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1

Geodynamics, Second Edition  

NASA Astrophysics Data System (ADS)

Turcotte and Schubert's first edition of Geodynamics has become the premier textbook on applications of continuum physics to geologic problems. After 20 years of widespread use by students, educators, and researchers, the second edition of Geodynamics is a welcome revision. All individuals working in the solid Earth sciences should own this textbook.Geodynamics provides practical insight into the governing physics of many processes in geology and geophysics. The general approach is to emphasize geological phenomena, derive the governing equations, and then expand to a variety of applications. Most of the applications are presented in one-spatial dimension, and this provides an effective starting point for conveying the basic theory Derivations in multi-dimensions are limited, however, largely because tensor and index notations are not used.

Ito, Garrett

2

NASA: Geodynamics Branch  

NSDL National Science Digital Library

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

3

Geodynamic basin classification  

SciTech Connect

Four criteria (continental margin type, basin position within a plate, crustal type, geodynamic models and processes of basin formation) are used to classify sedimentary basins. Within plate interiors, cratonic margin basins and interior cratonic basins are distinguished by position on a tectonic plate. In passive margins, rift basins, aulacogens, and flexure basins are distinguished by orientation with respect to margins (rifts parallel and aulacogens normal to margins) and geodynamic process (rifts and aulacogens form by stretching, flexure basins by elastic or viscoelastic flexure). Basins associated with active continental margins are distinguished by position with respect to margin, crustal type, and stress regimen. Trench-slope basins involve compressional-extensional regimens, whereas trench basins, forearc basins and retroarc basins form in compressional regimes (retroarc basins on continental crust; forearc and trench basins occupy different positions on margin boundaries). Extensional intra-arc basins form on continental crust whereas backarc basins form by rifting oceanic crust and rapid thermal subsidence. Both pull-apart and transform basins form in transform margins by rifting and thermal subsidence with different translational stress regimens. In collision margins, foreland basins occur within continental plates, and superposed (or collage) basins occur along suture zones. Polyhistory basins include successor basins involving changing tectonic styles, and resurgent basins involving repeated tectonic styles. Many mapped basins show polyhistory. Thus the cratonic Illinois basin evolved through stages of a rift basin, followed by thermal subsidence akin to passive margins, followed by viscoelastic basin formation akin to a foreland basin.

Klein, G.

1987-05-01

4

Seismological Constraints on Geodynamics  

NASA Astrophysics Data System (ADS)

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

Lomnitz, C.

2004-12-01

5

From Geodynamics to Simplicity  

NASA Astrophysics Data System (ADS)

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

Anderson, D. L.

2002-12-01

6

Exochemical Geodynamics and Potamochemistry  

NASA Astrophysics Data System (ADS)

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

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

2001-05-01

7

GLOBAL DISASTERS: Geodynamics and Society  

NASA Astrophysics Data System (ADS)

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

Vikulina, Marina; Vikulin, Alexander; Semenets, Nikolai

2013-04-01

8

Multiphase geodynamical modelling using Aspect  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

9

Information Technology Developments for Geodynamics  

NASA Astrophysics Data System (ADS)

Some recent research at UNAVCO and the University of Colorado has been focused on Rocky Mountain tectonics, and Information Technology (IT) in the areas of data visualization and distributed data serving. At UNAVCO, we are participating in the geodynamics work in the Rocky Mountain Testbed of the GEON NSF funded (IT) Research project (www.geongrid.org). As part of this work, a variety of seismic tomography models, GPS velocity vector data, strain rate models and other data have been recompiled into a standard format. These data and models are being incorporated into our OPeNDAP server and the Integrated Data Viewer (IDV). OPeNDAP servers are platform independent, self-describing distributed data servers allowing easy access to a wide audience. The IDV is a freely distributed visualization and analysis tool developed by UCAR that has several exciting capabilities such as online collaboration, and a variety of 1-d, 2-d and 3-d viewing options. Necessary solid earth viewing capabilities (earthquakes, focal mechanisms, faults, etc.) are currently being added to the IDV. Both our OPeNDAP server and visualization tool are being integrated into the GEON portal, a website for data searching, analysis, and visualization. Designing and implementing such systems now allows us to be more prepared for the volumes of data anticipated from various EarthScope projects. As part of the scientific research for GEON, we have also begun investigations of Colorado seismicity. The 1992 Rocky Mountain Front IRIS/PASSCAL seismic experiment recorded many local earthquakes. We have begun to locate these events and are working to create focal mechanisms and calculations of stress drop for this region. These will aid in improving seismic hazard and risk assessments for the rapidly growing Rocky Mountain population. New IT capabilities will help augment the quality of this work through sharing the data with a larger audience, providing a means to view and analyze integrated data, and quickly providing a computationally intensive baseline by which results can be checked.

Bensen, G. D.; Meertens, C. M.; Sheehan, A. F.

2004-12-01

10

Geodynamics - Tracking satellites to monitor global change  

SciTech Connect

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

Beutler, G.; Morgan, P.; Neilan, R.E. (Bern Univ., (Switzerland) Canberra Univ. (Australia) JPL, Pasadena, CA (United States))

1993-02-01

11

Time-domain parallelization for geodynamic modeling  

NASA Astrophysics Data System (ADS)

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

Samuel, H.

2012-04-01

12

Iranian Permanent GPS Network for Geodynamics (IPGN)  

NASA Astrophysics Data System (ADS)

Iran is one of the most tectonically active zone in Alpine-Himalayan seismic belt where has been shaken by largely destroying historical and instrumental earthquakes. Iran is located in the convergence zone between Arabia and Eurasia with a velocity of 22 mm/yr nearly to the North. The shortening between Arabian and Eurasian plates in Iran is mainly distributed on Zagros and Alborz belts. Despite the historical and scientific awareness of seismic hazard in Iran, unfortunately this country lacked a Continuous GPS network to study geodynamic and tectonic movements. Such geodetic measurement can play an important role to understand the tectonic deformation then to evaluate the seismic hazard on Iran. Since early 2005 National Cartographic Center of Iran (NCC) is establishing a continuous GPS network named Iranian Permanent GPS Network for Geodynamics (IPGN). Taking into account the number of provided GPS receivers, (108) we made a priority based on two factors of seismicity and population. At the first, in order to study general tectonic behavior in Iran 41 stations, globally distributed in whole of Iran, were been considered. Three other areas in the priority list were: Centeral Alborz, North-West of Iran and North-East of Iran. The rest of receivers, i.e. ~60, were considered for these areas as local networks. These four networks are daily processed and give us a continuous monitoring of any surface deformation. In this paper we try to present the results obtained from the network

Tavakoli, F.; Nankali, H. R.; Sedighi, M.; Djamour, Y.; Mosavi, Z.

2009-04-01

13

Geodynamical Evolution and Tectonic Framework of China  

NASA Astrophysics Data System (ADS)

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

LIU, Guangding

14

Persistent sand bars explained by geodynamic effects  

NASA Astrophysics Data System (ADS)

The persistent nature of intertidal sand bars has been the subject of much speculation concerning the hydrodynamic mechanisms involved, but its origin remains enigmatic. Here, we introduce salient geophysics in contrast to the physics of fluids above the sediments. The geophysical evidence combined with theoretical modeling and analysis demonstrates that the geodynamic processes ensuing during exposure periods have a profound impact, yielding the persistent nature of the intertidal bars under severe hydrodynamic forcing which would otherwise lead to unstable bar behavior. The feedback between the effects of the dynamics of suction, i.e. negative pore water pressure relative to atmospheric air pressure, and sediment transport and morphology is found to play a crucial role in the intertidal bar morphodynamics. Our finding may fundamentally alter the current perspective, leading to a new level of understanding, of sediment transport and bar behavior at waterfronts that are ubiquitous in rivers, estuaries, and coastal seas.

Sassa, Shinji; Watabe, Yoichi

2009-01-01

15

Linking mineral physics and geodynamic mantle models  

NASA Astrophysics Data System (ADS)

Recent geophysical studies of deep Earth structure have provided considerable insight into the physical state of our planet, including detailed seismic images of the Earth's interior and geodynamic models that simulate 3D spherical convection at high resolution. Despite this progress, many important features in mantle structure remain unexplained by geodynamics, as the chemical state and the mineralogical thermodynamics of the deep Earth are not sufficiently well understood and described in mantle convection models. In addition to mantle structure the, the mantle phase transitions could interact with upwelling and downwelling thermal structures in a complex way that cannot be easily modeled by parameterized buoyancy force, e.g. based only on the post-spinel transition in the Mg2SiO4 part of mantle mineralogy. Recent experimental and theoretical progress in Mineral Physics has made it possible to build self-consistent models of the (dry) phases of the Earth's mantle. The models are based exclusively on physical and thermodynamic measurements. Here we have constructed a new thermodynamic database for the mantle and have coupled the resulting density dynamically (through the buoyancy term) with mantle convection models. The database is build on a self-consistent Gibb's free energy minimisation of the system MgO-FeO-SiO2-CaO-Al2O3 that is appropriate for standard chemical models of the Earth's mantle (e.g. pyrolite) for relevant high pressure and temperature phases. We have linked the database with a high-resolution 2-D convection code (2DTERRA), dynamically coupling the thermodynamic model (density) with the conservation equations of mantle flow. The coupled model is run for different parameterisations of viscosity, initial temperature conditions, and varying the internal vs. external heating. We compare the resulting flow and temperature fields to convection cases based on the Boussinesq approximation or other standard descriptions of the equation of state in mantle dynamics to assess the influence of realistic mineralogical density on mantle convection.

Piazzoni, A.; Steinle-Neumann, G.; Bunge, H.

2006-12-01

16

Modern Geodynamic Model of the Arctic Ocean  

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

17

A petrological view of early Earth geodynamics  

NASA Astrophysics Data System (ADS)

Xenoliths of low T Archean cratonic mantle consist mostly of harzburgite and lherzolite with geochemical depletions that are characterisitc of igneous residues. Many authors have identified the complementary magmas as komatiites. This model is re-examined in light of work presented in Herzberg & O'Hara (2002) and found to be problematic. Munro-type alumina-undepleted komatiites from Alexo, Pyke Hill, and other locations often contain olivine phenocrysts with maximum Mg# \\cong 94. Residues of fractional melting would consist of pure dunite having Mg# = 97-98, but these are not observed. Residues of equilibrium melting would also be pure dunite with Mg# = 94, but these are also not observed. Olivines with Mg# = 94 are found in rare harzburgites, indicating that residues of alumina-undepleted komatiite have either been overprinted by subsequent magmatism or they have been geodynamically eroded. Alumina-undepleted komatiites can be successfully modeled with a primary magma containing 30% MgO produced by 0.5 mass fractions of equilibrium melting of depleted peridotite. A hot plume interpretation is consistent with both the petrology and helium isotopic compositions of alumina-undepleted komatiites. But what about cratonic mantle? The FeO and MgO contents of residues of fertile mantle peridotite formed by both equilibrium and fractional melting can be predicted and applied to xenoliths of cratonic mantle in most cases. Application to xenoliths from the Kaapvaal and Slave cratons is not possible owing to a second stage of Opx enrichment, but results can be applied to most xenoliths from Siberia, Tanzania, Somerset Island, and east Greenland as they contain less than 45% SiO_2. These xenoliths are very similar to residues produced by fractional melting. Pressures of initial melting were mostly 3 to 5 GPa, but can be as high 7 GPa. Pressures of final melting were highly variable and can be as low as 1 GPa. Potential temperatures (T_P) were typically 1450 to 1600oC and primary magmas contained 14 to 22% MgO, similar to Reykjanes MORB, Gorgona, Hawaii, and the early Icelandic plume in the model of Herzberg & O'Hara (2002). However, a few xenoliths record T_P as low as 1300oC. Two geodynamic interpretations follow: 1) Archean cratonic mantle formed as residues below ridges and hotspots similar to those of today, except the lithosphere was somewhat thinner in some cases, 2) Archean cratonic mantle formed as residues below hot ridges in most cases. Early Proterozoic sheeted dikes and eruptives from the Cape Smith Belt in Canada are consistent with the hot ridge interpretation. Ridge potential temperatures could have been 1520-1570oC, higher than modern ridges (1300-1450oC) but similar to those for the Gorgona and early Tertiary Icelandic plumes.

Herzberg, C.

2003-04-01

18

Modeling petrological geodynamics in the Earth's mantle  

NASA Astrophysics Data System (ADS)

We have developed an approach that combines principles of fluid dynamics and chemical thermodynamics into a fully coupled scheme to model geodynamic and petrological evolution of the Earth's mantle. Transport equations involving pressure, temperature, velocities, and bulk chemical composition are solved for one or more dynamic phases and interfaced with the thermodynamic solutions for equilibrium mineralogical assemblages and compositions. The mineralogical assemblage and composition are computed on a space-time grid, assuming that local thermodynamic equilibrium is effectively achieved. This approach allows us to simultaneously compute geophysical, geochemical, and petrological properties that can be compared with a large mass of observational data to gain insights into a variety of solid Earth problems and melting phenomena. We describe the salient features of our numerical scheme and the underlying mathematical principles and discuss a few selected applications to petrological and geophysical problems. First, it is shown that during the initial stage of passive spreading of plates, the composition of the melt near Earth's surface is in reasonable agreement with the average major element composition of worldwide flood basalts. Only the silica content from our model is slightly higher that in observational data. The amount of melt produced is somewhat lower than the estimated volumes for extrusive and upper crustal intrusive igneous rocks from large igneous provinces suggesting that an active upwelling of a larger mantle region should be considered in the process. Second, we have modeled a plume upwelling under a moving plate incorporating the effects of mineralogy on the density structure and viscous dissipation on the heat transport equation. The results show how these effects promote mantle instability at the base of the lithosphere. Third, we have considered a mantle convection model with viscosity and density directly related to the local equilibrium mineralogical assemblage. Interesting lateral variations and significant differences in the viscosity structure of the upper and lower mantle are revealed from our model results. The averaged viscosity variations with depth retrieved from our numerical simulations seem to reproduce the main features of the mantle viscosity structure under the Pacific ocean obtained from recent studies based on inversion of seismic data.

Tirone, M.; Ganguly, J.; Morgan, J. P.

2009-04-01

19

Application of VLBI and satellite laser ranging to geodynamics  

Microsoft Academic Search

The NASA Crustal Dynamics Project has developed very-long baseline interferometer (VLBI) systems and satellite laser ranging (SLR) systems for geodynamics measurements. In VLBI, a radio noise signal from a distant quasar is received by two or more radio antennas and coherently recorded. These recordings are cross-correlated to determine the relative signal delays between stations which are used to derive the

R. J. Coates

1983-01-01

20

Numerical Modeling in Geodynamics: Success, Failure and Perspective  

Microsoft Academic Search

A real success in numerical modeling of dynamics of the Earth can be achieved only by multidisciplinary research teams of experts in geodynamics, applied and pure mathematics, and computer science. The success in numerical modeling is based on the following basic, but simple, rules. (i) People need simplicity most, but they understand intricacies best (B. Pasternak, writer). Start from a

A. Ismail-Zadeh

2005-01-01

21

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

Microsoft Academic Search

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

Thomas Varghese; Michael Selden

1990-01-01

22

Study of a Close-Grid Geodynamic Measurement System.  

National Technical Information Service (NTIS)

The Clogeos (Close-Grid Geodynamic Measurement System) concept, a complete range or range-rate measurement terminal installed in a satellite in a near-polar orbit with a network of relatively simple transponders or retro-reflectors on the ground at interv...

1977-01-01

23

Applications of deformation analysis in geodesy and geodynamics  

Microsoft Academic Search

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

Athanasios Dermanis; Evangelos Livieratos

1983-01-01

24

On the geodynamic model of the earth and the plate tectonic hypothesis. I - The geodynamic model and fundamental equations  

Microsoft Academic Search

A geodynamic model of the earth is discussed. This model serves as the basis for a global mathematical earth model and as a mathematical model for individual earth regions. It utilizes the theory of plate tectonics, the assumption of a stepwise differentiation of mass density inside the earth, and the theory of thermoelastic viscoplasticity. System of equations of motion for

J. Nedoma

1986-01-01

25

Neogene stratigraphy and Andean geodynamics of southern Ecuador  

Microsoft Academic Search

The present paper reviews Tertiary volcanic and sedimentary formations in the Inter-Andean region of southern Ecuador (between 2°S and 4°20?S) in order to develop a geodynamic model of the region. The formations occur in the southern shallow prolongation of the Inter-Andean Valley between the Cordillera Real to the east, and the Cordillera Occidental and Amotape–Tahu??n Provinces to the west. One

Dominik Hungerbühler; Michael Steinmann; Wilfried Winkler; Diane Seward; Arturo Egüez; Dawn E. Peterson; Urs Helg; Cliff Hammer

2002-01-01

26

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

Microsoft Academic Search

Dubois, J., Deplus, C., Diament, M., Daniel, J. and Collot, J.-Y., 1988. Subduction of the Bougainville seamount (Vanuatu): mechanical and geodynamic implications. Tecfonoph.vics, 149: 111-119. New bathymetric data gathered during a Seabeam survey (SEAPSO cruise, leg 1) enable us to re-examine the flexural response of the oceanic lithosphere subducting under the New Hebrides (Vanuatuj island arc. The Bougainville seamount and

J. Dubois; C. DEPLUS; M. DIAMENT; J. DANIEL; J.-Y. COLLOT

1988-01-01

27

Calculation of satellite orbits for purposes of geodynamical research  

NASA Astrophysics Data System (ADS)

It is shown that the calculation of satellite orbits for the determination of geodynamical parameters can be carried out efficiently through the use of current numerical-integration algorithms combined with regularized equations of satellite motion (KS theory). It is demonstrated that Lageos observations can be analyzed using the direct integration of equations in rectangular coordinates by the Adams algorithm of variable order (based on divided differences, for example).

Taradii, V. K.; Tsesis, M. L.

1985-02-01

28

Concept of Spatial Information System for Pieniny geodynamic polygon  

NASA Astrophysics Data System (ADS)

The poster presents the conception of Spatial Information System (SIS) for geodynamic polygon of Pieniny Klippen Belt (PKB). Geodynamic research of the region, conducted by the staff of Faculty of Geodesy and Cartography of Warsaw University of Technology since the sixties of twentieth century, concern the vertical and horizontal movements and changes of Earth gravity parameters. The collected material all this time, very rich in observations and documentations, as well as further research planned in the region were an inspiration to establish the SIS. The designed system is concerned to be useful basically for collection of the results received so far and planned observation epochs as well. Its target functionality will allow to support the data presentations, analyses of the obtained results and planning process for next research in the future. The proposed conception of the database is described in the poster. The database of the considered SIS contains the following elements: information about geological structures of PKB, localizations of control points of geodynamic polygon and collected observations like: measurements of angles and distances, GNSS, precise and trigonometric levelling, gravimetric. The selected pilot layers of the SIS are based on: DTM, topographic maps, administrative and geologic maps. The data in the project are used to cover and characterize the three tectonic units distinguished in the study area. The ESRI software was used for main part of the work in the project.

Pasnikowski, M.; Chmiel, J.; Choromanski, M.; Pillich, A.; Szynal, P.; Galecka, M.; Jarmuz, D.

2009-04-01

29

The solution of fundamental problems of geodynamics, geophysics, geology and planetology  

Microsoft Academic Search

On the base of geodynamic model of the forced gravitational swing and displacement of shells of a planet under action of a gravitational attraction of surrounding (external) celestial bodies [1], [2] the fundamental problems of geodynamics, geology, planetology, geophysics, etc. have been studied and solved. 1). The mechanism of cyclic variations of activity of natural processes in various time scales.

Yury Barkin

2010-01-01

30

Overview of adaptive finite element analysis in computational geodynamics  

NASA Astrophysics Data System (ADS)

The use of numerical models to develop insight and intuition into the dynamics of the Earth over geological time scales is a firmly established practice in the geodynamics community. As our depth of understanding grows, and hand-in-hand with improvements in analytical techniques and higher resolution remote sensing of the physical structure and state of the Earth, there is a continual need to develop more efficient, accurate and reliable numerical techniques. This is necessary to ensure that we can meet the challenge of generating robust conclusions, interpretations and predictions from improved observations.

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

2013-10-01

31

Geodynamic Study In The Region of Southwest Bulgaria  

NASA Astrophysics Data System (ADS)

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

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

32

Recent advances in data assimilation in computational geodynamic models  

NASA Astrophysics Data System (ADS)

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

Ismail-Zadeh, Alik

2010-05-01

33

Geodynamic reconstructions of the South America-Antarctica plate system  

NASA Astrophysics Data System (ADS)

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

Vérard, Christian; Flores, Kennet; Stampfli, Gérard

2012-01-01

34

Geodynamics--where are we and what lies ahead?  

PubMed

The introduction and evolution of the plate tectonics hypothesis during the past two decades has sparked the current renaissance of research in the earth sciences. An outgrowth of active geophysical and geological exploration of the oceans, the plate tectonics model has come under intense scrutiny by geologists, geochemists, and geophysicists who have attempted to apply the model to the origin and growth of continents, the generation of oceanic and continental crust, and the nature of the lithosphere, asthenosphere, and underlying mantle with respect to their evolution through time and to the driving mechanism or mechanisms for plate tectonics. The study of other terrestrial planets and moons has been helpful in understanding the earth model. The unequal distribution of geological features, both in the continents and oceans, emphasizes the need for ongoing studies of international scope such as the recently completed International Geodynamics Project and its successor, the International Lithosphere Program, both stressing studies related to the dynamics of the lithosphere. PMID:17741165

Drake, C L; Maxwell, J C

1981-07-01

35

The geodynamics of the Pamir-Punjab syntaxis  

NASA Astrophysics Data System (ADS)

The collision of Hindustan with Eurasia in the Oligocene-early Miocene resulted in the rearrangement of the convective system in the upper mantle of the Pamir-Karakoram margin of the Eurasian Plate with subduction of the Hindustan continental lithosphere beneath this margin. The Pamir-Punjab syntaxis was formed in the Miocene as a giant horizontal extrusion (protrusion). Extensive nappes developed in the southern and central Pamirs along with deformation of its outer zone. The Pamir-Punjab syntaxis continued to form in the Pliocene-Quaternary when the deformed Pamirs, which propagated northward, were being transformed into a giant allochthon. A fold-nappe system was formed in the outer zone of the Pamirs at the front of this allochthon. A geodynamic model of syntaxis formation is proposed here.

Burtman, V. S.

2013-01-01

36

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

NASA Astrophysics Data System (ADS)

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

Vartanyan, G. S.

2010-12-01

37

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

SciTech Connect

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

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

1996-02-10

38

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

SciTech Connect

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

Cabre, R.

1983-01-01

39

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

40

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

NASA Astrophysics Data System (ADS)

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

Besse, J.

2004-12-01

41

Exploring problems in tectonics and geodynamics with seismology  

NASA Astrophysics Data System (ADS)

I demonstrate in two different studies how seismology can be a powerful tool for exploring and testing tectonic/geodynamic problems. In the first study, I analyze, model, and interpret a deep marine seismic reflection/refraction, magnetics, gravity, and bathymetric profile collected across the Bristol Bay basin, a back-arc basin in the southeast Bering Sea. I test three leading models for basin subsidence, and show that the basin evolved due to both faulting and flexural subsidence associated with extension and volcanic loading of the arc. The second study is an investigation of mantle fabrics around hotspots (Eifel, Hawaii, and eastern Nevada) and beneath part of the East African Plateau (Tanzania and Kenya). I analyze, model, and interpret the splitting of teleseismic shear-waves that originate from earthquakes to determine the orientation and magnitude of seismic velocity anisotropy, which allows me to place constraints on the orientation, magnitude, and depth of mantle deformation fabrics. I show that the fabrics around hotspots are explained best as a result of current deformation associated with parabolic asthenospheric flow (PAF), the horizontal asthenospheric flow associated with the interaction of gravitationally spreading plume material with an asthenosphere that is being dragged in the direction of plate motion. The success of the PAF model in fitting the data suggests that strong anisotropy exists in the asthenosphere, which means that dislocation creep is an important deformation mechanism beneath some hotspots. It also suggests that plume-lithosphere interaction is dominated by laminar flow. Perhaps the most important implication is that shear-wave splitting can be used as a diagnostic to test between upwelling and non-upwelling sources for mantle hotspots, and can provide estimates of geodynamic parameters beneath regions of thin mantle lithosphere. Splitting beneath the East African Plateau appears to be due to asthenospheric anisotropy associated with southward flowing plume material beneath the East African rifts, asthenospheric flow around the moving Tanzania craton, and fossilized fabrics in the lithosphere beneath the Precambrian mobile belts. An unexpected finding is that the history of east-west lithospheric extension has not resulted in an east-west mantle fabric, suggesting that the mantle there has a low mechanical strength.

Walker, Kristoffer T.

42

Geodynamics of Continental Lithospheric Rupturing: Progress and Challenge  

NASA Astrophysics Data System (ADS)

The break-up and transition from rifting to drifting of continental lithosphere are vital for deciphering the formation and evolution of rift and ocean, marginal sea and associated resource consequences as well; however, the physics and mechanism of this rupturing process are controversial. Thanks to the endeavors of international geoscience community with large research programs such as IODP and MARGINS and mass geophysical and geological observations available, prominent advancements on this issue have been made during recent decade. Here we briefly review related progress on continental lithosphere rupturing and mainly focus on the topics as follows: nature of crustal structure of conjugated continental margin, conceptional model on continental lithospheric rupturing and geodynamic modeling. The existence of zone of exhumed continental mantle in the oceanic-continental transition of non-volcanic type continental margin, composed by serpentinized peridotite, is emphasized here, regarding its relatively weak rheology that facilitates the break up of lithosphere. The fault system of diverse types, especially the concave downward fault, absorbing the deformation from rifting to drifting should be taken into account in constructing conceptional mode for lithospheric rupturin. The configuration of pre-rifting lithosphere, for instance, the rheological heterogeneity, thermal structure and tectonic inheritance, are the key factors that control the rupturing process of continental lithosphere. Lastly, some challenges are all presented, and we conclude that multidisciplinary studies of the typical conjugated continental margins in the world are essential for better understanding on lithospheric rupturing.

Liu, S.

2008-12-01

43

Geodynamical analysis of the Iranian Plateau and surrounding regions  

NASA Astrophysics Data System (ADS)

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

Asgharzadeh, Mohammad Forman

44

Geodynamics of rapid voluminous felsic magmatism through time  

NASA Astrophysics Data System (ADS)

Two end member geodynamic settings produce the observed examples of rapid voluminous felsic (rhyolitic) magmatism through time. The first is driven by mantle plume head arrival underneath a continent and has operated in an identifiable and regular manner since at least 2.45 Ga. This style produces high temperature (? 1100 °C), low aspect ratio rheoignimbrites and lavas that exhibit high SiO2/Al2O3 ratios, high K2O/Na2O ratios, and where available data exists, high Ga/Al2O3 ratios (> 1.5) with high F (in thousands of parts per million) and low water content. F concentration is significant as it depolymerizes the silicate melt, influencing the magmas' physical behavior during development and emplacement. These rhyolites are erupted as part of rapidly emplaced (10-15 Myr) mafic LIPs and are formed primarily by efficient assimilation-fractional crystallization processes from a mafic mantle parent. The second is driven by lithospheric extension during continental rifting or back arc evolution and is exclusive to the Phanerozoic. SLIPs (silicic large igneous provinces) develop over periods < 40 Myr and manifest in elongate zones of magmatism that extend up to 2500 km, contrasting with the mafic LIP style. Some of the voluminous felsic magmas within SLIPs appear to have a very similar geochemistry and petrogenesis to that of the rhyolites within mafic LIPs. Other voluminous felsic magmas within SLIPs are sourced from hydrous lower crust, and contrast with those sourced from the mantle. They exhibit lower temperatures (< 900 °C), explosive ignimbrites with lower SiO2/Al2O3 ratios, and lower K2O/Na2O ratios. Rapid voluminous felsic magmatism represents both extreme examples of continental growth since the Archean, and also dramatic periods of crustal recycling and maturation during the Phanerozoic.

Pankhurst, M. J.; Schaefer, B. F.; Betts, P. G.

2011-04-01

45

Tectonics and geodynamics of the Eastern Venezuelan Ranges  

SciTech Connect

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

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

1993-02-01

46

Geodynamics of the Gulf of California from surface wave tomography  

NASA Astrophysics Data System (ADS)

The Gulf of California, which forms part of the Pacific-North American plate boundary, is an ideal place to investigate upper mantle dynamics in a continental rifting area. With 19 seismic stations located around the gulf, the NARS-Baja experiment (2002-2008) was designed to image its crustal and mantle structure. Here we present results of a tomographic inversion of Love and Rayleigh interstation phase velocity measurements for a radially anisotropic shear velocity model of the Gulf of California. This study confirms the overall low shear-wave velocities in the upper 200 km of the mantle found in other Rayleigh wave studies, and the presence of a positive shear-wave velocity anomaly at depths of roughly 80-160 km beneath the central gulf (Zhang et al., 2009). In addition, we find that the horizontal shear velocity (VSH) is generally higher than the vertical shear velocity (VSV). For the northern gulf, however, there is strong indication for VSV>VSH in the 40-60 km depth range. This region also has anomalously low shear-wave velocities down to 100 km depth. Combining these observations, we suggest that the low velocity anomaly and the negative radial anisotropy (VSHgeodynamics are caused by the cessation of subduction by stalled microplates in the central and southern gulf and the presence of a slab window in the north.

Zhang, Xiaomei; Paulssen, Hanneke

2012-02-01

47

Crisis of isotope geodynamics: Sm-Nd aspect  

NASA Astrophysics Data System (ADS)

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

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

2009-04-01

48

Second phase of the European Project CERGOP-2/Environment (Central Europe Regional Geodynamics Project)  

NASA Astrophysics Data System (ADS)

The paper includes concise information on the status of the international geodynamic project CERGOP (Central Europe Regional Geodynamics Project). The achievements of the realisation of the first phase of the Project are summarised. The enlarged objectives, the programme and scope of work of the second phase of the Project are shortly described. List of workpackages covering particular fields of activities within the Project is given. Project is supported financially by the European Commission. Project CERGOP was an impulse for the establishment of the CEGRN Consortium of institutes involved in realisation of the Project. The Consortium will also be a seedbed of new European projects and initiatives.

Sledzinski, Janusz

49

Geodynamic Evolution of the Southern Flank of the Corinth Rift  

NASA Astrophysics Data System (ADS)

The Gulf of Corinth is the most seismically active area of Europe extending in a N-S direction at a rate of 12mm/yr. Many studies have focused on currently active normal faults, which bound the southern flank of the Corinth rift. However, many prominent faults, that are considered no longer active, outcrop over a broader area along with their syn-rift sedimentary sequence. The normal fault network and related synrift succession have been mapped and studied at a scale of 1:25,000. The geometry of the fault network in 3D has been reconstructed in the gOcad 3D geomodelling package. Based on these detailed field data we propose a geodynamic model for the evolution of the region in three steps over the last two million years. From 2 to 1 Ma, extension affected a broad area at least twenty kilometers wide. Alluvial conglomerates and sandstones, deposited in grabens and half grabens, were derived from erosion of the pre-existing (Hellenic) high relief to the south in the Peloponnese massif. Around 1Ma, a regional uplift led to the migration of the depocenter to the north. New faults are activated closer to the coast, in places generating forced folds that tilted synrift fluvial formations northward over a 2-3 kilometers wide area. Considerable accommodation space was generated by these faults and, with an increased sediment supply from the south, a series of giant marine Gilbert deltas developed in their hangingwalls. Finally, from 0.5 Ma to present, the activation of a series of major new faults further to the north (near the current coastline) coincided with regional uplift of the south coastal belt, and initiated the formation of a second generation of Gilbert delta, currently building out into the gulf. The faults can be divided into three families. The main one (74 data) is oriented N110, dipping 45 to 60° to the north. It includes 5 major faults spaced 3 to 5 km from south to north, with a throw larger than 1000m. A secondary set (41 data) strikes N60, dipping to the NW, it includes only one fault with a throw larger than 500m; the other secondary set (43 data) is antithetic to the two first ones as it strikes N60 to N110, dipping to the south, the largest fault it includes has a throw of about 400m. Most faults are planar and the importance of listric faults seems minor in the rift history.

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

2005-12-01

50

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

Microsoft Academic Search

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

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

1992-01-01

51

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

Microsoft Academic Search

The Lengguru accretionary wedge (West Papua) is located in a very active geodynamical context. It results from the oblique convergence between the Pacific plate and the Australian plate. All the wedge has been build between 11 and 2 Ma (Bailly et al., 09). Exceptional boulders of fresh eclogites were discovered in the internal part of the Lengguru wedge, in the

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

2010-01-01

52

Mantle flow pattern and geodynamic cause of the North China Craton reactivation: Evidence from seismic anisotropy  

Microsoft Academic Search

We investigate the mantle flow pattern and geodynamic cause of North China Craton (NCC) reactivation using shear wave splitting measurements from 140 broadband stations. Using a newly developed method for simulating wave propagation in a two-dimensional anisotropic medium, we first examined the influence of sedimentary structures on SKS splitting measurements. The simulations show that a sedimentary layer, whether isotropic or

Liang Zhao; Mei Xue

2010-01-01

53

Designing a geodetic-geodynamic network: a comparative study of data processing tools  

Microsoft Academic Search

The geodetic-geodynamic network (G1) was established with the intention of monitoring recent crustal deformation and serving as the major control network in Israel. In 1996 the network was measured for the first time using GPS. This paper presents the second GPS measurement campaign of the G1 network, held in 2002. It presents the network configuration design and the data processing

G. Even-Tzur; E. Salmon; M. Kozakov; M. Rosenblum

2004-01-01

54

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

Microsoft Academic Search

The Solar system periodically passes through spiral arms of the Galaxy, which are stellar density waves. Processes due to the presence of galactic shocks (shock waves) may be responsible for the abrupt atmosphere changes (climate), geodynamics (supercontinental cycle, large tectonic processes, mantle convection, geomagnetic field and others) and biosphere. Galactic shocks (GS) are the narrow region of high gas compression

D. Khristoforova

2009-01-01

55

Geodynamic Evolution of the Nubia-Arabia-Somalia Plate Boundary System  

Microsoft Academic Search

We present a geodynamic scenario for the evolution of the Nubia (Nu)-Arabia (Ar)-Somalia (So) plate boundary system that is based on new geodetic constraints on the kinematics of active deformation, and published estimates of the timing of regional tectonic processes. This scenario supports two, long debated, principal hypotheses for plate dynamics, 1) plate motions are driven primarily by sinking of

R. E. Reilinger; S. McClusky; P. Vernant; G. Ogubazghi; S. Fisseha; A. Arrajehi; R. O. Bendick; J. Sholan

2009-01-01

56

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

Microsoft Academic Search

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

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

2005-01-01

57

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

Microsoft Academic Search

The northern part of the Greater Caucasus is one of the most geodynamically active regions of Russia. This is a zone of complex tectonics resulting from interaction between two of the Earth's major lithospheric plates, Arabia and Eurasia. Therefore, the region as a whole is characterized by a complex system of faults, with meridional and diagonal structures. The first GPS

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

2010-01-01

58

A Geodynamical Perspective on the Subduction of Cocos and Rivera plates beneath Mexico and Central America  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

59

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

SciTech Connect

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

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

1988-08-01

60

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

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

61

Geological Survey of Canada, Geodynamics Program: Earthquake Processes: Cascadia Subduction Zone  

NSDL National Science Digital Library

This page explains the tectonic setting of the west coast of North America. It explains the process of the subduction of the Juan de Fuca plate beneath the North American plate. It describes the methods used to observe tectonic deformation caused by subduction, and explains how they are used to estimate earthquake potential in the region. Links are provided to the Geological Survey of Canada's Geodynamics Program home page, and to their Pacific Geoscience Centre page.

62

Dynamics of interaction between fields of seismicity and surface deformations (Bishkek geodynamic test area)  

Microsoft Academic Search

The spatial-temporal dynamics of surface crustal movements revealed from GPS data is compared with seismicity in the Bishkek\\u000a geodynamic test area documented in the regional KNET catalog. The geological information system (GIS) GeoTaim 2.0 is substantially\\u000a improved, which allowed variations in seismicity and deformation fields to be analyzed in the 3D raster. It is shown that\\u000a seismicity and surface deformations

G. A. Sobolev; N. A. Zakrzhevskaya; K. N. Akatova; V. G. Gitis; A. B. Derendyaev; V. D. Bragin; N. A. Sycheva; S. I. Kuzikov

2010-01-01

63

Dynamics of interaction between fields of seismicity and surface deformations (Bishkek geodynamic test area)  

Microsoft Academic Search

The spatial-temporal dynamics of surface crustal movements revealed from GPS data is compared with seismicity in the Bishkek geodynamic test area documented in the regional KNET catalog. The geological information system (GIS) GeoTaim 2.0 is substantially improved, which allowed variations in seismicity and deformation fields to be analyzed in the 3D raster. It is shown that seismicity and surface deformations

G. A. Sobolev; N. A. Zakrzhevskaya; K. N. Akatova; V. G. Gitis; A. B. Derendyaev; V. D. Bragin; N. A. Sycheva; S. I. Kuzikov

2010-01-01

64

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

Microsoft Academic Search

The presented model of the Late Cenozoic geodynamic evolution of the central Andes and the complex tectonic, geological, and\\u000a geophysical model of the 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

T. V. Romanyuk

2009-01-01

65

Space geodesy in geodynamic studies: Recent movements in the Zeya-Bureya Basin  

Microsoft Academic Search

The Amur-Zeya geodynamic test ground was set up in 2000 to study recent intracontinental crustal deformations. The velocity\\u000a field calculations for the period of 2000 to 2003 describe three movements scales. The general level is characterized by the\\u000a vectors of IGS sites in the eastern part of Asia, the BLAG (Blagoveshchensk) site included. The southeast movement of the\\u000a IRKT (Irkutsk)

A. I. Miroshnichenko; A. P. Sorokin; V. A. San’kov; A. V. Lukhnev; S. V. Ashurkov; A. T. Sorokina; N. I. Panfilov; M. A. Serov; S. I. Sherman

2008-01-01

66

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

NASA Astrophysics Data System (ADS)

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

Hochard, C.; Vérard, C.

2011-12-01

67

Geology, Geochemistry and Geochronology of the Upper Cretaceous high-K volcanics in the southern Part of the Eastern Pontides: Implications for Mesozoic Geodynamic Evolution of NE Turkey  

Microsoft Academic Search

The Eastern Pontide Orogenic Belt is one of the most complex geodynamic settings in the Alpine-Mediterranean region. Its geodynamic evolution is very controversial due to lack of systematic, quantitative structural, geochemical and geochronological data. This belt is divided into three subgroups: northern, southern and axial zones, distinguished from north to south by different lithological units, facies changes and tectonic characteristics.

Y. Eyuboglu

2009-01-01

68

Programmes and achievements of the long term cooperation in geodesy and geodynamics of sixteen CEI (Central European Initiative) countries  

NASA Astrophysics Data System (ADS)

The paper includes concise information on geodetic and geodynamic projects that are realised in international cooperation of the Central European countries in the frame of the scientific programme of the CEI WG "Science and Technology" Section C "Geodesy". The main achievements of the first phase of the international European geodynamic project CERGOP (Central Europe Regional Geodynamics Project) are outlined. The general objectives of another CEI project UNIGRACE (Unification of Gravity Systems in Central and Eastern Europe) and the results of the 1998 campaign of absolute gravity measurements are pointed out. The programmes of activities of the Section C Working Group on Satellite Navigation Systems and actions realised by the Working Group on University Education Standards are summarised. The cooperation links between CEI WGST Section C and European Geophysical Society (EGS) and International Association of Geodesy (IAG) are shortly discussed.

?ledzi?ski, Janusz; International Coordinator of the CEI WGST Section C "Geodesy", Chairman of the IAG Subcommission "Geodetic; GeodynamicProgrammes of the CEI"

2002-07-01

69

Recent geodynamics of the faults and paradoxes of the rates of deformation  

NASA Astrophysics Data System (ADS)

The results of analyzing the long (20-50 years) time series of geodetic observations carried out in the regions with enhanced seismotectonic activity (Kopet Dag, Kamchatka, and California) are presented. It is established that recent vertical and horizontal displacements in the fault zones estimated by instrumental geodetic observations with increased spatiotemporal resolution indicate that the deformations in the fault zones paradoxically deviate from the movements inherited from the previous geological epochs. The paradoxes of high and low deformation rates in recent geodynamics lie in the reliably established empirical fact that extremely high local deformation rates (up to 10-5 per annum and higher) exist in the fault zones in the setting of weak regional deformations, whose annual rates are by two to three orders of magnitude lower. Very low annual average rates of relative horizontal deformations, which only measure 3-5 amplitudes of tidal deformations of the solid Earth, are revealed in the seismically active regions of Kopet Dag and Kamchatka as well as in the San Andreas Fault Zone in northern California. The fault-block dilemma arising in the interpretation of the observations of recent fault geodynamics is formulated. Either the role of active element, which forms the present anomalous deformations, is played by a block, while a fault plays the role of the passive element, or the fault zone itself is a source of anomalous movements, while the blocks are passive elements (hosting medium). It is shown that paradoxes of low and high deformation rates vanish if we assume that the recent anomalous geodynamics is formed by parametric excitation of the deformation processes in the fault zones in the conditions of quasi-static loading.

Kuzmin, Yu. O.

2013-09-01

70

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

NASA Astrophysics Data System (ADS)

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

Grose, C. J.

2008-05-01

71

Use of satellite geodesy for determination of geodetic and geodynamic parameters  

NASA Astrophysics Data System (ADS)

The relative efficiency attainable in determinations of different geodetic and geodynamic parameters are presently evaluated for cosmic-geodetic methods using laser- and radio-ranging satellites, lunar laser ranging, and quasar-based VLBI, in view of recent results thus obtained for the earth's rotation parameters, station coordinates, tectonic plate movements, the gravity field, the tides, and the earth's elastic parameters. Accuracies of 1-3 cm have been obtained for station positions referred to a geocentric frame for terrestrial distances and for pole coordinates.

Montag, H.

72

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

Microsoft Academic Search

\\u000a The Indian stratigraphic record with well documented Mesozoic and Early Tertiary terrestrial biotas is now adequate to shed\\u000a light on the geodynamic chronology of the subcontinent during the rift, drift and collision phases. The record provides one\\u000a of the best examples of the response of a biota that is undergoing considerable latitudinal displacement, dispersal, origination,\\u000a evolution and extinction.\\u000a \\u000a \\u000a This paper

A. Sahni

2010-01-01

73

Geodynamic factors in the formation of reef reservoirs of the Kama-Kinel rift  

NASA Astrophysics Data System (ADS)

Devonian and Carboniferous carbonate sedimentation in the eastern portion of the Russian Plate largely depended on the development of the complex Kama-Kinel rift zone dividing arched uplifts in the western region of the Volga-Ural province. Geodynamically, this zone was formed in several stages with the successive development of reef barriers. Individual elements of these reef masses with high permeability and porosity subsequently became hydrocarbon reservoirs and formed chains of major oil fields. The reef masses have a complex structure due to sedimentation and diagenetic processes in some reef zones. This causes the formation of specific types of void space in particular reef zones. The highest porosity is found in lumpy limestones formed in peripheral zones of intra-reef lagoons unaffected by diagenetic recrystallisation. Medium porosities are characteristic of partly recrystallised limestones of transitional zones of the lagoons. Low permeabilities and porosities are found in pelitomorphic limestones formed in central portions of the intra-reef lagoons. However, geodynamic unloading in limestones of this type produced secondary fractures and specific fractured reservoirs. Thus, some reef masses contain hydrocarbon deposits with complex reservoirs requiring specific technologies for their development.

Izotov, V.; Sitdikova, L.; Sadrlimanov, A.; Safin, A.

2009-04-01

74

Grid convergence study of the combined finite difference & Marker-In-Cell method for geodynamic applications  

NASA Astrophysics Data System (ADS)

The combined finite difference & Marker-In-Cell technique of Gerya and Yuen (2003) is a popular method for studying geodynamic processes involving many material phases with differing rheological properties. Numerous applied studies have demonstrated the versatility of the scheme for studying large viscous deformations. The principal reason why the method is flexible is the use of an interpolation technique to capture fluid properties at a subgrid level. Given the geodynamic applications, the discretisation is required to be robust when the domain contains sharp variations in viscosity and free surfaces. In our study, we measure the robustness of the spatial discretisation by computing the discretisation error and analysing the convergence rate of the velocity and pressure fields. We examine the convergence properties of the traditional staggered grid discretisation and show that introducing an interpolated viscosity constructed from the markers does not modify the convergence behaviour. Moreover, we introduce a free surface stabilisation algorithm and show that the stabilisation does not alter the convergence rate of the method. Gerya, T. V., Yuen, D. A., 2003. Charaterictics-based marker method with conservative[|#12#|]finite-difference schemes for modeling geological fows with strongly variable transport properties. Physics of the Earth and Planetary Interiors 140 (4), 293-318.

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

2010-12-01

75

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

NASA Astrophysics Data System (ADS)

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

May, D. A.

2012-05-01

76

Watching structural and geodynamic features of a plate boundary: Peceneaga-Camena Fault  

NASA Astrophysics Data System (ADS)

The Peceneaga - Camena Fault represents one of the major lithosphere contacts on the Romanian territory. Its nature and dynamics have been subject to many geological and geophysical researches since the beginning of the 20th century. Based on geophysical evidence some authors consider PCF as a plate boundary, the strike-slip contact between the Moesian Micro-Plate (MoP) and East European Plate (EEP). Deep seismic soundings along the international line II had revealed its trans-crustal nature, with a 10 km step at both Conrad and Moho discontinuities. It is likely that the geodynamic evolution of this major tectonic accident is tightly connected to the opening of the W Black Sea basin. Seismic tomography studies have outlined strong fingerprints of the W Black Sea opening within its NW inland. In depth extension of PCF may be clearly seen within the tomography images down to more than 150 km. It seems that lithosphere expelled by the rifting split MoP into several compartments by creating or reactivating a NW trending major fault system to which the PCF belongs. After the W Black Sea rifting ended its evolution, the geodynamic engine in the area seems to be the active rifting in the SW Arabian Plate (red Sea and Aden Bay) pushing northward the Arabian Plate by about 48 mm/yr, and further on, pushing a MoP segment towards the Carpathians. Under this pushing, the above-mentioned MoP compartments move towards the Carpathians, staying together by friction. However, when tectonic forces overcome the friction, the slivers may relatively slip each other, thus generating earthquakes along their wedges. The presence of some scarce seismicity along PCF seems to confirm the idea. To check up the above mentioned geodynamic scenario, a geodetic experiment has been imagined to monitor PCF flanks displacement. Two Leica TC 1201 total stations were installed on the southern flank of PCF (belonging to MoP) in order to measure the distance to a laser reflector installed on the northern PCF flank (within the neighbouring EEP). Each instrument measures the distance to the reflector every 6 seconds and records minute averages of the observations. This way time series related to movements of the PCF compartments were acquired and stored in a computer database. To diminish the record noise, mainly due to the temperature variation and terrestrial tides, some filtering techniques were applied to data in order to better reveal the existent trends. The analysis made lead to some interesting conclusions: (i) PCF is a geodynamical active contact, which explains earthquakes presence along it; (ii) flanks displacements are irregular in both speed and strike; (iii) according to the records, PCF has behaved both as a right-lateral and / or left-lateral contact. The results are fully consistent with the geodynamic model connected to W Black Sea evolution. When the PCF northern compartment escapes toward Carpathians, PCF appears as a left-lateral fault. On the opposite, if the southern compartment is moving under the action of tectonic forces, then PCF appears as right-lateral fault. These conclusions may provide important constraints for interpreting GPS data obtained during epoch campaigns.

Besutiu, L.; Zlagnean, L.

2009-04-01

77

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

Microsoft Academic Search

Geodynamic studies of Malaysia have been ventured upon in the South-East Asia region since the first GeodySEA project in 1996. Both East and West Malaysia lies on the Eurasian Plate, and assumed to have no linear distortion between any two joined points relative to one another. However, Malaysia lies at the southern tip of the plate encroached by two frequently

Rabieahtul Abu Bakar; Khamarrul Azahari Razak

2010-01-01

78

Geodynamics of flat-slab subduction, sedimentary basin development, and hydrocarbon systems along the southern Alaska convergent plate margin  

Microsoft Academic Search

Combining field-based geologic studies and numerical modeling provides a robust tool for evaluating the geodynamics of convergent margins. Southern Alaska is arguably the most tectonically active part of the convergent margin of western North America. This conceptual approach has been used to interpret the modern basin dynamics, as well as key stages in the Cenozoic development of this region, including

Emily S Finzel

2010-01-01

79

Late Palaeozoic to early Mesozoic geodynamic evolution of the Circum-Pacific orogenic belt in South Korea and Southwest Japan  

Microsoft Academic Search

A review of the overall features of the late Palaeozoic-early Mesozoic orogen of Southwest Japan and its Korean hinterland allows a new geodynamic model for the building of the east Asian margin to be proposed. During middle Carboniferous to early Permian times, an oceanic basin formed in a passive margin environment at a moderate spreading rate as the Honshu continental

Dominique Cluzel

1992-01-01

80

Grid-Enabling the Global Geodynamics Project: Automatic RDF Extraction from the ESML Data Description and Representation via GRDDL  

Microsoft Academic Search

An eXtensible Markup Language (XML) based data model for the Global Geodynamics Project (GGP) has been previously developed. Mindful of the need to incorporate metadata into the description and representation, a Resource Description Framework (RDF) based approach is introduced that extends the previous data model. Specifically, use of RDF allows relationships to be described and represented, and will eventually result

L. Ian Lumb; Keith D. Aldridge

2006-01-01

81

Gravitational Influence of the Sun and Moon on the Earth and Possible Geodynamic Consequences  

NASA Astrophysics Data System (ADS)

The goal of current research is to reconsider the role of tidal stresses and deformations in a planet’s life and to show the mechanisms that transform tidal deformations into geodynamic and other processes. 1. Tidal stress and strain oscillations have been acting on the Earth, uniformly and monotonously, for hundreds of millions of years. As such, these small tidal effects accumulate during geological time and can result in the following tectonic and geodynamic phenomenae: dilatation of the Earth’s material and separation of its components: solid, liquid, and gas; transformation of low-amplitude tidal deformations into lateral differential motion of the Earth’s layers, internal heating, and magnetic field generation. The “complex loading of a granular substance” (Revuzhenko, 2003) was considered as a possible mechanism that transforms radial tidal deformations into lateral displacements of the Earth’s layers. The governing equations were written. The Figure below shows the trajectory of a particle in the liquid core. A and B represent the initial and final (when calculation was terminated) positions of a particle; the Coriolis force was taken into account. It was shown that similar trajectories can be obtained also by solving the Navier-Stokes equations for a low-viscosity liquid and tidal force (see section 2) acting on a liquid. 2. The barycenter of the Earth and Moon binary planet system is 4670 km from the center of the Earth. The center of the Earth is orbiting around the Sun on a non-Keplerian, perturbed orbit. This requires a more careful consideration of inertial and tidal forces acting on the Earth and its structures. The formula for a tidal force is Fn=?i=1,nf Mi/?i3 ?i - a0, a0 = aK + ap, aK is Keplerian, and ap is the non-Keplerian (of the same order as a Keplerian one) acceleration of the center of mass of the Earth. The formula for the tidal force acting on the Earth from the Sun and the Moon was first obtained and studied by Yu. Avsyuk (1996, 2001, 2007). The shortest period of the tidal force according to this formula is 13.6 (not 27.5!) days. This formula was used for interpreting different geodynamic phenomenae, from Moon seismisity through the Chandler wobble. This work was supported by RFBR grant No 09-05-00426-a

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

2009-12-01

82

Radioactivity measurements in volcano-tectonic area for geodynamic process study  

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

83

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

SciTech Connect

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

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

1993-09-01

84

Croatian Permanent Stations within the International GPS-Service for Geodynamics  

NASA Astrophysics Data System (ADS)

During the year 2000, the first two GPS-permanent stations in the Republic of Croatia were established: Dubrovnik and Osijek. These stations became the part of two international networks designed for monitoring Earth's crustal movements: EUREF-Permanent and International GPS-service for Geodynamics. In this paper we describe the background of the IGS and EUREF Permanent projects, basic tectonic patterns of the Adriatic Microplate, establishment of permanent stations in Croatia, performed measurements, and the first results of their usage. In addition, a proposal for development of a Croatian GPS-permanent stations network is given. Such a network could be used for both numerous scientific investigations and practical real-time navigation on the land, at the sea and in air.

Medak, D.; Pribi?evi?, B.

85

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

SciTech Connect

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

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

1991-02-01

86

Testing Absolute Plate Reference Frames and the Implications for the Generation of Geodynamic Mantle Heterogeneity Structure  

NASA Astrophysics Data System (ADS)

Several absolute reference frames for Cretaceous-Tertiary plate tectonic reconstructions have been proposed over the last decade. They include reference frames based on hotspot tracks displaying age progression, and assuming either fixed or moving hotspots, as well as palaeomagnetically-based reference frames, a subduction reference frame and hybrid reference frames. All these alternative reference frames imply a particular history of the location of subduction zones through time, the associated subduction history, and the evolution of mantle heterogeneity via the mixing of subducted slab material with the mantle. Therefore it is possible to evaluate the observed distribution of subducted slab material in the mantle versus that predicted by a forward geodynamic model in which the plate kinematic history given by a particular absolute plate is coupled with a mantle convection model. We present a comparison of five alternative absolute plate motion models in terms of their consequences for global deep mantle structure by utilizing the 3-D spherical finite element mantle convection code TERRA, coupled with the global plate tectonic reconstruction software GPlates. We impose global palaeo-plate boundaries and plate velocities back to 140 Ma as surface boundary conditions for each absolute rotation model and forward model the associated subduction history. The correlation of seismic tomography with the predicted present-day mantle structure from each of plate models is then assessed using well-imaged slabs. We will present and discuss a comparison of geodynamically predicted mantle heterogeneity and seismic tomography to infer the robustness of each absolute reference frame through time, thus providing additional constraints for the integration of plate tectonics and mantle dynamics.

Shephard, G. E.; Bunge, H.; Schuberth, B. S.; Müller, D.; Talsma, A.; Moder, C.

2010-12-01

87

Geographic Information Systems (GIS) Spatial Data Compilation of Geodynamic, Tectonic, Metallorgenic, Mineral Deposit, and Geophysical Maps and Associated Descriptive Data for Northeast Asia.  

National Technical Information Service (NTIS)

The purpose of this publication is to provide a high-quality spatial data compilation (Geographical Information System or GIS) of geodynamic, mineral deposit, and metallogenic belt maps, and descriptive data for Northeast Asia for customers and users. Thi...

V. V. Naumova R. J. Miller M. I. Patuk M. Y. Kapitanchuk W. J. Nokleberg A. I. Khanchuk L. M. Parfenov S. M. Rodionov

2006-01-01

88

Geodynamic processes of Taiwan arc–continent collision and comparison with analogs in Timor, Papua New Guinea, Urals and Corsica  

Microsoft Academic Search

The Taiwan arc–continent collision involves four geodynamic processes: intra-oceanic subduction; initial arc–continent collision; advanced arc–continent collision; and arc collapse\\/subduction. These processes now occur simultaneously in 19–24°30?N but have operated sequentially southward since the Late Miocene. Although the geological and geophysical features appear to change progressively from north to south across the island, they are distinct within individual tectonic regimes. Using

Chi-Yue Huang; Peter B Yuan; Ching-Weei Lin; Tan K Wang; Chung-Pai Chang

2000-01-01

89

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

90

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

Microsoft Academic Search

Using the Earth Science Markup Language (ESML), an XML-based data model for the Global Geodynamics Project (GGP) was recently introduced [Lumb & Aldridge, Proc. HPCS 2005, Kotsireas & Stacey, eds., IEEE, 2005, 216-222]. This data model possesses several key attributes -i.e., it: makes use of XML schema; supports semi-structured ASCII format files; includes Earth Science affinities; and is on track

L. I. Lumb; K. D. Aldridge

2005-01-01

91

Measurements of the VLBI experiments during the first campaign of the Asian-Pacific space geodynamics (APSG) program  

Microsoft Academic Search

During the first campaign of the Asian-Pacific space geodynamics (APSG) program in October 1997, two VLBl experiments were\\u000a successfully organized and coordinated by the Astrometry and Geodesy VLBl Group of Shanghai Astronomical Observatory, the\\u000a Chinese Academy of Sciences, cooperated with geodetic VLBl group, GSFC, NASA, USA. Six VLBl stations participated in the experiments,\\u000a including Seshan and Urumqi station of China,

Guangli Wang; Shuhua Ye; Zhihan Qian; Jinling Li; Chopo Ma; Jim Ryan; David Gordon; Karen Baver; Jin Zhang; Xiang Liu; Kazuo Aoki; Misao Ishihara; Strand Rich; Cox Clyde

2001-01-01

92

Time series analysis of EPN stations as a criterion of choice of reference stations for local geodynamic networks  

NASA Astrophysics Data System (ADS)

Local and regional geodynamic studies require evaluation of inner (intraplate) velocities, primarily reference points' velocities. Relative velocities between selected European Permanent Network (EPN) stations can be evaluated using different approaches (time series analysis, ITRF2000 velocities, NUVEL1A-NNR velocities). The authors present the method of mean trend congruency analysis for EPN stations coordinate time series (from weekly EUREF solutions). The article includes results of time series analysis of EPN stations located no more than 700 km away from our local geodynamic network (LGN) SUDETES located in Sudety Mts. and Sudetic Foreland (Central Europe), performed for a selection of the best reference stations. Taking into account the results of performed classification and the distance between stations and local research area (Sudety Mts., SW Poland), the best conditions of local measurements' connection to the European network have been fulfilled for the stations: BOR1, PENC, GOPE, GRAZ WTZR and POTS. Stations, such as WROC and MOPI, located close to the research area are characterized by significantly worse quality parameters. Finally the influence of reference station selection on estimated velocities of local geodynamic network points is shown. The authors participate in EPN Special Project: Time series monitoring for geokinematics (Central Europe subjetwork).

Borkowski, Andrzej; Bosy, Jaroslaw; Kontny, Bernard

93

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

NASA Astrophysics Data System (ADS)

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

Vérard, C.; Hochard, C.

2011-12-01

94

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

95

Methods for computing internal flattening, with applications to the Earth's structure and geodynamics  

NASA Astrophysics Data System (ADS)

After general comments (Section 1) on using variational procedures to compute the oblateness of internal strata in the Earth and slowly rotating planets, we recall briefly some basic concepts about barotropic equilibrium figures (Section 2), and then proceed to discuss several accurate methods to derive the internal flattening. The algorithms given in Section 3 are based on the internal gravity field theory of Clairaut, Laplace and Lyapunov. They make explicit use of the concept of a level surface. The general formulation given here leads to a number of formulae which are of both theoretical and practical use in studying the Earth's structure, dynamics and rotational evolution. We provide exact solutions for the figure functions of three Earth models, and apply the formalism to yield curves for the internal flattening as a function of the spin frequency. Two more methods, which use the general deformation equations, are discussed in Section 4. The latter do not rely explicitly on the existence of level surfaces. They offer an alternative to the classical first-order internal field theory, and can actually be used to compute changes of the flattening on short timescales produced by variations in the LOD. For short durations, the Earth behaves elastically rather than hydrostatically. We discuss in some detail static deformations and Longman's static core paradox (Section 5), and demonstrate that in general no static solution exists for a realistic Earth model. In Section 6 we deal briefly with differential rotation occurring in cylindrical shells, and show why differential rotation of the inner core such as has been advocated recently is incompatible with the concept of level surfaces. In Section 7 we discuss first-order hydrostatic theory in relation to Earth structure, and show how to derive a consistent reference Earth model which is more suitable for geodynamical modelling than are modern Earth models such as 1066-A, PREM or CORE11. An important result is that a consistent application of hydrostatic theory leads to an inertia factor of about 0.332 instead of the value 0.3308 used until now. This change automatically brings `hydrostatic' values of the flattening, the dynamic shape factor and the precessional constant into much better agreement with their observed counterparts than has been assumed hitherto. Of course, we do not imply that non-hydrostatic effects are unimportant in modelling geodynamic processes. Finally, we discuss (Sections 7-8) some implications of our way of looking at things for Earth structure and some current problems of geodynamics. We suggest very significant changes for the structure of the core, in particular a strong reduction of the density jump at the inner core boundary. The theoretical value of the free core nutation period, which may be computed by means of our hydrostatic Earth models CGGM or PREMM, is in somewhat better agreement with the observed value than that based on PREM or 1066-A, although a significant residue remains. We attribute the latter to inadequate modelling of the deformation, and hence of the change in the inertia tensor, because the static deformation equations were used. We argue that non-hydrostatic effects, though present, cannot explain the large observed discrepancy of about 30 days.

Denis, C.; Amalvict, M.; Rogister, Y.; Tomecka-Sucho?, S.

1998-03-01

96

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

97

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

98

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

NASA Astrophysics Data System (ADS)

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

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

2005-12-01

99

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

100

Global paleo-lithospheric models for geodynamical analysis of plate reconstructions  

NASA Astrophysics Data System (ADS)

We present a general framework to generate time-dependent global subduction history models from kinematic plate reconstructions and explore their associated coupled plate-mantle dynamic behaviour. Slabs are constructed by advecting material into the mantle by prescribing its radial velocity and following the absolute tangential motion of the subducting plate. A simple geodynamic scenario where plates and slabs define isopycnic and isoviscous regions in an homogeneous or layered mantle was explored using the boundary element method-based software BEMEarth. The resulting dynamic behaviour was used to predict the absolute plate motion directions for the present day and a particular mid-cretaceous (125 Ma) kinematic model. We show how the methodology can be used to compare and revise kinematic reconstructions based on their effect on the balance of plate driving forces and the resulting Euler poles of subducting plates. As an example we compare the Farallon plate dynamics at 125 Ma in a global model with two reconstructions in the context of the evolution of the Western North American Cordillera. Our results suggest a method to identify episodes of absolute plate motions that are inconsistent with the expected plate dynamics.

Quevedo, L.; Morra, G.; Müller, R. D.

2012-12-01

101

The solution of fundamental problems of geodynamics, geophysics, geology and planetology  

NASA Astrophysics Data System (ADS)

On the base of geodynamic model of the forced gravitational swing and displacement of shells of a planet under action of a gravitational attraction of surrounding (external) celestial bodies [1], [2] the fundamental problems of geodynamics, geology, planetology, geophysics, etc. have been studied and solved. 1). The mechanism of cyclic variations of activity of natural processes in various time scales. 2). The nature of eccentric positions of the core and the mantle of the Earth. A role of the Moon, the Sun, Neptune and other celestial bodies in activization of the swing of core-mantle system of the Earth. 3). Power of endogenous activity of planetary natural processes on planets and satellites. 4). The nature of correlations of natural processes with features of motion of baricenter of the solar system. 5). An explanation of influence of bodies of solar system on excitation of variations of planetary processes with Milankovitch's periods (in tens and hundred thousand years). 6). A possible explanation of geological cycles as result of excitation of solar system at its motion in a gravitational field of the Galaxy. 7). The phenomenon of polar inversion of natural processes on the Earth, both other planets and satellites. 8). Spasmodic (step-by-step) and catastrophic changes of activity of natural processes. 9). Sawtooth (gear curve) variations of natural processes. 10). The phenomenon of twisting of hemispheres (latitude zones) of celestial bodies. 11). Formation of the pear-shaped form of celestial bodies and the mechanism of its change. 10). Ordered planetary structures in spatial distribution of geological formations. 12). The phenomena of bipolarity of celestial bodies and antipodality of formations. Many fundamental problems of natural sciences have been obtained an explanation on the basis of developed geodynamic model (Barkin, 2002, 2009). The fundamental problems of celestial mechanics and geodynamics, geophysics and the geology, excited of scintific community in current of last decades and even centuries have been solved. The fundamental phenomena in rotation of the Earth: secular drift of a pole of its axis of rotation and non-tidal acceleration of axial rotation of a planet have received an explanation. Observable secular variations of a gravity, variations of a geopotential coefficients, secular drift of the center of mass of the Earth, secular changes of a global level of ocean and change of average levels of ocean in northern and southern hemispheres of the Earth, secular geodetic changes of the Earth in present period have been explained, etc. It is shown, that there is a uniform mechanism for many bodies of solar system of excitation of natural processes in their polar areas. In particular it is shown, that polar regions of many celestial bodies, including their soil layers, are sated by fluids. The last position obtains the precise confirmation in researches of subsoil waters and a water ice on Mars, the Moon, Mercury, etc. bodies of solar system. A wide number of the natural phenomena has been predicted by the author and these predictions have already obtained and obtain confirmations and an explanations in the data of modern observations and space missions. An existence of the seas in polar regions of the Titan, concentration of water ice in polar regions of Mercury, the Moon, Mars and other bodies of solar system has been predicted. The conclusion about fluid consentrations at polar regions of celestial bodies is extremely important for revealing of carbon deposits on the Earth, first of all in regions of Arctic and Antarctic. Work is partially supported by RFBR grants: N 08-02-00367, N-09-02-92113-JF. References 1. Barkin Yu.V. (2002) An explanation of endogenous activity of planets and satellites and its cyclisity. Isvestia sekcii nauk o Zemle Rossiiskoi akademii ectestvennykh nauk. Vyp. 9, M., VINITI, pp. 45-97. In Russian. 2. Barkin Yu.V. (2009) Moons and planets: mechanism of their life. Proceedings of International Conference 'Astronomy and World Heritage: across Time and Continents' (Kazan, 19-

Barkin, Yury

2010-05-01

102

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

NASA Astrophysics Data System (ADS)

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

Raznitsin, Yu. N.

2012-01-01

103

Metamorphic history and geodynamic significance of the Early Cretaceous Sabzevar granulites (Sabzevar structural zone, NE Iran)  

NASA Astrophysics Data System (ADS)

The Iranian ophiolites are part of the vast orogenic suture zones that mark the Alpine-Himalayan convergence zone. Few petrological and geochronological data are available from these ophiolitic domains, hampering a full assessment of the timing and regimes of subduction zone metamorphism and orogenic construction in the region. This paper describes texture, geochemistry, and the pressure-temperature path of the Early Cretaceous mafic granulites that occur within the Tertiary Sabzevar ophiolitic suture zone of NE Iran. Whole rock geochemistry indicates that the Sabzevar granulites are likely derived from a MORB-type precursor. They are thus considered as remnants of a dismembered dynamo-thermal sole formed during subduction of a back-arc basin (proto-Sabzevar Ocean) formed in the upper-plate of the Neotethyan slab. The metamorphic history of the granulites suggests an anticlockwise pressure-temperature loop compatible with burial in a hot subduction zone, followed by cooling during exhumation. Transition from a nascent to a mature stage of oceanic subduction is the geodynamic scenario proposed to accomplish for the reconstructed thermobaric evolution. When framed with the regional scenario, results of this study point to diachronous and independent tectonic evolutions of the different ophiolitic domains of central Iran, for which a growing disparity in the timing of metamorphic equilibration and of pressure-temperature paths can be expected to emerge with further investigations.

Nasrabady, M.; Rossetti, F.; Theye, T.; Vignaroli, G.

2011-11-01

104

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

105

Geodynamic implications of paleomagnetic data from Tertiary sediments in Sakhalin, Russia (NW Pacific)  

NASA Astrophysics Data System (ADS)

N-S trending right-lateral strike-slip faults, which were active in the Tertiary, transect Sakhalin, Russia, while Mesozoic forearc and accretionary rocks testify to an earlier period of subduction. Several kinematic models have been proposed for the region, but the details required to constrain these models, such as the timing of the transition from subduction to strike-slip tectonics in Sakhalin, are still unknown. Even first-order tectonic features, such as the boundaries of the plates with which Sakhalin evolved during the Tertiary, are poorly known. Paleomagnetic results from around Sakhalin were obtained to constrain the geodynamic evolution of the region. Comparison of paleomagnetic inclination data with the apparent polar wander paths for the Eurasian, Pacific, and North American Plates suggests that Sakhalin probably evolved with the North American Plate, although a history including the Eurasian Plate cannot be ruled out. Paleomagnetic declination data suggest that significant clockwise vertical axis rotation has occurred in Sakhalin since the mid-Paleocene. It is likely that this rotational deformation was accommodated by Tertiary activity on right-lateral strike-slip faults, which may be associated with the opening of the Japan Sea, Tatar Strait, and Kuril Basin. These data contradict a published kinematic model for eastern Sakhalin, where counterclockwise vertical axis rotations were predicted for Neogene basins in the East Sakhalin Mountains. Agreement is better, however, with published paleomagnetic data from southern Sakhalin, where clockwise vertical axis rotations were documented.

Weaver, Richard; Roberts, Andrew P.; Flecker, Rachel; MacDonald, David I. M.; Fot'yanova, Lidiya M.

2003-02-01

106

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

107

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

NASA Astrophysics Data System (ADS)

We developed and tested a new 2D staggered grid method which is designed specifically for use on adaptive quad-tree meshes. The key to our new adaptive staggered grid (ASG) stencil is in the form of the stress conservative finite difference constraints which are enforced at the "hanging" velocity nodes between resolution transitions within the quad-tree mesh. We demonstrate numerically that the ASG stencil is (i) stable and does not produce spurious pressure oscillations across regions of grid refinement which intersect discontinuous viscosity struc-tures and (ii) possess the same order of accuracy as the classical non-adaptive staggered grid discretization. Additionally, we investigate the applicability of several pragmatic error indicators to demonstrate the superior performance of the ASG stencil over traditional non-adaptive grid approaches. We envisage broad applicability of this new numerical method for simulating mantle convection and lithospheric dynamics. Simplified examples of geodynamic applications are provided in the form of (a) extensional deformation of visco-plastic rocks with free surface and (b) planetary deformation.

Gerya, Taras; May, Dave; Duretz, Thibault

2013-04-01

108

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

NASA Astrophysics Data System (ADS)

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

Mentes, Gy.

2012-01-01

109

Petrography, geochemistry and geodynamic environment of potassic alkaline rocks in Eslamy peninsula, northwest of Iran  

NASA Astrophysics Data System (ADS)

Eslamy peninsula, 360 km2 in area, is located in the eastern coast of Urmieh lake in the northwest of Iran. This peninsula is a complex stratovolcano with a collapsed center, which is elevated due to later intrusions of sub-volcanic masses with trachytic to microsyenitic composition. The composite cone consists of a sequence of leucite tephrite, tephrite, leucite basanite, basanite and related pyroclastic rocks. Magmatic activities in the Eslamy peninsula begin with potassic alkaline to ultrapotassic and basic, silica-undersaturated shoshonitic rocks and they are followed by intrusions of lamprophyric dykes and end with acidic magmatism including trachytic, microsyenitic, syenitic and phonolitic domes. The original magma of the Eslamy peninsula rocks has a potassic alkaline nature (Roman type) rich in LREE and LILE and depleted of HREE. These characteristics suggest that the origin of magma can be from deep mantle with a garnet lherzolite composition, a low partial melting rate which has been contaminated by crustal materials in its way up. Fractional crystallization of olivine, diopsidic clinopyroxene and leucite played an important role in the evolution of magmas. Scrutinizing the geodynamic environment of Eslamy peninsula rocks in discrimination diagrams indicates that these rocks must have been formed in a post-collision magmatic arc setting.

Hajalilou, B.; Moayyed, M.; Hosseinzadeh, Gh.

2009-12-01

110

Mantle flow uplift of western Anatolia and the Aegean: Interpretations from geophysical analyses and geodynamic modeling  

NASA Astrophysics Data System (ADS)

The Western Anatolian and Aegean region demonstrates a complex geologic history of horizontal and vertical tectonics. Active normal faulting and exhumation zones indicate that Western Anatolia has experienced significant extension since the Oligocene-Early Miocene (˜30 Ma). Our geophysical analyses demonstrate that the region is also uplifted relative to an elevation that would be expected given an isostatic response to the lithosphere structure. Namely, topography "residuals" indicate a residual uplift of about 1500 m over ˜200 km sections of Western Anatolia and the Aegean. Admittance functions between free-air gravity and topography indicate that the regional topography is isostatically uncompensated and as it approaches ˜50 mGal/km at the longest wavelengths, the uncompensated topography is likely owing to an underlying mantle flow component. Using forward geodynamic modelling we consider an idealized section of Western Anatolian lithosphere based on tomographic inversions and examine the magnitude and pattern of surface topography to reconcile with the geophysical observables. The models consistently show a plateau-type uplift (and horizontal extension) through Western Anatolia with an amplitude and wavelength consistent with the residual topography calculations. Together, the geophysical analyses and modelling provide independent quantitative evidence that the thin Anatolian-Aegean lithosphere is being buoyed upwards by underlying mantle flow. The mantle flow may be associated with active lithosphere delamination beneath the region; a process that would also explain the ongoing crustal extension.

Komut, Tolga; Gray, Robert; Pysklywec, Russell; Gö?ü?, O?Uz H.

2012-11-01

111

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

PubMed

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

Mentes, Gy

2012-01-01

112

Which geodynamic roles for volatile-rich low melt fractions in the Earth's mantle?  

NASA Astrophysics Data System (ADS)

Volatiles and melts are thoroughly related in the Earth's mantle because volatiles facilitate melting and melts concentrate mantle volatiles. Mapping of mantle solidus by mean of experimental petrology has long established that melting can occur in numerous mantle regions provided that volatiles are present in the rocks. Volatile concentration in mantle rocks is however small and consequently, associated melt fractions are small. The produced liquids are carbonated melts, which can incorporate variable amount of silicate components and are extremely rich in volatiles (H-Cl-F-S). Because melting profoundly affects rock physical properties and geochemical mass transfers, the localization and recognition of such melts inside the Earth are critical for our understanding of global mantle geodynamics. Mantle electrical conductivity, rather than seismic methods is most suited to identify the presence of such low melt fractions, because low melt fraction likely to form at depth > 150 km are expected to constitute about 0.1% at the grain boundaries of mantle rocks. Recent electromagnetic surveys (see Tarits et al. this meeting) indicate that underneath Mid-Oceanic Ridges, mantle rocks are continuously conductive from 60 km, the depth of MOR-basalt formation, to >400 km depth. Such conductive mantle rocks are clearly attributed to small fractions of carbonated melts, which furthermore most likely contain high amounts of water (see Sifré and Gaillard, this session). This petrological interpretation of mantle electrical anomalies contrasts with the traditional mineral physic views that attributed high mantle conductivity to crystallographic defects associated to water incorporation in olivine. But the water in olivine model is disputed by nearly all existing experimental data. The amount of carbonated melts required to explain mantle conductivity suggests about 170-300 ppm CO2 in the mantle that sources MOR-basalts, which is in excellent agreement with geochemical estimations (180 +/- 100 ppm). The geochemical-geodynamic implications of continuous melt films wetting grain boundaries from the transition zone the MOR-basalt source regions are then discussed following several key observations: (1) The redox transition from carbonate to diamond expected from petrological models to occur at 200-250 km depth is not consistent with geophysical observations implying a revision of mantle redox state in up-welling regions; (2) The petrologically assessed depth of anhydrous melting of carbonate is 350km but high conductivity extends well below, implying a likely hydrous melting of mantle carbonates; (3) A continuous network of low melt fractions from the transition zone to the MOR-B melting regions has major implications regarding the rate of transfer of incompatible elements from the transition zone to the lithosphere-asthenosphere boundary, which might be faster than mantle convection rates; (4) these incompatible elements include volatile species such as water, which would not only sit in olivine and radioactive elements, implying that an important mantle heat source is in fact mobile.

Gaillard, F.

2012-04-01

113

The seismic cycle at subduction thrusts: benchmarking geodynamic numerical simulations and analogue models  

NASA Astrophysics Data System (ADS)

The physics governing the long-term seismic cycle in subduction zones remains poorly understood due to its spatial inaccessibility, complex tectonics and geometry, and the limited observation time. However, modeling approaches for large-scale subduction and small-scale dynamic rupture processes are well developed, and could help to overcome limited seismic observations for improved studies of the long-term seismic cycle at subduction thrusts. Such a continuum mechanic, geodynamic model includes a more realistic geometry and rheology with spontaneously developing faults, but also needs to transfer large spatial and temporal modeling scales such that short seismic events are resolved. We deploy a continuum mechanic numerical method that involves a plane-strain finite-difference scheme with marker-in-cell technique to solve the conservation of momentum, mass, and energy for a visco-elasto-plastic rheology. The simulated laboratory setup constitutes a triangular, visco-elastic crustal wedge that is underlain by a restricted, velocity-weakening zone. Both are driven toward a backstop by a subducting, straight slab. We benchmark our geodynamic numerical approach to a novel gelatin lab experiment that shows a cyclic seismic pattern. Our results demonstrate that the fluid-dynamic, viscous-elasto-plastic code simulates a series of regular rapid, short, elastic seismic events if velocity-weakening friction is incorporated. During the inter-seismic period the seismogenic zone subducts with the slab, thus focusing stresses near its down-dip end. Once material strength is exceeded, the seismogenic zone fails and ruptures predominantly in up-dip direction, thereby causing a short, rapid reversal of wedge displacements and acceleration of reversed velocities. After this stress release, healing (increase of friction coefficient) is essential to build up stresses for generating the next earthquake. Velocity strengthening in aseismogenic regions assists a) to limit the rupture up- and down-dip of the seismogenic zone, b) to move peak-velocity locations to just below the up-dip extent of the seismogenic zone, and c) to decrease the frequency of a rupture breaking up to the trench. Timing of events, spatial earthquake source parameters, and magnitudes are mainly affected by two material parameters: shear modulus (inversely related to the inter-seismic duration) and dynamic friction drop (affecting several source parameters through a differential stress drop). Within the range of material parameters constrained in the lab, we accomplish a first-order match between numerical and analogue models for the most important earthquake source properties. Therefore, we conclude that inertia and a non-steady-state state component in the friction formulation are not essential in the numerical study. After this promising benchmark we will apply our visco-elasto-plastic code with velocity-dependent friction to a more realistic subduction setup and regional subduction cases.

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

2012-04-01

114

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

NASA Astrophysics Data System (ADS)

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

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

2002-07-01

115

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

NASA Astrophysics Data System (ADS)

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 and deep seismic reflection profile was added considering the blank exploration areas. The Moho depth and variation character shows that: the Moho framework of the continent in China is strongly correlated with China’s tectonics and topography, expressed in two weftwise and two warpwise strips. Two weftwise strips are Tianshan-Yinshan-Yanshan orogeny and Kunlun-Qilian-Dabie range, while two warpwise ones are Daxing’anling-Taihangshan-Wulingshan gravity gradient zone and Helanshan-Longmenshan range. According to the Moho framework of China and other geological evidences, the continent in China could be divided into three geodynamic domains: western domain, middle domain and eastern domain. The western one lies to the west of the Helanshan-Longmengshan range and is affected by the collision of Indian and Eurasian paltes, The main character is crustal thickening in the margin of the Tibet plateau, crustal thinning in the heartland of the plateau and reactivation of Tianshan orogeny; the middle zone lies between Helanshan-Longmenshan zone and Daxin'anling-Taihangshan-Wulingshan gravity gradient zone, this zone has stable crust and minor Moho variation relatively, which reflect a buffer zone between western and eastern zones and a transfer zone from compression to extension; the eastern zone is located to the east of the gravity gradient zone, mainly affected by the peri-Pacific tectonic domain, and the strong extensional and thinning event have changed the Moho depth and character in the entire eastern zone.

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

2010-12-01

116

Timing, rates and geodynamical conditions of continental crust generation, destruction and reworking  

NASA Astrophysics Data System (ADS)

The timing, rates and the geodynamical conditions of continental crust generation, destruction and reworking remain a topic of considerable debate. Around 7% of the present-day exposed crust consists of rocks of Archaean age, yet models of continental growth suggest that 20-100% of the present-day volume of the continental crust had formed by the end of the Archaean. Continental growth models rely on understanding the balance between the generation of new crust and the reworking of old crust, and how these have changed with time throughout Earth's history. For that purpose, the variations in radiogenic isotope ratios in detrital rocks and minerals are a key archive. Two different approaches are considered to model the growth of continents: (1) the variation of Nd isotopes in continental shales with various deposition ages, which requires a correction of the bias induced by preferential erosion of younger rocks through an erosion parameter 'K'; and (2) the variations in U-Pb, Hf and O isotopes in detrital zircons sampled worldwide. These two approaches independently suggest that the continental crust was generated continuously, with a marked decrease in the continental growth rate at ca. 3 Ga. The >4 Ga to ~3 Ga period is characterised by relatively high net rates of continental growth (~3.0 km3.a-1), which are similar to the rates at which new crust is generated, and destroyed, at the present time. Since 3 Ga the net growth rates are much lower (~0.8 km3.a-1), and this may be attributed to higher rates of destruction of continental crust. The inflexion in the continental growth curve at ~3 Ga indicates a fundamental change in the way the crust was generated and preserved. This change may be linked to onset of subduction-driven plate tectonics and discrete subduction zones.

Dhuime, B.; Hawkesworth, C. J.; Cawood, P. A.

2012-04-01

117

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

NASA Astrophysics Data System (ADS)

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

Carminati, Eugenio; Lustrino, Michele; Doglioni, Carlo

2012-12-01

118

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

NASA Astrophysics Data System (ADS)

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

BräUer, Karin; KäMpf, Horst; Niedermann, Samuel; Strauch, Gerhard; Tesa?, Ji?I.

2008-04-01

119

Triassic redbeds in the Malaguide Complex (Betic Cordillera — Spain): Petrography, geochemistry and geodynamic implications  

NASA Astrophysics Data System (ADS)

Sandstone petrography and mudstone mineralogy and geochemistry of Triassic mudstones and sandstones from continental redbeds of the Malaguide Complex (Betic Cordillera, southern Spain) provide useful information on provenance, palaeoclimate and geodynamics during the early stages of the Pangea break-up, and on their diagenetic evolution. The sandstones are quartzarenites to sub-litharenites, with minor lithic fragments and rare feldspars. The mudstone samples show a PAAS like elemental distribution. The samples likely record recycling processes from their metasedimentary basement rocks that significantly affected the weathering indices, and monitors cumulative effects, including a first cycle of weathering at the source rocks. Sandstone composition and chemical-mineralogical features of mudstones record a provenance derived from continental block and recycled orogen that were weathered under warm and episodically wet climate. Source areas were located towards the east of the present-day Malaguide outcrops, and were formed by fairly silicic rock types, made up mainly of Palaezoic metasedimentary rocks, similar to those of the Paleozoic underlying series, with subordinate contributions from magmatic-metamorphic sources, and a rare supply from mafic metavolcanic rocks. Clay-mineral distribution of mudstones is dominated by illite and illite/smectite mixed-layer that result from differences in provenance, weathering, and burial/temperature history. Illite crystallinity values, illitization of kaolinite, occurrence of typical authigenic minerals and apatite fission-track studies, coupled with a subsidence analysis of the whole Malaguide succession suggest burial depths of at least 4-6 km with temperatures of 140-160 °C, typical of the burial diagenetic stage, and confirm the Middle Miocene exhumation of the Betic Internal Domain tectonic stack topped by the Malaguide Complex.

Perri, Francesco; Critelli, Salvatore; Martín-Algarra, Agustín; Martín-Martín, Manuel; Perrone, Vincenzo; Mongelli, Giovanni; Zattin, Massimiliano

2013-02-01

120

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

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

121

Emplacement of the Arzachena Pluton (Corsica-Sardinia Batholith) and the geodynamics of incoming Pangaea  

NASA Astrophysics Data System (ADS)

The assembly of the Corsica-Sardinia Batholith (C-SB) coincides with final shaping of the Variscan belt and represents a key structure to unravel the feedbacks between partial melting, rheology and the evolution of collisional orogens. This paper presents a model for the genesis of the Arzachena pluton (AZN), one of the major calc-alkaline massifs of the C-SB, based on U-Pb zircon dating, thermobarometry and structural analysis. Major and trace element compositions indicate that AZN has hybrid characteristics between that of typical S- and I-type granites, that could be explained in terms of incremental melting of a heterogeneous crustal source made of metatexites and Ordovician calc-alkaline granitoids. Growth of the pluton started around 320-315 Ma with the emplacement at middle crustal level (0.37-0.4 GPa) of granodioritic melts within narrow, conjugate, NW-SE sinistral and E-W dextral shear zones. The main growth stage (311 + 6/- 4 Ma) is marked by emplacement of large volumes of monzogranitic melts that induced a local decrease of the crustal strength expressed by horizontal channel flow driven by the gravity. Finally (307.6 ± 3.5 Ma), leucogranites emplaced within radial and peripheral dilatant fractures developed during the cooling of the main body. The transition from magmatic to sub-magmatic and HT-solid state fabric observed throughout AZN indicates that deformation plays a non-trivial role during the growth of the magmatic system. Restoring the position of the Corsica-Sardinia block to early Permian coordinates allow to recast the birth of the C-SB in a consistent geodynamic framework that conciliates the development of conjugates strike-slip structures, the oroclinal bending of the chain and the thermal relaxation. This study indicates that the C-SB had an active role during post-orogenic extension rather than being just a consequence of it.

Casini, Leonardo; Cuccuru, Stefano; Maino, Matteo; Oggiano, Giacomo; Tiepolo, Massimo

2012-05-01

122

Geodynamics of synconvergent extension and tectonic mode switching: Constraints from the Sevier-Laramide orogen  

NASA Astrophysics Data System (ADS)

Many orogenic belts experience alternations in shortening and extension (tectonic mode switches) during continuous plate convergence. The geodynamics of such alternations are not well understood. We present a record of Late Cretaceous to Eocene alternations of shortening and extension from the interior of the retroarc Sevier-Laramide orogen of the western United States. We integrate new Lu-Hf garnet geochronometry with revised PT paths utilizing differential thermobarometry combined with isochemical G-minimization plots, and monazite Th-Pb inclusion geochronometry to produce a well-constrained "M" shaped PTt path. Two burial events (86 and 65 Ma) are separated by ˜3 kbar of decompression. The first burial episode is Late Cretaceous, records a 2 kbar pressure increase at ˜515-550 °C and is dated by a Lu-Hf garnet isochron age of 85.5 ± 1.9 Ma (2?); the second burial episode records ˜1 kbar of pressure increase at ˜585-615 °C, and is dated by radially decreasing Th-Pb ages of monazite inclusions in garnet between ˜65 and 45 Ma. We propose a synconvergent lithospheric delamination cycle, superimposed on a dynamic orogenic wedge, as a viable mechanism. Wedge tapers may evolve from critical to subcritical (amplification), to supercritical (separation), and back to subcritical (re-equilibration) owing to elevation changes resulting from isostatic adjustments during the amplification and separation of Rayleigh-Taylor instabilities, and post-separation thermal and rheological re-equilibration. For the Sevier-Laramide hinterland, the sequence of Late Cretaceous delamination, low-angle subduction, and slab rollback/foundering during continued plate convergence explains the burial-exhumation-burial-exhumation record and the "M-shaped" PTt path.

Wells, Michael L.; Hoisch, Thomas D.; Cruz-Uribe, Alicia M.; Vervoort, Jeffrey D.

2012-02-01

123

Tectonics, stress state, and geodynamics of the Mesozoic and Cenozoic Rift basins in the Baikal region  

NASA Astrophysics Data System (ADS)

The results of geological, structural, tectonic, and geoelectric studies of the dry basins in the Baikal Rift Zone and western Transbaikalia, combined under the term Baikal region, are integrated. Deformations of the Cenozoic sediments related to pulsing and creeping tectonic processes are classified. The efficiency of mapping of the fault-block structure of the territories overlapped by loose and poorly cemented sediments is shown. The faults mapped at the ground surface within the basins are correlated with the deep structure of the sedimentary fill and the surface of the crystalline basement, where they are expressed in warping and zones of low electric resistance. It is established that the kinematics of the faults actively developing in the Late Cenozoic testifies to the relatively stable regional stress field during the Late Pliocene and Quaternary over the entire Baikal region, where the NW-SE-trending extension was predominant. At the local level, the stress field of the uppermost Earth’s crust is mosaic and controlled by variable orientation of the principal stress axes with the prevalence of extension. The integrated tectonophysical model of the Mesozoic and Cenozoic rift basin is primarily characterized by the occurrence of mountain thresholds, asymmetric morphostructure, and block-fault structure of the sedimentary beds and upper part of the crystalline basement. The geological evolution of the Baikal region from the Jurassic to Recent is determined by alternation of long (20-115 Ma) epochs of extension and relatively short (5.3-3.0 Ma) stages of compression. The basins of the Baikal Rift System and western Transbaikalia are derivatives of the same geodynamic processes.

Lunina, O. V.; Gladkov, A. S.; Nevedrova, N. N.

2010-05-01

124

New Insights on the Geodynamic Evolution of the Galapagos Volcanic Province  

NASA Astrophysics Data System (ADS)

We developed a simple quantitative framework based on crustal thickness observations along the Carnegie, Cocos, and Malpelo Ridges, to place first order constraints on the geodynamic evolution of the Galapagos Volcanic Province and on the along-axis intensity of the Galapagos melt anomaly during the last 20 Ma. Our results suggest that the Cocos - Nazca Spreading Center has moved northwards at 2 cm/yr with respect to the Galapagos anomaly during this period of time. The combined effect of this movement and that of the complicated geometry of the spreading center made that, at 20 Ma, the Galapagos anomaly was ridge-centered. At 12 Ma the center of the Galapagos anomaly was located around 70 km north of the spreading center, and the anomaly-related along-axis melt flux was around 50 % of that estimated at 20 Ma. At present day the anomaly is located around 170 km south of the spreading center and the along-axis melt flux is only 23 % of that observed at 20 Ma. This implies that the influence of the melt anomaly on the spreading center would become indistinguisheable for seismic refraction techniques at a distance of aroound 460 km. This results are used to infer that the center of the melt anomaly passed over the spreading center at 8.5 Ma. The main tectonic event of the area, the Panama Fracture Zone, initiated at 10 Ma, leading to the separation between Cocos and Malpelo Ridges. The present configuration of the Galapagos Volcanic Province is well recovered if symmetric spreading with a mean full spreading rate of 5 cm/yr has taken place in the spreading center after the initiation of the movement along the Panama Fracture Zone.

Sallares, V.; Charvis, P.

2002-12-01

125

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

126

Mantle Flow Uplift and Heating of the Anatolian Block: Interpretations from Geophysical Evidence and Geodynamic Modeling  

NASA Astrophysics Data System (ADS)

Western Anatolia and the eastern Aegean demonstrate an interesting geologic history of horizontal and vertical tectonics. Active normal faulting and exhumational zones indicate that western Anatolia has experienced significant extension since the Oligocene-Early Miocene ( ˜30 Ma). Geomorphological evidence indicates recent uplift: ˜700 m in the last 3 Myrs. We have conducted a series of geophysical analyses to demonstrate that the region is also uplifted relative to an elevation that would be expected given an isostatic response to the lithospheric structure. Namely, topography 'residuals' indicate a residual uplift of ˜1000 m over ˜500 km sections of western Anatolia and the eastern Aegean. We also calculate admittance functions between free-air gravity and topography to quantify the nature of the uplift. These data indicate that the regional topography is isostatically uncompensated and is likely owing to an underlying mantle flow component. Heat flow data indicate that the area is thermally elevated as well. Using forward geodynamic modeling we consider idealized sections of Anatolian lithosphere based on tomographic inversions and examine the magnitude and pattern of surface topography and heat flow to reconcile with the geophysical observables. The models test the response of the surface topography to various configurations of the Anatolian-Aegean surface plates, including variably strong lithosphere and the presence of a weak mantle wedge and weak zones in the crust. Together, the geophysical data and analyses and modeling provide independent quantitative evidence that the thin Anatolian/Aegean lithosphere is being buoyed upwards by underlying mantle flow. We propose that the mantle flow is associated with lithospheric delamination beneath the region; a process that would also explain the ongoing crustal extension.

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

2011-12-01

127

The long-term seismic cycle at subduction thrusts: benchmarking geodynamic numerical simulations and analogue models  

NASA Astrophysics Data System (ADS)

The physics governing the long-term seismic cycle in subduction zones remains elusive, largely due to its spatial inaccessibility, complex tectonic and geometric setting, and the short observational time span. To improve our understanding of the physics governing this seismic cycle, we benchmark a geodynamic numerical approach with a novel laboratory model. In this work we quantify and compare periodicity and source parameters of slip events (earth-quakes and gel-quakes) as a function of fault rheology (i.e. frictional properties), subduction velocity, slab dip, and seismogenic zone width. Our fluid-dynamic numerical method involves a plane-strain finite-difference scheme with marker-in-cell technique to solve the conservation of momentum, mass, and energy for a visco-elasto-plastic rheology. The simulated gelatin laboratory setup constitutes a triangular, visco-elastic crustal wedge on top of a straight subducting slab that includes a seismogenic zone. Numerical and analogue results show a regular and roughly comparable periodicity of short, rapid wedge velocity reversals. Ruptures nucleating mainly around the bottom of the seismogenic zone, and propagating upward, cause a distinct and rapid drop in stress within the wedge. To mimic the short duration, high speed and regularity of the analogue results, the numerical method requires a form of steady-state velocity-weakening friction for acceleration, and healing. The necessity of including a variable state component into the numerical simulations is subject of ongoing work. Finally, we extend this analysis by observing the role of different friction laws in large-scale, geometrically more realistic models.

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

2011-12-01

128

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

NASA Astrophysics Data System (ADS)

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.

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

2012-03-01

129

Samovar: a thermomechanical code for modeling of geodynamic processes in the lithosphere-application to basin evolution  

Microsoft Academic Search

We present a new 2D finite difference code, Samovar, for high-resolution\\u000a numerical modeling of complex geodynamic processes. Examples are\\u000a collision of lithospheric plates (including mountain building and\\u000a subduction) and lithosphere extension (including formation of\\u000a sedimentary basins, regions of extended crust, and rift zones). The code\\u000a models deformation of the lithosphere with viscoelastoplastic rheology,\\u000a including erosion\\/sedimentation processes and formation of shear

Yuriy Elesin; Taras Gerya; Irina M. Artemieva; Hans Thybo

2010-01-01

130

International Symposium on Space Techniques for Geodynamics, Sopron, Hungary, July 9-13, 1984, Proceedings. Volumes 1 & 2  

NASA Astrophysics Data System (ADS)

Among the topics discussed are: remote measurement techniques for geodesy and geodynamics earth gravity and its interpretation from satellite data; and earth rotation and polar motion measurements. Consideration is also given to: satellite techniques and geodetic measurements; plate kinematics and crustal deformation; refraction effects on geodetic measurements from space; and tropospheric calibration in radio interferometry. Among additional topics discussed are: the status of Global Positioning System (GPS) standardization; the African Doppler Survey (ADOS) program; and least squares spectral analysis of a Doppler coordinate time series which was obtained at the Penc Satellite Geodetic Observatory in Hungary.

131

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

NASA Astrophysics Data System (ADS)

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

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

2005-12-01

132

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

NASA Astrophysics Data System (ADS)

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

Rodnikov, Alexander; Sergeyeva, Natalia; Zabarinskaya, Ludmila

2010-05-01

133

Geodynamic Evolution of the Nubia-Arabia-Somalia Plate Boundary System  

NASA Astrophysics Data System (ADS)

We present a geodynamic scenario for the evolution of the Nubia (Nu)-Arabia (Ar)-Somalia (So) plate boundary system that is based on new geodetic constraints on the kinematics of active deformation, and published estimates of the timing of regional tectonic processes. This scenario supports two, long debated, principal hypotheses for plate dynamics, 1) plate motions are driven primarily by sinking of oceanic lithosphere at subduction zones, and 2) the lithosphere is strong in relation to plate boundaries and drag forces on the base of the lithosphere (and likely, resisting forces associate with continental collision). 1) During the Late Oligocene (~30 Ma), domal uplift of the Afar region due to the Afar hot spot caused regional extension and the initial development of the Afar Triple Junction (TJ) along pre-existing zones of weakness; 2) The So-Nu plate boundary, East African Rift (EAR), developed at a slow rate due to the absence of boundary-normal extensional stresses (i.e., no subduction “pulling” the So Plate), slow motion that continues to the present; 3) Larger extensional stresses across the Nu-Ar and Ar-So boundaries (Red Sea and Gulf of Aden) due to active subduction of the Neotethys ocean lithosphere beneath Eu caused more rapid extension of these early rifts, with full scale continental rifting beginning ~ 25-30 Ma; 4) Between 16 - 11 Ma full ocean rifting in the Gulf of Aden caused a decrease in the forces transmitted to the So and Nu plates, causing slowing of the Nu and So plates with respect to Eu and Ar, and (possibly) an additional component of N-S oriented extension across the Red Sea; 5) Around this time (~10 Ma), activity shifted from the Gulf of Suez to the DSF system in the N Red Sea, and the Danakil Block in the southern Red Sea began rotating with respect to Nu and Ar, both changes related to the change in Nu-Ar relative motion; and 6) The balance of forces on the plate system have remained roughly unchanged since ~10 Ma, as have relative plate motions.

Reilinger, R. E.; McClusky, S.; Vernant, P.; Ogubazghi, G.; Fisseha, S.; Arrajehi, A.; Bendick, R. O.; Sholan, J.

2009-12-01

134

AlpArray - an initiative to advance understanding of Alpine geodynamics  

NASA Astrophysics Data System (ADS)

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

Hetényi, György; AlpArray Working Group

2013-04-01

135

Correlating basaltic composition with stages of geodynamic settings associated with breakup of supercontinent Rodinia  

NASA Astrophysics Data System (ADS)

The breakup of supercontinents is often accompanied by magmatism associated with many possible geodynamic scenarios and interactions between the mantle and the overlying continental lithosphere. We examine the geochemical and isotopic signature of late Proterozoic basalts of the Catoctin Volcanic Province (CVP) along eastern North America to identify the temporal tectono-magmatic stages associated with dispersal. We model Stage I basalt generation to be associated with incipient supercontinent extension with its chemical/isotopic signature dominated by sub-continental lithosphere mantle (SCLM). Stage II basalts mark transition to an incipient oceanic rift where Ocean island basalt (plume) or mid-ocean ridge basalt sources are diluted by SCLM. Stage III basalts are related to a mature mid-ocean ridge system where the source is dominated by the depleted asthenosphere MORB source. New isotopic and geochemical data from the Catoctin Formation (type area of CVP) in the region of the central Appalachian orogen show incompatible element ratios of Zr/Y = 4.91, La/Yb = 5.73, Th/Ta = 1.37 and Hf/Th = 2.82, as well as primitive mantle normalized trace element abundances with OIB affinity like Hawaii. These lavas have similar low Nb/La (0.63-1.04) as Hawaii but slightly higher Th/Ta (1.1-2.12). In Pb-Pb isotope space define a pseudo- binary trend between continental lithosphere-like sources and an OIB-like source similar to a C-like plume component suggestive of Stage II. Basalts of the Unicoi, Bassett and Sams Creek Formations are similar to the Catoctin Formation and are modeled as Stage II magmatism. Other basalts hosted within the Lynchburg and Ashe-Alligator Back formations are of both high (>2 wt %) and low (<2%) TiO2 types, where the low Titanium group is best modeled as stage I, while higher TiO2 samples reflect stage II OIB dominated source similar to the basalts of the Catoctin Formation. We emphasize that in order to confirm these stages additional precise geochemical data, especially Pb, Nd, Hf and Sr isotopes are required for basalts along eastern North America

Sinha, A.; Hanan, B. B.

2010-12-01

136

Testing absolute plate reference frames and the implications for the generation of geodynamic mantle heterogeneity structure  

NASA Astrophysics Data System (ADS)

Absolute reference frames are a means of describing the motion of plates on the surface of the Earth over time, relative to a fixed point or "frame." Multiple models of absolute plate motion have been proposed for the Cretaceous-Tertiary period, however, estimating the robustness and limitations of each model remains a significant limitation for refining both regional and global models of plate motion as well as fully integrated and time dependent geodynamic models. Here, we use a novel approach to compare five models of absolute plate motion in terms of their consequences for forward modelled deep mantle structure since at least 140 Ma. We show that the use of hotspots, either fixed or moving, or palaeomagnetics, with or without corrections for true-polar wander, leads to significant differences in palaeo-plate velocities of over 10 cm/yr as well as differences in the location of palaeo-plate boundaries of up to 30° in longitude and latitude. Furthermore, we suggest that first order differences in forward predicted mantle structure between the models are due mostly to differences in palaeo-plate velocities, whereas variation in the location of plate boundaries may contribute to smaller wavelength offsets. We present a global comparison of the absolute reference frames in terms of mantle structure, which we have tomographically filtered to reflect the resolution of the seismic tomography model S20RTS. At very long wavelengths hotspot models best reproduce the mantle structure. However, when geometry and the match of smaller-scale subducted slab volumes are compared, a hybrid model based on moving hotspots after 100 Ma and palaeomagnetic data before (with no corrections for true-polar wander), best reproduces the overall mantle structure of slab burial grounds, even though no single model fits best at all mantle depths. We find also that the published subduction reference frame tested here results in a modelled mantle structure that agrees well with S20RTS for depths > 2500 km, equivalent to subduction before the Cretaceous, but not for shallower depths. This indicates that a careful assimilation of hotspot, palaeomagnetic and seismic tomography data into future absolute plate motion models is required to derive a more robust subduction reference frame.

Shephard, G. E.; Bunge, H.-P.; Schuberth, B. S. A.; Müller, R. D.; Talsma, A. S.; Moder, C.; Landgrebe, T. C. W.

2012-02-01

137

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

NASA Astrophysics Data System (ADS)

The Carpathian-Pannonian system of Eastern and Central Europe represents a unique opportunity to study the interaction between surface tectonic processes involving convergence, extension and convective overturn in the upper mantle. Here, we present high-resolution images of upper mantle structure beneath the region from P-wave finite-frequency teleseismic tomography to help constrain such geodynamical interactions. We have selected earthquakes with magnitude greater than 5.5 in the distance range 30°-95°, which occurred between 2006 and 2011. The data were recorded on 54 temporary stations deployed by the South Carpathian Project (2009-2011), 56 temporary stations deployed by the Carpathian Basins Project (2005-2007), and 131 national network broadband stations. The P-wave relative arrival times are measured in two frequency bands (0.5-2.0 Hz and 0.1-0.5 Hz), and are inverted for Vp perturbation maps in the upper mantle. Our images show a sub-vertical slab of fast material beneath the eastern Alps which extends eastward across the Pannonian basin at depths below ˜300km. The fast material extends down into the mantle transition zone (MTZ), where it spreads out beneath the entire basin. Above ˜300km, the upper mantle below the Pannonian basin is dominated by relatively slow velocities, the largest of which extends down to ˜200km. We suggest that cold mantle lithospheric downwelling occurred below the Pannonian Basin before detaching in the mid-Miocene. In the Vrancea Zone of SE Romania, intermediate-depth (75-180 km) seismicity occurs at the NE end of an upper mantle high velocity structure that extends SW under the Moesian Platform, oblique to the southern edge of the South Carpathians. At greater depths (180-400 km), a sub-circular high velocity anomaly is found directly beneath the seismicity. This sub-vertical high-velocity body is bounded by slow anomalies to the NW and SE, which extend down to the top of the MTZ. No clear evidence of a residual slab is observed above the MTZ beneath the Eastern Carpathians. These observations suggest that intermediate-depth seismicity in Vrancea Zone is unlikely to be due to slab tearing, but rather could be explained by either gravitational instability or delamination of mantle lithosphere.

Ren, Y.; Stuart, G. W.; Houseman, G. A.; Dando, B.; Ionescu, C.; Hegedüs, E.; Radovanovi?, S.; Shen, Y.; South Carpathian Project Working Group

138

Geodynamic Models of Active Tectonics in the South-East Carpathians (Romania)  

NASA Astrophysics Data System (ADS)

The Vrancea region in the South-East Carpathians is the last remainder of subduction-strike slip tectonics along the Alpine-Carpathian-Pannonian region. Here, a near vertical slab is imaged by seismic tomography to a depth of about 300 km, coincident with up to magnitude 7.5 earthquakes in the depth range 90-140 km. Focal mechanisms show vertical extension in the slab, probably indicating that the slab is mechanically continuous and that slab detachment is ongoing. Regional GPS measurements were initiated in 1995 and substantially expanded in 2001 to register the seismic and tectonic evidence of subcrustal processes. The current GPS network consists of more than 50 campaign points and six permanent GPS stations and is operated by ISES (Netherlands) in collaboration with SFB-461 (Germany), the National Institute for Earth Physics (Romania), and the University of Bucharest (Romania). Here, we seek to interpret the velocity solution of Van der Hoeven et al. (2005) which shows up to 4 mm/yr horizontal motions relative to stable Europe. We separately explore various possible causes of the observed velocity field; post-seismic relaxation, wedge collapse and slab-related processes. Using a finite element method, we compute the post-seismic relaxation of the 1977 (Mw=7.5), 1986 (Mw=7.2) and 1990 (Mw=6.9) events in a three-dimensional model with a slab geometry that is appropriate for the region. We consider a wide range of models with realistic visco-elastic rheologies to conclude that the current contribution of post-seismic relaxation to the observed horizontal velocity field is below the noise level of the data. The Carpathians are typically considered as a fold-and-thrust belt which is why we consider the possibility that GPS velocities are the response to post-collisional collapse. We show that site velocities are mostly not directed downhill (at different wavelengths) and conclude that wedge collapse is not causing the GPS velocities. Finally, we use our regional geodynamic model to compute the contribution of break-off and sinking of the Vrancea slab. The directions and magnitudes of the predicted surface velocities are roughly similar to the GPS velocities up to 5-10 (depending on model parameters) asthenospheric Maxwell times after detachment. For typical earth parameters this means that current GPS velocities may reflect the response to total failure of the Vrancea slab somewhere during the last 16,000 years.

Govers, R.; Langebroek, P.

2005-12-01

139

Tectonic Geomorphology and Geodynamics of Rifting: Goodenough Basin, Papua New Guinea  

NASA Astrophysics Data System (ADS)

Variations in deformation style are evident along the rift axis of the Woodlark Basin and Papuan Peninsula, where oceanic rifting is propagating westward into a more distributed zone of continental lithospheric extension. The Goodenough Basin lies west of the westernmost segment of the Woodlark oceanic spreading zone. To its north lie the D'Entrecasteaux Islands, metamorphic core complexes rapidly uplifted through the Late Tertiary due to a combination of continental extension and density contrasts within the continental crust. To its south lies the Papuan Peninsula, the southern rift margin, the structural geometry of which has not been characterized previously. Analysis of SRTM digital elevation data together with fieldwork in March 2006 has allowed basic mapping of rift-bounding normal faults, with offset fault segments having lengths of up to 60 km. Geomorphic features such as linear range fronts with faceted spurs, tilted hangingwall surfaces and linear footwall drainage basins typify an immature and active rift margin. Fault traces are however buried beneath rapidly accumulating colluvial soils in this zone of tropical weathering and largely basaltic and gabbroic pre-rift lithologies. Footwall-derived, deltaic coarse clastics are uplifted and exposed in transfer zones between fault segments. These deposits, previously described as tectonically folded, show dip variations that may be explained as low-angle topset fluviatile conglomerates and angle-of-repose grain flow and mass flow conglomerates of Gilbert-type delta foresets. Staircases of offlapping depositional terraces are inferred to be the product of forced regression due to Late Quaternary footwall uplift superimposed upon Late Pleistocene glacio-eustatic fluctuations. Away from loci of coarse clastic input, raised terraces and platforms of coral and carbonate detritus occur, with raised notches evidencing continued Holocene uplift. Instrumentally recorded seismicity within the Goodenough Basin has been limited in the last few decades. But the tectonic geomorphology and implied uplift rates on its southern margin imply a significant seismic hazard, if controlled by seismogenic displacement events. Continental lithospheric extension west of the propagating tip of the Woodlark Basin has two distinct behaviours: To the north of the Goodenough Basin lie the documented metamorphic core complexes, with evidence for shallow-dipping, seismogenic normal faults. The southern continental rift margin and the Goodenough Basin are characterized by high angle faults and tectonic geomorphologies analogous to rift margins in central Greece or the Gulf of Suez, suggesting different lithospheric conditions. The region thus offers an ideal locale for studying the crustal conditions that determine extensional geodynamic states.

Collier, R. E.

2006-12-01

140

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

Microsoft Academic Search

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

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

2000-01-01

141

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

Microsoft Academic Search

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

Mian Liu; Hui Wang; Qingsong Li

2010-01-01

142

Evolution of Plate Tectonics From Hadean to the Modern Geodynamic Regime According to 3D Spherical Models With Self-Consistently Generated Plates  

Microsoft Academic Search

It has been proposed that the plate tectonic style has changed from the Hadean to the modern geodynamic regime. In the past decade, several studies have documented the effectiveness of plastic yielding in causing a basic approximation of plate tectonic behavior in mantle convection models with strongly temperature dependent viscosity, strong enough to form a rigid lid in the absence

H. van Heck; P. Tackley

2007-01-01

143

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

NASA Astrophysics Data System (ADS)

The physics governing the seismic cycle at seismically active subduction zones remains poorly understood due to restricted direct observations in time and space. 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.

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

2013-04-01

144

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

NASA Astrophysics Data System (ADS)

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

Plotnikova, I.

2009-04-01

145

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

146

Fluidity: Unstructured Adaptive Mesh Modelling for Geodynamics with a Fully--Implicit Free Surface  

NASA Astrophysics Data System (ADS)

We have developed a new computational modeling framework, Fluidity, for application to a range of two-- and three--dimensional geodynamic problems (Davies et al. 2011). The approach centers upon a finite element discretization on unstructured simplex meshes, which represent complex geometries in a straightforward manner. Throughout a simulation, the mesh is dynamically adapted to optimize the representation of evolving solution structures. The adaptive algorithm makes use of anisotropic measures of solution complexity, to vary resolution and allow long, thin elements to align with features such as boundary layers. The modeling framework developed differs from the majority of current mantle convection codes, which are typically based upon fixed structured grids. A thorough and detailed validation was therefore necessary. This has been successfully completed (Davies et al. 2011). Such benchmark comparisons highlight not only the robustness and accuracy of Fluidity but also the advantages of anisotropic adaptive unstructured meshes, significantly reducing computational requirements when compared to a fixed mesh simulation. In this study, we extend Fluidity to handle a true free--surface. Most mantle convection models treat the top surface as a free--slip boundary and topography is computed diagnostically from the normal stress. This relies on the assumption that the normal stress is balanced instantaneously by a change in buoyancy associated with surface deformation. However, Zhong et al. (1996) demonstrate that for wavelengths shorter than 1000 km and/or high effective lithospheric viscosity, the viscous relaxation time becomes of the same order as the time scale of mantle convection. In such circumstances one must account for the history dependence when computing topography and model a true free surface. This has recently become even more important as massively parallel adaptive mesh models allow one to simulate such length scales within global models (e.g. Stadler et. al. 2010). The inclusion of a time dependent free surface in mantle convection models may introduce a severe limitation on the timestep, to ensure numerical stability. In Kaus et al. (2010) this problem is addressed by introducing additional stabilization terms. In this presentation however we will introduce a new free surface method, in which free surface elevation is treated as an independent variable that is solved for in conjunction with the momentum and continuity equation using an implicit time integration. This removes the timestep constraint without the need for additional stabilization. We will present a series of benchmarks that demonstrate the benefit of this implicit approach. References D.R. Davies, C.R. Wilson and S. C.Kramer, Geochem. Geophys. Geosys. 12, 2011 S. Zhong, M. Gurnis and L. Moresi, Geophys. J. Int. 127, 1996 B.J.P. Kaus, H, Mühlhaus and D.A. May Phys. Earth Planet. Int. 181, 2010 G. Stadler, M. Gurnis, C. Burstedde, L.C. Wilcox, L. Alisic, and O. Ghattas, Science 329, 2010

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

2011-12-01

147

Geodynamic evolution of the Apenninic-Maghrebian orogen based on geological and geophysical data  

NASA Astrophysics Data System (ADS)

The orogenic belt of the central Mediterranean, which extends from northern Africa to the southern Apennines across Sicily and the Calabrian Arc (Apenninic-Maghrebian Orogen), is a orocline located between a new oceanic area, the Tyrrhenian Basin and a foreland structural domain. The latter is represented by an oceanic area, the Ionian Basin, bounded by two continental blocks, the Apulia to the north and the Pelagian Block to the south. Both these blocks have the innermost sectors involved in the orogenic process, after that they were detached giving rise since late Miocene to the deepest structural layer of the orogen: the External Thrust System. The ETS consists of a regional thrust-fold system and tectonically underlies a pile of rootless nappes, that constitute a relevant portion of the orogenic domain. Two major regional structural levels can be distinguished: the Apenninian-Maghrebian Chain and the Kabilo-Calabride Chain. The AMC represents a roof thrust system composed of inner carbonate platform units (Panormide and Inner Apenninic Platforms) and of basinal sequences, ascribed to the innermost Tethyan units or to the deformed sector of an originally outermost Ionian palaeobasin. The AMC is also characterized by the general decoupling of the enormous volumes of Tertiary silicoclastics. The KKC is composed by basement nappes, originated by the delamination of the European margin. Prolongate geological observations, integrated with geophysical data, along the orogen allow to restore a palaeogeographic picture and permit to outline the geodynamic evolution. A wide Tethyan basin, in which the Sicilide and Liguride sequences deposited, can be identified; it originated since late Jurassic and was located between the European margin of the Sardinia Block and the Maghrebian Block, which has been recognized by CROP-Mare seismic lines in the southern Tyrrhenian Sea and interpreted as basement of the carbonate platform sequences of Panormide units. Between the latter and the Afro-Adriatic foreland a basinal area has been identified and ascribed to part of the original Ionian oceanic basin, in which Ionian sequences (Imerese, Sicanian, Lagonegro Units) deposited. After a previous alpine orogenesis, whose evidences occur only in northern Calabria, the convergence resulted in the final closure of the Tethys realm. The subduction of the Tethyan slab became established along with the structural organization of the units of the European margin into a sliced basement chain (Kabylo-Calabride Chain) and emplacement of an accretionary wedge constituted by the Sicilide and Liguride Units. This is evident from: the development of a back-arc basin with oceanic crust (Balearic Basin) with consequent anticlockwise rotation of the Sardo-Corsican Block, by the formation of the calc-alkaline volcanic arc of Sardinia, and by the structural organization of an Africa-vergent accretionary wedge (Sicilide/Liguride mèlange complex). The end of this first phase of convergence is testified by the cessation of calc-alkaline volcanic activity, which coincides with the stop of anticlockwise rotation of the Sardo-Corsican Block at the Burdigalian-Langhian boundary. Geological data show that, during the same time interval, the orogenic areas suffered a tectonic phase which resulted in the wide superposition of units of internal origin (Sicilide and Liguride Units) upon the siliciclastic covers belonging to external sectors. Since Middle Miocene, a second phase led to the structural organization of the inner carbonate platform units (Panormide Units), detached from their basement, represented by the continental Maghrebian crust. The platforms thrust onto the Ionian basinal units (Imerese/Sicanian/M. Judica Units). The involvement of these units in the deformation front of the chain marks the beginning of subduction of the Ionian crust, and the progressive collision of the crustal back-stop of the chain against the Afro-Adriatic margins. On the African foreland, the crustal lineaments inherited from the Mesozoic palaeogeography, show an oblique direction w

Lentini, F.; Guarnieri, P.; Carbone, S.; di Stefano, A.

2003-04-01

148

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

NASA Astrophysics Data System (ADS)

The Yellowstone hotspot resulted from interaction of a mantle plume with the overriding North America plate. This feature and related processes have influenced a large part of the western U.S., producing the 16 Ma Yellowstone-Snake River Plain-Newberry silicic-basalt volcanic field (YSRPN). We integrate results from a multi-institution experiment that deployed 80 seismic stations and 160 campaign and 21 permanent GPS stations for 1999-2003. Crust and mantle velocity models were derived from inversion of teleseismic and local earthquake data. Kinematic and dynamic models were derived from inversion of GPS velocities constrained by stresses associated the topography and the +15 m geoid anomaly. Tomography revealed a P- and S-wave low-velocity body at depths of 8-16 km beneath the caldera that is interpreted as partial melt of 8-15% that feeds the youthful Yellowstone volcanic field. Volume changes in the magma chamber are responsible for GPS-measured episodes of uplift and subsidence of the caldera at decadal scales with average rates of ~20 mm/yr but much higher short-term rates of up to 80 mm/yr. An upper-mantle low-velocity body was imaged by inverting teleseismic data constrained by the geoid structure, crustal structure, and the upper mantle discontinuities. This low P and S velocity body extends from 80 km to ~250 km directly beneath Yellowstone and then continues to 650 km with unexpected tilt to the west at ~60°. The tilt is consistent with the ascent of the buoyant magma entrained in eastward return-flow of the upper mantle. We estimate this body has an excess temperature from 85K to 120K, depending on the water content and with up to 1.5% melt. Using the inclined plume-geometry and plate motion history, we extrapolate the Yellowstone mantle source southwestward ~800 km as a plume-head in oceanic lithosphere centered beneath the Columbia Plateau basalt field at 16 Ma. Magma ascent was truncated there by the passage of thicker continental lithosphere over the plume beginning at 12 Ma, reducing the rate of large-scale volcanic eruptions in the YSRP. The decapitated plume head beneath Oregon underwent mantle return flow above the subducting Juan de Fuca plate and was responsible for the NW transgressive magmatism of the Newberry system. We then model the overall kinematics of the western U.S. from GPS data as SW motion for the YSRP, ~2 mm/yr, rotating into E-W motion in the Basin-Range, with a cumulative rate of ~4 mm/yr, and rotating to the northwest at rates of up to ~5 mm/yr in the Pacific Northwest, totaling ~10 mm/yr. Geodynamic models employing the GPS data and geometry of the crust-mantle structure suggests that southwest motion of the YSRP is dominated by stresses produced by the high potential energy of the Yellowstone hotspot while westward motion of the Basin-Range is driven by stress differences associated with the high topography of the Rocky Mountains.

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

2006-12-01

149

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

150

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

NASA Astrophysics Data System (ADS)

The Lengguru accretionary wedge (West Papua) is located in a very active geodynamical context. It results from the oblique convergence between the Pacific plate and the Australian plate. All the wedge has been build between 11 and 2 Ma (Bailly et al., 09). Exceptional boulders of fresh eclogites were discovered in the internal part of the Lengguru wedge, in the so called Wandamen peninsula. The Wandamen peninsula displays an increasing metamorphic gradient from West to East. This metamorphic peninsula may also be regarded as the continuation of the inner part of the Central range of Papua New Guinea farther east. The eclogites area embedded in metasediments that present similarities with Mesozoic and Cenozoic sediments of the Australian margin in the continuation of Lengguru wedge. According to geochemical analysis of major and traces elements on the two freshest eclogites, their protolith has a Fe-Ti gabbroic composition. The CIPW norm of these rocks suggest a protolith, with 32% of pyroxenes, 47% of anorthite, less than 3% of olivine, with 7% of ilmenite and 7% of magnetite. Major elements show a tholeiitic characters. Traces elements suggest a T MORB signature with a high content of TiO2. The eclogites are medium to coarse grained. The metamorphic paragenesis consists of clinopyroxenes, garnets, amphiboles, rutiles, quartz and accessory minerals like apatites. Clinopyroxenes with omphacitic composition (XJd: 0.3-0.4) are poecilitic, rare textures of retrogression (symplectites) are observed. Symplectites are composed by diopside or Na-Ca-Fe pyroxene XJd (0.18) and albite, locally calcic amphiboles can replace the clinopyroxene. Garnet of several millimeters (3-4 mm) result from the aggregation of smaller euhedral crystals (500-700 µm). Some of them display atoll microstructure and exhibit a core filled by omphacite, slightly green amphibole, or by quartz. They contain minute inclusions of omphacite, amphibole, apatite, quartz. Many rutiles exsolutions are observed within the garnets, suggesting high metamorphic conditions. Garnets have a mixed composition between almandine and grossular. Inclusions of quartz in both garnet and omphacite are surrounded by fractures suggesting the previous occurrence of coesite. The sodic calcic and calcic greenish amphiboles are also important minerals of these eclogites. The PT conditions deduced from the eclogitic paragenesis are 14±3 kbar, 650±50°C. The Lengguru accretionary wedge has been active during 8 millions years, (between 11 and 2 Ma). So far we do not know the age of eclogitisation. However it is probably related to the accretionary wedge. Miocene pebbles were found engulfed within unmetamorphozed conglomerate (no metamorphic or magmatic pebbles were in the conglomerate) that overlies the eastern flank of the Wandamen massif suggesting that exhumation of eclogite was active after Miocene. Most of blueschist and eclogitic rocks in the world require at least 15 Ma for their formation and exhumation. These eclogites require the exceptional rapid process. Agard, P.,Yamato, P., Jolivet, L., Burov, E., (2009) Exhumation of oceanic blueschists and eclogites in subduction zones:Timing and mechanisms, EPSL, , 53-79 Bailly V., Pubellier M., Ringenbach J-C., de Sigoyer J., Sapin F. Jumps of deformation zones in a young convergent setting; the Lengguru fold-and-thrust belt, New Guinea Island, Lithos, doi:10.1016/j.lithos.2009.08.013

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

2010-05-01

151

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

152

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

153

Daly Lecture: Geochemical Insights into Mantle Geodynamics and Plume Structure (Invited)  

NASA Astrophysics Data System (ADS)

It is almost 50 years since the first documentation of mantle heterogeneity through the study of ocean island basalts (OIB) [1]. The origin, scale and source of these heterogeneities have been the subject of debate since then. One of the most common approaches in the study of mantle heterogeneities is to analyze the geochemistry of oceanic basalts brought to the surface by mantle plumes. The composition of these ocean island basalts is usually different from those extruded at mid-ocean ridges (MORB), even if some of the post-shield/rejuvenated volcanism of some islands present depleted isotopic signatures. Improved analytical precision for radiogenic isotopes, combined with statistical data treatment, allow for more detailed investigations into the geochemical variations of basalts related to hotspots and mantle plumes and for modeling of the shallow and deep plume structure. Identification of two clear geochemical trends (Loa and Kea) among Hawaiian volcanoes [2, 3] in all isotope systems [4], together with the recurrence of similar isotopic signatures at >350 kyr intervals, have implications for the dynamics and internal structure of the Hawaiian mantle plume conduit [5]. In this lecture, I will present a compilation of recent isotopic data for samples from the shield, post-shield/late shield and rejuvenated stages on Hawaiian volcanoes, focusing specifically on high-precision Pb isotopic data (MC-ICP-MS or DS, TS TIMS) and integrated with Sr, Nd and Hf isotopes. The Hawaiian mantle plume represents >80 Myr of volcanic activity in a pure oceanic setting and corresponds to a high plume flux. All isotopic systems indicate source differences for Loa- and Kea-trend volcanoes that are maintained throughout the ~1 Myr activity of each volcano and that extend back in time on all the Hawaiian Islands (to ~5 Ma). The Loa-trend source is more heterogeneous in all isotopic systems by a factor of ~1.5 than the Kea-trend source. There are also different geochemical trends with time (such as an increase of Pb isotopic ratios). Hawaiian post-shield and rejuvenated lavas have more Kea-like geochemical characteristics than the underlying shield lavas with only two exceptions. Their isotopic compositions are much less variable and extend towards more depleted values that depart from the shield mixing trends and that do not intersect MORB-type compositions. Comparable observations have been made on other oceanic islands [6] and this implies that the depleted component in mantle plumes is distinct from the MORB source, and is most likely unique to each plume. These results from Hawaii will be compared to other hotspots in different tectonic settings, such as Kerguelen, Galapagos, and Iceland, and some implications for mantle geodynamics will be discussed. [1] Gast et al. (1964) Science 145, 1181-1185. [2] Tatsumoto (1978) Earth and Planetary Science Letters 38, 63-87. [3] Abouchami et al. (2005) Nature 434, 3401-3406. [4] Weis et al. (2009) Eos Trans. AGU, 90(52), Abstract V41F-03. [5] Farnetani and Hofmann (2009, 2010) Earth and Planetary Science Letters 282, 314-322; 295, 231-240. [6] White (2010) Annual Review of Earth and Planetary Sciences 38, 133-160.

Weis, D. A.

2010-12-01

154

Using garnet peridotites as tools to reconstruct paleo-geodynamic settings of fossil continental collision zones  

NASA Astrophysics Data System (ADS)

Orogenic garnet peridotites (metamorphic rocks containing the characteristic HP garnet-olivine mineral assemblage) form volumetrically minor, but important components of (ultra)high pressure (UHP) metamorphic terranes. Such terranes form along convergent plate margins where two adjacent plates collide and one of the plates is subducted below the other. After eduction back to the surface such fossil continental subduction/collision zones form the basic components of exposed (U)HP metamorphic terranes. In the absence of significant amounts of tectonic overpressure (Vrijmoed et al., 2010), the discovery of diamond and majoritic garnet in (U)HP metamorphic terranes provide evidence that subduction of continental crust into the mantle was deep enough to reach the garnet stability field in the overlying mantle wedge above the subduction zone. Brueckner (1998) was the first author who noticed that garnet peridotite bodies, present in such mantle wedges, could be transferred during collision from the mantle wedge into the subducted continental crust. Subsequent buoyancy, most likely generated by slab break off of previously subducted oceanic crust, is the most likely candidate to enable the subducted continental crust and its garnet peridotite "cargo" to return back to (sub)crustal levels. During the latter process mantle wedge garnet peridotite may recrystallize (partly or completely) into what will be called here subduction zone garnet peridotite. Alternatively subduction zone garnet peridotite may be formed by prograde subduction of ultramafic protoliths (serpentinites, Fe-Ti peridotite) that may be present in subducting continental crust prior to subduction. Subdivision between these two basic types of orogenic garnet peridotites (mantle wedge - versus subduction zone peridotite) allows however that in mantle wedge garnet peridotite the subcontinental lithospheric mantle (SCLM) - versus crustal-incorporation processes can be identified which a.o. has lead to the recent recognition of a complete new, deep-seated, subcratonic, lithospheric mantle setting. In addition better characterization of SCLM processes in mantle wedge garnet peridotite will also allow for further subdivision of SCLM wedges into different subtypes that all may be present during collision in the hanging wall of a fossil collision/subduction system. In the following we will present the basic outlines of such a mantle wedge classification system. A simple "conceptual" model will be presented that will allow orogenic mantle wedge garnet peridotite to be used as a tool to reconstruct the former paleo-geodynamic setting of the collision/subduction system. Using field, petrological, geochemical, geochronological and geothermobarometric criteria, all of which can be analysed directly in the mantle wedge garnet peridotite body itself, the model allows for discrimination between four different end-member types within the SCLM (equivalent to young/hot/dynamic- versus cold/old/static mantle in thick or thin garnet-olivine bearing mantle wedges). In addition our conceptual model is based on the fundamental assumption that all SCLM was once formed by rising, accretion and cooling of hot asthenospheric mantle. Note also that all mantle wedge end member types may become overprinted by the subduction zone type. The latter, when complete, may evidently erase all former mantle wedge evidences. To test the applicability of our model we have applied the proposed mantle wedge classification system to well studied orogenic garnet peridotites of the Caledonian Orogeny in Scandinavia and the Triassic Sulu-Dabie Orogeny in China. Results will be presented. References: Brueckner (1998). Geology 26, 631-634; Vrijmoed et al. (2010). Eur. J. Mineralogy.

Zhang, Cong; van Roermund, Herman; Zhang, Lifei

2010-05-01

155

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

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

156

Neotectonics and Geodynamics In The Region of The Town of Bankya, Sofia Kettle (bulgaria)  

NASA Astrophysics Data System (ADS)

The Bankya tectonic node represents one of the most active contemporary mor- phostructural nodes in the SW part of the Sofia kettle. It is characterized geomorphp- logically as a region with active relief formation since the Upper Cretaceous till now. The emphasis in the present work is laid on the endogenic predetermination of the relief, formed in a zone with a dense network of fault structures along which slow and rapid tectonic movements have repeatedly proceeded. Lithostratigraphic units from the Upper Cretaceous series and the Paleogene, Neogene and Quaternary sys- tems are found in the studied region. The old tectonics is characterized by well pre- served fragments of the Late Cretaceous Lyulin volcanic apparatus. It was formed under island-arc conditions. The Senonian synsedimentary olistostromes and olisto- plates connected with tectonic landslides and klippes of a local thrust were related to the gravitation tectonics. The Middle Miocene thrust over Lyulin to the N was re- lated to the post-sedimentary processes. The following stage was that of the regional Neogene-Quaternary extension and the formation of the Sofia graben. The Lyulin Mt. morphostructure was formed starting with its orogenic (volcanic) stage and passing through the building and transformation of the younger geological cycles. The con- trast between the mountain and the Sofia kettle was not significant until the final cycle of the Neogene. Active movements took place along the faults striking to the between 30-40 to the E of the town of Bankya. A local widely opened to the NE graben was formed and loaded with sediments. The terrain was subjected to vertical compression. The organogenic construction of the Lyulin Mt. was formed and the contrast between the two morphostructures became stronger. The process of construction still contin- ues as seen from the incomplete profile, the anomalous falls, the deformations and displacements of the river terraces, the different alluvium thickness, etc. The gravi- tation process including almost entirely the valley slopes is tectonically and erosion- tectonically predetermined. Most of the landslides are of the circus type but there are landslides of the linear type too. The erosion incision of the riverbeds resulting from the contemporary tectonic movements is in the range of 10-12 to 20 m. There was a local earthquake (intensity of VI degree, epicentre depth between 8 and 10 km) in the region of Bankya in 1910. This earthquake disturbed the Plio-Pleistocene 1 erosion-accumulation level. Considerable relief deformations took place due to a pa- leoearthquake of the seismic-gravitational type and three landslide terraces with a slope height of more than 10 m were formed. The analysis shows that the relief of the Bankya tectonic node is a result of long-term endogenic processes. The fault structures are characterized by high activity, which is classified as potentially seismic hazardous in combination with their complex morphology. The relief is under the conditions of unstable dynamic equilibrium that provides the grounds to presume that there is a change in the local stress field. It is necessary to build a geodynamic monitoring polygon. 2

Angelova, D.

157

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

NASA Astrophysics Data System (ADS)

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

Georgiev, Ivan; Ganas, Athanassios

2013-04-01

158

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

NASA Astrophysics Data System (ADS)

Chronological succession in the formation of spreading basins is considered in the context of reconstruction of breakdown of Wegener’s Pangea and the development of the geodynamic system of the Arctic Ocean. This study made it possible to indentify three temporally and spatially isolated generations of spreading basins: Late Jurassic-Early Cretaceous, Late Cretaceous-Early Cenozoic, and Cenozoic. The first generation is determined by the formation, evolution, and extinction of the spreading center in the Canada Basin as a tectonic element of the Amerasia Basin. The second generation is connected to the development of the Labrador-Baffin-Makarov spreading branch that ceased to function in the Eocene. The third generation pertains to the formation of the spreading system of interrelated ultraslow Mohna, Knipovich, and Gakkel mid-ocean ridges that has functioned until now in the Norwegian-Greenland and Eurasia basins. The interpretation of the available geological and geophysical data shows that after the formation of the Canada Basin, the Arctic region escaped the geodynamic influence of the Paleopacific, characterized by spreading, subduction, formation of backarc basins, collision-related processes, etc. The origination of the Makarov Basin marks the onset of the oceanic regime characteristic of the North Atlantic (intercontinental rifting, slow and ultraslow spreading, separation of continental blocks (microcontinents), extinction of spreading centers of primary basins, spreading jumps, formation of young spreading ridges and centers, etc., are typical) along with retention of northward propagation of spreading systems both from the Pacific and Atlantic sides. The aforesaid indicates that the Arctic Ocean is in fact a hybrid basin or, in other words, a composite heterogeneous ocean in respect to its architectonics. The Arctic Ocean was formed as a result of spatial juxtaposition of two geodynamic systems different in age and geodynamic style: the Paleopacific system of the Canada Basin that finished its evolution in the Late Cretaceous and the North Atlantic system of the Makarov and Eurasia basins that came to take the place of the Paleopacific system. In contrast to traditional views, it has been suggested that asymmetry of the northern Norwegian-Greenland Basin is explained by two-stage development of this Atlantic segment with formation of primary and secondary spreading centers. The secondary spreading center of the Knipovich Ridge started to evolve approximately at the Oligocene-Miocene transition. This process resulted in the breaking off of the Hovgard continental block from the Barents Sea margin. Thus, the breakdown of Wegener’s Pangea and its Laurasian fragments with the formation of young spreading basins was a staged process that developed nearly from opposite sides. Before the Late Cretaceous (the first stage), the Pangea broke down from the side of Paleopacific to form the Canada Basin, an element of the Amerasia Basin (first phase of ocean formation). Since the Late Cretaceous, destructive pulses came from the side of the North Atlantic and resulted in the separation of Greenland from North America and the development of the Labrador-Baffin-Makarov spreading system (second phase of ocean formation). The Cenozoic was marked by the development of the second spreading branch and the formation of the Norwegian-Greenland and Eurasia oceanic basins (third phase of ocean formation). Spreading centers of this branch are functioning currently but at an extremely low rate.

Shipilov, E. V.

2008-03-01

159

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

NASA Astrophysics Data System (ADS)

The 1167 published cooling unit (CU) palaeointensity estimates contained in the 400-10 Ma portion of the PINT global database were rigorously filtered according to accurate age determinations, palaeodirectional reliability, recognition of polarity and the method of palaeointensity acquisition. The remaining 865 estimates (group 1) were further filtered to ensure self-consistency, reducing the data set to 425 estimates (group 2). Group 1 and 2 data were clustered into temporally and/or spatially distinct rock suites (RS) enabling each part of the record to be assessed for potential biasing by overrepresentation of palaeosecular variation (PSV). The record was segmented according to the distribution of the data, rather than using arbitrary time windows, to ensure quasi-consistent behaviour within each segment. Differences between these segments clearly indicate that a significant long-timescale (107 and 108 yr) variation of the mean geomagnetic poloidal field intensity (GPFI) occurred during the 400-10 Ma period and hence that changing lowermost mantle conditions affect the capacity of the geodynamo to generate a poloidal field. Both the mean dipole moment and its standard deviation appear to be a function of the range of values each CU may adopt at one particular time. This range is itself controlled by the variation of the maximum limit of dipole moment, while the value of the minimum limit remains relatively constant. Tentative support is provided for the recent suggestion that PSV may have been reduced during the Cretaceous normal superchron (CNS), though more data are needed in the range 120-60 Ma to confirm this. No conclusive evidence was found to support the suggestion that the GPFI record may be biased towards low or high values by palaeointensity determinations obtained using methods that do not adopt pTRM checks. Indeed, offsets caused by unreliable data in well-represented parts of the record are likely to be random and cancel one another out. When GPFI variation is analysed at a sufficiently high resolution to allow comparisons with the geomagnetic polarity reversal frequency (RF), it is not possible to confirm whether the two parameters are anticorrelated, decoupled or related in some more complex way. However, it is clear that GPFI and RF are definitely not positively correlated as has been previously suggested. The present database documents sharp increases in GPFI around the onset times of the two recognized superchrons, itself implying an anticorrelation. The implications, for geodynamo and mantle modelling, of both an anticorrelation and a decoupling of the geomagnetic parameters are discussed briefly. A generic geodynamic model is proposed to explain the relationship between observed long-term changes in GPFI and global geodynamic processes. The model predicts that changes in GPFI result from a chain of geodynamic processes extending from crust to core, beginning with plate reorganizations at the surface and culminating in increases in the vigour of outer core convection. Supercontinents are transient surface expressions of such geodynamic processes and provide the potential to test the generic model. Four time stages are proposed to describe the major long-term changes in GPFI since the Early Devonian: 400-350, 350-250, 250-175 and 175-10 Ma. The GPFI features within these stages are convincingly explained within the context of major events in the evolutionary cycle of Pangaea. Two major avalanching and mantle reorganization events, facilitating whole-mantle convection, are proposed; one linked with the amalgamation of Pangaea, the other (possibly less catastrophic) with the dispersal phase of the supercontinent. These events were separated by a period of mantle insulation during the time when the supercontinent was assembled and a layered mantle convection regime existed. The explanations are consistent with independent evidence from seismology, mantle modelling and mantle dynamics, though some ambiguities and intriguing relationships remain, which can only be addressed by the addition of high-quality

Biggin, A. J.; Thomas, D. N.

2003-02-01

160

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

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

161

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

162

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

NASA Astrophysics Data System (ADS)

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

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

2009-04-01

163

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

NASA Astrophysics Data System (ADS)

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

Muslimov, R.; Plotnikova, I.

2012-04-01

164

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

Microsoft Academic Search

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

N. I. Filatova

2006-01-01

165

Geomorphology and Geodynamics of the Cook-Austral Island-Seamount Chain in the South Pacific Ocean: Implications for Hotspots and Plumes  

Microsoft Academic Search

Among Pacific hotspot tracks, the Cook-Austral island-seamount chain is distinctly anomalous in geodynamic behavior, exhibiting repetitive episodes of volcanism at multiple sites, uplift of selected islands long after initial immersion by subsidence, and multiple alignments of volcanic edifices. Cook-Austral islands include a variety of disparate geomorphic types: volcanic islands without reefs, with fringing reefs, and with barrier reefs enclosing shallow

William R. Dickinson

1998-01-01

166

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

167

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

USGS Publications Warehouse

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

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

2004-01-01

168

Geodynamics of the Carpathian-Pannonian region: Insights from low temperature thermochronology of the Polish and Ukrainian Carpathians  

NASA Astrophysics Data System (ADS)

In recent years, the geodynamic evolution of the Carpathian-Pannonian region has been the subject of a heated scientific debate. This orogenic system formed between the Late Jurassic and the Neogene by the collision of the Alcapa and Tisza-Dacia microplates with the European Platform, and assumed its present-day configuration mainly during the Miocene, when the extensional Pannonian Basin formed in a retro wedge position, while compression was still active along the Carpathian front. The most common and widely accepted interpretation for the Miocene evolution of this region is based on a classical back-arc extension model and subsequent astenospheric upwelling and slab break-off. Nonetheless several authors proposed other possible driving mechanisms for the formation of the Pannonian Basin, such as lithosphere delamination or lithospheric gravitational instability. Thermochronometry provides important constrains to the depths of burial and to the timing and rates of exhumation. Each geodynamic scenario proposed for the Carpathian-Pannonian region implies a different spatial distribution of burial and a different timing of exhumation. In this work we use a compilation of several low-temperature thermochronometric datasets, referred to the Polish and Ukrainian Carpathians, to evaluate their compatibility with the different geodynamic models proposed so far. In order to achieve this goal we examine the spatial distribution of burial depths and of ages and rates of exhumation and we put them in relation with (i) the spatial trend of the relief, (ii) heat flow, (iii) crustal and lithospheric thickness, and (iv) structural setting. We propose a subdivision of the Polish and Ukrainian Carpathians in three different tectonic domains, based on geophysical and structural parameters. Each single area is characterized also by different burial-exhumation history and requires a specific explanation in terms of driving processes. In particular, we infer that exhumation occurred by erosion of the wedge during thrusting in the western area, by erosion and tectonic denudation driven by post-thrusting extension in the central sector, and by erosion of the uplifting wedge after the end of thrusting in the eastern sector. Based on the non-homogeneous burial depths inferred for the western and central sectors, we suggest the lack of a subducting slab and subsequent break-off in these areas. Furthermore, the distribution of exhumation ages along the chain is not compatible with a clockwise (E to SE ward) progressive slab break-off, the youngest ages being located in the central area, at the Polish-Ukraine boundary. Our results are consistent with the hypothesis that Miocene extension of the Carpathian-Pannonian region was triggered by gravitational instability and subsequent lithosphere downwelling, below the Carpathians mountain belt, and astenosphere upwelling below the Pannonian Basin. This process is compatible with the burial-exhumation distribution observed along the study region. Furthermore, it is able to explain both the coupled crustal extension and lithospheric thickening observed in the central sector (Poland-Ukraine boundary) and the progressive transition between the extending and subsiding Pannonian Basin and the uplifting Carpathians in the eastern area.

Andreucci, Benedetta; Zattin, Massimiliano; Castelluccio, Ada; Mazzoli, Stefano; Szaniawski, Rafal; Jankowski, Leszek

2013-04-01

169

Geodynamical Interpretation of Crustal and Mantle Shear-Wave Velocity Structures Beneath the Carpathian-Pannonian Region  

NASA Astrophysics Data System (ADS)

The Carpathian-Pannonian system of Eastern and Central Europe represents a unique opportunity to study the interaction between surface tectonic processes involving convergence and extension, and convective processes in the upper mantle. The South Carpathian Project (SCP), a major temporary deployment (2009-2011) of seismic broadband systems extending across the eastern Pannonian Basin and the South Carpathian Mountains was set up with the purpose of bringing constraints on the geodynamical processes that have shaped the region. Imaging the seismic velocity structure of the crust and the upper mantle helps us to understand the structure and geodynamical evolution of this part of central Europe. Here, we present high-resolution images of both crustal and upper mantle shear-wave velocity structures beneath the Carpathian-Pannonian region using surface waves obtained from ambient noise tomography, and finite-frequency teleseismic tomography using S-wave arrivals, from 54 stations of the South Carpathian Project (SCP, 2009-2011), 56 stations of the Carpathian Basins Project (CBP, 2005-2007) and 131 national network broadband stations. For ambient noise tomography, we computed cross-correlations of vertical component continuous ambient seismic noise recordings for all possible pairs of stations and stacked the correlated waveforms over 1-2 years for the temporary stations and up to 5 years for permanent stations to estimate Rayleigh wave empirical Green's functions. Over 5700 final Rayleigh wave Green's functions were selected for the measurement of group velocity dispersion curves between 4s and 40s using the multiple-filter analysis technique. Group velocity maps are first computed on a grid discretized with 0.2°x0.2° steps from a non-linear 2-D tomographic inversion of measured group velocity dispersion curves. We then inverted the Rayleigh wave group velocity at each location to obtain the 3-D shear-wave velocity structure of the crust and uppermost mantle beneath the Carpathian-Pannonian region. In the finite-frequency teleseismic tomography of S waves, we have selected earthquakes with magnitude greater than 5.5 in the distance range 30°-95°, which occurred between 2006 and 2011. Using multi-channel cross-correlation technique, over 29661 and 41875 relative S arrival times were measured in high and intermediate frequency bands (0.1-0.5 Hz and 0.05-0.1 Hz) respectively. The relative arrival times are inverted for S-wave velocity distribution in the upper mantle according to the 3-D finite frequency kernel formulation. Our shear-wave velocity models provide a uniquely complete and relatively high-resolution view of the crustal and upper mantle structures in the region. We will discuss the interpretations of these velocity variations for the formation and geodynamical evolution of the lithosphere and upper mantle of the Carpathian-Pannonian region.

Ren, Yong; Stuart, Graham; Houseman, Gregory; Grecu, Bogdan; Ionescu, Constantin; Hegedüs, Endre; Radovanovi?, Slavica; Shen, Yang; South Carpathian Project working group

2013-04-01

170

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

NASA Astrophysics Data System (ADS)

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

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

2005-12-01

171

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

NASA Astrophysics Data System (ADS)

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

Chelidze, Tamaz; Eppelbaum, Lev

2013-04-01

172

About Geodynamic Situation of the Formation and Development of the Inside Formation Throughs of the Volga-Ural Region  

NASA Astrophysics Data System (ADS)

The study area is the South Tatarstan Arch located in the Volgo-Ural Region, which is an enigmatic crustal segment occupying one third of the East European Platform. Tatarstan remains the oil-richest region of the Volga-Urals petroleum province. Sedimentary geological section consists of terrigenous-carbonate rocks of Devonian, Carboniferous and Permian systems. Its thickness is as much as 1,6 - 1,7 km in the most elevated parts of South Tatarsky Arch. It is supposed that deposits of Semilukian horizon (D3fm) represented by carbonate and argillo-carbonate silicified rocks characterized by the 3-5% abundance of organic carbon are major oil-generating complexes within the limits of this area. Oil accumulations are confined mostly to terrigenous reservoirs of the Lower Frasnian stage and to a lesser extent to sandy-aleurolite rocks of the Lower and Middle Carboniferous. Submeridional, latitudinal and diagonal faults related to processes taking place in the crystalline basement at the Early Paleozoic stage are predominating among faults identified within the limits of the studied area. The traces of discontinuities are identified from the gabbro - diabase dykes, products of the volcanic activity encountered in the Middle Devonian deposits, and from increased fracturing of rocks. Faults of various ranks are distinctly exhibited in the up-to-date relief. In the sedimentary cover faults are exhibited as flexure - discontinuity zones or structural terraces, they serve as boundaries between sharply replaced facies and sharp changes in the thickness of deposits. Problem of the origin and development of the Kama-Kinel inside formation through (KKIFT) as before is topical and significant for understanding of geodynamic situation of paleoshelf of East-European platform in Middle-Upper Devonian. Absence in KKIFT of thick, massive carbonaceous rocks and occurrence of decreased thickness of clay- silicon-carbonaceous organic-rich sediments - result of the different conditions of the sedimentation processes, different conditions of the gas-water composition characteristics of the marine basin, different conditions of the lithosphere. Paleogeografical, paleotectonical, lithofacies conditions - result of the specific geodynamic and fluid regime of the sedimentftion. Similar forms are widespread on the territory of the Volga-Ural antecline (from Samara area in the south to Perm in the north) and are of significant interest for regional petroleum geology as a whole. Section correlation of recognized components demonstrates their tectonic regime was deal with lithosphere decompression, active gas-fluid regime of the reduced system. Problem of studying carbonate deposits and their reservoir potential is related to the most important for board parts of the KKIFT.

Plotnikova, Irina

2010-05-01

173

Development of the New Zealand and San Andreas Continental Transforms: From Plate Kinematics to Lithospheric Geodynamics (Invited)  

NASA Astrophysics Data System (ADS)

Although oftentimes compared as being two similar continental transforms, the development of the San Andreas and Alpine Fault plate boundary systems reflect two distinctly different geodynamic paths to formation, localization, and evolution. Characteristics that lead to fundamental differences in their present-day tectonic behavior. The San Andreas system has formed in response to the migration of two triple junctions, and it lengthens over time at these transitions from subduction to translation. The San Andreas system forms within the region of thin lithosphere left in the wake of slab removal or subduction cessation, and therefore thermal processes dominate in the development of a localized plate boundary. There are associated short-lived deformational events including significant crustal thickening and subsequent crustal thinning that serve to substantially modify the overlying North American crust during this 3-5 million year transition time. In contrast the development of the Alpine Fault plate boundary system through New Zealand follows a different geodynamic path, and this transform boundary reflects an intermediate point in the overall transition of that Australia-Pacific plate boundary through New Zealand from an extensional to convergent boundary. Since approximately 25 Ma, with rapid changes in Australia-Pacific plate interactions, the plate boundary structure through continental New Zealand rapidly changed from extensional to translation/transpression. This transpression was accommodated by the initiation of two subduction regimes, whose positions were controlled by continent-ocean transitions linked by the translational/transpressional (proto) Alpine Fault system. This trench-transform-trench plate boundary system has migrated southward, maintaining essentially a constant length, but not constant localization, and along the way, ephemerally incorporating segments of the Australia and Pacific plates into the boundary - modifying, exhuming, and removing lithosphere. In spite of some present kinematic similarities, the history and ongoing tectonic evolution of these two prototypical continental transforms demonstrates the importance of the tectonic pathway to the development of a plate boundary and provides critical constraints on using these boundaries to understand fundamental plate boundary processes.

Furlong, K. P.

2009-12-01

174

Joint Modelling of Seismic, Geodynamic and Mineral Physics Data: Implications for the Origin of 3-D Density and Seismic Velocity Anomalies in the Mantle.  

NASA Astrophysics Data System (ADS)

Models of instantaneous (present-day) mantle dynamics provide strong constraints on the distribution and amplitude of 3-D density anomalies. In recent work [Forte, Mitrovica & Espesset, Phil. Trans., 2002], we developed models of 3-D mantle flow based on high-resolution tomographic models of global seismic shear velocity heterogeneity [e.g., Grand, Phil. Trans., 2002] which reconcile a wide variety of surface manifestations of mantle convection which include global gravity anomalies, plate tectonic motions, dynamic surface topography and the dynamic ellipticity of the core-mantle boundary. These diverse geodynamic observables provide direct constraints on the mantle density anomalies which are the driving force of the convective flow field. These density anomalies may be inferred by carrying out joint inversions of the geodynamic data sets, in which we assume a correlation between mantle density anomalies and the seismic velocity anomalies in a given tomography model. Neither the sign of the correlation (which may be positive or negative), nor the amplitude of the density anomalies is constrained to a-priori values in these inversions but are instead allowed to vary in order to provide optimal fits to the surface geodynamic data sets. The relationship between the geodynamically inferred density anomalies and seismic anomalies, when taken in conjunction with the separate mineral physical constraints on thermal and compositional derivatives [e.g., Karato, 1993; Wang & Weidner, 1996; Stacey, 1998], provide direct insights on the relative importance of thermal and chemical contributions to mantle heterogeneity [e.g., Forte & Mitrovica, Nature, 2001]. We will present the results of new density inversions employing mantle flow models based on the most recent mantle viscosity profiles derived by jointly inverting an updated and enlarged set of glacial isostatic adjustment data and mantle convection data sets [Mitrovica & Forte, 2003]. We have also devised a new and independent test of the origin of mantle heterogeneity by carrying out joint global inversions of seismic and geodynamic data [Grand & Forte, this meeting] assuming different scalings between density and seismic velocity which may be derived from mineral physics data. These hypothesis tests, as well as the direct inversions for mantle density, show a simple positive correlation between seismic shear velocity and density which is in accord with a dominant thermal origin for this heterogeneity.

Forte, A. M.; Mitrovica, J. X.; Grand, S. P.

2003-12-01

175

Functioning analysis of reference station in Hornsund and its possibilities of usage in geodynamic research of Spitsbergen  

NASA Astrophysics Data System (ADS)

Poster presents the analysis of observations collected during the measurements made by two reference stations working in surroundings of the Polish Polar Station in Hornsund. One of them, ASTR station has been working since 2005. Its functioning in the first period indicates significant multipath effect caused by the proximity of facilities of the Polish Polar Station. The effect occurred to be high enough to decide about the change of location of the antenna, which was possible only after completion of the building works of the polar station. During the expedition in 2008 the final location of the reference station, where conditions comply with the requirements, was chosen. So, the second station - HORN - was started, and series of test measurements were conducted, which allowed to determine the position of the station and to analyze GNSS signal quality. The poster presents comparative analysis of the observations collected by the old (ASTR) and new (HORN) localisation of antenna and contains description of the surroundings of the antenna and their influence on the multipath effect. Authors present as well the possibility of usage of the reference station in scientific research conducted nearby the Polish Polar Station in Hornsund. Moreover, the poster presents a concept of establishment of "the system of reference stations around Spitsbergen" and possibilities of participation of the planned system in global environmental and geodynamic research.

Wezka, K.; Pasnikowski, M.; Walo, J.

2009-04-01

176

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

NASA Astrophysics Data System (ADS)

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.

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

2007-07-01

177

Three-dimensional geodynamic framework for the central Southern Alps, New Zealand: Integrating Geology, Geophysics and Mechanical Observations  

NASA Astrophysics Data System (ADS)

Vertical and horizontal strain within oblique convergence reflects imposed tectonic and surficial boundary conditions as transmitted via the rheological structure of the deforming crust. We combine three-dimensional mechanical modeling with geological and geophysical observations to develop a geodynamic framework for the central Southern Alps of New Zealand. We propose that an along-strike variation in crustal thickness and strength exists within South Island, with Otago having a thicker and weaker crust. This rheological structure and the presence of elevated pore pressure beneath the Mt Cook-Aoraki region results in predictable distribution of strain and stress conditions which are compatible with observations of surface strain. The models predict that these two features lead to enhanced rates of rock uplift against the Alpine Fault adjacent to Mt Cook-Aoraki region. This results from two components of vertical stretching: the first caused by strong Canterbury lower crust pushing into weak Otago lower crust, causing vertical extrusion; and the second a result of elevated pore pressure in the mid-crust. Extensional strain predicted in the upper crust is confirmed by the presence of sub-vertical mineralized veins and earthquakes with a normal fault solution in the upper 5-8 kms of the Main Divide region.

Upton, Phaedra; Koons, Peter O.

178

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

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

179

Present-day geodynamics in the bend of the western and central Alps as constrained by earthquake analysis  

NASA Astrophysics Data System (ADS)

The contrasted tectonics of the western/central Alps is examined using a synthesis of 389 reliable focal mechanisms. The present-day strain regime is mapped and interpolated for the entire Alpine belt based on a newly developed method of regionalization. The most striking feature is a continuous area of extension which closely follows the large-scale topographic crest line of the Alpine arc. Thrusting is observed locally, limited to areas near the border of the Alpine chain. A majority of earthquakes within the Alps and its forelands are in strike-slip mode. Stress inversion methods have been applied to homogenous subsets of focal plane mechanisms in order to map regional variations in stress orientation. The stress state is confirmed to be orogen-perpendicular both for ?3 in the inner extensional zones and ?1 in the outer transcurrent/transpressional zones. Extensional areas are well correlated with the part of the belt which presents the thickest crust, as shown by the comparison with the Bouguer anomaly and the average topography of the belt. In the northwestern Swiss Alps, extension is also correlated with currently uplifting zones. These observations and our strain/stress analyses support a geodynamic model for the western Alps in which the current activity is mostly a result of gravitational `body' forces. Earthquakes do not provide any direct evidence for ongoing convergence in the Alpine system, but a relationship with ongoing activity of complex block rotations of the Apulian microplate cannot be ruled out.

Delacou, Bastien; Sue, Christian; Champagnac, Jean-Daniel; Burkhard, Martin

2004-08-01

180

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

NASA Astrophysics Data System (ADS)

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

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

181

3-D velocity model beneath the Middle–Lower Yangtze River and its implication to the deep geodynamics  

NASA Astrophysics Data System (ADS)

A mineralization zone exists in the Middle and Lower Yangtze River (MLYR) region. Previous studies have shown that this zone might be caused by the rich ejection of magma in the Mesozoic. We have applied the teleseismic tomography method to determine a 3-D P-wave velocity structure of the mantle down to 500 km depth beneath this region by using 14,740 P-wave arrival times collected from 519 teleseismic events recorded by 46 portable and 47 static seismic stations located in this region. The relative residual times used for the tomography are calculated by the modified multi-channel cross-correlation method which increases not only the efficiency but also the data precisions up to 0.01 s. The grid space is set as 1° × 1° horizontally and 50–100 km vertically. Our tomographic results show that the lithosphere with high velocity anomalies is separated into two parts: one locates above the depth of 100 km and the other at the depths between 250 km and 400 km, and the asthenosphere with low velocity anomalies locates between these two parts of lithosphere, which indicates that the lithosphere delaminated together with the asthenosphere upwelling. The detachment of lithosphere might relate to the subduction of the western Pacific slab. Therefore, our study provides clear evidence to geoscientists for understanding the deep dynamic process beneath this region and a three-stage geodynamic process is developed based on the new evidence.

Jiang, Guoming; Zhang, Guibin; Lü, Qingtian; Shi, Danian; Xu, Yao

2013-10-01

182

Two-Dimensional Geothermal Modelling Along the Central Pontides Magmatic Arc: Implications for the Geodynamic Evolution of Northern Turkey  

NASA Astrophysics Data System (ADS)

The Pontides, which can be divided tectonically into three main segments as Eastern, Central, and Western Pontides, is one of the most complex geodynamic settings within the Alpine belt. The Central Pontides, where the Eastern and Western Pontides met and formed a tectonic knot, represent an amalgamated tectonic mosaic consisting of remnants of oceanic, continental, and island arc segments. Subduction polarity, which is responsible for the formation of the Pontides, is still under debate because of limited geological, geophysical, and geochemical data. Two-dimensional (2-D) thermal modelling studies along the Central Pontides magmatic arc (Northern Turkey), Sakarya and K?r?ehir continents are investigated in order to delineate the crustal thermal structure and subduction polarity. The obtained numerical results indicate that arc and back-arc regions are hot because of the cooling effects of a subducting plate. Moho temperatures in the investigated region are found between 992°C in the south (back-arc) and 415°C in the north (arc). Moreover, mantle heat flow values vary from 57.2 mWm-2 in the south (back-arc) to 34.7 mWm-2 in the north (arc). It is shown from this study that the Eurasia plate had moved from north to south under the Anatolia plate along the south Black Sea coast.

Maden, Nafiz

2012-03-01

183

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

184

Time-dependent convection models of mantle thermal structure constrained by seismic tomography and geodynamics: implications for mantle plume dynamics and CMB heat flux  

NASA Astrophysics Data System (ADS)

One of the outstanding problems in modern geodynamics is the development of thermal convection models that are consistent with the present-day flow dynamics in the Earth's mantle, in accord with seismic tomographic images of 3-D Earth structure, and that are also capable of providing a time-dependent evolution of the mantle thermal structure that is as 'realistic' (Earth-like) as possible. A successful realization of this objective would provide a realistic model of 3-D mantle convection that has optimal consistency with a wide suite of seismic, geodynamic and mineral physical constraints on mantle structure and thermodynamic properties. To address this challenge, we have constructed a time-dependent, compressible convection model in 3-D spherical geometry that is consistent with tomography-based instantaneous flow dynamics, using an updated and revised pseudo-spectral numerical method. The novel feature of our numerical solutions is that the equations of conservation of mass and momentum are solved only once in terms of spectral Green's functions. We initially focus on the theory and numerical methods employed to solve the equation of thermal energy conservation using the Green's function solutions for the equation of motion, with special attention placed on the numerical accuracy and stability of the convection solutions. A particular concern is the verification of the global energy balance in the dissipative, compressible-mantle formulation we adopt. Such validation is essential because we then present geodynamically constrained convection solutions over billion-year timescales, starting from present-day seismically constrained thermal images of the mantle. The use of geodynamically constrained spectral Green's functions facilitates the modelling of the dynamic impact on the mantle evolution of: (1) depth-dependent thermal conductivity profiles, (2) extreme variations of viscosity over depth and (3) different surface boundary conditions, in this case mobile surface plates and a rigid surface. The thermal interpretation of seismic tomography models does not provide a radial profile of the horizontally averaged temperature (i.e. the geotherm) in the mantle. One important goal of this study is to obtain a steady-state geotherm with boundary layers which satisfies energy balance of the system and provides the starting point for more realistic numerical simulations of the Earth's evolution. We obtain surface heat flux in the range of Earth-like values : 37 TW for a rigid surface and 44 TW for a surface with tectonic plates coupled to the mantle flow. Also, our convection simulations deliver CMB heat flux that is on the high end of previously estimated values, namely 13 TW and 20 TW, for rigid and plate-like surface boundary conditions, respectively. We finally employ these two end-member surface boundary conditions to explore the very-long-time scale evolution of convection over billion-year time windows. These billion-year-scale simulations will allow us to determine the extent to which a 'memory' of the starting tomography-based thermal structure is preserved and hence to explore the longevity of the structures in the present-day mantle. The two surface boundary conditions, along with the geodynamically inferred radial viscosity profiles, yield steady-state convective flows that are dominated by long wavelengths throughout the lower mantle. The rigid-surface condition yields a spectrum of mantle heterogeneity dominated by spherical harmonic degree 3 and 4, and the plate-like surface condition yields a pattern dominated by degree 1. Our exploration of the time-dependence of the spatial heterogeneity shows that, for both types of surface boundary condition, deep-mantle hot upwellings resolved in the present-day tomography model are durable and stable features. These deeply rooted mantle plumes show remarkable longevity over very long geological time spans, mainly owing to the geodynamically inferred high viscosity in the lower mantle.

Glišovi?, P.; Forte, A. M.; Moucha, R.

2012-08-01

185

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

NASA Astrophysics Data System (ADS)

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

Besutiu, L.

2012-04-01

186

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

NASA Astrophysics Data System (ADS)

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

Hall, P. S.

2011-12-01

187

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

NASA Astrophysics Data System (ADS)

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.

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

2009-04-01

188

Alpine geodynamic evolution of passive and active continental margin sequences in the Tauern Window (eastern Alps, Austria, Italy): a review  

NASA Astrophysics Data System (ADS)

The Penninic oceanic sequence of the Glockner nappe and the foot-wall Penninic continental margin sequences exposed within the Tauern Window (eastern Alps) have been investigated in detail. Field data as well as structural and petrological data have been combined with data from the literature in order to constrain the geodynamic evolution of these units. Volcanic and sedimentary sequences document the evolution from a stable continent that was formed subsequent to the Variscan orogeny, to its disintegration associated with subsidence and rifting in the Triassic and Jurassic, the formation of the Glockner oceanic basin and its consumption during the Upper Cretaceous and the Paleogene. These units are incorporated into a nappe stack that was formed during the collision between a Penninic Zentralgneis block in the north and a southern Austroalpine block. The Venediger nappe and the Storz nappe are characterized by metamorphic Jurassic shelf deposits (Hochstegen group) and Cretaceous flysch sediments (Kaserer and Murtörl groups), the Eclogite Zone and the Rote Wand-Modereck nappe comprise Permian to Triassic clastic sequences (Wustkogel quartzite) and remnants of platform carbonates (Seidlwinkl group) as well as Jurassic volcanoclastic material and rift sediments (Brennkogel facies), covered by Cretaceous flyschoid sequences. Nappe stacking was contemporaneous to and postdated subduction-related (high-pressure) eclogite and blueschist facies metamorphism. Emplacement of the eclogite-bearing units of the Eclogite zone and the Glockner nappe onto Penninic continental units (Zentralgneis block) occurred subsequent to eclogite facies metamorphism. The Eclogite zone, a former extended continental margin, was subsequently overridden by a pile of basement-cover nappes (Rote Wand-Modereck nappe) along a ductile out-of-sequence thrust. Low-angle normal faults that have developed during the Jurassic extensional phase might have been inverted during nappe emplacement.

Kurz, W.; Neubauer, F.; Genser, J.; Dachs, E.

189

Discovery of Lower Cretaceous synmetamorphic thrust tectonics in French Lesser Antilles (La Désirade Island, Guadeloupe): Implications for Caribbean geodynamics  

NASA Astrophysics Data System (ADS)

Located east of Guadeloupe, the island of La Désirade exhibits the oldest rocks of the Lesser Antilles arc and the eastern Caribbean plate. An old magmatic basement is composed of (1) late Jurassic ophiolitic complex with meta-basaltic pillow lavas and interbedded radiolarites, (2) acid igneous complex comprising meta-quartz-diorite and meta-rhyolitic lavas flows, and (3) meta-diabasic/microdioritic dyke swarm complex. We present and discuss the discovery of synmetamorphic thrust tectonics in this island. Based on detailed structural analysis we evidenced two main compressive events. The first event (D1) is characterized by pervasive folding associated with thrust development. In the northeastern part of the island, a major thrust fault, the Grand Abaque Thrust, has been discovered which displaces for several kilometers the acid igneous complex onto the ophiolitic unit. The second deformation event (D2) is featured by a main pervasive cleavage S2 observed at the regional scale associated with upright folding (F2) and by the development of two sets of conjugated steeply dipping strike-slip shear zones, dextral 130°N and sinistral 20°N striking, respectively. Microstructural observations indicate that Greenschist facies metamorphism is clearly contemporaneous with the development of D1 and D2 superimposed tectonic structures. Ar/Ar geochronology was performed on two bulk of adularia minerals sampled in the northeast volcanic complex within a deformed zone related to a D2 event. These analyses yield well-defined and concordant plateau ages at 106.2 ± 1.7 Ma and 107.2 ± 1.8 Ma. Thus, shortening and thickening tectonics occurred during Lower Cretaceous (Albian). In the available framework of Caribbean geodynamics, the synmetamorphic thrust tectonics we discovered in the French Lesser Antilles is related to the collision between an Aptian-Albian oceanic plateau and the Andean-Cordilleran east-dipping subduction zone. Our results support subduction polarity reversal during Lower Cretaceous.

Corsini, M.; Lardeaux, J. M.; Verati, C.; Voitus, E.; Balagne, M.

2011-08-01

190

The post-orogenic evolution of the Northeast Greenland Caledonides constrained from apatite fission track analysis and inverse geodynamic modelling  

NASA Astrophysics Data System (ADS)

We present new apatite fission track (AFT) data from the Northeast Greenland passive margin, between 75.8 and 81°N, where elevations reach over 1000 m and no signs of magmatism related to the opening of the North Atlantic exist. The AFT ages are old, ranging from just less than 200 Ma up to more than 350 Ma, and the length distributions are predominantly narrow unimodal, with c-axis projected mean track lengths between 13.3 and 15.0 ?m. The passive margin of Northeast Greenland differs from other studied passive margins in terms of AFT age trends, as we observe no correlation with elevation or characteristic trends relative to mean track length.Using these new data and inverse geodynamic modelling, we constrain the evolution in the area since the orogenic collapse of the Caledonides. Exhumation histories are inferred using a uniform stretching model, incorporating variable rates of erosion or deposition, and thermal histories are found by solving the one-dimensional transient conduction-advection heat equation. These thermal histories are used with the observed fission track data to constrain acceptable strain rate histories and exhumation paths.The results suggest that rifting has been focused mainly in the now offshore regions since ~ 300 Ma, or in minor local areas onshore, not affecting the sampled areas significantly. The present-day high topography is therefore suggested simply to represent remnants of the original Caledonian topography, modified during early rifting and, other than the flexural isostatic response to erosional unloading, we find no need for introducing post-rift related uplift mechanisms.

Pedersen, Vivi Kathrine; Nielsen, Søren Bom; Gallagher, Kerry

2012-03-01

191

Magnetic fabrics and microstructures of the Jurassic Shah-Kuh granite pluton (Lut Block, Eastern Iran) and geodynamic inference  

NASA Astrophysics Data System (ADS)

The Jurassic Shah-Kuh granite pluton was emplaced in the northeastern part of the Lut Block (Eastern Iran) while this block was a part of the active margin under which the Tethys ocean, that separated Arabia from Central Iran, was subducting. Since this time, the Lut Block has rotated and migrated northward up to its present position. This structural study of the Shah-Kuh aims at strengthening the evidence of its original geodynamical location. Thanks to a systematic collection of oriented samples in the field, well-defined fabric and microstructural patterns were deduced from magnetic fabric measurements and optical microscopy observations. The overall magnetic fabric of the pluton yields vertical, north south striking foliations and shallow lineations plunging to the north. The corresponding microstructures attest to their formation in the magmatic stage, i.e. during emplacement. Subsequent deformation, characterized by (sub)mylonitic microstructures, has modified the original fabric into a northwest and locally a west northwest trend inside a two kilometre-wide corridor. This corridor reflects the trace of a sinistral shear zone that offsets the previous north south magmatic pattern of the pluton. The latter magmatic pattern is proposed to result from the shear component of strain that was parallel to the ancient active margin during pluton emplacement, as a result of strain partitioning, a situation frequently documented at convergent margins. Sinistral shear along an ˜ E W directed south-facing active margin, assuming a northeastward slip vector for the Tethys ocean during the Jurassic, and accepting a ˜ 150° counterclockwise rotation of the Lut Block after emplacement of the Shah-Kuh pluton, best explains both the magmatic and the solid-state lineation patterns.

Esmaeily, D.; Bouchez, J. L.; Siqueira, R.

2007-07-01

192

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

NASA Astrophysics Data System (ADS)

U-Pb zircon dating, Sr-Nd isotope tracing and major/trace/RE element analyses were performed to constrain the age, origin and geodynamic significance of plagiogranites that intrude lherzolites and gabbros in the Ligurian Alps and the Northern Apennines. In addition, a host Fe-diorite was investigated. Samples from the Ligurian Alps were collected from the Voltri Group and the Sestri-Voltaggio Zone, whereas the plagiogranites from the Northern Apennines were taken in the Bracco unit. All these units have been affected by Alpine metamorphism reaching eclogite facies in the Voltri Group, blueschist degree in the Sestri Voltaggio samples, and prehnite-pumpellyite facies in the Bracco Unit, which has additionally been affected by rodingitization. U-Pb zircon ages of 150 ± 1, 153 ± 1 and 156 Ma were obtained, respectively, for two plagiogranites and the host Fe-diorite in the Ligurian Alps, and an age of 153 ± 1 Ma was determined for the plagiogranite in Northern Apennines. Inherited components in zircon and initial Pb in plagioclase indicate mixing of variously differentiated basaltic magmas with small amounts of roughly 1.7-2.1 Ga old continental crust material. REE patterns in both the plagiogranites and the host diorite are characterized by high REE abundance, and moderate LREE enrichment. Nd isotopic compositions lie in the range of N-MORB sources, yielding initial epsilon Nd values between +8.8 and +9.7, whereas Sr is isotopically heterogeneous. The geochemical pattern of the plagiogranites and the host Fe-diorite requires melting of a MORB-type mantle source that experienced LREE enrichment shortly before melting. The most likely explanation for such enrichment is the injection of melts derived by small degrees of melting from an adjacent mantle region. The basaltic, LREE-enriched parent magmas generated from this enriched domain have probably undergone up to about 72% of low-pressure fractional crystallization prior to their emplacement into the gabbro-peridotite complex. The 156-150 Ma magmatism occurred in close relation to normal faulting, sedimentation of breccias, and detachment of the mantle complex from its overlying continental crust, followed by exposure on the ocean floor. This tectono-magmatic event in the Ligurian Alps and the Northern Apennines reflects rifting of the Adriatic-Iberian continental plate segment, preceding wider opening of the Piedmont-Ligurian ocean basin and pillow basalt deposition.

Borsi, Laura; Schärer, Urs; Gaggero, Laura; Crispini, Laura

1996-05-01

193

Geological and geodynamical studies of the origin and history of the Tharsis and Valles Marineris regions of Mars  

NASA Astrophysics Data System (ADS)

In this thesis I use data from the Mars Global Surveyor (MGS) spacecraft to examine the physical and geological properties of the lithosphere and crust of the Tharsis region of Mars, a vast volcanic and tectonic province. Two geodynamical studies utilize line-of-sight spacecraft accelerations from the Radio Science Experiment and topography from the Mars Laser Orbiter Altimeter (MOLA) for the primary purpose of estimating the effective elastic thickness (Te) for various regions of Tharsis. The value of Te provides temporal and spatial information regarding the formation of crustal features and the values derived in this study are used to infer the evolution of Tharsis over its ˜4.5 billion year history. Thaumasia, the oldest preserved region of Tharsis, is identified in this study as a large corona (a volcanic-tectonic feature identified on Venus). Using corona as an analog, a thin, elastic shell model is developed. Thaumasia is found to be in near-isostatic equilibrium consistent with an ancient formation age. Admittances for three regions of Tharsis are determined and fit with theoretical admittances. From this, Te across Tharsis is inferred to have varied over time and topographic loading appears to have become increasingly confined to the western margin. A photogeologic study of Valles Marineris, a vast canyon system that incises the crust of Tharsis to a depth exceeding 10 km, provides lithologic information regarding the composition of the crust. The rocks that comprise the upper crust of Thaumasia are interpreted to be primarily resulting from effusive flood basalt volcanism and near-surface magmatic intrusion. From these studies, it is concluded that: (1) Tharsis is largely the result of volcanic construction, (2) Thuamasia is the remnant of a large corona-like feature similar to Artemis Corona on Venus and formed within 500 Ma after planetary accretion, (3) volcanic effusion rates were very high during this time with the bulk of Tharsis being emplaced within the first billion years of the planet's history and quickly diminishing thereafter, and (4) volcanic activity has persisted throughout the last ˜3.5 billion years of Martian history in more localized regions confined to the western half of the province.

Williams, Jean-Pierre

194

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

195

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

NASA Astrophysics Data System (ADS)

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

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

2004-12-01

196

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

197

Dormation of the Xigaze ophiolite (Tibet): implications for the geodynamic evolution of the Neo-Tethys Ocean  

NASA Astrophysics Data System (ADS)

Recent tomography studies and paleo-geographic reconstructions argue for the presence of an active intra-oceanic subduction zone in the Neo-Tethys ocean. The inferred subduction zone extended from in front of the Arabian margin of Africa to southern Tibet via Ladakh and Kohistan. This intra-oceanic subduction zone implies the presence of an island arc in which the ophiolite massifs present along the Tethyan suture zoned may have evolved. Here we present the results of an extensive major, trace element and isotopic study of mineral separates from the ultramafic sequence of the Xigaze Ophiolite. This geochemical data set is used to identify and quantify the mantle processes that formed the Xigaze massif. These results constrain the geodynamic environment in which the massif has evolved and hence contribute to the paleo-reconstruction of the Neo-Tethys Ocean. The Xigaze ophiolite is situated along the Yarlung-Zangbo suture zone, 250 km west of Lhasa (Tibet). The massif forms an east-west 250 km long sub-linear belt with a N-S width ranging from 1-30 km. The harzburgitic mantle sequence is 5 km and was sampled along three sub-massifs: Luqu, Dazhuqu and Dazhuka sections. Mineral data define systematic east-west trends as do clinopyroxenes REE abundances. The Luqu clinopyroxenes are the most depleted in MREE and HREE with (Dy)N and (Yb)N as low as 0.5 and 2.1 respectively. They also record the lowest degree of LREE abundances but have variable LREE/MREE enrichment. The Dazhuku clinopyroxenes have spoon-shaped REE patterns characterised by sub-parallel HREE and constant MREE depletion but more variable LREE. In contrast, the Dazhuka clinopyroxenes are characterised by LREE depletion. The clinopyroxenes REE patterns are best modelled by 2-8% fractional melting in the garnet stability field followed by variable degree of hydrous melting also involving trace element refertilisation. The east-west increase in the degree of LREE enrichment, high degree of partial melting in hydrous conditions all attest to changes in melting condition along the ophiolite. These variation are interpreted as a record of changing tectonic environment. Evolution from MOR to back-arc setting with decreasing influence of the subduction zone is proposed. This study provides the first geochemical evidence that an intra-oceanic subduction was present in the Neo-Tethys Ocean at the time of formation of the Xigaze Ophiolite (110Ma) and confirm recent tomography and paleo-geographic studies.

Griselin, M.; Davies, G. R.; Pearson, D. G.

2003-04-01

198

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

NASA Astrophysics Data System (ADS)

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

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

2005-12-01

199

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

NASA Astrophysics Data System (ADS)

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

Abu Bakar, Rabieahtul; Azahari Razak, Khamarrul

2010-05-01

200

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

Microsoft Academic Search

Since 1975 until 2003 in the Geodynamic Laboratory in Ksiaz there were continuously performed clinometric observations with help of quartz horizontal pendulums only. In 2003 new tiltmeters were installed in galleries of the laboratory in Ksiaz. Tiltmeters consist of two several dozen meters length tubes partially filled with water. Principle of work of instruments bases on the law of hydrostatic

Marek Kaczorowski

2010-01-01

201

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

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

202

A Geodynamic Template for Super-Continent Dispersal Based on CAMP Geochemical and Isotopic Signatures From the Culpepper Basin of Virginia  

NASA Astrophysics Data System (ADS)

We present new geochemical data for the Mesozoic age Central Atlantic Magmatic Province (CAMP) LIP associated with the dispersal of the super-continent, Pangea. Data for the CAMP from the Culpepper Basin of Virginia, as well as previously published data for Mesozoic to recent North Atlantic MORB and OIB define an ordered sequence of geodynamic events for the rifting of Pangea and formation and evolution of the Atlantic ocean basin. CAMP data have Nb/La (0.36-0.62) and Th/Ta (4.61-9.14), similar to island arc lavas. The isotope signatures for the CAMP show island arc-SCLM and/or lower crust affinities. As rifting progressed and the ocean basin opened up (160-120 Ma to present), Central Atlantic MORB geochemical signatures require plume pollution of their asthenosphere source. Numerous plumes, dating back to the early opening of the ocean basin, occur along the western African continental margin in the Central Atlantic. We model this source evolution to reflect 200 Ma melting of the SCLM (CAMP event) associated with a thermal anomaly related to edge effect convection and thinned lithosphere produced during the breakup of the previous super-continent Rodinia (ca. late Proterozoic), followed (<200Ma) by continued upwelling of asthenosphere and buoyant mantle plumes rooted along the peripheries of the African superswell. We use the geochemistry of the Mesozoic to recent basalts as time markers to suggest that the sources of the basalts are linked to three recognizable stages of extension. Stage I basalt generation is associated with incipient supercontinent extension with its geochemical/isotopic signature dominated by sub-continental lithosphere mantle (SCLM). Stage II basalts mark transition to an incipient oceanic rift where ocean island basalt (plume) and/or mid-ocean ridge basalt sources are diluted by SCLM. Stage III basalts are related to a mature mid-ocean ridge system where the source is dominated by the depleted asthenosphere MORB source, variably polluted by SCLM and OIB conponents. Application of this geodynamic template has the potential to constrain the geodynamic enviroment of ancient LIPS.

Hanan, B. B.; Sinha, A.; Shervais, J. W.

2010-12-01

203

Finite-frequency tomography of P and S waves in the Carpathian-Pannonian region: Implications for geodynamics of the continental collision  

NASA Astrophysics Data System (ADS)

The Carpathian-Pannonian system which is the most tectonically active region in Eastern and Central Europe, represents an unique geodynamical case in continental collision zone for studying the interaction between the surface tectonic processes and the deep lithospheric and mantle processes. Particularly, the geodynamical processes involved in the formation of both Pannonian basin and Vrancea seismogenic zone are still debated today. Here, we present high-resolution upper mantle structures beneath the region from finite-frequency tomography using P and S waves in order to bring constraints on geodynamical models. We have selected teleseismic earthquakes with magnitude greater than 5.5, which occurred between 2005 and 2010. The data were recorded on 57 temporary stations deployed in the South Carpathian Project, 56 temporary stations deployed in the earlier Carpathian Basins Project (CBP), and 50 permanent broadband stations. The differential travel times are measured in high, intermediate and low frequencies (0.5-2.0 Hz, 0.1-0.5 Hz and 0.03-0.1 Hz for both P-wave, 0.1-0.5 Hz, 0.05-0.1 Hz and 0.02-0.05 Hz for S-wave), and are inverted according to the 3-D finite-frequency formulation to produce P and S-wave velocity maps at different depths in the mantle. Our images show the presence of a sub-vertical fast material beneath the eastern Alps which extends across the centre of the Pannonian region below ~ 300 km depth. It extends downward into the mantle transition zone and appears to spread outward beneath the entire basin. The upper mantle below the Pannonian basin is dominated by a slow anomaly extending down to ~ 300 km depth. We suggest that a late stage of gravitational instability with detachment of cold mantle lithospheric downwellings is occurring beneath the eastern Alps in the present-day. The same mechanism could also have occurred below the Pannonian basin in the past and though explain the mantle lithospheric extension. In the Vrancea Zone, the seismicity occurs at the NE end of a tabular upper mantle high velocity structure that trends SW along the southern edge of the South Carpathians and extends in depth to ~ 400 km. This sub-vertical high-velocity body is bounded by two slow anomalies to the NW and SE sides. No clear evidence of residual slabs has been observed in the mid upper mantle beneath Eastern Carpathians. These observations suggest that intermediate depth seismicity in Vrancea Zone is unlikely due to slab tearing, but rather could be explained by the gravitational instability or delamination of mantle lithosphere. However, our results cannot discriminate these two mechanisms.

Ren, Y.; Stuart, G. W.; Houseman, G. A.; Dando, B. D.; Ionescu, C.; Hegedus, E.; Radovanovic, S.

2011-12-01

204

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

NASA Astrophysics Data System (ADS)

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

Slabunov, Alexander

2013-04-01

205

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

206

Major types and time-space distribution of Mesozoic ore deposits in South China and their geodynamic settings  

NASA Astrophysics Data System (ADS)

The ore deposits of the Mesozoic age in South China can be divided into three groups, each with different metal associations and spatial distributions and each related to major magmatic events. The first event occurred in the Late Triassic (230-210 Ma), the second in the Mid-Late Jurassic (170-150 Ma), and the third in the Early-Mid Cretaceous (120-80 Ma). The Late Triassic magmatic event and associated mineralization is characterized by peraluminous granite-related W-Sn-Nb-Ta mineral deposits. The Triassic ore deposits are considerably disturbed or overprinted by the later Jurassic and Cretaceous tectono-thermal episodes. The Mid-Late Jurassic magmatic and mineralization events consist of 170-160 Ma porphyry-skarn Cu and Pb-Zn-Ag vein deposits associated with I-type granites and 160-150 Ma metaluminous granite-related polymetallic W-Sn deposits. The Late Jurassic metaluminous granite-related W-Sn deposits occur in a NE-trending cluster in the interior of South China, such as in the Nanling area. In the Early-Mid Cretaceous, from about 120 to 80 Ma, but peaking at 100-90 Ma, subvolcanic-related Fe deposits developed and I-type calc-alkaline granitic intrusions formed porphyry Cu-Mo and porphyry-epithermal Cu-Au-Ag mineral systems, whereas S-type peraluminous and/or metaluminous granitic intrusions formed polymetallic Sn deposits. These Cretaceous mineral deposits cluster in distinct areas and are controlled by pull-apart basins along the South China continental margin. Based on mineral assemblage, age, and space-time distribution of these mineral systems, integrated with regional geological data and field observations, we suggest that the three magmatic-mineralization episodes are the result of distinct geodynamic regimes. The Triassic peraluminous granites and associated W-Sn-Nb-Ta mineralization formed during post-collisional processes involving the South China Block, the North China Craton, and the Indo-China Block, mostly along the Dabie-Sulu and Songma sutures. Jurassic events were initially related to the shallow oblique subduction of the Izanagi plate beneath the Eurasian continent at about 175 Ma, but I-type granitoids with porphyry Cu and vein-type Pb-Zn-Ag deposits only began to form as a result of the breakup of the subducted plate at 170-160 Ma, along the NNE-trending Qinzhou-Hangzhou belt (also referred to as Qin-Hang or Shi-Hang belt), which is the Neoproterozoic suture that amalgamates the Yangtze Craton and Cathaysia Block. A large subduction slab window is assumed to have formed in the Nanling and adjacent areas in the interior of South China, triggering the uprise of asthenospheric mantle into the upper crust and leading to the emplacement of metaluminous granitic magma and associated polymetallic W-Sn mineralization. A relatively tectonically quiet period followed between 150 and 135 Ma in South China. From 135 Ma onward, the angle of convergence of the Izanagi plate changed from oblique to parallel to the coastline, resulting in continental extensional tectonics and reactivation of regional-scale NE-trending faults, such as the Tan-Lu fault. This widespread extension also promoted the development of NE-trending pull-apart basins and metamorphic core complexes, accompanied by volcanism and the formation of epithermal Cu-Au deposits, granite-related polymetallic Sn-(W) deposits and hydrothermal U deposits between 120 and 80 Ma (with a peak activity at 100-90 Ma).

Jingwen, Mao; Yanbo, Cheng; Maohong, Chen; Pirajno, Franco

2012-10-01

207

Major types and time-space distribution of Mesozoic ore deposits in South China and their geodynamic settings  

NASA Astrophysics Data System (ADS)

The ore deposits of the Mesozoic age in South China can be divided into three groups, each with different metal associations and spatial distributions and each related to major magmatic events. The first event occurred in the Late Triassic (230-210 Ma), the second in the Mid-Late Jurassic (170-150 Ma), and the third in the Early-Mid Cretaceous (120-80 Ma). The Late Triassic magmatic event and associated mineralization is characterized by peraluminous granite-related W-Sn-Nb-Ta mineral deposits. The Triassic ore deposits are considerably disturbed or overprinted by the later Jurassic and Cretaceous tectono-thermal episodes. The Mid-Late Jurassic magmatic and mineralization events consist of 170-160 Ma porphyry-skarn Cu and Pb-Zn-Ag vein deposits associated with I-type granites and 160-150 Ma metaluminous granite-related polymetallic W-Sn deposits. The Late Jurassic metaluminous granite-related W-Sn deposits occur in a NE-trending cluster in the interior of South China, such as in the Nanling area. In the Early-Mid Cretaceous, from about 120 to 80 Ma, but peaking at 100-90 Ma, subvolcanic-related Fe deposits developed and I-type calc-alkaline granitic intrusions formed porphyry Cu-Mo and porphyry-epithermal Cu-Au-Ag mineral systems, whereas S-type peraluminous and/or metaluminous granitic intrusions formed polymetallic Sn deposits. These Cretaceous mineral deposits cluster in distinct areas and are controlled by pull-apart basins along the South China continental margin. Based on mineral assemblage, age, and space-time distribution of these mineral systems, integrated with regional geological data and field observations, we suggest that the three magmatic-mineralization episodes are the result of distinct geodynamic regimes. The Triassic peraluminous granites and associated W-Sn-Nb-Ta mineralization formed during post-collisional processes involving the South China Block, the North China Craton, and the Indo-China Block, mostly along the Dabie-Sulu and Songma sutures. Jurassic events were initially related to the shallow oblique subduction of the Izanagi plate beneath the Eurasian continent at about 175 Ma, but I-type granitoids with porphyry Cu and vein-type Pb-Zn-Ag deposits only began to form as a result of the breakup of the subducted plate at 170-160 Ma, along the NNE-trending Qinzhou-Hangzhou belt (also referred to as Qin-Hang or Shi-Hang belt), which is the Neoproterozoic suture that amalgamates the Yangtze Craton and Cathaysia Block. A large subduction slab window is assumed to have formed in the Nanling and adjacent areas in the interior of South China, triggering the uprise of asthenospheric mantle into the upper crust and leading to the emplacement of metaluminous granitic magma and associated polymetallic W-Sn mineralization. A relatively tectonically quiet period followed between 150 and 135 Ma in South China. From 135 Ma onward, the angle of convergence of the Izanagi plate changed from oblique to parallel to the coastline, resulting in continental extensional tectonics and reactivation of regional-scale NE-trending faults, such as the Tan-Lu fault. This widespread extension also promoted the development of NE-trending pull-apart basins and metamorphic core complexes, accompanied by volcanism and the formation of epithermal Cu-Au deposits, granite-related polymetallic Sn-(W) deposits and hydrothermal U deposits between 120 and 80 Ma (with a peak activity at 100-90 Ma).

Jingwen, Mao; Yanbo, Cheng; Maohong, Chen; Pirajno, Franco

2013-03-01

208

Age and Geochemistry of Central American Forearc Basement Rocks (DSDP Leg 67 and 84) Reveal a Complex Geodynamic History  

NASA Astrophysics Data System (ADS)

The wide shelf between Costa Rica and southern Mexico hosts an unusually broad forearc basin. Geophysical investigations imply that the entire forearc basement is composed of ophiolitic rocks similar to exposed terranes of the widespread Caribbean Large Igneous Province (CLIP). Various geodynamic models have been suggested for the origin of the CLIP including its formation above the Galápagos plume head. Besides it's origin, the spatial extent and duration of CLIP volcanism are controversial. During DSDP Leg 67 and 84 the forearc basement was drilled and various igneous rocks including basalts, dolerites, gabbros and serpentinized peridotites were recovered. We present 40Ar/39Ar laser age and geochemical data (including major- and trace elements and Sr, Nd, Pb and Hf isotope ratios) of the drilled samples in order to determine if the igneous forearc basement represents old Pacific ocean crust, ancient arc volcanism, and/or accreted intraplate volcanic rocks possibly related to the CLIP? The igneous forearc basement can be subdivided into two groups: a geochemically strongly depleted group and an underlying geochemically enriched group. Mafic rocks of the depleted group have tholeiitic to basaltic andesitic compositions and display a strong depletion in incompatible elements but distinct enrichments of fluid-mobile elements such as Rb, Ba, U, K, Pb and Sr characteristic of arc volcanism. In contrast, alkali basaltic to hawaiitic rocks of the enriched group exhibit enriched incompatible element signatures with marked depletions in K, Pb and heavy rare earth elements similar to Ocean Island Basalt (OIB). Consistent with the trace element division, both groups form two separate fields in Sr, Nd, Pb, and Hf isotopic space with the depleted group showing isotopically depleted initial compositions (low 206Pb/204Pb=17.93-18.48 and 207Pb/204Pb=15.49-15.53 but elevated ^{143}Nd/^{144}Nd= 0.51294-0.51318 and ^{176}Hf/^{177}Hf= 0.28304-0.28316) and the enriched group having distinctly more enriched initial isotope ratios (e.g. high 206Pb/204Pb=19.42-20.34 and 207Pb/204Pb=15.65-15.70 but low ^{143}Nd/^{144}Nd=0.51272-0.51297, ^{176}Hf/^{177}Hf= 0.28281-0.28292). Preliminary results of step-heating 40Ar/39Ar age determinations of mineral separates range from ~100-143 Ma for the depleted group and 104-219 Ma for the enriched group. Because of a different mode and larger degree of isotopic enrichment it is highly questionable whether the enriched group samples are related to the CLIP or were derived from the Galápagos plume. Instead, these rocks most likely represent accreted Mesozoic intraplate seamounts/ocean islands of central Pacific origin. The depleted group can be interpreted as a submerged upper Cretaceous island arc, accreted to the Chortis Block subduction zone. Rocks of similar age and geochemistry to both groups can be found on the Santa Elena Peninsula in Costa Rica, which probably represents the subaerial exposed southern termination of the forarc basement.

Geldmacher, J.; Hoernle, K. A.; Hauff, F.; Kluegel, A.; Bogaard, P. V.

2006-12-01

209

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

SciTech Connect

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

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

1998-12-01

210

A geodynamic model of the evolution of the Arctic basin and adjacent territories in the Mesozoic and Cenozoic and the outer limit of the Russian Continental Shelf  

NASA Astrophysics Data System (ADS)

The tectonic evolution of the Arctic Region in the Mesozoic and Cenozoic is considered with allowance for the Paleozoic stage of evolution of the ancient Arctida continent. A new geodynamic model of the evolution of the Arctic is based on the idea of the development of upper mantle convection beneath the continent caused by subduction of the Pacific lithosphere under the Eurasian and North American lithospheric plates. The structure of the Amerasia and Eurasia basins of the Arctic is shown to have formed progressively due to destruction of the ancient Arctida continent, a retained fragment of which comprises the structural units of the central segment of the Arctic Ocean, including the Lomonosov Ridge, the Alpha-Mendeleev Rise, and the Podvodnikov and Makarov basins. The proposed model is considered to be a scientific substantiation of the updated Russian territorial claim to the UN Commission on the determination of the Limits of the Continental Shelf in the Arctic Region.

Laverov, N. P.; Lobkovsky, L. I.; Kononov, M. V.; Dobretsov, N. L.; Vernikovsky, V. A.; Sokolov, S. D.; Shipilov, E. V.

2013-01-01

211

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

212

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

NASA Astrophysics Data System (ADS)

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

Yakovlev, Fedor L.

2012-12-01

213

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)

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.

Stockli, D. F.

2009-05-01

214

The Temporal Spectrum of the Black Sea Level Fluctuations and its Possible Connection with the Dynamics of the Position Change of RT-22 of the Crao as AN Element of the European Geodynamic VLBI Network  

NASA Astrophysics Data System (ADS)

Using the international geodynamic VLBI program for 1994-2010 years, the coordinates of station "Simeiz" were determined. The results of measuring of the RT-22 Simeiz coordinates with the monthly averages of the data long-term measurements of the Black Sea level stations, located in Odessa, Ochakov, Sevastopol, Yalta and Katsively were estimated. All items of the sea level measuring have different water flows that gives the opportunity to explore the global geodynamic processes and their dependence on the solar activity cycle. The spectrum of the sea level variations in different points indicates the presence of the periods of one to 11 and 22 years. Using the wavelet analysis, the periods for each level station were estimated separately.

Ryabov, M. I.; Volvach, A. E.; Sukharev, A. L.; Donskikh, A. I.; Adobovskiy, V. V.; Kuklina, N. Y.; Shabalina, O. A.; Gubar, G. A.; Pokidaylo, S. L.

215

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)

Introduction After the Chernobyl Nuclear Power Plant (CNPP) disaster (04.26.1986) a huge amount (over 2000 sq. km) of nuclear wastes appeared within so-called "Cher- nobyl Exclusion Zone" (CEZ). At present there are not enough storage facilities in the Ukraine for safe disposal of nuclear wastes and hazardous chemical wastes. The urgent problem now is safe isolation of these dangerous wastes. According to the developed state program of radioactive waste management, the construction of a na- tional storage facility of nuclear wastes is planned. It is also possible to create regional storage facilities for hazardous chemical wastes. The region of our exploration cov- ers the eastern part of the Korosten Plutone and its slope, reaching the CNPP. 3D Space-Time Surface Imaging of Geophysical Fields. There are only three direct meth- ods of stress field reconstruction in present practice, namely the field investigations based on the large-scale fracturing tests, petrotectonic and optical polarization meth- ods. Unfortunately, all these methods are extremely laborious and need the regular field tests, which is difficult to conduct in the areas of anisotropic rock outcrops. A compilation of magnetic and gravity data covering the CNPP area was carried out as a prelude to an interpretation study. More than thirty map products were generated from magnetic, gravity and geodesy data to prepare the 3D Space-Time Surface Images (3D STSI). Multi-layer topography and geophysic surfaces included: total magnetic intensity, isostatically-corrected Bouguer gravity, aspect and slope, first and second derivatives, vertical and horizontal curvature, histogram characteristics and space cor- relation coefficients between the gradient fields. Many maps shows the first and sec- ond derivatives of the potential fields, with the results of lineament (edge) structure detection superimposed. The lineament or edges of the potential fields are located from maximal gradient in many directions extracted from the total vertical and hori- zontal gradient respectively, both shaded from the 5 northeast to 355 northwest. The dip of multi-layer surfaces indicates the down -"gradient" direction in the fields. The methodology of 3D STSI is based on the analysis of vertical and horizontal anisotropy of gravity and magnetic fields, as well as of multi-layer 3D space-time surface model (3D STSM) of the stress fields. The 3D STSM is multi-layer topology structure of 1 lineaments or gradients (edges) and surfaces calculated by uniform matrices of the geophysical fields. One of the information components of the stress fields character- istics is the aspects and slopes for compressive and tensile stresses. Overlaying of the 3D STSI and lineaments with maps of multi-layer gradients enables to create highly reliable 3D Space-Time Kinematic Model "3D STKM". The analysis of 3D STKM in- cluded: - the space-time reconstruct of forces direction and strain distribution scheme during formation of geological structures and structural paragenesis (lineaments) of potential fields; - predict the real location of expected tectonic dislocations, zones of rock fracturing and disintegration, and mass-stable blocks. Based on these data, the 3D STSM are drawn which reflect the geodynamics of territory development on the ground of paleotectonic reconstruction of successive activity stages having formed the present-day lithosphere. Thus three-dimensional STSM allows to construct an un- mixing geodynamic processes in any interval of fixed space-time in coordinates x, y, t(z). The integrated of the 3D STSM and 3D seismic models enables also to create structural-kinematic and geodynamic maps of the Earth's crust at different depth. As a result, the classification of CNPP areas is performed into zones of compressive and tensile stresses characterized by enhanced permeability of rocks, and zones of consoli- dation with minimal rocks permeability. In addition, the vertically alternating zones of extension and consolidation are identified. These data correlate with res

Bondarenko, Y.

216

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)

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.

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

2012-04-01

217

Probing the deep structure and geodynamics of the Gibraltar Arc System by integrating new data sets from the IberArray platform (Invited)  

NASA Astrophysics Data System (ADS)

The Gibraltar Arc system is a complex interaction zone between the Eurasia and African plates. This tectonically thickened arc with extended basins result from the interaction of slab roll back processes with upper plate deformation. Many different, often controversial evolutionary models have been proposed, from continental-scale thermal mantle source processes to regional-scale recycling of the lithosphere by either delamination, slab break-off, convective removal or the presence of active eastward subduction of oceanic crust. Structural features that could deserve prioritization between such models could not be properly constrained from geophysical results existing till now. However, the Topo-Iberia project currently on-going in Spain should provide such constraints. Topo-Iberia is a large-scale integrative research effort to achieve new, high resolution results on structure and geodynamics of the Iberian plate. It is based on the implementation of an IberArray platform, formed by GPS, MT and Broad-Band Seismic networks, similar to the Earthscope in US. Major features of the project and achieved results concerning the Gibraltar Arc System will be presented. Particularly, the seismic network, composed by more than 130 permanent and portable BB instruments, samples the Iberian-African domains of plate interaction in a 60km x 60km homogeneous grid and provides deep structural results from either tomographical methods (ambient noise, travel-time local + teleseismic events, or surface waves), Moho depths from receiver functions or mantle anisotropy from SKS splittings. As examples of results, significant variations on crustal thicknesses have been inferred within rather short distances, from more than 40 km Moho depths beneath the axes of the Betic and Rif chains to around 20 km towards the easternmost part of the study area, and the fast polarization directions (FPD) from SKS splitting measurements clearly show a spectacular rotation along the arc following the curvature of the Rif-Betic chain. These results support geodynamical processes invoking a fast retreating slab rather than convective-removal and delamination models. The FPD variations along the Gibraltar arc can be explained by fossil anisotropy acquired during the Western Mediterranean Eocene subduction, while changes to the South and South-East of the Rif-Betic chain could be the imprint of a flow episode around an Alboran high velocity slab during its Miocene fragmentation from the Algerian slab.

Gallart, J.

2010-12-01

218

Isotopic implications for the origin and the geodynamic nature of the Miocene granitic rocks in the northwest Anatolia (Turkey): comparison with the central Aegean magmatism  

NASA Astrophysics Data System (ADS)

Central Aegean magmatic belt including the northwestern Anatolia is interpreted in the literature as formed along magmatic arc which has migrated southwardly to its present position. During and after the closure of the Neo-Tethyan Ocean and progressive collision of the Tauride-Anatolide Platform with the Sakarya Continent, widespread magmatism occurred in NW Anatolia. These magmatic associations form a NW trending belt. In NW Anatolia, mostly Miocene I-type, shallow seated Egrigöz, Koyunoba, Alacam plutons expose along the suture zone called ?zmir-Ankara Zone. These granitoid rocks intruded into the basement rocks of the region which are from bottom to top consist of Menderes Massif, Afyon Zone and Bornova Flysch Zone. Due to the complex geodynamic evolution, the exact emplacement mode of the Miocene granitoids is still a subject for debate. New results give rise to re-consider the general mode of the Miocene magmatic activity and address the question if the magmatism was triggered by compression or extensional tectonic processes. The new data are also compared to those of the central Aegean granitoids. Initial isotopic signatures of these shallow seated granitoids of NW Anatolian are 87Sr/86Sr(I) = 0.70800-0.70975, ENd(I) = -4.9 to -7.3, ?18O = 9.4-10.6, 206Pb/204Pb = 18.85-18.918. These characteristics indicate an assimilation-dominated crystallization and most probably origin of a metaluminous older meta-sedimentary protolith which is also common in most of the central Aegean magmatic suites. However, the geodynamic scenario for the mode of emplacement of the Miocene granitoids along the NW Anatolia implies remarkable differences when comparing to the central Aegean granitoid suites. These differences can be summarized as: an extension related granitoid emplacement in the central Aegean occurred between 15 Ma to 10 Ma. However, in NW Anatolia, the granitoids emplaced after Eocene collision and continue till 20-22 Ma. Isotopic patterns with suggested mixing/mingling models imply a mantle derived source in the central Aegean granitoids. However, the granitoids in NW Anatolia are most likely affected from the lower crustal material rather than a mantle component. A post-collisional extensional emplacement model as suggested for the central Aegean granitic magmatism is not compatible with the petrogenetic and age implications of the NW Anatolian Miocene granites. According to their geological and new isotopic data, a collision-related progressive emplacement mode is more likely compatible in NW Anatolia.

Hasözbek, Altug; Satir, Muharrem; Erdogan, Burhan; Siebel, Wolfgang; Akay, Erhan; Deniz Dogan, Güllü

2010-05-01

219

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

NASA Astrophysics Data System (ADS)

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

Fuchs, L.; Schmeling, H.

2013-08-01

220

The use of caves as observatories for recent geodynamic activity and radon gas concentrations in the Western Carpathians and Bohemian Massif.  

PubMed

In recent years, many underground spaces such as caves and deep mines have been used to monitor geodynamic activity in the Western Carpathians and Bohemian Massif. In addition, long-term radon gas monitoring has also being undertaken in three of the caves. The observed radon concentrations have shown diurnal, seasonal and yearly variations. A significant correlation with external temperature has been registered. This pattern is considered to result from the movement of air caused by the contrast between the broadly constant internal and fluctuating external temperatures. The same seasonal effects have been observed in the record of active fault displacements at sites close to the surface. These seasonal effects lead to peak-to-peak massif dilation amplitude that affects the overall trend of fault displacement. It is also noted that a significant decrease in this amplitude occurs with increasing depth beneath the surface. However, high variability has also been observed in both the radon concentration and fault displacement activity recorded. Many events have been registered that link these two geofactors. PMID:21478172

Briestensky, M; Thinova, L; Stemberk, J; Rowberry, M D

2011-04-07

221

Geodynamic evolution of the SW Variscides: Orogenic collapse shown by new tectonometamorphic and isotopic data from western Ossa-Morena Zone, SW Iberia  

NASA Astrophysics Data System (ADS)

The pre-Mesozoic geodynamic evolution of SW Iberia has been investigated on the basis of detailed structural analysis, isotope dating, and petrologic study of high-pressure (HP) rocks, revealing the superposition of several tectonometamorphic events: (1) An HP event older than circa 358 Ma is recorded in basic rocks preserved inside marbles, which suggests subduction of a continental margin. The deformation associated with this stage is recorded by a refractory graphite fabric and noncoaxial mesoscopic structures found within the host metasediments. The sense of shear is top to south, revealing thrusting synthetic with subduction (underthrusting) to the north. (2) Recrystallization before circa 358 Ma is due to a regional-scale thermal episode and magmatism. (3) Noncoaxial deformation with top to north sense of shear in northward dipping large-scale shear zones is associated with pervasive hydration and metamorphic retrogression under mostly greenschist facies. This indicates exhumation by normal faulting in a detachment zone confined to the top to north and north dipping shear zones during postorogenic collapse soon after 358 Ma ago (inversion of earlier top to south thrusts). (4) Static recrystallization at circa 318 Ma is due to regional-scale granitic intrusions.

Rosas, F. M.; Marques, F. O.; BallèVre, M.; Tassinari, C.

2008-12-01

222

Multiple generations of mafic–ultramafic rocks from the Hongseong suture zone, western South Korea: Implications for the geodynamic evolution of NE Asia  

NASA Astrophysics Data System (ADS)

Dismembered mafic and serpentinized ultramafic bodies within the Hongseong suture zone of the Gyeonggi massif, southwestern Korean Peninsula are tectonically correlated with those from the Chinese Qinling–Dabie–Sulu collisional belt. We report sensitive high-resolution ion microprobe (SHRIMP) U–Pb zircon ages, detailed mineral compositions and whole rock geochemical data from the mafic rocks including eclogite and garnetite from the Hongseong suture zone. The zircon U–Pb data show multiple protolith ages corresponding to Neoproterozoic (ca. 815–770 Ma), Paleozoic (ca. 310 Ma) and Middle Triassic (ca. 240 Ma). The peak high-pressure and retrograde regional intermediate-pressure metamorphic events of Middle Triassic (ca. 240–230 Ma) are also recorded in zircons from the mafic rocks in the Hongseong suture zone. The ages and P–T estimates presented in this study match well with those of the peak ultra-high-pressure metamorphism in the Sulu area of China. Our results from the Hongseong suture zone provide important insights into the geodynamic history of the NE Asian region, with evidence for both Neoproterozoic subduction and a Paleozoic to Triassic subduction/accretion event.

Kwon, Sanghoon; Kim, Sung Won; Santosh, M.

2013-02-01

223

Joint seismic, geodynamic and mineral physical constraints on three-dimensional mantle heterogeneity: Implications for the relative importance of thermal versus compositional heterogeneity  

NASA Astrophysics Data System (ADS)

The joint interpretation of seismic and geodynamic data requires mineral physical parameters linking seismic velocity to density perturbations in the Earth's mantle. The most common approach is to link velocity and density through relative scaling or conversion factors: R?/s = dln?/dlnVS. However, the range of possible R?/s values remains large even when only considering thermal effects. We directly test the validity of several proposed depth-dependent conversion profiles developed from mineral physics studies for thermally-varying properties of mantle materials. The tests are conducted by simultaneously inverting shear wave traveltime data and a diverse suite of convection-related constraints interpreted with viscous-flow response functions of the mantle. These geodynamic constraints are represented by surface spherical harmonic basis functions (up to harmonic degree 16) and they consist of the global free-air gravity field, tectonic plate divergences, dynamic surface topography and the excess ellipticity of the core-mantle boundary (CMB). The tests yield an optimum 1-D thermal R?/s profile that is generally compatible with all considered data, with the exception of the dynamic surface topography that is most sensitive to the shallow upper mantle. This result is not surprising given that cratonic roots are known to be compositionally-distinct from the surrounding ambient mantle. Moreover, it is expected that the temperature-dependence of the thermal R?/s in the upper mantle is significant due to the temperature-dependence of seismic attenuation or Q. Therefore, a simple 1-D density-velocity relationship is insufficient. To address this problem, we obtained independent estimates of the first-order correction factors to the selected R?/s profile within the cratonic roots and in the ambient (thermal) upper mantle. These correction factors, defined as ?R?/s/?lnVS, are highly negative within the cratons signifying considerable compositional buoyancy. This result confirms that the negative buoyancy associated with the low temperatures in the cratons is significantly counteracted by the composition-induced positive buoyancy resulting in near-neutral buoyancy of the cratonic roots. Within the ambient upper mantle, the correction factors are found to be positive which is consistent with the expected behaviour of the R?/s relationship in thermally-varying upper-mantle material. We obtain a significantly greater reconciliation of the global gravity anomalies and dynamic surface topography when applying these laterally-varying corrections compared to a simple 1-D R?/s relationship. Inversion for a fully 3-D R?/s relationship reveals secondary effects including additional compositional variation within the cratonic roots and the deep-mantle superplume structures. We estimate the relative magnitude of the thermal and compositional (non-thermal) contributions to mantle density anomalies and conclude that thermal effects dominate shear wave and density heterogeneity throughout the non-cratonic mantle. We also demonstrate the potential pitfalls of scaling a purely seismically-derived model to obtain density rather than performing a true joint inversion to obtain velocity and density simultaneously.

Simmons, Nathan A.; Forte, Alessandro M.; Grand, Stephen P.

2009-06-01

224

Mantle Response to Collision, Slab Breakoff & Lithospheric Tearing in Anatolian Orogenic Belts, and Cenozoic Geodynamics of the Aegean-Eastern Mediterranean Region  

NASA Astrophysics Data System (ADS)

The geochemical and temporal evolution of the Cenozoic magmatism in the Aegean, Western Anatolian and peri-Arabian regions shows that plate tectonic events, mantle dynamics, and magmatism were closely linked in space and time. The mantle responded to collision-driven crustal thickening, slab breakoff, delamination, and lithospheric tearing swiftly, within geologically short time scales (few million years). This geodynamic continuum resulted in lateral mantle flow, whole-sale extension and accompanying magmatism that in turn caused the collapse of tectonically and magmatically weakened orogenic crust. Initial stages of post-collisional magmatism (~45 Ma) thermally weakened the orogenic crust in Tethyan continental collision zones, giving way into large-scale extension and lower crustal exhumation via core complex formation starting around 25-23 Ma. Slab breakoff was the most common driving force for the early stages of post-collisional magmatism in the Tethyan mountain belts in the eastern Mediterranean region. Magmatic rocks produced at this stage are represented by calc-alkaline-shoshonitic to transitional (in composition) igneous suites. Subsequent lithospheric delamination or partial convective removal of the sub-continental lithospheric mantle in collision-induced, overthickened orogenic lithosphere caused decompressional melting of the upwelling asthenosphere that in turn resulted in alkaline basaltic magmatism (<12 Ma). Attendant crustal extension and widespread thinning of the lithosphere facilitated rapid ascent of basaltic (OIB) magmas without much residence time in the crust and hence the eruption of relatively uncontaminated, asthenosphere-derived magmas at the surface (i.e. Kula lavas in SW Anatolia). Subduction of the Tethyan mantle lithosphere northward beneath Eurasia was nearly continuous since the latest Cretaceous, only temporarily punctuated by the collisional accretion of several ribbon continents (i.e. Pelagonia, Sakarya, Tauride-South Armenian) to the southern margin of Eurasia, and by related slab breakoff events. Exhumation of middle to lower crustal rocks and the formation of extensional metamorphic domes occurred in the backarc region of this progressively southward-migrated trench and the Tethyan (Afro-Arabian) slab throughout the Cenozoic. Thus, slab retreat played a major role in the Cenozoic geodynamic evolution of the Aegean and Western Anatolian regions. However, the subducting African lithospheric slab beneath the Aegean-Western Anatolian region is delimited to the east by a subduction-transform edge propagator (STEP) fault, which corresponds to the sharp cusp between the Hellenic and Cyprus trenches whose surface expression is marked by the Isparta Angle in the Western Taurides. This lithospheric tear in the downgoing African plate allowed the mantle to rise beneath SW Anatolia, inducing decompressional melting of shallow asthenosphere and producing linearly distributed alkaline magmatism younging in the direction of tear propagation (southward). The N-S-trending potassic and ultra-potassic volcanic fields stretching from the Kirka and Afyon-Suhut region (~17 Ma) in the north to the Isparta-Gölcük area (4.6 Ma-Recent) in the south are the result of this melting of the sub-slab (asthenospheric) mantle, which was metasomatized by recent subduction events in the region. Asthenospheric low velocities detected through Pn tomographic imaging in this region support the existence of shallow asthenosphere beneath the Isparta Angle at present. These observations suggest that currently there is no active subduction underneath much of Western Anatolia.

Dilek, Yildirim; Altunkaynak, Safak

2010-05-01

225

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

NASA Astrophysics Data System (ADS)

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

Pasqui, Valeria; Viti, Marcello; Mantovani, Enzo

2013-04-01

226

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

227

Geology, Geochemistry and Geochronology of the Upper Cretaceous high-K volcanics in the southern Part of the Eastern Pontides: Implications for Mesozoic Geodynamic Evolution of NE Turkey  

NASA Astrophysics Data System (ADS)

The Eastern Pontide Orogenic Belt is one of the most complex geodynamic settings in the Alpine-Mediterranean region. Its geodynamic evolution is very controversial due to lack of systematic, quantitative structural, geochemical and geochronological data. This belt is divided into three subgroups: northern, southern and axial zones, distinguished from north to south by different lithological units, facies changes and tectonic characteristics. Especially, the southern zone is very attractive with its numerous rock associations such as alaskan-type mafic-ultramafic intrusions, shoshonitic and ultrapotassic volcanics, adakitic magmatics, glaucophane-bearing gabbros, metamorphic and ultramafic massifes. This study focuses on the petrology, geotectonic setting and evidence for subduction polarity of the Upper Cretaceous shoshonitic and ultrapotassic volcanics exposed in the most southerly part of the eastern Pontide magmatic arc. Geological, geochemical and isotopic data indicate that there were two distinct cycles of high-K volcanic activity in the southern part of the eastern Pontide magmatic arc during the Late Cretaceous. The first cycle (Early Campanian), represented by shoshonitic trachyandesites and associated pyroclastics, containing high K2O (2.74-4.81 wt %) and Na2O (3.60-5.51 wt %), overlies the Middle-Cretaceous ophiolitic-olistostromal melange formed during the rifting stage of a back-arc basin (Neotethys). The second cycle of high-K volcanism is characterized by potassic or ultrapotassic analcime-bearing volcanics, erupted in a lagoonal environment during the Maastrichtian. Progressive shallowing of the basin indicates that Upper Cretaceous high-K volcanism developed during the final stage of pull-apart basin development in the southern zone of the eastern Pontides. These volcanic rocks, intercalated with continental detritus, are characterized by high Na2O (3.22-7.16 wt %) concentrated in secondary analcime crystals. Their K2O contents also range between 0.83 and 6.05 (wt %). Volcanic rocks belonging to both cycles have remarkable similarity in their trace and rare earth element concentrations and display variable enrichment in large ion lithophile elements (LILE), high field strength elements (HFSE), light rare earth elements (LREE) and heavy rare earth elements (HREE) with respect to primitive mantle and chondrite. Negative Nb, Ta, Zr, Hf and Ti anomalies are typical of subduction-related arc magmas. In addition, Nd-Sr and Pb isotope ratios of the investigated volcanics support that they are products of a similar mantle source. Undoubtedly, the existence of the subduction-related high-K volcanics in the southern part of the eastern Pontide magmatic arc is very important for interpretation of subduction polarity. Southward subduction of the Paleotethys oceanic crust during Mesozoic can be separated into two main stages. The first stage of southward subduction ended with slab break-off of the old and dense part of the Paleotethys oceanic crust during the Mid-Cretaceous. This process caused upwelling of the asthenospheric mantle and opening of the back-arc basins in the eastern Pontides. Middle Cretaceous olistostromal ophiolitic mélange formed on the transitional crust or on true oceanic crust restricted by deep spreading troughs of the pull-apart basins. Deformation of the deep-spreading troughs, in which the mélange formed, was initially extensional (drifting stage) but became increasingly compressional (infilling stage) as the strike-slip cycle was completed. Southward migration of the Upper Cretaceous volcanism in the eastern Pontides (arranged TH-CA in the north, CA-A in the south and shoshonitic-ultrapotassic in the far south) implies that the remaining undepleted part of Paleotethys oceanic crust continued to subduct southward. In addition, intense volcanic activity and emplacement of granite, gabbro and diorite intrusions in the northern part of the arc caused break-up of the Malm-Lower Cretaceous carbonate platform during the Upper Cretaceous.

Eyuboglu, Y.

2009-04-01

228

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

NASA Astrophysics Data System (ADS)

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

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

2012-07-01

229

Dripping of a Mantle Lithosphere Root and Tectonics in the Sierra Nevada Region: Reconciling Geodynamic Modeling with Geodetic/Geological Constraints  

NASA Astrophysics Data System (ADS)

Recent geophysical and geochemical studies in the Sierra Nevada region indicate that mantle lithosphere may be actively descending as a Rayleigh-Taylor-type instability. It has been postulated that this "drip" instability influenced the structural evolution of the crust and may be responsible for anomalous present-day topography in the area. Here, we consider in more detail this type of geodynamic mechanism in controlling the active and recent tectonics in the southern Sierra Nevada and surrounding region. Specifically, we conduct a series of scaled 2D numerical and 3D physical analogue experiments to examine quantitatively the evolution of the crust in response to underlying mantle instability. In the experiments, an idealized crust-mantle lithosphere-mantle system is configured in an upper mantle-scale solution space and a density perturbation is introduced into the model mantle lithosphere to initiate the gravitational instability. Observables from the experiments include surface topography, accumulated crustal deformation, and instantaneous strain rate. We compare the latter to crustal strain accumulation inferred from GPS measurements. In particular, an attempt is made to isolate the regional velocity field from the larger-scale North America-Pacific relative plate boundary motion, and to determine the contribution of steady (vs. episodic) strain accumulation in the measurements. In conjunction with the geodetic constraints, we reconcile the predicted deformation in the experiments with geological/geophysical observations of crust and mantle lithosphere structure, and compare the pattern of surface topography. The results provide integrated insights into the role of a local tectonic forcing in driving active and recent tectonic activity in the Sierra Nevada region.

Gogus, O. H.; Pysklywec, R. N.; Davis, J. L.; Cruden, A. R.

2005-05-01

230

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

NASA Astrophysics Data System (ADS)

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

Kaczorowski, Marek

231

Integrated studies of the recent evolution of Deception Island in the geodynamic setting of the Bransfield Basin opening (Antarctica): GEOMAGDEC Project  

NASA Astrophysics Data System (ADS)

Deception Island shows the most recent active volcanism, evidence of several eruptions since the late 18th century, and well-known eruptions in 1967, 1969, and 1970 at the western end of the volcanic ridge of the Bransfield Trough, between the South Shetland Islands and the Antarctic Peninsula. The recent tectonic activity of the Bransfield Trough is not well defined, and it presents a controversial origin. It is currently explained by two different models: (1) Opening of the basin may be related to passive subduction of the former Phoenix Plate and subsequent rollback of the South Shetland Trench; or (2) an oblique extension along the Antarctic Peninsula continental margin generated by the sinistral movement between the Antarctic and Scotia plates. This extension develops the Bransfield Trough and spread away the South Shetland tectonic block. The GEOMAGDEC project involves a multidisciplinary and integrated research of the Deception Island based on geophysical and geological methods. The purpose of this project, funded by the Spanish research agency, is the understanding of the main processes that govern the evolution of the Deception Island into the development of Bransfield Basin during recent times. Main aims are: (1) Study of the anisotropy of the magnetic susceptibility of volcanic deposits of emerged area of Deception Island to determine the relationship between magmatism (intrusive and extrusive) with the recent tectonic activity. This task allows the reconstruction of igneous flow directions of the different volcanic units established in the island, dikes emplacement modelling in active tectonic regime, and the integration of the results obtained in a kinematic and dynamic emplacement model of the different volcanic units of the Deception Island into recent geodynamic setting of Bransfield Basin opening. (2) Lito- and crono-stratigraphy analysis of the quaternary sedimentary units that filled Port Foster (inner bay of Deception Island) on the basis of the ultra-high seismic profiles and gravity cores data acquired during oceanographic campaigns carried out using the RV. BIO/HESPERIDES. (3) Recovery of the Hydrothermal Precipitation Cells (HPCs) emplaced in Port Foster during 2001 austral summer and the mineralogical and geochemical analysis of the precipitate deposits located in the inner walls of the HPCs. The analysis of these samples will provide important information about the recent volcanic activity.

Maestro, Adolfo; Gil-Imaz, Andrés.; Gil-Peña, Inmaculada; Galindo-Zaldívar, Jesús; Rey, Jorge; Soto, Ruth; López-Martínez, Jerónimo; Llave, Estefanía.; Bohoyo, Fernando; Rull, Fernando; Martínez-Frías, Jesús; Galán, Luis; Casas, David; Lunar, Rosario; Ercilla, Gemma; Somoza, Luis

2010-05-01

232

Preliminary analysis of the connection between ocean dynamics and the noise of gravity tide observed at the Sopronbánfalva Geodynamical Observatory, Hungary  

NASA Astrophysics Data System (ADS)

An experimental development of a PC controlled CCD ocular system applied for the LaCoste and Romberg G949 gravimeter of the Geodetic and Geophysical Research Institute of the Hung. Acad. Sci. made the continuous observation of time variation of gravity possible. The system was operated for half a year in the Sopronbánfalva Geodynamical Observatory to test its capabilities. The primary aim of this development was to provide an alternative and self-manageable solution for the standard/factory CPI reading of this type of gravimeter and use it for the monitoring of earth tide phenomenon. It, however, turned out that this system is sensitive enough to observe the effect of variable seismic noise (microseisms) due to the changes of ocean weather in the North Atlantic and North Sea regions at microGal level (1 ?Gal=10-8 m/s2). Up to now much attention was not paid to its influence on the quality and accuracy of gravity observations because of the large distance (> 1000 km) between the observation place (generally the Carpathian-Pannonian basin) and the source locations (centers of storm zones of the northern hydrosphere). Based on an elementary single wave surface deformation model the noise levels of gravity observations were compared to the spectral characteristics of seismic time series recorded at the same time in the Observatory. Although the sampling rate of gravity records was 120 s the daily variation of gravity noise level could be correlated to the variation of spectral amplitude distribution of the analyzed high pass filtered (cut-off frequency = 0.005 Hz) seismograms in the frequency band between 0.005 Hz and 10 Hz. Also available daily maps of ocean weather parameters were used to support both the correlation analysis and the parametrization of the source of microseisms for further statistical investigations. These maps which were processed by standard image processing algorithms provide numerical data about geometrical (distance and azimuth of the source relative to the observation point) and physical (mass of swelling water) quantities. The information can be applied for characterizing the state of ocean weather at a given day which may help the prediction of its influence in the future. Probably it is the first attempt to analyse quantitatively the effect of ocean weather on gravity observations in this specific area of the Carpathian-Pannonian region.

Papp, G.; Sz?cs, E.; Battha, L.

2012-04-01

233

Preliminary analysis of the connection between ocean dynamics and the noise of gravity tide observed at the Sopronbánfalva Geodynamical Observatory, Hungary  

NASA Astrophysics Data System (ADS)

An experimental development of a computer controlled photoelectric ocular system applied for the LaCoste and Romberg G949 gravimeter made the continuous observation of time variation of gravity possible. The system was operated for half a year in the Sopronbánfalva Geodynamical Observatory to test its capabilities. The primary aim of this development was to provide an alternative and self-manageable solution instead of the standard electronic (Capacitive Position Indicator) reading of this type of gravimeter and use it for the monitoring of Earth tide. It, however, turned out that this system is sensitive enough to observe the effect of variable seismic noise (microseisms) due to the changes of ocean weather in the North Atlantic and North Sea regions at microGal level (1 ?Gal = 10-8 m/s2). Up to now not much attention was paid to its influence on the quality and accuracy of gravity observations because of the large distance (>1000 km) between the observation place (generally the Carpathian-Pannonian basin) and the locations (centres of storm zones of the northern hydrosphere) of triggering events. Based on an elementary harmonic surface deformation model the noise level of gravity observations was compared to the spectral characteristics of seismic time series recorded at the same time in the observatory. Although the sampling rate of gravity records was 120 s the daily variation of gravity noise level showed significant correlation with the variation of spectral amplitude distribution of the analysed high pass filtered (cut-off frequency = 0.005 Hz) seismograms up to 10 Hz. Also available daily maps of ocean weather parameters were used to support both the correlation analysis and the parameterization of the triggering events of microseisms for further statistical investigations. These maps, which were processed by standard image processing algorithms, provide numerical data about geometrical (distance and azimuth of the storm centres relative to the observation point) and physical (mass of swelling water) quantities. The information can be applied for characterizing the state of ocean weather at a given day which may help the prediction of its influence on gravity measurements in the future. Probably it is the first attempt to analyse quantitatively the effect of ocean weather on gravity observations in this specific area of the Carpathian-Pannonian region.

Papp, G.; Sz?cs, E.; Battha, L.

2012-10-01

234

Evolution of the Cretaceous magmatism in the Apuseni-Timok-Srednogorie metallogenic belt and implications for the geodynamic reconstructions: new insight from geochronology, geochemistry and isotope studies  

NASA Astrophysics Data System (ADS)

Most major Cu-Au (-PGE) deposits in the Carpathian Balkan orogen are related to a 1500 km long belt of Upper Cretaceous magmatism extending from southern Romania through Yugoslavia to Bulgaria, with a likely continuation southeast of the Black Sea into Turkey, known as the Apuseni Banat Timok Srednogorie (ABTS) belt (Popov et al., 2000). In the frame of ABTS belt a new investigation was started to reveal the relation between Cretaceous magmatism and the Cu-Au-PGE deposits across the belt in East Serbia (Yugoslavia) and the Panagyurishte district (Bulgaria). The Late Cretaceous (Palaeogene?) magmatism of East Serbia developed along the Timok Magmatic Complex (TMC) in the east and the Ridanj Krepoljin Zone (RKZ) in the west. High precision U-Pb single zircon dating and a combination of isotope tracing, geochronological data as well as petrological data were used to provide additional data for the geodynamic evolution. A maximum life span of 2.5 Ma could be calculated for the first phase of volcanic activity in TMC, starting with the Amf-andesites of Veliki Kravelj (86.29 ± 0.32 Ma) and finishing with the Timozites (84.66 ± 0.5 Ma). Ore bearing magmatism in a single deposit (Veliki Kravelj) extended a maximum of 0.6 Ma ("pre-ore": 86.29 ± 0.32 Ma, "post-ore": 86.17 ± 0.15 Ma). Preliminary data for the dacites (70.3 ± 3.5 Ma) outcropping near Krepoljin give evidence for a shifting of the volcanic activity from TMC to RKZ together with changing the ore-deposit type from Cu-Au-PGE (TMC) to Pb-Zn-Cu (RKZ). Isotope tracing give evidence for mantle dominated source with increasing of crustal contamination in the same direction: (87Sr/86Sr ratios: 0.70388 to 0.706050, e-Hf-zircon data: +12 in TMC to +4.5 in RKZ). The Panagyurishte district (Bulgaria) show a duration time of the magmatic activity of 14 Ma, starting in the north at 92 Ma and finishing in the south at 78 Ma. Ore-related magmatism becomes younger in the same direction but finishes with 86 Ma. Multiple short magmatic pulses (< 1.Ma) led to several important Cu-Au-PGE ore deposits within the Central Srednogorie zone. Sr-, Nd-, Pb- and Hf-isotope tracing on whole rocks and minerals provides evidence for mixed crust-mantle origin of the magma with specific trends in the single deposits. Presented data suggest subduction related magmatism in the Upper Cretaceous with subduction rollback.

von Quadt, A.; Peytcheva, I.; Heinrich, C. A.; Frank, M.; Cvetkovic, V.

2003-04-01

235

Comparisons of the kinematics and deep structures of the Zagros and Himalaya and of the Iranian and Tibetan plateaus and geodynamic implications  

NASA Astrophysics Data System (ADS)

We compare the geologic histories, the deep structures, and the present-day kinematics of deformation of the Himalaya and the adjacent Tibetan Plateau with those of the Zagros and Iranian Plateau to test geodynamic processes of continental collision. Shortly after India and Arabia collided with Eurasia, horizontal shortening manifested itself by folding and thrust faulting of sedimentary rock detached from India's and Arabia's underlying crystalline basement. Subsequently, slip on thrust faults stacked slices of India's basement to build the Himalaya on India's northern margin. Such faulting has not yet developed in the Zagros, where collision is more recent and Arabia penetrates into Eurasia more slowly than India does, so that postcollision convergence with Eurasia is less. The greater elevation, thicker crust, and more marked heterogeneity of the upper mantle beneath the Tibetan than beneath the Iranian Plateau also reflect a more advanced stage of development. Moreover, while thrust or reverse faulting and crustal shortening continue on the margins of both plateaus, normal faulting, suggesting horizontal extension and crustal thinning, occurs within Tibet but not in Iran. Hence, the balance of forces that built the high Tibetan Plateau must have changed, apparently some time since ˜15 Ma. Removal of Tibetan mantle lithosphere could have altered that balance. If mantle lithosphere beneath the Iranian Plateau has been removed, however, the change in force balance has been too small to initiate normal faulting. Low seismic wave speeds in the uppermost mantle just beneath the Moho of both plateaus suggest (to us) that lithosphere beneath both is thin, consistent with late Cenozoic removal of it, but alternative explanations might account for these low speeds. Despite its apparently thin, and hence presumably weak, mantle lithosphere, much of central Iran undergoes little deformation. It illustrates how a crustal block can behave rigidly not necessarily because it is strong but because deviatoric stresses can be small. Whereas differences between the two regions clearly depend on the amount that Arabia and India have penetrated into Eurasia, which scales with both the dates of collision and rates of convergence, we see no differences in the operative processes that depend on the present-day rates of convergence.

Hatzfeld, Denis; Molnar, Peter

2010-06-01

236

The long-term rheology of continental lithosphere: validating experimental data from real-scale observations and physically consistent models of geodynamic processes  

NASA Astrophysics Data System (ADS)

The lithosphere may exhibit elastic, brittle-plastic and viscous-ductile properties. Rock mechanics experiments infer that a large part of the long-term lithospheric strength may be supported in the visco(ductile)-elastic regime. Yet, rock mechanics data refer to very high strain rates (10 orders of magnitude faster than natural ones), small, often mono-mineral, rock samples, simple loading conditions and specific fluid contents. Therefore they cannot be univocally applied to aggregated rocks at real conditions, geological time and spatial scales without additional parameterization. The only adequate parameterization would be based on real-time and space scale observations of lithosphere deformation in-situ. On practice, such observations refer to indirect interpretations of various kinds of data. New, solid insights may be obtained from large-scale thermo-mechanical models that reproduce lithospheric behavior while fitting multi-disciplinary sets of large-scale geophysical and geological data. For oceans, Goetze and Evan's brittle-elastic-ductile yield strength envelopes were successfully validated by models of plate flexure that have yielded robust estimates for the integrated strength of the lithosphere (EET) through correlating the observed gravity and bathymetry. In continents, the uncertainties of flexural models and of other data are much stronger due to the complex structure and history of continental plates. We suggest that continental rheology can be assessed and validated from a direct physical approach. For that we explore, by numerical thermo-mechanical modeling, the implications of a weak and strong mantle for tectonic structural styles to show which experimental rheology data sets are more physically compatible with tectonic scale deformation. We therefore suggest a new approach allowing for validation of extrapolations of the experimental rock mechanics data. We show, in particular, that the evolution of most continental convergence zones appeal for generalized "Jelly-Sandwich" rheology (strong mantle and strong upper crust with various possibilities for the intermediate and lower crust), which parameters can be robustly constrained , for each particular geodynamic context, from coupled dynamic thermo-mechanical models.

Burov, Evgueni

2010-05-01

237

Geodynamic evolution of the Eastern Sierras Pampeanas (Central Argentina) based on geochemical, Sm-Nd, Pb-Pb and SHRIMP data  

NASA Astrophysics Data System (ADS)

Whole-rock geochemical analyses using major and trace elements in combination with the Sm-Nd and Pb-Pb isotope systems, together with SHRIMP age dating on metasedimentary rocks from the Sierras de Chepes, the Sierras de Córdoba, the Sierra Norte and the San Luis Formation in the Sierra de San Luis, have been carried out to unravel the provenance and the geodynamic history of the Eastern Sierras Pampeanas, Central Argentina. The geochemical and the Sm-Nd data point to a slightly stronger mafic and less-fractionated material in the provenance area of the Sierras de Córdoba when compared to the other units. The TDM model ages from the Sierras de Chepes (~1.82 Ga) and the Sierra Norte (~1.79 Ga) are significantly older than the data from the Sierras de Córdoba (1.67 Ga). The Pb data are homogeneous for the different units. Only the 208Pb/204Pb ratios of some samples from the Sierras de Córdoba are higher. A late Pampean detrital zircon peak around 520 Ma from the Sierras de Chepes is in accordance with the new data from the San Luis Formation. This is similar to the literature data from the Famatina Belt located to the northwest of the Sierras de Chepes and also fits the detrital zircon peaks in the Mesón group. These maximum depositional ages were also reported from some locations in the Puncoviscana Formation but are absent in the Sierras de Córdoba. An improved model for the development of the Eastern Sierras Pampeanas in the area between the Sierras de Córdoba and the Puncoviscana Formation is provided. This gives new insights into the late Pampean development of the Sierra de San Luis and the complex development of the Eastern Sierras Pampeanas. This new model explains the younger detrital ages in the Puncoviscana Formation compared with the older ages of the Sierras de Córdoba. Another model of the Sierra de San Luis explains the younger depositional ages of the Pringles Metamorphic Complex and the San Luis Formation when compared to the Nogolí Metamorphic Complex and the Conlara Metamorphic Complex. Additionally, the rather fast change of the high-grade metamorphic conditions in the Pringles Metamorphic Complex and the low-grade metamorphic conditions in the San Luis Formation is explained by extension, the ascent of (ultra) mafic material and later folding and erosion.

Drobe, Malte; de Luchi, Mónica López; Steenken, André; Wemmer, Klaus; Naumann, Rudolf; Frei, Robert; Siegesmund, Siegfried

2011-04-01

238

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

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

239

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

NASA Astrophysics Data System (ADS)

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

Kerrich, R.; Feng, R.

1992-01-01

240

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

241

The Alps 1: A working geodynamic model for burial and exhumation of (ultra)high-pressure rocks in Alpine-type orogens  

NASA Astrophysics Data System (ADS)

Eocene (ultra)high-pressure ((U)HP) rocks exposed in the Western Alps are generally interpreted to result from subduction of European continental crust beneath Adria and its subsequent exhumation. However, the roles of extension (either from plate divergence or internal to the orogen) and erosion during exhumation remain controversial. Here we use 2D numerical geodynamic models to explain the formation and exhumation of (U)HP rocks in an Alpine-type orogen and interpret the results in the conceptual Prowedge–Uplifted Plug–Retrowedge–Conduit (PURC) framework. (U)HP metamorphism of oceanic and microcontinent crust in the models results from burial and accretion to a subduction channel/conduit formed beneath an advancing retrocontinent. Rapid exhumation from (U)HP conditions is achieved by the buoyancy-driven transport of a composite plume of stacked (U)HP oceanic and microcontinent crust from the subduction conduit to the overlying orogenic prowedge, accommodated by coeval thrusting and normal-sense shearing. Subsequent 'trans-crustal' exhumation is achieved by a combination of doming/internal extension and later retrotransport of the (U)HP plume through the uplifted plug, during underthrusting of the thick continental margin crust, coupled with increased erosion. Our proposed mechanism implies that exhumation-related normal-sense shearing in the Western Alps, per se, was driven from below by the buoyancy of the ascending plume, and that extension owing to plate divergence is not required to explain (U)HP rock exhumation. The efficiency of the exhumation mechanism depends strongly on the buoyancy and strength of the (U)HP plume, suggesting that in order to exhume rapidly, it must achieve a critical size. By implication, the multiple small Eocene (U)HP complexes within the Internal Crystalline Massifs may have been exhumed as part of a single composite body comprising diverse units aggregated from different levels of the subduction conduit during burial or ascent, rather than as individual small bodies exhumed in separate pulses.

Butler, Jared P.; Beaumont, Christopher; Jamieson, Rebecca A.

2013-09-01

242

Dating intrusion and cooling of Cenozoic granitoids in the Dinarides of Southern Serbia and discussion of the geodynamic setting of Paleocene-Miocene magmatism in the Balkan Peninsula  

NASA Astrophysics Data System (ADS)

This paper presents the results of high precision single grain U-Pb dating and Hf isotope analyses of thermally annealed and chemically abraded zircons from the Kopaonik, Drenje, Željin, Golija and Polumir intrusions in the inner Dinarides of southern Serbia. In addition, new zircon and apatite fission-track data together with local structural observations, allow for constraining the subsequent exhumation history of these intrusions. Two age groups were determined for the granitoid intrusions: (i) Oligocene intrusive bodies (Kopaonik, Drenje, Željin) ranging in age from 31.7 to 30.6 Ma and (ii) Miocene Golija and Polumir intrusions which emplaced at 20.58-20.17 and 18.06-17.74 Ma, respectively. The apatite fission-track modelling combined with zircon central ages show rapid cooling from above 300 to ca. 80 °C between 16 and 10 Ma for granitoids of both age groups, followed by rather slow cooling to surface temperatures for the last 10 Ma. Fast Middle Miocene cooling between 16 and 10 Ma is caused by extensional exhumation of the plutons that are located in the footwall of core-complexes. This documents that Miocene magmatism and core-complex formation leading to formation of the Pannonian basin also affected a part of the mountainous areas of the internal Dinarides. The discussion of an extensive set of age data from the literature and the geodynamic setting of the Balkan Peninsula reveals that there is no direct connection of the Dinaridic Late Eocene to earliest Miocene magmatic belt with contemporaneous Periadriatic intrusions in the Alps and along the Mid-Hungarian fault zone as proposed in the literature. We insist on the fact that the subduction polarity in the Alps, including that within the Western Carpathians north of the Mid-Hungarian fault zone, is opposite to that of the Dinarides during the given time span. Instead, we propose that Late Eocene to Oligocene magmatism, which affects the Adria-derived lower plate units of the internal Dinarides, may be caused by delamination of the Adriatic mantle from the overlying crust, associated with intra-plate convergence that propagates outward into the external Dinarides during this time interval. Miocene magmatism, on the other hand, is associated with core-complex formation at the southern rim of the Pannonian basin probably associated with the W-directed subduction of the European lithosphere beneath the Carpathians, possibly interfering with ongoing Dinaridic-Hellenic back-arc extension.

Senecio, Schefer; Cvetkovi?, Vladica; Fügenschuh, Bernhard; Kounov, Alexandre; Ovtcharova, Maria; Schaltegger, Urs; Schmid, Stefan

2010-05-01

243

Geodynamic implications of xenolith geotherms  

Microsoft Academic Search

Studies of xenolith suites yield depth-temperature arrays for the lithosphere at the time of eruption. These studies constrain the conductive heat flow through the lithosphere and limit the temperature range across the rheological boundary layer to <300 K. Numerical models of convection illustrate features that may be found within suites of samples. An individual dike may sample the geotherm along

Norman H. Sleep

2003-01-01

244

Geodynamic implications of xenolith geotherms  

NASA Astrophysics Data System (ADS)

Studies of xenolith suites yield depth-temperature arrays for the lithosphere at the time of eruption. These studies constrain the conductive heat flow through the lithosphere and limit the temperature range across the rheological boundary layer to <300 K. Numerical models of convection illustrate features that may be found within suites of samples. An individual dike may sample the geotherm along a finite length of its strike having variable geotherms, causing scatter in the depth-temperature array. In a suite from the Slave Province of Canada, local heating within a deep stockwork is a more likely cause of scatter. Plume material ponded beneath a craton may yield a linear array extrapolating to the shallow geotherm without any noticeable kink or curvature. This situation existed beneath Lesotho in South Africa at ˜90 Ma. Convection at the base of the lithosphere may produce stress concentrations that trigger dike formation. Dikes may stagnate and form stockworks in low-stress regions above the thermal boundary layer.

Sleep, Norman H.

2003-09-01

245

Geodynamic models of deep subduction  

NASA Astrophysics Data System (ADS)

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

Christensen, Ulrich

2001-12-01

246

KALMAR - "Kurile-Kamchatka and Aleutean Marginal Sea-Island Arc Systems: Geodynamic and Climate Interaction in Space and Time" - an integrated science approach between Russia and Germany  

NASA Astrophysics Data System (ADS)

The exploration of the arctic seas require an integrated approach applying different infrastructures. In Fall 2009 German and Russian scientists performed a geo marine cruise off Kamchatka and in the western Bering Sea within the frame of the KALMAR-Project. Two main research subjects formed the scientific backbone of the cruise: The first objective focuses on the geodynamic and volcanological-magmatic development of the Kuril-Kamchatka island arc system and the Kamchatka Aleutean Islands Triple-Junction. Very little is known about the composition of the mantle and the oceanic crust as well as of the seamounts including their ages. The best studied site is the Volcanologist's Massif located between the Bering- and the Alpha Fracture Zone (Tsvetkov 1990, Volynets et al. 1992, Yogodzinsky et al. 1994), which structurally belongs to the Komandorsky Basin. The oldest rocks of the Volcanologist's Massif show very similar trace element and isotope signatures like those rocks cropping out in the volcanoes on Kamchatka in the prolongation of the Alpha Fracture Zone (Portnyagin et al. 2005a), indicating similar conditions of magma formation. The top of the Volcanologist's Massif is characterized by the young (< 0.5 Ma) and hydrothermally active Piip volcano, which consists of special magnesium rich andesites ("Piip type"). Another hot site was the Meiji-Seamount which is the northernmost Seamount of the hotspot spur of the Hawaii-Emperor-Seamount chain, having an age of probably > 85 Ma. The only existing basement rocks from this seamount were gained during DSDP Leg 19. These are basalts with MORB like trace element and isotope signatures (Keller et al. 2000, Regelous et al. 2003). These data indicate that the Hawaii-Hotspot was at a MOR in Cretaceous time and that large volumes of depleted mantle material played a role during the magma formation. The second objective focuses on paleo-oceanographic investigations concentrating on the sediments along the eastern continental slope of Kamchatka, in the Komandorsky Basin, and on the Shirshov Ridge in order to explore paleoclimate archives to better understand the subpolar water mass transfer and the oceanographic and climatic development in the subarctic NW-Pacific. Comparisons of Late Pleistocene and Holocene temperature changes within the near surface water masses between the NW-Pacific and the N-Atlantic resulted in a new hypothesis, the "Atlantic-Pacific seesaw" (Kiefer et al. 2001, Kim et al. 2004, Kiefer and Kienast, 2005). This Atlantic-Pacific pattern of opposite temperature variations dominates the last 60ka on millennial timescales. Modelling results of Saenko et al. (2004) support the hypothesis of the "Atlantic-Pacific seesaw" and they postulate a mechanistic connection between the two regions driven by salinity variations, which couples both regions through the thermohaline circulation. A different model relates the Holocene Atlantic-Pacific dipole to the atmospheric tele-connection between the Arctic Oscillation/N-Atlantic Oscillation and the Pacific N-American Oscillation (Kim et al. 2004). http://kalmar.ifm-geomar.de

Dullo, Wolf-Christian; Baranov, Boris; van den Bogaard, Christel

2010-05-01

247

Extending a thickened crustal bulge: toward a new geodynamic evolution model of the paleozoic NW Bohemian Massif, German Continental Deep Drilling site (SE Germany)  

NASA Astrophysics Data System (ADS)

Fault-bounded (tectonic) metamorphic complexes assembling the NW Bohemian Massif around the German Continental Deep Drilling (KTB) site are seen to be extremely heterogeneous in tectonic and metamorphic histories. In current models, the different complexes were supposed to reflect a puzzle of small pre-Devonian microplates, and the related collision events supposedly lasted until the Carboniferous. Opposed to these models, it will be shown that all the boundaries among the complexes were formed by detachment, late in a prolonged overall geodynamic history of a thickened crustal bulge, during extensional tectonics and associated thermal events that outlasted the onset of collision in the Silurian/Lower Devonian by about 70-80 Ma. (Micro-)structures, petrological and geochronological data of individual complexes predominantly preserve the late stages rather than the unbroken record of their tectonometamorphic histories. Such partial histories strongly different among individual complexes, depict diverse snapshots taken at different places in the evolving thickened crustal bulge and at different instants in its overall evolution, and do not define different precollisional microplates. Predominantly P- T and deformation episodes after terrane juxtaposition are preserved. This article presents an integrated view of the structural geology, microscopic fabrics, P- T data and geochronology of such diverse metamorphic complexes. This integrated view provides a new understanding of (1) the tectonic evolution during Upper Silurian/Devonian collision of the Gondwana-derived Central European lithosphere with Laurussia, (2) the postaccretionary events that lasted through the Upper Carboniferous and (3), the earlier (Lower Ordovician) metamorphic and magmatic history, which is only locally recorded. Metamorphic complexes occupying the structurally highest position (upper tectonic complexes) record Devonian and earlier tectonometamorphic and magmatic events. After the Mid-Devonian, such complexes did not experience any metamorphism. The recorded Devonian events consist of subduction and exhumation of HP-rocks and their exhumation involved thrusting and extensional tectonics. Upper tectonic complexes comprise fragments of both the plate that was subducted in this period and the overriding plate. In the footwall, Carboniferous extension has brought upper tectonic complexes against metamorphic complexes that essentially record Lower and Upper Carboniferous tectonometamorphic and magmatic events (lower tectonic complexes). In the lower tectonic complexes, such events are (1) consecutive extensional stages that created at least three sets of ductile normal detachment systems intersecting each other, and various associated thermal pulses, as well as (2) predetachment events that are only recorded as petrologic and structural relics transposed during extension. Inferred as predetachment events are crustal subduction as well as stacking that outlasted thrusting and exhumation of the upper tectonic complexes. In the deeper portion of the thickened crustal bulge represented by the lower tectonic complexes, spatial variations of P- T- t- d histories during decompression occurred as a result of continued differential exhumation on the three sets of detachment systems, and also from various thermal pulses that have affected different parts of this section during progressive shearing and exhumation to various degrees. Whereas the lower tectonic complexes of the Erzgebirge Gneiss Dome preserve the record of a Lower Carboniferous history of HP-metamorphism and crustal thickening followed by extension, in those of the Oberpfalz region (KTB site), a major Upper Carboniferous thermal pulse mostly erased the pre-Upper Carboniferous strain fabrics and metamorphic record. In the Oberpfalz region, ongoing extension emplaced mid-crustal rocks that pervasively equilibrated in the Upper Carboniferous at high temperatures and low pressures (low P/T ratio) against rocks not exposed to high temperatures at that time. In summary, a prolonged postaccretionary history

Krohe, Alexander

1998-09-01

248

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

NASA Astrophysics Data System (ADS)

The Fiskenæsset Complex, SW Greenland, is one of the best preserved layered Archean intrusions in the world, consisting of an association of ca. 550-meter-thick anorthosite, leucogabbro, gabbro, and ultramafic rocks (dunite, peridotite, pyroxenite, and hornblendite). Despite poly-phase deformation and amphibolite to granulite facies metamorphism, primary cumulate textures and igneous layering are well-preserved in the complex.This study reports new major and trace element data for three variably thick (1 to 5 m) differentiated (dunite, through peridotite, pyroxenite, gabbro leucogabbro, to anorthosite) sequences (Sequences 1, 2 and 3) in the Sinarssuk area of the Fiskenæsset region. On several variation diagrams, samples from these sequences plot along a well-defined liquid line of descent, consistent with in situ fractional crystallization. The average chemical compositions of these sequences are used to constrain their approximate parental magma compositions. Petrographic observations and geochemical data suggest that Sequences 2 and 3 solidified from evolved magmas that underwent olivine fractionation prior to their intrusion. In contrast, Sequence 1 appears to have been derived from a near-primary parental magma (SiO2 = 43 wt.%, MgO = 20 wt.%, Al2O3 = 16 wt.%, CaO = 9.3 wt.%, Ni = 840 ppm, Mg-number = 80). The trace element patterns of this parental magma are comparable to those of Phanerozoic boninites, consistent with a supra-subduction zone geodynamic setting.If the relative thickness of ultramafic layers, the sum of dunite, peridotite and pyroxenite layers, in differentiated sequences is taken as an analog for the original complex emplaced into Archean oceanic crust, the Fiskenæsset Complex might have had a minimum thickness of 1000 m, with a 500 m thick ultramafic unit at the bottom. The thickness of the ultramafic unit in the preserved complex is less than 50 m, suggesting that more than 90% of the original ultramafic unit was either delaminated and recycled back into the mantle as a residual cumulate, or was destroyed during thrusting and TTG intrusion.Both the Fiskenæsset Complex and associated tholeiitic basalts display similar Th-Nb-LREE patterns and plot along the same differentiation trend on Zr versus incompatible trace element diagrams, suggesting a possible petrogenetic link between the two suites of rocks. However, basalts do not display the same differentiation trend as the complex on several major and trace element diagrams. In addition, basalts and parental magma to the complex do not plot along the same fractionation line on Al2O3/TiO2 versus incompatible trace element diagrams, implying that the Fiskenæsset layered intrusive rocks were not derived from tholeiitic basalts through fractional crystallization, as previously thought. Accordingly, we infer that the Fiskenæsset Complex and spatially associated basalts were derived from different mantle sources. Parental magmas to the Fiskenæsset Complex originated from a mantle source that was metasomatized by highly aluminous slab-derived melts.Layered anorthosite complexes are mostly restricted to the Archean and typically associated with tonalite-trondhjemite-granodiorite (TTG) gneisses. The petrogenesis of both suites appears to have been controlled mainly by slab melting, endorsing independent evidence for a secular change from slab-dominated melting to wedge-dominated melting in arc magmatism at the end of the Archean, reflecting higher geothermal gradients in Archean arcs than post-Archean counterparts.

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

2011-04-01

249

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

250

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)

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.

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

2012-04-01

251

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

252

Cenozoic geodynamics of the Bering Sea region  

NASA Astrophysics Data System (ADS)

In the Early Cenozoic before origination of the Aleutian subduction zone 50-47 Ma ago, the northwestern (Asian) and northeastern (North American) parts of the continental framework of the Pacific Ocean were active continental margins. In the northwestern part, the island-arc situation, which arose in the Coniacian, remained with retention of the normal lateral series: continent-marginal sea-island arc-ocean. In the northeastern part, consumption of the oceanic crust beneath the southern margin of the continental Bering shelf also continued from the Late Cretaceous with the formation of the suprasubduction volcanic belt. The northwestern and northeastern parts of the Paleopacific were probably separated by a continuation of the Kula-Pacific Transform Fracture Zone. Change of the movement of the Pacific oceanic plates from the NNW to NW in the middle Eocene (50-47 Ma ago) was a cause of the origin of the Aleutian subduction zone and related Aleutian island arc. In the captured part of the Paleopacific (proto-Bering Sea), the ongoing displacement of North America relative to Eurasia in the middle-late Eocene gave rise to the formation of internal structural elements of the marginal sea: the imbricate nappe structure of the Shirshov Ridge and the island arc of the Bowers Ridge. The Late Cenozoic evolution was controlled by subduction beneath the Kamchatka margin and its convergence with the Kronotsky Terrane in the south. A similar convergence of the Koryak margin with the Goven Terrane occurred in the north. The Komandorsky minor oceanic basin opened in the back zone of this terrane. Paleotectonic reconstructions for 68-60, 56-52, 50-38, 30-15, and 15-6 Ma are presented.

Chekhovich, V. D.; Sukhov, A. N.; Sheremet, O. G.; Kononov, M. V.

2012-05-01

253

Aral Sea Basin Evolution: Geodynamic Aspect  

Microsoft Academic Search

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

Bakhtiar Nurtaev

254

Magmatism and Geodynamics of Eastern Turkey  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

255

Metamorphic chemical geodynamics of subduction zones  

Microsoft Academic Search

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

Gray E. Bebout

2007-01-01

256

Putting the Dynamics in Chemical Geodynamics  

NASA Astrophysics Data System (ADS)

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

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

2007-12-01

257

Geodynamics: A tale of a trail  

NASA Astrophysics Data System (ADS)

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

Gordon, Richard G.

2008-09-01

258

Recent geodynamics and evolution of the Moma rift, Northeast Asia.  

NASA Astrophysics Data System (ADS)

The Cenozoic Moma rift system is a major tectonic feature in northeast Russia. It is composed of a series of basins (Selennyakh, Kyrin,Lower Moma,Upper Moma,etc.) filled with up to one km thick and bounded by the Chersky Range (up to 3100 m high) on the southwest and the Moma Range (up to 2400 m high) on the northeast. Northeast of the Moma Range is the Indigirka-Zyryanka foreland basin, composed of thick, up to 2.5 km, Eocene, Oligocene, and Miocene coal-bearing sequences, while on the southwestern side of the Chersky Range there are a number of piedmont basins (Tuostakh, Upper Adycha, Derbeke, etc.) containing up to several hundred meters of Miocene and Oligocene coal-bearing deposits. Despite considerable study over the past half-century, there is considerable debate over the origin, present-day tectonics, and evolution of the Moma rift system. The Cenozoic deposits of the basins generally become younger from northwest to southeast with the exception of the Seimchan-Buyunda basin. In the northeast, fan-shaped coal-bearing basins (e.g., Nenneli, Olzhoi, Selennyakh, Uyandina, Tommot, and others) are filled with Miocene to Pliocene deposits, while basins in the southeast (e.g., Taskan) are filled with Neogene sediments. The Seimchan-Buyunda basin, however, has sediments of Oligocene age. The Moma rift system is reflected a major step in the gravity field, presumably separating denser rocks of the Kolyma-Omolon superterrain from somewhat less dense rocks of the Verkhoyansk fold belt (margin of the North Asian Craton). Analysis of travel-times of Pn and Pg waves from local earthquakes indicates an area of thinned crust (30-35 km) southwest of the Moma rift system, extending as a "tongue" from the Lena River delta and the Laptev Sea to the upper part of the Kolyma River, as compared to 40-45 km in the surrounding areas. This region of thinned crust also coincides with a region of high heat flow values measured in boreholes of the Chersky Range (up to 88 mW/m2). Hot springs with temperatures up to +20°C are found within the Moma and Selnnyakh basins proper.The crustal inhomogeneity is also reflected in the upper mantle as indicated by a 40° rotation of the Rayleigh wave polarization angle from teleseisms recorded at Tiksi that cross the Moma rift system as opposed to those that do not. Cenozoic volcanism, chemically similar to basalts and rhyolites from rift zones elsewhere is found in the Moma rift proper. Balagan-Tas is a basaltic cinder cone which has been dated at 286,000 years based on Ar-Ar dating, while Uraga-Khaya is an undated, presumed Quaternary, rhyolitic dome. All these factors indicate that the Moma rift system originated as a continental rift, probably as an extension of the Arctic (Gakkel) Mid-Ocean Ridge. At the present, however, compressional conditions prevail within the Moma rift zone. Seismicity is generally absent from the rift basins proper or their margins; most seismicity is concentrated to the southwest of the Moma rift basins along major strike-slip fault systems. Focal mechanisms of the largest earthquakes in the Chersky Range also all show transpression. Field mapping indicates that the majority of the faults mapped in the field are strike-slip, thrust and reverse faults (86%) with only a small number of normal faults (14%) and that the Cenozoic deposits within the Moma rift are intensely folded. Re-leveling surveys conducted along the Indigirka River, which cuts across the Moma rift system, reveal a moderate rate of presnt-day vertical uplift (up to +4 mm/yr). Thus, the Moma rift system is no longer acting as a rift, but is undergoing transpression. This conclusion is also supported by recent plate motion calculations based on GPS and VLBI data, as well as slip-vectors of earthquakes, which indicates that the Euler pole between North America and Eurasia is located around 68-70°N, near the coast of the Laptev Sea. This places the Moma rift system in a zone of convergence between North America and Eurasia; this geometry also supports the extrusion of the Okhotsk Sea plate. Poles of ro

Imaev, V. S.; Imaeva, L. P.; Kozmin, B. M.; Fujita, K. S.; Mackey, K. G.

2009-04-01

259

Geodynamic Evolution of the Southern Flank of the Corinth Rift  

Microsoft Academic Search

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

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

2005-01-01

260

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

SciTech Connect

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.

Miller, W.A.

1997-08-01

261

Erosion, Himalayan Geodynamics, and the Geomorphology of Metamorphism  

Microsoft Academic Search

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

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

2001-01-01

262

Seismicity of oceanic and continental rifts—a geodynamic approach  

NASA Astrophysics Data System (ADS)

Two major kinds of divergent structures—oceanic and intracontinental rifts—were compared in principal seismic and tectonic characteristics. First, the role of main components of the mid-oceanic ridges (MOR) was estimated for the whole Earth. We considered two levels of the MOR segmentation. The first-order structures are the segments of MOR between triple junctions and the second-order structures are a transform faults and rift parts of MOR. The seismic catalogues NEIC and CMT were used to assess the seismic moment release. The seismic moment release was calculated another way using the global plate tectonic model NUVEL-1 and Brune's formulae. Comparison of these two values shows that the seismic coupling coefficient, ?, varies from 1 to 10% for most of MOR and is always higher for transform faults. Most of the deformation, therefore, is aseismic slip. Most seismicity of MOR is confined to transform faults. The energy contribution of transform faults is one to two orders magnitude higher than that of the rift, and increases with the spreading rate. There is a strong correlation between the seismic moment release of strike-slip faults and their total lengths. The correlation shows that the seismic moment release depends on the total transform area and confirms the simple thermal model of transform seismicity that was given by Burr and Solomon. The seismic moment release and the spreading rate have opposite patterns. For the rifts, there is an inverse correlation between the seismic moment of normal faults and spreading velocity, while it seems for transforms that these parameters are independent. Finally, these results show that the seismicity of transforms and rifts depends first of all on the thermal structure of oceanic lithosphere. In the case of continental rifts, one can distinguish in the degree of seismic activity depending on the stage of rifting. Hence, analysis of the continental seismicity requires the consideration of factors of a geological evolution that play practically no role in the case of oceanic lithosphere. The comparison of geological and seismic data for the East African region has allowed us to outline the regular changes of the seismic regime during development of the rift zone from the stage of incipient rift to mature oceanic rift. In the evolutionary series [intracontinental incipient rift]-[intracontinental mature rift]-[intercontinental rift]-[oceanic slow-spreading rift]-[oceanic fast-spreading rift], there is a gradual decrease of the role of rifts (sensu stricto, as tension structures) and increase of the role of strike-slip faults. Epicenters concentrate along major faults as well. The level of seismic energy becomes lower, although the rate of deformation increases.

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

1999-03-01

263

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

Microsoft Academic Search

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

Stephen E. Haggerty

1994-01-01

264

Plume capture by a migrating ridge: Analog geodynamic experiments  

NASA Astrophysics Data System (ADS)

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

Mendez, J. S.; Hall, P.

2010-12-01

265

Impurity elements as geodynamic indicators of oil accumulation conditions  

NASA Astrophysics Data System (ADS)

In view of the development of the naphtide polygenesis concept including the role of endogenous fluids in the processes of oil accumulations, the applicability of several geochemical coefficients characterizing the ratios of microelements (MEs) in oil is considered in order to identify the oil sources. By means of discrimination diagrams drawn for the average ME concentrations in oil, including the distribution coefficients of impurity elements in the systems of the melts of various alkalinity (rocks) and fluids (bitumens), it is shown that the oils of different regions are considerably different in their geochemical features.

Gottikh, R. P.; Pisotskii, B. I.

2010-08-01

266

Geodynamics of Africa from continuous GPS data: analyses and implications  

Microsoft Academic Search

The advent of space-geodetic techniques has dramatically improved the estimation of present-day plate motions: the velocity of discrete points on the Earth's surface can currently be obtained at sub-centimetre level in the ITRF2000 global reference frame, using a multitude of systems amongst which GPS (Global Positioning System) is prominent. Although the distribution of the reference GPS stations globally has a

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

2003-01-01

267

RAEGE: An Atlantic Network of Geodynamical Fundamental Stations.  

National Technical Information Service (NTIS)

Project RAEGE (Red Atlantica de Estaciones Geodinamicas y Espaciales) intends to set up a Spanish-Portuguese network of four Geodetic Fundamental Stations in Yebes (1), Canary Islands (1), and A cores Islands (2), as part of the developments needed for th...

F. Colomer J. A. LopezFernandez J. G. Gonzalez M. C. S. Assis

2010-01-01

268

Bridging Geodynamics, Hazards, and Capacity Building in East Africa  

Microsoft Academic Search

Advanced Workshop on Evaluating, Monitoring, and Communicating Volcanic and Seismic Hazards in East Africa; Trieste, Italy, 17-28 August 2009; Africa exhibits some of the most spectacular volcanic and tectonic features on Earth. Hazards associated with these features include volcanic eruptions, earthquakes, and carbon dioxide (CO2) degassing. For example, in 2002 an eruption destroyed 25% of the city of Goma, Congo,

Tobias P. Fischer

2010-01-01

269

Prelaunch testing of the laser geodynamic satellite (LAGEOS)  

Microsoft Academic Search

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

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

1977-01-01

270

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

Microsoft Academic Search

The optical range correction (the distance between the apparent retroreflective skin of the satellite and the center of mass) of the LAGEOS 2 was determined using computer analysis of theoretical and experimentally measured far field diffraction patterns, and with short pulse lasers using both streak camera-based range receivers and more conventional PMT-based range receivers. The three measurement techniques yielded range

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

1993-01-01

271

Tertiary geodynamical evolution of northwestern Greece: paleomagnetic results  

Microsoft Academic Search

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

Catherine Kissel; Carlo Laj; Carla Müller

1985-01-01

272

The geodynamic reasons of decade changes of climate  

NASA Astrophysics Data System (ADS)

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

Sidorenkov, N. S.

2012-11-01

273

Geodynamics applications of continuum physics to geological problems  

Microsoft Academic Search

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

D. L. Turcotte; G. Schubert

1982-01-01

274

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

PubMed

The Shallow Radar (SHARAD) on the Mars Reconnaissance Orbiter has imaged the internal stratigraphy of the north polar layered deposits of Mars. Radar reflections within the deposits reveal a laterally continuous deposition of layers, which typically consist of four packets of finely spaced reflectors separated by homogeneous interpacket regions of nearly pure ice. The packet/interpacket structure can be explained by approximately million-year periodicities in Mars' obliquity or orbital eccentricity. The observed approximately 100-meter maximum deflection of the underlying substrate in response to the ice load implies that the present-day thickness of an equilibrium elastic lithosphere is greater than 300 kilometers. Alternatively, the response to the load may be in a transient state controlled by mantle viscosity. Both scenarios probably require that Mars has a subchondritic abundance of heat-producing elements. PMID:18483402

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

2008-05-15

275

Mars North Polar Deposits: Stratigraphy, Age, and Geodynamical Response  

Microsoft Academic Search

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

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

2008-01-01

276

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

Microsoft Academic Search

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

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

2007-01-01

277

International coordination of space techniques for geodesy and geodynamics  

NASA Astrophysics Data System (ADS)

Highlights are given of the extensive activities of the CSTG that are under way and the progress made during the last four years. Activities covered include: the African Doppler Survey (ADOS); activities coordinated by NASA; activities in Japan; activities in Australia; and activities of the European Space Agency. Also discussed are other Western Euroepan activities and activities in Eastern Europe and the USSR, including Intercosmos and Geoss-REA.

Mueller, I. I.

278

The Coming Role of GPU in Computational Geodynamics (Invited)  

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

279

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

USGS Publications Warehouse

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

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

2008-01-01

280

Geodynamic modelling of terrane accretion, subduction, and collision  

NASA Astrophysics Data System (ADS)

Accretion, subduction, or collision of terranes can significantly affect subduction zone evolution and lead to reversed subduction polarity, trench jumping, or breaking off the slab. Terranes such as oceanic plateaus, volcanic arcs, and continental fragments have relatively thick crusts, and their size and buoyancy can therefore can be expected to influence subduction dynamics. Geological observations point out that accretion of terranes can lead to continental growth or accretionary orogenesis as evident by the collage of allochthonous terranes composing the western North American margin. Alternatively, subduction of terranes, as in the Andean subduction zone, has been posited to lead to flat slab subduction. We examine basic models of subduction zones to define the controlling parameters in accretion, subduction, or collision of such terranes with the thermo-mechanical numerical code SULEC. SULEC is a 2-D, Arbitrary Lagrangian-Eulerian, finite element code that incorporates a free surface and a visco-elasto-plastic rheology. Our models test the buoyancy of three end-member terranes; oceanic plateaus, volcanic arcs, and continental fragments by varying terrane length, terrane crustal thickness, and terrane rheology. We seek to evaluate whether terrane buoyancy is enough to induce subduction zone rearrangement or if another variable, such as terrane crustal detachment or a thick subduction accretionary channel, are necessary.

Tetreault, Joya; Buiter, Susanne

2010-05-01

281

Tectonic evolution at rift zones: Geodynamics and Numerical Modeling  

NASA Astrophysics Data System (ADS)

Tectonic evolution at rift zones is commonly considered symmetric along mid-ocean ridges, when modeling with relative plate motions and steady-state processes. However, the bathymetry of rift zones is generally asymmetric, being the eastern flank in average slightly shallower (100-300 m) than the western one. Also, based on surface wave tomographic models, shear wave velocities in the upper mantle indicate a difference between the western and eastern flanks of an oceanic basin. A better way to understand dynamics of the lithosphere at rift zones, and lithosphere/mantle interactions corresponds to absolute plate kinematic analyses, i.e., with respect to the mantle, modeling time-dependent tectonic processes. We performed numerical simulations of plate-driven mantle flow beneath mid-ocean ridges and we considered a time-dipendent flow induced by the relative motion of overlying rigid plates in an incompressible viscous mantle. In mantle reference frames, a net "westward" rotation of the lithosphere relative to the mantle can be observed, and we used velocities obtained in the hotspot reference frame, as boundary conditions. This implies that plates along a ridge, and the ridge itself, move toward the west but with different velocities, relative to the mantle, and the separation between plates triggers mantle upwelling. Numerical solutions for viscosity flow beneath plates that thicken with increasing age are presented. The mantle can be modeled as a viscous fluid, and its dynamics can be described using the Stokes equations. At a first approximation the fluid is considered Newtonian. A further step in the description of the phenomena would require the inclusion of thermal effects: in this case the fluid viscosity and density have to be considered as a function of the temperature. For solving both the Stokes equations and the thermal effects, a finite element approach has been adopted. Results show an asymmetric thickening of plates along the ridge, as suggested by geological a geophysical observations, and provide useful relationships between mantle temperature and thickness of the oceanic lithosphere.

Cuffaro, M.; Miglio, E.; Doglioni, C.

2010-12-01

282

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

Microsoft Academic Search

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

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

2004-01-01

283

The Geodynamics Models of the Active Continental of Eurasia-Pacific Margins Transition Zone  

Microsoft Academic Search

The active continental margins of the transition zone from Eurasian continent to the Pacific Ocean are characterized by high seismicity, volcanic eruption and natural cataclysms hazardous for the people living there. It is also area of recent intense tectonic movements and hydrothermal processes, place of accumulation of different kinds of useful minerals. The task of the research is (1) to

Alexander Rodnikov; Natalia Sergeyeva; Ludmila Zabarinskaya

2010-01-01

284

The Geodynamics Models of the Active Continental of Eurasia-Pacific Margins Transition Zone  

NASA Astrophysics Data System (ADS)

The active continental margins of the transition zone from Eurasian continent to the Pacific Ocean are characterized by high seismicity, volcanic eruption and natural cataclysms hazardous for the people living there. It is also area of recent intense tectonic movements and hydrothermal processes, place of accumulation of different kinds of useful minerals. The task of the research is (1) to study the deep structure and processes in the subduction and paleosubduction zones, beneath seismic hazardous zones, volcanic areas, mineragenetic fields, and sedimentary basins; (2) to determine the role of the deep processes going on in the upper mantle in the formation of major structural units of active continental and oceanic margins; (3) the study of the deep causes of geological phenomena to assess, predict and mitigate the natural disasters, specifically earthquakes, and volcanic eruptions. The distinctive feature of the deep structure of the continental margins is the presence of an asthenosphere in the upper mantle. The tectonically active regions, such as the island arcs and the rifts of the marginal seas, correlate with a thick asthenosphere. The asthenosphere resides in a depth of 50-80 km under the old Paleogene deep basins of the marginal seas, at about 30 km under the Neogene basins, and at a depth of 10-20 km under the Pliocene-Quaternary and recent inter-arc basins, causing the breaks of the lithosphere, the formation of rifts, basalt lava eruptions, and hydrothermal activity. The asthenospheric diapirs are marked on the surface by rift formations and mainly tholeiitic magma eruption. Rifts in the marginal seas and island arcs may by accompanied by intense mineralization. The asthenospheric diapirs represent the channels by which hot mantle fluids from the asthenosphere penetrate to the geological structures of the transition zone from Eurasian Continent to the Pacific Ocean. The work was supported by Russian Foundation for Basic Research. No 09-05-00406-a

Rodnikov, Alexander; Sergeyeva, Natalia; Zabarinskaya, Ludmila

2010-05-01

285

Geodynamics of the Yellowstone Hotspot and Mantle Plume: Seismic and GPS Imaging, Kinematics, and Mantle Flow  

NASA Astrophysics Data System (ADS)

The Yellowstone hotspot resulted from interaction of a mantle plume with the overriding N. America plate producing a ~800-km wide, ~300 m high topographic swell centered on Yellowstone National Park and produced the 800 km-long, 17 Ma Yellowstone-Snake River Plain (YSRP) volcanic field. The Yellowstone Plateau has extensive seismicity including a deadly M7.5 1959 earthquake and extensive swarms, the latest in late 2008-early 2009 experienced a thousand events on the caldera edge and whose activity migrated at ~1,000 m per day beginning with an explosive M4 earthquake. Heat flow is extraordinarily high, ~ 2,000 mWm2, indicative of the thermal energetics of this active volcano-tectonic system. Large-scale geophysical experiments provided seismic and GPS images of the hotspot and data on its kinematic and dynamic properties. Tomography reveals a caldera-wide Yellowstone crustal magma reservoir, that is fed by an upper-mantle plume composed of melt blobs, 80 km to 650 km deep, titled 60° NW. Deformation of Yellowstone is dominated by SW-extension at up to ~0.3 cm/yr, a fourth of the total Basin-Range opening rate, but with superimposed volcanic related uplift and subsidence at decadal scales, averaging ~2 cm/yr. An unprecedented episode of caldera uplift, up to 7 cm/yr from 2004-2008, was modeled as recharge of the crustal magma body at 10-km depth. Upper mantle convection models for Yellowstone are characterized by eastward flow beneath Yellowstone at 5 cm/yr. This suggests that the strong eastward mantle flow that deflects ascending melt into a tilted configuration, i.e. “bending the plume in the mantle wind”. Dynamic models reveal relatively low plume temperatures, up to 150°K excess temperatures, consistent with a weak buoyancy flux of ~0.25 Mg/s, but strong enough to produce the Yellowstone swell. Kinematic and dynamic modeling suggest that the excess gravitational potential of the swell drives the SW motion of the YSRP lithosphere “downhill” where it becomes part of clockwise rotation of western U.S. intraplate blocks. Extrapolating the location of the Yellowstone mantle-source southwestward t an initial position at 17 million years ago beneath eastern Oregon and the southern LIP Columbia Plateau basalt field, suggests a common mantle source for these features. This idea is consistent with the concept that the original plume ascended vertically behind the subducting Juan de Fuca plate, but at ~12 Ma became entrained in faster mantle flow beneath continental lithosphere and became tilted into its present configuration.

Smith, R. B.; Jordan, M.; Steinberger, B. M.; Farrell, J.; Puskas, C. M.; Waite, G. P.; Husen, S.; Chang, W.; O'Connell, R. J.

2009-12-01

286

Isotopic Variations in River Waters, Geodynamic Models and Exogenic Geochemical Cycles  

Microsoft Academic Search

Measurements of radiogenic isotope ratios (Nd, Sr, Pb, Os) and trace elements (REE, Re\\/Os, Sm\\/Nd, U-Th-Pb) in suspended and dissolved loads of rivers provide important constraints both on crust mantle-evolution models as well as on exogenic geochemical cycles. A coherent negative correlation of 206Pb\\/204Pb, 207Pb\\/204Pb, 208Pb\\/204Pb and 187Os\\/188Os isotope ratios with 143Nd\\/144Nd in river suspended loads and a positive correlation

S. B. Jacobsen

2001-01-01

287

Meso-Cenozoic geodynamic evolution of the Paris Basin: 3D stratigraphic constraints  

Microsoft Academic Search

3D stratigraphic geometries of the intracratonic Meso-Cenozoic Paris Basin were obtained by sequence stratigraphic correlations of around 1 100 wells (well-logs). The basin records the major tectonic events of the western part of the Eurasian Plate, i.e. opening and closure of the Tethys and opening of the Atlantic. From earlier Triassic to Late Jurassic, the Paris Basin was a broad

François Guillocheau; Cécile Robin; Pascal Allemand; Sylvie Bourquin; Nicolas Brault; Gilles Dromart; Roselyne Friedenberg; Jean-Pierre Garcia; Jean-Michel Gaulier; Fabrice Gaumet; Bernard Grosdoy; Franck Hanot; Paul Le Strat; Monique Mettraux; Thierry Nalpas; Christophe Prijac; Christophe Rigollet; Olivier Serrano; Gilles Grandjean

2000-01-01

288

Manifestation of solar and geodynamic activity in the dynamics of the Earth's rotation  

NASA Astrophysics Data System (ADS)

The relationships between different manifestations of solar and geomagnetic activity and the structural peculiarities of the dynamics of the pole wobble and irregularities in the Earth's rotation are studied using singular spectrum analysis. There are two close major peaks and several lower ones in the same frequency range (1.1-1.3 years) in the Chandler wobble (CW) spectrum. Components in the geomagnetic activity were distinguished in the same frequency band (by the Dst and Ap indices). Six- to seven-year oscillations in the Earth's rotation rate with a complex dynamics of amplitude variations are shown in variations in geomagnetic activity. It is revealed that secular (decade) variations in the Earth's rotation rate on average repeat global variations in the secular trend of the Earth's geomagnetic field with a delay of eight years during the whole observation period.

Gorshkov, V. L.; Miller, N. O.; Vorotkov, M. V.

2012-12-01

289

Cenozoic volcanic rocks from central Myanmar: Age, geochemical characteristics and geodynamic significance  

NASA Astrophysics Data System (ADS)

Late Cenozoic volcanism occurs in the central Myanmar basin, a region that is marked by the existence of the dextral Sagaing fault linking the eastern Himalayan Syntaxis in the north and the Andaman Sea in the south. This region is located in a unique and transitional position between compressional/Himalayan and extensional/Andaman Sea tectonic settings. Here we report new 40Ar/39Ar age results for the volcanic rocks from Mt. Popa and two volcanoes in Monywa, central Myanmar. The results suggest two distinct stages of eruptions, a mid-Miocene stage from ~16 to 13 Ma and a Quaternary stage <1 Ma, with a >10-m.y. magmatic gap in between. While calc-alkaline rocks showing arc lava geochemistry are abundant, an apparent change in magma composition is observed between the two stages. The mid-Miocene rocks are typical of high-K calc-alkaline nature and dominated by intermediate compositions (SiO2=53-62 wt.%). By contrast, the Quaternary rocks are mainly basalts but show heterogeneous compositions, including (1) high-Al basalts from Mt. Popa: ?Nd=+3.0 to +2.1, ?Hf=+17.4 to +10.7, (2) absarokites and high-Al basalts from Monywa: ?Nd?+3.6, ?Hf?+12.1 for the former and ?Nd?+3.0, ?Hf?+11.8 for the latter, and (3) OIB-type alkali basalts from Singu, a locality off the Sagaing fault: ?Nd?+0.9, ?Hf?+3.7. We interpret the long magmatic gap as a consequence of cessation of the oblique subduction of the Indian oceanic lithosphere beneath this part of Asia that occurred in the mid-Miocene, when the dextral motion of the Sagaing fault system initiated and opening of the Andaman Sea began. All these processes were related to the India-Asia collision that caused plate reorganization in the region and eventually transformed the subduction system from oblique convergence to dextral movement. Under this framework, the Quaternary volcanism renewed owing to small-degree melting of different types of pre-Miocene subduction-enriched mantle domains beneath central Myanmar related to an extensional or transtensional setting created by the stress partitioning along the Sagaing fault system.

Lee, H.; Chung, S.; Yang, H.; Chu, C.; Lo, C.; Mitchell, A.

2010-12-01

290

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

Microsoft Academic Search

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

C. Klootwijk

2009-01-01

291

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

Microsoft Academic Search

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

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

1997-01-01

292

The Geodynamic Evolution of the Central and South East European Tethyan Chains  

NASA Astrophysics Data System (ADS)

Together with the Main Tethyan Suture Zone (disrupted fragments of the Tethyan oceanic domain ), built up of ophiolitic complexes and their overlying sedimentary sequences, three deformed continental margins (continental crust overlaped by tethyan sedimentary formations) may be recognized within the Central and South-East European area, i.g. the European, the Fore-Apulian and the Apulian margins. The Main Tethyan Suture Zone groups together the : Vardar Zone, South Pannonian-Insubric Suture, Transylvaniadian and Pienidian units. The European Margin cover the Northern and Eastern Carpathains, the South Carpathians,the Balkan, Rhodope and Serebo-Maceonein Massiv. To the Fore-Apulian microcontinent belogs the North Apuseni, Central West Carpathians and Austrialpine units, as well as the most important basement of the Pannonian Depression. Apulia covers the most important part of the Dinarides and Hellenides. The Tethyan Ocean opened, in the central and southern part of the area, during the Late Anisian or Early Ladinian and spread, with different rates since the early Upper Jurassic. The rifting which precede the opening may be Late Permian (?) and Lower Triassic. In the same time within the European Plate the intracontinental aulacogene north Dobrogea-South Crimea start to develop as a pull-apart basin connected with the southeasternmost segment of the Tornquist-Teisseyre Zone. In the northern part (West Carpathains and Alps) the Tethyan Ocean opened in the Middle Jurassic being a prolongation (?) of the Central Atlantic opening. The Bukk Terrane drifted since the end of the Lower Triasic from the Apulian Margin and collided the Fore-Apulian microcontinent until the earlly Jurassic. The first compressive events occur at the Jurassic/Cretaceous boundary stressed out by kalk-alkaline volcanics developed upon oceanic crust (Mariane-type subduction) and the “closing” of the North Dobrogea-South Crimea Aulacogene. Since the Middle Jurassic within the European Continetal Margin develops a rift (Ceahlau-Severin) with withinplate ophiolites. The Mid-Cretaceous tectogenetic events were registerd within the Oceanic Tethys and the European Continental Margin.

Sandulescu, M.

2003-04-01

293

The Geodynamic Evolution of the Central and South East European Tethyan Chains  

Microsoft Academic Search

Together with the Main Tethyan Suture Zone (disrupted fragments of the Tethyan oceanic domain ), built up of ophiolitic complexes and their overlying sedimentary sequences, three deformed continental margins (continental crust overlaped by tethyan sedimentary formations) may be recognized within the Central and South-East European area, i.g. the European, the Fore-Apulian and the Apulian margins. The Main Tethyan Suture Zone

M. Sandulescu

2003-01-01

294

Insights on the kinematics of the India-Eurasia collision from global geodynamic models  

NASA Astrophysics Data System (ADS)

The Eocene India-Eurasia collision is a first order tectonic event whose nature and chronology remains controversial. We test two end-member collision scenarios using coupled global plate motion-subduction models. The first, conventional model, invokes a continental collision soon after ˜60 Ma between a maximum extent Greater India and an Andean-style Eurasian margin. The alternative scenario involves a collision between a minimum extent Greater India and a NeoTethyan back-arc at ˜60 Ma that is subsequently subducted along southern Lhasa at an Andean-style margin, culminating with continent-continent contact at ˜40 Ma. Our numerical models suggest the conventional scenario does not adequately reproduce mantle structure related to Tethyan convergence. The alternative scenario better reproduces the discrete slab volumes and their lateral and vertical distribution in the mantle, and is also supported by the distribution of ophiolites indicative of Tethyan intraoceanic subduction, magmatic gaps along southern Lhasa and a two-stage slowdown of India. Our models show a strong component of southward mantle return flow for the Tethyan region, suggesting that the common assumption of near-vertical slab sinking is an oversimplification with significant consequences for interpretations of seismic tomography in the context of subduction reference frames.

Zahirovic, Sabin; Müller, R. Dietmar; Seton, Maria; Flament, Nicolas; Gurnis, Michael; Whittaker, Joanne

2012-04-01

295

Metamorphic history and geodynamic significance of the Early Cretaceous Sabzevar granulites (Sabzevar structural zone, NE Iran)  

NASA Astrophysics Data System (ADS)

The Iranian ophiolites are part of the vast orogenic suture zones that mark the Alpine-Himalayan convergence zone. Few petrological and geochronological data are available from these ophiolitic domains, hampering a full assessment of the timing and regimes of subduction zone metamorphism and orogenic construction in the region. This paper describes texture, geochemistry and the pressure-temperature path of the Early Cretaceous granulites that occur within the Tertiary Sabzevar suture zone of NE Iran. The geochemical data set document that the granulites are remnants of a MORB-type oceanic crust and thus of a (Early Cretaceous ?) back-arc basin formed in the upper plate of the Neotethyan subduction and thus interpreted as portions of a dismembered dynamothermal sole formed during oceanic subduction. The metamorphic history of the granulites suggests an anticlockwise pressure-temperature loop, compatible with burial in a hot subduction zone followed by cooling during exhumation. This is interpreted as the evidence of a nascent subduction zone formed at the expenses of hot and hence young oceanic lithosphere. These data point to diachronous and independent tectonic evolutions of the different ophiolitic domains of central Iran, for which a growing heterogeneity in the timing of metamorphic equilibration and of pressure-temperature paths can be expected with further investigations.

Nasrabady, M.; Rossetti, F.; Theye, T.; Vignaroli, G.

2011-05-01

296

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

Microsoft Academic Search

The NW Borneo Margin is a complex structural domain where deformation style is a mix of compression and extension features associated with transverse structures. Review of outcrops, geomorphologic and magmatism studies show two imbricate wedges in Sabah\\/Brunei: - The Rajang-Crocker Wedge, mainly onshore, is oriented N-S in Sabah, curving to E-W in Sarawak. It is characterized by short wavelength thrusted

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

2009-01-01

297

Relict landscapes in active mountain belts: their age, interpretation and geodynamic significance  

NASA Astrophysics Data System (ADS)

Planar topographic markers have been widely used to infer the topographic and erosional history of mountain belts. During the last two decades, attention has focused on high-elevation low-relief surfaces in orogenic belts, the interpretation of which has generated considerable controversy regarding their age, mechanism of formation and tectonic or climatic significance. I will review three case studies to illustrate these issues. In the Pyrenees, high-elevation, low-relief surfaces have been mapped throughout the mountain belt and were suggested to have developed at high elevations due to significant base-level rise as a result of backfilling of the southern foreland basin, which developed under endorheic conditions between Late Eocene and Late Miocene times. Isolation of these surface remnants has been suggested to result from a more erosive climate since the Pliocene. However, an alternative study suggests that such relict landscape elements are restricted to the Eastern Pyrenees, developed at low elevations during the Miocene and were subsequently tectonically uplifted. This second hypothesis appears to be comforted by a suite of thermochronological, stratigraphic and geophysical data from the Eastern Pyrenees. We have used a thermo-kinematic model integrating the existing thermochronometry data from the central Pyrenees to constrain the amount and timing of base-level change in that area and find that, while significant filling and re-excavation of the southern flank must have occurred, the timing of exhumation is Late Miocene rather than Pliocene-Quaternary and the relationship with hypothetical relict landscape elements in the high chain remains unclear. In the western European Alps, widespread high-elevation low-relief surfaces develop close to the interface between crystalline basement and sedimentary cover in the "external crystalline massifs" (e.g., Pelvoux-Ecrins, Belledonne, Aar). These surfaces clearly appear to be lithologically controlled and to have been extended by cirque retreat where they occur in an elevation range around the glacial equilibrium line altitude, giving rise to apparently paradoxical observations of "paleosurface" preservation concurrent with widespread glacial erosion. Recent high-resolution thermochronology data suggests the final exhumation of these surfaces to be of Pliocene age. While they can be used as markers of glacial incision as well as integrated vertical motions since their formation in Triassic times, their use as markers of tectonic uplift during mountain building is limited. Finally, we have recently described high-elevation relict landscape elements dating from Eocene times in the northwest Himalaya. We interpret these as remnants of a once more widespread Tibetan Plateau, which was subsequently incised due to onset of large-scale strike slip faulting and drainage rearrangement. These surfaces have previously been suggested to result from efficient glacial erosion, but thermochronological data imply a much older age of formation. As is generally the case, the thermochronology data do not provide any constraint on the uplift history of the surfaces, but the simplest scenario suggests they were formed at high elevations and have since been passively eroded. The question remains as to how their morphologies have survived despite km-scale exhumation since Eocene times, as recorded by the thermochronology data. The above examples illustrate the conceptual and interpretational problems generally encountered when dealing with relict landscapes in mountainous regions. Similar arguments and controversies have developed for the Rocky Mountains and Sierra Nevada in the western US. Thermochronology data can put bounds on the age of exhumation of such landscape elements but the resolution of most thermochronological methods remains rather coarse and no direct information on uplift history is gained. The data do show that high-elevation low-relief landscape elements can record substantial amounts of exhumation, justifying their description as "relict landscape

van der Beek, Peter

2010-05-01

298

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

Microsoft Academic Search

Recent field and geochronological studies have demonstrated the importance of granitic magmatism in the evolution of the Neoproterozoic Bras??lia Belt, in Central Brazil. This is an orogenic belt developed in response to the convergence between the Amazon, 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

Márcio M Pimentel; Reinhardt A Fuck; Nilson F Botelho

1999-01-01

299

Geophysical and geochemical constraints on the geodynamic origin of the Vrancea Seismogenic Zone Romania  

Microsoft Academic Search

The Vrancea Seismogenic Zone (VSZ) of Romania is a steeply NW-dipping volume (30 x 70 x 200 km) of intermediate-depth seismicity in the upper mantle beneath the bend zone of the Eastern Carpathians. The majority of tectonic models lean heavily on subduction processes to explain the Vrancea mantle seismicity and the presence of a Miocene age calc-alkaline volcanic arc in

Melvin A. Fillerup

2010-01-01

300

Geodynamics of the Yellowstone hotspot and mantle plume: Seismic and GPS imaging, kinematics, and mantle flow  

Microsoft Academic Search

Integration of geophysical and geological data show that the Yellowstone hotspot resulted from a mantle plume interacting with the overriding North America plate, a process that has highly modified continental lithosphere by magmatic and tectonic processes and produced the 16-17Ma, 700-km-long Yellowstone-Snake River Plain (YSRP) silicic volcanic system. Accessibility of the YSRP allowed large-scale geophysical projects to seismically image the

Robert B. Smith; Michael Jordan; Bernhard Steinberger; Christine M. Puskas; Jamie Farrell; Gregory P. Waite; Stephan Husen; Wu-Lung Chang; Richard O'Connell

2009-01-01

301

Polyphased geodynamical evolution of the Ougarta (Algeria) magmatic complexes evidenced by paleomagnetic and AMS studies  

NASA Astrophysics Data System (ADS)

Magnetic fabric and remanent magnetization of the Ougarta magmatic complexes are carried essentially by secondary hematite, probably related to hydrothermal events at the origin of ore deposits in the Ougarta belt, and are both not of primary origin. Magnetic foliation is of tectonic origin, while magnetic lineation could be related to hydrothermalism. Obtained paleomagnetic directions correspond to syn-folding or post-folding remagnetizations. The comparison with the African APWP indicates Famenian-Tournaisian and Visean ages for these remagnetizations. At least, two deformation phases with different folding orientations, much older than previously assumed, affected the studied area.

Lamali, A.; Merabet, N.; Henry, B.; Maouche, S.; Graine–Tazerout, K.; Mekkaoui, A.; Ayache, M.

2013-03-01

302

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

NASA Astrophysics Data System (ADS)

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

Rass, Irene

2010-05-01

303

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

NASA Astrophysics Data System (ADS)

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. This yielded information on the 3D distribution of P-waves within the most heterogeneous and poorly investigated uppermost layer of the Black Sea region (down to a depth of 60 km). The interpretation of these results, together with new data on the velocity structure of the crust of the Black Sea led to the conclusion about the different lithosphere beneath the West and the East Black Sea Basins. This can be explained by origination of the depressions in the western and eastern parts of the Black Sea at different microplates and by specific features in their development at rifting and post-rifting stages.

Gobarenko, V. S.; Yegorova, T. P.

2010-06-01

304

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

Microsoft Academic Search

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

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

1997-01-01

305

Seismic constraints on the 660 km discontinuity and its mineral physical and geodynamical interpretation  

NASA Astrophysics Data System (ADS)

The 660 km discontinuity, which seperates the Earth's upper and lower mantle, has been detected routinely on a global scale in underside reflections of precursors to SS waves. The characteristics of this discontinuity determine the convective style of the mantle, distinguishing potentially between whole-mantle and layered- mantle convection. The key question is whether this discontinuity is caused by a phase transition in olivine or by a change in chemical composition. Answers have been sought in seismology by studying the detailed seismic characteristics of this discontinuity and comparing them with predictions from mineral physical models of the mantle. Here, we report observations of this discontinuity in many different regions, using precursors to PP waves. The apparent absence of the 660 km discontinuity in previous seismic studies of PP precursors has posed major problems for models of mantle composition. We find a complicated structure, showing single and double reflections ranging in depth from 640 km to 720 km, that requires the existence of multiple phase transitions in olivine and garnet at the base of the mantle transition zone. The combination of these phase changes leads to a delicate balance that can impede or enhance convection and also lead to multiple discontinuities around 660 km depth, depending on the local temperature and mantle models (Weidner &Wang, 1998, Hirose, 2002). Our results are consistent with a pyrolite mantle composition, but require additional lateral variations in temperature and/or minor elements such as Al in the mantle transition zone. This will influence lower mantle slab penetration and upwelling of plumes differently from region to region. Thus, the characteristics of the 660 km discontinuity and its impedance contrast can no longer be taken as a global constant when modelling mantle convection.

Deuss, A.; Redfern, S. A.

2006-12-01

306

Lower Oligocene Alpine geodynamic change: tectonic and sedimentary evidences in the western arc  

NASA Astrophysics Data System (ADS)

The formation of the western Alpine arc started during the earliest Oligocene, after a drastic kinematic change in the collisional regime. (A) Previously, south-southeast dipping subduction of the European lithosphere (including Briançonnais) underneath Adria resulted in an underfilled flexural basin propagating towards the north-northwest on the European foreland, which had already been moderately deformed due to the Iberian microplate motion. This propagation appears consistent with the Africa-Europe relative motion (Rosenbaum et al., 2002). During this early stage of collision, some oceanic units were obducted over the southern part of European continent (Corsica, Briançonnais). (B) From the early Oligocene on, the western Alps kinematics were dominated by lateral (westward) escape of the Internal Alps indenter, whose displacement with anticlockwise rotation progressively formed the arc. The structures of this mature stage of collision crosscut the buildup issued from (A), and its kinematics were probably more driven by local lithospheric forces of the Mediterranean domain (Jolivet et al., 1999) than by Africa-Europe convergence. The western and southern parts of the western Alpine arc display many evidences for this major syn-collisional change: - Structural interferences are found at various scales. For example, the circular-shape Pelvoux massif resulted in part from crossed shortening stages (SE-NW and E-W; Dumont et al., 2008). It is located in the footwall of two nappes stacks having propagated northwestwards and west- to southwestwards, respectively. The latter crosscuts the former south of Briançon city. - Tectonic transport directions are strongly variable both in the external and in the internal zones, but they consistently display anticlockwise rotation through time. The most important changes are found in the southern part of the western Alps, giving birth to a radial distribution propagating into the external zone. - Instead of beeing gradual, the propagation of syn-orogenic basins changed abruptly in earliest Oligocene times. In the southern Subalpine domain, previously SE-NW gradients (sedimentary transport, onlaps, thickness changes) shifted to westwards or southwestwards ones. This major syn-collisional change must have occurred in a short time interval bracketed between thrusting of the earliest, gravity-driven nappes over the Paleogene flexural basin, whose youngest sediments are dated as lowermost Oligocene, and eastwards underthrusting of the Pelvoux basement in the footwall of the Internal Alps indenter, having yielded Ar39/Ar40 ages of 31,2 ± 0,3 Ma to 33,7 ± 0,2 Ma (Simon-Labric et al. et al., in press). This 32 to 34 Ma old event can be traced all over the Alpine chain through its kinematic, structural, metamorphic and magmatic consequences. It played a key role in the generation of the modern, arcuate shape of the Western Alps. References: Dumont T., Champagnac J.D., Crouzet C. & Rochat P. (2008). Multistage shortening in the Dauphiné zone (French Alps): the record of Alpine collision and implications for pre-Alpine restoration. Swiss J. Geosci., 101, suppl. 1, p. 89-110. Jolivet L., Frizon De Lamothte D., Mascle A. & Séranne M. (1999). The Mediterranean Basins : Tertiary extension within the Alpine orogen - an introduction. In: Durand B., Jolivet L., Horwath F. & Séranne M. (eds.), Geological Soc. Spec. Publication, 156, p. 1-34. Simon-Labric T., Rolland Y., Dumont T., Heymes T., Authemayou C., Corsini M. & Fornari M. (in press). Ar39/Ar40 dating of Penninic Front tectonic displacement (W. Alps) during the Lower Oligocene (31-34 Ma). Terra Nova, in press. Rosenbaum G. & Lister G.S (2005). The Western Alps from the Jurassic to Oligocene: spatio-temporal constraints and evolutionary reconstructions. Earth-Sc. Rev., 69, p. 281-306.

Dumont, T.; Rolland, Y.; Simon-Labric, T.

2009-04-01

307

Geodynamic evolution of the Apenninic-Maghrebian orogen based on geological and geophysical data  

Microsoft Academic Search

The orogenic belt of the central Mediterranean, which extends from northern Africa to the southern Apennines across Sicily and the Calabrian Arc (Apenninic-Maghrebian Orogen), is a orocline located between a new oceanic area, the Tyrrhenian Basin and a foreland structural domain. The latter is represented by an oceanic area, the Ionian Basin, bounded by two continental blocks, the Apulia to

F. Lentini; P. Guarnieri; S. Carbone; A. di Stefano

2003-01-01

308

The Focal Mechanism Solutions of the Tohoku Earthquake Series and Their Geodynamical Implications  

NASA Astrophysics Data System (ADS)

We mainly employ centroid-moment tensor solutions (CMTs) for the March 11, 2011 Tohoku Earthquake and its aftershocks reported by Harvard University in studying deformation and stress state around Japan Sea area. After confirming the validity of CMTs by P-wave first motion polarity data from IRIS, we do cluster analysis and find that the solutions can be divided into three groups. The first group events are the kind of the main shock which is a low-angle thrust event, mainly occurred on the interface between the Pacific Plate and the North American Plate. The second group events are normal-fault earthquakes with principal extensional directions roughly pointing East-West direction. Most of these earthquakes located in the forearc uplift region of the Pacific plate. Some others occurred in the forearc accretionary wedge. The third group events are also normal-fault earthquakes though their principal extensional directions are roughly along the direction of the trench. These events located to the west of the Japan trench. We employ finite element method to simulate the stress state and deformation revealed by the focal mechanism solutions as well as GPS observations. Results show that the March 11, 2011 Tohoku Earthquake and some of its aftershocks released much of the East-West directional compressional stress accumulated in hundreds of years and resulted in at least a temporary East-West tensile state in the Japan Sea region which extends to China mainland. The normal-fault aftershocks located to the west of the Japan trench with East-West principal extensional direction were produced by this stress condition, while the existence of the normal-fault aftershocks with North-South principal extensional direction expressed the values of the tension along North-South direction and along East-West direction are roughly equal.

Yu, H.; TAO, K.; YU, C.; Cai, C.; Zheng, X.; Ning, J.

2011-12-01

309

Structure beneath the Alboran from geodynamic flow models and seismic anisotropy  

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

310

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

NASA Astrophysics Data System (ADS)

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.

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

2012-03-01

311

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

Microsoft Academic Search

We show that the anomalously low frictional resistance to the motion of large rock ava-lanches, gigantic blockslides and large faults can be explained quantitatively by including the energetics of rock breakage in a simulation model. Griffith (1920) defined fracture energy as the amount of energy needed to create unit area of new rock surface by breaking rocks into smaller fragments,

T. R. Davies; M. J. McSaveney

2010-01-01

312

Main Stages of Geodynamic Evolution of the Caucasian Segment of the Alpine-Mediterranean Belt  

NASA Astrophysics Data System (ADS)

Within the oceanic area of Tethys, with a typical oceanic crust, in geological past relatively small continental or subcontinental plates (terranes) were situated. The Greater Caucasian, Black Sea - Central Transcaucasian, Baiburt - Sevanian and Iran - Afghanian accretionary terranes, which in geological past represented island arcs or microcontinents, are identified in the Caucasian segment of the Alpine-Mediterranean belt. They are separated by ophiolite sutures (relics of small or large oceanic basins) of different age. During the Late Precambrian, Paleozoic and Early Mesozoic these terranes underwent horizontal displacement in different directions and ultimately they joined the Eurasian continent. New LA-ICP-MS U-Pb zircon dating along with available geologic, petrologic and geochemical investigations, allow to trace with confidence the main stages of regional metamorphism, granite formation and, consequently, pre-Alpine continental crust making within the Caucasus. At the pre-Grenville stage (1200 Ma and more) between the Baltica and Gondvana ancient continents, on the oceanic crust of Prototethys accumulation mainly of terrigenous sediments and of basic volcanites took place. At the Grenville stage (1000-800 Ma) subcontinental or primitive continental crust (gneiss-migmatite complex and synmetamorphic grenitoids of sodium series) were formed in suprasubduction conditions by both sides of Proto-Paleotethys and along the northern peripheries of comparatively small oceanic basins of the Arkhiz and Southern Slope of the Greater Caucasus. At the Baikalian stage (650-550 Ma) plagiogneissic complex has been cut by Precambrian gabbroids and intruded by large bodies of quartz-diorites. The next, Late Baikalian stage (540-500 Ma) is determined by the intrusion of Cambrian basites and Late Baikalian granitoids and by manifestation of intensive suprasubduction regional metamorphism. Late Baikalian tectogenesis is accompanied by contraction of the small oceanic basin of the Southern slope of the Greater Caucasus and obduction of its oceanic crust on the island arc of the Greater Caucasus. With the Early Variscan (Bretonian) orogeny regional metamorphism of the most Lower-Middle Paleozoic rocks of the Caucasus and formation of synmetamorphic granitoids is con-nected. Saurian orog¬eny (seemingly in Turneasian) corresponds to the most important pre-Alpine time of nappe formation in the Caucasus. And here, at last, Late Variscan orogeny with processes of intensive granite formation took place. Early Cimmerian (Indosinian) orogeny completes the formation of the Caucasian pre-Alpine structure. In the rear of the gradually closing Paleotethys generation of Mesotethys (Neotethys) had been taking place already since the Triassic. But Lesser Caucasus branch of the latter was formed since the end of the Middle Jurassic. In terms of geologic and paleomagnetic data Paleotethys became entirely closed only in the Bathonian phase of compression. The movement of the Austrian phase closed the Lesser Caucasian branch of Neotethys. In Alpine time one can distinguished: pre-orogenic (Adigean, Andean, Austrian, Subhercynian, Laramian and Pyrenean), early orogenic (Styrian and Attic) and Late orogenic or collision (Rodanian, Wallachian, Pasadenian) folding stages. In Late Alpine time maximum compression vast transsecting transverse fissures of extention, responsible for the penetration of orogenic volcanism far into the continent, in a zone of Transcaucasian transverse uplift occurred.

Gamkrelidze, Irakli; Shengelia, David; Maisadze, Ferando; Tsutsunava, Tamara; Chichinadze, Giorgi

2013-04-01

313

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

SciTech Connect

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

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

1994-11-01

314

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

SciTech Connect

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

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

1995-08-01

315

Geodynamic Interpretations of Global Topography and Gravity on Venus and Mars  

NASA Astrophysics Data System (ADS)

The topography and gravity measurements from missions to Venus and Mars are among a few data available to constrain models of the interior structure and dynamics of these planets. These measurements reveal various intriguing features whose origins have generated debates in the planetary science community. On Venus, these include a high correlation between the long-wavelength topography and the geoid. A common explanation is that the Venusian topography is a result of dynamic uplift caused by mantle convection (dynamic topography). Our analysis of convection models shows that in strongly temperature-dependent viscosity fluids, such as planetary mantles, the dynamic topography is actually small. The lithosphere is close to a state of hydrostatic equilibrium (thermal isostasy) and the largest contributions to topography and geoid anomalies come from the lithospheric thickness variations caused by sublithospheric convection. The Venusian topography and geoid can be fully explained by the thermal isostasy associated with lithospheric thickness variations and the compositional isostasy associated with crustal thickness variations. A prominent feature on Mars is the hemispherical dichotomy where the southern highlands stand several kilometers elevated above the northern lowlands. One of the most common explanations for its formation is that the dichotomy formed as a result of a giant impact in the northern lowlands. We show that the impact could have been on the opposite side of the planet. A sufficiently large impact can melt the mantle to such extent that upon isostatic adjustment and crystallization of the melted part of the mantle it forms a region of high standing topography (a megadome) instead of a crater. A topographic low forms antipodal to the impact (a megabasin).

Orth, Christopher P.

316

Geodynamic evolution of an UHP Suture Zone in the Greek Rhodope  

NASA Astrophysics Data System (ADS)

Detailed mapping of Alpine suture zone areas in the Greek Rhodope Metamorphic Complex and characterisation in terms of structures, petrology and geochronology reveal a tectonic wedge geometry with synmetamorphic SW shear at the base and NE shear on-top. These areas define a suture zone (Rhodope Suture Zone, RSZ) which developed between two continental plates of Variscan and Late Jurassic age (Turpaud & Reischmann 2005). It is subdivided into the Lower Rhodope Suture Zone (LRSZ) with material of mainly continental provenance and the Upper Rhodope Suture Zone (URSZ) with constituents of continental and oceanic origin. Both subunits contain microdiamond-bearing metapelites (Perraki et al. 2006) and record metamorphic stages starting from UHP in the Early/Middle Jurassic (? 180 Ma) to amphibolite facies conditions in the Late Cretaceous (? 79 Ma) (Bauer et al. 2007). The rocks of the LRSZ underwent uniaxial stretch during upward movements to lower crustal levels (? 12 kbar; 650°C) at ca. 144 Ma forming L\\ggS tectonites (deformation stage D1). The rocks of the URSZ experienced delayed exhumation and static annealing near 16 kbar and ~800°C at ca. 160 Ma. For both subunits subsequent exhumation was controlled by NE-SW shear along the Rhodope Normal Fault (RNF), which kinematically divides the two subunits of the RSZ (deformation stage D2). The duration of activity along the RNF is constrained by the formation of large-scale folds which formed during shear-partitioning (deformation stage D3) at conditions of <8 kbar and 650°C. D3 probably emerged along a discrete steep fault (Avren Fault in Bulgaria), re-orients earlier high-grade structures and separates central and eastern parts of the Rhodope Metamorphic Complex. D3 characterizes the Mid- to Late Cretaceous amphibolite/greenschist facies thrust tectonics in the Aegean region. N-vergent thrusting of low-grade Mesozoic schists including Jurassic ophiolites east of the fault is coeval with SSW vergent nappe consolidation in the central and western region. The source rocks of the RSZ are proposed to originate from a Variscan microcontinent and an ocean basin to the north. This ocean is interpreted as the easternmost branch of the Triassic/Jurassic Neotethyan ocean (Meliata ocean - eo-Alpine phase), which underwent subduction and metamorphism together with the microcontinent since the Early Jurassic. REFERENCESBAUER, C., RUBATTO, D., KRENN, K., PROYER, A. & HOINKES, G. 2007. A zircon study from the Rhodope Metamorphic Complex, N-Greece: Time record of a multistage evolution. Lithos, in press. PERRAKI, M., PROYER, A., MPOSKOS, E., KAINDL, R. & HOINKES, G. 2006. Raman micro-spectroscopy on DIAMOND, graphite and other carbon polymorphs from the ultrahigh-pressure metamorphic Kimi Complex of the Rhodope Metamorphic Province, NE Greece. Earth and Planetary Science Letters 241, 672-685.TURPAUD, P. & REISCHMANN, T. 2005. Relationships between crustal blocks and UHP relicts, an example from Northern Greece. Geophysical Research Abstracts 0453, 7.

Krenn, K.; Bauer, C.; Proyer, A.; Hoinkes, G.

2007-12-01

317

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

318

1D and 2D Benchmark of Two phase flow In Geodynamics  

NASA Astrophysics Data System (ADS)

It has long been recognized that the arc volcanism is directly related to the slab dehydration and water is necessary to explain the low temperature melting of the mantle wedge and possibly of the subducting oceanic crust and the composition of arc magma. To better understand the dynamics of geophysical fluid viz. water, melts in the mantle wedge related to subduction zone, we have developed a numerical model for two-phase flow which takes into account the effects of compaction of the matrix. In this numerical model, we solve mass and momentum conservation equations of matrix and of fluid following the formulation of Bercovici et al. (2001) using potential formulation of velocities of matrix and fluid. We use several numerical schemes that are Finite Difference (FD) method, Direct Solver method using band diagonal system of matrices to solve potential equations, Multidimensional Positive Definite Advection Transport Algorithm (MPDATA) scheme [Smolarkiewicz et al. (1998)] to solve advection equation i.e. mass conservation equation. We have benchmarked our code in 1D and 2D by comparing it with semi analytical solution [Richard et al.(2011)] under variable (porosity dependent) and constant bulk viscosity respectively. Here we present the formulation of our code and the results.

Kanjilal, S.

2012-04-01

319

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

NASA Astrophysics Data System (ADS)

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.

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

2011-08-01

320

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

Microsoft Academic Search

The East Tianshan is a remote Gobi area located in eastern Xinjiang, northwestern China. In the past sev- eral years, a number of gold, porphyry copper, and Fe(-Cu) and Cu-Ag-Pb-Zn skarn deposits have been discovered there and are attracting exploration interest. The East Tianshan is located between the Junggar block to the north and early Paleozoic terranes of the Middle

Jingwen Mao; Richard J. Goldfarb; Yitian Wang; Craig J. Hart; Zhiliang Wang; Jianmin Yang

321

First 40Ar/39Ar age determinations on the Malkhan granite-pegmatite system: Geodynamic implications  

NASA Astrophysics Data System (ADS)

The Malkhan granite-pegmatite system located in Central Transbaikalia, in the southwestern portion of the Malkhan-Yablonovy structure-formational zone of the Caledonian folding comprises two granite massifs (Bolsherechensk and Oreshny) and a miarolitic pegmatite field of the same name, which adjoins the Chikoi deep-seated fault and Lower Cretaceous Chikoi rift depression in the north. The first 40Ar/39Ar data were obtained on porphyritic biotite granites of the Oreshny massif and on K-feldspar, muscovite, and lepidolite from the Oktyabrskaya pegmatite vein. According to these data, the age of the granitepegmatite system is 123.8-127.6 Ma, which is consistent with the age of Lower Cretaceous rocks from the Chikoi depression. The intimate spatial relationship and isochronism between the Chikoi depression and the Malkhan granite-pegmatite system are strongly suggestive of a rift regime that affected its evolution, thus highlighting the need to regard the evolution of this system as being intimately related to depression development. Such a model can easily be realized within the framework of the concept of a metamorphic core complex, which was used to explain the nature of Transbaikal-type rift depressions and conjugate granite-gneiss swells.

Zagorsky, V. E.; Peretyazhko, I. S.

2010-02-01

322

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

NASA Astrophysics Data System (ADS)

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

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

2003-12-01

323

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

Microsoft Academic Search

Laboratory studies on deformation of olivine in response to applied stress suggest two distinct deformation mechanisms in the earth's upper mantle: diffusion creep through diffusion of atoms along grain boundaries and dislocation creep by slipping along crystallographic glide planes. Each mechanism has very different and important consequences on the dynamical evolution of the mantle and the development of mantle fabric.

Jeroen van Hunen; Shijie Zhong; Nikolai M. Shapiro; Michael H. Ritzwoller

2005-01-01

324

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

NASA Astrophysics Data System (ADS)

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.

Lorinczi, Piroska; Houseman, Gregory

2010-05-01

325

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

NASA Astrophysics Data System (ADS)

G. Beutler's Methods of Celestial Mechanics is a coherent textbook for students as well as an excellent reference for practitioners. Volume II is devoted to the applications and to the presentation of the program system CelestialMechanics. Three major areas of applications are covered: (1) Orbital and rotational motion of extended celestial bodies. The properties of the Earth-Moon system are developed from the simplest case (rigid bodies) to more general cases, including the rotation of an elastic Earth, the rotation of an Earth partly covered by oceans and surrounded by an atmosphere, and the rotation of an Earth composed of a liquid core and a rigid shell (Poincaré model). (2) Artificial Earth satellites. The oblateness perturbation acting on a satellite and the exploitation of its properties in practice is discussed using simulation methods (CelestialMechanics) and (simplified) first order perturbation methods. The perturbations due to the higher-order terms of the Earth's gravitational potential and resonant perturbations are considered thereafter. Special attention is paid to satellites of the Global Navigation Satellite Systems and to geostationary satellites. The characteristics of and models for the two most important non-gravitational forces, atmospheric drag and radiation pressure, are presented as well as the most relevant forces acting on high- and low-orbiting satellites. (3) Evolution of the planetary system. The outer planetary system consisting of the planets Jupiter to Pluto is studied over long time intervals relevant for climate change. The distribution of minor planets and their orbital properties, regular orbits, and chaotic orbits are easily generated and analyzed using CelestialMechanics. The volume concludes with the discussion of important mathematical tools of the program system and of the principles of spectral analysis.

Beutler, Gerhard

326

The geodynamic evolution of the Precaspian Basin (Kazakhstan) along a north–south section  

Microsoft Academic Search

Several hypotheses exist for the origin and evolution of the Precaspian Basin. There are more than 20 km of sediments deposited, yet there is little consensus on the causes of the subsidence. Except for the presence of a thick salt layer (Lower Permian), the main problem is the chronostratigraphic interpretation of the sediments in the centre of the basin, where

Marie-Françoise Brunet; Yuri A. Volozh; Mikhail P. Antipov; Leopold I. Lobkovsky

1999-01-01

327

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

Microsoft Academic Search

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

Zholtayev

1994-01-01

328

Metamorphic history and geodynamic significance of the Early Cretaceous Sabzevar granulites (Sabzevar structural zone, NE Iran)  

Microsoft Academic Search

The Iranian ophiolites are part of the vast orogenic suture zones that mark the Alpine-Himalayan convergence zone. Few petrological and geochronological data are available from these ophiolitic domains, hampering a full assessment of the timing and regimes of subduction zone metamorphism and orogenic construction in the region. This paper describes texture, geochemistry and the pressure-temperature path of the Early Cretaceous

M. Nasrabady; F. Rossetti; T. Theye; G. Vignaroli

2011-01-01

329

The Rio Sassito sedimentary succession (Ordovician): a pinpoint in the geodynamic evolution of the Argentine Precordillera  

NASA Astrophysics Data System (ADS)

In the Precordillera of western Argentina, an isolated outcrop of Llandeilian siliciclastics and Caradocian limestones (Rio Sassito succession) reveals a complex interplay between the tectonic and the sedimentary history of the Precordillera during Middle and Late Ordovician times. The succession is composed of a lower siliciclastic interval and an upper carbonate interval and is bounded below and above by erosional unconformities. Dating of these unconformities, which in many places merged to form one single surface, demonstrates that the most important erosional event took place prior to the deposition of the Rio Sassito succession. This erosional event is correlated to extensional tectonics during continental breakup and the separatio