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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

Journal of Geodynamics  

NSDL National Science Digital Library

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

3

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

4

Fundamental studies in geodynamics  

NASA Technical Reports Server (NTRS)

Research in fundamental studies in geodynamics continued in a number of fields including seismic observations and analysis, synthesis of geochemical data, theoretical investigation of geoid anomalies, extensive numerical experiments in a number of geodynamical contexts, and a new field seismic volcanology. Summaries of work in progress or completed during this report period are given. Abstracts of publications submitted from work in progress during this report period are attached as an appendix.

Anderson, D. L.; Hager, B. H.; Kanamori, H.

1981-01-01

5

Geodynamics from satellites  

NASA Technical Reports Server (NTRS)

The NASA Geodynamics Program is developing a variety of techniques in support of national programs in geodynamics, geomagnetics and earthquake hazard reduction. Global tectonics are to be observed by satellite laser tracking and radio interferometry, which will be used to measure the movements of extended (greater than 200 km) regions to an accuracy of 3 cm, while for shorter distances, lasers enable a more rapid measuring of regional strain accumulation patterns than ground systems. The techniques of Doppler tracking between two satellites to measure the gravity field over the ocean is also under NASA study

Kaula, W. M.

1979-01-01

6

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

7

GS of CAS Geodesy & Geodynamics Beijing June 20041 Geodesy and Geodynamics  

E-print Network

GS of CAS ­ Geodesy & Geodynamics ­ Beijing June 20041 Geodesy and Geodynamics By Christophe Vigny://www.geologie.ens.fr/~vigny #12;GS of CAS ­ Geodesy & Geodynamics ­ Beijing June 20042 Addressed topics Geodesy and Earth remote surface deformation and plate tectonics Measuring the Earth deformation : terrestrial and spatial geodesy

Vigny, Christophe

8

Laser geodynamic satellite (LAGEOS II)  

NASA Technical Reports Server (NTRS)

The Laser Geodynamic Satellite 2 (LAGEOS 2) is nearly identical to the LAGEOS 1 satellite, which was launched by NASA in 1976. However, LAGEOS 2 is completely passive, and is equipped with fused silian corner reflectors for ranging with ground-based lasers. The addition of LAGEOS 2 will provide the GSFC laser network with significantly increased satellite tracking opportunities, because LAGEOS 1 is at a 110-degree inclination and LAGEOS 2 will be at a 52-degree inclination. The flight profile is given, and information is presented in tabular form on the following topics: Deep Space Network support, frequency assignments, telemetry, tracking, and tracking support responsibility.

Portelli, C.; Ousley, G. W., Sr.

1991-01-01

9

International GPS Service for Geodynamics  

NASA Technical Reports Server (NTRS)

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

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

1996-01-01

10

GLOBAL DISASTERS: Geodynamics and Society  

NASA Astrophysics Data System (ADS)

The problem of reducing the damage caused by geodynamic and social disasters is a high priority and urgent task facing the humanity. The vivid examples of the earthquake in Japan in March 2011 that generated a new kind of threat - the radiation pollution, and the events in the Arabic world that began in the same year, are dramatic evidences. By the middle of this century, the damage from such disastrous events is supposed to exceed the combined GDP of all countries of the world. The database of 287 large-scale natural and social disasters and global social phenomena that have occurred in the period of II B.C.E. - XXI A.D. was compiled by the authors for the first time. We have proposed the following phenomenological model: the scale of disasters over the time does not decrease, there is a minimum of accidents in the XV century; the numbers of accidents have cycles lasting until the first thousand years, natural and social disasters in the aggregate are uniformly distributed in time, but separately natural and social disasters are nonuniform. Thus, due to the evaluation, a 500-year cycle of catastrophes and 200-300 and 700-800-year periodicities are identified. It is shown that catastrophes are grouped into natural and social types by forming clusters. The hypothesis of the united geo-bio-social planetary process is founded. A fundamentally new feature of this research is the assumptions about the statistical significance of the biosphere and the impact of society on the geodynamic processes. The results allow to formulate a new understanding of global disaster as an event the damage from which the humanity will be unable to liquidate even by means of the total resource potential and the consequence of which may turn into the irreversible destruction of civilization. The correlation between the natural and social phenomena and the possible action mechanism is suggested.

Vikulina, Marina; Vikulin, Alexander; Semenets, Nikolai

2013-04-01

11

GS of CAS Geodesy & Geodynamics Beijing June 20041 SEISMIC CYCLE  

E-print Network

GS of CAS ­ Geodesy & Geodynamics ­ Beijing June 20041 SEISMIC CYCLE · Elastic accumulation-seismic motions · Triggering of earthquake · Precursors ? #12;GS of CAS ­ Geodesy & Geodynamics ­ Beijing June 20042 Arctang profiles Uy = 2.V0 / arctang (x/h) #12;GS of CAS ­ Geodesy & Geodynamics ­ Beijing June

Vigny, Christophe

12

Geodynamics - Tracking satellites to monitor global change  

NASA Technical Reports Server (NTRS)

The major goals and organizational structure of the International GPS Geodynamics Service (IGS), a new Navstar satellite tracking service, are described. IGS activities are aimed at providing the scientific community with data on GPS orbits accurate enough for performing regional and local GPS analysis and daily earth rotation information.

Beutler, Gerhard; Morgan, Peter; Neilan, Ruth E.

1993-01-01

13

Geodynamical Evolution and Tectonic Framework of China  

Microsoft Academic Search

In this paper, we show that the tectonic framework of mainland China consists of three latitudinal strips, namely, Tianshan-Yinshan-Yanshan, Qinling-Dabie, and Nanling; two longitudinal strips namely, Daxing'anling Taihangshan Wulingshan, Helanshan-Longmenshan; and two triangles, Songpan-Ganzi, and Chaidamu. The geodynamic evolution of China can be considered in five-stages, which can be summarised as a kind of teeterboard-like process. The evolutionary process is

Guangding LIU

2007-01-01

14

Research activities of the Geodynamics Branch  

NASA Technical Reports Server (NTRS)

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

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

1984-01-01

15

Time-domain parallelization for geodynamic modeling  

NASA Astrophysics Data System (ADS)

Modern computational Geodynamics increasingly relies on parallel algorithms to speed up calculations. Currently, parallelization in Geodynamic codes is achieved via spatial decomposition, where the physical computational space (or its associated matrix system) is subdivided into domains that are attributed to one processor or to a set of processors. Such an approach that distributes the computational load is efficient as long as the size of the sub-domains is large enough so that the computational time remains larger than the communication time between processors. However, when the size of the sub-domains becomes too small, the parallel speed-up stagnates, which puts bounds on the maximum performances of the parallel calculations. This limitation can be overcome using a time-domain parallelization algorithm. This approach, named parareal, relies on the use of coarse sequential and fine parallel propagators to predict and to iteratively correct the solution over a given time interval. Although this method has been successfully used to solve parabolic and hyperbolic equations in various scientific areas, it has never been applied in geodynamic studies, where motions relevant to the Earth and other planetary mantles are that of a convective fluid at infinite Prandtl number. In that case, the time dependence of the mass and momentum equations is only implicit, due to thermal and/or viscous couplings with the explicitly time-dependent energy equation. This requires a number of modifications to the original algorithm. The performances of this adapted version of the parareal algorithm were investigated using theoretical model predictions in good agreement with numerical experiments. I show that under optimum conditions, the parallel speedup increases linearly with the number of processors, and speedups close to 25 were measured, using only few tens of CPUs. This parareal approach can be used alone or combined with any spatial parallel algorithm, allowing significant additional increase in speedup with increasing the number of processors.

Samuel, H.

2012-04-01

16

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

17

Geodynamical Evolution and Tectonic Framework of China  

NASA Astrophysics Data System (ADS)

In this paper, we show that the tectonic framework of mainland China consists of "three latitudinal strips", namely, Tianshan-Yinshan-Yanshan, Qinling-Dabie, and Nanling; "two longitudinal strips" namely, Daxing'anling Taihangshan Wulingshan, Helanshan-Longmenshan; and "two triangles", Songpan-Ganzi, and Chaidamu. The geodynamic evolution of China can be considered in five-stages, which can be summarised as a kind of "teeterboard-like" process. The evolutionary process is that in the Palaeozoic era, the China mainland had lower elevation in the west and higher in the east, with OrdosSichuan as an axis. After the Mesozoic era, because the blocks of Qiangtang, Gangdese, and India collided and sutured with the Tarim block. During this time closure of the Tethys ocean occurred, and the Qinghai-Tibet Plateau formed. In the Cenozoic subduction of the Pacific plate northwestwards under the Philippine Sea began, and the Philippine Sea block converged towards the Eurasian plate. This was associated with extension and thinning of the crust in East China, which resulted in the uplift of the land in the west and subsidence in the east of China. Finally, we point out that research on the geodynamic evolution of the terranes is of practical significance in prospecting for mineral deposits and hydrocarbon resources.

LIU, Guangding

18

The evolution of Hadean-Eoarchaean geodynamics  

NASA Astrophysics Data System (ADS)

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

O'Neill, C.; Debaille, V.

2014-11-01

19

Scientific Data Analysis and Software Support: Geodynamics  

NASA Technical Reports Server (NTRS)

The support on this contract centers on development of data analysis strategies, geodynamic models, and software codes to study four-dimensional geodynamic and oceanographic processes, as well as studies and mission support for near-Earth and interplanetary satellite missions. SRE had a subcontract to maintain the optical laboratory for the LTP, where instruments such as MOLA and GLAS are developed. NVI performed work on a Raytheon laser altimetry task through a subcontract, providing data analysis and final data production for distribution to users. HBG had a subcontract for specialized digital topography analysis and map generation. Over the course of this contract, Raytheon ITSS staff have supported over 60 individual tasks. Some tasks have remained in place during this entire interval whereas others have been completed and were of shorter duration. Over the course of events, task numbers were changed to reflect changes in the character of the work or new funding sources. The description presented below will detail the technical accomplishments that have been achieved according to their science and technology areas. What will be shown is a brief overview of the progress that has been made in each of these investigative and software development areas. Raytheon ITSS staff members have received many awards for their work on this contract, including GSFC Group Achievement Awards for TOPEX Precision Orbit Determination and the Joint Gravity Model One Team. NASA JPL gave the TOPEX/POSEIDON team a medal commemorating the completion of the primary mission and a Certificate of Appreciation. Raytheon ITSS has also received a Certificate of Appreciation from GSFC for its extensive support of the Shuttle Laser Altimeter Experiment.

Klosko, Steven; Sanchez, B. (Technical Monitor)

2000-01-01

20

Advanced cyberinfrastructure for research in Geodynamics  

NASA Astrophysics Data System (ADS)

Today's scientists need access to new information technology capabilities, able to perform high-resolution complex computing simulations in a reasonable time frame. Sophisticated simulation tools allow us to study phenomena that can never be observed or replicated by standard laboratory experiments. Modeling complex natural processes in general, and numerical computation in particular, represents today an essential need of research, and all modern research centers benefit from a computing center of one form or another. The combined power of hardware and sophisticated software, visualization tools, and scientific applications produced and used by interdisciplinary research teams make possible nowadays to advance the frontiers of science and to pose new key scientific questions. Cyberinfrastructure integrates hardware for high speed computing, a collection of highly specialized software and tools, and a powerful visualization tool. A new interdisciplinary research domain is emerging at the interface of geosciences and computing with essential inputs from geology and geophysics. In this study we show how to rapidly deploy a low-cost high-performance computing cluster (HPCC) and a 3D visualization system that can be used both in teaching and research in geosciences. Also, we present several geodynamic simulations performed with such systems.

Manea, Marina; Constantin Manea, Vlad

2010-05-01

21

Geodynamic contributions to global climatic change  

NASA Technical Reports Server (NTRS)

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

Bills, Bruce G.

1992-01-01

22

Basic research for the geodynamics program  

NASA Technical Reports Server (NTRS)

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

1991-01-01

23

Time domain parallelization for computational geodynamics  

NASA Astrophysics Data System (ADS)

I present a time domain parallelization approach for geodynamic modeling. This algorithm, named parareal, is based on the use of coarse sequential and fine parallel propagators to predict and to iteratively correct the solution of the governing equations over a given time interal. Although the method has been successfully used to solve differential equations, in various scientific areas, it has not been applied to model solid-state convective motions relevant to the Earth and other planetary mantles. In that case, the time-dependence of the velocity is only implicit, which requires modifications to the original algorithm. The performances of this adapted version of the parareal algorithm were investigated using theoretical model predictions in good agreement with numerical experiments. I show that under optimum conditions, the parallel speedup increases linearly with the number of processors, and speedups close to 10 were measured, using only few tens of CPUs. This parareal approach can be used alone or combined with any spatial parallel algorithm, allowing significant additional increase in speedup with increasing number of processors.

Samuel, Henri

2012-01-01

24

GS of CAS Geodesy & Geodynamics Beijing June 20041 RIGID PLATE TECTONICS  

E-print Network

GS of CAS ­ Geodesy & Geodynamics ­ Beijing June 20041 RIGID PLATE TECTONICS · Plate definition · Plate deformation : strain and rotation tensors #12;GS of CAS ­ Geodesy & Geodynamics ­ Beijing June.e. plates. #12;GS of CAS ­ Geodesy & Geodynamics ­ Beijing June 20043 Plate geometry and plate tecctonics

Vigny, Christophe

25

GS of CAS Geodesy & Geodynamics Beijing June 20041 Fundamentals of GPS  

E-print Network

GS of CAS ­ Geodesy & Geodynamics ­ Beijing June 20041 Fundamentals of GPS #12;GS of CAS ­ Geodesy of CAS ­ Geodesy & Geodynamics ­ Beijing June 20043 Phase measurement precision The precision-cycles) representing phase ambiguity #12;GS of CAS ­ Geodesy & Geodynamics ­ Beijing June 20044 Double differences One

Vigny, Christophe

26

GS of CAS Geodesy & Geodynamics Beijing June 20041 DEFORMATION PATTERN IN ELASTIC CRUST  

E-print Network

GS of CAS ­ Geodesy & Geodynamics ­ Beijing June 20041 DEFORMATION PATTERN IN ELASTIC CRUST ­ Geodesy & Geodynamics ­ Beijing June 20042 Stress () in 2D - Force = x surface - no rotation => xy = yx of CAS ­ Geodesy & Geodynamics ­ Beijing June 20043 Applied forces Normal forces on x axis : = xx(x). y

Vigny, Christophe

27

Eclogites and their geodynamic interpretation: a history  

NASA Astrophysics Data System (ADS)

Hay 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

28

The Overshoot Phenomenon in Geodynamics Codes  

NASA Astrophysics Data System (ADS)

The overshoot phenomenon is a common occurrence in numerical software when a continuous function on a finite dimensional discretized space is used to approximate a discontinuous jump, in temperature and material concentration, for example. The resulting solution overshoots, and undershoots, the discontinuous jump. Numerical simulations play an extremely important role in mantle convection research. This is both due to the strong temperature and stress dependence of viscosity and also due to the inaccessibility of deep earth. Under these circumstances, it is essential that mantle convection simulations be extremely accurate and reliable. CitcomS and ASPECT are two finite element based mantle convection simulations developed and maintained by the Computational Infrastructure for Geodynamics. CitcomS is a finite element based mantle convection code that is designed to run on multiple high-performance computing platforms. ASPECT, an adaptive mesh refinement (AMR) code built on the Deal.II library, is also a finite element based mantle convection code that scales well on various HPC platforms. CitcomS and ASPECT both exhibit the overshoot phenomenon. One attempt at controlling the overshoot uses the Entropy Viscosity method, which introduces an artificial diffusion term in the energy equation of mantle convection. This artificial diffusion term is small where the temperature field is smooth. We present results from CitcomS and ASPECT that quantify the effect of the Entropy Viscosity method in reducing the overshoot phenomenon. In the discontinuous Galerkin (DG) finite element method, the test functions used in the method are continuous within each element but are discontinuous across inter-element boundaries. The solution space in the DG method is discontinuous. FEniCS is a collection of free software tools that automate the solution of differential equations using finite element methods. In this work we also present results from a finite element mantle convection simulation implemented in FEniCS that investigates the effect of using DG elements in reducing the overshoot problem.

Kommu, R. K.; Heien, E. M.; Kellogg, L. H.; Bangerth, W.; Heister, T.; Studley, E. H.

2013-12-01

29

Exploring the asthenophere via geodynamic modeling  

NASA Astrophysics Data System (ADS)

The rheologically weak (i.e. low viscosity) layer known as the asthenosphere was first proposed to provide a mechanism for isostatic compensation [Barrell, 1914], and its existence has since been validated by studies of post-glacial rebound. Further evidence has come recently from geodynamic models that demonstrate a need for a weak rheological layer to facilitate a plate-like mode of mantle convection. Independent of these rheological considerations, magneto-telluric and seismic surveys have shown that the Earths oceanic upper mantle has relatively low seismic velocities, high seismic attenuation, and high electrical conductivity at depths of ~80-200km. Since these geophysical anomalies correlate well spatially with the low viscosity of the asthenosphere, it follows that there is likely a single mechanism responsible. Three competing hypotheses have been proffered: 1. the presence of volatiles, namely water [Hirth and Kohlstedt, 1996; Karato and Jung, 1998; Yang et al., 2007]; 2. the presence of small-degree partial melt [Anderson and Sammis, 1970; Shankland and Waff, 1977; Yoshino et al., 2005; Hirano et al., 2006; Mierdel et al., 2007]; 3. natural variations in the physical properties of dry, melt-free peridotite with temperature and pressure [Faul and Jackson, 2005; Stixrude and Lithgow-Bertelloni, 2005; Priestly and McKenzie, 2006]; Each of these mechanisms requires a unique distribution of volatiles and melt in the upper mantle, leading to corresponding spatial variations in viscosity and density. Each scenario will thus lead to a characteristic onset time and scale of dense thermal instabilities at the base of the overriding lithosphere, and thereby heat flow, bathymetry, and seismic structure. In an attempt to differentiate between these three hypotheses, we employ the CitcomCU finite element package to model the upper mantle beneath an oceanic plate. We explicitly include melting due to decompression beneath a mid-ocean ridge in the model using Lagrangian particles. These particles are used to track melting and volatiles within the model domain. The effects of melting [Cooper and Kohlstedt, 1986; Hirth and Kohlstedt, 1995] and volatiles [Hirth and Kohlstedt, 1996] on rheology, based on laboratory studies of olivine deformation, are included. We systematically vary plate velocity, mantle potential temperature, residual porosity, and water content to match the conditions of each hypothesis with the model output from each scenario then compared to geophysical observations. Specifically, heat flow and bathymetry can then be compared directly with field measurements in ocean basins. Likewise model output of temperature, composition and porosity can be used to infer seismic velocities and attenuation, which can in turn be compared to regional seismic models.

Fahy, E. H.; Hall, P.; Faul, U. H.

2009-12-01

30

Geodynamic and metabolic cycles in the Hadean  

NASA Astrophysics Data System (ADS)

High-degree melting of hot dry Hadean mantle at ocean ridges and plumes resulted in a crust about 30km thick, overlain in places by extensive and thick mafic volcanic plateaus. Continental crust, by contrast, was relatively thin and mostly submarine. At constructive and destructive plate boundaries, and above the many mantle plumes, acidic hydrothermal springs at ~400C contributed Fe and other transition elements as well as P and H2 to the deep ocean made acidulous by dissolved CO2 and minor HCl derived from volcanoes. Away from ocean ridges, submarine hydrothermal fluids were cool (?100C), alkaline (pH ~10), highly reduced and also H2-rich. Reaction of solvents in this fluid with those in ocean water was catalyzed in a hydrothermal mound, a natural self-restoring flow reactor and fractionation column made up of carbonates and freshly precipitated Fe-Ni sulfide and greenrust pores and bubbles, developed above the alkaline spring. Acetate and the amino acetate glycine were the main products, much of which was eluted to the ocean. Other organic byproducts were retained, concentrated and reacted within the compartments. These compartments comprising the natural hydrothermal reactor consisted partly of greigite (Fe5NiS8). It was from reactions between organic modules confined within these inorganic compartments that the first prokaryotic organism evolved. These acetogenic precursors to the Bacteria diversified and migrated down the mound and into the ocean floor to inaugurate the "deep biosphere". Once there the Bacteria, and the recently differentiated Archaea, were protected from cataclysmic heating events caused by large bolide impacts. Geodynamic forces led to the eventual obduction of the deep biosphere into the photic zone where, initially protected by a thin veneer of sediment, the use of solar energy was mastered and photosynthesis emerged. The further evolution to oxygenic photosynthesis was effected as catalytic [CaMn4+] bearing molecules that otherwise would have been interred in the mineral ranciéite in the shallow marine manganiferous sediments, were sequestered and invaginated within the cyanobacterial precursor where, energized by light, they could oxidize water with greater efficiency. Thus, chemical sediments were required both for the emergence of chemosynthesis and of oxygenic photosynthesis, the two innovations that did most to change the nature of our planet.

Russell, M. J.; Arndt, N. T.

2004-09-01

31

Metamorphic chemical geodynamics of subduction zones Gray E. Bebout  

E-print Network

Frontiers Metamorphic chemical geodynamics of subduction zones Gray E. Bebout Lehigh University.N. Halliday Available online 12 June 2007 Abstract Study of metamorphic suites directly representing the deep-pressure (UHP) metamorphic suites incorporating knowledge of mineral chemistry and reactions, kinetics

Bebout, Gray E.

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

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

34

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

35

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

36

Geochemical discrimination of basalts formed in major geodynamic settings  

NASA Astrophysics Data System (ADS)

New tectonomagmatic discriminant diagrams are proposed to determine the geodynamic settings of basalt formation from geochemical data. The reference (training) sets, on which the diagrams are based, comprise (1) recent island-arc basalts (IAB, n = 2902); (2) within-plate basalts (WPB, n = 12379); (3) mid-ocean ridge basalts (MORB, n = 1828); and (4) postcollision basic rocks, including dikes and sills (PCB, n = 1823). To determine the geodynamic settings of basalt formation, the belonging of a tested object to one of WPB + PCB, MORB, or IAB + PCB groups is first established, and then PCB is discriminated from WPB or IAB. The average weighted uncertainty of IAB, MORB, and WPB identification is about 10%. The use of new diagrams results in a substantial decrease in classification errors as compared with previously elaborated plots.

Velikoslavinsky, S. D.; Krylov, D. P.

2014-11-01

37

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

38

Monitoring of global geodynamic processes using satellite observations  

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

39

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

40

Paleomagnetic and geochronologic constraints on the geodynamic evolution of the Central Dinarides  

E-print Network

?? ? ??? ? ?? Paleomagnetic and geochronologic constraints on the geodynamic evolution, Paleomagnetic and geochronologic constraints on the geodynamic evolution of the Central Dinarides of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before

Utrecht, Universiteit

41

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

E-print Network

GS of CAS ­ Geodesy & Geodynamics ­ Beijing June 20041 Monitoring the Earth Surface from space bandwith. Shape of the surface from radar imagery Surface deformation from satellite geodesy : SLR, VLBI, DORIS, GPS #12;GS of CAS ­ Geodesy & Geodynamics ­ Beijing June 20042 Optical Imagery : basic principles

Vigny, Christophe

42

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

43

Geodynamics of oroclinal bending: Insights from the Mediterranean  

NASA Astrophysics Data System (ADS)

The Alpine Orogen in the Mediterranean region exhibits a series of orogenic curvatures (oroclines). The evolution of these oroclines is relatively well constrained by a plethora of geophysical and geological data, and therefore, their origin can inform us on the fundamental processes controlling oroclinal bending. Here, a synthesis of the geometry of Mediterranean oroclines, followed by a discussion on their geodynamic origin is presented. The geometrical synthesis is based on a new classification of Mediterranean oroclines, which defines a first-order orocline (Adriatic Orocline) by the general northward-convex shape of the Alpine Orogen from Cyprus to Gibraltar. Superimposed on the limbs of this orocline, are second-, third- and fourth-order oroclines. The major process that led to the formation of the Adriatic Orocline is the indentation of Adria into Europe, whereas second- and third-order oroclines (e.g., Western Mediterranean and Gibraltar oroclines, respectively) were primarily controlled by a combination of trench retreat and slab tearing. It appears, therefore, that the geodynamics of Mediterranean oroclines has been entirely dependent on plate boundary migration and segmentation, as expressed in the interlinked processes of indentation, trench retreat and slab tearing. The relative contribution of specific geodynamic processes, and their maturity, could be inferred from geometrical characteristics, such as the amplitude-to-width ratio, the orientation of the curvature (convex or concave) relative to the convergence vector, and their geometrical relationship with backarc extensional basins (e.g., in the concave side of the orocline). Based on the information from the Mediterranean oroclines, it is concluded that oroclinal bending commonly involves lithospheric-scale processes, and is not restricted to thin-skinned deformation. However, contrary to previous suggestions that assume that the whole lithosphere can buckle, there is no clear evidence that such processes occur in modern tectonic environments.

Rosenbaum, Gideon

2014-12-01

44

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

45

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

46

Geodynamic reconstructions of the South America-Antarctica plate system  

NASA Astrophysics Data System (ADS)

The South America-Antarctica plate system shows many oceanic accretionary systems and subduction zones that initiated and then stopped. To better apprehend the evolution of the system, geodynamic reconstructions (global) have been created from Jurassic (165 Ma) to present, following the techniques used at the University of Lausanne. However, additional synthetic magnetic anomalies were used to refine the geodynamics between 33 Ma and present. The reconstructions show the break up of Gondwana with oceanisation between South America (SAM) and Antarctica (ANT), together with the break off of 'Andean' geodynamical units (GDUs). We propose that oceanisation occurs also east and south of the Scotian GDUs. Andean GDUs collide with other GDUs crossing the Pacific. The west coast of SAM and ANT undergo a subsequent collision with all those GDUs between 103 Ma and 84 Ma, and the Antarctic Peninsula also collides with Tierra del Fuego. The SAM-ANT plate boundary experienced a series of extension and shortening with large strike-slip component, culminating with intra-oceanic subduction leading to the presence of the 'V-' and 'T-' anomalies in the Weddell Sea. From 84 Ma, a transpressive collision takes place in the Scotia region, with active margin to the east. As subduction propagates northwards into an old and dense oceanic crust, slab roll-back initiates, giving rise to the western Scotia Sea and the Powell Basin opening. The Drake Passage opens. As the Scotian GDUs migrate eastwards, there is enough space for them to spread and allow a north-south divergence with a spreading axis acting simultaneously with the western Scotia ridge. Discovery Bank stops the migration of South Orkney and 'collides with' the SAM-ANT spreading axis, while the northern Scotian GDUs are blocked against the Falkland Plateau and the North-East Georgia Rise. The western and central Scotia and the Powell Basin spreading axes must cease, and the ridge jumps to create the South Sandwich Islands Sea. The Tierra del Fuego-Patagonia region has always experienced mid-oceanic ridge subduction since 84 Ma. Slab window location is also presented (57-0 Ma), because of its important implication for heat flux and magmatism.

Vrard, Christian; Flores, Kennet; Stampfli, Grard

2012-01-01

47

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

48

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

49

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

50

Effects of turbulence on the geodynamic laser ranging system  

NASA Astrophysics Data System (ADS)

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.

1993-06-01

51

Coupling a geodynamic seismic cycling model to rupture dynamic simulations  

NASA Astrophysics Data System (ADS)

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

Gabriel, Alice; van Dinther, Ylona

2014-05-01

52

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

E-print Network

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 or in the interstellar medium; (ii) High-pressure, high-temperature condensation from solar matter associated with planetary-formation by raining out from the interiors of giant-gaseous protoplanets, and; (iii) Stripping of the primordial volatile components from the inner portion of the Solar System by super-intense solar wind associated with T-Tauri phase mass-ejections, presumably during the thermonuclear ignition of the Sun. As described herein, these processes lead logically, in a causally related manner, to a coherent vision of planetary formation with profound implications including, but not limited to, (a) Earth formation as a giant gaseous Jupiter-like planet with vast amounts of stored energy of protoplanetary compression in its rock-plus-alloy kernel; (b) Removal of approximately 300 Earth-masses of primordial gases from the Earth, which began Earth's decompression process, making available the stored energy of protoplanetary compression for driving geodynamic processes, which I have described by the new whole-Earth decompression dynamics and which is responsible for emplacing heat at the mantle-crust-interface at the base of the crust through the process I have described, called mantle decompression thermal-tsunami; and, (c)Uranium accumulations at the planetary centers capable of self-sustained nuclear fission chain reactions.

J. Marvin Herndon

2006-02-10

53

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

E-print Network

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

Gregg, Patricia Michelle Marie

2008-01-01

54

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

55

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

E-print Network

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

Georgen, Jennifer E

2001-01-01

56

APWPs: Critical Building Steps and Potential for Future Geodynamical Studies.  

NASA Astrophysics Data System (ADS)

Among other items, the Apparent Polar Wander Paths (APWP) of individual tectonic blocks contain information on geodynamical events from both shallower lithospheric sources (e.g. continental breakups and collisions) and deeper mantle sources affected by convection. Recent advances in the Earth Sciences, such as provided by global tomography or climate modeling, have emphasized the essential need for accurate reconstructions of the Earth's surface (blocks, plates and their boundaries and topographies), in order for instance to compare the initial positions of downgoing slabs or emerging hot spots with deeper mantle features, or to understand why and how time-varying climates and biomes may be related. A half century after its initial pionneering contributions to the formulation of continental drift and plate tectonics, paleomagnetism remains an invaluable tool which will allow us to solve a very large range of problems concerning both internal and external geodynamics (solid, fluid and bio-spheres). The accurate determination of the APWPs of crustal and lithospheric blocks remains one of the main goals that must be pursued by the paleomagnetic community. Based on two examples, one extending from Permian to Present, the other in the Late Proterozoic to Early Paleozoic, I will discuss various aspects of the construction of APWPs and reconstruction of past plate positions. Critical steps involve: 1) how are original paleomagnetic data selected? 2) how are the kinematic models used to transfer data from one plate to the other determined ? 3) how can poles coming from deformed (e.g. rotated) regions be used ? and 4) how good is the geocentric axial dipole (GAD) assumption, which is fundamental for reliable plate reconstructions ? Particular emphasis will be given to this last topic, since the GAD hypothesis has recently been challenged, with suggestions that significant long-term octupolar contributions might have existed from the Precambrian throughout to the early Tertiary. These might account for the low inclinations observed in central Asia in the Cretaceous and early Tertiary, or for the misfits of Pangea (Pangea A or B?). GAD hypothesis appears to be essentially correct and APWPs still have a bright future.

Besse, J.

2004-12-01

57

Structural Analysis and Geodynamic Implications of Tessera Terrain, Venus  

NASA Astrophysics Data System (ADS)

Understanding processes of tessera formation is fundamental to Venus tectonic and geodynamic models. We examined tessera terrain in Ishtar Terra, crustal plateaus, and as inliers within the plains using high-resolution Magellan SAR imagery. We describe several major types of tesseraeeach found in specific geologic or geomorphic regions. Fold and S-C tessera terrain are found only in Ishtar Terra; lava flow and basin-and-dome terrains reside within the interior of crustal plateaus, whereas folded ribbon terrain and extended folded terrain comprise margins of crustal plateaus; and star terrain lies within central Phoebe. Inliers are divisible into fracture-dominated and graben-dominated tesserae, which may represent ancient flooded coronae-chasmata and crustal plateaus, respectively. Thus tesserae might form in several tectonic environments, including as a result of (1) subsurface flow in Ishtar Terra, (2) as sequences of surface-layer extension and contraction in crustal plateaus, (3) as highly-extended, previously-deformed crustal plateaus which have deflated or sunken, and become flooded and thus preserved as large plains inliers, and (4) as densely-fractured surface layersfractured as a result of corona and chasma formationwhich have since sunken and become flooded, and thus preserved as isolated, scattered, highly-fractured inliers. If these models of formation are correct, tesserae would not form a global onion skin; they would not represent a globally synchronous unit; they would not record a single period of deformation; and it would not infer a single mechanism for tesserae formation.

Hansen, V. L.; Willis, J. J.

1996-03-01

58

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

59

EH vs. CI chondrite derived mantle: A geodynamical comparison  

NASA Astrophysics Data System (ADS)

It is generally assumed that the Earth's bulk composition is derived from carbonaceous CI chondrites. However, arguments based on stable isotopes and redox considerations favor another type of material from which the Earth could be derived: the enstatite EH chondrites. The latter implies substantial heterogeneities either in minor and major elements within the mantle which is strongly suggested by seismological observations and further reinforced by noble gas constraints. Here we investigate the geodynamical consequences of CI and EH derived Earth's mantle compositions. Using numerical simulations in cylindrical geometry with an appropriate scaling to approximate the spherical Earth, we compare the evolution of mantles derived from EH and from CI chondrites from 4.5 Gyr B.P. to present day. For both EH and CI models the upper part of the mantle (from which continental crust is extracted) has a pyrolitic-like composition, therefore the differences between the two models are shifted to the lower part of the mantle mantle, implying substantial differences in heat producing elements concentrations and Si, Fe and Mg content. Both models consider the extraction of continental crust, heterogeneous internal heating related to local concentrations of heat producing elements, and the presence of chemically denser material in the lowermost mantle, as suggested by tomographic studies. The thermal and chemical evolution of these two models is therefore compared and the implications on present day mantle heterogeneity in both major and trace elements as well as the consequences on seismological observables are investigated.

Samuel, H.; Farnetani, C. G.; Javoy, M.

2004-12-01

60

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

61

Global Distribution of the Ozone Component Resulting from Earth's Geodynamics  

NASA Astrophysics Data System (ADS)

Here we propose that the global ozone component, unexplained by solar radiation and galactic cosmic rays, results from sources of the terrestrial origin. We call this component the residual ozone (RO). Our hypothesis is based on correlations between distribution of RO, tectonic plate motions estimated by space geodesy and seismic tomography of the Earth's core surface. The pattern of a present-day global map of RO is remarkably simple; it comprises two regions: positive and negative. We provide arguments that this pattern evolved following the break-up of the Pangaea supercontinent 175 Ma ago, together with motion of tectonic plates to their current locations. We recovered the location of where the RO distribution "broke-up" at the time of the Pangaea break-up. This line of the initial RO break-up is mostly located over modern oceanic areas of the Earth and over Africa. This line also lies very close to the 0-contour of the Earth's core surface. Thus the following geodynamic process can be regarded: the mantle convective currents starting at the core surface provoke the break-up of Pangaea and of RO. Then the plates move to their current locations and RO evolves to its current pattern.

Steblova, R. S.

2011-12-01

62

Geodynamically Consistent Interpretation of Seismic Tomography under the Hawaiian Hotspot  

NASA Astrophysics Data System (ADS)

Recent theoretical developments as well as increased data quality and coverage have allowed seismic tomographic imaging to better resolve narrower structures at both shallow and deep mantle depths. However, despite these improvements, the interpretation of tomographic images remains problematic mainly because of: (1) the trade off between temperature and composition and their different influence on mantle flow; (2) the difficulty in determining the extent and continuity of structures revealed by seismic tomography. We present a study on mantle thermal plumes, which illustrate the need to consider both geodynamic and mineral physics for a consistent interpretation of tomographic images in terms of temperature composition and flow. We focus on the identification of thermal plume by seismic tomography beneath the Hawaiian hot spot: a set of 3D numerical experiments is performed in a spherical shell to model a rising plume beneath a moving plate. The thermal structure obtained is converted into body waves seismic velocities using mineral physics considerations. We then build synthetic travel time data by propagating front waves in the obtained seismic structure. This synthetic data will be used to construct a travel time tomographic model, which is compared with actual tomographic models based on data from the ongoing PLUME seismic experiment. This comparison will allow a more consistent and quantitative interpretation of seismic tomography and plume structure under Hawaii.

Bercovici, D.; Samuel, H.

2006-12-01

63

Geodynamics of Venice tidal marshes observed by radar interferometry  

NASA Astrophysics Data System (ADS)

Inter-tidal environments, such as lagoons and deltas, are naturally dynamic coastal systems that are unique in their close links to both land-based fluvial and coastal sea processes. These landscapes are generally experiencing a destructing phase over the last decades primarily caused by river sediment trapping in the upland drainage basins, sea level rise due to climate changes, and land subsidence. Accurate monitoring of the geodynamics of tidal environments is very difficult because of various concurrent causes: i) the logistical difficulties (or inaccessibility) to reach the areas precluding the use of traditional leveling and differential GPS surveys; b) the limited effectiveness of permanents GPS stations due to the significant small-scale variability of the litho-stratigraphy and the soil hydro-geomechanical properties because of the recent development of these environments, usually occurred over the late Holocene; and c) the lack of permanent natural/anthropogenic structures that reduces the capability of SAR interferometry. Because land subsidence is expected to give an important contribution to the cumulative sediment budget of the Venice Lagoon, Italy, the Venice Water Authority has supported a research aimed at improving the quantification of the present land subsidence by exploring the use of radar interferometry on a number of artificial corner reflectors. A network of 58 trihedral corner reflectors (TCR) was installed in the salt marshes of the Venice Lagoon before the summer 2007. The TCR are characterized by 60 cm long edge, made of aluminium to reduce their weight, placed in areas without any other strong scatterer, and oriented to be visible with ENVISAT ASAR and TerraSAR-X acquisitions of descending orbits. Salt marshes are constantly visible, except when the tide rises. The TCR, usually installed at a height of 1 m above the mean sea level, are therefore constantly outside the water. In order to mitigate atmospheric artifacts and to properly resolve the radar phase ambiguity, the TCR network has been planned to keep to a value of about 1.0-1.5 km the maximum distance between the TCR or between an "artificial" and the adjacent "natural" reflector. Persistent scatterer interferometry has been applied on a number of 65 ENVISAT scenes spanning the time interval form February 2003 to December 2009. Specific procedures have been implemented to improve the accuracy of the interferometric solution on the TCR and to include it into the global interferometric point target analysis on natural targets. For the first time we have so proved the possibility of precisely quantifying the geodynamic evolution of large-scale tidal environments. As expected, a significant variability of the displacement rates has been recorded, ranging between a general stability to subsidence up to 5 mm/yr. Very interesting general and site-specific results have been obtained relating the observed displacements with the morphological evolution of the tidal marshes.

Tosi, L.; Teatini, P.; Strozzi, T.

2010-12-01

64

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

65

Geodynamical analysis of the Iranian Plateau and surrounding regions  

NASA Astrophysics Data System (ADS)

The Middle East is a tectonically active region where the interaction between crustal units produce devastating earthquakes and volcanic eruptions. The region holds within its boundaries the Tethyside Orogeny and is limited to the north by the Intermediate Orogeny. The Iranian Plateau sets within the Tethyside collage and has been affected by the closure of Paleo- and Neo-Tethys Oceans during the Mesozoic and Cenozoic. For instance, large oil and gas fields have formed along the sutures of these two former oceans in northeastern Iran, the Persian Gulf and the Zagros Mountains. This dissertation involves analyzing the geodynamical processes of the Iranian Plateau by studying surface, airborne and satellite gravity and magnetic data collected across the Plateau and its surrounding regions. To provide a basis for a more accurate analysis of the region's lithospheric stresses, a high-resolution crustal thickness model is developed using spectral correlation analysis and gravity inversion. The results of this modeling suggest a thickened crust beneath the Anatolian Plateau, Sistan and Zagros Mountains, plus the Caspian Sea. Next, a regional scale morpho-tectonic interpretation of Iran's aeromagnetic data is developed that characterizes the magnetic anomalies of the country. The results of this analysis suggest that the crust of Iran is divided into a number of small plates, with boundaries that are characterized by strong positive magnetic anomalies. Large magmatic assemblages in northern and western Iran are characterized by strong negative magnetic anomalies. In support of the objectives of the pending GOCE gravity and SWARM magnetic low-Earth orbiting satellite missions, the theory for numerically estimating the full gravity and magnetic scalar, vector and tensor fields of the spherical prism is summarized. As an application, the gravity and magnetic fields that the GOCE satellite and SWARM constellation of satellites may observe over the tectonically active region of the Middle East, roughly centered on Iran are estimated.

Asgharzadeh, Mohammad Forman

66

Error analysis for the proposed close grid geodynamic satellite measurement system (CLOGEOS)  

NASA Technical Reports Server (NTRS)

The close grid geodynamic measurement system experiment which envisages an active ranging satellite and a grid of retro-reflectors or transponders in the San Andreas fault area is a detailed simulated study for recovering the relative positions in the grid. The close grid geodynamic measurement system for determining the relative motion of two plates in the California region (if feasible) could be used in other areas of the world to delineate and complete the picture of crustal motions over the entire globe and serve as a geodetic survey system. In addition, with less stringent accuracy standards, the system would also find usage in allied geological and marine geodesy fields.

Mueller, I. I.; Vangelder, B. H. W.; Kumar, M.

1975-01-01

67

ELSEVIER Tectonophysics 298 (1998) 259269 On the post-25 Ma geodynamic evolution of the western Mediterranean  

E-print Network

Mediterranean Erwan Gueguena , Carlo Doglionib,L , Manuel Fernandez c a Centro di Geodinamica, Universita`, Via Abstract During the Neogene and Quaternary western Mediterranean geodynamics were dominated­S converge occurred between Africa and Europe during the same time span. The western Mediterranean was thus

Doglioni, Carlo

68

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

E-print Network

Journal of Geodynamics 41 (2006) 128­132 Advances in Southern Ocean tide modeling Yuchan Yia,, Koji Kingdom Accepted 30 August 2005 Abstract Tides in the polar region play a major role in the dynamics of sea ice and floating glacial ice shelves. Existing ocean tide models are much less accurate in coastal

69

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

Microsoft Academic Search

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

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

1992-01-01

70

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

E-print Network

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

Tingley, Joseph V.

71

Geology and geodynamics of Iceland R.G. Trnnes, Nordic volcanological Institute, University of Iceland  

E-print Network

Geology and geodynamics of Iceland R.G. Trønnes, Nordic volcanological Institute, University of Iceland Iceland is located where the asthenosperic flow under the the NE Atlantic plate boundary interacts and mixes with a deep-seated mantle plume. The buoyancy of the Iceland plume leads to dynamic uplift

Ingólfsson, ?lafur

72

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

Microsoft Academic Search

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.

Alexander Rodnikov; Natalia Sergeyeva; Ludmila Zabarinskaya

2010-01-01

73

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

74

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, Tendrek and Sphan 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-Ptrge 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

75

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

76

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

Microsoft Academic Search

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

Cristina Pauselli; Costanzo Federico; Jean Braun

2004-01-01

77

Prospects of Global Navigation Satellite System (GNSS) reflectometry for geodynamic studies  

Microsoft Academic Search

Innovative processing of satellite radar altimetry over solid Earth has been successfully applied for observing geodynamic process of glacial isostatic adjustment over the former Laurentide Ice Sheet in the present-day Hudson Bay land region. In this contribution, a simulation is conducted to study the prospects of the applications of space-\\/airborne and land-based Global Navigation Satellite System (GNSS) reflectometry to synoptically

C. K. Shum; Hyongki Lee; P. A. M. Abusali; Alexander Braun; Guy de Carufel; Georgia Fotopoulos; Attila Komjathy; Chungyen Kuo

2011-01-01

78

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

Microsoft Academic Search

The presented model of the Late Cenozoic geodynamic evolution of the central Andes and the complex tectonic, geological, and\\u000a geophysical model of the Earths crust and upper mantle along the Central Andean Transect, which crosses the Andean subduction\\u000a zone along 21S, are based on the integration of voluminous and diverse data. The onset of the recent evolution of the central

T. V. Romanyuk

2009-01-01

79

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

NASA Astrophysics Data System (ADS)

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

Schenk, V.

80

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

81

Geodynamics and rate of volcanism on massive Earth-like planets Edwin S.Kite* and Michael Manga -University of California,Berkeley  

E-print Network

Geodynamics and rate of volcanism on massive Earth-like planets (1) Edwin S.Kite* and Michael Manga to that of the known terrestrial planets, at least 3 modes of mantle convection are possible: a) Earth-like - Plate not explicitly model mush ocean geodynamics. Instead, we track the lithosphere's Peclet number (i.e., the ratio

Kite, Edwin

82

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

83

The Lageos satellite. [for accurate determination of geodynamic motion with ground based lasers  

NASA Technical Reports Server (NTRS)

The fundamental concept of Lageos is a long-lived, dense, electrically and mechanically inert spherical satellite with its surface speckled with retroreflecting cube corners, designed such that range measurements between duly equipped laser ground stations and the satellite are possible with an ultimate accuracy of 2 cm when data from a single satellite pass are appropriately averaged. The Lageos concept requires that the satellite be placed in an orbit for which an ephemeris can be determined ultimately to 5 cm rms uncertainty for a 24-hour arc. These required satellite characteristics should allow the several geodynamic motions experienced by ground stations to be determined typically with 2 cm accuracy.

Johnson, C. W.; Lundquist, C. A.; Zurasky, J. L.

1976-01-01

84

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

USGS Publications Warehouse

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

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

2011-01-01

85

Great earthquakes in the 21st century and geodynamics of the Tibetan Plateau  

NASA Astrophysics Data System (ADS)

What are the geodynamic processes that caused these deadly earthquakes? Why have these earthquakes caused so much damage? What are the key lessons that we have learned from these devastating earthquakes? Answers to these questions will significantly enhance not only our understanding of earthquake occurrence but also our ability to reduce seismic hazard. Under the framework of bi-lateral cooperation on earthquake sciences between China and USA, the Second Bi-Lateral Workshop on Earthquake Sciences was held in Chengdu, Sichuan Province, China, from April 22 to 25, 2011. Among the goals of this workshop was a review of recent advances in the study of great earthquakes and the exchange of ideas on earthquake disaster reduction. The principle theme of the workshop was "Great Earthquakes in the 21st Century and Geodynamics." This Special Issue contains a total of 24 papers presented during the workshop. The contributions cover a wide-range of topics associated with the theme. This preface summarizes the main points of the papers presented in this issue.

Zhang, Pei-Zhen; Engdahl, Eric Robert

2013-01-01

86

Recent geodynamic pattern of the eastern part of the Bohemian Massif  

NASA Astrophysics Data System (ADS)

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

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

2009-04-01

87

Investigation some algorithms for solving problems of local geodynamics with using base GlonassGps stations. (Russian Title: ???????????? ????????? ?????????? ??????? ????? ????????? ??????????? ? ?????????????? ??????? ???????/Gps ???????)  

NASA Astrophysics Data System (ADS)

In this paper mathematical modeling results of some algorithms for solving problems of local geodynamics by using base GLONASSGPS stations are presented. The statistical algorithm for trend discovering in coordinates of the point and ways of reduction of influencing random errors on results of coordinate determination with using third differences of measured distances are discussed.

Kuznetsova, E. V.; Bordovitsyna, T. V.; Chernitsov, A. M.

2011-07-01

88

Plate motion changes, the Hawaiian-Emperor bend, and the apparent success and failure of geodynamic models  

Microsoft Academic Search

Geodynamic models explain present-day plate motions in terms of mantle buoyancy forces arising from subducted lithosphere and lithospheric thickening, or from velocity anomalies mapped by seismic tomography. However, such models do not account for sudden plate tectonic reorganizations, such as the dramatic change in Pacific plate motion implied by the sharp bend in the Hawaiian-Emperor seamount chain about 43 million

Mark A. Richards; Carolina Lithgow-Bertelloni

1996-01-01

89

A new geodynamic interpretation for the South Portuguese Zone (SW Iberia) and the Iberian Pyrite Belt genesis  

E-print Network

A new geodynamic interpretation for the South Portuguese Zone (SW Iberia) and the Iberian Pyrite the Iberian Pyrite Belt (IPB) and flysch deposits forming the southern extent of the zone. Structural analysis, tectonics, volcanism, me´lange, VMS, pyrite. Citation: One´zime, J., J. Charvet, M. Faure, J.-L. Bourdier

Paris-Sud XI, Université de

90

Achievements and Planned Programmes of Activities of The Csg.5/6 "geodynamics of Northern Carpathians"  

NASA Astrophysics Data System (ADS)

Within the programme of the regional group CSG.5/6 "Geodynamics of Northern Carpathians", the following main lines are carried out. (1) Geodetic and geophysical investigations of the recent crustal movements and geophysical analysis of deep struc- ture on the Carpathian geodynamic test field. (2) Subsequent study of geological struc- tures in the region of Northern Carpathians. On the initiative of the Main Astronomical Observatory, the National Space Agency and the Aerogeodetic Enterprise of Ukraine two permanent GPS stations, UZHL and SULP, were being established during last 1.5 years. The first one is situated in the zone of Transcarpathian flexure (Uzhgorod, University) and the second one - in the west of East-European plate (the Precarpathi- ans, Lviv, Polytechnic University). In addition to the long-term project "Restoration of Ukrainian-Polish complex geophysical station at Pip Ivan Mount in Charnohora (Ukrainian Carpathians)", the following actions are planned for 2002-2004. (1) To carry out the complex geodetic, geophysical, geological and geomorphological in- vestigations in this region, which is less studied in comparison with other areas in Carpathians. The comparison of simultaneous appearance of geophysical processes in these regions will allow detect a degree of influence of endogenic, exogenic, and antro- pogenig factors on present day hydro-geological processes in the whole Carpathian region. (2) To create a network of permanent stations for the complex geophysical and geodynamic monitoring, which will include measurements of intensity of Earth's surface deformation field, remote photogrammetric measurements of intensity of de- structive and shift processes, the determination of parameters of gravity and mag- netic fields, seismic and electrometric measurements, spectral analysis of space im- ages for quality and quantity estimations of technogenic and antropogenic activity, generalization of data on evolution and dynamics of river systems and monitoring of hydro-geological phenomena. On the basis of results of the mentioned observations, a relation will be detected between phenomena and fields of various physical nature, antropogenic factors and hazard hydro-geological phenomena in Carpathian region.

Zablotskyj, F.; Tretyak, K.

91

Putting Phase Equilibria into Geodynamic Models: An Equation of State Approach (Invited)  

NASA Astrophysics Data System (ADS)

The use of free energy minimization codes to calculate the proportions and properties of minerals and consequently bulk rock properties is now commonplace in geophysical modeling. In effect such applications imply the existence of an equation of state, which is the optimized free energy as a function of its independent variables, for the rocks of interest. The essential feature of the equation of state is that all thermodynamic properties can be derived from it, a feature that requires that its derivatives are continuous. The equation of state may be calculated dynamically within the larger framework of a geodynamic code or it may be implemented statically via tables that are calculated prior to the solution of the geodynamic application. The virtues of static implementation is its extreme simplicity, computational efficiency, and that the finite resolution of the table assures that the equation of state is numerically differentiable for any choice of independent state variables. However, the memory required to store the requisite multidimensional tables may necessitate dynamic implementations for problems involving multi-component mass transfer, e.g., as in reactive melt transport. Paradoxically, the unlimited accuracy of dynamic solutions creates a potential numerical instability, the Stefan problem, for geodynamic governing equations formulated in terms of pressure and temperature. This instability arises because the derivatives of an equation of state for a polyphase aggregate as a function of pressure and temperature are singular at the conditions of a low order phase transformation. An equation of state as a function of specific entropy, specific volume and chemical composition eliminates this difficulty and, additionally, leads to a robust formulation of the energy and mass conservation equations. In this formulation, energy and mass conservation furnish evolution equations for entropy and volume and the equation of state serves as an update rule for temperature and pressure. Although this formulation is straightforward, the computation of phase equilibria as a function of entropy and volume is challenging because the equations of state for individual phases are usually expressed as a function of temperature and pressure. This challenge can be met by an algorithm in which continuous equations of state are approximated by a series of discrete states; a representation that reduces the phase equilibrium problem to a linear optimization problem that is independent of the functional form used for the equations of state of individual phases and readily solved by successive linear programming. Regardless of the way free energy minimization is implemented and the choice of independent variables, a consistent definition of pressure, and the coupling of equilibrium kinetics to deformation, is only possible if the continuity equation accounts for dilational strain.

Connolly, J.

2009-12-01

92

The Lanzarote Geodynamic Laboratory: new capabilities for monitoring of volcanic activity at Canary Islands  

NASA Astrophysics Data System (ADS)

The volcanic island of Lanzarote is located at the northeastern end of the Canary Islands. Together with Fuerteventura Island, Lanzarote constitutes the emergent part of the East Canary Ridge, which presents a NNE-SSW volcanic alignment. Last eruptive events took place in 1824 and during the period 1730-1736, which is the largest to occur in the archipelago and throw out about 1.3 km3 of volcanic materials. The Lanzarote Geodynamic Laboratory (LGL) was created in 1986 with the idea of making Lanzarote as a natural laboratory to carry out studies in order to acquire more knowledge about its origin, present status and evolution (Vieira et al., 1991; 2006). The LGL has a multidisciplinary scientific purpose and, among others, various objectives are devoted to investigate mass distribution in the Earth system and surface displacements associated to volcanic and/or seismic activity in the island. The influence of LGL is extended throughout the whole geographical area of Lanzarote, including small islands located at the north. The laboratory has 3 observing modules distributed along the island according to its infrastructure and scientific objectives, where more than 70 sensors are recording continuously gravity variations, ground deformations, sea level, seismic activity, meteorological parameters, etc. All these observations are supplemented by periodic measurement of geodetic and geophysical networks that allow us to make studies at local, insular and regional scales. The application of geodetic and geophysical techniques to identify geodynamic signals related to volcanic processes is then a permanent research activity of the laboratory. Nowadays, this fact becomes more interesting due to the ongoing volcanic eruption that is taking place in other island of the Canary Archipelago, El Hierro, since past July 2011. That is, the multidisciplinary research carry on up to now at the LGL allow us to apply multiparameter observations of different kinds of volcanic manifestations at the surface level, and to compare geodynamic processes associated with an active area of the Earth's crust. In turn, the results obtained can provide new inputs for studying precursor of volcanic activity and also contribute to volcanic hazard mitigation. The LGL aims to be a permanent status of renewal, using new technologies for data recording and real time transmission, as well as for testing new sensors, scientific equipment and observational techniques related to monitoring and observation of volcanic activity. All these capabilities are necessary when high-resolution ground based observations must provide us the basis for studying the sources of volcanic deformation. The laboratory is thus open to support and to enhance the collaboration among scientists, as well as national and international institutions involved in research at active volcanic areas.

Arnoso, J.; Vlez, E. J.; Soler, V.; Montesinos, F. G.; Benavent, M.

2012-04-01

93

New age constraints for the geodynamic evolution of the Sistan Suture Zone, eastern Iran  

NASA Astrophysics Data System (ADS)

The Sistan Suture Zone (SSZ) in eastern Iran extends as a N-S trending belt over more than 700 km along the border area between Iran and Afghanistan. The SSZ formed as a result of eastward-directed subduction of a Neotethyan ocean basin beneath the Afghan block and includes a tectonic mlange consisting of disrupted meta-ophiolitic rocks within a low-grade matrix of ultramafic, mafic and pelitic schists. Some mlange blocks were affected by eclogite-, blueschist- and/or epidote amphibolite-facies P-T conditions. Understanding of the petrological and geochronological record of these rocks plays a key role in unravelling the geodynamic evolution of the SSZ. The main aim of the present study was to assess the geological significance of previously published 40Ar/39Ar ages (c. 116-139 Ma) which have not provided robust age constraints for geodynamic reconstructions on a regional scale. For this purpose, samples were collected within a NNW-SSE trending belt spanning a distance of c. 120 km that exposes the major occurrences of high-pressure/low temperature rocks and epidote amphibolites. Multi-point Rbsbnd Sr mineral isochrons indicate a regional consistent pattern with ages ranging between c. 83 and c. 87 Ma for eight samples representing different metamorphic grade and widely separated locations (weighted mean = 85.7 0.8 Ma). Additional 40Ar/39Ar dating for five of these samples yielded in most cases ages that are identical to the Rbsbnd Sr results within analytical uncertainty. For one sample the 40Ar/39Ar age of 81.3 1.3 Ma is about 3 myr younger than the corresponding Rbsbnd Sr age. A still younger Rbsbnd Sr age of 78.9 0.5 Ma was determined for a retrograde epidote-biotite assemblage in an overprinted domain of an eclogite. Ion probe Usbnd Pb zircon ages for two eclogites and two meta-acidic rocks from the mlange yielded weighted mean 206Pb/238U ages of 87.3 1.4 Ma, 86.1 1.5 Ma, 88.7 1.4 Ma and 87.2 1.2 Ma, respectively. The results of this study do not support previous interpretations suggesting > 125 Ma high-pressure/low-temperature metamorphism and amphibolite-facies overprinting, but instead document the importance of Late Cretaceous subduction zone processes for the geodynamic evolution of the SSZ.

Brcker, Michael; Fotoohi Rad, Gholamreza; Burgess, Ray; Theunissen, Stephanie; Paderin, Ilya; Rodionov, Nikolay; Salimi, Zohre

2013-06-01

94

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

95

Chemical geodynamics  

Microsoft Academic Search

Consideration is given to the following three principal boundary conditions relating to the nature and development of chemical structure in the earth's mantle: (1) inferred scale lengths for mantle chemical heterogeneities, (2) interrelationships of the various isotopic tracers, and (3) the bulk composition of the earth. These boundary conditions are integrated with geophysical constraints in order to evaluate models for

A. Zindler; S. R. Hart

1986-01-01

96

Geophysical Imprints of the Geodynamic Evolution of Moesia Following the Black Sea Opening  

NASA Astrophysics Data System (ADS)

Genesis of the two types of the Moesia basement (the so called Walachian, and Dobrogean sectors) along with the complex fault system affecting its cover and basement are still debated issues. Besides, there are two other intriguing aspects raised by the seismicity map of Romania: the sub-crustal events in the bending zone of East Carpathians, and the crust seismicity of the eastern Moesian Plate (MoP). Both the intermediate-depth earthquakes within full intra-continental environment and the intense craton seismicity are unusual aspects, and their apparent association difficult to explain. The paper proposes an integrated geodynamic model of MoP able to justify its current tectonics and both the crustal events in front of Carpathians, and the intermediate-depth earthquakes in the Vrancea zone within the frame of a unique geodynamic process. It starts from the idea that tectonic and geodynamic evolution of the E MoP and the bending zone of East Carpathians has been strongly affected by the opening of the W Black Sea basin, and is currently maintained by active rifting in SW Arabian Plate. The model is supported by geophysical and geodetic evidence. Unlike some previous geology-based models assuming that Black Sea opened during a singular geodynamic event (northward subduction of the Neo-Tethys Ocean floor), the pattern of the gravity and geomagnetic field, along with off-shore seismics bring convincing evidence on the distinct timing of the W and E Black Sea basins opening. Fingerprints of the lithosphere expelled by the W Black Sea rifting in the NW inland may be seen in the distribution of compression (P) wave velocity. In-depth development of NW striking major faults (splitting MoP into numerous vertical compartments) is also well revealed by seismic tomography (e.g. Peceneaga-Camena Fault, as the limit between MoP and East European Plate (EEP), still separates two distinct P wave velocity domains at 150 km depth). A second major fault system was created by the downward bending of MoP pushed towards vertical edge of Intra-Alpine Plate. It seems that W Black Sea opening also created the necessary environment for a FFT unstable triple junction within the bending zone of East Carpathians (VTJ), to which intermediate-depth earthquakes should be associated through thermo-baric accommodation phenomena occurring within the lithosphere sunken into the upper mantle. The triangle-shape and in-depth increase of the lateral extension of the VTJ high velocity seismic body are revealed by the high accuracy P wave tomography performed within Vrancea zone. Current geodetic and geophysical monitoring in the area has suggested a close link between crust and intermediate-depth seismic events. The intensification in tectonic forces may firstly led to the intensification of crust seismicity in the Carpathians foreland (by provoking slips between the MoP vertical compartments), followed, after a time-span depending on the force intensity and upper mantle viscosity, by VTJ sinking and consequent intermediate-depth seismic events in the Vrancea zone.

Besutiu, Lucian

2014-05-01

97

An attempt to monitor tectonic forces in the Vrancea active geodynamic zone: The Baspunar experiment  

NASA Astrophysics Data System (ADS)

An alternative model attempting to explain the unusual sub-crustal seismicity occurring in the bending zone of East Carpathians within full intra-continental environment (the so-called Vrancea zone) has assumed the presence of a FFT unstable triple junction between the three lithospheric compartments joining the area: East European Plate (EEP), Intra-Alpine Microplate (IaP) and the Moesian Microplate (MoP). Geophysical imprints (e.g. EM data, potential fields, seismic tomography), and indirect geological evidence (e.g. absence of the volcanism associated to subduction zones, the unusual high Neogene tectonic subsidence, symmetry and normal faulting within compressional environment of Focsani basin) support the hypothesis. The above-mentioned model considers the intermediate-depth seismicity as the result of the thermo-baric-accommodation phenomena generated within the colder lithosphere collapsed into the hotter upper mantle. Therefore, the amount of seismic energy thus released should be related to the volume of the lithosphere brought into thermo-baric disequilibrium by sinking into the upper mantle. Vertical dynamics of the Vrancea unstable triple junction (VTJ) seems to be controlled by the both tangential tectonic forces driving the neighbouring plates and the gravitational pull created by the eclogitization of VTJ lower crust. But, while eclogitization provides a relatively constant force, acceleration of sinking is expected to be provided by changes in the tectonic forces acting on VTJ. As changes in tectonic forces should reflect in changes of the dynamics of lithospheric compartments, geodetic means were considered for helping in their monitoring. The Peceneaga-Camena Fault (PCF) is a major lithospheric contact separating MoP and EEP, starting from the W Black Sea basin to the Vrancea zone. Geological evidence advocate for its variable geodynamic behaviour during the time, both as left-lateral or right-lateral fault. Unfortunately, GPS campaigns, so far (sparsely) run in the area, have provided inconsistent results on the PCF current dynamics. The Baspunar Geodynamic Observatory (BGO) has been designed and implemented by the Solid Earth Dynamics Department in the Institute of Geodynamics of the Romanian Academy in order to reveal and monitor eventual motions along PCF in the attempt to correlate variations in the slip rate with changes in the seismicity released within Vrancea zone. The first BGO records were strongly affected by changes in the atmospheric parameters. Consequently, technical measures and special corrections for the removal or at least mitigation of the effects created by changes in temperature, air pressure and humidity have been applied to the observations. In order to improve the signal to noise ratio, some mathematical filters have been applied too. The paper is aimed at revealing results of the geodetic observations along with preliminary geodynamic considerations. On the overall, after about two years of monitoring, PCF appears as an active tectonic contact. It mainly behaves as a left-lateral fault, but some short episodes with a reverse slip (dextral) were also pointed out. Correlations with crustal and intermediate-depth earthquakes occurring in both cases within the bending zone of East Carpathians are illustrated and discussed.

Besutiu, Lucian; Zlagnean, Luminita; Plopeanu, Marin

2013-04-01

98

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

99

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 Jlich high-performance computing center.

Popov, Anton; Kaus, Boris

2014-05-01

100

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

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

101

Spatial and temporal patterns of exhumation across the Venezuelan Andes: Implications for Cenozoic Caribbean geodynamics  

NASA Astrophysics Data System (ADS)

The Venezuelan Andes formed by complex geodynamic interaction between the Caribbean Plate, the Panam Arc, the South American Plate and the continental Maracaibo block. We study the spatial and temporal patterns of exhumation across the Venezuelan Andes using 47 new apatite fission track (AFT) ages as well as topographic analyses. This approach permits the identification of at least seven tectonic blocks (Escalante, Cerro Azul, Trujillo, Caparo, Sierra Nevada, Sierra La Culata and El Carmen blocks) with contrasting exhumation and cooling histories. The Sierra Nevada, Sierra La Culata and El Carmen blocks, located in the central part of the Venezuelan Andes and separated by the Bocon fault system, cooled rapidly but diachronously during the late Miocene-Pliocene. Major surface uplift and exhumation occurred in the Sierra Nevada block since before 8 Ma. A second phase of uplift and exhumation affected the El Carmen and Sierra La Culata blocks to the north of the Bocon fault during the late Miocene-Pliocene. The highest topography and steepest relief of the belt coincides with these blocks. The Caparo and Trujillo blocks, located at the northeastern and southwestern ends of the orogen, cooled more slowly from the Oligocene to the late Miocene. These blocks are characterized by significantly lower mean elevations and slightly lower mean slopes than the central blocks. Unraveling the cooling history of the individual blocks is important to better understand the control of preexisting faults and regional Caribbean geodynamics on the evolution of the Venezuelan Andes. Our data indicate a strong control of major preexisting fault zones on exhumation patterns and temporal correlation between phases of rapid exhumation in different blocks with major tectonic events (e.g., collision of the Panam arc; rotation of the Maracaibo block).

Bermdez, Mauricio A.; Kohn, Barry P.; van der Beek, Peter A.; Bernet, Matthias; O'Sullivan, Paul B.; Shagam, Reginald

2010-10-01

102

Geodynamics of the Dead Sea Fault: Do active faulting and past earthquakes determine the seismic gaps?  

NASA Astrophysics Data System (ADS)

The ~1000-km-long North-South trending Dead Sea transform fault (DSF) presents structural discontinuities and includes segments that experienced large earthquakes (Mw>7) in historical times. The Wadi Araba and Jordan Valley, the Lebanese restraining bend, the Missyaf and Ghab fault segments in Syria and the Ziyaret Fault segment in Turkey display geometrical complexities made of step overs, restraining and releasing bends that may constitute major obstacles to earthquake rupture propagation. Using active tectonics, GPS measurements and paleoseismology we investigate the kinematics and long-term/short term slip rates along the DSF. Tectonic geomorphology with paleoseismic trenching and archeoseismic investigations indicate repeated faulting events and left-lateral slip rate ranging from 4 mm/yr in the southern fault section to 6 mm/yr in the northern fault section. Except for the northernmost DSF section, these estimates of fault slip rate are consistent with GPS measurements that show 4 to 5 mm/yr deformation rate across the plate boundary. However, recent GPS results showing ~2.5 mm/yr velocity rate of the northern DSF appears to be quite different than the ~6 mm/yr paleoseismic slip rate. The kinematic modeling that combines GPS and seismotectonic results implies a complex geodynamic pattern where the DSF transforms the Cyprus arc subduction zone into transpressive tectonics on the East Anatolian fault. The timing of past earthquake ruptures shows the occurrence of seismic sequences and a southward migration of large earthquakes, with the existence of major seismic gaps along strike. In this paper, we discuss the role of the DSF in the regional geodynamics and its implication on the identification of seismic gaps.

Meghraoui, Mustapha

2014-05-01

103

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

104

The seismic cycle at subduction thrusts: 2. Dynamic implications of geodynamic simulations validated 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 validate a continuum, visco-elasto-plastic numerical model with a new laboratory approach (Paper 1). The analogous laboratory setup includes a visco-elastic gelatin wedge underthrusted by a rigid plate with defined velocity-weakening and -strengthening regions. Our geodynamic simulation 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 the rupture. Spontaneous evolution of absolute stresses leads to nucleation by coalescence of neighboring patches, mainly occurring at evolving asperities near the seismogenic zone limits. 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, until it arrests on a barrier. 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. This slip increases adjacent stresses, which are relaxed postseismically by afterslip and thereby produce persistent seaward motions. The wide range of observed physical phenomena, including back-propagation and repeated slip, and the agreement with laboratory results demonstrate that visco-elasto-plastic geodynamic models with rate-dependent friction form a new tool that can greatly contribute to our understanding of the seismic cycle at subduction zones.

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

2013-04-01

105

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

106

A geodynamic and mineral physics model of a solid-state ultralow-velocity zone Dan J. Bower a,b,  

E-print Network

A geodynamic and mineral physics model of a solid-state ultralow-velocity zone Dan J. Bower a seismic tradeoff between ULVZ thickness and wavespeed reduction. Seismic data are compatible with a solid-state

Jackson, Jennifer M.

107

Age, origin and geodynamic significance of plagiogranites in lherzolites and gabbros of the Piedmont-Ligurian ocean basin  

Microsoft Academic Search

U-Pb zircon dating, Sr-Nd isotope tracing and major\\/trace\\/RE element analyses were performed to constrain the age, origin and geodynamic significance of plagiogranites that intrude lherzolites and gabbros in the Ligurian Alps and the Northern Apennines. In addition, a host Fe-diorite was investigated. Samples from the Ligurian Alps were collected from the Voltri Group and the Sestri-Voltaggio Zone, whereas the plagiogranites

Laura Borsi; Urs Schrer; Laura Gaggero; Laura Crispini

1996-01-01

108

Ground deformation and gravity changes on the island of Pantelleria in the geodynamic framework of the Sicily Channel  

NASA Astrophysics Data System (ADS)

The island of Pantelleria is an active volcano located in the Sicily Channel (Southern Italy), in the middle of a continental rift system. Since the 1980s the island was periodically surveyed by using geodetic techniques (EDM, levelling, GPS and high precise gravimetry) to monitor the regional and local volcanic dynamics. Gravity data, collected between 1990 and 1998, show short and long wavelength changes due to the combined effect of shallow and deep sources. They reflect, to some degree, the structural setting of the island as delineated by the Bouguer anomaly field, which indicates that the island is broken up into two main basement blocks. The latter are bordered by two lineaments, probably regional faults related to the global geodynamics of the Sicily Channel Rift Zone. Moreover, the inverse correlation between the gravity and altimetric variations suggests that: i) Pantelleria is kinematically divided in two blocks; ii) the observed behaviour is strongly influenced by the geodynamics of the Sicily Channel. A new interpretation of the fully reprocessed data sets is presented, focusing on the spatial-temporal features of the horizontal ground deformation and gravity changes compared to the Bouguer anomaly and altimetric data. This leads to conclude that volcanism on the island has been probably strongly influenced by the global geodynamics of the Sicily Channel, and future eruptions are most likely to occur at the structural boundary separating the two blocks.

Behncke, Boris; Berrino, Giovanna; Corrado, Gennaro; Velardita, Rosanna

2006-02-01

109

Using Interactive Visualization to Analyze Solid Earth Data and Geodynamics Models  

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

110

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

111

Structural Geology of Graciosa Island - a contribution for the geodynamics of the Azores triple junction  

NASA Astrophysics Data System (ADS)

The Azores geodynamic setting, its geological, geochemical and geophysical characteristics, and the frequent seismic and volcanic activity, motivated the development of multidisciplinary studies aiming at the creation of a coherent model explaining the geodynamic and kinematic particularities that characterize the Azores triple junction - the contact between the North American, Eurasian and Nubian lithospheric plates. The tectonic regime determination at any given region, through the identification and characterisation of active faults, is a major contribution to the development of geodynamic models. In this domain the geometric and kinematic characterisation of Graciosa Island active faults was performed and a structural map was produced. The stress fields responsible for the development of the identified tectonic structures were also deduced. Two main fault systems were identified at Graciosa. One system (A) is composed of two sets of conjugated faults, one trending NW-SE and dipping to SW, presenting normal-dextral or dextral-normal oblique slip, and another striking NNE-SSW and dipping to ESE, with oblique normal-left lateral or left lateral-normal slip. The second fault system (B) includes NNE-SSW to NE-SW trending faults, dipping to WNW or NW, presenting normal-dextral or dextral-normal oblique slip. A family of conjugated faults with these structures was not found. The structural data indicate two distinct stress fields acting in Graciosa region that could be separated in time and/or in space. A stress field I, responsible for the occurrence of fault system A, with ?1 (maximum horizontal compressive stress axis) NNW-SSE to N-S, ?3 (maximum horizontal tensile stress axis) trending ENE-WSW to E-W, and an intermediate vertical compressive stress axis (?2); permutations between ?1 and ?2 may occur according to the alternation between transtensile and tensile tectonic regimes. A second stress field, II, is characterised by horizontal ?1, trending E-W to WSW-ENE, horizontal ?3, trending NNW-SSE to N-S, and vertical ?2. Permutation may also occur between ?2 and ?1 after events of stress drop during transtensile phases. Fault system B is associated to stress field II. The kinematic solutions shown in recent geodetic works and the stress fields determined from neotectonic analysis seem to point out to the presence of two distinct stress fields on the islands located near the margins of the shear zone where the Azorean islands of the central and eastern groups stand. Stress field I agrees with the local stress regime proposed by several authors for the shear zone that constitutes the western segment of the Eurasia - Nubia plate boundary. To explain the existence of stress field II, two hypothesis are proposed: (1) an intermediate region, with a transtensile regime, making the transition between the area subjected to the Mid-Atlantic Ridge tensile stress field and the more distal region with a compressive stress field; or (2) an intermediate region (established when the interplate shear stress is weaker), with a transtensile regime, defining a narrow band between the region of dextral transtension (resulting from the differential motion between the Eurasian and the Nubian plates) and the external compressive stress field established as the sea-floor moves away from the Ridge. Narrowing or widening of the area under influence of local stress field (I) may justify that the margins of the sheared region will become temporarily under the influence of the external stress field (II).

Hiplito, Ana; Madeira, Jos; Gaspar, Joo.; Carmo, Rita

2010-05-01

112

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

113

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

NASA Astrophysics Data System (ADS)

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

Hawie, N.

2013-12-01

114

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

115

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

116

Geodynamically Consistent Interpretation of Seismic Tomography for Thermal and Thermochemical Mantle Plumes  

NASA Astrophysics Data System (ADS)

Recent theoretical developments as well as increased data quality and coverage have allowed seismic tomographic imaging to better resolve narrower structures at both shallow and deep mantle depths. However, despite these improvements, the interpretation of tomographic images remains problematic mainly because of: (1) the trade off between temperature and composition and their different influence on mantle flow; (2) the difficulty in determining the extent and continuity of structures revealed by seismic tomography. We present two geodynamic studies on mantle plumes which illustrate the need to consider both geodynamic and mineral physics for a consistent interpretation of tomographic images in terms of temperature composition and flow. The first study aims to investigate the coupled effect of pressure and composition on thermochemical plumes. Using both high resolution 2D numerical modeling and simple analytical theory we show that the coupled effect of composition and pressure have a first order impact on the dynamics of mantle thermochemical plumes in the lower mantle: (1) For low Si enrichment of the plume relative to a reference pyrolitic mantle, an oscillatory behavior of the plume head is observed; (2) For Si-enriched plume compositions, the chemical density excess of the plume increases with height, leading to stagnation of large plume heads at various depths in the lower mantle. As a consequence, these thermochemical plumes may display broad (~ 1200 km wide and more) negative seismic velocity anomalies at various lower mantle depths, which may not necessarily be associated with upwelling currents. The second study focuses on the identification of thermal mantle plumes by seismic tomography beneath the Hawaiian hot spot: we performed a set of 3D numerical experiments in a spherical shell to model a rising plume beneath a moving plate. The thermal structure obtained is converted into P and S wave seismic velocities using mineral physics considerations. We then build synthetic travel time data by propagating front waves in the obtained seismic structure. This synthetic data will be used to construct a travel time tomographic model which is compared with actual tomographic models based on data from the PLUME seismic experiment. This comparison will allow a more consistent and quantitative interpretation of seismic tomography and plume structure under Hawaii.

Samuel, H.; Bercovici, D.

2006-05-01

117

Geodetic GNSS measurements as a basis for geodynamic and glaciological research in Antarctica  

NASA Astrophysics Data System (ADS)

For about twenty years our institute has been carrying out geodetic GNSS measurements and has been actively working in international collaboration for Antarctic research. Episodic GPS (and later GNSS) measurements of all contributing nations enter the "Database of the SCAR Epoch Crustal Movement Campaigns" which is being maintained at the institute in the framework of SCAR-GIANT. GNSS measurements form a basis for the realization of the International Terrestrial Reference Frame (ITRF) and its densification in Antarctica. Linked to respective products of an ongoing activity to re-process GNSS data of globally distributed stations a consistent and precise TRF realization can be reached. We will give an overview on the latest developments and the subsequent applications for geodynamic and glaciological investigations in Antarctica. Complementary to continuous GNSS observations episodic GNSS measurements have the potential to provide independent data on vertical deformations, which can be used to investigate the present-day ice-mass balance and to refine models of the glacial-isostatic adjustment. Repeated and properly referenced GNSS measurements at the ice surface yield ice-flow velocities and local ice-surface height changes. We will present latest results, e.g. for the Amundsen Sea sector, the subglacial Lake Vostok region and near-coastal regions of Dronning Maud Land or Enderby Land. Thus, it will be discussed how geodetic GNSS measurements form an important and indispensable basis for geodetic Earth system research with the focus on Antarctica.

Scheinert, Mirko; Dietrich, Reinhard; Knfel, Christoph; Fritsche, Mathias; Rlke, Axel; Schrder, Ludwig; Richter, Andreas; Eberlein, Lutz

2013-04-01

118

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

119

Geodynamic setting of mesothermal gold deposits: An association with accretionary tectonic regimes  

NASA Astrophysics Data System (ADS)

Mesothermal gold provinces of Phanerozoic age are characteristically associated with regional structures along which allochthonous terranes have been accreted onto continental margins or arcs. A recurring sequence of transpressive deformation, uplift, late kinematic mineralization, and shoshonitic magmatism is consistent with thermal reequilibration of tectonically thickened crust. Mesothermal gold camps in the Superior province are spatially associated with large-scale structures that have been interpreted as zones of transpressive accretion of individual subprovinces or allochthonous terranes: these boundary structures are characterized by the sequence of significant horizontal shortening, uplift, late-kinematic mineralization, and shoshonitic lamprophyres and therefore may have the same geodynamic significance as Phanerozoic counterparts. In this model, thermal re-equilibration of underplated and subducted oceanic lithosphere and sediments in a transpressive regime, over time scales of 10 to 40 m.y., is a necessary precursor to gold mineralization. Hydrothermal fluids are released along boundary faults and their splays during uplift: the uniform temperature, low salinity and mole% CO2 signify uniform source conditions, whereas the variable O, C, Sr, and Pb isotopic compositions of fluids reflect lithological complexity of the source regions and conduits. Ou the basis of this model it is suggested that mesothermal lode gold deposits are the product of subduction-related crustal underplating and deep, late metamorphism, rather than magmatic or metamorphic events in the supracrustal rocks. Secular variations in the generation of Archean, Proterozoic, and Phanerozoic mesothermal Au provinces reflect the timing of collisional orogenies within terranes of these eras.

Kerrich, Robert; Wyman, Derek

1990-09-01

120

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

121

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

NASA Astrophysics Data System (ADS)

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

Batalev, V. Yu.

2013-02-01

122

A new borehole wire extensometer with high accuracy and stability for observation of local geodynamic processes  

NASA Astrophysics Data System (ADS)

Very stable and reliable instruments with high accuracy are required in field measurements for continuous monitoring local geodynamic processes, such as tectonic movements, ground motions in landslide prone areas, etc. A sensitive borehole wire extensometer with low energy consumption was developed in the Geodetic and Geophysical Research Institute of the Hungarian Academy of Sciences to observe very small vertical movements (in the order of a few millimeters) of the upper layer of the soil due to hydrological, meteorological and biological processes. The newly developed instrument eliminates the disadvantages of the borehole wire extensometers which are presently used. Its sensitivity and stability are much higher than these parameters of the previous instruments. The instrument is able to measure distance variations without instrumental drift in a range of 0-4 mm with a resolution of better than 1 ?m. Since the effect of the yearly temperature variations can be easily removed from the extensometric data record, the compensation for the short-periodic (daily) thermal effects on the instrument was of high priority during the design of the instrument. This paper describes the construction and calibration of the extensometer. The extensometer was installed for monitoring vertical ground movements due to hydro-meteorological processes on the high loess wall of the Danube River at Dunafldvr, Hungary. The efficiency of the temperature compensation of the instrument was investigated in detail on the basis of the measured data series.

Mentes, Gy.

2012-01-01

123

Development of the Cte Ivoire Basin: reading provenance, sediment dispersal, and geodynamic implications from heavy minerals  

NASA Astrophysics Data System (ADS)

The combined approach of conventional and varietal heavy mineral analysis was applied to constrain changes in source rock area, dispersal routes of detritus, and geodynamic setting of the Upper Cretaceous to Neogene Cte d'Ivoire basin. The heavy mineral assemblage of Albian to Turonian sediments reflect a narrow source rock area and short transport distances. A prominent change in the heavy mineral association of Late Cenomanian to Neogene sediments indicates enlargement of source area and longer fluvial transport distances, or longer storage of sediment within the littoral energy fence. The sudden change within the heavy mineral associations marks the transition from the late syn-rift stage to the early passive margin stage of the Southern Atlantic. During Albian to Late Cenomanian time, the basin geometry was mainly controlled by steep slopes and sediments were transported directly to the depocenter. The situation changed in Late Cenomanian time. A small shelf area developed where sediments from different sources were mixed and reworked before deposition. We believe that the W-E direction of the long-shore drift, which transports today huge quantities of near-shore sand, was established at the end of the Paleogene. This resulted from the drifting of southern West Africa across the paleoequator and subsequent change in surface wind directions.

Wozazek, Stefan; Krawinkel, Hannelore

2002-05-01

124

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

125

Detection of metastable olivine wedge in the western Pacific slab and its geodynamic implications  

NASA Astrophysics Data System (ADS)

Seismic tomography and numerical simulations show that the western Pacific slab bends horizontally when it reaches the boundary between the upper mantle and lower mantle beneath northeast Asia. It is expected that a metastable olivine wedge (MOW) exists in the cold core of the slab because of a delayed phase transition from olivine to its high-pressure polymorphs. However, it is still debated whether the MOW actually exists or not, and even if it exists, its physical properties, such as seismic velocity and density, are still unclear. In this work we use high-quality arrival-time data of 17 deep earthquakes occurring within the Pacific slab under northeast Asia to study the detailed structure of the slab. The deep earthquakes are relocated precisely by applying a modified double-difference location method to arrival-time data recorded at both Chinese and Japanese stations. Based on the precise hypocentral locations, a forward modeling method and differential travel-time residuals data are used to estimate seismic velocity within the deep source zone, which can decrease or remove the influence of ambient velocity heterogeneities. Our results show that the MOW does exist within the Pacific slab under northeast Asia, and the MOW has a mean velocity anomaly of 7-9% lower than the iasp91 Earth model. The existence of MOW in the slab has important geodynamic implications. It can reduce the speed of slab subduction and affect the generation of deep earthquakes.

Jiang, Guoming; Zhao, Dapeng; Zhang, Guibin

2015-01-01

126

Large-scale changes of the atmosphere (climate), geodynamics and biosphere due to the galactic shocks  

NASA Astrophysics Data System (ADS)

The Solar system periodically passes through spiral arms of the Galaxy, which are stellar density waves. Processes due to the presence of galactic shocks (shock waves) may be responsible for the abrupt atmosphere changes (climate), geodynamics (supercontinental cycle, large tectonic processes, mantle convection, geomagnetic field and others) and biosphere. Galactic shocks (GS) are the narrow region of high gas compression along the inner edge of spiral wave. Shock wave leads to the interstellar dust compression and to the phase transition in the interstellar gas. GS are large-scale trigger mechanism of active star formation. GS ultimately changes temperature, pressure and the radiation balance. It is quite surprisingly that majority of the "data points" of the geochronological and stratigraphic scales are closely related to the time moments when the Solar system has passed through the galactic shocks. This extraterrestrial cause for the change of physical and chemical conditions on the Earth had profound effects on the biologic extinction and explosions. This hypothesis explains the biologic explosion in Cambrian, the Permian - Triassic and Cretaceous-Tertiary extinctions, i.e., the beginning of Paleozoic, Mesozoic and Cenozoic. It is valid in the frame of galactic shock model that any discussion time estimates of these past events and their implications for the future must be quantitative. It will permit an evaluation of age of greater catastrophes and changes in the Earth history, of the future meets with the spiral arms of the Galaxy. It predicts the existence of chronological scales of other planets.

Khristoforova, D.

2009-04-01

127

Tectonics and geodynamics of granulite-gneiss complexes in the East European Craton  

NASA Astrophysics Data System (ADS)

The Neoarchean and Paleoproterozoic granulite-gneiss complexes of the northern East European Craton, including their tectonic setting, accompanying igneous and sedimentary rocks, character of metamorphism and deep structure are considered in this paper. A similar approach was applied to the description and interpretation of the granulite-gneiss complexes of the Grenville-Sveconorwegian Orogen localized in the present-day structure of the European and North American continents. One of the most important results of this study is the recognition of a new type of tectonic structures called intracontinental oval orogens. These orogens were formed in the inner domain of the Neoarchean-Proterozoic supercontinent (2.8-0.85 Ga), which is called Lauroscandia. The extensional setting, which was initiated by a series of mantle plumes, locally passing to spreading but did not lead to the eventual breakup of the supercontinent and was followed by intracontinental collisional compression accompanied by closure of short-lived local oceans, subduction, and obduction. The Neoarchean and Proterozoic granulite-gneiss belts and areas of the East European Craton are components of the Karelian-Belomorian, Kola, Volgo-Uralia, Lauro-Russian, and Grenville-Sveconorwegian intracontinental oval orogens formed in the inner domain of Lauroscandia as a result of mantle-plume and plate-tectonic processes initiated by mantle superplumes. The geodynamic settings and tectonic processes in the Neoarchean-Proterozoic supercontinent differed markedly from both the Archean tectonics of miniplates and the Phanerozoic plate tectonics.

Mints, M. V.

2014-11-01

128

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

NASA Astrophysics Data System (ADS)

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

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

2003-04-01

129

A new borehole wire extensometer with high accuracy and stability for observation of local geodynamic processes.  

PubMed

Very stable and reliable instruments with high accuracy are required in field measurements for continuous monitoring local geodynamic processes, such as tectonic movements, ground motions in landslide prone areas, etc. A sensitive borehole wire extensometer with low energy consumption was developed in the Geodetic and Geophysical Research Institute of the Hungarian Academy of Sciences to observe very small vertical movements (in the order of a few millimeters) of the upper layer of the soil due to hydrological, meteorological and biological processes. The newly developed instrument eliminates the disadvantages of the borehole wire extensometers which are presently used. Its sensitivity and stability are much higher than these parameters of the previous instruments. The instrument is able to measure distance variations without instrumental drift in a range of 0-4 mm with a resolution of better than 1 ?m. Since the effect of the yearly temperature variations can be easily removed from the extensometric data record, the compensation for the short-periodic (daily) thermal effects on the instrument was of high priority during the design of the instrument. This paper describes the construction and calibration of the extensometer. The extensometer was installed for monitoring vertical ground movements due to hydro-meteorological processes on the high loess wall of the Danube River at Dunafo?ldva?r, Hungary. The efficiency of the temperature compensation of the instrument was investigated in detail on the basis of the measured data series. PMID:22299988

Mentes, Gy

2012-01-01

130

Some remarks on the structure and geodynamics of the Kenya Rift  

NASA Astrophysics Data System (ADS)

Since 1985 the KRISP working group has recorded a number of seismic profiles and carried out array experiments in the Kenya Rift valley. Long range profiling has shown that across the Rift at latitude 0.5, the crust thins from 40 km beneath the western flank to 30 km beneath the graben proper, and thickens again to 35 km beneath the eastern flank. The crustal thickness beneath the graben decreases northwards from 35 km beneath the culmination of the Kenya dome to 20 km under Lake Turkana, suggesting a change to a highly extended terrain in the northern Kenya Rift. Furthermore, the anomalous low mantle velocities of 7.5-7.6 km/s suggest that the upper mantle immediately beneath the Rift may contain reservoirs of magmas, which were generated at greater depth. The anomalous mantle under the graben proper, as seen by the tomographic imaging, is characterized by a large, steep walled low velocity zone with a velocity decrease of at least 10% in the central part between 65 and 100 km depth which reaches down to more than 150 km. A comparison of the shape and size of the observed Bouguer anomaly with the LVZ suggests that the upper mantle beneath the Rift probably includes some 5% partial melt, concentrated in the areas with lowest velocities. These results provide new constraints for geodynamic models of the evolution of the Kenya Rift.

Achauer, U.; Maguire, P. K. H.; Mechie, J.; Green, W. V.; Krisp Working Group

1992-10-01

131

Geodynamic Inferences from Integrated Ocean Drilling Program Expedition 330 to the Louisville Seamount Trail  

NASA Astrophysics Data System (ADS)

Integrated Ocean Drilling Program (IODP) Expedition 330 drilled five different guyots in the Louisville Seamount Trail ranging in age between 80 and 50 Ma. The primary goals of this expedition were to drill a sufficiently large number of in situ lava flows at each seamount for high-quality estimates of their paleolatitudes using paleomagnetic measurements, for improving the overall age progression using high-precision 40Ar/39Ar geochronology, and for detailed geochemical studies of the volcanic evolution of these seamounts. With these data we can provide the unique record of the paleolatitude shift (or lack thereof) of the Louisville mantle plume and compare it with the ~15 paleolatitude shift observed for seamounts in the Hawaiian-Emperor Seamount Trail over the same time period. These comparisons are of fundamental importance to determine whether these two primary hotspots have moved coherently or not, to understand the nature of hotspots and convection in the Earth's mantle, and to evaluate the possibility of true polar wander. We will present new 40Ar/39Ar age data for Sites U1372, U1373, U1374 and U1376 in conjunction with Expedition 330 shipboard paleomagnetic inclination data to discuss the geodynamic inferences from the resulting paleolatitude history of the Louisville hotspot between 80 and 65 Ma.

Koppers, A. A.; Yamazaki, T.; Geldmacher, J.; Scientific Party, E. 3; IODP Expedition 330 Scientific Party

2011-12-01

132

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, Gayan; Zambetakis-Lekkas, Alexandra; Galoyan, Ghazar; Sosson, Marc; Seyler, Monique; Sahakyan, Lilit; Grigoryan, Araiyk

2014-05-01

133

Gravity Changes and kinematic behaviour of the Island of Pantelleria in the Geodynamic Framework of the Sicily Channel (Southern Italy)  

NASA Astrophysics Data System (ADS)

The island of Pantelleria is an active volcano located in the Sicily Channel (Southern Italy), in the middle of a continental rift system. Since the 1980s the island is periodically surveyed by means of geodetic techniques (levelling, EDM, GPS and high precise gravimetry) to monitor the local and regional volcanic dynamics. The analysis of the gravity data, collected during several field surveys from 1990 to 1998, have shown that the gravity field changes generally appear resulting by the superposition of short and long wavelengths, due to the combined effect of shallow and deep sources. Gravity changes fields also reflect, to some degree, the structural setting of the island as sketched by the Bouguer anomaly field which indicates that the island is constituted by a basement dislocated in two main blocks. These latter are also bordered by two lineaments, probably regional faults related to the global geodynamics of the Sicily Channel Rift Zone. Moreover, there is an inverse correlation between the gravity and height variations and their joined analysis implies that: i) Pantelleria appears to be divided in two blocks also from the kinematic behaviour; ii) the observed phenomena may be also ascribed to the influence of the geodynamics of the Sicily Channel. Moreover, a combined analysis of the time-space features of the horizontal ground deformation and gravity changes has been done to check if the characteristics previously detected are present in all the aspects of the kinematic behaviour of the island. On the basis of the previous conclusions the EDM data have been reprocessed for a proper comparison with the gravity data, the Bouguer anomaly and the altimetric data. This allows a joint interpretation taking also into account the structural setting and the geodynamics of the Sicily Channel to evaluate its influence on the local volcanic dynamics of the island.

Berrino, G.; Velardita, R.; Behncke, B.; Corrado, G.

2004-12-01

134

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

135

New data on the Vrancea Nappe (Moldavidian Basin, Outer Carpathian Domain, Romania): paleogeographic and geodynamic reconstructions  

NASA Astrophysics Data System (ADS)

A study has been performed on the Cretaceous to Early Miocene succession of the Vrancea Nappe (Outer Carpathians, Romania), based on field reconstruction of the stratigraphic record, mineralogical-petrographic and geochemical analyses. Extra-basinal clastic supply and intra-basinal autochthonous deposits have been differentiated, appearing laterally inter-fingered and/or interbedded. The main clastic petrofacies consist of calcarenites, sub-litharenites, quartzarenites, sub-arkoses, and polygenic conglomerates derived from extra-basinal margins. An alternate internal and external provenance of the different supplies is the result of the paleogeographic re-organization of the basin/margins system due to tectonic activation and exhumation of rising areas. The intra-basinal deposits consist of black shales and siliceous sediments (silexites and cherty beds), evidencing major environmental changes in the Moldavidian Basin. Organic-matter-rich black shales were deposited during anoxic episodes related to sediment starvation and high nutrient influx due to paleogeographic isolation of the basin caused by plate drifting. The black shales display relatively high contents in sub-mature to mature, Type II lipidic organic matter (good oil and gas-prone source rocks) constituting a potentially active petroleum system. The intra-basinal siliceous sediments are related to oxic pelagic or hemipelagic environments under tectonic quiescence conditions although its increase in the Oligocene part of the succession can be correlated with volcanic supplies. The integration of all the data in the "progressive reorientation of convergence direction" Carpathian model, and their consideration in the framework of a foreland basin, led to propose some constrains on the paleogeographic-geodynamic evolutionary model of the Moldavidian Basin from the Late Cretaceous to the Burdigalian.

Amadori, Maria Letizia; Belayouni, Habib; Guerrera, Francesco; Martn-Martn, Manuel; Martin-Rojas, Ivn; Micl?u?, Crina; Raffaelli, Giuliana

2012-09-01

136

New age, isotopic composition, and geodynamic constraints on the Neoarchean Fiskenaesset anorthosite complex, SW Greenland  

NASA Astrophysics Data System (ADS)

The Neoarchean Fiskenaesset Complex, SW Greenland, is characterized by about 550 meter thick layered anorthosites, leucogabbros, gabbros, and ultramafic rocks. The complex is spatially associated with basaltic amphibolites displaying a tholeiitic composition. The major and trace element compositions of tholeiitic basalts suggest that they are petrogenetically related to the Fiskensset Complex by fractional crystallization. The complex appears to have been emplaced as multiple sills of magma and crystal mush into oceanic crust (tholeiitic basalts and gabbros). Anorthosites, gabbros, leucogabbros and ultramafic rocks (45 samples) yield a Sm-Nd isochron age of 2972 28 Ma, constraining the maximum age of the complex. All rock types in the complex are characterized by large positive initial epsilon-Nd values (+2.9 to +5.4), consistent with a long term depleted mantle source. The Fiskenaesset rocks yield a Pb-Pb isochron age of 2945 36 Ma. The Pb isochron intercepts the average depleted mantle growth curve at 3036 Ma, suggesting a Mesoarchean depleted mantle source. The trace element systematics of the least-altered anorthosites, gabbros, leucogabbros, ultramafic rocks, and tholeiitic basalts is collectively consistent with a supra-subduction zone geodynamic setting. On the log-transformed tectonic discrimination diagram, including La/Th, Sm/Th, Yb/Th, and Nb/Th ratios, tholeiitic basalts display a trend projecting from mid-ocean ridge basalt (MORB) to island arc basalt (IAB) field. This trend is interpreted as reflecting a transition from the depleted Neoarchean upper mantle to a subarc mantle wedge following the initiation of intra-oceanic subduction and arc migration. Collectively, on the basis of field relationships and geochemical characteristics, we interpret the Fiskensset Complex as a fragment of a Neoarchean oceanic island arc.

Polat, A.; Frei, R.

2009-12-01

137

AlpArray - an initiative to advance understanding of Alpine geodynamics  

NASA Astrophysics Data System (ADS)

AlpArray is a new initiative to study the greater Alpine area with a large-scale broadband seismological network. The interested parties (currently 32 institutes in 12 countries) plan to combine their existing infrastructures into an all-out transnational effort that includes data acquisition, processing, imaging and interpretation. The experiment will encompass the greater Alpine area from the Black Forest in the north to the Northern Apennines in the south and from the Pannonian Basin in the east to the French Massif Central in the west. We aim to cover this region with high-quality broadband seismometers by combining the ~400 existing permanent stations with an additional 400+ instruments from mobile pools. In this way, we plan to achieve homogeneous and high resolution coverage while also deploying densely spaced stations along swaths across key parts of the Alpine chain. These efforts on land will be combined with deployments of ocean bottom seismometers in the Mediterranean Sea. We also aim to implement the best practice for synchronizing mobile pool operation procedures and data handling. The main scientific goal of AlpArray is to investigate the structure and evolution of the lithosphere beneath the Alps, especially where the polarity of subduction is known to change, along with numerous regional questions. These targets will be imaged at several depths (e.g., near-surface structure to upper mantle anisotropy), scales (e.g., local seismicity to mantle transition zone thickness variations), using different methodologies in the sub-regions of interest. An overview of these in connection with the seismological measurements will be presented at the conference. The geodynamic interpretation of the acquired data will be complemented by other Earth Science subdisciplines such as numerical and analogue modelling, gravity and magneto-telluric measurements, as well as structural geology. In conclusion, we hope to turn the strong community interest into a truly interdisciplinary and collaborative project.

Hetnyi, G.; AlpArray Working Group

2012-04-01

138

Project MANTIS: A MANTle Induction Simulator for coupling geodynamic and electromagnetic modeling  

NASA Astrophysics Data System (ADS)

A key component to testing geodynamic hypotheses resulting from the 3D mantle convection simulations is the ability to easily translate the predicted physiochemical state to the model space relevant for an independent geophysical observation, such as earth's seismic, geodetic or electromagnetic response. In this contribution a new parallel code for simulating low-frequency, global-scale electromagnetic induction phenomena is introduced that has the same Earth discretization as the popular CitcomS mantle convection code. Hence, projection of the CitcomS model into the model space of electrical conductivity is greatly simplified, and focuses solely on the node-to-node, physics-based relationship between these Earth parameters without the need for "upscaling", "downscaling", averaging or harmonizing with some other model basis such as spherical harmonics. Preliminary performance tests of the MANTIS code on shared and distributed memory parallel compute platforms shows favorable scaling (>70% efficiency) for up to 500 processors. As with CitcomS, an OpenDX visualization widget (VISMAN) is also provided for 3D rendering and interactive interrogation of model results. Details of the MANTIS code will be briefly discussed here, focusing on compatibility with CitcomS modeling, as will be preliminary results in which the electromagnetic response of a CitcomS model is evaluated. VISMAN rendering of electrical tomography-derived electrical conductivity model overlain by an a 1x1 deg crustal conductivity map. Grey scale represents the log_10 magnitude of conductivity [S/m]. Arrows are horiztonal components of a hypothetical magnetospheric source field used to electromagnetically excite the conductivity model.

Weiss, C. J.

2009-12-01

139

The Tertiary dike magmatism in the Southern Alps: geochronological data and geodynamic significance  

NASA Astrophysics Data System (ADS)

The relationships between tectonics and magmatic activity in the Alps are still debated. Despite an active subduction since the Late Cretaceous, no arc-related magmatism is recorded prior of the Middle Eocene. The emplacement of plutons along the Insubric Fault in a short time span (~34-28 Ma) has been generally interpreted in terms of the slab break-off model. The Tertiary magmatism, however, is also characterized by the occurrence of widespread calcalkaline dikes not necessarily intruded along the Insubric Fault. The geochemical features of dikes vary along the Alps belt and are interpreted in terms of mantle source heterogeneity and degree of crustal contamination. U-Pb zircon dating of studied dikes indicates intrusion ages in the 42- to 34-Ma time interval. These data provide evidence for a pre-Oligocene magmatic activity that was not solely limited to the Adamello batholith. Moreover, it appears that dikes rejuvenate from SE to NW, in an opposite direction with respect to the Alpine subduction polarity. Thus, a more complex geodynamic scenario than the slab break-off model must be envisaged. The absence of arc magmatism prior to the Middle Eocene can be explained by the low-angle subduction of the Tethyan slab that confined the mantle partial melting zone away from the orogenic wedge. The onset of the Apennines subduction at 55-50 Ma caused the Alpine slab to retreat. The partial melting zone progressively migrated beneath the orogenic wedge and finally reached the axial belt in the Late Eocene, when the Alpine collision was completed. Only at this stage, slab break-off occurred and promoted the intrusion of the Periadriatic plutons.

Bergomi, Maria Aldina; Zanchetta, Stefano; Tunesi, Annalisa

2014-11-01

140

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 segmentstransform 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

141

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

142

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

143

Study of the recent geodynamic processes in the Kopet-Dag region  

NASA Astrophysics Data System (ADS)

The time series of the uniquely long geodetic observations of recent geodynamic processes in the Kopet-Dag region are analyzed. The regional observations of contemporary vertical movements cover a 75-year period; the zonal and local systems of leveling measurements, which provide an increased degree of spatiotemporal detail (the distance between the benchmarks is less than 1 km and the measurements are repeated with a frequency of once per month to two times per annum), have been functioning for 50 years. It is shown that during the last 40-50 years, the regional stress field in the forefront of the Main Kopet-Dag thrust and collision zone of the Turanian and Iranian plates is quasi static. The annual average trend rate of strains estimated from a set of the time series of uniquely long geodetic observations is (3-5) 10-8 yr-1, which is only one to two amplitudes of tidal deformations of the solid Earth. The local deformations in the fault zone reach the rates that are by 1.5-2 orders of magnitude higher than in the block part of the region. It is found that the segments of the Earth's surface within the axial part of the depression experience persistent uplifting, which indicates that they do not follow the scheme of inherited evolution characteristic of the fault-block structures of the region. It is demonstrated that these anomalous uplifts can be caused by the variations in the weak seismicity in the zone of the North Ashgabat Fault.

Izyumov, S. F.; Kuzmin, Yu. O.

2014-11-01

144

Flexural Rigidity Around Ross Island, Antarctica Based On Geodynamic Modeling And Seismic Stratigraphy  

NASA Astrophysics Data System (ADS)

Quantifying the flexural subsidence history around Mt. Erebus, located on Ross Island in the southern Ross Sea of West Antarctica, is essential to separating the tectonic, volcanic, and climatic signals in the stratigraphic record contained in regional seismic reflection and borehole data. Toward this end, we analyze both broken and continuous plate models of flexural subsidence due to volcanic loading around Mt. Erebus. Seismic reflection data from the IT90AR71, NBP0401-118m and NBP0401-126m seismic surveys are used to identify stratigraphic horizons associated with loading during different eruptive events. Based on results obtained by ANTOSTRAT, we have identified 5 seismic horizons RSb1 (early Oligocene), RSb2 (late Oligocene to early Miocene), RSb3 (early Miocene), RSb4(early to middle Miocene) and RSb5 (middle Miocene), which are correlated with the CIROS-1 drill hole, in the Eastern Ross Sea to identify 5 episodes of flexural subsidence related to Ross Island volcanic loading. The seismic data indicate that the flexural bulge associated with all 5 volcanic loading events is located at an average distance of 250 km from Mt. Erebus. We use the position of the flexural bulge and the dip of strata within the basin to constrain geodynamic models of flexural subsidence due to volcanic loading. We assume a mantle density of 3200 kg/m^3 and density of sedimentary basin infill of 2700 kg/m^3. Our preliminary results suggest that a broken plate, point load model is the most ideal case for Ross Island. The flexural rigidity is approximately 10^22.5 N-m, and the cumulative load of all volcanic episodes of Mt. Erebus is 9x10^11 N.

Jha, S.; Witt, D. R.; Harry, D. L.

2013-12-01

145

Volcanic Stratigraphy and Lithogeochemistry of the Northern Section of the Lynn Lake Greenstone Belt: Implications for Regional Geodynamics and Metallogenesis  

NASA Astrophysics Data System (ADS)

The MacLellan Au-Ag deposit, located in the Paleoproterozoic Lynn Lake greenstone belt of the Trans-Hudson Orogen, Manitoba, is hosted by a package of plagioclase-amphibole, chlorite-amphibole, and quartz-plagioclase-biotite schists that are considered to be representative of the geodynamic evolution of the northern section of the Lynn Lake greenstone belt. A combination of field and petrographic observations and high-precision trace element chemistry have identified the protoliths to the host rock sequence as transitional aluminous basalt with subordinate picrite and biotite-altered aluminous basalt, respectively. The Th-Nb-La-REE systematics of these rocks are consistent with a rifted continental margin environment. Volcanic rocks with similar Th-Nb-La-REE systematics to those from the MacLellan host rock sequence have been identified throughout the Lynn Lake region. Therefore, it is proposed that the Lynn Lake greenstone belt represents a rifted continental margin and based on this revised geodynamic model, the mineral potential of the belt should be reassessed.

Glendenning, Michael W. P., Jr.

146

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-Provenal Ocean).

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

2013-06-01

147

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

148

AlpArray - an initiative to advance understanding of Alpine geodynamics  

NASA Astrophysics Data System (ADS)

AlpArray is an initiative to study the greater Alpine area with a large-scale broadband seismological network. The interested parties (currently 57 institutes in 16 countries) plan to combine their existing infrastructures into an all-out transnational effort that includes data acquisition, processing, imaging and interpretation. The experiment will encompass the greater Alpine area from the Black Forest and the Bohemian Massif in the north to the Northern Apennines in the south and from the Pannonian Basin in the east to the French Massif Central in the west. We aim to cover this region with a high-quality broadband seismometer backbone by combining the ca. 220 existing permanent stations with additional 300-340 instruments from mobile pools, all of them to be deployed from 2014-2015 until 2017. In this way, we plan to achieve homogeneous and high resolution coverage (ca. 40 km average station spacing). Furthermore, we also plan to deploy a few densely spaced targeted networks along swaths across - and in regions of - key parts of the Alpine chain on shorter time scales. These efforts on land will be combined with deployments of ca. 40-45 ocean bottom seismometers in the Mediterranean Sea. We also aim to implement the best practice for synchronizing mobile pool operation procedures and data handling: common data centre and data management procedure, free access to data to participants as soon as possible through EIDA. Data will be open to the public 3 years after the experiment ends. The main scientific goal of AlpArray is to investigate the structure and evolution of the lithosphere beneath the Alps. A primary target is the geometry and configuration of subducting slabs and their polarity switch beneath the arc. Numerous regional questions such as seismic hazard will be tackled. Targets will be imaged at several depths (e.g., from near-surface structure down to upper mantle anisotropy), scales (e.g., from local seismicity to mantle transition zone thickness variations), using different methodologies in the sub-regions of interest. An overview of these targets and the methodologies intended to be applied in connection with the seismological measurements will be presented. The geodynamic interpretation of the acquired data will be complemented by other Earth Science disciplines such as state-of-the-art numerical and analogue modelling, gravity and magneto-telluric measurements, as well as structural geology. In conclusion, we hope to turn the strong community interest into a truly interdisciplinary and collaborative project in the key region for seismotectonic activity and dynamics of Europe.

Hetnyi, Gyrgy; AlpArray Working Group

2013-04-01

149

Geodynamic evolution of the Atlas system (Morocco) in post-palaeozoic times  

NASA Astrophysics Data System (ADS)

The Atlas system of Morocco comprises the Mediterranean Rif orogen and three foreland intracontinental ranges: Middle, High and Anti-Atlas, which behave as mobile zones within the stable platform. For this region, a review is given on the major structural elements, the sedimentary and volcanic evolution from Triassic to recent, the crustal and upper mantle structure and the seismicity. Based on these data the following geodynamic model has been derived: The break-up of Pangaea and the subsequent formation of the North Atlantic and the western Tethys affected to some extent the northwestern margin of the African continent. During the Triassic-Dogger interval, rift grabens, pull-apart basins and accompanying volcanism are features of these moderate mobilizations. From Upper Jurassic onward the rifting processes slowed down and ceased during the Eocene. The accompanying magmatism changed from basaltic effusions to alcaline intrusions, thus indicating a change from a tensional to a compressional stress-field. The third period of the evolution, from Oligocene to recent, was governed by compressional movements between Africa and Europe, culminating in collisional structures of the Betic Cordilleras and the Rif. Compression and uplift of the Rif Atlas and of the three intracontinental belts took place within the same time intervals, thus implying a common relationship to certain plate tectonic events. As evidence by magnetotelluric and seismic studies intracrustal shearing and detachment have been facilitated by the existence of intracrustal high conductivity and low velocity layers, caused by Mesozoic and Tertiary thermal activities. A mechanism of transferring compressional stress from the active margin to its foreland is provided by the BALLY model of thin-skinned thrusting. The combination of these principles with the structural situation in northern Africa suggests the formation of an inclined thrust plain structure, which has penetrated the sedimentary cover and deeper crustal complexes. A stronger compression had taken place within the fractured and weakened former rift zones, causing the observed young uplift of the ranges. A final stage of collision is marked by the NE/SW striking Transalboran fault zone, extending over a length of 1100 km from southeastern Spain across the Alboran Sea and along the Middle Atlas to Agadir.

Jacobshagen, Volker; Grler, Konrad; Giese, Peter

150

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

151

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

152

Long-term monitoring of geodynamic surface deformation using SAR interferometry  

NASA Astrophysics Data System (ADS)

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

Gong, Wenyu

153

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

154

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

155

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 Sr Rondane and central DML that had never been visited previously (from Blklettane and Bergekongen in the E to Urna and Srsteinen 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. Sr 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, Lufer; Clark, Chris; Kleinhanns, Ilka; Elburg, Marlina; Ruppel, Antonia; Estrada, Solveig; Damaske, Detlef; Jokat, Wilfried; Riedel, Sven; Lucka, Nicole

2013-04-01

156

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

NASA Astrophysics Data System (ADS)

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

Keskin, Mehmet

2014-05-01

157

Eclogite in West Papua (Wandamen Peninsula), petrological and geochemical characterization : geodynamical implications  

NASA Astrophysics Data System (ADS)

The Lengguru accretionary wedge (West Papua) is located in a very active geodynamical context. It results from the oblique convergence between the Pacific plate and the Australian plate. All the wedge has been build between 11 and 2 Ma (Bailly et al., 09). Exceptional boulders of fresh eclogites were discovered in the internal part of the Lengguru wedge, in the so called Wandamen peninsula. The Wandamen peninsula displays an increasing metamorphic gradient from West to East. This metamorphic peninsula may also be regarded as the continuation of the inner part of the Central range of Papua New Guinea farther east. The eclogites area embedded in metasediments that present similarities with Mesozoic and Cenozoic sediments of the Australian margin in the continuation of Lengguru wedge. According to geochemical analysis of major and traces elements on the two freshest eclogites, their protolith has a Fe-Ti gabbroic composition. The CIPW norm of these rocks suggest a protolith, with 32% of pyroxenes, 47% of anorthite, less than 3% of olivine, with 7% of ilmenite and 7% of magnetite. Major elements show a tholeiitic characters. Traces elements suggest a T MORB signature with a high content of TiO2. The eclogites are medium to coarse grained. The metamorphic paragenesis consists of clinopyroxenes, garnets, amphiboles, rutiles, quartz and accessory minerals like apatites. Clinopyroxenes with omphacitic composition (XJd: 0.3-0.4) are poecilitic, rare textures of retrogression (symplectites) are observed. Symplectites are composed by diopside or Na-Ca-Fe pyroxene XJd (0.18) and albite, locally calcic amphiboles can replace the clinopyroxene. Garnet of several millimeters (3-4 mm) result from the aggregation of smaller euhedral crystals (500-700 m). Some of them display atoll microstructure and exhibit a core filled by omphacite, slightly green amphibole, or by quartz. They contain minute inclusions of omphacite, amphibole, apatite, quartz. Many rutiles exsolutions are observed within the garnets, suggesting high metamorphic conditions. Garnets have a mixed composition between almandine and grossular. Inclusions of quartz in both garnet and omphacite are surrounded by fractures suggesting the previous occurrence of coesite. The sodic calcic and calcic greenish amphiboles are also important minerals of these eclogites. The PT conditions deduced from the eclogitic paragenesis are 143 kbar, 65050C. The Lengguru accretionary wedge has been active during 8 millions years, (between 11 and 2 Ma). So far we do not know the age of eclogitisation. However it is probably related to the accretionary wedge. Miocene pebbles were found engulfed within unmetamorphozed conglomerate (no metamorphic or magmatic pebbles were in the conglomerate) that overlies the eastern flank of the Wandamen massif suggesting that exhumation of eclogite was active after Miocene. Most of blueschist and eclogitic rocks in the world require at least 15 Ma for their formation and exhumation. These eclogites require the exceptional rapid process. Agard, P.,Yamato, P., Jolivet, L., Burov, E., (2009) Exhumation of oceanic blueschists and eclogites in subduction zones:Timing and mechanisms, EPSL, , 53-79 Bailly V., Pubellier M., Ringenbach J-C., de Sigoyer J., Sapin F. Jumps of deformation zones in a young convergent setting; the Lengguru fold-and-thrust belt, New Guinea Island, Lithos, doi:10.1016/j.lithos.2009.08.013

de Sigoyer, Julia; Pubellier, Manuel; Bailly, Vivien; Ringenbach, Jean-Claude

2010-05-01

158

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

159

Neoproterozoic geodynamic evolution of SW-Gondwana: a southern African perspective  

NASA Astrophysics Data System (ADS)

Our current understanding of the tectonic history of the principal Pan-African orogenic belts in southwestern Africa, reaching from the West Congo Belt in the north to the Lufilian/Zambezi, Kaoko, Damara, Gariep and finally the Saldania Belt in the south, is briefly summarized. On that basis, possible links with tectono-stratigraphic units and major structures on the eastern side of the Ro de la Plata Craton are suggested, and a revised geodynamic model for the amalgamation of SW-Gondwana is proposed. The Ro de la Plata and Kalahari Cratons are considered to have become juxtaposed already by the end of the Mesoproterozoic. Early Neoproterozoic rifting led to the fragmentation of the northwestern (in today's coordinates) Kalahari Craton and the splitting off of several small cratonic blocks. The largest of these ex-Kalahari cratonic fragments is probably the Angola Block. Smaller fragments include the Luis Alves and Curitiba microplates in eastern Brazil, several basement inliers within the Damara Belt, and an elongate fragment off the western margin, named Arachania. The main suture between the Kalahari and the Congo-So Francisco Cratons is suspected to be hidden beneath younger cover between the West Congo Belt and the Lufilian/Zambezi Belts and probably continues westwards via the Cabo Fro Terrane into the Gois magmatic arc along the Brasilia Belt. Many of the rift grabens that separated the various former Kalahari cratonic fragments did not evolve into oceanic basins, such as the Northern Nosib Rift in the Damara Belt and the Gariep rift basin. Following latest Cryogenian/early Ediacaran closure of the Brazilides Ocean between the Ro de la Plata Craton and the westernmost fragment of the Kalahari Craton, the latter, Arachania, became the locus of a more than 1,000-km-long continental magmatic arc, the Cuchilla Dionisio-Pelotas Arc. A correspondingly long back-arc basin (Marmora Basin) on the eastern flank of that arc is recognized, remnants of which are found in the Marmora Terranethe largest accumulation of oceanic crustal material known from any of the Pan-African orogenic belts in the region. Corresponding foredeep deposits that emerged from the late Ediacaran closure of this back-arc basin are well preserved in the southern areas, i.e. the Punta del Este Terrane, the Marmora Terrane and the Tygerberg Terrane. Further to the north, present erosion levels correspond with much deeper crustal sections and comparable deposits are not preserved anymore. Closure of the Brazilides Ocean, and in consequence of the Marmora back-arc basin, resulted from a change in the Ro de la Plata plate motion when the Iapetus Ocean opened between the latter and Laurentia towards the end of the Ediacaran. Later break-up of Gondwana and opening of the modern South Atlantic would have followed largely along the axis of the Marmora back-arc basin and not along major continental sutures.

Frimmel, H. E.; Basei, M. S.; Gaucher, C.

2011-04-01

160

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

161

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

162

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

163

Geodynamical aspects of the Eurasia-Nubia collision zone in Sicily (Italy): new data from a dense CGPS network  

NASA Astrophysics Data System (ADS)

The collisional processes acting along the boundary between the Eurasian and Nubian plates in Sicily (Italy) is a critical geological context for the definition of the hazard related to intense volcanic activity and to a diffuse low-to-medium seismic activity. The Catania section of the Istituto Nazionale di Geofisica e Vulcanologia (INGV-Ct) currently manage a network of about 40 continuous GPS stations. Many of these stations are devoted to the monitoring of active volcanic areas (Etna, Stromboli, Vulcano and Pantelleria), but some of these stations can help to improve the current knowledge of the geodynamical aspects of Sicily. In this work we show the first results of the analysis of the data from the INGV-Ct GPS network finalised to the estimation of velocity fields. The time span covered by our stations is different, ranging from 10 years to, at least, 3 years. We analysed the data using the GAMIT/GLOBK software (King and Bock, 1995; Herring, 1995) in a two step approach: in the first step we used double-differenced phase observations from each day to estimate station coordinates, atmospheric zenith delays at each station, and orbital and Earth orientation parameters, applying loose constrains to all parameters. In the second step we used the estimated station coordinates and their covariances from each day as quasi-observations to estimate a consistent set of coordinates and velocities for the entire period (10 years). Our estimates are computed in ITRF00 system with respect to an Eurasia and also Nubia-fixed reference frame, in order to distinguish the kinematic of the different plates. The analysis of these velocities and of the main strain parameters in some peculiar areas more densely covered by our network (Aeolian Islands, Eastern Sicily) gives new insights in the small scale processes linking the geodynamical aspects and the volcanic activity and a description of the features related to the large scale process of the collision.

Bruno, V.; Mattia, M.; Palano, D.; Rossi, M.; Gresta, S.

2006-12-01

164

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

NASA Astrophysics Data System (ADS)

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

Muslimov, R.; Plotnikova, I.

2012-04-01

165

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.

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

166

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

167

New Structural, Geochronological and Geochemical Constraints on the Late Paleozoic Geodynamic Evolution of Northwestern Tianshan, NW China  

NASA Astrophysics Data System (ADS)

The Tianshan Belt is one of the main elements of the Central Asia Orogenic collage, which builds up the Eurasian continent during the Paleozoic. The Tianshan Belt is often divided into North, Central and South Tianshan domains, the Yili Block is a continental piece that wedges eastward between the North and Central Tianshan. Our study provides some new structural, geochronological and geochemical evidence to better understand the Late Paleozoic geodynamic amalgamation of the western part of the North Tianshan and the Yili Block. The North Tianshan is composed of relics of oceanic lithosphere and Mid-Carboniferous turbidite. Blocks of serpentinized peridotite, gabbro, pillow basalt, chert and detrital rocks derived from ophiolite make up an ophiolitic mlange, refered to as the `Bayingou ophiolite'. Sedimentological and structural features indicate that this mlange is a sheared olistostrome with exotic blocks, which experienced polyphase tectonic processes. In the ophiolitic mlange, Famennian-Tournaisian radiolarians in chert, N-MORB, OIB and IAT-type mafic rocks with SHRIMP U-Pb age of 325-A7 Ma on Zircon from gabbro, indicate that these ophiolites developed within a Late Devonian to Mid-Carboniferous oceanic basin. This mlange separates the turbidite into two parts. The northern one is deformed by north-verging recumbent folds, and the southern one is characterized by a syn-metamorphic ductile deformation. Sandstone and pelite exhibit a steeply dipping slaty cleavage and a sub-horizontal stretching and mineral lineation. Kinematic criteria indicate ductile dextral shearing. A new 40Ar/39Ar dating on biotite of deformed schist shows that the shearing took place around 250 Ma. The Paleozoic rocks of the Yili Block consist of Carboniferous platform sediments associated with volcanic and volcaniclastic rocks and intruded by granitoids. Geochemical analyses (ICP-MS) on 60 volcanic rocks and granites from 8 representative sections show that (1) these rocks belong to the calc-alkaline series; (2) they are enriched in LILE while depleted in HFSE, and display a moderate negative anomaly of Nb and Ta relative to Th and Ce. These characters are consistent with subduction-related magmas; (3) they emplaced in a continental active margin. Zircon ICPMS-LA U-Pb ages of the andesites, granodiorites and granites range from 360 to 310 Ma. On the basis of above evidences, a Late Paleozoic geodynamic evolution of Northwestern Tianshan is proposed as follows. During Late Devonian-Early Carboniferous, a southward directed subduction closed an oceanic basin located between the Northern Tianshan and Junggar continent, and generated the Yili continental margin arc magmatism. Within the basin, intraoceanic tectonics (possibly along transform faults) might account for the development of the ophiolitic mlange. In Late Carboniferous, the subduction was followed by collision of the Yili Block with the Junggar continent. During the Early Permian, this suture zone was re-activated by dextral wrench faulting. In the Yili Block, the Permian tectonics is also responsible for the opening of pull-apart basins and emplacement of post-orogenic alkaline magmas. Keywords: Structure, geochronology, geochemistry, geodynamic evolution, Late Paleozoic, Tianshan

Wang, B.; Faure, M.; Cluzel, D.; Shu, L.; Charvet, J.

2005-12-01

168

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

NASA Astrophysics Data System (ADS)

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

Lu, Q.; Chang, Y.

2010-12-01

169

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

170

New advances in using seismic anisotropy, mineral physics and geodynamics to understand deformation in the lowermost mantle  

NASA Astrophysics Data System (ADS)

The D'' region, which lies in the lowermost few hundred kilometres of the mantle, is a central cog in the Earth's heat engine, influencing convection in the underlying core and overlying mantle. In recent years dense seismic networks have revealed a wealth of information about the seismic properties of this region, which are distinct from those of the mantle above. Here we review observations of seismic anisotropy in this region. In the past it has been assumed that the region exhibits a simple form of transverse isotropy with a vertical symmetry axis (VTI anisotropy). We summarise new methodologies for characterising a more general style of anisotropy using observations from a range of azimuths. The observations can be then used to constrain the mineralogy of the region and its style of deformation by a lattice preferred orientation (LPO) of the constituent minerals. Of specific interest is the recent discovery of the stability of the post-perovskite phase in this region, which might explain many enigmatic properties of D''. Mantle flow models based on density models derived from global tomographic seismic velocity models can be used to test plausible mineralogies, such as post-perovskite, and their deformation mechanisms. Here we show how linked predictions from mineral physics, geodynamical modelling and seismic observations can be used to better constrain the dynamics, mineralogy and physical properties of the lowermost mantle.

Nowacki, Andy; Wookey, James; Kendall, J.-Michael

2011-10-01

171

Present-day geodynamics of the Mediterranean-Lesser Caucasus part of the Alpine-Indonesian Mobile Belt  

NASA Astrophysics Data System (ADS)

At present, the concept of plate tectonics is predominant in the Earth sciences. However, there are also other, less popular ideas concerning the geodynamics of the Earth's crust/lithosphere. The highly accurate modern geodetic measurements such as GPS, SLR, and VLBI provide a new framework for assessing different standpoints. The results of global-scale geodetic measurements are in close agreement with the global plate tectonic reconstructions. However, the same measurements of regional networks in the Mediterranean part of the Alpine-Indonesian Mobile Belt yield results that disagree with the plate's tectonic reconstructions for this region. These measurements show that the belt's width in many areas of Eurasian and African lithospheric plates' convergence is not decreasing at present, as follows from the plate reconstructions, but increasing. At the same time, the segments of the belt under consideration are in a state of stress characterized by near-horizontal compression oriented across the strike of the belt. This contradiction can only be explained if it is assumed that the formation of the tectonic structure of the mobile belt is related to the active growth of the volume of the bedded rocks of the belt, i.e., of the plate's convergence zone. This growth is apparently due to the additional mineral material gained by the ascending mantle fluid flows. This implies that local, autonomous dynamic processes are required in addition to the lithospheric plate's interactions to account for the tectonic deformations observed in the mobile belt.

Shevchenko, V. I.; Lukk, A. A.; Prilepin, M. T.; Reilinger, R. E.

2014-01-01

172

Tilt Observations in the Normal Mode Frequency Band at the Geodynamic Observatory Cueva de los Verdes, Lanzarote  

NASA Astrophysics Data System (ADS)

We have conducted observations with the aid of a seismo-tiltmeter station, which is based on the Ostrovsky pendulum and installed at the Geodynamic Observatory Cueva de los Verdes at Lanzarote Island since 1995. In this station the signal is separated into two frequency bands - tidal tilts (from 0 to 5 mHz) and ground oscillations in the frequency range of free Earth's normal modes (from 0.2 to 5 mHz). The later band, called accelerometer channel, has additional amplification. We analyzed the background records in the frequency range of Earth's free oscillations from August 2000 to September 2001, as well as, Earth's normal modes after strong earthquakes. We found several distinctive persistent peaks in the spectra of background oscillations. Both amplitudes of distinguished peaks and noises have seasonal variations. We found that spectra of background oscillations are different in the frequency interval between 1.4 and 2.5 mHz for North- South and East-West components.

Kalinina, A. V.; Volkov, V. A.; Gorbatikov, A. V.; Arnoso, J.; Vieira, R.; Benavent, M.

173

Separation of the long-term thermal effects from the strain measurements in the Geodynamics Laboratory of Lanzarote  

NASA Astrophysics Data System (ADS)

A 12-year series (1992-2004) of strain measurements recorded in the Geodynamics Laboratory of Lanzarote is investigated. Through a tidal analysis the non-tidal component of the data is separated in order to use it for studying signals, useful for monitoring of the volcanic activity on the island. This component contains various perturbations of meteorological and oceanic origin, which should be eliminated in order to make the useful signals discernible. The paper is devoted to the estimation and elimination of the effect of the air temperature inside the station, which strongly dominates the strainmeter data. For solving this task, a regression model is applied, which includes a linear relation with the temperature and time-dependant polynomials. The regression includes nonlinearly a set of parameters, which are estimated by a properly applied Bayesian approach. The results obtained are: the regression coefficient of the strain data on temperature is equal to (-367.4 0.8) 10 -9 C -1, the curve of the non-tidal component reduced by the effect of the temperature and a polynomial approximation of the reduced curve. The technique used here can be helpful to investigators in the domain of the earthquake and volcano monitoring. However, the fundamental and extremely difficult problem of what kind of signals in the reduced curves might be useful in this field is not considered here.

Venedikov, A. P.; Arnoso, J.; Cai, W.; Vieira, R.; Tan, S.; Velez, E. J.

2006-01-01

174

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.

2012-08-01

175

Paleogeographic and geodynamic Miocene evolution of the Tunisian Tell (Numidian and Post-Numidian Successions): bearing with the Maghrebian Chain  

NASA Astrophysics Data System (ADS)

The Numidian and Post-Numidian stratigraphy of the Tunisian Tell has been updated based on 16 stratigraphic sections belonging to the Massylian sub-domain of the Maghrebian Flysch Basin and to the External Domain. The new data concern detailed litho- and biostratigraphy, gaps, synchronous marker levels, lateral correlations, tectonic contacts, etc. The successions studied show many diachronous and unconformity boundaries delimiting sedimentary depositional sequences related to some tectonic/sedimentary processes. Two main Miocene sedimentary successions (Numidian and Post-Numidian) are recognized overlying the Sub-Numidian Succession (pre-Early Aquitanian) by new integrated (planktonic foraminifera and calcareous nannoplankton) chronostratigraphic analyses, allowing an update of the formations studied. The Miocene tectonic/sedimentary relationships and the timing of the deformation are summarized as follows: (1) the activation of a foredeep stage and a tectogenesis phase gives rise to an accretionary orogenic wedge during mainly the Early Miocene; (2) a late-orogenic phase is checked in the Late Burdigalian-Early Langhian characterized by a marine glauconitic terrigenous sedimentation; (3) a post-orogenic generalized phase is confirmed from the Middle Miocene on in shallow marine or continental sedimentation. These results show good correlation along the Maghrebian Chain and Betic Cordillera. Finally, a paleogeographic and geodynamic evolutionary model concerning the Miocene African Tunisian Margin is postulated.

Belayouni, Habib; Guerrera, Francesco; Martn-Martn, Manuel; Serrano, Francisco

2013-04-01

176

Methodical questions and accuracy problems of GPS observations by the example of the geodynamic proving ground in Bishkek  

NASA Astrophysics Data System (ADS)

The key questions concerning the modern methodical tasks and accuracy of GPS measurements of crustal motion spanning are discussed for a full cycle of the survey from the organization of the field operations to the interpretation of the final results. The presented data rely on the 20-year experience of the geophysicists of the Research Station of the Russian Academy of Sciences in Bishkek (RS RAS) in GPS monitoring at the Geodynamic Proving Ground in Bishkek (GPGB) and in a large part of Central Asia. The comparative characteristics of the constellations of visible GPS and GLONASS satellites are analyzed from the standpoint of their practical application for precise scientific observations of crustal motions. The studies of the contemporary movements of the Earth's crust by the methods of satellite geodesy generally comprise three stages: (1) organization of the measurement networks and acquisition of the data; (2) data processing; and (3) interpretation of the results. Each stage is associated with its own block of the tasks and problems, and neither is guaranteed against uncertainties and errors which may affect the results, conclusions, and reconstructions.

Kuzikov, S. I.

2014-11-01

177

New insights on the deep geodynamic processes within Vrancea active seismic zone as inferred from non-tidal gravity changes  

NASA Astrophysics Data System (ADS)

Vrancea experiment Located in the bending zone of East Carpathians, just at the junction of three major lithospheric compartments, the so-called Vrancea zone exhibits unusual intermediate-depth seismicity within full intra-continental environment. The dominant idea is that the upper mantle seismicity is due to a slab relict hanging below the Vrancea crust. However, several aspects, among which the issues of its connection with the crust, are under debate. The presence of the intermediate-depth earthquakes with vertical-extension mechanism advocate for an active attachment of the oceanic lithosphere relict sinking into the upper mantle, but some seismic tomography images seem to point out a completely detached high velocity body. However, the low resolution makes the results questionable. A gravity experiment has been conducted in order to infer the lithosphere dynamics within the Vrancea seismic region from the space-time change of the gravity field in the area. Systematic high accuracy gravity observations have been performed within a dedicated gravity network consisting of 13 epoch-stations regularly spread over the study area and a geo-traverse crossing the epicentre zone. Instruments and methodology Using a Scintrex CG-5 relative meter, absolute gravity values have been transferred on each pillar from the both second order Romanian national gravity reference network and the Central Europe UNIGRACE network. Gravity values on the base stations located along the geo-traverse have been referred to one of the end base-stations, located outside the active geodynamic area in a stable environment. All gravity observations were corrected for tide and drift. Due to the short distance between the stations, corrections for atmospheric pressure change have not been considered. Main results As the second order Romanian national gravity network provides absolute gravity for the 1980's epoch, and the UNIGRACE network offers absolute gravity for 2000's epoch, pairs of absolute gravity values separated by a 20 years time-span have been obtained and compared on each pillar of the gravity network. Overall, a gravity decrease has been revealed in the area. The lowest gravity low has been recorded just within the epicentre area, along with a slight subsidence of topography. This unusual coupling of altitude decrease and gravity lowering looks clearly connected to deep geodynamic processes. 2D and 3D computer models simulating the gravity change have revealed a mass deficit (starting at approx 10 km depth) located in the epicentre area of the intermediate-depth earthquakes. It has been interpreted in terms of volume increase caused by an assumed lithosphere stretching created by the eclogitization of the lower crust penetrating the upper mantle. Sets of gravity values obtained along the geo-traverse from successive yearly campaigns have confirmed the previous assumption revealing the crust stretching as an on-going process. Based on the gravity results and their interpretation along with other kind of observations (e.g. high resolution tomography provided by joint inversion of the seismic and gravity data), some concluding remarks and speculations on the genesis of the intermediate-depth seismicity are finally presented. Acknowledgement. The research has been supported through the grant POS CCE O 2.1.2. ID 593 (contract 182/2010).

Besutiu, L.

2012-04-01

178

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

179

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

180

Geodynamic modeling of the capture and release of a plume conduit by a migrating mid-ocean ridge  

NASA Astrophysics Data System (ADS)

plates over the relatively stationary, long-lived conduits of mantle plumes. However, paleomagnetic data from the Hawaii-Emperor Seamount Chain suggests that the Hawaiian hotspot moved rapidly (~40 mm/yr) between 81 - 47 Ma [Tarduno et al., 2003]. Recently, Tarduno et al. [2009] suggested that this period of rapid motion might be the surface expression of a plume conduit returning to a largely vertical orientation after having been captured and tilted as the result of being "run over" by migrating mid-ocean ridge. I report on a series of analog geodynamic experiments designed to characterize the evolution of a plume conduit as a mid-ocean ridge migrates over. Experiments were conducted in a clear acrylic tank (100 cm x 70 cm x 50 cm) filled with commercial grade high-fructose corn syrup. Plate-driven flow is modeled by dragging two sheets of Mylar film (driven by independent DC motors) in opposite directions over the surface of the fluid. Ridge migration is achieved by moving the point at which the mylar sheets diverge using a separate motor drive. Buoyant plume flow is generated using a small electrical heater placed at the bottom of the tank. Plate velocities and ridge migration rate are controlled and plume temperature monitored using LabView software. Experiments are recorded using digital video which is then analyzed using digital image analysis software to track the position and shape of the plume conduit throughout the course of the experiment. The intersection of the plume conduit with the surface of the fluid is taken as an analog for the locus of hotspot volcanism and tracked as a function of time to obtain a hotspot migration rate. Results show that the plume conduit experiences significant tilting immediately following the passage of the migrating ridge.

Hall, P. S.

2011-12-01

181

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

182

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

NASA Astrophysics Data System (ADS)

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

Ayd?nak?r, Emre

2014-11-01

183

Geodynamic and Climate Interaction in the Kurile-Kamchatka and Aleutean Marginal Sea-Island Arc System  

NASA Astrophysics Data System (ADS)

The Kurile-Kamchatka and Aleutean Marginal Sea-Island Arc System is a complex climate driving region. To better understand the processes that control the subduction and the geodynamic and climatic development in this region a joint group of German and Russian scientists work together under the frame of the KALMAR project. In five closely coupled subprojects multidisciplinary research is carried out that involves a wide range of geophysical, tectonic, volcanological and petrological approaches as well as paleo-oceanographic and climate research. Several land expeditions on Kamchatka and three geomarine cruises in the NW-Pacific and the western Bering Sea are the bases for the research. The cruises with the German research vessel SONNE in 2009 concentrated on the geophysical investigation of the subducting plate offshore Kamchatka (SO201 Leg 1a), and on volcanological, petrological, tectonic and paleoceanographic questions (SO201 Leg 1b, SO201 Leg 2). The focus of the cruises was the study on the composition of the mantle and the oceanic crust, the seamounts and their ages as well as paleo-oceanographic investigations on the sediments along the eastern continental slope of Kamchatka, in the Komandorsky Basin, and on the Shirshov Ridge to explore paleoclimate archives to get an insight in the subpolar water mass transfer and the oceanographic and climatic development in the subarctic NW-Pacific. The geochemical refinement of a tephrostratigraphic framework of Pleistocene and Holocene tephra in Kamchatka provided a detailed chronology of Holocene Kamchatkan eruptions. It served as a basis for understanding temporal patterns in the eruption sequence and geochemical variations of magmas. It provides independent time markers for an exact correlation of the various climate archives from land and marine sites from the NW-Pacific and the Bering Sea. It needs to be proved, if Kamchatkan ashes can be traced into the Eastern Bering Sea and offshore Alaska.

van den Bogaard, C.; Dullo, W.; Baranov, B.; Hoernle, K.; Nuernberg, D.; Werner, R.

2011-12-01

184

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

NASA Astrophysics Data System (ADS)

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

Erenoglu, Oya; Bozcu, Mustafa

2014-05-01

185

Anomalous crustal and lithospheric mantle structure of southern part of the Vindhyan Basin and its geodynamic implications  

NASA Astrophysics Data System (ADS)

Tectonically active Vindhyan intracratonic basin situated in central India, forms one of the largest Proterozoic sedimentary basins of the world. Possibility of hydrocarbon occurrences in thick sediments of the southern part of this basin, has led to surge in geological and geophysical investigations by various agencies. An attempt to synthesize such multiparametric data in an integrated manner, has provided a new understanding to the prevailing crustal configuration, thermal regime and nature of its geodynamic evolution. Apparently, this region has been subjected to sustained uplift, erosion and magmatism followed by crustal extension, rifting and subsidence due to episodic thermal interaction of the crust with the hot underlying mantle. Almost 5-6 km thick sedimentation took place in the deep faulted Jabera Basin, either directly over the Bijawar/Mahakoshal group of mafic rocks or high velocity-high density exhumed middle part of the crust. Detailed gravity observations indicate further extension of the basin probably beyond NSL rift in the south. A high heat flow of about 78 mW/m2 has also been estimated for this basin, which is characterized by extremely high Moho temperatures (exceeding 1000 C) and mantle heat flow (56 mW/m2) besides a very thin lithospheric lid of only about 50 km. Many areas of this terrain are thickly underplated by infused magmas and from some segments, granitic-gneissic upper crust has either been completely eroded or now only a thin veneer of such rocks exists due to sustained exhumation of deep seated rocks. A 5-8 km thick retrogressed metasomatized zone, with significantly reduced velocities, has also been identified around mid to lower crustal transition.

Pandey, O. P.; Srivastava, R. P.; Vedanti, N.; Dutta, S.; Dimri, V. P.

2014-09-01

186

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

187

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

188

Stress Field in the Tonga Benioff Zone and Geodynamical Model for the First Stages of the Lau Basin Opening.  

NASA Astrophysics Data System (ADS)

This study aims at resolving the stress field in the Tonga convergence zone to further constrain the ongoing tectonic processes and their origin in this region. We investigate both the upper plate and the Benioff zone stress regime. The Tonga Benioff zone is characterized, among others, by an anomalous large seismic gap beneath the Lau Basin that triggers the question of the slab continuity between its intermediate (100-350km) and deep parts (400-700km). To address this problem, we studied the space distribution of the stress tensor in the Tonga Benioff zone using the global seismicity focal mechanisms catalogues (Engdahl et al., 1998; CMTS from Dziewonski et al., 1981). The stress tensors were computed using the Gephart's program (Gephart et al., 1984). Based on the distribution of the seismicity and on the identification of the main tectonic features, we carefully divided the slab in 100 km thick layers in depth and four sectors in latitude (14-18S, 18-21S, 21- 24S and 24-27S) to perform the stress tensor analysis. From 21 to 27S, the slab has a quite homogeneous downdip compressional regime down to 700 km, whereas the two other areas show strong variations of the stress orientation in the depth range 300 to 700 km. These variations are located on both sides of the gap and argue for a structural discontinuity across the seismic gap. Within the slab in the depth range 60 to 300 km and within the sectors 14-18S and 18-21S, there are evidences that downdip compressional mechanisms cluster close to the upper surface of the slab. These internal variations evidence the lateral segmentation of the slab and suggest locally the existence of a double seismic zone that seems to be preferentially localized in the slab which is decoupled from its deepest part. We also re-examined some of the main tectonic structures, such as the Futuna-Niua Fo'ou segment and the 17S boundary (Bonnardot et al., submitted) and we attempted to link them with the deep complex pattern of the Benioff zone as consequences of a subduction jump. We finally built up a 3D image of the Tonga slab that provides a new geodynamical model for the evolution of the Tonga-Lau system. We propose that the subduction jump was induced by the subduction of the Louisville Ridge 6 My ago and then followed by a multistage subduction roll- back to accommodate the Lau basin opening. This eventually yielded to a major tear in the slab beneath the basin that explains the present seismic gap.

Bonnardot, M.; Regnier, M.; Christova, C.; Ruellan, E.; Tric, E.

2006-12-01

189

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.

Martnez-Loriente, Sara; Sallars, Valent; Grcia, Eullia; Bartolome, Rafael

2014-05-01

190

A new strain rate model for the Great Basin and its application to tectonic and geodynamic studies  

NASA Astrophysics Data System (ADS)

The Great Basin in the western United States covers a large portion of the diffuse PA-NA plate boundary zone. Yet the seismic potential of its many faults as well as the evolution of, and the driving forces behind, the deformation remain largely unknown or disputed. To advance our understanding it is important to quantify the spatial distribution of the rate, style and direction of the present-day deformation field. GPS velocity measurements are the single most important input to fulfill this objective, and many data are now available from continuous (e.g., BARGEN network) and campaign style measurements (USGS and others). We use the Haines and Holt technique to present a new strain rate model, which is superior in its use of the latest GPS solutions and a denser model grid. Furthermore, the release of the 2003 USGS fault database makes it possible to use geologic data (i.e., slip rate and/or fault geometry) either as an additional constraint in or as a comparison with models based on the interpolation of GPS velocities alone. The ultimate aim of this work is; 1) to compare present-day style and rate of deformation with finite strain markers to place constraints on the Quaternary evolution of deformation, particularly in the northern Walker Lane, 2) to use objective means in distinguishing potential rigid blocks, 3) to identify zones of transient deformation, 4) to further develop the observed relationship between shear strain rate, fault orientation and geothermal output, and 5) to improve geodynamic models by comparing modeled present-day strain rate directions with finite strain orientations in the middle to lower crust as shown in metamorphic complexes and in the lithosphere as inferred from seismic anisotropy. For this presentation we will discuss the data synthesis as well as the resolution and reliability of the model. Furthermore, a few examples will be highlighted to underline the potential of the model in addressing the goals described above. Finally, a brief introduction will be given to the semi-permanent Mobile Array of GPS for NEvada Transtension (MAGNET) network (currently 40-50 stations, and growing) that will greatly improve our spatial resolution and velocity precision in the western Great Basin.

Kreemer, C.; Blewitt, G.; Hammond, W. C.; Coolbaugh, M. F.

2004-12-01

191

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.

Kksal, Serhat; Toksoy-Kksal, Fatma; Gnco?lu, M. Cemal; Mller, Andreas; Gerdes, Axel; Frei, Dirk

2013-04-01

192

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

193

Geological and geodynamic investigations of Alaskan tectonics: Responses in the ancient and modern geologic records to oblique plate convergence  

NASA Astrophysics Data System (ADS)

Stratigraphic, structural, and geophysical modeling studies focusing on both the Mesozoic and modern development of southern Alaska aid in understanding the nature of tectonic responses to oblique plate convergence. Analyses of the Lower to Upper (?) Cretaceous Kahiltna assemblage of the western Alaska Range and the Upper Cretaceous Kuskokwim Group of the northern Kuskokwim Mountains provide a stratigraphic record of orogenic growth in southwestern Alaska. The Kahiltna assemblage records dominantly west-directed gravity-flow transport of sediment to the axis of an obliquely closing basin that made up the suture zone between the allochthonous Wrangellia composite terrane and the North American pericratonic margin. Stratigraphic, compositional, and geochronologic analyses suggest that submarine-fan systems of the Kahiltna basin were fed from the subearial suture zone and contain detrital grains derived from both allochthonous and pericratonic sources, thereby implying a relatively close proximity of the island-arc terrane to the North American margin by late Early Cretaceous time. In contrast, Upper Cretaceous strata exposed immediately west of the Kahiltna assemblage record marine deposition during a period of transition from island arc accretion to strike-slip tectonics. The new stratigraphic model presented here recognizes diverse bathyal- to shelfal-marine depositional systems within the Kuskokwim Group that represent distinctive regional sediment entry points to the basin. Collectively, these strata suggest that the Kuskokwim Group represents the waning stages of marine deposition in a long-lived intra-oceanic and continental margin basin. Geodynamic studies focus on the mechanics of contemporary fault systems in southern Alaska inboard of the collisional Yakutat microplate. Finite-element analyses predict that a poorly understood Holocene strike-slip fault in the St. Elias Mountains transfers shear from the Queen Charlotte fault northward to the Denali fault, thereby forming a continuous transform system that accommodates right-lateral motion of the Pacific plate and Yakutat microplate relative to the stable North American craton. Although the best-fit model implies some component of anelastic deformation in the vicinity of the St. Elias Mountains and the western Alaska Range, results imply overall block-like behavior throughout the area of interest.

Kalbas, James L.

194

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

195

Sulphur geodynamic cycle  

PubMed Central

Evaluation of volcanic and hydrothermal fluxes to the surface environments is important to elucidate the geochemical cycle of sulphur and the evolution of ocean chemistry. This paper presents S/3He ratios of vesicles in mid-ocean ridge (MOR) basalt glass together with the ratios of high-temperature hydrothermal fluids to calculate the sulphur flux of 100?Gmol/y at MOR. The S/3He ratios of high-temperature volcanic gases show sulphur flux of 720?Gmol/y at arc volcanoes (ARC) with a contribution from the mantle of 2.9%, which is calculated as 21?Gmol/y. The C/S flux ratio of 12 from the mantle at MOR and ARC is comparable to the C/S ratio in the surface inventory, which suggests that these elements in the surface environments originated from the upper mantle. PMID:25660256

Kagoshima, Takanori; Sano, Yuji; Takahata, Naoto; Maruoka, Teruyuki; Fischer, Tobias P.; Hattori, Keiko

2015-01-01

196

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 150K, 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

197

Sulphur geodynamic cycle.  

PubMed

Evaluation of volcanic and hydrothermal fluxes to the surface environments is important to elucidate the geochemical cycle of sulphur and the evolution of ocean chemistry. This paper presents S/(3)He ratios of vesicles in mid-ocean ridge (MOR) basalt glass together with the ratios of high-temperature hydrothermal fluids to calculate the sulphur flux of 100?Gmol/y at MOR. The S/(3)He ratios of high-temperature volcanic gases show sulphur flux of 720?Gmol/y at arc volcanoes (ARC) with a contribution from the mantle of 2.9%, which is calculated as 21?Gmol/y. The C/S flux ratio of 12 from the mantle at MOR and ARC is comparable to the C/S ratio in the surface inventory, which suggests that these elements in the surface environments originated from the upper mantle. PMID:25660256

Kagoshima, Takanori; Sano, Yuji; Takahata, Naoto; Maruoka, Teruyuki; Fischer, Tobias P; Hattori, Keiko

2015-01-01

198

Fundamental studies in geodynamics  

NASA Technical Reports Server (NTRS)

Progress in modeling instantaneous plate kinematics is reviewed, with emphasis on recently developed models of present day plate motions derived by the systematic inversion of globally distributed data sets. Rivera plate motions, the Caribbean South American boundary, Indian plate deformation, Pacific-North America, seismicity and subduction processes, and the study of slow earthquakes and free oscillations are discussed.

Anderson, D. L.

1980-01-01

199

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

200

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

201

Unraveling the geodynamic evolution and tectonic history of the Guatemala Suture Zone: a world-class natural laboratory  

NASA Astrophysics Data System (ADS)

The Guatemala Suture Zone (GSZ) is the fault-bound region in central Guatemala that contains the present North American-Caribbean plate boundary. It is bounded by the Maya Block to the north and by the Chorts Block to the south. This major composite geotectonic unit contains a variety of ophiolites, serpentinite mlanges, and metavolcano-sedimentary sequences along with high-grade schist, gneisses, low-grade metasediments and metagranites thrusted north and south of the active Motagua fault system (MFS). This modern plate boundary has accommodated at least ~1100 km of left-lateral strike-slip motion over the Cenozoic and brings into contact the geological provinces described above. Classically, the GSZ has been interpreted as the result of a single progressive collision of a Chorts Block-related island arc with the passive margin of the Maya Block. This model was based on geochemical signatures of basaltic rocks in oceanic crust sequences both north and south of the MFS. However, results from our research challenge this single collision hypothesis. Oceanic and continental high-pressure-low-temperature (HP-LT) rocks astride the MFS have recorded multiple tectonic events revealed by their multiple metamorphic ages (Sm-Nd, U-Pb and Ar-Ar) and distinct PT paths. These tectonic events differ in age north and south of the MFS. Moreover, the continental and oceanic sequences across the MFS are geochemically and stratigraphically distinct, suggesting different tectonic origins. The southern margin of the Maya Block and the northern section of the GSZ can be clearly interpreted as a Cretaceous-Paleocene flexural passive margin tectonically overridden by ultramafic rocks and a Cretaceous island arc sequence. In contrast, the southern section of the GSZ is composed of a Carboniferous-Jurassic active margin tectonically imbricated with ultramafic rocks and a circum-Pacific Jurassic MORB and IAT metavolcano-sedimentary sequence. Thus, based on these results, we identify at least three major tectonic events within the GSZ: (i) A Jurassic-Early Cretaceous accretion and/or collision along a circum-Pacific active margin and the subsequent exhumation of oceanic HP-LT rocks now found on the southern section of the GSZ (ii) A Late Cretaceous closure of a back-arc basin that led to island arc-passive margin collision, which triggered exhumation of oceanic and continental HP-LT rocks and succeeding obduction onto the southern margin of the Maya Block (iii) A major Cenozoic left-lateral displacement along the then active margin that restructured the original tectonic arrangement into the present complex scenario. This new tectonic scenario hypothesis integrates all relevant geodynamic constraints reported on the GSZ and satisfactorily explains the occurrence of (i) an older circum-Pacific suture zone probably originated in southern Mexico in contact with (ii) a younger suture zone perhaps related to the closure of the proto Caribbean basin.

Flores, K. E.; Brocard, G. Y.; Harlow, G. E.

2013-12-01

202

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

NASA Astrophysics Data System (ADS)

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

Slabunov, Alexander

2013-04-01

203

The Early Miocene "Bisciaro volcaniclastic event" (northern Apennines, Italy): a key study for the geodynamic evolution of the central-western Mediterranean  

NASA Astrophysics Data System (ADS)

The Early Miocene Bisciaro Fm., a marly limestone succession cropping out widely in the Umbria-Romagna-Marche Apennines, is characterized by a high amount of volcaniclastic content, characterizing this unit as a peculiar event of the Adria Plate margin. Because of this volcaniclastic event, also recognizable in different sectors of the central-western Mediterranean chains, this formation is proposed as a "marker" for the geodynamic evolution of the area. In the Bisciaro Fm., the volcaniclastic supply starts with the "Raffaello" bed (Earliest Aquitanian) that marks the base of the formation and ends in the lower portion of the Schlier Fm. (Late Burdigalian-Langhian p.p.). Forty-one studied successions allowed the recognition of three main petrofacies: (1) Pyroclastic Deposits (volcanic materials more than 90 %) including the sub-petrofacies 1A, Vitroclastic/crystallo-vitroclastic tuffs; 1B, Bentonitic deposits; and 1C, Ocraceous and blackish layers; (2) Resedimented Syn-Eruptive Volcanogenic Deposits (volcanic material 30-90 %) including the sub-petrofacies 2A, High-density volcanogenic turbidites; 2B, Low-density volcanogenic turbidites; 2C, Crystal-rich volcanogenic deposits; and 2D, Glauconitic-rich volcaniclastites; (3) Mixing of Volcaniclastic Sediments with Marine Deposits (volcanic material 5-30 %, mixed with marine sediments: marls, calcareous marls, and marly limestones). Coeval volcaniclastic deposits recognizable in different tectonic units of the Apennines, Maghrebian, and Betic Chains show petrofacies and chemical-geochemical features related to a similar calc-alkaline magmatism. The characterization of this event led to the hypothesis of a co-genetic relationship between volcanic activity centres (primary volcanic systems) and depositional basins (depositional processes) in the Early Miocene palaeogeographic and palaeotectonic evolution of the central-western Mediterranean region. The results support the proposal of a geodynamic model of this area that considers previously proposed interpretations.

Guerrera, Francesco; Martn-Martn, Manuel; Raffaelli, Giuliana; Tramontana, Mario

2015-01-01

204

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

205

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

206

3-D geodynamic models of the India-Eurasia collision zone: investigating the role of lithospheric strength variation Sarah Bischoff and Lucy Flesch EAPS, Purdue University  

NASA Astrophysics Data System (ADS)

The India-Eurasia collision zone is the largest zone of continental deformation on the Earth's surface. A proliferation of geodetic, seismic, and geologic data across the zone provides a unique opportunity for constraining geodynamic models and increasing our understanding of mountain building and plateau growth. We present a 3-D, spherical, Stokes flow, finite volume, geodynamic model of the India-Eurasia collision. Lithospheric volume is constrained by seismic data. Continuous surface velocities, inferred from GPS and Quaternary fault slip data, are used to approximate velocity boundary conditions. We assume a stress-free surface, and free-slip along the model base. Model viscosity varies with depth and is calculated assuming the laterally-varying, depth-averaged viscosities of Flesch et al. (2001) and a cratonic Indian plate. Laterally the model extends from the southern tip of India northward to the Tian Shan, and from the Pamir Mountains eastward to the South China block. Vertically the model volume extends to a depth of 100 km, and is divided into three layers: upper crust, lower crust, and upper-lithospheric mantle. We use COMSOL Multiphysics (www.comsol.com) to investigate the role of vertical viscosity variation on surface deformation by holding the dynamics constant, adjusting the viscosity substructure, and determining the resultant stress and velocity fields. Solved model surface velocities are compared to the observed surface velocities inferred from GPS and Quaternary fault slip rates. A two-layer model employing laterally-variant viscosity estimates throughout the crust and mantle is ineffective at replicating the observed force balance. The weak crustal viscosities necessary for attaining the observed clockwise rotation around the eastern Himalayan syntaxis also result in erroneous southward velocities in southern Tibet, driven by excessive gravitational collapse. Strengthening crustal viscosities balances the boundary/body forces and allows for accommodation of Indian plate motion across Tibet, but no longer produces clockwise rotation around the eastern syntaxis. The best-fit velocity magnitude and rotation solution is achieved by a full three-layer model incorporating an upper crust of intermediate strength, a weaker lower crust, and a stronger upper mantle. Our three-layer model achieves rotation around the indenter without excessive gravitational collapse. Model and observed velocities diverge slightly in the Tarim Basin, the southern Gobi, and the northern South China block. Model velocities in the Tarim Basin are shifted in an easterly direction; possibly indicating a weaker than previously assumed Altyn Tagh fault, while Gobi and South China model velocities are shifted to the north; suggesting the presence of an additional level of complexity.

Bischoff, S. H.; Flesch, L. M.

2013-12-01

207

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

208

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

209

Tectonic framework and extensional pattern of the Malaguide Complex from Sierra Espua (Internal Betic Zone) during Jurassic-Cretaceous: implications for the Westernmost Tethys geodynamic evolution  

NASA Astrophysics Data System (ADS)

Mapping, lithostratigraphic, biostratigraphic and structural detailed analyses in Sierra Espua area (Internal Betic Zone, SE Spain) have allowed us to reconstruct the Jurassic-Cretaceous evolution of the Westernmost Mesomediterranean Microplate palaeomargin and, by correlation with other sectors (Northern Rift, central and western Internal Betic Zone), to propose a geodynamic evolution for the Westernmost Tethys. Extension began from Late Toarcian, when listric normal faults activated; these faults are arranged in three categories: large-scale faults, separating hectometric cortical blocks; main faults, dividing the former blocks into some kilometre-length blocks; and secondary faults, affecting the kilometric blocks. This fault ensemble, actually outcropping, in the Sierra Espua area, broke the palaeomargin allowing the westerly Tethyan Oceanic aperture with an extension at about 17.2%. Extension was not homogeneous in time, being the Late Toarcian to the Dogger-Malm boundary the period when blocks underwent the greatest movement (rifting phase), leading to the drowning of the area (8.2% extension). During the Malm (drifting phase) extension followed (5.7%), while during the Cretaceous a change to pelagic facies is recorded with an extension of about 3.3% ( post-drift stage). This evolution in the Westernmost Tethys seems to be related to areas out of the limit of significant crustal extension in the hanging wall block of the main cortical low-angle fault of the rifting.

Martn-Martn, Manuel; Martn-Rojas, Ivn; Caracuel, Jess E.; Estvez-Rubio, Antonio; Algarra, Agustn Martn; Sandoval, Jos

2006-09-01

210

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

211

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 (Dvoluy 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), Mgabrches de resdimentation, lacunes mcaniques et pseudo- hard-grounds sur la marge vocontienne au Barrmien et l'Aptien infrieur (SE France). Gologie 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. Gol. Fr., 181, p. 565-581.

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

2012-04-01

212

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

213

Geochemistry and zircon U-Pb-Hf isotopes of the granitoids of Baolidao and Halatu plutons in Sonidzuoqi area, Inner Mongolia: Implications for petrogenesis and geodynamic setting  

NASA Astrophysics Data System (ADS)

The Baolidao and Halatu plutons are located in the Northern Orogenic Belt (NOB) in Sonidzuoqi area of Inner Mongolia, which has an important significance for the tectonic evolution of Xing-Meng Orogenic Belt (XMOB). The two plutons have been intensively studied but the conclusions are still controversial. Combined with the previous study, this paper gives new geological data about the two correlative plutons for gaining a better understanding of their petrogenesis and the geodynamic setting. The Baolidao granitoids contain two different series, calc-alkaline series mainly formed in the Ordovician and high K calc-alkaline series mainly formed in the Carboniferous. The Halatu granites are formed in the Triassic and belong to high-K calc-alkaline series. This study got the zircon U-Pb ages of 316-322 Ma for the Baolidao granitoids and 233 2 Ma for the Halatu syenogranites, respectively. In the tectonic discrimination diagrams, they mainly fall into the area of post-orogenic granites (POG). Hf isotopic analyses for the Baolidao granitoids (Sample BLD-1 and 3) shows ?Hf (t) = 3.0-14.0, with two-stage Hf model age (TDM2) of 436-1138 Ma. The Halatu syenogranite (Sample HLT-1) also shows a depleted ?Hf (t) = 3.8-8.2, with TDM2 of 741-1024 Ma, suggesting the major involvement of juvenile crustal components. The various ?Hf values of the Carboniferous Baolidao and Triassic Halatu granitoids indicates a hybrid magma source of juvenile material with old crustal component, and the ?Hf (t) values decrease from the Carboniferous to Triassic, suggesting the increasing proportion of old continental material during this period. Combined with the regional geology, the Carboniferous Baolidao granitoids are possibly not arc rocks, but originated from the post-collisional setting. The Triassic Halatu granites were formed in the subsequently extensional environment.

Hu, Chuansheng; Li, Wenbo; Xu, Cheng; Zhong, Richen; Zhu, Feng

2015-01-01

214

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

NASA Astrophysics Data System (ADS)

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

Mariani, Patrizia; Braitenberg, Carla

2014-05-01

215

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.

Martnez-Loriente, Sara; Sallars, Valent; Grcia, Eullia; Bartolome, Rafael; Daobeitia, Juan Jos; Zitellini, Nevio

2014-01-01

216

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

217

Mafic Rocks of the Bowers Terrane and Along the Wilson-Bowers Terrane Boundary: Implications for a Geodynamic Model of the Ross Orogeny in Northern Victoria Land, Antarctica  

NASA Astrophysics Data System (ADS)

A key area for the construction of a geodynamic model for the Ross Orogeny in northern Victoria Land is the boundary zone between the Wilson and Bowers terranes, along with the Bowers terrane itself. These areas are characterized by the occurrence of an abundance of mafic volcanic and plutonic rocks (locally with variable metamorphic overprint) that is unparalleled in the remainder of the Wilson Terrane. The age of these mafic igneous rocks is not always unequivocally related to the Ross Orogeny. In the Lanterman Range, the Wilson Terrane close to the boundary to the Bowers Terrane is characterized by the occurrence of mafic and ultramafic rocks with a metamorphic grade ranging from amphibolite to greenschist facies, locally including lenses of well preserved medium-temperature eclogites and their variously retrogressed products (Gateway Hills Metamorphic Complex). All these mafic rocks are included within an amphibolite-grade metasedimentary sequence consisting of dominant gneisses and minor quartzites. The age of the mafic protoliths is still poorly constrained. The geochemical affinity is variable from E-MORB throughout T-MORB to orogenic calc-alkaline. A mafic-ultramafic cumulate intrusive complex (Tiger Gabbro) crops out at the SE termination of the Bowers terrane; the age of intrusion is close to 500 Ma. The geochemical affinity is orogenic calc-alkaline. As the Tiger Gabbro is in fault contact with the adjoining rocks of the Bowers Terrane, no constraints exist regarding the original country rock. The Bowers terrane includes formations of mafic volcanic rocks (Glasgow Volcanics) and metamorphosed volcaniclastic sediments (Molar Formation). The age of deposition could be middle-late Cambrian. Geochemical data indicate affinities including N-MORB, E-MORB, T-MORB, arc tholeiite, calc-alkaline and OIB products. Scattered paleontological evidence suggests that volcanism, erosion, and sedimentation of the Bowers mafic rocks occurred within middle-late Cambrian time. If this is the case, the geochemical affinities of the Bowers mafic rocks precludes that this elongated belt simply represented the remnants of a disrupted island arc. Rather, the variety of igneous rocks seems to be more typical of a marginal back arc basin in an extensional setting, associated with a primitive island-arc. The striking similarity of the variety of geochemical signature between Bowers mafic rocks and the protoliths of eclogites and amphibolites suggests that scattered mafic rocks, included within continental material at the border between the Wilson terrane and the arc-back arc (Bowers terrane), could have been subducted/underthrusted at depths in excess of 90 km.

Capponi, G.; Crispini, L.; di Vincenzo, G.; Ghezzo, C.; Meccheri, M.; Palmeri, R.; Rocchi, S.

2003-04-01

218

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

NASA Astrophysics Data System (ADS)

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

Kerrich, R.; Feng, R.

1992-01-01

219

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; Grber, Claudia; Baykiev, Eldar; Zaroli, Christophe

2014-05-01

220

Divergence between Antarctic and South American marine invertebrates: What molecular biology tells us about Scotia Arc geodynamics and the intensification of the Antarctic Circumpolar Current  

NASA Astrophysics Data System (ADS)

Continental drift processes such as major gateway openings have been historically advocated to explain the distribution of marine benthic taxa in the Southern Ocean (SO). The separation between Antarctic Peninsula and the southern tip of South America together with the onset of the Antarctic Circumpolar Current (ACC) represent the final step for the complete isolation of the Antarctic region. However, there is still controversy concerning the timing and mode of this process, and especially about the role of the Scotia Arc geodynamics in the development of a fully deep and intensified ACC circulation. Based on mitochondrial Cytochrome c Oxidase Subunit I (COI) sequences obtained from different taxa, we performed molecular comparisons between Antarctic and South American relatives to provide independent time estimations of Antarctica's isolation. We include in the analyses congeneric Antarctic and Patagonian near-shore marine benthic invertebrates including indirect developers (Nacella, Yoldia, Sterechinus, and Parbolasia) and brooders (Xymenopsis and Trophonella). Considering the levels of genetic differentiation between relatives from both regions and assuming the molecular clock hypothesis, we estimated the onset of their respective divergence. On one hand, similar levels of genetic distance in broadcast-spawners (7%-8.3%) support the hypothesis that the development of an effective barrier between Antarctica and South America occurred almost simultaneously for these groups. Divergence time estimations based on specific substitution rates indicate that the separation occurred near the Mio-Pliocene transition, long after the physical separation of both continents. Genetic distance and divergence time estimation in direct developers indicate an older separation time, close to the mid-Miocene. Even when the analyzed groups included both broadcast-spawners and brooder organisms, the divergence between Antarctic and South America lineages rather than being related to processes of continental drift, seems to be associated more to major changes in the Southern Ocean such as the evolution of the Scotia Arc and the deepening of the Drake Passage. Accordingly, these results support a genetic continuity between Antarctica and South America, probably along the Scotia Ridge, until the middle Miocene and a late ACC intensification at the Mio-Pliocene boundary.

Poulin, Elie; Gonzlez-Wevar, Claudio; Daz, Angie; Grard, Karin; Hne, Mathias

2014-12-01

221

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

NASA Astrophysics Data System (ADS)

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

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

2011-04-01

222

The Urumieh Plutonic Complex (NW Iran): Record of the geodynamic evolution of the Sanandaj-Sirjan zone during Cretaceous times - Part II: Magnetic fabrics and plate tectonic reconstruction  

NASA Astrophysics Data System (ADS)

The Urumieh complex, to the north of the Sanandaj-Sirjan zone (NW Iran), belongs to a plutonic arc that took place above the northeastward dipping subduction of Arabia under Iran during Late Cretaceous times. Seven granitoid bodies occupying an area of 300 km 2 can be sorted into three suites. According to the isotope chronology study of Ghalamghash et al. [Ghalamghash, J., Ndlec, A., Bellon, H., Vousoughi-Abedini, M., Bouchez, J.L., in press. The Urumieh Plutonic Complex: a magmatic record of the geodynamic evolution of the Sanandaj-Sirjan zone (NW Iran) during Cretaceous times - Part II: petrogenesis and 40K/40Ar dating. Journal of Asian Earth Sciences], the two first suites were emplaced during the same event at 100 Ma, and the third one was emplaced 20 Ma later: (1) the diorites form the largest bodies and comprise the Ghamishlu and Dourbeh stocks; (2) the biotite-granites are composed by the Sehkani, Nari and Doustak bodies, and (3) the younger bodies are represented by the Bardkish syenite and the Dourbeh granite. These bodies were subjected to systematic microstructural observations, and magnetic fabric measurements that yield information about their emplacement kinematics. The magnetic lineations of the diorites and biotite-granites (the early suites) call for a dominant NW-trending stretching during their intrusion, attributed to the transpressive deformation of the overriding Sanandaj-Sirjan microplate during the north-to northeastward motion of the subducting western branch of the Neo-Tethys. Oblique plate motion with 20% of strain partitioning along a NNW-trending plate boundary accounts for the observed magmatic structures. Intrusion of the younger bodies took place after consumption of this western oceanic domain at about 80 Ma. The NW-trending lineations of the syenite suggest that the transpressive regime was continuing, while the steep lineations and the peculiar microstructures of the Dourbeh granite call for a forceful intrusion. Our study suggests that the motion of Arabia with respect to Central Iran was more northerly directed than estimated before, for the 100-80 Ma time interval during which plate tectonic markers are not available.

Ghalamghash, J.; Bouchez, J. L.; Vosoughi-Abedini, M.; Ndlec, A.

2009-10-01

223

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

224

Geodynamic models of deep subduction  

NASA Astrophysics Data System (ADS)

Numerical and laboratory models that highlight the mechanisms leading to a complex morphology of subducted lithospheric slabs in the mantle transition zone are reviewed. An increase of intrinsic density with depth, an increase of viscosity, or phase transitions with negative Clapeyron slope have an inhibiting influence on deep subduction. The impingement of slabs on a viscosity and density interface has been studied in laboratory tanks using corn syrup. Slab interaction with equilibrium and non-equilibrium phase transitions has been modelled numerically in two dimensions. Both the laboratory and the numerical experiments can reproduce the variety of slab behaviour that is found in tomographic images of subduction zones, including cases of straight penetration into the lower mantle, flattening at the 660-km discontinuity, folding and thickening of slabs, and sinking of slabs into the lower mantle at the endpoint of a flat-lying segment. Aside from the material and phase transition properties, the tectonic conditions play an important role. In particular, the retrograde motion of the point of subduction (trench-rollback) has an influence on slab penetration into the lower mantle. A question that still needs to be clarified is the mutual interaction between plate kinematics and the subduction process through the transition zone.

Christensen, Ulrich

2001-12-01

225

Mesozoic units in SE Rhodope (Bulgaria): new structural and petrologic data and geodynamic implications for the Early Jurassic to Mid-Cretaceous evolution of the Vardar ocean basin  

NASA Astrophysics Data System (ADS)

In the southeastern Rhodope, both in southern Bulgaria and northern Greece, Mesozoic low-grade to non-metamorphic units, together with similar units in the eastern Vardar zone, were designated as the Circum-Rhodope Belt (CRB) that fringes the Rhodope high-grade metamorphic complex. In the Bulgarian southeastern Rhodope, Mesozoic units show a complicated tectono-stratigraphy underlaid by amphibolite-facies basement units. The basement sequence includes a lower orthogneiss unit with eclogite and meta-ophiolite lenses overlain by an upper marble-schist unit, presumably along a SSW-directed detachment fault as indicated by shear sense indicators. The Mesozoic sequence starts with greenschist units at the base, overlaying the basement along the tectonic contact. Mineral assemblages such as actinolite-chlorite-white mica garnet in schists and phyllites indicate medium greenschist facies metamorphism. Kinematic indicators in the same unit demonstrate a top-to-the NNW and NNE shear deformation coeval with metamorphism, subparallel to NW-SE to NE-SW trending mineral elongation lineation and axis of NW vergent small-scale folds. The greenschist unit is overlain by tectonic or depositional contact of melange-like unit that consists of diabases with Lower Jurassic radiolarian chert interlayers, Upper Permian siliciclastics and Middle-Upper Triassic limestones found as blocks in olistostromic member, embedded in Jurassic-Lower Cretaceous turbiditic matrix. The uppermost sedimentary-volcanogenic unit is represented by andesito-basalt lavas and gabbro-diorites, interbedded with terrigeneous-marl and tufaceous sediments that yield Upper Cretaceous (Campanian) fossils, related to the Late Cretaceous back-arc magmatic activity to the north in Sredna Gora zone. Petrologic and geochemical data indicates sub-alkaline and tholeiitic character of the greenschists and ophiolitic basaltic lavas, and the latter are classified as low-K and very low-Ti basalts with some boninitic affinity. Immobile trace element discrimination of both rock types constrains the volcanic (oceanic)-arc origin. They generally show low total REE concentrations (LREE>HREE) with enrichment of LIL elements relative to the HFS elements, and also very low Nb and relatively high Ce content consistent with an island-arc tectonic setting. We consider that the Meliata-Maliac ocean northern passive margin could be the source provenance for the Upper Permian clastics and Middle-Upper Triassic limestone blocks within the olistostromic melange-like unit, whereas turbidites and magmatic blocks may originate in an island arc-accretionary complex that relates to the southward subduction of the Maliac ocean under the supra-subduction back-arc Vardar ocean/island arc system. These new structural and petrologic data allow to precise the tectonic setting of the Mesozoic units and their geodynamic context in the frame of the Early Jurassic to Late Cretaceous evolution of the Vardar ocean.

Bonev, N.; Stampfli, G.

2003-04-01

226

Geochemistry of anorthositic differentiated sills in the Archean (~ 2970 Ma) Fiskensset Complex, SW Greenland: Implications for parental magma compositions, geodynamic setting, and secular heat flow in arcs  

NASA Astrophysics Data System (ADS)

The Fiskensset Complex, SW Greenland, is one of the best preserved layered Archean intrusions in the world, consisting of an association of ca. 550-meter-thick anorthosite, leucogabbro, gabbro, and ultramafic rocks (dunite, peridotite, pyroxenite, and hornblendite). Despite poly-phase deformation and amphibolite to granulite facies metamorphism, primary cumulate textures and igneous layering are well-preserved in the complex. This study reports new major and trace element data for three variably thick (1 to 5 m) differentiated (dunite, through peridotite, pyroxenite, gabbro leucogabbro, to anorthosite) sequences (Sequences 1, 2 and 3) in the Sinarssuk area of the Fiskensset region. On several variation diagrams, samples from these sequences plot along a well-defined liquid line of descent, consistent with in situ fractional crystallization. The average chemical compositions of these sequences are used to constrain their approximate parental magma compositions. Petrographic observations and geochemical data suggest that Sequences 2 and 3 solidified from evolved magmas that underwent olivine fractionation prior to their intrusion. In contrast, Sequence 1 appears to have been derived from a near-primary parental magma (SiO 2 = 43 wt.%, MgO = 20 wt.%, Al 2O 3 = 16 wt.%, CaO = 9.3 wt.%, Ni = 840 ppm, Mg-number = 80). The trace element patterns of this parental magma are comparable to those of Phanerozoic boninites, consistent with a supra-subduction zone geodynamic setting. If the relative thickness of ultramafic layers, the sum of dunite, peridotite and pyroxenite layers, in differentiated sequences is taken as an analog for the original complex emplaced into Archean oceanic crust, the Fiskensset Complex might have had a minimum thickness of 1000 m, with a 500 m thick ultramafic unit at the bottom. The thickness of the ultramafic unit in the preserved complex is less than 50 m, suggesting that more than 90% of the original ultramafic unit was either delaminated and recycled back into the mantle as a residual cumulate, or was destroyed during thrusting and TTG intrusion. Both the Fiskensset Complex and associated tholeiitic basalts display similar Th-Nb-LREE patterns and plot along the same differentiation trend on Zr versus incompatible trace element diagrams, suggesting a possible petrogenetic link between the two suites of rocks. However, basalts do not display the same differentiation trend as the complex on several major and trace element diagrams. In addition, basalts and parental magma to the complex do not plot along the same fractionation line on Al 2O 3/TiO 2 versus incompatible trace element diagrams, implying that the Fiskensset layered intrusive rocks were not derived from tholeiitic basalts through fractional crystallization, as previously thought. Accordingly, we infer that the Fiskensset Complex and spatially associated basalts were derived from different mantle sources. Parental magmas to the Fiskensset Complex originated from a mantle source that was metasomatized by highly aluminous slab-derived melts. Layered anorthosite complexes are mostly restricted to the Archean and typically associated with tonalite-trondhjemite-granodiorite (TTG) gneisses. The petrogenesis of both suites appears to have been controlled mainly by slab melting, endorsing independent evidence for a secular change from slab-dominated melting to wedge-dominated melting in arc magmatism at the end of the Archean, reflecting higher geothermal gradients in Archean arcs than post-Archean counterparts.

Polat, Ali; Fryer, Brian J.; Appel, Peter W. U.; Kalvig, Per; Kerrich, Robert; Dilek, Yildirim; Yang, Zhaoping

2011-04-01

227

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

228

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 Cheraa 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 16.960.09 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; Herv, Bellon; Ren, Maury; Olivier, Bruguier

2014-05-01

229

Petrogenesis and U-Pb zircon chronology of felsic tuffs interbedded with turbidites (Eastern Pontides Orogenic Belt, NE Turkey): Implications for Mesozoic geodynamic evolution of the eastern Mediterranean region and accumulation rates of turbidite sequences  

NASA Astrophysics Data System (ADS)

The Meso-Cenozoic geodynamic evolution of the Eastern Pontides Orogenic Belt, which is one of the key areas of the Alpine-Himalayan system, is still controversial due to lack of systematic geological, geophysical, geochemical and chronological data. The prevailing interpretation is that this belt represents the southern margin of Eurasia during the Mesozoic and its geodynamic evolution is related to northward subduction of oceanic lithosphere. This paper reports the first detailed geological, geochemical and chronological data from felsic tuffs interbedded with late Cretaceous turbidites in the Southern Zone of the Eastern Pontides Orogenic Belt. Individual tuff layers are thin, mostly < 2 m in thickness, implying that these are dominantly air-fall tuffs. Petrographic data indicate that the felsic tuffs, which exhibit various degrees of alteration, can be classified as crystal-rich and crystal-poor tuffs. The crystal-poor tuffs consist mainly of 45-65% devitrified glass shards and 10-20% broken quartz crystals, whereas the crystal-rich tuffs consist of > 50% crystals. The zircon U-Pb data show three statistically distinct ages at 84, 81 and 77 Ma, with uncertainties of about 1 Ma, suggesting that tuff-forming late Cretaceous magmatism started about 84 Ma ago and was episodically active over a minimum of 7 Ma. The age data also indicate that the average accumulation rate of the turbiditic sequence that hosts the felsic tuffs remained constant between 36 and 40 cm/10 ky. Their enrichment in LIL and LRE elements relative to HFS and HRE elements, and also strongly negative Nb, Ta and Ti anomalies, are consistent with those of magmas generated by subduction-related processes. The tuffs have relatively low initial ratios of 143Nd/144Nd (0.512296-0.512484; ?Nd: - 2.1 and - 7.2) and 87Sr/86Sr (0.704896-0.706159). Their initial Pb isotopic compositions range from 18.604 to 18.646 for 206Pb/204Pb, from 15.644 to 15.654 for 207Pb/206Pb and from 38.712 to 38.763 for 208Pb/204Pb. The distribution of Sr-Nd isotopic compositions in the late Cretaceous igneous rocks from different locations of the Eastern Pontides Orogenic Belt is consistent with two-component mixing between depleted mantle and crust. However, the Pb isotopic data are not compatible with two-component mixing and require at least a third component. Considering all of the new data and also previous data such as southward migration and increasing potassium content of the late Cretaceous arc volcanism, the northward migration of Cenozoic igneous activity, northward drift of the belt since the late Cretaceous and the existence of south-dipping reverse fault systems in the whole region, the Meso-Cenozoic geodynamic evolution of the Eastern Pontides Orogenic Belt can be best explained by southward subduction of Tethys oceanic lithosphere, rather than northward subduction.

Eyuboglu, Yener

2015-01-01

230

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

231

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 8E  

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 Cheraa. 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 Chetabi-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

232

New geochronological ages (U-Pb/Lu-Hf) from high-pressure rocks of the Escambray terrane and Santa Clara serpentinite mlange, central Cuba. Regional correlations and geodynamic implications  

NASA Astrophysics Data System (ADS)

Petrological and geochronological data of high pressure (HP) rocks from Cuba and Dominican Republic indicate continuous subduction in the northern edge of the Caribbean since ca. 120 Ma. However, expected correlation of the associated subduction zone towards the west in Guatemala is uncertain, for similar HP rocks in this region have metamorphic ages as old as 150 Ma. In this contribution we present new geochemical and U-Pb/Lu-Hf ages of HP rocks from the Escambray terrane and the central Cuba serpentinite mlange that allow geodynamic correlations between the Greater Antilles and Guatemala during the early and late Cretaceous. The Escambray composite terrane constitutes a metamorphic accretionary complex containing oceanic and platform-derived metasedimentary and metaigneous rocks that were tectonically assembled in the Caribbean subduction environment during the latest Cretaceous. The complex crops out as two domes, named Trinidad to the west and Sancti Spiritus to the east, forming a tectonic window below the arc-related Mabujina amphibolite complex and the allochthonous Cretaceous volcanic arc terrane. The latter overrides the central Cuba mlange, which contains low-pressure ophiolitic blocks and HP blocks of eclogite, garnet amphibolite and blueschist facies rocks within a serpentinitic matrix. This serpentinite mlange and similar melange bodies within the Escambray complex have been interpreted as fragments of the Caribbean subduction channel. The studied HP samples are of basaltic composition, poor in K2O (<0.34 wt %) and Rb (< 3.05 ppm), relatively rich in Ta (0.07-0.77 ppm) and Hf (0.74-4.17 ppm), and rich in Nb (0.68- 13.53 ppm). Most samples show a REE chondrite-normalised patterns characterized by a subtle LREE depletion, except a few samples which are characterized by slight enrichment in LREE. Based on their distinctive trace-element contents, most of the basaltic protholiths of the samples are identified as E- to N-MORB signature. Some samples of the Escambray complex show, however, enrichment in alkali and LIL elements, suggesting a) a passive continental margin origin of the protoliths or b) contamination of (altered) MOR-derived rocks by fluids in the subduction environment. A single zircon U-Pb age of 131.11.3 Ma for a block of garnet amphibolite from a sliver of oceanic serpentinite mlange from the Gavilanes unit (Trinidad Dome, Escambray terrane) is interpreted as reflecting the time of basaltic protolith crystallization or the time of HP metamorphism. The last interpretation, though still uncertain, is supported by a new garnet Lu-Hf age of 126,04 0.54 Ma for a block of eclogite from the central Cuba serpentinite mlange. SHRIMP analyses of single-grain zircons from two eclogite samples from the Gavilanes unit on the Cipiabo River (Sancti Spiritus dome, Escambray terrane) show a broad spectrum of ages between 172 Ma and 2.4 Ga. We interpret the occurrence of Middle Jurassic to Paleoproterozoic zircons in these eclogites as inherited, suggesting crustal contamination of the basaltic protoliths. A new garnet Lu-Hf age of 70,3 1.1 Ma for an eclogite on the Higuanojo River (Sancti Spiritus dome) agrees with most geochronological data from the Escambray terrane obtained so far. These data, combined with previously published age data of HP and low pressure (MOR- and arc-related) rocks, indicate continuous subduction in the Cuban branch of the northern leading edge of the Caribbean plate since ca. 130 Ma until, at least, 70 Ma and corroborate the interpretation that the onset of terrane(Caribeana)-trench collision took place during the latest Cretaceous, in agreement with geodynamic models for the region. The data also allow correlating paleosubduction zones of the Antilles and Guatemala in the same period, for ages of high pressure rocks from the Motagua valley serpentinite mlanges, the Chuacs complex, and the basement of the Maya block range 150-70 Ma.

Rojas-Agramonte, Y.; Garca-Casco, A.; Krner, A.; Herwartz, D.; Ibis Despaigne, A.; Wilde, S.

2012-04-01

233

Seimic Images and Wide-angle Velocity constrains of the structure and geodynamic origin of the Gibraltar Arc system: A geological interpretation of the Gulf of Cadiz imbricated wedge, the western and eastern Alboran basins, and the South-Balearic basin.  

NASA Astrophysics Data System (ADS)

The current geodynamics of the region between north Africa and the Iberian Peninsula are dominated by the collision between the Eurasian and African plates. The ongoing deformation is mainly driven by the NW-SE, slow 4-5 mm/yr convergence that is partitioned across numerous faults and diffused through a broad region with no clear plate boundary defined. However, this region is characterized by the a series of geological structures that appear unrelated to the current dominant plate kinematics. The region is formed by the Gibraltar Arc system, an arcuate structure that is fronted by a large imbricated wedge of tectonically piled sediment slices in the Gulf of Cadiz, and a series of basins in the Mediterranean part of the region. The western, little deformed Alboran basin is located on the rear of the Gibraltar stacked units. The eastern Alboran basin is characterized by numerous volcanic ridges and is transitional to the South Balearic - North Algerian basin that displays a generally lower topography. The different tectonic elements are floored by a poorly known crystalline basement and their age, evolution and geodynamic origin is still strongly debated. Part of the uncertainty arises from the lack of deep penetrating modern geophysical data in much of the region. In the last 5 years, 3 successive cruise in the region have produced an extensive coverage of the different tectonic elements collection a series of wide angle seismic profiles in 2006 during the WestMed cruise with German R/V Meteor and two multichannel seismic reflection cruises with the R/V Sarmiento de Gamboa from mid September to late October (TopoMed-Gassis cruise) and late October to late November (Geomargen-1 cruise) 2011. In this contribution we present the new images of the tectonic structures and sedimentary basin and the wide-angle seismic velocity models across key regions of the system. We also present an interpretation of the entire system in the context of a geodynamic model of eastward Miocene subduction, currently inactive, that may explain the structures observed in the data from the 3 cruises.

Gracia, E.; Ranero, C. R.; Grevemeryer, I.; WestMed, TopoMed, , T. h. e.; cruise parties, Geomargen-1

2012-04-01

234

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

235

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

236

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

237

Geodynamics: A tale of a trail  

NASA Astrophysics Data System (ADS)

A mantle plume origin for the Samoan hotspot has been contested because the ages along its putative trail did not seem to increase monotonically. New dates from the island of Savai'i resolve the controversy and favour a plume origin.

Gordon, Richard G.

2008-09-01

238

Geodynamics: How plumes help to break plates  

NASA Astrophysics Data System (ADS)

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

Buiter, Susanne

2014-09-01

239

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

240

12.520 Geodynamics, Fall 2004  

E-print Network

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

Hager, Bradford H.

241

12.520 Geodynamics, Fall 2005  

E-print Network

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

Hager, Bradford H.

242

Projection for Space Geodynamics, 1988-1998  

NASA Technical Reports Server (NTRS)

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

1984-01-01

243

CONSTRAINTS ON SUBDUCTION GEODYNAMICS FROM SEISMIC ANISOTROPY  

E-print Network

planet's interior. Subducting slabs represent the main driving mechanism for plate motion and also represent prime sites for natural hazards such as earthquakes, volcanoes, and tsunamis seismic anisotropy. (In contrast, inferences on mantle dynamics from other observations can be somewhat

244

Geodynamic evolution of the SW Europe Variscides  

Microsoft Academic Search

The early evolution of SW Europe Variscides started by opening of the Rheic ocean at ~500 Ma, splitting Avalonia from Armorica\\/Iberia. Subduction on the SE side of Rheic generated the Paleotethys back-arc basin (430-390 Ma, splitting Armorica from Iberia), with development of Porto-Tomar-Ferreira do Alentejo (PTFA) dextral transform defining the boundary between continental Armorica and Finisterra microplate to the W.

Antnio Ribeiro; Jos Munh; Rui Dias; Antnio Mateus; Eurico Pereira; Lusa Ribeiro; Paulo Fonseca; Alexandre Arajo; Toms Oliveira; Jos Romo; Hlder Chamin; Carlos Coke; Jorge Pedro

2007-01-01

245

Geodynamic Information in Peridotite CLAUDE HERZBERG*  

E-print Network

in kimberlite. Some of these differences reflect variable temperature and pressure conditions of melt extraction's mantle occur as xenoliths in kimberlite and alkali basalt, tectonic crustal emplacements (i.e. Alpine

246

On the geodynamic setting of kimberlite genesis  

NASA Technical Reports Server (NTRS)

The emplacement of kimberlites in the North American and African continents since the early Palaeozoic appears to have occurred during periods of relatively slow motion of these continents. The distribution of kimberlites in time may reflect the global pattern of convection, which forces individual plates to move faster or slower at different times. Two-dimensional numerical experiments on a convecting layer with a moving upper boundary show two different regimes: in the first, when the upper boundary velocity is high, heat is transferred by the large-scale circulation and in the second, when the upper boundary velocity is lower, heat is predominantly transferred by thermal plumes rising from the lower boundary layer. For a reasonable mantle solidus, this second regime can give rise to partial melting beneath the moving plate, far from the plate boundaries. The transition between these modes takes place over a small range of plate velocities; for a Rayleigh number of 1,000,000 it occurs around 20 mm/yr. It is suggested that the generation of kimberlite magmas may result from thermal plumes incident on the base of a slowly moving plate.

England, P.; Houseman, G.

1984-01-01

247

Magmatism and Geodynamics of Eastern Turkey  

NASA Astrophysics Data System (ADS)

Eastern Turkey has been an active collision zone for the last 15 My between the Arabian Plate and Eurasian continent. The collision initiated after the closure of the southern branch of the Neotethys Ocean by northward subduction beneath E Anatolia at ~15 Ma. The collision-related volcanism started immediately after the closure of the ocean (again at around 15 Ma) in the north of the present day Lake Van with the eruption of mostly intermediate to acid lavas displaying distinct subduction characteristics. Both continental collision and the magmatism are still active, because the Arabian plate still converges to Anatolia with a velocity of ~2.5 cm/y. The overriding Anatolian block experienced a major uplift event around 10 Ma. The region once resided below the sea level merged as a widespread plateau ~2 km above the sea level as part of a regional dome structure with ~1000 km diameter, extending from Central Anatolia in the West to Azerbaijan in the East. The first alkaline lavas derived from a relatively more enriched source erupted to the surface in the N of Lake Van coeval with the initiation of the uplift at around 10 Ma. The underthrusting Arabian platform, on the other hand, was deformed as a result of both crustal-scale east-west folds adjacent to the major thrust zone and extensional deformations perpendicular to the suture zone. Alkaline within-plate lavas with no subduction component erupted through these extension zones. This intraplate volcanism focused on the Karacada? volcanic complex that covers an area of ~10,000 km2. Early Stage volcanism of Karacada? was dominated by magmas derived from a shallower metasomatized (litospheric) mantle source, while magmas of the later stages were derived from deeper (asthenospheric) sources. The Karacada? volcanic area of SE Anatolia was sourced by a garnet bearing, deep asthenospheric mantle which is similar to that of Afar in terms of its Pb isotopic ratios. This brings into question whether the mantle material from the Afar plume reached beneath Eastern Anatolian by a mantle convection cell. We argue that both the uplift and the widespread volcanism across the region share a common reason: a major "slab-steepening and breakoff event beneath the large Eastern Anatolian Accretionary Complex". We argue that the older intermediate calc-alkaline volcanic products displaying a distinct subduction signature were possibly derived from the mantle wedge that opened out due to the steepening of the slab after the continental collision. Being unsupported by the subduction, the slab started to be steepened beneath the region, possibly resulting in widening, invasion and upwelling of the mantle wedge beneath E Anatolian accretionary complex. This possibly created a sucking effect on the asthenosphere, creating a mantle flow from the Pontides in the north to the south. The inferred asthenospheric flow perhaps pulled a portion of the asthenosphere that once had resided beneath the Pontide arc. Therefore, the subduction component was inherited from the previous Pontide arc magmatism. The widespread decompressional melting generated voluminous magmas with the aforementioned inherited subduction signature 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 asthenospheric mantle with no subduction component beneath the Arabian continent to flow to the north through a slab-window. As a result, the subduction-modified E Anatolian and the enriched Arabian asthenospheric mantles started to mix into each other. We interpret the eruption of the first alkaline lavas in the region at around 10 Ma (e.g. tephrites and alkaline basalts in the N of Lake Van) as the indication of the formation of the slab-window beneath the region due to tearing of the slab. The volcanism in the collision zone continued till the historical times. The region includes some of the largest volcanic centers (e.g. Ararat, Nemrut, Tendrek and Sphan volcanoes) and plateaus (e.g. The Erzurum-Kars Plateau) around the Mediterranean

Keskin, Mehmet; Oyan, Vural; Sharkov, Evgenii V.; Chugaev, Andrey V.; Gen, ?. Can; nal, Esin; Aysal, Nam?k; Duru, Olgun; Kavak, Orhan

2013-04-01

248

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

249

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

250

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

251

Geodynamic simulations using the fast multipole boundary element method  

NASA Astrophysics Data System (ADS)

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

Drombosky, Tyler W.

252

Anisotropic measurements in South Korea and geodynamic implications  

NASA Astrophysics Data System (ADS)

Seismic anisotropy beneath the southern Korean Peninsula was investigated. The most striking feature of the observed splitting patterns is the preference of the fast directions (NW-SE) that are nearly parallel to the direction of the absolute plate motion in the region. However, the splitting patterns over the region show significant variation in splitting parameters indicating a complex anisotropic structure. Variations of the splitting directions and dissimilarity in the source domains of basaltic volcanisms suggest that the asthenospheric mantle flow since at least the late Cenozoic cannot explain the seismic anisotropy beneath the region. Comparison to shear-wave splitting measurements from eastern China revealed that the NW-SE fast direction of splitting measurements in the the southern Korean Peninsula is close to that in the North China Block while the NE-SW fast direction might be related to that in the South China Block. The shallow mantle lithosphere beneath the southern Korean Peninsula retains the fossil anisotropy amalgamated prior to the late Paleozoic before the collision between the North China Block and South China Block, and the anisotropic structure was not completely realigned by the major orogenic events during the late Paleozoic to Mesozoic eras.

Kang, Tae-Seob

2010-05-01

253

Plume capture by a migrating ridge: Analog geodynamic experiments  

NASA Astrophysics Data System (ADS)

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

Mendez, J. S.; Hall, P.

2010-12-01

254

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

255

Phanerozoic growth of Asia: Geodynamic processes and evolution  

NASA Astrophysics Data System (ADS)

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

Pubellier, Manuel; Meresse, Florian

2013-08-01

256

Seismic anisotropy surrounding South China Sea and its geodynamic implications  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

257

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

258

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

259

Archean Geodynamics and Environments Geophysical Monograph Series 164  

E-print Network

that roughly offsets the craton's negative thermal buoyancy associated with its cooler thermal state are discussed: (1) high-degree melting in a very hot plume head with a potential temperature >1650°C, (2) accretion of oceanic lithosphere, and (3) accretion of arc lithosphere. The hot plume scenario predicts

Lee, Cin-Ty Aeolus

260

Seismicity of oceanic and continental riftsa geodynamic approach  

Microsoft Academic Search

Two major kinds of divergent structuresoceanic and intracontinental riftswere compared in principal seismic and tectonic characteristics. First, the role of main components of the mid-oceanic ridges (MOR) was estimated for the whole Earth. We considered two levels of the MOR segmentation. The first-order structures are the segments of MOR between triple junctions and the second-order structures are a transform faults

P. O. Sobolev; D. V. Rundquist

1999-01-01

261

The geodynamic reasons of decade changes of climate  

NASA Astrophysics Data System (ADS)

An analysis of meteorological observations and the spectral analysis of the daily air temperature anomalies have shown that the hot summers and the severe winters caused by the beats (slow periodic variations in the resulting amplitude) of the interacting temperature oscillations with close frequencies. The 35-year basic period of beats in the temperature and other hydrometeorological characteristics takes place due to the interference between their oscillations with periods of solar (365 days) and lunar (355 days) years. In 2010 over European Russia, the phases of the "solar" annual oscillations of hydrometeorological characteristics coincided with those of their basic "lunar" oscillations. As a result, the amplitudes of these oscillations added up and reached extreme values. Time series of the amount of sunshine are analyzed. It is shown that cycle with characteristic time about 35 years and quasi four-year fluctuations of the large amplitude manifest themselves in changes in cloud amount and the amount of sunshine. The revealed cycles are generated by lunisolar tides. The quasi 35-year changes of the cloud amount lead to fluctuations of the radiating balance. The amplitude of these fluctuations increases with the growth of latitude and becomes especially high in polar areas where the day (summer) and the night (winter) can last half a year. Big fluctuations of the thermal regime of polar areas generate radical disturbances of the interhemisphere circulation that lead to greater anomalies of the exchange of the air masses, heat, water vapour and pollution between the northern and southern hemispheres. These processes are responsible for the epochs of the atmospheric circulation, the decade variations in the intensity of the Indian monsoon, changes of the ice masses in Antarctica and Greenland that lead to the decade variations in the parameters of the Earth's rotation.

Sidorenkov, N. S.

2012-11-01

262

Geodynamics of Africa from continuous GPS data: analyses and implications  

NASA Astrophysics Data System (ADS)

The advent of space-geodetic techniques has dramatically improved the estimation of present-day plate motions: the velocity of discrete points on the Earth's surface can currently be obtained at sub-centimetre level in the ITRF2000 global reference frame, using a multitude of systems amongst which GPS (Global Positioning System) is prominent. Although the distribution of the reference GPS stations globally has a biased concentration towards Europe and North America, a significant number of stations have been installed during the last few years in areas previously void of stations that meet IGS (International GPS Service) quality requirements. In Africa, the number of continuous stations has increased significantly in the last two to three years, in particular due to the efforts of the Hartebeesthoek Radio Astronomy Observatory (HartRAO) in collaboration with the Jet Propulsion Laboratory (JPL). Daily processing of a network of continuous GPS stations commenced during 2002 in the framework of a research program dedicated to Africa. Although most of the stations are part of the IGS network, stations managed by the groups that are collaborating in this project are also included. For the entire network, all available data have been processed since 1996 (at the time, just three sites). Currently, this network contains nearly 30 stations located on Africa and surrounding continents. The solutions processed by the Delft Institute for Earth-Oriented Space Research (DEOS) are compared with the solutions produced by HartRAO for a similar network. This allows a direct evaluation of the reliability of both solutions that are estimated using different software packages (GIPSY and GAMIT) and different strategies to obtain solutions in ITRF2000. This aspect is investigated considering the disadvantages brought about by the continental scale of the networks and the sparse and non-uniform distribution of reference stations in the region. Finally, the derived velocity field is discussed in the frame of the tectonic settings of Africa. The implications on the relative motions, with respect to other plates, are discussed in detail using a global plate model developed using the entire ITRF2000 data set updated with the Africa GPS network solutions. Although data are limited for the Somalia region, the division of the African plate in two blocks: Nubia and Somalia, is also debated in detail.

Fernandes, R. M. S.; Combrinck, L.; Ambrosius, B. A. C.; Noomen, R.; Bastos, L.; Spakman, W.; Sucure, J.

2003-04-01

263

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

264

On the geodynamics of the Aegean rift Samuele Agostini a,  

E-print Network

,a , Piero Manetti a,d , Sonia Tonarini a a Istituto di Geoscienze e Georisorse-CNR, Pisa, Italy b the extension with the westward extrusion of the Anatolia plate (e.g. McKenzie, 1972; McClusky et al., 2000

Doglioni, Carlo

265

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

266

Tertiary geodynamical evolution of northwestern Greece: paleomagnetic results  

Microsoft Academic Search

Paleomagnetic results have been obtained from 29 sites sampled in Lower to Upper Oligocene flysch sections of the Ionian Zone in northwestern Greece. They indicate a clockwise rotation of about 45 of the entire region. A comparison with previously published results relative to both younger and older formations shows that this rotation has occurred in two phases of comparable amplitude,

Catherine Kissel; Carlo Laj; Carla Mller

1985-01-01

267

On the geodynamics of the northern Adriatic plate  

Microsoft Academic Search

The northern Adriatic plate underwent Permian-Mesozoic rifting and was later shortened by three orogenic belts (i.e., Apennines,\\u000a Alps and Dinarides) developed along three independent subduction zones. The inherited Mesozoic horst and graben grain determined\\u000a structural undulations of the three thrust belts. Salients developed in grabens or more shaly basins, whereas recesses formed\\u000a regularly around horsts. A new interpretation of seismic

Marco Cuffaro; Federica Riguzzi; Davide Scrocca; Fabrizio Antonioli; Eugenio Carminati; Michele Livani; Carlo Doglioni

2010-01-01

268

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

269

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

PubMed

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 approximately 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. PMID:18483402

Phillips, Roger J; Zuber, Maria T; Smrekar, Suzanne E; Mellon, Michael T; Head, James W; Tanaka, Kenneth L; Putzig, Nathaniel E; Milkovich, Sarah M; Campbell, Bruce A; Plaut, Jeffrey J; Safaeinili, Ali; Seu, Roberto; Biccari, Daniela; Carter, Lynn M; Picardi, Giovanni; Orosei, Roberto; Mohit, P Surdas; Heggy, Essam; Zurek, Richard W; Egan, Anthony F; Giacomoni, Emanuele; Russo, Federica; Cutigni, Marco; Pettinelli, Elena; Holt, John W; Leuschen, Carl J; Marinangeli, Lucia

2008-05-30

270

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

E-print Network

perovskite ·Cation-exchange coupling: --garnet; -pv-mw-gt ·Temperature-dependent transitions: (Mg,Fe)2SiO4 properties, survive the statistical averaging associated with a transition to a macroscopic description ­ they are electric dipole moments, magnetic dipole moments, various multipole moments, and the like. The study

Cerveny, Vlastislav

271

Plume capture by a migrating ridge: Analog geodynamic experiments  

Microsoft Academic Search

Paleomagnetic data from the Hawaii-Emperor Seamount Chain (HESC) suggests that the Hawaiian hotspot moved rapidly (~40 mm\\/yr) between 81 - 47 Ma but has remained relatively stationary since that time. This implies that the iconic bend in the HESC may in fact reflect the transition from a period of rapid hotspot motion to a stationary state, rather than a change

J. S. Mendez; P. Hall

2010-01-01

272

The Role of Carbon in Extrasolar Planetary Geodynamics and Habitability  

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

273

35. DIORITIC BASEMENT, SITE 493: PETROLOGY, GEOCHEMISTRY, AND GEODYNAMICS1  

Microsoft Academic Search

At Site 493, DSDP Leg 66, dioritic basement was reached below lower Miocene (NN1 Zone, 22-24 Ma) terrigenous sediments. Petrographical, mineralogical (including microprobe analyses), and chemical features of the dioritic rocks reveal their magmatic affinity with the calc-alkaline series. Furthermore, their radiometric age (35.3 m.y.) links the basement to the Sierra Madre Occidental in Mexico and to mid-Tertiary volcanic arcs

H. Bellon; R. C. Maury; J. F. Stephan

274

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

275

C. R. Geoscience 335 (2003) 6578 Geodynamics / Godynamique  

E-print Network

these deposits back to the Tropics, where they gradually warmed and were subjected to regional-scale thermohaline caractérisé par des 1631-0713/03/$ ­ see front matter 2003 Académie des sciences/?ditions scientifiques et

276

Joint seismic-geodynamic-mineral physical modelling of African geodynamics: A reconciliation of deep-mantle convection with surface geophysical constraints  

SciTech Connect

Recent progress in seismic tomography provides the first complete 3-D images of the combined thermal and chemical anomalies that characterise the unique deep mantle structure below the African continent. With these latest tomography results we predict flow patterns under Africa that reveal a large-scale, active hot upwelling, or superplume, below the western margin of Africa under the Cape Verde Islands. The scale and dynamical intensity of this West African superplume (WASP) is comparable to that of the south African superplume (SASP) that has long been assumed to dominate the flow dynamics under Africa. On the basis of this new tomography model, we find the dynamics of the SASP is strongly controlled by chemical contributions to deep mantle buoyancy that significantly compensate its thermal buoyancy. In contrast, the WASP appears to be entirely dominated by thermal buoyancy. New calculations of mantle convection incorporating these two superplumes reveal that the plate-driving forces due to the flow generated by the WASP is as strong as that due to the SASP. We find that the chemical buoyancy of the SASP exerts a strong stabilising control on the pattern and amplitude of shallow mantle flow in the asthenosphere below the southern half of the African plate. The asthenospheric flow predictions provide the first high resolution maps of focussed upwellings that lie below the major centres of Late Cenozoic volcanism, including the Kenya domes and Hoggar massif that lies above a remnant plume head in the upper mantle. Inferences of sublithospheric deformation from seismic anisotropy data are shown to be sensitive to the contributions of chemical buoyancy in the SASP.

Forte, A M; Quere, S; Moucha, R; Simmons, N A; Grand, S P; Mitrovica, J X; Rowley, D B

2008-08-22

277

Geodynamics Of The Yellowstone Hotspot From S Eismic And Gps Imaging: Progress Report  

NASA Astrophysics Data System (ADS)

An integrated study of the Yellowstone hotspot and it's interaction with the continental lithosphere is focused on understanding the evolution and effects of plume interaction with the continental lithosphere. Our basic goal is to develop a unified dynamic model of the Yellowstone hotspot and to resolve the question of whether there it has a deep mantle plume source. The 800-km-track of the 16Myr. Yellowstone-Snake River Plain (YSRP) volcanic system extends NE across the western U.S. with associated active seismicity and faulting. We will discuss the initial results of seismic tomography experiments: 1) an 80-instrument, NW-SE trending 500 km x 400 km broadband and high frequency array centered over Yellowstone planned to resolve structural geometry and composition of a presumed mantle plume and to record presumed plume-penetrating rays to ~600 km depth; and 2) an array of ~350 seismic stations of regional seismic networks focusing on the magmatically modified crust using local earthquake and controlled sources. Crustal deformation was assessed by 160-station campaign GPS surveys (1987-2000) complimented by a 15-station permanent GPS network planned to resolve the velocity vectors around the hotspot needed for kinematic and dynamic modeling. Initial tomographic results reveal a low-velocity, upper-crustal body beneath Yellowstone, interpreted to be the source of its active silicic volcanism; conversely, a high-velocity mid crustal body extends along the cooled hotspot track is interpreted to an Fe-rich residuum of the rhyolitic-basaltic volcanism. Teleseismic images within the Yellowstone swell that, combined with isostatic considerations, suggests that convective overturn has left partially molten mantle beneath the hotspot track to depths of about 180 km, and depleted residuum beneath the swell adjacent to the hotspot track. Also the fast axis of mantle anisotropy is oriented in the direction of plate transport; this differs from the anisotropy away from the swell. We can account for the current observations with either a plume or a non -plume source. Initial GPS determinations suggest NE-SW extension of ~2 mm/yr of the across the SRP that is notably slower than the 4-5 mm/yr of NE extension across Yellowstone. Possible mechanisms for the aseismic extension of the SRP include dike intrusion or elastic deformation of a homogeneous, high -strength block. Initial 3D finite element models of GPS and L. Quat. fault slip data reveal s clockwise opening of the YSRP that rotates to general EW extension south of the hotspot track. On a larger scale, 3D numerical simulations of thermal, compositional, and melt buoyancy -driven small-scale (ca. 100 km) convection beneaththe western U.S. indicates a tendency for melting to form lineations aligned with the plate (and extension) direction, although these lineations do not display straightforward hotspot-like propagation. One speculative augment for systematic volcanic propagation of the YSRP and observed seismic images and deformation fields is the interaction between an actively melting asthenosphere, the depleted residuum that it creates, and the upper mantle plate shear that "drags" the depleted residuum downstream of an active melt event for propagating melt instabilities.

Smith, R. B.; Humphreys, E.; Dueker, K.; Tackley, P.; Waite, G.; Schutt, D.; Hernland, J.

278

Fluid seepage variability across the external Northern Apennines (Italy): Structural controls with seismotectonic and geodynamic implications  

NASA Astrophysics Data System (ADS)

The relations between fluid seeps and tectonic structures have been targeted in some key areas of the axial sector, and partly at the edge of the exposed Northern Apennines (Pede-Apennine margin). In the axial zone, fluid seepage is dominated by methane venting, which may occur in the form of dry seeps or associated with mineral springs. Surface venting is linked to the presence of foreland-dipping normal faults, or related to reservoirs localised at inactive anticlines. The Pede-Apennine margin is instead dominated by thrusting and mud volcanism. The two different categories of fluid seepage appear strongly coupled to the dissimilar stress fields (compressional or extensional) operating in these sectors. Pressure data inferred from deep wells delineate an overall fluid pressure increase from the axial zone toward the Pede-Apennine margin, possibly as a result of the growth of tectonic compaction in this direction. The increase of fluid pressure at the Pede-Apennine margin is thus interpreted as the primary control on the transition from dry vents to mud volcanism. The intimate association between seepage modes and distinct tectonic structures involves relevant consequences on fluid-fault interactions and seismotectonics, and also shows connections with processes dictating the internal deformation of evolving fold-and-thrust belts.

Bonini, Marco

2013-04-01

279

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

NASA Astrophysics Data System (ADS)

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

Saria, Elifuraha E.

280

Late Neoproterozoic strongly peraluminous leucogranites, South Eastern Desert, Egypt petrogenesis and geodynamic significance  

Microsoft Academic Search

Summary Late Neoproterozoic garnet-bearing leucogranites are developed locally along thrust faults in the South Eastern Desert, Egypt. This work presents field observations, whole rock major and trace element abundances, RbSr isotope data and mineral chemistry for three occurrences in the Sikait-Nugrus area. Field observations show that the leucogranites cut the faults and their contact with the country rocks is sharp

A. M. Moghazi; M. A. Hassanen; F. H. Mohamed; S. Ali

2004-01-01

281

Tomographic filtering of geodynamic models: Implications for model interpretation and large-scale mantle structure  

NASA Astrophysics Data System (ADS)

The resolution operator ? is a critical accompaniment to tomographic models of the mantle. ? facilitates the comparison between conceptual three-dimensional velocity models and tomographic models because it can filter these theoretical models to the spatial resolution of the tomographic model. We compute ? for the tomographic model S20RTS (Ritsema et al., 1999, 2004) and two companion models that are based on the same data but derived with different norm damping values. The three models explain (within measurement uncertainty) S-SKS and S-SKKS travel times equally well. To demonstrate how artifacts distort tomographic images and complicate model interpretation, we apply ? to (1) a thermochemical and (2) an isochemical model of convection in the mantle that feature different patterns of shear velocity heterogeneity in the deep mantle if we assume that shear velocity heterogeneity is caused by temperature variations only. ? suppresses short-wavelength structures, removes strong velocity gradients, and introduces artificial stretching and tilting of velocity anomalies. Temperature anomalies in the thermochemical model resemble the spatial extent of low seismic velocity anomalies and the shear velocity spectrum in the D" region better than the isochemical model. However, the thermochemical model overpredicts the amplitude of shear velocity variation and places the African and Pacific anomalies imperfectly. We suspect that inaccurate velocity scaling laws and uncertain initial conditions control these mismatches. Extensive hypothesis testing is required to identify successful models.

Ritsema, Jeroen; McNamara, Allen K.; Bull, Abigail L.

2007-01-01

282

Building topography in Cyprus and south Turkey: geological constraints and geodynamic models  

NASA Astrophysics Data System (ADS)

We present a regional synthesis of the geometries and Neogene vertical motions and horizontal deformations of the central sector of the Cyprus arc-trench system, which are used to constrain 2D thermo-mechanical numerical models. We used depth-converted seismic reflection lines, basin analysis techniques and fieldwork observations, combined with available literature. From the Cyprus arc trench to the Central Anatolia Plateau, three independent vertical motion domains are identified: the Cyprus structural high; the Cilicia Basin and the Tauride Range. Early Miocene regional subsidence that still continues in the Cilicia Basin was disrupted by surface uplift in the north and south domains during Late Miocene or younger times. Coevally, N-S shortening developed regional contractional structures along the margin. The large-wavelength Miocene monocline fold that formed in S Turkey reveals relative vertical displacement rates of 0.5 mm/y and horizontal shortening values of <1%, along our studied sections. Shortening led to S-dipping thrusts in the center of the Cilicia Basin, and further developed the S-verging Kyrenia thrust system in N Cyprus. The observed deformation patterns and associated vertical motions suggest that the Anatolian upper-plate topography, including the uplifted south Turkey, results from wedge deformation in relation to the Cyprus arc. We use numerical finite element models to test this hypothesis. Models show that the mechanical growth of both the Anatolian accretionary complex and its forearc basin system caused sedimentary thickening and overburden, which led to the development of a sedimentary blanket that started to control the thermal distribution in the margin; relative temperatures decreased within the blanket and increased underneath it. This resulted in thermally weakened viscous deformation of the lower crust, which eventually forced the surface uplift of the landward side of the forearc basin and created a forearc-high, the modern Taurides. We also analyzed the influence of factors such as viscous properties of the crust and sedimentary accumulation rates. These parameters have a strong impact in the overall evolution of the margin as well as in when and whether surface uplift in the forearc-high occurs. Higher values in the viscous parameters drive older, more pronounced uplift, than lower viscosity values. Decreasing values change the shape and time-evolution of uplift, from older rounded-shaped uplift to mid-aged box-shaped uplift to absence of uplift. Large accumulation rates develop thicker basins that stabilize the margin and shift deformation towards their margins. This also induces surface uplift to take place at younger times and can lead to avoid its happening, i.e, if sediment accumulation rates are large, the subduction system needs longer times to develop the forearc-high. We conclude that the Cyprian subduction system drives mechanical accretion in Cyprus and deep-seated deformation in S Turkey, which in turn control vertical tectonic motions and topography development in the margin.

Fernndez-Blanco, David; Bertotti, Giovanni; Cassola, Teodoro; Willett, Sean

2014-05-01

283

Cenozoic denudation of the Menderes Massif and its geodynamic framework: slab tear or not?  

NASA Astrophysics Data System (ADS)

Despite having experienced similar rates of convergence during the Alpine Orogeny, the Hellenides and Anatolides display fundamental differences in crust and mantle structure across a region that broadly coincides with the Aegean coastline of the Anatolian peninsula. The Menderes Massif experienced early Miocene tectonic denudation and surface uplift in the footwall of a north-directed extensional detachment system, followed by late Miocene to recent fragmentation by E-W and NW-SE trending graben systems, resulting in one of Earth's largest metamorphic core complexes. Based on the interpretation of geological and geophysical data we propose that the tectonic denudation of the Menderes Massif was caused by late Oligocene/early Miocene lithosphere scale transtension along the boundary of the Adriatic and Anatolian lithospheric domains, when rollback of the Aegean slab affected the Aegean-Menderes section of the Tethyan Orogen. In addition to previously hypothesized crustal discontinuities, gravity data, earthquake locations and seismic velocity anomalies highlight a north-south oriented boundary in the upper mantle between a fast slab below the Aegean and a slow asthenospheric region below western Turkey. As an alternative to the common interpretation of this discontinuity representing the western edge of a slab tear, we propose that the change in lithospheric structure is the result of how different lithosphere domains responded to roll-back: relatively slow removal of lithospheric mantle below western Anatolia versus trench retreat in the rapidly extending Aegean Sea region. Our findings highlight the significance of lateral variations in subduction-collision systems for the formation of continental plateaux and metamorphic core complexes.

Gessner, Klaus; Gallardo, Luis; Markwitz, Vanessa; Ring, Uwe; Thomson, Stuart

2014-05-01

284

Postmiocene geodynamic evolution of the drake passage, Western Antarctic Region, southern ocean  

NASA Astrophysics Data System (ADS)

In 1994-2006, the German research vessel, Polarstern, and the Russian research vessel, Akademik Boris Petrov, carried out marine geologic and geophysical explorations in the Western Antarctic Region within the Bellingshausen, Amundsen, and Scotia marginal Seas and the Drake Passage. In these expeditions, new unique data on submarine topography have been collected by a multibeam echosounder, gravity and magnetic measurements have been carried out, multichannel seismic profiling has been performed, and the collections of rock samples have been acquired. The analysis and interpretation of new evidence together with previous geologic and geophysical data for the Drake Passage region have shown that end of spreading in the Aluk Ridge three million years ago resulted in the redistribution of stresses associated with the relative motion of the Antarctic, Scotia, and Phoenix Plates, which, in turn, caused significant tectonic reconstruction of the entire transition zone of the Drake Passage.

Teterin, D. E.

2011-08-01

285

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

SciTech Connect

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

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

1994-11-01

286

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

SciTech Connect

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

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

1995-08-01

287

Interface deformation in low reynolds number multiphase flows: Applications to selected problems in geodynamics  

SciTech Connect

Flow in the mantle of terrestrial planets produces stresses and topography on the planet`s surface which may allow us to infer the dynamics and evolution of the planet`s -interior. This project is directed towards understanding the relationship between dynamical processes related to buoyancy-driven flow and the observable expression (e.g. earthquakes, surface topography) of the flow. Problems considered include the ascent of mantle plumes and their interaction with compositional discontinuities, the deformation of subducted slabs, and effects of lateral viscosity variations on post-glacial rebound. We find that plumes rising from the lower mantle into a lower-viscosity upper mantle become extended vertically. As the plume spreads beneath the planet`s surface, the dynamic topography changes from a bell-shape to a plateau shape. The topography and surface stresses associated . with surface features called arachnoids, novae and coronae on Venus are consistent with the surface expression of a rising and spreading buoyant volume of fluid. Short wavelength viscosity variations, or sharp variations of lithosphere thickness, have a large effect on surface stresses. This study also considers the interaction and deformation of buoyancy-driven drops and bubbles in low Reynolds number multiphase systems. Applications include bubbles in magmas, the coalescence of liquid iron drops during core formation, and a wide range of industrial applications. Our methodology involves a combination of numerical boundary integral calculations, experiments and analytical work. For example, we find that for deformable drops the effects of deformation result in the vertical alignment of initially horizontally offset drops, thus enhancing the rate of coalescence.

Gable, C.; Travis, B.J. [Los Alamos National Lab., NM (United States); O`Connell, R.J.; Stone, H.A. [Harvard Univ., Cambridge, MA (United States)

1995-06-01

288

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

NASA Astrophysics Data System (ADS)

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

Kite, Edwin Stephen

289

Structure beneath the Alboran from geodynamic flow models and seismic anisotropy  

NASA Astrophysics Data System (ADS)

Upper mantle heterogeneity beneath the Alboran Sea (western Mediterranean) as inferred from seismology has been associated with a range of subduction and lithospheric delamination scenarios. However, better constraints on the deep dynamics of the region are needed to determine the cause and consequence of complex surface tectonics. Here, we use an improved set of shear wave splitting observations and a suite of mantle flow models to test a range of suggested structures. We find that the observed seismic anisotropy is best reproduced by mantle flow models that include a continuous, deeply extending slab beneath the Alboran which elongates along the Iberian margin from Granada to Gibraltar and curves southward toward the High Atlas. Other models with detached slabs, slabs with spatial gaps, or drip-like features produce results inconsistent with the splitting observations. SW-directed shear flow, when combined with sublithospheric deflection in response to a dense sinker, generates NNW-splitting orientations most similar to the patterns observed along Gibraltar. Slab viscosities of 250 times that of the upper mantle are preferred because they provide a balance between the poloidal flow induced by any sinker and toroidal flow induced by stiff slabs. The best match to anisotropy across the Atlas is a model with a stiff continental keel in northwestern Africa which deflects flow northward. Our results show that quantitative predictions of seismic anisotropy are useful in distinguishing the spatial and depth extent of regional density structures which may otherwise be ambiguous.

Alpert, Lisa A.; Miller, Meghan S.; Becker, Thorsten W.; Allam, Amir A.

2013-08-01

290

Micro-geodynamics of the Karakoram Fault Zone, Ladakh, NW Himalaya.  

E-print Network

??Microgeodynamics relates grain-scale deformation microstructures to macroscopic tectonic processes. Here the microgeodynamic approach combines optical and electron microscopy, including electron backscattered diffraction (EBSD), with field (more)

Wallis, David

2014-01-01

291

Geochemical similarities between the Vesuvius, Phlegraean Fields and Stromboli Volcanoes: petrogenetic, geodynamic and volcanological implications  

Microsoft Academic Search

Summary Vesuvius and Stromboli are two active and extensively studied volcanoes that traditionally have been considered as having\\u000a different styles of eruption, rock composition and tectonic setting. Data reveal close compositional affinities between these\\u000a two volcanoes. The abundant 1315?Ka old Stromboli leucite-tephritic rocks have radiogenic isotope signatures, and abundances\\u000a and ratios of incompatible elements with the exception of Rb and

A. Peccerillo

2001-01-01

292

Rock Breakage Energy and Large-Scale Low-Friction Geodynamic Phenomena  

NASA Astrophysics Data System (ADS)

We show that the anomalously low frictional resistance to the motion of large rock ava-lanches, gigantic blockslides and large faults can be explained quantitatively by including the energetics of rock breakage in a simulation model. Griffith (1920) defined fracture energy as the amount of energy needed to create unit area of new rock surface by breaking rocks into smaller fragments, and assumed that fracture energy was entirely consumed in the fracture process, manifesting as unavailable surface energy. This concept is widely accepted and used in rock breakage analysis and in earthquake and landslide energy budgets. While the first use is sensi-ble, the latter two are not. Breakage of an intact rock clast by applied force first involves elastic deformation of the whole clast, and elastic strain energy accumulates in the clast interior. At failure, this strain en-ergy is a maximum and (by definition) equal to the fracture energy. During failure, the strain energy suddenly reduces to zero as through-going cracks release the applied forces, and frag-ments recover their unstressed shapes. The strain energy released is equal to the work done in stressing the clast to breakage, again equalling the fracture energy. Evidently some of the re-leased strain energy is initially present in the kinetic energy of fragment shape recovery. If Griffiths assumption, that all the fracture energy used to break the rock becomes surface energy, were true, no mechanical energy would be available to provide rock fragments with kinetic energy, and rock fragments smaller than a few microns cannot be broken in two. How-ever, experiments show that fragment KE is at least 50% of the stored elastic strain energy in breakage of rock, and up to 85% with Pyrex; evidently the surface energy is substantially less than the fracture energy. In the energetics of earthquakes and large landslides this is fundamen-tally important, because the mechanical energy recycled by breaking grains to their environment is significant in the dynamics of the process - particularly when the grains involved are very small, as are many in large landslides and faults. Rock bursts in deep mines generate fragment velocities of many tens of metres per second, showing that large mechanical forces are exerted on the environment by grain breakage. We show that the average pressure exerted on its surroundings by a breaking clast is of the order of one-third of its average failure strength, which for unconfined intact crustal rock is in the order of 108 Pa - this is clearly significant in the dynamics of geophysical phenomena. Under high geostatic stresses, such as at the base of a large rock avalanche or in a fault at seismic depth, the failure strength is substantially higher and local dynamic pressures resulting from grain frag-mentation can be in the GPa range. We demonstrate, using a specific case study, that consideration of the dynamic pressures ex-erted by breaking rocks provides a simple and quantitative explanation for the anomalously low frictional resistance to the motion of a large debris avalanche. Griffith, A.A. (1920), The phenomena of rupture and flowing solids. Philosophical transactions of the Royal Society of London. A221: 163-198

Davies, T. R.; McSaveney, M. J.

2010-12-01

293

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

NASA Technical Reports Server (NTRS)

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

1974-01-01

294

On the origin of El Chichn volcano and subduction of Tehuantepec Ridge: A geodynamical perspective  

NASA Astrophysics Data System (ADS)

The origin of El Chichn volcano is poorly understood, and we attempt in this study to demonstrate that the Tehuantepec Ridge (TR), a major tectonic discontinuity on the Cocos plate, plays a key role in determining the location of the volcano by enhancing the slab dehydration budget beneath it. Using marine magnetic anomalies we show that the upper mantle beneath TR undergoes strong serpentinization, carrying significant amounts of water into subduction. Another key aspect of the magnetic anomaly over southern Mexico is a long-wavelength ( 150 km) high amplitude ( 500 nT) magnetic anomaly located between the trench and the coast. Using a 2D joint magnetic-gravity forward model, constrained by the subduction P- T structure, slab geometry and seismicity, we find a highly magnetic and low-density source located at 40-80 km depth that we interpret as a partially serpentinized mantle wedge formed by fluids expelled from the subducting Cocos plate. Using phase diagrams for sediments, basalt and peridotite, and the thermal structure of the subduction zone beneath El Chichn we find that 40% of sediments and basalt dehydrate at depths corresponding with the location of the serpentinized mantle wedge, whereas the serpentinized root beneath TR strongly dehydrates (90%) at depths of 180-200 km comparable with the slab depths beneath El Chichn (200-220 km). We conclude that this strong deserpentinization pulse of mantle lithosphere beneath TR at great depths is responsible for the unusual location, singularity and, probably, the geochemically distinct signature (adakitic-like) of El Chichn volcano.

Manea, Marina; Manea, Vlad C.

2008-08-01

295

Geodynamics of collision and collapse at the AfricaArabiaEurasia subduction zone an introduction  

E-print Network

; (2) continental drift, sea-floor spreading and formation of ocean basins; (3) subduction initiation and drifting in the Western Mediterranean (Dercourt et al. 1986), and with initiation of the Tyrrhenian oceanic subduction stage closes the oceanic basin, even- tually resulting in the arrival of a continental

Utrecht, Universiteit

296

A model of late Pleistocene ice sheet growth with realistic geography and simplified cryodynamics and geodynamics  

Microsoft Academic Search

A global two-dimensional one-level seasonal energy-balance model is asynchronously coupled to vertically integrated ice-flow models (which depend both on latitude and longitude) to study the response of the atmosphere-ocean-cryosphere-lithosphere system to solar forcing for the last ice age cycle of the late Pleistocene. The model simulates the position of the North American and European ice sheet complexes at the last

G. Deblonde; W R Peltier

1990-01-01

297

The enigmatic Mongol-Okhotsk Belt in NE Mongolia - a preliminary evaluation of the geodynamic development  

NASA Astrophysics Data System (ADS)

The Mongol-Okhotsk Belt (MOB) extends from Central Mongolia across eastern Siberia towards the Okhotsk Sea in the northwestern Pacific. The belt formed in a late stage of Jurassic orogeny in the composite Central Asian Orogenic Belt by the consumption of the Mongol-Okhotsk ocean (MOO). The Late Paleozoic-Mesozoic sediments associated with the belt in Mongolia are investigated in order to evaluate the timing and mode of ocean formation, the subduction and the collision of the framing margins. We apply an advanced provenance analysis including (1) heavy mineral and sandstone framework grain analysis and (2) U/Pb laser ablation ICPMS dating, trace element, and Hf isotope analysis of detrital zircons. We differentiate three tectono-stratigraphic units: (1) the Adaatsag and Doschgol terranes, which are supposed to represent the suture zone, (2) the Hangai-Hentei basin to the northwest of the suture, and (3) the Ereendavaa terrane and the Middle Gobi volcanic belt to the southeast. The latter two are concurrent with the northern and southern margins of the former MOO (in modern coordinates) respectively. The northern margin development is documented by ophiolitic accretionary wedge and fore-arc deposits. The southern margin is represented by Devonian-Carboniferous sediments presumably laid down on deformed and metamorphosed Neoproterozoic-Early Paleozoic continental and ophiolitic basement, which initially was accreted against the North Asia Craton (Siberia) by the closure of the Paleoasian ocean in the Ordovician. The available tectono-stratigraphic arguments together with biostratigraphic and radiometric age data suggest that the Mongol-Okhotsk ocean opened in Late Silurian, possibly by back-arc spreading within the Early Paleozoic collage due to northward subduction of the Paleotethys/Paleopacific ocean under the accreted Mongolian margin. The syn-sedimentary U/Pb detrital zircon age patterns and Hf isotopic values (epsilon Hf +6 - +7 in Devonian and Permo-Carboniferous time) show similar subduction related magma production processes in the northern and southern margin. However, the two continental margins of the MOO were presumably active at different periods. Our preliminary data propose that along the northern margin, from Silurian to Early Carboniferous subduction and accretion prevailed, which was re-initiated during the Permian. Reworking of older basement zircons is sparse. The contemporaneous Silurian-Devonian southern margin represented an extensional continental margin showing reworking of Neoproterozoic-Early Paleozoic zircons from the basement. It presumably turned into an active continental margin with starting arc magmatism in the Carboniferous. Continued subduction is manifested by the occurrence of Permian and Triassic zircons. On both margins Triassic and Jurassic continental sediments unconformably overlie tectonically deformed fore-arc series. In the suture zone in-between, Permo-Triassic and Jurassic samples contain Permian zircon grains, and an irregular mixing with Cambrian to Carboniferous zircons is documented. The pre-Permian zircon age spectra closer compare with the southern margin age distributions. Synsedimentary magmatic activity is documented until Late Triassic-Liassic (? 202 Ma). This volcanic source age approximately correlates with the time of closure of the MOO in the Mongolian segment of the mountain belt.

Denise, Bussien; Nergui, Martin-Gombojav; Wilfried, Winkler; Quadt Albrecht, Von

2010-05-01

298

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

NASA Astrophysics Data System (ADS)

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

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

299

Comparison of two differential interferometry techniques for the monitoring of geodynamic events  

NASA Astrophysics Data System (ADS)

The synthetic aperture radar (SAR) data acquired from the satellites ERS-1 and ERS-2 facilitate the extensive and astonishingly precise investigation of small displacements of the Earth's surface. Measurements of displacements are possible by differential SAR interferometry (D-InSAR) with centimeter accuracy. A detailed description of the D-InSAR system is presented to clarify the basic observation procedure. The D-InSAR system is an extension of the operational InSAR processor 'GENESIS' developed by the German Aerospace Research Establishment (DLR). The modular concept of the D-InSAR system permits a choice of different algorithms. Accordingly, the displacement can be extracted from an interferogram using a digital elevation model (DEM) as well as from two interferograms. Both techniques are illustrated and compared by a common data set. The geocoding and the various visualizations of the resulting data set support an easy application of this monitoring procedure in geosciences. Iceland is an especially suitable test site for differential SAR interferometry, because of its active tectonics, volcanism and flowing glaciers. Results of two Icelandic test sites are presented as applications.

Adam, Nico; Jonsson, Sigurjon

1997-12-01

300

Geodynamics of late Paleozoic magmatism in the Tien Shan and its framework  

NASA Astrophysics Data System (ADS)

The Devonian-Permian history of magmatic activity in the Tien Shan and its framework has been considered using new isotopic datings. It has been shown that the intensity of magmatism and composition of igneous rocks are controlled by interaction of the local thermal upper mantle state (plumes) and dynamics of the lithosphere on a broader regional scale (plate motion). The Kazakhstan paleocontinent, which partly included the present-day Tien Shan and Kyzylkum, was formed in the Late Ordovician-Early Silurian as a result of amalgamation of ancient continental masses and island arcs. In the Early Devonian, heating of the mantle resulted in the within-plate basaltic volcanism in the southern framework of the Kazakhstan paleocontinent (Turkestan paleoocean) and development of suprasubduction magmatism over an extensive area at its margin. In the Middle-Late Devonian, the margins of the Turkestan paleoocean were passive; the area of within-plate oceanic magmatism shifted eastward, and the active margin was retained at the junction with the Balkhash-Junggar paleoocean. A new period of active magmatism was induced by an overall shortening of the region under the settings of plate convergence. The process started in the Early Carboniferous at the Junggar-Balkhash margin of the Kazakhstan paleocontinent and the southern (Paleotethian) margin of the Karakum-Tajik paleocontinent. In the Late Carboniferous, magmatism developed along the northern boundary of the Turkestan paleoocean, which was closing between them. The disappearance of deepwater oceanic basins by the end of the Carboniferous was accompanied by collisional granitic magmatism, which inherited the paleolocations of subduction zones. Postcollision magmatism fell in the Early Permian with a peak at 280 Ma ago. In contrast to Late Carboniferous granitic rocks, the localization of Early Permian granitoids is more independent of collision sutures. The magmatism of this time comprises: (1) continuation of the suprasubduction process (I-granites, etc.) with transition to the bimodal type in the Tien Shan segment of the Kazakhstan paleocontinent that formed; (2) superposition of A-granites on the outer Hercynides and foredeep at the margin of the Tarim paleocontinent (Kokshaal-Halyktau) and emplacement of various granitoids (I, S, and A types, up to alkali syenite) in the linear Kyzylkum-Alay Orogen; and (3) within-plate basalts and alkaline intrusions in the Tarim paleocontinent. Synchronism of the maximum manifestation and atypical combination of igneous rock associations with spreading of magmatism over the foreland can be readily explained by the effect of the Tarim plume on the lithosphere. Having reached maximum intensity by the Early Permian, this plume could have imparted a more distinct thermal expression to collision. The localization of granitoids in the upper crust was controlled by postcollision regional strike-slip faults and antiforms at the last stage of Paleozoic convergence.

Biske, Yu. S.; Konopelko, D. L.; Seltmann, R.

2013-07-01

301

Metamorphic diamonds in a garnet megacryst from the Edough Massif (northeastern Algeria). Recognition and geodynamic consequences  

NASA Astrophysics Data System (ADS)

We report for the first time the discovery of diamond inclusions (5-30 ?m in size), identified by Raman spectroscopy and the characteristic sharp band at 1332 cm- 1 for crystalline diamond, in a garnet megacryst (? 5 cm) from the Edough Massif (NE Algeria). The garnet is adjacent to actinolite and ultramafic boudins and slices of marbles that are inserted within a major mylonite-ultramylonite band. This tectonic contact sharply delineates the Kef Lakhal oceanic unit from the granite-gneiss core below. The host garnet is almandine-dominant and is rich in exsolution of acicular rutile needles. Major and trace elements show a gradual but significant zonation from core to rim, and a sharp increase in grossular component in the rim. Trace element analyses of prismatic rutile inclusions up to 300 ?m in size indicate that the host metamorphic rock was a mafic protolith of MORB affinity. The Zr-in-rutile thermometry indicates a temperature range of 724-778 C that we relate to rutile growth, either during prograde metamorphism or under peak UHP metamorphic conditions of ? 3.6 GPa that were reached during subduction of the UHP-rock precursors. We suggest that the mafic protolith originates from the subducted retreating Calabrian branch of the Tethyan slab, that broke or tore, and which fragments were dragged upward and thrust onto the North African margin along with the Kef Lakhal unit, shortly followed by formation of the Edough dome and opening of the Algerian basin.

Caby, Renaud; Bruguier, Olivier; Fernandez, Laure; Hammor, Dalila; Bosch, Delphine; Mechati, Mehdi; Laouar, Rabah; Ouabadi, Aziouz; Abdallah, Nachida; Douchet, Chantal

2014-12-01

302

Geodynamic implications for the formation of the Betic-Rif orogen from magnetotelluric studies  

Microsoft Academic Search

Magnetotelluric data from the central Betics mountains (Spain) have been used to determine the electrical resistivity of the crust after a three-dimensional (3D) interpretive approach. At shallow levels (3 km), the most striking and well-resolved feature of the model is an upper-middle crust conductive body, located at the core of the Internal Betics antiform. This approximately 14-km-thick body is interpreted

A. Mart; P. Queralt; E. Roca; J. Ledo; J. Galindo-Zaldvar

2009-01-01

303

Geodynamics of the Carpathian Bend Zone: interconnection between surface and deep processes  

NASA Astrophysics Data System (ADS)

The Carpathian Bend Zone is a key segment of the Alpine-Himalyan Belt and represent the home of a very particular seismic activity: regular very strong earthquakes are being generated in a very narrow, deep volume of a finger-shape, vertically distributed. The nature of processes involved is instill not yet understood and could be eventually related to several main hypothesis, like: (1) subduction of an oceanic lithosphere (and eventually a remnant of this is just now detaching from the continental lithosphere of the East European and Moesian Platforms, (2) the oceanic slab subduction ended sometimes in (late) Miocene and then a part of the continental lithosphere of the mentioned platforms has been delaminated. Various models of the lithosphere - astenosphere system take into account for example the seismic attenuation and share wave splitting. The intricate geometry of the lithosphere - astenosphere system as well as the mantle flow around the "slab" generates intriguing questions. We add another constraint to the various methodological approaches by taking into account the kinematics of the crustal blocks as suggested by robust outcomes of an extended and long-term investigated satellite geodesy network consisting of permanent and campaign stations. We will integrate results of GPS investigations with other, complementary results from other investigations techniques in order to test the deep feedback to the Tethyan closure, including the astenosphere - lithosphere system, trying to explain the very unusual high Carpathian seismicity and the geometry of the high velocity body beneath the Carpathian Bend Zone and the mantle flow around it and related surface processes.

Mocanu, V.; Munteanu, L.; Munteanu, A.

2007-12-01

304

High-precision two-colour spaceborne laser ranging system for monitoring of geodynamic processes  

Microsoft Academic Search

The design concept of a spaceborne two-color picosecond-pulse laser ranging system operating at a pulse rate of about 20 Hz from a 1600 km circular orbit is presented. The system is designed to estimate distances to ground-based passive arrays of retroreflector targets, which are deployed in tectonically highly active zones, with a precision within + or - 1 cm. Since

H. P. Lutz; W. Krause; G. Barthel

1982-01-01

305

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

USGS Publications Warehouse

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

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

2009-01-01

306

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

307

Late Proterozoic older granitoids from the North Eastern desert of Egypt: petrogenesis and geodynamic implications  

Microsoft Academic Search

Major, trace, and REE data for three localities of calcalkaline older granitoid rocks exposed in the north Eastern Desert\\u000a of Egypt are presented. These rocks were selected to cover wide compositional spectrum of the Egyptian older granitoid varieties.\\u000a They are petrographically represented by granodiorite, tonalite, quartzdiorite, and quartzmonzodiorite. The rocks are comparable\\u000a with the peraluminous, unfractionated calcalkaline suites and fall

Mahmoud M. El Mahallawi; A. F. Ahmed

308

Deformation of slabs in the deep mantle: constraints from mineral physics and geodynamic implications  

Microsoft Academic Search

Temperature dependence of energy dissipation has a decisive control over the rate of convective heat transfer and the thermal evolution of a planet. Deformation of the lithosphere is a key process in mantle convection where a large amount of energy is likely dissipated. The lithosphere is strong and hence large energy dissipation likely occurs by the deformation of the lithosphere.

Shun-Ichiro Karato

2010-01-01

309

Investigations on the hierarchy of reference frames in geodesy and geodynamics  

NASA Technical Reports Server (NTRS)

Problems related to reference directions were investigated. Space and time variant angular parameters are illustrated in hierarchic structures or towers. Using least squares techniques, model towers of triads are presented which allow the formation of linear observation equations. Translational and rotational degrees of freedom (origin and orientation) are discussed along with and the notion of length and scale degrees of freedom. According to the notion of scale parallelism, scale factors with respect to a unit length are given. Three-dimensional geodesy was constructed from the set of three base vectors (gravity, earth-rotation and the ecliptic normal vector). Space and time variations are given with respect to a polar and singular value decomposition or in terms of changes in translation, rotation, deformation (shear, dilatation or angular and scale distortions).

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

1979-01-01

310

Large-scale Geodynamics Controls the Origin of the Residual Ozone Field  

NASA Astrophysics Data System (ADS)

Here we analyze the residual ozone field (ROF), which is the global ozone component unexplained by the solar radiation. Spatially, ROF mainly consists of two areas: positive and negative divided by the "break-up" line. Morphology of ROF was discussed in detail in [Seblova, Dokl. Earth Sci, 414, 582-586, 2007]. We argue that the spatial and temporal patterns of ROF point to its terrestrial origin. To confirm this hypothesis, we studied the following data sets: (1) global distribution of the total ozone from the TOMS satellite observations; (2) tectonic plate motion from GPS. (3) topography of the core-mantle boundary (CMB) from seismic data. We trace in time the evolution of the initial pattern of ROF as defined by the mantle upwelling and the break-up of Pangaea

Steblova, R. S.

2012-12-01

311

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

NASA Astrophysics Data System (ADS)

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

Ferraro, Pietro; De Natale, Giuseppe

2002-02-01

312

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

313

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

Microsoft Academic Search

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

Daniel Meshesha; Ryuichi Shinjo

2008-01-01

314

Using (222)Rn as a tracer of geodynamical processes in underground environments.  

PubMed

Radon levels in two old mines in San Luis, Argentina, were measured and analyzed, with the aim to assess the potential use of this radioactive noble gas as a tracer of geological processes in underground environments. La Carolina gold mine and Los Cndores tungsten mine are today used as tourism mines. CR-39 nuclear track detectors were used for this purpose. Measurements were performed during both winter and summer seasons. The findings show that in these environments, significant radon concentrations are subject to large seasonal fluctuations, due to the strong dependence on natural ventilation with the outside temperature variations. For both mines, higher concentration values of (222)Rn were observed in summer than in winter; with an extreme ratio of 2.5 times between summer and winter seasons for Los Cndores mine. The pattern of radon transport inside La Carolina mine revealed, contrary to what was believed, that this mine behaves as a system with two entrances located at different levels. However, this feature can only be observed in the winter season, when there is a marked difference between the inside and outside temperatures of the mine. In the case of Los Cndores mine, the radon concentration pattern distribution is principally established by air current due to chimney-effect in summer and winter seasons. In both cases, the analyses of radon pattern distribution appear as a good method to trace air currents, and then localize unknown ducts, fissures or secondary tunnels in subterranean environments. PMID:24012891

Valladares, D L; da Silva, A A R; Lacerda, T; Anjos, R M; Rizzotto, M; Velasco, H; de Rosas, J P; Tognelli, G; Yoshimura, E M; Ayub, J Juri

2014-01-15

315

Metallogenic geodynamic background of Mesozoic gold deposits in granite-greenstone terrains of North China Craton  

Microsoft Academic Search

The spatial distribution map of 65 mid-large gold-deposits hosted in the granite-greenstone terrains of the North China Craton\\u000a is first drawn. These gold deposits mainly concentrate in the Mesozoic remobilized Yinshan-Yan-shan-Liaoning-Jilin intracontinental\\u000a collisional orogenic belt, the northern Qinling and the Jiaodong Mesozoic collisional orogenic belts, and the Mesozoic intracontinental\\u000a fault-magmatic belts developed along the Taihangshan and the Tan-Lu faults; their

Yanjing Chen; Guangjun Guo; Xin Li

1998-01-01

316

Geodynamic setting of mesothermal gold deposits: An association with accretionary tectonic regimes  

Microsoft Academic Search

Mesothermal gold provinces of Phanerozoic age are characteristically associated with regional structures along which allochthonous terranes have been accreted onto continental margins or arcs. A recurring sequence of transpressive deformation, uplift, late kinematic mineralization, and shoshonitic magmatism is consistent with thermal reequilibration of tectonically thickened crust. Mesothermal gold camps in the Superior province are spatially associated with large-scale structures that

Robert Kerrich; Derek Wyman

1990-01-01

317

The characteristics, origins, and geodynamic settings of supergiant gold metallogenic provinces  

Microsoft Academic Search

There are six distinct classes of gold deposits, each represented by metallogenic provinces, having 100's to >1000 tonne gold\\u000a production. The deposit classes are: (1) orogenic gold; (2) Carlin and Carlin-like gold deposits; (3) epithermal gold-silver\\u000a deposits; (4) copper-gold porphyry deposits; (5) iron-oxide copper-gold deposits; and (6) gold-rich volcanic hosted massive\\u000a sulfide (VMS) to sedimentary exhalative (SEDEX) deposits. This classification

Robert Kerrich; Richard Goldfarb; David Groves; Steven Garwin; Yiefei Jia

2000-01-01

318

Early Eocene ArcContinent Collision in Kamchatka, Russia: Structural Evolution and Geodynamic Model  

Microsoft Academic Search

\\u000a The major event in the Cenozoic evolution of the Kamchatka orogen was the Early Eocene collision of the Ozernoy-Valagina (Olutorsky)\\u000a arc terrane with the continental margin of Asia. The arccontinent collision developed progressively from southwest to northeast\\u000a from the Early Eocene in South Kamchatka to the early Mid Eocene in the Olutorsky region. The nature of the continental margin\\u000a of

E. Konstantinovskaya

319

Determining crustal strain rates with spaceborne geodynamics ranging system data. 1: Baseline analysis  

NASA Technical Reports Server (NTRS)

A satellite-borne laser ranging system is proposed that is capable of making highly precise geodetic measurements over baselines ranging from a few tens of kilometers to several hundred kilometers. The precision with which crustal strain rates are derived from measurements made with this system is analyzed by using simple site configurations, intersite distances of about 25-70 kilometers, and measurement programs ranging from a few years to fifteen years. It is concluded that precisions of several parts in 10 to the 9th power per year are achievable. Compared to the expected shear strain rates of about 7 x 10 to the minus 7th power yr/1, this produces very favorable signal-to-noise ratios.

Cohen, S. C.; Cook, G. R.

1978-01-01

320

Granites and the geodynamic history of the neoproterozoic Bras??lia belt, Central Brazil: a review  

Microsoft Academic Search

Recent field and geochronological studies have demonstrated the importance of granitic magmatism in the evolution of the Neoproterozoic Bras??lia Belt, in Central Brazil. This is an orogenic belt developed in response to the convergence between the Amazon, So FranciscoCongo and Paran continental blocks. The presence of Neoproterozoic juvenile arc rocks and syn-collisional peraluminous granites challenged previous intracontinental evolution models for

Mrcio M Pimentel; Reinhardt A Fuck; Nilson F Botelho

1999-01-01

321

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

322

Petrology, geochemistry and geodynamics of basic granulite from the Altay area, North Xinjiang, China.  

PubMed

The basic granulite of the Altay orogenic belt occurs as tectonic lens in the Devonian medium- to lower-grade metamorphic beds through fault contact. The Altay granulite (AG) is an amphibole plagioclase two-pyroxene granulite and is mainly composed of two pyroxenes, plagioclase, amphibole and biotite. Its melano-minerals are rich in Mg/(Mg+Fe2+), and its amphibole and biotite are rich in TiO2. The AG is rich in Mg/(Mg+Fe2+), Al2O3 and depletion of U, Th and Rb contents. The AG has moderate SigmaREE and LREE-enriched with weak positive Eu anomaly. The AG shows island-arc pattern with negative Nb, P and Ti anomalies, reflecting that formation of the AG may be associated with subduction. Geochemical and mineral composition data reflect that the protolith of the AG is calc-alkaline basalt and formed by granulite facies metamorphism having peak P-T conditions of 750 degrees C-780 degrees C and 0.6-0.7 Gpa. The AG formation underwent two stages was suggested. In the early stage of oceanic crustal subduction, calc-alkaline basalt with island-arc environment underwent granulite facies metamorphism to form the AG in deep crust, and in the late stage, the AG was thrust into the upper crust. PMID:15236485

Li, Zi-Long; Chen, Han-Lin; Yang, Shu-Feng; Dong, Chuan-Wan; Xiao, Wen-Jiao

2004-08-01

323

Spatiotemporal Complexity of Continental Intraplate Seismicity: Insights from Geodynamic Modeling and Implications  

E-print Network

earthquakes can occur on the same fault zone even in the absence of strong tectonic loading. These complex earthquakes often occur in temporal clusters on faults that remain active for some time and then have long faults, earthquakes in continental in- traplate regions also appear to occur in temporal clusters

Liu, Mian

324

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

Microsoft Academic Search

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

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

1997-01-01

325

Geodynamic evolution of the NW Borneo Wedge: Subduction of a crustal asperity model  

NASA Astrophysics Data System (ADS)

The NW Borneo Margin is a complex structural domain where deformation style is a mix of compression and extension features associated with transverse structures. Review of outcrops, geomorphologic and magmatism studies show two imbricate wedges in Sabah/Brunei: - The Rajang-Crocker Wedge, mainly onshore, is oriented N-S in Sabah, curving to E-W in Sarawak. It is characterized by short wavelength thrusted folds. The age of deformation is Eocene-Oligocene with sequence of thrusting propagating westward. This wedge has been lately refolded by large wavelength anticlines generating well-known geomorphologic domains such as the Crocker Ranges, the Trusmadi Ranges and the Mulu Mountains. - The offshore NW Borneo Wedge is oriented NE-SW from North Sarawak to Palawan Island. This wedge can be divided into four structurally different domains, two compressive and two extensive basins rooted on the Mid-Miocene Unconformity (MMU). The formation of this wedge is contemporaneous with Mid-Miocene uplifts in the Rajang-Crocker Wedge. The timing of deformations and relationships between the different morpho-tectonic domains leads to reconsider the evolution of the entire NW Borneo Margin. The offshore NW Borneo Margin is characterized by the coeval NW Borneo Thrust Belt (offshore Northern Sabah) and the Outer Thrust Zone (offshore Brunei and Southern Sabah) of contrasted structural styles (difference of folds wavelength, occurrence of out-of-sequence thrusting, passive-roofing). The Outer Thrust Zone is associated both in time and space, to the large Baram-Champion deltaic province. This recent (Late Miocene) deltaic province results of a drastic change of sediment source during the Early/Mid-Miocene (~16Myr) from the SW (Schwanner Mountains) to the SE (Central Rajang-Crocker Wedge). The new model proposed here integrates the emplacement of the Baram-Champion deltaic province as the result of the docking and subduction into the NW Borneo Subduction of a crustal asperity named "Mulu Block". The subduction of a crustal asperity generates both large uplifts within the accretionary wedge and greater subsidence of the subducting plate; characterized here by: - Tremendous uplifts (South of Mulu Area and Central Rajang-Crocker Wedge), modifying the zone of sediment source and leaving a "scar" - geomorphologic anomaly without structural trend - within the wedge; - A deep "gluttonous" basin capturing 10km thick sediments into a deltaic province (The Baram-Champion Basin). New temperature data acquired from outcrop sampling in the central Borneo Wedge area support this new model, showing two domains: low temperature domain (frontal Balingian and Baram Basins) and high temperature domain (central Borneo Wedge). The jump of temperature is estimated around 100C and corresponds to what we interpret as the "scar" of the asperity.

Sapin, F.; Pubellier, M.; Ringenbach, J.-C.; Rives, T.

2009-04-01

326

Highlights of Recent CORK Hydrologic Borehole Observatory Results: Applications to Oceanography, Seismology, and Geodynamics  

NASA Astrophysics Data System (ADS)

Initial motivation for borehole hydrologic observatories came from the desire to observe natural temperatures and pressures and to sample fluids in permeable formations, where observations made at the time of drilling were dominated by drilling perturbations. As initial monitoring experiments proceeded, it became clear that sealed-hole CORK (circulation obviation retrofit kit) instrumentation could be used for other objectives, so their use expanded. Progressive improvements in power consumption and measurement resolution, and in some cases connections to shore provided recently by NEPTUNE-Canada (and in the future by DONET -Japan and OOI -U.S.A.), have further expanded the utility of borehole observatories well beyond that of early installations. Recent examples include documenting quasi-periodic turbidity currents in the Middle America Trench triggered by tidally stimulated sediment resuspension, slow slip across the full width of the subduction zone thrust off Costa Rica, post-seismic regional deformation in the Nankai Trough, and seismic noise generation in the northeast Pacific. In all cases, great value has been added to the data as a result of the borehole observations being placed in the context of concurrent observations from other types of monitoring instruments (e.g., current meters, seismometers, GPS receivers) deployed locally or regionally. Long observation periods have also been critical, since many of the phenomena of interest (e.g., slow slip events, earthquakes, and seasonally variable oceanographic events) occur infrequently. Coupling borehole observatories to seafloor cable systems will enhance many studies by allowing increased sampling rates, extended lifetime, precise timing, and coordinated complementary observations.

Davis, E. E.; Heesemann, M. L.

2010-12-01

327

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

NASA Astrophysics Data System (ADS)

The inclusion mineralogy of 1450 zircons over 4 billion years in age from the Jack Hills, Western Australia, was characterized for composition and phase assemblage. Results confirm that the inclusion population of these largely igneous zircons is dominated by muscovite and quartz (~ 75%). If the inclusions are original to the igneous zircons, this observation alone restricts the host melts to formation at pressure-temperature ( P- T) conditions of ~ 650-800 C and > 4 kbar. Several lines of evidence support the view that most of the analyzed mineral inclusions are primary, including their lack of association with cracks, magmatic crystal forms, and lack of exchange with fuchsitic (Cr-rich) micas in the host conglomerate. The application of Ti-in-zircon thermometry, and phengite, Ti-in-quartz, and Al-in-hornblende barometry to these inclusion assemblages yields estimates of magmatic P-T conditions from 5 to > 12 kbar and 700 40 C. These data indicate zircon formation along geotherms of ? 60 C/km and imply conductive near-surface heat flow of < 40 to 85 mW/m 2 a range that is substantially lower than most estimates of global Hadean heat flow. Of the possible environments capable of generating melting under such locally low heat flow early in Earth history, underthrusting, possibly in a manner similar to modern convergent margins, appears most consistent with numerous other geochemical constraints derived from investigation of Hadean zircons.

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

2010-10-01

328

Mineral inclusion thermobarometry in >4 Ga Jack Hills zircons provide further constraints on Hadean geodynamics  

Microsoft Academic Search

Detrital zircons from the Jack Hills of Western Australia provide an important record of terrestrial conditions during the Hadean Eon (ca. >4 Ga). Mineral inclusions captured in these ancient zircons add an extra dimension to our knowledge of Hadean Earth. The inclusion population is dominated by the presence of quartz and muscovite, most apparently primary to these igneous zircons. Several

M. Hopkins; T. M. Harrison; C. E. Manning

2010-01-01

329

Mineral inclusion thermobarometry in >4 Ga Jack Hills zircons provide further constraints on Hadean geodynamics  

NASA Astrophysics Data System (ADS)

Detrital zircons from the Jack Hills of Western Australia provide an important record of terrestrial conditions during the Hadean Eon (ca. >4 Ga). Mineral inclusions captured in these ancient zircons add an extra dimension to our knowledge of Hadean Earth. The inclusion population is dominated by the presence of quartz and muscovite, most apparently primary to these igneous zircons. Several lines of evidence support this view and argue against widespread exchange between most of these inclusions and their environment: (i) lack of association with cracks; (ii) magmatic crystal forms; (iii) absence of exchange with fuchsitic (Cr-rich) micas in the host conglomerate; and (iv) the heterogeneity in Sipfu values. We report new data on Ti concentration in quartz inclusions within Hadean zircons. The factor-of-10 difference in Ti content among included quartz grains is evidence against chemical communication between the host quartzite and inclusions, since the Jack Hills quartzite contains rutile which was mobile during metamorphism at ca. 2.5 Ga. Using the recently calibrated Ti-in-quartz thermobarometer yields a narrow range of pressure (202 kbar) for the three samples. This is in broad accord with the pressure range estimated for included muscovites with ~3.4 Sipfu (189 kbar). Taken together, the Hadean zircon inclusion assemblages yield estimates of magmatic P-T conditions from 5 to ca. 20 kbar at 70040C further supporting their formation under geotherms of ?60C/km thus implying conductive near-surface heat flow of ca. 20 to 80 mW/m2. Of all formational environments that satisfy the spectrum of geochemical constraints available and the inference of melt generation under suppressed heat flow, the most plausible appears to be partial melting of both juvenile and mature continental sediment via continuous underthrusting beneath a stable upper plate. We postulate that this melting could occur two different ways: fluxed melting of underthust sedimentary material, or fluxed melting of the upper plate due to plate dehydration or degassing of hydrous magma in the underthrust environment.

Hopkins, M.; Harrison, T. M.; Manning, C. E.

2010-12-01

330

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

SciTech Connect

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 with weathering crusts. The origins of certain terrigenous rocks, as well as products of low-temperature chemical processing, are connected with deep-volume decompression (brecciation, stockwork formation, formation of pipes and columns of igneous rocks, and chamber pegmatite and karst formation). The ore concentrations associated with such entities and appearing as stratiform deposits are most likely not exogenous, but they complete the endogenous history of the block concerned. The means and methods tested on typical endogenous deposits may therefore prove valuable in predicting certain varieties of stratiform deposits.

Goryainov, P.M.

1984-05-01

331

Geodynamics and Rate of Volcanism on Massive Earth-like Planets  

NASA Astrophysics Data System (ADS)

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

Kite, E. S.; Manga, M.; Gaidos, E.

2009-08-01

332

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

E-print Network

and the Dinarides, respectively. The wide chemical composition of the igneous rocks emplaced during this tectonic the geochemical composition of igneous rocks to infer the coeval tectonic setting characteristics cannot be used, structures, igneous and metamorphic rocks having been described in detail. Also the crustal and the upper

Doglioni, Carlo

333

Cenozoic and Mesozoic metamorphism in the Longmenshan orogen: Implications for geodynamic models of eastern Tibet  

NASA Astrophysics Data System (ADS)

The Tibetan Plateau is characterized by both its great height (much of it above 5,000 m) and flatness. It has been proposed that the flat topography is due to ductile flow of highly mobile lower crustal rocks. This idea has lead to a radical new idea in continental tectonics that horizontal outflow of mobile lower-crustal rock from topographic highs is one of the principal mechanisms by which plateaus grow laterally. It has been proposed that the large-scale topography of the whole of the SE Asian continent has been strongly influenced by this process. The best case for such a mechanism is made in the eastern border of Tibet in the Longmenshan orogen. The Longmenshan region lies on the western fringe of the S-China craton and has been involved in two stages of orogenesis: one event at 200 Ma associated with the collision between the N- and S-China cratons and a second, the Cenozoic Himalayan orogeny related to the collision between India and Asia. However, a number of studies have emphasized that the upper crustal deformation in the Longmenshan is almost entirely Mesozoic and, therefore, unrelated to the India-Asia collision, which began around 54 Ma. This discrepancy can be explained if the crustal thickening in the Longmenshan was caused by solid-state inflow of mobile lower-crustal metamorphic rocks from a topographic high. New zircon U-Pb and mica 40Ar/39Ar dating combined with structural studies confirm that most of the upper crustal deformation in the eastern margin of Tibet is Mesozoic. The deepest exposed parts of the orogen have undergone Barrovian facies metamorphism with estimated peak conditions around 8 kbar and 725 C (Huang et al, 2003) and associated deformation generally thought to have occurred around 200 Ma. However, new apatite U-Pb and monazite electron microprobe dating in the sillimanite zone give ages around 65 Ma. Metamorphic minerals occur both surrounding and as inclusions of the dated monazite suggesting 65 Ma is the age of metamorphism. The main phase of syn-metamorphic deformation is overprinted by a phase of folding associated with N-S fold axes and steep axial planes with geometries that indicate an E-W shortening of 10 - 50%. The evidence for originally thick crust existing around the time of the India-Asia collision and the presence of moderate amounts of Cenozoic E-W shortening can account for most if not all of the present thickness of the continental crust in the Longmenshan area. These results do not, therefore, support models of crustal thickening in the region caused by solid-state lateral flow of mid-crustal metamorphic rocks. Reference: Huang, M.-H., Buick, I. S. & Hou, W. 2003. Tectonometamorphic evolution of the Eastern Tibet plateau: evidence from the central Sogpan-Garze orogenic belt, western China. Journal of Petrology, 44 255-278

Wallis, S. R.; Tsujimori, T.; Aoya, M.; Kawakami, T.; Terada, K.; Suzuki, K.; Hyodo, H.

2003-12-01

334

Constraining Cretaceous subduction polarity in eastern Pacific from seismic tomography and geodynamic modeling  

NASA Astrophysics Data System (ADS)

of recent mantle seismic images below the America ignited a debate on the Cretaceous subduction polarity in the eastern Pacific Ocean. The traditional view is that the massive vertical slab wall under eastern North America resulted from an eastward Farallon subduction. An alternative interpretation attributes this prominent seismic structure to a westward subduction of the North American Plate against a stationary intraoceanic trench. Here I design quantitative subduction models to test these two scenarios, using their implied plate kinematics as velocity boundary conditions. Modeling results suggest that the westward subduction scenario could not produce enough slab volume as seismic images reveal, as is due to the overall slow subduction rate (~2.5 cm/yr). The results favor the continuous eastward Farallon subduction scenario, which, with an average convergence rate of >10 cm/yr prior to the Eocene, can properly generate both the volume and the geometry of the imaged lower mantle slab pile. The eastward subduction model is also consistent with most Cretaceous geological records along the west coast of North America.

Liu, Lijun

2014-11-01

335

Garnet reequilibration and growth in the eclogite facies and geodynamical evolution near peak metamorphic conditions  

Microsoft Academic Search

Caledonian eclogite-facies metamorphism partially reworking Grenvillian granulite-facies anorthosite allows us to study the processes of garnet reequilibration at high pressure and to reconstruct the evolution of the unit near metamorphic peak conditions. Our results indicate that eclogite-facies metamorphism happened in two successive phases: first, inherited granulitic garnet was fractured and reequilibrated from their boundaries (crystal or fracture rims); then eclogite-facies

Hugues Raimbourg; Bruno Goff; Laurent Jolivet

2007-01-01

336

GEODYNAMICS AND RATE OF VOLCANISM ON MASSIVE EARTH-LIKE PLANETS  

SciTech Connect

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

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

2009-08-01

337

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

PubMed

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

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

2012-03-16

338

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

SciTech Connect

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

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

1994-07-01

339

Metallogeny and geodynamics of the Aktiuz Boordu Mining District, Northern Tien Shan, Kyrgyzstan  

NASA Astrophysics Data System (ADS)

The Aktiuz-Boordu Mining District is located in the Northern Tien Shan in the eastern part of Kyrgyzstan. The region is characterized by nappe-folding structures and comprises strongly deformed Precambrian and Lower Paleozoic sedimentary, volcano-sedimentary, and metamorphic sequences. Metamorphic rocks are represented by crystalline schists, para- and orthogneisses, marble, migmatite, amphibolite and eclogite lenses. These rocks are thought to be the oldest in the Northern Tien Shan. The 2780-Ma Aktiuz complex has a total thickness of 2800-2900 m. Available U-Pb zircon age data for the Kemin Group migmatites yield ages of 2200 50 Ma. Based upon their geological setting, multistage metamorphism and isotopic ages of retrograde metamorphism (1.1-1.9 Ga), these rocks reach a few kilometers in thickness and are subdivided into Archaean and Paleoproterozoic. The Archaean and Paleoproterozoic basement metamorphic rocks contain mineralization of various ages and types, including porphyry Cu, Au-sulphide, Au-Bi, barite, epithermal base metal and Au-Ag, REE and rare-metals. Two ore fields have been identified within the Aktiuz-Boordu Mining District, they are: (1) Taldybulak-Boordu, with Au, base metal, and porphyry Cu systems; (2) Aktiuz, with REE, rare- and base-metal deposits. Within the Paleozoic Taldybulak-Boordu volcanic structure, deposits and occurrences of Au are present at Taldybulak Levoberezhny, Chimbulak Zapadny, Karamoko and Kuranjailyau; of Pb at Boordu, Taldybulak Stary, Chimbulak Vostochny and Chimbulak Zapadny; of Mo at Karabulak, and of Cu at Berkut-Kashka. Almost all are found along the periphery of deeply eroded volcanoes. Rock types in the Taldybulak-Boordu ore field mainly comprise chlorite-amphibole and amphibole schists, amphibolites, and migmatites of the Paleoproterozoic Kuperlisay suite. The younger Paleoproterozoic Kokbulak and Kapchigay suites are represented by mica schists and granite gneisses, which are separated from the Kuperlisay suite by a fault. The basement rocks are cut by a complex network of Paleozoic sub-1 volcanic intrusions, accompanied by eruptive rocks and breccia pipes. These represent the root system of Middle and Late Paleozoic volcanoes. At the Taldybulak Levoberezhny Au deposit, the principal ore-controlling structures are inter- and intraformational shear, thrust-fault zones and tectonic mlange injected by intrusions that underwent metasomatic alteration. Gold-sulphide disseminated mineralization is associated with the upper part of Taldybulak shear zone and is associated with monzodiorites and quartz-tourmaline veinlets. The Aktiuz ore field is located in an uplifted block of the basement rocks, including gneisses and crystalline schists (the Archean Aktiuz complex and Paleoproterozoic Kemin Group). They are intruded by Neoproterozoic mafic and ultramafics rocks, Late Ordovician-Silurian collision granites and granodiorites, Devonian monzodiorites, alaskites, alkalic and subalkalic two-feldspar granites, and Permian-Triassic syenites, subalkalic leucogranites, granophyres and granite-porphyries. The Kuperlisay leucogranite intrusion is an elongated body with several ridge-like projections of granophyres. For the Kuperlisay leucogranite a K-Ar age of 260 Ma was obtained, whereas the K-Ar age of granophyre is 225-230 Ma. Analyses of the Aktiuz granite samples taken from the Kutessay open pit yielded an age of 416 Ma (U-Pb zircon SHRIMP method). The Aktiuz ore field contains deposits of Th at Kuperlisay and Kutessay II, and of REE and base metals at Aktiuz and at Kalesay. All are hosted by leucocratic alkali granites, granophyres, granite-porphyries and albitites. Significant reserves and resources of REE and base metals ores for the Aktiuz and Kutessay II deposits make them economically important.

Djenchuraeva, R. D.; Borisov, F. I.; Pak, N. T.; Malyukova, N. N.

2008-03-01

340

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

341

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

Microsoft Academic Search

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

Philip England; Peter Molnar; Frank Richter

2007-01-01

342

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

343

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

Microsoft Academic Search

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

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

2002-01-01

344

Available online at www.sciencedirect.com Journal of Geodynamics 45 (2008) 99119  

E-print Network

simultaneously with D3 hinterland-directed tectonic transport at the boundary between the external and internal and are the result of four major tectonic events: (1) an initial Middle to Late Ordovician tectonic accretion and thrusting were initiated during Early Ordovician time (ca. 490 Ma) and culminated with the out

Long, Bernard

345

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

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

346

Permian age of the Burpala alkaline pluton, Northern Transbaikalia: Geodynamic implications  

NASA Astrophysics Data System (ADS)

This paper presents the U-Pb zircon age of pulaskite of the main phase (294 1 Ma) and the rare metal syenite (283 8 Ma) of the Burpala alkaline pluton. The geochronological data show that it was formed in the Early Permian. By age, it is comparable with the Synnyr pluton of the Synnyr rift zone, alkaline granitic rocks and bimodal volcanic associations of the Uda-Vitim rift zone, and carbonatites of the Saizhen rift zone of the Central Asian foldbelt. These intraplate igneous complexes were formed almost simultaneously with crustal granitic rocks of the Angara-Vitim batholite. All of this gives ground to suppose that the origination of their parental melts is a result of the influence of the mantle hot spot or mantle plume on the lithosphere that led to extensive crustal anatexis.

Kotov, A. B.; Vladykin, N. V.; Yarmolyuk, V. V.; Sal'nikova, E. B.; Sotnikova, I. A.; Yakovleva, S. Z.

2013-11-01

347

Geodynamic evolution of the Baguio Mineral District: Unlocking the Cenozoic record from clastic rocks  

NASA Astrophysics Data System (ADS)

Geochemical studies done on the Baguio Mineral District had dominantly looked at the igneous rocks. A major gap is the scarcity of studies dealing with the sedimentary rock geochemistry for this district which this paper intends to address. The petrographic data and major and trace element compositions of the siltstones-sandstones from the lower member of the Late Oligocene to Early Miocene Zigzag Formation show that they are generally quartz-rich and have high K2O, Th and La/Sc contents. The chondrite-normalized REE pattern exhibits a negative Eu anomaly, enrichment in LREEs and flat HREEs similar to typical post-Archean shales. Taken together, the data indicate derivation of the lower member of the Zigzag Formation from intermediate to acid igneous rock sources generated in an active margin setting. A likely candidate source is the Cordon Syenite Complex/Palali Formation in the Northern Sierra Madre - Caraballo Mountains. Derivation from mafic source rocks in an oceanic island arc setting is inferred for samples of the Middle to Late Miocene Klondyke, Late Miocene to Early Pliocene Amlang and Late Pliocene Cataguintingan Formations. These samples are characterized by low K2O, Th and La/Sc but high Cr/Th values. Unroofing of the Pugo Metavolcanics and the younger plutons in the Central Cordillera provided the materials which eventually produced the Klondyke and Amlang Formations. Continuous uplift and shallowing of the basin resulted in the deposition of the Cataguintingan Formation. The petrography, geochemistry and geological features of the sedimentary rocks clearly define the change in sediment provenance from quartz-rich during the Oligocene to quartz-deficit in the Miocene. This offers additional constraints in understanding the geological evolution of the mineral district.

Dimalanta, Carla B.; Yumul, Graciano P.; Imai, Akira

2013-03-01

348

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

349

Present day geodynamics in Iceland monitored by a permanent network of continuous GPS stations  

NASA Astrophysics Data System (ADS)

Iceland is located on the Mid-Atlantic Ridge and thereby offers a rare opportunity to study crustal movements at a divergent plate boundary. Iceland is not only characterized by the divergence of the Eurasian and North American Plates, as several active volcanoes are located on the island. Moderate size earthquakes occur in the transform zones, causing measurable crustal deformation. In 1999 the installation of a permanent network of continuous GPS stations (ISGPS) was initiated in order to observe deformation due to unrest in the Hengill volcanic system and at the Katla volcano. The ISGPS network has been enlarged over the years and consists today of more than 25 CGPS stations. Most of the stations are located along the plate boundary, where most of the active deformation takes place. Uplift due to post-glacial rebound due to the melting of the largest glacier in Europe, Vatnajkull, is also detected by the ISGPS network. This study presents results from analysis of 9 years of data from the ISGPS network, in the global reference frame PDR05, which has been evaluated by the Potsdam-Dresden-Reprocessing group with reprocessed GPS data only. We thus determine subsidence or land uplift in a global frame. The horizontal station velocities clearly show spreading across the plate boundary of about 20 mm/a. Stations in the vicinity of the glacier Vatnajkull indicate uplift in the range of 12 mm/a, while a station in the central part of Iceland shows uplift rates of about 25 mm/a. Tide gauge readings in Reykjavik and current subsidence rates observed with CGPS agree also quite well.

Vlksen, Christof; rnadttir, Thra; Geirsson, Halldr; Valsson, Gumundur

2009-12-01

350

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

E-print Network

INTRODUCTION Planet Earth is an extremely complex system, partly because of the existence of plate tectonics. Plate tectonics is an expression of slow convection of the Earth's mantle over geological timesEarthlosesitsinternalheat(seeglossarypagexx).Onageologicaltimescale(i.e.millions of years), plate tectonics exerts major controls on global sea-level changes and geochemical cycles. We

Müller, Dietmar

351

Quantitative analysis of the extensional tectonics of Tharsis bulge, Mars - Geodynamic implications  

NASA Astrophysics Data System (ADS)

The amount of horizontal strain on the Martian Tharsis bulge is quantified in order to provide further information on the tectonic evolution of this province. About 10 percent of the Tharsis surface bulge exhibits elliptical impact craters, which are the largest strain markers in the solar system. It is shown that these strain ellipses indicate more strain than could be due to the bulge building alone. The existence of such intensely deformed areas, the direction of the extensive strain, the localization of these areas on the bulge crest or on the top of topographic slopes, and the evidence of nonthinned crust under these areas may all be explained by gravitational slidings of the bulge surface over the topographic slope. This sliding would be possible because of the presence of a decollement level two kilometers below the surface, and because of the prefracturation which have made the detachment possible.

Thomas, P. G.; Allemand, P.

1993-07-01

352

K\\/Ar ages and stress pattern in the Azores: Geodynamic implications  

Microsoft Academic Search

We have dated by the K\\/Ar method the oldest volcanic formations known in the Azores archipelago. The results show a development of this oceanic island system from 5.5 m.y. to the present day. The age pattern is not compatible with a simple migration over a small fixed hot spot, but, plotting tectonic directions which control the volcanism versus age and

Gilbert Feraud; Ishiro Kaneoka; Claude Jean Allgre

1980-01-01

353

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

354

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

NASA Technical Reports Server (NTRS)

A program to study a LAGEOS retroreflector design change for optical performance improvement is described. The study objectives, the study approach, the principal assumptions, the type of basic data generated, and the significant results are discussed. Study limitations, implications for research, and suggested additional efforts are also summarized.

1975-01-01

355

Quantitative analysis of the extensional tectonics of Tharsis bulge, Mars - Geodynamic implications  

Microsoft Academic Search

The amount of horizontal strain on the Martian Tharsis bulge is quantified in order to provide further information on the tectonic evolution of this province. About 10 percent of the Tharsis surface bulge exhibits elliptical impact craters, which are the largest strain markers in the solar system. It is shown that these strain ellipses indicate more strain than could be

P. G. Thomas; Pascal Allemand

1993-01-01

356

Evaluation of geodynamic activity of the Dead Sea transform Fault by radon gas concentrations  

NASA Astrophysics Data System (ADS)

Twelve radon lines of dosimeters (detectors) were placed across the Jordan Valley active fault, which is a segment of the active Dead Sea transform fault system. Each line of the dosimeters shows one or more peaks of radon anomaly concentrations. Some of these peaks prove the intersection of the fault trace with these lines in areas where the fault plane is inferred. In other lines, the peaks correspond to the arrangement of faults in areas of pull-apart basins (sag ponds) or pressure ridges, formed due to the left or right step of the fault. Sag ponds usually show low radon emanations, because they are the place for the accumulation of very fine sediments, which decreases their porosity and hence the upward migration of the radon gas. The northern part of the Jordan valley relatively shows high radon emnation, which could be attributed to the presence of a seismic gap in the upper Jordan valley

Al-Bataina, B. A.; Altaj, M. M.; Atallah, M. Y.

2007-12-01

357

Geochemistry and geodynamic implications of the Triassic bimodal magmatism from Western Kunlun Orogen, northwest China  

NASA Astrophysics Data System (ADS)

The Western Kunlun Orogen occupies a key tectonic position at the junction between the Tarim block and the Tethyan domain. However, the late Paleozoic to early Mesozoic, especially the middle to late Triassic tectonic evolution history of the Western Kunlun Orogen remains controversial. This study reports SHRIMP zircon U-Pb ages and geochemical as well as Sr-Nd-Hf isotopic data for middle to late Triassic Taer pluton in Western Kunlun Orogen, Northwest China. The Taer pluton shows a strong bimodal distribution of compositions, with the felsic rocks dominant and the mafic rocks subordinate. Zircon U-Pb dating reveals that the coexisting mafic and felsic rocks are coeval, both emplacing in a period between 234 and 225 Ma. Most of the studied rocks are potassium rich and can be classified into high-K calc-alkaline to shoshonitic series. They are also strongly enriched in LREE, LILE and depleted in HFSE with strong negative Ti and Nb anomalies, and characterized by enriched Sr-Nd-Hf isotopic signatures. Detailed geochemical and isotopic studies indicate that the Taer pluton was emplaced in a post-collisional extensional setting, with the mafic rocks derived from partial melting of the enriched continental lithospheric mantle in the spinel facies field, and the felsic rocks formed by anatexis of newly underplated basaltic rocks. The existence of middle to late Triassic post-collisional magmas in Western Kunlun region suggests that the final closure of Paleo-Tethys and the initial collision between the Western Kunlun and the Qiangtang terranes may have happened before ~234 Ma, most probably in late Permian, rather than in late Triassic or early Jurassic. In assistance with other geological evidences, such as the presence of early Triassic to late Triassic/early Jurassic S-type magmatism, terrestrial molasse depositions, regional unconformities, and strong deformation, we propose that the Western Kunlun Orogen may have undergone a long post-collisional intracontinental process from early Triassic to late Triassic/early Jurassic.

Liao, Shiyong; Jiang, Yaohui; Zhou, Qin; Yang, Wanzhi; Jin, Guodong; Zhao, Peng

2012-03-01

358

Tien Shan, Pamir, and Tibet: History and geodynamics of phanerozoic oceanic basins  

NASA Astrophysics Data System (ADS)

Geological and biogeographical data on the paleooceanic basins of the Tien Shan and High Asia are summarized. The oceanic crustal rocks in the Tien Shan, Pamir, and Tibet belong to the Tethian and Turkestan-Paleoasian systems of paleooceanic basins. The tectonic evolution of these systems in the Phanerozoic was not coeval and unidirectional. The sialic blocks of the future Tien Shan, Pamir, and Tibet were incorporated into the Eurasian continent during several stages. In the Late Ordovician and Silurian several microcontinents were preliminarily combined into the Kazakh-Kyrgyz continent as a composite aggregation. The territories of the Tien Shan and Tarim became a part of Eurasia after the closure of the Turkestan, Ural, and Paleotethian oceans in the Late Carboniferous and Early Permian. The territories of the Pamir, Karakorum, Kunlun, and most of Tibet attached to the Eurasian continent in the Triassic. The Lhasa and Kohistan blocks were incorporated into Eurasia in the Cretaceous, whereas Hindustan was docked to Eurasia in the Paleogene.

Burtman, V. S.

2010-09-01

359

Genesis and geodynamic significance of Mesoproterozoic and Early Cretaceous tholeiitic dyke swarms from the So Francisco craton (Brazil)  

NASA Astrophysics Data System (ADS)

The eastern border of the So Francisco craton is characterized by widespread Mesoproterozoic (1.0 Ga) tholeiitic dykes and minor analogues of Early Cretaceous age (130 Ma). The Mesoproterozoic dykes (Salvador, Olivena, Espinhao, Diamantina) show large elemental and Sr-Nd isotopic variations that suggest different parental melts related to a small-scale heterogeneous mantle of depleted residua and enriched components (Statistical Upper Mantle Assemblage, SUMA), responsible for plume- and crust-type signatures. The Mesoproterozoic intrusions, compatible with early stages of Rodinia breakup, may represent the initial breakup of the So Francisco-Congo junction. Early Cretaceous dykes (Espinhao) reveal normal and reversed polarities, indicating two distinct intrusive periods. These intrusions have elemental and Sr-Nd isotopic compositions similar to those of the coeval (132 Ma) high-TiO 2 tholeiites from southern Paran Basin (Urubic-type, Brazil) and northern Etendeka (Khumib-type, Namibia). The genesis of these tholeiites requires lithospheric mantle components, as represented by K-alkaline (and carbonatitic) rocks from the Asuncion-Sapucai graben (Paraguay), that highlight the intriguing Pb-isotope relationships involving the Urubic-Khumib tholeiites. The essential role of the Tristan plume is difficult to determine. The spatial distribution of such uncommon high-TiO 2 tholeiites reveals that similar lithospheric components may exist in different cratonic blocks and associated mobile belts.

Rosset, A.; De Min, A.; Marques, L. S.; Macambira, M. J. B.; Ernesto, M.; Renne, P. R.; Piccirillo, E. M.

2007-06-01

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Geological and archaeological evidence of active faulting on the Martana Fault (Umbria-Marche Apennines, Italy) and its geodynamic implications  

NASA Astrophysics Data System (ADS)

This paper examines the morphotectonic and structural-geological characteristics of the Quaternary Martana Fault in the Umbria-Marche Apennines fold-and-thrust belt. This structure is more than 30 km long and comprises two segments: a N-NNW-trending longer segment and a 100°N-trending segment. After developing as a normal fault in Early Pleistocene times, the N-NNW Martana Fault segment experienced a phase of dextral faulting extending from the Early to Middle Pleistocene boundary until around 0.39 Ma, the absolute age of volcanics erupted in correspondence to releasing bends. The establishment of a stress field with a NE-ENE-trending 3 axis and NW-NNW 1 axis in Late Pleistocene to Holocene times resulted in a strong component of sinistral faulting along N-NNW-trending fault segments and almost pure normal faulting on newly formed NW-SE faults. Fresh fault scarps, the interaction of faulting with drainage systems and displacement of alluvial fan apexes provide evidence of the ongoing activity of this fault. The active left-lateral kinematic along N-NNW-trending fault segments is also revealed by the 1.8 m horizontal offset of the E-W-trending Decumanus road, at the Roman town of Carsulae. We interpret the present-day kinematics of the Martana Fault as consistent with a model connecting surface structures to the inferred north-northwest trending lithospheric shear zone m