using anisotropic elements, which are particularly useful for resolving one-dimensional flow features and material interfaces. Uses implicit solvers thus allowing for large time-steps with minimal loss of accuracy. PETSc provides some of these, though multigrid preconditioning methods have been developed in-house. Is optimized to run on parallel processors and has the ability to perform parallel mesh adaptivity - the subdomains used in parallel computing automatically adjust themselves to balance the computational load on each processor, as the mesh evolves. Has a novel interface-preserving advection scheme for maintaining sharp interfaces between multiple materials / components. Has an automated test-bed for verification of model developments. Such attributes provide an extremely powerful base on which to build a new geodynamical model. Incorporating into Fluidity the necessary physics and numerical technology for geodynamical flows is an ongoing task, though progress, to date, includes: Development and implementation of parallel, scalable solvers for Stokes flow, which can handle sharp, orders of magnitude variations in viscosity and, significantly, an anisotropic viscosity tensor. Modification of the multi-material interface-preserving scheme to allow for tracking of chemical heterogeneities in mantle convection models. Incorporation of a suite of geodynamic benchmarks into the automated test-bed. These recent advances, which all work in combination with the parallel mesh-optimization technology, enable Fluidity to simulate geodynamical flows accurately and efficiently. Initial results will be presented from: (i) a range of 2-D and 3-D thermal convection benchmarks; kinematic and dynamic subduction zone simulations; (iii) Comparisons between model predictions and laboratory experiments of plume dynamics. These results all clearly demonstrate the benefits of adaptive, unstructured meshes for geodynamical flows.

Davies, D. R.; Wilson, C. R.; Kramer, S. C.; Piggott, M. D.; Le Voci, G.; Collins, G. S.

2010-05-01

33

Precambrian geodynamics: models vs. concepts and constrains (Invited)  

NASA Astrophysics Data System (ADS)

In contrast to modern-day plate tectonics, studying Precambrian geodynamics presents a unique challenge as currently there is no agreement upon paradigm concerning the global geodynamics and lithosphere tectonics for the early Earth. Further progress in this direction requires cross-disciplinary efforts with a special emphasis placed upon quantitative testing of existing geodynamic concepts and extrapolating back in geological time, using both global and regional scale thermomechanical numerical models, which have been validated for present day Earth conditions. Here, we focus on discussing results of recent modeling studies in the context of existing concepts and constraints for Precambrian geodynamics. The three key features of Precambrian Earth evolution are outlined based on combining available observations and thermomechanical models (cf. review by Gerya, 2013): (1) Early Archean pre-subduction geodynamics was dominated by plume tectonics and the development of hot accretionary orogens with low topography, three-dimensional deformation and pronounced gravitational tectonics. Mantle downwellings and lithospheric delamination (dripping-off) processes are likely to have played a key role in assembling and stabilizing the hot orogens on a timescale up to hundreds of millions of years. Both oceanic-like and continental-like lithospheres were rheologically weak due to the high Moho temperature (>800 C) and melt percolation from hot partially molten sublithospheric mantle (Sizova et al., 2010). (2) Wide spread development of modern-style subduction on Earth started during Mesoarchean-Neoarchean at 3.2-2.5 Ga. This is marked by the appearance of paired metamorphic complexes and oldest eclogite ages in subcontinental lithospheric mantle. Numerical models suggest that the transition occurred at mantle temperatures 175-250 C higher than present day values, and was triggered by stabilization of rheologically strong plates of both continental and oceanic type (Sizova et al., 2010). Due to the hot mantle temperature, slab break-off was more frequent in the Precambrian time causing more episodic subduction compared to present day. (3) Wide spread development of modern-style (cold) collision on Earth started during Neoproterozoic at 600-800 Ma and is thus decoupled from the onset of modern-style subduction. Cold collision created favorable conditions for the generation of ultrahigh-pressure (UHP) metamorphic complexes which become widespread in Phanerozoic orogens. Numerical models suggest that the transition occurred at mantle temperatures 80-150 C higher than present day values and was associated with stabilization of the continental subduction (Sizova et al., 2013). Frequent shallow slab break-off limited occurrence of UHP rocks in the Precambrian time. References Gerya, T.V. (2013) Precambrian geodynamics: Concepts and models. Gondwana Research, DOI: http://dx.doi.org/10.1016/j.gr.2012.11.008 Sizova, E., Gerya, T., Brown, M., Perchuk, L.L. (2010) Subduction styles in the Precambrian: Insight from numerical experiments, Lithos, 116, 209-229. Sizova, E.V., Gerya, T.V., Brown, M. (2013) Contrasting styles of Phanerozoic and Precambrian continental collision, Gondwana Research, DOI: http://dx.doi.org/10.1016/j.gr.2012.12.011

Gerya, T.; Sizova, E.; Brown, M.

2013-12-01

34

Numerical Modeling in Geodynamics: Success, Failure and Perspective  

NASA Astrophysics Data System (ADS)

A real success in numerical modeling of dynamics of the Earth can be achieved only by multidisciplinary research teams of experts in geodynamics, applied and pure mathematics, and computer science. The success in numerical modeling is based on the following basic, but simple, rules. (i) People need simplicity most, but they understand intricacies best (B. Pasternak, writer). Start from a simple numerical model, which describes basic physical laws by a set of mathematical equations, and move then to a complex model. Never start from a complex model, because you cannot understand the contribution of each term of the equations to the modeled geophysical phenomenon. (ii) Study the numerical methods behind your computer code. Otherwise it becomes difficult to distinguish true and erroneous solutions to the geodynamic problem, especially when your problem is complex enough. (iii) Test your model versus analytical and asymptotic solutions, simple 2D and 3D model examples. Develop benchmark analysis of different numerical codes and compare numerical results with laboratory experiments. Remember that the numerical tool you employ is not perfect, and there are small bugs in every computer code. Therefore the testing is the most important part of your numerical modeling. (iv) Prove (if possible) or learn relevant statements concerning the existence, uniqueness and stability of the solution to the mathematical and discrete problems. Otherwise you can solve an improperly-posed problem, and the results of the modeling will be far from the true solution of your model problem. (v) Try to analyze numerical models of a geological phenomenon using as less as possible tuning model variables. Already two tuning variables give enough possibilities to constrain your model well enough with respect to observations. The data fitting sometimes is quite attractive and can take you far from a principal aim of your numerical modeling: to understand geophysical phenomena. (vi) If the number of tuning model variables are greater than two, test carefully the effect of each of the variables on the modeled phenomenon. Remember: With four exponents I can fit an elephant (E. Fermi, physicist). (vii) Make your numerical model as accurate as possible, but never put the aim to reach a great accuracy: Undue precision of computations is the first symptom of mathematical illiteracy (N. Krylov, mathematician). How complex should be a numerical model? A model which images any detail of the reality is as useful as a map of scale 1:1 (J. Robinson, economist). This message is quite important for geoscientists, who study numerical models of complex geodynamical processes. I believe that geoscientists will never create a model of the real Earth dynamics, but we should try to model the dynamics such a way to simulate basic geophysical processes and phenomena. Does a particular model have a predictive power? Each numerical model has a predictive power, otherwise the model is useless. The predictability of the model varies with its complexity. Remember that a solution to the numerical model is an approximate solution to the equations, which have been chosen in believe that they describe dynamic processes of the Earth. Hence a numerical model predicts dynamics of the Earth as well as the mathematical equations describe this dynamics. What methodological advances are still needed for testable geodynamic modeling? Inverse (time-reverse) numerical modeling and data assimilation are new methodologies in geodynamics. The inverse modeling can allow to test geodynamic models forward in time using restored (from present-day observations) initial conditions instead of unknown conditions.

Ismail-Zadeh, A.

2005-12-01

35

Strike-slip faults on Mars: Observations and implications for global tectonics and geodynamics  

E-print Network

Strike-slip faults on Mars: Observations and implications for global tectonics and geodynamics January 2008; accepted 1 May 2008; published 5 August 2008. [1] The tectonic evolution of Mars has been and geodynamic evolution of Mars. We model the tectonic evolution of the planet in response to the evolving

Hauck II, Steven A.

36

Constraining effective rheology through parallel joint geodynamic inversion  

NASA Astrophysics Data System (ADS)

The dynamics of crust and lithosphere is to a large extent controlled by its effective viscosity. Unfortunately, extrapolation of laboratory experiments indicates that viscosity is likely to vary over many orders of magnitude. Additional methods are thus required to constrain the effective viscosity of the present-day lithosphere using more direct geophysical observations. Here we discuss a method, which couples 3D geodynamic models with observations (surface velocities and gravity anomalies) and with a Bayesian inversion scheme on massively parallel high performance computers. We illustrate that the basic principle of a joint geodynamic and gravity inversion works well with a simple analytical example. In a next step, we test our approach using a synthetic 3D model of salt tectonics with erosion and sedimentation, and check how much noise conditions, model resolution, and sparse data coverage affect the resolving power of the method. Results show that it is possible to constrain the effective viscosity and density of layers that contribute to the large-scale dynamics, provided that those layers are numerically well resolved. The properties of thin layers that do not contribute much to the overall dynamics cannot be constrained, but noise or sparse data sampling does not significantly affect the inversion results. This thus illustrates that a joint geodynamic and gravity inversion is a potentially powerful method to constrain the dynamics of the crust and lithosphere. Having better constraints on the structure of the present-day crust and lithosphere will help to narrow the parameter space for models that aim to unravel lithosphere dynamics on a geological time scale.

Baumann, Tobias S.; Kaus, Boris J. P.; Popov, Anton A.

2014-09-01

37

Finding a suitable finite element for 3D geodynamic modeling  

NASA Astrophysics Data System (ADS)

Numerical modeling of geodynamic processes has become an important research topic in the recent decades. Apart from the correct interpretation of the model results, it is also vastly important to clearly understand the technical aspects of the model formulation, the weaknesses and advantages of different numerical schemes. The majority of numerical models considered to date are two-dimensional. The increased computational complexity of the 3D models make the selection of a suitable numerical scheme even more important compared to 2D. The geodynamic models can be very ill-posed from the numerical point of view. They usually contain large abrupt viscosity variations, and mixture of compressible and incompressible material behavior. In such a context the spatial discretization becomes very important, because it must provide an accurate and convergent solution, preferably with minimal cost and maximal geometrical flexibility. Practice shows that there is always a trade-of between the accuracy (stability) and the cost. Almost entire 3D finite element codes employed in geodynamic modeling community use some form of spatial discretization that violates the mathematical criteria of stability, the so-called Ladyzhenskaya-Babushka-Brezzi (LBB) condition. The explanation behind this fact is that instabilities do not necessarily show up in practice, but unstable discretization is relatively computationally inexpensive. The stability of LBB-stable elements itself is also conditional and strongly problem-depended. In the Rayleigh-Taylor benchmark with large (>1000) abrupt viscosity contrasts, discretized with non-fitted mesh, the meaningless velocity solutions can be obtained even with stable elements. Altogether these results bring us to a conclusion that the optimal choice of the finite element still remains unclear and deserves further study. In this work we bring our recent results concerning the selection of a suitable 3D finite element discretization to the attention of the modeling community. We consider different types of LBB-stable (including quite rear ones) and unstable (stabilized) formulations, both in the context of a standard continuous Galerkin, as well as a discontinuous Galerkin finite element methods. We believe that our findings will be interesting both for the code developers and for the practical researchers in the field of geodynamic modeling.

Popov, Anton; Sobolev, Stephan

2010-05-01

38

Software for Geodynamical Researches Used in the LSGER IAA  

E-print Network

Laboratory of Space Geodesy and Earth Rotation (LSGER) of the Institute of Applied Astronomy (IAA) of the Russian Academy of Sciences has been carrying on, since its creation, the computation of geodynamical products: Earth Orientation Parameters (EOP) and station coordinates (TRF) based on observations of space geodesy techniques: Very Long Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR), Global Positioning System (GPS). Principal software components, used for these investigations, include: package GROSS for processing of SLR observations, package Bernese for processing of GPS observations, package OCCAM for processing of VLBI observations, software for data exchange, and software for combination of space geodesy products.

Malkin, Zinovy; Skurikhina, Elena

2014-01-01

39

International GPS (Global Positioning System) Service for Geodynamics  

NASA Technical Reports Server (NTRS)

The International GPS (Global Positioning System) Service for Geodynamics (IGS) began formal operation on January 1, 1994. This first annual report is divided into sections, which mirror different aspects of the service. Section (1) contains general information, including the history of the IGS, its organization, and the global network of GPS tracking sites; (2) contains information on the Central Bureau Information System; (3) describes the International Earth Rotation Service (IERS); (4) details collecting and distributing IGS data in Data Center reports; (6) describes how the IGS Analysis Centers generate their products; (7) contains miscellaneous contributions from other organizations that share common interests with the IGS.

Zumberge, J. F. (Editor); Liu, R. (Editor); Neilan, R. E. (Editor)

1995-01-01

40

Unified Gravimetric Reference Frame for Polish IGS/EPN Stations and Geodynamic Test Fields  

NASA Astrophysics Data System (ADS)

Absolute gravity values are useful to regional geodynamic purposes as a complement of position monitoring at IGS/EPN permanent stations. Absolute gravity stations in region of geodynamic test field are also necessary as precise reference level for relative gravimetric measurements and long-period gravity monitoring. Absolute gravimetric network to unify gravimetric reference level for GNSS permanent stations and geodynamic test fields had been established in Poland in 2007-2008. Within a framework of this project six absolute gravity stations were established nearby IGS/EPN stations and seven points in two geodynamic test fields: Pieniny Test Field (3 points) and Sudetes Network (4 points). Final results of establishment of Unified Gravimetric Reference Frame for Polish IGS/EPN Stations and Geodynamic Test Fields are presented in the paper. Some issues with gravity reference level (comparing to Polish Fundamental Gravimetric Network), instruments parameters, observation elaboration and points stabilisation are also discussed.

Walo, Janusz; Olszak, Tomasz; Pachuta, Andrzej; Prchniewicz, Dominik; Szpunar, Ryszard

2010-05-01

41

Coupling a geodynamic seismic cycling model to rupture dynamic simulations  

NASA Astrophysics Data System (ADS)

The relevance and results of dynamic rupture scenarios are implicitly linked to the geometry and pre-existing stress and strength state on a fault. The absolute stresses stored along faults during interseismic periods, are largely unquantifiable. They are, however, pivotal in defining coseismic rupture styles, near-field ground motion, and macroscopic source properties (Gabriel et al., 2012). Obtaining these in a physically consistent manner requires seismic cycling models, which directly couple long-term deformation processes (over 1000 year periods), the self-consistent development of faults, and the resulting dynamic ruptures. One promising approach to study seismic cycling enables both the generation of spontaneous fault geometries and the development of thermo-mechanically consistent fault stresses. This seismo-thermo-mechanical model has been developed using a methodology similar to that employed to study long-term lithospheric deformation (van Dinther et al., 2013a,b, using I2ELVIS of Gerya and Yuen, 2007). We will innovatively include the absolute stress and strength values along physically consistent evolving non-finite fault zones (regions of strain accumulation) from the geodynamic model into dynamic rupture simulations as an initial condition. The dynamic rupture simulations will be performed using SeisSol, an arbitrary high-order derivative Discontinuous Galerkin (ADER-DG) scheme (Pelties et al., 2012). The dynamic rupture models are able to incorporate the large degree of fault geometry complexity arising in naturally evolving geodynamic models. We focus on subduction zone settings with and without a splay fault. Due to the novelty of the coupling, we first focus on methodological challenges, e.g. the synchronization of both methods regarding the nucleation of events, the localization of fault planes, and the incorporation of similar frictional constitutive relations. We then study the importance of physically consistent fault stress, strength, and geometry input for dynamic rupture propagation in terms of rupture path and dynamics. On the other hand, it will provide the opportunity to compare slow earthquake akin events developing in quasi-static geodynamic model to fully dynamic ruptures in terms of coseismic displacements and stress changes. Gabriel, A.-A. (2012), J.-P. Ampuero, L. A. Dalguer, and P. M. Mai, The transition of dynamic rupture modes in elastic media, J. Geophys. Res., 117(B9), 01480227. Gerya, T., and D. Yuen (2007), Robust characteristics method for modelling multiphase visco-elasto-plastic thermo-mechanical problems, Phys. Earth Planet In., 163(1-4), 83-105. Pelties, C. (2012), J. De la Puente, J.-P. Ampuero, G. B. Brietzke, and M. Kser Three-Dimensional Dynamic Rupture, Simulation with a High-order Discontinuous Galerkin Method on Unstructured Tetrahedral Meshes, J. Geophys. Res., 117(B2), B02309. van Dinther, Y. (2013a), T.V. Gerya, L.A. Dalguer, F. Corbi, F. Funiciello, and P.M. Mai, The seismic cycle at subduction thrusts: 2. Dynamic implications of geodynamic simulations validated with laboratory models, J. Geophys. Res., 118(4), 1502-1525. van Dinther, Y. (2013b), T.V. Gerya, L.A. Dalguer, P.M. Mai, G. Morra, and D. Giardini, The seismic cycle at subduction thrusts: insights from seismo-thermo-mechanical models, J. Geophys. Res., 118, 6183-6202.

Gabriel, Alice; van Dinther, Ylona

2014-05-01

42

Ophiolites in European Variscides and Uralides: Geodynamic settings and metamorphism  

NASA Astrophysics Data System (ADS)

The most important tectonic and magmatic events in the history of ophiolites in the Uralides and the European Variscides occurred almost sinchronously. The rocks of paleooceanic complexes in the both regions have similar paleontological and isotopic ages. The formation of the Ural and Variscan ophiolites is brought into correlation with a wide range of geodynamic settings. The Ural ophiolites mainly correspond to the suprasubduction setting, whereas the Variscan ophiolites are commonly related to rifts and mid-ocean spreading centers of the oceanic crust. The main difference is related to the origin of metamorphic rocks associated with ophiolites. The high-pressure-low-temperature metamorphism of the Ural ophiolites mainly related to the island arc-continent collision, whereas the Barrow-type metamorphism of ophiolites in the European Variscides developed at a higher temperature under medium-low pressure.

Savelieva, G. N.

2011-11-01

43

Geomorphology and Geodynamics at Crustal Boundaries within Asia and Africa  

NASA Technical Reports Server (NTRS)

The release of SRTM images by NASA over the past two years year has been greeted by foreign Earth scientist's as "NASA's gift to the World". The goodwill that this has engendered in parts of Africa. India, Pakistan and Bangladesh, as scientists in those countries contemplated what many of them considered an unprovoked and unjustifiable US invasion of Iraq, cannot be underestimated. We have used SRTM images from Africa and India and elsewhere to examine aspects of tectonism, geodynamics and tsunami and earthquake hazards. Highlights of this research are itemized in this final report. One difficulty that has arisen is , of course, that the funding for the science lead the availability of the data by more than a year. and as a result many of the findings are as yet unpublished.

2004-01-01

44

Geodynamical Analysis of Plate Reconstructions based on Subduction History Models  

NASA Astrophysics Data System (ADS)

We present a novel method to produce global subduction history models from plate reconstructions and use their predicted geodynamic behaviour as a quality metric for the physical consistency of absolute motions. We show that modelled slabs constructed by advecting material into the mantle according to absolute and relative plate motions given by a particular reconstruction are better correlated with the present day slab dips observed in mantle tomography than instantaneous kinematic quantities like present convergence rate. A complete simulation incorporating lithospheric thickness derived from oceanic age and a rheological model of the lithosphere was run using the Boundary Element Method-based software BEMEarth to infer the global pattern of mantle flow. The predicted plate motion orientations in the form of Euler pole location for the present day and mid-Cretaceous (125 Ma) were compared with the kinematic model for a set of rheologies and mantle structures, and found to be a robust and efficient indicator of the physical consistency of kinematic reconstructions based on their effect on the balance of plate driving forces. As an application example, during the Early Cretaceous, the predicted motion of the Farallon plate was found to be more consistent with the regional geology of the Western North American Cordillera system than the instantaneous motion suggested by a reconstruction at 125 Ma based on sparse hotspot track data on the Pacific Plate. This suggests that a methodology based on forward geodynamic modellling could be used to predict absolute plate motions in reconstructions for times that are ill-constrained by observations constraining absolute plate motions.

Quevedo, L. E.; Butterworth, N. P.; Matthews, K. J.; Morra, G.; Mller, R. D.

2011-12-01

45

Present-day geodynamics of the northern North American Cordillera  

NASA Astrophysics Data System (ADS)

Diffuse continental deformation results from interactions at plate boundaries, buoyancy forces generated by gradients in gravitational potential energy, and loads applied to the base of the lithosphere. Using finite element models, we calculate a deviatoric stress field associated with buoyancy forces, and then perform an iterative inversion to calculate deviatoric stress fields associated with boundary forces in the northern North American Cordillera. Our results reveal the presence of two distinct geodynamic domains. In the outboard domain, approximately equal magnitudes of boundary and buoyancy forces can account for the observed deformation along the Aleutian megathrust. In contrast, large boundary forces related to subduction of the Pacific and Yakutat slabs dominate the force-balance in south-central Alaska and combine with relatively small buoyancy forces to reproduce the observed kinematic indicators. In the inboard domain, encompassed by interior and northern Alaska and western Canada, boundary and buoyancy forces alone cannot reproduce the observed deformation. Therefore, we infer that deviatoric stresses due to basal tractions from a deeper mantle convection cell contribute to surface deformation in the inboard domain. Low effective lithospheric viscosity in south-central Alaska and the balancing effect of an independent geodynamic system driven by basal tractions in northern Alaska combine to confine the anomalously large Yakutat-related boundary deviatoric stresses to south-central Alaska. Deviatoric stresses associated with flat-slab subduction of the Yakutat microplate are a factor of two greater than boundary force estimates for the Andean and Indian-Eurasian convergent margins, where buoyancy and boundary forces are roughly equal in magnitude and dominate the force-balance.

Finzel, Emily S.; Flesch, Lucy M.; Ridgway, Kenneth D.

2014-10-01

46

The dynamics of oceanic transform faults : constraints from geophysical, geochemical, and geodynamical modeling  

E-print Network

Segmentation and crustal accretion at oceanic transform fault systems are investigated through a combination of geophysical data analysis and geodynamical and geochemical modeling. Chapter 1 examines the effect of fault ...

Gregg, Patricia Michelle Marie

2008-01-01

47

Anisotropy and deformation in the Earth's mantle : seismological observations, geodynamical models, and laboratory experiments  

E-print Network

In this thesis I report the results of several studies of elastic anisotropy and deformation in the Earth's mantle, using shear wave splitting measurements, numerical models of geodynamical processes, and laboratory ...

Long, Maureen Devaney

2006-01-01

48

Implementation of Newton-Rapshon iterations for parallel staggered-grid geodynamic models  

NASA Astrophysics Data System (ADS)

Staggered-grid finite differences discretization has a good potential for solving highly heterogeneous geodynamic models on parallel computers (e.g. Tackey, 2008; Gerya &Yuen, 2007). They are inherently stable, computationally inexpensive and relatively easy to implement. However, currently used staggered-grid geodynamic codes employ almost exclusively the sub-optimal Picard linearization scheme to deal with nonlinearities. It was shown that Newton-Rapshon linearization can lead to substantial improvements of the solution quality in geodynamic problems, simultaneously with reduction of computer time (e.g. Popov & Sobolev, 2008). This work is aimed at implementation of the Newton-Rapshon linearization in the parallel geodynamic code LaMEM together with staggered-grid discretization and viso-(elasto)-plastic rock rheologies. We present the expressions for the approximate Jacobian matrix, and give detailed comparisons with the currently employed Picard linearization scheme, in terms of solution quality and number of iterations.

Popov, A. A.; Kaus, B. J. P.

2012-04-01

49

Interactions between mantle plumes and mid-ocean ridges : constraints from geophysics, geochemistry, and geodynamical modeling  

E-print Network

This thesis studies interactions between mid-ocean ridges and mantle plumes using geophysics, geochemistry, and geodynamical modeling. Chapter 1 investigates the effects of the Marion and Bouvet hotspots on the ultra-slow ...

Georgen, Jennifer E

2001-01-01

50

The continental collision zone, South Island, New Zealand: Comparison of geodynamical models and observations  

SciTech Connect

In this report geodynamical models are used to test the applicability of the mantle subduction model to the compressional character and evaluation of the South Island continental convergence zone of New Zealand.

Beaumont, C.; Hamilton, J.; Fullsack, P. [Dalhousie Univ., Halifax, Nova Scotia (Canada)] [Dalhousie Univ., Halifax, Nova Scotia (Canada); Kamp, P.J.J. [Univ. of Waikato, Hamilton (New Zealand)] [Univ. of Waikato, Hamilton (New Zealand)

1996-02-10

51

Geodynamics of the Eastern Pacific Region, Caribbean and Scotia Arcs. Volume 9  

SciTech Connect

This book analyze the geodynamic phenomena related to the interaction of the eastern Pacific with the Americas between Canada and the Antarctic peninsula. Studies include the Cordilleran arcs and Juan de Fuca plate.

Cabre, R.

1983-01-01

52

GEOPHYSICS & GEODYNAMICS D. McKenzie, J.A. Jackson, R.S. White, A. Deuss,  

E-print Network

and geodynamic modelling. This is a vibrant training environment, for a career either in industry or academia Iceland, Iran, India, New Zealand, Chile and Indonesia and the Himalaya-Tibet region. Passive marine

Cambridge, University of

53

The mathematical representation of time-dependent parameters in some global geodynamics problems. II - Results  

NASA Astrophysics Data System (ADS)

Practical aspects of the construction of a mathematically homogeneous representation of time-dependent parameters are considered in the solution of global geodynamics problems related to the processing of satellite data. Expansions are obtained in the form of a finite series of Chebyshev polynomials for nutation, the tidal variation of UT1, and the influence of earth tides. A time-dependent geodynamic model of the geopotential is constructed.

Marchenko, A. N.

1988-08-01

54

Geodynamics and temporal variations in the gravity field  

NASA Technical Reports Server (NTRS)

Just as the Earth's surface deforms tectonically, so too does the gravity field evolve with time. Now that precise geodesy is yielding observations of these deformations it is important that concomitant, temporal changes in the gravity field be monitored. Although these temporal changes are minute they are observable: changes in the J2 component of the gravity field were inferred from satellite (LAGEOS) tracking data; changes in other components of the gravity field would likely be detected by Geopotential Research Mission (GRM), a proposed but unapproved NASA gravity field mission. Satellite gradiometers were also proposed for high-precision gravity field mapping. Using simple models of geodynamic processes such as viscous postglacial rebound of the solid Earth, great subduction zone earthquakes and seasonal glacial mass fluctuations, we predict temporal changes in gravity gradients at spacecraft altitudes. It was found that these proposed gravity gradient satellite missions should have sensitivities equal to or better than 10(exp -4) E in order to reliably detect these changes. It was also found that satellite altimetry yields little promise of useful detection of time variations in gravity.

Mcadoo, D. C.; Wagner, C. A.

1989-01-01

55

Global Biomass Variation and its Geodynamic Effects, 1982-1998  

NASA Technical Reports Server (NTRS)

Redistribution of mass near Earth's surface alters its rotation, gravity field, and geocenter location. Advanced techniques for measuring these geodetic variations now exist, but the ability to attribute the observed modes to individual Earth system processes has been hampered by a shortage of reliable global data on such processes, especially hydrospheric processes. To address one aspect of this deficiency, 17 yrs of monthly, global maps of vegetation biomass were produced by applying field-based relationships to satellite-derived vegetation type and leaf area index. The seasonal variability of biomass was estimated to be as large as 5 kg m(exp -2). Of this amount, approximately 4 kg m(exp -2) is due to vegetation water storage variations. The time series of maps was used to compute geodetic anomalies, which were then compared with existing geodetic observations as well as the estimated measurement sensitivity of the Gravity Recovery and Climate Experiment (GRACE). For gravity, the seasonal amplitude of biomass variations may be just within GRACE'S limits of detectability, but it is still an order of magnitude smaller than current observation uncertainty using the satellite-laser-ranging technique. The contribution of total biomass variations to seasonal polar motion amplitude is detectable in today's measurement, but it is obscured by contributions from various other sources, some of which are two orders of magnitude larger. The influence on the length of day is below current limits of detectability. Although the nonseasonal geodynamic signals show clear interannual variability, they are too small to be detected.

Rodell, M.; Chao, B. F.; Au, A. Y.; Kimball, J. S.; McDonald, K. C.

2005-01-01

56

Chronological constraints on the Permian geodynamic evolution of eastern Australia  

NASA Astrophysics Data System (ADS)

The New England Orogen in eastern Australia developed as a subduction-related orogen in the Late Devonian to Carboniferous, and was modified in the Permian by deformation, magmatism and oroclinal bending. The geodynamics associated with the development of the New England oroclines and the exact timing of major tectonic events is still enigmatic. Here we present new 40Ar/39Ar results from metasedimentary and volcanic rocks from the southern New England Orogen. Eight grains from four metasedimentary samples (Texas beds) that originated in the Late Devonian to Carboniferous accretionary wedge yielded reproducible plateau ages of ~ 293, ~ 280, ~ 270 and ~ 260 Ma. These results suggest a complex thermal history associated with multiple thermal events, possibly due to the proximity to Permian intrusions. Two samples from mafic volcanic rocks in the southernmost New England Orogen (Alum Mountain Volcanics and Werrie Basalt) yielded eruption ages of 271.8 1.8 and 266.4 3.0 Ma. The origin of these rocks was previously attributed to slab breakoff, following a period of widespread extension in the early Permian. We suggest that this phase of volcanism marked the transition from backarc extension assisted by trench retreat to overriding-plate contraction. The main phase of oroclinal bending has likely occurred during backarc extension in the early Permian, and terminated at 271-266 Ma with the processes of slab segmentation and breakoff.

Li, Pengfei; Rosenbaum, Gideon; Vasconcelos, Paulo

2014-03-01

57

Geodynamics of the northern Andes: Subductions and intracontinental deformation (Colombia)  

NASA Astrophysics Data System (ADS)

New regional seismological data acquired in Colombia during 1993 to 1996 and tectonic field data from the Eastern Cordillera (EC) permit a reexamination of the complex geodynamics of northwestern South America. The effect of the accretion of the Baud-Panama oceanic arc, which began 12 Myr ago, is highlighted in connection with mountain building in the EC. The Istmina and Ibagu faults in the south and the Santa Marta-Bucaramanga fault to the northeast limit an E-SE moving continental wedge. Progressive indentation of the wedge is absorbed along reverse faults located in the foothills of the Cordilleras (northward of 5N) and transpressive deformation in the Santander Massif. Crustal seismicity in Colombia is accurately correlated with active faults showing neotectonic morphological evidences. Intermediate seismicity allows to identify a N-NE trending subduction segment beneath the EC, which plunges toward the E-SE. This subduction is interpreted as a remnant of the paleo-Caribbean plateau (PCP) as suggested by geological and tomographic profiles. The PCP shows a low-angle subduction northward of 5.2N and is limited southward by a major E-W transpressive shear zone. Normal oceanic subduction of the Nazca plate (NP) ends abruptly at the southern limit of the Baud Range. Northward, the NP subducts beneath the Choc block, overlapping the southern part of the PCP. Cenozoic shortening in the EC estimated from a balanced section is 120 km. Stress analysis of fault slip data in the EC (northward of 4N), indicates an E-SE orientation of ?1 in agreement with the PCP subduction direction. Northward, near Bucaramanga, two stress solutions were observed: (1) a late Andean N80E compression and (2) an early Andean NW-SE compression.

Taboada, Alfredo; Rivera, Luis A.; Fuenzalida, AndrS.; Cisternas, Armando; Philip, Herv; Bijwaard, Harmen; Olaya, Jos; Rivera, Clara

2000-10-01

58

Tectonics and geodynamics of the Eastern Venezuelan Ranges  

SciTech Connect

The eastern Venezuelan Ranges result from oblique convergence along the South American-Caribbean plate boundary, whose main surface expression is the El Pilar dextral strike-slip fault. Crustal scale balanced cross-sections have been here completed from available surface and subsurface data across this major transfer zone which links the oceanic subduction of the Lesser Antilles with the continental subduction of the Andes. The present geometries of the sectons show a major discrepancy between the cover and basement lengths, which could be explained by tectonic inheritance from the Tethyan margin. A careful analysis of both the chronostratigraphy and the internal geometry of the foredeep and piggy-back syntectonic deposits are also used to establish the kinematics of each individual structure. Basement involved is postulated for the Pirital Thrust which cuts previously emplaced cover structures like the El Furrial structural unit. Reactivation of ancient thrust faults occurs also at the rear of the Pirital out-of-sequence thrust in the west. As in the Alps or the Pyrenees, a high density intracrustal wedge is required to fit the gravimetric high imaged north of the Serrania; the solutions require a deep crustal root beneath the belt and a north-dipping South American Moho. A consistent geodynamical model, involving the north-dipping subduction of at least 70 km of South American continental lithosphere is thus proposed. An important strain partitioning occurs along the El Pilar Fault and underneath the deep crustal indenter (backstop), which decouples the south-verging allochthon of the Serrania from the north-dipping subducted South American lithosphere and from the eastward-migrating metamorphic belt.

Roure, F. (IFP, Rueil-Malmaison (France)); Passalacqua, H. (Intevep, Caracas (Venezuela)); Gou, I. (Beicip, Rueil-Malmaison (France))

1993-02-01

59

Generating volumetric composition maps from particle based computational geodynamic simulations.  

NASA Astrophysics Data System (ADS)

The advent of using large scale, high resolution three-dimensional hybrid particle-grid based methods to study geodynamics processes is upon us. Visualizing and interpreting the three-dimensional geometry of the material configuration after severe deformation has occurred is a challenging task when adopting such a point based representation. In two-dimensions, the material configuration is readily visualized by creating a simple (x,y) scatter plot, using the particles position vector and coloring the points according to the lithology which each particle represents. Using only colored points (which do not need to be rendered as spheres), this approach unambiguous fills the 2D model domain with information defining the current material configuration. Along with an increased volume (i.e. MBytes) of output data generated by three-dimensional simulations, the higher dimensionality introduces additional complexities for visualization. The geometry of the deformed material in three-space will become topologically more complex than its two-dimensional counterpart. Secondly, the scatter plot approach used in 2D to represent the material configuration simply does not extend to three-dimensions as technique is unable to provide any sense of depth. To address some of the visualization challenges posed by such methods, we describe how an Approximate Voronoi Diagram (AVD) can be used to produce a volumetric representation of point based data. The AVD approach allows us to efficiently construct a volumetric partitioning of any subset of the model domain amongst a set points. From this representation, we can efficiently generate a representation of the material configuration which can be volume rendered, contoured, or from which cross sections can be extracted. The type of volumetric representations possible, and the performance characteristics of the AVD algorithm were demonstrated by applying the technique to simulation results from models of continental collision and salt tectonics.

May, D. A.

2012-04-01

60

Software and Algorithms for Solving Computational Geodynamic Problems using Next Generation Hardware  

NASA Astrophysics Data System (ADS)

Numerical geodynamic modeling is typically based on solving a series of partial differential equations which describe the long-term behavior of the solid visco-elasto-brittle/plastic Earth as a highly viscous incompressible fluid with strongly variable non-Newtonian viscosity. Coding for solving geodynamic equations is catching up with the advance of modern high performance computing. In the past five years, newly developed many-core computing technology, including GPU (Graphics Processing Unit) and MIC (Many Integrated Core), has also been utilized for geodynamic modeling. However, the lack of easy-to-expand or easy-to-use geo-computing toolkits limits the high performance software catching up with the endless updating of high performance hardware. In this presentation, we will firstly show two examples of the implementation of solving geodynamic problems based on Stokes and continuity equations with strongly variable viscosity using many-core hardware, with a specific focus on the GPU. The first example is a geometric multi-grid (GMG) solver, which solves a synthetic sinking cube problem using a staggered grid finite difference discretization. The second example is a preconditioned minimal residual (MINRES) solver for incompressible Stokes flow problem with many viscous inclusions which is discretized using the finite element method. Through these two implementation examples, we will analyze the cost of coding and running advantages and disadvantages of the two kinds of coding methodologies, and in a hope to discuss a potential general coding flowchart for solving geodynamic equations using many-core devices. Finally, a software stack based many-core computing framework oriented to geodynamic modeling is proposed for the future.

Zheng, Liang; Gerya, Taras

2014-05-01

61

Geodynamics, Seismicity, Minerageny and Ecology of Arctic Regions  

NASA Astrophysics Data System (ADS)

The researches of Arctic region is necessary for beginning from delimitation of Arctic. Geographically concept "Arctic" uncertain enough. There is a set of approach to definition of its borders and set the variants of these borders (eternal permafrost, boreal tayga, drifting ice, temperature, etc.). Most correct the point of view of Ecology is realization of Arctic borders on borders of the Arctic geo - depression. Such approach allows to consider in a complex migration of natural substance and polluting substance from orogenes to deep-water hollows of Arctic Ocean. On other hand, it is necessary to take into account natural power flows from zone of Mid-Arctic ridge system at Arctic Ocean to continental land, that is opposition direction process. The certificates of such influence at different levels of Earth's crust already has collected enough (speed of seismic wave on Moho discontinuity; modern vertical movement of Earth's crust; distribution of temperature on depth; structure of basement, etc.). During the last 250 million years the Arctic geo-depression has been developing as an autonomous region with circumpolar zonality, and mass-and-energy transfer in its bowlers as well as shitting of lithospheric plates and expansion of the ocean are caused by rotational forces under conditions of an expanding planet. Four types of geoecological structures have been recorded on the basis of deep structures, position in the over-all structures of regions, place in geological history of its evolution, time of appearance, geodynamic regimes , seismicity, structural-morphological features, specific form of appearance and composition of magmatic and sedimentary formations, compositions of soil, specific metallogenic nature, types of human activity, etc. It is tectonic Segments of Earth, as geoecological global structures; the continental marginal perioceanic zones; the branches of continental marginal perioceanic zones; the mineragenic province. The main criteria of ecological unity of territory under consideration are established to the following: circumpolar position; rigorous climate with short vegetation period and a long winter; extremely wide prevalence of permafrost rocks; multitude of bogs and lake per square unit in basis of many rivers flowing into Arctic Ocean; proximity of the structure and formation of ecosystem; fragility of the Arctic environment; specificity of national economic structure; uniqueness of the raw material base having no equals in the word in its resources and content minerals of certain components; availability of the word's largest Arctic shelf oil-and-gas super basin; common geoecological natural belts; circumpolar belt of earthquakes.

Kutinov, Y. G.

62

Izanagi-Pacific Ridge Subduction and its Geodynamic Consequences  

NASA Astrophysics Data System (ADS)

As part of a global plate tectonic model for 140 Ma to the present we present a revised plate reconstruction for the western Pacific and investigate its geodynamic consequences. In our plate model, mid-ocean ridge subduction beneath southern Japan occurs at 60-55 Ma, 20 million years later than proposed for Kula-Pacific or Farallon- Izanagi ridge subduction. The difference arises because Izanagi-Pacific (I-P) spreading ceases in previous models after 110 Ma while our model incorporates continued spreading until the I-P ridge subducts beneath eastern Asia at 60-55 Ma. We regard cessation of spreading at the I-P ridge between 110 and 80 Ma as unlikely as the Izanagi plate was undergoing rapid motion, driven by net slab-pull force, from the north-northwest, immediately prior to the proposed spreading cessation. Metamorphism of the Ryoke Belt in southern Japan has previously been attributed to Kula-Pacific ridge subduction at 85 Ma, but the high-T/low-P Ryoke Belt cannot be uniquely linked to a ridge subduction event. We propose that sub-parallel subduction of the I-P mid-ocean ridge beneath Japan at 60-55 Ma resulted in nearly simultaneous slab break-off along the length of the Japanese trench (approximately 2700 km). Geological evidence for this model includes cessation of a major accretion phase in the late Cretaceous, emplacement of the Okitsu Melange due to subduction of hot, buoyant material at 55 Ma, and cross-cutting fault fabrics that indicate a counter-clockwise rotation in relative plate motions between Eurasia and the I-P plate, consistent with palaeothermal and palaeopressure data, some time between 55 and 34 Ma. Rapid subduction of the I-P ridge, over a vast distance, may have triggered a chain reaction of tectonic plate reorganizations. With complete subduction of the I-P ridge at 55 Ma, forces acting on the western edge of the Pacific Plate would have changed from ridge-push to slab pull, changing Pacific absolute plate motions from northwest to west. A combination of Australian and Pacific plate motion changes between 53 Ma and 50 Ma then initiated both the Tonga-Kermadec subduction system and the Izu-Bonin-Marianas subduction systems around 50Ma, likely due to convergence across a fracture zone caused by the Pacific plate motion change. We suggest that the observed slowdown of sub-Pacific mantle flow at 47 Ma was due to progressive impediment of lateral sub-Pacific mantle flow by the descending slabs of the Izu-Bonin-Marianas and Tonga-Kermadec subduction zones.

Mller, R. D.; Whittaker, J. M.; Sdrolias, M.

2007-12-01

63

Geodynamical models of lithospheric deformation, rotation and extension of the Pannonian Basin of Central Europe  

Microsoft Academic Search

The two major crustal blocks of the Pannonian basin, Alcapa (AlpineCarpathianPannonian) and Tisza, underwent a complex process of rotation and extension of variable magnitude during the Tertiary. The northward push of the Adriatic Block initiated the eastward displacement and rotation of both the Alcapa and Tisza blocks. We have constructed geodynamical models of the rotation and extension of the two

Piroska Lorinczi; Gregory Houseman

2010-01-01

64

Mentawai fault zone off Sumatra: A new key to the geodynamics of western Indonesia  

Microsoft Academic Search

The geodynamic evolution of the western part of the Sunda arc is controlled by the change from frontal subduction of the Indo-Australian plate along Java to oblique subduction along Sumatra. This obliquity gives rise to the Sumatra fault zone that links the accretionary zone of the Andaman Sea to the Sunda Strait. Previous studies have shown a decrease of displacement

M. Diament; H. Harjono; K. Karta; C. Deplus; D. Dahrin; M. T. Zen Jr.; M. Grard; O. Lassal; A. Martin; J. Malod

1992-01-01

65

Radon Along the Dead Sea Transform: a Proxy of Geodynamic and Geophysical Processes  

Microsoft Academic Search

Radon (Rn-222) occurring in geogas and water phases in upper crustal levels is often mentioned as a proxy of active geodynamics, with a potential as a precursor of earthquakes. So far the reported variability and complexity of its signals limits establishment of a verifiable scientific basis for this proposition. Most investigations tried to relate the temporal variations to different combinations

G. Steinitz

2007-01-01

66

Advances in Global Positioning System Technology for Geodynamics Investigations: 1978-1992  

E-print Network

Advances in Global Positioning System Technology for Geodynamics Investigations: 1978 of the Global Positioning System (GPS) have developed the technology capable of meeting the stringent class of technical development. The last decade has witnessed the rise of the Global Positioning System

Tingley, Joseph V.

67

Indian Cretaceous Terrestrial Vertebrates: Cosmopolitanism and Endemism in a Geodynamic Plate Tectonic Framework  

NASA Astrophysics Data System (ADS)

The Indian stratigraphic record with well documented Mesozoic and Early Tertiary terrestrial biotas is now adequate to shed light on the geodynamic chronology of the subcontinent during the rift, drift and collision phases. The record provides one of the best examples of the response of a biota that is undergoing considerable latitudinal displacement, dispersal, origination, evolution and extinction.

Sahni, A.

68

Geodynamic models and their application in the combined interpretation of geological and geophysical data (a review)  

Microsoft Academic Search

The paper presents a review of investigations in the field of the theory and practice of the interpretation of geological and geophysical data with geodynamic models that were carried out mainly by researchers of the Institute of Physics of the Earth, Russian Academy of Sciences. Evolutionary models of platform structures, passive continental margins, rift zones, and orogens are examined. The

V. O. Mikhailov; V. M. Gordin; E. P. Timoshkina; E. A. Kiseleva; E. I. Smolyaninova

2007-01-01

69

Applications of Global Positioning System (GPS) in geodynamics: with three examples from Turkey  

Microsoft Academic Search

Global Positioning System (GPS) has been very useful tool for the last two decades in the area of geodynamics because or the validation of the GPS results by the Very Long Baseline Interferometry (VLBI) and Satellite Laser Ranging (SLR) observations. The modest budget requirement and the high accuracy relative positioning availability of GPS increased the use of it in determination

H. Yavasoglu; E. Tari; M. Sahin; H. Karaman; T. Erden; S. Bilgi; S. Erdogan

2005-01-01

70

True Polar Wander: linking Deep and Shallow Geodynamics to Hydro-and Bio-Spheric Hypotheses  

E-print Network

True Polar Wander: linking Deep and Shallow Geodynamics to Hydro- and Bio-Spheric Hypotheses T. D and Circulation Chemical Oceanographic Effects: Carbon Oxidation and Burial Critical Testing of Cryogenian-Cambrian TPW Ediacaran-Cambrian TPW: 'Spinner Diagrams' in the TPW Reference Frame Proof of Concept

71

A geodynamical perspective on the subduction of Cocos and Rivera plates beneath Mexico and Central America  

NASA Astrophysics Data System (ADS)

The Middle America subduction zone (MASZ) is one of the world most complex convergent margins as it involves the subduction of the Rivera and Cocos young oceanic plates beneath the North American and Caribbean plates and is bounded by the Gulf of California rift and the Panama slab window. Characterized by contorted and unusual slab geometry, irregularly distributed seismicity and volcanism, exceptionally large slow slip events (SSE) and non-volcanic tremors (NVT), this subduction system represents a great natural laboratory for better understanding geodynamic processes at a fundamental level. Based on a solid observational foundation, and incorporating the latest experimental results into a coherent geodynamical framework, we shed light on the main processes controlling the subduction system evolution in this region. The tectonics, volcanism, slab geometry and segmentation along the margin are reviewed from a geodynamical perspective. We proposed and discussed a series of evolutionary scenarios for the Mexican and Central American subduction zones, providing a coherent starting base for future geodynamical modeling studies tailored to this active margin. We discuss comparatively the recently discovered SSEs and NVTs along the MASZ, and try to differentiate among the proposed mechanisms responsible for these observations. Finally we discuss the recent seismic anisotropy observations in a geodynamic context, offering an integrated view of mantle flow pattern along the entire active margin. Although the MASZ as a whole may be considered a fairly complicated region with many unusual features and sometimes controversial interpretations, its complexity and unusual characteristics can improve our knowledge about the linkage between deep and surface processes associated with subduction zone dynamics.

Manea, V. C.; Manea, M.; Ferrari, L.

2013-12-01

72

Petrological geodynamic modeling of mid-ocean ridges  

NASA Astrophysics Data System (ADS)

Mid-ocean ridges are the primary location where the Earth's oceanic crust is formed. Beneath spreading ridges several processes such as dynamic melting and partial crystallization modify the petrology of the upper mantle and affect the Earth's global geochemical evolution. A unified picture of the temporal and spatial evolution of melt and residual mantle, as well as crustal production and melt dynamics requires a comprehensive model that takes into account simultaneously the complexity of the physical processes involved and the petrological variations of the ridge system. Here we present the first results of a 2-D numerical approach applied to a spreading ridge that fully couples a two-phase flow model for melt and solid mantle and a chemical thermodynamic model which provides a spatial and temporal description of the minerals and melt abundance and composition. The most significant features found by this study are the following. (1) Accumulation of melt is observed at the base of the lithosphere in the off-axis region (<50 km from the ridge axis). (2) Crustal production (thickness) shows temporal variations which are mainly induced by periodic discharge of the melt accumulated underplate. (3) Magma waves develop between 10 and 30 km depth in proximity of the ridge axis. However to accurately resolve melt fluctuations, the grid size must be smaller than the compaction length for porous flow. Since in this study the compaction length decreases with depth, we have used a simplified 1-D melt model incorporating the two-phase flow dynamics and the thermodynamic formulation to show that the depth at which magma waves start to form increases by increasing the numerical resolution. Despite the limitation of the numerical grid resolution, we have observed that variations of the melt content do not appear to have significant influence on major elements composition of the residual solid and melt. (4) In the initial stage of the ridge evolution, a melting area detaches from the main melting region around the ridge axis. It is possible that this type of development may repeat over time beyond the duration of the simulation model of this study (15 Ma). Sluggish coupling between the dynamics of the lithosphere and the asthenospheric mantle flow suggests that accretion of the lithosphere by conductive cooling away from the ridge center involves portions of the upper mantle that not necessarily passed through the spreading ridge. (5) During the development of the spreading ridge, the asthenosphere affected by the melting process deflects downwards, creating in this way a chemical heterogeneity in the large mantle circulation. (6) Composition of major elements in the residual solid after partial melting is in agreement with the chemical pattern observed in abyssal peridotites. However, in order to explain the large variation of major elements content found in abyssal peridotite, a consistent petrological and geodynamic model of the evolution of the mid-ocean ridge, requires that partial crystallization of small amount of melt refertilizes the depleted mantle. The petrological model presented in this study accounts for the complexity of polybaric dynamic melting and the continuous reactions between the residual solid and melt, but it is limited by the assumption of local thermodynamic equilibrium within a domain defined by the numerical grid size. The interpretation of the petrological results needs to be carefully evaluated to ensure that the time and space scale of the numerical model complies with the constraints provided by solid-melt reactive experiments and the spatial scale of the petrological structures observed in mid-ocean ridges. (7) Melt distribution and thermal structure are revealed by the seismic shear wave map computed from the numerical model. Certain observations, such as the extent of the melting region, overall agree quite well with the evidences from seismic studies from various ridge settings.

Tirone, M.; Sen, G.; Morgan, J. P.

2012-01-01

73

Cenozoic geodynamic evolution of the western Mediterranean domain: A view from the Neogene peri-Tyrrhenian basins  

SciTech Connect

Biostratigraphic and structural studies of synorogenic Neogene deposits in the southern Apennines, Calabria, and Cicily are compared to similar data from Sardinia and the Tyrrhenian Sea to trace the geodynamic evolution of the western Mediterranean domain.

Roure, F.; Montadert, L.; Mueller, C. (Institut Francais du Petrole, Rueil-Malmaison)

1988-08-01

74

Subduction to the lower mantle - a comparison between geodynamic and tomographic models  

NASA Astrophysics Data System (ADS)

It is generally believed that subduction of lithospheric slabs is a major contribution to thermal heterogeneity in Earth's entire mantle and provides a main driving force for mantle flow. Mantle structure can, on the one hand, be inferred from plate tectonic models of subduction history and geodynamic models of mantle flow. On the other hand, seismic tomography models provide important information on mantle heterogeneity. Yet, the two kinds of models are only similar on the largest (1000 s of km) scales and are quite different in their detailed structure. Here, we provide a quantitative assessment how good a fit can be currently achieved with a simple viscous flow geodynamic model. The discrepancy between geodynamic and tomography models can indicate where further model refinement could possibly yield an improved fit. Our geodynamical model is based on 300 Myr of subduction history inferred from a global plate reconstruction. Density anomalies are inserted into the upper mantle beneath subduction zones, and flow and advection of these anomalies is calculated with a spherical harmonic code for a radial viscosity structure constrained by mineral physics and surface observations. Model viscosities in the upper mantle beneath the lithosphere are ~1020 Pas, and viscosity increases to ~1023 Pas in the lower mantle above D". Comparison with tomography models is assessed in terms of correlation, both overall and as a function of depth and spherical harmonic degree. We find that, compared to previous geodynamic and tomography models, correlation is improved, presumably because of advances in both plate reconstructions and mantle flow computations. However, high correlation is still limited to lowest spherical harmonic degrees. An important ingredient to achieve high correlation - in particular at spherical harmonic degree two - is a basal chemical layer. Subduction shapes this layer into two rather stable hot but chemically dense "piles", corresponding to the Pacific and African Large Low Shear Velocity Provinces. Visual comparison along cross sections indicates that sinking speeds in the geodynamic model are somewhat too fast, and should be 2 0.8 cm yr-1 to achieve a better fit.

Steinberger, B.; Torsvik, T. H.; Becker, T. W.

2012-11-01

75

Subduction to the lower mantle - a comparison between geodynamic and tomographic models  

NASA Astrophysics Data System (ADS)

It is generally believed that subduction of lithospheric slabs is a major contribution to thermal heterogeneity in Earth's entire mantle and provides a main driving force for mantle flow. Mantle structure can, on the one hand, be inferred from plate tectonic models of subduction history and geodynamic models of mantle flow. On the other hand, seismic tomography models provide important information on mantle heterogeneity. Yet, the two kinds of models are only similar on the largest (1000s of km) scales and are quite different in their detailed structure. Here, we provide a quantitative assessment how good a fit can be currently achieved with a simple viscous flow geodynamic model. The discrepancy between geodynamic and tomography models can indicate where further model refinement could possibly yield an improved fit. Our geodynamical model is based on 300 Myr of subduction history inferred from a global plate reconstruction. Density anomalies are inserted into the upper mantle beneath subduction zones, and flow and advection of these anomalies is calculated with a spherical harmonic code for a radial viscosity structure constrained by mineral physics and surface observations. Model viscosities in the upper mantle beneath the lithosphere are ~1020 Pas, and viscosity increases to ~1023 Pas in the lower mantle above D". Comparison with tomography models is assessed in terms of correlation, both overall and as a function of depth and spherical harmonic degree. We find that, compared to previous geodynamic and tomography models, correlation is improved significantly, presumably because of improvements in both plate reconstructions and mantle flow computation. However, high correlation is still limited to lowest spherical harmonic degrees. An important ingredient to achieve high correlation - in particular at spherical harmonic degree two - is a basal chemical layer. Subduction shapes this layer into two rather stable hot but chemically dense "piles", corresponding to the Pacific and African Large Low Shear Velocity Provinces. Visual comparison along cross sections indicates that sinking speeds in the geodynamic model are somewhat too fast, and should be 20.8 cm yr-1 to achieve a better fit.

Steinberger, B.; Torsvik, T. H.; Becker, T. W.

2012-07-01

76

Geodynamic model for the development of the Cameroon Hot Line (Equatorial Africa)  

NASA Astrophysics Data System (ADS)

This work proposes a new geodynamic model for the development of the Cameroon Hot Line (CHL) in Equatorial Africa. It is based on the analysis of the distribution of lineaments and of magmatic bodies (Paleogene anorogenic ring-complexes and Neogene volcanic centres). Two successive geodynamic models are proposed to explain the distribution of the Cainozoic to recent magmatic activity. They are both sinistral. The first one, during the Paleogene, developed around the N ? 70E direction while the second one (Neogene) is oriented around the N ? 130E direction. The two periods are separated by a short transition. The emplacement follows the local reactivation of pre-existing (Pan-African) faults in relation to the collision between the Afro-Arabian and Eurasian plates, during the Alpine history.

Nkono, Collin; Fmnias, Olivier; Demaiffe, Daniel

2014-12-01

77

Geological remarks on the relationships between extension and convergent geodynamic settings  

Microsoft Academic Search

In convergent geodynamic settings, extensional and compressional tectonics occur contemporaneously or in different times and places, but they are deeply linked to each other in a number of different ways. The main types of extensional regimes here considered are for west-dipping subduction zones: (1) back-arc extension (e.g., Tyrrhenian Sea); (2) uplift and related extension due to asthenospheric wedging (e.g., Apennines);

Carlo Doglioni

1995-01-01

78

Journal of Geodynamics 41 (2006) 128132 Advances in Southern Ocean tide modeling  

E-print Network

02.01) in the Southern Ocean. Solutions for the M2, O1, N2, and Q1 tides that are obtained from frequency (cycle/day) True amplitude (cm) Vector difference (cm) True Aliased M2 1.932274 1.932273 16.6 0Journal of Geodynamics 41 (2006) 128­132 Advances in Southern Ocean tide modeling Yuchan Yia,, Koji

79

The geodynamical evolution of the Northern Apennines chain (Central Italy): an exploring numerical model  

Microsoft Academic Search

In this paper, 2D thermo-mechanical models with crustal deformation, driven by subduction, are performed to test the geodynamical scenario of a slab-retreat for the Northern Apennines chain (Central Italy). In the models, the lithosphere is regarded as a non-linear Maxwell visco-elastic body capable of brittle failure at low pressure and temperature and of viscous creep at elevated temperature, in Lagrangian

Cristina Pauselli; Costanzo Federico; Jean Braun

2004-01-01

80

Geodynamics of Central Europe Based On Observations of The GPS Euref Stations  

NASA Astrophysics Data System (ADS)

When azimuths of the horizontal movement vectors processed from GPS data mon- itored during several campaigns on regional networks situated in the Central Europe (the East Sudeten, the West Alps, the Trans-Alpen area) were compared, they dis- played remarkable changed in their values evaluated from two sequential campaigns with respect to next ones. As adopted, the GPS data processed of one campaign are ordinarily linked to a close EUREF station (or stations) to be joined to an Interna- tional Terrestrial Reference Frame (ITRF). Even though the interconnection to the ITRF, the vector azimuths for one site evaluated from different campaigns can still show changes. To eliminate this effect, available movements of the Central European EUREF stations were analysed with respect to geological structural units in that rela- tively coincident character of geodynamic movements are expected. Several "geody- namic" units were identified and delineated for an area of the Central Europe. Then, directions of the horizontal vector azimuths of network sites were incorporated into the unit scheme above mentioned. The paper will present data analysis of the EU- REF stations, the geodynamic unit scheme for the Central Europe and comparisons of geodynamic horizontal movements of the EUREF stations and the network sites. Fur- ther, an assessment of interrelated movements among the individual structural units was estimated. The geodynamic pattern of Central European unit movements brings more transparent understanding of mutual relations between EUREF stations and the regional GPS networks observations. The data analyse of GPS observations were sup- ported by the program of Ministry of Education, Youth and Sport 'Research Centre', No. LN00A005, and by the project of the Grant Agency of the Czech Republic, No. 205/01/0480.

Schenk, V.

81

Geodynamic models and their application in the combined interpretation of geological and geophysical data (a review)  

Microsoft Academic Search

The paper presents a review of investigations in the field of the theory and practice of the interpretation of geological\\u000a and geophysical data with geodynamic models that were carried out mainly by researchers of the Institute of Physics of the\\u000a Earth, Russian Academy of Sciences. Evolutionary models of platform structures, passive continental margins, rift zones, and\\u000a orogens are examined. The

V. O. Mikhailov; V. M. Gordin; E. P. Timoshkina; E. A. Kiseleva; E. I. Smolyaninova

2007-01-01

82

Seismological and Geodynamic Monitoring Network in the "javakheti" Test Zone in the Southern Caucasus  

NASA Astrophysics Data System (ADS)

The Javakheti Highland located in the border region between Armenia and Georgia (sharing a border with Turkey) is an area in the Southern Caucasus of young Holocene-Quaternary volcanism and a region with convergence of a number of active faults. Issues related to the geometry, kinematics and slip-rate of these faults and assessment of their seismic hazard remain unclear in part due to the fragmentary nature of the studies carried out soley within the borders of each of the countries as opposed to region wide. In the frame of the ISTC A-1418 Project "Open network of scientific Centers for mitigation risk of natural hazards in the Southern Caucasus and Central Asia" the Javakheti Highland was selected as a trans-border test-zone. This designation allowed for the expansion and upgrading of the seismological and geodynamic monitoring networks under the auspices of several international projects (ISTC CSP-053 Project "Development of Communication System for seismic hazard situations in the Southern Caucasus and Central Asia", NATO SfP- 983284 Project "Caucasus Seismic Emergency Response") as well as through joint research programs with the National Taiwan University and Institute of Earth Sciences (IES, Taiwan), Universite Montpellier II (France) and Ecole et Observatoire des Sciences de la Terre-Universit de Strasbourg (France). Studies of geodynamic processes, and seismicity of the region and their interaction have been carried out utilizing the newly established seismological and geodynamic monitoring networks and have served as a basis for the study of the geologic and tectonic structure . Upgrading and expansion of seismological and geodynamic networks required urgent solutions to the following tasks: Introduction of efficient online systems for information acquisition, accumulation and transmission (including sattelite systems) from permanent and temporary installed stations, Adoption of international standards for organization and management of databases in GIS format, Utilization of data archiving system working in intrnationally adopted formats and data exchange systems for communication with other international and national centers.

Arakelyan, A.; Babayan, H.; Karakhanyan, A.; Durgaryan, R.; Basilaia, G.; Sokhadze, G.; Bidzinashvili, G.

2012-12-01

83

Concepts for reference frames in geodesy and geodynamics: The reference directions  

Microsoft Academic Search

Modern high accuracy measurements of the non-rigid earth are to be referred to four-dimensional, i.e., time- and space-dependent\\u000a reference frames. Geodynamic phenomena derived from these measurements are to be described in a terrestrial reference frame\\u000a in which both space- and time-like variations can be monitored. Existing conventional terrestrial reference frames (e.g. CIO,\\u000a BIH) are no longer suitable for such purposes.

Erik W. Grafarend; Ivan I. Mueller; Haim B. Papo; Burghard Richter

1979-01-01

84

Concepts for reference frames in geodesy and geodynamics: The reference directions  

Microsoft Academic Search

Modern high accuracy measurements of the non-rigid earth are to be referred to four-dimensional, i.e., time- and space-dependent reference frames. Geodynamic phenomena derived from these measurements are to be described in a terrestrial reference frame in which both space- and time-like variations can be monitored. Existing conventional terrestrial reference frames (e.g. CIO, BIH) are no longer suitable for such purposes.

Erik W. Grafarend; Ivan I. Mueller; Haim B. Papo; Burghard Richter

1979-01-01

85

Online Geodynamics: interactive web-applications for graduate students in Earth Sciences  

NASA Astrophysics Data System (ADS)

In teaching geosciences classes it is essential to provide students with the possibility of having hands-on experiences, even if sometimes they happen to be only in the virtual world. In the portal created for the Computational Geodynamics Laboratory (http://www.geociencias.unam.mx/geodinamica), we present web-based applications, which will help students to manipulate and visualize not only data but also to understand concepts like mantle convection, plate reconstruction or plate deformation. The "Toolbox" option provides a set of state of the art applications (WebMap, WebPlates, WebFlexure, WebGravity, and WebConvec), in which logged-in users can run on-line various programs, without previous knowledge of advanced programming. WebPlates is used in Plate Tectonics classes, helping students to identify and familiarize themselves with various tectonic plates, different tectonic limits, hotspots, etc. WebFlexure is used to study the mechanical behavior of oceanic plates at trenches. WebConvec comes with four cases, analyzing the thermal and thermo-chemical convection in different conditions. In this way the students can be aware of how variation of various physical parameters can affect the modeling results. The "Models" section presents a collection of dynamic numerical models created in the Computational Geodynamics Laboratory. In this section, the logged-in user can visualize convection and deformation models, tectonic plate reconstructions, or geophysical field data, like geoid, gravity, etc. All these applications are actively used in the Geodynamics classes.

Manea, M.; Manea, V. C.

2009-04-01

86

Geodynamic evolution of the Earth over 600 Ma: implications for palaeo-climatic indicators  

NASA Astrophysics Data System (ADS)

During the last decades numerous local reconstructions were developed by the Geodynamic School of Lausanne. They participated to the elaboration of a 600Ma to present global plate tectonics model* based on field geology and controlled by geometric and kinematic constraints. Plate tectonics principles and lithospheric behaviour were applied to the model that drastically differs from the continental drift approach (i.e. based on palaeomagnetic data). Step after step lithospheric plates were reconstructed by adding or removing oceanic material (symbolized by synthetic isochrones) to major continents. The geodynamic evolution obtained is thus physically coherent and covers the whole surface of the Earth for the Phanerozoic. In the present contribution, we detail the basic tectonic features making up the model and the way they can be tested against the main palaeoclimatic indicators. Using synthetic isochrones, we developed a series of ocean lithosphere age maps. Based on plate rotation poles we computed velocity maps showing accretion and convergence rates. Converting ages into lithosphere thicknesses we quantified the volume of subducting material. Such tectonic parameters can be compared with the evolution of chemical proxies (e.g. CO2, ?18O, 87Sr/86Sr, Mg/Ca, SO4) offering a different way to decipher long-term climate changes. * This work was carried out as part of work done within the research program of the University of Lausanne on the Stampfli geodynamic model, model which is now owned by Neftex Petroleum Consultants Ltd. and is now attached to the "Neftex Earth Model ".

Hochard, C.; Vrard, C.

2011-12-01

87

Thermal and geodynamic contributions to the elevation of the Altiplano-Puna plateau  

NASA Astrophysics Data System (ADS)

The most remarkable feature of the Central Andes is the Altiplano-Puna plateau. This plateau is characterized by 3.5 km average elevation, approximately 70 km crustal thickness and very high heat flow. The upper mantle structure changes along strike below the plateau. The upper mantle below the Puna becomes hotter, and the lithosphere becomes thinner and weaker. These features suggest that thermal isostasy could play a role in the compensation of the Altiplano-Puna. Thermal isostasy is the geodynamic process whereby regional variations in the lithospheric thermal regime cause changes in elevation. Elevation changes result from variations in rock density in response to thermal expansion. The aim of this study is to estimate the thermal and geodynamic contributions to the elevation. While the thermal component of the Altiplano elevation would be of 1 km, the thermal contribution to the southern Puna elevation would be of 1.5 km. However, in the case of the southern Puna a portion of the actual topography (?20%) cannot be explained considering only compositional and thermal effects, suggesting additional geodynamical support. The obtained results suggest that the thermal state of the lithosphere would play a significant role in the elevation of the Central Andes, and may be responsible of some of the geological differences displayed by the Altiplano and the Puna.

Prezzi, Claudia; Iglesia Llanos, Mara Paula; Gtze, Hans-Jrgen; Schmidt, Sabine

2014-12-01

88

Use of high precision Satellite Laser Ranging Data in Space Geodynamics  

NASA Astrophysics Data System (ADS)

Satellite laser ranging (SLR) data analysis is one of the modern techniques used to derive the Earth rotation parameters (ERP) and to establish a Terrestrial Reference Frame (TRF) realization. Information on the ERP and TRF is widely used in astrometry, geodynamics and geodesy, in particular, in the Terrestrial and Celestial Reference Frames transformation. Algorithms developed to model the geodynamic satellite Lageos-1 and Lageos-2 motion are described in the paper. The model precision is at a few centimeter level at two-week intervals. The paper presents the recent results of the joint processing of Lageos-1 and Lageos-2 SLR data acquired by the global network of 103 stations in 1983--1996. The data were mainly obtained from the Crustal Dynamics Data Information System (CDDIS), NASA. The data analysis has been performed using KIEV-GEODYNAMICS 5.2 software which basically follows the IERS Conventions [2] with some exceptions. The aim of the analysis was to derive the Earth rotation parameters at 13.3-year time interval and SLR tracking stations coordinates and velocities. We have obtained a set of the Earth rotation parameters (xp, yp pole coordinates, UT1-UTC) on three-day intervals since MJD 45583 till MJD 50445, coordinates of 101 SLR stations at epoch January 1, 1993 (MJD 48898) and velocities of 50 sites (66 collocated stations) with good observing histories and sufficient amount of high quality data. The formal rms errors of the station coordinates are at the level of 0.1--1 cm for the majority of the stations. The derived station coordinates and velocities have been compared with ITRF94 [1]. The Terrestrial Reference Frame realization given by our solution is at the centimeter level in agreement with the ITRF94. Our solution for ERP has been compared with the {EOP(IERS) C 04} series. The formal errors are 0.4 milliarc second for pole coordinates and 0.03 millisecond for the Universal Time.

Rudenko, S.

89

Geodynamics for Everyone: Robust Finite-Difference Heat Transfer Models using MS Excel 2007 Spreadsheets  

NASA Astrophysics Data System (ADS)

Numerical geodynamics models of heat transfer are typically thought of as specialized topics of research requiring knowledge of specialized modelling software, linux platforms, and state-of-the-art finite-element codes. I have implemented analytical and numerical finite-difference techniques with Microsoft Excel 2007 spreadsheets to solve for complex solid-earth heat transfer problems for use by students, teachers, and practicing scientists without specialty in geodynamics modelling techniques and applications. While implementation of equations for use in Excel spreadsheets is occasionally cumbersome, once case boundary structure and node equations are developed, spreadsheet manipulation becomes routine. Model experimentation by modifying parameter values, geometry, and grid resolution makes Excel a useful tool whether in the classroom at the undergraduate or graduate level or for more engaging student projects. Furthermore, the ability to incorporate complex geometries and heat-transfer characteristics makes it ideal for first and occasionally higher order geodynamics simulations to better understand and constrain the results of professional field research in a setting that does not require the constraints of state-of-the-art modelling codes. The straightforward expression and manipulation of model equations in excel can also serve as a medium to better understand the confusing notations of advanced mathematical problems. To illustrate the power and robustness of computation and visualization in spreadsheet models I focus primarily on one-dimensional analytical and two-dimensional numerical solutions to two case problems: (i) the cooling of oceanic lithosphere and (ii) temperatures within subducting slabs. Excel source documents will be made available.

Grose, C. J.

2008-05-01

90

Preconditioned iterative methods for Stokes flow problems arising in computational geodynamics  

NASA Astrophysics Data System (ADS)

The numerical solution of a discrete Stokes flow problem is a common component of many computational geodynamic models. We compare using the Schur complement reduction (SCR) and a fully coupled (FC) approach to solve geodynamic problems which are characterized by incompressible fluids containing large variations in viscosity. The scalability and robustness of these methods is assessed by examining their sensitivity to the discretization parameter h and the viscosity contrast ??, respectively. We demonstrate that the scaled BFBt preconditioner [Elman, H.C., Howle, V.E., Shadid, J., Shuttleworth, R., Tuminaro, R., 2006. Block preconditioners based on approximate commutators. SIAM J. Sci. Comput. 27 (5), 1651-1668] can be an effective preconditioner for S=GK-1G, even when the fluid viscosity varies in space, provided an appropriate scaling is used. The performance of this preconditioner is strongly linked to the scaling employed. Through a number of numerical experiments, we demonstrate that our new scaling strategy ensures that the scaled BFBt preconditioner remains effective in scenarios where the viscosity variations are either locally smooth or discontinuous. Of the solvers considered, applying FGMRES to the pressure Schur complement in combination with BFBt and our choice of scaling matrices was the most scalable and robust approach.

May, Dave A.; Moresi, Louis

2008-12-01

91

Recent geodynamic pattern of the eastern part of the Bohemian Massif  

NASA Astrophysics Data System (ADS)

The Bohemian Massif, a Precambrian cratonic terrane, had been affected by several orogeneses forming its tectonic pattern. To detect the recent geodynamic motions going on fundamental geological structures of the Massif four regional geodynamic networks were established for epoch GPS measurements and one countrywide GEONAS network for permanent GPS satellite signals monitoring. In the east part of the Bohemian Massif sinistral movements on the Sudetic NW-SE faults and as well on the NNE-SSW faults of the Moravo-Silesian tectonic system have been detected. The sinistral trends dominate on many faults situated close to the contact of the Moldanuabian and Lugian parts and the Moravo-Silesian part of the Bohemian Massif. Because of tectonic systems intersections an existence of dextral movements cannot be excluded. Additional analyses displayed that eastern part of the Massif could be under extending trends. The preliminary site velocities assessed from GPS data for the eastern part of the Bohemian Massif are discussed from a viewpoint of regional geological structure motions. The work was supported by the Grant Agency of the Academy of Sciences of the Czech Republic (Project IAA300460507), the Targeted Research Programme of the Academy of Sciences of the CR (1QS300460551) and by the Ministry of Education, Youth and Sport of the Czech Republic (Projects LC506 and 1P05ME781).

Schenk, V.; Schenkov, Z.; Grcov, M.

2009-04-01

92

Chapter 4: Regional magnetic domains of the Circum-Arctic: A framework for geodynamic interpretation  

USGS Publications Warehouse

We identify and discuss 57 magnetic anomaly pattern domains spanning the Circum-Arctic. The domains are based on analysis of a new Circum-Arctic data compilation. The magnetic anomaly patterns can be broadly related to general geodynamic classification of the crust into stable, deformed (magnetic and nonmagnetic), deep magnetic high, oceanic and large igneous province domains. We compare the magnetic domains with topography/bathymetry, regional geology, regional free air gravity anomalies and estimates of the relative magnetic 'thickness' of the crust. Most of the domains and their geodynamic classification assignments are consistent with their topographic/bathymetric and geological expression. A few of the domains are potentially controversial. For example, the extent of the Iceland Faroe large igneous province as identified by magnetic anomalies may disagree with other definitions for this feature. Also the lack of definitive magnetic expression of oceanic crust in Baffin Bay, the Norwegian-Greenland Sea and the Amerasian Basin is at odds with some previous interpretations. The magnetic domains and their boundaries provide clues for tectonic models and boundaries within this poorly understood portion of the globe. ?? 2011 The Geological Society of London.

Saltus, R.W.; Miller, E.L.; Gaina, C.; Brown, P.J.

2011-01-01

93

Geodynamic insights into patterns of shear wave anisotropy in subduction zones  

NASA Astrophysics Data System (ADS)

Shear wave splitting observations from many subduction zones show complex patterns of seismic anisotropy that have trench-parallel fast directions and abrupt rotations. Several hypotheses have been proposed to explain these unexpected patterns. This work shows tests of the olivine fabric transition and three-dimensional flow hypotheses. The tool used to carry out this investigation is geodynamic modeling with seismological constraints on subduction zone geometry and rheological parameters based on rock deformation experiments. The geodynamic models presented in this work show that a transition to B-type olivine fabric can produce trench-parallel shear wave splitting with delay times greater than 1 s above the cold fore-arc mantle of subduction zones. The olivine fabric transition model adequately reproduces local-S splitting parameters associated with phases that sample the deep fore-arc mantle of the Ryukyu subduction system. The three-dimensional subduction zone models presented in this work show that both a transition to flat-slab subduction and strong trench curvature generate trench-parallel stretching in the warm are and back arc mantle. These models may explain trench-parallel shear wave splitting and abrupt rotations in fast direction in the are and back arc-mantle of the Andean and Marianas subduction systems. This thesis demonstrates that a variety of mechanisms may be necessary to account for trench-parallel anisotropy in subduction zones.

Kneller, Erik Arthur

94

Initiation of the San Jacinto Fault and its Interaction with the San Andreas Fault: Insights from Geodynamic Modeling  

E-print Network

Initiation of the San Jacinto Fault and its Interaction with the San Andreas Fault: Insights from Geodynamic Modeling QINGSONG LI 1,2 and MIAN LIU 1 Abstract--The San Andreas Fault (SAF) is the Pacific plate motion. Key words: Strain localization, fault interaction, San Andreas Fault, restraining bend

Liu, Mian

95

An analytical-numerical method for satellite movement determination of an intermediate orbit base for geodetical and geodynamical investigations  

Microsoft Academic Search

An analytical theory for determining accurately the coordinates of a satellite at any time during its movement around the earth was developed using a power series of regularized time and a spheroidal coordinate system. The theory is used to design a computer program for determining orbits of geodynamical satellites. The results of determining the orbit of Lageos with this program

Nikola Georgiev; Iavor Chapanov

1990-01-01

96

Gnss Geodetic Monitoring as Support of Geodynamics Research in Colombia, South America  

NASA Astrophysics Data System (ADS)

To support the geodynamics research at the northwestern corner of South America, GEORED, the acronym for "Geodesia: Red de Estudios de Deformacin" has been adopted for the Project "Implementation of the National GNSS Network for Geodynamics" carried out by the Colombian Geological Survey, (SGC), formerly INGEOMINAS. Beginning in 2007, discussions within the GEORED group led to a master plan for the distribution of the base permanent GPS/GNSS station array and specific areas of interest for campaign site construction. The use of previously identified active faults as preferred structures along which stresses are transferred through the deformational area led to the idea of segmentation of the North Andes within Colombia into 20 tectonic sub-blocks. Each of the 20 sub-blocks is expected to have, at least, three-four permanent GPS/GNSS stations within the block along with construction of campaign sites along the boundaries. Currently, the GEORED Network is managing 46 continuously including: 40 GEORED GPS/GNSS continuously operating stations; 4 GNSS continuously operating stations provided by the COCONet (Continuously Operating Caribbean GPS Observational Network) Project; the Bogot IGS GPS station (BOGT), installed in 1994 under the agreement between JPL-NASA and the SGC; and the San Andres Island station, installed in 2007 under the MOU between UCAR and the SGC. In addition to the permanent installations, more than 230 GPS campaign sites have been constructed and are being occupied one time per year. The Authority of the Panama Canal and the Escuela Politecnica de Quito have also provided data of 4 and 5 GPS/GNSS stations respectively. The GPS data are processed using the GIPSY-OASIS II software, and the GPS time series of daily station positions give fundamental information for both regional and local geodynamics studies. Until now, we have obtained 100 quality vector velocities for Colombia, 23 of them as part of the permanent network. The GPS/GNSS stations are located on the three major plates that interact within the Wide Plate Margin Deformation Zone including existing permanent installations on IGS Galapagos and Malpelo Islands on the Nazca Plate, and San Andres Island on the Caribbean plate. The velocity vectors confirm the oblique subduction of the Nazca Plate and Carnegie aseismic ridge collision processes at the Colombia-Ecuador trench which are assumed to be the mechanism for the transpressional deformation and the "escape" of the North Andes Block (NAB). The northernmost vectors in Colombia are indicative of the ongoing collision of the Panama Arc with northwestern Colombia. Planned for the year 2013 is the installation of 10 additional GNSS continuously operating stations, and construction of 20 GPS campaign sites.

Mora-Paez, H.; Acero-Patino, N.; Rodriguez-Zuluaga, J. S.; Diederix, H.; Bohorquez-Orozco, O. P.; Martinez-Diaz, G. P.; Diaz-Mila, F.; Giraldo-Londono, L. S.; Cardozo-Giraldo, S.; Vasquez-Ospina, A. F.; Lizarazo, S. C.

2013-05-01

97

Radioactivity measurements in volcano-tectonic area for geodynamic process study  

NASA Astrophysics Data System (ADS)

In the last ten years we carried out several radioactivity investigations in the aetnean area, a peculiar site characterized by both tectonicand volcanic features. In particular, continuous measurements in-soilradon gas carried out from 2001 until 2006 in the eastern flank of Mt. Etna, while several volcanic events occurred, showed a possible correlation between radon concentration and geodynamic activity, in particular magma uprising. We report in particular on the survey performedin order to determine vertical radon concentration profiles at differentdepths in sites near active faults in order to extract radon diffusion coefficients for the different sites. Moreover laboratory analysis alloweddetermining radionuclide contents (via ?-spectroscopy) and radon exhalation rate (via Can-technique) for different rock samples from themonitored sites. This study represents a contribution to better definethe radon transport process through fractured media, in particular in volcanic area.

Morelli, D.; Imm, G.; Cammisa, S.; Catalano, R.; Mangano, G.; La Delfa, S.; Patan, G.

2012-04-01

98

Arctic geodynamics: Continental shelf and deep ocean geophysics. ERS-1 satellite altimetry: A first look  

NASA Technical Reports Server (NTRS)

An overall review of the Arctic Geodynamics project is presented. A composite gravity field model of the region based upon altimetry data from ERS-1, Geosat, and Seasat is made. ERS-1 altimetry covers unique Arctic and Antarctic latitudes above 72 deg. Both areas contain large continental shelf areas, passive margins, as well as recently formed deep ocean areas. Until ERS-1 it was not possible to study these areas with satellite altimetry. Gravity field solutions for the Barents sea, portions of the Arctic ocean, and the Norwegian sea north of Iceland are shown. The gravity anomalies around Svalbard (Spitsbergen) and Bear island are particularly large, indicating large isostatic anomalies which remain from the recent breakup of Greenland from Scandinavian. Recently released gravity data from the Armed Forces Topographic Service of Russia cover a portion of the Barents and Kara seas. A comparison of this data with the ERS-1 produced gravity field is shown.

Anderson, Allen Joel; Sandwell, David T.; Marquart, Gabriele; Scherneck, Hans-Georg

1993-01-01

99

Isostasy of aseismic tectonic units in the South Atlantic Ocean and geodynamic implications  

NASA Astrophysics Data System (ADS)

Mechanical isostasy of the lithosphere in the South Atlantic Ocean was studied using information on gravity anomalies and bathymetry with additional constraints imposed by the altimetric geoid. The isostatic responses (admittances) over the Walvis Ridge, Rio Grande Rise and Trindade Seamount Chain were computed using a three-dimensional algorithm. The eastern Walvis Ridge and the Rio Grande Rise have the same response, which is well explained by an Airy model of isostasy. The other features are regionally supported. A variation in the thickness of the elastic plate was found along the western Walvis Ridge. A high value of the elastic plate thickness (20 km) was found under the Trindade Chain. Geodynamic implications are discussed in the light of these results.

Bulot, A.; Diament, M.; Dubois, J.; Kogan, M. G.

1984-10-01

100

On the post-25 Ma geodynamic evolution of the western Mediterranean  

NASA Astrophysics Data System (ADS)

During the Neogene and Quaternary western Mediterranean geodynamics were dominated by the `eastward' migration of the Apenninic arc and associated back-arc basins. The migration was controlled by retreat of the Apenninic slab and was associated with `boudinage' of the lithosphere in the back-arc area. Palaeo-reconstruction of the kinematics of the arc suggests about 775 km of migration from the Late Oligocene to present along a transect from the Gulf of Lions to Calabria. A maximum of 135 km of N-S converge occurred between Africa and Europe during the same time span. The western Mediterranean was thus mainly shaped by the migration of the slab related to west-directed subduction. It is hypothesized that minor N-S convergence deformed the arc but was not the cause of its formation.

Gueguen, Erwan; Doglioni, Carlo; Fernandez, Manuel

1998-11-01

101

Tectonic and geodynamic setting of oil and gas basins of the Soviet Union  

SciTech Connect

Within the territory of the Soviet Union and its off-shore economic zone are about 70 sedimentary basins containing oil and gas. The basins include almost all basin types described in present-day plate-tectonic classifications, namely (1) intracontinental and pericontinental rifts, suprarift syneclises, and zones of pericratonic downwarps; (2) ancient passive margins of continents with adjacent overthrust fold system; (3) modern passive margins of continents; (4) zones of convergence of lithospheric plates (i.e., zones of subduction of oceanic plates below continental plates); and (5) zones of collision of continental lithospheric plates. So, far, the only type of basin not identified within the territory of the Soviet Union is the pull-apart basin. The location and distribution of oil and gas deposits in the section of a basin, prevailing types of traps, and scale of potential resources are all features influenced by the geodynamic type of the basin.

Khain, V.E.; Sokolov, B.A. (Lomonosov State Univ., Moscow (Russian Federation)); Kleshchev, K.A.; Shein, V.S. (All-Union Petroleum Geological Research Inst., Moscow (Russian Federation))

1991-02-01

102

Strong intracontinental lithospheric deformation in South China: Implications from seismic observations and geodynamic modeling  

NASA Astrophysics Data System (ADS)

Classical plate tectonics theory predicts concentrated deformation at plate boundaries and weak deformation within plates. Yet, the existence of intracontinental orogens shows that highly deformed regions can occur within continental plates, which is geodynamically incompletely understood. Shear wave splitting measurements in South China show belt-parallel (i.e. NE-SW) fast directions beneath the Wulingshan-Xuefengshan Belts, while no dominant fast direction is found in the cratonic Sichuan Basin. Tomographic studies in the mantle in the same area show that the thickness of lithosphere beneath the intracontinental orogen is larger than that beneath the cratonic Sichuan Basin. In order to better understand these seismic observations, we performed numerical experiments of intracontinental lithospheric deformation with the presence of cratonic basin.

Lu, Gang; Zhao, Liang; Zheng, Tianyu; Kaus, Boris J. P.

2014-06-01

103

Numerical modeling of seismicity and geodynamics of the Kachchh rift zone, Gujarat, India  

NASA Astrophysics Data System (ADS)

The numerical block-and-fault model of lithosphere dynamics and seismicity (BAFD) is used to understand crustal motion and features of the observed seismicity in the Kachchh rift zone, Gujarat, Western India. The block-model allows simulating seismicity and geodynamics simultaneously unlike other modeling approaches for studying seismicity or geodynamics. The model structure of Kachchh rift zone is composed of seven major crustal blocks separated by fault planes. Based on the orientation of boundary crustal block movements, we develop a set of numerical experiments to analyze the spatial distribution of earthquakes, frequency-to-magnitude relationships, earthquake focal mechanisms, velocity field, and fault slip rates in the model. The main results of our modeling suggest that an NNW-SSE trending compression is a principal driving force in the Kachchh rift zone that explains basic features of the regional seismicity, direction of block motions, and the presence of an extensional stress regime associated with the Cambay rift zone. Large synthetic events occur on the fault segments associated with the Allah-Bund fault, Katrol hill fault and north Wagad fault which have been causative faults for the 1819 Mw7.7 Allah-Bund, 1956 Mw6.0 Anjar and 2001 Mw7.7 Bhuj earthquakes. The frequency-magnitude distribution for both synthetic seismicity and observed seismicity shows a similar slope. The focal mechanisms of the synthetic events are found to be consistent with those of earthquakes in the region. A special attention has been paid to study long-term and post-seismic deformations. Our results are in a qualitative agreement with the GPS post-seismic observations in the Kachchh rift zone. We infer that the observed seismicity and crustal block motions are a consequence of the dynamics of the entire regional fault and block system rather than that of a single causative fault only.

Vorobieva, Inessa; Mandal, Prantik; Gorshkov, Alexander

2014-11-01

104

Fast and Robust Newton strategies for non-linear geodynamics problems  

NASA Astrophysics Data System (ADS)

Geodynamic problems are inherently non-linear, with sources of non-inearities arising from the (i) rheology, (ii) boundary conditions and (iii) the choice of time integration scheme. We have developed a robust non-linear scheme utilizing PETSc's non-linear solver framework; SNES. Through the SNES framework, we have access to a wide range of globalization techniques. In this work we extensively use line search implementation. We explored a wide range different strategies for solving a variety of non-linear problems specific to geodynamics. In this presentation, we report of the most robust line-searching techniques which we have found for the three classes of non-linearities previously identified. Among the class of rheological non-linearities, the shear banding instability using visco-plastic flow rules is the most difficult to solve. Distinctively from its sibling, the elasto-plastic rheology, the visco-plastic rheology causes instantaneous shear localisation. As a results, decreasing time-stepping is not a viable approach to better capture the initial phase of localisation. Furthermore, return map algorithms based on a consistent tangent cannot be used as the slope of the tangent is infinite. Obtaining a converged non-linear solution to this problem only relies on the robustness non-linear solver. After presenting a Newton methodology suitable for rheological non-linearities, we examine the performance of this formulation when frictional sliding boundary conditions are introduced. We assess the robustness of the non-linear solver when applied to critical taper type problems.

Le Pourhiet, Laetitia; May, Dave

2014-05-01

105

Neogene volcanism and extension in Western Anatolian-Aegean area: A new geodynamic model  

NASA Astrophysics Data System (ADS)

The widespread Western Anatolian-Aegean Neogene volcanism presents a complex geochemical evolution reflecting the uncommon space-time variability of the geodynamic setting of the region. In the Western Anatolian and Central Aegean, a widespread supra-subduction magmatism, with calc-alkaline to shoshonitic affinity, took place from Early to Middle Miocene; this phase of activity ends with spots of ultra-K lavas and dykes. From Late Miocene onwards scattered alkali basaltic lavas with intraplate affinity were emitted, while calc-alkaline activity occurred in the South Aegean arc. Since Late Oligocene-Early Miocene, the region was, and still is, affected by extensional tectonics generally ascribed to a backarc rift. However the Aegean region should rather be considered as an unconventional backarc since its characteristics rather differ from 'typical' backarcs. In fact, in spite of a long lasting(>40Ma) active NE-directed subduction of Africa, the backarc area still maintains a relatively thick continental crust (>20-25 km). Moreover, the upper Eurasian plate is overriding the lower Africa plate with separate segments, with Greece moving faster, and Turkey moving slower. The differential velocity between Greece and Turkey determines extension in the upper plate, unrelated to the loss of subducted retreating lithosphere, which is the usual setting for the origin of 'classic' backarc settings. The geodynamic framework is supported by the geochemical and isotopic features of the supra-subduction magmas revealing the occurrence of a trapped, drying slab, with progressive decreasing of Fluid Mobile Elements/Fluid Immobile Elements ratios, ?11B and ?7Li, coupled with scarce variations of Sr and Nd isotopes. Moreover, the differential motion between the Greek and Anatolian micro-plates creates tear zones with the formation of slab ruptures or vertical slab windows. The occurrence of such windows is, in fact, outlined by the presence of alkali basalts with intraplate affinity sourced in the sub-slab mantle.

Agostini, S.; Doglioni, C.; Innocenti, F.; Manetti, P.; Tonarini, S.

2008-07-01

106

"Numerical techniques for thermo-mechanical-fluid-flow modelling in geosciences" 3D geodynamic modelling of lithospheric-scale deformation remains a challenge as it requires  

E-print Network

geodynamic modelling of lithospheric-scale deformation remains a challenge as it requires scalable multigrid developed LaMEM (Lithosphere and Mantle Evolution Model), which was originally a finite element code

Hanke-Bourgeois, Martin

107

Atmospheric excitation of polar motion during the GIG '91 measurement campaign. [GPS International Earth Rotation Service and Geodynamics experiment  

NASA Technical Reports Server (NTRS)

Daily determinations of the earth's pole position from GPS observations obtained during the first GPS IERS and Geodynamics (GIG) experiment are interpreted in terms of atmospheric wind and pressure fluctuations. Evidence is reported for atmospheric excitation of the rapid polar motions observed during the 23-day period from 22 January to 13 February, 1991. It is demonstrated that atmospheric wind and pressure fluctuations are mostly responsible for exciting the rapid polar motions observed during GIG '91.

Gross, Richard S.; Lindqwister, Ulf J.

1992-01-01

108

Results from parallel observations of superconducting and absolute gravimeters and GPS at the Hsinchu station of Global Geodynamics Project, Taiwan  

Microsoft Academic Search

The Hsinchu (HS) superconducting gravimeter (SG, serial T48) station is a newly established site in the Global Geodynamics Project (GGP). Simultaneous observations of T48, three FG5 absolute gravimeters, and GPS at four stations are studied. GPS shows few mm a?1 of horizontal and vertical motions around HS. The calibration factor and drifting rate of T48 are ?75.96 0.07 ?Gal

Cheinway Hwang; Ricky Kao; Ching-Chung Cheng; Jiu-Fu Huang; Chiung-Wu Lee; Tadahiro Sato

2009-01-01

109

Chemical geodynamics of continental subduction-zone metamorphism: Insights from studies of the Chinese Continental Scientific Drilling (CCSD) core samples  

Microsoft Academic Search

The DabieSulu orogenic belt of east-central China has long been a type location for the study of geodynamic processes associated with ultrahigh-pressure (UHP) tectonics. Much of our understanding of the world's most enigmatic processes in continental deep-subduction zones has been deduced from various records in this belt. By taking advantage of having depth profiles from core samples of the Chinese

Yong-Fei Zheng; Ren-Xu Chen; Zi-Fu Zhao

2009-01-01

110

Geodynamic evolution and sedimentary infill of the northern Levant Basin: A source to sink-perspective  

NASA Astrophysics Data System (ADS)

Nicolas Hawie a,b,c (nicolas.hawie@upmc.fr) Didier Granjeon c (didier.granjeon@ifpen.fr) Christian Gorini a,b (christian.gorini@upmc.fr) Remy Deschamps c (remy.deschamps@ifpen.fr) Fadi H. Nader c (fadi-henri.nader@ifpen.fr) Carla Mller Delphine Desmares f (delphine.desmares@upmc.fr) Lucien Montadert e (lucien.montadert@beicip.com) Franois Baudin a (francois.baudin@upmc.fr) a UMR 7193 Institut des Sciences de la Terre de Paris, Universit Pierre et Marie Curie/ Univ. Paris 06, case 117. 4, place Jussieu 75252 Paris Cedex 05, France b iSTEP, UMR 7193, CNRS, F-75005, Paris, France c IFP Energies nouvelles, 1-4 avenue du Bois Prau 92852 Rueil Malmaison Cedex, France d UMR 7207, Centre de Recherche sur la Paleobiodiversit et les Paleoenvironnements. Universit Pierre et Marie Curie, Tour 46-56 5me. 4, place Jussieu 75252 Paris Cedex 05, France e Beicip Franlab, 232 Av. Napolon Bonaparte, 95502 Rueil-Malmaison, France Sedimentological and biostratigraphic investigations onshore Lebanon coupled with 2D offshore reflection seismic data allowed proposing a new Mesozoic-Present tectono-stratigraphic framework for the northern Levant Margin and Basin. The seismic interpretation supported by in-depth facies analysis permitted to depict the potential depositional environments offshore Lebanon as no well has yet been drilled. The Levant region has been affected by successive geodynamic events that modified the architecture of its margin and basin from a Late Triassic to Middle Jurassic rift into a Late Cretaceous subduction followed by collision and Miocene-Present strike slip motion. The interplay between major geodynamic events as well as sea level fluctuations impacted on the sedimentary infill of the basin. During Jurassic and Cretaceous, the Levant Margin is dominated by the aggradation of a carbonate platform while deepwater mixed-systems prevailed in the basin. During the Oligo-Miocene, three major sedimentary pathways are expected to drive important quantities of clastic material into the Levant Basin: (1) the marginal canyons along the Levant Margin, (2) the Latakia region and the Palmyrides Basin (Syria) and (3) the Red Sea area and Nile Delta. Regional drainage system analysis was performed to estimate the contribution to the infill of the basin of the different sediment sources, and in particular, to estimate erosion of Nubian siliciclastic material, granitic Red Sea rift shoulders and Arabian Shield. A numerical stratigraphic forward model, Dionisos, was used to test these source-to-sink assumptions; a sensitivity analysis was then performed to understand better the impact of the different geodynamic and stratigraphic scenarios on the architecture and sedimentary infill of the Levant Basin, and thus on the expected petroleum systems of this frontier basin

Hawie, N.

2013-12-01

111

Impact of geodynamic development of the Barents Sea deep rift on evolving petroleum systems  

NASA Astrophysics Data System (ADS)

All the Barents Sea deposits are situated in the epicenter on active geodynamic development of the Barents Sea rift and, most important, over the zone of listric faults intersection, which consist a knot system over the mantle diapir. This is confirmed by prospecting seismology. Intrusion of hot mantle matter with further cooling down of abnormal lense might be a possible cause of appearance and evolution of ultradeep depressions. A high "seismic stratification" of the lower crust (nearly reaching the basement surface) at time scale about 8 sec. is typical for the inner, the deepest part of the depression. Supposing the "seismic stratified" lower crust correspond to "basalt" layer, this area is nearly upper crust ("granitic-gneiss") free. This fact confurmes conception on development of "granite free gaps" in the depression basement. Thick blocks of "seismically transparent" upper crust corresponding to the "granitic-gneiss" layer are marked out within Kolsk-Kanin monocline. An abrupt thickness decrease and appearance of "stratified" areas takes place at the southern edge of the depression. A filling of the over-rift sag with sediments, revival of the faults and their effect on the filtration processes and gas hydrates formation took place in the South Barents Sea depression. Repeating activation of the fault blocks in the basement, especially during late Jurassic - early Cretaceous period contributed to formation of the structures related to the greatest deposits of the South Barents Sea depression. An extended field acoustic data collected in the Barents Sea led to understanding of general fundamental problems for all Arctic Seas and, first of all, the problem of Quaternary glaciations. An analysis of Eurasian-Arctic continental margin shows correspondence between the rift systems of the shelf with those of the ocean. This relation can be observed by an example of the central Arctic region. All the rift systems underlying the sediment basin are expressed in the sea bed relief as spacious and extensive graben valleys burnished by lobes. The rift structures and the sediment cover are connected by the systems of transversal (or oblique) faults. A study of the regional geologic structure of basins affords believing in the very complicated inner riftogenic structure of the base and the lower part of the sediment cover, which is represented by a combination of grabens and horsts bound by the same tectonic border in the form of high amplitude fault zones, and have a very high density of fault-fractured tectonics. In the same time, a branching of the rift structures related to rounding of large solid blocks of the crust, represented by Archaean or Baikal base prominences, takes place. Their frequent structural connection with the continental paleo-rift structures is ascertained, but the shelf rift system are not their straight prolongation and separated by base thresholds concealed under the sediment cover or by bulkheads expressed even in the modern relief. Filling of over rift flexure by sediments, revival of faults and their impact on flow processes and gas hydrate formation in under sea bed sediments have occurred in the South Barents depression. Geodynamic development of the Barents sea rift not only played a substantial role in formation of as unique fields as Shtokman, Prirazlomnoe and others, but created prerequisites for possible gas outbursts into near-surface sediments of the Barents Sea that could result, in some cases, in gas hydrate formation. Periodic activation of basic fault blocks, especially in late Jurassic - early Cretaceous time significantly contributed to formation of the structures related to the greatest fields of South Barents depression. The information on geodynamic development of the region, thermal convection and modern sedimentation enable assessment of the real potentiality for underwater works in the region, potential gas hydrates resources, and will help to assign a strategy of prospecting work, to range the known

Balanyuk, I.; Dmitrievsky, A.

2009-04-01

112

Using Interactive Visualization to Analyze Solid Earth Data and Geodynamics Models  

NASA Astrophysics Data System (ADS)

The geological sciences are challenged to manage and interpret increasing volumes of data as observations and simulations increase in size and complexity. Major projects such as EarthScope and GeoEarthScope are producing the data needed to characterize the structure and kinematics of Earth's surface and interior at unprecedented resolution. At the same time, high-performance computing enables high-precision and fine- detail simulation of geodynamics processes, complementing the observational data. To facilitate interpretation and analysis of these datasets, to evaluate models, and to drive future calculations, we have developed methods of interactive visualization with a special focus on using immersive virtual reality (VR) environments to interact with models of Earth's surface and interior. VR has traditionally been used primarily as a presentation tool allowing active navigation through data. Reaping the full intellectual benefits of immersive VR as a tool for accelerated scientific analysis requires building on the method's strengths, that is, using both 3D perception and interaction with observed or simulated data. Our approach to VR takes advantage of the specialized skills of geoscientists who are trained to interpret geological and geophysical data generated from field observations. Interactive tools allow the scientist to explore and interpret geodynamic models, tomographic models, and topographic observations, while feature extraction tools support quantitative measurement of structures that emerge from numerical simulations or field observations. The use of VR technology enables us to improve our interpretation of crust and mantle structure and of geodynamical processes. Mapping tools based on computer visualization allow virtual "field studies" in inaccessible regions, and an interactive tool allows us to construct digital fault models for use in numerical models. Using the interactive tools on a high-end platform such as an immersive virtual reality room known as a Cave Automatic Virtual Environment (CAVE), enables the scientist to stand in data three-dimensional dataset while taking measurements. The CAVE involves three or more projection surfaces arranged as walls in a room. Stereo projectors combined with a motion tracking system and immersion recreates the experience of carrying out research in the field. This high-end system provides significant advantages for scientists working with complex volumetric data. The interactive tools also work on low-cost platforms that provide stereo views and the potential for interactivity such as a Geowall or a 3D enabled TV. The Geowall is also a well-established tool for education, and in combination with the tools we have developed, enables the rapid transfer of research data and new knowledge to the classroom. The interactive visualization tools can also be used on a desktop or laptop with or without stereo capability. Further information about the Virtual Reality User Interface (VRUI), the 3DVisualizer, the Virtual mapping tools, and the LIDAR viewer, can be found on the KeckCAVES website, www.keckcaves.org.

Kellogg, L. H.; Kreylos, O.; Billen, M. I.; Hamann, B.; Jadamec, M. A.; Rundle, J. B.; van Aalsburg, J.; Yikilmaz, M. B.

2008-12-01

113

Geodynamic models of the deep structure of the natural disaster regions of the Earth  

NASA Astrophysics Data System (ADS)

Investigation of the deep structure and creation of geodynamic models of natural disaster regions are important for understanding of the nature of such phenomena as earthquakes, eruptions of volcanoes, tsunami and others. Carrying out of such researches is necessary for definition of areas of potential risk, forecasting and the prevention of negative consequences of acts of nature. Research region is active continental margins of the Sea of Okhotsk, and especially the area of Neftegorsk earthquake which has occurred on May, 28th 1995 in the North Sakhalin and caused many victims and destructions. The geodynamic model of the lithosphere in the region of Neftegorsk earthquake has been constructed along the profile crossing the North Sakhalin Basin, Deryugin Basin and ophiolite complex between them. The Deryugin Basin was formed at the site of an ancient deep trench after the subduction of the Okhotsk Sea Plate under Sakhalin. The basin is located above a hot plume in the mantle at a depth of 25 km. The ophiolite belt of ultramafic magmatic rocks is an ancient (K2-Pg) paleosubduction zone separating the Deryugin basin from the North Sakhalin Basin. The thickness of the ancient seismic focal zone is 80 km. It is probably that the structures of the North Sakhalin have been formed in the following way. In the Late Cretaceous the oceanic Okhotsk Sea Plate subducted under Sakhalin, the eastern part of which was an andesite island arc. Approximately in Miocene the subduction of the plate apparently ceased. In that time the Tatar Rift Strait was formed. Ophiolite rocks of the subduction zones as a result of compression have been squeezed out on a surface. The ophiolite complex combined by the ultrabasic rocks, fixes position of ancient subduction zone. It is probable that the manifestation of the Neftegorsk earthquake was a result of activization of this ancient subduction zone. On a surface the subduction zone manifests itself as deep faults running along Sakhalin. The center of the Neftegorsk earthquake was directly formed by burst of activity of this ancient subduction zone. From a position of the ancient subduction zone under Sakhalin, which is a cause of strong earthquakes here, it follows that the region is one of seismic dangerous in Russia. Constructed on the basis of complex interpretation of the geologic-geophysical data the geodynamic models of natural disaster regions give the chance: to study a deep structure under seismic dangerous zones; to investigate a role of deep processes in the upper mantle in formation of structures of earth crust; to relate the geological features, tectonomagmatic, hydrothermal activity with the processes in the upper mantle; to plot maps in detail with zones of increasing risks to prevent active building or other economic activities in such dangerous regions.

Rodnikov, A. G.; Sergeyeva, N. A.; Zabarinskaya, L. P.

2012-04-01

114

The wave-like geodynamic reorganizations revealed by the change in orientation of the paleostress axes  

NASA Astrophysics Data System (ADS)

Sedimentary rock fracturing is a reliable stress indicator when properly measured, processed and interpreted. Our long-term field observations and theoretical considerations show that the primary joint sets are formed at the stage of diagenesis of sediments at horizontal bedding. Most likely, it happens due to internal instability of sediments manifested in localised form, which leads to formation of two conjugate systems of shear discontinuities. This model allows us to reconstruct the orientation of the axis of the maximum horizontal paleo-compression SH,max and to determine the period of its existence up to the scale of geological time. During more than 30 years of our field observations, we collected about 400,000 individual joint measurements in many regions of Eurasia. These data were applied to paleostress reconstruction by using interpretation of primary jointing formation mentioned above. Both spatial distributions of paleostress axes and the evolution of these distributions in time determined by our techniques are in reasonably good agreement with paleogeodynamic reconstructions obtained by other approaches. A distinctive feature of the paleostress evolution is that at certain times orientation of the SH,max axes changes abruptly, turning at an angle up to 90 . Sometimes these changes are gradually spreading to neighboring regions. We attribute this phenomenon to the geodynamic reorganization which spreads over the space at a certain speed. Such wave-like spreading was observed in the East-European platform, the Tien-Shan, along the arc Pamirs-Tibet-Vietnam and in other regions. From the perspective of this phenomenon, the Caucasus-Zagros region is of particular interest. Here from the end of the Early Cretaceous to the present time the SH,max axis with small spatial variations was NE oriented. However, we identified a relatively short period in the Miocene characterized by geodynamic reorganization. In the early middle Miocene in the south-east of the region (the south-eastern part of the Zagros) the SH,max axis changed orientation from NE to NW. At this time in the north of the region (Central Pre-Caucasus) the SH,max axis was still directed towards NE. But in the middle Sarmatian, when the southern part of the region already had NE orientation of compression, in the northern part the SH,max axis reoriented in NNW direction. As in the south of the region, this reorientation was short and in late Sarmatian the SH,max axis regained his usual NE orientation. The identified short-term restructuring that began in the south-east of the region in the early middle Miocene and which reached the northern part of the region in the early Late Miocene can be interpreted as the process of the south to north moving of the solitary wave of geodynamic perturbation. The velocity of the wave is estimated as 0.1-1.0 m/year.

Mukhamediev, Shamil; Belousov, Tomas

2014-05-01

115

Geodynamic evolution of the Earth over 600 Ma: palaeo-topography & -bathymetry (from 2D to 3D)  

NASA Astrophysics Data System (ADS)

A full global, physically coherent geodynamical model over 600 million years (Ma) has been developed at the University of Lausanne* during the past 20 years, based on the PaleoDyn database, compiling geological, palaeogeographical, and geophysical information of geodynamical interest. The 2D model (series of 48 maps) allows us, now, to investigate world bathymetry (or sea-floor topography) and continental topography. A theoretical approach of the relief is shown here, based on lithospheric plate cooling model and best-fit of present-day topographic (s.l.) data. Although such general and actualistic method may be valid to first order only, it has the advantage of being applicable anywhere in the world and for the whole Phanerozoic. Our wish is to combine our model with global oceanic and/or atmospheric circulation models (GCM). The model is a powerful tool to test whether tectonics is the predominant parameter on long-term global climate changes or not. Such 3D development, therefore, may have endless repercussions not only for Earth Sciences but also for the present-day debate upon climate changes. * This work was carried out as part of work done within the research program of the University of Lausanne on the Stampfli geodynamic model, model which is now owned by Neftex Petroleum Consultants Ltd. and is now attached to the "Neftex Earth Model".

Vrard, C.; Hochard, C.

2011-12-01

116

Geophysical Monitoring of Geodynamic Processes of Earth Crust of Central Armenia  

NASA Astrophysics Data System (ADS)

At present methods of monitoring are widely used and implemented in the different fields of science to receive non stop information about the observed object in time. The method of geophysical monitoring of earth crust is developed in Garny Geophysical Observatory. It is based on the abilities of geophysical and hydrogeological indicators to react to the changes of stressedly deformative state of earth crust. The study of variations of magnetic observations connected with the deformation processes which took place during the preparation of earthquake source or of other tectonic movements will significantly increase the informational and effective character of monitoring. The changes of hydrogeological indicators depending on the deformation of water-bearing rocks are defined by the parameters of deformational fields and by the elastic and filtration characters of rocks. Methodological means of monitoring are brought to the signal appearing which reflects the deformation of rock massive. The methods of noise elimination and singling out 'deformational signals' allow to delete or mention the trend, to compensate the influence of variations on atmospheric pressure on time rows of geophysical rows and underground water level, to allocate earth tide induced fluctuations of level. But not all the noise may be deleted by calculation. The following is included in the group of non-controlled noise: the influence of infiltration on atmospheric precipitations, effects of certain technogenic influences. Deformation indicators may be not only the deflection of geophysical indicators from certain phone values but also the parametres of variations of these indicators. There exists data on the changes of parameters of barometric effectiveness and saw tooth fluctuations of underground water level before seismic events. In some cases the noise which hinders the appearance of deformational signal may itself carry useful information. Method of geophysical monitoring of earth crust was applied which allows with the help of hydrogeodynamic observations, observations of geochemistry of underground water, module of full vector of magnetic field and seismic regime of the region to carry out the monitoring of modern geodynamic processes of Armenia. The character of distribution of hydrogeodeformational processes in time and space was studied. The character of time-spatial distribution of geodynamic stress was defined. Key Words: Deformation , Geophysical Monitoring, Earthqukae Source

Pashayan, R.

2012-12-01

117

Sink or swim? Geodynamic and petrological model constraints on the fate of Archaean primary crust  

NASA Astrophysics Data System (ADS)

Ambient mantle potential temperatures in the Archaean were significantly higher than 1500 C, leading to a high percent of melting and generating thick MgO-rich primary crust underlain by highly residual mantle. However, the preserved volume of this crust is low suggesting much of it was recycled. Here we couple calculated phase equilibria for hydrated and anhydrous low to high MgO crust compositions and their complementary mantle residues with 2-D numerical geodynamic models to investigate lithosphere dynamics in the early Earth. We show that, with increasing ambient mantle potential temperature, the density of primary crust increases more dramatically than the density of residual mantle decreases and the base of MgO-rich primary crust becomes gravitationally unstable with respect to the underlying mantle even when fully hydrated. To study this process we use geodynamic models that include the effects of melt extraction, crust formation and depletion of the mantle in combination with laboratory-constrained dislocation and diffusion creep rheologies for the mantle. The models show that the base of the gravitationally unstable lithosphere delaminates through relatively small-scale Rayleigh-Taylor instabilities, but only if the viscosity of the mantle lithosphere is sufficiently low. Thickening of the crust above upwelling mantle and heating at the base of the crust are the main mechanisms that trigger the delamination process. Scaling laws were developed that are in good agreement with the numerical simulations and show that the key parameters that control the instability are the density contrast between crust and underlying mantle lithosphere, the thickness of the unstable layer and the effective viscosity of the upper mantle. Depending on uncertainties in the melting relations and rheology (hydrous or anhydrous) of the mantle, this process is shown to efficiently recycle the crust above potential temperatures of 1550-1600 C. However, below these temperatures this process ceases to work, mainly because the percent of melting in the upper mantle is insufficient to generate locally thickened new crust. We further show that melting at the base of overthickened hydrated primary crust is also plausible at the predicted temperatures and would have led to intracrustal differentiation. The tonalite-trondhjemite-granodiorite gneisses that comprise exposed Archaean crust cannot have been generated directly from primary MgO-rich crust, but could have been derived from hydrated basaltic crust formed by crystal fractionation or intracrustal differentiation.

Kaus, B.; Johnson, T.; Brown, M.; VanTongeren, J. A.

2013-12-01

118

Integrated crustal models, characterisation of crustal lithology and geodynamic implications - southwestern Barents Sea.  

NASA Astrophysics Data System (ADS)

Our 3D model covers the offshore extension of the Norwegian Caledonides, which constitutes of a series of basement high and deep basins. Our 3D model integrates density and magnetic modelling with the interpretation of seismic refraction and reflection data and helps to characterize the different basement units. Furthermore, the 3D model allows characterizing the crustal configuration and contributes to our understanding of the geodynamics processes that affected the region and are expressed in the basement lithology variability. The model is based on interpretation of profiles constrained by refraction and reflection seismic. Well data were integrated to adjust the depth of the sedimentary layers. The geological interpretations are based on onshore- offshore links and onshore petrophysical sampling. The distribution of density, magnetic susceptibility and Q- ratio values allows distinguishing the different basement units (Precambrian gneiss, Caledonian Nappes, granitic plutons and mafic intrusions). One model explains the long-term persistence of the Loppa High as a high since Devonian times. The 3D model allows mapping the gneiss dome sitting along the west side of the Loppa High and other localised intrusions. At the east of the Loppa High, the model highlights a thickening of the Caledonian nappes important enough to overprint the Precambrian basement magnetic signature. Our basement unit map raises the question why the magnetic signal of the Caledonian basement is so representative at the east of the Loppa High whereas onshore its signal is weak and does not cover the Precambrian basement signal. The combination of our regional geophysical modelling with a more detailed study of the seismic interpretation allows proposing a geodynamic scenario for the Loppa High installation. We link the Loppa High geometry and composition to the installation of a gneiss dome syn-tectonic with the development of the Bjrnyrenna Fault Complex. Initiated in Devonian times, the development of the Bjrnyrenna Fault Complex and installation of the gneiss dome installations led to a rotation of the basement blocks rotations. As a consequence the Caledonian nappes in the east have been preserved, while the Caledonian layers have been eroded due to an uplift of the western part.

Barrere, C.; Ebbing, J.; Gernigon, L.

2007-12-01

119

Research on absolute gravity variations in geodynamic laboratory in Ksi?? in the period of 2007- 2011  

NASA Astrophysics Data System (ADS)

In 2006 a gravimetric pavilion was installed inside the Geodynamic Laboratory (LG) in Ksi??. The pavilion was equipped with two pillars intended to serve relative and absolute gravimetric measurements. Installation of measurement platform for absolute gravity measurements inside gravimetric pavilion of LG made it possible to perform four sessions of absolute gravity measurements: two of them in 2007 (June 10-12 and Nov. 21-22), one in 2008 (Apr. 21-22) and one in 2011 (June 19-21). In 2007 the absolute measurements were performed using two FG5 ballistic gravimeters. In April 2007 the measurements were performed by Dr Makinen from Geodetic Institute of Finnish Academy of Science with application of FG5 No. 221 absolute gravimeter. In June 2007 and in the years 2008 and 2011 such gravimetric measurements were performed by the team from Department of Geodesy and Astronomical Geodesy of Warsaw University of Technology using FG5 No. 230 absolute gravimeter. Elaboration of observation sessions from both gravimeters was performed in the Department of Higher Geodesy following the procedures used in constituting of uniform gravimetric system of geodynamic polygons reference. This constituting of gravimetric system comprised inter alia application of identical models of lithospheric tides (global model by Wenzel, 1997) and ocean tides (Schwiderski, 1980) (reduction of absolute measurements with tidal signals). Observations performed during summer of 2007, autumn of 2007, and spring of 2008 and 2011 indicated existence of small changes of absolute gravity of the order of 1 Gal. Maxima of accelerations appear in the spring period, and minima in the autumn period. This effect is connected with the influence of global hydrological factors the annual amplitude of which is ca 1,5 Gal and achieve extreme values in the spring-autumn interval. Very small value of observed amplitude of gravity changes in the period of extreme variability suggests that the observed gravity changes in LG are caused only by global phenomenon. This proves high degree of "independence" of gravimetric measurement base in LG from the local environmental factors such as ground water level variations, ground humidity, impact of snow cover, etc. At this moment the instrumental environment of absolute measurements obtains particular value, especially in the case of the tiltmeters and relative the gravimeter Lacoste& Romberg (LR-648). The relative gravity measurements as performed simultaneously with absolute gravity measurements enable us to determine the local tidal ephemeredes which makes it possible to replace the global tidal modal with ocean tidal model with the more realistic, locally determined tidal parameters (the local tidal ephemeredes).

Kaczorowski, Marek; Olszak, Tomasz; Walo, Janusz; Barlik, Marcin

2012-12-01

120

The Variscan Belt in Central Europe: Main structures, geodynamic implications, open questions  

NASA Astrophysics Data System (ADS)

The Variscan Belt of Europe originated from the confrontation of northern Europe and Gondwana, with intervening pre-Variscan blocks (Cadomian and older: Armorica, Tepla-Barrandean, Moravo-Silesian). Though a strike-slip component cannot be excluded, geological evidence suggests a subduction/collision process. Newly discovered features include basaltic rocks with MORB affinities, high-pressure metamorphic rocks, trench deposits, and large-scale allochthonism, which also affects the pre-Variscan basement, and has often led to an inversion of the metamorphic isogrades. Large-scale thrusting is evident at all crustal levels, and is also observable by geophysical methods. The structure of the Variscan crust is best described as horizontal-tectonic layering. Late Ordovician through Carboniferous convergence closed one Rhenohercynian and one Saxo-thuringian basin to the north, and at least one Mediterranean basin to the south of the pre-Variscan blocks. Subduction occurred from the north as well as from the south down under the dorsal core region. The exact timing and the driving mechanism of this bilateral activity remains a problem. Likewise uncertain are the exact limination of the pre-Variscan blocks, and the existence and width of oceanic areas. In the Saxothuringian Zone and in the south-facing part of the Moldanubian Zone, there is good evidence of early Palaeozoic rifting and of late Ordovician through Carboniferous plate convergence. Palaeomagnetic and palaeoclimatic constraints, however, suggest only a limited extent of oceanic basins in these areas, while they appear to allow a wider ocean at the Rhenohercynian-Saxothuringian boundary, which is relatively unobtrusive from the geological point of view. Research during the past decade has produced a wealth of information on the Variscan Fold belt in Europe. The resulting geodynamic models, however, are extremely diverging. Evidently, it is not the time yet for definitive statements. The present paper intends to review the state of knowledge, to deduce such basic items of a geodynamic model as appear reasonably well documented, and to point out the most urgent open questions. Stress will be laid on Central Europe, which offers a complete cross section through the northern flank of the Variscan Belt, and where we have carried out most of our studies during the last years.

Behr, H.-J.; Engel, W.; Franke, W.; Giese, P.; Weber, K.

1984-10-01

121

From StGermain to Underworld: Enabling Community-based code Development in Geodynamics  

NASA Astrophysics Data System (ADS)

Each discipline of geophysics has traditionally focused on limited sets of closely related phenomena using methodologies and data sets optimized for its specific area of interest. Why is that? Single discipline, single scale, foundation physics problems are relatively easy to code in Fortran, and hence they eventually become optimized for best performance whilst simultaneously becoming difficult to adapt to new interests. Yet geodynamicists want to break these ``out-of-scope'' barriers, and incorporate signals of interests beyond their immediate phenomena of interest. In turn this often entails a multi physics, multi scale and multi discipline development model. Multi physics is potentially easy to code, but application limited by the choice of numerical technique of the code. Multi scale is a numerical and discretisation issue that is closely related to the fundamental data structures of the code. This is difficult to change, and the ideal is hybrids of optimized solutions at desired scales. Multi discipline is much more focused on people and how they form problem constraints, the language / ontology they use, and their expectation in usability. In summary: facilitating a multi scale, multi physics , multi disciplinary development environment is difficult, complicated and generally not of core interest to a geodynamicist. However, today, with more powerful CPU architectures, we can move away from Fortran style coding with little wall-time cost. We have more powerful numerical techniques and models for constitutive laws, where disciplines beyond those specific to geodynamics such as numerical science, material science and computational science have progressed. Furthermore, more well proven and established libraries are available, when chosen and applied appropriately, lead to less work and for better results. How can we capitalize on this? We propose a multi-level community development model that allows computational scientists, numerical scientists, material scientists and phenomena modelers to develop their core interests and leverage off each other's work. In turn, we aim to produce adaptable code bases where core technologies can be interchanged. That is to provide modelers with the tools to venture beyond their present scope, whilst proving infrastructure builders real problems to test against. Furthermore we aim to match the language to the expectations of the people at those levels. We facilitate this environment through a fundamental framework named StGermain. We demonstrate its application to a spectrum of (long time scale) geodynamics problems encapsulated in the Underworld package. In particular we show three phenomena models from Underworld: mantle convection, roll back, and basin extension modeling. These are all at different scales, incorporate different physics, different work flows and maintained by different people. The methodology and technology is being applied to solve multi scale, multi physics modeling of materials manufacturing problems.

Quenette, S. M.; Moresi, L.; Sunter, P. D.; Hodkinson, L.; Lo, A.; Hassan, R.; Appelbe, B.; Turnbull, R.

2005-12-01

122

THERIAK_D: An add-on to implement equilibrium computations in geodynamic models  

NASA Astrophysics Data System (ADS)

This study presents the theory, applicability, and merits of the new THERIAK_D add-on for the open source Theriak/Domino software package. The add-on works as an interface between Theriak and user-generated scripts, providing the opportunity to process phase equilibrium computation parameters in a programming environment (e.g., C or MATLAB). THERIAK_D supports a wide range of features such as calculating the solid rock density or testing the stability of mineral phases along any pressure-temperature (P-T) path and P-T grid. To demonstrate applicability, an example is given in which the solid rock density of a 2-D-temperature-pressure field is calculated, portraying a simplified subduction zone. Consequently, the add-on effectively combines thermodynamics and geodynamic modeling. The carefully documented examples could be easily adapted for a broad range of applications. THERIAK_D is free, and the program, user manual, and source codes may be downloaded from http://www.min.uni-kiel.de/ed/theriakd/.

Duesterhoeft, Erik; Capitani, Christian

2013-11-01

123

An adaptive staggered grid finite difference method for modeling geodynamic Stokes flows with strongly variable viscosity  

NASA Astrophysics Data System (ADS)

Here we describe a new staggered grid formulation for discretizing incompressible Stokes flow which has been specifically designed for use on adaptive quadtree-type meshes. The key to our new adaptive staggered grid (ASG) stencil is in the form of the stress-conservative finite difference constraints which are enforced at the "hanging" velocity nodes between resolution transitions within the mesh. The new ASG discretization maintains a compact stencil, thus preserving the sparsity within the matrix which both minimizes the computational cost and enables the discrete system to be efficiently solved via sparse direct factorizations or iterative methods. We demonstrate numerically that the ASG stencil (1) is stable and does not produce spurious pressure oscillations across regions of grid refinement, which intersect discontinuous viscosity structures, and (2) possesses the same order of accuracy as the classical nonadaptive staggered grid discretization. Several pragmatic error indicators that are used to drive adaptivity are introduced in order to demonstrate the superior performance of the ASG stencil over traditional nonadaptive grid approaches. Furthermore, to demonstrate the potential of this new methodology, we present geodynamic examples of both lithospheric and planetary scales models.

Gerya, T. V.; May, D. A.; Duretz, T.

2013-04-01

124

Numerical approach to inverse problems in geodynamics: Application to lithosphere subduction  

NASA Astrophysics Data System (ADS)

To restore mantle thermal structures and convective flow in the geological past, mathematical and computational techniques for inverse retrospective problems should be employed to constrain the initial (in the past) conditions for the temperature and velocity in the mantle from present seismic, heat flow, geodetic and some other observations. The basic principle of inverse retrospective problems in geodynamics is to consider the initial temperature as a control variable and to optimise the model temperature and flow in order to minimize the discrepancy between the present observations and the solution to a model of the inverse thermo-convective mantle flow. Our model is based on the set of the Stokes, heat flux and continuity equations at the extended Boussinesq approximation and at the appropriate initial and boundary conditions and incorporates mantle phase transformations. We use a quasi-reversibility technique (Ismail-Zadeh et al., GJI, 2007) for assimilation of the present data and discuss applicability of this technique to restoration of a descending lithosphere. A sensitivity analysis has been performed to clarify the influence of the model boundary conditions and the model viscosity on model results. We apply the methodology to study the evolution of the Pacific and Philippine plates subducting beneath the Japanese islands and present several scenarios for the evolution of the descending lithosphere.

Ismail-Zadeh, A.; Tsepelev, I.; Honda, S.

2012-04-01

125

Intracontinental Deformation and Surface Uplift - Geodynamic Evolution of the Hangay Dome, Mongolia Central Asia  

NASA Astrophysics Data System (ADS)

The origin of high topography in continental interiors is a first-order question in continental dynamics. Standing significantly above the median continental freeboard, higher-elevation surfaces having relatively low relief and wavelengths of hundreds to thousands of kilometers are common on the continents and are excellent sites to investigate the interplay of solid-earth and surface processes. Continental plateaus occur in a number of tectonic settings and explanations for their origin such as asthenospheric upwelling, magmatic underplating, and delamination, are as diverse as their tectonic settings. The Hangay in Mongolia occupy a broad domal upland (~200,000 km2) embedded in the greater Mongolian Plateau (~425,000 km2) of Central Asia. The high interior of the dome sits at elevations ~1.5 km above the regional trend, locally reaches elevations over 4000 m, contains a high-elevation low-relief surface cut into crystalline basement and a 30 my record of basalt magmatism including mantle and crustal xenoliths. Global seismic tomography indicates a poorly resolved low-velocity zone in the upper mantle. Uplift, faulting, and volcanism are active. We present results from initial fieldwork in the Hangay in geomorphology, geochronology, paleoaltimetry, biogeography, petrology, geochemistry, and seismology designed to document the geodynamics, timing, rate, and pattern of surface uplift in the Hangay located deep in the Asian continental interior.

Meltzer, A.; Ancuta, L. D.; Carlson, R. W.; Caves, J. K.; Chamberlain, P.; Gosse, J. C.; Idleman, B. D.; Ionov, D. A.; Mcdannell, K. T.; Mendelson, T.; Mix, H. T.; Munkhuu, U.; Proussevitch, A. A.; Russo, R. M.; Sabaj-Perez, M.; Sahagian, D. L.; Sjostrom, D. J.; Stachnik, J. C.; Tsagaan, B.; Wegmann, K. W.; Winnick, M. J.; Zeitler, P. K.

2012-12-01

126

Application of the pseudorelief method for the territory of the Bishkek geodynamic polygon  

NASA Astrophysics Data System (ADS)

Based on 143 magnetotelluric soundings, the Berdichevskii impedance, the WieseParkinson matrix, and the phase tensor component are calculated for the Bishkek geodynamic polygon 50 150 km in size. The pseudoreliefs of the apparent resistance Ro brd , phase Fi brd , Wiese-Parkinson matrix norm, and apparent phase Fi k calculated from the phase tensor are constructed. An area of the crustal conductor with elevated conductivity located below the northern part of the Chui depression is distinguished during analysis of pseudoreliefs. Its characteristics will be used for solution of the 3D direct task and creation of the starting model of 2D inversion. The reliability of anomalous objects and estimation of their size during the use of real data is caused by the fact that the anomalies are displayed by different parts of the observation system for the various parameters of the MT-field: the phases vary directly over the anomalous object, and magnetovariational parameters form the rim around it. This allows us more completely and effectively to use the network of real data.

Batalev, V. Yu.

2013-02-01

127

Magnetostratigraphic dating of the uplifted atoll of Mar: Geodynamics of the Loyalty Ridge, SW Pacific  

NASA Astrophysics Data System (ADS)

The Loyalty Islands (SW Pacific) are uplifted as they are progressively affected by the lithospheric flexure of the Australian plate, before its subduction under the New Hebrides Arc. These geodynamic changes are constrained by magnetostratigraphically dating two sections from Mar Island, where mineral extractions coupled with rock-magnetic experiments suggest that the magnetic remanence is mostly carried by a mixture of single-domain to multidomain magnetite/maghemite. With the help of faunal determinations and radiometric dating, the sequences of polarity reversals, correlated to the geomagnetic polarity timescale, range from the top of Chron C4n (late Miocene) to the top of the Gauss Chron (late Pliocene). This new chronostratigraphy refines the timing of two distinctive carbonate units (rhodolith platform/coral reefs) separated by a hardground whose transition is known to coincide approximately with a regional event around the Miocene/Pliocene boundary. The magnetostratigraphic dating indicates that the hardground represents about a 1.9 m.y. hiatus and suggests variable sedimentation rates ranging from 4.7 to 65.4 m/m.y. during the atoll construction. The lithospheric bulge seems to have influenced the evolution of Mar Island some 3.1 m.y. ago, leading to a diachronous emersion of the northeast and southwest rim of the atoll with a mean uplift rate of the order of 4 cm/kyr.

Guyomard, T. S.; ASsaoui, D. M.; McNeill, D. F.

1996-01-01

128

The topical problems of identifying the results of the observations in recent geodynamics  

NASA Astrophysics Data System (ADS)

The paper addresses the problems of identifying the results of deformational observations on the Earth, which arise from the new measurement technologies and lead to the ambiguity relationships such as the "spatial size of the anomalydensity of the observation sites" and the "duration of the anomaliesdegree of temporal detail of the measurements." It is found that many "paradoxical" conclusions concerning the rates and scales of the recent geodynamical processes are removed if the parameters of the measurement system match the properties of the studied object and if the relative character of the observational means is taken into account. It is shown that the time variation in the uniaxial deviatoric stress leads to the variation in the volumetric strain and, consequently, to the variation in gravity. The ambiguity in determining the ground displacement vectors by SAR interferometry is demonstrated. It is concluded that the autonomous use of the interferometry data leads to the significant distortions of the results, and these data should be necessarily used in combination with the ground-based geodetic observations.

Kuzmin, Yu. O.

2014-09-01

129

Geodynamics of ophiolites and formation of hydrocarbon fields on the shelf of eastern Sakhalin  

NASA Astrophysics Data System (ADS)

A model is proposed showing the formation of hydrocarbon fields on the shelf of eastern Sakhalin as being caused by sustained (from the Late Cretaceous to the present) extension in the adjacent deepwater Deryugin Basin with exposure of the upper mantle rocks at the bottom of the sedimentary basin. The thrust faults and detachments formed through this process facilitated the penetration of seawater into ultramafic rocks, thus providing large-scale serpentinization accompanied by generation of hydrocarbons. Extension in the Deryugin Basin was compensated by horizontal shortening at its margins, and as a result, by the formation of ophiolitic allochthons as constituents of the accretionary prism of eastern Sakhalin. Hydrocarbons were injected and pumped in the root zones of the allochthons, giving rise to their westward migration and the formation of petroleum pools in fault-line and underthrust traps on the shelf of Sakhalin Island. The Deryugin Basin is a petroleum-collecting area for oil and gas fields localized in the upper part of its western margin. More broadly, the work considers interrelations between hydrocarbon generation and the geodynamics of tectonic couples of ophiolitic allochthons and adjacent deepwater basins of marginal seas, in particular, in the western Pacific.

Raznitsin, Yu. N.

2012-01-01

130

Geodynamic movements and deformations of the Sudetic structural unit of the Bohemian Massif  

NASA Astrophysics Data System (ADS)

The African plate pushes to European orogenic Alpine structures that transfer the compression further to Variscan structural units, including the Bohemian Massif. Central parts of the Bohemian Massif are relatively deep-seated and, therefore, some of marginal parts of the Massif and its border geological structures should be affected intensively and moved distinctly with respect to the central parts. The geodynamical GPS network EAST SUDETEN is located just over the area mentioned above, i.e. it covers both kinetically quasi-effected and quasi-non-effected structural blocks. GPS data observed already for six annual campaigns (1997-2002) were processed and movement vectors of individual network sites were assessed. Applied data processing did not allow errors in the horizontal direction 2 mm and in the vertical direction 5-6 mm to be exceeded. Since time series of coordinate changes for several network sites gave rather pronounce movement trends, preliminary deformations among individual structural blocks were evaluated and compared to other geological, geophysical and geodetic materials. The investigation has been supported by the Grant Agency of the Czech Republic, projects 205/97/0679 and 205/01/0480, and by the research programme of the Ministry of Education, Youth and Sport of the Czech Republic, project LN00A005 "Dynamics of the Earth".

Schenk, V.; Jechumtlov, Z.; Schenkov, Z.; Kottnauer, P.

2003-04-01

131

Performance of Basic Geodynamic Solvers on BG/p and on Modern Mid-sized CPU Clusters  

NASA Astrophysics Data System (ADS)

Nowadays, most researchers have access to computer clusters. For the community developing numerical applications in geodynamics, this constitutes a very important potential: besides that current applications can be speeded up, much bigger problems can be solved. This is particularly relevant in 3D applications. However, current practical experiments in geodynamic high-performance applications normally end with the successful demonstration of the potential by exploring the performance of the simplest example (typically the Poisson solver); more advanced practical examples are rare. For this reason, we optimize algorithms for 3D scalar problems and 3D mechanics and design concise, educational Fortran 90 templates that allow other researchers to easily plug in their own geodynamic computations: in these templates, the geodynamic computations are entirely separated from the technical programming needed for the parallelized running on a computer cluster; additionally, we develop our code with minimal syntactical differences from the MATLAB language, such that prototypes of the desired geodynamic computations can be programmed in MATLAB and then copied into the template with only minimal syntactical changes. High-performance programming requires to a big extent taking into account the specificities of the available hardware. The hardware of the world's largest CPU clusters is very different from the one of a modern mid-sized CPU cluster. In this context, we investigate the performance of basic memory-bounded geodynamic solvers on the large-sized BlueGene/P cluster, having 13 Gb/s peak memory bandwidth, and compare it with the performance of a typical modern mid-sized CPU cluster, having 100 Gb/s peak memory bandwidth. A memory-bounded solver's performance depends only on the amount of data required for its computations and on the speed this data can be read from memory (or from the CPUs' cache). In consequence, we speed up the solvers by optimizing memory access and CPU cache use: we avoid random memory access and multiple read of the same data by rearranging mutually independent computations. More precisely, we group operations that act on the same small parts of data as much as possible together, assuring that these small data parts fit into the CPU cache. In fact, reading from CPU cache requires nearly no time compared to reading from memory. We also optimize the technical programming needed for a parallelized running of the solvers on a computer cluster. The parallelization of a solver requires a spatial decomposition of the computational domain; each processor solves then the problem for one sub-domain, synchronizing at every iteration the sub-domain's boundaries with the ones of its neighbours. We optimize boundary synchronization between processors by developing optimal methods based on the full range of advanced MPI-features (MPI is the standard interface for developing parallel applications on CPU clusters with distributed memory). A geodynamic solver solves at every iteration a system of equations. This can be solved implicitly - by using a direct solver - or explicitly - by updating all variables in the system of equations based on a update rule derived from the system. We compare the performance of implicit and explicit solving for our applications.

Omlin, S.; Keller, V.; Podladchikov, Y.

2012-04-01

132

A scalable, parallel matrix-free Stokes solver for geodynamic applications  

NASA Astrophysics Data System (ADS)

Here I describe a numerical method suitable for studying non-linear, large deformation processes in crustal and lithopspheric dynamics. The method utilizes a hybrid spatial discretisation which consists of mixed finite elements for the Stokes flow problem, coupled to a Lagrangian marker based discretisation to represent the material properties (viscosity and density). This approach is akin to the classical Marker-And-Cell (MAC) scheme of Harlow and the subsequently developed Material Point Method (MPM) of Sulsky and co-workers. The geometric flexibility and ease of modelling large deformation processes afforded by such mesh-particle methods has been exploited by the lithospheric dynamics community over the last 20 years. The strength of the Stokes preconditioner fundamentally controls the scientific throughput achievable and represents the largest bottleneck in the development of our understanding of geodynamic processes. The possibility to develop a 'cheap' and efficient preconditioning methodology which is suitable for the mixed Q2-P1 element is explored here. I describe a flexible strategy, which aims to address the Stokes preconditioning issue using an upper block triangular preconditioner, together with a geometric multi-grid preconditioner for the viscous block. The key to the approach is to utilize algorithms and data-structures that exploit current multi-core hardware and avoid the need for excessive global reductions. In order to develop a scalable method, special consideration is given to; the definition of the coarse grid operator, the smoother and the coarse grid solver. The performance characteristics of this hybrid matrix-free / partially assembled multi-level preconditioning strategy is examined. The robustness of the preconditioner with respect to the viscosity contrast and the topology of the viscosity field, together with the parallel scalability is demonstrated.

May, D.

2013-12-01

133

Geodynamics of the southeastern Tibetan Plateau from seismic anisotropy and geodesy  

NASA Astrophysics Data System (ADS)

Ongoing plate convergence between India and Eurasia provides a natural laboratory for studying the dynamics of continental collision, a first-order process in the evolution of continents, regional climate, and natural hazards. In southeastern Tibet, the fast directions of seismic anisotropy determined using shear-wave splitting analysis correlate with the surficial geology including major sutures and shear zones and with the surface strain derived from the global positioning system velocity field. These observations are consistent with a clockwise rotation of material around the eastern Himalayan syntaxis and suggest coherent distributed lithospheric deformation beneath much of southeastern Tibet. At the southeastern edge of the Tibetan Plateau we observe a sharp transition in mantle anisotropy with a change in fast directions to a consistent E-W direction and a clockwise rotation of the surface velocity, surface strain field, and fault network toward Burma. Around the eastern Himalayan syntaxis, the coincidence between structural crustal features, surface strain, and mantle anisotropy suggests that the deformation in the lithosphere is mechanically coupled across the crust-mantle interface and that the lower crust is sufficiently strong to transmit stress. At the southeastern margin of the plateau in Yunnan province, a change in orientation between mantle anisotropy and surface strain suggests a change in the relationship between crustal and mantle deformation. Lateral variations in boundary conditions and rheological properties of the lithosphere play an important role in the geodynamic evolution of the Himalayan orogen and Tibetan Plateau and require the development of three-dimensional models that incorporate lateral heterogeneity.

Sol, S.; Meltzer, A.; Brgmann, R.; van der Hilst, R. D.; King, R.; Chen, Z.; Koons, P. O.; Lev, E.; Liu, Y. P.; Zeitler, P. K.; Zhang, X.; Zhang, J.; Zurek, B.

2007-06-01

134

Moving-mass gravimeter calibration in the Mtyshegy Gravity and Geodynamical Observatory (Budapest)  

NASA Astrophysics Data System (ADS)

A gravimeter calibration facility exists in the Mtyshegy Gravity and Geodynamical Observatory of Geological and Geophysical Institute in Hungary. During the calibration a cylindrical ring of 3200 kg mass is vertically moving around the equipment, generating gravity variations. The effect of the moving mass can be precisely calculated from the known mass and geometrical parameters. The main target of the calibration device was to reach a relative accuracy of 0.1-0.2% for the calibration of Earth-tide registering gravimeters. The maximum theoretical gravity variation produced by the vertical movement of the mass is ab. 110 microGal, so it provides excellent possibility for the fine calibration of gravimeters in the tidal range. The instrument was out of order for many years and in 2012 and 2013 it was renovated and automatized. The calibration process is aided by intelligent controller electronics. A new PLC-based system has been developed to allow easy control of the movement of the calibrating mass and to measure the mass position. It enables also programmed steps of movements (waiting positions and waiting times) for refined gravity changes. All parameters (position of the mass, CPI data, X/Y leveling positions) are recorded with 1/sec. sampling rate. The system can be controlled remotely through the internet. As it is well known that variations of the magnetic field can influence the measurements of metal-spring gravimeters, authors carried out magnetic experiments on the pillar of the calibration device as well, in order to analyze the magnetic effect of the moving stainless steel-mass. During the movements of the mass, the observed magnetic field has been changed significantly. According to the magnetic measurements, a correction for the magnetic effect was applied on the measured gravimetric data series. In this presentation authors show the facility in details and the numerical results of tests carried out by applying LCR G gravimeters.

Kis, Mrta; Koppn, Andras; Kovcs, Pter; Mernyi, Lszl

2014-05-01

135

Continental Flood Basalts of Bennett Island, East Siberian Sea: High Arctic Geodynamics  

NASA Astrophysics Data System (ADS)

Volcanism provides a means of tracing mantle melting events and crustal evolution. The High Arctic includes a rich portfolio of volcanic rocks outcropping in the Circum-Arctic borderlands and imaged geophysically beneath the Alpha-Mendeleev Ridge that have been lumped together as a High-Arctic Large Igneous Province (HALIP). However, the ages (c. 440-60 Ma) and compositions (tholeiitic-alkaline-calc-alkaline) reported varies considerably and geological correlations remain elusive. One of the possible correlative events is the formation of continental flood basalts and sills in the Canadian Arctic Islands, Svalbard, Franz Josef Land and Bennett Island. These flood basalts have previously been linked to mantle plume melting and may represent a short-lived LIP event at c. 124-122 Ma. We present new data for a 350 m thick continental flood basalt succession at Bennett Island examined during fieldwork in Septemer 2013 on a joint Russian (VSEGEI) - Swedish (SWEDARCTIC) expedition to the De Long Archipelago. This volcanic succession is composed of 20 near-horisontal, undeformed flow units overlying a thin sedimentary succession of Cretaceous age (?) including coal seams and possibly volcaniclastic material that, in turn, unconformably overlies a more steeply dipping succession of Cambrian and Ordovician sediments. The flows are thinnest (c. 2-10 m) and aphyric to very-sparsely olivine-phyric in the lower portion. In contrast, the flows in the upper portion are thicker (>20 m) and aphyric to sparsely plagioclase-phyric. We will discuss new petrographic and compositional data for the Bennett Island flood basalts, possibly including new U-Pb age data. The aim is to evaluate their petrogenesis, to discuss their possible correlation to the flood basalt and sill successions of the Canadian Arctic Islands, Svalbard and Franz Josef Land and evaluate the geodynamic evolution of the High Arctic.

Tegner, Christian; Pease, Victoria

2014-05-01

136

Shear wave splitting intensity tomography: theory, application, and coupling with geodynamical models  

NASA Astrophysics Data System (ADS)

The interpretation of shear wave splitting observations in complex regions where the geometry of anisotropy is highly heterogeneous is extremely difficult. This is particularly true for subduction zone regions, where the processes that control the three-dimensional distribution of anisotropy are not well understood. The inversion of splitting measurements for anisotropic stucture is not often attempted due to the limitations imposed by sparse data, but carefully constructed splitting data sets from dense broadband arrays can potentially illuminate regions of the upper mantle and facilitate a tomographic approach. We have developed a method for 2.5-D splitting intensity tomography that incorporates constraints from numerical models of geodynamical processes. We apply this method to study upper mantle anisotropy beneath southwestern Japan, using a previously published set of local and teleseismic shear wave splitting measurements. We use the splitting intensity metric introduced by Chevrot (2000) and calculate finite-frequency sensitivity kernels for the orientation and strength of anisotropy using the Born approximation. We calculate sensitivity kernels in a heterogeneous starting model that is taken from a numerical modeling study of anisotropy development in the mantle wedge due to a subducting lithospheric plate, and use these kernels in the inversion. The calculation of such kernels in realistic 2D or 3D heterogeneity is essential for true multi-scale, finite frequency splitting intensity tomography. Finally, we use the results of the inversion to refine our flow models with control parameters that best fit the splitting observations, and further improve the models by using perturbed flow models as new starting models for the inversion.

Long, M. D.; de Hoop, M. V.; van der Hilst, R. D.; Hager, B. H.

2006-12-01

137

Natural laboratory NW Bohemia: Comprehensive fluid studies between 1992 and 2005 used to trace geodynamic processes  

NASA Astrophysics Data System (ADS)

Comprehensive studies of CO2-rich fluids close to the swarm earthquake region Nov Kostel at the Czech-German border have been started 15 years ago and have in particular included two extended chemical and isotope monitoring studies lasting for several years each. The regional surface distribution patterns of the fluid signatures including the identification of the origin of fluid components are the focus of the detailed studies. Three degassing centers (Cheb basin, Marinsk Lzn?, and Karlovy Vary) with high CO2 flux and the same level of ?13C values, but different levels of 3He/4He ratios, have been identified. The studies have located the CO2 source and have investigated seismically induced changes in fluid characteristics on the basis of unique weekly sampling campaigns at selected locations. A seismically triggered release of crustal helium was confirmed by both monitoring campaigns. Finally, indications for a presently active magmatic process beneath the Cheb basin have been found. In contrast to volcanically active regions, magma accumulation in the study area takes place at the crust-mantle boundary and is not yet accompanied by heat transfer to the surface. Likewise, reactive magma-derived components are absent in the degassing fluids. The area of investigation has the potential to be a natural laboratory for fundamental studies of active geodynamic processes. The results of our fluid monitoring, including the stunning observation of mantle-derived free fluids marked by 3He/4He ratios within the subcontinental mantle range, are supported by geophysical findings from seismic studies and geologic indications.

BrUer, Karin; KMpf, Horst; Niedermann, Samuel; Strauch, Gerhard; Tesa?, Ji?I.

2008-04-01

138

A tectonic pressure pulse and increased geodynamic activity recorded from the long-term monitoring of faults in Europe  

NASA Astrophysics Data System (ADS)

This paper presents the results of a long-term monitoring study undertaken during the period 2002-2007. The study recorded the displacement of various widely-distributed tectonic structures along the generally aseismic Bohemian Massif (Czech Republic) and specifically along the Sudeten Marginal Fault Zone. The derived results were compared with data recorded over the same time period in the Upper Rhine Graben (Germany), Central Apennines (Italy), and the Gulf of Corinth (Greece). It is clear that a tectonic pressure pulse initiated a period of increased geodynamic activity across central and southern Europe during the course of our monitoring. Within the Bohemian Massif, the pressure pulse was first recorded in mid 2003 and the ensuing period of increased geodynamic activity lasted for nearly three years. This period is associated with compression along the Sudeten Marginal Fault Zone. The southern flank was repeatedly downthrust beneath the northern flank, which caused the latter to continually uplift and subside. The period of increased geodynamic activity was terminated by two strong local earthquakes. Consequently, it is considered that this period induced earthquake activity within the Bohemian Massif. When taken together, the presented data provides robust evidence for the reconfiguration of stress and strain relationships within central and southern Europe. Whilst it is possible that tectonic activity in the Alps produced a north-verging pressure pulse that affected central Europe (e.g. in the Bohemian Massif and Upper Rhine Graben), it cannot account for the pressure pulse recognised to the south (e.g. in the Central Apennines and the Gulf of Corinth). Due to the predominance of vertical movements, it is suggested that this reconfiguration results from deep seated processes within the lithosphere-asthenosphere. However, the influence of horizontal movements transmitted from the compressional zone between Africa and Europe cannot be discounted.

Stemberk, Josef; Ko?k, Blahoslav; Caco?, Stefan

2010-05-01

139

An analytical-numerical method for satellite movement determination of an intermediate orbit base for geodetical and geodynamical investigations  

NASA Astrophysics Data System (ADS)

An analytical theory for determining accurately the coordinates of a satellite at any time during its movement around the earth was developed using a power series of regularized time and a spheroidal coordinate system. The theory is used to design a computer program for determining orbits of geodynamical satellites. The results of determining the orbit of Lageos with this program are compared with those obtained by means of a numerical integration, showing a coincidence greater than 1 cm for a six-day period and greater than 3 mm for a two-week period.

Georgiev, Nikola; Chapanov, Iavor

140

Analysis of The Network of Permanent GPS Stations In Central Europe and Its Significance For Geodynamical Studies In The Region  

NASA Astrophysics Data System (ADS)

The network of 15-20 permanent GPS stations situated in central and southeast Eu- rope is routinely analyzed at the Slovak University of Technology since 2000.0. The products of the regular network solutions are the station coordinates with 24-hour and 3-hour resolution, station troposphere zenith delays and regional ionosphere models. The network analysis is performed with consistent strategy using the Bernese GPS V4.2 software. From the two-year interval (2000.0 - 2002.0) we obtained the homo- geneous time series applicable for geodynamical and geophysical research. The coor- dinate time series with 24-hour resolution are used for checking the GPS positioning continuity and for determination of parameters of linear trend and seasonal variations of station position. In the next step the residuals are submitted to spectral analysis and evaluation of parameters of autoregressive moving average representation of the series. The coordinate time series with 3-hour resolution are analyzed with the aim to estimate unmodeled tidal variations of station positions. In the paper first results from permanent station coordinate time series modeling will be presented with respect to their consequences for geodynamic investigations in the Central Europe region.

Hefty, J.; Kartikova, H.; Igondova, M.

141

Long-term monitoring of geodynamic surface deformation using SAR interferometry  

NASA Astrophysics Data System (ADS)

Synthetic Aperture Radar Interferometry (InSAR) is a powerful tool to measure surface deformation and is well suited for surveying active volcanoes using historical and existing satellites. However, the value and applicability of InSAR for geodynamic monitoring problems is limited by the influence of temporal decorrelation and electromagnetic path delay variations in the atmosphere, both of which reduce the sensitivity and accuracy of the technique. The aim of this PhD thesis research is: how to optimize the quantity and quality of deformation signals extracted from InSAR stacks that contain only a low number of images in order to facilitate volcano monitoring and the study of their geophysical signatures. In particular, the focus is on methods of mitigating atmospheric artifacts in interferograms by combining time-series InSAR techniques and external atmospheric delay maps derived by Numerical Weather Prediction (NWP) models. In the first chapter of the thesis, the potential of the NWP Weather Research & Forecasting (WRF) model for InSAR data correction has been studied extensively. Forecasted atmospheric delays derived from operational High Resolution Rapid Refresh for the Alaska region (HRRR-AK) products have been compared to radiosonding measurements in the first chapter. The result suggests that the HRRR-AK operational products are a good data source for correcting atmospheric delays in spaceborne geodetic radar observations, if the geophysical signal to be observed is larger than 20 mm. In the second chapter, an advanced method for integrating NWP products into the time series InSAR workflow is developed. The efficiency of the algorithm is tested via simulated data experiments, which demonstrate the method outperforms other more conventional methods. In Chapter 3, a geophysical case study is performed by applying the developed algorithm to the active volcanoes of Unimak Island Alaska (Westdahl, Fisher and Shishaldin) for long term volcano deformation monitoring. The volcano source location at Westdahl is determined to be approx. 7 km below sea level and approx. 3.5 km north of the Westdahl peak. This study demonstrates that Fisher caldera has had continuous subsidence over more than 10 years and there is no evident deformation signal around Shishaldin peak.

Gong, Wenyu

142

Cenozoic fluid-magmatic centers, geodynamics and volcanism in Northern Caucasus  

NASA Astrophysics Data System (ADS)

The central segment of Alpine mobile folded system of the Greater Caucasus is characterized by complex crossing of the active faults of different structural directions. On the crossings of disjunctive knots of Caucasian WNW and Trans-Caucasian NS faults the two Cenozoic fluid-magmatic centers are located featuring dormant yet not extinct volcanoes of Elbrus and Kazbek. Mentioned centers are known as the Elbrus volcano-plutonic center, the Kazbek volcano-plutonic center, they are outlined according to the results of geological, geomorphological and geophysical studies. Geodynamic position of the Elbrus volcano within the Transcaucasia uplift is considered with respect to evolution of volcanic processes and possible resumption of volcanic activity in this region. In order to carry out the multidisciplinary study of geological and geophysical processes in the vicinity of the volcanic dome it is essential to obtain reliable information about basic parameters of local magmatic structures. The satellite imagery processing carried out according to original technology based on determination of surface lineaments and consequent transition to analysis of the field of tectonic disintegration of the lithosphere may allow one to obtain independent knowledge about deep subsurface structures for the given territory. As a result, the 3D model of tectonic disintegration field under the Elbrus volcano has been constructed. The two anomalous domains have been outlined and they were associated with local deep magmatic source and peripheral magmatic chamber of the Elbrus volcano. Comparative analysis of experimental geophysical data obtained by means of microgravity studies over the same territory, magneto-telluric profiling and search for thermal anomalies has shown appropriate correlation in terms of shape, size and position of magmatic structures in the vicinity if the Elbrus volcanic center. Thus, the position and size of the magmatic chamber and the deep magmatic source of the Elbrus volcano have been determined as well as possible pathways of migration of fluids of deep origin. The map of modern fluid permeability of the Earth's crust for the territory of Northern Caucasus has been produced.

Sobissevitch, A. L.; Nechaev, Yu. V.; Masurenkov, Yu. P.; Pouzich, I. N.; Pronin, A. P.; Laverova, N. I.

2009-04-01

143

The Late Cenozoic geodynamic evolution of the central segment of the Andean subduction zone  

NASA Astrophysics Data System (ADS)

The presented model of the Late Cenozoic geodynamic evolution of the central Andes and the complex tectonic, geological, and geophysical model of the Earths crust and upper mantle along the Central Andean Transect, which crosses the Andean subduction zone along 21S, are based on the integration of voluminous and diverse data. The onset of the recent evolution of the central Andes is dated at the late Oligocene (27 Ma ago), when the local fluid-induced rheological attenuation of the continental lithosphere occurred far back of the subduction zone. Tectonic deformation started to develop in thick-skinned style above the attenuated domain in the upper mantle and then in the Earths crust, creating the bivergent system of the present-day Eastern Cordillera. The destruction of the continental lithosphere is correlated with ore mineralization in the Bolivian tin belt, which presumably started at 16 S and spread to the north and to the south. Approximately 19 Ma ago, the gently dipping Subandean Thrust Fault was formed beneath the Eastern Cordillera, along which the South American Platform began to thrust under the Andes with rapid thickening of the crust in the eastern Andean Orogen owing to its doubling. The style of deformation in the upper crust above the Subandean Thrust Fault changed from thick- to thin-skinned, and the deformation front migrated to the east inland, forming the Subandean system of folds and thrust faults verging largely eastward. The thickening of the crust was accompanied by flows at the lower and/or middle crustal levels, delamination, and collapse of fragments of the lower crust and lithospheric mantle beneath the Eastern Cordillera and Altiplano-Puna Plateau. As the thickness of the middle and lower crustal layers reached a critical thickness about 10 Ma ago, the viscoplastic flow in the meridional direction became more intense. Extension of the upper brittle crust was realized mainly in gliding and rotation of blocks along a rhombic fault system. Some blocks sank, creating sedimentary basins. The rate of southward migration estimated from the age of these basins is 26 km/Ma. Tectonic deformation was accompanied by diverse magmatic activity (ignimbrite complexes, basaltic flows, shoshonitic volcanism, etc.) within the tract from the Western Cordillera to the western edge of the Eastern Cordillera 27-5 Ma ago with a peak at 7 Ma; after this, it began to recede westward; by 5 Ma ago, the magmatic activity reached only the western part of the Altiplano-Puna Plateau, and it has been concentrated in the volcanic arc of the Western Cordillera during the last 2 Ma.

Romanyuk, T. V.

2009-07-01

144

Intraplate geodynamics and magmatism in the evolution of the Central Asian Orogenic Belt  

NASA Astrophysics Data System (ADS)

The Central Asian Orogenic Belt (CAOB) was produced as a consequence of the successive closure of the Paleoasian Ocean and the accretion of structures formed within it (island arcs, oceanic islands, and backarc basins) to the Siberian continent. The belt started developing in the latest Late Neoproterozoic, and this process terminated in the latest Permian in response to the collision of the Siberian and North China continents that resulted in closure of the Paleoasian ocean (Metcalfe, 2006; Li et al., 2014; Liu et al., 2009; Xiao et al., 2010; Didenko et al., 2010). Throughout the whole evolutionary history of this Orogenic Belt, a leading role in its evolution was played by convergent processes. Along with these processes, an important contribution to the evolution of the composition and structure of the crust in the belt was made by deep geodynamic processes related to the activity of mantle plumes. Indicator complexes of the activity of mantle plumes are identified, and their major distribution patterns in CAOB structures are determined. A number of epochs and areas of intraplate magmatism are distinguished, including the Neoproterozoic one (Rodinia breakup and the origin of alkaline rock belt in the marginal part of the Siberian craton); Neoproterozoic-Early Cambrian (origin of oceanic islands in the Paleoasian Ocean); Late Cambrian-Early Ordovician (origin of LIP within the region of Early Caledonian structures in CAOB); Middle Paleozoic (origin of LIP in the Altai-Sayan rift system); Late Paleozoic-Early Mesozoic (origin of the Tarim flood-basalt province, Central Asian rift system, and a number of related zonal magmatic areas); Late Mesozoic-Cenozoic (origin of continental volcanic areas in Central Asia). Geochemical and isotopic characteristics are determined for magmatic complexes that are indicator complexes for areas of intraplate magmatism of various age, and their major evolutionary trends are discussed. Available data indicate that mantle plumes practically did not cease to affect crustal growth and transformations in CAOB in relation to the migration of the Siberian continent throughout the whole time span when the belt was formed above a cluster of hotspots, which is compared with the African superplume.

Yarmolyuk, V. V.; Kuzmin, M. I.; Ernst, R. E.

2014-10-01

145

3D lithospheric structure beneath the eastern Tien-Shan and its geodynamic implication  

NASA Astrophysics Data System (ADS)

The Tien-Shan mountains straddle the border between Kyrgyztan and northwestern China. The geodynamics of this orogeny is a subject of an ongoing debate (e.g., crustal shortening vs. subduction). Most of the recent investigations focused on the western part of the mountain range (west of 80 deg. E). That leaves the dynamics of the eastern part of the orogeny less clear. We perform tomographic inversion using local and regional seismic data for the eastern part of the Tien-Shan, and provide more observations to this argument. We use seismic data from the Xinjiang Earthquake Administration which has operated a regional seismic network in northwestern China since 1988, with 54 sites in the region between 80 and 93 deg. E. Since that time nearly 35,000 earthquakes with ML larger than 2 have been recorded. P and S waves were picked from records of these earthquakes, making up a database of over 521,000 picks. We use a finite-difference tomographic inversion code that performs both earthquake relocation and wavespeed inversion. We carry out inversions for 3D distribution of P wavespeed and also for Vp/Vs values, using seismic events with 8 or more phases and travel time residuals under 3 seconds. This selection leaves 24308 earthquakes, resulting in 231098 P wave picks and 194251 S wave picks. After 8 iterations the variation of travel time residual become insignificant, suggesting that our inversion has converged. We present results of the final (8th) iteration, in which the RMS travel time residual has been reduced from 1.12 s to 0.51 s (more then 50% reduction). A checkerboard test suggests the resolution of the P wavespeed is better than that of the Vp/Vs structure, which likely reflects the larger number of P wave picks yielding excellent ray coverage. The upper crust is well resolved, while the resolution decreases with depth. We see evidence for layering of the crust in our study area. Vertical changes in the wavespeed reveal at least three layers beneath the eastern Tien-Shan: upper, middle and lower crust. Inspection of the 3D distribution of wavespeed suggests crustal thickening due to lateral compression in our study area: a sudden change of the geometry of wavespeed contours (VP= 7.9-8.1km/sec) beneath the northern edge of the Tien-Shan, implying that the crustal thickness increases abruptly beneath the Tien-Shan.

Li, Z.; Wang, H.; Huang, G.; Levin, V. L.; Roecker, S. W.; Li, Z.

2010-12-01

146

Petrologic-geodynamic models of the geochemical evolution of the segmented Siqueiros transform fault (Invited)  

NASA Astrophysics Data System (ADS)

Recent investigations of the dynamics of fast-slipping oceanic transform faults have illustrated the highly transient nature of these systems. Rather than focusing deformation along single long-lived fault strands, many fast-slipping transform fault systems exhibit complex plate boundaries and tectonic histories. Along the fast-spreading East Pacific Rise (EPR) plate motion reorganizations have resulted in the segmentation of 8 of the 9 major transform fault systems. We focus our investigation on the Siqueiros transform fault, which has been the site of detailed surveying and sampling along its four intra-transform spreading centers (ITSCs) and connecting fault strands. The structural history of the Siqueiros transform fault is complex with several counterclockwise changes in spreading direction of the EPR causing transtension within the fault domain, resulting in the formation of four ITSCs at discrete time intervals. Geochemical analyses of lavas from the western portion of Siqueiros generally fit into a similar compositional space as the northern EPR ridge axis lavas, while lavas collected from the eastern Siqueiros appear more closely linked in composition to rocks from the adjacent EPR south of the transform. However, no systematic along-transform chemical gradient is observed and a few lavas collected along the eastern Siqueiros are more similar in composition to the northern EPR ridge segment. Furthermore, the only E-MORB from the transform domain were recovered from the western ridge-transform intersection. In contrast, some of the most incompatible depleted and primitive basalts erupted along one of the western fault strands. These geochemical observations suggest that the Siqueiros transform preserves small-scale mantle heterogeneities beneath the transform domain. We utilize time-dependent, three-dimensional petrologic-geodynamic models to investigate the chemical evolution of the mantle beneath the Siqueiros transform fault in response to changes in plate divergence. The evolution of the residual mantle and mantle melt compositions are tracked during subsequent 're-melting' events caused by plate motion reorganizations. Of particular interest is whether the geochemical heterogeneities observed in the Siqueiros transform can be explained by its dynamic history, or if the Siqueiros transform lavas sample smaller mantle regions than the adjacent ridge axes, preserving small-scale geochemical heterogeneities in the mantle beneath the fault zone. Furthermore, we explore the geochemical implications of ridge migration (e.g., Carbotte et al., 2004) on transform fault lavas. Initial results suggest that variations in composition observed within Siqueiros likely result from both large-scale mantle processes as well as local mantle heterogeneities and illustrate the complex evolutionary history of segmented transform fault systems.

Gregg, P. M.; Perfit, M. R.; Fornari, D. J.

2013-12-01

147

Geodynamic and Magmatic Evolution of the Eastern Anatolian-Arabian Collision Zone, Turkey  

NASA Astrophysics Data System (ADS)

The Eastern Anatolian-Arabian Collision Zone represents a crucial site within the Tethyan domain where a subduction system involving a volcanic arc (i.e. Cretaceous to Oligocene Pontide volcanic arc in the north) associated with a large subduction-accretion complex (i.e. Cretaceous to Oligocene Eastern Anatolian Accretionary Complex i.e. "EAAC" in the south) turned later into a major continental collision zone that experienced a series of geodynamic events including lithospheric delamination, slab-steepening & breakoff, regional domal uplift, widespread volcanism and tectonic escape via strike slip fault systems. The region includes some of the largest volcanic centers (e.g. Karacada?, A??rkaya caldera, Ararat, Nemrut, Tendrek and Sphan volcanoes) and plateaus (e.g. The Erzurum-Kars Plateau) as well as the largest transform fault zones in the Mediterranean region. A recent geodynamic modeling study (Faccenna et al., 2013) has suggested that both the closure of the Tethys Ocean and the resultant collision were driven by a large scale and northerly directed asthenospheric mantle flow named the "Tethyan convection cell". This convection cell initiated around 25 Ma by combined effects of mantle upwelling of the Afar super plume located in the south, around 3,000 km away from the collision zone and the slab-pull of the Tethyan oceanic lithosphere beneath Anatolia in the north. The aforementioned mantle flow dragged Arabia to the north towards Eastern Anatolia with an average velocity of 2 cm/y for the last 20 My, twice as fast as the convergence of the African continent (i.e. 1 cm/y) with western and Central Turkey. This 1 cm/y difference resulted in the formation of the left lateral Dead Sea Strike Slip Fault between the African and Arabian plates. Not only did this mantle flow result in the formation of a positive dynamic topography in the west of Arabian block, but also created a dynamic tilting toward the Persian Gulf (Faccenna et al., 2013). Another remarkable indication of the advance of the mantle flow below Arabia is the northward propagation of within-plate alkaline basaltic volcanism which initiated ~30 Ma around the Afar region to SE Turkey in a time period of ~20 My. The northernmost portion of this alkaline basaltic province is represented by the Karacada? volcanic complex in SE Turkey which covers a footprint area of 10,000 km2 and consists of lavas ranging in age from ~11 Ma to 100 Ky. The Early Stage volcanism of Karacada? was dominated by magmas derived from a shallower metasomatized lithospheric mantle source, in contrast to the Late Stage volcanism which was sourced by a garnet-bearing, deep asthenospheric mantle with Sr, Nd and Pb isotopic composition transitional between Red Sea MORB and Afar plume (Keskin et al., 2012). After the initial contact of the Arabian and Eurasian continents at ~15 Ma, the subducted Tethyan slab steepened beneath the large EAAC, possibly resulting in widening, invasion and upwelling of the mantle wedge beneath E Anatolian accretionary complex. This possibly caused a sucking effect on the asthenosphere, creating a mantle flow from the Pontides in the north to the south (Keskin, 2003). A hot and buoyant asthenosphere emplaced beneath the thinned lithosphere, which is represented mostly by a mlange material, and resulted in the formation of a regional domal uplift. Dehydration of the sunken slab accompanied with decompression of the upwelling asthenospheric mantle generated magmas with a subduction signature which was imprinted on a relatively enriched source chemistry across E Anatolia in a period from 15 to 10 Ma. The slab broke off beneath the region, creating a slab window at around 10 Ma. This caused the enriched Afar-type asthenospheric mantle to flow to the north through the slab-window. As a result, the subduction-modified (i.e. due to slab dehydration) E Anatolian and the enriched Arabian asthenospheric mantles started to mix into each other. The eruption of the first alkaline lavas in the region at around 10 Ma (e.g. tephrites and alkali

Keskin, Mehmet

2014-05-01

148

Inception of the eastern California shear zone and evolution of the Pacific-North American plate boundary: From kinematics to geodynamics  

Microsoft Academic Search

The San Andreas Fault (SAF) is the transform boundary between the Pacific and the North American plates, yet up to 25% of the relative plate motion is now accommodated by the eastern California shear zone (ECSZ). Here we investigate the inception of the ECSZ and its geodynamic interactions with the SAF using a 3-D viscoelastoplastic finite element model. For a

Mian Liu; Hui Wang; Qingsong Li

2010-01-01

149

The Surface of Venus and Implications for its Geological and Geodynamical Evolution: The View Before Venus Express and Outstanding Questions for the Future  

Microsoft Academic Search

Prior to the Venera 15\\/16 and the Magellan missions to Venus, a wide range of ideas existed concerning the nature of the surface of Venus, the geological processes currently operating there, their link to interior processes, the implied geological and geodynamical history of the planet, and how all this compared with the nature and history of other terrestrial planetary bodies.

J. W. Head; M. A. Ivanov; A. T. Basilevsky

2008-01-01

150

Constraints on Hadean geodynamics from mineral inclusions in N4 Ga zircons Michelle D. Hopkins , T. Mark Harrison, Craig E. Manning  

E-print Network

Constraints on Hadean geodynamics from mineral inclusions in N4 Ga zircons Michelle D. Hopkins , T.W. Carlson Keywords: zircon Hadean inclusion thermobarometry U­Pb Jack Hills The inclusion mineralogy of 1450 that is substantially lower than most estimates of global Hadean heat ow. Of the possible environments capable

Manning, Craig

151

International Tectonic Map of the Circumpolar Arctic and its Significance for Geodynamic Interpretations  

NASA Astrophysics Data System (ADS)

In 2003 geological surveys of circum-arctic states initiated the international project "Atlas of Geological Maps of Circumpolar Arctic at 1:5 000000 scale". The project received active support of the UNESCO Commission for the Geological Map of the World (CGMW) and engaged a number of scientists from national academies of sciences and universities. Magnetic and gravity maps were prepared and printed by the Norwegian Geological Survey, and geological map was produced by the Geological Survey of Canada. Completion of these maps made possible compilation of a new Tectonic Map of the Arctic (TeMAr), and this work is now in progress with Russian Geological Research Institute (VSEGEI) in the lead of joint international activities. The map area (north of 60o N) includes three distinct roughly concentric zones. The outer onshore rim is composed of predominantly mature continental crust whose structure and history are illustrated on the map by the age of consolidation of craton basements and orogenic belts. The zone of offshore shelf basins is unique in dimensions with respect to other continental margins of the world. Its deep structure can in most cases be positively related to thinning and rifting of consolidated crust, sometimes to the extent of disruption of its upper layer, whereas the pre-rift evolution can be inferred from geophysical data and extrapolation of geological evidence from the mainland and island archipelagoes. The central Arctic core is occupied by abyssal deeps and intervening bathymetric highs. The Eurasia basin is commonly recognized as a typical oceanic opening separating the Barents-Kara and Lomonosov Ridge passive margins, but geodynamic evolution of Amerasia basin are subject to much controversy, despite significant intensification of earth science researchin the recent years. A growing support to the concept of predominance in the Amerasia basin of continental crust, particularly in the area concealed under High Arctic Large Igneous Province, is based on two lines of evidence: (1) seismic studies and gravity modeling of deep structure of the Earth's crust suggesting a continuity of its main layers from Central Arctic bathymetric highs to the adjoining shelves, and (2) geochrolology and isotope geochemistry of bottom rocks in the central Arctic Ocean indicating the likely occurrence here of Paleozoic supracrustal bedrock possibly resting on a Precambrian basement. In the process of compilation activities all possible effort will be made to reflect in the new international tectonic map our current understanding of present-day distribution of crust types in the Arctic. It will be illustrated by smaller-scale insets depicting, along with the crust types, additional information used for their recognition (e.g. depth to Moho, total sediment thickness, geotransects, etc. This will help to integrate geological history of Central Arctic Ocean with its continental rim and provide a sound basis for testing various paleogeodynamic models.

Petrov, O. V.; Morozov, A.; Shokalsky, S.; Leonov, Y.; Grikurov, G.; Poselov, V.; Pospelov, I.; Kashubin, S.

2011-12-01

152

Geochemistry and petrogenesis of mafic magmatic rocks of the Jharol Belt, India: geodynamic implication  

NASA Astrophysics Data System (ADS)

The belt consisting of deep-water meta-sediments of the Aravalli Supergroup hosts numerous mafic and ultramafic rocks occurring at two different structural levels. These are the basal Bagdunda volcanics and the Gopir magmatic rocks represented by Gopir dikes and flows associated with the ultramafic rocks along the Kaliguman lineament. The Bagdunda and Gopir mafic volcanic rocks are sub-alkaline, varying in composition from high Mg-tholeiite to basaltic komatiite. They are predominantly LREE depleted, but some flat REE patterns are also observed. Bulk geochemical data, especially the incompatible trace elements discount the possibility of crustal contamination. Gopir dikes are highly enriched in terms of their REE [(Ce/Sm) N and (Ce/Yb) N] and other incompatible trace elements and closely resemble the basal Aravalli volcanics. Their ratio (rock)/ratio (PM) and normalized multi-element abundance patterns depict their overall enriched nature compared to N-MORB and primitive mantle. The Gopir and Bagdunda volcanics reflect trace element characteristics transitional between E-MORB and OIB. Gopir dikes show remarkable similarity with continental tholeiite and Continental Flood Basalts (CFBs) with negative Nb, P and Ti anomalies and low Nb/Ce ratio unlike the volcanics of both the suites. Petrogenetic modeling based on the compositionally corrected [Mg] and [Fe] abundances for Gopir dikes, Gopir and Bagdunda volcanics indicates (a) their derivation from non-pyrolitic sources (b) their derivation from sources that were variably enriched in [Fe/Mg] ratios with large variation in their [Fe] contents and (c) olivine was a major phase to fractionate, followed by a lesser amount of clinopyroxene in the case of Gopir volcanics, whereas in Bagdunda volcanics a combination of olivine and clinopyroxene fractionation is suggested. Based on the geochemical data, supported by field evidence, we propose a geodynamic model for the development of the Jharol Belt in which we suggest that the basement rock, i.e. the Banded Gneissic Complex (BGC) started rifting probably under influence of a mantle plume during the late Archaean-early Proterozoic period. During the opening of the basin, magma derived from asthenospheric mantle reached the surface contemporaneously with sedimentation. The first phase of volcanism is represented by Bagdunda volcanics. With continuous rifting, the crust became highly attenuated and facilitated asthenospheric upwelling, causing high degrees of melting (indicated by a large volume of mafic and ultramafic rocks) during the second phase of magmatism (Gopir volcanics) that occurred at later stages of Jharol sedimentation. Coeval melting of the sub-continental lithosphere under the adjoining BGC craton probably caused the emplacement of dikes along with the Gopir volcanics. At this stage of progressive rifting, an oceanic crust very similar to that in marginal basins developed in the Jharol Belt.

Abu-Hamatteh, Z. S. H.

2005-07-01

153

Geodynamical and Geochemical Features of Oil Generation in Sedimentary Basin of Volga-Ural Region  

NASA Astrophysics Data System (ADS)

Oil and gas prospects of Paleozoic sedimentary rocks of Volga-Ural Anticline (VUA) various researchers evaluate in different ways. More than 150 oil fields in Paleozoic formations were discovered in the eastern half of Republic of Tatarstan of the East European Platform. There were not found any significant fields in the western areas of investigation region. According to many investigators, the western part of the Tatarstan has unfavourable geological structure from oil and gas potential view. Solution of problem concerning revealing HC source for the fields of Volga-Ural oil and gas province certainly would alow to discuss about further prospects of this territory. Data available evidence that during Paleozoic time, an area of the present-day South-Tatarian Arch (STA) and North-Tatarian Arch was a passive continental margin along which a sediments rocks up to 2 km thick was accumulated. Generation potential of organic matter containing in increased concentrations in domanikoid deposits was obtained. It has been discovered that the cumulative production in some oil areas of the Romashkino oil field substantially exceeds formerly proven, recoverable, reserves. Moreover, the volume of oil produced has already significantly exceeded the amount of oil that the Domanik strata could have generated as supposed source rocks of the South Tatarstan arch and the adjacent areas. Cumulative oil production in Tatarstan has already reached 3.0B tons, thus substantially exceeding 709M tons, calculated geochemically on the basis of the Paleozoic source rock potentials of all sedimentary strata. This discrepancy obviously shows the impossibility for the commercial amounts of hydrocarbons of being generated from the available material of the sedimentary cover. Some experts explain this phenomenon by the errors made in the reserve estimates. But another consider this as the inflow or replenishment by the hydrocarbon flow from the crystalline basement along the faults. Who is right? It is very difficult and debatable scientific problem. Based on numerous facts of many years studies of Archean-Proterozoic basement and it role in oil field formation of sedimentary cover it is being developed a working hypothesis about sources of oil. Oil from the Paleozoic of the STA is genetically identical to bitumoids of the basement, which is in itself indicative of the vertical migration of oil, for the sedimentary cover above STA has no adequate petroleum source. It is possible, source of oil don't connected with only sedimentary rocks of STA and the adjacent areas. This fact is forced us to search for another reasons of formation such gigantic oil field as Romashkino. As result of this there is appear the hypothesis of vertical migration of oil and oil saturated fluid from source located below the surface of crystalline basement. Existence of process of the modern fluid migration is confirmed by results of different examinations, which have carry out independently in different field of science. Analysis of a variety of elements by several methods of rocks, oil, bitumen samples from sedimentary cover and crystalline basement was performed. New geodynamical features of generation of Kamsko-Kinelskaia intraformational flexure were investigated.

Plotnikova, I.

2009-04-01

154

Tracing lithosphere amalgamation through time: chemical geodynamics of sub-continental lithospheric mantle  

NASA Astrophysics Data System (ADS)

The theory of plate tectonics is a relatively young concept in the Earth Sciences and describes the surface expression of planetary cooling via magmatism and reconciles mantle convection and plate movement with orogenesis, earthquakes and volcanism. Detailed observation of current tectonic plate movement has purported a relatively clear picture of the planet's geodynamics. Modern oceanic basins are the predominant sites of thermal equilibration of Earth interior resulting from decompressional, convective melting of peridotites. This magmatism generates mid-ocean ridge mafic crust and depleted upper mantle and in this model, oceanic crust becomes associated with buoyant mantle to form oceanic lithosphere. Subduction zones return this material together with sediments into the deeper mantle and presumably aid the formation of continental crust via arc magmatism. The mechanisms of continental crust amalgamation with buoyant mantle are less clear, and distinctly more difficult to trace back in time because metamorphism and metasomatism render the processes associating convecting mantle with continental crust elusive. Paramount in assessing these mechanisms is understanding the timing of crust and mantle formation so that the onset of plate tectonics and potential changes in modi operandi with respect to convection, mantle composition and melting pressure and temperature may be traced from the early Hadean to the present day. Typically the formation age of continental crust is more easily determined from felsic samples that contain accessory and relatively robust phases such as zircon and monazite that render a geochronological approach feasible. The lack of equally robust minerals and pervasive and ubiquitous metasomatism afflicting obducted orogenic peridotites and mantle xenoliths obliterates primary mineralogical and geochemical information. Hence it has proven difficult to acquire mantle depletion ages from continental lithospheric mantle, perhaps with the exception of Re-Os isotope dating of cratonic peridotites. Empiric mineralogical and geochemical data of continental and oceanic lithospheric mantle has been examined extensively and metasomatism has been studied in great detail. I will present a numerical modelling approach generating a comprehensive catalogue of variously depleted plagioclase-, spinel- and garnet-peridotite major and trace element compositions. In addition primary Pb, Sr, Nd, Hf and Os isotope data will approximate refractory mantle generated during Earth's major episodes of depletion and continental crust formation (1.2, 1.8, 2.9, 3.8 Ga). These hypothetical compositions will be compared to natural peridotites from on- and off-cratonic xenoliths, abyssal and orogenic peridotites to identify those rare samples least altered by interaction with silicate, hydrous and carbonatitic melts. Extremely depleted mantle has the potential to harbour Pb, Sr, Nd, Hf and Os isotope compositions that would be easily recognized if silicate melts were generated from this type of pristine mantle and the record of volcanic rocks will be examined to identify potential lithospheric melts.

Wittig, Nadine

2014-05-01

155

Short-term groundwater level variations in a seismic region as an indicator of the geodynamic regime  

NASA Astrophysics Data System (ADS)

An analysis of short-term (up to 5 days) variations in the groundwater level has been made for a group of wells in Turkmenistan, where observations in search of earthquake precursors have been carried out for many years. A great number of groundwater level variations, which reflect active geodynamic processes, were found in wells located in the Main Kopetdag Fault Zone. These variations are a response to relatively rapid movements in the fault zone. A number of specific features of the recent crustal movements were determined from the character of the groundwater level variations. These features are the preferential coincidence of the directions of rapid and slow movements, variation in the deformation rates in different portions of the fault, and a change in the movement rate with time. About 56% of the short-term groundwater level variations proceded or accompanied earthquakes, the rest of the variations were a response to aseismic movements. The characteristics of the precursory variations imply that before the earthquake, in the fracture zone, substantial short-term deformations occur at a rate 1-4 orders larger than the estimated values of deformations. The dependence of the amplitudes of short-term groundwater level variations and earth-tide level fluctuations on the position of observation wells with respect to the fault has been elucidated. These amplitudes and the number of recorded variations are larger near the fault, indicating intensified deformations and enhanced strain sensitivity of the well-reservoir system in the vicinity of major tectonic disturbances. The investigations conducted point to the high information content of special hydrogeological observations for monitoring recent geodynamic activity.

Kissin, I. G.; Belikov, V. M.; Ishankuliev, G. A.

1996-11-01

156

Paleogeographic evolution of the central segment of the South Atlantic during Early Cretaceous times: Paleotopographic and geodynamic implications  

NASA Astrophysics Data System (ADS)

The geodynamic processes that control the opening of the central segment of the South Atlantic Ocean (between the Walvis Ridge and the Ascension FZ) are debated. In this paper, we discuss the timing of the sedimentary and tectonic evolution of the Early Cretaceous rift by drawing eight paleogeographic and geodynamic maps from the Berriasian to the Middle-Late Aptian, based on a biostratigraphic (ostracodes and pollen) chart recalibrated on absolute ages (chemostratigraphy, interstratified volcanics, Re-Os dating of the organic matter). The central segment of the South Atlantic is composed of two domains, with a two phases evolution of the pre-drift ("rifting") times: a rift phase characterized by tilted blocks and growth strata, followed by a sag basin. The southern domain includes the Namibe, Santos and Campos Basins. The northern domain extends from the Espirito Santo and North Kwanza Basins, in the south, to the Sergipe-Alagoas and North Gabon Basins to the north. Extension started in the northern domain during the Late Berriasian (Congo-Camamu Basin to the Sergipe-Alagoas-North Gabon Basins) and migrated southward. At that time, the southern domain was not a subsiding domain (emplacement of the Parana-Etendeka Trapp). Extension started in this southern domain during the Early Barremian. The rift phase is shorter in the south (5-6 Ma, Barremian to base Aptian) than in the north (19 to 20 Myr, Upper Berriasian to base Aptian). The sag phase is of Middle to Late Aptian age. In the northern domain, this transition corresponds to a hiatus of Early to Middle Aptian age. From the Late Berriasian to base Aptian, the northern domain evolves from a deep lake with lateral highs to a shallower organic-rich one with no more highs. The lake migrates southward in two steps, until the Valanginian at the border between the northern and southern domains, until the Early Barremian, north of Walvis Ridge.

Chaboureau, Anne-Claire; Guillocheau, Franois; Robin, Ccile; Rohais, Sbastien; Moulin, Maryline; Aslanian, Daniel

2013-09-01

157

Geodynamic constraints on stress and strength of the continental lithosphere during India-Asia collision.  

NASA Astrophysics Data System (ADS)

There has been quite some debate in recent years on what the long-term strength of the continental lithosphere is and how it is related to the occurrence of earthquakes. One of the best studied areas in this respect is the India-Asia collision zone, where -in some profiles- the Moho depth is known to within a few km's. A relocation of earthquake source locations revealed that in India earthquakes occur throughout the whole lithosphere whereas in Tibet, earthquakes are restricted to the upper 10-15 km of the crust with few exceptions slightly above or below the Moho. The lack of substantial earthquake activity in the sub-Moho mantle lithosphere seems puzzling since (1D) strength envelop models for the continental lithosphere predict large differential stresses (and brittle failure) in these locations. A way out of this paradox is to assume that the rheology of the mantle lithosphere (i.e. the effective viscosity) is significantly smaller than usually assumed, either because of the effects of hydration, or because of increased Moho temperatures. As a consequence, the strength of the lithosphere resides in the crust and not in the upper mantle as previously assumed. This conclusion gets some support from spectral-based inverse models of the effective elastic thickness (using topography and gravity as input data), which is typically smaller than the seismogenic thickness. Even though this explanation might appear appealing at first, there are at least two major problems with it: (1) Estimations of the effective elastic thickness (EET) of the lithosphere are non-unique and model-dependent. Others, using a direct (non-spectral) modelling approach, find significantly larger values of the EET in the same locations (again using gravity & topography as constraints). (2) Long term geodynamic models indicate that if the mantle lithosphere would indeed be as weak as suggested, it would be very difficult to generate plate-tectonics like behavior: Subducting slabs behave more like vertical drips; and topography cannot be sustained for geologically relevant timescales. Yet, despite those problems, the relative lack of earthquakes underneath the Moho remains an intriguing fact, which is also found in other mountain belts such as the Swiss Alps. The two modelling approaches that are used to interpret the data, however, are based on highly simplified assumptions. The 1D Christmas-tree approach assumes that strain rates are homogeneous throughout a vertical section of the lithosphere. EET-based estimations assume that the lithosphere is an elastic layer over an infinite half space. In reality, however, the lithosphere is expected to have depth- and temperature-dependent material properties, and it is unclear whether strain rates in such a lithosphere are indeed constant with depth. For this reason, we here use a 2D modelling approach that takes geometrical complexities as well as mantle-lithosphere interaction into account. Rather than modelling the evolution of the India-Asia collision over a million-year timescale, as would typically be done with such an approach, we here restrict ourselves to the present-day rheological stratification of the lithosphere. The advantage of such quasi-instantaneous lithospheric models is that they require only a few time steps per simulations and can therefore cover a wide parameter space. As input we use relatively well-constrained datasets such as surface topography, Moho depth (where available), and far field convergence velocity. From this, the state-of-stress of the lithosphere, its surface velocity, gravity anomalies and mantle flow fields are computed as a function of lithospheric geometry and rheological stratification. Model results show that the response of the lithosphere and flow in the underlying mantle are significantly influenced by the rheology of the lithosphere, in particular by the effective viscosity of the mantle lithosphere. Models, in which the mantle lithosphere and lower crust are weak' become unstable and result in a Tibetan plateau that disappears in geologically small time

Kaus, B. J. P.; Schmalholz, S. M.; Lebedev, S.; Deschamps, F.

2009-04-01

158

About the Relation Between Geodynamics of the Sedimentary Basin and the Properties of Crude Oil  

NASA Astrophysics Data System (ADS)

Earlier, we wrote and reported about the modern geodynamic activity of the territory of South-Tatar arch, where the Romashkino oil field. We identified a periodic change in flow rates of oil and oil density at Romashkino and other oil fields of the South Tatar arch. Now we have studied the composition of oils and bitumoids from uneven (in terms of age) deposites of the sedimentary cover and basement rocks in the zones of possible hydrocarbon seepage in the central squares of Romashkinskoye field. The results of the comparative studies allowed us to come to the conclusion that the formation of oil-bearing deposits of Romashkinskoye field owes to the income and mixing of hydrocarbons (HC) fluids from different sources. The analysis of geological and production data (GPD) that was held during the many years of exploitation of the development wells of Romashkinskoye field by TatNIPIneft under the direction of I.F. Glumov suggests contemporary inflow of hydrocarbons in the industrial oil reservoir of the Pashi horizon of Romashkinskoye field and the existence of localized areas of inflow of new portions of HC. A number of criteria was worked out in the analysis of the GPD; that allowed us to identify among the total number of wells those, in which the process of hydrocarbon seepage was recorded with the greatest probability. Such wells were called anomalous. One of the directions of this research was to study the geochemical characteristics of oil from anomalous wells and to determine the degree of similarity and difference between this oil and the oil from both normal wells (in which the signs of deep seepage is not recorded), and bituminoid from the crystalline basement and sedimentary cover. If the hypothesis of a recurrent (also in modern times) influx of deep hydrocarbon is correct, then the oil from the anomalous wells should have specific features in comparison with the wells located outside the areas of the expected inflow. The results of geochemical studies of oil and organic matter in sedimentary cover rocks that were carried out within the last decade gave us new and unexpected conclusions. First, on the basis of pyrolysis it was found that the top agent of domanikits of the upper Devonian (which were traditionally considered to be a source rock for most crudes of the Volga-Ural region) is characterized by a low degree of catagenetic maturity. These rocks were not submerged to the depth of more than 2.5 km and were not included in the main area of oil and gas formation in most parts of its distribution within the Republic of Tatarstan, which corresponds to the main territory of North- and South-Tatar arch with surrounding areas of deflections and depressions. Comprehensive study of oil from the anomalous wells showed that these oils have certain characteristics different from normal oil wells, therefore, the hypothesis of a modern inflow of hydrocarbons is consistent and specific studies of this process should be continued. The estimated (by biomarker parameters) lack of genetic relationship between oil from producing under-domanik horizons (Pashi, Timansky, Ardatovsky and Vorobyevsky) and the top agent in domanikits indicates the need for searching of the sources of oil generation and confirms the viability of the hypothesis of deep origin of HC and their inflow into the sedimentary cover through the crystalline base. The oil from the anomalous wells should be subject to special investigations in the monitoring mode designed to examine the isotopic systematics of Sr and Nd, isotope characteristics of helium, carbon, hydrogen, nitrogen in the dissolved gases. The design of these studies needs to be linked, in the first place, with the seismic events continuing on the territory of Tatarstan, as the relationship between the change of the carbon isotopic composition and the seismic events has previously been established. Also in the condition of a recurrent inflow of new portions of the deep HC, it would be logical to assume the changes in the isotopic composition of elements of the dissolved gas.

Muslimov, R.; Plotnikova, I.

2012-04-01

159

Stages of geodynamic rearrangements of the eastern margin of the Eurasian continent in the Cenozoic: The amur river-sea of the Okhotsk region  

Microsoft Academic Search

It is widely believed in literature that the convergent boundary between the Pacific Plate and the eastern margin of the Eurasian continent permanently existed through the Late Mesozoic and Cenozoic. However, new data in combination with recent publications on the Sikhote Alin?Sakhalin [1?5] and the East China? Japan [6?8] regions testify to geodynamic and tectonic instability of the eastern margin

N. I. Filatova

2006-01-01

160

Joint seismic and geodynamic evidence for a long-lived, stable mantle upwelling under the East Pacific Rise  

NASA Astrophysics Data System (ADS)

Global seismic tomography has consistently imaged large-scale structures in the lower mantle under the Pacific Ocean and under Africa that are characterised by strongly reduced seismic shear velocities. These so-called "low shear-velocity provinces" (LVSP) have been variously interpreted as hot, stagnant thermochemical "piles" that are compositionally dense, or as deeply rooted expressions of positively buoyant, active upwellings. To distinguish which of these two end-member models is relevant to the actual dynamics in the deep mantle requires robust constraints on the density structure of these LVSP. Recent global tomography models reveal what appear to be three distinct 'lobes' of the Pacific LVSP: one located in the Western-Pacific mantle under the Caroline Islands, another in the South-Central-Pacific mantle under French Polynesia, and another below the East Pacific Rise (EPR), centred under Easter Island. To understand the dynamics and time-dependent evolution of these structures we employ recent tomography models derived from the joint inversion of global seismic and geodynamic data sets, which also include constraints from mineral physics (Simmons et al., GJI 2009, JGR 2010). A critically important feature of these joint tomography models is the inclusion of a laterally variable scaling between density and seismic shear velocity, thereby accounting for the spatially localized effect of compositional heterogeneity in the lower mantle. These lower-mantle compositional contributions to density are directly constrained by long-wavelength gravity anomaly data and the excess ellipticity of the CMB. We show that it is not possible to properly account for this compositional heterogeneity using a constant, or simple depth-dependent density-velocity scaling. We have carried out very-long-time mantle convection simulations employing as a starting condition the joint seismic-geodynamic inferences of mantle density structure (Glisovic et al., GJI 2012). We demonstrate with both time-reversed and forward integration of the thermal convective evolution of the LVSP under the Pacific, that the principal plume-like upwellings are directly under the EPR and under the Caroline Islands. The deep-mantle anomaly at the centre of the LVSP, under French Polynesia, yields almost no upwelling, owing to the joint seismic-geodynamic inference of significant compositional heterogeneity that opposes its thermal buoyancy. We find that the EPR 'superplume' is particularly long-lived and stable, over time spans in excess of a hundred million years (Glisovic et al., GJI 2012). Time-reversed simulations over the past 65 Ma also show a stable upwelling under the EPR (Glisovic & Forte, EPSL submitted 2013). This remarkable stability provides a direct explanation for the recent inference of strong lateral fixity of the EPR spreading centre from geological reconstructions of plate kinematics over the past 83 Ma (Rowley et al., AGU 2011, Nature submitted 2012).

Forte, A. M.; Glisovic, P.; Rowley, D. B.; Simmons, N. A.; Grand, S. P.

2013-12-01

161

Crust structure, geodynamic and metallogenisis of major metallogenic belts in East China: an introduction to SinoProbe-03 (Invited)  

NASA Astrophysics Data System (ADS)

SinoProbe is a new Chinese government-founded scientific Project with the overall aims of exploring the deep structure and geogynamic evolution of the continental crust and lithosphere beneath China. As a third sub-Project, the SinoProbe-03 is focus on two typical metallogenic belts: the South range and the middle and lower Yangtze River of Eastern China. The former is characterized by its world-class tungsten, tin and multimetal (Sb-Bi-Pb-Zn) metallogenisis which was considered to be related to crust-derived magma; whereas, the later is characterized by its iron, cupper and multimetal (Au-S-Pb-Zn) metallogenisis which was thought to be related to mantle-derived magma. The main questions related to two metallogenic belts that SinoProbe-03 plan to address are: (1) the crustal structure and geodynamic processes for generation and migration of magma, whats the sources characteristics that eventually control the metal types; (2) the fine upper-crust structure(<10km) of the major ore district ( e.g. Luzong, Tongling and Yudu-Ganxian), and how they control the ore-forming process, and the spatial distribution of major ore-bearing strata and ore-controlling structure; (3) the efficiency of integrated geophysical methods ( e.g. AMT, CSAMT, SIP, TEM), especially the seismic reflection method, in direct detection of deep ( 2km) ore-bearing formations or ore-controlling structure. SinoProbe-03 is therefore an multidisciplinary programme, combining surface observations with deep geophysical (near-vertical reflection, wide-angle reflection, broadband seismic array and magnetotellurics) and geochemical probing, applying, adapting and developing the latest technology to obtain an integrated image of the whole crust of the two metallogenic belts. Through this programme, we try to better understanding how the mineral systems (or large deposits) was initiated and evolved under the framework of geodynamic evolution. Acknowledgment: We acknowledge the financial support of SinoProbe by the Ministry of Finance and Ministry of Land and Resources, P. R. China, under Grant sinoprobe-03, and financial support by National Natural Science Foundation of China under Grant 40930418

Lu, Q.; Chang, Y.

2010-12-01

162

New evidence of delamination in the Western Alboran Sea. Geodynamic evolution of the Alboran domain and its margins  

NASA Astrophysics Data System (ADS)

The presence of continuous upper crustal blocks between the Iberian Betics and Moroccan Rif in the western and middle Alboran Sea, detected with tomography, can add new information about the lithosphere structure and geodynamic evolution in this region. A large volume of seismic data (P and S wave arrival times) has been collected for the period between 1 December 1988 and 31 December 2008 by 57 stations located in northern Morocco (National Institute of Geophysics, CNRST, Rabat), southern Portugal (Instituto de Meteorologia, Lisbon) and Spain (Instituto Geografico National, Madrid) and used to investigate the lithosphere in the western Alboran Sea region. We use a linearized inversion procedure comprising two steps: (1) finding the minimal 1-D model and simultaneous relocation of hypocenters and (2) determination of local velocity structure using linearized inversion. The model parameterization in this method assumes a continuous velocity field. The resolution tests indicate that the calculated images give near true structure imaged at 5 km depth for the Tanger peninsula, the Alhoceima region and southern Spain. At 15, 30 and 45 km depth we observe a near true structure imaged in northern Morocco, and southern Spain. At 60 and 100 km, southern Spain and the SW region of the Alboran Sea give a near true structure. The resulting tomographic image shows the presence of two upper crustal bodies (velocity 6.5 km/s) at 5-10 km depth between the Betics, Rif, western and central Alboran Sea. Low velocities at the base of these two bodies favor the presence of melt. This new evidence proves that the Tethysian ocean upper crust was not totally collapsed or broken down during the late Oligocene-early Miocene. These two blocks of upper crust were initially one block. The geodynamic process in the eastern of the Mediterranean is driven by slab rollback. The delamination process of the lithospheric mantle terminates with the proposed slab rollback in the western part of the Mediterranean. This can be explained by the removal of the major part of the lithosphere beneath the area, except in the SW part of the Alboran Sea where a small part of the lithospheric mantle is still attached and is extends and dips to SE beneath the Rif, slowly peeled back to the west. A second detached lithospheric mantle is located and extends to eastern part of the Rif and dips to the SE. The removal of lithosphere mantle from the base of the crust was replaced and heated by extrusion of asthenospheric material coming from depth to replace the part of crust detached. A combination of isostatic surface/topographic uplift and erosion induced a rapid exhumation and cooling of deep crustal rocks.

Timoulali, Youssef; Djellit, Hamou; Hahou, Youssef; Jabour, Nacer; Merrouch, Redouane

2014-07-01

163

Seismoacoustic responses to high-power electric pulses from well logging data at the Bishkek geodynamical test area  

NASA Astrophysics Data System (ADS)

The results of recording seismoacoustic emission (SAE) in the boreholes of the Bishkek geodynamical test area in Tien Shan, Kyrgyzstan, are presented. The spectral structure of SAE signals and the pattern of variations in SAE intensity during electromagnetic (EM) sounding of the Earth's crust by the highpower ERGU-600-2 generator unit are studied. The statistical methods for SAE data processing are adjusted for the problem of revealing the correlations between SAE responses and pulsed electrical impacts (i.e., energy input into the medium). The response of the medium to EM soundings, which are conducted for monitoring the apparent resistivity of the rocks, is revealed. The response of the medium manifests itself as the increase in SAE intensity (the responses to the electric current pulses generated during the soundings). The SAE responses belong to the same group of the effects (the signs of external forcing of rock destruction) as the variations in seismicity during the runs of the geophysical magneto-hydrodynamic (MHD) generators in 1983-1989 or experimental soundings in 2000-2005. The sources of SAE signals are located at shallow depths, near the geophone installation place. This accounts for the difference between the variations in SAE intensity and microseismicity in response to the same impact.

Zakupin, A. S.; Bogomolov, L. M.; Mubassarova, V. A.; Il'ichev, P. V.

2014-09-01

164

Robust coupled fluid-particle simulation scheme in Stokes-flow regime: Toward the geodynamic simulation including granular media  

NASA Astrophysics Data System (ADS)

present a simulation scheme for solving high-viscosity fluid and particle dynamics in a coupled computational fluid dynamics and discrete element method (CFD-DEM) framework. This simulation scheme is intended to be used for geodynamical magmatic studies such as crystal settling at the melting roof of a magma chamber. The high-viscosity fluid is treated by the Stokes-flow approximation, where the fluid interacts with particles via the drag force in a cell-averaged manner. The particles are tracked with contact forces by DEM. To efficiently solve such Stokes-DEM coupled equations, we propose two key techniques. One is formulation of particle motion without the inertial term, allowing a larger time step at higher viscosities. The other is a semi-implicit treatment of the cell-averaged particle velocity in the fluid equation to stabilize the calculation. We simulate the settling particles in strongly viscous fluids in three dimensions and compare the results with the experimental and theoretical results. Our solution strategy is found to be robust and successfully captures the collective behavior of the particles. The simulation method presented here will be useful in various fields interested in long-term dynamics of high-viscosity granular media.

Furuichi, Mikito; Nishiura, Daisuke

2014-07-01

165

Seismic-geodynamic constraints on three-dimensional structure, vertical flow, and heat transfer in the mantle  

USGS Publications Warehouse

Joint inversions of seismic and geodynamic data are carried out in which we simultaneously constrain global-scale seismic heterogeneity in the mantle as well as the amplitude of vertical mantle flow across the 670 km seismic discontinuity. These inversions reveal the existence of a family of three-dimensional (3-D) mantle models that satisfy the data while at the same time yielding predictions of layered mantle flow. The new 3-D mantle models we obtain demonstrate that the buoyancy forces due to the undulations of the 670 km phase-change boundary strongly inhibit the vertical flow between the upper and lower mantle. The strong stabilizing effect of the 670 km topography also has an important impact on the predicted dynamic topography of the Earth's solid surface and on the surface gravity anomalies. The new 3-D models that predict strongly or partially layered mantle flow provide essentially identical fits to the global seismic data as previous models that have, until now, predicted only whole-mantle flow. The convective vertical transport of heat across the mantle predicted on the basis of the new 3-D models shows that the heat flow is a minimum at 1000 km depth. This suggests the presence at this depth of a globally defined horizon across which the pattern of lateral heterogeneity changes rapidly. Copyright 1997 by the American Geophysical Union.

Forte, A. M.; Woodward, R. L.

1997-01-01

166

Geodynamic significance of the TRM segment in the East African Rift: active tectonics and paleostress in western Tanzania  

NASA Astrophysics Data System (ADS)

The Tanganyika-Rukwa-Malawi (TRM) rift segment in western Tanzania is a key sector for understanding the opening dynamics of the East African rift system (EARS). In an oblique opening model, it is considered as a dextral transfer fault zone that accommodates the general opening of the EARS in a NW-SE direction. In an orthogonal opening model, it accommodates pure dip-slip normal faulting with extension orthogonal to the rift segments and a general E-W extension for the entire EARS. We investigated the active tectonic architecture and paleostress evolution of the Ufipa plateau and adjacent Rukwa basin and in order to define their geodynamic role in the development of the EARS and highlight their pre-rift brittle tectonic history. The active fault architecture, fault-kinematic analysis and paleostress reconstruction show that the recent to active fault systems that control the rift structure develop in a pure extensional setting with extension direction orthogonal to the trend of the TRM segment. Two pre-rift brittle events are evidenced. An older brittle thrusting is related to the interaction between the Bangweulu block and the Tanzanian craton during the late Pan-African (early Paleozoic). It was followed by a transpressional inversion during the early Mesozoic. This inversion stage caused dextral strike-slip faulting along the fault systems that now control the major rift structures. It has been erroneously interpreted as related to the late Cenozoic EARS which instead is characterized by pure normal faulting.

Delvaux, D.; Kervyn, F.; Macheyeki, A. S.; Temu, E. B.

2012-04-01

167

Understanding the geodynamic setting of So Miguel, Azores: A peculiar bit of mantle in the Central Atlantic  

NASA Astrophysics Data System (ADS)

The Azores Plateau and Archipelago in the Central Atlantic Ocean has traditionally been considered as the surface expression of a deep mantle plume or hotspot that has interacted with a mid-ocean ridge. It is geodynamically associated with the triple junction between the North American, African and Eurasian plates. (Yang et al., 2006) used finite frequency seismic tomography to demonstrate the presence of a zone of low P-wave velocities (peak magnitude -1.5%) in the uppermost 200km of the mantle beneath the plateau. The tomographic model is consistent with SW deflection of a mantle plume by regional upper mantle shear flow driven by absolute plate motions. The volcanic island of Sao Miguel is located within the Terceira Rift, believed to represent the boundary between the African and Eurasian plates; magmatic activity has been characterised by abundant basaltic eruptions in the past 30,000 years. The basalts are distinctive within the spectrum of global ocean island basalts for their wide range in isotopic composition, particularly in 87Sr/86Sr. Their Sr-Nd-Pb isotopic compositions show systematic variations from west to east across the island which can be interpreted in terms of melting of a two-component mantle source. The low melting point (enriched) component in the source has been attributed to recycled ancient (~3 Ga) oceanic crust(Elliott et al., 2007). Using the thermo-barometry approach of (Lee et al., 2009) we demonstrate that the pressure and temperature of magma generation below Sao Miguel increase from west (2 GPa, 1425 C) to east (3.8 GPa, 1575 C), consistent with partial melting along a mantle geotherm with a potential temperature of ~ 1500 C. This is consistent with the magnitude of the thermal anomaly beneath the Azores Plateau (?T ~ 150-200 C) inferred on the basis of the seismic tomography study. The site of primary magma generation extends from the base of the local lithosphere (~ 50 km) to ~ 125 km depth. To understand the geodynamic setting of the Sao Miguel magmatism we combine GPS data and mantle convection models with our interpretation of the geochemistry of the basalts. We demonstrate strong south-westerly and downward flow in the asthenospheric mantle above the Transition Zone (410 km seismic discontinuity), consistent with a zone of upper mantle shearing below the base of the lithosphere. The maximum flow velocity is broadly consistent with the depth of magma generation. The advection of the mantle with respect to the oceanic plate "moves" an isotopically distinct mantle source component beneath the active volcanoes of Sao Miguel and carries its previous melting residues to the south-west. We discuss the nature of this mantle source and its contribution to the mantle velocity anomalies determined by seismic tomography. This study opens-up new perspectives for seismic tomography and potentially new connections between the fields of geophysics and geochemistry in oceanic domains.

Wilson, M.; Houlie, N.; Khan, A.; Lithgow-Bertelloni, C. R.

2012-12-01

168

Estimates of geodynamic state and structure of the local crust on the base of microseismic noise analysis  

NASA Astrophysics Data System (ADS)

A method for obtaining estimates of geodynamic state of the local crust and rock masses on the base of microseismic noise analysis is discussed. Microseismic noise is considered as a superposition of background microvibrations and a discrete component in the form of weak microseismic pulses generated by relaxational processes in the medium [1]. Currently active tectonic faults can be identified as zones with clustered sources of microseismic pulses and more intense amplitude variations of background microvibrations in tidal waves and baric variations in the atmosphere [2,3]. The presence of underground nonheterogeneities (i.e. contrasts in mechanic properties) and their scales are obtained from analysis of spectral characteristics of microseismic noise [4]. In the epicentral zone of an underground inhomogeneity we evidence characteristic quasi-chromatic pulses, stronger spectral density of local noise at high frequencies (more than 10 Hz) as well as maximum of spatial distribution of horizontal to vertical component spectral noise ratio (Nakamura parameter). The size of structural elements (blocks) of the Earth's crust is estimated by peak frequencies of momochromatic components of the spectrum on the base of the elaborated analytical model [1]. Parameters of weak pulses generated by relaxation (such as max velocity of oscillations, dominating (observed) period, etc.) yield estimates of differential movements of structural blocks in the medium as well as max stresses in the latter [5,6]. Examples are given to illustrate application of the proposed method to locating and mapping fault zones and underground nonheterogeneities in the Earth's crust, as well as to estimating scales of active structural blocks and their mobility potential when assessing places for nuclear atomic plants and underground nuclear waste storages. The method has also been successfully used for ranging hillsides of South Alps in terms of their liability to landslides. [1]. A.A. Spivak, S.B. Kishkina. The use of microseismic background for the identification of active geotectonic structure and determination of geodynamic characteristics// Izvestiya, Physics of the Solid Earth. 2004. Vol. 40. No. 7. Pp. 573-586. [2]. V.V. Adushkin, A.A. Spivak. Near-surface geophysics: complex investigations of the lithosphere-atmosphere interactions// Izvestiya, Physics of the Solid Earth. 2012. Vol. 48. No. 3. Pp. 181-198. [3]. A.A. Spivak. The specific features of geophysical fields in the fault zones// Izvestiya, Physics of the Solid Earth. 2010. Vol. 46. No. 4. Pp. 327-338. [4] A.A. Spivak, B.G. Lukishov. Seismoresonance methods of disclosure of the contrast zones in the Earth's crust// Physical fields and dynamics of interactive geospheres. Moscow, GEOS, 2007. Pp. 226-276. (In Russian). [5]. A.A. Spivak. Relaxation processes and mechanical conditions in the local areas of the Earth' crust// Doklady Earth Science. 1998. Vol. 363. No. 8. Pp. 1172-1175. [6]. A.A. Spivak. Structure of the stress state in tectonic faults zones// Doklady Earth Science. 1999. Vol. 364. No. 4. Pp. 544-548.

Loktev, D.; Spivak, A.

2013-05-01

169

The petrogenesis of Early Eocene non-adakitic volcanism in NE Turkey: Constraints on the geodynamic implications  

NASA Astrophysics Data System (ADS)

Whole-rock geochemistry, mineral chemistry, the 40Ar-39Ar age, and Sr-Nd isotopic data are presented for the Early Eocene non-adakitic volcanic rocks on the eastern corner of the Eastern Pontides orogenic belt (NE Turkey). The tectonic setting of the Eastern Pontides during the Late Mesozoic to Early Cenozoic remains a topic of debate. Here, for the first time, we describe the Early Eocene non-adakitic volcanic rocks from the Eastern Pontides. These rocks contain plagioclase, hornblende phenocrysts, and magnetite/titanomagnetite and apatite microphenocrysts. Geochronology studies based on the 40Ar-39Ar ratio of the amphibole separates reveal that the non-adakitic porphyritic volcanic rocks have a crystallization age of 50.04 0.10 to 50.47 0.22 Ma (Ypresian). The volcanic rocks show tholeiitic to calc-alkaline affinities and have low-to-medium K contents. They are also enriched in large-ion lithophile elements (LILE), light rare-earth elements (LREE), and depleted in high field strength elements (HFSE), with a no negative Eu anomaly (Eun/Eu* = 1.03-1.08) in mantle-normalized trace element spidergrams. The samples (Lacn/Lucn = 2.60-4.28) show low-to-medium enrichment in LREEs relative to HREEs, in chondrite-normalized REE patterns indicating similar sources for the rock suite. These rocks display a range of ISr (50 Ma) values from 0.70451 to 0.70485, and ?Nd (50 Ma) 2.9 and 3.7. The main solidification processes involved in the evolution of these volcanics consist of fractional crystallization, with minor amounts of crustal contamination. All of our evidence supports the conclusion that the parental magma of the rocks probably derived from an enriched mantle, previously metasomatized by fluids derived from the subducted slab, in a post-collisional, geodynamic setting.

Ayd?nak?r, Emre

2014-11-01

170

Quartz tube extensometer for observation of Earth tides and local tectonic deformations at the Sopronbanfalva Geodynamic Observatory, Hungary  

SciTech Connect

In May 1990, a quartz tube extensometer was installed in the Sopronbanfalva Geodynamic Observatory of the Geodetic and Geophysical Research Institute (GGRI) of the Hungarian Academy of Sciences for recording Earth tides and recent tectonic movements. The paper describes the construction of the extensometer and a portable calibrator used for the in situ calibration of the instrument. The extensometer is very sensitive. Its scale factor is 2.093{+-}0.032 nm/mV according to the highly precise calibration method developed at the GGRI. Since the stability of extensometers is strongly influenced by the geological structure and properties of the rocks in the vicinity of the recording site, the observatory instrument system was tested by coherence analysis between theoretical (as the input signal) and measured tidal data series (as the output signal). In the semidiurnal tidal frequency band the coherence is better than 0.95, while in the diurnal band it is about 0.8. Probably this is due to the fact that the noise is higher in the diurnal band (0.4-0.5 nstr) than in the semidiurnal band (0.19-0.22 nstr). Coherence analysis between theoretical and measured data corrected for barometric changes yielded a small improvement of coherence in both frequency bands, while using temperature data correction, no observable improvement was obtained. Results of the tidal analysis also show that the observatory instrument system is suitable for recording very small tectonic movements. The 18 years of continuous data series measured by the extensometer prove the high quality of the extensometer. On the basis of investigations, it was pointed out that further efforts should be done to improve the barometric correction method and that correction for ocean load, as well as considering topographic and cavity effects are necessary to increase the accuracy of determining tidal parameters.

Mentes, Gy. [Geodetic and Geophysical Research Institute of the Hungarian Academy of Sciences, Csatkai Endre u. 6-8, H-9400 Sopron (Hungary)

2010-07-15

171

Petrological and Geodynamic Evolution of Post-Collisional Eocene-Oligocene Magmatic Rocks In The Biga Peninsula, NW Anatolia  

NASA Astrophysics Data System (ADS)

The post-collisional Eocene-Oligocene magmatic activity in the Biga Peninsula (NWAnatolia) started in the Middle Eocene and produced widespread volcano-plutonic complexes. Two main magmatic episodes (Eocene and Oligocene) formed the igneous assemblages in the region. We classified 6 different magmatic units based on their lithostratigraphic and chonorostratigraphic properties, determined by 40Ar/39Ar methods (Eocene-Early Oligocene, 42.080.09 to 29.020.29 Ma). The Eocene sequence is associated with calc-alkaline composition Laleda? granodiorite, Beyay?r (andesite, dacite) volcanics and alkaline K?z?ldam volcanics (basaltic trachyandesite, trachybasalt). Subsequent, Oligocene volcanism results in calc-alkaline Dededa? volcanics (trachydacite to ryholit), K?rcalar volcanics (basalts, basaltic andesites) and calcalkaline/alkaline Harmanc?k volcanics (basalt to rhyolite). The calcalkaline magmatic suites are in middle, high-K and alkaline suites high-K, shoshonitic chemical composition. Trace and rare earth elements (REE) diagrams show enrichment in large-ion lithophile elements (LILE), light rare earth elements (LREE) relative to the high field strength elements (HFSE) and a significant increase in heavy rare earth element consumption (HREE). The enrichment of incompatible elements suggests derivation from a metasomatized mantle source, whereas the troughs in Nb and Ta indicate a subduction influence in the mantle melt sources. Mantle-derived magmas partially were modified by AFC/FC processes for all volcanic sequences. Geochemical features and compositional variations of Eocene volcanic group indicate decreasing amounts of partial melting, whereas Oligocene volcanic group indicate the effects of increasing crustal contamination and/or assimilation. However, crustal contamination and/or assimilation was not an important process in the evolution of Eocene-Oligocene alkaline group. The Eocene-Oligocene post-collisional volcanism in Biga Peninsula displays lithospheric mantle source enriched by subduction which controlled by slab break-off and lithospheric delamination. Keywords: NW Anatolia, post-collisional volcanism, geodynamic evolution, geochronology

Erenoglu, Oya; Bozcu, Mustafa

2014-05-01

172

Mechanism and timing of tectonic inversion in Cyrenaica (Libya): Integration in the geodynamics of the East Mediterranean  

NASA Astrophysics Data System (ADS)

In the eastern Mediterranean, the South-Tethys paleo-margin experienced poly-phased rifting episodes during Paleozoic and Mesozoic times. This domain has been subsequently inverted by discontinuous events occurring since the Late Cretaceous as a consequence of the Africa-Eurasia convergence. The Cyrenaica promontory (northeast Libya), including the Jabal Al Akhdar antiformal ridge, is not yet involved in the Africa-Eurasia collision zone. It thus gives an opportunity to analyze tectonic inversions occurring early in the development of the system and their possible causal links with events occurring along the plate boundary (i.e., within the Hellenic subduction). For this purpose, we present new geological cross-sections supported by offshore industrial 2D seismic profiles imaging the northeast prolongation of the antiformal ridge indenting the Mediterranean Ridge accretionary prism. The onshore part of this ENE-WSW trending structure exposes Upper Cretaceous to recent sedimentary rocks. Well calibrations allow us to be precise about the geometry of the structure, inherited from a Lower Cretaceous rift basin, and the timing of the main tectonic events. Oligocene sediments seal unconformably the main episodes of contractional deformation. Just below, growth strata of Late Ypresian to Priabonian age indicate a protracted folding episode during the Middle-Late Eocene, post-dating an older Late Cretaceous inversion. This evolution contrasts with what is observed in the adjacent Sirt Basin, characterized at the same time by extensional deformation and subsidence. Finally, we appraise how far these tectonic scenarios match the geodynamic evolution of the Hellenic domain.

Arsenikos, Stavros; Frizon de Lamotte, Dominique; Chamot-Rooke, Nicolas; Mohn, Geoffroy; Bonneau, Marie-Claude; Blanpied, Christian

2013-11-01

173

The fluids' geochemistry along the "Sperchios Basin - Northern Evoikos Gulf" Graben, a geodynamically complex area of Central Greece  

NASA Astrophysics Data System (ADS)

The study area is a 130 km long fast spreading graben in Central Greece. Its complex geodynamical setting includes both the presence at depth of a subduction slab responsible for the recent (Quaternary) volcanic activity in the area and the western termination of a tectonic lineament of regional importance (the North-Anatolian fault). Its high geothermal gradient is evidenced by the presence of many thermal springs with temperatures from 19 to 82 C, issuing along the normal faults bordering the graben. In the period 2004-2012 about 50 gas and water samples have been collected and their chemical and isotopic analysis revealed a wide range of compositions. Going from west to east the gas composition changes from CH4- to CO2-dominated passing through mixed N2-CH4 and N2-CO2 compositions, while at the same time the He isotopic composition goes from typical crustal values (0.05 R/Ra) up to 0.87 R/Ra (corrected for air contamination), showing in the easternmost sites a small but significant mantle input. Isotopic composition of CH4-C indicates a thermogenic origin for the CH4-rich samples and hydrothermal origin for the remaining samples. Positive ?15N values indicate a contribution of crustal derived nitrogen for the N2-rich samples. The ?13C values of most the CO2-enriched samples show a mixed origin (mantle and marine carbonates). Also the chemical composition of the waters shows differences along the graben and two main groups can be separated. The first, represented by dilute waters (E.C. < 600 ?S/cm), is found in the westernmost sites characterised by the presence of CH4-rich and mixed N2-CH4 gases. The remaining waters display higher salinities (E.C. from 12 to 56 mS/cm) due to the mixing with a modified marine component. Only the water composition of easternmost sites in the Giggenbach's cation triangular graph plots in the field of the partially equilibrated waters giving estimated temperatures at depth of 150-160C.

D'Alessandro, Walter; Bellomo, Sergio; Brusca, Lorenzo; Calabrese, Sergio; Kyriakopoulos, Konstantinos

2013-04-01

174

Paleozoic and Lower Mesozoic magmas from the eastern Klamath Mountains (North California) and the geodynamic evolution of northwestern America  

NASA Astrophysics Data System (ADS)

The Paleozoic to Early Mesozoic geology of the eastern Klamath Mountains (N California) is characterized by three major magmatic events of Ordovician, Late Ordovician to Early Devonian, and Permo-Triassic ages. The Ordovician event is represented by a calc-alkalic island-arc sequence (Lovers Leap Butte sequence) developed in the vicinity of a continental margin. The Late Ordovician to Early Devonian event consists of the 430-480 Ma old Trinity ophiolite formed during the early development of a marginal basin, and a series of low-K tholeiitic volcanic suites (Lovers Leap BasaltKeratophyre unit, Copley and Balaklala Formations) belonging to intraoceanic island-arcs. Finally, the Permo-Triassic event gave rise to three successives phases of volcanic activity (Nosoni, Dekkas and Bully Hill) represented by the highly differentiated basalt-to-rhyolite low-K tholeiitic series of mature island-arcs. The Permo-Triassic sediments are indicative of shallow to moderate depth in an open, warm sea. The geodynamic evolution of the eastern Klamath Mountains during Paleozoic to Early Mesozoic times is therefore constrained by the geological, petrological and geochemical features of its island-arcs and related marginal basin. A consistent plate-tectonic model is proposed for the area, consisting of six main stages: (1) development during Ordovician times of a calc-alkalic island-arc in the vicinity of a continental margin; (2) extrusion during Late Ordovician to Silurian times of a primitive basalt-andesite intraoceanic island-arc suite, which terminated with boninites, the latter suggest rifting in the fore-arc, followed by the breakup of the arc; (3) opening and development of the Trinity back-arc basin around 430-480 Ma ago; (4) eruption of the Balaklala Rhyolite either in the arc or in the fore-arc, ending in Early Devonian time with intrusion of the 400 Ma Mule Mountain stock; (5) break in volcanic activity from the Early Devonian to the Early Permian; and (6) development of a mature island-arc from the Early Permian to the Late Triassic. The eastern Klamath Mountains island-arc formations and ophiolitic suite are part of the "Cordilleran suspect terranes", considered to be Gondwana margin fragments, that have undergone large northward translations before final collision with the North American craton during Late Mesozoic or Cenozoic times. These eastern Klamath Mountains island-arcs could be associated with the paleo-Pacific oceanic plate that led to accretion of these allochthonous terranes to the American margin.

Lapierre, H.; Brouxel, M.; Albarede, F.; Coulin, C.; Lecuyer, C.; Martin, P.; Mascle, G.; Rouer, O.

1987-09-01

175

Palaeogeographic evolution of the central segment of the South Atlantic during Early Cretaceous times: palaeotopographic and geodynamic implications  

NASA Astrophysics Data System (ADS)

The tectonic and sedimentary evolution of the Early Cretaceous rift of the central segment of the South Atlantic Ocean is debated. Our objective is to better constraint the timing of its evolution by drawing palaeogeographic and deformation maps. Eight palaeogeographic and deformations maps were drawn from the Berriasian to the Middle-Late Aptian, based on a biostratigraphic (ostracodes and pollens) chart recalibrated on absolute ages (chemostratigraphy, interstratified volcanics, Re-Os dating of the organic matter). The central segment of the South Atlantic is composed of two domains that have a different history in terms of deformation and palaeogeography. The southern domain includes Namibe, Santos and Campos Basins. The northern domain extends from Espirito Santo and North Kwanza Basins, in the South, to Sergipe-Alagoas and North Gabon Basins to the North. Extension started in the northern domain during Late Berriasian (Congo-Camamu Basin to Sergipe-Alagoas-North Gabon Basins) and migrated southward. At that time, the southern domain was not a subsiding domain. This is time of emplacement of the Parana-Etendeka Trapp (Late Hauterivian-Early Barremian). Extension started in this southern domain during Early Barremian. The brittle extensional period is shorter in the South (5-6 Ma, Barremian to base Aptian) than in the North (19 to 20 Myr, Upper Berriasian to Base Aptian). From Late Berriasian to base Aptian, the northern domain evolves from a deep lake with lateral highs to a shallower one, organic-rich with no more highs. The lake migrates southward in two steps, until Valanginian at the border between the northern and southern domains, until Early Barremian, North of Walvis Ridge. The Sag phase is of Middle to Late Aptian age. In the southern domain, the transition between the brittle rift and the sag phase is continuous. In the northern domain, this transition corresponds to a hiatus of Early to Middle Aptian age, possible period of mantle exhumation. Marine influences were clearly occurring since the Early Aptian in the Northern domain and the Campos Basin. They seem sharp, brief flooding coming from the North, i.e. from the Tethys-Central Atlantic, trough a seaway crossing South America from Sao Luis, Parnaiba, Araripe and Almada basins (Arai, 1989). In the absence of data, the importance of those marine flooding during the Middle Aptian in the Santos Basin is still discussed. Keywords: South Atlantic Ocean, Early Cretaceous, Rift, Palaeogeography, Geodynamic

Chaboureau, A. C.; Guillocheau, F.; Robin, C.; Rohais, S.; Moulin, M.; Aslanian, D.

2012-04-01

176

Deformation of the Western Caribbean: Insights from Block and Geodynamic Models of Geodetic, Seismic and Geologic Data  

NASA Astrophysics Data System (ADS)

Cocos - Caribbean convergence along the Middle America Trench, including subduction of the Cocos Ridge and seamount domain, and Nazca - Caribbean oblique convergence along the South Panama Deformed Belt have resulted in complex plate boundary zone deformation since Miocene - Pliocene time. Plate boundary evolution and upper plate deformation in the western Caribbean is well studied and indicates, 1) Quaternary migration of the volcanic arc toward the back-arc northwest of the Cocos Ridge; 2) Pleistocene to present northwestward motion of the Central American Fore Arc (CAFA); 3) Quaternary to present deformation within the Central Costa Rica Deformed Belt; 4) Miocene-Pliocene cessation of volcanism and uplift of the Cordillera de Talamanca inboard the ridge; 5) Quaternary to present shortening across the fore-arc Fila Costea fold and thrust belt and back-arc North Panama Deformed Belt (NPDB); 6) Quaternary to present outer fore-arc uplift above the seamount domain (Nicoya Peninsula), and above (Osa Peninsula) and flanking (Burica Peninsula) the ridge; and 7) Quaternary to present faulting along the Sona-Azuero and Canal Discontinuity fault systems. We investigate the dynamic effects of Cocos and Nazca convergence along the entire Central American margin, and the implications on western Caribbean plate boundary evolution with a new GPS derived three-dimensional (horizontal and vertical) velocity field and kinematic block and geodynamic models. Specifically, we test the hypotheses that the Cocos Ridge is the main driver for upper plate deformation and that there is an independent Panama block. Our model results provide new Euler vectors for the CAFA and Panama block, rates of relative plate and block motions in the region, and constraints on interseismic coupling along the Middle America Trench and other major block bounding fault systems. These results are compared to existing geophysical and geologic data for the region and add insights into the rates of deformation across the regions listed above. We demonstrate that Cocos Ridge collision drives northwest-directed motion of the CAFA and the northeast-directed motion of the Panama region. The Panama region is driven into the Caribbean across the NPDB and into the Choco and North Andes blocks of northwestern South America, which are also converging with the Panama region, pushing it toward the west-northwest. Motion of the Panama region can be fit by an Euler vector suggesting that it is a rigid block, however, this is not in agreement with Quaternary faulting across the isthmus.

La Femina, P. C.; Geirsson, H.; Kobayashi, D.

2012-12-01

177

R/V Sonne Cruise SO193: New Insights Into the Geodynamic History of the Manihiki Plateau, SW-Pacific  

NASA Astrophysics Data System (ADS)

The Manihiki Plateau represents a Cretaceous Large Igneous Province (LIP) in the SW-Pacific. In May/June 2007, R/V Sonne cruise SO193 conducted ~4,700 nm of bathymetric mapping in key areas of the Manihiki Plateau region, and the first hard rock sampling of all major geomorphological units of the plateau as well as of seamounts on adjacent oceanic crust. The research project SO193 MANIHIKI aims to reconstruct the origin as well as spatial and temporal evolution of the Manihiki Plateau and to characterize the relationship between Manihiki and the other LIPs in the western Pacific. SO193 recovered magmatic or sedimentary rocks from 77 locations in the Manihiki Plateau region. Olivine-bearing sheet and pillow lavas dominate, but various types of volcaniclastic rocks are also common, some of them indicating subaerial or shallow water volcanic activity. Minor lithologies are, among others, picritic lavas, serpentinites, evolved lavas, and subvolcanic intrusives. Unexpectedly, the upper, directly accessible portions in some areas of the Manihiki Plateau (e.g., Suvorov Trough, North Plateau, the NE corner of the High Plateau) appear to mainly consist of solidified, indurated or lithified sediments which suggests secondary heating and/or intense tectonic movements. In contrast to the previously surveyed Hikurangi LIP east of New Zealand, guyot-type seamounts only exist in a few restricted areas of the Manihiki Plateau. The recent depth of their erosional platforms vary unsystematically between 1,600 m and 2,500 m below sea level (b.s.l.), implying different ages of these volcanoes or non-uniform subsidence rates. On the other hand, uneroded seamounts rising up to ~600 m b.s.l. occur on and close to the Manihiki Plateau. Pillow lavas dredged at a ~600 m high ridge on the High Plateau, which is believed to have formed under subaerial conditions, also indicate late-stage volcanic activity, after subsidence of the High Plateau. Taken together, the preliminary results of mapping and sampling of SO193 suggest a complex geodynamic history for the Manihiki Plateau, including long-term or repeated volcanism and intense tectonic movements (see also Coffin et al. abstract).

Werner, R.; Hauff, F.; Hoernle, K.; Coffin, M. F.; Scientific Party, S.

2007-12-01

178

Towards an Ontology for the Global Geodynamics Project: Automated Extraction of Resource Descriptions from an XML-Based Data Model  

NASA Astrophysics Data System (ADS)

Using the Earth Science Markup Language (ESML), an XML-based data model for the Global Geodynamics Project (GGP) was recently introduced [Lumb & Aldridge, Proc. HPCS 2005, Kotsireas & Stacey, eds., IEEE, 2005, 216-222]. This data model possesses several key attributes -i.e., it: makes use of XML schema; supports semi-structured ASCII format files; includes Earth Science affinities; and is on track for compliance with emerging Grid computing standards (e.g., the Global Grid Forum's Data Format Description Language, DFDL). Favorable attributes notwithstanding, metadata (i.e., data about data) was identified [Lumb & Aldridge, 2005] as a key challenge for progress in enabling the GGP for Grid computing. Even in projects of small-to-medium scale like the GGP, the manual introduction of metadata has the potential to be the rate-determining metric for progress. Fortunately, an automated approach for metadata introduction has recently emerged. Based on Gleaning Resource Descriptions from Dialects of Languages (GRDDL, http://www.w3.org/2004/01/rdxh/spec), this bottom-up approach allows for the extraction of Resource Description Format (RDF) representations from the XML-based data model (i.e., the ESML representation of GGP data) subject to rules of transformation articulated via eXtensible Stylesheet Language Transformations (XSLT). In addition to introducing relationships into the GGP data model, and thereby addressing the metadata requirement, the syntax and semantics of RDF comprise a requisite for a GGP ontology - i.e., ``the common words and concepts (the meaning) used to describe and represent an area of knowledge'' [Daconta et al., The Semantic Web, Wiley, 2003]. After briefly reviewing the XML-based model for the GGP, attention focuses on the automated extraction of an RDF representation via GRDDL with XSLT-delineated templates. This bottom-up approach, in tandem with a top-down approach based on the Protege integrated development environment for ontologies (http://protege.stanford.edu/), allows for initial scoping of an ontology for the GGP. Such ontological approaches are key to enabling the use of formerly specific-purpose GGP data into broader systems and frameworks such as those demanded by current challenges in tsunami research following the devastating 26 December 2004 Sumatra-Andaman event.

Lumb, L. I.; Aldridge, K. D.

2005-12-01

179

Contributions of Fe-K subalkaline granites for the geodynamic evolution of the Iberian Massif (Northern Portugal)  

NASA Astrophysics Data System (ADS)

In the Iberian Massif large volumes of granitic rocks were emplaced during the Variscan orogeny, mainly during the last ductile deformation phase D3. After that, an extensional tectonic regime controls the emplacement of several Fe-K subalkaline post-D3 plutons. Geochemical and isotopic results of post-D3 biotite granites in northern Portugal (Peneda-Gers, Vila Pouca de Aguiar, Mono-Porrio and guas Frias plutons) are presented and their contributions to the geodynamic evolution of the Iberian Variscides. They are porphyritic to coarse-medium grained biotite granites with potassium feldspar megacrysts, with rare mafic microgranular enclaves and some are associated to minor bodies of intermediate rocks and/or two mica granites. Accessory minerals include zircon, apatite, allanite, xenotime, ilmenite and sphene. Amphibole is present only in the Peneda-Gers and Mono-Porrio plutons. Emplacement ages based on U-Pb zircon analyses indicate a value of 290-299 Ma. They are meta- to peraluminous granitoids, having evolved chemical compositions, with high SiO2. Isotopic studies reveals initial 87Sr/86Sr ratios of 0.7033 to 0.7079 and ?Nd of -1.5 to -2.6 while rare hectometric intermediate rock bodies outcrop in the Mono-Porrio shows initial 87Sr/86Sr ratios of 0.7054 to 0.7061 and ?Ndi of 0.4 to -0.7. The isotopic composition of these post-D3 biotite granites is clearly less evolved than that of the synorogenic granites in the region, indicating that the mantle sources were distinct, and shows an important change in magma composition associated to the extensional regime. An origin by mantle input followed by mantle-crust interaction is proposed, implying the contribution of a less enriched mantle component than that involved in the genesis of synorogenic granites in northern Portugal (hybrid Mg-K subalkaline granites and calc-alkaline to aluminopotassic granites) This study permits to envisage that the extensional tectonics triggered the ascension of liquids from a more depleted mantle source implying an input of juvenile magma with mixing of crustal magmas, probably derivate from metaigneous sources, in lower crust, to produce hybrid granites. This also indicates an accretion process with a crustal growth episode.

Simes, P. P.; Martins, H. C. B.; Dias, G.

2012-04-01

180

Chemical geodynamics of continental subduction-zone metamorphism: Insights from studies of the Chinese Continental Scientific Drilling (CCSD) core samples  

NASA Astrophysics Data System (ADS)

The Dabie-Sulu orogenic belt of east-central China has long been a type location for the study of geodynamic processes associated with ultrahigh-pressure (UHP) tectonics. Much of our understanding of the world's most enigmatic processes in continental deep-subduction zones has been deduced from various records in this belt. By taking advantage of having depth profiles from core samples of the Chinese Continental Scientific Drilling (CCSD) project in the Sulu orogen, a series of combined studies were carried out for UHP metamorphic rocks from the main hole (MH) at continuous depths of 100 to 5000 m. The results provide new insights into the chemical geodynamics of continental subduction-zone metamorphism, especially on the issues that are not able to be resolved from the surface outcrops. Available results from our geochemical studies of CCSD-MH core samples can be outlined as follows. (1) An O isotope profile of 100 to 5000 m is established for the UHP metamorphic minerals, with finding of 18O depletion as deep as 3300 m. Along with areal 18O depletion of over 30,000 km 2 along the Dabie-Sulu orogenic belt, three-dimensional 18O depletion of over 100,000 km 3 occurs along the northern margin of the South China Block. (2) Changes in mineral O isotope, H isotope and water content occur in eclogite-gneiss transitions, concordant with petrographic changes. The contact between different lithologies is thus the most favorable place for fluid action; fluid for retrogression of the eclogites away from the eclogite-gneiss boundary was derived from the decompression exsolution. For the eclogites adjacent to gneiss, in contrast, the retrograde metamorphism was principally caused by aqueous fluid from the gneiss that is relatively rich in water. Inspection of the relationship between the distance, petrography and ?18O values of adjacent samples shows O isotope heterogeneities between the different and same lithologies on scales of 20 to 50 cm, corresponding to the maximum scales of fluid mobility during the continental collision. (3) Studies of major and trace elements in the two continuous core segments indicate high mobility of LILE and LREE but immobility of HFSE and HREE. Some eclogites have andesitic compositions with high SiO 2, alkalis, LREE and LILE but low CaO, MgO and FeO contents. These features likely result from chemical exchange with gneisses, possibly due to the metasomatism of felsic melt produced by partial melting of the associated gneisses during the exhumation. On the other hand, some eclogites appear to have geochemical affinity to refractory rocks formed by melt extraction as evidence by strong LREE and LILE depletion and the absence of hydrous minerals. These results provide evidence for melt-induced element mobility in the UHP metamorphic rocks, and thus the possible presence of supercritical fluid during exhumation. In particular, large variations in the abundance of such elements as SiO 2, LREE and LILE occur at the contact between eclogite and gneiss. This indicates their mobility between different slab components, although it only occurs on small scales and is thus limited in local open-systems. (4) Despite the widespread retrogression, retrograde fluid was internally buffered in stable isotope compositions, and the retrograde fluid was of deuteric origin and thus was derived from the decompression exsolution of structural hydroxyl and molecular water in nominally anhydrous minerals. (5) A combined study of petrography and geochronology reveals the episode of HP eclogite-facies recrystallization at 216 3 Ma, with timescale of 1.9 to 9.3 Myr or less. Collectively, the Dabie-Sulu UHP terrenes underwent the protracted exhumation (2-3 mm/yr) in the HP-UHP regime. (6) Zircon U-Pb ages and Hf isotopes indicate that mid-Neoproterozoic protoliths of bimodal UHP metaigneous rocks formed during supercontinental rifting along preexisting arc-continent collision orogen, corresponding to dual bimodal magmatism in response to the attempted breakup of the supercontinent Rodinia at about 780 Ma. The first type of bim

Zheng, Yong-Fei; Chen, Ren-Xu; Zhao, Zi-Fu

2009-09-01

181

Geodynamics: Christmas recycling  

NASA Astrophysics Data System (ADS)

The mechanisms for forming the abundant volcanic islands on ocean floors are debated. The geochemical signature of volcanic rocks from the northeast Indian Ocean suggests that seamounts there formed from melting recycled ancient continental rocks.

Gibson, Sally A.

2011-12-01

182

Archaean associations of volcanics, granulites and eclogites of the Belomorian province, Fennoscandian Shield and its geodynamic interpretation  

NASA Astrophysics Data System (ADS)

An assembly of igneous (TTG-granitoids and S-type leucogranites and calc-alkaline-, tholeiite-, kometiite-, boninite- and adakite-series metavolcanics) and metamorphic (eclogite-, moderate-pressure (MP) granulite- and MP amphibolite-facies rocks) complexes, strikingly complete for Archaean structures, is preserved in the Belomorian province of the Fennoscandian Shield. At least four Meso-Neoarchaean different-aged (2.88-2.82; 2.81-2.78; ca. 2.75 and 2.735-2.72 Ga) calc-alkaline and adakitic subduction-type volcanics were identified as part of greenstone belts in the Belomorian province (Slabunov, 2008). 2.88-2.82 and ca. 2.78 Ga fore-arc type graywacke units were identified in this province too (Bibikova et al., 2001; Mil'kevich et al., 2007). Ca.2.7 Ga volcanics were generated in extension structures which arose upon the collapse of an orogen. The occurrence of basalt-komatiite complexes, formed in most greenstone belts in oceanic plateau settings under the influence of mantle plumes, shows the abundance of these rocks in subducting oceanic slabs. Multiple (2.82-2.79; 2.78-2.76; 2.73-2.72; 2.69-2.64 Ga) granulite-facies moderate-pressure metamorphic events were identified in the Belomorian province (Volodichev, 1990; Slabunov et al., 2006). The earliest (2.82-2.79 Ga) event is presumably associated with accretionary processes upon the formation of an old continental crust block. Two other events (2.78-2.76; 2.73-2.72 Ga) are understood as metamorphic processes in suprasubduction setting. Late locally active metamorphism is attributed to the emplacement of mafic intrusions upon orogen collapse. Three groups of crustal eclogites with different age were identified in the Belomorian province: Mesoarchaean (2.88-2.86 and 2.82-2.80 Ga) eclogites formed from MORB and oceanic plateau type basalts and oceanic high-Mg rocks (Mints et al., 2011; Shchipansky at al., 2012); Neoarchaean (2.72 Ga) eclogites formed from MORB and oceanic plateau type basalts. The formation of eclogites is attributed to processes in a subducting slab. Correlation of the above complexes has revealed four alternating subduction systems: 2.88-2.82 Ga which comprises both suprasubduction (island-arc volcanics, graywackes) complexes and those from a subduction slab (eclogites), 2.81-2.78 Ga - island-arc volcanics, graywackes, granulites and eclogites; 2.75 Ga - island-arc volcanics only; 2.73-2.72 Ga - island-arc volcanics, granulites and eclogites. The duration of functioning of Meso-Neoarchaean subduction systems varies from 60 (or probably 30) to 15 Ma, which is consistent with the results of the numerical modelling (van Hunen, 2001) of subduction at mantle temperatures 125-150 degrees higher than the present temperature. This is a contribution to RFBR Project 11-05-00168 a References: Bibikova, E.V., Glebovitskii, V.A., Claesson, S. et al., 2001. Geochemistry International, 39(1) Mil'kevich, R.I., Myskova, T.A., Glebovitsky, V.A. et al. 2007. Geochemistry International, 45 Mints, M.V., Belousova, E.A., Konilov, A.N. et al., 2011. Geology, 38 Shchipansky, A.A., Khodorevskaya, L.I., Konilov, A.N., Slabunov, A.I., 2012. Russian Geology and Geophysics 53 Slabunov, A.I., Lobach-Zhuchenko, S.B., Bibikova, E.V. et al., 2006. European Lithosphere Dynamics, Memoir 32 Slabunov, A.I., 2008. Geology and geodynamics of Archean mobile belts (example from the Belomorian province of the Fennoscandian Shield van Hunen, J., 2001. Shallow and buoyant lithospheric subduction: couses and implications from thrmo-chemical numerical modelling. Theses PhD Volodichev, O.I., 1990. The Belomorian complex of Karelia: geology and petrology

Slabunov, Alexander

2013-04-01

183

Pre-collisional geodynamic context of the southern margin of the Pan-African fold belt in Cameroon  

NASA Astrophysics Data System (ADS)

We reassess the geodynamic context close to the Congo craton during the pre-collisional period of the Pan-African orogeny from whole-rock major and trace element compositions and isotopic data obtained in the westward extension of the Yaounde series (Boumnyebel area, Cameroon). The series consists of metasediments (micaschists, minor calc-silicate rocks and marbles) and meta-igneous rocks (hornblende gneisses, amphibolites, metagabbros, pyroxenites and talcschists) recrystallized under high-pressure conditions. Chemically, the micaschists correspond to shales and greywackes similar to the Yaounde high-grade gneisses. 87Sr/86Sr initial ratios (0.7084-0.7134), moderately negative ?Nd(620 Ma) values (-5.75 to -7.81), Nd model ages (1.66 < TDM < 1.74 Ga) and radiometric ages point to the conclusion that the Yaounde basin was filled with siliciclastic sediments derived from both reworked older continental crust (Palaeoproterozoic to Archaean in age) and Neoproterozoic juvenile volcanogenic material. This occurred in the same time span (625-1100 Ma) as the deposition of the Lower Dja, Yokadouma, Nola and Mintom series (Tonian-Cryogenian). Dolomitic marble associated with mafic/ultramafic rocks and characterized by high Cr (854-1371 ppm) and Ni (517-875 ppm) contents, are considered to result from chemical precipitation in relation with submarine magmatic activity. Talcschists (orthopyroxenitic to harzburgitic in composition) show primitive-mantle-normalized multi-element patterns with significant negative Nb-Ta anomalies, and slopes similar to that of average metasomatically altered lithospheric mantle. These rocks could be mantle slices involved in the collision tectonics. Amphibolites show the compositions of island-arc basalts with systematic negative Nb-Ta anomalies, 87Sr/86Sr initial ratios mostly <0.7047 and positive ?Nd(620 Ma) values (+1.41 to +6.58). They are considered to be the expression of incipient oceanisation to the north of the Congo craton during the early Neoproterozoic. Hornblende gneisses show andesitic compositions, with high 87Sr/86Sr initial ratios (0.7105 and 0.7125) and low ?Nd(620) values (-14.0 and -20.7) suggesting that their genesis involved juvenile and recycled older crustal materials. Syn-metamorphic metagabbro (Mamb) and metadiorite (Yaounde) intrusions show negative Nb-Ta negative anomalies but enrichment in light rare-earth and large-ion lithophile elements, suggesting a metasomatized mantle source. Overall, meta-igneous rocks seem to be representative of distinct magmatic events that accompanied the evolution of the Yaounde sedimentary basin, from opening and oceanisation to convergence and closure in relation with the collisional process. These data suggest that the Yaounde basin should not be considered as a back-arc basin, but more likely represents the expression of extensional processes to the north of the Congo craton, which led to rifting, fragmentation and limited oceanisation. In this view, the Adamawa-Yade block may represent a micro-continent detached from the Congo craton during the early Neoproterozoic.

Nkoumbou, C.; Barbey, P.; Yonta-Ngoun, C.; Paquette, J. L.; Villiras, F.

2014-11-01

184

On information-provided monitoring of geodynamic processes in the Kuznetsk Coal Basin in the conditions of highly intensive sub-soil usage  

SciTech Connect

It is shown that formation of underground hollows of the Kuznetsk Coal Basin (Kuzbass), induced by opencut and underground mining has reached an intensity of 1.3-1.5 million m{sup 3}/day. In the conditions of high concentration of mines and open-cuts in small areas, a regional monitoring network is required in view of a generated geomechanical space, hazardous in geodynamic manifestations. A developed information support of this network is presented, including information models of a geological environment and database obtained from instrumental observations on geomechanical processes. The equations of connection between structural and strength characteristics of rocks, their metamorphization grade and occurrence depth are given for five geological-tectonic zones of the Kuzbass as a way of prediction of their properties.

Oparin, V.N.; Potapov, V.P.; Tanaino, A.S. [Russian Academy of Science, Novosibirsk (Russian Federation). Inst. of Mining

2006-09-15

185

Evidence for Late Devonian vertical movements and extensional deformation in northern Africa and Arabia: Integration in the geodynamics of the Devonian world  

NASA Astrophysics Data System (ADS)

The Upper Paleozoic geodynamic evolution is discussed at the scale of a wide part of Gondwana from North Africa to Arabia. With the aim of giving an integrated tectonic scenario for the study domain, we revisit six key areas, namely, the Anti-Atlas Belt (Morocco), the Bechar Basin (west Algeria), the Hassi R'Mel High (central Algeria), the Talemezane Arch (south Tunisia), the Western Desert (Egypt), and, finally, the High Zagros Belt (Iran). Below the so-called "Hercynian unconformity," which is in reality a highly composite discontinuity, surface and subsurface data display a well-known arch-and-basin geometry, with basement highs and intervening Paleozoic basins. We show that this major feature results mainly from a Late Devonian event and can no longer be interpreted as a far effect of the Variscan Orogeny. This event is characterized by a more or less diffuse extensional deformation and accompanied either by subsidence, in the western part of the system, or by an important uplift of probable thermal origin followed by erosion and peneplanation. By the end of the Devonian, the whole region suffered a general subsidence governed by the progressive cooling of the lithosphere. Such a primary configuration is preserved in Arabia with typical sag geometry of the Carboniferous and Permian deposits but strongly disturbed elsewhere by the conjugated effects of the Variscan Orogeny during the Carboniferous and/or by subsequent uplifts linked to the central Atlantic and Neo-Tethys rifting episodes. In conclusion, we try to integrate this new understanding in the geodynamics of the Late Devonian, which at world scale is characterized by the onset of the Variscan Orogeny on the one hand and by magmatism, rifting, and basement uplift on the other hand.

Frizon de Lamotte, Dominique; Tavakoli-Shirazi, Saeid; Leturmy, Pascale; Averbuch, Olivier; Mouchot, Nicolas; Raulin, Camille; Leparmentier, FranOis; Blanpied, Christian; Ringenbach, Jean-Claude

2013-03-01

186

Rheological and geodynamic controls on the mechanisms of subduction, HP/UHP exhumation and PT conditions within crustal rocks during continental collision: insights from numerical models  

NASA Astrophysics Data System (ADS)

Mechanisms of continental convergence are so versatile that it is impossible to elucidate them from conventional set of observations. Additional discriminatory data are needed such as those derived from petrology data, since burial/exhumation dynamics inferred from metamorphic P-T-t paths potentially provides independent constraints on the collision mechanism. While subduction of crustal rocks is increasingly accepted as common phenomenon inherent to convergent processes involving continental plates and micro-continents, the conditions of their formation and mechanisms of their exhumation in the form of high- and ultra-high-pressure (HP/UHP) units remain a subject of controversy. In particular, deep burial and exhumation of continental crust occur in various settings, including subduction of micro-continental terrains carried down with the subducting oceanic lithosphere and transition between the oceanic and continental subduction. Geodynamic inferences from P-T data can be made only after providing a consistent approach to decryption of both pressure and temperature in terms of depth or at least in terms of characteristic geodynamic conditions. Thermo-mechanical thermodynamically coupled numerical models of continental collision provide some elements of solution to this problem through testing various geodynamic scenarios within relatively unconstrained framework which allows for account of non-lithostatic pressure variations and for deviations of temperature from commonly inferred thermal models. We here explore several possible scenarios of subduction and exhumation of continental crust, and their relation to PT conditions and mechanisms of HP/UHP exhumation inferred from conceptual and thermo-mechanical numerical models accounting for thermo-rheological complexity and diversity of the continental lithosphere. Numerical experiments suggest that in most cases both exhumation and continental subduction are transient processes, so that long-lasting (> 10-15 Myr) continental subduction occurs in very specific cases of cold strong lithospheres while in general this process takes less than 5 Myr. During the active subduction phase (simple shear accommodation of convergence) we do not detect significant deviations (+-20%) of total pressure in the subduction channel from lithostatic values , that can be rather lower than the lithostatic pressure, while intra-channel temperatures vary in quite large limits. Hence, large volumes of HP/UHP metamorphic rocks generated and brought to the surface during subduction phase would not record significant deviations from the lithostatic pressure conditions. At the same time, strong non-lithostatic pressures (extensional and compressional) are predicted for some internal parts of the colliding plates that, however, are not prone to yield "extractable" metamorphic material. The experiments also show that high non-lithostatic pressures develop in the former subduction channel at its lock-up , during and after the transition from subduction to pure shear collision or folding, while the metamorphic material generated at this stage appears to be blocked at depth and does not return to the surface (at least if the channel is not unlocked due some external conditions). We suggest that most continental orogenic belts could have started their formation from continental subduction. This process has been generally limited in time while pressures recorded in the HP and UHP material generated at this stage can be largely treated in terms of the lithostatic approximation. In case of subduction of continental terrains embedded in the oceanic lithosphere, it can be shown that their exhumation, resulting in formation of metaphoric belts and domes, may initiate series of slab roll-back and exhumation events associated with remarkably complex and spatially variable P-T-t paths.

Burov, Evgueni

2014-05-01

187

A late Tortonian paleotectonic restoration of the Gibraltar Arc System (GAS) based on the restoration of block rotations. Consequences on the GAS geodynamic evolution  

NASA Astrophysics Data System (ADS)

The Gibraltar Arc System (GAS) closes the Alpine-Mediterranean orogenic system to the west and includes the Betic-Rif orogenic belt, the Alboran and Argelian-Balearic basins and the accretionary prism present in the Cadiz Gulf. Previous investigations on this orogenic system, both onshore and offshore have permit to establish the first order milestones of its Miocene to Recent geodynamic evolution. In most of the models of the geodynamic evolution of the GAS, the external boundary of the Betic-Rif orogenic wedge, initially N-S directed, sweeps from east to west the Gibraltar Arc area, acquiring his arcuate geometry during this westward movement. Nevertheless, most of these models are generally at scale equivalent to 1:10.000.000 or even smaller, and frequently based on 2D schematic cross-sections from which a model for the whole arc is deduced. This fact under evaluates not only the mass movements oblique to the selected cross-section plane, but also the diachronism of the deformation, in turn expected in a so closed arc. In this communication, we want to zoom on the Gibraltar Arc area, to draw a detailed Late Tortonian paleotectonic restoration and to highlight the consequence of this reconstruction on the final evolution of the westernmost Mediterranean. Our approach is based on: 1) the identification and characterization of structural domains of the Gibraltar Arc orogenic system and the transfer fault zones that separate them, 2) an accurate dating of the superposed events of deformations for each one of these domains, 3) the restoration of vertical axis-rotations of some of these structural domains (evidenced by paleomagnetic data previously published), and 4) the quantification of Miocene shortening in the External zones. This exercise makes us to put all together the results of twenty years of research of our teams on this natural case-study, mainly with field and marine geology techniques, and to test it through the revision of an extensive bibliography. It will be shown that the proposed reconstruction permit to simplify most the kinematics models proposed at the moment. Although some key points are still problematic, this paleotectonic restoration may solve more problems than arise them. Acknowledgements: This study was supported by grants RNM-3713, RNM-215, CGL2008-03474 E/BTE, CTM2009-07715/MAR and CGL2009-11384.

Crespo-Blanc, Ana; Comas, Menchu; Balany, Juan Carlos

2014-05-01

188

The Arkot Da? Mlange in Ara area, central Turkey: Evidence of its origin within the geodynamic evolution of the Intra-Pontide suture zone  

NASA Astrophysics Data System (ADS)

In northern Turkey, the Intra-Pontide suture zone is represented by an east-west trending belt of deformed and/or metamorphic units located at the boundary between the Istanbul-Zonguldak terrane to the north and the Sakarya terrane to the south. These units can be regarded as issued from the Intra-Pontide domain, whose geodynamic history is still a matter of debate. Along the Akpinar-Ara-Bayramoren geotraverse, located in central Turkey, an ophiolite-bearing mlange known as the Arkot Da? Mlange, is well-exposed along the Intra-Pontide suture zone. The Arkot Da? Mlange plays a key role in the interpretation of the geodynamic history of the Intra-Pontide domain and can be described as a Late Santonian chaotic sedimentary deposit consisting of an up to 1000-m-thick succession of slide-blocks of different sizes and lithologies enclosed in a sedimentary matrix consisting of shales, coarse-grained arenites, pebbly mudstones and pebbly sandstones. The slide-blocks, from a few meters to hectometers in size, are represented by metamorphic rocks (mainly micaschists and gneisses), by ophiolites (peridotites, gabbros, IAT and BABB basalts and cherts) and by sedimentary rocks (cherts, neritic and pelagic limestone, marly limestone and ophiolite-bearing turbidites). The youngest age among the slide-blocks has been provided by the ophiolite-bearing turbidites where a late Coniacian nannofossil assemblage has been found. The cherts have provided a wide range of ages from the Middle Triassic to Late Cretaceous, whereas the fossils found in the limestone indicate Late Jurassic to Early Cretaceous ages. The matrix of the Arkot Da? Mlange, even if unaffected by metamorphism, shows deformations represented by multiple meters-thick cataclastic shear zones at the boundaries of the mlange slices or inside of them. According to its features, the source area of the Arkot Da? Mlange was most likely a continental and oceanic thrust sheet emplaced in the Late Cretaceous onto a continental margin. The data collected from the different slide-blocks suggest that the Intra-Pontide domain was characterised by an oceanic basin opened at the latest in the Early Jurassic. The opening of the Intra-Pontide oceanic basin was followed by the development of a subduction zone with a subsequent opening of suprasubduction oceanic basin in the Middle Jurassic-Early Cretaceous. The convergence in this suprasubduction oceanic basin started at the Early/Late Cretaceous boundary by an obduction process, whereas its final closure can be regarded as Late Paleocene in age.

Gncoglu, M. Cemal; Marroni, Michele; Pandolfi, Luca; Ellero, Alessandro; Ottria, Giuseppe; Catanzariti, Rita; Tekin, U. Kagan; Sayit, Kaan

2014-05-01

189

Geodynamic interpretation of the 40Ar/39Ar dating of ophiolitic and arc-related mafics and metamafics of the northern part of the Anadyr-Koryak region  

USGS Publications Warehouse

Isotope datings of amphibole-bearing mafics and metamafics in the northern part of the Anadyr-Koryak region allow clarification of the time of magmatic and metamorphic processes, which are synchronous with certain stages of the geodynamic development of the northwest segment of the Pacific mobile belt in the Phanerozoic. To define the 40Ar/39Ar age of amphiboles, eight samples of amphibole gabbroids and metamafics were selected during field work from five massifs representing ophiolites and mafic plutons of the island arc. Rocks from terranes of three foldbelts: 1) Pekulnei (Chukotka region), 2) Ust-Belaya (West Koryak region), and 3) the Tamvatnei and El'gevayam subterranes of the Mainits terrane (Koryak-Kamchatka region), were studied. The isotope investigations enabled us to divide the studied amphiboles into two groups varying in rock petrographic features. The first was represented by gabbroids of the Svetlorechensk massif of the Pekulnei Range and by ophiolites of the Tamvatnei Mts.; their magmatic amphiboles show the distribution of argon isotopes in the form of clearly distinguished plateau with an age ranging within 120-129 Ma. The second group includes metamorphic amphiboles of metagabbroids and apogabbro amphibolites of the Ust-Belaya Mts., Pekulnei and Kenkeren ranges (El'gevayam subterranes). Their age spectra show loss of argon and do not provide well defined plateaus the datings obtained for them are interpreted as minimum ages. Dates of amphiboles from the metagabbro of the upper tectonic plate of the Ust-Belaya allochthon points to metamorphism in the suprasubduction environment in the fragment of Late Neoproterozoic oceanic lithosphere in Middle-Late Devonian time, long before the Uda-Murgal island arc system was formed. The amphibolite metamorphism in the dunite-clinopyroxenite-metagabbro Pekulnei sequence was dated to occur at the Permian-Triassic boundary. The age of amphiboles from gabbrodiorites of the Kenkeren Range was dated to be Early Jurassic that confirmed their assignment to the El'gevayam volcanic-plutonic assemblage. These data are consistent with geological concepts and make more precise the available age dates. Neocomian-Aptian 40Ar/39Ar age of amphibolites from the Pekulnei and Tamvatnei gabbroids make evident that mafics of these terranes (varying in geodynamic formation settings and in petrogenesis) were generated in later stages of the development of the West Pekulnei and Mainits-Algan Middle-Late Jurassic-Early Cretaceous island arc systems, presumably due to breakup of island arcs in the Neocomian. ?? 2011 Pleiades Publishing, Ltd.

Palandzhyan, S.A.; Layer, P.W.; Patton, W.W., Jr.; Khanchuk, A.I.

2011-01-01

190

A new numerical method to calculate inhomogeneous and time-dependent large deformation of two-dimensional geodynamic flows with application to diapirism  

NASA Astrophysics Data System (ADS)

A key to understand many geodynamic processes is studying the associated large deformation fields. Finite deformation can be measured in the field by using geological strain markers giving the logarithmic strain f = log 10(R), where R is the ellipticity of the strain ellipse. It has been challenging to accurately quantify finite deformation of geodynamic models for inhomogeneous and time-dependent large deformation cases. We present a new formulation invoking a 2-D marker-in-cell approach. Mathematically, one can describe finite deformation by a coordinate transformation to a Lagrangian reference frame. For a known velocity field the deformation gradient tensor, F, can be calculated by integrating the differential equation DtFij = LikFkj, where L is the velocity gradient tensor and Dt the Lagrangian derivative. The tensor F contains all information about the minor and major semi-half axes and orientation of the strain ellipse and the rotation. To integrate the equation centrally in time and space along a particle's path, we use the numerical 2-D finite difference code FDCON in combination with a marker-in-cell approach. For a sufficiently high marker density we can accurately calculate F for any 2-D inhomogeneous and time-dependent creeping flow at any point for a deformation f up to 4. Comparison between the analytical and numerical solution for the finite deformation within a Poiseuille-Couette flow shows an error of less than 2 per cent for a deformation up to f = 1.7. Moreover, we determine the finite deformation and strain partitioning within Rayleigh-Taylor instabilities (RTIs) of different viscosity and layer thickness ratios. These models provide a finite strain complement to the RTI benchmark of van Keken et al. Large finite deformation of up to f = 4 accumulates in RTIs within the stem and near the compositional boundaries. Distinction between different stages of diapirism shows a strong correlation between a maximum occurring deformation of f = 1, 3 and 4, and the early, intermediate and late stages of diapirism, respectively. Furthermore, we find that the overall strain of a RTI is concentrated in the less viscous regions. Thus, spatial distributions and magnitudes of finite deformation may be used to identify stages and viscosity ratios of natural cases.

Fuchs, L.; Schmeling, H.

2013-08-01

191

Isostatic gravity anomaly, lithospheric scale density structure of the northern Tibetan plateau and geodynamic causes for potassic lava eruption in Neogene  

NASA Astrophysics Data System (ADS)

This paper will help to further constrain geodynamic models for the evolution of northern Tibet through two techniques that employ Bouguer gravity anomaly data: the first is isostatic correction of Bouguer gravity anomalies and the second is 2-D density modeling along a profile at 88.5E from 30N to 37N within the Tibetan Plateau. Areas dominated by volcanic rocks exhibit ultra-low Bouguer gravity anomalies and low isostatic residual anomalies. The 2-D density structure beneath Profile 88.5E shows a giant upward dome distributed body of low density in the middle-lower crust and mantle beneath the high-to-ultra-potassic areas, suggesting that the original middle and lower crusts were reformed and replaced extensively in the area. Based on existing regional geology and tectonics, geochemical data from magmatic rocks, and geophysical information, this paper proposes that the sustained northward subduction of the Indian plate has resulted in breaking off of the frontal margin of the Asian lithospheric mantle. Subsequently, the original lithosphere was reactivated by thermal-tectonic changes, high-to-ultra potassic volcanoes erupted extensively in the northern Tibetan Plateau during Neogene, and the plateau experienced rapid NE-trending uplift.

He, Rizheng; Liu, Guocheng; Golos, Eva; Gao, Rui; Zheng, Hongwei

2014-07-01

192

Palaeoproterozoic (1.83 Ga) zircons in a Bajocian (169 Ma) granite within a Middle Jurassic ophiolite (Rubiku, central Albania): a challenge for geodynamic models  

NASA Astrophysics Data System (ADS)

Two distinct zircon populations, 1,827 17 and 169 2 Ma in age, have been found in the Rubiku granite dyke in the Middle Jurassic Mirdita ophiolite in central Albania. The old inherited zircons represent a homogeneous population formed during a discrete Palaeoproterozoic, likely magmatic, zircon crystallization event. These older zircons were likely incorporated, in large part, into the granite magma that crystallized broadly at the time of the ophiolite emplacement (around 169 Ma). The limited data available do not allow for the construction of an unequivocal petrogenetic model, though several palaeotectonic scenarios are discussed as possible settings for the granite formation. The models refer to recent findings of old inherited zircons in rocks at recent mid-ocean ridge settings, but also consider likely contributions of crustal materials to primary basic ophiolitic magmas within supra-subduction settings and subsequent accretion/collision circumstances. The presence of old zircons in much younger rocks within ophiolite successions runs counter to geodynamic models of interaction between the oceanic lithosphere and continental crust, but constraining their genesis would require further systematic studies on these old inherited zircons, both in mafic (if present) and in felsic rocks of the ophiolites.

Kryza, Ryszard; Beqiraj, Arjan

2014-04-01

193

Permian geodynamic setting of Northeast China and adjacent regions: closure of the Paleo-Asian Ocean and subduction of the Paleo-Pacific Plate  

NASA Astrophysics Data System (ADS)

Northeast China and adjacent regions are located in the central East Asian continent and consist tectonically of both the Paleo-Asian and Paleo-Pacific orogens between the Siberian platform and Sino-Korean (North China) block. This paper discusses some hotly-debated issues concerning the Permian geodynamic setting of these regions, based on a comprehensive analysis of available geological, geochemical, paleobiogeographical and paleomagnetic data. Spatial and temporal distribution of ophiolites and associated continental marginal sequences, Permian sedimentary sequences, spatial distribution and geochemistry of Permian magmatic rocks, and the evolution of paleobiogeographical realms imply: (1) that the Permian marine basins in northeast China and adjacent regions include remnants of the Paleo-Asian Ocean in southeastern Inner Mongolia and central Jilin Province, and active continental margins of the Paleo-Pacific Ocean; (2) that the suture between the Siberian and Sino-Korean paleoplates was finally emplaced in the Permian and is located in areas from Suolunshan (Solonker) eastwards through regions north to the Xar Moron river in southeastern Inner Mongolia, and then central Jilin province to the Yanji area; and (3) that the Permian crustal evolution of northeast China and adjacent regions, as well as parts of the Siberian paleoplate, was influenced by subduction of the Paleo-Pacific oceanic plate. Finally, the Permian tectonic framework and paleogeography of northeast China and adjacent regions in central East Asia are discussed briefly, and Early and Late Permian palinspastic reconstruction maps are provided.

Li, J.-Y.

2006-03-01

194

Early Miocene strike-slip tectonics and granite emplacement in the Alboran Domain (Rif Chain, Morocco): significance for the geodynamic evolution of Western Mediterranean  

NASA Astrophysics Data System (ADS)

The Neogene tectonic evolution of the western Mediterranean region is accompanied and outlasted by diffuse magmatism. This study describes the tectonic setting, the petrography and geochemistry of the Early Miocene granitic dyke swarm that occurs in the Oued Amter area, in the core of the Alboran Domain of the Moroccan Rif. The structural setting indicates dyke intrusion assisted and controlled by strike-slip tectonics that operated through conjugate, NW-SE left-lateral and NE-SW right-lateral fault strands. The overall composition of the dykes (the high SiO2 contents (69-77 wt.%), coupled with low concentrations of TiO2, MgO, FeO, CaO), the high 87Sr/86Sr (0.719-0.722) and the low 143Nd/144Nd (ca. 0.5120) values point to a predominantly crustal origin of these magmatic bodies, compatible with a process involving muscovite-(biotite) dehydration melting of fertile metasedimentary sources. The isotopic signature is similar to that of the basement rocks of the Alboran Sea, suggesting for a similar crustal source for the Early Miocene felsic magmatism of the Betic-Rif realm. When framed within the regional setting, these data are used to propose a synthetic geodynamic model for the Early Miocene tectonic and magmatic evolution of the western Mediterranean region.

Rossetti, Federico; Dini, Andrea; Lucci, Federico; Bouybaouenne, Mohamed; Faccenna, Claudio

2013-11-01

195

Kinematic analysis of recent and active faults of the southern Umbria-Marche domain, Northern Apennines, Italy: geological constraints to geodynamic models  

NASA Astrophysics Data System (ADS)

The recent and active deformation that affects the crest zone of the Umbria-Marche belt (Northern Apennines, Italy) displays a remarkable extensional character, outlined by development of normal fault sets that overprint pre-existing folds and thrusts of Late Miocene-Early Pliocene age. The main extensional fault systems often bound intermontane depressions hosting recent, mainly continental, i.e. fluvial or lacustrine deposits, separating the latter from Triassic-Miocene, mainly carbonatic and siliciclastic marine rocks that belong to the Romagna-Umbria-Marche stratigraphic succession. Stratigraphic data indicate that the extensional strain responsible for the development of normal fault-bounded continental basins in the outer zones of the Northern Apennines was active until Middle Pleistocene time. Since Middle Pleistocene time onwards a major geodynamic change has affected the Central Mediterranean region, with local reorganization of the kinematics in the Adria domain and adjacent Apennine belt. A wide literature illustrates that the overall deformation field of the Central Mediterranean area is presently governed by the relative movements between the Eurasia and Africa plates. The complex interaction of the Africa-Adria and the Anatolian-Aegean-Balkan domains has led the Adria microplate to migrate NW-ward and to collide against Eurasia along the Eastern Southern Alps. As a consequence Adria is presently moving with a general left-lateral displacement with respect to the Apennine mountain belt. The sinistral component of active deformations is also supported by analysis of earthquake focal mechanisms. A comparison between geophysical and geological evidence outlines an apparent discrepancy: most recognized recent and active faults display a remarkable extensional character, as shown by the geometry of continental basin-bounding structutes, whereas geodetic and seismologic evidence indicates the persistency of an active strike-slip, left-lateral dominated strain field. The coexistence of extensional and strike-slip regimes, in principle difficult to achieve, may be explained in the framework of a transtensional deformation model where extensional components, normal to the main NW-directed structural trends, are associated to left-lateral strike-slip movements parallel to the main NW-directed structural trends. Critical for the evaluation of the internal consistency of a deformation model for the brittle upper crustal levels is the definition of the kinematics of active faults. In this study we illustrate the preliminary results of a kinematic analysis carried out along 20, exceptionally well exposed, recent and active fault surfaces cropping out in the southernmost portion of the Umbria-Marche belt adjacent to its termination against the the Latium-Abruzzi domain to the East. The collected data indicate that the investigated faults reflect a kinematically oblique character, and that development of these structures may be explained in the framework of a left-dominated transtensional strain field. More important, the data indicate that fault kinematic analysis is an effective tool in testing geodynamic models for actively deforming crustal domains.

Pasqui, Valeria; Viti, Marcello; Mantovani, Enzo

2013-04-01

196

The Surface of Venus and Implications for its Geological and Geodynamical Evolution: The View Before Venus Express and Outstanding Questions for the Future  

NASA Astrophysics Data System (ADS)

Prior to the Venera 15/16 and the Magellan missions to Venus, a wide range of ideas existed concerning the nature of the surface of Venus, the geological processes currently operating there, their link to interior processes, the implied geological and geodynamical history of the planet, and how all this compared with the nature and history of other terrestrial planetary bodies. The history of exploration of the surface of Venus represents the acquisition of data with increasing spatial and areal coverage, culminating in the near-global high-resolution image, altimetry, physical property and gravity data obtained by the Magellan mission. Among the most fundamental findings of the global Magellan image data are: 1) that volcanism and tectonism represent the most abundant geological processes operating on the observed surface, 2) that the styles and abundance of volcanism and tectonism combine attributes of both the Earth (e.g., very heavily tectonically deformed regions such as tessera) and the smaller terrestrial planetary bodies (e.g., vast volcanic plains deformed by wrinkle ridges), 3) that the distribution and nature of impact craters precludes active plate tectonics despite many Earth-like tectonic features (e.g., folded mountain belts), 4) that some features (e.g., coronae) are somewhat unique to Venus and may provide important information on mantle convection and lithospheric evolution processes, 5) that the number of impact craters is very small, indicating that the surface geological record is very young, less than 20% of the history of the planet itself, 6) that 80% of the geological record of Venus is no longer obviously preserved in the surface morphology, but may be preserved in the surface rocks, 7) that the distribution and state of preservation of existing impact craters may be consistent with a range of catastrophic resurfacing models, and 8) that the geological record and sequence of events can be correlated with geophysical data to assess crustal thickness variations and mantle convection patterns. The relationships of major elements of global topography and the sequence of events in the observed geological history (as recorded by major geologic units and structures) suggest that much of the current long-wavelength topography of Venus (tessera highlands and lowlands with regional plains) may have formed prior to emplacement of regional plains and been preserved since that time. These observations may favor evolutionary geodynamic models that are characterized by changes in geological style and rates, and may involve non-linear heat loss mechanisms that could have profound influence on the atmosphere. Although the observed surface of Venus dates from relatively recent planetary history, comparative planetology permits inferences to be made about the major stages in the earlier history of Venus. The evolution of the understanding of the surface from early speculations to present observations and interpretations provides an important context for: 1) establishing the relationships of the surface of Venus to the nature of the atmosphere and its evolution as assessed by Venus Express, 2) the comparison of the geological features and history of Venus relative to the Moon, Mars, Mercury and the Earth, and 3) defining the major outstanding problems and questions to be addressed by future experiments and missions to Venus.

Head, J. W.; Ivanov, M. A.; Basilevsky, A. T.

2008-12-01

197

The lithosphere architecture and geodynamic of the Middle and Lower Yangtze metallogenic belt in eastern China: constraints from integrated geophysical data  

NASA Astrophysics Data System (ADS)

The lithosphere structure and deep processes are keys to understanding mineral system and ore-forming processes. Lithosphere-scale process could create big footprints or signatures which can be observed by geophysics methods. SinoProbe has conducted an integrated deep exploration across middle and lower reaches of Yangtze Metallogenic Belt (YMB) in Eastern China, these included broadband seismic, reflection seismic, wide-angle reflection and magnetotellurics survey. Seismic reflection profiles and MT survey were also performed in Luzong, Tongling and Ningwu ore districts to construct 3D geological model. The resulting geophysical data provides new information which help to better understanding the lithosphere structure, geodynamic, deformation and heat and mass transportation that lead to the formation of the Metallogenic Belt. The major results are: (1) Lower velocity body at the top of upper mantle and a SE dipping high velocity body were imaged by teleseismic tomography beneath YMB; (2) Shear wave splitting results show NE parallel fast-wave polarization direction which parallel with tectonic lineament; (3) The reflection seismic data support the crustal-detachment model, the lower and upper crust was detached during contraction deformation near Tanlu fault and Ningwu volcanic basin; (4) Broadband and reflection seismic confirm the shallow Moho beneath YMB; (5) Strong correlation of lower crust reflectivity with magmatism; (6) The lower crust below Luzong Volcanics shows obvious reflective anisotropy both at the crust-mantle transition and the brittle-ductile transition in the crust. All these features suggest that introcontinental subduction, lithosphere delamination, mantle sources magmatic underplating, and MASH process are responsible for the formation of this Mesozoic metallogenic belt. Acknowledgment: We acknowledge the financial support of SinoProbe by the Ministry of Finance and Ministry of Land and Resources, P. R. China, under Grant sinoprobe-03, and financial support by National Natural Science Foundation of China under Grant 40930418

L, Qingtian; Shi, Danian; Jiang, Guoming; Dong, Shuwen

2014-05-01

198

Cryogenian transpression and granite intrusion along the western margin of Rodinia (Mt. Abu region): Magnetic fabric and geochemical inferences on Neoproterozoic geodynamics of the NW Indian block  

NASA Astrophysics Data System (ADS)

The Mt. Abu batholith in NW India comprises variably deformed porphyritic, granophyric to medium-grained granites and granite gneisses. They are intruded by rhyolitic and mafic dykes; the latter also mark the terminal magmatic phase in this batholith. Granitoids and rhyolitic dykes form a coherent group; petrographic and geochemical characteristics indicate high level intrusion of felsic magma generated from high temperature melting of a lower crustal source. Geochemical similarity, spatial contiguity and coeval emplacement (766 to 763 Ma) of Mt. Abu granitoids with the Neoproterozoic (770 to 750 Ma) Malani Igneous Suite (MIS) underline that both are related to the same thermal event with Mt. Abu batholith as southeastern continuity of the MIS. Anisotropy of magnetic susceptibility data shows parallel fabric orientation in all granitoid types (NE trend, steep SW dip) as well as in a prominent shear zone (Delwara Shear Zone) along the western margin of the batholith with continued deformation during and after the emplacement of granitic magma as inferred from deformation of late-stage mafic dykes. Including coeval shear zones and associated melting in the region NE of Mt. Abu shear-controlled magma generation and ascent along a > 50 km NE trending corridor (Mt. Abu-Sirohi fault zone) is inferred. Structural elements and microstructural criteria (steep foliations, vertical lineations, dextral displacement) indicate a transpressional setting for this Cryogenian event. In regional geodynamic context the Mt. Abu-MIS can be regarded as northeastern continuation of the Neoproterozoic (800-700 Ma) magmatic belt extending from northern Madagascar, the Seychelles into NW India. This magmatic belt, located along the western margin of supercontinent Rodinia, was formed during eastward subduction of the Mozambique Ocean. Transpressional forces responsible for shaping the structural architecture in the Mt. Abu-Sirohi region were most likely induced during closure of the Mozambique Ocean and related translation of the Marwar craton.

de Wall, Helga; Pandit, Manoj K.; Dotzler, Ramona; Just, Jana

2012-07-01

199

GOCE observations and geophysical constraints to better understand the lithosphere and geodynamical processes under the Paran-Etendeka region: preliminary results of PERLA project  

NASA Astrophysics Data System (ADS)

In the light of the considerable progress made by the modern geodetic satellite mission GOCE, one of the challenges of the European Space Agency (ESA) is to improve knowledge of physical properties and geodynamic processes of the lithosphere and the Earth deep interior, and their relationship to Earth-surface changes. In this context we propose a study that aims to understand the two pieces of lithosphere underlying the Paran-Etendeka conjugate margins (Brazil, and Angola-Namibia). It is essential to collect the geological and geophysical information about the thickness and the density of sedimentary layers, crustal thickness and mantle inhomogeneities. Our methodology integrates the geophysical database with the GOCE data, product of the innovative gravity satellite mission, that was concluded November 2013. Crustal thickness was obtained from all available seismological datasets. The density-depth relation of the shallow layers is modeled by geophysical data collected from literature and from the on-shore and off-shore drilling programs. Several compaction laws are used to estimate the density of each layer. This information is necessary to reduce the observations considering the gravity effect of all intracrustal known layers, to resolve the deep crustal structures (e.g. Moho and intracrustal bodies). A positive gravity anomaly is expected due to the magmatic activity of the Paran-Etendeka province. The smaller-scale and shallow gravity anomaly should be due to the occurrence of the volcanic activity close to the alkaline-carbonatite complexes, while the large-scale anomaly is expected from the underplating of a wide denser body at the depth of the crustal mantle boundary. In the present work some preliminary results of the inversion of the residual gravity anomaly in terms of densities in the middle and shallow lithosphere under the Paran-Etendeka region will be presented and interpreted.

Mariani, Patrizia; Braitenberg, Carla

2014-05-01

200

Geodynamic significance of the TRM segment in the East African Rift (W-Tanzania): Active tectonics and paleostress in the Ufipa plateau and Rukwa basin  

NASA Astrophysics Data System (ADS)

The Tanganyika-Rukwa-Malawi (TRM) rift segment in western Tanzania is a key sector for understanding the opening dynamics of the East African rift system (EARS). In an oblique opening model, it is considered as a dextral transfer fault zone that accommodates the general opening of the EARS in an NW-SE direction. In an orthogonal opening model, it accommodates pure dip-slip normal faulting with extension orthogonal to the rift segments and a general E-W extension for the entire EARS. The central part of the TRM rift segment is well exposed in the Ufipa plateau and Rukwa basin, within the Paleoproterozoic Ubende belt. It is also one of the most seismically active regions of the EARS. We investigated the active tectonic architecture and paleostress evolution of the Ufipa plateau and adjacent Rukwa basin and in order to define their geodynamic role in the development of the EARS and highlight their pre-rift brittle tectonic history. The active fault architecture, fault-kinematic analysis and paleostress reconstruction show that the recent to active fault systems that control the rift structure develop in a pure extensional setting with extension direction orthogonal to the trend of the TRM segment. Two pre-rift brittle events are evidenced. An older brittle thrusting is related to the interaction between the Bangweulu block and the Tanzanian craton during the late Pan-African (early Paleozoic). It was followed by a transpressional inversion during the early Mesozoic. This inversion stage is the best expressed in the field and caused dextral strike-slip faulting along the fault systems that now control the major rift structures. It has been erroneously interpreted as related to the late Cenozoic EARS which instead is characterized by pure normal faulting (our third and last stress stage).

Delvaux, D.; Kervyn, F.; Macheyeki, A. S.; Temu, E. B.

2012-04-01

201

Geochemistry and petrogenesis of high-K "sanukitoids" from the Bulai pluton, Central Limpopo Belt, South Africa: Implications for geodynamic changes at the Archaean-Proterozoic boundary  

NASA Astrophysics Data System (ADS)

The Neoarchaean Bulai pluton is a magmatic complex intrusive in the Central Zone of the Limpopo Belt (Limpopo Province, South Africa). It is made up of large volumes of porphyritic granodiorites with subordinate enclaves and dykes of monzodioritic, enderbitic and granitic compositions. New U-Pb LA-ICP-MS dating on zircon yield pluton-emplacement ages ranging between 2.58 and 2.61 Ga. The whole pluton underwent a high-grade thermal overprint at ~ 2.0 Ga, which did not affect the whole-rock compositions for most of the major and trace-elements, as suggested by a Sm-Nd isochron built up with 16 samples and yielding an age consistent with U-Pb dating. The whole-rock major- and trace-element compositions evidence that the Bulai pluton belongs to a high-K, calc-alkaline to shoshonitic suite, as well as unequivocal affinities with "high-Ti" sanukitoids. Monzodioritic enclaves and enderbites have both "juvenile" affinities and a strongly enriched signature in terms of incompatible trace elements (LREE, HFSE and LILE), pointing to an enriched mantle source. Based on trace-element compositions, we propose the metasomatic agent at their origin to be a melt deriving from terrigenous sediments. We therefore suggest a two-step petrogenetic model for the Bulai pluton: (1) a liquid produced by melting of subducted terrigenous sediments is consumed by reactions with mantle peridotite, producing a metasomatic assemblage; (2) low-degree melting of this metasomatized mantle gives rise to Bulai mafic magmas. Such a model is supported by geochemical modelling and is consistent with previous studies concluding that sanukitoids result from interactions between slab melts and the overlying mantle wedge. Before 2.5 Ga, melting of hydrous subducted metabasalts produced large volumes of TTG (Tonalite-Trondhjemite-Granodiorite) forming most of the volume of Archaean continental crust. By constrast, our geochemical study failed in demonstrating any significant role played by melting of subducted metabasalts, which points to lower thermal regimes as metasediments melt at lower temperature than metabasalts. This suggests that the geodynamic changes that took place at the Archaean-Proterozoic transition and witnessed by sanukitoid-related rocks are mainly the result of progressive and global cooling of Earth. On the other hand, melting of subducted detrital material is uncommon during the Archaean, which would also indicate that significant recycling of continental material within the mantle roughly began at the Archaean-Proterozoic transition.

Laurent, Oscar; Martin, Herv; Doucelance, Rgis; Moyen, Jean-Franois; Paquette, Jean-Louis

2011-04-01

202

Petrology and geochemistry of orthoamphibolites from the Variscan metamorphic sequences of the South Tisia in Croatia - an overview with geodynamic implications  

NASA Astrophysics Data System (ADS)

In the southern Pannonian Basin, the Variscan Barrovian- and overprinted Abukuma-type progressive metamorphic sequences of the South Tisia in Slavonian Mts. (SM) and Mt. Moslava?ka Gora (MG) are interlayered with orthoamphibolites. These sequences represent part of a disrupted Variscan belt that extends southeastwards of the Bohemian Massif through the Carpathians to the Caucasus. Orthoamphibolites contain hornblende (Mg-hornblende, tschermakite, pargasite, and edenite), plagioclase An48-98 (MG) and An26-35 (SM), biotite, grossular (MG) and almandine (SM) enriched garnet, diopside (MG), with accessory ilmenite, titanite, and clinozoisite. Based on major and trace element analyses and CIPW norms, these orthoamphibolites, which originally were olivine tholeiites to slightly alkalic basalts, can be correlated with tholeiites of consuming plate margins. ?18O of orthoamphibolites varies from 5.8 to 7.1, the measured 87Sr/86Sr ratio from 0.70435 to 0.70665, which indicates slight continental crust contamination, and the calculated ratio from 0.70262 to 0.70535, indicating an upper mantle origin of the original basaltic melts. For associated penecontemporaneous I-type granitoids, the calculated initial 87Sr/86Sr ratio also have upper mantle values ranging between 0.70293 and 0.70368. Geochemical data for orthoamphibolites and the associated penecontemporaneous I-type granites, and the occurrence of alpine-type ultramafic bodies within the Barrovian sequence, indicate that they have many features in common with orogenic associations related to recent subduction-related settings. Some characteristic element ratios suggest back-arc basin environments and the Ce/K vs. Ce diagram suggests a pargasite-lherzolite source. Its partial melting gave primitive basaltic melts of olivine tholeiite to slight alkalic affinities that produced at first differentiated mafic rocks by olivine fractionation (future orthoamphibolites) and, afterwards, a strongly differentiated suite of I-type granitoids by amphibole fractionation. Magma emplacement and subsequent AFC processes took place in subduction environments preceding the main Variscan deformational metamorphic event during which orthoamphibolites were generated. This interpretation is compatible with geodynamic modeling of this part of the Paleotethys.

Pami?, Jakob; Balen, Draen; Tiblja, Darko

2002-02-01

203

Potential geodynamic relationships between the development of peripheral orogens along the northern margin of Gondwana and the amalgamation of West Gondwana  

NASA Astrophysics Data System (ADS)

The Neoproterozoic-Early Cambrian evolution of peri-Gondwanan terranes (e.g. Avalonia, Carolinia, Cadomia) along the northern (Amazonia, West Africa) margin of Gondwana provides insights into the amalgamation of West Gondwana. The main phase of tectonothermal activity occurred between ca. 640-540 Ma and produced voluminous arc-related igneous and sedimentary successions related to subduction beneath the northern Gondwana margin. Subduction was not terminated by continental collision so that these terranes continued to face an open ocean into the Cambrian. Prior to the main phase of tectonothermal activity, Sm-Nd isotopic studies suggest that the basement of Avalonia, Carolinia and part of Cadomia was juvenile lithosphere generated between 0.8 and 1.1 Ga within the peri-Rodinian (Mirovoi) ocean. Vestiges of primitive 760-670 Ma arcs developed upon this lithosphere are preserved. Juvenile lithosphere generated between 0.8 and 1.1 Ga also underlies arcs formed in the Brazilide Ocean between the converging Congo/So Francisco and West Africa/Amazonia cratons (e.g. the Tocantins province of Brazil). Together, these juvenile arc assemblages with similar isotopic characteristics may reflect subduction in the Mirovoi and Brazilide oceans as a compensation for the ongoing breakup of Rodinia and the generation of the Paleopacific. Unlike the peri-Gondwanan terranes, however, arc magmatism in the Brazilide Ocean was terminated by continent-continent collisions and the resulting orogens became located within the interior of an amalgamated West Gondwana. Accretion of juvenile peri-Gondwanan terranes to the northern Gondwanan margin occurred in a piecemeal fashion between 650 and 600 Ma, after which subduction stepped outboard to produce the relatively mature and voluminous main arc phase along the periphery of West Gondwana. This accretionary event may be a far-field response to the breakup of Rodinia. The geodynamic relationship between the closure of the Brazilide Ocean, the collision between the Congo/So Francisco and Amazonia/West Africa cratons, and the tectonic evolution of the peri-Gondwanan terranes may be broadly analogous to the Mesozoic-Cenozoic closure of the Tethys Ocean, the collision between India and Asia beginning at ca. 50 Ma, and the tectonic evolution of the western Pacific Ocean.

Murphy, J. Brendan; Pisarevsky, Sergei; Nance, R. Damian

2013-10-01

204

Discovery of Miocene adakitic dacite from the Eastern Pontides Belt (NE Turkey) and a revised geodynamic model for the late Cenozoic evolution of the Eastern Mediterranean region  

NASA Astrophysics Data System (ADS)

The Cenozoic magmatic record within the ca. 500 km long eastern Pontides orogen, located within the Alpine metallogenic belt, is critical to evaluate the tectonic history and geodynamic evolution of the eastern Mediterranean region. In this paper we report for the first time late Miocene adakitic rocks from the southeastern part of the eastern Pontides belt and present results from geochemical and Sr-Nd isotopic studies as well as zircon U-Pb geochronology. The Tavdagi dacite that we investigate in this study is exposed as round or ellipsoidal shaped bodies, sills, and dikes in the southeastern part of the belt. Zircons in the dacite show euhedral crystal morphology with oscillatory zoning and high Th/U values (up to 1.69) typical of magmatic origin. Zircon LA-ICPMS analysis yielded a weighted mean 206Pb/238U age of 7.86 0.15 Ma. SHRIMP analyses of zircons with typical magmatic zoning from another sample yielded a weighted mean 206Pb/238U age of 8.79 0.19 Ma. Both ages are identical and constrain the timing of dacitic magmatism as late Miocene. The Miocene Tavdagi dacite shows adakitic affinity with high SiO2 (68.95-71.41 wt.%), Al2O3 (14.88-16.02 wt.%), Na2O (3.27-4.12 wt.%), Sr (331.4-462.1 ppm), Sr/Y (85-103.7), LaN/YbN (34.3-50.9) and low Y (3.2-5 ppm) values. Their initial 143Nd/144Nd (0.512723-0.512736) and 87Sr/86Sr (0.70484-0.70494) ratios are, respectively, lower and higher than those of normal oceanic crust. The geological, geochemical and isotopic data suggest that the adakitic magmatism was generated by partial melting of the mafic lower crust in the southeastern part of the eastern Pontide belt during the late Miocene. Based on the results presented in this study and a synthesis of the geological and tectonic information on the region, we propose that the entire northern edge of the eastern Pontides-Lesser Caucasus-Elbruz magmatic arc was an active continental margin during the Cenozoic. We identify a migration of the Cenozoic magmatism towards north over time resulting from the roll-back of the southward subducted Tethys oceanic lithosphere. Slab break-off during Pliocene is proposed to have triggered asthenospheric upwelling and partial melting of the subduction-modified mantle wedge which generated the alkaline magmatic rocks exposed in the northern part of the magmatic arc.

Eyuboglu, Yener; Santosh, M.; Yi, Keewook; Bekta?, Osman; Kwon, Sanghoon

2012-08-01

205

Archean geodynamics and the Abitibi-Pontiac collision: implications for advection of fluids at transpressive collisional boundaries and the origin of giant quartz vein systems  

NASA Astrophysics Data System (ADS)

Giant quartz vein systems of all ages, from the Archean to Cenozoic, are characterised by similarities of geodynamic setting, local structure, paragenesis, metal budget, P-T-t paths, and chemical, fluid dynamic and isotopic properties that collectively imply a singular hydrothermal process. Such quartz vein provinces form in regional brittle-ductile shear zones that define terrane boundaries, including closure of back-arc basins, and arc-continent or continent-continent collisions. Examples include the SVZ of the Archean Abitibi belt; the Norseman Wiluna belt, Yilgarn block; Kolar schist belt, India; Foothills Metamorphic Belt, California, and Coast Ranges Megalineament, in the Cordillera; and the Cenozoic Monte Rosa district, Insubric line. Evidence for an Archean collisional environment comes from the Abitibi and Pontiac Subprovince tectonic boundary, which hosts giant quartz vein systems. In this region, the amphibolite facies Lacorne tectonic block in the Archean Abitibi greenstone belt is anomalous with respect to the prevalent low-grade supracrustal sequences in neighbouring blocks. The Lacorne block has mature clastic sediments with a zircon provenance age spectrum from 3040-2691 Ma, and two granitic magma series; a late syntectonic monzodiorite-monzonite-granodiorite-syenite series formed over 2685-2670 Ma, similar to Phanerozoic volcanic arc granites, and post-tectonic garnet-muscovite granites emplaced at 2650-2630 Ma, which compositionally resemble Phanerozic collisional S-type granites. The Pontiac subprovince to the south of the Abitibi greenstone belt shares all the above features with the Lacorne block, and collided with and was locally thrust under the Abitibi belt, with differential uplift of the Lacorne block following collision to generate a tectonic window. Following collision of allochthonous terranes, the conjuction of large volumes of subcreted oceanic crust and sediments between accreted terranes, displaced isotherms rise, and metamorphic dehydration are all necessary conditions for forming giant quartz vein systems. Metamorphic fluids are expelled along the terrane boundary structures at deep levels, and focussed into second and higher order splays at mid-crustal levels where quartz and Au precipitation occurs. Hydrothermal fluids that formed the giant quartz veins are remarkably uniform in H, O, C, and Sr isotopic compositions, albeit with small provincial variations. The veins and gold precipitated at 270-360C, from fluids with low salinity and moderate CO 2 at 2-3 kbar in the brittle-ductile transition.

Kerrich, R.; Feng, R.

1992-01-01

206

A Study of Short-Period Surface Wave Data, Geodynamic Models, and the Rheology and Dynamics of the Mantle Beneath the East Pacific Rise  

NASA Astrophysics Data System (ADS)

This study uses inversions of isotropic and anisotropic seismic structure with geodynamic models to examine the mantle dynamics and rheology beneath the MELT region of the East Pacific Rise (EPR). A joint inversion of short-period Love (5-16 s) and Rayleigh (15-30 s) waves traveling from regional earthquakes northward along the EPR images the fine-scale structure of the shallowest (depths < 100 km) upper mantle in a two-dimensional cross-section, perpendicular to the rise axis. We image strong anisotropy in which horizontally propagating, E-W polarized S-waves would be faster than vertically polarized S-waves (i.e., VSH - VSV >0) at distances > 50-100 km from the ridge. These findings are consistent with those of azimuthal variations in longer-period Rayleigh wave velocity as well as shear-wave splitting (SWS) of teleseismic body waves. Beneath the rise axis, we see a narrow (50-100 km) zone of weakly negative radial anisotropy (VSH - VSV ? 0) extending from a depth of ~20 km and downward. The origin of the inverted pattern of anisotropy as well as the SWS results are examined using numerical models of mantle flow, assuming seismic anisotropy is caused by lattice preferred orientation of olivine and enstatite during dislocation creep. The westward migration of the EPR plus an eastward mantle return flow are considered much like prior models of the region. Results show that a transition between deeper Newtonian (diffusion) creep and shallower power-law (dislocation) creep occurring 100-150 km below the near-axis region can explain the amplitudes of the negative (VSH - VSV < 0) anisotropy beneath the ridge axis and positive (VSH - VSV >0) anisotropy below the flanks of the EPR. Greater transition depths result in too much anisotropy, smaller transition depths produce too little. Cases in which mantle rheology depends on pressure and temperature but not composition predict a zone of negative anisotropy beneath the EPR that is 7-8 times broader than that observed at a depth of 100 km. Cases that include the stiffening of the mantle as it dehydrates by partial melting predict a narrower zone of negative anisotropy beneath the ridge axis, which is more compatible with but is still wider than observed. Cases that include dynamic upwelling due to the buoyancy of retained partial melt in the mantle predict more strongly negative anisotropy beneath the ridge axis and in some cases negative, rather than positive anisotropy beneath the plate on the east. Thus the cases with a stiff, dehydrated shallow asthenosphere and passive mantle flow (i.e., little or no buoyant flow due to retained melt) provide the best fits to the observations.

Ito, G.; Dunn, R.; Forsyth, D. W.

2010-12-01

207

Geophysical and petrological modelling of the structure and composition of the crust and upper mantle in complex geodynamic settings: The Tyrrhenian Sea and surroundings  

NASA Astrophysics Data System (ADS)

Information on the physical and chemical properties of the lithosphere-asthenosphere system (LAS) can be obtained by geophysical investigation and by studies of petrology-geochemistry of magmatic rocks and entrained xenoliths. Integration of petrological and geophysical studies is particularly useful in geodynamically complex areas characterised by abundant and compositionally variable young magmatism, such as in the Tyrrhenian Sea and surroundings. A thin crust, less than 10 km, overlying a soft mantle (where partial melting can reach about 10%) is observed for Magnaghi, Vavilov and Marsili, which belong to the Central Tyrrhenian Sea backarc volcanism where subalkaline rocks dominate. Similar characteristics are seen for the uppermost crust of Ischia. A crust about 20 km thick is observed for the majority of the continental volcanoes, including Amiata-Vulsini, Roccamonfina, Phlegraean Fields-Vesuvius, Vulture, Stromboli, Vulcano-Lipari, Etna and Ustica. A thicker crust is present at Albani - about 25 km - and at Cimino-Vico-Sabatini about 30 km. The structure of the upper mantle, in contrast, shows striking differences among various volcanic provinces. Volcanoes of the Roman region (Vulsini-Sabatini-Alban Hills) sit over an upper mantle characterised by Vs mostly ranging from about 4.2 to 4.4 km/s. At the Alban Hills, however, slightly lower Vs values of about 4.1 km/s are detected between 60 and 120 km of depth. This parallels the similar and rather homogeneous compositional features of the Roman volcanoes, whereas the lower Vs values detected at the Alban Hills may reflect the occurrence of small amounts of melts within the mantle, in agreement with the younger age of this volcano. The axial zone of the Apennines, where ultrapotassic kamafugitic volcanoes are present, has a mantle structure with high-velocity lid ( Vs 4.5 km/s) occurring at the base of a 40-km-thick crust. Beneath the Campanian volcanoes of Vesuvius and Phlegraean Fields, the mantle structure shows a rigid body dipping westward, a feature that continues southward, up to the eastern Aeolian arc. In contrast, at Ischia the upper mantle contains a shallow low-velocity layer ( Vs = 3.5-4.0 km/s) just beneath a thin but complex crust. The western Aeolian arc and Ustica sit over an upper mantle with Vs 4.2-4.4 km/s, although a rigid layer ( Vs = 4.55 km/s) from about 80 to 150 km occurs beneath the western Aeolian arc. In Sardinia, no significant differences in the LAS structure are detected from north to south. The petrological-geochemical signatures of Italian volcanoes show strong variations that allow us to distinguish several magmatic provinces. These often coincide with mantle sectors identified by Vs tomography. For instance, the Roman volcanoes show remarkable similar petrological and geochemical characteristics, mirroring similar structure of the LAS. The structure and geochemical-isotopic composition of the upper mantle change significantly when we move to the Stromboli-Campanian volcanoes. The geochemical signatures of Ischia and Procida volcanoes are similar to other Campanian centres, but Sr-Pb isotopic ratios are lower marking a transition to the backarc mantle of the Central Tyrrhenian Sea. The structural variations from Stromboli to the central (Vulcano and Lipari) and western Aeolian arc are accompanied by strong variations of geochemical signatures, such as a decrease of Sr-isotope ratios and an increase of Nd-, Pb-isotope and LILE/HFSE ratios. The dominance of mafic subalkaline magmatism in the Tyrrhenian Sea basin denotes large degrees of partial melting, well in agreement with the soft characteristics of the uppermost mantle in this area. In contrast, striking isotopic differences of Plio-Quaternary volcanic rocks from southern to northern Sardinia does not find a match in the LAS geophysical characteristics. The combination of petrological and geophysical constraints allows us to propose a 3D schematic geodynamic model of the Tyrrhenian basin and bordering volcanic areas, including the subduction of the Ionian-Adria lithosphe

Panza, G. F.; Peccerillo, A.; Aoudia, A.; Farina, B.

2007-01-01

208

La Mamora, charnire entre la Meseta et le Rif: son importance dans l'volution godynamique postpalozoque du Maroc \\/ The Mamora Plain, a hinge between the Meseta and the Rif. Its importance in the post-Paleozoic geodynamic evolution of Morocco  

Microsoft Academic Search

The Mamora area (Morocco) is located in the northern part of the Meseta and the southern part of Rharb. The recent formations (Mesozoic to Quaternary) lie unconformably on a Paleozoic basement. This study based on hydrogeological, sedimentological, drilling data and seismic reflection profiles interpretation, proposes new interpretations of geodynamical evolution of this area particularly in terms of tectonic patterns. The

Lahcen Zouhri; Christian Lamouroux; Christophe Buret

2001-01-01

209

Magnetic Probing of Core Geodynamics  

NASA Astrophysics Data System (ADS)

To better understand geomagnetic theory and observation, we can use spatial magnetic spectra for the main field and secular variation to test core dynamical hypotheses against seismology. The hypotheses lead to theoretical spectra which are fitted to observational spectra. Each fit yields an estimate of the radius of Earth's core and uncertainty. If this agrees with the seismologic value, then the hypotheses pass the test. A new way to obtain theoretical spectra extends the hydromagnetic scale analysis of Benton [1992; GAFD] to scale-variant field and flow [Voorhies, 2004; JGR-SE, in press]. For narrow scale flow and a dynamically weak field by the top of Earth's core, this yields a generalized Stevenson-McLeod spectrum for the core-source field [Voorhies, Sabaka and Purucker, 2002; JGR-P], and a secular variation spectrum modulated by a cubic polynomial in spherical harmonic degree n. The former passes the tests. The latter passes many tests, but does not describe rapid dipole decline and quadrupole rebound; some tests suggest it is a bit hard, or rich in narrow scale change. In a core geodynamo, motion of the fluid conductor does work against the Lorentz force. This converts kinetic into magnetic energy which, in turn, is lost to heat via Ohmic dissipation. In the analysis at length-scale 1/k, if one presumes kinetic energy is converted in either eddy-overturning or magnetic free-decay time-scales, then Kolmogorov or other spectra in conflict with observational spectra can result. Instead, the rate work is done roughly balances the dissipation rate, which is consistent with small scale flow. The conversion time-scale depends on dynamical constraints. These are summarized by the magneto-geostrophic vertical vorticity balance by the top of the core, which includes anisotropic effects of rotation, the magnetic field, and the core-mantle boundary. The resulting theoretical spectra for the core-source field and its SV are far more compatible with observation. The conversion time-scale of order 120 years is pseudo-scale-invariant. Magnetic spectra of other planets may differ; however, if a transition to non-conducting fluid hydrogen in Jupiter acts as barrier to vertical flow, as well as current, then the shape of the jovi-magnetic spectrum could be remarkably Earth-like.

Voorhies, C. V.

2004-05-01

210

Petrogenesis and geodynamic setting of Neoproterozoic and Late Paleozoic magmatism in the Manzhouli-Erguna area of Inner Mongolia, China: Geochronological, geochemical and Hf isotopic evidence  

NASA Astrophysics Data System (ADS)

U-Pb dating and Hf isotopic analyses of zircons from various granitoids, combined with major and trace element analyses, were undertaken to determine the petrogenesis and geodynamic setting of Neoproterozoic and Late Paleozoic magmatism in the Manzhouli-Erguna area of Inner Mongolia, China. The Neoproterozoic granitoids are mainly biotite monzogranites with zircon U-Pb ages of 894 13 Ma and 880 10 Ma, and they are characterised by enrichment in large ion lithophile elements (LILEs; e.g., Rb, Ba, K) and light rare earth elements (LREEs), depletion in high field strength elements (HFSEs; e.g., Nb, Ta, Ti) and heavy rare earth elements (HREEs). The Late Devonian granitoids are dominantly syenogranites and mylonitised syenogranites with zircon U-Pb ages of 360 4 Ma, and they form a bimodal magmatic association with subordinate gabbroic rocks of the same age. The Late Devonian syenogranites have A-type characteristics including high total alkalis, Zr, Nb, Ce and Y contents, and high FeOt/MgO, Ga/Al and Rb/Sr ratios. The Carboniferous granitoids are mainly tonalites, granodiorites and monzogranites with U-Pb ages varying from 319 to 306 Ma, and they show very strong adakitic characteristics such as high La/Yb and Sr/Y ratios but low Y and Yb contents. The Late Permian granitoids are dominated by monzogranites and syenogranites with zircon U-Pb ages ranging between 257 and 251 Ma. Isotopically, the ?Hf(t) values of the Neoproterozoic granitoids range from +4.3 to +8.3, and the two-stage model ages (TDM2) from 1.2 to 1.5 Ga. The Late Devonian granitoids are less radiogenic [?Hf(t) from +12.0 to +12.8 and TDM2 from 545 to 598 Ma] than the Carboniferous [?Hf(t) from +6.8 to +9.5 and TDM2 from 722 to 894 Ma] and Late Permian granitoids [?Hf(t) from +6.1 to +9.4 and TDM2 in the range of 680-895 Ma]. These data indicate (1) the Neoproterozoic granitoids may have been generated by melting of a juvenile crust extracted from the mantle during the Mesoproterozoic, probably during or following the final stages of assembly of Rodinia as a result of the collision and amalgamation of Australia and the Tarim Craton; (2) the Late Devonian granitoids may have formed by partial melting of a new mantle-derived juvenile crust in a post-orogenic extensional setting; (3) the Carboniferous granitoids appear to have been produced by melting of garnet-bearing amphibolites within a thickened continental crust during and following the collision of the Songnen and Erguna-Xing'an terranes; and (4) the Late Permian granitoids may have been generated by melting of garnet-free amphibolites within the Neoproterozoic juvenile continental crust, probably in the post-collisional tectonic setting that followed the collision of the North China and Siberian cratons.

Gou, Jun; Sun, De-You; Ren, Yun-Sheng; Liu, Yong-Jiang; Zhang, Shu-Yi; Fu, Chang-Liang; Wang, Tian-Hao; Wu, Peng-Fei; Liu, Xiao-Ming

2013-05-01

211

Geochemistry and petrogenesis of Mashhad granitoids: An insight into the geodynamic history of the Paleo-Tethys in northeast of Iran  

NASA Astrophysics Data System (ADS)

Mashhad granitoids in northeast Iran are part of the so-called Silk Road arc that extended for 8300 km along the entire southern margin of Eurasia from North China to Europe and formed as the result of a north-dipping subduction of the Paleo-Tethys. The exact timing of the final coalescence of the Iran and Turan plates in the Silk Road arc is poorly constrained and thus the study of the Mashhad granitoids provides valuable information on the geodynamic history of the Paleo-Tethys. Three distinct granitoid suites are developed in space and time (ca. 217-200 Ma) during evolution of the Paleo-Tethys in the Mashhad area. They are: 1) the quartz diorite-tonalite-granodiorite, 2) the granodiorite, and 3) the monzogranite. Quartz diorite-tonalite-granodiorite stock from Dehnow-Vakilabad (217 4-215 4 Ma) intruded the pre-Late Triassic metamorphosed rocks. Large granodiorite and monzogranite intrusions, comprising the Mashhad batholith, were emplaced at 212 5.2 Ma and 199.8 3.7 Ma, respectively. The high initial 87Sr/86Sr ratios (0.708042-0.708368), low initial 143Nd/144Nd ratios (0.512044-0.51078) and low ?Nd(t) values (- 5.5 to - 6.1) of quartz diorite-tonalite-granodiorite stock along with its metaluminous to mildly peraluminous character (Al2O3/(CaO + Na2O + K2O) Mol. = 0.94-1.15) is consistent with geochemical features of I-type granitoid magma. This magma was derived from a mafic mantle source that was enriched by subducted slab materials. The granodiorite suite has low contents of Y (? 18 ppm) and heavy REE (HREE) (Yb < 1.53 ppm) and high contents of Sr (> 594 ppm) and high ratio of Sr/Y (> 35) that resemble geochemical characteristics of adakite intrusions. The metaluminous to mildly peraluminous nature of granodiorite from Mashhad batholiths as well as its initial 87Sr/86Sr ratios (0.705469-0.706356), initial 143Nd/144Nd ratios (0.512204-0.512225) and ?Nd(t) values (- 2.7 to - 3.2) are typical of adakitic magmas generated by partial melting of a subducted slab. These magmas were then hybridized in the mantle wedge with peridotite melt. The quartz diorite-tonalite-granodiorite stock and granodiorite batholith could be considered as arc-related granitoid intrusions, which were emplaced during the northward subduction of Paleo-Tethys Ocean crust beneath the Turan micro-continent. The monzogranite is strongly peraluminous (Al2O3/(CaO + Na2O + K2O) Mol. = 1.07-1.17), alkali-rich with normative corundum ranging between 1.19% and 2.37%, has high initial 87Sr/86Sr ratios (0.707457-0.709710) and low initial 143Nd/144Nd ratios (0.512042-0.512111) and ?Nd(t) values (- 5.3 to - 6.6) that substantiate with geochemical attributes of S-type granites formed by dehydration-melting of heterogeneous metasedimentary assemblages in thickened lower continental crust. The monzogranite was emplaced as a consequence of high-temperature metamorphism during the final integration of Turan and Iran plates. The ages found in the Mashhad granites show that the subduction of Paleo-Tethys under the Turan plate that led to the generation of arc-related Mashhad granites in late-Triassic, finally ceased due to the collision of Iran and Turan micro-plates in early Jurassic.

Mirnejad, H.; Lalonde, A. E.; Obeid, M.; Hassanzadeh, J.

2013-06-01

212

New insights into the origin of the subduction component in Late Oligocene magmatism in the Ronda peridotite (southern Spain): geodynamic implications for the western Mediterranean  

NASA Astrophysics Data System (ADS)

Several tectonic scenarios have been proposed for the Tertiary evolution of the Betic-Rif chain in the westernmost Mediterranean. Recent studies on late, mantle-derived Cr-rich websterite dykes in the Ronda peridotite have revealed recycling the involvement of sources of continental detrital sediments in the waning magmatic stage of the Ronda peridotite (Marchesi et al., 2012). This new data are consistent with a subduction-related setting for the late evolution of the Alboran lithospheric mantle before its final intracrustal emplacement in the early Miocene (Garrido et al., 2011). Detailed structural studies of Ronda plagioclase peridotites show that large-scale, ductile folding of peridotites-associated to the development of LT-LP plagioclase peridotite tectonites and ultramylonites-occurred during a contractional event before intracrustal emplacement of peridotites (Hidas et al., 2013). These authors have proposed that this event was related to inversion of a back-arc basin, followed by failed subduction initiation that ended into the intracrustal emplacement of peridotite into the Alboran wedge. This new structural data leads us to hypothesize that the crustal component observed in late, Cr-rich websterite might come from fluids produced by dehydration of underthrusted crustal units in the earliest stages of subduction initiation. Here we present new trace element and Sr-Nd-Pb-Hf isotopic data in whole rocks from Flysch sediments from the Betic cordillera and the underlying crustal units of the Ronda massif, which may account for the timing and geochemical signature of the Ronda Cr-rich pyroxenites dykes. These units correspond to the Flysch trough composed of turbiditic deposits, formed in the region between Iberia and Africa during Late Oligocene-Early Miocene, and the underlying crustal unit of the Ronda peridotite known as the Blanca unit. These new data are used to constrain the potential role of different crustal sources in the generation of the Late Oligocene subduction-related magmatism in the Ronda peridotite, and its implications for geodynamic models of the western Mediterranean in the Cenozoic. REFERENCES Garrido, C. J., F. Gueydan, G. Booth-Rea, J. Precigout, K. Hidas, J. A. Padrn-Navarta, and Marchesi C. . (2011) Garnet lherzolite and garnet-spinel mylonite in the Ronda peridotite: Vestiges of Oligocene backarc mantle lithospheric extension in the western Mediterranean, Geology, 39(10), 927-930. Hidas, K., Booth-Rea, G, Garrido, C. J., Martnez-Martnez, J. M., Padrn-Navarta, J. A., Konc, Z., Giaconia, F., Frets, E., and Marchesi, C. (2013) . Backarc basin inversion and subcontinental mantle emplacement in the crust: kilometre-scale folding and shearing at the base of the proto-Alborn lithospheric mantle (Betic Cordillera, southern Spain): Journal of the Geological Society, London. Marchesi, C., Garrido, C. J., Bosch, D., Bodinier, J.-L., Hidas, K., Padrn-Navarta, J. A., and Gervilla, F. (2012) A Late Oligocene Suprasubduction Setting in the Westernmost Mediterranean Revealed by Intrusive Pyroxenite Dikes in the Ronda Peridotite (Southern Spain): The Journal of Geology, 120 (2), 237-247.

Varas-Reus, Mara Isabel; Garrido, Carlos J.; Marchesi, Claudio; Bosch, Delphine; Hidas, Kroly; Acosta-Vigil, Antonio

2013-04-01

213

Early Cambrian Post-collisional volcanosedimentary Rey Bouba greenstone belt in northern Cameroun: LA-MC-ICP-MS U-Pb geochronology and implications for the geodynamic evolution of the Central African Fold Belt (CAFB).  

NASA Astrophysics Data System (ADS)

The Rey Bouba Greenstone Belt (RBGB) is a greenschist volcanosedimentary basin representing the youngest accretion event that characterized the geodynamic evolution of the CAFB of Northern Cameroon. LA-MC-ICP-MS U-Pb detrital zircon data indicate that both older PP to MP and younger NP to Early Cambrian sources from ca 2000 to ca 540 Ma, with main provenance being zircon grains from Cryogenian igneous rocks (between ca 850 and ca 650 Ma) were involved in the formation of the RBGB basin. Considering the age of metamorphism inferred from high pressure granulites at ca 600 Ma within the CAFB of northern Cameroon as the most direct evidence for the timing of continental collision, we conclude that the deformation associated with migmatites and post-collisional granites which fed the Rey Bouba basin mostly with NP zircon lasts until post 540 Ma, in correlation with the final amalgamation of the Gondwana Supercontinent during Latest Neoproterozoic-Earliest Cambrian. Therefore, the RBGB may represent the youngest post-collisional metavolcanosedimentary basin within the CAFB.

Bouyo, Merlain

2014-05-01

214

End-Permian to mid-Triassic termination of the accretionary processes of the southern Altaids: implications for the geodynamic evolution, Phanerozoic continental growth, and metallogeny of Central Asia  

NASA Astrophysics Data System (ADS)

The Altaids is one of the largest accretionary orogenic collages in the world with the highest rate of Phanerozoic continental growth and significant metallogenic importance. It is widely accepted that subduction-related orogenesis of the Altaids started in the late Precambrian and gradually migrated southward (present coordinates). However, it is uncertain when and how the building of the Altaids was finally completed. Based on structural geology, geochemical, geochronological, and paleomagnetic data, this paper presents late Paleozoic to early Mesozoic accretionary tectonics of two key areas, North Xinjiang in the west and Inner Mongolia in the east, together with neighboring Mongolia. The late Paleozoic tectonics of North Xinjiang and adjacent areas were characterized by continuous southward accretion along the wide southern active margin of Siberia and its final amalgamation with the passive margin of Tarim, which may have lasted to the end-Permian to early/mid-Triassic. In contrast, in Inner Mongolia and adjacent areas two wide accretionary wedges developed along the southern active margin of Siberia and the northern active margin of the North China craton, which may have lasted to the mid-Triassic. The final products of the long-lived accretionary processes in the southern Altaids include late Paleozoic to Permian arcs, late Paleozoic to mid-Triassic accretionary wedges composed of radiolarian cherts, pillow lavas, and ophiolitic fragments, and high-pressure/ultrahigh-pressure metamorphic rocks. Permian Alaskan-type zoned mafic-ultramafic complexes intruded along some major faults of the Tien Shan. We define a new Tarim suture zone immediately north of the Tarim craton that is probably now buried below the Tien Shan as a result of northward subduction of the Tarim block in the Cenozoic. The docking of the Tarim and North China cratons against the southern active margin of Siberia in the end-Permian to mid-Triassic resulted in the final closure of the Paleoasian Ocean and terminated the accretionary orogenesis of the southern Altaids in this part of Central Asia. This complex geodynamic evolution led to formation of giant metal deposits in Central Asia and to substantial continental growth.

Xiao, W. J.; Windley, B. F.; Huang, B. C.; Han, C. M.; Yuan, C.; Chen, H. L.; Sun, M.; Sun, S.; Li, J. L.

2009-09-01

215

Sr-Nd constraints and trace-elements geochemistry of selected Paleo and Mesoproterozoic mafic dikes and related intrusions from the South American Platform: Insights into their mantle sources and geodynamic implications  

NASA Astrophysics Data System (ADS)

The study of selected mafic intrusions from cratonic areas of the South American Platform shows considerable differences among their mantle sources and geodynamic features, particularly regarding the dikes from the SW Amazonian and So Francisco Cratons. The tholeiites from the SW Amazonian Craton, which belong to the Serra da Providncia Intrusive Suite (1.55 Ga), the Nova Lacerda swarm (1.44 Ga), the Colorado Complex (1.35 Ga), and the Nova Brasilndia Group (1.10 Ga), originated from a mantle source composed mainly of a N-MORB end-member, with a variable addition of slab fluids (up to 30%, according to the adopted model) from oceanic lithosphere due to episodic subductions during the Mesoproterozoic. Mafic intrusions from Nova Lacerda swarm and Colorado Complex are related to arc settings formed during the 1.47-1.35 Ga closure of the oceanic domain separating the Amazonian Craton and the Paragu Terrane, whereas the tholeiites from the Serra da Providncia Intrusive Suite and the Nova Brasilndia Group are considered intracratonic. The dike swarms of the So Francisco Craton are associated with intra-plate events. The inferred composition of the mantle source of the Lavras swarm (1.9 Ga) has a predominant E-MORB signature, and a modest contribution of up to 10% of an OIB component. The mantle composition underwent considerable changes during the Proterozoic, as indicated by the sources of the younger dikes, represented by the Diamantina (0.93 Ga) and the Salvador-Olivena swarms (0.92 Ga), to which considerable amount of slab derived fluids, probably from recycled crustal material, and OIB component were added. Changes in mantle composition and dikes intrusions could be related to the initial disruption of the Rodinia Supercontinent. The Florida (1.79 Ga) and Tandil (2.0 Ga) dikes are associated with extensional events of the Rio de La Plata Craton. In spite of the similarities between the tectonic framework of these swarms and that of Lavras (1.9 Ga), the composition of the Paleoproterozoic mantle of both cratons is very different. The parent mantle of the Florida dikes is more enriched and more heterogeneous than the others, probably due to the recycling of old crusts and OIB metasomatism. Isotopic data from the Tandil dikes also suggest an enriched original source, which could be a characteristic feature of the mantle of the Rio de La Plata Craton in Paleoproterozoic times. The Crixs-Gois (2.49 Ga) swarm originated from a very heterogeneous mantle source, probably contaminated by OIB metasomatic fluids and crustal addition, suggesting that crustal recycling has occurred since Archean times.

Girardi, V. A. V.; Teixeira, W.; Mazzucchelli, M.; Corra da Costa, P. C.

2013-01-01

216

Projection for Space Geodynamics, 1988-1998  

NASA Technical Reports Server (NTRS)

Premises defining the technical and operational environment of the next decade are listed. Observational programs required to satisfy scientific objectives in the study of geopotential fields, global dynamics, tectonics, and regional tectonics/crustal hazards are defined. Capabilities and applications of the Geopotential Research Mission to be launched in the early 1990's are explored and the benefits of more detailed measurements of the Moon and planets are indicated. Earthquake prediction in the western part of the U.S. is discussed. The use of decimeter, centimeter, and millimeter systems for very long baseline interferometry, satellite laser ranging, and lunar ranging techniques are discussed. Geographic regions of particular interest are identified.

1984-01-01

217

Geodynamic processes and deformation in orogenic belts  

NASA Astrophysics Data System (ADS)

The development of geosynclines and orogenic belts is related to lithosphere convergence. Initial sediment accumulation implying subsidence, and volcanic activity implying extension and rise of geotherms, are in most cases followed by folding and thrusting suggesting compression and by uplift. In terms of recent analogs, sediment accumulation and crustal extension are characteristic of back-arc spreading; subsequent compression would indicate continentcontinent collision; and rise of geotherms most likely requires localized thermal flow (convection) in the asthenosphere. These events are here shown to agree with Andrews and Sleep's (1974) numerical model of asthenosphere flow at converging plate margins. Orthogeosynclinal subsidence appears to be a consequence of subcrustal ablation and lithosphere extension and thinning in active marginal basins. Arc and Andean type magmatism mark the reappearance of ablated and transported, relatively low-density subcrustal material. Collision slows and eventually stops the local convection cell, resulting in local heat accumulation and hence high- T, low- P metamorphism and granitization while marginal basin (orthogeosynclinal) deposits are being compressed into Alpine style orogenic structures. Moreover, closing of the marginal basin leads to subsidiary subduction, which in turn may be responsible for some Alpine style structures. Oceanic trench deposits may become incorporated in orogenic zones, as high- P, low- T metamorphic belts (thalassogeosynclines). Dynamic uplift is a fundamental characteristic of orogeny. Most rising and sinking in orogenic zones can be linked to those asthenosphere processes which are a consequence of Andrews-Sleep convection.

Dennis, John G.; Jacoby, Wolfgang R.

1980-03-01

218

Hydrothermal Systems Rock Deformation and Geodynamics  

E-print Network

industry, univer- sities and governmental institutions interested in processes and simulation tech- niques of hydrogeological, geothermal and reactive transport applications. Post- graduate students specialising in one of this course is on coupled numerical simulation of fluid flow, heat trans- fer, multi species transport

219

Aral Sea Basin Evolution: Geodynamic Aspect  

Microsoft Academic Search

\\u000a The Aral Sea lies in the Aral-Sarykamysh depression, which is bordered by the low plains of Central Asia. The climate is continental\\u000a and extremely dry, and surface runoff is virtually zero. Since direct precipitation over the lake comprises only 10% of the\\u000a water budget, lake-level fluctuations are largely determined by changes in inflow from the Amu Darya and Syr Darya

Bakhtiar Nurtaev

220

Basic research for the geodynamics program  

NASA Technical Reports Server (NTRS)

Additional results are presented concerning a study that considers improvements over present Earth Rotation Parameter (ERP) determination methods by directly combining observations from various space geodetic systems in one adjustment. Earlier results are extended, showing that in addition to slight improvements in accuracy, substantial (a factor of three or more) improvements in precision and significant reductions in correlations between various parameters can be obtained (by combining Lunar Laser Ranging - LLR, Satellite Laser Ranging - SLR to Lageos, and Very Long Baseline Interferometry - VLBI data in one adjustment) as compared to results from individual systems. Smaller improvements are also seen over the weighted means of the individual system results. Although data transmission would not be significantly reduced, negligible additional computer time would be required if (standardized) normal equations were available from individual solutions. Suggestions for future work and implications for the New Earth Rotation Service (IERS) are also presented.

Mueller, Ivan I.

1988-01-01

221

12.520 Geodynamics, Fall 2005  

E-print Network

This course deals with mechanics of deformation of the crust and mantle, with emphasis on the importance of different rheological descriptions: brittle, elastic, linear and nonlinear fluids, and viscoelastic.

Hager, Bradford H.

222

12.520 Geodynamics, Fall 2004  

E-print Network

This course deals with mechanics of deformation of the crust and mantle, with emphasis on the importance of different rheological descriptions: brittle, elastic, linear and nonlinear fluids, and viscoelastic.

Hager, Bradford H.

223

Metamorphic chemical geodynamics of subduction zones  

Microsoft Academic Search

Study of metamorphic suites directly representing the deep subduction of altered oceanic crust and sediments can help elucidate the geochemical evolution of the forearc-to-subarc slab mantle interface, the nature of slab-derived fluids added to arc lava source regions, and the chemical changes in subducting rocks potentially contributing to the geochemical heterogeneity of the deeper mantle. The stage is set for

Gray E. Bebout

2007-01-01

224

Arctic region: new model of geodynamic history  

NASA Astrophysics Data System (ADS)

Basement of the Arctic shelf areas is characterizes with a complex structure. Age of the defined domains is early Pre-Cambrian, Neoproterozoic to Cambrian (Timanian and Baykalian), early-middle Paleozoic (Caledonian) and late Paleozoic (Uralian, Taimyrian and Ellesmerian). Mesozoic deformations affected Novaya Zemlya, Southern Taimyr and southern parts of the Laptev Sea, the East Siberian Sea, and the Chukchi Sea regions. There are several Paleozoic rift-postrift basins. The North Kara Basin and the Timan-Pechora Basin was formed during the early Ordovician time as subduction-related back-arc rift systems. The East-Barents Basin has the same origin but the age of its formation is late Devonian. Carboniferous rifting took place in the Norwegian part of the Barents Sea, the Chukchi Sea (Hanna Trough Basin) and the Sverdrup Basin. There are also rift-postrift basins of the Mesozoic age. Late Permian to Early Triassic rifting took place in the South Kara Basin; it was connected with both collapse of the Uralian Orogen and activity of the Siberian mantle plume. Aptian to Albian rifting was affected with really big area in the Laptev Sea, the East Siberian Sea and the Chukchi Sea right after the De-Long plume-related magmatic event. Paleogene (mainly Eocene) rifting was also widely spread in these areas. The Arctic Ocean consists of three main domains: the Canada Basin, Alpha-Mendeleev-Podvodnikov-Makarov domain, and the Eurasia Basin. The Canada Basin is a typical oceanic one. There are many uncertainties in the definition of spreading age, but in accordance with the prevalent point of view, it should be early Cretaceous, Neocomian. Alpha-Mendeleev-Podvodnikov-Makarov domain is an enigmatic region. We propose the following scenario for the formation of this domain: Aptian to Cenomanian plume-related large-scale intraplate basalt magmatism was followed by Albian to late Cretaceous rifting. Few axes of rifting were nearly orthogonal to the pre-existing one in the Canada Basin. The Alpha-Mendeleev Ridge is a rifted continental terrane covered by pre-rift basalts. The Eurasian Basin is a small oceanic one. Defined age of spreading is 56-0 Ma. The basin is characterized by a very slow spreading rate. Eocene to recent sediments covers the system of prominent linear ranges and valleys of former mid-oceanic ridge. The Lomonosov Ridge is a well known continental terrane dissected by Neogene-Quaternary faults. New data shows that the area of the Lomonosov and the Alpha-Mendeleev ridges was affected by strong Neogene to recent extension or transtension tectonics with the formation of numerous normal faults and related topographic highs and valleys. Recent bathymetry of these ridges is a result of this Neogene to recent tectonics. Our report is based on a new set of seismic lines in the Russian part of the Arctic region.

Nikishin, Anatoly; Kazmin, Yuriy; Malyshev, Nikolay; Morozov, Andrey; Petrov, Eugene

2014-05-01

225

Geodynamics of Cenozoic deformation in central Asia  

NASA Technical Reports Server (NTRS)

This paper presents a study of the tectonic stresses in central Asia based on an interpretation of satellite gravity data for mantle convection and supplemented with published fault plane solutions of earthquakes. Northwest-southeast to north-south compressional stresses exist in the Tien Shan region where reverse faulting dominates. The maximum compressive stress is oriented approximately northeast-southwest in the regions of Altai and southern Mongolia. Farther north, compressive stress gives way to tensional stress which causes normal faulting in the Baikal rift system. It is also shown that all of the tectonic stresses in the Tibetan plateau and Himalayan frontal thrust are related to the convection-generated stress patterns inferred from satellite gravity data. These results suggest that the complex crustal deformation in central Asia can be convincingly described by the deformation of the lithosphere on top of the up- and down-welling asthenospheric material beneath it. This observational fact may not only upset the simple view of the fluid crustal model of the Tibetan plateau, but also provide some useful constraints for the future development of deformation theory of continental crust.

Liu, H.-S.

1981-01-01

226

Geodynamic Motion at European SLR Sites  

NASA Astrophysics Data System (ADS)

The twenty year (1980-2000) time series of the positions at Satellite Laser Ranging (SLR) sites tracking the LAGEOS I satellite (launched May, 1976) contain signals with periods between hours and years, as well as the long-term effects of crustal movements or post-glacial rebound. Improved temporal sampling from a second similar satellite, LAGEOS II (launched Oct. 1992), aids in the separation of the geophysical from the SLR instrumental effects better than would be possible from LAGEOS I data analysis alone. Since these satellites are at the same altitude, but in different inclination orbits, the effect of some of the orbital errors on the analysis is also eliminated. During the past two decades the advances in overall system accuracy, in conjunction with improved satellite, Earth, and orbit perturbation modeling, now enable these observations to reveal a variety of features in geocentric position in time. Both the horizontal and the vertical components of station velocity can be determined to better than one mm/year at a majority of the European SLR sites. This facilitates the use of the European SLR sites to geodetically connect regional and local positioning networks monitoring sea level change in a geocentric reference frame.

Kolenkiewicz, R.; Smith, D. E.; Torrence, M. H.; Dunn, P. J.

2001-12-01

227

Geodynamics: How plumes help to break plates  

NASA Astrophysics Data System (ADS)

Computer models show how hot material that rises from Earth's interior is affected by plate tectonics, producing unexpected irregularities in Earth's topography and assisting in the break-up of continental plates. See Letter p.85

Buiter, Susanne

2014-09-01

228

Putting the Dynamics in Chemical Geodynamics  

NASA Astrophysics Data System (ADS)

An outstanding goal for both geochemists and geophysicists is to understand how to use the wide range of proxy geochemical (and geophysical) data to make useful inferences about the current and past dynamics of the planet. To relate data to dynamics, however, requires models that include the fundamental processes that affect chemical variability: i.e. source heterogeneity, chemical fractionation (melting/reactions), chemical transport and mixing. In particular, most models of chemical evolution do not include explicit fluid or magma transport and questions remain as to how much observed chemical variability can be attributed to magma dynamics. We discuss recent developments and models that suggest that at least some of the observed variability arises from transport processes. Driven by field observations, experiments and computational models, there is an emerging picture of partially molten regions as highly localized, channelized plumbing systems. Computations suggest that melt localization can arise from both chemical/physical and purely mechanical instabilities and can provide non-trivial mixing pathways through the mantle. Questions remain as to how the different instabilities interact and which may be dominant in the mantle. Regardless, a highly localized melt transport system can lead to significant trace element (and U-series) variability and fractionation even for a homogeneous source. Recent work extends these results to consider the interaction of a channelized melt system with a heterogeneous source and suggests that small scale spatial variations in partitioning can lead to significant scatter in the ratios of highly incompatible elements (Fang, Spiegelman & Kelemen). Current work is extending these approaches to try to understand the variability of major elements and reaction in open systems (Collier, Kelemen & Spiegelman) Looking forward, the integration of magma dynamics and small-scale localization into global mantle dynamics presents a major scientific and computational challenge. A key addition to magma dynamics models will be the consistent coupling of fluid/solid mechanics with thermodynamics to resolve both melting and crystallization of magmas (e.g. see Katz U06, this meeting). These models will also require advanced methods for the efficient solution of highly multi-scale problems. The CIG Magma dynamics project is actively pursuing these computational objectives with the long-term goal of developing true dynamic geochemistry models whose output can be directly compared to observations.

Spiegelman, M.; Katz, R. F.; Kelemen, P. B.; Fang, Y.; Collier, M.; Holtzman, B.

2007-12-01

229

Applied Geodynamics Laboratory Salt Tectonics Sandbox Animations  

NSDL National Science Digital Library

This collection of salt tectonics sandbox animation movies done by Giovanni Guglielmo, and available at UT Austin website, can be used to illustrate concepts and processes in a structural geology course. To access the animations, click on the 'animations' link in the menu on the left side of the web page. The animations are excellent for illustrating that the path from undeformed strata to final cross section is highly dynamic and can include a world of unrealized intermediate geometries. For example, the animations 'Rising and falling diapirs' can be used to introduce the concepts, and 'Raft Tectonics - Kwanza Basin' to illustrate the possibilities.

Guglielmo, Giovanni; Laboratory, Applied G.

230

Geochemistry and zircon U-Pb-Hf isotopic systematics of the Ningshan granitoid batholith, middle segment of the south Qinling belt, Central China: Constraints on petrogenesis and geodynamic processes  

NASA Astrophysics Data System (ADS)

The Ningshan Granitoid Batholith (NGB) is located in the middle segment of the South Qinling Belt (SQB) section of the Qinling orogenic belt, in Shaanxi Province, China, and consists of the Laocheng, Yanzhiba and Lanbandeng intrusions. The Laocheng intrusion is dominated by quartz diorites, granodiorites and monzogranites, with the Yanzhiba intrusion being granodiorite dominated, and the Lanbandeng intrusion predominantly consisting of two-mica monzogranites. LA-ICP-MS zircon U-Pb isotopic dating indicates that the NGB formed during two distinct episodes of magmatism, with an earlier episode at 222-216 Ma and a later episode at 210 Ma. Whole-rock geochemistry and geochronology data have allowed us to divide the NGB into three groups, with Group #1 rocks consisting of Laocheng intrusion quartz diorites and granodiorites, and Yanzhiba intrusion granodiorites that were produced in the early magmatic episode. Group #1 samples have high-K calc-alkaline compositions, and are characterized by high Mg# values, high Sr, Cr, and Ni concentrations, and high (La/Yb)N and Sr/Y ratios, but low Yb and Y concentrations, implying that these rocks were formed from a mixed magma derived from melting of Neoproterozoic crustal basaltic rocks and magmas sourced from a region of depleted mantle. Group #2 rocks are composed of the mid-K calc-alkaline monzogranites in the Laocheng intrusion that were formed in the later magmatic episode, and are characterized by lower Mg# values, and lower Cr, Ni, and Co concentrations than the Group #1 samples, but with high Sr concentrations and (La/Yb)N and Sr/Y ratios, low Y and Yb concentrations, negligible Eu anomalies, and a significant range in zircon ?Hf(t) values. The highest zircon ?Hf(t) values of the Group #2 samples plot close to the depleted mantle evolutionary line, indicating that these rocks were derived from a mixed magma with both crustal- and mantle-derived components. Group #3 samples consist of high-K calc-alkaline two-mica monzogranites of the Lanbandeng intrusion that were formed during the later magmatic episode. These rocks are characterized by high SiO2, Al2O3, and K2O concentrations, with low MgO and Sr concentrations, low (La/Yb)N and Sr/Y ratios, Nb, Ta, P and Ti depletions, and significantly negative Eu anomalies, implying that the magmas from which these rocks formed were derived from partial melting of sedimentary rocks and minor amount of basalt. The early magmatic episode associated with formation of the NGB occurred in a continental arc environment at 222-216 Ma, with 210 Ma magmatism during a geodynamic transition from syn-collisional to post-collisional tectonics across the SQB.

Yang, Pengtao; Liu, Shuwen; Li, Qiugen; Wang, Zongqi; Wang, Ruiting; Wang, Wei

2012-11-01

231

Introduction to Special Section on Physical Processes in Geodynamics  

NASA Astrophysics Data System (ADS)

On May 16 and 17, 1992, a meeting was held at Cornell University as part of activities to honor Donald L. Turcotte on the occasion of his 60th birthday (which actually occurred on April 22, 1992). The papers in the following special section are a result of that meeting, which included invited presentations and posters representing the diverse areas of geology and geophysics to which Donald Turcotte has contributed. Three of the papers deal with aspects of mantle convection. A. C. Fowler addresses the problem of initiation of subduction by extending boundary layer theory to a viscoplastic rheology. Turcotte and Oxburgh [1967] pioneered such studies by showing how boundary layer theory could be used to describe the dependence of geophysical observables such as heat flux on distance from a midocean ridge or age of the oceanic crust. D. W. Sparks et al. use a model of three-dimensional convection beneath a segmented ridge to explore how buoyancy effects and melt production beneath a spreading center influence ridge-parallel variations in crustal thickness and gravity. Magma migration and the dynamics of midocean ridges have been major focuses of Donald Turcotte's research in papers dating back to 1978 [e.g., Turcotte and Ahern, 1978; Ahern and Turcotte, 1979; Turcotte, 1982a; Kenyon and Turcotte, 1987]. G. A. Glatzmaier and G. Schubert calculate models of three-dimensional two-layer mantle convection in a spherical shell and compare with whole layer, spherical shell, three-dimensional convection models. These models represent the end-member states of a spectrum of possible modes of mantle convection [Turcotte and Oxburgh, 1972; Oxburgh and Turcotte, 1978; Turcotte, 1979a; Silver et al., 1988].

Schubert, G.

1993-12-01

232

Kinematics and geodynamics of the India-Eurasia collision  

NASA Astrophysics Data System (ADS)

The collision between the Indian and Eurasian continents produced the world's most pronounced mountain range, impacted long-term global climate and oceanic circulation, and deformed vast swathes of Southeast Asia. However, the collision chronology remains controversial largely due to uncertain pre-collision margin geometries. We embed two end-member scenarios of pre-collision geometries within a global plate motion model in our plate reconstruction software, GPlates. A scenario that implies long-lived Andean-style subduction along southern Eurasia was chosen to represent conventional models of convergence that require a very large Greater India. An alternative scenario, based on interpretations of ophiolite emplacements, present-day mantle structure, volcanogenic episodes, convergence rate trends and deformation events, suggests the existence of long-lived Tethyan intra-oceanic subduction. In this scenario, a smaller Greater India collides with an intra-oceanic island arc at ~60 Ma at equatorial latitudes, coinciding with a convergence rate drop, ophiolite emplacement and the onset of back-arc subduction. A final continent-continent collision occurs at ~40 Ma to consume the back-arc basin and induce extreme crustal deformation and lateral expulsion of Southeast Asian continental blocks. Plate velocities were sampled using a 50 km global mesh on the surface and were applied as the kinematic surface boundary layer to drive subduction from 200 Ma to the present using the mantle convection code CitcomS. The predicted mantle structure from end-member scenarios was validated using P- and S- wave seismic tomographic models, where long-term Andean-style subduction failed to reproduce the discrete slab volumes and the large latitudinal range of mid-mantle Tethyan slabs. The alternative scenario better reproduces the present-day mantle structure and the evidence for a multi-stage collision, volcanogenic episodes and characteristics of long-lived intra-oceanic Tethyan subduction.

Zahirovic, S.; Mller, R.; Seton, M.; Flament, N.; Gurnis, M.; Whittaker, J.

2012-12-01

233

Phanerozoic growth of Asia: Geodynamic processes and evolution  

NASA Astrophysics Data System (ADS)

Accretion processes often obscured in mountain belts can be documented with great detail in SE Asia where these have taken place during the Tertiary. The resulting configuration showing accreted continental strips and tectonised wedges is illustrated by the Tethysides jammed between the northern Laurasian cratons (Baltica and Siberia) and Gondwanian cratons (Africa, Arabia, India and Australia). Eurasia increased progressively in size due to the amalgamation of crustal and sedimentary belts. At places where the processes are documented in the recent times, they can be included within a "collision factory" which displays the opening of basins by rifting and sea floor spreading within the upper plate, until they undergo a process of shortening, both stages being subduction-controlled. In SE Asia the early stages are illustrated in the eastern Sunda arc where the subduction of the Sunda Trench is blocked in Sumba and Timor region, and flipped into the Flores Trough in less than 2 My. The incipient shortening is at present taking place in the Pliocene Damar basins. Another stage, where half of the upper plate basin has disappeared, is documented in the Celebes Sea. The examples of deformation being transferred further inland exist in the northern Celebes Sea and the Makassar Basin. The next important stage is the complete consumption of the marginal basin where both margins collide and the accretionary wedge is thrust over the margin, as illustrated in NW Borneo and Palawan. Each of these stages is responsible for a single short-lived tectonic event, the succession of several events composes an orogen which may last for over 10 My. These events predate the arrival of the conjugate margin of the large ocean, which marks the beginning of continental subduction as observed in the Himalaya-Tibet region. These examples show that the closure is generally diachronous through time as illustrated in the Philippines. We observe that the ophiolite obducted in such context is generally of back-arc origin (upper plate) rather than the relict of the vanishing large ocean which is rarely preserved. In the Philippines, once the crust is accreted the subduction zone progressively moved southward until its present position. We propose that the lithospheric mantle of the accreted block is delaminated and rolls back in a continuous manner, whereas the crust is deformed and accreted.

Pubellier, Manuel; Meresse, Florian

2013-08-01

234

The global geodynamic effect of the Macquarie Ridge earthquake  

SciTech Connect

Besides generating seismic waves, which eventually dissipate, an earthquake also generates a static displacement field everywhere within the Earth. This global displacement field rearranges the Earth's mass distribution, causing the Earth's rotational properties and gravitational field to change. The size of these changes depends, in general, upon the size of the earthquake. The Macquarie Ridge earthquake of May 23, 1989 is considered to be the largest earthquake to have occurred since the 1977 Sumba and Tonga events. As such, the coseismic effect of this earthquake upon the Earth's length-of-day, polar motion, and low-degree harmonic coefficients of the gravitational field are computed. It is found that this earthquake should have caused the length-of-day to decrease by 0.06 {mu}sec, the position of the mean rotation pole to shift 0.11 milli-arcsec towards 323{degree}E longitude, and selected degree l = 2-5 gravitational field coefficients to change by about 1 part in 10{sup 13}. These changes are all smaller than can be detected by current observational techniques. However, changes of this size could perhaps be detected in the future with the implementation of proposed improvements to the techniques of monitoring the Earth's rotation, and (especially for the low-degree gravitational field coefficients) with the placement of GPS receivers onboard orbiting spacecraft.

Gross, R.S.; Chao, B. Fong

1990-06-01

235

The global geodynamic effect of the Macquarie Ridge earthquake  

NASA Technical Reports Server (NTRS)

The coseismic effect of the Macquarie Ridge earthquake on the earth's length-of-day, polar motion, and low-degree harmonic coefficients of the gravitational field are compared. It is found that this earthquake should have caused the length-of-day to decrease by 0.06, the position of the mean rotation pole to shift 0.11 milliarcsec towards 323 E longitude, and selected degree l = 2-5 gravitational field coefficients to change by about 1 part in 10 to the 13th.

Gross, Richard S.; Chao, Fong B.

1990-01-01

236

SKS splitting and upper mantle geodynamic under California  

NASA Astrophysics Data System (ADS)

We performed teleseismic shear wave splitting measurements for 65 permanent (Berkeley, Caltech and Geoscope) and temporary (USArray and California Transect) broadband stations in Central California to study the vertical and lateral extent of the deformation beneath the San Andreas Fault System and to investigate interactions between lithosphere and asthenosphere in a transpressional plate boundary. The type of anisotropy detected at the different stations fall into two categories: either one with clear E/W trending fast directions and delay times in the range 1.5 to 2.0s, found at stations far from the San Andreas fault (SAF) system, or one where both the fast azimuth and delay times scatter considerably, for stations closer to the SAF system. In the latter case, the scatter is related to azimuthal variations of the splitting parameters that can be modeled by two anisotropic layers. The upper of the two layers provides fast directions in the range N30W to N50W, close to the strike of the main Californian faults (N35W to N45W) and averaged delay times of 0.7s; the lower layers show E/W directions and delay times in the range 1.5 to 2.5s and are therefore close to what is observed in stations that require only a single layer. We propose that the E/W trending anisotropic layer observed beneath all of California is 150 to 200 km thick and is located within the asthenosphere. Its deformation is likely due to absolute motion of the North American lithosphere overlying the asthenosphere and it may therefore be characterized by a horizontal foliation with E/W lineation. The other anisotropic layer ought to be related to the dynamics of the San Andreas Fault system and is probably characterized by a lithospheric vertical foliation with lineation parallel to the strike of the faults. Using the large amounts of data and the dense seismological coverage available in California, we are able to propose that this anisotropic layer is about 40 km broad at 70 kilometers depth beneath each fault of the San Andreas Fault System, and that the faults extend into the lithospheric mantle.

Bonnin, Mickael; Barruol, Guilem; Bokelmann, Goetz

2010-05-01

237

A proposed test area for the spaceborne geodynamic ranging system  

NASA Technical Reports Server (NTRS)

Precise geodetic measurements are proposed in which an orbiting laser obtains intersite distance between retroreflectors 25 to 100 km apart on the ground. The recommended area is a rectangle 200 by 400 km in southern California and adjacent Nevada, trending northeast. It includes the entire width of the San Andreas fault zone, the Garlock fault, the thrust faults of the Transverse Ranges, and the active strike-slip faults of the Mojave Desert.

Lowman, P. D., Jr.

1978-01-01

238

GS of CAS Geodesy & Geodynamics Beijing June 20041 SEISMIC CYCLE  

E-print Network

hundred years (200 on the plot). This time interval is called recurrence time interval. READ modified at recurrence time interval, plus or minus many decades (or centuries) 3. Physical and/or rheological conditions

Vigny, Christophe

239

Seismic anisotropy surrounding South China Sea and its geodynamic implications  

NASA Astrophysics Data System (ADS)

Several mechanisms have been proposed for the opening of the South China Sea. Here, we use SKS splitting analysis to investigate the mantle flow surrounding the South China Sea. We use a total of 23 seismic stations and 87 events. We applied spectral analysis and cluster analysis to find a stable splitting solution for each event. The main conclusions are: (1) In northern Vietnam, the NW-SE fast direction is parallel to the absolute plate motion as well as GPS observations with splitting times larger than 1 s, indicating a coupled lithosphere and mantle. In contrast, in southern Vietnam, the NE-SW fast direction suggests that the lithosphere and asthenosphere are decoupled. (2) The fast directions beneath the South China Block and central Taiwan are NE-SW and NS respectively, both parallel to surface deformations with splitting times greater than 1 s, indicating that mantle flow and surface deformation are related. (3) The observed NW-SE fast directions beneath Hainan Island reflect the India-Eurasia collision, and show no signatures of an upwelling mantle plume directly underneath Hainan Island. This implies that Hainan Island is tectonically closely related to the Red River Fault, not the South China Block. (4) In Borneo, the observed NE-SW direction is parallel to the Palawan Trench, consistent with flow associated with the inactive proto-South China Sea subduction system. The SKS splitting observations surrounding South China Sea cannot be explained by a single geologic process, with either the collision-driven extrusion model or the slab pull model fitting the data presented here.

Xue, Mei; Le, Khanh Phon; Yang, Ting

2013-12-01

240

Erosion, Himalayan Geodynamics, and the Geomorphology of Metamorphism  

Microsoft Academic Search

Is erosion important to the structural and petrological evolution of mountain belts? The nature of active metamorphic massifs co-located with deep gorges in the syntaxes at each end of the Himalayan range, together with the magnitude of erosional fluxes that occur in these regions, leads us to concur with suggestions that erosion plays an integral role in collisional dynamics. At

Peter K. Zeitler; Anne S. Meltzer; Peter O. Koons; David Craw; Bernard Hallet; C. Page Chamberlain; William S. F. Kidd; Stephen K. Park; Leonardo Seeber; Michael Bishop; John Shroder

2001-01-01

241

Geodynamic simulations using the fast multipole boundary element method  

NASA Astrophysics Data System (ADS)

Interaction between viscous fluids models two important phenomena in geophysics: (i) the evolution of partially molten rocks, and (ii) the dynamics of Ultralow-Velocity Zones. Previous attempts to numerically model these behaviors have been plagued either by poor resolution at the fluid interfaces or high computational costs. We employ the Fast Multipole Boundary Element Method, which tracks the evolution of the fluid interfaces explicitly and is scalable to large problems, to model these systems. The microstructure of partially molten rocks strongly influences the macroscopic physical properties. The fractional area of intergranular contact, contiguity, is a key parameter that controls the elastic strength of the grain network in the partially molten aggregate. We study the influence of matrix deformation on the contiguity of an aggregate by carrying out pure shear and simple shear deformations of an aggregate. We observe that the differential shortening, the normalized difference between the major and minor axes of grains is inversely related to the ratio between the principal components of the contiguity tensor. From the numerical results, we calculate the seismic anisotropy resulting from melt redistribution during pure and simple shear deformation. During deformation, the melt is expelled from tubules along three grain corners to films along grain edges. The initially isotropic fractional area of intergranular contact, contiguity, becomes anisotropic due to deformation. Consequently, the component of contiguity evaluated on the plane parallel to the axis of maximum compressive stress decreases. We demonstrate that the observed global shear wave anisotropy and shear wave speed reduction of the Lithosphere-Asthenosphere Boundary are best explained by 0.1 vol% partial melt distributed in horizontal films created by deformation. We use our microsimulation in conjunction with a large scale mantle deep Earth simulation to gain insight into the formation of anisotropy within dense and transient regions known as Ultralow-Velocity Zones, where there is an observed slowdown of shear waves. The results demonstrate a geometric steady state of the dynamic reservoirs by mechanical processes. Within the steady state Ultralow-Velocity Zones, we find significant anisotropy that can explain the speed reduction in shear waves passing through the region.

Drombosky, Tyler W.

242

Aegean crustal thickness inferred from gravity inversion. Geodynamical implications  

E-print Network

, the Aegean domain has undergone regional extension due to the southward retreat of the Hellenic subduction by the southward retreat of the south Hellenic subduction zone [5­9]. Since the late Miocene, the effects

Demouchy, Sylvie

243

Meteorites, Continents, Heat, and Non-Steady State Geodynamics  

NASA Astrophysics Data System (ADS)

Previous geochemical estimates of terrestrial radiogenic heat production were based on the assumption that refractory lithophile elements, such as the REE, U, and Th, are present in the Earth in chondritic relative proportions (the 'modified chondritic Earth' model, e.g., McDonough & Sun, Chem. Geol., 120: 223, 1995). However, 142Nd/144Nd ratios in modern terrestrial materials are 10 and 18 ppm higher than in enstatite and ordinary chondrites, respectively. One explanation is that the Sm/Nd ratio in the Earth, or at least the observable part of it, is 3 to 6% higher than chondritic, implying the Earth is non-chondritic, even for refractory lithophile elements. The most likely explanation is that a low Sm/Nd igneous protocrust formed as the Earth accreted and was lost through collisional erosion. A protocrust 3 to 6% enriched in Nd relative to Sm would have been even more strongly enriched in the more highly incompatible elements K, U, and Th. Calculations based on a model of protocrust formation and collisional erosion (O'Neill, & Palme, Phil. Trans. R. Soc. A366: 4205, 2008) that satisfy both Sm-Nd and Lu-Hf isotopic constraints imply U and Th concentrations in the bulk silicate Earth (BSE) that are 20 to 40% lower than in the 'modified chondritic Earth' model. Assuming a K/U = 13800 for the BSE, the K concentration is 10 to 30% lower than previously believed. This corresponds to a terrestrial heat production of 3.0 to 3.9 pW/kg or 11.9 to 15.8 TW. At the high end, these estimates are in excellent agreement with those of Lyubetskaya & Korenaga (JGR, 112: B03211, 2007), but are much lower than the 20 TW value derived from the 'modified chondritic Earth' model. Of this, some 5 to 10 TW of heat production is in the continental crust, leaving ?10 TW of heat production in the mantle. For comparison, recent estimates of U, Th, and K in the depleted mantle imply heat production in the range of 0.7-1.0 pW/kg; if the depleted mantle occupies the entire mantle, this translates into mantle heat production of 3-4 TW. Mantle heat losses are roughly 28 TW, hence the mantle Urey ratio (ratio of heat production to heat loss) is <0.3. If this mantle energy loss is supplied by secular cooling, it implies a cooling rate of >120C/Ga after accounting for adiabatic contraction, much higher than petrological and geophysical estimates. At present, heat generated by viscous dissipation of the gravitational energy released by sinking slabs is 12 to 15 TW, and <5 TW is released by the cooling core. Of this power, only a fraction, 3.8 to 4.8 TW, can produce new gravitational power to drive convection and plate tectonics. Thus gravitational energy is being consumed at a much higher rate than it is being regenerated through radioactive heating and viscous dissipation. These observations a clear indication that the present rate of slab subduction is not sustainable and that the mantle is in a phase of faster than normal plate motion. The Cretaceous superplume event may have marked the beginning of an episode of faster than average heat loss and seafloor spreading that continues to the present.

White, W. M.; Morgan, J. P.

2011-12-01

244

Subduction of the Bougainville seamount (Vanuatu): mechanical and geodynamic implications  

NASA Astrophysics Data System (ADS)

New bathymetric data gathered during a Seabeam survey (SEAPSO cruise, leg 1) enable us to re-examine the flexural response of the oceanic lithosphere subducting under the New Hebrides (Vanuatu) island arc. The Bougainville seamount and Sabine bank are interpreted as immerged fossil atolls, the recent subsidence of which is related to the subduction of the oceanic lithosphere. The position and altitude of the different fossil atolls which belong to the d'Entrecasteaux or Loyalty ridges are in good agreement with predictions of elastic flexure of the lithosphere. We deduce an average effective elastic thickness of the lithosphere of about 22 km for the area under study. This value is slightly smaller than the one corresponding to the lithospheric age as given by the magnetic anomalies, but is in good agreement with the age after a correction for thermal rejuvenation. This assumption of a thermal rejuvenation of the North Loyalty basin is also supported by previously reported high heat-flow values and attenuation of Sn seismic waves. However, the location and depth of the trench in front of the North Loyalty basin do not agree with the model which fits the other data. This discrepancy is interpreted as the result of variations of the value of Pb (vertical force per unit length of trench applied at the edge of the plate) along the subduction zone. Such variations may be related to the length of the subducted slab, which is shorter in front of the d'Entrecasteaux and Loyalty ridges than in front of the North Loyalty basin, according to the hypocentral distribution of earthquakes and a tomographic image of the slab.

Dubois, J.; Deplus, C.; Diament, M.; Daniel, J.; Collot, J.-Y.

1988-06-01

245

The Role of Carbon in Extrasolar Planetary Geodynamics and Habitability  

NASA Astrophysics Data System (ADS)

The proportions of oxygen, carbon, and major rock-forming elements (e.g., Mg, Fe, Si) determine a planet's dominant mineralogy. Variation in a planet's mineralogy subsequently affects planetary mantle dynamics as well as any deep water or carbon cycle. Through thermodynamic models and high pressure diamond anvil cell experiments, we demonstrate that the oxidation potential of C is above that of Fe at all pressures and temperatures, indicative of 0.1-2 Earth-mass planets. This means that for a planet with (Mg+2Si+Fe+2C)/O > 1, excess C in the mantle will be in the form of diamond. We find that an increase in C, and thus diamond, concentration slows convection relative to a silicate-dominated planet, due to diamond's ~3 order of magnitude increase in both viscosity and thermal conductivity. We assert then that in the C-(Mg+2Si+Fe)-O system, there is a compositional range in which a planet can be habitable. Planets outside of this range will be dynamically sluggish or stagnant, thus having limited carbon or water cycles leading to surface conditions inhospitable to life as we know it.

Unterborn, Cayman T.; Kabbes, Jason E.; Pigott, Jeffrey S.; Reaman, Daniel M.; Panero, Wendy R.

2014-10-01

246

The Gurupi Belt, northern Brazil: Lithostratigraphy, geochronology, and geodynamic evolution  

Microsoft Academic Search

The Gurupi Belt is located in northern Brazil on the southern margin of the So Lus Craton, which is dominated by juvenile calc-alkaline rocks formed in intra-oceanic island arcs between 2240 and 2150Ma. The Gurupi Belt consists of: (i) small lenses of an Archean metatonalite of 2594Ma; (ii) calc-alkaline\\/TTG tonalites and gneisses of 21472168Ma and juvenile Nd isotope signature, formed

Evandro L. Klein; Candido A. V. Moura; Robert S. Krymsky; William L. Griffin

2005-01-01

247

(C.Bina, 9/2011) From thermodynamics to geodynamics  

E-print Network

/2011) podrobnjsímetamorfnífacie(stupnmetamorfózy) Note increasing dehydration at higher T and characteristic shape of dehydration increasing dehydration at higher T and characteristic shape of dehydration reactions. Examine the amphibolite characteristic shape of dehydration reactions. General form of reaction progress: hbl-(Ca,Na)2­3(Mg,Fe,Al)5(Al

Cerveny, Vlastislav

248

Geodynamics of the Earth according to the altimeter measurements  

NASA Astrophysics Data System (ADS)

We performed a comprehensive analysis of observations of the Black Sea level variations by different methods. The first method is a coastal monitoring by sea-level tide gauges which measures sea level changes relative to a moving reference frame - the state geodetic network. The second one is the satellite altimetry which results are performed in the fixed global reference frame. At the first stage we studied the mean monthly data smoothed over three points for the period 1993-2009. We found that during years 1994-1995, 1999-2001, and 2006, changes of the sea level registered by two different methods were almost identical. Hence both methods have high accuracy. Difference between results of the two methods is an indicator of errors. Changes in the shape of the geoid result in the satellite data errors. Systematic errors of this method have period of 10.3 months. Errors in the coastal sea level measurements are associated with vertical movements of the gauge instruments. Systematic errors of this method has 14.6 months period which coincides with the Chandler one. We performed cross-spectral analysis of the errors caused by global changes of the geoid shape and regional geodeformations in the Black Sea region. We found that results of the sea level measurements by two different methods are the same during short periods of phase overlapping of these incoherent cyclic errors. At the second stage we studied the sea level changes averaged over 24 hours for the period May - July 2009. We concluded that the Earth' geomagnetic field variations during 10-15 May generated changes of the geoid. Main ruptures of the high-pressure gas pipe-lines which occurred at 9, 10, 16, 28 May could be related to corresponding geodeformations. We found that rapid changes of the distance from the satellite to the sea surface during May 2009 were preceded by geodeformations. During July 2009 we registered maximal geodeformations caused by increase of the amplitude of the solid Earth tides. In July, the sea level rose up to 12 cm during 20 days. In this period measurement errors associated with vertical movements of the tide gauges reached 21 cm. Their period is 7 days. Recorded ruptures of the gas pipeline networks during July occurred almost every 7 days also. The phase shift between periodic component of the vertical movements and ruptures of the gas pipelines was 180 degrees.

Uchytel, Igor; Jaroshenko, Victor; Mituchenko, Vadim; Kapochkin, Borys; Kucherenko, Nataliya

2010-05-01

249

Plume capture by a migrating ridge: Analog geodynamic experiments  

NASA Astrophysics Data System (ADS)

Paleomagnetic data from the Hawaii-Emperor Seamount Chain (HESC) suggests that the Hawaiian hotspot moved rapidly (~40 mm/yr) between 81 - 47 Ma but has remained relatively stationary since that time. This implies that the iconic bend in the HESC may in fact reflect the transition from a period of rapid hotspot motion to a stationary state, rather than a change in motion of the Pacific plate. Tarduno et al. (2009) have suggested that this period of rapid hotspot motion might be the surface expression of a plume conduit returning to a largely vertical orientation after having been captured and tilted by a migrating mid-ocean ridge. We report on a series of analog fluid dynamic experiments designed to characterize the interaction between a migrating spreading center and a thermally buoyant mantle plume. Experiments were conducted in a clear acrylic tank (100 cm x 70 cm x 50 cm) filled with commercial grade high-fructose corn syrup. Plate-driven flow is modeled by dragging two sheets of Mylar film (driven by independent DC motors) in opposite directions over the surface of the fluid. Ridge migration is achieved by moving the point at which the mylar sheets diverge using a separate motor drive. Buoyant plume flow is modeled using corn syrup introduced into the bottom of the tank from an external, heated, pressurized reservoir. Small (~2 mm diameter), neutrally buoyant Delrin spheres are mixed into reservoir of plume material to aid in visualization. Plate velocities and ridge migration rate are controlled and plume temperature monitored using LabView software. Experiments are recorded using digital video which is then analyzed using digital image analysis software to track the position and shape of the plume conduit throughout the course of the experiment. The intersection of the plume conduit with the surface of the fluid is taken as an analog for the locus of hotspot volcanism and tracked as a function of time to obtain a hotspot migration rate. Experiments are scaled to the Earth's mantle through a combination of a Peclet number and a plume buoyancy number. A range of spreading rates, ridge migration rates, and plume excess temperatures representative of the Earth are considered.

Mendez, J. S.; Hall, P.

2010-12-01

250

Geodynamical constraint on the history of Earth's ocean volume  

Microsoft Academic Search

The chemical composition of the bulk silicate Earth indicates that the present-day thermal budget is likely to be characterized by a significant excess of surface heat loss over internal heat generation. When combined with the notion of continental freeboard, this thermal budget places a tight constraint on the history of Earth's ocean volume. The capacity of Earth's oceans is determined

J. Korenaga

2008-01-01

251

Arctic geodynamics: Arctic science and ERS-1 satellite altimetry  

NASA Technical Reports Server (NTRS)

A detailed gravity field map of the mid Arctic Ocean, spreading ridge system was produced on the basis of ERS-1 satellite altimetry data. Areas of special concern, the Barents and Kara Seas, and areas surrounding the islands of Svalbard, Frans Josef Land and Novoya Zemlya are reviewed. ERS-1 altimetry covers unique Arctic and Antarctic latitudes above 72 degrees. Before ERS-1 it was not possible to study these areas with satellite altimetry. Gravity field solutions for the Barents Sea, portions of the Arctic Ocean and the Norwegian sea are shown. The largest gravity anomalies occur along the Greenland fracture zone as well as along transform faults near Svalbard.

Anderson, Allen Joel; Sandwell, David T.

1994-01-01

252

Paleomagnetic constrains on the geodynamic history of Romania  

Microsoft Academic Search

statistically significant number of samples and sites, can give a reliable record of the ancient geomagnetic field at the site of rock formation. The basic hypothesis that the geomagnetic field was, on average, that of an axial and geocentric dipole permits the paleomagnetist to interpret his results in terms of paleolatitude of the sampling site and its location with respect

Cristian Panaiotu

253

Geodynamic Evolution of the Southern Flank of the Corinth Rift  

Microsoft Academic Search

The Gulf of Corinth is the most seismically active area of Europe extending in a N-S direction at a rate of 12mm\\/yr. Many studies have focused on currently active normal faults, which bound the southern flank of the Corinth rift. However, many prominent faults, that are considered no longer active, outcrop over a broader area along with their syn-rift sedimentary

D. Jousselin; S. Bourlange; M. Ford; C. Le Carlier; S. Rohais

2005-01-01

254

Geodynamics applications of continuum physics to geological problems  

SciTech Connect

This textbook deals with the fundamental physical processes necessary for an understanding of plate tectonics and a variety of geologic phenomena. The first chapter reviews plate tectonics; its main purpose is to provide physics, chemistry, and engineering students with the geologic background necessary to understand the applications throughout the rest of the book. It goes on to discuss in following chapters: stress and strain relationships in the earths crust; basic principles of linear elasticity and the lithosphere; heat conduction in the earths crust; principles of gravity measurements; problems involving mantle convection and post glacial rebound; rock mechanics and rheology; principles of fluid flow in porous media; and, fault displacement measurements.

Turcotte, D.L.; Schubert, G.

1982-01-01

255

Geodynamics applications of continuum physics to geological problems  

Microsoft Academic Search

This textbook deals with the fundamental physical processes necessary for an understanding of plate tectonics and a variety of geologic phenomena. The first chapter reviews plate tectonics; its main purpose is to provide physics, chemistry, and engineering students with the geologic background necessary to understand the applications throughout the rest of the book. It goes on to discuss in following

D. L. Turcotte; G. Schubert

1982-01-01

256

Geodynamics of the Western Pacific-Indonesian region. Vol. II  

SciTech Connect

This book contains papers which are grouped into general studies and regional studies. The first section examines the dynamic processes as well as the systematic geological and geophysical relationships found in the region as a whole. The second section focuses on specific areas and features of the Western Pacific.

Hilde, T.W.C.; Uyeda, S.

1983-01-01

257

(C.Bina, 9/2011) From thermodynamics to geodynamics  

E-print Network

temperature) (isochoric Gruneisen parameter) (q value) (isochoric) #12;(C.Bina, 9/2011) Thermoelastic give complete illustration of parameter trade-offs. Contour values are of where the normal estimator 2 of state (Table 1, line 1). Four panels give complete illustration of parameter trade-offs. Contour values

Cerveny, Vlastislav

258

Geodynamical basis for crustal deformation under the Tibetan Plateau  

NASA Technical Reports Server (NTRS)

Plate tectonics and satellite-derived gravity data are used to examine crustal deformation under the Tibetan Plateau. A spherical harmonic analysis is given for the global plate boundary system, and the crustal stresses in Tibet are calculated from satellite gravity data. A superimposed stress system is constructed. The stress patterns reveal that the cold downwelling mantle convection flow beneath southern Tibet pulls the Indian plate down but applies a bending moment on the end of the plate to uplift and support the mass of the Himalayas.

Liu, H.-S.

1985-01-01

259

EAS 4312/6312: Geodynamics The Georgia Institute of Technology  

E-print Network

, and crustal faulting as mechanisms and consequences of plate tectonics. Office Hours: Hours will be held in my throughout the semester. Week Date Topic Exam 1,2 Aug. 24 - Sept. 2 Introduction to Plate Tectonics

Black, Robert X.

260

Emplacement of volcanic vents and geodynamics of Central Anatolia, Turkey  

Microsoft Academic Search

Observations on Synthetic Aperture Radar (SAR) scenes of the European Remote Sensing (ERS) satellite and Digital Elevation Models (DEMs), complemented by field structural analysis permit a new understanding of relationships between tectonics and volcanism since the late Miocene (10 Ma) in Central Anatolia. Volcanic edifices form elongate stratovolcanoes, linear clusters and volcanic ridges. They indicate emplacement on tension fractures and

D. Dhont; J. Chorowicz; T. Yurur; J.-L. Froger; O. Kose; N. Gundogdu

1998-01-01

261

Emplacement of volcanic vents and geodynamics of Central Anatolia, Turkey  

NASA Astrophysics Data System (ADS)

Observations on Synthetic Aperture Radar (SAR) scenes of the European Remote Sensing (ERS) satellite and Digital Elevation Models (DEMs), complemented by field structural analysis permit a new understanding of relationships between tectonics and volcanism since the late Miocene (10 Ma) in Central Anatolia. Volcanic edifices form elongate stratovolcanoes, linear clusters and volcanic ridges. They indicate emplacement on tension fractures and tail-crack or horsetail features. For instance, the Kara Dag volcano is rooted on a tail-crack which accommodates a horizontal left-lateral throw component at a fault termination. Caldera complexes of Cappadocia are associated with horsetail fault patterns. The emplacement of volcanoes also benefits from larger-scale tectonic structures: the Erciyes Dag volcano is localized by the Sultan Saz releasing bend which opens along the sinistral strike-slip Ecemis fault. Deformation has been analysed from tension fractureswhich are perpendicular to the direction of extensionand from field structural analysis. On a regional scale, the tectonic regime responsible for the distribution of volcanic vents in this area of convergence and lateral extrusion, is not compression but extension. The Central Taurus range is the thermally uplifted shoulder of the Adana-Cilicia basin, which is related to lithosphere thinning. Westward movements in the northwestern part of the studied area are influenced by the active back-arc Aegean extension situated to the west. Farther to the south, the direction of motion turns southwest and south, under the influence of the opening of the Adana-Cilicia basin. We interpreted that extension in the Central Anatolian plateau is related to crustal blocks moving above sub-horizontal detachment surfaces located in the lower crust. This is based on several facts: the Tuz Gl fault zone is a within-crust detachment; the Tuz Gl basin does not affect the whole lithosphere because otherwise it would have been bordered by thermally uplifted shoulders; movements change trend within a small (50 km) region.

Dhont, D.; Chorowicz, J.; Yrr, T.; Froger, J.-L.; Kse, O.; Gndogdu, N.

1998-10-01

262

Recent geodynamic evolution of the north Fiji basin (southwest Pacific)  

NASA Astrophysics Data System (ADS)

A cruise of the R/V Jean Charcot (Seapso III, December 1985) in the north Fiji basin between 16 and 22S obtained new structural and magnetic data concerning the central part of the basin. These have been used for the reinterpretation of the National Oceanic and Atmospheric Administration and U.S. Naval Research Project aeromagnetic survey (1979). The structural, surface-ship magnetic, and aeromagnetic data allow us to present a sketch of the evolution in four stages of the north Fiji basin for the past 10 m.y.

Auzende, Jean-Marie; Lafoy, Yves; Marsset, Bruno

1988-10-01

263

Prelaunch optical characterization of the Laser Geodynamic Satellite (LAGEOS 2)  

NASA Technical Reports Server (NTRS)

The optical range correction (the distance between the apparent retroreflective skin of the satellite and the center of mass) of the LAGEOS 2 was determined using computer analysis of theoretical and experimentally measured far field diffraction patterns, and with short pulse lasers using both streak camera-based range receivers and more conventional PMT-based range receivers. The three measurement techniques yielded range correction values from 248 to 253 millimeters dependent on laser wavelength, pulsewidth, and polarization, location of the receiver in the far field diffraction pattern and detection technique (peak, half maximum, centroid, or constant fraction). The Lidar cross section of LAGEOS 2 was measured at 4 to 10 million square meters, comparable to the LAGEOS 1.

Minott, Peter O.; Zagwodzki, Thomas W.; Varghese, Thomas; Seldon, Michael

1993-01-01

264

Origin of Siberian Large Igneous Province : link between petrology and geodynamics  

NASA Astrophysics Data System (ADS)

The composition of parental melts and their mantle sources were recently reconstructed for different types of Siberian Flood basalts [1] and meimechites [2] based on the compositions of olivine phenocrysts and their melt inclusions. It was shown that mantle source of early flood basalts (Gudchikhinskaya suite) was composed entirely from olivine-free pyroxenite, produced by reaction of recycled oceanic crust and peridotite. The composition of these lavas suggests that they were likely produced at depths of more than 130 km. However, in a very short time (150 m or 5% of lava column) afterwards the source composition of lavas (Tuklonskaya suite) has drastically changed incorporating up to 60% of peridotite. In addition, source of lavas has moved upwards to the depths of less than 70 km, where the major volume of Siberian traps have been produced. These observations suggest very fast, even catastrophic removal of at least 60 km of lithosphere, which led to massive melt production. Based on experimental and modeling results it was suggested that a Permian-Triassic plume, with potential temperature of up to 1650C transported a large amount of recycled ancient oceanic crust (up to 15-20%) as SiO2-oversaturated carbonated eclogite. Low-degree partial melting of eclogite at depths of 250-300 km produced carbonate-silicate melt that metasomatized the lithospheric roots of the Siberian shield. Further rise of the plume under relatively attenuated lithosphere (eg. 130-140 km in Norilsk area) led to progressive melting of eclogite and formation of reaction pyroxenite, which then melted at depths of 130-180 km. Consequently, a large volume of melt(Gudchikhinskaya suite) penetrated into the lithosphere and caused its Relay-Taylor instability and destruction. Delaminated lithosphere that included fragments of locally metasomatized depleted harzburgite subsided into the plume and was heated to the temperatures of the plume interior with subsequent generation of meimechite magma. Meimechites showed up at the surface only under thicker part of the lithosphere aside from major melting zone above because otherwise they were mixed up in more voluminous flood basalts. I further show that meimechites, uncontaminated Siberian flood basalts and kimberlites all likely share the same source of strongly incompatible elements, the carbonated recycled oceanic crust carried up by hot mantle plume. References: 1. Sobolev, A.V., Krivolutskaya N.A., and Kuzmin, D.V. (2009). Petrology of the parental melts and mantle sources of Siberian trap magmatism. Petrology, 17 (3), 253-286. 2. Sobolev, A.V., Sobolev, S.V., Kuzmin, D.V. , Malitch, K.N., and Petrunin, A.G. (2009). Siberian meimechites: origin and relation to flood basalts and kimberlites. Russian Geology and Geophysics, 50, 1-33.

Sobolev, A. V.

2010-05-01

265

Geochemistry and geodynamics of the Mawat mafic complex in the Zagros Suture zone, northeast Iraq  

NASA Astrophysics Data System (ADS)

The Iraqi Zagros Orogenic Belt includes two separate ophiolite belts, which extend along a northwest-southeast trend near the Iranian border. The outer belt shows ophiolite sequences and originated in the oceanic ridge or supra-subduction zone. The inner belt includes the Mawat complex, which is parallel to the outer belt and is separated by the Biston Avoraman block. The Mawat complex with zoning structures includes sedimentary rocks with mafic interbedded lava and tuff, and thick mafic and ultramafic rocks. This complex does not show a typical ophiolite sequences such as those in Penjween and Bulfat. The Mawat complex shows evidence of dynamic deformation during the Late Cretaceous. Geochemical data suggest that basic rocks have high MgO and are significantly depleted in LREE relative to HREE. In addition they show positive ? Nd values (+5 to+8) and low 87Sr/86Sr ratios. The occurrence of some OIB type rocks, high Mg basaltic rocks and some intermediate compositions between these two indicate the evolution of the Mawat complex from primary and depleted source mantle. The absence of a typical ophiolite sequence and the presence of good compatibility of the source magma with magma extracted from the mantle plume suggests that a mantle plume from the D? layer is more consistent as the source of this complex than the oceanic ridge or supra-subduction zone settings. Based on our proposed model the Mawat basin represents an extensional basin formed during the Late Paleozoic to younger along the Arabian passive margin oriented parallel to the Neo-Tethys oceanic ridge or spreading center. The Mawat extensional basin formed without creation of new oceanic basement. During the extension, huge volumes of mafic lava were intruded into this basin. This basin was squeezed between the Arabian Plate and Biston Avoraman block during the Late Cretaceous.

Azizi, Hossein; Hadi, Ayten; Asahara, Yoshihiro; Mohammad, Youssef Osman

2013-12-01

266

Along-Strike Variations in Crustal Seismicity in the Central Andes and Geodynamic Implications  

NASA Astrophysics Data System (ADS)

For the central Andes, we compiled relocated crustal earthquakes (magnitude ? 4.5) from the EHB Bulletin and Nipress et al. [2007] and focal mechanisms from the Global CMT catalog and published literature [Alvarado et al., 2005]. These data were plotted in map, cross section, and 3D views in the context of local tomography [Koulakov et al., 2006] and lithospheric boundaries [Tassara et al., in prep]. The results imply major along-strike variations in the mechanisms of crustal deformation. At the latitude of the Altiplano, there is scarce forearc seismicity. The thin-skinned Bolivian retroarc thrust belt shows no seismic events (magnitude ? 4.5), suggesting that it is deforming aseismically or locked. In contrast, at the latitude of the Puna to the south (20-25S), crustal seismicity is more prevalent in both the forearc and retroarc. Within this region, active deformation in the Coastal Cordillera near Antofagasta is occurring along steeply east-dipping normal faults at 15-41 km depth; this is the only part of the central Andean forearc that displays prominent extension. Outboard of this, thrust events at ~15 km depth in the forearc wedge display gently dipping nodal planes, and may be signatures of underplating crust that was tectonically eroded at the trench. Underplating is a likely process by which this region of the forearc has undergone ~1 km of surface uplift during the Neogene. Seismicity with thrust or reverse and oblique focal mechanisms in the retroarc wedge is localized beneath the frontal part of the thick-skinned Eastern Cordilleran thrust belt and the Santa Barbara ranges. Seismicity along discrete, east- and west-dipping planes occurs to near Moho depths (~50 km). While retroarc crustal seismicity continues to the south toward the Juan Fernandez flat slab, there is a concentration of seismic events in the retroarc at the latitude (22-23S) where there is prominent normal faulting in the forearc. We interpret the compiled data to suggest that at the latitude of the Puna, orogenic wedge tapers of both the forearc and retroarc wedges may be supercritical as a result of late Miocene to Recent lithosphere removal from beneath the hinterland.

Metcalf, K.; Pearson, D. M.; Kapp, P. A.; McGroder, M.; Kendall, J. J.

2011-12-01

267

NeogeneQuaternary magmatism and geodynamics in the CarpathianPannonian region: a synthesis  

Microsoft Academic Search

In the CarpathianPannonian region in Neogene times, westward-dipping subduction in a land-locked basin caused collision of two lithospheric blocks (Alcapa and Tisia) with the southeastern border of the European plate. Calc-alkaline and alkaline magmatism was closely related to subduction, rollback, collision and extension. From the spatial distribution of the magmatic activity, four segments can be defined: Western Segment (magmatism occurring

Ioan Seghedi; Hilary Downes; Alexandru Szakcs; Paul R. D. Mason; Matthew F. Thirlwall; Emilian Ro?u; Zoltn Pcskay; Em Mrton; Cristian Panaiotu

2004-01-01

268

John Perry's neglected critique of Kelvin's age for the Earth: A missed opportunity in geodynamics  

Microsoft Academic Search

Many readers know the tale of how William Thomson (later Lord Kelvin) calculated the age of the Earth from physical prin- ciples and adhered for over 50 years to an estimate that was far younger than geologists' estimates, despite the virtually unani- mous opposition of the geological community of the time. The prevalent version of this tale alleges that the

Philip England; Peter Molnar; Frank Richter

2007-01-01

269

The composition of hydrous partial melt at 410 km: Geodynamic implications (Invited)  

NASA Astrophysics Data System (ADS)

Geophysical observations of low S-wave velocities and high electrical conductivities at 410 km depth have been interpreted as evidence for the presence of silicate melt on top of the Earths transition zone. It has been suggested that the difference in the water storage capacity of upper mantle versus transition zone minerals may cause dehydration melting as material up-wells across the 410. A key question is whether this hydrous partial melt is neutrally buoyant in the mantle at these conditions. In order to assess these possibilities it is important to determine the likely composition of small degree hydrous melts at these conditions and to measure the H2O contents of mantle minerals coexisting with this melt phase. The composition of a hydrous melt in equilibrium with a mantle peridotite composition has been determined at conditions equivalent to the top of the 410 km seismic discontinuity i.e. 13 GPa and 1550 oC. Sandwich experiments were performed in the Fe-free CMASH system where an initial-guess hydrous melt composition was equilibrated with 50% anhydrous peridotite. Fe-free compositions ensured that H2O was not lost during the experiments as H2, because H2O contents must be determined through mass balance using the starting bulk composition. The resulting melt composition was used to assemble a further melt, which was then equilibrated in the same way. After several iterations it was possible to derive a melt composition, which was in equilibrium with a mineral assemblage identical to that observed for an anhydrous peridotite composition at the same conditions. In addition we performed further experiments to assess the Fe-Mg partitioning between hydrous silicate melt and mineral phases at the same conditions. With these partition coefficients the composition of the melt phase could be calculated. We found the equilibrium melt to contain 7 wt % H2O but to have a lower FeO content then previously predicted. The results of melt density calculations indicate that this melt would not be neutrally buoyant at conditions compatible with the base of the upper mantle.

Mookherjee, M.; Frost, D. J.

2010-12-01

270

Petrogenesis and geodynamic significance of silicic volcanism in the western Trans-Mexican Volcanic Belt  

NASA Astrophysics Data System (ADS)

Silicic volcanism in the western Trans-Mexican Volcanic Belt (WTMVB) was defined a Pliocene ignimbrite flare-up associated with the rifting of the Jalisco block from mainland Mexico (Frey et al., 2007; GSAB). With the integration of new and published geochronologic, geochemical, and isotope data we revise this interpretation and propose a new petrogenetic model. The oldest silicic volcanism consists of large silicic domes and minor pyroclastic flows (~370 km3) emplaced to the north of Guadalajara above a thick succession of ~11 to 8.7 Ma basaltic lavas, which yielded Ar-Ar and obsidian FT ages of ~7.5 to 5 Ma. Shortly after (4.9 to 2.9 Ma) large amount of rhyolitic lavas and ash flow tuffs (~500 km3) were emplaced in a WNW-ESE trending belt from Guadalajara to Compostela. Rhyolitic domes and flows (~430 km3) were emplaced also in the Pleistocene mostly between Tequila and Guadalajara with the late Pleistocene La Primavera caldera (~35 km3) as the sole explosive volcanic episodes. As a whole, silicic volcanism occurred from Late Miocene to the Pleistocene, and was dominated by dome and lava flows. Most rhyolites have high LILE/HFSE values and negative spikes at Nb, P and Ti. They also show the same Ba/Nb and K/Rb values and slightly higher Rb/Sr ratios as the 11-8 Ma basalts. Rhyolite Sr isotope data (87Sr/86Sr init = 0.70371 - 070598) are only slightly more radiogenic than the 11-8 basalts (87Sr/86Sr init = 0.70349-0.70410), whereas Nd isotope ratios are indistinguishable from them. Sr and Nd isotope ratios of the rhyolites are also similar to the crust nearby, indicating that they can be compatible either with fractional crystallization (FC) of basalts or with crust assimilation/melting. However REE contents are too low to be the result of basalt FC. Isotope and REE data can be successfully modelled with an initial crustal melt which subsequently undergone fractional crystallization of feldspar and quartz. Late Miocene slab detachment and subsequent slab rollback produced pulses of mafic magma that were partly trapped in the crust yielding crustal melting. Extensional faulting since the Pliocene favours the eruption of silicic magma as effusive dome and lava flows. Rifting at the boundaries of the Jalisco block is seen as a rollback induced reactivation of crustal structures but is unlike to evolve into a Jalisco microplate.

Petrone, C. M.; Ferrari, L.; Orozco, M. A.; Lopez Martinez, M.

2012-04-01

271

Late Cainozoic geodynamic evolution of Thessaly and surroundings (central-northern Greece)  

NASA Astrophysics Data System (ADS)

In the framework of the late Alpide deformation of Greece and of the recent and active extensional tectonism of the Aegean region, the geotectonic evolution of the Thessaly region (central-northern Greece) has been examined, using a quantitative and qualitative structural analysis; stratigraphie, sedimentological, morphotectonic and seismological data. The geometry of the faults, their architecture and the knowledge of the stress pattern are used to explain some aspects of the tectonics and crustal dynamics of Thessaly and the surrounding area. The oldest compressional phases taken into account show a mean ENE-WSW trending direction of shortening and have been defined as late Alpide (early Aquitanian and Langhian). A later (Late Miocene-Pliocene) NE-SW oriented extensional phase has been related to the Hellenic post-orogenic collapse which developed behind the collisional front between the Aegean (Eurasia) and African plates. This phenomenon diachronically migrated from the east (Central Macedonia, Thermaikos Basin) towards the west (Epirus, Albania) where it is still active. As a consequence of this second phase, the area forms a basin and range like structure. The third, and last, phase (Middle Pleistocene-present) is characterized by a N-S direction of extension and affects the entire Aegean region. It generated new E-W trending basins, superimposed on the inherited ones. This gave as a final result, the complex block pattern we can see today. The recent and active right-lateral strike-slip movements along the North Aegean Trough seem to stop in the Sporades Basin and do not affect the uppermost crust of mainland Greece. A further WNW-ESE directed extension observed occasionally in central and northern Greece could be explained by local events or as block-related deformation.

Caputo, Riccardo; Pavlides, Spyros

1993-08-01

272

Magmatic evolution of Sulawesi (Indonesia): constraints on the Cenozoic geodynamic history of the Sundaland active margin  

Microsoft Academic Search

Tertiary and Quaternary magmatic rocks from West Sulawesi record the complex history of part of the Sundaland margin where subduction and collision have been and are still active. The present study, based on petrographic data, major- and trace-element chemistry and 40K?40Ar dating aims to document the age and chemical characteristics of the magmatic formations from West Sulawesi and to determine

M. Polve; R. C. Maury; H. Bellon; C. Rangin; B. Priadi; S. Yuwono; J. L. Joron; R. Soeria Atmadja

1997-01-01

273

Crustal and Mantle Deformation in the Aegean Region: Evidence From Seismic Anisotropy and Geodynamic Modelling  

Microsoft Academic Search

Unlike the nearly rigid oceanic lithospheric plates, continental plates can undergo pervasive internal deformation. The mechanisms of this deformation are disputed, with observational constraints on three-dimensional flow at depth currently insifficient. New measurements of Rayleigh-wave dispersion in the Aegean region provide such constraints and reveal layered seismic anisotropy indicative of distributed deformation within the lithosphere. Across the northern Aegean, fast

S. Lebedev; B. Endrun; C. Tirel; T. M. Meier

2009-01-01

274

Laser geodynamic satellite thermal/optical/vibrational analyses and testing. Volume 1: Executive summary  

NASA Technical Reports Server (NTRS)

The results of the LAGEOS Thermal/Optical/Vibrational Analyses and test program conducted for the National Aeronautics and Space Administration are presented. The purpose of this study is to verify, through analysis and test, that the MSFC LAGEOS design inherently provides a retroreflector thermal environment which maintains acceptable retroreflector internal thermal gradients. Acceptable thermal gradients are those which result in less than 50% degradation of optical performance from isothermal optical performance. This volume provides an executive summary of the study program. It summarizes the study objectives, the study approach, the principal assumptions, the type of basic data generated and the significant results.

1974-01-01

275

Late paleozoic base and precious metal deposits, East Tianshan, Xinjiang, China: Characteristics and geodynamic setting  

USGS Publications Warehouse

The East Tianshan is a remote Gobi area located in eastern Xinjiang, northwestern China. In the past several years, a number of gold, porphyry copper, and Fe(-Cu) and Cu-Ag-Pb-Zn skarn deposits have been discovered there and are attracting exploration interest. The East Tianshan is located between the Junggar block to the north and early Paleozoic terranes of the Middle Tianshan to the south. It is part of a Hercynian orogen with three distinct E-W-trending tectonic belts: the Devonian-Early Carboniferous Tousuquan-Dananhu island arc on the north and the Carboniferous Aqishan - Yamansu rift basin to the south, which are separated by rocks of the Kanggurtag shear zone. The porphyry deposits, dated at 322 Ma, are related to the late evolutionary stages of a subduction-related oceanic or continental margin arc. In contrast, the skarn, gold, and magmatic Ni-Cu deposits are associated with post-collisional tectonics at ca. 290-270 Ma. These Late Carboniferous - Early Permian deposits are associated with large-scale emplacement and eruption of magmas possibly caused by lithosphere delamination and rifting within the East Tianshan.

Mao, J.; Goldfarb, R. J.; Wang, Y.; Hart, C. J.; Wang, Z.; Yang, J.

2005-01-01

276

Chapter 8: Understanding How the Earth Works: A Geodynamic Revolution Based on Linux Computing INTRODUCTION  

E-print Network

-caps, or are there other mechanisms that may result in major fluctuations of relative sea-level? LINUX BEOWULF PARALLEL. This approach was pioneered by The Beowulf Project, a collaboration between Red Hat Software, NASA Goddard Space supercomputer. The modular design of the Beowulf concept allows scientists and industry to build machines, which

Müller, Dietmar

277

Deep Structure of the Earth and Concentration of Metals in the Lithosphere: A Geodynamic Approach  

NASA Technical Reports Server (NTRS)

A discussion of and introduction to satellite-altitude geopotential fields studies and their interpretation with emphasis on results from metalliferous regions will be given. The magnetic and gravimetric measurements from satellite altitudes show heterogeneity in deeper parts of the lithosphere. These patterns of magnetic anomalies do not only reveal the largest iron ore deposits such as Kiruna, Sweden and Kursk, Russia, but also linear features indicating structural discontinuities. Changes of magnetic amplitude of these patterns are caused by intersecting transverse fractures localizing magmatism and concentration of metals. The role of trans-regional mantle-rooted structural discontinuities in the concentration of metals will be discussed and a new type of mineral prognosis map will be presented. Deep-rooted structural discontinuities, defined by combination of geological and geophysical criteria, with spacing of several hundred kilometers, reveal a quite uniform pattern in the deeper parts of the lithosphere. As these structures provide favorable pathways for the ascent of heat, magmas and ore-forming fluids, their recognition is of crucial importance and can be used in the compilation of a new type of mineral prognosis map. Examples are shown from the United States, Canada, China, Burma, South America, Europe and Australia. The European example includes a pattern of east west trending structural discontinuities or belts and their junction with the NW-trending Tornqvist-Teisseyre Line. The Upper Silesian-Cracovian Zn-Pb district occurs along one of the latitudinal belts. Leslaw Teper of the University of Silesia has been invited to show the fractures in crystalline basement beneath the sediments hosting the Zn-Pb ores.

Taylor, Patrick T.; Kutina, J.; Pei, R.

2004-01-01

278

Concepts for reference frames in geodesy and geodynamics - The reference directions  

NASA Technical Reports Server (NTRS)

The paper discusses a study that establishes a reference frame, moving with the earth (in some average sense), in which the geometric and dynamical behavior of the earth can be monitored, and whose motion with respect to inertial space can also be determined. Emphasis is placed on the fact that the reference directions at an observation point on the earth surface, are defined by fundamental vectors for both space and time. The interrelationships between this space- and time-variant angular parameter are illustrated in a commutative diagram and tower of triads. Although the model tower is also space- and time-variant, its variations are described by adopted parameters using our current knowledge of the earth.

Grafarend, E. W.; Richter, B.; Mueller, I. I.; Papo, H. B.

1979-01-01

279

Paleostress reconstructions and geodynamics of the Baikal region, Central Asia, Part 2. Cenozoic rifting  

Microsoft Academic Search

Investigations on the kinematics of rift opening and the associated stress field present a renewed interest since it has recently been shown that the control of the origin and evolution of sedimentary basins depends to a large extent on the interplay between lithospheric strength and applied stresses. It appears that changes of stress field with time are an important factor

Damien Delvaux; Rikkert Moeys; Gerco Stapel; Carole Petit; Kirill Levi; Andrei Miroshnichenko; Valery Ruzhich; Volodia San'kov

1997-01-01

280

Late Paleozoic paleogeographic reconstruction of Western Central Asia based upon paleomagnetic data and its geodynamic implications  

E-print Network

Late Paleozoic paleogeographic reconstruction of Western Central Asia based upon paleomagnetic data Paleozoic poles of Central Asia blocks show: (1) counter clockwise rotation of West Junggar with respect;1. Introduction Paleozoic continental growth in Central Asia results from successive accretion, collision

Paris-Sud XI, Université de

281

Calculation of derivatives of the earth's gravitational potential for use in satellite geodesy and geodynamics  

NASA Astrophysics Data System (ADS)

The derivatives of the earth's gravitational potential are expressed in terms of series of normalized spherical harmonics, and their coefficients are obtained in the form of linear combinations of normalized Stokes constants. The resulting expressions are used to develop an efficient algorithm for calculating the derivatives. The use of this algorithm instead of the well-known Cunningham's (1970) algorithm makes it possible to reduce the time required for the computation.

Abrikosov, O. A.

1986-04-01

282

Lower Carboniferous carbonates rocks in Chukotka (North-East of Russia): paleogeographical reconstruction and geodynamic events  

NASA Astrophysics Data System (ADS)

Carbonates of Anyui-Chukotka fold belt are widespread in Devonian and Carboniferous age. Missisipian limestones of different tectonic structure were investigated. We examine limestones from i) South-Anyui Suture (Polarny Creek); ii) Alarmaut uplift, iii) Kibera Cape and iv) Wrangel island. Limestones of Polarny Creek contain fragments of fauna and they occur with basalt-chert rocks (Sizhykh et al., 1977; Sokolov et al., 2006). Carbonates of Alarmaut uplift have terrigenous materials (sandstones) and are associated with schists. Carboniferous rocks of Kibera Cape consist of sandstones, gravels and conglomerates in the lower part of Mississipian unit. In the upper part they replaced by limestones and dolostones. Lower Carboniferous formation of Wrangel Island is composed of clastic and carbonate rocks with evaporates (Kos'ko et al., 1993, 2003). The lower unit of the Lower Carboniferous formation is composed of conglomerate or gravelstone with fragments of locally derived Devonian rocks. All carbonate rocks contain lenses and interlayers of cherts. We used geochemical criteria and isotopic data for understanding the Paleogeographic position of different Carboniferous blocks. Sedimentation of carbonates of Wrangel Island and Kibera Cape was in shallow-marine shelf of carbonate platform with lagoon shoal. Carbonates of Alarmaut uplift accumulating in the shallow-marine environment, in active hydrodynamics conditions. Sedimentation of Polarny Creek (SAS) was not near from bioherm reef. We have demonstrated the different paleogeographic environments for Chukotka's carbonate platform. Sedimentological, geochemical and isotopic data indicate shallow sea-water of carbonate platform for limestones of Alarmaut uplift, Kibera Cape and Wrangel island. Limestones of Polarny Creek (South-Anyui Suture) may be a part of a carbonate sequence formed on a volcanic atoll. Paleozoic deposits of Wrangel Island are presented as fragment of Arctida-Crockerland basement (Shatsky, 1935; Eardly, 1948; Embry, 1993, 2011). In our opinion, Carboniferous carbonates rocks of Chukotka are the part of carbonate platform of Old continental block, that was existent in the north of Arctic. Lower Carboniferous limestones of South-Anyui Suture cannot be considered an element of the exhumed Paleozoic section of Anyui-Chukotka fold belt (Sokolov et al., 2006). Acknowledgments: This work is financially supported by RFBR Project nos. 11-05-00074, 11-05-00787, 14-05-00031 and Scientific School NSh - 2981.2014.5

Tuchkova, Marianna; Sokolov, Sergey; Khudoley, Andrey; Pokrovsky, Boris; Vatrushkina, Elena

2014-05-01

283

Geodynamics and metallogeny of the central Eurasian porphyry and related epithermal mineral systems: A review  

NASA Astrophysics Data System (ADS)

Major porphyry Cu-Au and Cu-Mo deposits are distributed across almost 5000 km across central Eurasia, from the Urals Mountains in Russia in the west, to Inner Mongolia in north-eastern China. These deposits were formed during multiple magmatic episodes from the Ordovician to the Jurassic. They are associated with magmatic arcs within the extensive subduction-accretion complex of the Altaid and Transbaikal-Mongolian orogenic collages that developed from the late Neoproterozoic, through the Palaeozoic, to the Jurassic intracratonic extension. The arcs formed predominantly on the Palaeo-Tethys Ocean margin of the proto-Asian continent, but also within two back-arc basins. The development of the collages commenced when slivers of an older Proterozoic subduction complex were rifted from an existing cratonic mass and accreted to the Palaeo-Tethys Ocean margin of the combined Eastern Europe and Siberian cratons. Subduction of the Palaeo-Tethys Ocean beneath the Karakum and Altai-Tarim microcontinents and the associated back-arc basin produced the overlapping late Neoproterozoic to early Palaeozoic Tuva-Mongol and Kipchak magmatic arcs. Contemporaneous intra-oceanic subduction within the back-arc basin from the Late Ordovician produced the parallel Urals-Zharma magmatic arc, and separated the main Khanty-Mansi back-arc basin from the inboard Sakmara marginal sea. By the Late Devonian, the Tuva-Mongol and Kipchak arcs had amalgamated to form the Kazakh-Mongol arc. By the mid Palaeozoic, the two principal cratonic elements, the Siberian and Eastern European cratons, had begun to rotate relative to each other, "drawing-in" the two sets of parallel arcs to form the Kazakh Orocline between the two cratons. During the Late Devonian to Early Carboniferous, the Palaeo-Pacific Ocean began subducting below the Siberian craton to form the Sayan-Transbaikal arc, which expanded by the Permian to become the Selanga-Gobi-Khanka arc. By the Middle to Late Permian, as the Kazakh Orocline continued to develop, both the Sakmara and Khanty-Mansi back-arc basins were closed and the collage of cratons and arcs were sutured by accretionary complexes. During the Permian and Triassic, the North China craton approached and docked with the continent, closing the Mongol-Okhotsk Sea, an embayment on the Palaeo-Pacific margin, to form the Mongolian Orocline. Subduction and arc-building activity on the Palaeo-Pacific Ocean margin continued to the mid Mesozoic as the Indosinian and Yanshanian orogens.

Seltmann, Reimar; Porter, T. Mike; Pirajno, Franco

2014-01-01

284

Geodynamical model of development the gold ore deposit Muruntau in Central Kyzylkums /Western Uzbekistan/  

NASA Astrophysics Data System (ADS)

Recent advances in geology and sciences dealing with planets resulted in ever-growing information on the internal structure and composition of upper and lower mantle and its role in the development of mineral deposits. Thus, the analysis of geologic-geophysical velocity sections on DSS-MOVZ profiles, that cross Central Kyzylkum, has revealed a number of features, which are characteristic of the upper mantle rocks, related to morphology of bodies, their physical properties, consisting mainly in their contrasting values for contiquous blocks, and general increased velocity and density of the rocks they contain. Petrologic-geophysical analysis of the same profiles proved the previous conclusions, and besides it allowed us to create the geodinamical model of development of a complicated continental lithosphere within Central Kyzylkum Ore Magmatic Concenter (CKOMC). CKOMC is a part of Western Uzbekistan's territory, that has maximum concentration of gold ore deposits of different scale, including the gigantic one- Muruntau. There are two main factors, that condition the area of the concenter: 1.Obduction of crust of the ocean to continental one during the Upper Paleozoic collision of Kyrgiz-Kazakh and Karakum-Tadjik microcontinents; 2.Geochemical gold specialization of Turkestan paleo-ocean's lithosphere. As a result of obduction of doubled, and sometimes even trebled crust of the ocean to continental, the front of rock granitization shifted to the sphere of ocean sediments development, and granite-gneiss layer of the continental crust went down to granulite zone. The latter factor provoked mass penetration of fluids from the former granite-gneiss and sedimentary-metamorphic layers, which due to their uprush to the surface, formed fluid-hydrothermal system , enriched with gold, in the new upper crust. This, in its turn, conditioned the formation of numerous gold ore deposits of different facies and formations observed in Central Kyzylkums. Abrupt increase in the crust's thickness has broken the balance of the crust and mantle, melts of which also rushed upwards along the rift zones and faults, replacing the ancient and the newly formed granite-gneiss layer. Such a mechanism of the continental lithosphere formation explains the formation of blocks of crust, conditioned by the abrupt change of rocks having different density (1), and the presence single parts waveguides in lower parts of the upper crust, which are considered to be relics of the primary granite-gneiss layer enriched with fluids. Only the wedge of crust of the ocean thrusted over the continental crust could cause formation of rock blocks of unusual shape and content, but of the same metallogenic gold ore trend. The studied profiles allowed us to determine one more magmatogene structure of mantle formation. It has funnel shape, with its basement directed to the surface. Complex ring plutons and tectonic ring-shaped disturbances these can be seen during the analysis of space images. The narrowed part of the structure goes down to the lower mantle, and can form a shape of sand-glass, the surface of which served as a conductor of mantle plumes to the upper crust. Evidence of this are bodies of alkaline mafites and ultramafites in the upper crust of Central Kyzylkums, and presence of non-coherent elements containing gold (such as platinum and rare earth elements) at gold ore deposits.

Sidorova, I. P.

2004-12-01

285

Investigation of dynamic noise affecting geodynamics information in a tethered subsatellite  

NASA Technical Reports Server (NTRS)

Measurement of the gradient of the gravitational acceleration from a satellite platform is likely to provide the next improvement in knowledge of the Earth's gravity field after the upcoming Geopotential Research Mission. Observations from the subsatellite of a tethered satellite system (TSS) would increase sensitivity and resolution due to the low altitude possible. However, the TSS is a dynamically noisy system and would be perturbed by atmospheric drag fluctuations. The dynamic noise is being modeled in order to evaluate the feasibility of TSS gradiometry and to design methods of abating the error caused by this noise. The demonstration flights of the TSS are to provide an opportunity to directly observe the dynamical environment and refine modeling techniques. Random vibration analysis as a technique for modeling the TSS under atmospheric perturbation was studied.

Gullahorn, G. E.

1985-01-01

286

Contribution to defining a geodetic reference frame for Africa (AFREF): Geodynamics implications  

NASA Astrophysics Data System (ADS)

African Reference Frame (AFREF) is the proposed regional three-dimensional standard frame, which will be used to reference positions and velocities for geodetic sites in Africa and surrounding. This frame will play a crucial role in scientific application for example plate motion and crustal deformation studies, and also in mapping when it involves for example national boundary surveying, remote sensing, GIS, engineering projects and other development programs in Africa. To contribute to the definition of geodetic reference frame for Africa and provide the first continent-wide position/velocity solution for Africa, we processed and analyzed 16 years of GPS and 17 years of DORIS data at 133 GPS sites and 9 DORIS sites continuously operating geodetic sites in Africa and surroundings to describe the present-day kinematics of the Nubian and Somalian plates and constrain relative motions across the East African Rift. We use the resulting horizontal velocities to determine the level of rigidity of Nubia and updated a plate motion model for the East African Rift and revise the counter clockwise rotation of the Victoria plate and clockwise rotation of the Rovuma plate with respect to Nubia. The vertical velocity ranges from -2 to +2 mm/yr, close to their uncertainties with no clear geographical pattern. This study provides the first continent-wide position/velocity solution for Africa, expressed in International Terrestrial Reference Frame (ITRF2008), a contribution to the upcoming African Reference Frame (AFREF). In the next step we used the substantial increase in the geologic, geophysical and geodetic data in Africa to improve our understanding of the rift geometry and the block kinematics of the EAR. We determined the best-fit fault structure of the rift in terms of the locking depth and dip angle and use a block modeling approach where observed velocities are described as the contribution of rigid block rotation and strain accumulation on locked faults. Our results show a better fit with three sub-plates (Victoria, Rovuma and Lwandle) between the major plates Nubia and Somalia. We show that the earthquake slip vectors provide information that is consistent with the GPS velocities and significantly help reduce the uncertainties in plate angular velocity estimates. However, we find that 3.16 My average spreading rates along the Southwest Indian Ridge (SWIR) from MORVEL model are systematically faster than GPS-derived motions across that ridge, possibly reflecting the need to revise the MORVEL outward displacement correction. In the final step, we attempt to understand the hydrological loading in Africa, which may affect our geodetic estimates, particularly the uplift rates. In this work, we analyze 10 years (2002 - 2012) of continuous GPS measurements operating in Africa, and compare with the modeled hydrological loading deformation inferred from the Gravity Recovery and Climate Experiment (GRACE) at the same GPS location and for the same time period. We estimated hydrological loading deformation based on the Equivalent Water Height (EWH) derived from the 10-days interval reprocessed GRACE solution second release (RL02). We took in to account in both GPS and GRACE the systematic errors from atmospheric pressure and non-tidal ocean loading effects and model the Earth as perfect elastic and compute the deformation using appropriate Greens function. We analyze the strength of association between the observation (GPS) and the model (GRACE) in terms of annual amplitude and phase as well as the original data (time-series). We find a good correlation mainly in regions associated with strong seasonal hydrological variations. To improve the correlation between the two solutions, we subtract the GRACE-derived vertical displacement from GPS-observed time series and determine the variance reduction. Our solution shows average variance between the model and the observation reduced to ~40%. (Abstract shortened by UMI.)

Saria, Elifuraha E.

287

Paleomagnetic dating of continental geological formations: Strong diachronism evidenced in the Saharan platform and geodynamical implications  

NASA Astrophysics Data System (ADS)

The paleomagnetism is a powerful tool to date formations that have age not constrained by paleontological, stratigraphical or radiochronological data. It was applied, on the western border of the Murzuq basin in Algeria (Saharan platform), to the Zarzatine formation, attributed to a Middle-Upper Triassic-Lower Jurassic age. Comparison of the obtained paleomagnetic pole with previous poles from the same geological formation outcropping in another basin and from other Carboniferous to Lower Mesozoic African formations yielded a clearly older age (Late Permian) than expected. That evidences a strong diachronism (at least 40 My) of the deposition of this formation on the Saharan platform. The post-Hercynian structural evolution was therefore different according to the parts of this platform, with significant differential vertical tectonic movements. The latter were at the origin of erosion, hiatus or sediments deposition according to areas.

Henry, B.; Derder, M. E. M.; Amenna, M.; Maouche, S.; Bayou, B.; Ouabadi, A.; Bouabdallah, H.; Beddiaf, M.; Ayache, M.; Bestandji, R.

2014-11-01

288

Paleomagnetic and AMS data evidencing a polyphased geodynamical evolution in the Ougarta magmatic complexes (Algerian Sahara)  

NASA Astrophysics Data System (ADS)

The Ougarta fold belt is located at the junction between the West African Craton and the Panafrican domain of the Saharan platform. It is mainly related to the Variscan orogeny and was assumed to be of Post-Moscovian age. It mainly consists of NW-SE trending folds system. The magmatic complexes outcrop in the core of exhumed and eroded anticlines. They are identified as ignimbritic, andesitic to basaltic volcanism and as volcano-sedimentary levels Magnetic fabric and remanent magnetization of these magmatic complexes are carried essentially by secondary hematite, probably related to hydrothermal events at the origin of ore deposits in the Ougarta belt. Magnetic foliation is of tectonic origin, while magnetic lineation could be related to hydrothermalism. The two obtained paleomagnetic directions correspond to syn-folding and post-folding remagnetizations. The comparison with the African APWP indicates Famenian-Tournaisian and Visean ages for these remagnetizations. These differents results imply that at least, two deformation phases, with different folding orientations and much older than previously assumed, affected the studied area.

Eddine Merabet, Nacer-; Henry, Bernard; Lamali, Atmane; Maouche, Said; GraineTazerout, Khadidja; Mekkaoui, Abderrahmane; Ayache, Mohamed

2014-05-01

289

Polymetamorphic complexes in the eastern parts of the Balkan Peninsula: 600 Ma of geodynamic evolution  

NASA Astrophysics Data System (ADS)

Polymetamorphic amphibolite-facies complexes are exposed in the eastern and central parts of the Balkan Peninsula in different Alpine tectonic zones and under different Cadomian to Alpine collisional and exhumation histories and regimes. All complexes consist mostly of biotite and two-mica gneisses and schists, and amphibolites. Strong Cadomian overprint led to intimate mixing (tectonometamorphic amalgamation) of crustal and mantle (and/or oceanic crust)-derived (serpentinized ultramafics, eclogites) products. The pre-Cadomian complex in Central Sredna-gora Mountains evolved through Cadomian collision with c. 617 Ma granites, Hercynian 340 to 250 Ma granitoids, Late Permian exhumation, and Triassic-Jurassic sedimentation followed by Mid-Cretaceous exhumation. P-T conditions never reached amphibolite facies in post-Cadomian times except for some shear zones. The pre-Cadomian amphibolite-facies complex in Sakar Mt. was intruded by c. 500 Ma old granites, deeply eroded in late Permian time, and covered with depositional contact by Triassic terrestrial and marine sediments. Both basement and Triassic cover suffered folding and amphibolite-facies metamorphism (c. 150 Ma BP) followed by exhumation. Included in the Srednogorie Late Cretaceous volcanic arc as crystalline cores, these complexes have been affected by latest Cretaceous exhumation. Amphibolite-facies polymetamorphic cores (Ograzhdenian complex) within the Serbo-Macedonian massif and other units in SW Bulgaria and the adjacent countries were subjected to intense Cadomian (560 - 520 Ma BP) synmetamorphic collision and granite activity. Some units suffered Cadomian collision under greenschist-facies with a Neoproterozoic to Cambrian diabase-phyllitoid complex or have been exhumed and directly covered by Cambrian (followed by Cambrian limestones) or Tremadocian marine sandstones. After Palaeozoic exhumation, their structure was sealed by Permian, Triassic and Jurassic terrestrial and marine sediments, and after intense Mid-Cretaceous folding and thrusting, exhumed again in Palaeogene times. In the Rhodope region, the Mesoproterozoic? to Neoproterozoic supracrustal Rhodopian complex is built up of kyanite-, garnet- and staurolite-bearing biotite and two-mica gneisses and schists, amphibolites, marbles, calcareous schists, quartzo-feldspathic gneisses (derived of possible arkosic or rhyolitic protoliths), and orthoamphibolite, metaperidotite and eclogite rootless bodies. Migmatites and anatexites crop out in the cores of Rhodopian domes. Mid-Cretaceous thrusting in greenschist-facies conditions is documented at the peripheries of the Rhodope massif, and probably contributed to considerable (up to 70 km; now about 50 km) crustal thickening in the interior. The cores underwent very late (Early to Late Palaeogene) exhumation. Eclogitic rootless bodies that witness HP to UHP metamorphic events crop out in all complexes mentioned. Eclogite formation is referred to different mechanisms (burial through subduction of oceanic crust; amalgamation of mantle and crustal slivers in depth; metamorphism of deep norite to troctolite intrusions; local increase of pressure and temperature along minor shear zones) and times (Cadomian, Hercynian, Cimmerian and/or Alpine).

Zagorchev, I.

2007-12-01

290

Effect of geodynamics on the reliability of the dam behind the Chirkey hydroelectric power plant  

SciTech Connect

The chirkey hydraulic facility is located in the territory of one of the most seismically active sections of the Caucasus - the Dagestan wedge seismofocal region (SFR). Large-scale paleoseismodeformations have been observed here, and a series of destructive earthquakes with magnitudes of 5.3-6.7 and intensities of 7-8 ponts occurred in 1970 through 1976.

Marchuk, A.N.; Misrikhanov, M.S.; Abakarov, A.R. [and others

1994-11-01

291

Geodynamic evolution of southwestern Pre-Caspian region and neighboring areas of Northern Caucasus  

SciTech Connect

The study area includes two hydrocarbon-bearing basins. They are the southwestern Pre-Caspian basin and the eastern Northern Caucasus basin. They formed by the interaction of East-European, Aravia, Kazakhstan, Northern Caucasus, Guriev, and Ustyurt continental and sub-continental blocks. In the southwestern Pre-Caspian basin, sedimentation began at passive margins (Early-Middle Paleozoic), included salt deposition while the passive margins deformed in continental collisions (Late Paleozoic), and continued during isostatic compensation (Mesozoic-Cenozoic). Source rocks accumulated on upper Devonian to Carboniferous continental shelves and slopes. Oil and gas are trapped in sub-salt carbonate reservoirs and in clastic and carbonate rocks in complex post-salt structures. Devonian to Permian rocks, which accumulated on the margins of the Guriev continental block, are the most prospective reservoirs. The eroding Caucasus orogen produced the sediments in the Northern Caucasus basin. Clays (Oligocene-Miocene) deposited on the deep shelf in front of the orogen are the local source rocks. In the northern part of the basin, faulted anticlines are traps in the Mesozoic sequence. Traps are in thrust structures in the southern part of the basin. Carbonate and clastic rocks of the Tersko-Caspian trough are prospective in the basin.

Kleshchev K.; Shein, V. [VNIGNI, Moscow (Russian Federation)

1995-08-01

292

Relationships between fracture patterns, geodynamics and mechanical stratigraphy in Carbonates (South-East Basin, France)  

NASA Astrophysics Data System (ADS)

This study aims at improving the understanding of fracture genesis in layered carbonate sedimentary sequences, focusing on field analysis of Jurassic to Maastrichtian age carbonates of Provence (France). Fracture patterns of 9 outcrops were characterized in 3D: 6 of Urgonian, 1 of Tithonian and 2 of Campanian-Late Maastrichtian ages. Seven sites are located in relatively weakly deformed areas away from larges fault and fold zones where strain partitioning and stress localization effects may take place. Two sites are located in fold flanks for the purpose of relative dating and for comparison with the sites in the weakly deformed areas. Patterns and detailed fracture attributes were compared to host rock sedimentary facies, porosity and P-wave velocities. Fracture chronology was determined with cross-cutting relationships and compared to burial/uplift history reconstructed from subsidence curves and from a regional structural analysis. Our results show that fractures are clustered in two perpendicular joint sets whatever the host rock age. We observe an average spacing of 20 cm and no control of strike, age, facies, or bed thickness on fracture size. There is no mechanical stratigraphy. The fracture sequence compared to subsidence curves indicates that fractures occurred before tectonic inversion, during early and rapid burial, whatever the host rock age and facies. The abundance of burial stylolites does not correlate with maximum burial depth but with fracture frequency, host rock porosity and P-wave velocity. We conclude that the studied carbonates had early brittle properties controlled by their geographic position rather than by depositional facies types and undergone early diagenesis. The porosity loss/gain and the mechanical differentiation in carbonates of Provence could have been acquired during very early burial and diagenesis and have preserved through time. This study also demonstrates that regional fracturing is not necessarily driven by large scale structural events as it is often assumed in fractured reservoir modelling.

Lamarche, Juliette; Lavenu, Arthur P. C.; Gauthier, Bertrand D. M.; Guglielmi, Yves; Jayet, Ocane

2012-12-01

293

Journal of Geodynamics 65 (2013) 94116 Contents lists available at SciVerse ScienceDirect  

E-print Network

The Cenozoic deformation and related basin formation in west- ern Anatolia is one of the hot topics-slip deformation in the Izmir­Balikesir transfer zone and consequences for late Cenozoic evolution of western deformation between the Cycladic and Menderes core complexes within the Aegean Extensional System. Here, we

Utrecht, Universiteit

294

Low frequency electromagnetic signals in the atmosphere caused by geodynamics and solar activity  

NASA Astrophysics Data System (ADS)

Due to the composed structure of the medium and large portions of energy transferred, a seismic excitation in the oceanic or continental lithosphere disturbs all types of geophysical fields. To investigate the problem of electromagnetic (EM) forcing on the atmosphere from the seismically activated lithosphere, we have formulated two mathematical models of interaction of fields of different physical nature resulting in arising of the low-frequency (from 0.1 to 10 Hz by amplitude of a few hundreds of pT) EM signals in the atmosphere. First we have considered the EM field generation in the moving oceanic lithosphere and then in the moving continental one. For both cases, the main physical principles and geological data were applied for formulation of the model and characteristics of the computed signals of different nature agree with measurements of other authors. On the basis of the 2D model of the seismo-hydro-EM-temperature interaction in a lithosphere-Ocean-atmosphere domain, a block-scheme of a multisensory vertically distributed (from a seafloor up to the ionosphere) tsunami precursors detection system is described. On the basis of the 3D model of the seismo-EM interaction in a lithosphere-atmosphere domain, we explain effect of location of the future seismic epicenter area (obtained by Prof. Kopytenko, Yu. A. from Inst. IZMIRAN of Russian Acad. Sci. and co-authors) as the result of the magnetic field measurements in the atmosphere near the earths surface. We believe that the biosphere effects of forcing on the atmosphere may not be ignored. We formulate the result of our measurements with the system of micro-voltmeters: low-frequency EM disturbances of the atmosphere caused by solar activity (namely, geomagnetic storms with the geomagnetic index values K = 5 and K = 6), are decreasing temporarily the coherence of oscillations of the electric potentials of different points on the surface of a head, i.e. the coherence of the human brain EM processes. We are grateful to Prof. Kopytenko, Yu. A. and participants of the scientific seminars and conferences in IZMIRAN and Space Research Institute, Russian Acad. Sci., for discussions and researchers of the IZMIRAN observatory for data about the K index dynamics.

Novik, Oleg; Ruzhin, Yuri; Ershov, Sergey; Volgin, Max; Smirnov, Fedor

295

Geodynamic scenario and structural styles of Mesozoic and Cenozoic basins in China  

SciTech Connect

The continental lithosphere of China is situated at the junction of the Marginal-Pacific and Tethys-Himalayan tectonic domains. The most manifest tectonic movements responsible for the deformation of the continental lithosphere of China are taphrogenic, collisional, and shearing. These movements played an important role in the Mesozoic and Cenozoic tectonic evolution of China and formed various types of Mesozoic and Cenozoic basins in China. The Marginal-Pacific crust in eastern China was attenuated by rifting and developed north-northeast-trending Mesozoic and Cenozoic basins, e.g., the Songliao, Bohai Bay, and Jianghan basins. Rifting mainly followed preexisting lineaments or shear zones in the basement. Then basin-range (graben-horst) structures and large fault-bounded basins developed. Extensional structural styles have prevailed in Mesozoic and Cenozoic basins in eastern China, with listric faults and tilted blocks in the basement, and detached faults, growth faults, and rollover anticlines or drape folds in the cover rocks. These structures are favorable for hydrocarbon accumulation; thus, the famous Daqing and Zhongyuan oil fields formed in Songliao basin and Bohai Bay basin, respectively. In western China the continental crust thickened by collision and formed a series of Mesozoic and Cenozoic intermontane and foreland basins, such as the Junggar (Dzungaria), Tarim, and Qaidam basins. Contraction structural styles are predominant in Mesozoic and Cenozoic basins in western China, with shortened fault blocks and ramps in basement, and thrust faults and folds in the cover rocks. The Kelamayi and Laojunmiao oil fields formed in these compressional basins. 22 figures, 1 table.

Hefu, L.

1986-04-01

296

The Neoproterozoic-Paleozoic Arctic Margins: early stages of geodynamic evolution and plate reconstructions  

NASA Astrophysics Data System (ADS)

Available data on the existence of Precambrian metamorphic complexes among the main structures of the Arctic led to the suggestion that a large continental mass existed between Laurentia, Baltica and Siberia - an Arctic continent, more often called Arctida (Zonenshain, Natapov, 1987). It is inferred that as an independent continental mass Arctida was formed after the breakup of Rodinia, and in general it can have a pre-Grenvillian (including Grenvillian) basement age. The breakup of this mass and the collision of its fragments with adjacent cratons led to the formation of heterochronous collisional systems. Arctida probably included the Kara, Novosibirsk, Alaska-Chukotka blocks, the blocks of northern Alaska and the submerged Lomonosov Ridge, small fragments of the Inuit fold belt in the north of Greenland and the Canadian archipelago, the structures of the Svalbard and maybe the Timan-Pechora plates. However the inner structure of this paleocontinent, the mutual configuration of the blocks and its evolution in the Neoproterozoic-Paleozoic is still a matter of discussion. The most accurate way of solving these issues is by using paleomagnetic data, but those are nonexistent for most of the defined blocks. Reliable paleomagnetic determinations for the Neoproterozoic-Paleozoic time interval we are concerned with are available only for fragments of an island arc from Central Taimyr, which are 960 m.y. old (Vernikovsky et al., 2011) and for which the paleomagnetic pole is very close to the pole of Siberia from (Pavlov et al., 2002), and of the Kara microcontinent. This includes three paleomagnetic poles for 500, 450 and 420 Ma (Metelkin et al., 2000; Metelkin et al., 2005). It is those data that made up the basis of the presented paleotectonic reconstructions along with an extensive paleomagnetic database for the cratons of Laurentia, Baltica, Siberia and Gondwana. The paleogeographic position of the cratons is corrected (within the confidence levels for the paleomagnetic poles) according to the general model and the available global reconstructions that include the structures of the Arctic (Scotese, 1997; Lawyer et al., 2002; Golonka et al., 2003, 2006; Cocks, Torsvik, 2002, 2007). The position of those Arctida blocks that lack paleomagnetic data is reconstructed based on geological data.

Vernikovsky, V. A.; Metelkin, D. V.; Vernikovskaya, A. E.; Matushkin, N. Yu.; Lobkovsky, L. I.; Shipilov, E. V.

2012-04-01

297

Journal of Geodynamics Offshore Oligo-Miocene volcanic fields within the Corsica-Liguria Basin  

E-print Network

of plutonic bodies of adakitic affinity, such as the quartz microdiorite laccolith locally referred and trace elements) and their whole-rock K-Ar ages and mineral 40 Ar-39 Ar plateau ages. Around 15 Ma, minor to the coast, contemporaneous calc-alkaline rocks erupted insu-00693261,version1-2May2012 Author manuscript

Paris-Sud XI, Université de

298

Paleomagnetic Evidence For A 80 Ccw Rotation of The Apenninic Platform (southern Apennines): Geodynamic Implications  

NASA Astrophysics Data System (ADS)

The tectonic evolution of the Apennine belt / southern Tyrrhenian Sea system is addressed through a paleomagnetic study of Lias to Langhian sediments from the Apenninic carbonate platform (southern Apennines). Paleomagnetic data from 21 sites document a regional-scale 80 counterclockwise (CCW) rotation occurring after Langhian. Since previous studies of the Plio-Pleistocene clays spread over the oro- genic belt had previously documented a ~20 CCW rotation, we conclude that the southern Apennines rotated by 60 during Middle-Late Miocene. Our data prove that the southeastward drift of Calabrian block (and synchronous spreading of the south- ern Tyrrhenian Sea) induced saloon-door like deformation of the southern Apennines and Sicily which underwent similar-magnitude (although opposite in sign) orogenic rotations. Our paleogeographic reconstruction shows that at 15 Ma (Late Langhian) the Alpine-Apennine belt collided with a NNE-oriented carbonate platform corridor surrounded by oceanic basins. We speculate that both the end of the Corsica-Sardinia rotation and the eastward jump of the locus of back-arc extension (from the Liguro- Provenal to the Tyrrhenian Sea) may have been consequences of this event.

Gattacceca, J.; Speranza, F.

299

InSAR application for geodynamic study of the 14 August 2003 Lefkada, Greece earthquake  

NASA Astrophysics Data System (ADS)

The area of the Central Ionian Islands, one of which is the Lefkada Island, is the transition zone between the West Hellenic arc and the Apulian plate and it is recognized as Kephalonia Fault Zone (KFZ) with strike-slip faulting. This zone is characterized by high seismicity and natural hazard potential. One of the most significant recent events (Mw = 6.3) occurred on August 14, 2003 northwest of the Lefkada island. The maximum intensity has been evaluated as Io = VII+ to VIII in the town of Lefkada. Using 20 available SAR images acquired by the ESA ENVISAT satellite, we produced 191 interferograms that we used to examine the co- and post-seismic crustal deformations caused by this earthquake. On the base of quality of the backscattered signal the results are divided in groups and from each group a map of coherence is produced. As a result an analysis of the coherent quality of the terrain and a choice of the most proper group for crustal deformation detecting is made. Whereupon seven ascending and nine descending ENVISAT images are used for generating of 21 best ascending and 36 best descending interferograms, respectively. From them, 6 ascending and 8 descending are co-seismic interferograms, sufficiently coherent to show a deformation of the Earth's surface of 5.6 cm in the western part of the Lefkada Island. These results are compared with the GPS measurements available on the island, and show adequate agreement. A dislocation model using the Okada formalism is proposed. References: Hollenstein Ch., M.D. Mller, A.Geiger, H.-G. Kahle (2008). GPS-Derived Coseismic Displacements Associated with the 2001 Skyros and 2003 Lefkada Earthquakes in Greece. Bulletin of the Seismological Society of America, Vol. 98, No. 1, pp. 149-161.

Ilieva, M.; Elias, P.; Briole, P.; Dimitrov, D.

2009-04-01

300

Fluid mixing and ore deposition during the geodynamic evolution of the Sierra Almagrera (Betics, Spain)  

NASA Astrophysics Data System (ADS)

Marine and continental intramountaineous basins developed during the Neogene orographic evolution of the Betico-rifan orogenic wedge, as well as the related uplifted ranges within the Sierra Almagrera Metamorphic Core Complexes (MCC). The NNE-SSW striking trans-Alboran transcurrent fault system crosscuts the MCC post-dating the extensional exhumation stages recorded in the metamorphic fabric. Iron ores ( Pb, Cu, Zn) are encountered either as stratabound ore deposits in the Neogene basins or as vein networks crosscutting the metamorphic fabric of graphitic phyllites from the Sierra Almagrera. These Late Miocene ore deposits are related to the activity of the N-S striking Palomares fault segment of the Trans-Alboran fault system. Three sets of quartz veins (V?, V?? and V?) and one set of mineralized vein (V?, siderite, barite) are distinguished. The V? and V?? respectively are totally or partially transposed into the foliation. The V? and V? veins are discordant to the foliation. The problem addressed in this study concerns the nature of the fluids involved in the metal deposits and their relationships with the main reservoir fluids, e.g. the deep metamorphic fluids, the basinal fluids, and eventually the recharge meteoric fluids. This study focuses thus on the evolution of the fluids at different stages of ductile-brittle exhumation of the metamorphic ranges (Sierras) and their role during the exhumation and later on in relation with the hydrothermalism and metal deposition at a regional scale. Paleofluids were studied as inclusions in quartz, siderite and barite from veins by microthermometry and Raman spectroscopy, and a stable isotope study is in progress. Earliest fluids recorded in (V??) quartz veins are H2O- NaCl + CaCl2 (17 wt. %) - (traces of CO2, CH4, N2) metamorphic brines trapped at the ductile brittle transition at a minimum trapping temperatures (Th) of 340 C. Older metamorphic fluids in (V?) veins were lost during the complete recrystallization of the original quartz grains during transposition. The second fluid type is characterized by very low salinity inclusions (1.2 wt.% NaCl) found in veins discordant to the foliation (V?), and precedes brines (23 wt. % NaCl + CaCl2 with Th of 320 C) trapped in transgranular fluid inclusion planes (FIP). The NW-SE to N-S directions of these FIP appears coherent with shortening directions related to Tortonian and Messinian basin development (Montenat, 1990). The halogen signatures of the latest brines confirm that they derive from primary brines issued from sea water evaporation. Fluid inclusions in barites and siderites from (V?) veins display a Br/Cl ratio more typical of secondary brines and a rather large range of salinities, this indicating distinct fluid movements and the dissolution of evaporates by dilute fluids may be of meteoric origin. Fluids in siderites show the lowest trapping temperature conditions around 190 C. The existence of a sea water component in fluids was previously mentioned by Morales Ruano et al. (1995) indicate a ?34S of 22,1-23.9 for barite from Sierra Almagrera. In conclusion, during the Neogene multistage evolution of the Almagrera MCC, fluids of different origins e.g. basinal, meteoric and metamorphic fluids have circulated within the crust, and locally interacted with evaporites. The resulting brines formed Fe-(Ba, Pb, Cu) ores in discontinuities affecting both the metamorphic and sedimentary rocks. Morales Ruano, S., Both, R., and Fenoll Hach-Ali, P., 1995, Fluid evolution and mineral deposition in the Aguilas - Sierra Almagrera base metal ores, southeastern Spain.: Mineral Deposits, p. 365-368. Montenat, C., 1990, Les Bassins nognes du domaine btique oriental (Espagne), Documents et Travaux IGAL n12-13, 392 p.

Dyja, Vanessa; Tarantola, Alexandre; Hibsch, Christian; Boiron, Marie-Christine; Cathelineau, Michel

2013-04-01

301

Convergent plate margin dynamics: New perspectives from structural geology, geophysics and geodynamic modelling  

E-print Network

: Convergent plate margin Subduction Collision Orogenesis Slab Plate tectonics Convergent plate margins occur when two adjoining tectonic plates come together to form either a subduction zone, where at least one and discussions since the advent of plate tectonic theory. This paper provides a historical background

Rawlinson, Nick

302

Techniques to achieve geodynamic self-consistency in data-assimilation models of mantle convection  

NASA Astrophysics Data System (ADS)

Recent models of mantle convection that incorporate data-assimilation such as paleogeography reconstructions of plate boundary locations, the history of global plate motions used as surface velocity boundary conditions and paleo-age of seafloor as a proxy for oceanic plate thickness, have been employed to generate mantle thermal structures that can be directly compared to present-day mantle structure as inferred from seismic tomography. However, previous models contained significant mismatch, particularly in areas with complex tectonic histories such as western North America. We present several techniques used in some recent models (Liu and Stegman, EPSL, 2011) that achieve an unprecedented level of agreement between modeled thermal mantle structure and several recent tomography models using EarthScope's USArray data. In particular, these models are able to forward predict a rupture in the subducting Farallon-Juan de Fuca slab that laterally tears open across the face of the slab and allows an asthenospheric upwelling to occur (Liu and Stegman, Nature, 2012). The surface projection of the tear's development agrees remarkably well with the temporal-spatial evolution of Steens-Columbia River Basalt volcansim. To achieve this level of agreement, there are four major technical aspects, all of which work in concert and are critical for success: 1) a weak hinge is prescribed as the region behind the trench 2) a low-viscosity wedge that helps to reduce coupling to the surface 3) a pseudo-free surface boundary condition consisting of a layer of "sticky air" that allows for more natural plate bending and single-sided subduction 4) because the convective system (including the tectonic plates) are separated from the surface velocity boundary condition, we introduce a phase change that allows the "sticky air" to be viscous enough for the surface plate motions applied above to actually drive the plates below. Since the bending of the plate is driven by the negative buoyancy of the slab (i.e. slab pull), the sinking velocity of the slab is also critical such that slab-plate continuity is maintained at all times. Only then will continuous slab bending and progressive subduction occur. Using previous studies (Stegman et al., 2010; Schellart et al., 2007, 2010) as a guide for the strength of the hinge, we eventually found a value that allows the plate to bend and enter the mantle at the exact same speed as the prescribed trench motion. We then ensure the subducted slab sinks at the appropriate speed, and this is sensitive to both the plate thickness as prescribed by the paleo-age of seafloor and the specific radial viscosity profile. The seismic tomography provides an incredibly robust constraint on the mantle dynamics because it reflects the time-integrated history of subduction. In order to recover excellent agreement, the sinking of all slab material in the model must follow a very specific trajectory such that the final state matches observations. This can only be achieved if convective motions arising from driving forces (slab buoyancy) and resisting forces (viscosity structure including weak hinge, low-viscosity wedge, and radial viscosity profile) are all in perfect harmony with the imposed surface boundary conditions.

Liu, L.; Stegman, D. R.

2012-04-01

303

Uranium groundwater anomalies at LNGS: From the neutron flux background to the geodynamic processes  

NASA Astrophysics Data System (ADS)

Monitoring of chemical and physical groundwater parameters has been carried out worldwide in seismogenic areas with the aim to test possible correlations between their spatial and temporal variations and strain processes. It is shown in this paper that uranium groundwater anomalies, which were observed in cataclastic rocks crossing the underground Gran Sasso National Laboratory (LNGS), can be used as a possible strain meter in domains where continental lithosphre is subducted. Moreover, whereas at the Gran Sasso National Laboratory only the natural radioactivity in the rock, the concrete, as well as the induced part coming from interaction of cosmic ray muons with the rock or the detector materials itself were considered as possible sources for the neutron flux background, the water-rock interaction and its spatial-temporal variation induced by the hydrological pattern of the Gran Sasso aquifer must be taken into account. Water must be considered not only as moderator in concrete, but also as additional source for neutron flux modulation due to its variable concentration and its radioactivity.

Plastino, W.; Laubenstein, M.; Aprili, P.; Balata, M.; Bella, F.; Cardarelli, A.; Gallese, B.; Ioannucci, L.; De Vincenzi, M.; Nisi, S.; Ruggieri, F.

2012-04-01

304

Origin and Evolution of the Yellowstone Hotspot from Seismic-GPS Imaging and Geodynamic Modeling  

Microsoft Academic Search

The Yellowstone hotspot resulted from interaction of a mantle plume with the overriding North America plate. This feature and related processes have influenced a large part of the western U.S., producing the 16 Ma Yellowstone-Snake River Plain-Newberry silicic-basalt volcanic field (YSRPN). We integrate results from a multi-institution experiment that deployed 80 seismic stations and 160 campaign and 21 permanent GPS

R. B. Smith; M. Jordan; C. M. Puskas; J. Farrell; G. P. Waite

2006-01-01

305

The Binalud Mountains: A key piece for the geodynamic puzzle of NE Iran  

NASA Astrophysics Data System (ADS)

We applied a combined approach of morphotectonic analyzes of SPOT-5 satellite images and field surveys complemented by in situ-produced10Be exposure dating to determine the kinematics and rate of active faulting in the Binalud Mountains bounded by the Neyshabur Fault System to the southwest and the Mashhad Fault Zone to the northeast. Three regional episodes of alluvial surface abandonment were dated at 4.8 ka (Q1), 105 ka (Q3), and 255 ka (S3). Along the Neyshabur Fault System, cumulative offsets recorded by Q3fan surfaces yield slip rates of 2.4 0.5 and 2.8 0.6 mm/yr for right-lateral and reverse components of active faulting (corresponding to an oblique slip rate of 3.6 1.0 mm/yr), respectively. Reconstructing the cumulative right-lateral offset recorded by S3surfaces, a maximum slip rate of 1.3 0.1 mm/yr is suggested for the Mashhad Fault Zone. These imply an overall rate of 3.7 0.6 mm/yr for the range-parallel displacement and an uplift rate of 2.8 mm/yr due to the range-normal shortening (1.6-2.2 mm/yr) during late Quaternary. The Binalud Mountains are deformed as a soft-linked restraining relay zone, taking up the motion between central Iran and Eurasia at a rate of 4.0 1.3 mm/yr; this translates central Iran in the N340E direction. Our data favor localized faulting, instead of distributed deformation, at the northeastern boundary of the Arabia-Eurasia collision zone.

Shabanian, Esmaeil; Bellier, Olivier; Siame, Lionel; Abbassi, Mohammad R.; BourlS, Didier; Braucher, RGis; Farbod, Yassaman

2012-12-01

306

Ophiolites of the Kamchatsky Mys Peninsula, eastern Kamchatka: Structure, composition, and geodynamic setting  

Microsoft Academic Search

Ophiolites of the Afrika Mys Block of the Kamchatsky Mys Peninsula, eastern Kamchatka, are a fragment of an accretionary prism\\u000a that formed in the Late Cretaceous-Eocene on the southern side of the Kronotsky island arc as a result of its collision with\\u000a the Smagino volcanic uplift that arose at the post-Neocomian time on the subducting plate. On the basis of

M. Yu. Khotin; M. N. Shapiro

2006-01-01

307

The geodynamic province of transitional crust adjacent to magma-poor continental margins  

NASA Astrophysics Data System (ADS)

Two types of 'transitional crust' have been documented along magma-poor rifted margins. One consists of apparently sub-continental mantle that has been exhumed and serpentinized in a regime of brittle deformation during late stages of rifting. A second is highly thinned continental crust, which in some cases is known to have been supported near sea level until very late in the rift history and thus is interpreted to reflect depth-dependent extension. In both cases it is typically assumed that formation of oceanic crust occurs shortly after the breakup of brittle continental crust and thus that the transitional crust has relatively limited width. We here examine two representative cases of transitional crust, one in the Newfoundland-Iberia rift (exhumed mantle) and one off the Angola-Gabon margin (highly thinned continental crust). Considering the geological and geophysical evidence, we propose that depth-dependent extension (riftward flow of weak lower/middle continental crust and/or upper mantle) may be a common phenomenon on magma-poor margins and that this can result in a much broader zone of transitional crust than has hitherto been assumed. Transitional crust in this extended zone may consist of sub-continental mantle, lower to middle continental crust, or some combination thereof, depending on the strength profile of the pre-rift continental lithosphere. Transitional crust ceases to be emplaced (i.e., final 'breakup' occurs) only when emplacement of heat and melt from the rising asthenosphere becomes dominant over lateral flow of the weak lower lithosphere. This model implies a two-stage breakup: first the rupture of the brittle upper crust and second, the eventual emplacement of oceanic crust. Well-defined magnetic anomalies can form in transitional crust consisting of highly serpentinized, exhumed mantle, and they therefore are not diagnostic of oceanic crust. Where present in transitional crust, these anomalies can be helpful in interpreting the rifting history.

Sibuet, J.; Tucholke, B. E.

2011-12-01

308

Sedimentary basins of eastern Australia: paleomagnetic constraints on geodynamic evolution in a global context  

Microsoft Academic Search

Changes in plate movements cause intraplate deformation and lead to basin development, fluid flow and mineralisation phases. Movement changes are detailed by seafloor-spreading data, back to the Oxfordian, and by paleomagnetic data before that time. Paleomagnetism records and interprets plate movement changes as pole path featuresloops, bends, overprintsand these are applicable as tectonic and stratigraphic baselines at continental and global

C. Klootwijk

2009-01-01

309

AlpArray - Probing Alpine geodynamics with the next generation of geophysical experiments and techniques  

NASA Astrophysics Data System (ADS)

AlpArray is a European initiative to advance our understanding of orogenesis and its relationship to mantle and plate dynamics, surface processes, seismotectonics and seismic hazard in the Alps and the surrounding Apennines-Carpathians-Dinarides orogenic system. The initiative will integrate present-day Earth observables with high-resolution geophysical imaging of 3D structure and physical properties of the lithosphere and of the upper mantle, with focus on a high-end seismological array. With nearly three years of scientific and technical preparation, the start of AlpArray experiments is now on the horizon. In this presentation we overview the general idea and purpose of AlpArray, reason why the initiative focuses on the greater Alpine area and discuss some of the outstanding scientific questions. We provide an overview of the planned field efforts, mainly the overall AlpArray seismic network with 40 km average station spacing and a large aerial coverage. Further plans of targeted seismological experiments with regional interests as well as of other field measurement techniques (magnetotellurics, gravity) are also presented. The outline of collaborative projects between the numerous participating institutions and researchers are described in the frame of seven main AlpArray themes. These include state-of-the-art modelling techniques that will ultimately describe the dynamic evolution of the orogenic system in great detail. Finally, the most recent news regarding the organization of the AlpArray project will be summarized.

Kissling, Edi; Hetenyi, Gyrgy; AlpArray Working Group

2014-05-01

310

Tectonics, Deep-Seated Structure and Recent Geodynamics of the Caucasus  

NASA Astrophysics Data System (ADS)

The tectonics and deep-seated structure of the Caucasus are determined by its position between the still converging Eurasian and Africa-Arabian plates, within a wide zone of continental collision. The region in the Late Proterozoic - Early Cenozoic belonged to the Tethys Ocean and its Eurasian and Africa-Arabian margins. During Oligocene-Middle Miocene and Late Miocene-Quaternary time as a result of collision back-arc basins were inverted to form fold-thrust mountain belts and the Transcaucasian intermontane lowlands. The Caucasus is divided into platform and fold-thrust units, and forelands superimposed mainly on the rigid platform zones. The youngest structural units composed of Neogene-Quaternary continental volcanic formations of the Armenian and Javakheti highlands and extinct volcanoes of the Great Caucasus. As a result of detailed geophysical study of the gravity, magnetic, seismic, and thermal fields, the main features of the deep crustal structure of the Caucasus have been determined. Knowledge on the deep lithospheric structure of the Caucasus region is based on surface geology and deep and super deep drilling data combined with gravity, seismic, heat flow, and magnetic investigations. Close correlation between the geology and its deep-seated structures appears in the peculiarities of spatial distribution of gravitational, thermal and magnetic fields, particularly generally expressed in orientation of regional anomalies that is in good agreement with general tectonic structures. In this study we present two tomographic models derived for the region based on two different tomographic approaches. In the first case, we use the travel time data on regional seismicity recorded by networks located in Caucasus. The tomographic inversion is based on the LOTOS code which enables simultaneous determination of P and S velocity distributions and source locations. The obtained model covers the crustal and uppermost mantle depths. The second model, which is constructed for the upper mantle down to 700 km depth, is based on the data from the global ISC catalogue. We use travel times corresponding to rays which travel, at least partly, through the study volume. These data include rays from events in the study area recorded by worldwide stations, as well as teleseismic data recorded at regional stations. The computed seismic models reveal some deep traces of recent tectonic processes in the Caucasus: For the 5, 15, 25 and 60-km-depth, there appears a clear coincidence between anomalous low velocities of P and S-waves with the fold-thrust mountainous belts of the Great and Lesser Caucasus, and also connection of high-velocity anomalies with the Trasncaucasian forelands. Lowest-velocity anomalies are characteristic of the areas of Neogene-Quaternary volcanism of the Great and Lesser Caucasus. Areas with the lowest velocities of P- and S-waves coincide with the mountainous-folded belts, whereas the areas of high-velocity predominantly coincide with the platformal structures and forelands, as well as with basins of the Black and Caspian Seas. Clear spatial correlation of the areas of lowest values of P- and S-velocities with the areas of Neogene-Quaternary volcanism occurs up to the depth of 150-200km that evidences location of magma sources within the crust - upper mantle - asthenosphere. Tomographic data unambiguously confirm spatial unity of the main structures of the Caucasus and its basement, the location of the structures in situ in Late Cenozoic and connection of the volcanic constructions with their roots - magma chambers.

Amanatashvili, I.; Adamia, Sh.; Lursmanashvili, N.; Sadradze, N.; Meskhia, V.; Koulakov, I.; Zabelina, I.; Jakovlev, A.

2012-04-01

311

I. Climate change on ancient Mars. II. Exoplanet geodynamics and climate  

NASA Astrophysics Data System (ADS)

This thesis describes work related to long-term climate stability, on Mars and exoplanets. Mars is the only planet known to record a major transition in planetary habitability. The evidence for surface temperatures near the melting point of water on Early Mars is difficult to explain, because theory predicts a faint young Sun. Seasonal snowmelt need not require high annual mean temperatures, but surface water ice tends to migrate away from the warmer regions of the planet where melting is energetically possible. In the first part of this thesis I use geological analysis, mesoscale models, and idealized surface energy balance models to examine two possible solutions to this problem. Impacts into icy targets, groundwater outbursts, and phreatic explosions are all expected to inject water vapor into the Mars atmosphere. I use mesoscale models to track the atmospheric response to these transient, localized vapor sources. Using idealized boundary conditions, I show that storms with updraft speeds >50 m/s and localized precipitation are expected near transient lakes >103 km2 in size. Snow deposited in this way is out of equilibrium with orbital forcing, and correspondingly more likely to melt. Canyon paleolakes in the Valles Marineris are frequently associated with streams preserved on the plateaux just downwind of the canyons. Using geologically realistic boundary conditions, I study the atmospheric response to two short-lived paleolakes. In each case, the plateau streams are in the locations expected for localized precipitation. Liquid water availability favors lithification, so the Martian sedimentary rock record is a wet-pass filter. Orbital variability strongly affects liquid water availability, so considering only averaged orbital conditions is neither sufficient not appropriate. To find the likelihood of snow melting, I consider all possible orbital forcings using an idealized but self-consistent model of snowpack energy balance and the CO2 greenhouse effect. Seasonal snowmelt on Early Mars is possible under unusual orbital conditions provided that the snow is dust-contaminated. The predicted distribution of snowmelt can explain the distribution of sedimentary rocks on Mars, but only if Mars had a thin atmosphere when the sedimentary rocks formed. This framework is the first to link upcoming observations by the Mars Science Laboratory Curiosity rover at the lower Gale Crater mound to past global climate on Mars. The model makes predictions about the lower Gale Crater mound that can be tested using Curiosity rover data. Earth is the only example of long term climate stability that is available for study, so long term climate stability is difficult to understand. Extrasolar planets may ameliorate this problem of uniqueness. It is clear that rates of volcanic activity and of surface weathering are important in regulating long term climate. In the second part of this thesis, I model the rate of volcanism on massive Earth-like planets, and the surface weathering rate on planets in 1:1 spin:orbit resonance. "Super-Earths" in the range 1-10 Earth masses have been detected by radial velocity and transit methods. Using an idealized mantle thermal evolution model to drive mantle-melting models, I show that the rate of volcanism on massive Earth like planets is a weak function of planet mass. Planet mass can, however, affect tectonics by changing the mode of mantle convection. Earth's climate stability depends on a negative feedback involving the temperature-dependent rate of weathering and mean surface temperature. I use an idealized model to show that for intermediate surface pressures and for low-opacity atmospheres, nonlinearities in the surface energy balance can reverse the sign of this dependence on tidally-locked planets. This leads to climate instability. I conclude by discussing future observations and research aimed at understanding long-term climate stability.

Kite, Edwin Stephen

312

GEODYNAMICS AND RATE OF VOLCANISM ON MASSIVE EARTH-LIKE PLANETS  

SciTech Connect

We provide estimates of volcanism versus time for planets with Earth-like composition and masses 0.25-25 M {sub +}, as a step toward predicting atmospheric mass on extrasolar rocky planets. Volcanism requires melting of the silicate mantle. We use a thermal evolution model, calibrated against Earth, in combination with standard melting models, to explore the dependence of convection-driven decompression mantle melting on planet mass. We show that (1) volcanism is likely to proceed on massive planets with plate tectonics over the main-sequence lifetime of the parent star; (2) crustal thickness (and melting rate normalized to planet mass) is weakly dependent on planet mass; (3) stagnant lid planets live fast (they have higher rates of melting than their plate tectonic counterparts early in their thermal evolution), but die young (melting shuts down after a few Gyr); (4) plate tectonics may not operate on high-mass planets because of the production of buoyant crust which is difficult to subduct; and (5) melting is necessary but insufficient for efficient volcanic degassing-volatiles partition into the earliest, deepest melts, which may be denser than the residue and sink to the base of the mantle on young, massive planets. Magma must also crystallize at or near the surface, and the pressure of overlying volatiles must be fairly low, if volatiles are to reach the surface. If volcanism is detected in the 10 Gyr-old {tau} Ceti system, and tidal forcing can be shown to be weak, this would be evidence for plate tectonics.

Kite, E. S.; Manga, M. [Department of Earth and Planetary Science, University of California at Berkeley, Berkeley, CA 94720 (United States); Gaidos, E. [Department of Geology and Geophysics, University of Hawaii at Manoa, Honolulu, HI 96822 (United States)], E-mail: kite@berkeley.edu

2009-08-01

313

A change in the geodynamics of continental growth 3 billion years ago.  

PubMed

Models for the growth of continental crust rely on knowing the balance between the generation of new crust and the reworking of old crust throughout Earth's history. The oxygen isotopic composition of zircons, for which uranium-lead and hafnium isotopic data provide age constraints, is a key archive of crustal reworking. We identified systematic variations in hafnium and oxygen isotopes in zircons of different ages that reveal the relative proportions of reworked crust and of new crust through time. Growth of continental crust appears to have been a continuous process, albeit at variable rates. A marked decrease in the rate of crustal growth at ~3 billion years ago may be linked to the onset of subduction-driven plate tectonics. PMID:22422979

Dhuime, Bruno; Hawkesworth, Chris J; Cawood, Peter A; Storey, Craig D

2012-03-16

314

Plate Tectonics: Geodynamic models of evolution of oil and gas bearing basins of Kazakhstan  

SciTech Connect

Five types of sedimentary basins in Kazakhstan have been recognized by using plate tectonics to reinterpret geological and geophysical data: (1) intracontinental, central pre-Caspian, above rift, south pre-Caspian; (2) passive margin, east pre-Caspian; (3) back-arc, Turgan and Sir-Daria; (4) intra-arc, north Kisil-Koum, interior, Tengis and Chu-Sarisiu; and (5) marginal, north Usturt. Paleozoic history of these basins was connected with the spreading and collision of two lithospheric plates: east European and Kazakhstanian, which were separated by the paleo-Ural Ocean. Different tectonic positions of sedimentary basins were the reason for their different oil and gas potential.

Zholtayev, G. (Kazakhpolitecnic Institute, Almaty (Kazakhstan))

1994-07-01

315

Reprocessing of the CEGRN network and its impact on the geodynamics of Central Europe  

NASA Astrophysics Data System (ADS)

The IAG Working Group on "Integration of Dense Velocity Fields in the ITRF", the EUREF Working Group on Deformation Models and the project EPOS encourage initiatives aiming at estimating velocities of GNSS sites in a rigorous manner, both for reference frame applications and 3D tectonic deformation problems. Thirteen measurement campaigns between 1994 and 2013 with epoch and permanent GNSS stations make the CEGRN network one of the most regularly and accurately surveyed networks for scientific applications in Europe. We have reprocessed the CEGRN GNSS (GPS+GLONASS) data with the Bernese Software 5.2 using consistent IGb08 orbits and antenna models and aligned the resulting network to ETRF2000 Reference Frame using the position and velocities of Class A stations of the EUREF Permanent Network (EPN). The intent is to bring down to regional, i.e. Central European scale the same standard of accuracy as the EPN long-term solution. This paper presents first results of the CEGRN densification of the EPN: we review the input data, the processing strategies and the results, in terms of positions, velocities and Helmert parameters. Possible further combination, in a rigorous geodetic sense, with multiyear regional solutions, for example in Greece and Italy, processed with similar standards have an important potential to quantify the deformation field, for example in the Balkans. Preliminary results on possible locking depths and areas of higher probability of failure are reviewed.

Caporali, Alessandro

2014-05-01

316

On the possible use of optical fiber Bragg gratings as strain sensors for geodynamical monitoring  

NASA Astrophysics Data System (ADS)

Optical fiber sensors can be used to measure many different parameters including strain, temperature, pressure, displacement, electrical field, refractive index, rotation, position and vibrations. Among a variety of fiber sensors, fiber Bragg gratings (FBG) have numerous advantages over other optical fiber sensors. One of the major advantages of this type of sensors is attributed to wavelength-encoded information given by the Bragg grating. Since the wavelength is an absolute parameter, signal from FBG may be processed such that its information remains immune to power fluctuations along the optical path. This inherent characteristic makes the FBG sensors very attractive for application in harsh environments, "smart structures" and on-site measurements. This paper reviews the achievements about the FBG as a strain and temperature sensor and describes the potential applications of FBG sensors for applications in the field of geophysics and its expected development in the near future. The applications could include: rock deformation, fiber-optic geophone, optical based seismograph, vertical seismic profiling and structural monitoring of civil structures. Different techniques to detect strains and various applications will be reviewed and discussed. The problem of temperature-strain cross sensitivity, that is particularly difficult to eliminate, is addressed and approaches to overcome it are discussed.

Ferraro, Pietro; De Natale, Giuseppe

2002-02-01

317

Geodynamical and Geochemical Features of Oil Generation in Sedimentary Basin of Volga-Ural Region  

Microsoft Academic Search

Oil and gas prospects of Paleozoic sedimentary rocks of Volga-Ural Anticline (VUA) various researchers evaluate in different ways. More than 150 oil fields in Paleozoic formations were discovered in the eastern half of Republic of Tatarstan of the East European Platform. There were not found any significant fields in the western areas of investigation region. According to many investigators, the

I. Plotnikova

2009-01-01

318

A numerical treatment of geodynamic viscous flow problems involving the advection of material interfaces  

NASA Technical Reports Server (NTRS)

Effective numerical treatment of multicomponent viscous flow problems involving the advection of sharp interfaces between materials of differing physical properties requires correction techniques to prevent spurious diffusion and dispersion. We develop a particular algorithm, based on modern shock-capture techniques, employing a two-step nonlinear method. The first step involves the global application of a high-order upwind scheme to a hyperbolic advection equation used to model the distribution of distinct material components in a flow field. The second step is corrective and involves the application of a global filter designed to remove dispersion errors that result from the advection of discontinuities (e.g., material interfaces) by high-order, minimally dissipative schemes. The filter introduces no additional diffusion error. Nonuniform viscosity across a material interface is allowed for by the implementation of a compositionally weighted-inverse interface viscosity scheme. The combined method approaches the optimal accuracy of modern shock-capture techniques with a minimal increase in computational time and memory. A key advantage of this method is its simplicity to incorporate into preexisting codes be they finite difference, element, or volume of two or three dimensions.

Lenardic, A.; Kaula, W. M.

1993-01-01

319

Contrasting seismicity between the north China and south China blocks: Kinematics and geodynamics  

E-print Network

regions in the world. The south China block (SCB), another major craton in East Asia, has been seismically conditions are the primary cause of the contrasting seismicity. The SCB, facilitated by large strike (SCB), another ancient craton that collided with the NCB in the Mesozoic, has remained seismically

Liu, Mian

320

Geodynamic evolution of the European Variscan fold belt: palaeomagnetic and geological constraints  

NASA Astrophysics Data System (ADS)

The Variscan fold belt of Europe resulted from the collision of Africa, Baltica, Laurentia and the intervening microplates in early Paleozoic times. Over the past few years, many geological, palaeobiogeographic and palaeomagnetic studies have led to significant improvements in our understanding of this orogenic belt. Whereas it is now fairly well established that Avalonia drifted from the northern margin of Gondwana in Early Ordovician times and collided with Baltica in the late Ordovician/early Silurian, the nature of the Gondwana derived Armorican microplate is more enigmatic. Geological and new palaeomagnetic data suggest Armorica comprises an assemblage of terranes or microblocks. Palaeobiogeographic data indicate that these terranes had similar drift histories, and the Rheic Ocean separating Avalonia from the Armorican Terrane Assemblage closed in late Silurian/early Devonian times. An early to mid Devonian phase of extensional tectonics along this suture zone resulted in formation of the relatively narrow Rhenohercynian basin which closed progressively between the late Devonian and early Carboniferous. In this contribution, we review the constraints provided by palaeomagnetic data, compare these with geological and palaeobiogeographic evidence, and present a sequence of palaeogeographic reconstructions for these circum-Atlantic plates and microplates from Ordovician through to Devonian times.

Tait, J. A.; Bachtadse, V.; Franke, W.; Soffel, H. C.

321

GS of CAS Geodesy & Geodynamics Beijing June 20041 Monitoring the Earth Surface from space  

E-print Network

­ Beijing June 200417 Satellite Laser Ranging High energy laser firing at satellites enable to determine bandwith. Shape of the surface from radar imagery Surface deformation from satellite geodesy : SLR, VLBI SPOT example : The satellite has 2 telescopes : The first one acquires ahead, the second one behind

Vigny, Christophe

322

Journal of Geodynamics 53 (2012) 3442 Contents lists available at SciVerse ScienceDirect  

E-print Network

determination. Compared to the satellite laser ranging (SLR) technique that can only obtain one- dimensional of COSMIC and GRACE satellite missions Tingjung Lina , Cheinway Hwanga, , Tzu-Pang Tsenga,c , B.F. Chaob coefficients from GPS data of COS- MIC and GRACE satellite missions. The kinematic orbits of COSMIC and GRACE

Hwang, Cheinway

323

Tectonic structure and geodynamics of the divide between the Atlantic and Arctic oceans  

NASA Astrophysics Data System (ADS)

Tectonic analysis of the divide between the Atlantic and Arctic oceans, where Greenland and Eurasia are located close to each other, is accompanied by description of the main structural units of this region, including the Lena Trough, continental Yermak Block (Plateau), Molloy and Spitsbergen fracture zones, and Molloy interfault tectonic complex. The tectonic features of these structural units allow us to combine them into a single domain of the interoceanic tectonic divide, which separates the spreading zones of the North Atlantic and the Gakkel Ridge of the Arctic Ocean. This dividing domain is compared with other interoceanic divides of the Earth, the classification of which is proposed in my previous publications. Their common feature is the development of fault systems particularly pronounced in the Australian-Antarctic and African-Antarctic oceanic domains. The morphology, crustal structure, and magmatism of the considered region show that it is currently undergoing rifting, which probably predates oceanic spreading.

Pushcharovsky, Yu. M.

2010-05-01

324

Assessment of the geodynamical setting around the main active faults at Aswan area, Egypt  

NASA Astrophysics Data System (ADS)

The proper evaluation of crustal deformations in the Aswan region especially around the main active faults is crucial due to the existence of one major artificial structure: the Aswan High Dam. This construction created one of the major artificial lakes: Lake Nasser. The Aswan area is considered as an active seismic area in Egypt since many recent and historical felted earthquakes occurred such as the impressive earthquake occurred on November 14, 1981 at Kalabsha fault with a local magnitude ML=5.7. Lately, on 26 December 2011, a moderate earthquake with a local magnitude Ml=4.1 occurred at Kalabsha area too. The main target of this study is to evaluate the active geological structures that can potentially affect the Aswan High Dam and that are being monitored in detail. For implementing this objective, two different geophysical tools (magnetic, seismic) in addition to the Global Positioning System (GPS) have been utilized. Detailed land magnetic survey was carried out for the total component of geomagnetic field using two proton magnetometers. The obtained magnetic results reveal that there are three major faults parallel {F1 (Kalabsha), F2 (Seiyal) and F3} affecting the area. The most dominant magnetic trend strikes those faults in the WNW-ESE direction. The seismicity and fault plain solutions of the 26 December 2011 earthquake and its two aftershocks have been investigated. The source mechanisms of those events delineate two nodal plains. The trending ENE-WSW to E-W is consistent with the direction of Kalabsha fault and its extension towards east for the events located over it. The trending NNW-SSE to N-S is consistent with the N-S fault trending. The movement along the ENE-WSW plain is right lateral, but it is left lateral along the NNW-SSE plain. Based on the estimated relative motions using GPS, dextral strike-slip motion at the Kalabsha and Seiyal fault systems is clearly identified by changing in the velocity gradient between south and north stations. However, at the area between Kalabha and Seiyal faults, the movement has been changed in a different direction which is consistent with the other set of faults (N-S).

Ali, Radwan; Hosny, Ahmed; Kotb, Ahmed; Khalil, Ahmed; Azza, Abed; Rayan, Ali

2013-04-01

325

Methods of celestial mechanics. Vol. II: Application to planetary system geodynamics and satellite geodesy  

Microsoft Academic Search

G. Beutler's Methods of Celestial Mechanics is a coherent textbook for students as well as an excellent reference for practitioners. Volume II is devoted to the applications and to the presentation of the program system CelestialMechanics. Three major areas of applications are covered: (1) Orbital and rotational motion of extended celestial bodies. The properties of the Earth-Moon system are developed

Gerhard Beutler

2005-01-01

326

Laser geodynamic satellite/thermal/optical vibrational analyses and testing. Volume 2: Technical report, book 3  

NASA Technical Reports Server (NTRS)

The overall plan for accomplishing the various tests required to achieve the program objectives and tasks of the LAGEOS thermal/optical/vibration analysis and test program is described. The requirements for each test are identified for the purpose of program review for the design and fabrication of the required test article and test fixtures, for the allocation of test facilities, equipment and expendables, and for the generation of the detail test procedures by which the specified data will be obtained at specified test conditions. The current internal test program schedules, by which the various individual preparatory subtasks are to be accomplished to ensure that the individual test will be conducted within the time period required to meet program objectives are included.

1974-01-01

327

Appendix B: Description of Map Units for Northeast Asia Summary Geodynamics Map  

USGS Publications Warehouse

The major purposes of this chapter are to provide (1) an overview of the regional geology, tectonics, and metallogenesis of Northeast Asia for readers who are unfamiliar with the region, (2) a general scientific introduction to the succeeding chapters of this volume, and (3) an overview of the methodology of metallogenic and tectonic analysis used in this study. We also describe how a high-quality metallogenic and tectonic analysis, including construction of an associated metallogenic-tectonic model will greatly benefit other mineral resource studies, including synthesis of mineral-deposit models; improve prediction of undiscovered mineral deposit as part of a quantitative mineral-resource-assessment studies; assist land-use and mineral-exploration planning; improve interpretations of the origins of host rocks, mineral deposits, and metallogenic belts, and suggest new research. Research on the metallogenesis and tectonics of such major regions as Northeast Asia (eastern Russia, Mongolia, northern China, South Korea, and Japan) and the Circum-North Pacific (the Russian Far East, Alaska, and the Canadian Cordillera) requires a complex methodology including (1) definitions of key terms, (2) compilation of a regional geologic base map that can be interpreted according to modern tectonic concepts and definitions, (3) compilation of a mineral-deposit database that enables a determination of mineral-deposit models and clarification of the relations of deposits to host rocks and tectonic origins, (4) synthesis of a series of mineral-deposit models that characterize the known mineral deposits and inferred undiscovered deposits in the region, (5) compilation of a series of metallogenic-belt belts constructed on the regional geologic base map, and (6) construction of a unified metallogenic and tectonic model. The summary of regional geology and metallogenesis presented here is based on publications of the major international collaborative studies of the metallogenesis and tectonics of Northeast Asia that have been led by the U.S. Geological Survey (USGS). These studies have produced two broad types of publications (1) a series of regional geologic, mineral-deposit, and metallogenic-belt maps, with companion descriptions of the region, and (2) a suite of metallogenic and tectonic analyses of the same region. The study area consists of eastern Russia (most of eastern Siberia and the Russian Far East), Mongolia, northern China, South Korea, Japan, and adjacent offshore areas. The major cooperative agencies are the Russian Academy of Sciences; the Academy of Sciences of the Sakha Republic (Yakutia); VNIIOkeangeologia and Ministry of Natural Resources of the Russian Federation; the Mongolian Academy of Sciences; the Mongolian University of Science and Technology; the Mongolian National University; Jilin University, Changchun, People?s Republic of China, the China Geological Survey; the Korea Institute of Geosciences and Mineral Resources; the Geological Survey of Japan/AIST; the University of Texas, Arlington, and the U.S. Geological Survey (USGS). This study builds on and extends the data and interpretations from a previous project on the Major Mineral Deposits, Metallogenesis, and Tectonics of the Russian Far East, Alaska, and the Canadian Cordillera conducted by the USGS, the Russian Academy of Sciences, the Alaska Division of Geological and Geophysical Surveys, and the Geological Survey of Canada. The major products of this project were summarized by Naumova and others (2006) and are described in appendix A.

Parfenov, Leonid M.; Badarch, Gombosuren; Berzin, Nikolai A.; Hwang, Duk-Hwan; Khanchuk, Alexander I.; Kuzmin, Mikhail I.; Nokleberg, Warren J.; Obolenskiy, Alexander A.; Ogasawara, Masatsugu; Prokopiev, Andrei V.; Rodionov, Sergey M.; Smelov, Alexander P.; Yan, Hongquan

2009-01-01

328

Xainxa ultramafic rocks, central Tibet, China: Tectonic environment and geodynamic significance  

Microsoft Academic Search

The Xainxa ultramafic rocks, 200 km south of the Donqiao ophiolite, Bangong Nu Jiang suture zone, central Tibet, form a 1-km-thick sheet in tectonic contact with Paleozoic sediments to the south and with Mesozoic sediments to the north through roughly east-west, south-dipping reverse faults. The ultramafic rocks consist of depleted harzburgites with minor dunite patches and 1-m-sized deposits of podiform

J. Girardeau; J. Marcoux; E. Fourcade; J. P. Bassoullet; Tang Youking

1985-01-01

329

Journal of Geodynamics 46 (2008) 6977 Contents lists available at ScienceDirect  

E-print Network

of GRACE gravity coefficients for deter- mining the Earth's secular component of gravity change over models Time-varying gravity a b s t r a c t The measurement of glacial isostatic adjustment (GIA) is one are related to the high-resolution space­gravity data recovered from the Gravity and Climate Experiment (GRACE

Stuttgart, Universität

330

Investigations on the hierarchy of reference frames in geodesy and geodynamics  

Microsoft Academic Search

Problems related to reference directions were investigated. Space and time variant angular parameters are illustrated in hierarchic structures or towers. Using least squares techniques, model towers of triads are presented which allow the formation of linear observation equations. Translational and rotational degrees of freedom (origin and orientation) are discussed along with and the notion of length and scale degrees of

E. W. Grafarend; I. I. Mueller; H. B. Papo; B. Richter

1979-01-01

331

Discussion of The Eclogite Engine: Chemical geodynamics as a Galileo thermometer  

E-print Network

...given the temperature difference between a subducting slab and the MORB source region...?" The simple answer the temperatures in the surface boundary layer except at the delamination site and where the fertile blobs re and that variations in magma temperatures reflect lateral variations in mantle temperature. The potential temperature

Anderson, Don L.

332

Origin of hotspot lavas geochemical zoning: a geodynamics perspective Cinzia G. Farnetani(1)  

E-print Network

/yr Temperature dependent viscosity. Dry peridotite solidus by Katz plume? Left : Calculated conduit structure at 660 km depth, after 80 My of flow in the lower mantle). Center: Calculated 2 0 8 Pb* / 2 0 6 Pb* map across the melting zone of the Hawaiian plume. White circles

Geist, Dennis

333

The Fanos granite: structure, emplacement and geodynamic significance (Eastern Axios/Vardar Zone, Northern Greece)  

NASA Astrophysics Data System (ADS)

The Fanos granite occurs in the Peonia Subzone of the Eastern Axios-Vardar Zone in Northern Greece. It is a Late Jurassic (1581 Ma), N-S trending granite, intruding the Mesozoic back-arc Geuvgeuli ophiolitic complex (Peonia Subzone). It is composed of three main rock types namely aplitic granite, granite and microgranite evolved by fractional crystallization. At the eastern contact of the Fanos granite with the host ophiolitic rocks the initial intrusion character of the granitic bodies is well preserved. On the other hand, the western contact is overprinted by a few meters thick, westward-vergent semiductile thrust zone, probably of Late Jurassic-Early Cretaceous age. For the better understanding of the geotectonic evolution of the broader area, the Fanos granite is compared with the Mid-Late Jurassic Kastaneri volcano-sedimentary formation allocated on the eastern part of the Paikon Massif, on which the Guevgeuli ophiolites were obducted. In our study we address three major topics: a) the origin of the Fanos granite, b) the geochemical correlation between Fanos granite and Kastaneri formation and c) the relationship of the granite with the remnants of an oceanic island-arc or an active continental margin geotectonic setting situated in the Neotethys (=Axios/Vardar ocean). The collected rock samples are granites, aplitic granites, microgranites, rhyolites, quartz diorites, migmatites and amphibolites. These samples were analysed by X-ray fluorence for major and trace elements. The granite shows peraluminous characteristics, high-K calc-alkaline affinities and I-type features. The Sr initial isotopic ratios of the granite range between 0.70519 and 0.70559, while the Nd initial isotopic ratios range between 0.51236 and 0.51239, reflecting EM-I (Enriched Mantle-I) component. The trace element patterns along with the isotopic composition of the rocks indicate absence of continental crustal material contamination. Moreover, the geochemical data imply a common origin between the Fanos granite and the Kastaneri formation. Taking into account our structural and geochemical data along with the existing isotopic and geotectonic data of the broader Axios/Vardar Zone, we suggest that the studied granitic rocks were formed during an intraoceanic-subduction within the Neotethys ocean, approximately at the same time with the amphibolite sole formation, rather than during the evolution of an active continental margin. In the Late Jurassic, a general westward ophiolite obduction on the Pelagonian continental margin, resulted to the thrusting of the Fanos granite together with the obducted ophiolites.

Michail, Maria; Kilias, Adamantios; Koroneos, Antonios; Ntaflos, Theodoros; Pipera, Kyriaki

2014-05-01

334

Constraints on Hadean geodynamics from mineral inclusions in > 4 Ga zircons  

Microsoft Academic Search

The inclusion mineralogy of 1450 zircons over 4billion years in age from the Jack Hills, Western Australia, was characterized for composition and phase assemblage. Results confirm that the inclusion population of these largely igneous zircons is dominated by muscovite and quartz (~75%). If the inclusions are original to the igneous zircons, this observation alone restricts the host melts to formation

Michelle D. Hopkins; T. Mark Harrison; Craig E. Manning

2010-01-01

335

Constraints on Hadean geodynamics from mineral inclusions in > 4 Ga zircons  

Microsoft Academic Search

The inclusion mineralogy of 1450 zircons over 4 billion years in age from the Jack Hills, Western Australia, was characterized for composition and phase assemblage. Results confirm that the inclusion population of these largely igneous zircons is dominated by muscovite and quartz (~ 75%). If the inclusions are original to the igneous zircons, this observation alone restricts the host melts

Michelle D. Hopkins; T. Mark Harrison; Craig E. Manning

2010-01-01

336

Deformation driven by subduction and microplate collision: Geodynamics of Cook Inlet basin, Alaska  

USGS Publications Warehouse

Late Neogene and younger deformation in Cook Inlet basin is caused by dextral transpression in the plate margin of south-central Alaska. Collision and subduction of the Yakutat microplate at the northeastern end of the Aleutian subduction zone is driving the accretionary complex of the Chugach and Kenai Mountains toward the Alaska Range on the opposite side of the basin. This deformation creates belts of fault-cored anticlines that are prolific traps of hydrocarbons and are also potential sources for damaging earthquakes. The faults dip steeply, extend into the Mesozoic basement beneath the Tertiary basin fill, and form conjugate flower structures at some localities. Comparing the geometry of the natural faults and folds with analog models created in a sandbox deformation apparatus suggests that some of the faults accommodate significant dextral as well as reverse-slip motion. We develop a tectonic model in which dextral shearing and horizontal shortening of the basin is driven by microplate collision with an additional component of thrust-type strain caused by plate subduction. This model predicts temporally fluctuating stress fields that are coupled to the recurrence intervals of large-magnitude subduction zone earthquakes. The maximum principal compressive stress is oriented east-southeast to east-northeast with nearly vertical least compressive stress when the basin's lithosphere is mostly decoupled from the underlying subduction megathrust. This stress tensor is compatible with principal stresses inferred from focal mechanisms of earthquakes that occur within the crust beneath Cook Inlet basin. Locking of the megathrust between great magnitude earthquakes may cause the maximum principal compressive stress to rotate toward the northwest. Moderate dipping faults that strike north to northeast may be optimally oriented for rupture in the ambient stress field, but steeply dipping faults within the cores of some anticlines are unfavorably oriented with respect to both modeled and observed stress fields, suggesting that elevated fluid pressure may be required to trigger fault rupture. ?? 2006 Geological Society of America.

Bruhn, R. L.; Haeussler, P. J.

2006-01-01

337

Rethinking geochemical feature of the Afar and Kenya mantle plumes and geodynamic implications  

Microsoft Academic Search

We discuss the spatial and temporal variation in the geochemistry of mantle sources which were sampled by the Eocene to Quaternary mafic magmas in the vicinity of the Afar and Kenya plume upwelling zones, East Africa. Despite the contributions of lithospheric and crustal sources, carefully screened Eocene to Quaternary mafic lavas display wide range of Sr-Nd-Pb isotopic and incompatible trace

Daniel Meshesha; Ryuichi Shinjo

2008-01-01

338

Investigation of dynamic noise affecting geodynamics information in a tethered subsatellite  

NASA Technical Reports Server (NTRS)

Work performed as part of an investigation of noise affecting instrumentation in a tethered subsatellite, was studied. The following specific topics were addressed during the reporting period: a method for stabilizing the subsatellite against the rotational effects of atmospheric perturbation was developed; a variety of analytic studies of tether dynamics aimed at elucidating dynamic noise processes were performed; a novel mechanism for coupling longitudinal and latitudinal oscillations of the tether was discovered, and random vibration analysis for modeling the tethered subsatellite under atmospheric perturbation were studied.

Gullahorn, G. E.

1985-01-01

339

Geodynamic modelling of non-volcanic rifted margins: sedimentation process and effects  

NASA Astrophysics Data System (ADS)

Non-volcanic rifted margins (NVRMs) are characterized by an anomalous lack of magmatism and a wide continental-ocean transition which has been interpreted as an expanse of exhumed and serpentinized mantle. NVRMs are represented all over the world as in Labrador Sea, Southeast Australia, Newfoundland, and West Iberian Margin (WIM), where a serpentinized peridotite ridge is found. Erosion and sedimentation are surficial processes that redistribute material along the margins, changing the forces along the margin and affecting its thermal structure. In order to study coupled mantle dynamics and sedimentation processes during rifting, we used a modified version of the dynamic 2D code MILAMIN (Dabrowski et al. 2008). Our modified version includes a free surface together with a free-surface stabilization algorithm to generate stable topographies, strain softening to simulate faulting, serpentinization, magmatism, erosion and sedimentation. Erosion and sedimentation algorithm is based on diffusion and transport equations in 1D. The code allow us to investigate how sedimentation process conditions the architecture of the margins during rifting and in which magnitude the width of the margins and the height of the rift shoulders are affected by surficial processes. Furthermore, we can study how sediments influence the temperature distribution and evolution and, ultimately, the rheology of the crust during rifting. We are also working on modelling sedimentation with high resolution meshes to try to reproduce break-up uncomformities and to study the thermal evolution of the sediments.

Andres-Martinez, Miguel; Perez-Gussinye, Marta; Phipps Morgan, Jason; Armitage, John; Monteiro da Silva, Rafael

2014-05-01

340

Real episodic growth of continental crust or artifact of preservation? A 3-D geodynamic model  

NASA Astrophysics Data System (ADS)

Abstract We investigate whether the observed zircon age distribution of continental crust (CC) is produced by real crustal growth episodes or is only an artifact of preservation. In connection with the second alternative of this question, other authors proposed that there was little episodicity in the production of new CC and that modeling corroborates this opinion. We conclude that a combination of the two answers might be possible. In matters of modeling, however, we ascertain that a dynamic modeling of the convection-differentiation system of the mantle reveals the high probability of magmatic episodes. We solve the full set of balance equations in a 3-D spherical-shell mantle. The heat-producing elements are redistributed by chemical differentiation. A realistic solidus model of mantle peridotite is essential for an applicable model. The solidus depends not only on depth but also on the volatile concentration. Furthermore, we introduced realistic profiles of Grneisen parameter, viscosity, adiabatic temperature, thermal expansivity, and specific heat. Our model automatically produces lithospheric plates and growing continents. Regarding number, size, form, distribution, and surface velocity of the continents, no constraints have been prescribed. Regions of the input parameter space (Ra,?y,k,f3) that are favorable with respect to geophysical quantities show simultaneously not only episodicity of CC growth but also a reproduction of the observed zircon-age maxima referring to the instants of time. We also obtain Archean events for ages greater than 3000 Ma that are not or scarcely visible in the observed zircon ages. Sinusoidal parts of the evolution curve of qob, Ur, and Ekin are superposed with a monotonous decrease. The volumetrically averaged mantle temperature, Tmean, however, decreases smoothly and slowly, nearly without pronounced variations. Therefore, we can dismiss catastrophic mechanisms that simultaneously incorporate the whole mantle.</p> <div class="credits"> <p class="dwt_author">Walzer, Uwe; Hendel, Roland</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-05-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_16");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' 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showDiv("page_19");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">341</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/40447569"> <span id="translatedtitle">Palaeostress analysis, a contribution to the understanding of basin tectonics and <span class="hlt">geodynamic</span> evolution. Example of the Permian\\/Cenozoic tectonics of Great Britain and <span class="hlt">geodynamic</span> implications in western Europe</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Microtectonic analysis in association with tectonic-sedimentological observations enables us not only to define palaeostress tensors but also to date each of them. Such a study, carried out in central and northeastern England and in southernmost Wales has permitted us to point out several tectonic stages during the Permian-Cenozoic period. (1) Inferred from syn-sedimentary faulting in the Late Permian series, the</p> <div class="credits"> <p class="dwt_author">Christian Hibsch; Jean-Jacques Jarrige; Edward Marc Cushing; Jacques Mercier</p> <p class="dwt_publisher"></p> <p class="publishDate">1995-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">342</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/55906633"> <span id="translatedtitle"><span class="hlt">Geodynamical</span> Models of the Rotation and Extension of Alcapa and Tisza Blocks in the Pannonian Basin of Central Europe</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The two major crustal blocks of the Pannonian basin, Alcapa (Alpine-Carpathian Pannonian) and Tisza, underwent a complex process of rotation and extension of variable magnitude during the Tertiary. The northward push of the Adriatic Block initiated the eastward displacement and rotation of both the Alcapa and Tisza blocks. Emplacement was accompanied by substantial strike-slip movements, together with shortening and possible</p> <div class="credits"> <p class="dwt_author">P. Lorinczi; G. Houseman</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">343</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/56411784"> <span id="translatedtitle"><span class="hlt">Geodynamical</span> Models of the Rotation and Extension of Alcapa and Tisza Blocks in the Pannonian Basin of Central Europe</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The two major crustal blocks of the Pannonian basin, Alcapa (Alpine-Carpathian-Pannonian) and Tisza, underwent a complex process of rotation and extension of variable magnitude during the Tertiary. The northward push of the Adriatic Block initiated the eastward displacement and rotation of both the Alcapa and Tisza blocks. Emplacement was accompanied by substantial strike-slip movements, together with shortening and possible extension</p> <div class="credits"> <p class="dwt_author">P. Lorinczi; G. A. Houseman</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">344</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/40845495"> <span id="translatedtitle">Mesozoic and cenozoic volcanic rocks from central and southern Tibet: 39Ar40Ar dating, petrological characteristics and <span class="hlt">geodynamical</span> significance</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Field relations, radiometric ages and mineralogical and chemical characteristics of the orogenic volcanic rocks from the Lhasa block (Tibet) are studied. Volcanic activity started before the deposition of the Albian-Aptian sedimentary units (Takena Formation and Xigaze Group). Volcanism is volumetrically limited in the northern part of the Lhasa block: basalts, andesites and dacites are present while ignimbrites are scarce. Radiometric</p> <div class="credits"> <p class="dwt_author">C. Coulon; H. Maluski; C. Bollinger; S. Wang</p> <p class="dwt_publisher"></p> <p class="publishDate">1986-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">345</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/40449194"> <span id="translatedtitle">Overheated, Cu-bearing magmas in the Zald??var porphyry-Cu deposit, Northern Chile. <span class="hlt">Geodynamic</span> consequences</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The Zald??var porphyry copper deposit, Northern Chile, consists of two major intrusions, the 290 Ma Zald??var, and the more recent Miocene (38.7 Ma) Llamo porphyry. Five types of inclusions have been identified in quartz phenocrysts from Llamo porphyry, including melt inclusions (M), and four types of fluid inclusions, called MS (multi solids), B (brines), G (vapor-rich) and W (aqueous), respectively.Melt</p> <div class="credits"> <p class="dwt_author">E. Campos; J. L. R Touret; I Nikogosian; J Delgado</p> <p class="dwt_publisher"></p> <p class="publishDate">2002-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">346</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013PhDT.......194P"> <span id="translatedtitle">Sequence stratigraphy, <span class="hlt">geodynamics</span>, and detrital geothermochronology of Cretaceous foreland basin deposits, western interior U.S.A</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Three studies on Cordilleran foreland basin deposits in the western U.S.A. constitute this dissertation. These studies differ in scale, time and discipline. The first two studies include basin analysis, flexural modeling and detailed stratigraphic analysis of Upper Cretaceous depocenters and strata in the western U.S.A. The third study consists of detrital zircon U-Pb analysis (DZ U-Pb) and thermochronology, both zircon (U-Th)/He and apatite fission track (AFT), of Upper Jurassic to Upper Cretaceous foreland-basin conglomerates and sandstones. Five electronic supplementary files are a part of this dissertation and are available online; these include 3 raw data files (Appendix_A_raw_isopach_data.txt, Appendix_C_DZ_Data.xls, Appendix_C_U-Pb_apatite.xls), 1 oversized stratigraphic cross section (Appendix_B_figure_5.pdf), and 1 figure containing apatite U-Pb concordia plots (Appendix_C_Concordia.pdf). Appendix A is a combination of detailed isopach maps of the Upper Cretaceous Western Interior, flexural modeling and a comparison to dynamic subsidence models as applied to the region. Using these new isopach maps and modeling, I place the previously recognized but poorly constrained shift from flexural to non-flexural subsidence at 81 Ma. Appendix B is a detailed stratigraphic study of the Upper Cretaceous, (Campanian, ~76 Ma) Sego Sandstone Member of the Mesaverde Group in northwestern Colorado, an area where little research has been done on this formation. Appendix C is a geo-thermochronologic study to measure the lag time of Upper Jurassic to Upper Cretaceous conglomerates and sandstones in the Cordilleran foreland basin. The maximum depositional ages using DZ U-Pb match existing biostratigraphic age controls. AFT is an effective thermochronometer for Lower to Upper Cretaceous foreland stratigraphy and indicates that source material was exhumed from >4--5 km depth in the Cordilleran orogenic belt between 118 and 66 Ma, and zircon (U-Th)/He suggests that it was exhumed from <8--9 km depth. Apatite U-Pb analyses indicate that volcanic contamination is a significant issue, without which, one cannot exclude the possibility that the youngest detrital AFT population is contaminated with significant amounts of volcanogenic apatite and does not represent source exhumation. AFT lag times are <5 Myr with relatively steady-state to slightly increasing exhumation rates. Lag time measurements indicate exhumation rates of ~0.9->>1 km/Myr.</p> <div class="credits"> <p class="dwt_author">Painter, Clayton S.</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">347</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19750005832&hterms=BSR&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3DBSR"> <span id="translatedtitle">Laser <span class="hlt">geodynamic</span> satellite thermal/optical/ vibrational analyses and testing. Volume 2: Technical report, book 2. [retroreflector design</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">A detailed analysis of a fused silica cube-corner retroreflector is presented. The effects of manufacturing errors and temperature variations, which may affect the performance of the cube-corner retroreflector are included. The process used in the cube-corner performance is illustrated. The effect of manufacturing error and the effects of manufacturing error combined with various temperature profiles were examined. The effects of a nonuniform wedge angle with manufacturing error and with a manufacturing/temperature profile combination were also analyzed.</p> <div class="credits"> <p class="dwt_author"></p> <p class="dwt_publisher"></p> <p class="publishDate">1974-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">348</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://dspace.mit.edu/handle/1721.1/45774"> <span id="translatedtitle">Surface uplift, fluvial incision, and <span class="hlt">geodynamics</span> of plateau evolution, from the western margin of the Central Andean plateau</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/epsearch/">E-print Network</a></p> <p class="result-summary">The Colca-Majes and Cotahuasi-Ocona rivers in southwest Peru that cut through the western margin of the Andean plateau en route to the Pacific Ocean incised canyons over 3 km deep in response to late Cenozoic surface uplift. ...</p> <div class="credits"> <p class="dwt_author">Schildgen, Taylor F. (Taylor Frances)</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">349</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/49521654"> <span id="translatedtitle">Tectonics and <span class="hlt">geodynamics</span> of the Central Asian Foldbelt: the role of Late Paleozoic large-amplitude strike-slip faults</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The following structural elements have been recognized to constitute the tectonic demarcation of Central Asian Foldbelt: (1) The KazakhstanBaikal composite continent, its basement formed in VendianCambrian as a result of Paleoasian oceanic crust, along with Precambrian microcontinents and Gondwana-type terranes, subduction beneath the southeastern margin of the Siberian continent (western margin in present-day coordinates). The subduction and subsequent collision of</p> <div class="credits"> <p class="dwt_author">M. M. Buslov</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">350</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013EGUGA..1513614E"> <span id="translatedtitle">Geology, geochemistry and <span class="hlt">geodynamic</span> implications of the mafic-ultramafic rocks from the Antalya Complex, SW Turkey</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Antalya Complex is bounded on the east and the west by the opposing carbonate platforms (the eastern Anamas-Akseki and the western Bey Da?lar?) forming a north pointing cusp (so-called the Isparta Angle) in SW Turkey, and is made of an assemblage of allochthonous Mesozoic slope-basin deposits and ophiolitic thrust sheets. The allochthonous rock assemblages in the northern part of the Antalya Complex are mainly characterized by slope-basin deposits that are spatially associated with: Upper Triassic volcanic rocks varying in composition from alkali basalt to fractionated trachyandesite; Upper Jurassic-Lower Cretaceous tholeiitic volcanic rocks ranging in composition from basalt to rhyolite; and, MORB-type volcanic rocks, most likely in Cretaceous age, that are spatially associated with olistostromal and subophiolitic tectonic mlanges. Whole rock chemistry of the harzburgitic mantle peridotites (E?ridir K?z?l Da? peridotites) within the apex region of the Isparta Angle and of the isolated dolerite dykes intruding the peridotites, and the mineral chemistry of the harzburgitic spinels collectively suggest a depleted residual mantle peridotite character that is characteristic of forearc tectonic settings. Also, the Upper Triassic volcanic rocks associated with different basin deposits can be traced to the south within the Isparta Angle area and within the Mamonia Complex (SW Cyprus) in the eastern Mediterranean region. Upper Triassic alkaline volcanic rocks are underlain by rift-related siliciclastic rocks, massive limestones, and are, in turn, locally overlain by small patchy carbonate deposits, indicative of an intra-continental rift basin, which may have evolved in the apex region of the Isparta Angle. In the southern part of the Isparta Angle (in the eastern and western side of the Gulf of Antalya), the Triassic lavas are interbedded with and/or overlain by Upper Triassic pelagic sedimentary rocks. The Upper Triassic lavas of the Mamonia Complex are also locally overlain by the Upper Triassic reefal limestones and pelagic sedimentary rocks. Moreover, the Triassic lavas of the southern part of the Isparta Angle and the Mamonia Complex range compositionally from WPB-type to transitional and MORB-type with small age differences, suggesting rapid rifting and drifting in the southern part of the Antalya ocean. Constrains on the geological and geochemical characteristics of the Mesozoic mafic and ultramafic rocks associated with the allochthonous assemblages between the apex of the Isparta Angle and the Mamonia Complex suggest a continental rifting in the Isparta Angle area that was followed by nearly northward propagated opening and wedge-shaped ocean basin evolution with MORB-type oceanic crust and the evolution of a supra-subduction type ophiolite with forearc affinity within the same ocean basin.</p> <div class="credits"> <p class="dwt_author">Elitok, mer</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-04-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">351</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/40778932"> <span id="translatedtitle">Low-latitude meteoric fluid flow along the Cloncurry Fault, Cloncurry district, NW Queensland, Australia: <span class="hlt">geodynamic</span> and metallogenic implications</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Hydrothermal alteration within the Mount Isa Block (MIB) is typically largely to have ceased at the end of the Isan Orogeny (ca. 1.50 Ga). However, late, large brittle quartz-rich vein systems, including those of the Cloncurry Fault, cut Mesoproterozoic tectonic fabrics, intrusions and products of regional NaCa hydrothermal alteration. Associated features display affinities to iron oxideCuAu ore deposits, including specular</p> <div class="credits"> <p class="dwt_author">Geordie Mark; Patrick J Williams; Adrian J Boyce</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">352</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014CoMP..168.1078A"> <span id="translatedtitle">Quaternary bimodal volcanism in the Ni?de Volcanic Complex (Cappadocia, central Anatolia, Turkey): age, petrogenesis and <span class="hlt">geodynamic</span> implications</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The late Neogene to Quaternary Cappadocian Volcanic Province (CVP) in central Anatolia is one of the most impressive volcanic fields of Turkey because of its extent and spectacular erosionally sculptured landscape. The late Neogene evolution of the CVP started with the eruption of extensive andesitic-dacitic lavas and ignimbrites with minor basaltic lavas. This stage was followed by Quaternary bimodal volcanism. Here, we present geochemical, isotopic (Sr-Nd-Pb and ?18O isotopes) and geochronological (U-Pb zircon and Ar-Ar amphibole and whole-rock ages) data for bimodal volcanic rocks of the Ni?de Volcanic Complex (NVC) in the western part of the CVP to determine mantle melting dynamics and magmatic processes within the overlying continental crust during the Quaternary. Geochronological data suggest that the bimodal volcanic activity in the study area occurred between ca. 1.1 and ca. 0.2 Ma (Pleistocene) and comprises (1) mafic lavas consisting of basalts, trachybasalts, basaltic andesites and scoria lapilli fallout deposits with mainly basaltic composition, (2) felsic lavas consisting of mostly rhyolites and pumice lapilli fall-out and surge deposits with dacitic to rhyolitic composition. The most mafic sample is basalt from a monogenetic cone, which is characterized by 87Sr/86Sr = 0.7038, 143Nd/144Nd = 0.5128, 206Pb/204Pb = 18.80, 207Pb/204Pb = 15.60 and 208Pb/204Pb = 38.68, suggesting a moderately depleted signature of the mantle source. Felsic volcanic rocks define a narrow range of 143Nd/144Nd isotope ratios (0.5126-0.5128) and are homogeneous in Pb isotope composition (206Pb/204Pb = 18.84-18.87, 207Pb/204Pb = 15.64-15.67 and 208Pb/204Pb = 38.93-38.99). 87Sr/86Sr isotopic compositions of mafic (0.7038-0.7053) and felsic (0.7040-0.7052) samples are similar, reflecting a common mantle source. The felsic rocks have relatively low zircon ?18O values (5.6 0.6 ) overlapping mantle values (5.3 0.3 %), consistent with an origin by fractional crystallization from a mafic melt with very minor continental crustal contamination. The geochronological and geochemical data suggest that mafic and felsic volcanic rocks of the NVC are genetically closely related to each other. Mafic rocks show a positive trend between 87Sr/86Sr and Th, suggesting simultaneous assimilation and fractional crystallization, whereas the felsic rocks are characterized by a flat or slightly negative variation. High 87Sr/86Sr gneisses are a potential crustal contaminant of the mafic magmas, but the comparatively low and invariant 87Sr/86Sr in the felsic volcanics suggests that these evolved dominantly by fractional crystallization. Mantle-derived basaltic melts, which experienced low degree of crustal assimilation, are proposed to be the parent melt of the felsic volcanics. Geochronological and geochemical results combined with regional geological and geophysical data suggest that bimodal volcanism of the NVC and the CVP, in general, developed in a post-collisional extensional tectonic regime that is caused by ascending asthenosphere, which played a key role during magma genesis.</p> <div class="credits"> <p class="dwt_author">Aydin, Faruk; Schmitt, Axel K.; Siebel, Wolfgang; Snmez, Mustafa; Ersoy, Yal?n; Lermi, Abdurrahman; Dirik, Kadir; Duncan, Robert</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-11-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">353</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014IJEaS.103.1533F"> <span id="translatedtitle">Variscan orogeny in Corsica: new structural and geochronological insights, and its place in the Variscan <span class="hlt">geodynamic</span> framework</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">In Western Corsica, remnants of pre-batholitic lithological and metamorphic assemblages are preserved as km-scale septa enclosed within Lower Carboniferous to Early Permian plutons. Two groups of septa were recognized: (1) the Argentella and Agriates-Tenda fragments correspond to Neoproterozoic rocks deformed and metamorphosed during the Cadomian-Panafrican orogeny, and (2) the Zicavo, Porto-Vecchio, Solenzara-Fautea, Belgodre, Topiti, and Vignola fragments consist of Variscan metamorphic rocks. The lithological content and the main ductile deformation events for each septum are presented. In the Zicavo, Porto-Vecchio, and Topiti septa, a top-to-the-SW ductile shearing (D1 event) coeval with an amphibolite facies metamorphism is responsible for crustal thickening at ca 360 Ma. This main event was preceded by eclogite and granulite facies metamorphic events preserved as restites within migmatites dated at ca 345-330 Ma. A top-to-the-SE ductile shearing (D2 event) coeval with the crustal melting accommodated the exhumation of the D1 event. In contrast, the Belgodre segment is peculiar as it exhibits a top-to-the-E vergence, although retrogressed high-pressure rocks are also recognized. The pre-Permian fragments are arranged in four NW-SE-striking stripes that define a SW-NE zoning with (1) a Western domain in Topiti, Vignola, Zicavo, Porto-Vecchio, and Solenzara-Fautea; (2) a Neoproterozoic basement with its unconformable Early Paleozoic sedimentary cover in Argentella; (3) an Eastern metamorphic domain in Belgodre; (4) another Neoproterozoic basement with its Upper Paleozoic sedimentary cover in Agriates-Tenda. The Argentella basement is separated from the Western and Eastern domains by two sutures: S1 and S2. The Variscan Corsica represents the Eastern part of the Sardinia-Corsica-Maures segment. The comparison of this segment with other Variscan domains allows us to propose some possible correlations. We argue that the Western domain, Argentella, Belgodre, and Agriates-Tenda domains can be compared with the Southern Variscan belt exposed in French Massif Central-Southern Massif Armoricain, Armorica microblock, Lon block, respectively.</p> <div class="credits"> <p class="dwt_author">Faure, Michel; Rossi, Philippe; Gach, Julien; Melleton, Jrmie; Frei, Dirk; Li, Xianhua; Lin, Wei</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-09-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">354</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/10927514"> <span id="translatedtitle">The Miocene igneous rocks in the Basal Unit of Lavrion (SE Attica, Greece): petrology and <span class="hlt">geodynamic</span> implications</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The Miocene igneous rocks in the Basal Unit of the Lavrion area form part of the granitoid province of the central Aegean. Undeformed, subvertical dykes of quartz-syenite to granodiorite and granite porphyries, and a little deformed but variably altered granodiorite stock intrude metamorphic rocks of the Basal Unit. A 9.4 0.3 Ma K-Ar age on feldspar for a dyke</p> <div class="credits"> <p class="dwt_author">NIKOS S KARPELIS; BASILIOS T SIKOURAS; GEORGIA PE-PIPER</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">355</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/55679997"> <span id="translatedtitle">Echoes from the Transylvanian Lithosphere: Preliminary Results From the DRACULA I Profile and Implications for <span class="hlt">Geodynamics</span> of the Vrancea Zone</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Preliminary examination of new deep seismic reflection data in the Transylvanian Basin of Romania, collected through Project DRACULA, reveals strongly layered subhorizontal reflectivity throughout the middle and lower crust, as well as the upper mantle. Collected with 20 kg shots every 1 km recorded to 60 s by a 32-km active spread (640 channels at 50 m) with Reftek-125 seismometers</p> <div class="credits"> <p class="dwt_author">M. A. Fillerup; J. H. Knapp; C. C. Knapp; L. Munteanu; V. Mocanu; V. Raileanu</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">356</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1998Litho..43..135M"> <span id="translatedtitle">The importance of geochemical data for <span class="hlt">geodynamic</span> reconstruction: formation of the Olkhon metamorphic complex, Lake Baikal, Russia</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Olkhon metamorphic complex consists of two geochemically distinct unitsthe Olkhon unit and the Anga formation. The basic crystalline schists of the Olkhon group are interpreted as marginal basin tholeiites. Garnet-biotite gneisses, quartzites and marbles have large contents of C, Cr, V, Mo and Ag, which is typical of black shales that are interpreted to be accumulating under reducing conditions. In the Anga unit, the amphibolites are interpreted as metaandesite-basalts and alkaline basalts with associated metalaterites. Anga unit gneisses, quartzites and marbles display an absence of graphite and low concentrations of Cr and V, and high Mn, P, F and Ba grading into gonditic compositions. These data indicate that these rocks were originally deposited under oxidizing conditions in shallow water or in an onshore environment. The geochemical features of both the metavolcanics and metasediments suggest that the Anga and Olkhon successions accumulated within a marginal basin to mature island arc tectonic setting. The structure of the Olkhon region is essentially nappe-thrust stack that has resulted from compressional thrust tectonics that was later transformed into strike-slip dominated tectonics. The structure and age (450-530 Ma) of the complex accord with a Caledonian collisional history. The entire volcanogenic-sedimentary sequence underwent folding and zonal metamorphism at 800-55040C and 8-51 kb due to the thrust tectonics. Metasomatic granitization and local melting caused the formation of K-leucogranites within the gneiss beds. These granites differ greatly geochemically from slab to slab, reflecting a heterogeneous parental composition, variable P- T conditions, and variable degrees of partial melting.</p> <div class="credits"> <p class="dwt_author">Makrygina, V. A.; Petrova, Z. I.</p> <p class="dwt_publisher"></p> <p class="publishDate">1998-07-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">357</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.geologie.ens.fr/~rooke/NCRpdf4web/ChamotRookeGaulierJestin1999.pdf"> <span id="translatedtitle">Constraints on Moho depth and crustal thickness in the Liguro-Provencal basin from a 3D gravity inversion: <span class="hlt">geodynamic</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/epsearch/">E-print Network</a></p> <p class="result-summary">extension mechanism since late Oligocene time driven by the African trench retreat. Determination the Gulf of Lion margin and adjacent deep basin: multi- channel seismics of ECORS type and wide) in the Gulf of Lion area. However, seismic data remain sparse. Variability of the crustal structure is high</p> <div class="credits"> <p class="dwt_author">Nicolas, Chamot-Rooke</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">358</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013EGUGA..15.9917R"> <span id="translatedtitle">The Main Shear Zone in Sr Rondane: A key feature for reconstructing the <span class="hlt">geodynamic</span> evolution of East Antarctica</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Structural investigations were carried out along the Main Shear Zone (MSZ) of western Sr Rondane (22-25E, 71.5-72.5S) to gain new information about the position of the East-/West-Gondwana suture and the ancient plate tectonic configuration during Gondwana amalgamation. The WSW-ENE striking MSZ divides south-western Sr Rondane in a northern amphibolite-facies terrane and a southern tonalite-trondhjemite-granodiorite (TTG) terrane. The structure can be traced over a distance of ca. 100 km and reaches several hundred meters in width. It is characterized by a right-lateral sense of movement and marked by a transpressional and also transtensional regime. Ductilely deformed granitoids (ca. 560 Ma: SHRIMP U-Pb of zircon) and ductile - brittle structures, which evolved in a transitional ductile to brittle regime in an undeformed syenite (ca. 499-459 Ma, Ar-Ar mica), provide a late Proterozoic/ early Paleozoic time limit for the activity of the shear zone (Shiraishi et al., 2008; Shiraishi et al., 1997). Documentation of ductile and brittle deformation allows reconstructing up to eight deformation stages. Cross-cutting relationships of structural features mapped in the field complemented by published kinematic data reveal the following relative age succession: [i] Dn+1 - formation of the main foliation during peak metamorphism, [ii] Dn+2 - isoclinal, intrafolial folding of the main foliation, mostly foliation-parallel mylonitic shear zones (1-2 meter thick), [iii] Dn+3 - formation of tight to closed folds, [iv] Dn+4 - formation of relatively upright, large-scale open folds, [v] Dn+5 - granitoid intrusion (e.g. Vengen granite), [vi] Dn+6 - dextral shearing between amphibolite and TTG terranes, formation of the MSZ, [vii] Dn+7 - intrusion of late- to post-tectonic granitoids, first stage of brittle deformation (late shearing along MSZ), intrusion of post-kinematic mafic dykes, [viii] Dn+8 - second stage of brittle deformation including formation of conjugate fault systems. The latter point to a WNW-ESE respectively NW-SE oriented maximum paleostress direction and indicate the latest deformation event; they are possibly related to the break-up and fragmentation of Gondwana. Two contrasting models describe the configuration of East Gondwana during the Neoproterozoic and the final amalgamation of Gondwana. The first model proposes the existence of a Pan-African Orogen (East African/ Antarctic Orogen). The Main Shear Zone could represent the eastern extension of this orogen and may be related to a NE-directed lateral-escape tectonic model. Both published structural data from Sr Rondane and adjacent regions and the outcome of this study agree with this model and propose a suture of East- and West Gondwana located between Mhlig-Hofmann-Gebirge and Sr Rondane. The second model of an overlap of two orogens with different formation ages cannot be proved by structural data from the MSZ. Instead, tight test constraints of the second model may be provided by new magnetic anomaly maps based on a 2012/13 aerogeophysical survey. Shiraishi, K.; Dunkley, D.J.; Hokada, T.; Fanning, C.M.; Kagami, H.; and Hamamoto, T. (2008): Geochronological constraints on the Late Proterozoic to Cambrian crustal evolution of eastern Dronning Maud Land, East Antarctica: a synthesis of SHRIMP U-Pb age and Nd model age data. Geological Society, 308(1):21-67. Shiraishi, K.; Osanai, Y.; Ishizuka, H.; and Asami, M. (1997): Geological map of the Sr Rondane Mountains, Antarctica. Antarctica Geological Map Series, sheet 35, scale 1 : 25 0000. National Institute of PolarResearch, Tokyo.</p> <div class="credits"> <p class="dwt_author">Ruppel, Antonia; Lufer, Andreas; Lisker, Frank; Jacobs, Joachim; Elburg, Marlina; Damaske, Detlef; Lucka, Nicole</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-04-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">359</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013IJEaS.102..783B"> <span id="translatedtitle"><span class="hlt">Geodynamic</span> evolution of ophiolites from Albania and Greece (Dinaric-Hellenic belt): one, two, or more oceanic basins?</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">All the geological constraints for an exhaustive reconstruction of the Triassic to Tertiary tectonic history of the southern Dinaric-Hellenic belt can be found in Albania and Greece. This article aims to schematically reconstruct this long tectonic evolution primarily based on a detailed analysis of the tectonic setting, the stratigraphy, the geochemistry, and the age of the ophiolites. In contrast to what was previously reported in the literature, we propose a new subdivision on a regional scale of the ophiolite complexes cropping out in Albania and Greece. This new subdivision includes six types of ophiolite occurrences, each corresponding to different tectonic units derived from a single obducted sheet. These units are represented by: (1) sub-ophiolite mlange, (2) Triassic ocean-floor ophiolites, (3) metamorphic soles, (4) Jurassic fore-arc ophiolites, (5) Jurassic intra-oceanic-arc ophiolites, and (6) Jurassic back-arc basin ophiolites. The overall features of these ophiolites are coherent with the existence of a single, though composite, oceanic basin located east of the Adria/Pelagonian continental margin. This oceanic basin was originated during the Middle Triassic and was subsequently (Early Jurassic) affected by an east-dipping intra-oceanic subduction. This subduction was responsible for the birth of intra-oceanic-arc and back-arc oceanic basins separated by a continental volcanic arc during the Early to Middle Jurassic. From the uppermost Middle Jurassic to the Early Cretaceous, an obduction developed, during which the ophiolites were thrust westwards firstly onto the neighboring oceanic lithosphere and then onto the Adria margin.</p> <div class="credits"> <p class="dwt_author">Bortolotti, Valerio; Chiari, Marco; Marroni, Michele; Pandolfi, Luca; Principi, Gianfranco; Saccani, Emilio</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">360</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/3544584"> <span id="translatedtitle">Paleomagnetic constraints on the <span class="hlt">geodynamic</span> history of the major blocks of China from the Permian to the present</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">All available paleomagnetic poles of Upper Permian to Tertiary age from the main blocks of China are critically reviewed with the aim of placing constraints on models of the formation and the subsequent deformation of the region. For first-order analysis, apparent polar wander paths are constructed for the major blocks. The compatibilities and contradictions between the geological and paleomagnetic records</p> <div class="credits"> <p class="dwt_author">Randolph J. Enkin; Zhenyu Yang; Yan Chen; Vincent Courtillot</p> <p class="dwt_publisher"></p> <p class="publishDate">1992-01-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_17");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' href="#">4</a> <a onClick='return showDiv("page_5");' href="#">5</a> <a onClick='return showDiv("page_6");' href="#">6</a> <a onClick='return showDiv("page_7");' href="#">7</a> <a onClick='return showDiv("page_8");' href="#">8</a> <a onClick='return showDiv("page_9");' href="#">9</a> <a onClick='return showDiv("page_10");' href="#">10</a> <a onClick='return showDiv("page_11");' href="#">11</a> <a onClick='return showDiv("page_12");' href="#">12</a> <a onClick='return showDiv("page_13");' href="#">13</a> <a onClick='return showDiv("page_14");' href="#">14</a> <a onClick='return showDiv("page_15");' href="#">15</a> <