Note: This page contains sample records for the topic geodynamics from Science.gov.
While these samples are representative of the content of Science.gov,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of Science.gov
to obtain the most current and comprehensive results.
Last update: August 15, 2014.
1

Geodynamics  

NASA Technical Reports Server (NTRS)

The status of space geodynamics is examined, major scientific questions that need to be addressed are identified, and program activities are recommended for the next decade. Progress made in measuring tectonic plates, polar motion, and coupling of fluid motion of the Earth's core to the mantle is reviewed.

Walter, L. S.

1984-01-01

2

Geodynamics Project  

ERIC Educational Resources Information Center

Describes activities of Geodynamics Project of the Federal Council on Science and Technology, such as the application of multichannel seismic-reflection techniques to study the nature of the deep crust and upper mantle. (MLH)

Drake, Charles L.

1977-01-01

3

Nasa Geodynamics Program.  

National Technical Information Service (NTIS)

Activities and achievements for the period of May 1983 to May 1984 for the NASA geodynamics program are summarized. Abstracts of papers presented at the Conference are inlcuded. Current publications associated with the NASA Geodynamics Program are listed.

1984-01-01

4

NASA Geodynamics Program  

NASA Technical Reports Server (NTRS)

Activities and achievements for the period of May 1983 to May 1984 for the NASA geodynamics program are summarized. Abstracts of papers presented at the Conference are inlcuded. Current publications associated with the NASA Geodynamics Program are listed.

1984-01-01

5

NASA geodynamics program  

NASA Technical Reports Server (NTRS)

The history and development of the geodynamics program are described, in addition to accomplishments and plans for the future years activities. Extramural grant titles are listed for general research, Lageos investigations, and Magsat investigations.

1980-01-01

6

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.

7

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

8

The NASA Geodynamics Program: An overview  

NASA Technical Reports Server (NTRS)

This NASA Geodynamics Program overview collectively examines the history, scientific basis, status, and results of the NASA Program and outlines plans for the next five to eight years. It is intended as an informative nontechnical discussion of geodynamics research.

1983-01-01

9

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

10

Exochemical Geodynamics and Potamochemistry  

NASA Astrophysics Data System (ADS)

The processes which operate at the surface of the earth to weather the rocks and to erode the relief can be studied with the same methodology as we have used to study the geodynamics of internal processes (isotope tracers, trace element systematics, budget modeling by inverse approach). The rivers are like the basalts. They are messengers of erosion processes integrating a large number of microphenomena in all. We have applied to the river materials (both soluble and particulate) the same approach as we have done for basalts. What are the results? 1) We can determine accurately what are the contributors to the river chemistry. Case by case, but also at the whole earth level we can obtain the proportions of rain, carbonates, evaporites, silicates, and granitoids, which determine the composition of river water. 2) The complementary study of the particulates as well as the dissolved load permit us to measure the degree of weathering case by case, as well as the proportion of shales/granitoids. 3) Isotopic ratios of Sr, Pb, Nd, Os measured as particulates, and Sr, Os, Nd in the dissolved load permit us to obtain a reliable average continental crust for today. 4) For the "insoluble" elements, we can also obtain average reliable ratios representative of the bulk continental crust. 5) Systematic relationships can be established between chemical/physical erosion rates, chemical/physical erosion rates with temperature, with runoff, with pH. These scaling laws permit one to describe quantitatively the erosion process and a model can be built on such relationships. 6) The uses of various complementary techniques, including Pb isotopes, tracer element ratios, uranium disequilibrium series, permits one to establish the different regime of erosion: equilibrium, soil development, soil destruction. These cases can be quantitatively described. 7) With reference to the ocean, these results permit one to propose a new scale of residence time and a test of the Whitfield global equilibrium theory of the hydrosphere-lithosphere systems.

Allègre, C. J.; Dupré, B.; Gaillardet, J.

2001-05-01

11

Basic research for the geodynamics program  

NASA Technical Reports Server (NTRS)

The current technical objectives for the geodynamics program consist of (1) optimal utilization of laser and Very Long Baseline Interferometry (VLBI) observations for reference frames for geodynamics; (2) utilization of range difference observations in geodynamics; and (3) estimation techniques in crustal deformation analysis.

Mueller, I. I.

1985-01-01

12

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

13

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

14

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

15

Geodynamic monitoring in real times  

NASA Astrophysics Data System (ADS)

For the decision of problems of the short-term and intermediate term forecast of tectonic earthquakes the technique conditionally named - geodynamic monitoring which does not use the data of seismic monitoring for the operative decision of problems of the forecast is offered. Geodynamic monitoring (GDM) is to studying tensely - deformed conditions of the separate block of rock on change of activity natural radioactive gas is carried out by accommodation in the chosen file of specially designed monitors of radon - devices fixing change in time (VAR). The monitor of radon, (the detector of radon) as the basic measuring device located in the block of rocks, possesses enormous tensosensitivity to relative strain condition of a file. Depending on the enclosed pressure choose three characteristic points: 1) 30-35 % of "background" size VAR - the beginning of accumulation of inelastic energy; 2) 50 % of background VAR - the process of stabilization of an elastic condition of a file; 3) 70-75 % "background" VAR - a critical pressure in the mountain block, an opportunity as spontaneous dump of elastic energy, and under action external "triggerring" forces. If the size of the saved up energy is close to critical dump needs energy at a level of energy of variations of rotation of the Earth. Such significant energy causes "plenty" of earthquakes on all planet simultaneously. This fact confirms an opportunity of the short-term forecast of strong (destructive) earthquakes: dump of elastic pressure of the Earth in this case occurs in 25-30 hours after passage of variations of rotation of the Earth. It is for the notification of the population about coming nearer earthquake. External power functions (mechanical, electromagnetic, etc.), preparations influencing system and occurrence of tectonic earthquakes, are divided on two big classes: 1) "forecasting " functions - processes functionally connected to accumulation of elastic pressure and to dump by its rather small dozes; 2) external mechanical actions which initiate dump of the saved up elastic pressure - "triggirring functions", promoting dump of the elastic pressure resulting in earthquake. The short-term forecast of especially large earthquakes is entirely based on use of monitoring of rotation of the Earth: essential "triggerring functions" (variations of rotation of the Earth) dump(reset) the saved up pressure on all surface of the Earth, causing thus large earthquakes. Therefore the prevention(warning) of large earthquakes should be formed on the basis of monitoring variations of heterogeneity of rotation of the Earth, that usually precedes dump of elastic pressure(voltage) at 25-30 o'clock.

Outkin, V.; Yurkov, A.; Klimshin, A.; Kozlova, I.

2011-12-01

16

Multiphase geodynamical modelling using Aspect  

NASA Astrophysics Data System (ADS)

Aspect (Advanced Solver for Problems in Earth's ConvecTion) is a 2D/3D FEM code to simulate problems in thermal convection. It is a promising and powerful tool, implementing state-of-the-art numerical methods and is vowed to become a standard tool in the mantle convection numerical modelling community. Its primary focus is on the simulation of processes in the earth's mantle, but its design is more general than that and we therefore explore the (recent) algorithmic additions made to the code: these include for instance the ability to implement complex in/outflow boundary conditions, the tracking of any number of compositional fields which are passively advected by the computed velocity fields, and the use of various adaptive mesh refinement strategies. Several benchmarks of the geodynamical community involving multiphase flow will be shown and compared with results obtained with a FEM code using the particle-in-cell technique and a FEM code using the level set method. The use of Aspect in the case when a free surface is present will also be investigated.

Thieulot, Cedric; Glerum, Anne; Hillebrand, Bram; Spakman, Wim; Torsvik, Trond

2013-04-01

17

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

18

Proceedings of the International Committee on Geodynamics  

Microsoft Academic Search

This special volume, vol. 13, 1980, of the Geological Bulletin, University of Peshawar, Pakistan, on the Geodynamics of the NW Himalayas, contains 213 pages, 23 articles with 96 figures and 28 tables, authored by 36 contributors from 7 countries (Pakistan, U.S., France, India, Switzerland, Italy, U.K.). The volume truthfully reflects the diversity and intensity of the recent international scientific effort

Klaus Jacob

1982-01-01

19

Geodynamic laser ranging system laser transmitter  

Microsoft Academic Search

A description is given of the requirements and design options in the development of a spaceborne laser transmitter for NASA's Geodynamic Laser Ranging System. Three different oscillators are considered. The first is an injection-seeded ring oscillator yielding 1 mJ of energy within a 120-ps pulse. The second is a frequency-modulated mode-locked oscillator emitting 0.30 nJ in a 20-ps pulse. The

J. L. Dallas; J. P. Czechanski; D. B. Coyle; B. J. Zukowski; B. D. Seery

1991-01-01

20

Basic research for the geodynamics program  

NASA Technical Reports Server (NTRS)

Further development of utility program software for analyzing final results of Earth rotation parameter determination from different space geodetic systems was completed. Main simulation experiments were performed. Results and conclusions were compiled. The utilization of range-difference observations in geodynamics is also examined. A method based on the Bayesian philosophy and entropy measure of information is given for the elucidation of time-dependent models of crustal motions as part of a proposed algorithm. The strategy of model discrimination and design of measurements is illustrated in an example for the case of crustal deformation models.

1986-01-01

21

Geodynamic laser ranging system laser transmitter  

NASA Technical Reports Server (NTRS)

A description is given of the requirements and design options in the development of a spaceborne laser transmitter for NASA's Geodynamic Laser Ranging System. Three different oscillators are considered. The first is an injection-seeded ring oscillator yielding 1 mJ of energy within a 120-ps pulse. The second is a frequency-modulated mode-locked oscillator emitting 0.30 nJ in a 20-ps pulse. The third is a self-starting, additive pulse mode-locked laser. Detailed design considerations and preliminary results of these lasers are reported as well as the design of a unique multipass amplifier.

Dallas, J. L.; Czechanski, J. P.; Coyle, D. B.; Zukowski, B. J.; Seery, B. D.

1991-01-01

22

Application of space technology to geodynamics.  

PubMed

Measurements of the movement and deformation of tectonic plates are needed for many research areas in geodynamics, but observations with adequate accuracy and frequency of measurement are not feasible if classical geodetic methods are used. Long-baseline microwave interferometry and laser ranging to Earth satellites are among the new techniques that have been developed within the past decade to make the required measurements. Fixed and mobile stations using both these methods have been constructed in several countries and are now being used in an internationally coordinated research program. Baseline length accuracy better than 2 to 3 centimeters (1 standard deviation) is expected within the next 5 years. PMID:17741174

Flinn, E A

1981-07-01

23

Modern Geodynamic Model of the Arctic Ocean  

NASA Astrophysics Data System (ADS)

In 2011 at VSEGEI (Russia) within the international project "Atlas of Geological Maps of the Circumpolar Arctic", a draft of the structural tectonic map of the Arctic at 1: 5,000,000 scale was prepared. This map is accompanied by a model of deep lithospheric structure of the Russian Arctic, which reflects thickness, types and specific features of crustal structure, and by geodynamic reconstructions. Analysis of the geological and geophysical data enables distinguishing a set of features in the Arctic evolution: - Differences in geological structure and geodynamic evolution of the Western and Eastern Arctic have been spotted no less than since the Early Paleozoic, which was reflected in the formation of caledonides in the West of the Arctic, and ellesmerides in the East. - In the Middle Paleozoic-Mesozoic (Late Devonian-Early Cretaceous), the eastern parts of the Arctic were affected by geodynamic processes taking place in the Paleo-Pacific. The formation of the Canadian basin was a result of the Late Jurassic-Early Cretaceous riftogenesis. A set of features of this basin - such as constrained spreading, considerable depth and topography of the floor, sedimentation specifics - allows us to consider it as a marginal basin of the Paleo-Pacific that moved into an island-arc evolution stage in the Late Jurassic. Collision orogenic activities that widely manifested themselves in the Northern-Eastern part of Asia on the verge of the Early-Late Cretaceous are related to intraplate riftogenic processes in the Central Arctic that were followed by basic magmatism manifestations in Svalbard, Franz Josef Land and New Siberian Islands. Cretaceous stage of the intraplate riftogenesis determined to a great extent the modern-day structure of the Eastern Arctic. - The opening of the Northern Atlantic was accompanied by tectonic compression in the Eastern parts of the Arctic. The formation of the Eurasian basin was preceded by Late Cretaceous-Paleogene period of amplitude differentiated vertical tectonic movements. At that time, the Barents-Kara plate suffered lifting whose amplitude reached as many as 2000-3000 meters. Within the Amerasian basin prevailed descending movement that determined the generation of the cover of Late Cretaceous-Cenozoic formations. - Analysis of seismic data shows that the mid-oceanic Gakkel Ridge takes over older - presumably Early Cretaceous - riftogenic structure. Young oceanic Eurasian spreading basin changes into the riftogenic Laptev Sea basin. The Eastern and Western Eurasian basin passive margins are different. Within the Barents and Kara marginal seas, sedimentary paleobasins are reconstructed with a thick (up to 20 km) Paleozoic and Mesozoic (Triassic-Early Cretaceous) sedimentary cover and a heterogeneous basement. Amerasian basin was formed in the Late Jurassic-Early Cretaceous similar to the marginal basin of Paleo-Pacific. In the Late Cretaceous, it transformed into a residual basin, and beginning from the Neogene it evolved into an intraplate basin of the passive margin of the newly formed Eurasian Oceanic basin.

Petrov, O.; Sobolev, N.; Morozov, A.; Grikurov, G.; Shokalsky, S.; Kashubin, S.; Petrov, E.

2012-04-01

24

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

25

Singular Spectrum Analysis in Astrometry and Geodynamics  

NASA Astrophysics Data System (ADS)

The paper presents the possibilities of the Singular Spectrum Analyses on the examples of its application to several astrometric and geodynamic time series. The comparisons of results obtained by other often used methods (Fourier transform, Wavelet Transform, different filter methods) are given. The Singular Spectrum Analyses method was used for the investigation of the Chandler wobble (CW), which was extracted from the IERS Pole coordinates and latitude variations at Pulkovo. The CW amplitude and phase variations were examined by means of the Hilbert transform. The main conclusion which can be made from this study is: we have found two epochs of deep CW amplitude decreases near 1850 and 2005, which are also accompanied by a large phase jump, similar to well known event in 1920s. The investigation of first latitude observations at Pulkovo (1840-1855) was executed with the aim to gain and analyse the sum of Chandler and annual components from very small quantity of very noisy observations. The SSA is applied for investigation of the zenith troposphere delay time-series derived from observations of several VLBI stations. Combined IVS time-series of the zenith wet and total troposphere delays obtained in IGG were used for analysis. For all stations under consideration the non-linear trends and the seasonal components with annual and semiannual periods were found. Some interesting peculiarities were found to be individual for every stations. Comparison of the trends with meteorological parameters is also presented.

Vityazev, V. V.; Miller, N. O.; Prudnikova, E. Ja.

2010-10-01

26

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

27

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

28

Eclogites and their geodynamic interpretation: a history  

NASA Astrophysics Data System (ADS)

Haüy coined the term eclogite, meaning "chosen rock", in 1822, but de Saussure had already observed rocks of this type in the Alps four decades earlier. Throughout the 19th century, the origin of eclogite remained an enigma, in spite of great progress in our knowledge of this rock. The first chemical analyses, carried out around 1870, showed that its bulk composition was the same as gabbro. Therefore, eclogite was thought to be either an igneous rock of gabbroic composition or a metamorphosed gabbro. This second hypothesis became preferred when progressive transitions were observed between gabbros and eclogites. In 1903, simply by comparing the molar volumes of gabbroic and eclogite parageneses, Becke inferred that eclogite was the high-pressure equivalent of gabbro. In 1920, eclogite was involved in the conception of the metamorphic facies by Eskola. However, a few researchers denied the existence of an eclogite facies, and claimed that high stress instead of high lithostatic pressure could generate eclogites. In the 1960s, consideration of the water pressure parameter also favoured the belief that eclogite was simply the anhydrous equivalent of amphibolite. Finally, eclogite was definitely considered as a high-pressure metamorphic rock following the development of experimental petrology and the application of thermodynamics. In recent years, the discovery of ultrahigh-pressure coesite-bearing rocks in the crust has drastically changed geologists' ideas concerning the limits of eclogite-facies crustal metamorphism. Eclogites have been involved in several geodynamic theories. Around 1900, kimberlite studies favoured the idea that eclogite might be abundant in the interior of the Earth. In 1912, Fermor predicted the existence of a dense eclogite-bearing zone in the mantle. This "eclogite layer" hypothesis was still envisaged as late as 1970. The alternative "peridotite" hypothesis became preferred when experimental investigations demonstrated that the gabbro-to-eclogite transition could not coincide with a sharp Mohorovi?i? discontinuity. Before plate tectonics, high-pressure belts were interpreted as remnants of ophiolite-bearing "geosynclines", metamorphosed by loading during thrust faulting. After the acceptance of plate tectonics, around 1970, the same high-pressure Alpine-type belts came to be considered as former oceanic crust, transformed into eclogite within subduction zones, and subsequently incorporated into mountain belts. Surprisingly, formation of eclogite in "subsidence" zones (i.e. subduction zones) had already been envisaged as early as 1931 by Holmes, the inventor of a convection-current theory. In the 1980s, many authors tried to apply the model of Alpine-type high-pressure belts to eclogites enclosed within the gneisses of ancient orogens, but the question remains obscure nowadays. These eclogites have been involved in the "in situ versus foreign" controversy and in the unresolved enigma of ultrahigh-pressure metamorphism. The latter came under scrutiny in 1984 after the discovery of coesite and diamond in some eclogite-facies rocks. It has been a matter of considerable interest during the last two decades. Currently, the debate is focused on the geodynamic mechanisms responsible for the exhumation of these rocks, a question that will probably remain unresolved for part of the coming century.

Godard, Gaston

2001-09-01

29

Cenozoic geodynamic evolution of the Aegean  

NASA Astrophysics Data System (ADS)

The Aegean region is a concentrate of the main geodynamic processes that shaped the Mediterranean region: oceanic and continental subduction, mountain building, high-pressure and low-temperature metamorphism, backarc extension, post-orogenic collapse, metamorphic core complexes, gneiss domes are the ingredients of a complex evolution that started at the end of the Cretaceous with the closure of the Tethyan ocean along the Vardar suture zone. Using available plate kinematic, geophysical, petrological and structural data, we present a synthetic tectonic map of the whole region encompassing the Balkans, Western Turkey, the Aegean Sea, the Hellenic Arc, the Mediterranean Ridge and continental Greece and we build a lithospheric-scale N-S cross-section from Crete to the Rhodope massif. We then describe the tectonic evolution of this cross-section with a series of reconstructions from ~70 Ma to the Present. We follow on the hypothesis that a single subduction has been active throughout most of the Mesozoic and the entire Cenozoic, and we show that the geological record is compatible with this hypothesis. The reconstructions show that continental subduction (Apulian and Pelagonian continental blocks) did not induce slab break-off in this case. Using this evolution, we discuss the mechanisms leading to the exhumation of metamorphic rocks and the subsequent formation of extensional metamorphic domes in the backarc region during slab retreat. The tectonic histories of the two regions showing large-scale extension, the Rhodope and the Cyclades are then compared. The respective contributions to slab retreat, post-orogenic extension and lower crust partial melting of changes in kinematic boundary conditions and in nature of subducting material, from continental to oceanic, are discussed.

Jolivet, Laurent; Brun, Jean-Pierre

2010-01-01

30

2D Geodynamic models of Microcontinent Formation  

NASA Astrophysics Data System (ADS)

Continental fragments (microcontinents and continental ribbons) are rifted-off blocks of relatively unthinned continental crust situated among the severely thinned crust of passive margins. The existence of these large crustal blocks would suggest that the passive margin containing them either underwent simultaneous differential rifting or multi-stage rifting in order to produce continental breakup and seafloor spreading in more than one location in the span of approximately 100 km. Also, because continental fragments do not occur on every passive margin, there must be something particular about the crust and/or lithosphere that led to the production of these features. Some proposed mechanisms for microcontinent and continental ribbon formation include (1) structural inheritance, (2) strain localization by serpentinized mantle or magmatic underplating, and (3) plume interaction with an active rift. Pre-existing weakness and inherited structural fabrics in typical continental crust from past tectonic events, such as varying rheology of accreted terranes and collisional suture zones, could be reactivated and serve as foci for deformation. The second theory is that strain is localized in certain regions by large amounts of weakened material that are either serpentinized mantle or mafic bodies underplating the thinned crust. Another possible process that could lead to continental fragment formation is magmatic influence of hot plume material that focuses in various regions, producing rifts in separate areas. The Jan Mayen and Seychelles microcontinents both have geological and plate reconstruction evidence to support the plume interaction theory. We use 2-D geodynamic experiments to assess the importance of structural inheritance, strain localization by regions of weakened mantle material, and contributions to rifting from plume material on producing crustal blocks surrounded by seafloor or thinned/hyperextended crust. Our preliminary results suggest that each of these three mechanisms, working alone, cannot produce concurrent or multi-stage differential thinning and continental break-up. We infer that multistage extension produced by a combination of these mechanisms could be necessary to produce microcontinents and continental ribbons.

Tetreault, Joya; Buiter, Susanne

2013-04-01

31

Contributions to the geodynamics of western Canada  

NASA Astrophysics Data System (ADS)

Western Canada exhibits a large variation in continental lithosphere from very old rocks in the Canadian Shield across the younger Cordillera to the current accretion of the Yakutat Terrane in the Gulf of Alaska. The geodynamics are driven by the Pacific-North America plate motion resulting in deformation, seismicity, and mountain building across the Canadian Cordillera. The way the lithosphere reacts to deformation or loading depends on its thickness and strength. The effective elastic thickness of the lithosphere, Te , has been estimated in this thesis study using a coherence analysis of Bouguer gravity and topography. There is very thick and strong lithosphere in the old Canadian Shield (Te > 100 km) and thin and weak lithosphere in the Cordillera (Te = 20--30 km). Lithospheric temperature, derived from surface heat flow and upper crust radioactive heat generation, is the most important control on the strength of the lithosphere. Calculated temperatures at the base of the crust are high in the young and hot Cordillera (˜900--1000°C) and very low in the old and cold Craton (˜400--450°C). The depths to the thermally controlled brittle-ductile transition are in general agreement with the Te estimates. The high temperatures in the lower crust and upper mantle of the Cordillera reduce the density by thermal expansion. This thermal isostasy explains the surprising observation of high topography over thin crust. The estimated lithospheric temperatures are used to calculate lithospheric strength profiles. In agreement with the Te estimates, the Cordillera has a weak zone in the lower crust facilitating detachment of the upper crust. Analysis of GPS continuous and campaign data show that the Northern Cordillera is moving at ˜5--10 mm/y in a northward direction driven by the collision of the Yakutat Block in the Gulf of Alaska and is overthrusting the strong lithosphere of the Canadian Shield.* *This dissertation is multimedia (contains text and other applications not available in printed format). The CD requires the following system applications: Internet Browser; Adobe Acrobat; Microsoft Office.

Fluck, Paul

32

Applications of deformation analysis in geodesy and geodynamics  

Microsoft Academic Search

The role of deformation analysis is discussed with respect to its existing or possible future applications in geodesy and geodynamics. Expressions for strain tensors are given in the more general case of Riemannian spaces and specialized for Euclidean spaces and the case of infinitesimal deformation. Among the various applications, special emphasis is given to the study of crustal deformations of

Athanasios Dermanis; Evangelos Livieratos

1983-01-01

33

Time-dependent, irreversible entropy production and geodynamics  

Microsoft Academic Search

We present an application of entropy production as an abstraction tool for complex processes in geodynamics. We relate the thermodynamic the- ory to the underlying energy conservation principles and their application to continuum mechanics. In plasticity theory extremum principles of plastic work (upper and lower bound principles) have long proven to be extremely useful in understanding basic modes of plastic

Klaus Regenauer-Lieb; Ali Karrech; H. T. Chua; F. G. Horowitz; Dave A. Yuen

2009-01-01

34

Effects of turbulence on the geodynamic laser ranging system  

Microsoft Academic Search

The Geodynamic Laser Ranging System (GLRS) is one of several instruments being developed by the National Aeronautics and Space Administration (NASA) for implementation as part of the Earth Observing System in the mid-1990s (Cohen et al., 1987; Bruno et al., 1988). It consists of a laser transmitter and receiver in space and an array of retroreflectors on the ground. The

James H. Churnside

1993-01-01

35

Overview of adaptive finite element analysis in computational geodynamics  

NASA Astrophysics Data System (ADS)

The use of numerical models to develop insight and intuition into the dynamics of the Earth over geological time scales is a firmly established practice in the geodynamics community. As our depth of understanding grows, and hand-in-hand with improvements in analytical techniques and higher resolution remote sensing of the physical structure and state of the Earth, there is a continual need to develop more efficient, accurate and reliable numerical techniques. This is necessary to ensure that we can meet the challenge of generating robust conclusions, interpretations and predictions from improved observations. In adaptive numerical methods, the desire is generally to maximise the quality of the numerical solution for a given amount of computational effort. Neither of these terms has a unique, universal definition, but typically there is a trade off between the number of unknowns we can calculate to obtain a more accurate representation of the Earth, and the resources (time and computational memory) required to compute them. In the engineering community, this topic has been extensively examined using the adaptive finite element (AFE) method. Recently, the applicability of this technique to geodynamic processes has started to be explored. In this review we report on the current status and usage of spatially adaptive finite element analysis in the field of geodynamics. The objective of this review is to provide a brief introduction to the area of spatially adaptive finite analysis, including a summary of different techniques to define spatial adaptation and of different approaches to guide the adaptive process in order to control the discretisation error inherent within the numerical solution. An overview of the current state of the art in adaptive modelling in geodynamics is provided, together with a discussion pertaining to the issues related to using adaptive analysis techniques and perspectives for future research in this area. Additionally, we also provide a summary of available open source software relevant to AFE analysis in geodynamics with the intent to provide interested practitioners of computational geodynamics with a starting point for "first hand" geodynamic experimentation using AFE analysis.

May, D. A.; Schellart, W. P.; Moresi, L.

2013-10-01

36

Geodynamic Evolution of the Banda Sea Region  

NASA Astrophysics Data System (ADS)

We've carried out a large on- and offshore study in Eastern Indonesia to characterize the major structures and to provide constraints on the Neogene geodynamic evolution of the Banda Sea region. The onshore portion utilized remote sensing data and published geology. We tied the onshore to the offshore using recently acquired high resolution bathymetric data (16m and 25m bin size) and 2D seismic profiles that extend from Sulawesi in the west to Irian Jaya in the east across the northern part of the Banda Arc. We interpret the northern boundary of the 'Birds Head' (BH) of Papua, the Sorong Fault, to be a sinistral strike-slip fault zone with a minimum of 48 km displacement over the last few million years. The western boundary fault of Cendrawasih Basin defines the eastern boundary of BH and corresponds to the Wandamen Peninsula which comprises high pressure metamorphic rocks, including eclogite and granulite facies rocks, with exhumation ages from 4 to 1 Ma. Earthquake focal mechanism solutions indicate that the eastern boundary of BH is linked with a large scale offshore normal fault which we suggest may be related to the exhumation of the Wandamen Peninsula. The eastern boundary of Cendrawasih Basin is defined by a large transpressive belt along which BH is decoupled from the rest of Papua / Irian Jaya. This interpretation is supported by recent GPS studies. We propose that the BH and the Pacific plate are coupled, and therefore the Birds Head is therefore completely detached from Irian Jaya. Furthermore, Aru Basin, located at the NE corner of Banda Arc, is a Fault-Fault-Transform (FFT) type triple junction. According to available literature information the Banda Sea includes three distinct basins with different geologic histories; the North Banda Sea Basin (NBSB) was opened during 12-7 Ma, Wetar-Damar Basin (WDB) during 7-3.5 Ma and Weber Basin (WB) 3-0 Ma. Our bathymetric and seismic data indicated that the NBSB and Weber Basin lack normal oceanic crust and are probably floored by exhumed mantle, while WDB seems to have normal oceanic crust. These basins thought to be developed sequentially from north to south, possibly due to back arc extension resulting from trench retreat and roll-back of the northwards subducting Indo-Australian oceanic plate below the SE Eurasian margin along the Sunda-Banda subduction zone. We suggest that a trench-perpendicular tear in the subducting slab extends from the southwestern corner of Celebes Sea to the northeastern corner of Seram Island. It defines the southern boundary of the Banggai-Sula and Bird's Head (BH) blocks and northern boundary of Banda Sea micro-plate. The dominant character of this structure is sinistral strike-slip fault zone that eastward gradually become transpressional to ultimately thrusting at the tip of the tear east of Seram Island. Here, deformation results in a large accretionary wedge, the Seram Accretionary Belt (SAB) that is partitioned by intensely sheared strike-slip faults. The deformation mechanisms within the SAB is difficult to interpret due to poor seismic imaging below a shallow (Pliocene?) unconformity and the inferred complexity of the deformation within the belt. However, geometries of faults and fault blocks are very well pronounced on bathymetric data which provide hints for the deformation style of the belt.

Kaymakci, N.; Decker, J.; Orange, D.; Teas, P.; Van Heiningen, P.

2013-12-01

37

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

38

Solar System Processes Underlying Planetary Formation, Geodynamics, and the Georeactor  

Microsoft Academic Search

Only three processes, operant during the formation of the Solar System, are responsible for the diversity of matter in the\\u000a Solar System and are directly responsible for planetary internal-structures, including planetocentric nuclear fission reactors,\\u000a and for dynamical processes, including and especially, geodynamics. These processes are: (i) Low-pressure, low-temperature\\u000a condensation from solar matter in the remote reaches of the Solar System

J. Marvin Herndon

2006-01-01

39

Solar System Processes Underlying Planetary Formation, Geodynamics, and the Georeactor  

Microsoft Academic Search

Only three processes, operant during the formation of the Solar System, are responsible for the diversity of matter in the Solar System and are directly responsible for planetary internal-structures, including planetocentric nuclear fission reactors, and for dynamical processes, including and especially, geodynamics. These processes are: (i) Low-pressure, low-temperature condensation from solar matter in the remote reaches of the Solar System

J. Marvin Herndon

2006-01-01

40

Role of the Earth's rotation in global geodynamics  

Microsoft Academic Search

Role of the Earth's rotation in the global geodynamics. Pavlenkova N.I., Institute of Physics of the Earth of Russian Academy of Science, B.Grusinskaja 10, 123995, Moscow, ninapav@ifz.ru Geophysical studies show several regularities in Earth's structures which are not explained by the traditional global tectonics conceptions. (1) The surface of the Earth, as well as a surface of other planets, precisely

N. Pavlenkova

2009-01-01

41

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

42

8: Precambrian geodynamics and ore formation: The Fennoscandian Shield  

Microsoft Academic Search

Compared with present-day global plate tectonics, Archaean and Palaeoproterozoic plate tectonics may have involved faster moving, hotter plates that accumulated less sediment and contained a thinner section of lithospheric mantle. This scenario also fits with the complex geodynamic evolution of the Fennoscandian Shield from 2.06 to 1.78 Ga when rapid accretion of island arcs and several microcontinent–continent collisions in a

Pär Weihed; Nicholas Arndt; Kjell Billström; Jean-Clair Duchesne; Pasi Eilu; Olof Martinsson; Heikki Papunen; Raimo Lahtinen

2005-01-01

43

Turbulence effects on the geodynamic laser ranging system  

Microsoft Academic Search

The possible effects of refractive turbulence in the atmosphere on the Geodynamic Laser Ranging System are considered. For reasonable propagation conditions, beam steering effects can generally be neglected. Turbulence-induced beam spreading must be considered under conditions of high path-integrated turbulence. However, the most important effect is scintillation of the retroreflected beam. The weak-turbulence theory suggests that scintillations can be severe

J. H. Churnside

1992-01-01

44

Automated Testing Infrastructure and Result Comparison for Geodynamics Codes  

NASA Astrophysics Data System (ADS)

The geodynamics community uses a wide variety of codes on a wide variety of both software and hardware platforms to simulate geophysical phenomenon. These codes are generally variants of finite difference or finite element calculations involving Stokes flow or wave propagation. A significant problem is that codes of even low complexity will return different results depending on the platform due to slight differences in hardware, software, compiler, and libraries. Furthermore, changes to the codes during development may affect solutions in unexpected ways such that previously validated results are altered. The Computational Infrastructure for Geodynamics (CIG) is funded by the NSF to enhance the capabilities of the geodynamics community through software development. CIG has recently done extensive work in setting up an automated testing and result validation system based on the BaTLab system developed at the University of Wisconsin, Madison. This system uses 16 variants of Linux and Mac platforms on both 32 and 64-bit processors to test several CIG codes, and has also recently been extended to support testing on the XSEDE TACC (Texas Advanced Computing Center) Stampede cluster. In this work we overview the system design and demonstrate how automated testing and validation occurs and results are reported. We also examine several results from the system from different codes and discuss how changes in compilers and libraries affect the results. Finally we detail some result comparison tools for different types of output (scalar fields, velocity fields, seismogram data), and discuss within what margins different results can be considered equivalent.

Heien, E. M.; Kellogg, L. H.

2013-12-01

45

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

46

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

47

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

48

Geodynamics Studies in the active seismic regions in Egypt  

NASA Astrophysics Data System (ADS)

The recent crustal movement studies have a great role for evaluating the geodynamics of the seismo-active areas in the country. The crustal deformations must be in mind where it connecting significantly with the human life and its resources. From the historical point of view and recent instrumental records, there are some seismo-active areas in Egypt, where some significant earthquakes gad been occurred in different places. The special tectonic features in Egypt, Cairo, Aswan, Red Sea, Sinia and Nile Delta regions are the territories of a high seismic risk, which have to be monitored by up-to date technologies. The investigations of the seismic events and interpretations led to evaluate the seismic hazard for disaster prevention and for the safety of the dense populated areas and the vital national projects as the High Dam. In addition to the monitoring of the seismic events, the most powerful technique of satellite geodesy GPS will be used where geodetic networks are covering such seismic-active areas, around Nasser Lake, gulf of Suez, Cairo, Sinai and the Nile Delta. The main goal of these studies are monitoring of the crustal deformations associated with the earthquake occurrence in these seismo-active areas in order to study its geodynamical behavior and reducing the earthquake losses. The results of these movements at all networks in Egypt represent the form of the dynamic models for the deformations occurred during the different epochs of measurements. The final compiled output from the seismological and geodetic analysis will threw lights upon the geodynamical regime of these seismo-active areas.

Mohamed, A. S.

2003-04-01

49

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

50

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

51

The Allegresque History of Chemical Geodynamics: the Tenth Anniversary Revision  

NASA Astrophysics Data System (ADS)

Chemical geodynamics is a field of studies of the dynamic workings of the earth using chemical and isotopic tracers. It is a forum where geophysicists and geochemists exchange thoughts and ideas, and Prof. Allegre's contributions to the field go much beyond the term he coined. At the Allegre Symposium in 1997 in Paris, a tapestry depicting the history of chemical geodynamics was unveiled. The evolution of the field, creatures and denizens in it, and some historical defining moments of the field were pictorially woven into it, covering a period of 1960 - 1997 CE (i.e., 23 - 60 ACA, or Anno Claude Allegre). For the occasion of the second Allegre Symposium, a new segment of the tapestry has been woven, depicting significant advances made in the field over the past ten years. Highlights emphasize expanding collaboration of dynamicists, geochemists and mineral physicists, and include chemical structure of mantle plumes, convective stirring and scale lengths of mantle heterogeneity, early earth, and deep earth. Days of Enlightenment are near?

Shimizu, N.

2007-12-01

52

Recent advances in data assimilation in computational geodynamic models  

NASA Astrophysics Data System (ADS)

To restore dynamics of mantle structures in the geological past, data assimilation can be used to constrain the initial conditions for the mantle temperature and velocity from their present observations and estimations. The initial conditions so obtained can then be used to run forward models of mantle dynamics to restore the evolution of mantle structures. If heat diffusion is neglected, the present mantle temperature and flow can be assimilated using the backward advection (BAD) into the past. Two- and three-dimensional numerical approaches to the solution of the inverse problem of the Rayleigh-Taylor instability were developed for a dynamic restoration of diapiric structures to their earlier stages (e.g., Ismail-Zadeh et al., 1998, 2001, 2004; Kaus and Podladchikov, 2001). The mantle flow was modelled backwards in time from present-day mantle density heterogeneities inferred from seismic observations (e.g., Steinberger and O'Connell, 1998; Conrad and Gurnis, 2003). The variational (VAR) (or also called adjoint) data assimilation has been pioneered by meteorologists and widely used in oceanography and in hydrological studies. The use of VAR data assimilation in models of geodynamics has been put forward by Bunge et al. (2003) and Ismail-Zadeh et al. (2003). The VAR data assimilation algorithm was employed to restore numerically models of mantle plumes (Ismail-Zadeh et al., 2004, 2006; Hier-Majumder et al., 2005; Liu and Gurnis, 2008; Liu et al., 2008). The use of the quasi-reversibility (QRV) technique (more robust computationally) implies the introduction into the backward heat equation of the additional term involving the product of a small regularization parameter and a higher order temperature derivative (the resulting regularized heat equation is based on the Riemann law of heat conduction). The data assimilation in this case is based on a search of the best fit between the forecast model state and the observations by minimizing the regularization parameter. The QRV method was most recently introduced in geodynamic modelling (Ismail-Zadeh et al., 2007, 2008; Tantsyrev, 2008; Glisovic et al., 2009). The advances in computational geodynamics and in data assimilation attract an interest of the community dealing with lithosphere, mantle and core dynamics.

Ismail-Zadeh, Alik

2010-05-01

53

Frontiers in mineral physics relevant to geodynamics issues  

NASA Astrophysics Data System (ADS)

Mineral physics plays a critical role in understanding geodynamics for two reasons. First, properties of mineral play an important role in mass and energy transport in Earth's interior. Particularly important are the rheological properties that control the nature of mantle convection. Key issues in this area are the rheological properties of deep mantle and those of the lithosphere. Second, mineral physics knowledge is critical in interpreting various geophysical observations in terms of geodynamics. Interpretation of geophysical observations such as anomalies in seismic wave velocities, seismic anisotropy and electrical conductivity is not straightforward, and requires understanding of subtle details such as the role of minor element, hydrogen. In this talk, I will present a review of some of the recent advances in these areas focusing on the results obtained in my group. Understanding of rheological properties under the deep mantle conditions is challenging because of technical difficulties. We have developed a new deformation apparatus (RDA: rotational Drickamer apparatus) to study rheological properties under deep mantle conditions. This apparatus has been operated to P~25 GPa and T~2200 K. Even the study of rheological properties under the lithospheric conditions requires some technical development because orthopyroxene that is stable only above ~1 GPa plays a key role (commonly used gas apparatus cannot be used under these conditions). I will review some new results using these new techniques including the first quantitative results on the rheological properties of a perovskite + (Mg,Fe)O mixture and the strain weakening of a model peridotite under the lithospheric conditions. These new results provide some hints as to plausible models of dynamics and evolution of Earth's interior. However, Earth is complex and geodynamic studies must also be constrained by observations. Seismological observations including seismic discontinuities, lateral variation in velocities and seismic anisotropy are the key to the understanding of the dynamics of Earth's interior. Although the resolution is less, observations on electrical conductivity are also important particularly in inferring the distribution of hydrogen (water). Current status of these studies will be reviewed and key issues that require further studies will be discussed.

Karato, Shun-ichiro

2014-05-01

54

Geodynamic Study In The Region of Southwest Bulgaria  

NASA Astrophysics Data System (ADS)

Southwestern (SW) Bulgaria is a region of the most expressed tectonic and seismic activity in the whole territory of Bulgaria. The area belongs to the zone of recent ex- tension of the earth crust with the complex interference the horizontal and vertical movements of geological structures. The tectonic activity is confirmed with the re- cent high seismicity in the region. The largest earthquake in Europe in the last two centuries had happened near the Krupnik-Kresna area in 04.04.1904 with magnitude M = 7.8 (Karnik, 1969). A complex geodynamic study of recent deformations in the SW Bulgaria is of particular importance because of the possibility the seismogenic faults to provoke strong earthquakes. Since 1970 the Central Laboratory of Geodesy has carried out a geodetic monitoring of the vertical movements in the local seismic active zone of Krupnik-Kresna. We present the results of this monitoring along with the analysis of the precise spirit levelling from tree epochs - 1978, 1986 and 2000 of the 1st class state levelling line crossing the Krupnik fault. They show significant ver- tical crustal movements in the neighbourhood of the main Krupnik normal fault and confirm its recent tectonic activity. In 2001 the Central Laboratory of Geodesy, the Ge- ological Institute and the Geophysical Institute at the Bulgarian Academy of Sciences in cooperation with the Geodetic Department of the University of Architecture, Civil Engineering and Geodesy initiated a research project: "Multidisciplinary study on the active geodynamic setting of the Southwest Bulgaria". A regional GPS geodynamic network for long term monitoring of the recent crustal movements in this region was established. The GPS site locations were chosen after a detail study of the available seismotectonic and geologic data. The first GPS campaign was performed in the late summer of the last year. Some main seismotectonic features of the SW Bulgaria re- gion are discussed based on the new geological data and the recently recorded seismic activity in the period 1990 - 2001. We expect that the results obtained in the frame- work of this project could be a valuable contribution to assess the stress accumulation and to make a reliable evaluation of the seismic risk in the region.

Georgiev, I.; Pashova, L.; Nikolov, G.; Dimitrov, D.; Botev, E.

55

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

56

Geodynamics branch data base for main magnetic field analysis  

NASA Technical Reports Server (NTRS)

The data sets used in geomagnetic field modeling at GSFC are described. Data are measured and obtained from a variety of information and sources. For clarity, data sets from different sources are categorized and processed separately. The data base is composed of magnetic observatory data, surface data, high quality aeromagnetic, high quality total intensity marine data, satellite data, and repeat data. These individual data categories are described in detail in a series of notebooks in the Geodynamics Branch, GSFC. This catalog reviews the original data sets, the processing history, and the final data sets available for each individual category of the data base and is to be used as a reference manual for the notebooks. Each data type used in geomagnetic field modeling has varying levels of complexity requiring specialized processing routines for satellite and observatory data and two general routines for processing aeromagnetic, marine, land survey, and repeat data.

Langel, Robert A.; Baldwin, R. T.

1991-01-01

57

Linking plate reconstructions with deforming lithosphere to geodynamic models  

NASA Astrophysics Data System (ADS)

While global computational models are rapidly advancing in terms of their capabilities, there is an increasing need for assimilating observations into these models and/or ground-truthing model outputs. The open-source and platform independent GPlates software fills this gap. It was originally conceived as a tool to interactively visualize and manipulate classical rigid plate reconstructions and represent them as time-dependent topological networks of editable plate boundaries. The user can export time-dependent plate velocity meshes that can be used either to define initial surface boundary conditions for geodynamic models or alternatively impose plate motions throughout a geodynamic model run. However, tectonic plates are not rigid, and neglecting plate deformation, especially that of the edges of overriding plates, can result in significant misplacing of plate boundaries through time. A new, substantially re-engineered version of GPlates is now being developed that allows an embedding of deforming plates into topological plate boundary networks. We use geophysical and geological data to define the limit between rigid and deforming areas, and the deformation history of non-rigid blocks. The velocity field predicted by these reconstructions can then be used as a time-dependent surface boundary condition in regional or global 3-D geodynamic models, or alternatively as an initial boundary condition for a particular plate configuration at a given time. For time-dependent models with imposed plate motions (e.g. using CitcomS) we incorporate the continental lithosphere by embedding compositionally distinct crust and continental lithosphere within the thermal lithosphere. We define three isostatic columns of different thickness and buoyancy based on the tectonothermal age of the continents: Archean, Proterozoic and Phanerozoic. In the fourth isostatic column, the oceans, the thickness of the thermal lithosphere is assimilated using a half-space cooling model. We also define the thickness of the thermal lithosphere for different continental types, with the exception of the deforming areas that are fully dynamic. Finally, we introduce a "slab assimilation" method in which the thermal structure of the slab, derived analytically, is progressively assimilated into the upper mantle through time. This method not only improves the continuity of slabs in forward models with imposed plate motions, but it also allows us to model flat slab segments that are particularly relevant for understanding dynamic surface topography. When it comes to post-processing and visualisation, GPlates allows the user to import time-dependent model output image stacks to visualise mantle properties (e.g. temperature) at a given depth through time, with plate boundaries and other data attached to plates overlain. This approach provides an avenue to simultaneously investigate the contributions of lithospheric deformation and mantle flow to surface topography. Currently GPlates is being used in conjunction with the codes CitcomS, Terra, BEMEarth and the adaptive mesh refinement code Rhea. A GPlates python plugin infrastructure makes it easy to extend interoperability with other geodynamic modelling codes.

Müller, R. D.; Gurnis, M.; Flament, N.; Seton, M.; Spasojevic, S.; Williams, S.; Zahirovic, S.

2011-12-01

58

Geodynamics of the Gibraltar Arc and the Alboran Sea region  

NASA Astrophysics Data System (ADS)

Located at the Westernmost tip of the Mediterranean sea, the Gibraltar Arc is a very complex zone. The Betics in Spain and the Rif belt in Morocco surround the Alboran sea characterized by a thinned continental crust. The geodynamic evolution of this region results from the convergence of African and Iberian margins since the Late Cretaceous. It is controlled both by plate convergence and mantle dynamics, which significantly impact on morphology, sedimentary environments, tectonics, metamorphism and magmatism. We present here the contents of the special issue on the Gibraltar Arc and nearby regions, following the workshop organized at the University Abdelmalek Essaadi of Tetouan in Morocco from 27 to 28 October, 2011. The goal of this international workshop was to have an overview of the actual advance in research concerning the Rif and Betics chains, the Alboran basin, and their influence on the Iberian and African forelands.

Corsini, M.; Chalouan, A.; Galindo-Zaldivar, J.

2014-07-01

59

Effects of turbulence on the geodynamic laser ranging system  

NASA Technical Reports Server (NTRS)

The Geodynamic Laser Ranging System (GLRS) is one of several instruments being developed by the National Aeronautics and Space Administration (NASA) for implementation as part of the Earth Observing System in the mid-1990s (Cohen et al., 1987; Bruno et al., 1988). It consists of a laser transmitter and receiver in space and an array of retroreflectors on the ground. The transmitter produces short (100 ps) pulses of light at two harmonics (0.532 and 0.355 microns) of the Nd:YAG laser. These propagate to a retroreflector on the ground and return. The receiver collects the reflected light and measures the round-trip transit time. Ranging from several angles accurately determines the position of the retroreflector, and changes in position caused by geophysical processes can be monitored.

Churnside, James H.

1993-01-01

60

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. Käser 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

61

Paleomagnetic reconstruction of geodynamic events in the Eastern Alpine Neogene  

NASA Astrophysics Data System (ADS)

A new, comprehensive paleomagnetic database from the Eastern Alpine Neogene basins was developed in order to construct a paleogeographic model of the geodynamic development of the Eastern Alps. The origin of the basins is explained largely through Miocene kinematics (late collision stage) in the Eastern Alps. In the last decade, the combination between the new tectonic models "tectonic escape" and "extensional collapse" (Platt 1987, Dewey 1988) provided the basis for interpretations of the development of the Carpathian Arc and the Pannonian Basin. Earlier studies gave evidence for paleomagnetically detectable tectonic movements during the Miocene. For instance, Mauritsch (1972, 1975) and Pohl &Soffel (1982) observed large rotations of the Neogene volcanics in the Styrian Basin. Sediments of Ottnangian to Sarmatian age from several intramontane basins of the Eastern Alps yielded a tendency of larger rotations in the older rocks indicating essentially Middle Miocene rotation (Marton et al., 1997). In Slovenia, Marton &Jelen (1997) found moderate rotations that matched those of the Lavant Valley Basin and the Styrian Basin of Austria as well as the Transdanubian Central Range of Hungary. Results from the Molasse zone showed indications for counterclockwise rotations, which are consistent with our paleomagnetic data from the Korneuburg Basin, as well as with new results from the foredeep of the West Carpathians (Marton et al., 2002). The new results from basins located North, East and South of the Eastern Alps show a general trend for synsedimentary counterclockwise rotations of 20 degrees with respect to the Eurasian paleopoles during the Karpatian and Badenian stages. A second period of counterclockwise rotation occurs during the Pannonian stage, while the uppermost Miocene results are in accordance with the Eurasion geodynamic reconstructions. Such a pattern of rotations cannot be explained be individual movements of the subbasins. At the same time, rotations in a clockwise sense are observed in the Eastern and South-Eastern parts of the study area.

Scholger, R.; Stingl, K.

2003-04-01

62

The Geodynamics of Intraplate Earthquakes: A preliminary study  

NASA Astrophysics Data System (ADS)

Interaction between plates along plate boundaries is the primary cause for most earthquakes. Although there is only relatively small number of intraplate earthquakes, some of them are devastating, for example the 1811-1812 New Madrid earthquakes (M=7.5 - 8.0), and the geodynamics of intraplate earthquakes are poorly understood. We have investigated the basic geodynamics controlling intraplate and interplate earthquakes in a viscoelastic finite element model. We used an infinitesimally long weak zone to approximate the plate boundary, and a weak zone of finite length for intraplate seismic zones. Systematic numerical experiments are conducted to simulate the stress evolution between seismic cycles as well as steady-state stress patterns with various rheological structures, fault geometries, and boundary conditions. Our results show fundamental differences in stress evolution between intraplate and interplate earthquakes. After an interplate earthquake, stress migrates to the neighboring segments of the fault zone, leading to sequential earthquakes along the fault zone. Similar results have been shown in previous studies. However, following a large intraplate earthquake, stress is released from the fault zone and migrated into the surrounding crust. A strong ambient crust would support the deviatoric stresses, leading to slow re-accumulation of stress and strain in the intraplate seismic zone. Applying this model to the New Madrid Seismic Zone (NMSZ), our model predicted slow stress accumulation within the NMSZ following the 1811-1812 events, consistent with the low rate of strain accumulation indicated by the GPS data. The amplified stresses within the surrounding crust, together with crustal heterogeneities, may help to explain the relatively scattered seismicity around the NMSZ, including the recent event (Mw=4.5) in Evansville, Indiana.

Li, Q.; Liu, M.; Sandvol, E.

2002-12-01

63

Lithosphere-scale geodynamics in the Rhodope: assumptions and implications  

NASA Astrophysics Data System (ADS)

The Rhodope Metamorphic Complex (RMC) is a synmetamorphic nappe stack located in the hinterland of the Hellenide orogen which is part of the Alpine-Himalayan chain. Advances in analytical instrumentation in petrology over the last 10 years made possible the documentation of high-to ultrahigh-pressure conditions in this complex. Despite the wealth of petrologic P-T-t data and the multitude of generic models on the evolution of the RMC, only few geodynamic restorations project long enough back in time to cover the entire life span of the orogen since the Jurassic. There are many reasons for the different (and often contrasting) models proposed for the RMC that deserve to be mentioned. Here, we present the different reconstructions published together with the assumptions on which they were built and their geodynamic implications. We then proceed to carefully assess those implications individually from the mineral to the lithosphere scale. Our assessment poses important constrains on the pressure, temperature and deformation history of the complex on a regional scale that cannot be satisfied by all reconstructions. Such constrains involve the length of the subducting plate, the thermal histories of the metamorphic rocks, the age response of the isotopic systems and last, but not least, the structural record of km-scale movements that can be identified in the field. In addition, the presence of ultrahigh-pressure rocks is restricted to shear zones all across the RMC and this requires an explanation. We examine the possibility of non-lithostatic pressure variations within crustal-scale ductile shear zones.

Moulas, Evangelos; Burg, Jean-Pierre; Kostopoulos, Dimitrios; Schenker, Filippo

2014-05-01

64

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

NASA Astrophysics Data System (ADS)

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

Vartanyan, G. S.

2010-12-01

65

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

66

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

67

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

68

Geodynamic Effects of Ocean Tides: Progress and Problems  

NASA Technical Reports Server (NTRS)

Satellite altimetry, particularly Topex/Poseidon, has markedly improved our knowledge of global tides, thereby allowing significant progress on some longstanding problems in geodynamics. This paper reviews some of that progress. Emphasis is given to global-scale problems, particularly those falling within the mandate of the new IERS Special Bureau for Tides: angular momentum, gravitational field, geocenter motion. For this discussion I use primarily the new ocean tide solutions GOT99.2, CSR4.0, and TPXO.4 (for which G. Egbert has computed inverse-theoretic error estimates), and I concentrate on new results in angular momentum and gravity and their solid-earth implications. One example is a new estimate of the effective tidal Q at the M_2 frequency, based on combining these ocean models with tidal estimates from satellite laser ranging. Three especially intractable problems are also addressed: (1) determining long-period tides in the Arctic [large unknown effect on the inertia tensor, particularly for Mf]; (2) determining the global psi_l tide [large unknown effect on interpretations of gravimetry for the near-diurnal free wobble]; and (3) determining radiational tides [large unknown temporal variations at important frequencies]. Problems (2) and (3) are related.

Richard, Ray

1999-01-01

69

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

70

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

71

Application of VLBI and satellite laser ranging to geodynamics  

NASA Technical Reports Server (NTRS)

The NASA Crustal Dynamics Project has developed very-long baseline interferometer (VLBI) systems and satellite laser ranging (SLR) systems for geodynamics measurements. In VLBI, a radio noise signal from a distant quasar is received by two or more radio antennas and coherently recorded. These recordings are cross-correlated to determine the relative signal delays between stations which are used to derive the vector baselines between the stations. The SLR systems accurately determine the range to a retroreflector satellite as a function of time with short laser pulses. These range measurements from several stations to the same satellite are used in orbit analysis programs to determine the position of the stations and the vector baselines between the stations. Measurements with these systems have achieved precisions of a few centimeters in length for distances of several thousand km. These systems are now operating in a global network for measuring the relative motion of the N. American, Pacific, S. American, Nazca, Eurasian and Australian tectonic plates. Highly mobile VLBI and SLR systems are being operated at many sites in the active earthquake areas in western N. America in order to determine the crustal deformation and strain accumulation.

Coates, R. J.

1983-01-01

72

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

73

Tightly Coupled Geodynamic Systems: Software, Implicit Solvers & Applications  

NASA Astrophysics Data System (ADS)

The generic term "multi-physics" is used to define physical processes which are described by a collection of partial differential equations, or "physics". Numerous processes in geodynamics fall into this category. For example, the evolution of viscous fluid flow and heat transport within the mantle (Stokes flow + energy conservation), the dynamics of melt migration (Stokes flow + Darcy flow + porosity evolution) and landscape evolution (Stokes + diffusion/advection over a surface). The development of software to numerically investigate processes that are described through the composition of different physics components are typically (a) designed for one particular set of physics and are never intended to be extended, or coupled to other processes (b) enforce that certain non-linearity's (or coupling) are explicitly removed from the system for reasons of computational efficiency, or due the lack of a robust non-linear solver (e.g. most models in the mantle convection community). We describe a software infrastructure which enables us to easily introduce new physics with minimal code modifications; tightly couple all physics without introducing splitting errors; exploit modern linear/non-linear solvers and permit the re-use of monolithic preconditioners for individual physics blocks (e.g. saddle point preconditioners for Stokes). Here we present a number of examples to illustrate the flexibility and importance of using this software infra-structure. Using the Stokes system as a prototype, we show results illustrating (i) visco-plastic shear banding experiments, (ii) how coupling Stokes flow with the evolution of the material coordinates can yield temporal stability in the free surface evolution and (iii) the discretisation error associated with decoupling Stokes equation from the heat transport equation in models of mantle convection with various rheologies.

May, D.; Le Pourhiet, L.; Brown, J.

2011-12-01

74

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

75

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 Baudó-Panama oceanic arc, which began 12 Myr ago, is highlighted in connection with mountain building in the EC. The Istmina and Ibagué 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 5°N) 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 5.2°N 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 Baudó Range. Northward, the NP subducts beneath the Chocó 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 4°N), 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 N80°E compression and (2) an early Andean NW-SE compression.

Taboada, Alfredo; Rivera, Luis A.; Fuenzalida, AndréS.; Cisternas, Armando; Philip, Hervé; Bijwaard, Harmen; Olaya, José; Rivera, Clara

2000-10-01

76

Geodynamic setting of the mineral deposits of the Urals  

NASA Astrophysics Data System (ADS)

The first-order geodynamic domains of the Uralide orogen constitute a relatively simple pattern across the orogenic belt. Continental rifting along the western margin is expressed by a system of Vendian-early Palaeozoic structures with shale-hosted siderite and magnesite and basalt-hosted base metals. It is superimposed on a Middle Riphean rift system with layered mafic-ultramafic complexes with chromite and ilmenite-titano-magnetite and subordinate ophiolite massifs with gold and magnetite. An oceanic spreading domain, immediately east of the Main Uralian Fault is associated with chromite, titano-magnetite and massive sulphide deposits (Dombarovsky or Cyprus type). Further east, bimodal volcanic associations in island arcs with oceanic crust have formed copper-zinc massive volcanic sulphide deposits (Uralian type). Subsequently, complex volcanic sulphide deposits are associated with belts of andesite-dacite and co-magmatic diorite (Baymak or Kuroko type). The eastern, destructive, margin of the orogen is characterized by magnetite and copper-magnetite skarns and porphyry systems. Relatively small plagiogranite to granodiorite complexes, related to oceanic crust, carry scheelite and gold. Calc-alkaline granitic massifs have formed associations of tungsten, tantalum and beryllium. This pattern was dissected by major thrusts and transcurrent shear zones. Increased fluid activity in the course of deformation, inferred to have been involved in complex multi-phase gold mineralization was most probably controlled by deep-reaching faults and shears. Although the recognition of the first-order domains represents a guideline for exploration, detailed structural geological studies of the kinematics of the major faults and shear zones are required in conjunction with radiometric dating of suitable fault- and ore-associated minerals, in association with on-going deep-reaching geophysical investigations.

Koroteev, V. A.; de Boorder, H.; Necheukhin, V. M.; Sazonov, V. N.

1997-07-01

77

Crisis of isotope geodynamics: Sm-Nd aspect  

NASA Astrophysics Data System (ADS)

Isotope geochemistry for many years contributes to improve our understanding of the Earth's interiors. There are a lot of models of the crust-mantle system evolution based on the isotope data. Indeed, identification of various types of the mantle material on the basis of isotope composition of its magmatic derivatives has opened perspective to fill geophysical models with the geochemical content. Study of the mantle material composition, changing in time and in space, with the same approach originated a new branch of geology, which was named chemical geodynamics or isotope geodynamics. Opportunities of the new approach have been unambiguously admitted more than 30 years ago after DePaolo & D.Wasserburg pioneer works, dedicated to development of Sm-Nd isotope systematics. This systematics became the most considerable component in the basement of isotope geodynamics as a whole. Since then nobody ever discussed the constrains of this siystematics. At the same time there are many contradictions in it. There are numerous mantle xenoliths depleted in main elements (Pearson et al., 2003), for which the whole variation curve normalized to chondrite is plotted below chondrite level. Paradox of the situation is that this mantle material has REE pattern which displays a continuous decrease of their concentration from La to Lu. Accordingly, Sm/Nd ratio in such material is lower than in chondrites. Through some time this material will be able to generate melts with ENd<0, which is considered to be the characteristic of the enriched mantle. At the same time, the material producing such melts in terms of the total REE concentration and the main elements concentration is high depleted. Another example, which demonstrates the independent variations of the main elements concentration, of the total REE contents, of Sm/Nd ratio and of Nd isotope composition in a source of the mantle magmatic derivatives, is connected with tholeiites of the middle ocean ridges and ocean islands. Tholeiites represent perhaps the most widespread terrestrial magmatic rocks. At the same time about 40 % of them are represented by rocks in which REE relative concentration continuously decreases from Eu to La while the total REE content exceeds the chondritic one ten times. Naturally in this case the Sm/Nd ratio in tholeiites is higher than the same ratio in chondritic. As for the concentration of the main and rare-earth elements in tholeiites these rocks are undoubtedly enriched material. They compose a considerable part of an oceanic crust and, apparently, are an essential component of lower crust as a result of underplating. However during melting of the tholeiites, in which Sm/Nd ratio is higher, than in PM, and which had enough time to change Nd isotope composition according to this ratio, the melts will be marked by values of ENd>0. In common Sm-Nd isotope systematics these isotope characteristics correspond to derivatives of the depleted material. So, in terms of the Nd isotope analysis the derivatives of the enriched material of oceanic or even of lower continental crust will be referred to derivatives of the depleted mantle. The same situation is observed in Lu-Hf isotope systematics of tholeiites. Isotope-petrochemical identification of xenoliths corresponding to the material of geochemically closed primitive mantle, has shown that MORB source is not depleted mantle as it was considered to be earlier, but a primitive mantle - PM (Pushkarev, 2006, 2007). It means that deficiency of Nd relative to Sm in PM in comparison with their concentrations in chondrites is caused not by crust formation. This peculiarity is either a primary feature of protoplanetary material, whose composition was different from chondritic one, or it reflects predominant capture of LREE by a component of segregating core, or it is a consequence of both reasons simultaneously. Identity of MORB source to primitive mantle and its discrepancy with the composition of chondrits in Sm-Nd isotope systematics was discovered earlier by J.A.Kostitsyn (2004) on the basis of the represe

Pushkarev, Y. D.; Nikitina, L. P.

2009-04-01

78

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

79

Visualization of P-T Paths Derived From Numerical Thermomechanical Experiments: new Insights Into Geodynamic Problems  

NASA Astrophysics Data System (ADS)

The pressure (P)-temperature (T)-time (t) path of a rock is a direct record of its movement within the Earth's interior. Thus P-T-t paths are powerful tools for understanding geodynamic processes, and in the last 25 years many P-T-t paths have been worked out for rocks of the crust and upper mantle. Although one-dimensional modelling of P-T-t paths during regional metamorphism (e.g., [1]) has allowed many important features of the P-T-t evolution of metamorphic rocks to be explained, and the necessary further progress can be achieved with 2D and 3D numerical approaches (e.g., [2-5]), the majority of numerical studies on geodynamic processes at present do not specifically address the details of P-T-t trajectories. Thus, the huge amount of empirical data available on the P-T-t evolution of crustal and mantle rocks is at present not adequately used to check and interactively optimize numerical models of geodynamic processes. This is especially true in those geodynamic settings where rocks must evolve contrasting P-T-t trajectories within the same rock complex (e.g., [3-4]). We suggest that there is a general major problem in visualizing the results of numerical geodynamic modelling in terms of the P-T-t evolution of the rocks involved. We have developed a user-friendly dynamic visualisation and animation technique to allow direct interactive comparison between P-T-t paths and numerical experiments of different geodynamic situations. In addition, we have implemented a new, robust Gibbs energy minimization approach to allow petrologically oriented internally consistent thermodynamic data bases to be used as independent constraints on P-T-t trajectories (e.g., [6]). References: [1] England, PC and AB Thompson, J. Petrol., 25, 894-928, 1984; [2] Peacock, S, Tectonics, 9, 1197-1211, 1990; [3] Gerya, TV, LL Perchuk, DD van Reenen and CA Smit, J. Geodynamics, 30, 17-35, 2000; [4] Willner AP, E Sebazungu, TV Gerya, WV Maresch and A Krohe, J. Geodynamics, 33, 281-314, 2002; [5] Beaumont, C, RA Jamieson, MH Nguyen and B Lee, Nature, 414, 738-742, 2001; [6] Gerya, TV, LL Perchuk, WV Maresch, AP Willner, DD Van Reenen, and CA Smit, Eur. J. Mineralogy, 14, 687-699.

Maresch, W.; Gerya, T.

2002-12-01

80

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.

81

Radon as a proxy of subtle geodynamic activity in the volcanic context - Tenerife (Canary Islands)  

Microsoft Academic Search

A monitoring system at the surface and mainly in the sub-surface of the volcanic edifice of Tenerife is installed for monitoring and studying the radon flux as an indicator of geodynamic activity. The steep topography of Tenerife and the existence of a dense network of underground galleries enable setting up a 3D network of monitoring stations (located: at 400 to

G. Steinitz; C. Martin; N. Gazit-Yaari; A. Eff-Darwich; J. de La Nuez; M. Quesada; V. Soler; M. Zimmer; J. Erzinger; C. Fernandez; Tern

2003-01-01

82

Chemical Geodynamics of Cenozoic Magmatism in the Turkish-Iranian and Tibetan High Plateaus  

Microsoft Academic Search

We analyze the chemical geodynamics of Cenozoic magmatism in the Turkish-Iranian and Tibetan high plateaus within the framework of their collisional tectonic evolution. Post-collisional magmatism in both plateaus shows systematic spatial and temporal variations as a direct result of mantle response to plate tectonic events and hence changes in mantle dynamics through time. Continental collision and crustal accretion events along

Yildirim Dilek; Zhidan Zhao

2010-01-01

83

Geodynamic implications of Devonian silicic arc magmatism in the Sierra Nevada and Klamath Mountains, California  

Microsoft Academic Search

Most proposed geodynamic models integrate the northern Sierra Nevada and eastern Klamath Mountains in a single island-arc system. New petrological and geochemical data show that the Upper Devonian Sierra Buttes Formation of the northern Sierra Nevada displays important differences from the Lower Devonian Balaklala Formation of the eastern Klamath Mountains. The cale-alkalic affinity of the Sierra Buttes rhyolites (light rare

O. Rouer; H. Lapierre; G. Mascle; C. Coulon; J. Albers

1989-01-01

84

Geodynamics laser ranging system: Performance simulations and development of the EOS facility  

Microsoft Academic Search

The NASA Geodynamics Laser Ranging System is a spaceborne multicolor laser ranger to be used for studying regional and local scale crustal movements and will provide a capability for height profiling of ice-sheets, land terrains, cloud-tops, and other surfaces. Ranging measurements to retroreflector targets will produce intersite distances and relative heights with subcentimeter accuracy over baselines up to several hundred

S. C. Cohen

1988-01-01

85

Geodynamic Effects on the Dams in Cascade of the Sulak Hydraulic Power Systems  

Microsoft Academic Search

In view of the passage of the Federal statute, ”On the safety of hydraulic structures,” in 1999 and 2000 the Institute of Physics of the Earth of the Russian Academy of Sciences, the Dagestan Power Authority, and the Dagestan Scientific Center (Russian Academy of Sciences) carried out field investigations of geodynamic effects on the safety of the cascade of Sulak

A. N. Marchuk; A. R. Abakarov; M. G. Daniyalov; O. A. Asmanov; M. M. Mirzaliev; R. A. Levkovich

2001-01-01

86

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.; Manea, M.; Ferrari, L.

2013-05-01

87

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.

Constantin Manea, Vlad; Manea, Marina; Ferrari, Luca

2013-04-01

88

Miocene to Recent Magmatism and Geodynamics of Eastern Turkey  

NASA Astrophysics Data System (ADS)

Eastern Turkey has been an active continental collision zone for the last 15 My between the African and Eurasian continents. The collision started at around 15 Ma after the total consumption of oceanic lithosphere of the southern branch of the Neotethys Ocean beneath E Anatolia and is still going on, as Africa still converges to E Anatolia with a velocity of ~2.5 cm/y. The overriding Anatolian plate, resided below the sea level till the collision, was subjected to a major block uplift event around 10 Ma, emerging as a widespread plateau ~2 km above the sea level, which has been roughened by later erosion and volcanic activities. The aforementioned plateau is considered as part of a regional dome structure with ~1000 km diameter extending from E Anatolia up to Azerbaijan. Immediately after the collision, a widespread volcanism emerged on the Eastern Anatolian Plateau, whose products covered almost over half of the region. Characteristically, all these products contain a distinct subduction component. The volcanism in the collision zone continued to the historical times and is considered to be still active. The region includes some of the largest volcanic centers (e.g. Ararat, Nemrut, Tendürek and Süphan volcanoes) and plateaus (e.g. The Erzurum-Kars Plateau) around the circum-Mediterranean region. The collision-related volcanic province is not only confined into Anatolia but also continues into the neighboring countries through Georgia, Armenia, Iran and up to Russia, spanning ~1000 km. In contrast, the underthrusting Arabian platform was subjected to both crustal-scale east-west folding close to the thrust front and extensional deformations perpendicular to the suture zone. Along these extensional fractures, within-plate lavas with no subduction component erupted. This intraplate volcanism focused on the Karacada? volcanic complex, covering an area ~10,000 km2. Early Stage volcanism of Karacada? was dominated by magmas derived from a shallower (litospheric) mantle source, while magmas of the later stages were derived from deeper (asthenospheric) sources. Based on the results of seismic tomography, tectonics and geochemical/isotopic studies of the volcanic successions, it has now been well established that both uplift and widespread volcanism across the region have a common reason: a major "slab-steepening and breakoff event beneath a large accretionary complex". After the collision, being unsupported by the subduction, the slab started to be steepened beneath the region. This possibly resulted in widening, invasion and upwelling of the mantle wedge beneath E Anatolian accretionary complex, followed by a widespread decompressional melting, generating voluminous magmas with an inherited subduction signature. The subducted slab broke off beneath the Bitlis-Pötürge massif ~10 Ma, causing the enriched asthenospheric mantle with no subduction component beneath the Arabian continent to flow to the north through a slab-window. This resulted in mixing between the subduction-modified E Anatolian and the Arabian asthenospheres. On the basis of the results from our geochemical/ geochronologic/isotopic data and petrologic models, we argue that the temporal and spatial changes in the chemistry of volcanics across the region are the artifacts of these geodynamic events that controlled the movement and interaction of mantle domains with contrasting geochemical, isotopic and mineralogical identities. Compositions of some of the primitive magmas were further modified via interactions with the lithospheric mantle and/or crustal material coupled with fractionation en route to the surface.

Keskin, M.; Sharkov, E. V.; Lebedev, V. A.; Chugaev, A. V.; Oyan, V.; Genc, S. C.; Unal, E.; Aysal, N.

2012-04-01

89

Role of the Earth's rotation in global geodynamics  

NASA Astrophysics Data System (ADS)

Role of the Earth's rotation in the global geodynamics. Pavlenkova N.I., Institute of Physics of the Earth of Russian Academy of Science, B.Grusinskaja 10, 123995, Moscow, ninapav@ifz.ru Geophysical studies show several regularities in Earth's structures which are not explained by the traditional global tectonics conceptions. (1) The surface of the Earth, as well as a surface of other planets, precisely shares on two hemispheres with a different relief and structure of an earth's crust: on the Pacific (oceanic) hemisphere with the lowered relief and a thin oceanic crust, and a continental hemisphere with prevalence of the raised relief and a thick continental crust. (2) There is a regular system of global lineaments and ring structures which are stretched on thousand kilometers, covering continents and oceans. As one of examples it is possible to result system of rift zones (mid-oceanic ridges), forming a ring around of the Antarctica with rift branches from it through everyone of 90 degrees. (3) Asymmetry with a relief of a day time surface when to each raised structure there corresponds the lowered surface on the opposite side of globe is observed. (4) The continental and oceanic mantles have different compositions and deep roots (>300 km) beneath the continents are prominent as regions with relatively high seismic velocities. There are regular connections between geological structures and deep mantle roots. (5) The classical lithosphere-asthenosphere model is not confirmed by seismic data. The asthenosphere can not be traced as a continuous layer, there are disconnected lenses (asthenolenses) even beneath mid-oceanic ridges. Significant horizontal movements of the lithosphere, as proposed by the global plate tectonics, would destroy all these regularities and crust-mantle interaction. To make an agreement between all observed data, the fluids-rotation hypothesis is proposed. The hypothesis supposes two main energy sources of the global tectonics: the degasification of the Earth (the fluids advection) and changes in the Earth rotation. At formation of the core there was the Earth's expansion and was formed system of global lineaments and the Pacific ring. Bipolar convection in the core has created a magnetic field and the increased advection of deep fluids in the southern hemisphere. The last promoted formation of thick continental lithosphere in this hemisphere in Archean-Proterozoi. This thick lithosphere has led to asymmetry of the planet and to relative displacement of the mass centers of the Earth's spheres. It produced high pressure between the spheres (Barkin, 2002) and could have initiated their relative displacements. As a uniform asthenosphere does not exist and the continents have deep roots such displacements were most probable on a surface of a liquid outer core. The marked mass centre dislocation has caused the turning of the mantle around the core with movement of the continental hemisphere from South Pole to the equator. It corresponds to the data on movement of paleomagnetic and paleoclimate poles that took place in Paleozoic era. The rotation of the mantle around the core passed non-uniformly: the tidal forces connected to periodic change of Earth's rotation axis position in system the Earth-Lund-Sun (Avsyuk, 1996) were imposed on the basic moving forces restoring the mass center balance. The periodic displacements of the mantle created conditions for alternation of tectonic activity epochs. Rotation of the mantle around the core created a new nonequilibrium system. Therefore in Mesozoic era a new stage begins: an expansion of the southern hemisphere which radius is now bigger, than the northern one. Such expansion created the regular system of the mid-oceanic ridges forming a ring around Antarctica with the symmetric Mid-Atlantic, Indian and Pacific ridges. Supposedly at the last stage the formation of the continent on South Pole (Antarctica) and destruction of a continental crust on the northern hemisphere (formation of the Arctic ocean) took place to mount on the mass center balance.

Pavlenkova, N.

2009-04-01

90

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

91

Is the geodynamic process in preparation of strong earthquakes reflected in the geomagnetic field?  

NASA Astrophysics Data System (ADS)

A methodology of detecting geomagnetic variations caused by dangerous geodynamic processes at depth has been developed. This methodology was tested using data from three Japanese observatories within the network of the International project ‘Intermagnet’ (www.intermagnet.org 2011). Anomalous behaviour of the geomagnetic field was detected during the period of the great Tohoku-oki earthquake on 11 March 2011. Theoretical evaluation of the possible mechanisms of these anomalous geomagnetic variations (AGV) has been examined. The possibility of the emergence of an AGV in the vicinity of earthquake epicentres in Japan and their rapid monitoring (online or with a delay of one day) is demonstrated. The main tool of the developed methodology is delineation of the geodynamic magnetic effect by the use of a differential function.

Finkelstein, M.; Price, C.; Eppelbaum, L.

2012-10-01

92

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-Université 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

93

Geodynamic impact on the stable isotope signatures in a shallow epicontinental sea  

Microsoft Academic Search

Analyses were made of a mollusc-based meta dataset of 859 d13C and d18O data of Miocene nearshore settings in the European Paratethys Sea and its descendant Lake Pannon. The observed trends document a strong tie to geodynamics, which are largely decoupled from Miocene open ocean isotope curves. Semi- to fully enclosed, initially marine water bodies such as the Paratethys Sea

Mathias Harzhauser; Werner E. Piller; Christine Latal

2007-01-01

94

Geological, tomographic, kinematic and geodynamic constraints on the dynamics of sinking slabs  

NASA Astrophysics Data System (ADS)

We use geodynamic models with imposed plate velocities to test the forward-modeled history of subduction based on a particular plate motion model against alternative seismic tomography models. We utilize three alternative published reference frames: a hybrid moving hotspot-palaeomagnetic, a hybrid moving hotspot-true polar wander corrected-palaeomagnetic, and a Subduction Reference Frame, a plate model including longitudinal shifts of subduction zones by matching subduction volumes imaged by P-wave tomography, to assess which model best predicts present day mantle structure compared with seismic tomography and volumetrically derived subduction history. Geodynamic modeling suggests paleo-longitudinal corrections applied to the Subduction Reference Frame result in lower mantle slab material beneath North America and East Asia accumulating up to 10-15° westward of that imaged by tomography, whereas the hybrid models develop material offset by 2-9°. However, the Subduction Reference Frame geodynamic model produces slab material beneath the Tethyan Domain coinciding with slab volumes imaged by tomography, whereas the hybrid reference frame models do not, suggesting regional paleo-longitudinal corrections are required to constrain slab locations. We use our models to test inferred slab sinking rates in the mantle focusing on well-constrained regions. We derive a globally averaged slab-sinking rate of 13 ± 3 mm/yr by combining the ages of onset and cessation of subduction from geological data and kinematic reconstructions with images of subducted slabs in the mantle. Our global average slab-sinking rate overlaps with the 15-20 mm/yr rate implied by mantle convection models using a lower mantle viscosity 100 times higher than the upper mantle.

Butterworth, N. P.; Talsma, A. S.; Müller, R. D.; Seton, M.; Bunge, H.-P.; Schuberth, B. S. A.; Shephard, G. E.; Heine, C.

2014-01-01

95

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.

96

Combination of solutions for geodetic and geodynamic applications of the Global Positioning System (GPS).  

NASA Astrophysics Data System (ADS)

The increasing number of permanent GPS stations all over the world was the motivation to develop a new program, called ADDNEQ, to be able to derive from sequentially processed session solutions a statistically correct combined parameters estimate. Only original coordinate- and velocity parameters are considered. The program ADDNEQ is intended to meet the growing requirements of the CODE (Center for Orbit Determination in Europe) Analysis Center of the IGS (International GPS Service for Geodynamics). The Analysis Centers of the IGS produce the following data: (1) high accuracy GPS ephemerides, (2) Earth rotation parameters, (3) coordinates and velocities of the IGS tracking stations, (4) GPS satellite and tracking station clock information, (5) ionospheric information.

Brockmann, E.

97

Gravity anomalies, compensation mechanisms, and the geodynamics of western Ishtar Terra, Venus  

NASA Technical Reports Server (NTRS)

Pioneer Venus line-of-sight orbital accelerations were utilized to calculate the geoid and vertical gravity anomalies for western Ishtar Terra on various planes of altitude z sub 0. The apparent depth of isostatic compensation at z sub 0 = 1400 km is 180 + or - 20 km based on the usual method of minimum variance in the isostatic anomaly. An attempt is made here to explain this observation, as well as the regional elevation, peripheral mountain belts, and inferred age of western Ishtar Terra, in terms of one or three broad geodynamic models.

Grimm, Robert E.; Phillips, Roger J.

1991-01-01

98

Geodynamics laser ranging system: Performance simulations and development of the EOS facility. [Earth Observing System (EOS)  

NASA Technical Reports Server (NTRS)

The NASA Geodynamics Laser Ranging System is a spaceborne multicolor laser ranger to be used for studying regional and local scale crustal movements and will provide a capability for height profiling of ice-sheets, land terrains, cloud-tops, and other surfaces. Ranging measurements to retroreflector targets will produce intersite distances and relative heights with subcentimeter accuracy over baselines up to several hundred kilometers long. Arrays containing up to a few hundred targets can be surveyed nearly simultaneously. Altimetric profiling can be performed with spatial resolution of 80m and vertical accuracy of 10cm with the latter depending on the roughness and slope of the terrain.

Cohen, S. C.

1988-01-01

99

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.; Schenková, Z.; Grácová, M.

2009-04-01

100

Inferencing Core-Mantle Geodynamics with Angular-Momentum Excitation of Length-of-Day Variations  

NASA Astrophysics Data System (ADS)

Under the conservation of angular momentum (AM), any variation in the AM (delta-AM) of the geophysical fluids should be accompanied by an equal and opposite variation in the solid Earth's delta-AM, which in turn will manifest as variation in the Earth's rotation. However, the conversion factor involves the physical inertia for the delta-AM to excite Earth rotational variation, that is, the moments of inertia of the solid Earth. The question is: to what extent, does the core participate in the delta-AM excitation process of the Earth rotational variations from intra-seasonal to inter-annual time scales? Using length of day change and general circulation model delta-AMs including ECMWF atmospheric AM, ECCO oceanic AM and GLDAS hydrological AM, we show that core-mantle is decoupled in intra-seasonal time scales and slightly coupled in inter-annual time scales, at a least squares fit criterion. In the frequency domain, the geodynamics of core-mantle varies with frequency slightly. The geodynamics of core-mantle tends from decoupling in intra-seasonal time scales to slightly coupling in inter-annual time scales. To avoid the inverted barometer (IB) effects between atmospheric delta-AM and oceanic delta-AM, we also substitute the mass term of delta-AM by delta-C20 gravity coefficients observed from SLR. However, we acquire the similar results.

Yan, H.; Chao, B.

2012-04-01

101

Volume reconstruction of point cloud data sets derived from computational geodynamic simulations  

NASA Astrophysics Data System (ADS)

One of the most widely used numerical modeling techniques in geodynamics to study the evolution of geomaterials is the "marker-and-cell" technique. In such methods the material lithology is represented by Lagrangian particles (markers), while the continuum equations are solved on a background mesh. Significant research has been devoted to improving the efficiency and scalability of these numerical methods to enable high-resolution simulations to be performed on modest computational resources. In contrast, little attention has been given to developing visualization techniques suitable for interrogation high-resolution 3D particle data sets. We describe an efficient algorithm for performing a volume reconstruction of the lithology field defined via particles (code available upon request from the author). The algorithm generates an Approximate Voronoi Diagram (AVD) which transforms particle data sets into a cell-based, volumetric data set. The volumetric representation enables cross sections of the material configuration to be constructed efficiently and unambiguously, thereby enabling the interior material structure of the simulation results to be analyzed. Examples from geodynamic simulations are used to demonstrate visual results possible using this visualization technique. Performance comparisons are made between existing implementations of exact and approximate Voronoi diagrams. Overall, the AVD developed herein is found to be extremely competitive as a visualizing tool for massive particle data sets as it is extremely efficient, has low memory requirements and can be trivially used in a distributed memory computing environment.

May, D. A.

2012-05-01

102

On the use of satellite positioning systems for the regional geodynamic studies  

NASA Astrophysics Data System (ADS)

During the last decade an accuracy of the three-dimensional positioning with the use of GPS techniques was improved for more than an order, simultaneously with a significant sinking of the prices of ground receivers. Using an example of the satellite positioning system GPS-NAVSTAR now widely used for the civilian and scientific aims one can show that a potential and precision of similar systems is not yet exausted and if an appropriate modification of the onboard segment as well as a general approach to the error sources studies and an improvement of the time synchronization channel, will be carried out, a field of application of the GPS system for the basic problems of Geophysics and Geodynamics will be practically infinite. The main applications of the GPS technique are plate tectonic studies in regional and global scale, sea-level control and studies, as well as rapid EOP determinations. Several international geodynamic projects like WEGENER, SELF, MOST, CAT, EUROPROBE, Baltic Sea and oth. are carried out at the Russian territory and adjacent countries. 14 core sites of the IGS network with the TURBO/ROGUE and ZI2 receivers are operating regularly.

Tatevian, S. K.

103

On principles, methods and recent advances in studies towards a GPS-based control system for geodesy and geodynamics  

Microsoft Academic Search

Although Very Long Baseline Interferometry (VLBI) and Satellite Laser Ranging (SLR) are becoming increasingly important tools for geodynamic studies, their future role may well be fulfilled by using alternative techniques such as those utilizing the signals from the Global Positioning System (GPS). GPS, without the full implementation of the system, already offers a favorable combination of cost and accuracy and

Demitris Delikaraoglou

1989-01-01

104

New aspects on the interconnection between precursory seismic electric signal lead time and geodynamics in the northern Aegean Sea  

NASA Astrophysics Data System (ADS)

New insights on the deformation process of a confined region in the northern Aegean Sea corroborates the claims that the observed long lead times of the precursory seismic electric signals of the two largest earthquakes which occurred within the last 15 years in the area are attributed to specific geodynamics. Possible underlying physics are also discussed.

Dologlou, Elizabeth

2014-04-01

105

Noble Gases and Siderophile Elements in the Mantle: Unconventional Experimental Results and Their Implications for Chemical Geodynamics  

Microsoft Academic Search

Recent and ongoing experimental studies reveal unexpected behavior of noble gases and siderophile elements that may affect future geodynamic interpretations. Ar-uptake experiments on mantle minerals provide insight into Ar compatibility (solubility) and diffusivity in these phases. Contrary to expectation, solubility results suggest that Ar behaves as a compatible element during mantle melting, favoring residence in point defects in minerals over

E. B. Watson; L. A. Hayden; J. B. Thomas; D. J. Cherniak

2007-01-01

106

Problems of the application of an analytical theory of satellite motion to geodynamics and satellite geodesy problems  

Microsoft Academic Search

The merits of an analytical theory of satellite motion are examined in comparison with numerical integration, in order to identify a suitable technique for geodynamics and satellite geodesy calculations. The theory is based on an integration of Aksenov's (1977) first and second order differential equations for intermediate orbital elements. The equations are derived to account for the oblateness of the

N. V. Emelianov

1984-01-01

107

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 Deformación" 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 Bogotá 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

108

Geoelectrical, strain and tilt investigations of hydrological processes at the broadband Geodynamical Observatory Moxa, Germany  

NASA Astrophysics Data System (ADS)

The Geodynamic Observatory Moxa, located in Thuringia/Germany, is dedicated to studies of temporal deformations of the earth's crust and of variations of the gravity field. One of the essential issues with respect to these investigations is the reduction of the hydrological impact on the data of the gravimeters, strainmeters and tiltmeters. In order to optimise the reductions, we investigated the changes in the hydrological conditions in the woody mountain slope above the observatory with time-lapse electrical resistivity tomography (ERT), and analysed the strain and tilt measurements for prominent signatures of pore pressure induced subsurface deformations. Here we present the results for two profiles - parallel and perpendicular to the slope - measured with ERT during 33 campaigns between June 2007 and April 2010. Resistivity changes and variations of apparent soil moisture, inferred from ERT sections, were found to primarily occur in the first two metres of the subsurface. These variations can be related to subsurface flow in the upper two metres induced by precipitation events and snowmelts. Trees close to the profiles only show a minimum impact on the resistivity and soil moisture changes. Furthermore, systematic hydrologically induced deformations can be observed in hodographs of strain and tilt measurements for large precipitation events (> 80 mm) and snowmelts. In the strain data a short-term (< 3 days) dilatational signal is found with an amplitude of 20 nstrain to 60 nstrain and a long-term (> 7 days) compressional signal between 40 nstrain and 180 nstrain. The preferential N-S direction of long-term deformational signals (> 1 week) is also observed in the tilt data. The direction of tilt changes (25 nrad-120 nrad) is nearly parallel to the drainage direction of the nearby Silberleite creek indicating variations of pore pressure gradients during hydrological events. The results of these hydrological studies at the Geodynamic Observatory Moxa can be used for removing the time dependent hydrological signal in strain and tilt data and, thus, better correction algorithms for hydrological impacts can be developed to enhance the value of the data for geodynamic studies.

Hermann, Tobias; Kroner, Corinna; Jahr, Thomas

2013-11-01

109

Fluidity: a fully-unstructured adaptive mesh computational framework for geodynamics  

NASA Astrophysics Data System (ADS)

Fluidity is a finite element, finite volume fluid dynamics model developed by the Applied Modelling and Computation Group at Imperial College London. Several features of the model make it attractive for use in geodynamics. A core finite element library enables the rapid implementation and investigation of new numerical schemes. For example, the function spaces used for each variable can be changed allowing properties of the discretisation, such as stability, conservation and balance, to be easily varied and investigated. Furthermore, unstructured, simplex meshes allow the underlying resolution to vary rapidly across the computational domain. Combined with dynamic mesh adaptivity, where the mesh is periodically optimised to the current conditions, this allows significant savings in computational cost over traditional chessboard-like structured mesh simulations [1]. In this study we extend Fluidity (using the Portable, Extensible Toolkit for Scientific Computation [PETSc, 2]) to Stokes flow problems relevant to geodynamics. However, due to the assumptions inherent in all models, it is necessary to properly verify and validate the code before applying it to any large-scale problems. In recent years this has been made easier by the publication of a series of ‘community benchmarks’ for geodynamic modelling. We discuss the use of several of these to help validate Fluidity [e.g. 3, 4]. The experimental results of Vatteville et al. [5] are then used to validate Fluidity against laboratory measurements. This test case is also used to highlight the computational advantages of using adaptive, unstructured meshes - significantly reducing the number of nodes and total CPU time required to match a fixed mesh simulation. References: 1. C. C. Pain et al. Comput. Meth. Appl. M, 190:3771-3796, 2001. doi:10.1016/S0045-7825(00)00294-2. 2. B. Satish et al. http://www.mcs.anl.gov/petsc/petsc-2/, 2001. 3. Blankenbach et al. Geophys. J. Int., 98:23-28, 1989. 4. Busse et al. Geophys. Astrophys. Fluid 75:39-59, 1994. 5. J. Vatteville et al. Geochem. Geophy. Geosy., 10, 2009. doi:200910.1029/2009GC002739. Numerical simulation of a thermal plume showing contours of temperature and the dynamically optimised unstructured mesh.

Kramer, S. C.; Davies, D.; Wilson, C. R.

2010-12-01

110

Constraining the rheology of the lithosphere through joint geodynamic and gravity inversion  

NASA Astrophysics Data System (ADS)

Understanding the physics of lithospheric deformation and continental collision requires good constraints on lithospheric rheology. Typically, rheology is determined from laboratory experiments on small rock samples, which are extrapolated to geological conditions - an extrapolation over 10 orders of magnitude in deformation rates. These laboratory experiments generally show that small changes in the composition of the rocks, such as adding a bit of water, can dramatically change its viscosity. Moreover, it is unclear which rock type gives the best mechanical description of, for example, the upper crust and whether a small sample is even appropriate to describe the large scale mechanical behavior of the crust. So the viscosity of the lithosphere is probably the least constrained parameter in geodynamics. Ideally, we thus need a new independent method that allows constraining the effective rheology of the lithosphere directly from geophysical data, which is the aim of this work. Our method uses the fact that the geodynamically controlling parameters of lithospheric deformation are its effective viscosity and density structure. By appropriately parameterising the rheological structure of the lithosphere we perform instantaneous forward simulations of present-day lithospheric deformation scenarios with a finite element method to compute the gravity field and surface velocities. The forward modelling results can be compared with observations such as Bouguer anomalies and GPS-derived surface velocities. More precisely, we automatize the forward modelling procedure with a Monte Carlo method, and in fact solve a joint geodynamic and gravity inverse problem. The resulting misfit can be illustrated as a function of rheological model parameters and a more detailed analysis allows constraining probabilistic parameter ranges. For a simplified setup with linear viscous rheologies we can demonstrate mathematically that a joint geodynamic-gravity inversion approach results in a unique solution as opposed to inverting for gravity alone. This is shown to work as well in combination with 3D forward models of salt tectonics on an upper crustal scale. Yet, the lithosphere has nonlinear rheologies that can be plastic or temperature-dependent powerlaw creep depending on stresses. As the thermal structure of the lithosphere is in general poorly constrained, and only affects the dynamics of the lithosphere in an indirect manner, we developed a parameterized rheology that does not include temperature but includes other nonlinearities (such as stress-dependent viscosity). To test the accuracy of this method we perform lithospheric-scale collision forward models that incorporate a temperature-dependent viscoelastic-plastic rheology to create synthetic gravity and surface velocities data. In a second step, we deploy these synthetic data sets to perform the joint inversion, using our simplified parameterized rheology. Results show that we can recover the rheology of the lithosphere reasonably well, provided that lithospheric layers contribute to the large-scale dynamics. In addition, we will show an application of our method to 2D cross-sections of the India-Asia collision system. Acknowledgements Funding was provided by the ERC under the European Community's Seventh Framework Program (FP7/2007-2013) / ERC Grant agreement #258830

Baumann, T.; Kaus, B.; Popov, A.

2013-12-01

111

Geodynamic model and oil and gas prospects of the Pre-Caspian basin  

SciTech Connect

The Pre-Caspian basin has gone through three cycles of dynamic development. The third cycle, starting in the Devonian, included all the stages of geodynamic evolution: crustal destruction, spreading, convergence, collision, and isostatic compensation. In the Paleozoic, within the present boundaries of the Pre-Caspian basin were three sedimentary subbasins, which were fundamentally different from one another in terms of the dynamics of subsidence, rates of sedimentation, and heat flow, as reflected in the conversion of organic matter into hydrocarbons and the formation oil and gas accumulation zones. The eastern, south-eastern, and southern edges of the Pre-Caspian basin are complicated by overthrusts, and there are exploration prospects under the allochthons in the autochthonous carbonate complex.

Zholtaev, G.Z. (Kazakhstan Polytechnic Institute, Alma Ata (Kazakhstan))

1993-09-01

112

Nonlinearities and multigrid solvers for geodynamic applications using staggered grid finite differences.  

NASA Astrophysics Data System (ADS)

We report on the state of the development of the massively parallel staggered-grid finite difference version of the LaMEM code, parts of which have scaled to over 260'000 cores. In particular we present i) our matrix-free nonlinear solution strategy for visco-elasto-plasticity, ii) updated linear solver that includes a coupled velocity-pressure geometric multigrid preconditioner, and iii) an optimized treatment of the makers with approximate stress-rotation algorithm generalized from 2D to 3D formulation. The capabilities of the solver are demonstrated with a set of geodynamically-relevant benchmarks and example problems on the massively parallel computers. Acknowledgements. Funding was provided by the European Research Council under the European Community's Seventh Framework Program (FP7/2007-2013) / ERC Grant agreement #258830. Numerical computations have been performed on JUQUEEN of the Jülich high-performance computing center.

Popov, Anton; Kaus, Boris

2014-05-01

113

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.; Immé, G.; Cammisa, S.; Catalano, R.; Mangano, G.; La Delfa, S.; Patanè, G.

2012-04-01

114

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

115

The Seismic Cycle at Subduction Thrusts: Implications of Geodynamic Simulations Benchmarked with Laboratory Models  

NASA Astrophysics Data System (ADS)

The physics governing the seismic cycle at seismically active subduction zones remains poorly understood due to restricted direct observations in time and space. To investigate subduction zone dynamics and associated interplate seismicity, we benchmark a quasi-static, visco-elasto-plastic numerical model to a new laboratory approach. We demonstrate that our numerical method reproduces seismic cycle behavior and source parameter estimates of the laboratory setup that includes a visco-elastic gelatin wedge underthrusted by a plate with defined velocity-weakening and -strengthening regions. Our innovative geodynamic approach includes velocity-weakening friction to spontaneously generate a series of fast frictional instabilities that correspond to analog earthquakes. A match between numerical and laboratory source parameters is obtained when velocity-strengthening is applied in the aseismic regions to stabilize and limit the rupture, while promoting slip complexity. Spontaneous nucleation by coalescence of neighboring patches mainly occurs at evolving asperities near the seismogenic zone limits, with a preference for the downdip region. Consequently, a crack-, or occasionally even pulse-like, rupture propagates toward the opposite side of the seismogenic zone by increasing stresses ahead of its rupture front. The resulting surface displacements qualitatively agree with geodetic observations and show landward and, from near the downdip limit, upward interseismic motions. These are rebound and reversed coseismically as the fault slips (Figure 1). Slip produces stress shadows that are relaxed afterwards by postseismic accelerated creep or afterslip. The agreement with laboratory results and the wide range of observed physical phenomena, including back-propagation and repeated slip, demonstrate that visco-elasto-plastic geodynamic models with rate-dependent friction represent a new tool that can greatly contribute to our understanding of the seismic cycle at subduction zones.orizontal displacement of six particles at the surface.

van Dinther, Y.; Gerya, T.; Dalguer, L. A.; Corbi, F.; Funiciello, F.; Mai, P. M.

2012-12-01

116

Plio-Quaternary coastal sequences, sea-level changes and coastal geodynamics :  

NASA Astrophysics Data System (ADS)

Sequences of Plio-Quaternary shorelines generated by sea-level cyclicity and tectonics massively shape the coasts worldwide. Here, we compile a worldwide synthesis of sea-level changes for the following highstands : MIS 1, MIS 3, MIS5e, and MIS 11 and explore the relationships to regional geodynamics. We identified 896 sequences including the MIS 5e benchmark, out of which 177 also feature the highest Holocene shorelines, 6 where the elevation of the MIS 3 shorelines are known, and 40 including that of MIS 11 shorelines. We considered 8 main geodynamical contexts for a statistical analysis: passive margin (337 sites, 14 domains, U=0.06 ± 0.01 mm/a), hot spot chains (45 sites, 14 domains, U=0.02 ± 0.02 mm/a), rifts (45 sites, 2 domains, U=0.12 ± 0.02 mm/a), ridges (3 sites, 1 domain, U=0.14 ± 0.02 mm/a), transform plate boundaries (119 sites, 7 domains, U=0.25 ± 0.03 mm/a), intra-oceanic subductions (131 sites, 4 domains, U=0.43 ± 0.04 mm/a), continental subductions underneath oceanic plates (12 sites, 1 domain, U=0.54+/- 0.04 mm/a), oceanic subductions underneath continental plates (166 sites, 7 domains, U=0.06 ± 0.01 mm/a), intra-continental convergence (10 sites, 2 domains, U=1.47 ± 0.08 mm/a). Counter-intuitive is the fact that passive margin are ubiquitously uplifting, while tectonic segmentation is more important on active margins. Additionally, 511 sites document the elevation of the highest shoreline of the sequence, from which we extrapolate a minimum age of onset for the sequence (based on MIS 5e uplift rates). 99% (511 sites) were formed at least during Pliocene and/or Quaternary, showing that potentially more ancient records are either eroded or non-existent.

Pedoja, Kevin; Husson, Laurent; Nexer, Maëlle; Regard, Vincent; Delcaillau, Bernard

2013-04-01

117

A 3-D Geodynamic Model of Strain Partitioning in Southern California  

NASA Astrophysics Data System (ADS)

In southern California, strain resulting from the relative motion between the Pacific and the North American plates is partitioned in a complex system of transcurrent, transcompressional, and transtensional faults. High-precision GPS measurements in this region have enabled kinematic modeling of the present-day strain partitioning between major faults in southern California. However, geodynamic models are needed to understand the cause of strain partitioning and to determine strain in regions where faults are blind or diffuse. We have developed a regional-scale geodynamic model of strain partitioning in southern California. This 3-D viscoelasto-plastic finite element model incorporates first-order fault geometry of the major active faults in the region. The model domain includes an elastoplastic upper crust on top of a viscoelastic lower lithospheric layer. Deformation is driven by the relative motion between the Pacific and the North American plates, imposed as a displacement boundary condition. Plastic deformation both within the fault zones and in the unfaulted surrounding crust is calculated. Our results show that the Big Bend of the San Andreas Fault, and other geometric complexity of faults in southern California, plays a major role in strain partitioning. The observed variations of strain portioning in southern California can be explained by the geometric configuration of fault systems relative to the relative plate motion, without appealing to basal traction of a flowing lower lithosphere. The model predicts concentrated plastic strain under the reverse fault systems in the Transverse Ranges and the young and diffuse faults in the Eastern California Shear Zone across the Mojave Desert, where a number damaging earthquakes occurred in the past decades.

Ye, J.; Liu, M.; Lin, F.

2012-12-01

118

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

119

Upper mantle and crustal structure of the East Greenland Caledonides: New geophysical evidence and geodynamic implications  

NASA Astrophysics Data System (ADS)

The East Greenland and Scandinavian Caledonides once formed a major coherent mountain range, as a consequence of the collision of the continents of Laurentia and Baltica. The crustal and upper mantle structure was furthermore influenced by several geodynamic processes leading to the formation of the North Atlantic passive margins, including the gravitational collapse, extension, rifting and a possible influence by volcanism related to the Iceland hot spot. The landscape and topography were finally shaped by extensive erosion, finding its peak in the quaternary glaciations. Seismological data were acquired in the East Greenland Caledonides by the Ella-Ø-array for a period of two years (2009-2011). The array containing 11 broadband seismometers was situated at approximately 73 °N covering a distance of 270 km from the Greenland Ice Sheet to the Atlantic coast, north of the Iceland Ridge. A Receiver Function study based on an average of 36 events per station reveals a clear eastward dipping high-velocity structure underneath the study area. The geophysical character, supported by synthetic modelling, is consistent with a 10 km thick subducted slab of eclogitized oceanic crust. This might be the key for unravelling of a complex geodynamic setting and development leading to the formation of the Caledonides. The distinct preservation of structures in the upper mantle to depths of 100 km or more, limits the impact of subsequent collision and extension related deformation. In support of this interpretation, we present selected results from on-going detailed studies of the crustal and upper mantle, including a Receiver Function inversion, seismic P-wave travel time tomography and gravity modelling.

Schiffer, C.; Balling, N.; Jacobsen, B. H.; Hejrani, B.; Nielsen, S. B.

2013-12-01

120

A Geodynamic Grand Challenge: Time-Reversed Mantle Convection Reconstructions From Tomographic Images of Present-Day Mantle Structure  

NASA Astrophysics Data System (ADS)

One of the most complex challenges in current geodynamics research is the reconstruction of the past evolution of 3-D mantle temperature structure from seismic tomographic images of present-day lateral heterogeneity in the mantle. Early efforts to address this problem have been based on backward advection approximations based on the assumption that mantle convection is a very-high Rayleigh number process (e.g. Forte & Mitrovica 1997; Steinberger & O'Connell 1997). Over the past decade further progress has been achieved and new techniques have been proposed, such as the 4-D variational (Bunge et al. 2003) and quasi-reversible (Ismail-Zadeh et al. 2007) approaches. An enduring challenge is the construction of time-reversed mantle convection simulations that yield maximum consistency with a wide suite of surface geodynamic constraints on mantle rheology and 3-D structure inferred from seismic tomography. Resolving this outstanding problem is of crucial importance, because a successful reconstruction of the time-dependent, 3-D mantle convective structure in the geological past provides unique insights into the origin and evolution of a number of fundamental surface processes that include topography changes, eustatic sea level variations, state of stress in the lithosphere, and Earth rotation variations. A key concern in these reconstructions is quantifying the inherent uncertainties and the implications for surface geodynamic observables. We will explore these issues and compare the efficacy of different backward convection techniques using a new mantle convection model based on recent joint seismic-geodynamic tomography inversions (Simmons et al., GJI, 2009).

Glisovic, P.; Forte, A. M.; Moucha, R.

2009-12-01

121

The Deep Structure and 3D Thermo-geodynamics of the Caucasus by Geophysical Data.  

NASA Astrophysics Data System (ADS)

The Caucasus is a continental collision zone, representing a connecting link between the Western and Eastern parts of the Alpine-Himalayan Belt. The structure and geodynamics have been studied rather well in both of the above mentioned segments of Alpine-Himalayan Belt, but remained problematic on the Caucasus. Compilation of detailed digital geophysical data bases and their numerical interpretation by modern methods are needed for the quantitative solution of the problem of structure and tectonics of the Caucasus. The first steps in these directions are made in this paper. The Caucasus is crossed by deep seismic sounding profiles "Gali-Safaraliev" (from the West of East) and "Bakuriani-Stepnoe" (from The North to South). Besides, there are the measurements of gravitational and magnetic fields at different heights along these lines. Integrated interpretation of the set of these geophysical fields by modern geophysical technique supplemented by the existing geological data allows approaching closely the solution of problems, related to structure and evolution of Caucasus. Three-dimensional stationary and non-stationary geothermal and thermo-elastic models of the Caucasus and the Black and Caspian seas areas are developed and their geological interpretation is given. The temperature field has been defined for the period 410 Ma on the basis of the stationary model of the investigated region. The thermo-elastic equations were solved and both horizontal and vertical thermo-elastic displacements have been calculated on the basis of the thermal field using Hook's rheology. These models revealed a number of interesting features in the geodynamics of the region. Nevertheless, they did not give us an opportunity to consider the dynamics of models, taking into account the process of sedimentation. That is why afterwards, computations were carried out on the basis of a non-stationary thermal model beginning from the period of the sedimentary cover formation. Such approach allows the construction of three-dimensional non-stationary geothermal and thermo-elastic models of the Caucasus and the Black and the Caspian seas water areas proposed by the authors of this paper. Paleo-reconstruction schemes of development of sedimentary cover of the Caucasus (Sholpo, 1978) and the Black sea area (Kasmin at al. 2000) and a lot of other data regarding the Caspian sea area have been used for the construction of three-dimensional non-stationary models of investigated region. Numerical modeling of thermal and thermo-elastic processes allows revealing the temporal distribution of a number of thermo-geodynamic events including the formation of some deep faults and active seismic zones. The above preliminary results on 3D structure and temperature fields in Caucasus were compared to recent publication on 3D crust structure and thermal model of Western and Central Europe (Tesauro, Kaban, and Cloetingh, 2010) and quite satisfactory agreement with our results was found for matching areas (North Turley, Black Sea, Crimea) of considered regions.

Chelidze, T.; Gugunava, G.; Gamkrelidze, N.; Mindeli, P.; Kiria, J.; Ghonghadze, S.; Janovskaya, O.

2012-04-01

122

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 Müller Delphine Desmares f (delphine.desmares@upmc.fr) Lucien Montadert e (lucien.montadert@beicip.com) François Baudin a (francois.baudin@upmc.fr) a UMR 7193 Institut des Sciences de la Terre de Paris, Université 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 Préau 92852 Rueil Malmaison Cedex, France d UMR 7207, Centre de Recherche sur la Paleobiodiversité et les Paleoenvironnements. Université Pierre et Marie Curie, Tour 46-56 5ème. 4, place Jussieu 75252 Paris Cedex 05, France e Beicip Franlab, 232 Av. Napoléon 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

123

Investigations of gravity and plumb line variations in Geodynamic Laboratory of Space Research Center in Ksiaz  

NASA Astrophysics Data System (ADS)

The Geodynamic Laboratory of Space Research Centre exists in Ksiaz since 1974 year. The Laboratory is placed in horizontal galleries built in slope of valley. Underground galleries are situated 340 meters above sea level and 50 meters below the Earth surface. Stability of bedrocks and good propagation of geodynamic signals by orogen were confirmed by long-standing seismic and tiltmeter measurements. In 1974 in laboratory there were begun measurements carried with help of two quartz horizontal pendulums equipped with photographic system of registration. Photographic system of registration was applied until 2002. In 2006 we resumed pendulums measurements with help of new system of electronic registration. Since 1974 the pendulums measurements are carried out at the fixed place in azimuths closed to fundamental directions NS and EW. In 2002 in geodynamic laboratory there appeared long water-tube tiltmeter. Instrument consists of two perpendicular tubes 65 and 83 meters-long, partially filled with water. The idea of measurements bases on phenomenon of hydrostatic equilibrium. Tilting of tubes in relation to gravity field produces variations of water level inside the hydrodynamic system of the instrument. Variations of water level are measured with the help of interference technique. This technique allowed us to achieve internal sensitivity of tiltmeter close to 1 microarcsecond. Furthermore, stability of length of the He-Ne lasers light and application of differential method for data elaboration caused elimination of the instrumental drift. In 2007 in laboratory we installed relative gravimeter LaCoste&Romberg G-648 of tidal resolution. Initiation of gravity measurements was possible after construction in underground gravimetric room equipped with thermostatic system and pillar for relative gravimetry. Long-standing series of plumb line variations obtained with help of horizontal pendulums allowed us to lead investigations of tidal signals. Permanent observations carried out using horizontal pendulums suggest also existence of strong, irregular non-tidal signal of plumb line variations. During tens of years of pendulums measurements several times we observed epochs of instability of pendulums equilibrium position. Almost every year the azimuths of equilibrium of the pendulums have been changing rapidly. Existence of strong non-tidal signals was also confirmed by plumb line measurements carried out with help of long water-tube tiltmeter. Special peculiarities of new tiltmeter such as high resolution and possibility of reduction of instrumental drift opened possibility of investigation of the long period or systematic plumb line variations. In 2004 property of water-tube tiltmeter allowed us to observe phenomenon of the Earth free oscillation caused by extremely strong seismic event which took place near the coast of Sumatra-Andaman Islands. Introduction to laboratory gravimetry opens for us perspective of investigation of Love'a numbers h and k for Sudeten Mountain area.

Kaczorowski, M.

2009-04-01

124

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

125

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

126

Gravity, Magnetics and Geodynamic evolution of the Vavilov and Marsili Backarc Basins in the Tyrrhenian Sea  

NASA Astrophysics Data System (ADS)

The Southern Tyrrhenian Sea, the youngest basin of the West Mediterranean, is made of two sub-basins partly carpeted by oceanic crust. One is the Vavilov Basin, with crust as old as 5-6 Ma; the other is the Marsili Basin where the seafloor spreading process occurred about 2.0 Ma. Each of the two basins displays a prominent volcanic ridge oriented NNE/SSW that mask the former oceanic spreading axes. In this paper, we present new potential field data obtained from Vavilov and Marsili volcanic systems during the recent cruises R/V Universitatis PROMETHEOUS 2006 and R/V Urania MAVA2011. We performed a detailed description and interpretation of the peculiar patterns of magnetic and gravity anomalies considering the morphostructural features of the oceanic seafloor basin and the particular setting of the two seamounts. Both the Vavilov and Marsili volcanic systems have a similar gravity signature with low average density (2.2 g/cm3) due probably to the eruptive mechanisms that prevailed in the two volcanoes. Both systems show NNE-SSW magnetic stripes, particularly well developed at Marsili. The two seamounts present shallow manifestation of hydrothermal alteration that in the case of Vavilov is completely extinct while in the case of the Marsili, it is still active as confirmed by the presence, on the volcano's summit of hydrothermal chimneys rich in Fe-Mn-oxyhydroxides. The similarity between the two basins may be due to similar geodynamic processes affecting the southern Tyrrhenian at different times. Since the Oligocene, the geodynamic evolution of western Mediterranean Sea was mainly driven by passive sinking of the Ionian-African plate within the European mantle modifying, step by step, the crustal setting of the Valencia region, of the Provençal basin and of the Tyrrhenian Sea. The roll back movement triggered stretching of upper-middle crust of the European plate with a different stress rate inducing variable depleting effects that can recall a typical boudinage-like style. In the Tyrrhenian basin the roll back occurred since the Tortonian striking along a preferential east/southern-eastward direction causing crustal stretching and the formation of new oceanic basins. The Marsili basin oceanic crust formed by seafloor spreading that about 1 Ma shifted to a regime of prevailing vertical accretion of the volcanic ridge due to a new intense magmatic pulse related probably to slab tearing in the subduction system. The Vavilov ridge underwent a similar evolution during the Matuyama reverse chron (about 2.5 Ma). Our data suggest that the evolution of the entire Tyrrhenian sea was driven by two asynchronous geodynamic stages resulting in a common style: high-rate of eastward rollback during the initial phase, drastic decrease of the seafloor spreading rate and finally slab tearing with the formation of the volcanic ridges at the centre of the basins.

Cocchi, L.; Muccini, F.; Carmisciano, C.; Caratori Tontini, F.; Bortoluzzi, G.; Ligi, M.; D'Oriano, F.; Bonatti, E.

2012-12-01

127

An Investigation Into the Effect of Composition on the Geometry of Thermochemical Piles in Tomographically-filtered Geodynamic Models  

NASA Astrophysics Data System (ADS)

Broad, low velocity anomalies in the lower mantle beneath Africa and the Pacific are conspicuous features in all tomographic images. However, it remains uncertain whether these structures are dense thermo-chemical piles or whether they are relatively narrow thermal upwellings in an iso-chemical lower mantle, that have been blurred in the tomographic process. In previous work we have analysed conceptual geodynamical models that have been filtered by the resolution matrix of the tomographic model S20RTS. This enabled us to quantify the effects of heterogeneous resolution in seismic images. We considered both spherical thermo-chemical and iso-chemical geodynamic convection models with imposed plate history for the past 119 million years, concluding that the thermo-chemical models best explain, although not exclusively, the broad extent of the imaged low-velocity anomalies. Here, we further investigate the influence which composition has on the geometry of the anomalous structures in filtered geodynamical models, and estimate the required physical conditions of thermo-chemical structures that optimally match the seismic data.

Bull, A. L.; McNamara, A. K.; Ritsema, J.

2006-12-01

128

Seismic Velocity Structure of the Mantle beneath the Hawaiian Hotspot and Geodynamic Perspectives  

NASA Astrophysics Data System (ADS)

Data from the PLUME deployments of land and ocean bottom seismometers have provided unprecedented new constraints on regional seismic structure of the mantle beneath the Hawaiian Islands and motivated a new generation of geodynamic models for understanding hotspot origins. Three-dimensional finite-frequency body-wave tomographic images of S- and P-wave velocity structure reveal an upper-mantle low-velocity anomaly beneath Hawaii that is elongated in the direction of the island chain and surrounded by a high-velocity anomaly in the shallow upper mantle that is parabolic in map view. Low velocities continue downward to the mantle transition zone between 410 and 660 km depth and extend into the topmost lower mantle southeast of Hawaii. Upper mantle structure from both S and P waves is asymmetric about the island chain, with lower velocities just southwest of the island of Hawaii and higher velocities to the east. Independent Rayleigh-wave tomography displays a similarly asymmetric structure in the lower lithosphere and asthenosphere, and also reveals a low-velocity anomaly (with horizontal dimensions of 100 by 300 km across and along the chain, respectively) beneath the hotspot swell that reaches to depths of at least 140 km. Shear-wave splitting observations dominantly reflect fossil lithospheric anisotropy, although a signature of asthenospheric flow also may be resolvable. S-to-P receiver function imaging of the lithosphere-asthenosphere boundary suggests shoaling from 100 km west of Hawaii to 80 km beneath the island, a pattern consistent with results from Rayleigh wave imaging. In terms of mantle plume geodynamic models, the broad upper-mantle low-velocity region beneath the Hawaiian Islands may reflect the "diverging pancake" at the top of the upwelling zone; the surrounding region of high velocities could represent a downwelling curtain of relatively cool sublithospheric material; and the low-velocity anomalies southeast of Hawaii in the transition zone and topmost lower mantle are consistent with predictions of a plume conduit tilted by mantle flow. Dynamic models of a thermochemical plume containing eclogite predict a double layering of plume material in the upper mantle and may explain the large apparent thickness of the low velocity anomaly in the upper mantle. Shear wave splitting predicted from lattice preferred orientation that develops in response to modeled plume deformation shows promise for understanding the rheology and layered seismic anisotropy at Hawaii.

Wolfe, C. J.; Laske, G.; Ballmer, M. D.; Ito, G.; Collins, J. A.; Solomon, S. C.; Rychert, C. A.

2012-12-01

129

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

130

Geodynamic Regimes of the Mantle - Constraints From a He-Inclusive Global Data Compilation  

NASA Astrophysics Data System (ADS)

27 years after the introduction of Chemical Geodynamics by Allègre (1982), fundamental issues about the geodynamic evolution of the Earth's mantle remain to be resolved. Geophysical evidence for whole mantle convection combined with the difficulty to preserve mantle heterogeneity since the early Earth contrast with geochemical evidence for longterm isolation of parts of the Earth's mantle. Noble gases, in particular helium, remain central to this discussion with three contrasting models considered here: (1) The layered mantle by Allègre et al. (1983) with the lower mantle preserving high 3He/4He ratios since early Earth; (2) The D" layer model by Tolstikhin & Hofmann (1995) with D" preserving high 3He/4He ratios since early Earth; (3) The incompletely degassing mantle model of Class and Goldstein (1995) with depleted mantle domains in the lower mantle preserving high 3He/4He ratios since 1-2 Ga. Here we present new constraints from our updated He-inclusive global data compilation. Ocean island basalts show a correlation between 3He/4He and Th contents, consistent with He isotope ratios reflecting the radiogenic production rate of the variably enriched OIB mantle sources. A high 3He/4He - low Th component is required to explain the global systematics. Constraints on the Th-U content in the three models place tight constraints on the absolute and relative contribution from the high 3He/4He reservoir to OIB mantle sources. Both the layered mantle model and the D" model requires small and extremely uniform contributions of a few percent or permil respectively; contributions outside of this small range, even if slightly higher or lower, are inconsistent with the global OIB data. Only the incompletely degassing mantle model allows for variability in the scale of contributions from old depleted mantle preserving higher 3He/4He ratios and from sources having a variety of ages. This model is also consistent with the requirement of dominantly peridotitic mantle sources for OIB. Allègre, C.J. (1982) Tectonophysics 81, 109-132. Allègre, C.J. et al. (1983) Nature 303, 762-766. Tolstikhin, I.N. & Hofmann, A.W. (2005) Phys. Earth Planet. Int. 148, 109-130. Class, C. & Goldstein, S.L. (2005) Nature 436, 1107-1112.

Class, C.; Goldstein, S. L.

2007-12-01

131

Constraining the rheology of the lithosphere through joint geodynamic and gravity inversion  

NASA Astrophysics Data System (ADS)

Understanding the physics of lithospheric deformation requires good constraints on lithospheric rheology and in particular on the effective viscosity. Typically, rheology is determined from laboratory experiments on small rock samples, which are extrapolated to geological conditions - an extrapolation over 10 orders of magnitude in deformation rates. Ideally, we thus need a new independent method that allows constraining the effective rheology of the lithosphere directly from geophysical data, which is the aim of this work. Our method uses the fact that the geodynamically controlling parameters of lithospheric deformation are its effective viscosity and density structure. By appropriately parametrising the rheological structure of the lithosphere we perform instantaneous forward simulations of present-day lithospheric deformation scenarios with a finite element method to compute the gravity field as well as surface velocities. The forward modelling results can be compared with observations such as Bouguer anomalies and GPS-derived surface velocities. More precisely, we automatise the forward modelling procedure with a Markov-Chain Monte Carlo method, and in fact solve a joint geodynamic and gravity inverse problem. The resulting misfit can be illustrated as a function of rheological model parameters and a more detailed analysis allows constraining probabilistic parameter ranges. Yet, the lithosphere has non-linear rheologies that can be plastic or temperature-dependent powerlaw creep depending on stresses. As the thermal structure of the lithosphere is in general poorly constrained, and only affects the dynamics of the lithosphere in an indirect manner, we developed a parameterised rheology that excludes a direct temperature dependency. To test the accuracy of this approximation we perform lithospheric-scale collision forward models that incorporate a temperature-dependent visco-plastic rheology to create synthetic surface observations. In a second step, we deploy these synthetic data sets to perform a joint inversion, using our simplified parameterized rheology. Results show that we can recover the rheology of the lithosphere reasonably well, provided that lithospheric layers contribute to the large-scale dynamics. In addition, we have applied the models to the India-Asia collision zone, and first results are consistent with the Tibetan plateau having a weak lower crust, but the Indian mantle lithosphere having large viscosities.

Kaus, Boris; Baumann, Tobias; Popov, Anton

2014-05-01

132

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

NASA Astrophysics Data System (ADS)

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 shear-wave propagation directions within the mantle lithosphere are parallel to the direction of current extension. In the presently non-deforming Cyclades, anisotropic fabric in the lower crust trends parallel to the direction of paleo-extension in the Miocene. These results imply that the region-scale extension in the Aegean is accommodated, at least in part, by diffuse, continuous deformation in the lower crust and lithospheric mantle. Visco-elasto-plastic geodynamic modelling of the lithospheric extension in the Aegean confirms that the retreat of the Hellenic subduction zone is sufficient as a force driving the pervasive extension and flow of the weakened lithosphere of the Aegean. The large finite strains modelled in the lower crust and lithospheric mantle and associated with the extension and formation of metamorphic core complexes are consistent with the strong anisotropy observed seismically.

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

2009-12-01

133

Comparison of Noise Levels of Superconducting Gravimeters of The Ggp (global Geodynamics Project) Network  

NASA Astrophysics Data System (ADS)

Since 1997 a network of superconducting gravimeters has been monitoring the varia- tions of the Earth's gravity field. Data from the network, under the coordination of the Global Geodynamics Project (GGP), allows a comparison of the noise levels of the different contributing stations. We use a standardized processing procedure to evalu- ate the combined instrument plus site noise, based on averaging the five quietest days at each station. The stations at Boulder (USA), Canberra (Australia) and Strasbourg (France) are the least noisy sites in terms of the residual power spectral densities (PSD) and a nominal measure called the Seismic Noise Magnitude. Most of the stations have PSDs in the range [-180 dB,-150 dB] from 0 Hz to the Nyquist frequency (8.33 mHz). For frequencies higher than 0.8 mHz, the PSDs are 1 to 2 orders of magnitude higher than the New Low Noise Model of Peterson (NLNM). For frequencies less than 0.8 mHz, including the long period seismic and subseismic bands, the PSDs are smaller than the NLNM. Knowledge of the noise levels of each station is important in a num- ber of studies that combine the data to determine global Earth parameters. We cite for example the stacking of the data to determine the period of the free core nutation and the Chandler wobble, and the potential use of the data in the search for the gravity variations associated with the translational mode of the inner core.

Rosat, S.; Hinderer, J.; Crossley, D.

134

Crustal tomographic imaging and geodynamic implications toward south of Southern Granulite Terrain (SGT), India  

NASA Astrophysics Data System (ADS)

The crustal structure toward southern part of SGT is poorly defined leaving an opportunity to understand the tectonic and geodynamic evolution of this high-grade granulite terrain surrounded by major shear and tectonically disturbed zones like Achankovil Shear Zone (AKSZ) and Palghat Cauvery Shear Zone (PCSZ). To develop a geologically plausible crustal tectonic model depicting major structural elements, a comprehensive tomographic image was derived using deep-seismic-sounding data corroborated by Bouguer gravity modeling, coincident-reflection-seismic, heat-flow and available geological/geochronological informations along the N-S trending Vattalkundu-Kanyakumari geotransect. The final tectonic model represents large compositional changes of subsurface rocks accompanied by velocity heterogeneities with crustal thinning (44-36 km) and Moho upwarping from north to south. This study also reveals and successfully imaged anomalous zone of exhumation near AKSZ having transpression of exhumed rocks at mid-to-lower crustal level (20-30 km) with significant underplating and mantle upwelling forming a complex metamorphic province. The presence of shear zones with high-grade charnockite massifs in the upper-crust exposed in several places reveal large scale exhumation of granulites during the Pan-African rifting (~ 550 Ma) and provide important insights of plume-continental lithosphere interaction with reconstruction of the Gondwanaland.

Behera, Laxmidhar

2011-09-01

135

Ophiolites as indicators of the geodynamic evolution of the Tethyan ocean  

NASA Astrophysics Data System (ADS)

Reviewing the ophiolites of the Alpine chain from the Western Mediterranean to the Indian Ocean, we subdivide them into ten groups of outcrops. The geological environment through time, the internal composition and history are given for each. Emphasis is put on the variegated and successive geodynamic processes which can be reconstructed for the different ophiolitic belts since their birth as an ocean-like crust to their incorporation through accretion to a continent. One can distinguish: low versus high tholeiitic partial melting; fairly or poorly established ridges; simple ridge-type crust versus complex ridge + ensimatic arc (and even more complex) type; long-lived versus short-lived oceanic crust stages; abrupt, large-scale, pure obduction versus progressive collision-related obduction or simple progressive juxtaposition to continent. The major events through time in the Tethyan ophiolitic belts can be listed as follows: spreading ridge activity during the Jurassic (Liguria, Dinaro-Hellenides, Lesser Caucasus) and the Cretaceous (Peri-Arabic, Nain Sabzewar) with a jump of ridge in between; repeated change from ridge to ensimatic arc (Dinaro-Hellenic, Lesser Caucasus, Peri-Arabic, ? West Indian) during the latest Jurassic and Cretaceous; Upper Cretaceous (+Tertiary) collision-related obductions (Pontic-Lesser Caucasus, Liguria) squeezing out the elevated portions of these basins; lack of oceanic magmatism during the Cenozoic but progressive accretion along accretionary wedges of the elevated portions of the remaining Mesozoic crust (Van, Naïn, Sabzewar, Zahedan, MeKran).

Knipper, A.; Ricou, L.-E.; Dercourt, J.

1986-03-01

136

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 Wiese—Parkinson 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

137

Geodynamics of a retreating Mediterranean arc: what are the geologic constraints?  

NASA Astrophysics Data System (ADS)

The Betic-Rif arc is a classic example of a retreating Mediterranean arc accommodated by an extending back-arc basin - the Alboran Sea. The driving forces in this system are debated, because of uncertainties in the structure of the underlying upper mantle, the total displacement, and the kinematics of deformation in the overlying crust. Geological data place constraints on the directions, amounts, and timing of displacement of various parts of the system, which need to be taken into account in constructing geodynamic models. The external thrust belt records displacements produced during the Miocene by a combination of Africa-Iberia convergence, westward motion of the Alboran Domain, and extension within the Alboran Domain. Analysis is complicated by the effects of vertical axis rotation, but the combination of abundant paleomagnetic data, slip-vector data on faults, and shortening estimates from balanced cross-sections allow a fairly precise reconstruction, which indicates that the Alboran Domain moved 250 km west between Africa and Iberia between 19 and 7 Ma. Prior to this, displacement estimates depend largely on the record of early Miocene crustal thinning, and pre-Miocene accretion and crustal thickening, in the Alboran Domain, both of which are poorly constrained. Progressive reconstructions of the Betic-Rif arc and Alboran Domain through time, with an estimate of the uncertainties, are presented, together with suggestions for the evolution of upper mantle structure during this history.

Platt, J. P.

2011-12-01

138

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

139

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

140

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

141

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

142

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

143

Progress in understanding the geodynamic and palaeoenvironmental evolution of the Tethys in the Lesser Caucasus  

NASA Astrophysics Data System (ADS)

The remnants of a Mesozoic oceanic realm exist in the Lesser Caucasus (mainly in Armenia and Karabagh); this realm was once part of the Tethyan oceanic branch positioned between Eurasia and the South-Armenian Block, a Gondwana-derived terrain that can be considered as part of the Tauride-Anatolide plate. The existing Tethyan rocks of Lesser Caucasus are part of an over 2,000 Km long suture zone, running through the northern part of Turkey towards Iran. Biostratigraphic studies of the aforementioned rocks contribute vastly to get a better understanding of the geodynamic, paleogeographic and paleoenvironmental evolution of this geologically complex area. When radiolarites are the sedimentary cover of submarine ophiolitic lavas their dating provides important time constraints for the evolution of the complex Mesozoic oceanic realm. In spite of extensive sampling during the last ten years across the Sevan-Hakari (Akera) suture zone and the Vedi ophiolite we found no Triassic or Lower Jurassic radiolarites. However, as testified by some previous studies, it is likely that oceanic floor spreading was initiated during the Late Triassic. Radiolarian biostratigraphic results we have obtained establish that radiolarian ooze accumulated, and it was occasionally interrupted by lava flows, during (at least) the Bajocian to Cenomanian time interval. The Bajocian is widely established (Vedi, Sevan and Hakari ophiolites), while we have recently obtained a Cenomanian radiolarian fauna from Amasia (NW Armenia). Two late Tithonian - Valanginian radiolarian assemblages, recovered from the NE of Lake Sevan (Dzknaged and Dali sections) are of particular significance, as radiolarites are intercalated with mafic rocks formed after episodes of submarine volcanic activity. The Dali basaltic sequence overlies (with a contact displaying cataclastic structures) layered dioritic cumulates with a few plagiogranites representing the crust of an intra-oceanic island arc. Both radiolarite sequences accumulated around the Jurassic/Cretaceous transition contain rounded blocks of oolitic grainstones with fragments of crinoids; they provide evidence for shallow water platform carbonates in the neighbourhood, fragments of which slid into a bathymetrically complex oceanic sea floor. New radiolarian ages obtained recently on numerous tuffites intercalated in siliceous sequences along the Amasia-Sevan zone (Amasia, Sarinar, Old Sodk pass sections) suggest that subaerial volcanic activity was underway for most of the Middle Jurassic to Lower Cretaceous (Bajocian/Bathonian to Albian). The Vedi area (SE of Yerevan) is important in many ways, especially because it allows the detailed study of the obduction of ophiolites to the South-Armenian carbonate sequence; the latter is overlain stratigraphically by a flysch that ends with an olistostome containing a large variety of ophiolite-derived blocks. Microfacies observation of the last 150 m of the carbonate sequence suggests a back-reef inner platform depositional environment, with the presence of benthic foraminifera characteristic of a Cenomanian age. Results from the Amasia ophiolite and the Vedi carbonate sequence point to a major geodynamic change that took place during the Cenomanian, involving both the late stage of submarine oceanic magmatic activity and the obduction of ophiolites onto the South-Armenian Block.

Danelian, Taniel; Asatryan, Gayané; Zambetakis-Lekkas, Alexandra; Galoyan, Ghazar; Sosson, Marc; Seyler, Monique; Sahakyan, Lilit; Grigoryan, Araiyk

2014-05-01

144

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

145

Crustal architecture and geodynamics of North Queensland, Australia: Insights from deep seismic reflection profiling  

NASA Astrophysics Data System (ADS)

A deep crustal seismic reflection and magnetotelluric survey, conducted in 2007, established the architecture and geodynamic framework of north Queensland, Australia. Results based on the interpretation of the deep seismic data include the discovery of a major, west-dipping, Paleoproterozoic (or older) crustal boundary, considered to be an ancient suture zone, separating relatively nonreflective, thick crust of the Mount Isa Province from thinner, two layered crust to the east. Farther to the east, a second major crustal boundary also dips west or southwest, offsetting the Moho and extending below it, and is interpreted as a fossil subduction zone. Across the region, the lower crust is mostly highly reflective and is subdivided into three mappable seismic provinces, but they have not been tracked to the surface. In the east, the Greenvale and Charters Towers Provinces, part of the Thomson Orogen, have been mapped on the surface as two discrete provinces, but the seismic interpretation raises the possibility that these two provinces are continuous in the subsurface, and also extend northwards to beneath the Hodgkinson Province, originally forming part of an extensive Neoproterozoic-Cambrian passive margin. Continuation of the Thomson Orogen at depth beneath the Hodgkinson and Broken River Provinces suggests that these provinces (which formed in an oceanic environment, possibly as an accretionary wedge at a convergent margin) have been thrust westwards onto the older continental passive margin. The Tasman Line, originally defined to represent the eastern limit of Precambrian rocks in Australia, has a complicated geometry in three dimensions, which is related to regional deformational events during the Paleozoic. Overall, the seismic data show evidence for a continental margin with a long history (Paleoproterozoic to early Mesozoic) but showing only limited outward growth by crustal accretion, because of a repeated history of overthrust shortening during repeated phases of orogenesis.

Korsch, R. J.; Huston, D. L.; Henderson, R. A.; Blewett, R. S.; Withnall, I. W.; Fergusson, C. L.; Collins, W. J.; Saygin, E.; Kositcin, N.; Meixner, A. J.; Chopping, R.; Henson, P. A.; Champion, D. C.; Hutton, L. J.; Wormald, R.; Holzschuh, J.; Costelloe, R. D.

2012-10-01

146

Geodynamic evolution of the central and western Mediterranean: Tectonics vs. igneous petrology constraints  

NASA Astrophysics Data System (ADS)

We present a geodynamic reconstruction of the Central-Western Mediterranean and neighboring areas during the last 50 Myr, including magmatological and tectonic observations. This area was interested by different styles of evolution and polarity of subduction zones influenced by the fragmented Mesozoic and Early Cenozoic paleogeography between Africa and Eurasia. Both oceanic and continental lithospheric plates were diachronously consumed along plate boundaries. The hinge of subducting slabs converged toward the upper plate in the double-vergent thick-skinned Alps-Betics and Dinarides, characterized by two slowly-subsiding foredeeps. The hinge diverged from the upper plate in the single-vergent thin-skinned Apennines-Maghrebides and Carpathians orogens, characterized by a single fast-subsiding foredeep. The retreating lithosphere deficit was compensated by asthenosphere upwelling and by the opening of several back-arc basins (the Ligurian-Provençal, Valencia Trough, Northern Algerian, Tyrrhenian and Pannonian basins). In our reconstruction, the W-directed Apennines-Maghrebides and Carpathians subductions nucleated along the retro-belt of the Alps and the Dinarides, respectively. The wide chemical composition of the igneous rocks emplaced during this tectonic evolution confirms a strong heterogeneity of the Mediterranean upper mantle and of the subducting plates. In the Apennine-Maghrebide and Carpathian systems the subduction-related igneous activity (mostly medium- to high-K calcalkaline melts) is commonly followed in time by mildly sodic alkaline and tholeiitic melts. The magmatic evolution of the Mediterranean area cannot be easily reconciled with simple magmatological models proposed for the Pacific subductions. This is most probably due to synchronous occurrence of several subduction zones that strongly perturbed the chemical composition of the upper mantle in the Mediterranean region and, above all, to the presence of ancient modifications related to past orogeneses. The classical approach of using the geochemical composition of igneous rocks to infer the coeval tectonic setting characteristics cannot be used in geologically complex systems like the Mediterranean area.

Carminati, Eugenio; Lustrino, Michele; Doglioni, Carlo

2012-12-01

147

Geodynamic and ionospheric disturbances during Kultuk earthquake (27 August 2008) in the southern Baikal region  

NASA Astrophysics Data System (ADS)

Coordinated investigations of geodynamic and ionospheric disturbances following the strong earthquake near the village Kultuk (the southern tip of Lake Baikal) were made by the Insti-tute of Solar-Terrestrial Physics, Institute of the Earth`s Crust, and Department of Physical Problems of the Buryat Scientific Center (Russian Academy of Sciences, Siberian Branch). The earthquake in Kultuk (27 August 2008, Mw=6.3) was the greatest seismic event ever registered within Baikal basin during the instrumental observation period. The normal fault displacement with a significant strike-slip component prevailed in the earthquake foci. To reveal deformation effects in the Earth`s crust related with coseismic and postseismic processes of this earthquake, we calculated characteristics of the velocity field of horizontal displacements and deformations in the southern Baikal region using GPS geodesy data. Measurement data before, right after and a year after the earthquake were compared. The earthquake focal mechanism was shown to correspond completely to the stress condition before the earthquake. Measurements made right after the earthquake did not reveal changes in velocity fields of displacements and defor-mations. Presence of relaxation deformations for a year after the earthquake was revealed near the epicenter. High-precision GPS measurements during the earthquake revealed changes on the long baselines (Ulan-Ude -Irkutsk and Ulan-Ude -Listvyanka). Deviations on the baseline lengths after the earthquake reached 125 mm and 150 mm, respectively. The baselines regained the initial level by midday of 28 August 2008. Ionospheric responses to the main shock and aftershocks of the Kultuk earthquake were investigated using GPS sounding data. The work was supported by the SB RAS interdisciplinary collaboration project No. 56.

Perevalova, Natalia; Zherebtsov, Gelii; Sankov, Vladimir; Loukhnev, Andrey; Bashkuev, Yury; Dembelov, Mikhail; Ashurkov, Sergey; Voeykov, Sergey; Yasyukevich, Yury; Kurkin, Vladimir; Astafyeva, Elvira

148

Seismicity and geodynamics in the central part of the Vanuatu Arc  

NASA Astrophysics Data System (ADS)

The Vanuatu Arc (VA) in the southwest Pacific ocean (167°E, 13-20°S), is highly seismically active, with more than 35 events of magnitude Mw ? 7 since 1973 (USGS catalog). The geodynamics are dominated by the east-dipping subduction of the Australian Plate under the North Fiji Basin microplate. Convergence rates are estimated to be between 130 and 170 mm/yr, except in the central part of the VA where convergence slows to 30-40 mm/yr. This slowing appears to be the result of blockage by the subducting d'Entrecastaux ridge. To quantify the tectonics of this blocked section, we deployed 30 seismometers in 2008-2009 and 8 GPS stations since 2008, in the forearc region of the central VA. The seismometers recorded more than 100 events/day. Detailed analysis of the earthquake catalog reveals: 1) a seismic gap between 40 and 60 km deep under the two largest islands of the VA (Santo and Malekula); 2) subduction plane and intraplate faulting within the down-going plate; and 3) reduced activity beneath Malekula island , perhaps indicating a locked patch on the subduction plane. We infer the geometry of the subduction interface by combining our catalog with unpublished data from the 2000 Santo Mw 6.9 earthquake and aftershocks and the USGS and Global CMT catalogs. The subduction interface appears to be composed of two different panels: a shallow one with a small dip angle and a deeper one with higher dip starting at a depth of ~50 km. We compare finite-element modeling of these panels to the geodetic data to test the connectedness of the two panels and their degree of locking.

Baillard, C.; Crawford, W. C.; Ballu, V.; Regnier, M. M.; Pelletier, B.; Garaebiti, E.

2013-12-01

149

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

150

Seismicity of mid-oceanic ridges and its geodynamic implications: a review [review article  

NASA Astrophysics Data System (ADS)

The global system of mid-oceanic ridges (MOR) is one of the longest active seismic belts where most of the earthquake epicenters are located continuously within a narrow axial zone. We summarized the principal results of the studies in MOR seismicity and their implications for geodynamics. The studies of epicenter distribution along the ridges and of focal mechanisms make an important contribution to the development of plate tectonics. During recent decades, a great amount of information on MOR structure and sea-floor spreading has become available. Geological and geophysical observations revealed a partitioning of the ridge by numerous discontinuities of several orders, which is reflected in the seismicity. There is a clear difference in seismic regime between two kinds of first-order segments—transform faults and spreading centers. The first have seismic moment release one-two orders higher; their contribution into the total seismic budget of MOR increases with higher spreading rate. The relationships between the seismic moment release, fault length and spreading rate are quite different for transform and rift parts of MOR; this confirms the difference in the geometry of their respective earthquake source volumes. In both these cases, the principal factor controlling the ridge seismicity is the thermal structure of the lithosphere. Microseismic experiments using ocean bottom seismometers, hydrophones and sonobuoys have perceptibly reduced the cutoff magnitude of complete reporting and the location uncertainty. Large numbers of microearthquakes are usually recorded almost everywhere near the ridge axis, even during relatively short recording times. More detailed location of epicenters and focal depths acquired great significance in the studies of magmatism, hydrothermal circulation and fracturing on MOR. Some spatial relationships seem to emerge between epicenter distribution and the location of hydrothermal sulfide deposits along the MOR. Several hierarchical levels could be distinguished; the nature of the relationship depends on the level of interest.

Rundquist, D. V.; Sobolev, P. O.

2002-07-01

151

Geodynamic Constraints on the Flow of Samoan-Plume Mantle Into the Northern Lau Basin  

NASA Astrophysics Data System (ADS)

The northernmost portion of the Lau Basin features numerous geochemical and geophysical anomalies. These include a strong north-to-south gradient in the trace element and isotopic (Sr-Nd-Pb) enrichment of basalts erupted along the various back-arc spreading centers (BASCs) within the basin, high 3He/4He (up to 28 times Ra, the ratio in Earth's atmosphere) in basalts erupted along some portions of the BASCs (e.g., Rochambeau Bank), and the presence of trench parallel shear wave splitting near the Tonga arc. The presence of these anomalies has been attributed to the southward flow of material from the nearby Samoan hotspot into the northern Lau Basin. Here, we present results from a series of numerical geodynamic experiments undertaken to test the viability of this hypothesis and to constrain both the total extent and the spatial distribution of any incursion of Samoan mantle into the Lau Basin. Numerical experiments were conducted using the COMSOL Multiphysics Finite Element Modeling package to model mantle flow and melting within a 2-dimensional model domain corresponding to a north-south cross-section through the upper 400 km of the mantle and extending from the Pacific plate north of the Vitiaz Lineament through the northern Lau Basin. Experiments indicate that, if it is hotter than ambient mantle, southward-flowing Samoan mantle would experience extensive melting due to adiabatic decompression as it moves from beneath older, thicker Pacific lithosphere to the younger, thinner lithosphere of the Lau Basin south of the Vitiaz Lineament. Experimental predictions of melt production are compared to bathymetric data from the northern Lau Basin to constrain both the physical characteristics (e.g., temperature) and spatial distribution of the flow of Samoan mantle into the Lau Basin.

Katsiaficas, N. J.; Hall, P. S.; Jackson, M. G.

2011-12-01

152

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

NASA Astrophysics Data System (ADS)

A gravimeter calibration facility exists in the Mátyáshegy 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, Márta; Koppán, Andras; Kovács, Péter; Merényi, László

2014-05-01

153

Retrieving past geodynamic events by unlocking rock archives with ?-XRF and ?-spectroscopy  

NASA Astrophysics Data System (ADS)

Rocks are commonly polycrystalline systems presenting multi-scale chemical and structural heterogeneities inherited from crystallization processes or successive metamorphic events. This work illustrates how spatially resolved analytical techniques coupled with thermodynamic approaches allow rock compositional variations to be related to large-scale geodynamic processes. Emphasis is placed on the contribution of quantitative chemical imaging to the study of 2.2-2.0 Gy old metamorphic rocks from the West African Craton. A thorough analysis of elemental chemical maps acquired on rock thin sections enabled high pressure relic minerals to be located and re-analyzed later with precise point analyses. The pressure-temperature conditions of crystallization calculated from these analyses are typical of modern subduction zones. These results push back the onset of modern-style plate tectonics to 2.15 Gy, i.e. more than one billion years earlier than was consensually accepted. The second part of the paper describes the imaging capabilities offered by the new ultra-bright diffraction limited synchrotron sources. Experimental data acquired with the Maia detector at beamline P06 at Petra III as well as simulations of ?-XRF spectra that will be generated at the SRX beamline at NSLS-II are presented. These results demonstrate that cm2 large chemical maps can be acquired with submicron spatial resolution and a precision suitable for thermobarometric estimates, with dwell time smaller than 1 millisecond. The last part of the paper discusses the relevance of utilizing recent X-ray fluorescence nanoprobes for diagenetic to low grade metamorphism applications.

De Andrade, V.; Ganne, J.; Dubacq, B.; Ryan, C. G.; Bourdelle, F.; Plunder, A.; Falkenberg, G.; Thieme, J.

2014-04-01

154

On principles, methods and recent advances in studies towards a GPS-based control system for geodesy and geodynamics  

NASA Technical Reports Server (NTRS)

Although Very Long Baseline Interferometry (VLBI) and Satellite Laser Ranging (SLR) are becoming increasingly important tools for geodynamic studies, their future role may well be fulfilled by using alternative techniques such as those utilizing the signals from the Global Positioning System (GPS). GPS, without the full implementation of the system, already offers a favorable combination of cost and accuracy and has consistently demonstrated the capability to provide high precision densification control in the regional and local areas of the VLBI and SLR networks. This report reviews VLBI and SLR vis-a-vis GPS and outlines the capabilities and limitations of each technique and how their complementary application can be of benefit to geodetic and geodynamic operations. It demonstrates, albeit with a limited data set, that dual-frequency GPS observations and interferometric type analysis techniques make possible the modelling of the GPS orbits for several days with an accuracy of a few meters. The use of VLBI or SLR sites as fiducial stations together with refinements in the orbit determination procedures can greatly reduce the systematic errors in the GPS satellite orbits used to compute the positions of non-fiducial locations. In general, repeatability and comparison with VLBI of the GPS determined locations are of the order of between 2 parts in 10 to the 7th power and 5 parts in 10 to the 8th power for baseline lengths less than 2000 km. This report is mainly a synthesis of problems, assumptions, methods and recent advances in the studies towards the establishment of a GPS-based system for geodesy and geodynamics and is one phase in the continuing effort for the development of such a system. To some, including the author, it seems reasonable to expect within the next few years that more evidence will show GPS to be as a powerful and reliable a tool as mobile VLBI and SLR are today, but largely more economical.

Delikaraoglou, Demitris

1989-01-01

155

Tectono-sedimentary evolution of the Tertiary Piedmont Basin (NW Italy) within the Oligo-Miocene central Mediterranean geodynamics  

NASA Astrophysics Data System (ADS)

analyze the tectono-sedimentary and thermochronometric constraints of the Tertiary Piedmont Basin (TPB) and its adjoining orogen, the Ligurian Alps, providing new insights on the basin evolution in response to a changing geodynamic setting. The geometry of the post-metamorphic faults of the Ligurian belt as well as the fault network that controlled the Oligo-Miocene TPB deposition has been characterized through a detailed structural analysis. Three main faulting stages have been distinguished and dated thanks to the relationships among faults and basin stratigraphy and thermochronometric data. The first stage (F1, Rupelian-Early Chattian) is related to the development of extensional NNW-directed faults, which controlled the exhumation of the orogen and the deposition of nearshore clastics. During the Late Chattian, the basin drowning is marked by mudstones and turbidites, which deposition was influenced by the second faulting stage (F2). This phase was mainly characterized by NE- to ENE-striking faults developed within a transtensional zone. Since the Miocene, the whole area was dominated by transpressive tectonics. The sedimentation was represented by a condensed succession followed by a very thick, turbiditic complex. At the regional scale, this succession of events reflects the major geodynamic reorganization in the central Mediterranean region during the Oligo-Miocene times, induced by the late-collisional processes of the Alps, by the eastward migration of the Apennines subduction and by the opening of extensional basins (i. e., the Liguro-Provençal Ocean).

Maino, Matteo; Decarlis, Alessandro; Felletti, Fabrizio; Seno, Silvio

2013-06-01

156

Transformation of Tidal Deformations into Geodynamic Processes and Fractal Rheology of the Earth's Substance  

NASA Astrophysics Data System (ADS)

The kinematics and dynamics of a binary "Earth-Moon" planet system have been studied with respect to the rotational motion of the Earth and Moon about the barycenter of the system, situated at a distance of 4641 km from the center of the Earth. The Earth's orbital motion, rotation and tidal deformations have a significant influence on the geodynamic processes, generation and support of the magnetic field, and climate changes of the planet. It has been shown that the tidal force causes displacements of the inner core; the corresponding gravitational effect on the Earth's surface has been evaluated (Avsyuk, 2001; Avsyuk, Suvorova, 2006). To explain these correlations, a number of mechanisms of transformations of radial tidal deformations into lateral displacements of the Earth's substance have been considered. In addition, three rheological models were taken to model tidal deformations: viscous, granular, and a fractal model based on Zener's standard rheological element. Mathematical modeling of tidal deformations for different rheologies of the substances of Earth demonstrated that the radial planetary tides are being transformed into lateral motion of planetary layers. Evaluation of the rate of lateral motion shows that this mechanism can be responsible for the westward drift of the lithosphere. The rate of lateral motion of planetary layers depends on the magnitude of the rate of radial tidal deformations, k(r). Mathematical modeling of tidal deformations for different distributions k(r) showed that the radial variation of this coefficient produces differential motion of deep planetary layers resulting in internal frictional heating of deep layers which can raise temperatures at given depths to the melting point of this material (Maslov, Anokhin, 2007; Maslov, 2007). This melting can be one of the factors influencing and amplifying the Earth's magnetic field. It is shown that the rate and energy of differential lateral motion of material in the core are enough to generate and support Earth's magnetic field. Experimental modeling (Revuzhenko, 2006) of tidal deformations in granular substance is in good agreement with the results of mathematical modeling.

Maslov, L. A.; Avsyuk, Y. N.

2008-12-01

157

The Three-dimensional Geodynamic Model of The Pechenga Ore District (baltic Shield, Russia)  

NASA Astrophysics Data System (ADS)

The drilling and investigation of the Kola superdeep borehole SG-3 for the first time provided direct data on the structure and composition of the ancient continental crust at previously inaccessible depths. They stimulated the elaboration of alternative three- dimensional models of the Pechenga ore district equally. These models consider the Pechenga structure that hosts large sulfide copper-nickel deposits as a graben-syncline, asymmetrical syncline, explosive volcanic center, and two-continent collision suture zone. The paper comprises the reappraisal of the alternative models and the charac- teristics of an integrated three-dimensional geodynamic model of the Pechenga ore district. Rock density and their anisotropy in elastic properties were used as the main parameters for the formalized description of the borehole SG-3 section and the refer- ence profile on the day surface. The first parameter reflects the rocks' lithology, the second accounts for the intensity of synmetamorphic tectonic deformations. In addi- tion, new age datings and morphology of the gravity field of the Pechenga district were considered. The computer-based technology insured reappraisal of the alterna- tive models by comparison of observed and calculated gravity profiles going through the borehole SG-3. The constraints of the proposed integrated model are based both on the investigations of the borehole SG-3 and on the additional surface studies. The model regards the Pechenga ore district as a horizontal section of a mantle-derived volcano-plutonic ore-forming system of the central type. The model defines the north- ern limb of the Pechenga structure as an imbricated fragment of a volcanic caldera and describes its southern limb as a combination of a sheeted monocline in a jux- taposition with rheomorphic granitoid domes. Development of the system was pre- ceded by rifting of the consolidated sialic crust. The model implies a co-genetic re- lationship between the Early Proterozoic basaltoid volcanism and the nickel-bearing basic-ultramafic plutonism. The basic and younger intermediate volcanic rocks filled two volcano-tectonic depressions associated with a thick zone of northwestern faults. Later on, the volcano-tectonic depressions experienced intense compression and meta- morphism that influenced the basement rocks, too. Finally, steep-dipping zones of cataclasis and retrograde metamorphism originated in an extension environment. The integrated model entails a new interpretation of localization conditions of the sulfide copper-nickel deposits and helps to understand the position of the Pechenga ore dis- 1 trict in the Pechenga-Imandra-Varzuga suture zone. This study was supported by the RFBR (projects nos. 01-05-64294, 01-05-64295). 2

Lobanov, K.; Kazansky, V.

158

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

159

Self-organized geodynamics of karst limestone landscapes and coupled terra rossa/bauxite formation  

NASA Astrophysics Data System (ADS)

Why do flat limestones overlain by terra rossa or bauxite systematically adopt so-called karst geomorphology, which consists of sets of roughly regularly spaced wormholes, or funnels, or sinkholes, or tower karst? The idea that the funnels and sinkholes are located at the intersections of preexisting sets of subvertical fractures is untenable. New field and petrographic evidence (Merino & Banerjee, J. Geology, 2008) revealed that, rather than 'residual' or 'detrital' (the only options that have been on the table for decades), the terra rossa/bauxite clays and Al- and Fe-oxyhydroxides grow authigenically at the base of the terra rossa, replacing the underlying limestone at a generally downward-moving reaction front several centimeters thick. The clay-for-limestone replacement, which preserves solid volume (because it takes place by clay-growth-driven pressure solution of calcite), releases H+ ions. These dissolve more calcite, generating considerable leached porosity in a narrow zone that travels with the replacement front. We proposed (Merino & Banerjee, J. Geology, 2008) that the moving leached-porosity maximum created at the front could trigger the reactive-infiltration instability (Chadam et al, IMA J. Appl. Math., 1986), causing the replacement-and-leaching reaction front to become regularly fingered, with the fingers jumping in scale to funnels, these to sinks, and these, when deep enough and merged together laterally, to tower karst. This new geodynamics would account both for the world-wide association of terra rossa and bauxite with karst limestones, and for the stunning, self-organized geomorphology of karst itself. We are testing these ideas through linear stability analysis of a simplified reaction-transport system of equations and through numerical solution of the full non-linear system of reaction-transport equations applicable, including aqueous speciation. Preliminary calculations (Banerjee & Merino, J. Geology, 2011) suggest that the replacement-and-leaching front is self-accelerating. The linear stability analysis may help to delineate climatic and hydrologic conditions for the development of spatial patterns of karst landscape and to predict the spacing of the patterns.

Merino, E.; Wang, Y.; Banerjee, A.

2012-12-01

160

Neoproterozoic/Lower Palaeozoic geodynamic evolution of Dronning Maud Land: integrating geology and geophysics  

NASA Astrophysics Data System (ADS)

East Antarctica probably formed by amalgamation of a number of cratons along distinct Ediacaran mobile belts, including the ca. 600-500 Ma East African-Antarctic Orogen (EAAO) that dissects Dronning Maud Land (DML). New field-work during the international expeditions Geodynamic Evolution of East Antarctica (GEA) I + II in the austral summers 2010/11 and 2011/12, and first geochronological results from eastern DML reveal a complex tectonic architecture across the belt. In western DML, the EAAO reworks older Mesoproterozoic crust of the Maud Belt; the westernmost boundary of the mobile belt is characterized by a major dextral transpressional shear zone. In central DML, a major magnetic anomaly, the Forster anomaly, was interpreted as a cryptic suture of the EAAO (Riedel et al. 2012). The area where the Forster anomaly crosses the DML mountains is poorly investigated so far, but appears to coincide with a major strike slip shear zone in the southern Kurze Mts. and the occurrence of major Ediacaran granulite bodies. East of the Forster anomaly, the magnetic anomaly pattern changes significantly and typical Maud type crust is not present any longer. GEA II targeted a range of nunataks between Sør Rondane and central DML that had never been visited previously (from Blåklettane and Bergekongen in the E to Urna and Sørsteinen in the W). These nunataks are dominated by medium- to high-grade metasedimentary and metavolcanic rocks of possibly Neoproterozoic age, including abundant marble and graphite schists. Sør Rondane in eastern DML, is dominated by two distinct blocks separated by the dextral Main Shear Zone. The northwestern block is still part of the eastern EAAO, where new SHRIMP zircon data from metamorphic rims provide ages of ca. 560 Ma. The southeastern block is made up of a TTG terrane, which provides four new SHRIMP zircon dates between 990-980 Ma, interpreted as igneous crystallization ages (oceanic arc). The TTG terrane shows limited tectonic overprint and is likely the southeastern foreland of the EAAO. Close to the contact of the two blocks grey geisses and augen-gneisses gave zircon crystallization ages of ca. 750 Ma, ages which were previously unknown from the EAAO. The Forster anomaly therefore separates distinctly different parts of the EAAO: a) a reworked, mainly Grenville-age crust to the W (the overprinted margin of the Kalahari Craton) and b) a part of the orogen dominated by Neoproterozoic accretionary tectonics to the E. This difference is also reflected in the geochemistry of voluminous late-tectonics granitoids across the belt. Riedel, S. et al., 2012, Tectonophysics, doi.org/10.1016/j.tecto.2012.10.011

Jacobs, Joachim; Andreas, Läufer; Clark, Chris; Kleinhanns, Ilka; Elburg, Marlina; Ruppel, Antonia; Estrada, Solveig; Damaske, Detlef; Jokat, Wilfried; Riedel, Sven; Lucka, Nicole

2013-04-01

161

The geodynamic evolution of the Alps: what can we learn further from the metasediments  

NASA Astrophysics Data System (ADS)

Based on mineralogical works, Ernst (1971) was able to use the plate tectonic concept for proposing a first modern model for the evolution of the Alps. In the meantime, Frey (1969), as well as Trommsdorff (1966), started to investigate metamorphism in isochemical systems provided by shales and siliceous carbonates, respectively. This allowed for quantitatively constraining the Cenozoic temperature evolution in the Central Alps. Frey et al. (1999) compiled all available information on the peak temperature distribution, and used the occurrence of eclogites to display the dynamics of the Alpine evolution. The regional distribution of late Cretaceous-Tertiary metamorphic conditions, documented in post-Hercynian metasediments across the entire Alpine belt from Corsica-Tuscany in the West to Vienna in the East, will be presented. Based on metamorphic studies in metasediments, we evidence substantial differences in the metamorphic, and hence the geodynamical evolution along strike the Alpine orogen. The Western Alps did not reach the mature stage of a head-on colliding belt as is indicated by a continuous metamorphic evolution, representing all the subduction related processes ranging from lower greenschist to UHP conditions. All the metamorphic rocks behind the Pennine frontal thrust were already exhumed to upper crustal level during ongoing oceanic and continental subduction and before collision with the Dauphinois domain from around 32 Ma onwards. Hence, the Western Alps represent a frozen-in subduction zone. Since then only exhumation by erosional processes affected the inner parts of the orogen. The rest of the Alpine orogen later underwent a more important collision process due to the ongoing head-on geometry of subduction and collision. It therefore often but not always shows a bimodal metamorphic evolution with two distinct P and T peaks. The intensity of the thermal overprint relates to the amount of crustal material incorporated to the orogenic wedge. Thermal overprint is primarily related to the amount of crust involved in the subduction and collision processes rather than to processes of shear or viscous heating. The latter mechanism, which suppose high deformation rate will not allow for the preservation of HP-LT assemblages within high-grade rocks. The relation between the volume of continental crust imbricated and intensity of high-temperature orogenic metamorphism can be generalized over the entire alpine edifice, except for Tuscany where the late (< 8 Ma) thermal overprint is clearly related to lithospheric thinning.

Bousquet, R.; Oberhänsli, R.; Wiederkehr(1), M.; Schuster, R.; Schmid(2), S. M.; Koller, F.; Goffé, B.

2009-04-01

162

gLucifer: Next-generation visualization framework for high-perfomance computational geodynamic models  

NASA Astrophysics Data System (ADS)

High performance computing provides unprecedented capabilities to produce higher resolution 4-D models in a fraction of the time. Thus, the need exists for a new generation of visualization systems able to maintain parity with the enormous volume of data generated from state-of-the-art numerical models. However, this volume of data is too large to be written to disk, even if only temporarily, as it introduces a significant performance bottleneck and therefore requires an innovation to circumvene the assumption that most existing visualization software make at a quite fundamental level, which is that model data is input from a dump file. This issue, in conjunction with the fact that available packages do not scale well for plotting very large numbers of specialized particles, necessitates the creation of a new visualization system that meets the needs of large-scale geodynamic modeling. We have successfully developed such a system, gLucifer, using a software framework approach that allows efficient re-use of our efforts in other areas of research. gLucifer is capable of producing movies of a 4-D data set ``on the fly'' (simultaneously with running the parallel scientific application) and sampled at the finest spatial and temporal scales (the highest resolution every timestep), without creating a performance bottleneck. By eliminating most of the human effort involved in visualizing results through post-processing, gLucifer reconnects the scientist to the numerical experiment as it unfolds in real time. gLucifer further provides a novel type of interactivity, termed iterative visualization, that exploits the ever-increasing availability of computational resources. Through the use of multiple windows with multiple viewports, generating custom fields ``on the fly'' with variables and operators, and fully distributed rendering and scene compositing, data sets that were previously very difficult to even manage may be efficiently explored and interrogated. Future developments include the ability to post-process fully rendered movies and harness the potential of remote visualization enabled with grid computing.

Duboz, C.; Stegman, D.; Moresi, L.; Turnbull, R.; Lo, A.; Quenette, S.

2005-12-01

163

Gradient Recovery Methods for Improved Stresses and Strain Rates in Geodynamic Models  

NASA Astrophysics Data System (ADS)

Deformation of the lithosphere is characterized by strongly non-linear constitutive laws which produce strong localization in response to tectonic stresses. In geodynamics models the structures developed during localizaton may be represented by discontinuous means such as crack or fault models, or as very fine shear bands. However, in each case, the orientation of the fabric and the evolving damage is controlled by the modelled stress and strain rate fields. In order to ensure the evolution is well resolved and not dominated by numerical artifacts, it is essential to compute accurate stresses, pressures and strain-rates. The same issue arises in models where strong shear heating is present as this is computed throughout the domain as the product of local stress and strain rates. In standard Finite Element Methods, limitations in accuracy exist as the stress and strain-rate are not primary variables and are typically discontinuous across element boundaries. Several recovery methods can be employed to recreate a continuous field with a rate of convergence (with mesh refinement) equivalent to that for to the primary variables. For hybrid FE Methods, not all of these recovery schemes are possible. We have made extensive use of a Finite Element method combined with a Lagrangian Integration Points, (FELIP) (L. Mores et al 2003) which is very well suited to describing strain-dependent localization in highly deforming media. Here we discuss methods for obtaining highly convergent stresses and strain rates for FE methods where standard superconvergent patch methods cannot be applied. We have found that the best post-processing recovery methods, considering computational cost, element type and precision, are Superconvergent Patch Recovery (O. C. Zienkiewicz, J. Z. Zhu 1992) which is only suitable for elements with superconvergent points and Recovery By Equilibrium in Patches (REP --- B. Boroomand O.C Zienkiewicz 1997) which is suitable for all element types and quantities. Results using the above methods, will be discussed when applying them to geological applications as well as analytic solutions, comparing time taken, memory used and accuracy of the recovered variables.

Sharples, W. K.; Moresi, L. N.; May, D. A.; Giordani, J.; Lemiale, V.

2006-12-01

164

Geodynamic evolution of eastern Dronning Maud Land: research highlights from an international geological-geophysical approach  

NASA Astrophysics Data System (ADS)

East Antarctica formed by amalgamation of a number of cratons along distinct Ediacaran mobile belts, including the ca. 600-500 Ma East African-Antarctic Orogen (EAAO) and the Kuunga Orogen that apparently converge in Dronning Maud Land (DML). In central DML, the major Forster Magnetic Anomaly separates rocks with Grenville-age protolith ages of ca. 1130-1000 Ma to the W, from rocks with Early Neoproterozic protolith ages, c. 1000-930 Ma, to the East. The Forster Magnetic Anomaly is therefore interpreted as a suture. New field-work during two recent international expeditions, Geodynamic Evolution of East Antarctica (GEA) I + II, and first geoscientic results reveal a complex tectonic architecture between Sør Rondane and central DML. East of the Forster anomaly, the magnetic anomaly pattern changes significantly and typical Maud type crust is not present any longer. GEA II targeted a range of nunataks between Sør Rondane and central DML that had never been visited previously (from Blåklettane and Bergekongen in the E to Urna and Sørsteinen in the W). These nunataks are dominated by medium- to high-grade metasedimentary and metavolcanic rocks of possibly Neoproterozoic age, including abundant marble and graphite schists. Sør Rondane in eastern DML, is dominated by two distinct blocks separated by the dextral Main Shear Zone. The northwestern block appears as part of the EAAO or the Kuunga Orogen, where new SHRIMP zircon data from metamorphic rims provide ages of ca. 560 Ma. The southeastern block is made up of a TTG terrane, which provides 12 new zircon crystallistation ages ranging from 1000-930 Ma. The TTG terrane has predominantly oceanic affinities and the wide range of ages might indicate long-lasting accretionary tectonics. The TTG terrane shows in part limited tectonic overprint and could be the southeastern foreland of the EAAO or the Kuunga Orogen. Close to the contact of the two blocks, grey geisses and augen-gneisses gave zircon crystallization ages of ca. 750 Ma, ages which were previously unknown from the EAAO. The Forster anomaly therefore separates distinctly different parts of the EAAO: a) a reworked, mainly Grenville-age crust to the W (the overprinted margin of the Kalahari Craton) and b) a part of the orogen dominated by Neoproterozoic accretionary tectonics to the E. This difference is also reflected in the geochemistry of voluminous late-tectonics granitoids across the belt.

Jacobs, Joachim; Ehlburg, Marlina; Laeufer, Andreas; Clark, Chris; Kleinhanns, Ilka; Andersen, Tom; Mieth, Matthias; Ruppel, Antonia; Damaske, Detlef; Lucka, Nicole; Estrada, Solveig; Jokat, Wilfried

2014-05-01

165

Stratigraphic signatures of crustal shortening and central Andean geodynamics in the Altiplano plateau, southern Peru  

NASA Astrophysics Data System (ADS)

The initiation and evolution of hinterland basins along convergent margins has been variably attributed to partitioning of pre-existing flexural foreland basins, drainage closure by uplift of flanking topographic barriers, and/or isolated strike-slip or extensional processes. In the central Andean plateau, the upper Oligocene to middle Miocene basin fill of the northernmost Altiplano in southern Peru preserves a record of orogenesis between the Western Cordillera magmatic arc and the Eastern Cordillera fold-thrust belt. New stratigraphic, provenance, geochronologic and structural datasets from the ~3.7-km-high Ayaviri hinterland basin suggest that upper-crustal shortening was the dominant factor controlling basin evolution. The basin preserves a ~2300 m thick succession (Puno Group and Lower Tinajani Formation) of fluvial sandstone and overbank siltstone capped abruptly by ~400 m of alluvial fan pebble-boulder conglomerate (Upper Tinajani Formation). New U-Pb zircon geochronologic constraints from 8 tuff horizons and the youngest age populations from 10 sandstone horizons constrain the depositional age between 29.6 ± 1.2 Ma and 15.71 ± 0.97 Ma. The resulting ~15 Myr basin record yields sediment accumulation rates between 110 and 660 m/Myr, comparable to those of major lowland foreland basins. A prominent shift in basin provenance is recorded by detrital zircon U-Pb spectra, conglomerate clast compositions, modal sandstone compositions and paleocurrent data. Newly dated growth strata along the two basin-bounding thrust faults highlight the role of Andean shortening on basin evolution. Footwall growth strata along the southwest-directed Ayaviri fault defining the Eastern Cordillera margin suggests deformation at ~28 Ma. Younger footwall growth strata along the northeast-directed Pasani fault defining the Western Cordillera margin demonstrate an episode of out-of-sequence thrusting at ~16.4 Ma. This event is associated with the provenance and depositional shift of the coarse-grained Upper Tinajani Formation. Oligocene to early Miocene basin evolution was controlled by flexural subsidence driven by shortening along the Ayaviri fault and broader Eastern Cordillera. Subsequent basin reorganization was initiated by punctuated out-of-sequence motion along the southwest basin margin (Pasani fault). The record of variable, punctuated shortening and subsidence emphasizes the role of upper-crustal thrusting in driving hinterland tectonics. However, it remains unclear if out-of-sequence thrusting in the northern Altiplano was a localized deformation event indicative of critical wedge dynamics, changing magmatic-arc processes, or a geodynamic response to complex patterns of lithospheric removal and pulses of surface uplift.

Perez, Nicholas D.; Horton, Brian K.

2014-05-01

166

Geodynamic Models of the Active Continental Margins of the Sea of Okhotsk  

NASA Astrophysics Data System (ADS)

The deep structure models of the lithosphere on the Okhotsk Sea Region and the region of Neftegorsk earthquake which has occurred on May 28, 1995 in the northern part of Sakhalin, caused victims and destructions are examined. The geodynamic model shows that North Sakhalin consists of the North Sakhalin basin, the Deryugin basin and the ophiolite complex located between them. The Deryugin basin was formed in position of an ancient deep trench after subducting the Okhotsk Sea Plate under Sakhalin in Late Cretaceous-Paleogene. The North Sakhalin basin was formed on a place of back-arc basin at that time. The ophiolite complex combined by the ultrabasic rocks, fixes position of ancient subduction zone acting about 100-60 million years ago. It is probably that the Deryugin basin and the North Sakhalin basin have been formed in the following way. Approximately 100 million years ago, the oceanic lithosphere of the Sea of Okhotsk subsided under Sakhalin, the eastern part of which was an andesite island arc. Behind it, in western Sakhalin there was a basin where sandy - clayey deposits accumulated in the Late Cretaceous, which subsequently formed the basement of Cenozoic North Sakhalin oil and gas basin. Approximately 10 - 15 million years ago subduction of the lithosphere of the Sea of Okhotsk apparently ceased. The remains of subduction zone, in the form of an ophiolite complex were revealed by geological and geophysical data. On a surface the subduction zone is shown as deep faults stretched along Sakhalin. It is probable that the manifestation of the Neftegorsk earthquake was a result of activization of this ancient subduction zone. As a result of mobile components along ancient subduction zone under Sakhalin, considerable displacements in earth crust along numerous faults and deformation of an earth surface go on. 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. The work was supported by Russian Foundation for Basic Research. No: 09-05-00406-a

Rodnikov, Alexander; Sergeyeva, Natalia; Zabarinskaya, Ludmila

2010-05-01

167

Factors that control the angle of shear bands in geodynamic numerical models of brittle deformation  

NASA Astrophysics Data System (ADS)

Numerical models of brittle deformation on geological timescales typically use a pressure-dependent (Mohr-Coulomb or Drucker-Prager) plastic flow law to simulate plastic failure. Despite its widespread usage in geodynamic models of lithospheric deformation, however, certain aspects of such plasticity models remain poorly understood. One of the most prominent questions in this respect is: what are the factors that control the angle of the resulting shear bands? Recent theoretical work suggest that both Roscoe (45°), Coulomb angles (45 +/- ?/2, where ? is the angle of internal friction) and Arthur angles (45° +/- ( ? + ?/4) where ? is the dilation angle), as well as all intermediate angles are possible. Published numerical models, however, show a large range of shear band angles with some codes favoring Arthur angles, whereas others yield Coulomb angles. In order to understand what causes the differences between the various numerical models, here I perform systematic numerical simulations of shear localization around an inclusion of given length scale. Both numerical (element type), geometrical and rheological (viscoplastic versus viscoelastoplastic) effects are studied. Results indicate that the main factor, controlling shear band angle, is the non-dimensional ratio between the length scale of the heterogeneity d and the size of the numerical mesh ?x. Coulomb angles are observed only in cases where the inclusion is resolved well ( d/ ?x > 5-10), and in which it is located sufficiently far from the boundary of the box. In most other cases, either Arthur or Roscoe orientations are observed. If heterogeneities are one element in size, Coulomb angles are thus unlikely to develop irrespective of the employed numerical resolution. Whereas differences in element types and rheology do have consequences for the maximum obtainable strain rates inside the shear bands, they only have a minor effect on shear band angles. Shear bands, initiated from random noise or from interactions of shear bands with model boundaries or other shear bands, result in stress heterogeneities with dimensionless length scales d/?x ~ 1-2. Such shear bands are thus expected to form Roscoe or Arthur orientations, consistent with the findings in previous numerical models.

Kaus, Boris J. P.

2010-03-01

168

Paleogene retroarc flexural basin beneath the Neogene Pannonian Basin: A geodynamic model  

NASA Astrophysics Data System (ADS)

The Neogene (Middle Miocene-Recent) Pannonian Basin is superimposed on an earlier Paleogene (Middle Eocene-Early Miocene) basin complex as a result of back-arc extension. Although the stratigraphy of the latter is very well known due to raw material exploration, its formation and structural evolution is much less understood. A transtensional origin was generally proposed for the Paleogene Basin of Hungary, assuming an origin analogous to that of the overlying Neogene Pannonian Basin. We suggest an alternative geodynamic scenario for the development of the Paleogene basin complex, as we think that the observations are better understood in terms of a retroarc foredeep basin model. According to this, a flexural basin developed south of the backthrust inner West Carpathian units. The thrust load resulted in a generally deep, underfilled "flysch" basin during Middle Eocene-Early Oligocene times. In the Late Oligocene-Early Miocene predominantly shallow marine and continental deposition occurred indicating the gradual cessation of thrusting in the adjacent thrust-fold belt and the beginning of "molasse" sedimentation. Throughout the whole Paleogene, a shift can be observed of the bathyal, dominantly siliciclastic (in the axis of the foredeep) and neritic, partly carbonate (in the foreland flank of the foredeep) facies belts. This migration of the Middle Eocene-Early Miocene depocenters of the HPB (Hungarian Paleogene Basin) to the east-northeast in present-day coordinates is the result of two processes: (1) the advancement of backthrusting to the southeast; (2) along-strike shift of thrusting to the northeast. While a thin-skinned thrust front can be reconstructed for the Late Eocene (Buda Anticline), the Diósjenö-Hurbanovo line is interpreted as the result of a major thick-skinned thrusting event at the base of the NP24 zone ( $˜31 Ma). The subsidence pattern, the distinct depositional environments and the structural observations can be more easily integrated into a flexural basin model than into a wrench basin model. Based on the flexural basin model of this work the early Tertiary Western Carpathians formed a compressional arc. While this arc probably developed above a B-subduction zone, during the Late Eocene with a corresponding trench (Magura), a forearc basin (Central Carpathian or Podhale) and a retroarc flexural basin (Hungarian Paleogene), from the Early Oligocene to the Early Miocene it was characterized by A-subduction with a corresponding peripheral foredeep (Dukla and Silesian) and a retroarc flexural basin (Hungarian Paleogene).

Tari, G.; Báldi, T.; Báldi-Beke, M.

1993-11-01

169

Seismic source parameters and geodynamical features in the Vrancea region, Romania  

NASA Astrophysics Data System (ADS)

The earthquakes clustered in a confined volume at intermediate depths beneath the Vrancea (Romania) seismic region are severely affecting an extended area of Romania and its neighboring countries. During the last century, five events with magnitudes larger than 6.5 occurred within this narrowly confined focal volume. A better understanding of the source process of Vrancea earthquakes is of crucial importance in order to properly assess the ground motion level that has to be expected from future large events and to model the geodynamics of this complex intra-continental convergence area. A substantial new amount of high-quality earthquake data have been recently gained through the progress of seismic networks on the Romanian territory within the cooperation programme with the University of Karlsruhe (Germany): Collaborative Research Centre 461 programme (Bonjer et al., 2000) and the tomography experiment CALIXTO'99 (Wenzel et al., 1999). On the basis of the new digital accelerometer and velocity data (Kinemetrics K2 and broadband instruments) we retrieve the source parameters of small-to-moderate earthquakes (duration magnitude below 5.8) generated in the Vrancea subducting slab. Empirical Green's function deconvolution and spectral ratio methods are applied for a set of 130 earthquakes. Pairs of collocated events with similar focal mechanism are selected in order to retrieve source parameters and to inspect the source scaling properties over the entire seismic active depth domain (between 60 and 180 km). The tests of stability of the source time function parameters are carried out using all the elements (9 short-period and 1 broad band borehole instruments over a 5km x 5km area) of the BURAR array, installed in the northern part of Romania (Bucovina area) within a cooperation with Air Force Technical Applications Center - Florida (USA). Source parametrization and scaling are correlated with clustering properties of earthquake time, space and size distributions as well as with differences in specific source mechanisms or/and structural inhomogeneity properties along the subducting lithosphere. Our results confirm previous research focused on seismicity, tomography and seismic source scaling in the Vrancea region revealing significant subducting slab irregularity which was assumed to be in connection with differences in the physical, geochemical and tectonic processes at different scale lengths.

Radulian, M.; Popa, M.; Popescu, E.

2007-05-01

170

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, Tendürek and Süphan 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 mélange 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

171

Geodynamic setting of the high-grade amphibolites and associated igneous rocks from the accretionary complex of Povorotny Cape, Taiganos Peninsula, northeastern Russia  

Microsoft Academic Search

The petrology and geochemistry of high-grade amphibolites and associated gabbro, volcanic rocks and peridotites from Povorotny Cape (northeastern Russia) are considered with the aim to examine the geodynamic setting of different rock complexes related with the accretionary structure of this area. Geochemical and petrological evidence indicates that the following two predominant groups of igneous rocks were involved in the construction

Sergei Silantyev; Sergei Sokolov; Grigori Bondarenko; Odin Morozov; Boris Bazylev; Suren Palandzhyan; Alexander Ganelin

2000-01-01

172

Geodynamic evolution of the lithosphere and upper mantle beneath the Alboran region of the western Mediterranean: Constraints from travel time tomography  

Microsoft Academic Search

A number of different geodynamic models have been proposed to explain the extension that occurred during the Miocene in the Alboran Sea region of the western Mediterranean despite the continued convergence and shortening of northern Africa and southern Iberia. In an effort to provide additional geophysical constraints on these models, we performed a local, regional, and teleseismic tomographic travel time

Alexander Calvert; Eric Sandvol; Dogan Seber; Muawia Barazangi; Steven Roecker; Taoufik Mourabit; Francisco Vidal; Gerardo Alguacil; Nacer Jabour

2000-01-01

173

Triassic and Jurassic-Cretaceous deposits in the Western Chukotka: geodynamic implications, provenance studies and deformation  

NASA Astrophysics Data System (ADS)

Studied region is situated in western Chukotka, in Northeast Russia. We examine the part of Chukotka microplate, the key element in the evolution of the Amerasian basin. The Triassic of Chukotka is represented by up to 5 km of deposits. Triassic terrigeneous deposits consist of three different complexes: Lower-Middle Triassic, Upper Triassic Carnian, and Norian. All the complexes are represented by rhythmic intercalation of sandstones, siltstones and mudstones. Clastic material was carried by large rivers, possessing large reservoir on neighbouring continent. Progradation of delta system in deeper regions is observed. During the Triassic, sedimentation was represented by continental slope progradation. Petrographic study of mineral composition has established the sandstones as graywackes and lithic arenites, according to Pettijohn classification (1981). Sandstones with clasts of rock fragments of lower metamorphic grade rocks dominate at the base of Triassic deposits, sandstones with fragments of higher grade metamorphic rocks dominate in the Later Triassic deposits. This different shows that the Triassic represents an unroofing sequence sours of erosional processes that produced the clastic material eroded more deeply buried rocks through time. Detrital zircons from Triassic sedimentary rocks were collected for constain its paleogeographic links to source terranes. Zircons populations from these three samples are very similar, and youngest zircon ages show peaks at 236-255 Ma. Besides, we are dating the 9 samples for K-Ar and Rb-Sr methods. Data are similar and show 200-204 Ma, and we suppose that this isotopic data indicate the age of first stage of deformation in Chukotka's basin. The Jurassic-Cretaceous of Chukotka is represented by up to 3 km of deposits. The sedimentary complexes are enriched by organic matter, and fresh clastic materials. Fragments of shales, sometimes laminated or cleaved are their indicator constituents. Sandstones are arkosic. The chemical composition and mineral assemblages are different from Triassic sandstone. Besides, Upper Jurassic sandstones differs from Cretaceous sandstones. Our investigations indicate that Triassic, Upper Jurassic, and Lower Cretaceous sedimentary basins were related to different source provenance. In the paper will discuss the sedimentation, provenances, and geodynamic settings of Triassic and Jurassic-Cretaceous deposits. The studied part of western Chukotka is composed of variably deformed, folded and cleaved rhythmic deposits. Widely distributed and intensively deformed Triassic sequences (Tuchkova et al., 2007) and J-K units both intruded by Aptian-Albian postcollisional plutons and dikes (Katkov et al., 2010). Collisional-related fabric and subsequent granitoids are complicated by small-scale latest normal faults, in particular related to the westernmost segment of South Chukchi (Hope) basin development in Upper Cretaceous (?)-Cenozoic. Intensity of the compressional deformation of Jurassic-Cretaceous rocks is significantly less than in Triassic sequence. Work was supported by RBRR projects 11-05-00787, 11-05-00074, Scientific school # NSh-5177.2012.5, kontrakts No. 04.740.11.0190, and 01/14/20/11.

Tuchkova, M.

2012-04-01

174

Geodynamic modeling of passive margin systems from tectonic reconstructions with deforming plate boundaries  

NASA Astrophysics Data System (ADS)

The effect of mantle flow on surface topography has been the subject of considerable interest over the last few years. A common approach to the problem is to link plate tectonic reconstructions and global geodynamic models. An important limitation of this approach is that traditional plate tectonic reconstructions do not take the deformation of the lithosphere into account. We introduce quantitative models of surface plate kinematics that include areas of deforming continental crust. We present a series of global reconstructions including deforming plates in key areas, derived using tools developed within the open source plate modeling software GPlates. In traditional plate reconstructions, the continents are represented as rigid blocks that overlap in full-fit reconstructions. Models that use topological polygons avoid continental overlaps, but plate velocities are still derived on the basis of Euler poles for rigid blocks. To resolve these issues, we use a methodology that requires at minimum two inputs; (1) the relative motions of the rigid blocks within continents; (2) a definition of the regions in which continental crust deformed between these blocks. We use geological and geophysical data to interpret the landward limit of significant extension and crustal thinning along conjugate passive margins. These boundaries are used to construct polygons along both margins that define the extent of the stretched continental crust on either side of the rift. We derive individual motion histories for each point on the conjugate continent/ocean boundaries (COBs). Joined together, these COB points form the topological boundaries of deforming domains in which each vertex moves independently. The deforming domains represented by topological meshes extend forward in time as the major rigid plates drift apart. In our tectonic reconstruction with deforming plates, the timing and the intensity of continental extension is imposed by the progressive, diachronous breakup and initiation of seafloor spreading for each major margin system. The velocity field derived from the plate reconstructions is used as a time-dependent surface boundary condition in mantle convection models that include compositionally distinct crust and continental lithosphere embedded within the thermal lithosphere. In deforming areas, the velocity field is obtained by linearly interpolating velocities from adjacent non-deforming areas within GPlates. We computed forward global mantle flow models using 3D-spherical finite-element code CitcomS to simultaneously quantify the relative contributions of lithospheric stretching, thermal subsidence, and deep mantle flow to the subsidence of passive margins. Applied to the South Atlantic, the method reproduces the first-order asymmetry of the margins. In particular, the large subsidence of the Argentinian margin is due to the dynamic topography induced by ongoing subduction along the narrow southern portion of South America. This result illustrates the importance of dynamic topography to the total subsidence at passive margins.

Williams, S.; Flament, N.; Heine, C.; Hosseinpour Vazifehshenas, M.; Seton, M.; Gurnis, M.; Müller, R. D.

2012-04-01

175

Upper mantle structures beneath the Carpathian-Pannonian region: Implications for the geodynamics of continental collision  

NASA Astrophysics Data System (ADS)

The Carpathian-Pannonian system of Eastern and Central Europe represents a unique opportunity to study the interaction between surface tectonic processes involving convergence and extension and convective processes in the upper mantle. Here, we present high-resolution images of upper mantle structure beneath the region obtained using P- and S-wave finite-frequency teleseismic tomography to help constrain the geodynamical interpretation of the region. We have selected earthquakes with magnitude greater than 5.5 in the distance range 30°-95°, which occurred between 2006 and 2011. The data were recorded on 54 temporary stations deployed in the South Carpathian Project (2009-2011), 56 temporary stations deployed in the Carpathian Basins Project (2005-2007), and 131 permanent broadband stations of national networks. The relative arrival times are measured in high, intermediate and low frequency bands (0.5-2.0 Hz, 0.1-0.5 Hz and 0.03-0.1 Hz for both P-waves, 0.1-0.5 Hz, 0.05-0.1 Hz and 0.02-0.05 Hz for S-waves), and are inverted using a 3-D finite-frequency formulation to produce P- and S-wave velocity maps at depths between 75 and 600 km in the mantle. Our images show a sub-vertical slab of fast material beneath the eastern Alps which extends eastward across the Pannonian basin at depths below ~300 km. The fast material extends down into the mantle transition zone (MTZ), where it spreads out beneath the entire basin. Above ~300 km, the upper mantle below the Pannonian basin is dominated by relatively slow velocities, the most dominant of which extends down to nearly 200 km and underlies the >7km thick sediments of the Mako-Békés rift basins. We suggest that cold mantle lithospheric downwelling occurred below the Pannonian Basin before detaching in the mid-Miocene. In the Vrancea Zone, intermediate depth seismicity occurs at the NE end of a tabular upper mantle high velocity structure that trends SW along the southern edge of the South Carpathians and extends to depths of ~400 km. This sub-vertical high-velocity body is bounded by slow anomalies to the NW and SE, which extend down to the top of the MTZ. The slow anomalies correlate with outcrops of Neogene-Quaternary volcanic activities in the East Carpathians and Apuseni Mountains. No clear evidence of residual slabs is observed in the mid upper mantle beneath Eastern Carpathians; the eastern Carpathians are underlain by slow velocities everywhere above the transition zone. These observations suggest that intermediate depth seismicity in the Vrancea Zone is unlikely to be due to slab tearing, but rather could be explained by either gravitational instability or delamination of mantle lithosphere.

Ren, Y.; Stuart, G. W.; Houseman, G. A.; Dando, B.; Ionescu, C.; Hegedus, E.; Radovanovic, S.; South Carpathian Project Working Group

2012-04-01

176

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

177

Geodynamic evolution and the history of the atmospheres of Mars and Venus  

NASA Astrophysics Data System (ADS)

To investigate in what measure the interactions between the mantle and the atmosphere would have caused the divergent evolutions of the terrestrial planets in our solar system, we propose to model the effects of mantle dynamics on the evolution of CO2, H2O and other species like Argon or Nitrogen in the atmosphere, but also of the surface temperature. We consider several processes that are considered to have a strong influence on the atmosphere of terrestrial planets. First, the main source of volatiles in our model is the degassing from the mantle. We use and adapt the StagYY code developed by Tackley (Tackley, 2008) for the geodynamic part of the study. This modeling gives a realistic and advanced account of the mantle convection processes. When possible, we compare those results to published modeling (Breuer and Spohn, 2006; Grott et al., 2011) and observation. Atmospheric escape is considered as the main volatile loss flux. Early escape is thermal, caused by hydrodynamic escape. Its effects can be modeled, as we did for Venus. After the first few hundred of million years, the main atmospheric escape flux becomes non-thermal. We model the evolution of the present escape flux by comparing recent study on these processes and ASPERA (Analyzer of Space Plasma and EneRgetic Atoms) measurements. Differences in present-day escape depending on solar activity are used to extrapolate early escape. We combine these models to calculate the state of the atmosphere of Venus and Mars. This lets us estimate the surface temperature of those planets either from a Mars Global Circulation Model (e.g. Forget at al., 1999), or with a gray radiative-convective atmosphere model, for Venus. In the case of Mars, Ar appears to be a tracer of volcanic degassing. We also show that the present-day atmosphere of Mars is likely to be constituted by a large part of volcanic gases. Even with a low CO2 concentration in the magma (150 ppm), present-day atmosphere is constructed of 50% of volcanic gases emitted since 4 billion years ago, which corresponds to an age of 1.9 to 2.3 Gyr. The variations of CO2 pressure over this period seem relatively low (50 mbar at most). This seems in line with the assumption that the heavy loss of volatiles occurred before 500 Myr. Surface temperature variations are likely to be small (several Kelvin) and would not be responsible for periods of flowing liquid surface water by themselves. Water is abundant on Mars during the whole 4 billion years evolution (between 30% and 150% of the present day water) but is unlikely to reside in the atmosphere or in liquid form. In the case of Venus, we are able to reproduce a mantle convection behaviour showing what could be interpreted as resurfacing events with times of high activity separated by quieter periods. Atmospheric escape is also different; it is much lower than on Mars. During the last 4 Gyr, CO2 pressure doesn't seem to vary significantly, while water pressure decreased by several millibars, which induced a surface temperature variation of several tens of kelvins and illustrates the dry state of present-day Venus.This is in agreement with calculated isotopic ratios for noble gases such as Neon and Argon.

Gillmann, C.; Tackley, P. J.; Lognonne, P.

2011-12-01

178

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

179

Modern geodynamical motion of the Northern Caucasus from data of GPS/GLONASS observations  

NASA Astrophysics Data System (ADS)

The northern part of the Greater Caucasus is one of the most geodynamically active regions of Russia. This is a zone of complex tectonics resulting from interaction between two of the Earth's major lithospheric plates, Arabia and Eurasia. Therefore, the region as a whole is characterized by a complex system of faults, with meridional and diagonal structures. The first GPS and absolute gravity campaign in the Black Sea and Northern Caucasus regions was carried out between 1993 and 1994 as part of the SELF project. One of the points of the GPS measurements was transformed in the stationary station. This station is located in Karatchay-Cherkessia Republic of the Russian Federation. Since 1997 the Zelenchukskaya station has been part of the European Reference Frame (EUREF) GPS network with a code ZECK. Within the last few years we have established three new stationary GPS/GLONASS stations in the Northern Caucasus. The first (site code TRSK) is located in the Kabardino-Balkaria Republic, near the Elbrus volcano. It began to operate in 2005. The second one is located in Karatchay-Cherkessia Republic (site code KISL). This station has been in operation since 2006. The third is located in Vladikavkaz, the capital of North Ossetia Republic (site code VLAD). The continuous GPS measurements began in 2008. These four stationary stations form the base for the regional Northern Caucasus GPS network, which can be called the Northern Caucasus Deformation Array (NCDA). We analyse the GPS data using BERNESE 5.0 GPS software. As a reference site we use the Mendeleevo station, located in the Moscow region (IGS site code MDVJ). The striking aspect of the velocity field of the Northern Caucasus derived from the NDCA stations is the rapid motion in the north-east direction with almost equal velocities of about 28 mm/yr. The motion of the feducial site MDVJ (Moscow region) is characterised by a similar velocity value (25 mm/yr) in the same direction. Therefore the motion of the Northern Caucasus region is mainly defined by the general tectonic movement of the Eurasian plate with respect to ITRF. At the same time the analysis defines excess NE movement of stations in the NCDA with respect to Eurasia (as defined here by the Moscow station) at rates of 3-4 mm/yr. Apparently the excess velocities of NCDA reflect tectonic activity of this region. With respect to the uplift of the Northern Caucasus region, the situation is ambiguous. The uplift of the ZECK site derived from the GPS data coincides with an estimation obtained on the basis of absolute gravity measurements over a thirteen-years period (2 mm/yr). The station Terskol shows the greatest uplift (9 mm/yr). The local effect connected with inflation of magmatic chambers of the Elbrus volcano may be one of the possible explanations of the uplift value of the TRSK site. Nevertheless the question of the uplift estimate for the Northern Caucasus region demands further study. This work is supported by the Russian Foundation for Basic Research under Grants No 09-05-90365 and No 10-05-00262.

Milyukov, Vadim; Zharov, Vladimir; Mironov, Alexey; Myasnikov, Andrey; Kaufman, Mark

2010-05-01

180

Geo-information approach to the study of Romashkino oil field geodynamics  

NASA Astrophysics Data System (ADS)

Geodynamic processes have an immediate influence on a fluid dynamics, for that version they are of significant importance in the formation and reformation processes of oil and gas deposits. The object of our analysis was Romashkino oil field, which is confined to the anticlinal structure of the arch part of the South Tatar Arch. The initial data in our project include the series of a paper maps, which contain the location of the intersection of production and injection wells with the Kyn horizont at the Romashkino oil field and geologic engineering information, which contains the flow rates's inversions data of the well's production activity. Inversion occurs as a periodic increasing of the flow rates which is not caused by the external special influence on the well, against the long-term production activity's decreasing by the decreasing of oil's flow rates. During the analysis of the data we identified the anomalous wells in which the hydrocarbon feed process was observed with the highest probability based on several criteria. By the using of modern GIS technology we have compared the plots, in which an anomal wells are located, with a block structure of the basement and the sedimentary cover, and with the deconsolidated and fluid's penetrability zones of the crystalline basement. For analysis of tabular data array we used ArcGis software package. Romashkino's map was vectorized by using the EasyTrase and when we assigned a number to each object. When the project was exported to ArcGIS and data obtained the geographic coordinates. We obtained the following attributes for the testing wells: the year of exploitation's beginning, the period of the inversion, the ratio of flow rates before and after inversion, and others. We created a series of maps with location of wells, with a flow rate's inversion by the year (1957-1998) for Minnibayevo area and by the five-year intervals for Minnibayevo area separately and for the Romashkino oil field. The maps of the inversion's density were built by the interpolation from the values of the ratio of oil flow rates before and after the inversion in the wells. These data was selected as a characterizing of the inversion strength. Thereby we created the convenient and informative geodata base through using GIS technology. The comprehensive interpretation of a series of maps, created by ArcGIS software package, is in progress. Firstly an analysis of the location of arrangement of the production wells, in which was occurred inversion of oil production in the process of production activity was made. After this, we compared their location with the block structure scheme. We noticed that the wells are grouped in linear- elongated zone along the fault, there is an affinity of this well to the certain parts of the small-sized blocks. The development of scientific and practical research in this direction is of a high significant because it can lead to a change in the strategy and methodology of the geological prospecting on the one hand and of the exploration of hydrocarbon deposits on the other hand.

Usmanov, S.; Sharipov, B.; Akhmetov, A.; Delev, A.

2012-04-01

181

Six years analysis of HemusNET permanent GPS network data - impact on geodynamics of the Balkans  

NASA Astrophysics Data System (ADS)

The presentation outlines results for horizontal motion of the crust in the Balkans, mainly Bulgaria and Northern Greece, obtained by processing and analyzing of data from permanent GPS sites during the period 2007 - 2012. Estimates of horizontal velocities of stations in Bulgaria and Northern Greece obtained by GAMIT/GLOBK along with geological and seismotectonic information give the opportunity to draw inferences about the recent tectonic activity in this area and its position within the East Mediterranean geodynamic processes. The GPS velocities in Bulgaria and Northern Greece exhibit a clear tendency to increase from north to south. The obtained results suggest that the transition zone between "stable" Eurasia and the Aegean extensional province is located south from the Balkan (Hemus) Mountain and to the western parts of the North Anatolian Fault - the so-called South Balkan extensional region.

Georgiev, Ivan; Ganas, Athanassios

2013-04-01

182

Absolute gravity measurements in Switzerland: Definition of a base network for geodynamic investigations and for the Swiss fundamental gravity net  

NASA Astrophysics Data System (ADS)

Results of two absolute gravity surveys performed in Switzerland between 1978 and 1979 are presented and discussed in the framework of the uplift history of the Swiss Alps. Five absolute stations have been established as a contribution to the Swiss fundamental gravity net as well as to geodynamic investigations on the Alpine uplift. Two sites (Interlaken-Jungfraujoch) form the end points of a calibration line for field gravimeters. The gravity range of this line amounts to 605 × 10-5 ms-2 (=605 mgal). It can be traversed in a relatively short time interval of less than 3 hours. Two other sites (Brig and Chur) are located in the area of the most negative gravity anomalies and highest uplift rates encountered in Switzerland. They serve as reference stations for a more extended gravity net for studying non-periodic secular gravity variations associated with the Alpine uplift.

Marson, I.; Kahle, H.-G.; Chaperon, F.; Mueller, St.; Alasia, F.

1981-09-01

183

Quantitative geodynamics - Lithospheric processes, convection and global dynamics; Proceedings of the Symposium, Hamburg, West Germany, August 19, 1983  

NASA Astrophysics Data System (ADS)

A collection of papers dealing with quantitative geodynamics, devoted to the topics of lithospheric processes and convection and global dynamics, are presented. Lithospheric growth, thinning, and strength are discussed on the basis of thermomechanical approximations. Improved numerical finite element techniques are adopted in the study of continent-continent collisions and the relaxation of the lithosphere due to dip-slip deformation. The penetration of fluid bodies through a solid medium is considered, and flow problems of the lithosphere-asthenosphere system are approximated using an image system technique. Convective mixing and the related development of the fine mantle structure are studied, and improvements in numerical techniques for studying dynamical earth processes are discussed. Finally, constraints on the mechanical structure of the earth derived from quantitative polar motion modeling are addressed.

Neugebauer, H. J.; Olson, P.

1984-12-01

184

Practical analytical solutions for benchmarking of 2-D and 3-D geodynamic Stokes problems with variable viscosity  

NASA Astrophysics Data System (ADS)

Geodynamic modeling is often related with challenging computations involving solution of the Stokes and continuity equations under the condition of highly variable viscosity. Based on a new analytical approach we have developed particular analytical solutions for 2-D and 3-D incompressible Stokes flows with both linearly and exponentially variable viscosity. We demonstrate how these particular solutions can be converted into 2-D and 3-D test problems suitable for benchmarking numerical codes aimed at modeling various mantle convection and lithospheric dynamics problems. The Main advantage of this new generalized approach is that a large variety of benchmark solutions can be generated, including relatively complex cases with open model boundaries, non-vertical gravity and variable gradients of the viscosity and density fields, which are not parallel to the Cartesian axes. Examples of respective 2-D and 3-D MatLab codes are provided with this paper.

Popov, I. Yu.; Lobanov, I. S.; Popov, S. I.; Popov, A. I.; Gerya, T. V.

2014-06-01

185

Practical analytical solutions for benchmarking of 2-D and 3-D geodynamic Stokes problems with variable viscosity  

NASA Astrophysics Data System (ADS)

Geodynamic modeling often involves challenging computations involving solution of Stokes and continuity equations under condition of highly variable viscosity. Based on new analytical approach we developed generalized analytical solutions for 2-D and 3-D incompressible Stokes flows with both linearly and exponentially variable viscosity. We demonstrated how these generalized solutions can be converted into 2-D and 3-D test problems suitable for benchmarking numerical codes aimed at modeling various mantle convection and lithospheric dynamics problems. Main advantage of this new generalized approach is that large variety of benchmark solutions can be generated including relatively complex cases with open model boundaries, non-vertical gravity and variable gradients of viscosity and density fields, which are not parallel to Cartesian axes. Examples of respective 2-D and 3-D MatLab codes are provided with this paper.

Popov, I. Yu.; Lobanov, I. S.; Popov, S. I.; Popov, A. I.; Gerya, T. V.

2013-12-01

186

Installation of two high-sensitivity laser strainmeters in a new underground geodynamical observatory (GEODYN) at Canfranc (Spain)  

NASA Astrophysics Data System (ADS)

High-sensitivity wide-band strain measurements allow an advanced study of different geodynamic phenomena, both local and global, in a spectrum ranging from short period seismic waves to tectonic deformation. Among the latest results produced by the few high-sensitivity wide-band laser interferometers operating allover the world, the analysis of the strain recorded by the Gran Sasso (Italy) laser interferometers before and after the 2009 L'Aquila earthquake allowed putting tight constraints on earthquake nucleation processes and other pre-seismic phenomena, and detecting the slow diffusive propagation of an aseismic rupture during the first hours following the main event.The Gran Sasso interferometers are operating since several years, proving their high reliability. An improved version of the Gran Sasso interferometers have been recently installed in the Canfranc (Spain) underground Laboratory (LSC). The LSC is located at depth in one of the most seismically active areas in Western Europe, at the Pyrenean chain that marks the boundary between the European plate and the Iberian microplate. These features make it particularly suitable and interesting for hosting an advanced integrated geodynamic observatory (GEODYN), of which the interferometers are part. The first tests on strain data evidence a much lower noise level with respect that the Gran Sasso installations, expecially in the frequency band 0.0001 to 0.1 Hz, suggesting the capability of producing clear records of low-frequency seismic waves, Earth free oscillations, and possible local aseismic stress release. We will give a technical description of the installation, show some examples of recordings, and discuss the local distortion of the deformation field, as obtained by comparing Earth tide predictions and observations.

Crescentini, L.; Botta, V.; Amoruso, A.; Bettini, A.

2012-04-01

187

A geodynamical view on the steadiness of geodetically-derived rigid plate-motions over geological time  

NASA Astrophysics Data System (ADS)

Plate-motion changes probe Earth's lithosphere dynamics. The ability to map ocean-floor magnetisation is key to infer past plate motions over Myr-time-scales. The advent of space geodesy in the Earth Sciences offered an independent snapshot of contemporary plate kinematics, averaged over decades. Early studies supported the notion of plate-motions steadiness through geological time, because contemporary rates were remarkably similar to past-3-Myr averages. Data collected since two decades, however, favour the opposite inference: geodetic and paleo-magnetic motions exhibit differences beyond confidence ranges, and the current view of the scientific community is that geodetically-derived motions generally represent kinematics over time-scales shorter than a few centuries. These differences pose important questions on the characteristics of plate kinematic variability through time. Here I make inferences on the steadiness of geodetically-derived plate-motions over geological time by combining geodynamical arguments with kinematic datasets. I exploit datasets to build putative scenarios for the recent kinematic evolution of major plates. I then compare the minimum rate at which plate torques need to vary to generate these scenarios, with the maximum rate at which large-scale geological processes can contribute torques. This allows assessing the geodynamical plausibility of each scenario. Results indicate that plate-motion changes must have taken no less than 1 Myr to occur, more likely 2 Myr. It is plausible that geodetically-observed plate-motions remained steady since 1 Myr ago, possibly for longer. This calls for a shift in the way we regard the contemporary figure of geodetic plate-motions, which might have remained steady for much longer over geological time than we think.

Iaffaldano, G.

2013-12-01

188

Reconstructing palaeo-volcanic geometries using a Geodynamic Regression Model (GRM): Application to Deception Island volcano (South Shetland Islands, Antarctica)  

NASA Astrophysics Data System (ADS)

This article describes a reconstruction made of the palaeo-volcanic edifice on Deception Island (South Shetland Islands, Antarctica) prior to the formation of its present caldera. Deception Island is an active Quaternary volcano located in the Bransfield Strait, between the South Shetland Islands and the Antarctic Peninsula. The morphology of the island has been influenced mainly by the volcanic activity but geodynamics and volcanic deformation have also contributed. A volcanic reconstruction method, the Geodynamic Regression Model (GRM), which includes a terrain deformation factor, is proposed. In the case of Deception Island, the directions of this deformation are NW-SE and NE-SW, and match both the observed deformation of the Bransfield Strait and the volcanic deformation monitored over the last 20 years in the island, using Global Navigation Satellite System (GNSS) techniques. Based on these data, possible volcanic deformation values of 5-15 mm/yr in these directions have been derived. A possible coastline derived from a current bathymetry is transformed, according to values for the chosen date, to obtain the palaeo-coastline of Deception Island of 100 k years ago. Topographic, geomorphologic, volcanological and geological data in a GIS system have been considered, for computation of the outside caldera slope, palaeo-coastline, palaeo-summit height and palaeo digital elevation model (DEM). The result is a 3D palaeo-geomorphological surface model of a volcano, reaching 640 m in height, with an increase of 4 km3 in volume compared to the current edifice, covering 4 km2 more surface area and the method reveals the previous existence of parasite volcanoes. Two photorealistic images of the island are obtained by superposition of textures extracted from a current Quick Bird satellite image also. This technique for reconstructing the terrain of an existing volcano could be useful for analysing the past and future geomorphology of this island and similar locations.

Torrecillas, C.; Berrocoso, M.; Felpeto, A.; Torrecillas, M. D.; Garcia, A.

2013-01-01

189

Estimation of Non-Seasonal Oceanic Mass Redistribution and its Geodynamic Effects from the Topex/Poseidon Observation  

NASA Technical Reports Server (NTRS)

Mass redistribution in terms of angular momentum will change the Earth's rotation under the conservation of angular momentum. It also changes the external gravitational field according to Newton's gravitational law. These small geodynamic variations can be measured very accurately by modem space geodetic techniques. We report on new estimates of the oceanic tidal angular momentum and hence the tidal variations in the Earth's rotation rate and polar motion. These are deduced from the new tidal solutions GOT99 and TPXO.3, plus M2 and Mf estimates (with error bars) from TPXO.4a. Comparisons with observed diurnal/semidiurnal tidal variations are generally similar to previous model estimates. Comparisons of models and observations of Mf polar motion are confused, with neither models nor observations agreeing among themselves or with each other. Part of this is caused by differences in Mf currents; model TPXO.4 shows current-intensive Rossby modes along western boundaries of major basins, which are indeed expected on theoretical grounds. Unfortunately, there are no reliable in situ observations of Mf currents useful for comparing models. On non-tidal oceanic mass redistribution we compute the principal components of the multi-year T/P sea surface height (SSH) field using EOF (empirical orthogonal functions) taking into consideration of the latitude-dependent area weighting. Emphasis is placed upon non-seasonal and interannual oscillations on regional scales, including ENSO and the North Atlantic Oscillation. Steric corrections to the observed SSH due to sea surface temperature changes (which has no geodynamic effects) is now under study using POCM ocean model output.

Chao, Benjamin F.; Ray, Richard D.; Au, A. Y.

1999-01-01

190

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

191

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

NASA Astrophysics Data System (ADS)

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 the corresponding constraints on the geodynamic evolution of the Sundaland border. The West Sulawesi magmatic province includes the South Arm of Sulawesi (Ujung Pandang area), the western part of Central Sulawesi with the Toraja and Palu areas, and finally, the North Arm, extending from Palu to Manado, which includes the Tolitoli and Manado areas. Paleocene magmatic activity seems to be restricted to an episode of calc-alkaline magmatism in the Ujung Pandang area (61-59 Ma). The major Eocene (50-40 Ma) magmatic event is tholeiitic and is documented in all areas except in Ujung Pandang. It led to the emplacement of tholeiitic pillow-lavas and basaltic dykes of back-arc basin (BAB) affinity. These rocks are potential equivalents to the Celebes Sea basaltic basement. From Oligocene to Miocene, magmatic eruptions produced successively island-arc tholeiitic (IAT) and calc-alkaline (CA) rock series. The youngest IAT activity occurred around 18 Ma in the central part (Palu area) and around 14 Ma in the North Arm (Tolitoli area) while CA magmas were emplaced in the North Arm at ca. 18 Ma (Tolitoli and Manado areas). Typical calc-alkaline activity resumed only in the North Arm (Tolitoli and Manado areas) during the Late Miocene (9 Ma) and is still active in the Manado region. In other areas (Palu, Toraja and Ujung Pandang areas) an important and widespread magmatic event occurred between 13 and 10 Ma and emplaced K-rich magmas, either silica-undersaturated alkali-potassic basalts (AK), ultrapotassic basanites (UK) or shoshonites (SH). K-rich activity continued in the south until the Pleistocene (0.77 Ma) with alkali-potassic, ultrapotassic and shoshonitic magmas. In Central Sulawesi (Toraja and Palu areas) the most recent magmatic event occurred between 6.5 and 0.6 Ma. The corresponding products are granitic rocks and widely distributed rhyolitic pyroclastic flow deposits. All these rocks are acidic in character (SiO 2 > 60%), with trace-element and isotopic signatures (Sr?Nd?Pb) typical of a strong continental imprint. The most striking tectonic implication of this magmatic evolution is that West Sulawesi can no longer be considered as a typical magmatic arc as previously assumed. With the exception of the Manado area beneath which subduction is still active, calc-alkaline and island-arc tholeiitic lavas and plutonics are volumetrically minor with respect to K-rich magmas. Their occurrence through time is also fairly restricted, mostly to the period between 30 and 15 Ma. Another important feature is the occurrence of island-arc tholeiitic and calc-alkaline magmas crosscutting an older terrane of BAB affinity, the Tinombo Formation (Manado, Tolitoli and Palu areas). As this formation is being regarded as an equivalent to the Celebes Sea floor, the most likely explanation for this feature is the hypothesis of tectonic erosion linked to the NW-dipping subduction beneath the North Arm. The Late Miocene high-K magmatic activity in Central and South Sulawesi reflects the prevalence of a post-collisional tectonic regime following the docking of microcontinents of Australian origin to Central Sulawesi during Neogene times. The incompatible element-enriched character of these high-K rocks might reflect their derivation from a mantle source enriched through metasomatism related to a previous subduction event. Such a model cannot account for the Plio-Pleistocene CAK magmatism of Central Sulawesi, the acidic composition of which does not support a derivation from an ultrabasic source. The trace-element patterns of the CAK rocks are very similar to those of the high-grade metamorphics of Central Sulawesi, suggesting that the

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

1997-04-01

192

Generations of spreading basins and stages of breakdown of Wegener’s Pangea in the geodynamic evolution of the Arctic Ocean  

Microsoft Academic Search

Chronological succession in the formation of spreading basins is considered in the context of reconstruction of breakdown\\u000a of Wegener’s Pangea and the development of the geodynamic system of the Arctic Ocean. This study made it possible to indentify\\u000a three temporally and spatially isolated generations of spreading basins: Late Jurassic-Early Cretaceous, Late Cretaceous-Early\\u000a Cenozoic, and Cenozoic. The first generation is determined

E. V. Shipilov

2008-01-01

193

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

194

Comparative analysis of geodynamic activity of the Caucasian and Eastern Mediterranean segments of the Alpine-Himalayan convergence zone  

NASA Astrophysics Data System (ADS)

The Alpine-Himalayan convergence zone (AHCZ) underwent recent transverse shortening under the effect of collisional compression. The process was accompanied by rotation of separate microplates. The Caucasian and Eastern Mediterranean regions are segments of the of the AHCZ and are characterized by intensive endogenous and exogenous geodynamic processes, which manifest themselves in occurrence of powerful (with magnitude of 8-9) earthquakes accompanied by development of secondary catastrophic processes. Large landslides, rock falls, avalanches, mud flows, etc. cause human deaths and great material losses. The development of the aforesaid endogenous processes is set forth by peculiarities of the deep structure of the region and an impact of deep geological processes. The Caucasus is divided into several main tectonic terranes: platform (sub-platform, quasi-platform) and fold-thrust units. Existing data enable to perform a division of the Caucasian region into two large-scale geological provinces: southern Tethyan and northern Tethyan located to the south of and to the north of the Lesser Caucasian ophiolite suture, respectively. The recent investigations show that the assessments of the seismic hazard in these regions are not quite correct - for example in the West Caucasus the seismic hazard can be significantly underestimated, which affects the corresponding risk assessments. Integrated analysis of gravity, magnetic, seismic and thermal data enables to refine the assessment of the seismic hazard of the region, taking into account real rates of the geodynamic movements. Important role play the last rheological constructions. According to Reilinger et al. (2006) tectonic scheme, the West flanking of the Arabian Plate manifests strike-slip motion, when the East Caucasian block is converging and shortening. The Eastern Mediterranean is a tectonically complex region located in the midst of the progressive Afro-Eurasian collision. The recent increasing geotectonic activity in this region highlights the need for combined analysis of seismo-neotectonic signatures. For this purpose, this article presents the key features of the tectonic zonation of the Eastern Mediterranean. Map of derivatives of the gravity field retracked from the Geosat satellite and novel map of the Moho discontinuity illustrate the most important tectonic features of the region. The Post-Jurassic map of the deformation of surface leveling reflects the modern tectonic stage of Eastern Mediterranean evolution. The developed tectono-geophysical zonation map integrates the potential geophysical field analysis and seismic section utilization, as well as tectonic-structural, paleogeographical and facial analyses. Tectonically the map agrees with the earlier model of continental accretion (Ben-Avraham and Ginzburg, 1990). Overlaying the seismicity map of the Eastern Mediterranean tectonic region (for the period between 1900 and 2012) on the tectonic zonation chart reveals the key features of the seismo-neotectonic pattern of the Eastern Mediterranean. The results have important implications for tectonic-seismological analysis in this region (Eppelbaum and Katz, 2012). A difference in the geotectonic patterns makes interesting comparison of geodynamic activity and seismic hazard of the Caucasian and Eastern Mediterranean segments of the AHCZ.

Chelidze, Tamaz; Eppelbaum, Lev

2013-04-01

195

High precision deformation monitoring at the Geodynamic Observatory Moxa/Thuringia, Germany: The new three-component laser-strainmeter assembly  

NASA Astrophysics Data System (ADS)

High precision observations at the surface of the Earth are relevant for several geodynamic investigations regarding long- and short-term changes of position in tectonically active regions, periodic changes due to Earth tides, free modes or seismic waves, fluid induced deformations and control monitoring of constructions. Observations based on satellites, e.g. INSAR are convenient in particular for the acquisition of large-scale deformation field changes. Terrestrially installed strainmeters are restricted to stationary locations, but they enable the deformation observation with a significantly higher accuracy of better than 10-9 m. Since 1964 at the Geodynamic Observatory Moxa in Thuringia/Germany two quartz-tube strainmeters are installed, in 2002 a laser-strainmeter, and in 2005 a borehole strainmeter were added. This arrangement enabled the observation of load and deformation effects of barometric pressure fields moving above the observatory, which were also accompanied by numerical modelling explaining the whole process. Two further laser-strain components with a new laser technology have recently been installed in June 2011 and will now improve the strainmeter assembly significantly. Here we show two main results of the comparative investigations: the improvement of quality of data due to the new laser component installation and the environmental effects like barometric pressure or groundwater level changes on the strainmeter assembly at the Geodynamic Observatory Moxa.

Kukowski, N.; Jahr, T.; Schindler, P.; Jentzsch, M.

2011-12-01

196

Digital files for northeast Asia geodynamics, mineral deposit location, and metallogenic belt maps, stratigraphic columns, descriptions of map units, and descriptions of metallogenic belts  

USGS Publications Warehouse

This is the online version of a CD-ROM publication. It contains all of the data that are on the disc but extra files have been removed: index files, software installers, and Windows autolaunch files. This publication contains a a series of files for Northeast Asia geodynamics, mineral deposit location, and metallogenic belt maps descriptions of map units and metallogenic belts, and stratigraphic columns. This region includes Eastern Siberia, Russian Far East, Mongolia, Northeast China, South Korea, and Japan. The files include: (1) a geodynamics map at a scale of 1:5,000,000; (2) page-size stratigraphic columns for major terranes; (3) a generalized geodynamics map at a scale of 1:15,000,000; (4) a mineral deposit location map at a scale of 1:7,500,000; (5) metallogenic belt maps at a scale of 1:15,000,000; (6) detailed descriptions of geologic units with references; (7) detailed descriptions of metallogenic belts with references; and (8) summary mineral deposit and metallogenic belt tables. The purpose of this publication is to provide high-quality, digital graphic files for maps and figures, and Word files for explanations, descriptions, and references to customers and users.

edited by Nokleberg, Warren J.; Badarch, Gombosuren; Berzin, Nikolai A.; Diggles, Michael F.; Hwang, Duk Hwan; Khanchuk, Alexander I.; Miller, Robert J.; Naumova, Vera V.; Obolensky, Alexander A.; Ogasawara, Masatsugu; Parfenov, Leonid M.; Prokopiev, Andrei V.; Rodionov, Sergey M.; Yan, Hongquan

2004-01-01

197

Noble Gases and Siderophile Elements in the Mantle: Unconventional Experimental Results and Their Implications for Chemical Geodynamics  

NASA Astrophysics Data System (ADS)

Recent and ongoing experimental studies reveal unexpected behavior of noble gases and siderophile elements that may affect future geodynamic interpretations. Ar-uptake experiments on mantle minerals provide insight into Ar compatibility (solubility) and diffusivity in these phases. Contrary to expectation, solubility results suggest that Ar behaves as a compatible element during mantle melting, favoring residence in point defects in minerals over 'escape' to the melt. In terms of diffusion, Ar is sufficiently mobile in olivine and orthopyroxene to ensure effective dispersal from relatively K-rich minerals on a geodynamically short time scale. Solid-liquid equilibration during melting of the MORB source is also likely; however, Ar diffusion is slow enough for disequilibrium to arise during phenocryst growth in a pre-eruption setting. The main implications of these results are that: 1) Ar degassing of the mantle through MORB volcanism may be an inefficient process; and 2) the existence of deeply-sequestered Ar (and other noble gases?) is plausible. New data on the behavior of siderophile elements (Os, Ir, Ru, Rh, Pt, Re, Au, W, Mo, Co, Cu and C) in polycrystalline MgO and synthetic peridotite reveal that these elements are highly mobile in the grain boundaries of mantle assemblages and analogs. W, Au and C have the highest diffusivities (10-8 to 10-7 m2/s); Ir, Ru, Re and Os are at the low end of the range (~10-12 to 10-11 m2/s). There is no discernible correlation between grain-boundary diffusivity and any particular property of the atoms or elements. These new data imply that Earth's outer core may 'leak' siderophile elements into the lower mantle over distances exceeding 100 km in 4 GYr for W, Au and C. Although not significant in itself as a whole-mantle transport process, grain boundary diffusion appears capable of 'contaminating' the lower mantle over a sufficient distance to enable entrainment of a core signature into plume- or convective mantle flow. If the outer core contains C, our data suggest that there may be a significant core-to-mantle flux of this element.

Watson, E. B.; Hayden, L. A.; Thomas, J. B.; Cherniak, D. J.

2007-12-01

198

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

199

Geodynamic models of terrane accretion: Testing the fate of island arcs, oceanic plateaus, and continental fragments in subduction zones  

NASA Astrophysics Data System (ADS)

Crustal growth at convergent margins can occur by the accretion of future allochthonous terranes (FATs), such as island arcs, oceanic plateaus, submarine ridges, and continental fragments. Using geodynamic numerical experiments, we demonstrate how crustal properties of FATs impact the amount of FAT crust that is accreted or subducted, the type of accretionary process, and the style of deformation on the overriding plate. Our results show that (1) accretion of crustal units occurs when there is a weak detachment layer within the FAT, (2) the depth of detachment controls the amount of crust accreted onto the overriding plate, and (3) lithospheric buoyancy does not prevent FAT subduction during constant convergence. Island arcs, oceanic plateaus, and continental fragments will completely subduct, despite having buoyant lithospheric densities, if they have rheologically strong crusts. Weak basal layers, representing pre-existing weaknesses or detachment layers, will either lead to underplating of faulted blocks of FAT crust to the overriding plate or collision and suturing of an unbroken FAT crust. Our experiments show that the weak, ultramafic layer found at the base of island arcs and oceanic plateaus plays a significant role in terrane accretion. The different types of accretionary processes also affect deformation and uplift patterns in the overriding plate, trench migration and jumping, and the dip of the plate interface. The resulting accreted terranes produced from our numerical experiments resemble observed accreted terranes, such as the Wrangellia Terrane and Klamath Mountain terranes in the North American Cordilleran Belt.

Tetreault, J. L.; Buiter, S. J. H.

200

The Sinemurian carbonate mud-mounds from central High Atlas (Morocco): stratigraphy, geometry, sedimentology and geodynamic patterns  

NASA Astrophysics Data System (ADS)

The Moroccan Central High Atlasic mud-mounds correspond to carbonate sponge-algal buildups developed in open marine conditions towards the Lower-Upper Sinemurian boundary. The structures gradually increase in size through time, from the small-sized lenses included in the Idikel coarse-bedded Lower Sinemurian grainstones to the high domes observed in the succeeding Aberdouz and Ouchbis Upper Sinemurian thin-bedded mudstones. The biological communities (mainly algae, sponges, thrombolites, stromatolites, annelids, bryozoans, brachiopods, pelecypods, gastropods, echinoderms, corals and scarce foraminifera) comprise common, well conserved remains in the rising core frameworks and small reworked bioclasts in the surrounding sedimentary depressions. These buildups are closely linked to tectonic processes as they grew on the normal synsedimentary faults which affected the central Atlasic area during the Lower Liassic period, leading to the breakup of the Early Sinemurian carbonate platform and the resultant initiation of the Upper Sinemurian subsiding basin. Silting conditions under hernipelagic sedimentation led to their death. Similar palaeogeographic changes and geodynamic evolution have been described recently from different structures in North Africa, Western Europe and North America.

Chafiki, Driss; Canérot, Joseph; Souhel, Abdellatif; el Hariri, Khadija; Eddine, Kamal Taj

2004-06-01

201

High resolution strain observations: Installation and first results of new laser strainmeters at the Geodynamic Observatory Moxa/Germany  

NASA Astrophysics Data System (ADS)

Since 1964 two quartz tube strainmeters (SN & EW) have been operating as long-period seismometers in the gallery of the Geodynamic Observatory Moxa, located approx. 30 km south of Jena (Germany). In the last 15 years, also the longperiodic signals have been recorded and investigated. The mechanical strainmeters were complemented by a third component in 2003, a laser strainmeter which is oriented NW-SE and connects the endpoints of the quartz tube strainmeters. In 2005 a borehole strainmeter was added to the whole arragement. In 2011 parallel to the east-west and north-south oriented quartz tubes, two new laser strainmeters were installed. Comparing the first time series of all strainmeters shows a significantly higher data quality of the new laser systems, especially regarding the long- and aperiodic drift behaviour, the signal to noise ratio of the diurnal and semidiurnal tidal periods as well as the high frequency parts of the signal. As such laser strainmeter systems could also operate with small base lengths of e.g. one meter, it is potentially feasible to construct mobile systems, which can be used, e.g. in connection with monitoring hazard related phenomena, such as cockpits or collapse sinks as well as tectonically highly active regions.

Schindler, P.; Jahr, T.; Jentzsch, G.; Kukowski, N.

2012-04-01

202

Pressure-temperature history of the Brooks Range and Seward Peninsula, Alaska HP-LT units and geodynamic implications  

NASA Astrophysics Data System (ADS)

Metamorphic rocks in the inner zones of mountain belts constitute a marker of vertical movements within orogenic wedges, themselves controled by balance between boundary conditions and volume forces. They provide key evidence for paleogeographic and tectonic reconstruction of convergence zones. In the Arctic, the Amerasian basin opened in cretaceous time and evolved in the upper plate of the Pacific subduction system. The tectonic evolution of the Brooks Range, northern Alaska, is a key issue for understanding possible coupling between these two dynamics. HP-LT metamorphic rocks, now exposed in the Schist belt, Brooks Range, and the Nome Complex, Seward Peninsula, were brought to the surface during Early Cretaceous to Paleocene time. The processes responsible for their exhumation (syn-collisional nappe-stacking or post-collisional extensional detachment) are still a matter of debate, and have direct implications in terms of orogenic boundary conditions and coupling between subduction processes (to the south) and basin response (to the north; the North Slope). Systematic thermometry via Raman Spectrometry (RSCM) on carbonaceous material from regional transects in the Schist Belt and the Seward Peninsula as well as pseudosections calculations allow the determination of units with contrasting pressure-temperature histories and a comparison of thermal evolution of the two areas. Geodynamic implications of their exhumation is then discussed.

Lemonnier, N.; Labrousse, L.; Agard, P.; Till, A. B.

2013-12-01

203

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

204

Anomalies in the variations of the radon concentration related to geodynamical processes in the volcano Popocatepetl, Mexico  

NASA Astrophysics Data System (ADS)

Analysis of the variation of the concentration of radon (noble gas with natural radioactivity) measured in the area of the volcano Popocatepetl is presented. Permanent observations were performed at different places (Tlamacas station, Paso de Cortes, and the referent site in Amecameca) during December 2007 - January 2009, data were collected by identical Radon Scout instruments (manufactured by SARAD company) with integration time 1 hour per sample. Our analysis reveals certain stable tendencies. First of all, averaged values of the radon concentration observed in the volcano sites (Tlamacas and Paso de Cortes) are 4-10 greater of those measured in the Amecameca referent site. Then, there is a distinct difference between the data recorded at 2 volcano sites. Paso de Cortes (20 km away from volcano) data regularly manifest high level values with only diurnal variation, unlike the Tlamacas station (4 km away) data display considerable variations possibly associated with volcano geodynamics. Thus, there are numerous gradual depletions of the radon concentration with duration from about 12 hours up to several days. We associate most of observed anomalies with 2 volcano-related events: 1) in major cases radon depletions anticipates moderate volcano eruptions, and 2) some of the observed anomalies accompany tectono-volcanic events.

Kotsarenko, A.; Grimalsky, V.; Koshevaya, S.; Yutsis, V.; Pérez-Enríquez, R.; Cruz Abeyro, J. A. L.; Villegas Cerón, R. A.; Valdés-Gonzáles, C.

2009-04-01

205

Time Series Analysis of Epn Stations As A Criterion of Choice of Reference Stations For Local Geodynamic Networks  

NASA Astrophysics Data System (ADS)

The definition of a geodetic reference system by modern techniques (GPS) requires systematic temporal changes of the position of the defining stations. Authors present the results of time series analysis of EPN stations located no more then 700 km from our LGN in Sudety Mts. and Sudety Foreland (e.g. WTZR, BOR1, GRAZ, PENC, POTS, JOZE, GOPE, BOGO, LAMA, WROC), performed for the selection of the best reference stations. The proposed methods of coordinates time series analysis using Matlab libraries and own Matlab toolboxes are discussed. The results of comparison of analysis results with tectonic background for EPN stations are presented. Taking into account the results of performed classification as well as the distance between stations and the local research area (Sudety Mts., SW Poland), the best conditions of connection of local measurements to the European network have been fulfilled for the stations: BOR1, PENC, GOPE, GRAZ and POTS. Stations as WROC and MOPI, located also close to the research area possesses significantly worse quality parameters. Finally the influence of reference station selection on estimated velocities of local geodynamic network points is shown. Presented analysis have been related only to the horizontal coordinates and velocities. This work has been supported by the Polish State Committee for Scientific Research grants No 9T12E00518 and 9T12E02918.

Borkowski, A.; Bosy, J.; Kontny, B.

206

The Multi-factor Predictive Seis &Gis Model of Ecological, Genetical, Population Health Risk and Bio-geodynamic Processes In Geopathogenic Zones  

NASA Astrophysics Data System (ADS)

I. Goal and Scope. Human birth rate decrease, death-rate growth and increase of mu- tagenic deviations risk take place in geopathogenic and anthropogenic hazard zones. Such zones create unfavourable conditions for reproductive process of future genera- tions. These negative trends should be considered as a protective answer of the com- plex biosocial system to the appearance of natural and anthropogenic risk factors that are unfavourable for human health. The major goals of scientific evaluation and de- crease of risk of appearance of hazardous processes on the territory of Dnipropetrovsk, along with creation of the multi-factor predictive Spirit-Energy-Information Space "SEIS" & GIS Model of ecological, genetical and population health risk in connection with dangerous bio-geodynamic processes, were: multi-factor modeling and correla- tion of natural and anthropogenic environmental changes and those of human health; determination of indicators that show the risk of destruction structures appearance on different levels of organization and functioning of the city ecosystem (geophys- ical and geochemical fields, soil, hydrosphere, atmosphere, biosphere); analysis of regularities of natural, anthropogenic, and biological rhythms' interactions. II. Meth- ods. The long spatio-temporal researches (Y. Bondarenko, 1996, 2000) have proved that the ecological, genetic and epidemiological processes are in connection with de- velopment of dangerous bio-geophysical and bio-geodynamic processes. Mathemat- ical processing of space photos, lithogeochemical and geophysical maps with use of JEIS o and ERDAS o computer systems was executed at the first stage of forma- tion of multi-layer geoinformation model "Dnipropetrovsk ARC View GIS o. The multi-factor nonlinear correlation between solar activity and cosmic ray variations, geophysical, geodynamic, geochemical, atmospheric, technological, biological, socio- economical processes and oncologic case rate frequency, general and primary popula- tion sickness cases in Dnipropetrovsk City (1.2 million persons) are described by the multi-factor predictive SEIS & GIS model of geopathogenic zones that determines the human health risk and hazards. Results and Conclusions. We have created the SEIS system and multi-factor predictive SEIS model for the analysis of phase-metric spatio- 1 temporal nonlinear correlation and variations of rhythms of human health, ecological, genetic, epidemiological risks, demographic, socio-economic, bio-geophysical, bio- geodynamic processes in geopathogenic hazard zones. Cosmophotomaps "CPM" of vegetation index, anthropogenic-landscape and landscape-geophysical human health risk of Dnipropetrovsk City present synthesis-based elements of multi-layer GIS, which include multispectral images SPOT o, maps of different geophysical, geochem- ical, anthropogenic and citogenic risk factors, maps of integral oncologic case rate frequency, general and primary population sickness cases for administrative districts. Results of multi-layer spatio-temporal correlation of geophysical field parameters and variations of population sickness rate rhythms have enabled us to state grounds and to develop medico-biological and bio-geodynamic classification of geopathogenic zones. Bio-geodynamic model has served to define contours of anthropogenic-landscape and landscape-geophysical human health risk in Dnipropetrovsk City. Biorhythmic vari- ations give foundation for understanding physiological mechanisms of organism`s adaptation to extreme helio-geophysical and bio-geodynamic environmental condi- tions, which are dictated by changes in Multi-factor Correlation Stress Field "MCSF" with deformation of 5D SEIS. Interaction between organism and environment results in continuous superpositioning of external (exogenic) Nuclear-Molecular-Cristallic "NMC" MCSF rhythms on internal (endogenic) Nuclear-Molecular-Cellular "NMCl" MCSF rhythms. Their resonance wave (energy-information) integration and disinte- gration are responsible for struc

Bondarenko, Y.

207

Present Day Hot Spot Melting Inferred from Geodynamics and Thermodynamics Modeling and the Thermal History of the Mantle  

NASA Astrophysics Data System (ADS)

Hot spot melting is the end-product of a complex sequence of processes that most likely starts at the CMB boundary. To provide a complete description and a better constrained understanding of the melting process from the petrological and geophysical point of view, two requirements appear to be essential. 1) accurate knowledge of the physico-chemical and thermodynamic properties of the mantle, and characterization of the thermal and geodynamic conditions for the generation and evolution of a thermal plume. 2) development of a geodynamic numerical procedure that incorporates the properties of the mantle and is capable of simulate the thermal evolution of a plume and the petrological evolution of the melting process. The thermodynamic approach is best suited to accomplish the latter objective. By following these requirements, the model allows us to compute several features that can be independently compared with petrological and geophysical observations which ultimately provide a validation for the whole procedure. The viscosity and the thermal conditions leading to the formation of a thermal plume are retrieved from a separate study of the thermal history of the mantle that is mainly constrained by the requirement for melting in the upper mantle in the past and recent time (session DI19, contribution entitled: A Viscosity Model for the Mantle Based on Diffusion in Minerals and Constrained by the Thermal History and Melting of the Mantle). The main topic of this contribution is the final stage of the plume evolution, that is the the thermal structure and melting in a hot spot setting, focusing in particular on the magmatism associated to the Hawaiian-Emperor seamount chain. The numerical study is a work in progress that reveals several key features. Perhaps the most important aspect that emerge from the modeling work is the formation of periodic instabilities and the thermal erosion of the base of the lithosphere which are mainly induced by the formation and transport of melt. The dynamic evolution of the base of the lithosphere shows a significant correspondence with the bathymetry and topography of the seamount chain. The sequence of pre-shield, shield and post-shield magmatism is also consistent with this scenario. The combined two-phase flow model and thermodynamic formulation for melting describes a polybaric dynamic melting process. One important observation is that volcanism and emplacement of melt on the surface can take place much later and at some lateral distance from the vertical location where melting originally started. This observation applies for the development of tholeiitic basalts but also for pyroxenite cumulates that, even though are associated to post-erosional events, may have actually formed in an earlier stage. The model reveals also that a lithospheric component contributes to the generation of the melt, which is not necessarily in contradiction with the isotopic evidence of an ancient mantle reservoir. Magma permeability plays a crucial role on the characterization of the extent of the melt production and local abundance because it affects melt transport and chemical variations of the residual solid.

Tirone, M.; Ganguly, J.

2011-12-01

208

Understanding the geodynamic setting of São 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

209

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

210

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

211

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

212

Petrogenesis and Geodynamic Significance of Late Precambrian-Early Paleozoic Metagranites in Istranca (Strandja) Zone, NW Pontides, Turkey  

NASA Astrophysics Data System (ADS)

The existence of Cadomian arc magmatism in Istranca Zone within the Western part of the Pontides was determined according to new zircon U-Pb dating and whole-rock geochemical analysis of the Çatalca and ?hsaniye metagranites. Magmatic evolution of the Late Precambrian-Early Paleozoic metagranites in Istrandja Zone related to the Cadomian orogeny along the northern Gondwana margin. The Istranca zone is composed of metamorphic basement intruded by large granitic bodies and overlain by a Paleozoic-Mesozoic meta-sedimentary cover. The metamorphic rocks of the Istranca zone extend from Bulgaria, Istranca Mountains to NW Turkey and reach the area near Istanbul (Çatalca region). The Çatalca and ?hsaniye metagranites have a subalkaline, high-K calc-alkaline and peraluminous character. Trace element geochemistry displays decreasing normalized concentrations from large-ion lithophile (LIL) elements to high field strength (HFSE) elements and from light (LREE) to heavy rare earth elements (HREE). A negative Eu anomaly is both types of metagranites. On tectonic discrimination diagrams, the samples from both metagranites plot in the subduction-related fields. The SHRIMP-II U-Pb zircon ages of the Çatalca metagranite range from 534.5 ± 4.7 Ma to 546.0 ± 3.9 Ma and LA-ICP-MS U-Pb zircon dating yields 535.5 ± 3.6 Ma age for the ?hsaniye metagranite. The new ages together with the geochemical constraints allow a new geodynamic interpretation for the Istranca zone and we compare these metagranites with other Upper Ediacaran to Lower Cambrian granitoids of Turkey and Alpine-Himalayan orogenic belt. We deduce an origin of these elements from the northern Gondwana-Land margin.

Yilmaz Sahin, Sabah; Aysal, Nam?k; Gungor, Y?ld?r?m; Peytcheva, Irena; Neubauer, Franz

2014-05-01

213

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

NASA Astrophysics Data System (ADS)

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 V-1 and 0.2 ± 0.7 ?Gal a-1 (1 ?Gal = 10-8 m s-2). Both the SG and absolute gravity records contain trends of about 2-3 ?Gal a-1. The ocean tide gravity effects (OTGEs) were estimated from NAO.99b, FES2004, and CSR4.0, and their amplitudes agree with the SG observations at the submicroGal level, but their phases differ from the observations up to 10°. The Newtonian effect of ocean tide contributes 20% to the total OTGE at HS, and it is larger at islands in the Taiwan Strait. The inelastic body tide model of Dehant et al. (1999) is more consistent with the SG observations than the elastic model. Modeled gravity-atmosphere admittances based on an exponential distribution of air mass explain well the observed admittances. The average gravity-atmosphere admittance during typhoons is 30% larger than that in a nontyphoon time. A list of coseismic gravity changes from T48 caused by earthquakes over 2006-2007 is given for potential studies of fault parameters. The modeled effects of atmospheric pressure, groundwater, soil moisture, and polar motion explain the FG5 observed gravity trend to 1.1 ?Gal a-1. Seasonally, the groundwater-induced gravity change contributes the most to the SG residual gravity, but its phase leads the latter by 63 days.

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

2009-07-01

214

Geodynamical modeling and multiscale seismic expression of thermo-chemical heterogeneity and phase transitions in the lowermost mantle  

NASA Astrophysics Data System (ADS)

The D region at the base of the mantle is characterized by seismologically inferred 3D heterogeneity, including multiple interfaces, localized low velocity zones, and anisotropy. The occurrence of the post-perovskite (PPV) phase transition with a steep Clapeyron slope of 11.5-13 MPa/K, close to the core-mantle boundary, is a prime candidate for explaining observed seismic layering in the D. To examine the effect of the PPV phase transition on seismic structure we have carried out finite-element simulations with high-resolution (up to 3 km) in a cylindrical geometry. The rheology of the mantle has both Newtonian diffusion and non-Newtonian components, with a much greater propensity to non-Newtonian for PPV. From the temperature output we computed the 2D variations in shear wavespeed using a seismic equation of state based on mineral physics data. We then use a wave-packet decomposition of the wavespeed variations, which accounts for the events-to-stations illumination to obtain the seismic expressions of the geodynamically modeled structures. The results reveal lens-shaped PPV structures, much like the patterns obtained from seismic imaging with ScS data. A similar analysis of thermo-chemical anomalies from a subducting slab with crustal material shows that structures with a spatial scale of MORB crustal thickness produce characteristic features reminiscent of the small scale detail in the seismic imaging results. These experiments illustrate the high sensitivity of the seismic expression near the CMB to the wavespeed coefficients of the oceanic crust under high pressure conditions.

van den Berg, Arie P.; De Hoop, Maarten V.; Yuen, David A.; Duchkov, Anton; van der Hilst, Robert D.; Jacobs, Michael H. G.

2010-06-01

215

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, 42.08±0.09 to 29.02±0.29 Ma). The Eocene sequence is associated with calc-alkaline composition Laleda? granodiorite, Beyçay?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

216

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

PubMed

In May 1990, a quartz tube extensometer was installed in the Sopronbánfalva 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. PMID:20687746

Mentes, Gy

2010-07-01

217

Visualizing 3D mantle structure from seismic tomography and geodynamic model predictions of the India-Eurasia and East Asia convergence zone  

NASA Astrophysics Data System (ADS)

In light of the extremely deformed and complex surface geology in the Central and Eastern Asian convergence zones, the subsurface mantle structure holds vital clues to the evolution of the subduction zones and collisional chronologies. This is especially true for the Tethyan convergence zone, where the mantle structure has been used to suggest intra-oceanic subduction preceded the terminal collision between the Indian and Eurasian continents. Geodynamic models of such a scenario have confirmed that a two-stage collision better reproduces the present-day mantle structure, and particularly the latitudinal range of discrete Tethyan mid-mantle slabs. Using our plate reconstruction software, GPlates (www.gplates.org), we visualise our evolving geodynamic models of subduction and the mantle structure interpreted from seismic tomographic models to account for the evolution of subduction zones in Central and East Asia in a combined plate tectonic and 3D mantle structure context for times since the Jurassic. By visualising the source and trajectory of slabs in the mantle over time enables correlations with positive seismic velocity anomalies at present day with improved confidence. Our approach emphasises the need to capture mantle convection that includes slab advection resulting from return flow and the complex slab interactions from multiple nearby subduction zones such as the Pacific and Tethyan domains. Mantle temperature isosurface with semi-transparent deviation window and surface mask excluding Eurasian plate.

Cannon, J.; Pfaffelmoser, T.; Zahirovic, S.; Müller, R.; Seton, M.

2012-12-01

218

Nature and distribution of geological domains at the Africa-Eurasia plate boundary off SW Iberia and regional geodynamic implications  

NASA Astrophysics Data System (ADS)

We present a new classification of geological domains at the Africa-Eurasia plate boundary off SW Iberia, together with a regional geodynamic reconstruction spanning from the Mesozoic extension to the Neogene-to-present-day convergence. It is based on seismic velocity and density models along two regional wide-angle seismic transects, one running NW-SE from the Horseshoe to the Seine abyssal plains, and the other running N-S from S Portugal to the Seine Abyssal Plain, combined with previously available information. The seismic velocity and density structure at the Seine Abyssal Plain and the internal Gulf of Cadiz indicates the presence of a highly heterogeneous oceanic crust, similar to that described in ultra-slow spreading centers, whereas in the Horseshoe and Tagus abyssal plains, the basement structure resembles that of exhumed mantle sections identified in the Northern Atlantic margin. The integration of all this new information allows defining the presence of three oceanic domains offshore SW Iberia: (1) the Seine Abyssal Plain domain, generated during the first stages of slow seafloor spreading in the NE Central Atlantic (Early Jurassic); (2) the Gulf of Cadiz domain, made of oceanic crust generated in the Alpine-Tethys spreading system between Iberia and Africa, which was coeval with the formation of the Seine Abyssal Plain domain and lasted up to the North Atlantic continental break-up (Late Jurassic); and (3) the Gorringe Bank domain, mainly made of rocks exhumed from the mantle with little synchronous magmatism, which formed during the first stages of North Atlantic opening. Our models suggest that the Seine Abyssal Plain and Gulf of Cadiz domains are separated by the Lineament South strike-slip fault, whereas the Gulf of Cadiz and Gorringe Bank domains appear to be limited by a deep thrust fault located at the center of the Horseshoe Abyssal Plain. The formation and evolution of these three domains during the Mesozoic is key to understand the sequence of events that occurred during the first stages of opening of the Northern Atlantic.

Martínez-Loriente, Sara; Sallarès, Valentí; Gràcia, Eulàlia; Bartolome, Rafael

2014-05-01

219

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 Costeña 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

220

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 Basalt—Keratophyre 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

221

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 150-160°C.

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

2013-04-01

222

Crustal source of the Late Cretaceous Satansar? monzonite stock (central Anatolia - Turkey) and its significance for the Alpine geodynamic evolution  

NASA Astrophysics Data System (ADS)

The Late Cretaceous granitic rocks within central Anatolia (Turkey) not only date and show the magmatic aspects of the Alpine realm, but also give clues about its geodynamic character. Among them, the Satansar? monzonite stock (SMS), part of the Terlemez pluton (Aksaray), characterizing the inception of an extensional tectonic regime in central Anatolia, has a subalkaline, metaluminous and magnesian geochemical nature with depletion in Ba, Nb, P and Ti, and with enrichment of Th, U, K and Pb relative to primitive mantle. The SMS has LREE enriched patterns ([La/Yb]N = 18.45-21.21) with moderately negative Eu-anomalies ([Eu/Eu*]N = 0.65-0.73). The geochemical data infer a crustal source with an inherited subduction-related component, and fractionation of plagioclase and amphibole. A crustal signature for the SMS is also inferred from high 87Sr/86Sr(t) ratios (0.70826-0.70917), and low ?Nd(t) values (-6.9 to -7.6). Zircon crystals from the SMS typically have magmatic rims overgrowing inherited cores that are reworked, resorbed and overgrown. Completely new zircon crystals grown in a single magmatic episode have also been identified. Laser ablation ICP-MS U-Pb zircon analyses yield a mean 206Pb/238U age of 74.4 ± 0.6 Ma (2?) for the intrusion of the SMS. Rare discordant analyses range from the Devonian to the Proterozoic (i.e., 207Pb/206Pb ages between 364 Ma and 1263 Ma). In situ zircon Hf isotope analyses reveal low 176Lu/177Hf ratios and negative ?Hf(t) values, which is consistent with a predominantly crustal source of the SMS. We suggest that the water-rich magmas were generated in a hot zone within the crust produced by residual melts from basalt crystallization and partial melts of pre-existing metamorphic and igneous rocks within the lower crust of central Anatolia. The SMS likely formed by episodic injections of these hybrid monzonite melts by adiabatic ascent to shallow crust where they crystallized. This interpretation may be useful in interpreting the involvement of crustal sources for other monzonitic rocks in central Anatolia and granitic magmatism in other similar tectonic environments.

Köksal, Serhat; Toksoy-Köksal, Fatma; Göncüo?lu, M. Cemal; Möller, Andreas; Gerdes, Axel; Frei, Dirk

2013-04-01

223

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

224

Miocene shoshonite volcanism in Sardinia: Implications for magma sources and geodynamic evolution of the central-western Mediterranean  

NASA Astrophysics Data System (ADS)

In this paper we document the existence of a Miocene shoshonite (SHO) volcanism in Northern Sardinia (Anglona). This occurrence completes the spectrum of orogenic magmas related to the subduction process which developed from the Eocene along the Palaeo-European continental margin, in concert with the opening of the Ligurian-Balearic back-arc basin and southeastward drift/rotation of the Sardinia-Corsica continental block. K-Ar ages show that the oldest volcanics of the area are calcalkaline (CA) basalts and andesites (~ 21 Ma), overlain by 19.7-18.4 Ma-old more potassic products such as high-potassium calcalkaline (HK-CA) and SHO lavas. CA, HK-CA and SHO suites include basalts and differentiated lavas of andesite and latite composition, respectively, that (according to the PELE software modelling) represent ~ 40-45% residual liquid fraction after shallow fractional crystallization. Application of the "Arc Magma Simulator" software suggests that the generation of primary melts of the distinct suites may occur at similar degrees of partial melting (5-8%) and melting pressures (2-2.2 GPa, ~ 60-70 km depth) in the mantle wedge. By contrast, the potassic character of parental melts of CA, HK-CA and SHO suites is controlled by 1) the amount of subducted continental components (possibly terrigenous sediments) and 2) the pressure (depth) at which these metasomatic agents are released from the slab. Results suggest that the slab depth beneath the volcanic district increased from ~ 80-100 to 100-120 km for CA and SHO magmas, respectively. Accordingly, the evolution from CA to SHO magmatism in the same plumbing system could be related to slab deepening and increase of the subduction angle of ~ 5-10° in the time span of 2-3 Ma. This tectono-magmatic scenario conforms to the major anticlockwise rotation (~ 30°) event of the Sardinia block (between 20.5 and 18 Ma). This geodynamic evolution preludes the development of the volcanism in the Apennine-Tyrrhenian domains, where the final collisional/post-collisional stages of subduction were characterized by accentuated slab retreat and roll back, inter-arc extension and eruption of highly potassic magmas in the frontal arc (Roman and Aeolian Provinces).

Beccaluva, Luigi; Bianchini, Gianluca; Mameli, Paola; Natali, Claudio

2013-11-01

225

Geodynamic models of plumes from the margins of large thermo-chemical piles in the Earth's lowermost mantle  

NASA Astrophysics Data System (ADS)

We present geodynamic models featuring mantle plumes that are almost exclusively created at the margins of large thermo-chemical piles in the lowermost mantle. The models are based on global plate reconstructions since 300 Ma. Sinking subducted slabs not only push a heavy chemical layer ahead, such that dome-shaped structures form, but also push the thermal boundary layer (TBL) toward the chemical domes. At the steep edges it is forced upwards and begins to rise — in the lower part of the mantle as sheets, which then split into individual plumes higher in the mantle. The models explain why Large Igneous Provinces - commonly assumed to be caused by plumes forming in the TBL above the core-mantle boundary (CMB) - and kimberlites during the last few hundred Myr erupted mostly above the margins of the African and Pacific Large Low Shear Velocity Provinces (LLSVPs) of the lowermost mantle, which are probably chemically distinct from and heavier than the overlying mantle. Computations are done with two different codes, one based on spherical harmonic expansion, and CITCOM-S. The latter is combined with a self-consistent thermodynamic material model for basalt, harzburgite, and peridotite, which is used to derive a temperature- and presssure dependent database for parameters like density, thermal expansivity and specific heat. In terms of number and distribution of plumes, results are similar in both cases, but in the latter model, plume conduits are narrower, due to consideration of realistic lateral - in addition to radial - viscosity variations. For the latter case, we quantitatively compare the computed plume locations with actual hotspots and find that the good agreement is very unlikely (probability < 0.1 %) to result by chance. We also compare with results obtained without a chemical layer in the lowermost mantle. In addition to the 3-D models with earthlike geometry, we also show results obtained with a 2-D finite element code. These results allow us to assess how much the computed long-term stability of the piles is affected by numerical diffusion. We have also conducted a systematic investigation, which configurations of piles and plumes can exhibit long-term stability, and under what conditions (in particular, amount and location of subduction, thermal expansivity vs. depth) thermo-chemical piles can remain stable, if subduction occurs above or near them. Our models support that mantle plumes are more intimately linked to plate tectonics than commonly believed. Not only can plumes cause continental break-up, but conversely subducted plates may trigger plumes at the margins of LLSVPs near the CMB.

Steinberger, B. M.; Gassmoeller, R.; Mulyukova, E.

2012-12-01

226

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

227

The utilization of Malaysian Active GPS System data for geodynamic applications: a case study in East and West Malaysia  

NASA Astrophysics Data System (ADS)

Geodynamic studies of Malaysia have been ventured upon in the South-East Asia region since the first GeodySEA project in 1996. Both East and West Malaysia lies on the Eurasian Plate, and assumed to have no linear distortion between any two joined points relative to one another. However, Malaysia lies at the southern tip of the plate encroached by two frequently ruptured boundaries, the Indian-Australian plate and the Philippines plate, and it is also within the buffer of the Ring of fire. Hence, this paper is essential to determine the relative movement of Malaysia, and with the possibilities to identify the presences of slip-fault formation which might be of threat to the stable platform that we have taken for granted. Availability of uninterrupted GPS observations over the Malaysian Active GPS System known as MASS stations situated across the country established by the Department of Survey and Mapping (DSMM) evidently help provides the data for this study. There are currently eighteen MASS stations mounted with Trimble 4000 dual frequency antenna and data recorded at fine second interval made accessible in hourly files. Satellite data collected continuously over a long period of time are processed by Bernese GPS processing software. Fifteen International GNSS Service (IGS) stations were selected within similar period of observations were gathered, processed, later act as tie points to the MASS stations. Apparently with this Malaysia will form a network to the globe. In this research the author will output the relative MASS stations coordinates and velocity estimates in International terrestrial reference frame (ITRF) 2000 since GPS data used are before the derivation of ITRF2005. At present the measures of quality for GPS derived coordinates given by commercial software packages tend to be unrealistic because unmodelled errors remain unaccounted for. The commercial software packages are either over-optimistic or conversely, therefore, have low fidelity. Thus, Bernese GPS processing software was used here due to its capability to provide high precision result for long baselines observables and able to parameterize the atmosphere, earth rotation, earth and ocean tide from the terrestrial observations. The output of this study showed that the velocity of the relative movement of Malaysia have a magnitude of 3cm per year for the year 2000 till 2002 and towards the South-Eastern direction. For future research, data should be processed with the latest version of Bernese GPS processing software 5.0 which allows for a fully combined processing of data from both GPS and GLONASS receivers with standard ambiguity resolution strategies taking reference to ITRF2005.

Abu Bakar, Rabieahtul; Azahari Razak, Khamarrul

2010-05-01

228

Unraveling the tectonic history of northwest Africa: Insights from shear-wave splitting, receiver functions, and geodynamic modeling  

NASA Astrophysics Data System (ADS)

The complex tectonic history and orogenesis in the westernmost Mediterranean are primarily due to Cenozoic convergence of Africa with Eurasia. The Gibraltar system, which includes the Rif Mountains of Morocco and the Betics in Spain, forms a tight arc around the Alboran Basin. Further to the south the Atlas Mountains of Morocco, an example of an intracontinental fold and thrust belt, display only modest tectonic shortening, yet have unusually high topography. To the south of the Atlas, the anti-Atlas is the oldest mountain range in the region, has the lowest relief, and extends toward the northern extent of the West African Craton. To help unravel the regional tectonics, we use new broadband seismic data from 105 stations across the Gibraltar arc into southern Morocco. We use shear wave splitting analysis for a deep (617 km) local S event and over 230 SKS events to infer azimuthal seismic anisotropy and we image the lithospheric structure with receiver functions. One of the most striking discoveries from these methods is evidence for localized, near vertical-offset deformation of both crust-mantle and lithosphere-asthenosphere interfaces at the flanks of the High Atlas. These offsets coincide with the locations of Jurassic-aged normal faults that were reactivated during the Cenozoic. This suggests that these lithospheric-scale discontinuities were involved in the formation of the Atlas and are still active. Shear wave splitting results show that the inferred stretching axes are aligned with the highest topography in the Atlas, suggesting asthenospheric shearing in mantle flow guided by lithospheric topography. Geodynamic modeling shows that the inferred seismic anisotropy may be produced by the interaction of mantle flow with the subducted slab beneath the Alboran, the West African Craton, and the thinned lithosphere beneath the Atlas. Isostatic modeling based on these lithospheric structure estimates indicates that lithospheric thinning alone does not explain the anomalous Atlas topography. Instead, an upwelling component induced by a mantle anomaly is also required to support the Atlas, suggesting that the timing of uplift is contemporaneous with recent volcanism in the Middle Atlas.

Miller, M. S.; Becker, T. W.; Allam, A. A.; Alpert, L. A.; Di Leo, J. F.; Wookey, J. M.

2013-12-01

229

Markers for geodynamic stability of the Variscan basement: case study for the Montseny-Guilleries High (NE Iberia)  

NASA Astrophysics Data System (ADS)

The Montseny-Guilleries High is a Miocene horst composed of Variscan basement rocks, situated in the northeastern part of the Catalan Coastal Ranges (NE Iberia). The Montseny-Guilleries High has an asymmetric profile with an abrupt faulted scarp at the southeastern margin and a smooth surface dipping to the Northwest; here Paleocene sediments of the Ebro basin margin are to some extend in onlap. The stratigraphic arrangement of the Mesozoic units in the Catalan Coastal Ranges indicate that the Montseny-Guilleries area was a relief during the Mesozoic, remaining exposed probably from the Permian to the Cretaceous [Anadón et al., 1979; Gómez-Gras, 1993]. The high subsequently has been faulted due to a rifting phase that took place during the Miocene [Anadón et al., 1979]. The geodynamic history (burial-exhumation processes and denudation rate) of the Montseny-Guilleries High can be deciphered from cooling markers, such as for example apatite fission tracks [Juez-Larré & Andriessen, 2006]. However, the cooling history of an area depends on many factors (i.e. denudation rate, variations of the geothermal gradient) that complicate interpretations [Juez-Larré & Ter Voorde, 2009]. Another solution is to search for datable paleoweathering records in order to obtain benchmarks for ancient surfaces of continental exposure. This is the case for the Permian-Triassic paleosurface, at which an extensive albitization-hematisation alteration occurred at shallow depth [Thiry et al., 2009]. Several paleoalterations have been identified in the Montsent-Guilleries High [Gómez-Gras & Ferrer, 1999]. These alterations are coupled to the smooth surface or peneplain of the northwestern margin of the high and form a paleoprofile with less altered rocks on the lower parts of the relief and more altered rocks located at the higher parts of the relief (i.e. on the peneplain). From base to top, the profile starts with week albitization-hematisation of the facies developed mainly in the fractures; the degree of albitization-hematisation progressively increases towards the top affecting the whole rock, which acquires a characteristic pink color. Finally, the top of the profile is formed by strongly altered to hematite and kaolinite rich reddish facies. These uppermost parts of the alteration profile are formed by a relatively soft rock and are therefore usually not preserved, but the intermediate albitized parts are more resistant to surface alteration than unaltered facies and protect the peneplain from weathering and erosion. The albitization-hematisation alterations observed in the Montseny-Guilleries peneplain are very similar to the Permian-Triassic paleoalteration profiles observed in other parts of Europe, affecting the Variscan basement [Ricordel et al., 2007; Parcerisa et al., 2009]. Dating these profiles using paleomagnetic methods will help us to identify the location of the Permian-Triassic surface in the area and deduce its geodynamic history during the Mesozoic and Tertiary periods. Anadón, P., Colombo, F., Esteban, M., Marzo, M., Robles, S., Santanach, P., Solé-Sugrañes, L., 1979, Evolución tectonostratigráfica de los Catalánides, Acta Geol. Hisp., 14: 242-270. Gómez-Gras, D., 1993, El Permotrias de la Cordillera Costero Catalana: facies y petrologia sedimentaria (Parte I), Bol. Geol. Min., 104 (2): 115-161. Gómez-Gras, D., Ferrer, C., 1999, Caracterización petrológica de perfiles de meteorización antiguos desarrollados en granitos tardihercínicos de la Cordillera Costero Catalana, Rev. Soc. Geol. Esp., 12(2): 281-299. Juez-Larre, J., Andriessen, P.A.M., 2006, Tectonothermal evolution of the northeastern margin of Iberia since the break-up of Pangea to present, revealed by low-temperature fission-track and (U-Th)/He thermochronology: A case history of the Catalan Coastal Ranges, Earth Planet. Sci. Let., 243 (1-2): 159-180. Juez-Larré, J., Ter Voorde, M., 2009, Thermal impact of the break-up of Pangea on the Iberian Peninsula, assessed by thermochronological dating and numerical modeling, Tectonophysics, v.

Parcerisa, David; Franke, Christine; Gómez-Gras, David; Thiry, Médard

2010-05-01

230

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

231

Geodynamics: Progress and prospects  

Microsoft Academic Search

The tectonic history of the Western Pacific is considered along with the Nazca Plate, Ophiolites and pelagic sediments in the Alpine-Mediterranean region, Messinian events in the Mediterranean, paleomagnetic studies in the Alpine-Mediterranean area, a geotraverse through the Eastern and Southern Alps, a report on contemporary movements, and the dynamics of the North Anatolian fault. Attention is also given to the

C. L. Drake

1976-01-01

232

Yellowstone Hotspot Geodynamics  

NASA Astrophysics Data System (ADS)

The Yellowstone hotspot results from the interaction of a mantle plume with the overriding N. America plate producing a ~300-m high topographic swell centered on the Late Quaternary Yellowstone volcanic field. The Yellowstone area is dominated by earthquake swarms including a deadly M7.3 earthquake, extraordinary high heat flow up to ~40,000 mWm-2, and unprecedented episodes of crustal deformation. Seismic tomography and gravity data reveal a crustal magma reservoir, 6 to 15 km deep beneath the Yellowstone caldera but extending laterally ~20 km NE of the caldera and is ~30% larger than previously hypothesized. Kinematically, deformation of Yellowstone is dominated by regional crustal extension at up to ~0.4 cm/yr but with superimposed decadal-scale uplift and subsidence episodes, averaging ~2 cm/yr from 1923. From 2004 to 2009 Yellowstone experienced an accelerated uplift episode of up to 7 cm/yr whose source is modeled as magmatic recharge of a sill at the top of the crustal magma reservoir at 8-10-km depth. New mantle tomography suggest that Yellowstone volcanism is fed by an upper-mantle plume-shaped low velocity body that is composed of melt "blobs", extending from 80 km to 650 km in depth, tilting 60° NW, but then reversing tilt to ~60° SE to a depth of ~1500 km. Moreover, images of upper mantle conductivity from inversion of MT data reveal a high conductivity annulus around the north side of the plume in the upper mantle to resolved depths of ~300 km. On a larger scale, upper mantle flow beneath the western U.S. is characterized by eastward flow beneath Yellowstone at 5 cm/yr that deflects the plume to the west, and is underlain by a deeper zone of westerly return flow in the lower mantle reversing the deflection of the plume body to the SE. Dynamic modeling of the Yellowstone plume including a +15 m geoid anomaly reveals low excess plume temperatures, up to 150°K, consistent with a weak buoyancy flux of ~0.25 Mg/s. Integrated kinematic modeling of GPS, Quaternary fault slip, and seismic data suggest that the gravitational potential of the Yellowstone swell creates a regional extension affecting much of the western U.S. Overall, the Yellowstone hotspot swell is the vertex of tensional stress axes rotation from E-W in the Basin-Range to NE-SW at the Yellowstone Plateau as well as the cause of edge faulting, nucleating the nearby Teton and Centennial faults. We extrapolate the original location of the Yellowstone mantle-source southwestward 800 km to an initial position at 17 million years ago beneath eastern Oregon and Washington suggesting a common origin for the YSRP and Columbia Plateau volcanism. We propose that the original plume head ascended vertically behind the subducting Juan de Fuca plate, but was entrained ~12 Ma ago in a faster mantle flow beneath the continental lithosphere and tilted into its present configuration.

Smith, R. B.; Farrell, J.; Massin, F.; Chang, W.; Puskas, C. M.; Steinberger, B. M.; Husen, S.

2012-12-01

233

Integration of permanent and periodic GPS/GNSS measurements for local and regional geodynamic research in the area of the Polish-Czech Network SUDETEN  

NASA Astrophysics Data System (ADS)

Since 1997 all current local geodynamic studies in the area of the Polish and Czech parts of the Sudeten and the Sudetic Foreland have been associated with annual periodic GPS campaigns, epoch measurements. The most epochs consisted of more than twelve observation hours and some of them kept on two or three 24-hour observations. Experience collected by international research teams carrying out geodynamic researches with the GPS technique in seismically active areas (USA, Japan) proved that more information can give permanent measurements. However, the Sudeten area, regarded as an area of the weak tectonic activity, can be hardly covered with the dense network of GNSS stations from economic reasons. Hence rational using of existing permanent GPS stations located in studied area and in its vicinity detects the coordinate changes that cannot be appointed from periodic campaign data and that, on the other hand, have rather regional than local character. Creating the spatial models of irregularities of the continuous signals should improve results of the epoch measurements. From this viewpoint, in this project authors used measurement data of chosen permanent GPS stations located in the area: the EPN stations, ASG-EUPOS stations, GEONAS stations and all epoch observations. These data were gained as part of research projects carried out within 1997-2009 period, as well as during new supplementing campaigns realized in the frame of the project N526278940 in the 2011 and 2012 years. Reprocessing of all the permanent and epoch data performed by the latest version of Bernese GNSS Software (V5.2) was performed using EPN guidelines for the processing, reference frame realization and the usage of physical models (atmosphere, Earth rotation, etc.). Standardized results of processing the aggregated GPS network, including permanent stations and all local networks on the area of research, serve for conducting new geodynamic interpretation. Further parameters that estimate the linear model of position changes of test point coordinates based on results of the permanent and epoch observations had been performed. Then, applying linear site velocities, the surface deformation model for the Sudeten area was compiled. Results of this research constitute the base both for recognizing tectonic impacts to the area and for potential hazard assessments. This research had been granted by the Polish National Science Centre, project No. N526 278940, and accomplished in cooperation of specialists from the Institute of Geodesy and Geoinformatics, Wroclaw University of Environmental and Life Sciences, the Institute of Rock Structure and Mechanics of the Czech Academy of Sciences in Prague and the Polish State Geological Institute, Lower Silesia Branch in Wroclaw.

Kontny, Bernard; Kaplon, Jan; Schenk, Vladimir; Schenkova, Zdenka; Badura, Janusz

2014-05-01

234

Development of fluid-particle coupled simulation method in the Stokes flow regime: toward 3-D geodynamic simulation including granular media  

NASA Astrophysics Data System (ADS)

A fluid-particle two-phase flow has been widely studied in geodynamics, because particle-saturated fluid layer is important for understanding the dynamics of solidifying and melting process in the magma chamber or magma ocean. In order to deal with such particle-fluid systems as the geodynamical modeling in 3-D geometry, we develop a new coupled simulation code of Finite Difference method (FDM) for fluid flow and Discrete Element method (DEM) for solid particles. Although this type of numerical method has been well developed in the engineering field to investigate the fluidized bed especially for the high Reynolds number in short time scales, the method for the low Reynolds number over long time scales has not yet been fully addressed. In the geodynamic modeling with highly viscous fluid, the fluid motion can be treated as the Stokes flow. We employ empirically derived a coupling term between fluid flow and particle motion providing good fit with experimental data of the creeping flow. When this coupling force is directly introduced to the normal DEM equation of particles, we have to numerically solve dumped oscillation with a small time step dt ~1/? for high fluid viscosity ?. Thus the normal DEM does not seem to be suitable solution method for our target problems. We therefore propose to drop off the inertial term from the governing equation of DEM based on the Stokes flow approximation and solve the force balance equation as same as that for the fluid. With this approach, we can employ the large dt~? for the problems with highly viscos fluid. Since our original solution algorithms for both of FDM and DEM are designed for the massively vector parallel architectures with two characteristic numerical techniques, we can solve large size of problems in 3-D geometry. 1. The geometric multi grid method of our robust Stokes flow solver is implemented with agglomeration technique to enhance the parallel efficiency in coarse grid operations. 2. Our DEM utilizes the parallel algorithms for a summation of contact force and search of particle pairs using particle labels sorted by the cell number to improve computational efficiency of the code. In the presentation, we introduce details of our coupled model treatment of the granular medium and demonstrate the validation test with an analogue experiment.

Furuichi, M.; Nishiura, D.; Nakagawa, T.

2012-12-01

235

Contrasts in Archean and Paleoproterozoic Dome-and-Keel Structure: Evidence for Secular Change in Precambrian Geodynamic Processes?  

NASA Astrophysics Data System (ADS)

Many regions of Archean and Paleoproterozoic continental crust consist of granite-greenstone belts. In these belts, deep troughs (keels) of deformed and metamorphosed cover (supracrustal volcanic and sedimentary rocks) surround regional-scale domes of basement (gneiss, granitoid, and migmatite) creating dome-and-keel structure. Three models for the development of dome-and-keel structure remain the subject of debate: (1) Domes are solid-state diapirs, meaning domes rise and supracrustal rocks sink triggered by a density inversion that develops when denser supracrustal rocks (mafic/ultramafic volcanics and iron-rich sediments) accumulate over radiogenic felsic basement, and the basement becomes hot and mobile (due to insulation by the supracrustals); (2) Domes develop because of crustal shortening, meaning domes represent either the products of fold interference, or are culminations of stacked thrust slices or folds; (3) Domes are Cordilleran-type metamorphic-core complexes, meaning surfaces of domes are regional extensional detachments that arch upwards when exhumed by extreme stretching of overburden. It has been tacitly assumed that dome-and-keel structures formed both during Archean and Paleoproterozoic time reflect the same processes. Whether such structures formed in the Phanerozoic remains unclear. Based on field relationships in two examples, the Quadrilatero Ferrifero (QF) of Minas Gerais in eastern Brazil, and the Penokean orogen of northern Michigan, it appears that Archean dome-and-keel structure and Paleoproterozoic dome-and-keel structure differ markedly from each other in terms of the process by which they formed. In the QF, two distinct deformation events may have produced the dome-and-keel structure. The first was Archean (ca. 2.7 Ga) and involved rise of basement, and possibly magma, into overlying greenstone/sedimentary cover of comparable age. Based on map relations and kinematic features, this phase is compatible with a solid-state diapir model; the rise of diapirs may have been triggered by extensional collapse of a thick greenstone assemblage built on felsic crust that became progressively warmer and weaker due to insulation. Interior structure and radiometric dating of domes in the Republic area of northern Michigan suggest a similar history there. The second, in both the QF and the Republic areas, was Paleoproterozoic, about 0.5 b.y. after greenstone formation, when slip on normal-sense shear zones dropped Paleoproterozoic strata (including BIF), which had just previously been involved in fold-thrust-belt deformation, down into a network of steep-sided grabens. In places, the new Paleoproterozoic keels were superimposed on Archean keels, but locally they cross-cut Archean ones. Based on its timing, this second phase of keel formation in the QF is a consequence of the extensional collapse in the fold-thrust belt of the 2.1 Ga Transamazonian orogen. In Republic, this keel-forming event immediately post-dates the Penokean collisional orogeny. Thus, both events appear to be a manifestation of extensional collapse of a fold-thrust belt of a collisional orogen; such a style of extension is kinematically and geometrically very different from Cenozoic Cordilleran core-complexes, and thus is not typical of Phanerozoic orogens. A progressive change from diapiric dome emplacement, to steep-sided graben formation (effectively, crustal-scale boudinage), to core-complex formation, if correct, implies secular evolution of geodynamic processes from the latter part of the Archean into the Paleoproterozoic. Such evolution may reflect a change in the thermal structure of the crust and/or in the densities of crustal materials.

Marshak, S.

2004-05-01

236

Cratonic roots under North America are shifted by basal drag: new evidence from gravity and geodynamic modeling  

NASA Astrophysics Data System (ADS)

The impact of basal drag on the long-lived cratonic roots has been debated since the discovering of plate tectonics. Previously, evidence for a shifted mantle structure under North America was postulated from a comparison of the surface expression of the Great Meteor hotspot track versus its location at 200 km depth as inferred from seismic tomography (Eaton and Frederiksen, 2007). We present new results that are based on the integrative modeling of gravity and seismic data. The starting point is the residual gravity anomaly and residual topography, which are computed by removing of the crustal effect and of the effect of temperature variations in the upper mantle from the observed fields (Mooney and Kaban, 2010). After the temperature correction both residual fields chiefly reflect compositional density heterogeneity of the upper mantle. The residual gravity and topography are jointly inverted to determine the 3D density structure of the upper mantle. The inversion technique accounts for the fact that although these parameters are controlled by the same factors, the effect depends on depth and wavelength. Therefore, we can resolve the vertical distribution of density more reliable than by interpreting only one parameter. We found a strong negative anomaly under the North American craton, as expected for a depleted mantle. However, starting from a depth of about 200 km the depleted root is shifted west-southwest. The maximal shift reaches about 1000 km at a depth of 300 km. The direction agrees with the North American plate movement and with the anisotropy pattern in the upper mantle (e.g. Bokelmann, 2002). The results of the gravity modeling are confirmed by geodynamic modeling. The mantle flow is estimated from the density and temperature distribution derived from seismic tomography models. A 3D viscosity model is supplemented with weak boundaries based on an integrated model of plate boundary deformations. The calculated plate velocities are in a good agreement with the GPS-based models. We found a vertical gradient of the horizontal mantle flow velocity under the North American craton that relates to shear stresses deforming the cratonic root. The lateral velocity within the lowermost part of the lithosphere is about 2 mm/y faster than the overlying plate velocity. If we extrapolate this value to the past, the observed shift of the cratonic root could be achieved in about 500 Ma. Bokelmann GHR, (2002) Convection-driven motion of the North American craton: Evidence from P-wave anisotropy, Geoph. J. Int., 148, 278-287. Eaton DW and Frederiksen A, (2007) Seismic evidence for convection-driven motion of the North American plate, Nature 446, 428-431. Mooney WD, Kaban, MK., (2010). The North American Upper Mantle: Density, Composition, and Evolution, J. Geophys. Res., 115, B12424.

Kaban, M. K.; Petrunin, A.; Mooney, W. D.

2013-12-01

237

Geodynamics of magmatic Cu-Ni-PGE sulfide deposits: new insights from the Re-Os isotope system  

USGS Publications Warehouse

In this study, we reassess crustal contamination and sulfide ore-forming processes in some of the largest magmatic ore deposits, using published Re-Os isotope data and a modeling methodology that incorporates the R factor, defined as the effective mass of silicate magma with which a given mass of sulfide magma has equilibrated, in an Re-Os isotope mixing equation. We show that there is less disparity between conclusions based on Re-Os isotope data compared to other isotopic systems if the R factor is considered, Komatiite-associated Ni sulfide ore systems typically have high Os concentrations, low Re/Os ratios, and near-chondritic initial Os isotope compositions. For magmatic sulfide ores that are interpreted to have experienced relatively low R factors (2,000). Sulfide saturation in these ore systems may, therefore, have been achieved via changes in intensive parameters of the komatiite lavas (cooling or decompression) or changes in compositional parameters transparent to the Re-Os isotope system (e.g., fo2/fs2/fH2O)- Basalt-gabbro-associated Cu-Ni sulfide ore systems at Duluth, Sudbury, and Stillwater are quite distinct from those at Kambalda by having comparatively low Os concentrations, high Re/Os ratios, and high initial Os isotope compositions, These chemical and isotopic characteristics are indicative of significant interactions between their parental basaltic magmas and old crust because there are no known mantle reservoirs with such extreme geocheinical characteristics. Our modeling suggests that for Cu-Ni sulfide ores at Duluth, Sudbury, and Stillwater to maintain the observed high initial Os isotope compositions inherited from a crustal contaminant, R factors for these systems must have been low (< 10,000), consistent with their low metal concentrations. Thus, we interpret this style of base metal sulfide mineralization to be derived from crustally contaminated but less dynamic magmatic systems that did not permit extensive equilibration of sulfide magma with silicate magma, For basalt-gabbro-associated Cu-Ni-PGE-rich sulfide ore systems that have Re-Os geochemical characteristics more similar to those associated with komatiites, R factors must have been high (??? 10,000 for Noril'sk-Talnakh and the J-M reef, Stillwater Complex). In these very dynamic magmatic ore systems, crustal contamination processes are more difficult to assess using Re-Os isotopes as the effects of contamination are masked by the R factor process in which sulfide magma equilibrates with extensive amounts of asthenospheric mantle-derived magma. Sulfide protore for these systems may, then, have been very radiogenic and of crustal origin prior to R factor processes that occurred during transport in feeder conduits and in upper crustal magma chambers. This study, therefore, highlights the need for caution when interpreting the Re-Os isotope geochemistry of sulfide ores from dynamic magmatic systems. The results of our reinvestigation of these giant ore deposits suggest that geodynamic processes associated with large magmatic systems, including major lithospheric pathways to the surface, changes in flow regime, coupled magma flow-through and magma mixing (providing enhanced R factors), may be critical to our understanding of the emplacement, localization, and quality of magmatic sulfide deposits. Thus, the timing and exact mechanism of sulfide saturation may be subordinate to dynamic magmatic processes in the localization of economic concentrations of magmatic sulfides.

Lambert, D. D.; Foster, J. G.; Frick, L. R.; Ripley, E. M.; Zientek, M. L.

1998-01-01

238

An Empirical Approach to Simulating the Development of Various Olivine Fabric and Associated Seismic Anisotropy in Complex Geodynamic Flow Models  

NASA Astrophysics Data System (ADS)

Kevin J. Miller; Laurent G.J. Montési strat944@umd.edu ; montesi@umd.edu Department of Physics, Department of Geology University of Maryland, College Park, MD 20742, United States The detection of seismic anisotropy has become one of the most useful tools for characterizing flow in the Earth’s upper mantle. Thus, it is crucial for geodynamic models to include predictions of anisotropy so that their relevance for the Earth can be easily evaluated. Rigorous fabric development models, which utilize the deformation and rotation of a large number of grains, have already been created for the purpose of analyzing flow models. Such models include D-REX. However, it is important to have simpler tools that provide rapidly first order prediction of mantle fabric and anisotropy. The simplest proxy for anisotropy is provided by the instantaneous flow field, with the fast axis of olivine oriented along the direction for shear. More rigorously, it is possible to integrate finite strain and associate the fast axis of olivine with the direction of maximum elongation. However, the recognition that different fabric types can dominate in different regions of the mantle motivates a more general, albeit empirical model of fabric development. Our empirical approach is motivated as follows: 1) The intensity of the fabric should grow proportionally with the strain rate; 2) The fast, intermediate, and low axes of the crystals should rotate and align towards target directions related to the principal axes of strain rate. To achieve these goals, we developed a 4-step algorithm: 1) The flow field is decomposed into strain rate and rotation rate tensors; 2) We determine the eigenvalues and eigenvectors of the instantaneous strain rate tensor; 3) We switch the order of these eigenvalues, recombining them to produce a fabric development tensor; 4) We return the fabric development tensor to the global reference frame and add the rotation rate tensor. After integration along flow lines, this algorithm produces a tensor that represents the orientation of the olivine axes and can be converted into an anisotropic seismic wave speed tensor. If the switch is skipped, the result is a 3D strain tensor, often represented as a strain ellipse. However, if the second and third eigenvalues (intermediate value and minimum elongation rate) are switched, the [001] axis rotates in the shear plane to be perpendicular to direction of shear whereas the slow axis [010] becomes perpendicular to the shear plane, forming an A-type fabric. Other substitutions produce other target fabrics, such as B- or C-type. It is also possible to adjust the rate at which a fabric develops or add a component of fabric eraser. Thus, we can model how rapidly fabric adjusts to a change of deformation condition without tracking many grains. We will present an example application of fabric transition in the mantle wedge, where a rock with a preexisting A- or C- type fabric may enter a region where B-fabric is expected.

Miller, K. J.; Montesi, L. G.

2009-12-01

239

Geomorphology and geodynamics of the Cook-Austral island-seamount chain in the South Pacific Ocean: Implications for hotspots and plumes  

SciTech Connect

Among Pacific hotspot tracks, the Cook-Austral island-seamount chain is distinctly anomalous in geodynamic behavior, exhibiting repetitive episodes of volcanism at multiple sites, uplift of selected islands long after initial immersion by subsidence, and multiple alignments of volcanic edifices. Cook-Austral islands include a variety of disparate geomorphic types: volcanic islands without reefs, with fringing reefs, and with barrier reefs enclosing shallow lagoons, low-lying atolls; and makatea islands composted of volcanic cores surrounded by annular limestone tablelands. The distribution of subsided and uplifted islands along the Cook-Austral chain reflects multiple hotspot activity, probably related to multiple mantle diapirs of local character rather than to deep-seated plumes. Rapid Pacific plate motion can generate elongate hotspot tracks from transient hotspot activity unrelated to columnar advective plumes.

Dickinson, W.R. [Univ. of Arizona, Tucson, AZ (United States). Dept. of Geosciences

1998-12-01

240

Characteristics of mantle sources in Jurassic to Quaternary magmatic history of the territory of Armenia, as a guide to diverse geodynamic settings  

NASA Astrophysics Data System (ADS)

Complex geological mosaic of the territory of Armenia is presented by units consisting by fragments of continental blocks of Gondwanaland origin, Mesozoic Tethian island arc and Mesozoic ophiolitic complexes. Extensive magmatic activity traced from Early Jurassic to Holocene developed in diverse geological settings, such as Jurassic Tethyian MORB lavas, Upper Cretaceous and Eocene rift-related magmas and post-collisional Pliocene-Quaternary volcanic series. Despite the remarkable existence of subduction, obduction and collisional orogenic processes, accompanied by extensional and compressional tectonics, little is known about the relation between geodynamics and magma generation conditions, as mantles sources types and primary melts characteristics during the evolution of the region. Current study is intended to get new information that help to fill the gaps between the geodynamical puzzle and conditions of the mantle sources melting within the selected key areas of the territory of Armenia and Lesser Caucasus in general. In this contribution we focus on discussion of results of detailed geochemical and petrological studies of representative, highest-MgO samples of Jurassic picrites within Vedi ophiolites, picrite dyke of Alaverdi cutting Mesozoic Tethian island arc complexes, Upper Cretaceous rift-related sub-alkaline/alkaline basaltic series of Idjevan and Gochas, Late Eocene alkaline basaltic dyke of Jajur cutting Eocene volcanic and sedimentary complexes and Pliocene - Quaternary post-collisional volcanism, presented by 1) rifting-related flood basalts (dolerites); 2) HKCA basaltic series of Aragats stratovolcano and Gegham monogenetic volcanic upland and 3) high-alkaline, silica-undersaturated basaltic series of Syunik and Kapan. Geochemical signatures of most studied samples are characterised by enrichments in LILE and LREE, but depleted in HFSE, reflecting to OIB/MORB-type mantle source that may have been modified by subduction-related processes. Exceptions are the Jurasic Vedi and Alaverdi picrites reflecting the typical Tethyan MORB-type mantle, as well the Late Cretaceous Gochas, Martuni and Idjevan and Late Eocene Djajur showing absence of pronounced subduction-related modification of OIB-type mantle sources. Detail mineralogical study of early liquidus assemblages demonstrates that most studied samples consist high-Fo (>88) olivine that are considered to have crystallized from primary mantle-derived melts. Exceptions are low-Fo olivines characterized for Quaternary Aragats, Gegham and partially volcanoes of Syunik upland, those probably crystallized from crust contaminated AFC melts and/or melt resulting from the mixture of primary and crust-melted (adakite-type) melts. Spinel inclusions trapped in high-Fo olivine contain variable amounts of Ti, Al, and Cr, pointing to involvement of heterogeneous (MORB-type, OIB-type and subduction-type) mantle sources, that well agree with differ mantle-lithosphere domains and geodynamic controls during magma generations within the region from Jurassic to Quaternary time. Geochemical signature of melts, those could be maximally close to the primary or parental magmas, we obtained from LA-ICP-MS analyses of melt inclusions trapped in high-Fo olivines from all studied samples. Wide heterogeneity of melts within the individual and between differ magmatic systems, as well the link with geodynamical control and mantle sources melting scenarios will be discussed.

Nikoghosyan, Igor; Meliksetian, Khachatur; van Bergen, Manfred; Mason, Paul; Jrbashyan, Ruben; Navasardyan, Gevorg; Ghukasyan, Yura; Melkonyan, Rafael; Karapetyan, Sergey

2014-05-01

241

Tectonic setting of the Late Triassic volcaniclastic series of the Luang Prabang Basin, Laos, and geodynamic implications from the Triassic to Jurassic in SE Asia  

NASA Astrophysics Data System (ADS)

The Luang Prabang Basin, located on the eastern margin of the Indochina block, is mainly composed of volcaniclastic continental deposits. The interpretation of U-Pb zircon geochronological dates shows that volcanism is contemporaneous with the sedimentation during the Late Triassic (c.a. 225 to 215 Ma; Blanchard et al., 2013, J. Asian Earth Sci., 70-71; 8-26). At the same time, volcanism is also known along the Eastern margin of the Indochina block (present day Thailand). There are currently two main contrasting interpretations concerning the tectonic setting related to these volcanic events: are they arc-related (e.g. Barr et al., 2006, J. Geol. Soc. London, 163; 1037-1046) or post collisional (e.g. Srichan et al., 2009, Island Arc, 18; 32-51)? We have performed geochemical analysis on both sedimentary and volcanic rocks of the Luang Prabang Basin in order to evaluate the relationships between the volcanic events and to propose a geodynamic interpretation. The geochemical characteristics of the Luang Prabang Late Triassic volcaniclastic and volcanic rocks are compatible with a volcanic arc setting. The confrontation of these results with the stratigraphic evolution of the eastern margin of the Indochina block leads to reconsider the Late Triassic to Jurassic geodynamic evolution of this area. Arc-related volcanism seems to occur during nearly the whole Triassic, implying a subduction of the Paleotethys beneath the Indochina block. As the stratigraphic record of north-eastern Thailand and western Myanmar shows an important stratigraphic gap spanning from the Early to the Middle Jurassic, the collision between the Indochina and the Sibumasu blocks likely occurred at that period.

Rossignol, Camille; Bourquin, Sylvie; Dabard, Marie-Pierre; Hallot, Erwan; Poujol, Marc; Nalpas, Thierry

2014-05-01

242

Identification of geodynamic setting and of folding formation mechanisms using of strain ellipsoid concept for multi-scale structures of Greater Caucasus  

NASA Astrophysics Data System (ADS)

For recognition of folding formation mechanisms and of geodynamic setting of development of inner parts of mobile belts, the idea of a deforming description with use of parameters of strain ellipsoid is used. Such description includes for a separate fold a dip of an axial plain and a shortening value in axis perpendicular to axial plain as strain ellipse axes. For a homogeneous series of folds (folded domains) there are three parameters: folds shortening value, axial plain dip (axes of strain ellipsoid) and dip of folds envelope plain. Folds in the Vorontsov nappe of North-West Caucasus were investigated. Possible trends of change of parameters "dip of axial plain"/"shortening value" have been described and compared for two kinematic models: lateral shortening (flattening) and simple horizontal shearing. Trend of natural fold strain parameters has shown the coincidence with horizontal simple shearing trend which corresponds to gravitational sliding in geodynamic relation. Distinctions in formation mechanisms of small and large structures are discussed. Large structures (tectonic zones) should be split on a series of folded domains. Aggregate description of deformations of these domains helps to give the characteristic of complicated mechanisms in models and in nature. Several different types of experiments were investigated. It was shown that different mechanisms have specific clouds of domain geometry in 3D space of three parameters. Discrepancies of such clouds were used as key features for mechanisms identification. Mechanisms of lateral pressure, gravitational sliding, theoretical and experimental models of diapirism, numerical model of mesobuckling are shortly described. Structural cross-sections for main three zones of the Greater Caucasus have been described using strain parameters of domains. Conventional models of accretionary prism type have not been confirmed. Complex mechanism of mesobuckling combining with simple shearing in "near-thrust" inclined zones well describes the structure in a first approximation.

Yakovlev, Fedor L.

2012-12-01

243

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

244

The Arkot Da? Mélange in Araç 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-Araç-Bayramoren geotraverse, located in central Turkey, an ophiolite-bearing mélange known as the Arkot Da? Mélange, is well-exposed along the Intra-Pontide suture zone. The Arkot Da? Mélange 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? Mélange, even if unaffected by metamorphism, shows deformations represented by multiple meters-thick cataclastic shear zones at the boundaries of the mélange slices or inside of them. According to its features, the source area of the Arkot Da? Mélange 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.

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

2014-05-01

245

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; Balanyá, Juan Carlos

2014-05-01

246

What can hafnium isotope ratios arrays tell us about orogenic processes? An insight into geodynamic processes operating in the Alpine/Mediterranean region  

NASA Astrophysics Data System (ADS)

Over the last decade, technological advances in laser-ablation sampling techniques have resulted in an increase in the number of combined U-Pb-Hf zircon isotope studies used to investigate crustal evolution on a local, regional and global scale. Hafnium isotope arrays over large time scales (>500 myr) have been interpreted to track evolving plate tectonic configurations, and the geological outputs associated with changing plate boundaries. We use the Alpine-Mediterranean region as an example of how hafnium isotope arrays record the geodynamic processes associated with the complex geological evolution of a region. The geology of Alpine-Mediterranean region preserves a complex, semi-continuous tectonic history that extends from the Neoproterozoic to the present day. Major components of the Variscan and Alpine orogens are microcontinental ribbons derived from the northern Gondwanan margin, which were transferred to the Eurasian plate during the opening and closing of the Rheic and Paleo-Tethys Oceans. Convergence of the Eurasian and African plates commenced in the Mid-Late Cretaceous, following the destruction of the Alpine-Tethys Ocean during the terminal breakup of Pangea. In general, convergence occurred slowly and is characterised by northward accretion of Gondwanan fragments, interspersed with subduction of African lithosphere and intermittent roll-back events. A consequence of this geodynamic scenario was periods of granite-dominated magmatism in an arc-backarc setting. New Hf isotope data from the peri-Gondwanan terranes (Iberia, Meguma and Avalonia) and a compilation of existing Phanerozoic data from the Alpine-Mediterranean region, indicate ~500 myr (Cambrian-Recent) of reworking of peri-Gondwanan crust. The eHf array follows a typical crustal evolution pattern (Lu/Hf=0.015) and is considered to reflect reworking of juvenile peri-Gondwanan (Neoproterozoic) crust variably mixed with an older (~1.8-2.0 Ga) source component, probably Eburnian crust from the West Africa Craton. The Phanerozoic Hf isotopic data from Variscan and Alpine Europe suggest that slow translation of continental fragments from one continent to another produces a characteristic, long-term crustal reworking eHf array, which strongly contrasts with the Hf array defined by Phanerozoic circum-Pacific orogens.

Henderson, B.; Murphy, J.; Collins, W. J.; Hand, M. P.

2013-12-01

247

AGrav—The New International Absolute Gravity Database of BGI and BKG and its benefit for the Global Geodynamics Project (GGP)  

NASA Astrophysics Data System (ADS)

A new database for absolute gravity (AG) measurements has been implemented at BGI and BKG and is operational now for storing absolute gravity data either in the form of metadata or as detailed measurement results. The database development was proposed by the IGFS (International Gravity Field Service) and is expected to have a great importance for the GGOS (Global Geodetic Observing System) initiative. This database will provide an overview about AG stations and observations and by this improve the cooperation between gravity groups and foster the combination with other geodetic observation techniques. The international community of absolute gravimeter users is asked to contribute to this database. In addition to its primary purposes, demonstration of the global site distribution and information about available observations, the database could also provide an important contribution to the Global Geodynamics Project (GGP). Precise repeated absolute gravity measurements at the superconducting gravimeter (SG) sites are necessary for the determination of SG drift parameters and can be used for checking SG instrument calibration factors. The AGrav database is capable of storing the necessary AG observations at the SG location in detail up to the "single drop level" and provides this information for the combination with SG time series. An example for a selected station is presented. It is proposed to establish an interface between the AGrav and GGP databases.

Wilmes, H.; Wziontek, H.; Falk, R.; Bonvalot, S.

2009-12-01

248

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

249

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

250

Gravity sliding in basinal setting, a surficial record of tectonic and geodynamic evolution; examples from the southern W. Alps and their foreland  

NASA Astrophysics Data System (ADS)

The occurrence of large-scale submarine landslides, although commonly observed in the present basins, is only exceptionally mentioned in the Alpine orogen and foreland. The southern part of the Western Alpine arc and the SE basin of France provide examples of such features which could be related with particular geodynamic events, in relation with the motion of the Iberian and Adriatic microplates : - A >50km2 slump scar formed in Aptian times at the northwestern edge of the SE France (so-called Vocontian) basin, giving a low-angle detachment surface which was onlapped by Albian hemipelagic marls (Ferry & Flandrin, 1979). The latter mark the maximum deepening stage of the basin, and the head of the scar is located over a deep-seated fault bounding the platform, which strongly suggest that sliding was caused by differential subsidence due to Middle Cretaceous extension, as a consequence of Iberia-Europe divergence. - Later on, a deep-marine erosion surface developed further down the basin over a >100km2 area (Dévoluy massif; Michard et al., 2010), which had been previously affected by Mid-Cretaceous extension. Typical inversion structures are found beneath the surface, which indicate that NS shortening overprinted the extensional pattern. The removal of up to 400m of Mesozoic sediments was controlled by gravity processes, probably triggered by the deformation of the basin floor following tectonic inversion. The overlying pelagic carbonates indicate that shortening occurred before the Campanian, which is closely comparable with the earliest stages of tectonic inversion in the Pyrenees. - The transition slope between the Paleogene Alpine flexural basin and the NW-ward propagating accretionary prism provides examples of basin floor degradation and of gravity-driven emplacement of large-scale blocks, generally regarded as thrust-sheets in the Alps. These features allow to reconstruct the early stages of the Adria-Europe collision, which strongly differ from the Oligo-Miocene dynamics and which are overprinted or crosscut by the modern orogen (Dumont et al., 2011). Theses examples show that, in different structural and geodynamic settings, detailed analysis of basin floor morphology, (re)sediments transport directions, syndepositional deformations and provenance of exotic blocks can provide useful information about the regional kinematics, which can be integrated with other datasets, i.e. tectonic, metamorphic, thermochronologic, etc. Dumont T., Schwartz S., Guillot S., Simon-Labric T., Tricart P. & Jourdan S. (2011), Structural and sedimentary records of the Oligocene revolution in the Western Alpine arc. Jour. Geodyn., in press. Ferry S. & Flandrin J. (1979), Mégabrèches de resédimentation, lacunes mécaniques et pseudo-« hard-grounds » sur la marge vocontienne au Barrémien et à l'Aptien inférieur (SE France). Géologie Alpine, 55, p. 75-92. Michard A., Dumont T., Andreani L. & Loget N. (2010), Structural and sedimentary records of the Oligocene revolution in the Western Alpine arc. Bull. Soc. Géol. Fr., 181, p. 565-581.

Dumont, T.; Franzi, V.; Matthews, S. J.

2012-04-01

251

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

252

The Permian volcanism of Sardinia revisited: new geochronological and geochemical data as a key for geodynamic evolution of the western Peri-Tethian sector  

NASA Astrophysics Data System (ADS)

Recent studies have confirmed the important role played by magmatism affecting Sardinian basins during the latest Carboniferous and Permian age (Cortesogno et al. 1998; Buzzi et al., 2008; Casini et al., 2012). To-date, most of the geochronological analysis performed on the Permian volcanic events in the island are methodologically overcome and frequently not in tune with the stratigraphy. In the north-western and central-southeastern Sardinian basins (Nurra, Perdasdefogu, Seui-Seulo and Escalaplano), the late-post Variscan tectonic collapse favored the emplacement of a calc-alkaline products not only in the form of generally shallow intrusions but also volcanism within intramontane strike-slip basins. This magmatism is expressed both as pyroclastic rocks-lava flows filling small half-graben basins and hypabyssal intrusions (lava-domes and dykes). These volcano-sedimentary troughs generally include both external and internal igneous eruptions as well as the detrital products eroded from the surrounding structural highs. Rhyolites, andesites and dacites are the main rock types while trachydacites and trachyandesites are less represented. Our goal is to couple the petrographic and geochemical features of 17 selected samples stratigraphically constrained and new U-Pb ages data on zircons from the post-Variscan effusive rocks in Sardinia. The whole-rock and REE geochemical features confirm a progressive evolution in the post-Variscan extensional, trans-tensile regime in with and fits an origin in a stacking of nappes associated with thermal re-equilibration of lithospheric mantle and telescopic partial melting of the thickened crust. The process is dominated by AFC. As far as the geochronological analysis is concerned, a preliminary cathodoluminescence study has been performed on all mounted crystals in order to select the precise location of the shot points. Each crystal has been analyzed for U, Th and Pb in the epoxy mount by laser-ablation inductively coupled plasma mass spectrometry (LA ICP-MS) at the Institute of Geosciences and Earth Resources IGG-CNR of Pavia. The time lag of Permian ages recorded along the Sardinia cross section is significant in the modeling of the post- Variscan tectonic, sedimentary evolution and in the perspective of the geodynamic evolution of Southern Variscides. REFERENCES Casini L., Cuccuru S., Maino M., Oggiano G., Tiepolo M 2012. Emplacement of the Arzachena Pluton (Corsica-Sardinia Batholith) and the geodynamics of incoming Pangaea. Tectonophysics 544-545 (2012) 31-49. Buzzi L., Gaggero L., Oggiano G. 2008. The Santa Giusta ignimbrite (NW Sardinia): a clue for the magmatic, structural and sedimentary evolution of a Variscan segment between Early Permian and Triassic. Italian Journal of Geoscience 127(3), 683-695. Cortesogno L., Cassinis G., Dallagiovanna G., Gaggero L., Oggiano G., Ronchi A., Seno S., Vanossi M. 1998. The Variscan post-collisional volcanism in Late Carboniferous-Permian sequences of Ligurian Alps, Southern Alps and Sardinia (Italy): a synthesis. Lithos 45, 305-328.

Gaggero, Laura; Gretter, Nicola; Lago, Marceliano; Langone, Antonio; Oggiano, Giacomo; Ronchi, Ausonio

2014-05-01

253

Seismic and gravity constraints on the nature of the basement in the Africa-Eurasia plate boundary: New insights for the geodynamic evolution of the SW Iberian margin  

NASA Astrophysics Data System (ADS)

present a new classification of geological domains at the Africa-Eurasia plate boundary off SW Iberia, together with a regional geodynamic reconstruction spanning from the Mesozoic extension to the Neogene-to-present-day convergence. It is based on seismic velocity and density models along a new transect running from the Horseshoe to the Seine abyssal plains, which is combined with previously available geophysical models from the region. The basement velocity structure at the Seine Abyssal Plain indicates the presence of a highly heterogeneous, thin oceanic crust with local high-velocity anomalies possibly representing zones related to the presence of ultramafic rocks. The integration of this model with previous ones reveals the presence of three oceanic domains offshore SW Iberia: (1) the Seine Abyssal Plain domain, generated during the first stages of slow seafloor spreading in the NE Central Atlantic (Early Jurassic); (2) the Gulf of Cadiz domain, made of oceanic crust generated in the Alpine-Tethys spreading system between Iberia and Africa, which was coeval with the formation of the Seine Abyssal Plain domain and lasted up to the North Atlantic continental breakup (Late Jurassic); and (3) the Gorringe Bank domain, made of exhumed mantle rocks, which formed during the first stages of North Atlantic opening. Our models suggest that the Seine Abyssal Plain and Gulf of Cadiz domains are separated by the Lineament South strike-slip fault, whereas the Gulf of Cadiz and Gorringe Bank domains appear to be limited by a deep thrust fault located at the center of the Horseshoe Abyssal Plain.

Martínez-Loriente, Sara; Sallarès, Valentí; Grácia, Eulália; Bartolome, Rafael; Dañobeitia, Juan José; Zitellini, Nevio

2014-01-01

254

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

255

Macro- and micro- geodynamic of Terebliya-Riksk geodetic man-caused polygon of Ukrainian Carpathians influenced by specificities of structure-geological and hydro-geological conditions  

NASA Astrophysics Data System (ADS)

Terebliya-Riksk diversion power station is located on two levels ( with difference of 180m ) of south mountainside of Ukrainian Carpathians and separate parts of this power station lie inside rock. Therefore influential parameters of it's stability are geological, tectonic and hydrogeological conditions in complex. Monitoring of intensity and nature of displacements of flow ( pressure) pipe and other objects of power station with geoditic methods indicates that fluctuations of water-level in reservoir caused bouth by natural and artificial efects are of great influence on objects mentioned. Based on geodetical high-precision observations made by LeicaTPS 1201 robotic total station short-periodic components of fundamental vibrations which result in their destructive deformation were determined. Mathematical apparatus ( which uses function of Fourie series and theory of cinematic coefficients ) for displacements determinations of pressure pipe was disigned. Complex of engineering-geological surveys gave an opportunity to define the origin of macro- and micro- geodynamics movements of Terebliya-Riksk diversion power station region. Engineering-geological conditions which influence on power station structure most of all were determined as following : small foldings and cleavage areas appearances, also fluctuations of level of underground water (refered to hydrogeological conditions). Periodic micro-displacemets appearances ( which operate on reducing-stretching scheme) fixed on power station structure are turned to be in direct relation on to what exend reservoir is filled up. Permanent macro- displacements appearances ( which operates in north-west direction ) fixed on pressure pipe are the result sum of residual micro-displacements caused by return periodic movements and are determined by structure-geological, engineering-geological and tectonic conditions.

Kulchyzkyy, A.; Serebryannyy, Y.; Tretyak, K.; Trevogo, I.; Zadoroznnyy, V.

2009-04-01

256

GOCE observations and geophysical constraints to better understand the lithosphere and geodynamical processes under the Paraná-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 Paraná-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 Paraná-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 Paraná-Etendeka region will be presented and interpreted.

Mariani, Patrizia; Braitenberg, Carla

2014-05-01

257

The geochemical variations of the upper cenozoic volcanism along the Calama Olacapato El Toro transversal fault system in central Andes (˜24°S): petrogenetic and geodynamic implications  

NASA Astrophysics Data System (ADS)

In this paper, we present new geochemical and Sr-Nd isotopic data for several Upper Miocene volcanic centres aligned along one of the most extensive transcurrent lineament in the Central Andes, the Calama-Olacapato-El Toro (COT). The transversal volcanic belt along COT is constituted by large composite volcanoes and a caldera structure; they are, from NW to SE, Puntas Negras, Rincon, Tul Tul, Del Medio and Pocitos (TUMEPO), Quevar Aguas Calientes and Tastil. In order to compare chemical data from the different centres along the COT transect, differentiation effects were minimised by using data extrapolated at 60% SiO 2 with least-square regression method. In the western sector of the COT, the volcanic products of Puntas Negras and Rincon show relatively high K 2O and 87Sr/ 86Sr and low Rb/Cs, Ta/Th, La/Yb, 143Nd/ 144Nd. To the east, the TUMEPO products have high Sr and 143Nd/ 144Nd, La/Yb and Ba/Rb and low Y, 87Sr/ 86Sr. In the easternmost COT sector, Quevar, Aguas Calientes and Tastil volcanic complexes exhibit low La/Yb, high 87Sr/Sr 86 and low 143Nd/ 144Nd. On the basis of these data, we propose a petrogenetic and geodynamical model for Central Andes at 24°S. In correspondence of Miocene-Quaternary volcanic arc (Puntas Negras and Rincon), the magmas inherited a calcalkaline signature partly modified by upper crustal and/or sediment assimilation. In the central eastern sector, melting, assimilation, storage and homogenisation (MASH) processes occurred at the base of a thickened crust. In this COT sector, TUMEPO products show an evident lower crust signature and could be considered representative for MASH derived magmas. In the easternmost sector, Quevar, Aguas Calientes and Tastil products could represent magmas generated by partial melting of underthrusted Brasilian shield and mixed with magmas derived by MASH processes.

Matteini, M.; Mazzuoli, R.; Omarini, R.; Cas, R.; Maas, R.

2002-02-01

258

Irregular effects of tilting of foundation and probable connection with plate tectonic motions Results of many years standing measurements of long water-tubes and horizontal pendulums tiltmeters in Geodynamic Laboratory of SRC in Ksiaz  

NASA Astrophysics Data System (ADS)

Since 1975 until 2003 in the Geodynamic Laboratory in Ksiaz there were continuously performed clinometric observations with help of quartz horizontal pendulums only. In 2003 new tiltmeters were installed in galleries of the laboratory in Ksiaz. Tiltmeters consist of two several dozen meters length tubes partially filled with water. Principle of work of instruments bases on the law of hydrostatic equilibrium. The interferometer system for continuous measurements and registrations of ultra small variations of water level was applied. This system enables permanent measurements of water level variations with nanometer accuracy corresponding to 0.005 [mas] of plumb line variation. Water-tube tiltmeters (WT) possess several advantages such as: high and stable resolution of measurements, stable sensitivity of measurements, stable and well determined azimuth of measurements, lack of instrumental drift, make possible investigation of long period or systematic effects of tilting of foundation. Possibility of elimination instrumental drift from WT measurements allowed us to investigate long-standing, non-tidal clinometric signals. Since 2003 until 2007 we observed five epochs of extremely strong clinometric signals. The largest signals happened without seasonal correlations in different months. Magnitudes of strong signals exceeded hundred of [mas] and time of durations amount dozen or so days. First information of existence of the large clinometric effects comes from long lasting measurements carried on with help of the quartz horizontal pendulums. Almost every year of measurements we observed one or two epochs of unstable work of pendulums associated with rapid variations of azimuths of equilibrium of pendulums until their contact with limiters. Similarities of strong clinometric signals registered by two different classes of tiltmeters as well as their correlation confirm thesis that large signals are geodynamic, not instrumental origin. We are able to exclude phenomena such as air pressure loading effects, seasonal variations of mean temperature, non-tidal loading effects of ocean origin, variations of level of ground water, and other seasonal effects as reasons of large clinometric signals. Azimuths of resultant tilts of these signals are close to direction of plate tectonic motions observed by GPS and laser permanent stations in surrounding of Geodynamic Laboratory. Probability that large clinometric signals are produced by recent plate tectonic motions is increasing by special geometry of orogen in which laboratory was situated as well as its contact with Sudetic marginal fold. Keywords: Geodynamic, Earth tides, plumb line variations, non-tidal effects, tiltmeters, plate tectonic.

Kaczorowski, Marek

259

Geochemistry and geodynamics of a Late Cretaceous bimodal volcanic association from the southern part of the Pannonian Basin in Slavonija (Northern Croatia)  

USGS Publications Warehouse

In this paper we present petrological and geochemical information on a bimodal basaltrhyolite suite associated with A-type granites of Late Cretaceous age from the South Pannonian Basin in Slavonija (Croatia). Basalts and alkali-feldspar rhyolites, associated in some places with ignimbrites, occur in volcanic bodies that are interlayered with pyroclastic and fossiliferous Upper Cretaceus sedimentary rocks. The petrology and geochemistry of the basalts and alkali-feldspar rhyolites are constrained by microprobe analyses, major and trace element analyses including REE, and radiogenic and stable isotope data. Basalts that are mostly transformed into metabasalts (mainly spilites), are alkalic to subalkalic and their geochemical signatures, particularly trace element and REE patterns, are similar to recent back-arc basalts. Alkali-feldspar rhyolites have similar geochemical features to the associated cogenetic A-type granites, as shown by their large variation of Na2O and K2O (total 8-9%), very low MgO and CaO, and very high Zr contents ranging between 710 and 149ppm. Geochemical data indicate an amphibole lherzolite source within a metasomatized upper mantle wedge, with the influence of upper mantle diapir with MORB signatures and continental crust contamination. Sr incorporated in the primary basalt melt had an initial 87Sr/86Sr ratio of 0.7039 indicating an upper mantle origin, whereas the 87Sr/86Sr ratio for the alkalifeldspar rhyolites and associated A-type granites is 0.7073 indicating an apparent continental crust origin. However, some other geochemical data favour the idea that they might have mainly originated by fractionation of primary mafic melt coupled with contamination of continental crust. Only one rhyolite sample appears to be the product of melting of continental crust. Geological and geodynamic data indicate that the basalt-rhyolite association was probably related to Alpine subduction processes in the Dinaridic Tethys which can be correlated with recent back-arc basins. The difference in geological and isotope ages between the bimodal basalt-rhyolite volcanism with A-type granite plutonism (72 Ma) and the final synkinematic S-type granite plutonism (48 Ma) can be taken as a lifetime of the presumed BARB system of the Dinaridic Tethys. Remnants of this presumed subduction zone can be traced for 300 km along the surrounding northernmost Dinarides.

Pamic, J.; Belak, M.; Bullen, T. D.; Lanphere, M. A.; McKee, E. H.

2000-01-01

260

Seismic structure of the Helan–Liupan–Ordos western margin tectonic belt in North-Central China and its geodynamic implications  

NASA Astrophysics Data System (ADS)

We study high-resolution three-dimensional P-wave velocity (Vp) tomography and anisotropic structure of the crust and uppermost mantle under the Helan-Liupan-Ordos western margin tectonic belt in North-Central China using 13,506 high-quality P-wave arrival times from 2666 local earthquakes recorded by 87 seismic stations during 1980-2008. Our results show that prominent low-velocity (low-V) anomalies exist widely in the lower crust beneath the study region and the low-V zones extend to the uppermost mantle in some local areas, suggesting that the lower crust contains higher-temperature materials and fluids. The major fault zones, especially the large boundary faults of major tectonic units, are located at the edge portion of the low-V anomalies or transition zones between the low-V and high-V anomalies in the upper crust, whereas low-V anomalies are revealed in the lower crust under most of the faults. Most of large historical earthquakes are located in the boundary zones where P-wave velocity changes drastically in a short distance. Beneath the source zones of most of the large historical earthquakes, prominent low-V anomalies are visible in the lower crust. Significant P-wave azimuthal anisotropy is revealed in the study region, and the pattern of anisotropy in the upper crust is consistent with the surface geologic features. In the lower crust and uppermost mantle, the predominant fast velocity direction (FVD) is NNE-SSW under the Yinchuan Graben and NWW-SEE or NW-SE beneath the Corridor transitional zone, Qilian Orogenic Belt and Western Qinling Orogenic Belt, and the FVD is NE-SW under the eastern Qilian Orogenic Belt. The anisotropy in the lower crust may be caused by the lattice-preferred orientation of minerals, which may reflect the lower-crustal ductile flow with varied directions. The present results shed new light on the seismotectonics and geodynamic processes of the Qinghai-Tibetan Plateau and its northeastern margin.

Cheng, Bin; Cheng, Shunyou; Zhang, Guowei; Zhao, Dapeng

2014-06-01

261

Anatomy of an ancient subduction interface at 40 km depth: Insights from P-T-t-d data, and geodynamic implications (Dent Blanche, Western Alps)  

NASA Astrophysics Data System (ADS)

An exhumed metamorphic suture zone over 40 km long is exposed in the Dent Blanche Region of the Western Alps belt, along the Swiss-Italian border. In this region, the metasediment-bearing ophiolitic remnants of the Liguro-Piemontese ocean (Tsaté complex) are overthrusted by a continental, km-sized complex (Dent Blanche Tectonic System: DBTS) of Austro-Alpine affinity. The DBTS represents a strongly deformed composite terrane with independent tectonic slices of continental and oceanic origin. In order to better understand the nature and the geodynamic meaning of the shear zone at the base of the DBTS (Dent Blanche Thrust, DBT) we re-evaluated the pressure-temperature-time-deformation (P-T-t-d) history of these two units using modern thermobarometric tools, Rb/Sr deformation ages and field relationships. Our results show that the Tsaté complex is formed by a stack of km-thick calcschists-bearing tectonic slices, having experienced variable maximum burial temperatures of between 360°C and 490°C at depths of ca. 25-40 km, between 41 Ma and 37 Ma. The Arolla gneissic mylonites constituting the base of the DBTS experienced a continuous record of protracted high-pressure (12-14 kbar), top-to-NW D1 deformation at 450-500°C between 43 and 55 Ma. Some of these primary, peak metamorphic fabrics have been sheared (top-to-SE D2) and backfolded during exhumation and collisional overprint (20 km depth, 35-40 Ma) leading to the regional greenschist facies retrogression particularly prominent within Tsaté metasediments. The final juxtaposition of the DBTS with the Tsaté complex occurred between 350 and 500°C during this later, exhumation-related D2 event. Although some exhumation-related deformation partially reworked D1 primary features, we emphasize that the DBT can be viewed as a remnant of the Alpine early Eocene blueschist-facies subduction interface region. The DBT therefore constitutes the deeper equivalent of some shallower portions of the Alpine subduction interface exposed 200 km eastwards in eastern Switzerland (e.g. Bachmann et al., 2009). Our results shed light on deep (25-45 km) subduction zone structures and dynamics and are therefore of major interest for geophysical studies imaging the plate interface region in active subduction zones.

Angiboust, Samuel; Glodny, Johannes; Oncken, Onno; Chopin, Christian

2014-05-01

262

Geodynamic models for the Neoproterozoic Yenisey Ridge orogenic belt (western Siberian Craton continental margin) and evolution of granitoid and alkaline magmatism  

NASA Astrophysics Data System (ADS)

We assume that the genesis of the Yenisey Ridge accretional orogen is a result of three events: a) syn-collisional events (probably outside the Siberian craton), which resulted in the forming of the S- and I-type 880-860 Ma Teya granites in the Central Angara terrane; b) the collision between the Central Angara terrane and the Siberian craton and the forming of the syn- and post-collisional S- and A- type 760-720 Ma Ayakhta and Glushikha granites; c) the forming of island arcs and ophiolites along the margin of the Siberian craton, their accretion and obduction onto the continent in the interval of 700-630 Ma. The last event is of special interest because at the same time in the Tatarka-Ishimba suture zone of the Yenisey Ridge, which is subparallel to the continental margin, the forming of intrusive and volcanic rocks of various composition and heightened alkalinity was taking place, including alkaline syenites as well as carbonatites and A-type granites, whose magmatic sources vary from mantle to mantle-crustal and crustal. These rocks form small plutons of round or oval shape, dikes, bedded bodies, tracing this tectonic zone along its entire length. Some of the A-type granites may be considered as hybrid rocks as suggested by mineralogical-petrographical features: inclusions of rocks of basic composition and magma-mingling structures. These granites are slightly peraluminous rocks. In contrast to the 760-720 Ma A-type granites, they have higher REE and Nb and Ta contents. They formed synchronously with the rocks of the island arc complex and their accretion and obduction onto the continental margin of Siberia in the interval of 700-630 Ma. It is quite probable that their forming in the back-arc suprasubduction zone was taking place at the same time that the oceanic plate was subducting below the continent from the western margin of the Siberian craton and reached the asthenospheric layer. The obtained data and the developed models uncover the geodynamic evolution of the forming of accretional orogens in the western margin of the Siberian craton in the Neoproterozoic.

Vernikovsky, Valery; Vernikovskaya, Antonina

2010-05-01

263

Influence of anelastic corrections to the temperature derivatives of seismic velocities on 3-D wavefields in geodynamically derived seismic mantle heterogeneity  

NASA Astrophysics Data System (ADS)

Recently, we have developed a new joint forward modeling approach to test geodynamic hypotheses directly against seismic data: Seismic heterogeneity is predicted by converting the temperature field of a high-resolution 3-D mantle circulation model into seismic velocities using thermodynamic models of mantle mineralogy. 3-D global wave propagation in the synthetic elastic structures is then simulated using a spectral element method. Being based on forward modelling only, this approach allows us to generate synthetic wavefields and seismograms independently of seismic observations. The statistics of observed long-period body wave traveltime variations show a markedly different behaviour for P- and S-waves: the standard deviation of P-wave delay times stays almost constant with ray turning depth, while that of the S-wave delay times increases strongly throughout the mantle. In an earlier study, we showed that synthetic traveltime variations computed for an isochemical mantle circulation model with strong core heating can reproduce these different trends. This was taken as a strong indication that seismic heterogeneity in the lower mantle is likely dominated by thermal variations on large length-scales; that is, relevant for long-period body waves. To test the robustness of our earlier conclusion, we address now the question on the influence of anelasticity on the standard deviation of synthetic traveltime variations. Owing to the differences in seismic frequency content between laboratory measurements (MHz to GHz) and the Earth (mHz to Hz), the seismic velocities given in the mineralogical model need to be adjusted; that is, corrected for dispersion due to anelastic effects. This correction will increase the sensitivity of the seismic velocities to temperature variations. The magnitude of this increase in sensitivity depends on absolute temperature, frequency, the frequency dependence of attenuation and the activation enthalpy of the dissipative process. Especially the latter two are poorly known for mantle minerals and our results show that variations in activation enthalpy produce the largest differences in temperature sensitivity with respect to the purely elastic case. We will present new wave propagation simulations and corresponding statistical analyses of traveltime measurements for different synthetic seismic models spanning the possible range of anelastic velocity conversions while being based on the same mantle circulation model.

Schuberth, Bernhard; Gräber, Claudia; Baykiev, Eldar; Zaroli, Christophe

2014-05-01

264

Geodynamical evolution of Central Andes at 24°S as inferred by magma composition along the Calama-Olacapato-El Toro transversal volcanic belt  

NASA Astrophysics Data System (ADS)

Miocene to Recent volcanism on the Puna plateau (Central Andes) developed in three geological settings: (a) volcanic arc in the Western Cordillera (Miocene-Recent); (b) trans-arc along the main NW-SE transverse fault systems (Miocene); and (c) back-arc, mainly monogenic volcanic centres (Pliocene-Quaternary). We have studied the evolution of the arc-trans-arc volcanism along one of the most extensive transverse structures of Central Andes, the Calama-Olacapato-El Toro, at 24°S. Compositional variations from arc to trans-arc volcanism provide insights into petrogenesis and magma source regions. Puntas Negras and Rincon volcanic centres are arc-type and have typical calc-alkaline geochemical and Sr-Nd-Pb isotopic characteristics. East of the arc, lavas of the Tul-Tul, Del Medio and Pocitos complexes (TUMEPO) are heavy rare earth element-depleted and could be derived from 20-30% of partial melting of a lower crustal garnet-bearing metabasite. These liquids could be variably mixed with arc magmas at the base of the crust (MASH). This suggests important contributions from lower crustal sources to TUMEPO centres. Products at the Quevar and Aguas Calientes volcanic complexes to the east of TUMEPO show a prominent upper crustal signature (high 86Sr/ 87Sr, low 143Nd/ 144Nd) and could represent mixtures of 20-30% TUMEPO-type liquids with up to 70-80% of upper crustal melts. We propose a geodynamic model to explain geochemical variations for the arc-trans-arc transverse volcanism from the Upper Miocene to Recent. In our model, arc volcanism is linked to dehydration of the subducting Nazca plate, which produces typical calc-alkaline compositions. During the Upper Miocene (10-5 Ma), lithospheric evolution in the Puna plateau was dominated by thickening of ductile lower crust and thinning of the lithosphere. Lower crustal melting was promoted by concomitant asthenospheric upwelling and water release from the amphibolite-eclogite transformation, yielding TUMEPO magmas with lower crustal signatures. At the same time, the eastern sector of the Puna plateau experienced westward underthrusting of the Brazilian shield and upper crustal brittle deformation. Partial melts from underthrust upper crustal wedges mixed with lower crustal magmas to produce lavas at Aguas Calientes and Quevar. During Pliocene to Quaternary, delamination of the lithosphere and lowermost crust promoted a widespread monogenetic ocean island basalt-type and shoshonitic volcanism.

Matteini, M.; Mazzuoli, R.; Omarini, R.; Cas, R.; Maas, R.

2002-11-01

265

Geodynamics: Mantle plume chemical diversity  

NASA Astrophysics Data System (ADS)

Ocean island lavas have complex geochemical signatures. Numerical simulations suggest that these signatures may reflect the entrainment and transport to Earth's surface of both primordial material and recycled oceanic crust by deeply rooted mantle plumes.

Deschamps, Frédéric

2014-05-01

266

The geodynamic characteristics of Cretaceous (Paleogene) magmatic belts between the southeastern coast of China and Japan: Implication from ductile deformations time and diagenetic manner  

NASA Astrophysics Data System (ADS)

1.Introduction It is generally believed that the Yanshanian orogeny outlined the present-day geological configuration that has developed since the Jurassic (Li 2000), by which the Early Yanshanian (J3) dominated the Cathaysia interior, whereas the Late Yanshanian (K1) dominated the southeast coastal area. Basically, products of the early Cretaceous magmatism are more restricted in a NE-SW trending zone-the Southeast Coast of China Magmatic Belt (SECMB) in China. Previous investigations have revealed that volcano-intrusive rock assemblages are mainly shallow-level, calc-alkaline, I-type felsic rocks ranging from granodioritic to alkali feldspar granitic, and succeeding A-type granites(Chen et al. 2000). The Cretaceous to Paleogene volcano-intrusive complex rocks are extensively distributed in the WS Japan Magmatic Belt (WSJMB). Note that the majority of granitic intrusions were emplaced in the Cretaceous, and they intruded into the pre-Cretaceous accretionary complexes which include regional metamorphic rocks. The intrusive granitoids are associated with coeval gabbros, diorites, rhyolites and ignimbrites.The formation of the Japanese Islands has been taken as the classic model for accretionary orogeny and often serves as an example for understanding the crustal evolution of the CAOB and other accretionary orogens (Sengor and Natal'in, 1996; Condie, 2007; Cawood and others, 2009). 2. Correlation with two Cretaceous magmatic belts 2.1 The beginning and end times for magmatic activity as well as dynamics deformation time. 2.2 Beginning of high-Mg andesite and adakite produced by melting of subducting oceanic slab in Japan. 2.3 The finishing marks of magmatic activity. 2.4 Approximatively resembling diagenetic manner. 3. Geodynamic characteristics of two magmatic belts The WSJMB is a plutonic-metamorphic terrane that comprises unmetamorphosed pre-Cretaceous accretionary complexes with shallow-level, calc-alkaline, I-type granites-rhyolites, metasediments with migmatites and gneissose granites. The volcano-intrusive complex rocks are dominant over metamorphic rocks, Based on the apparent along-arc variation of isotopic ages, it has been suggested that the Ryoke and Sanyo granitoids were produced by Cretaceous subduction of the Kula-Pacific ridge. Thus, the felsic rocks in WSJMB were formed by partial melting of derived-younger crust all long under subducted compressive setting. Contrarily, the volcano-intrusive complex rocks in SECMB were produced by an immense melting of the Proterozoic crustal material through basaltic underplating, which the upwelled mantle brought up extra heat. As the collision compressive of paleo-Pacific plate during the early Cretaceous (about 125-120Ma) resulted in crustal thickening, succeeding lithospheric delamination or detachment took place, magmas thus were emplaced at extensional environments. The an-orogenic magmatism occured under lithospheric extension-break up environments.

Mao, J.; Takahashi, Y.; Ye, H.; Zhao, X.; Li, Z.; Kee, W.; Liu, K.; Hu, Q.

2011-12-01

267

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

268

Geodynamic implications of Collo-Bougaroun Miocene magmatic complex (Eastern Algerian margin): a review of U-Pb, K-Ar chronology and geochemistry  

NASA Astrophysics Data System (ADS)

The ''Petite-Kabylie' comprises all eastern Algerian coastal magmatic chain outcropping from Jijel to the west, up to the plain of Annaba, to the east. At the western part of this area, the Kabylie of Collo stretches between 6° and 7° E and 36° 30 'and 37° 06' N towards Skikda. The Bougaroun magmatic complex form a large elliptical batholith oriented ENE-WSW over 20 km that intrudes serpentinized peridotites and kinzigites of the Bougaroun basement to the east. This granitic pluton gives time constraints as it induces deformation and contact metamorphism of the Oligo-Miocene Kabyle sedimentary cover which are well observed at ''Collo-Oued Zhour' basin in the south. The Collo-Bougaroun volcano-plutonic complex, of ca. 300 km2, comprises (1) granular rocks, mainly cordierite bearing peraluminous granites (Bougaroun pluton to the north, the BeniToufout to the south and the Filfila to the east), (2) gabbros that occur at the northern and southern parts of Cap Bougaroun pluton where they are associated with ultramafic (3) microgranular rocks, mainly microgranites, that outcrop at the eastern part of the Bougaroun pluton, in Collo basin and El Milia, microdiorites in Bouserdoum and some doleritic or microgabbroic metric veins at Cap Bougaroun and (4) of lava in the Kef Cheraïa rhyolitic complex. Rocks from Collo-Bougaroun sites belong either to low-K, medium-K or high-K calc-alkaline series. The geochemistry of basic rocks (gabbros and dolerites) places strong constraints on their origin. Their LREE-depleted patterns, enrichment in LILE and slight depletion in HFSE are discussed in the very particular geodynamic context of the northern Algerian margin. Indeed, such depleted magmas could hardly have been emplaced over the African basement without experiencing any contamination imprint. Whole rock K/Ar ages were performed on 150-300 ?m grains from a set of representative magmatic rocks from Collo-Bougaroun region. The mafic rocks ages show a probable rejuvenation from (21.25 ± 6.01 (large error linked to the K2O wt% of 0.04) to 16.45 ± 0.52 Ma). This feature is attributed to a late K-gain during hydrothermal processes. This interpretation is supported by the occurrence of low temperature minerals (Adularia) in microgabbros and fine grained gabbros (microprobe analyses). The granite ages scatter between 20.85 ± 0.51 and 17.88 ± 0.5 Ma. The latter is consistent with 206U-238Pb age of 16.96±0.09 Ma obtained from 28 laser ablation spots analyses performed on zircon grains. Microgranites usually outcropping in Langhian ''post-nappes' basins, yield ages ranging from 14.17 ± 0.35 to 13.59 ± 0.33 Ma.

Fatiha, Abbassene; Aziouz, Ouabadi; Gilles, Chazot; Hervé, Bellon; René, Maury; Olivier, Bruguier

2014-05-01

269

Gas isotopic signatures (He, C, and Ar) in the Lake Kivu region (western branch of the East African rift system): Geodynamic and volcanological implications  

NASA Astrophysics Data System (ADS)

On 17 January 2002, the city of Goma was partly destroyed by two of the several lava flows erupted from a roughly N-S oriented fracture system opened along the southern flank of Mount Nyiragongo (Democratic Republic of Congo), in the western branch of the East African rift system. A humanitarian and scientific response was promptly organized by international, governmental, and nongovernmental agencies coordinated by the United Nations and the European Union. Among the different scientific projects undertaken to study the mechanisms triggering this and possible future eruptions, we focused on the isotopic (He, C, and Ar) analysis of the magmatic-hydrothermal and cold gas discharges related to the Nyiragongo volcanic system, the Kivu and Virunga region. The studied area includes the Nyiragongo volcano, its surroundings, and peripheral areas inside and outside the rift. They have been subdivided into seven regions characterized by distinct 3He/4He (expressed as R/Rair) ratios and/or ?13C-CO2 values. The Nyiragongo summit crater fumaroles, whose R/Rair and ?13C-CO2 values are up to 8.73 and from -3.5‰ to -4.0‰ VPDB, respectively, show a clear mantle, mid-ocean ridge basalt (MORB)-like contribution. Similar mantle-like He isotopic values (6.5-8.3 R/Rair) are also found in CO2-rich gas emanations (mazukus) along the northern shoreline of Lake Kivu main basin, whereas the 13?C-CO2 values range from -5.3‰ to -6.8‰ VPDB. The mantle influence progressively decreases in (1) dissolved gases of Lake Kivu (2.6-5.5 R/Rair) and (2) the distal gas discharges within and outside the two sides of the rift (from 0.1 to 1.7 R/Rair). Similarly, ?13C-CO2 ratios of the peripheral gas emissions are lighter (from -5.9‰ to -11.6‰ VPDB) than those of the crater fumaroles. Therefore, the spatial distribution of He and C signatures in the Lake Kivu region is mainly produced by mixing of mantle-related (e.g., Nyiragongo crater fumaroles and/or mazukus gases) and crustal-related (e.g., gas discharges in the Archean craton) fluids. The CO2/3He ratio (up to 10 × 1010) is 1 order of magnitude higher than those found in MORB, and it is due to the increasing solubility of CO2 in the foiditic magma feeding the Nyiragongo volcano. However, the exceptionally high 40Ar*/4He ratio (up to 8.7) of the Nyiragongo crater fumaroles may be related to the difference between He and Ar solubility in the magmatic source. The results of the present investigation suggest that in this area the uprising of mantle-originated f luids seems strongly controlled by regional tectonics in relation to the geodynamic assessment of the rift. These fluids are mainly localized in a relatively small zone between Lake Kivu and Nyiragongo volcano, with important implications in terms of volcanic activity.

Tedesco, D.; Tassi, F.; Vaselli, O.; Poreda, R. J.; Darrah, T.; Cuoco, E.; Yalire, M. M.

2010-01-01

270

New insights on the Gibraltar Arc geodynamics from SKS splitting: first contribution from the IberArray broad-band seismic network  

NASA Astrophysics Data System (ADS)

The Rif-Betic region, comprising the Gibraltar Arc and the extensional Alboran basin and including the diffuse limit between the Eurasia and African plates, is complex and there is still not a commonly accepted hypothesis about the mechanism responsible for its formation, as models including lithospheric delamination, convective removal or subduction have been proposed. In this context, the knowledge about the presence and properties of upper mantle anisotropy from SKS splitting measurements can provide valuable information to constrain the different geodynamical models. The installation of new permanent and semi-permanent broadband stations in the region has allowed obtaining a first insight into the anisotropic properties (Buontempo et al, 2008) and evidenced the presence of geographical variations in the anisotropic parameters, even if the lack of data in the Northern part of Morocco did not allow to obtain a detailed image. We present here the first analysis of the data provided by the IberArray broad-band seismic network that will allow a significant improvement the coverage of this area. The IberArray broad-band seismic network was deployed over this region for about 18 months, beginning in summer/fall 2007 in the framework of the large-scale Topo-Iberia project. This portable array, formed by up to 55 new generation dataloggers equipped with broad-band seismometers, has covered the southern part of Iberia (35 stations) and northern Morocco (20 stations) in an approximately regular grid, with a nominal spacing of 60 km. Data from more than 35 permanent broadband stations maintained by different institutions operating in the region has also been integrated into the IberArray database. Events with epicentral distances between 85 and 120 degrees and magnitude greater than 6.0 are systematically extracted from the continuous dataset and SKS and SKKS phases are inspected for anisotropy using the SplitLab software. Processing of the whole dataset is still ongoing, but the available results, including those for the entire year 2008, significantly improve the spatial resolution of SKS measurements in this region. The inferred fast velocity directions (FVD) clearly show a spectacular rotation along the Gibraltar arc, following the curvature of the Rif-Betic chain, from roughly N65E beneath the Betics to close to N65W beneath the Rif chain. Stations located in the South and South-east edges of the array, show a distinct pattern, with FVD oriented NE-SW to E-W. The results for some sites suggest the presence of complex anisotropy features, probably including two anisotropic layers. The obtained FVD results are compatible with rollback / subduction models, while convective-removal and delamination models seem unlikely to be compatible with our results. The FVD variations along the Gibraltar arc could be explained by fossil anisotropy acquired during the Eocene Western Mediterranean subduction, while the change in FVD observed to the South and South-East of the Rif-Betic chain can be related to the imprint of a flow episode around the Alboran high velocity slab during its Miocene fragmentation from the Algerian slab.

Diaz Cusí, Jordi; Gallart, Josep; Villaseñor, Antonio

2010-05-01

271

Combined geological and gravimetric mapping and modelling for an improved understanding of observed high-resolution gravity variations: a case study for the Global Geodynamics Project (GGP) station Moxa, Germany  

NASA Astrophysics Data System (ADS)

Geodynamic observatories around the globe continuously monitor signals like gravity, tilt and strain as a function of time. However, global signals are often masked by local effects, caused by the direct surroundings of the station, including the local geological setting. This link is well established for superconducting gravimeters (SG) that observe the gravity field variations at very high resolution. An enhancement of the SG time series by the application of local correction is exemplarily shown here in a very practicable procedure for the Geodynamic Observatory Moxa, Germany. We show how the combination of geological and gravimetrical mapping and modelling around Moxa results in a significant correction of the original gravity data, as can be proven by comparison with the satellite-derived gravity field. Detailed geological mapping of the observatory surroundings, including measurements of fold axes, foliations and joints, was the basis of the present study. The fold structure in the area of interest was interpreted by geometrical 3D modelling. The complete representation of different rock types in space also provides a better understanding of the local hydro-geological situation. Using a combination of the 3D geological model with the high-resolution Bouguer map of the observatory surroundings, we developed a 3D density model. This model enables the correction of small gravity effects caused by mass variations close to the SG, in particular local hydro-geological mass changes. Thus, the procedure presented here, based on a close connection of geology and gravimetry, is a powerful tool for the reduction of local gravity effects on SG recordings. It should be applicable to SG stations worldwide, where similar hydrologically driven mass changes can be assumed.

Kasch, Norbert; Naujoks, Marco; Kley, Jonas; Jahr, Thomas

2013-07-01

272

Comments on “Arc magmatism and subduction history beneath the Zagros Mountains, Iran: A new report of adakites and geodynamic consequences” by J. Omrani, P. Agard, H. Whitechurch, M. Bennoit, G. Prouteau, L. Jolivet  

NASA Astrophysics Data System (ADS)

Based on the imprecise geochemical data for 62 samples from Qom, Anar and Baft regions in central Iranian magmatic arc Omrani et al. (Omrani, J., Agard, P., Witechurch, H., Benoit, M., Prouteau, G., Jolivet, L., 2008. Arc magmatism and subduction history beneath the Zagsros Mountains, Iran: A new report of adakites and geodynamic consequences. Lithos 106, 380-398.), suggested that all studied magmatic rocks display the geochemical affinity of subduction-related calc-alkalic rock suites. Here, we demonstrate that the incorrect altered and variable geochemical data (e.g., Al 2O 3, Sr, Y, Ni, Cr, SiO 2, Na 2O, La/Yb and Th/Ce), show that most of the samples actually display calc-alkaline, shoshonitic and calc-alkalic-adakitic affinities. Furthermore, as a result of alteration, rock samples of similar age (e.g., Qom) indicate both adakitic and non-adakitic compositional signatures, which is misleading. On the basis of more than 400 previously published geochemical analyses, we suggest that, after eliminating the false geochemical signatures, the calc-alkaline and adakitic affinities of the central Iranian magmatic arc are due to flat subduction and might be related to a second phase of Miocene- Pliocene porphyry copper mineralization, which is a considerable exploration target and thus merits further investigation.

Aftabi, Alijan; Atapour, Habibeh

2009-12-01

273

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

274

K-Ar chronology and geochemistry of the Miocene magmatism of Collo-Bougaroun and Edough-Cap de Fer areas (NE Algeria). Temporal constraints on geodynamic evolution of the Eastern Algerian margin between 6° and 8°E  

NASA Astrophysics Data System (ADS)

The ''Petite Kabylie'' corresponds to the eastern Algerian coastal magmatic chain outcropping from Jijel to the west, up to the plain of Annaba to the east. In this area, the Collo-Bougaroun volcano-plutonic complex, of ca. 300 km2, comprises (1) granular rocks, mainly cordierite bearing peraluminous granites, (2) gabbros that occur at the northern and southern parts of Cap Bougaroun pluton where they are associated with ultramafic rocks and form the layered complex of Yadene?; (3) microgranular rocks, mainly microgranites, that outcrop at the eastern part of the Bougaroun pluton, in Collo basin and El Milia, microdiorites in Bouserdoum and some doleritic or microgabbroic metric veins at Cap Bougaroun and (4) of rhyolitic lava in Kef Cheraïa. The Bougaroun complex form a huge elliptical batholite along a major axis of 20km oriented ENE- WSW that intrudes serpentinized peridotites and kinzigites of the Bougaroun basement to the east. This granitic pluton gives time constraints as it induces deformation and contact metamorphism of the Oligo-Miocene Kabyle sediments of Collo-Oued Zhour basin in the south. These sediments reach the Upper Burdigalien which suggests that the lower limit of emplacement of this granite is coeval at least with this age. The majority of these magmatic rocks show subalkaline affinity with strong enrichment (0.13 to 4.13 %) in K2O during fractionation to calc-alkaline and high-K calc-alkaline affinity for the most differentiated rocks. The felsic rocks (granites, microgranites and rhyolites) are marked by a significant crustal contamination (?Nd = -10, I Sr = 0.720, ?18O = +12 ‰ [1], [2]) during their petrogenesis. However, the presence of basic rocks (gabbros and dolerites) that are depleted in K2O (0.13 to 0.44%) provides information on mantle composition and origin of magmas. The geochemical data on these rocks are discussed in the very particular geodynamic context of the northern Algerian margin.Twenty-four 40K-40Ar analyses were performed on whole rock and separated grain minerals (biotite, quartz and feldspar) from some granites. Grains were chosen in 150-300 ?m separates. The obtained results from mineral separates from the granites and gabbros scatter between 21 and 16 Ma. These results appear older compared to field observations that fixe the age of pluton intrusion around 16-17 Ma. Several assumptions are made on the possible origin of the possible excess argon, particularly during crustal contamination of magmas and differentiation processes. Syn-late or post-magmatic hydrothermal alteration is also considered. The Chetaïbi-Cap Fer area shows mafic (gabbro, basalt), intermediate (diorite) and felsic rocks (microgranite and rhyolite) that were emplaced either as lava-flows, sills, dykes or laccoliths intruding Miocene sediments. 14 samples were dated by K/Ar whole rock method and in some cases biotite and quartz & feldspar separates. The results show three groups: between 16 and 15Ma, about 14Ma and about 13Ma. We consider that three distinct magmatic events are responsible for their emplacement.These results agree well with the overall geodynamic context of Algerian margin which was structured during three tangential tectonic events, dated respectively 17 Ma, 15 Ma and 9 Ma.

Abbassene, F.; Bellon, H.; Chazot, G.; Ouabadi, A.

2013-12-01

275

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 São Francisco Cratons. The tholeiites from the SW Amazonian Craton, which belong to the Serra da Providência Intrusive Suite (1.55 Ga), the Nova Lacerda swarm (1.44 Ga), the Colorado Complex (1.35 Ga), and the Nova Brasilândia 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 Paraguá Terrane, whereas the tholeiites from the Serra da Providência Intrusive Suite and the Nova Brasilândia Group are considered intracratonic. The dike swarms of the São 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-Olivença 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 Crixás-Goiás (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.; Corrêa da Costa, P. C.

2013-01-01

276

Phanerozoic burial and unroofing of the western Slave craton and Wopmay orogen from apatite (U-Th)/He thermochronometry: assessing links between surface and deep-seated geodynamic processes  

NASA Astrophysics Data System (ADS)

Low temperature thermochronology of cratonic regions offers the potential for elucidating linkages between burial and unroofing patterns, surface uplift and subsidence, and lithosphere-asthenosphere interactions. The Slave craton contains >4.0 Ga rocks, is underlain by a cold, thick, chemically depleted lithospheric mantle root, was stabilized by late Archean time, and then surrounded by Proterozoic orogens. Despite its insulation from plate margin processes and apparent stability, both mafic dikes and kimberlites have repeatedly disrupted the Slave craton in the Proterozoic and Phanerozoic. Phanerozoic sedimentary xenoliths contained in kimberlites that range in age from ca. 610 to 0.45 Ma record the past extent of strata that were subsequently denuded, indicating that the Slave craton underwent a more dynamic history of burial and unroofing than widely recognized. These observations raise the question of whether cratonic deposition and denudation was influenced by Phanerozoic thermal and mechanical perturbations associated with kimberlite emplacement, changing mantle flow regimes, and/or far-field plate boundary processes. We present new apatite (U-Th)/He thermochronometry data for nine samples along an E-W transect from the interior of the Slave craton into the adjacent Paleoproterozoic Wopmay orogen to more comprehensively constrain the region's burial and unroofing history. The transect was designed both to address the issues outlined above and to specifically assess how the cratonic architecture across the Paleoproterozoic suture between these two terranes may have controlled the lithospheric response to Phanerozoic perturbations. All samples yielded Permian to mid-Triassic apatite (U-Th)/He dates. When combined with geologic and stratigraphic constraints, the results can be modeled as consistent with a history characterized by complete He loss from the apatites between the Devonian and Triassic. Assuming a surface temperature of 5°C and a 20°C/km geotherm, this corresponds to burial depths of >2.2 km during this time interval, followed by cooling and unroofing to near-surface conditions in the Late Jurassic, and lesser reheating or reburial during Cretaceous and Early Tertiary time. The broad uniformity of the apatite (U-Th)/He dates indicates that rocks across the more than 250 km covered by our sample transect underwent similar thermal histories. This pattern suggests this area behaved as a single, broadly coherent cratonic region since at least ca. 250 Ma. The results allow a preliminary assessment of potential relationships between the burial and unroofing history, tectonic events at the plate margins, and/or deep-seated geodynamic processes.

Ault, A. K.; Flowers, R. M.; Bowring, S. A.

2008-12-01

277

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

278

A geodynamic constraint on Archean continental geotherms  

NASA Astrophysics Data System (ADS)

Dewey (1988) observed that gravitational collapse appears to currently limit the altitudes of large plateaus on Earth to about 3 to 5 km above sea level. Arndt (1999) summarized the evidence for the failure of large parts of the continental crust to reach even sea-level during the Archean. If this property of Archean continental elevations was also enforced by gravitational collapse, it permits an estimation of the geothermal gradient in Archean continental crust. If extensional (collapse) tectonics is primarily a balance between gravitational power and the power consumed by extensional (normal) faulting in the upper brittle crust, as analysed by Bailey (1999), then it occurs when continental elevations above ocean bottoms exceed about 0.4 times the thickness of the brittle crust (Bailey, 2000). Assuming an Archean oceanic depth of about 5 km, it follows that that the typical thickness of Archean continental brittle crustal must have been less than about 12 km. Assuming the brittle-ductile transition to occur at about 350 degrees Celsius, this suggests a steep geothermal gradient of at least 30 degrees Celsius per kilometer for Archean continents, during that part of the Archean when continents were primarily submarine. This result does not help resolve the Archean thermal paradox (England and Bickle, 1984) whereby the high global heat flow of the Archean conflicts with the rather shallow crustal Archean geotherms inferred from geobarometry. In fact, the low elevation of Archean continental platforms raises another paradox, a barometric one: that continents were significantly below sea-level implies, by isostasy, that continental crustal thicknesses were significantly less than 30 km, yet the geobarometric data utilized by England and Bickle indicated burial pressures of Archean continental material of up to 10 kb. One resolution of both paradoxes (as discussed by England and Bickle) would be to interpret such deep burials as transient crustal thickening events of duration less than the crustal thermal equilibriation time (about 10 to 30 Ma). Temporary entrainment in the wake of basal eclogite ``sinkers'' might provide such transient burial. Vlaar's (1994) modelling of this eclogite delamination process (tectonically elaborated by Zegers and van Keken (2001)) indicates such sinker events would be significantly shorter than 10 Ma. The topographic re-equilibriation of a hot moho above such a process would be similarly short (Kaufmann and Royden, 1994).

Bailey, R. C.

2003-04-01

279

Geodynamic aspects of the Loma Prieta Earthquake  

NASA Astrophysics Data System (ADS)

The Loma Prieta earthquake differs from most of the observed seismicity along the San Andreas in northern California in its depth and style of rupture. The combination of crustal and thermal structure in the Loma Prieta region allowed strain accumulation to 18-20 km in the crust, leading to rupture at that depth during the event. A discrepancy in displacement direction of crust and mantle components of the Pacific plate near Loma Prieta led to a decoupling of the crust from the mantle within the ductile lower crust. This played a key part in the rupture initiation at the base of the seismogenic layer.

Furlong, Kevin P.; Langston, Charles A.

280

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

281

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.

282

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

283

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

284

Precise leveling, space geodesy and geodynamics  

NASA Technical Reports Server (NTRS)

The implications of currently available leveling data on understanding the crustal dynamics of the continental United States are investigated. Neotectonic deformation, near surface movements, systematic errors in releveling measurements, and the implications of this information for earthquake prediction are described. Vertical crustal movements in the vicinity of the 1931 Valentine, Texas, earthquake which may represent coseismic deformation are investigated. The detection of vertical fault displacements by precise leveling in western Kentucky is reported. An empirical basis for defining releveling anomalies and its implications for crustal deformation in southern California is presented. Releveling measurements in the eastern United States and their meaning in the context of possible crustal deformation, including uplift of the Appalachian Mountains, eastward tilting of the Atlantic Coastal Plain, and apparent movements associated with a number of structural features along the east coast, are reported.

Reilinger, R.

1981-01-01

285

Starlette geodynamics - The earth's tidal response  

NASA Technical Reports Server (NTRS)

The French Starlette satellite, launched in 1975, had the primary geophysical objective of providing information regarding 'solid' earth and ocean tides. The present paper is concerned with an analysis of the 1980 Starlette laser-ranging data for tides, geodetic parameters, and orbital parameters. The obtained solution represents a simultaneous least squares solution based upon normal equations constructed from seventy 5-day orbital arcs. It is pointed out that this new method has produced far better tidal results than would be achievable on the basis of the previous long periodic mean orbit evolution approach described by Felsentreger et al. (1979). It was possible to recover reasonable tidal values for periods on the Starlette orbit ranging from 6 days to over 90 days.

Williamson, R. G.; Marsh, J. G.

1985-01-01

286

Basic research for the geodynamics program  

NASA Technical Reports Server (NTRS)

Laser systems deployed in satellite tracking were upgraded to accuracy levels where biases from systematic unmodelled effects constitute the basic factor that prohibits extraction of the full amount of information contained in the observations. Taking into consideration that the quality of the instrument advances at a faster pace compared to the understanding and modeling of the physical processes involved, one can foresee that in the near future when all lasers are replaced with third generation ones the limiting factor for the estimated accuracies will be the aforementioned biases. Therefore, for the reduction of the observations, methods should be deployed in such a way that the effect of the biases will be kept well below the noise level. Such a method was proposed and studied. This method consists of using the observed part of the satellite pass and converting the laser ranges into range differences in hopes that they will be less affected by biases in the orbital models, the reference system, and the observations themselves.

1983-01-01

287

A climate model with cryodynamics and geodynamics  

Microsoft Academic Search

We represent a highly simplified, zero-dimensional model of the climatic system. The model attempts to incorporate mechanisms important on the time scale of glaciation cycles, namely, 104-105 years. In particular, the radiation balance of the ocean-atmosphere, the plastic flow of continental ice sheets, and the viscous flow of the upper mantle are taken into account. The stress is on the

Michael Ghil; Hervé Le Treut

1981-01-01

288

A climate model with cryodynamics and geodynamics  

NASA Technical Reports Server (NTRS)

A simplified, zero-dimensional model of the climatic system is presented which attempts to incorporate mechanisms important on the time scale of glaciation cycles: 10,000 to 100,000 years. The ocean-atmosphere radiation balance, continental ice sheet plastic flow, and upper mantle viscous flow are taken into account, with stress on the interaction between the ice sheets and the upper mantle. The model exhibits free, self-sustained oscillations of an amplitude and period comparable to those found in the paleoclimatic record of glaciations, offering mild support for the idea that unforced oscillations can actually exist in the real climatic system itself. The careful study of the interplay between internal mechanisms and external forcing is held to represent an interesting challenge to the theory of ice ages.

Ghil, M.; Le Treut, H.

1981-01-01

289

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

290

International lithosphere program - Exploiting the geodynamics revolution  

NASA Technical Reports Server (NTRS)

After presenting a development history of the application of spacecraft technology in the field of earth dynamics, which encompasses the measurement of the motion and the large scale deformation of the tectonic plates as well as the monitoring of earth's gravity and magnetic fields, attention is given to the International Lithosphere Program (ILP). ILP studies the dynamics and evolution of the lithosphere, with a view to earth resources identification and geological hazard reduction. Among the major problems being addressed is the mechanism by which magmas are generated, extruded, and intruded, at convergent and divergent plate boundaries and within plates. By contrast to current understanding of rifting, almost nothing is known about how the process of subduction begins. The methods used to measure tectonic plate phenomena are: laser ranging to both the moon and man-made satellites, and VLBI.

Flinn, E. A.

1984-01-01

291

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

292

Geodynamic control on melt production in the central Azores : new insights from major and trace elements, Sr, Nd, Pb, Hf isotopic data and K/Ar ages on the islands of Terceira, Sao Jorge and Faial  

NASA Astrophysics Data System (ADS)

A combined geochronological and geochemical study has been carried out on the volcanic islands of Terceira, São Jorge, and Faial (central Azores) to examine the relationships between mantle dynamics, melt production and regional deformation close to the triple junction between the American, the Eurasian and the Nubian lithospheric plates. The lavas analyzed span the last 1.3 Myr, and have been erupted during two main periods prior to 800 ka and after 750 ka, respectively. They range in composition from alkaline basalts/basanites to trachytes, and overall exhibit a strong enrichment in highly incompatible elements. The whole range of isotopic compositions here reported (87Sr/86Sr: 0.703508-0.703913; 143Nd/144Nd: 0.512882-0.513010; 206Pb/204Pb: 19.0840- 20.0932; 207Pb/204Pb: 15.5388-15.6409; 208Pb/204Pb: 38.7416-39.3921; 176Hf/177Hf: 0.282956-0.283111) suggests the involvement of three components: (1) a weakly radiogenic component reflecting the source of regional MORBs, (2) a main HIMU-type component represented in the three islands, and (3) an additional component in Faial recent lavas, which appears similar to the EM type end-member previously recognized on other Azores eruptive complexes. The geographical distribution of the enriched components and the synchronous construction of various islands at the regional scale rules out a single narrow active plume. They suggest in turn the presence of dispersed residual enriched mantle blobs, interpreted as remnants from a large heterogeneous plume probably responsible for edification of the Azores plateau several Myr ago. The lavas erupted in São Jorge and Faial prior to 800 ka have similar and homogeneous isotopic ratios, which partly overlap the compositional field of MORBs from the adjacent portion of the Mid-Atlantic Ridge (MAR). Their genesis can be explained by the regional development of N150 transtensive tectonic structures, which promoted significant decompression melting of the upper mantle, with correlative dilute expression of the enriched components. In contrast, the youngest lavas (< 750 ka) erupted along the N110 main structural direction on the three islands are significantly enriched in LILE and LREE, and generally have variable but more radiogenic isotopic compositions. Such characteristics suggest low-degree partial melting and greater incorporation of fertile residual mantle anomalies during passive tectonic reactivation of pre-existing transform faults promoted by recent ridge-push at the MAR. We propose that sub-aerial volcanism over the last 1.3 Myr in the central Azores recorded a sudden change in the conditions of melt generation which most probably reveals a major reconfiguration of regional deformation accompanying the recent geodynamic reorganization of the Eurasia-Nubia plate boundary.

Hildenbrand, A.; Weis, D. A.; Madureira, P.; Marques, F. O.

2012-12-01

293

NASA geodynamics program investigations summaries: A supplement to the NASA geodynamics program overview  

NASA Technical Reports Server (NTRS)

The development of a time series of global atmospheric motion and mass fields through April 1984 to compare with changes in length of day and polar motion was investigated. Earth rotation was studied and the following topics are discussed: (1) computation of atmospheric angular momentum through April 1984; (2) comparisons of psi sub values with variations in length of day obtained by several groups utilizing B.I.H., lunar laser ranging, VLBI, or Lageos measurements; (3) computation of atmospheric excitation of polar motion using daily fields of atmospheric winds and pressures for a short test period. Daily calculations may be extended over a longer period to examine the forcing of the annual and Chandler wobbles, in addition to higher frequency nutations.

1982-01-01

294

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.; Müller, R.; Seton, M.; Flament, N.; Gurnis, M.; Whittaker, J.

2012-12-01

295

Solar System Processes Underlying Planetary Formation, Geodynamics, and the Georeactor  

Microsoft Academic Search

Only three processes, operant during the formation of the Solar System, are\\u000aresponsible for the diversity of matter in the Solar System and are directly\\u000aresponsible for planetary internal-structures, including planetocentric nuclear\\u000afission reactors, and for dynamical processes, including and especially,\\u000ageodynamics. These processes are: (i) Low-pressure, low-temperature\\u000acondensation from solar matter in the remote reaches of the Solar System

J. Marvin Herndon

2006-01-01

296

Ecological-geodynamic evaluation of the Chuya earthquake  

Microsoft Academic Search

Disruptions of the Gornyi Altai ecologic-geological systems due to the Chuya earthquake were examined. The energy bond between\\u000a abiotic Earth spheres (the lithosphere and atmosphere) and biota were investigated during the period of seismic activity of\\u000a the Earth’s mantle, particularly with respect to population morbidity.

A. V. Shitov; V. E. Kats; M. A. Khar’kina

2008-01-01

297

Mars north polar deposits: stratigraphy, age, and geodynamical response  

USGS Publications Warehouse

The Shallow Radar (SHARAD) on the Mars Reconnaissance Orbiter has imaged the internal stratigraphy of the north polar layered deposits of Mars. Radar reflections within the deposits reveal a laterally continuous deposition of layers, which typically consist of four packets of finely spaced reflectors separated by homogeneous interpacket regions of nearly pure ice. The packet/interpacket structure can be explained by approximately million-year periodicities in Mars' obliquity or orbital eccentricity. The observed ???100-meter maximum deflection of the underlying substrate in response to the ice load implies that the present-day thickness of an equilibrium elastic lithosphere is greater than 300 kilometers. Alternatively, the response to the load may be in a transient state controlled by mantle viscosity. Both scenarios probably require that Mars has a subchondritic abundance of heat-producing elements.

Phillips, R. J.; Zuber, M. T.; Smrekar, S. E.; Mellon, M. T.; Head, J. W.; Tanaka, K. L.; Putzig, N. E.; Milkovich, S. M.; Campbell, B. A.; Plaut, J. J.; Safaeinili, A.; Seu, R.; Biccari, D.; Carter, L. M.; Picardi, G.; Orosei, R.; Surdas, Mohit, P.; Heggy, E.; Zurek, R. W.; Egan, A. F.; Giacomoni, E.; Russo, F.; Cutigni, M.; Pettinelli, E.; Holt, J. W.; Leuschen, C. J.; Marinangeli, L.

2008-01-01

298

Wilson study cycles: Research relative to ocean geodynamic cycles  

NASA Technical Reports Server (NTRS)

The effects of conversion of Atlantic (rifted) margins to convergent plate boundaries; oceanic plateaus at subduction zones; continental collision and tectonic escape; southern Africa rifts; and global hot spot distribution on long term development of the continental lithosphere were studied.

Kidd, W. S. F.

1985-01-01

299

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

300

Argon isotopic composition of Archaean atmosphere probes early Earth geodynamics.  

PubMed

Understanding the growth rate of the continental crust through time is a fundamental issue in Earth sciences. The isotopic signatures of noble gases in the silicate Earth (mantle, crust) and in the atmosphere afford exceptional insight into the evolution through time of these geochemical reservoirs. However, no data for the compositions of these reservoirs exists for the distant past, and temporal exchange rates between Earth's interior and its surface are severely under-constrained owing to a lack of samples preserving the original signature of the atmosphere at the time of their formation. Here, we report the analysis of argon in Archaean (3.5-billion-year-old) hydrothermal quartz. Noble gases are hosted in primary fluid inclusions containing a mixture of Archaean freshwater and hydrothermal fluid. Our analysis reveals Archaean atmospheric argon with a (40)Ar/(36)Ar value of 143?±?24, lower than the present-day value of 298.6 (for which (40)Ar has been produced by the radioactive decay of the potassium isotope (40)K, with a half-life of 1.25 billion years; (36)Ar is primordial in origin). This ratio is consistent with an early development of the felsic crust, which might have had an important role in climate variability during the first half of Earth's history. PMID:23739427

Pujol, Magali; Marty, Bernard; Burgess, Ray; Turner, Grenville; Philippot, Pascal

2013-06-01

301

Geodynamics of the Sichuan earthquake region in May 12, 2008  

Microsoft Academic Search

A disastrous earthquake with a magnitude of M 7.8? 7.9 occurred 93 km northwest of the administrative center Chengdu, Sichuan Province, China, on May 12, 2008. The hypocenter depth was about 30 km. Aftershocks with magnitudes up to M 6.1?6.4 went on until the first half of June. Their epicenters were confined to the north-northwest?trending zone extending for 315 km

Yu. G. Gatinsky; D. V. Rundkvist; G. L. Vladova; T. V. Prokhorova

2008-01-01

302

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 fractures—which are perpendicular to the direction of extension—and 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 Gölü fault zone is a within-crust detachment; the Tuz Gölü 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.; Yürür, T.; Froger, J.-L.; Köse, O.; Gündogdu, N.

1998-10-01

303

A Proposed Test Area for the Spaceborne Geodynamic Ranging System.  

National Technical Information Service (NTIS)

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, trendi...

P. D. Lowman

1978-01-01

304

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

305

Prelaunch testing of the laser geodynamic satellite (LAGEOS)  

NASA Technical Reports Server (NTRS)

The LAGEOS was extensively tested optically prior to launch. The measurement techniques used are described and resulting data is presented. Principal emphasis was placed on pulse spreading characteristics, range correction for center of mass tracking, and pulse distortion due to coherent effects. A mode-locked freqeuncy doubled Nd:YAG laser with a pulse width of about 60 ps was used as the ranging transmitter and a crossfield photo-multiplier was used in the receiver. High speed sampling electronics were employed to increase receiver bandwidth. LAGEOS reflected pulses typically had a width of 250 ps with a variability in the range correction of less than 2 mm rms. Pulse distortion due to coherent effects was inferred from average waveforms and appears to introduce less than + or - 50 ps jitter in the location of the pulse peak. Analytic results on this effect based on computer simulations are also presented. Theoretical and experimental data on the lidar cross section were developed in order to predict the strength of lidar echoes from the satellite. Cross section was measured using a large aperture laser collimating system to illuminate the LAGEOS. Reflected radiation far-field patterns were measured using the collimator in an autocollimating mode. Data were collected with an optical data digitzer and displayed as a three-dimensional plot of intensity versus the two far-field coordinates. Measurements were made at several wavelengths, for several types of polarizations, and as a function of satellite orientation.

Fitzmaurice, M. W.; Minott, P. O.; Abshire, J. B.; Rowe, H. E.

1977-01-01

306

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

307

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

Microsoft Academic Search

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

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

1993-01-01

308

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

NASA Astrophysics Data System (ADS)

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

1993-09-01

309

The Coming Role of GPU in Computational Geodynamics (Invited)  

NASA Astrophysics Data System (ADS)

With the proliferation of GPU ( graphics accelerator board) the computing landscape has changed enormously in the last 3 years. The new additional capabilities of the GPU , such as larger shared memories and load-store operations , allow it to be considered as a viable stand-alone computational and visualization engine. Today the massive threading and computing capability of GPU can deliver at least an order of magnitude performance over the multi-core CPU architecture. The cost of a GPU system is also considerably cheaper than a CPU cluster by more than an order of magnitude.The introduction of CUDA and ancillary software aids, such as Jackets, have allowed the rapid translation of many venerable codes into software usable on GPU. We will discuss our experience acquired over the past year in attacking five different computational problems in the geosciences, using the GPU. They include (1.) 3-D seismic wave propagation with the spectral-element method (2.)2-D shallow water equation as applied to tsunami wave propagation, using finite-differences (3.) 3-D mantle convection with constant viscosity using a 4th order compact finite-difference operator (4.) non-linear heat-diffusion equation in 2-D using a collocation method based on radial basis functions over an elliptical area . Grid points are divided so as to lie on a centroidal Voronoi mesh . Derivatives are calculated at each grid point using a point-dependent stencil computed from the nearest neighbors .(5.) Stokes flow with variable viscosity by means of a pre-conditioner calculated on the GPU based on the vortex method using Green’s functions, along with the radial basis functions and the fast multi-pole method. The Krylov method is used on the CPU for the final iterative step .We will discuss the relative speed-ups of the GPU over the CPU in each of these cases. We will point out the need to go to more computationally intensive mode with multiple GPUs, which calls for key CPUs to control the message passing between the different computational domains by means of MPI. In our CPU-GPU system a separate GPU, the Nvidia GTX 295 , is also devoted for visualizing the ongoing computed results. According to some circles, the future roadmap of GPU seems to be at least one and a half order of magnitude brighter than the CPU in the next 6 years.

Yuen, D. A.; Knepley, M. G.; Erlebacher, G.; Wright, G. B.

2009-12-01

310

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

311

Techniques for the analysis of geodynamic effects using laser data  

NASA Technical Reports Server (NTRS)

New orbit computation techniques have been developed to realize the full precision of laser ranging measurements from a single tracking station used to accurately determine the orbital inclination of a satellite. In order to evaluate earth and ocean tidal effects on the satellite and polar motion effects on the station latitude, improved computational techniques are described for perturbations significantly influencing the satellite's inclination, such as solar radiation pressure and geopotential resonance. By using the time independent value of maximum latitude reached by the satellite as the experimental variable, orbit tracking errors caused by imprecise modelling of the gravity field and atmospheric drag have been largely overcome and made possible long term analysis of osculating elements. With these techniques, quarter day spans of laser data have been employed to monitor the inclination of the satellite to the order 0.01 arcseconds precision over a period of seventeen months.

Dunn, P. J.; Smith, D. E.; Kolenkiewicz, R.

1973-01-01

312

Messinian Erosional Surface in the Levantin margins: geodynamic implications.  

NASA Astrophysics Data System (ADS)

During the Messinian salinity crisis (5.96-5.33 Ma), the Mediterranean Sea was disconnected from the Atlantic Ocean. As a consequence, a dramatic sea-level fall occurred during part of the crisis and deep erosion has been observed on the Mediterranean margins as well as on the continent. The origin and evolution of the Messinian Salinity Crisis (MSC) and associated deposits beneath the Mediterranean seafloor is still subject of considerable debate, mainly focused on their depositional environment, age and correlation from the basinal to marginal series. One of the key problems concerns the lack of biostratigraphy data and 3D geometrical control of main stratigraphic surfaces. Recent studies in three areas in the Eastern Mediterranean basins, Hatay (Turkey), Lattakie (Syria), and Psematismenos (Cyprus) basins confirm the presence of the Messinian Erosional Surface which separates the uppermost Miocene deposits from the Pliocene, clearly encased in incises valleys. Systematic cartography of this unconformity shows fluvial erosion in relation with the peak of the Messinian Salinity Crisis. On the edges of the Psematismenos incised valleys or subareal canyons, the Messinian Erosional Surface impacts the previously deposited Messinian marginal evaporites linked to a first step of the Messinian Salinity Crisis. Huge Mass Transport Deposits are often locally preserved along the canyons edges and made of breccias with blocks of variable size and nature, gypsum and other pre-Messinian rocks. Fan delta complexes infilled the Messinian canyons flooded during the Zanclean. The most spectacular is described in the Nahr El Khabir Valley in northern Syria. These observations consists in distinct steps of the Messinian Salinity Crisis: 1- circum-Mediterranean deposition of marginal evaporite between 5.96 and 5.6 Ma in suspended basins, and 2- the downcutting of the Messinian fluvial canyons between 5.6 and 5.32Ma ending with the complex Pliocene marine reflooding, caracterised by a catastrophic sea level rise.

Mocochain, L.; Clauzon, G.; Robinet, J.; Blanpied, C.; Suc, J. P.; Gorini, C.; Abdalla, A. Al; Azki, F.

2012-04-01

313

Neogene basanites in western Kamchatka: Mineralogy, geochemistry, and geodynamic setting  

Microsoft Academic Search

Neogene (N\\u000a 1\\u000a 2\\u000a -N\\u000a 2\\u000a 1\\u000a ?) K-Na alkaline rocks were found in western Kamchatka as a subvolcanic basanite body at Mount Khukhch. The basanites have\\u000a a microphyric texture with olivine phenocrysts in a fine-grained doleritic groundmass. The olivine contains inclusions of\\u000a Al-Cr spinel. The microlites consist of clinopyroxene, plagioclase, magnetite, and apatite, and the interstitial phases are\\u000a leucite,

A. B. Perepelov; M. Yu. Puzankov; A. V. Ivanov; T. M. Filosofova; E. I. Demonterova; E. V. Smirnova; L. A. Chuvashova; T. A. Yasnygina

2007-01-01

314

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

315

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

316

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

317

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

318

Subduction thrust seismicity in geodynamic numerical simulations compared to observations  

NASA Astrophysics Data System (ADS)

Subduction thrust earthquakes occur over different spatial and temporal scales. In this study, the long-term earthquake cycle is investigated in a 4000x200 km ocean-continent subduction setting. Events or periods of rapid deformation, present within spontaneously formed localizations of plastic strain, are collected and quantified for comparison to observations and scaling to nature. The resulting database gives insight into the cyclic nature and timing of large earthquakes. The characteristics of the subduction zone seismic cycle also differ for different convergent margins. Subduction zones that are weakly coupled and receive a lot of sediment are likely to produce large mega-thrust earthquakes, while more and smaller earthquakes are observed next to compressive overriding plates, where the coupled fault receives less sediment. This distinction is tested in our model by producing different databases with events for different overriding plate tectonic regimes, different inter-plate frictions and different amounts of sediments. To model the long-term seismic cycle in a subduction zone we use a plane-strain finite-difference scheme with marker-in-cell technique to solve the conservation of momentum, mass, and energy for a visco-elasto-plastic rheology (code I2ELVIS). In a generic, petrologically complex continent-ocean subduction zone, localizations of plastic strain are formed when the second invariant of the deviatoric stress tensor exceeds the Drucker-Prager yield criterion, leading to a correction to the pressure-dependent yield stress by decreasing a viscosity-like parameter. We assume a seismic event occurs when a sudden considerable stress drop occurs simultaneously with an immediate strong increase in strain rate. For these events we collect estimates of depth, stress drop, and slip area, assuming equi-dimensional slip areas, and thereby acquire a very rough indication of earthquake size. Previous results have shown the existence of several clusters of plastic strain localizations, at the thrust interface, bending outer-rise, back-arc, and accretionary wedge, whose cycle is related to the by far most energetic events at the thrust interface. These thrust events spread over depths of about 15 km and occur about every 10.000 years within a seismogenic zone extending from about 20 to 35 km depth. They also showed the presence of a long-term cycle in dissipated strain energy rate of the order of 30.000 years.

van Dinther, Ylona; Gerya, Taras; Dalguer, Luis A.; Mai, P. Martin; Morra, Gabriele

2010-05-01

319

The kinematic and geodynamic significance of the Atacama fault zone, northern Chile  

NASA Astrophysics Data System (ADS)

The Atacama fault zone (AFZ) is the dominant feature in the structure of the North Chilean Coastal Cordillera. Left lateral displacement took place along its system of longitudinal faults during the Jurassic and early Cretaceous. This development was contemporaneous with arc magmatism and was later reactivated, resulting in a steep normal fault. Strike-slip movements along the AFZ consist of two sets of ductile shear zones of different ages: one Jurassic, formed under amphibolite-facies conditions; the other early Cretaceous, with greenschist-facies mylonites. Structural asymmetries point to a sinistral sense of shear in both sets. The AFZ can be interpreted as a magmatic arc structure which accommodated the oblique subduction of an oceanic plate (trench-linked strike-slip fault). The sinistral sense of shear is consistent with reconstructions of late Jurassic to early Cretaceous plate configurations in the SE Pacific.

Scheuber, Ekkehard; Andriessen, Paul A. M.

320

The kinematic and geodynamic significance of the Atacama fault zone, northern Chile  

Microsoft Academic Search

The Atacama fault zone (AFZ) is the dominant feature in the structure of the North Chilean Coastal Cordillera. Left lateral displacement took place along its system of longitudinal faults during the Jurassic and early Cretaceous. This development was contemporaneous with arc magmatism and was later reactivated, resulting in a steep normal fault. Strike-slip movements along the AFZ consist of two

Ekkehard Scheuber; Paul A. M. Andriessen

1990-01-01

321

Investigation of dynamic noise affecting geodynamics information in a tethered subsatellite  

NASA Technical Reports Server (NTRS)

The effects of a tethered satellite system's internal dynamics on the subsatellite were calculated including both overall motions (libration and attitude oscillations) and internal tether oscillations. The SKYHOOK tether simulation program was modified to operate with atmospheric density variations and to output quantities of interest. Techniques and software for analyzing the results were developed including noise spectral analysis. A program was begun for computing a stable configuration of a tether system subject to air drag. These configurations will be of use as initial conditions for SKYHOOK and, through linearized analysis, directly for stability and dynamical studies. A case study in which the subsatellite traverses an atmospheric density enhancement confirmed some theoretical calculations, and pointed out some aspects of the interaction with the tether system dynamics.

Gullahorn, G. E.

1984-01-01

322

Geodynamic implications of Pleistocene ultrarapid vertical-axis rotations in the Southern Apennines, Italy  

NASA Astrophysics Data System (ADS)

Paleomagnetic analysis from lower Pleistocene (Sicilian) mudstones in the Sant'Arcangelo basin (Southern Apennines, Italy) shows no vertical-axis rotations. These results define the upper time constraint on the 23° counterclockwise rotations previously measured in the underlying lower Pleistocene (Santernian Emilian) units of the Sant'Arcangelo basin. These rotations occurred before the Jaramillo subchron in a time span of <0.5 m.y. Paleomagnetic rotations are coeval with the major phases of thrusting along the outer front of the Apennines, do not extend to the Adriatic foreland, and were limited to the hanging wall of the active thrust sheets along the outer front of the Apennines. Rapid counterclockwise rotations, coeval with thrusting and offset on left-lateral faults, represent the surface manifestation of the differential slab retreat and southwestward rollback of the trench in the Calabrian arc region. The unusually fast vertical-axis rotations indicate that the left-lateral component of deformation was particularly intense during the early Pleistocene in the Sant'Arcangelo region, located along the edge of the retreating subduction zone. These data suggest that the lateral breakoff of the African-Ionian-Adriatic subducting lithosphere, imaged by seismic tomography and deep seismicity, occurred in the Sant'Arcangelo region during the early Pleistocene.

Mattei, Massimo; Petrocelli, Vincenzo; Lacava, Donato; Schiattarella, Marcello

2004-09-01

323

Geodynamically unusual settings of sedimentary rock and ore formation due to tectonic-decompression effects  

Microsoft Academic Search

The traditional views of terrigenous rocks as products of classical sedimentary cycle, ''mobilization-transport-deposition,'' are not universal. Detrital rocks are sometimes formed due to flaking and fracturation of rocks of rising blocks. The process is produced by tectonic-decompression mechanisms - the origination of a gradient of excessive stress and its discharge. It is incorrect to classify rocks created by this phenomenon

Goryainov

1984-01-01

324

Late Cretaceous to Early Tertiary Motion of the Hawaiian Hotspot and its Geodynamic Implications  

NASA Astrophysics Data System (ADS)

Many of our ideas of where mantle plumes originate, how they interact with the convecting mantle and how plates have moved in the past rely on interpretations of the Hawaiian-Emperor hotspot track. One reason this volcanic lineament has attained this conceptual stature lies in its prominent bend at 43 Ma. The bend, which separates the westward trending Hawaiian islands from the northward-trending Emperor seamounts has no equal among the Earth's hotspot tracks; it is the clearest physical manifestation of a change in plate motion in a fixed hotspot reference frame. However, paleomagnetic data available from Suiko Seamount and Detroit Seamount of the Emperor trend (Tarduno and Cottrell, EPSL, 1997) suggest that the Emperor seamounts might primarily record drift of the Hawaiian hotspot in the mantle. ODP Leg 197 was designed to test this idea through drilling on Emperor trend seamounts. Record-setting basement penetration at five holes drilled during the leg has allowed us to both test this idea and learn more about the source and melting history of the Hawaiian hotspot. The paleolatitudes suggested from our preliminary paleomagnetic analysis of basement cores clearly differ from the latitude of Hawaii. The values are consistent with the hypothesis that the Hawaiian hotspot moved southward from 81 to 43 Ma at rates of 30 to 50 mm yr-1. These values, which are within the range of velocities typical of lithospheric plates, force us to reconsider the cause of the Hawaiian-Emperor bend, rates of mantle convection and Pacific plate reconstructions based on the fixed hotspot assumption. This motion also precludes use of hotspots as a reference frame to calculate true polar wander, estimates of which may be too large by a factor of 5 when compared with global paleomagnetic data sets (Tarduno and Smirnov, EPSL, 2001).

Tarduno, J. A.; Duncan, R. A.; Cottrell, R. D.; Scholl, D. W.

2002-05-01

325

The application of continuum damage mechanics to solve problems in geodynamics  

NASA Astrophysics Data System (ADS)

Deformation within the Earth's lithosphere is largely controlled by the rheology of the rock. Ductile behavior in rocks is often associated with plasticity due to dislocation motion or diffusion under high pressures and temperatures. However, ductile behavior can also occur in brittle materials. An example would be cataclastic flow associated with folding at shallow crustal levels, steep subduction zones, and large-scale deformation at plate boundaries. Engineers utilize damage mechanics to model the continuum deformation of brittle materials. We utilize a modified form of damage mechanics where damage represents a reduction in frictional strength and includes a yield stress. We use this empirical approach to simulate the bending of the lithosphere. We use numerical simulations to obtain elastostatic solutions for plate bending and where the stress exceeds a yield stress, we apply damage to reduce the elastic moduli. Damage is calculated at each time step by a power-law relationship of the ratio of the yield stress to stress and the yield strain to the strain. To test our method, we apply our damage rheology to a plate deforming under applied shear, a constant bending moment, and a constant load. We simulate a wide range of behaviors from slow relaxation to instantaneous failure, over timescales that span six orders of magnitude. Stress relaxation produces elastic-perfectly plastic behavior in cases where failure does not occur. For cases of failure, we observe a rapid increase in damage leading to failure. The changes in the rate of damage accumulation in failure cases are similar to the changes in b-values of acoustic emissions observed in triaxial compression tests of fractured rock and b-value changes prior to some large earthquakes. Thus continuum damage mechanics can simulate ductile behavior due to brittle mechanisms as well as observations of laboratory experiments and seismicity.

Manaker, David Martin

326

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

327

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

328

Proterozoic sedimentation and Pan-African geodynamic development in the Himalaya  

Microsoft Academic Search

The Purana or Proterozoic-Lower Cambrian continental-margin sedimentary succession of the Lesser Himalaya comprises three lithological divisions: a lower argillo-arenaceous group, a middle carbonate succession and an upper argillo-calcareous assemblage. The poorly sorted basal sediments consisting of wacke-slate alternations of the lower group were emplaced by currents, including turbidity currents, which in the early stage flowed northwards from the Aravalli and

K. S. Valdiya

1995-01-01

329

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

330