Sample records for geodynamics

  1. Geodynamics.

    ERIC Educational Resources Information Center

    Flinn, Edward A.

    1983-01-01

    Discusses trends, research activities, and conferences in geodynamics. These include topics on the lithosphere and lower continental crust formation discussed at a U.S. Geodynamics Committee workshop (Austin, Texas 1982) and symposia (each dealing with specific topics) sponsored by the Inter-Union Commission on Dynamics and Evolution of the…

  2. NASA geodynamics program: Bibliography

    NASA Technical Reports Server (NTRS)

    1990-01-01

    The Seventh Geodynamics Program report summarizes program activities and achievements during 1988 and 1989. Included is a 115 page bibliography of the publications associated with the NASA Geodynamics Program since its initiation in 1979.

  3. NASA Geodynamics Program

    NASA Technical Reports Server (NTRS)

    1984-01-01

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

  4. Fundamentals studies in geodynamics

    NASA Technical Reports Server (NTRS)

    Anderson, D. L.

    1980-01-01

    Research in geodynamics, seismology, and planetary quakes is presented. Terradynamics and plate tectonics are described using dynamic models. The early evolution of the Earth's mantle is also discussed.

  5. NASA geodynamics program

    NASA Technical Reports Server (NTRS)

    1980-01-01

    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.

  6. Fundamental studies in geodynamics

    NASA Technical Reports Server (NTRS)

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

    1981-01-01

    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.

  7. Geodynamics Branch research report, 1982

    NASA Technical Reports Server (NTRS)

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

    1983-01-01

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

  8. The NASA Geodynamics Program: An overview

    NASA Technical Reports Server (NTRS)

    1983-01-01

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

  9. Chemical geodynamics of Western Anatolia

    Microsoft Academic Search

    Ramananda Chakrabarti; Asish R. Basu; Arundhuti Ghatak

    2011-01-01

    We report major and trace element concentrations and Nd–Sr–Pb isotopic data of 10 post-collisional volcanic domains in Western Anatolia, a seismically active part of the Alpine–Himalayan belt in the Aegean extensional province. Our objective is to provide geochemical constraints for tectono-magmatic processes shaping the late Cenozoic geodynamic evolution of Western Anatolia.Calc-alkaline volcanic rocks occurring to the north of the Izmir–Ankara–Erzincan

  10. Chemical geodynamics of Western Anatolia

    Microsoft Academic Search

    Ramananda Chakrabarti; Asish R. Basu; Arundhuti Ghatak

    2012-01-01

    We report major and trace element concentrations and Nd–Sr–Pb isotopic data of 10 post-collisional volcanic domains in Western Anatolia, a seismically active part of the Alpine–Himalayan belt in the Aegean extensional province. Our objective is to provide geochemical constraints for tectono-magmatic processes shaping the late Cenozoic geodynamic evolution of Western Anatolia.Calc-alkaline volcanic rocks occurring to the north of the Izmir–Ankara–Erzincan

  11. Geodynamics map of northeast Asia

    USGS Publications Warehouse

    Parfenov, Leonid M., (compiler); Khanchuk, Alexander I.; Badarch, Gombosuren; Miller, Robert J.; Naumova, Vera V.; Nokleberg, Warren J.; Ogasawara, Masatsugu; Prokopiev, Andrei V.; Yan, Hongquan

    2013-01-01

    This map portrays the geodynamics of Northeast Asia at a scale of 1:5,000,000 using the concepts of plate tectonics and analysis of terranes and overlap assemblages. The map is the result of a detailed compilation and synthesis at 5 million scale and is part of a major international collaborative study of the mineral resources, metallogenesis, and tectonics of northeast Asia conducted from 1997 through 2002 by geologists from earth science agencies and universities in Russia, Mongolia, northeastern China, South Korea, Japan, and the USA.

  12. The NASA Geodynamics Program report, 1981

    NASA Technical Reports Server (NTRS)

    1982-01-01

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

  13. Research program of the Geodynamics Branch

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

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

  14. Geodynamical Evolution and Tectonic Framework of China

    Microsoft Academic Search

    Guangding LIU

    2007-01-01

    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

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

    E-print Network

    Vigny, Christophe

    themselves : what is the shape and the size of the earth ? If the Earth were flat, then one could see very://www.geologie.ens.fr/~vigny #12;GS of CAS ­ Geodesy & Geodynamics ­ Beijing June 20042 Addressed topics Geodesy and Earth remote sensing : general introduction Global properties of the Earth : Topography, gravity and Geoïd, Global

  16. Geodynamic environments of ultra-slow spreading

    NASA Astrophysics Data System (ADS)

    Kokhan, Andrey; Dubinin, Evgeny

    2015-04-01

    Ultra-slow spreading is clearly distinguished as an outstanding type of crustal accretion by recent studies. Spreading ridges with ultra-slow velocities of extension are studied rather well. But ultra-slow spreading is characteristic feature of not only spreading ridges, it can be observed also on convergent and transform plate boundaries. Ultra-slow spreading is observed now or could have been observed in the past in the following geodynamic environments on divergent plate boundaries: 1. On spreading ridges with ultra-slow spreading, both modern (f.e. Gakkel, South-West Indian, Aden spreading center) and ceased (Labrador spreading center, Aegir ridge); 2. During transition from continental rifting to early stages of oceanic spreading (all spreading ridges during incipient stages of their formation); 3. During incipient stages of formation of spreading ridges on oceanic crust as a result of ridge jumps and reorganization of plate boundaries (f.e. Mathematicians rise and East Pacific rise); 4. During propagation of spreading ridge into the continental crust under influence of hotspot (Aden spreading center and Afar triple junction), under presence of strike-slip faults preceding propagation (possibly, rift zone of California Bay). Ultra-slow spreading is observed now or could have been observed in the past in the following geodynamic environments on transform plate boundaries: 1. In transit zones between two "typical" spreading ridges (f.e. Knipovich ridge); 2. In semi strike-slip/extension zones on the oceanic crust (f.e. American-Antarctic ridge); 3. In the zones of local extension in regional strike-slip areas in pull-apart basins along transform boundaries (Cayman trough, pull-apart basins of the southern border of Scotia plate). Ultra-slow spreading is observed now or could have been observed in the past in the following geodynamic environments on convergent plate boundaries: 1. During back-arc rifting on the stage of transition into back-arc spreading (central part of Bransfield rift); 2. During back-arc inter-subduction spreading (Ayu trough, northern Fiji basin), 3. During diffuse back-arc spreading (area on the south-eastern border of Scotia sea), 4. During back-arc spreading under splitting of island arc (northern extremity of Mariana trough). Each of the geodynamic environments is characterized by peculiar topographic, geological and geophysical features forming under the same spreading velocities. Development of ultra-slow spreading in each of these environments results in formation of peculiar extension sedimentary basins.

  17. Geodynamical Evolution and Tectonic Framework of China

    NASA Astrophysics Data System (ADS)

    LIU, Guangding

    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.

  18. Venus Exploration Priorities for Understanding Tectonic and Geodynamic Evolution

    NASA Astrophysics Data System (ADS)

    Glaze, L. S.

    2015-05-01

    Geodynamic science objectives figure prominently in the VEXAG goals and objectives, as well as the roadmap, for Venus exploration. Although some measurements can be made from orbit, many challenges remain for long-term observations from the surface.

  19. Experimental, Numerical and Observational Models in Geodynamics

    NASA Astrophysics Data System (ADS)

    Lithgow-Bertelloni, Carolina

    2015-04-01

    Geodynamics, the study of the forces that drives all Earth's processes is a rich field that deeply connects all aspects of geological and geophysical studies, from surface observations of the sedimentary record to knowledge of deep Earth structure from mineral physics and seismology. In the context of the solid Earth geodynamics primarily focuses on lithosphere and mantle dynamics, while core dynamics is the purview of geomagnetism. I will focus this talk on the former, its historical context and future developments. We have known the equations of motion and mechanics for ~200 years, but only relatively recently can they be solved with enough accuracy and resolution to do geology. We have made great strides since Arthur Holmes conceptual models of mantle flow, thanks to computational and experimental advances. We can know model plate boundaries globally with resolutions in the order of a few kms and image temperature and velocity simultaneously in the laboratory in 3D and non-intrusively. We have also learned a great deal about the physics of the Earth, from composition to rheology. New theories on plate boundary rheology are paving the way for self-consistent generation of plates from mantle flow. New computational methods allow for adaptive meshing, fabric development and history, so we can study deformation and compare directly to geological observations in mountain ranges and continental rifts. We can use ever more sophisticated images of mantle structure from seismic and other geophysical data to probe the relationship between melting, flow and dynamical processes. We can reconstruct landscapes and relief, plate motions and sedimentation and ask how much the mantle has contributed to drainage reversal, sedimentation and climate change. The future of the field is ever brighter.

  20. Scientific Data Analysis and Software Support: Geodynamics

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

    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.

  1. Geodynamic contributions to global climatic change

    NASA Technical Reports Server (NTRS)

    Bills, Bruce G.

    1992-01-01

    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.

  2. Singular Spectrum Analysis in Astrometry and Geodynamics

    NASA Astrophysics Data System (ADS)

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

    2010-10-01

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

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

    E-print Network

    Vigny, Christophe

    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

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

    E-print Network

    Vigny, Christophe

    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

  5. Radar altimetry methods for solid earth geodynamics studies

    Microsoft Academic Search

    Hyong Ki Lee

    2008-01-01

    Satellite radar altimetry, which was initially designed for accurate measurements of sea surface height, has been demonstrated to be applicable to non-ocean surfaces as well. In this study, three different applications of satellite altimetry to geodynamics studies have been examined: solid Earth crustal deformation due to Glacial Isostatic Adjustment (GIA) over Hudson Bay, North America, water level fluctuation over vegetated

  6. Towards High Accuracy (millimeter) Laser Ranging Using Laser Geodynamic Satellites

    Microsoft Academic Search

    Thomas Varghese; Michael Selden

    1990-01-01

    Laser Geodynamic Satellite (LAGEOS) is a passive spherical satellite of 60cm diameter with a symmetrical distribution of 426 cube corners. It will be launched by NASA for laser ranging from ground stations. The temporal response of the spacecraft was studied using short pulse lasers and a high speed streak camera. Experimental results suggest that range measurements from the ground to

  7. Overview and Observational Constraints on Venus' Geodynamics and Tectonics

    NASA Astrophysics Data System (ADS)

    Smrekar, S. E.

    2015-05-01

    Today Venus is a single plate, uninhabitable planet. Why doesn’t it have plate tectonics? Did it ever have plate tectonics or a more mobile lid? This paper reviews what is known about Venus’ tectonics and geodynamics, as well as what is debated.

  8. The Allegresque History of Chemical Geodynamics: the Tenth Anniversary Revision

    Microsoft Academic Search

    N. Shimizu

    2007-01-01

    Chemical geodynamics is a field of studies of the dynamic workings of the earth using chemical and isotopic tracers. It is a forum where geophysicists and geochemists exchange thoughts and ideas, and Prof. Allegre's contributions to the field go much beyond the term he coined. At the Allegre Symposium in 1997 in Paris, a tapestry depicting the history of chemical

  9. Applications of deformation analysis in geodesy and geodynamics

    Microsoft Academic Search

    Athanasios Dermanis; Evangelos Livieratos

    1983-01-01

    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

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

    Microsoft Academic Search

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

    2000-01-01

    New regional seismological data acquired in Colombia during 1993 to 1996 and tectonic field data from the Eastern Cordillera (EC) permit a reexamination of the complex geodynamics of northwestern South America. The effect of the accretion of the Baudó-Panama oceanic arc, which began 12 Myr ago, is highlighted in connection with mountain building in the EC. The Istmina and Ibagué

  11. Geodynamic Evolution of the Banda Sea Region

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    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.

  12. Geochemical discrimination of basalts formed in major geodynamic settings

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

    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.

  13. Cultural and Technological Issues and Solutions for Geodynamics Software Citation

    NASA Astrophysics Data System (ADS)

    Heien, E. M.; Hwang, L.; Fish, A. E.; Smith, M.; Dumit, J.; Kellogg, L. H.

    2014-12-01

    Computational software and custom-written codes play a key role in scientific research and teaching, providing tools to perform data analysis and forward modeling through numerical computation. However, development of these codes is often hampered by the fact that there is no well-defined way for the authors to receive credit or professional recognition for their work through the standard methods of scientific publication and subsequent citation of the work. This in turn may discourage researchers from publishing their codes or making them easier for other scientists to use. We investigate the issues involved in citing software in a scientific context, and introduce features that should be components of a citation infrastructure, particularly oriented towards the codes and scientific culture in the area of geodynamics research. The codes used in geodynamics are primarily specialized numerical modeling codes for continuum mechanics problems; they may be developed by individual researchers, teams of researchers, geophysicists in collaboration with computational scientists and applied mathematicians, or by coordinated community efforts such as the Computational Infrastructure for Geodynamics. Some but not all geodynamics codes are open-source. These characteristics are common to many areas of geophysical software development and use. We provide background on the problem of software citation and discuss some of the barriers preventing adoption of such citations, including social/cultural barriers, insufficient technological support infrastructure, and an overall lack of agreement about what a software citation should consist of. We suggest solutions in an initial effort to create a system to support citation of software and promotion of scientific software development.

  14. Late Cambrian-Ordovician tectonics and geodynamics of Central Asia

    Microsoft Academic Search

    N. L. Dobretsov; M. M. Buslov

    2007-01-01

    In the Late Cambrian-Ordovician, Gondwana-derived microcontinents such as Kokchetav, Altai-Mongolian, Tuva-Mongolian, and Barguzin, as well as the Kazakhstan-Tuva-Mongolian island arc or a system of island arcs were involved in intense accretion-collision processes in similar geodynamic settings on a vast territory of Central Asia — from West Kazakhstan to Lake Baikal. The processes were likely to be the result of a

  15. Geodynamic setting of recent volcanism in North Eurasia

    Microsoft Academic Search

    V. I. Kovalenko; V. V. Yarmolyuk; O. A. Bogatikov

    2009-01-01

    A GIS layout of the map of recent volcanism in North Eurasia is used to estimate the geodynamic setting of this volcanism.\\u000a The fields of recent volcanic activity surround the Russian and Siberian platforms—the largest ancient tectonic blocks of\\u000a Eurasia—from the arctic part of North Eurasia to the Russian Northeast and Far East and then via Central Asia to the

  16. Applications of Geodesy to Geodynamics, an International Symposium

    NASA Technical Reports Server (NTRS)

    Mueller, I. I. (editor)

    1978-01-01

    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.

  17. Role of the Earth's rotation in global geodynamics

    Microsoft Academic Search

    N. Pavlenkova

    2009-01-01

    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

  18. Mud Volcanism, Geodynamics and Seismicity of Azerbaijan and the Caspian Sea Region

    Microsoft Academic Search

    Behrouz M. Panahi

    A dramatic activation of geodynamic processes of a natural and technogenic origin has been observed within the Azerbaijan and the Caspian Sea area for the last decade. It is evident this activation observed due to the unique geodynamics of the region which associated with peculiarities of geological structure — in particular, with a very thick and young sedimentary cover. Geological

  19. International GPS (Global Positioning System) Service for Geodynamics

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

    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.

  20. Geodynamic reconstructions of the South America-Antarctica plate system

    NASA Astrophysics Data System (ADS)

    Vérard, Christian; Flores, Kennet; Stampfli, Gérard

    2012-01-01

    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.

  1. Effects of turbulence on the geodynamic laser ranging system

    NASA Technical Reports Server (NTRS)

    Churnside, James H.

    1993-01-01

    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.

  2. Mantle Plume Dynamics Constrained by Seismic Tomography and Geodynamics

    NASA Astrophysics Data System (ADS)

    Glisovic, P.; Forte, A. M.

    2012-12-01

    We construct a time-dependent, compressible mantle convection model in three-dimensional spherical geometry that is consistent with tomography-based instantaneous flow dynamics, using an updated and revised pseudo-spectral numerical method [Glisovic et al., Geophys. J. Int. 2012]. We explored the impact of two end-member surface boundary conditions, for a rigid and plate-like surface, along with geodynamically-inferred radial viscosity profiles. In each case we find that deep-mantle hot upwellings are durable and stable features in the mantle-wide convective circulation. These deeply-rooted mantle plumes show remarkable longevity over very long geological time spans (several hundred million years), mainly owing to the high viscosity in the lower mantle. Our very-long time convection simulations suggest that the deep-mantle plumes beneath the following hotspots: Pitcairn, Easter, Galapagos, Crozet, Kerguelen, Caroline and Cape Verde, are most reliably resolved in the present-day tomographic images.

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

    E-print Network

    Georgen, Jennifer E

    2001-01-01

    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 ...

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

    E-print Network

    Vigny, Christophe

    GS of CAS ­ Geodesy & Geodynamics ­ Beijing June 20041 Fundamentals of GPS #12;GS of CAS ­ Geodesy the travel time of radio waves. But the troposphere is not dispersive (effect not inversely proportional

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

    E-print Network

    Long, Maureen Devaney

    2006-01-01

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

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

    SciTech Connect

    Cabre, R.

    1983-01-01

    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.

  7. Geodynamic Evolution of the Eurekan Orogen of Ellesmere Island

    NASA Astrophysics Data System (ADS)

    Heron, P. J.; Pysklywec, R. N.; Stephenson, R.

    2014-12-01

    The Eurekan Orogeny, which created much of the high topography of Ellesmere Island and adjacent Greenland, occurred as a result of mountain-building processes the dynamics of which are not well understood. It is generally considered that the rotation of Greenland in the Eocene (related to sedimentary basin formation in Baffin Bay) produced compressional tectonics between Greenland and Ellesmere Island. As part of this process, the Eurekan Orogeny formed away from a traditional convergent ocean-closure plate boundary, and represents a style of "intraplate" deformation. In this work, the geodynamic evolution of the Eurekan Orogeny and its relationship to the tectonics of the Canadian polar margin and northern Baffin Basin is explored using high-resolution thermal-mechanical numerical experiments with the modelling code SOPALE. The modelling of the High Arctic is constrained by the first-order crustal structure of the region (deduced by local gravity field and passive seismological data). Presented are suites of numerical experiments that investigate how the pre-existing lithospheric structures (both crustal and sub-crustal) control the evolution of the resulting intraplate orogen. The influence of other primary modelling parameters, such as plate convergence velocity and assumed rheology, are also explored. To highlight the role of surface processes on plate and lithosphere deformation, the importance of climate-controlled erosion and deposition in influencing the tectonics of High Arctic orogenesis is considered. As the tectonic evolution of the region is poorly resolved, we present some of the first interpretations of the development of Ellesmerian and northern Baffin lithosphere from the Earth's surface down to the base of the lithosphere. The numerical experiments evaluate and refine the geodynamical interpretations for enigmatic intraplate tectonics—applicable to this Arctic region and other instances globally.

  8. Magnetohydrodynamic Convection in the Outer Core and its Geodynamic Consequences

    NASA Technical Reports Server (NTRS)

    Kuang, Weijia; Chao, Benjamin F.; Fang, Ming

    2004-01-01

    The Earth's fluid outer core is in vigorous convection through much of the Earth's history. In addition to generating and maintaining Earth s time-varying magnetic field (geodynamo), the core convection also generates mass redistribution in the core and a dynamical pressure field on the core-mantle boundary (CMB). All these shall result in various core-mantle interactions, and contribute to surface geodynamic observables. For example, electromagnetic core-mantle coupling arises from finite electrically conducting lower mantle; gravitational interaction occurs between the cores and the heterogeneous mantle; mechanical coupling may also occur when the CMB topography is aspherical. Besides changing the mantle rotation via the coupling torques, the mass-redistribution in the core shall produce a spatial-temporal gravity anomaly. Numerical modeling of the core dynamical processes contributes in several geophysical disciplines. It helps explain the physical causes of surface geodynamic observables via space geodetic techniques and other means, e.g. Earth's rotation variation on decadal time scales, and secular time-variable gravity. Conversely, identification of the sources of the observables can provide additional insights on the dynamics of the fluid core, leading to better constraints on the physics in the numerical modeling. In the past few years, our core dynamics modeling efforts, with respect to our MoSST model, have made significant progress in understanding individual geophysical consequences. However, integrated studies are desirable, not only because of more mature numerical core dynamics models, but also because of inter-correlation among the geophysical phenomena, e.g. mass redistribution in the outer core produces not only time-variable gravity, but also gravitational core-mantle coupling and thus the Earth's rotation variation. They are expected to further facilitate multidisciplinary studies of core dynamics and interactions of the core with other components of the Earth.

  9. Present-day geodynamics of the northern North American Cordillera

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

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

    E-print Network

    J. Marvin Herndon

    2007-01-02

    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.

  11. Chronological constraints on the Permian geodynamic evolution of eastern Australia

    NASA Astrophysics Data System (ADS)

    Li, Pengfei; Rosenbaum, Gideon; Vasconcelos, Paulo

    2014-03-01

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

  12. Geodynamics and temporal variations in the gravity field

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

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

  13. A free surface method for Eulerian finite difference geodynamic codes

    NASA Astrophysics Data System (ADS)

    Thibault, Duretz

    2015-04-01

    In geodynamic simulations, the surface of the Earth is generally represented by a free surface. Whereas some methods offer natural free surface boundary (e. g. Lagrangian Finite Elements), the implementation of a free surface is not trivial in Eulerian finite difference codes. Therefore, the so-called "sticky air" method is often employed. This method is straightforward to implement but suffers from a number of drawbacks. Alternatively a Eulerian discretisation of the free surface is here proposed. The free surface boundary condition is applied on the staggered grid and the resulting free surface is advected using a set of marker points. Numerical tests show that this free surface representation is convergent and offers first order spatial accuracy. Classical community benchmarks test were successfully reproduced and a number of real-life applications (large strain, thermo-mechanical, visco-elasto-plastic models) are presented. Moreover, we show the benefits of this method when an iterative Stokes solvers is employed. This free surface representation is hence a promising tool for three-dimensional numerical simulations.

  14. Geodynamic Effects of Ocean Tides: Progress and Problems

    NASA Technical Reports Server (NTRS)

    Richard, Ray

    1999-01-01

    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.

  15. Geodynamics of Venice tidal marshes observed by radar interferometry

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

    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.

  16. ELEFANT: a user-friendly multipurpose geodynamics code

    NASA Astrophysics Data System (ADS)

    Thieulot, C.

    2014-07-01

    A new finite element code for the solution of the Stokes and heat transport equations is presented. It has purposely been designed to address geological flow problems in two and three dimensions at crustal and lithospheric scales. The code relies on the Marker-in-Cell technique and Lagrangian markers are used to track materials in the simulation domain which allows recording of the integrated history of deformation; their (number) density is variable and dynamically adapted. A variety of rheologies has been implemented including nonlinear thermally activated dislocation and diffusion creep and brittle (or plastic) frictional models. The code is built on the Arbitrary Lagrangian Eulerian kinematic description: the computational grid deforms vertically and allows for a true free surface while the computational domain remains of constant width in the horizontal direction. The solution to the large system of algebraic equations resulting from the finite element discretisation and linearisation of the set of coupled partial differential equations to be solved is obtained by means of the efficient parallel direct solver MUMPS whose performance is thoroughly tested, or by means of the WISMP and AGMG iterative solvers. The code accuracy is assessed by means of many geodynamically relevant benchmark experiments which highlight specific features or algorithms, e.g., the implementation of the free surface stabilisation algorithm, the (visco-)plastic rheology implementation, the temperature advection, the capacity of the code to handle large viscosity contrasts. A two-dimensional application to salt tectonics presented as case study illustrates the potential of the code to model large scale high resolution thermo-mechanically coupled free surface flows.

  17. Tectonics and geodynamics of the Eastern Venezuelan Ranges

    SciTech Connect

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

    1993-02-01

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

  18. The DORIS benefits as seen from flight dynamics to geodynamics

    NASA Astrophysics Data System (ADS)

    Nouel, F.; Berthias, J. P.; Broca, P.; Comps, A.; Deleuze, M.; Guitart, A.; Jayles, C.; Laudet, Ph.; Pierret, C.; Piuzzi, A.

    DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite) is a radio receiver designed to accurately measure the carrier frequencies of incoming signals generated by a worldwide beacon network. The DORIS concept is to minimize error sources so that the submeter level on the low Earth orbit satellite position can be reached almost permanently. The DORIS ground segment includes a control center and an orbit determination service, which were conceived to adequately process DORIS measurements and to maintain this high accuracy objective. Since February 1991, DORIS has been used to track the Earth observation satellite SPOT 2 and will also be a passenger for the following SPOT platforms. DORIS is the French tracking system of the oceanographic altimetry satellite TOPEX/POSEIDON which includes laser and experimental global positioning system (GPS) tracking on the US data. During 1990 and 1991, the SPOT Precise Orbit Determination (POD) was performed allowing an orbit time coverage of more than 70% (including frequent system tests during the first year). Taking the SPOT POD as a reference other tracking systems were evaluated and calibrated. Range, range rate, angular measurements have now generated adequate statistics characterizing their noises and their bias behavior, in terms of instrumental and propagation and time tag. Actual station keeping maneuver performances can also be estimated to the millimeter per second level in the three dimension space. Ionospheric daily maps are a by-product of the DORIS concept with its two coherent stable frequencies 2.03625 GHz and 401.24 MHz. As the measurements are performed on board, an autonomous orbit determination system prototype has been developed and performance estimated. As far as geodynamics are concerned, new Earth gravity fields have been developed by several groups from Europe and United States. These models will allow better orbit determination, especially for sun-synchronous orbits.

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

    NASA Technical Reports Server (NTRS)

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

    1975-01-01

    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.

  20. Geodynamics, Seismicity, Minerageny and Ecology of Arctic Regions

    NASA Astrophysics Data System (ADS)

    Kutinov, Y. G.

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

  1. Numerical Geodynamic Experiments of Continental Collision: Past and Present

    NASA Astrophysics Data System (ADS)

    Gray, Robert

    Research explores deep continental lithosphere (i.e., the continental lower crust and mantle lithosphere) deformation during continental collision. I found that depending on the composition/rheology of the crust and the amount of radiogenic heat production in the crust, three dominant modes of mantle lithosphere deformation evolve under Neoarchean-like conditions: (1) a pure-shear thickening style; (2) an imbrication style; (3) and a "flat-subduction" style. The imbrication and the flat-subduction styles result in the emplacement of "plate-like" mantle lithosphere at depths between 200 km and 325 km. The imbrication style behavior shifts to the "flat-subduction" style behavior after a crustal inversion event. I investigated mature Phanerozoic-style collision and found that it is sensitive to mantle lithosphere density, mantle lithosphere yield stress, lower-crustal strength and to the presence of phase change-related density changes in the lower crust. The early stages of collision are accommodated by subduction of lower crust and mantle lithosphere along a discrete shear zone beneath the overriding plate. Next, the subducting lower crust and mantle lithosphere retreat from the collision zone, permitting the sub-lithospheric mantle to upwell and intrude the overriding plate. Next, the lower crust and mantle lithosphere of the overriding plate delaminate from the overlying crust. This process produces plateau-like uplift. These modeling results are interpreted in the context of available geological and geophysical observables for the Himalayan-Tibetan orogen. I quantitatively investigated the effects that sediment deposition may have on continental lithosphere deformation during collision. In the absence of sedimentation, the early stages of collision are accommodated by subduction of lower crust and mantle lithosphere beneath the overriding plate. Next, the subducting lower crust and mantle lithosphere retreat from the collision zone. This permits the sub-lithospheric mantle to upwell and come into contact with the thickened upper crust. When sedimentation is imposed subduction-like consumption of the subducting plate remains stable. Using numerical geodynamic models, I studied the influence of the pressure-dependence of viscosity on tectonic deformation during collision. At low activation volumes, high convergence rates, and low to moderate initial Moho temperatures the subduction style of mantle lithosphere deformation is dominant. At low activation volumes, high convergence rates, and high initial Moho temperatures distributed pure-shear style deformation occurs. At low activation volumes, low convergence rate, and moderate to high initial Moho temperatures the mantle lithosphere prefers a convective removal style of deformation. Increasing the activation volume of mantle material in either of these three cases changes the style of mantle lithosphere deformation because its viscosity increases non-linearly.

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

    E-print Network

    Tingley, Joseph V.

    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

  3. Late Cretaceous synsedimentary diapirism of Bazina–Sidi Bou Krime Triassic evaporites (northern Tunisia): Geodynamic implications

    Microsoft Academic Search

    Fahmi Ben Mehrez; Jamel Kacem; Mahmoud Dlala

    2009-01-01

    The structural and sedimentary analyses of the surrounding area of the Bazina–Sidi Bou Krime Triassic outcrops (Hedil country, northern Tunisia) show that the geodynamic evolution of this sector has been mainly guided by the diapiric movement of this evaporitic mass in association with synsedimentary extensive tectonics. These results allowed us to imply a new interpretation which excludes the presence of

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

    E-print Network

    Kaus, Boris

    Factors that control the angle of shear bands in geodynamic numerical models of brittle deformation Viscoplasticity Numerical modelling Long-term tectonics Numerical models of brittle deformation on geological. Introduction Numerical modelling of the deformation of brittle crust on geo- logical timescales is an important

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

    E-print Network

    Paris-Sud XI, Université de

    1 Journal of Geodynamics Offshore Oligo-Miocene volcanic fields within the Corsica-Liguria Basin-rich calc-alkaline. Miocene volcanic activity was important in Sardinia, where andesites and ignimbrites to our initial project. Key-Words: Mediterranean, Ligurian margins and Basin, Offshore Corsica, Miocene

  6. Heat flow and geodynamics in the Tyrrhenian Sea F. Mongelli,1

    E-print Network

    Doglioni, Carlo

    the first measurements of heat flow in the Tyrrhenian basin for 12 stations; the average value of the bestHeat flow and geodynamics in the Tyrrhenian Sea G. Zito,1 F. Mongelli,1 S. de Lorenzo1 and C.g. Kastens et al., 1988; Bigi et al., 1989; Sartori, 1989; Savelli, 2001). Extension evolved to ocean

  7. CretaceousTertiary geodynamics: a North Atlantic exercise Trond H. Torsvik,1,2

    E-print Network

    Torsvik, Trond Helge

    Cretaceous­Tertiary geodynamics: a North Atlantic exercise Trond H. Torsvik,1,2 Jon Mosar1 reconstructions are presented for the Cretaceous­Early Tertiary North Atlantic using a combination described misfits between the North Atlantic Plate elements at successive intervals during this time period

  8. Structural Analysis of a Sampling of Tesserae: Implications for Venus Geodynamics

    Microsoft Academic Search

    Vicki L. Hansen; James A. Willis

    1996-01-01

    Understanding the nature and timing of tessera formation is fundamental to Venus tectonic and geodynamic models. Tesserae are commonly considered to exhibit complex deformation histories, to represent the oldest global stratigraphic unit, to have formed during a global phase of tesserization, and to require weak lithosphere for their formation. Although these characterizations of tesserae are gaining widespread mention in the

  9. New evidence for dislocation creep from 3-D geodynamic modeling of the Pacific upper mantle structure

    E-print Network

    Zhong, Shijie

    New evidence for dislocation creep from 3-D geodynamic modeling of the Pacific upper mantle mantle: diffusion creep through diffusion of atoms along grain boundaries and dislocation creep on the dynamical evolution of the mantle and the development of mantle fabric. Due to the lack of in situ

  10. Constraining mantle flow with seismic and geodynamic data: A joint approach

    E-print Network

    Long, Bernard

    Constraining mantle flow with seismic and geodynamic data: A joint approach Nathan A. Simmons a the style of convective flow occurring in the mantle is essential to understand the thermal and chemical evolution of Earth's interior as well as the forces driving plate tectonics. Models of mantle convection

  11. Monitoring global geodynamical parameter variations with GPS and low earth satellites

    Microsoft Academic Search

    S. C. Wu; S. M. Lichten; R. P. Malla

    1992-01-01

    A low earth satellite enhances global geodynamical parameters determination with GPS in two ways. First, it improves the GPS orbits, which in turn improve the estimates of other parameters. Secondly, a low earth satellite completes an orbit cycle in far shorter time (90 to 120 minutes) than do GPS satellites (12 hours); it observes more GPS satellites than a ground

  12. Geodynamic evolution of the Neogene intermontane Chota basin, Northern Andes of Ecuador

    Microsoft Academic Search

    Roberto Barragán; Roger Baudino; René Marocco

    1996-01-01

    The development of intermontane basins with a thick non-marine sedimentary pile is one of the main characteristics of the Andean geodynamic evolution during the Neogene. The Chota basin is the northernmost Neogene intermontane basin recognized in the Andes of Ecuador. This basin is located in the Interandean Depression and presents a sedimentary fill of continental deposits.The detailed stratigraphic and tectonic

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

    E-print Network

    2006-01-01

    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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  15. Miocene to Recent Magmatism and Geodynamics of Eastern Turkey

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

  16. Role of the Earth's rotation in global geodynamics

    NASA Astrophysics Data System (ADS)

    Pavlenkova, N.

    2009-04-01

    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.

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

    SciTech Connect

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

    1988-08-01

    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.

  18. Geodynamics of the Southern Tethyan Margin in Tunisia and Maghrebian domain: new constraints from integrated geophysical study

    Microsoft Academic Search

    Hakim Gabtni; Chokri Jallouli; Kevin Lee Mickus; Mohamed Moncef Turki

    The geodynamic evolution of the Southern Tethyan Margin of Tunisia is investigated using geophysical studies. Analysis of\\u000a gravity and seismic reflection data in the Maghrebian domain and Southern Tunisia reveals the geodynamic role played by the\\u000a North Saharan Flexure (NSF) in the evolution of the Southern Tethyan Margin. The Saharan Atlas Mountains (Atlasic Basin) and\\u000a the African Craton (Telemzan High)

  19. Monitoring global geodynamical parameter variations with GPS and low earth satellites

    NASA Technical Reports Server (NTRS)

    Wu, S. C.; Lichten, S. M.; Malla, R. P.

    1992-01-01

    A low earth satellite enhances global geodynamical parameters determination with GPS in two ways. First, it improves the GPS orbits, which in turn improve the estimates of other parameters. Secondly, a low earth satellite completes an orbit cycle in far shorter time (90 to 120 minutes) than do GPS satellites (12 hours); it observes more GPS satellites than a ground receiver does in shorter time and increases the correlation between GPS orbit errors. This reduces the error in the determination of nonrotational coordinate parameters, i.e., geocentric offset of ground tracking sites. Covariance results with the global geodynamical parameters modeled as constants, and as random-walk parameters to closer reflect the actual variations, are compared. The effects of using different GPS data quality and different ground tracking network are studied. The case of using two earth satellites in orthogonal orbital planes is also investigated.

  20. Rapid Plate Motion Variations Through Geological Time: Observations Serving Geodynamic Interpretation

    NASA Astrophysics Data System (ADS)

    Iaffaldano, Giampiero; Bunge, Hans-Peter

    2015-05-01

    Past and current plate motions are increasingly well mapped from high-temporal-resolution paleomagnetic and geodetic studies, revealing rapid variations that occur on short timescales relative to the time it takes for the large-scale structure associated with mantle buoyancy to evolve. The rates of change of plate velocities hold key information on the geodynamic, tectonic, and Earth's surface processes that may have caused them. Rapid plate motion changes thus provide us with a unique opportunity to quantify the forcing associated with these processes. Important mechanisms capable of inducing such rapid changes include evolving plate boundary forces, for example, those associated with slab sinking or orogeny along convergent margins, as well as temporal variations in pressure-driven flow within the asthenosphere that link plate velocity variations explicitly to changes in dynamic topography. Here, we focus on (a) findings from recent kinematic observations and (b) the quantitative framework that allows their geodynamic interpretation.

  1. Origin and geodynamic significance of Tertiary postcollisional basaltic magmatism in Serbia (central Balkan Peninsula)

    Microsoft Academic Search

    V Cvetkovi?; D. Prelevic; H. Downes; M. Jovanovic; O. Vaselli; Z. Pecskay

    2004-01-01

    Tertiary basaltic magmatism in Serbia occurred through three episodes: (i) Paleocene\\/Eocene, when mostly east Serbian mafic alkaline rocks (ESPEMAR) formed, (ii) Oligocene\\/Miocene, dominated by high-K calc–alkaline basalts, shoshonites (HKCA–SHO) and ultrapotassic (UP) rocks, and (iii) Pliocene episode when rocks similar to (ii) originated. In this study, the geodynamics inferred from petrogenesis of the (i) and (ii) episodes are discussed.The ESPEMAR

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

    Microsoft Academic Search

    Boris J. P. Kaus

    2010-01-01

    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

  3. Geodynamic implications of deep mantle upwelling in the source of Tertiary volcanics from the Veneto region

    E-print Network

    Demouchy, Sylvie

    Geodynamic implications of deep mantle upwelling in the source of Tertiary volcanics from by a depleted asthenospheric mantle component (87 Sr/86 Sri=0.70306­0.70378; "Ndi=+3.9 to +6.8; "Hfi=+6.4 to +8.1, 206 Pb/204 Pbi=18.786­19.574). P-wave seismic tomography of the mantle below the Veneto region shows

  4. Using Zircon Chemistry as a Discriminating Tool for Geodynamical Context of Magma Formation

    NASA Astrophysics Data System (ADS)

    Bussien Grosjean, D.; Chazot, G.; Bollinger, C.; Langlade, J.; Vonlanthen, P.; Guillong, M.; Bachmann, O.; Rouget, M. L.; Liorzou, C.

    2014-12-01

    Zircon, a widespread accessory mineral in rocks of felsic composition, is frequently used in various disciplines of geosciences as a petrogenetic, geochronologic and geothermometric tool. It can survive metamorphism and partial melting, and it is chemically and physically very resistant to erosion. As a consequence, zircon is very common in sedimentary rocks of terrigenous origin. Over the last decades, several studies have focused on detrital zircon grains to track the eroded source of sedimentary rocks. However, despite the fact that zircon chemistry allows its source rock to be dated and characterized in terms of crystallization temperature and composition, the detailed geodynamical context of the source rock is still very difficult to reconstruct. The goal of this study is to infer the geodynamical crystallization environment of zircon from its geochemical signature. Differentiated igneous rocks from several geodynamic environments, including intraplate, active margin, ocean rift, and pre-, syn-, and post-collisional settings, were sampled, and zircon grains were separated, mounted in epoxy, and imaged by cathodoluminescence. The trace element signature of zircon was determined using (in-situ) laser ablation-high-resolution-inductively coupled plasma-mass spectrometry (LA-HR-ICP-MS). Zircons non representative of original magmatic values (LaN(ormalised) > 1, PrN > 10 and SmN/LaN < 10) had been disregarded. Y and Yb seem to behave similarly if we compare zircons from all our samples. But preliminary observation of trace elements such as Nb, Ta, and Th plotted against rare earth elements allows us to characterise and discriminate several geodynamic environments. More particularly, Y/Th ratio and Eu anomaly seem to be significant to distinguish ocean rift and intraplate settings, thus confirming the geochemical control of the zircon crystallisation.

  5. Toward Studying the Variability of Earthquake Seismicity in Geodynamic Numerical Simulations of a Subduction Zone

    Microsoft Academic Search

    Y. V. Dinther; T. Gerya; P. M. Mai; L. A. Dalguer Gudiel; G. Morra

    2009-01-01

    Earthquakes and their faulting dynamics evolve over a broad range of space and time-scales. In this study, we model the long-term earthquake cycle on a convergent margin, starting from geodynamic large space-time scales, sequentially progressing to small space-time scales to cover the range of interest. Our numerical simulations link kinematic observables and long-term deformation phenomena to earthquake occurrences. Observed outer-rise

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

    Microsoft Academic Search

    T. V. Romanyuk

    2009-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  8. 2011-: PhD in petrophysics, Gosciences Montpellier, Universit Montpellier II, France. 2009-2011: Masters in Geodynamics, Gosciences Montpellier, magna cum laude,

    E-print Network

    Demouchy, Sylvie

    . 2009-2011: Masters in Geodynamics, Géosciences Montpellier, magna cum laude, Université de Montpellier in Earth and Environmental Sciences, magna cum laude, Université de Bourgogne, Dijon, France. Research

  9. Multi-disciplinary contributions of HartRAO to global geodesy and geodynamics

    NASA Astrophysics Data System (ADS)

    Combrinck, Ludwig

    2015-04-01

    The Hartebeesthoek Radio Astronomy Observatory (South Africa) supports global initiatives in both geodesy and geodynamics through an active programme of science platform provision in Africa, the Atlantic Ocean, Indian Ocean and Antarctica. Our involvement ranges from the installation of tide gauges, Global Navigation Satellite Systems stations, seismometers and accelerometers on remote islands to the installation of radar reflectors in Antarctica which enable accurate, geo-referenced maps of the Antarctic coast line to be made. Currently we also participate in the African VLBI Network (AVN), with the aim to densify not only astronomical observatories in Africa, but to improve the geometry and distribution of advanced geodetic and geophysical equipment to facilitate development of research platforms in Africa, which can be used for geodynamics and related sciences, supporting international projects such as the WEGENER initiative. We present our multi-disciplinary activities during the last decade and sketch the way forward. Participation of Africa in the global arena of astronomy, geodesy, geodynamics and related fields will receive a major boost during the next decade. This is partially due to the development of a component of the Square Kilometre Array (SKA) in Africa but also due to the Global Geodetic Observing System (GGOS) project and the international objectives of higher geodetic accuracies and more stable reference frames. Consequent spinoffs into many disciplines relying on global reference frames and sub-cm positional accuracies stand to benefit and Africa can play a major role in improving both science and network geometries.

  10. Constraining Mantle Heterogeneities with Joint Inversions of Seismic, Geodynamic, and Mineral Physics Data

    NASA Astrophysics Data System (ADS)

    Lu, C.; Grand, S. P.; Forte, A. M.; Simmons, N. A.

    2014-12-01

    Two outstanding goals of solid earth geophysics are to determine the chemical structure of the Earth and to understand the dynamics of its interior. The dynamics of the mantle are controlled by density variations and combined knowledge of density structure and seismic velocities provide the strongest constraints on chemical heterogeneity. Unfortunately, most of the traditional geophysical methods such as seismic tomography and geodynamic modeling alone cannot adequately resolve the density structure within the mantle. Thus, seismic, geodynamic and mineral physics joint inversion methods have been applied to better understand the dynamics of the mantle in recent years (e.g. Simmons et al. 2010). In these joint inversions, P wave and S wave travel times, as well as four convection-related geodynamic observations (free air gravity, tectonic plate motion, dynamic topography, and the excess ellipticity of the core-mantle boundary) can be used to produce 3-D models of density and seismic velocities simultaneously. The approach initially attempts to find a model that assuming temperature controls lateral variations in mantle properties and then to consider more complicated lateral variations that account for the presence of chemical heterogeneity to further fit data. Here we present new joint inversion results include 50% more new S wave travel time data than in previous work and geodynamic data that extend to larger spherical harmonic degrees. In addition, temperature derivatives of P and S velocity and density have been determined using an updated mineral physics dataset. For the first time we include non-linear anelastic temperature effects on velocities in the joint inversion. The anelastic effects decrease the required high density component within the lower mantle superplumes. The hypothesis that temperature variations explain most observed heterogeneity within the mantle is consistent with our data. Reference: Simmons, N. A., A. M. Forte, L. Boschi, and S. P. Grand (2010), GyPSuM: A joint tomographic model of mantle density and seismic wave speeds, Journal of Geophysical Research: Solid Earth, 115(B12), B12310, doi:10.1029/2010JB007631.

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

    USGS Publications Warehouse

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

    2011-01-01

    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.

  12. Recent geodynamic pattern of the eastern part of the Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Schenk, V.; Schenková, Z.; Grácová, M.

    2009-04-01

    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).

  13. Monitoring deep geodynamic processes within Vrancea intermediate-depth seismic zone by geodetic means

    NASA Astrophysics Data System (ADS)

    Besutiu, Lucian; Zlagnean, Luminita

    2015-04-01

    Background Located in the bending zone of East Carpathians, the so-called Vrancea zone is one of the most active seismic regions in Europe. Despite many years of international research, its intermediate-depth seismicity within full intra-continental environment still represents a challenge of the 21st century. Infrastructure In the attempt to join the above-mentioned efforts, the Solid Earth Dynamics Department (SEDD) in the Institute of Geodynamics of the Romanian Academy has developed a special research infrastructure, mainly devoted to gravity and space geodesy observations. A geodetic network covering the epicentre area of the intermediate-depth earthquakes has been designed and implemented for monitoring deep geodynamic processes and their surface echoes. Within each base-station of the above-mentioned network, a still-reinforced concrete pillar allows for high accuracy repeated gravity and GPS determinations. Results Starting from some results of the previously run CERGOP and UNIGRACE European programmes, to which additional SEDD repeated field campaigns were added, an unusual geodynamic behaviour has been revealed in the area. 1) Crust deformation: unlike the overall uprising of East Carpathians, as a result of denudation followed by erosion, their SE bending zone, with Vrancea epicentre area exhibits a slight subsidence. 2) Gravity change: more than 200 microgals non-tidal gravity decrease over a 20 years time-span has been noticed within the subsiding area. Extended observations showed the gravity lowering as a nowadays continuing process. Interpretation This strange combination of topography subsidence and gravity lowering has been interpreted in terms of crust stretching in the Vrancea epicentre zone due to the gravity pull created by densification of the lower crust as a result of phase-transform processes taking place in the lithospheric compartment sunken into the upper mantle. The occurrence of crust earthquakes with vertical-extension focal mechanism exclusively in the Vrancea seismic zone support the assumption. Recent studies on the Vrancea echoes of 2013 Galati-Izvoarele quake swarm have also confirmed our hypotheses. Based on numerical modelling of the geodynamic process, an estimate of the stretching rate has been obtained, fully consistent with results inferred from studies on the seismic energy released by the Vrancea intermediate earthquakes. Concluding remarks Looking further, the sinking of the Vrancea lithosphere into the upper mantle (and consequent crust stretching, appropriately reflected in the non-tidal gravity change) appears as an ongoing geodynamic process, tightly connected to the intermediate-depth seismicity generated within the lithosphere penetrating the upper mantle by thermo-baric accommodation phenomena. Time series provided by repeated gravity observations conducted on the above-mentioned infrastructure for about ten years have clearly revealed: (i) the persistence of the gravity lowering, and (ii) some apparent connection between the rate of the gravity change, and the amount of seismic energy released by intermediate-depth earthquakes. Acknowledgements. The research has been partly performed through CYBERDYNE project, funded through the EU structural programme (contract #184/2010).

  14. Development of the Côte d´Ivoire Basin: reading provenance, sediment dispersal, and geodynamic implications from heavy minerals

    Microsoft Academic Search

    Stefan Wozazek; Hannelore Krawinkel

    2002-01-01

    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 Côte 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

  15. Constraints from Moho geometry and crustal thickness on the geodynamic origin of the Vrancea Seismogenic Zone (Romania)

    E-print Network

    Knapp, Camelia Cristina

    Constraints from Moho geometry and crustal thickness on the geodynamic origin of the Vrancea to be the Moho at 15s (40­42km) on the Ramnicu Sarat line to 16s (47­48km) on the Braila line, (2) a thick, (5) a lack of notable west-dipping structures in the crust and across the Moho, and (6) variable

  16. Constraints from Moho geometry and crustal thickness on the geodynamic origin of the Vrancea Seismogenic Zone (Romania)

    Microsoft Academic Search

    Dana M. Mucuta; Camelia C. Knapp; James H. Knapp

    2006-01-01

    Reprocessing of industry deep seismic reflection data (Ramnicu Sarat and Braila profiles) from the SE Carpathian foreland of Romania provides important new constraints on geodynamic models for the origin of the intermediate depth Vrancea Seismogenic Zone (VSZ). Mantle (70 200 km) earthquakes of the VSZ are characterized by high magnitudes (greater than 6.5), frequent occurrence rates (approximately 25 years), and

  17. Application of a long-range terrestrial laser scanner in research on lowland geodynamic processes

    NASA Astrophysics Data System (ADS)

    Wi?niewska, Daria; Kramkowski, Mateusz; Tyszkowski, Sebastian

    2015-04-01

    Progress in the LIDAR technology allows collection of data over a longer range and with a higher precision than most of geodetic measurement methods. It is particularly useful in areas that are inaccessible, dangerous, or with a highly variable morphology. These include mountains, steep slopes of river valleys, and edges of water bodies. Because of a high variation in altitude, they are particularly prone to geodynamic processes. In recent years, such areas have been surveyed more and more often with the use of Airborne Laser Scanning, but the high costs and low frequency of surveys make it difficult to trace the dynamics of phenomena and recorded processes. A few years ago, a new method for imaging of land surfaces started to be used: Terrestrial Laser Scanning. The latest scanners make long-distance scanning possible, up to several kilometres), which until recently had been reserved exclusively for Airborne Laser Scanning. The ease and mobility of scanning allows recording of geodynamic processes immediately after their initiation and their constant monitoring, with a high frequency of data collection. The usefulness of long-distance Terrestrial Laser Scanning is presented here on the basis of mass movements on slopes of a large river valley (the lower Vistula valley) and edges of artificial water bodies. These areas were selected because of a high dynamics of geodynamic processes. The scanning was performed at a distance of 2-4 km from the objects, with a resolution of 0.002°. Such parameters of the equipment and the broad scope and long range enable researchers simultaneous scanning of wide belts of the marginal zone. They also allow precise imaging of slopes, including the microforms that cannot be recorded with any other method. Thanks to the characteristics of laser beam reflection, it is also possible to perform analyses that allow identification of landslide initiation, as well as initial stages of erosion of river banks and edges of water bodies. In this study, we used an innovative method, Multi Station Adjustment, enabling easy linking of scans and their georeferencing without the need to establish benchmarks in the field. In practice, this allows further processing of the scans with GIS software. This study is a contribution to the Virtual Institute of Integrated Climate and Landscape Evolution (ICLEA) of the Helmholtz Association

  18. Geodynamic Mechanisms of plateau uplift and strain distribution in Eastern Anatolia

    NASA Astrophysics Data System (ADS)

    Caner Memi?, Ömer; Hakan Gö?ü?, O?uz; Pysklywec, Russell N.; Karabulut, Hayrullah; Keskin, Mehmet

    2015-04-01

    The Eastern Anatolia region (with an average ~2 km elevation) is dominated by N-S shortening and it represents one of the best examples for active/young continental collision between the Arabian and Eurasian plates. Studies suggest that the entire plateau began to rise since the plate collision (about 13 Ma) along the Bitlis-Zagros suture zone and this collision follows the accretion of the units of the Neotethyan ocean where oceanic lithosphere fragments (e.g., ophiolites) underlies the younger units across most of the plateau at present. Seismic imaging of the deep lithosphere in the region suggests that most of the plateau is underlain by 65 km thick total lithosphere and 45 km thick crust. Corroborating the seismological work, petrological interpretations of younger volcanic rocks from the central part of the plateau (e.g., Erzurum-Kars plateau) suggest an asthenospheric source, therefore the mantle lithosphere most likely have been removed form beneath the plateau in the last 10-13 Myr. Proposed geodynamic models that accounts for the observed tectonic anomalies and inferred lithospheric removal in the east Anatolia include: (1) slab steepening/ and break off under the subduction-accretion complex in the south; and (2) mantle lithosphere delamination in the north. A series of numerical geodynamic experiments are carried out to explain the near-surface characteristics (crustal thickness, surface strain rate and heat flow) of the each hypothesis, including combined styles of break-off and delamination. We investigate the role of various controlling parameters in these experiments (e.g., plate convergence velocity, mantle lithosphere density, and crustal density) and relate the model predictions against observed geological, geophysical, and petrological anomalies for Eastern Anatolia. Model results are also considered in the context of the last 30 Myrs geodynamic evolution of the Tibetan plateau (with an elevation average of 5 km), where both Eastern Anatolia and Tibet share several common geologic histories. Our preliminary results suggest the large-scale mantle lithosphere removal under the plateaus can drive significant thermal and topographic perturpations which may be due to the delamination type rather than the localized break-off tectonics.

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

    NASA Astrophysics Data System (ADS)

    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

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

  1. Chemical geodynamics

    Microsoft Academic Search

    A. Zindler; S. R. Hart

    1986-01-01

    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

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

    SciTech Connect

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

    1993-09-01

    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.

  3. Plate Tectonics, the Wilson Cycle, and Mantle Plumes: Geodynamics from the Top

    NASA Astrophysics Data System (ADS)

    Burke, Kevin

    2011-05-01

    By 1968, J. Tuzo Wilson had identified three basic elements of geodynamics: plate tectonics, mantle plumes of deep origin, and the Wilson Cycle of ocean opening and closing, which provides evidence of plate tectonic behavior in times before quantifiable plate rotations. My pre-1968 experience disposed me to try to play a part in testing these ideas. Most recently, with colleagues, I have been able to show that deep-seated plumes of the past ˜5.5 × 108 years have risen only from narrow plume generation zones (PGZs) at the core-mantle boundary (CMB) mostly on the edges of two Large Low Shear wave Velocity Provinces (LLSVPs) that have been stable, antipodal, and equatorial in their present positions for hundreds of millions of years and perhaps much longer. A need now is to develop an understanding of Earth that embodies plate tectonics, deeply subducted slabs, and stable LLSVPs with plumes that rise from PGZs on the CMB.

  4. MLDs, LABs, and Moho's, Oh My! Using Geodynamical Models to Guide Interpretations of Geophysical Observations

    NASA Astrophysics Data System (ADS)

    Cooper, C. M.; Miller, M. S.

    2014-12-01

    As we peer deeper and in more detail into cratonic lithosphere, intriguing structures arise to peak our curiosity and imagination. Seismic discontinuity imaging reveals anomalous features that appear as depths (~100-160 km) that appear to be shallower than the base of the tomographically inferred cratonic lithosphere (~150-300 km). These are now been known as mid-lithospheric discontinuities (MLD). Magnetotelluric data shows regions of low resistivity suggesting regions of hydration or presence of carbon in graphite form. But how do we interpret these observations and how do we use them to learn more about craton formation and evolution? Some explanations for these anomalies include melt accumulation, the lithosphere-asthenosphere boundary (LAB), and phase transitions. We propose that many of the structures might actually be related to the initial formation of the cratonic lithosphere. We use a combination of geodynamic models and observations of the depths and orientations of mid-lithospheric seismic discontinuities from a compilation of recent receiver function observations within various regions of cratonic lithosphere around the world and new results from the West African Craton to test whether some of the imaged structure can be attributed to the initial formation of thickened cratonic lithosphere. The formation of thick, cratonic lithosphere should introduce complex structures that could then be preserved within the long-lived regions (to then be later captured by eager geophysicists). We performed numerical simulations of the thickening of lithosphere. We considered two types of thickening - either a process akin to (1) thrust stacking or (2) viscous thickening of the lithospheric material.. In particular, we looked to delineate regions that showed regions with mid-lithospheric discontinuities occurring at variable depths and orientations. Our geodynamic models provide an explanation for the observation that some cratonic regions exhibit mid-lithospheric discontinuities at variable depths and orientations, but others may not.

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

    NASA Astrophysics Data System (ADS)

    Meghraoui, Mustapha

    2014-05-01

    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.

  6. Program of Geodynamic Investigation for the Site of a New Nuclear Power Plant in Hungary

    NASA Astrophysics Data System (ADS)

    Trosits, D.; Horvath, F.; Katona, T.; Gerstenkorn, A.

    2014-12-01

    Preparation of a new nuclear power plant project is going on in Hungary at Paks site. Although there is an operating plant at the site, comprehensive geological, geophysical investigation has to be implemented in accordance with Hungarian nuclear safety regulation and international norms for confirming the site acceptability and providing a neotectonic basis for site seismic hazard assessment. The scope, techniques and methods of investigations have to be adapted to the geotectonic environment of the site and Pannonian Basin as a whole. The poster presents a brief summary of the program and provides a detailed description of the seismic survey focusing on the 3D subsurface imaging that is the most important task of planned geophysical investigations. The 3D geophysical imaging provides essential geodynamic information to assess the capability of near site faults and for the seismic hazard analysis, as well as for the hydrogeological modeling. The planned seismic survey gives a unique dataset for understanding the spatial relationship between individual fault segments. The 3D survey allows predicting and characterization of deformations induced by recent lithospheric stresses that is crucial for assessing the tectonic stability of the area. 3D seismic survey has to be combined with appropriate 2D and 3D shallow seismic profiling. The obtained 3D seismic data are also used for numerical geodynamic modeling. Rheology of rocks fundamentally influences the frequency of seismic activity, i.e. the accumulation and release of seismic energy. Regarding this the Pannonian Basin has specific features: the crust is thin and thermal gradients are high. This implies the whole lithosphere can be considered rheologically weak and its behavior is mostly plastic. It is suspected that most of the fault zones in the Pannonian basin are restricted to the sedimentary fill and the uppermost crust, and rest of the lithosphere experiences aseismic deformation.

  7. The demise of the Oligo-Miocene fluvial system of the Levant and its geodynamic significance

    NASA Astrophysics Data System (ADS)

    Vachtman, Dina; Mart, Yossi

    2015-04-01

    The Levant rift system is a linear assemblage of axial rifts and their mountainous flanks that comprises two structurally distinct sections. The southern segment is built of series of secondary axial grabens, which trend northwards and are separated from each other by poorly rifted threshold zones, which is the northern extension of the Red Sea continental break-up. The northern section comprises the SW-trending Karasu - Hatay rifts, from which the Ghab graben branches southwards, which is tectonically attributed to the westward migration of Anatolia. A system of large rivers transected the southern section of the Levant from central Arabia in the east to the Mediterranean Sea in the west during the Oligo-Miocene, leaving behind 5 km thick series of clastic deposits at sea, and sandstones and conglomerates of variable thickness on land. The demise of that fluvial system was gradual, stretching from the late Miocene to the early Pleistocene, where coastal rivers were truncated from their sources due to the growth of segmented rift. The geodynamic process that constrains the development of the rifts of the southern Levant and their elevated flanks is oblique rifting, where several small rifts start the evolution along a weakness zone concurrently, separated by wide and inactive threshold zones. Gradually the rifts grow along their long axes to interconnect, shrinking the threshold zone to their disappearence. Such geodynamic history best accounts for the observations of relicts of late Miocene fluvial deposits on mountaintops, large river beds dated to the late Miocene-early Pliocene, and large marine fan deposits of early Pliocene age, where rivers continued to flow in the threshold zones, but truncated by the emerging rifts.

  8. Unravelling the driving forces of Anatolian tectonics: geodynamic models and constraints (Invited)

    NASA Astrophysics Data System (ADS)

    Pysklywec, R. N.; Gogus, O. H.; Komut, T.; Gray, R.

    2013-12-01

    Western and Eastern Anatolia both demonstrate a complex geologic history of horizontal and vertical tectonics. Western Anatolia has been extending significantly since the early Miocene and is associated with normal faulting, rift basins and exhumed zones of Menderes Massif Metamorphic rocks. On the other hand, the East Anatolia plateau has been shortening, uplifting and accommodating plate convergence between Arabian and Eurasian plates along the Bitlis suture zone. At the same time as the tectonic deformation both regions are also experiencing large-scale anomalous vertical motions. For example, admittance functions between free-air gravity and topography for Western Anatolia indicate that the regional topography is isostatically uncompensated and consistent in magnitude with support by an underlying mantle flow component. In this work, we propose that the regional plate deformation is the result of the interplay between lithospheric and mantle (sub-lithospheric) dynamics. Using forward geodynamic models we consider idealized sections of Anatolian lithosphere based on tomographic inversions and examine the magnitude and pattern of surface topography and crustal deformation to reconcile with the observational constraints. The models--driven by the inferred local mantle structure--consistently show a plateau-type uplift and horizontal extension through Western Anatolia with an amplitude and wavelength consistent with the residual topography calculations. There is also a breadth of petrological and seismological research that suggests the absence of mantle lithosphere beneath both Eastern and Western Anatolia. We use the geodynamic experiments to test whether gravitational instability/delamination of the lithosphere in the region may be coupling the forces driving the (horizontal) surface deformation and (vertical) topography.

  9. La Galite Archipelago (Tunisia, North Africa): Stratigraphic and petrographic revision and insights for geodynamic evolution of the Maghrebian Chain

    Microsoft Academic Search

    Habib Belayouni; Daniele Brunelli; Roberto Clocchiatti; Angelida Di Staso; Iz-Eddine El Amrani El Hassani; Francesco Guerrera; Samia Kassaa; Nejia Laridhi Ouazaa; Manuel Martín Martín; Francisco Serrano; Mario Tramontana

    2010-01-01

    The location of the La Galite Archipelago on the Internal\\/External Zones of the Maghrebian Chain holds strong interest for the reconstruction of the geodynamic evolution of the Mesomediterranean Microplate-Africa Plate Boundary Zone.New stratigraphic and petrographic data on sedimentary successions intruded upon by plutonic rocks enabled a better definition of the palaeogeographic and palaeotectonic evolutionary model of the area during the

  10. Tomographic-Geodynamic Model Comparisons and the Presence of Post-Perovskite and Chemical Heterogeneity in Earth's Lowermost Mantle

    NASA Astrophysics Data System (ADS)

    Koelemeijer, P.; Deuss, A. F.; Ritsema, J.; van Heijst, H. J.; Davies, R.; Schuberth, B. S. A.; Chust, T.

    2014-12-01

    Dynamic processes occurring in the mantle and core interact at the core-mantle boundary (CMB), which marks the largest thermal and compositional interface inside the Earth. This interplay has produced a myriad of complex structures in the lowermost mantle that offer valuable insights into the dynamics of this region. Large-low-shear velocity provinces (LLSVPs) dominate shear wave velocity (Vs) models of the deep mantle. In addition, global tomography studies generally find an increase in the ratio of shear wave to compressional wave velocity (Vp) variations, accompanied by a significant anti-correlation between shear wave and bulk sound velocity (Vc) variations. These seismic characteristics, also observed in the recent SP12RTS tomographic model, have primarily been interpreted in terms of chemical variations but could potentially also be explained by the presence of the deep mantle post-perovskite (pPv) phase. In this contribution, we attempt to interpret the observed seismic characteristics by linking them to dynamic processes occurring in the deep mantle. For this purpose, we compare the shear and compressional wave velocity structure of SP12RTS to mantle structure derived from geodynamic models of mantle convection. We project the geodynamic models into the SP12RTS model parametrization and use its resolution operator to account for the limited tomographic resolution. We include geodynamic models with and without the post-perovskite phase and/or chemical variations and in addition vary the CMB temperature. Although the reparametrization and tomographic filtering significantly affect the obtained mantle structure, we demonstrate that the patterns observed in the ratios and correlations of seismic velocities are robust features. Our tomographic-geodynamic model comparison suggests that the seismic characteristics can be explained by the presence of post-perovskite but it allows no discrimination between isochemical and thermochemical models of mantle convection.

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

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Hawie, N.

    2013-12-01

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

  13. Influences of a ridge subduction on seismicity and geodynamics in the central Vanuatu arc.

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    The central part of the Vanuatu arc is characterized by the subduction of the d'Entrecasteaux ridge under the North Fiji Basin. This ridge influences directly the seismicity and the geodynamics in the proximal region. By analyzing the hypocenters from a local microseismic catalog (2008-2009) and global catalogs we show that the subduction interface, in the first 50 km depth, presents a small dipping angle where the ridge is subducting. This bump highlights the buoyancy of the ridge associated to the excess of fluids present in the seamount. This underplating could explain 20% to 60% of the vertical displacement estimated on the forearc islands from corals datations and that can reach a maximum of 6 mm/yr. The high concentration of hydrous minerals in the subducting ridge might also explain the important activity of intermediate depth earthquakes (half of the total activity in the studied region), we observed a very good correlation between the supposed extension of the ridge in depth and the location of these earthquakes. We propose that they are associated to crust minerals dehydration that causes hydrous fracturation trough preexistent faults. This dehydration process is maintained to a maximum depth of 190 km due to the high thermal parameter of the australian plate.Using the geometry of the Wadati-Benioff plane derived from earthquakes localisations, we established a 2D mechanical model to explain the horizontal interseismic displacement observed by GPS on islands of the upper plate. We show that the subduction interface alone cannot explain the GPS velocities observed, the system of thrust faults located below the back arc islands of Maewo and Pentecost, plays a major role in the region geodynamics and accommodate as much convergence as the subduction interface (between ~16 and 34 mm/yr). Using the model we were also able to explain the closing of the Aoba basin during interseismic phase (~25 mm/an). Finally, the mechanical model suggests the existence of a 23 km wide locked patch that reaches the trench.

  14. AlpArray Austria - Illuminating the subsurface of Austria and understanding of Alpine geodynamics

    NASA Astrophysics Data System (ADS)

    Fuchs, Florian; Bokelmann, Götz; Bianchi, Irene; Apoloner, Maria-Theresia; AlpArray Working Group

    2015-04-01

    AlpArray Austria is a research project to study the geodynamics of the Eastern Alps and the subsurface of Austria with a large-scale mobile broadband seismological network. AlpArray Austria is part of the AlpArray project - a unique European transnational research initiative in which 64 research institutes from 17 countries join their expertise to advance our knowledge about the structure and evolution of the lithosphere beneath the entire Alpine area. AlpArray Austria is coordinated by the Department of Meteorology and Geophysics (IMGW) at the University of Vienna and funded by the Austrian Science Fund (FWF). During spring 2015 the deployment of 42 mobile broadband seismometers (and two permanent stations) will commence and by autumn 2015 Austria will be completely covered by a dense seismological network with an average station spacing of about 40 kilometers. The mobile network consisting of 27 Reftek 151 60s sensors (provided by IMGW) and 15 Trillium 120s instruments (provided by the Dublin Institute for Advanced Studies, DIAS, Ireland) will complement the permanent Austrian seismic network operated by the Austrian Zentralanstalt für Meteorologie und Geodynamik (ZAMG) that will also install the two permanent stations. AlpArray Austria will be continuously recording high-quality ground motion data for three years. Seismic data will be distributed through the European Integrated Data Archive (EIDA) and shared with the collaborating AlpArray institutes. AlpArray Austria will shed light on the detailed geological structure and geodynamical evolution of the Eastern Alps and the subsurface of Austria. Utilizing seismic analysis methods such as shear wave splitting, receiver functions and body wave dispersion the AlpArray Austria working group at IMGW will, together with the international partners, focus on seismic anisotropy in the upper mantle, the location of interfaces and tomography, to answer outstanding questions on slab geometry and subduction polarity under the Eastern Alps. While the primary scope of AlpArray Austria is fundamental research the unique dataset will also improve our knowledge about near-surface geologic structures and help to assess the seismic hazard in Austria.

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    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).

  16. Brittle Solvers: Lessons and insights into effective solvers for visco-plasticity in geodynamics

    NASA Astrophysics Data System (ADS)

    Spiegelman, M. W.; May, D.; Wilson, C. R.

    2014-12-01

    Plasticity/Fracture and rock failure are essential ingredients in geodynamic models as terrestrial rocks do not possess an infinite yield strength. Numerous physical mechanisms have been proposed to limit the strength of rocks, including low temperature plasticity and brittle fracture. While ductile and creep behavior of rocks at depth is largely accepted, the constitutive relations associated with brittle failure, or shear localisation, are more controversial. Nevertheless, there are really only a few macroscopic constitutive laws for visco-plasticity that are regularly used in geodynamics models. Independent of derivation, all of these can be cast as simple effective viscosities which act as stress limiters with different choices for yield surfaces; the most common being a von Mises (constant yield stress) or Drucker-Prager (pressure dependent yield-stress) criterion. The choice of plasticity model, however, can have significant consequences for the degree of non-linearity in a problem and the choice and efficiency of non-linear solvers. Here we describe a series of simplified 2 and 3-D model problems to elucidate several issues associated with obtaining accurate description and solution of visco-plastic problems. We demonstrate that1) Picard/Successive substitution schemes for solution of the non-linear problems can often stall at large values of the non-linear residual, thus producing spurious solutions2) Combined Picard/Newton schemes can be effective for a range of plasticity models, however, they can produce serious convergence problems for strongly pressure dependent plasticity models such as Drucker-Prager.3) Nevertheless, full Drucker-Prager may not be the plasticity model of choice for strong materials as the dynamic pressures produced in these layers can develop pathological behavior with Drucker-Prager, leading to stress strengthening rather than stress weakening behavior.4) In general, for any incompressible Stoke's problem, it is highly advisable to look at the predicted dynamic pressure fields, particularly if they are being fed back into the rheology. Given a range of well described model problems, we discuss broader issues of what, if any, are appropriate plasticity models and under what circumstances we can expect to obtain accurate solutions from such formulations.

  17. Solution of geodynamical Problems from the Point of View of Synergeric

    NASA Astrophysics Data System (ADS)

    Hachay, Olga

    2015-04-01

    It is considered the relation of solution geodynamic problems by geosynergetical approach. A new algorithm of seismological information processing of detailed mines catalogue with use kinematic and dynamical characteristics of deformation waves, which propagate with different velocities in the rock massif under heavy influence of single blasts and technological explosions had been developed. It is estimated that the waves, which propagate with the velocities from 10 to 1 m/hour are primary carrier of the energy in the massif and promote its releasing. Events, which occur in the massive with these waves with releasing energy less than 104 joules promote to the creep rebuilding of the massif. Events, which occur in the massive with these waves with releasing energy more, than 105 joules, can be used as rock burst precursory and it is recommend taking into account by changing of explosions in the indicated part of the massif. The whole absence of such events indicates the growing of the stress massif state in the mine as a whole. The received joined information from the seismic catalogue is very significant for forecasting of dangerous events in the rock mines. It is developed an algorithm for scenario of rock shocks treatment in the rock massif. It can be used for analyze massif natural state on seismological polygons. References 1. Hachay O.A. Geosynergetic: theory, method, experiment. Complex analyze of electromagnetic and other geophysical data. M.: KRASAND, 2011.

  18. Low strength of the shallow mantle lithosphere: Data and geodynamical consequences

    NASA Astrophysics Data System (ADS)

    Tommasi, A.; Demouchy, S. A.; Cordier, P.

    2014-12-01

    The shallow mantle is, except in extremely thin and hot plates, the stronger part of the lithosphere and hence a key layer for understanding plate tectonics. We will present mechanical and microstructural data (EBSD and TEM) from deformation experiments on olivine single crystals and polycrystals performed at low temperature (850-1100°C) and moderate pressure (300 MPa) under dry conditions. These results indicate that the shallow lithospheric mantle may deform by dislocation-based processes at much lower stresses than those predicted from the extrapolation of high-temperature experimental data for olivine. Although the experiments show heterogeneous mechanical behaviors, with hardening, the microstructural observations highlight that, even at the high strain rate of the experimental conditions, recovery processes are at play, suggesting that in nature, at lower strain rates and higher pressure, hardening by dislocation entanglement might be counteracted. Consistently, mantle rocks deformed in natural shear zones active at temperatures 850-900°C show microstructures characterized by coarse recrystallized grain sizes (?100µm) and strong crystal preferred orientations, which are consistent with deformation dominantly by dislocation creep at rather low stresses (<100MPa). Based on our experimental results and on a compilation of previously published data on olivine deformation between 500 and 1000 °C, we propose a new semi-empirical exponential flow law, which might represent an upper limit to the uppermost mantle strength. Such a low strength shallow mantle lithosphere suggests a higher equilibrium recrystallized grain sizes, and less shear heating; further geodynamic implications will then be discussed.

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

    NASA Astrophysics Data System (ADS)

    Raznitsin, Yu. N.

    2012-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Batalev, V. Yu.

    2013-02-01

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

  1. Seismicity and geodynamics of the low- to high-grade transition zone of peninsular India

    NASA Astrophysics Data System (ADS)

    Rao, B. Ramalingeswara

    1992-01-01

    A new seismogenetic belt has been identified in the well-known transition zone of peninsular India (lat. 12°-14° N and long. 74°-80° E) based on a critical analysis of historical and recent seismic data. The diffused and weak seismicity in the area could be attributed to the reactivation of adjoining shear zones. A seismic energy release map has been prepared for southern peninsular India, which depicts the long-term seismicity in this region. Temporal variations in seismic activity in space indicate migration of seismic activity from east to west within the transition zone. This phenomenon is discussed in relation to the mobility of shear belts adjacent to the Dharwar Craton. Further, the maximum horizontal principal compressive stress directions on the Indian continent are also briefly discussed. These stresses may be mainly responsible for the mobility of the major shear zones adjacent to the Dharwar Craton. The analysis of the seismic data in space and time, thus, suggests two possible geodynamic models viz., (1) a stick-slip model and (2) a crustal shortening model.

  2. Tracing the origin of Geodynamics: The Alfred Wegener Memorial Expedition 2014

    NASA Astrophysics Data System (ADS)

    Stüwe, Kurt

    2015-04-01

    2012 marked the 100st anniversary of the seminal publications on Continental Drift Theory by Alfred Wegener. These publications (and Wegener's book "On the origin of the continents", published three years later) are widely accepted to be the fundamental breakthrough that opened the path to the Theory of Plate Tectoncis and ultimately the path to modern Geodynamics some 50 years later. In the same historic year of the 1912 publications, Alfred Wegener set off for what was to become the most dramatic of his three Greenland expeditions. On this expedition Wegener and Koch crossed the entire northern icecap of Greenland. In honour of the hundreds anniversary of Wegener's publications, the Austrian Academy of Sciences funded an expedition to trace the footsteps of the 1912 expedition in the spirit of Alfred Wegener, while also conducting modern Earth Science. This expedition that was conducted in summer 2014. For the expedition, a 1952 Cessna180 was acquired in Alaska, adapted with bush wheels, wing extensions and extra tanks and was flown by the author and one of the worlds most renown bush pilots from Alaska in a 10 day effort to Greenland. There, the entire NE Greenland Caledonides were covered and photographed. Field work for a masters projects was conducted and samples were collected from a series of some of the most remote locations in the Caledonides ever visited. Most spectacularly, the original sled of Wegeners 1912 expedition was found some 30 kilometers from its expected location in the Dove Bugt Region of northeastern Greenland.

  3. Late Permian to Late Triassic basin evolution of North Vietnam: geodynamic implications for the South China and Indochina blocks

    NASA Astrophysics Data System (ADS)

    Rossignol, Camille; Bourquin, Sylvie; Hallot, Erwan; Poujol, Marc; Roger, Françoise

    2015-04-01

    The core of South East Asia is composed of a mosaic of continental blocks, among which the Indochina and the South China blocks (present day northern Vietnam), amalgamated during the Permian and/or the Triassic. Late Permian to Late Triassic geodynamic evolution of these two blocks remains controversial. The main discussion points concern the existence and the closure of an oceanic domain separating the Indochina and the South China blocks during this period. Especially, the polarity and the timing of the subduction zone that led to the collision between the blocks as well as the present location of the suture delimiting them are a matter of debate. Despite the valuable information they can provide, the sedimentary basins from northern Vietnam have been neglected in the previous studies dealing with the geodynamic evolution of South East Asia. To determine the geodynamic evolution of the area, the basins of Sam Nua and Song Da, presently located in North Vietnam, have been investigated using a combined approach involving sedimentology, geochronology (U-Pb/zircon) and geochemistry (whole-rock major and trace elements composition of both volcanic and volcaniclastic rocks). The palaeoenvironment evolution, the main unconformities, their age and the tectonic affinities of the interbedded volcanic and volcaniclastics series have been characterized for these two basins. Our results demonstrate (i) that the Song Da Basin exhibits a palaeogeographic affinity with the South China block, (ii) the occurrence of extensive calk-alkaline volcanism and associated volcaniclastic deposits in the Sam Nua Basin, related to the existence of an active magmatic arc during the Early and the lower Middle Triassic, (iii) a South dipping (present day coordinate) oceanic lithosphere beneath the Indochina block, deduced from the location of the magmatic arc south of the potential suture zones, (iv) that an angular unconformity postdates the lower Middle Triassic volcaniclastic deposits in the Sam Nua basin. This unconformity, crosscutting the subduction related deposits, is interpreted as the result of the collision between the Indochina and the South China blocks.

  4. Geodynamics and intermediate-depth seismicity in Vrancea (the south-eastern Carpathians): Current state-of-the art

    NASA Astrophysics Data System (ADS)

    Ismail-Zadeh, Alik; Matenco, Liviu; Radulian, Mircea; Cloetingh, Sierd; Panza, Giuliano

    2012-03-01

    The Vrancea region of the south-eastern Carpathians is a remarkable site of intra-continental intermediate-depth seismicity. A large set of geological, geophysical, and geodetic observations has been accumulated for the last few decades and utilised to improve our knowledge of the shallow and deep structures beneath Vrancea, the crustal and mantle dynamics, and the linkage between deep and surface processes in the region. In this article we review geology and tectonics of the Vrancea region including post-collisional to recent deformations, syn- to post-collisional magmatism, and orogenic exhumation along the East and South Carpathians. The regional seismicity is analysed, and the recent seismic studies including reflection, refraction, body and surface wave tomography are reviewed. We discuss new geodetic measurements of horizontal and vertical movements in the region, geoelectric studies, density/gravity and thermal modelling. Qualitative and quantitative (including retrospective) geodynamic models developed for Vrancea are analysed. The knowledge of regional tectonics, geodynamics, seismicity, lithospheric deformation, and stress regime in the Vrancea earthquake-prone region assists in an assessment of strong ground motion, seismic hazard and risk. The earthquake simulation, seismic hazard, and earthquake forecasting models have also been reviewed providing a link between deep geodynamic processes and their manifestation on the surface. Finally we discuss unresolved problems in Vrancea in order to improve our understanding of the regional evolution, present tectonics, mantle dynamics, intermediate-depth seismicity, and surface manifestations of the lithosphere dynamics and to enhance our ability to forecast strong earthquakes in the Vrancea region. The problems to be solved include: (i) the origin of the high-velocity body revealed by seismic tomography studies (oceanic versus continental); (ii) the lithospheric scale mechanism driving the Miocene subsidence of the Transylvania basin; (iii) sub-crustal structure between 40 and 70 km; (iv) contemporary regional horizontal and vertical movements; and (v) a comprehensive seismic hazard assessment in the region.

  5. GIS-project: geodynamic globe for global monitoring of geological processes

    NASA Astrophysics Data System (ADS)

    Ryakhovsky, V.; Rundquist, D.; Gatinsky, Yu.; Chesalova, E.

    2003-04-01

    A multilayer geodynamic globe at the scale 1:10,000,000 was created at the end of the nineties in the GIS Center of the Vernadsky Museum. A special soft-and-hardware complex was elaborated for its visualization with a set of multitarget object directed databases. The globe includes separate thematic covers represented by digital sets of spatial geological, geochemical, and geophysical information (maps, schemes, profiles, stratigraphic columns, arranged databases etc.). At present the largest databases included in the globe program are connected with petrochemical and isotopic data on magmatic rocks of the World Ocean and with the large and supperlarge mineral deposits. Software by the Environmental Scientific Research Institute (ESRI), USA as well as ArcScan vectrorizator were used for covers digitizing and database adaptation (ARC/INFO 7.0, 8.0). All layers of the geoinformational project were obtained by scanning of separate objects and their transfer to the real geographic co-ordinates of an equiintermediate conic projection. Then the covers were projected on plane degree-system geographic co-ordinates. Some attributive databases were formed for each thematic layer, and in the last stage all covers were combined into the single information system. Separate digital covers represent mathematical descriptions of geological objects and relations between them, such as Earth's altimetry, active fault systems, seismicity etc. Some grounds of the cartographic generalization were taken into consideration in time of covers compilation with projection and co-ordinate systems precisely answered a given scale. The globe allows us to carry out in the interactive regime the formation of coordinated with each other object-oriented databases and thematic covers directly connected with them. They can be spread for all the Earth and the near-Earth space, and for the most well known parts of divergent and convergent boundaries of the lithosphere plates. Such covers and time series reflect in diagram form a total combination and dynamics of data on the geological structure, geophysical fields, seismicity, geomagnetism, composition of rock complexes, and metalloge-ny of different areas on the Earth's surface. They give us possibility to scale, detail, and develop 3D spatial visualization. Information filling the covers could be replenished as in the existing so in newly formed databases with new data. The integrated analyses of the data allows us more precisely to define our ideas on regularities in development of lithosphere and mantle unhomogeneities using some original technologies. It also enables us to work out 3D digital models for geodynamic development of tectonic zones in convergent and divergent plate boundaries with the purpose of integrated monitoring of mineral resources and establishing correlation between seismicity, magmatic activity, and metallogeny in time-spatial co-ordinates. The created multifold geoinformation system gives a chance to execute an integral analyses of geoinformation flows in the interactive regime and, in particular, to establish some regularities in the time-spatial distribution and dynamics of main structural units in the lithosphere, as well as illuminate the connection between stages of their development and epochs of large and supperlarge mineral deposit formation. Now we try to use the system for prediction of large oil and gas concentration in the main sedimentary basins. The work was supported by RFBR, (grants 93-07-14680, 96-07-89499, 99-07-90030, 00-15-98535, 02-07-90140) and MTC.

  6. AlpArray - an initiative to advance understanding of Alpine geodynamics

    NASA Astrophysics Data System (ADS)

    Hetényi, G.; AlpArray Working Group

    2012-04-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Carminati, Eugenio; Lustrino, Michele; Doglioni, Carlo

    2012-12-01

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

  8. Seismicity and geodynamics in the central part of the Vanuatu Arc

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  9. Geodynamics of flat subduction: Seismicity and tomographic constraints from the Andean margin

    NASA Astrophysics Data System (ADS)

    Gutscher, Marc-André; Spakman, Wim; Bijwaard, Harmen; Engdahl, E. Robert

    2000-10-01

    The cause and geodynamic impact of flat subduction are investigated. First, the 1500 km long Peru flat slab segment is examined. Earthquake hypocenter data image two morphologic highs in the subducting Nazca Plate which correlate with the positions of subducted oceanic plateaus. Travel time tomographic images confirm the three-dimensional slab geometry and suggest a lithospheric tear may bound the NW edge of the flat slab segment, with possible slab detachment occurring down dip as well. Other flat slab regions worldwide are discussed: central Chile, Ecuador, NW Colombia, Costa Rica, Mexico, southern Alaska, SW Japan, and western New Guinea. Flat subduction is shown to be a widespread phenomenon, occuring in 10% of modern convergent margins. In nearly all these cases, as a spatial and temporal correlation is observed between subducting oceanic plateaus and flat subduction, we conclude that flat subduction is caused primarily by (1) the buoyancy of thickened oceanic crust of moderate to young age and (2) a delay in the basalt to eclogite transition due to the cool thermal structure of two overlapping lithospheres. A statistical analysis of seismicity along the entire length of the Andes demonstrates that seismic energy release in the upper plate at a distance of 250-800 km from the trench is on average 3-5 times greater above flat slab segments than for adjacent steep slab segments. We propose this is due to higher interplate coupling and the cold, strong rheology of the overriding lithosphere which thus enables stress and deformation to be transmitted hundreds of kilometers into the heart of the upper plate.

  10. Modeling of geodynamic processes on Ganymede and Callisto: Insight into thermal and tectonic histories

    NASA Astrophysics Data System (ADS)

    Dombard, Andrew John

    Geodynamic processes on Ganymede and Callisto, the two largest icy satellites of Jupiter, are modeled, providing insight into the thermal and tectonic histories of these two geophysically similar, yet geologically different, moons. A model for unstable lithospheric extension is applied to Ganymede's grooved terrain, a ubiquitous tectonic form composed of subparallel ridge-and-trough sets. By using updated water-ice ductile parameters and by recognizing that low surface temperatures prevailed during groove formation, the model is shown to be viable (especially if local extension exceeds 10%), predicting sufficiently strong instabilities over proper wavelengths, although requiring large near-surface thermal gradients (>10 K km-1) and strain rates (generally >10-15 s-1). The model, however, ignores elasticity, and instability behavior under viscoelasticity is next shown to be different from that under a viscous rheology, lacking constant growth rates and the presence of a dominant wavelength. While such studies provide information on Ganymede during groove formation, study of relaxed impact craters provides information on thermal state for both moons and throughout their lifetimes. Topography creates stresses that temperature-sensitive ductile creep works to relax. Thus, study of crater populations on Ganymede and Callisto, which display a continuum of relaxation states, can be used to probe thermal evolution. Previous analyses had difficulty reconciling rheological parameters for ice with apparent multi-Gyr ages of some terrains. Here, an elastoviscoplastic model for topographic relaxation is developed, wherein under high heat flow, an elastic flexural effect can develop that leads to greater amounts of degradation and to plastic (i.e., brittle) failure at the surface, particularly on the uplifting crater floor. Under reasonable input parameters, the full range of relaxation states can be reproduced. In order to effectively degrade craters in polar regions, the presence of an insulating regolith or a thick frost deposit, to modulate surface temperatures, is indicated. Plastic strains are less than 1%; it is uncertain whether such magnitudes would be observable in available imagery.

  11. Geological remarks on the relationships between extension and convergent geodynamic settings

    NASA Astrophysics Data System (ADS)

    Doglioni, Carlo

    1995-12-01

    In convergent geodynamic settings, extensional and compressional tectonics occur contemporaneously or in different times and places, but they are deeply linked to each other in a number of different ways. The main types of extensional regimes here considered are for west-dipping subduction zones: (1) back-arc extension (e.g., Tyrrhenian Sea); (2) uplift and related extension due to asthenospheric wedging (e.g., Apennines); (3) extension at the subduction hinge (e.g., Marianas); (4) extension due to increasing length of arcs (e.g., Apennines). For east-, northeast- or north-northeast-dipping subduction zones: (5) extension induced by collapse of orogens (e.g., Alps, Himalayas); (6) extension induced by differential lithosphere-asthenosphere coupling in the hanging wall of a subduction zone (e.g., Aegean rift); (7) rifting induced by orogenic roots anchored into the mantle (e.g., Atlantic and Tethys). Other types may be considered: (8) inversion of plate motion, from convergent to divergent relative plate vectors due to external velocity fields (e.g., Basin and Range); (9) transtension may occur along oblique ramps of thrust arcs due to differential forward propagation of thrusts planes (e.g., southern arm of the Barbados accretionary prism?); transtension and transpression also occur contemporaneously along an undulate strike-slip setting, or extension can accompany foreland dipping duplexes; (10) apparent extension due to down-section cut of thrust planes along subduction zones. Each type of extension generates different shape, depth and relationships between hanging wall and footwall of the associated normal faults and shear zones.

  12. GNSS strain rate patterns and their application to investigate geodynamical credibility of the GNSS velocities

    NASA Astrophysics Data System (ADS)

    Araszkiewicz, Andrzej; Figurski, Mariusz

    2015-04-01

    The potential that lies in the use of GNSS measurements for crustal deformation studies have already noticed in the beginning of the first of such a system (GPS). Today thanks to the development of satellite positioning techniques it is possible to detect displacement on the Earth surface with an accuracy less than 1 cm. With long-term observations we can determine the velocities even more accurately. Growing demand in the last years for GNSS applications, both for scientific and civil use, meant that new networks of the reference stations were created. Such a dense GNSS networks allow to conduct research in the field of crust deformation at a higher spatial resolution than before. In Europe most of the research focuses on Mediterranean regions, where we can monitor events resulting from the tectonic plates collision. But even in Central Europe we can see effect of Africa push. In our research we focused on Polish territory, where in the past 5 years a nearly 300 reference stations were established. With minimal movements that have been observed in Poland, a key issue in this type of research is to determine the geodynamic reliability of the estimated stations velocities. While the long-term observations enable us to determine the very accurate velocities, it hard to indicate how reliably they reflect actual tectonic movements is. In this paper we proposed a method for testing the reliability of stations velocities based on the strain rate field analysis. The method is based on the analysis of the distribution of the rate of deformation tensor components obtained for triangular elements built on the basis of assessed station. The paper presents the results of numerical simulations and initial use of the method for the Polish network of reference stations: ASG-EUPOS

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

    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.

  14. Grain size evolution in the mantle and its effect on geodynamics and seismic observables

    NASA Astrophysics Data System (ADS)

    Myhill, R.; Dannberg, J.; Eilon, Z.; Gassmoeller, R.; Moulik, P.; Faul, U.; Asimow, P. D.

    2014-12-01

    Dynamic models of Earth's convecting mantle usually implement flow laws with constant grain size, stress-independent viscosity and a limited treatment of variations associated with changes in mineral assemblage. These simplifications greatly reduce computational requirements but preclude effects such as shear localisation and transient changes in rheology associated with phase transitions, which have the potential to fundamentally change flow patterns in the mantle. Here we use the finite-element code ASPECT (Bangerth et al., 2013) to model grain size evolution and the interplay between grain size, stress and strain rate in the convecting mantle. We include the simultaneous and competing effects of dynamic recrystallisation resulting from work done by dislocation creep, grain growth and recrystallisation at phase transitions. Further expressions account for slow growth in multiphase assemblages resulting from pinning. Grain size variations also affect seismic properties of mantle materials. We use several formulations from the literature to relate intrinsic variables (P, T, and grain size) from our numerical models to seismic velocity (Vs) and attenuation (Q). Our calculations use thermodynamically self-consistent anharmonic elastic moduli determined for the mineral assemblages in the mantle using HeFESTo (Stixrude and Lithgow-Bertelloni, 2013). We investigate the effect of realistically heterogeneous grain sizes by computing seismic observables such as body wave travel times, ray paths, and attenuation (t*) as well as mode eigenfrequencies and quality factors at different frequencies. We highlight the frequency-dependent sensitivity of seismic waves to grain size, which is important when interpreting Vs and Q observations in terms of mineral assemblage and temperature. This work is based on a project started at the CIDER 2014 summer program. References: Bangerth, W. et al., 2014, ASPECT: Advanced Solver for Problems in Earth's ConvecTion. Computational Infrastructure for Geodynamics, 2014. Stixrude, L. and Lithgow-Bertelloni, C., HeFESTo: Thermodynamics and Elasticity of the Mantle, AGU Fall Meeting 2013.

  15. The role of modern geodynamics in the transformation of the local erosion basis in the Arctic river systems

    NASA Astrophysics Data System (ADS)

    Shapovalova, Elizaveta

    2015-04-01

    To assess the impact of modern geodynamic processes in the erosion of river channels in the area of oil and gas field, located in the permafrost region the following studies were made: interpretation of satellite images to identify fault zones in the structure of the landscape oil and gas field, located in the subarctic zone; mathematical modeling of extensive and local subsidence in the found faults areas; field measurements within the territory of the field. These studies led to conclusions about influence of modern geodynamic processes on activization of erosive processes. Dimensions of the studied field is approximately 40*60 km. As a result of extensive sagging modeling on its territory for the period of the end of the development the sag depth of the Earth's surface equal to 90 cm was obtained. In this case, the slope of the Earth's surface with respect to the central part of the study area will be 4.5 * 10-5. This slope is comparable with the values of the average slope of lowland rivers. For example, for the Ob River it is 4 * 10-5. This case shows that the river flowing through the field, due to changes in the local erosion basis may be experiencing channel deformation in its central part. According to the observations and model calculations local subsidence of the Earth's surface in fault zones induced by mining, lead to the Earth's surface inclines order 7 * 10-5 - 1.2 * 10-3. Field observations in 2014 in areas where active faults identified revealed a number of factors of changes in the river channel. There were areas overdeepened channel, tear off and slipped down blocks of rocks, leading to the subsequent transformation of the channel, as well as additional thermal erosion gullies that increase the accumulation of sediments and alter the structure of the river network. The combination of modern geodynamics with thermokarst processes in perennial permafrost layer enhances erosion. This investigations have shown that the factor of modern geodynamics of natural or man-made influences on the transformation of the river system at the present stage of its development. This is a new factor. Previously, it was not taken into account, among other geomorphological factors in the analysis of structure changes of the Earth's surface.

  16. AlpArray - an initiative to advance understanding of Alpine geodynamics

    NASA Astrophysics Data System (ADS)

    Hetényi, György; AlpArray Working Group

    2013-04-01

    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.

  17. Long-term monitoring of geodynamic surface deformation using SAR interferometry

    NASA Astrophysics Data System (ADS)

    Gong, Wenyu

    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.

  18. Landscape evolution in Lower Austria: Geodynamic processes comprised in time based on luminescence dating of loess

    NASA Astrophysics Data System (ADS)

    Thiel, Christine; Terhorst, Birgit; Jaburova, Iva; Buylaert, Jan-Pieter; Murray, Andrew S.; Frechen, Manfred

    2010-05-01

    Numerous geodynamic processes have formed the present-day landscape. To understand regional landscape dynamics, it is very important to investigate sedimentary outcrops that reflect these different processes. But it is equally important to constrain these processes in time. Loess and loess-like deposits contain considerable information on palaeoenvironmental changes and landscape evolution. Moreover loess is potentially very suitable for luminescence dating because of the long distance atmospheric transport; this allows full resetting of the prior luminescence signal in the mineral grains. The technique also covers a wide time span (from a few years to several hundred thousand years) and it is very suitable for bracketing most landscape evolutionary processes in time, because it directly measures the last exposure to daylight of the mineral grains. At Langenlois, Lower Austria, Pliocene fluvial sediments and Pleistocence loess and loess-like deposits are exposed; the latter are of interest for our study. We present sedimentological data and luminescence ages for several profiles exposed in an abandoned brickyard in Langenlois. Luminescence ages were derived using polymineral silt-sized grains and a SAR-protocol (Murray and Wintle, 2000) with a preheat of 250°C (60 s), IR stimulation at 50°C (100 s) and a subsequent IR stimulation at 225°C for 100 s (referred to as elevated temperature post-IR IRSL protocol; Buylaert et al., 2009). The luminescence (mainly from feldspars) was detected in the blue-violet region through a Schott BG39/Corning 7-59 filter combination. Our data suggest that distinct landscape evolutionary processes have taken place, represented by a gradual shift from fluvial to terrestrial-aeolian deposition. Two different depositional phases could be distinguished by luminescence dating, one of which lies in the Middle Pleistocene (~ 250 ka), whereas the other phase is dated to 35-45 ka. Buylaert, J. P., Murray, A. S., Thomsen, K. J., Jain, M., 2009. Testing the potential of an elevated temperature IRSL signal from K-feldspar. Radiation Measurements, 44, 560-565. Murray, A. S., Wintle, A. G., 2000. Luminescence dating of quartz using an improved single-aliquot regenerative-dose protocol. Radiation Measurements, 32, 57-73.

  19. ENVIMINE - developing environmental and geodynamical safety related to mine closure in the Barents region

    NASA Astrophysics Data System (ADS)

    Väisänen, Ulpu; Kupila, Juho; Kozyrev, Anatoly; Konukhin, Vladimir; Alakangas, Lena

    2015-04-01

    A project of mining environmental research in the Barents region was carried out in 2012-2014, in cooperation between Geological Survey of Finland, Mining Institute of Kola Science Centre, Russian Academy of Sciences, Russia, and Luleå University of Technology, Sweden. The study areas were the active chrome mine of Kemi in Northern Finland, and the closed mines of Umbozero in Murmansk region, Northwestern Russia, and Laver in Northern Sweden. Umbozero mine, producing rare earth metals, was in operation 1984-2004. Laver mine with iron sulphide ore, producing copper, was in operation 1936-1946. The objectives of the project were to develop a methodology for environmentally safe mine closure by cross border cooperation, and to produce information of the mining environment for target groups. The aim was also to find out solutions for minimizing environmental impacts and to develop multilateral relations between Finnish, Russian and Swedish organizations, responsible for environmental management. The studies were carried out by sampling and analyzing of groundwater and surface water, surficial deposits and organic sediments of streams in the mine sites and reference areas. Composition of deposits in the tailings was carried out by means of geophysical measurements (GPR, XRF). Research data of Kemi mine indicate diminished emissions, especially after open pit mining was finished in 2006. The results in Laver, Sweden, indicate that the oxidation rate in the tailings has decreased over time, which may be due to the increased distance over which oxygen needs to diffuse to reach unoxidised sulphide grains in the tailings. Problems in Umbozero are seismic instability, high pH values of waters (max. 10.4), fluorine and aluminum concentrations in the mine site, due to the rock type. Concentrations were decreasing downstream, also heavy metal concentrations were low. Results of the project are the basis for updated database of environmental condition of the study areas and for assessment of environmental impacts. Database will be used for developing recommendations for providing environmental and geodynamical safety of Umbozero. The project was partly funded by the European Union.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  1. Red Sea Rift-Related Quseir Basalts, Central Eastern Desert, Egypt: Petrogenetic and Geodynamic Evolution

    NASA Astrophysics Data System (ADS)

    Farahat, Esam; Ali, Shehata; Hauzenberger, Christoph

    2015-04-01

    Mineral and whole rock chemistry of Tertiary Red Sea rift-related basalts occurred in south Quseir city, Central Eastern Desert, Egypt has been presented to investigate their petrogenetic and geodynamic evolution. The South Quseir basalts (SQB) have been classified as high-Ti tholeiitic lava (TiO2 >2 wt. %) emplaced in anorogenic tectonic setting. Their Mg# varies from 48 to 53. Pearce element ratios (PER) suggest that the SQB magmas have evolved through fractional crystallization of olivine + clinopyroxene ± plagioclase assemblages, however, the absence of Eu-anomaly argues against plagioclase fractionation. The clinopyroxene compositions provide evidence for polybaric fractionation of the parental mafic magma. Estimated temperatures of crystallization range from 1143 to 1323 oC for olivines, 1031 to 1207 oC for clinopyroxenes, 600 to 900 oC for feldspars, and 638 to 787 oC for Fe-Ti oxides. Oxygen fugacity (ƒO2) values range from -15.16 to -19.5. The incompatible trace element signatures of the SQB (La/Ba = 0.08-0.10 and La/Nb = 0.89-1.04) are similar to those of ocean island basalts (OIB) generated from asthenospheric mantle source unaffected by subduction components. Modelling calculations indicate that the SQB primary magmas were derived from 4-5% partial melting of a garnet-bearing lherzolite mantle source which had a potential temperature (Tp= 1334-1432 °C; based on olivine liquid equilibria) corresponding to ambient temperature of MORB (i.e. passive rifting). This ambient mantle would have to rise to shallower depths (< 100 km) in the upper mantle to cross the dry mantle solidus and stimulate adiabatic partial melting. These estimates along with absence of HIMU (high ? refers to high 238U/204Pb) components (based on trace element data) show that the SQB volcanism isn't associated with thermally driven mantle plumes. Thus, the SQB magma generation is related to extensional regime through passive upwelling and adiabatic decompression melting of an asthenospheric mantle source associated with Red Sea rifting.

  2. Tectonic reconstructions with deforming plates and geodynamic modeling of passive margin systems

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

    The effect of mantle flow on surface topography has been the subject of considerable interest over the last few years. A common approach to the problem is to link plate tectonic reconstructions and global geodynamic models. An important limitation of this approach is that traditional plate tectonic reconstructions do not take the deformation of the lithosphere into account. We introduce quantitative models of surface plate kinematics that include areas of deforming continental crust. We present a series of global reconstructions including deforming plates in key areas, derived using tools developed within the open source plate modeling software GPlates. In traditional plate models, the continents are represented as rigid blocks that overlap in full-fit reconstructions. Models that use topological polygons avoid continental overlaps, but plate velocities are still derived on the basis of the Euler poles for the rigid blocks. To resolve these issues, we use a methodology that requires at minimum two inputs; (1) the relative motions of the major rigid blocks within the continents; (2) a definition of the regions in which continental crust between these blocks deformed. We use geological and geophysical data to interpret the landward limit of significant extension and crustal thinning along both conjugate margins. These boundaries are used to construct polygons along both margins that define the extent of the stretched continental crust on either side of the rift. We derive individual motion histories for each point on the conjugate COBs. Joined together, these COB points form the topological boundaries of deforming domains in which each vertex moves independently. The deforming domains represented by topological meshes extend as the major rigid plates either side diverge. In our tectonic reconstruction with deforming plates, the timing and the intensity of continental extension is imposed by the progressive, diachronous breakup and initiation of seafloor spreading for each major margin system. Our methodology allows us to investigate different models for the full-fit reconstruction of major ocean basins such as the North and South Atlantic and the South East Indian Ocean, and revise them if necessary to yield a better fit to available crustal thickness estimates. Once the kinematic models are constructed, the surface velocities within the deforming regions of our reconstruction are calculated within GPlates by linearly interpolating velocities from adjacent non-deforming areas. Velocities derived from the global reconstruction are used as a time-dependent surface boundary condition in mantle convection models that include compositionally distinct crust and continental lithosphere embedded within the thermal lithosphere. These models are the first step towards investigating the effect of both lithospheric stretching and of mantle flow on the total tectonic subsidence of these margins.

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

    E-print Network

    Manning, Craig

    Constraints on Hadean geodynamics from mineral inclusions in N4 Ga zircons Michelle D. Hopkins , T.W. Carlson Keywords: zircon Hadean inclusion thermobarometry U­Pb Jack Hills The inclusion mineralogy of 1450 zircons over 4 billion years in age from the Jack Hills, Western Australia, was characterized

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

    NASA Astrophysics Data System (ADS)

    Keskin, Mehmet

    2014-05-01

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

  5. The seismic cycle on subduction thrusts: a laboratory validation and implications from large-scale geodynamic simulations

    NASA Astrophysics Data System (ADS)

    van Dinther, Ylona; Gerya, Taras; Dalguer, Luis; Mai, Martin; Corbi, Fabio; Funiciello, Francesca; Morra, Gabriele

    2013-04-01

    The physics governing the seismic cycle at seismically active subduction zones remains poorly understood due to restricted direct observations in time and space. In this study, we present visco-elasto-plastic continuum numerical simulations as a new tool that may help to shed light onto the interaction of subduction mechanics and associated seismicity. First, we validate that these models, typically used in long-term geodynamic simulations, are able to reproduce seismological observables. Its ability to model cycles of large analogue earthquakes is demonstrated through a validation with innovative laboratory models (van Dinther et al., 2013). This benchmark shows cycles of fast frictional instabilities can be simulated (and matched), if velocity-weakening (and velocity-strengthening) friction are incorporated in the analogue seismogenic zone (and up- and downdip of it). The resulting model captures a wide range of physical phenomena observed in nature, including a) ruptures propagating as cracks or self-healing pulses; b) repeated slip on a single patch; and c) afterslip leading to postseismic surface displacements that complement a qualitative agreement with geodetic observations. In subsequent large-scale simulations, we include slip rate dependent friction into a thermo-mechanical model of a petrologically realistic continental margin to simulate earthquake-like events with recurrence intervals of a thousand years. These events exhibit surface displacements and earthquake source parameters comparable to nature, including the amount of slip, stress drop, and rupture width. However, rupture propagation is much slower than observed. These models reveal interesting geodynamic and seismological implications, including a) a reconciliation of low effective friction expected from geodynamic models (? < 0.1) with high strengths attained in laboratory experiments (static friction of ~0.7); b) a spontaneous downdip seismogenic limit near the Moho due to plastic strength increase and stress decrease as ductile flow becomes dominant; and c) a spontaneous deceleration of the rupture speed in the up-dip direction, though velocity-strengthening friction is needed to prevent the rupture from regularly breaking the trench.

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

    NASA Astrophysics Data System (ADS)

    Tuchkova, M.

    2012-04-01

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

  7. A study on parameters for implicit penalizing-load algorithms for stabilization of free surfaces in geodynamic models

    NASA Astrophysics Data System (ADS)

    Andres-Martinez, Miguel; Phipps Morgan, Jason; Perez-Gussinye, Marta; Ruepke, Lars H.

    2014-05-01

    Earth surface in geodynamic codes has been typically modeled as a free-stress surface, which means that the total stresses applied to the surface are considered zero value. Free surface allows topography to be generated in response to the inner forces of geodynamic models. Surficial processes, such as erosion and sedimentation, reshape topography and, therefore, change the loads to be considered in the geodynamic processes. Therefore, a free surface is also needed to couple modeling of surficial processes together with mantle dynamics. Real free surface models also allow to study relaxation of topography, such as isostatic post-glacial rebound, in a geodynamic setting. However, free surfaces have typically confronted stability problems when the time step chosen to run the model is bigger than the viscous relaxation time. Time steps small enough to avoid free-surface instabilities usually result in computationally expensive models. We have developed a free-surface stabilization algorithm (FSSA) to avoid instabilities for bigger time steps (>10 Kyr), which penalizes the system with a load calculated implicitly from a portion of the difference between the topography for an initial time step, and the future topography in the next time step. The penalization load is formulated based on the velocities at the nodes for the beginning of the time step, and applied to the nodes at the beginning of the same time step. Additionally, we have coded the FSSA described in Kaus, Mühlhaus and May (2010), for comparison. Their algorithm also penalizes the system with a load which is calculated deriving the surface traction terms from the time discretization of the momentum equation. The penalizing terms in both our and Kaus' FSSAs are controlled by a factor which value ranges between 0 and 1. Several simplistic viscous tests have been run in order to find the optimal (more accurate and more stable) control factor for both algorithms. These tests showed that both methods produce very similar and accurate results (error ~<0.01), and that 2/3 is the optimal control factor for together stability and accuracy, for both FSSAs. The penalizing terms account for a vertical component and an horizontal component, which are symmetric and asymmetric in Stiffness-shape form, respectively. Consequently, the horizontal component of the penalization makes the Stiffness matrix to be asymmetric, so Cholesky factorization cannot be applied, which results into a slower solution of the system. We have developed a scheme to apply Cholesky factorization to the symmetric terms, and use Uzawa-like iterations to include the asymmetric terms in the system. This should intuitively give more stable results than FSSAs that omit the horizontal penalization terms, especially for topographies with steep slopes, where the horizontal component of the velocities is an important term for the surface displacement.

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

    NASA Astrophysics Data System (ADS)

    Chaboureau, Anne-Claire; Guillocheau, François; Robin, Cécile; Rohais, Sébastien; Moulin, Maryline; Aslanian, Daniel

    2013-09-01

    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.

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

    Microsoft Academic Search

    J.-Y. Li

    2006-01-01

    Northeast China and adjacent regions are located in the central East Asian continent and consist tectonically of both the Paleo-Asian and Paleo-Pacific orogens between the Siberian platform and Sino-Korean (North China) block. This paper discusses some hotly-debated issues concerning the Permian geodynamic setting of these regions, based on a comprehensive analysis of available geological, geochemical, paleobiogeographical and paleomagnetic data. Spatial

  10. Tectono-sedimentary events and geodynamic evolution of the Mesozoic and Cenozoic basins of the Alpine Margin, Gulf of Tunis, north-eastern Tunisia offshore

    Microsoft Academic Search

    Fetheddine Melki; Taher Zouaghi; Mohamed Ben Chelbi; Mourad Bédir; Fouad Zargouni

    2010-01-01

    The structural pattern, tectono-sedimentary framework and geodynamic evolution for Mesozoic and Cenozoic deep structures of the Gulf of Tunis (north-eastern Tunisia) are proposed using petroleum well data and a 2-D seismic interpretation. The structural system of the study area is marked by two sets of faults that control the Mesozoic subsidence and inversions during the Paleogene and Neogene times: (i)

  11. Isotopic and geochemical zoning of Devonian magmatism in the Altai–Sayan rift system: Composition and geodynamic nature of mantle sources

    Microsoft Academic Search

    A. A. Vorontsov; V. V. Yarmolyuk; G. S. Fedoseev; A. V. Nikiforov; G. P. Sandimirova

    2010-01-01

    Based on the systematic investigation of the geochemical and isotopic (Sr and Nd) characteristics of basic rocks from various\\u000a volcanic areas of the Devonian Altai-Sayan rift system, the compositions of mantle magma sources were characterized, and the\\u000a geodynamic scenarios of their entrainment into rifting processes were reconstructed. It was found that the titanium-rich basic\\u000a rocks (2.5 2 < 4.2 wt

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  13. What can zircon ages from the Jack Hills detrital zircon suite really tell us about Hadean geodynamics?

    NASA Astrophysics Data System (ADS)

    Whitehouse, Martin; Nemchin, Alexander

    2015-04-01

    As the only direct sample of the Hadean Earth, detrital zircon grains from the Jack Hills, Western Australia, have been the subject of intense investigation over the almost three decades since their discovery. A wide variety of geochemical and isotopic analyses of these grains, as well as their mineral inclusions, have been used variously to support two fundamentally different models for Hadean geodynamics: (i) Some form of (not necessarily modern-style) plate recycling generating felsic (continental-type?) crust at the boundaries [1, 2], or conversely (ii) the persistence of a long-lived, stagnant basaltic lid within which magmatism occurred as a result of internal temperature perturbations and/or impacts [3, 4], a model also generally consistent with a wide range of observations from post-Hadean geochemical reservoirs. Despite the considerable time and resources expended, the majority of these studies uncritically accept the individual U-Pb zircon ages, even though their veracity is key to many of the interpretations [5, 6]. We report here the results of an in-depth evaluation of all published (and new) U-Pb ages from the Jack Hills zircon suite in order to define age populations that can be used with a high degree of confidence in geodynamic interpretations. A notable problem in the interpretation of U-Pb data from ancient zircon grains (including those as young as the Neoarchean) is that disturbance of the systematics even several 100 Ma after crystallization causes data to spread along the concordia curve without becoming discernably discordant within the relatively large error bounds associated with U/Pb ages from in situ dating methods (e.g. SIMS). While 207Pb/206Pb ages are typically more precise, individually they provide no means to detect Pb-loss-induced younging. However, if two or preferably more analyses have been made in the same zircon growth zone, a reasonable evaluation of the possibility of Pb-loss can be made. In the available Jack Hills zircon dataset, only 111 grains have been analysed at least twice and of these, only 48 give a consistent internal age, while only 14 have been analysed more than twice and can strictly be considered to yield true ages. Two resulting age peaks at 4.18 - 4.08 Ga and 4.05 - 3.98 Ga potentially represent major magmatic events in the Hadean. In order to explain ages >4.18 Ga, a magmatic event as old as the oldest reliable Jack Hills zircon age of 4.374 Ga is also required. The significance of this limited number of magmatic events for Hadean global geodynamic models will be discussed. References: [1] Harrison, T.M. et al. Geochim Cosmochim Ac 69 (10), A390-A390 (2005), [2] Peck, et al. Geochim Cosmochim Acta 65 (22), 4215-4229 (2001), [3] Kemp, A.I.S. et al. EPSL, 296 (1-2), 45-56 (2010), [4] Kamber, B.S., et al., Contrib Mineral Petr 145 (1), 25-46 (2003), [5] Cavosie, A.J., et al., Precambrian Res 135 (4), 251-279 (2004). [6] Holden P, et al., Int. J. Masspectrometry, 286, 53-63 (2009)

  14. Comparison of a parallel installation of laser and quartz tube strainmeters at the Geodynamic Observatory Moxa in Thuringia, Germany

    NASA Astrophysics Data System (ADS)

    Kobe, Martin; Jahr, Thomas; Kukowski, Nina; Methe, Pascal; Goepel, Andreas

    2015-04-01

    High-resolution continuous deformation measurements provide an important data base for studies on deformation of the solid Earth (e.g. due to tides or hydrologically-induced deformation) that has strain amplitudes from ?m to nm. Time series can be obtained by different strainmeters that measure relative changes in length between two fixed points on the Earth's surface with a resolution up to 10-10 m. In order to improve the signal-to-noise ratio strainmeters are installed in galleries or caves with a thick mountain overburden. The Geodynamic Observatory Moxa operates beside seismological and gravimetrical sensor systems an extensive strainmeter array. It consists of a borehole extensometer, two quartz tubes at right angles and one diagonally-installed laser strainmeter. In 2011, two new laser strainmeters were added in cooperation with the company SIOS/Ilmenau. They are installed parallel to the quartz tubes and fixed to the bedrock by the same pylon. This kind of parallel installation is unique in the world and allows the direct comparison of measurements of horizontal length changes with different types of strainmeters for the first time. For the comparison of the data we used mainly the tidal analysis of three-years long time series, as well as the signal from a research borehole on the observatory's perimeter. The first results show a decrease of the long lasting device-specific drift by a factor of 2.3 - 2.5 × 10 of the laser strainmeters (LS) with respect to the quartz systems (QS). Furthermore, the signal-to-noise ratio of the LS is significantly higher than for the QS, as can be seen, for example, in the tidal amplitude factors (AF). In the north-south direction we determined AF ˜ 1.0 (LS) and AF ˜ 0.6 (QS) that yields LS- QS ˜ 1.66. In the east-west direction we found AF ˜ 0.67 (LS), AF ˜ 0.16 (QS), and therefore -LS QS ˜ 4.3. The tidal parameters are used to evaluate the new laser strainmeter system. Furthermore the determination of LS- QS provides a method to calibrate the quartz tubes for the first time. The comparison of other deformation signals in the time series reveals that LS- QS changes with the considered signal period. A transfer function is required to calibrate QS using LS. The new laser strainmeter array is a significant step towards the measurement of subsurface deformation at the Geodynamic Observatory Moxa. Furthermore it is presently being used to develop a transportable laser strainmeter system for areal applications, for example, across fault zones.

  15. George V Land paragneisses xenoliths dating. New insights for the Antarctica-Australia connection and geodynamic reconstructions.

    NASA Astrophysics Data System (ADS)

    Lamarque, Gaëlle; Bascou, Jérôme; Ménot, René-Pierre; Paquette, Jean-Louis; Rolland, Yann; Cottin, Jean-Yves

    2015-04-01

    George V Land is constituted of terrains that are considered as the southern extension of Australia in Antarctica. This region plays a key role to better understand the assembly, evolution and separation of the Gondwana and Rodinia supercontinents. In the studied area two distinct continental domains in ages, nature, structures and crustal thicknesses are juxtaposed: the 1.7-2.4 Ga Terre Adélie Craton to the west and a younger domain, comprised of 500 Ma old intrusive complex to the east. The latter is mainly composed of granitoids and is associated with the Ross Orogeny. From field evidences, these two domains are likely separated by a major dextral strike-slip structure: the Mertz shear zone (MSZ, 145°E). The MSZ was activated at 1.7 and 1.5 Ga respectively in amphibolite and greenschists facies conditions. The tectonic evolution of the eastern region between 1.5 Ga (last activation of the MSZ) and 500 Ma (age of the domain bordering the craton) is a key question to geodynamic reconstructions. For this purpose we studied samples of paragneisses xenoliths hosted by the Palaeozoic granitoids, as they represent relics from the underlying basement of this domain. Xenoliths are few-centimeters to several decimeters in size and include different types of paragneisses that may coexist. U-Pb analyses were carried out on 130 zircons from three different xenoliths. Extracted detritic zircons have similar ages from a sample to another showing a common origin of the sedimentary protolith. A large variety of ages were found from 580 Ma to 3.4 Ga and the best-represented age is about 580 Ga that may correspond to a metamorphic stage predating the intrusive event. Another interesting result is that almost no 1.6 to 2.4 Ga zircons were found, suggesting that sedimentary protolithes cannot be derived from erosion of the neighbouring Terre Adélie Craton. This result argues for a tectonic collage between the two domains. By comparing our results with previous similar studies in South Australia and West Antarctica, we propose a new scenario for the geodynamic evolution of the region before the opening of the Southern Ocean.

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

    NASA Astrophysics Data System (ADS)

    Bondarenko, Y.

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

  19. Late Cretaceous transgression on a Cimmerian high (Neka Valley, Eastern Alborz, Iran): A geodynamic event recorded by glauconitic sands

    NASA Astrophysics Data System (ADS)

    Berra, Fabrizio; Zanchi, Andrea; Mattei, Massimo; Nawab, Amir

    2007-07-01

    In the Neka Valley (Eastern Alborz, Iran), glaucony-bearing marine sediments of early-middle Santonian age directly overlie Palaeozoic to Triassic units deformed during the Eo-cimmerian orogenic event (Late Triassic). The Upper Cretaceous open marine sediments were deposited on a flat surface lacking any evidence of pedogenesis. The geochemical and morphological features of glaucony grains, which characterize the base (1 to 1.5 m) of the Upper Cretaceous succession, indicate an autochthonous origin of the highly-evolved glaucony, denoting a long-lasting period of low sedimentation rate. The development of glaucony in the observed stratigraphic position is indicative of a rapid drowning of the former Cimmerian relief that cannot be explained by a eustatic rise alone: the palaeo-depth needed for the development of glaucony and for the presence of the observed bathyal foraminifera assemblages is greater than the maximum eustatic excursion documented in the Cretaceous. The occurrence of glaucony in this stratigraphic position reflects thus an important episode of increased subsidence rates, related to a geodynamic event framed in a time-interval of major plate reorganization in the complex puzzle of the Iranian plates: the subsidence event that caused the development of the glauconitic horizon in the Neka Valley could likely represent the effect of a Santonian stage of the complex and long-lasting story of the opening of the Caspian Sea.

  20. High uplift rates highlight the major role of erosion in the present-day geodynamics of the Western Alps

    NASA Astrophysics Data System (ADS)

    Vernant, P.; Nguyen, H.; Mazzotti, S.; chery, J.; Genti, M.; Cattin, R.

    2013-12-01

    We presents the velocity field of ~160 continuous GNSS sites in France. No significant horizontal motion can be detected to the level of ×0.5 mm/yr (95% confidence), but significant uplift rates up to 1 - 2 mm/yr are observed for sites in the Western Alps, an area underlined by moderate, but frequent, seismicity. Focal mechanisms in the upper crust show extension normal to the range axis in the axial zone, and compression in the foothills. This deformation has usually been interpreted as the result of gravitational collapse of the range under its own weight. Classical models of gravitational collapse suggest horizontal flow of the range, and imply horizontal strain rates higher than the vertical ones. The present day velocity field does not support this idea since the vertical rates are at least 5 times larger that the horizontal ones. Based on 2D finite element modeling taking into account ad hoc geotherms and rheology laws for the crust and the upper mantle, we show that erosion-induced uplift displacements of the mountain range can trigger extension below the high topography region and compression in the foothills. We further suggest that deciphering vertical motion in low convergence mountain ranges is key to better understand their geodynamics. Combining vertical rates together with seismology and gravimetry in numerical models will take us a step further in the comprehension of the earth dynamics.

  1. Tectono-sedimentary events and geodynamic evolution of the Mesozoic and Cenozoic basins of the Alpine Margin, Gulf of Tunis, north-eastern Tunisia offshore

    NASA Astrophysics Data System (ADS)

    Melki, Fetheddine; Zouaghi, Taher; Chelbi, Mohamed Ben; Bédir, Mourad; Zargouni, Fouad

    2010-09-01

    The structural pattern, tectono-sedimentary framework and geodynamic evolution for Mesozoic and Cenozoic deep structures of the Gulf of Tunis (north-eastern Tunisia) are proposed using petroleum well data and a 2-D seismic interpretation. The structural system of the study area is marked by two sets of faults that control the Mesozoic subsidence and inversions during the Paleogene and Neogene times: (i) a NE-SW striking set associated with folds and faults, which have a reverse component; and (ii) a NW-SE striking set active during the Tertiary extension episodes and delineating grabens and subsiding synclines. In order to better characterize the tectono-sedimentary evolution of the Gulf of Tunis structures, seismic data interpretations are compared to stratigraphic and structural data from wells and neighbouring outcrops. The Atlas and external Tell belonged to the southernmost Tethyan margin record a geodynamic evolution including: (i) rifting periods of subsidence and Tethyan oceanic accretions from Triassic until Early Cretaceous: we recognized high subsiding zones (Raja and Carthage domains), less subsiding zones (Gamart domain) and a completely emerged area (Raouad domain); (ii) compressive events during the Cenozoic with relaxation periods of the Oligocene-Aquitanian and Messinian-Early Pliocene. The NW-SE Late Eocene and Tortonian compressive events caused local inversions with sealed and eroded folded structures. During Middle to Late Miocene and Early Pliocene, we have identified depocentre structures corresponding to half-grabens and synclines in the Carthage and Karkouane domains. The north-south contractional events at the end of Early Pliocene and Late Pliocene periods are associated with significant inversion of subsidence and synsedimentary folded structures. Structuring and major tectonic events, recognized in the Gulf of Tunis, are linked to the common geodynamic evolution of the north African and western Mediterranean basins.

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

    NASA Astrophysics Data System (ADS)

    Besutiu, L.

    2012-04-01

    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).

  3. Simple Lu-Hf isotope patterns resulting from complex Archean geodynamics: example of the Pietersburg block (South Africa)

    NASA Astrophysics Data System (ADS)

    Laurent, Oscar; Zeh, Armin

    2015-04-01

    The combined use of U-Pb and Lu-Hf isotope data from Hadean and Archean zircons is widely used to constrain the mechanisms of continental crust formation and evolution in the early Earth. Such data generally define ?Hf-time arrays, interpreted as reflecting the closed-system, protracted reworking of single crustal reservoirs episodically extracted from depleted mantle (DM) sources. Many models about early Earth evolution and continental growth rely on this interpretation and its consequences (i.e. determination of Hf model ages and crustal residence times). However, this straightforward interpretation is difficult to reconcile with the complex evolution of Archean terranes, involving progressive crustal maturation and a range of crustal and mantle sources to granitoid magmas. Here we present a database of U-Pb and Lu-Hf isotopes measured in situ by LA-(MC-)ICPMS in zircons from >30 samples, representative of the temporal and spatial record of a single segment of Archean crust, the Pietersburg block (Kaapvaal Craton, South Africa). Coupling of age-Hf data with petrological and geochemical constraints shows that >1 Ga-long crustal evolution in the PB is characterized by (i) crustal nucleation in an intra-oceanic setting between 3.4 and 3.1 Ga; (ii) rapid formation of large volumes of juvenile TTG crust in an accretionary orogen at the northern edge of the proto-Kaapvaal craton between 3.1 and 2.9 Ga; (iii) intracrustal reworking and subduction of TTG-derived sediments along an Andean-type continental margin between 2.9 and 2.75 Ga; (iv) continental collision with the Central Zone of the Limpopo Belt at 2.75-2.69 Ga, resulting in magmatism derived from local crust and metasomatized mantle; (v) a discrete anorogenic event at ~2.05 Ga with the emplacement of SCLM-derived alkaline magmas. Despite the diversity of magmas and geodynamic settings depicted by this evolution, all samples emplaced between 3.0 and 2.0 Ga plot along a single, robust array of decreasing ?Hf with time, demonstrating that such arrays do not provide relevant information about Hadean-Archean geodynamics, unless independent constraints are considered. The Hf-time array of the PB is moreover characterized by a notably low 176Lu/177Hf of ~0.003, typical of the ~2.95 Ga-old TTGs that represent the largest volume of juvenile crust in the area. Yet, the petrogenesis of granitoid magmas plotting along the array involve other source components and crust-mantle interactions. This paradox may be solved considering that the bulk crust-mantle system behaved as a closed-system reservoir for Lu/Hf once large volumes of TTG crust and complementary SCLM were formed, enhancing the stability of the lithosphere. Regardless the mechanisms involved in its reworking, the incompatible element budget of this lithosphere is then dominated by the most voluminous, "enriched" crustal component (~2.95 Ga TTGs in that case). Models of early Earth evolution may therefore be reconsidered according to this alternative interpretation of Lu-Hf isotope arrays.

  4. La Galite Archipelago (Tunisia, North Africa): Stratigraphic and petrographic revision and insights for geodynamic evolution of the Maghrebian Chain

    NASA Astrophysics Data System (ADS)

    Belayouni, Habib; Brunelli, Daniele; Clocchiatti, Roberto; Di Staso, Angelida; El Hassani, Iz-Eddine El Amrani; Guerrera, Francesco; Kassaa, Samia; Ouazaa, Nejia Laridhi; Martín, Manuel Martín; Serrano, Francisco; Tramontana, Mario

    2010-01-01

    The location of the La Galite Archipelago on the Internal/External Zones of the Maghrebian Chain holds strong interest for the reconstruction of the geodynamic evolution of the Mesomediterranean Microplate-Africa Plate Boundary Zone. New stratigraphic and petrographic data on sedimentary successions intruded upon by plutonic rocks enabled a better definition of the palaeogeographic and palaeotectonic evolutionary model of the area during the early-middle Miocene. The lower Miocene sedimentary units ( La Galite Flysch and Numidian-like Flysch) belong to the Mauritanian (internal) and Massylian (external) sub-Domains of the Maghrebian Chain, respectively. These deposits are related to a typical syn-orogenic deposition in the Maghrebian Flysch Basin Domain, successively backthrusted above the internal units. The backthrusting age is post-Burdigalian (probably Langhian-Serravallian) and the compressional phase represents the last stage in the building of the accretionary wedge of the Maghrebian orogen. These flysch units may be co-relatable to the similar well-known formations along the Maghrebian and Betic Chains. The emplacement of potassic peraluminous magmatism, caused local metamorphism in the Late Serravallian-Early Tortonian (14-10 Ma), after the last compressional phase (backthrusting), during an extensional tectonic event. This extensional phase is probably due to the opening of a slab break-off in the deep subduction system. La Galite Archipelago represents a portion of the Maghrebian Flysch Basin tectonically emplaced above the southern margin of the "Mesomediterranean Microplate" which separated the Piemontese-Ligurian Ocean from a southern oceanic branch of the Tethys (i.e. the Maghrebian Flysch Basin). The possible presence of an imbricate thrust system between La Galite Archipelago and northern Tunisia may be useful to exclude the petroleum exploration from the deformed sectors of the offshore area considered.

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

    NASA Astrophysics Data System (ADS)

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

    2009-07-01

    The Hsinchu (HS) superconducting gravimeter (SG, serial T48) station is a newly established site in the Global Geodynamics Project (GGP). Simultaneous observations of T48, three FG5 absolute gravimeters, and GPS at four stations are studied. GPS shows few mm a-1 of horizontal and vertical motions around HS. The calibration factor and drifting rate of T48 are -75.96 ± 0.07 ?Gal V-1 and 0.2 ± 0.7 ?Gal a-1 (1 ?Gal = 10-8 m s-2). Both the SG and absolute gravity records contain trends of about 2-3 ?Gal a-1. The ocean tide gravity effects (OTGEs) were estimated from NAO.99b, FES2004, and CSR4.0, and their amplitudes agree with the SG observations at the submicroGal level, but their phases differ from the observations up to 10°. The Newtonian effect of ocean tide contributes 20% to the total OTGE at HS, and it is larger at islands in the Taiwan Strait. The inelastic body tide model of Dehant et al. (1999) is more consistent with the SG observations than the elastic model. Modeled gravity-atmosphere admittances based on an exponential distribution of air mass explain well the observed admittances. The average gravity-atmosphere admittance during typhoons is 30% larger than that in a nontyphoon time. A list of coseismic gravity changes from T48 caused by earthquakes over 2006-2007 is given for potential studies of fault parameters. The modeled effects of atmospheric pressure, groundwater, soil moisture, and polar motion explain the FG5 observed gravity trend to 1.1 ?Gal a-1. Seasonally, the groundwater-induced gravity change contributes the most to the SG residual gravity, but its phase leads the latter by 63 days.

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

    NASA Astrophysics Data System (ADS)

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

    2013-11-01

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

  7. Jurassic-Cretaceous clastic sequences of Chukotka: sedimentation, structural style and geodynamic implications for Russian East Arctic shelf.

    NASA Astrophysics Data System (ADS)

    Tuchkova, M. I.; Sokolov, S. D.; Verzhbitsky, V. E.

    2009-04-01

    Jurassic-Lower Cretaceous sedimentary sequence, exposed on the Chukotka continental margin is critical for understanding the timing, dynamics and sedimentary setting evolution of Chukotka-Eurasia collisional process (e.g., Sokolov et al., 2002) and so, represents one of the key regional stratigraphic units (Til'man,1973, Tibilov,1982; Miller et al., 2002, 2007). From the other hand, this research may shed the light on the widely discussing problem of the Canadian and Makarov basins opening (e.g., Miller, Verzhbitsky, in press). Jurassic-Lower Cretaceous sedimentary complexes of the Chukotka microcontinent are composed of terrigeneous deposites. Those sedimentary complexes are enriched by organic matter, and fresh clastic materials. Fragments of shales, sometimes laminated or cleaved are their indicator constituents. Sandstones are arkosic. The percentage of types of rocks fragments is different in Jurassic and Cretaceous deposits. Chemical composition of the Jurassic-Cretaceous rocks is not uniform too: Upper Jurassic sandstones form one group depleted in Na2O+K2O, Cretaceous sandstones, enriched in Na2O+K2O. Thus, our investigations indicate that Jurassic-Cretaceous sedimentary basins were related to different source provenance. We believe, that the stratigraphy and composition of Jurassic-Lower Cretaceous onshore sequences are crucial for prediction of the geological structure of East Siberian and Chukchi Sea shelf (1), understanding the evolution of Mesozoic sedimentary basins of East Arctic (2) and testifying the existing geodynamic models of Amerasian Basin opening (3). The work is supported by the Russian Foundation for Basic Research (grant 08-05-00547), program of ONZ RAS 14, and NSH-3172.2008.5.

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

    SciTech Connect

    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

    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.

  9. A simulation to study the feasibility of improving the temporal resolution of LAGEOS geodynamic solutions by using a sequential process noise filter

    NASA Technical Reports Server (NTRS)

    Hartman, Brian Davis

    1995-01-01

    A key drawback to estimating geodetic and geodynamic parameters over time based on satellite laser ranging (SLR) observations is the inability to accurately model all the forces acting on the satellite. Errors associated with the observations and the measurement model can detract from the estimates as well. These 'model errors' corrupt the solutions obtained from the satellite orbit determination process. Dynamical models for satellite motion utilize known geophysical parameters to mathematically detail the forces acting on the satellite. However, these parameters, while estimated as constants, vary over time. These temporal variations must be accounted for in some fashion to maintain meaningful solutions. The primary goal of this study is to analyze the feasibility of using a sequential process noise filter for estimating geodynamic parameters over time from the Laser Geodynamics Satellite (LAGEOS) SLR data. This evaluation is achieved by first simulating a sequence of realistic LAGEOS laser ranging observations. These observations are generated using models with known temporal variations in several geodynamic parameters (along track drag and the J(sub 2), J(sub 3), J(sub 4), and J(sub 5) geopotential coefficients). A standard (non-stochastic) filter and a stochastic process noise filter are then utilized to estimate the model parameters from the simulated observations. The standard non-stochastic filter estimates these parameters as constants over consecutive fixed time intervals. Thus, the resulting solutions contain constant estimates of parameters that vary in time which limits the temporal resolution and accuracy of the solution. The stochastic process noise filter estimates these parameters as correlated process noise variables. As a result, the stochastic process noise filter has the potential to estimate the temporal variations more accurately since the constraint of estimating the parameters as constants is eliminated. A comparison of the temporal resolution of solutions obtained from standard sequential filtering methods and process noise sequential filtering methods shows that the accuracy is significantly improved using process noise. The results show that the positional accuracy of the orbit is improved as well. The temporal resolution of the resulting solutions are detailed, and conclusions drawn about the results. Benefits and drawbacks of using process noise filtering in this type of scenario are also identified.

  10. Constraints on the Thermochemical Structure of the Earth's Deep Mantle Using Seismic, Geodynamic and Mineral Physics Data

    NASA Astrophysics Data System (ADS)

    Mitrovica, J. X.; Forte, A. M.

    2003-12-01

    The integration of seismic, geodynamic and mineral physics data to constrain the large scale composition and dynamics of the Earth's mantle is a widely stated goal of global geophysics; however, the appropriate methodology for this integration is a matter of debate. In recent work [Forte and Mitrovica, Phil. Trans., 2002] we outlined, atleast for a simple compositional model of the mantle, an approach for combining joint (shear and bulk sound) seismic models, seismic velocity derivatives obtained from results in mineral physics, and convection related observations (plate motions, gravity anomalies and the excess ellipticity of the CMB). Our inversions yielded a mantle viscosity profile characterized by two viscosity maxima within the lower mantle. The deepest of the two, at 2000 km depth, suppresses all but the longest horizontal wavelengths of the present-day flow in the bottom 1000 km of the lower mantle, thereby providing a simple interpretation for the `red' spectrum of seismically-inferred heterogeneity in this region. The integration also suggested that while chemical anomalies in the lower-most mantle are required to explain seismic observations, these anomalies are unable to inhibit the dominant thermal buoyancy of the deep-mantle mega-plumes below the Pacific and Africa. In this talk we describe the results of a large set of new inversions that: (1) extend the viscosity inferences to include a suite of data related to glacial isostatic adjustment (GIA; these data include site-specific post-glacial decay times from Fennoscandia and Hudson Bay, and a relaxation spectrum which provides the decay time versus wavelength of Fennoscandian deformation); and (2) map out, using Monte-Carlo simulations, plausible variations in thermochemical structure (summarized by the so-called buoyancy ratio) associated with uncertainties in the seismic models, mineral physics data and mantle viscosity (including the presence of the lateral variations). The GIA data provide an important, independent constraint on absolute viscosity and significantly improve the resolution of the resulting viscosity inferences, particularly in the transition zone and top half of the lower mantle. However, the viscosity peak at 2000 km depth remains a robust feature of these new inversions, reinforcing our earlier conclusion that this structure plays a pre-eminent role in deep mantle flow dynamics. Furthermore, the Monte-Carlo simulations indicate a positive correlation between density and shear wave velocity in the deep mantle and thus a dominance of thermal buoyancy within that region.

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

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

    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

  12. Variability in forearc deformation during subduction: Insight from geodynamic models and application to the Calabria subduction zone

    NASA Astrophysics Data System (ADS)

    Chen, Zhihao; Schellart, Wouter; Duarte, Joao

    2015-04-01

    In nature subducting slabs and overriding plate segments bordering subduction zones are generally embedded within larger plates. Such large plates can impose far-field boundary conditions that impact the style of subduction and overriding plate deformation. Here we present 3D dynamic analogue models of subduction, in which the far-field boundary conditions at the trailing edges of the subducting plate (SP) and overriding plate (OP) are varied. Four configurations are presented: Free (both plates free), SP-Fixed, OP-Fixed and SP-OP-Fixed. We investigate their impact on the kinematics and dynamics of subduction, with a special focus on overriding plate deformation. Our models indicate that in natural (narrow) subduction zones, assuming a homogeneous overriding plate, the formation of backarc basins (e.g., Tyrrhenian Sea, Aegean Sea, Scotia Sea) is generally expected to occur at a comparable location (300-500 km from the trench), irrespective of the boundary condition. Furthermore, our models indicate that the style of forearc deformation (shortening or extension) is determined by the mobility of the overriding plate through controlling the force normal to the subduction zone interface (trench suction). Our geodynamic model that uses the SP-OP-Fixed set-up is comparable to the Calabria subduction zone with respect to subduction kinematics, slab geometry, trench curvature and accretionary wedge configuration. Furthermore, it provides explanation for the natural observations of both backarc extension in the Tyrrhenian Sea and forearc extension in the Calabria region, which have been active since the Miocene. We explain the observations as a consequence of subduction of the narrow Calabrian slab and the immobility of the subducting African plate and overriding Eurasian plate. This setting forced subduction to be accommodated almost entirely by slab rollback (not trenchward overriding plate motion), while trench retreat was accommodated almost entirely by backarc and forearc extension (not trenchward overriding plate motion), similarly to our SP-OP-Fixed model. This tectonic setting induced strong trench suction, which caused the forearc extension in Calabria.

  13. Active intraplate deformation as geodynamic responses to oblique shallow subduction of a flat slab: example from central and southwest Japan

    NASA Astrophysics Data System (ADS)

    Ishiyama, Tatsuya; Sato, Hiroshi

    2015-04-01

    Subduction of a flat slab has been recognized as one of the primary driving mechanism of wide intracontinental subsidence farther away from the subduction leading edge in many subduction margins. In most cases, however, quantitative and qualitative limitations on chronological constraints prevent comprehensive understanding of these geodynamic linkages. In this study, we show distinct, geologic and seismic evidence for spatial and temporal correlation between plate subduction and intercontinental deformation, mainly driven by dynamic interaction between subducting Philippine Sea (PHS) plate and overriding continental crusts of central and southwest Japan (Eurasian plate) along the Nankai-Tonankai subduction zone since Pliocene. Based on analyses of Pliocene to Pleistocene tectonic histories by use of rich dataset of Neogene stratigraphy, drainage network evolution, and shallow to deep seismic reflection profiles, depocenters of wide sedimentary basins and active thrusting have migrated northward since ca. 5 Ma to present from forearc to backarc of the southwest Japan arc. Median tectonic line, active dextral strike-slip fault as a forearc sliver along the Nankai, is located north of the upward extension of the downdip limit of the interseismic locked zone. Southwest Japan north of the MTL, underlain by the subducting slab with steady state slip (Nakanishi et al., 2002; Kodaira et al., 2004), appears tectonically less inactive than central Japan and has behaved as a less deformed rigid block. Contrastingly, Quaternary active intraplate deformation has been prominent north of the inactive MTL above a shallow flat segment of the PHS plate along the Tonankai. Deep seismic reflection profile images upward corrugated very shallow PHS slab being contact with continental lower crust beneath actively deforming area. We interpreted temporal and spatial correlation of oblique subduction of the shallow and flat, corrugated PHS slab as an essential mechanical role to enhance downward drag of the overriding plate and synchronous strong compressional stress field in the crust. More westerly PHS subduction since middle Pleistocene, suggested by unconformity in the forearc basin deposits and change of sense of fault slip along the active MTL cause stronger horizontal stress in the overriding plate, consistent with increasing geologic slip rate on active structures with this plate configurations. In shorter timescales, during four repetitions of the Nankai subduction zone earthquakes since 17th century, numbers of intraplate large (M>6.5) earthquakes occurred above or near the PHS flat slab are much larger than other surrounding regions. This also may suggest mechanical link between subduction processes and seismicity in the overriding plate.

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

    NASA Astrophysics Data System (ADS)

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

    2009-09-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

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

  16. Rotational waves in geodynamics

    NASA Astrophysics Data System (ADS)

    Gerus, Artyom; Vikulin, Alexander

    2015-04-01

    The rotation model of a geoblock with intrinsic momentum was constructed by A.V. Vikulin and A.G. Ivanchin [9, 10] to describe seismicity within the Pacific Ocean margin. It is based on the idea of a rotational motion of geoblocks as the parts of the rotating body of the Earth that generates rotary deformation waves. The law of the block motion was derived in the form of the sine-Gordon equation (SG) [5, 9]; the dimensionless form of the equation is: ?2? ?2? ??2 - ??2 = sin?, (1) where ? = ?/2, ? = k0z and ? = v0k0t are dimensionless coordinates, z - length of the chain of masses (blocks), t - time, ? - turn angle, ?0 - representative velocity of the process, k0 - wave number. Another case analyzed was a chain of nonuniformly rotating blocks, with deviation of force moments from equilibrium positions ?, considering friction forces ? along boundaries, which better matched a real-life seismic process. As a result, the authors obtained the law of motion for a block in a chain in the form of the modified SG equation [8]: ?2? ?2? ??- ??2 - ? ?2 = sin ?+ ? ?? + ??(?)sin ? (2)

  17. Sulphur geodynamic cycle

    PubMed Central

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

    2015-01-01

    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

  18. Fundamental studies in geodynamics

    NASA Technical Reports Server (NTRS)

    Anderson, D. L.

    1980-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Slabunov, Alexander

    2013-04-01

    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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

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

    SciTech Connect

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

    2006-09-15

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

  2. 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)

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

    2015-01-01

    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.

  3. 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)

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

    2015-06-01

    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.

  4. The tectonometamorphic evolution of the Apuseni Mountains (Romania): Geodynamic constraints for the evolution of the Alps-Carpathians-Dinaride system of orogens

    NASA Astrophysics Data System (ADS)

    Reiser, Martin; Schuster, Ralf; Fügenschuh, Bernhard

    2015-04-01

    New structural, thermobarometric and geochronological data allow integrating kinematics, timing and intensity of tectonic phases into a geodynamic model of the Apuseni Mountain, which provides new constraints for the evolution of the Alps-Carpathians-Dinaride system of orogens. Strong differences in terms of deformation directions between Early and Late Cretaceous events provide new constraints on the regional geodynamic evolution during the Cretaceous. Geochronological and structural data evidence a Late Jurassic emplacement of the South Apuseni Ophiolites on top of the Biharia Nappe System (Dacia Mega-Unit), situated in an external position at the European margin. Following the emplacement of the ophiolites, three compressive deformation phases affected the Apuseni Mountains during Alpine orogeny: a) NE-directed in-sequence nappe stacking and regional metamorphic overprinting under amphibolite-facies conditions during the Early Cretaceous ("Austrian Phase"), b) NW-directed thrusting and folding, associated with greenschist-facies overprinting, during the early Late Cretaceous ("Turonian Phase") and c) E-W internal folding together with brittle thrusting during the latest Cretaceous ("Laramian Phase"). Major tectonic unroofing and exhumation at the transition from Early to Late Cretaceous times is documented through new Sm-Nd Grt, Ar-Ar Ms and Rb-Sr Bt ages from the study area and resulted in a complex thermal structure with strong lateral and vertical thermal gradients. Nappe stacking and medium-grade metamorphic overprinting during the Early Cretaceous exhibits striking parallels between the evolution of the Tisza-Dacia Mega-Units and the Austroalpine Nappes (ALCAPA Mega-Unit) and evidences a close connection. However, Late Cretaceous tectonic events in the study area exhibit strong similarities with the Dinarides. Thus, the Apuseni Mountains represent the "missing link" between the Early Cretaceous Meliata subduction (associated with obduction of ophiolites) and the Neotethys subduction during Late Cretaceous times.

  5. Beyond Apatite (U-Th)/He thermochronometry: Detailed low-T thermal history reconstructions and applicability to a wider range of geodynamic environments

    NASA Astrophysics Data System (ADS)

    Stockli, D. F.

    2009-05-01

    Low-T thermochronometric dating techniques have proven to be powerful tools to constrain the cooling of rocks exhumed by a wide-range of tectonic and geologic processes and are widely used to elucidate time- temperature and exhumation histories of mountain belts, metamorphic terranes, and sedimentary basins. The approach is fundamentally based on the fact that rocks cool during tectonic or erosional unroofing such that the timing, rate, and magnitude of exhumation can be quantified by low-temperature thermochronometric data. While (U-Th)/He dating of apatite (Tc of ˜55- 70°C) and zircon (˜190°C) are now a well- established thermochronometric techniques, (U-Th)/He dating of other refractory and metamorphic minerals such titanite (˜200°C), monazite (˜180-240°C), rutile (˜220°C), magnetite (˜250°C), and other silicate and oxide phases have been developed as new tools and have attracted significant attention. These novel tools and the potential of multi-mineral and multi- thermochronometer dating offer new and exciting possibilities of resolving different portions of a rock's low-T thermal history and their overall thermal history in greater detail. The combination of multiple (U-Th)/He thermochronometers has the potential to quantify the t-T path between 4°C and 250°C. Furthermore, expansion of low-T thermochronometry to wider range of lithologies and geological environments through development of new mineral phases offers exciting new tools for a more detailed understanding of tectonic and thermal processes in different geodynamic environments. A more complete understanding of He diffusion kinetics, careful integration with petrologic and mineralogical context, and advanced numerical modeling of thermochronometric data have significantly improved our ability to more fully elucidate and quantify thermal processes in response to structural, petrologic, and erosional processes. Development and refinement of new thermochronometers and systematic incorporation of new analytical techniques is enabling us to derive high-resolution reconstructions of tectonic processes in different geodynamic settings.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  7. Les manifestations tectono-sédimentaires d'âge Campanien Maastrichtien en Tunisie : implications sur l'évolution géodynamique de la marge Nord-AfricaineThe Campanian Maastrichtian synsedimentary tectonic activity: implication in the geodynamic evolution of the North African Margin

    NASA Astrophysics Data System (ADS)

    Dlala, Mahmoud

    The synsedimentary tectonic activity evidenced in central and northern Tunisia points out the fact that the Campanian-Maastrichtian deposits are associated with several NW-SE and east-west normal faults. These results suggest that the east-west transform fault of North African Margin is still active during this stage. These data allow us to discuss a new geodynamic model for the North African Margin. To cite this article: M. Dlala, C. R. Geoscience 334 (2002) 135-140.

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

    NASA Astrophysics Data System (ADS)

    Burov, Evgueni

    2014-05-01

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

  9. Relating geodynamic setting to periods of crustal growth and reworking as illustrated by the Phanerozoic granitoids of the Eastern Cordillera of South Peru

    NASA Astrophysics Data System (ADS)

    Reitsma, M.; Schaltegger, U.; Spikings, R.; Ulianov, A.; Gerdes, A.; Chiaradia, M.

    2012-04-01

    The granitoids that form the backbone of the Eastern Cordillera of Peru between 12 and 14°S, are the ideal material for a case study to relate geodynamic setting to crustal growth over the period of a Wilson cycle. Extension related plutons were emplaced in the back-arc region of the Western Gondwana margin during the Ordovician, Permo-Carboniferous, Triassic and Early Jurassic. With the onset of the Andean cycle in the Middle Jurassic the South American margin was under compression, the plutonic record of this period is in the study area restricted to the Eocene and Miocene. The Ordovician to Triassic back-arc related plutons share many geochemical characteristics that point to dominant crustal reworking as the main process during their formation. These are 1) their mainly felsic and peraluminous nature; 2) the similarity of whole rock REE and trace element compositions compared to those of average continental crust; 3) the presence of negative Nb-Ta anomalies only in the more evolved samples which indicates that these excursions have been obtained by crustal melting rather than from a slab fluid and 4) the presence of significant amounts of xenocrystic cores in zircon. According to the literature the last major episode of juvenile crust formation was during the Grenvillian age Sunsas event (1.2 - 0.9 Ga) related to the collision of Laurentia and south-western Amazonia during the assembly of Rodinia. Hf-isotopes on zircons from the Ordovician, Permo-Carboniferous and Triassic plutons confirm their origin as mainly crustal melts generated by reworking of Sunsas-age crust. Under these geodynamic conditions it is mainly the crust that melts due to an elevated geothermal gradient as the result of crustal thinning. However, data from Jurassic nepheline bearing syenite and Eocene hornblende diorite and monzonite have epsilon Hfi values well above those of Sunsas crust, indicating an important mantle component in the melts. The Jurassic geodynamic setting is interpreted as extreme back-arc extension at the verge of spreading, peralkaline, SiO2-undersaturated syenites formed by small degrees of partial melting of the shallowest asthenospheric mantle but constitute only a volumetrically subordinate magmatic pulse, hence it did not contribute significantly to crustal growth. On the other hand, the Eocene Andahuaylas-Yauri batholith also has an important mantle component in its melt and at the same time is volumetrically the largest magmatic episode in the study area. Therefore we conclude that most Phanerozoic crustal growth took place during this compressional regime related to flat slab subduction. In other words, Eocene melting of the mantle assisted by slab derived fluids was much more efficient than Jurassic decompression melting of a relatively dry mantle during back-arc extension.

  10. Geological setting and geochemical signatures of the mafic rocks from the Intra-Pontide Suture Zone: implications for the geodynamic reconstruction of the Mesozoic Neotethys

    NASA Astrophysics Data System (ADS)

    Sayit, Kaan; Marroni, Michele; Göncüoglu, M. Cemal; Pandolfi, Luca; Ellero, Alessandro; Ottria, Giuseppe; Frassi, Chiara

    2015-06-01

    A number of suture zones exist in Turkey, which is believed to represent the closure of Paleo and NeoTethyan oceanic basins. Regarding the development of the latter oceanic entity, namely Neotethys, the geodynamic evolution of the Intra-Pontide branch, the northernmost one of a number of oceanic basins remains enigmatic. The Intra-Pontide Suture Zone in Northwest Turkey includes several tectonic units most of which are characterized by the occurrence of mafic rocks with distinct geochemical signatures. In this paper, the mafic rocks collected from four of these units (the Domuz Da? Unit, the Saka Unit, the Daday Unit and the Arkot Da? Mèlange) have been studied in detail along two selected transects. The Domuz Da? Unit is characterized by amphibolites, micaschists and marbles, which have been overprinted by low-grade metamorphism.The Saka Unit is in turn represented by an assemblage of slices of amphibolites, marbles and micaschists metamorphosed under upper amphibolite facies metamorphic conditions in the Late Jurassic time. In these units, the amphibolites and their retrograded counterparts display E-MORB-, OIB- BABB- and IAT-type signatures. The Daday Unit is characterized by metasedimentary and metamafic rocks metamorphosed under blueschist to sub-greenschist facies conditions. The metamafic rocks comprise actinolite-bearing schists and Na-amphibole-bearing varieties possibly derived from basaltic and gabbroic protoliths. They have a wide range of chemical compositions, displaying N-MORB-, E-MORB-, OIB- BABB- and IAT-type signatures. The Arkot Da? Mèlange consists of a Late Santonian assemblage of slide-blocks mainly represented by basaltic lithologies showing affinities ranging from N-MORB- and IAT- to BABB-type magmas. The geochemical signature of the studied mafic rocks indicates that the tectonic units documented along the two studied transects of the Intra-Pontide Suture Zone have been derived from a supra-subduction zone. This hypothesis corroborates the available data collected from the Ayl? Da? Ophiolite Unit cropping out in the westernmost studied transect. This finding can provide new insights for the reconstruction of the geodynamic history of the Intra-Pontide domain.

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

    USGS Publications Warehouse

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

    2011-01-01

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

  12. 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)

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

    2014-05-01

    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.

  13. 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)

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

    2012-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

  15. Géodynamique et évolution thermique de la matière organique: exemple du bassin de Qasbat-Tadla, Maroc centralBasin geodynamics and thermal evolution of organic material: example from the Qasbat-Tadla Basin, central Morocco

    NASA Astrophysics Data System (ADS)

    Er-Raïoui, H.; Bouabdelli, M.; Bélayouni, H.; Chellai, H.

    2001-05-01

    Seismic data analysis of the Qasbat-Tadla Basin allows the deciphering of the main tectonic and sedimentary events that characterised the Hercynian orogen and its role in the basin's structural development. The global tectono-sedimentary framework involves structural evolution of an orogenic foreland basin and was the source of rising geotherms in an epizonal metamorphic environment. The complementary effects of these parameters has led to different source rock maturity levels, ranging from oil producing to graphite domains. Different maturity levels result from three distinct structural domains within the basin, each of which exhibit characteristic geodynamic features (tectonic contraints, rate of subsidence, etc.).

  16. Configuration of geological domains and geodynamic evolution of the Africa-Eurasia plate boundary off SW Iberia revisited based on seismic velocity and density models

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    We present a new classification of geological (basement) domains at the Africa-Eurasia plate boundary offshore 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 Tagus 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 off SW Iberia: (1) the Seine Abyssal Plain domain, generated during the first stages of slow seafloor spreading in the NE segment of the 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 (Early Cretaceous). 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, which coincides with the seismicity cluster nucleated in the middle of the plain that shows moment tensor solutions of reverse faulting at depths of 40-60 km. 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 and its connection and interplay with the Western Mediterranean basin.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  18. 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)

    Poulin, Elie; González-Wevar, Claudio; Díaz, Angie; Gérard, Karin; Hüne, Mathias

    2014-12-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

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

  20. New insights in the geodynamics of the Lipari-Vulcano area (Aeolian Archipelago, southern Italy) from geological, geodetic and seismological data

    NASA Astrophysics Data System (ADS)

    Barreca, G.; Bruno, V.; Cultrera, F.; Mattia, M.; Monaco, C.; Scarfì, L.

    2014-12-01

    Geological, geodetic and seismological data have been analyzed in order to frame the Lipari-Vulcano complex (Aeolian archipelago, southern Italy) into the geodynamic context of the southeastern Tyrrhenian Sea. It is located at the northern end of a major NNW-SSE trending right-lateral strike-slip fault system named "Aeolian-Tindari-Letojanni" which has been interpreted as a lithospheric discontinuity extending from the Aeolian Islands to the Ionian coast of Sicily and separating two different tectonic domains: a contractional one to the west and an extensional one to the north-east. Structural field data consist of structural measurements performed on well-exposed fault planes and fractures. The mesostructures are mostly represented by NW-SE striking normal faults with a dextral-oblique component of motion. Minor structures are represented by N-S oriented joints and tension gashes widespread over the whole analyzed area and particularly along fumarolized sectors. The analyzed seismological dataset (from 1994 to 2013) is based on earthquakes with magnitude ranging between 1.0 and 4.8. The hypocenter distribution depicts two major alignments corresponding to the NNW-SSE trending Aeolian-Tindari-Letojanni fault system and to the WNW-ESE oriented Sisifo-Alicudi fault system. GPS data analysis displays ?3.0 mm/yr of active shortening between the two islands, with a maximum shortening rate of about 1.0 × 10-13 s-1, between La Fossa Caldera and south of Vulcanello. This region is bounded to the north by an area where the maximum values of shear strain rates, of about 0.7 × 10-13 s-1 are observed. This major change occurs in the area south of Vulcanello that is also characterized by a transition in the way of the vertical axis rotation. Moreover, both the islands show a clear subsidence process, as suggested by negative vertical velocities of all GPS stations which exhibit a decrease from about -15 to -7 mm/yr from north to south. New data suggest that the current kinematics of the Lipari-Vulcano complex can be framed in the tectonic context of the eastward migrating Sisifo-Alicudi fault system. This is dominated by transpressive tectonics in which contractional and minor extensional structures can coexist with strike-slip motion.

  1. Please cite this article in press as: Kaus, B.J.P., et al., A stabilization algorithm for geodynamic numerical simulations with a free surface. Phys. Earth Planet. In. (2010), doi:10.1016/j.pepi.2010.04.007

    E-print Network

    Kaus, Boris

    2010-01-01

    with a free surface Boris J.P. Kausa,b, , Hans Mühlhausc , Dave A. Maya a Geophysical Fluid Dynamics ESCC, University of Queensland, Australia a r t i c l e i n f o Article history: Received 14 December: Lithospheric deformation Rheology Stress state Numerical modelling Free surface Computational geodynamics a b

  2. 1, 591624, 2004 Hadean geodynamic

    E-print Network

    Boyer, Edmond

    that the first prokaryotic organism evolved. These acetogenic precursors to the Bacteria diver- sified there the Bacteria, and the recently differentiated Archaea, were pro-20 tected from cataclysmic heating events into the photic zone where, initially protected by a thin veneer of sediment, the use of solar energy was mastered

  3. 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)

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

    2014-05-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-06-01

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

  7. Structural and geodynamic study in central Tunisia using field and geophysical data: new structural interpretation of the N-S axis and associated Atlassic structures

    NASA Astrophysics Data System (ADS)

    Dhahri, Ferid; Tanfous, Dorra; Gabtni, Hakim; Boukadi, Noureddine

    2015-02-01

    A structural and geodynamic evolution of central Tunisia is constructed from field studies and geophysical data within the Tunisian Atlassic domain. Bouguer gravity and horizontal gradient magnitude (HGM) maps indicate that computed anomalies are related to subsurface structures and are in accordance with the general structural trends of central Tunisia. Near Cherichira fault, the strike is ENE-WSW, whereas it is N-S along the N-S axis, a major discontinuity between the Pelagian shelf to the east and Central Atlas Mountains to the west. E-W-oriented HGM profiles on the north side of the Cherichira fault show moderate HGM variations, which correspond to the NE-SW fault system of the Ousselet-Bou Dabbous. This trend is also expressed by the second-order vertical derivative map of this area. However, on the south side of the fault, a dominant peak is indicated rather than the anomalies characteristic of the north side of the fault. This anomaly is associated with the N-S axis discontinuity. Seismic reflection data are also used to elucidate the structural configuration and style north and south of the Cherichira fault. The seismic lines demonstrate that faulting and associate halokinesis in Ousselet-Bou Dabbous area are not comparable to the paleogeographic fault system of the N-S axis southward. To the south of Cherichira fault, the seismic lines show massive Triassic evaporates piercing along the major paleogeographic faults associated with thickness variations of Mesozoic and Cenozoic stratigraphic units and a reverse slip of western structural elements. It seems that the N-S axis corresponds to a steeply dipping major zone of weakness in the Tunisian Atlassic Mountains and indicates evidence of several stages of activity, including the rise of Triassic evaporates rise up which outcrop at several localities such as Rheouis and Mezzouna. The loading and upward rise of Triassic evaporites along this weak zone are a key factor in the thinning of the Mesozoic-Cenozoic sedimentary cover along this paleogeographic discontinuity. These new data indicate the northeast extrapolation of fold and grabens of the Central Atlas of Tunisia to the northeast of Kairouan, whereas the northern extent of the N-S axis is limited to south of the Cherichira fault. The Cherichira fault is NE-SW oriented and parallels the Ballouta-Zaghouan fault system, which reflects the regional strike of the Tellian orogeny and the associated nappes to the north. The geometry and kinematics of these Tellian features are linked to the tectonic evolution of the northern African margin, including Mesozoic extension separating the African and European plates to the inversion of these structures since the Late Cretaceous. The N-S axis is correlated in its direction and tectonic framework to the strike-slip fault system of the African craton, which is present to the south in the Algerian Saharan domain of Hoggar.

  8. 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)

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

    2013-04-01

    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. Padrón-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., Martínez-Martínez, J. M., Padrón-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-Alborán lithospheric mantle (Betic Cordillera, southern Spain): Journal of the Geological Society, London. Marchesi, C., Garrido, C. J., Bosch, D., Bodinier, J.-L., Hidas, K., Padrón-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.

  9. Le Carbonifère du Maroc central : les formations de Migoumess, de Tirhela et d'Idmarrach. Lithologie, biostratigraphie et conséquences géodynamiquesThe Carboniferous formations of Migoumess, Tirhela and Idmarrach (central Morocco): lithology, biostratigraphy and geodynamic consequences

    NASA Astrophysics Data System (ADS)

    Berkhli, Mostafa; Vachard, Daniel

    2002-01-01

    New biostratigraphical data based on foraminifers, algae and pseudo-algae indicate that the limestone pebbles of the channelized polygenic conglomerates of the Migoumess formation contain Late Visean (V3b ?-V3c) assemblages. That confirms the Westphalian age attributed to this formation by Hollard [Zdt. Geol. Ges. 129 (1978) 495-512]. The Tournaisian age assigned to it by palynology [C. R. Acad. Sci. Paris, série II 310 (1990) 1573-1576] cannot be retained. The Tirhela formation, Late Visean and Serpukhovian (E1) in age, is coeval with the Akerchi formation [Berkhli, thèse d'État, 1999; Berkhli et al., J. Afr. Earth Sci. (accepté)]. The Idmarrach formation, mapped as a thrust sheet [C. R. Acad. Sci. Paris, série II 310 (1990) 1573-1576], is dated as Serpukhovian (E1) and its thrusting is consequently post-Serpukhovian. Palaeogeographic and geodynamic consequences are listed. To cite this article: M. Berkhli, D. Vachard, C. R. Geoscience 334 (2002) 67-72

  10. 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)

    Bouyo, Merlain

    2014-05-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Rojas-Agramonte, Y.; García-Casco, A.; Kröner, A.; Herwartz, D.; Ibis Despaigne, A.; Wilde, S.

    2012-04-01

    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 mélange 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 mélange, which contains low-pressure ophiolitic blocks and HP blocks of eclogite, garnet amphibolite and blueschist facies rocks within a serpentinitic matrix. This serpentinite mélange 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 131.1±1.3 Ma for a block of garnet amphibolite from a sliver of oceanic serpentinite mélange 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 mélange. 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 mélanges, the Chuacús complex, and the basement of the Maya block range 150-70 Ma.

  14. 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)

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

    2012-04-01

    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.

  15. 12.520 Geodynamics, Fall 2005

    E-print Network

    Hager, Bradford H.

    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.

  16. 12.520 Geodynamics, Fall 2004

    E-print Network

    Hager, Bradford H.

    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.

  17. The geodynamics of the Levant margin

    NASA Astrophysics Data System (ADS)

    Ben-Avraham, Z.

    2006-12-01

    The Levant continental margin, offshore Israel, Lebanon and Syria, is usually defined as a passive margin that was formed through rifting processes. During the formation two major continental fragments are assumed to separate from the northern edge of the Afro-Arabian plate to form the Levant basin: the Tauride and Eratosthenes blocks. Today an oceanic crust and, in places, a very thin continental crust are present between the Levant margin and Eratosthenes seamount. The margin can be divided into two distinct provinces that are separated by the Carmel Structure, which extends from seawards to the northwest across the continental shelf and slope. The preservation of segmentation, both in the shallow and in the deep structure, insinuates that the two segments were formed through different continental breakup processes, which continue to dictate the style of sediment accumulation. The nature and development of the continental margin offshore Israel were the subject of numerous studies, which suggest that the southern Levant segment (south of the Carmel Structure) was formed through continental rifting processes. In contrast, the northern segment, from the Carmel structure northwards and offshore southern Lebanon, was hardly studied before. Recent studies however indicate that the northern segment shows a strong similarity to classical transform margins in the world. In view of the new classification of the northern Levant margin a modified scenario is suggested for: (a) the initial stages in which the Levant margin was formed; and (b) the present day structural differences between the two segments of the margin. At present, the northern Levant continental margin is being reactivated by transpressional faulting of the marine continuation of the Carmel fault which bends northward at the base of the continental slope due to the rheological discontinuity in this region. This fault system coincides with the sharp continental-oceanic crustal transition, and acts as an isolator between the Levant basin and its land counterpart. To the north, this feature may initiate the formation of a new triple junction, with the Latakia ridge (part of the eastern Cyprian arc) and the East Anatolian fault.

  18. The geodynamics of super-sized Earths

    Microsoft Academic Search

    C. O'Neill; A. Lenardic

    2007-01-01

    The habitability of a planet is strongly contingent on its tectonic regime. Recently, the discovery of giant Earth-like planets has led to speculation on their surface conditions and dynamics. Here we explore the tectonic regimes of super-sized Earths, which are a function of the balance between driving forces, and the resistive strength of the lithosphere. We use mantle convection simulations

  19. A geodynamic framework for eastern Mediterranean kinematics

    Microsoft Academic Search

    Paul Lundgren; Domenico Giardini; Raymond M. Russo

    1998-01-01

    We use a finite element model incorporating plate motion boundary conditions, fault constraints, and space geodetic velocities to calculate eastern Mediterranean plate kinematics and to estimate the motion of the region's major faults. We then use subsets of these constraints to generate models testing different scenarios of driving forces (slab roll-back at the Hellenic arc, Arabian plate push, gravitational collapse

  20. Magmatism and Geodynamics of Eastern Turkey

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

    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, Tendürek and Süphan volcanoes) and plateaus (e.g. The Erzurum-Kars Plateau) around the Mediterranean

  1. Geodynamic evolution of the SW Europe Variscides

    Microsoft Academic Search

    António Ribeiro; José Munhá; Rui Dias; António Mateus; Eurico Pereira; Luísa Ribeiro; Paulo Fonseca; Alexandre Araújo; Tomás Oliveira; José Romão; Hélder Chaminé; Carlos Coke; Jorge Pedro

    2007-01-01

    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.

  2. Water, Life, and Planetary Geodynamical Evolution

    Microsoft Academic Search

    P. van Thienen; K. Benzerara; D. Breuer; C. Gillmann; S. Labrosse; P. Lognonné; T. Spohn

    2007-01-01

    In our search for life on other planets over the past decades, we have come to understand that the solid terrestrial planets\\u000a provide much more than merely a substrate on which life may develop. Large-scale exchange of heat and volatile species between\\u000a planetary interiors and hydrospheres\\/atmospheres, as well as the presence of a magnetic field, are important factors contributing\\u000a to

  3. Water, Life, and Planetary Geodynamical Evolution

    Microsoft Academic Search

    P. van Thienen; K. Benzerara; D. Breuer; C. Gillmann; S. Labrosse; P. Lognonné; T. Spohn

    \\u000a In our search for life on other planets over the past decades, we have come to understand that the solid terrestrial planets\\u000a provide much more than merely a substrate on which life may develop. Large-scale exchange of heat and volatile species between\\u000a planetary interiors and hydrospheres\\/atmospheres, as well as the presence of a magnetic field, are important factors contributing\\u000a to

  4. Precise leveling, space geodesy and geodynamics

    NASA Technical Reports Server (NTRS)

    Reilinger, R.

    1981-01-01

    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.

  5. Geodynamic and metabolic cycles in the Hadean

    Microsoft Academic Search

    M. J. Russell; N. T. Arndt

    2004-01-01

    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 ~400°C contributed Fe and other

  6. Arctic region: new model of geodynamic history

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    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.

  7. The Year at geodynamics regional processes

    E-print Network

    Colorado at Boulder, University of

    of landforms in paleo- climates has yielded interesting new insights on past ENSO events. Earthquake hazards as part of the Space Weather Program. New forecast models of the ionosphere are leading to a better for new modeling efforts in air-quality forecasting. The development of the new Science and Technology

  8. Geodynamics and The Evolution of Continental Lithosphere

    NASA Astrophysics Data System (ADS)

    Hamilton, W. B.

    R.L. ArmstrongSs (1991) posthumous paper demonstrated that, contrary to conven- tional (and still dominant) geochemical assumption, isotopic data require most con- tinental material to have been fractionated into crust early in Earth history and to have been variably recycled since through the mantle. Recent information confirms predictions implicit in his recycling model. Archean cratonic crust mostly lacks a thick, mafic basal layer and is in bulk more felsic than Proterozoic and younger crust, whereas Archean lithospheric mantle is much more refractory than younger litho- sphere, which becomes markedly more enriched in fusible components with decreas- ing age. The oldest rocks in all Archean cratons are felsic migmatites, plus abundant but subordinate ultramafic, mafic, and anorthositic rocks. Ion-microprobe ages of zir- cons in these gneisses typically scatter from a maximum (currently 4.4 Ga in Yilgarn, and 4.1-3.6 Ga in other cratons) to minima near ages of overlying supracrustal rocks or of remobilization into late domiform batholiths. The gneisses were near wet-solidus temperature for long periods, the felsic protolith may have been mostly fractionated into crust by 4.4 Ga, and these ancient gneisses may dominate middle and lower Archean crust. Setting of formation is unknown, although steep REE patterns sug- gest derivation, by hydrous magmatic fractionation or partial melting, complementary to garnet-rich rocks that comprise geophysical mantle. Waterlaid supracrustal rocksU-° first quartzite, then mostly mafic and ultramafic lavaUwere deposited on the basement ° rocks after 3.5 Ga, and were deformed by gravitational rise of domiform batholiths and sinking of dense synclines. Indicators of plate-tectonic rifting and convergence are widespread in terrains younger than 2 Ga but are wholly lacking in the Archean. Plate tectonics is driven by subduction, which is enabled by top-down cooling of light asthenosphere to form dense oceanic lithosphere. Hinges roll back into subducting plates, and slabs sink broadside, pushing sub-lithospheric mantle back into the oceans from whence they came, forcing spreading therein. Slabs are plated down on, and de- press, the 660-km discontinuity, and are overpassed by overriding plates, like tanks above basal treads, transferring mantle to passively spreading oceans. No compelling evidence indicates plate-tectonic circulation to extend deeper than the 660-km discon- tinuity, and cosmologic and thermodynamic data are incompatible with deep circula- tion. Post-2.0 Ga circulation, with lessening re-fractionation, has made crust gradually more mafic, and upper mantle gradually more felsic.

  9. South Aegean Geodynamic And Tsunami Monitoring Platform

    NASA Astrophysics Data System (ADS)

    Paradissis, Demitris; Drakatos, George; Marinou, Aggeliki; Anastasiou, Demitris; Alatza, Stauroula; Zacharis, Vangelis; Papanikolaou, Xanthos; Melis, Nicolaos; Kalogeras, Ioannis; Chouliaras, Gerasimos; Evangelidis, Christos; Makropoulos, Konstantinos

    2015-04-01

    The Aegean Sea is one of the most tectonically and seismically active areas in the world, thus constituting a Natural Laboratory. For the first time, a permanent multiparametric platform of networks that combine different (both terrestrial and space oriented) techniques, is established, in order to monitor the tectonic and volcanic activity in the area and produce an on-line database available both to the scientific community and the public. This platform includes continuous GNSS networks, tide-gauge sensors, accelerometers and seismographs. All the available existing infrastructure has been upgraded, enlarged and modernized resulting in a collaborative operation. New instrumentation has been installed in carefully selected sites. All the available data are analysed using state of the art processing software. Raw data and products will be available through a project dedicated portal. The multiparametric data and results gathered will be integrated and combined with the existing archive owned by the participating institutes to produce a thoroughgoing view of the underlying geophysical processes. The island of Santorini will serve as a focused study case for the project, due to the special tectono-volcanic interest and because of the already existing dense multiparametric network. Our goal is to provide permanent infrastructure and knowledge both to enlighten ambiguous scientific hypothesis and serve as a focal point for further scientific research.

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

    NASA Technical Reports Server (NTRS)

    1982-01-01

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

  11. EH vs. CI chondrite derived mantle: A geodynamical comparison

    Microsoft Academic Search

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

    2004-01-01

    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

  12. Late Paleozoic-Early Mesozoic Geodynamics of Central Asia

    Microsoft Academic Search

    M. M. Buslov; Y. Fujiwara; K. Iwata; N. N. Semakov

    2004-01-01

    Correlation and synthesis of published and new structural, paleomagnetic and geochronological data from Central Asia show the important role of strike-slip faulting in their evolution. The pattern of major strike-slip faults outlines a terrane collage produced by a Late Devonian-Early Carboniferous collision of the Gondwana-derived Altai-Mongolia-Tuva composite microcontinent with Siberia, and a Late Carboniferous-Permian collision of East Europe and Kazakhstan,

  13. Seismic Tomogram of the Earth's Mantle: Geodynamic Implications.

    PubMed

    Fukao, Y

    1992-10-23

    Recent seismic tomography of the Earth's mantle has revealed a large-scale pattern of mantle convection comprising upwelling columnar plumes in the Pacific and Africa and downwelling planar sheets along the Circum Pacific. Upwelling and downwelling occur most extensively under the south Pacific and west Pacific, respectively. High-resolution image of plate subduction has been obtained from the dense seismic networks around Japan. Japanese seismologists are in the best position to resolve the internal structure of downwelling current as an integral part of the whole convection system. PMID:17748897

  14. Seismic anisotropy surrounding South China Sea and its geodynamic implications

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    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.

  15. Complex seismic anisotropy beneath western Tibet and its geodynamic implications

    NASA Astrophysics Data System (ADS)

    Wu, Jing; Zhang, Zhongjie; Kong, Fansheng; Yang, Bin B.; Yu, Youqiang; Liu, Kelly H.; Gao, Stephen S.

    2015-03-01

    Shear wave splitting parameters obtained along a linear array of 23 stations deployed in western Tibet during a two-year period from 2011 to 2013 demonstrate strong and systematic azimuthal variations with a 90-degree periodicity, suggesting the existence of double-layer anisotropy with a horizontal axis of symmetry. The predominant fast orientations are mostly E-W for events from the east and southeast, and NE-SW or N-S for events from the northwestern quadrant. Under the assumption of a two-layer anisotropic structure, we grid-search for the two pairs of parameters that characterize the complex anisotropy. The resulting fast orientation for the lower layer is mostly N-S, which is consistent with the direction of mantle flow caused by the subduction of the Indian continent beneath Tibet. For the upper layer, the fast orientation is NE-SW, which is significantly different from the strike of dominant surface structures, and can be explained by lower crustal flow in western Tibet. This interpretation is supported by the NE-SW orientation and significant strength (with splitting times as large as 1.3 s) of crustal anisotropy revealed using the sinusoidal moveout of the P-to-S converted phases from the Moho. To our knowledge, this is the first time when upper layer anisotropy revealed from SWS analysis is reliably constrained in the crust using independently determined crustal anisotropy measured by the P-to-S converted phase from the Moho. The observations provide additional evidence for the existence of a subducted Indian slab that is undeformed and is decoupled from the significantly shortened crust, extending to the northern margin of the Qiangtang block.

  16. Lower Mantle melting model and it's geodynamical applications

    NASA Astrophysics Data System (ADS)

    Fomin, I.; Tackley, P. J.

    2014-12-01

    Model of solid-liquid equilibrium laws and substances properties in lower mantle conditions is important to understand the early stages of evolution of terrestrial planets, such as core formation and magma ocean crystallization. This model is also necessary to prove theories on some modern seismic features of the Earth (e.g. ultra-low velocity zones) and petrological observations (e.g. lower mantle mineral assemblage inclusions in diamonds). Numerous experimental and numerical studies of the lower mantle phases provide sufficient amount of data to build up a thermodynamic model, which can be used in geophysical fluid dynamics research. Experimental studies are the direct source of soliduses values, but other thermodynamic parameters stay unclear. Molecular Dynamics modeling provides data on thermodynamic properties of solids and liquids (density, heat capacity, latent heat of melting etc.). But absence of minor components (iron, alkali etc.) and some numerical issues (e.g. [Belonoshko, 2001]) make it to overestimate melting temperatures significantly (up to 20-30%). Our approach is to develop a model based on MD data by [de Koker et al., 2013] with evaluation of all important parameters according to classical thermodynamic equations. But melting temperatures (especially at eutectic points) are corrected along Clausius-Clapeyron slopes to agree with modern experimental data ([Andrault et al., 2011], [Andrault et al., 2014], [Fiquet et al., 2010], [Hirose et al., 1999], [Mosenfelder et al., 2007], [Nomura et al., 2014],[Ozawa et al., 2011], [Zerr et al., 1998]). Notable effect on melt and solid densities has iron partitioning, so KD value reported by [Andrault et al., 2012] was used. Proposed model was implemented into StagYY software (e.g. [Tackley, 2008]). It is a finite-volume discretization code for advection of solid and liquid in a planetary scale. CMB temperature was set to be 4000-4400 K. Calculations predict appearing and disappearing batches containing up to 5-7% of melt. Amount of FeO in liquid is up to 18%, so melts are 2 % denser than solid counterpart, resulting in total density increase up to 1 %. This data fits properties proposed for Ultra-Low Velocity Zones (melt fraction between 5 and 30 % [Garnero et al., 1998], and density increase of at least 1% [Beuchert & Schmeling, 2013]).

  17. Prelaunch testing of the laser geodynamic satellite (LAGEOS)

    Microsoft Academic Search

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

    1977-01-01

    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

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

    Microsoft Academic Search

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

    1993-01-01

    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

  19. Moho topography in the central Andes and its geodynamic implications

    Microsoft Academic Search

    X. Yuan; S. V. Sobolev; R. Kind

    2002-01-01

    P-to-S converted waves at the continental Moho together with waves multiply reflected between the Earth’s surface and the Moho have been used to estimate the Moho depth and average crustal Vp\\/Vs variations in the central Andes. Our analysis confirms and significantly complements the Moho depth estimates previously obtained from wide-angle seismic studies and receiver functions. The resulting crustal thickness varies

  20. Aegean crustal thickness inferred from gravity inversion. Geodynamical implications

    E-print Network

    Demouchy, Sylvie

    ­Miocene times. Moho topography is obtained by inversion of satellite marine gravity data. Data are first by a rather flat Moho at 25 km. A two-stage model of the Aegean extension could well explain the observed

  1. Tertiary geodynamical evolution of northwestern Greece: paleomagnetic results

    Microsoft Academic Search

    Catherine Kissel; Carlo Laj; Carla Müller

    1985-01-01

    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,

  2. Wilson study cycles: Research relative to ocean geodynamic cycles

    NASA Technical Reports Server (NTRS)

    Kidd, W. S. F.

    1985-01-01

    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.

  3. Plume capture by a migrating ridge: Analog geodynamic experiments

    Microsoft Academic Search

    J. S. Mendez; P. Hall

    2010-01-01

    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

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

    E-print Network

    Cerveny, Vlastislav

    #12;(C.Bina, 9/2011) (fromB.Hacker) podrobnjsímetamorfnífacie(stupnmetamorfózy) #12;(C.Bina, 9 reactions. (faciesboundariesfromB.Hacker) Precise boundaries involve several reactions and depend upon bulk (over a temperature interval of more than 50°). (faciesboundariesfromB.Hacker) Precise boundaries

  5. Crystalline Basement of Junggar Basin and Its Geodynamic Analysis

    NASA Astrophysics Data System (ADS)

    Zhao, J.

    2013-12-01

    Understanding the structure and properties of the crystalline basement of the Junggar basin is a key issue in interpreting regional tectonics in northwest China. We conducted a wide-angle seismic reflection/refraction survey along a ~600km long transect through the Junggar basin from Emin to Qitai. Combining detailed gravity and geomagnetic survey (1:200000 scale) in the Junggar basin and adjacent regions, we preformed joint inversion of seismic, gravity, and aeromagnetic data and inverted for the P-wave velocity structure, the density and magnetic intensity of materials in the crust and the uppermost mantle along this profile. In the context of Global Geosciences Transect, we proposed a comprehensive interpretation by integrating seismic, geological, stratigraphic, geochemical, and geochronological data. Along the profile, the total crustal thickness for the Junggar basin ranges from 46 km to 56 km. The upper crust of the Junggar basin consists of two layers: the 1-12km thick sedimentary cover overlying a 12-20km thick crystalline basement. A spindly-shaped middle crust is comparatively thin, with thicknesses ranging from 4 km to 15 km. The lower crust is characterized by a uniform thickness of ~15 km despite having clear lateral velocity variations. Velocity contours in the uppermost mantle of the Junggar basin are convex geometrically, indicating the velocity is higher at the center of the basin than at either side. Several N-S trending faults were imaged, which cut through the crust and are associated with low seismic reflectivity, low Q values, and no obvious dislocation and are considered to be 'extensional' faults. High seismic velocities, high densities and high magnetic intensities indicate that upper mantle masses of basic to ultra-basic rocks have been added to the crystalline basement in several sections along these faults. The basement of the Junggar basin is composed of the Junggar block and the Variscian Kelameili continental margin accretion zone. The lithology of the Junggar basement is complicated especially towards its center. It is composed of mafic, ultra-mafic, and acidic rocks, such as basalt, granite, and sandstone. The basement of the Junggar basin is divided into two distinct terranes: the Manasi terrain in the south and Wulungu terrain in the north. The Dishuiquan-Halatelashan suture zone separates these two terranes. The southern Manasi terrain shows strong geomagnetism likely to be associated with deep faults which may provide potential channels for deep magnetic materials to migrate and intrude into the crust. The basement of the Junggar basin is composed of two layers. To the north of the Dishuiquan-Halatelashan suture zone, the upper layer is the Kelameili continental margin accretion zone, or the folded basement composed of Devonian and Lower Carboniferous rocks. The lower layer may be the original crystal basement from the early Paleozoic age. To the south of the suture zone the upper layer is the same and the lower layer may be the original crystalline basement from the Middle-Later Proterozoic.

  6. Superkimberlites: A geodynamic diamond window to the Earth's core

    NASA Astrophysics Data System (ADS)

    Haggerty, Stephen E.

    1994-03-01

    Carbon is the fourth most abundant element in the solar system. In the Earth carbon is in atmospheric CO2, limestone, other organic products, graphite and trace diamond; interstellar diamond, however, is ubiquitous. Diamond is well known for some unique physical and chemical properties, but it is perhaps less well known that the mineral is geologically ancient (3.3 Ga), that its origins are deep in the mantle (greater than 180 km), and that diamonds are among the deepest solid objects to reach the surface of the Earth; rare diamonds are from the transition zone (400-670 km), and other diamonds possibly nucleated in the lower mantle (greater than 670 km). Transport to the surface is in volatile (C-O-H-N-S)-charged highly explosive kimberlite and lamproite volcanoes. These volcanoes are sited exclusively in the oldest (greater than 1.7 Ga), tectonically most stable, and thickest (approximately 200 km) regions of crust and upper mantle lithosphere. The energetics required for volcanism are so exceptional and the sources so deep that possible connections between and among the core, geomagnetism, plumes and diamonds are explored. Some correlations are established and others are implied. The results are sufficiently enticing to propose that kimberlites and geographically and temporally associated carbonatites are continental recorders of plumes dating back to at least 2.8 Ga, and that some diamonds may have recorded core events dating back to 3.3 Ga, or possibly earlier. Peaks in kimberlite magmatic activity correlate , on average, with normal and reverse superchron and subchron behavior of the geomagnetic field. The time lag between magnetohydrodynamic activity in the core and kimberlite eruptive cycles at the Earth's surface is of the order of 25-50 Ma, consistent with the travel times modeled for the passage of plumes from the D'' layer to the subcontinental lithosphere. Although the existence of plumes and the nature of D'' are debated, the correlations established for the past 500 Ma between and among superchrons, subchrons, kimberlites and entrained diamonds weigh heavily in favor of the following scenario: solid core growth, the consequent release of Si, O, C, H, S, K and possibly N and B to D'', disruption of D'' at some critically unstable threshold thickness (200-300 km), enhanced core convection and the stabilization of a constant non-reversing magnetic dipole field, rising plumes and subsequent volcanism. If protokimberlitic magma and entrainment begin at the core-mantle boundary, a number of geochemical and mineralogical anomalies in diamonds are at present best satisfied if D'' is invoked. These include but are not limited to intensely reduced (i.e., oxygen deficient) SiC, metallic Fe, an abundance of sulfides, silicate perovskite and wuestite-periclase mineral inclusions in diamonds.

  7. The DORIS benefits as seen from flight dynamics to geodynamics

    Microsoft Academic Search

    F. Nouel; J. P. Berthias; P. Broca; A. Comps; M. Deleuze; A. Guitart; C. Jayles; Ph. Laudet; C. Pierret; A. Piuzzi

    1992-01-01

    DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite) is a radio receiver designed to accurately measure the carrier frequencies of incoming signals generated by a worldwide beacon network. The DORIS concept is to minimize error sources so that the submeter level on the low Earth orbit satellite position can be reached almost permanently. The DORIS ground segment includes a control

  8. Long-term orbit determination and prediction for geodynamic investigations

    Microsoft Academic Search

    B. E. Douglas

    1976-01-01

    Comparison of artificial earth satellite orbits determined with different data types and\\/or force model parameters indicates that the error in such orbits is essentially short periodic with respect to the satellite motion. Therefore the mean elements of satellite orbits can be expected to be very precisely known. A precision of a few centimeters in mean semi-major axis and a few

  9. Geodynamic modelling of low-buoyancy thermo-chemical plumes

    NASA Astrophysics Data System (ADS)

    Dannberg, Juliane; Sobolev, Stephan

    2015-04-01

    The Earth's biggest magmatic events that form Large Igneous Provinces are believed to originate from massive melting when hot mantle plumes rising from the lowermost mantle reach the base of the lithosphere. Classical models of thermal mantle plumes predict a flattening of the plume head to a disk-like structure, a kilometer-scale surface uplift just before the initiation of LIPs and thin plume tails. However, there are seismic observations and paleo-topography data that are difficult to explain with this classical approach. Here, using numerical models, we show that the issue can be resolved if major mantle plumes are thermo-chemical rather than purely thermal. It has been suggested a long time ago that subducted oceanic crust could be recycled by mantle plumes; and based on geochemical data, they may contain up to 15-20% of this recycled material in the form of dense eclogite, which drastically decreases their buoyancy and makes it depth-dependent. We perform numerical experiments in a 3D spherical shell geometry to investigate the dynamics of the plume ascent, the interaction between plume- and plate-driven flow and the dynamics of melting in a plume head. For this purpose, we use the finite-element code ASPECT, which allows for complex temperature-, pressure- and composition-dependent material properties. Moreover, our models incorporate phase transitions (including melting) with the accompanying rheological and density changes, Clapeyron slopes and latent heat effects for both peridotite and eclogite, mantle compressibility and a strong temperature- and depth-dependent viscosity. We demonstrate that despite their low buoyancy, such plumes can rise through the whole mantle causing only negligible surface uplift. Conditions for this ascent are high plume volume and moderate lower mantle subadiabaticity. While high plume buoyancy results in plumes directly advancing to the base of the lithosphere, plumes with slightly lower buoyancy pond in a depth of 300-400 km and form pools or a second layer of hot material. These structures are caused by phase transitions occurring in different depths in peridotite and eclogite; and they become asymmetric and finger-like channels begin to form when the plume gets entrained by a quickly moving overlying plate. We also show that the bulky tails of large and hot low-buoyancy plumes are stable for several tens of millions of years and that their shapes fit seismic tomography data much better than the narrow tails of thermal plumes.

  10. (C.Bina, 5/2012) From thermodynamics to geodynamics

    E-print Network

    Cerveny, Vlastislav

    . Nelson, 2011) #12;(C.Bina, 5/2012) (J. Winter) Diopside (CaMgSi2O6) ­ Anorthite (CaAl2Si2O8) No Solid) Eutectic MeltingTwo-Component Systems: Diopside (CaMgSi2O6) ­ Anorthite (CaAl2Si2O8) No Solid Solution: Diopside (CaMgSi2O6) ­ Anorthite (CaAl2Si2O8) No Solid Solution ­ Congruently Melting End-Members Note

  11. Anisotropic measurements in South Korea and geodynamic implications

    NASA Astrophysics Data System (ADS)

    Kang, Tae-Seob

    2010-05-01

    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.

  12. ORIGINAL ARTICLE Increasing the usability and accessibility of geodynamic modelling

    E-print Network

    Müller, Dietmar

    that represent obstacles to the development of realistic simulation of deep earth processes. Realistic 4D thermo of the Un- derworldGUI are available at the web site http:// www, advantageous for geo- scientists to employ 4D computer simulations in their re- search (Moresi et al. 2003

  13. Geodynamic inversion to constrain the nonlinear rheology of the lithosphere

    NASA Astrophysics Data System (ADS)

    Baumann, Tobias; Kaus, Boris

    2015-04-01

    A common method to determine the strength of the lithosphere is through estimating its effective elastic thickness from the coherence between gravity and topography. This method assumes a priori that the lithosphere is a thin elastic plate floating on a viscous mantle. Whereas this seems to work well with oceanic plates, it has given controversial results in continental collision zones. Usually, continental collisions zones are well-studied areas for which additional geophysical datasets such as receiver functions and seismic tomography exist that constrain the geometry of the lithosphere and often show that it is rather complex. Yet, lithospheric geometry by itself is insufficient to understand the dynamics of the lithosphere, as this also requires knowledge of the rheology of the lithosphere. Experimental results show significant variability between various rock types and there are large uncertainties in extrapolating laboratory values to nature, which leaves room for speculation. An independent approach is thus required to better understand the rheology and dynamics of the lithosphere in collision zones. Our method combines numerical thermo-mechanical forward models of the present-day lithosphere with a massively parallel Bayesian inversion approach. The geometry of the forward models is part of the a priori knowledge and is constructed from seismological data. We jointly invert topography, gravity, horizontal and vertical surface velocities to constrain the unknown rheological material parameters of the forward models in a probabilistic sense. The model rheology is described with experimentally determined viscous creep laws and other parameters describing the plastic behaviour. As viscosity is temperature dependent, the temperature structure of the forward models is parameterised as well. We apply the method to cross-sections of the India-Asia collision system. In this case, we deal with 17 to 20 model parameters, which requires solving up to 2 × 106 forward models. The resulting models fit the data within their respective uncertainty bounds, and show that the Indian mantle lithosphere must have a high viscosity. Results for the Tibetan plateau are less clear, and both models with a weak Asian mantle lithosphere and with a weak Asian lower crust fit the data nearly equally well.

  14. A proposed test area for the spaceborne geodynamic ranging system

    NASA Technical Reports Server (NTRS)

    Lowman, P. D., Jr.

    1978-01-01

    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.

  15. Geodynamical aspects of the Hoggar Shield (Algeria) from Aeromagnetic data

    Microsoft Academic Search

    N. Bournas; M. Hamoudi; A. Galdeano; K. Ouzegane; J. R. Kienast

    2003-01-01

    The Hoggar is a wide region situated in the central part of northwest Africa. It represents the main component of the Tuareg shield, which is a part of the Panafrican Transaharan belt. The Hoggar is mainly composed of metamorphic rocks formed during the Panafrican orogeny and is crossed by several north-south mega-shear zones separating crustal blocks with different lithology. This

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

    USGS Publications Warehouse

    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

    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.

  17. Thermal rocketing and the Laser Geodynamic Satellite (LAGEOS-1)

    SciTech Connect

    Miller, W.A.

    1997-08-01

    This is the final report of a one-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory. LAGEOS is the most accurately tracked satellite in orbit. It is a totally passive, dense spherical satellite covered with 426 cube corner reflectors. Besides its great utility in measuring the Earth`s length of day and polar wobble, this satellite can be used to measure, for the first time, the general relativistic frame-dragging effect. Of the five dominant error sources in such an experiment, the largest one involves surface interaction of thermal forces (thermal rocketing) and its influence on the orbital nodal precession. The project objective was to enhance an already available theoretical model (computer code) developed at Los Alamos based on new optical-spin data obtained at the University of Maryland. The project objective was met and the enhanced code will serve as the new spin-dynamics model for future LAGEOS satellite missions.

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

    Microsoft Academic Search

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

    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

  19. GS of CAS Geodesy & Geodynamics Beijing June 20041 SEISMIC CYCLE

    E-print Network

    Vigny, Christophe

    June 20048 Difficulty of earthquake prediction Even though a given fault can have a characteristic Earthquake repeating itself over a characteristic time, earthquake prediction is difficult because : 1. Those and rupture on a fault. Example on a Strike-slip fault and a Subduction fault · Size of an earthquake · Time

  20. Geodynamics applications of continuum physics to geological problems

    Microsoft Academic Search

    D. L. Turcotte; G. Schubert

    1982-01-01

    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

  1. Earthquake source characteristics along the arcuate Himalayan belt: Geodynamic implications

    NASA Astrophysics Data System (ADS)

    Khan, Prosanta Kumar; Ansari, Md Afroz; Mohanty, S.

    2014-06-01

    The occurrences of moderate to large magnitude earthquakes and associated subsurface geological processes were critically examined in the backdrop of Indian plate obliquity, stress obliquity, topography, and the late Tertiary regional tectonics for understanding the evolving dynamics and kinematics in the central part of the Himalayas. The higher topographic areas are likely associated with the zones of depressions, and the lower topographic areas are found around the ridges located in the frontal part of the orogen. A positive correlation between plate and stress obliquities is established for this diffuse plate boundary. We propose that the zone of sharp bending of the descending Indian lithosphere is the nodal area of major stress accumulation which is released occasionally in form of earthquakes. The lateral geometry of the Himalayas shows clusters of seismicity at an angle of ˜20? from the centre part of the arc. Such spatial distribution is interpreted in terms of compression across the arc and extension parallel to the arc. This biaxial deformation results in the development of dilational shear fractures, observed along the orogenic belt, at an angle of ˜20? from the principal compressive stress axis.

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

    SciTech Connect

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

    2008-08-22

    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.

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

    NASA Technical Reports Server (NTRS)

    1974-01-01

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

  4. Le volcanisme cambrien du Maroc central : implications géodynamiquesThe Central Morocco Cambrian volcanism: geodynamic implications

    NASA Astrophysics Data System (ADS)

    Ouali, Houssa; Briand, Bernard; Bouchardon, Jean-Luc; Capiez, Paul

    2003-05-01

    In southeastern Central Morocco, the Bou-Acila volcanic complex is considered of Cambrian age. In spite of low-grade metamorphic effect, initial volcanic texture and mineralogy can be recognized and volcanic rocks are dominated by dolerites and porphyric dolerites. The initial mineralogy is composed of plagioclases, pyroxenes and dark minerals. A secondary mineral assemblage is composed of albite, epidote, chlorite and calcite. According to their immobile elements compositions, the southeastern central Morocco metavolcanites are of within-plate continental tholeiites. This volcanism and those recognized in many other areas in Morocco confirm a Cambrian extensive episode within the Gondwana supercontinent. To cite this article: H. Ouali et al., C. R. Geoscience 335 (2003).To cite this article: H. Ouali et al., C. R. Geoscience 335 (2003).

  5. Late Paleozoic geodynamic evolution of the Junggar Basin (Northwestern China) : insights from new paleomagnetic results

    Microsoft Academic Search

    F. Choulet; Y. Chen; B. Wang; M. Faure; D. Cluzel; W. Lin; B. Xu

    2009-01-01

    The continental or oceanic nature and the geographic extent of the Junggar basement remain controversial; nevertheless this area presents special interests in order to better understand the Paleozoic tectonic framework of Central Asia. A paleomagnetic study has been performed on Late Paleozoic rocks around Junggar Basin in order to check if it can be regarded as a rigid block at

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

    Microsoft Academic Search

    F. Choulet; Y. Chen; B. Wang; M. Faure; D. Cluzel; J. Charvet; W. Lin; B. Xu

    2011-01-01

    Carboniferous to Permian volcanoclastic rocks have been collected from South Junggar and West Junggar. Primary magnetizations have been observed from the characteristic components of 10 sites of Early Permian (P1) and Late Permian (P2) red beds of South Junggar area. The 14 Early Carboniferous sites from West Junggar Mountains expose post-folding secondary magnetizations and according to their spatial distribution, 9

  7. Generation of felsic crust in the Archean: a geodynamic modeling perspective

    NASA Astrophysics Data System (ADS)

    Sizova, Elena; Gerya, Taras; Stüwe, Kurt; Brown, Michael

    2015-04-01

    The relevance of contemporary tectonics to the formation of the Archean terrains is a matter of vigorous debate. Higher mantle temperatures and higher radiogenic heat production in the past would have impacted on the thickness and composition of the oceanic and continental crust. As a consequence of secular cooling, there is generally no modern analog to assist in understanding the tectonic style that may have operated in the Archean. For this reason, well-constrained numerical modeling, based on the fragmentary evidence preserved in the geological record, is the most appropriate tool to evaluate hypotheses of Archean crust formation. The main lithology of Archean terrains is the sodic tonalite-trondhjemite-granodiorite (TTG) suite. Melting of hydrated basalt at garnet-amphibolite to eclogite facies conditions is considered to be the dominant process for the generation of the Archean TTG crust. Taking into account geochemical signatures of possible mantle contributions to some TTGs, models proposed for the formation of Archean crust include subduction, melting at the bottom of thickened continental crust and fractional crystallization of mantle-derived melts under water-saturated conditions. We evaluated these hypotheses using a 2D coupled petrological-thermomechanical numerical model with initial conditions appropriate to the Eoarchean-Mesoarchean. As a result, we identified three tectonic settings in which intermediate to felsic melts are generated by melting of hydrated primitive basaltic crust: 1) delamination and dripping of the lower primitive basaltic crust into the mantle; 2) local thickening of the primitive basaltic crust; and, 3) small-scale crustal overturns. In addition, we consider remelting of the fractionated products derived from underplated dry basalts as an alternative mechanism for the formation of some Archean granitoids. In the context of a stagnant lid tectonic regime which is intermittently terminated by short-lived subduction, we identified two distinct types of continent crust. The first type is a pristine granite-greenstone-like crust with dome-and-keel geometry formed over delaminating-upwelling mantle which is mostly subjected to vertical tectonics processes. By contrast, the second type is a reworked (accreted) crust comprising strongly deformed granite-greenstone and subduction-related sequences and subjected to both strong horizontal compression and vertical tectonics processes. Thus, our study has identified a possible spatial and temporal transition from the lower-grade granite-greenstone terrains to higher-grade gneiss terrains in the Archean as each tectonic cycle is terminated by short-lived subduction. We suggest that the contemporaneity of the proposed mechanisms for the generation of TTGs explains the variety and complexity of the Archean geological record.

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

  9. Geodynamics of the Emile Baudot Escarpment and the Balearic Promontory, western Mediterranean

    Microsoft Academic Search

    J Acosta; A Muñoz; P Herranz; C Palomo; M Ballesteros; M Vaquero; E Uchupi

    2001-01-01

    The 348km long, 105–155km wide and 1000–2000m high northeast trending Balearic Promontory separates the Valencia Trough to the northwest from the South Balearic–Algerian Basin to the southeast. It consists of three blocks, Ibiza at the southwest end, Mallorca in the center and Menorca at the northeast end of the Promontory. The Ibiza and Mallorca blocks were thrust faulted and folded

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

    Microsoft Academic Search

    Jeffrey C. Andrews-Hanna; Maria T. Zuber; Steven A. Hauck II

    2008-01-01

    The tectonic evolution of Mars has been driven primarily by the interaction of Tharsis-induced loading stresses with a uniform contractional stress field, leading to global assemblages of graben and wrinkle ridges. Until recently, strike-slip faults have appeared to be largely absent from the tectonic record. We here present evidence for a new set of Noachian to Early Hesperian strike-slip faults

  11. Petrogenesis and geodynamic implications of the Mid-Triassic lavas from East Kunlun, northern Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Li, Xiaowei; Huang, Xiongfei; Luo, Mingfei; Dong, Guochen; Mo, Xuanxue

    2015-06-01

    Lying in the northern margin of the Tibetan Plateau, the East Kunlun Orogenic Belt (EKOB) is characterized by widespread of the late Permian to Late Triassic magmatic rocks. In order to better understand magma genesis and evolution during the waning stage of the Paleo-Tethyan oceanic subduction and subsequent collision, we present zircon U-Pb dating and Lu-Hf isotopes, whole-rock major and trace elements, and Sr-Nd isotope data for the Triassic volcanic lavas in the Haishigou area of the EKOB, northern Tibet. Lithologically, the Haishigou volcanic lavas are mainly composed of dacites and rhyolites. The LA-ICP-MS zircon U-Pb analyses for rhyolites have shown that the Haishigou volcanic rocks formed during the Middle Triassic with ages of ca. 244-245 Ma. The Haishigou volcanic lavas actually belong to part of the Middle Triassic Naocangjiangou Formation, rather than the Late Triassic Elashan Formation. Geochemically, Haishigou volcanic lavas have SiO2 = 60.31-76.19 wt% and K2O = 2.60-4.18 wt%, placing them in high-K calc-alkaline series. These lavas are characterized by enrichment in some large-ion lithophile elements (e.g., Rb, K and Pb) and light rare earth elements and depletion in some high field strength elements (e.g., Nb, Ta, and Ti), with geochemical affinities to those rocks forming in a continental or an oceanic arc setting. All the volcanic rocks exhibit high initial 87Sr/86Sr ratios (0.70614-0.70841) and moderately negative ?Nd(t) values (-5.9 to -4.3) that imply a continental rather than oceanic type magma source. The rhyolites in the Haishigou volcanics exhibit moderately negative to slightly positive ?Hf(t) values (-4.2 to 1.4). Combined with their zircon Hf two-stage model ages of 1187-1538 Ma and whole-rock Nd two-stage model ages of 1.37-1.38 Ga, it can be inferred that the crustal growth of East Kunlun occurred during the Mesoproterozoic, making them similar in age to the lower crust metamorphic basement beneath the EKOB (i.e., the Xiaomiao Group). We suggest that the Haishigou dacites were generated by partial melting of the mafic lower crust beneath the EKOB with addition of a mantle-derived mafic component and that the rhyolites were produced by fractional crystallization from a dacitic parent. Taking into account the Late Permian to Triassic geological record from the EKOB and surrounding regions, we argue that the Middle Triassic volcanic rocks in the Haishigou area erupted during the northward subduction of the Paleo-Tethyan oceanic plate. Consequently, the timing of closure of the Paleo-Tethyan Ocean just south of the EKOB is no earlier than the Middle Triassic.

  12. Geodynamic and seismic constraints on the thermochemical structure and dynamics of convection in the deep mantle.

    PubMed

    Forte, Alessandro M; Mitrovica, Jerry X; Espesset, Aude

    2002-11-15

    We revisit a recent study by Forte & Mitrovica in which global geophysical observables associated with mantle convection were inverted and the existence of a strong increase in viscosity near a depth of 2000 km was inferred. Employing mineral-physics data and theory we also showed that, although there are chemical anomalies in the lowermost mantle, they are unable to inhibit the dominant thermal buoyancy of the deep-mantle mega-plumes below Africa and the Pacific Ocean. New Monte Carlo simulations are employed to explore the impact of uncertainties in current mineral-physics constraints on inferences of deep-mantle thermochemical structure. To explore the impact of the high-viscosity peak at a depth of 2000 km on the evolution of lower-mantle structure, we carried out time-dependent convection simulations. The latter show that the stability and longevity of the dominant long-wavelength heterogeneity in the lowermost mantle are controlled by this viscosity peak. PMID:12460479

  13. Deep-mantle high-viscosity flow and thermochemical structure inferred from seismic and geodynamic data.

    PubMed

    Forte, A M; Mitrovica, J X

    2001-04-26

    Surface geophysical data that are related to the process of thermal convection in the Earth's mantle provide constraints on the rheological properties and density structure of the mantle. We show that these convection-related data imply the existence of a region of very high effective viscosity near 2,000 km depth. This inference is obtained using a viscous-flow model based on recent high-resolution seismic models of three-dimensional structure in the mantle. The high-viscosity layer near 2,000 km depth results in a re-organization of flow from short to long horizontal length scales, which agrees with seismic tomographic observations of very long wavelength structures in the deep mantle. The high-viscosity region also strongly suppresses flow-induced deformation and convective mixing in the deep mantle. Here we predict compositional and thermal heterogeneity in this region, using viscous-flow calculations based on the new viscosity profile, together with independent mineral physics data. These maps are consistent with the anti-correlation of anomalies in seismic shear and bulk sound velocity in the deep mantle. The maps also show that mega-plumes in the lower mantle below the central Pacific and Africa are, despite the presence of compositional heterogeneity, buoyant and actively upwelling structures. PMID:11323661

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  15. Neogene and quaternary volcanism in Eastern Azerbaijan (Iran): some KAr age determinations and geodynamic implications

    Microsoft Academic Search

    A. A. Alberti; P. Comin-Chiaramonti; S. Sinigoi; M. Nicoletti; C. Petrucciani

    1980-01-01

    Zusammenfassung  Vier K\\/Ar Altersbestimmungen von Vulkaniten verschiedener Bildungen des Savalan Vulkans (Ost-Azerbaijan, Iran), der eine große Struktur mit andesitischen bis riodazitischen Produkten ist, und der für lange Zeit als Quaternär betrachtet worden ist, lassen auf eine lange vulkanische Geschichte schließen, die mindestens im oberen Miozän begann. K\\/Ar Altersbestimmungen von drei Vulkanit-Proben aus anderen Orten derselben Provinz weisen auch kalk-alkaline Aktivität ab

  16. Psematismenos-Maroni Basin in Cyprus: geomorphology and biostratigraphic contributions to its Tertiary geodynamic evolution

    NASA Astrophysics Data System (ADS)

    Blanpied, Christian; Mocochain, Ludovic; Müller, Carla

    2015-04-01

    The Tertiary regressive sedimentary succession which forms the sedimentary cover of the Troodos Ophiolic Massif has been studied in the Psematismenos-Maroni Basin (PMB) located in southern Cyprus. Identification of key surfaces, morphologies, and sedimentary facies permit to propose a new interpretation of the geologic history of this basin. The series of unconformity surfaces are conforted by numerous new datings, and they are related to tectonic, eustatic, and biostratigraphic hiatuses. This eventually leads to a new geologic vision of the Psematismenos-Maroni Basin from the Neogene Pakhna formation up to the first alluvial deposits of the Quaternary. In the meantime, and for what concerns the Messinian salinity crisis; similarities and differences from the 2008 Messinian consensus (Lofi et al. 2008) are highlighted.

  17. Upper Jurassic-Lower Cretaceous sincollisional sedimentary sequences of Chukotka: sedimentation, structural style and geodynamic implications

    Microsoft Academic Search

    M. I. Tuchkova; S. D. Sokolov; V. E. Verzhbitsky

    2008-01-01

    Upper Jurassic-Lower Cretaceous sincollisional sedimentary sequence, exposed on the Central part of Northern Chukotka is critical for understanding the timing, dynamics and sedimentary setting evolution of Chukotka-Eurasia collisional process (e.g., Sokolov et al., 2002) and so, represents one of the key regional stratigraphic units (Til'man, 1973; Tibilov, 1982; Miller et al., 2002,2007). From the other hand, this research may shed

  18. Upper Jurassic-Lower Cretaceous sincollisional sedimentary sequences of Chukotka: sedimentation, structural style and geodynamic implications

    NASA Astrophysics Data System (ADS)

    Tuchkova, M. I.; Sokolov, S. D.; Verzhbitsky, V. E.

    2008-12-01

    Upper Jurassic-Lower Cretaceous sincollisional sedimentary sequence, exposed on the Central part of Northern Chukotka is critical for understanding the timing, dynamics and sedimentary setting evolution of Chukotka-Eurasia collisional process (e.g., Sokolov et al., 2002) and so, represents one of the key regional stratigraphic units (Til'man, 1973; Tibilov, 1982; Miller et al., 2002,2007). From the other hand, this research may shed the light on the widely discussing problem of the Canadian and Makarov basins opening (e.g., Miller, Verzhbitsky, in press). Field observations reveal moderately to weakly deformed terrigenous sediments of the first stage of deposition with visible and dispersal plants remnants and containing organic-rich beds. Widely distributed and intensively deformed Triassic sequences (Tuchkova et al., 2007) and discussing Jurassic-Cretaceous units both intruded by Aptian-Albian postcollisional plutons and dikes (e.g., Katkov et al., 2006). Collisional-related fabric and subsequent granitoids are complicated by small-scale latest normal faults, in particular related to the westernmost segment of South Chukchi (Hope) basin development in Upper Cretaceous(?)-Cenozoic. We believe, that Upper Jurassic-Lower Cretaceous chukotkian formation, overthrusted by Triassic (and Paleozoic?) sequences (Tibilov, 1982; Baranov, 1995), continues offshore to the Eastern Siberian and Chukchi Seas and play significant role in the structure of the Eastern Arctic Russian shelf. The work is supported by the Russian Foundation for Basic Research (grant 08-05-00547), program of ONZ RAS, and NSH-3172.2008.5.

  19. Cretaceous Rocks of the Penzhina Bay: Mineralogy, Petrography, and Geodynamic Sedimentation Conditions

    Microsoft Academic Search

    M. I. Tuchkova; P. V. Markevich; K. A. Krylov; V. I. Koporulin; V. N. Grigor'ev

    2003-01-01

    Cretaceous sedimentary and volcanosedimentary rocks from northwestern Kamchatka are considered. The stadial analysis has revealed variable impacts of three major provenances upon the Cretaceous Penzhina sedimentary basin. The provenances were composed of volcanic and volcanosedimentary rocks (Uda–Murgal island arc and Okhotsk–Chukotka volcanic belt) and granitic–metamorphic rocks (the mature Asian continental margin). Sediments were largely accumulated owing to the erosion of

  20. Investigation of dynamic noise affecting geodynamics information in a tethered subsatellite

    NASA Technical Reports Server (NTRS)

    Gullahorn, G. E.

    1985-01-01

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

  1. Investigation of dynamic noise affecting geodynamics information in a tethered subsatellite

    NASA Technical Reports Server (NTRS)

    Gullahorn, G. E.

    1985-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    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 earth’s 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.

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

    E-print Network

    Cambridge, University of

    controlled-source seismic acquisition, data modelling and inversion to study large scale crustal processes national and international collaboration in aspects of space-based observation combined with fieldwork. We have expanded our activities in marine seismology through collaboration with Schlumberger. We

  4. The Moho depth and variation character of the continent in China and its geodynamic implications

    Microsoft Academic Search

    X. Xiong; R. Gao; Q. Li; Y. Guan; R. He; H. Wang; Z. Lu; H. Hou; W. Li; G. Deng

    2010-01-01

    From the 1950s, lots of seismic exploration work has been implemented in the continent of China, which spread all over China's main tectonic units. We summarized this datum systemically, and discussed the Moho depth and variation character in China. The Moho depth was sampled along 84 deep seismic sounding profiles per 20-30 km, and the datum of the receiver function

  5. A New Seismic Model of the Eastern Alps and its Relevance for Geodesy and Geodynamics

    E-print Network

    Brückl, Ewald

    -wave velocity in the crust and a map of the Mohorovicic discontinuity (Moho) and interpretations of two and the new Moho map enable to determine a significant fragmentation of the lithosphere. The inferred

  6. Magmatic constraints on geodynamic models of subduction in the East Carpathians, Romania

    Microsoft Academic Search

    Paul R. D. Mason; Ioan Seghedi; Alexandru Szákacs; Hilary Downes

    1998-01-01

    The East Carpathian volcanic arc is the youngest region of calc-alkaline magmatic activity in Eastern Europe. A general age progression of the onset and cessation of magmatic activity occurs along the East Carpathian arc from older volcanic structures (ca. 12 Ma) in the NW to the youngest (

  7. Neogene–Quaternary magmatism and geodynamics in the Carpathian–Pannonian region: a synthesis

    Microsoft Academic Search

    Ioan Seghedi; Hilary Downes; Alexandru Szakács; Paul R. D. Mason; Matthew F. Thirlwall; Emilian Ro?u; Zoltán Pécskay; Emö Márton; Cristian Panaiotu

    2004-01-01

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

  8. On the origin of El Chichón volcano and subduction of Tehuantepec Ridge: A geodynamical perspective

    Microsoft Academic Search

    Marina Manea; Vlad C. Manea

    2008-01-01

    The origin of El Chichón 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

  9. Habitability of the Goldilocks planet Gliese 581g: results from geodynamic models

    NASA Astrophysics Data System (ADS)

    von Bloh, W.; Cuntz, M.; Franck, S.; Bounama, C.

    2011-04-01

    Aims: In 2010, detailed observations have been published that seem to indicate another super-Earth planet in the system of Gliese 581, which is located in the midst of the stellar climatological habitable zone. The mass of the planet, known as Gl 581g, has been estimated to be between 3.1 and 4.3 M?. In this study, we investigate the habitability of Gl 581g based on a previously used concept that explores its long-term possibility of photosynthetic biomass production, which has already been used to gauge the principal possibility of life regarding the super-Earths Gl 581c and Gl 581d. Methods: A thermal evolution model for super-Earths is used to calculate the sources and sinks of atmospheric carbon dioxide. The habitable zone is determined by the limits of photosynthetic biological productivity on the planetary surface. Models with different ratios of land/ocean coverage are pursued. Results: The maximum time span for habitable conditions is attained for water worlds at a position of about 0.14 ± 0.015 AU, which deviates by just a few percent (depending on the adopted stellar luminosity) from the actual position of Gl 581g, an estimate that does however not reflect systematic uncertainties inherent in our model. Therefore, in the framework of our model an almost perfect Goldilock position is realized. The existence of habitability is found to critically depend on the relative planetary continental area, lending a considerable advantage to the possibility of life if Gl 581g's ocean coverage is relatively high. Conclusions: Our results are another step toward identifying the possibility of life beyond the Solar System, especially concerning super-Earth planets, which appear to be more abundant than previously surmised.

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    We applied a combined approach of morphotectonic analyzes of SPOT-5 satellite images and field surveys complemented by in situ-produced10Be exposure dating to determine the kinematics and rate of active faulting in the Binalud Mountains bounded by the Neyshabur Fault System to the southwest and the Mashhad Fault Zone to the northeast. Three regional episodes of alluvial surface abandonment were dated at ˜4.8 ka (Q1), ˜105 ka (Q3), and ˜255 ka (S3). Along the Neyshabur Fault System, cumulative offsets recorded by Q3fan surfaces yield slip rates of 2.4 ± 0.5 and 2.8 ± 0.6 mm/yr for right-lateral and reverse components of active faulting (corresponding to an oblique slip rate of 3.6 ± 1.0 mm/yr), respectively. Reconstructing the cumulative right-lateral offset recorded by S3surfaces, a maximum slip rate of 1.3 ± 0.1 mm/yr is suggested for the Mashhad Fault Zone. These imply an overall rate of 3.7 ± 0.6 mm/yr for the range-parallel displacement and an uplift rate of ˜2.8 mm/yr due to the range-normal shortening (1.6-2.2 mm/yr) during late Quaternary. The Binalud Mountains are deformed as a soft-linked restraining relay zone, taking up the motion between central Iran and Eurasia at a rate of 4.0 ± 1.3 mm/yr; this translates central Iran in the ˜N340°E direction. Our data favor localized faulting, instead of distributed deformation, at the northeastern boundary of the Arabia-Eurasia collision zone.

  11. Crustal heterogeneity in the 2007 Noto-Hanto earthquake area and its geodynamical implications

    NASA Astrophysics Data System (ADS)

    Padhy, Simanchal; Mishra, O. P.; Zhao, Dapeng; Wei, Wei

    2011-08-01

    To understand the genesis of the 25 March 2007 Noto-Hanto earthquake (Mw 6.6), we determined high-resolution 3-D seismic velocity (Vp and Vs) and Poisson's ratio (?) images in the epicenter area using 24,698 P-wave and 22,927 S-wave arrival times from 809 earthquakes and 265 sP depth-phase data collected from seismograms of 162 earthquakes beneath the Japan Sea. The sub-oceanic events are relocated accurately by using P-, S- and sP depth-phase arrival time data jointly. Our results demonstrate that the seismic velocity (Vp and Vs) and Poisson's ratio (?) vary markedly in the source area. In and around the main shock hypocenter, low-velocity and high-? anomalies are revealed, which are apt for accumulation of differential strain to bring the brittle failure. We infer that the zone with pronounced low-velocity and high Poisson's ratio beneath the source area reflects fluid-related anomalies derived either from the dehydration of the subducting Pacific slab or from permeation of sea-water through deep-seated active faults or both to the main shock hypocenter, which in turn may have facilitated the rupture initiation of the main shock and its aftershock sequence by weakening the overlying seismogenic layer beneath the region. Our study reinforces the concept of fluid-driven earthquakes in the peninsular regions, elsewhere in the world.

  12. Evaluation of geodynamic activity of the Dead Sea transform fault by radon gas concentrations

    Microsoft Academic Search

    M. Al-Taj; B. Al-Bataina; M. Atallah

    2004-01-01

    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

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

    Microsoft Academic Search

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

    2007-01-01

    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

  14. Predictions from the Geodynamic Model of a Pull-Apart Basin

    NASA Astrophysics Data System (ADS)

    Petrunin, A.; Sobolev, S. V.

    2005-12-01

    Pull-apart basins belong to a special type of sedimentary basins associated with continental transform faults. They are depressions that are formed as a result of crustal extension in domains where the sense of fault overstepping or bending coincides with the fault motion sense. The outstanding classic example of a pull-apart basin is the 150 km long Dead Sea basin which is located at the Dead Sea Transform and where more than 8 km of sedimentary cover has accumulated since 15-17 Ma. It remains unclear what determines the length of a pull-apart basin and the thickness of its sediments and how the associated extension strain is distributed at depth beneath the basin. We present a simplified 3-D thermomechanical model of a pull-apart basin formed at an overstepping of an active continental transform fault. The modelling shows that, in addition to the magnitude of strike-slip displacement, the major parameters, which control basin length, thickness of sediments and deformation pattern beneath the basin are thickness of the brittle layer and friction strength at major faults. The unusually large length and sediment thickness of the Dead Sea basin can be explained by 100 km of the strike-slip motion, thick (up to 27 km) brittle part of the cold lithosphere beneath the basin and friction coefficient of less than 0.15 at major faults. The much thinner sedimentary cover in the Gulf of Aqaba basin, located at the southernmost part of the Dead Sea Transform, close to the Red Sea Rift, is likely due to a thinner brittle part (12-15 km) of the warmer lithosphere. Based on our model and observed distribution of seismicity in the deepest part of the Dead Sea basin, we predict relation between depth of the basin and friction coefficient at major faults. Moreover, we also predict that uplift of the Moho beneath the basin is less than 3 km. We also infer that the values of surface heat flow of 40 mW/m2, reported for the Dead Sea, are probably much too low (by 15-20 mW/m2), because, otherwise, either the depth of the Dead Sea pull-apart basin would be more than 16 km or no pull-apart deformation would occur in such cold lithosphere. All these predictions can be tested in a multidisciplinary project including seismic, geothermic and stress-field observations.

  15. A Change in the Geodynamics of Continental Growth 3 Billion Years Ago

    NASA Astrophysics Data System (ADS)

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

    2012-03-01

    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.

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

    E-print Network

    Doglioni, Carlo

    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

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

    Microsoft Academic Search

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

    2000-01-01

    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

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

    Microsoft Academic Search

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

    1997-01-01

    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

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

    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.

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

    Microsoft Academic Search

    Márcio M Pimentel; Reinhardt A Fuck; Nilson F Botelho

    1999-01-01

    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, São Francisco–Congo and Paraná continental blocks. The presence of Neoproterozoic juvenile arc rocks and syn-collisional peraluminous granites challenged previous intracontinental evolution models for

  1. Geodynamics of the zone of continental continuation of Mid-Arctic earthquakes belt (Laptev Sea)

    Microsoft Academic Search

    G. P. Avetisov

    1999-01-01

    On the basis of a generalization of all available data on the distribution of earthquake epicenters and their focal mechanisms, the opinion is expressed that there is no thorough splitting of Laptev Sea lithosphere associated with the divergent boundary between the Eurasia and North American plates. There are two fragments of this boundary which are laterally separated by hundreds of

  2. Magmatic sources and geodynamics of the early Mesozoic Northern Mongolia-Western Transbaikalia rift zone

    Microsoft Academic Search

    A. A. Vorontsov; V. V. Yarmolyuk; D. A. Lykhin; S. I. Dril; S. A. Tatarnikov; G. P. Sandimirova

    2007-01-01

    The Northern Mongolia-Western Transbaikalia rift zone is the largest Mesozoic riftogenic structure in eastern Asia and extends\\u000a for a distance of more than 1200 km. The zone consists of depressions and grabens, which were formed between 233 and 188 Ma\\u000a and are filled with basaltic and basalt-comendite (bimodal) volcanic associations accompanied by numerous peralkaline granite\\u000a massifs. Geochemical and isotope (Sr,

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

    NASA Astrophysics Data System (ADS)

    Thomas, P. G.; Allemand, P.

    1993-07-01

    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.

  4. A Geodynamic Model of the Evolution of the Earth’s Chemical Mantle Reservoirs

    Microsoft Academic Search

    Uwe Walzer; Roland Hendel

    \\u000a A dynamic 3-D spherical-shell model for the chemical evolution of the Earth’s mantle is presented. Chemical differentiation,\\u000a convection, stirring, and thermal evolution constitute an inseparable dynamic system. Our model is based on the solution of\\u000a the balance equations of mass, momentum, energy, angular momentum, and four sums of the number of atoms of the pairs 238U-206Pb, 235U-207Pb, 232Th-208Pb, and 40K-40Ar.

  5. Sn Attenuation Model in Tibetan Region and its Geodynamic Implications to Plateau Formation

    NASA Astrophysics Data System (ADS)

    Zhao, L.; Xie, X. B.; Fan, N.; Yao, Z.

    2014-12-01

    We collected 23,940 tangential broadband regional seismic records with their ray paths cross the Tibetan plateau. The waveforms are selected based on criteria that these earthquakes were located in the crust, with magnitudes ranging 3.5-6.6, and epicentral distances 200-2000 km. We extract Sn waveforms using a 0.7 km/s group-velocity window around the IASP91 arrival times, and collect the noise in an equal-length time window before the first arriving P wave. By correcting Sn spectra with the noise, we obtain the source-station amplitudes between 0.05 and 10.0 Hz. Both dual- and single-station data are used in the joint inversion for the Sn Q distribution and Sn-wave excitation functions. The wave paths are calculated using the CRUST1.0 model, and the source radiation patterns are obtained from the Harvard CMT. Strong Sn attenuations are observed in the Tibetan plateau, particularly in its northern part, which are correlated with strong Lg wave attenuations in this area. The part of the Tibetan plateau with elevations above 4,000 m has an average Sn Q of 210. On the contrast, regions surrounding the Tibetan plateau are mostly characterized by high Q values except for Yungui plateau, where a relatively low Q of 203 is observed. The dynamic processes of plateau formation are accompanied by strong thermal activities. The temperature variations affect both material rheology and seismic velocity and attenuation. Thus, seismic attenuations may serve as indicators for material flow. We use attenuation data to constrain the flow pattern in the low crust and uppermost mantle. Combining the Lg- and Sn-wave Q models with other geophysical data, a lower-crustal flow channel is found from north Tibet to east and then towards the southeast along the western edge of the rigid Sichuan basin. This work was supported by the National Natural Science Foundation of China (grants 41374065, 41174048).

  6. Statistical properties of seismic anisotropy predicted by upper mantle geodynamic models

    Microsoft Academic Search

    Thorsten W. Becker; Sebastien Chevrot; Vera Schulte-Pelkum; Donna K. Blackman

    2006-01-01

    We study how numerically predicted seismic anisotropy in the upper mantle is affected by several common assumptions about the rheology of the convecting mantle and deformation-induced lattice preferred orientations (LPO) of minerals. We also use these global circulation and texturing models to investigate what bias may be introduced by assumptions about the symmetry of the elastic tensor for anisotropic mineral

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

    E-print Network

    Utrecht, Universiteit

    ; (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

  8. Investigation of dynamic noise affecting geodynamics information in a tethered subsatellite

    NASA Technical Reports Server (NTRS)

    Gullahorn, G. E.

    1984-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

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

    Microsoft Academic Search

    Pietro Ferraro; Giuseppe De Natale

    2002-01-01

    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

  11. Grain size evolution in the mantle and its effect on geodynamics, seismic velocities and attenuation

    NASA Astrophysics Data System (ADS)

    Dannberg, Juliane; Eilon, Zach; Gassmoeller, Rene; Moulik, Pritwiraj; Myhill, Robert; Faul, Ulrich; Asimow, Paul

    2015-04-01

    Dynamic models of Earth's convecting mantle usually implement flow laws with constant grain size, stress-independent viscosity and a limited treatment of variations associated with changes in mineral assemblage. These simplifications greatly reduce computational requirements but preclude effects such as shear localisation and transient changes in rheology associated with phase transitions, which have the potential to fundamentally change flow patterns in the mantle. Here we use the finite-element code ASPECT (Bangerth et al., 2013) to model grain size evolution and the interplay between grain size, stress and strain rate in the convecting mantle. We include the simultaneous and competing effects of dynamic recrystallisation resulting from work done by dislocation creep, grain growth in multiphase assemblages and recrystallisation at phase transitions. Grain size variations also affect seismic properties of mantle materials. We use several published formulations to relate intrinsic variables (P, T, and grain size) from our numerical models to seismic velocity (Vs) and attenuation (Q). Our calculations use thermodynamically self-consistent anharmonic elastic moduli determined for the mineral assemblages in the mantle using HeFESTo (Stixrude and Lithgow-Bertelloni, 2013). We investigate the effect of realistically heterogeneous grain sizes by computing body wave travel times, ray paths, and attenuation (t*) at different frequencies. We highlight the frequency-dependent sensitivity of seismic waves to grain size, which is important when interpreting Vs and Q observations in terms of mineral assemblage and temperature. Our models show that rapid metamorphic reactions in mantle upwellings and downwellings lead to high lateral viscosity contrasts, as a result of gradual grain size evolution. Positive feedback between grain size reduction and viscosity reduction results in shear localisation. As a result, the edges of thermal plumes have smaller grain sizes and lower viscosities than their cores. Dynamic recrystallisation in subducting slabs results in lower seismic velocities and Q than would be predicted from purely thermal models. A change in physical parameters such as activation volume is required across the 660 km discontinuity to match the higher Q observed seismically in the lower mantle. The very slow grain growth in the lower mantle predicted by high pressure experiments produces unrealistically large travel time delays (>20 s) and t* values (>4 s) in our synthetic calculations with our current constitutive relationships for deriving Vs and Q. Benchmarking our dynamic models against seismic observations will involve further adjustments to the grain size evolution in the lower mantle as well as the tuning of these constitutive relationships.

  12. The role of rift inheritance during Cenozoic mountain building of the central Pyrenees and geodynamic implications

    NASA Astrophysics Data System (ADS)

    Filleaudeau, P.-Y.; Mouthereau, F.; Lacombe, O.; Pik, R.; Fellin, M. G.

    2012-04-01

    Providing accurate estimates of shortening, as well as the duration and vertical amplitudes of tectonic events in collisional orogens is critical to better understanding the retroactions between the distribution of crustal deformation and surface processes during mountain building. However, structural and bedrock geochronological constraints are usually lacking accuracy for the early stages of convergence that are generally overprinted by complex deformation patterns and synorogenic burial. In this aim, we present new detrital low-temperature thermochronometry (detrital AFT dating, zircon (U-Th)/He ages) and geochronology (zircon U/Pb ages) on both flanks of the Pyrenean orogen. Combined with available in-situ thermochronometric constraints we examine the role of rift inheritance on the early stages of orogenesis. Together with foreland tectono-stratigraphic constraints and re-appraisal of the distribution of crustal deformation in the central Pyrenees, these new data offer the unique opportunity to precisely determine the kinematics on both sides of the Pyrenean mountain belt from Late Cretaceous to Miocene. Intermediate restorations are then produced for well-suited and key time intervals (Early Oligocene, Middle Eocene, Cretaceous-Paleogene transition, Late Campanian and Late Santonian) in order to examine the mass balance within the orogenic wedge. This study shows that during the initial stage of contraction (83-68 Ma) exhumation rates were accommodated by a limited amount of underthrusting. Acceleration of plate convergence in the Late Cretaceous, as inferred from plate reconstructions, is supported an exhumational event at ~65 Ma. At this time, the North Pyrenean flysch basins were inverted on top of an inherited S-dipping crustal detachment that previously exposed lithospheric mantle (Pyrenean Lherzolites) to the surface during the mid-Cretaceous extension phase . The amount of accreted material from the Iberian crust increased significantly after the Paleocene continuing until the late Oligocene to form an antiformal stack of basement units in the backbone of the chain. Mass balance estimates show a long-term unsteady pattern of orogenic evolution characterized by a remarkable increase of erosional fluxes during the Late Eocene-Oligocene with no commensurate incoming flux of crustal material. This result appears consistent with a major renewal of rapid exhumation in the hinterland for which both internal and external drivers are discussed.

  13. The lithosphere structure and geodynamics of the West and East Black Sea Basins

    Microsoft Academic Search

    V. S. Gobarenko; T. P. Yegorova

    2010-01-01

    The velocity structure of the Black Sea lithosphere has been studied using the local seismic tomography method based on the\\u000a Backus-Gilbert approach and applied for a quite large amount of seismological data. As seismic sources, we used the earthquakes\\u000a that occurred within the Black Sea and adjoining regions and generated seismic waves recorded by seismic stations around the\\u000a Black Sea.

  14. The lithosphere structure and geodynamics of the West and East Black Sea Basins

    Microsoft Academic Search

    V. S. Gobarenko; T. P. Yegorova

    2010-01-01

    The velocity structure of the Black Sea lithosphere has been studied using the local seismic tomography method based on the Backus-Gilbert approach and applied for a quite large amount of seismological data. As seismic sources, we used the earthquakes that occurred within the Black Sea and adjoining regions and generated seismic waves recorded by seismic stations around the Black Sea.

  15. Molybdenum deposits in the eastern Qinling, central China: constraints on the geodynamics

    Microsoft Academic Search

    Zhengwei Zhang; Xiaoyong Yang; You Dong; Bingquan Zhu; Duofu Chen

    2011-01-01

    More than a dozen molybdenum prospects, distributed within a zone about 200 km long and 20 km wide, have been discovered in the Eastern Qinling orogenic belt, central China. These deposits are mainly hosted within small, dominantly granoporphyritic and quartz monzonitic intrusions of Cretaceous age. They can be classified into five groups based on spatial relationships between the ores and intrusions: porphyry-type,

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

    NASA Astrophysics Data System (ADS)

    Burtman, V. S.

    2010-09-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Teterin, D. E.

    2011-08-01

    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.

  18. Geodynamical evolution of the Southern Carpathians: inferences from computational models of lithospheric gravitational instability

    NASA Astrophysics Data System (ADS)

    Lorinczi, Piroska; Houseman, Gregory

    2010-05-01

    The Carpathians are a geologically young mountain chain which, together with the Alps and the Dinarides, surround the extensional Pannonian and Transylvanian basins of Central Europe. The tectonic evolution of the Alpine-Carpathian-Pannonian system was controlled by convergence between the Adriatic and European plates, by the extensional collapse of thickened Alpine crust and by the retreat of the Eastern Carpathians driven by either a brief episode of subduction or by gravitational instability of the continental lithospheric mantle. The Southeast corner of the Carpathians has been widely studied due to its strong seismic activity. The distribution and rate of moment release of this seismic activity provides convincing evidence of a mantle drip produced by gravitational instability of the lithospheric mantle developing beneath the Vrancea region now. The question of why gravitational instability is strongly evident beneath Vrancea and not elsewhere beneath the Southern Carpathians is unresolved. Geological and geophysical interpretations of the Southern Carpathians emphasise the transcurrent deformation that has dominated recent tectonic evolution of this mountain belt. We use computational models of gravitational instability in order to address the question of why the instability appears to have developed strongly only at the eastern end of this mountain chain. We use a parallelised 3D Lagrangean-frame finite deformation algorithm, which solves the equations of momentum and mass conservation in an incompressible viscous fluid, assuming a non-linear power-law that relates deviatoric stress and strain-rate. We consider a gravitationally unstable system, with a dense mantle lithosphere overlying a less dense asthenosphere, subject to boundary conditions which simulate the combination of shear and convergence that are thought to have governed the evolution of the South Carpathians. This program (OREGANO) allows 3D viscous flow fields to be computed for spatially variable density and viscosity and we assume that deformation is initially localized in the Carpathian region because its crust and/or mantle layers are weakened by some prior tectonic or magmatic process.

  19. Constraints on the Geodynamical History of Venus from Argon Degassing and the Cratering Record

    NASA Astrophysics Data System (ADS)

    O'Rourke, J. G.; Korenaga, J.

    2015-05-01

    Thermal evolution models of Venus featuring continuous evolution in the stagnant-lid regime possibly satisfy all available constraints, including the present-day atmospheric mass of radiogenic argon and the statistical properties of impact craters.

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

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

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

  1. Geodynamics of crustal deformation and seismotectonic block movements in central Europe

    NASA Technical Reports Server (NTRS)

    Liu, H. S.

    1984-01-01

    Geological observations reveal the style of neotectonic near-surface stresses and deformations in central Europe. Seismic activity, focal depths and fault plane solutions of earthquakes indicate kinematic reactions within the crust. A crustal deformation model which may account for the Rhine graben systems and the associated seismotectonic block movements in Europe is presented. A computer aided tomography to gravity anomalies is used in determining the crustal stresses in central Europe. Tomographical interpretations of gravity data with respect to seismic stresses are discussed. Kinematics and dynamics are integrated to show that the measured regional stresses in central Europe are derivable from the convection generated traction on the boundary of the elastic spherical shell of the crust as inferred from satellite derived gravity data.

  2. Petrological-thermomechanical modeling of Precambrian continental collision: geodynamical effects of subcontinental lithospheric mantle thickness

    NASA Astrophysics Data System (ADS)

    Zakharov, Vladimir; Perchuk, Alexei; Zavyalov, Sergei; Sineva, Tamara; Gerya, Taras

    2015-04-01

    The Precambrian collision and orogeny remains enigmatic and contentious. Different tectonic styles of orogeny in the Precambrian compared to modern Earth are suggested by interpretations of geological, petrological and geochemical observations from Proterozoic and Archean orogenic belts. Here, we present results of 2D petrological-thermomechanical numerical modeling of continental collision at crustal thickness of 35 km and convergence rate of 5 cm/year with variable thickness of subcontinental lithospheric mantle (SCLM). The numerical experiments cover the range of SCLM thickness from 65 km to 165 km, the upper mantle temperature exceeded the modern temperature by 150 oC, and the radiogenic heat production of continental crust is 1.5 times higher than that at present. The numerical modeling has shown that in the case of SCLM thickness of 65 to 125 km the subduction terminates with slab break-off followed by the formation of a large igneous province in between the two continents instead of an orogenic belt. The time and the place of the slab break-off depend on SCLM thickness. The thinner it is, the earlier and the closer to the surface the slab breaks-off. For instance, the slab is detached in 10.3 m.y. at the depth 150 km when the model with SCLM of 115 km, whereas in the case of SCLM of 65 km the slab detaches in 5.1 m.y. almost near the very surface. In the latter case, the magmatic province is very large due to development at the both sides of the oceanic slab (instead of one side provinces in the other experiments). Continental collision with a very thick SCLM (of 165 km and more) proceeds without slab break-off and rather limited volcanism. This work was supported by the Russian Foundation for Basic Research, grant 13-05-01033 and by the Supercomputing Centre of Lomonosov Moscow State University.

  3. Density variability - fundamental basis of structure formation and tectonic-geodynamic evolution of the Earth

    NASA Astrophysics Data System (ADS)

    Guliyev, Hatam; Guliyev, Ibrahim; Yetirmishli, Gurban

    2014-05-01

    It was shown that there are some common geomechanical basis of process of consolidation, deconsolidation, phase transitions, formation of zones of small shear stiffness (waveguides), realization of material and energetic mass flow in the internal structures of the Earth based on fundamental properties of basic systems of equations of nonlinear mechanics of the deformed bodies, data and results of Green, Ringwood, Liu's known experimental studies. Its instability for different geological media was shown studying the distribution of medium density depending on deformation changes. Distinguishing various forms of instability it was shown that there is general deformation mechanism of consolidation process of compressible medium according to which transfer to deconsolidation occurs at certain stages due to specific change of equilibrium states. Instability of deformation process contributes to emergence of geometric structures in composition of geological medium which are favorable to form deconsolidation zones and zones of small shear stiffness. Destruction by delamination at various depth of the Earth's interior can lead to formation of voids of various scale. Various forms of instability can be realized in the process of further evolution in the vicinity of these free surfaces, and voids can be filled by the loosened mass, i.e. deconsolidation process occurs under compression conditions. More hard bodies of local scale in the form of rod, strips, plates, cylindrical bodies, voids etc. can exist at different depth of mantle. These bodies can lose the stability under compression conditions. Therefore, part of their material and environment are loosened and deconsolidation process occurs again. The above described cases significantly depends on the realized form of deformation. Unevenness of deformation has a great value. Partial melting and magma formation can occur in these deconsolidated zones depending on mineral associations, petrochemical properties, thermobaric conditions and depth. This process becomes more feasible in case, when water appears as a result of dehydration in the considered zones. Some of these zones of deconsolidation can turn to focus of liquefied mass and give the beginning to mass flow on various directions in further evolution.

  4. Petrogenesis and geodynamic implications of the Gejiu igneous complex in the western Cathaysia block, South China

    NASA Astrophysics Data System (ADS)

    Cheng, Yanbo; Mao, Jingwen; Spandler, Carl

    2013-08-01

    The Gejiu tin district in western Cathaysia block comprises a series of igneous rocks including equigranular and porphyritic granites, gabbro and nepheline syenite. Systematic SHRIMP or LA-ICP-MS zircon U-Pb analyses of 15 representative samples from various phases of the Gejiu complex yielded Late Cretaceous ages of 78-85 Ma. Based on their mineralogical, geochemical and Sr-Nd-Hf isotope characteristics, these rocks are categorized into three groups: felsic rocks, alkaline rocks and mafic rocks. The felsic rock group includes the equigranular and porphyritic granites. Geochemical characteristics include high SiO2 contents, enrichment in Rb, Th, U, Nb, Ta, Nd and Hf and depletion in Ba, K, Sr, P, Eu and Ti compared to primitive mantle. REE patterns feature slight LREE enrichment with pronounced negative Eu anomalies. Geochemical data and Sr-, Nd- and Hf-isotopic compositions indicate that the felsic rocks were probably generated by partial melting of crustal source rocks with a minor input from mantle materials. The mafic rocks (gabbro and mafic microgranular enclaves) have distinct geochemical and isotopic features consistent with derivation from an enriched mantle source, with variable degrees of mixing with crustal-derived magmas. Strontium-, Nd- and Hf-isotopic compositions of the alkaline rocks are similar with those of the mafic rocks, suggesting that they have a similar source. Nevertheless, petrological and geochemical characteristics of these rocks indicate that they experienced extensive crystal fractionation and limited crustal contamination. Based on the emplacement of the gabbro-mafic microgranular enclaves-syenite-granites in the Gejiu district, together with contemporaneous geological events in other parts of the western Cathaysia block, we suggest that a widespread extension-related magmatic episode affected the entire region in the late Cretaceous, possibly as a result of lithospheric thinning, basaltic underplating and associated crustal melting.

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

    NASA Astrophysics Data System (ADS)

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

    2013-07-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-11-01

    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.

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

    Microsoft Academic Search

    Mian Liu; Youqing Yang

    2005-01-01

    The north China block (NCB), part of the Sino-Korean craton, is surprisingly one of the most active seismic regions in the world. The south China block (SCB), another major craton in East Asia, has been seismically quiescent. Using the updated GPS data and finite element modeling, we show that the kinematic boundary conditions are the primary cause of the contrasting

  8. Local hydrology, the Global Geodynamics Project and CHAMP\\/GRACE perspective: some case studies

    Microsoft Academic Search

    M. Llubes; N. Florsch; J. Hinderer; L. Longuevergne; M. Amalvict

    2004-01-01

    We first quantify the influence of aquifers on gravity variations by considering local, regional and continental scales. We show that locally only the direct attraction of the underlying aquifer has to be taken into account. At continental (or global scales), the underground water masses act by direct attraction (due to the earth curvature), loading flexure and potential redistribution. We show

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

    SciTech Connect

    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

    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.

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

    NASA Technical Reports Server (NTRS)

    Lenardic, A.; Kaula, W. M.

    1993-01-01

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

  11. Detrital glaucophane in graywackes of the Rhenohercynian Harz mountains and the geodynamic implications

    Microsoft Academic Search

    M. Ganssloser; T. Theye; H. Wachendorf

    1996-01-01

    Detrital blue amphibole was found for the first time in two samples of the Famennian section of the South Harz-Selke Graywacke and the Tanne Graywacke (Middle Visean) of the Harz Mountains. Microprobe analyses reveal that the blue amphiboles represent glaucophane with Fe3+\\/(Fe3++AlVI)=0.22 molar ratio. The minimum pressure required for the formation of glaucophane of this composition is estimated to be

  12. Detrital glaucophane in graywackes of the Rhenohercynian Harz mountains and the geodynamic implications

    Microsoft Academic Search

    M. Ganssloser; T. Theye; H. Wachendorf

    1996-01-01

    Detrital blue amphibole was found for the first time in two samples of the Famennian section of the South Harz-Selke Graywacke\\u000a and the Tanne Graywacke (Middle Visean) of the Harz Mountains. Microprobe analyses reveal that the blue amphiboles represent\\u000a glaucophane with Fe3+\\/(Fe3++AlVI)=0.22 molar ratio. The minimum pressure required for the formation of glaucophane of this composition is estimated to be

  13. Detrital glaucophane in graywackes of the Rhenohercynian Harz mountains and the geodynamic implications

    NASA Astrophysics Data System (ADS)

    Ganssloser, M.; Theye, T.; Wachendorf, H.

    1996-12-01

    Detrital blue amphibole was found for the first time in two samples of the Famennian section of the South Harz-Selke Graywacke and the Tanne Graywacke (Middle Visean) of the Harz Mountains. Microprobe analyses reveal that the blue amphiboles represent glaucophane with Fe3+/(Fe3++AlVI)=0.22 molar ratio. The minimum pressure required for the formation of glaucophane of this composition is estimated to be approximately 8 kbar. The source area of the detrital glaucophane is assumed to be located between the Northern Phyllite Zone and the Mid-German Crystalline Rise, in areas which have been downfaulted (?subducted) during the Variscan orogeny. The age of blueschist-facies metamorphism in the source area must be of pre-Upper Devonian age. This metamorphic event is significantly older than the Lower Carboniferous high-pressure/low-temperature metamorphism documented in parts of the northern Phyllite zone. Hence, the convergent tectonics connected with blueschist-facies metamorphism is not restricted to the Lower Carboniferous, but can be traced back at least to the early Upper Devonian. These data are in accordance with a southerly directed underplating (?subduction) at the northern margin of the Saxothuringian zone active during at least from early Upper Devonian to Lower Carboniferous.

  14. Detrital glaucophane in graywackes of the Rhenohercynian Harz mountains and the geodynamic implications

    NASA Astrophysics Data System (ADS)

    Ganssloser, M.; Theye, T.; Wachendorf, H.

    Detrital blue amphibole was found for the first time in two samples of the Famennian section of the South Harz-Selke Graywacke and the Tanne Graywacke (Middle Visean) of the Harz Mountains. Microprobe analyses reveal that the blue amphiboles represent glaucophane with Fe3+/(Fe3++AlVI)=0.22 molar ratio. The minimum pressure required for the formation of glaucophane of this composition is estimated to be approximately 8kbar. The source area of the detrital glaucophane is assumed to be located between the Northern Phyllite Zone and the Mid-German Crystalline Rise, in areas which have been downfaulted (?subducted) during the Variscan orogeny. The age of blueschist-facies metamorphism in the source area must be of pre-Upper Devonian age. This metamorphic event is significantly older than the Lower Carboniferous high-pressure/low-temperature metamorphism documented in parts of the northern Phyllite zone. Hence, the convergent tectonics connected with blueschist-facies metamorphism is not restricted to the Lower Carboniferous, but can be traced back at least to the early Upper Devonian. These data are in accordance with a southerly directed underplating (?subduction) at the northern margin of the Saxothuringian zone active during at least from early Upper Devonian to Lower Carboniferous.

  15. Analysis of surface wave azimuthal anisotropy with geodynamic models and application to the Iceland hotspot

    NASA Astrophysics Data System (ADS)

    Gallego, A.; Ito, G.; Dunn, R.

    2011-12-01

    In this study we characterize seismic anisotropy in complex mantle flow systems using synthetic models. Anisotropy retrieved from inversions of Rayleigh and Love waves has been widely used to understand the dynamics of mantle flow. However in areas with complex flow, such as plume-ridge interaction near Iceland, the interpretation of seismic models is difficult due to incomplete depth resolution, limited azimuthal coverage, and the non-uniqueness of the flow history that produces anisotropy. Seismic models that solve for radial anisotropy only, where there exists azimuthal anisotropy in the data, may not be interpreted correctly. The upper mantle is composed primarily of olivine (75%) and exhibits strong anisotropies due to preferred orientation of crystal lattices. In a weakly anisotropic media the elastic tensor can be considered as a sum of an isotropic elastic tensor plus a small anisotropic component. Using the method of Montagner and Nataf (1986), we calculated dispersion curves (synthetic data) from the depth integral functions involving the linear combination of the elastic parameters and the azimuthal direction of the surface wave propagation. We then inverted this synthetic data to retrieve an anisotropic shear wave model. The models used to generate the synthetic data were progressively increased in complexity and include: 1D models with one and two distinct anisotropic layers, 2D half-space cooling models with one and two distinct anisotropic layers and fully 3D finite-element models (citcom) with complex plume-ridge flow. For the 1D and 2D models the anisotropy was calculated from the anisotropic component of the olivine elastic tensor for different orientations of the fast axis. For the 3D models, anisotropy was calculated from the fabric evolution of olivine-enstatite aggregates in steady-flow. Preliminary results reveal that when the synthetic data include azimuthal anisotropy with the olivine fast axis oriented parallel to the direction of wave propagation, retrieved radial anisotropy via data inversion exhibits vertical polarization of around 2%. Similar anisotropy can be obtained with a weaker initial anisotropy and the fast axis oriented vertically. These results have important implications for the interpretation of seismic anisotropy for complex systems of mantle flow. For instance, if seismic data has poor azimuthal coverage, then recovered vertical anisotropy in a ridge-plume system can be interpreted as either horizontal flow of the plume near the top of the mantle or as vertical upwelling of convective upper mantle near the ridge axis.

  16. ARTICLE IN PRESS New evidence for dislocation creep from 3-D geodynamic

    E-print Network

    Ritzwolle, Mike

    July 2005 Editor: R.D. van der Hilst Abstract Laboratory studies on deformation of olivine in response to applied stress suggest two distinct deformation mechanisms in the earth's upper mantle: diffusion creep of the mantle and the development of mantle fabric. Due to the lack of in situ observations, it is unclear which

  17. Metamorphism in Taiwan : state of the art and some geodynamic interpretation

    Microsoft Academic Search

    O. Beyssac; M. Simoes; J. Avouac; J. Malavieille; Y. Chen; Y. Chan

    2009-01-01

    The central range (CR) of Taiwan is composed of a Cenozoic slate belt and the pre-Tertiary Tananao schists. Ongoing crustal shortening has resulted from the collision between the Chinese continental margin and the Luzon volcanic arc, which started ~6.5 Myr ago. Due to the obliquity of the subduction relative to the continental margin, the collision started in the north and

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

    E-print Network

    Vigny, Christophe

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

  19. A consistent geodynamic model for predicting the velocity and plate-internal deformation of Eurasia

    NASA Astrophysics Data System (ADS)

    Govers, Rob; Garcia-Sancho, Candela; Warners-Ruckstuhl, Karin; van der Burgt, Janneke; Wortel, Rinus

    2015-04-01

    The motion and deformation of tectonic plates is driven by gravity and resisted by frictional forces. In principle it should thus be possible to build mechanical models that reproduce plate velocities and surface deformation. Here we present a new approach that overcomes many of the previous obstacles to achieving this goal. Our approach to quantify the forces is based on mechanical equilibrium of the whole Eurasian plate, meaning that an increase in, for instance collision, forces must be matched by other plate tectonic forces. We first focus on present-day Eurasia. We include basal tractions from a global convection model, lithospheric body forces, and edge forces resulting from the interaction of the Eurasian plate with neighboring plates. The resulting force distribution is constrained by observed plate motion and by stress observations. Eurasia's stress field turns out to be most sensitive to the distribution of collision forces on the plate's southern margin and, to a lesser extent, to lithospheric density structure and normal pressure from mantle flow. Stress observations require collision forces on the India-Eurasia boundary of 7.0 - 10.5 TN/m. A similar analysis is performed for Eurasia at 20 Ma and 40 Ma. Plate geometry is taken from the global Lausanne (Stampfli) reconstruction, as are plate velocities and oceanic ages. Lithospheric body forces are accounted for in a simplified way because we lack detailed enough information on the plate scale topography. For the Miocene, we find ˜1.2 TN/m for the collision force on the India-Eurasia boundary. In the Eocene, the collision force we find is ˜0.4 TN/m. We conclude that the magnitude of the collision force on Tibet increased significantly after 20 Ma: from 40-20 Ma, the plate contact force on the India/Tibet plate boundary segment was of the same order of magnitude as resistive forces on subduction plate boundaries elsewhere. Our timing of the collision force on Eurasia, is substantially younger than the often quoted collision age of ˜50Ma. Forces (and the corresponding stresses) drive permanent deformation on both geological time scales and short time scales, e.g., earthquakes. Low stress magnitudes may result in strain if the material is weak, high stresses may give no strain in strong materials. Our next step therefore is to use geological information on the strength of the lithosphere. We show new results of our work on using estimates of the mechanical properties of the lithosphere to predict surface deformation.

  20. Geodynamic models of the Wilson Cycle: From rifts to mountains to rifts

    NASA Astrophysics Data System (ADS)

    Buiter, Susanne; Tetreault, Joya; Torsvik, Trond

    2015-04-01

    The Wilson Cycle theory that oceans close and reopen along the former suture is a fundamental concept in plate tectonics. The theory suggests that subduction initiates at a passive margin, closing the ocean, and that future continental extension localises at the ensuing collision zone. Each stage of the Wilson Cycle will therefore be characterised by inherited structural and thermal heterogeneities. Here we investigate the role of Wilson Cycle inheritance by considering the influence of (1) passive margin structure on continental collision and (2) collision zones on passive margin formation. Passive margins may be preferred locations for subduction initiation because inherited faults and areas of exhumed serpentinized mantle may weaken a margin enough to localise shortening. If subduction initiates at a passive margin, the shape and structure of the passive margins will affect future continental collision. Our review of present-day passive margins along the Atlantic and Indian Oceans reveals that most passive margins are located on former collision zones. Continental break-up occurs on relatively young sutures, such as Morocco-Nova Scotia, and on very old sutures, such as the Greenland-Labrador and East Antarctica-Australia systems. This implies that it is not always post-collisional collapse that initiates the extensional phase of a Wilson Cycle. We highlight the impact of collision zone inheritance on continental extension and rifted margin architecture. We show numerical experiments of one Wilson Cycle of subduction, collision, and extension. Subduction initiates at a tapered passive margin. Closure of a 60 Ma ocean leads to continental collision and slab break-off, followed by some tens of kilometres of slab eduction. Mantle flow above the sinking detached slab enhances deformation in the rift area. The resulting rift exposes not only continental crust, but also subduction-related sediments and oceanic crust remnants. Renewed subduction in the post-collision phase is enabled by lithosphere delamination and slab rollback, leading to back-arc extension in a style similar to the Tyrrhenian Sea.

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

    E-print Network

    Müller, Dietmar

    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

  2. A link between geochemistry and geodynamics: carbonatites and kimberlites, Polar Siberia

    NASA Astrophysics Data System (ADS)

    Rass, Irene

    2010-05-01

    Geophysical evidence indicates that the Moho surface beneath the northern Siberian Platform composes crests (or ranges) up to 14 km high above deeper areas and 50-80 to 150 km wide (Chernyshov and Bokaya, 1983). These ranges at the Moho likely mark ancient rift zones with a thinner crust. More than 70% kimberlites in structures surrounding the Anabar Shield occur along these Moho crests (Kravchenko et al., 1997; Rosen and Kostyuchenko, 1998). Carbonate-rich rocks that compose pipes, along with kimberlites, in kimberlite fields, were recognized as an individual type of carbonatite rocks: kimberlitic carbonatites (Lapin and Marshintsev, 1984). They abound in kimberlite fields of both Paleozoic and Mesozoic age southeast and east of the Anabar Shield. The liquidus temperatures of related kimberlites, determined based on their major-component chemistries, are 1429-1441?C and 1349-1518?C, respectively (Perchuk and Vaganov, 1980). Compared to classic carbonatites in ring complexes, kimberlitic carbonatites are characterized by the lowest relative concentrations of P and Sr, slightly lower REE, and high contents of Cr, Ti, and Zr (Rass, 1998). Mesozoic kimberlitic carbonatites exhibit a dependence of their geochemistry, position relative to the axial zones of the Moho crests, and the temperatures of the associated kimberlites, from the Kuoika to the Lower Kuonamka field: from <42 km and 1518 ?C to ~50 km and 1395 ?C (Rass et al., 2000). Away from the maximum heights of the Moho crests, which mark ancient rifts in the northern part of the Siberian Platform and with a decrease in the liquidus temperatures of the associated kimberlites, the relative P and Nb concentrations in these rocks increase, and those of REE, Cr, and, to a lesser extent, Ni and Co decrease. The depths of the Moho surface beneath carbonatites in Mesozoic ring structures of the Odikhincha, Guli, Magan, and Yraas complexes in the Maymecha-Kotui alkaline-ultrabasic-carbonatite province west of the Anabar Shield and in Maldzhangarka complex south of the Shield are 36, <42, 42-46, and 50 km, respectively. Their geochemical characteristics show analogous zoning relative to the axial zones of the Moho crests. The geochemical features of kimberlitic carbonatites are controlled, first of all, by the partition coefficients of trace elements between the silicate and carbonate components of the deep-sitting magmas. Their experimentally determined parameters are still scarce (Green, 1994) and obviously insufficient for any conclusions about the physicochemical conditions of the exsolution and/or melting of the parental magmas, so that any empirical dependences the identified in them provide information on the lateral heterogeneity of the mantle material in the northern Siberian Platform. References Chernyshov N.V. and Bokaya L.I., in: Structural Elements of the Earth's Crust and Their Evolution. Nauka, Novosibirsk, 1983: 144-150 (in Russ.) Green T.H. Chemical Geology, 1994, vol.117: 1-36 Kravchenko S.M., Schakhotko L.I., Rass I.T. Global Tectonics and Metallogeny, 1997, vol.6, No.2: 137-140 Lapin A.V., Marshintsev V.K. Geology of Ore Deposits, 1984, No.3: 28-42 Perchuk L.L., Vaganov V.I. Contrib.Mineral.Petrol., 1980, vol.72: 219-228 Rass I.T. Geochem. Int., 1998, vol.36, No.2: 107-116 Rass I.T., Ilupin I.P., Marchenko T.M., Schakhotko L.I., in: The 2nd Russ. Conf. Transactions, Syctyvkar, 2000, vol.4: 307-308 (in Russ.) Rosen O.M., Kostyuchenko S.L., in: Khain V.Ye. (Ed.) Explanatory notes for the tectonic map..., Moskow, 1998: 10-42

  3. Geodynamics and seismic hazard in the Calabrian Arc: towards a Messina earthquake supersite

    NASA Astrophysics Data System (ADS)

    Chiarabba, Claudio; Dell'Acqua, Fabio; Faccenna, Claudio; Lanari, Riccardo; Matteuzzi, Francesco; Mattia, Mario; Neri, Giancarlo; Patané, Domenico; Polonia, Alina; Prati, Claudio; Tinti, Stefano; Zerbini, Susanna; Ozener, Haluk

    2015-04-01

    The Messina region represents a key site of the Mediterranean, where active faulting, seismic shaking, volcanism, rapid uplift and landslides represent the surface manifestation of deep processes. Fast deformation results in one of the highest seismic hazard of the Mediterranean, as testified by historic destructive earthquakes occasionally accompanied by submarine mass flows and tsunami-events that added death and destruction to the already devastating effects of the earthquakes. Several geophysical and geological studies carried out during the last decades help defining the kinematics and the dynamics of the system. The tectonic evolution of the Messina region is strictly linked with the Southern Tyrrhenian and Calabrian Arc system, the retreat of the Ionian slab and the back-arc basin opening. The present-day geometry of the Calabrian slab, as well imaged by tomographic analyses and shallow-to-deep seismicity, shows a narrow slab plunging down steeply into the mantle. At 100-150 km depth, the southern edge of the slab is positioned beneath Northeastern Sicily, approximately between Tindari and Messina. Within this frame, several relevant questions are still unsolved. For example, it is not clear how the upper plate may deform as a response of a differential sinking of the subducting slabs, or how deep mantle flow at the slab edge may influence the pattern of surface deformation. Structural and geodetic data show the first-order pattern of deformation in Northeastern Sicily, and define the Tindari-Messina area as the boundary between a region in compression to the west, dominated by the Africa convergence, and a region in extension to the east-northeast, dominated by slab rollback. In addition, geodetic studies also show an increase of crustal motion velocity from Sicily to Calabria with an overall clockwise rotation of the velocity vector. This pattern of surface deformation evidences a sharp extension process active in the Messina region. The elevation of marine terraces indicates that vertical uplift in this region is occurring at a very high rate, locally more than 1 mm/yr, and of the same order of magnitude estimated for horizontal deformation. This pattern is also indicative of non-isostatic deformation that may be related to deep mantle dynamics. The Messina Straits region represents a very rare opportunity to investigate a wide variety of interrelated geological processes resulting in different types of high-impact geo-hazards affecting a single region. Notwithstanding the disastrous societal and economic impacts that these geo-hazards might cause in the study area, this opportunity, along with the ambition of revealing fundamental aspects of how mantle processes are coupled to shallow and surface ones, are among the main scientific motivations to propose the Messina Straits as a GEO earthquake supersite.

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

    Microsoft Academic Search

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

    2005-01-01

    Each discipline of geophysics has traditionally focused on limited sets of closely related phenomena using methodologies and data sets optimized for its specific area of interest. Why is that? Single discipline, single scale, foundation physics problems are relatively easy to code in Fortran, and hence they eventually become optimized for best performance whilst simultaneously becoming difficult to adapt to new

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

    SciTech Connect

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

    1994-07-01

    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.

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

    PubMed

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

    2012-03-16

    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

  7. GEODYNAMICS AND RATE OF VOLCANISM ON MASSIVE EARTH-LIKE PLANETS

    SciTech Connect

    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

    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.

  8. Joint Analysis of GOCE Gravity Gradients Data with Seismological and Geodynamic Observations to Infer Mantle Properties

    NASA Astrophysics Data System (ADS)

    Metivier, L.; Greff-Lefftz, M.; Panet, I.; Pajot-Métivier, G.; Caron, L.

    2014-12-01

    Joint inversion of the observed geoid and seismic velocities has been commonly used to constrain the viscosity profile within the mantle as well as the lateral density variations. Recent satellite measurements of the second-order derivatives of the Earth's gravity potential give new possibilities to understand these mantle properties. We use lateral density variations in the Earth's mantle based on slab history or deduced from seismic tomography. The main uncertainties are the relationship between seismic velocity and density -the so-called density/velocity scaling factor- and the variation with depth of the density contrast between the cold slabs and the surrounding mantle, introduced here as a scaling factor with respect to a constant value. The geoid, gravity and gravity gradients at the altitude of the GOCE satellite (about 255 km) are derived using geoid kernels for given viscosity depth profiles. We assume a layered mantle model with viscosity and conversion factor constant in each layer, and we fix the viscosity of the lithosphere. We perform a Monte Carlo search for the viscosity and the density/velocity scaling factor profiles within the mantle which allow to fit the observed geoid, gravity and gradients of gravity. We test a 2-layer, a 3-layer and 4-layer mantle. For each model, we compute the posterior probability distribution of the unknown parameters, and we discuss the respective contributions of the geoid, gravity and gravity gradients in the inversion. Finally, for the best fit, we present the viscosity and scaling factor profiles obtained for the lateral density variations derived from seismic velocities and for slabs sinking into the mantle.

  9. Comparative Analysis of Biogeographic, Sedimentologic and Paleomagnetic Data and the Geodynamics of Terranes of Northeast Asia in Late Permian

    Microsoft Academic Search

    A. Biakov; E. Kolosev

    2004-01-01

    We present the first consistent model of the relative locations of the most important tectonic structures in Northeast of Asia for Late Paleozoic time. This model is based on comparative analysis of paleomagnetic, sedimentologic and biogeographic data. Results of research by the authors and critically reviewed data of the other researchers are used. The current paleomagnetic data for Permian rocks

  10. Palaeostress reconstructions and geodynamics of the Baikal region, Central Asia, Part I. Palaeozoic and Mesozoic pre-rift evolution

    Microsoft Academic Search

    D. Delvaux; R. Moeys; G. Stapel; A. Melnikov; V. Ermikov

    1995-01-01

    This paper presents the first palaeostress results obtained for the basement of the Baikal rift system, in southern Siberia (Russia). Large-scale structural analysis and palaeostress reconstructions show that the Palaeozoic-Mesozoic kinematic history, precursor of the Baikal Cenozoic rifting, is characterized by the succession of six regional palaeostress stages. Stress inversion of fault-slip data and earthquake focal mechanisms is performed using

  11. Paleomagnetism and geodynamics of the onshore High Arctic Large Igneous Province and its connection to the offshore Alpha Ridge

    NASA Astrophysics Data System (ADS)

    Tarduno, J. A.

    2009-05-01

    Here I summarize findings from the University of Rochester paleomagnetic expeditions to the High Canadian Arctic dedicated to understanding the tectonic and magmatic evolution of the region, together with recovering data useful for defining the history of the geomagnetic field. Our work has focused on what we now recognize as two distinct episodes of volcanism: i. massive flood basalt volcanism at ca. 92 Ma and ii. smaller volume, spatially restricted volcanism at ca 77 Ma. Lava flows from the older event have provided key paleomagnetic data that exclude significant latitudinal motion of the Canadian Arctic Islands relative to North America. When combined with other North American sites, these data define a time-averaged dipolar magnetic field. The younger volcanics, preserved in small basins on remote northern Ellesmere Island, may define a failed rifting event; their extent in the Arctic Ocean is uncertain, but they may correlate with dikes reported from northern Greenland. The older flood basalts thicken to the north in the Canadian Arctic (Axel Heiberg Island), near the region where Alpha Ridge of the Arctic Ocean abuts the coastline. Following results of seismic analyses, I interpret this, together with Mendeleev Ridge as a volcanic oceanic plateau, potentially with continental blocks similar in structure to Kerguelen Plateau of the Indian Ocean. Simple hotspot track models fail to predict a tie of this feature to an extant hotspot (although a tie to the Iceland hotspot has been suggested). A new model of plume tilt at mid-mantle depths toward an upper mantle upwelling may better explain the observations.

  12. Dinosaurs ''re-write'' the geodynamics of the eastern Mediterranean and the paleogeography of the Apulia Platform

    NASA Astrophysics Data System (ADS)

    Bosellini, A.

    2002-11-01

    Evidence of a sizeable population of large dinosaurs on the Apulia carbonate platform calls for a revision of the current paleotectonic and paleogeographic scenario of the eastern Mediterranean area. A review of geophysical and geological data of the Ionian Sea and surrounding areas leads to envisage the Late Jurassic-Early Cretaceous Ionian Sea region as a "cul-de-sac"-type basin enclosed by shallow-water carbonate banks, connecting the Apulia carbonate platform to Peloponnesus, northern Cyrenaica, Cyrene Seamount and Medina Ridge. These banks were repeatedly and periodically exposed to subaerial conditions, and offered vast land areas for migration of dinosaurs. As regards the nature of the Mesozoic Ionian basin, interpretations are quite controversial. The "continental" vs. "oceanic" crust debate will likely be solved only when the Ionian basin crust will be reached by drilling. The conclusion of the present review leads to consider Adria as a true African Promontory and the Apulia Platform as a sort of Florida Peninsula, attached to North Africa (Cyrenaica spur), subdividing the oceanic(?) "Mesozoic Mediterranean" into a western Ionian basin and an eastern Levantine basin.

  13. Mineral chemistry, crystallization conditions and geodynamic implications of the Oligo-Miocene granitoids in the Biga Peninsula, Northwest Turkey

    NASA Astrophysics Data System (ADS)

    Aysal, Nam?k

    2015-06-01

    Widespread plutonic rocks in NW Turkey occur within the southward-younging and overlapping magmatic belts across the Aegean region. Post-collisional magmatism is represented by a series of granitoidic intrusions and volcanic successions. K-Ar and U-Pb LA-ICP-MS zircon dating of the Kazda? and Yenice plutons yielded ages between 20.5 ± 0.5 Ma and 27.89 ± 0.17 Ma (Late Oligocene-Early Miocene). The granitoid samples are high-K calc-alkaline and metaluminous to slightly peraluminous. The 87Sr/86Sr values for the granitoids, enclaves and leucocratic rocks range between 0.705168 and 0.708357. The initial 143Nd/144Nd ratios calculated for the crystallization ages of ca. 23-27 Ma are between 0.512425 and 0.512614, and the ?Nd values vary from -3.5 to 0.2. The Nd TDM model ages range between 0.73 and 1.13 Ga. These samples are enriched in LILEs and LREE and depleted in HFSEs with negative Eu anomalies, indicating that the melts were derived from an enriched lithospheric mantle modified by subducted slab-derived melts. Energy constrained-assimilation and fractional crystallization (EC-AFC) modelling indicates that fractional crystallization and crustal assimilation modified the parent magma's composition during its residence in the upper crust. The mineral chemistry of amphiboles, pyroxenes, biotites and feldspars is used to constrain the pressure (P), temperature (T), oxygen fugacity (logƒO2) and water contents (H2Omelt) during the crystallization of the magmas in the studied granitoids. The clinopyroxene temperatures are in the range of 823-910 ± 45 °C. The amphibole temperatures for the studied plutonic rocks are in the range of 707-926 °C (mean = 798 ± 45 °C), and the crystallization depths are estimated to be in the interval of 1.02-10.2 km. The NW Anatolian plutonic rocks can be considered to have been equilibrated at the oxygen fugacities of calcic amphiboles (logƒO2) between -8.99 and -13.96 bars (mean = -12.11 bar) and H2Omelt contents between 1.63% and 6.79% (mean = 4.15%). Meanwhile, the biotites, which display consistent oxygen fugacity values (-10.65 to -13.22), suggest their reliability with the typical values of calc-alkaline magma crystallization. These values suggest a relatively higher oxidation state during crystallization and are related to arc magmatism. All of the calculated values indicate that all of the plutons were emplaced at shallow crustal levels. It can be inferred that the Oligo-Miocene magmatism in NW Turkey may be linked to crustal thinning that resulted from slab roll-back and a back-arc extensional regime after the collision between the Sakarya Zone and Anatolide-Tauride Platform.

  14. Geochronological and geochemical constraints on the petrogenesis and geodynamic setting of the Qianlishan granitic pluton, Southeast China

    NASA Astrophysics Data System (ADS)

    Guo, Chun-Li; Wang, Ru-Cheng; Yuan, Shun-Da; Wu, Sheng-Hua; Yin, Bing

    2015-04-01

    The Qianlishan is a well-known granitic pluton directly related to the super large W-Sn-Mo-Bi polymetallic Shizhuyuan deposit in southeast China. The pluton is composed of three intrusive phases: the first phase of microfine-grained porphyritic biotite granite, the second phase of fine-grained porphyritic biotite granite, and the third phase of medium-grained equigranular zinnwaldite granite. SIMS zircon U-Pb dating yields precise ages for three phases; they are 154.5 and 152.3 Ma, 153.4 and 152.5 Ma, 152.4 and 151.6 Ma, respectively. Overall, all three granite phases contain high SiO2 (73.2-77.7 wt.%) and total alkalis (K2O+Na2O = 7.27-9.36 wt.%). Their aluminum saturation index values increase from 0.91-0.99 for Phase 1, through 0.92-1.01 for Phase 2, to 1.01-1.27 for Phase 3. Average (La/Yb)N ratios are 3.88, 4.12, and 1.06, respectively, in three phases. Compared with Phase 3 granite, the Phase 1 and 2 granites have less conspicuous negative Eu anomalies (Phases 1, 2 Eu/Eu* = 0.13-0.28; Phase 3 Eu/Eu* = 0.01-0.02); Phase 3 granite also shows stronger depletion in Sr, P, Zr, and Ti. Mica compositions change from Mg- and Fe- to Al, F, Li-rich, whereas plagioclase compositions evolve from andesine/oligoclase to albite from Phases 1 to 3 granites. Mineralogical features and whole-rock geochemistry indicate that Phase 3 granite experienced more intensive fractional crystallization than others. The Qianlishan granites have low ? Nd(t) values (-12.9 to -7.9). Zircon ? Hf(t) and ?18O values are -11.1‰ to -5.14‰ and 7.97‰ to 10.35‰, respectively. Two-stage model ages of whole-rock Nd isotopes (1.2-1.9 Ga) and zircon Hf isotopes (1.5-1.9 Ga) indicate that these granites were derived from partial melting of late Paleoproterozoic to early Mesoproterozoic crustal material. Phase 1 and 2 are fractionated I-type granites, and Phase 3 is high-degree fractionated S-type granite. High zirconium saturation temperature (~780 °C) and presence of diopside indicate that these granites originated from partial melting under the relatively high temperature environment. Combined with alkaline basalts, tholeiitic basalts, and intraplate shoshonitic intrusions in time and space, the Qianlishan pluton occurs right within an intercontinental rift along the Qin-Hang deep fault zone in the middle to late Jurassic.

  15. Geodynamics of the western part of the Mongolia–Okhotsk collisional belt, Trans-Baikal region (Russia) and Mongolia

    Microsoft Academic Search

    Yu. A Zorin

    1999-01-01

    After the western edge of the Mongolian microcontinent joined the Siberian continent in the region of Central Mongolia in the earliest Permian, these two continental blocks remained turned at an angle of about 120° with respect to each other and separated (on greater extent of their present-day boundary) by an enormous gulf of the Paleopacific called the Mongolia–Okhotsk ocean. Closure

  16. Introduction. The large-scale geodynamics of the present-day Earth is to a large extent connected to

    E-print Network

    van Thienen, Peter

    connected to plate tectonics. The formation of oceanic lithosphere at the spreading centers of mid- ocean and atmosphere and finally radiated into space. This effectively cools the Earth's interior. At mid-ocean ridges, new basaltic crust is formed by solidification of melt which is produced by pressure release partial

  17. 11. GEODYNAMIC EVOLUTION OF THE CÔTE D'IVOIRE-GHANA TRANSFORM MARGIN: AN OVERVIEW OF LEG 159 RESULTS1

    Microsoft Academic Search

    Christophe Basile; Jean Mascle; Jean Benkhelil; Jean-Pierre Bouillin

    A synthesis of shipboard and postcruise studies performed on Ocean Drilling Program (ODP) Leg 159 data leads to several important modifications on previously proposed models for the Côte d'Ivoire-Ghana Transform Continental Margin evolution. Siliciclastic sedimentation occurred from Aptian through late Albian times in a wrench tectonic (possibly pull-apart basin) set - ting and was submitted to high geothermal gradients. This

  18. Role of preexisting faults in the geodynamic evolution of Northern Tunisia, insights from gravity data from the Medjerda valley

    Microsoft Academic Search

    A. Amiri; A. Chaqui; I. Hamdi Nasr; M. H. Inoubli; N. Ben Ayed; S. Tlig

    2011-01-01

    The middle Medjerda valley belongs to the Tellian zone of Tunisia; it behaves as a post-orogenic basin where surface structural indices are almost completely absent. It is noteworthy to recall that Alpine and Atlasic tectonic prints are well expressed on both sides of this basin.This paper presents an integrated study comprising geology and gravity data.Subsurface geological modeling was based on

  19. Jurassic-Cretaceous clastic sequences of Chukotka: sedimentation, structural style and geodynamic implications for Russian East Arctic shelf

    Microsoft Academic Search

    M. I. Tuchkova; S. D. Sokolov; V. E. Verzhbitsky

    2009-01-01

    Jurassic-Lower Cretaceous sedimentary sequence, exposed on the Chukotka continental margin is critical for understanding the timing, dynamics and sedimentary setting evolution of Chukotka-Eurasia collisional process (e.g., Sokolov et al., 2002) and so, represents one of the key regional stratigraphic units (Til'man,1973, Tibilov,1982; Miller et al., 2002, 2007). From the other hand, this research may shed the light on the widely

  20. Structure and geodynamics of the post-collision zone between the Nazca-Antarctic spreading center and South America

    NASA Astrophysics Data System (ADS)

    Maksymowicz, Andrei; Contreras-Reyes, Eduardo; Grevemeyer, Ingo; Flueh, Ernst R.

    2012-09-01

    The Chile Triple Junction (CTJ) is the place where the Chile Ridge (Nazca-Antarctic spreading center) is subducting beneath the continental South American plate. Sediment accretion is active to the south of the CTJ in the area where the northward migrating Chile Ridge has collided with the continent since 14 Ma. At the CTJ, tectonic erosion of the overriding plate narrows and steepens the continental slope. We present here a detailed tomographic image of the upper lithospheric Antarctic-South America subduction zone where the Chile Ridge collided with the continent 3-6 Ma off Golfo de Penas. Results reveal that a large portion of trench sediment has been scraped off and frontally accreted to the forearc forming a 70-80 km wide accretionary prism. The velocity-depth model shows a discontinuity at 30-40 km landward of the deformation front, which is interpreted as the contact between the frontal (poorly consolidated sedimentary unit) and middle (more compacted sedimentary unit) accretionary prism. The formation of this discontinuity could be related to a short term episode of reduced trench sedimentation. In addition, we model the shape of the continental slope using a Newtonian fluid rheology to study the convergence rate at which the accretionary prism was formed. Results are consistent with an accretionary prism formed after the collision of the Chile Ridge under slow convergence rate similar to those observed at present between Antarctic and South America (?2.0 cm/a). Based on the kinematics of the Chile Ridge subduction during the last 13 Ma, we propose that the accretionary prism off Golfo de Penas was formed recently (?5 Ma) after the collision of the Chile Ridge with South America.

  1. Blocks or Continuous Deformation in Large-Scale Continental Geodynamics: Ptolemy Versus Copernicus, Kepler, and Newton (Invited)

    NASA Astrophysics Data System (ADS)

    Molnar, P. H.

    2010-12-01

    The enhanced precision and resolution of GPS velocity fields within active continental regions have highlighted two views of how best to describe these fields: (1) as relative movements of effectively rigid (or elastic) blocks, essentially plate tectonics with many plates, or (2) as continuous deformation of a (non-Newtonian) viscous fluid in a gravity field. The operative question is not: Are there blocks? Of course, there are. It is: Do blocks help us understand the deformation? Dan McKenzie used to say, 40 years ago, that the reason plate tectonics was accepted so easily was that the kinematics of plate motion could be analyzed separately from the dynamics that underlies that motion. No such separation seems to work for continental tectonics, where crust thickens or thins, and where the dynamics, both stresses and the gravitational body force, and kinematics are intimately connected via a constitutive relation that links strain rate to stress. Treating continental deformation in terms of blocks is like treating planetary orbits in terms of Ptolemaic epicycles; such a treatment provides an accurate description of the kinematics, but obscures dynamics. (Sea captains in the 15th Century would have been wise to use Ptolemy’s epicycles, not yet a Copernican system, to navigate their ships). A description in terms of blocks, however, seems unlikely to reveal insights into the dynamic processes and the viscosity structure of the deforming lithosphere. In Tibet, most hypothesized blocks are cut by obvious faults and must deform, if GPS measurements are not yet accurate enough to resolve such deformation. Presumably as the number of GPS control points and the precision of their velocities increase, so will numbers of blocks needed to describe the velocity field, with numbers of GPS points and numbers of blocks obeying a fractal relationship. The important unanswered question concerns how best to describe the constitutive equation for continental lithosphere? The Tibetan Plateau illustrates this failing of plate tectonics (or crustal blocks) especially well. In particular, because of the large lateral variations in gravitational potential energy, it offers the best region in which to study dynamics of continental deformation.

  2. Constraints on Moho depth and crustal thickness in the Liguro-Provencal basin from a 3D gravity inversion: geodynamic

    E-print Network

    Nicolas, Chamot-Rooke

    Constraints on Moho depth and crustal thickness in the Liguro- Provencal basin from a 3D gravity and reflection data to constrain a new Moho depth map in the Liguro-Proven~al basin (Western Mediterranean Sea for a range of Moho depths between 12 km (deep basin) and 30 km (mainland). The oceanic crust thickness

  3. 3-D Structure and geodynamic evolution of accreted igneous layer in the Narmada-Tapti region (India)

    Microsoft Academic Search

    A. P. Singh

    1998-01-01

    The Narmada-Tapti rift system is an unusual feature crossing the west coast of India. A recent 2-D analysis of Bouguer gravity anomaly combined with four deep seismic sounding profiles in the region has revealed a 15–20 km thick high-density (3.02 g cm?3) accreted igneous layer at the base of the crust. For a more realistic approximation a 3-D density model

  4. Crustal structure in the Carpatho-Pannonian region: insights from three-dimensional gravity modelling and their geodynamic significance

    Microsoft Academic Search

    Péter Szafián; Frank Horváth

    2006-01-01

    A three-dimensional gravity modelling of the Carpatho-Pannonian region was carried out to get a better image of the Moho boundary\\u000a and the most prominent intra-crustal density heterogeneities. At first, only the major density boundaries were considered:\\u000a the bottom of the Tertiary basin fill, the Moho discontinuity and the lithosphere to asthenosphere boundary. Density contrasts\\u000a were represented by relative densities. The

  5. Multiple Variscan nappes in Limousin, western Massif Central, France: geophysical constraints to the geological model and geodynamic implications

    NASA Astrophysics Data System (ADS)

    Dubuisson, G.; Hirn, A.; Girardeau, J.; Mercier, J.-C. C.; Veinante, J.-L.

    1988-03-01

    The upper crustal structure of Limousin, western Massif Central, France, results from tectonic superposition of major Variscan high-grade metamorphic crystalline nappes, one of them containing well preserved relicts of an early Paleozoic oceanic lithosphere. Three of these nappes outcrop in the studied area as evidenced by surface geological observations. Their overall present synclinorium structure is confirmed by the gravimetric data. Results from three short refraction seismic profiles recorded in this area are totally compatible either with the local tectonic model or with the global one recently proposed for Limousin. Although it would be an over-interpretation to derive a geological model from the only seismic profiles presented, this study shows that short seismic profiles are critical for 3-D extrapolation of the geological surface data in old orogenic regions. As ophiolites are located within a peculiar unit representing an early major thrust contact, the origin of the various nappes above and below may be defined in terms of plate tectonics.

  6. Paleomagnetic constraints on the geodynamic history of the major blocks of China from the Permian to the present

    Microsoft Academic Search

    Randolph J. Enkin; Zhenyu Yang; Yan Chen; Vincent Courtillot

    1992-01-01

    All available paleomagnetic poles of Upper Permian to Tertiary age from the main blocks of China are critically reviewed with the aim of placing constraints on models of the formation and the subsequent deformation of the region. For first-order analysis, apparent polar wander paths are constructed for the major blocks. The compatibilities and contradictions between the geological and paleomagnetic records

  7. Comparative Analysis of Biogeographic, Sedimentologic and Paleomagnetic Data and the Geodynamics of Terranes of Northeast Asia in Late Permian

    NASA Astrophysics Data System (ADS)

    Biakov, A.; Kolosev, E.

    2004-12-01

    We present the first consistent model of the relative locations of the most important tectonic structures in Northeast of Asia for Late Paleozoic time. This model is based on comparative analysis of paleomagnetic, sedimentologic and biogeographic data. Results of research by the authors and critically reviewed data of the other researchers are used. The current paleomagnetic data for Permian rocks from the Northeast region still remain scanty and are practically non-existent for some tectonic structures such as the Okhotsk microcontinent. Nevertheless we believe that it can be shown that there was no major (thousands of kilometers) horizontal motion between the separate tectonic blocks of Yana-Kolyma fold-and-thrust area, at least starting Middle Paleozoic. In paleogeographic terms Northeast Asia in the Permian represented a system of marine basins of various types. Okhotsk microcontinent was outboard from the Siberian craton to the southeast (present day coordinates). A system of deepwater marginal type marine basins lay to the east of the Siberian craton. The Koni-Taigonos volcanic arc was along the south edge, and. its erosion products formed deepwater fore-arc basins. Significant differences between the Permian bivalve communities on the Omolon microcontinent and contemporary communities of Verkhoyansk indicate the existence of the deepwater Ayan-Yuryakh trough basin. The strata of the latter are characterized as thick (up to 7 km) flysch deposits plus thick diamictites. Paleobiogeographic studies show that major biogeographic units can be clearly distinguished in the Verkhoyansk-Okhotsk on one side and Kolyma-Omolon biochores on the other, which can be currently ranked as sub regions. Verkhoyansk-Okhotsk sub region includes Verkhoyansk epicontinental sea shelf and the Okhotsk microcontinent shelf. These can be further subdivided into a number of provinces. The Kolyma-Omolon sub region includes continental shelves of the Omolon, Omulevka, Prykolyma microcontinents and the Koni-Taigonos arc. The degree of diversity of these two biochores is so great that it requires separate development and indicates the existence of a major biogeographical barrier during the Permian. The distinctions between the Verkhoyansk-Okhotsk and Kolyma-Omolon sub regions are found througout the whole Permian and over other faunal groups such as brachiopods and ammonites as well as over the rest of bivalve taxons. Multiple use of biogeographic, sedimentologic and paleomagnetic materials including new original data on sedimentology and paleomagnetism allowed a model of the relative positions of the basic tectonic structures of Verkhoyansk-Kolyma fold-and-thrust area in the second half of the Permian. . These studies have been supported by the Russian Foundation for Basic Research, grant N 03-05-96012-Arctic and Far East Branch Russian Academy of Sciences, Grant N 04-3-A-08-014.

  8. Remagnetization of Lower Cretaceous limestones from the southern Pyrenees and relation to the Iberian plate geodynamic evolution

    Microsoft Academic Search

    Jaume Dinarès-Turell; Jesús García-Senz

    2000-01-01

    Paleomagnetic study (34 sites) of thick Cretaceous ~5000 m marine carbonate strata from the Organyà Basin (OB) in the southern Pyrenees reveals a uniformly normal polarity characteristic remanence with varying declination (D) (Berriasian-Barremian, D=295° Aptian-Albian, D=348°, upper Cretaceous, D=354°) that resides in magnetite and predates Late Cretaceous\\/Tertiary folding. The lack of reverse polarity magnetizations in the Berriasian-Barremian series, together with

  9. UPb chronology of the Northampton Complex, Western Australia – evidence for Grenvillian sedimentation, metamorphism and deformation and geodynamic implications

    Microsoft Academic Search

    O. Bruguier; D. Bosch; R. T. Pidgeon; D. I. Byrne; L. B. Harris

    1999-01-01

    Conventional and SHRIMP U-Pb analyses of zircon, monazite, titanite and apatite from the high grade rocks of the Northampton\\u000a Complex in Western Australia provide constraints on the timing of metamorphic processes and deformation events in the northern\\u000a Darling Mobile Belt (western margin of the Archean Yilgarn Craton). Paragneisses and mafic volcanics and\\/or intrusions have\\u000a undergone granulite facies metamorphism in a

  10. Two stages of granite formation in the Sredinny Range, Kamchatka: Tectonic and geodynamic setting of granitic rocks

    Microsoft Academic Search

    M. V. Luchitskaya; A. V. Solov’ev; J. K. Hourigan

    2008-01-01

    The newly formed continental crust in southern Kamchatka was created as a result of the Eocene collision of the Cretaceous-Paleocene\\u000a Achaivayam-Valagin island arc and the northeastern Asian margin. Widespread migmatization and granite formation accompanied\\u000a this process in the Sredinny Range of Kamchatka. The tectonic setting and composition of granitic rocks in the Malka Uplift\\u000a of the Sredinny Range are characterized

  11. A long-term rock uplift rate for eastern Crete and geodynamic implications for the Hellenic subduction zone

    NASA Astrophysics Data System (ADS)

    Strobl, M.; Hetzel, R.; Fassoulas, C.; Kubik, P. W.

    2014-08-01

    The island of Crete in the forearc of the Hellenic subduction zone has a rugged topography with local relief exceeding 2 km. Based on the elevation of marine shorelines, rates of rock uplift during the Late Holocene were previously estimated to range between 1 and 4 mm/a in different parts of the island. These rates may, however, not be representative for longer timescales, because subduction earthquakes with up to 9 m of vertical coseismic displacement have affected Crete in the Late Holocene. Here we use a well preserved sequence of marine terraces near Kato Zakros in eastern Crete to determine the rate of rock uplift over the last ?600 ka. Field investigations and topographic profiles document a flight of more than 13 marine bedrock terraces that were carved into limestones of the Tripolitza unit. Preliminary age constraints for the terraces were obtained by 10Be exposure dating of rare quartz-bearing sandstone clasts, which are present on some terraces. The 10Be ages of these samples, which have been corrected for an inherited nuclide component, yielded exposure ages between ?100 ka and zero. Combined with geomorphologic evidence the two oldest 10Be ages suggest that the terraces T4 and T5, with shoreline angles at an elevation of ?68 and ?76 m above sea level, respectively, formed during the marine isotope stage 5e about 120 ka ago. The correlation of the higher terraces (T6 to T13) with regional sea-level highstands indicates sustained rock uplift at a rate of ?0.5 m/ka since at least ?600 ka. As normal faulting has dominated the tectonics of Crete during the last several million years, upper crustal shortening can be ruled out as a cause for rock uplift. We argue that the sustained uplift of the island results from the continuous underplating of sediments, which are transferred from the subducting African plate to the base of the crust beneath Crete.

  12. Provenance analysis and detrital zircon geochronology on the onshore Makran accretionary wedge, SE Iran: implication for the geodynamic setting

    NASA Astrophysics Data System (ADS)

    Mohammadi, Ali; Burg, Jean-Pierre; Winkler, Wilfried; Ruh, Jonas

    2014-05-01

    The Makran, located in Southeast Iran and South Pakistan, is one of the largest accretionary wedges on Earth. In Iran it comprises turbiditic sediments ranging in age from Late Cretaceous to Holocene. We present a provenance analysis on sandstones, which is aimed at reconstructing the assemblages of source rocks and the tectonic setting from which the clastic material was derived. Sandstone samples collected from different units span the regional stratigraphy from Late Cretaceous to Miocene. Laser ablation ICP-MS resulted in ca 2800 new U-Pb ages of individual detrital zircons from 18 samples collected in onshore Makran. 101 detrital zircons from a Late Cretaceous fine grained sandstone range from 180 to 160 Ma (Middle Jurassic). 478 detrital zircons from mid- to late Eocene sandstones allow differentiating a NE and NW sector of the Makran Basin. Zircon grains in the NE basin belong to two populations peaking at 180 to 160 Ma (late Early to Middle Jurassic) and 50 to 40 Ma (Mid-Eocene), with the noticeable absence of Cretaceous grains. In the NW basin, detrital zircons are 120 to 40 Ma (late Early Cretaceous to Lutetian, Eocene). 587 detrital zircon grains from fine to medium grained Oligocene sandstones collected over the whole area also range from 120 to 40 Ma (late Early Cretaceous to Eocene, Lutetian). 1611 detrital zircons from early Miocene sandstones show again distinctly different ages in the eastern and western parts of the basin. They range from 120 to 40 Ma (late Early Cretaceous to Eocene) in the eastern and from 80 to 40 Ma (Late Cretaceous to Eocene) in the western basin. Hf isotopes analyses were performed on 120 zircon grains from 6 samples. Negative values (-2 to -15) in Middle Jurassic and late Early Cretaceous zircons indicate minor or no influence of mantle reservoirs which implies a rifting setting during crystallization of the zircons. Low negative to positive (-5 to +10) values in Late Cretaceous and Eocene zircons indicate mixed crustal and juvenile magma sources, which are common in continental arc environments. Point counts of 32 sandstone thin sections were performed following the Gazzi-Dikinson method. 300-400 points were counted in each thin section. The sandstones are feldspathic litharenites and litharenites. Feldspar is dominantly plagioclase (> 90%) with minor amounts of K-feldspar. Most of the quartz grains (75%) are mono-crystalline but poly-crystalline ones (maximum 25%) also occur. Rock fragments are represented by sedimentary, volcanic and metamorphic grains. Volcanic rock-fragments mostly are andesites and volcanic chert. Sedimentary lithic grains comprise mostly sandstone, siltstone, limestone and dolomite. Metamorphic lithic grains generally are low-grade schists and phyllites. In various compositional ternary diagrams, the sources of the sandstones plot in the transitional to dissected arc and recycled orogenic fields. We selected 26 samples for heavy mineral study. 200-300 grain were identified and counted in each sample. Heavy mineral suites show a highly variable composition including (1) a group of ultra-stable minerals (zircon, monazite, tourmaline, rutile, brookite, anatase and sphene) derived from a granitic continental crust sources, (2) metastable minerals delivered from variable metamorphic-grade source rocks (epidote group, garnet, staurolite, chloritoid, kyanite, andalusite, glaucophane), (3) chromian spinel from ultrabasic rocks, (4) common hornblende either supplied from metamorphic or basic igneous series, and (5) a local pyroxene-rich source in the pyroclastic sandstone formation overlying pillow lavas. Glaucophane (5-20%) occurs in several samples, which indicates high-pressure/low-temperature metamorphic rocks in the detrital source areas for Eocene and Miocene sandstones. Earlier work in the Pakistani Makran suggested that pre-Miocene sediments were supplied from the Himalaya, whereas Miocene to Recent deposits were reworked older sediments of the accretionary wedge. Our data do not support this conclusion. Instead, we identified rifting-related detrital so

  13. Submitted for publication in AGU Monograph Series Self-gravity, Self-consistency & Self-organization in Geodynamics &

    E-print Network

    Anderson, Don L.

    , including the interpretation of tomographic images. Pressure compresses a solid and changes physical processes. The 650-km discontinuity is an isochemical phase change but major chemical boundaries may occur, with the former favoring whole-mantle convection and the later favoring layered convection. However, a different

  14. Geodynamic settings and formation conditions of crystalline complexes in the south Altai and south Gobi metamorphic belts

    Microsoft Academic Search

    I. K. Kozakov; A. N. Didenko; P. Ya. Azimov; T. I. Kirnozova; E. B. Sal’nikova; I. V. Anisimova; Ch. Erdenejargal

    2011-01-01

    The Hercynian mobile belts in Central Asia comprise the Hercynian proper and the Late Hercynian (Indosinian) belts separated\\u000a by the South Gobi microcontinent, the origin of which is related to the evolution of the South Mongolian and Inner Mongolian\\u000a basins with the oceanic crust. Crystalline complexes within these belts occur as tectonic sheets of a variety of sizes. At\\u000a the

  15. Tectonic environment and geodynamic significance of the Neo-Cimmerian Donqiao ophiolite, Bangong-Nujiang suture zone, Tibet

    Microsoft Academic Search

    J. Girardeau; J. Marcoux; C. J. Allègre; J. P. Bassoullet; Tang Youking; Xiao Xuchang; Zao Yougong; Wang Xibin

    1984-01-01

    The Bangong-Nujiang suture zone is underlain by a discontinuous and roughly EW ophiolite belt. Around Donqiao-Gyanco, ophiolitic and metasedimentary Palaeozoic series form nappes thrusted over Jurassic flysch series. All these series have undergone a late symmetrical folding accompanied by generally northward reverse faulting. Although strongly dismembered, a complete ophiolitic sequence comprising harzburgites with large podiform-type chromite deposits, wehrlites, cumulate gabbros,

  16. Numerical models of a dense layer at the base of the mantle and implications for the geodynamics of D?

    NASA Astrophysics Data System (ADS)

    Montague, Nancy L.; Kellogg, Louise H.

    2000-05-01

    To investigate the dynamics of the mantle's D? layer, we explore numerical models of mantle convection which feature a dense basal boundary layer. We use a double-diffusive finite element convection scheme and vary thermal and chemical Rayleigh numbers and properties including viscosity, thermal conductivity, and internal heating. For isoviscous models with heating only from below, the thermal Rayleigh number (Ra) is set at either 106 or 107. The negative chemical buoyancy of a dense layer produces a stable boundary layer when the ratio of chemical to thermal buoyancy (the buoyancy number B) is around 1. For B = 0.5 the layer is unstable, while B = 0.6 may produce a layer which remains stable for long periods, depending on other factors (such as Rayleigh number, layer thickness, and thermal diffusivity of the layer). At high enough Ra, small-scale convection can occur within the layer. Using Ra = 107, we look at changes in layer thickness from 100 to 300 km at two values of B(0.6 and 1). Convection within the layer takes place most easily when the layer has a greater initial thickness. For B = 0.6, the layer is not always continuous along the lower boundary, so convection within the layer does not occur unless the initial thickness is fairly high (300 km). Increasing the thermal diffusivity of the layer (to simulate enrichment in metals) enhances heat conduction across the layer and can suppress internal convection within D?. Enhanced conduction also leads to higher plume temperatures. Including internal heating mainly increases the overall heat flow through the mantle, leading to higher surface heat flux. Finally, we examine models with temperature-dependent viscosity and pressure-dependent viscosity using Rayleigh numbers in the range of 107. Convection within the dense layer is enhanced by the relative reduction in viscosity. Our models exhibit only a modest decrease in viscosity (an order of magnitude) but illustrate how a dense, low-viscosity layer interacts with cold, viscous downwellings.

  17. Laser geodynamic satellite thermal/optical/ vibrational analyses and testing. Volume 2: Technical report, book 1. [retroreflector design

    NASA Technical Reports Server (NTRS)

    1974-01-01

    The results of the LAGEOS thermal/optical/vibrational analysis and test program are reported. Through analyses and tests it is verified that the MSFC LAGEOS design provides a retroreflector thermal environment which maintains acceptable retroflector internal thermal gradients. The technical results of the study, organized by the major task areas are presented. The interrelationships of the major tasks are described and the major decisions are identified.

  18. Laser geodynamic satellite thermal/optical/vibrational analyses and testing, volume 2, book 1 technical report. [retroreflector performance

    NASA Technical Reports Server (NTRS)

    1975-01-01

    The results are presented of a retroreflector performance improvement program. The following areas of the program are discussed: retroreflector dimensional verification, initial optical performance analysis, LAGEOS test retroreflector rework, final optical performance analysis, optical performance tests, evaluations and conclusions, and laser wavelength evaluation and dihedral angle selection. Data tables, diagrams, graphs, and photographs are included.

  19. Paleozoic ophiolitic mélanges from the South Tianshan Orogen, NW China: Geological, geochemical and geochronological implications for the geodynamic setting

    NASA Astrophysics Data System (ADS)

    Jiang, Tuo; Gao, Jun; Klemd, Reiner; Qian, Qing; Zhang, Xi; Xiong, Xianming; Wang, Xinshui; Tan, Zhou; Chen, Bangxue

    2014-02-01

    Two ophiolitic mélange belts, the South Central Tianshan Ophiolite Belt (SCTOB) and the South Tianshan Ophiolite Belt (STOB), extend almost parallel to the Chinese South Tianshan Orogen - the southernmost part of the Central Asian Orogenic Belt (CAOB). The SCTOB occurs interlayered in the South Central Tianshan Suture Zone, the STOB as exotic blocks in Palaeozoic sedimentary strata. However, their tectonic settings and ages, which are crucial for understanding the formation of the CAOB, are still controversially discussed. In order to better understand these geological problems, geological, geochemical and geochronological investigations were conducted on the Guluogou (SCTOB) as well as on the Serikeyayilake and Aertengkesi ophiolitic mélanges (STOB). The ophiolitic suites are composed of basalts, gabbros and mantle peridotites. Laser ablation ICP-MS (LA-ICP-MS) U-Pb zircon ages of 334 ± 5 Ma and 332 ± 7 Ma were obtained for the Guluogou gabbros, while SHRIMP U-Pb zircon ages of 423 ± 10 Ma and 423 ± 4 Ma were determined for the Serikeyayilake and Aertengkesi gabbros. The mineral composition of the mantle peridotites and the geochemical characteristics of the basalts suggest a mid-ocean ridge (MOR) type affinity for the Guluogou ophiolite and a SSZ type affinity for the Serikeyayilake and Aertengkesi ophiolites. The present data, combined with previously published results, indicate that the STOB may have been derived from a forearc rifting setting that existed during the early Silurian to the early Carboniferous (ca. 439-356 Ma), whereas the SCTOB may represent fragments of a normal wide ocean that lasted to the early Carboniferous (ca. 332 Ma).

  20. Granitoids of the Ufalei block (South Urals): Sr-Nd isotope systematics, geodynamic position and genetic reconstructions

    NASA Astrophysics Data System (ADS)

    Ronkin, Yu. L.; Shardakova, G. Yu.; Maslov, A. V.; Shagalov, E. S.; Lepikhina, O. P.

    2009-04-01

    Petrogeochemical and isotopic-geochronological signatures in granitoids developed in structures with complex geological history represent an important feature for reconstructing paleogeodynamic settings. Granitoids are widespread in the western slope of the Urals, where the Uralian Orogen contacts via a collage of different-age blocks of the east European Platform. The Ufalei block located in the Central Urals megazone at the junction between the South and Middle Urals’ segments represents one such boundary structure with multistage geological evolution. The isotopic ages obtained by different methods for acid igneous rocks range from 1290 to 245 Ma. We determined close Rb-Sr and Sm-Nd ages (317 Ma) for granites of the Nizhnii Ufalei Massif. By their petrochemical parameters, granitoids and host granite-gneisses differ principally from each other: the former are close to subduction-related, while the latter, to continental-riftogenic varieties. The primary ratio (87Sr/86Sr)0 = 0.70428 and ?Nd ? +4 values indicate significant contribution of oceanic (island-arc?) material to the substrate, which served as a source for granites of the Nizhnii Ufalei Massif. Model Nd ages of granites vary from 641 to 550 Ma. Distinct oceanic rocks and varieties with such ages are missing from the surrounding structures. New isotopic dates obtained for ultramafic and mafic rocks from different zones of the Urals related to the Cadomian cycle imply development of unexposed Upper Riphean-Vendian “oceanic” rocks in the central part of the Ufalei block, which played a substantial role in the formation of the Nizhnii Ufalei granitoids. Such rocks could be represented, for example, by fragments of the Precambrian Timanide-type ophiolite association. The analysis of original materials combined with published data point to the heterogeneous composition and structure of the Ufalei block and a significant part of the western segment of the Central Uralian Uplift and extremely complex geological history of the region coupling the Uralian Orogen with the East European Platform in the present-day structure.

  1. Tectonic magnetic lineation and oroclinal bending of the Alborz range: Implications on the Iran-Southern Caspian geodynamics

    NASA Astrophysics Data System (ADS)

    Cifelli, Francesca; Ballato, Paolo; Alimohammadian, Habib; Sabouri, Jafar; Mattei, Massimo

    2015-01-01

    In this study we use the anisotropy of magnetic susceptibility (AMS) and paleomagnetic data for deciphering the origin of magnetic lineation in weakly deformed sedimentary rocks and for evaluating oroclinal processes within the Arabia-Eurasia collision zone. In particular, we have analyzed the Miocene Upper Red Formation (URF) from the outer curved front of the southern Central Alborz Mountains of north Iran, to test for the first time with paleomagnetic data the origin (primary versus secondary) of this orogenic arc. AMS data document the existence of a magnetic lineation parallel to the orientation of the major tectonic structures, which vary along strike from WNW to ENE. These directions are highly oblique to the paleoflow directions and hence suggest that the magnetic lineation in the URF was produced by compressional deformation during layer-parallel shortening. In addition, our paleomagnetic data document clockwise and anticlockwise rotations along vertical axis for the western and eastern sectors of the Central Alborz Mountains, respectively. Combined, our results suggest that the orogen represents an orocline, which formed not earlier than circa 7.6 Ma most likely through bending processes caused by the relative motion between the rigid crustal blocks of the collision zone. Moreover, our study provides new insights into the Iran-Southern Caspian Basin kinematic evolution suggesting that the present-day SW motion of the South Caspian Basin with respect to Central Iran postdates oroclinal bending and hence cannot be as old as late Miocene to early Pliocene but a rather recent configuration (i.e., 3 to <1 Ma).

  2. Ages and geodynamic settings of Xilamulun Mo–Cu metallogenic belt in the northern part of the North China Craton

    Microsoft Academic Search

    Lian-chang Zhang; Hua-ying Wu; Bo Wan; Zhi-guang Chen

    2009-01-01

    The Xilamulun belt along the northern part of the North China Craton is located in eastern segment of the Central Asian Orogenic Belt and has great economic potential for Mo–Cu mineralization. More than ten medium to large ore deposits have been discovered in this region in the recent years. The major types of mineralization type include porphyry (Chehugou Mo–Cu, Kulitou

  3. Evidence of low density sub-crustal underplating beneath western continental region of India and adjacent Arabian Sea: Geodynamical considerations

    NASA Astrophysics Data System (ADS)

    Pandey, O. P.; Agrawal, P. K.; Negi, J. G.

    1996-07-01

    The known high mobility of the Indian subcontinent during the period from 80 to 53 Ma has evoked considerable interest in recent times. It appears to have played an important role in shaping the subcontinental structures of western India and the adjoining Arabian Sea. During this period, a major catastrophic event took place in the form of Deccan volcanism, which coincides with the biological mass extinction at the K-T boundary, including the death of dinosaurs. The origin of Deccan volcanism is still being debated. Geophysically, western India and its offshore regions exhibit numerous prominent anomalies which testify to the abnormal nature of the underlying crust-lithosphere. In this work, we develop a two-dimensional structural model of these areas along two long profiles extending from the eastern basin of the Arabian Sea to about 1000 km inland. The model, derived from the available gravity data in the oceanic and continental regions, is constrained by seismic and other relevant information in the area, and suggests, for the first time, the presence of an extensive low-density (2.95-3.05 g/cm 3) sub-crustal underplating. Such a layer is found to occur between depths of 11 and 20 km in the eastern basin of the Arabian Sea, and betweeen 45 and 60 km in the continental region where it is sandwiched in the lower lithosphere. The low density may have been caused as a result of serpentinization or fractionation of magma by a process related in some way to the Deccan volcanic event. Substantial depletion of both oceanic and continental lithosphere is indicated. We hypothesize that the present anatomy of the deformed lithosphere of the region at the K-T boundary is the result of substantial melt generated owing to frictional heat possibly giving rise to a hot cell like condition at the base of the lithosphere, resulting from the rapid movement of the Indian subcontinent between 80 and 53 Ma.

  4. A long-term rock uplift rate for eastern Crete and geodynamic implications for the Hellenic subduction zone

    NASA Astrophysics Data System (ADS)

    Strobl, M.; Hetzel, R.; Fassoulas, C.; Kubik, P.

    2014-12-01

    The island of Crete in the forearc of the Hellenic subduction zone has a rugged topography with a local relief exceeding 2 km. Based on the elevation of marine shorelines, rates of rock uplift during the Late Holocene were previously estimated to range between 1 and 4 mm/a in different parts of the island (e.g. Lambeck, 1995). These rates may, however, not be representative for longer timescales, because subduction earthquakes with up to 9 m of vertical coseismic displacement have recently affected Crete (Stiros, 2001). Here we use a well preserved sequence of marine terraces near Kato Zakros in eastern Crete to determine the rate of rock uplift over the last ˜600 ka. Field investigations and topographic profiles document a flight of more than 13 marine bedrock terraces that were carved into limestones of the Tripolitza unit. Preliminary age constraints for the terraces were obtained by 10Be exposure dating of rare quartz-bearing sandstone clasts, which are present on some terraces. The 10Be ages of these samples, which have been corrected for an inherited nuclide component, yielded exposure ages between ˜100 ka and zero. Combined with geomorphologic evidence the two oldest 10Be ages suggest that the terraces T4 and T5, with shoreline angles at an elevation of ca. 68 and ca. 76 m above sea level, respectively, formed during the marine isotope stage 5e about 120 ka ago. The correlation of the higher terraces (T6 to T13) with regional sea-level high-stands (Siddall et al., 2003) indicates sustained rock uplift at a rate of ˜0.5 m/ka since at least ˜600 ka. As normal faulting has dominated the tectonics of Crete during the last several million years, upper crustal shortening can be ruled out as a cause for rock uplift. We argue that the sustained uplift of the island results from the continuous underplating of sediments, which are transferred from the subducting African plate to the base of the crust beneath Crete. Lambeck, 1995, Geophys. J. Int. 122, 1022-1044.Siddall et al., 2003, Nature, 423, 853-858.Stiros, 2001, J. Struct. Geol., 23, 545-562.

  5. Crustal Deformation of Luzon Island, Philippines from GPS-based Geodynamic Models and Structural Analyses of Satellite Imagery

    Microsoft Academic Search

    G. A. Galgana; M. W. Hamburger; R. C. Torres; R. McCaffrey; Q. Chen

    2004-01-01

    We develop a comprehensive model of plate boundary deformation, based on satellite-based structural analyses combined with geodetic and seismic evidence of present-day deformation of Luzon Island, Philippines. The region comprises the northern part of the Philippine Mobile Belt, a plate boundary zone situated between two active, opposing subduction zones. Correlation of geodetic and seismic evidences with the structural map generated

  6. Crustal Deformation of Luzon Island, Philippines from GPS-based Geodynamic Models and Structural Analyses of Satellite Imagery

    NASA Astrophysics Data System (ADS)

    Galgana, G. A.; Hamburger, M. W.; Torres, R. C.; McCaffrey, R.; Chen, Q.

    2004-12-01

    We develop a comprehensive model of plate boundary deformation, based on satellite-based structural analyses combined with geodetic and seismic evidence of present-day deformation of Luzon Island, Philippines. The region comprises the northern part of the Philippine Mobile Belt, a plate boundary zone situated between two active, opposing subduction zones. Correlation of geodetic and seismic evidences with the structural map generated from the Shuttle Radar Topography Mission (SRTM) DEM and Landsat images reveal the complexity of recent deformation style of the island. Geologic structures were mapped using co-registered sets of SRTM DEM shaded relief images and Landsat 7 images. The SRTM shaded reliefs were processed at different illumination directions and overlaid with cloud-free Landsat 7 mosaic. We then use the satellite-based identification of active faults to develop a microplate model for active deformation in the Philippine arc. We apply an elastic block model to describe active deformation within the region, utilizing simultaneous inversions of GPS-observed site velocity vectors and earthquake slip vectors to solve for block rotations, elastic fault strain accumulation on block boundaries, and internal block strain. Campaign-based GPS observations acquired from 1996-2002, and focal mechanism data from the Harvard-CMT catalogue from 1972-2003 were primary inputs for deriving the block models. Findings for slip across the major faults show 35-44 mm/y sinistral slip along the Philippine fault system, 19-28 mm/y along the Digdig fault and 21-28 mm/y motion along the northern Cordillera fault. Slower slip rates are detected along the Macolod Corridor System , with 11-13 mm/y left lateral, trans-tensional motion. Strain across the Philippine fault is modeled as a near vertical strike-slip fault, with elastic strain accumulation on a fully locked fault to 15 km. depth.

  7. Relationships between pore pressure, stresses, and present-day geodynamics in the Scotian Shelf, offshore eastern Canada

    SciTech Connect

    Yassir, N.A. [Univ. of Waterloo, Ontario (Canada); Bell, J.S. [Geological Survey of Canada, Calgary, Alberta (Canada)

    1994-12-01

    A geomechanical study of the Mesozoic and Tertiary sediments beneath the Scotian Shelf shows that two major weak layers exist at depth: the over-pressured unit at 4000 m and the basal Argo salt, which is ductile and diapiric. A consistent relationships is observed between the overpressures and the stress state in the basin. First, the smaller horizontal principal stress increases dramatically just above the onset of overpressuring, and secondly, borehole breakouts, indicators of stress anisotropy-decrease in abundance within the overpressure zone. Neither tectonic shear nor rapid burial can explain these observations; however, overpressuring by fluid generation will result in horizontal stress increase and eventually lead to an isotropic stress state. Compelling evidence is found for hydrocarbon generation being a key cause of overpressuring in the Scotian Shelf.

  8. Laser geodynamic satellite thermal/optical/ vibrational analyses and testing. Volume 2: Technical report, book 2. [retroreflector design

    NASA Technical Reports Server (NTRS)

    1974-01-01

    A detailed analysis of a fused silica cube-corner retroreflector is presented. The effects of manufacturing errors and temperature variations, which may affect the performance of the cube-corner retroreflector are included. The process used in the cube-corner performance is illustrated. The effect of manufacturing error and the effects of manufacturing error combined with various temperature profiles were examined. The effects of a nonuniform wedge angle with manufacturing error and with a manufacturing/temperature profile combination were also analyzed.

  9. Evolution of bimodal volcanism in Gona, Ethiopia: geochemical associations and geodynamic implications for the East African Rift System

    NASA Astrophysics Data System (ADS)

    Ghosh, N.; Basu, A. R.; Gregory, R. T.; Richards, I.; Quade, J.; Ebinger, C. J.

    2013-12-01

    The East African rift system in Ethiopia formed in the Earth's youngest flood basalt province, and provides a natural laboratory to study the geochemistry of bimodal volcanism and its implications for plume-derived magmatism, mantle-lithosphere interactions and evolution of continental rifts from plate extension to rupture. Our geochemical studies of the ~6 Ma to recent eruptive products from Gona within the Afar Rift Zone are understood in context of crustal and upper mantle seismic imaging studies that provide constraints on spatial variations. Geochemical (major element, trace element and isotope) analyses of basalts and rhyolitic tuff from Gona indicate a common magma source for these bimodal volcanics. Light rare earth elements (LREEs) are enriched with a strong negative Eu anomaly and a positive Ce anomaly in some of the silicic volcanic rocks. We observe strong depletions in Sr and higher concentrations of Zr, Hf, Th, Nb and Ta. We hypothesize that the silicic rocks may be residues from a plume-derived enriched magma source, following partial melting with fractional crystallization of plagioclase at shallow magma chambers. The absence of Nb-Ta anomaly shows no crustal assimilation by magmas. Sr isotopes, in conjunction with Nd and Pb isotopes and a strong Ce anomaly could reflect interaction of the parent magma with a deep saline aquifer or brine. Nd isotopic ratios (?Nd = 1.9 to 4.6) show similarity of the silicic tuffs and basalts in their isotopic compositions except for some ~6 Ma lavas showing MORB-like values (?Nd = 5 to 8.7) that suggest involvement of the asthenosphere with the plume source. Except for one basaltic tuff, the whole rock oxygen isotopic ratios of the Gona basalts range from +5.8‰ to +7.9‰, higher than the ? values for typical MORB, +5.7. The oxygen isotopes in whole rocks from the rhyolite tuffs vary from 14.6‰ to 20.9‰ while their Sr isotope ratios <0.706, indicative of post-depositional low T alteration of these silicic rocks by a fluid derived from seawater or some crustal fluid not enriched in radiogenic Sr. The bimodality of the volcanic rocks may be genetically related by fractional crystallization or by partial melting of a hydrothermally altered mafic crust from earlier magma generation in the rift, without continental crustal assimilation. The geochemical data, along with geophysical and geodetic studies, assist our understanding of the tectonics of continental break up and plume magmatism in the Afar depression and the East African Rift system.

  10. Density, stress, and gravity anomalies in the interiors of the earth and mars and the probable geodynamical implications: Comparative analysis

    NASA Astrophysics Data System (ADS)

    Chujkova, N. A.; Nasonova, L. P.; Maximova, T. G.

    2014-05-01

    The formulas that allow, within the quadratic approximation, for the contribution of the anomalous masses, distributed along the height relative to the reference ellipsoid, in the Stokes parameters are derived. It is shown that the contribution of the quadratic terms is largest and commensurate, by the order of magnitude, with the linear contribution if the anomalous masses have a dipole distribution along the height. The quadratic contribution is particularly significant for Mars, where the span of relative variations in the surface topography is by an order of magnitude larger than in the Earth. The problem is solved and the method is developed for finding the depths of compensation for the topographical harmonics of different order and degree. The most probable levels of compensation for topographic irregularities are determined by the analysis of the distribution histograms for the depths of compensation. The maps of lateral distributions of the compensating masses at the selected levels are calculated. It is shown that the observed anomalous structures generate the anomalies in the internal gravity field, which may serve as a cause for the convective motion in the mantle and core of the planet. Besides, the probable nonisostatic vertical stresses in the crust and mantle of the Earth and Mars are calculated.

  11. Petrology, geochemistry and geochronology of the magmatic suite from the Jianzha Complex, central China: Petrogenesis and geodynamic implications

    NASA Astrophysics Data System (ADS)

    Li, Xiaowei; Mo, Xuanxue; Bader, Thomas; Scheltens, Mark; Yu, Xuehui; Dong, Guochen; Huang, Xiongfei

    2014-12-01

    The intermediate-mafic-ultramafic rocks in the Jianzha Complex (JZC) at the northern margin of the West Qinling Orogenic Belt have been interpreted to be a part of an ophiolite suite. In this study, we present new geochronological, petrological, geochemical and Sr-Nd-Hf isotopic data and provide a different interpretation. The JZC is composed of dunite, wehrlite, olivine clinopyroxenite, olivine gabbro, gabbro, and pyroxene diorite. The suite shows characteristics of Alaskan-type complexes, including (1) the low CaO concentrations in olivine; (2) evidence of crystal accumulation; (3) high calcic composition of clinopyroxene; and (4) negative correlation between FeOtot and Cr2O3 of spinels. Hornblende and phlogopite are ubiquitous in the wehrlites, but minor orthopyroxene is also present. Hornblende and biotite are abundant late crystallized phases in the gabbros and diorites. The two pyroxene-bearing diorite samples from JZC yield zircon U-Pb ages of 245.7 ± 1.3 Ma and 241.8 ± 1.3 Ma. The mafic and ultramafic rocks display slightly enriched LREE patterns. The wehrlites display moderate to weak negative Eu anomalies (0.74-0.94), whereas the olivine gabbros and gabbros have pronounced positive Eu anomalies. Diorites show slight LREE enrichment, with (La/Yb)N ratios ranging from 4.42 to 7.79, and moderate to weak negative Eu anomalies (Eu/Eu? = 0.64-0.86). The mafic and ultramafic rocks from this suite are characterized by negative Nb-Ta-Zr anomalies as well as positive Pb anomalies. Diorites show pronounced negative Ba, Nb-Ta and Ti spikes, and typical Th-U, K and Pb peaks. Combined with petrographic observations and chemical variations, we suggest that the magmatism was dominantly controlled by fractional crystallization and crystal accumulation, with limited crustal contamination. The arc-affinity signature and weekly negative to moderately positive ?Nd(t) values (-2.3 to 1.2) suggest that these rocks may have been generated by partial melting of the juvenile sub-continental lithospheric mantle that was metasomatized previously by slab-derived fluids. The lithologies in the JZC are related in space and time and originated from a common parental magma. Geochemical modeling suggests that their primitive parental magma had a basaltic composition. The ultramafic rocks were generated through olivine accumulation, and variable degrees of fractional crystallization with minor crustal contamination produced the diorites. The data presented here suggest that the subduction in West Qinling did not cease before the early stage of the Middle Triassic (?242 Ma), a back-arc developed in the northern part of West Qinling during this period, and the JZC formed within the incipient back-arc.

  12. Geodynamic Environment by Satellite Geodesy, Seismic Attenuation and S-wave Splitting. Example from Vrancea Seismogenic Zone, SE Carpathians

    NASA Astrophysics Data System (ADS)

    Mocanu, Victor; Russo, Raymond; Ambrosius, Boudewijn

    2010-05-01

    In the Vrancea seismogenic zone (SE Carpathians), where very strong earthquakes (Mw > 7) are reported several times a century, the seismotectonics is very complex. It develops beneath the contact between the Moldavian East European Platform, the Scythian Platform, and the Moesian Platform, to the east and southeast, and terranes of the Transylvania Basin lying within the Carpathian arc. Several hypothesis have been considered by scientists in order to explain the clustered foci of crustal and intermediate events (as deep as 200 km). However, until now, there is no tectonic scenario which could explain all geological and geophysical observations. We try to integrate long-term permanent and campaign GPS outcomes with contributions from seismic attenuation and S-wave splitting results. GPS contributions mainly refer to determination of velocity vectors. 15 campaigns and seven permanent stations are being used in order to determine the detailed kinematics of an area characterized by very small velocities (1-2 mm/y), bringing the satellite technique to almost its limit. The results suggest a counterclockwise mantle flow around the Vrancea seismogenic zone, which is a high velocity body developed in an almost vertical position, developing deeper than 200 km. This results is also supported by seismic attenuation studies. We found that models like delamination and subduction could be supported by seismic attenuation studies in this zone. The delamination model implies strong upwelling and horizontal inflow of asthenosphere into the gap between the delaminating and remnant lithosphere. The other model implies downwelling and perhaps lateral-horizontal inflow along the slab detachment or tear. The models imply different distributions of density and rheological properties associated with the different lithosphere - asthenosphere structures. We use the ratio of spectral amplitudes of P and S waves from vertical and transverse seismograms to estimate the S to P ratio in the frequency domain, and then we calculate Qs, the relative shear wave attenuation via two complementary techniques: We find that stations located near and above the Vrancea zone and in the Transylvanian Basin, attenuation is high (low Q). Stations situated on the East European, Moesian, and Scythian Platforms are characterized by higher Qs (low attenuation). We interpret the high attenuation in the Vrancea and Transylvanian Basin is the result of shallow hot asthenosphere present in this area. Observations of source-side shear wave splitting clearly show that upper mantle anisotropy is strongly variable in the region of the tightly curved Carpathian Arc: shear waves taking off from Vrancea along paths that sample the East and Southern Carpathians have fast anisotropy axes parallel to these ranges, whereas those leaving the source region to traverse the upper mantle beneath the Transylvanian Basin (i.e., mantle wedge side) trend NE-SW. Shear waves sampling the East European and Scythian Platforms are separable into two groups, one characterized by fast shear trends to the NE-SW, and a second, deeper group, with trends to NW-SE; also, the majority of null splits occur along paths leaving Vrancea in these NE-E azimuths. Deeper fabric with E-W trend marking asthenospheric flow beneath the craton's base. This more complex anisotropy beneath the western edge of the East European Platform would account for both the variability of observed splitting of waves that sample this volume.

  13. Reconstructing the Late Cretaceous geodynamics of Neotethys by geochemical study of the mudstones in the Central Sakarya Region, NW Anatolia

    NASA Astrophysics Data System (ADS)

    Ac?kal?n, Sanem; Ocakoglu, Faruk; Ömer Y?lmaz, Ä.°Smail

    2010-05-01

    In this study geochemical composition of the Late Campanian - Early Danian deep-marine mudstones were investigated to enlighten the provenance of the Central Sakarya Basin. Changes in the ratios of elements related with ultramafic/mafic (Ni, Cr, Ti, Rb) to felsic (Zr, Y, K2O) provenances were examined through the section. Furthermore some trace element based graphs were used to understand the tectonic setting. The 725 m thick ?smailler section is composed of mostly mudstones; only the Early Danian shows alternation of thin limestones with mudstones. To understand the characteristics of source rocks Rb/K2O, Ti/Zr, Ni/Zr, Ni/Y and Cr/Zr ratios (mafic/felsic ratios) were used and similarities of trends in all ratios were remarkable. According to the trends of graphs the section can be divided in to three parts: 0-254 m (latest Early Campanian - earliest Early Maastrichtian), 254 - 709 m (earliest Early Maastrichtian - Early Danian), and 709th m to the top (Early Danian). Mafic/felsic ratios increase over the first 254 m and thereafter remain nearly constant. After the K/T Boundary (709th m) a major decrease occurs. When the trends in all ratios are considered it can be suggested that in the first 254 m of the section, source area was firstly dominated by felsic rocks. Towards the top mafic/ultramafic sources become abundant and till the K/T Boundary changes in the provenance were not significant. Although in all graphs major shifts can be seen at K/T Boundary, these should be controlled by the impact rather than change in provenance. To understand the tectonic setting of the ?smailler Section, graphs of La vs Th, La/Th vs Hf and Th/Sc vs Zr/Sc were used. In these graphs each part of the section is investigated separately. In the La vs Th graph, 0-254 m of the section corresponds to a continental island arc while upper levels belong to an oceanic arc setting. La/Th vs Hf graph plots Late Campanian levels in to a felsic arc setting, however towards the top first a mixed arc and later an andesitic arc setting becomes significant. According to the Th/Sc vs Zr/Sc graph, contribution of upper continental crust is obvious for first 254 meters, but at the end of the Cretaceous contribution of mantle becomes more dominant. The chemical composition of the mudstones summarized above, suggest that the basin was fed from a continental island arc/continental crust (felsic source) in Late Campanian and from the beginning of the Late Maastrichtian, oceanic arc or most probably uplifted slices of oceanic crust (mafic source) became dominant source area due to the beginning of collision.

  14. Late Cretaceous high?K volcanism in the eastern Pontide orogenic belt: implications for the geodynamic evolution of NE Turkey

    Microsoft Academic Search

    Yener Eyübo?lu

    2010-01-01

    High?K volcanics were produced in two different Late Cretaceous cycles during the infilling of back?arc basins of the eastern Pontides. The first cycle, represented by shoshonitic trachyandesites and associated pyroclastics, containing high K2O (2.74–4.81 wt?%) and Na2O (3.60–5.51 wt?%), overlies a mid?Cretaceous ophiolitic?olistostromal melange formed during the rifting stage of a back?arc basin (Neotethys). Ar\\/Ar dating of biotite from trachyandesite

  15. Laser geodynamic satellite thermal/optical/vibrational analysis and testing, volume 2, book 2. [cubes and far fields

    NASA Technical Reports Server (NTRS)

    1975-01-01

    The main tasks described involved an interferometric evaluation of several cubes, a prediction of their dihedral angles, a comparison of these predictions with independent measurements, a prediction and comparison of far field performance, recommendations as to revised dihedral angles and a subsequent analysis of cubes which were reworked to confirm the recommendations. A tolerance study and theoretical evaluation of several cubes was also performed to aid in understanding the results. The far field characteristics evaluated included polarization effects and treated both intensity distribution and encircled energy data. The energy in the 13.2 - 16.9 arc-sec annular region was tabulated as an indicator of performance sensitivity. The results are provided in viewgraph form, and show the average dihedral angle of an original set of test cubes to have been 1.8 arc-sec with an average far field annulus diameter of 18 arc-sec. Since the peak energy in the 13.2 - 16.9 arc-sec annulus was found to occur for a 1.35 arc-sec cube, and since cube tolerances were shown to increase the annulus diameter slightly, a nominal dihedral angle of 1.25 arc-sec was recommended.

  16. Petrogenesis and geodynamic significance of silicic volcanism in the western Trans-Mexican Volcanic Belt: role of gabbroic cumulates

    NASA Astrophysics Data System (ADS)

    Petrone, Chiara Maria; Orozco-Esquivel, Teresa; Ferrari, Luca

    2014-05-01

    In the western Trans-Mexican Volcanic Belt voluminous silicic volcanism has been associated with the rifting of the Jalisco block from mainland Mexico. Rhyolitic volcanism started at 7.5 Ma after a major pulse of basaltic volcanism aged 11-8.5 Ma associated with slab detachment. This was followed by a second period, between 4.9 and 2.9 Ma, associated with rhyolitic domes and ignimbrite coexisting with basaltic volcanism. The similarity in rare earth element contents between basalts and rhyolites excludes a simple liquid line of descent. The low Ba and Sr contents and the ferroan character of the rhyolites suggest extensive fractional crystallization. Late Miocene-early Pliocene rhyolite Sr isotope values are only slightly more radiogenic than the basalts, whereas Nd isotope ratios are indistinguishable. We successfully modelled the 7.5-3 Ma silicic magmatism as a result of partial melting of crustal gabbroic complexes that we infer to have formed in the mid-lower crust due to the high-density Fe-enriched composition of the late Miocene basaltic volcanism. Slab rollback since ~7.5 Ma favoured decompression melting and arrival of additional mafic magmas that intruded in the lower crust. These basalts heated and melted the gabbroic complexes forming the silicic magmas, which subsequently underwent assimilation and fractional crystallization processes. The first silicic pulse was emplaced during a period of low tectonic activity. Extensional faulting since the Pliocene favours the eruption of both silicic magma and lesser amount of mafic lavas.

  17. Paper in press in Journal of Geodynamics, 2011; author's version Structural and Sedimentary records of the Oligocene revolution

    E-print Network

    Paris-Sud XI, Université de

    with deep lithospheric causes, i.e. partial detachment of the Tethyan slab and/or a change in motion and the incipient Ligurian rifting. insu-00663367,version1-26Jan2012 Author manuscript, published in "Journal

  18. Consequences of Chixculub Impact for the Tectonic and Geodynamic Evolution of the Gulf of Mexico North Carribean Region

    NASA Astrophysics Data System (ADS)

    Rangin, C.; Crespy, A.; Martinez-Reyes, J.

    2013-05-01

    The debate for Pacific exotic origin versus in situ inter American plate Atlantic origin of the Caribbean plate is active in the scientific community since decades. Independently of the origin of this plate, its fast motion towards the east at a present rate of 2cm/yr is accepted to have been initiated during the early-most Cenozoic. The Paleocene is a key period in the global evolution of Central America mainly marked also by the Chicxulub multiring meteor impact in Yucatan. We question here the genetic relationship between this impact event and the incipient tectonic escape of the Caribbean plate. The mostly recent published models suggest this impact has affected the whole crust down to the Moho, the upper mantle being rapidly and considerably uplifted. The crust was then fragmented 600km at least from the point of impact, and large circular depressions were rapidly filled by clastic sediments from Cantarell to Western Cuba via Chiapas and Belize. North of the impact, the whole Gulf of Mexico was affected by mass gravity sliding, initiated also during the Paleocene in Texas, remaining active in this basin up to present time. South of the impact, in the Caribbean plate, the Yucatan basin was rapidly opened, indicating a fast escape of the crustal material towards the unique free boundary, the paleo-Antilles subduction zone. Shear waves velocity data below the Caribbean plate suggest this crustal tectonic escape was enhanced by the fast eastward flowing mantle supporting a fragmented and stretched crust. The proposed model suggests Chicxulub impact (but also the hypothetic Beata impact) have fragmented brittle crust, then easily drifted towards the east. This could explain the Paleogene evolution of the Caribbean plate largely stretched during its early evolution. Geologically, this evolution could explain the absence of evident Paleogene oblique subduction along the Caribbean plate northern and southern margins, marked only by Mid Cretaceous dragged volcanic complexes, but also the relatively recent motion along the Cayman Fault zone (Miocene instead of Eocene). These results are part of a cooperative research-industry programm conducted by CEREGE/EGERIE, Aix-en-Provence and GeoAzur, Nice, with Frontier Basin study group TOTAL S.A., Paris.

  19. Earthquake mechanisms in the Gulfs of Gökova, S??ac?k, Ku?adas?, and the Simav Region (western Turkey): Neotectonics, seismotectonics and geodynamic implications

    NASA Astrophysics Data System (ADS)

    Yolsal-Çevikbilen, Seda; Taymaz, Tuncay; Helvac?, Cahit

    2014-11-01

    The mechanical behavior of continental lithosphere of Aegean region and western Turkey is one of the foremost interesting geological disputes in earth sciences. This region provides complex tectonic events which produced a strong heterogeneity in the crust as such in among most continental regions. The reasons of the ongoing lithospheric-scale extension within the Aegean region can be revealed by the correlation with the prevailing kinematic and dynamic factors such as roll-back of the subduction slab and back arc extension, westward extrusion of the Anatolian micro-plate, block rotations and transtensional transform faults. Seismological studies of earthquake source mechanisms and slip inversions play important roles on deciphering the current deformation and seismotectonic characteristics of the region. In recent years, several moderate earthquakes have occurred in the Gulfs of Gökova, S??ac?k, Ku?adas?, and Simav Graben. We studied source mechanisms and rupture histories of those earthquakes to retrieve the geometry of active faulting, source characteristics, kinematic and dynamic fault parameters and current deformations in western Turkey. We used teleseismic body-waveform inversions of long-period P- and SH-, and broad-band P-waveforms. We also checked first motion polarities of P-waves recorded at both regional and teleseismic stations. Inversion results revealed E-W striking normal faulting mechanisms with small amount of left-lateral strike-slip components in the Gulf of Gökova, and NE-SW oriented right-lateral strike-slip faulting mechanisms in the Gulf of S??ac?k. In Simav Graben, earthquake source parameters show dominantly normal faulting mechanisms with strike-slip components. Our inversions resulted in focal depths for the earthquake ranging from 10 to 15 km and NE-SW trending T-axes directions. The finite-fault slip distribution and rupture propagation models exhibit seismic moment releases and large displacement values which essentially occurred at hypocenters of the earthquakes. The overall results exhibited uniform and circular-shaped rupture propagations along dip directions of fault planes. Although most of the focal mechanism solutions show dominantly normal faulting mechanisms associated with the E-W oriented horst-graben structures in western Turkey, there are also strike-slip faulting mechanisms related to remarkable strike-slip faults which are capable of generating damaging earthquakes, particularly in the Gulf of S??ac?k and Karaburun Peninsula. Thus, we suggest that present-day deformation in the Gulfs of Gökova, S??ac?k, Ku?adas?, and Simav Graben (western Turkey) is still mainly driven by the N-S extensional tectonics, but we tentatively further emphasize the importance of strike-slip faults in shaping tectonic structures in the Aegean region.

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

    E-print Network

    Hanke-Bourgeois, Martin

    to obtain the correct surface topography with a sticky-air approach, provided that the viscosity algorithms that perform well in the presence of large and abrupt jumps in viscosity. In recent years, we have competitive method compared to finite element methods in terms of accuracy and in case the jumps of viscosity

  1. Petrography, geochemistry and U-Pb zircon age of the Matongo carbonatite Massif (Burundi): Implication for the Neoproterozoic geodynamic evolution of Central Africa

    NASA Astrophysics Data System (ADS)

    Midende, Gilbert; Boulvais, Philippe; Tack, Luc; Melcher, Frank; Gerdes, Axel; Dewaele, Stijn; Demaiffe, Daniel; Decrée, Sophie

    2014-12-01

    The Matongo carbonatite intrusion belongs to the Neoproterozoic Upper Ruvubu alkaline plutonic complex (URAPC), that is located in Burundi along the western branch of the East African Rift. Beside the Matongo carbonatite, the URAPC alkaline complex comprises feldspathoidal syenites, diorites, quartz-bearing syenites and granites. Three main facies have been recognized in the Matongo carbonatite: (1) Sövites represent the dominant facies. Two varieties have been recognized. A scarce coarse-grained sövite (sövite I), which is altered and poorly enriched in REE (4 < ?REE < 8 ppm), is encountered in highly fractured zones. A fine-grained sövite (sövite II), which is made of saccharoidal calcite, commonly associated with apatite, aegirine and amphibole, is abundant in the intrusion. Sövite II is enriched in LREE (442 < ?REE < 1550 ppm, 49 < LaN/YbN < 175). (2) Ferrocarbonatites, that form decimeter-wide veins crosscutting the sövites, are characterized by a LREE enriched patterns (225 < ?REE < 1048 ppm, 17 < LaN/YbN < 64). (3) K-feldspar and biotite-rich fenite facies (silicocarbonatites) have been recognized at the contact between the carbonatites and the country rock. They are likewise LREE-enriched (134 < ?REE < 681 ppm, 25 < LaN/YbN < 46). Additionaly, "late" hydrothermal MREE-rich carbonatite veinlets can be found in sövite I. They are characterized by moderate enrichment in REE (?REE = 397 ppm), with a MREE-humped pattern (LaN/YbN = 3.7). The different facies represent the typical magmatic evolution of a carbonatite, while the silicocarbonatites are interpreted as resulting from the fenitisation of the country host-rocks. In addition, the most REE-depleted and fractionated facies, i.e. the coarse-grained sövite facies and the "late" calcite veinlets testify for hydrothermal processes that occurred after carbonatite emplacement and result from REE mobilization and redistribution. Large idiomorphic zircon crystals (megacrysts), found in the vicinity of the carbonatite can directly be related to the carbonatite evolution. They have been dated at 705.5 ± 4.5 Ma (U-Pb concordant age, LA-ICP-MS). Similar zircon megacrysts of the Lueshe carbonatite (DRCongo) have been dated and give a concordant age at 798.5 ± 4.9 Ma (U-Pb, LA-ICP-MS). Considering that an extensional tectonic regime occured at that time in Central Africa - what remains debated - both ages could relate to different stages of Rodinia breakup, with uprise of mantle-derived magmas along Palaeoproterozoic lithospheric zones of weakness.

  2. Whole-Rock Geochemistry and Zircon U-Pb Isotopes of the Late Cretaceous Granitoids of the Eastern Taurus (turkey): Implications for Petrogenesis and Geodynamic Setting

    NASA Astrophysics Data System (ADS)

    Beyarslan, Melahat; Lin, Yu-Chin; Chung, Sun-Lin; Feyzi Bingol, Ahmet; Yildirim, Esra

    2015-04-01

    The granitoid plutons out crop largely in the Eastern Taurus, in Turkey. New data, including a combination of field relation, U-Pb zircon geochronology and rock geochemistry on the granitoids in the Eastern Taurus of the Tethyan orogen in Turkey, come from four plutons ( Pertek, Baskil, Göksun and ?ifrin). Pertek, Baskil and Göksun plutons consist mainly of diorite, quartz-diorites, tonalite, granodiorites and granites of I-type, with minor monzonite, the ?ifrin pluton consists of syenogranite, syenite, monzogranite, monzonite. U-Pb zircon geochronology of four samples of diorite and granite from Pertek and Baskil plutons indicate ages of 86±2 - 79 ± 1Ma. U-Pb zircon geochronology of four samples from the ?ifrin granitoid yield ages 77±1-72±1 Ma. Considering these ages, emplacement of the plutons took place during Late Cretaceous (Santonian-Campanian), from 86 to 72 Ma. Although the SiO2 of rocks forming granitoids varies in wide range ( 46.792- 74.092 wt%), they show arc and syn-collision geochemical affinity, with enrichment of LILE (K, Rb, Sr and Ba) and depletion of HFSE (Nb, Ta and Ti) and P. Geochemical data indice that the diorite, tonalite and granodiorite are low-K tholeiite, monzodiorite, monzogranite, granite and K-granite are calc-alkaline and high-K calc-alkaline and monzonite, syenomonzonite and syenite of ?ifrin pluton and some samples of the Pertek pluton are shoshonitic. The Eastern Taurus granitoids would be formed by partial melting of possible juvenile arc-derived rocks during subduction of the South Branch of the Neo-Tethyan oceanic crust and subsequent arc-continent collision.

  3. U-Pb zircon geochronology, geochemical and Sr-Nd-Hf isotopic compositions of the Early Indosinian Tongren Pluton in West Qinling: Petrogenesis and geodynamic implications

    NASA Astrophysics Data System (ADS)

    Li, Xiaowei; Mo, Xuanxue; Huang, Xiongfei; Dong, Guochen; Yu, Xuehui; Luo, Mingfei; Liu, Yanbin

    2015-01-01

    The West Qinling Orogenic Belt (WQOB), an important part of the Qinling-Dabie-Sulu Orogen (Central Orogen), is essential to understand the prolonged evolution of the northeastern branch of the Paleo-Tethys in East Asia. Zircon LA-ICP-MS U-Pb age and Lu-Hf isotopes, bulk-rock major and trace element, and Sr-Nd isotope data for the granodiorite intrusion from the Tongren area, West Qinling are presented. LA-ICP-MS zircon U-Pb dating analyses from two samples constrain the time of crystallization of the granodiorite to ca. 241 Ma. Combined with newly published age data from other coeval intrusive rocks in West Qinling, it is concluded that an Early Indosinian magmatic event occurred in West Qinling. In-situ zircon Hf isotope data on the two samples dated exhibit ?Hf(t) values of -0.6 to -5.8 and -0.8 to -3.9, with corresponding TDMC ages of 1312 to 1637 Ma and 1321 to 1516 Ma, respectively. Granodiorites are characterized by relatively high Mg# values (51.4-58.0), intermediate SiO2 (63.75-67.04 wt.%), high Al2O3 (14.24-15.58 wt.%) and total alkalies (6.60-8.00 wt.%) and relatively low A/CNK values (0.93-1.10). Granodiorites have I-type, high-K to shoshonitic, and metaluminous to weakly peraluminous character, showing bulk-rock geochemical features of arc-related granitoids. They are enriched in large-ion lithophile and light rare-earth elements, and depleted in some high-field-strength elements. The rocks show uniformly high (87Sr/86Sr)t (0.707616-0.708237) and low ?Nd(t) values (-7.9 to -7.5). Estimated crystallization temperatures for the rocks range from 720 ± 48 °C (Ti-in-zircon thermometer) to 759 ± 25 °C (zircon saturation thermometer). The data suggest that magmas were generated by dehydration melting of a mafic lower crustal component with additional input of a mafic component derived from the subcontinental lithospheric mantle. We conclude that the Tongren granodiorite formed in a subduction-related regime in response to slab roll-back of the northward-subducting A'nyemaqen-Mianlue oceanic lithosphere.

  4. Late Panafrican Geodynamical Evolution of the Tuareg Shield: An AMS Study of Neoproterozoic Granitoids Intrusions around the Raghane Mega Shear-Zone

    NASA Astrophysics Data System (ADS)

    Henry, B.; Nouar, O.; Derder, M. E.; Bayou, B.; Ouabadi, A.; Amenna, M.; Hemmi, A.; Ayache, M.

    2009-05-01

    Magnetic fabric studies have been carried out in three plutons emplaced during Late Panafrican times (600 - 540 Ma) around the Raghane N-S mega-shear zone in southeastern Algeria. This shear zone, which can be observed across all the Aïr and Hoggar shield, is one of the most important in Africa. It separates two metacratons (LATEA and eastern Saharan), which present very different degree of deformation and of metamorphism. The studied plutons are apparently undeformed, except close to NNE-SSW and WNW-ESE faults. No clearly oriented magmatic structures have been observed in all these intrusions, except in only few sites with green lengthened enclaves. This study represents the last part (southern area) of an extensive work made along the Raghane shear zone in Algeria. In most previously studied plutons, the magnetic fabric has the same dominant characteristics, with a sub-horizontal magnetic lineation. This lineation is mainly N-S to NNE-SSW, underlying the dominant role of the Raghane shear zone and of its associated NNE-SSW structures during and after the emplacement of the plutons. The new study of three plutons (Abdou, Hanane and Yvonne) points that they are all with a composite character, only part of each of them showing sub-horizontal lineation related to stresses around the shear zones during the late-magmatic period. Their other part has a clearly different magnetic fabric. In fact, the southern part of the Hanane pluton presents fabric clearly due to post-magmatic deformation along a reactivated NNE-SSW fault. For the Abdou and Yvonne plutons, this other part represents other intrusive episodes having occurred in different geological contexts. The granodioritic part of the Yvonne pluton has a deformational magnetic fabric very similar to that of the relatively old (594 Ma) neighboring granodioritic Ohergehem pluton and could belong to this generation of plutons emplaced during the main northward movement of the Assodé-Issalane terrane along the western boundary of the Saharan metacraton. On the contrary, the northern part of Adjou present a fabric still related to the magma emplacement, with magnetic lineation close to the direction of lengthening of the enclaves. Like the other plutons of this region, the northern part of Adjou emplaced in a context of local extension related to movements along the Raghane shear zone, but, contrary to the others, it was not submitted during its late magmatic period to compressive context due to new movements along the shear zone. Similar magnetic fabric, with sub-horizontal lineation related to shear zones, has been already obtained in all the other intrusions of different parts of the Hoggar shield. All these magnetic fabric data therefore show that homogeneous compressive conditions continued in whole Hoggar during a very long period after the Panafrican orogeny.

  5. Miocene incorporation of peridotite into the Hercynian basement of the Maghrebides (Edough massif, NE Algeria): Implications for the geodynamic evolution of the Western Mediterranean

    Microsoft Academic Search

    O. Bruguier; D. Hammor; D. Bosch; R. Caby

    2009-01-01

    A laser ablation ICP-MS U–Pb age of 17.84±0.12 Ma (late Burdigalian) was obtained from monazites separated from a leucocratic diatexite collected in close proximity to a small peridotite massif incorporated into the lower crustal sequence of the Edough Massif (north-eastern Algeria), a southern segment of the peri-Mediterranean Alpine Belt. Monazites extracted from a neighbouring deformed leucogranite intruding early Paleozoic phyllites yield

  6. A Lost Realm in the Internal Domains of the Betic-Rif Orogen (Spain and Morocco): Evidence from Conglomerates and Consequences for Alpine Geodynamic Evolution.

    PubMed

    Martín-Algarra; Messina; Perrone; Russo; Maate; Martín-Martín

    2000-07-01

    The Malaguide-Ghomaride Complex is capped by Upper Oligocene-Aquitanian clastic deposits postdating early Alpine orogenesis but predating the main tectonic-metamorphic evolution, end of nappe emplacement, unroofing, and exhumation of the metamorphic units of the Betic-Rif Orogen. Two conglomerate intervals within these deposits are characterized by clasts of sedimentary, epimetamorphic, and mafic volcanic rocks derived from Malaguide-Ghomaride units and by clasts of acidic magmatic and orthogneissic rocks of unknown provenance, here studied. Magmatic rocks originated from late-Variscan two-mica cordierite-bearing granitoids and, subordinately, from aplitic dikes. Orthogneisses derive from similar plutonic rocks but are affected by an Alpine metamorphic overprint evolving from greenschist (T=510&j0;-530 degrees C and P=5-6 kbar) to low-temperature amphibolite facies (T>550&j0;C and P<3 kbar). Such a plutonic rock suite is unknown in any Betic-Rif unit or in the basement of the Alboran Sea, and the metamorphic evolution in the orthogneisses is different from (and older than) that of Alpujarride-Sebtide rocks to which they were formerly ascribed. Magmatic and metamorphic rocks very similar to those studied characterize the basements of some Kabylia and Calabria-Peloritani units. Therefore, the source area is a currently lost continental-crust realm of Calabria-Peloritani-Kabylia type, located to the ESE of the Malaguide-Ghomaride Domain and affected by a pre-latest Oligocene Alpine metamorphism. Increasingly active tectonics transformed this realm into rising areas from which erosion fed small subsiding synorogenic basins formed on the Malaguide-Ghomaride Complex. This provenance analysis demonstrates that all these domains constituted a single continental-crust block until Aquitanian-Burdigalian times, before its dispersal around nascent western Mediterranean basins. PMID:10856014

  7. Development of the Khao Khwang Fold and Thrust Belt: Implications for the geodynamic setting of Thailand and Cambodia during the Indosinian Orogeny

    NASA Astrophysics Data System (ADS)

    Morley, C. K.; Ampaiwan, P.; Thanudamrong, S.; Kuenphan, N.; Warren, J.

    2013-01-01

    The Indosinian Orogeny in Thailand is often viewed as having developed between strongly linear terranes, which today trend approximately N-S. The terranes were subsequently disrupted by later tectonics, particularly NW-SE trending Cenozoic strike-slip faults. The ENE-WSW to NE-SW striking thrusts and folds in the Khao Khwang Platform area of the Saraburi Group on the SW margin of the Indochina Terrane are not easily explained in the context of this traditional view. Reversal of the clockwise rotation shown to have affected the block north of the Mae Ping Fault zone only enhances the E-W orientation of structures in the fold and thrust belt, and moves the belt further east towards Cambodia. One solution for the trend that fits better with regional understanding from hydrocarbon exploration of the Khorat Plateau is that the Indochina Terrane was actually a series of continental blocks, separated by Permian rifting. During the Early Triassic the early stages of collision (South China-Cathaysian Terrane collision with Vietnam Indochina) resulted in the amalgamation of disparate blocks that now form the Indochina Terrane by closure along the rifts. At the same time or following on from the collision there was closure of the back-arc area between Indochina and the Sukhothai zone. The rift basins, were thrusted and inverted during the early stages of the Indosinian orogeny, and only underwent minor reactivated when later Sibumasu collided with Sukhothai Zone-Indochina Terrane margin during the Late Triassic. The scenario described above requires the presence of a (minor) E-W trending suture in NW Cambodia. Evidence for this suture is suggested by the presence of Permo-Triassic calc-alkaline volcanism.

  8. New insights on the structural style of the subsurface of the Tell units in north-western Tunisia issued from seismic imaging: Geodynamic implications

    Microsoft Academic Search

    Sami Khomsi; Mohamed Soussi; Chokri Mahersi; Mourad Bédir; Héla Fakhfakh-Ben Jemia; Sami Riahi; Kamel Bou Khalfa

    2009-01-01

    Structural interpretations of seismic sections crossing the Tell area in Tunisia, allow us to outline the structural style of the subsurface along the thrust front of the Numidian “nappe” and its relationships with the substratum north of the Middle Mejerda valley. The seismic interpretations show a structural style characterized by large thrust sheets detached over the Triassic salt, whereas the

  9. New insights on the structural style of the subsurface of the Tell units in north-western Tunisia issued from seismic imaging: Geodynamic implications

    NASA Astrophysics Data System (ADS)

    Khomsi, Sami; Soussi, Mohamed; Mahersi, Chokri; Bédir, Mourad; Jemia, Héla Fakhfakh-Ben; Riahi, Sami; Khalfa, Kamel Bou

    2009-04-01

    Structural interpretations of seismic sections crossing the Tell area in Tunisia, allow us to outline the structural style of the subsurface along the thrust front of the Numidian "nappe" and its relationships with the substratum north of the Middle Mejerda valley. The seismic interpretations show a structural style characterized by large thrust sheets detached over the Triassic salt, whereas the autochthonous cover is affected by inherited faults and tilted blocks. These inherited faults are connected at depth on the major "décollement" level represented by the interface Triassic salt/Mesozoic-Cenozoic cover. This autochthonous Atlas type cover recorded the Eocene Atlas compressional event outlined by the angular unconformity of the Oligo-Miocene on top of folded Cretaceous strata. Seismic interpretation shows also the occurrence of important halokinetic movements deforming both the autochthonous and allochthonous series. Two types of diapirs can be distinguished: the first ones cutting the autochthonous sedimentary cover, the second ones the Tellian sheets specially the Numidian "nappe" which is the uppermost tectonic unit of the Tellian belt. These latter Triassic levels have pierced the allochthonous cover after the "nappes" emplacement i.e. after the Langhian and during the Late Miocene compressional events. Otherwise, Triassic salt is incorporated as sole thrust level beneath the Numidian "nappe". A regional structural transect crossing the whole Tunisia thrust belt from the Tell to the southeastern foreland and the Zaghoaun thrust-fault allows us to illustrate the overall structural style of the Domain. It outlines the occurrence, beneath the upper-most Tellian structural level (Numidian) of imbricated units issued from duplexing of the sedimentary cover. It appears that the Numidian "nappe" detaches over Middle-Late Eocene shales which represent the upper-most "décollement" level. The Triassic salts locally exposed at the base the Numidian "nappe" are incorporated mechanically during the southward gliding of the "nappe" above the duplex structures.

  10. High-heat geodynamic setting during the Palaeozoic evolution of the Mount Painter Province, SA, Australia: evidence from combined field structural geology and potential-field inversions

    NASA Astrophysics Data System (ADS)

    Armit, R. J.; Ailleres, L.; Betts, P. G.; Schaefer, B. F.; Blaikie, T. N.

    2014-10-01

    A method for subsurface recognition of blind geological bodies is presented using combined surface constraints and 3-D structural modelling that incorporates constraints from detailed mapping, and potential-field inversion modelling. This method is applied to the Mount Painter Province and demonstrates that addition of low density material is required to reconcile the gravity signature of the region. This method may be an effective way to construct 3-D models in regions of excellent structural control, and can be used to assess the validity of surface structures with 3-D architecture. Combined geological and potential-field constrained inversion modelling of the Mount Painter Province was conducted to assess the validity of the geological models of the region. Magnetic susceptibility constrained stochastic property inversions indicates that the northeast to southwest structural trend of the relatively magnetic meta-sedimentary rocks of the Radium Creek Group in the Mount Painter Inlier is reconcilable with the similar, northeast to southwest trending positive magnetic anomalies in the region. Radium Creek Group packages are the major contributor of the total magnetic response of the region. However field mapping and the results of initial density constrained stochastic property inversion modelling do not correlate with a large residual negative gravity anomaly central to the region. Further density constrained inversion modelling indicates that an additional large body of relatively low density material is needed within the model space to account for this negative density anomaly. Through sensitivity analysis of multiple geometrical and varied potential-field property inversions, the best-fitting model records a reduction in gravity rms misfit from 21.9 to 1.69 mGal, representing a reduction from 56 to 4.5 per cent in respect to the total dynamic range of 37.5 mGal of the residual anomaly. This best-fitting model incorporates a volumetrically significant source body of interpreted felsic, low density material (1012 m3) impinging on the central-west of the Mount Painter Inlier and overlying Neoproterozoic sequences, and the emplacement of more mafic affinities in the northeast and east. The spatial association and circular geometry of these granitoid bodies suggests an affinity with the Palaeozoic ˜460-440 Ma British Empire Granite that outcrops in the Mount Painter Inlier. The intrusion of this additional material in the Palaeozoic could either be the product of; or contributed to, an increased local geotherm and heat flow in the region during the Palaeozoic.

  11. Crustal structure of the eastern Algerian continental margin and adjacent deep basin: implications for late Cenozoic geodynamic evolution of the western Mediterranean

    NASA Astrophysics Data System (ADS)

    Bouyahiaoui, B.; Sage, F.; Abtout, A.; Klingelhoefer, F.; Yelles-Chaouche, K.; Schnürle, P.; Marok, A.; Déverchère, J.; Arab, M.; Galve, A.; Collot, J. Y.

    2015-06-01

    We determine the deep structure of the eastern Algerian basin and its southern margin in the Annaba region (easternmost Algeria), to better constrain the plate kinematic reconstruction in this region. This study is based on new geophysical data collected during the SPIRAL cruise in 2009, which included a wide-angle, 240-km-long, onshore-offshore seismic profile, multichannel seismic reflection lines and gravity and magnetic data, complemented by the available geophysical data for the study area. The analysis and modelling of the wide-angle seismic data including refracted and reflected arrival travel times, and integrated with the multichannel seismic reflection lines, reveal the detailed structure of an ocean-to-continent transition. In the deep basin, there is an ˜5.5-km-thick oceanic crust that is composed of two layers. The upper layer of the crust is defined by a high velocity gradient and P-wave velocities between 4.8 and 6.0 km s-1, from the top to the bottom. The lower crust is defined by a lower velocity gradient and P-wave velocity between 6.0 and 7.1 km s-1. The Poisson ratio in the lower crust deduced from S-wave modelling is 0.28, which indicates that the lower crust is composed mainly of gabbros. Below the continental edge, a typical continental crust with P-wave velocities between 5.2 and 7.0 km s-1, from the top to the bottom, shows a gradual seaward thinning of ˜15 km over an ˜35-km distance. This thinning is regularly distributed between the upper and lower crusts, and it characterizes a rifted margin, which has resulted from backarc extension at the rear of the Kabylian block, here represented by the Edough Massif at the shoreline. Above the continental basement, an ˜2-km-thick, pre-Messinian sediment layer with a complex internal structure is interpreted as allochthonous nappes of flysch backthrusted on the margin during the collision of Kabylia with the African margin. The crustal structure, moreover, provides evidence for Miocene emplacement of magmatic intrusions in both the deep basin and the continental margin. Based on the crustal structure, we propose that the eastern Algerian basin opened during the southeastward migration of the European forearc before the collision, along a NW-SE elongated spreading centre that ran perpendicular to the subduction trend. Such an atypical geometry is explained by the diverging directions of the subduction rollback during the backarc opening: eastward for the Corsica-Sardinia block, and southward for the Kabylian blocks. This geometry of the forearc can be interpreted as the surface expression of a slab tear at depth, which is responsible for atypical magmatism in the overlying backarc oceanic basin.

  12. Provenance of eclogitic metasediments in the north Qilian HP/LT metamorphic terrane, western China: Geodynamic implications for early Paleozoic subduction-erosion

    NASA Astrophysics Data System (ADS)

    Zhang, J. X.; Li, J. P.; Yu, S. Y.; Meng, F. C.; Mattinson, C. G.; Yang, H. J.; Ker, C. M.

    2012-10-01

    In this contribution, we present new petrological, geochemical, zircon U-Pb and Hf isotopic data for eclogitic metasediments from the north Qilian orogenic belt, in which early Paleozoic ophiolitic sequences and HP/LT metamorphic rocks have been previously recognized. The studied metasediments contain eclogite facies assemblages reflecting P-T conditions of 450-560 °C and 1.9-2.4 GPa, consistent with those of adjacent eclogites. REE compositions of the eclogitic metasediments overlap those of average upper continental crust. The SHRIMP and LA-MC-ICPMS U-Pb data of zircons from metasediments demonstrate input from sources with major age components about 500 Ma and 1600-1900 Ma (peak at ~ 1800 Ma), with a smaller population at 660-800 Ma (peak at 750 Ma), and minor > 1.9 Ga zircon ages. The youngest detrital zircons suggest a maximum depositional age of ca. 475 Ma, and combined with P-T conditions and previously determined metamorphic age suggest a burial rate of > 0.6-0.7 cm/yr. Zircon Hf isotopic analyses show that 500 Ma zircons have positive ?Hf(t) (mainly between + 8 and + 16). By contrast, Meso- to Paleoproterozoic detrital zircons show a broad spectrum of ?Hf(t) (mainly between - 5 and + 10) with TDMHf of 1800-2500 Ma. These data suggest that eclogitic metasediments are derived from a mixture of Proterozoic continent crust and juvenile early Paleozoic oceanic and/or island arc crust, and their protoliths likely were deposited in a terrigenous-dominated continental margin basin rather than a pelagic oceanic crust environment. The new results are consistent with subduction erosion of the active continental margin during south-dipping subduction, as these sediments, formed in a fore-arc environment close to the Qilian block to the south, were transported in the subduction zone to 60-70 km depth prior to their exhumation.

  13. Major geodynamic and sedimentary constraints on the chronostratigraphic correlation of the lower-middle Cambrian transition in the western Mediterranean region

    Microsoft Academic Search

    J. Javier Álvaro; Sébastien Clausen

    2005-01-01

    The sedimentary rocks of the lower-middle Cambrian transition in the western Mediterranean region have recorded a superposition\\u000a of extensive tectonic, volcanic, epeirogenic, and eustatic events that led to a complex sequence framework that, in some cases,\\u000a makes detailed chronostratigraphic correlations difficult. This paper summarizes and updates the relationships between event\\u000a stratigraphy, fluctuations of relative sea level, setting of major stratigraphic

  14. Plutonic ultramafic-mafic complexes of the Vel'may terrane, eastern Chukotka (Russia): first petrological results and preliminary geodynamic interpretations

    NASA Astrophysics Data System (ADS)

    Ledneva, G. V.; Bazylev, B. A.; Kuzmin, D.; Ishiwatari, A.; Kononkova, N. N.; Sokolov, S. D.

    2012-04-01

    The Vel'may terrane (eastern Chukotka) is commonly considered as a continuity of the South Anyui Suture (SAS) zone (western Chukotka) and the Angaucham terrane (Brooks Range, Alaska), which marks the southern boundary of the Arctic Alaska - Chukotka displaced continental microplate (AACM). The correlation of terranes bounding the microplate is based on findings of similar upper Triassic (Norian) faunas (Tynankergav, Bychkov, 1987; Sokolov et al., 2009) and the ubiquitous occurrence of ultramafic-mafic plutonic complexes attributed to be ophiolite fragments. However, plutonic complexes of the Vel'may terrane haven't been petrologically investigated till now. In the study area they spatially associate with upper Jurassic-lower Cretaceous deposits of the Cross Bay zone and upper Triassic sequences of the Kolyuchinskaya Bay zone. In the Cross Bay zone ultramafic and mafic rocks compose small tectonic slices and are represented by non-spreading subduction-related restite spinel harzburgites and shallow-level plagioclase peridotite and gabbro cumulates (crystallization pressure is estimated at 3.5±1 and 1.5±1 kb ((Schmidt, 1992), respectively) closely resembling fragments of an ophiolitic assemblage. In the Kolyuchinskaya Bay zone tectonic slices of ultramafic and mafic rocks are dominated by clinopyroxene-bearing dunites, hornblende wehrlites/olivine clinopyroxenites and hornblende gabbros. This rocks are high-pressure cumulates (crystallization pressure is estimated at 8±1 kb (Schmidt, 1992)) of lower crustal magma-chambers originated in a mature island-arc or an Andean-type active continental margins. Remnants of subduction-related ophiolite and magma-chambers are typical of sutures indicative of an arc-continent collision; and they occur widely in the SAS zone (Lychagin, 1985; Ganelin, Sylantyev, 2008) and the Angayucham terrane (Loney, Himmelberg, 1989). Thus, the Vel'may terrane can be considered as a possible marker of the AACM boundary. This work was supported by the Russian Foundation for Basic Research (project No 10-05-00529) and Program of the Leading Scientific Schools (grants No 3919.2010.5 and 7091.2010.5).

  15. Field and Geochemical Characteristics of the ca. 3.0-billion-years-old Ivisaartoq Greenstone Belt, West Greenland: Geodynamic Implications

    NASA Astrophysics Data System (ADS)

    Polat, A.

    2005-12-01

    The 3.0 Ga Ivisaartoq greenstone belt is the largest Mesoarchean (~3075 Ma) supracrustal assemblage in southern West Greenland. The belt is composed mainly of pillow basalts ultramafic flows, gabbros, and serpentinites. Pillow basalts display well-preserved core and rim structures. Many pillow cores have cavities at the centre, which are filled mainly with diopside-quartz-plagioclase-epidote assemblage, indicating Mesoarchean seafloor hydrothermal alteration processes. Pillow cores and gabbros have pre-alteration ocelli structures, composed predominantly of plagioclase-quartz assemblage. These ocelli structures are morphologically and mineralogically similar to those found in other Archean belts. Accordingly, they have been interpreted to represent immiscible liquids. The diopside-quartz-plagioclase-epidote metasomatic assemblage in the pillow cores is interpreted as metamorphosed epidosite formed under upper-greenschist to lower-amphibolite facies metamorphic conditions during hydrothermal alteration of the Mesoarchean oceanic crust. Early seafloor hydrothermal alteration was followed by amphibolite facies regional metamorphism, characterized by diopside-garnet-hornblende-plagioclase-quartz-vesuvianite calc-silicate metasomatic assemblage. Given the preservation of primary ocelli-matrix texture in the outer pillow cores, they are considered as the least altered sections of the pillow basalts. On chondrite- and primitive mantle-normalized diagrams, these pillow cores have the following trace element characteristics: (1) moderately enriched LREE patterns; (2) near-flat HREE patterns; and (3) variably negative Nb, Ti, and Zr anomalies. Ultramafic flows, with picritic geochemical characteristics, and gabbros also have similar trace element characteristics, consistent with a subduction zone geochemical signature. Given the observations that epidosites and subduction zone geochemical signatures have been identified in several Phanerozoic ophiolites, the Ivisaartoq belt is interpreted as the crustal section of a dismembered Mesoarchean supra-subduction zone ophiolite.

  16. Jurassic formation and Eocene subduction of the Zermatt–Saas-Fee ophiolites: implications for the geodynamic evolution of the Central and Western Alps

    Microsoft Academic Search

    Daniela Rubatto; Dieter Gebauer; Mark Fanning

    1998-01-01

    The Zermatt–Saas-Fee ophiolites (ZSFO) are one of the best preserved slices of eclogitic oceanic crust in the Alpine chain.\\u000a They formed during the opening of the Mesozoic Tethys and underwent subduction to HP\\/UHP conditions during Alpine compression. A cathodoluminescence-based ion microprobe (SHRIMP) dating of different zircon domains\\u000a from metagabbros and oceanic metasediments was carried out to constrain the timing of

  17. High-resolution sequence stratigraphy of an alluvial fan–fan delta environment: stratigraphic and geodynamic implications – An example from the Keuper Chaunoy Sandstones, Paris Basin

    Microsoft Academic Search

    Sylvie Bourquin; Christophe Rigollet; Philippe Bourges

    1998-01-01

    Facies analysis of the Chaunoy Formation, conducted as the first stage of this study, reveals that the corresponding fluvial system essentially involved bedload deposition, 2-D and 3-D megaripple migration, and debris-flow deposition. Such processes are characteristic of alluvial fan depositional environments. These alluvial fan deposits pass laterally eastward into a shallow lacustrine environment. In stage 2 of the study, electrofacies

  18. The deep seismic structure of the Earth's crust along the Antarctic Peninsula-A summary of the results from Polish geodynamical expeditions

    NASA Astrophysics Data System (ADS)

    Janik, Tomasz; Grad, Marek; Guterch, Aleksander; ?roda, Piotr

    2014-12-01

    A summary of the results of four Polish geophysical expeditions, which constituted an extensive programme of seismic wide-angle refraction experiments in the northern Antarctic Peninsula region between 1979 and 1991, is analysed here. The results include the interpretation of 20 deep seismic sounding profiles located along the western coast of the Antarctic Peninsula. Additionally, a few shallow seismic profiles in the Deception Island area and a total of 10 reflection profiles from the Bransfield Strait and Drake Passage area were carried out. Crustal velocity models extending across the Antarctic Peninsula continental shelf between the Adelaide Island and the Bransfield Strait show a typical continental crustal structure, with crustal thicknesses of 36-42 km near the coast that decreases to 25-28 km beneath the outer continental shelf. Farther north in the Bransfield Strait region, the models document a southeastward dip of the Moho discontinuity from a depth of 12 km beneath the South Shetland Trench to 40 km under the northern tip of the Antarctic Peninsula. Beneath the trough of the Bransfield Strait, a high-velocity body with P-wave velocities exceeding 7.0 km/s was detected in a depth range of 6-32 km.

  19. S. Lallemand and F. Funiciello (eds.), Subduction Zone Geodynamics, 63 DOI 10.1007/978-3-540-87974-9, Springer-Verlag Berlin Heidelberg 2009

    E-print Network

    Demouchy, Sylvie

    , and clinohumite (21.8%, Vs 15.9%). Brucite at 4GPa (Vp 26.5%, Vs 30.9%) and the dense hydrogen magnesium silicate anisotropy. It is the case for brucite and talc, in which increasing pressure from ambient to 4GPa reduces

  20. Field evidence of Eros-scale asteroids and impact-forcing of Precambrian geodynamic episodes, Kaapvaal (South Africa) and Pilbara (Western Australia) Cratons

    NASA Astrophysics Data System (ADS)

    Glikson, Andrew Y.

    2008-03-01

    The role of asteroid and comet impacts as triggers of mantle-crust processes poses one of the fundamental questions in Earth science. I present direct field evidence for close associations between impact ejecta/fallout units, major unconformities and lithostratigraphic boundaries in Archaean and early Proterozoic terrains, including abrupt changes in the composition of volcanic and sedimentary assemblages across stratigraphic impact boundaries, with implications for the nature and composition of their provenance terrains. As originally observed by D.R. Lowe and G.R. Byerly, in the Barberton Greenstone Belt, eastern Kaapvaal Craton, South Africa, 3.26-3.24 Ga asteroid mega-impact units are closely associated with the abrupt break between an underlying simatic mafic-ultramafic volcanic crust and an overlying association of turbidites, banded iron formations, felsic tuff and conglomerates of continental affinities. Contemporaneous stratigraphic relationships are identified in the Pilbara Craton, Western Australia. Evidence for enrichment of seawater in ferrous iron in the wake of major asteroid impacts reflects emergence of new source terrains, likely dominated by mafic compositions, attributed to impact-triggered oceanic volcanic activity. Relationships between impact and volcanic activity are supported by the onset of major mafic dyke systems associated with ~ 2.48 Ga and possibly the 2.56 Ga mega-impact events.

  1. 6th International Symposium on Andean Geodynamics (ISAG 2005, Barcelona), Extended Abstracts: 481-484 A Grenvillian anorthosite-mangerite-charnockite-granite suite in the

    E-print Network

    -484 481 A Grenvillian anorthosite-mangerite-charnockite-granite suite in the basement of the Andes Introduction Only a few anorthositic rocks of Proterozoic age are so far described from the basement al, 2005). A new occurrence (the Ilo Anorthosite) is located in the Arica elbow (southern Peru

  2. Geochemical and detrital zircon studies of meta-sedimentary rocks from the Teletsk and Ulagan blocks, Russian Altai: Implications on their tectonic affinity and geodynamic evolution

    NASA Astrophysics Data System (ADS)

    Chen, Ming; Sun, Min

    2015-04-01

    A combined whole-rock geochemical and detrital zircon geochronological and Hf-isotope study was conducted on meta-sedimentary sequences of the Teletsk and Ulagan blocks in order to trace their provenance, depositional setting and tectonic affinity. Samples from the Teletsk and Ulagan blocks underwent epidote-amphibole- and greenschist-facies metamorphism, respectively, but all of them show comparable geochemical characteristics. They are characterized by high Al2O3/SiO2 ratios and ICV (Index of Chemical Variability) values, while (Gd/Yb)N ratios and REEs compositions are comparable to those of the upper continental crust, indicating that their protoliths were immature and probably deposited proximal to the source areas without significant sedimentary sorting. The low CIA (Chemical Index of Alteration) values for these samples (47.3-74.5 and 52.5-74.5, respectively) further suggest that the source rocks underwent mild to moderate chemical weathering. All the samples show major elements (e.g., Al2O3/TiO2, TiO2/Fe2O3T, Fe2O3T/Al2O3), REEs concentrations, HFSEs and transition elements compositions between the typical andesites and granites, but deviate from those of basaltic rocks, implying that intermediate-felsic rocks served dominant sources during the sedimentation. These geochemical characteristics are consistent with the continental island arc setting, which is discriminated by the TiO2, Al2O3 and Fe2O3T + MgO concentrations higher than those of passive marginal depositions, but La/Sc, Ti/Zr, La/Th, La/Sc and Zr/Th ratios comparable to those of depositions in continental island arc settings. Two samples from the Teletsk and Ulagan blocks yield similar detrital zircon age spectra, with the most prominent population of ca. 620-470 Ma old and a subordinate one of ca. 943-743 Ma old. Comparison with surrounding tectonic units shows that the Tuva-Mongolian terrane and surrounding island arcs in western Mongolia probably provided substantial sources to the protoliths. The similarities in geochemical compositions and detrital zircon patterns with those for the Altai-Mongolian terrane suggest that the Teletsk and Ulagan blocks possibly represented the northern margin of this terrane with different crustal levels. Our study places further constraints that the whole Altai-Mongolian terrane possibly represented a large subduction-accretion complex built upon the active margin in the western Mongolia during the early Paleozoic.

  3. Prelimilary Geological and Geochemical Data from the Cangaldag Complex (Kastamonu-Turkey): Implications for the Geodynamic Evolution of the Central Pontides

    NASA Astrophysics Data System (ADS)

    Cimen, Okay; Sayit, Kaan; Goncuoglu, M. Cemal

    2015-04-01

    The Cangaldag Complex, one of the tectonic units lying in the Central Pontides of the Sakarya Composite Terrane, comprises variably deformed and metamorphosed rocks of mostly magmatic origin. These lithologies include both extrusive and intrusive varieties as well as volcaniclastic types, with a wide range of compositions from felsic to mafic. Petrographically the complex consists of diverse rock types, including basalt, tuff, diabase, gabbro, andesite, and rhyo-dacite. The mafic lithologies generally appear to be affected by greenschist facies metamorphism with typical assemblage of ab+act+chl+ep. A well-developed schistosity is observed in some cases. The dacitic types are generally slightly metamorphic, displaying porphyritic textures with quartz and feldspar phenocrysts embedded in a fine-grained groundmass. Mylonitic varieties of this type are also found. On the basis of geochemistry, the Cangaldag samples are of sub-alkaline character and represented by both primitive and evolved members. All rock types are variably depleted in Nb compared to LREE, similar to the lavas from subduction-related tectonic settings. In N-MORB normalized plots, the primitive members are separated into 3 groups on the basis of levels of enrichment. The first group display highly depleted characteristics akin to boninitic lavas. The second group is relatively enriched compared to the first group but still depleted than N-MORB. The third group, however, is the most enriched among the three, whose level of enrichment is around N-MORB. The overall geochemical features suggest that the Cangaldag meta-igneous rocks have been generated in an intra-oceanic system with the involvement of a subduction-modified mantle source. The chemistry of the primitive members further indicate that the melt generation within the Cangaldag Unit probably occurred on both arc and back-arc regions of the Intra-Pontide supra-subduction zone.

  4. Crustal Structure and Miocene Geodynamic Evolution of the Easternmost Algerian Back-Arc Basin and Continental Margin (western Mediterranean Sea) from Wide-Angle and Multichannel Seismics

    NASA Astrophysics Data System (ADS)

    Bouyahiaoui, B.; Sage, F.; Abtout, A.; Klingelhoefer, F.; Yelles-Chaouche, A.; Schenini, L.; Philippe, S.; Marok, A.; Deverchere, J.; Arab, M.; Galve, A.; Collot, J. Y.

    2014-12-01

    We use new wide-angle seismic and multichannel seismic reflection data (SPIRAL cruise, 2009) and additional geophysical data to study the crustal structure of the eastern Algerian back-arc basin that was born during the Miocene Tethys subduction rollback, before the collision of the European forearc (Kabylian blocks) with the northern African continent ~16-18 Ma ago. In the deep basin, the P-wave velocity model images a thin, 5.5-km-thick oceanic crust with velocity ranging between 4.8 km/s and 7.1 km/s. It is composed of two layers, with a velocity-gradient higher in the upper layer than in the lower one. S-wave modeling indicates a Poisson ratio of 0.28 in the lower crust, supporting a dominant gabbroic composition. Below the continental edge, we define two segments: (1) West of 7°45'E, a typical continental crust with P-wave velocities between 5.2 km/s and 7.0 km/s depicts a gradual seaward thinning of ~15 km over an ~35-km distance characterizing a stretched margin resulting from back-arc extension; (2) East of 7°45'E, the continental crust is a few kilometers thinner, arguing for a variable crustal thickness along the forearc before collision. Based on the deep basin crustal structure and magnetic anomalies, we propose that the eastern Algerian basin opened during the southeastward migration of the European forearc along a NW-SE elongated spreading center that ran perpendicular to the subduction trend, which is an unusual configuration for back-arc opening. Such an atypical geometry of the accretion and the oceanic crustal structure may result from a slab tear at depth related to diverging directions of the subduction rollback (and hence the forearc blocks) during back-arc opening: eastward for the Corsica-Sardinia block, and southward for the Kabylian blocks. The variable thickness of the continental crust along the margin may result from the crustal stretching along the forearc that accommodated the opening of the oceanic domain north of it.

  5. A new international tectonic map of the Arctic (TeMAr) at 1:5 M scale and geodynamic evolution in the Arctic region

    NASA Astrophysics Data System (ADS)

    Petrov, Oleg; Smelror, Morten; Shokalsky, Sergey; Morozov, Andrey; Kashubin, Sergey; Grikurov, Garrik; Sobolev, Nikolay; Petrov, Evgeny

    2013-04-01

    A new tectonic map of the Arctic (TeMAr) at 1:5 M scale is a part of the international Atlas of Geological Maps of the Circumpolar Arctic, which is being compiled under the aegis of the Commission for the Geological Map of the World (CGMW). Compilation of the TeMAr was initiated in 2009 after the publication of base maps of the Atlas - geological map (geological survey of Canada) and magnetic and gravity maps (geological survey of Norway) - with the use of a wide range of bathymetric, geophysical, geological, isotope and geochronological data, including new dated seabed samples and new bedrock samples obtained during recent field studies on the Arctic territory. Making use of these data in the map legend employing tectonic settings enabled correlation of various onshore and offshore fragments of the map. The map reflects Arctic regions' tectonic structure, which consists principally of orogenic belts of the Neoproterozoic to the Late Mesozoic age, platform and basin sediments that overlie them and rift structures formed in part as a consequence of seafloor spreading in the North East Atlantic. Furthermore, many structures are traced from the land throughout shelf regions and into deepwater parts of the Arctic Ocean and show a tendency to become younger northwards toward the Canada Basin. For example, collisional structures of South Ural were formed in the Late Carboniferous, those in the Middle Urals in the Permian, and those of Polar Ural, Pay-Khoy and Novaya Zemlya in the Late Permian and Triassic. The Triassic traps of Eastern and Western Siberia were followed by Cretaceous basalts of the High Arctic large igneous province (HALIP). Cenozoic rifting and subsequent spreading (ca. 56 Ma) was caused by the propagation of sea-floor spreading in the North East Atlantic penetration into the Central Arctic along the Gakkel Ridge

  6. Weak faults in a strong crust: Geodynamic constraints on fault strength, stress in the crust, and the vertical distribution of strength in the lithosphere.

    NASA Astrophysics Data System (ADS)

    Fay, N.; Humphreys, G.

    2005-12-01

    We present results of steady-state dynamic finite element numerical models for the state of stress and strain rate in the crust and upper mantle in the vicinity of a transform fault. Model rheology is elastic-viscous-plastic where plastic mechanical behavior is used as a proxy for pressure-dependent friction of the seismogenic crust. Viscous flow is incorporated as temperature dependent, power-law creep. We assume that the crust outside the fault zone is at or near its frictional yield strength (i.e., `strong', e.g., Townend and Zoback, 2001) predicted by Byerlee's Law and aim to determine the acceptable range of fault strength and viscosity distributions that satisfy the observations that seismic faulting extends to typically 15 km and that the tectonic strain rate of fault-bounding blocks is small. Assuming the traditional `christmas-tree' strength distribution of the lithosphere (e.g., Brace and Kohlstedt, 1980), our primary results are the following. The upper limit of fault strength is approximately 30 MPa (averaged over 15 km), the majority (>50%) of the vertically integrated strength of the lithosphere resides in the uppermost mantle, and the depth to which frictional deformation occurs in the crustal blocks depends on the strength of nearby faults and viscosity of the lower crust and should not exceed approximately 6-9 km, below which relatively low strain rate viscous creep is the dominant deformation mechanism. We also incorporate the thermal feedback effects of viscous and frictional shear heating and explore the controls on the distribution of shear strain in the lower crust and upper mantle.

  7. Geodynamic controls on Tertiary arc magmatism in Ecuador: Constraints from U-Pb zircon geochronology of Oligocene-Miocene intrusions and regional age distribution trends

    NASA Astrophysics Data System (ADS)

    Schütte, Philip; Chiaradia, Massimo; Beate, Bernardo

    2010-06-01

    We obtained U-Pb zircon ages of Late Tertiary intrusions in the northern Andes to provide robust time calibration points for the intrusive geochronologic framework of Ecuador which is mostly based on K-Ar data. Magmatism associated with intrusion emplacement ranges from 31 to 7 Ma, with ages mainly pooling in the Late Oligocene-Early Miocene. Where both K-Ar and U-Pb data exist for a given intrusive system, ages obtained by the different methods are usually concordant within 1-4 m.y. suggesting that K-Ar ages are accurate indicators for the timing of Tertiary arc magmatism on a regional multi-m.y. scale. Except for a single sample, the investigated intrusions completely lack externally inherited zircons, in agreement with dominantly zircon-poor, oceanic crustal basement domains. Spatio-temporal distribution trends of Tertiary arc magmatism inferred from screened U-Pb, K-Ar, and zircon fission track geochronologic data allow tracking of the progressive along-arc broadening of a flat slab segment below southernmost Ecuador in the Mid- to Late Miocene, and of moderate slab shallowing in northern-central Ecuador in the Late Miocene. These regional arc migration patterns correlate in time with the subduction of the buoyant Inca Plateau and the Carnegie Ridge seamount chain. The temporal distribution of Tertiary Ecuadorian arc magmatism indicates a Late Oligocene-Early Miocene arc magmatic flare-up event comprising widespread ignimbrite eruption and batholith construction. Initiation of the flare-up event coincides in time with accelerating, less oblique Farallon/Nazca-South America plate convergence, suggesting a positive feedback between convergence rates, asthenospheric melt production, mantle-crust melt flux, and upper crustal arc magmatic productivity in Ecuador.

  8. Geochemistry of the Jinduicheng Mo-bearing porphyry and deposit, and its implications for the geodynamic setting in East Qinling, P.R. China

    Microsoft Academic Search

    Laimin Zhu; Guowei Zhang; Bo Guo; Ben Lee; Hujun Gong; Fei Wang

    2010-01-01

    Simultaneous determinations of U–Pb dating and Hf isotopes on single zircon grains by excimer laser-ablation quadrupole and multiple-collector ICP-MS and petrologic and ore geochemical studies have been applied to the ore-bearing porphyry of the Jinduicheng porphyritic molybdenum deposit in East Qinling. Lithogeochemical data show that the porphyry is characteristic of high K2O, K-feldspar porphyritic calc-alkaline granitoids with 176Hf\\/177Hf=0.282020–0.282436 and ?Hf(t)=?23.7

  9. The Late Cretaceous-Paleogene active margin of Northeastern Asia: Geodynamic setting of terrigenous sedimentary basins in the Central Koryak terrane

    NASA Astrophysics Data System (ADS)

    Chekhovich, V. D.; Palandzhyan, S. A.; Sukhov, A. N.; Egorkin, A. V.; Ben'yamovsky, V. N.

    2008-01-01

    The northeastern segment of the Late Cretaceous suprasubduction Okhotsk-Chukotka volcanic belt is not an analogue of Andean-type continental margin. During its formation, the belt was separated from the Paleopacific by a complexly built assembly that comprised the Central Koryak continental block and the Essoveem volcanic arc at its margin. Various types of independent terrigenous sedimentary basins were formed in the Late Cretaceous and Early Paleogene at the subsided portion of the microcontinent and its slope. The Uchkhichkhil-type basin was characterized by deposition of polymictic clastic sediments produced during erosion of the volcanic arc and pyroclastic material derived from active volcanic centers of this arc that extended along the microcontinent margin that faced the Okhotsk-Chukotka volcanic belt. The deposition of quartz-feldspathic flyschoid sequences as products of scouring of sialic basement of the continental block was inherent to the Ukelayat type of sedimentation. The closure of the minor oceanic basin that separated the Asian margin from microcontinent in the late Campanian resulted in the cessation of subduction-related activity of the Okhotsk-Chukotka volcanic belt and the Essoveem arc and initiated the formation of the Late Cretaceous accretionary margin of Asia. The deep structure of the central Koryak Highland deduced from the results of seismic surveying with the earthquake converted-wave method has corroborated the geotectonic interpretation.

  10. Carbonate xenoliths hosted by the Mesoproterozoic Siddanpalli Kimberlite Cluster (Eastern Dharwar craton): implications for the geodynamic evolution of southern India and its diamond and uranium metallogenesis

    NASA Astrophysics Data System (ADS)

    Chalapathi Rao, N. V.; Anand, M.; Dongre, A.; Osborne, I.

    2010-12-01

    A number of limestone and metasomatised carbonate xenoliths occur in the 1,090 Ma Siddanpalli kimberlite cluster, Raichur kimberlite Field, Eastern Dharwar craton, southern India. These xenoliths are inferred to have been derived from the carbonate horizons of the Kurnool (Palnad) and Bhima Proterozoic basins and provide evidence for a connection between these basins in the geological past. A revised Mesoproterozoic age is proposed for the Bhima and Kurnool (Palnad) basins based on this kimberlite association and is in agreement with similar proposals made recently for the Chattisgarh and Upper Vindhyan sediments in Central India. The observed Bhima-Kurnool interbasinal uplift may have been caused by: (1) extension- or plume-related mafic alkaline magmatism that included the emplacement of the southern Indian kimberlites at ~1.1 Ga, (2) mantle plume-related doming of the peninsular India during the Cretaceous, or (3) Quaternary differential uplift in this region. It is not possible, with the currently available geological information to constrain the exact timing of this uplift. The deep erosion of primary diamond sources in the Raichur kimberlite Field in the upper reaches of the Krishna River caused by this uplift could be the elusive source of the alluvial diamonds of the Krishna valley. Mesoproterozoic sedimentary basins can host world class unconformity-type uranium deposits. In light of its inferred Mesoproterozoic age, a more detailed stratigraphic and metallogenic analysis of the Kurnool basin is suggested for uranium exploration.

  11. The 2013 Lunigiana (Central Italy) earthquake: Seismic source analysis from DInSAR and seismological data, and geodynamical implications for the northern Apennines

    NASA Astrophysics Data System (ADS)

    Pezzo, Giuseppe; Boncori, John Peter Merryman; Atzori, Simone; Piccinini, Davide; Antonioli, Andrea; Salvi, Stefano

    2014-12-01

    In this study we use Synthetic Aperture Radar Differential Interferometry (DInSAR) and seismological data to constrain the source of the mainshock of the 2013 Lunigiana (North-western Italy) seismic sequence, namely an Mw 5.1 event occurred on 2013 June 21. The sequence took place in a transfer zone located between the Lunigiana (North) and Garfagnana (South) graben. As the destructive Mw 6.2 earthquake occurred in 1920 has demonstrated, this area is seismically active and is considered the most hazardous area of the Northern Apennines. Hypocentre relocations of the Lunigiana sequence aftershocks are well fitted by a ~ 45° N-dipping fault plane, whereas the focal mechanism solution yields a dip-slip mechanism with a slight right-lateral strike-slip component. Surface displacements estimated from ascending COSMO-SkyMed imagery acquired in the time-span of a single day around the mainshock were used to derive an elastic dislocation model. The estimated slip distributions computed on fixed and variable size meshes show peak values of 30 cm and 40 cm respectively. Static stress variation analysis was performed to analyze possible stress overloads on the closest seismogenic sources. Our results provide insight into the tectonics of the Northern Apennines, suggesting the fundamental role of transfer fault zones in intra-mountain basin origin and in the assessment of seismic hazard in an extensional tectonic regime.

  12. Magmatic response to abrupt changes in geodynamic settings: Pliocene—Quaternary calc-alkaline and Nb-enriched lavas from Mindanao (Philippines)

    NASA Astrophysics Data System (ADS)

    Sajona, Fernando G.; Bellon, Hervé; Maury, RenéC.; Pubellier, Manuel; Cotten, Joseph; Rangin, Claude

    1994-10-01

    Mindanao, the largest island in the southern Philippine archipelago, is a composite of at least two terranes; one with Eurasian affinity (western Mindanao) and the other belonging to the Philippine Mobile Belt (eastern Mindanao), of Philippine Sea plate affinity. The island is surrounded by three subduction zones that have been installed only in the past 4 m.y. Prior to this, the two terranes were separated by an ocean that disappeared continuously by subduction of its two edges beneath western and eastern Mindanao, where mostly typical arc magmatic rocks, dated at 30 Ma, 19-15 Ma, 12-11 Ma and 7-4 Ma were emplaced. The suturing of the two terranes occurred at ca. 5 Ma. Following this major structural reorganization, abrupt changes are recorded in the < 3 Ma old magmatism of the island. The emplacement of adakites, dated from 1.80 to 0.10 Ma and 0.70 Ma in eastern and western Mindanao, respectively, is thought to result from the initiation of new subductions . In western Mindanao, associated Nb-enriched basalts (NEB) and basaltic andesites (2.58-1.08 Ma) might represent either melts of mantle having interacted with adakitic liquids or of heterogenous mantle containing an OIB component. Seismic data give evidence of the presence of a detached subducted slab beneath Central Mindanao, where the recent volcanism is post-collisional. Calc-alkaline lavas, dated at 2.31-0.29 Ma, pre-date potassic volcanism dated at 0.80-0.36 Ma. Among the calc-alkaline rocks, a group of relatively magnesian basalts and basaltic andesites is also considered to be enriched in Nb and one adakitic sample has been found. The geochemical diversity of magmatic types in Mindanao is attributed to: (1) the highly heterogenous character of their mantle source, which contains variable amounts of metasomatic pargasite and phlogopite, and, possibly, an additional OIB component that could contribute to Nb enrichment of NEB; (2) the contribution of melts from the ubducted oceanic crust; these melts are either emplaced directly on the surface (adakites) or act as metasomatic agents leading to a Nb-enriched mantle, a probable source of NEB. Garnet and amphibole fractionation could also account for additional variations in the MREE and the HREE.

  13. Geodynamic and climate controls in the formation of Mio-Pliocene world-class oxidized cobalt and manganese ores in the Katanga province, DR Congo

    NASA Astrophysics Data System (ADS)

    Decrée, Sophie; Deloule, Étienne; Ruffet, Gilles; Dewaele, Stijn; Mees, Florias; Marignac, Christian; Yans, Johan; de Putter, Thierry

    2010-10-01

    The Katanga province, Democratic Republic of Congo, hosts world-class cobalt deposits accounting for ~50% of the world reserves. They originated from sediment-hosted stratiform copper and cobalt sulfide deposits within Neoproterozoic metasedimentary rocks. Heterogenite, the main oxidized cobalt mineral, is concentrated as “cobalt caps” along the top of silicified dolomite inselbergs. The supergene cobalt enrichment process is part of a regional process of residual ore formation that also forms world-class “manganese cap” deposits in western Katanga, i.e., the “black earths” that are exploited by both industrial and artisanal mining. Here, we provide constraints on the genesis and the timing of these deposits. Ar-Ar analyses of oxidized Mn ore and in situ U-Pb SIMS measurements of heterogenite yield Mio-Pliocene ages. The Ar-Ar ages suggest a multi-phase process, starting in the Late Miocene (10-5 Ma), when the metal-rich substratum was exposed to the action of meteoric fluids, due to major regional uplift. Further oxidation took place in the Pliocene (3.7-2.3 Ma) and formed most of the observed deposits under humid conditions: Co- and Mn-caps on metal-rich substrata, and coeval Fe laterites on barren areas. These deposits formed prior to the regional shift toward more arid conditions in Central Africa. Arid conditions still prevailed during the Quaternary and resulted in erosion and valley incision, which dismantled the metal-bearing caps and led to ore accumulation in valleys and along foot slopes.

  14. Structure and petrology of Pan-African nepheline syenites from the South West Cameroon; Implications for their emplacement mode, petrogenesis and geodynamic significance

    NASA Astrophysics Data System (ADS)

    Emmanuel, Nsifa Nkonguin; Rigobert, Tchameni; Anne, Nédélec; Roberto, Siqueira; André, Pouclet; Jérôme, Bascou

    2013-11-01

    Three late-Neoproterozoic nepheline syenite intrusions crop out close to the late-Pan-African SW Cameroon shear zone, namely the Mont des Eléphants, Eboundja and Rocher du Loup intrusions. They are characterized by magmatic to solid-state deformation structures and microstructures. Their magmas were mainly derived from partial melting of the subcontinental lithospheric mantle. Magmatic differentiation may have occurred through fractionation of clinopyroxene, amphibole, plagioclase and accessory minerals (apatite, sphene, magnetite and zircon). Bulk magnetic susceptibilities are variable in intensity depending of the magnetite content. Their magnetic anisotropies are unusally high, especially in the Rocher du Loup intrusion. The trajectories of magnetic foliations and lineations display an arcuate shape from an E-W direction in the easternmost Mont des Eléphants to a N-S direction in the Rocher du Loup intrusion. These features are consistent with a synkinematic emplacement in relation with the sinistral motion along the SW Cameroon shear zone, whose age is therefore dated by the age of the syenites, i.e. 590 Ma. Magma genesis and ascent was likely favored by a large gradient in lithospheric thickness along the western margin of the Congo craton.

  15. Geochronology and geochemistry of Late Pan-African intrusive rocks in the Jiamusi-Khanka Block, NE China: Petrogenesis and geodynamic implications

    NASA Astrophysics Data System (ADS)

    Yang, Hao; Ge, Wen-chun; Zhao, Guo-chun; Dong, Yu; Bi, Jun-hui; Wang, Zhi-hui; Yu, Jie-jiang; Zhang, Yan-long

    2014-11-01

    To constrain the early Paleozoic tectonic evolution of the Jiamusi-Khanka Block and its relationship to the Late Pan-African event in Gondwana, we undertook zircon U-Pb dating and geochemical analyses (major and trace elements, and Hf isotopic compositions) of early Paleozoic intrusive rocks in the Jiamusi-Khanka Block, NE China. LA-ICP-MS zircon U-Pb age data demonstrate that these intrusive rocks were emplaced at three stages during the Late Pan-African event, represented by ~ 540 Ma syenogranite, ~ 515 Ma quartz syenite, and ~ 500 Ma monzogranite and gabbro. Geochemically, the ~ 500 Ma gabbros in the Jiamusi-Khanka Block have low SiO2 (50.26-51.21 wt.%), relatively high MgO (4.08-5.67 wt.%), Ni (13.1-14.1 ppm) and Cr (28.4-56.0 ppm), and are slightly enriched in LILEs (e.g., Ba, K) and LREEs, and depleted in Zr, Hf, Nb, Ta and P. The ?Hf(t) values of zircons in the gabbro range from + 2.6 to + 6.4. All these geochemical features indicate that the gabbros were likely produced by the partial melting of a depleted mantle that had been metasomatized by fluids derived from a subducted slab. In contrast, the ca.540-500 Ma granites and quartz syenites contain high SiO2 (64.49-72.20 wt.%) and low MgO (0.40-0.75 wt.%), Cr (1.69-6.88 ppm) and Ni (1.26-3.26 ppm). They have relatively low 176Hf/177Hf ratios of 0.282247-0.282599 with Hf two-stage model ages of 1173-2280 Ma, and most of the magmatic zircons have positive ?Hf(t) values varying from + 0.2 - + 4.8, indicating that these granites and quartz syenites were probably derived from a dominantly Paleo-Mesoproterozoic "old" crustal source with possible different degrees of addition of juvenile materials. According to the geochemical data and global geological investigations, we propose that the 541-498 Ma intrusive rocks in the Jiamusi-Khanka Block formed in a post-collisional or post-orogenic extensional setting linked to the collapse of a Late Pan-African orogen associated within the Gondwana.

  16. A Lower Mantle Origin for Megacryst Suite Pyroxene-Ilmenite Xenoliths in Kimberlites: High-Pressure Experimental Constraints and Geodynamic Significance

    NASA Astrophysics Data System (ADS)

    Collerson, K. D.; Terasaki, H.; Ohtani, E.; Suzuki, A.; Kondo, T.

    2004-12-01

    Megacryst suite xenoliths (MSX's) in kimberlites, alnoites and alkali basalts are an important and poorly understood association. MSX's comprise medium- to coarse-grained monomineralic, or rare, multi-grain aggregates of low Cr, high Ti-Na pyrope, Mg ilmenite, sub-calcic pyroxene, Fo85±3 olivine, orthopyroxene and zircon. Some MSX's exceed 30 cm in diameter. They are interpreted to form by fractional crystallization from their host magma, near the base of the lithosphere [1-2]. However, majorite, and other high-pressure phases in some garnetite MSX's, indicates a mantle transition zone (TZ) origin [3]. A sub-lithospheric, deeply subducted slab source is also supported by Hf isotopic data [4]. A common member of the MSX suite, are graphic intergrowths of pyroxene and Mg-ilmenite interpreted to reflect cotectic, or non-equilibrium crystallization [5-6] from the kimberlite magma. However, Pb isotopic data for Monastery [7], and Namibian [8] megacrysts shows that MSX's and their host magmas are unrelated. Thus the mineralogy of the Ti-rich px-ilm MSX's needs to be determined at TZ and higher P. We have conducted multi-anvil (MA) and diamond anvil (DA) experiments on natural px-ilm xenoliths from Monastery and Malaita with different TiO2 contents (17% and 12%), in an attempt to synthesize the pre-exsolution phase. MA experiments were carried out on both starting compositions at 18 and 21 GPa, at 1800° C and 2100° C. None of the experiments yielded a single phase. Phases identified (EPMA, Raman & XRD) include: majorite, Si-rich ilmenite and Ca-Si-Ti Pv. At 21 GPa and 2100° C wadsleyite formed part of the assemblage, and melt was locally developed. Majorite is the most abundant phase in all experiments. Maximum majorite TiO2 occurs at 18 GPa (i.e., 5.4% - Malaita and 6.2% - Monastery). In the lower Ti Malaita composition, at 25 GPa and 1800° C, the assemblage is dominated by almost equal amounts of majorite (TiO2 1.3% to 2.1%) and Ca-Si-Ti Pv, with a small amount of titaniferous Na2O-bearing magnesiowustite. Conclusions from MA experiments are: (1) a single homogeneous Ti-rich silicate phase is not stable in the TZ; (2) closest approach to a homogeneous phase occurs in the lower TiO2 Malaita composition at 25 GPa; (3) maximum solubility of TiO2 in majorite is 5-6% at 18 GPa; (4) at 2100° C and 21 GPa, melting occurs, and majorite plus Si-ilmenite reacts to form Ti-Ca-Si Pv and wadsleyite. Furthermore, in a DA experiment at 30 GPa and 1800° C a multi-phase, Ti-Ca-Si Pv dominated assemblage still prevails. Pyroxene-Mg ilmenite MSX's are therefore interpreted to form from Ti-rich protoliths, possibly ilmenite-rich cumulates, in subducted slabs of oceanic lithosphere. The homogeneous phase from which the pyroxene-Mg-ilmenite intergrowths were exsolved, is thus interpreted to be Ti-Ca-Si Pv, not Ti-rich majorite [cf., 9-10]. Results confirm large-scale transport of oceanic lithosphere into the upper lower mantle during subduction. [1] Nixon, et al., (1963) Am. Mineral. 48, 1090. [2] Jones et al., (1987) In: Mantle Xenoliths 711. [3] Collerson et al., (2000) Science, 288, 1215. [4] Nowell et al., (2004) J Petrol. 45, 1583. [5] Wyatt (1977) CMP 61, 1-9. [6] Mitchell (2004) Lithos (in press) [7] Collerson et al., (2001) EOS 82. [8] Davies et al., (2001) J Petrol. 42, 159. [9] Ringwood & Lovering (1970) EPSL, 7, 371. [10] Zhang et al., (2003) EPSL, 216, 591.

  17. Kinematics and active faults in Western Greece in the framework of Central and Eastern Mediterranean geodynamics: new insights from GPS and field work

    NASA Astrophysics Data System (ADS)

    Perouse, E.; Chamot-Rooke, N. R.; Sébrier, M.; Rabaute, A.; Sorel, D.; Arsenikos, S.; Briole, P.

    2011-12-01

    Western Greece is the transition area between fast extension in the Gulf of Corinth, dextral transpression in the Ionian islands associated to the NW termination of the Hellenic subduction zone and collision of the Apulian platform and Eurasia plate in Epirus. We use a multi-scale approach to investigate the kinematics of this challenging region. As the kinematic boundary conditions of this region are complex, we propose a large scale kinematic model that encompasses both Central and Eastern Mediterranean. We use Haines and Holt (1993) method to derive a continuous velocity and strain rate field by interpolating model velocities that are fitted in a least square sense to published GPS velocities. The main results of our model are: (1) We minimize the motion of the Hyblean plateau in Sicily and Apulia to derive a pole of rotation for the Ionian block following D'Agostino et al. (2008). This rotation pole also minimizes the Ionian basin motion; (2) We propose a "southward drag" of SW Balkans associated to the retreat of the Hellenic slab. The southward motion of the Aegean block with respect to Eurasia is gradually accommodated in the Balkans, so that the propagation of the North Anatolian Fault throughout is not required; (3) On absolute plates motion reference frame (Kreemer 2009), our results suggest a surface toroidal motion located above the NW edge of the Hellenic slab. We discuss whether this clockwise surface toroidal motion mimics toroidal astenospheric flow or not. At a smaller scale, we perform kinematic calculations to distinguish whether surface movements measured by GPS in Western Greece are due to block motion or diffuse deformation. Interseismic strain influence of the shallow subduction interface on surface velocity vectors is tested. To constrain the active structures that accommodate the present strain, we carried out a Quaternary geology and geomorphology field work in Etolo-Akarnania region (Western Greece). We establish a new map of active faults. Our main results are : (1) Along the NNW-sriking Katouna fault, which connects the Gulf of Ambrakia to the Gulf of Patras, several senestral offsets of drainages have been observed and, combined with new GPS velocities (Briole et al. in prep.), an Holocene slip-rate of ~ 4mm/yr may be assessed. An alluvial fan, which is offset along the Katouna fault, was sampled to perform 10Be and 36Cl cosmic ray exposure dating and then, accurately constrain the fault slip-rate; (2) Trichonida lake and the Gulf of Ambrakia are WNW-striking, active half grabens, with a N-dipping master fault as in the Gulf of Corinth; (3) The N-striking Neogene thrusts, which are exposed close to the SW coast of Etolo-Akarnania (Clews 1989, Underhill 1989), appear inactive as they are sealed by strongly cemented and weathered slope debris that are not younger than Middle Quaternary. This suggests that the Etolo-Akarnania region behaves as southward moving rigid "block".

  18. Ab initio thermodynamics and seismic properties of MgSiO3 polymorphs at mantle transition zone conditions: the geodynamic role of non-olivine phases

    NASA Astrophysics Data System (ADS)

    Belmonte, Donato; Ottonello, Giulio Armando; Vetuschi Zuccolini, Marino

    2014-05-01

    MgSiO3 polymorphs with the garnet, pyroxene and ilmenite structure play a key role in controlling phase equilibria and seismic velocity gradients in the mantle transition zone (440-660 km). Despite the relative abundance of structural and thermoelastic informations, thermodynamic data are still poorly constrained and their extrapolation at high pressure and temperature conditions is affected by large uncertainties. In this work, ab initio calculations of the thermodynamic properties of MgSiO3 polymorphs stable at MTZ conditions (tetragonal majorite, Mj; akimotoite, Ak; HP-clinoenstatite, HPCEn) have been carried out with the hybrid B3LYP density functional method. The static and vibrational features of these minerals (equation of state, elastic constants, seismic velocities and anisotropy, IR and Raman spectra, mode Grüneisen parameters) have been fully characterized in a broad range of P-T conditions. The vibrational density of states (vDOS) have been reproduced in the framework of quasi-harmonic approximation through a full phonon dispersion calculation or, alternatively, a modified Kieffer's model splitting the acoustic and optic modes contribution to the thermodynamic functions. The calculated heat capacities are in good agreement with the relatively few calorimetric investigations made so far on these minerals in the low- to medium-T range. However, physical unsoundness may affect the high-temperature extrapolation of calorimetric results, so that the use in phase equilibria calculation deserves great care. The calculated Gibbs free energies allow to define phase transition boundaries in the MgSiO3 phase diagram and locate the majorite-akimotite-perovskite triple point at P = 21.09 ± 0.13 GPa and T = 2247 ± 31 K. The effect of partial structural disorder in majorite, assessed via an interchange enthalpy (?Hint = 15 kJ/mol) and configurational entropy [Sconf = 1.9 J/(mol×K)] contribution, must be taken into account to accurately reproduce the Mj-Ak-Pv triple point. The predicted Clapeyron slopes of the phase boundaries Mj-Pv, Mj-Ak, Ak-Pv and HPCEn-Mj turn out to be 2.2, 8.3, -4.0 and -3.6 MPa/K, respectively, in good agreement with experimental observations and thermodynamic optimizations as well. The geophysical implications concerning the role of non-olivine mineral phases in mantle dynamics, deep seismic discontinuities, density change and slab stagnation at 660 km depth are briefly outlined and discussed.

  19. In situ zircon Hf-O isotopic analyses of late Mesozoic magmatic rocks in the Lower Yangtze River Belt, central eastern China: Implications for petrogenesis and geodynamic evolution

    NASA Astrophysics Data System (ADS)

    Yan, Jun; Liu, Jianmin; Li, Quanzhong; Xing, Guangfu; Liu, Xiaoqiang; Xie, Jiancheng; Chu, Xiaoqiang; Chen, Zhihong

    2015-06-01

    A combined study of whole-rock major and trace elements, Sr-Nd isotopes, zircon U-Pb dating, and in situ zircon Hf-O isotopes has been carried out for late Mesozoic magmatic rocks in the Lower Yangtze River Belt. The results provide insights into the origin of mantle sources of magma above a subduction zone, and thus into the petrogenesis of high-K calc-alkaline rocks, shoshonites, and A-type granites on continental margins, and the associated tectonic transformation from a continental arc to a back-arc extensional setting. The late Mesozoic magmatism can be subdivided into three stages: high-K calc-alkaline intrusions (148-133 Ma), shoshonitic rocks (133-127 Ma), and A-type granitoids (127-123 Ma). All the rocks have consistent arc-like trace element characteristics with positive anomalies of Rb, Th, U, Pb, and LREE, negative anomalies of Nb, Ta, and Ti, and enriched Sr-Nd-Hf isotopic signatures. The first-stage intrusions in the Tongling area usually host dark enclaves of diorite, have high Sr/Y ratios, and low Y contents, and contain zircons with relatively low ?Hf(t) values (- 38.6 to - 6.6) and high ?18O values (5.7‰ to 10.1‰). A few inherited zircons with Neoarchean to Paleoproterozoic ages and highly enriched Hf isotopic compositions were detected in both the host intrusive rocks and the enclaves. The second-stage Ningwu volcanics contain zircons with moderate ?Hf(t) values (- 13.3 to - 3.8) and elevated ?18O values (5.4‰ to 7.6‰). The third-stage intrusions can be divided into A1- and A2-type granitoids, and their zircons have relatively high ?18O values of 6.7‰ to 10.3‰ and high ?Hf(t) values of 0 to - 7.9. Based on these geochemical data we drew the following conclusions. Before 148 Ma, following metasomatism by slab-derived fluid/melts, partial melting of the lithospheric mantle produced basaltic magma in the context of a subducting paleo-Pacific plate. This basaltic magma mixed with magma derived from the Archean lower crust, and the underplated and thickened juvenile lower crust. From 148 to 133 Ma, continuous production of these mixed magma resulted in their intrusions as basic rocks at shallow levels. Meanwhile, partial melting of the thickened juvenile crust formed the intermediate-acid rocks of the first stage. As subduction continued, and the dip angle of the subducting plate increased, the continental arc tectonic setting was transformed to one of back-arc extensions. Metasomatism and decompression induced intensive partial melting of the lithospheric mantle, and these magmas, together with a limited amount of assimilated crustal materials, formed the second-stage volcanics. Roll-back of the subducted slab resulted in extension, causing disassembling of the lower lithosphere and lithospheric thinning, and the upwelling of hot asthenosphere. The A2-type granites were the result of the reworking of the Mesoproterozoic juvenile crust in this tectonic setting of extension. On the other hand, the A1-type granitoids were formed from magmas that were derived both from the matasomatized mantle and from the A2-type granitic material that had its origins in the Mesoproterozoic juvenile crust. We suggest that an integrated and comparative study of the multiple stages of development of these magmatic rocks is the key to understanding the tectonic evolution and associated magmatic activities in this continental intraplate setting.

  20. A Classical Science Transformed.

    ERIC Educational Resources Information Center

    Kovalevsky, Jean

    1979-01-01

    Describes how satellites and other tools of space technology have transformed classical geodesy into the science of space geodynamics. The establishment and the activities of the French Center for Geodynamic and Astronomical Research Studies (CERGA) are also included. (HM)

  1. Datation U_Pb : âge de mise en place du magmatisme bimodal des Jebilet centrales (chaîne Varisque, Maroc). Implications géodynamiquesU_Pb dating: emplacement age of the bimodal magmatism of central Jebilet (Variscan Belt, Morocco). Geodynamic implications

    NASA Astrophysics Data System (ADS)

    Essaifi, Abderrahim; Potrel, Alain; Capdevila, Ramon; Lagarde, Jean-Louis

    2003-01-01

    The bimodal magmatism of central Jebilet is dated to 330.5 +0.68-0.83 Ma by U?Pb dating on zircons. This age, similar to that of the syntectonic Jebilet cordierite-bearing granitoids, corresponds to the age of the local major tectonometamorphic event. The syntectonic plutonism of the Jebilet massif, composed of tholeiitic, alkaline, and peraluminous calc-alkaline series, is variegated. Magmas emplacement was favoured by the local extension induced by the motion along the western boundary of the Carboniferous basins of the Moroccan Meseta. The Jebilet massif exemplifies the activation of various magmas sources during an episode of continental convergence and crustal wrenching.

  2. Le magmatisme basique filonien néoprotérozoïque de la boutonnière de Zenaga, Anti-Atlas central, Maroc: pétrologie, géochimie et signification géodynamiqueNeoproterozoic basic dykes of the Zenaga Inlier, central Anti-Atlas, Morocco: petrology, geochemistry and geodynamic significance

    NASA Astrophysics Data System (ADS)

    Hafid, A.; Sagon, J. P.; Julivert, M.; Arboleya, M. L.; Saquaque, A.; El-Boukhari, A.; Saidi, A.; Soler, J. M. F.

    2001-05-01

    Before the Pan-African Orogeny, the Palæoproterozoic basement and its Neoproterozoic cover (limestones and quartzites) of the Zenaga Inlier were cross-cut by a swarm of doleritic dykes. They are more or less altered. The primary mineral assemblage consists of plagioclase, clinopyroxene, very rare orthopyroxene, ilmenite, apatite, micropegmatite and sometimes hornblende and biotite. Mineralogical and geochemical studies indicate that the dolerites are continental tholeiites. Two groups of dykes have been distinguished. Accordingly, rare earth elements, P 2O 5, Zr, Th, Ba and Sr contents are higher in group I than in group II, which is richer in V. Group I comprises the north-south and northwest-southeast swarms, while group II corresponds to northeast-southwest and east-west swarms, which were emplaced later. These geochemical variations may be explained by a higher degree of melting of the mantle source for the later group II. Doleritic dykes of Zenaga had been emplaced during an extensional episode, prior to Pan-African folding.

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

    Microsoft Academic Search

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

    2009-01-01

    The Altaids is one of the largest accretionary orogenic collages in the world with the highest rate of Phanerozoic continental\\u000a growth and significant metallogenic importance. It is widely accepted that subduction-related orogenesis of the Altaids started\\u000a in the late Precambrian and gradually migrated southward (present coordinates). However, it is uncertain when and how the\\u000a building of the Altaids was finally

  4. Sm-Nd and U-Pb isotopic constraints for crustal evolution during Late Neoproterozic from rocks of the Schirmacher Oasis, East Antarctica: geodynamic development coeval with the East African Orogeny

    USGS Publications Warehouse

    Ravikant, V.; Laux, J.H.; Pimentel, M.M.

    2007-01-01

    Recent post-750 Ma continental reconstructions constrain models for East African Orogeny formation and also the scattered remnants of ~640 Ma granulites, whose genesis is controversial. One such Neoproterozoic granulite belt is the Schirmacher Oasis in East Antarctica, isolated from the distinctly younger Pan-African orogen to the south in the central Droning Maud Land. To ascertain the duration of granulite-facies events in these remnants, garnet Sm-Nd and monazite and titanite U-Pb IDTIMS geochronology was carried out on a range of metamorphic rocks. Garnet formation ages from a websterite enclave and gabbro were 660±48 Ma and 587±9 Ma respectively, and those from Stype granites were 598±4 Ma and 577±4 Ma. Monazites from metapelite and metaquartzite yielded lower intercept UPb ages of 629±3 Ma and 639±5 Ma, respectively. U-Pb titanite age from calcsilicate gneiss was 580±5 Ma. These indicate peak metamorphism to have occurred between 640 and 630 Ma, followed by near isobaric cooling to ~580 Ma. Though an origin as an exotic terrane from the East African Orogen cannot be discounted, from the present data there is a greater likelihood that Mesoproterozoic microplate collision between Maud orogen and a northerly Lurio-Nampula block resulted in formation of these granulite belt(s).

  5. U-Pb, 39Ar/40Ar geochronology of the metamorphosed volcanic rocks of the Bainaimiao Group in central Inner Mongolia and its implications for ore genesis and geodynamic setting

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

    The greenschist facies volcano-sedimentary sequence of the Bainaimiao Group in central Inner Mongolia hosts the Bainaimiao Cu-Mo-Au deposit and the Bainaimiao lode gold deposit. But the ore classification and genetic process of the Bainaimiao Cu-Mo-Au deposit is still disputed. In this study we have selected the interbedded metamorphosed volcanic rocks of the Bainaimiao Group for LA-ICP-MS zircon U-Pb analysis. 17 analyses form a tight cluster on the concordia and yield a weighted mean 206Pb/238U age of 465 ± 1 Ma (95% confidence level, MSWD = 0.95, n = 17), which represents the best estimate of the crystallization age of the volcanic rocks of the Bainaimiao Group. Biotite from the greenschist of the Bainaimiao Group yielded a well-defined plateau with an age of 429.2 ± 4.1 Ma. The inverse isochron age is 429.1 ± 4.2 Ma with an elevated (40Ar/36Ar)i ratio of 299.9 ± 22.7, which represents the time of regional greenschist facies metamorphism. Previous studies showed that the Re-Os isochron age of the molybdenite from the Bainaimiao Cu-Mo-Au deposit is 445.0 ± 3.4 Ma and the mineralized granodiorite porphyry yielded a weighted mean 206Pb/238U age of 445 ± 6 Ma. These data indicate that the Bainaimiao volcanic rocks were formed at about 465 Ma and the porphyry Cu-Mo-Au mineralization took place at about 445 Ma. Volcanic rock emplacement is 20 Ma older than the Cu-Mo-Au mineralization indicates it is a porphyry deposit rather than VMS deposit. The dynamic setting for the porphyry mineralization is the Paleo-Asian Oceanic plate subduction along the northern margin of the North China Craton in early Paleozoic. Subsequently, the collision between the Bainaimiao arc and the North China Craton led to regional metamorphism and deformation at about 430 Ma and the old porphyry system may have been overprinted during this metamorphic process.

  6. First finding of microdiamond, coesite and other UHP phases in felsic granulites in the Moldanubian Zone: Implications for deep subduction and a revised geodynamic model for Variscan Orogeny in the Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Perraki, Maria; Faryad, Shah Wali

    2014-08-01

    Heavy mineral fractions and polished thin sections from felsic granulites from the Moldanubian Zone of the Bohemian Massif were thoroughly studied by means of Raman microspectroscopy combined with optical microscopy and scanning electron microscopy. The following phases were identified, among others, as inclusions in robust minerals such as garnet and zircon: Diamond, characterized by an intense narrow peak at 1332 cm- 1, was found in two inclusions in zircon. They have a size of ~ 5 ?m. Coesite, identified by its very characteristic peak at ~ 520 cm- 1, was found in an inclusion in garnet together with quartz. Coesite has been almost completely transformed into quartz; only minor coesite nano-domains remain. Kumdykolite, the orthorhombic polymorph of NaAlSi3O8, characterized by strong peaks at 220, 456 and 492 cm- 1, occurs either as single crystals or as a part of multiphase inclusions in garnet and in zircon along with other mineral phases such as K-feldspar, phengite, rutile. Moissanite, SiC, exhibiting the characteristic Raman bands at ~ 767, 788 and 969 cm- 1, occurs as inclusions in garnet. Diamond and coesite are considered to have formed at the peak ultrahigh-pressure metamorphic (UHPM) conditions. Kumdykolite has been proposed to be a metastable phase formed during rapid cooling from high temperature. Moissanite points to extremely reduced conditions during subduction to great depths. The finding of UHP phases in felsic granulites in the Moldanubian Zone is clear evidence for subduction of crustal materials to mantle depths. The garnet hosting the UHP phase inclusions usually preserves prograde compositional zoning; this in combination with the UHPM mineral inclusions suggests that the felsic material should have passed UHP metamorphism at a low-temperature gradient. Isothermal decompression (the commonly accepted model) at temperatures of 850-950 °C would have substantially modified and homogenized the garnet composition eliminating any compositional zoning. Therefore, the UHPM felsic rocks could have experienced only a short-term granulite facies metamorphism after they were exhumed to crustal levels.

  7. Experimental determination of salt partition coefficients between aqueous fluids, ice VI and ice VII: implication for the composition of the deep ocean and the geodynamics of large icy moons and water rich planets

    NASA Astrophysics Data System (ADS)

    Journaux, Baptiste; Daniel, Isabelle; Cardon, Hervé; Petitgirard, Sylvain; Perrillat, Jean-Philippe; Caracas, Razvan; Mezouar, Mohamed

    2015-04-01

    The potential habitability of extraterrestrial large aqueous reservoir in icy moons and exoplanets requires an input of nutrients and chemicals that may come from the rocky part of planetary body. Because of the presence of high pressure (HP) water ices (VI, VII, etc.) between the liquid ocean and the silicates, such interactions are considered to be limited in large icy moons, like Ganymede and Titan, and water rich exoplanets. In the case of salty-rich oceans, recent experimental and modeling works have shown that aqueous fluids can be stable at higher pressures [1, 2]. This can ultimately allow direct interaction with the rocky core of icy moons. This effect is nevertheless limited and for larger bodies such as water rich exoplanets with much higher pressures in their hydrosphere, HP ice should be present between the rocky core and a putative ocean. Salts are highly incompatible with low pressure ice Ih, but recent experimental work has shown that alkali metal and halogen salts are moderately incompatible with ice VII, that can incorporate up to several mol/kg of salts [3, 4, 5]. As far as we know, no similar study has been done on ice VI, a HP ice phase expected inside large icy moons. We present here the first experimental data on the partition coefficient of RbI salt between aqueous fluids, ice VI and ice VII using in-situ synchrotron X-Ray single crystal diffraction and X-Ray fluorescence mapping (ESRF - ID-27 beam line [6]). Our experiment enable us to observe a density inversion between ice VI and the salty fluid, and to measure the values of salt partition coefficients between the aqueous fluid and ice VI (strongly incompatible) and ice VII (moderately incompatible). Using the volumes determined with X-Ray diffraction, we were able to measure the density of salty ice VI and ice VII and determine that salty ice VI is lighter than pure H2O ice VI. These results are very relevant for the study of water rich planetary bodies interior because the partition coefficient will enable the computation of the chemical evolution in the deep ocean during the cooling of the hydrosphere. These results are also very important for the high pressure ice mantle dynamics as they show the great effects of dissolved salt on the ice phases densities and therefore the potential role of convecting ice to feed the overlaying ocean with life-sustaining chemicals. References [1] Journaux B, Daniel I, Caracas R, Montagnac G, Cardon H. Icarus. 2013; 226:35-63. [2] Vance S, Brown JM. Geochimica Cosmochimica Acta. 2013; 110:176-89. [3] Frank M, Runge C, Scott H, Maglio S, Olson J, Prakapenka V, et al. Physics of the Earth and Planetary Interiors. 2006; 155 :152-62. [4] Frank MR, Aarestad E, Scott HP, Prakapenka VB. Physics of the Earth and Planetary Interiors. 2013; 215:12-20. [5] Klotz S, Bove L, Strässle T, Hansen T, Saitta A. Nat Mater. 2009; 8:405-9. [6] Mezouar, M. et al. Journal of Synchrotron Radiation. 2005; 12, 659-664.

  8. Petrology of the Miocene igneous rocks in the Altar region, main Cordillera of San Juan, Argentina. A geodynamic model within the context of the Andean flat-slab segment and metallogenesis

    NASA Astrophysics Data System (ADS)

    Maydagán, Laura; Franchini, Marta; Chiaradia, Massimo; Pons, Josefina; Impiccini, Agnes; Toohey, Jeff; Rey, Roger

    2011-07-01

    The Altar porphyry Cu-(Au-Mo) deposit (31° 29' S, 70° 28' W) is located in the Andean Main Cordillera of San Juan Province (Argentina), in the southern portion of the flat-slab segment (28-33°S), 25 km north of the world-class porphyry Cu-Mo deposits of Los Pelambres and El Pachón. Igneous rocks in the area have been grouped into the Early Miocene Lower Volcanic Complex -composed of intercalations of lava flows and thin volcaniclastic units that grade upwards to a thick massive tuff- and the Middle-Late Miocene Upper Subvolcanic Suite that consists of a series of porphyritic stocks and dikes and magmatic and hydrothermal breccias. The Lower Volcanic Complex represents an Early Miocene arc (20.8 Ma ± 0.3 Ma; U-Pb age) erupted over a steep subduction zone. Their magmas equilibrated with an assemblage consisting of plagioclase- and pyroxene-dominated mineral residues, and experienced fractional crystallization and crustal contamination procesess. Their radiogenic signatures are interpreted to indicate conditions of relatively thickened continental crust in Altar during the Early Miocene, compared to the south and west. The Upper Subvolcanic Suite represents the development of a Middle-Late Miocene arc (11.75 ± 0.24 Ma, 10.35 ± 0.32 Ma; U-Pb ages) emplaced over a shallow subduction zone. A magmatic gap in Altar area betwen the Lower Volcanic Complex and Upper Subvolcanic Suite correlates with documented higher rates of compression in this period, that may have favored the storage of the USS magmas in cameras within the crust. Magmas of the Upper Subvolcanic Suite require a hornblende-bearing residual mineral assemblage that is interpreted to reflect their higher water contents. The relatively uniform radiogenic isotope compositions of the Upper Subvolcanic Suite magmas suggest a homogeneously mixed crust-mantle contribution in the source region. They have similar REE signatures as other fertile intrusives of the flat-slab. The differences observed in their isotopic signatures reflect an increase in the amount of crustal components incorporated into magmas from south (El Teniente) to north (El Indio) which correlate with an increase of crustal thickness. U-Pb ages of Altar rocks confirm a temporal connection between the ridge arrival and the magmatism associated with mineralization in this zone of the flat-slab segment. We argue that since the Middle-Late Miocene, mantle and lower crust may have been hydratated by fluids from the slab and from the Juan Fernández Ridge at the latitude of Altar, which favored the generation of the Middle-Late Miocene magmas. We also suggest that at this latitude the collision ridge-trench at ˜11 Ma and the subduction of the Juan Fernández Ridge beneath Altar region at ˜11-10 Ma may have promoted changes in the tectonic stress regime, allowing the USS magmas to rise to shallower levels in the crust. This may explain the location of a cluster of contemporaneous giant porphyry Cu-Mo deposits including El Pachón-Los Pelambres, the Altar Cu (Mo-Au) deposit, and other nearby recently discovered Cu prospects such as Piuquenes, La Coipa, Rincones de Araya and Los Azules.

  9. Patterns of seismic anisotropy and mantle flow around convergent margins: predictions from 3D geodynamic modelling, comparison with observations and implications for the interpretation of seismic tomographies (Arne Richter Award Lecture for OYS)

    NASA Astrophysics Data System (ADS)

    Faccenda, Manuele

    2015-04-01

    Seismic anisotropy generated by strain-induced lattice/crystal preferred orientation (LPO/CPO) of intrinsically anisotropic minerals is commonly used to study flow in the mantle and its relations with plate motions. In this contribution, I will present results from 3D petrological-thermomechanical models of subduction/collisional settings, where the strain-induced LPO of polycrystalline aggregates of the upper and mid mantle is computed. Overall, medium to strong fabrics develop in the upper and uppermost lower mantle around the convergent margin, with distinctive patterns that are related to the margin dynamic history. The full elastic tensors obtained from each polycrystalline aggregate is then used to carry out several seismological synthetic experiments. In particular: 1) seismogram synthetics of teleseismic waves propagating sub-vertically were computed to estimate SKS splitting patterns that are mostly controlled by the anisotropy in the upper mantle. Results are compared with observations from different subduction and collisional settings, yielding a strong constrain on the recent dynamics of these convergent margins. 2) synthetic seismic tomographies were produced using realistic ray path distributions around convergent margins, showing how the interpretation of seismic anomalies could potentially be biased by the presence of seismic anisotropy and a non-uniform seismic ray coverage.

  10. [The Journal of Geology, 2001, volume 109, p. 755770] 2001 by The University of Chicago. All rights reserved. 0022-1376/2001/10906-0005$01.00 Geodynamic Significance of the Kontum Massif in Central Vietnam

    E-print Network

    Nagy-Shadman, Elizabeth A.

    in Central Vietnam: Composite 40 Ar/39 Ar and U-Pb Ages from Paleozoic to Triassic Elizabeth A. Nagy,1 Henri-central Vietnam has long been classified as lower continental crust of Precambrian (Archean) age. U-Pb zircon of the Kontum massif in central Vietnam have traditionally been interpreted as an uplifted Precambrian (Archean

  11. Contribution to a geodynamic reconstruction of the Anti-Atlas (Morocco) during Pan-African times with the emphasis on inversion tectonics and metallogenic activity at the Precambrian–Cambrian transition

    Microsoft Academic Search

    Dominique Gasquet; Gilles Levresse; Alain Cheilletz; Moulay Rachid Azizi-Samir; Abdellah Mouttaqi

    2005-01-01

    New geochronological analyses (U–Pb SIMS zircon ages) have yielded ages of 552±5Ma for the Bou Madine rhyolitic dome (Ougnat, eastern Anti-Atlas), 543±9Ma for the Tachkakacht rhyolitic dyke (Saghro–Imiter, eastern Anti-Atlas), and 531±5Ma for the Aghbar trachytic sill (Bou Azzer, central Anti-Atlas). Inherited zircon cores from the Aghbar trachytic sill and from the Bou Madine rhyolitic dome have been shown to

  12. SHRIMP U–Pb and Sm–Nd data for the Araxá Group and associated magmatic rocks: constraints for the age of sedimentation and geodynamic context of the southern Bras??lia Belt, central Brazil

    Microsoft Academic Search

    Danielle Piuzana; Márcio Martins Pimentel; Reinhardt A Fuck; Richard Armstrong

    2003-01-01

    SHRIMP U–Pb and Sm–Nd isotopic data for Araxá Group micaschist, associated amphibolite and intrusive tonalite were used to estimate the age and tectonic setting of deposition of the original detrital sediments, in the southern part of the Neoproterozoic Bras??lia Fold Belt. One amphibolite sample from a layer interleaved tectonically within the metasedimentary rocks has the U–Pb zircon age of 838±20Ma.

  13. Flexure of the lithosphere and the geodynamical evolution of non-cylindrical rifted passive margins: Results from a numerical model incorporating variable elastic thickness, surface processes and 3D thermal subsidence

    NASA Astrophysics Data System (ADS)

    Braun, Jean; Deschamps, François; Rouby, Delphine; Dauteuil, Olivier

    2013-09-01

    We present a new numerical model to calculate the surface deflection of a two-dimensional, yet variable thickness, thin elastic plate. The model is based on a multi-grid, finite difference solution of the fourth-order differential equation that incorporates the terms arising from the non-uniform thickness assumption. The model has been developed to calculate the flexural response of the continental lithosphere subjected to an arbitrary, instantaneous stretching. The flexural model is coupled to (a) a finite element, three dimensional thermal model incorporating the conduction, advection and production terms that allows the computation of the thermal subsidence resulting from the stretching-induced perturbation of the isotherms, assuming that the effective elastic thickness is controlled by the depth to a given isotherm; and (b) a finite difference surface process model that assumes that transport is linearly proportional to slope leading to a second-order, diffusion-type partial differential equation. The model also incorporates the effect of sediment compaction. We present a series of simple benchmarks that demonstrate the accuracy of the model. We also present results of simple 2D and 3D stretching experiments highlighting the importance of 3D flexural effects and the assumed variable elastic thickness on the development of a passive margin and its thermal evolution. Finally, we perform a numerical experiment based on a stretching geometry derived from the present-day geometry of the Western AfricaTransform Margin to predict sediment accumulation patterns and a stratigraphic architecture which we can compare to observations.

  14. HeAr isotopic system of fluid inclusions in pyrite from the molybdenum deposits in south margin of North China Block and its trace to metallogenetic and geodynamic background

    Microsoft Academic Search

    LaiMin Zhu; GuoWei Zhang; Bo Guo; Ben Lee

    2009-01-01

    The helium and argon isotopic compositions of the ore-forming fluids from the molybdenum deposits such as Jinduicheng, Donggou,\\u000a Shijiawan, and Sandaozhuang, which are located in the East Qinling molybdenum belt in south margin of North China Block (SMCNB),\\u000a are reported in this paper. The origin and the evolution of the ore-forming fluids and their coupled-relationships with the\\u000a intra-continental collision and

  15. Geochemistry, zircon U-Pb and Lu-Hf isotopes of an Early Cretaceous intrusive suite in northeastern Jiangxi Province, South China Block: Implications for petrogenesis, crust/mantle interactions and geodynamic processes

    NASA Astrophysics Data System (ADS)

    Deng, Zhengbin; Liu, Shuwen; Zhang, Lifei; Wang, Zongqi; Wang, Wei; Yang, Pengtao; Luo, Ping; Guo, Boran

    2014-07-01

    The Early Cretaceous Tieshan intrusive suite, in northeastern Jiangxi Province along the northern margin of the Eastern Cathaysia Block, is composed of diabase porphyrites, monzodiorites, syenite porphyries, quartz monzonites, monzogranites and granite porphyries. LA-ICPMS zircon U-Pb isotopic analyses reveal that this intrusive complex was emplaced between 142 Ma and 117 Ma. The ~ 135 Ma diabase porphyrites, monzodiorites, and syenite porphyries are characterized by low to moderate SiO2 and MgO contents, with high K2O and total alkaline contents. These rocks exhibit slightly to strongly fractionated REE patterns and upper crust-like multi-element patterns with depletions of Nb, Ta and Ti, and show strongly negative ?Hf (t) values of - 9.0 to - 11.8. All these patterns are identical to those of the Caiyuan syenites, Huangtuling gabbros in the east, and Lengshuikeng trachyandesites and quartz syenites in the west. These geochemical and zircon Lu-Hf isotopic features indicate that their magmatic precursors were generated by 0.2%-2% partial melting of a phlogopite-bearing enriched subcontinental lithospheric mantle source that was metasomatized by sediments. The ~ 117 Ma quartz monzonite has slightly higher ?Hf (t) values (- 5.6 to - 8.7) like those of the Honggong syenites, indicating an interaction between the asthenosphere and the lithosphere. The ~ 142-134 Ma granite porphyries and monzogranites are characterized by high SiO2 levels but low concentrations of refractory elements, and show enrichment of LREEs and LILEs, with variable negative anomalies of Nb, Ta, Ti, Sr, P and Ba in multi-element diagrams normalized by primitive mantle. The monzogranite exhibits strongly negative ?Hf (t) values of - 10.5 to - 13.3 and TDM2 (Hf) values of 1849-2023 Ma, and the granite porphyries display relatively wide ?Hf (t) values of - 7.2 to - 13.4 and TDM2 (Hf) values of 1645-2043 Ma, indicating that these monzogranites and granite porphyries are highly fractionated granites derived from partial melting of the Paleoproterozoic basement with involvement of enriched mantle-derived magmas or juvenile components, and the primary magma experienced fractionation of K-feldspar, plagioclase, monazite, allanite and zircon during magma ascent and emplacement. The Tieshan intrusive suite, together with the Caiyuan syenites, Huangtuling gabbros, and Lengshuikeng trachyandesites and quartz syenites, forms a highly enriched shoshonitic rock belt in the northeastern margin of the Cathaysia Block. Integrating with previously published data, we propose that the subducted Paleo-Pacific plate extended into the central South China Block in the Middle Jurassic, and experienced slab rollback during the Early Cretaceous.

  16. Geodynamic setting of volcano-plutonic rocks in so-called ``paleo-accretionary prisms'': Fore-arc activity or post-collisional magmatism? The Shimanto belt as a case study

    NASA Astrophysics Data System (ADS)

    Stein, G.; Charvet, J.; Lapierre, H.; Fabbri, O.

    1994-10-01

    The Cretaceous-Tertiary Shimanto belt of southwestern Japan is usually considered to be a simple accretionary prism (Taira et al., 1982; Ogawa, 1985), whereas, based on structural and sedimentological evidences, Charvet and Fabbri (1987) and Charvet et al. (1990) proposed an alternative model in which a collision with an unknown microblock followed the formation of the accretionary prism, and induced the Early Miocene main tectonism. One characteristic of the Shimanto belt is the occurrence of well developed magmatic bodies of Middle Miocene age (14±1 Ma) which can be used for testing the model. They show numerous peculiarities. (1) They consist predominantly of acidic volcano-plutonic complexes. Mafic sills or lavas are present in a lesser amount. (2) With respect to the supposed position of the subduction trench during Miocene time and to the northern location of the Setouchi volcanics, considered as a volcanic front ca 13 Ma, this magmatism is a near-trench magmatism. (3) Various tectono-magmatic affinities are present. The basaltic sills or lavas have mostly T-to E-MORB type affinities. An alkaline complex is present at Ashizuri cape. The most abundant magmatism consists of calc-alkaline volcano-plutonic bodies, typically peraluminous in the southern part of Shimanto and metaluminous near the northern border of the belt. (4) Metamorphic enclaves inter alia are often included in the calc-alkaline complexes. Their highest P- T conditions range between 0.7-0.8 GPa and 630-860°C. A simple subduction model is not able to explain all these features. The first necessity is to find a mechanism which develops a high thermal anomaly allowing the formation of magmas close to the trench. According to thermal modelling, the subduction of an oceanic plate, even young, does not provide enough heat. Secondly, in well known mature accretionary prisms (e.g. the Barbados one), the thickest part of the complex does not exceed 15 km. In such conditions, it is difficult to obtain pressures ranging from 0.7 to 0.8 GPa. This is much more difficult if we consider that some granitic rocks were formed in the youngest part of the so-called prism, in the thinnest portion. Finally, a simple subduction model does not explain the various magmatic affinities. Geochemical data show that the magmatic source of the Ashizuri alkaline complex is likely to be an enriched mantle comparable to OIB sources. On the other hand, the calc-alkaline rocks may have been derived by mixing between mantellic components and crustal ones, or in some cases by pure anatectic processes. The upwelling of a hot asthenospheric mantle, from which the Ashizuri suite could have been derived, may represent a heating source strong enough to make crustal materials melt. The proposed collision model could explain (1) the heating source, (2) the various magmatic affinities and also (3) the 0.7-0.8 GPa pressure invoking crustal thickening induced by the collisional event.

  17. C O N T E N T S H e r n a n i S p i r i d o n o v Geodynamics of Bulgaria (part II) . . . . . . . . . . . . . . . . . .

    E-print Network

    Borissova, Daniela

    . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ve l i m i r a S t o y a n o v a ­ Applicability of the DRASTIC type index-methods for vulnerability assessment of groundwater arsenic contamination . . . . . . . . . . . . . . . Z o y a M e t e e v a, A n t o

  18. Geochemistry and geochronology of mafic rocks from the Vespor suite in the Juruena arc, Roosevelt-Juruena terrain, Brazil: Implications for Proterozoic crustal growth and geodynamic setting of the SW Amazonian craton

    NASA Astrophysics Data System (ADS)

    Scandolara, Jaime E.; Ribeiro, Pedro S. E.; Frasca, Antônio A. S.; Fuck, Reinhardt A.; Rodrigues, Joseneusa B.

    2014-08-01

    This study presents new geochemical data on rocks from the Vespor suite, an important mafic unit from the Juruena arc, Roosevelt-Juruena terrain, SW Amazonian craton, northwest Mato Grosso, Brazil, attempting to define their tectonic setting and type of mantle source. The Juruena arc may be part of a magmatic belt (Jamari and Juruena arcs) at the southwestern Amazonian craton during assembly of the Columbia supercontinent. The investigated rocks represent a Paleoproterozoic subduction-related mafic suite of sigmoidal bodies, composed mainly of gabbro, norite, gabbronorite and diorite, that underwent amphibolite facies metamorphism. Here we present also preliminary petrology aspects and zircon U-Pb geochronology. Geochemical character and variation trends of major and trace elements as well as selected trace element ratios suggest that Vespor suite rocks have a tholeiitic lineage of arc affinity controlled by fractional crystallization with a prominent iron enrichment trend. Gabbros, norites and gabbronorites are characterized by enrichment of LILE and weakly to moderately differentiated HFSE patterns, suggesting their deviation from an enriched heterogeneous lithospheric mantle source. Vespor suite rocks are characterized by depletion of Nb-Ta, P and Ti, with flat distribution of HFSE, markedly large variations in most of the LILE, positive anomalies displayed by Ba, K, Th, Sr, Pb and weak negative anomalies of Hf-Zr. These features reflect limited degrees of crustal contamination associated with a subduction-related magma process where the mantle wedge was chemically modified. In addition, the enrichment in LILE and Pb, low values of the ratios (Lan/Smn - 0.83 to 4.58) and (Nbn/Lan - 0.04 to 0.45), but high Th/Yb ratios, gently to moderately sloping REE profiles (La/Ybn = 2.53-7.37), negative anomalies in HFSE (Ta, Zr, Hf, and Ti), and positive anomalies in LILE (Th, Ba, Sr), suggest derivation from a metasomatized lithospheric mantle source above a subduction zone with weak crustal contamination. Both the composition of the mantle source and the degree of partial melting that produced the parental magmas of these rocks, determined by using REE abundance and ratios, indicate that gabbroic/dioritic melts were generated at different degrees of melting of the source: about 5-20% partial melting of a garnet-spinel lherzolite, around 1-10% partial melting of spinel lherzolite source, and approximately 1-5% partial melting of intermediate source composition, and crystallizing between 1.773 and 1.764 Ma.

  19. Structural Evolution From a Strike-Slip Transform Fault to a Non-transform Discontinuity: Examples From 57°-58°30'E on the SW Indian Ridge and Geodynamic Implications

    Microsoft Academic Search

    A. Hosford; J. Lin

    2002-01-01

    Observations of various oceanic spreading centers demonstrate that the difference in crustal age across a ridge offset, and the associated contrast in mechanical strength of the lithosphere, influence whether the ridge-axis discontinuity is a transform fault or a non-transform discontinuity (NTD). At the Mid-Atlantic Ridge, for example, discontinuities with age offsets greater than 2-3 Myr correspond to stable transforms while

  20. Authors' address: Geochemistry and Geodynamics Research Centre-Universit du Qubec Montral-McGill University (GEOTOP-UQAM-McGill). Universit du Qubec Montral, C. P. 8888 Suc. "Centre Ville", Montral, QC, Canada, H2X 3Y7

    E-print Network

    Long, Bernard

    Effects of top predators transmitted through the food webs in terrestrial and aquatic environments have been widely studied, generating a large amount of field and theoretical work under the designation

  1. Lithochemistry of the Paleoisland-arc complexes in the orogenic belts of the Russian Far East

    Microsoft Academic Search

    A. I. Malinovsky; M. I. Tuchkova

    2010-01-01

    New chemical data on terrigenous rocks from the Russian Far East paleobasins different in age and geodynamic style were compared\\u000a with similar data on the recent and old sediments accumulated in well-known geodynamic settings. The generalization and geodynamic\\u000a interpretation of the original results revealed the island-arc nature of the studied objects and demonstrated the possibility\\u000a of using the lithochemical approach,

  2. Journals and books

    NASA Astrophysics Data System (ADS)

    During the 1980-1982 biennium the publications program was marked by an enhanced spirit of cooperation with other organizations. Several joint ventures that capitalized on the strengths of both parties were undertaken.The Geodynamics Series, which focuses on the interaction between geophysics and traditional geology, is published jointly with the Geological Society of America. This series was initiated to publish the final reports of the International Geodynamics Program and required close cooperation with the Inter-Union Commission on Geodynamics.

  3. Are there really superposed Mohos in the southwestern Alps? New seismic data from fan-profiling reflections

    Microsoft Academic Search

    F. Thouvenot; A. Paul; J. Fréchet; N. Béthoux; L. Jenatton; R. Guiguet

    2007-01-01

    The Moho preserves imprints of the regional geodynamic evolution of the lithosphere. As such, its detailed topography in divergence or convergence zones has a strong bearing on any geodynamic model. This is still more critical where 3-D effects are expected, as in the case of the Alpine chain which exhibits in its western part a short radius of curvature while

  4. RESEARCH PAPER Earth curvature effects on subduction morphology

    E-print Network

    Tackley, Paul J.

    , and we suggest a general approach for modeling combined mantle convection and plate tectonics. The first geodynamics Á Nazca plate Á Pacific plate Á Plate tectonics Á Subduction 1 Introduction Mantle geodynamics] of 0.25, implying that plate tectonics is dominated by the largest plates. When strong inner het

  5. GEOBULLETIN FEBrUary 7Th

    E-print Network

    Carlson, Anders

    @wisc.edu. ********************************************************** JOB OPENINGS: · Durham University (UK) seeks a highly motivated postdoctoral researcher with geodynamical/geochemical modelling experience to study early Earth geodynamics, petrology and geochemistry. · Postdoctoral Research Associate in Mineral Self-Assembly and Chemical Coupling · Postdoctoral Research

  6. Plate tectonic reconstructions with continuously closing plates$ Michael Gurnis a,n

    E-print Network

    Müller, Dietmar

    Plate tectonic reconstructions with continuously closing plates$ Michael Gurnis a,n , Mark Turner: Geodynamics Plate tectonics a b s t r a c t We present a new algorithm for modeling a self-consistent set, traditional global plate tectonic reconstructions have become inadequate for geodynamics. The CCP algorithm

  7. Gravitational mechanism of active life of the Earth, planets and satellites

    Microsoft Academic Search

    Yury Barkin

    2010-01-01

    From positions of geodynamic model of the forced gravitational swing, wobble and displacements of shells of a planet are studied and fundamental problems of geodynamics, geology, geophysics, planetary sciences are solved etc.: 1) The mechanism of cyclic variations of activity of natural processes in various time scales. 2) The power of endogenous activity of planetary natural processes on planets and

  8. Geochemical constraints on Carboniferous volcanic rocks of the Yili Block (Xinjiang, NW China): Implication for

    E-print Network

    Paris-Sud XI, Université de

    for understanding the Late Paleozoic geodynamic evolution of Central Asia. It is bounded to the north was followed by Permian­Mesozoic polyphase transcurrent faulting. Keywords: Geochemistry; Volcanic rocks

  9. Sediment budget of the Napo River, Amazon basin, Ecuador and Peru A., Laraque1

    E-print Network

    Paris-Sud XI, Université de

    transfer and geodynamic processes at the Andean Piedmont. Key Words : Amazon River basin, Sediment yield and Meade, 1983). Most of the sediment discharged (95%) to the Atlantic Ocean by the Amazon River comes from

  10. Topside Driven 3D Convection Model of the East African Rift System with Comparison to Observed Rift-Parallel Surface Motions

    NASA Astrophysics Data System (ADS)

    Stamps, D. S.; Bangerth, W.; Hager, B.

    2015-05-01

    We test the hypothesis of basal shear driven tectonics where rift-parallel surface motions are observed in an active rift of the East African Rift System using a new 3D regional geodynamic model based on the code ASPECT.

  11. The telecommunications and data acquisition progress report 42-64

    NASA Technical Reports Server (NTRS)

    Renzetti, N. A. (editor)

    1981-01-01

    Progress in the development and operations of the Deep Space Network is reported. Developments in Earth-based radio technology as applied to geodynamics, astrophysics, and the radio search for extraterrestrial intelligence are included.

  12. The telecommunications and data acquisition report

    NASA Technical Reports Server (NTRS)

    1980-01-01

    Progress in the development and operations of the Deep Space Network along with developments in Earth-based radio technology as applied to geodynamics, astrophysics, and the search for extraterrestrial intelligence are reported.

  13. Vertical near surface conductivity-anomaly detected at the dead-sea-transform

    Microsoft Academic Search

    Olaf Koch; Stefan L. Helwig; Naser Meqbel

    SUMMARY Within the Dead-Sea-Rift-Transec-(DESERT)-project seismic, seismological, electromagnetic, gravity, magnetic, geodynamic and geological studies were done at the Dead Sea Rift\\/Dead Sea Transform (DST) to give answers to the question: \\

  14. LOTEM and SHOTEM measurements at the Dead-Sea-Transform within the DESERT-project

    Microsoft Academic Search

    O. Koch; C. Scholl; S. L. Helwig; R. Martin; N. Meqbel

    2004-01-01

    Within the Dead-Sea-Rift-Transec-(DESERT)-project seismic, seismological, electromagnetic, gravity, magnetic, geodynamic and geological studies were done at the Dead Sea Rift\\/Dead Sea Transform (DST) to give answers to the questions: \\

  15. NASA plan for international crustal dynamics studies

    NASA Technical Reports Server (NTRS)

    1979-01-01

    The international activities being planned as part of the NASA geodynamics program are described. Methods of studying the Earth's crustal movements and deformation characteristics are discussed. The significance of the eventual formalations of earthquake predictions methods is also discussed.

  16. ARTICLE IN PRESS UNCORRECTEDPROOF

    E-print Network

    Socquet, Anne

    / Rhakine range / Kampetlet schists / mica-chlorite thermobarometry / Himalayan ophiolite Résumé ­ L Kampetlet / thermobarometrie mica-chlorite / ophiolite himalayenne Abridged version 1. Introduction The Indo schists) as- sociated with ophiolite, suggests that the range underwent a more complex geodynamic

  17. New Insight into Mantle Rheology from Laboratory Experiments: Grain-Boundary Sliding and Viscous Anisotropy

    NASA Astrophysics Data System (ADS)

    Hansen, L. N.

    2015-05-01

    Strain-dependent rheologies are rarely incorporated into geodynamic simulations. Recent laboratory results yield strain-dependent models for grain-boundary sliding and viscous anisotropy, both of which lead to large-scale strain localization.

  18. Effects of Stellar Flux on Tidally Locked Terrestrial Planets: Degree-1 Mantle Convection and Local Magma Ponds

    E-print Network

    Gelman, S. E.

    We model the geodynamical evolution of super-Earth exoplanets in synchronous rotation about their star. While neglecting the effects of a potential atmosphere, we explore the parameter spaces of both the Rayleigh number ...

  19. Petrological and rheological controls on volcanism to terrestrial planets

    E-print Network

    Elkins Tanton, Linda Tarbox, 1965-

    2002-01-01

    Through experimental petrology and geodynamic modeling, processes of melting under thick lithospheres on the Earth and the moon are investigated. Phase equilibrium experiments were carried out on Apollo 14B and 15C picritic ...

  20. Balloon-Borne Electromagnetic Measurement of the Lithospheric Thickness of Venus

    NASA Astrophysics Data System (ADS)

    Grimm, R. E.

    2015-05-01

    The lithosphere controls the planetary geodynamic style. EM energy from lightning can be sensed globally and responds to the temperature structure of the lithosphere. This measurement can be performed from any altitude below the ionosphere.

  1. The Tectonics of Small Worlds

    NASA Astrophysics Data System (ADS)

    Buczkowski, D. L.; Wyrick, D. Y.

    2015-05-01

    Understanding small world tectonics may help us predict small rocky e