Science.gov

Sample records for active plate tectonics

  1. The seismicity of Ethiopia; active plate tectonics

    USGS Publications Warehouse

    Mohr, P.

    1981-01-01

    Ethiopia, descended from the semimythical Kingdom of Punt, lies at the strategic intersection of Schmidt's jigsaw puzzle where the Red Sea, Gulf of Aden, and the African Rift System meet. Because of geologically recent uplift combined with rapid downcutting erosion by rivers, notably the Blue Nile (Abbay), Ethiopia is the most mountainous country in Africa. It is also the most volcanically active, while its historical seismicity matches that of the midocean ridges. And, in a sense, Ethiopia is host to an evoloving ocean ridge system. 

  2. Tectonic Plate Movement.

    ERIC Educational Resources Information Center

    Landalf, Helen

    1998-01-01

    Presents an activity that employs movement to enable students to understand concepts related to plate tectonics. Argues that movement brings topics to life in a concrete way and helps children retain knowledge. (DDR)

  3. Earthquakes and plate tectonics.

    USGS Publications Warehouse

    Spall, H.

    1982-01-01

    Earthquakes occur at the following three kinds of plate boundary: ocean ridges where the plates are pulled apart, margins where the plates scrape past one another, and margins where one plate is thrust under the other. Thus, we can predict the general regions on the earth's surface where we can expect large earthquakes in the future. We know that each year about 140 earthquakes of magnitude 6 or greater will occur within this area which is 10% of the earth's surface. But on a worldwide basis we cannot say with much accuracy when these events will occur. The reason is that the processes in plate tectonics have been going on for millions of years. Averaged over this interval, plate motions amount to several mm per year. But at any instant in geologic time, for example the year 1982, we do not know, exactly where we are in the worldwide cycle of strain build-up and strain release. Only by monitoring the stress and strain in small areas, for instance, the San Andreas fault, in great detail can we hope to predict when renewed activity in that part of the plate tectonics arena is likely to take place. -from Author

  4. Earthquakes and plate tectonics

    USGS Publications Warehouse

    Spall, H.

    1977-01-01

    An explanation is to be found in plate tectonics, a concept which has revolutionized thinking in the Earth sciences in the last 10 years. The theory of plate tectonics combines many of the ideas about continental drift (originally proposed in 1912 by Alfred Wegener in Germany) and sea-floor spreading (suggested originally by Harry Hess of Princeton University). 

  5. Plate tectonics: Metamorphic myth

    NASA Astrophysics Data System (ADS)

    Korenaga, Jun

    2016-01-01

    Clear evidence for subduction-induced metamorphism, and thus the operation of plate tectonics on the ancient Earth has been lacking. Theoretical calculations indicate that we may have been looking for something that cannot exist.

  6. Earth's Decelerating Tectonic Plates

    SciTech Connect

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

    2008-08-22

    Space geodetic and oceanic magnetic anomaly constraints on tectonic plate motions are employed to determine a new global map of present-day rates of change of plate velocities. This map shows that Earth's largest plate, the Pacific, is presently decelerating along with several other plates in the Pacific and Indo-Atlantic hemispheres. These plate decelerations contribute to an overall, globally averaged slowdown in tectonic plate speeds. The map of plate decelerations provides new and unique constraints on the dynamics of time-dependent convection in Earth's mantle. We employ a recently developed convection model constrained by seismic, geodynamic and mineral physics data to show that time-dependent changes in mantle buoyancy forces can explain the deceleration of the major plates in the Pacific and Indo-Atlantic hemispheres.

  7. Plate tectonics conserves angular momentum

    NASA Astrophysics Data System (ADS)

    Bowin, C.

    2009-03-01

    of seafloor spreading) are adjustment zones that accommodate strains in the lithosphere. Further, the interlocked pattern of the Australian and Pacific plates the past 42 Million years (with their absolute plate motions near 90° to each other) is taken as strong evidence that large thermally driven "roller" convection cells previously inferred as the driving mechanism in earlier interpretations of continental drift and plate tectonics, have not been active in the Earth's mantle the past 42 Million years, if ever. This report also presents estimates of the changes in location and magnitude of the Earth's axis of total plate tectonic angular momentum for the past 62 million years.

  8. The Plate Tectonics Project

    ERIC Educational Resources Information Center

    Hein, Annamae J.

    2011-01-01

    The Plate Tectonics Project is a multiday, inquiry-based unit that facilitates students as self-motivated learners. Reliable Web sites are offered to assist with lessons, and a summative rubric is used to facilitate the holistic nature of the project. After each topic (parts of the Earth, continental drift, etc.) is covered, the students will…

  9. Plate tectonics conserves angular momentum

    NASA Astrophysics Data System (ADS)

    Bowin, C.

    2010-03-01

    velocity on the crests of convection cells driven by rising heat. The magnitude of these sinking mass anomalies is inferred also to be sufficient to overcome basal plate and transform fault frictions. These results imply that spreading centers are primarily passive reactive features, and fracture zones (and wedge-shaped sites of seafloor spreading) are adjustment zones that accommodate strains in the lithosphere. Further, the interlocked pattern of the Australian and Pacific plates the past 42 Million years (with their absolute plate motions near 90° to each other) is taken as strong evidence that large thermally driven "roller" convection cells previously inferred as the driving mechanism in earlier interpretations of continental drift and plate tectonics, have not been active in the Earth's mantle the past 42 Million years, if ever. This report also presents estimates of the changes in location and magnitude of the Earth's axis of total plate tectonic angular momentum for the past 62 million years.

  10. Martian plate tectonics

    NASA Astrophysics Data System (ADS)

    Sleep, N. H.

    1994-03-01

    The northern lowlands of Mars have been produced by plate tectonics. Preexisting old thick highland crust was subducted, while seafloor spreading produced thin lowland crust during late Noachian and Early Hesperian time. In the preferred reconstruction, a breakup margin extended north of Cimmeria Terra between Daedalia Planum and Isidis Planitia where the highland-lowland transition is relatively simple. South dipping subduction occured beneath Arabia Terra and east dipping subduction beneath Tharsis Montes and Tempe Terra. Lineations associated with Gordii Dorsum are attributed to ridge-parallel structures, while Phelegra Montes and Scandia Colles are interpreted as transfer-parallel structures or ridge-fault-fault triple junction tracks. Other than for these few features, there is little topographic roughness in the lowlands. Seafloor spreading, if it occurred, must have been relatively rapid. Quantitative estimates of spreading rate are obtained by considering the physics of seafloor spreading in the lower (approx. 0.4 g) gravity of Mars, the absence of vertical scarps from age differences across fracture zones, and the smooth axial topography. Crustal thickness at a given potential temperature in the mantle source region scales inversely with gravity. Thus, the velocity of the rough-smooth transition for axial topography also scales inversely with gravity. Plate reorganizations where young crust becomes difficult to subduct are another constraint on spreading age. Plate tectonics, if it occurred, dominated the thermal and stress history of the planet. A geochemical implication is that the lower gravity of Mars allows deeper hydrothermal circulation through cracks and hence more hydration of oceanic crust so that more water is easily subducted than on the Earth. Age and structural relationships from photogeology as well as median wavelength gravity anomalies across the now dead breakup and subduction margins are the data most likely to test and modify hypotheses

  11. Study provides data on active plate tectonics in southeast Asia region

    NASA Astrophysics Data System (ADS)

    Wilson, P.; Rais, J.; Reigber, Ch.; Reinhart, E.; Ambrosius, B. A. C.; Le Pichon, X.; Kasser, M.; Suharto, P.; Majid, Dato'Abdul; Yaakub, Dato'Paduka Awang Haji Othman Bin Haji; Almeda, R.; Boonphakdee, C.

    A major geodynamic study has provided significant new information about the location of active plate boundaries in and around Southeast Asia, as well as deformation processes in the Sulawesi region of Indonesia and tectonic activity in the Philippine archipelago. Results also have confirmed the existence of the so-called Sunda Block, which appears to be rotating with respect to adjacent plates.The study, known as the Geodynamics of South and South-East Asia (GEODYSSEA) project, has been a joint venture of the European Commission and the Association of South- East Asian Nations. It began in 1991 and involved a large team of European and Asian scientists and technicians studying the complex geodynamic processes and natural hazards of the region from the Southeast Asia mainland to the Philippines to northern Australia. Earthquakes, volcanic eruptions, tsunamis, and tectonically induced landslides endanger the lives of millions of people in the region, and the tectonic activity behind these natural hazards results from the convergence and collision of the Eurasian, Philippine, and Indo-Australian Plates at relative velocities of up to 10 cm per year.

  12. Tectonic activity evolution of the Scotia-Antarctic Plate boundary from mass transport deposit analysis

    NASA Astrophysics Data System (ADS)

    Pérez, Lara F.; Bohoyo, Fernando; Hernández-Molina, F. Javier; Casas, David; Galindo-Zaldívar, Jesús; Ruano, Patricia; Maldonado, Andrés.

    2016-04-01

    The spatial distribution and temporal occurrence of mass transport deposits (MTDs) in the sedimentary infill of basins and submerged banks near the Scotia-Antarctic plate boundary allowed us to decode the evolution of the tectonic activity of the relevant structures in the region from the Oligocene to present day. The 1020 MTDs identified in the available data set of multichannel seismic reflection profiles in the region are subdivided according to the geographic and chronological distributions of these features. Their spatial distribution reveals a preferential location along the eastern margins of the eastern basins. This reflects local deformation due to the evolution of the Scotia-Antarctic transcurrent plate boundary and the impact of oceanic spreading along the East Scotia Ridge (ESR). The vertical distribution of the MTDs in the sedimentary record evidences intensified regional tectonic deformation from the middle Miocene to Quaternary. Intensified deformation started at about 15 Ma, when the ESR progressively replaces the West Scotia Ridge (WSR) as the main oceanic spreading center in the Scotia Sea. Coevally with the WSR demise at about 6.5 Ma, increased spreading rates of the ESR and numerous MTDs were formed. The high frequency of MTDs during the Pliocene, mainly along the western basins, is also related to greater tectonic activity due to uplift of the Shackleton Fracture Zone by tectonic inversion and extinction of the Antarctic-Phoenix Ridge and involved changes at late Pliocene. The presence of MTDs in the southern Scotia Sea basins is a relevant indicator of the interplay between sedimentary instability and regional tectonics.

  13. Episodic plate tectonics on Venus

    NASA Technical Reports Server (NTRS)

    Turcotte, Donald

    1992-01-01

    Studies of impact craters on Venus from the Magellan images have placed important constraints on surface volcanism. Some 840 impact craters have been identified with diameters ranging from 2 to 280 km. Correlations of this impact flux with craters on the Moon, Earth, and Mars indicate a mean surface age of 0.5 +/- 0.3 Ga. Another important observation is that 52 percent of the craters are slightly fractured and only 4.5 percent are embayed by lava flows. These observations led researchers to hypothesize that a pervasive resurfacing event occurred about 500 m.y. ago and that relatively little surface volcanism has occurred since. Other researchers have pointed out that a global resurfacing event that ceased about 500 MYBP is consistent with the results given by a recent study. These authors carried out a series of numerical calculations of mantle convection in Venus yielding thermal evolution results. Their model considered crustal recycling and gave rapid planetary cooling. They, in fact, suggested that prior to 500 MYBP plate tectonics was active in Venus and since 500 MYBP the lithosphere has stabilized and only hot-spot volcanism has reached the surface. We propose an alternative hypothesis for the inferred cessation of surface volcanism on Venus. We hypothesize that plate tectonics on Venus is episodic. Periods of rapid plate tectonics result in high rates of subduction that cool the interior resulting in more sluggish mantle convection.

  14. Continental tectonics in the aftermath of plate tectonics

    NASA Technical Reports Server (NTRS)

    Molnar, Peter

    1988-01-01

    It is shown that the basic tenet of plate tectonics, rigid-body movements of large plates of lithosphere, fails to apply to continental interiors. There, buoyant continental crust can detach from the underlying mantle to form mountain ranges and broad zones of diffuse tectonic activity. The role of crustal blocks and of the detachment of crustal fragments in this process is discussed. Future areas of investigation are addressed.

  15. Tectonics of the Easter plate

    NASA Technical Reports Server (NTRS)

    Engeln, J. F.; Stein, S.

    1984-01-01

    A new model for the Easter plate is presented in which rift propagation has resulted in the formation of a rigid plate between the propagating and dying ridges. The distribution of earthquakes, eleven new focal mechanisms, and existing bathymetric and magnetic data are used to describe the tectonics of this area. Both the Easter-Nazca and Easter-Pacific Euler poles are sufficiently close to the Easter plate to cause rapid changes in rates and directions of motion along the boundaries. The east and west boundaries are propagating and dying ridges; the southwest boundary is a slow-spreading ridge and the northern boundary is a complex zone of convergent and transform motion. The Easter plate may reflect the tectonics of rift propagation on a large scale, where rigid plate tectonics requires boundary reorientation. Simple schematic models to illustrate the general features and processes which occur at plates resulting from large-scale rift propagation are used.

  16. Plate tectonics, damage and inheritance.

    PubMed

    Bercovici, David; Ricard, Yanick

    2014-04-24

    The initiation of plate tectonics on Earth is a critical event in our planet's history. The time lag between the first proto-subduction (about 4 billion years ago) and global tectonics (approximately 3 billion years ago) suggests that plates and plate boundaries became widespread over a period of 1 billion years. The reason for this time lag is unknown but fundamental to understanding the origin of plate tectonics. Here we suggest that when sufficient lithospheric damage (which promotes shear localization and long-lived weak zones) combines with transient mantle flow and migrating proto-subduction, it leads to the accumulation of weak plate boundaries and eventually to fully formed tectonic plates driven by subduction alone. We simulate this process using a grain evolution and damage mechanism with a composite rheology (which is compatible with field and laboratory observations of polycrystalline rocks), coupled to an idealized model of pressure-driven lithospheric flow in which a low-pressure zone is equivalent to the suction of convective downwellings. In the simplest case, for Earth-like conditions, a few successive rotations of the driving pressure field yield relic damaged weak zones that are inherited by the lithospheric flow to form a nearly perfect plate, with passive spreading and strike-slip margins that persist and localize further, even though flow is driven only by subduction. But for hotter surface conditions, such as those on Venus, accumulation and inheritance of damage is negligible; hence only subduction zones survive and plate tectonics does not spread, which corresponds to observations. After plates have developed, continued changes in driving forces, combined with inherited damage and weak zones, promote increased tectonic complexity, such as oblique subduction, strike-slip boundaries that are subparallel to plate motion, and spalling of minor plates. PMID:24717430

  17. Ridge push engine of plate tectonics

    NASA Astrophysics Data System (ADS)

    Swedan, N. H.

    2015-07-01

    Convection of the upper mantle drives the tectonic plates. This convection is a thermodynamic cycle that exchanges heat and mechanical work between mantle and tectonic plates. Thermodynamics and observations indicate that the energy of the geological activities resulting from plate tectonics is equal to the latent heat of melting, calculated at mantle's pressure, of the new ocean crust regenerated at midocean ridges. This energy varies with the temperature of ocean floor, which is correlated with surface temperature. The main objective of this manuscript is to demonstrate that plate tectonics is a thermodynamic engine and can be calculated as such. Unlike existing tectonic models, the thermodynamic model is very sensitive to variations of the temperature of ocean floor, which is correlated with surface temperature. Therefore, the observed increase of geological activities can be projected with surface temperature rise. Other objectives of the manuscript are to calculate the force that drives the tectonic plates, estimate the energy released, and validate the calculations based on experiments and observations. In addition to the scientific merit of projecting the geological activities, a good projection can have a broader impact at the societal and economical levels. Investment and insurance related decisions are affected by climate change, and our ability to project the geological activities is of paramount importance for the economy and public safety. This work can thus provide tools to assess the risks and hazards associated with the trend of geological activities with surface temperature rise.

  18. Plate tectonics on Venus

    NASA Technical Reports Server (NTRS)

    Anderson, D. L.

    1981-01-01

    The high surface temperature of Venus implies a permanently buoyant lithosphere and a thick basaltic crust. Terrestrial-style tectonics with deep subduction and crustal recycling is not possible. Overthickened basaltic crust partially melts instead of converting to eclogite. Because mantle magmas do not have convenient access to the surface the Ar-40 abundance in the atmosphere should be low. Venus may provide an analog to Archean tectonics on the earth.

  19. Plate tectonics on Venus

    NASA Astrophysics Data System (ADS)

    Anderson, D. L.

    1981-04-01

    The high surface temperature of Venus implies a permanently buoyant lithosphere and a thick basaltic crust. Terrestrial-style tectonics with deep subduction and crustal recycling is not possible. Overthickened basaltic crust partially melts instead of converting to eclogite. Because mantle magmas do not have convenient access to the surface the Ar-40 abundance in the atmosphere should be low. Venus may provide an analog to Archean tectonics on the earth.

  20. Accelerated plate tectonics.

    PubMed

    Anderson, D L

    1975-03-21

    The concept of a stressed elastic lithospheric plate riding on a viscous asthenosphere is used to calculate the recurrence interval of great earthquakes at convergent plate boundaries, the separation of decoupling and lithospheric earthquakes, and the migration pattern of large earthquakes along an arc. It is proposed that plate motions accelerate after great decoupling earthquakes and that most of the observed plate motions occur during short periods of time, separated by periods of relative quiescence. PMID:17799689

  1. Origin of Small Tectonic Plates

    NASA Astrophysics Data System (ADS)

    Mallard, C.; Coltice, N.; Seton, M.; Müller, D.; Tackley, P.

    2015-12-01

    The plate tectonic theory allowed to split the Earth surface into 6 (Le Pichon 1968) to 52 tectonic plates (Bird 2003). These plates are separated into two groups: the first of 7 large plates and the second of numerous smaller plates (Morra et al 2013). Previous studies using the reconstruction of the past 200 My, suggest that the size of large plates is driven by mantle flow. But the tools employed are descriptive (Morra et al 2013, Sornette and Pisarenko 2003), hence ignoring forces and physical principles within the lithosphere and the mantle. The processes at the origin of small plates remain unknown. We developed a new approach to explain the plate sizes. We demonstrate that the physics of convection drives it. We applied plate tectonics theory on 3D spherical convection models generating plate-like motions, which give access to a complete survey of data: velocities, viscosity and heat flow. Our data show that (1) the large plates depend on the dominating scale of the convective flow due to the initiation or the shutdown of subductions; (2) the smaller plates are generated thanks to large variability of regional stresses along subduction zone by slab pull and suction influenced by the geometry of trenches. Our results are consistent with the quick reorganizations of back-arc basins occuring synchronously with the modification of subduction zones geometry around the Pacific plate (Sdrolias et al 2004). Hence, we conclude that (1) the decreasing number of small plates in the plate reconstructions back in time is an artifact induced by their short lifetime, that is why they are artificially ignored; (2) the geometry of past trenches is simplified leading to an underestimation of the length of subduction zones.

  2. Lasting mantle scars lead to perennial plate tectonics

    PubMed Central

    Heron, Philip J.; Pysklywec, Russell N.; Stephenson, Randell

    2016-01-01

    Mid-ocean ridges, transform faults, subduction and continental collisions form the conventional theory of plate tectonics to explain non-rigid behaviour at plate boundaries. However, the theory does not explain directly the processes involved in intraplate deformation and seismicity. Recently, damage structures in the lithosphere have been linked to the origin of plate tectonics. Despite seismological imaging suggesting that inherited mantle lithosphere heterogeneities are ubiquitous, their plate tectonic role is rarely considered. Here we show that deep lithospheric anomalies can dominate shallow geological features in activating tectonics in plate interiors. In numerical experiments, we found that structures frozen into the mantle lithosphere through plate tectonic processes can behave as quasi-plate boundaries reactivated under far-field compressional forcing. Intraplate locations where proto-lithospheric plates have been scarred by earlier suturing could be regions where latent plate boundaries remain, and where plate tectonics processes are expressed as a ‘perennial' phenomenon. PMID:27282541

  3. Lasting mantle scars lead to perennial plate tectonics.

    PubMed

    Heron, Philip J; Pysklywec, Russell N; Stephenson, Randell

    2016-01-01

    Mid-ocean ridges, transform faults, subduction and continental collisions form the conventional theory of plate tectonics to explain non-rigid behaviour at plate boundaries. However, the theory does not explain directly the processes involved in intraplate deformation and seismicity. Recently, damage structures in the lithosphere have been linked to the origin of plate tectonics. Despite seismological imaging suggesting that inherited mantle lithosphere heterogeneities are ubiquitous, their plate tectonic role is rarely considered. Here we show that deep lithospheric anomalies can dominate shallow geological features in activating tectonics in plate interiors. In numerical experiments, we found that structures frozen into the mantle lithosphere through plate tectonic processes can behave as quasi-plate boundaries reactivated under far-field compressional forcing. Intraplate locations where proto-lithospheric plates have been scarred by earlier suturing could be regions where latent plate boundaries remain, and where plate tectonics processes are expressed as a 'perennial' phenomenon. PMID:27282541

  4. Lasting mantle scars lead to perennial plate tectonics

    NASA Astrophysics Data System (ADS)

    Heron, Philip J.; Pysklywec, Russell N.; Stephenson, Randell

    2016-06-01

    Mid-ocean ridges, transform faults, subduction and continental collisions form the conventional theory of plate tectonics to explain non-rigid behaviour at plate boundaries. However, the theory does not explain directly the processes involved in intraplate deformation and seismicity. Recently, damage structures in the lithosphere have been linked to the origin of plate tectonics. Despite seismological imaging suggesting that inherited mantle lithosphere heterogeneities are ubiquitous, their plate tectonic role is rarely considered. Here we show that deep lithospheric anomalies can dominate shallow geological features in activating tectonics in plate interiors. In numerical experiments, we found that structures frozen into the mantle lithosphere through plate tectonic processes can behave as quasi-plate boundaries reactivated under far-field compressional forcing. Intraplate locations where proto-lithospheric plates have been scarred by earlier suturing could be regions where latent plate boundaries remain, and where plate tectonics processes are expressed as a `perennial' phenomenon.

  5. Plate Tectonics: A Paradigm under Threat.

    ERIC Educational Resources Information Center

    Pratt, David

    2000-01-01

    Discusses the challenges confronting plate tectonics. Presents evidence that contradicts continental drift, seafloor spreading, and subduction. Reviews problems posed by vertical tectonic movements. (Contains 242 references.) (DDR)

  6. Active tectonics

    SciTech Connect

    Not Available

    1986-01-01

    This study is part of a series of Studies in Geophysics that have been undertaken for the Geophysics Research Forum by the Geophysics Study Committee. One purpose of each study is to provide assessments from the scientific community to aid policymakers in decisions on societal problems that involve geophysics. An important part of such assessments is an evaluation of the adequacy of current geophysical knowledge and the appropriateness of current research programs as a source of information required for those decisions. The study addresses our current scientific understanding of active tectonics --- particularly the patterns and rates of ongoing tectonic processes. Many of these processes cannot be described reasonably using the limited instrumental or historical records; however, most can be described adequately for practical purposes using the geologic record of the past 500,000 years. A program of fundamental research focusing especially on Quaternary tectonic geology and geomorphology, paleoseismology, neotectonics, and geodesy is recommended to better understand ongoing, active tectonic processes. This volume contains 16 papers. Individual papers are indexed separately on the Energy Database.

  7. Petroleum occurrences and plate tectonics

    SciTech Connect

    Olenin, V.B.; Sokolov, B.A.

    1983-01-01

    This paper analyzes the mechanisms of petroleum formation and petroleum accumulation proposed in recent years by some Russian and foreign investigators from the viewpoint of the new global or plate tectonics. On the basis of discussion and the facts, the authors conclude that the mechanisms proposed are in contradiction to reality and their use in practical application is at least premature.

  8. Jadeitites and Plate Tectonics

    NASA Astrophysics Data System (ADS)

    Harlow, George E.; Tsujimori, Tatsuki; Sorensen, Sorena S.

    2015-05-01

    Jadeitite is a relatively rare, very tough rock composed predominantly of jadeite and typically found associated with tectonic blocks of high-pressure/low-temperature metabasaltic rocks (e.g., eclogite, blueschist) in exhumed serpentinite-matrix mélanges. Studies over the past ˜20 years have interpreted jadeitite either as the direct hydrous fluid precipitate from subduction channel dewatering into the overlying mantle wedge or as the metasomatic replacement by such fluids of oceanic plagiogranite, graywacke, or metabasite along the channel margin. Thus, jadeitites directly sample and record fluid transport in the subduction factory and provide a window into this geochemical process that is critical to a major process in the Earth system. They record the remarkable transport of large ion lithophile elements, such as Li, Ba, Sr, and Pb, as well as elements generally considered more refractory, such as U, Th, Zr, and Hf. Jadeitite is also the precious form of jade, utilized since antiquity in the form of tools, adornments, and symbols of prestige.

  9. Stability of active mantle upwelling revealed by net characteristics of plate tectonics.

    PubMed

    Conrad, Clinton P; Steinberger, Bernhard; Torsvik, Trond H

    2013-06-27

    Viscous convection within the mantle is linked to tectonic plate motions and deforms Earth's surface across wide areas. Such close links between surface geology and deep mantle dynamics presumably operated throughout Earth's history, but are difficult to investigate for past times because the history of mantle flow is poorly known. Here we show that the time dependence of global-scale mantle flow can be deduced from the net behaviour of surface plate motions. In particular, we tracked the geographic locations of net convergence and divergence for harmonic degrees 1 and 2 by computing the dipole and quadrupole moments of plate motions from tectonic reconstructions extended back to the early Mesozoic era. For present-day plate motions, we find dipole convergence in eastern Asia and quadrupole divergence in both central Africa and the central Pacific. These orientations are nearly identical to the dipole and quadrupole orientations of underlying mantle flow, which indicates that these 'net characteristics' of plate motions reveal deeper flow patterns. The positions of quadrupole divergence have not moved significantly during the past 250 million years, which suggests long-term stability of mantle upwelling beneath Africa and the Pacific Ocean. These upwelling locations are positioned above two compositionally and seismologically distinct regions of the lowermost mantle, which may organize global mantle flow as they remain stationary over geologic time. PMID:23803848

  10. Plate Tectonics: From Plate Boundary Zone Tectonics To Extensive Intraplate Tectonics

    NASA Astrophysics Data System (ADS)

    Ishikawa, M.

    2004-12-01

    Plates makes up earth's surface, and tectonic activity is generally concentrated on plate boundary zones. In restrict meaning, plate tectonics of the earth is regarded as mixture of plate boundary zone tectonics and extensive intraplate tectonics. For example, the Asian continent never behaves as rigid plate that was deformed extensively when the Indian continent collided with it. I infer that extensive intraplate tectonics reflects rheological weakening of wet mantle. To demonstrate effect of H2O component on plate strength, one-dimensional rheological profiles of 100 km depth were constructed by assuming 20km thick upper crust and 20km thick lower crust. Temperature-depth profiles were calculated based on one-dimensional steady-state static heat transfer at given surface heat flows. Power law creep and Byerlee_fs law were used to estimate strength in ductile regime and brittle regime respectively. Creep strength for upper crust, lower crust, dry mantle and wet mantle were calculated using creep parameters of granite, granulite, dry dunite and wet dunite. The minimum value between power law creep strength and Byerlee_fs law strength gives the strength of the lithosphere. Strength profile at surface heat flow of 55mW/m2 (continental average is 56.5mW/m2) and strain rate of 10-15/s (intraplate deformation is about 10-15/s - 10-16/s in Asia) shows a significant difference in strength for using dry mantle and wet mantle. In case of dry mantle, the uppermost mantle is quite strong. However, if wet peridotite represent the upper mantle, there is very little strength in the uppermost mantle. The cumulative lithospheric strength, i.e. integral strength from surface to 100km depth, and the cumulative mantle strength, i.e. integral strength from 40km to 100km depth were calculated with changing strain rate. For example, to deform continental lithosphere at strain rate of 10-15/s, wet mantle has a cumulative strength of about 2x1012N/m whereas the cumulative strength of dry

  11. Plate tectonics, habitability and life

    NASA Astrophysics Data System (ADS)

    Spohn, Tilman; Breuer, Doris

    2016-04-01

    The role of plate tectonics in defining habitability of terrestrial planets is being increasingly discussed (e.g., Elkins-Tanton, 2015). Plate tectonics is a significantly evolved concept with a large variety of aspects. In the present context, cycling of material between near surface and mantle reservoirs is most important. But increased heat transport through mixing of cold lithosphere with the deep interior and formation of continental crust may also matter. An alternative mechanism of material cycling between these reservoirs is hot-spot volcanism combined with crust delamination. Hot-spot volcanism will transport volatiles to the atmosphere while delamination will mix crust, possibly altered by sedimentation and chemical reactions, with the mantle. The mechanism works as long as the stagnant lithosphere plate has not grown thicker than the crust and as long as volcanic material is added onto the crust. Thermal evolution studies suggest that the mechanism could work for the first 1-2 Ga of planetary evolution. The efficiency of the mechanism is limited by the ratio of extrusive to intrusive volcanism, which is thought to be less than 0.25. Plate tectonics would certainly have an advantage by working even for more evolved planets. A simple, most-used concept of habitability requires the thermodynamic stability of liquid water on the surface of a planet. Cycling of CO2between the atmosphere, oceans and interior through subduction and surface volcanism is an important element of the carbonate-silicate cycle, a thermostat feedback cycle that will keep the atmosphere from entering into a runaway greenhouse. Calculations for a model Earth lacking plate tectonics but degassing CO2, N, and H2O to form a surface ocean and a secondary atmosphere (Tosi et al, 2016) suggest that liquid water can be maintained on the surface for 4.5Ga. The model planet would then qualify as habitable. It is conceivable that the CO2 buffering capability of its ocean together with silicate

  12. When Did Plate Tectonics Begin

    NASA Astrophysics Data System (ADS)

    Brown, M.

    2015-12-01

    Present-day plate tectonics on Earth is characterized by asymmetric (one-sided) subduction, but how do we recognize the imprint of subduction in the geologic record? How do we weigh global (commonly younger) vs local (commonly older) datasets or distinguish initiation from episodic from continuous subduction? How reliable are data gaps? Characteristics of the Paleozoic record of subduction include calc-alkaline magmatism, blueschist/UHP metamorphism and collisional orogenesis, and ophiolites as representatives of former ocean lithosphere. Are these characteristic rocks preserved in Proterozoic, Archean and Hadean crust? Does a hotter mantle, higher heat production and weaker lithosphere modify or eliminate these features? What preceded subduction and how do we recognize that regime? Are rock associations or geochemical fingerprints reliable? Does reworking and overprinting modify geochemical fingerprints? Proposals for the start of plate tectonics have been based on: persistence of isotope anomalies/fractionated chemical domains in the mantle; changes in chemistry of magmatic rocks, rates of crustal growth vs reworking, and sites of growth; the metamorphic record, particularly the first appearance of contrasting thermal gradients or eclogite (including evidence from mineral inclusions in diamonds) or UHP metamorphic rocks; stabilization of cratonic lithosphere and formation of supercratons, and the beginning of the Proterozoic supercontinent cycle; the end of the flat Earth, emergence of continents, development of significant topography, changes in the style of orogeny and the rise in atmospheric oxygen; and, the appearance of passive margins and changes in the style of sedimentation. Estimates of the timing have varied from the Hadean to Neoproterozoic. I will summarize evidence for a growing consensus that the late Mesoarchean to early Paleoproterozoic was a 700 Myr long period of transition to continuous (?) subduction and global (?) mobile-lid plate tectonics.

  13. Caribbean plate tectonics from seismic tomography

    NASA Astrophysics Data System (ADS)

    Ten Brink, U. S.; Villasenor, A.

    2012-12-01

    New seismic tomography in the Caribbean shows close links between the geometry and dynamics of subducting slabs and the geology of the overriding plate. Unlike most oceanic plates, the Caribbean plate lacks identifiable seafloor magnetic anomalies and fracture zones. The plate's history has therefore been inferred primarily from land geology along the plate boundary, which is complicated by large-scale shear deformation, and from finite rotations of surrounding plates.We used more than 14 million arrival times from 300,000 earthquakes to identify P-wave velocity anomalies. We relate the anomalies to the geometry and dynamics of subducting slabs and to patterns of earthquake activity, volcanism, topographic relief, and tectonic deformation. For example, we detect two separate slabs belonging to the North and South American plates, respectively, which appear to be responsible for morphologic and tectonic differences between the arcs of the Northern (from Guadeloupe northward) and Southern (from Dominica southward) Lesser Antilles. Variations in earthquake activity between Haiti and the Dominican Republic can be explained by a change in slab geometry from an underplated slab beneath Haiti to a subducting slab under the Dominican Republic. A shallow tear in the slab may explain the anomalously deep Puerto Rico Trench and the frequent earthquake swarms there. The westward shift in volcanic activity in the Northern Lesser Antilles from the Miocene Limestone Caribbees to the present arc can be attributed to the limit on convective flow imposed by the 3-D geometry of the slab at depth. A thinned South America slab under the southern Lesser Antilles may result from traction imposed on the slab by a wide forearc wedge. Variations in tectonic deformation of northern South America could be related to the location of the Caribbean Large Igneous Province north of the Maracaibo Block.

  14. Relationship between plume and plate tectonics

    NASA Astrophysics Data System (ADS)

    Puchkov, V. N.

    2016-07-01

    The relationship between plate- and plume-tectonics is considered in view of the growth and breakdown of supercontinents, active rifting, the formation of passive volcanic-type continental margins, and the origin of time-progressive volcanic chains on oceanic and continental plates. The mantle wind phenomenon is described, as well as its effect on plume morphology and anisotropy of the ambient mantle. The interaction of plumes and mid-ocean ridges is discussed. The principles and problems of plume activity analysis in subduction- and collision-related foldbelts are considered and illustrated with examples.

  15. History and Evolution of Precambrian plate tectonics

    NASA Astrophysics Data System (ADS)

    Fischer, Ria; Gerya, Taras

    2014-05-01

    Plate tectonics is a global self-organising process driven by negative buoyancy at thermal boundary layers. Phanerozoic plate tectonics with its typical subduction and orogeny is relatively well understood and can be traced back in the geological records of the continents. Interpretations of geological, petrological and geochemical observations from Proterozoic and Archean orogenic belts however (e.g., Brown, 2006), suggest a different tectonic regime in the Precambrian. Due to higher radioactive heat production the Precambrian lithosphere shows lower internal strength and is strongly weakened by percolating melts. The fundamental difference between Precambrian and Phanerozoic tectonics is therefore the upper-mantle temperature, which determines the strength of the upper mantle (Brun, 2002) and the further tectonic history. 3D petrological-thermomechanical numerical modelling experiments of oceanic subduction at an active plate at different upper-mantle temperatures show these different subduction regimes. For upper-mantle temperatures < 175 K above the present day value a subduction style appears which is close to present day subduction but with more frequent slab break-off. At upper-mantle temperatures 175 - 250 K above present day values steep subduction continues but the plates are weakened enough to allow buckling and also lithospheric delamination and drip-offs. For upper-mantle temperatures > 250 K above the present day value no subduction occurs any more. The whole lithosphere is delaminating and due to strong volcanism and formation of a thicker crust subduction is inhibited. This stage of 200-250 K higher upper mantle temperature which corresponds roughly to the early Archean (Abbott, 1994) is marked by strong volcanism due to sublithospheric decompression melting which leads to an equal thickness for both oceanic and continental plates. As a consequence subduction is inhibited, but a compressional setup instead will lead to orogeny between a continental

  16. Plate Tectonic Cycle. K-6 Science Curriculum.

    ERIC Educational Resources Information Center

    Blueford, J. R.; And Others

    Plate Tectonics Cycle is one of the units of a K-6 unified science curriculum program. The unit consists of four organizing sub-themes: (1) volcanoes (covering formation, distribution, and major volcanic groups); (2) earthquakes (with investigations on wave movements, seismograms and sub-suface earth currents); (3) plate tectonics (providing maps…

  17. Petrologic implications of plate tectonics.

    PubMed

    Yoder, H S

    1971-07-30

    Petrologists can make significant contributions to the plate tectonic concept. Fixing the stability fields of the principal rock types involved will provide the limits of pressure and temperature of the various environments. Experimental determination of the partition coefficients of the trace elements will be helpful. Studies of the partial melting behavior of possible parental materials in the absence and presence of water, especially the undersaturated region, will contribute to the understanding of magma production. Experimental observations on the rheological properties of the peridotites below and just above the solidus will lead to a better evaluation of the convective mechanism. Measurement of the fundamental properties of rocks, such as the density of solids and liquids at high pressures and temperatures, would contribute to understanding the concepts of diapiric rise, magma segregation, and the low-velocity zone. Broader rock sampling of the oceanic areas of all environments will do much to define the petrologic provinces. The field petrologist specializing in the Paleozoic regions and Precambrian shields can contribute by examining those regions for old plate boundaries and devising new criteria for their recognition. PMID:17770454

  18. Writing and Visualization for Teaching Plate Tectonics

    NASA Astrophysics Data System (ADS)

    Thomas, S. F.

    2004-12-01

    The Theory of Plate Tectonics is probably the most important paradigm for understanding the workings of our planet. As such it is an integral part in any Introductory Geology course. Whereas geology majors usually easily embrace the Theory of Plate Tectonics, the enthusiasm for the coherence and elegance of this theory appears to be much more subdued among the majority of non-science majors. While visual and electronic media certainly support the teaching of the theory, pretty pictures and animations are not sufficient for many non-science majors to grasp the concepts of interacting lithospheric plates. It is well known that students do better in learning scientific concepts if they create their own understanding through research and inquiry-based learning, by working in the field, manipulating real earth-science data, and through writing. Writing assignments give instructors the opportunity to assess their students' learning and to clarify misconceptions yet they also have to be willing to teach students how to craft a science paper. Most electronic media and textbook-added CD-ROMs are not useful for making the structure of a science paper transparent. I found many of the necessary ingredients for effectively teaching plate tectonics in the interactive CD-ROM, "Our Dynamic Planet", developed by Wm. Prothero together with G. Kelly (University of California at Santa Barbara). It allows students to select and manipulate real earth-science data of plate-tectonically active regions, and provides an electronic interface that lets students create graphical representations of their collected data. A downloadable Teacher's Manual provides suggestions on teaching students to write a scientific argument, rooted in sound pedagogy. Originally designed for a large oceanography class, the material was modified for use in a small introductory geology class for non-science majors. Various assignments were given to instruct students in writing a scientific argument based on their

  19. Caribbean tectonics and relative plate motions

    NASA Technical Reports Server (NTRS)

    Burke, K.; Dewey, J. F.; Cooper, C.; Mann, P.; Pindell, J. L.

    1984-01-01

    During the last century, three different ways of interpreting the tectonic evolution of the Gulf of Mexico and the Caribbean have been proposed, taking into account the Bailey Willis School of a permanent pre-Jurassic deep sea basin, the Edward Suess School of a subsided continental terrain, and the Alfred Wegener School of continental separation. The present investigation is concerned with an outline of an interpretation which follows that of Pindell and Dewey (1982). An attempt is made to point out ways in which the advanced hypotheses can be tested. The fit of Africa, North America, and South America is considered along with aspects of relative motion between North and South America since the early Jurasic. Attention is given to a framework for reconstructing Caribbean plate evolution, the evolution of the Caribbean, the plate boundary zones of the northern and southern Caribbean, and the active deformation of the Caribbean plate.

  20. The jubilee of plate tectonics

    NASA Astrophysics Data System (ADS)

    Glen, William; Frankel, Henry

    What should one expect at a birthday gathering for an idea that suffered disdain from birth, but was later transformed overnight into the ruling global theory of the Earth sciences? Tom Hilde and Richard Carlson (Texas A&M University, College Station, Tex.), under the auspices of the Texas A&M Geodynamics Research Institute, with the cooperation of the National Aeronautics and Space Administration (NASA) , the Inter-Union Commission on the Lithosphere, and the U.S. Geodynamics Committee, convened an unprecedented gathering of the makers of Earth science's modern revolution and a large number of their foremost disciples at Texas A&M April 22- 24 , 1987.Those who missed the show will have to read for weeks to learn of the panoply of profound new developments across the broad front of research bearing on plate tectonics, but those with an interest in their own intellectual genealogy will not be able to recapture the sense of historic moment that pervaded Rudder Tower Conference Center as many of the old revolutionaries opened windows on the past. Of the 20 key participants or originators who were invited to speak, all but four sent abstracts. Pleased and surprised by this strong response, the convenors found themselves in the rather difficult position of having to limit the number of talks by nonoriginators to 20. The unique assembly also provided the first opportunity to video interviews with more than a dozen of the originators.

  1. Plate Tectonics: A Framework for Understanding Our Living Planet.

    ERIC Educational Resources Information Center

    Achache, Jose

    1987-01-01

    Discusses some of the events leading to the development of the theory of plate tectonics. Describes how seismic, volcanic, and tectonic features observed at the surface of the planet are now seen as a consequence of intense internal activity, and makes suggestions about their further investigation. (TW)

  2. How mantle slabs drive plate tectonics.

    PubMed

    Conrad, Clinton P; Lithgow-Bertelloni, Carolina

    2002-10-01

    The gravitational pull of subducted slabs is thought to drive the motions of Earth's tectonic plates, but the coupling between slabs and plates is not well established. If a slab is mechanically attached to a subducting plate, it can exert a direct pull on the plate. Alternatively, a detached slab may drive a plate by exciting flow in the mantle that exerts a shear traction on the base of the plate. From the geologic history of subduction, we estimated the relative importance of "pull" versus "suction" for the present-day plates. Observed plate motions are best predicted if slabs in the upper mantle are attached to plates and generate slab pull forces that account for about half of the total driving force on plates. Slabs in the lower mantle are supported by viscous mantle forces and drive plates through slab suction. PMID:12364804

  3. MACMA: a Virtual Lab for Plate Tectonics

    NASA Astrophysics Data System (ADS)

    Grigne, C.; Combes, M.; Tisseau, C.

    2013-12-01

    MACMA (Multi-Agent Convective MAntle) is a tool developed to simulate evolutive plate tectonics and mantle convection in a 2-D cylindrical geometry (Combes et al., 2012). The model relies mainly on a force balance to compute the velocity of each plate, and on empirical rules to determine how plate boundaries move and evolve. It includes first-order features of plate tectonics: (a) all plates on Earth do not have the same size, (b) subduction zones are asymmetric, (c) plates driven by subducting slabs and upper plates do not exhibit the same velocities, and (d) plate boundaries are mobile, can collide, merge and disappear, and new plate boundaries can be created. The MACMA interface was designed to be user-friendly and a simple use of the simulator can be achieved without any prerequisite knowledge in fluid dynamics, mantle rheology, nor in numerical methods. As a preliminary study, the simulator was used by a few students from bachelor's degree to master's degree levels. An initial configuration for plate tectonics has to be created before starting a simulation: the number and types of plate boundaries (ridge, subduction, passive margins) has to be defined and seafloor ages must be given. A simple but interesting exercise consists in letting students build such an initial configuration: they must analyze a map of tectonic plates, choose a 2-D section and examine carefully a map of seafloor ages. Students mentioned that the exercise made them realize that the 3-D spherical structure of plate tectonics does not translate directly in a simple 2-D section, as opposed to what is usually shown in books. Physical parameters: e.g. mantle viscosity, number of layers to consider in the mantle (upper and lower mantle, possible asthenosphere), initial time and mantle temperature, have to be chosen, and students can use this virtual lab to see how different scenarios emerge when parameters are varied. Very importantly, the direct visualization of the mobility of plate

  4. Tectonic Evolution of the Jurassic Pacific Plate

    NASA Astrophysics Data System (ADS)

    Nakanishi, M.; Ishihara, T.

    2015-12-01

    We present the tectonic evolution of the Jurassic Pacific plate based on magnetic anomly lineations and abyssal hills. The Pacific plate is the largest oceanic plate on Earth. It was born as a microplate aroud the Izanagi-Farallon-Phoenix triple junction about 192 Ma, Early Jurassic [Nakanishi et al., 1992]. The size of the Pacific plate at 190 Ma was nearly half that of the present Easter or Juan Fernandez microplates in the East Pacific Rise [Martinez et at, 1991; Larson et al., 1992]. The plate boundary surrounding the Pacific plate from Early Jurassic to Early Cretaceous involved the four triple junctions among Pacific, Izanagi, Farallon, and Phoenix plates. The major tectonic events as the formation of oceanic plateaus and microplates during the period occurred in the vicinity of the triple junctions [e.g., Nakanishi and Winterer, 1998; Nakanishi et al., 1999], implying that the study of the triple junctions is indispensable for understanding the tectonic evolution of the Pacific plate. Previous studies indicate instability of the configuration of the triple junctions from Late Jurassic to Early Cretaceous (155-125 Ma). On the other hand, the age of the birth of the Pacific plate was determined assuming that all triple junctions had kept their configurations for about 30 m.y. [Nakanishi et al., 1992] because of insufficient information of the tectonic history of the Pacific plate before Late Jurassic.Increase in the bathymetric and geomagnetic data over the past two decades enables us to reveal the tectonic evolution of the Pacific-Izanagi-Farallon triple junction before Late Jurassic. Our detailed identication of magnetic anomaly lineations exposes magnetic bights before anomaly M25. We found the curved abyssal hills originated near the triple junction, which trend is parallel to magnetic anomaly lineations. These results imply that the configuration of the Pacific-Izanagi-Farallon triple junction had been RRR before Late Jurassic.

  5. Spreading continents kick-started plate tectonics.

    PubMed

    Rey, Patrice F; Coltice, Nicolas; Flament, Nicolas

    2014-09-18

    Stresses acting on cold, thick and negatively buoyant oceanic lithosphere are thought to be crucial to the initiation of subduction and the operation of plate tectonics, which characterizes the present-day geodynamics of the Earth. Because the Earth's interior was hotter in the Archaean eon, the oceanic crust may have been thicker, thereby making the oceanic lithosphere more buoyant than at present, and whether subduction and plate tectonics occurred during this time is ambiguous, both in the geological record and in geodynamic models. Here we show that because the oceanic crust was thick and buoyant, early continents may have produced intra-lithospheric gravitational stresses large enough to drive their gravitational spreading, to initiate subduction at their margins and to trigger episodes of subduction. Our model predicts the co-occurrence of deep to progressively shallower mafic volcanics and arc magmatism within continents in a self-consistent geodynamic framework, explaining the enigmatic multimodal volcanism and tectonic record of Archaean cratons. Moreover, our model predicts a petrological stratification and tectonic structure of the sub-continental lithospheric mantle, two predictions that are consistent with xenolith and seismic studies, respectively, and consistent with the existence of a mid-lithospheric seismic discontinuity. The slow gravitational collapse of early continents could have kick-started transient episodes of plate tectonics until, as the Earth's interior cooled and oceanic lithosphere became heavier, plate tectonics became self-sustaining. PMID:25230662

  6. The interpretation of crustal dynamics data in terms of plate interactions and active tectonics of the Anatolian plate and surrounding regions in the Middle East

    NASA Technical Reports Server (NTRS)

    Toksoz, M. Nafi; Reilinger, Robert

    1992-01-01

    A detailed study was made of the consequences of the Arabian plate convergence against Eurasia and its effects on the tectonics of Anatolia and surrounding regions of the eastern Mediterranean. A primary source of information is time rates of change of baseline lengths and relative heights determined by repeated SLR measurements. These SLR observations are augmented by a network of GPS stations in Anatolia, Aegea, and Greece, established and twice surveyed since 1988. The existing SLR and GPS networks provide the spatial resolution necessary to reveal the details of ongoing tectonic processes in this area of continental collision. The effort has involved examining the state of stress in the lithosphere and relative plate motions as revealed by these space based geodetic measurements, seismicity, and earthquake mechanisms as well as the aseismic deformations of the plates from conventional geodetic data and geological evidence. These observations are used to constrain theoretical calculations of the relative effects of: (1) the push of the Arabian plate; (2) high topography of Eastern Anatolia; (3) the geometry and properties of African-Eurasian plate boundary; (4) subduction under the Hellenic Arc and southwestern Turkey; and (5) internal deformation and rotation of the Anatolian plate.

  7. Plate Tectonics in the Late Paleozoic

    NASA Astrophysics Data System (ADS)

    Domeier, Mat; Torsvik, Trond

    2014-05-01

    As the chronicle of plate motions through time, paleogeography is fundamental to our understanding of plate tectonics and its role in shaping the geology of the present-day. To properly appreciate the history of tectonics—and its influence on the deep Earth and climate—it is imperative to seek an accurate and global model of paleogeography. However, owing to the incessant loss of oceanic lithosphere through subduction, the paleogeographic reconstruction of 'full-plates' (including oceanic lithosphere) becomes increasingly challenging with age. Prior to 150 Ma ~60% of the lithosphere is missing and reconstructions are developed without explicit regard for oceanic lithosphere or plate tectonic principles; in effect, reflecting the earlier mobilistic paradigm of continental drift. Although these 'continental' reconstructions have been immensely useful, the next-generation of mantle models requires global plate kinematic descriptions with full-plate reconstructions. Moreover, in disregarding (or only loosely applying) plate tectonic rules, continental reconstructions fail to take advantage of a wealth of additional information in the form of practical constraints. Following a series of new developments, both in geodynamic theory and analytical tools, it is now feasible to construct full-plate models that lend themselves to testing by the wider Earth-science community. Such a model is presented here for the late Paleozoic (410-250 Ma). Although we expect this model to be particularly useful for numerical mantle modeling, we hope that it can also serve as a general framework for understanding late Paleozoic tectonics, one on which future improvements can be built and further tested.

  8. Plate Tectonics, Geographical Information System, paleogeography

    SciTech Connect

    Moore, Thomas L.; Scotese, Christopher

    2002-05-24

    The PaleoX.framwork is a dynamically linked/loaded framework for Cocoa applications. The primary goal of this library is to standardize several elements used for working with paleogeographic data. This includes objects designed to organize information for tectonic plates, including maps, rotation objects, plate names, and designations. In addition, PaleoX provides object-oriented solutions for handling standard paleogeographic file formats from the PALEOMAP Project.

  9. Plate Tectonics and Continental Drift: Classroom Ideas.

    ERIC Educational Resources Information Center

    Stout, Prentice K.

    1983-01-01

    Suggests various classroom studies related to plate tectonics and continental drift, including comments on and sources of resource materials useful in teaching the topics. A complete list of magazine articles on the topics from the Sawyer Marine Resource Collection may be obtained by contacting the author. (JN)

  10. Plate tectonics drive tropical reef biodiversity dynamics

    PubMed Central

    Leprieur, Fabien; Descombes, Patrice; Gaboriau, Théo; Cowman, Peter F.; Parravicini, Valeriano; Kulbicki, Michel; Melián, Carlos J.; de Santana, Charles N.; Heine, Christian; Mouillot, David; Bellwood, David R.; Pellissier, Loïc

    2016-01-01

    The Cretaceous breakup of Gondwana strongly modified the global distribution of shallow tropical seas reshaping the geographic configuration of marine basins. However, the links between tropical reef availability, plate tectonic processes and marine biodiversity distribution patterns are still unknown. Here, we show that a spatial diversification model constrained by absolute plate motions for the past 140 million years predicts the emergence and movement of diversity hotspots on tropical reefs. The spatial dynamics of tropical reefs explains marine fauna diversification in the Tethyan Ocean during the Cretaceous and early Cenozoic, and identifies an eastward movement of ancestral marine lineages towards the Indo-Australian Archipelago in the Miocene. A mechanistic model based only on habitat-driven diversification and dispersal yields realistic predictions of current biodiversity patterns for both corals and fishes. As in terrestrial systems, we demonstrate that plate tectonics played a major role in driving tropical marine shallow reef biodiversity dynamics. PMID:27151103

  11. Plate tectonics drive tropical reef biodiversity dynamics.

    PubMed

    Leprieur, Fabien; Descombes, Patrice; Gaboriau, Théo; Cowman, Peter F; Parravicini, Valeriano; Kulbicki, Michel; Melián, Carlos J; de Santana, Charles N; Heine, Christian; Mouillot, David; Bellwood, David R; Pellissier, Loïc

    2016-01-01

    The Cretaceous breakup of Gondwana strongly modified the global distribution of shallow tropical seas reshaping the geographic configuration of marine basins. However, the links between tropical reef availability, plate tectonic processes and marine biodiversity distribution patterns are still unknown. Here, we show that a spatial diversification model constrained by absolute plate motions for the past 140 million years predicts the emergence and movement of diversity hotspots on tropical reefs. The spatial dynamics of tropical reefs explains marine fauna diversification in the Tethyan Ocean during the Cretaceous and early Cenozoic, and identifies an eastward movement of ancestral marine lineages towards the Indo-Australian Archipelago in the Miocene. A mechanistic model based only on habitat-driven diversification and dispersal yields realistic predictions of current biodiversity patterns for both corals and fishes. As in terrestrial systems, we demonstrate that plate tectonics played a major role in driving tropical marine shallow reef biodiversity dynamics. PMID:27151103

  12. Plate tectonics drive tropical reef biodiversity dynamics

    NASA Astrophysics Data System (ADS)

    Leprieur, Fabien; Descombes, Patrice; Gaboriau, Théo; Cowman, Peter F.; Parravicini, Valeriano; Kulbicki, Michel; Melián, Carlos J.; de Santana, Charles N.; Heine, Christian; Mouillot, David; Bellwood, David R.; Pellissier, Loïc

    2016-05-01

    The Cretaceous breakup of Gondwana strongly modified the global distribution of shallow tropical seas reshaping the geographic configuration of marine basins. However, the links between tropical reef availability, plate tectonic processes and marine biodiversity distribution patterns are still unknown. Here, we show that a spatial diversification model constrained by absolute plate motions for the past 140 million years predicts the emergence and movement of diversity hotspots on tropical reefs. The spatial dynamics of tropical reefs explains marine fauna diversification in the Tethyan Ocean during the Cretaceous and early Cenozoic, and identifies an eastward movement of ancestral marine lineages towards the Indo-Australian Archipelago in the Miocene. A mechanistic model based only on habitat-driven diversification and dispersal yields realistic predictions of current biodiversity patterns for both corals and fishes. As in terrestrial systems, we demonstrate that plate tectonics played a major role in driving tropical marine shallow reef biodiversity dynamics.

  13. North Chilean forearc tectonics and cenozoic plate kinematics

    NASA Astrophysics Data System (ADS)

    Buddin, Tim S.; Stimpson, Ian G.; Williams, Graham D.

    1993-04-01

    The continental forearc of northern Chile has been subjected to contemporaneous extension and compression. Here, cross-sections constructed across the forearc are presented which show that since initial shortening, deformation of the forearc has occurred in two tectonically distinct areas. These inner and outer forearc areas are separated by the strain discontinuity of the Atacama fault system and the tectonically neutral Central Depression. The outer forearc, the Coastal Cordillera, exhibits extensional tectonics, with large (up to 300 m) normal fault scarps preserved. These faults cut the earlier thrusts responsible for the elevation of Jurassic rocks at the coast above their regional elevation. The normal faults have been re-activated, displacing Quaternary salt deposits in the Salar Grande. This re-activation of the basement faults is probably due to the subduction of anomalously thick oceanic crust, producing an isostatic imbalance in the outer forearc. In the inner forearc, cross-sections through the Sierra del Medio and Cordillera de Domeyko show that structures of the Pre-Cordillera are best explained by a thick-skinned thrust system, with localized thin-skinned tectonics controlled by evaporite detachment horizons. Current forearc deformation features indicate a strong degree of correlation between subduction zone geometry and forearc tectonics. The timing of Cenozoic tectonism also fits well with established plate motion parameters, and the spatial and temporal variation in the state of stress of the forearc shows a close relationship throughout the Cenozoic to the plate kinematics and morphology of the subducting Nazca plate.

  14. Teaching Plate Tectonic Concepts using GeoMapApp Learning Activities

    NASA Astrophysics Data System (ADS)

    Goodwillie, A. M.; Kluge, S.

    2012-12-01

    GeoMapApp Learning Activities ( http://serc.carleton.edu/geomapapp/collection.html ) can help educators to expose undergraduate students to a range of earth science concepts using high-quality data sets in an easy-to-use map-based interface called GeoMapApp. GeoMapApp Learning Activities require students to interact with and analyse research-quality geoscience data as a means to explore and enhance their understanding of underlying content and concepts. Each activity is freely available through the SERC-Carleton web site and offers step-by-step student instructions and answer sheets. Also provided are annotated educator versions of the worksheets that include teaching tips, additional content and suggestions for further work. The activities can be used "off-the-shelf". Or, since the educator may require flexibility to tailor the activities, the documents are provided in Word format for easy modification. Examples of activities include one on the concept of seafloor spreading that requires students to analyse global seafloor crustal age data to calculate spreading rates in different ocean basins. Another activity has students explore hot spots using radiometric age dating of rocks along the Hawaiian-Emperor seamount chain. A third focusses upon the interactive use of contours and profiles to help students visualise 3-D topography on 2-D computer screens. A fourth activity provides a study of mass wasting as revealed through geomorphological evidence. The step-by-step instructions and guided inquiry approach reduce the need for teacher intervention whilst boosting the time that students can spend on productive exploration and learning. The activities can be used, for example, in a classroom lab with the educator present and as self-paced assignments in an out-of-class setting. GeoMapApp Learning Activities are funded through the NSF GeoEd program and are aimed at students in the introductory undergraduate, community college and high school levels. The activities are

  15. Active Pacific North America Plate boundary tectonics as evidenced by seismicity in the oceanic lithosphere offshore Baja California, Mexico

    NASA Astrophysics Data System (ADS)

    Hauksson, Egill; Kanamori, Hiroo; Stock, Joann; Cormier, Marie-Helene; Legg, Mark

    2014-03-01

    Pacific Ocean crust west of southwest North America was formed by Cenozoic seafloor spreading between the large Pacific Plate and smaller microplates. The eastern limit of this seafloor, the continent-ocean boundary, is the fossil trench along which the microplates subducted and were mostly destroyed in Miocene time. The Pacific-North America Plate boundary motion today is concentrated on continental fault systems well to the east, and this region of oceanic crust is generally thought to be within the rigid Pacific Plate. Yet, the 2012 December 14 Mw 6.3 earthquake that occurred about 275 km west of Ensenada, Baja California, Mexico, is evidence for continued tectonism in this oceanic part of the Pacific Plate. The preferred main shock centroid depth of 20 km was located close to the bottom of the seismogenic thickness of the young oceanic lithosphere. The focal mechanism, derived from both teleseismic P-wave inversion and W-phase analysis of the main shock waveforms, and the 12 aftershocks of M ˜3-4 are consistent with normal faulting on northeast striking nodal planes, which align with surface mapped extensional tectonic trends such as volcanic features in the region. Previous Global Positioning System (GPS) measurements on offshore islands in the California Continental Borderland had detected some distributed Pacific and North America relative plate motion strain that could extend into the epicentral region. The release of this lithospheric strain along existing zones of weakness is a more likely cause of this seismicity than current thermal contraction of the oceanic lithosphere or volcanism. The main shock caused weak to moderate ground shaking in the coastal zones of southern California, USA, and Baja California, Mexico, but the tsunami was negligible.

  16. Tectonic speed limits from plate kinematic reconstructions

    NASA Astrophysics Data System (ADS)

    Zahirovic, Sabin; Müller, R. Dietmar; Seton, Maria; Flament, Nicolas

    2015-05-01

    The motion of plates and continents on the planet's surface are a manifestation of long-term mantle convection and plate tectonics. Present-day plate velocities provide a snapshot of this ongoing process, and have been used to infer controlling factors on the speeds of plates and continents. However, present-day velocities do not capture plate behaviour over geologically representative periods of time. To address this shortcoming, we use a plate tectonic reconstruction approach to extract time-dependent plate velocities and geometries from which root mean square (RMS) velocities are computed, resulting in a median RMS plate speed of ∼ 4 cm /yr over 200 Myr. Linking tectonothermal ages of continental lithosphere to the RMS plate velocity analysis, we find that the increasing portions of plate area composed of continental and/or cratonic lithosphere significantly reduces plate speeds. Plates with any cratonic portion have a median RMS velocity of ∼ 5.8 cm /yr, while plates with more than 25% of cratonic area have a median RMS speed of ∼ 2.8 cm /yr. The fastest plates (∼ 8.5 cm /yr RMS speed) have little continental fraction and tend to be bounded by subduction zones, while the slowest plates (∼ 2.6- 2.8 cm /yr RMS speed) have large continental fractions and usually have little to no subducting part of plate perimeter. More generally, oceanic plates tend to move 2-3 times faster than continental plates, consistent with predictions of numerical models of mantle convection. The slower motion of continental plates is compatible with deep keels impinging on asthenospheric flow and increasing shear traction, thus anchoring the plate in the more viscous mantle transition zone. We also find that short-lived (up to ∼ 10 Myr) rapid accelerations of Africa (∼100 and 65 Ma), North America (∼100 and 55 Ma) and India (∼ 130 , 80 and 65 Ma) appear to be correlated with plume head arrivals as recorded by large igneous province (LIPs) emplacement. By evaluating

  17. Seismology: tectonic strain in plate interiors?

    PubMed

    Calais, E; Mattioli, G; DeMets, C; Nocquet, J-M; Stein, S; Newman, A; Rydelek, P

    2005-12-15

    It is not fully understood how or why the inner areas of tectonic plates deform, leading to large, although infrequent, earthquakes. Smalley et al. offer a potential breakthrough by suggesting that surface deformation in the central United States accumulates at rates comparable to those across plate boundaries. However, we find no statistically significant deformation in three independent analyses of the data set used by Smalley et al., and conclude therefore that only the upper bounds of magnitude and repeat time for large earthquakes can be inferred at present. PMID:16355163

  18. The interpretation of crustal dynamics data in terms of plate interactions and active tectonics of the Anatolian Plate and surrounding regions in the Middle East

    NASA Technical Reports Server (NTRS)

    Toksoz, M. Nafi

    1988-01-01

    The long-term objective of this project is to interpret NASA's Crustal Dynamics measurements (SLR) in the Eastern Mediterranean region in terms of relative plate movements and intraplate deformation. The approach is to combine realistic modeling studies with analysis of available geophysical and geological observations to provide a framework for interpreting NASA's measurements. This semi-annual report concentrates on recent results regarding the tectonics of Anatolia and surrounding regions from ground based observations. Also reported on briefly is progress in the use of the Global Positioning System to densify SLR observations in the Eastern Mediterranean. Reference is made to the previous annual report for a discussion of modeling results.

  19. The interpretation of crustal dynamics data in terms of plate interactions and active tectonics of the Anatolian Plate and surrounding regions in the Middle East

    NASA Technical Reports Server (NTRS)

    Toksoz, M. Nafi

    1987-01-01

    The long term objective of this project is to interpret NASA's Crustal Dynamics measurements (SLR) in the Eastern Mediterranean region in terms of relative plate motions and intraplate deformation. The approach is to combine realistic modeling studies with an analysis of available geophysical and geological observations to provide a framework for interpreting NASA's measurements. This semi-annual report concentrates on recent results regarding the tectonics of Anatolia and surrounding regions from ground based observations. Also briefly reported on is progress made in using GPS measurements to densify SLR observations in the Eastern Mediterranean.

  20. Perennial plate tectonics with lasting mantle lithosphere scars

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    Although the conventional theory of plate tectonics can explain non-rigid behaviour at plate boundaries, it cannot adequately explain the processes involved in deformation and seismicity within plate interiors. Here, we consider that the pre-existing deformation or "scarring" within the mantle lithosphere may have a very long lived presence that could incorporate deformation of the plate interior and plate boundary. Mantle lithosphere scars from continent-continent collisions could generate virtual plate boundaries that remain over long timescales, producing "perennial" plate tectonics. Local geophysical studies can map the crustal environment well, and global whole mantle tomography models are rapidly improving, yet high-resolution images of the mantle lithosphere are often not available in regions where scarring may be present. Where mantle lithosphere heterogeneities have been observed (usually interpreted simply as subduction scars), the same attention has not been afforded to them as, for example, re-activation of faults within the Earth's crust. In idealized numerical simulations, we compare how relic scarring at varying depths in the lithosphere affects patterns of deformation. High-resolution thermal-mechanical numerical experiments explore continental lithospheric deformation featuring a weakened crust and mantle lithosphere scars. Our models show that deep lithospheric scars can control the tectonic evolution of a region over shallow geological features, indicating the importance of mantle lithosphere heterogeneities. The Altyn Tagh Fault (ATF) in central China is an example of an ancient continental collision zone that undergoes periodic deformation during times of regional compression. We suggest that the ATF may be a locale where a long-lasting mantle lithosphere scar can control the subsequent crustal evolution and deformation, with ancient plate boundaries having a "perennial" plate tectonic presence.

  1. Active tectonics west of New Zealand's Alpine Fault: South Westland Fault Zone activity shows Australian Plate instability

    NASA Astrophysics Data System (ADS)

    De Pascale, Gregory P.; Chandler-Yates, Nicholas; Dela Pena, Federico; Wilson, Pam; May, Elijah; Twiss, Amber; Cheng, Che

    2016-04-01

    The 300 km long South Westland Fault Zone (SWFZ) is within the footwall of the Central Alpine Fault (<20 km away) and has 3500 m of dip-slip displacement, but it has been unknown if the fault is active. Here the first evidence for SWFZ thrust faulting in the "stable" Australian Plate is shown with cumulative dip-slip displacements up to 5.9 m (with 3 m throw) on Pleistocene and Holocene sediments and gentle hanging wall anticlinal folding. Cone penetration test (CPT) stratigraphy shows repeated sequences within the fault scarp (consistent with thrusting). Optically stimulated luminescence (OSL) dating constrains the most recent rupture post-12.1 ± 1.7 ka with evidence for three to four events during earthquakes of at least Mw 6.8. This study shows significant deformation is accommodated on poorly characterized Australian Plate structures northwest of the Alpine Fault and demonstrates that major active and seismogenic structures remain uncharacterized in densely forested regions on Earth.

  2. Quantitative tests for plate tectonics on Venus

    NASA Technical Reports Server (NTRS)

    Kaula, W. M.; Phillips, R. J.

    1981-01-01

    Quantitative comparisons are made between the characteristics of plate tectonics on the earth and those which are possible on Venus. Considerations of the factors influencing rise height and relating the decrease in rise height to plate velocity indicate that the rate of topographic dropoff from spreading centers should be about half that on earth due to greater rock-fluid density contrast and lower temperature differential between the surface and interior. Statistical analyses of Pioneer Venus radar altimetry data and global earth elevation data is used to identify 21,000 km of ridge on Venus and 33,000 km on earth, and reveal Venus ridges to have a less well-defined mode in crest heights and a greater concavity than earth ridges. Comparison of the Venus results with the spreading rates and associated heat flow on earth reveals plate creation rates on Venus to be 0.7 sq km/year or less and indicates that not more than 15% of Venus's energy is delivered to the surface by plate tectonics, in contrast to values of 2.9 sq km a year and 70% for earth.

  3. The Biggest Plates on Earth. Submarine Ring of Fire--Grades 5-6. Plate Tectonics.

    ERIC Educational Resources Information Center

    National Oceanic and Atmospheric Administration (DOC), Rockville, MD.

    This activity is designed to teach how tectonic plates move, what some consequences of this motion are, and how magnetic anomalies document the motion at spreading centers do. The activity provides learning objectives, a list of needed materials, key vocabulary words, background information, day-to-day procedures, internet connections, career…

  4. Geology and plate-tectonic development

    SciTech Connect

    Irwin, W.P.

    1990-01-01

    The San Andreas fault is a transform fault along the boundary between the Pacific and North American plates. Bedrock along the fault includes various lithologic units that range in age from Precambrian to Tertiary and younger. Some bedrock units that can be matched across the fault suggest strike-slip displacement of as much as 560 km. This chapter describes geologic formations of northern and central California, including Franciscan rocks, Coast Range ophiolite, Great Valley sequence, Coast Range thrust, Salinian block, displacement of pre-Quaternary rocks by the San Andreas fault, and the relation of geologic structure to seismic behavior. Formations of southern California which are described are the Transverse Ranges and the Salton Trough and displacement of basement rocks by the San Andreas fault. Plate-tectonic development of the San Andreas fault is also discussed.

  5. Plate tectonics and hotspots: the third dimension.

    PubMed

    Anderson, D L; Tanimoto, T; Zhang, Y S

    1992-06-19

    High-resolution seismic tomographic models of the upper mantle provide powerful new constraints on theories of plate tectonics and hotspots. Midocean ridges have extremely low seismic velocities to a depth of 100 kilometers. These low velocities imply partial melting. At greater depths, low-velocity and high-velocity anomalies record, respectively, previous positions of migrating ridges and trenches. Extensional, rifting, and hotspot regions have deep (> 200 kilometers) low-velocity anomalies. The upper mantle is characterized by vast domains of high temperature rather than small regions surrounding hotspots; the asthenosphere is not homogeneous or isothermal. Extensive magmatism requires a combination of hot upper mantle and suitable lithospheric conditions. High-velocity regions of the upper 200 kilometers of the mantle correlate with Archean cratons. PMID:17841084

  6. Plate tectonics and crustal deformation around the Japanese Islands

    NASA Technical Reports Server (NTRS)

    Hashimoto, Manabu; Jackson, David D.

    1993-01-01

    We analyze over a century of geodetic data to study crustal deformation and plate motion around the Japanese Islands, using the block-fault model for crustal deformation developed by Matsu'ura et al. (1986). We model the area including the Japanese Islands with 19 crustal blocks and 104 faults based on the distribution of active faults and seismicity. Geodetic data are used to obtain block motions and average slip rates of faults. This geodetic model predicts that the Pacific plate moves N deg 69 +/- 2 deg W at about 80 +/- 3 mm/yr relative to the Eurasian plate which is much lower than that predicted in geologic models. Substantial aseismic slip occurs on the subduction boundaries. The block containing the Izu Peninsula may be separated from the rigid part of the Philippine Sea plate. The faults on the coast of Japan Sea and the western part of the Median Tectonic Line have slip rates exceeding 4 mm/yr, while the Fossa Magna does not play an important role in the tectonics of the central Japan. The geodetic model requires the division of northeastern Japan, contrary to the hypothesis that northeastern Japan is a part of the North American plate. Owing to rapid convergence, the seismic risk in the Nankai trough may be larger than that of the Tokai gap.

  7. Plate tectonics and planetary habitability: current status and future challenges.

    PubMed

    Korenaga, Jun

    2012-07-01

    Plate tectonics is one of the major factors affecting the potential habitability of a terrestrial planet. The physics of plate tectonics is, however, still far from being complete, leading to considerable uncertainty when discussing planetary habitability. Here, I summarize recent developments on the evolution of plate tectonics on Earth, which suggest a radically new view on Earth dynamics: convection in the mantle has been speeding up despite its secular cooling, and the operation of plate tectonics has been facilitated throughout Earth's history by the gradual subduction of water into an initially dry mantle. The role of plate tectonics in planetary habitability through its influence on atmospheric evolution is still difficult to quantify, and, to this end, it will be vital to better understand a coupled core-mantle-atmosphere system in the context of solar system evolution. PMID:22256796

  8. The Interpretation of Crustal Dynamics Data in Terms of Plate Interactions and Active Tectonics of the Anatolian Plate and Surrounding Regions in the Middle East

    NASA Technical Reports Server (NTRS)

    Toksoz, M. Nafi; Reilinger, Robert E.

    1990-01-01

    During the past 6 months, efforts were concentrated on the following areas: (1) Continued development of realistic, finite element modeling of plate interactions and associated deformation in the Eastern Mediterranean; (2) Neotectonic field investigations of seismic faulting along the active fault systems in Turkey with emphasis on identifying seismic gaps along the North Anatolian fault; and (3) Establishment of a GPS regional monitoring network in the zone of ongoing continental collision in eastern Turkey (supported in part by NSF).

  9. Oil prospection using the tectonic plate model

    NASA Astrophysics Data System (ADS)

    Pointu, Agnès

    2015-04-01

    Tectonic plate models are an intellectual setting to understand why oil deposits are so uncommon and unequally distributed and how models can be used in actual oil and gas prospection. In this case, we use the example of the Ghawar deposit (Saudi Arabia), one of the largest producing well in the world. In the first step, physical properties of rocks composing the oil accumulation are studied by laboratory experiments. Students estimate the porosity of limestone and clay by comparing their mass before and after water impregnation. Results are compared to microscopic observations. Thus, students come to the conclusion that oil accumulations are characterized by superposition of rocks with very different properties: a rich organic source rock (clays of the Hanifa formation), a porous reservoir rock to store the petroleum in (limestones of the Arab formation) and above an impermeable rock with very low porosity (evaporites of the Tithonien). In previous lessons, students have seen that organic matter is usually mineralized by bacteria and that this preservation requires particular conditions. The aim is to explain why biomass production has been so important during the deposit of the clays of the Hanifa formation. Tectonic plate models make it possible to estimate the location of the Arabian Peninsula during Jurassic times (age of Hanifa formation). In order to understand why the paleo-location of the Arabian Peninsula is important to preserve organic matter, students have different documents showing: - That primary production of biomass by phytoplankton is favored by climatic conditions, - That the position of continents determinate the ocean currents and the positions of upwelling zones and zones where organic matter will be able to be preserved, - That north of the peninsula there was a passive margin during Jurassic times. An actual seismic line is studied in order to highlight that this extensive area allowed thick sedimentary deposits to accumulate and that fast

  10. Convection and plate tectonics on extrasolar planets

    NASA Astrophysics Data System (ADS)

    Sotin, C.; Grasset, O.; Schubert, G.

    2012-04-01

    The number of potential Earth-like exoplanets is still very limited compared to the overall number of detected exoplanets. But the different methods keep improving, giving hope for this number to increase significantly in the coming years. Based on the relationship between mass and radius, two of the easiest parameters that can be known for exoplanets, four categories of planets have been identified: (i) the gas giants including hot Jupiters, (ii) the icy giants that can be like their solar system cousins Uranus and Neptune or that can have lost their H2-He atmosphere and have become the so-called ocean planets, (iii) the Earth-like planets with a fraction of silicates and iron similar to that of the Earth, and (iv) the Mercury like planet that have a much larger fraction of iron. The hunt for exoplanets is very much focused on Earth-like planets because of the desire to find alien forms of life and the science goal to understand how life started and developed on Earth. One science question is whether heat transfer by subsolidus convection can lead to plate tectonics, a process that allows material to be recycled in the interior on timescales of hundreds of millions of years. Earth-like exoplanets may have conditions quite different from Earth. For example, COROT-7b is so close to its star that it is likely locked in synchronous orbit with one very hot hemisphere and one very cold hemisphere. It is also worth noting that among the three Earth-like planets of the solar system (Earth, Venus and Mars), only Earth is subject to plate tectonics at present time. Venus may have experienced plate tectonics before the resurfacing event that erased any clue that such a process existed. This study investigates some of the parameters that can influence the transition from stagnant-lid convection to mobile-lid convection. Numerical simulations of convective heat transfer have been performed in 3D spherical geometry in order to determine the stress field generated by convection

  11. Studies in geophysics: Active tectonics

    NASA Technical Reports Server (NTRS)

    1986-01-01

    Active tectonics is defined within the study as tectonic movements that are expected to occur within a future time span of concern to society. Such movements and their associated hazards include earthquakes, volcanic eruptions, and land subsidence and emergence. The entire range of geology, geophysics, and geodesy is, to some extent, pertinent to this topic. The needs for useful forecasts of tectonic activity, so that actions may be taken to mitigate hazards, call for special attention to ongoing tectonic activity. Further progress in understanding active tectonics depends on continued research. Particularly important is improvement in the accuracy of dating techniques for recent geologic materials.

  12. Plate tectonics simulations using reduced viscosity contrasts - The simple approach?

    NASA Astrophysics Data System (ADS)

    Noack, L.; Breuer, D.

    2012-04-01

    In the last decades, more and more studies focussed on the simulation of plate tectonics for Earth and other terrestrial planets inside and outside the solar system. But only the recent development of new robust codes (e.g. GAIA [1] or RHEA [2]) and the usage of super-computers shifted the investigation of planetary mantles into more realistic regimes. One of the problems that many codes still cannot handle is the large viscosity contrast (global or local cell-to-cell contrasts) expected for terrestrial planets and the viscosity is typically simplified [3]. On Earth, the expected contrast varies with 10 or more orders of magnitude. On planets with higher mantle temperatures (e.g. as can be expected for young super-Earths), this viscosity contrast may be even higher with steeper viscosity gradients at the lower boundary of the lithosphere. To solve this problem one can either use a larger nondimensional surface temperature in the Arrhenius viscosity law (or analogously a smaller activation energy) or linearize the exponent of the viscosity, leading to the so-called Frank-Kamenetskii approximation. Several codes use one of these two approximations to be able to simulate terrestrial planets and try to investigate the trend of the likeliness of processes like plate tectonics, depending on factors as surface temperature, internal heating, or mantle thickness. However, our findings propose that the trends observed with these viscosity approximations differ from the ones obtained with the Newtonian Arrhenius law. The first observation is that the approximations lead more easily to plate tectonics than the Arrhenius law. In addition, the dependence of the critical yield stress (i.e. where the transition from plate-tectonics regime to stagnant-lid regime takes place) on the Rayleigh number strongly differs, and the plate tectonics regime is much more easily obtained than for the Arrhenius viscosity. The difference increases with planetary radius. Note, that a more realistic

  13. Active Tectonics in the Tibetan Plateau Region as a Consequence of Plate-Scale Forces on the Eurasian Plate: a Model Study

    NASA Astrophysics Data System (ADS)

    Garcia-Sancho, C.; Govers, R. M. A.; Tesauro, M.

    2015-12-01

    We study the forces acting on the Eurasian plate and the resulting present-day deformation. We use mechanically balanced models based on plate contact forces (continental collision, plate boundary friction at transform faults and subduction contacts, and slab roll-back forces), lithospheric body forces (from lateral variations in topography, density structure) and mantle convective tractions including dynamic topography. These forces drive Eurasia in the direction of absolute motion and fit observed horizontal stress directions to first order. We employ plane stress spherical finite elements and linear visco-elastic rheology to compute the lithosphere-averaged mechanical response. We consider the influence of including the major active faults in these models. Here we focus on intra-plate deformation in the Tibetan Plateau. We assume five different compositions for the upper and lower crust and one for the upper mantle, and we use geotherms and crustal thickness maps to constrain depth-dependent rheology profiles and to estimate vertically averaged viscosities. Predicted velocities show to be very sensitive to the reference point: Eurasia consists of cratonic regions surrounded by more recently active "mobile belts". Using the Siberian or the East European craton as a reference gives significantly different deformation solutions. Best-matching velocities are obtained using Eurasia's "center of deformation", defined on the basis of force moments and located in the southeastern Siberian craton. Comparison with horizontal GPS velocities shows a good correlation in velocity directions and magnitudes in the Tibetan Plateau, Tarim Basin and Tien Shan. Strain rate and vertical axis rotation rates also provide a good fit. Velocity field and clockwise rotation pattern in Southeast Asia are highly dependent on the vertically averaged horizontal viscosity distribution contrast and its geometry. Faults do not significantly affect the predicted surface velocity field

  14. This dynamic earth: the story of plate tectonics

    USGS Publications Warehouse

    Kious, W. Jacquelyne; Tilling, Robert I.

    1996-01-01

    In the early 1960s, the emergence of the theory of plate tectonics started a revolution in the earth sciences. Since then, scientists have verified and refined this theory, and now have a much better understanding of how our planet has been shaped by plate-tectonic processes. We now know that, directly or indirectly, plate tectonics influences nearly all geologic processes, past and present. Indeed, the notion that the entire Earth's surface is continually shifting has profoundly changed the way we view our world.People benefit from, and are at the mercy of, the forces and consequences of plate tectonics. With little or no warning, an earthquake or volcanic eruption can unleash bursts of energy far more powerful than anything we can generate. While we have no control over plate-tectonic processes, we now have the knowledge to learn from them. The more we know about plate tectonics, the better we can appreciate the grandeur and beauty of the land upon which we live, as well as the occasional violent displays of the Earth's awesome power.This booklet gives a brief introduction to the concept of plate tectonics and complements the visual and written information in This Dynamic Planet (see Further reading), a map published in 1994 by the U.S. Geological Survey (USGS) and the Smithsonian Institution. The booklet highlights some of the people and discoveries that advanced the development of the theory and traces its progress since its proposal. Although the general idea of plate tectonics is now widely accepted, many aspects still continue to confound and challenge scientists. The earth-science revolution launched by the theory of plate tectonics is not finished.

  15. The interpretation of crustal dynamics data in terms of plate interactions and active tectonics of the Anatolian Plate and surrounding regions in the Middle East

    NASA Technical Reports Server (NTRS)

    Toksoz, M. Nafi

    1987-01-01

    The primary effort in this study during the past year has been directed along two separate lines: (1) expanding finite element models to include the entire Anatolian plate, the Aegean Sea and the Northeastern Mediterranean Sea, and (2) investigating the relationship between fault geometry and earthquake activity for the North Anatolian and similar strike-slip faults (e.g., San Andreas Fault). Both efforts are designed to provide an improved basis for interpreting the Crustal Dynamics measurements NASA has planned for this region. The initial phases of both investigations have been completed and the results are being prepared for publication. These investigations are described briefly.

  16. Plate tectonics and the Gulf of California region

    SciTech Connect

    Schmidt, N.

    1990-11-01

    The geology and tectonism of California have been influenced greatly by the collision and interaction between the Pacific plate and the North American plate. The forces generated by this interaction caused substantial horizontal movement along the San Andreas fault system and created the Gulf of California rift zone. This article summarizes the unique features of the gulf, describes the theory of plate tectonics, explains how tectonism may have affected the geologic evolution and physiography of the gulf, and illustrates the process by which the Colorado River became linked to the gulf.

  17. Active tectonics of the Andes

    NASA Astrophysics Data System (ADS)

    Dewey, J. F.; Lamb, S. H.

    1992-04-01

    Nearly 90 mm a -1 of relative plate convergence is absorbed in the Andean plate-boundary zone. The pattern of active tectonics shows remarkable variations in the way in which the plate slip vector is partitioned into displacement and strain and the ways in which compatibility between different segments is solved. Along any traverse across the plate-boundary zone, the sum of relative velocities between points must equal the relative plate motion. We have developed a kinematic synthesis of displacement and strain partitioning in the Andes from 47°S to 5°N relevant for the last 5 Ma based upon: (1) relative plate motion deduced from oceanic circuits giving a roughly constant azimuth between 075 and 080; (2) moment tensor solutions for over 120 crustal earthquakes since 1960; (3) structural studies of deformed Plio-Pleistocene rocks; (4) topographic/geomorphic studies; (5) palaeomagnetic data; and (6) geodetic data. We recognize four neotectonic zones, with subzones and boundary transfer zones, that are partitioned in different ways. These zones are not coincident with the 'classic' zones defined by the presence or absence of a volcanic chain or differences in finite displacements and strains and tectonic form; the long-term segmentation and finite evolution of the Andes may not occur in constantly defined segments in space and time. In Segment 1 (47°-39°S), the slip vector is partitioned into roughly orthogonal Benioff Zone slip with large magnitude/large slip-surface earthquakes and both distributed dextral shear giving clockwise rotations of up to 50° and dextral slip in the curved Liquine-Ofqui Fault System giving 5°-10° of anticlockwise fore-arc rotation. In Segment 2 (39°-20°S), the slip vector is partitioned into Benioff Zone slip roughly parallel with the slip vector, Andean crustal shortening and a very small component of dextral slip, including that on the Atacama Fault System. Between 39° and 34°S, a cross-strike dextral transfer, which deflects

  18. Active compressional tectonics in central Africa and implications for plate tectonic models: evidence from fault mechanism studies of the 1998 earthquakes in the Congo Basin

    NASA Astrophysics Data System (ADS)

    Ayele, Atalay

    2002-07-01

    Two earthquakes occurred in the Congo Basin in March and April 1998. These two events are reported to have comparable size (5.5 m b) and nearly the same epicentral locations, far from the western branch of the East African Rift System (EARS). The P-wave groups of these two earthquakes as recorded at FURI station have nearly identical waveforms, which is indicative of similar rupture process. The epicentral distribution in the area has no apparent trend and the reported seismicity is relatively sporadic. The results of the fault mechanism study show that the two earthquakes have a similar rupture process with slight variation. The duration of the main shock (event 980426) is 3.3 s and its scalar seismic moment, M o, is 2.6×10 17 Nm. The style of the dominant deformation for both events is thrust type, which is not commonly observed in the African Plate. A compressive stress environment may be created by plate-boundary forces of the mid Atlantic Ridge and the EARS.

  19. Upper plate responses to active spreading ridge/transform subduction: The tectonics, basin evolution, and seismicity of the Taita area, Chile Triple Junction

    SciTech Connect

    Flint, S.; Prior, D. ); Styles, P.; Murdie, R. ); Agar, S.; Turner, P. )

    1993-02-01

    Integrated field geophysical, structural and stratigraphic studies are attempting to elucidate the mechanisms and consequences of the Late Miocene-present day subduction of the Chile Ridge triple junction system. Preliminary data indicate a shallow plane of seismicity at about 15 km to 20 km depth below the Taitao peninsula. The depths correspond to the predicted depth range of subducted upper ocean crust. The calculated Bouguer anomaly map cannot be explained by the upper plate geology, suggesting that gravity is influenced by heterogeneities in the subducting oceanic plate. Seismic data imply that a subducted transform system underlying the inner Taitao Peninsula is still an active structure. A series of Middle-Late Tertiary sedimentary basins lie inboard of the triple junction. Within the Cosmelli basin, abrupt marine to continental facies transitions give clear evidence of base level changes. The amount of basinward shift of facies across sequence boundaries gets progressively greater up stratigraphy, indicating progressively greater base level changes. The lower part of the basin fill is folded and then thrusted eastward as a series of imbricates, while the overlying, greater thickness of fluvial sediments are only gently tilted westwards. We provisionally interpret this geometry to indicate that the early basin fill was deforming due to contractional tectonics while the later basin fill was being deposited. This complex basin history may reflect initiation and development of triple junction subduction.

  20. On volcanism and thermal tectonics on one-plate planets

    NASA Technical Reports Server (NTRS)

    Solomon, S. C.

    1978-01-01

    For planets with a single global lithospheric shell or 'plate', the thermal evolution of the interior affects the surface geologic history through volumetric expansion and the resultant thermal stress. Interior warming of such planets gives rise to extensional tectonics and a lithospheric stress system conductive to widespread volcanism. Interior cooling leads to compressional tectonics and lithospheric stresses that act to shut off surface volcanism. On the basis of observed surface tectonics, it is concluded that the age of peak planetary volume, the degree of early heating, and the age of youngest major volcanism on the one-plate terrestrial planets likely decrease in the order Mercury, Moon, Mars.

  1. On the breakup of tectonic plates by polar wandering

    NASA Technical Reports Server (NTRS)

    Liu, H.-S.

    1974-01-01

    The equations for the stresses in a homogeneous shell of uniform thickness caused by a shift of the axis of rotation are derived. The magnitude of these stresses reaches a maximum value of the order of 10 to the 9th power dyn/sq cm, which is sufficient for explaining a tectonic breakup. In order to deduce the fracture pattern according to which the breakup of tectonic plates can be expected the theory of plastic deformation of shells is applied. The analysis of this pattern gives an explanation of the existing boundary systems of the major tectonic plates as described by Morgan (1968), LePichon (1968) and Isacks et al. (1968).

  2. Simulation of Evolutive Plate Tectonics: the Size of Plates Depends on Mantle Temperature

    NASA Astrophysics Data System (ADS)

    Grigne, C.; Combes, M.

    2013-12-01

    We use a dynamic model of plate tectonics based on a multiagent approach, in a 2D cylindrical geometry (Combes et al., 2012), to study how evolutive plate tectonics affect the long term thermal state of the mantle, and in return, to analyze the relationship between the mantle mean temperature and the geometry of plate tectonics. Our model accounts for first-order features of plate tectonics: (a) all plates on Earth do not have the same size, (b) subduction zones are asymmetric, (c) plates driven by subducting slabs and upper plates do not exhibit the same velocities, and (d) plate boundaries are mobile, can collide, merge and disappear, and new plate boundaries can be created. We show that when processes for plate boundary creation (subduction initiation and ridge creation) are relying on a brittle criterion, namely when a fixed yield strength has to be reached, the average size of plates adapts to the mantle thermal state: longer plates are obtained for a hotter mantle, which implies a maximum seafloor age that remains fairly high throughout Earth's thermal history and limits mantle heat loss. This is consistent with petrological and geochemical constraints on Earth's cooling history. Important fluctuations in the mantle heat flux and velocities of plates are obtained on a timescale of a few hundred Myr, but on the long term, the relationship between the average wavelength of plate tectonics and mantle temperature can be explained by a simple scaling law. Recent compilations of geological records infer that passive margins had longer lifespans in the past (e.g. Bradley 2008; 2011), which has been linked to 'sluggish' plate tectonics and slow plates in the Precambrian (Korenaga, 2006). Our simulations outputs include lifespans of tectonic entities such as passive margins, as well as statistical data about events of plates reorganizations. We obtain faster plates in the past than at present day, but counterintuitively we also observe a low episodicity of tectonic

  3. The present-day number of tectonic plates

    NASA Astrophysics Data System (ADS)

    Harrison, Christopher G. A.

    2016-03-01

    The number of tectonic plates on Earth described in the literature has expanded greatly since the start of the plate tectonic era, when only about a dozen plates were considered in global models of present-day plate motions. With new techniques of more accurate earthquake epicenter locations, modern ways of measuring ocean bathymetry using swath mapping, and the use of space based geodetic techniques, there has been a huge growth in the number of plates thought to exist. The study by Bird (2003) proposed 52 plates, many of which were delineated on the basis of earthquake locations. Because of the pattern of areas of these plates, he suggested that there should be more small plates than he could identify. In this paper, I gather together publications that have proposed a total of 107 new plates, giving 159 plates in all. The largest plate (Pacific) is about 20 % of the Earth's area or 104 Mm2, and the smallest of which (Plate number 5 from Hammond et al. 2011) is only 273 km2 in area. Sorting the plates by size allows us to investigate how size varies as a function of order. There are several changes of slope in the plots of plate number organized by size against plate size order which are discussed. The sizes of the largest seven plates is constrained by the area of the Earth. A middle set of 73 plates down to an area of 97,563 km2 (the Danakil plate at number 80, is the plate of median size) follows a fairly regular pattern of plate size as a function of plate number. For smaller plates, there is a break in the slope of the plate size/plate number plot and the next 32 plates follow a pattern of plate size proposed by the models of Koehn et al. (2008) down to an area of 11,638 km2 (West Mojave plate # 112). Smaller plates do not follow any regular pattern of area as a function of plate number, probably because we have not sampled enough of these very small plates to reveal any clear pattern.

  4. Optimal Planet Properties For Plate Tectonics Through Time And Space

    NASA Astrophysics Data System (ADS)

    Stamenkovic, Vlada; Seager, Sara

    2014-11-01

    Both the time and the location of planet formation shape a rocky planet’s mass, interior composition and structure, and hence also its tectonic mode. The tectonic mode of a planet can vary between two end-member solutions, plate tectonics and stagnant lid convection, and does significantly impact outgassing and biogeochemical cycles on any rocky planet. Therefore, estimating how the tectonic mode of a planet is affected by a planet’s age, mass, structure, and composition is a major step towards understanding habitability of exoplanets and geophysical false positives to biosignature gases. We connect geophysics to astronomy in order to understand how we could identify and where we could find planet candidates with optimal conditions for plate tectonics. To achieve this goal, we use thermal evolution models, account for the current wide range of uncertainties, and simulate various alien planets. Based on our best model estimates, we predict that the ideal targets for plate tectonics are oxygen-dominated (C/O<1) (solar system like) rocky planets of ~1 Earth mass with surface oceans, large metallic cores super-Mercury, rocky body densities of ~7000kgm-3), and with small mantle concentrations of iron 0%), water 0%), and radiogenic isotopes 10 times less than Earth). Super-Earths, undifferentiated planets, and especially hypothetical carbon planets, speculated to consist of SiC and C, are not optimal for the occurrence of plate tectonics. These results put Earth close to an ideal compositional and structural configuration for plate tectonics. Moreover, the results indicate that plate tectonics might have never existed on planets formed soon after the Big Bang—but instead is favored on planets formed from an evolved interstellar medium enriched in iron but depleted in silicon, oxygen, and especially in Th, K, and U relative to iron. This possibly sets a belated Galactic start for complex Earth-like surface life if plate tectonics significantly impacts the build up

  5. Active tectonics and human survival strategies

    NASA Astrophysics Data System (ADS)

    King, Geoffrey; Bailey, Geoffrey; Sturdy, Derek

    1994-10-01

    Tectonic movements continuously remould the surface of Earth in response to plate motion. Yet such deformation is rarely taken into account when assessing landscape change and its impact on human land use, except perhaps as an occasional hazard to human life or a temporary disruption in the longer term patterns of human history. However, active tectonics also create and sustain landscapes that can be beneficial to human survival, forming a complex topography of potentially fertile sedimentary basins enclosed by mountain barriers that can facilitate the control and explotation of food resources, especially animal prey. We discuss the tectonic history of northwest Greece and show how the Paleolithic sites of the region are located to take advantage of tectonically created features at both a local and a regional scale. We suggest that the association of significant concentrations of early Paleolithic sites with tectonically acitve regions is not coincidental and that on the longer time spans of human biological evolution, active tectonics has been an important selective agent contributing to the development of the human species as an intelligent predator.

  6. Plate Margin Deformation and Active Tectonics Along the Northern Edge of the Yakutat Terrane in the Saint Elias Orogen, Alaska and Yukon, Canada

    NASA Technical Reports Server (NTRS)

    Bruhn, Ronald L.; Sauber, Jeanne; Cotton, Michele M.; Pavlis, Terry L.; Burgess, Evan; Ruppert, Natalia; Forster, Richard R.

    2012-01-01

    The northwest directed motion of the Pacific plate is accompanied by migration and collision of the Yakutat terrane into the cusp of southern Alaska. The nature and magnitude of accretion and translation on upper crustal faults and folds is poorly constrained, however, due to pervasive glaciation. In this study we used high-resolution topography, geodetic imaging, seismic, and geologic data to advance understanding of the transition from strike-slip motion on the Fairweather fault to plate margin deformation on the Bagley fault, which cuts through the upper plate of the collisional suture above the subduction megathrust. The Fairweather fault terminates by oblique-extensional splay faulting within a structural syntaxis, allowing rapid tectonic upwelling of rocks driven by thrust faulting and crustal contraction. Plate motion is partly transferred from the Fairweather to the Bagley fault, which extends 125 km farther west as a dextral shear zone that is partly reactivated by reverse faulting. The Bagley fault dips steeply through the upper plate to intersect the subduction megathrust at depth, forming a narrow fault-bounded crustal sliver in the obliquely convergent plate margin. Since . 20 Ma the Bagley fault has accommodated more than 50 km of dextral shearing and several kilometers of reverse motion along its southern flank during terrane accretion. The fault is considered capable of generating earthquakes because it is linked to faults that generated large historic earthquakes, suitably oriented for reactivation in the contemporary stress field, and locally marked by seismicity. The fault may generate earthquakes of Mw <= 7.5.

  7. A window for plate tectonics in terrestrial planet evolution?

    NASA Astrophysics Data System (ADS)

    O'Neill, Craig; Lenardic, Adrian; Weller, Matthew; Moresi, Louis; Quenette, Steve; Zhang, Siqi

    2016-06-01

    The tectonic regime of a planet depends critically on the contributions of basal and internal heating to the planetary mantle, and how these evolve through time. We use viscoplastic mantle convection simulations, with evolving core-mantle boundary temperatures, and radiogenic heat decay, to explore how these factors affect tectonic regime over the lifetime of a planet. The simulations demonstrate (i) hot, mantle conditions, coming out of a magma ocean phase of evolution, can produce a "hot" stagnant-lid regime, whilst a cooler post magma ocean mantle may begin in a plate tectonic regime; (ii) planets may evolve from an initial hot stagnant-lid condition, through an episodic regime lasting 1-3 Gyr, into a plate-tectonic regime, and finally into a cold, senescent stagnant lid regime after ∼10 Gyr of evolution, as heat production and basal temperatures wane; and (iii) the thermal state of the post magma ocean mantle, which effectively sets the initial conditions for the sub-solidus mantle convection phase of planetary evolution, is one of the most sensitive parameters affecting planetary evolution - systems with exactly the same physical parameters may exhibit completely different tectonics depending on the initial state employed. Estimates of the early Earth's temperatures suggest Earth may have begun in a hot stagnant lid mode, evolving into an episodic regime throughout most of the Archaean, before finally passing into a plate tectonic regime. The implication of these results is that, for many cases, plate tectonics may be a phase in planetary evolution between hot and cold stagnant states, rather than an end-member.

  8. Generation and Initiation of Plate Tectonics on Terrestrail Planets

    NASA Astrophysics Data System (ADS)

    Foley, Bradford J.

    The question of why plate tectonics occurs on Earth, but not on the other planets of our solar system, is one of the most fundamental issues in geophysics and planetary science. I study this problem using numerical simulations of mantle convection with a damage-grainsize feedback (grain-damage) to constrain the conditions necessary for plate tectonics to occur on a terrestrial planet, and how plate tectonics initiates. In Chapter 2, I use numerical simulations to determine how large a viscosity ratio, between pristine lithosphere and mantle, damage can offset to allow mobile (plate-like) convection. I then use the numerical results to formulate a new scaling law to describe the boundary between stagnant lid and plate-like regimes of mantle convection. I hypothesize that damage must reduce the viscosity of shear zones in the lithosphere to a critical value, equivalent to the underlying mantle viscosity, in order for plate tectonics to occur, and demonstrate that a scaling law based on this hypothesis reproduces the numerical results. For the Earth, damage is efficient in the lithosphere and provides a viable mechanism for the operation of plate tectonics. I apply my theory to super-Earths and map out the transition between plate-like and stagnant lid convection with a "planetary plate-tectonic phase" diagram in planet size-surface temperature space. Both size and surface temperature are important, with plate tectonics being favored for larger, cooler planets. This gives a natural explanation for Earth, Venus, and Mars, and implies that plate tectonics on exoplanets should correlate with size, incident solar radiation, and atmospheric composition. In Chapters 3 and 4 I focus on the initiation of plate tectonics. In Chapter 3, I develop detailed scaling laws describing plate speed and heat flow for mantle convection with grain-damage across a wide parameter range, with the intention of applying these scaling laws to the early Earth in Chapter 4. Convection with grain

  9. Plate Tectonics on Earth-like Planets: Implications for Habitability

    NASA Astrophysics Data System (ADS)

    Noack, L.; Breuer, D.

    2011-12-01

    Plate tectonics has been suggested to be essential for life (see e.g. [1]) due to the replenishment of nutrients and its role in the stabilization of the atmosphere temperature through the carbon-silicate cycle. Whether plate tectonics can prevail on a planet should depend on several factors, e.g. planetary mass, age of the planet, water content (at the surface and in the interior), surface temperature, mantle rheology, density variations in the mantle due to partial melting, and life itself by promoting erosion processes and perhaps even the production of continental rock [2]. In the present study, we have investigated how planetary mass, internal heating, surface temperature and water content in the mantle would factor for the probability of plate tectonics to occur on a planet. We allow the viscosity to be a function of pressure [3], an effect mostly neglected in previous discussions of plate tectonics on exoplanets [4, 5]. With the pressure-dependence of viscosity allowed for, the lower mantle may become too viscous in massive planets for convection to occur. When varying the planetary mass between 0.1 and 10 Earth masses, we find a maximum for the likelihood of plate tectonics to occur for planetary masses around a few Earth masses. For these masses the convective stresses acting at the base of the lithosphere are strongest and may become larger than the lithosphere yield strength. The optimum planetary mass varies slightly depending on the parameter values used (e.g. wet or dry rheology; initial mantle temperature). However, the peak in likelihood of plate tectonics remains roughly in the range of one to five Earth masses for reasonable parameter choices. Internal heating has a similar effect on the occurrence of plate tectonics as the planetary mass, i.e. there is a peak in the probability of plate tectonics depending on the internal heating rate. This result suggests that a planet may evolve as a consequence of radioactive decay into and out of the plate

  10. Origin of plate tectonics: Grain-damage, inheritance and hysteresis

    NASA Astrophysics Data System (ADS)

    Bercovici, D.; Ricard, Y. R.

    2015-12-01

    The emergence of plate tectonics is enigmatic because of the lack of observations in the early Archean as well as the challenge of understanding how plates form. The damage theory of lithospheric weakening by grain-reduction provides a physical framework for plate generation. This model builds on grain-scale physics to describe planetary-scale processes, and is consistent with lab and field observations of polycrystalline rocks and lithospheric mylonites. Grain-damage accounts for the evolution of damage and healing by grain growth, hence predicts plate boundary formation and longevity, and how they depend on surface conditions. The establishment of global plate tectonics likely started between >4Ga and 2.7Ga, and may have taken over a billion years to develop. Under Earth-like conditions, grain-damage combined with intermittent Archean protosubduction produces persistent weak zones that accumulate into well developed plates by 3Ga. However, Venus' hotter surface promotes healing, suppresses damage and inhibits weak zone accumulation, which suggests why plate tectonics failed to spread on our sister planet. New work posits that interface damage is possibly suppressed at moderate grain-size; this induces a hysteresis loop wherein three equilibrium deformation branches coexist. These branches include a stable large-grain, weakly-deforming state in dislocation creep, a stable small-grain rapidly-deforming state in diffusion creep analogous to mylonites, and an unstable intermediate-grain state. At the right conditions, a lithosphere can acquire two stable deformation states characteristic of plate tectonics; i.e., both slowly deforming plate interiors and rapidly deforming plate boundaries can co-exist. Earth currently sits inside the hysteresis loop and can have coexisting deformation states, while Venus sits at the end of the loop where only the weakly deforming branch dominates. The hot post-Hadean Earth might have had peak deformation only on the weakly

  11. Plate tectonic history of the Arctic

    NASA Technical Reports Server (NTRS)

    Burke, K.

    1984-01-01

    Tectonic development of the Arctic Ocean is outlined, and geological maps are provided for the Arctic during the mid-Cenozoic, later Cretaceous, late Jurassic, early Cretaceous, early Jurassic and late Devonian. It is concluded that Arctic basin history is moulded by the events of the following intervals: (1) continental collision and immediately subsequent rifting and ocean formation in the Devonian, and continental rifting ocean formation, rapid rotation of microcontinents, and another episode of collision in the latest Jurassic and Cretaceous. It is noted that Cenozoic Arctic basin formation is a smaller scale event superimposed on the late Mesozoic ocean basin.

  12. Numerical modelling of instantaneous plate tectonics

    NASA Technical Reports Server (NTRS)

    Minster, J. B.; Haines, E.; Jordan, T. H.; Molnar, P.

    1974-01-01

    Assuming lithospheric plates to be rigid, 68 spreading rates, 62 fracture zones trends, and 106 earthquake slip vectors are systematically inverted to obtain a self-consistent model of instantaneous relative motions for eleven major plates. The inverse problem is linearized and solved iteratively by a maximum-likelihood procedure. Because the uncertainties in the data are small, Gaussian statistics are shown to be adequate. The use of a linear theory permits (1) the calculation of the uncertainties in the various angular velocity vectors caused by uncertainties in the data, and (2) quantitative examination of the distribution of information within the data set. The existence of a self-consistent model satisfying all the data is strong justification of the rigid plate assumption. Slow movement between North and South America is shown to be resolvable.

  13. Plate tectonics: Delayed response to mantle pull

    NASA Astrophysics Data System (ADS)

    Nedimović, Mladen R.

    2016-08-01

    At mid-ocean ridges, the directions in which plates spread and the underlying mantle flows were thought to broadly align. A synthesis of results from ridges that spread at a variety of rates reveals that instead there may be a systematic skew.

  14. A New Test of Plate Tectonics.

    ERIC Educational Resources Information Center

    Shea, James Herbert

    1989-01-01

    Discussed are two techniques that can be used to directly test the theory that the plates which make up the crust of the earth are still moving. Described are the use of satellite laser ranging and very long baseline interferometry. Samples of data and their analysis are provided. (CW)

  15. Crustal velocity model along the southern Cuban margin: implications for the tectonic regime at an active plate boundary

    NASA Astrophysics Data System (ADS)

    Moreno, Bladimir; Grandison, Margaret; Atakan, Kuvvet

    2002-11-01

    A new 1-D velocity model along the southern Cuban margin has been determined using local earthquake data, which are the result of the merged Cuban and Jamaican catalogues. Simultaneous inversion using joint-hypocentre determination was applied to solve the coupled hypocentre-velocity model problem. We obtained a seven-layer model with an average Moho interface at 20 km. The average velocity was found to be 7.6 km s-1 on the top of the crust-mantle transition zone and 6.9 km s-1 in the basaltic layer of the crust. The improvement in the earthquake locations allowed us for the first time to use local seismicity to characterize the activity on local faults and the stress regime in the area. For this purpose, 34 earthquake focal mechanisms were determined along the eastern segments of the Oriente Fault. These solutions are consistent with the known left-lateral strike-slip motion along this major structure as well as with the stress regime of two local structures: (1) the Cabo Cruz Basin and (2) the Santiago deformed belt. The first structure is dominated by normal faults with minor strike-slip components and the second by reverse faults. The shallow seismicity in the Cabo Cruz Basin is associated with fault planes trending N55°-58°E and dipping 38°-45° to the north. The Santiago deformed belt, on the other hand, exhibits diverse fault plane orientations. These local structures account for most of the earthquake activity along the southern Cuban margin. Deep seismicity observed in the Santiago deformed belt, supported by focal mechanisms, suggests underthrusting of the Gonave Microplate beneath the Cuban Block in this area. The principal stress orientations obtained from stress inversion of earthquake focal mechanisms suggest a thrust faulting regime along the Southern Cuban margin. We obtained a nearly horizontal σ1 and nearly vertical σ3, which indicates active compressional deformation along the major Oriente transcurrent fault in agreement with the dominant

  16. Plate Tectonism on Early Mars: Diverse Geological and Geophysical Evidence

    NASA Technical Reports Server (NTRS)

    Dohm, J. M.; Maruyama, S.; Baker, V. R.; Anderson, R. C.; Ferris, Justin C.; Hare, Trent M.

    2002-01-01

    Mars has been modified by endogenic and exogenic processes similar in many ways to Earth. However, evidence of Mars embryonic development is preserved because of low erosion rates and stagnant lid convective conditions since the Late Noachian. Early plate tectonism can explain such evidence. Additional information is contained in the original extended abstract.

  17. Inversion for the driving forces of plate tectonics

    NASA Technical Reports Server (NTRS)

    Richardson, R. M.

    1983-01-01

    Inverse modeling techniques have been applied to the problem of determining the roles of various forces that may drive and resist plate tectonic motions. Separate linear inverse problems have been solved to find the best fitting pole of rotation for finite element grid point velocities and to find the best combination of force models to fit the observed relative plate velocities for the earth's twelve major plates using the generalized inverse operator. Variance-covariance data on plate motion have also been included. Results emphasize the relative importance of ridge push forces in the driving mechanism. Convergent margin forces are smaller by at least a factor of two, and perhaps by as much as a factor of twenty. Slab pull, apparently, is poorly transmitted to the surface plate as a driving force. Drag forces at the base of the plate are smaller than ridge push forces, although the sign of the force remains in question.

  18. Cenozoic tectonic evolution of the Bohai Bay Basin and its coupling relationship with Pacific Plate subduction

    NASA Astrophysics Data System (ADS)

    Liang, Jintong; Wang, Hongliang; Bai, Ying; Ji, Xinyuan; Duo, Xuemei

    2016-09-01

    The Bohai Bay Basin is a Mesozoic-Cenozoic rift basin in eastern China. Based mainly on a balanced-section analysis, this study compares the spatio-temporal differences of tectonic evolution in relation to strike-slip faults among different depressions within the basin. In combination with the analysis of subsidence characteristics, the study also attempts to clarify the Cenozoic tectonic evolution of the basin and its coupling relationship with the subduction of the Pacific Plate. It was found that: (1) the strike-slip faults were activated generally from south to north and from west to east during the Cenozoic; (2) there is a negative correlation between the intensity of tectonic activity in the Bohai Bay Basin and subduction rate of the Pacific Plate; and (3) the migration direction of the basin depocenters is consistent with the direction of Pacific Plate subduction.

  19. Application of plate tectonics concepts in hydrocarbon exploration: Hokkaido Corner

    SciTech Connect

    Sabitay, A.; Shirley, J.

    1986-07-01

    An area prospective for hydrocarbon production is located offshore from south-central Hokkaido in northern Japan. The sediments there are contained in a forearc basin associated with the Japan-Kurile subduction system to the east. At the juncture of the Japan and Kurile Trenches, a major change in direction, associated with a transverse fault, is referred to as the Hokkaido Corner. The transverse fault is known to disrupt the subducting slab from measurements and studies of earthquake foci and focal mechanisms. The prospective forearc basin overlies the disrupted subducting slab, establishing a probable wrench-fault system. The history of deformation in the basin has been related to the northwesterly movement of the Pacific oceanic plate and its subduction under the Japanese Island arc. Seaward-dipping, stacked thrust sheets were found in wells drilled in the forearc basin. These sheets have been explained as resulting as resulting from gravity sliding of mountains at the eastern basin margin. The mountains formed as an uplifted belt above the toe of the continental mass overlying the subducting slab west of the Japan-Kurile Trenches. Further complications involve a history of submarine canyon erosion, wrench faulting, volcanic activity, and rapid uplift and subsidence with consequent complex sedimentation. Gravity, magnetics, seismic, well, and petrophysics information were integrated in order to interpret this area. Several localities in and near Australia are described where an interpretation using plate tectonics concepts is indicated.

  20. Beyond plate tectonics - Looking at plate deformation with space geodesy

    NASA Technical Reports Server (NTRS)

    Jordan, Thomas H.; Minster, J. Bernard

    1988-01-01

    The requirements that must be met by space-geodetic systems in order to constrain the horizontal secular motions associated with the geological deformation of the earth's surface are explored. It is suggested that in order to improve existing plate-motion models, the tangential components of relative velocities on interplate baselines must be resolved to an accuracy of less than 3 mm/yr. Results indicate that measuring the velocities between crustal blocks to + or - 5 mm/yr on 100-km to 1000-km scales can produce geologically significant constraints on the integrated deformation rates across continental plate-boundary zones such as the western United States.

  1. Mesozoic Plate Tectonic Evolution of the Northern Margin of Pangea

    NASA Astrophysics Data System (ADS)

    Miller, E. L.

    2011-12-01

    Asia joined Laurentia and Baltica during the formation of the Urals in the Early Permian. Subsequently, the northern margin of Pangea shared a paleo-Pacific facing margin. Analysis of events along this (mostly active) margin provides insight into the plate tectonic setting and evolution of the Arctic basins and their temporal links to Pacific margin events. A 3-phase tectonic evolution characterizes the northern margin of Pangea during the Mesozoic: 1. Permo-Triassic rifting (Siberian Trap magmatism)was linked to rifting in a series of back-arc basins developed along the northern margin of Pangea. Triassic-Jurasic deep-water sedimentary seqences deposited in these basins were subsequently deformed during phase 2 events. 2. Lithospheric shortening/convergence across this margin deformed these basinal sediments and shed syn-orogenic deposits cratonward in the Jura-Cretaceous. Syn-orogenic basinal successions are widespread from the Verkoyansk margin of Siberia to the Brooks Range fold and thrust belt. Their sources are well-characterized by U-Pb ages of detrital zircon suites and include Pennsylvanian-Permian, Triassic and Jurassic magmatic belts, implying convergence and emplacement of a long-lived arc system onto the continental margin. 3. Structures related to phase 2 are cut and overprinted by voluminous, syn-extensional, slab-related magmatism that developed during southward or Pacific-ward migration of a N-dipping subducting slab. It is inferred that the earliest part of the Amerasia Basin likely opened during part of this magmatic event, 135 to 90 Ma. The final culmination of this magmatic event is the Ohotsk-Chukotsk volcanic belt, ~90-75 Ma;after this, magmatism continues to migrate Pacific-ward in a series of steps. Utilizing plate models of the Arctic by Lawver et al.(2002) it can be shown that some of the differences in the timing and style of Mesozoic orogenesis along the northern paleo-Pacific margin of Pangea (and especially the differences between the

  2. Global Dynamic Numerical Simulations of Plate Tectonic Reorganizations

    NASA Astrophysics Data System (ADS)

    Morra, G.; Quevedo, L.; Butterworth, N.; Matthews, K. J.; Müller, D.

    2010-12-01

    We use a new numerical approach for global geodynamics to investigate the origin of present global plate motion and to identify the causes of the last two global tectonic reorganizations occurred about 50 and 100 million years ago (Ma) [1]. While the 50 Ma event is the most well-known global plate-mantle event, expressed by the bend in the Hawaiian-Emperor volcanic chain, a prominent plate reorganization at about 100 Ma, although presently little studied, is clearly indicated by a major bend in the fracture zones in the Indian Ocean and by a change in Pacific plate motion [2]. Our workflow involves turning plate reconstructions into surface meshes that are subsequently employed as initial conditions for global Boundary Element numerical models. The tectonic setting that anticipates the reorganizations is processed with the software GPlates, combining the 3D mesh of the paleo-plate morphology and the reconstruction of paleo-subducted slabs, elaborated from tectonic history [3]. All our models involve the entire planetary system, are fully dynamic, have free surface, are characterized by a spectacular computational speed due to the simultaneous use of the multi-pole algorithm and the Boundary Element formulation and are limited only by the use of sharp material property variations [4]. We employ this new tool to unravel the causes of plate tectonic reorganizations, producing and comparing global plate motion with the reconstructed ones. References: [1] Torsvik, T., Müller, R.D., Van der Voo, R., Steinberger, B., and Gaina, C., 2008, Global Plate Motion Frames: Toward a unified model: Reviews in Geophysics, VOL. 46, RG3004, 44 PP., 2008 [2] Wessel, P. and Kroenke, L.W. Pacific absolute plate motion since 145 Ma: An assessment of the fixed hot spot hypothesis. Journal of Geophysical Research, Vol 113, B06101, 2008 [3] L. Quevedo, G. Morra, R. D. Mueller. Parallel Fast Multipole Boundary Element Method for Crustal Dynamics, Proceeding 9th World Congress and 4th Asian

  3. Creep of phyllosilicates at the onset of plate tectonics

    SciTech Connect

    Amiguet, Elodie; Reynard, Bruno; Caracas, Razvan; Van de Moortele, Bertrand; Hilairet, Nadege; Wang, Yanbin

    2012-10-24

    Plate tectonics is the unifying paradigm of geodynamics yet the mechanisms and causes of its initiation remain controversial. Some models suggest that plate tectonics initiates when the strength of lithosphere is lower than 20-200 MPa, below the frictional strength of lithospheric rocks (>700 MPa). At present-day, major plate boundaries such as the subduction interface, transform faults, and extensional faults at mid-oceanic ridge core complexes indicate a transition from brittle behaviour to stable sliding at depths between 10 and 40 km, in association with water-rock interactions forming phyllosilicates. We explored the rheological behaviour of lizardite, an archetypal phyllosilicate of the serpentine group formed in oceanic and subduction contexts, and its potential influence on weakening of the lithospheric faults and shear zones. High-pressure deformation experiments were carried out on polycrystalline lizardite - the low temperature serpentine variety - using a D-DIA apparatus at a variety of pressure and temperature conditions from 1 to 8 GPa and 150 to 400 C and for strain rates between 10{sup -4} and 10{sup -6} s{sup -1}. Recovered samples show plastic deformation features and no evidence of brittle failure. Lizardite has a large rheological anisotropy, comparable to that observed in the micas. Mechanical results and first-principles calculations confirmed easy gliding on lizardite basal plane and show that the flow stress of phyllosilicate is in the range of the critical value of 20-200 MPa down to depths of about 200 km. Thus, foliated serpentine or chlorite-bearing rocks are sufficiently weak to account for plate tectonics initiation, aseismic sliding on the subduction interface below the seismogenic zone, and weakening of the oceanic lithosphere along hydrothermally altered fault zones. Serpentinisation easing the deformation of the early crust and shallow mantle reinforces the idea of a close link between the occurrence of plate tectonics and water at

  4. Plate Tectonics: The Way the Earth Works. Teacher's Guide. LHS GEMS.

    ERIC Educational Resources Information Center

    Cuff, Kevin

    This teacher guide presents a unit on plate tectonics and introduces hands-on activities for students in grades 6-8. In each unit, students act as real scientists and gather evidence by using science process skills such as observing, graphing, analyzing data, designing and making models, visualizing, communicating, theorizing, and drawing…

  5. Could plate tectonics on Venus be concealed by volcanic deposits

    NASA Technical Reports Server (NTRS)

    Kaula, W. M.; Muradian, L. M.

    1982-01-01

    The present investigation is supplementary to a study reported by Kaula and Phillips (1981). From an analysis of Pioneer Venus altimetry, Kaula and Phillips had inferred that any heat loss from the planet by plate tectonics must be small compared to that from the earth. However, it has been suggested by others that plate tectonic may exist on Venus, but that the expected 'square root of s' dependence of the topographic drop off is not observed because it is concealed by lava flows. The present investigation has the objective to conduct an examination whether this suggestion of concealment by lava flow is correct. On the basis of the performed analysis, it is concluded that the results obtained by Kaula and Phillips appear to be well justified.

  6. The magma ocean as an impediment to lunar plate tectonics

    NASA Technical Reports Server (NTRS)

    Warren, Paul H.

    1993-01-01

    The primary impediment to plate tectonics on the moon was probably the great thickness of its crust and particularly its high crust/lithosphere thickness ratio. This in turn can be attributed to the preponderance of low-density feldspar over all other Al-compatible phases in the lunar interior. During the magma ocean epoch, the moon's crust/lithosphere thickness ratio was at the maximum theoretical value, approximately 1, and it remained high for a long time afterwards. A few large regions of thin crust were produced by basin-scale cratering approximately contemporaneous with the demise of the magma ocean. However, these regions probably also tend to have uncommonly thin lithosphere, since they were directly heated and indirectly enriched in K, Th, and U by the same cratering process. Thus, plate tectonics on the moon in the form of systematic lithosphere subduction was impeded by the magma ocean.

  7. The magma ocean as an impediment to lunar plate tectonics

    NASA Astrophysics Data System (ADS)

    Warren, P. H.

    1993-03-01

    The primary impediment to plate tectonics on the moon was probably the great thickness of its crust and particularly its high crust/lithosphere thickness ratio. This in turn can be attributed to the preponderance of low-density feldspar over all other Al-compatible phases in the lunar interior. During the magma ocean epoch, the moon's crust/lithosphere thickness ratio was at the maximum theoretical value, approximately 1, and it remained high for a long time afterwards. A few large regions of thin crust were produced by basin-scale cratering approximately contemporaneous with the demise of the magma ocean. However, these regions probably also tend to have uncommonly thin lithosphere, since they were directly heated and indirectly enriched in K, Th, and U by the same cratering process. Thus, plate tectonics on the moon in the form of systematic lithosphere subduction was impeded by the magma ocean.

  8. Plate tectonic patterns and convection in the Phanerozoic

    NASA Astrophysics Data System (ADS)

    Kanasewich, E. R.; Evans, M. E.; Havskov, J.

    Paleomagnetic observations, oceanic magnetic lineations and the present continental margins are combined in an interactive computer program to generate maps for seven periods in the Phanerozoic era. Geological evidence on the position of geosynclines, volcanic assemblages, and zones of diastrophism are used to model a reconstruction of major plate boundaries in the past. Only six to nine major plates are necessary to describe satisfactorily the main geological events in the paleomagnetic reconstruction of the continents. The stability of these plates over time is strong evidence that mantle-wide convection was, and is, present. The formation of the supercontinent Pangaea results from a change in the convective pattern from a third-order to a second-order system, while the breakup of Pangaea resulted from a shift back to a third-order convective pattern. It is concluded that the 10 principles of plate tectonics are a valuable guide for reconstructing the geological past.

  9. A Simple Class Exercise on Plate Tectonic Motion.

    ERIC Educational Resources Information Center

    Bates, Denis E. B.

    1990-01-01

    Presented is an activity in which students construct a model of plate divergence with two sheets of paper to show the separation of two continental plates in a system of spreading ridges and faults. Diagrams and procedures are described. (CW)

  10. The transpressive tectonics and large earthquake distribution along the plate boundary in North Africa

    NASA Astrophysics Data System (ADS)

    Meghraoui, Mustapha; Pondrelli, Silvia

    2010-05-01

    The Tell Atlas and Rif Mountains of northern Africa have been the site of several large and moderate seismic events in the last decades. However, the thrust and fold system of NW Algeria experienced the largest earthquakes in the last centuries along the Africa-Eurasia plate boundary. This shallow seismic activity was very often associated with surface faulting and deformation as for the Mw 7.3 El Asnam (10/10/1980) and the Mw 6.8 Zemmouri-Boumerdes (21/05/2003) earthquakes. We study the active tectonics along the plate boundary in North Africa from the seismicity database, individual large and moderate earthquakes, the seismic moment tensor summation, the geodetic measurements (GPS and InSAR) and the structural and kinematic of active faults. Neotectonic structures and significant seismicity (Mw>5) indicate that coeval east-west trending right-lateral faulting and NE-SW thrust-related folding result from the oblique convergence at the plate boundary. A simple modeling of block tectonics suggests that transpression and block rotation govern the mechanics of the Africa - Eurasia plate boundary in the Tell Atlas and Rif Mountains. The tectonic restraining bend of NW Algeria combined with the ~ 5 mm/yr convergence between Africa and Eurasia justify the large seismic activity on the thrust and fold system of the Tell Atlas and the relatively passive active deformation along the adjacent sections of the plate boundary.

  11. Barrel organ of plate tectonics - a new tool for outreach and education

    NASA Astrophysics Data System (ADS)

    Broz, Petr; Machek, Matěj; Šorm, Zdar

    2016-04-01

    Plate tectonics is the major geological concept to explain dynamics and structure of Earth's outer shell, the lithosphere. In the plate tectonic theory processes in the Earth lithosphere and its dynamics is driven by the relative motion and interaction of lithospheric plates. Geologically most active regions on Earth often correlate with the lithospheric plate boundaries. Thus for explaining the earth surface evolution, mountain building, volcanism and earthquake origin it is important to understand processes at the plate boundaries. However these processes associated with plate tectonics usually require significant period of time to take effects, therefore, their entire cycles cannot be directly observed in the nature by humans. This makes a challenge for scientists studying these processes, but also for teachers and popularizers trying to explain them to students and to the general public. Therefore, to overcome this problem, we developed a mechanical model of plate tectonics enabling demonstration of most important processes associated with plate tectonics in real time. The mechanical model is a wooden box, more specifically a special type of barrel organ, with hand painted backdrops in the front side. These backdrops are divided into several components representing geodynamic processes associated with plate tectonics, specifically convective currents occurring in the mantle, sea-floor spreading, a subduction of the oceanic crust under the continental crust, partial melting and volcanism associated with subduction, a formation of magmatic stripes, an ascent of mantle plume throughout the mantle, a volcanic activity associated with hot spots, and a formation and degradation of volcanic islands on moving lithospheric plate. All components are set in motion by a handle controlled by a human operator, and the scene is illuminated with colored lights controlled automatically by an electric device embedded in the box. Operation of the model may be seen on www

  12. Structural regularities in the lithosphere of continents and plate tectonics

    NASA Astrophysics Data System (ADS)

    Pavlenkova, N. I.

    1995-03-01

    Two fundamental, but competing earth science concepts have been under discussion in Russia. The first one, that of endogenous regimes, is based on the assumption that permanent vertical relationships or long-term interactions between the crust and upper mantle control crustal evolution. Significant horizontal movements of the lithosphere, as required by the second concept, that of global plate tectonics, would destroy these crust-mantle interactions. Certain regular features of the crust and upper mantle support the endogenous regime concept and are difficult to explain in terms of conventional plate tectonics. In particular, the close correlation between near-surface features and deep (> 400 km) mantle inhomogeneities suggests that many geological structures are deeply rooted in the mantle. Moreover, geophysical studies have failed to reveal a well-defined and continuous asthenosphere at relatively shallow depths (˜ 100 km) that would allow lithospheric plates to be transported over large distances, and the rheology of the lithosphere itself is found to be sufficiently inhomogeneous as to cast doubt on the principle of thin rigid plates. In contrast, palaeomagnetic and other data require that horizontal movements of many near-surface geological structures must have taken place. To explain this apparent contradiction, it is suggested here that the crust and its connected deep root are capable of gliding along one of the deep mantle phase transition zones with respect to the inner Earth.

  13. The San Andreas fault experiment. [gross tectonic plates relative velocity

    NASA Technical Reports Server (NTRS)

    Smith, D. E.; Vonbun, F. O.

    1973-01-01

    A plan was developed during 1971 to determine gross tectonic plate motions along the San Andreas Fault System in California. Knowledge of the gross motion along the total fault system is an essential component in the construction of realistic deformation models of fault regions. Such mathematical models will be used in the future for studies which will eventually lead to prediction of major earthquakes. The main purpose of the experiment described is the determination of the relative velocity of the North American and the Pacific Plates. This motion being so extremely small, cannot be measured directly but can be deduced from distance measurements between points on opposite sites of the plate boundary taken over a number of years.

  14. Plate tectonics and petroleum potential of the Laptev Sea region

    SciTech Connect

    Savostin, L.; Drachev, S.; Baturin, D. )

    1991-08-01

    About 1,600 km of multichannel seismic data with simultaneous gravity and magnetic measurements were collected in the Laptev Sea during 1989. Additionally, a 100 km onshore seismic reflection profile transected the northern termination of the Verrkoyansky Mountains. Data interpretation showed the following. The tectonic patterns of the Laptev Sea region was formed as a result of two major tectonic phases. The first phase was associated with collisions between the Paleozoic passive margin of Siberia and a number of allochthonous terrains which were previously parts of the North American Paleo-Pacific plate. These tectonic events accompanied the opening of the Canadian basin and ended in the second half of the Early Cretaceous. The second phase was a result of the opening of the Makarov and the Europeo-Asiatic basins, which caused the rifting processes within the Laptev Sea Shelf. Seismic onshore data show that the orogenic sequence consists of allochthonous plates which were thrust onto the thick sedimentary cover the Siberia platform. An underthrusting sedimentary sequence is situated at depths from 3 to 5 km, which present a good possibility to reach by the drill. The geological analogy with Appalachian Mountains United States, permits one to propose a high petroleum potential for this area. A system of offshore Laptev Sea grabens consisting of a series of alternating tilted and thrusted blocks, along with intrablock pre-drift sediments, are promising as potential hydrocarbon traps. This is akin to structural setting within North Sea oil and gas province.

  15. Exploring Active Tectonics in the Dominican Republic

    NASA Astrophysics Data System (ADS)

    Carbó-Gorosabel, A.; Córdoba-Barba, D.; Martín-Dívila, J.; Granja-Bruña, J. L.; Llanes Estrada, P.; Muñoz-Martín, A.; ten Brink, U. S.

    2010-07-01

    The devastating 12 January 2010 Haiti earthquake (M = 7.0), which killed an estimated 230,000 people and caused extensive damage to homes and buildings, drew attention to the crucial need for improved knowledge of the active tectonics of the Caribbean region. But even before this disastrous event, interest in understanding the active and complex northeastern Caribbean plate boundary had been increasing, because this region has experienced significant seismic activity during the past century and has an extensively documented record of historical seismicity and tsunamis. Moreover, this is an easily accessible region in which to study the continuity of seismic faults offshore and to try to understand the transitions between strike-slip and convergent tectonic regimes. Interest in the region has led to several studies that have improved scientists' knowledge of subduction zone tectonics and earthquake and tsunami hazard assessments 005BMann et al., 2002; ten Brink et al., 2006, 2009; Grindlay et al., 2005; Manaker et al., 2008; Granja Bruña et al., 2009; Mondziel et al., 2010].

  16. Geophysical Limitations on the Habitable Zone: Volcanism and Plate Tectonics

    NASA Astrophysics Data System (ADS)

    Noack, Lena; Rivoldini, Attilio; Van Hoolst, Tim

    2016-04-01

    Planets are typically classified as potentially life-bearing planets (i.e. habitable planets) if they are rocky planets and if a liquid (e.g. water) could exist at the surface. The latter depends on several factors, like for example the amount of available solar energy, greenhouse effects in the atmosphere and an efficient CO2-cycle. However, the definition of the habitable zone should be updated to include possible geophysical constraints, that could potentially influence the CO2-cycle. Planets like Mars without plate tectonics and no or only limited volcanic events can only be considered to be habitable at the inner boundary of the habitable zone, since the greenhouse effect needed to ensure liquid surface water farther away from the sun is strongly reduced. We investigate if the planet mass as well as the interior structure can set constraints on the occurrence of plate tectonics and outgassing, and therefore affect the habitable zone, using both parameterized evolution models [1] and mantle convection simulations [1,2]. We find that plate tectonics, if it occurs, always leads to sufficient volcanic outgassing and therefore greenhouse effect needed for the outer boundary of the habitable zone (several tens of bar CO2), see also [3]. One-plate planets, however, may suffer strong volcanic limitations. The existence of a dense-enough CO2 atmosphere allowing for the carbon-silicate cycle and release of carbon at the outer boundary of the habitable zone may be strongly limited for planets: 1) without plate tectonics, 2) with a large planet mass, and/or 3) a high iron content. Acknowledgements This work has been funded by the Interuniversity Attraction Poles Programme initiated by the Belgian Science Policy Office through the Planet Topers alliance, and results within the collaboration of the COST Action TD 1308. References Noack, L., Rivoldini, A., and Van Hoolst, T.: CHIC - Coupling Habitability, Interior and Crust, INFOCOMP 2015, ISSN 2308-3484, ISBN 978

  17. Plate Tectonics on Earth and on Alien Worlds - Novel Insights into Mantle Dynamics

    NASA Astrophysics Data System (ADS)

    Stamenkovic, V.; Breuer, D.; Seager, S.

    2014-12-01

    We derive the framework of how common assumptions behind parameterized 1D and full convection 2D/3D models, as well as planet mass, interior structure and composition impact the evolution of plate tectonics on Earths and super-Earths. This approach additionally allows us to resolve previous disagreements between groups that studied plate tectonics on super-Earths and to unveil major problems when modeling the thermal evolution of plate tectonics with both 1D and 2D/3D models. How planet properties impact the evolution of plate tectonics is highly sensitive to a planet's initial thermal conditions, the rheology of mantle rock, the scaling of interior heat and yield stress with planet mass, and especially to whether shear or normal stresses drive plate tectonics. Based on the currently most likely model configuration and for planets starting molten, we find that plate tectonics is less likely to occur on super-Earths, for increasing iron and radiogenic heat contents within the mantle, and also with decreasing core to mantle mass fractions. Interestingly, we also find that water within a planet's mantle has a negative impact on plate tectonics and that only surface water can beneficially impact subduction (but not the initiation of plate tectonics). This emphasizes how the distribution and exchange of water between surface and mantle reservoirs are crucial for plate tectonics, and how difficult it is to find positive water-plate tectonics correlations.

  18. Extrusional Tectonics over Plate Corner: an Example in Northern Taiwan

    NASA Astrophysics Data System (ADS)

    Lu, Chia-Yu; Lee, Jian-Cheng; Li, Zhinuo; Lee, Ching-An; Yeh, Chia-Hung

    2016-04-01

    In northern Taiwan, contraction, transcurrent shearing, block rotation and extension are four essential tectonic deformation mechanisms involved in the progressive deformation of this arcuate collision mountain belt. The neotectonic evolution of the Taiwan mountain belt is mainly controlled not only by the oblique convergence between the Eurasian plate and the Philippine Sea plate but also the corner shape of the plate boundary. Based on field observations and analyses, and taking geophysical data (mostly GPS) and experimental modelling into account, we interpret the curved belt of northern Taiwan as a result of of contractional deformation (with compression, thrust-sheet stacking & folding, back thrust duplex & back folding) that induced vertical extrusion, combined with increasing transcurrent & rotational deformation (with transcurrent faulting, bookshelf-type strike-slip faulting and block rotation) that induced transcurrent/rotational extrusion and extension deformation which in turn induced extensional extrusion. As a consequence, a special type of extrusional folds was formed in association with contractional, transcurrent & rotational and extensional extrusions subsequently. The extrusional tectonics in northern Taiwan reflect a single, albeit complicated, regional pattern of deformation. The crescent-shaped mountain belt of Northeastern Taiwan develops in response to oblique indentation by an asymmetric wedge indenter, retreat of Ryukyu trench and opening of the Okinawa trough.

  19. Plate tectonics of the northern part of the Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Verzhbitsky, E. V.; Kononov, M. V.; Kotelkin, V. D.

    2007-10-01

    Geophysical data on the northern part of the Pacific Ocean were systematized to compile a map of geomagnetic and geothermal studies of the Bering Sea. The absence of reliable data about the formation time of the Bering Sea structures of oceanic and continental origins is noted; this hampered the assessment of the geodynamical processes in the North Pacific. Based on the geophysical data, we estimated the age of the structures of the Bering Sea floor such as the Commander Basin (21 My), the Shirshov Ridge (95 and 33 My in the northern and southern parts, respectively), the Aleutian Basin (70 My), the Vitus Arch (44 My), the Bowers Ridge (30 My), and the Bowers Basin (40 My). These values are confirmed by the geological, geophysical, and kinematic data. A numerical modeling of the formation of extensive regional structures (Emperor Fracture Zone, Chinook Trough, and others) in the Northern Pacific is carried out. A conclusion was made on the basis of the geological and geothermal analysis that the northern and southern parts of the Shirshov Ridge have different geological ages and different tectonic structures. The northern part of the ridge is characterized by an upthrust-nappe terrain origin, while the southern part has originated from a torn-away island arc similar to the origin of the Bowers Ridge. The sea floor of the Aleutian Basin represents a detached part of the Upper Cretaceous Kula plate, on which spreading processes took place in the Vitus Arch area in the Eocene. The final activity phase in the Bering Sea began 21 My B.P. by spreading of the ancient oceanic floor of the Commander Basin. Based on the age estimations of the structures of the Bering Sea floor, the results of the modeling of the process of formation of regional fracture zones and of the geomagnetic, geothermal, tectonic, geological, and structural data, we calculated and compiled a kinematic model (with respect to a hot spot reference system) of the northern part of the Pacific Ocean for 21

  20. Early Miocene transpression across the Pacific-North American plate margin, initiation of the San Andreas fault, and tectonic wedge activation

    SciTech Connect

    McLaughlin, R.J. ); Underwood, M.B. )

    1993-04-01

    Magnetic stripes on the Pacific plate (PAC) indicate that subduction along the North American plate (NAM) margin ceased about 26--28 Ma south of the Mendocino fracture zone (MFZ), when the Pacific-Farallon (PAC-FAR) ridge encountered the NAM. In this area the PAC-FAR ridge apparently was segmented and abandoned as it encountered the margin, and was thrust beneath the western lip of the NAM, possibly due to residual FAR slab-pull. Between [approximately] 26 and 23.5 Ma, compressional tectonism in the distal NAM overlying the hot, buoyant ridge, produced ocean floor volcanism and a series of borderland structural basins that filled with continent-derived clastics. Initiation of the San Andreas transform, and capture of a large segment of the NAM by the PAC appears to have occurred between [approximately] 24 and [approximately] 14 Ma. Beginning at least as early as 18 Ma, northeast of the San Andreas fault, blind thrusts, folding and tilting developed in the roof of a northeastwardly-propagating wedge complex beneath the length of the Coast Ranges. The wedge complex probably was multistage and may have been initiated as early as 70--60 Ma. In the Cape Mendocino and Loma Prieta regions, Miocene or younger northeast-vergent members of the roof thrust system root into the San Andreas fault and characteristically displace deep water marine rocks northeastward over the shallower margin. Total shortening across the transform margin based on deep crustal models must exceed 200 km since 70 Ma and is [ge]50 km since 28 Ma.

  1. The ERESE Project: Modeling Inquiry-Based Plate Tectonic Lessons

    NASA Astrophysics Data System (ADS)

    Symons, C. M.; Helly, M.; Helly, J.; Miller, S. P.; Staudigel, H.; Koppers, A.

    2004-12-01

    The Enduring Resources for Earth Science Education (ERESE) project is a collaborative effort between earth scientists, educators, librarians and data archive managers. Its goal is to develop and maintain a persistent online research and education archive in a digital library environment that supports earth science education in plate tectonics. A key to the library's effectiveness as an educational tool is the efficiency with which educators can access, use and contribute to the library. We have created a master template that educators use to develop inquiry-based curriculum. The central components of the master template include a teacher log, a student log and resource matrices. The teacher's log is divided into stages that reflect our approach to inquiry. This approach was used during a workshop as scientists worked with the teachers to model a reasonable pedagogical analog to scientific inquiry. The student log is similar in structure to a scientific method lab report. There are currently 17 resource matrices that directly access canonical education objects in the digital library, 3 of which relate to expedition planning and 14 to plate tectonics. The structure of the resource matrices allows teachers and students to traverse manageable packets of information relating to a specific topic by expert level (rows) and information type (columns). Teachers download and customize the master template using any web composer and are then invited to upload their lessons through a simple interface at Earthref.org. Once uploaded the lessons become part of the ERESE digital library collection. The upload process allows teachers to define keywords and metadata to allow useful searches by topic, concept or educational standard. The use of a single master template for inquiry lesson design means library contributions will share a common format as well as exploit identical plate tectonic resources.

  2. Geoid Data and Implications for Plate Tectonic Dynamics

    NASA Astrophysics Data System (ADS)

    Richardson, R. M.; Coblentz, D. D.

    2013-12-01

    It has long been recognized that the motion of the mechanically rigid lithospheric plates of the earth are the surface expression of large-scale convection in the mantle. It is also accepted that the stresses driving plate motion are an amalgam of the basal tractions associated with this convection and long-wavelength density variations within the plates themselves. Parsing the relative contribution from these two sources to the geodynamics of the lithosphere continues to be an important topic of plate dynamics research. Because geoid anomalies are directly related to the local dipole moment of the density-depth distribution, they provide an ideal method for evaluating density variations within the lithosphere and the associated tectonic stresses. The main challenge with this approach is isolating the lithospheric geoid contribution from the full geoid (which is dominated by sources from deeper in the earth, namely the lower mantle). We address this issue by using a high-pass spherical harmonic filtering of the EGM2008-WGS84 geoid (which is complete to spherical harmonic degree and order 2159), with a cosine taper between orders 9 to 13 and 78 to 82 to produce a 'lithospheric' geoid. In the present study we focus on tectonic implications of the lithospheric geoid in three different areas: 1) passive continental margins where we have evaluated over 150 margin-transects spaced roughly every three degrees. The global average geoid anomaly associated with the transition from old oceanic lithosphere to the continent was found to 6-9 meters and appears to be insensitive to a range of geoid filtering degrees and orders; 2) The geoid highs associated with the mid-ocean ridges and the cooling oceanic lithospheric, where we have examined a number of geoid profiles across ridges and find that previous estimates of a geoid anomaly of 10-15 meters associated with ridges to be valid; and 3) continental regions which are characterized by both elevated geoid anomalies (e.g., the

  3. The efficiency of plate tectonics and nonequilibrium dynamical evolution of planetary mantles

    NASA Astrophysics Data System (ADS)

    Moore, W. B.; Lenardic, A.

    2015-11-01

    Consideration of the structure of dynamical equilibria in terrestrial planets using simplified descriptions of the relevant heat transport processes (rigid-lid convection, plate tectonics, and heat pipe volcanism) reveals that if the efficiency of plate tectonic heat transport decreases at higher mantle temperature, then it cannot govern quasi-equilibrium dynamical evolution, and the system is always evolving away from the plate tectonic regime. A planet on which plate tectonics is less efficient at higher temperature stays in heat pipe mode longer, spends less time undergoing plate tectonics, and has a low and ever-decreasing Urey number during this phase. These conclusions are based solely on the structure of the equilibria in a system with less efficient plate tectonics in the past and are independent of the mechanisms leading to this behavior. Commonly used quasi-equilibrium approaches to planetary thermal evolution are likely not valid for planets in which heat transport becomes less efficient at higher temperature.

  4. A new plate tectonic concept for the eastern-most Mediterranean

    NASA Astrophysics Data System (ADS)

    Huebscher, C.; McGrandle, A.; Scaife, G.; Spoors, R.; Stieglitz, T.

    2012-04-01

    Owing to the seismogenic faults bordering the Levant-Sinai realm and the discovery of giant gas reservoirs in the marine Levant Basin the scientific interest in this tectonically complex setting increased in recent years. Here we provide a new model for the Levant Basin architecture and adjacent plate boundaries emphasizing the importance of industrial seismic data for frontier research in earth science. PSDM seismics, residual gravity and depth to basement maps give a clear line of evidence that the Levant Basin, formerly considered as a single tectonic entity, is divided into two different domains. Highly stretched continental crust in the southern domain is separated from deeper and presumably Tethyan oceanic crust in the north. A transform continuing from southwest Cyprus to the Carmel Fault in northern Israel is considered as the boundary. If this interpretation holds, the Carmel-Cyprus Transform represents a yet unknown continent-ocean boundary in the eastern Mediterranean, thus adding new constrains for the Mediterranean plate tectonic puzzle. The Eratosthenes Seamount, considered as the spearhead of incipient continental collision in the eastern Mediterranean, is interpreted as a carbonate platform that developed above a volcanic basement. NW-SE trending strike-slip faults are abundant in the entire Levant region. Since this trend also shapes the topography of the Levant hinterland including Quaternary deposits their recent tectonic activity is quite likely. Thus, our study supports previous studies which attributed the evolution of submarine canyons and Holocene triggering of mass failures not only to salt tectonics or depositional processes, but also to active plate-tectonics.

  5. On the breakup of tectonic plates by polar wandering

    NASA Technical Reports Server (NTRS)

    Liu, H. S.

    1973-01-01

    The observed boundary system of the major tectonic plates on the surface of the earth lends fresh support to the hypothesis of polar wandering. A dynamic model of the outer shell of the earth under the influence of polar shift is developed. The analysis falls into two parts: (1) deriving equations for stresses caused by polar shifting; and (2) deducing the pattern according to which the fracture of the shell can be expected. For stress analysis, the theory of plates and shells is the dominant feature of this model. In order to determine the fracture pattern, the existence of a mathematical theorem of plasticity is recalled: it says that the plastic flow begins to occur when a function in terms of the differences of the three principal stresses surpasses a certain critical value. By introducing the figures for the geophysical constants, this model generates stresses which could produce an initial break in the lithosphere.

  6. Observing tectonic plate motions and deformations from satellite laser ranging

    NASA Technical Reports Server (NTRS)

    Christodoulidis, D. C.; Smith, D. E.; Kolenkiewicz, R.; Klosko, S. M.; Torrence, M. H.

    1985-01-01

    The scope of geodesy has been greatly affected by the advent of artificial near-earth satellites. The present paper provides a description of the results obtained from the reduction of data collected with the aid of satellite laser ranging. It is pointed out that dynamic reduction of satellite laser ranging (SLR) data provides very precise positions in three dimensions for the laser tracking network. The vertical components of the stations, through the tracking geometry provided by the global network and the accurate knowledge of orbital dynamics, are uniquely related to the center of mass of the earth. Attention is given to the observations, the methodologies for reducing satellite observations to estimate station positions, Lageos-observed tectonic plate motions, an improved temporal resolution of SLR plate motions, and the SLR vertical datum.

  7. Plate tectonic evolution of circum-Antarctic passive margins

    SciTech Connect

    Scotese, C.R.; Lawver, L.A.; Sclater, J.G.; Mayes, C.L.; Norton, I.; Royer, J.

    1987-05-01

    Passive margins that formed during the Late Jurassic and Cretaceous account for approximately 80% of the 15,000-km circumference of Antarctica. There are no passive margins younger than Late Cretaceous. Approximately 28% of these margins are Late Jurassic in age, 24% are Early Cretaceous in age, and the remaining 48% formed during the Late Cretaceous. The tectonic style of the rifting events that formed these margins varies considerably along the perimeter of Antarctica. In several areas the initiation of sea-floor spreading was preceded by a long period of extension and predrift stretching (Wilkes Land). Along other portions of the margin, rifting proceeded rapidly with little evidence for a lengthy phase of pre-drift extension (Queen Maud Land). Though extension is the dominant tectonic style, there is evidence for large-scale strike-slip movement associated with the early phases of continental breakup along the coasts of Crown Princess Martha Land and Victoria Land. Except for a short segment of the margin between the West Antarctic peninsula and Marie Byrdland, the Antarctic passive margins have not been affected by subsequent subduction-related compressive deformation. This presentation will review the plate tectonic evolution of the Circum-Antarctic passive margins during five time intervals: Early Jurassic, Late Jurassic, Early Cretaceous, mid-Cretaceous, and latest Cretaceous. A map illustrating the relative amounts of extension along the margin of Antarctica will be presented, and a computer animation illustrating the breakup of Gondwana from an Antarctic perspective will be shown.

  8. Topography of Venus and earth - A test for the presence of plate tectonics

    NASA Technical Reports Server (NTRS)

    Head, J. W.; Yuter, S. E.; Solomon, S. C.

    1981-01-01

    Comparisons of earth and Venus topography by use of Pioneer/Venus radar altimetry are examined. Approximately 93% of the Venus surface has been mapped with a horizontal resolution of 200 km and a vertical resolution of 200 m. Tectonic troughs have been indicated in plains regions which cover 65% of Venus, and hypsometric comparisons between the two planets' elevation distributions revealed that while the earth has a bimodal height distribution, Venus displays a unimodal configuration, with 60% of the planet surface within 500 m of the modal planet radius. The effects of mapping the earth at the same resolution as the Venus observations were explored. Continents and oceans were apparent, and although folded mountains appeared as high spots, no indications of tectonic activity were discernible. A NASA Venus Orbiting Imaging radar is outlined, which is designed to detect volcanoes, folded mountain ranges, craters, and faults, and thereby allow definition of possible plate-tectonic activity on Venus.

  9. Plate tectonics from VLBI and SLR global data

    NASA Technical Reports Server (NTRS)

    Harrison, Christopher G. A.; Robaudo, Stefano

    1992-01-01

    This study is based on data derived from fifteen years of observations of the SLR (side-looking radar) network and six years of the VLBI (very long baseline interferometry) network. In order to use all available information VLBI and SLR global data sets were combined in a least squares fashion to calculate station horizontal velocities. All significant data pertaining to a single site contribute to the station horizontal motion. The only constraint on the solution is that no vertical motion is allowed. This restriction does not greatly affect the precision of the overall solution given the fact that the expected vertical motion for most stations, even those experiencing post glacial uplift, is well under 1 cm/yr. Since the average baseline is under 4,000 km, only a small fraction of the station vertical velocity is translated into baseline rates so that the error introduced in the solution by restricting up-down station movement is minimal. As a reference, station velocities were then compared to the ones predicted by the NUVEL-1 geological model of DeMets et al. (1990). The focus of the study is on analyzing these discrepancies for global plate tectonics as well as regional tectonic settings. The method used also allows us not only to derive horizontal motion for individual stations but also to calculate Euler vectors for those plates that have enough stations located on the stable interior like North America, Pacific, Eurasia, and Australia.

  10. A model for plate tectonic evolution of mantle layers.

    PubMed

    Dickinson, W R; Luth, W C

    1971-10-22

    In plate tectonic theory, lithosphere that descends into the mantle has a largely derivative composition, because it is produced as a refractory residue by partial melting, and cannot be resorbed readily by the parent mantle. We suggest that lithosphere sinks through the asthenosphere, or outer mantle, and accumulates progressively beneath to form an accretionary mesosphere, or inner mantle. According to this model, there is an irreversible physicochemical evolution of the mantle and its layers. We make the key assumption that the rate at which mass has been transferred from the lithosphere to the mesosphere is proportional to the rate of radiogenic heat production. Calculations of mass transfer with time demonstrate that the entire mass of the present mesosphere could have been produced in geologically reasonable times (3 x 10(9) to 4.5 x 10(9) years). The model is consistent with the generation of the continental crust during the last 3 x 1O(9) years and predicts an end to plate tectonic behavior within the next 10(9) years. PMID:17796091

  11. Global tectonic activity map with orbital photographic supplement

    SciTech Connect

    Lowman, P.D. Jr.

    1981-01-01

    A three part map showing equatorial and polar regions was compiled showing tectonic and volcanic activity of the past one million years, including the present. Features shown include actively spreading ridges, spreading rates, major active faults, subduction zones, well defined plates, and volcanic areas active within the past one million years. Activity within this period was inferred from seismicity (instrumental and historic), physiography, and published literature. The tectonic activity map was used for planning global geodetic programs of satellite laser ranging and very long base line interferometry and for geologic education.

  12. A global tectonic activity map with orbital photographic supplement

    NASA Technical Reports Server (NTRS)

    Lowman, P. D., Jr.

    1981-01-01

    A three part map showing equatorial and polar regions was compiled showing tectonic and volcanic activity of the past one million years, including the present. Features shown include actively spreading ridges, spreading rates, major active faults, subduction zones, well defined plates, and volcanic areas active within the past one million years. Activity within this period was inferred from seismicity (instrumental and historic), physiography, and published literature. The tectonic activity map was used for planning global geodetic programs of satellite laser ranging and very long base line interferometry and for geologic education.

  13. Paleomap PC: Plate tectonic reconstructions on IBM compatible computers

    SciTech Connect

    Walsh, D.B.; Scotese, C.R. . Dept. Geology)

    1993-02-01

    PALEOMAP-PC (PMAPPC) allows users to interactively view Phanerozoic plate reconstructions on IBM compatible personal computers. This software compliments Macintosh and Unix software developed to conjunction with the PALEOMAP Project at the University of Texas at Arlington. The past positions of the continents can be viewed on the PC monitor in a variety of map projections including the spherical projection which gives a 3-D perspective of the Earth. Once a reconstruction time has been entered, the total finite rotations for over 150 independently moving plates are calculated and the plates are rotated back through time and drawn in reconstructed coordinates. The user can zoom in and out focusing on particular areas of interest. Hard copy output is available to a variety of output devices, both as a screen dump utility and as a selected option within the program. Although visualizing continental configurations through time is the core of the program, its primary strength is that user-defined data, such as stratigraphic or structural data, can be incorporated and plotted on reconstructed basemaps. This allows the time aspect of all geological data to be united with other user-supplied data within the plate tectonic framework.

  14. Modelling continental deformation within global plate tectonic reconstructions

    NASA Astrophysics Data System (ADS)

    Williams, S.; Whittaker, J.; Heine, C.; Müller, P.

    2010-12-01

    A limitation of regional and global plate tectonic models is the way continental deformation is represented. Continental blocks are typically represented as rigid polygons - overlaps or gaps between adjacent continental blocks represent extension or compression respectively. Full-fit reconstructions of major ocean basins result in large overlaps between the conjugate continental plates, on the basis that the continental margins are highly extended compared to their pre-rift state. A fundamental challenge in generating more robust global-scale plate reconstructions is the incorporation of a more quantitative description of the kinematics within extended passive margins, based on observations. We have used the conjugate Southern Australia and Wilkes Land, Antarctica margins as a case study, and as part of this work have generated revised sediment thickness maps for these margins. These datasets are used to test different approaches for generating full-fit reconstructions in order to create a framework of methodologies that is globally applicable. One approach is to restore two conjugate continent-ocean boundaries (COBs) to their pre-rift configuration and then use the geometric fitting method of Hellinger (1981) and Royer and Chang (1991), used to generate fits of seafloor isochrons, to generate a “full-fit” Euler pole. To quantitatively restore the COBs to their palinspastic pre-rift configuration we integrate estimates of crustal thickness along small circle paths, defined by an initial estimate of the Euler stage pole describing plate motions during continental rifting. We then use the conjugate sets of restored COB’s as inputs to the geometric fitting method, treating them as isochrons, and so generate poles of rotation for the plate configuration prior to rifting. Two potential shortcomings of this methodology are that (1) the conjugate margins are treated independently, whereas in reality they were actually one continuous continental basin during rifting

  15. Using the Mesozoic History of the Canadian Cordillera as a Case Study in Teaching Plate Tectonics.

    ERIC Educational Resources Information Center

    Chamberlain, Valerie Elaine

    1989-01-01

    Reviews a model used in the teaching of plate tectonics which includes processes and concepts related to: terranes and the amalgamation of terranes, relative plate motion and oblique subduction, the effects of continent-continent collision, changes in plate motion, plate configuration, and the type of plate boundary. Diagrams are included.…

  16. New multi-beam bathymetric map of the Ionian Sea (Central Mediterranean): Evidence for active sedimentary and morpho-tectonic processes along the Africa-Eurasia plate boundary

    NASA Astrophysics Data System (ADS)

    Gutscher, M. A.; Kopp, H.; Krastel, S.; Bohrmann, G.; Garlan, T.; Zaragosi, S.; Klaucke, I.; Wintersteller, P.; Loubrieu, B.; Le Faou, Y.; San Pedro, L.; Dominguez, S.; Rovere, M.; Mercier De Lepinay, B. F.

    2015-12-01

    A combined dataset of multi-beam bathymetry, based on 5 recent marine geophysical surveys since 2010 as well as a compilation of earlier surveys, now spans the vast majority of the Ionian Sea and the active margin of East Sicily and Calabria. (The new surveys are: R/V Meteor cruise 86, 2010 PI - S. Krastel; MocoSed R/V PourquoiPas 2012 PI - T. Garlan; Circee R/V Suroit 2013 PI - M.-A. Gutscher; R/V Meteor cruise 111, 2014 PI's - H. Kopp, M.-A. Gutscher; R/V Meteor cruise 112, 2014 PI - G. Bohrmann). This new compilation of mostly unpublished bathymetric data is presented as a 2 arc-sec (60m) grid and reveals fine-scale structures on the seafloor in unprecedented detail. These include the deeply incised Malta-Hyblean Escarpment, numerous submarine canyons, broad regions of relatively flat seafloor dominated by fields of sediment waves, the gently undulating anticlinal fold-and-thrust belts of two accretionary wedge complexes related to the Hellenic subduction (W Mediterranean ridge) and to the Calabrian arc. These accretionary wedges intersect and overlap and define two of the three sides of the triangular Ionian abyssal plain. The internal structure of these morpho-tectonic provinces as well as the transition zones between them is also imaged by high-resolution 72-channel seismic reflection profiles. Together these data offer new insights into the interaction and competition between active sedimentary and tectonic processes shaping this part of the Central Mediterranean. Acknowledgment: The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 603839 (Project ASTARTE - Assessment, Strategy and Risk Reduction for Tsunamis in Europe).

  17. The effect of plate stresses and shallow mantle temperatures on tectonics of northwestern Europe

    NASA Astrophysics Data System (ADS)

    Goes, S.; Loohuis, J. J. P.; Wortel, M. J. R.; Govers, R.

    2000-12-01

    Northwestern Europe is tectonically more active, in terms of seismicity, vertical motions and volcanism, than would be expected from its location far from any plate boundaries. In the context of the Netherlands Earth System Dynamics Initiative, we investigated the implications of two recent modeling efforts, of Eurasian plate forces and European mantle structure, for our understanding of the dynamics of these intraplate tectonics. We find that: (1) a simple balance between ridge push and collision forces along the southern European boundary does not seem sufficient to explain the observed direction of maximum horizontal compression in northwestern Europe. Our stress model, which imposes dynamical equilibrium on the full Eurasian plate, predicts that collision forces along the African-European boundary are relatively weak and have only a minor effect on the stress field in northwestern Europe; (2) seismic velocity anomalies in the shallow mantle imply 100-300°C variations in temperature under northwestern Europe. This regional mantle structure probably plays a significant role in the high level of intraplate tectonic activity and the regional variations in stress and tectonic style. For most tectonically active areas in Europe, observed surface heat flow anomalies coincide with anomalies in mantle velocity. Low velocity anomalies under northwestern Europe coincide with areas of recent volcanism and uplift, but are offset from the regions of maximum surface heat flow. This suggests that the thermal regime of the central European lithosphere is not in a steady state, probably due to changing mantle conditions. The effect of strong variations in lithospheric strength, predicted from the modeled thermal gradients in the shallow mantle, and of dynamic stresses induced by proposed active mantle upwellings may account for (some of) the differences between the observed and modeled stress field and will be investigated in future stress models.

  18. Prototypical Concepts and Misconceptions of Plate Tectonic Boundaries

    NASA Astrophysics Data System (ADS)

    Sibley, D. F.; Patino, L. C.

    2003-12-01

    Students of geology encounter many prototypical/exemplar concepts* that include representative, but not necessarily defining, features and characteristics. This study of students' prototypical representations of plate tectonic boundaries indicates that their representations are rich sources of information about their misconceptions about plate tectonics. After lectures in plate tectonics and mountain building, 353 students in a general education geology class were asked to draw a continent-continent convergent boundary. For this study, a correct answer is defined as having the major features in correct proportions as depicted in the plate boundary diagrams on the USGS web. Fifty-two percent of the drawings were either incorrect or incomplete such that they could not be interpreted. Only 48% were readily interpretable, and of these 22% drew the boundary correctly, showing a thickening of crust where two continents collide. Thirty-three percent drew the boundary showing concave slabs of continental crust as one might imagine two pieces of firm rubber pushed together on a rigid surface and 45% depicted mountains as one might imagine inverted ice cream cones on a rigid plank. Twenty-one senior class geology majors and graduate students were given the same assignment. Forty-eight percent rendered a correct drawing, whereas 38% drew the same ice cream cone on a plank type picture that 45% of the general education students drew. In a second class of 12 geology majors, only 1 student drew a cross section of a continent-ocean boundary similar to standard representation. Four of 12 drew mountains on the top of continental crust over a subduction zone but did not draw a compensating mass within the crust or lithosphere. Prototypical drawings provide more information about students' concepts than do most multiple-choice questions. For example, sixty-two percent of theses students who drew mountains similar to foam rubber pads pushed together on a desk or ice cream cones on a

  19. Plate tectonics beyond plate boundaries: the role of ancient structures in intraplate orogenesis

    NASA Astrophysics Data System (ADS)

    Heron, Philip; Pysklywec, Russell; Stephenson, Randell

    2015-04-01

    The development of orogens that occur at a distance from plate boundaries (i.e., `intraplate' deformation) cannot be adequately explained through conventional plate tectonic theory. Intraplate deformation infers a more complex argument for lithospheric and mantle interaction than plate tectonic theory allows. As a result, the origins of intraplate orogenesis are enigmatic. One hypothesis is the amalgamation of continental material (i.e., micro-plates) leaves inherent scars on the crust and mantle lithosphere. Previous studies into continent-continent collisions identify a number of scenarios from accretionary tectonics that affect the crust and mantle (namely, the development of a Rayleigh-Taylor instability, lithospheric underplating, lithospheric delamination, and lithospheric subduction). Any of these processes may weaken the lithosphere allowing episodic reactivation of faults within continental interiors. Hence, continental convergence (i.e., shortening) at a time after continental collision may cause the already weakened crust and mantle lithosphere to produce intraplate deformation. In order to better understand the processes involved in deformation away from plate boundaries, we present suites of continental shortening models (using the high-resolution thermal-mechanical modelling code SOPALE) to identify the preferred style of deformation. We model ancient structures by applying weak subduction scarring, changing the rheological conditions, and modifying the thermal structure within the lithosphere. To highlight the role of surface processes on plate and lithosphere deformation, the effect of climate-driven erosion and deposition on the tectonic structure of intraplate deformation is also addressed. We explore the relevance of the models to previously studied regions of intraplate orogenesis, including the Pyrenees in Europe, the Laramide orogen in North America, Tien Shan orogen in Central Asia, and Central Australia. The findings of the simulations with

  20. Emerging Possibilities and Insuperable Limitations of Exogeophysics: The Example of Plate Tectonics

    NASA Astrophysics Data System (ADS)

    Stamenković, Vlada; Seager, Sara

    2016-07-01

    To understand the evolution and the habitability of any rocky exoplanet demands detailed knowledge about its geophysical state and history—such as predicting the tectonic mode of a planet. Yet no astronomical observation can directly confirm or rule out the occurrence of plate tectonics on a given exoplanet. Moreover, the field of plate tectonics is still young—questioning whether we should study plate tectonics on exoplanets at this point in time. In this work, we determine the limitations and the emerging possibilities of exogeophysics, the science of connecting geophysics to exoplanets, on the example of plate tectonics. Assuming current uncertainties in model and planet parameters, we develop a qualitatively probabilistic and conservative framework to estimate on what kind of planets and where in the Galaxy plate tectonics might occur. This we achieve by modeling how plate yielding, the most critical condition needed for plate mobility and subduction, is affected by directly observable (planet mass, size) or indirectly, to some degree, assessable planet properties (structure and composition). Our framework not only highlights the importance of a planet’s chemistry for the existence of plate tectonics and the path toward practical exogeophysics but also demonstrates how exoplanet science can actually help to better understand geophysics and the fundamentals of plate tectonics on Earth itself.

  1. Plate Tectonics: From Initiation of Subduction to Global Plate Motions (Augustus Love Medal Lecture)

    NASA Astrophysics Data System (ADS)

    Gurnis, Michael

    2013-04-01

    Plates are driven by buoyancy forces distributed in the mantle, within cooling oceanic plates (ridge push) and within subducted slabs. Although the case is often made that subducted slabs provide the principle driving force on plate motion, consensus has not been achieved. This is at least partially due to the great difficulty in realistically capturing the role of slabs in observationally-constrained models as slabs act to drive and resist plate motions through their high effective viscosity. Slab buoyancy acts directly on the edge of the plate (slab pull), while inducing mantle flow that tends to drag both subducting and overriding plates toward the trench. While plates bend during subduction they undergo a form of 'plastic failure' (as evident through faulting, seismicity and reduction of flexural parameters at the outer trench wall). The birth of a new subduction zone, subduction initiation, provides important insight into plate motions and subduction dynamics. About half of all subduction zones initiated over the Cenozoic and the geophysical and geological observations of them provide first order constraints on the mechanics of how these margins evolved from their preexisting tectonic state to self-sustaining subduction. We have examples of subduction initiation at different phases of the initiation process (e.g. early versus late) as well as how margins have responded to different tectonic forcings. The consequences of subduction initiation are variable: intense trench roll back and extensive boninitic volcanism followed initiation of the Izu-Bonin-Mariana arc while both were absent during Aleutian arc initiation. Such differences may be related to the character of the preexisting plates, the size of and forces on the plates, and how the lithosphere was initially bending during initiation. I will address issues associated with the forces driving plate tectonics and initiating new subduction zones from two perspectives. A common thread is the origin and

  2. Plate Tectonics and Taiwan Orogeny based on TAIGER Experiments

    NASA Astrophysics Data System (ADS)

    Wu, F. T.; Kuochen, H.; McIntosh, K. D.

    2014-12-01

    Plate tectonics framework is usually complex in a collision zone, where continental lithosphere is involved. In the young Taiwan orogeny, with geologic understanding and large new geodetic and subsurface datasets now available an environment has been created for testing tectonic hypotheses regarding collision and orogeny. Against the background of the commonly accepted view of Taiwan as a southward propagating, self-similar 2-D orogen, a fully 3-D structure is envisaged. Along the whole length of the island the convergence of the Eurasian plate (EUP) the Philippine Sea plate (PSP) takes shape with different plate configurations. In northern Taiwan the convergence occurs with simultaneous collision of the oceanic PSP with continental EUP and the northward subduction of the PSP; in the south, EUP, in the guise of the South China Sea rifted Eurasian continent, subducts toward the east; in central Taiwan collision of oceanic PSP with continental EUP dominates. When relocated seismicity and focal mechanisms are superposed on subsurface P and Vp/Vs velocity images the configurations and the kinematics of the PSP and EUP collision and subduction become clear. While in northern Taiwan the subduction/collision explains well the high peaks and their dwindling (accompanied by crustal thinning) toward the north. In the south, mountains rise above the east-dipping EUP subduction zone as the Eurasian continental shelf veers toward the southwest, divergent from the trend of the Luzon Arc - calling into question the frequently cited arc-continent collision model of Taiwan orogeny. High velocity anomaly and Benioff seismicity coexist in the south. Going north toward Central Taiwan the high velocity anomaly persists for another 150 km or so, but it becomes seismically quiescent. Above the quiescent section the PSP and EUP collide to build the main part of the Central Range and its parallel neighbor the eastern Coastal Range. Key implications regarding orogeny include: 1) Significant

  3. Constraining Initiation and Onset Time of Plate Tectonics on Earth

    NASA Astrophysics Data System (ADS)

    Roller, G.

    2014-12-01

    The onset time for modern-style plate tectonics is still heavily debated among geoscientists. Proposed timings range from the Phanerozoic to the Hadean. Here I present a new theoretical approach to tackle this question. I combine ideas of nuclear astrophysics and geochronology and apply the concept of sudden nucleosynthesis to calculate so-called nucleogeochronometric Rhenium-Osmium model ages. Sudden nucleosynthesis has been suggested by nuclear theory [1-2] as a possible mechanism for the creation of the heavy isotopes. Hence, this concept may generally be used to identify rapid (r-) neutron-capture process events. For Earth, nucleogeochronometric model age calculations based upon published pyroxenite and komatiite data [3-5] point to an r-process event around 3 Ga. Since the r-process requires high neutron densities and temperatures within seconds, a gravitational core collapse forming at least a part of the inner core is discussed as a possible cause, thus initiating modern-style plate tectonics at that time. This age is in line with an earlier proposed value of 2.7 Ga for an inner core forming event [6], pronounced changes in the magnitude of the geomagnetic field and geological evidence like the onset of extensive plutonism and crust formation starting around the Archean-Proterozoic transition. Besides, results from nucleogeochronometric age calculations for published peridotitic pentlandites [7] lead to corrections as to their previously inconsistent model ages: These are now in good agreement with their Proterozoic 1.43 Ga isochronous regression line, supporting the model. [1] Burbidge et al. (1957) Revs. Mod. Phys. 29, 547 - 650. [2] Hoyle et al. (1960) ApJ 132, 565 - 590. [3] Reisberg et al. (1991) Earth Planet. Sci. Lett. 105, 196 - 213. [4] Roy-Barman et al. (1996) Chem. Geol. 130, 55 - 64. [5] Luck et al. (1984) Earth Planet Sci. Lett. 68, 205 - 208. [6] Hale (1987) Nature 329, 233 -237. [7] Smit et al. (2010) Geochim. Cosmochim. Acta 74, 3292 - 3306.

  4. Identifying active interplate and intraplate fault zones in the western Caribbean plate from seismic reflection data and the significance of the Pedro Bank fault zone in the tectonic history of the Nicaraguan Rise

    NASA Astrophysics Data System (ADS)

    Ott, B.; Mann, P.

    2015-12-01

    The offshore Nicaraguan Rise in the western Caribbean Sea is an approximately 500,000 km2 area of Precambrian to Late Cretaceous tectonic terranes that have been assembled during the Late Cretaceous formation of the Caribbean plate and include: 1) the Chortis block, a continental fragment; 2) the Great Arc of the Caribbean, a deformed Cretaceous arc, and 3) the Caribbean large igneous province formed in late Cretaceous time. Middle Eocene to Recent eastward motion of the Caribbean plate has been largely controlled by strike-slip faulting along the northern Caribbean plate boundary zone that bounds the northern margin of the Nicaraguan Rise. These faults reactivate older rift structures near the island of Jamaica and form the transtensional basins of the Honduran Borderlands near Honduras. Recent GPS studies suggest that small amount of intraplate motion within the current margin of error of GPS measurements (1-3 mm/yr) may occur within the center of the western Caribbean plate at the Pedro Bank fault zone and Hess Escarpment. This study uses a database of over 54,000 km of modern and vintage 2D seismic data, combined with earthquake data and results from previous GPS studies to define the active areas of inter- and intraplate fault zones in the western Caribbean. Intraplate deformation occurs along the 700-km-long Pedro Bank fault zone that traverses the center of the Nicaraguan Rise and reactivates the paleo suture zone between the Great Arc of the Caribbean and the Caribbean large igneous province. The Pedro Bank fault zone also drives active extension at the 200-km-long San Andres rift along the southwest margin of the Nicaraguan Rise. Influence of the Cocos Ridge indentor may be contributing to reactivation of faulting along the southwesternmost, active segment of the Hess Escarpment.

  5. Structures in the Deep Mantle: Implications for the Onset of Plate Tectonics and the Viscosity Structure

    NASA Astrophysics Data System (ADS)

    Stein, Claudia; Hansen, Ulrich

    2016-04-01

    Recently deep structures have been studied intensively. The observed large anomalies with reduced seismic velocities (LLSVPs) beneath Africa and the Pacific are obtained in numerical models as an initial dense layer at the core-mantle boundary (CMB) is pushed up to piles by the convective flow (e.g., McNamara et al., EPSL 229, 1-9, 2010). Adding a dense CMB layer to a model featuring active plate tectonics, Trim et al. (EPSL 405, 1-14, 2014) find that surface mobility is strongly hindered by the dense material and can even vanish completely for a CMB layer that has a too high density or too large a volume. In a further study we employed a fully rheological model in which oceanic plates form self-consistently. We observe that an initial dense CMB layer strongly affects the formation of plates and therefore the onset time of plate tectonics. In a systematic 2D parameter study of thermochemical convection we discuss the resulting viscosity structure and time of plate initiation.

  6. Tsunamis from Tectonic Sources along Caribbean Plate Boundaries

    NASA Astrophysics Data System (ADS)

    Lopez, A. M.; Chacon, S.; Zamora, N.; Audemard, F. A.; Dondin, F. J. Y.; Clouard, V.; Løvholt, F.; Harbitz, C. B.; Vanacore, E. A.; Huerfano Moreno, V. A.

    2015-12-01

    The Working Group 2 (WG2) of the Intergovernmental Coordination Group for the Tsunami and Other Coastal Hazards Warning System for the Caribbean and Adjacent Regions (ICG/CARIBE-EWS) in charge of Tsunami Hazards Assessment, has generated a list of tsunami sources for the Caribbean region. Simulating these worst-case, most credible scenarios would provide an estimate of the resulting effects on coastal areas within the Caribbean. In the past few years, several publications have addressed this issue resulting in a collection of potential tsunami sources and scenarios. These publications come from a wide variety of sources; from government agencies to academic institutions. Although these provide the scientific community with a list of sources and scenarios, it was the interest of the WG2 to evaluate what has been proposed and develop a comprehensive list of sources, therefore leaving aside proposed scenarios. The seismo-tectonics experts of the Caribbean within the WG2 members were tasked to evaluate comprehensively which published sources are credible, worst-cases, and consider other sources that have been omitted from available reports. Among these published sources are the GEM Faulted Earth Subduction Characterization Project, and the LANTEX/Caribe Wave annual exercise publications (2009-2015). Caribbean tectonic features capable of generating tsunamis from seismic dislocation are located along the Northeastern Caribbean, the Lesser Antilles Trench, and the Panamá and Southern Caribbean Deformed Belts. The proposed sources have been evaluated based on historical and instrumental seismicity as well as geological and geophysical studies. This paper presents the sources and their justification as most-probable tsunami sources based on the context of crustal deformation due to Caribbean plate interacting with neighboring North and South America plates. Simulations of these sources is part of a subsequent phase in which effects of these tectonically induced tsunamis

  7. Grain-damage hysteresis and plate tectonic states

    NASA Astrophysics Data System (ADS)

    Bercovici, David; Ricard, Yanick

    2016-04-01

    Shear localization in the lithosphere is an essential ingredient for understanding how and why plate tectonics is generated from mantle convection on terrestrial planets. The theoretical model for grain-damage and pinning in two-phase polycrystalline rocks provides a frame-work for understanding lithospheric shear weakening and plate-generation, and is consistent with laboratory and field observations of mylonites. Grain size evolves through the competition between coarsening, which drives grain-growth, and damage, which drives grain reduction. The interface between crystalline phases controls Zener pinning, which impedes grain growth. Damage to the interface enhances the Zener pinning effect, which then reduces grain-size, forcing the rheology into the grain-size-dependent diffusion creep regime. This process thus allows damage and rheological weakening to co-exist, providing a necessary positive self-weakening feedback. Moreover, because pinning inhibits grain-growth it promotes shear-zone longevity and plate-boundary inheritance. However, the suppression of interface damage at low interface curvature (wherein inter-grain mixing is inefficient and other energy sinks of deformational work are potentially more facile) causes a hysteresis effect, in which three possible equilibrium grain-sizes for a given stress coexist: (1) a stable, large-grain, weakly-deforming state, (2) a stable, small-grain, rapidly-deforming state analogous to ultramylonites, and (3) an unstable, intermediate grain-size state perhaps comparable to protomylonites. A comparison of the model to field data suggests that shear-localized zones of small-grain mylonites and ultra-mylonites exist at a lower stress than the co-existing large-grain porphyroclasts, rather than, as predicted by paleopiezometers or paleowattmeters, at a much higher stress; this interpretation of field data thus allows localization to relieve instead of accumulate stress. The model also predicts that a lithosphere that

  8. Plate tectonics on the Earth triggered by plume-induced subduction initiation.

    PubMed

    Gerya, T V; Stern, R J; Baes, M; Sobolev, S V; Whattam, S A

    2015-11-12

    Scientific theories of how subduction and plate tectonics began on Earth--and what the tectonic structure of Earth was before this--remain enigmatic and contentious. Understanding viable scenarios for the onset of subduction and plate tectonics is hampered by the fact that subduction initiation processes must have been markedly different before the onset of global plate tectonics because most present-day subduction initiation mechanisms require acting plate forces and existing zones of lithospheric weakness, which are both consequences of plate tectonics. However, plume-induced subduction initiation could have started the first subduction zone without the help of plate tectonics. Here, we test this mechanism using high-resolution three-dimensional numerical thermomechanical modelling. We demonstrate that three key physical factors combine to trigger self-sustained subduction: (1) a strong, negatively buoyant oceanic lithosphere; (2) focused magmatic weakening and thinning of lithosphere above the plume; and (3) lubrication of the slab interface by hydrated crust. We also show that plume-induced subduction could only have been feasible in the hotter early Earth for old oceanic plates. In contrast, younger plates favoured episodic lithospheric drips rather than self-sustained subduction and global plate tectonics. PMID:26560300

  9. Plate tectonics on the Earth triggered by plume-induced subduction initiation

    NASA Astrophysics Data System (ADS)

    Gerya, T. V.; Stern, R. J.; Baes, M.; Sobolev, S. V.; Whattam, S. A.

    2015-11-01

    Scientific theories of how subduction and plate tectonics began on Earth—and what the tectonic structure of Earth was before this—remain enigmatic and contentious. Understanding viable scenarios for the onset of subduction and plate tectonics is hampered by the fact that subduction initiation processes must have been markedly different before the onset of global plate tectonics because most present-day subduction initiation mechanisms require acting plate forces and existing zones of lithospheric weakness, which are both consequences of plate tectonics. However, plume-induced subduction initiation could have started the first subduction zone without the help of plate tectonics. Here, we test this mechanism using high-resolution three-dimensional numerical thermomechanical modelling. We demonstrate that three key physical factors combine to trigger self-sustained subduction: (1) a strong, negatively buoyant oceanic lithosphere; (2) focused magmatic weakening and thinning of lithosphere above the plume; and (3) lubrication of the slab interface by hydrated crust. We also show that plume-induced subduction could only have been feasible in the hotter early Earth for old oceanic plates. In contrast, younger plates favoured episodic lithospheric drips rather than self-sustained subduction and global plate tectonics.

  10. Towards implementing plate tectonics in 3D mantle convection simulations

    NASA Astrophysics Data System (ADS)

    Bollada, Peter; Davies, Huw

    2010-05-01

    One of the great challenges in numerical mantle convection simulations is to achieve models that naturally develop plate tectonic like behaviour at the surface. In this work we are looking to achieve such models by investigating the set of models where a single consistent rheology is used for the whole model. We have started by investigating a viscoelastic rheology, related to the Oldroyd-B model from the field of polymers. The goal will be to have the parameter that controls the relaxation between elastic and viscous behaviour to depend upon temperature, pressure and strain-rate. With an appropriate choice of this dependence we have, on the near surface, high viscous/elastic regions interfaced with lower, pure viscous, regions of high strain-rate; while it also becomes more viscous at depth in the interior. In this way we hope to obtain plate like behaviour at the surface which naturally progresses to viscous convective behaviour in the interior. We have started to implement this model in the established mantle 3D finite element spherical mantle convection code TERRA (Baumgardner, 1984). Some parts of the model have been implemented as a force (to be combined with the gravitational body force) on the right hand side. The work has required us to develop and code in TERRA: (i) methods to overcome the continuity problem of the stress field stemming from the fact that the velocity field is represented by linear finite elements; (ii) new operators to handle stress and its gradients; (iii) methods to analyse plate-like behaviour at the surface (iv) the necessary functional dependence of viscosity and elastic relaxation time on temperature, strain-rate and pressure We will present the background to the work, its implementation and results.

  11. This Dynamic Planet: World map of volcanoes, earthquakes, impact craters and plate tectonics

    USGS Publications Warehouse

    Simkin, Tom; Tilling, Robert I.; Vogt, Peter R.; Kirby, Stephen H.; Kimberly, Paul; Stewart, David B.

    2006-01-01

    Our Earth is a dynamic planet, as clearly illustrated on the main map by its topography, over 1500 volcanoes, 44,000 earthquakes, and 170 impact craters. These features largely reflect the movements of Earth's major tectonic plates and many smaller plates or fragments of plates (including microplates). Volcanic eruptions and earthquakes are awe-inspiring displays of the powerful forces of nature and can be extraordinarily destructive. On average, about 60 of Earth's 550 historically active volcanoes are in eruption each year. In 2004 alone, over 160 earthquakes were magnitude 6.0 or above, some of which caused casualties and substantial damage. This map shows many of the features that have shaped--and continue to change--our dynamic planet. Most new crust forms at ocean ridge crests, is carried slowly away by plate movement, and is ultimately recycled deep into the earth--causing earthquakes and volcanism along the boundaries between moving tectonic plates. Oceans are continually opening (e.g., Red Sea, Atlantic) or closing (e.g., Mediterranean). Because continental crust is thicker and less dense than thinner, younger oceanic crust, most does not sink deep enough to be recycled, and remains largely preserved on land. Consequently, most continental bedrock is far older than the oldest oceanic bedrock. (see back of map) The earthquakes and volcanoes that mark plate boundaries are clearly shown on this map, as are craters made by impacts of extraterrestrial objects that punctuate Earth's history, some causing catastrophic ecological changes. Over geologic time, continuing plate movements, together with relentless erosion and redeposition of material, mask or obliterate traces of earlier plate-tectonic or impact processes, making the older chapters of Earth's 4,500-million-year history increasingly difficult to read. The recent activity shown on this map provides only a present-day snapshot of Earth's long history, helping to illustrate how its present surface came to

  12. Subduction controls the distribution and fragmentation of Earth’s tectonic plates.

    PubMed

    Mallard, Claire; Coltice, Nicolas; Seton, Maria; Müller, R Dietmar; Tackley, Paul J

    2016-07-01

    The theory of plate tectonics describes how the surface of Earth is split into an organized jigsaw of seven large plates of similar sizes and a population of smaller plates whose areas follow a fractal distribution. The reconstruction of global tectonics during the past 200 million years suggests that this layout is probably a long-term feature of Earth, but the forces governing it are unknown. Previous studies, primarily based on the statistical properties of plate distributions, were unable to resolve how the size of the plates is determined by the properties of the lithosphere and the underlying mantle convection. Here we demonstrate that the plate layout of Earth is produced by a dynamic feedback between mantle convection and the strength of the lithosphere. Using three-dimensional spherical models of mantle convection that self-consistently produce the plate size–frequency distribution observed for Earth, we show that subduction geometry drives the tectonic fragmentation that generates plates. The spacing between the slabs controls the layout of large plates, and the stresses caused by the bending of trenches break plates into smaller fragments. Our results explain why the fast evolution in small back-arc plates reflects the marked changes in plate motions during times of major reorganizations. Our study opens the way to using convection simulations with plate-like behaviour to unravel how global tectonics and mantle convection are dynamically connected. PMID:27309815

  13. Subduction controls the distribution and fragmentation of Earth’s tectonic plates

    NASA Astrophysics Data System (ADS)

    Mallard, Claire; Coltice, Nicolas; Seton, Maria; Müller, R. Dietmar; Tackley, Paul J.

    2016-07-01

    The theory of plate tectonics describes how the surface of Earth is split into an organized jigsaw of seven large plates of similar sizes and a population of smaller plates whose areas follow a fractal distribution. The reconstruction of global tectonics during the past 200 million years suggests that this layout is probably a long-term feature of Earth, but the forces governing it are unknown. Previous studies, primarily based on the statistical properties of plate distributions, were unable to resolve how the size of the plates is determined by the properties of the lithosphere and the underlying mantle convection. Here we demonstrate that the plate layout of Earth is produced by a dynamic feedback between mantle convection and the strength of the lithosphere. Using three-dimensional spherical models of mantle convection that self-consistently produce the plate size–frequency distribution observed for Earth, we show that subduction geometry drives the tectonic fragmentation that generates plates. The spacing between the slabs controls the layout of large plates, and the stresses caused by the bending of trenches break plates into smaller fragments. Our results explain why the fast evolution in small back-arc plates reflects the marked changes in plate motions during times of major reorganizations. Our study opens the way to using convection simulations with plate-like behaviour to unravel how global tectonics and mantle convection are dynamically connected.

  14. Plate tectonics hiati as the cause of global glaciations: 2. The late Proterozoic 'Snowball Earth'

    NASA Astrophysics Data System (ADS)

    Osmaston, M. F.

    2003-04-01

    A fundamental reappraisal of the mechanisms that drive plate tectonics has yielded the remarkable conclusion that, for at least the past 130 Ma, the principal agent has not been ridge-push or slab-pull but a CW-directed torque (probably of electromagnetic origin at the CMB) reaching the deep (>600 km, e.g.[1]) tectospheric keel of the Antarctica craton. Major changes in spreading direction marked both ends of the 122--85 Ma Cretaceous Superchron and started by forming the Ontong Java Plateau. Action of MORs as gearlike linkages has driven Africa and India CCW since Gondwana breakup and continues to drive the Pacific plate CCW. In the Arctic there is now no cratonic keel to pick up any corresponding polar torque, so northern hemisphere plate tectonics is far less active. The thesis of this contribution is that in the Neoproterozoic the lack of cratons at high latitudes would have deprived plate tectonics of this motivation, causing MORs to die (see below) and a major fall in sea-level, leading to global glaciation as outlined in Part 1 for the Huronian events. Like that seen during that first hiatus, dyke-swarm volcanism could have arisen from thermal shrinkage of the global lithosphere, providing CO2 and ash-covering that interrrupted glacial episodes. In oceanic settings this volcanism would have lowered pH and supplied Fe2+ for shallow bio-oxygenic action to deposit as BIF. My multifacet studies of the subduction process convince me that the rapid development of "flat-slab" interface profiles involves the physical removal of hanging-wall material in front of the downbend by basal subduction tectonic erosion (STE). Historically this, and its inferred ubiquity in the Archaean as the precursor to PSM (Part 1), suggests that the required subducting-plate buoyancy is thermal. Accordingly, a redesign [2] of the MOR process has incorporated the heat-containing LVZ as an integral part of the plate and luckily provides a lot more ridge-push to ensure the subduction of

  15. Shells on a Sphere: Tectonic Plate Motion and Plate Boundary Deformation

    NASA Astrophysics Data System (ADS)

    Apel, Edwin Victor, III

    Plate motion models have matured from being based only on geology and seismicity to incorporating space-based geodetic methods like GPS. I use a block modeling approach to incorporate both rigid block rotation and near-boundary elastic strain accumulation effects in a formal inversion of GPS velocities. Independent Okhotsk and Amurian microplate motions are tested using GPS velocities that constrain the plate kinematics of northeast Asia. Modeling favors scenarios with independent OKH and AMU motion, based on the application of F-test statistics. The plate-motion parameters of the independent plates are consistent with the kinematics inferred from earthquake focal mechanism solutions along their boundaries. GPS-measured velocities (15 from continuously recording stations within the stable India plate interior) geodetically constrain India plate motion, intraplate strain, and plate boundary deformation around the India plate. Dense station coverage from previously published studies allows rigorous testing of boundary parameterizations. I develop robust India plate motion parameters and see good agreement between predicted plate directions from the preferred model and the seismological data. Available GPS data in and around the Aegean region is combined and used to evaluate plate motion models, elastic plate boundary deformation and its relationship to seismogenic coupling along the Hellenic subduction zone. The A.D. 365 M ˜8.4, the A.D. 1303 M˜8 Crete suggest that portions of the plate interface must be locked. The primary focus of this study is to examine potential upper plate deformation resulting from a locked subduction interface, active hanging-wall extension, or both. I consider multiple model scenarios in an attempt to interpret the both the horizontal and vertical geodetic signals in the region and its implications for earthquake hazard assessment.

  16. Geodetic constraints on active tectonics of the Western Mediterranean: Implications for the kinematics and dynamics of the Nubia-Eurasia plate boundary zone

    NASA Astrophysics Data System (ADS)

    Vernant, Philippe; Fadil, Abdelali; Mourabit, Taoufik; Ouazar, Driss; Koulali, Achraf; Davila, Jose Martin; Garate, Jorge; McClusky, Simon; Reilinger, Robert

    2010-04-01

    We present GPS observations in Morocco and adjacent areas of Spain from 15 continuous (CGPS) and 31 survey-mode (SGPS) sites extending from the stable part of the Nubian plate to central Spain. We determine a robust velocity field for the W Mediterranean that we use to constrain models for the Iberia-Nubia plate boundary. South of the High Atlas Mountain system, GPS motions are consistent with Nubia plate motions from prior geodetic studies. We constrain shortening in the Atlas system to <1.5 mm/yr, 95% confidence level. North of the Atlas Mountains, the GPS velocities indicate Nubia motion with respect to Eurasia, but also a component of motion normal to the direction of Nubia-Eurasia motion, consisting of southward translation of the Rif Mountains in N Morocco at rates exceeding 5 mm/yr. This southward motion appears to be directly related to Miocene opening of the Alboran Sea. The Betic Mountain system north of the Alboran Sea is characterized by WNW motion with respect to Eurasia at ˜1-2 mm/yr, paralleling Nubia-Eurasia relative motion. In addition, sites located in the Betics north of the southerly moving Rif Mountains also indicate a component of southerly motion with respect to Eurasia. We interpret this as indicating that deformation associated with Nubia-Eurasia plate motion extends into the southern Betics, but also that the Betic system may be affected by the same processes that are causing southward motion of the Rif Mountains south of the Alboran Sea. Kinematic modeling indicates that plate boundary geometries that include a boundary through the Straits of Gibraltar are most compatible with the component of motion in the direction of relative plate motion, but that two additional blocks (Alboran-Rif block, Betic Mountain block), independent of both Nubia and Eurasia are needed to account for the motions of the Rif and Betic Mountains normal to the direction of relative plate motion. We speculate that the southward motions of the Alboran-Rif and Betic

  17. The Earth's Mantle Is Solid: Teachers' Misconceptions About the Earth and Plate Tectonics.

    ERIC Educational Resources Information Center

    King, Chris

    2000-01-01

    Discusses the misconceptions revealed by the teachers' answers and outlines more accurate answers and explanations based on established evidence and uses these to provide a more complete understanding of plate tectonic process and the structure of Earth. (Author/YDS)

  18. Students' mental model development during historically contextualized inquiry: how the `Tectonic Plate' metaphor impeded the process

    NASA Astrophysics Data System (ADS)

    Dolphin, Glenn; Benoit, Wendy

    2016-01-01

    At present, quality earth science education in grade school is rare, increasing the importance of post-secondary courses. Observations of post-secondary geoscience indicate students often maintain errant ideas about the earth, even after direct instruction. This qualitative case study documents model-building activities of students as they experienced classroom instruction that braids history, inquiry, and model-based-learning within the context of earth dynamics. Transcripts of students' conversations, and their written work indicate students primarily employed model accretion to enhance their mental models. Instances of accretion were descriptive, pertaining to what their model consisted of, as opposed to how it explained the target phenomenon. Participants also conflated "continent" with "tectonic plate" and had difficulty attributing elastic properties - the mechanism for earthquakes - to rocks or "plates". We assert that the documented learning difficulties resulted from use of the metaphor "tectonic plate", reinforced by other everyday experiences and meanings. We suggest students need time with new models or concepts to develop strong descriptions before developing explanations. They need concrete experiences and explicit discussions concerning mapping those experiences to concepts. Lastly, because students often apply common meanings to scientific terms, we should not ask if they understand, but ask how they understand the concept.

  19. Tectonic controls on the stratigraphic architecture and hydrocarbons systems of the Arabian Plate

    SciTech Connect

    Grabowski, G.J. Jr.; Norton, I.O.

    1995-12-31

    Arabian Platform sediments consist of major sequences separated by tectonically controlled unconformities. These tectonic events, at the plate margins, controlled the orientation and distribution of sedimentary facies on the stable platform. Eustacy and subsidence were the principle controls on the actual facies that formed.

  20. Northeast Basin and Range province active tectonics: An alternative view

    SciTech Connect

    Westaway, R. )

    1989-09-01

    Slip rates and slip vector azimuths on major active oblique normal faults are used to investigate whether circulation associated with the Yellowstone upwelling plume is driving tectonic deformation in the northeast Basin and Range province. Observed deformation is consistent with this suggestion; the plume is sheared to the southwest by motion of the North American plate. Testable predictions are made for structure and evolution of the region.

  1. Vernal Point and Plate Tectonics: Indo-Australian

    NASA Astrophysics Data System (ADS)

    Chavez C, Teodosio; Chavez-Sumarriva, Israel; Chavez S, Nadia

    2013-04-01

    A precession coordinate system (eccentricity -100Ka, obliquity -40Ka and precession -25Ka) developed by Milankovicht was the precession of the equinoxes, where the vernal point retrograde 1° every 72 years approximately and enter (0°) into the Aquarius constellation on March 20, 1940. On earth this entry was verify through: a) stability of the magnetic equator in the south central zone of Peru and in the north zone of Bolivia, b) the greater intensity of equatorial electrojet (EEJ) in Peru and Bolivia since 1940. The vernal point is a maximum conductivity sensitive axis in the EEJ given at the equinoxes. There was a relationship between the equatorial electrojet - magnetic equator - crust, and besides there was a long history of studies of coupling between earthquake-ionosphere that can be founded in the following revisions: Liperovsky et al. (1990); Gaivoronskaya (1991); Liperovsky et al. (1992); Parrot et al. (1993); Pulinets et al. (1994) and Gokhberg et al. (1995). In IUGG (2007), Cusco was propose as a prime meridian (72° W == 0°) that was parallel to the Andes; the objective was to synchronize the earth sciences phenomena (e.g. geology, geophysics, etc.). The coordinate system had the vernal point from meridian (72° W == 0°) and March 20, 1940. The retrograde movement of the vernal point was the first precessional degree (2012 = 1940 + 72); from the new prime meridian (72° W == 0°) it has obtained the opposite meridian (72° E == 180°). The first precessional degree (2012) near the meridian (72 ° E) was related to the date of April 11, 2012 where a massive earthquake of 8.6 on the Richter scale, followed by several aftershocks, one of 8.2 degrees struck Indonesia with epicenter near Banda Aceh. Five months after that date, Matthias Delescluse et.al (2012), Han Yue et.al (2012), and Fred F. Pollitz et.al, (2012), explained that the two violent earthquakes would be evidence of a break in the Indo-Australian Plate Tectonics caused earthquakes around

  2. Tertiary plate tectonics and high-pressure metamorphism in New Caledonia

    USGS Publications Warehouse

    Brothers, R.N.; Blake, M.C., Jr.

    1973-01-01

    The sialic basement of New Caledonia is a Permian-Jurassic greywacke sequence which was folded and metamorphosed to prehnite-pumpellyite or low-grade greenschist facies by the Late Jurassic. Succeeding Cretaceous-Eocene sediments unconformably overlie this basement and extend outwards onto oceanic crust. Tertiary tectonism occurred in three distinct phases. 1. (1) During the Late Eocene a nappe of peridotite was obducted onto southern New Caledonia from northeast to southwest, but without causing significant metamorphism in the underlying sialic rocks. 2. (2) Oligocene compressive thrust tectonics in the northern part of the island accompanied a major east-west subduction zone, at least 30 km wide, which is identified by an imbricate system of tectonically intruded melanges and by development of lawsonite-bearing assemblages in adjacent country rocks; this high-pressure mineralogy constituted a primary metamorphism for the Cretaceous-Eocene sedimentary pile, but was overprinted on the Mesozoic prehnite-pumpellyite metagreywackes. 3. (3) Post-Oligocene transcurrent faulting along a northwest-southeast line (the sillon) parallel to the west coast caused at least 150 km of dextral offset of the southwest frontal margin of the Eocene ultramafic nappe. At the present time, the tectonics of the southwest Pacific are related to a series of opposite facing subduction (Benioff) zones connected by transform faults extending from New Britain-Solomon Islands south through the New Hebrides to New Zealand and marking the boundary between the Australian and Pacific plates. Available geologic data from this region suggest that a similar geometry existed during the Tertiary and that the microcontinents of New Guinea, New Caledonia and New Zealand all lay along the former plate boundary which has since migrated north and east by a complex process of sea-floor spreading behind the active island arcs. ?? 1973.

  3. Ultraslow, slow, or fast spreading ridges: an interplay between plate tectonics and mantle convection

    NASA Astrophysics Data System (ADS)

    Husson, Laurent; Yamato, Philippe; Bézos, Antoine

    2015-04-01

    Oceanic spreading rates are highly variable. These variations are known to correlate to a variety of surface observables, like magmatic production, heat flow or bathymetry, which lead to classify ridges into fast and slow spreading ridges, but also as the more peculiar ultraslow spreading regime. Here we explore the dynamic relationships between spreading ridges, plate tectonics and mantle flow. For this, we first focus on the thermal signature at deeper levels that we infer from the global S-wave seismic tomography model of Debayle and Ricard (2012). We show that the thermal structure of ridges gradually departs from the half-space cooling model for slow, and above all ultraslow spreading ridges. We also infer that the sub- lithospheric mantle temperature decreases by more than 180K from fast spreading to ultraslow spreading regimes. Both observations indicate that the mantle convection pattern is increasingly altered underneath slow and ultraslow spreading ridges. We suggest that this is due to far-field tectonics on the other ends of lithospheric plates. Not only it modulates the spreading rates but it also alters the convection regime: collisions at active plate boundaries obstruct plate motion and decrease their velocities. We then test this hypothesis using a thermo-mechanical model that represents a convection cell carrying a positively buoyant continental lithosphere on top. The continent gradually drifts away from the spreading ridge, from which the oceanic lithosphere grows and cools while the continent eventually collides at the opposite side. In turn, this event drastically modifies the upper kinematic condition for the convecting mantle that evolves from a mobile lid regime to an almost stagnant lid regime. Implications on spreading ridges are prominent: heat advection is slower than thermal diffusion, which causes the oceanic lithosphere to thicken faster; the oceanic plates get compressed and destabilized by a growing number of small scale transient

  4. Tectonic escape of the Caribbean plate since the Paleocene: a consequence of the Chicxulub meteor impact?

    NASA Astrophysics Data System (ADS)

    Rangin, C.; Martinez-Reyes, J.; Crespy, A.; Zitter, T. A. C.

    2012-04-01

    The debate for Pacific exotic origin versus in situ inter American plate Atlantic origin of the Caribbean plate is active in the scientific community since decades. Independently of the origin of this plate, its fast motion towards the east at a present rate of 2cm/yr is accepted to have been initiated during the early-most Cenozoic. The Paleocene is a key period in the global evolution of Central America mainly marked also by the Chicxulub multiring meteor impact in Yucatan. We question here the genetic relationship between this impact event and the incipient tectonic escape of the Caribbean plate. The mostly recent published models suggest this impact has affected the whole crust down to the Moho, the upper mantle being rapidly and considerably uplifted. The crust was then fragmented 600km at least from the point of impact, and large circular depressions were rapidly filled by clastic sediments from Cantarell to Western Cuba via Chiapas and Belize. North of the impact, the whole Gulf of Mexico was affected by mass gravity sliding, initiated also during the Paleocene in Texas, remaining active in this basin up to present time. South of the impact, in the Caribbean plate, the Yucatan basin was rapidly opened, indicating a fast escape of the crustal material towards the unique free boundary, the paleo-Antilles subduction zone. Shear waves velocity data below the Caribbean plate suggest this crustal tectonic escape was enhanced by the fast eastward flowing mantle supporting a fragmented and stretched crust. The proposed model suggests Chicxulub impact (but also the hypothetic Beata impact) have fragmented brittle crust, then easily drifted towards the east. This could explain the Paleogene evolution of the Caribbean plate largely stretched during its early evolution. Geologically, this evolution could explain the absence of evident Paleogene oblique subduction along the Caribbean plate northern and southern margins, marked only by Mid Cretaceous dragged volcanic

  5. Ancient Tectonic and Volcanic Activity in the Tharsis Region

    NASA Astrophysics Data System (ADS)

    Werner, S. C.; Kronberg, P.; Hauber, E.; Grott, M.; Steinberger, B.; Torsvik, T. H.; Neukum, G.

    The two topographically dominating volcanic provinces on Mars are the Tharsis and the Elysium regions, situated close to the equator on the dichotomy boundary between the heavily cratered (older) highlands and the northern lowlands (about 100 degrees apart). The regions are characterized by volcanoes whose morphologies are analogous to volcanic landforms on Earth, and the huge volcanoes in the Tharsis region (Olympus Mons and Tharsis Montes) are prime examples resembling many characteristics of Hawaiian shield volcanoes. The main difference between the Martian and terrestrial volcanoes are their size and the length of the flows, possibly due to higher eruption rates, the "stationary" character of the source (no plate tectonics) and the lower gravity. The Tharsis plateau is the topographically most prominent region on Mars, and associated with an areoid high. On Earth, large geoid highs are related to longlived heterogeneities near the core-mantle boundary that are sources for large igneous provinces. The Tharsis' volcanic vent structures were active at least episodically over the past 4 billion years (based on crater count statistics), which indicates long-lived volcanic and magmatic activity. Two major groups of tectonic features are related to the Tharsis bulge: a concentric set of wrinkle ridges indicating compression radial to Tharsis,and several sets of extensional structures that radiate outward from different centers within Tharsis, indicating tension circumferential to Tharsis. No landforms imply ancient plate tectonics. Here, we present surface ages associated with volcanic and tectonic landforms with a special focus on the ancient magma-tectonic environment (see Grott et al. 2006, this volume). We will examine the long-lived volcanism and tectonic surface expressions and discuss whether Mars volcanism could represent deep mantle plumes.

  6. Using Google Earth to Explore Multiple Data Sets and Plate Tectonic Concepts

    NASA Astrophysics Data System (ADS)

    Goodell, L. P.

    2015-12-01

    Google Earth (GE) offers an engaging and dynamic environment for exploration of earth science data. While GIS software offers higher-level analytical capability, it comes with a steep learning curve and complex interface that is not easy for the novice, and in many cases the instructor, to negotiate. In contrast, the intuitive interface of GE makes it easy for students to quickly become proficient in manipulating the globe and independently exploring relationships between multiple data sets at a wide range of scales. Inquiry-based, data-rich exercises have been developed for both introductory and upper-level activities including: exploration of plate boundary characteristics and relative motion across plate boundaries; determination and comparison of short-term and long-term average plate velocities; crustal strain analysis (modeled after the UNAVCO activity); and determining earthquake epicenters, body-wave magnitudes, and focal plane solutions. Used successfully in undergraduate course settings, for TA training and for professional development programs for middle and high school teachers, the exercises use the following GE data sets (with sources) that have been collected/compiled by the author and are freely available for non-commercial use: 1) tectonic plate boundaries and plate names (Bird, 2003 model); 2) real-time earthquakes (USGS); 3) 30 years of M>=5.0 earthquakes, plotted by depth (USGS); 4) seafloor age (Mueller et al., 1997, 2008); 5) location and age data for hot spot tracks (published literature); 6) Holocene volcanoes (Smithsonian Global Volcanism Program); 7) GPS station locations with links to times series (JPL, NASA, UNAVCO); 8) short-term motion vectors derived from GPS times series; 9) long-term average motion vectors derived from plate motion models (UNAVCO plate motion calculator); 10) earthquake data sets consisting of seismic station locations and links to relevant seismograms (Rapid Earthquake Viewer, USC/IRIS/DELESE).

  7. Past and present seafloor age distributions and the temporal evolution of plate tectonic heat transport

    NASA Astrophysics Data System (ADS)

    Becker, T. W.; Conrad, C. P.; Buffett, B.; Muller, D.; Loyd, S.; Lithgow-Bertelloni, C.; Corsetti, F.

    2008-12-01

    Variations in the rates of seafloor generation and recycling have potentially far-reaching consequences for sea level, ocean chemistry and climate. A parameterized framework to describe such variations could guide the study of non-uniformitarian plate tectonic activity, but there is little agreement on the appropriate mechanical description of the surface boundary layer. A strong constraint on the statistics of oceanic convection systems comes from the preserved seafloor age distribution, and additional inferences are possible when paleo-seafloor is modeled based on plate motion reconstructions. Based on previously reconstructed seafloor ages, we recently inferred that oceanic heat flow was larger by ~15% at 60~Ma than today. This signal is mainly caused by the smaller plates that existed previously in the Pacific basin with relatively larger ridge-proximal area of young seafloor. The associated decrease in heat flow is larger than any plausible decrease due to cooling, and therefore hint at cyclic behavior in plate tectonics. We also consider area-per-age statistics for the present-day and back to 140~Ma from new paleo-age reconstructions. Using a simplified seafloor age evolution model we explore which physical parameterizations for the average behavior of the oceanic lithosphere are compatible with broad trends in the data. In particular, we show that a subduction probability based on lithospheric buoyancy ("sqrt(age)") leads to results that are comparable to, or better than, that of the probability distribution that is required to obtain the "triangular" age distribution with age-independent destruction of ocean floor. The current, near triangular distribution of ages and the relative lull in heat flow are likely only snapshots of a transient state during the Wilson cycle. Current seafloor ages still contain hints of a ≤sssim 60~Myr period, cyclic variation of seafloor production, and using paleo-ages for 140~Ma, we find a ~ 400~Myr best-fitting variation

  8. The importance of temporal stress variation and dynamic disequilibrium for the initiation of plate tectonics

    NASA Astrophysics Data System (ADS)

    Stamenković, V.; Höink, T.; Lenardic, A.

    2016-06-01

    We use 1-D thermal history models and 3-D numerical experiments to study the impact of dynamic thermal disequilibrium and large temporal variations of normal and shear stresses on the initiation of plate tectonics. Previous models that explored plate tectonics initiation from a steady state, single plate mode of convection concluded that normal stresses govern the initiation of plate tectonics, which based on our 1-D model leads to plate yielding being more likely with increasing interior heat and planet mass for a depth-dependent Byerlee yield stress. Using 3-D spherical shell mantle convection models in an episodic regime allows us to explore larger temporal stress variations than can be addressed by considering plate failure from a steady state stagnant lid configuration. The episodic models show that an increase in convective mantle shear stress at the lithospheric base initiates plate failure, which leads with our 1-D model to plate yielding being less likely with increasing interior heat and planet mass. In this out-of-equilibrium and strongly time-dependent stress scenario, the onset of lithospheric overturn events cannot be explained by boundary layer thickening and normal stresses alone. Our results indicate that in order to understand the initiation of plate tectonics, one should consider the temporal variation of stresses and dynamic disequilibrium.

  9. Plate tectonics on the early Earth: Limitations imposed by strength and buoyancy of subducted lithosphere

    NASA Astrophysics Data System (ADS)

    van Hunen, Jeroen; van den Berg, Arie P.

    2008-06-01

    The tectonic style and viability of modern plate tectonics in the early Earth is still debated. Field observations and theoretical arguments both in favor and against the uniformitarian view of plate tectonics back until the Archean continue to accumulate. Here, we present the first numerical modeling results that address for a hotter Earth the viability of subduction, one of the main requirements for plate tectonics. A hotter mantle has mainly two effects: 1) viscosity is lower, and 2) more melt is produced, which in a plate tectonic setting will lead to a thicker oceanic crust and harzburgite layer. Although compositional buoyancy resulting from these thick crust and harzburgite might be a serious limitation for subduction initiation, our modeling results show that eclogitization significantly relaxes this limitation for a developed, ongoing subduction process. Furthermore, the lower viscosity leads to more frequent slab breakoff, and sometimes to crustal separation from the mantle lithosphere. Unlike earlier propositions, not compositional buoyancy considerations, but this lithospheric weakness could be the principle limitation to the viability of plate tectonics in a hotter Earth. These results suggest a new explanation for the absence of ultrahigh-pressure metamorphism (UHPM) and blueschists in most of the Precambrian: early slabs were not too buoyant, but too weak to provide a mechanism for UHPM and exhumation.

  10. Tectonic lineaments in the cenozoic volcanics of southern Guatemala: Evidence for a broad continental plate boundary zone

    NASA Technical Reports Server (NTRS)

    Baltuck, M.; Dixon, T. H.

    1984-01-01

    The northern Caribbean plate boundary has been undergoing left lateral strike slip motion since middle Tertiary time. The western part of the boundary occurs in a complex tectonic zone in the continental crust of Guatemala and southernmost Mexico, along the Chixoy-Polochic, Motogua and possibly Jocotan-Chamelecon faults. Prominent lineaments visible in radar imagery in the Neogene volcanic belt of southern Guatemala and western El Salvador were mapped and interpreted to suggest southwest extensions of this already broad plate boundary zone. Because these extensions can be traced beneath Quaternary volcanic cover, it is thought that this newly mapped fault zone is active and is accommodating some of the strain related to motion between the North American and Caribbean plates. Onshore exposures of the Motoqua-Polochic fault systems are characterized by abundant, tectonically emplaced ultramafic rocks. A similar mode of emplacement for these off shore ultramafics, is suggested.

  11. Tectonic signatures on active margins

    NASA Astrophysics Data System (ADS)

    Hogarth, Leah Jolynn

    High-resolution Compressed High-Intensity Radar Pulse (CHIRP) surveys offshore of La Jolla in southern California and the Eel River in northern California provide the opportunity to investigate the role of tectonics in the formation of stratigraphic architecture and margin morphology. Both study sites are characterized by shore-parallel tectonic deformation, which is largely observed in the structure of the prominent angular unconformity interpreted as the transgressive surface. Based on stratal geometry and acoustic character, we identify three sedimentary sequences offshore of La Jolla: an acoustically laminated estuarine unit deposited during early transgression, an infilling or "healing-phase" unit formed during the transgression, and an upper transparent unit. The estuarine unit is confined to the canyon edges in what may have been embayments during the last sea-level rise. The healing-phase unit appears to infill rough areas on the transgressive surface that may be related to relict fault structures. The upper transparent unit is largely controlled by long-wavelength tectonic deformation due to the Rose Canyon Fault. This unit is also characterized by a mid-shelf (˜40 m water depth) thickness high, which is likely a result of hydrodynamic forces and sediment grain size. On the Eel margin, we observe three distinct facies: a seaward-thinning unit truncated by the transgressive surface, a healing-phase unit confined to the edges of a broad structural high, and a highly laminated upper unit. The seaward-thinning wedge of sediment below the transgressive surface is marked by a number of channels that we interpret as distributary channels based on their morphology. Regional divergence of the sequence boundary and transgressive surface with up to ˜8 m of sediment preserved across the interfluves suggests the formation of subaerial accommodation during the lowstand. The healing-phase, much like that in southern California, appears to infill rough areas in the

  12. Ophiolitic Chromitites from the Andriamena Greenstone Belt, Madagascar: Possible Evidence for mid-Archean Plate Tectonics

    NASA Astrophysics Data System (ADS)

    Reisberg, L. C.; Ohnenstetter, M.; Zimmermann, C.; Ratefiarimino, A.; Levy, D.

    2015-12-01

    . 186Os/188Os measurements are in progress. If the ophiolitic nature of the chromitites is confirmed, our results might imply that geodynamic mechanisms similar to present-day plate tectonic processes may already have been active in the mid-Archean Earth.

  13. Playing jigsaw with large igneous provinces - a plate-tectonic reconstruction of Ontong Java Nui

    NASA Astrophysics Data System (ADS)

    Hochmuth, Katharina; Gohl, Karsten; Uenzelmann-Neben, Gabriele; Werner, Reinhard

    2015-04-01

    Ontong Java Nui is a Cretaceous large igneous province (LIP), which was rifted apart into various smaller plateaus shortly after its emplacement around 125 Ma in the central Pacific. It incorporated the Ontong Java Plateau, the Hikurangi Plateau and the Manihiki Plateau as well as multiple smaller fragments, which have been subducted. Its size has been estimated to be approximately 0.8% of the Earth's surface. A volcanic edifice of this size has potentially had a great impact on the environment such as its CO2 release. The break-up of the "Super"-LIP is poorly constrained, because the break-up and subsequent seafloor spreading occurred within the Cretaceous Quiet Period. The Manihiki Plateau is presumably the centerpiece of this "Super"-LIP and shows by its margins and internal fragmentation that its tectonic and volcanic activity is related to the break-up of Ontong Java Nui. By incorporating two new seismic refraction/wide-angle reflection lines across two of the main sub-plateaus of the Manihiki Plateau, we can classify the break-up modes of the individual margins of the Manihiki Plateau. The Western Plateaus experienced crustal stretching due to the westward motion of the Ontong Java Plateau. The High Plateau shows sharp strike-slip movements at its eastern boundary towards an earlier part of Ontong Java Nui, which is has been subducted, and a rifted margin with a strong volcanic overprint at its southern edges towards the Hikurangi Plateau. These observations allow us a re-examination of the conjugate margins of the Hikurangi Plateau and the Ontong Java Plateau. The repositioning of the different plateaus leads to the conclusion that Ontong Java Nui was larger (~1.2% of the Earth's surface at emplacement) than previously anticipated. We use these finding to improve the plate tectonic reconstruction of the Cretaceous Pacific and to illuminate the role of the LIPs within the plate tectonic circuit in the western and central Pacific.

  14. Models of convection-driven tectonic plates - A comparison of methods and results

    NASA Technical Reports Server (NTRS)

    King, Scott D.; Gable, Carl W.; Weinstein, Stuart A.

    1992-01-01

    Recent numerical studies of convection in the earth's mantle have included various features of plate tectonics. This paper describes three methods of modeling plates: through material properties, through force balance, and through a thin power-law sheet approximation. The results obtained are compared using each method on a series of simple calculations. From these results, scaling relations between the different parameterizations are developed. While each method produces different degrees of deformation within the surface plate, the surface heat flux and average plate velocity agree to within a few percent. The main results are not dependent upon the plate modeling method and herefore are representative of the physical system modeled.

  15. Modeling the Philippine Mobile Belt: Tectonic blocks in a deforming plate boundary zone

    NASA Astrophysics Data System (ADS)

    Galgana, G. A.; Hamburger, M. W.; McCaffrey, R.; Bacolcol, T. C.; Aurelio, M. A.

    2007-12-01

    The Philippine Mobile Belt, a seismically active, rapidly deforming plate boundary zone situated along the convergent Philippine Sea/Eurasian plate boundary, is examined using geodetic and seismological data. Oblique convergence between the Philippine Sea Plate and the Eurasian plate is accommodated by nearly orthogonal subduction along the Philippine Trench and the Manila Trench, as well as by strike-slip faulting along the Philippine Fault system. We develop a model of active plate boundary deformation in this region, using elastic block models constrained by known fault geometries, published GPS observations and focal mechanism solutions. We then present an estimate of block rotations, fault coupling, and intra-block deformation, based on the best-fit model that minimizes the misfit between observed and predicted geodetic vectors and earthquake slip vectors. Slip rates along the Philippine fault vary from ~22 - 36 mm/yr in the Central Visayas and about 10 to 40 mm/yr in Luzon, trending almost parallel to the fault trace. In northern Luzon, Philippine Fault splays accommodate transpressional strain. The Central Visayas block experiences convergence with the Sundaland block along the Negros Trench and the Mindoro-Palawan collision zone. On the eastern side of Central Visayas, sinistral strike-slip faulting occurs along the NNW-SSE-trending Philippine Fault. Mindanao Island in southern Philippines is dominated by east-verging subduction along the Cotabato Trench, and strain partitioning (strike- slip faulting with west-verging subduction) in eastern Mindanao along the southern Philippine Fault and Philippine Trench, respectively. Oblique active sinistral strike slip faults in Central and Eastern Mindanao that were hypothesized to be responsible for basin formation are obvious boundaries for tectonic blocks. Located south of Mindanao Island we define an adjoining oceanic block defined by the N-S trending complex dual subduction zone of Sangihe and Halmahera

  16. Seismic Probing of the Base of a Tectonic Plate from Subduction Zone to Trench Outer Rise: Hikurangi Margin, New Zealand

    NASA Astrophysics Data System (ADS)

    Louie, J. N.; Kent, G. M.; Lamb, S. H.; Savage, M. K.; Stern, T. A.; Stratford, W. R.

    2015-12-01

    The nature of the base of a tectonic plate (LAB) is the 3rd dimension of plate tectonics. Recent seismic studies of the LAB have revealed planar features that show very different characteristics. In the oceans, the top of the S-wave low velocity zone shows a systematic deepening with plate age that fits plate-cooling models. However, the change in radial anisotropy has a markedly constant depth of ~70 km, regardless of plate age. A recent land-based study (SAHKE 2) of the subducted Pacific Plate in the southern Hikurangi margin has imaged a pair of distinct reflectors defining a ~10 km thick channel parallel to and ~70 km below the top of the ~15° dipping plate. Low velocities indicate that the channel is a zone of partial melt or high volatile content, acting as a weak base to the plate. Receiver function studies along the Japan margin have also imaged layers at these depths, parallel to the top of the plate and dipping up to 45°. We propose probing the base of the tectonic plate by tracing potential LAB seismic reflectors from their dipping portions in the subduction zone to where they bend in the trench outer rise. If the seismically identified boundary represents a 'frozen-in' feature, created at the mid ocean ridge, then it will remain parallel to the top of the plate, and its nature will remain unchanged as it is tracked over the outer rise. Alternatively, if the base of the plate is a thin channel of partial melt, then one would expect thickening of the channel beneath the outer rise due to melt ponding in the core of the flexure; this melt ponding may be the source of volcanic activity. A 500-km survey will trace the Pacific plate LAB from the subduction zone into the trench outer rise. The deeper part of the line coincides with the part of the plate where the ~10 km thick 'melt' channel was clearly imaged with the SAHKE 2 experiment. We show with synthetic experiments that given seismic energy scatter and attenuation comparable to that observed in the

  17. Tectonic-volcanic discontinuity at latitude 27° south Andean Range, associated with Nazca Plate Subduction

    NASA Astrophysics Data System (ADS)

    Gonzalez-Ferran, O.; Baker, P. E.; Rex, D. C.

    1985-03-01

    The area investigated lies between latitude 26°40' and 27°15' south and longitude 69°30' and 68°30' west in the Andean Range. A combination of K-Ar dating, petrology, geochemistry and geophysical data has led to the recognition of an important change in the tectonic control of volcanic activity during the early Pliocene. Five volcanic cycles are recognized and grouped into two units according to tectonic control. The first unit comprises the following cycles; (a) La Coipa-Maricunga 23.0-15.7 Ma; (b) Pastillito 13.9-12.9 Ma; and (c) Wheelwright 8.84-6.14 Ma; representing a progression of active belts, striking N5°E, towards the east. The second group is represented by Pen¯as Biancas 4.90-2.64 Ma and Ojos del Salado 1.84-Recent (active) having a N65°E strike, extending over a distance of some 250 km in the high Andes. The volcanic rocks of both groups belong to the calc-alkali series ranging from andesitic basalt to andesite, dacite and rhyolite, though with significant variations in total alkali content. Changes in the orientation of the volcanic belt may be related to changes in the spreading rate of the Nazca Plate or to changes in the angle of subduction on either side of latitude 27°S i.e. along the latitude of the Easter Hot Line.

  18. Constraints on plate tectonics initiation from scaling laws for single-cell convection

    NASA Astrophysics Data System (ADS)

    Wong, Teresa; Solomatov, Viatcheslav S.

    2016-08-01

    The Earth is the only planet known to have plate tectonics, while other planets are covered with a stagnant lid. On the Earth, the initiation of subduction, which is thought to be the fundamental process for plate tectonics initiation, is caused not only by the negative buoyancy of the lithosphere but also by the forces from plate motions. However, for planets which do not have plate tectonics, the very first episode of lithospheric failure has to be caused by forces other than plate motions. Sublithospheric convection has been proposed as a possible mechanism that provides lithospheric instability through inducing stresses in the lithosphere, and lithospheric failure can occur when the yield stress is below a critical value. We test the applicability of scaling laws for the critical yield stress obtained in single-cell convection simulations to strongly time-dependent multi-cell systems. We show that with an appropriate choice of characteristic aspect ratio for the convective system, the scaling laws from single-cell simulations can be used to evaluate the conditions on the terrestrial planets in the inner Solar System for plate tectonics to exist. In agreement with previous studies, the estimated values for critical yield stress and coefficient of friction are much lower than the expected values for the Earth's lithosphere.

  19. Plate tectonic models derived from multiple data sources: Examples from the Arctic

    NASA Astrophysics Data System (ADS)

    Webb, Peter; Masterton, Sheona; Eue, Dorothea

    2013-04-01

    Plate tectonic reconstructions are a useful tool in the modern exploration industry. A variety of interpretative applications and data sets require robust plate models; specific examples include the rotation of well data to their past locations, analysis of palaeogeographic environments and predictions of properties such as heat flux through time. As plate tectonic reconstructions become more widely used they become more ambitious, pushing further back in time and including older stratigraphic units, often with increasingly complex tectonic histories. Geological data becomes increasingly sparse for these older units, leading to more subjective choices when creating plate models. In our global plate tectonic model we collate data from numerous sources, including geological structure mapping, interpretation and analysis of potential field data and depth to basement maps, palaeomagnetism and geological relationships from published literature. The plate model is strongly interlinked with on-going global studies at Getech, such as palaeoenvironment mapping, palaeotopography and palaeoclimate; direct feedback from these studies is used to refine and test tectonic solutions both within a regional and global framework. Our global plate model is currently undergoing major improvements extending it back to the start of the Permian (300 Ma). This includes updates to oceanic structures and ocean-continent boundaries to better constrain the internal boundaries and fit of the Pangaea supercontinent. The update also includes Permian-Triassic modelling of South East Asia and China, improvements in Kazakhstan, Central Asia and the North American Cordillera and a re-evaluation of our existing Arctic tectonics. These regions also contain feedback from Jurassic palaeoenvironment mapping to improve the current tectonic reconstructions. We present the multi-disciplinary approach to plate modelling with particular focus on North America and the Arctic. Numerous and often conflicting

  20. Episodic tectonic plate reorganizations driven by mantle convection

    NASA Astrophysics Data System (ADS)

    King, Scott D.; Lowman, Julian P.; Gable, Carl W.

    2002-10-01

    Periods of relatively uniform plate motion were interrupted several times throughout the Cenozoic and Mesozoic by rapid plate reorganization events [R. Hey, Geol. Soc. Am. Bull. 88 (1977) 1404-1420; P.A. Rona, E.S. Richardson, Earth Planet. Sci. Lett. 40 (1978) 1-11; D.C. Engebretson, A. Cox, R.G. Gordon, Geol. Soc. Am. Spec. Pap. 206 (1985); R.G. Gordon, D.M. Jurdy, J. Geophys. Res. 91 (1986) 12389-12406; D.A. Clague, G.B. Dalrymple, US Geol. Surv. Prof. Pap. 1350 (1987) 5-54; J.M. Stock, P. Molnar, Nature 325 (1987) 495-499; C. Lithgow-Bertelloni, M.A. Richards, Geophys. Res. Lett. 22 (1995) 1317-1320; M.A. Richards, C. Lithgow-Bertelloni, Earth Planet. Sci. Lett. 137 (1996) 19-27; C. Lithgow-Bertelloni, M.A. Richards, Rev. Geophys. 36 (1998) 27-78]. It has been proposed that changes in plate boundary forces are responsible for these events [M.A. Richards, C. Lithgow-Bertelloni, Earth Planet. Sci. Lett. 137 (1996) 19-27; C. Lithgow-Bertelloni, M.A. Richards, Rev. Geophys. 36 (1998) 27-78]. We present an alternative hypothesis: convection-driven plate motions are intrinsically unstable due to a buoyant instability that develops as a result of the influence of plates on an internally heated mantle. This instability, which has not been described before, is responsible for episodic reorganizations of plate motion. Numerical mantle convection experiments demonstrate that high-Rayleigh number convection with internal heating and surface plates is sufficient to induce plate reorganization events, changes in plate boundary forces, or plate geometry, are not required.

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

    SciTech Connect

    Zholtayev, G. )

    1994-07-01

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

  2. Predicting earthquakes along the major plate tectonic boundaries in the Pacific

    USGS Publications Warehouse

    Spall, H.

    1978-01-01

    In an article in the last issue of the Earthquake Information Bulletin ("Earthquakes and Plate Tectonics," by Henry Spall), we saw how 90 percent of the world's earthquakes occur at the margins of the Earth's major crustal plates. however, when we look at the distribution of earthquakes in detail, we see that a number of nearly aseismic regions, or seismic gaps, can be found along the present-day plate boundaries. Why is this? And can we regard these areas as being more likely to be the sites for future larger earthquakes than those segments of the plate boundaries that have ruptured recently. 

  3. Neogene Caribbean plate rotation and associated Central American tectonic evolution

    NASA Technical Reports Server (NTRS)

    Wadge, G.; Burke, K.

    1983-01-01

    A theoretical model of the opening of the Cayman Trough is developed on the basis of geological evidence from a wide area. It is proposed that strike slip motion began about 30 Myr ago and proceeded at a rate of 37 + or - 6 mm/yr for a total of 1100 km of relative plate displacement, and that Central America Underwent an anticlockwise rotation with internal plate deformation. Maps of the reconstructed motion are provided.

  4. Plate-tectonic evolution of the western U.S.A.

    USGS Publications Warehouse

    Hamilton, W.

    1987-01-01

    Changing interactions of lithospheric plates provide the framework for this review of the 3100 m.y. geological history of some 3 million km2 of mountains, deserts, plateaux and plains. The Precambrian to Neogene development of the western U.S.A. is outlined in terms of plate collisions, subduction events and deformation of lithospheric slabs, with some interpretations based on SE Asia and other regions of complex tectonics.-R.A.H.

  5. Tectonics of the Nazca-Antarctic plate boundary

    NASA Technical Reports Server (NTRS)

    Anderson-Fontana, Sandra; Larson, Roger L.; Engeln, Joseph F.; Lundgren, Paul; Stein, Seth

    1987-01-01

    A new bathymetric chart of part of the Chile transform system is constructed, based mainly on an R/V Endeavor survey from 100 deg W to its intersection with the East Ridge of the Juan Fernandez microplate. A generally continuous lineated trend can be followed through the entire region, with the transform valley being relatively narrow and well-defined from 109 deg W to approximately 104 deg 30 min W. The fracture zone then widens to the east, with at least two probable en echelon offsets to the south at 104 deg and 102 deg W. Six new strike-slip mechanisms along the Chile Transform and one normal fault mechanism near the northern end of the Chile Rise, inverted together with other plate-motion data from the eastern portion of the boundary, produce a new best-fit Euler pole for the Nazca-Antarctic plate pair, providing tighter constraints on the relative plate motions.

  6. A diffuse plate boundary model for Indian Ocean tectonics

    NASA Technical Reports Server (NTRS)

    Wiens, D. A.; Demets, C.; Gordon, R. G.; Stein, S.; Argus, D.

    1985-01-01

    It is suggested that motion along the virtually aseismic Owen fracture zone is negligible, so that Arabia and India are contained within a single Indo-Arabian plate divided from the Australian plate by a diffuse boundary. The boundary is a zone of concentrated seismicity and deformation commonly characterized as 'intraplate'. The rotation vector of Australia relative to Indo-Arabia is consistent with the seismologically observed 2 cm/yr of left-lateral strike-slip along the Ninetyeast Ridge, north-south compression in the Central Indian Ocean, and the north-south extension near Chagos.

  7. Pacific Rim and Pacific Plate Tectonism Associated With the Hawaiian Emperor Bend

    NASA Astrophysics Data System (ADS)

    Sterling, A.; Kroenke, L. W.; Wessel, P.; Harada, Y.

    2002-12-01

    Widespread Pacific Rim and Pacific plate tectonism both appear to be closely associated with a pronounced change in Pacific absolute plate motion (APM) that occurred about 43 Ma as revealed by the Hawaiian Emperor Bend. In the Western Pacific prior to the change, as the Pacific plate moved toward the north, Proto Izu -- Bonin -- Mariana (IBM) subduction was already occurring by 49 Ma, perhaps as early as 52 Ma near the northern end of the Proto IBM, evidenced by the emplacement of boninites in the forearc (Cosca et al., 1998). If the Philippine Basin -- Pacific plate circuit is traced though the Coral Sea basin after closing the Ayu and Sorel troughs, it is evident that the alignment of the Proto IBM (Kyushu -- Palau) subduction zone roughly paralleled the Pacific APM during the initiation of subduction. At ~ 43 Ma, Proto-IBM Trench subduction rapidly increased, possibly causing the major change in Pacific (and Australia) APM that produced the prominent bend in the Hawaiian-Emperor chain. This change also produced a the minor bend in the Louisville chain, as the Pacific plate began to move west-northwestward, as well as at least five more noticeable bends in other seamount chains across the Central Pacific. In the Northeastern Pacific, the expansive magmatic activity, which occurred during the early stage of Aleutian Arc growth between 55--50 Ma, began to wane between 45 and 40 Ma (Scholl et al., 1987). After the 43 Ma change in Pacific APM, the Aleutian subduction zone began to accommodate dextral slip at its western end, as well as continuing convergence at its eastern end. To the south, in the Eastern Pacific, Ridge propagation began about 43 Ma both north and south of the Murray FZ (extending southward to the Clarion FZ). Much farther to the south, changes are also apparent in the Pacific -- Antarctic spreading pattern at ~43 Ma. In the Central Pacific, following the 43 Ma change in Pacific plate motion, intraplate subduction began along the Manus -- North

  8. Plate tectonics of the Red Sea and East Africa.

    PubMed

    McKenzie, D P; Davies, D; Molnar, P

    1970-04-18

    The relative motion between the plates on each side of the East African Rift Valley can be obtained from the opening of the Red Sea and the Gulf of Aden. The calculated direction of relative motion agrees well with fault plane solutions for earthquakes north of the equator. PMID:16057189

  9. Seismicity and plate tectonics in south central Alaska

    NASA Technical Reports Server (NTRS)

    Van Wormer, J. D.; Davies, J.; Gedney, L.

    1974-01-01

    Hypocenter distribution shows that the Benioff zone associated with the Aleutian arc terminates in interior Alaska some 75 km north of the Denali fault. There appears to be a break in the subducting Pacific plate in the Yentna River-Prince William Sound area which separates two seismically independent blocks, similar to the segmented structure reported for the central Aleutian arc.

  10. Early impact basins and the onset of plate tectonics. Ph.D. Thesis - Maryland Univ.

    NASA Technical Reports Server (NTRS)

    Frey, H.

    1977-01-01

    The fundamental crustal dichotomy of the Earth (high and low density crust) was established nearly 4 billion years ago. Therefore, subductable crust was concentrated at the surface of the Earth very early in its history, making possible an early onset for plate tectonics. Simple thermal history calculations spanning 1 billion years show that the basin forming impact thins the lithosphere by at least 25%, and increases the sublithosphere thermal gradients by roughly 20%. The corresponding increase in convective heat transport, combined with the highly fractured nature of the thinned basin lithosphere, suggest that lithospheric breakup or rifting occurred shortly after the formation of the basins. Conditions appropriate for early rifting persisted from some 100,000,000 years following impact. We suggest a very early stage of high temperature, fast spreading "microplate" tectonics, originating before 3.5 billion years ago, and gradually stabilizing over the Archaean into more modern large plate or Wilson Cycle tectonics.

  11. Introduction of the Concepts of Plate Tectonics into Secondary-School Earth Science Textbooks.

    ERIC Educational Resources Information Center

    Glenn, William Harold

    1992-01-01

    Secondary school earth-science textbooks in print from 1960 through 1979 were examined to determine how rapidly concepts of plate tectonics were incorporated into those texts during the period when scientists' views about these concepts were evolving most rapidly. Suggests that delays were probably due to an unwillingness to engage in speculation…

  12. Jules Verne Voyager, Jr: An Interactive Map Tool for Teaching Plate Tectonics

    NASA Astrophysics Data System (ADS)

    Hamburger, M. W.; Meertens, C. M.

    2010-12-01

    simultaneously and does not require any special software installation on users' systems. In addition, a javascript-based educational interface, dubbed "Exploring our Dynamic Planet", incorporates the map tool, explanatory material, background scientific material, and curricular activities that encourage users to explore Earth processes using the Jules Verne Voyager, Jr. tool. Exploring our Dynamic Planet can be viewed at http://www.dpc.ucar.edu/VoyagerJr/. Because of its flexibility, the map utilities can be used for hands-on exercises exploring plate interaction in a range of academic settings, from high school science classes to entry-level undergraduate to graduate-level tectonics courses.

  13. A seismic reflection image for the base of a tectonic plate.

    PubMed

    Stern, T A; Henrys, S A; Okaya, D; Louie, J N; Savage, M K; Lamb, S; Sato, H; Sutherland, R; Iwasaki, T

    2015-02-01

    Plate tectonics successfully describes the surface of Earth as a mosaic of moving lithospheric plates. But it is not clear what happens at the base of the plates, the lithosphere-asthenosphere boundary (LAB). The LAB has been well imaged with converted teleseismic waves, whose 10-40-kilometre wavelength controls the structural resolution. Here we use explosion-generated seismic waves (of about 0.5-kilometre wavelength) to form a high-resolution image for the base of an oceanic plate that is subducting beneath North Island, New Zealand. Our 80-kilometre-wide image is based on P-wave reflections and shows an approximately 15° dipping, abrupt, seismic wave-speed transition (less than 1 kilometre thick) at a depth of about 100 kilometres. The boundary is parallel to the top of the plate and seismic attributes indicate a P-wave speed decrease of at least 8 ± 3 per cent across it. A parallel reflection event approximately 10 kilometres deeper shows that the decrease in P-wave speed is confined to a channel at the base of the plate, which we interpret as a sheared zone of ponded partial melts or volatiles. This is independent, high-resolution evidence for a low-viscosity channel at the LAB that decouples plates from mantle flow beneath, and allows plate tectonics to work. PMID:25653000

  14. The dynamics of plate tectonics and mantle flow: from local to global scales.

    PubMed

    Stadler, Georg; Gurnis, Michael; Burstedde, Carsten; Wilcox, Lucas C; Alisic, Laura; Ghattas, Omar

    2010-08-27

    Plate tectonics is regulated by driving and resisting forces concentrated at plate boundaries, but observationally constrained high-resolution models of global mantle flow remain a computational challenge. We capitalized on advances in adaptive mesh refinement algorithms on parallel computers to simulate global mantle flow by incorporating plate motions, with individual plate margins resolved down to a scale of 1 kilometer. Back-arc extension and slab rollback are emergent consequences of slab descent in the upper mantle. Cold thermal anomalies within the lower mantle couple into oceanic plates through narrow high-viscosity slabs, altering the velocity of oceanic plates. Viscous dissipation within the bending lithosphere at trenches amounts to approximately 5 to 20% of the total dissipation through the entire lithosphere and mantle. PMID:20798311

  15. A model of convergent plate margins based on the recent tectonics of Shikoku, Japan

    NASA Technical Reports Server (NTRS)

    Bischke, R. E.

    1974-01-01

    A viscoelastic finite element plate tectonic model is applied to displacement data for the island of Shikoku, Japan. The flow properties and geometry of the upper portions of the earth are assumed known from geophysical evidence, and the loading characteristics are determined from the model. The nature of the forces acting on the Philippine Sea plate, particularly in the vicinity of the Nankai trough, is determined. Seismic displacement data related to the 1946 Nankaido earthquake are modeled in terms of a thick elastic plate overlying a fluidlike substratum. The sequence of preseismic and seismic displacements can be explained in terms of two independent processes operating on elastic lithospheric plates: a strain accumulation process caused by vertical downward forces acting on or within the lithosphere in the vicinity of the trench, and a strain release process caused by plate failure along a preexisting zone on weakness. This is a restatement of Reid's elastic rebound theory in terms of elastic lithospheric plates.

  16. Stress in the lithosphere from non-tectonic loads with implications for plate boundary processes

    NASA Astrophysics Data System (ADS)

    Luttrell, Karen Marie

    Stress in the lithosphere from non-tectonic loads is calculated, making use of semi-analytic Fourier models. Sources of non-tectonic stress include coastal lithospheric bending in response to the rise in eustatic sea level since the Last Glacial Maximum, lithospheric rebound and pore pressure changes in response to the intermittent load of Ancient Lake Cahuilla in the Salton trough, stress sustained through the formation and long-term support of local short-wavelength topography, and topography created by the ejecta debris from impact craters on the surface of the icy Galilean satellites. Stresses from time varying surface water loads are calculated along major plate boundaries globally to determine to what extent, if any, these loads influence the major tectonic processes at work in plate boundary regions, such as the earthquake cycle on major faults. It is determined that the stress perturbations from these loads are generally an order of magnitude smaller than the tectonic stress accumulation rate. Their ability to noticeably affect the seismic cycle is therefore restricted to specific circumstances including when the tectonic loading rate is particularly low, such as along secondary plate boundary fault structures, when the nontectonic loading rate is particularly high, such as in the case of catastrophic flooding events, or when the fault in question is already critically stressed to a near-failure level. Stresses from local topography are calculated along the global mid-ocean ridge and along the Chilean subduction megathrust. The predicted orientations of these stresses are compared to a presumed ridge-normal and transform-strike-slip faulting regime or the focal mechanism of a single large earthquake, respectively. Quantitative constraints for the coincident tectonic stresses are subsequently established with implications for the strength of the plate boundary faults and the necessity of particular topographic and bathymetric features.

  17. Upper Plate Tectonics and Fluid Flow Along the Middle America Convergent Margin

    NASA Astrophysics Data System (ADS)

    Huguen, C.; Ranero, C. R.; Weinrebe, W.; Sahling, H.; Borhmann, G.; Klaucke, I.

    2002-12-01

    We present new multibeam bathymetry, side scan sonar, sub-bottom profiling, deep towed video camera images and sampling from active structures related to tectonics and fluid flow at the overriding plate of the Middle America subduction zone. Data were collected during SONNE 163-1 cruise at key locations based on full bathymetric coverage of the margin with a ~ 100 m grid. We surveyed normal faults along the middle-upper continental slope and associated mounds. Also, the locus of seamount subduction was investigated. The new bathymetry has been gridded at ~ 25 m. Deep towed side scan sonar data have a resolution of ~ 1 m. Subbottom high resolution profiling images the upper ~ 100 m of slope sediment. Deep towed camera observations and sampling were used to ground truth the geophysical data. The canyon system present in the upper slope terminates abruptly at the ~ mid slope where normal faulting develops. Roughly coincident with the faulting development, groups of small mounds (few 100s m to 1 km long and < 100 m to 150 m high) occur along the upper-middle slope. These mounds, previously interpreted as mud volcanoes, do not show evidence of mud flows in the side scan data. Deep towed camera and dredging at numerous locations indicate that the surface of the mounds is made of chemoherm carbonates that yield a characteristic high reflectivity in back scatter images. The mounds seem to be areas of fluid discharge and chemosynthetic fauna was observed locally in all of the structures investigated. The mounds are spatially coincident and may be associated to the development of the faults. Their fate may also be related to the faulting: mounds disappear downslope as the fault throw increases. Data from the areas of active seamount subduction show clear evidence for recent/ongoing tectonism at the uplifted overriding plate. The largest deformation occurs at the summit of the uplift and at the trail of the seamount where sliding and slumping are active. Areas of the summit

  18. Tectonic Activity during the Harappan Civilization

    NASA Astrophysics Data System (ADS)

    Prasad, M.; Nur, A.

    2001-12-01

    The Harappan civilization in South Asia existed between 3,300 and 1,900 BC. Extensive remnants from this era are found in Pakistan and northwestern India. The region is far from plate boundaries and, until recently, has been considered tectonically inactive. A combination of data from current and historic seismicity, marine seismic surveys, and prevalent geologic and tectonic features with archeological findings, historical and scriptural records, and GIS mapping of large scale areas shows: \\begin{enumerate} Occurrence of earthquakes starting from the 26th January, 2001 event to as far back as 2500 BC Existence of an ancient river, Saraswati corroborated with historical records, GIS mapping, marine seismic surveys Sea level changes from archeological excavations of variations in fauna. We show how a cross-disciplinary study can provide ways of filling information gaps and providing new insights. A comparison between isoseismal lines from the Magnitude 8 event of 26th January, 2001 with location of Harappan cities shows that most cities would have been obliterated by such an event. >http://pangea.stanford.edu/ ~manika/harappa.html

  19. The rapid drift of the Indian tectonic plate.

    PubMed

    Kumar, Prakash; Yuan, Xiaohui; Kumar, M Ravi; Kind, Rainer; Li, Xueqing; Chadha, R K

    2007-10-18

    The breakup of the supercontinent Gondwanaland into Africa, Antarctica, Australia and India about 140 million years ago, and consequently the opening of the Indian Ocean, is thought to have been caused by heating of the lithosphere from below by a large plume whose relicts are now the Marion, Kerguelen and Réunion plumes. Plate reconstructions based on palaeomagnetic data suggest that the Indian plate attained a very high speed (18-20 cm yr(-1) during the late Cretaceous period) subsequent to its breakup from Gondwanaland, and then slowed to approximately 5 cm yr(-1) after the continental collision with Asia approximately 50 Myr ago. The Australian and African plates moved comparatively less distance and at much lower speeds of 2-4 cm yr(-1) (refs 3-5). Antarctica remained almost stationary. This mobility makes India unique among the fragments of Gondwanaland. Here we propose that when the fragments of Gondwanaland were separated by the plume, the penetration of their lithospheric roots into the asthenosphere were important in determining their speed. We estimated the thickness of the lithospheric plates of the different fragments of Gondwanaland around the Indian Ocean by using the shear-wave receiver function technique. We found that the fragment of Gondwanaland with clearly the thinnest lithosphere is India. The lithospheric roots in South Africa, Australia and Antarctica are between 180 and 300 km deep, whereas the Indian lithosphere extends only about 100 km deep. We infer that the plume that partitioned Gondwanaland may have also melted the lower half of the Indian lithosphere, thus permitting faster motion due to ridge push or slab pull. PMID:17943128

  20. Madagascar's Escape from Africa: New Constraints and Understanding for Plate Tectonic Reconstructions

    NASA Astrophysics Data System (ADS)

    Phethean, J. J. J.; Davies, R. J.; Van Hunen, J.; Kalnins, L. M.; McCaffrey, K. J. W.

    2015-12-01

    We present a new plate tectonic reconstruction for the drift of Madagascar away from East Africa using the new Sandwell and Smith gravity dataset (V23.1). Detailed interpretation of free-air and Bouguer anomalies, together with gravity gradients, has allowed interpretation of the extinct mid ocean ridge and associated fracture zone lineaments from the Western Somali Basin. Combined with temporal constraints from previous ocean magnetic anomaly interpretations, this analysis produces a reconstruction that supports Reeves' (2014) tight fit of Gondwana fragments. Furthermore, it sheds light on the nature of the Davie Fracture Zone (DFZ) and the position of the continent-ocean boundary (COB) in the region. The model predicts that the COB lies along the Rovuma Basin; and that offshore Tanzania is most likely a segmented and obliquely rifted margin, not a transform continental margin along the DFZ as previously thought. This places the COB up to several hundred kilometres farther inboard than previous interpretations, which is supported by new seismic evidence of oceanic crust inboard of the DFZ. We show the DFZ to be a major ocean-ocean fracture zone formed by the coalescence of several smaller fracture zones during a change in plate motions as Madagascar escaped from Africa. This new geodynamical understanding has important implications for petroleum industry activities in East Africa, as the expected heat flow varies dramatically between oceanic and continental crust. Reeves, C., 2014. The position of Madagascar within Gondwana and its movements during Gondwana dispersal. J. Afr. Earth. Sci. 94, 45-57.

  1. Paleozoic plate-tectonic evolution of the Tarim and western Tianshan regions, western China

    SciTech Connect

    Yangshen, S.; Huafu, L.; Dong, J.

    1994-11-01

    The plate-tectonic evolution of the Tarim basin and nearby western Tianshan region during Paleozoic time is reconstructed in an effort to further constrain the tectonic evolution of Central Asia, providing insights into the formation and distribution of oil and gas resources. The Tarim plate developed from continental rifting that progressed during early Paleozoic time into a passive continental margin. The Yili terrane (central Tianshan) broke away from the present eastern part of Tarim and became a microcontinent located somewhere between the Junggar ocean and the southern Tianshan ocean. The southern Tianshan ocean, between the Tarim craton and the Yili terrane, was subducting beneath the Yili terrane from Silurian to Devonian time. During the Late Devonian-Early Carboniferous, the Tarim plate collided with the Yili terrane by sinistral accretional docking that resulted in a late Paleozoic deformational episode. Intracontinental shortening (A-type subduction) continued through the Permian with the creation of a magmatic belt. 21 refs., 7 figs., 1 tab.

  2. Areas of Unsolved Problems in Caribbean Active Tectonics

    NASA Astrophysics Data System (ADS)

    Mann, P.

    2015-12-01

    I review some unsolved problems in Caribbean active tectonics. At the regional and plate scale: 1) confirm the existence of intraplate deformation zones of the central Caribbean plate that are within the margin of error of ongoing GPS measurements; 2) carry out field studies to evaluate block models versus models for distributed fault shear on the densely populated islands of Jamaica, Hispaniola, Puerto Rico, and the Virgin Islands; 3) carry out paleoseismological research of key plate boundary faults that may have accumulated large strains but have not been previously studied in detail; 4) determine the age of onset and far-field effects of the Cocos ridge and the Central America forearc sliver; 4) investigate the origin and earthquake-potential of obliquely-sheared rift basins along the northern coast of Venezuela; 5) determine the age of onset and regional active, tectonic effects of the Panama-South America collision including the continued activation of the Maracaibo block; and 6) validate longterm rates on active subduction zones with improving, tomographic maps of subducted slabs. At the individual fault scale: 1) determine the mode of termination of large and active strike -slip faults and application of the STEP model (Septentrional, Polochic, El Pilar, Bocono, Santa Marta-Bucaramanaga); 2) improve the understanding of the earthquake potential on the Enriquillo-Plantain Garden fault zone given "off-fault" events such as the 2010 Haiti earthquake; how widespread is this behavior?; and 3) estimate size of future tsunamis from studies of historic or prehistoric slump scars and mass transport deposits; what potential runups can be predicted from this information?; and 4) devise ways to keep rapidly growing, circum-Caribbean urban populations better informed and safer in the face of inevitable and future, large earthquakes.

  3. Delivery of volatiles to terrestrial planets during accretion: Setting the stage for plate tectonics

    NASA Astrophysics Data System (ADS)

    Elkins-Tanton, L.; Tikoo, S.

    2012-04-01

    A persistent problem in planetary science is how and when plate tectonics can begin in planetary evolution. On Earth, plate tectonics is thought to be facilitated by the low-viscosity asthenosphere, which obtains its low viscosity partly through low pressure, and partly through a water content on the order of hundreds of parts per million, likely trapped in the crystal structure of nominally anhydrous silicate minerals. Subduction zones introduce water contents of that magnitude to the mantle that circulates above the sinking oceanic plate, and subduction zones are sometimes cited as the process that hydrates an originally dry planetary interior. Thus there is a chicken-and-egg problem: If a damp asthenosphere is needed for plate tectonics, but plate tectonics itself creates the damp asthenosphere, how does the process initiate? Despite the existence of a metallic (reduced) core, both the compositions of meteorites and the certainty of radial mixing during accretion suggest that the Earth and other rocky planets accreted with some non-zero water content. Tracking water partitioning between magma ocean fluids and solidifying mantle minerals suggests that the planetary interior could begin with a non-zero water content. Here we present models for the interior water content of the Earth following accretion, and hypothesize about a dynamic processes that may have sped the development of plate tectonics. On an Earth-sized planet a magma ocean would solidify to produce very dense near-surface solids that also contain the bulk of the water held in the solid state, and the bulk of the incompatible elements. During gravitationally-driven overturn shallow, dense, damp solids carry their water as they sink into the perovskite stability zone and transform the bulk of their mineralogy into perovskite. The last solids that form near the surface exceed the likely water saturation levels of perovskite and will be forced to dewater as they cross the boundary into the lower mantle

  4. Correlation between plate motions and tectonic subsidence of sedimentary basins in Africa

    SciTech Connect

    Janssen, M.E. )

    1993-09-01

    From the early Mesozoic until the Holocene, the African continent was generally in a state of extension, based on plate tectonic reconstructions and sedimentary basin subsidence studies. Beginning with the breakup of Gondwana in the Permian-Triassic, this resulted in the formation of the present-day African continental margins and a series of intracontinental rift basins, located mainly on older (late Proterozoic) shear zones. Numerous wells from marginal, as well as intracontinental rift basins, have been backstripped to elucidate their Mesozoic and Tertiary tectonic histories. They show a generally consistent patterns of subsidence and uplift phases in all basins. During the evolution of these basins, the direction of African plate motion changed several times. This was related to the differential opening of the central and south Atlantic oceans, changes in spreading rates in both the Atlantic and Indian oceans, and the collision between Africa and Europe. Episodes of compressional deformation related to these plate tectonic changes are revealed in backstripped tectonic subsidence curves.

  5. The 2.0 Ga Usagaran eclogites, Tanzania: the onset of modern plate tectonics or a continuation of the norm?

    NASA Astrophysics Data System (ADS)

    Buchan, C.; Collins, A. S.; Reddy, S. M.; Mruma, A.

    2003-04-01

    formed during closure of a marginal basin, suggests that the plate tectonic processes active at this time were similar to those in modern settings. These results show that by 2.0 Ga, despite possibly elevated mantle temperatures, metamorphic conditions in subduction zones had evolved to produce and preserve low/med temperature eclogites.

  6. Active Tectonics in crossroads of an evolving orogen and morphological consequences: Anatolia

    NASA Astrophysics Data System (ADS)

    Koral, Hayrettin

    2016-04-01

    Anatolia lies in a curved setting of the active Alpine Mountain Range and is located in crossroads of the European and Asian terrains. It is one of the fastest deforming land in the world, manifested by seismicity, characteristic landforms and GPS measurements. Active tectonics in Anatolia provides not only a comparable geological model for the past orogens, but also a laboratory case for morphological consequences of an orogenic processes. Anatolia comprise different tectonic subsettings with its own characteristics. Northern part is influenced by tectonic characteristics of the Black Sea Basin, the Pontides and the Caucasian Range; northwestern part by the Balkanides; eastern-southeastern part by the Bitlis-Zagros suture; and south-southwestern part by the eastern Mediterranean subduction setting. Much of its present tectonic complexity was inherited from the convergence dominant plate tectonic setting of the platelets prior to the Middle-Neogene. Beginning about 11 Ma ago, the deformed and uplifted landmass unable to accommodate further deformation in Anatolia and ongoing tectonic activity gave rise to rearrangement of tectonic forces and westerly translational movements. Formation of major strike-slip faults in Anatolia including the North and East Anatolian Faults and a new platelet called the Anatolian Plate are the consequences of this episode. Such change in the tectonic regime has led to modification of previously-formed landscape, modification and sometimes termination of previously-formed basins. Evidence is present in the Plio-Quaternary stratigraphy, tectonic characteristics and morphology of the well-studied areas. This presentation will discuss active tectonic features of the northwestern, southwestern and eastern Anatolian subsettings and their influence on morphology that is closely related to sites of pre-historical human settlement.

  7. Integrating seismological and tectonic studies to constrain lithospheric evolution at complex plate boundaries

    NASA Astrophysics Data System (ADS)

    Hayes, Gavin Peter

    The relative motion of tectonic plates across their boundaries generates deformation in the surrounding lithosphere. How this deformation is expressed reflects both present-day plate configurations and how plate boundaries evolve. To understand the behavior of plate boundaries, we must study how they have developed. The advances made in seismology over the past fifty years---both in observation and application---provide tools ideal for such analysis. Here, I use these tools to investigate the tectonic evolution of complex plate boundaries. I focus on two areas that have experienced geologically recent plate tectonic variations---the Mendocino triple junction in northern California, and the Australia:Pacific plate boundary south of New Zealand. In northern California, the northward migration of the Mendocino triple junction over the past ˜10Ma has driven a synchronous pattern of thickening and thinning of North American crust. In studying this deformation I find major thinning is localized to a narrow region of crust in the Redwood Valley area. This thinning is accompanied by a steeply dipping Moho (>15°), and by high Poisson's Ratio's in the lower crust, characteristic of layers of melt. These melts may link to shallow (˜10km) dike injections that drive a migrating sequence of seismicity in the shallow crust near Lake Pillsbury. The limited data sets available led me to develop new tools in receiver function and crustal velocity ratio analyses that significantly improve our ability to resolve spatial changes in crustal properties. The application of these techniques forms a second major aspect of this thesis. Finally, I analyze the deformation of Australian lithosphere adjacent to the plate boundary south of New Zealand. I perform earthquake relocations on the distribution of intra- and inter-plate seismicity, and combined with plate reconstructions since the late Oligocene show that deformation occurs over a ˜150km wide area west of the current plate boundary

  8. Gravity anomalies, plate tectonics and the lateral growth of Precambrian North America

    NASA Technical Reports Server (NTRS)

    Thomas, M. D.; Grieve, R. A. F.; Sharpton, V. L.

    1988-01-01

    The widespread gravity coverage of North America provides a picture of the gross structural fabric of the continent via the trends of gravity anomalies. The structural picture so obtained reveals a mosaic of gravity trend domains, many of which correlate closely with structural provinces and orogenic terranes. The gravity trend map, interpreted in the light of plate-tectonic theory, thus provides a new perspective for examining the mode of assembly and growth of North America. Suture zones, palaeosubduction directions, and perhaps, contrasting tectonic histories may be identified using gravity patterns.

  9. New Internet software aids paleomagnetic analysis and plate tectonic reconstructions

    NASA Astrophysics Data System (ADS)

    Schettino, Antonio; Scotese, Christopher R.

    Internet server-side applications are becoming an invaluable source of information for many scientists. This is particularly evident in the case of molecular biology, where raw information and computation tools related to various genome projects are easily and quickly accessible through several Web servers. As illustrated by the pioneering efforts of the Ocean Drilling Stratigraphic Network (ODSN) service for making online plate reconstructions, the Cornell Interactive Mapping System, the Harvard Centroid-Moment Tensor Project, and the DRAGON project, geophysics has just begun to systematically use comparable network programming technology Within the next few years, many local resources that are currently accessible only at the scale of university departments will be rendered available to a wide public of researchers and students.

  10. Global plate tectonics and the secular motion of the pole

    NASA Technical Reports Server (NTRS)

    Soler, T.

    1977-01-01

    Astronomical data compiled during the last 70 years by the international organizations providing the coordinates of the instantaneous pole clearly shows a persistent drift of the mean pole. The differential contributions to the earth's second-order tensor of inertia were obtained and applied, resulting in no significant displacement of the earth's principal axis. In view of the above, the effect that theoretical geophysical models for absolute plate velocities may have on an apparent displacement of the mean pole as a consequence of station drifting was analyzed. The investigation also reports new values for the crustal tensor of inertia (assuming an ellipsoidal earth) and the orientation of its axis of figure, reopening the old speculation of a possible sliding of the whole crustover the upper mantle, including the supporting geophysical and astronomic evidence.

  11. Towards an Integrated Model of Earth's Thermo-Chemical Evolution and Plate Tectonics

    NASA Astrophysics Data System (ADS)

    Tackley, P. J.; Xie, S.

    2001-05-01

    It has long been a challenge for geodynamicists, who have typically modeled homogeneous mantles, to explain the geochemical evidence for the existence of several distinct chemical reservoirs, in terms of a dynamically and chemically self-consistent model. While the mixing behavior of generalized tracers has received much attention in the modeling community, a recent trend has been towards mantle convection models that track the evolution of specific chemical species, both major and minor, and can thus be related to geochemical observations. However, obtaining realistic chemical evolution in such models is dependent on their having a reasonable representation of plate tectonic behavior since the recycling of oceanic crust and complementary depleted residuum is a key process in Earth that other terrestrial planets may lack. In general, this has required inserting plate motions by hand in models. In recent years, however, we have learned how to perform numerical simulations of mantle convection in which plate tectonic behavior is introduced self-consistently through plastic yielding of the lithosphere. In this presentation, models of mantle convection that combine a treatment of geochemical evolution with self-consistently generated plate tectonics, will be presented. Preliminary results indicate that the system can self-consistently evolve regions which have a HIMU-like signature as well as regions with a high He3/He4 ratio.

  12. Late Miocene to recent plate tectonic history of the southern Central America convergent margin

    NASA Astrophysics Data System (ADS)

    Morell, Kristin D.

    2015-10-01

    New plate reconstructions constrain the tectonic evolution of the subducting Cocos and Nazca plates across the southern Central American subduction zone from late Miocene to recent. Because of the strong relationships between lower and upper (Caribbean) plate dynamics along this margin, these constraints have wide-ranging implications for the timing and growth of upper plate deformation and volcanism in southern Central America. The reconstructions outline three important events in the Neogene history of this margin: (1) the coeval development of the Panama Triple Junction with the initiation of oblique subduction of the Nazca plate at ˜8.5 Ma; (2) the initiation of seamount and rough crust subduction beginning at ˜3-4 Ma; and (3) Cocos Ridge subduction from ˜2 to 3 Ma. A comparison of these events with independent geologic, geomorphic, volcanic, and stratigraphic data sets reveals that the timing, rates, and origin of subducting crust directly impacted the Neogene growth of upper plate deformation and volcanism in southern Central America. These analyses constrain the timing, geometry, and causes of a number of significant tectonic and volcanic processes, including rapid Plio-Quaternary arc-fore arc contraction due to Cocos Ridge subduction, the detachment of the Panama microplate at ˜1-3 Ma, and the late Miocene cessation of mantle-wedge-derived volcanism across ˜300 km of the subduction zone.

  13. Earthquake stress drops, ambient tectonic stresses and stresses that drive plate motions

    USGS Publications Warehouse

    Hanks, T.C.

    1977-01-01

    A variety of geophysical observations suggests that the upper portion of the lithosphere, herein referred to as the elastic plate, has long-term material properties and frictional strength significantly greater than the lower lithosphere. If the average frictional stress along the non-ridge margin of the elastic plate is of the order of a kilobar, as suggested by the many observations of the frictional strength of rocks at mid-crustal conditions of pressure and temperature, the only viable mechanism for driving the motion of the elastic plate is a basal shear stress of several tens of bars. Kilobars of tectonic stress are then an ambient, steady condition of the earth's crust and uppermost mantle. The approximate equality of the basal shear stress and the average crustal earthquake stress drop, the localization of strain release for major plate margin earthquakes, and the rough equivalence of plate margin slip rates and gross plate motion rates suggest that the stress drops of major plate margin earthquakes are controlled by the elastic release of the basal shear stress in the vicinity of the plate margin, despite the existence of kilobars of tectonic stress existing across vertical planes parallel to the plate margin. If the stress differences available to be released at the time of faulting are distributed in a random, white fasbion with a mean-square value determined by the average earthquake stress drop, the frequency of occurrence of constant stress drop earthquakes will be proportional to reciprocal faulting area, in accordance with empirically known frequency of occurrence statistics. ?? 1977 Birkha??user Verlag.

  14. Punctuated equilibria plate tectonics and exploration strategies: Examples from Australia and South America

    SciTech Connect

    Ross, M.I.; Abreu, V.; Vail, P.R. )

    1996-01-01

    Understanding the interplay between plate tectonic events, subsidence, flexure, and depositional systems is critical to successful exploration, play concept development, and maturation modelling in frontier exploration. Conventional exploration techniques (seismic/well log mapping, geohistory, geophysical, and forward modelling) are used to quantitatively describe the stratigraphic packages observed in basins, but the driving force creating and destroying the packages has typically been qualitatively described as subsidence/uplift events. In order to predict depositional systems patterns, the driving force of these events must be more quantitatively understood. We observe that the tectonic history of plates is characterized by long periods of fairly constant motion interrupted by short events of re- organization ([open quotes]punctuated equilibria[close quotes]). We also observe that these events are usually regional in nature and cause changes in regional subsidence patterns. Furthermore, these changes cause changes in major depositional system locations and characteristics. Analysis of-the plate tectonic history of motion predicts times of quiescence and times of rapid change in basin stratigraphy and therefore produce more effective exploration strategies. We have performed integrated sequence stratigraphic analysis in three basins (Barrow/Dampier, Otway, Santos-Pelotas), on two widely displaced continents (Australia and South America), spanning the Cretaceous Period. Although the tectonic histories are different, each basin responds to its tectonic history in a similar fashion: slow (or negative) subsidence diminishes volume and recognizability of transgressive and highstand systems tract and increases the volume and recognizability of lowstand systems tracts. The alternate case (rapid subsidence) produces the alternate result.

  15. Punctuated equilibria plate tectonics and exploration strategies: Examples from Australia and South America

    SciTech Connect

    Ross, M.I.; Abreu, V.; Vail, P.R.

    1996-12-31

    Understanding the interplay between plate tectonic events, subsidence, flexure, and depositional systems is critical to successful exploration, play concept development, and maturation modelling in frontier exploration. Conventional exploration techniques (seismic/well log mapping, geohistory, geophysical, and forward modelling) are used to quantitatively describe the stratigraphic packages observed in basins, but the driving force creating and destroying the packages has typically been qualitatively described as subsidence/uplift events. In order to predict depositional systems patterns, the driving force of these events must be more quantitatively understood. We observe that the tectonic history of plates is characterized by long periods of fairly constant motion interrupted by short events of re- organization ({open_quotes}punctuated equilibria{close_quotes}). We also observe that these events are usually regional in nature and cause changes in regional subsidence patterns. Furthermore, these changes cause changes in major depositional system locations and characteristics. Analysis of-the plate tectonic history of motion predicts times of quiescence and times of rapid change in basin stratigraphy and therefore produce more effective exploration strategies. We have performed integrated sequence stratigraphic analysis in three basins (Barrow/Dampier, Otway, Santos-Pelotas), on two widely displaced continents (Australia and South America), spanning the Cretaceous Period. Although the tectonic histories are different, each basin responds to its tectonic history in a similar fashion: slow (or negative) subsidence diminishes volume and recognizability of transgressive and highstand systems tract and increases the volume and recognizability of lowstand systems tracts. The alternate case (rapid subsidence) produces the alternate result.

  16. Precambrian Plate Tectonics and the Formation of the Canadian Shield: Seismic Evidence from Hudson Bay

    NASA Astrophysics Data System (ADS)

    Bastow, I. D.; Thompson, D. A.; Kendall, J. M.; Helffrich, G. R.; Wookey, J.; Snyder, D. B.; Eaton, D. W.; Darbyshire, F. A.

    2010-12-01

    The Canadian Shield is one of the largest exposures of Precambrian rocks on Earth. It is a mosaic of several Archean terranes that were brought together during a series of Paleoproterozoic orogens culminating in the so-called Trans-Hudson Orogen (THO), which is thought to have been similar to the Himalayan orogen in scale and nature. The tectonic evolution and lithospheric subdivisions of this region are poorly understood, but new seismic networks in northern Hudson Bay provide fresh information sources to place constraints on the Precambrian processes that formed and shaped it. Using data from a network of 12 broadband seismic stations in the northern part of Hudson Bay that complement existing POLARIS and CNSN networks in the region, we report on a combined study of seismic anisotropy, travel-time tomography, and receiver functions. While tomographic images reveal no clear seismological distinction between Archean and Proterozoic mantle, results from the study of seismic anisotropy show that much of the northern Hudson Bay region retains a strong signature of Archean-to-Paleoproterozoic tectonics - in particular the THO. The receiver function study also provides evidence in support of this 1.8 Ga orogenic event, but the simplicity of crustal structure in the oldest terranes as well as the scale of orogenic belts provides little evidence in support modern-day-style plate tectonics. When reviewed in light of age and compositional constraints from the geological record, our seismic observations point towards a secular change from non-plate tectonic deformation during the Paleo- to Mesoarchean evolving towards fully-developed modern-style plate tectonic interactions during the Paleoproterozoic.

  17. Mobilization of evaporites in tectonically active terrains

    NASA Astrophysics Data System (ADS)

    Stiros, Stathis C.

    2015-04-01

    The role of evaporites, mostly halite, during seismic sequences is investigated using evidence from certain earthquakes with magnitude between approximately 6.0 and 7.2 which occurred in the last 60 years in the Zagros Mts. (Iran) and the Ionian Sea (Greece); i.e. two seismically active areas, characterized by evaporite-associated decollements and more shallow decollements combined with mature, along-thrusts intrusions. Studied earthquakes produced either large scale surface deformation, or were covered by high-resolution and accuracy GPS and INSAR data, permitting to fully recognize the deformation pattern. In all cases an "atypical", tectonic deformation pattern was observed, ranging from apparently "impossible" patterns (thrust and normal faults, sub-parallel and homothetic; 1953 Cephalonia earthquake, Greece) to rather diffuse tectonic patterns, even to "phantom" earthquakes (Zagros). Careful analysis and modeling of the surface deformation data, in combination with the available geological, geophysical and seismological data permits to recognize, and even to quantify differences between deformation observed, and that expected in ordinary environments. In particular, it was found that during earthquakes evaporites were mobilized, and this led either to a secondary deformation of the overburden, fully detached from the basement, or to significant aseismic (post-seismic) deformation. Anomalies in the distribution of seismic intensities due to evaporitic intrusions along faults were also observed. Apart from seismological implications (unpredictable post-seismic deformation, possibly also in the far-field), these results deriving from regions at different levels of evaporitic evolution, may prove useful to understand patterns of mobilization of evaporites during periods of tectonic activity.

  18. Evidence for long-lived subduction of an ancient tectonic plate beneath the southern Indian Ocean

    NASA Astrophysics Data System (ADS)

    Simmons, N. A.; Myers, S. C.; Johannesson, G.; Matzel, E.; Grand, S. P.

    2015-11-01

    Ancient subducted tectonic plates have been observed in past seismic images of the mantle beneath North America and Eurasia, and it is likely that other ancient slab structures have remained largely hidden, particularly in the seismic-data-limited regions beneath the vast oceans in the Southern Hemisphere. Here we present a new global tomographic image, which shows a slab-like structure beneath the southern Indian Ocean with coherency from the upper mantle to the core-mantle boundary region—a feature that has never been identified. We postulate that the structure is an ancient tectonic plate that sank into the mantle along an extensive intraoceanic subduction zone that migrated southwestward across the ancient Tethys Ocean in the Mesozoic Era. Slab material still trapped in the transition zone is positioned near the edge of East Gondwana at 140 Ma suggesting that subduction terminated near the margin of the ancient continent prior to breakup and subsequent dispersal of its subcontinents.

  19. Melting-induced crustal production helps plate tectonics on Earth-like planets

    NASA Astrophysics Data System (ADS)

    Lourenço, Diogo L.; Rozel, Antoine; Tackley, Paul J.

    2016-04-01

    Within our Solar System, Earth is the only planet to be in a mobile-lid regime. It is generally accepted that the other terrestrial planets are currently in a stagnant-lid regime, with the possible exception of Venus that may be in an episodic-lid regime. In this study, we use numerical simulations to address the question of whether melting-induced crustal production changes the critical yield stress needed to obtain mobile-lid behaviour (plate tectonics). Our results show that melting-induced crustal production strongly influences plate tectonics on Earth-like planets by strongly enhancing the mobility of the lid, replacing a stagnant lid with an episodic lid, or greatly extending the time in which a smoothly evolving mobile lid is present in a planet. Finally, we show that our results are consistent with analytically predicted critical yield stress obtained with boundary layer theory, whether melting-induced crustal production is considered or not.

  20. JaMBES: A "New" Way of Calculating Plate Tectonic Reconstruction

    NASA Astrophysics Data System (ADS)

    Chambord, A. I.; Smith, E. G. C.; Sutherland, R.

    2014-12-01

    Calculating the paleoposition of tectonic plates using marine geophysical data has been usually done by using the Hellinger criterion [Hellinger, 1981]. However, for the Hellinger software [Kirkwood et al., 1999] to produce stable results, we find that the input data must be abundant and spatially well distributed. Although magnetic anomalies and fracture zone data have been increasingly abundant since the 1960s, some parts of the globe remain too sparsely explored to provide enough data for the Hellinger code to provide satisfactory rotations. In this poster, we present new software to calculate the paleopositions of tectonic plates using magnetic anomalies and fracture zone data. Our method is based on the theory of plate tectonics as introduced by [Bullard et al., 1965] and [Morgan, 1968], which states that ridge segments (ie. magnetic lineations) and fracture zones are at right angles to each other. In order to test our software, we apply it to a region of the world where climatic conditions hinder the acquisition of magnetic data: the Southwest Pacific, between New Zealand and Antarctica from breakup time to chron 20 (c43Ma). Bullard, E., J. E. Everett, and A. G. Smith (1965), The fit of continents around the atlantic, Philosophical Transactions of the Royal Society of London, Series A: Mathematical and Physical Sciences, 258(1088), 41-51. Hellinger, S. J. (1981), The uncertainties of finite rotations in plate tectonics, Journal of Geophysical Research, 86(B10), 9312-9318. Kirkwood, B. H., J. Y. Royer, T. C. Chang, and R. G. Gordon (1999), Statistical tools for estimating and combining finite rotations and their uncertainties, Geophysical Journal International, 137(2), 408-428. Morgan, W. J. (1968), Rises, trenches, great faults, and crustal blocks, Journal of Geophysical Research, 73(6), 1959-1982.

  1. Using Google Earth to Teach Plate Tectonics and Science Explanations

    ERIC Educational Resources Information Center

    Blank, Lisa M.; Plautz, Mike; Almquist, Heather; Crews, Jeff; Estrada, Jen

    2012-01-01

    "A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas" emphasizes that the practice of science is inherently a model-building activity focused on constructing explanations using evidence and reasoning (NRC 2012). Because building and refining is an iterative process, middle school students may view this practice…

  2. Crustal structure and active tectonics in the Eastern Alps

    NASA Astrophysics Data System (ADS)

    Brückl, E.; Behm, M.; Decker, K.; Grad, M.; Guterch, A.; Keller, G. R.; Thybo, H.

    2010-04-01

    During the last decade, a series of controlled source seismic experiments brought new insight into the crustal and lithospheric structure of the Eastern Alps and their adjacent tectonic provinces. A fragmentation of the lithosphere into three blocks, Europe (EU), Adria (AD), and the new Pannonian fragment (PA), was interpreted and a triple junction was inferred. The goal of this study has been to relate these deep crustal structures to active tectonics. We used elastic plate modeling to reconsider the Moho fragmentation. We interpret subduction of EU below AD and PA from north to south and underthusting of AD mantle below PA from southwest to northeast. The Moho fragmentation correlates well with major upper crustal structures and is supported by gravity, seismic, and geodetic data. An analysis of crustal thickening suggests that active convergence is associated with continued thrusting and lateral extrusion in the central Eastern Alps and thickening of the Adriatic indenter under the Southern Alps. According to the velocity relations at the triple junction, PA moves relative to EU and AD along ENE and SE striking faults, mainly by strike slip. An eastward directed extensional component is compensated by the lateral extrusion of the central Eastern Alps. The Periadriatic (Insubric) line east of the triple junction and the mid-Hungarian fault zone have relatively recently lost their role as first-order active structures. We favor the idea that the Pannonian fragment and the TISZA block merged to a "soft" microplate surrounded by the Eastern and Southern Alpine, Carpathian, and Dinaric orogens.

  3. Active NE-SW Compressional Strain Within the Arabian Plate

    NASA Astrophysics Data System (ADS)

    Floyd, M. A.; ArRajehi, A.; King, R. W.; McClusky, S.; Reilinger, R. E.; Douad, M.; Sholan, J.; Bou-Rabee, F.

    2012-12-01

    Motion of the Arabian plate with respect to Eurasia has been remarkably steady over more than 25 Myr as revealed by comparison of geodetic and plate tectonic reconstructions (e.g., McQuarrie et al., 2003, GRL; ArRajehi et al., 2010, Tectonics). While internal plate deformation is small in comparison to the rate of Arabia-Eurasia convergence, the improved resolution of GPS observations indicate ~ NE-SW compressional strain that appears to affect much of the plate south of latitude ~ 30°N. Seven ~ NE-SW oriented inter-station baselines all indicated shortening at rates in the range of 0.5-2 mm/yr, for the most part with 1-sigma velocity uncertainties < 0.4 mm/yr. Plate-scale strain rates exceed 2×10-9/yr. The spatial distribution of strain can not be resolved from the sparse available data, but strain appears to extend at least to Riyadh, KSA, ~ 600 km west of the Zagros Fold and Thrust Belt that forms the eastern, collisional boundary of the Arabian plate with Eurasia (Iran). Geodetic velocities in the plate tectonic reference frame for Arabia, derived from magnetic anomalies in the Red Sea (Chu and Gordon, 1998, GJI), show no significant E-W motion for GPS stations located along the Red Sea coast (i.e., geodetic and plate tectonic spreading rates across the Red Sea agree within their resolution), in contrast to sites in the plate interior and along the east side of the plate that indicate east-directed motions. In addition, NE-SW contraction is roughly normal to ~ N-S striking major structural folds in the sedimentary rocks within the Arabian Platform. These relationships suggest that geodetically observed contraction has characterized the plate for at least the past ~ 3 Myr. Broad-scale contraction of the Arabian plate seems intuitively reasonable given that the east and north sides of the plate are dominated by active continental collision (Zagros, E Turkey/Caucasus) while the west and south sides are bordered by mid-ocean ridge spreading (Red Sea and Gulf of

  4. On the importance of plumes to initiate subduction and plate tectonics

    NASA Astrophysics Data System (ADS)

    Davaille, Anne

    2015-04-01

    Understanding the details of plate failure and the initiation of subduction remains a challenge due to the complexity of mantle rocks. We carried out experiments on convection in aqueous colloidal dispersions heated from below, and dried and cooled from above. The rheology of these fluids depends strongly on solid particle fraction fp, being Newtonian at low fp, and presenting memory, yield stress, elasticity, and brittle properties as fp increases. Such a behaviour is analogue to the rheology of mantle rocks as temperature decreases. When drying is sufficiently rapid in the laboratory, a visco-elasto-plastic skin ("lithosphere") forms on the fluid surface. Depending on its rheology, and on the different scales of convection existing in our laboratory mantle, we observed different modes of one-sided subduction initiation. However, not all of them lead to continuous plate tectonics. If subduction is definitely a necessary condition for plate tectonics, it is not sufficient. Amongst the different modes of subduction initiation, we observed two of them where one-sided subduction was induced by the impingement of a hot plume under the skin, the trench being localized on the rim of the plume impingement zone under the lithosphere. Then depending on the lithospheric rheology, the nascent subduction can then either stop as the result of subducted plate necking, or continue to sink smoothly. Due to the brittle character of the skin, the subduction trench will never describe a complete circle, but several tears and/or transform faults will develop as subduction and roll back proceed. Inspection of the geological record on Earth suggests that such a strong association between plumes and subduction may have been instrumental in the nucleation and growth of cratons, the onset of continuous plate tectonics, and present-day initiation of subduction around some large oceanic plateaus.

  5. Late middle ( ) Miocene Segmentation of an Eocene-early Miocene carbonate megabank on the Northern Nicaragua Rise tied to the tectonic activity at the North America/Caribbean plate boundary zone

    SciTech Connect

    Droxler, A.; Cunningham, A. ); Hine, A.C.; Hallock, P.; Duncan, D. ); Rosencrantz, E.; Buffler, R. ); Robinson, E. )

    1993-02-01

    The Northern Nicaragua Rise (NNR) is comprised today of the eastern Honduras/Nicaragua and southern Jamaica carbonate shelves, and a series of relatively small detached carbonate banks (i.e., Pedro, Rosalind, Serranilla, Diriangen, and Bawika Banks) separated from each other by intervening basins and seaways. The NNR basins and seaways, because of their common north trending orientation, have been previously interpreted as Paleocene, Eocene, and possibly Oligocene rifts, becoming progressively younger from the eastern to the western part of NNR. Results from three recent (1988 and 1992) high resolution seismic surveys within these major seaways and basins, (1) Walton Basin, (2) Pedro Channel, and (3) seaways and Serranilla Basin on the western side of the NNR, show that the present bank and basin configuration evolved from a once continuous megabank that covered the entire length of the NNR, including the Island of Jamaica from Eocene through early Miocene times. In the late middle ( ) Miocene, this megabank progressively broke up into a series of smaller banks, basins and seaways, mainly as the result of tectonic movements related to the overall strike-slip displacement within the North American and Caribbean Plate Boundary Zone of the Cayman Trough. At the same time (late middle Miocene), the most eastern portion of the megabank was uplifted and today forms most of central and south Jamaica. The timing of the megabank segmentation has tentatively been constrained by dating several blocks of shallow water limestone dredged from parts of the megabank outcropping on the sea floor of different seaways.

  6. This dynamic planet: A world map of volcanoes, earthquakes, and plate tectonics

    SciTech Connect

    Simkin, T.; Tilling, R.I.; Taggart, J.N.; Jones, W.J.; Spall, H.

    1989-01-01

    The Earth's physiographic features overlain by its volcanoes, earthquake epicenters, and the movement of its major tectonic plates are shown in this map. This computer-generated map of the world provides a base that shows the topography of the land surface and the sea floor; the additions of color and shaded relief help to distinguish significant features. From the Volcano Reference file of the Smithsonian Institution, nearly 1,450 volcanoes active during the past 10,000 yr are plotted on the map in four categories. From the files of the National Earthquake Information Center (US Geological Survey), epicenters selected from 1,300 large events (magnitude {>=} 7.0) from 1987 onward and from 140,000 instrumentally recorded earthquakes (magnitude {>=} 4.0) from 1960 to the present are plotted on this map according to two magnitude categories and two depth categories. This special map is intended as a teaching aid for classroom use and as a general reference for research. It is designed to show prominent global features when viewed from a distance; more detailed features are visible on closer inspection.

  7. Petrogenesis and Tectonic Evolution of Granitic Rocks in The Northern Margin of North China Plate

    NASA Astrophysics Data System (ADS)

    Xu, X.; Zhao, Q.; Zheng, C.; Liu, W.; Xu, B.

    2010-12-01

    The late Paleozoic-early Mesozoic granites in Daqingshan district of the northern margin of north China plate is classified into six types as follows.Aguigou intrusion is consists of gabbro, diorite, quartz diorite, and granodiorite.Its feature is rich in mafic compositions.The formation age is 284.5±2.9Ma or 283.7±3.7Ma for the quartz diorite, and 281.1±3.4Ma for granodiorite. The genesis of the intrusion belongs to I-type granite. Laoyinhada intrusion comprises fine biotite monzonitic granite and porphyritic biotite monzonitic granite. The age is 272±4Ma for the fine biotite monzonitic granite. The genesis of the body is I-type granite.Halaheshao intrusion is a group of medium-coarse biotite-bearing monzonitic granites and large porphyritic-bearing monzonitic granite. The age is 260±0.5Ma for the biotite-bearing monzonitic granite.The tectonic environment belongs to post-orogenic granites.Taolegai intrusion consists of medium-fine granite, medium-coarse granite, porphyritic-bearing granite, and fine granite. The age is 224±3Ma for medium-coarse granite.Its genesis is light color granite co-occurred with muscovite peraluminous granites. The tectonic environment belongs to post-orogenic granites.Gechoushan intrusion is medium-fine monzonitic granite, a kind of typical muscovite granites. Its formation era is late Triassic. The tectonic environment belongs to post-orogenic granite.Shadegai intrusion is mainly composed of biotite granites. The age is 211.2±0.7Ma for medium-coarse biotite granite. The tectonic setting belongs to post-orogenic granites. The different types granites in the area basically reveal all the magmatic events from late Palaeozoic orogeny, to post-orogeny, and to intracontinental orogeny in the north edge of the north China plate. Early Permian Aguigou intrusion is a magmatic arc granite, formed in the continental edge in the early period of the middle Asia ocean plate subduction. Mid-Permian Laoyinhada intrusion is a magmatic arc granite

  8. The role of image design in communicating the plate tectonic model

    NASA Astrophysics Data System (ADS)

    Clark, S. K.

    2009-12-01

    As the unifying concept of the geosciences, the plate tectonic model is arguably the most important concept for students to understand about the Earth. The scale of plate tectonic processes is far beyond the everyday scale of human lives. Maps and schematic images within textbooks, on-line, or on television are the only access that most lay people, students, and even geologists will ever have to these inherently intangible processes. This means that images play a critical role in communicating aspects of plate tectonics and in developing conceptual models of these earth-scale processes to both experts and novices. In this study, non-science majors to geoscience faculty answered questions about a simplified version of a well-known schematic cross-section that illustrates various plate tectonic processes. Findings from questionnaires and interviews, including eye-tracking data, reveal the differences in how experts and novices visually inspect and interpret the cross-section. Findings include: Experts will focus on the relevant aspects of the image and may completely filter and dismiss aspects of the image they deem irrelevant. However, those same, irrelevant aspects can pose significant distractions to novices, and may mislead novices either by creating new misconceptions or supporting prior misconceptions. Two examples of commonly seen and possibly distracting aspects in cross sections of the plate tectonic model are a red, orange, or yellow asthenosphere under a gray lithosphere, and subducting slabs that terminate in the asthenosphere. The color scheme supports a misconception held by some of a hot, liquid mantle. Subducting slabs that either terminate abruptly or fade away are frequently interpreted to be melting at the “tip”. These findings support research that has clearly indicated that experts attend to relevant aspects of visual stimuli whereas novices do not. Images designed for experts may simply be too confusing for novices to focus on the salient

  9. Maps, Plates, and Mount Saint Helens.

    ERIC Educational Resources Information Center

    Lary, Barbara E.; Krockover, Gerald H.

    1987-01-01

    Describes a laboratory activity on plate tectonics which focuses on the connection between plate tectonics and the different types of volcanoes. Provides questions for discussion and includes suggestions for extending the activity. (ML)

  10. The tectonic plates are shifting: cultural change vs. mural dyslexia.

    PubMed

    Cohn, Kenneth; Friedman, Leonard H; Allyn, Thomas R

    2007-01-01

    In response to a rapidly changing healthcare marketplace, a variety of new business models have arisen, including new specialties (hospitalists), selective care (concierge medicine), and joint ventures (ambulatory surgical centers, specialty hospitals), some with hospitals and others with independent vendors. Since both hospitals and physicians are feeling the squeeze of rising expenses, burdensome regulations, heightened consumer expectations, and stagnant or decreasing reimbursement, the response to global economic competition and the need to improve clinical and financial outcomes can bring physicians and hospitals together rather than drive them farther apart. In response to perceived threats, physicians and hospital executives can engage in defensive reasoning that may feel protective but can also lead to mural dyslexia, the inability or unwillingness to see the handwriting on the wall. The strategies of positive deviance (finding solutions that already exist in the community rather than importing best practices), appreciative inquiry (building on success rather than relying solely on root-cause analyses of problems), and structured dialogue (allowing practicing physicians to articulate clinical priorities rather than assuming they lack the maturity and will to come to consensus) are field-tested approaches that allow hospital leaders to engage practicing physicians and that can help both parties work more interdependently to improve patient care in a dynamically changing environment. Physician-hospital collaboration based on transparency, active listening, and prompt implementation can offer sustainable competitive advantage to those willing to embark on a lifetime learning journey. PMID:17907689

  11. Mantle Convection, Stagnant Lids and Plate Tectonics on Super-Earths

    NASA Astrophysics Data System (ADS)

    Tackley, P. J.; van Heck, H. J.

    2008-12-01

    The discovery of extra-solar super-Earths has prompted interest in their possible mantle dynamics and evolution, and in whether their lithospheres are most likely to be undergoing plate tectonics like on Earth, or be stagnant lids like on Mars and Venus. The origin of plate tectonics is poorly understood for the Earth, likely involving a complex interplay of rheological, compositional, melting and thermal effects, which makes it impossible to make reliable predictions for other planets. Nevertheless, as a starting point it is common to parameterize the complex processes involved as a simple yield stress that is either constant or has a linear "Byerlee's law" dependence on pressure (e.g., [Tackley, GCubed 2000ab] in 3D cartesian geometry; [van Heck and Tackley, GRL 2008] in 3D spherical geometry). For such a simple description, scaling with planet size is expected to depend on heating mode (internal versus basal) and lithospheric strength profile. Simple "back of the envelope" scaling laws (e.g., following Moresi and Solomatov, GJI 1998) ignoring the pressure- dependence of physical properties such as density and thermal expansivity, suggest that the threshold for plate tectonics (i.e., yield stress or friction coefficient) does not depend strongly on planet size, and plate tectonics is equally likely or more likely for larger planets. Scalings that take into account pressure-related changes in physical properties [Valencia et al., Astrophys. J., 2007] make a similar prediction for predominantly internally-heated convection. Because the simplifying assumptions made in developing analytical scalings may not be valid over all parameter ranges, numerical simulations are needed; the one numerical study on super-Earths to date (O'Neill and Lenardic, GRL 2007) finds that plate tectonics is less likely on a larger planet, in apparent contradiction of analytical results. To try and understand this we here present new calculations of yielding- induced plate tectonics as a

  12. Tectonic plates, D (double prime) thermal structure, and the nature of mantle plumes

    NASA Technical Reports Server (NTRS)

    Lenardic, A.; Kaula, W. M.

    1994-01-01

    It is proposed that subducting tectonic plates can affect the nature of thermal mantle plumes by determining the temperature drop across a plume source layer. The temperature drop affects source layer stability and the morphology of plumes emitted from it. Numerical models are presented to demonstrate how introduction of platelike behavior in a convecting temperature dependent medium, driven by a combination of internal and basal heating, can increase the temperature drop across the lower boundary layer. The temperature drop increases dramatically following introduction of platelike behavior due to formation of a cold temperature inversion above the lower boundary layer. This thermal inversion, induced by deposition of upper boundary layer material to the system base, decays in time, but the temperature drop across the lower boundary layer always remains considerably higher than in models lacking platelike behavior. On the basis of model-inferred boundary layer temperature drops and previous studies of plume dynamics, we argue that generally accepted notions as to the nature of mantle plumes on Earth may hinge on the presence of plates. The implication for Mars and Venus, planets apparently lacking plate tectonics, is that mantle plumes of these planets may differ morphologically from those of Earth. A corollary model-based argument is that as a result of slab-induced thermal inversions above the core mantle boundary the lower most mantle may be subadiabatic, on average (in space and time), if major plate reorganization timescales are less than those acquired to diffuse newly deposited slab material.

  13. Supercontinents, Plate Tectonics, Large Igneous Provinces and Deep Mantle Heterogeneities

    NASA Astrophysics Data System (ADS)

    Torsvik, T. H.; Steinberger, B.; Burke, K.; Smethurst, M. A.

    2008-12-01

    The formation and break-up of supercontinents is a spectacular demonstration of the Earth's dynamic nature. Pangea, the best-documented supercontinent, formed at the end of the Palaeozoic era (320 Ma) and its dispersal, starting in the Early Jurassic (190 Ma), was preceded by and associated with widespread volcanic activity, much of which produced Large Igneous Provinces (LIPs), but whether any of the heat or material involved in the generation of LIP rocks comes from greater depths has remained controversial. Two antipodal Large Low Shear wave Velocity Provinces with centre of mass somewhat south of the equator (African and Pacific LLSVPs), isolated within the faster parts of the deep mantle dominate all global shear- wave tomography models. We have tested eight global models and two D" models: They all show that deep- plume sourced hotspots and most reconstructed LIPs for the last 300 million years project radially downwards to the core-mantle-boundary near the edges of the LLSVPs showing that the plumes that made those hotspots and LIPS came only from those plume generation zones. This is a robust result because it is observed in multiple reference frames, i.e. fixed/moving hotspot and palaeomagnetic frames, and in the latter case whether the effect of True Polar Wander (TPW) is considered or not. Our observations show that the LLSVPs must have remained essentially stable in their present position for the last 300 million years. LIPs have erupted since the Archean and may all have been derived from the margins of LLSVPs but whether the African and Pacific LLSVPs have remained the same throughout Earth's history is less certain although analogous structures on Mars do indicate long-term stability on that planet. Deep mantle heterogeneities and the geoid have remained very stable for the last 300 million years, and the possibility is therefore open for speculating on links to Pangea assembly. In a numerical model, Zhong et al. (2007, EPSL) argued that Pangea

  14. Tectonic implications of post-30 Ma Pacific and North American relative plate motions

    USGS Publications Warehouse

    Bohannon, R.G.; Parsons, T.

    1995-01-01

    The Pacific plate moved northwest relative to North America since 42 Ma. The rapid half rate of Pacific-Farallon spreading allowed the ridge to approach the continent at about 29 Ma. Extinct spreading ridges that occur offshore along 65% of the margin document that fragments of the subducted Farallon slab became captured by the Pacific plate and assumed its motion proper to the actual subduction of the spreading ridge. This plate-capture process can be used to explain much of the post-29 Ma Cordilleran North America extension, strike slip, and the inland jump of oceanic spreading in the Gulf of California. Much of the post-29 Ma continental tectonism is the result of the strong traction imposed on the deep part of the continental crust by the gently inclined slab of subducted oceanic lithosphere as it moved to the northwest relative to the overlying continent. -from Authors

  15. The many impacts of building mountain belts on plate tectonics and mantle flow

    NASA Astrophysics Data System (ADS)

    Yamato, Philippe; Husson, Laurent

    2015-04-01

    During the Cenozoic, the number of orogens on Earth increased. This observation readily indicates that in the same time, compression in the lithosphere became gradually more and more important. Such an increase of stresses in the lithosphere can impact on plate tectonics and mantle dynamics. We show that mountain belts at plate boundaries increasingly obstruct plate tectonics, slowing down and reorienting their motions. In turn, this changes the dynamic and kinematic surface conditions of the underlying flowing mantle. Ultimately, this modifies the pattern of mantle flow. This forcing could explain many first order features of Cenozoic plate tectonics and mantle flow. Among these, one can cite the compression of passive margins, the important variations in the rates of spreading at oceanic ridges, or the initiation of subduction, the onset of obduction, for the lithosphere. In the mantle, such change in boundary condition redesigns the pattern of mantle flow and, consequently, the oceanic lithosphere cooling. In order to test this hypothesis we first present thermo-mechanical numerical models of mantle convection above which a lithosphere rests. Our results show that when collision occurs, the mantle flow is highly modified, which leads to (i) increasing shear stresses below the lithosphere and (ii) to a modification of the convection style. In turn, the transition between a 'free' convection (mobile lid) and an 'upset' convection (stagnant -or sluggish- lid) highly impacts the dynamics of the lithosphere at the surface of the Earth. Thereby, on the basis of these models and a variety of real examples, we show that on the other side of a collision zone, passive margins become squeezed and can undergo compression, which may ultimately evolve into subduction or obduction. We also show that much further, due to the blocking of the lithosphere, spreading rates decrease at the ridge, a fact that may explain a variety of features such as the low magmatism of ultraslow

  16. Integrating Geochemical and Geodynamic Numerical Models of Mantle Evolution and Plate Tectonics

    NASA Astrophysics Data System (ADS)

    Tackley, P. J.; Xie, S.

    2001-12-01

    The thermal and chemical evolution of Earth's mantle and plates are inextricably coupled by the plate tectonic - mantle convective system. Convection causes chemical differentiation, recycling and mixing, while chemical variations affect the convection through physical properties such as density and viscosity which depend on composition. It is now possible to construct numerical mantle convection models that track the thermo-chemical evolution of major and minor elements, and which can be used to test prospective models and hypotheses regarding Earth's chemical and thermal evolution. Model thermal and chemical structures can be compared to results from seismic tomography, while geochemical signatures (e.g., trace element ratios) can be compared to geochemical observations. The presented, two-dimensional model combines a simplified 2-component major element model with tracking of the most important trace elements, using a tracer method. Melting is self-consistently treated using a solidus, with melt placed on the surface as crust. Partitioning of trace elements occurs between melt and residue. Decaying heat-producing elements and secular cooling of the mantle and core provide the driving heat sources. Pseudo-plastic yielding of the lithosphere gives a first-order approximation of plate tectonics, and also allows planets with a rigid lid or intermittent plate tectonics to be modeled simply by increasing the yield strength. Preliminary models with an initially homogeneous mantle show that regions with a HIMU-like signature can be generated by crustal recycling, and regions with high 3He/4He ratios can be generated by residuum recycling. Outgassing of Argon is within the observed range. Models with initially layered mantles will also be investigated. In future it will be important to include a more realistic bulk compositional model that allows continental crust as well as oceanic crust to form, and to extend the model to three dimensions since toroidal flow may alter

  17. The stepwise growth of tectonic plates across Earth's evolving supercontinent cycle

    NASA Astrophysics Data System (ADS)

    Van Kranendonk, M. J.; Kirkland, C. L.

    2012-04-01

    Plate tectonics both creates and recycles crust, but the rate of continental growth over Earth history remains contentious: some believe it formed fast and early, others more gradually and, perhaps, episodically, through the supercontinent cycle. Time constrained analysis of both oxygen and hafnium isotopes in zircon grains and incompatible elements (Zr, Th) from magmatic rocks confirms the importance of Earth's supercontinent cycle not only on the degree of crustal recycling rates that arises from the aggregation and dispersal of supercontinents, but also on mantle temperatures, crustal growth rates, and climatic conditions. These changes are used to infer a conditioned duality of the Earth system between alternating periods of hot and cold mantle that arise in response to the supercontinent cycle. Hot mantle periods that accompany supercontinent aggregation events are characterised by mantle superplume events, increased crustal recycling and warm, reducing climatic conditions. Cool mantle periods during supercontinent rifting result from core insulation by slab graveyards and are characterised by low rates of crust production and cool, more oxidizing conditions. Changes in the intensity of the orogenic cycle through time since its inception at c. 3.2 Ga are ascribed to self-reorganisation of progressively larger tectonic plates (tessellation of a sphere) that accommodate the secular decrease in planetary heat. Bursts of crust extraction during Neoarchean and Mesoproterozoic supercontinent assembly led to overstep periods of large plates on subduction-cooled, melt-depleted mantle, accompanied by global ice ages. Optimal packing (pentagonal dodecahedron) of the plates was attained on dispersal of Nuna at 1.4 Ga, leading to a peak in geochemical and isotopic proxies of orogenic intensity during c. 1.2 Ga assembly of Rodinia (large plates on warmer Earth), with declining intensity thereafter as a function of decreasing heat with same-size plates.

  18. MANTLE CONVECTION, PLATE TECTONICS, AND VOLCANISM ON HOT EXO-EARTHS

    SciTech Connect

    Van Summeren, Joost; Conrad, Clinton P.; Gaidos, Eric

    2011-07-20

    Recently discovered exoplanets on close-in orbits should have surface temperatures of hundreds to thousands of Kelvin. They are likely tidally locked and synchronously rotating around their parent stars and, if an atmosphere is absent, have surface temperature contrasts of many hundreds to thousands of Kelvin between permanent day and night sides. We investigated the effect of elevated surface temperature and strong surface temperature contrasts for Earth-mass planets on the (1) pattern of mantle convection, (2) tectonic regime, and (3) rate and distribution of partial melting, using numerical simulations of mantle convection with a composite viscous/pseudo-plastic rheology. Our simulations indicate that if a close-in rocky exoplanet lacks an atmosphere to redistribute heat, a {approx}>400 K surface temperature contrast can maintain an asymmetric degree 1 pattern of mantle convection in which the surface of the planet moves preferentially toward subduction zones on the cold night side. The planetary surface features a hemispheric dichotomy, with plate-like tectonics on the night side and a continuously evolving mobile lid on the day side with diffuse surface deformation and vigorous volcanism. If volcanic outgassing establishes an atmosphere and redistributes heat, plate tectonics is globally replaced by diffuse surface deformation and volcanism accelerates and becomes distributed more uniformly across the planetary surface.

  19. A unit of instruction on the plate tectonic evolution of New England

    SciTech Connect

    Reusch, D. )

    1993-03-01

    A unit of instruction has been developed which enables high school students to decipher the plate tectonic evolution of a typical mountain belt, the New England segment of the Appalachian Orogen. It integrates a wide variety of geological topics including: geological time, the fossil record, global tectonics, geological environments, rocks, minerals, and representative sedimentary, igneous, and metamorphic processes. Students are provided with a simplified tectonic map of the New England area and data cards on each of 12 units. They use fossils and radiometric dates to sort the units chronologically and the map to sort them geographically. Next, they compare the fossil and geological data for each unit with modern tectonic settings and interpret each unit as either oceanic crust [+-] mantle, volcanic arc, arc margin, continental crust, passive margin (rift, shelf, or slope), granite system, or collision margin. Finally, they reconstruct the paleogeography for each time period which reveals the cycle of Iapetus Ocean growth and destruction and the initiation of the Atlantic Ocean cycle.

  20. Conception and realisation of educational models for an exhibition explaining the plate tectonics theory

    NASA Astrophysics Data System (ADS)

    Ouerghi, S.; Harchi, M.; Riadh chebbi, M.

    2012-04-01

    Alfred Wegener suggested in 1915 that the seven continents were once one large land mass that broke apart creating the continents, which then drifted to their current locations. The Atlantic Ocean was created by this process. The mid-Atlantic Ridge is an area where new sea floor is being created. The sea floor continues to spread and the plates get bigger and bigger. Therefore, when plates diverge and form new crust in one area, the plates must converge in another area and be destroyed. When two continental plates meet each other this results in the formation of a mountain. As the subducting oceanic crust melts as it goes deeper into the Earth, the newly-created magma rises to the surface and forms volcanoes. So, the plates move towards each other. The amount of crust on the surface of the earth remains relatively constant. In this context, the aim of this study is to elaborate some educational models to facilitate the comprehension of plate tectonics and there results for pupils and science city visitors.

  1. Development of the Plate Tectonics and Seismology markup languages with XML

    NASA Astrophysics Data System (ADS)

    Babaie, H.; Babaei, A.

    2003-04-01

    The Extensible Markup Language (XML) and its specifications such as the XSD Schema, allow geologists to design discipline-specific vocabularies such as Seismology Markup Language (SeismML) or Plate Tectonics Markup Language (TectML). These languages make it possible to store and interchange structured geological information over the Web. Development of a geological markup language requires mapping geological concepts, such as "Earthquake" or "Plate" into a UML object model, applying a modeling and design environment. We have selected four inter-related geological concepts: earthquake, fault, plate, and orogeny, and developed four XML Schema Definitions (XSD), that define the relationships, cardinalities, hierarchies, and semantics of these concepts. In such a geological concept model, the UML object "Earthquake" is related to one or more "Wave" objects, each arriving to a seismic station at a specific "DateTime", and relating to a specific "Epicenter" object that lies at a unique "Location". The "Earthquake" object occurs along a "Segment" of a "Fault" object, which is related to a specific "Plate" object. The "Fault" has its own associations with such things as "Bend", "Step", and "Segment", and could be of any kind (e.g., "Thrust", "Transform'). The "Plate" is related to many other objects such as "MOR", "Subduction", and "Forearc", and is associated with an "Orogeny" object that relates to "Deformation" and "Strain" and several other objects. These UML objects were mapped into XML Metadata Interchange (XMI) formats, which were then converted into four XSD Schemas. The schemas were used to create and validate the XML instance documents, and to create a relational database hosting the plate tectonics and seismological data in the Microsoft Access format. The SeismML and TectML allow seismologists and structural geologists, among others, to submit and retrieve structured geological data on the Internet. A seismologist, for example, can submit peer-reviewed and

  2. Archean upper crust transition from mafic to felsic marks the onset of plate tectonics.

    PubMed

    Tang, Ming; Chen, Kang; Rudnick, Roberta L

    2016-01-22

    The Archean Eon witnessed the production of early continental crust, the emergence of life, and fundamental changes to the atmosphere. The nature of the first continental crust, which was the interface between the surface and deep Earth, has been obscured by the weathering, erosion, and tectonism that followed its formation. We used Ni/Co and Cr/Zn ratios in Archean terrigenous sedimentary rocks and Archean igneous/metaigneous rocks to track the bulk MgO composition of the Archean upper continental crust. This crust evolved from a highly mafic bulk composition before 3.0 billion years ago to a felsic bulk composition by 2.5 billion years ago. This compositional change was attended by a fivefold increase in the mass of the upper continental crust due to addition of granitic rocks, suggesting the onset of global plate tectonics at ~3.0 billion years ago. PMID:26798012

  3. Archean upper crust transition from mafic to felsic marks the onset of plate tectonics

    NASA Astrophysics Data System (ADS)

    Tang, Ming; Chen, Kang; Rudnick, Roberta L.

    2016-01-01

    The Archean Eon witnessed the production of early continental crust, the emergence of life, and fundamental changes to the atmosphere. The nature of the first continental crust, which was the interface between the surface and deep Earth, has been obscured by the weathering, erosion, and tectonism that followed its formation. We used Ni/Co and Cr/Zn ratios in Archean terrigenous sedimentary rocks and Archean igneous/metaigneous rocks to track the bulk MgO composition of the Archean upper continental crust. This crust evolved from a highly mafic bulk composition before 3.0 billion years ago to a felsic bulk composition by 2.5 billion years ago. This compositional change was attended by a fivefold increase in the mass of the upper continental crust due to addition of granitic rocks, suggesting the onset of global plate tectonics at ~3.0 billion years ago.

  4. Numerical simulation of tectonic plates motion and seismic process in Central Asia

    SciTech Connect

    Peryshkin, A. Yu.; Makarov, P. V. Eremin, M. O.

    2014-11-14

    An evolutionary approach proposed in [1, 2] combining the achievements of traditional macroscopic theory of solid mechanics and basic ideas of nonlinear dynamics is applied in a numerical simulation of present-day tectonic plates motion and seismic process in Central Asia. Relative values of strength parameters of rigid blocks with respect to the soft zones were characterized by the δ parameter that was varied in the numerical experiments within δ = 1.1–1.8 for different groups of the zonal-block divisibility. In general, the numerical simulations of tectonic block motion and accompanying seismic process in the model geomedium indicate that the numerical solutions of the solid mechanics equations characterize its deformation as a typical behavior of a nonlinear dynamic system under conditions of self-organized criticality.

  5. EAG Eminent Speaker: Two types of Archean continental crust: plume and plate tectonics on early Earth

    NASA Astrophysics Data System (ADS)

    Van Kranendonk, M. J.

    2012-04-01

    Over 4.5 billion years, Earth has evolved from a molten ball to a cooler planet with large continental plates, but how and when continents grew and plate tectonics started remain poorly understood. In this paper, I review the evidence that 3.5-3.2 Ga continental nuclei of the Pilbara (Australia) and Kaapvaal (southern Africa) cratons formed as thick volcanic plateaux over hot, upwelling mantle and survived due to contemporaneous development of highly depleted, buoyant, unsubductable mantle roots. This type of crust is distinct from, but complimentary to, high-grade gneiss terranes, as exemplified by the North Atlantic Craton of West Greenland, which formed through subduction-accretion tectonics on what is envisaged as a vigorously convecting early Earth with small plates. Thus, it is proposed that two types of crust formed on early Earth, in much the same way as in modern Earth, but with distinct differences resulting from a hotter Archean mantle. Volcanic plateaux provided a variety of stable habitats for early life, including chemical nutrient rich, shallow-water hydrothermal systems and shallow marine carbonate platforms.

  6. Tectonomagmatic evolution of the Earth: from the primordial crust to plate tectonics

    NASA Astrophysics Data System (ADS)

    Sharkov, E. V.; Bogatikov, O. A.

    2009-12-01

    There are two dominating hypotheses about composition of the primordial Earth’s crust now: basic or sialic. Both models require a global melting of primary chondritic material, and final result would depend on degree of melt differentiation during hardening of global magmatic ocean. Such a solidification, due to difference in adiabatic and melting point gradients proceeded in bottom-top direction and resulted in accumulation of low-temperature derivates in outer shell of the planet. Geological data, namely granite-dominated Archean crust, composed mainly by tonalite-trondhjemite-granodiorite (TTG) rocks, and Hadean detrital zircons from Australia with U-Pb age 4.4-4.2 Ga supports the primordial-sialic crust hypothesis. Formation of the sialic crust was responsible for the depletion of the upper mantle matter. The early Precambrian (Archean, Early Paleoproterozoic) tectonomagmatic activity was rather different from the Phanerozoic: the major structures were granite-greenstone terranes and their separating granulite belts; high-Mg melts (komatiite-basaltic and boninite-like), derived from a depleted source of the first generation mantle superplumes, predominated. Situation can be described in terms of plume-tectonics. Cardinal change of tectonomagmatic processes occurred in the period of 2.3 to 2.0 Ga, which was characterized by voluminous eruption of Fe-Ti picrites and basalts similar to the Phanerozoic within-plate magmas, derived from geochemical-enriched mantle source. Simultaneously, important compositional changes occurred in the atmosphere, hydrosphere and biosphere (Melezhik et al., 2005). The first Phanerozoic-type orogens (Svecofennian of the Baltic Shield, Trans-Hudson and others of the Canadian Shield, etc.) appeared ca. 2 Ga. Since then, subduction of the ancient sialic continental crust (together with newly-formed oceanic crust) is a permanent process and the crustal material has stored in the “slab graveyard”, estimated in the mantle by seismic

  7. Active tectonics in the Moroccan High Atlas

    NASA Astrophysics Data System (ADS)

    Sébrier, Michel; Siame, Lionel; Zouine, El Mostafa; Winter, Thierry; Missenard, Yves; Leturmy, Pascale

    2006-01-01

    Review of seismological and structural data coupled with new data on topographical, geomorphology, and Quaternary geology allows delineating the major active faults of the High Atlas. These are the North and South border faults of which fault segmentations correspond to Mw ranging between 6.1 and 6.4. Detail active tectonics analyses were performed on the South Atlas Fault Zone in the Souss and Ouarzazate basins, where deformed Quaternary levels permit to estimate slip rates on individual faults in the order of 0.1 mm yr -1. Such low slip rates imply that large observational time-window is needed to analyze active deformation in low-seismicity regions. However, the complex 3D geometry of reverse or thrust faults may cause difficulty to relate surface observations with the deeper faults that have the potential to nucleate big earthquakes. Further studies are necessary to interpret the Anti Atlas seismicity. To cite this article: M. Sebrier et al., C. R. Geoscience 338 (2006).

  8. Plate Tectonic Modulation of Microbial Productivity in the Deep Ocean-A Keck-supported Proto-NEPTUNE Experiment

    NASA Astrophysics Data System (ADS)

    Delaney, J. R.; Keck Team

    2003-12-01

    Deformation and volcanic activity in a plate tectonic framework must result in fluid, and therefore nutrient, fluxes within the upper oceanic crust, and between the oceanic crust and the deep ocean. These fluxes support microbial activity of many types, but the linkages are difficult to define and the magnitude of the overall process is extremely difficult to characterize and quantify because of the episodic behavior of the processes involved. Solving this problem requires long-term commitment of instrumental arrays designed to simultaneously identify and measure interactions between the seafloor and the overlying ocean. Although largely operating in a plate tectonically dominated regime on earth, similar geo-biochemical processes may be active on any number of planets at some time following accretion. Understanding the interactions here on earth may inform exploration for life on other bodies in our solar system and beyond. As an initial step toward exploring these linked phenomena, three adjacent plate boundaries along the northern edge of the Juan de Fuca Plate, were instrumented in the summer of 2003 with support from the Keck Foundation and the NSF. The intent is to initiate a proto-NEPTUNE suite of experiments designed to define the basic relationships involved microbial productivity resulting from plate boundary deformation. Although deployed in an autonomous mode now, the instruments and the approaches involved will transition to the Regional Cabled Observatory planned for the NE Pacific within five years. The principal focus of this initial deployment was on a vigorously active ridge crest hydrothermal system overlying a known magma chamber. In the summer of 2003, a permanent installation of 8 seismometers, 7 seven-short period instruments and one broad band sensor, was completed at the northern end of the Juan de Fuca Ridge on the Endeavour Segment. The seismic array is complemented by a suite of temperature, fluid flow, and pressure measuring devices, as

  9. Pliocene eclogite exhumation at plate tectonic rates in eastern Papua New Guinea.

    PubMed

    Baldwin, Suzanne L; Monteleone, Brian D; Webb, Laura E; Fitzgerald, Paul G; Grove, Marty; Hill, E June

    2004-09-16

    As lithospheric plates are subducted, rocks are metamorphosed under high-pressure and ultrahigh-pressure conditions to produce eclogites and eclogite facies metamorphic rocks. Because chemical equilibrium is rarely fully achieved, eclogites may preserve in their distinctive mineral assemblages and textures a record of the pressures, temperatures and deformation the rock was subjected to during subduction and subsequent exhumation. Radioactive parent-daughter isotopic variations within minerals reveal the timing of these events. Here we present in situ zircon U/Pb ion microprobe data that dates the timing of eclogite facies metamorphism in eastern Papua New Guinea at 4.3 +/- 0.4 Myr ago, making this the youngest documented eclogite exposed at the Earth's surface. Eclogite exhumation from depths of approximately 75 km was extremely rapid and occurred at plate tectonic rates (cm yr(-1)). The eclogite was exhumed within a portion of the obliquely convergent Australian-Pacific plate boundary zone, in an extending region located west of the Woodlark basin sea floor spreading centre. Such rapid exhumation (> 1 cm yr(-1)) of high-pressure and, we infer, ultrahigh-pressure rocks is facilitated by extension within transient plate boundary zones associated with rapid oblique plate convergence. PMID:15372021

  10. The motion and rheology of the Indian plate, and their effects upon Tibetan tectonics

    NASA Astrophysics Data System (ADS)

    Copley, A.; Avouac, J.; Hollingsworth, J.; Leprince, S.

    2010-12-01

    We describe three inter-related studies which together shed new light on the rheology and dynamics of the Indian plate and the Tibetan Plateau. We begin by describing force-balance calculations in which we have estimated the forces acting upon the Indian plate, and quantified the effects of the India-Asia collision upon the motion of the plate. We then describe a joint inversion of seismic and geodetic data for the distribution of slip in the 2001 Mw 7.6 Bhuj earthquake. By comparing the stress drop in the earthquake with the total force exerted upon the Indian plate by the Tibetan Plateau (estimated from our force-balance calculations) we can infer that the majority of the forces exerted upon the plate are supported by stresses within the seismogenic crust. We show this model is consistent with the distribution of seismicity beneath the Ganges foreland basin. Finally, we discuss the effects of this strong Indian crust upon the deformation of the Tibetan Plateau. We show that spatial variations in tectonic regime within the plateau are the result of the underthrusting of strong Indian crust, and that the surface is mechanically coupled to the deep roots of the mountain range.

  11. Plate tectonics 2.5 billion years ago - Evidence at Kolar, south India

    NASA Technical Reports Server (NTRS)

    Krogstad, E. J.; Hanson, G. N.; Balakrishnan, S.; Rajamani, V.; Mukhopadhyay, D. K.

    1989-01-01

    The Archean Kolar Schist Belt, south India, is a suture zone where two gneiss terranes and at least two amphibolite terranes with distinct histories were accreted. Amphibolites from the eastern and western sides of the schist belt have distinct incompatible element and isotopic characteristics suggesting that their volcanic protoliths were derived from different mantle sources. The amphibolite and gneiss terranes were juxtaposed by horizontal compression and shearing between 2530 and 2420 million years ago (Ma) along a zone marked by the Kolar Schist Belt. This history of accretion of discrete crustal terranes resembles those of Phanerozoic convergent margins and thus suggests that plate tectonics operated on earth by 2500 Ma.

  12. Plate tectonics on large exoplanets and the importance of the initial conditions

    NASA Astrophysics Data System (ADS)

    Noack, Lena; Breuer, Doris

    2013-04-01

    Several numerical studies have been published in the past years speculating about the existence of plate tectonics on large exoplanets. These studies focus on various aspects like the mass of a planet [1,2,3,5], the interior heating rate and mantle temperatures [4,5] and the occurrence of water in the upper mantle [6]. Different trends in the propensity for plate tectonics have been observed in particular when varying the planetary mass: with increasing mass the surface mobilization is found to be either more [2,3,5], equally [3,6] or less [1,4] likely than on Earth. These studies and their implications are, however, difficult to compare as they assume different initial conditions and parameter sets, and either neglect the pressure effect on the viscosity or assume a rather small influence of the pressure on the rheology. Furthermore, the thermal evolution of the planets (i.e. cooling of core and decrease in radioactive heat sources with time) is typically neglected. In our study, we us the finite volume code GAIA [7] and apply a pseudo-plastic rheology. We investigate how a strong pressure-dependence of the viscosity [8] influences not only the convective regime in the lower mantle, but also the upper mantle and hence the likelihood to obtain plate tectonics. We investigate how our results change when assuming different initial conditions, focussing on the initial temperature in the lower mantle and at the core-mantle boundary. We find that the initial temperature conditions have a first-order influence on the likelihood of plate tectonics on large exoplanets and (as observed in earlier studies) surface mobilization may either be more, equally or less likely than on Earth. References [1] O'Neill, C. and A. Lenardic (2007), GRL 34, 1-4. [2] Valencia, D., O'Connell, R.J. and Sasselov, D.D. (2007), Astrophys. J. Let., 670(1):45-48. [3] van Heck, H.J. and Tackley, P.J. (2011), EPSL, 310:252-261. [4] Stein, C.; A. Finnenkötter, J. P. Lowman and U. Hansen (2011), GRL

  13. Drilling to investigate processes in active tectonics and magmatism

    NASA Astrophysics Data System (ADS)

    Shervais, J.; Evans, J.; Toy, V.; Kirkpatrick, J.; Clarke, A.; Eichelberger, J.

    2014-12-01

    convergent plate margins (subduction zones). This workshop brought together a diverse group of scientists with a broad range of scientific experience and interests. A particular strength was the involvement of both early-career scientists, who will initiate and carry out these new research programs, and more senior researchers with many years of experience in scientific drilling and active tectonics research. Each of the themes and questions outlined above has direct benefits to society, including improving hazard assessment, direct monitoring of active systems for early warning, renewable and non-renewable resource and energy exploitation, and predicting the environmental impacts of natural hazards, emphasizing the central role that scientific drilling will play in future scientific and societal developments.

  14. Tectonic plates, difficulties for pupils to link models and scientific data.

    NASA Astrophysics Data System (ADS)

    David-Ameline, Jacques

    2014-05-01

    In a secondary school in the west of France, I teach Biology and Geology to young pupils from 12 to 15 years old. This poster deals with the difficulties that pupils have to link the scientific data concerning the plate tectonics and the models. I choose to reproduce for pupils some situations that faced some first scientific people as they discovered arguments for the plate tectonics. For example, they have to discover the thickness of the plates by studying the speed of the seismic waves regarding the deepness. That means that they have to construct a curve starting with a table and then to analyze it. The first step is linked to math lessons and is quite easy for them. But the second one needs to mix the curve with its signification. This point is particularly hard and as we correct it, it appears like one moment of « pure science » because they seem to discover something none did before, with the power of their brain ! The second work on this subject is to study the representations of the subduction at an oceanic trench and of the mid-ocean ridge. They first look for drawing explaining what happens for the plates in those places and then they look for proofs that permitted to create those drawings. They really need help to make the difference between scientific data (pictures, curves...) and other drawings similar to the one they choose. For this subject working with documents is not easy because pupils have to ask themselves « what kind of document is it ?» before going further into their thinking. Nevertheless, they often succeed in those works because the teacher helps them a little. Those subjects open their eyes on what science is for a geological theme. It's also a good method to make them having fun doing science and to make them being seduced by making science.

  15. Thermochronology and tectonics of the Leeward Antilles: Evolution of the southern Caribbean Plate boundary zone

    USGS Publications Warehouse

    van der Lelij, Roelant; Spikings, Richard A.; Kerr, Andrew C.; Kounov, Alexandre; Cosca, Michael; Chew, David; Villagomez, Diego

    2010-01-01

    Tectonic reconstructions of the Caribbean Plate are severely hampered by a paucity of geochronologic and exhumation constraints from anastomosed basement blocks along its southern margin. New U/Pb, 40Ar/39Ar, apatite fission track, and apatite (U-Th)/He data constrain quantitative thermal and exhumation histories, which have been used to propose a model for the tectonic evolution of the emergent parts of the Bonaire Block and the southern Caribbean Plate boundary zone. An east facing arc system intruded through an oceanic plateau during ~90 to ~87 Ma and crops out on Aruba. Subsequent structural displacements resulted in >80°C of cooling on Aruba during 70–60 Ma. In contrast, exhumation of the island arc sequence exposed on Bonaire occurred at 85–80 Ma and 55–45 Ma. Santonian exhumation on Bonaire occurred immediately subsequent to burial metamorphism and may have been driven by the collision of a west facing island arc with the Caribbean Plate. Island arc rocks intruded oceanic plateau rocks on Gran Roque at ~65 Ma and exhumed rapidly at 55–45 Ma. We attribute Maastrichtian-Danian exhumation on Aruba and early Eocene exhumation on Bonaire and Gran Roque to sequential diachronous accretion of their basement units to the South American Plate. Widespread unconformities indicate late Eocene subaerial exposure. Late Oligocene–early Miocene dextral transtension within the Bonaire Block drove subsidence and burial of crystalline basement rocks of the Leeward Antilles to ≤1 km. Late Miocene–recent transpression caused inversion and ≤1 km of exhumation, possibly as a result of the northward escape of the Maracaibo Block.

  16. Plate tectonics and orogenic research after 25 years: Synopsis of a Tethyan perspective

    NASA Astrophysics Data System (ADS)

    Şengör, A. M. Celâl

    1991-02-01

    Orogeny, the process by which the earth's prominent mountain ranges are constructed, is herein defined as a collective term for convergent margin processes. The recognition that strains and displacements of very considerable magnitude occur along all of the three dimensions within an orogenic belt has grown gradually during the last two centuries. Investigation of orogenic belts along cross-sections reveals that there are a large number of types of orogenic belts. These are divided into four main orders ( transpressional, subduction-controlled, obduction-controlled, and collision-controlled) consisting of two superfamilies, eight families, and twenty genera. Cross-sectional studies of orogenic belts show that the cross-sectional area during orogeny is not conserved. Similarly, map-view studies of orogenic belts reveal that an absolute minimum of 60% (by length) of them display significant strike-slip motion along their trend which leads also to a non-conservation of the cross-sectional area during orogeny. Thus, rigorous line and area balancing across orogenic belts now is not possible. Large orogenic belts are commonly made up of tectonic collages of microcontinents, island arcs, and accretionary complexes, generally disrupted to form smaller, fault-bounded tectonic entities of diverse sorts. The recently developed "terrane analysis" was developed to aid the study of these but it resembles the early concepts of Alpine nappes and is found to be a retrogressive step in tectonic research mainly because of its disclaim of most genetic connotations. The temporal aspects of orogeny have been debated for over 200 years in terms of continuous vs. world-wide, synchronously episodic orogeny. Plate tectonics has provided a rigorous rationale and something approaching a consensus for continuous orogeny. I conclude that there are as yet no shortcuts to establishing the kinematics of continental deformation except by the traditional methods of field geology aided by relevant

  17. Evidence for long-lived subduction of an ancient tectonic plate beneath the southern Indian Ocean

    SciTech Connect

    Simmons, N. A.; Myers, S. C.; Johannesson, G.; Matzel, E.; Grand, S. P.

    2015-11-14

    In this study, ancient subducted tectonic plates have been observed in past seismic images of the mantle beneath North America and Eurasia, and it is likely that other ancient slab structures have remained largely hidden, particularly in the seismic-data-limited regions beneath the vast oceans in the Southern Hemisphere. Here we present a new global tomographic image, which shows a slab-like structure beneath the southern Indian Ocean with coherency from the upper mantle to the core-mantle boundary region—a feature that has never been identified. We postulate that the structure is an ancient tectonic plate that sank into the mantle along an extensive intraoceanic subduction zone that migrated southwestward across the ancient Tethys Ocean in the Mesozoic Era. Slab material still trapped in the transition zone is positioned near the edge of East Gondwana at 140 Ma suggesting that subduction terminated near the margin of the ancient continent prior to breakup and subsequent dispersal of its subcontinents.

  18. Evidence for long-lived subduction of an ancient tectonic plate beneath the southern Indian Ocean

    DOE PAGESBeta

    Simmons, N. A.; Myers, S. C.; Johannesson, G.; Matzel, E.; Grand, S. P.

    2015-11-14

    In this study, ancient subducted tectonic plates have been observed in past seismic images of the mantle beneath North America and Eurasia, and it is likely that other ancient slab structures have remained largely hidden, particularly in the seismic-data-limited regions beneath the vast oceans in the Southern Hemisphere. Here we present a new global tomographic image, which shows a slab-like structure beneath the southern Indian Ocean with coherency from the upper mantle to the core-mantle boundary region—a feature that has never been identified. We postulate that the structure is an ancient tectonic plate that sank into the mantle along anmore » extensive intraoceanic subduction zone that migrated southwestward across the ancient Tethys Ocean in the Mesozoic Era. Slab material still trapped in the transition zone is positioned near the edge of East Gondwana at 140 Ma suggesting that subduction terminated near the margin of the ancient continent prior to breakup and subsequent dispersal of its subcontinents.« less

  19. Permian and Pennsylvanian tectonic events in eastern California in relation to major plate motions

    SciTech Connect

    Stevens, C.H.; Sedlock, R. ); Stone, P. )

    1993-04-01

    Northwest-trending basins cutting across older northeast-trending facies belts in eastern California opened by Middle Pennsylvanian time and continued to develop and expand into the Early Permian. Basin development was accompanied by east-vergent thrust-faulting in the Early Permian and was followed by development of northeast-trending folds and regional uplift in middle and Late Permian time. These events have been considered products of long-tern sinistral truncation of the western North American continental margin. Later, in the Late Permian, extensional faulting created small northeast-trending basins in which deposition of terrestrial and shallow-marine rocks occurred. The author consider all late Paleozoic tectonism in eastern California to have been driven by plate interactions along the western margin of North America and to be only indirectly related to the late Paleozoic collision between North America and Gondwana. They propose that the truncated part of North America was part of the Paleo-pacific plate. In Nevada the margin of this plate, along which the Havallah assemblage eventually was emplaced, was convergent, but in California the margin bent sharply and became transform. This fault continued as the Mojave-Sonora mega-shear into Mexico where the oceanic part of the Paleopacific plate was subducted under Gondwana, forming an extensive arc now represented by rocks in S. America.

  20. Acoustic monitoring of earthquakes along the Blanco Transform Fault zone and Gorda Plate and their tectonic implications

    NASA Astrophysics Data System (ADS)

    Dziak, Robert Paul

    Hydroacoustic tertiary (T-) waves are seismically generated acoustic waves that propagate over great distances in the ocean sound channel with little loss in signal strength. Hydrophone recorded T-waves can provide a lower earthquake detection threshold and an improved epicenter location accuracy for oceanic earthquakes than land-based seismic networks. Thus detection and location of NE Pacific ocean earthquakes along the Blanco Transform Fault (BTFZ) and Gorda plate using the U.S. Navy's SOSUS (SOund SUrveillance System) hydrophone arrays afford greater insight into the current state of stress and crustal deformation mechanics than previously available. Acoustic earthquake information combined with bathymetry, submersible observations, earthquake source- parameter estimates, petrologic samples, and water-column chemistry renders a new tectonic view of the southern Juan de Fuca plate boundaries. Chapter 2 discusses development of seismo-acoustic analysis techniques using the well-documented April 1992 Cape Mendocino earthquake sequence. Findings include a hydrophone detection threshold estimate (M ~ 2.4), and T-wave propagation path modeling to approximate earthquake acoustic source energy. Empirical analyses indicate that acoustic energy provides a reasonable magnitude and seismic moment estimate of oceanic earthquakes not detected by seismic networks. Chapters 3 documents a probable volcanogenic T-wave event swarm along a pull-apart basin within the western BTFZ during January 1994. Response efforts yielded evidence of anomalous water-column 3He concentrations, pillow- lava volcanism, and the first discovery of active hydrothermal vents along an oceanic fracture zone. Chapter 4 discusses the detection of a NE-SW trending microearthquake band along the mid-Gorda plate which was active from initiation of SOSUS recording in August 1991 through July 1992, then abruptly ceased. It is proposed that eventual termination of the Gorda plate seismicity band is due to

  1. Tectonics

    NASA Astrophysics Data System (ADS)

    John Dewey will complete his term as editor-in-chief of Tectonics at the end of 1984. Clark Burchfiel's term as North American Editor will also end. Tectonics is published jointly with the European Geophysical Society. This newest of AGU's journals has already established itself as an important journal bridging the concerns of geophysics and geology.James A. Van Allen, president of AGU, has appointed a committee to recommend candidates for both editor-in-chief and North American editor for the 1985-1987 term.

  2. Investigating the Subduction History of the Southwest Pacific using Coupled Plate Tectonic-Mantle Convection Models

    NASA Astrophysics Data System (ADS)

    Matthews, K. J.; Flament, N. E.; Williams, S.; Müller, D.; Gurnis, M.

    2014-12-01

    The Late Cretaceous to mid Eocene (~85-45 Ma) evolution of the southwest Pacific has been the subject of starkly contrasting plate reconstruction models, reflecting sparse and ambiguous data. Disparate models of (1) west-dipping subduction and back-arc basin opening to the east of the Lord Howe Rise, (2) east-dipping subduction and back-arc basin closure to the east of the Lord Howe Rise, and (3) tectonic quiescence with no subduction have all been proposed for this time frame. To help resolve this long-standing problem we test a new southwest Pacific reconstruction using global mantle flow models with imposed plate motions. The kinematic model incorporates east to northeast directed rollback of a west-dipping subduction zone between 85 and 55 Ma, accommodating opening of the South Loyalty back-arc basin to the east of New Caledonia. At 55 Ma there is a plate boundary reorganization in the region. West-dipping subduction and back-arc basin spreading end, and there is initiation of northeast dipping subduction within the back-arc basin. Consumption of South Loyalty Basin seafloor continues until 45 Ma, when obduction onto New Caledonia begins. West-dipping Tonga-Kermadec subduction initiates at this time at the relict Late Cretaceous-earliest Eocene subduction boundary. We use the 3D spherical mantle convection code CitcomS coupled to the plate reconstruction software GPlates, with plate motions and evolving plate boundaries imposed since 230 Ma. The predicted present-day mantle structure is compared to S- and P-wave seismic tomography models, which can be used to infer the presence of slab material in the mantle at locations where fast velocity anomalies are imaged. This workflow enables us to assess the forward-modeled subduction history of the region.

  3. Tectonics of the Scotia-Antarctica plate boundary constrained from seismic and seismological data

    NASA Astrophysics Data System (ADS)

    Civile, D.; Lodolo, E.; Vuan, A.; Loreto, M. F.

    2012-07-01

    The plate boundary between the Scotia and Antarctic plates runs along the broadly E-W trending South Scotia Ridge. It is a mainly transcurrent margin that juxtaposes thinned continental and transitional crust elements with restricted oceanic basins and deep troughs. Seismic profiles and regional-scale seismological constraints are used to define the peculiarities of the crustal structures in and around the southern Scotia Sea, and focal solutions from recent earthquakes help to understand the present-day geodynamic setting. The northern edge of the western South Scotia Ridge is marked by a sub-vertical, left-lateral master fault. Locally, a narrow wedge of accreted sediments is present at the base of the slope. This segment represents the boundary between the Scotia plate and the independent South Shetland continental block. Along the northern margin of the South Orkney microcontinent, the largest fragment of the South Scotia Ridge, an accretionary prism is present at the base of the slope, which was possibly created by the eastward drift of the South Orkney microcontinent and the consequent subduction of the transitional crust present to the north. East of the South Orkney microcontinent, the physiography and structure of the plate boundary are less constrained. Here the tectonic regime exhibits mainly strike-slip behavior with some grade of extensional component, and the plate boundary is segmented by a series of NNW-SSE trending release zones which favored the fragmentation and dispersion of the crustal blocks. Seismic data have also identified, along the north-western edge of the South Scotia Ridge, an elevated region - the Ona Platform - which can be considered, along with the Terror Rise, as the conjugate margin of the Tierra del Fuego, before the Drake Passage opening. We propose here an evolutionary sketch for the plate boundary (from the Late Oligocene to the present) encompassing the segment from the Elephant Island platform to the Herdman Bank.

  4. Active Tectonics And Modern Geodynamics Of Sub-Yerevan Region

    NASA Astrophysics Data System (ADS)

    Avanesyan, M.

    2004-05-01

    The given work is dedicated to active tectonics and modern geodynamics of Sub-Yerevan region. This region is interesting as a one of regions with maximal seismic activity in Armenia. The high level of seismic risk of this region is conditioned by high level of seismic hazard, high density of the population, as well as presence of objects of special importance and industrial capacities. The modern structure of Sub-Yerevan region and the adjacent area, as well as the Caucasus entirely, has mosaic-block appearance, typical for collision zone of Arabian and Eurasian plates. Distinctively oriented active faults of various ranges and morphological types are distinguished. These faults, in their turn, form various-scale active blocks of the Earth's crust and their movement defines seismic activity of the region. The researches show, that all strong earthquakes in the region were caused by movements by newest and activated ancient faults. In order to reveal the character of Earth's crust active blocks movement, separation of high gradients of horizontal and vertical movements and definition of stress fields highest concentration regions by GPS observations, high-accuracy leveling and study of earthquake focal mechanisms a new seismotectonic model is developed, which represents a combination of tectonic structure, seismic data, newest and modern movements. On the basis of comparison and analysis of these data zones with potential maximal seismic hazard are separated. The zone of joint of Azat-Sevan active and Yerevan abysmal faults is the most active on the territory of Sub-Yerevan region. The directions relatively the Earth's crust movement in the zones of horizontal and vertical movement gradients lead to conclusion, that Aragats-Tsakhkunian and Gegam active blocks undergo clockwise rotation. This means, that additional concentration of stress must be observed in block corners, that is confirmed by location of strong earthquakes sources. Thus, on the North 1988 Spitak (M

  5. Evolution of the western segment of Juan Fernández Ridge (Nazca Plate): plume vs. plate tectonic processes

    NASA Astrophysics Data System (ADS)

    Lara, Luis E.; Rodrigo, Cristián; Reyes, Javier; Orozco, Gabriel

    2014-05-01

    The Juan Fernandez Ridge (Eastern Pacific, Nazca Plate) is thought to be a classic hot spot trail because of the apparent age progression observed in 40Ar-39Ar data. However, geological evidence and some thermochronological data suggest a more complex pattern with a rejuvenation stage in Robinson Crusoe Island, the most eroded of the Juan Fernandez Archipelago. In fact, a postshield stage at 900-700 ka separates the underlying shield-related pile from the post-erosional alkaline succession (Ba/Yb=38.15; La/Yb=15.66; Ba/Y=20.27; Ba/Zr=2.31). Shield volcanoes grew at high effusion rate at ca. 5-4 Ma erupting mostly tholeiitic to transitional magmas (Ba/Yb=18.07-8.32; La/Yb=4.59-9.84; Ba/Y=4.24-8.18; Ba/Zr=0.73-1.09). Taken together, shield volcanoes form a continuous plateau with a base at ca. 3900 mbsl. However, a more complex structural pattern can be inferred from geophysical data, which suggest some intracrustal magma storage and a more extended area of magma ascent. A role for the Challenger Fracture Zone is hypothesized fueling the controversy between pristine plume origin and the effect of plate tectonic processes in the origin of intraplate volcanism. This research is supported by FONDECYT Project 1110966.

  6. The emergence of seismic cycles from stress feedback between intra-plate faulting and far-field tectonic loading

    NASA Astrophysics Data System (ADS)

    So, Byung-Dal; Capitanio, Fabio A.

    2016-08-01

    Using numerical modeling we show the emergence of cyclic slip behavior of faults from stress feedback through an idealized fault, its surrounding plates and far-field tectonic stress. The tectonic stress is exerted on the fault through a force applied along an idealized plate margin, acting on the fault, resulting from the interactions of viscous embedding and external plates. We find that, in such coupled system, the interaction of plates results into feedback with periodic deformation, slip along the fault and episodic plate margin motions. The viscosity of the embedding and loading plates primarily control the stress-loading time and hence the slip recurrence interval. For an Earth-like range of lithospheric viscosities, we derive a power-law with negative exponent, -0.99 to -0.5, scaling the recurrence period with loading-rate, providing an explanation for the observables from paleoseismology and geodesy. The feedback between single fault and far-field stress that arises from interactions of deforming plates provides a context to understand the earthquake cycle within continents, while reconciling the short-term seismic deformation to the long-term plate tectonics frame.

  7. Rubidium-strontium geochronology and plate-tectonic evolution of the southern part of the Arabian Shield

    USGS Publications Warehouse

    Fleck, Robert J.; Greenwood, W.R.; Hadley, D.G.; Anderson, R.E.; Schmidt, D.L.

    1980-01-01

    Rubidium-strontium studies of Precambrian volcanic and plutonic rocks of the Arabian Shield document an early development of the Arabian craton between 900 and 680 m.y. (million years) ago. Geologic studies indicate an island-arc environment characterized by andesitic (dioritic) magmas, volcaniclastic sedimentation, rapid deposition, and contemporaneous deformation along north or northwest-trending axes. Magmatic trends show consistent variation in both composition and geographic location as a function of age. The oldest units belong to an assemblage of basaltic strata exposed in western Saudi Arabia that yield an age of 1165:!:110 m.y. The oldest andesitic strata studied yield an age of 912:!:76 m.y. The earliest plutonic units are diorite to trondhjemite batholiths that range from 800 to 9,00 m.y. in age and ,occur along the western and southern parts of Saudi Arabia. Younger plutonic units, 680 to 750 m.y. in age, range from quartz diorite to granodiodte and become more abundant in the central and northeastern parts of the Arabian Shield. Initial 'Sr/ 86 Sr ratios for both dioritic groups range from 0.7023 to 0.7030 and average 0.7027. The absence of sialic detritus in sedimentary units and the evidence for an island-arc environment suggest the early development of the Arabian craton at a convergent plate margin between plates of oceanic lithosphere. Active subduction apparently extended from at least 900 m.y. to about 680 m.y. Subsequent to this subduction-related magmatism and tectonism, called the Hijaz tectonic cycle, the Arabian craton was sutured to the late Precambrian African plate in a collisional event. This period of orogeny, represented in Arabia and eastern Africa by the Mozambiquian or Pan-African event, extended from some time before 650 m.y. to at least 540 m.y. and perhaps 520 m.y. B.P. Although the tectonic processes of subduction and continental collision during the 900+ to 500-m.y. period require similar directions of plate convergence, the

  8. Plate Tectonics Initiation on Earth-Like Planets: Insights From Numerical and Theoretical Analysis of Convection-Induced Lithospheric Failure

    NASA Astrophysics Data System (ADS)

    Wong, Teresa

    Plate tectonics is central to many aspects of the geology and evolution of terrestrial planets, yet it is only observed on the Earth while all other known planets are covered with a stagnant lithosphere. Plate motions on the Earth are mostly driven by the pull of subducting slabs, therefore understanding the initiation of subduction is crucial to understanding plate tectonics initiation. On a one-plate planet which lacks the forces due to plate motions, some other mechanisms will have to cause the first episode of subduction to mobilize the surface. Sublithospheric convection has been proposed as a possible mechanism that induce stresses in the lithosphere. The question is whether these stresses can initiate subduction. We develop scaling laws for the criterion of lithospheric failure from single-cell steady-state convection, which has more controlled flow and thus easier to analyze. We show that these scaling laws are applicable to time-dependent convection. We also investigate the time-dependent behavior of convection to understand the factors controlling the timing of lithospheric failure. We find that the variation in timing not only systematically depends on the physical parameters of the convecting mantle; for convective systems with the same set of parameters, small variations in initial conditions result in different structures of the lithosphere. This changes the stresses in the lithosphere and gives rise to different times of lithospheric failure. This study suggests that it is important to address the question of when plate tectonics can initiate on a planet, in addition to finding favorable conditions for lithospheric failure. We extrapolate the scaling laws to planetary conditions to assess the feasibility of plate tectonics for terrestrial planets, and estimate whether plate tectonics can happen in reasonable planetary lifetimes.

  9. Melting-induced crustal production helps plate tectonics on Earth-like planets

    NASA Astrophysics Data System (ADS)

    Lourenço, Diogo L.; Rozel, Antoine; Tackley, Paul J.

    2016-04-01

    Within our Solar System, Earth is the only planet to be in a mobile-lid regime. It is generally accepted that the other terrestrial planets are currently in a stagnant-lid regime, with the possible exception of Venus that may be in an episodic-lid regime (Armann and Tackley, JGR 2012). Using plastic yielding to self-consistently generate plate tectonics on an Earth-like planet with strongly temperature-dependent viscosity is now well-established, but such models typically focus on purely thermal convection, whereas compositional variations in the lithosphere can alter the stress state and greatly influence the likelihood of plate tectonics. For example, Rolf and Tackley (GRL, 2011) showed that the addition of a continent can reduce the critical yield stress for mobile-lid behaviour by a factor of around two. Moreover, it has been shown that the final tectonic state of the system can depend on the initial condition (Tackley, G3 2000 - part 2). Weller and Lenardic (GRL, 2012) found that the parameter range in which two solutions are obtained increases with viscosity contrast. We can also say that partial melting has a major role in the long-term evolution of rocky planets: (1) partial melting causes differentiation in both major elements and trace elements, which are generally incompatible (Hofmann, Nature 1997). Trace elements may contain heat-producing isotopes, which contribute to the heat loss from the interior; (2) melting and volcanism are an important heat loss mechanism at early times that act as a strong thermostat, buffering mantle temperatures and preventing it from getting too hot (Xie and Tackley, JGR 2004b); (3) mantle melting dehydrates and hardens the shallow part of the mantle (Hirth and Kohlstedt, EPSL 1996) and introduces viscosity and compositional stratifications in the shallow mantle due to viscosity variations with the loss of hydrogen upon melting (Faul and Jackson, JGR 2007; Korenaga and Karato, JGR 2008). We present a set of 2D spherical

  10. Past and present seafloor age distributions and the temporal evolution of plate tectonic heat transport

    NASA Astrophysics Data System (ADS)

    Becker, Thorsten W.; Conrad, Clinton P.; Buffett, Bruce; Müller, R. Dietmar

    2009-02-01

    Variations in Earth's rates of seafloor generation and recycling have far-reaching consequences for sea level, ocean chemistry, and climate. However, there is little agreement on the correct parameterization for the time-dependent evolution of plate motions. A strong constraint is given by seafloor age distributions, which are affected by variations in average spreading rate, ridge length, and the age distribution of seafloor being removed by subduction. Using a simplified evolution model, we explore which physical parameterizations of these quantities are compatible with broad trends in the area per seafloor age statistics for the present-day and back to 140 Ma from paleo-age reconstructions. We show that a probability of subduction based on plate buoyancy (slab-pull, or "sqrt(age)") and a time-varying spreading rate fits the observed age distributions as well as, or better than, a subduction probability consistent with an unvarying "triangular" age distribution and age-independent destruction of ocean floor. Instead, we interpret the present near-triangular distribution of ages as a snapshot of a transient state of the evolving oceanic plate system. Current seafloor ages still contain hints of a ˜ 60 Myr periodicity in seafloor production, and using paleoages, we find that a ˜ 250 Myr period variation is consistent with geologically-based reconstructions of production rate variations. These long-period variations also imply a decrease of oceanic heat flow by ˜ - 0.25%/Ma during the last 140 Ma, caused by a 25-50% decrease in the rate of seafloor production. Our study offers an improved understanding of the non-uniformitarian evolution of plate tectonics and the interplay between continental cycles and the self-organization of the oceanic plates.

  11. Micro-plate tectonics and kinematics in Northeast Asia inferred from a dense set of GPS observations

    NASA Astrophysics Data System (ADS)

    Jin, Shuanggen; Park, Pil-Ho; Zhu, Wenyao

    2007-05-01

    The plate tectonics of Northeast Asia are very complex with diffuse and sparse seismicity in the broad plate deformation zones embedded by a number of micro-plates, particularly the controversial Amurian plate. Now the increasingly dense GPS networks in this area provide an important tool to investigate plate tectonic kinematics and to identify the approximate plate tectonic geometries. In this paper, we have processed GPS data (1998-2005) collected by an extensive GPS network (China and South Korea) with more than 85 continuous sites and about 1000 campaign GPS stations. The kinematics of Northeast Asia is studied by modeling GPS-derived velocities with rigid block rotations and elastic deformation. We find that the deformation in Northeast Asia can be well described by a number of rotating blocks, which are independent of the Eurasian plate motion with statistical significance above the 99% confidence level. The tectonic boundary between the North China and Amuria plates is the Yin Shan-Yan Shan Mountain belts with about 2.4 mm/yr extension. Along the boundary between North China and South China, the Qinling-Dabie fault is moving left laterally at about 3.1 mm/yr. The Amuria and South Korea blocks are extending at about 1.8 mm/yr. The Baikal Rift between the Amurian and Eurasian plates is spreading at about 3.0 mm/yr. The 9-17 mm/yr relative motion between the Amuria and Okhotsk blocks is accommodated at the East Sea-Japan trench zone. Localized deformation near the Qinling-Dabie fault and Yin Shan-Yan Shan Mountain belts may be elastic strain accumulation due to interseismic locking of faults.

  12. New Paleomagnetic Justification for the Plate Tectonic Reconstruction of the Arctic

    NASA Astrophysics Data System (ADS)

    Metelkin, D. V.; Vernikovskiy, V. A.; Matushkin, N. Y.; Zhdanova, A.; Mikhaltsov, N. E.; Abashev, V. V.; Kulakov, E.

    2015-12-01

    We report paleomagnetic and geologic data that support a new plate tectonic reconstruction for the Arctic from the Neoproterozoic to Mesozoic. We propose a new outlook on the history of the Arctida paleocontinent, which combined sialic blocks of the present Eurasian shelf of the Arctic Ocean. Our model implies two Arctidas at that time. The earlier Arctida-I was located near equator and connected the continental margins of Laurentia, Baltica and Siberia within the supercontinent of Rodinia. The Arcrtida-I disintegration was caused by a breakup of Rodinia. As a result, small plates like on Svalbard, Kara, New Siberia Island (NSI) terrane and others were formed. We have reconstructed the main stages of later remobilization and global drift of these plates before Pangea assemblage. In contrast to traditional interpretation of the NSI as a part of the Chukchi-Alaska terrane, our observation suggest a linkage between the NSI and Kolyma-Omolon terrane that framed Siberia. As a result of Pangea assembly at Paleozoic-Mesozoic boundary the second recovery of Arctida took place. We assume that Arctida-II also connected Laurentia, Baltica, and Siberia but constituted the Pangean periphery in the temperate latitudes. The later Arctida-II disintegrated during the Mesozoic during the opening of Arctic Ocean.

  13. Integrating Plate Tectonic Reconstruction and Mantle Dynamics: A valuable Aid in Frontier Exploration

    NASA Astrophysics Data System (ADS)

    Hafkenscheid, Edith; Warners-Ruckstuhl, Karin; van Oosterhout, Cees; Bergman, Steve; Davies, J. Huw; Govers, Rob; Hochard, Cyril; Kennan, Lorcan; Ross, Malcolm; Stampfli, Gérard M.; Vérard, Christan; Webb, Peter; Wortel, Rinus

    2013-04-01

    Effective hydrocarbon exploration in frontier regions requires an understanding of the tectonic and thermal evolution of basins, among other parameters or conditions. This is especially challenging when high-resolution local data are lacking, requiring reasonable interpolation and extrapolation of more regional knowledge. Some of the key first-order parameters influencing the presence and preservation of an economic petroleum system are the basin's vertical motion history and its thermal and stress evolution. To quantify these parameters in a physically consistent manner over several hundred million years, an integrated lithosphere-mantle dynamics modeling approach is needed. To this purpose, we embarked on developing a 3D dynamic model for the whole earth that links surface phenomena to mantle convection and lithosphere dynamics. The project involved a close collaboration between Shell and three universities, and integration of many disciplines and techniques. University of Lausanne developed 600-0 Ma global plate reconstructions with consistently evolving plate boundaries. The 300-0 Ma period was then adapted to be used as surface boundary condition for forward mantle convection modeling by Cardiff University, producing global predictions of base lithosphere temperatures, heat flow and mantle induced vertical surface motion through time. As a last step, Utrecht University developed a method to predict the lithospheric stress field through time based on integration of these mantle modeling results with the plate reconstruction model. This approach offers predictive scenarios and grids relevant to petroleum exploration that can be validated with local geological and geophysical data.

  14. The boundary between the Indian and Asian tectonic plates below Tibet

    PubMed Central

    Zhao, Junmeng; Yuan, Xiaohui; Liu, Hongbing; Kumar, Prakash; Pei, Shunping; Kind, Rainer; Zhang, Zhongjie; Teng, Jiwen; Ding, Lin; Gao, Xing; Xu, Qiang; Wang, Wei

    2010-01-01

    The fate of the colliding Indian and Asian tectonic plates below the Tibetan high plateau may be visualized by, in addition to seismic tomography, mapping the deep seismic discontinuities, like the crust-mantle boundary (Moho), the lithosphere-asthenosphere boundary (LAB), or the discontinuities at 410 and 660 km depth. We herein present observations of seismic discontinuities with the P and S receiver function techniques beneath central and western Tibet along two new profiles and discuss the results in connection with results from earlier profiles, which did observe the LAB. The LAB of the Indian and Asian plates is well-imaged by several profiles and suggests a changing mode of India-Asia collision in the east-west direction. From eastern Himalayan syntaxis to the western edge of the Tarim Basin, the Indian lithosphere is underthrusting Tibet at an increasingly shallower angle and reaching progressively further to the north. A particular lithospheric region was formed in northern and eastern Tibet as a crush zone between the two colliding plates, the existence of which is marked by high temperature, low mantle seismic wavespeed (correlating with late arriving signals from the 410 discontinuity), poor Sn propagation, east and southeast oriented global positioning system displacements, and strikingly larger seismic (SKS) anisotropy. PMID:20534567

  15. The boundary between the Indian and Asian tectonic plates below Tibet.

    PubMed

    Zhao, Junmeng; Yuan, Xiaohui; Liu, Hongbing; Kumar, Prakash; Pei, Shunping; Kind, Rainer; Zhang, Zhongjie; Teng, Jiwen; Ding, Lin; Gao, Xing; Xu, Qiang; Wang, Wei

    2010-06-22

    The fate of the colliding Indian and Asian tectonic plates below the Tibetan high plateau may be visualized by, in addition to seismic tomography, mapping the deep seismic discontinuities, like the crust-mantle boundary (Moho), the lithosphere-asthenosphere boundary (LAB), or the discontinuities at 410 and 660 km depth. We herein present observations of seismic discontinuities with the P and S receiver function techniques beneath central and western Tibet along two new profiles and discuss the results in connection with results from earlier profiles, which did observe the LAB. The LAB of the Indian and Asian plates is well-imaged by several profiles and suggests a changing mode of India-Asia collision in the east-west direction. From eastern Himalayan syntaxis to the western edge of the Tarim Basin, the Indian lithosphere is underthrusting Tibet at an increasingly shallower angle and reaching progressively further to the north. A particular lithospheric region was formed in northern and eastern Tibet as a crush zone between the two colliding plates, the existence of which is marked by high temperature, low mantle seismic wavespeed (correlating with late arriving signals from the 410 discontinuity), poor Sn propagation, east and southeast oriented global positioning system displacements, and strikingly larger seismic (SKS) anisotropy. PMID:20534567

  16. Plate Tectonics 2.0: Using GPS to Refine Global Crustal Kinematics and Rewrite Textbooks

    NASA Astrophysics Data System (ADS)

    Kreemer, C.; Blewitt, G.; Stamps, D. S.; Saria, E.

    2015-12-01

    Any model of the Earth's inner workings should be consistent with the observed motion and deformation at its surface. The whole idea that the entire Earth's surface comprises of a dozen or so tectonic plates with no deformation in between them (as most textbooks will tell you) is embarrassingly outdated. The advent of high-precision GNSS measurements of crustal motion has led to the direct observation of plate motion, the confirmation of plate rigidity, and the refinement of crustal kinematics in diffuse plate boundary zones. With the rapidly growing number of continuous GPS (cGPS) stations (as well as campaign-style measurements) some of the earlier results can now be reassessed while at the same time we can continue to quantify the motion and deformation of a large part of the Earth's surface. We present the latest version (v. 2.2) of the Global Strain Rate Model (GSRM), which is almost entirely constrained by horizontal GPS velocities. The model contains the rigid-body rotations of 50 plates as well as strain rate and vorticity estimates at a high spatial resolution for the ~14% of the Earth's surface that is caught up in between the plates. Resulting global or regional maps of dilatation, vorticity, and strain tensor amplitude and style, are poised to augment standard textbook images of plate motions, and we anticipate that they will foster further scientific and educational inquiry. GSRM v2.2 is constrained by >24,000 velocities. Of those ~7900 were determined by us from time-series that we obtained through a routine processing of all globally available RINEX data. Many of these stations were not installed with the intention to track crustal motions, but often are very usable. This station category is currently the biggest contributor to the data explosion; our solution has >1100 more stations compared with the previous solution of just 18 months ago. We transform to our solution GPS velocities from >250 published studies, >30 more than in the previous

  17. The effect of melting and crustal production on plate tectonics on terrestrial planets

    NASA Astrophysics Data System (ADS)

    Louro Lourenço, D. J.; Tackley, P. J.

    2013-12-01

    Within the Solar System, Earth is the only planet to be in a mobile-lid regime, whilst it is generally accepted that all the other terrestrial planets are currently in a stagnant-lid regime, showing little or no surface motion. A transitional regime between these two, showing episodic overturns of an unstable stagnant lid, is also possible and has been proposed for Venus (Armann and Tackley, JGR 2012). Using plastic yielding to self-consistently generate plate tectonics on an Earth-like planet with strongly temperature-dependent viscosity is now well-established, but such models typically focus on purely thermal convection, whereas compositional variations in the lithosphere can alter the stress state and greatly influence the likelihood of plate tectonics. For example, Rolf and Tackley (GRL, 2011) showed that the addition of a continent can reduce the critical yield stress for mobile-lid behaviour by a factor of around 2. Moreover, it has been shown that the final state of the system (stagnant- or mobile-lid) can depend on the initial condition (Tackley, G3 2000 - part 2); Weller and Lenardic (GRL, 2012) found that the parameter range in which two solutions are obtained increases with viscosity contrast. We can also say that partial melting has a major role in the long-term evolution of rocky planets: (1) partial melting causes differentiation in both major elements (like Fe and Si) and trace elements, which are generally incompatible (Hofmann, Nature 1997). Trace elements may contain heat-producing isotopes, which contribute to the heat loss from the interior; (2) melting and volcanism are an important heat loss mechanism at early times that act as a strong thermostat, buffering mantle temperatures and preventing it from getting too hot (Xie and Tackley, JGR 2004b; Armann and Tackley, JGR 2012); (3) mantle melting dehydrates and hardens the shallow part of the mantle (Hirth and Kohlstedt, EPSL 1996) and introduces viscosity and compositional stratifications in

  18. A Pilot Search for Evidence of Extrasolar Earth-analog Plate Tectonics

    NASA Astrophysics Data System (ADS)

    Jura, M.; Klein, B.; Xu, S.; Young, E. D.

    2014-08-01

    Relative to calcium, both strontium and barium are markedly enriched in Earth's continental crust compared to the basaltic crusts of other differentiated rocky bodies within the solar system. Here, we both re-examine available archived Keck spectra to place upper bounds on n(Ba)/n(Ca) and revisit published results for n(Sr)/n(Ca) in two white dwarfs that have accreted rocky planetesimals. We find that at most only a small fraction of the pollution is from crustal material that has experienced the distinctive elemental enhancements induced by Earth-analog plate tectonics. In view of the intense theoretical interest in the physical structure of extrasolar rocky planets, this search should be extended to additional targets.

  19. Plate tectonics and offshore boundary delimitation: Tunisia-Libya case at the International Court of Justice

    NASA Astrophysics Data System (ADS)

    Stanley, Daniel Jean

    1982-03-01

    The first major offshore boundary dispute where plate tectonics constituted a significant argument was recently brought before the International Court of Justice by Libya and Tunisia concerning the delimitation of their continental shelves. Libya placed emphasis on this concept to determine natural prolongation of its land territory under the sea. Tunisia contested use of the entire African continental landmass as a reference unit and views geography, geomorphology and bathymetry as relevant as geology. The Court pronounced that “It is the outcome, not the evolution in the long-distant past, which is of importance.” Moreover, it is the present-day configuration of coasts and seabed that are the main factors, not geology.

  20. Satellite Elevation Magnetic and Gravity Models of Major South American Plate Tectonic Features

    NASA Technical Reports Server (NTRS)

    Vonfrese, R. R. B.; Hinze, W. J.; Braile, L. W.; Lidiak, E. G.; Keller, G. R. (Principal Investigator); Longacre, M. B.

    1984-01-01

    Some MAGSAT scalar and vector magnetic anomaly data together with regional gravity anomaly data are being used to investigate the regional tectonic features of the South American Plate. An initial step in this analysis is three dimensional modeling of magnetic and gravity anomalies of major structures such as the Andean subduction zone and the Amazon River Aulacogen at satellite elevations over an appropriate range of physical properties using Gaus-Legendre quadrature integration method. In addition, one degree average free-air gravity anomalies of South America and adjacent marine areas are projected to satellite elevations assuming a spherical Earth and available MAGSAT data are processed to obtain compatible data sets for correlation. Correlation of these data sets is enhanced by reduction of the MAGSAT data to radial polarization because of the profound effect of the variation of the magnetic inclination over South America.

  1. A PILOT SEARCH FOR EVIDENCE OF EXTRASOLAR EARTH-ANALOG PLATE TECTONICS

    SciTech Connect

    Jura, M.; Klein, B.; Xu, S.; Young, E. D. E-mail: kleinb@astro.ucla.edu E-mail: eyoung@ess.ucla.edu

    2014-08-20

    Relative to calcium, both strontium and barium are markedly enriched in Earth's continental crust compared to the basaltic crusts of other differentiated rocky bodies within the solar system. Here, we both re-examine available archived Keck spectra to place upper bounds on n(Ba)/n(Ca) and revisit published results for n(Sr)/n(Ca) in two white dwarfs that have accreted rocky planetesimals. We find that at most only a small fraction of the pollution is from crustal material that has experienced the distinctive elemental enhancements induced by Earth-analog plate tectonics. In view of the intense theoretical interest in the physical structure of extrasolar rocky planets, this search should be extended to additional targets.

  2. Break-up of Gondwana and opening of the South Atlantic: Review of existing plate tectonic models

    USGS Publications Warehouse

    Ghidella, M.E.; Lawver, L.A.; Gahagan, L.M.

    2007-01-01

    each model. We also plot reconstructions at four selected epochs for all models using the same projection and scale to facilitate comparison. The diverse simplifying assumptions that need to be made in every case regarding plate fragmentation to account for the numerous syn-rift basins and periods of stretching are strong indicators that rigid plate tectonics is too simple a model for the present problem.

  3. Subduction on Europa: Evidence for plate tectonics on an icy world (Invited)

    NASA Astrophysics Data System (ADS)

    Kattenhorn, S. A.; Prockter, L. M.

    2013-12-01

    Europa is the primary target in NASA's future outer solar system exploration strategy. A tidally heated global ocean beneath its ice shell is important for astrobiological considerations; however, habitability requires a source of chemical nutrients. Europa's radiolytically processed surface is a potential source, but a means of delivery of compounds to the ocean is required. Past studies of Europa's surface have been unable to explain an abundance of extensional features (e.g., dilational bands) yet scant evidence of contraction. Moreover, the crater-based surface age (40-90 Myr) indicates one of the solar system's youngest surfaces, implying Europa's surface (3.09 x 107 km2) may have been recycled in this time frame (i.e., 0.3-0.8 km2 per year). We address this enigma by presenting evidence for subduction, and hence plate tectonics, on Europa. We reconstruct geologic features in a 106,000 km2 candidate region to show that the current surface configuration involved numerous translations and rotations of rigid plates. The reconstruction reveals ~100 km of missing surface that seemingly vanished along a 20-km-wide, band-like zone with unusual color characteristics. Mismatching geological features across this zone suggest an ~80-km-wide region may have subducted along a ≥300-km-long plate boundary. The subduction zone is arcuate, has no topographic expression at image resolutions, and is partially bounded by transform faults. The overriding plate has numerous strike-slip faults consistent with strain partitioning related to oblique convergence. The surface of the overriding plate is also pervasively dotted with isolated patches of disrupted terrain, which we interpret as erupted cryolava, implying a significant subsurface thermal perturbation related to the potential subduction. If a subduction model for Europa is accurate, buoyancy constraints and a lack of contractional topography imply that the subducting slab does not enter the ocean directly. We thus interpret

  4. The ERESE Project: Enactment of Digital Library Inquiry-Based Plate Tectonic Lessons

    NASA Astrophysics Data System (ADS)

    Helly, M.; Symons, C. M.; Dow, N.; Miller, S. P.; Helly, J.; Staudigel, H.; Koppers, A.

    2004-12-01

    The Enduring Resources for Earth Science Education (ERESE) project is a collaborative effort between earth scientists, educators, librarians and data archive managers. Its goal is to develop and maintain a persistent online research and education archive in a digital library environment that supports earth science education in plate tectonics. A major contribution from educators has been the development of inquiry lessons included in the digital library. Fourteen middle and high school teachers from across the country participated in the ERESE Workshop in July 2004. The goal of the workshop was three-fold: to provide the teachers with a research experience based on the digital library materials, to model an inquiry process and to support teachers as they develop inquiry lessons for their students. This process was led by a team of scientists and expert educators. The team used a master template to facilitate the teacher's lesson development. The pedagogical approach outlined in the template reflects a model of scientific thinking the goal of which is to shift from direction by the teacher at the onset of a lesson to a self-directed experience on the part of the student as they engage in the inquiry process and complete the lesson. Two examples of inquiry lessons produced as part of the workshop are reported here. The first investigates the symmetry of magnetic stripes at the northern East Pacific Rise using real marine geophysical data from the digital library. The second inquiry lesson was developed by a participant teacher and has been implemented this academic year by a high school marine science teacher. The lesson investigates the evidence that supports plate tectonics on the basis of the Pangea model. Having already been implemented in the classroom this lesson provides a rigorous testing of the inquiry process and the robustness of the scientific content of the digital library.

  5. Opening of the Aden Gulf Ridge Derived from GPS Constraints and Plate Tectonic Models

    NASA Astrophysics Data System (ADS)

    Fernandes, R. M.; Rolandone, F.; Leroy, S.; Alothman, A.; Al-Aydrus, A.; Khalil, H.; Ahmed, A.; Khanbari, K.; Bos, M. S.; Nicolon, P.; Heydel, L.

    2012-12-01

    The Aden Gulf Ridge forms, together with the Red Sea and the Ethiopian Rift, the only emerged RRR-type (Ridge/Ridge/Ridge) triple junction in the globe: the Afar Triple Junction. The Aden Gulf Ridge defines the boundary between two major tectonic blocks: Arabia and Somalia, being Nubia the third unit in the triple junction (bordering Arabia along the Red Sea and Somalia along the Ethiopian Rift). Although the extensional behaviour of these structures are well known, the present-day magnitudes of their opening rates are still under evaluation, in particular for the opening rate between the Arabia and Somalia plates. This work uses GPS observations acquired in campaign and continuous mode in order to better constrain the opening rates of the three plate boundaries. For the Nubia-Arabia and Nubia-Somalia boundary plates, we use solely the velocity predictions given by our computed angular velocity models using the available continuous stations in Nubia, Somalia and Arabia. The available data set is augmented here with several stations in Saudi Arabia, which allow us to better constrain the angular velocity for the stable part of the Arabia plate. We estimate the angular velocity model with respect to ITRF2008 (the latest realization of the International Terrestrial Reference System) using the value of 2.5 years (although most of the stations have already a significantly longer time-series) as threshold data span for the processed time-series. Temporal correlations are used to properly estimate the uncertainty of the time-series and derived angular velocity model. In addition, to study the near-field in the Aden Gulf, data acquired in denser campaign networks in Yemen and Oman are used to also directly compute the extension rate in the Red Sea. We show that most of the Arabian Peninsula is stable (within the uncertainties) but the southwest part (Yemen) is influenced by the proximity with the Afar Triple Junction.

  6. Inherited segmentation of the Iberian-African margins and tectonic reconstruction of a diffuse plate boundary.

    NASA Astrophysics Data System (ADS)

    Fernàndez, Manel; Torne, Montserrat; Vergés, Jaume; Casciello, Emilio

    2016-04-01

    Diffuse plate-boundary regions are characterized by non-well defined contacts between tectonic plates thus making difficult their reconstruction through time. The Western Mediterranean is one of these regions, where the convergence between the African and Iberian plates since Late Cretaceous resulted in the Betic-Rif arcuate orogen, the Gulf of Cadiz imbricate wedge, and the Alboran back-arc basin. Whereas the Iberia-Africa plate boundary is well defined west to the Gorringe Bank and along the Gloria Fault, it becomes much more diffuse eastwards with seismicity spreading over both the south-Iberian and north-African margins. Gravity data, when filtered for short wavelengths, show conspicuous positive Bouguer anomalies associated with the Gorringe Bank, the Gulf of Cadiz High and the Ronda/Beni-Bousera peridotitic massifs reflecting an inherited Jurassic margin segmentation. The subsequent Alpine convergence between Africa and Iberia reactivated these domains, producing crustal-scale thrusting in the Atlantic segments and eventually subduction in the proto-Mediterranean segments. The Jurassic segmentation of the Iberia-Africa margins substantiates the double-polarity subduction model proposed for the region characterized by a change from SE-dipping polarity in the Gorringe, Gulf of Cadiz and Betic-Rif domains, to NW-dipping polarity in the proto-Algerian domain. Therefore, the Algerian and Tyrrhenian basins in the east and the Alboran basin in the west are the result of SSE-E and NW-W retreating slabs of oceanic and/or hyper-extended Tethyan domains, respectively.

  7. The Making of Early Continents and the Initiation of Plate Tectonics on Earth

    NASA Astrophysics Data System (ADS)

    Rey, P. F.; Coltice, N.; Flament, N. E.

    2014-12-01

    We propose a simple, self-consistent model to explain a range of puzzling observation made in many Archean cratons including 1/ the marked petrological stratification of the lithospheric mantle; 2/ the multimodal polybaric volcanism of greenstone covers; 3/ the regional and temporal overlap between komatiitic-tholeiitic basalts and arc-volcanism; and 4/ the mid-lithospheric seismic discontinuity mapped across several cratons. This model also explains the possible transition from a stagnant-lid regime to a transient then steady-state plate tectonic regime. We performed several series of 2D thermo-mechanical numerical experiments to investigate the effect of an early continent on mantle convection. We considered a composite lid including 1/ a continent consisting of 55 km thick crust - made of TTG and continental flood basalts - above a 170-km-thick strongly depleted, strong and buoyant lithospheric mantle, and 2/ an oceanic lid including a 15-km-thick basaltic crust. These experiments show that the continent slowly spreads laterally toward the adjacent oceanic lid. The spreading and thinning of the continent drives exhumation of the fertile sub-continental mantle, which in turn promotes polybaric decompression melting producing komatiitic and tholeiitic basalts. Continental boudinage and rifting accompanying the spreading drives further upwelling and decompression melting to even shallower depths. This partial melting produces a moderately depleted mantle layer, progressively incorporated through cooling to the base of the continent. Our numerical experiments also show that spreading continents force the adjacent oceanic lid into the convective mantle, promoting subduction of the oceanic lid and temporal overlap between Archean komatiitic-tholeiitic basalts with arc-volcanism. Spreading and thinning of the continent lead to a sub-horizontal litho-tectonic fabric in the mantle, with a possible major discontinuity between the older strongly depleted mantle, and the

  8. Playing jigsaw with Large Igneous Provinces—A plate tectonic reconstruction of Ontong Java Nui, West Pacific

    NASA Astrophysics Data System (ADS)

    Hochmuth, Katharina; Gohl, Karsten; Uenzelmann-Neben, Gabriele

    2015-11-01

    The three largest Large Igneous Provinces (LIP) of the western Pacific—Ontong Java, Manihiki, and Hikurangi Plateaus—were emplaced during the Cretaceous Normal Superchron and show strong similarities in their geochemistry and petrology. The plate tectonic relationship between those LIPs, herein referred to as Ontong Java Nui, is uncertain, but a joined emplacement was proposed by Taylor (2006). Since this hypothesis is still highly debated and struggles to explain features such as the strong differences in crustal thickness between the different plateaus, we revisited the joined emplacement of Ontong Java Nui in light of new data from the Manihiki Plateau. By evaluating seismic refraction/wide-angle reflection data along with seismic reflection records of the margins of the proposed "Super"-LIP, a detailed scenario for the emplacement and the initial phase of breakup has been developed. The LIP is a result of an interaction of the arriving plume head with the Phoenix-Pacific spreading ridge in the Early Cretaceous. The breakup of the LIP shows a complicated interplay between multiple microplates and tectonic forces such as rifting, shearing, and rotation. Our plate kinematic model of the western Pacific incorporates new evidence from the breakup margins of the LIPs, the tectonic fabric of the seafloor, as well as previously published tectonic concepts such as the rotation of the LIPs. The updated rotation poles of the western Pacific allow a detailed plate tectonic reconstruction of the region during the Cretaceous Normal Superchron and highlight the important role of LIPs in the plate tectonic framework.

  9. The effect of melting and crustal production on plate tectonics on terrestrial planets

    NASA Astrophysics Data System (ADS)

    Lourenço, Diogo L.; Tackley, Paul J.

    2014-05-01

    Within the Solar System, Earth is the only planet to be in a mobile-lid regime, whilst it is generally accepted that all the other terrestrial planets are currently in a stagnant-lid regime, showing little or no surface motion. A transitional regime between these two, showing episodic overturns of an unstable stagnant lid, is also possible and has been proposed for Venus (Armann and Tackley, JGR 2012). Using plastic yielding to self-consistently generate plate tectonics on an Earth-like planet with strongly temperature-dependent viscosity is now well-established, but such models typically focus on purely thermal convection, whereas compositional variations in the lithosphere can alter the stress state and greatly influence the likelihood of plate tectonics. For example, Rolf and Tackley (GRL, 2011) showed that the addition of a continent can reduce the critical yield stress for mobile-lid behaviour by a factor of around 2. Moreover, it has been shown that the final tectonic state of the system can depend on the initial condition (Tackley, G3 2000 - part 2); Weller and Lenardic (GRL, 2012) found that the parameter range in which two solutions are obtained increases with viscosity contrast. We can also say that partial melting has a major role in the long-term evolution of rocky planets: (1) partial melting causes differentiation in both major elements and trace elements, which are generally incompatible (Hofmann, Nature 1997). Trace elements may contain heat-producing isotopes, which contribute to the heat loss from the interior; (2) melting and volcanism are an important heat loss mechanism at early times that act as a strong thermostat, buffering mantle temperatures and preventing it from getting too hot (Xie and Tackley, JGR 2004b); (3) mantle melting dehydrates and hardens the shallow part of the mantle (Hirth and Kohlstedt, EPSL 1996) and introduces viscosity and compositional stratifications in the shallow mantle due to viscosity variations with the loss of

  10. The effect of melting and crustal production on plate tectonics on terrestrial planets

    NASA Astrophysics Data System (ADS)

    Lourenço, Diogo; Tackley, Paul

    2015-04-01

    Within the Solar System, Earth is the only planet to be in a mobile-lid regime, whilst it is generally accepted that all the other terrestrial planets are currently in a stagnant-lid regime, showing little or no surface motion. A transitional regime between these two, showing episodic overturns of an unstable stagnant lid, is also possible and has been proposed for Venus (Armann and Tackley, JGR 2012). Using plastic yielding to self-consistently generate plate tectonics on an Earth-like planet with strongly temperature-dependent viscosity is now well-established, but such models typically focus on purely thermal convection, whereas compositional variations in the lithosphere can alter the stress state and greatly influence the likelihood of plate tectonics. For example, Rolf and Tackley (GRL, 2011) showed that the addition of a continent can reduce the critical yield stress for mobile-lid behaviour by a factor of around 2. Moreover, it has been shown that the final tectonic state of the system can depend on the initial condition (Tackley, G3 2000 - part 2); Weller and Lenardic (GRL, 2012) found that the parameter range in which two solutions are obtained increases with viscosity contrast. We can also say that partial melting has a major role in the long-term evolution of rocky planets: (1) partial melting causes differentiation in both major elements and trace elements, which are generally incompatible (Hofmann, Nature 1997). Trace elements may contain heat-producing isotopes, which contribute to the heat loss from the interior; (2) melting and volcanism are an important heat loss mechanism at early times that act as a strong thermostat, buffering mantle temperatures and preventing it from getting too hot (Xie and Tackley, JGR 2004b); (3) mantle melting dehydrates and hardens the shallow part of the mantle (Hirth and Kohlstedt, EPSL 1996) and introduces viscosity and compositional stratifications in the shallow mantle due to viscosity variations with the loss of

  11. A plate tectonic-paleoceanographic hypothesis for Cretaceous source rocks and cherts of northern South America

    SciTech Connect

    Villamil, T.; Arango, C. )

    1996-01-01

    New paleocontinental reconstructions show a northern migration of the South American Plate with respect to the paleoequator from the Jurassic to the Late Cretaceous. This movement caused the northern margin of South America to migrate from a position south to a position north of the paleoequator. Ekman transport generated net surface water movement towards the south during times when northern South America was south of the paleoequator. This situation favored downwelling and prevented Jurassic and earliest Cretaceous marine source rocks from being deposited. When northern South America was north of the paleoequator Ekman transport forced net water movement to the north favoring upwelling, paleoproductivity, and the deposition of one of the best marine source rocks known (the La Luna, Villeta, and equivalents). This plate tectonic paleoceanographic hypothesis explains the origin of hydrocarbons in northern South America. The stratigraphic record reflects this increase in paleoproductivity through time. This can be observed in facies (non-calcareous shales to calcareous shales to siliceous shales and finally to bedded cherts) and in changing planktic communities which were initially dominated by healthy calcareous foraminifer assemblages, followed by stressed foraminifer populations and finally by radiolarians. Total organic carbon and source rock quality were affected by this long term increase in paleoproductivity but also, and more markedly, by a punctuated sequence stratigraphic record dominated by low- frequency changes in relative sea level. The magnitude of transgressive episodes caused by rise in sea level determined the extent of source rock intervals and indirectly the content of organic carbon.

  12. A plate tectonic-paleoceanographic hypothesis for Cretaceous source rocks and cherts of northern South America

    SciTech Connect

    Villamil, T.; Arango, C.

    1996-12-31

    New paleocontinental reconstructions show a northern migration of the South American Plate with respect to the paleoequator from the Jurassic to the Late Cretaceous. This movement caused the northern margin of South America to migrate from a position south to a position north of the paleoequator. Ekman transport generated net surface water movement towards the south during times when northern South America was south of the paleoequator. This situation favored downwelling and prevented Jurassic and earliest Cretaceous marine source rocks from being deposited. When northern South America was north of the paleoequator Ekman transport forced net water movement to the north favoring upwelling, paleoproductivity, and the deposition of one of the best marine source rocks known (the La Luna, Villeta, and equivalents). This plate tectonic paleoceanographic hypothesis explains the origin of hydrocarbons in northern South America. The stratigraphic record reflects this increase in paleoproductivity through time. This can be observed in facies (non-calcareous shales to calcareous shales to siliceous shales and finally to bedded cherts) and in changing planktic communities which were initially dominated by healthy calcareous foraminifer assemblages, followed by stressed foraminifer populations and finally by radiolarians. Total organic carbon and source rock quality were affected by this long term increase in paleoproductivity but also, and more markedly, by a punctuated sequence stratigraphic record dominated by low- frequency changes in relative sea level. The magnitude of transgressive episodes caused by rise in sea level determined the extent of source rock intervals and indirectly the content of organic carbon.

  13. The geochemical fingerprint of serpentinite- and crust-dominated plate-interface settings: some tectonic implications

    NASA Astrophysics Data System (ADS)

    Cannaò, Enrico; Scambelluri, Marco; Agostini, Samuele; Tonarini, Sonia

    2014-05-01

    The interface between converging plates is made of kilometre-thick domains where slab and upper plate mantle materials are tectonically slicied within a matrix dominated either by (meta)sedimentary/crustal rocks or by serpentinite. The latter may correspond to supra-subduction mantle altered by uprising slab fluids. Once formed, these plate-interface domains act as hydrated low-viscosity layers where tectonic stress and fluid-mediated mass transfer are strongly focussed. Here we present the geochemical study of two plate-interface environments: (1) serpentinite-rich, represented by the high-pressure serpentinites of the Ligurian Alps (Erro-Tobbio and Voltri Units); (2) sediment-dominated top slab mélange, represented by de-serpentinized garnet peridotite and chlorite harzburgite bodies (hosting eclogite and metarodingite) embedded in paragneiss and micaschist from Cima di Gagnone (Adula Unit, Central Alps). The Ligurian serpentinites derive from oceanic and wedge mantle tectonically coupled and dragged to depth during Alpine subduction: they may represent the hydrated precursors of the Cima di Gagnone peridotites. The B, Pb and Sr isotopic composition of the above sets of rocks helps defining tectonic and mass transfer processes during accretion of slab and suprasubduction mantle rocks in plate-interface domains, and to retrieve the imprint of fluids from these settings, which that ultimately affect arc magmatism. The serpentinized peridotites from Erro-Tobbio (ET) show high B (10-30 ppm), delta11B (10-25 per mil), B/Nb ratio (>380) and limited enrichment in 206Pb/204Pb (18.17-18,51) and 87Sr/86Sr (0.7046- 0.7060). Scambelluri & Tonarini (2012) interpreted the B and Sr isotopic imprint of ET as representative of upper plate mantle altered by slab-fluids. The B contents (up to 30 ppm), delta11B (18-30 per mil), B/Nb ratio (>900) and 206Pb/204Pb (18.09-18.22) of the Voltri serpentinites are similar to ET. Their 87Sr/86Sr (0.7079 to 0.7105) is higher than ET. The

  14. Plate tectonic controls on atmospheric CO2 levels since the Triassic.

    PubMed

    Van Der Meer, Douwe G; Zeebe, Richard E; van Hinsbergen, Douwe J J; Sluijs, Appy; Spakman, Wim; Torsvik, Trond H

    2014-03-25

    Climate trends on timescales of 10s to 100s of millions of years are controlled by changes in solar luminosity, continent distribution, and atmosphere composition. Plate tectonics affect geography, but also atmosphere composition through volcanic degassing of CO2 at subduction zones and midocean ridges. So far, such degassing estimates were based on reconstructions of ocean floor production for the last 150 My and indirectly, through sea level inversion before 150 My. Here we quantitatively estimate CO2 degassing by reconstructing lithosphere subduction evolution, using recent advances in combining global plate reconstructions and present-day structure of the mantle. First, we estimate that since the Triassic (250-200 My) until the present, the total paleosubduction-zone length reached up to ∼200% of the present-day value. Comparing our subduction-zone lengths with previously reconstructed ocean-crust production rates over the past 140 My suggests average global subduction rates have been constant, ∼6 cm/y: Higher ocean-crust production is associated with longer total subduction length. We compute a strontium isotope record based on subduction-zone length, which agrees well with geological records supporting the validity of our approach: The total subduction-zone length is proportional to the summed arc and ridge volcanic CO2 production and thereby to global volcanic degassing at plate boundaries. We therefore use our degassing curve as input for the GEOCARBSULF model to estimate atmospheric CO2 levels since the Triassic. Our calculated CO2 levels for the mid Mesozoic differ from previous modeling results and are more consistent with available proxy data. PMID:24616495

  15. Plate tectonic controls on atmospheric CO2 levels since the Triassic

    PubMed Central

    Van Der Meer, Douwe G.; Zeebe, Richard E.; van Hinsbergen, Douwe J. J.; Sluijs, Appy; Spakman, Wim; Torsvik, Trond H.

    2014-01-01

    Climate trends on timescales of 10s to 100s of millions of years are controlled by changes in solar luminosity, continent distribution, and atmosphere composition. Plate tectonics affect geography, but also atmosphere composition through volcanic degassing of CO2 at subduction zones and midocean ridges. So far, such degassing estimates were based on reconstructions of ocean floor production for the last 150 My and indirectly, through sea level inversion before 150 My. Here we quantitatively estimate CO2 degassing by reconstructing lithosphere subduction evolution, using recent advances in combining global plate reconstructions and present-day structure of the mantle. First, we estimate that since the Triassic (250–200 My) until the present, the total paleosubduction-zone length reached up to ∼200% of the present-day value. Comparing our subduction-zone lengths with previously reconstructed ocean-crust production rates over the past 140 My suggests average global subduction rates have been constant, ∼6 cm/y: Higher ocean-crust production is associated with longer total subduction length. We compute a strontium isotope record based on subduction-zone length, which agrees well with geological records supporting the validity of our approach: The total subduction-zone length is proportional to the summed arc and ridge volcanic CO2 production and thereby to global volcanic degassing at plate boundaries. We therefore use our degassing curve as input for the GEOCARBSULF model to estimate atmospheric CO2 levels since the Triassic. Our calculated CO2 levels for the mid Mesozoic differ from previous modeling results and are more consistent with available proxy data. PMID:24616495

  16. Cenozoic East Asia plate tectonic reconstructions using constraints of mapped and unfolded slabs from mantle seismic tomography

    NASA Astrophysics Data System (ADS)

    Wu, J. E.; Suppe, J.; Kanda, R. V.

    2012-12-01

    Subducted slabs were mapped in the mantle under East Asia using MITP08 global seismic tomography (Li et al., 2008), Benioff zone seismicities and published local tomography. 3D gridded slab surfaces were constructed by manually picking and correlating the midpoint of fast seismic anomalies along variable cross-section orientations. The mapped slabs were structurally 'unfolded' and restored to the spherical Earth surface to assess their pre-subduction geometries. Gplates software was used to constrain plate tectonic reconstructions using the unfolded slabs. The unfolded SE Asia upper mantle slabs reveal a 'picture puzzle' fit along their edges that suggests a larger NE Indo-Australian ocean once existed that included the Philippine Sea, Molucca Sea and Celebes Sea. Deeper lower mantle detached slabs indicate an early to mid-Cenozoic 'East Asia Sea' between east Sundaland and the Pacific that stretched from the Ryukyu Islands north of present-day Taiwan southward to Sulawesi. The unfolded slab constraints produced gap and overlap incompatibilities when used in published plate tectonic reconstructions. Here a plate tectonic reconstruction incorporating the unfolded slab constraints is proposed that has the Philippine Sea, Molucca Sea and Celebes Sea clustered at the northern margin of Australia during the early Cenozoic. At the mid-Cenozoic these plates moved NNE with 'Australia-like' plate motions and overrode the 'East Asia Sea'. Plate motions were accommodated by N-S transforms at the eastern margin of Sundaland. Between 25 to 15 Ma the Philippine Sea, Molucca Sea and Celebes Sea plates were fragmented from the greater Indo-Australian ocean. The Philippine Sea was captured by the Pacific plate and now has Pacific-like westward motions.

  17. Rapid Kinematic and Tectonic Variations Along the 1400-km-long Australia-Woodlark Plate Boundary Zone, Papua New Guinea and Woodlark Basin

    NASA Astrophysics Data System (ADS)

    Mann, P.; Taylor, F. W.; Gahagan, L.; Watson, L.

    2004-12-01

    Previous GPS studies have shown the wide variability in present-day plate motions across the highly arcuate, 1400-km-long Australia-Woodlark plate boundary extending from Papua New Guinea to the Solomon Islands. GPS-determined motions range from orthogonal oceanic spreading in the Woodlark basin, to continental transtension in the 2.5-km-high core complex area of easternmost Papua New Guinea, to continental strike-slip and transpression in 4-km-high mountains of the Papuan Peninsula. We use imagery, earthquake focal mechanisms, coral reef uplift data, and structural mapping studies to establish the along-strike continuity of the active plate boundary fault. Systematic angular changes in the direction of the plate vector along this continuous fault explain its varied tectonic geomorphology, Holocene uplift history, and geologic structure. We use a series of plate reconstructions to illustrate the longer term, Cenozoic evolution of this boundary including: its formation as an arcuate, N- and NE-dipping ophiolitic suture zone during Paleogene time, the progressive "unzippering" of this thrust over the past 6 Ma along a N- and NE-dipping, low-angle normal fault in easternmost Papua New Guinea, and its "zippering" or continued shortening on the suture thrust in the Owen Stanley Ranges of the Papuan Peninsula. Over the 1400-km-length of the fault, the length of segments of oceanic spreading, transtension, and transpression is 250-500 km; the time period separating one tectonic style from the succeeding style encroaching from the east is several million years. This systematic spatial and temporal superposition of tectonic styles, leads to complex - but predictable - along-strike variations in geologic history.

  18. GIS-based Reconstruction of Pangaea with Recent Progresses in Plate Tectonics

    NASA Astrophysics Data System (ADS)

    Kwon, O.-H.; Cheong, H.-B.; Lee, Y.-W.

    2012-04-01

    It is now widely accepted that the continents or land masses are constantly, slowly moving, or drifting over the asthenosphere as the sea floors spread in response to the mantle convection. These continents were joined together at one time, some 250 million years ago, in a single giant landmass called Pangaea. Alfred Wegener, who proposed originally the hypothesis of continental drift, succeeded in reconstructing the Pangaea in early 20th century, by gathering evidences such as land features, fossils, and climate change. The shape of Pangaea shown by Wegener is a huge landmass which is in rounded shape close to an oval. The Pangaea of Wegener was found to be in good agreement with the supercontinent which was reconstructed by modern scientists in late 1960s based on concrete and sophisticated sciences such as the plate tectonics. There are a couple of shapes describing the Pangaea by now, other than the Wegener's, that are recognized by the geological community. In spite of profound geological data and development of related-area sciences, uncertainties still remains on the precise shape of Pangaea before the stage of breaking up and drifting apart. In this study, the Pangaea is reconstructed taking the recent progresses of plate tectonics into full consideration with the use of an elaborate Geographical Information System (GIS) mapping technique. For a better visualization of the shape of the supercontinent the equidistant map projection is incorporated to display the Pangaea, where the central point of Pangaea is placed on the center of the map. The Pangaea reconstructed in this way appears in an almost circular shape, which has never been seen in previous studies (Fig. 1). The radius of the circle which circumscribes the Pangaea is about 9 000 km, giving the total area slightly above that of continents and lands of present day, because some of the continental margins were considered as a part of continents. This result suggests us that the Pangaea might have

  19. The Proto Southern Gulf of California represented by GIS Plate Tectonic Reconstructions

    NASA Astrophysics Data System (ADS)

    Skinner, L. A.; Umhoefer, P. J.; Kluesner, J. W.

    2012-12-01

    We present GIS-based plate tectonic reconstruction maps for the southern Gulf of California oblique rift. The maps track plate boundary deformation back to 14 Ma. Tectonic blocks are defined by faults, geology, seismic data, and bathymetry/topography. Spreading center and fault-slip rates were acquired from geologic data, cross-Gulf tie points, and GPS studies. Baja California-North America GPS rates (47 mm/yr across the Gulf; 4 mm/yr in the borderland) agree remarkably with ~6 Ma geologic offsets across the Gulf and are used during reconstruction steps back to 6 Ma. The Alarcon and Guaymas spreading centers initiated at 2.4 Ma and 6 Ma (Lizarralde et al., 2007), respectively, while the Farallon, Pescadero, and Carmen spreading centers began between ~2-1 Ma (Lonsdale, 1989). Therefore, the 2, 4, and 6 Ma reconstruction steps include a long transtensional fault zone along much of the southern Gulf, connecting the Guaymas spreading center with either the Alarcon spreading center or East Pacific Rise. For reconstructions at 8, 10, and 12 Ma, a range of across-Gulf and borderland fault rates fit the current constraints, but all models suggest an increase in across-Gulf faulting rates at 8 - 6 Ma. We used 30 mm/yr across the Gulf and 20 mm/yr across the borderland. These models result in ~470 km northwestward offset across the Gulf (we also account for a minor E-W offset) and ~145 km offset across the borderland. The 12 - 14 Ma reconstructions suggest that the Gulf of California formed along a 100 x 1600 km volcanic arc and narrow extensional belt between the Cretaceous batholith and the Sierra Madre Occidental. The initial seaway at 8 - 6.5 Ma was only ~200-250 km wide by 1600 km long. We will also combine our 12 Ma map with the McQuarrie and Werrnicke (2005) reconstruction to present a new reconstruction for the whole Walker Lane to Gulf of California belt.

  20. Tectonics of the Philippine Sea Plate as Seen From GPS Observations

    NASA Astrophysics Data System (ADS)

    Kato, T.; Kotake, Y.

    2002-12-01

    We analyzed the Global Positioning System (GPS) data in and around the Philippine Sea plate (PHS) to provide a velocity field for discussing tectonics of the plate and the mechanism of subduction process around PHS. In the present study, first, we revised the previously determined Euler vector of PHS relative to stable Eurasia using newly obtained data. Eastern part of Europe was assumed to be in a rigid block according to Nocquet et al. (2001) and we estimated the seven parameters of Helmert Transformation of this block relative to ITRF97. Then these parameters were used to estimate the Euler vector of PHS relative to stable Eurasia. For this purpose, we re-analyzed GPS data of up until 2001 at Chichi-jima, Okino-Tori Shima, Minami-Daito, Palau, Aogashima and Hachijo islands in ITRF97 reference together with surrounding IGS sites. Results suggest that the Euler vector of PHS relative to _gstable Eurasia_h is to be (61.4N, 163.7E, 1.003deg/my). Contrary to our previous estimate, the result suggests that Palau may be considered as in the rigid part of PHS. In contrast, the northern Izu islands are suggested to be affected by local volcanic disturbances. Then, we studied tectonic motions of Mariana arc and Palau-Yap arc. The Mariana Islands have been repeatedly observed since 1992. Kotake (2000) analyzed data at Anatahan, Guguan, Pagan and Agrigan as well as Saipan and Guam sites and showed that the velocities are much slower than what we expect from rigid motion of PHS. Residual velocities at these islands clearly show eastward motion of the Mariana Islands, suggesting that the Mariana Islands are subject to the spreading of the Mariana Trough. The rotation pole of the Mariana block was re-estimated as (20.6N, 145.2E) and angular velocity to be 4.17deg/ma, according to the re-estimated PHS motion. The position of the rotation pole is a few degrees south to the geographical hinge point of the Mariana arc and west Mariana ridge at about 24N. Estimated eastward

  1. Intraoceanic Arc Tectonic and Sedimentary Processes: Translation from Modern Activity to Ancient Records

    NASA Astrophysics Data System (ADS)

    Draut, A. E.; Clift, P. D.

    2013-12-01

    Records of ancient intraoceanic arc activity, now preserved in continental suture zones, are used to reconstruct paleogeography, plate motion, collision and accretion events, and to understand how continental crust is formed, recycled, and maintained through time. However, interpreting tectonic and sedimentary records after arc-continent collision is complicated by preservation of evidence for some processes and loss of evidence for others. We examine what is lost, and what is preserved, in the translation from modern processes to the ancient record of oceanic subduction zones. Composition of accreted arc terranes differs as a function of arc-continent collision geometry. ';Forward-facing' collision can accrete an oceanic arc onto either a passive or an active continental margin, with the arc facing the continent and colliding trench- and forearc-side first. In ';backward-facing' collision, involving two subduction zones with similar polarity, the arc collides backarc-first with an active continental margin. The preservation of evidence for contemporary sedimentary and tectonic arc processes in the geologic record depends greatly on how well the various parts of the arc survive collision and orogeny in each case. Preservation of arc terranes likely is biased towards those that were in tectonic accretion for tens of millions of years before collision, rather than tectonic erosion. The prevalence of tectonic erosion in modern oceanic subduction zones implies that valuable records of arc processes are commonly destroyed even before collision with a continent. Arc systems are most likely to undergo tectonic accretion shortly before forward-facing collision with a continent, and thus most forearc and accretionary-prism material in ancient arc terranes likely is temporally biased toward the final stages of arc activity, when sediment flux to the trench was greatest. Collision geometry and tectonic erosion vs. accretion are important controls on the ultimate survival of

  2. Dual subduction tectonics and plate dynamics of central Japan shown by three-dimensional P-wave anisotropic structure

    NASA Astrophysics Data System (ADS)

    Ishise, Motoko; Miyake, Hiroe; Koketsu, Kazuki

    2015-07-01

    The central Japanese subduction zone is characterized by a complex tectonic setting affected by the dual subduction of oceanic plates and collisions between the island arcs. To better understand of the subduction system, we performed an anisotropic tomography analysis using P-wave arrival times from local earthquakes to determine the three-dimensional structure of P-wave azimuthal anisotropy in the overriding plate and the Pacific and Philippine Sea (PHS) slabs. The principal characteristics of anisotropy in the subducted and subducting plates are (1) in the overriding plate, the distribution pattern of fast direction of crustal anisotropy coincides with that of the strike of geological structure, (2) in the two oceanic plates, fast propagation directions of P-wave were sub-parallel to the directions of seafloor spreading. Additionally, our tomographic images demonstrate that (1) the bottom of the Median Tectonic Line, the longest fault zone in Japan, reaches to the lower crust, and seems to link to the source region of an inter-plate earthquake along the PHS slab, (2) the segmentation of the PHS slab - the Izu Islands arc, the Nishi-Shichito ridge, and the Shikoku basin - due to the formation history, is reflected in the regional variation of anisotropy. The tomographic study further implies that there might be a fragment of the Pacific slab suggested by a previous study beneath the Tokyo metropolitan area. The overall findings strongly indicate that seismic anisotropy analysis provide potentially useful information to understand a subduction zone.

  3. On plate tectonics and the geologic evolution of southwestern North America

    NASA Astrophysics Data System (ADS)

    Ward, Peter L.

    1991-07-01

    Very rapid subduction of the Farallon plate under southwestern North America between 60 and 40 Ma was accompanied by a relatively low volume of magmatism throughout the southwestern United States and northern Mexico. Between 40 and 20 Ma, when subduction slowed significantly and in one area may have even stopped, magmatism became widespread and voluminous from Nevada and Utah to central Mexico. This correlation of rapid subduction with a relatively low volume of magmatism can be explained by the observation that subduction-related andesitic arc volcanism, often formed in a Laramide-style compressional regime, is relatively low volume compared to continental volcanism. The shallow roots of arc volcanic systems are clearly exposed in the porphyry copper deposits found in currently active arcs and common throughout southwestern North America between 60 and 50 Ma. By 43 Ma, worldwide plate motions changed, the Pacific plate began moving away from North America, and subduction of the Farallon plate slowed. By around 36 Ma, the easternmost part of the East Pacific Rise, which was located between the Pioneer and Murray fracture zones, approached the trench and the young, hot, buoyant lithosphere appears to have clogged part of the subduction zone. Uplift on land became widespread. Voluminous continental magmatism formed the Sierra Madre Occidental (SMO) of Mexico, one of the largest batholiths in the world, as well as volcanic centers now exposed in the San Juan Mountains of Colorado and the Rio Grande Rift of New Mexico. Vectors of motion of the Pacific plate relative to the North American plate determined by Stock and Molnar (1988) are consistent with formation of a transtensional environment along the plate boundary sufficient to create a 100- to 200-km-wide void just landward of the old volcanic arc. While the SMO batholith was forming within this void, the Monterey and Arguello microplates just offshore to the west were broken off from the Farallon plate and rotated

  4. New Insights into the Active Tectonics of Eastern Indonesia from GPS Measurements

    NASA Astrophysics Data System (ADS)

    Susilo, S.; Koulali Idrissi, A.; McClusky, S.; Meilano, I.; Cummins, P. R.; Tregoning, P.; Syafii, A.

    2014-12-01

    The Indonesian archipelago encompasses a wide range of tectonic environments, including island arc volcanism, subduction zones, and arc-continent collision. Many of the details of this tectonic activity are still poorly understood, especially where the Australian continent collides with Indonesia, separating the Sunda Arc in west from that at the Banda Arc in the east. While it seems clear that the Australian plate is subducted under both the Sunda and Banda Arcs, it is not clear what happens along the 1000 km -long stretch in between. The question of just where the plate motion is accommodated is of major importance to assessments of earthquake and tsunami hazard in the region. To help resolve these questions the Geospatial Information Agency of Indonesia has collaborated with the Australian National University and the Bandung Institute of Technology in a GPS campaign spanning much of eastern Indonesia, from Lombok in the west to Alor in the east. We have combined these data with those from previous campaigns, resulting in over 27 campaign and 18 continuous GPS sites being used in the analysis. The improvement in site density allowed us to develop of a more complete description of tectonic activity in this region than has been obtained in previous studies. Our preliminary results suggests that there is a relatively simple transition from subduction at the Java Trench off east Java, to a partitioned convergence along both the Timor Trough and the Flores Thrust in the Nusa Tenggara region.

  5. Tectonic and depositional model of the Arabian and adjoining plates during the Silurian-Devonian

    SciTech Connect

    Husseini, M.I. )

    1991-01-01

    During the Late Ordovician and Early Silurian, the western part of the Arabian Peninsula was covered by polar glaciers that advanced from the south pole in African Gondwana. During this period, nondeposition, erosion, or marginal marine conditions prevailed in eastern and northern Arabia. When the glaciers melted in the Early Silurian, sea level rose sharply and the paleo-Tethys Ocean transgressed the Arabian and adjoining plates depositing a thick, organic-rich shale directly over the glaciogenic and periglacial rocks and related unconformities. The post-glacial sequence coarsens upward reflecting the passage of a coastline prograding northward from African and Arabian Gondwana to northern Arabia. A sea level drop in the Late Silurian placed the study area in a terrestrial environment; however, as sea level recovered in the Early Devonian, a carbonate sequence blanketed most of the area. The transgression, however, was interrupted by regional uplift and local orogenic movements in the Middle and Late Devonian. These movements constitute the onset of Hercynian tectonism, which resulted in erosion of the older sequences, depositional hiatuses, and regional facies changes.

  6. Development of Caribbean plate tectonics: A contribution from oil exploration in Venezuela

    SciTech Connect

    Fuentes, J. ); Oum, S. ); Lander, R. )

    1990-05-01

    Following several huge oil and gas discoveries during the mid-1980s in the Northern Venezuela overthrust belt more detailed geological and geophysical studies have increased their perception of structural control on sedimentary basin development. Significant improvements in seismic data quality and seismic lines positioned close to outcrops of the frontal thrust give evidence of Miocene to Pleistocene thin-skinned tectonics as the mechanism of the formation of the overthrust belt of the Serrania del Interior. The authors conclude that the thrust sheet was formed by the effects of major right-lateral transcurrent movements along the El Pilar fault system, which forced metasediments against thick Miocene clastics in pull-apart basins. These basins were created earlier by strike-slip motions of preexisting parallel en-echelon normal faults. The eastwardly mobile Caribbean plate boundary and its evolution from a collision to a transpression zone is documented and a new approach to an evaluation of oil and gas potential is made of multiple reservoirs in stacked, folded thrust sheets.

  7. Relationship between observed upper mantle structures and recent tectonic activity across the Southeastern United States

    NASA Astrophysics Data System (ADS)

    Biryol, C. Berk; Wagner, Lara S.; Fischer, Karen M.; Hawman, Robert B.

    2016-05-01

    The lithospheric structure of the Southeastern United States is a product of earlier episodes of continental collision and breakup. The region is located in the interior of the North American Plate, away from active plate margins. However, there is ongoing tectonism in the region with multiple zones of seismicity, uplifting arches, and Cenozoic intraplate volcanism. The mechanisms controlling this activity and the state of stress remain enigmatic. Two important factors are plate strength and preexisting, inherited structures. Here we present new tomographic images of the upper mantle beneath the Southeastern United States, revealing large-scale structural variations in the upper mantle. Examples include the relatively thick lithospheric mantle of stable North America that abruptly thins beneath the Paleozoic Appalachian orogeny, and the slow upper mantle of the Proterozoic Reelfoot rift. Our results also indicate fast seismic velocity patterns that can be interpreted as ongoing lithospheric foundering. This provides a viable explanation for seismicity, uplifting, and young intraplate volcanism. We postulate that not only tectonic inheritance but also continuing lithospheric foundering may control the ongoing activity of the region long after it became a passive margin. Based on distinct variations in the geometry and thickness of the lithospheric mantle and foundered lithosphere, we propose that piecemeal delamination has occurred beneath the region throughout the Cenozoic, removing a significant amount of reworked/deformed mantle lithosphere. Ongoing lithospheric foundering beneath the eastern margin of stable North America explains significant variations in thickness of lithospheric mantle across the former Grenville deformation front.

  8. Relief Evolution in Tectonically Active Mountain Ranges

    NASA Technical Reports Server (NTRS)

    Whipple, Kelin X.

    2004-01-01

    The overall aims of this 3-yr project, as originally proposed were to: (1) investigate quantitatively the roles of fluvial and glacial erosion in the evolution of relief in mountainous regions, and (2) test rigorously the quality and accuracy of SRTM topographic data in areas of rugged relief - both the most challenging and of greatest interest to geomorphic, neotectonic, and hazards applications. Natural laboratories in both the western US and the Southern Alps of New Zealand were identified as most promising. The project has been both successful and productive, despite the fact that no SRTM data for our primary field sites in New Zealand were released on the time frame of the work effort. Given the delayed release of SRTM data, we pursued the scientific questions of the roles of fluvial and, especially, glacial erosion in the evolution of relief in mountainous regions using available digital elevation models (DEMs) for the Southern Alps of New Zealand (available at both 25m and 50m pixel sizes), and USGS 10m and 30m DEMs within the Western US. As emphasized in the original proposal, we chose the emphasis on the role of glacial modification of topographic relief because there has been little quantitative investigation of glacial erosion processes at landscape scale. This is particularly surprising considering the dramatic sculpting of most mid- and high-latitude mountain ranges, the prodigious quantities of glacially-derived sediment in terrestrial and marine basins, and the current cross-disciplinary interest in the role of denudational processes in orogenesis and the evolution of topography in general. Moreover, the evolution of glaciated landscapes is not only a fundamental problem in geomorphology in its own right, but also is at the heart of the debate over Late Cenozoic linkages between climate and tectonics.

  9. Tectonic Storytelling with Open Source and Digital Object Identifiers - a case study about Plate Tectonics and the Geopark Bergstraße-Odenwald

    NASA Astrophysics Data System (ADS)

    Löwe, Peter; Barmuta, Jan; Klump, Jens; Neumann, Janna; Plank, Margret

    2014-05-01

    The communication of advances in research to the common public for both education and decision making is an important aspect of scientific work. An even more crucial task is to gain recognition within the scientific community, which is judged by impact factor and citation counts. Recently, the latter concepts have been extended from textual publications to include data and software publications. This paper presents a case study for science communication and data citation. For this, tectonic models, Free and Open Source Software (FOSS), best practices for data citation and a multimedia online-portal for scientific content are combined. This approach creates mutual benefits for the stakeholders: Target audiences receive information on the latest research results, while the use of Digital Object Identifiers (DOI) increases the recognition and citation of underlying scientific data. This creates favourable conditions for every researcher as DOI names ensure citeability and long term availability of scientific research. In the developed application, the FOSS tool for tectonic modelling GPlates is used to visualise and manipulate plate-tectonic reconstructions and associated data through geological time. These capabilities are augmented by the Science on a Halfsphere project (SoaH) with a robust and intuitive visualisation hardware environment. The tectonic models used for science communication are provided by the AGH University of Science and Technology. They focus on the Silurian to Early Carboniferous evolution of Central Europe (Bohemian Massif) and were interpreted for the area of the Geopark Bergstraße Odenwald based on the GPlates/SoaH hardware- and software stack. As scientific story-telling is volatile by nature, recordings are a natural means of preservation for further use, reference and analysis. For this, the upcoming portal for audiovisual media of the German National Library of Science and Technology TIB is expected to become a critical service

  10. Allochthonous deep-water basin deposits of the western US: Implications for Paleozoic paleogeography and plate margin tectonics

    SciTech Connect

    Miller, E.L. . Geology Dept.)

    1993-04-01

    The stratigraphy and sedimentology of the lower Paleozoic Roberts Mts. and upper Paleozoic Golconda allochthons can be used to reconstruct their general paleogeographic setting in the Paleozoic. Basalt pillow lavas and radiolarian chert, were once considered straightforward evidence that the allochthons represented imbricated ocean crust formed at sites far removed from continental influences. Better stratigraphic definition, provenance studies and geochemistry of lavas now indicate that clastic components were derived from the continental shelf or interior and basalts in the Roberts Mountains allochthon were erupted in an intraplate setting through thinned continental crust (Madrid, 1987). Both in the earliest Mississippian and in the Late Permian, the Antler Basin (Roberts Mts.) and the Havallah Basin (Golconda) received proximal detritus from island arc sources to the west, immediately prior to closure of the basins by thrust-faulting. These data suggest that both systems of basins formed as marginal basins by rifting on the continental shelf (Antler Basin) and along the continental margin (Havallah Basin) and were flanked to the west by active island arcs at least during part of their history. As such, their stratigraphy provides a great deal of insight regarding tectonism along the western plate margin of North America during the Paleozoic.

  11. Crustal deformation and volcanism at active plate boundaries

    NASA Astrophysics Data System (ADS)

    Geirsson, Halldor

    Most of Earth's volcanoes are located near active tectonic plate boundaries, where the tectonic plates move relative to each other resulting in deformation. Likewise, subsurface magma movement and pressure changes in magmatic systems can cause measurable deformation of the Earth's surface. The study of the shape of Earth and therefore studies of surface deformation is called geodesy. Modern geodetic techniques allow precise measurements (˜1 mm accuracy) of deformation of tectonic and magmatic systems. Because of the spatial correlation between tectonic boundaries and volcanism, the tectonic and volcanic deformation signals can become intertwined. Thus it is often important to study both tectonic and volcanic deformation processes simultaneously, when one is trying to study one of the systems individually. In this thesis, I present research on crustal deformation and magmatic processes at active plate boundaries. The study areas cover divergent and transform plate boundaries in south Iceland and convergent and transform plate boundaries in Central America, specifically Nicaragua and El Salvador. The study is composed of four main chapters: two of the chapters focus on the magma plumbing system of Hekla volcano, Iceland and the plate boundary in south Iceland; one chapter focuses on shallow controls of explosive volcanism at Telica volcano, Nicaragua; and the fourth chapter focuses on co- and post-seismic deformation from a Mw = 7.3 earthquake which occurred offshore El Salvador in 2012. Hekla volcano is located at the intersection of a transform zone and a rift zone in Iceland and thus is affected by a combination of shear and extensional strains, in addition to co-seismic and co-rifting deformation. The inter-eruptive deformation signal from Hekla is subtle, as observed by a decade (2000-2010) of GPS data in south Iceland. A simultaneous inversion of this data for parameters describing the geometry and source characteristics of the magma chamber at Hekla, and

  12. Contrasting plate-tectonic styles of the Qinling-Dabie-Sulu and Franciscan metamorphic belts

    NASA Astrophysics Data System (ADS)

    Ernst, W. G.; Liou, J. G.

    1995-04-01

    The Dabie Mountains are part of the >2000-km-long Qinling-Dabie-Sulu suture zone juxtaposing the Sino-Korean and Yangtze cratons. An eastern extension apparently crosses Korea and lies along the Japan Sea side of Honshu as the Imjingang and Sangun terranes, respectively; a northeastern segment may be present in Sikhote-Alin, Russian Far East. This orogenic belt records late Paleozoic ocean-floor consumption and the Triassic collision of two Precambrian continental massifs in east-central China. Coesite and microdiamond inclusions in strong, refractory minerals of eclogite facies ultrahigh-pressure (UHP) metamorphic rocks in the Dabie-Sulu area attest to profound subduction of a leading salient of the old, cold Yangtze craton, now recovered through tectonic exhumation and erosion. Northward increase in intensity of subsolidus recrystallization of the suture complex is analogous to the internal progression in grade of high-pressure (HP) and UHP metamorphism documented in the Western Alps. In both regions, subduction of narrow prongs of continental material, UHP metamorphism, and return toward midcrustal levels of relatively lower density, buoyant microcontinental blocks resulted from delamination of these rocks from the descending, higher density, oceanic-crust-capped lithospheric plate. Such salients of continental crust represent an integral structural part of the downgoing slab, remain intact, and may be dragged to great depths before disengaging and rising differentially as coherent blocks. UHP parageneses include trace mineralogic relics requiring peak metamorphic conditions of 700 900 ° C and 28 35 kbar or more. In contrast, Pacific-type HP metamorphic belts, as represented by the Franciscan Complex of western California, recrystallized under physical conditions up to 200 500 ° C, 10 ± 3 kbar. In this setting, voluminous quartzo-feldspathic and graywacke debris was carried downward on oceanic-crust-capped lithosphere, choking the subduction zone with

  13. Plate tectonics and offshore boundary delimitation: Tunisia-Libya case at the International Court of Justice

    SciTech Connect

    Stanley, D.J.

    1983-03-01

    Advances in the technology for exploiting resources of the oceans, particularly recovery of hydrocarbons and minerals in deep water, is benefiting a growing number of nations. At the same time, however, economic and political pressures have induced concern and there is now a much increased emphasis on jurisdiction to divide the offshore areas between the 132 coastal nations. Negotiations affect research operations at sea and, in consequence, marine scientists have been made aware of offshore problems as highlighted by the Law of the Sea Treaty (UNCLOS III) and complications arising from the legal versus scientific definitions of continental shelves and margins. The first major offshore boundary case of international scope where plate tectonics has constituted a significant argument is the one recently brought before the International Court of Justice by Libya and Tunisia concerning the delimitation of their continental shelves. Of the two parties, Libya placed the greatest emphasis on this concept as a means to determine natural prolongation of its land territory into and under the sea. Tunisia contested Libya's use of the whole of the African continental landmass as a reference unit; in Tunisia's view, considerations of geography, geomorphology, and bathymetry are at least as relevant as are those of geology. In its landmark judgment (February 1982) - which almost certainly will have far-reaching consequences in future such boundary delimitation cases - the court pronounced that It is the outcome, not the evolution in the long-distant past, which is of importance, and that it is the present-day configuration of the coasts and sea bed which are the main factors to be considered, not geology.

  14. Dynamic Digital Maps: On-line Publication of Representative "Local" Geology in a Plate Tectonic Setting

    NASA Astrophysics Data System (ADS)

    Condit, C. D.

    2002-12-01

    The use of Dynamic Digital Maps (DDMs) offers the geologic community a combination of attributes which allow the on-line publication of spatially related, highly quantitative data, to be set in a local or regional environment which lets both professional and students make inquiry based observations, and makes these data easily available for analyses. The DDM does this by displaying analytical data, images and movies from links at sample site locations on maps or images in a friendly user interface. Macintosh-only prototypes of two of these DDMs [Springerville Volcanic Field (DDM-SVF) and Tatara-San Pedro volcanic complex (DDM-TSP)] have been used in university petrology classes; the latter program has been converted to a template from which other DDMs can be made. This DDM.Template is presently being ported to a cross-platform web-enabled programming environment (MetaCard - Revolution). An example of a map produced in the process of creating this port, the DDM of New England (DDM-NE) includes six geologic field trips and the State Geologic Map of Massachusetts, and can be obtained from the URL http://ddm.geo.umass.edu. The use of these three maps allows what is essentially access to representative "local" geology in three global plate tectonic settings: a subduction zone (the Andes, DDM-TSP), a continental interior monogenetic volcanic field (DDM-SVF) and a failed rift valley (the Deerfield Basin within the DDM.NE). Because the DDM.Template provides locations for text and captions to be inserted for use at several user levels (e.g. the professional geologist, the beginning geoscientist, and the layman or perhaps middle-school student) the use of DDMs also provides a much needed outreach mechanism for the geosciences.

  15. Quantitative assessment of growth plate activity

    SciTech Connect

    Harcke, H.T.; Macy, N.J.; Mandell, G.A.; MacEwen, G.D.

    1984-01-01

    In the immature skeleton the physis or growth plate is the area of bone least able to withstand external forces and is therefore prone to trauma. Such trauma often leads to premature closure of the plate and results in limb shortening and/or angular deformity (varus or valgus). Active localization of bone seeking tracers in the physis makes bone scintigraphy an excellent method for assessing growth plate physiology. To be most effective, however, physeal activity should be quantified so that serial evaluations are accurate and comparable. The authors have developed a quantitative method for assessing physeal activity and have applied it ot the hip and knee. Using computer acquired pinhole images of the abnormal and contralateral normal joints, ten regions of interest are placed at key locations around each joint and comparative ratios are generated to form a growth plate profile. The ratios compare segmental physeal activity to total growth plate activity on both ipsilateral and contralateral sides and to adjacent bone. In 25 patients, ages 2 to 15 years, with angular deformities of the legs secondary to trauma, Blount's disease, and Perthes disease, this technique is able to differentiate abnormal segmental physeal activity. This is important since plate closure does not usually occur uniformly across the physis. The technique may permit the use of scintigraphy in the prediction of early closure through the quantitative analysis of serial studies.

  16. Earthquake activity and crustal stresses in stable plate interiors

    NASA Astrophysics Data System (ADS)

    Camelbeeck, Thierry; Calais, Eric; Mazzotti, Stéphane; Stein, Seth

    2016-04-01

    Unlike plate-boundary earthquakes that are explained by plate motions and their recurrence interval inferred from the rate at which these motions are released seismically, we have a limited understanding on the triggering causes of earthquakes in stable plate interiors as well as on the mechanisms explaining their apparent episodic, clustered, and migrating nature. An alternative model explaining those characteristics of the seismic activity in those regions where no discernable strain is building up today is that earthquakes result from the release of strain from a long-term pre-stressed lithosphere, triggered by processes weakening fault zones, like fluid circulation, or modifying applied normal stress on well oriented faults, like regional or more local erosion, water or ice loadings. In this talk, we present examples of three complementary approaches that should permit better understanding the mechanisms of this intraplate earthquake activity. They rely on studying their possible triggering factors and regional stresses controlling their mechanism, and also on modelling the possible strain rates of geological domains in relationship to their geological history and their fabrics. Among other things, we question whether the spatial variations of the short wavelengths gravitational potential energy associated to lateral variations of surface topography and crustal density can induce local stress perturbations explaining the complexity of the present-day tectonics in Western Europe and its possible relationship to earthquake activity.

  17. Tectonics and Relative Plate Motions Around the Andaman Sea and Sumatra

    NASA Astrophysics Data System (ADS)

    Eguchi, T.; Murakoshi, T.

    2005-12-01

    There are several R-F-R models of the active back-arc opening system in the Andaman Sea proposed by authors, e.g., Curray et al. (1978), Eguchi et al. (1979), Eguchi (1991), Mantovani et al. (2001) and Nielsen et al. (2004). Most of the previous authors, except Eguchi et al. (1978) and Eguchi (1991), documented NW-SE or NNW-SSE striking relative plate motion at the Central Andaman Rift. Recent multi-beam bathymetry study by GEODYSSEA Project group confirmed the detailed configuration of the ENE-WSW striking Central Andaman Rift and adjacent transcurrent faults. All of data from the marine survey and recent shallow earthquakes as well as their strike-slip type focal mechanisms along the N-S striking fault segment at 95.2E from 11N to 12.5N support the approximate N-S opening at the adjacent Central Andaman Rift. The magnetic anomaly survey data of Curray et al. (1978) suggest that, in the case of N-S opening, the rate becomes 4.0 cm/y, although Curray et al. (1978) proposed the total rate of 3.7 cm/y in the case of NNW-SSE opening. We then studied the realistic geometry of plate boundaries from Sumatra through the Andaman sea including the Central Andaman Rift to Myanmar, using recent seismological data and GPS studies. As is important, the Sundaland is not part of the Eurasia plate as revealed by recent GPS surveys. Furthermore, based on data of GPS velocity vectors w.r.t. Eurasia plate (e.g., Pradirodirdjo et al., 1997; Michel et. al., 2001), we can recognize some differential motion within the NW-SE striking fore-arc block, which is bounded by the Sumatra transcurrent fault and Java trench. The GPS data indicate 'differential motion' in both the trench-parallel and trench-normal directions within the NW-SE striking fore-arc block. We must resolve whether such kind differential movement within the fore-arc block is steady or not, to investigate the detailed spatio-temporal nature of dynamic coupling at the subduction zones with intermittent activity of larger

  18. The Northern Caribbean Plate Boundary Offshore Hispaniola: Strike-slip and Compressive Tectonic Processes

    NASA Astrophysics Data System (ADS)

    Corbeau, J.; Rolandone, F.; Leroy, S. D.; Mercier De Lepinay, B. F.; Meyer, B.; Ellouz, N.

    2014-12-01

    The boundary between the Caribbean plate and the North American plate is transpressive due to the oblique collision between these two plates. The transpressive movement is partitioned and accommodated in the Hispaniola region along two left-lateral strike-slip structures surrounding a fold-and-thrust belt. New multibeam bathymetry data and multichannel seismic reflection profiles have been recently collected during the Haiti-SIS and Haiti-SIS 2 cruises, along part of the northern Caribbean plate boundary between Cuba, Jamaica and Hispaniola. From the north to the south, three types of deformations are observed. In the Windward Passage, the analysis of the data set reveals that the movement on the Oriente fault between Cuba and Hispaniola is purely left-lateral strike-slip according to the GPS measurements. In the Gonave basin, west of Hispaniola, the deformation is compressive. A series of folds is identified and moves toward the southwest. The Enriquillo-Plantain-Garden Fault (EPGF) is localized in the Jamaica Passage, between Jamaica and Hispaniola. The analysis of the data set reveals that the left-lateral EPGF recently intersects inherited basins from the eastern Cayman Trough margin. The study of the actual EPGF active trace shows that this fault moves with a pure strike-slip component, at least in its western part: the presence of a little push-up structure and a set of three en echelon folds is highlighting in the western part of the Jamaica Passage. The shortening rate in the inherited basins crossed by the EPGF increases from west to east (5.8% to 8.5%), indicating that a thrusting component is also accommodated around the EPGF.

  19. Miocene uplift of the NE Greenland margin linked to plate tectonics: Seismic evidence from the Greenland Fracture Zone, NE Atlantic.

    NASA Astrophysics Data System (ADS)

    Døssing, Arne; Japsen, Peter; Watts, Anthony; Nielsen, Tove; Jokat, Wilfried; Thybo, Hans

    2016-04-01

    Tectonic models predict that, following breakup, rift margins undergo only decaying thermal subsidence during their post-rift evolution. However, post-breakup stratigraphy beneath the NE Atlantic shelves shows evidence of regional-scale unconformities, commonly cited as outer margin responses to inner margin episodic uplift, including the formation of coastal mountains. The origin of these events remains enigmatic. We present a seismic reflection study from the Greenland Fracture Zone - East Greenland Ridge (GFZ-EGR) and the NE Greenland shelf. We document a regional intra-Miocene seismic unconformity (IMU), which marks the termination of syn-rift deposition in the deep-sea basins and onset of: (i) thermo-mechanical coupling across the GFZ, (ii) basin compression, and (iii) contourite deposition, north of the EGR. The onset of coupling across the GFZ is constrained by results of 2-D flexural backstripping. We explain the thermo-mechanical coupling and the deposition of contourites by the formation of a continuous plate boundary along the Mohns and Knipovich ridges, leading to an accelerated widening of the Fram Strait. We demonstrate that the IMU event is linked to onset of uplift and massive shelf-progradation on the NE Greenland margin. Given an estimated middle-to-late Miocene (~15-10 Ma) age of the IMU, we speculate that the event is synchronous with uplift of the East and West Greenland margins. The correlation between margin uplift and plate-motion changes further indicates that the uplift was triggered by plate tectonic forces, induced perhaps by a change in the Iceland plume (a hot pulse) and/or by changes in intra-plate stresses related to global tectonics.

  20. On the origin and tectonic significance of the intra-plate events of Grenvillian-type age in South America: A discussion

    NASA Astrophysics Data System (ADS)

    Cordani, Umberto G.; Fraga, Leda Maria; Reis, Nelson; Tassinari, Colombo C. G.; Brito-Neves, Benjamim B.

    2010-01-01

    The objective of this article is to examine the available evidence of intra-plate tectonic episodes of "Grenvillian-type age", affecting the South-American continent, assessing their possible causal correlation with the tectonic processes occurring within the orogenic belts active at their margins. For the Amazonian Craton, the active margin is represented by the Rondonian-San Ignacio and Sunsas belts. However, active margins of similar age are not recognized for the São Francisco and the Rio de La Plata Cratons, and the intra-plate events over them could be reflections of the Kibaran, Irumide or Namaqua orogenic collisions in Africa. Grenvillian-type age events over the Amazonian Craton can be described in four different aspects: shearing and tectonic reactivation along zones of weakness, cratogenic granitic magmatism, alkaline ring complexes, and pervasive regional heating in some localized regions. The first of them may reflect the compressional stresses at active margins, however the others may have different origins. Within the type-region of the K'Mudku tectono thermal episode, mylonites and pseudotachylites cut across the regional granitoid and metamorphic rocks. These shear belts developed under low-to-moderate temperature conditions, that induced resetting of K-Ar and Rb-Sr mineral ages. In the São Francisco Craton, extensional and compressional events of Grenvillian-type age are well registered by the structural features exhibited by the sedimentary rocks of the Espinhaço Supergroup. For example, in Bahia state, an Appalachian-style structure is observed, with large synclines and anticlines extending along hundreds of kilometers. The major difference between the Amazonian and the Congo-São Francisco Cratons is related to heat originated from the Earth's interior. Amazonia exhibits very large areas heated up to 350-400 °C, where the K'Mudku thermo-tectonic episodes were detected. In addition, Amazonia comprises a large amount of cratogenic granitic

  1. Crustal Structure at the North Eastern Tip of Rivera Plate, Nayarit- Marias Islands Region: Scenarios and Tectonic Implications. Tsujal Project

    NASA Astrophysics Data System (ADS)

    Danobeitia, J.; Bartolome, R.; Barba, D. C., Sr.; Nunez-Cornu, F. J.; Bandy, W. L.; Prada, M.; Cameselle, A. L.; Nunez, D.; Espindola, J. M.; Estrada, F.; Zamora, A.; Gomez, A.; Ortiz, M.

    2014-12-01

    A primarily analysis of marine geophysical data acquired aboard the RRS James Cook in the framework of the project "Characterization of seismic hazard and tsunami associated with cortical contact structure Rivera Jalisco Block Plate (TSUJAL)" is presented. This survey was held in the region of Nayarit-Tres Marias Islands between February and March 2014. The examination of data recorded by 16 OBS 's, deployed along 4 wide angle seismic profiles is presented, using an airgun-array seismic source of 6800 c.i., which allows sampling the crustal structure to the Moho. The profiles are located along the margin off the Marias Islands: a profile of over 200 km NNW-SSE direction and parallel to the western flank of the Islas Marias Islands and three orthogonal thereto. These perpendicular sections sample the lithosphere from the north of Maria Madre Island with a profile of 100 km length, across Maria Magdalena and Mari Cleofas Islands, with a profile of 50 km long, till south of Maria Cleofas with a profile of 100 km long. Coincident multichannel seismic profiles with refraction ones are also surveyed, although shooting with a source of 3,540 c. i., and acquired with a digital "streamer" of 6.0 km long. Simultaneously, multibeam, parametric and potential field data were recorded during seismic acquisition A first analysis shows an anomalously thickened crust in the western flank of the Marias Islands, as indicated by relatively short pre-critical distances of 30-35 km. While the moderate dip of 7 ° of the subduction of the Pacific oceanic plate favors somehow this effect, the existence of a remnant crustal fragment is also likely. Moreover, the images provided by the parametric sounding show abundant mass wasting deposits suggesting of recent active tectonics, possibly generated by earthquakes with moderate magnitude as those reported in the Marias Islands. This set of geophysical data, not only provide valuable information for the seismogenic characterization and

  2. Plate flexure and volcanism: Late Cenozoic tectonics of the Tabar-Lihir-Tanga-Feni alkalic province, New Ireland Basin, Papua New Guinea

    NASA Astrophysics Data System (ADS)

    Lindley, I. D.

    2016-05-01

    Late Cenozoic Tabar-Lihir-Tanga-Feni (TLTF) alkaline volcanism, New Ireland Basin, PNG, is associated with extensional cracks along the crests of flexed ridges developed on the New Ireland Microplate (New name). The tectonic alignment of the TLTF volcanic arc is essentially perpendicular to the flexed ridges, suggesting that fractures parallel to the direction of maximum horizontal compression facilitated the rapid ascent of alkaline magmas from the mantle region, perhaps 60-70 km depth. The mainly Pliocene to Pleistocene volcanoes were localized at the intersection of ridge-parallel Kabang structures and arc-parallel Niffin structures, suggesting that the Kabang-Niffin structural intersections underlying each of the TLTF island groups provided a well developed, clustered network of open conduits which tapped the mantle source region. Periodic post-Miocene locking and unlocking along the strike-slip Kilinailau Fault (New name) are thought to have functioned as a valve, turning on (Pliocene) and then turning off (Pleistocene) volcanic activity, respectively. Partial locking of the Kilinailau Fault during the Pliocene resulted in the accumulation of intraplate stresses within the New Ireland Microplate, and caused plate flexure and ridge development, plate-cracking along ridge crests and the development of arc-parallel regional fractures parallel to the direction of maximum compression. Unlocking of the Kilinailau Fault in the Pleistocene resulted in the release of intraplate stresses in the New Ireland Microplate and a cessation of volcanic activity across most of the TLTF arc. The style and scale of plate flexure and cracking, accompanied by within-plate alkaline volcanism from equally spaced ridge-top eruptive centers confined to a narrow, linear volcanic arc are unknown from any other tectonic province.

  3. Generation of plate tectonics with two-phase grain-damage and pinning: Source-sink model and toroidal flow

    NASA Astrophysics Data System (ADS)

    Bercovici, David; Ricard, Yanick

    2013-03-01

    theory therefore readily satisfies key plate-tectonic metrics of localized toroidal motion and plate-boundary inheritance, and thus provides a predictive theory for the generation of plate tectonics on Earth and other planets.

  4. Active tectonic studies in the United States, 1987-1990

    SciTech Connect

    Weldon, R.J., II )

    1991-01-01

    The techniques and instrumentation used in active tectonic studies are discussed, and recent results are reviewed. It is suggested that a critical mass of data on several particular regions has been accumulated, making possible critical debates and attempts to assess earthquake hazards. Particular attention is given to studies of the Pacific Northwest region, basin and range deformation studies, and distributed deformation and hidden earthquake sources. Also included is a comprehensive bibliography for the period.

  5. A Digital Tectonic Activity Map of the Earth

    NASA Technical Reports Server (NTRS)

    Lowman, Paul; Masuoka, Penny; Montgomery, Brian; OLeary, Jay; Salisbury, Demetra; Yates, Jacob

    1999-01-01

    The subject of neotectonics, covering the structures and structural activity of the last 5 million years (i.e., post-Miocene) is a well-recognized field, including "active tectonics," focussed on the last 500,000 years in a 1986 National Research Council report of that title. However, there is a cartographic gap between tectonic maps, generally showing all features regardless of age, and maps of current seismic or volcanic activity. We have compiled a map intended to bridge this gap, using modern data bases and computer-aided cartographic techniques. The maps presented here are conceptually descended from an earlier map showing tectonic and volcanic activity of the last one million years. Drawn by hand with the National Geographic Society's 1975 "The Physical World" map as a base, the 1981 map in various revisions has been widely reproduced in textbooks and various technical publications. However, two decades of progress call for a completely new map that can take advantage of new knowledge and cartographic techniques. The digital tectonic activity map (DTM), presented in shaded relief (Fig. 1) and schematic (Fig. 2) versions, is the result. The DTM is intended to show tectonism and volcanism of the last one million years, a period long enough to be representative of global activity, but short enough that features such as fault scarps and volcanos are still geomorphically recognizable. Data Sources and Cartographic Methods The DTM is based on a wide range of sources, summarized in Table 1. The most important is the digital elevation model, used to construct a shaded relief map. The bathymetry is largely from satellite altimetry, specifically the marine gravity compilations by Smith and Sandwell (1996). The shaded relief map was designed to match the new National Geographic Society world physical map (1992), although drawn independently, from the digital elevation model. The Robinson Projection is used instead of the earlier Van der Grinten one. Although neither

  6. Archean greenstone-tonalite duality: Thermochemical mantle convection models or plate tectonics in the early Earth global dynamics?

    NASA Astrophysics Data System (ADS)

    Kerrich, Robert; Polat, Ali

    2006-03-01

    Mantle convection and plate tectonics are one system, because oceanic plates are cold upper thermal boundary layers of the convection cells. As a corollary, Phanerozoic-style of plate tectonics or more likely a different version of it (i.e. a larger number of slowly moving plates, or similar number of faster plates) is expected to have operated in the hotter, vigorously convecting early Earth. Despite the recent advances in understanding the origin of Archean greenstone-granitoid terranes, the question regarding the operation of plate tectonics in the early Earth remains still controversial. Numerical model outputs for the Archean Earth range from predominantly shallow to flat subduction between 4.0 and 2.5 Ga and well-established steep subduction since 2.5 Ga [Abbott, D., Drury, R., Smith, W.H.F., 1994. Flat to steep transition in subduction style. Geology 22, 937-940], to no plate tectonics but rather foundering of 1000 km sectors of basaltic crust, then "resurfaced" by upper asthenospheric mantle basaltic melts that generate the observed duality of basalts and tonalities [van Thienen, P., van den Berg, A.P., Vlaar, N.J., 2004a. Production and recycling of oceanic crust in the early earth. Tectonophysics 386, 41-65; van Thienen, P., Van den Berg, A.P., Vlaar, N.J., 2004b. On the formation of continental silicic melts in thermochemical mantle convection models: implications for early Earth. Tectonophysics 394, 111-124]. These model outputs can be tested against the geological record. Greenstone belt volcanics are composites of komatiite-basalt plateau sequences erupted from deep mantle plumes and bimodal basalt-dacite sequences having the geochemical signatures of convergent margins; i.e. horizontally imbricated plateau and island arc crust. Greenstone belts from 3.8 to 2.5 Ga include volcanic types reported from Cenozoic convergent margins including: boninites; arc picrites; and the association of adakites-Mg andesites- and Nb-enriched basalts. Archean cratons

  7. Present-day kinematics of the Rivera plate and implications for tectonics in southwestern Mexico

    NASA Technical Reports Server (NTRS)

    Demets, Charles; Stein, Seth

    1990-01-01

    A model for the present-day motion of the Rivera plate relative to the North America, Cocos, and Pacific plates is derived using new data from the Pacific-Rivera rise and Rivera transform fault, together with new estimates of Pacific-Rivera motions. The results are combined with the closure-consistent NUVEL-1 global plate motion model of DeMets et al. (1990) to examine present-day deformation in southwestern Mexico. The analysis addresses several questions raised in previous studies of the Rivera plate. Namely, do plate motion data from the northern East Pacific rise require a distinct Rivera plate? Do plate kinematic data require the subduction of the Rivera plate along the seismically quiescent Acapulco trench? If so, what does the predicted subduction rate imply about the earthquake recurrence interval in the Jalisco region of southwestern Mexico?

  8. Present-day kinematics of the Rivera plate and implications for tectonics in southwestern Mexico

    NASA Astrophysics Data System (ADS)

    Demets, Charles; Stein, Seth

    1990-12-01

    A model for the present-day motion of the Rivera plate relative to the North America, Cocos, and Pacific plates is derived using new data from the Pacific-Rivera rise and Rivera transform fault, together with new estimates of Pacific-Rivera motions. The results are combined with the closure-consistent NUVEL-1 global plate motion model of DeMets et al. (1990) to examine present-day deformation in southwestern Mexico. The analysis addresses several questions raised in previous studies of the Rivera plate. Namely, do plate motion data from the northern East Pacific rise require a distinct Rivera plate? Do plate kinematic data require the subduction of the Rivera plate along the seismically quiescent Acapulco trench? If so, what does the predicted subduction rate imply about the earthquake recurrence interval in the Jalisco region of southwestern Mexico?

  9. Miocene uplift of the NE Greenland margin linked to plate tectonics: Seismic evidence from the Greenland Fracture Zone, NE Atlantic

    NASA Astrophysics Data System (ADS)

    Døssing, Arne; Japsen, Peter; Watts, Anthony B.; Nielsen, Tove; Jokat, Wilfried; Thybo, Hans; Dahl-Jensen, Trine

    2016-02-01

    Tectonic models predict that following breakup, rift margins undergo only decaying thermal subsidence during their postrift evolution. However, postbreakup stratigraphy beneath the NE Atlantic shelves shows evidence of regional-scale unconformities, commonly cited as outer margin responses to inner margin episodic uplift, including the formation of coastal mountains. The origin of these events remains enigmatic. We present a seismic reflection study from the Greenland Fracture Zone-East Greenland Ridge (GFZ-EGR) and the NE Greenland shelf. We document a regional intra-Miocene seismic unconformity (IMU), which marks the termination of synrift deposition in the deep-sea basins and onset of (i) thermomechanical coupling across the GFZ, (ii) basin compression, and (iii) contourite deposition, north of the EGR. The onset of coupling across the GFZ is constrained by results of 2-D flexural backstripping. We explain the thermomechanical coupling and the deposition of contourites by the formation of a continuous plate boundary along the Mohns and Knipovich ridges, leading to an accelerated widening of the Fram Strait. We demonstrate that the IMU event is linked to onset of uplift and massive shelf progradation on the NE Greenland margin. Given an estimated middle to late Miocene (~15-10 Ma) age of the IMU, we speculate that the event is synchronous with uplift of the east and west Greenland margins. The correlation between margin uplift and plate motion changes further indicates that the uplift was triggered by plate tectonic forces, induced perhaps by a change in the Iceland plume (a hot pulse) and/or by changes in intraplate stresses related to global tectonics.

  10. The Role of Plate Tectonic-Climate Coupling and Exposed Land Area in the Development of Habitable Climates on Rocky Planets

    NASA Astrophysics Data System (ADS)

    Foley, Bradford J.

    2015-10-01

    The long-term carbon cycle is vital for maintaining liquid water oceans on rocky planets due to the negative climate feedbacks involved in silicate weathering. Plate tectonics plays a crucial role in driving the long-term carbon cycle because it is responsible for CO2 degassing at ridges and arcs, the return of CO2 to the mantle through subduction, and supplying fresh, weatherable rock to the surface via uplift and orogeny. However, the presence of plate tectonics itself may depend on climate according to recent geodynamical studies showing that cool surface temperatures are important for maintaining vigorous plate tectonics. Using a simple carbon cycle model, I show that the negative climate feedbacks inherent in the long-term carbon cycle are uninhibited by climate's effect on plate tectonics. Furthermore, initial atmospheric CO2 conditions do not impact the final climate state reached when the carbon cycle comes to equilibrium, as long as liquid water is present and silicate weathering can occur. Thus an initially hot, CO2 rich atmosphere does not prevent the development of a temperate climate and plate tectonics on a planet. However, globally supply limited weathering does prevent the development of temperate climates on planets with small subaerial land areas and large total CO2 budgets because supply limited weathering lacks stabilizing climate feedbacks. Planets in the supply limited regime may become inhospitable for life and could experience significant water loss. Supply limited weathering is less likely on plate tectonic planets because plate tectonics promotes high erosion rates and thus a greater supply of bedrock to the surface.

  11. Seismic tomographic constraints on plate-tectonic reconstruction of Nazca subduction under South America since late Cretaceous (~80 Ma)

    NASA Astrophysics Data System (ADS)

    Chen, Yi-Wei; Wu, Jonny; Suppe, John; Liu, Han-Fang

    2016-04-01

    Our understanding of the global plate tectonics is based mainly on seafloor spreading and hotspot data obtained from the present earth surface, which records the growth of present ocean basins. However, in convergent tectonic settings vast amounts of lithosphere has been lost to subduction, contributing to increasing uncertainty in plate reconstruction with age. However, subducted lithosphere imaged in seismic tomography provides important information. By analyzing subducted slabs we identify the loci of subduction and assess the size and shape of subducted slabs, giving better constrained global plate tectonic models. The Andean margin of South America is a classic example of continuous subduction up to the present day, providing an opportunity to test the global plate prediction that ~24×10e6 km2 (4.7% of earth surface) lithosphere has been subducted since ~80 Ma. In this study, we used 10 different global seismic tomographies and Benioff zone seismicity under South America. To identify slabs, we first compared all data sets in horizontal slices and found the subducted Nazca slab is the most obvious structure between the surface and 750 km depth, well imaged between 10°N and 30°S. The bottom of the subducted Nazca slab reaches its greatest depth at 1400 km at 3°N (Carnegie Andes) and gradually shallows towards the south with 900 km minimum depth at 30°S (Pampean Andes). To assess the undeformed length of subducted slab, we used a refined cross-sectional area unfolding method from Wu et al. (in prep.) in the MITP08 seismic tomography (Li et al., 2008). Having cut spherical-Earth tomographic profiles that parallel to the Nazca-South America convergence direction, we measured slab areas as a function of depth based on edges defined by steep velocity gradients, calculating the raw length of the slab by the area and dividing an assumed initial thickness of oceanic lithosphere of 100km. Slab areas were corrected for density based on the PREM Earth model

  12. Geomorphic Indices in the Assessment of Tectonic Activity in Forearc of the Active Mexican Subduction Zone

    NASA Astrophysics Data System (ADS)

    Gaidzik, K.; Ramirez-Herrera, M. T.

    2015-12-01

    Rapid development of GIS techniques and constant advancement of digital elevation models significantly improved the accuracy of extraction of information on active tectonics from landscape features. Numerous attempts were made to quantitatively evaluate recent tectonic activity using GIS and DEMs, and a set of geomorphic indices (GI), however these studies focused mainly on sub-basins or small-scale areal units. In forearc regions where crustal deformation is usually large-scale and do not concentrate only along one specific fault, an assessment of the complete basin is more accurate. We present here the first attempt to implement thirteen GI in the assessment of active tectonics of a forearc region of an active convergent margin using the entire river basins. The GIs were divided into groups: BTAI - basin geomorphic indices (reflecting areal erosion vs. tectonics) and STAI - stream geomorphic indices (reflecting vertical erosion vs. tectonics). We calculated selected indices for 9 large (> 450 km2) drainage basins. Then we categorized the obtained results of each index into three classes of relative tectonic activity: 1 - high, 2 - moderate, and 3 - low. Finally we averaged these classes for each basin to determine the tectonic activity level (TAI). The analysis for the case study area, the Guerrero sector at the Mexican subduction zone, revealed high tectonic activity in this area, particularly in its central and, to a lesser degree, eastern part. This pattern agrees with and is supported by interpretation of satellite images and DEM, and field observations. The results proved that the proposed approach indeed allows identification and recognition of areas witnessing recent tectonic deformation. Moreover, our results indicated that, even though no large earthquake has been recorded in this sector for more than 100 years, the area is highly active and may represent a seismic hazard for the region.

  13. UAV's for active tectonics : case example from the Longitudinal Valley and the Chishan Faults (Southern Taiwan)

    NASA Astrophysics Data System (ADS)

    Deffontaines, Benoit; Chang, Kuo-Jen; Chan, Yu-Chang; Chen, Rou-Fei; Hsieh, Yu-Chung

    2015-04-01

    Taiwan is a case example to study active tectonics due to the active NW-SE collision of the Philippine and Eurasian Sea Plates as the whole convergence reaches 10cm/y. In order to decipher the structural active tectonics geometry, we used herein UAV's to get high resolution Digital Terrain Model (DTM) in local active tectonics key areas. Classical photo-interpretation where then developped in order to structurally interprete these data, confirmed by field studies. Two location had first been choosen in order to highlight the contribution of such high resolution DTM in SW Taiwan on the Longitudinal Valley Fault (SE Taiwan) on its southern branch from Pinting to Luyeh terraces (Pinanshan) where UAV's lead to better interprete the location of the outcropping active deformations. Combined with available GPS data and PALSAR interferometry (Deffontaines et Champenois et al., submitted) it is then possible to reconstruct the way of the present deformation in this local area. In the Pinting terraces, If the western branch of the fault correspond to an outcroping thrust fault, the eastern branch act as a a growing active anticline that may be characterized and quantified independantly. The interpretation of the UAV's high resolution DTM data on the Chishan Fault (SW Taiwan) reveals also the geometry of the outcropping active faults complex structural behaviour. If the Chishan Fault act as a thrusting in its northern tip (close to Chishan city), it acts as a right lateral strike-slip fault north of Chaoshan (Kaohsiung city) as described by Deffontaines et al. 2014. Therefore UAV's are a so useful tool to get very high resolution topographic data in Taiwan that are of great help to get the geometry of the active neotectonic structures in Taiwan.

  14. On the relationship between tectonic plates and thermal mantle plume morphology

    NASA Technical Reports Server (NTRS)

    Lenardic, A.; Kaula, W. M.

    1993-01-01

    Models incorporating plate-like behavior, i.e., near uniform surface velocity and deformation concentrated at plate boundaries, into a convective system, heated by a mix of internal and basal heating and allowing for temperature dependent viscosity, were constructed and compared to similar models not possessing plate-like behavior. The simplified numerical models are used to explore how plate-like behavior in a convective system can effect the lower boundary layer from which thermal plumes form. A principal conclusion is that plate-like behavior can significantly increase the temperature drop across the lower thermal boundary layer. This temperature drop affects the morphology of plumes by determining the viscosity drop across the boundary layer. Model results suggest that plumes on planets possessing plate-like behavior, e.g., the Earth, may differ in morphologic type from plumes on planets not possessing plate-like behavior, e.g., Venus and Mars.

  15. Tectonic earthquakes of October 22, 2005 and March 28, 2013 in the north of the Russian plate

    NASA Astrophysics Data System (ADS)

    Morozov, A. N.; Vaganova, N. V.; Konechnaya, Ya. V.

    2016-07-01

    The data from seismic stations of the Arkhangelsk network and the networks in the neighboring territories are analyzed for refining the focal parameters of the tectonic earthquakes recorded in the north of the Russian plate on October 22, 2005 ( M = 2.9) and March 28, 2013 ( M = 3.4). The epicenters of the earthquakes are confined to the large NW-SE striking faults which border the Arkhangelsk bulge starting from the Kara-Pinega rift in the northeast and Onega-Kandalaksha paleorift in the southwest. The calculated focal mechanism of the earthquake of March 28, 2013 agrees with the distribution of neotectonic stresses characteristic of the north of the Russian plate, and specifically, with the submeridional compression and sublatitudinal extension.

  16. A source-sink model of the generation of plate tectonics from non-Newtonian mantle flow

    SciTech Connect

    Bercovici, D.

    1995-02-01

    A model of mantle convection which generates plate tectonics requires strain rate- or stress-dependent rheology in order to produce strong platelike flows with weak margins as well as strike-slip deformation and plate spin (i.e., toroidal motion). Here, we employ a simple model of source-sink driven surface flow to determine the form of such a rheology that is appropriate for Earth`s present-day plate motions. In this model, lithospheric motion is treated as shallow layer flow driven by sources and sinks which correspond to spreading centers and subduction zones, respectively. Two plate motion models are used to derive the source sink field. As originally implied in the simpler Cartesian version of this model, the classical power law rheologies do not generate platelike flows as well as the hypothetical Whitehead-Gans stick-slip rheology (which incorporates a simple self-lubrication mechanism). None of the fluid rheologies examined, however, produce more than approximately 60% of the original maximum shear. For either plate model, the viscosity fields produced by the power law rheologies are diffuse, and the viscosity lows over strike-slip shear zones or pseudo-margins are not as small as over the prescribed convergent-divergent margins. In contrast, the stick-slip rheology generates very platelike viscosity fields, with sharp gradients at the plate boundaries, and margins with almost uniformly low viscosity. Power law rheologies with high viscosity contrasts, however, lead to almost equally favorable comparisons, though these also yield the least platelike viscosity fields. This implies that the magnitude of toroidal flow and platelike strength distributions are not necessarily related and thus may present independent constraints on the determination of a self-consistent plate-mantle rheology.

  17. A source-sink model of the generation of plate tectonics from non-Newtonian mantle flow

    NASA Technical Reports Server (NTRS)

    Bercovici, David

    1995-01-01

    A model of mantle convection which generates plate tectonics requires strain rate- or stress-dependent rheology in order to produce strong platelike flows with weak margins as well as strike-slip deformation and plate spin (i.e., toroidal motion). Here, we employ a simple model of source-sink driven surface flow to determine the form of such a rheology that is appropriate for Earth's present-day plate motions. In this model, lithospheric motion is treated as shallow layer flow driven by sources and sinks which correspond to spreading centers and subduction zones, respectively. Two plate motion models are used to derive the source sink field. As originally implied in the simpler Cartesian version of this model, the classical power law rheologies do not generate platelike flows as well as the hypothetical Whitehead-Gans stick-slip rheology (which incorporates a simple self-lubrication mechanism). None of the fluid rheologies examined, however, produce more than approximately 60% of the original maximum shear. For either plate model, the viscosity fields produced by the power law rheologies are diffuse, and the viscosity lows over strike-slip shear zones or pseudo-margins are not as small as over the prescribed convergent-divergent margins. In contrast, the stick-slip rheology generates very platelike viscosity fields, with sharp gradients at the plate boundaries, and margins with almost uniformly low viscosity. Power law rheologies with high viscosity contrasts, however, lead to almost equally favorable comparisons, though these also yield the least platelike viscosity fields. This implies that the magnitude of toroidal flow and platelike strength distributions are not necessarily related and thus may present independent constraints on the determination of a self-consistent plate-mantle rheology.

  18. Plate-Tectonic Analysis of Shallow Seismicity: Apparent Boundary Width, beta-Value, Corner Magnitude, Coupled Lithosphere Thickness, and Coupling in 7 Tectonic Settings

    NASA Astrophysics Data System (ADS)

    Bird, P.; Kagan, Y. Y.

    2003-12-01

    A new plate model [Bird, 2003, G3, 10.1029/2001GC000252] is used to analyze the mean seismicities of 7 types of plate boundary (CRB continental rift boundary, CTF continental transform fault, CCB continental convergent boundary, OSR oceanic spreading ridge, OTF oceanic transform fault, OCB oceanic convergent boundary, SUB subduction zone). We compare the plate-like (non-orogen) regions of model PB2002 with the CMT catalog to select apparent boundary half-widths, and then assign 95% of shallow earthquakes to one of these settings. A tapered Gutenberg-Richter model of the frequency/moment relation is fit to the subcatalog for each setting by maximum-likelihood. Best-fitting β values range from 0.53 to 0.92, but all 95%-confidence ranges are consistent with a common value of 0.61-0.66. To better determine some corner magnitudes we expand the subcatalogs by: (1) inclusion of orogens; and (2) inclusion of years 1900-1975 from the catalog of Pacheco and Sykes [1992]. Combining both earthquake statistics and the plate-tectonic constraint on moment rate, corner magnitudes include: CRB 7.64-.26+.76, CTF 8.01-.21+.45, CCB 8.46-.39+.21, OCB 8.04-.22+.52, and SUB 9.58-.46+.48. Coupled lithosphere thicknesses are found to be: CRB 3.0-1.4+7.0 km; CTF 8.6-4.1+11 km; CCB 18-11+? km; OSR 0.13-0.09+.13 km for normal-faulting and 0.40-.21+? km for strike-slip; OTF 12-7.1+?, 1.6-0.5+1.4, and 1.5-0.6+1.2 km at low, medium, and high velocities; OCB 3.8-2.3+13.7 km, and SUB 18.0-10.8+? km. Generally high coupling of subduction and continental plate boundaries suggests that here all seismic gaps are dangerous unless proven to be creeping. Generally low coupling within oceanic lithosphere suggests a different model of isolated seismic asperities surrounded by large seismic gaps which may be permanent.

  19. Application of Laser Ranging and VLBI Data to a Study of Plate Tectonic Driving Forces

    NASA Technical Reports Server (NTRS)

    Solomon, S. C.

    1980-01-01

    The conditions under which changes in plate driving or resistive forces associated with plate boundary earthquakes are measurable with laser ranging or very long base interferometry were investigated. Aspects of plate forces that can be characterized by such measurements were identified. Analytic solutions for two dimensional stress diffusion in a viscoelastic plate following earthquake faulting on a finite fault, finite element solutions for three dimensional stress diffusion in a viscoelastic Earth following earthquake faulting, and quantitative constraints from modeling of global intraplate stress on the magnitude of deviatoric stress in the lithosphere are among the topics discussed.

  20. Closure of the Africa-Eurasia-North America plate motion circuit and tectonics of the Gloria fault

    NASA Technical Reports Server (NTRS)

    Argus, Donald F.; Gordon, Richard G.; Demets, Charles; Stein, Seth

    1989-01-01

    The current motions of the African, Eurasian, and North American plates are examined. The problems addressed include whether there is resolvable motion of a Spitsbergen microplate, the direction of motion between the African and North American plates, whether the Gloria fault is an active transform fault, and the implications of plate circuit closures for rates of intraplate deformation. Marine geophysical data and magnetic profiles are used to construct a model which predicts about 4 mm/yr slip across the Azores-Gibraltar Ridge, and west-northwest convergence near Gibraltar. The analyzed data are consistent with a rigid plate model with the Gloria fault being a transform fault.

  1. The joint impact of ocean circulation and plate tectonics on the glacial South Pacific carbon pool

    NASA Astrophysics Data System (ADS)

    Ronge, T.; Tiedemann, R.; Lamy, F.; Köhler, P.; Alloway, B.; De Pol-Holz, R.; Pahnke, K.; Southon, J. R.

    2015-12-01

    To understand the whereabouts of CO2 during glacials and its pathways during deglacial transitions is one of the main priorities in paleoclimate research. The opposing patterns of atmospheric CO2 and Δ14C suggest that the bulk of CO2 was released from an old and therefore 14C-depleted carbon reservoir. As the modern deep ocean, below ~2000 m, stores up to 60-times more carbon than the entire atmosphere, it is considered to be a major driver of the atmospheric CO2 pattern, storing CO2 during glacials, releasing it during deglacial transitions. We use a South Pacific transect of sediment cores, covering the Antarctic Intermediate Water (AAIW), the Upper Circumpolar Deep Water (UCDW) and the Lower Circumpolar Deep Water (LCDW), to reconstruct the spatio-temporal evolution of oceanic Δ14C over the last 30,000 years. During the last glacial, we find significantly 14C-depleted waters between 2000 and 4300 m water depth, indicating a strong stratification and the storage of carbon in these water masses. However, two sediment cores from 2500 m and 3600 m water depth reveal an extreme glacial atmosphere-to-deep-water Δ14C offset of up to -1000‰ and ventilation ages (deep-water to atmosphere 14C-age difference) of ~8000 years. Such old water masses are expected to be anoxic, yet there is no evidence of anoxia in the glacial S-Pacific. Recent studies showed an increase of Mid Ocean Ridge (MOR) volcanism during glacials due to the low stand of global sea level. For this reason, we hypothesize that the admixture of 14C-dead carbon via tectonic activity along MORs might have contributed to these extremely low radiocarbon values. With a simple 1-box model, we calculated if the admixture of hydrothermal CO2 has the potential to lower the deep Pacific Δ14C signal. We show that if the oceanic turnover time is at least 2700 years, an increased hydrothermal flux of 1.2 μmol kg-1 yr-1 has the potential to reproduce the extreme radiocarbon values observed in our records.

  2. Tectono-stratigraphic evolution of the Canete Basin, Lima, Peru, a plate tectonic model for the Mesozoic evolution of the Central Andes

    SciTech Connect

    Aleman, A.M. )

    1993-02-01

    An arc-trench system has been active in the Central Andes since at least since Late Triassic. This Mesozoic margin was characterized by subduction-erosion processes, PreMesozoic metamorphic outer basement high, pervasive extension, tectonic inversion, sporadic igneous activity and segmentation of the arc. Episodic variations in the tectonic evolution of the associated basins were controlled by the variable angle of subduction, age of the subducted plate, rate and angle of convergence, and the relative motion of the Farallon and South America Plates. The Canete Basin is an elongate frontal arc basin, subparallel to the arc, which documents the early evolution of the Andean Orogeny. In the Canete Basin, the oldest arc volcanism is documented by the interbedded tuffs, lava flows and tuffaceous marine shales of the Late Jurassic Puente Piedra Group which was deposited along a series of isolated and elongated troughs that formed adjacent to the arc. During Late Berriasian the arc subsided and the lithofacies changed from arc to continental derived lithologies. The shallow marine, quartz rich Morro Solar Group was derived from the uplifted metamorphic basement high in the west, as the result of ensialic extension. Locally, volcanic quiescence was interrupted by deposition of the volcaniclastic rich Pucusana Formation. The Late Hauterivian to Aptian Lima Group consists of lime mudstones, shales and subordinated gypsum and bioclastic limestones with volcaniclastic and lava flow facies of the Chilca Group. Stratigraphic relationship rapid changes in thickness and facies of this unit document the development of an incipient arc and the persistence of ensialic extension prior to the maximum paroxysm of volcanic activity of the overlying Albian to Cenomanian Chillon Group. Interbedded volcaniclastic sandstones, lava flows, hyaloclastic breccias and the tuffaceous shales of the Chillon Group were coeval with the early phases of emplacement of the Coastal Batholith (CB).

  3. Philippine Sea and East Asian plate tectonics since 52 Ma constrained by new subducted slab reconstruction methods

    NASA Astrophysics Data System (ADS)

    Wu, Jonny; Suppe, John; Lu, Renqi; Kanda, Ravi

    2016-06-01

    We reconstructed Philippine Sea and East Asian plate tectonics since 52 Ma from 28 slabs mapped in 3-D from global tomography, with a subducted area of ~25% of present-day global oceanic lithosphere. Slab constraints include subducted parts of existing Pacific, Indian, and Philippine Sea oceans, plus wholly subducted proto-South China Sea and newly discovered "East Asian Sea." Mapped slabs were unfolded and restored to the Earth surface using three methodologies and input to globally consistent plate reconstructions. Important constraints include the following: (1) the Ryukyu slab is ~1000 km N-S, too short to account for ~20° Philippine Sea northward motion from paleolatitudes; (2) the Marianas-Pacific subduction zone was at its present location (±200 km) since 48 ± 10 Ma based on a >1000 km deep slab wall; (3) the 8000 × 2500 km East Asian Sea existed between the Pacific and Indian Oceans at 52 Ma based on lower mantle flat slabs; (4) the Caroline back-arc basin moved with the Pacific, based on the overlapping, coeval Caroline hot spot track. These new constraints allow two classes of Philippine Sea plate models, which we compared to paleomagnetic and geologic data. Our preferred model involves Philippine Sea nucleation above the Manus plume (0°/150°E) near the Pacific-East Asian Sea plate boundary. Large Philippine Sea westward motion and post-40 Ma maximum 80° clockwise rotation accompanied late Eocene-Oligocene collision with the Caroline/Pacific plate. The Philippine Sea moved northward post-25 Ma over the northern East Asian Sea, forming a northern Philippine Sea arc that collided with the SW Japan-Ryukyu margin in the Miocene (~20-14 Ma).

  4. Tectonic control on the drainage system in a piedmont region in tectonically active eastern Himalayas

    NASA Astrophysics Data System (ADS)

    Goswami, Chandreyee; Mukhopadhyay, Dhruba; Poddar, Bikash Chandra

    2012-03-01

    The impact of neotectonic activity on drainage system has been studied in a large alluvial fan in the eastern Himalayan piedmont area between the Mal River and the Murti River. Two distinct E-Wlineaments passing through this area had been identified by Nakata (1972, 1989) as active faults. The northern lineament manifested as Matiali scarp and the southern one manifested as Chalsa scarp represent the ramp anticlines over two blind faults, probably the Main Boundary Thrust (MBT) and the Himalayan Frontal Thrust (HFT), respectively. The fan surface is folded into two antiforms with a synform in between. These folds are interpreted as fault propagation folds over the two north dipping blind thrusts. Two lineaments trending NNE-SSW and nearly N-S, respectively, are identified, and parts of present day courses of the Murti and Neora Rivers follow them. These lineaments are named as Murti and Neora lineaments and are interpreted to represent a conjugate set of normal faults. The rivers have changed their courses by the influence of these normal faults along the Murti and Neora lineaments and their profiles show knick points where they cross E-W thrusts. The overall drainage pattern is changed from radial pattern in north of the Matiali scarp to a subparallel one in south due to these conjugate normal faults. The interfluve area between these two rivers is uplifted as a result of vertical movements on the above mentioned faults. Four major terraces and some minor terraces are present along the major river valleys and these are formed due to episodic upliftment of the ground and subsequent down-cutting of the rivers. The uppermost terrace shows a northerly slope north of the Chalsa scarp as a result of folding mentioned above. But rivers on this terrace form incised channels keeping their flow southerly suggesting that they are antecedent to the folding and their downcutting kept pace with the tectonism.

  5. Late Cenozoic tectonics of the Middle Atlas Mountains, Morocco: Continental deformation in the diffuse western Mediterranean plate boundary

    NASA Astrophysics Data System (ADS)

    Gomez, Francisco Gustavo

    The Atlas Mountains of North Africa, located in the African foreland of the Alpine mountain belts, comprise a 2,000 km long Cenozoic mountain chain whose development was guided by older Mesozoic rift structures. This dissertation examines one component, the Middle Atlas Mountains of Morocco, using geological and geophysical data to constrain the tectonic development of the mountain chain. These results are then placed in the broader context of regional deformation. The NE-SW trending Middle Atlas Mountains are obliquely oriented within the late Cenozoic regional stress field, resulting in deformation partitioned into strike-slip faulting and thrust-related folding. Kinematic analyses of fault-slip data and earthquake focal mechanisms demonstrate that compressional deformation dominates the Folded Middle Atlas, whereas strike-slip faulting, with possible horizontal extension, predominates in the Tabular Middle Atlas. Geological field observations, digital topography, LANDSAT imagery, and seismicity provide evidence for recent tectonics in the Middle Atlas. In the central Middle Atlas, cross-section balancing across the 20 km wide fold belt demonstrates about 4.7 km of Cenozoic horizontal shortening producing 800 m of structural relief. Other constraints on crustal thickening suggest a discrepancy between contraction and thickening. One possible explanation involves partitioning crustal deformation with depth: The upper crust shortens by thickening (faulting and folding), whereas the lower crust deforms laterally. At the northern extent of the mountain chain, the Guercif Basin developed where the Middle Atlas abut the Rif thrust belt. Similar timing of extensional deformation and proximity with the Rif, suggest that the Guercif Basin has been influenced by Rif tectonics. Stratal relations demonstrate that uplift of the Middle Atlas is a late Cenozoic phenomenon. In Morocco, shortening of the High and Middle Atlas Mountains accommodated 20--45% of the total African

  6. Plate tectonics and net lithosphere rotation over the past 150 My

    NASA Astrophysics Data System (ADS)

    Torsvik, Trond H.; Steinberger, Bernhard; Gurnis, Michael; Gaina, Carmen

    2010-03-01

    We have developed an improved model of global digital palaeo-plate boundaries and plate motion to describe the distribution and history of plates since the Late Jurassic. From this history we computed net lithospheric rotation (NR) through time confirming the so-called westward drift, but only for the past 30 Myr. The NR has significantly smaller magnitudes (0.13°/My, past 5 My) than for some other plate models; it averages to 0.11 ± 0.03°/My for the past 50 My with a small but systematic increase toward the present. The westward drift, seen only for the past 30 My, is attributed to the increased dominance of a steadily growing and accelerating Pacific plate. NR shows peaks with time but only an Early Tertiary peak of 0.33°/My (when the Indian plate was undergoing the largest known acceleration/deceleration) can be interpreted with some confidence. We find a linear decreasing trend in net rotation over the past 150 My, but attribute this trend to increasing reconstruction uncertainties back in time, as subduction consumed more than half of the oceanic crust since the Jurassic. After removing a linear time-trend, we find a NR average of about 0.12°/My for the past 150 My.

  7. An Integrated Geospatial System for earthquake precursors assessment in Vrancea tectonic active zone in Romania

    NASA Astrophysics Data System (ADS)

    Zoran, Maria A.; Savastru, Roxana S.; Savastru, Dan M.

    2015-10-01

    With the development of space-based technologies to measure surface geophysical parameters and deformation at the boundaries of tectonic plates and large faults, earthquake science has entered a new era. Using time series satellite data for earthquake prediction, it is possible to pursue the behaviors of earthquake precursors in the future and to announce early warnings when the differences between the predicted value and the observed value exceed the pre-define threshold value. Starting with almost one week prior to a moderate or strong earthquake a transient thermal infrared rise in LST of several Celsius degrees (oC) and the increased OLR values higher than the normal have been recorded around epicentral areas, function of the magnitude and focal depth, which disappeared after the main shock. Also are recorded associated geomagnetic and ionospheric distrurbances. Vrancea tectonic active zone in Romania is characterized by a high seismic hazard in European- Mediterranean region, being responsible of strong or moderate intermediate depth and normal earthquakes generation on a confined epicentral area. Based on recorded geophysical parameters anomalies was developed an integrated geospatial system for earthquake precursors assessment in Vrancea active seismic zone. This system integrates derived from time series MODIS Terra/Aqua, NOAA-AVHRR, ASTER, Landsat TM/ETM satellite data multi geophysical parameters (land surface temperature -LST, outgoing long-wave radiation- OLR, and mean air temperature- AT as well as geomagnetic and ionospheric data in synergy with in-situ data for surveillance and forecasting of seismic events.

  8. Mesozoic-Cenozoic history of subduction within the Tethyan region as inferred from seismic tomography and plate tectonic reconstructions

    NASA Astrophysics Data System (ADS)

    Hafkenscheid, E.; Wortel, R.; Spakman, W.

    2003-12-01

    We have studied the large-scale history of subduction within the Tethyan region, the Alpine-Himalayan-Indonesian mountain chain that stretches from the Mediterranean to Southeast Asia. From tomographic images of the present mantle structure, the volumes and locations of the positive seismic velocity anomalies are determined. The large tomographic volumes, and the large depths at which they are found, indicate that they must have resulted from long periods of subduction in Cenozoic and Mesozoic times. We therefore examine the large-scale surface motions within the region since 200 Ma, the time window that is thought to be necessary to explain the inferred tomographic anomalies. From plate tectonic reconstructions, the amount of convergence and velocities, both relative and absolute, are determined using the relevant poles of rotation. In general, we find the tomographic volumes in the upper mantle in the eastern Mediterranean and Middle East to be similar to the tectonic volumes that are expected to have subducted during the Cenozoic. On the contrary, the results indicate that the Cenozoic amount of shortening in the Indian region was probably not accompanied by lithosphere subducting into the mantle. For all regions, the tomographic volumes found in the lower mantle are larger than the tectonic volumes expected to have subducted during mainly Mesozoic times. The volumes in the Indian region and the Middle East approximately differ a factor 1-2. However, the results suggest that much more material must have been subducted in the eastern Mediterranean than is calculated for the African-Eurasian convergence alone. This points to a major role of oceanic spreading during lithospheric subduction in the area.

  9. Tectonic and deposition model of late Precambrian-Cambrian Arabian and adjoining plates

    SciTech Connect

    Husseini, M.I. )

    1989-09-01

    During the late Precambrian, the terranes of the Arabian and adjoining plates were fused along the northeastern flank of the African plate in Gondwanaland. This phase, which ended approximately 640 to 620 Ma, was followed by continental failure (620 to 580 Ma) and intracontinental extension (600 to approximately 550 Ma). During the Infracambrian extensional phase, a triple junction may have evolved near the Sinai Peninsula and may have consisted of the (1) Jordan Valley and Dead Sea rift branch, (2) Sinai and North Egypt rift branch, and (3) the Najd wrench-rift branch. The Najd, Hawasina, and Zagros fault systems may have been transverse faults that accompanied rifting in the Arabian Gulf and Zagros Mountains, southern Oman, Pakistan, and Kerman in central Iran. While the area was extending and subsiding, the Tethys Ocean flooded the eastern side of the Arabian plate and Iran and deposited calcareous clastics, carbonates, and evaporites (including the Hormuz and Ara halites). This transgression extended into the western part of the Arabian plate via the Najd rift system. The termination of the extensional phase during the late Early Cambrian was accompanied by a major regression and terrestrial conditions on the Arabian Peninsula. However, by the Early Ordovician, as sea level peaked to a highstand, the Arabian plate was blanketed with marginal marine sediments. 11 figs., 2 tabs.

  10. Faunal breaks and species composition of Indo-Pacific corals: the role of plate tectonics, environment and habitat distribution.

    PubMed

    Keith, S A; Baird, A H; Hughes, T P; Madin, J S; Connolly, S R

    2013-07-22

    Species richness gradients are ubiquitous in nature, but the mechanisms that generate and maintain these patterns at macroecological scales remain unresolved. We use a new approach that focuses on overlapping geographical ranges of species to reveal that Indo-Pacific corals are assembled within 11 distinct faunal provinces. Province limits are characterized by co-occurrence of multiple species range boundaries. Unexpectedly, these faunal breaks are poorly predicted by contemporary environmental conditions and the present-day distribution of habitat. Instead, faunal breaks show striking concordance with geological features (tectonic plates and mantle plume tracks). The depth range over which a species occurs, its larval development rate and genus age are important determinants of the likelihood that species will straddle faunal breaks. Our findings indicate that historical processes, habitat heterogeneity and species colonization ability account for more of the present-day biogeographical patterns of corals than explanations based on the contemporary distribution of reefs or environmental conditions. PMID:23698011

  11. Faunal breaks and species composition of Indo-Pacific corals: the role of plate tectonics, environment and habitat distribution

    PubMed Central

    Keith, S. A.; Baird, A. H.; Hughes, T. P.; Madin, J. S.; Connolly, S. R.

    2013-01-01

    Species richness gradients are ubiquitous in nature, but the mechanisms that generate and maintain these patterns at macroecological scales remain unresolved. We use a new approach that focuses on overlapping geographical ranges of species to reveal that Indo-Pacific corals are assembled within 11 distinct faunal provinces. Province limits are characterized by co-occurrence of multiple species range boundaries. Unexpectedly, these faunal breaks are poorly predicted by contemporary environmental conditions and the present-day distribution of habitat. Instead, faunal breaks show striking concordance with geological features (tectonic plates and mantle plume tracks). The depth range over which a species occurs, its larval development rate and genus age are important determinants of the likelihood that species will straddle faunal breaks. Our findings indicate that historical processes, habitat heterogeneity and species colonization ability account for more of the present-day biogeographical patterns of corals than explanations based on the contemporary distribution of reefs or environmental conditions. PMID:23698011

  12. Young tectonics of a complex plate boundary zone: Indentation, rotation, and escape in Alaska

    NASA Astrophysics Data System (ADS)

    Wallace, W. K.; Ruppert, N. A.

    2012-12-01

    Convergence of thick crust of the Yakutat block with the southern margin of Alaska is widely recognized as a dominant influence on the tectonics of Alaska since at least late Miocene time. It is less clear how this convergence relates to the distribution, type, and orientation of geologic structures, and to the boundaries between the tectonic provinces that they define. We propose that convergence of Yakutat block includes two distinct components that influence deformation and topography in different ways: 1) The crust of the exposed, southern Yakutat block is too thick to subduct, which has caused the collisional St. Elias orogen. Detachment of the upper part of the mafic basement allows delamination and sinking of the remaining mafic crust and lithospheric mantle. The collisional orogen drives rigid counterclockwise rotation of the southern Alaska block south of the arcuate, right-lateral Denali fault. The western boundary of this block is a zone of distributed contraction in the western Alaska Range and Cook Inlet. 2) The northern part of the Yakutat block is thin enough to subduct but thick and buoyant enough to cause localized flat-slab subduction orthogonal to rotation of the southern Alaska block. Consequences include the gently antiformal Talkeetna Mountains that span the forearc basin, a gap in the magmatic arc, and a basement-involved fold-and-thrust belt in the northern Alaska Range. An arcuate oroclinal hinge from southern Alaska to the northeastern Brooks Range reflects indentation since at least Paleocene time. Traction above the subducted Yakutat block along the southern part of this hinge drives current indentation. North of the subducted Yakutat block, indentation is reflected by left-lateral block rotation that accommodates shortening between the Denali and Tintina faults and by contraction farther north along the northern edge of the arcuate northeastern Brooks Range. Western Alaska accommodates both northward indentation and westward convergence

  13. New insights on 3-D plates interaction near Taiwan from tomography and tectonic implications

    NASA Astrophysics Data System (ADS)

    Lallemand, Serge; Font, Yvonne; Bijwaard, Harmen; Kao, Honn

    2001-07-01

    Recent tomographic results are used to trace the South China Sea and Philippine Sea subducting slabs, south and northeast of Taiwan along the Manila and Ryukyu trenches, respectively. In particular, the 3-D plates interaction beneath Taiwan is discussed based on a close-up view of the tomographic sections together with earthquake hypocenters distribution. Our study indicates that: (1) the east-dipping South China Sea slab can be followed to the north, up to the latitude of Hualien, (2) the Eurasian plate subducts beneath most part of the Taiwan island down to the 670 km-depth discontinuity, (3) the north-dipping Philippine Sea slab can be followed slightly west of the longitude of Hualien. Both plates thus interact beneath northern Taiwan where the arc-continent collision is paroxysmal. (4) Slab detachment is envisaged at the northern edge of the subducted Eurasian plate beneath the Coastal Range of Taiwan, which may facilitate the northwestward motion of the Philippine Sea plate with respect to Eurasia. Slabs geometries obtained from tomographic sections allow us to reconstruct the Late Neogene plate kinematics and dynamics in this region. Our main conclusions are: (1) The size of the original South China Sea was about twice its present size. (2) The subducted part of the West Philippine Basin i.e. the largest oceanic basin of the Philippine Sea Plate, extends only 400 km north of the Ryukyu Trench. (3) Slab detachment might have occurred 3-5 my ago beneath the central and northern Ryukyu Arc along a weak zone that is aligned with the Gagua Ridge: an ancient plate boundary. (4) The Ryukyu Trench has propagated westward from 126°E of longitude (southeast of Miyako Island) to the locus of the present arc-continent collision, along a major lithospheric tear that cut through the continent-ocean boundary first, and then through the continental lithosphere. As a consequence, the southern Ryukyu margin developed progressively from east to west as a subduction zone

  14. Origin of marginal basins of the NW Pacific and their plate tectonic reconstructions

    NASA Astrophysics Data System (ADS)

    Xu, Junyuan; Ben-Avraham, Zvi; Kelty, Tom; Yu, Ho-Shing

    2014-03-01

    Geometry of basins can indicate their tectonic origin whether they are small or large. The basins of Bohai Gulf, South China Sea, East China Sea, Japan Sea, Andaman Sea, Okhotsk Sea and Bering Sea have typical geometry of dextral pull-apart. The Java, Makassar, Celebes and Sulu Seas basins together with grabens in Borneo also comprise a local dextral, transform-margin type basin system similar to the central and southern parts of the Shanxi Basin in geometry. The overall configuration of the Philippine Sea resembles a typical sinistral transpressional "pop-up" structure. These marginal basins except the Philippine Sea basin generally have similar (or compatible) rift history in the Cenozoic, but there do be some differences in the rifting history between major basins or their sub-basins due to local differences in tectonic settings. Rifting kinematics of each of these marginal basins can be explained by dextral pull-apart or transtension. These marginal basins except the Philippine Sea basin constitute a gigantic linked, dextral pull-apart basin system.

  15. Early Miocene Tectonic Activity in the western Ross Sea (Antarctica)

    NASA Astrophysics Data System (ADS)

    Sauli, C.; Sorlien, C. C.; Busetti, M.; Geletti, R.; De Santis, L.

    2012-12-01

    In the framework of the Rossmap Italian PNRA work objectives to compile extended and revised digital maps of the main unconformities in Ross Sea, Antarctica, much additional seismic reflection data, that were not available to previous ANTOSTRAT compilation, were incorporated into a new ROSSMAP interpretation. The correlation across almost all of Ross Sea, from DSDP Site 270 and Site 272 in Eastern Basin to northern Victoria Land Basin, of additional early Miocene and late Oligocene horizons that were not part of ANTOSTRAT allows interpretations to be made of fault activity and glacial erosion or deposition at a finer time resolution. New conclusions include that extensional or transtensional fault activity within the zone between Victoria Land Basin and Northern Basin, initiated by 23 Ma or earlier, and continued after 18 Ma. Steep parallel-striking faults in southern Victoria Land Basin display both reverse and normal separation of 17.5 Ma (from Cape Roberts Program-core 1) and post-16 Ma horizons, suggesting an important strike-slip component. This result may be compared with published papers that proposed post-17 Ma extension in southern Victoria Land Basin, 16-17 Ma extension in the AdareTrough, north of the Ross Sea continental shelf, but no Miocene extension affecting the Northern Basin (Granot et al., 2010). Thus, our evidence for extension through the early Miocene is significant to post-spreading tectonic models. Reference Granot R., Cande S. C., Stock J. M., Davey F. J. and Clayton R. W. (2010) Postspreading rifting in the Adare Basin, Antarctica: Regional tectonic consequences. Geochem. Geophys. Geosyst., 8, Q08005, doi:10.1029/2010GC003105.

  16. The driving mechanism of plate tectonics: Relation to age of the lithosphere at trenches

    NASA Astrophysics Data System (ADS)

    Carlson, R. L.; Hilde, T. W. C.; Uyeda, S.

    1983-04-01

    Sea-floor age-depth and age-trench-depth relations suggest that the oceanic lithosphere continues to thicken and subside with age beyond 80 Ma. If so, slab-pull (FS) and ridge-push (FR) forces can be calculated from the age of the sea floor at trenches (t), and if the shear stress acting on the base of the plate increases with absolute velocity (νa), the approximate force balance equation isFD1 Dva2=Svat32+Rt where D, S and R are constants related to drag, slab pull and ridge push, respectively. The relation between velocity and age is FD2 va2=S‧vat12+R‧ We have tested this model by linear regression using rate and age data for 15 trenches: FD3 va(mm/a)2=(9.20±.32)vat12+(26±250) The strength of this correlation (r² = 0.98) is strong evidence in favor of the validity of this simple model. These results suggest that ridge push is just sufficient to overcome drag at the base of the plate, and does not contribute significantly to the motions of oceanic plates, though the value of R‧ is consistent with the motions of plates not attached to subducted slabs.

  17. An Experimental Study of Incremental Surface Loading of an Elastic Plate: Application to Volcano Tectonics

    NASA Technical Reports Server (NTRS)

    Williams, K. K.; Zuber, M. T.

    1995-01-01

    Models of surface fractures due to volcanic loading an elastic plate are commonly used to constrain thickness of planetary lithospheres, but discrepancies exist in predictions of the style of initial failure and in the nature of subsequent fracture evolution. In this study, we perform an experiment to determine the mode of initial failure due to the incremental addition of a conical load to the surface of an elastic plate and compare the location of initial failure with that predicted by elastic theory. In all experiments, the mode of initial failure was tension cracking at the surface of the plate, with cracks oriented circumferential to the load. The cracks nucleated at a distance from load center that corresponds the maximum radial stress predicted by analytical solutions, so a tensile failure criterion is appropriate for predictions of initial failure. With continued loading of the plate, migration of tensional cracks was observed. In the same azimuthal direction as the initial crack, subsequent cracks formed at a smaller radial distance than the initial crack. When forming in a different azimuthal direction, the subsequent cracks formed at a distance greater than the radial distance of the initial crack. The observed fracture pattern may explain the distribution of extensional structures in annular bands around many large scale, circular volcanic features.

  18. Rotational inertia of continents: A proposed link between polar wandering and plate tectonics

    USGS Publications Warehouse

    Kane, M.F.

    1972-01-01

    A mechanism is proposed whereby displacement between continents and the earth's pole of rotation (polar wandering) gives rise to latitudinal transport of continental plates (continental drift) because of their relatively greater rotational inertia. When extended to short-term polar wobble, the hypothesis predicts an energy change nearly equivalent to the seismic energy rate.

  19. Effects of Student-Generated Diagrams versus Student-Generated Summaries on Conceptual Understanding of Causal and Dynamic Knowledge in Plate Tectonics.

    ERIC Educational Resources Information Center

    Gobert, Janice D.; Clement, John J.

    1999-01-01

    Grade five students' (n=58) conceptual understanding of plate tectonics was measured by analysis of student-generated summaries and diagrams, and by posttest assessment of both the spatial/static and causal/dynamic aspects of the domain. The diagram group outperformed the summary and text-only groups on the posttest measures. Discusses the effects…

  20. Glacial reorganization of topography in a tectonically active mountain range

    NASA Astrophysics Data System (ADS)

    Adams, Byron; Ehlers, Todd

    2016-04-01

    Tests of the interactions between tectonic and climate forcing on Earth's topography often focus on the concept of steady-state whereby processes of rock deformation and erosion are opposing and equal. However, when conditions change such as the climate or tectonic rock uplift, then surface processes act to restore the balance between rock deformation and erosion by adjusting topography. Most examples of canonical steady-state mountain ranges lie within the northern hemisphere, which underwent a radical change in the Quaternary due to the onset of widespread glaciation. The activity of glaciers changed erosion rates and topography in many of these mountain ranges, which likely violates steady-state assumptions. With new topographic analysis, and existing patterns of climate and rock uplift, we explore a mountain range previously considered to be in steady-state, the Olympic Mountains, USA. The details of our analysis suggest the dominant topographic signal in the Olympic Mountains is a spatial, and likely temporal, variation in erosional efficiency dictated by orographic precipitation, and Pleistocene glacier ELA patterns, and not tectonic rock uplift rates. Alpine glaciers drastically altered the relief structure of the Olympic Mountains. The details of these relief changes are recorded in channel profiles as overdeepenings, reduced slopes, and associated knickpoints. We find the position of these relief changes within the orogen is dependent on the position of the Pleistocene ELA. While alpine glaciers overdeepened valleys in regions near the Pleistocene ELA (which has a tendency to increase relief), headward erosion of west and north flowing glacier systems captured significant area from opposing systems and caused drainage divide lowering. This divide lowering reduced relief throughout the range. We demonstrate similar topographic effects recorded in the basin hypsometries of other Cenozoic mountain ranges around the world. The significant glacial overprint on

  1. The River Network, Active Tectonics and the Mexican Subduction Zone, Southwest Mexico

    NASA Astrophysics Data System (ADS)

    Gaidzik, K.; Ramirez-Herrera, M. T.; Kostoglodov, V.; Basili, R.

    2014-12-01

    Rivers, their profiles and network reflect the integration of multiple processes and forces that are part of the fundamental controls on the relief structure of mountain belts. The motivation of this study is to understand active tectonic processes in the forearc region of subduction zones, by distinguishing evidence of active deformation using the river network and topography. To this end, morphotectonic and structural studies have been conducted on fifteen drainage basins on the mountain front, parallel to the Mexican subduction zone, where the Cocos plate underthrusts the North American plate. The southwest - northeast Cocos plate subduction stress regime initiated ca. 20 MA. NE-SW to NNE-SSW normal faults as well as sub-latitudinal to NW-SE strike-slip faults (both dextral and sinistral) constitute the majority of mesofaults recorded in the field within the studied drainage basins. Occasionally dextral N-S strike-slip faults also occur. The stress tensor reconstruction suggests two main evolution stages of these faults: 1) the older is dominated by a NW-SE to WNW-ESE extensional regime and 2) the younger is a transcurrent regime, with NNE-SSW σ1 axis. The drainage pattern is strongly controlled by tectonic features, whereas lithology is only a subordinate factor, with only one exception (Petatlán river). Generally, major rivers flow from north to south mainly through NE-SW and NNE-SSW normal faults, and/or sub-longitudinal dextral (also locally sinistral) strike-slip faults. In the central and eastern part of the studied area, rivers also follow NW-SE structures, which are generally normal or sinistral strike-slip faults (rarely reverse). In most cases, local deflections of the river main courses are related to sub-latitudinal strike-slip faults, both dextral and sinistral. Within the current stress field related to the active Cocos subduction, both normal and strike-slip fault sets could be reactivated. Our analysis suggests that strike-slip faults, mainly

  2. Active tectonics and Quaternary landscape evolution across the western Panama block, Costa Rica, Central America

    NASA Astrophysics Data System (ADS)

    Marshall, Jeffrey Scott

    Three aspects of active tectonism are examined across central Costa Rica: (1) fault kinematics; (2) volcanic arc retreat; and (3) spatially variable coastal uplift. Diffuse faulting along the Central Costa Rica Deformed Belt (CCRDB) defines the western margin of the Panama block and aligns with the rough-smooth boundary (RSB) on the subducting Cocos plate. Sub-horizontal subduction of rough, hotspot thickened crust (Cocos Ridge and seamounts) shifts active shortening into the volcanic arc along the CCRDB. Mesoscale faults express variable kinematics across three domains: transtension in the forearc, transcurrent motion across the volcanic arc, and transpression in the back arc. Fault kinematics agree with seismicity and GPS data, and isotopic ages confirm that faulting postdates the late Neogene onset of shallow subduction. Stratigraphic correlation augmented by 40Ar/39Ar dating constrain the timing of Quaternary arc migration from the Neogene Aguacate range to the modern Cordillera Central. The Valle Central basin, between the cordilleras, filled with thick sequences of lavas, pyroclastic flows, and lahars. Middle Pleistocene drainage capture across the Aguacate arc linked the Valle Central with the Pacific slope and ash flows descended onto the coastal Orotina debris fan. Arc retreat reflects slab shallowing and enhanced tectonic erosion as rough crust entered the subduction zone. Differing subduction parameters across the RSB (crustal age, slab dip, roughness) produce marked contrasts in coastal tectonism. Varying uplift rates across coastal faults reflect sub-horizontal subduction of seamount roughness. Three groups (I--III) of fluvial terraces are correlated along the coast by isotopic ages and geomorphic characteristics. Base level fluctuations and terrace genesis reflect interaction between eustatic sea level and spatially variable rock uplift. Low uplift rates (north of RSB), yield one surface per terrace group, whereas moderate rates (south of RSB

  3. Climate dominated topography in a tectonically active mountain range

    NASA Astrophysics Data System (ADS)

    Adams, B. A.; Ehlers, T. A.

    2015-12-01

    Tests of the interactions between tectonic and climate forcing on Earth's topography often focus on the concept of steady-state whereby processes of rock deformation and erosion are opposing and equal. However, when conditions change such as the climate or tectonic rock uplift, then surface processes act to restore the balance between rock deformation and erosion by adjusting topography. Most examples of canonical steady-state mountain ranges lie within the northern hemisphere, which underwent a radical change in the Quaternary due to the onset of widespread glaciation. The activity of glaciers changed erosion rates and topography in many of these mountain ranges, which likely violates steady-state assumptions. With new topographic analysis, and existing patterns of climate and rock uplift, we explore a mountain range previously considered to be in steady-state, the Olympic Mountains, USA. The broad spatial trend in channel steepness values suggests that the locus of high rock uplift rates is coincident with the rugged range core, in a similar position as high temperature and pressure lithologies, but not in the low lying foothills as has been previously suggested by low-temperature thermochronometry. The details of our analysis suggest the dominant topographic signal in the Olympic Mountains is a spatial, and likely temporal, variation in erosional efficiency dictated by orographic precipitation, and Pleistocene glacier ELA patterns. We demonstrate the same topographic effects are recorded in the basin hypsometries of other Cenozoic mountain ranges around the world. The significant glacial overprint on topography makes the argument of mountain range steadiness untenable in significantly glaciated settings. Furthermore, our results suggest that most glaciated Cenozoic ranges are likely still in a mode of readjustment as fluvial systems change topography and erosion rates to equilibrate with rock uplift rates.

  4. Quantifying the net slab pull force as a driving mechanism for plate tectonics

    NASA Astrophysics Data System (ADS)

    Schellart, W. P.

    2004-04-01

    It has remained unclear how much of the negative buoyancy force of the slab (FB) is used to pull the trailing plate at the surface into the mantle. Here I present three-dimensional laboratory experiments to quantify the net slab pull force (FNSP) with respect to FB during subduction. Results show that FNSP increases with increasing slab length and dip up to ~8-12% of FB, making FNSP up to twice as large as the ridge push force. The remainder of FB is primarily used to drive rollback-induced mantle flow (~70%), to bend the subducting plate at the trench (~15-30%) and to overcome shear resistance between slab and mantle (0-8%).

  5. Interactive Ocean Observatories are Essential for Global Assessment of Plate-tectonically Modulated Microbial Input to the Deep Ocean

    NASA Astrophysics Data System (ADS)

    Delaney, J.; Team, K.

    2004-12-01

    A major new planetary-scale research thrust can only be addressed with interactive, next-generation ocean-observatory capabilities. These new research opportunities arise from the possibility that input into the ocean of chemosynthetically derived microbial biomass from below the seafloor rivals the biomass from primary photosynthetic productivity near the top of the ocean. All three types of plate boundaries and many plate interiors vent microbe-bearing fluids into the deep ocean continuously AND episodically. Unpredicted episodes increase nutrient output and venting volume by as much as a factor of 100 for weeks to months at a time (Lilley et al.,2003, Nature). Because of the highly non-linear nature of these fluxes, quantification of such processes represents essential, but unconstrained, variables in equations for carbon budgets and bio-flux in the deep ocean. Triggering events and their induced fluxes must be detected, located, responded to, and quantified before their relative importance to the global-ocean system can be evaluated. Addressing these issues requires an essential new capability in the ocean sciences. High-power and high-bandwidth cabled systems will enable remote and long-term experimentation with processes via thousands of stationary and/or mobile sensor platforms on, below, and above the seafloor. The Ocean Research Interactive Observatory Networks (ORION) program is currently working with NEPTUNE Canada to produce a plate-tectonic-scale, regional cabled ocean observatory (RCO), an ideal platform for adaptive surveillance and quantitative response to fluid-flux generating events at the margins and interior of the Juan de Fuca (JdF) Plate. The W. M. Keck Foundation is supporting a pre-NEPTUNE exploration of the linked processes involved in the deformation-fluid/microbial flux concept. Thirteen seismometers (3 broadband, 10 short-period) and 45 fluid-movement/chemical sensors are co-deployed on three different, but adjacent, plate boundaries at

  6. Hydrothermal and tectonic activity in northern Yellowstone Lake, Wyoming

    USGS Publications Warehouse

    Johnson, S.Y.; Stephenson, W.J.; Morgan, L.A.; Shanks, Wayne C.; Pierce, K.L.

    2003-01-01

    Yellowstone National Park is the site of one of the world's largest calderas. The abundance of geothermal and tectonic activity in and around the caldera, including historic uplift and subsidence, makes it necessary to understand active geologic processes and their associated hazards. To that end, we here use an extensive grid of high-resolution seismic reflection profiles (???450 km) to document hydrothermal and tectonic features and deposits in northern Yellowstone Lake. Sublacustrine geothermal features in northern Yellowstone Lake include two of the largest known hydrothermal explosion craters, Mary Bay and Elliott's. Mary Bay explosion breccia is distributed uniformly around the crater, whereas Elliott's crater breccia has an asymmetric distribution and forms a distinctive, ???2-km-long, hummocky lobe on the lake floor. Hydrothermal vents and low-relief domes are abundant on the lake floor; their greatest abundance is in and near explosion craters and along linear fissures. Domed areas on the lake floor that are relatively unbreached (by vents) are considered the most likely sites of future large hydrothermal explosions. Four submerged shoreline terraces along the margins of northern Yellowstone Lake add to the Holocene record or postglacial lake-level fluctuations attributed to "heavy breathing" of the Yellowstone magma reservoir and associated geothermal system. The Lake Hotel fault cuts through northwestern Yellowstone Lake and represents part of a 25-km-long distributed extensional deformation zone. Three postglacial ruptures indicate a slip rate of ???0.27 to 0.34 mm/yr. The largest (3.0 m slip) and most recent event occurred in the past ???2100 yr. Although high heat flow in the crust limits the rupture area of this fault zone, future earthquakes of magnitude ???5.3 to 6.5 are possible. Earthquakes and hydrothermal explosions have probably triggered landslides, common features around the lake margins. Few high-resolution seismic reflection surveys have

  7. Exhumation and Coupling at the Plate Interface: Large Tectonic Slices V. Melange Formation? Key Contexts and Possible Controlling Parameters

    NASA Astrophysics Data System (ADS)

    Agard, P.; Angiboust, S.; Guillot, S.; Garcia-Casco, A.

    2011-12-01

    Fragments of subducted oceanic lithosphere returned along the plate interface convey crucial information regarding the thermal and rheological conditions of convergent plate boundaries. Geological evidence indicate that, unlike subduction, exhumation is non-steady (Agard et al., Earth Sci. Rev. 2009). We herein focus on deep processes along the plate interface (40-80 km depth), for which there is no counterflow (unlike in accretionary prisms) and no other known mechanisms to return eclogites than interplate friction or buoyancy. These eclogites are of two major types: large scale (>km) slices with coherent PT estimates (W. Alps) versus isolated fragments (frequently m-hm) in a serpentinite- or sedimentary-rich matrix showing contrasting equilibration depths (with hints of punctuated exhumation and even reburial; Franciscan, Cuba, Sistan; e.g., Garcia-Casco et al., Geol. Acta 2006). This latter type tends to show warmer equilibration paths, whereas the larger tectonic slices from the former type remain systematically cold. Serpentinites are crucial for both in permitting decoupling and acting as a buoy, and fluid budget is important too in enhancing floatability and allowing large slices to survive (Angiboust and Agard, Lithos 2010). Numerical models implementing free migration of fluids in the subduction zone also show that the plate interface is strongly localized in the absence of fluids: mechanical decoupling efficiently occurs along the sediment veneer and/or at the top of the highly hydrothermalized crust. Whenever fluids are released in greater amounts (depending on initial fluid content and/or thermal structure), deformation becomes much more distributed and affects both the mantle wedge and the top of the downgoing lithosphere (crust and hydrated mantle top), thereby increasing mechanical coupling between the two plates. Based on natural data and numerical modelling we herein propose that rheological contrast chiefly controls mechanical decoupling. On a

  8. Taiwan: a perfect field trip to study active tectonics and erosion processes

    NASA Astrophysics Data System (ADS)

    Bigot-Cormier, Florence; Beauval, Véronique; Martinez, Claire-Marie; Seyeux, Jana

    2014-05-01

    Taiwan is located at the boundary between the Philippine Sea Plate to the East and the Eurasian Plate to the West. This plate boundary is rather complex since it comprises two subduction zones of reverse polarities. Due to this specific geodynamic context, this field is a perfect area to answer the French program in 5th grade (erosion processes) and 4th grade (active tectonics) in Earth Science class. That's why for the second year, students from the Lycée Français de Shanghai (LFS) in 4th grade will go for a 4-day field trip to discover volcanoes (in the Yangminshan National Park) and para-seismic constructions in the 101 Tower at Taipei. It will remind them the program of their previous class (5ème) through the visit of Yehliu Geographic Park and some other areas in the North of the Island where they will be able to observe different erosion processes (wind or water) carving the landscape. The aim of this field trip is first to show them that Earth Sciences cannot be studied only in class but also on the field to get a better understanding of the processes. In this manner, after having understood the internal thermal system of our Earth in class, they will see its manifestations on the surface of the Earth, by seeing an active explosive volcano with gas ejection, specific mineralization, and hot springs. Furthermore on the field, they will be able to do a link between the external and internal geodynamics processes usually studied separately in middle school. The poster presented will detail the first field trip in Taiwan realized in May 2013 by the LFS 4th grade students and will be made by the students going in June 2014. Thus, this activity will allow them to get a perspective of the topic that they will discover on the field trip.

  9. Lithosphere-asthenosphere Structure and Active Tectonics In Central Italy

    NASA Astrophysics Data System (ADS)

    Chimera, G.; Aoudia, A.; Saraò, A.; Panza, G. F.

    We investigate the lithosphere-asthenosphere structure and the active tectonics along a stripe from the Tyrrhenian to the Adriatic with emphasis on the Umbria-Marche area by means of surface-wave tomography, and inversion studies for structure and seismic moment tensor retrieval. The data include seismic waveforms, a large compilation of local group velocities (0.8-4s) and regional phase and group velocity (10-100s) measurements. The local group velocity maps cover the area reactivated by the 1997 Umbria-Marche earthquake sequence. These maps suggest a relation between the lat- eral heterogeneity and distribution of the active faults and related basins. Such relation is confirmed by the non-linear inversion of the local dispersion curves. To image the deeper structure from the Tyrrhenian to the Adriatic coast, we fix the uppermost part of the crust using the Umbria-Marche models along with the CROP03 profile and related shear wave velocity, and invert the additional long period dispersion measure- ments. The results of the inversion show the geometry and lateral heterogeneity of the lithosphere-asthenosphere system. The retrieved models for the Umbria-Marche up- per crust reveal the importance of the inherited compression on the ongoing extension and related seismic activity. The reactivated 1997 normal fault zone displays a thrust fault geometry as evidenced by the lateral extent of the faulted Late Triassic evap- orites that did not yet balance the cumulative normal faulting deformation attesting therefore recent extensional tectonics within the thrust belt. Our data are in favor of a listric geometry of faulting at depth. Source inversion studies of the two main crustal events of September 26 and October 14, 1997 show the dominance of normal faulting mechanisms, whereas selected aftershocks between the reactivated fault segments re- veal that the prevailing deformation at the step-over is of strike-slip faulting type. The rupture of the three distinct and

  10. Structural and Tectonic Map Along the Pacific-North America Plate Boundary in Northern Gulf of California, Sonora Desert and Valle de Mexicali, Mexico, from Seismic Reflection Evidence

    NASA Astrophysics Data System (ADS)

    Gonzalez-Escobar, M.; Suarez-Vidal, F.; Mendoza-Borunda, R.; Martin Barajas, A.; Pacheco-Romero, M.; Arregui-Estrada, S.; Gallardo-Mata, C.; Sanchez-Garcia, C.; Chanes-Martinez, J.

    2012-12-01

    Between 1978 and 1983, Petróleos Mexicanos (PEMEX) carried on an intense exploration program in the northern Gulf of California, the Sonora Desert and the southern part of the Mexicali Valley. This program was supported by a seismic reflection field operation. The collected seismic data was 2D, with travel time of 6 s recording, in 48 channels, and the source energy was: dynamite, vibroseis and air guns. Since 2007 to present time, the existing seismic data has been re-processing and ire-interpreting as part of a collaboration project between the PEMEX's Subdirección de Exploración (PEMEX) and CICESE. The study area is located along a large portion of the Pacific-North America plate boundary in the northern Gulf of California and the Southern part of the Salton Trough tectonic province (Mexicali Valley). We present the result of the processes reflection seismic lines. Many of the previous reported known faults were identify along with the first time described located within the study region. We identified regions with different degree of tectonic activity. In structural map it can see the location of many of these known active faults and their associated seismic activity, as well as other structures with no associated seismicity. Where some faults are mist placed they were deleted or relocated based on new information. We included historical seismicity for the region. We present six reflection lines that cross the aftershocks zone of the El Mayor-Cucapah earthquake of April 4, 2010 (Mw7.2). The epicenter of this earthquake and most of the aftershocks are located in a region where pervious to this earthquake no major earthquakes are been reported. A major result of this study is to demonstrate that there are many buried faults that increase the seismic hazard.

  11. On plate tectonics and the geologic evolution of southwestern North America

    USGS Publications Warehouse

    Ward, P.L.

    1991-01-01

    Very rapid subduction of the Farallon plate under southwestern North America between 60 and 40 Ma was accompanied by a relatively low volume of magmatism throughout the southwestern United States and northern Mexico. Between 40 and 20 Ma, when subduction slowed significantly and in one area may have even stopped, magmatism became widespread and voluminous from Nevada and Utah to central Mexico. This correlation of rapid subduction with a relatively low volume of magmatism can be explained by the observation that subduction-related andesitic arc volcanism, often formed in a Laramide-style compressional regime, is relatively low volume compared to continental volcanism. -from Author

  12. Plate tectonics hiati as the cause of global glaciations: 1. Early Proterozoic events and the rise of oxygen

    NASA Astrophysics Data System (ADS)

    Osmaston, M. F.

    2003-04-01

    Plate tectonics is the main way in which the Earth's internal heat is brought to the surface and lost, so it seems that global tectonics should not stop and start. Consequently the long-standing fact that, globally, no orogenic granitoid or greenstone U-Pb ages have been found in the 2.45--2.22 Ga interval has been attributed to defective sampling. Here I argue that this interval was indeed a prolonged hiatus in plate tectonics, being the first of two. The other, but differently caused, was in the late Proterozoic and is the topic of Part 2. The feature common to both hiati, and relevant to global glaciation, is that mid-ocean ridges (MORs) die and subside, potentially lowering sea-level by several kilometres, causing loss of atmospheric CO2 by weathering and an increase in planetary albedo. For the origin of the first hiatus we must first go back to formation of the core. The current iron-percolation model is invalidated by the fact that its corollary, the arrival of a water and siderophile-rich "late veneer" at the end of percolation, would be required to arrive some 60 Ma after the Moon, which never had a late veneer, was already in Earth orbit. The available alternative [1] would have given the early Earth a wet and low-viscosity convecting mantle able to dispose of the early heat with high efficiency; so that by 2.8 Ga MORs began to deepen, exposing cratons to massive weathering which lowered atmospheric CO2. The well-documented late Archaean acceleration of crustal addition to cratons, or, more precisely, of TTG-granitoid intrusion of greenstone belts, is also, paradoxically, evidence of waning mantle heat. Such wide-belt intrusion, grouped into quasi-coeval 'events', are examples of post-subduction magmatism (PSM), marking interruption of flat-slab subduction under a greenstone belt when a microcraton arrived [2]. On each occasion the TTG, derived from the subducted and reheated oceanic crust, advected subducting-plate heat to the surface that would

  13. Coherence between geodetic and seismic deformation in a context of slow tectonic activity (SW Alps, France)

    NASA Astrophysics Data System (ADS)

    Walpersdorf, A.; Sue, C.; Baize, S.; Cotte, N.; Bascou, P.; Beauval, C.; Collard, P.; Daniel, G.; Dyer, H.; Grasso, J.-R.; Hautecoeur, O.; Helmstetter, A.; Hok, S.; Langlais, M.; Menard, G.; Mousavi, Z.; Ponton, F.; Rizza, M.; Rolland, L.; Souami, D.; Thirard, L.; Vaudey, P.; Voisin, C.; Martinod, J.

    2015-04-01

    A dense, local network of 30 geodetic markers covering a 50 × 60 km2 area in the southwestern European Alps (Briançon region) has been temporarily surveyed in 1996, 2006 and 2011 by GPS. The aim is to measure the current deformation in this seismically active area. The study zone is characterized by a majority of extensional and dextral focal mechanisms, along north-south to N160 oriented faults. The combined analysis of the three measurement campaigns over 15 years and up to 16 years of permanent GPS data from the French RENAG network now enables to assess horizontal velocities below 1 mm/year within the local network. The long observation interval and the redundancy of the dense campaign network measurement help to constrain a significant local deformation pattern in the Briançon region, yielding an average E-W extension of 16 ± 11 nanostrain/year. We compare the geodetic deformation field to the seismic deformation rate cumulated over 37 years, and obtain good coherencies both in amplitude and direction. Moreover, the horizontal deformation localized in the Briançon region represents a major part of the Adriatic-European relative plate motion. However, the average uplift of the network in an extensional setting needs the presence of buoyancy forces in addition to plate tectonics.

  14. The Central-Western Mediterranean: Anomalous igneous activity in an anomalous collisional tectonic setting

    NASA Astrophysics Data System (ADS)

    Lustrino, Michele; Duggen, Svend; Rosenberg, Claudio L.

    2011-01-01

    plate (Sardinia, Corsica, Balearic Islands, Kabylies, Calabria, Peloritani Mountains). The bulk of igneous activity in the central-western Mediterranean is believed to have tapped mantle 'wedge' regions, metasomatized by pressure-related dehydration of the subducting slabs. The presence of subduction-related igneous rocks with a wide range of chemical composition has been related to the interplay of several factors among which the pre-metasomatic composition of the mantle wedges (i.e., fertile vs. refractory mineralogy), the composition of the subducting plate (i.e., the type and amount of sediment cover and the alteration state of the crust), the variable thermo-baric conditions of magma formation, coupled with variable molar concentrations of CO 2 and H 2O in the fluid phase released by the subducting plates are the most important. Compared to classic collisional settings (e.g., Himalayas), the central-western Mediterranean area shows a range of unusual geological and magmatological features. These include: a) the rapid formation of extensional basins in an overall compressional setting related to Africa-Europe convergence; b) centrifugal wave of both compressive and extensional tectonics starting from a 'pivotal' region around the Gulf of Lyon; c) the development of concomitant Cenozoic subduction zones with different subduction and tectonic transport directions; d) subduction 'inversion' events (e.g., currently along the Maghrebian coast and in northern Sicily, previously at the southern paleo-European margin); e) a repeated temporal pattern whereby subduction-related magmatic activity gives way to magmas of intraplate geochemical type; f) the late-stage appearance of magmas with collision-related 'exotic' (potassic to ultrapotassic) compositions, generally absent from simple subduction settings; g) the relative scarcity of typical calcalkaline magmas along the Italian peninsula; h) the absence of igneous activity where it might well be expected (e.g., above the

  15. Actively controlling coolant-cooled cold plate configuration

    DOEpatents

    Chainer, Timothy J.; Parida, Pritish R.

    2016-04-26

    Cooling apparatuses are provided to facilitate active control of thermal and fluid dynamic performance of a coolant-cooled cold plate. The cooling apparatus includes the cold plate and a controller. The cold plate couples to one or more electronic components to be cooled, and includes an adjustable physical configuration. The controller dynamically varies the adjustable physical configuration of the cold plate based on a monitored variable associated with the cold plate or the electronic component(s) being cooled by the cold plate. By dynamically varying the physical configuration, the thermal and fluid dynamic performance of the cold plate are adjusted to, for example, optimally cool the electronic component(s), and at the same time, reduce cooling power consumption used in cooling the electronic component(s). The physical configuration can be adjusted by providing one or more adjustable plates within the cold plate, the positioning of which may be adjusted based on the monitored variable.

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

    NASA Astrophysics Data System (ADS)

    Besutiu, Lucian; Zlagnean, Luminita; Plopeanu, Marin

    2013-04-01

    An alternative model attempting to explain the unusual sub-crustal seismicity occurring in the bending zone of East Carpathians within full intra-continental environment (the so-called Vrancea zone) has assumed the presence of a FFT unstable triple junction between the three lithospheric compartments joining the area: East European Plate (EEP), Intra-Alpine Microplate (IaP) and the Moesian Microplate (MoP). Geophysical imprints (e.g. EM data, potential fields, seismic tomography), and indirect geological evidence (e.g. absence of the volcanism associated to subduction zones, the unusual high Neogene tectonic subsidence, symmetry and normal faulting within compressional environment of Focsani basin) support the hypothesis. The above-mentioned model considers the intermediate-depth seismicity as the result of the thermo-baric-accommodation phenomena generated within the colder lithosphere collapsed into the hotter upper mantle. Therefore, the amount of seismic energy thus released should be related to the volume of the lithosphere brought into thermo-baric disequilibrium by sinking into the upper mantle. Vertical dynamics of the Vrancea unstable triple junction (VTJ) seems to be controlled by the both tangential tectonic forces driving the neighbouring plates and the gravitational pull created by the eclogitization of VTJ lower crust. But, while eclogitization provides a relatively constant force, acceleration of sinking is expected to be provided by changes in the tectonic forces acting on VTJ. As changes in tectonic forces should reflect in changes of the dynamics of lithospheric compartments, geodetic means were considered for helping in their monitoring. The Peceneaga-Camena Fault (PCF) is a major lithospheric contact separating MoP and EEP, starting from the W Black Sea basin to the Vrancea zone. Geological evidence advocate for its variable geodynamic behaviour during the time, both as left-lateral or right-lateral fault. Unfortunately, GPS campaigns, so far

  17. Aperture of the northern and central Gulf of California since 9 to -1 Ma BP, using an instantaneous kinematic plate tectonics model

    NASA Astrophysics Data System (ADS)

    Gonzalez-Garcia, J.; Gonzalez-Ortega, J.

    2013-12-01

    The position of points over the earth surface is conveniently represented in a terrestrial (earth center fixed) reference frame, one that is rotating in some well defined way with the earth. In order to represent actual, past and future positions, we use the International Terrestrial Reference Frame, with kinematic plate tectonic models in a no-net rotation mode. Here we use the Pacific-Northamerica (PA-NA) plate motion model with Northamerica plate fixed. In our case, the actual shoreline of Mexico mainland is maintained fixed for visual purpose. We show the translation of the Baja California peninsula, traveling as PA-NA, since 9 Ma BP to 1 Ma AP. We made a 'calibration' of few kinematic plate tectonic models in PA-NA zone constraining the stable Mendocino Triple Junction (MTJ; 40.384°N ×2 km, 124.88°W +2, -4 km). Those models can be divided in two groups: space geodesy and geological. A preliminary result shows that geodesy models are a better representation of a constant kinematic plate tectonic motion, as compared with geological ones (using actual directions of transform faults, seafloor spreading anomalies with and without earthquake slip vectors). We select GEODVEL plate motion model, which uses four space geodesy techniques: VLBI, SLR, DORIS and GPS. The aperture of the northern and central Gulf of California is adjusted by the evolution of the MTJ and a 'virtual' southeastern end triple junction, which is not coincident with the Rivera Triple Junction. We also observe that GEODVEL is not well constrained at Guadalupe and Socorro islands, which are supposed to be part of Pacific plate, but with 2.5 and 7.0 mm/yr residual, respectively.

  18. Tree Tectonics

    NASA Astrophysics Data System (ADS)

    Vogt, Peter R.

    2004-09-01

    Nature often replicates her processes at different scales of space and time in differing media. Here a tree-trunk cross section I am preparing for a dendrochronological display at the Battle Creek Cypress Swamp Nature Sanctuary (Calvert County, Maryland) dried and cracked in a way that replicates practically all the planform features found along the Mid-Oceanic Ridge (see Figure 1). The left-lateral offset of saw marks, contrasting with the right-lateral ``rift'' offset, even illustrates the distinction between transcurrent (strike-slip) and transform faults, the latter only recognized as a geologic feature, by J. Tuzo Wilson, in 1965. However, wood cracking is but one of many examples of natural processes that replicate one or several elements of lithospheric plate tectonics. Many of these examples occur in everyday venues and thus make great teaching aids, ``teachable'' from primary school to university levels. Plate tectonics, the dominant process of Earth geology, also occurs in miniature on the surface of some lava lakes, and as ``ice plate tectonics'' on our frozen seas and lakes. Ice tectonics also happens at larger spatial and temporal scales on the Jovian moons Europa and perhaps Ganymede. Tabletop plate tectonics, in which a molten-paraffin ``asthenosphere'' is surfaced by a skin of congealing wax ``plates,'' first replicated Mid-Oceanic Ridge type seafloor spreading more than three decades ago. A seismologist (J. Brune, personal communication, 2004) discovered wax plate tectonics by casually and serendipitously pulling a stick across a container of molten wax his wife and daughters had used in making candles. Brune and his student D. Oldenburg followed up and mirabile dictu published the results in Science (178, 301-304).

  19. Model for suturing of Superior and Churchill plates: An example of double indentation tectonics

    NASA Astrophysics Data System (ADS)

    Gibb, R. A.

    1983-07-01

    Recent gravity surveys in eastern and southern Hudson Bay, Canada, have revealed, for the first time, the gravity anomaly pattern over the complete length of the proposed circum-Superior suture. A symmetrical distribution of linear, positive anomalies near the southern and eastern perimeters of Hudson Bay suggests a model in which suturing of Superior and Churchill protoplates was accomplished by subduction of oceanic lithosphere and by progressive double indentation of the rigid-plastic Churchill craton by the Thompson and Ungava salients of the rigid Superior protocontinent. Suturing was initiated at the Thompson salient with extrusion of Churchill material laterally along strike-slip faults into the Hudson Bay embayment. With continued subduction, indentation of the Churchill craton by the Ungava salient commenced, so that Churchill material was now extruded from two directions to fill the embayment of Hudson Bay. Following complete suturing of the Hudson Bay embayment, the motion of the Superior plate relative to the Churchill may have changed by about 90° E to facilitate complete closure of the predecessor of the Labrador Sea. The pattern of faulting and other major structural elements of northern Saskatchewan-Manitoba can be interpreted in terms of the proposed analogue model of plane indentation. The regional faults and their senses of motion correspond generally to that predicted by the theoretical pattern of slip lines associated with a wedge-shaped indenter.

  20. The Wisconsin magmatic terrane: An Early Proterozoic greenstone-granite terrane formed by plate tectonic processes

    NASA Technical Reports Server (NTRS)

    Schulz, K. J.; Laberge, G. L.

    1986-01-01

    The Wisconsin magmatic terrane (WMT) is an east trending belt of dominantly volcanic-plutonic complexes of Early Proterozoic age (approx. 1850 m.y.) that lies to the south of the Archean rocks and Early Proterozoic epicratonic sequence (Marquette Range Supergroup) in Michigan. It is separated from the epicratonic Marquette Range Supergroup by the high-angle Niagara fault, is bounded on the south, in central Wisconsin, by Archean gneisses, is truncated on the west by rocks of the Midcontinent rift system, and is intruded on the east by the post-orogenic Wolf river batholith. The overall lithologic, geochemical, metallogenic, metamorphic, and deformational characteristics of the WMT are similar to those observed in recent volcanic arc terranes formed at sites of plate convergence. It is concluded that the WMT represents an evolved oceanic island-arc terrane accreated to the Superior craton in the Early Proterozoic. This conclusion is strengthened by the apparent absence of Archean basement from most of the WMT, and the recent recognition of the passive margin character of the epicratonic Marquette Range Supergroup.

  1. Thick shell tectonics on one-plate planets - Applications to Mars

    NASA Technical Reports Server (NTRS)

    Banerdt, W. B.; Saunders, R. S.; Phillips, R. J.; Sleep, N. H.

    1982-01-01

    Using the zero frequency equations of a self-gravitating elastic spherical shell overlying a strengthless fluid, a theory for stress distribution in thick lithospheric shells on one-plate planets is developed. For both the compensated and flexural modes, stress distributions in lithospheres are reviewed. For compensated modes, surface stresses depend only on surface topography, whereas for flexural modes it is shown that, for long wavelengths, stress trajectories are mainly dependent on the lithospheric lateral density distribution and not on elastic properties. Computational analyses are performed for Mars, and it is found that isostatically compensated models correctly predict the graben structure in the immediate Tharsis region and a flexural loading model is satisfactory in explaining the graben in the regions surrounding Tharsis. A three-stage model for the evolution of Tharsis is hypothesized: isostasy with north-south graben formation on Tharsis, followed by flexural loading and radial graben formation on the perimeter of Tharsis, followed by a last stage of loading with little or no regional deformation.

  2. Spectrum of slip behaviour in Tohoku fault zone samples at plate tectonic slip rates

    NASA Astrophysics Data System (ADS)

    Ikari, Matt J.; Ito, Yoshihiro; Ujiie, Kohtaro; Kopf, Achim J.

    2015-11-01

    During the 2011 Tohoku-oki earthquake, extremely extensive coseismic slip ruptured shallow parts of the Japan Trench subduction zone and breached the sea floor. This part of the subduction zone also hosts slow slip events (SSE). The fault thus seems to have a propensity for slip instability or quasi-instability that is unexpected on the shallow portions of important fault zones. Here we use laboratory experiments to slowly shear samples of rock recovered from the Tohoku-oki earthquake fault zone as part of the Japan Trench Fast Drilling Project. We find that infrequent perturbations in rock strength appear spontaneously as long-term SSE when the samples are sheared at a constant rate of about 8.5 cm yr-1, equivalent to the plate-convergence rate. The shear strength of the rock drops by 3 to 6%, or 50 kPa to 120 kPa, over about 2 to 4 h. Slip during these events reaches peak velocities of up to 25 cm yr-1, similar to SSE observed in several circum-Pacific subduction zones. Furthermore, the sheared samples exhibit the full spectrum of fault-slip behaviours, from fast unstable slip to slow steady creep, which can explain the wide range of slip styles observed in the Japan Trench. We suggest that the occurrence of SSE at shallow depths may help identify fault segments that are frictionally unstable and susceptible to large coseismic slip propagation.

  3. Tectonic slicing of subducting oceanic crust along plate interfaces: Numerical modeling

    NASA Astrophysics Data System (ADS)

    Ruh, J. B.; Le Pourhiet, L.; Agard, Ph.; Burov, E.; Gerya, T.

    2015-10-01

    Multikilometer-sized slivers of high-pressure low-temperature metamorphic oceanic crust and mantle are observed in many mountain belts. These blueschist and eclogite units were detached from the descending plate during subduction. Large-scale thermo-mechanical numerical models based on finite difference marker-in-cell staggered grid technique are implemented to investigate slicing processes that lead to the detachment of oceanic slivers and their exhumation before the onset of the continental collision phase. In particular, we investigate the role of the serpentinized subcrustal slab mantle in the mechanisms of shallow and deep crustal slicing. Results show that spatially homogeneous serpentinization of the sub-Moho slab mantle leads to complete accretion of oceanic crust within the accretionary wedge. Spatially discontinuous serpentinization of the slab mantle in form of unconnected patches can lead to shallow slicing of the oceanic crust below the accretionary wedge and to its deep slicing at mantle depths depending on the patch length, slab angle, convergence velocity and continental geothermal gradient. P-T paths obtained in this study are compared to natural examples of shallow slicing of the Crescent Terrane below Vancouver Island and deeply sliced crust of the Lago Superiore and Saas-Zermatt units in the Western Alps.

  4. Collision tectonics

    SciTech Connect

    Coward, M.P.; Ries, A.C.

    1985-01-01

    The motions of lithospheric plates have produced most existing mountain ranges, but structures produced as a result of, and following the collision of continental plates need to be distinguished from those produced before by subduction. If subduction is normally only stopped when collision occurs, then most geologically ancient fold belts must be collisional, so it is essential to recognize and understand the effects of the collision process. This book consists of papers that review collision tectonics, covering tectonics, structure, geochemistry, paleomagnetism, metamorphism, and magmatism.

  5. Archean plate tectonics geodynamics: example from the Belomorian province, Fennoscandian Shield

    NASA Astrophysics Data System (ADS)

    Slabunov, Alexander

    2014-05-01

    A fragment of the Archean collisional Belomorian orogen has been identified as the Belomorian province (BP) of the Fennoscandian Shield (Slabunov, 2008; Holtta et al., 2014). The province consists dominantly of Archean rocks, Early Paleoproterozoic rocks being less abundant. Rock of BP exhumed from middle crustal depths in Paleoproterozoic time (1.94-1.8 Ga). Seismic (CDP) profiling data (Sharov et al., 2010) show that the internal structure of BP reflects nappe tectonics: in Archean time, a collage of numerous slides was formed, and in Paleoproterozoic time the BP was thrusted on the Karelian craton and, in turn, was thrusted by rocks of the Kola province. The BP consists dominantly of Meso- and Neoarchean rock association (Slabunov et al. 2006). Neoarchean granitoids predominate, but eclogite-bearing metam?lange (Volodichev et al., 2004; Mints et al., 2010; Shchipansky et al., 2012), island-arc volcanics, front-arc basin sediments, ophiolite-type oceanic plateau-type rocks, collisional S-granites, kyanite-facies metamorphic rocks, molassa-type rocks, subalkaline granitoids and leucogabbro have been revealed among supracrustal rock associations. Rocks of the Belomorian province were subjected to multiple metamorphism in Archean and Paleoproterozoic time at moderately high to high pressures and were considerably deformed. High-grade supracrustal complexes make up not more than 20 % of the BP, but as they probably host ore and are crucial for the understanding of the formation and evolution of the structure, they are given close attention. Five generations of greenstone complexes of different ages: 2.88-2.82 Ga, 2.8-2.78 Ga, ca. 2.75 Ga , ca. 2.72 Ga and not later than 2.66 Ga, and two paragneiss complex in which sediments were formed 2.89-2.82 and 2.78 Ga ago, are distinguished. The main stages of crustal evolution in the BP: ca 2.88-2.82 Ga - the first subduction-accretion event marked by the following complexes: island-arc volcanics of the Keret GB; metagraywacke

  6. Reidar Løvlie and Plate Tectonic consequences of sedimentary inclination shallowing

    NASA Astrophysics Data System (ADS)

    Torsvik, Trond H.

    2014-05-01

    Reidar Løvlie was my mentor and supervisor in the early 1980s and he thought me all about laboratory experiments and palaeomagnetic methods, but also various aspects of science philosophy. My first fieldworks were together with him and I enjoyed memorable trips to the Bear Island, Spitsbergen and Scotland. Acquisition of magnetism in sediments was always a favourite topic of Reidar and in the early 1980s he was particularly interested in sedimentary inclination shallowing. From one of our fieldtrips to Spitsbergen we sampled unconsolidated flood-plain deposits of hematite-bearing Devonian red sand/siltstone from Dicksonfjorden. These were used for redeposition experiments in a coil system that could simulate different latitudes (field inclinations) and in 1994 we published a paper entitled"Magnetic remanence and fabric properties of laboratory-deposited hematite-bearing red sandstone" that demonstrated the tangent relationship between inclinations of detrital remanent magnetization and the ambient magnetic field. Inclination (I) error in sediments is latitude dependent, antisymmetric and the bias closely mimics errors produced by octupole fields of the same sign as the dipole field. Inclination shallowing is commonly predicted from tan (Observed Inclination) = f * tan (Field Inclination) where f is the degree of inclination error. In our study we calculated a f value of 0.4 and this laboratory value (and many others) is significant lower than those estimated from the E/I or the magnetic fabric methods developed in the past decade (f typically around 0.6). There is now little doubt that inclination shallowing in detrital sediments is a serious problem that affects plate reconstructions and apparent polar wander paths. As an example, a f value of 0.6 amounts to a latitude error of 1600 km at around 50 degrees N or S (comparable to the effects of octupole contributions as high as 22%) and this have led to erroneous Pangea reconstructions.

  7. Pore pressure sensitivities to dynamic strains: Observations in active tectonic regions

    NASA Astrophysics Data System (ADS)

    Barbour, Andrew J.

    2015-08-01

    Triggered seismicity arising from dynamic stresses is often explained by the Mohr-Coulomb failure criterion, where elevated pore pressures reduce the effective strength of faults in fluid-saturated rock. The seismic response of a fluid-rock system naturally depends on its hydromechanical properties, but accurately assessing how pore fluid pressure responds to applied stress over large scales in situ remains a challenging task; hence, spatial variations in response are not well understood, especially around active faults. Here I analyze previously unutilized records of dynamic strain and pore pressure from regional and teleseismic earthquakes at Plate Boundary Observatory (PBO) stations from 2006 to 2012 to investigate variations in response along the Pacific/North American tectonic plate boundary. I find robust scaling response coefficients between excess pore pressure and dynamic strain at each station that are spatially correlated: around the San Andreas and San Jacinto fault systems, the response is lowest in regions of the crust undergoing the highest rates of secular shear strain. PBO stations in the Parkfield instrument cluster are at comparable distances to the San Andreas Fault (SAF), and spatial variations there follow patterns in dextral creep rates along the fault, with the highest response in the actively creeping section, which is consistent with a narrowing zone of strain accumulation seen in geodetic velocity profiles. At stations in the San Juan Bautista (SJB) and Anza instrument clusters, the response depends nonlinearly on the inverse fault-perpendicular distance, with the response decreasing toward the fault; the SJB cluster is at the northern transition from creeping-to-locked behavior along the SAF, where creep rates are at moderate to low levels, and the Anza cluster is around the San Jacinto Fault, where to date there have been no statistically significant creep rates observed at the surface. These results suggest that the strength of the

  8. Viscoelastic deformation near active plate boundaries

    NASA Technical Reports Server (NTRS)

    Ward, Steven N.

    1991-01-01

    Very Long Baseline Interferometry (VLBI) now has the capacity to monitor geodetic positions with precisions of a few 1 mm over continental baselines. For tectonic applications, one of the major products of the VLBI program is the determination of the rate of change of station locations. Vector site velocities are now routinely produced. One of the novel techniques, VLBI Euler poles, is discussed.

  9. Earthquake mechanisms and active tectonics of the Hellenic subduction zone

    NASA Astrophysics Data System (ADS)

    Shaw, Beth; Jackson, James

    2010-05-01

    We use improved focal mechanisms and centroid depth estimates of earthquakes, combined with GPS velocities, to examine the tectonics of the Hellenic subduction zone, and in particular the processes occurring at both ends of the Hellenic Arc. Nubia-Aegean convergence is accommodated by shallowly dipping thrust-faulting along the subduction-zone interface, as well as by steeper splay faults in the overriding material. From a comparison of observed and expected seismic moment release over the last 100 yr, combined with existing knowledge of the longer-term documented historical record, we confirm earlier suggestions that most (80 per cent) of this convergence is accommodated aseismically, that is, that the subduction zone is uncoupled. This conclusion is robust, even allowing for rare very large earthquakes on splay faults, such as that of AD 365, and also allowing for the contribution of small earthquakes. The downgoing Nubian plate deforms by arc-parallel contraction at all depths, from 200 km seaward of Crete to at least 100 km within the subducting slab. Extensional (T) axes of earthquakes are aligned downdip within the descending slab suggesting that, even if the aseismic prolongation of the slab has reached the 670 km mantle discontinuity, it does not transmit stresses to shallower depths. Shallow thrust-faulting earthquakes on the subduction interface show a divergence of slip vectors round the arc, and GPS measurements show that this is accommodated mainly by E-W extension on normal faults in the overriding Aegean material. The eastern end of the subduction zone, south of Rhodes, displays distributed deformation in the overriding material, including a mixture of strike-slip and splay-thrust faulting, and probably involves rotations about a vertical axes. Here slip on the interface itself is by thrust faulting with slip vectors oblique to the arc but parallel to the overall Nubia-Aegean convergence: there is no evidence for slip-partitioning in the traditional

  10. Late Pleistocene and Holocene uplift history of Cyprus: implications for active tectonics along the southern margin of the Anatolian microplate

    USGS Publications Warehouse

    Harrison, R.W.; Tsiolakis, E.; Stone, B.D.; Lord, A.; McGeehin, J.P.; Mahan, S.A.; Chirico, P.

    2013-01-01

    The nature of the southern margin of the Anatolian microplate during the Neogene is complex, controversial and fundamental in understanding active plate-margin tectonics and natural hazards in the Eastern Mediterranean region. Our investigation provides new insights into the Late Pleistocene uplift history of Cyprus and the Troodos Ophiolite. We provide isotopic (14C) and radiogenic (luminescence) dates of outcropping marine sediments in eastern Cyprus that identify periods of deposition during marine isotope stages (MIS) 3, 4, 5 and 6. Past sea-levels indicated by these deposits are c. 95±25 m higher in elevation than estimates of worldwide eustatic sea-level. An uplift rate of c. 1.8 mm/year and possibly as much as c. 4.1 mm/year in the past c. 26–40 ka is indicated. Holocene marine deposits also occur at elevations higher than those expected for past SL and suggest uplift rates of c. 1.2–2.1 mm/year. MIS-3 marine deposits that crop out in southern and western Cyprus indicate uniform island-wide uplift. We propose a model of tectonic wedging at a plate-bounding restraining bend as a mechanism for Late Pleistocene to Holocene uplift of Cyprus; uplift is accommodated by deformation and seismicity along the margins of the Troodos Ophiolite and re-activation of its low-angle, basal shear zone.

  11. The effect of plate movements in the northern region of South America on tectonics and sedimentation in the Eastern Llanos Basin

    SciTech Connect

    Pena, L.E. )

    1993-02-01

    The geological configuration of the Eastern Llanos pericratonic mega-basin has been directly affected by the overall tectonic regime experienced in the Northern part of South America. Interaction between the Pacific (Cocos), South American and Caribbean Plates generated a regional compressional dextral rotational force expressed as a regional North-South striking structural trend in the southern part of the basin and an east-west striking trend in portion nearest the Caribbean Plate Boundary. Nearly 90% of the strike-slip faults in this northern area show right lateral displacement. The majority of the structures in the East Llanos basin are related to the Late Miocene uplift of the Eastern Andes. Nevertheless we can subdivide the structures into two major groups: pre-Miocene and post-Miocene. By being able to recognize pre-Miocene Cretaceous age structures, much altered by later movements, we can envision remigration of hydrocarbons out of early traps into those created more recently. Plate tectonic events in the north of South America have produced a general regional structure strike directional through time. Sedimentary-tectonic relationships depend upon regional phenomena which, if interpreted correctly, help to sub-divide the mega-basin into genetically related parts. By understanding the mechanism that creates large scale structural features, the geologist is thus provided with an important tool that can aid him in exploring the Eastern Llanos basin.

  12. A Review of the Isotopic and Trace Element Evidence for Mantle and Crustal Processes in the Hadean and Archean: implications for the Onset of Plate Tectonic Subduction

    NASA Astrophysics Data System (ADS)

    Smart, Katie A.; Tappe, Sebastian; Stern, Richard A.; Webb, Susan J.; Ashwal, Lewis D.

    2016-03-01

    Plate tectonics plays a vital role in the evolution of our planet. Geochemical analysis of Earth’s oldest continental crust suggests that subduction may have begun episodically about 3.8 to 3.2 billion years ago, during the early Archaean or perhaps more than 3.8 billion years ago, during the Hadean. Yet, mantle rocks record evidence for modern-style plate tectonics beginning only in the late Archaean, about 3 billion years ago. Here we analyse the nitrogen abundance, as well as the nitrogen and carbon isotopic signatures of Archaean placer diamonds from the Kaapvaal craton, South Africa, which formed in the upper mantle 3.1 to 3.5 billion years ago. We find that the diamonds have enriched nitrogen contents and isotopic compositions compared with typical mantle values. This nitrogen geochemical fingerprint could have been caused by contamination of the mantle by nitrogen-rich Archaean sediments. Furthermore, the carbon isotopic signature suggests that the diamonds formed by reduction of an oxidized fluid or melt. Assuming that the Archaean mantle was more reduced than the modern mantle, we argue that the oxidized components were introduced to the mantle by crustal recycling at subduction zones. We conclude, on the basis of evidence from mantle-derived diamonds, that modern-style plate tectonics operated as early as 3.5 billion years ago.

  13. A Virtual Tour of Plate Tectonics: Using Google Earth for Inquiry Investigations

    ERIC Educational Resources Information Center

    Mulvey, Bridget; Bell, Randy

    2012-01-01

    Google Earth is an exciting way to engage students in scientific inquiry--the foundation of science education standards and reforms. The National Science Education Standards identify inquiry as an active process that incorporates questioning, gathering and analyzing data, and thinking critically about the interplay of evidence and explanations.…

  14. Students' Mental Model Development during Historically Contextualized Inquiry: How the "Tectonic Plate" Metaphor Impeded the Process

    ERIC Educational Resources Information Center

    Dolphin, Glenn; Benoit, Wendy

    2016-01-01

    At present, quality earth science education in grade school is rare, increasing the importance of post-secondary courses. Observations of post-secondary geoscience indicate students often maintain errant ideas about the earth, even after direct instruction. This qualitative case study documents model-building activities of students as they…

  15. Glacier Ice Mass Fluctuations and Fault Instability in Tectonically Active Southern Alaska

    NASA Technical Reports Server (NTRS)

    SauberRosenberg, Jeanne M.; Molnia, Bruce F.

    2003-01-01

    Across southern Alaska the northwest directed subduction of the Pacific plate is accompanied by accretion of the Yakutat terrane to continental Alaska. This has led to high tectonic strain rates and dramatic topographic relief of more than 5000 meters within 15 km of the Gulf of Alaska coast. The glaciers of this area are extensive and include large glaciers undergoing wastage (glacier retreat and thinning) and surges. The large glacier ice mass changes perturb the tectonic rate of deformation at a variety of temporal and spatial scales. We estimated surface displacements and stresses associated with ice mass fluctuations and tectonic loading by examining GPS geodetic observations and numerical model predictions. Although the glacial fluctuations perturb the tectonic stress field, especially at shallow depths, the largest contribution to ongoing crustal deformation is horizontal tectonic strain due to plate convergence. Tectonic forces are thus the primary force responsible for major earthquakes. However, for geodetic sites located < 10-20 km from major ice mass fluctuations, the changes of the solid Earth due to ice loading and unloading are an important aspect of interpreting geodetic results. The ice changes associated with Bering Glacier s most recent surge cycle are large enough to cause discernible surface displacements. Additionally, ice mass fluctuations associated with the surge cycle can modify the short-term seismicity rates in a local region. For the thrust faulting environment of the study region a large decrease in ice load may cause an increase in seismic rate in a region close to failure whereas ice loading may inhibit thrust faulting.

  16. Geodetic evidence for continuing tectonic activity of the Carboneras fault (SE Spain)

    NASA Astrophysics Data System (ADS)

    Echeverria, Anna; Khazaradze, Giorgi; Asensio, Eva; Masana, Eulalia

    2015-11-01

    The Carboneras fault zone (CFZ) is a prominent onshore-offshore strike-slip fault that forms part of the Eastern Betic Shear Zone (EBSZ), located in SE Spain. In this work, we show for the first time, the continuing tectonic activity of the CFZ and quantify its geodetic slip-rates using continuous and campaign GPS observations conducted during the last decade. We find that the left-lateral motion dominates the kinematics of the CFZ, with a strike-slip rate of 1.3 ± 0.2 mm/yr along the N48° direction. The shortening component is significantly lower and poorly constrained. Recent onshore and offshore paleoseismic and geomorphic results across the CFZ suggest a minimum Late Pleistocene to present-day strike-slip rate of 1.1 mm/yr. Considering the similarity of the geologic and geodetic slip rates measured at different points along the fault, the northern segment of the CFZ must have been slipping approximately at a constant rate during the Quaternary. Regarding the eastern Alpujarras fault zone corridor (AFZ), located to the north of the CFZ, our GPS measurements corroborate that this zone is active and exhibits a right-lateral motion. These opposite type strike-slip motion across the AFZ and CFZ is a result of a push-type force due to Nubia and Eurasia plate convergence, which, in turn, causes the westward escape of the block bounded by these two fault zones.

  17. Active Wave Propagation and Sensing in Plates

    NASA Technical Reports Server (NTRS)

    Ghoshal, Anindya; Martin, William N.; Sundaresan, Mannur J.; Schulz, Mark J.; Ferguson, Frederick

    2001-01-01

    Health monitoring of aerospace structures can be done using an active interrogation approach with diagnostic Lamb waves. Piezoelectric patches are often used to generate the waves, and it is helpful to understand how these waves propagate through a structure. To give a basic understanding of the actual physical process of wave propagation, a model is developed to simulate asymmetric wave propagation in a panel and to produce a movie of the wave motion. The waves can be generated using piezoceramic patches of any size or shape. The propagation, reflection, and interference of the waves are represented in the model. Measuring the wave propagation is the second important aspect of damage detection. Continuous sensors are useful for measuring waves because of the distributed nature of the sensor and the wave. Two sensor designs are modeled, and their effectiveness in measuring acoustic waves is studied. The simulation model developed is useful to understand wave propagation and to optimize the type of sensors that might be used for health monitoring of plate-like structures.

  18. Importance of active tectonics during karst formation. A Middle Eocene to Pleistocene example of the Lina Moutains (Irian Jaya, Indonesia)

    NASA Astrophysics Data System (ADS)

    Thery, J.-M.; Pubellier, M.; Thery, B.; Butterlin, J.; Blondeau, A.; Adams, C. G.

    1999-05-01

    The Lina Moutains show a typical example of karst formation associated to recent and active tectonics. The limestone samples were collected from giant potholes present beneath the heavy rainforest, during speleological expeditions to the Bird's Head of Irian-Jaya. Micropalaeontological data allow us to give a Middle Pleistocene age for the most recent karst formation. A detailed stratigraphy between the Upper Lutetian and the Middle Pleistocene was recorded, with tectonic events during the Oligocene and Pleistocene. The edge of the resurgence layer was also dated. We also conclude the probable existence of a subterraneous network downhill of the karst within the most recent levels of the Kais Limestone formation. We replace this formation within the tectonic evolution of this area between the Eocene and the Middle Pleistocene, in conjunction with the oblique convergence of the Pacific plate carrying volcanic arc fragments and the Australian margin, which resulted in folding, normal faulting associated with local extension, and wrench motion, which are settings capable of creating uplift of the carbonated platform.

  19. 4D Arctic: A Glimpse into the Structure and Evolution of the Arctic in the Light of New Geophysical Maps, Plate Tectonics and Tomographic Models

    NASA Astrophysics Data System (ADS)

    Gaina, Carmen; Medvedev, Sergei; Torsvik, Trond H.; Koulakov, Ivan; Werner, Stephanie C.

    2014-09-01

    Knowledge about the Arctic tectonic structure has changed in the last decade as a large number of new datasets have been collected and systematized. Here, we review the most updated, publicly available Circum-Arctic digital compilations of magnetic and gravity data together with new models of the Arctic's crust. Available tomographic models have also been scrutinized and evaluated for their potential to reveal the deeper structure of the Arctic region. Although the age and opening mechanisms of the Amerasia Basin are still difficult to establish in detail, interpreted subducted slabs that reside in the High Arctic's lower mantle point to one or two episodes of subduction that consumed crust of possibly Late Cretaceous-Jurassic age. The origin of major igneous activity during the Cretaceous in the central Arctic (the Alpha-Mendeleev Ridge) and in the proximity of rifted margins (the so-called High Arctic Large Igneous Province—HALIP) is still debated. Models of global plate circuits and the connection with the deep mantle are used here to re-evaluate a possible link between Arctic volcanism and mantle plumes.

  20. The Core as the Third Pivotal End Member of the Earth's Plate Tectonic Cycle: A New Theory

    NASA Astrophysics Data System (ADS)

    Carman, J. H.

    2005-05-01

    Existing data and use of a hypothetical model, post-Stishovite-Magnesiowustite-Iron, indicate that the Earth's core could be the the convertor end member of the Earth's Plate Tectonic Cycle (EPTC): a new theory. This third pivitol end member, the core, is the place where the cycle begins and ends, to begin again. The first pivotal end member of the EPTC, for a three end member system, is the global MORB end member where new oceanic crust and lithosphere are created. Sea-floor spreading connects it to the second end member, the subduction end member, where oceanic crust and lithosphere disappear to become cold lithospheric-crust complexes descending through the mantle toward the Earth's core. When complexes break into it they are slowed, turned and endothermally ingested. Partial melting frees lower mantle phases and iron while forming metallic liquid and a densified immiscible silicate liquid, of which 17 vol.% reduces the bulk density of a convecting outer core by 10 %. Freed crystalline phases form micro-phases of micrometer to millimeter in size that more or less fill mega-bodies of <83 vol.% metallic liquid and <17 vol.% immiscible silicate liquid, both of centimeters to kilometers in size. Excess core energy starting each cycle comes mainly from irreversible exothermal reactions at numerous unstable phase contacts by stable phases within and between mega-bodies to yield stable products of lower Gibbs free energy, only to make new contacts and react...and react again. Other sources of exothermal energy come from radioactive silicate liquid and friction at stable phase contacts during mega-body convection. Heat accumulated from these energy sources tends to expand the outer core as univariant boundary reactions of the core and the lower mantle reverse, with +5.0 cm3g-1comming from the inner core boundary reaction alone. The outer core's pervasive expansion against the passively resisting strength of the mantle results in explosive ejection of silicate liquid

  1. Actively controlling coolant-cooled cold plate configuration

    SciTech Connect

    Chainer, Timothy J.; Parida, Pritish R.

    2015-07-28

    A method is provided to facilitate active control of thermal and fluid dynamic performance of a coolant-cooled cold plate. The method includes: monitoring a variable associated with at least one of the coolant-cooled cold plate or one or more electronic components being cooled by the cold plate; and dynamically varying, based on the monitored variable, a physical configuration of the cold plate. By dynamically varying the physical configuration, the thermal and fluid dynamic performance of the cold plate are adjusted to, for example, optimally cool the one or more electronic components, and at the same time, reduce cooling power consumption used in cooling the electronic component(s). The physical configuration can be adjusted by providing one or more adjustable plates within the coolant-cooled cold plate, the positioning of which may be adjusted based on the monitored variable.

  2. Drainage response to active tectonics and evolution of tectonic geomorphology across the Himalayan Frontal Thrust, Kumaun Himalaya

    NASA Astrophysics Data System (ADS)

    Luirei, Khayingshing; Bhakuni, Surendra S.; Kothyari, Girish Ch.

    2015-06-01

    We present the results of integrated studies of geomorphic indices of drainage networks and landforms developed across the mountain front along the Himalayan Frontal Thrust (HFT) between the Dabka and Baur rivers, Kumaun Himalaya. The HFT is a morphogenic structure in nature, creating a 100-m-high E-W trending escarpment that extends ~ 21 km. Geomorphological evidence indicates ~ 10.5 km westward migration of the Dabka River and ~ 5.2 km eastward migration of the Baur River. These migrations are a result of uplift of the hanging wall along the HFT. The HFT is offset by a transverse fault, which suggests that the latter postdates the reactivation of the HFT between 500 and 100 ka. Presence of different levels of strath terraces along the mountain front suggests the active nature of the HFT. To assess the relative tectonic activity, morphometric indices such as stream-gradient (SL) index, mountain front sinuosity (Smf) index, and ratio of valley floor width to valley height (Vf) have been analyzed. Results of the former two are consistent with the tectonic landforms developed in thrust zones. Paleochannels of the Dabka and Baur rivers are characterized by high Vf values while other valleys show low Vf values. Quaternary alluvial sediments have been deformed along the Pawalgarth Thrust, a splay of the HFT. Deformation has resulted in the formation of the Pawalgarh Anticline, a thrust-related asymmetric fold.

  3. Significant Centers of Tectonic Activity as Identified by Wrinkle Ridges for the Western Hemisphere of Mars

    NASA Technical Reports Server (NTRS)

    Anderson, R.C.; Haldemann, A. F. C.; Golombek, M. P.; Franklin, B. J.; Dohm, J. M.; Lias, J.

    2000-01-01

    The western hemisphere region of Mars has been the site of numerous scientific investigations regarding its tectonic evolution. For this region of Mars, the dominant tectonic region is the Tharsis province. Tharsis is characterized by an enormous system of radiating grabens and a circumferential system of wrinkle ridges. Past investigations of grabens associated with Tharsis have identified specific centers of tectonic activity. A recent structural analysis of the western hemisphere region of Mars which includes the Tharsis region, utilized 25,000 structures to determine the history of local and regional centers of tectonic activity based primarily on the spatial and temporal relationships of extensional features. This investigation revealed that Tharsis is more structurally complex (heterogeneous) than has been previously identified: it consists of numerous regional and local centers of tectonic activity (some are more dominant and/or more long lived than others). Here we use the same approach as Anderson et al. to determine whether the centers of tectonic activity that formed the extensional features also contributed to wrinkle ridge (compressional) formation.

  4. Active Tectonics in the Ohrid Basin (Macedonia/Albania)

    NASA Astrophysics Data System (ADS)

    Reicherter, K.; Hoffmann, N.; Fernández-Steeger, T.

    2009-04-01

    (Aliaj et al., 2004). The Ohrid Basin meets all criteria of an active, seismogenic landscape: linear step-like fault scarps in the landscape and under water in the lake. Post-glacial (or Late Pleistocene) bedrock fault scarps at Lake Ohrid are long-lived expressions of repeated surface faulting in tectonically active regions, where erosion cannot outpace the fault slip. Other morphotectonic features are wineglass-shaped valleys and triangular facets, which are well preserved. Generally, the faults and fault scarps are getting younger towards the basin center, as depicted on seismic and hydroacoustic profiles. Additionally, mass movement bodies within the lake and also onshore (rockfalls, landslides, sub-aqueous slides, homogenites, turbidites) are likely to be seismically triggered, eventually damming the outflow of Lake Ohrid temporarily. References: Aliaj, S, Adams, J, Halchuk, S, Sulstarova, E, Peci, V, Muco, B, 2004. Probabilistic seismic hazard maps for Albania. 13th World Conf. Earthquake Engineering, Vancouver, B.C., Canada, paper no. 2469, 14 pp. Muço, B, 1998. Catalogue of ML 3,0 earthquakes in Albania from 1976 to 1995 and distribution of seismic energy released. Tectonophysics, 292, 311-319.

  5. The Physics of a Volcanic System: What is the Actual Role Played by Tectonic Setting in Controlling Volcanic Activity?

    NASA Astrophysics Data System (ADS)

    Canon-Tapia, E.

    2005-12-01

    Modern text-books commonly explain volcanic activity as a direct consequence of plate tectonics, overlooking the different scales characteristic of both types of processes. By acknowledging such differences, however, it is possible to envisage a model of a volcanic system that is based in the same principles of hydrostatics established by Blaise Pascal over 300 yrs ago. Such principles allow us to estimate the local conditions required for the occurrence of volcanism at a given location highlighting the importance of the rock strength and the density difference between melt and its surroundings. This model shows that the minimum thickness of the zone of partial melting in the mantle (or seismically defined Low Velocity Zone) that is required to feed volcanic activity might range from 5 to over 100 km, but also that under certain circumstances a rock strength < 200 MPa may suffice to keep magma trapped at depth whereas in other cases a strength > 600 MPa will not suffice to stop magma ascent resulting in volcanic activity at the surface. Consequently, the model of volcanism developed here explains why is that a given LVZ may lead to volcanic activity in some places whereas a completely identical LVZ may not result in volcanic activity in a different location. Consequently, this model provides a general framework that allows us to better understand the actual role played by tectonic setting in controlling volcanism at a planetary scale.

  6. Seafloor morphology of the Eurasia-Nubia (Africa) plate boundary between the Tore-Madeira Rise and the Straits of Gibraltar: a case of coexistent Mesozoic through Present day features of tectonic, oceanographic and sedimentary origin

    NASA Astrophysics Data System (ADS)

    Terrinha, Pedro; Duarte, João.; Valadares, Vasco; Batista, Luis; Zitellini, Nevio; Grácia, Eulalia; Lourenço, Nuno; Rosas, Filipe; Roque, Cristina

    2010-05-01

    The joint use of more than 10.000 km multichannel seismic reflection profiles and 180.000km2 of multibeam swath bathymetry and backscatter allowed for a new vision of the seafloor tectonic and geomorphic processes of the area that encompasses the present day plate boundary between Africa and Eurasia, between the Gibraltar Straits and the Tore-Madeira Rise, in the southern sector of the North Atlantic Ocean. The interpretation of this data allowed for the detailed description of the seafloor morphology (i.e. a morphologic map) and the classification of the morphologic features in what respects the genetic process and age. It can be seen that in the same region coexist morphologic features that result from tectonic processes associated with the Triassic-Cretaceous break-up of Pangea, the Paleogene-Miocene compressive phase, the Miocene through Present subduction under the Gibraltar Arc (Gutscher et al., 2002), the Pliocene-Quaternary wrench tectonics and possible coeval plate boundary (Zitellini et al., 2009), the Present day mud volcanism and propagation of the compressive deformation along the West Continental Margin of Portugal (Terrinha et al., 2009). Interpretation of the seismic profiles together with the bathymetry allows the understanding of endogenous and exogenous processes that creates reliefs associated with active structures (related to the Miocene through Present compressive stress field). Other reliefs generated in Mesozoic times by analogous processes can be as well preserved as these active ones. In what concerns exogenous processes, the analysis of the two datasets (reflection seismics and bathymetry) allowed for the description of morphologic features associated with oceanic currents that interact with the seafloor forming these important features. As is the case of the well known active contourites but also less known features, like giant scours at 4 km water depth that have recently been described, suggesting the interaction of deep currents and

  7. Epeirogeny and plate tectonics

    NASA Technical Reports Server (NTRS)

    Menard, H. W.

    1975-01-01

    Vertical motions of the earth crust and their causes are considered in relation to epeirogenic phenomena. Factors discussed include: external loading and unloading; bending at subduction zones; internal density changes; and dynamic effects of mantle motion. The relationship between epeirogeny and drift is briefly reviewed along with oceanic epeirogeny.

  8. Modern Tectonic Deformation in the Active Basin-And Province Northwest of Beijing, China

    NASA Astrophysics Data System (ADS)

    Mi, S.; Wen, X.

    2012-12-01

    Our study region is the northwest of Beijing, northern north China. The most typical extensional active tectonic area of the China continent, called the active basin-and-range province northwest of Beijing, exist there. This active tectonic province is made up of several NE-trending Quaternary graben basins and horst ranges between basins. An about 1500-year-long written historical record has suggested that there have been no major earthquakes with magnitude 7 or greater occurred in most of the study region since AD 512. So, the characteristic of modern tectonic deformation of the study region and its implication for the future seismic potential of major earthquakes are important scientific issues. In this study, based on data of regional GPS station velocities and active tectonics, combining relocated earthquake distribution, we make a preliminary analysis on the characteristic of the modern tectonic deformation of the study region. We design three zones across deferent segments of the active basin-and-range province to analyze both the present tectonic deformation from the GPS velocity profiles and the major fault's downward-extents from the relocated hypocenters. Our analyses reveal that: (1) Significant NNW-ward and SSE-ward horizontal extension exists on different segments of the active basin-and-range province northwest of Beijing at rates of 2 to 3mm /yr, accompanied with right-lateral shear deformation at 1 to 2mm/yr. (2) On the present tectonic deformation, the southeastern margin of the Datong-Yangyuan basin, the biggest graben basin of the active tectonic province, shows as a turning belt of the extensional rates, suggesting that relatively high tensile strain accumulation could exist there. (3)On the northeastern segment of the studied active basin-and-range province, both the Zhangjiakou-Yanhui graben basin and the Beijing graben basin have also been being in significant extensional and shear deformation. (4) The relocated hypocenter distribution have

  9. The feedback between active tectonics, fluid flow and mineralization in an Andean geotermal reservoir

    NASA Astrophysics Data System (ADS)

    Reich, M.; Arancibia, G.; Perez, P.; Sanchez, P.; Cembrano, J. M.; Stimac, J. A.; Lohmar, S.

    2012-12-01

    In the Andean Cordillera of Central-Southern Chile, geothermal resources occur in close spatial relationship with active volcanism. The nature of the relationship between tectonics and volcanism in this region is the result of interaction between the crustal structures of the basement and the ongoing regional stress field, which is primarily controlled by the oblique convergence of the Nazca and South America Plates. Between 39° and 46°S, the volcanic and geothermal activity is controlled by the NNE-trending, 1,000 km long Liquiñe-Ofqui Fault Zone (LOFZ), an intra-arc dextral strike-slip fault system. Although there is consensus that volcanism (and hence geothermal activity) in southern Chile is largely controlled by the regional-scale tectonic stress field and architecture of the volcanic arc, there is limited scientific information about the role of local kinematic conditions on fluid flow and mineralization during the development and evolution of geothermal reservoirs. In this report, we present the preliminary results of an undergoing structural, mineralogical and geochemical study of the Tolhuaca geothermal system in southern Chile. The Tolhuaca geothermal reservoir formed as a liquid-dominated hydrothermal system, where shallow upflow resulted in near-boiling temperatures in a roughly horizontal liquid reservoir at 100-200 m depth (Melosh et al., 2010, 2012). In an early stage of evolution, hydrothermal brecciation and phase-separation (boiling) episodes penetrated at least 950 m depth into the deeper reservoir, and boiling was followed by steam-heated water invasion that cooled the reservoir. In a later stage, the preliminary conceptual model involves boiling and reheating of the reservoir, forming a system with deep hot brines that is connected to the shallow steam zone by an upflow conduit that is characterized by high-temperature mineralogy. The structural analysis of veins, fault-veins and faults of the Tol-1 drillcore (~1080 m depth) provide insights

  10. A harbinger of plate tectonics: a commentary on Bullard, Everett and Smith (1965) ‘The fit of the continents around the Atlantic’

    PubMed Central

    Dewey, John F.

    2015-01-01

    In the 1960s, geology was transformed by the paradigm of plate tectonics. The 1965 paper of Bullard, Everett and Smith was a linking transition between the theories of continental drift and plate tectonics. They showed, conclusively, that the continents around the Atlantic were once contiguous and that the Atlantic Ocean had grown at rates of a few centimetres per year since the Early Jurassic, about 160 Ma. They achieved fits of the continental margins at the 500 fathom line (approx. 900 m), not the shorelines, by minimizing misfits between conjugate margins and finding axes, poles and angles of rotation, using Euler's theorem, that defined the unique single finite difference rotation that carried congruent continents from contiguity to their present positions, recognizing that the real motion may have been more complex around a number of finite motion poles. Critically, they were concerned only with kinematic reality and were not restricted by considerations of the mechanism by which continents split and oceans grow. Many of the defining features of plate tectonics were explicit or implicit in their reconstructions, such as the torsional rigidity of continents, Euler's theorem, closure of the Tethyan ocean(s), major continental margin shear zones, the rapid rotation of small continental blocks (Iberia) around nearby poles, the consequent opening of small wedge-shaped oceans (Bay of Biscay), and misfit overlaps (deltas and volcanic piles) and underlaps (stretched continental edges). This commentary was written to celebrate the 350th anniversary of the journal Philosophical Transactions of the Royal Society. PMID:25750142

  11. A harbinger of plate tectonics: a commentary on Bullard, Everett and Smith (1965) 'The fit of the continents around the Atlantic'.

    PubMed

    Dewey, John F

    2015-04-13

    In the 1960s, geology was transformed by the paradigm of plate tectonics. The 1965 paper of Bullard, Everett and Smith was a linking transition between the theories of continental drift and plate tectonics. They showed, conclusively, that the continents around the Atlantic were once contiguous and that the Atlantic Ocean had grown at rates of a few centimetres per year since the Early Jurassic, about 160 Ma. They achieved fits of the continental margins at the 500 fathom line (approx. 900 m), not the shorelines, by minimizing misfits between conjugate margins and finding axes, poles and angles of rotation, using Euler's theorem, that defined the unique single finite difference rotation that carried congruent continents from contiguity to their present positions, recognizing that the real motion may have been more complex around a number of finite motion poles. Critically, they were concerned only with kinematic reality and were not restricted by considerations of the mechanism by which continents split and oceans grow. Many of the defining features of plate tectonics were explicit or implicit in their reconstructions, such as the torsional rigidity of continents, Euler's theorem, closure of the Tethyan ocean(s), major continental margin shear zones, the rapid rotation of small continental blocks (Iberia) around nearby poles, the consequent opening of small wedge-shaped oceans (Bay of Biscay), and misfit overlaps (deltas and volcanic piles) and underlaps (stretched continental edges). This commentary was written to celebrate the 350th anniversary of the journal Philosophical Transactions of the Royal Society. PMID:25750142

  12. The importance of mineral physics and a free surface in large-scale numerical models of mantle convection and plate tectonics

    NASA Astrophysics Data System (ADS)

    Tackley, Paul; Nakagawa, Takashi; Crameri, Fabio; Connolly, James; Deschamps, Frédéric; Kaus, Boris; Gerya, Taras

    2010-05-01

    Here, our recent progress in understanding the large-scale dynamics of the mantle convection - plate tectonics system is summarised, with particular focus on the influence of realistic mineral physics and a free surface. High pressure and temperature experiments and calculations of the properties of mantle minerals show that many different mineral phases exist as a function of pressure, temperature and composition [e.g. Irifune and Ringwood, EPSL 1987], and that these have a first-order influence on density (which has a large effect on the dynamics) and elastic moduli (which influence seismic velocity). Numerical models of global thermo-chemical mantle convection have typically used a simple approximation such as the extended Boussinesq approximation to treat these complex variations in material properties. Instead, we calculate composition-dependent mineral assemblages and their physical properties using the code Perple_X, which minimizes free energy for a given combination of oxides as a function of temperature and pressure [Connolly, EPSL 2005], and use this in a numerical model of thermo-chemical mantle convection in a three-dimensional spherical shell, to calculate three-dimensionally-varying physical proporties. In this presentation we compare the results obtained with this new, self-consistently-calculated treatment with results using our old, approximate treatment, focusing particularly on thermo-chemical-phase structures and seismic anomalies in the transition zone and core-mantle boundary (CMB) region [Nakagawa and Tackley, G3 2009], which are strongly influenced by the coupling between compositional variations and phase transitions. The numerical models treat the evolution of a planet over billions of years, including self-consistent plate tectonics arising from plastic yielding, melting-induced differentiation, and a parameterised model of core evolution based on heat extracted by mantle convection. Self-consistent plate tectonics-like behaviour may be

  13. Application of laser ranging and VLBI data to a study of plate tectonic driving forces. [finite element method

    NASA Technical Reports Server (NTRS)

    Solomon, S. C.

    1980-01-01

    The measurability of changes in plate driving or resistive forces associated with plate boundary earthquakes by laser rangefinding or VLBI is considered with emphasis on those aspects of plate forces that can be characterized by such measurements. Topics covered include: (1) analytic solutions for two dimensional stress diffusion in a plate following earthquake faulting on a finite fault; (2) two dimensional finite-element solutions for the global state of stress at the Earth's surface for possible plate driving forces; and (3) finite-element solutions for three dimensional stress diffusion in a viscoelastic Earth following earthquake faulting.

  14. Active faults and minor plates in NE Asia

    NASA Astrophysics Data System (ADS)

    Kozhurin, Andrey I.; Zelenin, Egor A.

    2014-05-01

    Stated nearly 40 yr ago the uncertainty with plate boundaries location in NE Asia (Chapman, Solomon, 1976) still remains unresolved. Based on the prepositions that a plate boundary must, first, reveal itself in linear sets of active structures, and, second, be continuous and closed, we have undertaken interpretation of medium-resolution KH-9 Hexagon satellite imageries, mostly in stereoscopic regime, for nearly the entire region of NE Asia. Main findings are as follows. There are two major active fault zones in the region north of the Bering Sea. One of them, the Khatyrka-Vyvenka zone, stretches NE to ENE skirting the Bering Sea from the Kamchatka isthmus to the Navarin Cape. Judging by the kinematics of the Olyutorsky 2006 earthquake fault, the fault zones move both right-laterally and reversely. The second active fault zone, the Lankovaya-Omolon zone, starts close to the NE margin of the Okhotsk Sea and extends NE up to nearly the margin of the Chukcha Sea. The fault zone is mostly right-lateral, with topographically expressed cumulative horizontal offsets amounting to 2.5-2.6 km. There may be a third NE-SW zone between the major two coinciding with the Penzhina Range as several active faults found in the southern termination of the Range indicate. The two active fault zones divide the NE Asia area into two large domains, which both could be parts of the Bering Sea plate internally broken and with uncertain western limit. Another variant implies the Khatyrka-Vyvenka zone as the Bering Sea plate northern limit, and the Lankovaya-Omolon zone as separating an additional minor plate from the North-American plate. The choice is actually not crucial, and more important is that both variants leave the question of where the Bering Sea plate boundary is in Alaska. The Lankovaya-Omolon zone stretches just across the proposed northern boundary of the Okhorsk Sea plate. NW of the zone, there is a prominent left-lateral Ulakhan fault, which is commonly interpreted to be a

  15. Recent tectonic activity on Pluto driven by phase changes in the ice shell

    NASA Astrophysics Data System (ADS)

    Hammond, Noah P.; Barr, Amy C.; Parmentier, Edgar M.

    2016-07-01

    The New Horizons spacecraft has found evidence for geologic activity on the surface of Pluto, including extensional tectonic deformation of its water ice bedrock see Moore et al. (2016). One mechanism that could drive extensional tectonic activity is global surface expansion due to the partial freezing of an ocean. We use updated physical properties for Pluto and simulate its thermal evolution to understand the survival of a possible subsurface ocean. For thermal conductivities of rock less than 3 W m-1 K-1, an ocean forms and at least partially freezes, leading to recent extensional stresses in the ice shell. In scenarios where the ocean freezes and the ice shell is thicker than 260 km, ice II forms and causes global volume contraction. Since there is no evidence for recent compressional tectonic features, we argue that ice II has not formed and that Pluto's ocean has likely survived to present day.

  16. Applications of Morphochronology to the Active Tectonics of Tibet

    SciTech Connect

    Ryerson, F J; Tapponnier, P; Finkel, R C; Meriaux, A; der Woerd, J V; Lasserre, C; Chevalier, M; Xiwei, X; Haibing, L; King, G P

    2005-01-28

    The Himalayas and the Tibetan Plateau were formed as a result of the collision of India and Asia, and provide an excellent opportunity to study the mechanical response of the continental lithosphere to tectonic stress. Geophysicists are divided in their views on the nature of this response advocating either (1) homogeneously distributed deformation with the lithosphere deforming as a fluid continuum or (2) deformation is highly localized with the lithosphere that deforms as a system of blocks. The resolution of this issue has broad implications for understanding the tectonic response of continental lithosphere in general. Homogeneous deformation is supported by relatively low decadal, geodetic slip-rate estimates for the Altyn Tagh and Karakorum Faults. Localized deformation is supported by high millennial, geomorphic slip-rates constrained by both cosmogenic and radiocarbon dating on these faults. Based upon the agreement of rates determined by radiocarbon and cosmogenic dating, the overall linearity of offset versus age correlations, and on the plateau-wide correlation of landscape evolution and climate history, the disparity between geomorphic and geodetic slip-rate determinations is unlikely to be due to the effects of surface erosion on the cosmogenic age determinations. Similarly, based upon the consistency of slip-rates over various observation intervals, secular variations in slip-rate appear to persist no longer than 2000 years and are unlikely to provide reconciliation. Conversely, geodetic and geomorphic slip-rate estimates on the Kunlun fault, which does not have significant splays or associated thrust faults, are in good agreement, indicating that there is no fundamental reason why these complementary geodetic and geomorphic methods should disagree. Similarly, the geodetic and geomorphic estimates of shortening rates across the northeastern edge of the plateau are in reasonable agreement, and the geomorphic rates on individual thrust faults demonstrate

  17. Copernican tectonic activities in the northwestern Imbrium region of the Moon

    NASA Astrophysics Data System (ADS)

    Daket, Yuko; Yamaji, Atsushi; Sato, Katsushi

    2015-04-01

    Mare ridges and lobate scarps are the manifestations of horizontal compression in the shallow part of the Moon. Conventionally, tectonism within mascon basins has been thought to originate from mascon loading which is syndepositional tectonics (e.g., Solomon and Head, 1980). However, Ono et al. (2009) have pointed out that the subsurface tectonic structures beneath some mare ridges in Serenitatis appeared to be formed after the deposition of mare strata. Watters et al. (2010) also reported Copernican lobate scarps. Those young deformations cannot be explained by the mascon loading and are possibly ascribed to global cooling, orbital evolution and/or regional factors. Since mare ridges are topographically larger than lobate scarps, they might have large contribution to the recent contraction. In this study, we estimated until when the tectonic activities of mare ridges lasted in the northwestern Imbrium region. In order to infer the timing of the latest ages of tectonic activities, we used craters dislocated by the thrust faults that run along to the mare ridges in the study area. The ages of dislocated craters indicate the oldest estimate of the latest tectonic activity of the faults, because those craters must have existed during the tectonic activities. The ages of craters are inferred by the degradation levels classified by Trask (1971). We found ~450 dislocated craters in the study area. About 40 of them are smaller than 100 meter in diameter. Sub-hundred-meter-sized craters that still maintain their morphology sharp are classified into Copernican Period. Those small dislocated craters are interspersed all over the region, indicating that the most of the mare ridges in the study area were tectonically active in Copernican Period. In addition, we also found two sub-hundred-meter-sized craters dislocated by a graben at the west of Promontorium Laplace, indicating horizontal extension existed at Copernican Period. Consequently, tectonic activities in the study

  18. Salts as indicators of tectonic activity along Nesson anticline, North Dakota

    SciTech Connect

    Lefever, J.A.; Lefever, R.D.; Anderson, S.B.

    1988-07-01

    The Nesson anticline is the major north-south-trending structure in the North Dakota portion of the Williston basin. The trace of the anticline is marked by nearly continuous production for 110 mi (175 km) from the Canadian border south to Dunn County; production is from 13 different stratigraphic zones. Previous studies have shown that the central and southern parts of the anticline, from Beaver Lodge field south to Rattlesnake Point field, consist of at least nine structurally independent areas, each of which has an individual tectonic history. Isopach patterns indicate that most of the areas underwent their greatest tectonic activity during the Devonian and Early Mississippian, although a few areas were active during the early Mesozoic as well. Ten traceable salts are present along the anticline in the Prairie (Devonian), Charles (Mississippian), Opeche (Permian), Spearfish (Triassic), and Pipe Formations (Jurassic). The isopach patterns of the individual salts indicate contemporaneous tectonic activity through thickening or thinning of the salt. Postdepositional activity is indicated by the absence of a salt; the timing of the activity may be estimated from the presence of compensating section above the level of the salt. Their results indicate that, in addition to the times given above, significant tectonic activity took place along the anticline during the Late Mississippian, late Jurassic, and Early Cretaceous.

  19. Preliminary study on hydrogeology in tectonically active areas.

    SciTech Connect

    Lowry, Thomas Stephen; Lappin, Allen R.; Gettemy, Glen L.; Jensen, Richard Pearson; Arnold, Bill Walter; James, Scott Carlton; Lee, Moo Yul; Meier, Diane A.

    2006-09-01

    This report represents the final product of a background literature review conducted for the Nuclear Waste Management Organization of Japan (NUMO) by Sandia National Laboratories, Albuquerque, New Mexico, USA. Internationally, research of hydrological and transport processes in the context of high level waste (HLW) repository performance, has been extensive. However, most of these studies have been conducted for sites that are within tectonically stable regions. Therefore, in support of NUMO's goal of selecting a site for a HLW repository, this literature review has been conducted to assess the applicability of the output from some of these studies to the geological environment in Japan. Specifically, this review consists of two main tasks. The first was to review the major documents of the main HLW repository programs around the world to identify the most important hydrologic and transport parameters and processes relevant in each of these programs. The review was to assess the relative importance of processes and measured parameters to site characterization by interpretation of existing sensitivity analyses and expert judgment in these documents. The second task was to convene a workshop to discuss the findings of Task 1 and to prioritize hydrologic and transport parameters in the context of the geology of Japan. This report details the results and conclusions of both of these Tasks.

  20. Mixing in mantle convection models with self-consistent plate tectonics and melting and crustal production: Application to mixing in the early Earth

    NASA Astrophysics Data System (ADS)

    Tackley, Paul

    2016-04-01

    It is generally thought that the early Earth's mantle was hotter than today, which using conventional convective scalings should have led to vigorous convection and mixing. Geochemical observations, however, suggest that mixing was not as rapid as would be expected, leading to the suggestion that early Earth had stagnant lid convection (Debaille et al., EPSL 2013). Additionally, the mantle's thermal evolution is difficult to explain using conventional scalings because early heat loss would have been too rapid, which has led to the hypothesis that plate tectonics convection does not follow the conventional convective scalings (Korenaga, GRL 2003). One physical process that could be important in this context is partial melting leading to crustal production, which has been shown to have the major effects of buffering mantle temperature and carrying a significant fraction of the heat from hot mantle (Nakagawa and Tackley, EPSL 2012), making plate tectonics easier (Lourenco et al., submitted), and causing compositional differentiation of the mantle that can buffer core heat loss (Nakagawa and Tackley, GCubed 2010). Here, the influence of this process on mantle mixing is examined, using secular thermo-chemical models that simulate Earth's evolution over 4.5 billion years. Mixing is quantified both in terms of how rapidly stretching occurs, and in terms of dispersion: how rapidly initially close heterogeneities are dispersed horizontally and vertically through the mantle. These measures are quantified as a function of time through Earth's evolution. The results will then be related to geochemically-inferred mixing rates.

  1. Plate tectonic reconstruction of South and East Asia since 43 Ma using seismic tomographic constraints: role of the subducted ';East Asia Sea' (Invited)

    NASA Astrophysics Data System (ADS)

    Wu, J. E.; Suppe, J.; Renqi, L.; Kanda, R. V.

    2013-12-01

    Lithosphere that subducts at convergent plate boundaries provides a potentially decipherable plate tectonic record. In this study we use global seismic tomography to map subducted slabs in the upper and lower mantle under South and East Asia to constrain plate reconstructions. The mapped slabs include the Pacific, the Indian Ocean and Banda Sea, the Molucca Sea, Celebes Sea, the Philippine Sea and Eurasia, New Guinea and other lower mantle detached slabs. The mapped slabs were restored to the earth surface and used with Gplates software to constrain a globally-consistent, fully animated plate reconstruction of South and East Asia. Three principal slab elements dominate possible plate reconstructions: [1] The mapped Pacific slabs near the Izu-Bonin and the Marianas trenches form a subvertical slab curtain or wall extending down to 1500 km in the lower mantle. The ';slab curtain' geometry and restored slabs lengths indicate that the Pacific subduction zone has remained fixed within +/- 250 km of its present position since ~43 Ma. In contrast, the Tonga Pacific slab curtain records at least 1000 km trench rollback associated with expansion of back-arc basins. [2] West of the Pacific slab curtain, a set of flat slabs exist in the lower mantle and record a major 8000km by 2500-3000km ocean that existed at ~43 Ma. This now-subducted ocean, which we call the ';East Asian Sea', existed between the Ryukyu Asian margin and the Lord Howe hotspot, present-day eastern Australia, and fills a major gap in Cenozoic plate reconstructions between Indo-Australia, the Pacific Ocean and Asia. [3] An observed ';picture puzzle' fit between the restored edges of the Philippine Sea, Molucca Sea and Indian Ocean slabs suggests that the Philippine Sea was once part of a larger Indo-Australian Ocean. Previous models of Philippine Sea plate motions are in conflict with the location of the East Asian Sea lithosphere. Using the mapped slab constraints, we propose the following 43 Ma to 0 plate

  2. Tectonic activity and structural features of active intracontinental normal faults in the Weihe Graben, central China

    NASA Astrophysics Data System (ADS)

    Rao, Gang; Lin, Aiming; Yan, Bing; Jia, Dong; Wu, Xiaojun

    2014-12-01

    This study examines the tectonic activity and structural features of active normal faults in the Weihe Graben, central China. The Weihe Graben is an area with a high level of historic seismicity, and it is one of the intracontinental systems that developed since Tertiary in the extensional environment around the Ordos Block. Analysis of high-resolution remote-sensing imagery data, field observations, and radiocarbon dating results reveal the following: i) active normal faults are mainly developed within a zone < 500 m wide along the southern border of the eastern part of the Weihe Graben; ii) the active faults that have been identified are characterized by stepwise fault scarps dipping into the graben at angles of 40°-71°; iii) there are numerous discontinuous individual fault traces, ranging in length from a few tens of meters to 450 m (generally < 200 m); iv) fault zone structures, topographic features, and fault striations on the main fault planes indicate almost pure normal-slip; and v) late Pleistocene-Holocene terrace risers, loess, and alluvial deposits have been vertically offset by up to ~ 80 m, with a non-uniform dip-slip rate (throw-rates) ranging from ~ 2.1 to 5.7 mm/yr, mostly 2-3 mm/yr. Our results reveal that active normal faults have been developing in the Weihe Graben under an ongoing extensional environment, probably associated with the pre-existing graben and spreading of the continental crust, and this is in contrast with the Ordos Block and neighboring orogenic regions. These results provide new insights into the nature of extensional tectonic deformation in intracontinental graben systems.

  3. Modern Tectonic Deformation in the Active Basin-and-Range Province Northwest of Beijing, China

    NASA Astrophysics Data System (ADS)

    Mi, Suting; Wen, Xueze

    2013-04-01

    Our study region is the northwest of Beijing, northern north China. The most typical extensional active tectonic area of the China continent, called the active basin-and-range province northwest of Beijing, exist there. This active tectonic province is made up of several NE-trending Quaternary graben basins and horst ranges between basins. An about 1500-year-long written historical record has suggested that there have been no major earthquakes with magnitude 7 or greater occurred in most of the study region since AD 512. So, the characteristic of modern tectonic deformation of the study region and its implication for the future seismic potential of major earthquakes are important scientific issues. In this study, based on data of regional GPS station velocities and active tectonics, combining relocated earthquake distribution, we make a preliminary analysis on the characteristic of the modern tectonic deformation of the study region. We design three zones across deferent segments of the active basin-and-range province to analyze both the present tectonic deformation from the GPS velocity profiles and the major fault's downward-extents from the relocated hypocenters. Our analyses reveal that: (1) Significant NNW-ward and SSE-ward horizontal extension exists on different segments of the active basin-and-range province northwest of Beijing at rates of 2 to 3mm /yr, accompanied with right-lateral shear deformation at 1 to 2mm/yr. (2) On the western and middle segments of the active basin and range province, most of the total horizontal extension and shear deformation happen in the width from the Huangqihai basin to the Datong-Yanggao basin , suggesting that some major faults in this width could have had relatively-high strain build-up. (3) It is possible that one or more basement detachment belts exist under the active basins, and it or they possibly dip(s) southeastern-ward. (4) The modern tectonic extensional rate is up to 2 to 3mm /yr in the study region. However

  4. Mapping Active Faults and Tectonic Geomorphology offshore central California

    NASA Astrophysics Data System (ADS)

    Johnson, S. Y.; Watt, J. T.; Hart, P. E.; Sliter, R. W.; Wong, F. L.

    2009-12-01

    In June 2008, and July 2009, the USGS conducted two high-resolution, marine, seismic-reflection surveys across the continental shelf and upper slope between Piedras Blancas and Point Sal, central California, in order to better characterize regional earthquake sources. More than 1,300 km of single-channel seismic data were acquired aboard the USGS R/V Parke Snavely using a 500-joule mini-sparker source fired at a 0.5-second shot interval and recorded with a 15-meter streamer. Most tracklines were run perpendicular to the coast at 800-meter spacing, extending from the nearshore (~ 10-15 m water depth) to as far as 20 km offshore. Sub-bottom imaging varies with substrate, ranging from outstanding (100 to 150 m of penetration) in inferred Quaternary shallow marine, shelf and upper slope deposits to poor (0 to 10 m) in the Mesozoic basement rocks. Marine magnetic data were collected simultaneously on this survey, and both data sets are being integrated with new aeromagnetic data, publicly available industry seismic-reflection data, onshore geology, seismicity, and high-resolution bathymetry. Goals of the study are to map geology, structure, and sediment distribution; to document fault location, length, segmentation, shallow geometry and structure; and to identify possible sampling targets for constraining fault slip rates, earthquake recurrence, and tsunami hazard potential. The structure and tectonic geomorphology of the >100-km-long, right-lateral, Hosgri fault zone and its connections to the Los Osos, Pecho, Oceano and other northwest-trending inboard faults are the focus of this ongoing work. The Hosgri fault forms the eastern margin of the offshore Santa Maria basin and coincides in places with the outer edge of the narrow (5- to 15-km-wide), structurally complex continental shelf. The Hosgri is imaged as a relatively continuous, vertical fault zone that extends upward to the seafloor; varies significantly and rapidly along strike; and incorporates numerous

  5. Mega-Network GPS Solutions: Producing a Consistent, Global-Scale, and High-Resolution View of Plate Tectonic Stability, Rotation, and Deformation.

    NASA Astrophysics Data System (ADS)

    Blewitt, G.; Kreemer, C.

    2007-12-01

    We present a single self-consistent GPS solution for over 2000 stations with ambiguity resolution applied for the period 1994--2007. Here we demonstrate that such `mega-network' GPS solutions provide a consistent, global- scale, and high-resolution view of plate tectonics in action. Specifically our solution is used to investigate the stability of the North American plate, its rotation, intra-plate deformation, and deformation in the Pacific-North America Plate boundary zone. A significant improvement in precision and accuracy attributable to ambiguity resolution is quantified by (1) the reduction of variance of station position time series (`repeatability'), (2) the reduction of variance in motions between stations within stable plate interiors, and (3) the relative smoothness of the velocity field in the Great Basin of western North America. The software developed to produce this solution, AMBIZAP Version 2.0 (ftp://gneiss.nbmg.unr.edu/ambizap) was made publicly available in August 2007. The method builds seamlessly on the precise point positioning (PPP) method invented by Zumberge et al. in 1997, additionally providing improved accuracy at a fraction of the original computational cost. Like PPP, the computation time of AMBIZAP (including network adjustment) is linear with number of stations N, unlike previous algorithms that exhibit power-law behavior, which presents a barrier to processing N >> 100. The longer-term significance of this development is the ease with which the software could be applied to N ~ 10000 GPS networks worldwide within the foreseeable future, including the N > 1000 Plate Boundary Observatory, which is already nearing completion.

  6. Using high-resolution aeromagnetic survey to map tectonic elements of plate boundaries: An example from the Dead Sea Fault

    NASA Astrophysics Data System (ADS)

    Al-Zoubi, A. S.; ten Brink, U. S.; Rybakov, M.; Rotstein, Y.

    2004-12-01

    The Dead Sea Fault (DSF) is a transform plate boundary between the African and the Arabian plates. The 200-km-long DSF segment between the Gulf of Aqaba/Elat and the Dead Sea, which has the morphology of a rift valley, shows little seismic activity, and its surface trace is only intermittently visible. High-resolution magnetic data were collected in October 2003 aboard a Jordanian military helicopter flying at an altitude of 100 m over the southern 120-km-long section of this fault segment. The survey was part of a US-AID Middle Eastern Regional Cooperation project between Jordanian, Israeli, Palestinian, and American scientists. Data were collected along rift-perpendicular lines spaced 300 m apart, requiring frequent crossings between Israeli and Jordanian air spaces. The data were gridded at 75 m interval following resolution tests, reduced to pole, and incorporated into a GIS together with elevation, geology, and gravity maps to facilitate interpretation. The main findings of the magnetic survey are the absence of magnetic anomalies crossing the rift valley, and the presence of a rift-parallel regional lineament corresponding to the active trace of the DSF. The lineament extends NNE as an almost continuous trace from Elat, Israel, to the eastern side of the valley 5 km north of Rahmeh. Jordan. Another fault trace located 2-3 km to the west may overlap and continue NNE through Gebel A-Risha, and into the central Arava/Araba valley, where it is visible on the surface. Alternatively, the two traces may be connected. If an offset between the two traces exists, it may be small enough to allow an earthquake rupture to propagate across the offset, and generate an earthquake with a moment magnitude of up to 7.5. Traces of buried faults in the central Arava/Araba valley that were previously active in the DSF system, are visible as abrupt terminations of an area of short wavelength magnetic anomalies. These anomalies probably represent shallow subsurface magmatic

  7. Misconceptions and Conceptual Changes Concerning Continental Drift and Plate Tectonics among Portuguese Students Aged 16-17.

    ERIC Educational Resources Information Center

    Marques, Luis; Thompson, David

    1997-01-01

    This study investigates student misconceptions in the areas of continent, ocean, permanence of ocean basins, continental drift, Earth's magnetic field, and plates and plate motions. A teaching-learning model was designed based on a constructivist approach. Results show that students held a substantial number of misconceptions. (Author/DKM)

  8. Assessment of relative tectonic activity in the Trichonis Lake graben (Western Greece) using geomorphometry

    NASA Astrophysics Data System (ADS)

    Karymbalis, Efthimios; Valkanou, Kanella; Fubelli, Giandomenico; Ferentinou, Maria; Giles, Philip; Papanastassiou, Dimitris; Gaki-Papanastassiou, Kalliopi; Tsanakas, Konstantinos

    2016-04-01

    In tectonically active areas fluvial systems and mountain fronts are controlled by the type, geometry, and recent activity of faults. The aim of this study is to investigate the contribution of neotectonics to the development of the fluvial landscape of the broader Trichonis Lake area (located in western continental Greece) through quantitative geomorphological analysis. The Trichonis Lake graben is a well-known tectonic depression of Quaternary age, which cuts across the early Tertiary NW-SE fold and thrust structures of the Pindos Mountain belt. It strikes WNW-ESE for a distance of 32 km and has a width of 10 km. The graben at the north and south flanks of the lake is bounded by E-W and NW-SE trending faults. Recent seismic activity (a shallow earthquake sequence in 1975 and a 2007 earthquake swarm) showed the existence of a NNW-SSE normal fault that dips to the NE and bounds the south-eastern shore of the lake. The studied catchments are developed on the hanging walls of these active normal faults. To evaluate the relative tectonic activity in the study area, various morphometric indices were measured for 35 catchments (slope of the valley sides of the catchment, hypsometric integral, catchment asymmetry factor, relief ratio, Melton's ruggedness number, stream-gradient index, ratio of valley floor width to valley height, and catchment shape) and 20 mountain fronts (mountain-front sinuosity index) around the lake. For the measurement of the geomorphometric variables a digital elevation model (DEM) with 2-m spatial resolution was derived from topographic maps at 1:5000 scale with 4-m contour lines, and a series of maps showing the spatial distribution of the variables were produced in a GIS environment. For each morphometric variable the catchments were classified into three classes. The combination of these morphometric variables allowed us to yield two new indices of relative tectonic activity (named IRTA - Index of Relative Tectonic Activity and IAT - Index of

  9. Thermal History of Planetary Objects: From Asteroids to super-Earths, from plate-tectonics to life (Runcorn-Florensky Medal Lecture)

    NASA Astrophysics Data System (ADS)

    Spohn, Tilman

    2013-04-01

    planets - like the Earth - the volatile budget matters for the interior evolution. With plate tectonics, large-scale volatile cycles are invoked. On the Earth, even the biosphere is speculated to interact with the interior. It has been argued (e.g., Rosing et al. 2006; Sleep et al, 2012) that the formation of continents could be a consequence of bioactivity harvesting solar energy through photosynthesis to help build the continents and that the mantle should carry a chemical biosignature. A model is presented that includes mantle convection, mantle water vapor degassing at mid-oceanic ridges and regassing through subduction zones, continental crust formation and erosion and water storage and transport in a porous oceanic crust that includes hydrous mineral phases. The biosphere enters the model through its effect on continental erosion and through a reduction of the activation barrier to metamorphic reactions (e.g., Kim et al., 2004) in sediment layers. An abiotic world is found to have a much drier mantle than the present Earth but may have a similar surface coverage by continents. The reduced rate of continental crust production on the abiotic world would be balanced by a reduced rate of continent erosion. Through the effect of water on the mantle rheology, the biotic world would tend to be tectonically more active and have a more rapid long-term carbon-silicate cycle. J. Kim, H. Dong, J. Seabaugh, S. W. Newell, D. D. Eberl, Science 303, 830-832, 2004 N. H. Sleep, D. K. Bird, E. Pope, Annu. Rev. Earth Planet. Sci. 40, 277-300, 2012 M. T. Rosing, D. K. Bird, N. H. Sleep, W. Glassley, F. Albarede, Paleo3 232, 90-113, 2006

  10. Tectonic activity and the evolution of submarine canyons: The Cook Strait Canyon system, New Zealand

    NASA Astrophysics Data System (ADS)

    Micallef, Aaron; Mountjoy, Joshu; Barnes, Philip; Canals, Miquel; Lastras, Galderic

    2016-04-01

    Submarine canyons are Earth's most dramatic erosional features, comprising steep-walled valleys that originate in the continental shelf and slope. They play a key role in the evolution of continental margins by transferring sediments into deep water settings and are considered important biodiversity hotspots, pathways for nutrients and pollutants, and analogues of hydrocarbon reservoirs. Although comprising only one third of continental margins worldwide, active margins host more than half of global submarine canyons. We still lack of thorough understanding of the coupling between active tectonics and submarine canyon processes, which is necessary to improve the modelling of canyon evolution in active margins and derive tectonic information from canyon morphology. The objectives of this study are to: (i) understand how tectonic activity influences submarine canyon morphology, processes, and evolution in an active margin, and (2) formulate a generalised model of canyon development in response to tectonic forcing based on morphometric parameters. We fulfil these objectives by analysing high resolution geophysical data and imagery from Cook Strait Canyon system, offshore New Zealand. Using these data, we demonstrate that tectonic activity, in the form of major faults and structurally-generated tectonic ridges, leaves a clear topographic signature on submarine canyon location and morphology, in particular their dendritic and sinuous planform shapes, steep and linear longitudinal profiles, and cross-sectional asymmetry and width. We also report breaks/changes in canyon longitudinal slope gradient, relief and slope-area regression models at the intersection with faults. Tectonic activity gives rise to two types of knickpoints in the Cook Strait Canyon. The first type consists of low slope gradient, rounded and diffusive knickpoints forming as a result of short wavelength folds or fault break outs and being restored to an equilibrium profile by upstream erosion and

  11. Seismic activity of Tokyo area and Philippine Sea plate under Japanese Islands

    NASA Astrophysics Data System (ADS)

    Sakai, S.; Nakagawa, S.; Nanjo, K.; Kasahara, K.; Panayotopoulos, Y.; Tsuruoka, H.; Kurashimo, E.; Obara, K.; Hirata, N.; Kimura, H.; Honda, R.

    2012-12-01

    The Japanese government has estimated the probability of earthquake occurrence with magnitude 7-class during the next 30 years as 70 %. This estimation is based on five earthquakes that occurred in this area in the late 120 years. However, it has been revealed that this region is lying on more complicated tectonic condition due to the two subducted plates and the various types of earthquakes which have been caused by. Therefore, it is necessary to classify these earthquakes into inter-plate earthquakes and intra-plate ones. Then, we have been constructing a seismic observation network since 5 years ago. Tokyo Metropolitan area is a densely populated region of about 40 million people. It is the center of Japan both in politics and in economy. So that human activities have been conducting quite busily, this region is unsuitable for seismic observation. Then, we have decided to make an ultra high dense seismic observation network. We named it the Metropolitan Seismometer Observation Network; MeSO-net. MeSO-net consists of 296 seismic stations. Minimum interval is about 2km and average interval is about 5km.We picked the P- and S-wave arrival times manually. We applied double-difference tomography method to the dataset and estimated the velocity structure. We depicted the plate boundaries from the newly developed velocity model. And, we referred to the locations of the repeating earthquakes, the distributions of normal hypocenters and the focal mechanisms. Our plate model became relatively flat and a little shallower than previous one.Seismicity of Metropolitan area after the M9 event was compared to the one before M9 event. The seismic activity is about 4 times as high as before the M9 event occurred. We examined spatial distribution of the activated seismicity with respect to the newly developed plate configuration. The activated events are located on upper boundaries and they have almost thrust type mechanisms. Recently, a slow slip event has occurred on October in

  12. A kinematic model for Afar Depression lithospheric thinning and its implications for hominid evolution: an exercise in plate-tectonic paleoanthropology

    NASA Astrophysics Data System (ADS)

    Redfield, T.; Often, M.; Wheeler, W. H.

    2002-12-01

    We present a detailed Nubia-Arabia-Somalia (NU-AR-SOM) kinematic reconstruction based on magnetic sea floor isochrons in the Gulf of Aden and Red Sea and piercing points along the Red Sea margins. The reconstruction is combined with digital topographic and depth-to-Moho data to constrain in 4D the Late Oligocene to present-day evolution of the Afar supra-Moho crust. Opposite end-member models for crustal evolution are described. We conclude that less than 20% of the present-day Afar supra-Moho crust was constructed by magmatic processes such as diking and underplating. The reconstructions indicate that the greater percentage of crustal thinning (extension) occurred before 6.2 Ma. We model the thinning of the effective elastic lithosphere that accompanied extension, and show that the regional-scale topographic development of the Afar depression was virtually complete by Mid Pliocene time. The plate-tectonic model has paleoanthropological implications. Prior to 6.2 Ma the proximal positions of NU-SOM, AR, and the Danakil block suggest subaerial conditions prevailed between Yemen and Ethiopia. Uninhibited Africa-Eurasia faunal exchange through Afar and Arabia (corroborated by isotopic and paleontologic data) was tectonically permissible until the time of the earliest hominids. Continued stretching caused the Afar land bridge(s) to disappear during Early to Mid Pliocene time. Primitive hominid populations living within the Afar Depression became isolated from AR sometime before ~3.2 Ma. With the plateau becoming less habitable due to long-term Late Neogene cooling, hominids that remained in the Afar Depression were required to adapt to a smaller range that was effectively bounded by the already well-developed NU-SOM escarpments and the newly opened Straits of Bab el Mandeb. The combination of high quality habitat,topographic confinement, and a gradual (tectonic) reduction in range, exacerbated by potentially severe fluctuations in local climate (well documented by land

  13. Magma-tectonic interactions in an area of active extension; a review of recent observations, models and interpretations from Iceland

    NASA Astrophysics Data System (ADS)

    Pedersen, Rikke; Sigmundsson, Freysteinn; Drouin, Vincent; Rafn Heimisson, Elías; Parks, Michelle; Dumont, Stéphanie; Árnadóttir, Þóra; Masterlark, Timothy; Ófeigsson, Benedíkt G.; Jónsdóttir, Kristín; Hooper, Andrew

    2016-04-01

    The geological setting of Iceland provides rich opportunities of studying magma-tectonic interactions, as it constitutes Earth's largest part of the mid-oceanic ridge system exposed above sea level. A series of volcanic and seismic zones accommodate the ~2 cm/year spreading between the North-American and Eurasian plates, and the Icelandic hot-spot conveniently provides the means of exposing this oceanic crust-forming setting above sea-level. Both extinct and active plumbing system structures can be studied in Iceland, as the deeply eroded tertiary areas provide views into the structures of extinct volcanic systems, and active processes can be inferred on in the many active volcanic systems. A variety of volcanic and tectonic processes cause the Icelandic crust to deform continuously, and the availability of contemporaneous measurements of crustal deformation and seismicity provide a powerful data set, when trying to obtain insight into the processes working at depth, such as magma migration through the uppermost lithosphere, magma induced host rock deformation and volcanic eruption locations and styles. The inferences geodetic and seismic datasets allow on the active plate spreading processes and subsurface magma movements in Iceland will be reviewed, in particular in relation to the Northern Volcanic Zone (NVZ). There the three phases of a rifting cycle (rifting, post-rifting, inter-rifting) have been observed. The NVZ is an extensional rift segment, bounded to the south by the Icelandic mantle plume, and to the north by the Tjörnes transform zone. The NVZ has typically been divided into five partly overlapping en-echelon fissure swarms, each with a central main volcanic production area. Most recently, additional insight into controlling factors during active rifting has been provided by the Bárðarbunga activity in 2014-2015 that included a major rifting event, the largest effusive eruption in Iceland since 1783, and a gradual caldera collapse. It is evident

  14. DISCUSSION: When and How did Plate Tectonics Begin, What Came Before, and Why is this Controversy important for Understanding the Earth and Exoplanets?

    NASA Astrophysics Data System (ADS)

    Stern, R. J.; Gerya, T.; Sobolev, S. V.; Tackley, P.

    2015-12-01

    Because all 5 presentations in the Union session "When and How did Plate Tectonics Begin, What Came Before, and Why is this Controversy important for Understanding the Earth and Exoplanets?" will have 5 minute discussion periods, the scheduled 15 minute end-of-session discussion period is intended to allow other perspectives to be presented by the scientific community. We invite brief (2 powerpoint slides) comments from the community about any aspect of the topic at hand. We encourage anyone who has something pertinent or interesting to say to submit 2 powerpoint slides directly to any one of the four co-convenors listed on this abstract. The first slide should be a simple title with the name and affiliation of the commenter. The second slide should be the content of the comment. The convenors will compile all of these that are submitted up to the noon on the day before the session occurs, when we will upload the compiled files in the order that they were received (if we have received digital scans of signed waivers by that time, see below). During the discussion, we will call on those who have submitted 2 slides to the podium to make their points in 2 minutes or less (total time from being called to leaving the podium). Because this AGU Union session including the discussion period will be live-streamed and recorded, all Discussion Session commenters will be required to sign an AGU waiver acknowledging this and giving permission to be recorded. These will be sent via e-mail to those who submit 2 slide powerpoints. Commenters that do not sign and return the waiver will be scheduled after all commenters who have returned signed waivers and AGU will terminate live streaming and recording accordingly. If no one submits anything then we will have open discussion from the floor. We will also advertise the Monte Verita conference in Locarno Switzerland 17-22 July 2016. This conference will explore in greater detail the 5 key aspects of Plate Tectonic evolution briefly

  15. Evaluating influence of active tectonics on spatial distribution pattern of floods along eastern Tamil Nadu, India

    NASA Astrophysics Data System (ADS)

    Selvakumar, R.; Ramasamy, SM.

    2014-12-01

    Flooding is a naturally recurrent phenomenon that causes severe damage to lives and property. Predictions on flood-prone zones are made based on intensity-duration of rainfall, carrying capacity of drainage, and natural or man-made obstructions. Particularly, the lower part of the drainage system and its adjacent geomorphic landforms like floodplains and deltaic plains are considered for analysis, but stagnation in parts of basins that are far away from major riverine systems is less unveiled. Similarly, uncharacteristic flooding in the upper and middle parts of drainage, especially in zones of an anomalous drainage pattern, is also least understood. Even though topographic differences are attributed for such anomalous spatial occurrence of floods, its genetic cause has to be identified for effective management practice. Added to structural and lithological variations, tectonic movements too impart micro-scale terrain undulations. Because active tectonic movements are slow-occurring, long-term geological processes, its resultant topographical variations and drainage anomalies are least correlated with floods. The recent floods of Tamil Nadu also exhibit a unique distribution pattern emphasizing the role of tectonics over it. Hence a detailed geoinformatics-based analysis was carried out to envisage the relationship between spatial distribution of flood and active tectonic elements such as regional arches and deeps, block faults, and graben and drainage anomalies such as deflected drainage, compressed meander, and eyed drainages. The analysis reveals that micro-scale topographic highs and lows imparted by active tectonic movements and its further induced drainage anomalies have substantially controlled the distribution pattern of flood.

  16. Active tectonics of the Oran (Algeria) Quaternary plain

    NASA Astrophysics Data System (ADS)

    youcef, Bouhadad; rabah, Bensalem; e-hadi, oubaiche

    2016-04-01

    The Oran region, in north-western Algeria, has been hit several times in the past by destructive moderate-sized and strong earthquakes. The Oran October 9th , 1790 (I0= X) was among the strongest seismic events in the western Mediterranean area comparable, if we consider the described effects, to the El- Asnam (1980, Ms=7.3) and Zemmouri (2003, Mw=6.8) earthquakes. Such strong seismic events requires the presence of major active geological structures that are re-activated several times in the past. In this work we present results of a multi- disciplinary study combining geomorphic analysis, field earthquake geological investigations and geophysical methods, undertaken to study the southern border of the Oran Quaternary plain. A 50 km long, SW-dipping and NE-SW trending active fault has been identified that showing clear quaternary deformation. Keywords: earthquake geology, active fault, geomorphic, geophysics, Algeria.

  17. Two-dimensional numerical modeling of tectonic and metamorphic histories at active continental margins

    NASA Astrophysics Data System (ADS)

    Gerya, Taras; Stöckhert, Bernhard

    2006-04-01

    The evolution of an active continental margin is simulated in two dimensions, using a finite difference thermomechanical code with half-staggered grid and marker-in-cell technique. The effect of mechanical properties, changing as a function of P and T, assigned to different crustal layers and mantle materials in the simple starting structure is discussed for a set of numerical models. For each model, representative P T paths are displayed for selected markers. Both the intensity of subduction erosion and the size of the frontal accretionary wedge are strongly dependent on the rheology chosen for the overriding continental crust. Tectonically eroded upper and lower continental crust is carried down to form a broad orogenic wedge, intermingling with detached oceanic crust and sediments from the subducted plate and hydrated mantle material from the overriding plate. A small portion of the continental crust and trench sediments is carried further down into a narrow subduction channel, intermingling with oceanic crust and hydrated mantle material, and to some extent extruded to the rear of the orogenic wedge underplating the overriding continental crust. The exhumation rates for (ultra)high pressure rocks can exceed subduction and burial rates by a factor of 1.5 3, when forced return flow in the hanging wall portion of the self-organizing subduction channel is focused. The simulations suggest that a minimum rate of subduction is required for the formation of a subduction channel, because buoyancy forces may outweigh drag forces for slow subduction. For a weak upper continental crust, simulated by a high pore pressure coefficient in the brittle regime, the orogenic wedge and megascale melange reach a mid- to upper-crustal position within 10 20 Myr (after 400 600 km of subduction). For a strong upper crust, a continental lid persists over the entire time span covered by the simulation. The structural pattern is similar in all cases, with four zones from trench toward arc

  18. Change in biochemical and morphological characteristics of Lonicera caerulea in tectonically active zone of the Dzhazator River Valley (Altai Mountains)

    NASA Astrophysics Data System (ADS)

    Boyarskikh, I. G.; Khudyaev, S. A.; Platonova, S. G.; Kolotukhin, S. P.; Shitov, A. V.; Kukushkina, T. A.; Chankina, O. V.

    2012-12-01

    Local geophysical and geochemical anomalies affect the polymorphism of taste variations, berry shape, and content of some biologically active substances in Lonicera caerulea leaves in the tectonically active Altai Mountains (Dzhazator River basin).

  19. The giant coastal landslides of Northern Chile: Tectonic and climate interactions on a classic convergent plate margin

    NASA Astrophysics Data System (ADS)

    Mather, Anne E.; Hartley, Adrian J.; Griffiths, James S.

    2014-02-01

    Documented for the first time are an extensive suite of late Neogene giant terrestrial coastal landslides along the classic convergent margin of western South America (18° to 24° south). These are remarkable in terms of their unusual abundance and atypical setting, such failures previously being linked with oceanic volcanic edifices or over-steepened glaciated coastlines. Located within the hyper-arid Coastal Cordillera of the Atacama Desert of Northern Chile we report the presence of more than 60 individual large-scale landslides with individual volumes up to 9 km3 developed over a horizontal coastline distance of some 650 km. These landslides were emplaced as a combination of rock avalanches and multiple rotational failures. The majority terminated directly into the Pacific - likely generating significant tsunami hazard to the Chilean and south Peruvian coastline in a region which is today considered to be part of a notorious seismic gap. The proliferation and scale of these Late Neogene giant landslides in this actively uplifting, hyperarid terrain suggests they are the main geomorphic agent for relief reduction, probably triggered by megathrust earthquakes and potentially providing a unique palaeoseismic archive. The temporal and spatial distribution of these giant landslides corresponds with a period of surface steepening of the forearc wedge in the Central Andes and south to north differential uplift associated with factors such as aseismic ridge subduction. The resulting surface gradient increases, combined with the persistent climatic aridity of the region, have served to limit effective relief-reducing geomorphic processes in this oversteepened terrain to large-scale landsliding. The phenomena documented here geospatially link previously recognised large-scale slope failures from the off-shore environment and higher altitude areas of the Andean forearc, suggesting that large-scale landsliding is capable of transferring sediment on a regional scale to the

  20. Ganges-Brahmaputra Delta: Balance of Subsidence, Sea level and Sedimentation in a Tectonically-Active Delta (Invited)

    NASA Astrophysics Data System (ADS)

    Steckler, M. S.; Goodbred, S. L.; Akhter, S. H.; Seeber, L.; Reitz, M. D.; Paola, C.; Nooner, S. L.; DeWolf, S.; Ferguson, E. K.; Gale, J.; Hossain, S.; Howe, M.; Kim, W.; McHugh, C. M.; Mondal, D. R.; Petter, A. L.; Pickering, J.; Sincavage, R.; Williams, L. A.; Wilson, C.; Zumberge, M. A.

    2013-12-01

    Bangladesh is vulnerable to a host of short and long-term natural hazards - widespread seasonal flooding, river erosion and channel avulsions, permanent land loss from sea level rise, natural groundwater arsenic, recurrent cyclones, landslides and huge earthquakes. These hazards derive from active fluvial processes related to the growth of the delta and the tectonics at the India-Burma-Tibet plate junctions. The Ganges and Brahmaputra rivers drain 3/4 of the Himalayas and carry ~1 GT/y of sediment, 6-8% of the total world flux. In Bangladesh, these two great rivers combine with the Meghna River to form the Ganges-Brahmaputra-Meghna Delta (GBMD). The seasonality of the rivers' water and sediment discharge is a major influence causing widespread flooding during the summer monsoon. The mass of the water is so great that it causes 5-6 cm of seasonal elastic deformation of the delta discerned by our GPS data. Over the longer-term, the rivers are also dynamic. Two centuries ago, the Brahmaputra River avulsed westward up to 100 km and has since captured other rivers. The primary mouth of the Ganges has shifted 100s of km eastward from the Hooghly River over the last 400y, finally joining the Brahmaputra in the 19th century. These avulsions are influenced by the tectonics of the delta. On the east side of Bangladesh, the >16 km thick GBMD is being overridden by the Burma Arc where the attempted subduction of such a thick sediment pile has created a huge accretionary prism. The foldbelt is up to 250-km wide and its front is buried beneath the delta. The main Himalayan thrust front is <100 km north, but adjacent to the GBMD is the Shillong Massif, a 300-km long, 2-km high block of uplifted Indian basement that is overthrusting and depressing GBMD sediments to the south. The overthrusting Shillong Massif may represent a forward jump of the Himalayan front to a new plate boundary. This area ruptured in a ~M8 1897 earthquake. Subsidence from the tectonics and differential

  1. The Distribution and Composition Characteristics of Siliceous Rocks from Qinzhou Bay-Hangzhou Bay Joint Belt, South China: Constraint on the Tectonic Evolution of Plates in South China

    PubMed Central

    Li, Hongzhong; Zhai, Mingguo; Zhang, Lianchang; Zhou, Yongzhang; Yang, Zhijun; He, Junguo; Liang, Jin; Zhou, Liuyu

    2013-01-01

    The Qinzhou Bay-Hangzhou Bay joint belt is a significant tectonic zone between the Yangtze and Cathaysian plates, where plentiful hydrothermal siliceous rocks are generated. Here, the authors studied the distribution of the siliceous rocks in the whole tectonic zone, which indicated that the tensional setting was facilitating the development of siliceous rocks of hydrothermal genesis. According to the geochemical characteristics, the Neopalaeozoic siliceous rocks in the north segment of the Qinzhou Bay-Hangzhou Bay joint belt denoted its limited width. In comparison, the Neopalaeozoic Qinzhou Bay-Hangzhou Bay joint belt was diverse for its ocean basin in the different segments and possibly had subduction only in the south segment. The ocean basin of the north and middle segments was limited in its width without subduction and possibly existed as a rift trough that was unable to resist the terrigenous input. In the north segment of the Qinzhou Bay-Hangzhou Bay joint belt, the strata of hydrothermal siliceous rocks in Dongxiang copper-polymetallic ore deposit exhibited alternative cycles with the marine volcanic rocks, volcanic tuff, and metal sulphide. These sedimentary systems were formed in different circumstances, whose alternative cycles indicated the release of internal energy in several cycles gradually from strong to weak. PMID:24302882

  2. The distribution and composition characteristics of siliceous rocks from Qinzhou Bay-Hangzhou Bay joint belt, South China: constraint on the tectonic evolution of plates in South China.

    PubMed

    Li, Hongzhong; Zhai, Mingguo; Zhang, Lianchang; Zhou, Yongzhang; Yang, Zhijun; He, Junguo; Liang, Jin; Zhou, Liuyu

    2013-01-01

    The Qinzhou Bay-Hangzhou Bay joint belt is a significant tectonic zone between the Yangtze and Cathaysian plates, where plentiful hydrothermal siliceous rocks are generated. Here, the authors studied the distribution of the siliceous rocks in the whole tectonic zone, which indicated that the tensional setting was facilitating the development of siliceous rocks of hydrothermal genesis. According to the geochemical characteristics, the Neopalaeozoic siliceous rocks in the north segment of the Qinzhou Bay-Hangzhou Bay joint belt denoted its limited width. In comparison, the Neopalaeozoic Qinzhou Bay-Hangzhou Bay joint belt was diverse for its ocean basin in the different segments and possibly had subduction only in the south segment. The ocean basin of the north and middle segments was limited in its width without subduction and possibly existed as a rift trough that was unable to resist the terrigenous input. In the north segment of the Qinzhou Bay-Hangzhou Bay joint belt, the strata of hydrothermal siliceous rocks in Dongxiang copper-polymetallic ore deposit exhibited alternative cycles with the marine volcanic rocks, volcanic tuff, and metal sulphide. These sedimentary systems were formed in different circumstances, whose alternative cycles indicated the release of internal energy in several cycles gradually from strong to weak. PMID:24302882

  3. Plate motion

    SciTech Connect

    Gordon, R.G. )

    1991-01-01

    The motion of tectonic plates on the earth is characterized in a critical review of U.S. research from the period 1987-1990. Topics addressed include the NUVEL-1 global model of current plate motions, diffuse plate boundaries and the oceanic lithosphere, the relation between plate motions and distributed deformations, accelerations and the steadiness of plate motions, the distribution of current Pacific-North America motion across western North America and its margin, plate reconstructions and their uncertainties, hotspots, and plate dynamics. A comprehensive bibliography is provided. 126 refs.

  4. Linking Europa's plume activity to tides, tectonics, and liquid water

    NASA Astrophysics Data System (ADS)

    Rhoden, Alyssa Rose; Hurford, Terry A.; Roth, Lorenz; Retherford, Kurt

    2015-06-01

    Much of the geologic activity preserved on Europa's icy surface has been attributed to tidal deformation, mainly due to Europa's eccentric orbit. Although the surface is geologically young (30-80 Myr), there is little information as to whether tidally-driven surface processes are ongoing. However, a recent detection of water vapor near Europa's south pole suggests that it may be geologically active. Initial observations indicated that Europa's plume eruptions are time-variable and may be linked to its tidal cycle. Saturn's moon, Enceladus, which shares many similar traits with Europa, displays tidally-modulated plume eruptions, which bolstered this interpretation. However, additional observations of Europa at the same time in its orbit failed to yield a plume detection, casting doubt on the tidal control hypothesis. The purpose of this study is to analyze the timing of plume eruptions within the context of Europa's tidal cycle to determine whether such a link exists and examine the inferred similarities and differences between plume activity on Europa and Enceladus. To do this, we determine the locations and orientations of hypothetical tidally-driven fractures that best match the temporal variability of the plumes observed at Europa. Specifically, we identify model faults that are in tension at the time in Europa's orbit when a plume was detected and in compression at times when the plume was not detected. We find that tidal stress driven solely by eccentricity is incompatible with the observations unless additional mechanisms are controlling the eruption timing or restricting the longevity of the plumes. The addition of obliquity tides, and corresponding precession of the spin pole, can generate a number of model faults that are consistent with the pattern of plume detections. The locations and orientations of these hypothetical source fractures are robust across a broad range of precession rates and spin pole directions. Analysis of the stress variations across

  5. Nappes, tectonics of oblique plate convergence, and metamorphic evolution related to 140 million years of continuous subduction, Franciscan Complex, California

    SciTech Connect

    Wakabayashi, J. )

    1992-01-01

    This paper presents a new synthesis of Franciscan Complex tectonics, with the emphasis on the pre-San Andreas fault history of these rocks. Field relations suggest that the Franciscan is characterized by nappe structures that formed during sequential accretion at the trench. The presence of these structures along with other field relations, including the lack of evidence for large offset of conglomerate suites, indicates that strike-slip fault systems of large displacement ({gt}500 km) did not cut the Franciscan Complex during subduction. Regional geology and comparisons to modern arc-trench systems suggest that strike-slip faulting associated with oblique subduction took place inboard (east) of the Franciscan in the vicinity of the magmatic arc. The Franciscan varies along strike, because individual accreted elements (packets of trench sediment, seamounts, etc.) did not extend the full length of the trench. Different depths of underplating, distribution of post-metamorphic faulting, and level of erosion produced the present-day surface distribution of high P/T metamorphism. Franciscan Complex tectonic history is presented in this paper.

  6. Magnetic fields over active tectonic zones in ocean

    USGS Publications Warehouse

    Kopytenko, Yu. A.; Serebrianaya, P.M.; Nikitina, L.V.; Green, A.W.

    2002-01-01

    The aim of our work is to estimate the electromagnetic effects that can be detected in the submarine zones with hydrothermal activity. It is known that meso-scale flows appear in the regions over underwater volcanoes or hot rocks. Their origin is connected with heat flux and hot jets released from underwater volcanoes or faults in a sea bottom. Values of mean velocities and turbulent velocities in plumes were estimated. Quasiconstant magnetic fields induced by a hot jet and a vortex over a plume top are about 1-40 nT. Variable magnetic fields are about 0.1-1 nT. These magnetic disturbances in the sea medium create an additional natural electromagnetic background that must be considered when making detailed magnetic surveys. ?? 2002 Elsevier Science Ltd. All rights reserved.

  7. A tectonic interpretation of NW-SE strike-slip faulting during the 2004 off the Kii peninsula earthquakes, Japan: Probable tear of the Philippine Sea plate

    NASA Astrophysics Data System (ADS)

    Miyoshi, T.; Ishibashi, K.

    2005-11-01

    The 2004 off the Kii peninsula earthquakes (Mw 7.5 for the main shock) occurred within the subducting Philippine Sea (PHS) plate near its boundary, the Nankai trough, southwest Japan. The rupture mode of the foreshock-main shock-aftershock sequence was complicated, a combination of ENE-WSW striking (almost trough parallel) reverse faulting beneath the trough and NW-SE trending (almost trough normal) strike-slip faulting mostly on the landward side of the former. In this paper, we discuss the tectonic meaning of this NW-SE running strike-slip fault. We examined hypocenter distribution and focal mechanisms of slab earthquakes from October 1997 through September 2004 and confirmed a NW-SE striking tear of the PHS slab beneath the middle part of the Kii Peninsula pointed out by Miyoshi and Ishibashi (2004). According to the Earthquake Research Committee (2004) there is a NW-SE trending structural discontinuity in the PHS crust to the southeast of the main shock epicenter. Putting all features together, we interpret that there is a NW-SE striking fracture within the PHS plate continuously from the Nankai trough region to the slab beneath the Kii Peninsula, and that a partial rupture of this fracture occurred during the off the Kii peninsula earthquakes together with trough-parallel reverse faulting. It should be noted that two disastrous M 7-class slab earthquakes seem to have occurred along this tear beneath the peninsula in 1899 and 1952.

  8. Evolution of the Theory of the Earth: A Contextualized Approach for Teaching the History of the Theory of Plate Tectonics to Ninth Grade Students

    NASA Astrophysics Data System (ADS)

    Dolphin, Glenn

    2009-04-01

    Current high school Earth Science curricula and textbooks organize scientific content into isolated “units” of knowledge. Within this structure, content is taught, but in the absence of the context of fundamental understandings or the process of how the science was actually done to reach the conclusions. These are two key facets of scientific literacy. I have developed curriculum from a historical perspective that addresses two particular units of study in Earth Science (“geologic time” and “plate tectonics”). The curriculum traces the evolution of the theory of plate tectonics. It includes contextualized experiences for students such as telling stories, utilizing original historical texts, narratives, and essential questions, to name a few. All of the strategies are utilized with the goal of building understanding around a small set of common themes. Exploring the historical models in this way allows students to analyze the models, while looking for limitations and misconceptions. This methodology is used to encourage students to develop more scientifically accurate understandings about the way in which the world and the process of scientific discovery work. Observations of high student engagement during the utilization of this contextualized approach has demonstrated that a positive effect on student understanding is promising.

  9. A hypothesis for Proterozoic-Phanerozoic supercontinent cyclicity, with implications for mantle convection, plate tectonics and Earth system evolution

    NASA Astrophysics Data System (ADS)

    Grenholm, Mikael; Scherstén, Anders

    2015-11-01

    We present a conceptual model for supercontinent cycles in the Proterozoic-Phanerozoic Eons. It is based on the repetitive behavior of C and Sr isotopes in marine carbonates and U-Pb ages and εHf of detrital zircons seen during the Neoproterozoic-Paleozoic and Paleoproterozoic Eras, respectively. These records are considered to reflect secular changes in global tectonics, and it is hypothesized that the repetitive pattern is caused by the same type of changes in global tectonics. The fundamental premise of this paper is that such repetitive changes should also be recorded in orogenic belts worldwide. This carries the implication that Neoproterozoic-Paleozoic orogenic belts should have Paleoproterozoic equivalents. It is proposed that this is the case for the East African, Uralides and Ouachita-Alleghanian orogens, which have Paleoproterozoic analogs in the West African-Amazon, Laurentian and East European cratons, respectively. The Neoproterozoic-Paleozoic orogenic belts are not isolated features but occur in a specific global context, which correspond to the relatively well-constrained Neoproterozoic break-up of Rodinia, and the subsequent Late Paleozoic assembly of Pangea. The existence of Paleoproterozoic equivalents to Neoproterozoic-Paleozoic orogens requires that the same cycle defined the Paleoproterozoic. We therefore hypothesize that there were Paleoproterozoic supercontinents equivalent to Rodinia and Pangea, and that Proterozoic-Phanerozoic supercontinents are comprised of two basic types of configurations, equivalent to Rodinia (R-type) and Pangea (P-type). The Paleoproterozoic equivalent of Rodinia is likely the first supercontinent to have formed, and Proterozoic-Phanerozoic supercontinent cycles are therefore defined by R- to R-type cycles, each lasting approximately 1.5 Gyr. We use this cyclic pattern as a framework to develop a conceptual model that predicts the configuration and cycles of Proterozoic-Phanerozoic supercontinents, and their

  10. Active cloaking of flexural waves in thin plates

    NASA Astrophysics Data System (ADS)

    Futhazar, Gregory; Parnell, William J.; Norris, Andrew N.

    2015-11-01

    An active cloak consists of a set of discrete multipole sources distributed in space. When the source positions and amplitudes are carefully specified the active field destructively interferes with an incident time harmonic wave so as to nullify the total field in some finite domain and ensure that in the far field only the incident wave is present, i.e. the active field is non-radiating. Here it is shown how to efficiently determine the source coefficients explicitly in the context of flexural waves in thin plates. The work is carried out in the context of Kirchhoff plate theory, using the Rayleigh-Green theorem to derive the unique source amplitudes for a given incident flexural wave.

  11. Accretionary Complexes: Recorders of Plate Tectonism and Environmental Conditions Through Time on Earth and Possibly Those Early Noachian (Hadean-equivalent) in Age on Mars

    NASA Astrophysics Data System (ADS)

    Dohm, J. M.; Maruyama, S.; Miyamoto, H.; Viviano-Beck, C. E.; Anderson, R. C.

    2014-12-01

    On Ear