Science.gov

Sample records for plate tectonic events

  1. 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

  2. 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). 

  3. 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.

  4. 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.

  5. 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)

  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, 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.

  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. Intermittent Plate Tectonics

    NASA Astrophysics Data System (ADS)

    Silver, P. G.; Behn, M. D.

    2006-12-01

    Intermittent Plate Tectonics A basic premise of Earth Science is that plate tectonics has been continuously operating since it began early in Earth's history. Yet, plate-tectonic theory itself, specifically the collisional phase of the Wilson Cycle, constitutes a process that is capable of stopping all plate motion. The plausibility of a plate-tectonic hiatus is most easily illustrated by considering the expected future of the present-day plate-tectonic configuration. Since the opening of the Atlantic at ~200 ma, the area of the Atlantic basin has been growing at the expense of the Pacific. If this trend continues, relative plate motion models predict that in ~350 my, the Pacific Ocean basin will effectively close leading to widespread continent-continent collisions. Since a continent-continent collision represents the termination of subduction locally, the accumulated effect of all collisions is to stop subduction globally. In this scenario, ridges would then stop spreading and young oceanic lithosphere would cool, reaching a steady-state thickness of 100 km in about 80 my, based on the properties of oceanic lithosphere today. This would constitute the stoppage of plate tectonics. The presumption that plate tectonics never stops in the face of continental collisions is equivalent to requiring that subduction flux is approximately constant through time, such that subduction initiation roughly balances subduction termination. Such a balance then raises several questions about the subduction initiation process. When and how does subduction initiate? Is there a detectible relationship between subduction cessation and subduction initiation? We can gain some guidance into these questions by examining the plate motion history over the last 200 my. Subduction initiation has occurred over the last 80 my in three intra- oceanic subduction zones: Aleutians, Marianas-Izu-Bonin and Tonga-Kermadec in the Pacific basin. In these cases, however, subduction initiation would not

  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. 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.

  12. Intermittent plate tectonics?

    PubMed

    Silver, Paul G; Behn, Mark D

    2008-01-04

    Although it is commonly assumed that subduction has operated continuously on Earth without interruption, subduction zones are routinely terminated by ocean closure and supercontinent assembly. Under certain circumstances, this could lead to a dramatic loss of subduction, globally. Closure of a Pacific-type basin, for example, would eliminate most subduction, unless this loss were compensated for by comparable subduction initiation elsewhere. Given the evidence for Pacific-type closure in Earth's past, the absence of a direct mechanism for termination/initiation compensation, and recent data supporting a minimum in subduction flux in the Mesoproterozoic, we hypothesize that dramatic reductions or temporary cessations of subduction have occurred in Earth's history. Such deviations in the continuity of plate tectonics have important consequences for Earth's thermal and continental evolution.

  13. 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.

  14. Tectonics: Changing of the plates

    NASA Astrophysics Data System (ADS)

    Brandon, Alan

    2016-10-01

    The composition of Earth's crust depends on the style of plate tectonics and of the melting regimes in the mantle. Analyses of the oldest identified rocks suggest that these styles and the resulting crust have changed over Earth's history.

  15. 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.

  16. Earth's Decelerating Tectonic Plates (Invited)

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

    We employ a recently developed convection model constrained by seismic, geodynamic and mineral physics data (Simmons et al., GJI 2009) to explore the impact of time-dependent changes in mantle buoyancy forces on tectonic plate accelerations. This plate-coupled mantle convection model incorporates a viscosity structure that reconciles both glacial isostatic adjustment and global convection-related data sets (Mitrovica & Forte, EPSL 2004) and it successfully reproduces present-day plate velocities, global surface gravity and topography data. This convection model predicts the recent deceleration of several major plates in the Pacific and Indo-Atlantic hemispheres. Independent verification of these predictions is a fundamental test of the plausibility of the buoyancy forces and rheological structure in the convection model. To this end, we consider marine magnetic anomaly and space geodetic constraints on tectonic plate motions to determine a new global map of present-day rates of change of plate velocities. This map shows that several major plates, such as the Pacific, Africa and Nazca plates are presently decelerating and that they contribute to a globally-averaged slowdown in tectonic plate speeds. These joint geologic-geodetic inferences of plate decelerations are consistent with those predicted by our tomography-based convection model.

  17. 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.

  18. 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.

  19. 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.

  20. 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)

  1. 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

  2. Comment on "Intermittent plate tectonics?".

    PubMed

    Korenaga, Jun

    2008-06-06

    Silver and Behn (Reports, 4 January 2008, p. 85) proposed that intermittent plate tectonics may resolve a long-standing paradox in Earth's thermal evolution. However, their analysis misses one important term, which subsequently brings their main conclusion into question. In addition, the Phanerozoic eustasy record indicates that the claimed effect of intermittency is probably weak.

  3. 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.

  4. 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.

  5. 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

  6. 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.

  7. 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)

  8. 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…

  9. Plate tectonics of the Mediterranean region.

    PubMed

    McKenzie, D P

    1970-04-18

    The seismicity and fault plane solutions in the Mediterranean area show that two small rapidly moving plates exist in the Eastern Mediterranean, and such plates may be a common feature of contracting ocean basins. The results show that the concepts of plate tectonics apply to instantaneous motions across continental plate boundaries.

  10. 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.

  11. 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.

  12. Subduction Drive of Plate Tectonics

    NASA Astrophysics Data System (ADS)

    Hamilton, W. B.

    2003-12-01

    Don Anderson emphasizes that plate tectonics is self-organizing and is driven by subduction, which rights the density inversion generated as oceanic lithosphere forms by cooling of asthenosphere from the top. The following synthesis owes much to many discussions with him. Hinge rollback is the key to kinematics, and, like the rest of actual plate behavior, is incompatible with bottom-up convection drive. Subduction hinges (which are under, not in front of, thin leading parts of arcs and overriding plates) roll back into subducting plates. The Pacific shrinks because bounding hinges roll back into it. Colliding arcs, increasing arc curvatures, back-arc spreading, and advance of small arcs into large plates also require rollback. Forearcs of overriding plates commonly bear basins which preclude shortening of thin plate fronts throughout periods recorded by basin strata (100 Ma for Cretaceous and Paleogene California). This requires subequal rates of advance and rollback, and control of both by subduction. Convergence rate is equal to rates of rollback and advance in many systems but is greater in others. Plate-related circulation probably is closed above 650 km. Despite the popularity of concepts of plumes from, and subduction into, lower mantle, there is no convincing evidence for, and much evidence against, penetration of the 650 in either direction. That barrier not only has a crossing-inhibiting negative Clapeyron slope but also is a compositional boundary between fractionated (not "primitive"), sluggish lower mantle and fertile, mobile upper mantle. Slabs sink more steeply than they dip. Slabs older than about 60 Ma when their subduction began sink to, and lie down on and depress, the 650-km discontinuity, and are overpassed, whereas younger slabs become neutrally buoyant in mid-upper mantle, into which they are mixed as they too are overpassed. Broadside-sinking old slabs push all upper mantle, from base of oceanic lithosphere down to the 650, back under

  13. 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

  14. How mantle slabs drive plate tectonics.

    PubMed

    Conrad, Clinton P; Lithgow-Bertelloni, Carolina

    2002-10-04

    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.

  15. 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.

  16. Mesozoic/Cenozoic tectonic events around Australia

    NASA Astrophysics Data System (ADS)

    Müller, R. Dietmar; Gaina, Carmen; Tikku, Anahita; Mihut, Dona; Cande, Steven C.; Stock, Joann M.

    We use an absolute and relative plate motion model for the plates around Australia to identify major plate tectonic events, evaluate their causes, and investigate their effects on anomalous intraplate subsidence or uplift and on the history of oceanic crustal accretion. An event at ˜136 Ma is marked by the onset of sea floor spreading between Greater India and Australia. At about this time long-lived subduction east of Australia ceased, probably due to subduction of the Phoenix-Pacific spreading ridge, changing this plate boundary to a transform margin. Between 130 and 80 Ma, Australia and East Antarctica moved eastward in the Atlantic-Indian mantle hotspot reference frame. This can be plausibly linked to ridge push from the NW-SE oriented spreading center NW of Australia and to the inferred geometry and continued subduction of the Phoenix plate beneath the West Antarctic margin. A drastic change in spreading direction between the Indian and Australian plates from NE-SW to N-S occurred at about 99 Ma, possibly caused by a change in absolute motion of the Pacific Plate. Chron 27 (˜61 Ma) marks the onset of relative motion between East and West Antarctica, and a change in the relative motion between Australia and Antarctica. It may be linked to the subduction of a segment of the Neo-Tethyan Ridge. Both events caused anomalous subsidence on the Northwest Shelf of Australia. The almost stationary position of Australia w.r.t. the mantle from ˜80 Ma to ˜40 Ma may reflect the progressive subduction of the Pacific-Phoenix ridge to the east of New Zealand preceding 80 Ma, resulting in a diminished trench suction force east of Australia. Preliminary reconstructions to close the Pacific-Australian plate circuit based on recently collected geophysical data indicate that a tectonic event at 43 Ma may mark the onset of renewed subduction east of Australia. At the same time spreading in the Wharton Basin between India and Australia ceased, and tectonic reactivation is

  17. 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.

  18. On the Origin of Plate Tectonics

    NASA Astrophysics Data System (ADS)

    Bercovici, D.

    2014-12-01

    The emergence of plate tectonics was Earth's defining moment. How and when platetectonics started is shrouded in mystery because of the paucity of observations in theArchean as well the challenge of understanding how plates are generated. The damage theoryof lithospheric weakening by grain-reduction provides a physical framework for plategeneration. This model builds on grain-scale processes to elucidate planetary-scaletectonics, and is consistent with lab and field observations of polycrystalline rocks andlithospheric shear zones. The grain-damage model accounts for the evolution of damage andhealing (by grain growth) at various planetary conditions, hence predicts plate boundaryformation and longevity, and how they depend on surface environment. For example, the onset of prototectonics is predicted to require clement conditions tokeep healing from erasing weak zones; conversely, cool conditions possibly requiredtectonics to draw down primordial CO2. Thus whether tectonics preceded a cool climate (andwater) or vice versa is immaterial as they likely needed each other or neither wouldexist. Sparse evidence that prototectonics co-initiated with liquid water hints at thelink between tectonics, water and surface conditions. The establishment of wide-spread plate tectonics started between >4Ga and 2.7Ga, and mayhave taken over a billion years to develop. Under Earth-like conditions, combininggrain-damage with intermittent Archean protosubduction produces persistent weak zones thataccumulate to yield well developed plates within 1Gyrs. In contrast, Venus' hottersurface conditions promotes healing and prohibits weak zone accumulation, which explainswhy plate tectonics failed to spread on our sister planet. Damage and weak-zone inheritance may also influence plate evolution and reorganization inthe modern era. Changes in plate direction, such as reflected in the Emperor-Hawaiianbend, leave weak zones misaligned with plate motion, causing oblique plate boundaries

  19. 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.

  20. LOWLID FORMATION AND PLATE TECTONICS ON EXOPLANETS

    NASA Astrophysics Data System (ADS)

    Stamenkovic, V.; Noack, L.; Breuer, D.

    2009-12-01

    The last years of astronomical observation have opened the doors to a universe filled with extrasolar planets. Detection techniques still only offer the possibility to detect mainly Super-Earths above five Earth masses. But detection techniques do steadily improve and are offering the possibility to detect even smaller planets. The observations show that planets seem to exist in many possible sizes just as the planets and moons of our own solar system do. It is only a natural question to ask if planetary mass has an influence on some key habitability factors such as on plate tectonics, allowing us to test which exoplanets might be more likely habitable than others, and allowing us to understand if plate tectonics on Earth is a stable or a critical, instable process that could easily be perturbed. Here we present results derived from 1D parameterized thermal evolution and 2D/3D computer models, showing how planetary mass influences the propensity of plate tectonics for planets with masses ranging from 0.1 to 10 Earth masses. Lately [2, 3] studied the effect of planetary mass on the ability to break plates and hence initiate plate tectonics - but both derived results contradictory to the other. We think that one of the reasons why both studies [2, 3] are not acceptable in their current form is partly due to an oversimplification. Both treated viscosity only temperature-dependent but neglected the effect pressure has on enlarging the viscosity in the deep mantle. More massive planets have therefore a stronger pressure-viscosity-coupling making convection at high pressures sluggish or even impossible. For planets larger than two Earth masses we observe that a conductive lid (termed low-lid) forms above the core-mantle boundary and thus reduces the effective convective part of the mantle when including a pressure-dependent term into the viscosity laws as shown in [1]. Moreover [2, 3] use time independent steady state models neglecting the fact that plate tectonics is a

  1. Plate tectonic modelling: virtual reality with GMAP

    NASA Astrophysics Data System (ADS)

    Torsvik, Trond Helge; Smethurst, Mark Andrew

    1999-05-01

    Palaeogeographic reconstructions have been an integral part of global tectonic research since the advent of the plate tectonic paradigm, and GMAP is a state of the art computer program which performs all processing and plotting tasks associated with the generation of palaeogeographic reconstructions and plate tectonic modelling. GMAP is menu-driven and easy to use; the user is never far removed from the basic data from which palaeogeographic reconstructions are derived, and therefore has a sense of total control over the program's performance. GMAP can generate reconstructions based on known Euler rotation data poles or palaeomagnetic poles. The user is also free simply to move continents around on the screen, according to less tangible constraints. GMAP is supplied with a full range of continental outlines. It is also possible to import new continents via simple ASCII files. GMAP is in use at leading institutions world-wide, and has been the work-horse of the EUROPEAN GEOTRAVERSE and EUROPROBE projects.

  2. Laboratory plate tectonics: a new experiment.

    PubMed

    Gans, R F

    1976-03-26

    A "continent" made of a layer of hexagonally packed black polyethylene spheres floating in clear silicon oil breaks into subcontinents when illuminated by an ordinary incandescent light bulb. This experiment may be a useful model of plate tectonics driven by horizontal temperature gradients. Measurements of the spreading rate are made to establish the feasibility of this model.

  3. 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)

  4. Crustal genesis and plate tectonics

    NASA Astrophysics Data System (ADS)

    Yang-shen, Shi; Shu-feng, Yang; Ling-zhi, Guo; Huo-gen, Dong

    1991-02-01

    As a transitional zone between ocean and continent, the continental margins are important accreted belts of the granitic crust. Extensive granitoids of different geological ages and different genetic series occur in the continental margins of southeastern China. The granites in active continental margins of southeast China are divided into two genetic series by present authors as follows:(1) S-type granitoids in the interior of the continental plate; and (2) I-type granitoids in the margin of the continental plate. S-type and I-type granitoids of almost the same geological age are paired and belted in their spatial distribution parallel to the continental margin. These are referred to as "paired granite belts". Granitic continental crust genesis is closely related to the growth of paired granite belts. In Mt. Yunkai of southeastern China, Guangdong province, Early Paleozoic S-type granitoids have been produced as a result of transformation of Cambrian sediments during the processes of metamorphism, migmatization, granitization and remelting. Co-magmatic volcanic rocks are completely lacking in this area. Early Paleozoic I-type granitoids on the east side of Mt. Yunkai are distributed along the ancient continental margin. These rocks co-exist with comagmatic island-arc volcanic rocks of calc-alkaline series in this area. The above mentioned two types of granitoids are paired and belted. Similar paired granite belts exist around the world, such as in North America and southeastern Australia, and are interpreted to be products of post plate convergence, subduction and collision.

  5. 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.

  6. 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

    2016-05-06

    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.

  7. 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

  8. Global Cretaceous plate tectonics and paleogeography

    SciTech Connect

    Barron, E.J.; Beeson, D.; Chen, P.; Dingle, R.V.; Frakes, L.A; Funnell, B.M.; Kauffman, E.G.; Petri, S.; Reyment, R.A.; Riccardi, A.C.

    1985-01-01

    The International Geologic Correlation Program (IGCP) Project 191, The Cretaceous Paleoclimatic Atlas Project has compiled 89 Cretaceous paleogeographic maps representing ten regions or continents. The map resolution varies from stage by stage (e.g. North America, Europe, USSR, Australia) to four maps (e.g. China, Southern South America) to a compilation of localities (Antarctica). The paleogeography is plotted here on global plate tectonic reconstructions for each stage. The reconstructions include continental positions and latitude. In addition, the oceanic plates are reconstructed including bathymetry based on a thermal age-depth relationship. The compiled paleogeography and plate tectonic base maps represent the most comprehensive framework for plotting and analyzing sedimentologic, geochemical and paleontologic data with respect to geography and latitude for the Cretaceous time period.

  9. 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

  10. 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

  11. Lasting mantle scars lead to perennial plate tectonics.

    PubMed

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

    2016-06-10

    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.

  12. 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.

  13. Generation and Initiation of Plate Tectonics on Terrestrail Planets

    NASA Astrophysics Data System (ADS)

    Foley, Bradford J.

    , initial subduction event may help hasten the onset of modern style plate tectonics by drawing excess CO 2 out of the atmosphere and cooling the climate.

  14. 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.

  15. Mars plate tectonics (1) :An Earth prospective

    NASA Astrophysics Data System (ADS)

    Maruyama, S.; Dohm, J.; Baker, V.

    2001-12-01

    We hypothesize the existence of plate tectonism during the embryonic development of Mars, which resulted in the proposed Tharsis superplume (GSA, 2001). Similar to the major influence of superplume on the history of the Earth, we envision the Tharsis superplume to have dominated the geological and climatological history of Mars. Early Noachian plate tectonism is collectively explained by an array of prominent structures and features revealed through Viking-based geological investigations and through the recently acquired high-resolution topographic, imaginary, and geophysical coverage of the Mars Global Surveyor mission. These include: (1) highland-lowland boundary, (2) the Thaumasia highlands mountain range, (3) circular domes among distinct structures of similar trends (e.g., southwest margin of the Thaumasia highland mountain range), interpreted to be andesitic domes associated with subduction zone magma, (e.g., silicic-rich provenances that source andesitic materials to northern plains), and (4) geophysical anomalies such as those identified in the northern plain and regions located to the east-southeast of Hellas basin, interpreted to be the dead spreading centers and probably accreted terrains, respectively. Martian plate tectonism is thought to have continued after the core was frozen, resulting in the death of dynamo, because Mars potential temperature of mantle is expected to be higher than 1500° C, if 34% S-bearing Fe-Ni alloy core was consolidated. In this case, no magnetic stripes would remain in the northern lowland, whereas the proposed southern highland supercontinent that formed during the dynamo would have yielded strong magnetic signatures. For examples EW-trending narrow units with strong remanent magnetism in the southern highland may be accreted oceanic lithosphere. Moreover, the Archean hydrothermal system deposits located along the mid-oceanic ridges on the Earth suggest that the large amounts of carbonate and sulfate are expected to have

  16. Tectonics of oblique plate boundary systems

    NASA Astrophysics Data System (ADS)

    Díaz-Azpiroz, Manuel; Brune, Sascha; Leever, Karen A.; Fernández, Carlos; Czeck, Dyanna M.

    2016-12-01

    The relative displacement between lithospheric plates normally results in obliquely deforming plate boundaries. This is simply caused by the fact that, on plate tectonics basis, irregularly shaped plate boundaries are rarely perpendicular or parallel to small-circle rotation paths, which describe plate motion on a sphere (Fig. 1a). Global current relative plate motions estimated from geological data (DeMets et al., 2010; Argus et al., 2011) and GPS measurements (e.g., Kreemer et al., 2003; Argus et al., 2010) provide insight to the prevalent degrees of obliquity on Earth's surface. Based on these global data sets, Philippon and Corti (2016), statistically show that current orthogonal boundaries (obliquity angle smaller than 10°) represent around 8% of the total boundary length whereas strike-slip boundaries (obliquity angle larger than 80°) are encountered in < 10% of the total boundary length. Therefore, around 80% of active plate boundaries present oblique relative motions. Furthermore, changes in plate kinematics leading to migration or jumps in the rotation poles necessarily cause obliquity along former pure strike-slip or convergent/divergent boundaries (Fig. 1b).

  17. 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.

  18. 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.

  19. 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

  20. Tectonic development of the Maya plate

    SciTech Connect

    Charleston, S.; Concit, S.C.; Sanchez, R.

    1985-01-01

    The Maya Plate is located at the southern margin of the North American Plate, it comprises from north to south, the following tectonic provinces: The Yucatan Platform, (including the lowlands of Peten and the oil-rich offshore platform of the Campeche Bank), the Macuspana basin, the Salt Basin, the NW-SE trending Sierra de Chiapas Folded Belt, the Chiapas depression and the Ciapas Massif. During the past, the deformation of the Maya Plate, have been attributed to the Laramide Orogeny. The present study develops a model based on the interaction between the Maya, Caribbean and the oceanic Cocos-plates, assuming that during the Middle Miocene, the development of the left-lateral Motagua Fault between the Maya and Caribbean plates, displaced the Yucatan Platform in a southwestward direction. It is consider that the combine action of two opposite forces, was responsible for the development of most of the Sierra de Chiapas major anticlines and synclines. Finally the model suggests that these structures, were later affected by trans-compressive forces, originated as a secondary response, due to the development of several left-lateral transcurrent faults, associated with the Polochic Fault System.

  1. 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.

  2. 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.

  3. Learning Plate Tectonics Using a Pre-Analogy Step

    NASA Astrophysics Data System (ADS)

    Glesener, G. B.; Sandoval, W. A.

    2011-12-01

    Previous research has shown that children tend to demonstrate lower performance on analogical reasoning tasks at a causal relations level compared to most adults (Gentner & Toupin, 1986). This tendency is an obstacle that geoscience educators must overcome because of the high frequency of analogies used in geoscience pedagogy. In particular, analog models are used to convey complex systems of non-everyday/non-observable events found in nature, such as plate tectonics. Key factors in successful analogical reasoning that have been suggested by researchers include knowledge of the causal relations in the base analog (Brown & Kane, 1988; Gentner, 1988; Gentner & Toupin, 1986), and development of learning strategies and metaconceptual competence(Brown & Kane, 1988). External factors, such as guiding cues and hints have been useful cognitive supports that help students reason through analogical problems (Gick & Holyoak, 1980). Cognitive supports have been seen by researchers to decrease processing demands on retrieval and working memory (Richland, Zur, & Holyoak, 2007). We observed third and fourth graders learning about plate tectonics beginning with a pre-analogy step-a cognitive support activity a student can do before working with an analogy to understand the target. This activity was designed to aid students in developing their understanding of object attributes and relations within an analog model so that more focus can be placed on mapping the corresponding higher-order relations between the base and target. Students learned targeted concepts of plate tectonics, as measured by pre to post gains on items adapted from the Geosciences Concept Inventory. Analyses of classroom interaction showed that students used the object attributes and higher-order relations highlighted in the pre-analogy activity as resources to reason about plate boundaries and plate movement during earthquakes.

  4. 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.

  5. The integration of palaeogeography and tectonics in refining plate tectonic models: an example from SE Asia

    NASA Astrophysics Data System (ADS)

    Masterton, S. M.; Markwick, P.; Bailiff, R.; Campanile, D.; Edgecombe, E.; Eue, D.; Galsworthy, A.; Wilson, K.

    2012-04-01

    -mechanical events and regional tectonics. These data are interpreted to constrain depositional systems and tectonophysiographic terranes. Palaeotopography and palaeobathymetry are derived from these tectonophysiographic terranes and depositional systems, and are further constrained using geological relationships, thermochronometric data, palaeoaltimetry indicators and modern analogues. Throughout this process, our plate model is iteratively tested against our palaeogeographies and their environmental consequences. Both the plate model and the palaeogeographies are refined until we have obtained a consistent and scientifically robust result. In this presentation we show an example from Southeast Asia, where the plate model complexity and wide variation in hypotheses has huge implications for the palaeogeographic interpretation, which can then be tested using geological observations from well and seismic data. For example, the Khorat Plateau Basin, Northeastern Thailand, comprises a succession of fluvial clastics during the Cretaceous, which include the evaporites of the Maha Sarakham Formation. These have been variously interpreted as indicative of saline lake or marine incursion depositional environments. We show how the feasibility of these different hypotheses is dependent on the regional palaeogeography (whether a marine link is possible), which in turn depends on the underlying plate model. We show two models with widely different environmental consequences. A more robust model that takes into account all these consequences, as well as data, can be defined by iterating through the consequences of the plate model and geological observations.

  6. 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.

  7. 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

  8. 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

  9. 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.

  10. Silurian to Early Carboniferous plate tectonic model of Central Europe

    NASA Astrophysics Data System (ADS)

    Golonka, Jan; Barmuta, Jan; Barmuta, Maria

    2014-05-01

    The presented plate tectonic model focuses on Silurian to Early Carboniferous evolution of Central Europe with special attention given to the Sudetes region (north and north-east part of the Bohemian Massif). During our studies, we tested alternative models focused on the position of the Armorican terranes, known as the Armorican Terrane Assembly (ATA) (e.g.: Matte, 2001) and tried to refine the existing reconstructions, which describe Armorica as an individual continent during the Late Silurian and Devonian (e.g. Lewandowski, 2003, Winchester, 2002). Our plate tectonic model depict that these small blocks were scattered along the northern margin of Gondwana, where they formed the "Armorican Spour" as suggested by Kroner and Romer (2013). The seaways were present between blocks. Because of the north dipping subduction zone along the southern margin of the Laurussia continent the back-arc basin and island arc were formed. The narrowing of the Rheic ocean led to the complicated collision of Gondwana and Laurussia. Three main stages of this event can be distinguished: (1) collision of the Armorican Spour with the Laurussian island arc, (2) back-arc basin closure, (3) final Gondwana and Laurussian collision. Those stages correlate well with Variscan Subduction Zone System proposed by Kroner and Romer (2013). Interactive modeling performed in GPlates, shows that the presented model is valid from kinematic and geometrical point of view. Kroner U., Romer R., L., 2013, Two plates - many subduction zones: the Variscan orogeny reconsidered. Gondwana Research, 24: 298-329. Lewandowski M., 2003, Assembly of Pangea: Combined paleomagnetic and paleoclimatic approach, Advances in Geophysics, 46: 199-236 Matte P., 2001, The Variscan collage and orogeny (480 290 Ma) and the tectonic definition of the Armorica microplate: a review. Terra Nova, 13: 122¨C128. Winchester J., A., The Pace TMR Network Team, 2002, Palaeozoic amalgamation of Central Europe: new results from recent

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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).

  16. 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.

  17. 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

  18. 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.

  19. 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.

  20. 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

  1. Background events in microchannel plates

    NASA Technical Reports Server (NTRS)

    Siegmund, O. H. W.; Vallerga, J.; Wargelin, B.

    1988-01-01

    Measurements have been made to assess the characteristics and origins of background events in microchannel plates (MCPs). An overall background rate of about 0.4 events/sq cm persec has been achieved consistently for MCPs that have been baked and scrubbed. The temperature and gain of the MCPs are found to have no significant effect on the background rate. Detection of 1.46-MeV gamma rays from the MCP glass confirms the presence of K-40, with a concentration of 0.0007 percent, in MCP glass. It is shown that beta decay from K-40 is sufficient to cause the background rate and spectrum observed. Anticoincidence measurements indicate the the background rate caused by cosmic ray interactions is small (less than 0.016 events/sq cm per sec).

  2. 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

  3. 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.

  4. 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.

  5. 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)

  6. Extending Alaska's plate boundary: tectonic tremor generated by Yakutat subduction

    USGS Publications Warehouse

    Wech, Aaron G.

    2016-01-01

    The tectonics of the eastern end of the Alaska-Aleutian subduction zone are complicated by the inclusion of the Yakutat microplate, which is colliding into and subducting beneath continental North America at near-Pacific-plate rates. The interaction among these plates at depth is not well understood, and further east, even less is known about the plate boundary or the source of Wrangell volcanism. The drop-off in Wadati-Benioff zone (WBZ) seismicity could signal the end of the plate boundary, the start of aseismic subduction, or a tear in the downgoing plate. Further compounding the issue is the possible presence of the Wrangell slab, which is faintly outlined by an anemic, eastward-dipping WBZ beneath the Wrangell volcanoes. In this study, I performed a search for tectonic tremor to map slow, plate-boundary slip in south-central Alaska. I identified ∼11,000 tremor epicenters, which continue 85 km east of the inferred Pacific plate edge marked by WBZ seismicity. The tremor zone coincides with the edges of the downgoing Yakutat terrane, and tremors transition from periodic to continuous behavior as they near the aseismic Wrangell slab. I interpret tremor to mark slow, semicontinuous slip occurring at the interface between the Yakutat and North America plates. The slow slip region lengthens the megathrust interface beyond the WBZ and may provide evidence for a connection between the Yakutat slab and the aseismic Wrangell slab.

  7. 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.

  8. 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.

  9. 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

  10. Tectonics of one-plate planets

    SciTech Connect

    Janes, D.M.

    1990-01-01

    A general planetary shell model in spherical coordinates is developed that is capable of treating shells of arbitrary thickness and driving forces of arbitrary breadth. A methodology is then presented for finding the forces exerted on the shell from two processes. A treatment is developed for mantle convection driven by a density anomaly within a viscous mantle. This model is applied to the small moon of Uranus, Miranda, to study the three large coronae which dominate its surface and for which several competing hypotheses were offered, two of which invoked mantle convection driven by density anomalies of opposite sign. A general model is then developed for loading of the lithosphere and the effects of a range of loads breadths and lithosphere thicknesses are examined. The combinations of these two variables are mapped out where classical approximations such as the flat-plate and thin-shell models are applicable as well as the nature and extent of the transition between these two regimes are determined. Finite element modeling is employed to investigate the coronae on Venus, showing that morphological aspects of these features reported in the literature can be produced by flexure of the lithosphere beneath a volcanic load and gravitational sliding of a cooled crust off these volcanic mounds. Independent characteristic topographic profiles are produced for three of the more regular coronae which question how typical the reported morphologies are in the coronae in general.

  11. 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

    2015-02-05

    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.

  12. Mantle Rheology and Plate Tectonics: Damage and Inheritance

    NASA Astrophysics Data System (ADS)

    Ricard, Y. R.; Bercovici, D.; Schubert, G.

    2014-12-01

    The specific rheology of the lithosphere that allows the existence of plate tectonics on Earth is poorly understood. This rheology must explain why plate tectonics initiated on Earth but not on Venus, which has very similar size and gravity, but also how changes in plate motion can occur on time scales more rapid than that of the deeper convection (~100 myrs). We suggest that a key ingredient of this rheology is the coupling of the grain size evolution of the polycrystalline rocks that constitute the mantle, with the flow. We demonstrate this process using a grain evolution and damage mechanism (Bercovici and Ricard, 2012) with a composite rheology, which are compatible with field and laboratory observations. Our model predicts that the grain size is controlled by an dynamic equilibrium where deformation tends to reduce the grain sizes which otherwise would spontaneously increase. The presence of secondary phases is crucial as it eases the grain size reduction and inhibits their too fast recoveries. The resulting time-dependent rheology is non-linear, leads to localisation on time scales much shorter than those of the typical transit time of mantle convection but has also a long healing time. These characteristics of fast damage and long term memory is shown in simple models to spontaneously generate plates on a planet with Earth's parameters. For Venus hotter surface conditions, accumulation and inheritance of damage is negligible; hence only subduction zones survive and plate tectonics does not spread. This rheology also explains how subducting slabs can be rapidly detached when a buoyant crust is drawn into subduction and therefore how rapid plate changes can occur.

  13. 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.

  14. 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.

  15. Plate Tectonics and the Discrimination of Underground Explosions from Earthquakes

    DTIC Science & Technology

    1975-09-01

    insignificant (amounting to as much as 20% of the travel time for media such as plexi - glass ) and, if true, could require important correction of travel time...zones in Europe, Asia and South America, according to recent concepts of plate tectonics. - These models will include factors of focal depth, ray...minimum estimate for the radiated energy is low by a factor of 3-10 with respect to the estimate obtained from energy - magnitude relations for these

  16. 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.

  17. Linking mantle dynamics, plate tectonics and surface processes in the active plate boundary zones of eastern New Guinea (Invited)

    NASA Astrophysics Data System (ADS)

    Baldwin, S.; Moucha, R.; Fitzgerald, P. G.; Hoke, G. D.; Bermudez, M. A.; Webb, L. E.; Braun, J.; Rowley, D. B.; Insel, N.; Abers, G. A.; Wallace, L. M.; Vervoort, J. D.

    2013-12-01

    Eastern New Guinea lies within the rapidly obliquely converging Australian (AUS)- Pacific (PAC) plate boundary zone and is characterized by transient plate boundaries, rapidly rotating microplates and a globally significant geoid high. As the AUS plate moved northward in the Cenozoic, its leading edge has been a zone of subduction and arc accretion. The variety of tectonic settings in this region permits assessment of the complex interplay among mantle dynamics, plate tectonics, and surface processes. Importantly, the timescale of tectonic events (e.g., subduction, (U)HP exhumation, seafloor spreading) are within the valid bounds of mantle convection models. A record of changes in bathymetry and topography are preserved in high standing mountain belts, exhumed extensional gneiss domes and core complexes, uplifted coral terraces, and marine sedimentary basins. Global seismic tomography models indicate accumulation of subducted slabs beneath eastern New Guinea at the bottom of the upper mantle (i.e., <660km depth). Some of the deeply subducted material may indeed be buoyant subducted AUS continental margin (to depths of ~250-300 km), as well as subducted continental material that has reached the point of no return (i.e., > 250-300 km). Preliminary global-scale backward advected mantle convection models, driven by density inferred from joint seismic-geodynamic tomography models, exhibit large-scale flow associated with these subducted slab remnants and predict the timing and magnitude (up to 1500 m) of dynamic topography change (both subsidence and uplift) since the Oligocene. In this talk we will explore the effects of large-scale background mantle flow and plate tectonics on the evolution of topography and bathymetry in eastern New Guinea, and discuss possible mechanisms to explain basin subsidence and surface uplift in the region.

  18. Fluid flow paths and upper plate tectonics at erosional margins

    NASA Astrophysics Data System (ADS)

    Ranero, C. R.; Weinrebe, W.; von Huene, R.; Huguen, C.; Sahling, H.; Bohrmann, G.

    2003-04-01

    An understanding of fluid flow regime and tectonics of convergent margins dominated by subduction erosion processes lags behind that for accretionary margins. Recent seafloor mapping and seismic images along Middle America and North Chile indicate that tectonic processes that pervasively fracture the upper plate across the entire continental slope create a complex hydrological system characterizing erosional margins. The most spectacular fracturing occurs where seamounts underthrust the margin locally uplifting and breaking the upper plate. Fractures concentrate at the summit of the uplift and leave a trail of mass wasting. At the summit, high backscatter energy is coincident with outcrops of authigenic carbonates. Away from the areas of seamount subduction, a pervasive extensional tectonic fabric develops due to collapse of the margin from basal erosion (upper plate material removal along the plate boundary). High resolution bathymetry displays arrays of margin semiparallel normal faults across the middle-upper slope. Associated with the faults groups of mud diapirs pierce through the slope sediment cover and crop out at the seafloor. Photographs and dredging indicate that the mounds are partially covered by chemoherm carbonates and locally chemosynthetic fauna were observed. Seismic data image some of the normal faults cutting from the seafloor to great depths into the upper plate, in some cases perhaps reaching the plate boundary. Thus, mud diapirs and faults might be tapping fluids from that depth. In addition to those areas of focussed fluids flow, positive temperature anomalies over large areas, deduced from depth to Bottom Simulating Reflectors, indicate a diffuse fluid flow. The lower slope is fronted by a small sediment prism (typically 5-15 km wide) constructed from debris wasted from the margin that increases pore pressure along the decollement and facilitates subduction of the incoming sediment. In some cases mass wasting may fill the trench with up to

  19. 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

    , leaving water behind in a rapid flux as the dense material sinks. This event will form a kind of "water catastrophe," and would have the potential to partially melt the upper mantle, to produce a damp asthenosphere, and indeed to encourage convection. These results imply that planets in which perovskite is stable, that is, planets that are larger than Mars, are perhaps more likely to have an early initiation of plate tectonics, and that larger planets may have more violent and near-surface mantle volatile releases during any overturn event.

  20. Lithospheric response to plume- and plate-tectonic interactions

    NASA Astrophysics Data System (ADS)

    Puchkov, V.

    2012-04-01

    Plate movements and deformations of lithosphere are driven mostly by a thermochemical convection in asthenosphere. Contrariwise, plume-tectonic processes result from a larger-scale thermochemical convection in the whole mantle, starting at the core-mantle boundary (CMB) and depending on core-mantle interactions. The plate-tectonic processes affect lithosphere as a whole, dividing it into moving and deforming plates, while the plume-tectonic ones are manifested locally or regionally as LIPs (Large Igneous Provinces) and hot spots. Meeting in the lithosphere, these processes interact, resulting in a series of tectonic effects that deserve a special consideration. 1. It was noted (e.g. Sengor, 2001; Li et al., 2008) that destruction of supercontinents is accompanied by growth of a superplume (LIP) activity within continental territories. Meanwhile, there are cases when a superplume activity is not connected with continents and conversely, superplumes on continents do not necessarily lead to their splitting. According to V. Trubitsyn (2000), the break-up of a supercontinent is a result of a "blanketing effect" of heat accumulation under it, inducing a restructuring of a convection pattern. I suggested that superplumes simply add the heat to this effect, supplying the process with an additional energy and making the break-up of a supercontinent more easy. 2. One more example of a joint action of plate and plume processes is a formation of continental passive margins, that belong to two types: volcanic and avolcanic (Jeffroy,2005; Melankholina, 2008, 2011). Such characteristics of the volcanic type as a high volcanic activity, underplating, presence of specific seaward-dipping reflectors, are the result of an interference of a passive rifting with active plume processes after the break-up of a supercontinent. 3. Another example of a co-operation of plume- and plate tectonic mechanics is well known: it is a formation of time-progressive volcanic chains (Morgan,1971

  1. Extrusional Tectonics at Plate Corner: an Example in Northern Taiwan

    NASA Astrophysics Data System (ADS)

    Lu, C. Y.; Lee, J. C.; Li, Z.; Yeh, C. H.; Lee, C. A.

    2015-12-01

    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 and opening of the Okinawa trough at plate corner.

  2. Mantle convection and plate tectonics on Earth-like exoplanets

    NASA Astrophysics Data System (ADS)

    Sotin, C.; Schubert, G.

    2009-12-01

    The likelihood of plate tectonics on exoplanets larger than Earth can be assessed using either scaling laws or numerical models describing mantle thermal convection. We investigate the parameters which control the ratio of convective driving forces to lithosphere resisting forces. Two papers, Valencia et al. (AstroPhys. J., 670, L45-L48, 2007) and O’Neill and Lenardic (Geophys. Res. Lett., 34, L19204, 2007), came to opposite conclusions based on scaling laws and numerical calculations, respectively. The different assumptions and parameters used in each study are compared. The definition of thermal boundary layer and lithosphere and the use of their characteristics in the scaling laws are clarified. We show that Valencia et al. (2007) overestimate the ratio of driving forces to resistive forces because they infer too large values for both the thickness of the thermal boundary layer and the length of the plate and too small a value for the yield strength. We show that this ratio is so weakly dependent on the size of an Earth-like planet that other parameters such as presence of water, heating per unit mass, upper mantle thickness, etc., may actually determine the occurrence or not of plate tectonics. The numerical calculations of O’Neill and Lenardic (2007) show the importance of 2D simulations for determining the values of the velocity below the lithosphere, the convective stresses, and the plate dimensions. It demonstrates the need for 3D spherical numerical simulations. Their conclusion that super-Earths would not have plate tectonics depends on a number of assumptions including the constancy of heat-flux as a function of planetary size. We present a 3D spherical scaling including the increase of heat flux with the size of a planet showing that larger Earth-like planets would be marginally in the mobile lid convection regime reinforcing our caution that other factors may tip the balance. The present study points out the importance of the distance between

  3. 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.

  4. 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.

  5. 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…

  6. Ordovician-Silurian tectonism in northern California: The Callahan event

    SciTech Connect

    Cotkin, S.J. )

    1992-09-01

    Middle Ordovician to Early Silurian volcanism, plutonism, metamorphism, deformation, and sedimentation in the Yreka and Trinity terranes, eastern Klamath Mountains, northern California, are considered to be related phenomena that occurred in response to an episode of tectonism known as the Callahan event. A diverse array of evidence is used to construct a tectonic model for the Callahan event that involves a subduction zone, a magnetic arc, and a back-arc spreading center, and to show that tectonism likely occurred within the framework of the North American continental margin. Evidence pertaining to subduction polarity is meager, but is consistent with an eastward dip. The Callahan event represents the earliest Phanerozoic convergent-margin tectonic event recognized within the U.S. Cordillera.

  7. 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.

  8. 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.

  9. 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.

  10. 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

  11. 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.

  12. 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.

  13. 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.…

  14. 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.

  15. 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.

  16. 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

  17. 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

  18. Lessons learned while playing with the Arctic plate tectonic puzzle

    NASA Astrophysics Data System (ADS)

    Skogseid, J.; Meisling, K. E.; Miller, E. L.; Nikishin, A. M.

    2013-12-01

    The plate tectonic evolution of the Amerasia Basin in the Arctic Ocean is controversial, and a number of models have been suggested in which the common denominator is that they are all poorly constrained. In general the Canada Basin and the Makarov-Podvodnikov Basin, are separated by the Alpha-Mendeleev Ridge, which has a bathymetric and geophysical signature indicating either over-thickened oceanic crust or magmatically overprinted continental fragments. Both interpretations imply that the ridge has a connection to the High Arctic Large Igneous Province probably associated with a mantle plume emplacement beneath the lithosphere, causing excess magmatism in the region starting at about 125 Ma. It is widely accepted that the ';windshield wiper' model of Lawver et al. (2002) is applicable for the Canada Basin proper, yet it is still debated whether the boundary transform is located close to the Lomonosov Ridge, beneath the Alpha-Mendeleev Ridge, or on the Alaskan side of the Chukchi Borderland and Northwind Ridge. It remains a major uncertainty where large offset regional shear zones required by some models could be hidden beneath the Arctic continental shelves and how they were linked into the South Anhui Paleo-Ocean. The approach taken in this study is to dissect the Chukotka terranes, formed by long-lived compressional tectonism associated with the Pacific subduction system, to explore different scenarios for South Anhui Ocean evolution and consider potential Paleo-Pacific driving mechanisms for Amerasia Basin opening. The Chukotka terranes represent a complex of magmatic and sedimentary units younging towards the subduction zone, thus allowing restoration by ';undocking' them one by one. The remaining elements of the Alaskan and Siberian shelves are subsequently linked to conjugate elements on the North American and Eurasian plates based on correlation of geochemical and stratigraphic ';tie-points'. The study utilizes available geological markers, crustal cross

  19. 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.

  20. The Cariris Velhos tectonic event in Northeast Brazil

    NASA Astrophysics Data System (ADS)

    dos Santos, Edilton José; Van Schmus, William Randall; Kozuch, Marianne; Neves, Benjamim Bley de Brito

    2010-01-01

    The Borborema Province in northeastern South America is a typical Brasiliano-Pan-African branching system of Neoproterozoic orogens that forms part of the Western Gondwana assembly. The province is positioned between the São Luis-West Africa craton to the north and the São Francisco (Congo-Kasai) craton to the south. For this province the main characteristics are (a) its subdivision into five major tectonic domains, bounded mostly by long shear zones, as follows: Médio Coreaú, Ceará Central, Rio Grande do Norte, Transversal, and Southern; (b) the alternation of supracrustal belts with reworked basement inliers (Archean nuclei + Paleoproterozoic belts); and (c) the diversity of granitic plutonism, from Neoproterozoic to Early Cambrian ages, that affect supracrustal rocks as well as basement inliers. Recently, orogenic rock assemblages of early Tonian (1000-920 Ma) orogenic evolution have been recognized, which are restricted to the Transversal and Southern domains of the Province. Within the Transversal Zone, the Alto Pajeú terrane locally includes some remnants of oceanic crust along with island arc and continental arc rock assemblages, but the dominant supracrustal rocks are mature and immature pelitic metasedimentary and metavolcaniclastic rocks. Contiguous and parallel to the Alto Pajeú terrane, the Riacho Gravatá subterrane consists mainly of low-grade metamorphic successions of metarhythmites, some of which are clearly turbiditic in origin, metaconglomerates, and sporadic marbles, along with interbedded metarhyolitic and metadacitic volcanic or metavolcaniclastic rocks. Both terrane and subterrane are cut by syn-contractional intrusive sheets of dominantly peraluminous high-K calc-alkaline, granititic to granodioritic metaplutonic rocks. The geochemical patterns of both supracrustal and intrusive rocks show similarities with associations of mature continental arc volcano-sedimentary sequences, but some subordinate intra-plate characteristics are also

  1. 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

  2. Global Ocean Sedimentation Patterns: Plate Tectonic History Versus Climate Change

    NASA Astrophysics Data System (ADS)

    Goswami, A.; Reynolds, E.; Olson, P.; Hinnov, L. A.; Gnanadesikan, A.

    2014-12-01

    Global sediment data (Whittaker et al., 2013) and carbonate content data (Archer, 1996) allows examination of ocean sedimentation evolution with respect to age of the underlying ocean crust (Müller et al., 2008). From these data, we construct time series of ocean sediment thickness and carbonate deposition rate for the Atlantic, Pacific, and Indian ocean basins for the past 120 Ma. These time series are unique to each basin and reflect an integrated response to plate tectonics and climate change. The goal is to parameterize ocean sedimentation tied to crustal age for paleoclimate studies. For each basin, total sediment thickness and carbonate deposition rate from 0.1 x 0.1 degree cells are binned according to basement crustal age; area-corrected moments (mean, variance, etc.) are calculated for each bin. Segmented linear fits identify trends in present-day carbonate deposition rates and changes in ocean sedimentation from 0 to 120 Ma. In the North and South Atlantic and Indian oceans, mean sediment thickness versus crustal age is well represented by three linear segments, with the slope of each segment increasing with increasing crustal age. However, the transition age between linear segments varies among the three basins. In contrast, mean sediment thickness in the North and South Pacific oceans are numerically smaller and well represented by two linear segments with slopes that decrease with increasing crustal age. These opposing trends are more consistent with the plate tectonic history of each basin being the controlling factor in sedimentation rates, rather than climate change. Unlike total sediment thickness, carbonate deposition rates decrease smoothly with crustal age in all basins, with the primary controls being ocean chemistry and water column depth.References: Archer, D., 1996, Global Biogeochem. Cycles 10, 159-174.Müller, R.D., et al., 2008, Science, 319, 1357-1362.Whittaker, J., et al., 2013, Geochem., Geophys., Geosyst. DOI: 10.1002/ggge.20181

  3. Ever deeper phylogeographies: trees retain the genetic imprint of Tertiary plate tectonics.

    PubMed

    Hampe, Arndt; Petit, Rémy J

    2007-12-01

    Changes in species distributions after the last glacial maximum (c. 18 000 years bp) are beginning to be understood, but information diminishes quickly as one moves further back in time. In this issue of Molecular Ecology, Magri et al. (2007) present the fascinating case of a Mediterranean tree species whose populations preserve the genetic imprints of plate tectonic events that took place between 25 million years and 15 million years ago. The study provides a unique insight into the pace of evolution of trees, which, despite interspecific gene flow, can retain a cohesive species identity over timescales long enough to allow the diversification of entire plant and animal genera.

  4. 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.

  5. 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

  6. Tectonic Fabric of the Cocos Plate and Conjugate Pacific Plate Crust Near Mexico

    NASA Astrophysics Data System (ADS)

    Stock, J. M.

    2014-12-01

    Existing satellite gravity data, along with publicly available single beam bathymetry, multibeam bathymetry, and shipboard and satellite magnetic anomalies were compiled to make an updated map of tectonic features of the Cocos Plate offshore Mexico and the conjugate crust on the Pacific Plate. The area includes the northern Cocos plate as far south as the Tehuantepec Ridge, and Pacific plate crust on both sides of the Mathematician Rise. This thus includes the modern East Pacific Rise (EPR), the submarine rift margins that bound it - Moctezuma and Manzanillo Troughs - and features previously identified such as the Orozco and O'Gorman Fracture Zones near the Middle America Trench (MAT). The goal was to use existing data to evaluate the likely features that may have existed on the now subducted Cocos Plate crust north of the Clarion Fracture Zone-Tehuantepec Ridge. This can then be compared to seismic imaging of the downgoing slab and geochemical variations along the Mexican Volcanic Arc. Bathymetric slopes were computed automatically from multibeam data gridded at 200 m, 300 m, and 400 m pixel size, and processed to remove signals of circular features such as seamounts, and regions of low slope, while emphasizing higher slopes controlled by linear abyssal hill fabric and fracture zones. Tectonic fabrics at all 3 scales are generally similar. In the resulting tectonic fabric map, the domain of modern East Pacific Rise spreading is clearly visible, truncating older fabrics at the Manzanillo Trough on the east and the Moctezuma Trough on the west. The Orozco Fracture Zone lies entirely within the young part of this crustal province and does not reach the Manzanillo Trough or the MAT. Hence, it is not a feature of the downgoing Cocos Plate and should not be used to explain variations in geochemistry of the arc or geometric variations in the subducted plate. A zone of E-W to ENE-WSW oriented abyssal hills and lineated magnetic anomalies in a bathymetric low between the

  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. Initiation of plate tectonics from post-magma ocean thermochemical convection

    NASA Astrophysics Data System (ADS)

    Foley, Bradford J.; Bercovici, David; Elkins-Tanton, Linda T.

    2014-11-01

    Leading theories for the presence of plate tectonics on Earth typically appeal to the role of present day conditions in promoting rheological weakening of the lithosphere. However, it is unknown whether the conditions of the early Earth were favorable for plate tectonics, or any form of subduction, and thus, how subduction begins is unclear. Using physical models based on grain-damage, a grainsize-feedback mechanism capable of producing plate-like mantle convection, we demonstrate that subduction was possible on the Hadean Earth (hereafter referred to as proto-subduction or proto-plate tectonics), that proto-subduction differed from modern day plate tectonics, and that it could initiate rapidly. Scaling laws for convection with grain-damage show that though either higher mantle temperatures or higher surface temperatures lead to slower plates, proto-subduction, with plate speeds of ≈1.75 cm/yr, can still be maintained in the Hadean, even with a CO2 rich primordial atmosphere. Furthermore, when the mantle potential temperature is high (e.g., above ≈2000 K), the mode of subduction switches to a "sluggish subduction" style, where downwellings are drip like and plate boundaries are diffuse. Finally, numerical models of post-magma ocean mantle convection demonstrate that proto-plate tectonics likely initiates within ˜100 Myr of magma ocean solidification, consistent with evidence from Hadean zircons. After the initiation of proto-subduction, non-plate-tectonic "sluggish subduction" prevails, giving way to modern style plate tectonics as both the mantle interior and climate cool. Hadean proto-subduction may hasten the onset of modern plate tectonics by drawing excess CO2 out of the atmosphere and cooling the climate.

  9. How do tectonic plates deform? A case study from eastern Anatolia

    NASA Astrophysics Data System (ADS)

    Schultz, Colin

    2014-05-01

    The theory of plate tectonics, despite all its accomplishments, still has some sizeable gaps. For instance, scientists are not sure whether to treat tectonic plates as rigid elastic slabs or more as viscous wafers overlain by a thin brittle layer. A new study of the Anatolian plate by Cavalié and Jónsson should bring researchers a step closer to settling this debate.

  10. Precambrian plate tectonic setting of Africa from multidimensional discrimination diagrams

    NASA Astrophysics Data System (ADS)

    Verma, Sanjeet K.

    2017-01-01

    New multi-dimensional discrimination diagrams have been used to identify plate tectonic setting of Precambrian terrains. For this work, nine sets of new discriminant-function based multi-dimensional discrimination diagrams were applied for thirteen case studies of Precambrian basic, intermediate and acid magmas from Africa to highlight the application of these diagrams and probability calculations. The applications of these diagrams indicated the following results: For northern Africa: to Wadi Ghadir ophiolite, Egypt indicated an arc setting for Neoproterozoic (746 ± 19 Ma). For South Africa: Zandspruit greenstone and Bulai pluton showed a collision and a transitional continental arc to collision setting at about Mesoarchaean and Neoarchaean (3114 ± 2.3 Ma and 2610-2577 Ma); Mesoproterozoic (1109 ± 0.6 Ma and 1100 Ma) ages for Espungabera and Umkondo sills were consistent with an island arc setting. For eastern Africa, Iramba-Sekenke greenstone belt and Suguti area, Tanzania showed an arc setting for Neoarchaean (2742 ± 27 Ma and 2755 ± 1 Ma). Chila, Bulbul-Kenticha domain, and Werri area indicated a continental arc setting at about Neoproterozoic (800-789 Ma); For western Africa, Sangmelima region and Ebolowa area, southern Cameroon indicated a collision and continental arc setting, respectively for Neoarchaean (∼2800-2900 Ma and 2687-2666 Ma); Finally, Paleoproterozoic (2232-2169 Ma) for Birimian supergroup, southern Ghana a continental arc setting; and Paleoproterozoic (2123-2108 Ma) for Katiola-Marabadiassa, Côte d'Ivoire a transitional continental arc to collision setting. Although there were some inconsistencies in the inferences, most cases showed consistent results of tectonic settings. These inconsistencies may be related to mixed ages, magma mixing, crustal contamination, degree of mantle melting, and mantle versus crustal origin.

  11. 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.

  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

    2016-07-07

    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.

  13. 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.

  14. Mantle convection and plate tectonics: toward an integrated physical and chemical theory

    PubMed

    Tackley

    2000-06-16

    Plate tectonics and convection of the solid, rocky mantle are responsible for transporting heat out of Earth. However, the physics of plate tectonics is poorly understood; other planets do not exhibit it. Recent seismic evidence for convection and mixing throughout the mantle seems at odds with the chemical composition of erupted magmas requiring the presence of several chemically distinct reservoirs within the mantle. There has been rapid progress on these two problems, with the emergence of the first self-consistent models of plate tectonics and mantle convection, along with new geochemical models that may be consistent with seismic and dynamical constraints on mantle structure.

  15. Initiation of plate tectonics from post-magma ocean thermo-chemical convection

    NASA Astrophysics Data System (ADS)

    Foley, B. J.; Bercovici, D. A.

    2013-12-01

    We investigate the initiation of plate tectonics on Earth from scaling laws for plate tectonic style convection with grain-damage, and from numerical models of mantle convection immediately after magma ocean solidification. Using scaling laws for convection with grain-damage we constrain the likelihood of plate tectonics on the early Earth. Both mantle temperature and surface temperature play key roles in how plate speed and heat flow scale, and thus whether plate tectonics would be likely on the early Earth. Specifically either high mantle temperatures or high surface temperatures decrease plate speed because grain-growth (or healing) increases in lithospheric shear zones, causing viscosity to go up in these regions. When applied to the early Earth, we find that while higher mantle temperatures decrease plate speed, it is not enough to shut off plate tectonics; plate speed only decreases by a factor of 2 going from the present day to Hadean mantle temperatures. Surface temperature has a bigger influence as it more directly controls the temperature in lithospheric shear zones; at a Venusian surface temperature plate tectonics can be effectively shut off. Earth's surface temperature in the Hadean is unknown, however, given that Hadean zircons show evidence for liquid water, the surface temperature was lower than that of present day Venus. Even under hot greenhouse conditions plate speeds on the order of 1 cm/yr could exist in the Hadean. Therefore early Earth conditions were favorable for plate tectonics, even with a higher surface temperature, although Hadean plate tectonics would be sluggish (slower plate speed and thicker lithosphere) compared to the present day. We perform numerical convection experiments to constrain the timescales over which plate tectonics would initiate in the early Earth, starting from post-magma ocean conditions. Rapid solidification of the magma ocean leaves behind a solid mantle with a temperature profile following the solidus. There is

  16. 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

  17. [Comment on “Plate tectonics: Scientific revolution or scientific program?” by Jean-Claude Mareschal] Development of plate tectonics theory: The missing piece

    NASA Astrophysics Data System (ADS)

    Doe, Bruce R.

    The recent article by Jean-Claude Mareschal (“Plate Tectonics: Scientific Revolution or Scientific Program?” in Eos, May 19, 1987, p. 529) adds to the interesting literature on the evolution of the theory of plate tectonics. It is curious that an aspect of the general theory that seems to be little considered and mentioned by Mareschal or others who write about the history of development of the theory, but that was vitally important in my own acceptance of the theory, was the discovery of subduction and, to a lesser extent, abduction.

  18. 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)

  19. Tectonic Plate Parameters Estimated in the International Terrestrial Reference Frame ITRF2008 Based on SLR Stations

    NASA Astrophysics Data System (ADS)

    Kraszewska, Katarzyna; Jagoda, Marcin; Rutkowska, Miłosława

    2016-10-01

    This paper concerns an analysis of the accuracy of estimated parameters Ω (Φ, Λ, ω) which define the tectonic plate motions. The study is based on the velocities of station positions published by ITRF2008 for Satellite Laser Ranging (SLR) technique. The Eurasian, African, North American and Australian plates were used in the analysis. Influence of the number and location of stations on the plate surface on estimation accuracy of the tectonic plate motion parameters was discussed. The results were compared with the APKIM 2005 IGN model. In general, a remarkable concurrence agreement between our solutions and the APKIM 2005 model was found.

  20. 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

  1. Cenozoic geological and plate tectonic evolution of SE Asia and the SW Pacific: computer-based reconstructions, model and animations

    NASA Astrophysics Data System (ADS)

    Hall, Robert

    2002-04-01

    A plate tectonic model for the Cenozoic development of the region of SE Asia and the SW Pacific is presented and its implications are discussed. The model is accompanied by computer animations in a variety of formats, which can be viewed on most desktop computers. GPS measurements and present seismicity illustrate the high rates of motions and tectonic complexity of the region, but provide little help in long-term reconstruction. Plate boundaries shifted rapidly in the Cenozoic. During convergence of the major plates, there were numerous important episodes of extension, forming ocean basins and causing subsidence within continental regions, probably driven by subduction. Within eastern Indonesia, New Guinea and the Melanesian arcs, there are multiple Cenozoic sutures, with very short histories compared to most well-known older orogenic belts. They preserve a record of major changes in tectonics, including subduction polarity reversals, elimination of volcanic arcs, changing plate boundaries and extension within an overall contractional setting. Rapid tectonic changes have occurred within periods of less than 5 Ma. Many events would be overlooked or ignored in older orogenic belts, even when evidence is preserved, because high resolution dating is required to identify them, and the inference of almost simultaneous contraction and extension seems contradictory. There were three important periods in regional development: at about 45, 25 and 5 Ma. At these times, plate boundaries and motions changed, probably because of major collision events. The 45 Ma plate reorganisation may be related to India-Asia collision, although some important intra-Pacific events, such as voluminous Eocene boninite magmatism, seem to be older and require other causes. Indentation of Asia by India modified the Asian continent, but there is little indication that India has been the driving force of tectonics in most of SE Asia. The most important Cenozoic plate boundary reorganisation was at

  2. 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.

  3. 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.

  4. Initiation of plate tectonics from post-magma ocean chemical overturn

    NASA Astrophysics Data System (ADS)

    Foley, B. J.; Bercovici, D.; Elkins-Tanton, L. T.

    2011-12-01

    We investigate the initiation of plate tectonics on Earth from thermo-chemical mantle convection after magma ocean solidification. Plate tectonics likely began early in Earth's history, based on Archean arc and back-arc rock assemblages such as greenstone belts. Furthermore, the presence of zircons as early as 4.4 Ga indicates that plate tectonics, or at least some type of surface recycling, was active on Earth soon after magma ocean solidification. However, initiating plate tectonic style surface recycling is extremely difficult. In the modern day Earth weak zones created through plate tectonic processes, such as oceanic fracture zones and dormant spreading ridges, provide nucleation points for new subduction zones, and hence the maintenance of plate tectonics. In the early Earth, prior to plate tectonics, this mechanism is absent. Therefore another process responsible for forming the lithospheric weak zones that are requisite for the initiation of plate tectonics is necessary. We hypothesize that thermo-chemical convection in the mantle immediately following magma ocean solidification will create damaged weak zones before the proto-lithosphere cools and becomes to stiff to sink back into the mantle (i.e. before a stagnant lid forms). We model an initially hot mantle, cooling from the surface such that it undergoes convective instability. We use a damage-grainsize feedback mechanism (referred to as grain-damage) for lithospheric weak zone formation; this mechanism causes lithospheric weakening due to convective stresses, similar to the psuedoplastic yield stress rheology, and allows for dormant weak zones, which psuedoplasticity does not. We also include an initially unstable compositional density profile created by chemical differentiation during magma ocean solidification. Crystal settling at the bottom of the magma ocean, and compaction of melt out of this solid layer, isolates the solidifying mantle from the chemically evolving liquid. As a result, dense

  5. 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.

  6. 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.

  7. 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

  8. Plate tectonics on super-Earths: Equally or more likely than on Earth

    NASA Astrophysics Data System (ADS)

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

    2011-10-01

    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 active plate tectonics like on Earth, or be stagnant lids like on Mars and Venus. The origin of plate tectonics is poorly understood for Earth, likely involving a complex interplay of rheological, compositional, melting and thermal effects, which makes it challenging 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 Byerlee's law dependence on pressure. Because the simplifying assumptions made in developing analytical scalings may not be valid over all parameter ranges, numerical simulations are needed; one numerical study on super-Earths finds that plate tectonics is less likely on a larger planet (O'Neill and Lenardic (2007)), in apparent contradiction of an analytical scaling study (Valencia et al. (2007)). To try and understand this we here present new calculations of yielding-induced plate tectonics as a function of planet size, focusing on the idealized end members of internal heating or basal heating as well as different strength profiles, and compared to analytical scalings. In the present study we model super-Earths as simple scaled up versions of Earth, i.e., assuming constant physical properties, keeping the ratio of core/mantle radii constant and applying the same temperature difference between top/bottom boundaries and the same internal heating rate. Effects that originate outside of the planet, such as tidal forces, meteor impacts and intense surface heating from a nearby star are not considered. We find that for internally-heated convection plate tectonics is equally likely for terrestrial planets of any size, whereas for basally-heated convection plate tectonics becomes more likely with increasing planet size. This is

  9. 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.

  10. 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.

  11. Role of structural heritage and global tectonics events in evolution of Algerian Triassic basin: Tectonic inversion and reservoir distribution

    SciTech Connect

    Boudjema, A.; Tremolieres, P.

    1988-01-01

    Fieldwork and subsurface studies (350 bore holes and more than 100 seismic profiles) show the structural evolution of the Triassic Saharian basin. This evolution is controlled by the successive motions of ancient faults of the Paleozoic basement during the different compressional and distensional tectonic phases. These movements led to some tectonic inversions. Depending on the strike of the faults, the present results correspond to normal throw or reverse throw at the level of hydrocarbon reservoirs. These tectonic phases clearly result from relative motions between African, American, and European lithospheric plates. The Triassic basin, a mobile zone between two rigid shields, constitutes a very good indication of the successive motions. The distribution and the nature of hydrocarbon fields are clearly related to the proximity of the faults, the post-tectonic erosion of a part of the source rocks, the burial and maturation of the organic matter, and the age of structural traps.

  12. Was there a global-scale plate reorganisation event at 100 Ma?

    NASA Astrophysics Data System (ADS)

    Matthews, K. J.; Seton, M.; Müller, R. D.

    2011-12-01

    A plate reorganisation event that occurred at 50 Ma has received much attention due to its association with the well-known bend in the Hawaiian-Emperor seamount chain. We review the major tectonic events that occurred between 110 and 90 Ma and find strong evidence that a plate reorganisation at this time was global in scale, occurred over a period of 3-8 Myr, and may have been more dramatic than the 50 Ma event. While the Hawaiian-Emperor bend is synonymous with the 50 Ma event, prominent fracture zone bends in the Wharton Basin west of Australia record a drastic 50° change in the direction of spreading between Australia and India, and have long been discussed in terms of a mid-Cretaceous plate reorganisation in the Indian Ocean. Yet to-date there has been no attempt at a complete global investigation of this reorganisation to determine its magnitude and continental impact. Key tectonic events in the Atlantic-realm include a major compressional episode in the Antarctic Peninsula, a 75° counter-clockwise rotation of the Antarctic-South American spreading ridge in the Weddell Sea, an increase in spreading rate at the mid-Atlantic ridge, a change in the tectonic regime along the western convergent margin of South America from extensional to compressional, a subduction polarity reversal in the Caribbean, and changes in sedimentation patterns in African basins followed by a kimberlite emplacement pulse. The Indian-Pacific realm records back-arc basin closure, a magmatic pulse and a possible spreading ridge subduction event in the NeoTethys as well as rapid clockwise rotation of the Indian-Antarctic spreading ridge, the termination of long-lived eastern Gondwanaland subduction east of Australia, a swerve of the Pacific plate, a major unconformity in New Zealand, and a change in the geochemistry of igneous rocks in Marie Byrd Land (West Antarctica) signifying a transition from subduction-related to rift-related magmatism. The concentration of tectonic events occurred in

  13. Initiation of plate tectonics from post-magma ocean thermo-chemical convection

    NASA Astrophysics Data System (ADS)

    Foley, B. J.; Bercovici, D.

    2012-12-01

    We investigate the initiation of plate tectonics on Earth from a compositional overturn immediately after magma ocean solidification, and the early maintenance of plate tectonics through thermo-chemical penetrative convection in the Archean mantle. Plate tectonics likely began early in Earth's history based on Archean arc and back-arc rock assemblages such as greenstone belts. Furthermore, the presence of zircons as early as 4.4 Ga indicates that at least some type of surface recycling was active on Earth soon after magma ocean solidification. However, how plate tectonics initiates is unknown. In the modern day Earth weak zones created through plate tectonic processes, such as oceanic fracture zones and dormant spreading ridges, provide nucleation points for new subduction zones, and hence the maintenance of plate tectonics. In the early Earth, prior to plate tectonics, this mechanism is absent. Therefore another process responsible for forming lithospheric weak zones is necessary. We hypothesize that compositional overturn in the mantle immediately following magma ocean solidification will drive lithospheric weakening through grain-damage, and that subsequent penetrative thermo-chemical mantle convection will sustain weak zones in the lithosphere and plate tectonic style mantle convection in the early Earth. We model an initially hot mantle cooling from the surface such that it undergoes convective instability. We use a damage-grainsize feedback mechanism (grain-damage) for lithospheric weak zone formation; this mechanism causes lithospheric weakening due to convective stresses, and allows for dormant weak zones. We also include an initially unstable compositional density profile to account for chemical differentiation during magma ocean solidification. Crystal settling at the bottom of the magma ocean, and compaction of melt out of this solid layer, isolates the solidifying mantle from the chemically evolving liquid. As a result, dense material solidifies last

  14. 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.

  15. 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

  16. 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.

  17. 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.

  18. 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.

  19. 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…

  20. 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…

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. No-Net-Rotation and Indo-Atlantic Hotspot Reference Frames: Towards a New View of Tectonic Plate Motions and Earth Dynamics

    NASA Astrophysics Data System (ADS)

    Quere, S.; Rowley, D.; Forte, A.; Moucha, R.

    2007-12-01

    A new view of plate tectonics coupled to mantle dynamics is emerging from recent paleomagnetic reconstructions of tectonic plate histories obtained in the hotspot and no-net-rotation reference frames. A number of fundamental differences relative to past plate reconstructions have been discerned. Firstly, in previous models the difference between present-day plate motions in the global hotspot and no-net-rotation reference frames consisted of a westward drift of the lithosphere due to the dominant motion of the Pacific plate in the hotspot frame. In contrast, the new plate motion reconstructions based on the Indo-Atlantic hotspot reference frame now show that the present-day global rotation of the lithosphere is mainly in the South-North direction. Second, we find a more than 100% speed-up of the Nazca plate motion at 35 Ma which we have interpreted in terms of a slab avalanche event below the Nazca-South America plate boundary. This may be the first direct geological evidence for a mantle avalanche event occurring at a time which precedes a significant plate reorganisation. Third, the speed-up of the Nazca plate does not appear to be associated with a jump of the East-Pacific rise, therefore this feature may not be completely passive as previously thought. Fourth, the Hawaiian-Emperor bend which was a key element in previous plate reconstruction based on the assumption of a fixed Hawaiian hotspot, can no longer be explained by a change of direction of the Pacific plate and this corroborates recent studies showing a southward motion of the Hawaiian hotspot. Finally, the new Indo-Atlantic hotspot reconstruction of present-day plate motions is significantly different from the one previously established by Gripp and Gordon (1990) and the model appears to be in greater accord with plate motions predicted by seismic tomography-based mantle convection models.

  6. Plate Tectonics as a Far-From-Equilibrium Self-Organized Dissipative System

    NASA Astrophysics Data System (ADS)

    Anderson, D. L.

    2001-12-01

    A fluid above the critical Rayleigh number is far from equilibrium and spontaneously organizes itself into patterns involving the collective motion of large numbers of molecules which are resisted by the viscosity of the fluid. No external template is involved in forming the pattern. In 1928 Pearson showed that Bénard's experiments were driven by variations in surface tension at the top of the fluid and the surface motions drove convection in the fluid. In this case, the surface organized itself AND the underlying fluid. Both internal buoyancy driven flow and flow driven by surface forces can be far-from-equilibrium self-organized open systems that receive energy and matter from the environment. In the Earth, the cold thermal boundary layer at the surface drives plate tectonics and introduces temperature, shear and pressure gradients into the mantle that drive mantle convection. The mantle provides energy and material but may not provide the template. Plate tectonics is therefore a candidate for a far-from-equilibrium dissipative self-organizing system. Alternatively, one could view mantle convection as the self-organized system and the plates as simply the surface manifestation. Lithospheric architecture also imposes lateral temperature gradients onto the mantle which can drive and organize flow. Far-from-equilibrium self-organization requires; an open system, interacting parts, nonlinearities or feedbacks, an outside steady source of energy or matter, multiple possible states and a source of dissipation. In uniform fluids viscosity is the source of dissipation. Sources of dissipation in the plate system include bending, breaking, folding, shearing, tearing, collision and basal drag. These can change rapidly, in contrast to plate driving forces, and introduce the sort of fluctuations that can reorganize far-from-equilibrium systems. Global plate reorganizations can alternatively be thought of as convective overturns of the mantle, or thermal weakening of plates

  7. 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.

  8. Aegean tectonics, a record of slab-overriding plate interactions (Invited)

    NASA Astrophysics Data System (ADS)

    Jolivet, L.; Faccenna, C.; Huet, B.; Lecomte, E.; Labrousse, L.; Denèle, Y.; Le Pourhiet, L.; Lacombe, O.; Burov, E. B.; Meyer, B.; Suc, J.; Popescu, S.; Monié, P.; Philippon, M.; Gueydan, F.; Brun, J.; Paul, A.; Salaün, G.; Armijo, R.

    2010-12-01

    northern Aegean Sea and led to an easier coupling between upper mantle and upper crust, easing the localisation and propagation of the NAF. (7) A comparison between crustal and mantle finite strain suggests that mantle flow due to slab retreat controls the stretching of the crust. Our model involves progressive slab retreat and mantle flow below the overriding plate inducing the observed succession of tectonic episodes with a progressive localisation of extension due to several slab tearing events. There is no paradox in the tectonic history and rheological behaviour of the Aegean lithosphere but an evolution of the kinematic boundary conditions due to slab deformation at depth.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. Mantle Convection, Plate Tectonics, and the Asthenosphere: A Bootstrap Model of the Earth's Internal Dynamics

    NASA Astrophysics Data System (ADS)

    Lenardic, A.; Hoink, T.

    2008-12-01

    Several studies have highlighted the role of a low viscosity asthenosphere in promoting plate-like behavior in mantle convection models. It has also been argued that the asthenosphere is fed by mantle plumes (Phipps- Morgan et al. 1993; Deffeyes 1972) and that the existence of the specific plume types required for this depends on plate subduction (Lenardic and Kaula 1995; Jellinek et al. 2002). Independent of plumes, plate subduction can generate a non-adiabatic temperature gradient which, together with temperature dependent mantle viscosity, leads to a low viscosity near surface region. The above suggests a conceptual model in which the asthenosphere can not be defined solely in terms of material properties but must also be defined in terms of an active process, plate tectonics, which both maintains it and is maintained by it. The bootstrap aspect of the model is its circular causality between plates and the asthenosphere, neither being more fundamental than the other and the existence of each depending on the other. Several of the feedbacks key to the conceptual model will be quantified. The implications for modeling mantle convection in a plate-tectonic mode will also be discussed: 1) A key is to get numerical simulations into the bootstrap mode of operation and this is dependent on assumed initial conditions; 2) The model implies potentially strong hysteresis effects (e.g., transition between convection states, associated with variable yield stress, will occur at different values depending on whether the yield stress is systematically lowered or raised between successive models).

  16. 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.

  17. 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.

  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. 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.

  20. 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.

  1. 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.

  2. Mars Crustal Magnetism: Plate Tectonics and Flood Basalts

    NASA Astrophysics Data System (ADS)

    Connerney, J.; Acuna, M.; Ness, N.

    2006-12-01

    The crustal magnetic field of Mars, mapped in unprecedented detail by the Mars Global Surveyor spacecraft, bears a record of crustal formation and subsequent evolution. The magnetic field in Meridiani has characteristics (transform faulting, symmetry) associated with crustal spreading in the presence of a reversing dynamo. The detailed erasure of crustal fields in and around filled basins (Utopia, Isidis) and massive volcanic constructs (Tharsis Montes, Oylmpus Mons, Alba Patera, Elysium Mons) suggests that the northern plains were largely demagnetized by emplacement of ~km thick flood basalts in single cooling events. Thermal demagnetization under a few km of flood basalts would require that the pre-existing magnetic imprint be borne in a layer only a few km thick. This in turn implies very intense magnetization (order 100 A/m) if the same layer thickness is applied to the intensely magnetized southern highlands. Icelandic basalts are rarely as intensely magnetized, but some samples - characterized by single domain magnetite formed from high temperature oxidation of olivine - approach this number.

  3. 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

  4. 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

  5. The Krafla Magmatic and Tectonic Episode of 1974-1989 at the Divergent Plate Boundary in North Iceland

    NASA Astrophysics Data System (ADS)

    Einarsson, P.; Brandsdottir, B.

    2006-12-01

    The Krafla rifting episode was a sequence of magmatic and tectonic events along the plate boundary in N- Iceland, beginning in 1974 with increased seismicity within the Krafla caldera and lasting until 1989 when inflation of the caldera stopped. The activity was confined to the Krafla volcanic system and adjacent transform zone. The volcanic system consists of a central volcano with associated rift zones that extend for about 100 km along the plate boundary, perpendicular to the plate separation vector. A localized crustal magma chamber has been identified at about 3 km depth within the caldera, both by seismic methods and geodetic location of a source of variable pressure. The chamber sits on top of a 30 km wide intrusive dome extending from the base of the crust at 19 km depth. During most of the episode, magma ascending from depth accumulated in the magma chamber. The inflation periods were punctuated by sudden deflation events lasting from several hours to 3 months when the walls of the chamber were breeched and magma was injected into the adjacent rift zones. A total of about 20 discrete rifting events were identified, each one affecting only a portion of the plate boundary. The course of events was similar in all events, beginning with subsidence and spasmodic tremor in the caldera, followed by earthquakes that migrated away from the caldera into the rift zone. Subsidence within the Krafla caldera was concurrent with rifting. Large-scale extension with surface faulting correlated with regions of intensive seismicity. The rift zone earthquakes stopped at the same time as the deflation of the caldera. Re-inflation of the caldera began immediately following each deflation and rifting event. The rate of re-inflation was highest in the beginning, but gradually diminished with time. This indicates that the pressure difference driving the magma flow to the inflating magma chamber from the reservoir feeding it is highest in the beginning, then diminishing as the

  6. 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.

  7. Tectonics of the Verkhoyansk-Kolyma Mesozoides in the context of plate tectonics

    NASA Astrophysics Data System (ADS)

    Parfenov, L. M.

    1991-12-01

    The Verkhoyansk-Kolyma Mesozoides, located to the northeast of the ancient Siberian platform, form a part of a Mesozoic orogenic belt which lies between the Siberian and North American platforms, the Pacific Ocean and Arctic Ocean. The outer part of the Verkhoyansk-Kolyma Mesozoides is adjacent to the Siberian platform and comprises the Verkhoyansk foldbelt, composed primarily of Carboniferous-Middle Jurassic clastic sequences and lower-middle Paleozoic and Riphean terrigenous-carbonate series deposited on the Siberian passive continental margin. Northeastward, the passivemargin shelf deposits grade into Upper Permian to Lower Jurassic black-shale sequences of the Kular Nera slate belt which formed at a continental rise and in a marginal sea. Thick (up to 8-10 km), largely carbonate Ordovician-Devonian deposits of the Cherskiy, Selennyakh and Ulakhan-Tas ranges lie allochthonously over the Mesozoic and represent formations of the Omulevka carbonate platform. Ophiolites of uncertain age and a serpentinite melange have been tectonically juxtaposed against the latter. The time of emplacement for the Ophiolites is constrained by their occurrence in a Bathonian-Callovian olistostrome. The northeast-trending Alazeya volcanic arc, of Carboniferous to early Jurassic age, is located in the central part of what was once considered as the Kolyma massif. An accretionary wedge associated with the arc is buried beneath Late-Cenozoic deposits and can be traced by a large magnetic anomaly which extends to the south and east. The Omolon and Okhotsk massifs have an Archean granulite basement and are independent microcontinents. The available paleomagnetic data do not allow of the quantitative assessment of the amount ofseparation of the various allochthonous terranes, either from each other or from the Siberian continent. An affinity between Paleozoic and Mesozoic faunas of the Mesozoides and those ofthe Siberian platform indicates that their relative separation did not exceed a few

  8. Filling in the juvenile magmatic gap: Evidence for uninterrupted Paleoproterozoic plate tectonics

    NASA Astrophysics Data System (ADS)

    Partin, C. A.; Bekker, A.; Sylvester, P. J.; Wodicka, N.; Stern, R. A.; Chacko, T.; Heaman, L. M.

    2014-02-01

    Despite several decades of research on growth of the continental crust, it remains unclear whether the production of juvenile continental crust has been continuous or episodic throughout the Precambrian. Models for episodic crustal growth have gained traction recently through compilations of global U-Pb zircon age frequency distributions interpreted to delineate peaks and lulls in crustal growth through geologic time. One such apparent trough in zircon age frequency distributions between ∼2.45 and 2.22 Ga is thought to represent a pause in crustal addition, resulting from a global shutdown of magmatic and tectonic processes. The ∼2.45-2.22 Ga magmatic shutdown model envisions a causal relationship between the cessation of plate tectonics and accumulation of atmospheric oxygen over the same period. Here, we present new coupled U-Pb, Hf, and O isotope data for detrital and magmatic zircon from the western Churchill Province and Trans-Hudson orogen of Canada, covering an area of approximately 1.3 million km2, that demonstrate significant juvenile crustal production during the ∼2.45-2.22 Ga time interval, and thereby argue against the magmatic shutdown hypothesis. Our data is corroborated by literature data showing an extensive 2.22-2.45 Ga record in both detrital and magmatic rocks on every continent, and suggests that the operation of plate tectonics continued throughout the early Paleoproterozoic, while atmospheric oxygen rose over the same time interval. We argue that uninterrupted plate tectonics between ∼2.45 and 2.22 Ga would have contributed to efficient burial of organic matter and sedimentary pyrite, and the consequent rise in atmospheric oxygen documented for this time interval.

  9. New constraints of subducted mantle lithosphere on plate-tectonic reconstructions of deformed continental blocks

    NASA Astrophysics Data System (ADS)

    Suppe, J.; Wu, J.; Kanda, R. V. S.; Lu, R.; Lin, C. D. J.

    2012-04-01

    Global seismic tomography and earthquake locations are now sufficiently good that many subducted slabs can be mapped in 3D, unfolded and restored to the surface of the Earth, thereby providing important new quantitative constraints on plate-tectonic reconstructions. The size, shape, present horizontal and vertical positions and seismic velocities of subducted slabs provide rich data constraints on plate-tectonic reconstructions of past plate networks into which the deformed continental regions such as Eurasia and SE Asia must fit. Commonly, we find that well-imaged and restored slabs of mantle lithosphere fit together along their edges in approximate "picture-puzzle" fashion, within seismic resolution. The slab edges correspond to plate transforms, slab tears, initial positions of trenches and edges of slab windows. This use of subducted slabs provides for more data-rich reconstructions of lost ocean basins such as those consumed between India and Eurasia and between Southeast Asia and Australia, and thereby constrains deformation of the adjacent continents. We describe our methodologies for mapping and unfolding slabs in Gocad, and using these restored slabs in GPlates. Examples are shown from Taiwan, the India-Asia collision, Southeast Asia, and Greater northeast Australia.

  10. 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.

  11. Plate kinematics, origin and tectonic emplacement of supra-subduction ophiolites in SE Asia

    NASA Astrophysics Data System (ADS)

    Pubellier, Manuel; Monnier, Christophe; Maury, René; Tamayo, R.

    2004-11-01

    A unique feature of the Circum Pacific orogenic belts is the occurrence of ophiolitic bodies of various sizes, most of which display petrological and geochemical characteristics typical of supra-subduction zone oceanic crust. In SE Asia, a majority of the ophiolites appear to have originated at convergent margins, and specifically in backarc or island arc settings, which evolved either along the edge of the Sunda (Eurasia) and Australian cratons, or within the Philippine Sea Plate. These ophiolites were later accreted to continental margins during the Tertiary. Because of fast relative plate velocities, tectonic regimes at the active margins of these three plates also changed rapidly. Strain partitioning associated with oblique convergence caused arc-trench systems to move further away from the locus of their accretion. We distinguish "relatively autochthonous ophiolites" resulting from the shortening of marginal basins such as the present-day South China Sea or the Coral Sea, and "highly displaced ophiolites" developed in oblique convergent margins, where they were dismantled, transported and locally severely sheared during final docking. In peri-cratonic mobile belts (i.e. the Philippine Mobile Belt) we find a series of oceanic basins which have been slightly deformed and uplifted. Varying lithologies and geochemical compositions of tectonic units in these basins, as well as their age discrepancies, suggest important displacements along major wrench faults. We have used plate tectonic reconstructions to restore the former backarc basins and island arcs characterized by known petro-geochemical data to their original location and their former tectonic settings. Some of the ophiolites occurring in front of the Sunda plate represent supra-subduction zone basins formed along the Australian Craton margin during the Mesozoic. The Philippine Sea Basin, the Huatung basin south of Taiwan, and composite ophiolitic basements of the Philippines and Halmahera may represent

  12. 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

  13. 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

  14. 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.

  15. 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.

  16. 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.

  17. 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

  18. 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

    tomography. We believe that the ascending of the second generation mantle plumes (thermochemical), enriched in Fe, Ti, P, LREE, etc., was responsible for those changes. Those plumes were generated at the core-mantle boundary in D" layer and this process is active so far. The thermochemical plume matter possessed less density and could reach shallower depths; triggering plate tectonics processes. So, previously absent geochemical-enriched material started to involve from ~2.3 Ga in the Earth’s tectonomagmatic processes. Where such material was “conserved” and how it was activated? The established succession of events could be provided by a combination of two independent factors: (1) the Earth originally was heterogeneous, and (2) the downward heating of the Earth (from the surface to the core) was followed by the cooling of its outer shells. The most evidently cause of the centripetal heating of the Earth was a zone/wave of heat-generating deformation, appeared after it’s accretion completion, which moved inside the planet as a result of acceleration of the body’s rotation around axis due to momentum conservation law as a result of material compaction and it’s radius shortening.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

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

    USGS Publications Warehouse

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

    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.

  4. Characteristic Size of Tectonic Plates: Insights from Boundary Layer Theory with Grain-damage

    NASA Astrophysics Data System (ADS)

    Mulyukova, E.; Bercovici, D.

    2015-12-01

    The dominant degree-2 pattern of mantle convection is a commonly inferred feature from seismological observations (Dziewonski et al., 2010). This pattern is likely associated with large-scale structures like hotspot super-swells and Pacific subduction-zones. The mechanism that dictates this long-wavelength structure is currently a subject of debate. Interestingly, mantle convection models featuring temperature- and depth-dependent viscosity and Earth-like convective vigor typically predict a shorter characteristic wavelength, reflected in the spatial distribution of upwelling plumes and downwellings (Zhong et al., 2000). Plate generating physics is an additional effect that possibly governs the long-wavelength convective pattern; i.e., tectonic plates constitute the top cold thermal boundary layer, subduction of which is the most efficient component of the mantles convective heat transport. To address the effect of plate generation on convective wavelength, we combine a boundary-layer model of mantle convection (Turcotte & Oxburgh, 1967), with the grain-damage model of lithospheric shear-localization (Bercovici & Ricard, 2012). As shown by Solomatov (1995), the strongly temperature-dependent viscosity of Earth materials would render it in the stagnant lid regime of convection, much like what is observed on Venus. Grain-damage allows for self-weakening that remobilizes the lithosphere, making plate like flow possible. Such self-weakening necessarily has an effect on the length of the lithospheric boundary layer and hence convective wavelength. Our simple model thus infers a characteristic size of tectonic plates for a given convective vigor. Superposition of the long convective length-scale, dictated by the cold, stiff, yet damaged and deformable thermal boundary layer, onto the length-scale dictated by convective instability yields a range of material parameters for which the convective pattern is consistent with observations.

  5. 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

  6. 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

  7. Plate tectonics 2.5 billion years ago: evidence at kolar, South India.

    PubMed

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

    1989-03-10

    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 accrted. Amphibolites from the eastern and western sides of the schist belt have distinct incompatible element and isotopic characteristics sugesting that their volcanic protoliths were derived from dint 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.

  8. 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.

  9. Cenozoic Plate tectonic history of the northern Venezuela-Trinidad Area

    NASA Astrophysics Data System (ADS)

    Erlich, Robert N.; Barrett, S. F.

    1990-02-01

    Geological and geophysical data, coupled with recent plate tectonic reconstructions, suggest that the Cenozoic geologic history of the northern Venezuela-Trinidad area has been dominated by strike-slip displacement of discrete crustal blocks. Allochthonous terranes within the area include metavolcanic rocks of the Cretaceous Villa de Cura Group and metamorphic rocks of the Precambrian to Cretaceous Cordillera de la Costa. A relatively competent crustal block (Margarita Block) is defined by an outline around the metamorphic basement of Margarita Island, the Araya/Paria peninsula, the Northern Range of Trinidad, and Tobago Island. Reconstruction of the Margarita Block to its original position requires at least partial closure of the Falcon Basin, closure of the Bonaire and Cariaco basins, and restoration of about 50 km of motion on both the Oca and Bocono faults. Post middle Eocene eastward translation of the Caribbean plate caused eastward motion of the Margarita Block. A minor change in relative plate motion during the late Oligocene or early Miocene produced a right step in the Moron fault, forming the Cariaco pull-apart basin and El Pilar fault zone. Maximum offset on El Pilar fault is estimated to be no more than 125 km, though displacement along the entire fault zone may have been greater. Transpressional stresses between the Caribbean plate and northern South America caused folding of the Serrania del Interior of Venezuela and the Central Range of Trinidad. Eastward migration of transpressional stresses at the southeastern corner of the Caribbean-South American plate boundary is being accommodated by formation of oblique thrusts, transpressive anticlines, and downwarping of the crust. Bouguer gravity data suggest that Jurassic-aged Atlantic oceanic crust is being depressed as the Caribbean plate expands into the Demerara Plateau area. This study suggests that the faults and transtensional/transpressional/compressional structures identified in this study are

  10. 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).

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

    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.

  12. 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.

  13. 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.

  14. Effects of tectonic plate deformation on the geodetic reference frame of Mexico

    NASA Astrophysics Data System (ADS)

    Gonzalez Franco, G. A.; Avalos, D.; Esquivel, R.

    2013-05-01

    Positioning for geodetic applications is commonly determined at one observation epoch, but tectonic drift and tectonic deformation cause the coordinates to be different for any other epoch. Finding the right coordinates at a different epoch from that of the observation time is necessary in Mexico in order to comply the official reference frame, which requires all coordinates to be referred to the standard epoch 2010.0. Available models of horizontal movement in rigid tectonic plates are used to calculate the displacement of coordinates; however for a portion of Mexico these models fail because of miss-modeled regional deformation, decreasing the quality of users' data transformed to the standard epoch. In this work we present the progress achieved in measuring actual horizontal motion towards an improved modeling of horizontal displacements for some regions. Miss-modeled velocities found are as big as 23mm/a, affecting significantly applications like cadastral and geodetic control. Data from a large set of GNSS permanent stations in Mexico is being analyzed to produce the preliminary model of horizontal crustal movement that will be used to minimize distortions of the reference frame.

  15. 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

    Determining the time of the onset of plate tectonics is critical to understanding the geodynamic processes that controlled the evolution of the early Earth. The near absence of Archean ophiolites, as defined by the presence of a residual ultramafic section, has been considered to be one of the primary arguments against Archean plate tectonics. The Andriamena greenstone belt of Madagascar contains massive chromitite bodies consisting of about 90% chromite and about 10% gangue minerals, mostly secondary (talc, green amphibole, orthopyroxene, Ca and Mg carbonate). Numerous observations argue in favor of an ophiolitic origin for these chromitites, including the high Cr# (0.67-0.74), coupled with relatively high Mg# (0.6-0.78) of the constituent chromite. In addition, these phases display extremely low TiO2 contents (<0.25%), which are also characteristic of ophiolites and possibly suggestive of an arc environment. Though in many places the chromitite is in tectonic contact with a variety of unrelated igneous lithologies, remnants of apparently cogenetic ultramafic rock types, including dunites, harzburgites, and some pyroxenites are sometimes immediately juxtaposed with the chromitite. The very high Fo content of the olivine in the associated dunite, as high as 0.95, also attests to an ophiolitic provenance. Platinum group element (PGE) and 187Os/188Os analyses were performed on several chromitite samples. Chondrite normalized PGE spectra display marked depletions in PPGE relative to IPGE, with (Pt/Ir)N ranging from ~0 to 0.09, though Pd contents are somewhat less depleted than those of Pt. The observed PPGE depletion is another feature characteristic of ophiolitic chromitites. The IPGE enrichment is consistent with the presence of laurite microinclusions in the chromite revealed by SEM. Os isotopic compositions are tightly clustered, with 187Os/188Os ranging from 0.1057 to 0.1059, corresponding to TRD model ages of ~ 3.2 Ga, assuming primitive upper mantle parameters

  16. Learning by exploring planets, plate tectonics, and the process of inquiry

    NASA Astrophysics Data System (ADS)

    Bartlett, M. G.

    2006-12-01

    Inquiry-based instruction should be question driven, involve good triggers for learning, emphasize researchable questions, build research skills, provide mechanisms for students to monitor their progress, and draw on the expertise of the instruction to promote inquiry and reflection. At Brigham Young University Hawaii, we have implemented an inquiry based approach to teaching introductory Earth science which provides students with little or no background in the sciences immediate access to participation in current research of genuine scientific interest. An example of this process is presented in which students are engaged in reflecting on whether plate tectonics is a general theory of planetary organization and evolution. Students use topographic, magnetic, spectral, and other data from NASA and ESA missions to determine whether "Earth-style" plate tectonics is functional on planets and moons elsewhere in the solar system. Students are engaged in a data- rich environment from which they must formulate and test multiple hypotheses. Throughout the process, students are engaged in small groups to identify what they need to learn to answer their questions, what resources are available to them, how best to report their findings, and how they can assess the amount of learning that is taking place. Students' responses to the course have been overwhelmingly positive and suggest that many of the students are internalizing the meta-cognitive skills the course is designed to inculcate.

  17. Linking geological evidence from the Eurasian suture zones to a regional Indian Ocean plate tectonic model

    NASA Astrophysics Data System (ADS)

    Gibbons, A.; Aitchison, J.; Müller, R.; Whittaker, J.

    2012-12-01

    We present a revised regional plate tectonic model for the Indian Ocean from the Late Jurassic to present, which assimilates both marine geophysical data constraining the seafloor spreading history as well as a variety of geological observations from the Eurasian collision zone. This model includes relative motion between Greater India, Sri Lanka, West Australia, East Antarctica, East Madagascar, the Seychelles and Argoland, a continental sliver which began migrating towards Eurasia in the Late Jurassic, forming the northern margins of Greater India and western Australia. Recently collected data offshore northwest Australia suggest that the majority of Greater India reached only halfway along the West Australian margin in an Early Mesozoic reconstruction, bounded by the Wallaby-Zenith Fracture Zone. The revised geometries and relative motion histories redefine the timing and nature of collisional events, as well as the history of back-arc basins and intra-oceanic arcs, such as the Kohistan-Ladakh intra-oceanic arc in northwest India and Pakistan. Abundant ophiolites have been identified throughout the Yarlung-Tsangpo Suture Zone, between the Indian-Himalaya and Tibet, several have boninitic compositions and almost all date to either the Mid Jurassic or late Early Cretaceous. Further evidence suggests that an intra-oceanic arc collided with Greater India before colliding with Eurasia. Our model features a transform boundary running north of East Africa, which initiated an oceanic arc following short-lived compression between the western and central Mesotethys in the Late Jurassic, coinciding with the initial motion of Argoland. The arc developed through extension and ophiolite generation until at least the mid-Cretaceous and consumed a narrow thinned sliver of West Argoland between ~120-65 Ma. The arc remained active in the same position until its eventual collision with Greater India ~55 Ma. The eastern portion of the intra-oceanic arc accreted to eastern Eurasia

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. A global-scale plate reorganization event at 105-100 Ma

    NASA Astrophysics Data System (ADS)

    Matthews, Kara J.; Seton, Maria; Müller, R. Dietmar

    2012-11-01

    A major plate reorganization is postulated to have occurred at approximately 100 Ma. However, this reorganization has received limited attention, despite being associated with the most prominent suite of fracture zone bends on the planet and many other geological events. We investigate tectonic events from the period ˜110 to 90 Ma and show that the reorganization occurred between 105 and 100 Ma, was global in scale, and affected all major plates. Seafloor evidence for plate motion changes is abundant during this period, with either fracture zone bends or terminations preserved in all ocean basins. Long-lived eastern Gondwanaland subduction ended along a 7000 km long section of the margin, while elsewhere around the proto-Pacific rim subduction continued and there is evidence that compressional stresses increased in the overriding plates. Thrusting in western North America, transpression and basin inversion in eastern Asia, and development of the present-day Andean-style margin along western South America occurred contemporaneous with the development of an extensional regime in eastern Gondwanaland. Basin instability in Africa and western Europe further demonstrates that lithospheric stress regime changes were widespread at this time. Considering the timing of the reorganization and the nature of associated plate boundary changes, we suggest that eastern Gondwanaland subduction cessation is the most likely driving mechanism for the reorganization. Subduction is the dominant driver of plate motion and therefore this event had the potential to strongly modify the balance of driving forces acting on the plates in the southwestern proto-Pacific and neighboring plates, whereby producing widespread changes in plate motion and continental lithospheric stress patterns. We propose that major changes in ridge-trench interaction triggered the cessation of subduction. The progressive subduction of two closely spaced perpendicular mid ocean ridges at the eastern Gondwanaland

  5. 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

  6. 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.

  7. 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

  8. Miocene-Pliocene transition in the southern Cyprus basins: The sedimentary expression of regional tectonic events

    SciTech Connect

    Orzag-Sperber, F.; Rouchy, J.M. )

    1988-08-01

    In the southern part of Cyprus, a Maastrichtian-Pleistocene sedimentary area fringes Troodos Mountain, a fragment of an ancient crust. During the Neogene, three basins formed in this area: Polemi, Pissouri, and Psematismenos. A deep marine condition has prevailed since the Maastrichtian. During the Paleocene and early Miocene, the sea gradually become shallower until the Messinian, where the most spectacular sedimentary event concerns the deposition of evaporites contemporaneous with other Mediterranean evaporites. Some sedimentary phenomena express the tectonic instability during the upper Miocene. A well-known tectonic event affecting the east Mediterranean region generally referred to as the Miocene-Pliocene phase occurs at the Miocene-Pliocene limit. Recent sedimentological studies indicate this event is in fact complex. The Tortonian-lower Pliocene period is marked by a constraint involving an N20 distension in the Polemi and Pissouri basins and an N100 distension in the Psematismenos basin. Sedimentologic studies have demonstrated three tectonic pulsations during the Messinian prior to the Pliocene transgression. These are expressed by two episodes of seismic brecciation and a paleoemersion indicated by paleosols and detrital discharges. These phenomena suggest brief tectonic instability during the Messinian. Microtectonic studies reveal that the main change in tectonic constraint does not coincide with the Miocene-Pliocene contact but occurs at the top of the lower Pliocene.

  9. 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.

  10. The Tectonic Event of the Cenozoic in the Tasman Area, Western Pacific, and Its Role in Eocene Global Change

    NASA Astrophysics Data System (ADS)

    Collot, J.; Sutherland, R.; Rouillard, P.; Patriat, M.; Roest, W. R.; Bache, F.

    2014-12-01

    . Together, these evidences form a tectonic event, which is manifest as a regional Eocene-Oligocene unconformity, and which is named the "Tectonic Event of the Cenozoic in the Tasman Area" (TECTA). Studying the absolute timing of TECTA and the relative timing of its sub-events will allow to better understand its role and relation to Eocene global change.

  11. 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.

  12. 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

  13. 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.

  14. 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.

  15. 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

  16. 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

    We present an interactive, web-based map utility that can make new geological and geophysical results accessible to a large number and variety of users. The tool provides a user-friendly interface that allows users to access a variety of maps, satellite images, and geophysical data at a range of spatial scales. The map tool, dubbed 'Jules Verne Voyager, Jr.', allows users to interactively create maps of a variety of study areas around the world. The utility was developed in collaboration with the UNAVCO Consortium for study of global-scale tectonic processes. Users can choose from a variety of base maps (including "Face of the Earth" and "Earth at Night" satellite imagery mosaics, global topography, geoid, sea-floor age, strain rate and seismic hazard maps, and others), add a number of geographic and geophysical overlays (coastlines, political boundaries, rivers and lakes, earthquake and volcano locations, stress axes, etc.), and then superimpose both observed and model velocity vectors representing a compilation of 2933 GPS geodetic measurements from around the world. A remarkable characteristic of the geodetic compilation is that users can select from some 21 plates' frames of reference, allowing a visual representation of both 'absolute' plate motion (in a no-net rotation reference frame) and relative motion along all of the world's plate boundaries. The tool allows users to zoom among at least three map scales. The map tool can be viewed at http://jules.unavco.org/VoyagerJr/Earth. A more detailed version of the map utility, developed in conjunction with the EarthScope initiative, focuses on North America geodynamics, and provides more detailed geophysical and geographic information for the United States, Canada, and Mexico. The ‘EarthScope Voyager’ can be accessed at http://jules.unavco.org/VoyagerJr/EarthScope. Because the system uses pre-constructed gif images and overlays, the system can rapidly create and display maps to a large number of users

  17. Education Modules for Teaching About Earthquakes, Volcanoes and Plate Tectonics Using the SEISMIC Computer Program

    NASA Astrophysics Data System (ADS)

    Braile, L. W.; Braile, S. J.

    2002-12-01

    We are developing educational modules for teaching about earthquakes, volcano eruptions and related plate tectonic concepts using an interactive computer program called SEISMIC (written by Alan Jones). The program includes up-to-date earthquake and volcanic eruption catalogs and allows the user to display earthquake and volcanic eruption activity in "speeded up real time" on global, regional or local maps that also show the topography of the area in a shaded relief map image. SEISMIC is an interactive program that includes a number of tools that allow the user to analyze earthquake and volcanic eruption data and produce effective displays to illustrate seismicity and volcano patterns. The program can be used to sort data and provide results for statistical analysis, to generate detailed earthquake and volcano activity maps of specific areas or for specific purposes, to investigate earthquake sequences such as foreshocks and aftershocks, and to produce cross section or 3-D perspective views of earthquake locations. The program can be a powerful and effective tool for teaching about plate tectonics and geologic hazards using earthquake and volcano locations, and for learning (or practicing) fundamental science skills such as statistical analysis, graphing, and map skills. The teaching modules describe and illustrate how to use the SEISMIC program effectively in demonstrations, classroom presentations and interactive presentations, and independent study/research. Because the program has many useful options and can be used to examine earthquake activity and volcanic eruption data, the modules provide instructions and examples of quantitative analysis, graphing of results, creating useful maps and cross section diagrams, and performing in-depth exploration and research. The program and the teaching modules can be used effectively middle school, secondary school and college classes.

  18. Impact-related Events on Active Tectonic Regions Defined by Its Age, Shocked Minerals and Compositions

    NASA Astrophysics Data System (ADS)

    Miura, Y.; Hirota, A.; Gorton, M.; Kedves, M.

    2002-03-01

    New type of impact-related event is defined at active tectonic region by using semi-circular structure, bulk XRF compositions with mixed data, shocked quartz grains with the PDFs texture, and Fe-Ni content. Example is discussed in Takamatsu MKT crater in Japan.

  19. Tectonic Events May Have Triggered the Cambrian Explosion

    NASA Astrophysics Data System (ADS)

    Wendel, JoAnna

    2014-11-01

    Major geological changes causing sea level rise at the start of the Cambrian period (540-490 million years ago) could have kick-started the Cambrian Explosion—a geological time period when most major phyla of life suddenly appeared in the fossil record. A paper published in the November issue of Geology (doi:10.1130/G35886.1) proposes a new geological mechanism for this event.

  20. 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.

  1. 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.

  2. Tectonic stress state in NE Japan as part of the Okhotsk plate

    NASA Astrophysics Data System (ADS)

    Altis, Sungat

    2001-09-01

    An existing geodetic flow velocity model, obtained by using an internal free network adjustment technique, is used to derive estimates for various strain rates parameters in NE Japan. The greatest shortening rates of the principal strains, trending ˜E-W, are located in regions where much steady, internal, frame-invariant plastic flow deformation is observed to be taking place. The internal geodetic adjustment technique yielded the internal deformation in the Tohoku arc; most of the intraplate deformations, including the much folding deformations observed in the inner zone, are produced from within. An interseismic transient elastic loading at a strongly coupled/locked Japan trench would not be needed. The observed ongoing extensive ductile folding deformation in the inner zone of Tohoku may mean that the geodetic strain rates, causing shortening at ˜2-3 cm/yr, probably reflect the more correct level of the deformation, which is steady/permanent, in NE Japan as compared with seismic/faulting data, which indicate ˜0.5 cm/yr shortening. The calculated principal strain rates are used to make an interpretation for the origin of the deviatoric principal stresses within the greater regional plate tectonic framework. The tectonic stress state in NE Japan, as part of the Okhotsk plate, could mostly be influenced by the Okhotsk plate, which is extruding southward to lessen the significant accumulated contractional deformation in NE Asia in the Verkhoyansk-Cherskii mountains. The principal strain rates are ˜N-S extensional essentially everywhere in NE Japan, as a result of the southerly extrusion, except in its southernmost leading edge, in the Uetsu/Fossa Magna province, where the Japan Alps rampart rises in front of the extrusion. Here an ˜E-W compressional stress state prevails. A second ˜E-W contractional zone is found in north-central Tohoku, extending from the Sanriku province in the outer zone to the inner zone in the Japan Sea side, being more prevalent in the

  3. Characteristics of the Cenozoic crustal deformations in SE Korea and its vicinity due to major tectonic events

    NASA Astrophysics Data System (ADS)

    Son, M.; Kim, J.; Song, C.; Sohn, Y.; Kim, I.

    2010-12-01

    The southeastern Korean Peninsula has experienced multiple crustal deformations according to changes of global tectonic setting during the Cenozoic. Characteristics of the crustal deformations in relation to major Cenozoic tectonic events are summarized as follows. (1) Collision of Indian and Eurasian continents and abrupt change of movement direction of the Pacific plate (50 ~ 43 Ma): The collision of Indian and Eurasian continents caused the eastward extrusion of East Asia block as a trench-rollback, and then the movement direction of the Pacific plate was abruptly changed from NNW to WNW. As a result, the strong suction-force along the plate boundary produced a tensional stress field trending EW or WNW-ESE in southeastern Korea, which resultantly induced the passive intrusion of NS or NNE trending mafic dike swarm pervasively. (2) Opening of the East Sea (25 ~ 16 Ma): The NS or NNW-SSE trending opening of the East Sea generated a dextral shear stress regime trending NNW-SSE along the eastern coast line of the Korean Peninsula. As a result, pull-apart basins were developed in right bending and overstepping parts along major dextral strike slip faults trending NNW-SSE in southeastern Korea. The basins can be divided into two types on the basis of geometry and kinematics: Parallelogram-shaped basin (rhombochasm) and wedged-shaped basin (sphenochasm), respectively. At that time, the basins and adjacent basement blocks experienced clockwise rotation and northwestward tilting, and the eastward propagating rifting also occurred. At about 17 Ma, the Yeonil Tectonic Line, which is the westernmost border fault of the Miocene crustal deformation in southeastern Korea, began to move as a major dextral strike slip fault. (3) Clockwise rotation of southeastern Japan Island (16~15 Ma): The collision of the Izu-Bonin Arc and southeastern Japan Island, as a result of northward movement of the Philippine sea-plate, induced the clockwise rotation of southeastern Japan Islands. The

  4. 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

  5. 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

  6. 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.

  7. 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.

  8. 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.

  9. Meso-Cenozoic intraplate contraction in Central and Western Europe: a unique tectonic event?

    NASA Astrophysics Data System (ADS)

    Kley, Jonas; Jähne, Fabian; Malz, Alexander

    2014-05-01

    From the British Isles to Poland, Europe experienced contractional deformation in Late Cretaceous and Paleogene time. The closest contemporaneous plate margins were the incipient Mid-Atlantic rift in the west and northwest, and the Mediterranean system of subduction zones in the south. Each of these plate margins was located more than 1000 km away from the site of deformation. This tectonic event thus represents an outstanding example of large-scale intraplate shortening and may serve as a template for comparison with modern examples. Its effects are seen in a ca. 500 km wide strip that stretches in NW-SE-direction along the Tornquist Line, a regional fault zone separating thick lithosphere of the Baltic Shield from much thinner lithosphere to the southwest. Most faults and folds also trend NW-SE, but some are linked by large N-S-striking transfer zones. In the southeast, the shortening structures are truncated by the Neogene Carpathian thrust front; their original extent is unknown. In the west, the fault zones fan out into more northerly trends in the Central North Sea and more easterly trends in the Channel area before dying out on the shelf. Late Cretaceous (ca. 90-70 Ma) shortening dominates from Poland to the North Sea, while the main shortening event in Southern Britain is of Paleogene age. Many Late Cretaceous to Paleogene structures have been conditioned by Permian or Triassic through Early Cretaceous extensional faulting, whereas some large basement uplifts and reverse faults have no demonstrable inheritance from earlier extension. The thick, mobile Zechstein salt has modified extensional and contractional structures, but both extend beyond its depositional borders. Even where thick evaporates underlie the Mesozoic sedimentary cover, the basement is typically involved in the deformation, except for localized thin-skinned imbricate thrusting and salt-cored anticlines. Different structural styles do not appear to correlate with the magnitude of shortening

  10. Time variability in Cenozoic reconstructions of mantle heat flow: plate tectonic cycles and implications for Earth's thermal evolution.

    PubMed

    Loyd, S J; Becker, T W; Conrad, C P; Lithgow-Bertelloni, C; Corsetti, F A

    2007-09-04

    The thermal evolution of Earth is governed by the rate of secular cooling and the amount of radiogenic heating. If mantle heat sources are known, surface heat flow at different times may be used to deduce the efficiency of convective cooling and ultimately the temporal character of plate tectonics. We estimate global heat flow from 65 Ma to the present using seafloor age reconstructions and a modified half-space cooling model, and we find that heat flow has decreased by approximately 0.15% every million years during the Cenozoic. By examining geometric trends in plate reconstructions since 120 Ma, we show that the reduction in heat flow is due to a decrease in the area of ridge-proximal oceanic crust. Even accounting for uncertainties in plate reconstructions, the rate of heat flow decrease is an order of magnitude faster than estimates based on smooth, parameterized cooling models. This implies that heat flow experiences short-term fluctuations associated with plate tectonic cyclicity. Continental separation does not appear to directly control convective wavelengths, but rather indirectly affects how oceanic plate systems adjust to accommodate global heat transport. Given that today's heat flow may be unusually low, secular cooling rates estimated from present-day values will tend to underestimate the average cooling rate. Thus, a mechanism that causes less efficient tectonic heat transport at higher temperatures may be required to prevent an unreasonably hot mantle in the recent past.

  11. Time variability in Cenozoic reconstructions of mantle heat flow: Plate tectonic cycles and implications for Earth's thermal evolution

    PubMed Central

    Loyd, S. J.; Becker, T. W.; Conrad, C. P.; Lithgow-Bertelloni, C.; Corsetti, F. A.

    2007-01-01

    The thermal evolution of Earth is governed by the rate of secular cooling and the amount of radiogenic heating. If mantle heat sources are known, surface heat flow at different times may be used to deduce the efficiency of convective cooling and ultimately the temporal character of plate tectonics. We estimate global heat flow from 65 Ma to the present using seafloor age reconstructions and a modified half-space cooling model, and we find that heat flow has decreased by ∼0.15% every million years during the Cenozoic. By examining geometric trends in plate reconstructions since 120 Ma, we show that the reduction in heat flow is due to a decrease in the area of ridge-proximal oceanic crust. Even accounting for uncertainties in plate reconstructions, the rate of heat flow decrease is an order of magnitude faster than estimates based on smooth, parameterized cooling models. This implies that heat flow experiences short-term fluctuations associated with plate tectonic cyclicity. Continental separation does not appear to directly control convective wavelengths, but rather indirectly affects how oceanic plate systems adjust to accommodate global heat transport. Given that today's heat flow may be unusually low, secular cooling rates estimated from present-day values will tend to underestimate the average cooling rate. Thus, a mechanism that causes less efficient tectonic heat transport at higher temperatures may be required to prevent an unreasonably hot mantle in the recent past. PMID:17720806

  12. 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.

  13. 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

  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.

  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; 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.

  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. Simulation of gas hydrate dissociation caused by repeated tectonic uplift events

    NASA Astrophysics Data System (ADS)

    Goto, Shusaku; Matsubayashi, Osamu; Nagakubo, Sadao

    2016-05-01

    Gas hydrate dissociation by tectonic uplift is often used to explain geologic and geophysical phenomena, such as hydrate accumulation probably caused by hydrate recycling and the occurrence of double bottom-simulating reflectors in tectonically active areas. However, little is known of gas hydrate dissociation resulting from tectonic uplift. This study investigates gas hydrate dissociation in marine sediments caused by repeated tectonic uplift events using a numerical model incorporating the latent heat of gas hydrate dissociation. The simulations showed that tectonic uplift causes upward movement of some depth interval of hydrate-bearing sediment immediately above the base of gas hydrate stability (BGHS) to the gas hydrate instability zone because the sediment initially maintains its temperature: in that interval, gas hydrate dissociates while absorbing heat; consequently, the temperature of the interval decreases to that of the hydrate stability boundary at that depth. Until the next uplift event, endothermic gas hydrate dissociation proceeds at the BGHS using heat mainly supplied from the sediment around the BGHS, lowering the temperature of that sediment. The cumulative effects of these two endothermic gas hydrate dissociations caused by repeated uplift events lower the sediment temperature around the BGHS, suggesting that in a marine area in which sediment with a highly concentrated hydrate-bearing layer just above the BGHS has been frequently uplifted, the endothermic gas hydrate dissociation produces a gradual decrease in thermal gradient from the seafloor to the BGHS. Sensitivity analysis for model parameters showed that water depth, amount of uplift, gas hydrate saturation, and basal heat flow strongly influence the gas hydrate dissociation rate and sediment temperature around the BGHS.

  18. Plate Tectonics Constrained by Evidence-Based Magmatic Temperatures and Phase Relations of Fertile Lherzolite (Invited)

    NASA Astrophysics Data System (ADS)

    Green, D. H.; Falloon, T.

    2010-12-01

    In order to understand Earth’s plate tectonics we must interpret the most direct probes for mantle composition and temperature distribution i.e. the primitive basaltic magmas and peridotites representing partial melts and mantle residues. An evidence-based approach to identification of parental magmas and determination of their temperatures requires glass and phenocryst compositions and experimentally calibrated Fe/Mg partitioning between olivine and melt. We have compared magmatic crystallization temperatures between ‘hot-spot’(proposed to be plume-related) and normal mid-ocean ridge basalt (MORB) parental liquids, by examining three representative magmatic suites from both ocean island (Hawaii, Iceland, and Réunion) and mid-ocean ridge settings (Cocos-Nazca, East Pacific Rise, and Mid-Atlantic Ridge). We have glass and olivine phenocryst compositions, including volatile (H2O) contents, and have calculated parental liquid compositions at 0.2GPa by incrementally adding olivine back into the glass compositions until a liquid in equilibrium with the most-magnesian olivine phenocryst composition is obtained. The results of these calculations demonstrate that there is very little difference (maximum of ~20°C) between the ranges of crystallization temperatures of the parental liquids (MORB:1243-1351°C versus OIB:1286-1372°C) when volatile contents are taken into account. However while lacking temperature contrast, the source regions for ‘hot-spot’ parental magmas contain geochemical signatures of old subducted crust/lithosphere. The mantle depths of origin determined for both the MORB and OIB suites are similar (MORB:1-2 GPa; OIB:1-2.5 GPa). Calculations of mantle potential temperatures (Tp) are model dependent, particularly to melt fraction from an inferred source. Assuming similar fertile lherzolite sources, the differences in Tp values between the hottest MORB and the hottest ocean island tholeiite sources are ~80°C. These differences disappear if the

  19. 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

  20. Tectonic events recorded in the sediments and crust of the Caribbean sea floor

    SciTech Connect

    Holcombe, T.L.

    1985-01-01

    A reconnaissance review of reflection-seismic sections from the Caribbean, together with limited information derived from dredged rocks, sediment cores, and drillholes, yields or contributes to first-order conclusions regarding the tectonic history of the water-covered Caribbean. Broadly speaking, tectonic episodes for which there is some evidence are: (1) late Cenozoic convergence and accretion along deformed continental or island margins off Panama, Colombia/Venezuela, and Hispaniola/Puerto Rico; (2) late Cenozoic generation of oceanic crust within the Cayman Trough; (3) late Cenozoic secondary deformation along the Caribbean-North American plate boundary zone, in the form of small pull-apart basins, transcurrent faults, tensional rift basins, and compressional features; (4) late Cenozoic slow disintegration of the western part of the Caribbean plate; (5) Cenozoic rift-basin formation on the upper Nicaraguan rise; (6) early Cenozoic or late Cretaceous opening of the Yucatan Basin; (7) late Cretaceous through early Cenozoic island arc formation; and (8) late Cretaceous and earlier emplacement of flow basalts in the northwestern Venezuelan Basin and possibly beneath large areas of the Caribbean. There is no evidence that except along their active margins, the Venezuelan Basin, Beata Ridge, Colombian Basin, and Nicaraguan rise areas have been sites for large-scale relative movements which created or destroyed plate material since late Cretaceous time - or earlier.

  1. 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

  2. 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.

  3. Upper plate deformation and seismic barrier in front of Nazca subduction zone: The Chololo Fault System and active tectonics along the Coastal Cordillera, southern Peru

    NASA Astrophysics Data System (ADS)

    Audin, Laurence; Lacan, Pierre; Tavera, Hernando; Bondoux, Francis

    2008-11-01

    The South America plate boundary is one of the most active subduction zone. The recent Mw = 8.4 Arequipa 2001 earthquake ruptured the subduction plane toward the south over 400 km and stopped abruptly on the Ilo Peninsula. In this exact region, the subduction seismic crisis induced the reactivation of continental fault systems in the coastal area. We studied the main reactivated fault system that trends perpendicular to the trench by detailed mapping of fault related-geomorphic features. Also, at a longer time scale, a recurrent Quaternary transtensive tectonic activity of the CFS is expressed by offset river gullies and alluvial fans. The presence of such extensional fault systems trending orthogonal to the trench along the Coastal Cordillera in southern Peru is interpreted to reflect a strong coupling between the two plates. In this particular case, stress transfer to the upper plate, at least along the coastal fringe, appears to have induced crustal seismic events that were initiated mainly during and after the 2001 earthquake. The seafloor roughness of the subducting plate is usually thought to be a cause of segmentation along subduction zones. However, after comparing and discussing the role of inherited structures within the upper plate to the subduction zone segmentation in southern Peru, we suggest that the continental structure itself may exert some feedback control on the segmentation of the subduction zone and thus participate to define the rupture pattern of major subduction earthquakes along the southern Peru continental margin.

  4. Is a 50 Ma Event Recorded in the Absolute Plate Motion of Africa?

    NASA Astrophysics Data System (ADS)

    Maher, S. M.; Wessel, P.; Müller, R.; Harada, Y.

    2012-12-01

    There is considerable evidence for a global plate tectonic reorganization at ~Chron 21, as suggested by observed changes in global relative plate motion (RPM). The timings of these events appear to coincide with the age of the Hawaiian Emperor Bend (HEB), i.e., ~47-50 Ma. This 120° bend has traditionally been the poster child for the fixed hotspot hypothesis, suggesting the Pacific plate underwent a change in absolute plate motion (APM) as it moved over a more or less stationary Hawaiian hotspot. However, palaeomagnetic evidence favors southward motion of the Hawaii hotspot during the Emperor stage, limiting the amount of APM change required. In the Indo-Atlantic realm, RPMs involving Africa all seem compatible with a change in Africa APM around ~50 Ma. If this global plate reorganization took place there should also be physical evidence on the Africa plate itself due to the change in Africa APM. A candidate for such evidence may be the Réunion-Mascarene bend, which exhibits many HEB-like features. However, the Réunion hotspot also created the Chagos-Laccadive ridge as it encountered (and later crossed) the Carlsberg Ridge, and the oldest Mascarene section closest to the Seychelles may be continental in origin; thus there is some uncertainty in how to interpret the geometry. Furthermore, published APM models have had difficulty modeling this abrupt change in orientation. To reexamine this problem we derived a new Africa APM model that goes back to ~65 Ma using the Hybrid Polygonal Finite Rotation Method. The modeling incorporates the geometry and ages of seamount chains on the Africa plate and their associated hotspots as suitable constraints on an Africa APM model. The present as well as earlier positions of hotspots can be adjusted to get the best fit for the model. We examine how models with or without a ~50 Ma bend satisfy the geometries and age progressions of hotspot chains on the Africa plate and how well the predictions match observed paleolatitudes.

  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. Nature of ophiolite occurrences along the eastern margin of the Indian plate and their tectonic significance

    NASA Astrophysics Data System (ADS)

    Sengupta, S.; Ray, K. K.; Acharyya, S. K.; de Smeth, J. B.

    1990-05-01

    Upper Mesozoic to lower Eocene ophiolitic rocks occur in two parallel belts along the eastern margin of the Indian plate. The eastern belt passes through central Burma, Sumatra, and Java, and coincides with a zone of gravity highs resulting from steeply dipping mafic rocks. It denotes the locus of the subduction where these ophiolites were accreted just prior to middle Eocene time. In contrast, the western belt, which passes through Nagaland, Manipur, western Burma, and Andaman, is flanked to the east by a negative gravity anomaly zone. In it the ophiolites occur as rootless, subhorizontal bodies, tectonically overlying Eocene-Oligocene flysch sedimentary rocks. They are inferred to be nappes that propagated westward from the eastern belt during late Oligocene terminal collision of the Indian and Eurasian continental blocks. Ophiolite occurrences in Andaman and Mentawai islands belonging to the western belt are generally linked with active subduction west of the island arc. This subduction began only in late Miocene time, and thus it could not have produced the ophiolites, which had been emplaced on land much earlier.

  7. Effect of Rheology on Mantle Dynamics and Plate Tectonics in Super-Earths

    NASA Astrophysics Data System (ADS)

    Tackley, P. J.; Ammann, M. W.; Brodholt, J. P.; Dobson, D. P.; Valencia, D. C.

    2011-12-01

    The discovery of extra-solar "super-Earth" planets with sizes up to twice that of Earth has prompted interest in their possible lithosphere and mantle dynamics and evolution. Simple scalings [1,2] suggest that super-Earths are more likely than an equivalent Earth-sized planet to be undergoing plate tectonics. Generally, viscosity and thermal conductivity increase with pressure while thermal expansivity decreases, resulting in lower convective vigor in the deep mantle, which, if extralopated to the largest super-Earths might, according to conventional thinking, result a very low effective Rayleigh number in their deep mantles and possibly no convection there. Here we evaluate this. (i) As the mantle of a super-Earth is made mostly of post-perovskite we here extend the density functional theory (DFT) calculations of post-perovskite activation enthalpy of [3] to a pressure of 1 TPa. The activation volume for diffusion creep becomes very low at very high pressure, but nevertheless for the largest super-Earths the viscosity along an adiabat may approach 10^30 Pa s in the deep mantle, which would be too high for convection. (ii) We use these DFT-calculated values in numerical simulations of mantle convection and lithosphere dynamics of planets with up to ten Earth masses. The models assume a compressible mantle including depth-dependence of material properties and plastic yielding induced plate-like lithospheric behavior, solved using StagYY [4]. Results confirm the likelihood of plate tectonics and show a novel self-regulation of deep mantle temperature. The deep mantle is not adiabatic; instead internal heating raises the temperature until the viscosity is low enough to facilitate convective loss of the radiogenic heat, which results in a super-adiabatic temperature profile and a viscosity increase with depth of no more than ~3 orders of magnitude, regardless of what is calculated for an adiabat. It has recently been argued [5] that at very high pressures, deformation

  8. Mesozoic and Cenozoic plate tectonics in the High Arctic: new 2D seismic data and geodynamic models

    NASA Astrophysics Data System (ADS)

    Nikishin, Anatoly; Kazmin, Yuriy; Glumov, Ivan; Petrov, Eugene; Poselov, Viktor; Burov, Evgueni; Gaina, Carmen

    2014-05-01

    Our paper is mainly based on the interpretation of 2D seismic lines, obtained from Arctic-2001 and Arctic-2012 projects. We also analyzed all available open-source data concerning Arctic geology. Three domains are distinguished in the abyssal part of Arctic Ocean: (1) Canada Basin, (2) Lomonosov-Podvodnikov-Alpha-Mendeleev-Nautilus-Chukchi Plateau (LPAMNCP) area, (3) Eurasia Basin. Canada Basin has oceanic and transitional crust of different structure. The formation time of this oceanic basin is probably 134-117 Ma. New seismic data for LPAMNCP area shows numerous rift structures parallel to the Lomonosov Ridge and Mendeleev Ridge. These rift structures are also nearly orthogonal to the Canada Basin spreading axis, and this may indicate either a different mechanism for the formation of the LPAMNCP region and Canada Basin, or a very complicated basin architecture formed by processes we do not yet understand. We also observe at the base of the LPAMNCP area sedimentary cover packages of bright reflectors, they were interpreted as basalt flows probably related to the Cretaceous plume volcanism. Approximate time of the volcanism is about 125 Ma. After this event, the area experienced stretching and transtension as documented by large scale rifting structures. The younger Eurasian Basin has oceanic crust of Eocene to Recent age, and our new seismic data confirms that Gakkel Ridge has typical ultraslow-spreading zone topography. Perhaps, Eurasia Basin crust was partly formed by exhumed and serpentinized mantle. Lomonosov and Alpha-Mendeleev Ridges has typical present-day basin and range topography with Oligocene to Recent faults. It means, that all LPAMNCP area was subjected to regional intra-plate stretching during Neogene to Recent time. We assume, that this intra-plate stretching was related to the Gakkel Ridge extension. We suppose, that the deep-water part of Arctic Ocean was formed during three main stages: (1) Valanginian - Early Aptian: formation of Canada Basin

  9. Biogeographical consequences of Cenozoic tectonic events within East Asian margins: a case study of Hynobius biogeography.

    PubMed

    Li, Jun; Fu, Cuizhang; Lei, Guangchun

    2011-01-01

    Few studies have explored the role of Cenozoic tectonic evolution in shaping patterns and processes of extant animal distributions within East Asian margins. We select Hynobius salamanders (Amphibia: Hynobiidae) as a model to examine biogeographical consequences of Cenozoic tectonic events within East Asian margins. First, we use GenBank molecular data to reconstruct phylogenetic interrelationships of Hynobius by bayesian and maximum likelihood analyses. Second, we estimate the divergence time using the bayesian relaxed clock approach and infer dispersal/vicariance histories under the 'dispersal-extinction-cladogenesis' model. Finally, we test whether evolutionary history and biogeographical processes of Hynobius should coincide with the predictions of two major hypotheses (the 'vicariance'/'out of southwestern Japan' hypothesis). The resulting phylogeny confirmed Hynobius as a monophyletic group, which could be divided into nine major clades associated with six geographical areas. Our results show that: (1) the most recent common ancestor of Hynobius was distributed in southwestern Japan and Hokkaido Island, (2) a sister taxon relationship between Hynobius retardatus and all remaining species was the results of a vicariance event between Hokkaido Island and southwestern Japan in the Middle Eocene, (3) ancestral Hynobius in southwestern Japan dispersed into the Taiwan Island, central China, 'Korean Peninsula and northeastern China' as well as northeastern Honshu during the Late Eocene-Late Miocene. Our findings suggest that Cenozoic tectonic evolution plays an important role in shaping disjunctive distributions of extant Hynobius within East Asian margins.

  10. Tectonic events and structural configuration of the Barinas-Apure Basin

    SciTech Connect

    Portilla, A. )

    1993-02-01

    Among the Sub-Andean basins of northern South America is located the Barinas-Apure basin, in southwestern Venezuela. Through the analysis of high-resolution seismic-profiles and surface geology, three different tectonic events have affected the sediments of this basin: (a) a late Cretaceous-Paleocene event, related with the Larmidian orogenesis, (b) a late Middle Eocene event, related to north-Venezuelan flexure, and (c) a Miocene to Pleistocene event, under the influence of the Andean (Merida) orogenesis. Is the last one, the responsible of the present-day structural configuration on the basin, i.e., an assymetric syncline. Several complex structures and fault-systems are recognized in this basin, they are grouped in pre-Oligocene and Miocene-Pleistocene in origin. Among these, only the pre-Oligocene structures have accumulated important oil reservoirs.

  11. 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

  12. 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

    Phanerozoic eclogites are widely interpreted to have formed in subduction zone environments where fragments of oceanic crust have been buried to depths greater than 50 km. The formation and preservation of Phanerozoic eclogites is demonstrably linked to plate convergence and their study of eclogite-facies rocks underpins our understanding of subduction zones and plate tectonic models. Our understanding of more ancient, Precambrian tectonics is based on a uniformitarian model, which assumes that modern day tectonic processes are good analogues of those in the past. This assumption is limited because numerical modelling has shown that the driving force of plate tectonics, the thermal structure of the Earth, has changed dramatically over geological time. For example, at the start of the Palaeoproterozoic (2.5 Ga) the Earth's heat production was twice as high as at present. If these models are true then it is difficult to reconcile the formation of low-med temperature eclogite facies rocks in the Early Earth. The Palaeoproterozoic Usagaran orogenic belt of Tanzania contains the Earth’s oldest reported examples (2.0 Ga) of low/med temperature eclogites. The eclogites are reported to have MORB-like geochemical characteristics, which coupled with P-T estimates for their formation, suggests that they are subduction related. In this study detailed structural analysis and U-Th-Pb SHRIMP zircon dating of gneisses exposed in the high-grade, eclogite bearing part of the orogen (the Isimani Suite), has demonstrated that detrital grains in paragneisses yield ages between 2.4 &2.9 Ga. These are intercalated with 2.7 Ga orthogneisses of a similar age to the Tanzanian craton. The extensive distribution of 2.7 Ga crust in both the footwall and hangingwall of the Usagaran Orogen suggests that the most likely tectonic setting for the protoliths of the mafic eclogites was as oceanic crust in a marginal basin. The identification of Palaeoproterozoic subduction related eclogites that

  13. Kinematic History and Tectonic Evolution of the Amerasian Basin: Investigating Palaeo-Plate Boundaries around the Chukchi Borderlands

    NASA Astrophysics Data System (ADS)

    Brumley, K.; Coakley, B.; Stone, D.; Wallace, W.

    2007-12-01

    The multi-stage opening of the Arctic Ocean's Amerasian Basin is only partially understood due to the difficulty of utilizing traditional marine geologic and geophysical techniques in ice-covered waters. While the kinematic development of the Eurasian Basin is well-understood to be the northernmost extension of the Mid-Atlantic Ridge, the history of the morphologically complex Amerasian Basin may be due to multiple events, significantly complicating interpretation of its history. Any detailed model for the opening of the Amerasian Basin must both incorporate structures that accommodate spreading as well as explain the tectonic mechanisms that drove basin development. Cretaceous-age tholeiitic flood basalts and associated radiating dike swarms of the High Arctic Large Igneous Province (HALIP), found along the basin margin, provide a tectonic mechanism and geometry to substantiate sound reconstruction. Detailed models need also consider pre-existing zones of weakness such as the deformation front of the Devonian Caledonides, which may underlie Barents Shelf sediments (Gee and Bogolepova, 2003). Reactivation of these ancient structural trends along this suture zone may explain the motion of Mendeleev Ridge as it rifted from Lomonosov Ridge and created the rectangular pull-apart basin between them. We propose a revised plate model for the development of the Amerasian Basin. A Cretaceous magmatic source localized under the Alpha Ridge accompanied the onset of rifting. This generated the HALIP radiating dike swarms and tholeiitic flood basalts found on the DeLong Islands, Svalbard, Franz Joseph Land, Greenland, Sverdrup Basin and, possibly, the Alpha and Mendeleev Ridges. New bathymetric and sub-bottom profiling data also suggests the existence of igneous dikes on Chukchi Cap. The subsequent development of a triple junction resulted in dilational opening of the Canada Basin. Spreading was accommodated by the migration of the southern edges of the northeastern Siberian

  14. 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

  15. 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.

  16. Cretaceous alkaline intra-plate magmatism in the Ecuadorian Oriente Basin: Geochemical, geochronological and tectonic evidence

    NASA Astrophysics Data System (ADS)

    Barragán, Roberto; Baby, Patrice; Duncan, Robert

    2005-08-01

    Small volumes of Cretaceous alkaline basaltic magmas have been identified in the sedimentary infill of the Ecuadorian Oriente foreland basin. They are characterized by a restricted range of compositional variation, low LILE/HFSE ratios and Sr-Nd isotope values within the range of oceanic island basalts (OIB). Reflection seismic data show that a pre-existing NNE-SSW Triassic and Jurassic rift controls the location and occurrence of these alkaline eruptive sites. Radiometric ages ( 40Ar- 39Ar, incremental heating method) and the biostratigraphic record of their surrounding sediments indicate a NNE-SSW systematic age variation for the emplacement of this alkaline volcanism: from Albian (110 ± 5.2 Ma) in the northern part of the Oriente Basin, to Campanian (82.2 ± 2.0 Ma) in the west-central part. The geochemical, geochronological and tectonic evidences suggest that asthenospheric mantle has upwelled and migrated to the SSW, into the region underlying the pre-existing Triassic and Jurassic rift (thin-spot?). We propose that subduction was abandoned, subsequent to the accretion of allochthonous terranes onto the Ecuadorian and Colombian margin in the latest Jurassic-earliest Cretaceous, causing the relict slab material, corresponding to the eastwards-directed leading plate, to roll-back. Unmodified asthenospheric mantle migrated into the region previously occupied by the slab. This resulted in partial melting and the release of magmatic material to the surface in the northern part of the Oriente Basin since at least Aptian times. Then, magmatism migrated along the SSW-trending Central Wrench Corridor of the Oriente Basin during the Upper Cretaceous, probably as a consequence of the lateral propagation of the transpressive inversion of the Triassic-Jurassic rift. Eventually, the Late Cretaceous east-dipping Andean subduction system was renewed farther west, and the development of the compressional retro-foreland Oriente Basin system halted the Cretaceous alkaline

  17. Observational Constraints on Lithospheric Rheology and Their Implications for Lithospheric Dynamics and Plate Tectonics

    NASA Astrophysics Data System (ADS)

    Zhong, S.; Watts, A. B.

    2014-12-01

    Lithospheric rheology and strength are important for understanding crust and lithosphere dynamics, and the conditions for plate tectonics. Laboratory studies suggest that lithospheric rheology is controlled by frictional sliding, semi-brittle, low-temperature plasticity, and high-temperature creep deformation mechanisms as pressure and temperature increase from shallow to large depths. Although rheological equations for these deformation mechanisms have been determined in laboratory settings, it is necessary to validate them using field observations. Here we present an overview of lithospheric rheology constrained by observations of seismic structure and load-induced flexure. Together with mantle dynamic modeling, rheological equations for high-temperature creep derived from laboratory studies (Hirth and Kohlstedt, 2003; Karato and Jung, 2003) satisfactorily explain the seismic structure of the Pacific upper mantle (Hunen et al., 2005) and Hawaiian swell topography (Asaadi et al., 2011). In a recent study that compared modeled surface flexure and stress induced by volcano loads in the Hawaiian Islands region with the observed flexure and seismicity, Zhong and Watts (2013) showed that the coefficient of friction is between 0.25 and 0.7, and is consistent with laboratory studies and also in-situ borehole measurements. However, this study indicated that the rheological equation for the low-temperature plasticity from laboratory studies (e.g., Mei et al., 2010) significantly over-predicts lithospheric strength and viscosity. Zhong and Watts (2013) also showed that the maximum lithospheric stress beneath Hawaiian volcano loads is about 100-200 MPa, which may be viewed as the largest lithospheric stress in the Earth's lithosphere. We show that the relatively weak lithospheric strength in the low-temperature plasticity regime is consistent with seismic observation of reactivated mantle lithosphere in the western US and the eastern North China. We discuss here the causes

  18. 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.

  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

    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.

  20. 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.

  1. Earthly and Otherworldly Glaciers on Mars: Expressed Subsurface Subpolar Ice and "Plate Tectonic" South Polar Ices

    NASA Astrophysics Data System (ADS)

    Kargel, J. S.

    2003-12-01

    within the area of perennial CO2 ice. This part of the polar cap exhibits strong evidence for convergent flow tending to close the quasi-spiral structured troughs, as predicted by finite-element modelers. A rich phenomenology accompanies this closure. In some cases, good evidence exists for one icy sheet overriding another. Elastic plate flexural responses, with attendant small-scale tectonism, is quite common, as is evidence for ductile deformation. Analogs drawn from Earth's lithosphere provide compelling explanations for some of these features. Smooth, topographically enclosed flat areas in the south polar deposits may be the surface expressions of subglacial lakes or refrozen lakes.

  2. Far field effects of Alpine plate tectonism in the Iberian microplate recorded by fault-related denudation in the Spanish Central System

    NASA Astrophysics Data System (ADS)

    de Bruijne, C. H.; Andriessen, P. A. M.

    2002-05-01

    Apatite fission track analysis was performed on 56 samples from central Spain to unravel the far field effects of the Alpine plate tectonic history of Iberia. The modelled thermal histories reveal complex cooling in the Cenozoic, indicative of intermittent denudation. Accelerated cooling events occurred across the Spanish Central System (SCS) from the Middle Eocene to Recent. These accelerated cooling events resulted in up to 2.8±0.9 km of denudation in the western Sierra de Gredos and 3.6±1.0 km in the central and eastern Gredos (assuming a paleogeothermal gradient of 28±5 °C and a surface temperature of 10 °C). The greatest amount of denudation (5.0±1.6 km) occurred in the Sierra de Guadarrama. Accompanying rock uplift was 4.7±1.0 and 5.9±1.6 km in the eastern Gredos and Guadarrama, respectively. Most denudation in the Gredos occurred from the Middle Eocene to the Early Miocene and can be related to the N-S stress field, induced by the Pyrenean compression. In the Guadarrama, the greatest denudation was Pliocene to Recent of age and seems related to the ongoing NW-SE Betic compression. The fact that the formation of the E-W trending Gredos coincides with the N-S Pyrenean compression and the creation of the present day morphology of the NE-SW trending Guadarrama with the younger NW-SE Betic compression, indicates that they record the far field effects of Alpine plate tectonics on Iberia. The trend of pre-existing lineaments was of major importance in influencing the style and magnitude of these of far field effects.

  3. 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.

  4. 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

  5. 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?

  6. Crustal structure beneath southern Africa: insight into how tectonic events affect the Mohorovičić discontinuity

    NASA Astrophysics Data System (ADS)

    Delph, Jonathan R.; Porter, Ryan C.

    2015-01-01

    The long and complex history of southern Africa makes it a geological nexus for understanding how crust forms, evolves and survives plate tectonic processes over billions of years. The goal of this study is to characterize the crustal thickness, composition, and Moho impedance contrasts across the Kaapvaal and Zimbabwe Cratons and surrounding mobile belts, which range in age from Archean to Palaeozoic. We use data gathered from the 1997-1999 Southern Africa Seismic Experiment, the Africa Array (2006-2007) and the Global Seismographic Network (1993-2009) to generate P-wave receiver function Gaussian-weighted common conversion point stacks across the region in order to provide a continuous 3-D image of crustal variations throughout southern Africa. We observe thickened crust associated with mobile belts and the intrusion of the Bushveld Complex relative to the less-deformed cratons. The southern Kaapvaal and eastern Zimbabwe Cratons have a well-defined Moho with an average depth of ˜34 km and Vp/Vs of ˜1.73, indicative of felsic average crustal composition. We explain the felsic composition observed in the Kaapvaal Craton in the context of significant crustal modification related to the deposition of the Ventersdorp lavas. We find that the Bushveld Province, the site of the world's largest layered mafic intrusion, has a thick (>40 km) crust with a Vp/Vs > 1.8, indicative of a mafic average crustal composition. The magnitude of Moho conversions beneath the Bushveld Province is variable, with the lowest amplitude conversion appearing between the eastern and western limbs of the Bushveld Complex, indicative of mafic underplating beneath the region. In the Limpopo Belt and western Zimbabwe Craton, we observe low amplitude Moho conversions beneath the Okavango Dyke Swarm, and attribute this to the reworking of the crust by mafic underplating and intrusion during the Jurassic rifting of Gondwanaland. The Namaqua-Natal event thickened the crust and created a gradational

  7. 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

  8. What can seafloor fabric tell us about the nature of the 50 Ma plate-mantle event?

    NASA Astrophysics Data System (ADS)

    Müller, R. D.; Matthews, K. J.

    2011-12-01

    Several different mechanisms have been proposed to account for the 50 Ma plate-mantle event, including India-Eurasia collision, the time dependence of the Reunion plume-push force, the subduction of the Izanagi-Pacific mid-ocean ridge, and transient ridge capture of the Hawaiian plume. We use a recent digital global seafloor tectonic fabric map derived from vertical gravity gradients together with magnetic anomaly identifications to analyse the geometry and timing of Late Cretaceous-Early Cenozoic fracture zone (FZ) bends. Two sets of closely spaced FZ bends in the North Atlantic, Weddell Sea and at the Southwest Indian Ridge between Antarctica and Africa produce an S-shape in the seafloor fabric. The older spreading ridge reorganisation initiated close to 70 Ma, and was completed around 55 Ma. The younger FZ bends are sharper, were initiated approximately 55-49 Ma and completed around 40-42 Ma, after which time spreading returned to its pre-S-bend azimuth. Additionally there is a distinct increase in seafloor roughness at the mid-Atlantic ridge at about 70 Ma reflecting a decrease in spreading rate. Seafloor fabric indicators of plate motion change produced at around 70 Ma coincide with emplacement of the Reunion plume and are restricted to parts of the Atlantic-Indian realm. The Pacific domain appears unaffected by the mechanism that drove plate motion changes in the Atlantic and Indian Oceans at this time. Yet, from ~55-40 Ma Pacific FZ bends and other oceanic and plate margin events are widespread. Along with formation of the younger part of the Atlantic-Indian S-bends, FZ bends and changes in FZ morphology in the northeast Pacific signify a reorientation of the Pacific-Farallon spreading ridge, a northward propagation of the Pacific-Antarctic ridge, increases in spreading rates at the Australia-Pacific ridge and a change in the direction of plate motion, with spreading terminating in the Tasman Sea. And initiation of Izu-Bonin-Mariana subduction. This

  9. Tectonic Structure of the Middle America Pacific Margin and Incoming Cocos Plate From Costa Rica to Guatemala

    NASA Astrophysics Data System (ADS)

    Ranero, C. R.; Weinrebe, W.; Grevemeyer, I.; Phipps Morgan, J.; Vannucchi, P.; von Huene, R.

    2003-12-01

    A new multibeam bathymetry and magnetic survey with R/V SONNE in summer 2003 has mapped the continental margin and incoming plate of NW Nicaragua, El Salvador and Guatemala, extending existing coverage from offshore Costa Rica and part of Nicaragua to a full coverage map of about 1200 km long by 100 km wide area along the plate boundary. The incoming plate along Nicaragua, El Salvador and Guatemala is of similar age and was formed at superfast spreading rates; however, its morphology changes drastically along strike. The seafloor-spreading inherited morphology is very smooth along Nicaragua, but with ridges up to 800 m high in Guatemala, with a transition across El Salvador. The development and dimensions of the dominant inherited fabric seems to be related to discontinuities at the paleospreading center. A series of troughs oblique to the main fabric may indicate the location of pseudofaults and correspond to areas where the seafloor fabric is most prominent. Bending of the oceanic plate into the trench reactivates the inherited fabric forming a well pervasive faulting system along the oceanic trench slope. The continental slope displays three morphotectonic units that roughly correspond to the upper, middle and lower slope, although the across slope width of each unit is fairly variable. Small canyons and gullies that form at the sudden dip change across the shelf break carve the upper slope. The canyons coalesce and become shallower as the dip decreases downslope. Locally some large canyons continue into the slope toe. The middle slope is a rough terrain variable in width and dip sculptured by pervasive normal faulting and locally by mass wasting processes. The lower slope is formed by en echelon terraces striking similar to the rough terrain of the incoming plate and mimicking the half graben morphology of the underthusting plate. The three morphotectonic slope domains represent differences in tectonic activity, with more stable upper slope, a middle slope

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. Reinterpretation of Mesozoic and Cenozoic tectonic events, Mountain Pass area, northeastern San Bernardino County, California

    SciTech Connect

    Nance, M.A. . Geology Dept.)

    1993-04-01

    Detailed mapping, stratigraphic structural analysis in the Mountain Pass area has resulted in a reinterpretation of Mesozoic and Cenozoic tectonic events in the area. Mesozoic events are characterized by north vergent folds and thrust faults followed by east vergent thrusting. Folding created two synclines and an anticline which were than cut at different stratigraphic levels by subsequent thrust faults. Thrusting created composite tectono-stratigraphic sections containing autochthonous, para-autothonous, and allochthonous sections. Normal faults cutting these composite sections including North, Kokoweef, White Line, and Piute fault must be post-thrusting, not pre-thrusting as in previous interpretations. Detailed study of these faults results in differentiation of at least three orders of faults and suggest they represent Cenozoic extension correlated with regional extensional events between 11 and 19 my. Mesozoic stratigraphy reflects regional orogenic uplift, magmatic activity, and thrusting. Inclusion of Kaibab clasts in the Chinle, Kaibab and Chinle clasts in the Aztec, and Chinle, Aztec, and previously deposited Delfonte Volcanics clasts in the younger members of the Delfonte Volcanics suggest regional uplift prior to the thrusting of Cambrian Bonanza King over Delfonte Volcanics by the Mescal Thrust fault. The absence of clasts younger than Kaibab argues against pre-thrusting activity for the Kokoweef fault.

  17. 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).

  18. 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

  19. Tectonic events reflected by palaeocurrents, zircon geochronology, and palaeobotany in the Sierra Baguales of Chilean Patagonia

    NASA Astrophysics Data System (ADS)

    Gutiérrez, Nestor M.; Le Roux, Jacobus P.; Vásquez, Ana; Carreño, Catalina; Pedroza, Viviana; Araos, José; Oyarzún, José Luis; Pablo Pino, J.; Rivera, Huber A.; Hinojosa, L. F.

    2017-01-01

    The Sierra Baguales, situated north of the Torres Del Paine National Park in the Magallanes region of southern Chile, shows a well-exposed stratigraphic sequence ranging from the Late Cretaceous to late Pliocene, which presents a unique opportunity to study the evolution of sedimentological styles and trends, palaeoclimate changes, and tectonic events during this period. The depositional environment changed from a continental slope and shelf during the Cenomanian-Campanian (Tres Pasos Formation) to deltaic between the Campanian-Maastrichtian (Dorotea Formation) and estuarine in the Lutetian-Bartonian (Man Aike Formation). During the Rupelian, a continental environment with meandering rivers and overbank marshes was established (Río Leona Formation). This area was flooded in the early Burdigalian (Estancia 25 de Mayo Formation) during the Patagonian Transgression, but emerged again during the late Burdigalian (Santa Cruz Formation). Measured palaeocurrent directions in this Mesozoic-Cenozoic succession indicate source areas situated between the northeast and east-southeast during the Late Cretaceous, east-southeast during the middle Eocene, and southwest during the early Oligocene to early Miocene. This is confirmed by detrital zircon age populations in the different units, which can be linked to probable sources of similar ages in these areas. The east-southeastern provenance is here identified as the Antarctic Peninsula or its northeastern extension, which is postulated to have been attached to Fuegian Patagonia during the Eocene. The southwestern and western sources were exhumed during gradual uplift of the Southern Patagonian Andes, coinciding with a change from marine to continental conditions in the Magallanes-Austral Basin, as well as a decrease in mean annual temperature and precipitation indicated by fossil leaves in the Río Leona Formation. The rain shadow to the east of the Andes thus started to develop here during the late Eocene-early Oligocene ( 34

  20. 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.

  1. 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

  2. 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.

  3. Lithospheric Rheology Constrained by Loading of the Hawaiian Islands and its Implications for the Dynamics of Plate Tectonics

    NASA Astrophysics Data System (ADS)

    Zhong, S.; Watts, A. B.

    2013-12-01

    Lithospheric rheology is important for understanding crustal and lithospheric dynamics, and the conditions for plate tectonics. For example, numerical modeling studies suggest that plate tectonics emerge from the dynamics of mantle convection when a small coefficient of friction (<0.1) or small yield stress for lithosphere is used. However, lithospheric rheology is not well understood. In this study, we developed 3-D finite element models for computing load-induced surface deformation and stress for lithosphere and mantle with realistic non-linear viscoelastic rheology including the frictional sliding, low-temperature plasticity, and high-temperature creep. We determined the deformation and stress due to volcano loading in the Hawaiian region in the last few million years. By comparing model predictions with seismic observations of the depth to the top of oceanic crust and depth-dependence of seismicity in the Hawaiian region, we sought to constrain lithospheric rheology. Our calculations show that the load-induced surface deformation in the Hawaiian region is controlled by low-temperature plasticity and frictional sliding but is insensitive to high-temperature creep. Lithospheric strength predicted from laboratory derived low-temperature plasticity needs to be reduced significantly to match the observations, together with frictional coefficient in the range from 0.1 to 0.7. However, the small coefficient of friction weakens the shallow part of the lithosphere so much that it causes the minima in strain rate and stress to occur at too large depths to be consistent with the depth distribution of seismicity at Hawaii. Our results therefore suggest that the coefficient of friction is between 0.25 and 0.7. Finally, maximum lithospheric stress under Hawaiian loads is about 100-200 MPa for models that match the observations, and this stress may be viewed as the largest lithospheric stress on the Earth.

  4. 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 Earth, highlighted in Japan, North America, Europe, and Greenland, accretionary complexes comprehensively record information compiled while the oceanic crust is en route from the mid-oceanic ridge to the subduction zone, spanning hundreds of millions of years. At the zone, oceanic crustal materials are stacked along thrust faults and/or subducted to be eventually recycled into the mantle. The surviving accretionary-complex materials include Ocean Plate Stratigraphy (OPS). The ideal succession of the OPS (from oldest to youngest) is mid-ocean ridge basalt, pelagic sediment including radiolarian chert, hemipelagic sediment including siliceous shale, and trench turbidite deposits. Therefore, accretionary complexes often record diverse environmental conditions from deep- to shallow-marine environments, including those perturbed by magmatic, impact, and possibly extrasolar events. Stratigraphic, impact-crater, paleotectonic, and magnetic-anomaly information point to Early Noachian (Hadean-equivalent) Martian geologic terrains; they are extremely ancient environmental records compared to those destroyed on Earth due to differences in planetary mass and evolutional states. Such record a dynamic phase of the evolution of Mars, including interacting ocean, landmass, and atmosphere, as well as possible plate tectonism during an operating dynamo. A candidate accretionary complex and nearby outcrops of steeply dipping beds comprising olistostrome-like blocks, nearby and in the Claritas rise, respectively, may be key evidence of major crustal shortening related to plate tectonism, in addition to being extremely ancient environmental records. Claritas rise is a rugged promontory about 250 km across, which forms the northwest part of an extremely ancient and large mountain range, Thaumasia highlands, with a length nearing 2,400 km, or approximating that of the Himalayas. Future investigation of the ancient Martian basement, which includes geochemical analyses for possible OPS

  5. 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…

  6. 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.

  7. Rotational Inerfia of Continents: A Proposed Link between Polar Wandering and Plate Tectonics.

    PubMed

    Kane, M F

    1972-03-24

    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.

  8. 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.

  9. Tectonics of the Antarctic-Scotia plate boundary near Elephant and Clarence Islands, West Antarctica

    NASA Astrophysics Data System (ADS)

    Klepeis, Keith A.; Lawver, Lawrence A.

    1996-09-01

    Over 5000 km of new bathymetric data collected from near the northern Antarctic Peninsula (60°S-63.5°S latitude, 53.5°W-63°W longitude) show the morphology of an irregular segment of the Antarctic-Scotia plate boundary and nearby Shetland microplate. The irregular plate boundary is formed by an oblique intersection (>70°) of the sinistral transpressional Shackleton fracture zone (SFZ) and the sinistral transtensional South Scotia Ridge transform (SSR) near Elephant (EI) and Clarence (CI) Islands. Mapped boundaries of the Shetland microplate include the South Shetland Trench and the volcanic rift axis of Bransfield Strait marginal basin. Bathymetric data, single-channel seismic reflection profiles, and Geosat/ERS 1 free air gravity data show a southeast trending fault zone on the northeast side of a prominent ridge in the SFZ. The fault zone is defined by scarps that affect ocean floor sediments, fault-bounded subbasins, rotated sedimentary layers, angular unconformities, linear gravity trends, and transtensional followed by contractional deformation. Southeast of a termination of the SFZ ridge at the South Shetland Trench, the fault zone subdivides into segments displaying steep scarps (up to 23°) and canyons on the northeast margin of the EI platform. These features become east-west trending nearer to the western SSR. South of the islands, southwest trending extensional or transtensional fault zones disrupt the Bransfield Strait volcanic rift axis. These data suggest that (1) recent (<4 Ma) changes in the configuration of the Antarctic plate near the Antarctic Peninsula caused a segment of the SFZ transform to adjust to a more stable, rectilinear geometry with the SSR transform, and (2) diffuse transtension resulting from current Antarctic-Scotia relative motion is dissecting the Shetland microplate near EI and CI and transferring slivers of the Scotia plate onto the Antarctic plate.

  10. Potential use of Volcano Tectonic Events to Forecast and Predict Eruptions

    NASA Astrophysics Data System (ADS)

    Palacios, P. B.; Cordoba, G.; Yepes, H. A.

    2006-12-01

    The magnitude of volcano tectonic events is analyzed for some volcanoes of Ecuador and Colombia. In this study, sequential temporal samples are taken and confidence intervals for the population mean magnitude are computed. In each studied volcano the temporal variation of the confidence intervals are statistically significant and we assume this results as evidence of the inner stress changes. Before the eruptions the sequence of the confidence intervals form a pick, probably related to a strong inner stress change, and we propose use it as indicator to forecast eruptions. Each volcano has been considered as a single system and also using the confidence intervals, consecutive levels of the system stage have been defined. The time of transition on these levels has been used to propose a linear statistic model to predict the time of eruption. One successful forecast (before the eruption at July 21, 2004) and two successful predictions (before the eruptions at November 24, 2005 and July 12, 2006) about Galeras volcano are presented.

  11. Recent kinematics of the tectonic plates surrounding the Red Sea and Gulf of Aden

    NASA Astrophysics Data System (ADS)

    Schettino, Antonio; Macchiavelli, Chiara; Pierantoni, Pietro Paolo; Zanoni, Davide; Rasul, Najeeb

    2016-10-01

    The Red Sea and Gulf of Aden represent two young basins that formed between Africa and Arabia since the early Oligocene, floored by oceanic crust or by transitional and thinned continental crust. While in the easternmost Gulf of Aden, the rift-drift transition can be dated chron C6 (˜20.1 Ma), here we show that in the Red Sea the first pulse of seafloor spreading occurred during chron C3n.2n (˜4.6 Ma) around ˜17.1°N (present-day coordinates) and propagated southwards from this location, separating the Danakil microplate from Arabia. It is also shown that seafloor spreading between Arabia and Nubia started later, around chron 2A (˜2.58 Ma), and propagated northwards. At present, there is no magnetic evidence for the existence of a linear spreading centre in the northern Red Sea at latitudes higher than ˜24°N and in the southern Red Sea below ˜14.8°N. The present-day plate kinematics of this region can be described with high accuracy by a network of five interacting plates (Nubia, Arabia, Somalia, Sinai and Danakil) and six triple junctions. For times older than anomaly 2A (˜2.58 Ma) and up to anomaly 3, the absence of marine magnetic anomalies between Arabia and Nubia prevents a rigorous kinematic description of the five-plates system. However, there is strong evidence that the unique changes in plate motions during the last 5 Myr were a dramatic slowdown at chron C2 (˜1.77 Ma) in the spreading or extension rates along the ridge and rift axes, thereby a good representation of the real plate motions can be obtained anyway by backward extension of the oldest Arabia-Nubia and Arabia-Danakil stage rotations determined on the basis of marine magnetic anomalies, respectively, C2-C2A and C2A-C3. The proposed kinematic reconstructions are accompanied by a geodynamic explanation for the genesis of large continent-continent fracture zones at the rift-drift transition and by an analysis of the strain associated with plate motions in Afar, northeastern Egypt and

  12. Paleomagnetic data from the Philippine Sea Plate and their tectonic significance

    NASA Astrophysics Data System (ADS)

    Haston, Roger B.; Fuller, M.

    1991-04-01

    New paleomagnetic data from Guam and Saipan have been obtained and are used, in conjunction with previously published results from around the Philippine Sea plate, to interpret the origin and history of the Philippine Sea plate. A lower Miocene direction (I=3.5°, D=54.5°, a95=17.4°, k=20.3) and a middle Oligocene direction (I=5.3°, D=68.4°, a95=12.8°, k=52.4) have been obtained from the Palau Islands. Only one reliable result, a middle Oligocene direction (I=15.1°, D=66.1°, a95=11.1°, k=20.1), has been obtained from Guam. Many characteristic remanent magnetic directions have been obtained from the lower Eocene Facpi Formation; however, the results are too scattered (k=4.5) to be considered reliable. Two reliable directions have been obtained from Saipan: a middle Miocene result (I=30.7°, D=28.1°, a95=8.4°, k=64.6), and a lower Eocene result (I=-12.0°, D=43.0°, a95=12.5°, k=16.0). Two lower Eocene results from Chichijima (I=9.5°, D=105.3°, a95=12.6°, k=6.1) and Anijima (I=-0.8°, D=91.7°, a95=16.9°, k=4.9) are the reliable results from the Bonin islands. There are two end-member interpretations for these data: (1) small scale local rotation of blocks along the plate margin, or (2) rotation of the Philippine Sea plate as a whole. To distinguish between these interpretations, we reconstructed the East Philippine Sea province back to its prerifting configuration. The rotation caused by deformation can be estimated by comparing the paleomagnetism of Guam, Saipan, and the Bonin islands to Palau. Prior to reconstruction, the older declination values are scattered. Closing the marginal basins reduces the declination scatter, and all of the islands show increasing clockwise deflection with time. This suggests that the Philippine Sea plate has rotated up to 80° clockwise and moved northward around 20° since the Eocene, and deformational rotation is a second-order feature. The finite pole of rotation of the Philippine Sea plate relative to Eurasia must

  13. The effect of plumes and a free surface on mantle dynamics with continents and self-consistent plate tectonics

    NASA Astrophysics Data System (ADS)

    Jain, Charitra; Rozel, Antoine; Tackley, Paul

    2014-05-01

    Rolf et al. (EPSL, 2012) and Coltice et al. (Science, 2012) investigated the thermal and dynamical influences of continents on plate tectonics and the thermal state of Earth's mantle, but they did not explicitly consider the influence of mantle plumes. When present, strong mantle plumes arising from the deep mantle can impose additional stresses on the continents, thereby facilitating continental rifting (Storey, Nature 1995; Santosh et al., Gondwana Research 2009) and disrupting the supercontinent cycle (Philips and Bunge, Geology 2007). In recent years, several studies have characterized the relation between the location of the plumes and the continents, but with contradicting observations. While Heron and Lowman (GRL, 2010; Tectonophysics, 2011) propose regions where downwelling has ceased (irrespective of overlying plate) as the preferred location for plumes, O'Neill et al. (Gondwana Research, 2009) show an anti-correlation between the average positions of subducting slabs at continental margins, and mantle plumes at continental/oceanic interiors. Continental motion is attributed to the viscous stresses imparted by the convecting mantle and the extent of this motion depends on the heat budget of the mantle. Core-mantle boundary (CMB) heat flux, internal heating from decay of radioactive elements, and mantle cooling contribute to this heat budget. Out of these sources, CMB heat flux is not well defined; however, the recent determination that the core's thermal conductivity is much higher than previously thought requires a CMB heat flow of at least 12 TW (de Koker et al., PNAS 2012; Pozzo et al., Nature 2012; Gomi et al., PEPI 2013), much higher than early estimates of 3-4 TW (Lay et al., Nature 2008). Thus, it is necessary to characterize the effect of increased CMB heat flux on mantle dynamics. In almost all mantle convection simulations, the top boundary is treated as a free-slip surface whereas Earth's surface is a deformable free surface. With a free

  14. 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.

  15. Plate Tectonics at 3.8-3.7 Ga: Field Evidence from the Isua Accretionary Complex, Southern West Greenland.

    PubMed

    Komiya; Maruyama; Masuda; Nohda; Hayashi; Okamoto

    1999-09-01

    Archean oceanic lithosphere was rigid. These conclusions-rigidity and lateral plate movement-support the idea that the modern style of plate tectonics was in operation only 0.7-0.8 G.yr. after the formation of the Earth.

  16. 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

  17. Mantle-derived peridotites in southwestern Oregon: relation to plate tectonics.

    PubMed

    Medaris, L G; Dott, R H

    1970-09-04

    A group of peridotites in southwestern Oregon contains high-pressure mineral assemblages reflecting recrystallization at high temperatures (1100 degrees to 1200 degrees C) over a range of pressure decreasing from 19 to 5 kilobars. It is proposed that the peridotites represent upper-mantle material brought from depth along the ancestral Gorda-Juan de Fuca ridge system, transported eastward by the spreading Gorda lithosphere plate, and then emplaced by thrust-faulting in the western margin of the Cordillera during late Mesozoic time.

  18. 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

  19. Roles of plate locking and block rotation in the tectonics of the Pacific Northwest

    NASA Astrophysics Data System (ADS)

    Ning, Zuoli

    The Pacific Northwest has potential for huge megathrust earthquakes. The influence of plate locking in the Cascadia subduction zone dominates crustal deformation off the shores of Washington and Oregon, but does not much affect areas far from the trench. The maximum principal strain rate epsilon 1 is -0.013 +/- 0.007 mustrain/yr in the Olympic Peninsula, 0.007 +/- 0.005 mustrain/yr in the Puget Sound, -0.005 +/- 0.005 mustrain/yr at Mt. Rainier, -0.004 +/- 0.005 mustrain/yr along the northern Oregon coast, and 0.011 +/- 0.006 mustrain/yr in central Oregon. The minimum principal strain rate epsilon2 is -0.083 +/- 0.008 mustrain/yr N56°E in the Olympic Peninsula, -0.034 +/- 0.007 mustrain/yr N63°E in the Puget Sound, -0.020 +/- 0.006 mustrain/yr N53°E at Mt. Rainier, -0.051 +/- 0.014 mustrain/yr N85°E along the northern Oregon coast, and -0.010 +/- 0.006 mustrain/yr N71°E in central Oregon. A new model of plate locking on the Cascadia subduction zone is similar to a model (1997). The uncertainty of the widths of the locked and transition zone in the model is about 25km--40km. Guided by computed site velocities, seismicity patterns, heat flow, volcanic data, and geological structures, we find it is necessary to divide the crust in the Pacific Northwest into separate moving blocks. We have analyzed a model in which the Oregon block is separated from the Washington block at latitude 46°. The Washington block has been further divided into 5-subblocks, three in the forearc and two in eastern Washington. We remove contributions of JDF plate locking from the site velocity field and determine a rotation pole and a strain rate for each sub-block. We conclude that Juan de Fuca plate locking has little direct effect on crustal earthquake occurrence in the Pacific Northwest (except for periodic megathrust earthquakes). In the Oregon block, plate locking and rigid block rotation are sufficient to explain GPS observations and the lower rate of seismicity in Oregon. The

  20. Geology of the Eoarchean, > 3.95 Ga, Nulliak supracrustal rocks in the Saglek Block, northern Labrador, Canada: The oldest geological evidence for plate tectonics

    NASA Astrophysics Data System (ADS)

    Komiya, Tsuyoshi; Yamamoto, Shinji; Aoki, Shogo; Sawaki, Yusuke; Ishikawa, Akira; Tashiro, Takayuki; Koshida, Keiko; Shimojo, Masanori; Aoki, Kazumasa; Collerson, Kenneth D.

    2015-11-01

    The Earth is a unique planet, which has been highly evolved, diversified and complicated through geologic time, and underwent many key events, including giant impact, magma ocean, core formation, large-scale mantle differentiation and late heavy bombardment, especially in its dawn. But, our knowledge of early Earth is limited due to the lack of the Hadean supracrustal rocks. The supracrustal rocks with the Eoarchean ages provide key evidence for the Earth's early evolution, but few supracrustal rocks have been comprehensively investigated. Therefore, we mapped in seven areas of the Saglek Block, northern Labrador, where ancient supracrustal sequences are interleaved with a diverse assemblage of orthogneisses. Early studies suggested that some of them have the Mesoarchean ages because of the lack of the Mesoarchean Saglek dyke, but we found the Saglek dykes in the areas to recognize the Eoarchean Nulliak supracrustal rocks and Uivak Gneiss in all the areas. Recent reassessment of U-Pb dating and cathodoluminescence observation of zircons from the oldest suites of the Uivak Gneiss showed that the Uivak Gneiss has the Eoarchean age, > 3.95 Ga, and forms the Iqaluk-Uivak Gneiss series. Because our geological survey clearly showed that the Iqaluk-Uivak Gneisses were intruded into the Nulliak supracrustal belts, the Nulliak supracrustal rocks are the oldest supracrustal rock in the world. The supracrustal belts consist of piles of fault-bounded blocks, which are composed of the ultramafic rocks, mafic rocks and sedimentary rocks in ascending order, similar to modern ocean plate stratigraphy (OPS). In addition, small-scale duplex structures are found over the areas. The presence of duplex structure and OPS indicates that the > 3.95 Ga Nulliak supracrustal belts originate from an accretionary complex. The presence of the accretionary complex, ophiolite and granitic continental crust provides the oldest evidence for the plate tectonics on the early Earth.

  1. Metallogenic events and tectonic setting of the Duobaoshan ore field in Heilongjiang Province, NE China

    NASA Astrophysics Data System (ADS)

    Hao, Yu-Jie; Ren, Yun-Sheng; Duan, Ming-Xin; Tong, Kuang-Yin; Chen, Cong; Yang, Qun; Li, Chao

    2015-01-01

    The Duobaoshan ore field, a major center of metal production in Northeast China, is located in the northeast of the Xing'an-Mongolia Orogenic Belt (the eastern part of the Central Asian Orogenic Belt) and within the northern Greater Xing'an Mountains. Several types of ore deposits are mined in the Duobaoshan region, including the Duobaoshan and Tongshan porphyry copper-molybdenum deposits, the Sankuanggou skarn iron-copper deposit, and the Zhengguang epithermal gold deposit. Zircon grains from the Tongshan granodiorite and porphyritic granite yield laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb weighted mean ages of 475.9 ± 0.8 Ma and 230.9 ± 0.9 Ma to 240.7 ± 0.8 Ma, respectively. The Re-Os isochron age of molybdenites from the Tongshan deposit is 473 ± 4 Ma. Because both field observations and petrographic analysis identified disseminated chalcopyrite, pyrite, and malachite in the porphyritic granite, the isotope dating indicates that the Tongshan deposit underwent at least two magmatic-mineralization events, during the Ordovician and the Triassic. Zircon grains from the metallogenic granodiorite of the Sankuanggou skarn deposit yield an age of 176.1 ± 0.3 Ma, and Re-Os dating of molybdenite gives an age of 173 ± 6 Ma, indicating a Jurassic event. Based on previous research and the new geochemical analysis presented in this study, it is inferred that the magmatism and mineralization of the Sankuanggou deposit were associated with the subduction of the Paleo-Pacific Plate. The Duobaoshan region has therefore experienced at least three major magmatic and mineralization events, during the Ordovician (470-480 Ma), the Triassic (230-240 Ma), and the Early Jurassic (170-180 Ma).

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

    NASA Astrophysics Data System (ADS)

    Kalbas, James L.

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

  3. 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).

  4. Fault Slip Embedded in Creep: Insight into Tectonic Tremors and Slow Slip Events from Acoustic and Optical Monitoring of Fractures

    NASA Astrophysics Data System (ADS)

    Elkhoury, J. E.; Lengline, O.; Ampuero, J. P.; Schmittbuhl, J.

    2010-12-01

    Observations of temporal and spatial correlations between slow slip earthquakes and tectonic tremor activity suggest a physical relation between them. Early descriptions of mechanisms relating these phenomena simply attributed the relation between seismic and aseismic events to fluid mediated processes. More recent hypotheses suggest that tectonic tremors are bursts of seismic energy due to the rupturing of small asperities within slow slipping regions. Here we present laboratory results of a unique experimental setting aimed at understanding the response to transient loads of a system of small asperities embedded in creep as a model of tectonic tremor activity triggered by slow slip and modulated by tides. We performed mode I crack propagation experiments on glass bead blasted and annealed 2D interfaces of transparent material (Polymethylmethacrylate) where fracture fronts were confined to the 2D weakness plane of the heterogeneous interface. We monitored acoustic emissions (AE) with piezo-electric sensors surrounding the crack front line. We also optically monitored the rupture front line with up to 1000 frames per second. The experimental loading conditions produce quasi-static front propagation at slow average speeds. Image processing reveals de-pinning along the front that we characterize as intermittent opening during slow front propagation. AE locations strongly correlate to the spatiotemporal clustering of the de-penning events along the front. Moreover, this correlation is preserved at the time of imposed transient fluctuations in loading during front propagation. Using the analogy between mode I and modes II and III fractures, our results translate into intermittent slip on faults linked to clustering of seismic activity produced by the breakage of asperities embedded in creeping regions with no need of invoking fluid mediated processes. Thus our experiments help reveal the interplay between aseismic and seismic slip on faults. We also observe qualitative

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. Plate tectonics and biogeographical patterns of the Pseudophoxinus (Pisces: Cypriniformes) species complex of central Anatolia, Turkey.

    PubMed

    Hrbek, Tomas; Stölting, Kai N; Bardakci, Fevzi; Küçük, Fahrettin; Wildekamp, Rudolf H; Meyer, Axel

    2004-07-01

    We investigated the phylogenetic relationships of Pseudophoxinus (Cyprinidae: Leuciscinae) species from central Anatolia, Turkey to test the hypothesis of geographic speciation driven by early Pliocene orogenic events. We analyzed 1141 aligned base pairs of the complete cytochrome b mitochondrial gene. Phylogenetic relationships reconstructed by maximum likelihood, Bayesian likelihood, and maximum parsimony methods are identical, and generally well supported. Species and clades are restricted to geologically well-defined units, and are deeply divergent from each other. The basal diversification of central Anatolian Pseudophoxinus is estimated to have occurred approximately 15 million years ago. Our results are in agreement with a previous study of the Anatolian fish genus Aphanius that also shows a diversification pattern driven by the Pliocene orogenic events. The distribution of clades of Aphanius and Pseudophoxinus overlap, and areas of distribution comprise the same geological units. The geological history of Anatolia is likely to have had a major impact on the diversification history of many taxa occupying central Anatolia; many of these taxa are likely to be still unrecognized as distinct.

  11. 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

  12. Cenozoic tectonic and climatic events in southern Iberian Peninsula: Implications for the evolutionary history of freshwater fish of the genus Squalius (Actinopterygii, Cyprinidae).

    PubMed

    Perea, Silvia; Cobo-Simon, Marta; Doadrio, Ignacio

    2016-04-01

    Southern Iberian freshwater ecosystems located at the border between the European and African plates represent a tectonically complex region spanning several geological ages, from the uplifting of the Betic Mountains in the Serravalian-Tortonian periods to the present. This area has also been subjected to the influence of changing climate conditions since the Middle-Upper Pliocene when seasonal weather patterns were established. Consequently, the ichthyofauna of southern Iberia is an interesting model system for analyzing the influence of Cenozoic tectonic and climatic events on its evolutionary history. The cyprinids Squalius malacitanus and Squalius pyrenaicus are allopatrically distributed in southern Iberia and their evolutionary history may have been defined by Cenozoic tectonic and climatic events. We analyzed MT-CYB (510 specimens) and RAG1 (140 specimens) genes of both species to reconstruct phylogenetic relationships and to estimate divergence times and ancestral distribution ranges of the species and their populations. We also assessed their levels of genetic structure and diversity as well as the amount of gene flow between populations. To investigate recent paleogeographical and climatic factors in southern Iberia, we modeled changes-through-time in sea level from the LGM to the present. Phylogenetic, geographic and population structure analyses revealed two well-supported species (S. malacitanus and S. pyrenaicus) in southern Iberia and two subclades (Atlantic and Mediterranean) within S. malacitanus. The origin of S. malacitanus and the separation of its Atlantic and Mediterranean populations occurred during the Serravalian-Tortonian and Miocene-Pliocene periods, respectively. These divergence events occurred in the Middle Pliocene and Pleistocene in S. pyrenaicus. In both species, Atlantic basins possessed populations with higher genetic diversity than Mediterranean, which may be explained by the Janda Lagoon. The isolation of S. malacitanus was

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

    NASA Astrophysics Data System (ADS)

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

    2009-10-01

    The Urumieh complex, to the north of the Sanandaj-Sirjan zone (NW Iran), belongs to a plutonic arc that took place above the northeastward dipping subduction of Arabia under Iran during Late Cretaceous times. Seven granitoid bodies occupying an area of ˜300 km 2 can be sorted into three suites. According to the isotope chronology study of Ghalamghash et al. [Ghalamghash, J., Nédélec, A., Bellon, H., Vousoughi-Abedini, M., Bouchez, J.L., in press. The Urumieh Plutonic Complex: a magmatic record of the geodynamic evolution of the Sanandaj-Sirjan zone (NW Iran) during Cretaceous times - Part II: petrogenesis and 40K/40Ar dating. Journal of Asian Earth Sciences], the two first suites were emplaced during the same event at ˜100 Ma, and the third one was emplaced ˜20 Ma later: (1) the diorites form the largest bodies and comprise the Ghamishlu and Dourbeh stocks; (2) the biotite-granites are composed by the Sehkani, Nari and Doustak bodies, and (3) the younger bodies are represented by the Bardkish syenite and the Dourbeh granite. These bodies were subjected to systematic microstructural observations, and magnetic fabric measurements that yield information about their emplacement kinematics. The magnetic lineations of the diorites and biotite-granites (the early suites) call for a dominant NW-trending stretching during their intrusion, attributed to the transpressive deformation of the overriding Sanandaj-Sirjan microplate during the north-to northeastward motion of the subducting western branch of the Neo-Tethys. Oblique plate motion with ˜20% of strain partitioning along a NNW-trending plate boundary accounts for the observed magmatic structures. Intrusion of the younger bodies took place after consumption of this western oceanic domain at about 80 Ma. The NW-trending lineations of the syenite suggest that the transpressive regime was continuing, while the steep lineations and the peculiar microstructures of the Dourbeh granite call for a forceful intrusion. Our

  14. 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.

  15. 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.

  16. GPS and seismological constraints on active tectonics and arc-continent collision in Papua New Guinea: Implications for mechanics of microplate rotations in a plate boundary zone

    NASA Astrophysics Data System (ADS)

    Wallace, Laura M.; Stevens, Colleen; Silver, Eli; McCaffrey, Rob; Loratung, Wesley; Hasiata, Suvenia; Stanaway, Richard; Curley, Robert; Rosa, Robert; Taugaloidi, Jones

    2004-05-01

    The island of New Guinea is located within the deforming zone between the Pacific and Australian plates that converge obliquely at ˜110 mm/yr. New Guinea has been fragmented into a complex array of microplates, some of which rotate rapidly about nearby vertical axes. We present velocities from a network of 38 Global Positioning System (GPS) sites spanning much of the nation of Papua New Guinea (PNG). The GPS-derived velocities are used to explain the kinematics of major tectonic blocks in the region and the nature of strain accumulation on major faults in PNG. We simultaneously invert GPS velocities, earthquake slip vectors on faults, and transform orientations in the Woodlark Basin for the poles of rotation of the tectonic blocks and the degree of elastic strain accumulation on faults in the region. The data are best explained by six distinct tectonic blocks: the Australian, Pacific, South Bismarck, North Bismarck, and Woodlark plates and a previously unrecognized New Guinea Highlands Block. Significant portions of the Ramu-Markham Fault appear to be locked, which has implications for seismic hazard determination in the Markham Valley region. We also propose that rapid clockwise rotation of the South Bismarck plate is controlled by edge forces initiated by the collision between the Finisterre arc and the New Guinea Highlands.

  17. Azimuthal seismic anisotropy in the Earth's upper mantle and the thickness of tectonic plates

    NASA Astrophysics Data System (ADS)

    Schaeffer, A. J.; Lebedev, S.; Becker, T. W.

    2016-11-01

    Azimuthal seismic anisotropy, the dependence of seismic wave speeds on propagation azimuth, is largely due to fabrics within the Earth's crust and mantle, produced by deformation. It thus provides constraints on the distribution and evolution of deformation within the upper mantle. Here, we present a new global, azimuthally anisotropic model of the crust, upper mantle and transition zone. Two versions of this new model are computed: the rough SL2016svAr and the smooth SL2016svA. Both are constrained by a very large data set of waveform fits (˜750 000 vertical component seismogram fits). Automated, multimode waveform inversion was used to extract structural information from surface and S wave forms in broad period ranges (dominantly from 11 to 450 s, with the best global sampling in the 20-350 s range), yielding resolving power from the crust down to the transition zone. In our global tomographic inversion, regularization of anisotropy is implemented to more uniformly recover the amplitude and orientation of anisotropy, including near the poles. Our massive waveform data set, with complementary large global networks and high-density regional array data, produces improved resolution of global azimuthal anisotropy patterns. We show that regional scale variations, related to regional lithospheric deformation and mantle flow, can now be resolved by the global models, in particular in densely sampled regions. For oceanic regions, we compare quantitatively the directions of past and present plate motions and the fast-propagation orientations of anisotropy. By doing so, we infer the depth of the boundary between the rigid, high-viscosity lithosphere (preserving ancient, frozen fabric) and the rheologically weak asthenosphere (characterized by fabric developed recently). The average depth of thus inferred rheological lithosphere-asthenosphere boundary (LAB) beneath the world's oceans is ˜115 km. The LAB depth displays a clear dependence on the age of the oceanic

  18. 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.

  19. The Effect of Plumes on the Dynamics of Supercontinents in a Self-Consistent Plate Tectonics Setting

    NASA Astrophysics Data System (ADS)

    Jain, C.; Rozel, A.; Tackley, P. J.

    2014-12-01

    Strong mantle plumes arising from the deep mantle can impose stresses on the continents, thereby facilitating continental rifting and disrupting the supercontinent cycle (Storey, Nature 1995; Santosh et al., Gondwana Research 2009). In recent years, several studies have characterized the relation between the location of the plumes and the continents, but with contradicting observations. While Heron and Lowman (GRL, 2010; Tectonophysics, 2011) propose regions where downwelling has ceased (irrespective of overlying plate) as the preferred location for plumes, O'Neill et al. (Gondwana Research, 2009) show an anti-correlation between the average positions of subducting slabs at continental margins, and mantle plumes at continental/oceanic interiors. Extent of continental motion depends on the heat budget of the mantle (CMB heat flux, radiogenic heating, mantle cooling). CMB heat flux is not well defined; however, the recent determination of core's high thermal conductivity requires a CMB heat flow of at least 12 TW (de Koker et al., PNAS 2012; Pozzo et al., Nature 2012; Gomi et al., PEPI 2013), much higher than early estimates of 3-4 TW (Lay et al., Nature 2008). Thus, it is necessary to characterize the effect of increased CMB heat flux on mantle dynamics. In almost all mantle convection simulations, the top boundary is treated as a free-slip surface whereas Earth's surface is a deformable free surface. Unlike free-slip, a free surface boundary condition allows for the development of topography and leads to realistic single-sided (asymmetric) subduction (Crameri et al., GJI 2012; Crameri et al., GRL 2012). Using StagYY code (Tackley, PEPI 2008), we test (i) the impact of increased basal heating on mantle dynamics with continents and self-consistent plate tectonics, including whether plumes prefer to develop under continents; (ii) the influence of a free surface on continents using the 'sticky air' approach, in which a low density and a small viscosity fluid layer is

  20. Spatial analysis of an intra-plate basaltic volcanic field in a compressional tectonic setting: South-eastern Australia

    NASA Astrophysics Data System (ADS)

    van den Hove, Jackson; Grose, Lachlan; Betts, Peter G.; Ailleres, Laurent; Van Otterloo, Jozua; Cas, Ray A. F.

    2017-04-01

    The Newer Volcanics Province (NVP) is a Pliocene to Recent intra-plate basaltic volcanic field (BVF) that has formed in a compressive tectonic setting (σv < σhmin < σHmax) and is not readily attributed to a single geodynamic process. A comprehensive spatial analysis of both monogenetic eruption centres and coeval vents of the NVP constrain factors that control the distribution and emplacement of volcanoes. A point-set of 434 eruption centres totalling 726 vents are divided into three geographical sub-provinces for analysis. Kernel density estimation and Poisson nearest neighbour analysis are used to scrutinize the distribution of eruption centres. A simple and novel fitted regression line method is used to determine the orientation of coeval vents, and Hough transform and two-point azimuth methods are used to identify alignments and alignment trends between eruption centres. The distribution of eruption centres and their relative spatial density corresponds with the extent of thinner lithosphere. Eruption centres of the NVP have a clustered distribution whilst smaller sub-sets of eruption centres are distributed more uniformly. The main alignment trends between coeval vents related to individual dikes and between eruption centres related to successive temporally discrete dikes are primarily oriented nearly parallel with pre-existing crustal fault trends. The frequency of volcanic alignments shows faults oriented nearly parallel to the orientation of the regional maximum horizontal compressive stress (σ1) are favourably utilised by intrusions over other fault trends. The depth from which pre-existing faults facilitate dike propagation is not constrained. We interpret they are likely important in preventing dikes from stalling and forming sills under a compressive stress field in the case of the NVP. It is also observed that coeval vent alignments are more strongly aligned in areas overlying consolidated basement relative to areas of poorly consolidated basin

  1. Chemostratigraphy and geochronology of the Kaniapiskau Supergroup, Labrador Trough indicate a major tectonic reorganization event hidden in the first cycle

    NASA Astrophysics Data System (ADS)

    Bekker, A.; Davis, D.; Wing, B.

    2009-05-01

    Deposition of the Paleoproterozoic Kaniapiskau Supergroup in the Labrador Trough started before 2.16 Ga and continued until shortly after ca. 1.88 Ga and is conventionally viewed as the result of three cycles of sedimentation in a single basin. The lower part of the first cycle is usually interpreted as rift to passive margin deposits, while the second and third cycles were likely deposited in the foreland basin. The age and depositional setting of the middle and upper parts of the lower cycle remains poorly constrained. We combine results of chemostratigraphic study of carbonates of the Kaniapiskau Supergroup with U-Pb geochronology of detrital zircons from the basal and middle parts of the first cycle to improve age constraints, understanding of tectonic setting, and correlation with other Paleoproterozoic basins along the eastern margin of the Superior Craton. The basal Chakonipau Formation has the youngest detrital zircon with an age of 2241 +/- 18 Ma, further constraining rifting between 2.22 and 2.16 Ga. The overlying lower part of the first cycle contains carbonates with highly positive carbon isotope values, typical for the 2.22-2.1 Ga Lomagundi Event. It is capped by black shales representing a flooding event and overlying turbiditic greywackes. Carbonates in the overlying upper part of the first cycle do not carry a 13C-enrichment and were therefore deposited after ca. 2.1 Ga. We infer a major break in sedimentation at the base of the Bacchus Formation consistent with its transgressive position over various units from the lower part of the first cycle. The flooding and deposition of immature sediments suggests a major reorganization in the basin likely related to the distal response to tectonic stresses. Similar events are also recognized in the Mistassini Basin, ~400 km SW along the margin of the Superior Craton and in other basins worldwide (e.g. on the Wyoming and Fennoscandian cratons), where black shales and turbidites straddle the end of the

  2. 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.

  3. 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.

  4. Tectonic Plates of China

    DTIC Science & Technology

    1977-04-01

    Cambrian, Ordovician. 3. Greenlandite diorite facies or hornblendite hornstone facies, Presinian and Sinian. 4. Caledonian granite. 5. Mylonite and its...4. Yiliang-Suichen fault. 3. Granite. 5. illr-Sitongfaut.4. Quartz diorite batholith. 6. Shiaojiang fault. 5. Ophiolite suite. 7. zemhofaut.6. Quartz... diorite line. 8. Chujiang fault. 7. Radioactive dating. 9. Shiping-Jiansui fault.8.De fal zo. 10. Anningho fault. 11. Luyejiang fault. 12. Yuan fault

  5. The provenance and tectonic setting of the Lower Devonian sandstone of the Danlin Formation in southeast Yangtze Plate, with implications for the Wuyi-Yunkai orogeny in South China Block

    NASA Astrophysics Data System (ADS)

    Zhang, Jiawei; Ye, Taiping; Li, Shuangcheng; Yuan, Guohua; Dai, Chuangu; Zhang, Hui; Ma, Yibo

    2016-12-01

    The South China Block was subject to widespread tectonic and magmatic events during the middle Ordovician to earliest Devonian which are collectively called the Wuyi-Yunkai orogeny. Two different hypotheses were formulated about the origin of the orogeny: collisional orogenesis and intracontinental orogenesis. Ages of 215 detrital zircons were obtained from quartz sandstones in the Lower Devonian Danlin Formation exposed in Dushan County, south Guizhou Province. The results show that the detrital zircons came from multiple source areas but with little indication of the Wuyi-Yunkai orogeny. The detrital zircons of early Paleozoic age account only for 1.9% of all samples. These zircons range from 476 to 402 Ma and originated from the early Paleozoic granites situated east of Dushan County. The mean 206Pb/238U age of the two youngest detrital zircons was 404 Ma, which constrains the maximum depositional age of the Danlin Formation. The detrital zircons are mostly within Neoproterozoic age (59.5%) and in the range 997 to 557 Ma. The zircon age pattern, morphology, and trace element characteristics combined with paleogeographic reconstruction interpret that these detrital zircons were supplied from igneous rocks in the Neoproterozoic Sibao and Danzhou Groups within the west Jiangnan orogen to the east of the study area. Mesoproterozoic zircons made up 20.9% of the grains and range from 1569 to 1055 Ma; the ages of most of these zircons coincide with those of zircons indicating the Grenvillian orogeny (1300-1000 Ma) in the Cathaysia Plate. The detrital zircon age data reveal that the study area was located in an intracontinental tectonic setting, both before and after the Wuyi-Yunkai orogeny. Therefore, the Cathaysia Plate was not separated from the Yangtze Plate by an ocean and the study area received sediments primarily from the Cathaysia Plate located to the southeast since the middle Ordovician. By the early Devonian, the sediments were supplied by the west Jiangnan

  6. 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

  7. Upper Paleogene shallow-water events in the Sandino Forearc Basin, Nicaragua-Costa Rica - response to tectonic uplift

    NASA Astrophysics Data System (ADS)

    Andjic, Goran; Baumgartner-Mora, Claudia; Baumgartner, Peter O.

    2016-04-01

    The Upper Cretaceous-Neogene Sandino Forearc Basin is exposed in the southeastern Nicaraguan Isthmus and in the northwestern corner of Costa Rica. It consists of an elongated, slightly folded belt (160 km long/30 km wide). During Campanian to Oligocene, the predominantly deep-water pelagic, hemipelagic and turbiditic sequences were successively replaced by shelf siliciclastics and carbonates at different steps of the basin evolution. We have made an inventory of Tertiary shallow-water limestones in several areas of Nicaragua and northern Costa Rica. They always appear as isolated rock bodies, generally having an unconformable stratigraphic contact with the underlying detrital sequences. The presence of these short-lived carbonate shoals can be attributed to local or regional tectonic uplift in the forearc area. The best-preserved exposure of such a carbonate buildup is located on the small Isla Juanilla (0.15 km2, Junquillal Bay, NW Costa Rica). The whole island is made of reef carbonates, displaying corals in growth position, associated with coralline red algae (Juanilla Formation). Beds rich in Larger Benthic Foraminifera such as Lepidocyclina undosa -favosa group permit to date this reef as late Oligocene. A first uplift event affected the Nicaraguan Isthmus, that rose from deep-water to shelfal settings in the latest Eocene-earliest Oligocene. The upper Oligocene Juanilla Formation formed on an anticline that developed during the early Oligocene, contemporaneously with other folds observed in the offshore Sandino Forearc Basin. During the early Oligocene, a period of global sea-level fall, the folded tectonic high underwent deep erosion. During the late Oligocene, a time of overall stable eustatic sea level, tectonic uplift gave way to moderate subsidence, creating accommodation space for reef growth. A 4th or 5th order (Milankovic-type) glacio-eustatic sea level rise, could also have triggered reef growth, but its preservation implies at least moderate

  8. Gridino melange zone of the Belomorian eclogite province: Succession of tectonic events and structural position of mafic dyke swarms

    NASA Astrophysics Data System (ADS)

    Babarina, I. I.; Sibelev, O. S.; Stepanova, A. V.

    2014-07-01

    Based on relationships between Paleoproterozoic mafic dykes, lithotectonic complexes, and tectonic structures of the Gridino Zone in the Belomorian eclogite province of the Fennoscandian Shield, deformations have been divided into groups differing in age and the succession of tectonic events has been reconstructed. The formation of Neoarchean eclogite-bearing melange was related to disintegration of large eclogite sheets in the course of near-horizontal ductile flow accompanied by syntectonic granitoid magmatism, multiple migmatization, and granulite-to amphibolite-facies metamorphism. The exotic blocks, including eclogites, were incorporated into TTG gneisses as sheets and lenses up to a few hundreds of meters in thickness and oriented conformably with gneissic banding. As a result of ductile flow, the lithotectonic complexes were transported at the level of discrete brittle-ductile deformations expressed as strike-slip faults and associated folds. Under conditions of a relatively rigid medium, individual structural elements underwent rotation approximately through 90° in plan view. Under the extension regime in the Early Paleoproterozoic, several swarms of mafic dykes were injected into the already cold framework rocks, as is evident from dyke morphology. The dykes crosscut all predated structures, included turned blocks, and are therefore important reference points for subdivision of Neoarchean and Paleoproterozoic processes. The Svecofennian postdyke tectonic activity was accompanied by local shearing and boudinage of metabasic rocks, development of quartz and pegmatite veins along tension cracks, disharmonic folding, and discrete retrograde metamorphism up to amphibolite-facies conditions. The postdyke deformations did not exert a substantial effect on the previously formed regional structure.

  9. 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

  10. 3-D simulation of temporal change in tectonic deformation pattern and evolution of the plate boundary around the Kanto Region of Japan due to the collision of the Izu-Bonin Arc

    NASA Astrophysics Data System (ADS)

    Hashima, A.; Sato, T.; Ito, T.; Miyauchi, T.; Furuya, H.; Tsumura, N.; Kameo, K.; Yamamoto, S.

    2010-12-01

    The Kanto region of Japan is in a highly complex tectonic setting with four plates interacting with each other: beneath Kanto, situated on the Eurasian and North American plates, the Philippine sea plate subducts and the Pacific plate further descends beneath the North American and Philippine sea plates, forming the unique trench-trench-trench triple junction on the earth. In addition, the Izu-Bonin (Ogasawara) arc on the Philippine sea plate is colliding with the Japan islands, which is considered to be a significant effect on the tectonics of Kanto. To reveal the present crustal structure and the present internal stress fields in such a complex tectonic setting, it is essential to comprehend them through the long-term tectonic evolution process. In this study, we estimate the temporal change in tectonic deformation pattern along with the geometry of the plate boundary around Kanto by numerical simulation with a kinematic plate subduction model based on the elastic dislocation theory. This model is based on the idea that mechanical interaction between plates can rationally be represented by the increase of the displacement discontinuity (dislocation) across plate interfaces. Given the 3-D geometry of plate interfaces, the distribution of slip rate vectors for simple plate subduction can be obtained directly from relative plate velocities. In collision zones, the plate with arc crust cannot easily descend because of its buoyancy. This can be represented by giving slip-rate deficit. When crustal deformation occurs, it also causes change in geometry of the plate boundary itself. This geometry change sensitively affects mechanical interaction at the plate boundary. Then the renewed plate-to-plete interaction alters crustal deformation rates. This feedback system has a large effect on collision zones. Indeed, the plate boundary around the Izu peninsula, the northernmost end of the Izu-Bonin arc, intends landward as large as 100 km. Iterating this effect sequentially

  11. 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.

  12. Tectonic leakage of fault bounded aquifers subject to non-isothermal recharge: a mechanism generating thermal precursors to seismic events

    NASA Astrophysics Data System (ADS)

    Hamza, Valiya M.

    2001-11-01

    illustrating model fits to thermal transients, identified as precursors to seismic events, in Firjusa (Turkmenistan), Didiweli (Georgia) and Izu peninsula (Japan). The possibility of obtaining complementary information on processes responsible for fluid flow during pre-seismic periods is pointed out. It appears that the occurrence of thermal anomalies associated with small-scale tectonic deformation may not be uncommon. Its detection depends on availability of suitable boreholes and of the facilities for monitoring of temperatures using high precision sensors over periods comparable to local recurrence periods of earthquakes.

  13. Plate Coupling and Transient Events Detection from Geodetic Measurements in Nicoya Peninsula, Costa Rica

    NASA Astrophysics Data System (ADS)

    Jiang, Y.; McCaffrey, R.; Wdowinski, S.; Dixon, T.; Protti, M.; Gonzalez, V. M.; Newman, A. V.; Feng, L.

    2011-12-01

    Aseismic tremor and slow slip events (SSE) are known to perturb the stress field at the plate subduction interface. Nicoya Peninsula in northern Costa Rica is located near the Middle America Trench (MAT), where the Cocos plate subducts underneath Caribbean plate. The subducting Cocos plate contains two types of subducting oceanic crust, East Pacific Rise (EPR) in the northern peninsula and Cocos-Nazca Spreading center (CNS) in the southern peninsula. The two crust types differ in subducting speed and orientation, topography, age and heat flow. This unique geological setting provides an opportunity to investigate the kinematics and dynamics of SSE and tremor. In the Nicoya peninsula SSE are found in high b-value regions and occur approximately every 20 months. However, the location and magnitude of SSE are still uncertain due to limited observations. Here we report additional geodetic observations and use a new GPS time-series inversion scheme to investigate simultaneously both SSE and interseismic locking patterns in the study area and their evolution with time. We solve for the steady inter-seismic velocity field and parameters characterizing SSE including slip amount and duration. A preliminary analysis of continuous and campaign GPS data using the time dependent geodetic inversion software TDefnode [McCaffrey 2009] reveals three slow-slipping patches for events in 2003, 2005, 2007 and 2009. Previous inversion analysis of Outerbridge et al. [2010] of the 2007 SSE identified the two of the three patches, a deep on at depth of ~25 km, and a shallower patch at depth of ~7 km. The third patch identified by our inversion at depth of ~15 km is similar in area and location to that reported by Protti et al. [2004] for the 2003 event.

  14. 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.

  15. A delicate balance of magmatic-tectonic interaction at Kilauea Volcano, Hawai`i, revealed from slow slip events

    USGS Publications Warehouse

    Montgomery-Brown, Emily; Poland, Michael; Miklius, Asta

    2015-01-01

    Eleven slow slip events (SSEs) have occurred on the southern flank of Kilauea Volcano, Hawai’i, since 1997 through 2014. We analyze this series of SSEs in the context of Kilauea’s magma system to assess whether or not there are interactions between these tectonic events and eruptive/intrusive activity. Over time, SSEs have increased in magnitude and become more regular, with interevent times averaging 2.44 ± 0.15 years since 2003. Two notable SSEs that impacted both the flank and the magmatic system occurred in 2007, when an intrusion and small eruption on the East Rift Zone were part of a feedback with a SSE and 2012, when slow slip induced 2.5 cm of East Rift Zone opening (but without any change in eruptive activity). A summit inflation event and surge in East Rift Zone lava effusion was associated with a SSE in 2005, but the inferred triggering relation is not clear due to a poorly constrained slip onset time. Our results demonstrate that slow slip along Kilauea’s décollement has the potential to trigger and be triggered by activity within the volcano’s magma system. Since only three of the SSEs have been associated with changes in magmatic activity within the summit and rift zones, both the décollement and magma system must be close to failure for triggering to occur.

  16. Sequential Mesozoic and Cenozoic tectonic events in Grant range and Railroad Valley, Nye County, Nevada

    SciTech Connect

    Flanigan, D.M.H.

    1989-03-01

    A series of palinspastic geologic cross sections were constructed for the Grant Range-Railroad Valley (GR-RRV) area. This palinspastic reconstruction differs from previously published interpretations in two major ways. First, new granite age dates and a chronological framework deduced by Fryxell in 1984 in the central and southern Grant Range were applied, where possible, to the northern Grant Range. Second, recent drilling was correlated to outcrop interpretations. Results of this reconstruction suggest that significant tectonism affected the GR-RRV area earlier than previously believed. Mesozoic compression produced east-vergent folding in the GR-RRV area, followed by Late Cretaceous intrusion. Local, possibly blind thrusting may have been associated with the intrusion. Above the granite dome, shallow, brittle, listric faulting and deeper low-angle attenuation faulting accommodated intrusion. After intrusion, relative quiescence prevailed during the deposition of the Sheep Pass Formation and the lower Garrett Ranch Group ignimbrite. Uplift in the middle and late Oligocene produced pervasive listric, normal, east-dipping faulting that may in part be represented by apparent growth faults within volcanics. Subsequent west-dipping listric faulting was in part gravity driven. High-angle Miocene normal faulting initiated the present structure. All commercial oil fields in Railroad Valley are producing from Miocene and younger structures. However, an understanding of older structures will allow more accurate prediction of reservoirs within a particular, prospective, younger structure.

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

    DOE PAGES

    Simmons, N. A.; Myers, S. C.; Johannesson, G.; ...

    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

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

  19. 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.

  20. Spectral analysis of the gravity and elevation along the western Africa-Eurasia plate tectonic limit: Continental versus oceanic lithospheric folding signals

    NASA Astrophysics Data System (ADS)

    Muñoz-Martín, A.; De Vicente, G.; Fernández-Lozano, J.; Cloetingh, S.; Willingshofer, E.; Sokoutis, D.; Beekman, F.

    2010-12-01

    Large-scale folding is a key mechanism of lithospheric deformation and has been described in many parts of the Earth, both for the continental and oceanic lithospheres. Some aspects of this process such as the presence of coupling/decoupling between the crustal deformation and the mantle lithosphere, or between different lithospheres, make it necessary to accurately control the periodic characteristics of the elevation and of the gravity signal. 1D spectral analysis of gravity and topography profiles is sensitive to a series of factors: the location, length and orientation of the profiles, as well as the number of samples taken. We carry out a systematic analysis of the periodicities in the topography and gravity, both 1D and 2D, along the western border of the Africa-Eurasia plate tectonic boundary. We analyze the sensitivity of the 1D and 2D spectral analysis in order to compare the results along a plate boundary where oceanic and continental lithospheres are in contact with different tectonic, kinematic and rheological aspects. Our 1D spectral results indicate that the greater the profile length, the longer the wavelength peaks that are found. Nevertheless there are some periodic signals that appear in almost all the analyzed profiles: 100-250 km for the N-S profiles across oceanic plate boundary and 150-250 km where the plate boundary is developed over continental lithospheres. The 2D spectral analysis avoids the problems found in relation to the particular location of the profile but the resulting wavelengths are slightly higher than those obtained from the 1D spectral analysis. The wavelengths estimated for both oceanic and continental lithospheres at the Africa-Eurasia boundary (> 250 km) show low values of mean mantle strength (< 10 13 Pa m). The presence of lithospheric folds means that the continental and oceanic lithospheres are mechanically coupled. This had previously been suggested for Iberia but not for the limit between S Iberia and the Terceira

  1. 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)

  2. A multigap resistive plate chamber array for the Extreme Energy Events project

    NASA Astrophysics Data System (ADS)

    De Gruttola, D.; Abbrescia, M.; Agocs, A.; Aiola, S.; Antolini, R.; Avanzini, C.; Baldini Ferroli, R.; Bencivenni, G.; Bossini, E.; Bressan, E.; Chiavassa, A.; Cicalò, C.; Cifarelli, L.; Coccia, E.; De Pasquale, S.; Di Giovanni, A.; D'Incecco, M.; Dreucci, M.; Fabbri, F. L.; Frolov, V.; Garbini, M.; Gemme, G.; Gnesi, I.; Gustavino, C.; Hatzifotiadou, D.; La Rocca, P.; Li, S.; Librizzi, F.; Maggiora, A.; Massai, M.; Miozzi, S.; Panareo, M.; Paoletti, R.; Perasso, L.; Pilo, F.; Piragino, G.; Regano, A.; Riggi, F.; Righini, G. C.; Sartorelli, G.; Scapparone, E.; Scribano, A.; Selvi, M.; Serci, S.; Siddi, E.; Spandre, G.; Squarcia, S.; Taiuti, M.; Tosello, F.; Votano, L.; Williams, M. C. S.; Yanez, G.; Zichichi, A.; Zouyevski, R.

    2014-10-01

    The Extreme Energy Events (EEE) Project is a Centro Fermi - CERN - INFN - MIUR Collaboration Project for the study of extremely high energy cosmic rays, which exploits the Multigap Resistive Plate Chamber (MRPC) technology. The excellent time resolution and good tracking capability of this kind of detector allows us to study Extensive Air Showers (EAS) with an array of MRPC telescopes distributed across the Italian territory. Each telescope is installed in a high school, with the further goal to introduce students to particle and astroparticle Physics. The status of the experiment and the results obtained are reported.

  3. Forced relative displacements of the core and mantle as the basic mechanism of secular changes of the Earth shape and lithosphere plates tectonics

    NASA Astrophysics Data System (ADS)

    Barkin, Yury

    2010-05-01

    The summary. In the work planetary changes of a figure of the Earth and geoid in present epoch are discussed. Contrast and asymmetric geodetic changes of northern and southern hemispheres are revealed. The phenomenon of lengthening of latitude circles of a southern hemisphere and shortening of lengths of latitude circles of northern hemisphere, the phenomenon of expansion of a southern hemisphere and, accordingly, compression of northern hemisphere in relation to the center of mass of the Earth have been predicted. The reasons of the planetary tendency of displacement (drift) of plates in northern direction are studied. The geodynamic model is developed, on which the basic moving force in tectonics of plates is a gravitational influence of a moveable core of the Earth on all layers of the mantle, and also on blocks of the crust and lithosphere plates. In a base of all tectonic and geological reorganizations the mechanism of the forced relative oscillations and swings of the core and the mantle of the Earth in various time scales, including geological timescale lays. 1 Mechanism of formation and changes of the pear-shaped form of the Earth. According to developed geodynamic model a pear-shaped form of planets is not their given property for all time (as believed before scientists), and is the dynamic response to the slow forced relative displacements of the core and mantle [1]. Than more a relative displacement of the core and mantle (eccentricity of the core in some geology epoch), is especially clearly expressed pear-shaped form. The planet Mars possesses a big pear-shaped form and by our estimations the core of this planet is displaced in northern direction (to latitude in approximately 60° N) on 20-25 km [2]. An eccentricity of the Earth core is less (estimations give displacement about 3-4 km in direction to Brazil [3]) and it pear-shaped form is much less. 2 The phenomenon of asymmetric lengthening of latitude circles of southern and northern hemispheres of

  4. 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

  5. Tree ring correlation between prehistoric landslides and abrupt tectonic events in Seattle, washington.

    PubMed

    Jacoby, G C; Williams, P L; Buckley, B M

    1992-12-04

    Radiocarbon ages of submerged trees on landslide deposits in Lake Washington, Seattle, indicate that the most recent slides in three separate areas may have occurred simultaneously about 1000 years ago. Tree ring crossdating shows that seven bark-bearing trees from one of these recent slides and a tree 23 kilometers to the northwest in a probable tsunami deposit on the shore of Puget Sound died in the same season of the same year. The close coincidence among the most recent lake landslides, a probable tsunami, abrupt subsidence, and other possible seismic events gives evidence for a strong prehistoric earthquake in the Seattle region.

  6. Long Range Hydroacoustic Propagation from Small Explosives to Large Tectonic Events (Invited)

    NASA Astrophysics Data System (ADS)

    Degroot-Hedlin, C. D.

    2009-12-01

    A wide variety of hydroacoustic signals have been detected near Diego Garcia, in the Indian Ocean, and at other hydro-acoustic stations operated by the Comprehensive Test Ban Treaty Organization. The durations range from several seconds for signals from explosive shots in temperate latitudes, tens of seconds for explosions within the Antarctic Circumpolar Current (ACC), several minutes for small earthquakes near the continental shelf, to over half an hour for propagation from a large tsunamigenic event, for source-receiver distances of several thousands of kilometers. The primary mechanisms used to explain the variability in duration are the existence of a distributed source region, source size, and dispersion. Travel time, and hence dispersion is computed using normal modes; bottom interacting higher order modes are neglected. For the explosive shots, the observed and predicted travel times and signal dispersion agree to within 2 s, under the assumptions that propagation is adiabatic and follows a geodesic path. Dispersion is predicted and observed to increase with propagation distance through the ACC. The duration of the underwater earthquakes along the continental shelf are independent of source size, and significantly exceeds the dispersion times computed for the given location, indicating a distributed source region; the azimuths derived from the hydro-acoustic signals further corroborate this. Finally, the long duration of the acoustic signal from the tsunamigenic event is used to derive the velocity and direction of rupture.

  7. 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

  8. The assessment of the transformation of global tectonic plate models and the global terrestrial reference frames using the Velocity Decomposition Analysis

    NASA Astrophysics Data System (ADS)

    Ampatzidis, Dimitrios; König, Rolf; Glaser, Susanne; Heinkelmann, Robert; Schuh, Harald; Flechtner, Frank; Nilsson, Tobias

    2016-04-01

    The aim of our study is to assess the classical Helmert similarity transformation using the Velocity Decomposition Analysis (VEDA). The VEDA is a new methodology, developed by GFZ for the assessment of the reference frames' temporal variation and it is based on the separation of the velocities into two specified parts: The first is related to the reference system choice (the so called datum effect) and the latter one which refers to the real deformation of the terrestrial points. The advantage of the VEDA is its ability to detect the relative biases and reference system effects between two different frames or two different realizations of the same frame, respectively. We apply the VEDA for the assessment between several modern tectonic plate models and the recent global terrestrial reference frames.

  9. 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.

  10. 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

  11. 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).

  12. Evolution of the Late Pleistocene Aspe River (Western Pyrenees, France). Signature of climatic events and active tectonics

    NASA Astrophysics Data System (ADS)

    Nivière, Bertrand; Lacan, Pierre; Regard, Vincent; Delmas, Magali; Calvet, Marc; Huyghe, Damien; Roddaz, Bernard

    2016-03-01

    We make use of the cosmogenic nuclide 10Be exposure to date an alluvial terrace of the Aspe River in the foothills of the northwestern Pyrenees. Initially ascribed to the Rissian glaciation, our dating shows that the terrace was abandoned at 18 ± 2 kyr. In reference to the Late Pleistocene climatic chronology, two kinds of terraces can be distinguished: high-standing fill terraces probably deposited during glacial events and lower cut-in-fill and strath terraces cut during the postglacial river incision. A part of the terrace aggradations could have occurred during the Würmian glacial episodes. Hence, the dated terrace fits in with the prevailing view of incision during climate transitions. Our study also shows that elevation is not a good criterion of terrace correlation, which should be better carried out on the basis of absolute dating. In addition, this dating also suggests a potential Late Pleistocene fault reactivation of the Mail Arrouy thrust in this tectonically active area of the Western Pyrenees.

  13. 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.

  14. 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).

  15. 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.

  16. Temporal change in plate coupling and long-term slow slip events in southwestern Japan

    NASA Astrophysics Data System (ADS)

    Ochi, Tadafumi

    2015-12-01

    In the southwestern part of Japan, many large earthquakes have been reported and many geodetic or seismic observations have been performed to monitor crustal deformation due to the interaction between the subducting Philippine Sea plate and the overriding continental plate along the Suruga-Nankai trough. These precise observations provide insight into aseismic stress-releasing processes such as slow slip events (SSEs). In this study, I focus on the effect of SSEs on interplate coupling to reveal the overall temporal evolution of interplate states along the trough in southwestern Japan. I focus mainly on the western part of the subduction zone, called the Nankai region. In this part, three SSEs (in 1997, 2003, and 2010) were detected during the period in which observations are available. Interplate coupling recovered quickly after the SSEs terminated. The eastern part of this region shows consistently strong coupling whether SSEs occur or not. Long-term SSEs are distributed between the coupling area and the area where tremors occur. I also examine the balance between stress accumulation and release at four points in the region. Below the eastern part of the strongly coupled area, at a depth of ∼15 km, constant coupling of about 7 cm/yr takes place. In the center of the SSE region, at a depth of ∼25 km, ∼40% of the accumulated stress is released through SSEs, with the rest contributing to the stress accumulation process.

  17. 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.

  18. 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.

  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. A revised estimate of Pacific-North America motion and implications for Western North America plate boundary zone tectonics

    NASA Technical Reports Server (NTRS)

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

    1987-01-01

    Marine magnetic profiles from the Gulf of Californa are studied in order to revise the estimate of Pacific-North America motion. It is found that since 3 Ma spreading has averaged 48 mm/yr, consistent with a new global plate motion model derived without any data. The present data suggest that strike-slip motion on faults west of the San Andreas is less than previously thought, reducing the San Andreas discrepancy with geodetic, seismological, and other geologic observations.

  1. Neutron star crustal plate tectonics. I. Magnetic dipole evolution in millisecond pulsars and low-mass X-ray binaries

    SciTech Connect

    Ruderman, M. )

    1991-01-01

    Crust lattices in spinning-up or spinning-down neutron stars have growing shear stresses caused by neutron superfluid vortex lines pinned to lattice nuclei. For the most rapidly spinning stars, this stress will break and move the crust before vortex unpinning occurs. In spinning-down neutron stars, crustal plates will move an equatorial subduction zone in which the plates are forced into the stellar core below the crust. The opposite plate motion occurs in spinning-up stars. Magnetic fields which pass through the crust or have sources in it move with the crust. Spun-up neutron stars in accreting low-mass X-ray binaries LMXBs should then have almost axially symmetric magnetic fields. Spun-down ones with very weak magnetic fields should have external magnetic fields which enter and leave the neutron star surface only near its equator. The lowest field millisecond radiopulsars seem to be orthogonal rotators implying that they have not previously been spun-up in LMXBs but are neutron stars initially formed with periods near 0.001 s that subsequently spin down to their present periods. Accretion-induced white dwarf collapse is then the most plausible genesis for them. 29 refs.

  2. Late Carboniferous-early Permian events in the Trans-European Suture Zone: Tectonic and acid magmatic evidence from Poland

    NASA Astrophysics Data System (ADS)

    Żelaźniewicz, A.; Oberc-Dziedzic, T.; Fanning, C. M.; Protas, A.; Muszyński, A.

    2016-04-01

    The Trans-European Suture Zone (TESZ) links the East and West European Platforms. It is concealed under Meso-Cenozoic cover. Available seismic data show that the lower crustal layer in the TESZ is an attenuated, 200 km wide, SW margin of Baltica. The attenuation occurred when Rodinia broke-up, which gave rise to evolution of the thinned, thus relatively unstable margin of Baltica. It accommodated accretions during Phanerozoic events. We focus on acid magmatism, specifically granitoid, observed close to the SW border of the TESZ in Poland. This border is defined by the Dolsk Fault Zone (DFZ) and the Kraków-Lubliniec Fault Zone (KLFZ) on which dextral wrenching developed as a result of the Variscan collision between Laurussia and Gondwana. The granitoids at the DFZ and KLFZ were dated at 300 Ma. In the Variscan foreland that overlaps the TESZ, orogenic thickening continued to 307-306 Ma, possibly contributed to melting of the thickened upper continental crust (εNd300 = - 6.0 to - 4.5) and triggered the tectonically controlled magmatism. The wrenching on the TESZ border faults caused tensional openings in the basement, which promoted magmatic centers with extrusions of rhyolites and extensive ignimbrites. The Chrzypsko-Paproć and Małopolska magmatic centers were developed at the DFZ and KLFZ, respectively. The magmatic edifices commenced at 302 Ma with relatively poorly evolved granites, which carried both suprasubduction and anorogenic signatures, then followed by more evolved volcanic rocks (up to 293 Ma). Their geochemistry and inherited zircons suggest that the felsic magmas were mainly derived from upper crustal rocks, with some mantle additions, which included Sveconorwegian and older Baltican components. The complex TESZ, with Baltica basement in the lower crust, was susceptible to transient effects of mantle upwelling that occurred by the end of the Variscan orogeny and resulted in an episode of the "flare-up" magmatism in the North German-Polish Basin.

  3. Temporal correlation of magmatic-tectonic events in the lower and upper crust in north-east Australia

    NASA Astrophysics Data System (ADS)

    Murgulov, Valeria; Griffin, William L.; O'Reilly, Suzanne Y.

    2012-07-01

    Hf model ages yielded by rutiles in a garnet-rich lower-crustal granulite xenolith from the McBride Province and whole-rock Nd and Hf model ages for the plagioclase- and garnet-rich Chudleigh and McBride granulites overlap with the well-defined U-Pb ages for detrital zircons and zircons in granitoids (Murgulov et al. Chem Geol 245:198-218, 2007; Mineral Petrol 95:17-45, 2009), suggesting temporal correlation of magmatic-tectonic events in the lower and upper crust in the north-east Australian craton. Intrusion of basaltic magmas into and below the lower crust beneath the Chudleigh Province around 1.4, 1.7 and 2.3 Ga and beneath the McBride Province around 1.5, 1.7, 2.3 and 2.5 Ga provided heat for remelting and supplied magmas with juvenile mantle isotope signatures to the upper crust. Similar magmas provided enough heat to cause melting in the lower crust beneath the Chudleigh Province around 0.12 and 0.8-0.9 Ga and beneath the McBride Province around 0.42, 0.8-0.9 Ga, 1.1 and 1.3 Ga but were not sufficient to cause significant melting in the upper crust. A wide range in initial 176Hf/177Hf values and a ~1.55 Ga Hf model age yielded by rutiles in the McBride granulite provide a link to the genesis of ~420 Ma granitoids. The data for a plagioclase-rich granulite from the Atherton Province are similar to those for the Chudleigh and McBride granulites. However, additional samples are required to test whether the lower crust of the Tasman orogenic belt is lithologically and isotopically similar to the lower crust of the craton.

  4. Using Paleomagnetic, Geochemical and Structural Data to Recognize Post-metamorphic Tectonic Events in the Caledonide Terranes of Western Svalbard.

    NASA Astrophysics Data System (ADS)

    Michalski, K.; Manby, G.; Nejbert, K.; Domańska Siuda, J.; Burzyński, M.

    2015-12-01

    A total of 170 oriented palaeomagnetic samples of Proterozoic-Lower Palaeozoic metacarbonates and metabasites from 28 sites in Hornsund and Oscar II Land, Western Spitsbergen (Fig. 1A) were investigated at the Polish Academy of Sciences Institute of Geophysics . Petrographic and rock-magnetic analyses revealed that the ferromagnetic carriers are dominated by metamorphic pyrrhotite and Low-Ti magnetite. Simultaneous in situ laser ablation 40Ar/39Ar age determination of the samples indicate that a 426-380 Ma Caledonian sensu lato thermal overprint was followed by younger events in the 377-326 Ma and ca. 300 Ma intervals (Fig. 1B). The latter two ages appear to coincide with recently published seismic data indicating that Late Devonian - Carboniferous rifting was followed by similar crustal extension in the SW Barents shelf area in Late Carboniferous time. Published in situ palaeomagnetic directions from Hornsund area in SW Svalbard fit the Silurian sector of the Baltica reference path suggesting that the geometry of the sampled Caledonian Sofekammen Syncline was not modified during following Svalbardian or Eurekan deformation events (Fig. 1C). In contrast, palaeomagnetic directions obtained from Oscar II Land are distant from Caledonian sector of Baltica reference path (Fig. 1C). It is suggested here, that the most significant mechanism responsible for the rotation of the palaeomagnetic directions and modification of geometry of Caledonian tectonic structures of Oscar II Land was listric normal faulting related to the opening of the North Atlantic -Arctic Ocean Basins. Late Cretaceous- Early Tertiary Eurekan folding and thrust faulting appear to have had minor influence on the palaeomagnetic directions obtained. This study is part of the Polish National Science Centre - DEC 2011/03/D/ST10/05193 PALMAG 2012-2016 funded project . Fig. 1. A. Geological sketch map of Western Spitsbergen. B. Probability diagrams derived from insitu 40Ar/39Ar laser ablation age

  5. Plio-Quaternary paleostresses in the Atlantic passive margin of the Moroccan Meseta: Influence of the Central Rif escape tectonics related to Eurasian-African plate convergence

    NASA Astrophysics Data System (ADS)

    Chabli, Ahmed; Chalouan, Ahmed; Akil, Mostapha; Galindo-Zaldívar, Jesús; Ruano, Patricia; Sanz de Galdeano, Carlos; López-Garrido, Angel Carlos; Marín-Lechado, Carlos; Pedrera, Antonio

    2014-07-01

    The Atlantic Moroccan Meseta margin is affected by far field recent tectonic stresses. The basement belongs to the variscan orogen and was deformed by hercynian folding and metamorphism followed by a post-Permian erosional stage, producing the flat paleorelief of the region. Tabular Mesozoic and Mio-Plio-Quaternary deposits locally cover the Meseta, which has undergone recent uplift, while north of Rabat the subsidence continues in the Gharb basin, constituting the foreland basin of the Rif Cordillera. The Plio-Quaternary sedimentary cover of the Moroccan Meseta, mainly formed by aeolian and marine terraces deposits, is affected by brittle deformations (joints and small-scale faults) that evidence that this region - considered up to date as stable - is affected by the far field stresses. Striated faults are recognized in the oldest Plio-Quaternary deposits and show strike-slip and normal kinematics, while joints affect up to the most recent sediments. Paleostress may be sorted into extensional, only affecting Rabat sector, and three main compressive groups deforming whole the region: (1) ENE-WSW to ESE-WNW compression; (2) NNW-SSE to NE-SW compression and (3) NNE-SSW compression. These stresses can be attributed mainly to the NW-SE oriented Eurasian-African plate convergence in the western Mediterranean and the escape toward the SW of the Rif Cordillera. Local paleostress deviations may be related to basement fault reactivation. These new results reveal the tectonic instability during Plio-Quaternary of the Moroccan Meseta margin in contrast to the standard passive margins, generally considered stable.

  6. 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.

  7. Precambrian and Mesozoic plate margins: Montana, Idaho and Wyoming with field guides for the 8th international conference on basement tectonics

    SciTech Connect

    Lewis, S.E.; Berg, R.B.

    1988-07-01

    Two field trips held in conjunction with the 8th International Conference on Basement Tectonics are the raison d'etre for this volume, which would perhaps otherwise seem an eclectic association. The unifying theme is an investigation of the nature of plate margins in time and space, consonant with the main theme of the conference, Characterization and Comparison of Precambrian Through Mesozoic Continental Margins. Papers presented at the conference will be published in a separate volume by the International Basement Tectonics Association, Inc. The first field trip is at least a preliminary attempt at an overview of the Precambrian (predominantly Archean) crystalline basement of southwestern Montana. A number of interesting investigations have been focused on this region in recent years. Thus, papers in the first part of this volume take the reader from the Stillwater Complex across the Beartooth Plateau, to the northern borders of Yellowstone National Park on to the southern Madison Range, and finally to some of the western-most (probable) Archean exposures in the Highland Mountains south of Butte. Moving considerably forward on the geologic time scale, the other broad topic dealt with in a second field trip and complementary articles is a relatively recent collisional terrane in central Idaho and eastern Oregon. Examined are portions of the Idaho batholith and its enigmatic and fascinating marginal rocks, and to the west, the heart of the suture zone itself in the Wallowa-Seven Devils terrane with its group of exotic intrusive, metavolcanic, and metasedimentary rocks. Individual papers are processed separately for the data base.

  8. Cenozoic prograding sequences of the Antarctic continental margin: a record of glacio-eustatic and tectonic events

    USGS Publications Warehouse

    Cooper, A. K.; Barrett, P.J.; Hinz, K.; Traube, V.; Letichenkov, G.; Stagg, H.M.J.

    1991-01-01

    times, like today, by little or no clastic sedimentation on the continental shelf other than beneath retreated ice shelves lying far from the continental sheld edge. Ice streams carve broad depressions across the shelf and carry abundant basal sediments directly to the continental shelf edge, thereby creating troughmouth fans and sheet-like prograding sequences (i.e. type IA sequences). Numerous acoustic unconformities and multiple overcompacted layers within the prograding sequences suggest major fluctuations of the Antarctic Ice Sheet. The available drilling and seismic interpretations provide the following history: (1) Cenozoic ice sheets have existed in places near the continental shelf since middle to late Eocene time. (2) A grounded Antarctic ice sheet first expanded to the continental shelf edge, with probable overdeepening of the outer shelf, in late Eucene to early Oligocene time in Prydz Bay, possibly in early Miocene time in the Ross Sea, and at least by middle Miocene time in the Weddell Sea. (3) The relative amounts of shelf prograding and inferred ice-volume variations (and related sea-level changes) have increased since middle to late Miocene time in the eastern Ross Sea, Prydz Bay, and possibly Weddell Sea. Our analysis is preliminary. Further acoustic surveys and scientific drilling are needed to resolve the proximal Antarctic record of glacio-eustatic, climatic, and tectonic events recorded by the prograding sequences. ?? 1991.

  9. Dynamic evolution of continental and oceanic lithosphere in global mantle convection model with plate-like tectonics and one sided subduction.

    NASA Astrophysics Data System (ADS)

    Ulvrova, Martina; Coltice, Nicolas; Tackley, Paul

    2015-04-01

    Drifting of continents, spreading of the seafloor and subduction at convergent boundaries shape the surface of the Earth. On the timescales of several hundreds of millions of years, divergent boundaries at mid-ocean ridges are created and destroyed in within the Wilson cycle. This controls the evolution of the Earth as it determines the heat loss out. Presence of floating continents facilitates the Earth-like mobile lid style of convection as convective stresses are concentrated on the rheological boundary between oceanic and continental lithosphere. Subducting slabs allow for the surface material to be buried down into the mantle and have an important effect on surface tectonics. The main feature of the subduction zones observed on Earth is that it is single-sided forming the deep trenches. Recently, different numerical models were successful in reproducing one-sided subduction by allowing for the vertical deformation of the Earth surface (Crameri and Tackley 2014). In the meantime, advances were made in modelling continental break-up and formation (Rolf et al. 2014). In this study we perform numerical simulations of global mantle convection in spherical annulus geometry with strongly depth and temperature dependent rheology using StagYY code (Tackley 2008). In these models plate tectonics is generated self-consistently and features one-sided subduction on ocean-ocean plate boundary as well as floating continents. We focus on determining (1) the influence of one-sided subduction on the dynamics of the system (2) formation and breakup of continents. Rerefences: Crameri, F. and P. J. Tackley, Spontaneous development of arcuate single-sided subduction in global 3-D mantle convection models with a free surface, J. Geophys. Res., 119(7), 5921-5942, 2014. Rolf, T., N. Coltice and P. J. Tackley (2014), Statistical cyclicity of the supercontinent cycle, Geophys. Res. Lett. 41, 2014. Tackley, P. J., Modellng compressible mantle convection with large viscosity contrasts in

  10. Analysis of geometry of volcanoes and faults in Terceira Island (Azores): Evidence for reactivation tectonics at the EUR/AFR plate boundary in the Azores triple junction

    NASA Astrophysics Data System (ADS)

    Navarro, A.; Lourenço, N.; Chorowicz, J.; Miranda, J. M.; Catalão, J.

    2009-02-01

    The late Pliocene to Quaternary (5 Ma) volcanism in the central and eastern Azores Archipelago is related to the Eurasia/Africa divergence, but a clear deformation pattern has not yet been established at this location. This work focuses on the contribution of Synthetic Aperture Radar (SAR) scenes and Digital Elevation Models (DEM), complemented with geophysical, geodetic and morpho-structural data, to establish the geometric relationships between volcanic edifices and tectonic structures in the central and eastern Azores Archipelago. Bathymetric data were also used to extend field observations to the significant submarine area of the Azores plateau. Strikes of extension fractures, directly observed or inferred from elongated volcanic vents or linear volcanic clusters in Terceira Island, indicate that volcanism is mainly controlled by regional extension as given by NUVEL-1A plate motion model. Additionally, other directions were also detected for extension fractures around the Santa Barbara volcano (defining a radial pattern) and in the central part of the island (exhibiting an S-shape pattern). Although most of the volcanic vents are controlled by extension fractures, some seem to be controlled by faulting, such as the case of the ones rooted in releasing bends along strike-slip or oblique-slip faults in the central part of the island. Concerning the Azores plateau, most of the structures have directions that do not directly fit with present-day direction of relative motion (˜ N70°) between Eurasia and Africa. Directions ranging from N110° to N125°, found mainly along the Terceira rift, are interpreted as ancient transform directions, reactivating as transtensional fault zones due to the present-day plate motion. N-S directions are also visible in the plateau, being interpreted as former middle-oceanic rift faults reactivated as left-lateral fault zones. These results contrast with the volcanic expression in other hotspot dominated oceanic islands such as the

  11. Formation and metasomatism of continental lithospheric mantle in intra-plate and subduction-related tectonic settings

    NASA Astrophysics Data System (ADS)

    Ionov, Dmitri

    2010-05-01

    Our knowledge of the origin and evolution of the continental lithospheric mantle (CLM) remains fragmentary and partly controversial in spite of recent advances in petrologic, geochemical and geophysical studies of the deep Earth and experimental work. Debate continues on a number of essential topics, like relative contributions of partial melting, metasomatism and ‘re-fertilisation' as well as the timing, conditions and tectonic settings of those processes. These topics can be addressed by studies of ultramafic xenoliths in volcanic rocks which arguably provide the least altered samples of modern and ancient CLM. The subcontinental lithosphere is thought to be a mantle region from which melts have been extracted, thus making the lithosphere more refractory. Melting degrees can be estimated from Al contents while the depth of melt extraction can be assessed from Al-Fe (Mg#) relations in unmetasomatized melting residues in comparison with experimental data, e.g. [1]. High silica and opx in the residues may indicate melting in water-rich conditions. High-precision Mg# and Mn for olivine may constrain degrees and conditions of partial melting and/or metasomatism, tectonic settings, modal compositions (e.g. presence of garnet) and equilibration conditions of mantle peridotites [2]. These estimates require both adequate sampling and high-quality major element and modal data; sampling and analytical uncertainties in published work may contribute substantially to chemical heterogeneities (and different origins) inferred for CLM domains [3]. Very fertile peridotite xenolith suites are rare worldwide [3]. They were initially viewed as representing mantle domains that experienced only very small degrees of melt extraction but are attributed by some workers to ‘refertilization' of refractory mantle by percolating asthenospheric melts. Such alternative mechanisms might be valid for some rare hybrid and Fe-enriched peridotites but they fail to comprehensively explain modal

  12. 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.

  13. Stratigraphic responses to a major tectonic event in a foreland basin: the Ecuadorian Oriente Basin from Eocene to Oligocene times

    NASA Astrophysics Data System (ADS)

    Christophoul, Frédéric; Baby, Patrice; Dávila, Celso

    2002-02-01

    The Eocene to Oligocene sediments of the Ecuadorian Oriente Basin record two kinds of second-order stratigraphic response to the tectonic evolution. Lower Eocene shows evidences of local scale syntectonic deposits. This tectonic activity can be related to right lateral convergent movements inverting pre-cretaceous extensional structures. Upper Eocene and Oligocene sediments are integrated as the expression of an isostatic rebound characterizing a basin scale syntectonic deposition. This response is evidenced by a reciprocal architecture of the depositional sequences identified in the sedimentary formations. These data have allowed us to propose a new geodynamic model for the Paleogene evolution of the Oriente Basin.

  14. 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

  15. 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.

  16. 4D Arctic: A Glimpse into the Structure and Evolution of the Arctic in the Light of New Geophysical Maps, Plate Tectonics and Tomographic Models.

    PubMed

    Gaina, Carmen; Medvedev, Sergei; Torsvik, Trond H; Koulakov, Ivan; Werner, Stephanie C

    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.

  17. Evolution of the Earth as an andesite planet: water, plate tectonics, and delamination of anti-continent

    NASA Astrophysics Data System (ADS)

    Tatsumi, Yoshiyuki; Sato, Takeshi; Kodaira, Shuichi

    2015-06-01

    The Earth is unique in our solar system in having a buoyant, highland-forming continental crust with a differentiated, andesitic composition; thus, it can be referred to as an "andesite planet." Andesitic magmatism is associated with convergent plate margins such as subduction zones, leading to a broad consensus that this setting has been the major site of continental crust formation. However, while andesites are dominant in mature continental arcs, they are subordinate in juvenile oceanic arcs, resulting in a great conflict regarding the creation of the continental crust. We focused on the Izu-Bonin-Mariana arc to assess this problem, as it is a juvenile intra-oceanic arc with a mid-crustal layer that has a seismic velocity identical to that of the bulk continental crust. Petrological modeling of the production of andesitic melts by the mixing of mantle-derived basalt with crust-derived, rhyolite magmas successfully reproduced the crust/mantle structure observed in seismic profiles of the Izu-Bonin-Mariana arc. As a result, we presented a challenging hypothesis: the continent was created in the ocean. One key mechanism that differentiates initial basaltic arc crust to evolved, andesitic continental crust may be the delamination of SiO2-depleted residues of crustal melting, termed "anti-continent," from the arc crust.

  18. Tectonics and metallogenic provinces

    USGS Publications Warehouse

    Guild, P.W.

    1983-01-01

    Various theories have been advanced to explain the well-known uneven distribution of metals and ore-deposit types in space and time. Primordial differences in the mantle, preferential concentration of elements in the crust, the prevalence of ore-forming processes at certain times and (or) places, and combinations of one or several of these factors have all been called upon to account for the "metallogenic provinces," which can be defined loosely as regions containing similar deposits of one or a group of metals or minerals. Because many, perhaps most, provinces have complex, multistage origins, the relative importance of inheritance vs. process is still controversial. In recent years the geographic relationship of many geologically young provinces to present-day plate-tectonic positions (accreting or consuming margins, intraplate structures, etc.) has been widely recognized, and the presumption is strong that older provinces had similar relationships to former plates. As most ore deposits resulted from a favorable conjunction of geological processes that are no longer operative, elucidation of their genesis requires reconstruction of the geologic history of the province, with particular emphasis on events coeval with mineralization. Tectonic analysis is an important aspect of this reconstruction; data from orbiting satellites have contributed greatly to this analysis, as the voluminous literature of the past decade testifies. Both the synoptic view of large areas and the ability to emphasize faint contrasts have revealed linear, curvilinear, and circular features not previously recognized from field studies. Some of these undoubtedly reflect basement structures that have contributed to the development, or limit the extent, of metallogenic provinces. Their recognition and delineation will be increasingly valuable to the assessment of resources available and as guides to exploration for the ores needed by future generations. ?? 1983.

  19. Introducing tectonically and thermo-mechanically realistic lithosphere in the models of plume head -lithosphere interactions (PLI) including intra-continental plate boundaries.

    NASA Astrophysics Data System (ADS)

    Guillou-Frottier, L.; Burov, E.; Cloetingh, S.

    2007-12-01

    Plume-Lithosphere Interactions (PLI) in continets have complex topographic and magmatic signatures and are often identified near boundaries between younger plates (e.g., orogenic) and older stable plates (e.g., cratons), which represent important geometrical, thermal and rheological barriers that interact with the emplacement of the plume head (e.g., Archean West Africa, East Africa, Pannonian - Carpathian system). The observable PLI signatures are conditioned by plume dynamics but also by complex rheology and structure of continental lithosphere. We address this problem by considering a new free-surface thermo-mechanical numerical model of PLI with two stratified elasto-viscous-plastic (EVP) continental plates of contrasting age, thickness and structure. The results show that: (1) surface deformation is poly-harmonic and contains smaller wavelengths (50-500 km) than that associated with the plume head (>1000 km). (2) below intra-plate boundaries, plume head flattening is asymmetric, it is blocked from one side by the cold vertical boundary of the older plate, which leads to mechanical decoupling of crust from mantle lithosphere, and to localized faulting at the cratonic margin; (2) the return flow from the plume head results in sub-vertical down-thrusting (delamination) of the lithosphere at the margin, producing sharp vertical cold boundary down to the 400 km depth; (3) plume head flattening and migration towards the younger plate results in concurrent surface extension above the centre of the plume and in compression (pushing), down-thrusting and magmatic events at the cratonic margin (down-thrusting is also produced at the opposite border of the younger plate); these processes may result in continental growth at the "craton side"; (4) topographic signatures of PLI show basin-scale uplifts and subsidences preferentially located at cratonic margins. Negative Rayleigh-Taylor instabilities in the lithosphere above the plume head provide a mechanism for crustal

  20. 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

    off-shore Peru-Chile trench. This has implications for the friction of the subducting Nazca plate and associated seismicity and uplift.

  1. Incorporation of New and Old Tectonics Concepts Into a Modern Course in Tectonics.

    ERIC Educational Resources Information Center

    Hatcher, Robert D., Jr.

    1983-01-01

    Describes a graduate-level tectonics course which includes the historical basis for modern tectonics concepts and an in-depth review of pros/cons of plate tectonics. Tectonic features discussed include: ocean basins; volcanic arcs; continental margins; continents; orogenic belts; foreland fold and thrust belts; volcanic/plutonic belts of orogens;…

  2. Tectonic isolation of the Levant basin offshore Galilee-Lebanon effects of the Dead Sea fault plate boundary on the Levant continental margin, eastern Mediterranean

    NASA Astrophysics Data System (ADS)

    Schattner, U.; Ben-Avraham, Z.; Lazar, M.; Hüebscher, C.

    2006-11-01

    The continental margin of the central Levant, offshore northern Israel and southern Lebanon is characterized by a sharp continental-oceanic crustal transition, exhibited on the bathymetry as a steep continental slope. At the base of the slope a narrow zone of faulting deforms the upper Messinian-recent sedimentary sequence. Further into the basin no major deformations are observed. However, onland a restraining bend along the Dead Sea fault plate boundary results in the formation of the Lebanon and anti-Lebanon mountain ranges, which exhibit a large positive isostatic anomaly not compensated at depth. All these geologic features follow a NNE-SSW trend. A dense network of multi-channel and single-channel seismic profiles, covering 5000 km of ship-track offshore northern Israel and southern Lebanon, was analyzed for the purpose of characterizing the continental margin. Additional seismic surveys covering the area between the Levant margin and the Cyprean arc were examined. Data were then incorporated with magnetic, gravity and earthquake measurements to reveal the deep crustal structure of the area and integrated with bathymetry data to describe the behavior of the young sedimentary basin fill. Results indicate that the Levant basin, offshore northern Israel and southern Lebanon (up to Beirut) is more-or-less unaffected by the intense tectonic deformation occurring onland. The transition between the deformed area onland and the undeformed Levant basin occurs along the base of the continental slope. Along the base, the upper Messinian-recent sedimentary sequence is cut by two sets of faults: shallow growth faults resulting from salt tectonics and high angle faults, marking the surface expression of a deeper crustal discontinuity - the marine extension of the Carmel fault zone. The central Levant continental margin is being reactivated by transpressional faulting of the marine continuation of the Carmel fault, at the base of the continental slope. This fault system

  3. Tectonic events, sequence stratigraphy and prediction of petroleum play elements in the Cretaceous and Tertiary of the northern Carnarvon Basin, north west shelf, Australia

    SciTech Connect

    Romine, K.K.; Durrant, J.D.

    1996-12-31

    The Carnarvon Basin is one of Australia`s most prolific oil and gas provinces. A recent Paleocene discovery has initiated a shift in exploration interest from traditional Jurassic/Triassic plays to the younger Cretaceous and Tertiary section. To improve play element prediction, a sequence stratigraphic study has been completed, utilizing newly acquired, regional high-resolution seismic data and 80 wells. The occurrence and distribution of the key play elements, reservoir, source and seal, is controlled by the interaction of tectonic subsidence, eustasy and paleogeography, with traps and migration pathways set up and modified by regional tectonic events. For example, a major rifting event commenced in the latest Kimmeridgian-Tithonian that resulted in structuring of older Jurassic sediments and initiation of seafloor spreading in the adjacent Cuvier-Gascoyne Abyssal Plain in the Valanginian. This event was accompanied by a dramatic fall in eustasy that initiated the deposition of high-quality reservoir sandstones of the Tithonian-Valanginian age Barrow Delta. The post-rift phase of thermal cooling and rapid subsidence resulted in transgression, accompanied by deposition of backstepping parasequences of the Mardie Greensand, a potential thief zone and reservoir, and culminated in maximum transgression and deposition of seal and source facies of the Muclerong Shale. The improved sequence stratigraphic framework established in this study provides a predictive tool for the development and assessment of new plays.

  4. Tectonic events, sequence stratigraphy and prediction of petroleum play elements in the Cretaceous and Tertiary of the northern Carnarvon Basin, north west shelf, Australia

    SciTech Connect

    Romine, K.K. ); Durrant, J.D. )

    1996-01-01

    The Carnarvon Basin is one of Australia's most prolific oil and gas provinces. A recent Paleocene discovery has initiated a shift in exploration interest from traditional Jurassic/Triassic plays to the younger Cretaceous and Tertiary section. To improve play element prediction, a sequence stratigraphic study has been completed, utilizing newly acquired, regional high-resolution seismic data and 80 wells. The occurrence and distribution of the key play elements, reservoir, source and seal, is controlled by the interaction of tectonic subsidence, eustasy and paleogeography, with traps and migration pathways set up and modified by regional tectonic events. For example, a major rifting event commenced in the latest Kimmeridgian-Tithonian that resulted in structuring of older Jurassic sediments and initiation of seafloor spreading in the adjacent Cuvier-Gascoyne Abyssal Plain in the Valanginian. This event was accompanied by a dramatic fall in eustasy that initiated the deposition of high-quality reservoir sandstones of the Tithonian-Valanginian age Barrow Delta. The post-rift phase of thermal cooling and rapid subsidence resulted in transgression, accompanied by deposition of backstepping parasequences of the Mardie Greensand, a potential thief zone and reservoir, and culminated in maximum transgression and deposition of seal and source facies of the Muclerong Shale. The improved sequence stratigraphic framework established in this study provides a predictive tool for the development and assessment of new plays.

  5. Slow slip events in plate-rate laboratory experiments on samples from shallow regions of subduction megathrusts

    NASA Astrophysics Data System (ADS)

    Ikari, M.; Ito, Y.; Ujiie, K.; Kopf, A.

    2015-12-01

    It is now recognized that slow slip events on plate-boundary fault zones occur not only downdip of the seismogenic zone, but also updip within several km from the seafloor. These shallower events are advantageous because the fault material can be sampled by drilling, and in-situ conditions can be replicated in the laboratory. We report here on results of laboratory friction experiments investigating fault zone material sampled during Ocean Drilling Program and International Ocean Drilling Program expeditions to subduction zones in Japan and Costa Rica. We employ laboratory conditions of 7-16 MPa effective stress and ~20 °C simulating ~1-2.5 km burial depth. Additionally, we shear the samples at plate convergence rates of less than 10 cm/yr. When driven at plate convergence rates, friction perturbations analogous to slow slip events are sometimes observed. In plate-boundary fault zone samples from the Tohoku region at the Japan Trench, these events exhibit stress drops of 3-7% over several hours with a maximum slip rate of 10-25 cm/yr under 7 MPa effective normal stress. Increasing the effective normal stress to 16 kPa results in a corresponding increase in stress drop up to 15% and slip rates up to 57 cm/yr, consistent with critical stiffness theory which predicts that increasing effective normal stress decreases frictional stability. A sample from the plate boundary décollement from the Costa Rica margin exhibited similar slow slip behavior, with stress drops of 3-12% and maximum slip velocities up to 16 cm/yr. This sample is described as a hemipelagic clay, whereas a sample of nannofossil chalk from the same region did not exhibit such behavior. For the Nankai Trough offshore Japan, samples from the megasplay fault zone and décollement did not exhibit the slow slip events observed in the Japan Trench and Costa Rica samples. Analyses of velocity-stepping data from these tests indicate a propensity for velocity-weakening frictional behavior at slow rates

  6. Relocating Seismicity on the Arctic Plate Boundary Using Teleseismic and Regional Phases and a Bayesian Multiple Event Locator

    NASA Astrophysics Data System (ADS)

    Gibbons, Steven J.; Dahl-Jensen, Trine; Kværna, Tormod; Larsen, Tine B.; Paulsen, Berit; Voss, Peter

    2016-04-01

    The tectonophysics of plate boundaries are illuminated by the pattern of seismicity - and the ability to locate seismic events accurately depends upon the number and quality of observations, the distribution of recording stations, and how well the traveltimes of seismic phases are modelled. The boundary between the Eurasian and North American plates between 70 and 84 degrees North hosts large seismic events which are well recorded teleseismically and many more events at far lower magnitudes that are well recorded only at regional distances. Existing seismic bulletins have considerable spread and bias resulting from limited station coverage and deficiencies in the velocity models applied; this is particularly acute for the lower magnitude events which may only be constrained by a small number of Pn and Sn arrivals. Over the past 15 years, there has been a significant improvement in the seismic network in the Arctic - a difficult region to instrument due to the harsh climate, a sparsity of quiet and accessible sites, and the expense and difficult logistics of deploying and maintaining stations. New deployments and upgrades to stations on Greenland, Svalbard, and the islands Jan Mayen, Hopen, and Bjørnøya have resulted in a sparse but stable regional seismic network which results in events down to magnitudes below 3 generating high quality Pn and Sn signals on multiple stations. A catalog of over 1000 events in the region since 1998 has been generated using many new phase readings on stations on both sides of the spreading ridge in addition to teleseismic P phases. The Bayesloc program, a Bayesian hierarchical multiple event location algorithm, has been used to relocate the full set of events iteratively and this has resulted in a significant reduction in the spread in hypocenter estimates for both large and small events. Whereas single event location algorithms minimize the vector of time residuals on an event-by-event basis, Bayesloc favours the hypocenters which

  7. Thermal Histories of Earth, Moon, Mars and Vesta, and A Thermal Signal for the Onset of Terrestrial-like Plate Tectonics

    NASA Astrophysics Data System (ADS)

    Putirka, K. D.

    2015-12-01

    Mantle potential temperatures (Tp) reflect mantle circulation and planetary cooling, and thus may provide clues as to why Earth is unique amongst the terrestrial planetary bodies. A re-evaluation of Tp estimates for Earth, Mars, Moon, and Vesta, reveals an anticipated decrease in maximum Tp as planet size decreases, at least if we apply a 4.3 Ga age to shergottites (e.g., Bouvier et al., 2009; Werner et al., 2014), and use the highest MgO komatiites from Earth's Archean eon (27-30% MgO, e.g., Green et al., 1975). With these assumptions, Earth and Mars yield time-Tp paths indicative of secular cooling that appears to be largely monotonic following the end of accretion. These two cooling trends further provide intriguing support for Stevenson's (2003) hypothesis that smaller planets cool at similar rates, but always maintain lower temperatures. One key difference between Earth and the other bodies, though, is that Earth exhibits a clear split in Phanerozoic terrestrial mantle temperatures, into plume- and ambient-Tp, although there is a hint of a parallel process on Mars at 1.3 Ga, if we accept that the high MgO Nakhla D composition is a liquid (Longhi and Pan, 1989; Treiman 1986). The onset of Tp bi-modality may be a harbinger of a transition from a stagnant lid to a plume/plate convective regime; in the former, only hot plumes from the core-mantle boundary contribute to volcanism, whereas in a plume/plate mode, small-scale convection of cooler ambient mantle, mostly at rifts and subduction zones, also contributes to surface volcanism. The contrasts between Earth and the other bodies imply that planetary radii and initial temperatures exert the primary control on whether or not modern terrestrial tectonics is able to develop. Exploration of Mars is still at too early a stage to infer much regarding its internal thermal state at 1.3 Ga, but clearly the study of young volcanic features there are of prime importance, perhaps much more so for understanding planetary and

  8. Role of the offshore Pedro Banks left-lateral strike-slip fault zone in the plate tectonic evolution of the northern Caribbean

    NASA Astrophysics Data System (ADS)

    Ott, B.; Mann, P.; Saunders, M.

    2013-12-01

    Previous workers, mainly mapping onland active faults on Caribbean islands, defined the northern Caribbean plate boundary zone as a 200-km-wide bounded by two active and parallel strike-slip faults: the Oriente fault along the northern edge of the Cayman trough with a GPS rate of 14 mm/yr, and and the Enriquillo-Plaintain Garden fault zone (EPGFZ) with a rate of 5-7 mm/yr. In this study we use 5,000 km of industry and academic data from the Nicaraguan Rise south and southwest of the EPGFZ in the maritime areas of Jamaica, Honduras, and Colombia to define an offshore, 700-km-long, active, left-lateral strike-slip fault in what has previously been considered the stable interior of the Caribbean plate as determined from plate-wide GPS studies. The fault was named by previous workers as the Pedro Banks fault zone because a 100-km-long segment of the fault forms an escarpment along the Pedro carbonate bank of the Nicaraguan Rise. Two fault segments of the PBFZ are defined: the 400-km-long eastern segment that exhibits large negative flower structures 10-50 km in width, with faults segments rupturing the sea floor as defined by high resolution 2D seismic data, and a 300-km-long western segment that is defined by a narrow zone of anomalous seismicity first observed by previous workers. The western end of the PBFZ terminates on a Quaternary rift structure, the San Andres rift, associated with Plio-Pleistocene volcanism and thickening trends indicating initial rifting in the Late Miocene. The southern end of the San Andreas rift terminates on the western Hess fault which also exhibits active strands consistent with left-lateral, strike-slip faults. The total length of the PBFZ-San Andres rift-Southern Hess escarpment fault is 1,200 km and traverses the entire western end of the Caribbean plate. Our interpretation is similar to previous models that have proposed the "stable" western Caribbean plate is broken by this fault whose rate of displacement is less than the threshold

  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. Tectonic Terminology: Some Proposed Changes

    ERIC Educational Resources Information Center

    Hill, Mason L.

    1978-01-01

    Plate tectonics concepts require a definition of fault, a new term to compliment epeirogeny, and a clarification of transform fault characteristics. This article makes proposals for these changes. (Author/MA)

  11. Spiral tectonics

    NASA Astrophysics Data System (ADS)

    Hassan Asadiyan, Mohammad

    2014-05-01

    Spiral Tectonics (ST) is a new window to global tectonics introduced as alternative model for Plate Tectonics (PT). ST based upon Dahw(rolling) and Tahw(spreading) dynamics. Analogues to electric and magnetic components in the electromagnetic theory we could consider Dahw and Tahw as components of geodynamics, when one component increases the other decreases and vice versa. They are changed to each other during geological history. D-component represents continental crust and T-component represents oceanic crust. D and T are two arm of spiral-cell. T-arm 180 degree lags behind D-arm so named Retard-arm with respect to D or Forward-arm. It seems primary cell injected several billions years ago from Earth's center therefore the Earth's core was built up first then mantel and finally the crust was build up. Crust building initiate from Arabia (Mecca). As the universe extended gravitation wave swirled the earth fractaly along cycloid path from big to small scale. In global scale (order-0) ST collect continents in one side and abandoned Pacific Ocean in the other side. Recent researches also show two mantels upwelling in opposite side of the Earth: one under Africa (tectonic pose) and the other under Pacific Ocean (tectonic tail). In higher order (order-1) ST build up Africa in one side and S.America in the other side therefore left Atlantic Ocean meandered in between. In order-n e.g. Khoor Musa and Bandar-Deylam bay are seen meandered easterly in the Iranian part but Khoor Abdullah and Kuwait bay meandered westerly in the Arabian part, they are distributed symmetrically with respect to axis of Persian Gulf(PG), these two are fractal components of easterly Caspian-wing and westerly Black Sea-wing which split up from Anatoly. Caspian Sea and Black Sea make two legs of Y-like structure, this shape completely fitted with GPS-velocity map which start from PG and split up in the Catastrophic Point(Anatoly). We could consider PG as remnants of Ancient Ocean which spent up

  12. Kinematic Evolution of fold-and-thrust Belts in the Yubei Area: Implications for the Tectonic Events of Ordovician at the Southern Tarim Basin

    NASA Astrophysics Data System (ADS)

    Zhang, Y.

    2015-12-01

    As a response to tecto-orogenic processes of the South Altun and the West Kunlun (Monlar P, 1975; He Bizhu, 2011), early Paleozoic tectonic evolution of the southern Tarim craton was distinctively one of the extensions and was followed by compression (Morris W.Leighton, 1990; Gao Zhiqian, 2015). From the late Ordovician, the Yubei area developed distinctively NE-SW trending fold-and-thrust belts in rows which were eroded and deformed through multiphase tectonic movement (Dengfa He, 2007), with similarities and dissimilarities between each other rows in many aspects, at the Southern Tarim inner basin (Fig. 1). The northern of Hetian paleo-uplift and the northwestern of NE-trending folds zone on Caledonian in Tangguzibasi depression should be favorable to the potential exploration area for the first large-scale period of hydrocarbon migration and accumulation (Brown LF, 1979). In this contribution, based on geophysical log, core and 2D/3D seismic data, we constructed its tectonic geometry morphology, controlled by detailed chronostratigraphic framework. According to the fault-related fold theory, rows of asymmetric fault-propagation folds grew in the Yubei area during the late Caledonian period, with the evidence of interpreted growth strata from the high resolution 3D seismic data (Suppe J et al., 1990). That intercontinental tecto-orogenic events from southern Tarim basin, leading to the transformation of its margins, affected inner basin at that time, modified the basin into the Tarim metacraton (Jean-Paul Liégeois, 2013; Zieglar P.A., 1998). Correlating the four tectonic groups of the identified with the axis variation of strata and fold amplitude distribution showed that fault evolution progressed in several superimposed stages: Precambrian, late Ordovician to early Carboniferous (Zhao Zongju, 2009), Carboniferous to Permian, Cenozoic. Analyzing the sedimentary development and structure evolution the tectonic paleo-geographic setting is reconstructed, providing

  13. Lithospheric Models of the Middle East to Improve Seismic Source Parameter Determination/Event Location Accuracy

    DTIC Science & Technology

    2012-09-01

    structure of Saudi Arabia through data collection from broadband stations. Figure 2. (Left) Map of Arabian Plate showing major tectonic ...State Award Nos. DE-AC52-07NA27344/24.2.3.2 and DOS_SIAA-11-AVC/NMA-1 ABSTRACT The Middle East is a tectonically complex and seismically...active region. The ability to accurately locate earthquakes and other seismic events in this region is complicated by tectonics , the uneven

  14. Seismic sequence stratigraphy of Miocene deposits related to eustatic, tectonic and climatic events, Cap Bon Peninsula, northeastern Tunisia

    NASA Astrophysics Data System (ADS)

    Gharsalli, Ramzi; Zouaghi, Taher; Soussi, Mohamed; Chebbi, Riadh; Khomsi, Sami; Bédir, Mourad

    2013-09-01

    The Cap Bon Peninsula, belonging to northeastern Tunisia, is located in the Maghrebian Alpine foreland and in the North of the Pelagian block. By its paleoposition, during the Cenozoic, in the edge of the southern Tethyan margin, this peninsula constitutes a geological entity that fossilized the eustatic, tectonic and climatic interactions. Surface and subsurface study carried out in the Cap Bon onshore area and surrounding offshore of Hammamet interests the Miocene deposits from the Langhian-to-Messinian interval time. Related to the basin and the platform positions, sequence and seismic stratigraphy studies have been conducted to identify seven third-order seismic sequences in subsurface (SM1-SM7), six depositional sequences on the Zinnia-1 petroleum well (SDM1-SDM6), and five depositional sequences on the El Oudiane section of the Jebel Abderrahmane (SDM1-SDM5). Each sequence shows a succession of high-frequency systems tract and parasequences. These sequences are separated by remarkable sequence boundaries and maximum flooding surfaces (SB and MFS) that have been correlated to the eustatic cycles and supercycles of the Global Sea Level Chart of Haq et al. (1987). The sequences have been also correlated with Sequence Chronostratigraphic Chart of Hardenbol et al. (1998), related to European basins, allows us to arise some major differences in number and in size. The major discontinuities, which limit the sequences resulted from the interplay between tectonic and climatic phenomena. It thus appears very judicious to bring back these chronological surfaces to eustatic and/or local tectonic activity and global eustatic and climatic controls.

  15. The global tectonic pattern

    NASA Astrophysics Data System (ADS)

    Doglioni, Carlo

    1990-07-01

    The relative motion vectors between the lithosphere and the underlying mantle appear to follow global flow lines which can be constructed by linking axes of extension and compression over the Earth's surface. The flow lines for the last 40 Ma are generally WNW-ESE (E-W), with an undulation of an about 15,000 km wavelength, showing a gradual and progressive variation in orientation. The undulation, which is sharper to the east, may reflect the mantle flow around an unstable rotation axis. The westward motion of the lithospheric plates could be interpreted as a result of differential angular velocity induced by the deceleration of the earth's rotation or, in a toroidal field, by the effects induced by lateral heterogeneities both in the lithosphere and in the mantle. In this light, plate tectonics is a consequence of variable decoupling at the base of the lithosphere as a function of mantle anisotropies. Simply stated, when there is compression or transpression between two plates, it is the eastern plate which moves more rapidly westwards relative to the underlying mantle. If there is extension or transtension, it is the western plate that moves faster westwards. Lithospheric subduction, especially if it dips westward, produces an obstacle to the eastward flow of the mantle. This is referred to as the Nail Effect. The eastward roll-back of the subduction hinge due to the mantle push will generate back-arc extension. Subductions following the mantle flow (E or NE-dipping) are associated to thicker thrust belts with huge exposures of basement rocks in the hinterland and shallow foreland basins. The subductions contrasting the mantle flow (W or SW-dipping) are characterized by shallow thrust belts with deep foreland basin and coeval extension in the back. E-dipping subductions are passive responses to actively thrusting plates: the base plate and intra-lithospheric decollements are connected to the surface and can uplift deep rocks. The W-dipping subductions are

  16. NASA Now: Plate Tectonics: Earthquakes

    NASA Video Gallery

    Dr. Greg Lyzenga is a research scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., and a professor of physics at Harvey Mudd College in Claremont, Calif. Lyzenga explains how frict...

  17. Plate tectonics: A supercontinental boost

    NASA Astrophysics Data System (ADS)

    Lenardic, Adrian

    2017-01-01

    180 million years ago Earth's continents were amalgamated into one supercontinent called Pangaea. Analysis of oceanic crust formed since that time suggests that the cooling rate of Earth was enhanced in the wake of Pangaea's dispersal.

  18. Tectonic stress in the plates

    NASA Technical Reports Server (NTRS)

    Richardson, R. M.; Solomon, S. C.; Sleep, N. H.

    1979-01-01

    In the present paper, the basic set of global intraplate stress orientation data is plotted and tabulated. Although the global intraplate stress field is complicated, several large-scale patterns can be seen. Much of stable North America is characterized by an E-W to NE-SW trend for the maximum compressive stress. South American lithosphere beneath the Andes, and perhaps farther east in the stable interior, has horizontal compressive stresses trending E-W to NW-SE. Western Europe north of the Alps is characterized by a NW-SE trending maximum horizontal compression, while Asia has the maximum horizontal compressive stress trending more nearly N-S, especially near the Himalayan front.

  19. Plate boundaries and extensional tectonics

    NASA Astrophysics Data System (ADS)

    Le Pichon, Xavier; Angelier, Jacques; Sibuet, Jean-claude

    1982-01-01

    The behaviour of the lithosphere under extensional strain is different whether the surface of the lithosphere is above or below the level that would be reached by the asthenosphere in its absence. Below this level, the continuity of the old lithosphere may be rapidly broken and oceanic accretion starts. Above this level, extensive thinning of the old lithosphère occurs until the level is reached, and then the asthenospheric material may break out to the surface. The thinning probably depends on the strain rate. Two extreme cases must be distinguished. For low strain rates: the lower lithosphere may be thinned by diapiric intrusions and lithospheric sinking; the upper one is much less affected, as occurs in the African Rifts or the Rhine Graben. For high strain rates, the whole lithosphère is thinned rather uniformly, as occurs in the Aegean region and probably on many continental margins. The greatest portion of the lithosphere is extended plastically, while the upper brittle portion, about 10 km thick, is extended by normal faulting. The pattern of faulting in these widely extended areas is compared to a pack of cards resting at an angle on a plane, with each card (tilted block) making a slight angle with the preceding one. Using this simple model, we discuss the case of the Pindos basin of the Hellenides. Similar intra-continental basins 150 to 400 km wide may be created before the subsidence increases sufficiently for oceanic accretion to begin. We point out that these basins are especially susceptible to compressional failure whenever the stress system changes from extensional to compressional. Consequently, many orogens are localized along such zones of earlier extension, as shown by geological studies of the Western Alpine system.

  20. Simulation of tectonic evolution of the Kanto basin of Japan since 1 Ma due to subduction of the Pacific and Philippine sea plates and collision of the Izu-Bonin arc

    NASA Astrophysics Data System (ADS)

    Hashima, Akinori; Sato, Toshinori; Sato, Hiroshi; Asao, Kazumi; Furuya, Hiroshi; Yamamoto, Shuji; Kameo, Koji; Miyauchi, Takahiro; Ito, Tanio; Tsumura, Noriko; Kaneda, Heitaro

    2015-04-01

    The Kanto basin, the largest lowland in Japan, developed by flexure as a result of (1) the subduction of the Philippine Sea (PHS) and the Pacific (PAC) plates and (2) the collision of the Izu-Bonin arc with the Japanese island arc. Geomorphological, geological, and thermochronological data on long-term vertical movements over the last 1 My suggest that subsidence initially affected the entire Kanto basin after which the area of subsidence gradually narrowed until, finally, the basin began to experience uplift. In this study, we modelled the tectonic evolution of the Kanto basin following the method of Matsu'ura and Sato (1989) for a kinematic subduction model with dislocations, in order to quantitatively assess the effects of PHS and PAC subduction. We include the steady slip-rate deficit (permanent locking rate at the plate interface) in our model to account for collision process. We explore how the arc-arc collision process has been affected by a westerly shift in the PHS plate motion vector with respect to the Eurasian plate, thought to have occurred between 1.0-0.5 Ma, using long-term vertical deformation data to constrain extent of the locked zone on the plate interface. We evaluated the change in vertical deformation rate for two scenarios: (1) a synchronous shift in the orientation of the locked zone as PHS plate motion shifts and (2) a delayed shift in the orientation of the locked zone following a change in plate motion. Observed changes in the subsidence/uplift pattern are better explained by scenario (2), suggesting that recent (<1 My) deformation in the Kanto basin shows a lag in crustal response to the shift in plate motion. We also calculated recent stress accumulation rates and found a good match with observed earthquake mechanisms, which shows that intraplate earthquakes serve to release stress accumulated through long-term plate interactions.

  1. Simulation of tectonic evolution of the Kanto Basin of Japan since 1 Ma due to subduction of the Pacific and Philippine Sea plates and the collision of the Izu-Bonin arc

    NASA Astrophysics Data System (ADS)

    Hashima, Akinori; Sato, Toshinori; Sato, Hiroshi; Asao, Kazumi; Furuya, Hiroshi; Yamamoto, Shuji; Kameo, Koji; Miyauchi, Takahiro; Ito, Tanio; Tsumura, Noriko; Kaneda, Heitaro

    2016-06-01

    The Kanto Basin, the largest lowland in Japan, developed by flexure as a result of (1) the subduction of the Philippine Sea (PHS) and the Pacific (PAC) plates and (2) the repeated collision of the Izu-Bonin arc fragments with the Japanese island arc. Geomorphological, geological, and thermochronological data on vertical movements over the last 1 My suggest that subsidence initially affected the entire basin after which the area of subsidence gradually narrowed until, finally, the basin began to experience uplift. In this study, we modeled the tectonic evolution of the Kanto Basin following the method of Matsu'ura and Sato (1989) for a kinematic subduction model with dislocations, in order to quantitatively assess the effects of PHS and PAC subduction. We include the steady slip-rate deficit (permanent locking rate at the plate interface) in our model to account for collision process. We explore how the latest collision of the Izu Peninsula block has been affected by a westerly shift in the PHS plate motion vector with respect to the Eurasian plate, thought to have occurred between 1.0-0.5 Ma, using long-term vertical deformation data to constrain extent of the locked zone on the plate interface. We evaluated the change in vertical deformation rate for two scenarios: (1) a synchronous shift in the orientation of the locked zone as PHS plate motion shifts and (2) a delayed shift in the orientation of the locked zone following the shift in plate motion. Observed changes in the uplift/subsidence pattern are better explained by scenario (2), suggesting that recent (< 1 My) deformation in the Kanto Basin shows a lag in crustal response to the plate motion shift. We also calculated stress accumulation rates and found a good match with observed earthquake mechanisms, which shows that intraplate earthquakes serve to release stress accumulated through long-term plate interactions.

  2. Linking serpentinite geochemistry with tectonic evolution at the subduction plate-interface: The Voltri Massif case study (Ligurian Western Alps, Italy)

    NASA Astrophysics Data System (ADS)

    Cannaò, E.; Scambelluri, M.; Agostini, S.; Tonarini, S.; Godard, M.

    2016-10-01

    , whereas mylonitic serpentinite is reset in its concentrations of FME and its B, Sr and Pb isotope compositions, due to interaction with sediment- and crust-derived fluids. The environment of this interaction is either compatible with (i) an outer-rise zone setting, with percolation of seawater-derived fluids enriched in sedimentary components into bending-related fault structures, or with (ii) subduction channel domains, where ascending sediment-derived slab fluids infiltrate slices of former oceanic serpentinite accreted to the plate interface domain. Influx of sediment-derived subduction fluids along major deformation zones in serpentinite modifies the element budget of the rocks, with important implications for element recycling and the tectonic history of serpentinite. The B, Sr and Pb isotopic systematics, coupled with FME concentration in serpentinites are particularly helpful geochemical tracers of interaction between different reservoirs in subduction-interface environments, and are more sensitive than the traditionally applied stable oxygen and hydrogen isotope compositions.

  3. 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

  4. Holistic microstructural techniques reveal synchronous and alternating andalusite and staurolite growth during three tectonic events resulted from shifting partitioning of growth vs deformation

    NASA Astrophysics Data System (ADS)

    Bell, T. H.; Fay, C.

    2016-10-01

    Excellent inclusion trails in a sample containing both staurolite and andalusite porphyroblasts are used to demonstrate techniques that allow the intimate relationships between deformation and porphyroblast growth to be recognized, described in detail and understood. This approach reveals three main phases of growth of both mineral phases, some of which was demonstrably synchronous, during three tectonic events. Each main period of growth occurred during the early stages of three deformations that were successively near orthogonal. However, extra periods are distinguishable in andalusite in some of these events because this phase occurs as clusters of large crystals that vary in orientation by 2° to > 10°. All foliations defined by all inclusion trails within every porphyroblast inflect/intersect about an axis trending at 025° (called a FIA). This indicates that the direction of the horizontal component of bulk shortening was identical for the first and third of the three deformations recorded by porphyroblast growth. Portions of sigmoidal to slightly spiral-shaped inclusion trails in most porphyroblast clusters locally diverge in opposite directions due to overprinting orthogonal bulk shortening typical of that which forms millipede geometries. These microstructures confirm the role of coaxial bulk shortening in initiating porphyroblast growth in an environment that locally becomes strongly non-coaxial as the deformation intensifies in the same event. In this sample, increasing non-coaxiality as the deformation intensified resulted in the same asymmetry for each of the three events and thus an overall spiral-like shape. Differing stages in the development of these bulk-shortening geometries preserved in adjacent or touching phases negate any role for porphyroblast rotation during ductile deformation. Andalusite and staurolite grew without any inter-reaction in locations where they lie in contact. This multiply repeated growth behaviour initiated within zones of

  5. Gondwana to Asia: Plate tectonics, paleogeography and the biological connectivity of the Indian sub-continent from the Middle Jurassic through latest Eocene (166 35 Ma)

    NASA Astrophysics Data System (ADS)

    Ali, Jason R.; Aitchison, Jonathan C.

    2008-06-01

    Using the most up-to-the-date information available, we present a considerably revised plate tectonic and paleogeographic model for the Indian Ocean bordering continents, from Gondwana's Middle Jurassic break-up through to India's collision with Asia in the middle Cenozoic. The landmass framework is then used to explore the sometimes complex and occasionally counter-intuitive patterns that have been observed in the fossil and extant biological records of India, Madagascar, Africa and eastern Eurasia, as well those of the more distal continents. Although the paleogeographic model confirms the traditional view that India became progressively more isolated from the major landmasses during the Cretaceous and Paleocene, it is likely that at various times minor physiographic features (principally ocean islands) provided causeways and/or stepping-stone trails along which land animals could have migrated to/from the sub-continent. Aside from a likely link (albeit broken by several marine gaps) to Africa for much of this time (it is notable, that the present-day/recent biota of Madagascar indicates that the ancestors of five land-mammal orders, plus bats, crossed the > 400-km-wide Mozambique Channel at different times in the Cenozoic), it is possible that the Kerguelen Plateau connected India and Australia-Antarctica in the mid-Cretaceous (approximately 115-90 Ma). Later, the Seychelles-Mascarene Plateau and nearby elevated sea-floor areas could have allowed faunas to pass between southern India and Madagascar in the Late Cretaceous, from around 85-65 Ma, with an early Cenozoic extension to this path forming as a result of the Reunion hot-spot trace islands growing on the ocean floor to the SSW of India. The modelling also suggests that India's northward passage towards Asia, with eventual collision at 35 Ma, involved the NE corner of the sub-continent making a glancing contact with Sumatra, followed by Burma from ~ 57 Ma (late Paleocene) onwards, a scenario which is

  6. Active tectonics of the western tethyan himalaya above the underthrusting indian plate: The upper sutlej river basin as a pull-apart structure

    NASA Astrophysics Data System (ADS)

    Ni, James; Barazangi, Muawia

    1985-03-01

    Fault-bounded blocks and structural elements were mapped in the eastern Ladakh-Spiti and upper Sutlej River Basin located within the Tethyan Himalaya and to the southwest of the Karakorum fault zone mainly using LANDSAT Multispectral Scanner (MSS) band 5, band 7 (near-infrared) images with detailed analysis of smaller areas by interactive digital processing of false color images, and Returned Beam Vidicon (RBV) imagery in conjunction with available topographical, geological and seismological data. For the first time the Leo Pargil Horst and other nearby fault-bounded blocks located at the northwestern end of the upper Setlej River Basin were clearly revealed on the LANDSAT color composites. Shallow crustal seismicity is systematically related to the NNE-trending and N-trending normal faults of the Leo Pargil and nearby regions. Some of the aftershocks of the Kinnaur earthquake of January 19,1975 ( Ms = 6.8), appear to be associated with movement along the NNE-trending westbound fault of the Leo Pargil Horst and the nearby Kaurik-Chango fault. The main shock, however, is teleseismically located at about 30 km to the northwest of the Kaurik-Chango fault. Fault plane solutions of the main shock and two aftershocks indicate a large component of normal faulting. In map view, the upper Sutlej River Basin has an approximately rhomboidal shape and is located to the southwest of the Karakorum fault system. We suggest that this basin is a pull-apart between the NW-SE oriented, right-lateral, strike-slip Karakorum fault system and the high-angle faults near the southern boundary of the Tethyan Himalaya. The Leo Pargil Horst is the northwestern bounding fault block of this pull-apart. The active tectonic features in this part of the Tethyan Himalaya appear to reflect right-shear within the crust, and this is probably a consequence of oblique underthrusting of the Indian continental plate beneath the western Himalaya and southwestern Tibet during the Neogene and Quaternary

  7. Uplift of Zagros Mountains slows plate convergence

    NASA Astrophysics Data System (ADS)

    Balcerak, Ernie

    2013-05-01

    Research has indicated that mountain ranges can slow down the convergence between two tectonic plates on timescales as short as a few million years, as the growing mountains provide enough tectonic force to impact plate motions. Focusing on the convergence of the Arabian and Eurasian plates at the Zagros mountain range, which runs across Iran and Iraq, Austermann and Iaffaldano reconstructed the relative motion of the plates using published paleomagnetic data covering the past 13 million years, as well as current geodetic measurements. They show that the convergence of the two plates has decreased by about 30% over the past 5 million years. Looking at the geological record to infer past topography and using a computer model of the mantle-lithosphere system, the authors examined whether the recent uplift across the Zagros Mountains could have caused the observed slowdown. They also considered several other geological events that might have influenced the convergence rate, but the authors were able to rule those out as dominant controls. The authors conclude that the uplift across the Zagros Mountains in the past 5 million years did indeed play a key role in slowing down the convergence between the Eurasian and Arabian plates. (Tectonics, doi:10.1002/tect.20027, 2013)

  8. Intra Plate Stresses Using Finite Element Modelling

    NASA Astrophysics Data System (ADS)

    Jayalakshmi, S.; Raghukanth, S. T. G.

    2016-10-01

    One of the most challenging problems in the estimation of seismic hazard is the ability to quantify seismic activity. Empirical models based on the available earthquake catalogue are often used to obtain activity of source regions. The major limitation with this approach is the lack of sufficient data near a specified source. The non-availability of data poses difficulties in obtaining distribution of earthquakes with large return periods. Such events recur over geological time scales during which tectonic processes, including mantle convection, formation of faults and new plate boundaries, are likely to take place. The availability of geometries of plate boundaries, plate driving forces, lithospheric stress field and GPS measurements has provided numerous insights on the mechanics of tectonic plates. In this article, a 2D finite element model of Indo-Australian plate is developed with the focus of representing seismic activity in India. The effect of large scale geological features including sedimentary basins, fold belts and cratons on the stress field in India is explored in this study. In order to address long term behaviour, the orientation of stress field and tectonic faults of the present Indo- Australian plate are compared with a reconstructed stress field from the early Miocene (20 Ma).

  9. Global tectonics and space geodesy.

    PubMed

    Gordon, R G; Stein, S

    1992-04-17

    Much of the success of plate tectonics can be attributed to the near rigidity of tectonic plates and the availability of data that describe the rates and directions of motion across narrow plate boundaries \\m=~\\1 to 60 kilometers wide. Nonetheless, many plate boundaries in both continental and oceanic lithosphere are not narrow but are hundreds to thousands of kilometers wide. Wide plate boundary zones cover \\m=~\\15 percent of Earth's surface area. Space geodesy, which includes very long baseline radio interferometry, satellite laser ranging, and the global positioning system, is providing the accurate long-distance measurements needed to estimate the present motion across and within wide plate boundary zones. Space geodetic data show that plate velocities averaged over years are remarkably similar to velocities averaged over millions of years.

  10. Global tectonics and space geodesy

    NASA Technical Reports Server (NTRS)

    Gordon, Richard G.; Stein, Seth

    1992-01-01

    Much of the success of plate tectonics can be attributed to the near rigidity of tectonic plates and the availability of data that describe the rates and directions of motion across narrow plate boundaries of about 1 to 60 kilometers. Nonetheless, many plate boundaries in both continental and oceanic lithosphere are not narrow but are hundreds to thousands of kilometers wide. Wide plate boundary zones cover approximately 15 percent of earth's surface area. Space geodesy, which includes very long baseline radio interferometry, satellite laser ranging, and the global positioning system, provides the accurate long-distance measurements needed to estimate the present motion across and within wide plate boundary zones. Space geodetic data show that plate velocities averaged over years are remarkably similar to velocities avaraged over millions of years.

  11. Inter- and intra-plate deformation at North American plate boundaries

    NASA Technical Reports Server (NTRS)

    Beavan, John

    1986-01-01

    Alaska tectonics and earthquake hazard studies; Southern California tectonics (block rotation); spreading near the Salton Trough; California plate motion (fault zone kinematics); and Caribbean plate motion investigations are examined.

  12. Tectonic evolution and paleogeography of Europe

    SciTech Connect

    Yilmaz, P.O.; Norton, I.O.; Chuchla, R.J. ); Leary, D.A. )

    1993-09-01

    The goal of this study was to use the tectonic framework of European craton to constrain our understanding of the sedimentary basins of Europe. An understanding of the amalgamation of the crustal blocks of Europe during the Caledonian, Hercynian, and Alpine orogenies was accomplished using an Evans and Sutherland system. Paleogeographic maps were ;made and integrated with the plate reconstruction with an eye toward how regional plate-scale events affect play elements in the basins. Europe is an artifact of Phanerozoic tectonic history, an amalgamation of crustal blocks without a precambrian nucleus of it own. This is in direct contrast of Africa, Asia, and North America. Multiple riftings and collisions created extremely complex mountain building during the Caledonian, Hercynian, Cimmerian, and Alpine orogenies. Basins are diverse, superimposed, and have long-lived tectonic histories with complex structuring and highly variable play elements. The Hercynian orogene set up the framework for northern European hydrocarbon systems. Its collapse set up the Apulian Mesozoic hydrocarbon system. Alpine deformation and tectonically related extension in turn set up the Neogene hydrocarbon systems of the Carpathians Pannonian basin and the Apennines. Eleven paleogeographic maps were completed at a scale of 1:5,000,000. There are four for the Paleozoic to show the Hercynian orogeny and its subsequent foredeeps, and four for the Mesozoic, showing Tethyan rifting and associated subsidence, as well as the Cimmerian orogenies and start of Alpine deformation. The three time slices in the Cenozoic show the Alpine orogene and its foredeeps and the tectonically related extensional basins.

  13. Gunbarrel mafic magmatic event: A key 780 Ma time marker for Rodinia plate reconstructions

    USGS Publications Warehouse

    Harlan, S.S.; Heaman, L.; LeCheminant, A.N.; Premo, W.R.

    2003-01-01

    Precise U-Pb baddeleyite dating of mafic igneous rocks provides evidence for a widespread and synchronous magmatic event that extended for >2400 km along the western margin of the Neoproterozoic Laurentian craton. U-Pb baddeleyite analyses for eight intrusions from seven localities ranging from the northern Canadian Shield to northwestern Wyoming-southwestern Montana are statistically indistinguishable and yield a composite U-Pb concordia age for this event of 780.3 ?? 1.4 Ma (95% confidence level). This 780 Ma event is herein termed the Gunbarrel magmatic event. The mafic magmatism of the Gunbarrel event represents the largest mafic dike swarm yet identified along the Neoproterozoic margin of Laurentia. The origin of the mafic magmatism is not clear, but may be related to mantle-plume activity or upwelling asthenosphere leading to crustal extension accompanying initial breakup of the supercontinent Rodinia and development of the proto-Pacific Ocean. The mafic magmatism of the Gunbarrel magmatic event at 780 Ma predates the voluminous magmatism of the 723 Ma Franklin igneous event of the northwestern Canadian Shield by ???60 m.y. The precise dating of the extensive Neoproterozoic Gunbarrel and Franklin magmatic events provides unique time markers that can ultimately be used for robust testing of Neoproterozoic continental reconstructions.

  14. Heat transport in the Hadean mantle: From heat pipes to plates

    NASA Astrophysics Data System (ADS)

    Kankanamge, Duminda G. J.; Moore, William B.

    2016-04-01

    Plate tectonics is a unique feature of Earth, and it plays a dominant role in transporting Earth's internally generated heat. It also governs the nature, shape, and the motion of the surface of Earth. The initiation of plate tectonics on Earth has been difficult to establish observationally, and modeling of the plate breaking process has not consistently accounted for the nature of the preplate tectonic Earth. We have performed numerical simulations of heat transport in the preplate tectonic Earth to understand the transition to plate tectonic behavior. This period of time is dominated by volcanic heat transport called the heat pipe mode of planetary cooling. These simulations of Earth's mantle include heat transport by melting and melt segregation (volcanism), Newtonian temperature-dependent viscosity, and internal heating. We show that when heat pipes are active, the lithosphere thickens and lithospheric isotherms are kept flat by the solidus. Both of these effects act to suppress plate tectonics. As volcanism wanes, conduction begins to control lithospheric thickness, and large slopes arise at the base of the lithosphere. This produces large lithospheric stress and focuses it on the thinner regions of the lithosphere resulting in plate breaking events.

  15. Tectonic and Kinematic Regime along the Northern Caribbean Plate Boundary: New Insights from Broad-band Modeling of the May 25, 1992, Ms = 6.9 Cabo Cruz, Cuba, Earthquake

    NASA Astrophysics Data System (ADS)

    Perrot, J.; Calais, E.; Mercier de Lépinay, B.

    On May 25th, 1992, an Ms = 6.9 earthquake occurred off the southwestern tip of Cuba, along the boundary between the Caribbean and North American plates. This earthquake was the largest to strike southern Cuba since 1917 and the largest ever recorded in that region by global seismic networks. It is therefore a key element for our understanding of the tectonic and kinematic regime along the northern Caribbean plate boundary. In order to test the previously proposed source parameters of the Cabo Cruz earthquake and to better constrain its focal mechanism, we derived a new set of source parameters from unfiltered broad-band teleseismic records. We used a hybrid ray tracing method that allows us to take into account propagation effects of seismic waves in a realistic crustal model around the source. Our solution is consistent with the long-period focal mechanism solution of Virieux et al. (1992). Our solution also models the higher frequency crustal and water layer phases. The primarily strike-slip focal mechanism has a small thrust component. Its shows an east-west trending nodal plane dipping 55° to the north that we interpret as the rupture plane since it corresponds to the geometry of the major active fault in that area. The displacement on this plane is a left-lateral strike-slip combined with a small amount of southward thrust. The result is in good agreement with the active tectonic structures observed along the Oriente fault south of Cuba. The small thrust component demonstrates that, contrary to prior belief, the transpressive regime extends along this whole segment of the Caribbean/North American plate boundary. Together with historical seismicity, it suggests that most of the stress accumulated by the Caribbean/North American plate motion is released seismically along the southern Cuban margin during relatively few but large earthquakes.

  16. 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

  17. Two Cenozoic tectonic events of N-S and E-W extension in the Lhasa Terrane: Evidence from geology and geochronology

    NASA Astrophysics Data System (ADS)

    Huang, Feng; Xu, Ji-Feng; Chen, Jian-Lin; Wu, Jian-Bin; Zeng, Yun-Chuan; Xiong, Qiu-Wei; Chen, Xue-Feng; Yu, Hong-Xia

    2016-02-01

    Cenozoic active structures in the Tibetan Plateau are mainly regional N-S trending extensional faults and grabens, and E-W trending extensional tracks that are related to the transition from syn- to post-collision between India and Asia. E-W trending tracks are parallel to the direction of Neo-Tethyan oceanic convergence and consist of extensional volcanic-sedimentary basins and magmatic dykes in the southern Lhasa Terrane, Tibet. N-S trending tracks comprise faults and grabens, which are widely developed in Tibet. It remains unknown how and when the geodynamic transition from E-W to N-S trending tectonic tracks occurred. This study describes both E-W and N-S trending tectonic tracks identified at Dazi area of southern Lhasa Terrane, where E-W trending mafic dykes intruded a granitoid and late-stage N-S trending felsic dykes cut across E-W trending mafic dykes. Zircons from four granitoid samples yield consistent crystallization ages of ca. 60 Ma and positive εHf(t) values (~+ 9). An altered dioritic vein, which cuts the mafic dykes, yields an age of ca. 53 Ma. These new dating results indicate that E-W trending dykes, which formed due to regional N-S extension, were emplaced between 60 and 53 Ma. In addition, two N-S trending monzonitic porphyritic dykes, which cut the mafic dykes, yield U-Pb zircon ages of ca. 17 Ma with moderate positive εHf(t) values (+ 3 to + 9.6), as well as a NNE-SSW trending quartz monzonitic dyke, which cuts all other types of dykes, yields U-Pb ages of ca. 13 Ma. This suggests that E-W extension took place between 17 and 13 Ma. These results, in combination with existing age data for Gangdese granitoids and mafic magmatism, indicate the occurrence of two major extensional events at 60-53 Ma and 17-13 Ma. In turn, this implies that the transition from E-W to N-S trending tectonic and the onset of E-W extension occurred at ca. 17 Ma or slightly earlier. Paleocene granitoids have geochemical characteristics that are indicative of both

  18. Is subduction really in the plate tectonics driving seat, or do two other global mechanisms do the driving? A review in the 'deep-keeled cratons' frame for global dynamics

    NASA Astrophysics Data System (ADS)

    Osmaston, M. F.

    2012-04-01

    mantle boundary layer habitually assumed, but its LVZ content gives it (i) residual heat content, (ii) corresponding buoyancy, and (iii) a flexural strength which demands a reconsideration of its mode of downbend, hitherto widely regarded as flexural, but still be able to explain outer rises and their differences. Solutions for (ii) and (iii) are convincingly supported by widespread exposure of the resulting rocks in the Alps, telling us how they and other UHP metamorphic mountain belts have been built [11]. I will illustrate the essential points. In particular, the buoyancy (ii) provides the upward mechanical contact essential for the shallow basal subduction tectonic erosion of the upper plate as preparation of thin imbricate crustal slices to subduct to UHP. And a seismologically supported through-plate step-faulting mode of downbend copes with the flexure problem (iii) and provides the tectonic erosion mechanism. In tackling these matters, important intrinsic properties of the materials are, notably:- (1) the thermal conductivity of non-migrating interstitial melt is >20 times less than its parent rock, so the LVZ heat is effectively trapped during the plate's journey across the ocean, only to be released when subduction raises the pressure and the melt freezes; (2) the garnet-to-spinel peridotite phase change, typically at 50 to 90 km depth, gives some 50 times more volume change per joule than pure expansivity, and it does so with the big force of solid-state recrystallization. This force is the crack-wall push-apart force provided by our thick-plate MOR model, which thereby develops at least an order more ridge push than the divergent flow model. We now consider the post-downbend evolution of the subducting plate, recognizing both the heat content of its ex-LVZ material and that, within the 2-layer mantle picture established by the plate dynamics of 'deep-keeled cratons' [2 - 5], there is no substantial mantle transport across the 660 km level. Examination of

  19. A review of the tectonic evolution of the Northern Pacific and adjacent Cordilleran Orogen

    NASA Astrophysics Data System (ADS)

    Jakob, Johannes; Gaina, Carmen; Johnston, Stephen T.

    2014-05-01

    Numerous plate kinematic models for the North Pacific realm have been developed since the advent of plate tectonics in the early seventies (e.g Atwater (1970), Mammerickx and Sharman (1988)). Although published kinematic models are consistent with the broad scale features of the North Pacific, the link between plate motions and the evolution of the North American Cordillera remains poorly understood. Part of the problem lies in conflicting interpretations of geological versus paleomagnetic data sets, with the result being a lack of consensus regarding: the paleolocation of key geological units; the paleogeography of terrane formation and amalgamation; the motion, boundaries and even existence of oceanic plates; and the character (e.g. trend of subduction) and position of plate boundaries within the northern Pacific basin. Remnants of the Farallon and Kula plates, and some short-lived microplates, demonstrate the complicated tectonic evolution of the oceanic realm west of the North American margin (e.g. Rea and Dixon (1983); McCrory and Wilson (2013); Shephard et al. (2013)). The creation and destruction of major tectonic plates and microplates has presumably left a record in the Cordilleran orogen of western North America. However, working backward from the geological relationships to plate reconstructions remains difficult. Here we investigate the relationship between the plate motions of the Pacific Ocean and the terrane movements in the North American Cordillera by revising the marine magnetic and gravity anomalies of the northern Pacific. In particular, we reevaluate plate boundaries at times of major changes in plate geometry of the Pacific, Kula, Chinook and Farallon plates from C34n onward. Our focus is also on the plate geometries of the Resurrection, Eshamy and Siletz-Crescent plates during the time between anomaly C26 and C12, and the links between plate interactions and on-shore tectonic events recorded in the geological record of Vancouver Island

  20. On the PETM and ETM2 global warming events: New evidence for a tectonic-magmatic trigger mechanism (Invited)

    NASA Astrophysics Data System (ADS)

    Storey, M.; Condon, D.; Stecher, O.; Hald, N.

    2009-12-01

    The climate record covering the past 70 my shows that global temperatures peaked during the Early Eocene around ˜54 to 52 Ma; the Early Eocene Climatic Optimum (EECO) (1). Preceding and during the EECO were three ephemeral global warming events, each with approximately half the intensity of its predecessor: the Paleocene Eocene Thermal Maximum (PETM), the Eocene Thermal Maximum 2 (ETM2) and the Eocene Thermal Maximum 3 (ETM3). Each is marked by an abrupt decrease in the δ13C of sedimentary carbon, consistent with the rapid addition of massive amounts of 13C-depleted C, in the form of carbon dioxide and/or methane, into the hydrosphere/atmosphere. These events are regarded as the best deep-time analogues to future climate scenarios through higher CO2 concentration in the atmosphere. There is, however, no consensus on the source of the carbon for these ancient warming events or the triggering mechanism/s for the release. Two ideas are (i) breakdown of marine methane hydrate (2), possibly related to orbital cycles forcing and/or (ii) for the PETM, thermogenic release of methane by massive sill intrusion into C-rich sedimentary basins, with the gas being released via a complex of thousands of hydrothermal vents (3). These two potential carbon sources have quite different isotopic ratios, which in mass balance calculations determine the amount of carbon required to account for the carbon isotope excursions. Better knowledge of the carbon sources/s is essential if these events are to be factored in to models of climate sensitivity to atmospheric CO2 concentration. The PETM has been shown to be synchronous with the onset of peak, continental-breakup related, magmatic activity during the formation of the East Greenland and the Faeroes flood basalt province (4), supporting the sill intrusion model for the source of the methane/CO2 (3). One perceived weakness of this explanation, however, is that it apparently fails to explain the younger ETM2 and ETM3 events. Here we

  1. CRUSTAL TECTONICS AND SEISMICITY OF THE MIDDLE EAST

    NASA Astrophysics Data System (ADS)

    Ghalib, H. A.; Gritto, R.; Sibol, M. S.; Herrmann, R. B.; Aleqabi, G. I.; Caron, P. F.; Wagner, R. A.; Ali, B. S.; Ali, A. A.

    2009-12-01

    The Arabian plate describes a geological entity and a dynamic system that has been in continuous interaction with the African plate to the west and south and the Eurasian plate to the north and east. The western and southern boundaries are distinguished by see floor spreading along the Gulf of Aden and Red Sea and transform faulting along the Dead Sea, whereas the northern and eastern boundaries are portrayed by compressional suture zones under thrusting the Turkish and Iranian plateaus. Despite this favorable juxtaposition of continental land masses and the plethora of national seismic networks in every country of the Middle East, the majority of published research on the Arabian plate and surrounding tectonic blocks still depends primarily on global seismographic stations and occasional local networks. Since 2005, we deployed a number of seismic stations, and more recently a five elements array, in close proximity to the northeastern boundary of the Arabian plate. The primary objective of the effort is to better understand the regional seismicity and seismotectonics of the Arabian plate and surrounding regions. To date over a terabyte of high quality 100 sps continuous three-component broadband data have been collected and being analyzed to derive models representative of the greater Middle East tectonic setting. This goal is, in part, achieved by estimating local and regional seismic velocity models using receiver function and surface wave dispersion analyses, and by using these models to obtain accurate hypocenter locations and event focal mechanisms. The resulting events distribution reveals a distinct picture of the interaction between the seismicity and tectonics of the region. The highest seismicity rate seems to be confined to the active northern section of the Zagros thrust zone, while it decreases towards the southern end, before the intensity increases again in the Bandar Abbas region. Spatial distribution of the events and stations provide thorough

  2. Spatio-temporal autocorrelation of Neogene-Quaternary volcanic and clastic sedimentary rocks in SW Montana and SE Idaho: Relationship to Cenozoic tectonic and thermally induced extensional events

    NASA Astrophysics Data System (ADS)

    Davarpanah, A.; Babaie, H. A.; Dai, D.

    2013-12-01

    Two systems of full and half grabens have been forming since the mid-Tertiary through tectonic and thermally induced extensional events in SW Montana and neighboring SE Idaho. The earlier mid-Tertiary Basin and Range (BR) tectonic event formed the NW- and NE-striking mountains around the Snake River Plain (SRP) in Idaho and SW Montana, respectively. Since the mid-Tertiary, partially synchronous with the BR event, diachronous bulging and subsidence due to the thermally induced stress field of the Yellowstone hotspot (YHS) has produced the second system of variably-oriented grabens through faulting across the older BR fault blocks. The track of the migration of the YHS is defined by the presence of six prominent volcanic calderas along the SRP which become younger toward the present location of the YHS. Graben basins bounded by both the BR faults and thermally induced cross-faults (CF) systems are now filled with Tertiary-Quaternary clastic sedimentary and volcanic-volcaniclastic rocks. Neogene mafic and felsic lava which erupted along the SRP and clastic sedimentary units (Sixmile Creek Fm., Ts) deposited in both types of graben basins were classified based on their lithology and age, and mapped in ArcGIS 10 as polygon using a combination of MBMG and USGS databases and geological maps at scales of 1:250.000, 1:100,000, and 1:48,000. The spatio-temporal distributions of the lava polygons were then analyzed applying the Global and Local Moran`s I methods to detect any possible spatial or temporal autocorrelation relative to the track of the YHS. The results reveal the spatial autocorrelation of the lithology and age of the Neogene lavas, and suggest a spatio-temporal sequence of eruption of extrusive rocks between Miocene and late Pleistocene along the SRP. The sequence of eruptions, which progressively becomes younger toward the Yellowstone National Park, may track the migration of the YSH. The sub-parallelism of the trend of the SRP with the long axis of the

  3. The golden transformation of the Cretaceous plate subduction in the west Pacific

    NASA Astrophysics Data System (ADS)

    Sun, Weidong; Ding, Xing; Hu, Yan-Hua; Li, Xian-Hua

    2007-10-01

    Long-term couplings between the subducting and overlying plates are very important to understanding plate tectonics, in particular intraplate evolutions. Geological records of this coupling however, are usually not well preserved. Here we show a good example in eastern China where Cretaceous tectonic evolution matches remarkably well with the drifting history of the Pacific plate. The most pronounced phenomenon is that the eastern China large-scale orogenic lode gold (Au) mineralization occurred contemporaneously with an abrupt change of ~ 80° in the drifting direction of the subducting Pacific plate, concurrent with the formation of the Ontong Java Plateau. Given that lode Au deposits usually form at the onset of compressional or transpressional deformations, the Au deposits dated the major tectonic change from extension to transpression in eastern China, coherent with the subduction regime. The Cretaceous drifting history of the Pacific plate also tallies with other major geological events in eastern China, e.g., the evolution of the Tan-Lu fault and magmatic activities, suggesting that the major geological events in eastern China in the Cretaceous were mainly controlled by the subduction of the Pacific plate, and that plate interactions during su