Sample records for plate tectonic events

  1. Plate TectonicsPlate Tectonics Plate TectonicsPlate Tectonics

    E-print Network

    Siebel, Wolfgang

    Plate TectonicsPlate Tectonics #12;Plate TectonicsPlate Tectonics · Lithosphere ­ strong, rigid, transform boundaries ­ travel 1 to 11 cm/yr relative to one another #12;14 tectonic plates today #12;Mid asthenosphere that flows · 8 large lithospheric plates and 6 smaller ones ­ separated by divergent, convergent

  2. Plate Tectonics

    NSDL National Science Digital Library

    Mrs. Walls

    2011-01-30

    Create a poster all about Plate Tectonics! Directions: Make a poster about Plate Tectonics. (20 points) Include at least (1) large picture (15 points) on your poster complete with labels of every part (10 points). (15 points) Include at least three (3) facts about Plate Tectonics. (5 points ...

  3. Plate Tectonics

    NSDL National Science Digital Library

    2006-01-01

    In this lesson, students are introduced to the theory of plate tectonics and explore how the theory was developed and supported by evidence. Through class discussion, videos, and activities, students seek connections between tectonic activity and geologic features and investigate how the theory of plate tectonics evolved.

  4. Plate Tectonics

    NSDL National Science Digital Library

    Mrs. Rohlfing

    2011-02-03

    Students will go over the main points of plate tectonics, including the theory of continental drift, different types of plate boundaries, seafloor spreading, and convection currents. We have been spending time learning about plate tectonics. We have discussed the theory of continental drift, we have talked about the different types of plate boundaries, we have also learned about seafloor spreading and convection currents. Plate Boundary Diagram Now is your chance ...

  5. Plate Tectonics

    NSDL National Science Digital Library

    National Science Teachers Association (NSTA)

    2007-03-21

    The Plate Tectonics SciPack explores the various materials that make up Earth and the processes they undergo to provide a framework for understanding how continents are created and change over time. The focus is on Standards and Benchmarks related to Earth's layers, oceanic and continental plates and the interactions between plates.In addition to comprehensive inquiry-based learning materials tied to Science Education Standards and Benchmarks, the SciPack includes the following additional components:? Pedagogical Implications section addressing common misconceptions, teaching resources and strand maps linking grade band appropriate content to standards. ? Access to one-on-one support via e-mail to content "Wizards".? Final Assessment which can be used to certify mastery of the concepts.Learning Outcomes:Plate Tectonics: Layered Earth? Identify that Earth has layers (not necessarily name them), and that the interior is hotter and more dense than the crust.? Identify the crust as mechanically strong, and the underlying mantle as deformable and convecting.Plate Tectonics: Plates? Identify that the outermost layer of Earth is made up of separate plates.? Choose the correct speed of the motion of plates.? Identify the ocean floor as plate, in addition to the continents (to combat the common idea that only continents are plates, floating around on the oceans).? Recognize that oceans and continents can coexist on the same plate.Plate Tectonics: Plate Interactions? Identify the different interactions between plates.? Discuss what happens as a result of those interactions.Plate Tectonics: Consequences of Plate Interactions? Explain why volcanoes and earthquakes occur along plate boundaries. ? Explain how new sea floor is created and destroyed.? Describe features that may be seen on the surface as a result of plate interactions.Plate Tectonics: Lines of Evidence? Use plate tectonics to explain changes in continents and their positions over geologic time.? Provide evidence for the idea of plates, including the location of earthquakes and volcanoes, continental drift, magnetic orientation of rocks in the ocean floor, etc.

  6. Plate Tectonics: Plate Interactions

    NSDL National Science Digital Library

    National Science Teachers Association (NSTA)

    2006-11-01

    This Science Object is the fourth of five Science Objects in the Plate Tectonic SciPack. It identifies the events that may occur and landscapes that form as a result of different plate interactions. The areas along plate margins are active. Plates pushing against one another can cause earthquakes, volcanoes, mountain formation, and very deep ocean trenches. Plates pulling apart from one another can cause smaller earthquakes, magma rising to the surface, volcanoes, and oceanic valleys and mountains from sea-floor spreading. Plates sliding past one another can cause earthquakes and rock deformation. Learning Outcomes:? Explain why volcanoes and earthquakes occur along plate boundaries. ? Explain how new sea floor is created and destroyed.? Describe features that may be seen on the surface as a result of plate interactions.

  7. Plate Tectonics

    NSDL National Science Digital Library

    Smoothstone

    This interactive Flash explores plate tectonics and provides an interactive map where users can identify plate boundaries with name and velocities as well as locations of earthquakes, volcanoes, and hotspots. The site also provides animations and supplementary information about plate movement and subduction. This resource is a helpful overview or review for introductory level high school or undergraduate physical geology or Earth science students.

  8. Plate Tectonics

    NSDL National Science Digital Library

    This data tip from Bridge, the Ocean Sciences Education Teacher Resource Center archive, includes a variety of educational sites to visit on plate tectonic theory. Learners can use underwater earthquake data to identify plate boundaries with links to the National Oceanic and Atmospheric Administration's Acoustic Monitoring Program Ocean Seismicity data. Data from the Northeast Pacific, eastern Equatorial Pacific, and North Atlantic are examined in more detail.

  9. Mapping Plate Tectonic Boundaries

    NSDL National Science Digital Library

    Michael Kerwin

    To prepare for this activity, students do background reading on Plate Tectonics from the course textbook. Students also participate in a lecture on the discovery and formulation of the unifying theory of plate tectonics, and the relationship between plate boundaries and geologic features such as volcanoes. Lastly, in lecture, students are introduced to a series of geologic hazards caused by certain plate tectonic interactions. The activity gives students practices at identifying plate boundaries and allows them to explore lesser known tectonically active regions.

  10. Plate Tectonics as Expressed in Geological Landforms and Events

    NSDL National Science Digital Library

    Jeff Ryan

    This activity seeks to have students analyze global data sets on earthquake and volcano distributions toward identifying major plate boundary types in different regions on the Earth. A secondary objective is to familiarize students with two publicly available resources for viewing and manipulating geologically-relevant geospatial data: Google Earth(TM) and GeoMapApp.

  11. External Resource: Plate Tectonics

    NSDL National Science Digital Library

    1900-01-01

    This Windows to the Universe interactive webpage connects students to the study and understanding of plate tectonics, the main force that shapes our planets surface. Topics: plate tectonics, lithosphere, subduction zones, faults, ridges.

  12. Plate Tectonic Theory

    NSDL National Science Digital Library

    John Louie

    This is the web site for a Plate Tectonics Theory class at The University of Nevada, Reno. The home page/syllabus contains links to several of the topics covered in the course. The topics with web based lecture materials are earthquake seismology, structure of the Earth, composition of the Earth, lithospheric deformation, the plate tectonics paradigm, and the driving mechanisms of plate tectonics.

  13. Tectonic Plates and Plate Boundaries

    NSDL National Science Digital Library

    WGBH Educational Foundation

    2005-12-17

    This interactive activity adapted from NASA features world maps that identify different sections of the Earth's crust called tectonic plates. The locations of different types of plate boundaries are also identified, including convergent, divergent, and transform boundaries.

  14. Plate Tectonics Animation

    NSDL National Science Digital Library

    2002-01-01

    Plate tectonics describes the behavior of Earth's outer shell, with pieces (plates) bumping and grinding and jostling each other about. Explore these maps and animations to get a jump start on understanding plate tectonic processes, history, and how motion of the plates affects our planet today.

  15. 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

  16. Caribbean plate tectonics

    NSDL National Science Digital Library

    Sting

    This illustration available at Wikimedia Commons shows the plate tectonic setting in the Caribbean. Plate boundaries are color-coded by margin type and plate motions are noted with direction and magnitude in mm/yr.

  17. Earthquakes and Plate Tectonics

    NSDL National Science Digital Library

    This article describes the theory of plate tectonics and its relation to earthquakes and seismic zones. Materials include an overview of plate tectonics, a description of Earth's crustal plates and their motions, and descriptions of the four types of seismic zones.

  18. Plate Tectonics Prof. Thomas Herring

    E-print Network

    Herring, Thomas

    1 Plate Tectonics Prof. Thomas Herring MIT 05/14/02 Lexington HS Plate tectonics 2 Contact/14/02 Lexington HS Plate tectonics 3 Overview · Development of the Plate tectonic theory · Geological Data ­ Sea-floor spreading ­ Fault types from earthquakes ­ Transform faults ­ Today's measurements of plate tectonics 05

  19. PLATE TECTONICS USING GIS Understanding plate tectonics using real

    E-print Network

    PLATE TECTONICS USING GIS Understanding plate tectonics using real global data sets pertaining OF THE UPSTATE, SC An afternoon field trip to observe the evidences for plate tectonic history, and to witness

  20. Plate Tectonics: Further Evidence

    NSDL National Science Digital Library

    The representation depicts the spreading of the sea floor along the mid-ocean ridges. The resource generally describes the theory of plate tectonics, including the movement of plates with regard to one another.

  1. Geology - Plate Tectonics

    NSDL National Science Digital Library

    Visitors to this site can learn about the theory of plate tectonics, the history of its development, and the mechanisms that drive the formation, movement, and destruction of continents and tectonic plates. A selection of animations depicts the movements of crustal plates and continents through time. Each animation is accompanied by an interactive time scale that provides links to descriptions of the geology and paleontology of the selected era or period.

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

    SciTech Connect

    Stevens, C.H.; Sedlock, R. (San Jose State Univ., CA (United States)); Stone, P. (Geological Survey, Reston, VA (United States))

    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.

  3. Plate Tectonic Primer

    NSDL National Science Digital Library

    Lynn Fichter

    This site gives an in-depth look at the theory of plate tectonics and how it works. The structure of the Earth is discussed, with brief rock type descriptions. The structure of the lithosphere, plate boundaries, interplate relationships, and types of plates are all covered in detail.

  4. 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)

  5. Plate tectonics, damage and inheritance.

    PubMed

    Bercovici, David; Ricard, Yanick

    2014-04-24

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

  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: Consequences of Plate Interactions

    NSDL National Science Digital Library

    National Science Teachers Association (NSTA)

    2006-11-01

    This Science Object is the fourth of five Science Objects in the Plate Tectonic SciPack. It identifies the events that may occur and landscapes that form as a result of different plate interactions. The areas along plate margins are active. Plates pushing against one another can cause earthquakes, volcanoes, mountain formation, and very deep ocean trenches. Plates pulling apart from one another can cause smaller earthquakes, magma rising to the surface, volcanoes, and oceanic valleys and mountains from sea-floor spreading. Plates sliding past one another can cause earthquakes and rock deformation. Learning Outcomes:? Explain why volcanoes and earthquakes occur along plate boundaries. ? Explain how new sea floor is created and destroyed.? Describe features that may be seen on the surface as a result of plate interactions.

  8. Internet Geography: Plate Tectonics

    NSDL National Science Digital Library

    This site is part of GeoNet Internet Geography, a resource for pre-collegiate British geography students and their instructors. This page focuses on the structure of the Earth and the theory of plate tectonics, including continental drift, plate boundaries, the Ring of Fire, and mountains.

  9. Plate Tectonics at Work

    NSDL National Science Digital Library

    This is a brief description of the results of plate movement according to the Theory of Plate Tectonics. It explains how divergence at the mid-ocean ridges accounts for the discoveries of Harry Hess. The site also refers to the invention of the magnetometer and the discovery of the young age of the ocean floor basalt. It concludes that these are the kinds of discoveries and thinking that ultimately led to the development of the theory of plate tectonics and that in just a few decades, have greatly changed our view of and notions about our planet and the sciences that attempt to explain its existence and development.

  10. An Introduction to Plate Tectonics

    NSDL National Science Digital Library

    This page is a brief introduction to plate tectonics. It starts with a discussion of the evolution of the theory of plate tectonics and the arguments supporting it. It then discusses the processes associated with tectonics and the types of plate boundaries: divergent, convergent and transform boundaries. It concludes with a discussion of the current hypotheses of what causes plates to move.

  11. Tectonic Plates and Plate Boundaries

    NSDL National Science Digital Library

    Continents were once thought to be static, locked tight in their positions in Earth's crust. Similarities between distant coastlines, such as those on opposite sides of the Atlantic, were thought to be the work of a scientist's overactive imagination, or, if real, the result of erosion on a massive scale. This interactive feature shows 11 tectonic plates and their names, the continents that occupy them, and the types of boundaries between them.

  12. Plate Tectonics Learning Module

    NSDL National Science Digital Library

    Rita Haberlin

    This plate tectonics unit was designed to be used with a college course in physical geography. Subject matter covered includes: the development of the theory including Wegener's Continental Drift Hypothesis and the existence of Pangaea, Harry Hess and his work on sea-floor spreading, and the final theory. It points out that global features such as deep oceanic trenches, mid-ocean ridges, volcanic activity, and the location of earthquake epicenters can now be related to the story of plate tectonics, since most geological activity occurs along plate boundaries. Divergent, convergent and transform plate boundaries are discussed in detail. This module contains a study guide and outline notes, study questions, and practice quizzes. One feature of the module is a web exploration section with links to twelve outside sites that augment the instruction.

  13. Plate Tectonic Movement Visualizations

    NSDL National Science Digital Library

    This collection provides a wide array of visual resources and supporting material about plate tectonic movements. Visualizations include simple animations, GIS-based animated maps, paleogeographic maps and globes, and numerous illustrations and photos. This collection is not exhaustive but does represent some of the best sources for teaching. Resources can be incorporated into lectures, labs, or other activities.

  14. 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…

  15. Lesson 3. Plate Tectonics Overview

    E-print Network

    Chen, Po

    Lesson 3. Plate Tectonics #12;Overview · Prior to the 1970s that with the development of the theory of plate tectonics. · Knowledge of the ocean floors of the Earth #12;Overview · Plate tectonics explains the formaBon of the Earth's two

  16. The Biggest Plates on Earth: Plate Tectonics

    NSDL National Science Digital Library

    In this lesson, students investigate the movement of Earth's tectonic plates, the results of these movements, and how magnetic anomalies present at spreading centers document the motion of the crust. As a result of this activity, students will be able to describe the motion of tectonic plates, differentiate between three types of plate boundaries, infer what type of boundary exists between two tectonic plates, and understand how magnetic anomalies provide a record of geologic history and crustal motion around spreading centers. As an example, they will also describe plate boundaries and tectonic activity in the vicinity of the Juan de Fuca plate adjacent to the Pacific Northwest coast of North America.

  17. Plate Tectonics: Lines of Evidence

    NSDL National Science Digital Library

    National Science Teachers Association (NSTA)

    2006-11-01

    This Science Object is the fifth of five Science Objects in the Plate Tectonics SciPack. It explores the physical, geographical, and geological evidence for the theory of continental drift and plate tectonics. Plate tectonics provide a unifying framework for understanding Earth processes and history, and is supported by many lines of evidence. Over geologic time, plates move across the globe creating different continents (and positions of continents). Learning Outcomes:? Use plate tectonics to explain changes in continents and their positions over geologic time.? Provide evidence for the idea of plates, including the location of earthquakes and volcanoes, continental drift, magnetic orientation of rocks in the ocean floor, etc.

  18. Plate Tectonics: The Mechanism

    NSDL National Science Digital Library

    This text explains how detailed mapping of the ocean floor led scientists like Howard Hess and R. Deitz to revive the Holmes convection theory. Hess and Deitz modified the theory considerably and called their new theory Sea-floor Spreading. Among the seafloor features that supported the sea-floor spreading hypothesis were: mid-oceanic ridges, deep sea trenches, island arcs, geomagnetic patterns, and fault patterns. These features are treated in detail and related to the current Theory of Plate Tectonics.

  19. Plate Tectonics and Volcanism

    NSDL National Science Digital Library

    This is a lesson where learners explore plate movement and the relationship between plate tectonics and volcanoes. The lesson models scientific inquiry using the 5E instructional model and includes teacher notes, prerequisite concepts, common misconceptions, student journal and reading. This is lesson five in the Astro-Venture Geology Training Unit that was developed to increase students' awareness of and interest in astrobiology and the many career opportunities that utilize science, math and technology skills. The lessons are designed for educators to use with the Astro-Venture multimedia modules.

  20. 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.

  1. 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 about Mars plate tectonics.

  2. Global Topography and Tectonic Plates

    NSDL National Science Digital Library

    David Greene

    The goal of this activity is to investigate global topographic and tectonic features, especially the tectonic plates and their boundaries. Using a double-page size digital topographic map of the Earth that includes both land and sea floor topography, students are asked to draw plate boundaries, deduce plate motions and interactions, and explore the connections between topography and tectonic processes at the global scale.

  3. Dynamics of Tectonic Plates

    E-print Network

    Pechersky, E; Sadowski, G; Yambartsev, A

    2014-01-01

    We suggest a model that describes a mutual dynamic of tectonic plates. The dynamic is a sort of stick-slip one which is modeled by a Markov random process. The process defines a microlevel of the dynamic. A macrolevel is obtained by a scaling limit which leads to a system of integro-differential equations which determines a kind of mean field systems. Conditions when Gutenberg-Richter empirical law are presented on the mean field level. These conditions are rather universal and do not depend on features of resistant forces.

  4. A plate tectonic model for the Paleozoic and Mesozoic constrained by dynamic plate boundaries and restored

    E-print Network

    Cerveny, Vlastislav

    A plate tectonic model for the Paleozoic and Mesozoic constrained by dynamic plate boundaries November 2001; accepted 15 November 2001 Abstract We developed a plate tectonic model for the Paleozoic rates and major tectonic and magmatic events. Plates were constructed through time by adding

  5. Intermittent plate tectonics?

    PubMed

    Silver, Paul G; Behn, Mark D

    2008-01-01

    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. PMID:18174440

  6. The science behind Plate Tectonics

    NSDL National Science Digital Library

    John Weber

    Plate tectonics is a quantitative, robust and testable, geologic model describing the surface motions of Earth's outer skin. It is based on real data and assumptions, and built using the scientific method. New space geodesy data provide important quantitative (and independent) tests of this model. In general, these new data show a close match to model predictions, and suggest that plate motion is steady and uniform over millions of years. Active research continues to refine the model and to better our understanding of plate motion and tectonics. The exercise presented here aims to help students experience the process of doing science and to understand the science underlying the plate tectonic theory. Key words: plate tectonics, global plate motion models, assumptions, geologic data (spreading rates, transform fault azimuths, earthquake slip vectors), space geodesy tests.

  7. Tectonic stress in the plates

    Microsoft Academic Search

    Randall M. Richardson; Sean C. Solomon; Norman H. Sleep

    1979-01-01

    The state of stress in the lithosphere provides strong constraints on the forces acting on the plates. The directions of principal stresses in the plates as indicated by midplate earthquake mechanisms, in situ stress measurements, and stress-sensitive geological features are used to test plate tectonic driving force models, under the premises that enough data exist in selected areas to define

  8. 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.

  9. Tectonic Plate Movement in Alaska

    NSDL National Science Digital Library

    2008-11-04

    In this video adapted from KUAC-TV and the Geophysical Institute at the University of Alaska, Fairbanks, learn how tectonic plate movement is responsible for building mountains, such as the Wrangell and St. Elias Mountains.

  10. The Nature of Tectonic Plates

    NSDL National Science Digital Library

    2008-12-30

    This lesson provides an overview of the various types of interactions between tectonic plates. The discussion uses the analogy of a cracked egg to describe the tectonic plates composing Earth's crust. Other topics include the concentrated earthquake and volcanic activity associated with plate boundaries, types of interactions at the boundaries, and how plate motions are affecting the Atlantic and Pacific Oceans. The lesson includes an activity in which students will use online references to locate a hypothetical nuclear power plant in a geologically safe area, investigate the history of large earthquakes in South Carolina, provide a likely location for a hypothetical geothermal power plant, and others.

  11. Earthquakes, Volcanoes, and Plate Tectonics

    NSDL National Science Digital Library

    This page consists of two maps of the world, showing how earthquakes define the boundaries of tectonic plates. Volcanoes are also distributed at plate boundaries (the "Ring of Fire" in the Pacific) and at oceanic ridges. It is part of the U.S. Geological Survey's Cascades Volcano Observatory website, which features written material, images, maps, and links to related topics.

  12. Subduction Drive of Plate Tectonics

    Microsoft Academic Search

    W. B. Hamilton

    2003-01-01

    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

  13. CENOZOIC PLATE TECTONICS OF SE ASIA 11 Cenozoic plate tectonic reconstructions of SE Asia

    E-print Network

    Royal Holloway, University of London

    CENOZOIC PLATE TECTONICS OF SE ASIA 11 Cenozoic plate tectonic reconstructions of SE Asia ROBERT TW20 0EX, UK (e-mail: robert.hall@gl.rhul.ac.uk) Abstract: A new plate tectonic model to present regional tectonics. Plate tectonic reconstructions of SE Asia may help in understanding

  14. 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.

  15. 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)

  16. Author's personal copy Plate tectonic reconstructions with continuously closing plates$

    E-print Network

    Bower, Dan J.

    Author's personal copy Plate tectonic reconstructions with continuously closing plates$ Michael May 2011 Keywords: Geodynamics Plate tectonics a b s t r a c t We present a new algorithm for modeling margins and plates, traditional global plate tectonic reconstructions have become inadequate

  17. Learning Assessment #1 - Plate Tectonics

    NSDL National Science Digital Library

    Michelle Speta

    In Part 1 of this activity, students are provided with a blank topographic profile and an associated tectonic plate boundary map. Students are asked to draw a schematic cross-section on the profile down to the asthenosphere including tectonic plates (with relative thicknesses of crust etc. appropriately illustrated), arrows indicating directions of plate movement, tectonic features (mid-ocean ridges, trenches and volcanic arcs) and symbols indicating where melting is occurring at depth. In Part 2, students are asked to provide geological and geophysical lines of evidence to support their placement of convergent and divergent boundaries, respectively. A bonus question asks students to predict what would happen if spreading along the Atlantic mid-ocean ridge were to stop. Students are referred to appropriate sections of the textbook to guide them in completing all the parts of this activity. Students are also provided with a checklist of required elements for both parts of the assignment.

  18. Plate Tectonics Jigsaw

    NSDL National Science Digital Library

    Anne Egger

    This activity is a slight variation on an original activity, Discovering Plate Boundaries, developed by Dale Sawyer at Rice University. I made different maps, including more detail in all of the datasets, and used a different map projection, but otherwise the general progression of the activity is the same. More information about jigsaw activities in general can be found in the Jigsaws module. The activity occurs in several sections, which can be completed in one or multiple classes. In the first section, students are divided into "specialist" groups, and each group is given a global map with a single dataset: global seismicity, volcanoes, topography, age of the seafloor, and free-air gravity. Each student is also given a map of plate boundaries. Their task in the specialist group is to become familiar with their dataset and develop categories of plate boundaries based only on their dataset. Each group then presents their results to the class. In the second section, students reorganize into groups with 1-2 of each type of specialist per group. Each new group is given a plate, and they combine their different datasets on that one plate and look for patterns. Again, each plate group presents to the class. The common patterns and connections between the different datasets quickly become apparent, and the final section of the activity involves a short lecture from the instructor about types of plate boundaries and why the common features are generated at those plate boundaries. A follow-up section or class involves using a problem-solving approach to explain the areas that don't "fit" into the typical boundary types - intra-plate volcanism, earthquakes in the Eastern California Shear Zone, etc.

  19. Metamorphic Rocks and Plate Tectonics

    NSDL National Science Digital Library

    Smoothstone

    This interactive Flash explores the processes and products of metamorphism, including rock examples, types of metamorphism, and facies, and relates them to plate tectonics. It is a useful overview or review suitable for high school or introductory level undergraduate students in Earth science or physical geology courses. It includes diagrams, animations, and supplementary information about metamorphic rocks.

  20. 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.

  1. Comment on "Intermittent plate tectonics?".

    PubMed

    Korenaga, Jun

    2008-06-01

    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. PMID:18535229

  2. First Draft 1 April 2003 Plate Tectonics ;

    E-print Network

    Anderson, Don L.

    1 4/18/04 First Draft 1 April 2003 Plate Tectonics ; The General Theory The Complex Earth is difficult to overturn. After more than 20 years some implications of plate tectonics have yet to be fully convective systems. It relies on a theory of plate tectonics unconstrained by assumptions about absolute

  3. 6, 793830, 2014 Plate tectonic raster

    E-print Network

    Müller, Dietmar

    SED 6, 793­830, 2014 Plate tectonic raster reconstruction in GPlates J. Cannon et al. Title Page if available. Plate tectonic raster reconstruction in GPlates J. Cannon 1 , E. Lau 1, * , and R. D. Müller 1 1 of the European Geosciences Union. 793 #12;SED 6, 793­830, 2014 Plate tectonic raster reconstruction in GPlates J

  4. Tectonic Plate Motion

    NSDL National Science Digital Library

    The representation shows the direction of motion of the Earth's major plates as measured through NASA's satellite laser ranging (SLR) technology. A series of world maps, accompanying text, and the subsequent links explain this technology in great detail. One can click on the Index Map for Satellite Laser Ranging site Velocity and see the vectors (arrows) that indicate the direction and rate of movement of Earth's plates in much more detail. Accompanying text gives a more detailed explanation of what each sub map is showing.

  5. Plate Tectonics Quiz

    NSDL National Science Digital Library

    This quiz for younger students asks them 10 questions about plate motions, rock types in continental and oceanic crust, crustal formation and mountain building, the supercontinent Pangea, and the theory of continental drift. A link to a page on continental drift provides information to answer the questions.

  6. 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.

  7. 26 ENGINEERING & SCIENCE fall 2011 Tectonic plates

    E-print Network

    26 ENGINEERING & SCIENCE fall 2011 Tectonic plates worldwide have been slipping, sliding such as this one occurs when one tectonic plate is being jammed underneath its neighbor in a region called GPs technology for nationwide tectonic monitoring, and the Geographical Survey Institute of Japan

  8. Musical Plates: A Study of Plate Tectonics

    NSDL National Science Digital Library

    2007-01-01

    In this project, students use Real-Time earthquake and volcano data from the Internet to explore the relationship between earthquakes, plate tectonics, and volcanoes. There is a teachers guide that explains how to use real time data, and in the same section, there is a section for curriculum standards, Supplement and enrichment activities, and assessment suggestions. Included on this webpage are four core activities, and three enrichment activities, including an activity where the student writes a letter to the president. There is also a link to reference materials that might also interest you and your students.

  9. Continental tectonics in the aftermath of plate tectonics

    Microsoft Academic Search

    Peter Molnar

    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

  10. 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)

  11. How Mantle Slabs Drive Plate Tectonics

    Microsoft Academic Search

    Clinton P. Conrad; Carolina Lithgow-Bertelloni

    2002-01-01

    The gravitational pull of subducted slabs is thought to drive the motions of Earth's tectonic plates, but the coupling between slabs and plates is not well established. If a slab is mechanically attached to a subducting plate, it can exert a direct pull on the plate. Alternatively, a detached slab may drive a plate by exciting flow in the mantle

  12. LETTER doi:10.1038/nature13072 Plate tectonics, damage and inheritance

    E-print Network

    LETTER doi:10.1038/nature13072 Plate tectonics, damage and inheritance David Bercovici1 & Yanick Ricard2 The initiation of plate tectonics on Earth is a critical event in our planet's history. The time and inher- itance of damage is negligible; hence only subduction zones survive and plate tectonics does

  13. ConcepTest: Plate Tectonic Theory

    NSDL National Science Digital Library

    Which of the following statements is not consistent with plate tectonic theory? a. Continental crust is generally older than oceanic crust. b. The number of plates has changed through time. c. Mountain chains are ...

  14. A plate tectonic model for the Paleozoic and Mesozoic constrained by dynamic plate boundaries and restored synthetic oceanic isochrons

    Microsoft Academic Search

    G. M Stampfli; G. D. Borel

    2002-01-01

    We developed a plate tectonic model for the Paleozoic and Mesozoic (Ordovician to Cretaceous) integrating dynamic plate boundaries, plate buoyancy, ocean spreading rates and major tectonic and magmatic events. Plates were constructed through time by adding\\/removing oceanic material, symbolized by synthetic isochrons, to major continents and terranes. Driving forces like slab pull and slab buoyancy were used to constrain the

  15. The Plate Tectonic Story: A Scientific Jigsaw

    NSDL National Science Digital Library

    This activity has students read and answer questions based upon the article 'The plate tectonic story: a scientific jigsaw.' The article starts with the continental drift theory of Alfred Wegener and adds the evidence from the seafloor to arrive at plate tectonics. It concludes with remarks about mantle dynamics and the future ability to predict earthquakes.

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

    ERIC Educational Resources Information Center

    Blueford, J. R.; And Others

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

  17. Mantle dynamics with induced plate tectonics

    Microsoft Academic Search

    Yanick Ricard; Christophe Vigny

    1989-01-01

    A new model of mantle dynamics and plate tectonics which takes into account the existence of rigid and independent plates has been developed. These plates, which break the spherical symmetry assumed in all earlier models, modify the mantle circulation and hence the predicted surface observables such as displacement and gravity. This paper uses a very simple two-plate model to explain

  18. Life with and Life without Plate Tectonics

    NASA Astrophysics Data System (ADS)

    Lenardic, A.; Hoeink, T.; Jellinek, M.; Johnson, C. L.; Cowan, N. B.; Pierrehumbert, R.; Stamenkovic, V.; O'Neill, C.; Dasgupta, R.

    2014-12-01

    The long standing notion that plate tectonics is key to planetary habitability is critically evaluated. The purported necessity of plate tectonics for planetary habitability is tied to volatile cycling, atmosphere retention, and carbon burial. Plate tectonics is not unique in allowing for cycling of volatiles between the interior of a planet and its atmosphere. Volcanism can be maintained on a single plate planet over geologic time scales and several non-plate tectonic recycling mechanisms are viable on such a planet. The frequency and efficiency of these modes of volatile recycling and volcanism are critical to evaluating whether they are sufficient to stabilize climate. An episodic mode of a volcanism and subduction also has the potential to provide the level of volatile cycling needed to maintain habitability. We combine solid planet models of degassing and regassing with climate, surface processes, and carbon sequestration models to determine the level to which habitable conditions can be maintained in the absence of plate tectonics. We also review arguments that the Earth operated in a different tectonic mode over its initial 2-3 billion years of geologic evolution, a time period over which the planet was habitable. Collectively our results suggests that habitable conditions can exist independent of the tectonic mode of a planet. However, O-rich atmospheres and complex life might require continuous recycling processes and ocean floor uplift to bury carbon onto stable platforms as provided by plate tectonics.

  19. 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.

  20. Igneous Rock Compositions and Plate Tectonics

    NSDL National Science Digital Library

    Allen Glazner

    In this exercise, students are split into groups to gather whole-rock geochemical data (major-, trace-, and rare-earth elements) from the GEOROC database for igneous rocks sampled from four different plate tectonic settings: mid-ocean ridges, subduction zones, oceanic islands, and oceanic plateaus. Each group is assigned a different plate tectonic setting and collects three datasets from different locations for their tectonic setting. Geochemical data is graphed as major-element variation and REE diagrams to quantify igneous diversity both within the same tectonic setting and between different tectonic settings. The main goal of this exercise is to demonstrate that igneous rock compositions are a strong function of plate tectonic setting.

  1. Hierarchical self-organization of tectonic plates

    E-print Network

    Morra, Gabriele; Müller, R Dietmar

    2010-01-01

    The Earth's surface is subdivided into eight large tectonic plates and many smaller ones. We reconstruct the plate tessellation history and demonstrate that both large and small plates display two distinct hierarchical patterns, described by different power-law size-relationships. While small plates display little organisational change through time, the structure of the large plates oscillate between minimum and maximum hierarchical tessellations. The organization of large plates rapidly changes from a weak hierarchy at 120-100 million years ago (Ma) towards a strong hierarchy, which peaked at 65-50, Ma subsequently relaxing back towards a minimum hierarchical structure. We suggest that this fluctuation reflects an alternation between top and bottom driven plate tectonics, revealing a previously undiscovered tectonic cyclicity at a timescale of 100 million years.

  2. Cenozoic plate tectonics of SE Asia 99 The plate tectonics of Cenozoic SE Asia and the distribution of land

    E-print Network

    Sheldon, Nathan D.

    Cenozoic plate tectonics of SE Asia 99 The plate tectonics of Cenozoic SE Asia and the distribution, plate tectonics, Cenozoic Abstract A plate tectonic model for the development of SE Asia and the SW. There are three important periods in regional development: at about 45 Ma, 25 Ma and 5 Ma. At these times plate

  3. Google Earth Plate Tectonics File (.kmz)

    NSDL National Science Digital Library

    UNAVCO

    This Google Earth .kmz file contains a number of data sets that can be used to help students learn about plate tectonics. These include: earthquake epicenters, plate boundaries, plate motion vectors, GPS station motion vectors, US Array seismic station locations, LiDAR hillshades, strain rates, volcano locations, magnetic anomalies, gravity anomalies (GRACE), geologic map, and meteor crater locations.

  4. Plate Tectonics-Discover Our Earth

    NSDL National Science Digital Library

    Institute for the Study of the Continents (INSTOC)

    This site from Cornell University presents an illustrated and interactive description of plate tectonics. Topics covered include an introduction to plate boundaries and sea floor spreading, and the use of earthquake activity to locate plate boundaries. After each topic is established, it is followed by a series of exercises using the QUEST interactive program.

  5. FAQ: Earthquakes, Faults, Plate Tectonics, Earth Structure

    NSDL National Science Digital Library

    This frequently-asked-questions feature provides answers about earthquakes, faults, plate tectonics, and earth structure. Maps and diagrams are provided with some answers, and links to additional information and to related topics are included.

  6. Investigating Plate Tectonics with Google Earth

    NSDL National Science Digital Library

    Beth Pratt-Sitaula

    Students examine data sets of topography, bathymetry, volcano location, earthquake location and size, and ocean floor age in Google Earth to determine the location and attributes of different types of plate tectonic boundaries.

  7. Investigating Students' Ideas About Plate Tectonics

    NSDL National Science Digital Library

    Brent Ford

    2006-09-01

    As part of a project designed to develop, among other tools, an assessment for measuring middle school understanding in plate tectonics, researches from Horizon Research, Inc. (HRI)--a research firm specializing in science and mathematics education--interviewed middle school students about their ideas in plate tectonics and processes that shape the Earth. The purpose of the interviews was to uncover common, incorrect student ideas that could serve as distractors for the multiple-choice test being developed.

  8. Plate Tectonics, The Cause of Earthquakes

    NSDL National Science Digital Library

    John Louie

    This page provides an overview of the role of plate tectonics in the generation of earthquakes. It provides a map of plate locations and figures that illustrate fault types and tectonic environments (extensional, transform, and compressional). Examples of surface features in the Pacific Northwest, Nevada, Indonesia, the San Andreas Fault, the Red Sea, the Zagoros Mountains in Iran, and on the planet Venus are provided.

  9. Plate tectonics on the terrestrial Plate tectonics is largely controlled by the buoyancy distribution in oceanic litho-

    E-print Network

    van Thienen, Peter

    Chapter 4 Plate tectonics on the terrestrial planets Abstract Plate tectonics is largely controlled), and surface temperatures in order to inves- tigate under which conditions plate tectonics is a viable indicates that plate tectonics could only operate on reasonable time scales at a potential mantle

  10. Tectonic Plates and Plate Boundaries (WMS)

    NSDL National Science Digital Library

    Eric Sokolowsky

    2004-06-14

    The earths crust is constantly in motion. Sections of the crust, called plates, push against each other due to forces from the molten interior of the earth. The areas where these plates collide often have increased volcanic and earthquake activity. These images show the locations of the plates and their boundaries in the earths crust. Convergent boundaries are areas where two plates are pushing against each other and one plate may be subducting under another. Divergent boundaries have two plates pulling away from each other and indicate regions where new land could be created. Transform boundaries are places where two plates are sliding against each other in opposite directions, and diffuse boundaries are places where two plates have the same relative motion. Numerous small microplates have been omitted from the plate image. These images have been derived from images made available by the United States Geological Surveys Earthquake Hazards Program.

  11. Whole Earth Structure and Plate Tectonics

    E-print Network

    Whole Earth Structure and Plate Tectonics Earth Structure (2nd Edition), 2004 W.W. Norton & Co, New York Slide show by Ben van der Pluijm © WW Norton; unless noted otherwise #12;© EarthStructure (2nd ed evolution of Earth: from continental drift (early 1900's) to sea-floor spreading (early 1960's) to plate

  12. Plate Tectonics: The Scientist Behind the Theory

    NSDL National Science Digital Library

    2005-12-17

    This video segment adapted from A Science Odyssey profiles Alfred Wegener, the scientist who first proposed the theory of continental drift. Initially criticized, his theory was accepted after further evidence revealed the existence of tectonic plates and showed that these plates move.

  13. Plate Tectonics: Moving Middle School Science

    NSDL National Science Digital Library

    Carolee Barber

    This resource guide from the Middle School Portal 2 project, written specifically for teachers, provides links to exemplary resources including background information, lessons, career information, and related national science education standards. This wiki page is about plate tectonics and features online resources that were hand-picked for middle school teachers. The resources are organized into three sets: background information (for teachers and students), activities (single-day and multiple-day), and animations. National Science Education Standards related to plate tectonics are also provided. Each resource set begins with a discussion of its strengths. For example, students work with models and data in the activities, many of which are discovery-oriented. Teaching tips and usage suggestions are offered in the set introductions and in the descriptions of individual resources. Together, the resources address topics such as the development of the plate tectonics theory and the types of plate boundaries and their locations.

  14. Spreading continents kick-started plate tectonics.

    PubMed

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

    2014-09-18

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

  15. A planetary perspective on Earth evolution: Lid Tectonics before Plate Tectonics

    NASA Astrophysics Data System (ADS)

    Piper, John D. A.

    2013-03-01

    Plate Tectonics requires a specific range of thermal, fluid and compositional conditions before it will operate to mobilise planetary lithospheres. The response to interior heat dispersion ranges from mobile lids in constant motion able to generate zones of subduction and spreading (Plate Tectonics), through styles of Lid Tectonics expressed by stagnant lids punctured by volcanism, to lids alternating between static and mobile. The palaeomagnetic record through Earth history provides a test for tectonic style because a mobile Earth of multiple continents is recorded by diverse apparent polar wander paths, whilst Lid Tectonics is recorded by conformity to a single position. The former is difficult to isolate without extreme selection whereas the latter is a demanding requirement and easily recognised. In the event, the Precambrian palaeomagnetic database closely conforms to this latter property over very long periods of time (~ 2.7-2.2 Ga, 1.5-1.3 Ga and 0.75-0.6 Ga); intervening intervals are characterised by focussed loops compatible with episodes of true polar wander stimulated by disturbances to the planetary figure. Because of this singular property, the Precambrian palaeomagnetic record is highly effective in showing that a dominant Lid Tectonics operated throughout most of Earth history. A continental lid comprising at least 60% of the present continental area and volume had achieved quasi-integrity by 2.7 Ga. Reconfiguration of mantle and continental lid at ~ 2.2 Ga correlates with isotopic signatures and the Great Oxygenation Event and is the closest analogy in Earth history to the resurfacing of Venus. Change from Lid Tectonics to Plate Tectonics is transitional and the geological record identifies incipient development of Plate Tectonics on an orogenic scale especially after 1.1 Ga, but only following break-up of the continental lid (Palaeopangaea) in Ediacaran times beginning at ~ 0.6 Ga has it become comprehensive in the style evident during the Phanerozoic Eon (< 0.54 Ga).

  16. Tectonic Plates, Earthquakes, and Volcanoes

    NSDL National Science Digital Library

    The representation shows earthquake and volcanic activity corresponds to plate boundaries. This interactive topographical map with the ocean water removed shows the boundaries of major plates and the locations of major volcanic eruptions and earthquakes worldwide.

  17. The generation of plate tectonics from mantle convection David Bercovici

    E-print Network

    Frontiers The generation of plate tectonics from mantle convection David Bercovici à Department In the last decade, significant progress has been made toward understanding how plate tectonics is generated changes in plate motion, and the Archaean initiation of the plate-tectonic mode of convection. This paper

  18. Teaching Box: Evidence for Plate Tectonics

    NSDL National Science Digital Library

    This Teaching Box is an online assembly of interrelated learning concepts that focuses on finding the evidence for plate tectonics. Digital resources, education standards, and comprehensive lesson plans are combined to provide an inquiry-based exploration of each of three lines of evidence for plate tectonics: fossil distribution, locations, depths, and types of earthquakes; and locations and types of volcanoes. For each line of evidence there is a map showing supporting concepts and their associated standards, preconceptions, lessons organized into teachable units, and a reference section describing the resources used in the box. An introductory activity is also included to engage the students and to provide a segue into the theory.

  19. Tectonic Plate Movements and Hotspots

    NSDL National Science Digital Library

    Ken Rhinehart

    This lesson introduces the idea that rates and directions of plate movements can be measured. The discussion centers on the use of mantle 'hotspots' to determine plate motions. Examples include the Hawaiian Islands, the Galapagos Islands, and the Yellowstone hotspot. The lesson includes an activity in which students use online resources to answer questions about the Galapagos Islands and measure plate movement rates using online data for the Hawaiian Islands hotspot.

  20. 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 thatpersist for the age of the plate. Grain-damage within a cold subducting slab may alsocause its very rapid detachment, and the abrupt loss of the slab-pull force could accountfor precipitous changes in plate motion, such as for the Pacific plate at both 47Ma and6Ma.

  1. Plate Tectonics: Recycling the Seafloor

    NSDL National Science Digital Library

    Lisa Ayers Lawrence

    2012-12-27

    In this activity, learners work in teams to predict and outline the location of plate boundaries using the National Oceanic and Atmospheric Administration's Acoustic Monitoring Program's underwater earthquake data. Then, learners compare their estimates to the USGS's map of the plates and discuss.

  2. Tracking Tectonic Plates Using Two Independent Methods

    NSDL National Science Digital Library

    Laurel Goodell

    Students come to this activity familiar with the basic assumptions of plate tectonics. Using a Google Earth platform showing commonly accepted lithospheric plate boundaries as well as locations of GPS stations, students form a hypothesis about motions expected across a particular boundary. They then set about testing their hypotheses by plotting motion vectors using two independent methods. METHOD 1: LONG-TERM "MODEL" RATES OF PLATE MOTION Students use a "Plate Motion Calculator" to determine "model" rates of plate motion averaged over millions of years. METHOD 2: GPS MEASUREMENTS INTERPRETED IN TERMS OF PLATE MOTION Students interpret GPS data as near real-time rates of plate motion. RESULTS Students find that in general, plate tectonic theory holds up. However, they also discover sophisticated detail rates are not constant, internal deformation of plates does occur and some boundaries are "wider" than others. Student evaluations of the activity demonstrate that they feel engaged and empowered as they work with authentic data, and gain a sophisticated understanding of a fundamental theory as well as the process of doing science.

  3. 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 dynamic process changing with time. By combining 1D thermal time evolution models and 2D/3D steady state models we are able to conclude that planetary mass does influence the propensity of plate tectonics on planets. The pressure dependence changes the scaling laws for parameterized models and influences the scaling of stresses associated with breaking of plates and thus the initiation of plate tectonics. The results indicate that for planets with masses larger than Earth lithospheric plates are either becoming thicker or remain similar in thickness and yield stresses to break the plates increase - making it harder to assume that plate tectonics is more likely on Super-Earths. Moreover, convective stresses decrease more than yield stresses do for planets smaller than Earth, leading to the fact that planets with masses close to one Earth mass seem to have better chances to exhibit plate tectonics than larger or smaller planets with similar composition and structure. References [1] Noack, L. Stamenkovic, V., and Breuer, D. (2009) ESLAB 09, P1.04. [2] Valencia, D., O’Connell, R.J., and Sasselov, D.D. (2007) Astroph. J., 670, 45-48. [3] O’Neill, C. and Lenardic, A. (2007) GRL, 34, L19204

  4. Reducing Plate Tectonic Misconceptions with Lecture Tutorials

    Microsoft Academic Search

    K. M. Kortz; J. M. Smay; A. V. Mattera; S. K. Clark

    2009-01-01

    In order to address student difficulties with and common misconceptions about plate tectonics, we created five Lecture Tutorials suitable for introductory geoscience courses. Lecture Tutorials are 10-15 minute worksheets that students complete in class in small groups to make learning more student-centered. Students build their knowledge with questions that progressively become more difficult, requiring them think about their misconceptions. Our

  5. 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)

  6. Plate tectonics and hotspots - The third dimension

    Microsoft Academic Search

    Don L. Anderson; Toshiro Tanimoto; Yu-Shen Zhang

    1992-01-01

    An evaluation is made of the constraining influence exerted by high resolution seismic tomographic models of the upper mantle on theories of plate tectonics and hotspots. While extensional, rifting, and hotspot regions are noted to have low velocity anomalies of depth exceeding 200 km, the upper mantle is composed of vast domains of high temperature, rather than small regions surrounding

  7. Assessment of the cooling capacity of plate tectonics and

    E-print Network

    van Thienen, Peter

    Chapter 5 Assessment of the cooling capacity of plate tectonics and flood volcanism in the evolution of Earth, Mars and Venus Abstract Geophysical arguments against plate tectonics in a hotter Earth mechanisms: plate tectonics and basalt extrusion / flood vol- canism. Our model results show

  8. Lab 4: Plate Tectonics Locating Geologic Hazards Introduction

    E-print Network

    Chen, Po

    1 Lab 4: Plate Tectonics ­ Locating Geologic Hazards Introduction The likelihood of major that moved around the Earth's surface. Thus, the theory of plate tectonics was developed. This theory of the theory of plate tectonics is useful for understanding the major geologic hazards. (It is also helpful

  9. FUNDAMENTALS OF PLATE TECTONICS Fall Semester 2012-13

    E-print Network

    Polly, David

    FUNDAMENTALS OF PLATE TECTONICS Fall Semester 2012-13 Geological Sciences G454/G554 Section 32565, paleomagnetism, petrology, and structural geology that led to the development of plate tectonic theory student will prepare a paper on some aspect or applica- tion of plate tectonic theory. The paper should

  10. Afrotheria: Plate tectonics meets genomics S. Blair Hedges*

    E-print Network

    Hedges, Blair

    Commentary Afrotheria: Plate tectonics meets genomics S. Blair Hedges* Department of Biology that evolved on Africa when that continent was isolated from others through plate tectonics (1). Although places more importance on plate tectonics in the early evolution of placental mammals (2, 13). However

  11. Tour of Park Geology: Plate Tectonics

    NSDL National Science Digital Library

    This National Park Service (NPS) site provides links to geology field notes providing information about National Parks, National Monuments, and National Recreation Areas that have to do with plate tectonics. The site also has illustrations and descriptions of different plate boundaries. The parks are divided into categories depending on which type of plate boundary they are located on. This includes divergent boundaries(active and ancient), convergent boundaries (ocean-ocean, continent-continent, continent-ocean), transform faults, hot spots, and accreted terrains. Parks referenced include Virgin Islands National Park, Florissant Fossil Beds National Monument, Hawaii Volcanoes National Park, and many more.

  12. Dangerous Earth: A Plate Tectonic Story

    NSDL National Science Digital Library

    This article and accompanying questions discusses the fact that several of the Earth's tectonic plates move at about the same speed as fingernails grow - around 35 mm per year - and that the plates are made of lithosphere (crust plus the upper part of the mantle). Students will also learn that beneath the lithosphere is the asthenosphere, part of the upper mantle that is ductile because it contains 1-10 percent molten material as films around the crystals. In addition they will find that the Earth's magnetic field has flipped (the N pole becoming the S pole, and vice versa) many times throughout geological time, resulting in rocks with varying directions of magnetism. They will also find that as tectonic plates move apart, new rock is formed and this locks in the direction of the magnetic field at the time.

  13. A plate tectonic model of the Palaeozoic tectonic history of New South Wales

    Microsoft Academic Search

    Erwin Scheibner

    1973-01-01

    An updated* tectonic model for the Palaeozoic tectonic history of New South Wales, based on actualistic models of plate tectonics, has resulted from tectonic analyses and syntheses during the compilation of the Tectonic Map of New South Wales.Most emphasis is given to marginal seas, which characterize Pacific marginal mobile zones. Marginal seas form in the regime of lithospheric tension under

  14. Tectonic speed limits from plate kinematic reconstructions

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    The motion of plates and continents on the planet's surface are a manifestation of long-term mantle convection and plate tectonics. Present-day plate velocities provide a snapshot of this ongoing process, and have been used to infer controlling factors on the speeds of plates and continents. However, present-day velocities do not capture plate behaviour over geologically representative periods of time. To address this shortcoming, we use a plate tectonic reconstruction approach to extract time-dependent plate velocities and geometries from which root mean square (RMS) velocities are computed, resulting in a median RMS plate speed of ? 4 cm /yr over 200 Myr. Linking tectonothermal ages of continental lithosphere to the RMS plate velocity analysis, we find that the increasing portions of plate area composed of continental and/or cratonic lithosphere significantly reduces plate speeds. Plates with any cratonic portion have a median RMS velocity of ? 5.8 cm /yr, while plates with more than 25% of cratonic area have a median RMS speed of ? 2.8 cm /yr. The fastest plates (? 8.5 cm /yr RMS speed) have little continental fraction and tend to be bounded by subduction zones, while the slowest plates (? 2.6- 2.8 cm /yr RMS speed) have large continental fractions and usually have little to no subducting part of plate perimeter. More generally, oceanic plates tend to move 2-3 times faster than continental plates, consistent with predictions of numerical models of mantle convection. The slower motion of continental plates is compatible with deep keels impinging on asthenospheric flow and increasing shear traction, thus anchoring the plate in the more viscous mantle transition zone. We also find that short-lived (up to ? 10 Myr) rapid accelerations of Africa (?100 and 65 Ma), North America (?100 and 55 Ma) and India (? 130 , 80 and 65 Ma) appear to be correlated with plume head arrivals as recorded by large igneous province (LIPs) emplacement. By evaluating factors influencing plate speeds over the Mesozoic and Cenozoic, our temporal analysis reveals simple principles that can guide the construction and evaluation of absolute plate motion models for times before the Cretaceous in the absence of hotspot tracks and seafloor spreading histories. Based on the post-Pangea plate motions, one principle that can be applied to pre-Pangea times is that plates with less than ? 50% continental area can reach RMS velocities of ? 20 cm /yr, while plates with more than 50% continental fraction do not exceed RMS velocities of ? 10 cm /yr. Similarly, plates with large portions of continental or cratonic area with RMS velocities exceeding ? 15 cm /yr for more than ? 10 Myr should be considered as potential artefacts requiring further justification of plate driving forces in such scenarios.

  15. Plate Tectonics: The Hawaiian Archipelago

    NSDL National Science Digital Library

    Since the Hawaiian Islands were all created by volcanic activity, it is somewhat surprising that only the island of Hawaii now possesses any active volcanoes. Why did the volcanoes that built the other islands stop erupting and why are those on the big island still active? This video segment, adapted from a NOVA television broadcast, shows how plumes of hot material rise from the Earth's interior to create 'hot spots' in the crust which are the locations of volcanic activity. Movement of the Pacific Plate causes volcanic islands to continually form, migrate away from the hot spot, and become extinct, forming chains of islands like the Hawaiian Islands. The segment is four minutes thirty-seven seconds in length.

  16. Plate tectonic reconstructions with continuously closing plates$ Michael Gurnis a,n

    E-print Network

    Müller, Dietmar

    Plate tectonic reconstructions with continuously closing plates$ Michael Gurnis a,n , Mark Turner: Geodynamics Plate tectonics a b s t r a c t We present a new algorithm for modeling a self-consistent set, traditional global plate tectonic reconstructions have become inadequate for geodynamics. The CCP algorithm

  17. What on Earth is Plate Tectonics?

    NSDL National Science Digital Library

    This abbreviated explanation of the subject of plate tectonics is divided into several parts. The first section, entitled Into the Earth, describes the crust, mantle and core of the Earth, while the next section shows a world map with the plates delineated. The section called Action at the Edges uses text and diagrams to explain what is occurring at the plate boundaries. Links lead to a detailed discussion of converging boundaries including ocean-ocean, ocean-continental, and continental-continental. A wide range illustration shows both surface and cross-section views of plate interaction and a link leads to a similar diagram with labels. In the Moving through Time section, a series of color-coded maps is shown, illustrating the relative position of the continents over the past 650 million years. The last section shows a paleogeographic reconstruction of the Earth and explains how paleomagnetism, magnetic anomalies, paleobiogeography, paleoclimatology, and geologic history are used to create it.

  18. 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.

  19. Caribbean tectonics and relative plate motions

    NASA Astrophysics Data System (ADS)

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

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

  20. 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.

  1. Inevitability of Plate Tectonics on Super-Earths

    E-print Network

    Diana Valencia; Richard J. O'Connell; Dimitar D. Sasselov

    2007-10-03

    The recent discovery of super-Earths (masses less or equal to 10 earth-masses) has initiated a discussion about conditions for habitable worlds. Among these is the mode of convection, which influences a planet's thermal evolution and surface conditions. On Earth, plate tectonics has been proposed as a necessary condition for life. Here we show, that super-Earths will also have plate tectonics. We demonstrate that as planetary mass increases, the shear stress available to overcome resistance to plate motion increases while the plate thickness decreases, thereby enhancing plate weakness. These effects contribute favorably to the subduction of the lithosphere, an essential component of plate tectonics. Moreover, uncertainties in achieving plate tectonics in the one earth-mass regime disappear as mass increases: super-Earths, even if dry, will exhibit plate tectonic behaviour.

  2. Inevitability of Plate Tectonics on Super-Earths

    E-print Network

    Valencia, Diana; Sasselov, Dimitar D

    2007-01-01

    The recent discovery of super-Earths (masses less or equal to 10 earth-masses) has initiated a discussion about conditions for habitable worlds. Among these is the mode of convection, which influences a planet's thermal evolution and surface conditions. On Earth, plate tectonics has been proposed as a necessary condition for life. Here we show, that super-Earths will also have plate tectonics. We demonstrate that as planetary mass increases, the shear stress available to overcome resistance to plate motion increases while the plate thickness decreases, thereby enhancing plate weakness. These effects contribute favorably to the subduction of the lithosphere, an essential component of plate tectonics. Moreover, uncertainties in achieving plate tectonics in the one earth-mass regime disappear as mass increases: super-Earths, even if dry, will exhibit plate tectonic behaviour.

  3. Geological and plate tectonic setting of the Longitudinal Valley

    E-print Network

    Winfree, Erik

    3 Chapter 1 Geological and plate tectonic setting of the Longitudinal Valley Fault 1.1 Tectonic and the Philippine Sea Plate (Figure 1.1a). South of Taiwan this convergence is absorbed along the Manila trench by the eastward subduction of the oceanic crust of the South China Sea beneath the Philippine Sea Plate, leading

  4. 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.

  5. 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.

  6. Musical Plates: A Study of Earthquakes and Plate Tectonics

    NSDL National Science Digital Library

    This on-line project is part of the Center for Improved Engineering and Science Education (CIESE) program. As they complete this series of lessons, students will use real-time data to solve a problem, study the correlation between earthquakes and tectonic plates, and determine whether or not there is a relationship between volcanoes and plate boundaries. Musical Plates has four Core Activities that will teach students how to access and interpret real-time earthquake and volcano data and to how use the information to solve a real-world problem. Each of the core activities is designed to be used in a 45-minute class period. This unit also has three enrichment lessons and a final project lesson that can also be used for assessment.

  7. Geology and plate-tectonic development

    SciTech Connect

    Irwin, W.P.

    1990-01-01

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

  8. 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.

  9. External Resource: Plate Tectonics: Diverging, Converging, and Transform Boundaries

    NSDL National Science Digital Library

    1900-01-01

    This activity allows learners to explore the meaning of plate tectonics, to distinguish the different layers of the Earth, to model the effects caused by plate movements, to explore the reasons for earthquakes and volcanoes, and to discovering how conver

  10. Teaching About Plate Tectonics and Faulting Using Foam Models

    NSDL National Science Digital Library

    Larry Braile

    This teacher's guide provides directions for building three-dimensional models from foam blocks to demonstrate plate tectonic principles, plate boundary interactions and the geometry and relative motions of faulting of geologic layers. References are included.

  11. This Dynamic Earth: the Story of Plate Tectonics

    NSDL National Science Digital Library

    2000-03-28

    This publication provides an introduction to the theory of plate tectonics. It was intended as a companion to the map entitled 'This Dynamic Planet', published by the U.S. Geological Survey (USGS) and the Smithsonian Institution. Topics include the history and development of the theory, lines of evidence, plate motions and interactions, hotspots, what drives plate motion, and extraterrestrial plate tectonics. It can be viewed online, downloaded, or purchased in hardcopy. Ordering information is provided.

  12. 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.

  13. INTRODUCTION One of the paradigms of plate tectonics is that plate bound-

    E-print Network

    Doglioni, Carlo

    INTRODUCTION One of the paradigms of plate tectonics is that plate bound- aries record the deformation related to the ongoing geodynamic processes, assuming a single tectonic setting. This article that represents the sum of distinct tectonic styles that we may consider independent. The coexistence of four

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

    PubMed

    Korenaga, Jun

    2012-07-01

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

  15. Earthquakes Living Lab: The Theory of Plate Tectonics

    NSDL National Science Digital Library

    Civil and Environmental Engineering Department,

    Students gather evidence to explain the theory of plate tectonics. Using the online resources at the Earthquakes Living Lab, students examine information and gather evidence supporting the theory. They also look at how volcanoes and earthquakes are explained by tectonic plate movement, and how engineers use this information. Working in pairs, students think like engineers and connect what they understand about the theory of plate tectonics to the design of structures for earthquake-resistance. A worksheet serves as a student guide for the activity.

  16. Plate tectonics and the Gulf of California region

    SciTech Connect

    Schmidt, N.

    1990-11-01

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

  17. 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 sedimentation rate is necessary to bury organic matter and to restrict the mineralization. Consequences of crustal extension are also studied by using an experimental sand box model. The creation of faults is related to the subsidence of the margin. This subsidence allows the crossing of the oil window, leading to pyrolysis of organic matter and its transformation into oil. Afterwards, students compare the structures obtained after extension in their sand box to the actual organization of the Ghawar oil accumulation (seismic line). They can see that faults created by extension forces have not been preserved and can assume that compression forces have caused formation of the traps. An animation of paleo-location of continents during the upper Jurassic helps them to think that compression forces are linked to the closure of the Tethys Sea. A model using gravel and clay is used to show the principle of oil trapping. This way, students understand how the tectonic plate models explain the actual location of oil deposits and then how it can be used to look for new deposits.

  18. Driving forces of plate tectonics and the importance of inertia

    NSDL National Science Digital Library

    Donald Forsyth

    To demonstrate how unimportant inertia is in plate tectonic problems, as part of a lecture, we calculate momentum and moment of inertia of both a supertanker and a plate. A supertanker running into a dock will do more than a million times more damage than a plate. This activity addresses student misconceptions and has a small quantitative component.

  19. The Uncertainties of Finite Rotations in Plate Tectonics

    Microsoft Academic Search

    S. J. Hellinger

    1981-01-01

    During the past decade the hypothesis of plate tectonics has successfully explained many of the features of the upper layer of the earth. This hypothesis states that the strong outer layer of the earth is composed of a small number of large rigid plates. It is the interaction of these rigid plates at their boundaries that accounts for most of

  20. Seismic gaps and plate tectonics: Seismic potential for major boundaries

    Microsoft Academic Search

    W. R. McCann; S. P. Nishenko; L. R. Sykes; J. Krause

    1979-01-01

    The theory of plate tectonics provides a basic framework for evaluating the potential for future great earthquakes to occur along major plate boundaries. Along most of the transform and convergent plate boundaries considered in this paper, the majority of seismic slip occurs during large earthquakes, i.e., those of magnitude 7 or greater. The concepts that rupture zones, as delineated by

  1. 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.

  2. Origin of Plate Tectonics by Grain-Damage: Hysteresis and Plate-Like States

    NASA Astrophysics Data System (ADS)

    Bercovici, D.

    2015-05-01

    Grain-damage theory provides a physical framework to explain the conditions for generating plate tectonics on rocky planets. I present new work exploring grain-damage hysteresis which predicts when plate-like states on planets can exist.

  3. The driving force of plate tectonics evaluated in spherical coordinates 

    E-print Network

    Donahue, John Michael

    1985-01-01

    THE DRIVING FORCE OF PLATE TECTONICS EVALUATED IN SPHERICAL COORDINATES A Thesis by JOHN MICHAEL DONAHUE Approved as to style and content by: Richard L. Carlson (Chairman) ond J. Willemann (Member) William Sage (Member) Earl R. Ho ins... (Head of D artment) May 1985 ABSTRACT The Driving Force of Plate Tectonics Evaluated in Spherical Coordinates. (Hay 1985) John Michael Donahue, B. S. , Texas Tech University Chairman of Advisory Committee: Dr. R. L. Carlson A slab-pull driving...

  4. The driving force of plate tectonics evaluated in spherical coordinates

    E-print Network

    Donahue, John Michael

    1985-01-01

    THE DRIVING FORCE OF PLATE TECTONICS EVALUATED IN SPHERICAL COORDINATES A Thesis by JOHN MICHAEL DONAHUE Approved as to style and content by: Richard L. Carlson (Chairman) ond J. Willemann (Member) William Sage (Member) Earl R. Ho ins... (Head of D artment) May 1985 ABSTRACT The Driving Force of Plate Tectonics Evaluated in Spherical Coordinates. (Hay 1985) John Michael Donahue, B. S. , Texas Tech University Chairman of Advisory Committee: Dr. R. L. Carlson A slab-pull driving...

  5. 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.

  6. 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).

  7. GEOPHYSICAL JOURNAL INTERNATIONAL, 133, 379389, 1998 1 A continuous plate-tectonic model using geophysical data

    E-print Network

    GEOPHYSICAL JOURNAL INTERNATIONAL, 133, 379­389, 1998 1 A continuous plate-tectonic model using kinetic energy in the continuous plate model. Short title: The continuous model of plate tectonics Keywords: Plate-tectonics; plate boundaries; intraplate deformation, toroidal-poloidal partitioning. 1 Now

  8. Plate tectonic modelling: virtual reality with GMAPp Trond Helge Torsvika, b,

    E-print Network

    Torsvik, Trond Helge

    Plate tectonic modelling: virtual reality with GMAPp Trond Helge Torsvika, b, *, Mark Andrew an integral part of global tectonic research since the advent of the plate tectonic paradigm, and GMAP with the generation of palaeogeographic reconstructions and plate tectonic modelling. GMAP is menu-driven and easy

  9. Organization of the tectonic plates in the last 200 Myr Gabriele Morra a,n

    E-print Network

    Müller, Dietmar

    Organization of the tectonic plates in the last 200 Myr Gabriele Morra a,n , Maria Seton b reconstructions global geodynamics plate size top­down tectonics mantle convection bottom­up tectonics a b s t r a c t The present tessellation of the Earth's surface into tectonic plates displays a remarkably

  10. Growth of the hemispheric dichotomy and the cessation of plate tectonics on Mars

    E-print Network

    Nimmo, Francis

    Growth of the hemispheric dichotomy and the cessation of plate tectonics on Mars A. Lenardic 2004. [1] Although Mars is currently not tectonically active, it may have experienced plate tectonics for the Earth predict that it should operate in the plate tectonic regime now but that it may have experienced

  11. Your Mission: To become familiar with the major plate boundaries through exploration of plate tectonic features using Google Earth.

    E-print Network

    Smith-Konter, Bridget

    boundaries through exploration of plate tectonic features using Google Earth. Your Supplies: (1) A computer with internet access and the Google Earth program of Earth's tectonic plates using Google Earth. To do this, login

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

    USGS Publications Warehouse

    Hamilton, W.

    1987-01-01

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

  13. Archean magmatism and deformation were not products of plate tectonics

    Microsoft Academic Search

    Warren B. Hamilton

    1998-01-01

    The granite-and-greenstone terrains that dominate upper crust formed from about 3.6 to about 2.6 Ga, and record magmatic and tectonic processes very different from those of a younger time. They indicate heat loss by the Archean Earth primarily by voluminous magmatism from a mantle much hotter than that of the present. Plate-tectonic processes were not then operating. The distinctive array

  14. Mantle convection models featuring plate tectonic behaviour: an overview of methods

    E-print Network

    Wells, Mathew G. - Department of Physical and Environmental Sciences, University of Toronto

    convection models featuring plate tectonic behaviour: an overview of methods and progress Julian P. Lowman ,1 53 54 55 56 57 58 59 60 61 62 63 64 65 Abstract Arguably, the presence of plate-tectonic-type surface observations of plate tectonics as well as how the plates and deep mantle interact. Fledgling studies

  15. Author's personal copy Plate tectonics and net lithosphere rotation over the past 150 My

    E-print Network

    Torsvik, Trond Helge

    Author's personal copy Plate tectonics and net lithosphere rotation over the past 150 My Trond H online 27 January 2010 Editor: Y. Ricard Keywords: plate tectonics global digital palaeo-plate boundaries (Wegener 1915) into Sea-Floor Spreading (Hess 1962) and to the theory of Plate Tectonics (Wilson, 1966, Mc

  16. Tectonic stresses in the African plate: Constraints on the ambient lithospheric stress state

    E-print Network

    Sandiford, Mike

    Tectonic stresses in the African plate: Constraints on the ambient lithospheric stress state David. Predicted tectonic stresses in the oceanic regions of the African plate range from tension along the mid surrounded by mid-ocean ridges. Thus, of Earth's tectonic plates, these two plates can be expected to best

  17. The influence of tectonic plates on mantle convection patterns, temperature and heat flow

    E-print Network

    Gable, Carl W.

    The influence of tectonic plates on mantle convection patterns, temperature and heat flow Julian P, mantle, plate tectonics. 1 I N T R O D U C T I O N Calculations based on boundary layer theory by the geometry of tectonic plates. In comparison with a small plate, less heat per unit area must be lost through

  18. Plate Tectonics as a Far-From-Equilibrium Self-Organized System Don L. Anderson

    E-print Network

    Anderson, Don L.

    Plate Tectonics as a Far- From- Equilibrium Self-Organized System By Don L. Anderson Word Count: 3 and other forces at the top. Plate tectonics was once regarded as passive motion of plates on top of mantle convection cells but it now appears that continents and plate tectonics organize the flow in the mantle

  19. Plate Tectonics: Diverging, Converging, and Transform Boundaries

    NSDL National Science Digital Library

    In this lesson, students will learn to distinguish the different layers of the Earth, observe the effects of plate movements, and explore the reasons for earthquakes and volcanoes. They will label and measure the thicknesses of each layer of the Earth (lithosphere, asthenosphere, etc.) and record their results, construct models from sand and clay to illustrate what happens at the three types of plate boundaries (transform, diverging, and converging), and investigate convergent plate boundaries to see which scenarios may create earthquakes and/or volcanoes.

  20. Azores–Tunisia, A Tectonically Complex Plate Boundary

    Microsoft Academic Search

    Elisa Buforn; Agustín Udías

    2010-01-01

    The seismically active region from Tunisia to the Azores Islands constitutes the westernmost part of the plate boundary between Eurasia and Africa. From the point of view of tectonics, this is a complex structure which involves volcanism and rifting at the Azores, strike-slip motion at the center of the Atlantic, and horizontal N-S compressions at its eastern part, with complex

  1. INTRODUCTION Unlike Earth, Venus apparently lacks plate tectonics. Thus

    E-print Network

    Jurdy, Donna M.

    INTRODUCTION Unlike Earth, Venus apparently lacks plate tectonics. Thus plumes may be an important at different scales has been attributed to plume or diapiric activ- ity on Venus. Examples of these include activity in the Beta-Atla-Themis region, Venus Audeliz Matias Donna M. Jurdy* Department of Geological

  2. Intraplate Stress as an Indicator of Plate Tectonic Driving Forces

    Microsoft Academic Search

    Randall M. Richardson; Sean C. Solomon; Norman H. Sleep

    1976-01-01

    To test driving force models for plate tectonics, the global intraplate stress fields predicted by various force systems are compared with the long-wavelength features of the observed stress field as determined by midplate earthquake mechanisms, in situ measurements, and stress-induced geolo, gic structures. The calculated stresses are obtained by a finite difference solution to the equilibriumequations for thin elastic spherical

  3. 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.

  4. Focussing of stress by continents in 3D spherical mantle convection with selfconsistent plate tectonics

    E-print Network

    Tackley, Paul J.

    . In this study we present 3D spherical mantle convection models with selfconsistent plate tectonics and a mobile at the margins, which allows for plate tectonics at higher yield strength and leads to better agreement convection with selfconsistent plate tectonics, Geophys. Res. Lett., 38, L18301, doi:10.1029/ 2011GL048677. 1

  5. The Quest for Self-Consistent Generation of Plate Tectonics in Mantle Convection Models

    E-print Network

    Tackley, Paul J.

    The Quest for Self-Consistent Generation of Plate Tectonics in Mantle Convection Models Paul J. Tackley Department of Earth and Space Sciences, University of California, Los Angeles Plate tectonics do not exhibit plate tectonic behavior unless it is imposed by the modeler. This paper explores

  6. Mechanisms for the generation of plate tectonics by two-phase grain-damage and pinning

    E-print Network

    Mechanisms for the generation of plate tectonics by two-phase grain-damage and pinning David localization in the lithosphere are essential ingredients for understanding how and whether plate tectonics tectonics on Earth and other planets. Keywords: Keywords: Plate generation; mantle convection; damage

  7. Recent tectonic plate decelerations driven by mantle convection A. M. Forte,1

    E-print Network

    Long, Bernard

    Recent tectonic plate decelerations driven by mantle convection A. M. Forte,1 R. Moucha,1 D. B in tectonic plate velocities using a model of mantle flow that is based on a new high- resolution global of these predicted plate decelerations using space geodetic and oceanic magnetic anomaly constraints on tectonic

  8. The problem of fitting of the zero-range model of the tectonic plate under

    E-print Network

    The problem of fitting of the zero-range model of the tectonic plate under a localized boundary of fitting of the zero-range model of the tectonic plate under the boundary stress based on comparison on the boundary of the tectonic plate and estimate the risk of a powerful earthquake at this zone. Key-words Thin

  9. Mechanisms for the generation of plate tectonics by two-phase grain-damage and pinning

    E-print Network

    Mechanisms for the generation of plate tectonics by two-phase grain-damage and pinning David for understanding how and whether plate tectonics is generated from mantle convection on terrestrial planets. We therefore provides a key ingredient and predictive theory for the generation of plate tectonics on Earth

  10. Can Earth's rotation and tidal despinning drive plate tectonics? Federica Riguzzi a,c,

    E-print Network

    Doglioni, Carlo

    Can Earth's rotation and tidal despinning drive plate tectonics? Federica Riguzzi a,c, , Giuliano January 2009 Accepted 10 June 2009 Available online xxxx Keywords: Plate tectonics Earth's rotation Tidal tectonics on the basis of the following observations: 1) plates move along a westerly polarized flow

  11. Self-consistent generation of tectonic plates in time-dependent, three-dimensional mantle

    E-print Network

    Tackley, Paul J.

    Self-consistent generation of tectonic plates in time-dependent, three-dimensional mantle, some of which display an approximation of plate tectonic behavior that is continuous in space and time dependence than three-dimensional models. Keywords: Mantle convection; plate tectonics; rheology; lithosphere

  12. Science to understand our land: terranes, tectonic plates and how BC came to be

    E-print Network

    Pedersen, Tom

    Science to understand our land: terranes, tectonic plates and how BC came to be What's it about the land we call BC came to be. The science is about tectonic plates and pieces of land from elsewhere the tectonic plates interact in the western part of North America and offshore. 3. But how did the bits of land

  13. Hands On Science with NOAA TITLE: Plate Tectonics and Lava Lamps

    E-print Network

    Hands ­ On Science with NOAA TITLE: Plate Tectonics and Lava Lamps OVERVIEW: Participants use move. SCIENCE BACKGROUND: Tectonic plates are portions of the Earth's outer crust (the lithosphere). These convection currents cause the tectonic plates to move several centimeters per year relative to each other

  14. 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.

  15. Generation of plate tectonics via grain-damage and pinning

    NASA Astrophysics Data System (ADS)

    Bercovici, D.; Ricard, Y. R.

    2012-12-01

    Weakening and shear localization in the lithosphere are essential ingredients for understanding how and whether plate tectonics is generated from mantle convection on terrestrial planets. The grain-damage and pinning mechanism of Bercovici & Ricard (2012) for lithospheric shear--localization proposes that damage to the interface between phases in a polycrystalline material like peridotite (composed primarily of olivine and pyroxene) increases the number of small Zener pinning surfaces that constrain mineral grains to ever smaller sizes regardless of creep mechanism. This effect allows a self-softening feedback in which damage and grain-reduction can co-exist with a grain-size dependent diffusion creep rheology; moreoever, grain growth and weak-zone healing are greatly impeded by Zener pinning thereby leading to long-lived relic weak zones. This mechanism is employed in two-dimensional flow calculations to test its ability to generate toroidal (strike-slip) motion from convective type flow and to influence plate evolution. The fluid dynamical calculations employ source-sink driven flow as a proxy for convective poloidal flow (upwelling/downwelling and divergent/convergent motion), and the coupling of this flow with non-linear rheological mechanisms excites toroidal or strike-slip motion. The numerical experiments show that pure dislocation-creep rheology, and grain-damage without Zener pinning (as occurs in a single-phase assemblages) permit only weak localization and toroidal flow; however, the full grain-damage with pinning readily allows focussed localization and intense, plate-like toroidal motion and strike-slip deformation. Rapid plate motion changes are also tested with abrupt rotations of the source-sink field after a plate-like configuration is developed; the post-rotation flow and material property fields are found to never recover or lose memory of the original configuration, leading to suboptimally aligned plate boundaries (e.g., strike-slip margins non-parallel to plate motion), oblique subduction and highly localized, weak and long lived acute plate-boundary junctions such as at the Aleution-Kurile intersection. The grain-damage and pinning theory therefore readily satisfies key plate-tectonic metrics of localized toroidal motion and plate-boundary inheritance, and thus provides a predictive theory for the generation of plate tectonics on Earth and other planets. References: Bercovici, D., Ricard, Y., 2012. Mechanisms for the generation of plate tectonics by two-phase grain-damage and pinning. Phys. Earth Planet. Int. 202-203, 27--55.

  16. Scaling of plate-tectonic convection with pseudoplastic rheology

    E-print Network

    Korenaga, Jun

    2010-01-01

    The scaling of plate-tectonic convection is investigated by simulating thermal convection with pseudoplastic rheology and strongly temperature-dependent viscosity. The effect of mantle melting is also explored with additional depth-dependent viscosity. Heat-flow scaling can be constructed with only two parameters, the internal Rayleigh number and the lithospheric viscosity contrast, the latter of which is determined entirely by rheological properties. The critical viscosity contrast for the transition between plate-tectonic and stagnant-lid convection is found to be proportional to the square root of the internal Rayleigh number. The relation between mantle temperature and surface heat flux on Earth is discussed on the basis of these scaling laws, and the inverse relationship between them, as previously suggested from the consideration of global energy balance, is confirmed by this fully dynamic approach. In the presence of surface water to reduce the effective friction coefficient, the operation of plate tec...

  17. 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)

  18. Investigation of Newtonian Forces on Plate Tectonics

    NSDL National Science Digital Library

    This model-making activity gives students an opportunity visualize Newtonian forces acting on a single point as well as combined forces acting to produce synclines and anticlines in Earth's crust. Students will analyze models to interpret findings of plate movements.

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

    SciTech Connect

    Ross, M.I.; Abreu, V.; Vail, P.R. [Rice Univ., Houston, TX (United States)

    1996-12-31

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

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

    PubMed

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

    2015-02-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

  2. 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 (ENSL); (UC)

    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 the surface of the Earth.

  3. Senonian basin inversion and rejuvenation of rifting in Africa and Arabia: synthesis and implications to plate-scale tectonics

    Microsoft Academic Search

    René Guiraud; William Bosworth

    1997-01-01

    The late Paleozoic to Tertiary stratigraphic record of much of the African plate reflects the effects of continental rifting and passive margin development. Several short-lived, but widespread and tectonically important, compressional or wrench-dominated events occurred, however, during the Permian to Recent evolution of Africa. We focus here on the best documented of these events, which occurred during the late Santonian.

  4. 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.

  5. 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).

  6. 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.

  7. 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.

  8. 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.

  9. Teaching Earth Dynamics: What's Wrong with Plate Tectonics Theory?

    E-print Network

    Herndon, J M

    2005-01-01

    Textbooks frequently extol plate tectonics theory without questioning what might be wrong with the theory or without discussing a competitive theory. How can students be taught to challenge popular ideas when they are only presented a one-sided view? In just a few pages, I describe more than a century of geodynamic ideas. I review what is wrong with plate tectonics theory and with Earth expansion theory, and describe my new Whole-Earth Decompression Dynamics Theory, which unifies the two previous dominant theories in a self- consistent manner. Along the way, I disclose details of what real science is all about, details all too often absent in textbooks and classroom discussions. In these few pages, I only touch on highlights and just part the curtain a bit so that teachers might glimpse ways to bring to their students some of the richness and excitement of discovery that becomes evident when one begins to question prevailing, currently popular perceptions of our world.

  10. 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.

  11. 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.

  12. Global aspects of volcanism: the perspectives of “plate tectonics” and “volcanic systems”

    Microsoft Academic Search

    Edgardo Cañón-Tapia; George P. L Walker

    2004-01-01

    The concept of plate tectonics provides a general framework to fit the distribution and general characteristics of volcanoes. There remain, however, many details of volcanic activity that are difficult to explain solely by this paradigm. For example, plate tectonics predicts that volcanic activity should take place continuously along all convergent and divergent tectonic margins, where in fact we observe a

  13. 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 1 km of fluid-rich sediment that is then subducted. Tectonic erosion implies that the subduction channel is also fed by material from the upper plate, but the volume, composition and fluid content are poorly constrained.

  14. Revised tectonic boundaries in the Cocos Plate off Costa Rica: Implications for the segmentation of the convergent margin and for plate tectonic models

    Microsoft Academic Search

    Udo Barckhausen; Cesar R. Ranero; R. von Huene; Steven C. Cande; Hans A. Roeser

    2001-01-01

    The oceanic Cocos Plate subducting beneath Costa Rica has a complex plate tectonic history resulting in segmentation. New lines of magnetic data clearly define tectonic boundaries which separate lithosphere formed at the East Pacific Rise from lithosphere formed at the Cocos-Nazca spreading center. They also define two early phase Cocos-Nazca spreading regimes and a major propagator. In addition to these

  15. 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). Recently, the author (Puchkov, 2009) compiled an upgraded scheme of such chains in the modern oceans. A comparison of this scheme with vectors of lithospheric plate motions (http://itrf.ensg.ign.fr) have shown a very good correlation. 4. A special evidence of a co-operation between plume and plate tectonic mechanics comes from rare places where a plume coincides with a MOR. The most bright example is Iceland, where a very proliferous "non-MORB" volcanism occurs, and a conspicuous bend of the spreading axis with its small jumps in the eastward direction takes place. It can be explained by a slight westward drift of the spreading axis as a whole, relative to the plume, while the plume "attracts' and bends the MOR axis, being mechanically the weakest area. Such interactions ought to take place between Karlsberg MOR and Kerguelen and Reunion plumes 38-33 Ma ago. A different example of such an interaction is the Galapagos plume, coinciding with the Cocos-Nasca branch of the East Pacific spreading system (O'Connor et al., 2007). Here the drift direction of the spreading ridge is parallel to the ridge itself, and therefore the volcanoes activated by the plume are split and make two branching chains. These interactions give an additional perspective to development of a modern global tectonic theory.

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

    E-print Network

    Vigny, Christophe

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

  17. Plate tectonic history of the Arctic

    SciTech Connect

    Burke, K.

    1985-02-01

    The Arctic Ocean represents the last great challenge in establishing the broad outlines of the histories of the present oceans of the earth. The rotation of the Lomonosov Ridge away from the Barents Shelf during the Cenozoic is well established, and a unique present relationship has been demonstrated between the Gakkel Ridge and the Poloussnoye graben system. Earlier history of the Arctic is poorly known, but a possible and testable scenario involves rifting of the North Slope Alaska-Chukotsk block (NSAC) from the Canadian Arctic islands during the Early Cretaceous and rifting of the New Siberian block (NSB) along strike on the same margin a little later. Both NSAC and NSB were involved, after rapid rotation, in the assembly of northeastern Asia with such other blocks as Greater Japan (much of Kyushu, Honshu, Hokkaido, Sakhalin, Sikhote Alin, Kamchatka, and Koryak) and Omolon. During earlier Mesozoic, Permian, and Carboniferous times, NSB and NSAC occupied one Atlantic-type margin of the triangular Boreal embayment of the Pacific, while the Verkhoyansk Atlantic-type margin of Siberia (with the prominent Vilyuy rift embayment) occupied the other. These 2 rifted margins, which are now caught up respectively in the Brooks Range-South Anyui-Sviatory Nos suture zone and the Sette Daban-Chirskiy suture zone, had formed during the Late Devonian close to the site of and shortly after the Innuitian suturing event between Siberia and North America.

  18. 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.

  19. 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…

  20. The generation of plate tectonics on a planet

    NASA Astrophysics Data System (ADS)

    Landuyt, William, III

    A major question in Earth and planetary science is why does Earth exhibit plate tectonics and the other terrestrial planets do not? The difference in tectonic behavior between Earth and Venus is even more striking given their similarity in size, composition, and average density. While our general knowledge of material behavior suggests that all the terrestrial planets, Earth included, should not exhibit plate tectonics, the requisite weakening allowing this tectonic style is in operation on our planet but not Venus. To address this set of questions I have taken a two-part approach: development and implementation of a two-phase damage rheology in models of lithospheric deformation and planetary convection to determine the plate generating capabilities of such a shear localizing model, and consideration of the effect of a planet's climate on a lithospheric damage rheology and how this can explain the different modes of convection displayed by Earth and Venus. I have implemented a two-phase damage rheology into a two-dimensional simple-shear calculation as a means for understanding the depth-dependent localization occurring in the lithosphere. The results from this work imply that while void-generating damage is likely only important in the upper 15 km of the lithosphere, grain size reducing damage is able to produce strong localization. The combined interaction of void and grain size reducing damage can also lead to the formation of a central shear zone dominated by small grains with high porosity bands bordering this region. Implementation of two-phase damage rheology into a convectively driven lithospheric-mantle model suggests similar behaviors, namely that grain size reducing damage is far more efficacious at producing localization necessary for plate generation. The hypothesis regarding the effect of climate on planetary convection suggests that temperate surface temperatures (due to the role of free surface water controlling the carbon cycle) moderate healing due to grain-growth in the lithosphere, thereby leading to enhanced damage and localization necessary for plate boundary formation. Venus on the other hand has much higher surface temperatures 400 K higher), which leads to increased healing and a suppression of localization and plate tectonics. I tested this hypothesis in a convectively driven lithospheric-mantle model along with a scaling analysis, and I found that variations in the lithospheric healing rate (which serves as a proxy for surface temperature) can lead to a transition in planetary convective modes. A more rigorous test of this hypothesis was attempted by developing a variable viscosity convection model for planetary convection. Here I tested the effect of varying surface temperature on the development of localization with a grain size and temperature dependent rheology. The results from this work suggest that a surface temperature increase of approximately 250 K relative to Earth values could lead to a transition from plate tectonic convection to an episodic mode of convection potentially similar to what is exhibited by Venus.

  1. The effectiveness of teaching from smaller concepts to larger using data and observations in plate tectonics

    Microsoft Academic Search

    Matthew L. Schuchardt

    2010-01-01

    This purpose of this project was to test the effectiveness of teaching from smaller concepts toward larger concepts, using data and observations in plate tectonics. By following this method the students became more like the scientists themselves who took observations from the physical world to build theories of plate tectonics. It was presented in three sections earthquakes, volcanoes, and plate

  2. Plate Tectonic Evolution of Eastern Australian Marginal Ocean M. Sdrolias1

    E-print Network

    Müller, Dietmar

    Plate Tectonic Evolution of Eastern Australian Marginal Ocean Basins M. Sdrolias1 , R.D. Müller2-arc ridge (remnant arc) on the other (Keary & Vine 1996). Plate tectonic reconstructions accounting exploration target is an accurate and self-consistent plate kinematic reconstruction of the region of interest

  3. Plate Tectonics GEY 443/643 -Fall 2005 Room LFG 202 MW 2:30 3:45 pm

    E-print Network

    Ahmad, Sajjad

    Plate Tectonics ­ GEY 443/643 - Fall 2005 Room LFG 202 ­ MW 2:30 ­ 3:45 pm Instructors: Michael@unlv.nevada.edu Required Text: Global Tectonics by Philip Kearey and Frederick J. Vine Supplementary Text: Plate Tectonics and Policies GEY 443/643 ­ Plate Tectonics ­ Fall 2005 ­ Wells & Snelson 1 #12;1. Participation: You

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

    Microsoft Academic Search

    P. Einarsson; B. Brandsdottir

    2006-01-01

    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

  5. G141 Earthquakes & Volcanoes Lab 2 Plate Tectonics Name _____________________________ G141 Lab 2: Exploring Plate Motion and Deformation in California Using GPS Data

    E-print Network

    Polly, David

    G141 Earthquakes & Volcanoes Lab 2 ­ Plate Tectonics Name _____________________________ 1 G141 Lab of modern GPS technology, we can actually observe the process of plate tectonics as the plates are moving of that segment of the Earth's tectonic plate. We will be using data recorded by UNAVCO consort- ium (www

  6. 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.…

  7. 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.

  8. 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.

  9. Plate tectonics from VLBI and SLR global data

    NASA Technical Reports Server (NTRS)

    Harrison, Christopher G. A.; Robaudo, Stefano

    1992-01-01

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

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

    E-print Network

    Generation of plate tectonics with two-phase grain-damage and pinning: Source-sink model theory therefore readily satisfies key plate-tectonic metrics of localized toroidal motion and plate-boundary inheritance, and thus provides a predictive theory for the generation of plate tectonics on Earth and other

  11. Geophys. J. Int. (1994) 119,595-610 A continuous kinematic model of plate-tectonic motions

    E-print Network

    1994-01-01

    Geophys. J. Int. (1994) 119,595-610 A continuous kinematic model of plate-tectonic motions David of mantle dynamics-which involves continuum physics-and the theory of plate tectonics-which employs to adjust the plate-tectonic model to allow for continuous surface motions. Here we present a model of plate

  12. Multi-Agent Modelling of Earth's Dynamics: Towards a Virtual Laboratory of Plate Tectonics Cecile Grigne(1)

    E-print Network

    Paris-Sud XI, Université de

    Multi-Agent Modelling of Earth's Dynamics: Towards a Virtual Laboratory of Plate Tectonics C-Agent Convective MAntle) is a new tool developed to simulate plate tectonics and mantle convection in a 2-D). Evolutive plate tectonics We obtain an evolutive system where the geometry and the number of plates

  13. Subduction and Plate Edge Tectonics in the Southern Caribbean

    NASA Astrophysics Data System (ADS)

    Levander, A.; Schmitz, M.; Niu, F.; Bezada, M. J.; Miller, M. S.; Masy, J.; Ave Lallemant, H. G.; Pindell, J. L.; Bolivar Working Group

    2013-05-01

    The southern Caribbean plate boundary consists of a subduction zone at at either end of a complex strike-slip fault system: In the east at the Lesser Antilles subduction zone, the Atlantic part of the South American plate subducts beneath the Caribbean. In the north and west in the Colombia basin, the Caribbean subducts under South America. In a manner of speaking, the two plates subduct beneath each other. Finite-frequency teleseismic P-wave tomography confirms this, imaging the Atlantic and the Caribbean plates subducting steeply in opposite directions to transition zone depths under northern South America (Bezada et al, 2010). The two subduction zones are connected by the El Pilar-San Sebastian strike-slip fault system, a San Andreas scale system that has been cut off at the Bocono fault, the southeastern boundary fault of the Maracaibo block. A variety of seismic probes identify subduction features at either end of the system (Niu et al, 2007; Clark et al., 2008; Miller et al. 2009; Growdon et al., 2009; Huang et al., 2010; Masy et al, 2011). The El Pilar system forms at the southeastern corner of the Antilles subduction zone with the Atlantic plate tearing from South America. The deforming plate edges control mountain building and basin formation at the eastern end of the strike-slip system. Tearing the Atlantic plate from the rest of South America appears to cause further lithospheric instability continentward. In northwestern South America the Caribbean plate very likely also tears, as its southernmost element subducts at shallow angles under northernmost Colombia but then rapidly descends to the transition zone under Lake Maracaibo (Bezada et al., 2010). We believe that the flat slab controls the tectonics of the Neogene Merida Andes, Perija, and Santa Marta ranges. The nonsubducting part of the Caribbean plate also underthrusts northern Venezuela to about the width of the coastal mountains (Miller et al., 2009). We infer that the edge of the underthrust Caribbean plate supports the elevations of the coastal mountains and controls continuing deformation.

  14. How Much Surface Deformation Results from Slab Processes Rather than Surface Plate Tectonics?

    NASA Astrophysics Data System (ADS)

    Freymueller, J. T.; Steblov, G. M.; Kogan, M. G.; Titkov, N. N.; Vasilenko, N. F.; Prytkov, A. S.; Frolov, D. I.

    2013-12-01

    The largest deep focus earthquake yet recorded (Mw 8.3) occurred 24 May 2013 at 607 km depth beneath the Sea of Okhotsk. Unlike past deep focus events, this earthquake caused significant displacements at the surface, which were measured using continuous GPS sites in Kamchatka, the Kuril Islands, Komandorsky (Russian Aleutian) Islands, and adjacent areas of the Russian Far East (Steblov et al., this meeting). The surface displacements can be explained by extensional faulting using either the GCMT primary or auxiliary fault plane consistent with the seismic moment magnitude, although the GPS displacements do not constrain the rupture area or slip independently. Although the largest measured displacements for this event are only ~15 mm, this raises the question of how much does deformation of the slab contribute to the surface displacement/velocity field? For example, is there an 'interseismic' signal associated with the stress/strain buildup prior to these events? If there is no equivalent to 'elastic rebound' for such events, then each large deep focus earthquake must produce permanent, although every long wavelength, strain of the surface plate. Like other deep focus earthquakes, this event represents deformation within the slab long after subduction. Intermediate depth earthquakes also result from slab deformation. Although plate tectonics is responsible for putting the slab in this situation, and the forces acting on the slab influence plate motions, the details of how the slab deforms have generally been thought to be irrelevant for measurements of surface plate motions. In this presentation I will quantify the global surface deformation rate from intermediate and deep focus events and explore the consequences of this deformation for geodetic estimates of plate motion and plate boundary deformation. Predicted coseismic displacements based on the GCMT moment tensor.

  15. 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 about 25 Ma. The New Guinea passive margin collided with the East Philippines-Halmahera-South Caroline Arc system. The Australian margin, in the Bird's Head region, also began to collide with the SE Asian margin in Sulawesi. The Ontong Java Plateau collided with the Melanesian Arc. These collisions caused a major change in the character of plate boundaries between about 25 and 20 Ma. Since 25 Ma, tectonic events east of Eurasia were driven by motion of the Pacific Plate. Further, west, the movement of Australia northwards caused rotations of blocks and accretion of microcontinental fragments to SE Asia. Plate motions and boundaries changed again at about 5 Ma, for uncertain reasons, possibly as a consequence of Pacific Plate motion changes, arc-continent collision in Taiwan, or other boundary changes at the Pacific margin, for example in the Philippines. Areas to the west and east of New Guinea, the Banda Sea and Woodlark Basin, illustrate the speed of change, the unexpected interplay of convergence and extension, and the importance of subduction as the engine of change. Subduction has been the principal driving mechanism for tectonic change, although its manifestations are varied. They include collision-related phenomena, partitioning of oblique convergence, and effects of hinge roll-back and pull forces of subducting slabs. Magmatism is not always associated with subduction, depending on the movement of subduction hinge, and there may be important extension of the upper plate both perpendicular and parallel to the length of subduction zones. Strike-slip faulting is observably very important within the Pacific-Australia-Eurasia convergent setting, yet appears in few tectonic models. Long-term strike-slip deformation can explain some of the complexities of areas such as New Guinea, including magmatism and its absence, and thermo-chronological data showing very young and rapid cooling of the mobile belt and fold belt. The inadequacies of the tectonic model reflect in part the difficulties of applying rigid plate tectonics, when there is clear evidence of changing

  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 regards to past and future North American intraplate deformation are also discussed. Our results indicate that there exists a number of tectonic environments that can be produced relating to continental accretion, and that specific observational constraints to the local area (e.g., geological, geophysical, geodetic) are required to be integrated directly into the analyses for better interpretation. The models shown here find that although rheological changes to the lithosphere can produce a range of deformation during continental convergence (i.e., crustal thickening, thinning, and folding), mantle weak zones from ancient subduction can generate more localized deformation and topography.

  17. Linking continental drift, plate tectonics and the thermal state of the Earth's mantle

    E-print Network

    Tackley, Paul J.

    Linking continental drift, plate tectonics and the thermal state of the Earth's mantle T. Rolf a between continental drift, oceanic plate tectonics and the thermal state of the Earth's mantle, by using Arthur Holmes proposed that continental drift and seafloor kinematics are surface expressions of large

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

    E-print Network

    Becker, Thorsten W.

    : seafloor age distributions plate tectonics oceanic heat flow Variations in Earth's rates of seafloorPast and present seafloor age distributions and the temporal evolution of plate tectonic heat of Earth Sciences, University of Southern California, Los Angeles, CA, USA b Department of Geology

  19. Time variability in Cenozoic reconstructions of mantle heat flow: Plate tectonic cycles and implications for

    E-print Network

    Conrad, Clint

    the average cooling rate. Thus, a mechanism that causes less efficient tectonic heat transport at higher convection plate reconstructions seafloor spreading Earth's heat loss is fueled by two dominant sources: (iTime variability in Cenozoic reconstructions of mantle heat flow: Plate tectonic cycles

  20. 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. PMID:18092990

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

  2. Plate Tectonics: The Rocky History of an Idea

    NSDL National Science Digital Library

    Information on this site about the early history of the Theory of Plate Tectonics begins in 1912 with Alfred Wegener (1880-1930), who noticed that most of the continents seem to fit together like a puzzle. The west African coastline seems to fit nicely into the east coast of South America and the Caribbean sea, and a similar fit appears across the Pacific. He proposed that the continents were once compressed into a single protocontinent, which he called Pangaea, and over time they have drifted apart into their current distribution. The site includes further information that convinced Wegener of his theory and also the suggestion of Arthur Holmes that there were convection currents in the mantle. Lastly there is mention of sea floor spreading as suggested by Harry Hess and R. Deitz.

  3. The Onset of Plate tectonics in a Compositionally Stratified mantle

    NASA Astrophysics Data System (ADS)

    Hansen, U.; Dude, S.

    2013-12-01

    We investigate the geodynamical evolution of the Earth after the crystallization of the magma ocean. This situation is resembled by a scenario, displaying a compositionally stratified mantle being heated from below and within, while also cooled from above. The evolution of the system is dependent on initial conditions and further strongly on the assumed rheology. We have employed numerical models in 2D and 3d cartesian , as well as in spherical geometry to explore possible evolutionary paths of the Early Earth. A common feature of all models featuring a strongly temperature dependent viscosity is the self-organized generation of separately convecting layers. Such layers reduce the heat flow from the core and also delay instabilities from the top layer. Thus this type of model favors a late onset of l arge scale plate tectonics, possibly as late as 2Gyears after formation. A typical feature of this scenario is the intermittent breakdown of layers in the mantle leading to strong pulses of the heat flow. A different picture emerges for a more pressure dominated rheology. Even a slightly stable compositional stratification is sufficient to suppress global convection. Instead the surface is destabilized and small scale plate tectonics sets in immediately. We further investigated the effect of fractional crystallization and a resulting unstable compositional gradient. In all models we observed an Rayleigh-Taylor instability and subseuqtly a long term evolution being very similar to the scenario with the initially stable gradient. According to these results both, a fractional or homogeneous crystallization would lead to a similar long term evolution of the mantle.

  4. 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 petrological changes may accompany the crustal thickening, e.g., eclogitization, and delamination, 2) Rather than the detachment the exhumation of the metamorphic core of the Central Range is the main engine of the orogeny, and 3) The lithosphere has a complex rheological structure, indicated, in part, by the spatial distribution of seismicity.

  5. 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 Moctezuma Trough and the Mathematician Rise forms a separate crustal province, truncated by the Moctezuma Trough. There is a possible conjugate fragment of this older province preserved east of the Manzanillo Trough, next to the MAT. Thus, features of the downgoing Cocos Plate appear to be more complicated than has been envisioned in most previous interpretations.

  6. Z .Earth and Planetary Science Letters 154 1998 139151 Generation of plate tectonics from lithospheremantle flow and

    E-print Network

    Z .Earth and Planetary Science Letters 154 1998 139­151 Generation of plate tectonics from The formation of plate tectonics from mantle convection necessarily requires nonlinear rheological behavior has long been suspected to be a key ingredient for the existence of plate tectonics, i.e., water. q

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

    E-print Network

    Royal Holloway, University of London

    Cenozoic geological and plate tectonic evolution of SE Asia and the SW Paci®c: computer A plate tectonic model for the Cenozoic development of the region of SE Asia and the SW Paci the driving force of tectonics in most of SE Asia. The most important Cenozoic plate boundary reorganisation

  8. How plate tectonics is recorded in chalk deposits along the eastern English Channel in Normandy (France) and Sussex (UK)

    E-print Network

    Boyer, Edmond

    01/12/2011 - 1 - How plate tectonics is recorded in chalk deposits along the eastern English provides an excellent record of brittle tectonics generated by far-field stresses of plate tectonics re Kutzenhausen, France Abstract Intra-plate stresses that occurred in the Anglo-Paris Basin and English Channel

  9. Rifting beneath Antarctica's ice sheet: A plate tectonic Supervisors: Graeme Eagles (RHUL) & Fausto Feraccioli (British Antarctic Survey)

    E-print Network

    Royal Holloway, University of London

    Rifting beneath Antarctica's ice sheet: A plate tectonic approach Supervisors: Graeme Eagles (RHUL rapid sea level changes by more than 100 m; it forms a crucial plate tectonic link between the African traditional geological techniques. Instead, studies of the circuit of plate tectonic motions in the South

  10. The original kinematic plate tectonic model proposed that the outer shell (lithosphere) of the Earth is divided into a small

    E-print Network

    Sandwell, David T.

    The original kinematic plate tectonic model proposed that the outer shell (lithosphere driver of plate tectonics and mantle convection, but much of the energy dissipation may be in this part rele- vant to plate tectonics. Here we have compiled a series of global maps that help to confirm

  11. Timing of Plate Tectonics Initiation on a One-Plate Planet: Insights from Numerical Simulations of Time-Dependent Convection

    NASA Astrophysics Data System (ADS)

    Wong, T.; Solomatov, V. S.

    2015-05-01

    Plate tectonics initiation may be favored under certain conditions, yet due to the chaotic nature of time-dependent convection the timing of initiation could be different for the same planetary conditions depending on initial conditions.

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

    NASA Astrophysics Data System (ADS)

    Husson, Laurent; Yamato, Philippe; Bézos, Antoine

    2015-04-01

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

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

    E-print Network

    Demouchy, Sylvie

    New insights on 3-D plates interaction near Taiwan from tomography and tectonic implications Serge trenches, respectively. In particular, the 3-D plates interaction beneath Taiwan is discussed based of Hualien, (2) the Eurasian plate subducts beneath most part of the Taiwan island down to the 670 km

  14. Strain weakening enables continental plate tectonics Frdric GUEYDAN (1), Jacques PRCIGOUT (2) and Laurent G.J. MONTESI (3)

    E-print Network

    Paris-Sud XI, Université de

    1 Strain weakening enables continental plate tectonics Frédéric GUEYDAN (1), Jacques PRÉCIGOUT (2-scale strain localization and hence enables plate tectonics. No rheological model proposed to date is comprehensive enough to describe both the weakness of plate boundary and rigid-like behaviour of plate interiors

  15. JOURNAL OF GEOPHYSICAL RESEARCH, VOL. ???, XXXX, DOI:10.1029/, Tectonic plate generation and two-phase damage: void

    E-print Network

    Paris-Sud XI, Université de

    JOURNAL OF GEOPHYSICAL RESEARCH, VOL. ???, XXXX, DOI:10.1029/, Tectonic plate generation and two-PHASE DAMAGE AND PLATE GENERATION X - 3 1. Introduction Although the theory of plate tectonics is a well-PHASE DAMAGE AND PLATE GENERATION Abstract. The two-phase theory for compaction and damage employs a nonequi

  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 complexes, but also the relatively recent motion along the Cayman Fault zone (Miocene instead of Eocene). These results are part of a cooperative research-industry programm conducted by CEREGE/EGERIE, Aix-en-Provence and GeoAzur, Nice, with Frontier Basin study group, TOTAL S.A., Paris.

  17. Connecting Cross-Sectional Data from the Red Sea to Plate Tectonics

    NSDL National Science Digital Library

    Laura Guertin

    Students will use map views and cross-sectional profiles across the Red Sea to determine plate tectonic processes in the region. Google Earth is a technological tool used to facilitate the investigation.

  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. Late Palaeozoic Biogeography of East Asia and Palaeontological Constraints on Plate Tectonic Reconstructions

    Microsoft Academic Search

    A. B. Smith

    1988-01-01

    Biogeographical patterns of late Palaeozoic rugose coral genera are analysed for the Lower Carboniferous (Visean), early Lower Permian (Asselian\\/Sakmarian), late Lower Permian (Qixian) and early Upper Permian (Maokoan) of East Asia. Boundaries to the biotic regions are defined to coincide with tectonically significant suture zones to test rival hypotheses about the plate tectonic reconstruction of that region. Three numerical techniques

  20. Plate tectonic evolution of the southern margin of Eurasia in the Mesozoic and Cenozoic

    Microsoft Academic Search

    J. Golonka

    2004-01-01

    Thirteen time interval maps were constructed, which depict the Triassic to Neogene plate tectonic configuration, paleogeography and general lithofacies of the southern margin of Eurasia. The aim of this paper is to provide an outline of the geodynamic evolution and position of the major tectonic elements of the area within a global framework. The Hercynian Orogeny was completed by the

  1. Young Tectonic Events in Martian Chaotic Terrain

    NASA Astrophysics Data System (ADS)

    Martel, L. M. V.

    2012-03-01

    Examples of recent tectonic activity and subsidence on Mars are expressed in Aureum Chaos, the area of chaotic terrain east of Valles Marineris. So say researchers who have studied the layered deposits of Aureum Chaos and the cross-cutting relationships between scarps, dunes, and a landslide. Mauro Spagnuolo (Universidad de Buenos Aires), Angelo Rossi (International Space Science Institute and Jacobs University Bremen), Ernst Hauber (German Aerospace Center), and Stephan van Gasselt (Freie Universität Berlin) identified fault-related geomorphic features in remote sensing data, specifically a disrupted landslide that they determine to be less than 1.9 million years old. If indeed very recent activity has occurred along faults in Aureum Chaos, then these may be very important sites for studies related to the circulation of fluid or gas through, or out of, these fractures or fissures. Both geologists and astrobiologists would be interested in the implications for the distribution of water in the crust, the aqueous alteration of minerals, and the potential for microenvironments to harbor or sustain life.

  2. Neotectonic and structural characteristics along the Chaochou fault system in SW Taiwan: implications for tectonic escape during oblique plate convergence

    Microsoft Academic Search

    Y. Chan; J. Lee; C. Lu; J. Hu; H. Chu; C. Hou; R. Rau; K. Ching

    2002-01-01

    Tectonic escape has been recognized as a common geologic process that relates to the lateral expulsion of a tectonic block during oblique plate convergence and collision. To better understand fault behaviors in such tectonically active regions, we characterized short-term and recent deformation in the SW Taiwan, where deformation largely associates with tectonic escape. This study focuses on a prominent boundary

  3. EVIDENCE FOR EARLY PROTEROZOIC PLATE TECTONICS FROM SEISMIC REFLECTION PROFILES IN THE BALTIC SHIELD

    Microsoft Academic Search

    T. Dahl-Jensen; R. W. Hobbs; SL Klemperer; DH Matthews; DB Snyder; R Long; T Matthews; DJ Blundell; CE Lund; H Palm; LB Pedersen; RG Roberts; SA Elming; P Heikkinen; H Korhonen; U Luosto; SE Hjelt; K Komminaho; J Yliniemi; R Meissner; P Sadowiak; T Wever; T Dickmann; ER Fleuh; A Berthelsen; H Thybo; N Balling; E Normark

    1990-01-01

    Plate tectonics provides the linking framework for all tectonic and\\u000a magmatic activity seen today, but it is not known when plate tectonics\\u000a first developed on Earth. New deep seismic reflection and coincident\\u000a refraction profiles across an exposed, 1.89-Gyr-old volcanic arc complex\\u000a show a 10-km-thick offset in the Moho and bivergent reflectors in the\\u000a crust, which were most probably created by

  4. Numerical Models of Plate Tectonics and Mantle Convection in Three Dimensions

    Microsoft Academic Search

    Carl Walter Gable

    1989-01-01

    Up to now, numerical models of mantle convection have not included two important features of the earth; the earth is three dimensional and tectonic plates on the surface translate as rigid blocks. This work incorporates surface plates into a dynamic, three dimensional Cartesian convection model allowing quantitative investigation of geodynamic phenomena which were previously inaccessible. The power spectra of the

  5. New Constraints on Carribean Plate Tectonic Evolution Caribbean Basins included in the series Sedimentary Basins of the World, 4 Elsevier

    E-print Network

    Müller, Dietmar

    New Constraints on Carribean Plate Tectonic Evolution Caribbean Basins included in the series rotations North America-South America plate motions in the Caribbean are Discussion Lesser Antilles to Mid Acknowledgment References Abstract We review the plate tectonic evolution of the Caribbean area based

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

    NASA Astrophysics Data System (ADS)

    Burke, Kevin

    2011-05-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  8. Initiation of Plate Tectonics from Post-Magma Ocean Thermo-Chemical Convection

    E-print Network

    Foley, Bradford J; Elkins-Tanton, Linda T

    2014-01-01

    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 $\\approx 1.75$ cm/yr, can still be maintained in the Hadean, even with a CO$_2$ rich primordial atmosphere. Furthermore, when the...

  9. 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.

  10. Focal Mechanisms and Plate Tectonics of the Southwest Pacific

    Microsoft Academic Search

    Tracy Johnson; Peter Molnar

    1972-01-01

    Ninety-six new focal mechanisms were determined for earthquakes on the belt of seismic activity separating the Pacific and Australian plates. The direction of convergence of these plates varies from Ntg-SW to E-W. The Australian plate underthrusts the Pacific plate to the ENE under the Solomon and New Hebrides islands and overthrusts the Pacific to the east along the Tonga-Kermadec arc

  11. Middle Miocene to present plate tectonic history of the southern Central American Volcanic Arc

    NASA Astrophysics Data System (ADS)

    MacMillan, Ian; Gans, Phillip B.; Alvarado, Guillermo

    2004-11-01

    New mid Miocene to present plate tectonic reconstructions of the southern Central American Volcanic Arc (CAVA) reveal that the inception of Cocos Ridge subduction began no earlier than 3 Ma, and possibly as late as 2 Ma. The Cocos Ridge has been displaced from the Malpelo Ridge to the southeast since ˜9 Ma along the Panama Fracture Zone (PFZ) system. Ambiguous PFZ and Coiba Fracture Zone (CFZ) interaction since ˜9 Ma precludes conclusively establishing the age of initial Cocos Ridge subduction. Detailed reconstructions based on magnetic anomalies offshore reveal several other variations in subduction parameters beneath southern Central America that preceded subduction of the Cocos Ridge, including southeastward migration of the Nazca-Cocos-Caribbean triple junction along the Middle America Trench (MAT) from 12 Ma to present, and subduction of ?2 km high scarps both parallel and perpendicular to the trench from 6 to ˜1 Ma. The timing of changes in subduction processes has commonly been determined by (and correlated with) geologic changes in the upper plate. However, reliable 40Ar/ 39Ar dating of these events has become available only recently [Abstr. Programs-Geol. Soc. Am. (2002)]. These new dates better constrain the magmatic and structural history of southern Costa Rica. Observations from this data set include: a gap in the volcanic record from 11 to 6 Ma, which coincides temporally with emplacement of most plutons in southern Costa Rica, normal arc volcanism ceased after 3.5 Ma in southern Costa Rica, and Pliocene (mostly ˜1.5 Ma) adakite volcanism was widely distributed from central Panama to southern Costa Rica (though volumetrically insignificant). This new data reveals that many geologic phenomena, commonly attributed to subduction and underplating of the buoyant Cocos Ridge, in fact precede inception of Cocos Ridge subduction and seem to correlate more favorably in time with earlier tectonic events. Adakite volcanic activity corresponds in space and time with the subduction of a large scarp associated with a tectonic boundary off southern Panama. Regional unconformities and an 11-6 Ma gap in arc volcanism match temporally with oblique subduction of the Nazca plate beneath central and southern Costa Rica. Cessation of volcanic activity, low-temperature cooling of plutons in the Cordillera de Talamanca (CT), and rapid increases in sedimentation in the fore-arc and back-arc basins coincide with passage of the Nazca-Cocos-Caribbean triple junction and initiation of subduction of "rough" crust associated with Cocos-Nazca rifting 3.5 Ma, closely followed by initial subduction of the Cocos Ridge 2-3 Ma. None of the aforementioned geologic events occurred at a time that would allow for underplating by the Cocos Ridge. Rather they are probably related to complex interactions with subduction of complicated plates offshore. All of the aforementioned events indicate that the southern Central American subduction system has been in flux since at least ˜12 Ma.

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

    SciTech Connect

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

    1994-07-01

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

  13. Identifying Plate Tectonic Boundaries for a Virtual Ocean Basin

    NSDL National Science Digital Library

    Stephen Reynolds

    Students observe a virtual ocean basin and two adjacent continental margins. From the characteristics of the sea floor and adjacent land, students infer where plate boundaries might be present. They then predict where earthquakes and volcanoes might occur. Finally, they draw their inferred plate boundaries in cross section.

  14. 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, at the surface, and the solid mantle is chemically unstable. The effect of compositional buoyancy is crucial; in its absence convection does not begin until a thick, rigid lid has formed, and thus stagnant lid convection results. Initiating plate tectonics from this state is extremely difficult. We therefore perform numerical calculations with initially unstable compositional profiles to map out the conditions that allow for weak zone formation and plate tectonic style convection in the early Earth. In calculations without damage, compositional overturn is followed immediately by penetrative convection, which eventually develops into full mantle convection as mixing eliminates the chemical heterogeneity. With strongly temperature dependent viscosity, the penetrative convection is suppressed and the lag time to full mantle convection is prolonged significantly. We propose that with grain-damage the initial overturn will form lithospheric weak zones; these weak zones will then allow for penetrative convection to occur, sustaining the damaged zones and surface mobility until full mantle convection develops. We present a suite of numerical calculations to assess the viability of this mechanism for initiating plate tectonics on the early Earth.

  15. Mesozoic plate tectonic reconstruction of the Carpathian region

    Microsoft Academic Search

    László Csontos; Attila Vörös

    2004-01-01

    Palaeomagnetic, palaeobiogeographic and structural comparisons of different parts of the Alpine–Carpathian region suggest that four terranes comprise this area: the Alcapa, Tisza, Dacia and Adria terranes. These terranes are composed of different Mesozoic continental and oceanic fragments that were each assembled during a complex Late Jurassic–Cretaceous–Palaeogene history. Palaeomagnetic and tectonic data suggest that the Carpathians are built up by two

  16. 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 the reconstructed-southern hemisphere, thereby signifying that the ultimate trigger for the reorganisation was located in the southern hemisphere. We describe two potential driving mechanisms for the 100 Ma event: (1) termination of the long-lived eastern Gondwanaland subduction zone (a top-down mechanism), and (2) intersection of the Bouvet Plume with the Africa-South America-Antarctica ridge-ridge-ridge triple junction (a bottom-up mechanism). Our review of the 100 Ma reorganisation may help in re-assessing the driving forces of global tectonic events and aid hypothesis testing using geodynamic models, including those for the 50 Ma event.

  17. 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.

  18. 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.

  19. Mantle transition zone beneath the Caribbean-South American plate boundary and its tectonic implications

    E-print Network

    Niu, Fenglin

    Mantle transition zone beneath the Caribbean-South American plate boundary and its tectonic seismic network of Venezuela to study the mantle transition zone structure beneath the Caribbean Caribbean, the 410-km is featured by a narrow (200 km EW) 25-km uplift extending in the NS direction around

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

    Microsoft Academic Search

    Daniel Jean Stanley

    1982-01-01

    The first major offshore boundary dispute where plate tectonics constituted a significant argument was recently brought before the International Court of Justice by Libya and Tunisia concerning the delimitation of their continental shelves. Libya placed emphasis on this concept to determine natural prolongation of its land territory under the sea. Tunisia contested use of the entire African continental landmass as

  1. Supercontinents, mantle dynamics and plate tectonics: A perspective based on conceptual vs. numerical models

    Microsoft Academic Search

    Masaki Yoshida; M. Santosh

    2011-01-01

    The periodic assembly and dispersal of supercontinents through the history of the Earth had considerable impact on mantle dynamics and surface processes. Here we synthesize some of the conceptual models on supercontinent amalgamation and disruption and combine it with recent information from numerical studies to provide a unified approach in understanding Wilson Cycle and supercontinent cycle. Plate tectonic models predict

  2. Miocene faulting at plate tectonic velocity in the Himalaya of central Nepal

    E-print Network

    Miocene faulting at plate tectonic velocity in the Himalaya of central Nepal Matthew J. Kohna, Tri-Chandra Campus, Ghantaghar, Kathmandu, Nepal, United States Received 7 April 2004; received (MCT) and affiliated faults in central Nepal. Inferred rates were 1.5F0.9 cm/yr (Langtang Thrust, ~19

  3. Influence of early plate tectonics on the thermal evolution and magnetic field of Mars

    Microsoft Academic Search

    F. Nimmo; D. J. Stevenson

    2000-01-01

    Recent magnetic studies of Mars suggest that (1) it possessed a periodically reversing magnetic field for the first ~500 Myr of its existence and (2) plate tectonics may have been operating during this time. On Earth the geodynamo is thought to occur because of convection in the outer core. This paper estimates the amount of heat the Martian core can

  4. 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…

  5. A new class of ``pseudofaults'' and their bearing on plate tectonics: A propagating rift model

    Microsoft Academic Search

    Richard Hey

    1977-01-01

    The pattern of magnetic anomaly offsets striking obliquely to the Blanco fracture zone near the Juan de Fuca spreading center appears to be incompatible with the rigid-plate hypothesis. Previous workers have thus called upon complex, or anomalous, mechanisms to explain the tectonic evolution of this area. According to the ``propagating rift'' model developed here, the basic observations that previous hypotheses

  6. 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…

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

    PubMed

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

    2010-08-27

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

  8. 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.

  9. Plate tectonics on super-Earths: Equally or more likely than on Earth H.J. van Heck , P.J. Tackley

    E-print Network

    Tackley, Paul J.

    Plate tectonics on super-Earths: Equally or more likely than on Earth H.J. van Heck , P.J. Tackley 29 July 2011 Available online xxxx Editor: Y. Ricard Keywords: super-Earths plate tectonics mantle and evo- lution, and in whether their lithospheres are most likely to be undergoing active plate tectonics

  10. 578 R. J. STERN Chinese Science Bulletin | March 2007 | vol. 52 | no. 5 | 578-591 When and how did plate tectonics begin? Theoretical

    E-print Network

    Stern, Robert J.

    plate tectonics begin? Theoretical and empirical considerations R. J. STERN Geosciences Department mantle (asthenosphere) and is mostly driven by lithosphere sinking in subduction zones. Plate tectonics and viscous mantle. Plate tectonics is an unusual way for a silicate planet to lose heat, as it exists on only

  11. 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.

  12. 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.

  13. Micro plate tectonics in the Virgin Islands Basin, north eastern Caribbean

    NASA Astrophysics Data System (ADS)

    Raussen, S.; Lykke-Andersen, H.

    2009-12-01

    The formation of the Virgin Islands Basin in the north eastern part of the Caribbean is controlled by the plate boundary between the Puerto Rico-Virgin Islands Micro Plate and the stable part of the Caribbean Plate. The Puerto Rico-Virgin Islands Micro Plate is one of three micro plates located in a complex plate boundary zone in the north eastern part of the Caribbean where the Caribbean Plate borders the North American Plate. These micro plates move differently than the stable part of the Caribbean plate. There exists a lot of contradicting theories about the course of formation of the Virgin Islands Basin, including counter clockwise rotation of the micro plate and dextral or sinistral strike-slip movements between the plates. In connection with the Danish Galathea 3 expedition, the most extensive exploration of the basin to date was conducted in March 2007. Cores, CTD measurements, multi beam bathymetric data and 2D seismic data were acquired. The results from the multi beam and seismic data are presented in this study. The main observations are of extensional features, which show both on the sea bed and in the sedimentary package. Furthermore, evidence of strike-slip movements is found. Based on the observations, a tectonic model is presented. The model consists of a primary north-south to north west-south east directed extension combined with east-west trending sinistral strike-slip. It implies that the Puerto Rico-Virgin Islands Micro Plate is moving slower towards the east-north east than the stable part of the Caribbean Plate. The model is supported by the newest GPS-measurements. The Virgin Islands Basin is located in The Anegada Passage, which comprises the south eastern boundary between the Puerto Rico-Virgin Islands Micro Plate and the stable part of the Caribbean Plate.

  14. Plate Tectonics of the Red Sea and East Africa

    Microsoft Academic Search

    D. P. McKenzie; D. Davies; P. MOLNAR

    1970-01-01

    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.

  15. 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.

  16. Plate-tectonic boundary formation by grain-damage and pinning

    NASA Astrophysics Data System (ADS)

    Bercovici, David

    2015-04-01

    Shear weakening in the lithosphere is an essential ingredient for understanding how and why plate tectonics is generated from mantle convection on terrestrial planets. I present continued work on a theoretical model for lithospheric shear-localization and plate generation through damage, grain evolution and Zener pinning in two-phase (polycrystalline) lithospheric rocks. Grain size evolves through the competition between coarsening, which drives grain-growth, with damage, which drives grain reduction. The interface between 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 shear-localizing feedback. Moreover, because pinning inhibits grain-growth it promotes shear-zone longevity and plate-boundary inheritance. This theory has been applied recently to the emergence of plate tectonics in the Archean by transient subduction and accumulation of plate boundaries over 1Gyr, as well as to rapid slab detachment and abrupt tectonic changes. New work explores the saturation of interface damage at low interface curvature (e.g., because it is associated with larger grains that take up more of the damage, and/or because interface area is reduced). This effect allows three possible equilibrium grain-sizes for a given stress; a small-grain-size high-shear state in diffusion creep, a large grain-size low shear state in dislocation creep, and an intermediate state (often near the deformation map phase-boundary). The low and high grain-size states are stable, while the intermediate one is unstable. This implies that a material deformed at a given stress can acquire two stable deformation regimes, a low- and high- shear state; these are indicative of plate-like flows, i.e, the coexistence of both slowly deforming plates and rapidly deforming plate boundaries.

  17. A combined rigid/deformable plate tectonic model for the evolution of the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Watson, J. G.; Glover, C. T.; Adriasola Munoz, A. C.; Harris, J. P.; Goodrich, M.

    2012-04-01

    Plate tectonic reconstructions are essential for placing geological information in its correct spatial context, understanding depositional environments, defining basin dimensions and evolution, and serve as a basis for palaeogeographic mapping and for palaeo-climate modelling. Traditional 'rigid' plate reconstructions often result in misfits (overlaps and underfits) in the geometries of juxtaposed plate margins when restored to their pre-rift positions. This has been attributed to internal deformation pre- and/or syn- continental break-up. Poorly defined continent-ocean boundaries add to these problems. To date, few studies have integrated continental extension within a global model. Recent plate tectonic reconstructions based on the relative motions of Africa, Madagascar, India and Antarctica during the break-up of eastern Gondwana have not taken into account the effects of deformation; particularly between India and Madagascar, and India and the Seychelles. A deformable plate model is in development that builds on the current rigid plate model to describe the complex multiphase break-up history between Africa, Madagascar, Seychelles and India, the associated magmatic activity and subsequent India/Eurasia collision. The break-up of eastern Gondwana occurred in the mid Jurassic by rifting between Africa and the India-Madagascar-Australian-Antarctica plates, followed by the Late Jurassic drift of India away from Australia and the Cretaceous break-up of Australia and Antarctica. The northwards drift of the Seychelles-India block in the Tertiary was accommodated by the opening of the Laxmi Basin. This was followed by the eruption of the extensive Deccan flood basalts and the separation of India and the Seychelles. Crustal domains on volcanic margins can be very difficult to define due to the accretion of magmatic material. On these margins, there is much speculation on the position of the continent-ocean boundary and the timing of rifting and sea-floor spreading. The presence of magnetic anomalies indicating variable rates of seafloor spreading and 'jumps' in the axis of seafloor spreading have not as yet been satisfactorily resolved by existing plate models. Integration of detailed geophysical and geological datasets, combined with published data will be used to produce an enhanced plate tectonic model. This will be coupled with deformable modelling of the extensional margins, incorporating stretching (?) factors and deformation trajectories to calculate the extent of crustal deformation for the main episodes of continental break-up. This will result in more accurate plate tectonic reconstructions for the determination of pre-rift geometries, palaeo-positions of the plates and exploration datasets intersected with them, to aid hydrocarbon exploration in the region.

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

    SciTech Connect

    Janssen, M.E. (Vrije Universiteit, Amsterdam (Netherlands))

    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.

  19. 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.

  20. Seismicity and tectonics of the subducted Cocos Plate

    NASA Astrophysics Data System (ADS)

    Burbach, George Vanness; Frohlich, Cliff; Pennington, Wayne D.; Matumoto, Tosimatu

    1984-09-01

    We have examined teleseismic earthquake locations reported by the International Seismological Centre (ISC) for the Middle America region and selected 220 as the most reliable. These hypocenters and other data are used to delineate the deep structure of the subducted Cocos Plate. The results indicate that the subducted plate consists of three major segments: Segment I extends from the Panama Fracture Zone to the Nicoya Peninsula. The structure of this segment is poorly defined. Segment II is the largest and best-defined segment. This segment consists of two parts, IIA and IIB. Part IIA extends from the Nicoya Peninsula to western Guatemala and is very well defined and continuous in structure. Its strike follows the curvature of the trench and dips at about 60°. Part IIB extends from western Guatemala to Orizaba, Mexico. The dip of this part of the segment decreases slightly toward the northwest, and its strike is more northward than that of the trench. Segment III extends from Orizaba to the Rivera Fracture Zone, and is not well defined due to a lack of earthquake activity beneath about 100 km. Its orientation differs markedly from segment II and strikes somewhat more westward than the trench. Between parts IIA and IIB of segment II the subducted plate seems to be continuous, bending smoothly to accommodate the change in geometry. Local network data from Costa Rica suggest there may be a tear between segments I and II. Between segments II and III there is a gap in the hypocenters which makes it difficult to define the boundary. The change in geometry between these two segments indicates that there may be a tear, and two strike-slip focal mechanisms in the region support this conclusion. We find no convincing evidence supporting the existence of segments smaller than the three described above. If there is smaller-scale segmentation in the shallow part of the subducting plate the plate must still maintain enough continuity to appear continuous at greater depths. There is no evidence for any major tear in the subducted plate associated directly with either the Tehuantepec Ridge or the Orozco Fracture zone. The shallow subduction at the northwestern end of segment II may be related to the bouyancy of the Tehuantepec Ridge. The Cocos Ridge is probably directly responsible for the change in geometry between segments I and II and may even be slowing or stopping subduction in segment I. The structure of the subducted plate in segment II and the changes in the character of volcanism along the arc can be related to the relative motion of the North American and Caribbean Plates. The present geometry of part IIB of segment II is more consistent with the probable configuration of the trench about 7 Ma ago than with the present configuration, indicating that the North American plate is overriding the subduction zone. Appendices 2, 3, and 4 are available with entire article on microfiche. Order from American Geophysical Union, 2000 Florida Avenue, N.W., Washington, DC 20009. Document B84-009; $2.50.

  1. in press, AGU Monograph on The History and Dynamics of Global Plate Motions, ed. M. Richards, 1999 The Quest for Self-Consistent Generation of Plate Tectonics in Mantle

    E-print Network

    Tackley, Paul J.

    1 The Quest for Self-Consistent Generation of Plate Tectonics in Mantle Convection Models Paul J. Tackley Department of Earth and Space Sciences, University of California, Los Angeles Plate tectonics do not exhibit plate tectonic behavior unless it is imposed by the modeler. This paper explores

  2. The class material is designed to address fundamental yet extremely interesting questions about earthquakes and plate tectonic activity and their cyclicity. For example: Just why and how are earthquakes generated at plate edges and

    E-print Network

    earthquakes and plate tectonic activity and their cyclicity. For example: Just why and how are earthquakes? Ideas about interactions of the various components of the plate tectonic model and its attendant of crustal deformation produced during complex plate tectonic interactions. Earth is a gigantic heat engine

  3. Proterozoic plate tectonics, glaciation and iron-formations

    NASA Astrophysics Data System (ADS)

    Young, Grant M.

    1988-08-01

    Glacigenic diamictites and associated rocks are common in Early and Late Proterozoic sequences. Most of the preserved Proterozoic glacigenic rocks formed in marine basins in an extensional tectonic regime at or close to the rift-drift transition. The reasons for glaciation in this tectonic setting are not known but two possible contributing factors, given an initially cool climatic regime, are the formation of new seaways by continental fragmentation and uplift of the rift shoulders during early stages of breakup. The absence of such glacigenic deposits in the classical miogeoclines of the peri-Atlantic region may be due to an anomalously warm global climatic regime in the late Mesozoic. Iron-formations in the Archean and Early Proterozoic formed in many different environments; the critical factor was a dearth of siliciclastic deposition. Starved basins commonly developed during the transition from miogeocline to foreland basin in the Wilson cycle of ocean opening and closure, when drainage from the craton was replaced by that from a rising orogen. Early Proterozoic iron-rich sediments in the Great Lakes region, in southeast Wyoming and in the Northwest Territories of Canada are interpreted as the earliest deposits of such foreland basins. They are considered to be chemical precipitates from iron-rich sea water. Late Proterozoic iron-formations formed under an extensional regime, possibly in small Red Sea-type ocean basins where hydrothermal circulation produced metal-rich brines. These brines were displaced by movement of cold waters derived from sea-going glaciers, leading to dilution and precipitation of Fe and Si. Thus, in the Late Proterozoic, there was a critical association of continental rifting, glaciation and hydrothermal circulation. This combination of environmental parameters led to the production of the unique Late Proterozoic class of hydrothermal iron-formations.

  4. 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.

  5. The rapid drift of the Indian tectonic plate.

    PubMed

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

    2007-10-18

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

  6. Giant impacts and the initiation of plate tectonics on terrestrial planets

    NASA Astrophysics Data System (ADS)

    Ruiz, Javier

    2011-06-01

    Earth is the only terrestrial planet with present-day lithosphere recycling through plate tectonics. However, theoretical models of mantle convection based on general considerations find that all the terrestrial planets should be operating in the stagnant lid regime, in which the planets are one-plated and there is no lithosphere recycling. The stagnant lid regime is a consequence of the strong viscosity contrast across the convective layer, and therefore the upper lid (roughly equivalent to the lithosphere) must be sufficiently weakened in order to be mobilized. Here I propose that giant impacts could have provided the upper layer weakening required for surface recycling, and hence for plate tectonics, to initiate on the early Earth. Additionally, giant impacts originated lithosphere thickness and density differences, which might contribute to the initiation of subduction. Impacts are more energetic for Earth than for Mars, which could explain the likely early existence of plate tectonics on the Earth whereas Mars never had lithosphere recycling. On the other hand, convection on Mercury and the Moon might be sluggish or even inexistent, implying a reduced influence of giant impacts on their internal dynamics, whereas there is no record of the earliest geological history of Venus, which obscures any discussion on the influence of giant impacts on their internal dynamics.

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1981-01-01

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

  9. 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.

  10. California takes earthquakes very seriously. The state straddles two major tectonic plates and is subject to relatively frequent, often major, potentially devastating quakes.

    E-print Network

    California takes earthquakes very seriously. The state straddles two major tectonic plates the Pacific and North American tectonic plates. The Pacific Plate includes a sliver of California and Baja California, as well as Hawaii and most of the Pacific Ocean, while the North American Plate includes

  11. Continental Margin Tectonics Along the Convergent Plate Boundary of Central Chile

    NASA Astrophysics Data System (ADS)

    Weinrebe, W.; Ranero, C. R.; Diaz, J.; Reichert, C.; Vera, E. E.

    2003-12-01

    Multibeam bathymetry along central Chile provides a detailed map of recent tectonic deformation of the margin and incoming oceanic plate from about 28? S to 36? S. The data were collected during R/V SONNE cruises 101, 102, 104 and 161 and a cruise with R/V Vidal Gormaz. Individual pings were edited and cleaned and the different surveys have been merged after depth calculations using a different measured velocity function for each of them. The oceanic Nazca plate is covered by about 100 m of pelagic sediment and the morphology of the igneous basement is displayed well in the bathymetric maps. The oceanic plate topography changes markedly along the subduction zone and exerts a first order control in the distribution of trench sediment infill and in the tectonic style of deformation of the margin. A major boundary occurs at latitude 32?-33? S where the hotspot volcanic chain of Juan Fernadez is currently subducting. The chain subducts oblique to the margin strike and thus the tectonic boundary has been migrating along the subduction zone through time. South of the area of ridge subduction the trench is filled with turbidites and a 20-40 km wide accretionary prism occurs at the front of the continental slope. The upper slope has a smooth morphology indicative of a quiet tectonic domain. At the current area of ridge subduction and north of it (28?-33?S) the trench has a reduced turbiditic infill. The trench infill seems to be at minimum at 31-32S and slightly larger to the north as the trench axis becomes deeper. Here, a small ridge at the slope toe may indicate that reduced accretion is active. The continental slope is deeper and more rugged that to the south displaying a series of small midslope basins. Here, the continental slope morphotectonic structure is the product of tectonic erosion due to the passage of the volcanic ridge.

  12. Plate tectonic model for the oligo-miocene evolution of the western Mediterranean

    NASA Astrophysics Data System (ADS)

    Cohen, Curtis R.

    1980-10-01

    This paper outlines a plate tectonic model for the Oligo-Miocene evolution of the western Mediterranean which incorporates recent data from several tectonic domains (Corsica, Sardinia, the Kabylies, Balearic promontory, Iberia, Algero-Provençal Basin and Tunisian Atlas). Following late Mesozoic anticlockwise rotation of the Iberian peninsula (including the Balearic promontory and Sardinia), late Eocene collision occurred between the Kabylies and Balearic promontory forming a NE-trending suture with NW-tectonic polarity. As a result of continued convergence between the African and European plates, a polarity flip occurred and a southward-facing trench formed south of the Kabylie—Balearic promontory suture. During late Oligocene time an E-W-trending arc and marginal basin developed behind the southward-facing trench in the area of the present-day Gulf of Lion. Opening of this basin moved the Corsica—Sardinia—Calabria—Petit Kabylie—Menorca plate southward, relative to the African plate. Early Miocene back-arc spreading in the area between the Balearic promontory and Grand Kabylie emplaced the latter in northern Algeria and formed the South Balearic Basin. Coeval with early Miocene back-arc basin development, the N-S-extension in the Gulf of Lion marginal basin changed to a more NW-SE direction causing short-lived extension in the area of the present-day Valencia trough and a 30° anticlockwise rotation of the Corsica-Sardinia-Calabria—Petit Kabylie plate away from the European plate. Early—middle Miocene deformation along the western Italian and northeastern African continental margins resulted from this rotation. During the early late Miocene (Tortonian), spreading within a sphenochasm to the southwest of Sardinia resulted in the emplacement of Petit Kabylie in northeastern Algeria.

  13. Petroleum formation by Fischer-Tropsch synthesis in plate tectonics

    SciTech Connect

    Szatmari, P. (Petrobras Research Center, Rio de Janeiro (Brazil))

    1989-08-01

    A somewhat speculative hypothesis of petroleum genesis in the upper lithosphere is proposed, based on Fischer-Tropsch synthesis. This hypothesis is distinct from both the organic (biogenic) model and the inorganic model of hydrocarbon degassing from the Earth's interior. The hypothesis presented in this paper proposes that petroleum liquids form by Fischer-Tropsch synthesis on magnetite and hematite catalysts when carbon dioxide (derived by massive metamorphic or igneous decarbonation of subducted sedimentary carbonates) reacts with hydrogen generated by the serpentinization (in the absence of air) of shallow-mantle lithosphere and ophiolite thrust sheets. Oblique plate movements may favor hydrocarbon formation by creating deep faults that aid fluid flow and serpentinization. The world's richest oil provinces, including those of the Middle East, may be tentatively interpreted to have formed by this mechanism. 8 figs., 1 tab.

  14. Changes in electrical resistivity track changes in tectonic plate coupling

    NASA Astrophysics Data System (ADS)

    Heise, Wiebke; Caldwell, T. Grant; Bertrand, Edward A.; Hill, Graham J.; Bennie, Stewart L.; Ogawa, Yasuo

    2013-10-01

    coupling on the Hikurangi subduction margin along the east coast of New Zealand's North Island changes north to south from almost uncoupled to locked. Clay-rich sediments and aqueous fluids at the subduction interface have been invoked as key factors in the frictional processes that control interplate coupling. Here we use magnetotelluric data to show that the subduction interface in the weakly coupled region is electrically conductive but is resistive in the locked region. These results indicate the presence of a layer of fluid- and clay-rich sediments in the weakly coupled region and support the idea that the presence of fluid and hydrated clays at the interface is a major factor controlling plate coupling.

  15. 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.

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

    Microsoft Academic Search

    Daniel Jean Stanley

    1982-01-01

    The first major offshore boundary dispute where plate tectonics constituted a significant argument was recently brought before\\u000a the International Court of Justice by Libya and Tunisia concerning the delimitation of their continental shelves. Libya placed\\u000a emphasis on this concept to determine natural prolongation of its land territory under the sea. Tunisia contested use of the\\u000a entire African continental landmass as

  17. 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.

  18. An Integrated Alternative Conceptual Framework to Heat Engine Earth, Plate Tectonics, and Elastic Rebound

    Microsoft Academic Search

    STAVROS T. TASSOS; DAVID J. FORD

    2005-01-01

    Physical evidence indicates that a thermally driven Earth, plate tectonics, and elastic rebound theory violate fundamental physical principles, and that Earth is a quantified solid body, the size of which possibly increases with time. Earth's core is considered as a low-temperature, high-energy\\/high- frequency, high-tension material, wherein new elements form, constituting the Excess Mass (EM), which is then added atom-by-atom to

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

    PubMed

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

    2013-06-27

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

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

    Microsoft Academic Search

    Robert Hall

    2002-01-01

    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

  1. Seismological studies of the tectonics of divergent plate boundaries

    Microsoft Academic Search

    J. F. Engeln

    1985-01-01

    Earthquakes on major Atlantic transform faults were studied. Most of the events show transform-parallel strike-slip motion on steeply dipping planes. A number of earthquakes with anomalous mechanisms occur near ridge-transform intersections where the thermal contrast is greatest and stress orientations can be oblique to both the ridge and transform. Centroid depths, determined by body wave waveform inversion, occur above the

  2. High-resolution global upper mantle structure and plate tectonics

    Microsoft Academic Search

    Yu-Shen Zhang; Toshiro Tanimoto

    1993-01-01

    A global high-resolution S wave velocity model RG5.5 is obtained for the upper 500 km of Earth's mantle using a 5 x 5 deg equal-area block parameterization. The data set consists of some 18,000 seismograms associated with 971 events with magnitudes larger than 5.5. Fundamental modes are used with periods from 75 to 250 s. The horizontal resolution length is

  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 differences in magmatic and tectonic. styles of Hijaz orogenesis from those of the Pan-African and the temporal break between them in much of the southern part of the Arabian Shield support division into at least two events. As defined by the ages of major plutonic units, the axis of magmatic and tectonic activity migrated eastward or northeastward during the Hijaz cycle, the predominantly dioritic plutonic rocks becoming younger and more siliceous to the east. Granodiorite to granite pl}.1tonism of the Pan-African event, however, shows no geographic bias, being distributed throughout the Arabian Shield. Although the Hijaz diorites and Pan-African granitic rocks exhibit strong contrasts in composition and age differences as great as 250 m.y. in the westernmost parts of the area, the two groups are less distinct compositionally and nearly the same age in the eastern part.

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

    NASA Astrophysics Data System (ADS)

    Davaille, Anne

    2015-04-01

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

  5. 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 be. The map is designed to show the most prominent features when viewed from a distance, and more detailed features upon closer inspection. The back of the map zooms in further, highlighting examples of fundamental features, while providing text, timelines, references, and other resources to enhance understanding of this dynamic planet. Both the front and back of this map illustrate the enormous recent growth in our knowledge of planet Earth. Yet, much remains unknown, particularly about the processes operating below the ever-shifting plates and the detailed geological history during all but the most recent stage of Earth's development.

  6. A plate-tectonic model for the Mesozoic and Early Cenozoic history of the Caribbean plate

    Microsoft Academic Search

    Martin Meschede; Wolfgang Frisch

    1998-01-01

    We present a model in which the Caribbean plate is an intra-American feature formed along the Caribbean spreading center as opposed to the current model that considers the Caribbean plate as a far-travelled crustal segment that formed in the Pacific region. Paleomagnetic data, which cover an age range from Jurassic through Paleocene, indicate the ophiolite complexes in Costa Rica and

  7. A model of present-day tectonic plate motions from 12 years of DORIS measurements

    NASA Astrophysics Data System (ADS)

    Soudarin, Laurent; Crétaux, Jean-François

    2006-11-01

    In the frame of the International DORIS Service (IDS), the Laboratoire d’Etudes en Géophysique et Océanographie Spatiales (LEGOS)/ Collecte Localisation Satellites (CLS) Analysis Center (LCA) processes DORIS measurements from the SPOT, TOPEX/Poseidon and Envisat satellites and provides weekly station coordinates of the whole network to the IDS. Based on DORIS measurements, the horizontal and vertical velocities of 57 DORIS sites are computed. The 3D positions and velocities of the stations with linear motion are estimated simultaneously from the 12-year (1993 2004) combined normal equation matrix. We include 35 DORIS sites assumed to be located in the stable zones of 9 tectonic plates. For the motion of these plates, we propose a model (LCAVEL-1) of angular velocities in the ITRF2000 reference frame. Based on external comparison with the most recent global plate models (PB2002, REVEL, GSRM-1 and APKIM2000) and on internal analysis, we estimate an average velocity error of the DORIS solution of less than 3 mm/year. The LCAVEL-1 model presents new insights of the Somalia/Nubia pair of plates, as the DORIS technique has the advantage of having a few stations located on those two plates. We also computed (and provide in this article) the horizontal motion of the sites located close to plate boundaries or in the deformation zones defined in contemporary models. These computations could be used in further analysis for these particular regions of the Earth not moving as rigid plates.

  8. Mars Plate Tectonics: Surface Geology and Analyses of Topographic and Geophysical Data

    NASA Astrophysics Data System (ADS)

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

    2001-12-01

    We propose plate tectonism for the embryonic stage (Early Noachian) of development of Mars to help explain distinct features and landforms (also see Maruyama et al. and Baker et al., this volume), including the long-lived Tharsis magmatic complex. The Tharsis magmatic complex has been recently recognized as an Earth-like superplume (GSA Boston meeting, 2001--Maruyama et al., 2001; Baker et al., 2001; and Dohm et al., 2001), similar to the proposed long-lived, fixed mantle/core-sourcing wet Africa and Pacific superplumes of Earth (Maruyama, 1994, J. Geol. Soc. Japan, v. 100, 24-49; Fukao et al., 1994, J. Geol. Soc. Japan, v. 100, 4-23). Other features and landforms of Mars that may be collectively explained by an Early Noachian plate tectonic phase include: (1) the ancient mountain range of Thaumasia highlands (Dohm and Tanaka, 1999, Planetary and Space Science, v 47, 411-431), (2) the highland-lowland boundary (e.g., Scott and Tanaka, 1986, USGS I-Map 1802-A), (3) tectonic macrostructures, many of which are interpreted to be thrust structures (e.g., Schultz and Tanaka, 1994, J. Geophys. Res., v. 99, 8371-8385), (4) circular domes located near the southwestern margin of the Thaumasia plateau (Dohm and Tanaka, 1999, Planetary and Space Science, v 47, 411-431), many of which (a) occur among the tectonic macrostructures of (3), (b) are interpreted to represent explosive volcanism (e.g., andesitic constructs), and (c) are considered to mark former zones of subduction, and (5) gravity and magnetic anomalies identified in parts of the northern plains and Terra Cimmeria and Terra Sirenum regions (Acuna et al., 1999, Science, v. 284, 790-793; Yuan et al., in press, J. Geophys. Res., Planets), which may symbolize former remnant ocean plates with hotspot tracks of island arcs that are transparent through thick sedimentary covers and zones of accreted terrains, respectively.

  9. Neogene tectonic stress fields of northeast Honshu Arc and implications for plate boundary conditions

    NASA Astrophysics Data System (ADS)

    Otsuki, Kenshiro

    1990-09-01

    More than 3300 metalliferous veins were analyzed to reconstruct the Neogene tectonic stress field of the northeast Honshu Arc using basic fracture mechanics. The veins are grouped into a dominant NE system and subordinate E-W, N-S and NW systems. The NE system is associated with assemblages of conjugate strike-slip faults and extension joints or normal faults which were formed during a period from 15 to 5 Ma. The fractures suggest that ?1or?2 was oriented ENE and ?3 was oriented NNW. ?3 is thought to have been tensional, because no veins are associated with thrust faults. This stress orientation is neither perpendicular nor parallel to the axis of the Japan Trench where the Pacific plate was moving west-northwest and was subducted under the northeast Honshu Arc. The inconsistency between the stress orientation and the plate kinematics can be explained by the dynamic effects related to other plate boundaries surrounding the northeast Honshu Arc, namely compression on the Hokkaido Axial Zone and the Itoigawa-Shizuoka Tectonic Line. In addition, the triple junction of the Japan Trench, Izu-Bonnin Trench and the Sagami Trough was probably located 300-400 km northeast from its present position and the subduction zone of Nankai Trough-Sagami Trough is assumed to have been a tensional plate boundary. The reconstructed stress field is consistent with transtensional backarc rifting at about 15 Ma.

  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 remnants of such marginal basins. The portion of the Philippine Sea Plate carrying the Taiwan-Philippine arc and its composite ophiolitic/continental crustal basement might have actually originated in a different setting, closer to that of the Papua New Guinea Ophiolite, and then have been displaced rapidly as a result of shearing associated with fast oblique convergence.

  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. Relating plate tectonics, mantle convection and variations in paleomagnetic reversal frequency

    NASA Astrophysics Data System (ADS)

    Choblet, Gael; Amit, Hagay; Husson, Laurent

    2014-05-01

    Mantle control through time-dependent CMB heat flux pattern and magnitude is a possible external cause to variable reversal frequency of the geodynamo. Necessary CMB heat flux characteristics for reversals in numerical dynamos include most notably a strong average value and a heat flux larger than average at low latitudes. Since plate tectonics affect mantle convection, and thus CMB heat flux and core dynamics, they constitute a possible influence on reversal frequency . We perform numerical experiments of mantle convection with a prescribed plate velocity history at the surface and analyze the time evolution of CMB heat flux in the light of specific criteria promoting or inhibiting reversals. These are systematically compared to the observed reversal frequency for the Earth. The main parameters we investigate for mantle convection are the rheology and the nature of a possibly denser layer in the lowermost region of the mantle. Our study includes a larger number of mantle convection models than previously considered by the few pioneering studies on the same topic and lead to methodological conclusions concerning which of the CMB heat flux criteria are most pertinent and on the time period during which a comparison with paleomagnetic data is meaningful. Preferred mantle models as well as general considerations on the buffering effect of mantle dynamics between plate tectonics and CMB heat flux will be presented. Combining paleomagnetic observations, models for the time-evolution of plate tectonics, inferences from numerical dynamos and mantle convection simulations, our results may provide an important constraint on the structure and dynamics of Earth's mantle.

  14. Relating plate tectonics, mantle convection and variations in paleomagnetic reversal frequency

    NASA Astrophysics Data System (ADS)

    Choblet, G.; Amit, H.

    2013-12-01

    Mantle control through time-dependent CMB heat flux pattern and magnitude is a possible external cause to variable reversal frequency of the geodynamo. Necessary CMB heat flux characteristics for reversals in numerical dynamos include most notably a strong average value and a heat flux larger than average at low latitudes. Since plate tectonics affect mantle convection, and thus CMB heat flux and core dynamics, they constitute a possible influence on reversal frequency . We perform numerical experiments of mantle convection with a prescribed plate velocity history at the surface and analyze the time evolution of CMB heat flux in the light of specific criteria promoting or inhibiting reversals. These are systematically compared to the observed reversal frequency for the Earth. The main parameters we investigate for mantle convection are the rheology and the nature of a possibly denser layer in the lowermost region of the mantle. Our study includes a larger number of mantle convection models than previously considered by the few pioneering studies on the same topic and lead to methodoligical conclusions concerning which of the CMB heat flux criteria are most pertinent and on the time period during which a comparison with magnetic data is meaninful. Preferred mantle models as well as general considerations on the buffering effect of mantle dynamics between plate tectonics and CMB heat flux will be presented. Combining paleomagnetic observations, models for the time-evolution of plate tectonics, inferences from numerical dynamos and mantle convection simulations, our results may provide an important constraint on the on the structure and dynamics of Earth's mantle.

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

    NASA Astrophysics Data System (ADS)

    Yamato, Philippe; Husson, Laurent

    2015-04-01

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

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

    SciTech Connect

    Van Summeren, Joost; Conrad, Clinton P.; Gaidos, Eric, E-mail: summeren@hawaii.edu [Department of Geology and Geophysics, University of Hawaii at Manoa, Honolulu, HI 96822 (United States)

    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.

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

    SciTech Connect

    Reusch, D. (Maine Geological Survey, Augusta, ME (United States))

    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.

  18. 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 thousand kilometers. Remnants of basins with oceanic crust found in the inner areas of the Verkhoyansk-Kolyma Mesozoides indicate that they are more comparable to present-day marginal seas of eastern Asia than to the open Pacific Ocean. Early folding occurred as a result of the pre-mid-Jurassic attachment of the Prikolyma and Omolon terranes to the Alazeya arc, which led to the formation of the large, heterogeneous, Kolyma-Omolon microcontinent. Later folding was due to a collision of the Kolyma-Omolon microcontinent with the Omulevka platform and the Verkhoyansk passive margin. This deformation propagated from the inner (Cherskiy) areas, in Bathonian time, towards the Siberian platform, where it culminated in frontal thrusts in the latest Cretaceous. Transverse and longitudinal belts of Upper-Mesozoic granitoids are closely related to collision processes. Their long history (about 90 m.y.) reflects the duration of the collision.

  19. An alternative plate tectonic model for the Palaeozoic–Early Mesozoic Palaeotethyan evolution of Southeast Asia (Northern Thailand–Burma)

    Microsoft Academic Search

    O. M. Ferrari; C. Hochard; G. M. Stampfli

    2008-01-01

    An alternative model for the geodynamic evolution of Southeast Asia is proposed and inserted in a modern plate tectonic model. The reconstruction methodology is based on dynamic plate boundaries, constrained by data such as spreading rates and subduction velocities; in this way it differs from classical continental drift models proposed so far. The different interpretations about the location of the

  20. Thrust -wrench interference tectonics in the Gulf of Cadiz (Africa -Iberia plate boundary in the North-East Atlantic): insights from

    E-print Network

    Paris-Sud XI, Université de

    Thrust - wrench interference tectonics in the Gulf of Cadiz (Africa - Iberia plate boundary to a segment of the Africa- Eurasia plate boundary previously described as tectonically diffuse (e.g. Sartori key segment of the Africa-Iberia plate boundary (North- East Atlantic ocean), three main different

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

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

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

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

    USGS Publications Warehouse

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

    1973-01-01

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

  3. 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 that is broadly consistent with geologically based reconstructions of production rate variations. From the new reconstructions, a consistent decrease of total oceanic heat flow by ~ -0.25%/Myr over the last 140~Ma is inferred. Our study provides some of the required input for 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.

  4. 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 38, L21201. [5] Foley, B.J., Bercovici, D. and Landuyt, W. (2012), EPSL 331-332, 281-290. [6] Korenaga, J. (2010), Astrophys. J. Let. 725, L43-L46. [7] Hüttig, C. and K. Stemmer (2008), PEPI 171, 137-146. [8] Stamenkovic, V.; L. Noack, D. Breuer and T. Spohn (2012), Astroph. J. 748(1), 41.

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

    NASA Astrophysics Data System (ADS)

    Stanley, Daniel Jean

    1982-03-01

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

  6. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

  8. 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. (Empresa Colombiana de Petroleos, Santafe de Bogota (Colombia))

    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.

  9. Tectonic plate under a localized boundary stress: fitting of a zero-range solvable model

    E-print Network

    Petrova, L

    2008-01-01

    We suggest a method of fitting of a zero-range model of a tectonic plate under a boundary stress on the basis of comparison of the theoretical formulae for the corresponding eigenfunctions/eigenvalues with the results extraction under monitoring, in the remote zone, of non-random (regular) oscillations of the Earth with periods 0.2-6 hours, on the background seismic process, in case of low seismic activity. Observations of changes of the characteristics of the oscillations (frequency, amplitude and polarization) in course of time, together with the theoretical analysis of the fitted model, would enable us to localize the stressed zone on the boundary of the plate and estimate the risk of a powerful earthquake at the zone.

  10. Tectonic plate under a localized boundary stress: fitting of a zero-range solvable model

    E-print Network

    L. Petrova; B. Pavlov

    2008-01-18

    We suggest a method of fitting of a zero-range model of a tectonic plate under a boundary stress on the basis of comparison of the theoretical formulae for the corresponding eigenfunctions/eigenvalues with the results extraction under monitoring, in the remote zone, of non-random (regular) oscillations of the Earth with periods 0.2-6 hours, on the background seismic process, in case of low seismic activity. Observations of changes of the characteristics of the oscillations (frequency, amplitude and polarization) in course of time, together with the theoretical analysis of the fitted model, would enable us to localize the stressed zone on the boundary of the plate and estimate the risk of a powerful earthquake at the zone.

  11. 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.

  12. Tectonics and plate boundary processes along the Southeast Indian Ridge and the East Pacific Rise

    NASA Astrophysics Data System (ADS)

    Conder, James Andrew

    Classical plate tectonics describes crustal deformation in a simple kinematic way, with deformation occurring only at narrow boundaries of plates with rigid interiors. Many dynamic processes at these boundaries are not well understood. There are also apparent deviations from classical plate tectonics where significant intraplate deformation occurs. In this thesis, we analyze and model geophysical data from the Southeast Indian Ridge (SEIR) and the East Pacific Rise (EPR) to address some of these issues. Hotspots often affect the dynamics of nearby spreading centers. As shown by bathymetry, side-scan sonar, and magnetic anomaly data, the Amsterdam-St. Paul (ASP) hotspot has altered the spreading history and geometry of nearby SEIR spreading axes. The hotspot thickened the oceanic crust near the spreading center and reorganized the plate boundary through rift propagation and ridge jumps, creating the youngest known transform fault in the process. The region near the ASP plateau has been suggested as where a wide, diffuse, NW-SE trending oceanic plate boundary meets the SEIR. Using data from the SEIR, we perform a statistical analysis and examine predictions of the model to test its validity. The boundary is not confirmed on statistical grounds, but evidence suggests that it does exist. However, it does not extend south of the St. Paul Fracture Zone, narrowing the previously proposed boundary by 800 km where it meets the SEIR. We also test the hypothesis that deformation near the eastern end of the SEIR, including a large intraplate earthquake can be explained by an additional plate boundary. If the earthquake lies on a plate boundary, its sense of slip should be right-lateral rather than the observed left-lateral motion, ruling out the hypothesis. Asymmetric geophysical properties of the EPR near 17°S suggest more melt beneath the Pacific side than the Nazca side. Numerical modeling results indicate that the asymmetry may be produced by pressure-driven across-axis mantle flow from the Pacific superswell. Across-axis flow extends upwelling and melting to the west of the axis, but limits upwelling to the east, shutting off melting and accounting for the observed asymmetry.

  13. A revised plate tectonic model for the western Tethys from Paleozoic to Cretaceous

    NASA Astrophysics Data System (ADS)

    Stampfli, G. M.; Borel, G. D.

    2003-04-01

    In the light of a broad array of new data going from deep seismic to detailed field work , we reconsidered the geodynamic evolution of the Adria and Apulia micro-continents in space and time. This evolution has been described in many ways so far, rich with controversies, but recent approaches have shown that more could be added, mainly in the field of plate tectonics, supported by new geophysical datasets. The main concern is the Late Palaeozoic and Mesozoic evolution of terrains that were separated and united several times, but always with a large component of lateral displacement. A key point is the age of the East Mediterranean-Ionian sea basin, and the nature of the sea-floor in this area. This, in turn, influences the way that continental re-assembly for the Mesozoic can be done. An agreement is now emerging about the Permo-Triassic age of the E-Mediterranean-Ionian sea floor and its direct connection with the Neotethys. A new continental fit was built up in an attempt at reconciling plate tectonics with geophysical data, it differs significantly from previous proposed models, mainly regarding the position of Adria. This new model is based on the necessity for having already a close to the present day position of Adria versus Apulia already since Late Triassic times. This, in turn influences the scenario for the opening and closing of the Alpine Tethys, keeping in mind that Iberia followed the wander path of Africa during most of the Cretaceous period.

  14. C:/ITOOLS/WMS/CUP-NEW/2476231/WORKINGFOLDER/KKE/9780521897150C07.3D 95 [95114] 10.1.2011 9:06PM Next-generation plate-tectonic reconstructions

    E-print Network

    Torsvik, Trond Helge

    Next-generation plate-tectonic reconstructions using GPlates james a. boyden, r. dietmar mu¨ ller s. cannon 7.1 Introduction Plate tectonics is the kinematic theory that describes the large and interactions of large, rigid, interlocking fragments of lithosphere called tectonic plates. Plates form

  15. 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 (near Burma) causing anticlockwise rotation/retreat of the margin until collision between the main portion of Greater India and central Eurasian margin took place ~36 Ma. This relatively young collision between India and Eurasia is supported by subduction-related magmatism, which continued into the Late Eocene. The Upper Eocene Pengqu Formation also suggests that marine conditions prevailed south of the suture zone until that time, while the Upper Oligocene to Lower Miocene Gangrinboche conglomerates mark the initial mixing and deposition of both Eurasian and Indian-sourced sediments.

  16. Marine Magnetic Anomaly Compilations in the Indian Ocean for Plate Tectonics and Beyond (Invited)

    NASA Astrophysics Data System (ADS)

    Dyment, J.; Bhattacharya, G. C.; Vadakkeyakath, Y.; Bissessur, D.; Jacob, J.; Kattoju, K. R.; Ramprasad, T.; Royer, J.; Patriat, P.; Chaubey, A. K.; Srinivas, K.; Choi, Y.

    2009-12-01

    The French territories in the western and southern parts of the Indian Ocean (i.e. Reunion and Mayotte islands, islands in the Mozambique Channel, Kerguelen and Crozet archipelagos, Saint Paul and Amsterdam islands…) have triggered significant scientific activities, including marine geophysics, by French scientists in this area. French marine magnetic data in this ocean span more than four decades, with records as old as 1966 and as recent as early 2009. Similarly, Indian scientists have collected a large amount of geophysical data in the northern Indian Ocean, with a focus on the Arabian Sea, the Bay of Bengal, the Central Indian Basin, and surrounding areas. To take advantage of the obvious complementarity of the French and Indian data sets for plate tectonics studies, we have conducted two projects funded by the Indo-French Centre for the Promotion of Advanced Research, the first one regarding the Arabian and eastern Somali basins, the second one the Central Indian, Madagascar and Crozet basins. These projects have been complemented by more localized work over the Mascarene Basin and Wharton basins, both characterized by an abandoned spreading centre. The purpose of this presentation is to show how such a compilation is being used to conduct plate tectonic studies, from the identification of the magnetic anomalies to their unambiguous picking using the analytic signal, the construction of isochrons and tectonic chart, and the paleogeographic reconstructions. Beyond this classical use, the compiled data can be used to produce magnetic anomaly grids and maps in areas with sufficient data coverage: such grids may help to improve and/or complement future versions of the World Digital Magnetic Anomaly Map (WDMAM).

  17. 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.

  18. 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.

  19. Parameters controlling dynamically self-consistent plate tectonics and single-sided subduction in global models of mantle convection

    NASA Astrophysics Data System (ADS)

    Crameri, Fabio; Tackley, Paul J.

    2015-05-01

    Recent advances in numerical modeling allow global models of mantle convection to more realistically reproduce the behavior at convergent plate boundaries; in particular, the inclusion of a free surface at the outer boundary has been shown to facilitate self-consistent development of single-sided subduction. This allows for a more extensive study of subduction in the context of global mantle convection, as opposed to commonly used regional models. Our first study already indicated important differences between mantle convection with single-sided subduction and mantle convection with double-sided subduction. Here we further investigate the effect of various physical parameters and complexities on inducing Earth-like plate tectonics and its evolution in time. Results reinforce the previous finding that using a free surface instead of a free-slip outer boundary dramatically changes subduction style, with free surface cases displaying many episodes of single-sided subduction, which leads to more realistic slab dip, stress state, trench retreat rate, and slab-induced mantle flow. Longevity of single-sided subduction is promoted by a layer of hydrated crust with a low yield strength to lubricate the subduction channel, a low-viscosity asthenosphere, and a high strength of the slab (determined by a combination of high-diffusion creep viscosity and intermediate friction coefficient), although its effective viscosity is in the observationally constrained range in the bending region. The time evolution displays interesting events including subduction polarity reversals, subduction shut-off, and slab break-off.

  20. 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, primarily delineated by seismicity, bathymetric profiles and E-W thrust mechanisms. In our preferred model, the Philippine Mobile Belt can be represented by at least 12 independently moving rigid tectonic blocks, separated by active faults and subduction zones.

  1. 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.

  2. Evidence for relative motions between the Indian and Australian Plates during the last 20 m.y. From plate tectonic reconstructions: Implication for the deformation of the Indo-Australian plate

    Microsoft Academic Search

    Jean-Yves Royer; Ted Chang

    1991-01-01

    We use plate tectonic reconstructions to establish whether motions between India and Australia occurred since chron 18 (43 Ma). We test the Africa\\/Antarctica\\/Australia\\/India plate circuit closure at chrons 5 (10 Ma), 6 (21 Ma) and 13 (36 Ma) using a complication of magnetic anomalies and fracture zone traces from the Southeast, Southwest, Central Indian and the Carlsberg ridges. Additional reconstructions

  3. 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 the shallow mantle due to viscosity variations with the loss of hydrogen upon melting (Faul and Jackson, JGR 2007; Korenaga and Karato, JGR 2008). In this work we present a set of 2D spherical annulus simulations (Hernlund and Tackley, PEPI 2008) using StagYY (Tackley, PEPI 2008), which uses a finite-volume scheme for advection of temperature, a multigrid solver to obtain a velocity-pressure solution at each timestep, tracers to track composition, and a treatment of partial melting and crustal formation. We address the question whether melting-induced crustal production changes the critical yield stress needed to obtain mobile-lid behaviour as a function of governing parameters. Our results show that melting and crustal production strongly influence plate tectonics on terrestrial planets, by making plate tectonics both easier and harder; i.e., for the same yield stress and reference viscosity the use or not of a treatment for melting and crustal production may result in a change from a stagnant-lid regime into an episodic-lid regime or a change from mobile-lid regime to an episodic-lid regime. Several factors can play a role on these, namely lateral heterogeneities and differences in the lid thickness induced by melting and crustal production, the maximum depth of melting, etc.

  4. 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 investigators); 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.

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

    E-print Network

    Jura, M; Xu, S; Young, E D

    2014-01-01

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

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

    Microsoft Academic Search

    J. R. Delaney

    2003-01-01

    Deformation and volcanic activity in a plate tectonic framework must result in fluid, and therefore nutrient, fluxes within the upper oceanic crust, and between the oceanic crust and the deep ocean. These fluxes support microbial activity of many types, but the linkages are difficult to define and the magnitude of the overall process is extremely difficult to characterize and quantify

  7. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2004-12-01

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

  9. Magnetic anomalies and early plate tectonics at Lamont-Doherty Geological Observatory

    NASA Astrophysics Data System (ADS)

    Heirtzler, J. R.

    1991-02-01

    A marine magnetics program was begun at Lamont Geological Observatory in the late 1950's. It consisted of developing the magnetometers, acquiring data from all the oceans, establishing computer processing techniques, and new interpretative methods. Areas off the east coast of North America and over the Reykjanes Ridge showed the linear nature of the magnetic anomalies. The Mid-Atlantic Ridge showed a characteristic anomaly over its entire length. A long magnetic profile obtained in the South Pacific showed that the anomalies were symmetric about the ridge axis and were caused by the same sequence of magnetic bodies as were the anomalies of the Reykjanes Ridge. Similar sequences of anomalies were found in all the oceans and they were best interpreted in terms of the Vine-Matthews-Morley theory of seafloor spreading. The history of the Indian, South Pacific, South Atlantic, and North Atlantic Oceans, the Galapagos, and other areas was published, ushering in the age of plate tectonics. The history of geomagnetic reversals for the last 75 million years was revealed and the age of the sediment layers of the ocean could then be determined with this geomagnetic chronology. These results, which were first made public in 19S7, provided much excitement in the scientific community and much interaction among different disciplines. It is here suggested that the rotational motion of the earth could be the ultimate cause of tectonic plate motion, the behavior of the geomagnetic field, variations of climate and the extinction of certain species. A large extraterrestrial impact could perturb all of these phenomena.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    Europa is the primary target in NASA's future outer solar system exploration strategy. A tidally heated global ocean beneath its ice shell is important for astrobiological considerations; however, habitability requires a source of chemical nutrients. Europa's radiolytically processed surface is a potential source, but a means of delivery of compounds to the ocean is required. Past studies of Europa's surface have been unable to explain an abundance of extensional features (e.g., dilational bands) yet scant evidence of contraction. Moreover, the crater-based surface age (40-90 Myr) indicates one of the solar system's youngest surfaces, implying Europa's surface (3.09 x 107 km2) may have been recycled in this time frame (i.e., 0.3-0.8 km2 per year). We address this enigma by presenting evidence for subduction, and hence plate tectonics, on Europa. We reconstruct geologic features in a 106,000 km2 candidate region to show that the current surface configuration involved numerous translations and rotations of rigid plates. The reconstruction reveals ~100 km of missing surface that seemingly vanished along a 20-km-wide, band-like zone with unusual color characteristics. Mismatching geological features across this zone suggest an ~80-km-wide region may have subducted along a ?300-km-long plate boundary. The subduction zone is arcuate, has no topographic expression at image resolutions, and is partially bounded by transform faults. The overriding plate has numerous strike-slip faults consistent with strain partitioning related to oblique convergence. The surface of the overriding plate is also pervasively dotted with isolated patches of disrupted terrain, which we interpret as erupted cryolava, implying a significant subsurface thermal perturbation related to the potential subduction. If a subduction model for Europa is accurate, buoyancy constraints and a lack of contractional topography imply that the subducting slab does not enter the ocean directly. We thus interpret a thin (~several km), brittle lid overlying a thicker, convecting ice layer, with plate motions and subduction restricted to the brittle lid. The subducting plate is presumably consumed at a rate conducive to complete subsumption into the convecting layer. On Earth, oceanic lithosphere recycling occurred along 55,000 km of subduction zones in <200 Myr at 20-80 mm/yr. On Europa, similar subduction rates (11-26 mm/yr), if valid, are possible for 30,000 km of subduction boundaries. Europa's surface area (~6% of Earth's) would accordingly recycle over a shorter time frame, consistent with the surface age. Our work potentially provides a new paradigm for interpreting Europa's surface features and age, and provides a mechanism to deliver nutrients from the surface to the ocean: crucial for astrobiology and habitability. If subduction exists, Europa would become the only other solar system body beyond Earth to exhibit plate tectonics, involving subduction (surface area removal), mid-ocean-ridge-like spreading (surface area creation at dilational bands), and transform motions. Such motions are presumably driven by convection in the deeper, warmer ice, evidenced by thermal upwellings at sites of chaos and lenticulae.

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

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

    SciTech Connect

    Orzag-Sperber, F.; Rouchy, J.M. (Universite Paris XI, Orsay (France))

    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.

  13. 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

    The geometry and age progression of Emperor and Hawaii seamounts provide compelling evidence for a major change in Pacific plate motion over a short period of geological time at c. 50 Ma. This time approximately coincides with significant changes in plate boundary configuration and rate in the Indian Ocean, Antarctica, and with the onset of subduction zones in the western Pacific from Japan to New Zealand. This new subduction system that initiated during Eocene time can be divided into two sectors: The northern sector formed at the eastern boundary of the Philippine Sea plate and evolved into the Izu-Bonin-Mariana system. It has and is being extensively studied (2014 IODP expedition 351) to determine the magmatic products, but is limited in the record that is preserved because it is entirely intra-oceanic in character. The southern sector, the Tasman Area sector, borders continental fragments of Gondwana from Papua New Guinea, New Caledonia and New Zealand. This subduction zone evolved into the Tonga-Kemadec system. Because most of the southwest Pacific remained in marine conditions throughout Paleogene time and because rapid seawards roll-back of the subduction is inferred to have happened, it presents extensive well-preserved stratigraphic records to study the Eocene-Oligocene plate boundary evolution. The recent compilation of c. 100.000 km of 2D seismic data in the Tasman Frontier database has allowed us to describe, in the overriding plate of the proto subduction, stratigraphic evidence for large Cenozoic vertical movements (2-4 km) over a lateral extension of 2000 km (from New Caledonia to New Zealand), long-wavelength (~500 km) warping and large amounts of reverse faulting and folding near the proto-trench. These recent observations from the Lord Howe Rise, New Caledonia Trough and South Norfolk Ridge system reveal clear evidence for convergent deformation (uplift and erosion) and subsequent subsidence recorded in Eocene and Oligocene stratal relationships. 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.

  14. 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 hydrogen upon melting (Faul and Jackson, JGR 2007; Korenaga and Karato, JGR 2008). We present a set of 2D spherical annulus simulations (Hernlund and Tackley, PEPI 2008) using StagYY (Tackley, PEPI 2008), which uses a finite-volume scheme for advection of temperature, a multigrid solver to obtain a velocity-pressure solution at each timestep, tracers to track composition, and a treatment of partial melting and crustal formation. We address the question whether melting-induced crustal production changes the critical yield stress needed to obtain mobile-lid behaviour as a function of governing parameters. Our results show that melting and crustal production strongly influence plate tectonics on terrestrial planets. For the same parameters the use of a treatment for melting and crustal production facilitates breaking the stagnant-lid, replacing it with episodic-lid; however, a smoothly evolving mobile lid can also be replaced by episode-lid. Several factors can play a role on these, namely lateral heterogeneities, differences in the lid thickness and internal planetary temperatures induced by melting and crustal production.

  15. 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 hydrogen upon melting (Faul and Jackson, JGR 2007; Korenaga and Karato, JGR 2008). We present a set of 2D spherical annulus simulations (Hernlund and Tackley, PEPI 2008) using StagYY (Tackley, PEPI 2008), which uses a finite-volume scheme for advection of temperature, a multigrid solver to obtain a velocity-pressure solution at each timestep, tracers to track composition, and a treatment of partial melting and crustal formation. We address the question whether melting-induced crustal production changes the critical yield stress needed to obtain mobile-lid behaviour as a function of governing parameters. Our results show that melting and crustal production strongly influence plate tectonics on terrestrial planets. For the same parameters the use of a treatment for melting and crustal production facilitates breaking the stagnant-lid, replacing it with episodic-lid; however, a smoothly evolving mobile lid can also be replaced by episode-lid. Several factors can play a role on these, namely lateral heterogeneities, differences in the lid thickness and internal planetary temperatures induced by melting and crustal production.

  16. Time Variability in Cenozoic Reconstructions of Mantle Heat Flow: Plate Tectonic Cycles and Implications for Earth's Thermal Evolution

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

    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.

  17. 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

  18. 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

    2007-09-01

    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 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. PMID:17720806

  19. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    The interface between converging plates is made of kilometre-thick domains where slab and upper plate mantle materials are tectonically slicied within a matrix dominated either by (meta)sedimentary/crustal rocks or by serpentinite. The latter may correspond to supra-subduction mantle altered by uprising slab fluids. Once formed, these plate-interface domains act as hydrated low-viscosity layers where tectonic stress and fluid-mediated mass transfer are strongly focussed. Here we present the geochemical study of two plate-interface environments: (1) serpentinite-rich, represented by the high-pressure serpentinites of the Ligurian Alps (Erro-Tobbio and Voltri Units); (2) sediment-dominated top slab mélange, represented by de-serpentinized garnet peridotite and chlorite harzburgite bodies (hosting eclogite and metarodingite) embedded in paragneiss and micaschist from Cima di Gagnone (Adula Unit, Central Alps). The Ligurian serpentinites derive from oceanic and wedge mantle tectonically coupled and dragged to depth during Alpine subduction: they may represent the hydrated precursors of the Cima di Gagnone peridotites. The B, Pb and Sr isotopic composition of the above sets of rocks helps defining tectonic and mass transfer processes during accretion of slab and suprasubduction mantle rocks in plate-interface domains, and to retrieve the imprint of fluids from these settings, which that ultimately affect arc magmatism. The serpentinized peridotites from Erro-Tobbio (ET) show high B (10-30 ppm), delta11B (10-25 per mil), B/Nb ratio (>380) and limited enrichment in 206Pb/204Pb (18.17-18,51) and 87Sr/86Sr (0.7046- 0.7060). Scambelluri & Tonarini (2012) interpreted the B and Sr isotopic imprint of ET as representative of upper plate mantle altered by slab-fluids. The B contents (up to 30 ppm), delta11B (18-30 per mil), B/Nb ratio (>900) and 206Pb/204Pb (18.09-18.22) of the Voltri serpentinites are similar to ET. Their 87Sr/86Sr (0.7079 to 0.7105) is higher than ET. The garnet peridotite and harzburgite from Gagnone have low B (up to 9 ppm), low B/Nb (<100) and high Pb and Sr isotopic ratios (206Pb/204Pb up to 18.84; 87Sr/86Sr 0.7124). Eclogite and HP metarodingite in the Gagnone peridotite show comparable values. The host metasediments and gneiss show higher B (6-16 ppm), 206Pb/204Pb (up to 18.98) and 87Sr/86Sr (0.7275). than peridotites and mafic rocks. All the Gagnone rocks have negative delta11B (ultramafic and mafic rocks = 0 to -10 per mil; country rocks = -3 to -12 per mil). The Gagnone peridotites reveal geochemical mixing between ultramafic and host crustal reservoirs. Considering that these peridotites derive from serpentinized protoliths, we expect that the initial high 11B of serpentinites was modified by two combined processes: (1) serpentine dehydration, releasing heavy B to fluids, and (2) exchange between ultramafic rocks and sediment-derived subduction fluids during burial and exhumation. The geochemical signature of the Voltri serpentinites is indicative of interaction with slab fluids enriched in heavy B-rich and in crust-derived components, such as in mantle rocks which evolved atop of the subducting slab. This implies that the slices of the downgoing slab are emplaced early during their burial history atop of the subducting plate. The geochemical signature of peridotites and host metasediments from Gagnone, points to significant exchange between ultramafic bodies and host rocks during prograde subduction prior to peak metamorphism. This again indicates accretion to the plate interface of slab and wedge materials during an early stage of subduction. Moreover, Voltri and Gagnone represent distinct reservoirs, showing positive versus negative delta11B. Serpentinite-dominated settings, like Voltri, produce high B and 11B fluids which can explain 11B-enrichment of much Pacific arcs. Differently, the sediment- and gneiss-dominated Gagnone mélange shows high B, negative ?11B, high radiogenic Pb and Sr: fluids released from such a mélange fit the composition of lavas from convergent margins affecte

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

    SciTech Connect

    Villamil, T.; Arango, C. (Univ. of Colorado, Boulder, CO (United States))

    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.

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

    SciTech Connect

    Villamil, T.; Arango, C. [Univ. of Colorado, Boulder, CO (United States)

    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.

  3. From nanoparticles to plate tectonics : insights for laboratory experiments using colloidal dispersions

    NASA Astrophysics Data System (ADS)

    Davaille, A.

    2014-12-01

    We recently discovered a material, aqueous dispersions of colloidal nanoparticles, whose rheology depends strongly on solid particle fraction fp, being Newtonian at low fp, and presenting yield stress, shear thinning, elasticity, and brittle properties as fp increases. Moreover, the rheology is time-dependent, with shear stress causing damage, which can heal due to electrostatic interactions between the colloidal particles. The competition between damage and healing results in long-term weak zones. Such a behaviour is analogue to the rheology of mantle rocks as temperature decreases. We therefore undertake a systematic laboratory study of convection in such fluids, where the system is continuously cooled and dried from above and heated or not from below. As the dispersion is dried, a skin ("lithosphere") forms at the surface on the convective fluid, and instabilities develop on several scales as shear bands (0.01 mm-scale), folds (mm-scale), fractures (0.1-10 mm-scale), small-scale convection (cm-scale) and plates (2-20 cm-scale). The system always describes several dynamic regimes through time: an initially very soft lithosphere would result in a stagnant lid regime of convection, which can then evolve in episodic and/or partial subduction, sometimes continuous plate tectonics, and finally stagnant lid. Regime diagrams will be presented as a function of the effective rheology of lithosphere. This "effective" rheology depends on the cascade of instabilities at smaller scales, thanks to which it is much weaker than the material properties measured on small samples.

  4. 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.

  5. 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.

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

    PubMed

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

    2014-03-25

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

  7. Tectonics

    NSDL National Science Digital Library

    Benjamin, Jane

    In this activity, developed by the Lane Community College Geo-STAC programâ??, students will "describe spatial occurrence of earthquakes and tectonic landforms. Students practice Boolean logic queries to select data and describe spatial patterns. In part two, students develop and test hypotheses to explore the relationship between earthquake magnitude, location depth and the impact on human life and property." This activity was created as part of the Introductory Physical Geography course. On the site, visitors will find a link to the student activity and teaching guide, as well as link to the web-based GIS map. This is an excellent activity for high school or early undergraduate students for hands-on work with GIS and coordinate systems.

  8. Discovering Plate Boundaries

    NSDL National Science Digital Library

    Alison Henning

    Students are initially assigned to one of four maps of the world: Seismology, Volcanology, Geochronology or Topography. They are also given a map of the world's plate boundaries and are asked to classify the boundaries based upon the data from their assigned map. Students are then assigned to a tectonic plate, such that each plate group contains at least one "expert" on each map. As a group, they must classify their plate's boundaries using data from all four maps. Recent volcanic and seismic events are discussed in the plate tectonic context. Has minimal/no quantitative component Uses geophysics to solve problems in other fields

  9. Shear-wave splitting beneath western United States in relation to plate tectonics

    NASA Astrophysics Data System (ADS)

    Özalaybey, Serdar; Savage, Martha K.

    1995-09-01

    We have examined shear wave splitting in teleseismic shear waves from 26 broadband stations in the western United States. Fast polarization directions (?) and delay times (?t) show spatial variations that are coherent within geologic provinces. Stations located near the San Andreas fault show clear evidence for fault-parallel anisotropy in the crust and upper mantle (115-125 km thickness). This can be explained by the finite strain associated with the relative plate motion between the North American and Pacific plates. The lateral extent of this strain field is probably narrow to the west, because stations 55 km west of the San Andreas fault do not show fault-parallel anisotropy in southern California. Station LAC located 80 km east of the San Andreas fault shows large fault-parallel anisotropy. This suggests that the Pacific-North American plate boundary in the mantle might be displaced to the east in southern California. A deeper E-W oriented fast direction of anisotropy underlies the fault-parallel anisotropic layer in the vicinity of the San Andreas fault. An E-W fast feature is also present beneath the western Basin and Range and the foothills of the Sierra-Nevada, although local variations are present. The magnitude of delay times suggests that this feature resides in the asthenosphere. We interpret this feature as the asthenospheric flow in the slabless window left behind the Farallon plate. The flow-induced anisotropy may partially be frozen-in at shallow depths. Station ORV is located near the southern edge of the Gorda slab where no anisotropy is detected. The absence of anisotropy at this location could therefore mark a boundary between Farallon associated flow and regions where E-W oriented asthenospheric flow did not occur. The lack of evidence for NE-SW fast orientation within the Walker Lane Shear Belt of western Nevada suggests that this crustal feature does not extend into the mantle or that is not as well developed as that beneath the San Andreas fault. Stations located over the young subducting Gorda plate mark a change in the fast direction to nearly NE-SW. This direction aligns well with the maximum compressive stress direction in the overlying North American plate and the NE-SW directed internal shearing of the Gorda plate. The anisotropic thicknesses calculated from delay times suggest roughly double that expected for purely lithospheric contributions. This implies that the anisotropic thickness may include some of the asthenosphere. Alternatively, using a higher anisotropy of 8% can bring thicknesses in line with other measures of lithospheric thicknesses. The correspondence between the fast directions and the present plate tectonic deformations suggest that mapping upper mantle deformation through seismic anisotropy is a viable method, and that asthenospheric flow may be a significant contributor to seismic anisotropy.

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

    NASA Astrophysics Data System (ADS)

    Ishise, Motoko; Miyake, Hiroe; Koketsu, Kazuki

    2015-07-01

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

  11. 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 which is similar for transects across the inverted Lower Saxony Basin and areas of predominant basement thrusting. Bulk contraction of the entire deformed belt is unlikely to exceed a few tens of kilometers, corresponding to <<10% of horizontal shortening. Shortening rate estimates are around 1 mm/yr both for well-constrained local structures and for order-of-magnitude estimates of the entire belt, suggesting that a limited number of faults were active at any given time. Space geodetic data indicate similar modern shortening rates across Central Europe on a decade scale, but there is no geologic evidence for focused deformation comparable to the Mesozoic event. Fold orientations, fault slip data and stylolite teeth indicate relatively uniform, SSW-NNE-directed shortening. This direction is consistent with the convergence direction of Africa, Iberia and Eurasia that was established between ca. 120 Ma and 85 Ma in the course of global plate motion reorganization. The European short-lived pulse of intraplate deformation was apparently caused by a switch to near-orthogonal convergence across former transform boundaries, whereas modern examples of intraplate shortening seem to be bound to coeval orogens.

  12. Holocene tectonics south of the Indus Suture, Lahaul-Ladakh Himalaya, India: a consequence of Indian Plate motion

    NASA Astrophysics Data System (ADS)

    Bhargava, O. N.

    1990-03-01

    The continued northward drift of the Indian Plate after the cessation of its further subduction was successively forced upon other planes of dislocations along old lineaments south of the Indus Suture Zone (ISZ). The active tectonics chiefly confined to the Main Central Thrust, the Main Boundary Thrust, the thrust between the Siwalik rocks and the older Alluvium and along certain tensional/extensional faults are steady but not spectacular. The youngest major tectonic activity in the Himalaya, leaving visible signatures, occurred south of ISZ after the last Quaternary glaciation. This activity rejuvenated older faults causing deflection and disorganization of several rivers which had come to occupy the U-shaped glacial valleys in the Ladakh and Lahaul. The strike-slip movements discretely folded the terraces and also formed the pull-apart Tso Morari and Kiogar Tso basins. The Indian Plate motion also affected the Peninsular part, although less intensely.

  13. Plate Tectonic Consequences of competing models for the origin and history of the Banda Sea subducted oceanic lithosphere

    E-print Network

    Heine, Christian; McKay, Hamish; Müller, R Dietmar

    2012-01-01

    The Banda Arc, situated west of Irian Jaya and in the easternmost extension of the Sunda subduction zone system, reveals a characteristic bowl-shaped geometry in seismic tomographic images. This indicates that the oceanic lithosphere still remains attached to the surrounding continental margins of northern Australia and the Bird's Head microcontinent. Major controversies exist between authors proposing an allochthonous or autochthonous origin of the Bird's Head block. Either scenario has important implications for plate kinematic models aiming to reconstruct the tectonic evolution of the region and the late Jurassic seaoor spreading geometry of this now subducted Argo-Tanimbar-Seram (ATS) ocean basin. Wider implications affect the tectonic conguration of the Tethyan-Pacic realm, the distribution of plate boundaries as well as the shape and size of continental blocks which have been rifted off the northeastern Gondwana margin during the Late Jurassic and are now accreted to the SE Asia margin. We apply structu...

  14. How plate tectonics is recorded in chalk deposits along the eastern English Channel in Normandy (France) and Sussex (UK)

    NASA Astrophysics Data System (ADS)

    Duperret, Anne; Vandycke, Sara; Mortimore, Rory N.; Genter, Albert

    2012-12-01

    Intra-plate stresses that occurred in the Anglo-Paris Basin and English Channel during Upper Cretaceous and Cenozoic times are a consequence of the convergence between Eurasia and Africa and the opening of the North Atlantic area. This geodynamic re-organisation is recorded on each side of the English Channel, with the emergence of regional structures such as the the Weald-Artois anticline and the reactivation of large-scale strike-slip faults. We analyse the Anglo-Paris Basin Chalk fracture system, on each side of the eastern English Channel, using a set of 1600 meso-scale fractures data collected on coastal chalk cliffs in Normandy (NW France) and Sussex (UK). Meso-scale fracture system is precisely dated using chalk lithostratigraphy correlations within the basin. Moreover, an inversion method is used on fault slip data to evidence a paleostress chronology in the Anglo-Paris Basin. Three main Upper Cretaceous extensive events, characterized by normal faults and jointing are recorded in Normandy and two Cenozoic compressive and extensive events with strike-slip and normal faults appear in Sussex. Paleostress records vary on each part of the eastern English Channel. The meso-scale fracture system is thus used to better define the type of relationship between meso-scale and large-scale brittle deformation in the Chalk during Meso-Cenozoic. A first NE-SW extension is recorded in Normandy in relation with local anticlines structures and related to the Lower Rhine graben opening. A second event is a WNW-ESE extension of local origin in relation with the subsidence axis of the Paris Basin. The third event is a NNE-SSW extension, well marked in Normandy and related to the activation of E-W normal faults in the western approaches of the English Channel. This event is also recorded in Sussex and reactivates locally older fractures in strike-slip. The Oligocene N-S compression/E-W extension related to the Pyrenean tectonics and the last E-W extension relative to the North Sea graben opening are well recorded in Sussex, but not in Normandy. Recent far-field stresses developed in the NW European platform are focused on deep crustal structures like the Artois hills and the Cotentin areas in France. These structures act as a stress barrier by protecting the Normandy Chalk from recent far-field stresses. On the contrary, recent far-field stresses are easily recorded by meso-scale brittle deformation on the folded Chalk in Sussex.

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

    SciTech Connect

    Fuentes, J. (Corpoven, Puerta La Cruz (Venezuela)); Oum, S. (TOTAL-CFP, Paris (France)); Lander, R. (Corpoven, Puerta La Cruz (Venezeula))

    1990-05-01

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

  16. Origin and evolution of marginal basins of the NW Pacific: Diffuse-plate tectonic reconstructions

    E-print Network

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

    2012-01-01

    Formation of the gigantic linked dextral pull-apart basin system in the NW Pacific is due to NNE- to ENE-ward motion of east Eurasia. This mainly was a response to the Indo-Asia collision which started about 50 Ma ago. The displacement of east Eurasia can be estimated using three aspects: (1) the magnitude of pull-apart of the dextral pull-apart basin system, (2) paleomagnetic data from eastern Eurasia and the region around the Arctic, and (3) the shortening deficits in the Large Tibetan Plateau. All the three aspects indicate that there was a large amount (about 1200 km) of northward motion of the South China block and compatible movements of other blocks in eastern Eurasia during the rifting period of the basin system. Such large motion of the eastern Eurasia region contradicts any traditional rigid plate tectonic reconstruction, but agrees with the more recent concepts of non-rigidity of both continental and oceanic lithosphere over geological times. Based on these estimates, the method developed for resto...

  17. Indentation and Lateral Escape in Western Ishtar Terra, Venus — An Analog for Deformation of the Archean Abitibi Subprovince, Superior Craton, Canada Without Plate Tectonics

    NASA Astrophysics Data System (ADS)

    Harris, L. B.; Bédard, J. H.

    2015-05-01

    Radar about Lakshmi Planum, Venus, shows regional transcurrent shear zones, folds and thrusts formed by indentation and lateral escape. The Archean Abitibi subprovince Canada shows identical structures suggesting a similar, non-plate tectonic origin.

  18. 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.

  19. TOPSIDE TECTONICS Don L. Anderson

    E-print Network

    Anderson, Don L.

    Science #12;07/19/01 2 TABLE 1: Convection and Plate Tectonics Style of Convection Successful ? Problems-forming plates TBD Freely-evolving plates TBD #12;07/19/01 3 Abstract Plate tectonics is a far in and between the plates. Without plate tectonics and with simple boundary conditions the mantle would

  20. Formation of the world's largest molybdenum metallogenic belt: a plate-tectonic perspective on the Qinling molybdenum deposits

    Microsoft Academic Search

    Cong-Ying Li; Fang-Yue Wang; Xi-Luo Hao; Xing Ding; Hong Zhang; Ming-Xing Ling; Ji-Bin Zhou; Yi-Liang Li; Wei-Ming Fan; Wei-Dong Sun

    2012-01-01

    Qinling ore belt is the largest known molybdenum belt in the world with a total reserve of >5 Mt of Mo metal. Based on the geochemical behaviour of Mo, the structural settings of the Qinling orogenic belt, and geological events in eastern China, we propose that tectonic settings are of critical importance to the formation of these ore deposits. Molybdenum

  1. Formation of the world's largest molybdenum metallogenic belt: a plate-tectonic perspective on the Qinling molybdenum deposits

    Microsoft Academic Search

    Cong-Ying Li; Fang-Yue Wang; Xi-Luo Hao; Xing Ding; Hong Zhang; Ming-Xing Ling; Ji-Bin Zhou; Yi-Liang Li; Wei-Ming Fan; Wei-Dong Sun

    2011-01-01

    Qinling ore belt is the largest known molybdenum belt in the world with a total reserve of >5 Mt of Mo metal. Based on the geochemical behaviour of Mo, the structural settings of the Qinling orogenic belt, and geological events in eastern China, we propose that tectonic settings are of critical importance to the formation of these ore deposits. Molybdenum

  2. 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 infrastructure. It allows complex search queries, including metadata such as DOI and media fragment identifiers (MFI), thereby linking data citation and science communication.

  3. Cenozoic tectonic events at the border of the Paraná Basin, São Paulo, Brazil

    NASA Astrophysics Data System (ADS)

    Fernandes, A. J.; Amaral, G.

    2002-03-01

    In the last decade, even in areas that had been considered tectonically stable, a great amount of Cenozoic, including the Quaternary period, structural data have been collected throughout Brazil. The main goal of this study is to describe the Cenozoic structures and tectonic evolution of an area that is located at the border of the Paraná Basin in the state of São Paulo. The research methods consisted of the analysis of: (1) brittle structure data, mainly conjugate fractures and fault slip data; (2) lineaments traced on air photos and TM Landsat and radar images; and (3) a second-order base surface map. The study area, during the Cenozoic, has been affected by five strike-slip tectonic events, which generated mainly strike-slip faults, and secondarily normal and reverse ones. The events were named, from the oldest to the youngest, E1-NE, E2-EW, E3-NW, E4-NS, and E5-NNE; and the maximum principal stresses ?1 strike approximately NE-SW, E-W, NW-SE, N-S, and NNE-SSW, respectively. Event E2-EW seems to have been contemporaneous with the deposition of the Rio Claro Formation, the most important Cenozoic deposit of probable Neogenic age, and also to have controlled the distribution of its deposits. Event E3-NW was the strongest one in the area, as is pointed out by structural data, and the maximum principal stress ?1 of event E5-NNE is partially concordant with the orientation of ?H-max of well break-out data in the Paraná Basin, suggesting a Neotectonic activity for this event. Finally, discontinuities parallel and correlated to the directions of strike-slip faults of the Cenozoic events seem to have actively controlled the sculpturing of the relief in the study area.

  4. Regional Tectonics emphasizes the

    E-print Network

    . Generally the class utilizes aspects of structural geology and plate tectonic theory to provide a broad and interests. Other topics included a careful assessment of the plate tectonics model, Wilson cycle, firstRegional Tectonics emphasizes the tectonic development of major mountain ranges across the globe

  5. Plate-scale Seismic Studies of Anatolia: Implications on Tectonic Interpretations (Invited)

    NASA Astrophysics Data System (ADS)

    Taymaz, T.; Fichtner, A.; Vanacore, E. A.; Saygin, E.; Cevikbilen, S. Y.; Fielding, E. J.

    2013-12-01

    Dense coverage of high-quality seismic data combined with modern modeling and tomography techniques are in the process reshaping and refining our understanding of Anatolian tectonics. Recently conducted receiver function analyses and multiscale full waveform inversion, in particular, provide new information on the interaction between upper-mantle dynamics and near-surface processes and observations. Receiver functions covering the wider Anatolian region reveal a sharp drop in Moho depth across the East Anatolian Fault, suggesting that the fault demarks the boundary between the Anatolian and Arabian plates. Moho depths beneath the East Anatolian Plateau are 40-55 km with the deepest measurements to the North and Northeast. These signals are consistent with observed high topography of around 2 km being supported by mantle forces or slab break-off models rather than crustal thickening. In addition to the Moho depths, the shear wave velocity crustal structure is independently determined from Bayesian inversion of receiver functions. Results underline the complex nature of Anatolian crust. Full waveform inversion of complete broadband seismograms constrains the crustal and upper-mantle signature of the North Anatolian Fault Zone. The fault zone is bound by high-velocity blocks within the crust suggesting that it developed along the edges of continental fragments with high rigidity. Below the crust, the surface expression of the North Anatolian Fault Zone correlates with a 600 km long low-velocity band. This is interpreted as the upper-mantle expression of Tethyan sutures that formed 60-15 Ma ago. The structurally weak suture facilitated the formation of the younger crustal fault zone.

  6. 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 of this weakening in the context of the potential effects on laboratory studies of reduced grain size and Peierls stress on the low-temperature deformation regime.

  7. 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 incompetent material. Sited between both plates, and strongly adhering to neither, this buoyant, largely sedimentary complex decoupled at 25 30 km depth, and ascended toward the surface. In both Alpine-type intracontinental collision and Pacific-type underflow, light sialic material displaced dense mantle; thus, the return to midcrustal levels was propelled dominantly by body forces.

  8. Magma and tectonics along divergent plate boundaries: insights from field and modelling data

    NASA Astrophysics Data System (ADS)

    Acocella, V.; Trippanera, D.; Ruch, J.; Abebe, B.; Giordano, A.; Thordarson, T.

    2013-12-01

    Recent data have demonstrated that magma emplacement may play the major role during discrete rifting episodes. Here we use field data and analogue modeling to better constrain the role of magma and regional tectonics on the development of rift structures. We performed field surveys along the Neo Volcanic Zone (Iceland) and the Main Ethiopian Rift, focusing on 1) single eruptive fissures and related structures (Laki and Eldgjà, Iceland) and 2) on mature rifts where several diking events occurred (Sveinagja, Krafla in Iceland and Fantale in Ethiopia). Systematic measurements of fault geometry and kinematics and extension fractures have been carried out. To better understand any role of magma on the evolution of the geometry and kinematics of rift, we use analogue models of dike intrusion. Laser-scanner and Particle Image Velocimetry (PIV) techniques have been used allowing us to quantify and reconstruct the time evolution of the rift development. Results of field surveys and analogue models suggest a correlation between the surface deformation pattern along rift zones (width and depth of grabens; normal and/or reverse kinematics, fault termination and opening of the normal faults) and the intrusion of magma at depth (injection of single or multiple dikes, at deeper or shallower levels). Different types of graben-like structures formed according to different depths and openings of rift zones.

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

    NASA Astrophysics Data System (ADS)

    Bercovici, David; Ricard, Yanick

    2013-03-01

    The grain-damage and pinning mechanism of Bercovici and Ricard (2012) for lithospheric shear-localization is employed in two-dimensional flow calculations to test its ability to generate toroidal (strike-slip) motion and influence plate evolution. This mechanism posits that damage to the interface between phases in a polycrystalline material like peridotite (composed primarily of olivine and pyroxene) increases the number of small Zener pinning surfaces, which then constrain mineral grains to ever smaller sizes, regardless of creep mechanism. This effect allows a self-softening feedback in which damage and grain-reduction can co-exist with a grain-size dependent diffusion creep rheology; moreover, grain growth and weak-zone healing are greatly impeded by Zener pinning thereby leading to long-lived relic weak zones. The fluid dynamical calculations employ source-sink driven flow as a proxy for convective poloidal flow (upwelling/downwelling and divergent/convergent motion), and the coupling of this flow with non-linear rheological mechanisms excites toroidal or strike-slip motion. The numerical experiments show that pure dislocation-creep rheology, and grain-damage without Zener pinning (as occurs in a single-phase assemblages) permit only weak localization and toroidal flow; however, the full grain-damage with pinning readily allows focussed localization and intense, plate-like toroidal motion and strike-slip deformation. Rapid plate motion changes are also tested with abrupt rotations of the source-sink field after a plate-like configuration is developed; the post-rotation flow and material property fields retain memory of the original configuration for extensive periods, leading to suboptimally aligned plate boundaries (e.g., strike-slip margins non-parallel to plate motion), oblique subduction, and highly localized, weak and long lived acute plate-boundary junctions such as at what is observed at the Aleutian-Kurile intersection. The grain-damage and pinning theory therefore readily satisfies key plate-tectonic metrics of localized toroidal motion and plate-boundary inheritance, and thus provides a predictive theory for the generation of plate tectonics on Earth and other planets.

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

    SciTech Connect

    Portilla, A. (Corpoven S.A., Puerto la Cruz (Venezuela))

    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. Oregon offers something for everyone who loves the outdoors --especially geologists. Oregon is a land filled with wonder and intrigue. Over the state's long history, plate tectonic and volcanic activity

    E-print Network

    Tullos, Desiree

    . Oregon is a land filled with wonder and intrigue. Over the state's long history, plate tectonic tectonic plate under- neath the Pacific Ocean produced the Coast Range over millions of years. Hot fluids coming off the diving plate, beginning about 35 million years ago, resulted in the volcanic eruptions

  12. 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.

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

    Microsoft Academic Search

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

    2007-01-01

    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

  14. 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.

  15. Siberian Arctic Continental Margin: Constraints and Uncertainties of Plate Tectonic Models

    NASA Astrophysics Data System (ADS)

    Drachev, S. S.

    2004-12-01

    Siberian Arctic Continental Margin (SACM) reveals a complicated tectonic history resulted from three major events: (1) Mesozoic collisions of various allochtonous blocks with Paleo-Siberian continental margin, (2) Opening of Canada Basin, and (3) Opening of Eurasia Basin. Despite considerable progress was achieved in the past 15 years owing to CDP seismic reflection surveys and satellite observations, some major points of SACM's structure and history are still poorly understood. According to the most accepted model, opening of the Canada Basin led to separation and counterclockwise rotation of North Alaskan-Chukchi Microplate until it collided with Siberian/Omolon margin along South Anyui Suture. However, the time and geometry of the opening are not properly constrained yet. Uniform rotation of North Alaskan-Chukchi Microplate by 66 deg. causes a significant overlap in the East Siberian Sea that cannot be explained by later extension of the SACM. Accepted age of the basin opening is 130-80 Ma, however, geological data show that South Anyui Suture was already completely closed by Aptian. In contrast, Cretaceous flood basalts suggest even later opening of the Canada Basin, which may have begun around 125 Ma. Chukchi Borderland, when remained at its present position, prevents closure of the Amerasia Basin. We suggest it was conjugated to what now the northeastern margin of East Siberian Sea is. Then it was detached from the SACM and moved to the present-day position during spreading episodes within the Arctic basins. However, the time of this event is unconstrained yet. Late Cretaceous-Cenozoic extension of the SACM was related to opening of the Eurasia Basin, and, probably, North Atlantic and Labrador Sea. It led to significant modification of SACM's initial architecture and created several profound rift systems. Extension of northern Laptev Shelf totals at least 190 km, which is about 47 % of the total divergence within adjacent Eurasia Basin. The northern East Siberian and Chukchi seas and Chukchi Borderland are the best candidates to account for some 200 km of the "missing extension". Using all available data we have revised structure and geological history of the SACM and speculated its relationships to the Canadian Arctic Margin in a "pre-Canada Basin" Arctic.

  16. 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?

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

    SciTech Connect

    Bercovici, D. [Univ. of Hawaii, Honolulu, HI (United States)] [Univ. of Hawaii, Honolulu, HI (United States)

    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.

  18. 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.

  19. Pre-plate tectonics and structure of the Archean mantle lithosphere imaged by seismic anisotropy - inferences from the LAPNET array in northern Fennoscandia

    NASA Astrophysics Data System (ADS)

    Plomerova, Jaroslava; Vecsey, Ludek; Babuska, Vladislav; Lapnet Working Group

    2013-04-01

    Various studies of seismic anisotropy clearly demonstrate the Archean mantle lithosphere consists of domains with different fabrics reflecting fossil anisotropic structures. We detect anisotropic signal both in the P-wave travel-time deviations and shear-wave splitting recorded by the LAPNET array (2007-2009) in the Archean craton of Fennoscandia (Plomerova et al., 2011). The anisotropic parameters change across the array and stations with similar characteristics form groups. The geographical variations of seismic-wave anisotropy delimit individual sharply bounded domains of the mantle lithosphere, each of them having a consistent fabric. The domains can be modelled in 3D by peridotite aggregates with dipping lineation a, or foliation (a,c). Also radial anisotropy of the Archean lithosphere derived from surface waves indicates inclined structure of all the cratonic regions of the continents, though with less detailed lateral resolution in comparison with body-wave anisotropy. These findings allow us to interpret the domains as micro-plate fragments retaining fossil fabrics in the mantle lithosphere, reflecting thus an olivine LPO created before the micro-plates assembled. Successive subductions of oceanic lithosphere is a mechanism which can work in modern-style plate tectonics as we know it now, being considered as widespread since 2.7 Ga. Though the modern plate tectonics is the most distinct tectonic style acting up to now, we have to consider a mechanism creating oriented structures (fabrics) in a pre-plate-tectonic style. The early lithosphere formed in dynamic conditions far from simple cooling which would result in sub-horizontal layered structure of the lithosphere. Earlier tectonic modes in a hotter and more dynamic Earth might be similar in some respects to those of the modern-plate tectonics. Basaltic "rockbergs" on convecting magma ocean in the Hadean Earth are supposed to turn to either proto-plate tectonics with platelets and supercratonal, or, to unstable stagnant lithospheric lid models in the Archean (~4.0 Ga), both evolving into the modern-style plate tectonics (Ernst 2007). The stage of platelets or supercratonal lasted during the deep mantle and plume-driven circulations, when plate motions were controlled by asthenospheric convection dragging buoyant lithosphere along and down. Differential motions between pairs of Precambrian cratons indicated in paleomagnetic records suggest supercontinental amalgamation and dispersal involving Archean cratons. Current thick and cold Archean cratons are thus formed by a collage of fragments of old lithosphere, each of them retaining its fabric. Studies of fossil anisotropy preserved in the mantle lithosphere contribute both to mapping the lithosphere-asthenosphere boundary and deciphering boundaries of individual blocks building the continental lithosphere (Plomerova and Babuska, Lithos 2010).

  20. 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.

  1. Pacific-North America Plate Tectonics of the Neogene Southwestern United States: An Update

    Microsoft Academic Search

    Tanya Atwater; Joann Stock

    1998-01-01

    We use updated rotations within the Pacific-Antarctica-Africa-North America plate circuit to calculate Pacific-North America plate reconstructions for times since chron 13 (33 Ma). The direction of motion of the Pacific plate relative to stable North America was fairly steady between chrons 13 and 4, and then changed and moved in a more northerly direction from chron 4 to the present

  2. 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.

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

    Microsoft Academic Search

    Thomas C. Hanks

    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

  4. Tectonically emplaced ultra-depleted lithospheric mantle records garnet, spinel and plagioclase facies events

    NASA Astrophysics Data System (ADS)

    Czertowicz, Thomas; Scott, James; Palin, Mike

    2014-05-01

    The poorly studied Anita Ultramafites in western New Zealand represent a several km wide slice of lithospheric mantle that was tectonically emplaced onto the Gondwana supercontinent margin. The peridotites are almost exclusively spinel facies dunite and harzburgite, although spinel-orthopyroxene symplectites indicate the former presence of Cr-garnet. Pyroxenite dikes are uncommon, and there is no sign of an ophiolitic type structure. Olivine (~Fo93) and chromite (~Cr# 70) attest to extreme degrees of melt depletion, likely under hydrous conditions. The rocks were decompressed and equilibrated at the spinel facies. The ultramafites were then refertilised by a fluid that was rich in Si, Ca, K, OH and LREE, and probably equates to a low-degree silicate melt. The occurrence of negative and positive Eu and Sr anomalies in amphibole points to the influence of plagioclase, and suggests that refertilisation occurred at a very shallow lithospheric level. An added complication is that the peridotite was metamorphosed to upper amphibolite facies in the Cretaceous after tectonic emplacement. This generated talc, tremolite and chlorite. P-T conditions from adjacent gneisses indicate that this event occurred at ~ 10-12 kbar in association with crustal thickening. Thus, the peridotite may have been pushed back out of plagioclase facies conditions, partially melted, and re-equilibrated back in the spinel facies. The Anita Ultramafics therefore record a sequence of attempts to equilibrate at garnet - spinel - plagioclase - spinel facies, before final exhumation.

  5. Coupling volcanism and tectonics along divergent plate boundaries: collapsed rifts from Central Afar, Ethiopia

    Microsoft Academic Search

    Valerio Acocella

    2010-01-01

    Magma along divergent plate boundaries is erupted from fissures or vents from central volcanoes, with limited impact on rift architecture. Here I summarize the geological and structural features accompanying the eruption of part of a km-thick volcanic sequence (\\

  6. Active Volcanoes and Plate Tectonics, Hot Spots and the Ring of Fire

    NSDL National Science Digital Library

    This world map shows the major plates and plate boundaries, including such notables as the Mid-Atlantic Ridge, the San Andreas Fault, and the Java and Aleutian Trenches. The Pacific Ring of Fire is shown, including the Cascade Range. The location of major volcanoes is also depicted. A feature of this site is a black and white version that can be printed out for greater clarity.

  7. 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

  8. Global coupling at 660 km is proposed to explain plate tectonics and the generation of the earth's magnetic field

    E-print Network

    Jozsef Garai

    2007-09-10

    The presence of low viscosity layers in the mantle is supported by line of geological and geophysical observations. Recent high pressure and temperature investigations indicated that partial carbonate melt should exist at the bottom of the lithosphere and at 660 km. The presence of few percent carbonate melt reduces the viscosity by several order of magnitude. The globally existing 660 km very low viscosity layer allows the development of differential rotation between the upper and lower mantle. This differential rotation between the 660 km outer shell and the rest of the earth offers a plausible explanation for plate tectonics and for the generation of the earth's magnetic field. Simple dynamo model is proposed, which able to reproduce all of the features of the contemporary and, within reasonable uncertainty, the paleomagnetic field. The model is also consistent with geological and geophysical observations.

  9. Global coupling at 660 km is proposed to explain plate tectonics and the generation of the earth's magnetic field

    E-print Network

    Garai, Jozsef

    2007-01-01

    The presence of low viscosity layers in the mantle is supported by line of geological and geophysical observations. Recent high pressure and temperature investigations indicated that partial carbonate melt should exist at the bottom of the lithosphere and at 660 km. The presence of few percent carbonate melt reduces the viscosity by several order of magnitude. The globally existing 660 km very low viscosity layer allows the development of differential rotation between the upper and lower mantle. This differential rotation between the 660 km outer shell and the rest of the earth offers a plausible explanation for plate tectonics and for the generation of the earth's magnetic field. Simple dynamo model is proposed, which able to reproduce all of the features of the contemporary and, within reasonable uncertainty, the paleomagnetic field. The model is also consistent with geological and geophysical observations.

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

    PubMed

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

    2013-07-22

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

  11. Magmatic activity tends to concentrate at tectonic plate bound-aries. At rapidly convergent margins, such as the Andes, intense mag-

    E-print Network

    Galland, Olivier

    of magma influences the deformation pattern in the brittle crust. The influence of deep magma bodies deformation structures in the upper crust, we describe the structure of an active volcano (Tromen, Argentina activity mostly occurs at plate boundaries, where tectonic deformation also concentrates. Because magmatic

  12. 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…

  13. Timing of Late Pliocene to Middle Pleistocene tectonic events in Rhodes (Greece) inferred from magneto-biostratigraphy and

    E-print Network

    Utrecht, Universiteit

    Timing of Late Pliocene to Middle Pleistocene tectonic events in Rhodes (Greece) inferred from sequences on the island of Rhodes (Aegean fore-arc, Greece). Here, we present an integrated isotopic; Pliocene; Pleistocene; Rhodes; Greece; Mediterranean Sea 1. Introduction The island of Rhodes (Greece

  14. Kattenhorn and Hurford: Tectonics of Europa 199 Tectonics of Europa

    E-print Network

    Kattenhorn, Simon

    and diapirism, and secondary effects driven by strike-slip faulting and plate flex- ure. (3) TectonicKattenhorn and Hurford: Tectonics of Europa 199 199 Tectonics of Europa Simon A. Kattenhorn tectonic disruption over its visible history. The descrip- tion, interpretation, and modeling of tectonic

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

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

  16. Plate tectonic model for the Carboniferous evolution of the New England Fold Belt

    Microsoft Academic Search

    C. G. Murray; C. L. Fergusson; P. G. Flood; W. G. Whitaker; R. J. Korsch

    1987-01-01

    The New England Fold Belt forms the easternmost, youngest part of the Tasman Fold Belt System. For much of Late Palaeozoic time, it was a convergent plate margin at the edge of the Australian continent. At present, the New England Fold Belt is separated into the Yarrol Province in the north and the New England Province in the south by

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

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

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

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

    USGS Publications Warehouse

    Kane, M.F.

    1972-01-01

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

  19. The 1946 Hispaniola earthquakes and the tectonics of the North America-Caribbean plate boundary zone, northeastern Hispaniola

    NASA Astrophysics Data System (ADS)

    Russo, R. M.; Villasenor, A.

    1995-04-01

    We have determined focal mechanisms for the largest earthquake (M(sub s) = 7.8) recorded instrumentally in the Caribbean Basin, the August 4, 1946, Hispaniola earthquake, and three of its large-magnitude (M(sub s) greater than or equal to 6.1) aftershocks. We also relocated 63 aftershocks and one foreshock of the event series. The aftershock series is elongate, trends WNW, and is centered on the Samana Peninsula of northeast Hispaniola. Shallow aftershocks are in a 75-km-wide linear zone, and intermediate depth (70 to 130 km) aftershocks apparently delineate a moderately south or SSW dipping slab. It is not clear, however, whether these events indicate active subduction of North American Atlantic Ocean lithosphere or are strike-slip events on the interface between subducted but no longer sinking slab and Caribbean mantle. We constrained focal mechanisms of the main shock and three aftershocks by combining observed P and S polarities and amplitude ratios and also by waveform modeling. The two methods yield consistent results. The mechanisms include strike-slip and thrust dispacements on NW striking nodal planes. Fault dip is variable, NE or SW. The NW striking fault planes parallel mapped terrane boundaries and faults in the North America (NA)-Caribbean (Ca) plate boundary zone and are also parallel to the aftershock series trend. We interpret the events to be motions on a WNW trending restraining bend segment of the NA-Ca plate boundary in eastern Hispaniola. We have calculated magnitudes for eight of the earthquakes in the series; for the three events (including the main shock) for which data are available, our magnitudes are systematically less than the previously published magnitude estimates. Given the high magnitude and large aftershock area of the August 4, 1946, event, these earthquakes probably represent the true long-term interplate motions between North America and the terranes in this portion of the plate boundary zone.

  20. Stopping the tectonic conveyor belt

    E-print Network

    Bercovici Geology students today are presented with the theory of plate tectonics as the grand model of how. Thephysicaltheorythatbestaccountsfor plate tectonics is that of thermal convection in the mantle. In this theory, Earth's solid mantle. Mantleconvectionisthusamorefundamen- tal theory of geology than is plate tectonics, although its presentation in most Earth- science

  1. Mantle Convection, Plate Tectonics, and Volcanism on Hot Exo-Earths

    E-print Network

    van Summeren, Joost; Gaidos, Eric

    2011-01-01

    Recently discovered exoplanets on close-in orbits should have surface temperatures of 100's to 1000's of K. They are likely tidally locked and synchronously rotating around their parent stars and, if an atmosphere is absent, have surface temperature contrasts of many 100's to 1000's K 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 (i) pattern of mantle convection, (ii) tectonic regime, and (iii) 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 >~ 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 dicho...

  2. A tale of two arcs? Plate tectonics of the Izu-Bonin-Mariana (IBM) arc using subducted slab constraints

    NASA Astrophysics Data System (ADS)

    Wu, J. E.; Suppe, J.; Renqi, L.; Kanda, R. V. S.

    2014-12-01

    Published plate reconstructions typically show the Izu-Bonin Marianas arc (IBM) forming as a result of long-lived ~50 Ma Pacific subduction beneath the Philippine Sea. These reconstructions rely on the critical assumption that the Philippine Sea was continuously coupled to the Pacific during the lifetime of the IBM arc. Because of this assumption, significant (up to 1500 km) Pacific trench retreat is required to accommodate the 2000 km of Philippine Sea/IBM northward motion since the Eocene that is constrained by paleomagnetic data. In this study, we have mapped subducted slabs of mantle lithosphere from MITP08 global seismic tomography (Li et al., 2008) and restored them to a model Earth surface to constrain plate tectonic reconstructions. Here we present two subducted slab constraints that call into question current IBM arc reconstructions: 1) The northern and central Marianas slabs form a sub-vertical 'slab wall' down to maximum 1500 km depths in the lower mantle. This slab geometry is best explained by a near-stationary Marianas trench that has remained +/- 250 km E-W of its present-day position since ~45 Ma, and does not support any significant Pacific slab retreat. 2) A vanished ocean is revealed by an extensive swath of sub-horizontal slabs at 700 to 1000 km depths in the lower mantle below present-day Philippine Sea to Papua New Guinea. We call this vanished ocean the 'East Asian Sea'. When placed in an Eocene plate reconstruction, the East Asian Sea fits west of the reconstructed Marianas Pacific trench position and north of the Philippine Sea plate. This implies that the Philippine Sea and Pacific were not adjacent at IBM initiation, but were in fact separated by a lost ocean. Here we propose a new IBM arc reconstruction constrained by subducted slabs mapped under East Asia. At ~50 Ma, the present-day IBM arc initiated at equatorial latitudes from East Asian Sea subduction below the Philippine Sea. A separate arc was formed from Pacific subduction below the East Asian Sea. The Philippine Sea plate moved northwards, overrunning the East Asian Sea and the two arcs collided between 15 to 20 Ma. From 15 Ma to the present, IBM arc magmatism was produced by Pacific subduction beneath the Philippine Sea.

  3. Stress Transfer Processes during Great Plate Boundary Thrusting Events: A Study from the Andaman and Nicobar Segments

    NASA Astrophysics Data System (ADS)

    Andrade, V.; Rajendran, K.

    2010-12-01

    The response of subduction zones to large earthquakes varies along their strike, both during the interseismic and post-seismic periods. The December 26, 2004 earthquake nucleated at 3° N latitude and its rupture propagated northward, along the Andaman-Sumatra subduction zone, terminating at 15°N. Rupture speed was estimated at about 2.0 km per second in the northern part under the Andaman region and 2.5 - 2.7 km per second under southern Nicobar and North Sumatra. We have examined the pre and post-2004 seismicity to understand the stress transfer processes within the subducting plate, in the Andaman (10° - 15° N ) and Nicobar (5° - 10° N) segments. The seismicity pattern in these segments shows distinctive characteristics associated with the outer rise, accretionary prism and the spreading ridge, all of which are relatively better developed in the Andaman segment. The Ninety East ridge and the Sumatra Fault System are significant tectonic features in the Nicobar segment. The pre-2004 seismicity in both these segments conform to the steady-state conditions wherein large earthquakes are fewer and compressive stresses dominate along the plate interface. Among the pre-2004 great earthquakes are the 1881 Nicobar and 1941 Andaman events. The former is considered to be a shallow thrust event that generated a small tsunami. Studies in other subduction zones suggest that large outer-rise tensional events follow great plate boundary breaking earthquakes due to the the up-dip transfer of stresses within the subducting plate. The seismicity of the Andaman segment (1977-2004) concurs with the steady-state stress conditions where earthquakes occur dominantly by thrust faulting. The post-2004 seismicity shows up-dip migration along the plate interface, with dominance of shallow normal faulting, including a few outer rise events and some deeper (> 100 km) strike-slip faulting events within the subducting plate. The September 13, 2002, Mw 6.5 thrust faulting earthquake at Diglipur (depth: 21 km) and the August 10, 2009, Mw 7.5 normal faulting earthquake near Coco Island (depth: 22 km), within the northern terminus of the 2004 rupture are cited as examples of the alternating pre and post earthquake stress conditions. The major pre and post 2004 clusters were associated with the Andaman Spreading Ridge (ASR). In the Nicobar segment, the most recent earthquake on June 12, 2010, Mw 7.5 (focal depth: 35 km) occurred very close to the plate boundary, through left lateral strike-slip faulting. A segment that does not feature any active volcanoes unlike its northern and southern counterparts, this part of the plate boundary has generated several right lateral strike-slip earthquakes, mostly on the Sumatra Fault System. The left-lateral strike-slip faulting associated with the June 12 event on a nearly N-S oriented fault plane consistent with the trend of the Ninety East ridge and the occasional left-lateral earthquakes prior to the 2004 mega-thrust event suggest the involvement of the Ninety East ridge in the subduction process.

  4. 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.

  5. Structuration of the lithosphere in plate tectonics as a self-organized critical phenomenon

    Microsoft Academic Search

    Didier Sornette; Anne Sornette; Philippe Davy

    1990-01-01

    In order to clarify the basic physical and geological mechanisms responsible for the self-organization of the crust within a continental plate, a field theory, deduced from symmetry and conservation laws, is proposed. The relevant parameter is the coarse-grained fluctuating strain tensor. On the basis of a diffusion-like conservation equation and the symmetries imposed by the tensorial character of the order

  6. 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).

  7. 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.

  8. 5th - How the Earth Changes: Landforms, Plate Tectonics, Erosion, and Weathering

    NSDL National Science Digital Library

    Miss B

    2011-09-08

    These are a list of links and activities about how the Earth's surface changes. There is also a list of titles to look for on eMedia to learn more about this topic. To get the username and password for Pioneer Library and eMedia talk to your local librarian. ACTIVITIES Shape It Up - Fun game, it sometimes repeats a landform but there are lots to figure out so keep trying. Learner Interactives: Dynamic Earth - I think that the "Plate Boundaries," and "Slip, Slide, Collide," tabs were the most useful. You can just select those from the top. BEST PICK! Changing Earth s Surface (UEN) - Click through ...

  9. 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

  10. It's "Your" Fault!: An Investigation into Earthquakes, Plate Tectonics, and Geologic Time

    ERIC Educational Resources Information Center

    Clary, Renee; Wandersee, James

    2011-01-01

    Earthquakes "have" been in the news of late--from the disastrous 2010 Haitian temblor that killed more than 300,000 people to the March 2011 earthquake and devastating tsunami in Honshu, Japan, to the unexpected August 2011 earthquake in Mineral, Virginia, felt from Alabama to Maine and as far west as Illinois. As expected, these events aroused…

  11. Tectonic slicing of subducted oceanic crust along plate interfaces: numerical modeling

    NASA Astrophysics Data System (ADS)

    Ruh, Jonas B.; Burov, Evgenii; Gerya, Taras; Agard, Philippe; Le Pourhiet, Laetitia

    2015-04-01

    Remains of high-pressure low-temperature metamorphic oceanic crust are observed within orogenic belts and along recent subduction zones all around the globe. Such blueshist and eclogite "slivers" can strongly vary in extend and experienced P-T-t evolution. To reveal the surficial occurrence of oceanic rocks that occasionally have been at depths down to ~ 80 km within subduction zones, two main processes have to be investigated individually: (i) Detachment of oceanic slivers from the down going plate preventing rocks to be consumed by the mantle, and (ii) exhumation of detached oceanic material to the surface. It has often been stated that the process of slicing and exhumation of oceanic blueshists and eclogites is closely related to continental subduction. Nevertheless, several examples worldwide show exhumation (and therefore latest possible detachment from slab) occurring early or intermediate of the subduction process. We present new insight into the mechanical processes of detachment of oceanic slivers and their exhumation independent of continental collision by using numerical modelling tools. Large-scale thermo-mechanical models (600 * 200 km) based on finite difference, marker-in-cell technique, are applied to test how serpentinised upper slab mantle (mantle serpentinisation at oceanic ridges or/and along to outer-rise normal faults) influences shallow and deep crustal detachment. Preliminary results show that a through-going serpentinite layer below the oceanic crust, if serpentinisation exceeds 50%, triggers slicing at wedge depths. Even if mechanical coupling mainly occurs at intermediate depths along the subduction interface, stresses within the oceanic crust are dispersed upward due to the weak, decoupling serpentinite layer. Unconnected patches of serpentinised upper slab mantle eventually lead to deep slicing, depending on upper plate serpentinisation due to slab dewatering. Furthermore, we investigated the effect of pressure-dependent fluid migration and according weakening (increasing fluid pressure) of subducted crust and its implications on slicing.

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

    SciTech Connect

    Miller, E.L. (Stanford Univ., CA (United States). 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.

  13. Global tectonics and space geodesy

    Microsoft Academic Search

    Richard G. Gordon; Seth Stein

    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

  14. 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

  15. 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 associated hazard with Rivera-Plate/Jalisco block, but it will also contribute to decipher the complex interplay between the accretion of the East Pacific Rise, the Magdalena Crest and the opening of the Gulf of California in the northeastern part of the diffuse Middle America Trench.

  16. 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.

  17. 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).

  18. 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 added to the top of the model. The existing model from Rolf et al. (EPSL 2012) is developed further but with weaker continents.

  19. Plate Puzzle Page 1 of 20 Plate Puzzle 1

    E-print Network

    Benitez-Nelson, Claudia

    plotting activities. Good follow-up activities are: plate tectonics flip book, epicenter plotting using tectonics. The map is an attractive display of plate tectonic features such earthquake epicenters boundaries so that one can examine the relationship of the tectonic features to the plate boundaries. The map

  20. 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.

  1. Intraplate Deformation Adjacent to the Macquarie Ridge South of New Zealand - The Tectonic Evolution of a Complex Plate Boundary

    NASA Astrophysics Data System (ADS)

    Hayes, G. P.; Furlong, K. P.

    2007-12-01

    The response of lithospheric plate boundaries to rapid changes in plate motions provide constraints used to determine the manner in which transitions in plate motions and plate boundary configurations can occur. In the case of the Australia - Pacific plate boundary in the Macquarie Ridge region south of New Zealand a substantial change in plate motions has occurred since the Oligocene. Over a period of less than 15Ma, this boundary changed from mid-ocean ridge spreading to simple translation, the record of which is recorded in the fabric and fracture zones of the oceanic lithosphere. Application of available well-constrained plate motions imply that substantial deformation of the oceanic lithosphere must have occurred after fracture zone formation to create the arcuate structure of these fracture zones today. Plate reconstructions of this plate boundary system from the Oligocene through the Early-Mid Miocene are used here to isolate the timing of transitions in plate motion from divergence to translational motion. These reconstructions identify rapid rotations in plate motions after approximately 25Ma. By 20Ma, the majority of crust created along this plate boundary was already in place, and the Australian Plate was translating northwards relative to the Pacific towards New Zealand, where a corner of Australian Plate is ultimately subducted. The timing of this transition in plate motions implies that the onset of subduction at the Puysegur Trench may have been as early as approximately 20Ma. These reconstructions also identify the shape of fracture zones either side of the relic mid-ocean ridge through the time of their formation. Comparison of these restored fracture zones with their present-day appearance delineates a broad zone of deformation extending ~150km into the plate interior from the Macquarie Ridge Complex, the modern plate boundary structure. This area of deformation coincides with a broad distribution of seismicity in the Australian Plate on both inter- and intra-plate structures, including two great (M8+) earthquakes over the past twenty years, one of which occurred over 130km from the plate boundary. The persistence of this deformation through time indicates a link with the evolution of the plate boundary from divergence to translation and subduction, and may be a result of stress build-up within the Australian Plate as a consequence of the impingement of the subducting plate on the thickened lithosphere of southern New Zealand. Such a collision may act as a resisting force to subduction, and if it continues, further deformation internal to the Macquarie Block may lead to a southward migration of the Australia:Pacific subduction interface and the capturing of this section of lithosphere onto the Pacific Plate.

  2. A Seismo-Tectonic Signal From Offshore Sedimentation: The 2010 Haiti Earthquake and Prior Events

    NASA Astrophysics Data System (ADS)

    McHugh, C. M.; Seeber, L.; Cormier, M.; Hornbach, M.; Momplaisir, R.; Waldhauser, F.; Sorlien, C. C.; Steckler, M. S.; Gulick, S.

    2011-12-01

    The Mw 7.0 January 2010 earthquake in Haiti was one of the deadliest in history. It involved multiple faults along or near the main Enriquillo-Plantain Garden Fault (EPGF). This left-lateral transform is a branch of the northern Caribbean plate boundary across southern Hispaniola. The main rupture was strike-slip but almost all aftershocks had thrust mechanisms, and surface deformation may have been concentrated on anticline forelimbs driven by blind thrust faults. Earthquake generated mass-wasting and turbidity currents were sampled from the Canal du Sud slope (~1000 m water depth), a basin at 1500 m, and the deepest part of the strait at 1700 m. The turbidites were strongly correlated by 234Th with a half-life of 24 days. In the deepest area, a turbidite-homogenite unit (T-H) extends over 50 km2 and is composed of basal sand beds 5 cm thick and 50 cm of mud above. The sedimentary structures in the sand were linked to oscillatory motions by internal seiches. The T-H units recovered from the slope and deep basin are similar in composition. The Leogane Delta, upslope from the sampling sites, is rich in this lithology that has been linked to oceanic basement rocks exposed on the southern Haitian peninsula. In contrast, the T-H unit recovered from the basin at 1500 m is perched behind a thrust anticline and has a greater concentration of Ca derived from Ca rich sources such as the Tapion Ridge on the southern peninsula. The Tapion Ridge is a compressional structure associated with a restraining bend along the EPGF. The T-H unit beneath the 2010 deposit has a 14C age of 2400 cal yrs BP, and interpreted as an earthquake triggered deposit. It is nearly identical in thickness, composition and fine structures to the 2010 T-H. Notably absent from the record are younger turbidites that could have been linked to the historic 1770 AD and other similar earthquakes expected from GPS rates across the EPGF. Two hypotheses are being considered for this long gap in T-H sedimentation. One proposes that during relative high stands of sea level fringing reefs are trapping sediment on the shelf and that a critical accumulation is needed to generate failure. Many large local earthquakes could have occurred before reaching this critical thickness. Low sedimentation rates (6 cm/1000 yrs) support this possibility. Our preferred hypothesis, alternatively, links T-Hs to earthquakes with a large thrust component such as the 2010 event in order to generate failure. This latter hypothesis accounts for some earthquakes producing no turbidites while others, such as the 2010 event, do. It also accounts for the fracturing sampled along 8 km of the perched basin. We propose that thrust earthquakes along the Tapion Ridge segment of the EPGF reoccur at ~2000-year intervals and this sedimentary signal is preserved in Canal du Sud.

  3. 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.

  4. Late Tertiary paleogeographic and tectonic evolution of the Mediterranean area

    SciTech Connect

    Arnott, R.J.; Haan, E.A.

    1988-08-01

    The present geography of the Mediterranean Sea is the result of late Tertiary tectonic processes and hardly reflects its Mesozoic and early Tertiary evolution. This paper outlines a plate tectonics model for the Mediterranean area from the Oligocene to the Pliocene. Seismic and well data have been integrated into the regional structural framework to produce a set of paleogeographic maps, which includes the Oligocene, early and middle Miocene, late Miocene, and Pliocene. These maps highlight the changes in sedimentation patterns in response to the tectonic development of the Mediterranean area. Special attention will be given to the Messinian desiccation event.

  5. Plate tectonic reconstruction of South and East Asia since 43 Ma using seismic tomographic constraints: role of the subducted ';East Asia Sea' (Invited)

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    Lithosphere that subducts at convergent plate boundaries provides a potentially decipherable plate tectonic record. In this study we use global seismic tomography to map subducted slabs in the upper and lower mantle under South and East Asia to constrain plate reconstructions. The mapped slabs include the Pacific, the Indian Ocean and Banda Sea, the Molucca Sea, Celebes Sea, the Philippine Sea and Eurasia, New Guinea and other lower mantle detached slabs. The mapped slabs were restored to the earth surface and used with Gplates software to constrain a globally-consistent, fully animated plate reconstruction of South and East Asia. Three principal slab elements dominate possible plate reconstructions: [1] The mapped Pacific slabs near the Izu-Bonin and the Marianas trenches form a subvertical slab curtain or wall extending down to 1500 km in the lower mantle. The ';slab curtain' geometry and restored slabs lengths indicate that the Pacific subduction zone has remained fixed within +/- 250 km of its present position since ~43 Ma. In contrast, the Tonga Pacific slab curtain records at least 1000 km trench rollback associated with expansion of back-arc basins. [2] West of the Pacific slab curtain, a set of flat slabs exist in the lower mantle and record a major 8000km by 2500-3000km ocean that existed at ~43 Ma. This now-subducted ocean, which we call the ';East Asian Sea', existed between the Ryukyu Asian margin and the Lord Howe hotspot, present-day eastern Australia, and fills a major gap in Cenozoic plate reconstructions between Indo-Australia, the Pacific Ocean and Asia. [3] An observed ';picture puzzle' fit between the restored edges of the Philippine Sea, Molucca Sea and Indian Ocean slabs suggests that the Philippine Sea was once part of a larger Indo-Australian Ocean. Previous models of Philippine Sea plate motions are in conflict with the location of the East Asian Sea lithosphere. Using the mapped slab constraints, we propose the following 43 Ma to 0 plate tectonic reconstruction. At ~43 Ma a major plate reorganization occurred in South and East Asia marked by Indian Ocean Wharton ridge extinction, initiation of Pacific Ocean WNW motions and the rapid northward motion of the Australian plate. The Philippine Sea and Molucca Sea were clustered at the northern margin of Australia, northwest of New Guinea. During the mid-Cenozoic these plates moved NNE with Australia, accommodated by N-S transforms at the eastern margin of Sundaland. The East Asian Sea was subducted under the northward-moving Philippine Sea and Australia plates, and the expanding Melanesian and Shikoku-Parece Vela backarc basins. At ~20 to 25 Ma the Philippine Sea and Molucca Sea were fragmented from Indo-Australia and began to have a westward component of motion due to partial Pacific capture. Around 1-2 Ma the Philippine Sea was more fully captured by the Pacific and now has rapid Pacific-like northwestward motions.

  6. Tectonic implications of Mars crustal magnetism J. E. P. Connerney*

    E-print Network

    California at Berkeley, University of

    crust formed during an early era of plate tectonics. magnetic planetary plate tectonics Precisely how of plate tectonics, retaining, in places, the magnetic imprint acquired when it formed, billions of yearsTectonic implications of Mars crustal magnetism J. E. P. Connerney* , M. H. Acun~ a*, N. F. Ness

  7. Widespread remagnetizations and a new view of Neogene tectonic rotations within the Australia-Pacific plate boundary zone, New Zealand

    Microsoft Academic Search

    Christopher J. Rowan; Andrew P. Roberts

    2008-01-01

    Large, clockwise, vertical axis tectonic rotations of the Hikurangi margin, East Coast, New Zealand, have been inferred over both geological and contemporary timescales, from paleomagnetic and geodetic data, respectively. Previous interpretations of paleomagnetic data have laterally divided the margin into independently rotating domains; this is not a feature of the short-term velocity field, and it is also difficult to reconcile

  8. 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.

  9. SIGNIFICANT TECTONIC AND CLIMATIC EVENTS FOR THE YAKUTAT BLOCK COLLISION, GULF OF ALASKA

    E-print Network

    New Hampshire, University of

    terminus of the Aleutian trench and a mismatch between GPS recorded motion and plate slip vectors; the latter may be accommodated in part by oblique-slip motion at the base of the slope between the Yakutat-resolution seismic data suggest that the Transition fault is caused by an incipient step-over of the Fairweather

  10. Were the Great April 2012 Indian Ocean Earthquakes Triggered by the 2004 Plate Boundary Event?

    NASA Astrophysics Data System (ADS)

    M P, R.; Rajendran, K.

    2013-12-01

    The Andaman-Sumatra subduction zone is the only plate boundary known to have generated two great strike-slip earthquakes following a great plate boundary earthquake. Thus, the 2004, Mw 9.2 thrust event and the Mw 8.6 and Mw 8.2 pair of earthquakes on 11 April, 2012 on the subducting oceanic plate form an intriguing sequence. The April events throw up some interesting questions. Could the twin earthquakes ~430 km from the Aceh coast of Northern Sumatra (~100 km away from the plate boundary) and at a depth of ~45 km be a consequence of the post-2004 visco-easltic processes and consequent changes in static stress? In a stress regime altered by a great plate boundary earthquake, can the pre-existing fractures be activated to generate great earthquakes? Based on our observations of the pre and post 2004 seismicity, we divide the subduction zone in to two segments- the northern Andaman segment (10-15 N) and the southern Nicobar segment (0-10 N). We focus more on the southern segment which features one of the most active oceanic plates in the world, being part of the diffused Indo-Australian plate boundary. The northern portion of this diffused plate boundary consists of the north-east or NNE trending linear feature known as the Ninety-east ridge. The 2012 sequence of great earthquakes occurred to the east of this ridge. The faulting mechanisms of these earthquakes remain debated. The Ninety-east ridge and paleo-transform faults that run parallel to the ridge justify the near N-S fault plane. Rupture models based on back projection of seismic data however suggests predominance of E-W faults, although they are not geomorphologically well expressed. The next important question is how these events are linked to the 2004 earthquake and how they are related to each other. We use the static stress change due to the 2004 event and alternate fault geometries to compute the static stress changes based on Coulomb's criterion, caused by the 2004 earthquake. Stress changes are computed for both the fault planes and at different depths (10km, 45km). Our studies suggest that the Mw 8.6 event occurred in a region of higher stress and one could argue that it was triggered by the stress changes that followed the 2004 earthquake. The subducting oceanic plate west of the Nicobar segment had actually been experiencing an increase in moment release after the 2004 earthquake. What triggered the Mw 8.2 soon after is another interesting question. Could it be similar to its predecessor, in response to the static stress changes caused by the 2004 event, but on a different fault? Or was it a static or dynamic response to the first earthquake?

  11. Tectonics, Earthquakes, Volcanoes

    NSDL National Science Digital Library

    Camille Holmgren

    Students do background reading on plate tectonics and associated geologic hazards. In the first part of this exercise, students use on-line courseware from California State University, Los Angeles (Virtual Earthquake) to investigate seismograph records and use these records to determine earthquake epicenters and magnitudes. In the second part, they complete a crossword puzzle designed to help them master new vocabulary related to plate tectonics.

  12. Are there other tectonics than tidal despinning, global contraction and Caloris related events on Mercury? A review of questions and problems

    NASA Astrophysics Data System (ADS)

    Thomas, Pierre G.

    1997-01-01

    Mercury's tectonic activity was confined to its early history. A synthesis of classical references indicates that its tectonic activity was principally related to (1) a small change in the shape of its lithosphere by tidal despinning, (2) a small change in radius and area by shrinkage due to secular cooling, and (3) the Caloris related events. These activities produced the ancient tectonic grid, the lobate scarps, and the Calorian ridges scarps and grabens, respectively. This low degree of activity was ultimately due to Mercury's small size. In spite of this apparent simplicity, some features are still intriguing. Detailed compilation of lineaments on the entire planet indicates that the grid is not similar to the theoretical despinning grid. Some trends are explained by despinning, but only with unusual mechanical properties of the Mercurian lithosphere, while some other trends are not explained at all by despinning. Examples of unexplained tectonic features in the same region are presented in this paper. Some circular depressions may be interpreted as the result of tectonic or volcano-tectonic subsidence (caldera?). Some exibit narrow and particularly straight grooves which cannot be explained as impact related features, and may be interpreted as open tectonic cracks. The Tolstoj area exhibits hills and grooves which cannot be interpreted as Tolstoj impact related features. Morphological and chronological studies indicate that these features would consist of the extensional tectonic features (horsts and grabens) developed on the convex top of a tectonically uplifted bulge. The tectonic development of this area occurred over a long period of time, and is probably due to a deep and long-lived internal source. These examples show the existence of large- and small-scale internal activities which affect Mercury's surface independently from global or impact related tectonics. Such activities must be taken into account in further models of Mercurian internal structure and history and must be searched in data of future missions. A new Mercurian mission with a complete coverage of image and altimetric/gravimetric data is thus necessary to understand the geology and the tectonic of Mercury.

  13. 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 and marine paleoclimate proxies) appears to have been unique to Afar in Mid Pliocene Africa, and may have caused hominids living in the Depression to undergo physical and cultural evolution more rapidly and successfully than hominids inhabiting equally productive but less confined ranges elsewhere. We suggest that plate-tectonic induced isolation caused the Afar Depression to become the cauldron within which genus Homo arose to prominence. If our interpretation is correct, continental drift played a major role in hominid-to-human evolution.

  14. 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)

  15. Plate motion

    SciTech Connect

    Gordon, R.G. (USAF, Geophysics Laboratory, Hanscom AFB, MA (United States))

    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.

  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. Climatic, volcanic and tectonic events recorded in recent sediments of the Rukwa rift, Western Tanzania

    NASA Astrophysics Data System (ADS)

    Delvaux, D.; Mees, F.; Williamson, D.; Macheyeki, A. S.

    2009-04-01

    Lake Rukwa is now a shallow lake occupying the floor of the closed Rukwa depression in the western branch of the East African Rift System. Sediment records of the paleo-lake level show that during the Late Pleistocene to Early Holocene, Lake Rukwa reached the level of the overflow sill, 180 m higher than its present level, and was overflowing into Lake Tanganyika. Lacustrine sediments from this period are now exposed on the margin of the depression, and in particular along the Songwe River, where several large sections up to 35 meters high can be studied. Investigation of selected sections reveals a complex evolution in alternating fluvio-deltaic to lacustrine environment, punctuated by episodic inflow of volcanic material from the nearby Rungwe Volcanic Province. Macroscopic description of the sedimentary packages and their geometry, combined with C14 dating, diatom analysis, and optical microscopy allow to propose a preliminary evolution scheme in which climatically induced lake level change, volcanic input and tectonic influence can be reconstructed. In particular, correlations between sections at different altitudes allow to better constrain the lake level fluctuation than previous estimates based on drill core analysis.

  18. 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. (Amoco Production Company, Houston, TX (United States))

    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).

  19. Nappes, tectonics of oblique plate convergence, and metamorphic evolution related to 140 million years of continuous subduction, Franciscan Complex, California

    SciTech Connect

    Wakabayashi, J. (Earth Sciences Associates Inc., Palo Alto, CA (United States))

    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.

  20. Oceanic anoxic events and plankton evolution: Biotic response to tectonic forcing during the mid-Cretaceous

    Microsoft Academic Search

    R. Mark Leckie; Timothy J. Bralower; Richard Cashman

    2002-01-01

    Mid-Cretaceous (Barremian-Turonian) plankton preserved in deep-sea marl, organic-rich shale, and pelagic carbonate hold an important record of how the marine biosphere responded to short- and long-term changes in the ocean-climate system. Oceanic anoxic events (OAEs) were short-lived episodes of organic carbon burial that are distinguished by their widespread distribution as discrete beds of black shale and\\/or pronounced carbon isotopic excursions.

  1. 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).

  2. 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. (Liverpool Univ. (United Kingdom)); Styles, P.; Murdie, R. (Northwestern Univ., Evanston, IL (United States)); Agar, S.; Turner, P. (Birmingham Univ. (United Kingdom))

    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.

  3. Plate kinematics in the western Pacific derived from geodetic observations

    E-print Network

    Tregoning, Paul

    Tectonophysics: Plate motions­present and recent (3040), 3040 Marine Geology and Geophysics: Plate tectonics (8150, 8155, 8157, 8158); KEYWORDS: GPS, North Bismarck Plate, Australian Plate, Pacific Plate, tectonic spanning the Australian Plate and the western Pacific region to derive new tectonic models of the motions

  4. Plate Boundaries

    NSDL National Science Digital Library

    This site provides information on plate boundaries, which are found at the edge of the lithospheric plates and are of three types: convergent, divergent and conservative. Wide zones of deformation are usually characteristic of plate boundaries because of the interaction between two plates. The three boundaries are characterized by their distinct motions which are described in the text and depicted with block diagram illustrations, all of which are animated. There are also two maps that show the direction of motion of the plates. Active links lead to more information on plate tectonics.

  5. 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.

  6. 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.

  7. Plate motion at the surface of the Earth can now be directly measured using space geodetic techniques.

    E-print Network

    Nicolas, Chamot-Rooke

    tectonics. Introduction Plate kinematics deals with the motion of tectonic plates at the surface elsewhere. We present here a new map that shows the current plate tectonics framework in the light. The plate tectonics revolution in the mid-1960s Plate tectonics was discovered in the mid-1960s. It merely

  8. 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.

  9. 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. (eds.)

    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.

  10. Tectonic Emplacement of the Ophiolitic Mélange in the West Junggar, NW China: Comment on the Plate Boundary Significance of Ophiolitic Mélange Belt

    NASA Astrophysics Data System (ADS)

    Wang, G.; Xu, Y.; Xiao, L.; Chen, C.

    2014-12-01

    Many ophiolitic mélanges distribute in the West Junggar, NW China. They are fault-contacted with Carboniferous turbidites with mostly NE trend and some NS trend with ages mostly Ordovician-Silurian and some Late Devonian. The boundary faults and the foliation inside the mélanges are of high-angle or nearly vertical. The NE trend ophiolitic mélange belts were structurally emplaced into the Carboniferous strata mainly by dextral transpressive deformation, but the NS trend ophiolitic mélange belts mainly by lateral extrusion deformation or pure shearing, suggesting a uniform stress field of nearly EW compression controlled the emplacements. The tectonic relationship between the ophiolitic mélanges and the Carboniferous turbidites imply that the ophiolitic mélanges are the main components of the basement of the Carboniferous strata. The geophysical data also reveal that high gravity, high magnetic and medium resistivity exist under the Carboniferous strata, matching well to the distribution of the ophiolitic mélanges on the surface. The neodymium model ages (TDM) of widely distributed Late Carboniferous-Permian granites are mostly between 0.352-0.923Ga and concentrate in 0.45-0.6Ga with positive eNd(t) mostly between 5~10, suggesting the Early Paleozoic rocks as the main magma source, consistent with the age of the ophiolitic mélanges, also coinciding with the conclusion of the ophiolitic mélanges as the basement of the Carboniferous strata. The Carboniferous turbidites primarily formed in residual basin. Early Permian terrestrial coarse molasses deposits unconformitily cover on the Carboniferous turbidites, suggesting the residual basin closed in Late Carboniferous. The accretionary complex or residual oceanic crust emplaced into the overlying Carboniferous turbidites through the dextral transpression or lateral extrusion due to EW convergent when the residual basin closed. The tectonic juxtaposition relationship between the ophiolitic mélanges and the younger lateral strata with same stratigraphic system suggests that the ophiolitic mélange belts do not separate different tectonic palaeogeographic or stratigraphic divisions. The traditional understanding of the ophiolitic mélange belt as plate or terrane boundary should be carefully to apply to the West Jungar.

  11. 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;…

  12. Mid-continent tectonic inversions, Northwest Territories, Canada

    NASA Astrophysics Data System (ADS)

    Cook, D. G.; MacLean, B. C.

    1996-06-01

    Four types of tectonic inversion are recorded on reflection seismic data from the area northwest of Great Bear Lake in the Northwest Territories, Canada. The strata involved span about 1.7 Ga of Proterozoic and Phanerozoic history, and have been subjected to at least five tectonic events, two extensional, two compressional and one transpressional. Two types of positive inversion, one type of negative inversion, and one type of double inversion (positive following negative) are documented. One of the positive inversions is atypical in that it involves no reversal in tectonic polarity; it was effected by a renewal of compression. During the entire 1.7 Ga time span the successive tectonic phases occurred in a mid-continental setting far from any known active plate margin(s).

  13. Pulsating Mantle Hypothesis "PMH" and its Applications on Apparent Solar Day Length Variations, Geodynamo and Plate Tectonics Theories, Tide, Earth's Axis Tilted and Earthquake Forecasting

    NASA Astrophysics Data System (ADS)

    Gholibeigian, H.; Amirshakarami, A.

    2012-12-01

    In this hypothesis, two phenomena; Inner Core Dislocation (ICD) and Outer Core Bulge (OCB) have appeared inside the Earth due to unbalanced gravitational attraction of the Sun and the Moon, and consequently the mantle is under diurnal cyclic pulsating load by it. In the other words, the inner core's center and axis (Earth's magnetic axis) do not crossed or overlapped on the Earth's center and axis (geographic axis) and distance between these two centers vary permanently in magnitude and direction. See Fig 1,2. ( C is geo-center, C' is inner core's center and always CC'>>0 ). These two phenomena which have diurnal, monthly and yearly cycles, have generated hydro-magneto-thermo-mechanical load including high kinetic energy which produces forced convection system in the outer core and pressurizes the mantle from its bottom. In this paper, we briefly discuss the six scientific results and applications of the hypothesis which are derived from ICD&OCB 1- Cause of apparent solar day length variations, and its overlapping with ICD&OCB variations spectrum, Fig 2, as the first observable factor for proving the PMH. In this section we use data for apparent solar day length variations in year 1998, and Figure's sheet is the same equatorial sheet, minimum of length day is in September 16 which is 24h-21.3 sec., as we can see the length of the ICD&OCB's vector which is result of the Sun and Moon's gravity forces, is minimum but in Dec. 22 which length day is 24h+29 sec, its vector is bigger 2- Generation and diurnal variation of the Earth's magnetic field and its overlapping with ICD&OCB variation as the second observable factor for proving the PMH. In this section we develop the Geodynamo Theory. 3- The ICD&OCB as the main engine of the tectonic plate's motion is discussed. In this section we develop the Plate Tectonics Theory. 4- How four Earth's systems; ICD&OCB, Sun's thermal energy, Sun and Moon's gravity forces interact and work together for generation of tide. 5- Eight factors for diverting ICD&OCB from their regular motion and consequently Earth's inclination changes. 6- Proposing computational procedure including Von Mises model which has residual stress that developed by the authors and mathematical representation of the PMH fin form of an energy equation for calculation of strain energy, W, versus time in a fault for earthquake (big >4.5 earthquakes) forecasting.

  14. 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 a three-dimensional spherical shell using the yin-yang grid, Phys. Earth Planet. Inter, 171 (1-4), 7-18, 2008.

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

    NASA Astrophysics Data System (ADS)

    Smrekar, S. E.

    2015-05-01

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

  16. A comparison of tectonic tremor and microseismicity associated with the 2010 and 2011 slow slip events in the northern Hikurangi subduction zone

    NASA Astrophysics Data System (ADS)

    Todd, E. K.; Schwartz, S. Y.

    2012-12-01

    Tectonic tremor has been identified in New Zealand along the Alpine Fault, triggered by large teleseismic events and associated with slow slip events (SSEs) along the Hikurangi subduction margin. Both long-term and short-term SSEs occur at various intervals along the Hikurangi subduction zone. The SSEs in New Zealand are shallower than SSEs in Cascadia and Japan, and are among the shallowest in the world. Northern Hikurangi short-term slow slip events are associated with an increase in both tectonic tremor and microseismicity, which have been challenging to distinguish. We investigate tremor and seismicity patterns associated with two co-located SSEs in March 2010 (Mw =6.7, maximum slip ~ 120 mm, duration 16 days) and December 2011 (Mw = 6.52, maximum slip ~50 mm, duration 11 days). Using a modified version of the popular envelope cross-correlation technique, we find that tremor locations are similar for both SSEs. The number of earthquakes from the GeoNet catalog for the time periods before, during, and after both SSEs show a stronger seismicity increase during the 2010 event compared with the 2011 event. We will present an analysis of tremor and microseismicity associated with both the 2010 and 2011 short-term slow slip events in the Gisbourne region of the Hikurangi subduction zone.

  17. Digital Tectonic Activity Map

    NSDL National Science Digital Library

    NASA explains that their new site: "The Digital Tectonic Activity Map (DTAM) is a new visualization tool for both researcher and educator alike to better understand tectonic activity of our planet for the past 1 million years. DTAM is a Geographical Information System (GIS) that displays a realistic synoptic view of present global tectonism by filling in the cartographic gap between conventional geological maps and plate reconstruction maps." Maps displaying seismic, interferometry (VLBA), digital tectonic activity (DTA), and global tectonic activity (GTA) can be downloaded in postscript, .gif, or .tiff formats. The DTAM team is under the direction of NASA's Goddard Space Center. This site is an extraordinary resource; for the first time these maps are available in digital format, making current seismic data easily accessible.

  18. Towards community-driven paleogeographic reconstructions: integrating open-access paleogeographic and paleobiology data with plate tectonics

    NASA Astrophysics Data System (ADS)

    Wright, N.; Zahirovic, S.; Müller, R. D.; Seton, M.

    2013-03-01

    A variety of paleogeographic reconstructions have been published, with applications ranging from paleoclimate, ocean circulation and faunal radiation models to resource exploration; yet their uncertainties remain difficult to assess as they are generally presented as low-resolution static maps. We present a methodology for ground-truthing the digital Palaeogeographic Atlas of Australia by linking the GPlates plate reconstruction tool to the global Paleobiology Database and a Phanerozoic plate motion model. We develop a spatio-temporal data mining workflow to validate the Phanerozoic Palaeogeographic Atlas of Australia with paleoenvironments derived from fossil data. While there is general agreement between fossil data and the paleogeographic model, the methodology highlights key inconsistencies. The Early Devonian paleogeographic model of southeastern Australia insufficiently describes the Emsian inundation that may be refined using biofacies distributions. Additionally, the paleogeographic model and fossil data can be used to strengthen numerical models, such as the dynamic topography and the associated inundation of eastern Australia during the Cretaceous. Although paleobiology data provide constraints only for paleoenvironments with high preservation potential of organisms, our approach enables the use of additional proxy data to generate improved paleogeographic reconstructions.

  19. The PLATES Project

    NSDL National Science Digital Library

    This is the web page for PLATES, a program of research into plate tectonic and geologic reconstructions at the University of Texas at Austin Institute for Geophysics. The page contains links to a brief overview of plate tectonics and plate reconstructions using the PLATES Project's global plate reconstruction model, in addition to movies in the format of powerpoint animations which can be downloaded for later use. Models are shown on the evolution of the earth's oceans and the movement of the earth's tectonic plates from the Late Precambrian through the present day, reconstructing (i.e. "predicting") geological environments through geologic history. Maps of the following can be accessed: late Neo-Proterozoic, Silurian, early Jurassic, early Cretaceous, Cretaceous-Tertiary Boundary, and Oligocene. Movies are available on the following subjects: global plate motion, Jurassic to present day, opening of the Indian Ocean, and tectonic evolution of the Arctic region.

  20. Tectonics of East Indonesia

    NASA Astrophysics Data System (ADS)

    Nishimura, Susumu; Suparka, S.

    1990-09-01

    The complex processes resulting in basin formation and inversion during the Tertiary tectonic evolution of Indonesia owe their origin to the interplay between the Indian, Eurasian, Australian and Pacific plates. Within the framework of these major plates and their relative motions, some microplates may be recognized whose tectonic development was constrained by motions of the large plates. Treated as small ridged microplates, their boundaries define the sites of basin formation. Their dynamic development results in the formation and subsequent inversion of basins throughout the region. This paper outlines the tectonic framework of Indonesia throughout Tertiary time in a series of reconstructions and considers the constraints that this implies for microplate motions and basin histories.

  1. Streaking in Cascadia ETS Events and Implications for the Subduction Plate Interface

    NASA Astrophysics Data System (ADS)

    Houston, H.; Ghosh, A.

    2011-12-01

    The manner in which episodic tremor and slow slip (ETS) propagates across the subduction plate interface provides constraints on its properties and the physical processes involved. We have been examining catalogs of tremor locations to study propagation patterns during ETS. Tremor in the large Cascadia ETS events propagates mainly via three modes: 1) the slow along-strike advance of ETS, 2) rapid tremor reversals (RTRs) that propagate back from the tremor front in an opposite direction to the along-strike advance, but at speeds 10-40 times faster (Houston et al., Nature Geoscience, 2011), and 3) streaks, even faster migrations of tremor parallel to the plate-convergence direction at speeds ~ 70 km/hr (Ghosh et al., G3, 2011). The UW Seismology group has recently deployed an EarthScope-funded seismic experiment, the Array of Arrays, to image tremor more precisely with eight subarrays. A 15-month catalog of high-resolution tremor locations has been generated based on the triangulation of back-projected beams from the subarrays. We detect tremor streaks in this catalog automatically and systematically determine streak propagation properties. Key issues for constraining streak-generation processes include systematic differences between up- and down-dip traveling streaks, how streak properties may depend on depth, and whether streaks accelerate or decelerate during propagation. Stacking automatically-detected streaks can address some of these issues. Two approaches to automatically detecting streaks have been developed and applied to the M6.8 2010 ETS. One method declares a streak when averaged epicenters continue to move in a roughly constant direction for more than 10 km. The second declares a streak if epicenters during a specified time interval, say 20 min, are sufficiently well-correlated with time. The two methods agree well and detect several streaks per day of 15-30 min duration with speeds consistent with those inferred for the 2008 ETS. Although the detection methods have no azimuthal bias, most of the detected streaks align with one direction; furthermore, that direction lies much closer to the plate convergence direction than directly down-dip (the down-dip and plate convergence directions differ significantly along most of Cascadia). Many more streaks are detected in the actual catalog than in randomized versions, in which the times within each hour are permuted. These results lend substantial credence to convergence-parallel streaks as real features of ETS. Streak propagation patterns suggest the plate interface is anisotropic along the slip direction. The ubiquity of streaking parallel to plate convergence implies control by corrugated or smeared structures on the plate interface. This could occur via such structures controlling the orientation of an advancing slip pulse, which could carry streaks along its peak (Rubin, G3, 2011), or more directly via heterogeneous physical properties (such as rheology or permeability) elongated in the convergence direction. In this connection, we note that daily tremor bands in Cascadia ETS are also often oriented parallel to the convergence direction whether the ETS is advancing north or south, even though the direction of ETS advance would be expected to affect the orientation of a slip pulse on a homogeneous interface.

  2. Active upper plate thrust faulting in regions of low plate interface coupling, repeated slow slip events, and coastal uplift: Example from the Hikurangi Margin, New Zealand

    NASA Astrophysics Data System (ADS)

    Mountjoy, Joshu J.; Barnes, Philip M.

    2011-01-01

    Contractional fore-arc faulting and deformation is a characteristic feature of many subduction systems. Definition of the three-dimensional geometry and displacement rates of active, upper plate, out-of-sequence thrust faults along ˜250 km of the upper Hikurangi Margin enables us to examine the relationship between fore-arc deformation and the subduction interface in light of interseismic coupling estimates and distribution of slow slip events, both modeled from GPS measurements. These mid-fore-arc structures include the seaward vergent, outer shelf Lachlan and Ariel faults, with vertical separation rates up to 5 mm/yr, and several other major inner shelf faults with rates that are up to 3.8 mm/yr and comparable with Holocene coastal uplift rates. Seismic reflection imaging and geometric projection of these faults at depth indicate that they splay from the region of the plate interface where geodetic inversions for interseismic coupling and slow slip events suggest that the plate boundary undergoes aseismic slip. This observation may indicate either (1) that frictional properties and interseismic coupling on the plate interface are independent and unrelated to the active splay fault deformation in the inner-middle fore arc or (2) that the active splay faulting reflects long-term mechanical coupling related to higher shear stress, or the relative yield strength of the plate interface to the overriding plate, and that the current pattern of interseismic coupling may not be persistent over geological time scales of 20 ka. We compare structure and processes on the northern Hikurangi and Costa Rican margins and find similarities and significant differences astride these subduction systems.

  3. 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)

  4. 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 intrusions. The closest exposed intrusion is dated at 20.7 Ma, shortly before the development of the DSF. Other anomalies can be traced at the edges of our survey area and are likely related to Precambrian outcrops along the rift shoulders. Comparison of the magnetic and the sparser land-gravity data shows the same general azimuth of the magnetic lineament and of the segmented fault system as derived from the gravity and a surprisingly good coincidence between local gravity and magnetic anomalies over the Timna pull-apart basin, owing perhaps to the sensitivity of the high-resolution magnetic data to the thickness of the sedimentary cover.

  5. 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

    Sedimentary sections up to 6-14 km thick lie beneath many areas of the Antarctic continental margin. The upper parts of the sections contain up to 6 km of Cenozoic glacial and possibly non-glacial sequences that have prograded the continental shelf up to 85 km. We describe the Cenozoic sequences using two general categories based on their acoustic geometries. Type IA sequences, which account for most prograding of the Antarctic continental shelf, have complex sigmoidal geometries and some acoustic characteristics atypical of low-latitude margins, such as troughs and mounds lying parallel and normal to the shelf edge and high velocities (2.0-2.6 km/s) for flat layers within 150 m of the seafloor. Type IIA sequences, which principally aggrade the paleoshelf, lie beneath type IA sequences and have mostly simple geometries and gently dipping reflections. The prograding sequences are commonly located near the seaward edges of major Mesozoic and older margin structures. Relatively rapid Cenozoic subsidence has occured due to the probable rifting in the Ross Sea, thermal subsidence in the Antarctic Peninsula, and isostatic crustal flexure in Wilkes Land. In Prydz Bay and the Weddell Sea, prograding sequences cover Mesozoic basins that have undergone little apparent Cenozoic tectonism. Grounded ice sheets are viewed by us, and others, as the principal mechanism for depositing the Antarctic prograding sequences. During the initial advance of grounded ice the continental shelf is flexurally overdeepened, the inner shelf is heavily eroded, and gently dipping glacial strata are deposited on the shelf (i.e type IIA sequences). The overdeepened shelf profile is preserved (a) during glacial times, by grounded ice sheets episodically crossing the shelf, eroding sediments from onshore and inner shelf areas, and depositing sediments at the front of the ice sheet as outer shelf topset-banks and continental slope foreset-aprons (i.e. type IA sequences), and (b) during interglacial 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.

  6. Tectonic development of the SW Arabian Plate margin within the central Arabian flank of the Red Sea rift system

    NASA Astrophysics Data System (ADS)

    Szymanski, E.; Stockli, D. F.; Johnson, P. R.; Kattan, F. H.; Cosca, M. A.

    2009-12-01

    The Red Sea rift system is a prime example of continental rifting and has contributed significantly to our understanding of the geologic processes that manage the rupture of continental lithosphere. Using a combined geo- and thermochronometric approach, we explore the modes and mechanisms of rift margin development by studying Red Sea rift-related geologic products along the central Saudi Arabian flank of the rift system, north of Jeddah. We use apatite and zircon (U-Th)/He thermochronometry and whole-rock 40Ar/39Ar dating of basalt to define the spatiotemporal relationship between rift flank extensional structures and rift-related harrat volcanism. This technical approach permits the reconstruction of the tectonic margin from early rift architecture, to strain distribution during progressive rifting, and through subsequent whole-scale modifications of the rift flank due to thermal and isostatic factors. Constraints on the dynamics of rift flank deformation are achieved through the collection of geologic samples along long-baseline thermochronometric transects that traverse the entire Arabian shield from the coastal escarpment to the inland Paleozoic sedimentary cover sequences. Long-baseline transects resolve the timing of rift flank uplift and reveal the pattern of lithospheric modification during the rupturing of continental lithosphere. Locally, short-baseline elevation transects map the footwall exhumation of major normal faults that delineate both the modern rift margin and inland extensional basins such as the NW-trending Hamd-Jizil basin, a prominent syn-extensional basin comprised of two distinct half-grabens (Jizil and Hamd) located NW of Medina. Diffuse lithospheric extension during the Oligo-Miocene affected a widespread area well inboard from the modern rift margin; samples from footwall blocks that bound the inland Jizil and Hamd half-grabens yield apatite (U-Th)/He cooling ages of 14.7 ± 0.9 Ma and 24.5 ± 1.5 Ma, respectively. The mid-Miocene age is doubly-significant since it reveals not only a Red Sea rift signal 140 km inboard from the modern border fault complex but also underscores the importance of fault reactivation during progressive rifting since the Jizil half-graben is structurally delineated by faults formed within the Neoproterozoic Najd shear zone fabric. Oligo-Miocene apatite (U-Th)/He ages from Jabal Radwa, a pluton exhumed within the border fault complex, show that rift flank exhumation and extensional faulting occurred within the central portion of the Arabian rift flank penecontemporaneous to faulting in the Hamd-Jizil half-graben system. Within the rift flank fault systems, an absence of footwall exhumation ages younger than ~13 Ma confirms that major extensional faulting migrated basin-ward in the middle Miocene during a time of rift reorganization and the establishment of the Dead Sea-Gulf of Aqaba transform. However, minor deepening of the inland Hamd-Jizil basin continued through the late Miocene as relatively young, basin-internal faults cut 17 Ma - 10 Ma basalt flows from harrat Khaybar that had blanketed the region.

  7. 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)

  8. Recent Advances in Mars Tectonics

    NSDL National Science Digital Library

    M.P. Golombek

    This short article from the Jet Propulsion Laboratory features a pre-plate tectonic overview of the tectonic features and processes on Mars. The summary discusses how advances in knowledge expected from the Mars Global Surveyor will be used to explore remaining questions.

  9. Tectonic setting of kimberlites

    NASA Astrophysics Data System (ADS)

    Jelsma, Hielke; Barnett, Wayne; Richards, Simon; Lister, Gordon

    2009-11-01

    Kimberlites can be viewed as time capsules in a global plate tectonic framework. Their distribution illustrates clustering in time and space. Kimberlite ages span the assembly and break-up of a number of supercontinents, such as Rodinia and Gondwana. These supercontinents show time lines with (i) broad periods devoid of kimberlite magmatism corresponding to times of continent stability, and (ii) narrow kimberlite emplacement windows corresponding to times of fundamental plate reorganizations. This episodicity implies that kimberlite emplacement events are intrinsically related to particular stages in the life cycle of supercontinents. The onset of kimberlite magmatism is closely associated with thermal perturbations (thermal insulation, mantle upwelling?) beneath a stagnant or sluggish supercontinent. These perturbations may have caused uplift and the onset of continental break-up through fracture zones propagating into the supercontinent. Subsequent spreading and ocean floor development is marked by apparent cusps and jogs in plate motion paths. Resultant strain is accommodated along trans-lithospheric corridors with episodic uplift and erosion and focused kimberlite melt migration. The corridors are manifest as discontinuities in the lithosphere mantle, measured as geophysical gradients and as changes in mantle lithosphere composition. Within the crust, these corridors are expressed as (a) terrane boundaries, (b) incipient continental rifts, (c) fracture zones, or (d) major dyke swarms. Some kimberlite populations are clustered along parallel sets of corridors widely distributed across a large part of a subcontinent and repeated magmatism is seen within many of the clusters. The association of kimberlite occurrences with discontinuities may be ascribed to favorable conditions for melt production and to resultant melt focusing along high strain zones that contain fractures and faults. Such conditions may be attained during different stages in the evolution of continents: (a) supercontinent formation; (b) incipient rifting (driven by far-field stresses?) and onset of continental break-up; and (c) strain accommodation along the continental continuation of oceanic fracture zones during spreading. Type (c) may show concomitant kimberlite magmatism in separate continents after break-up.

  10. Transverse drainage development along a tectonically active transform plate boundary (San Lorenzo River and Pancho Rico Creek, Monterey County, California)

    NASA Astrophysics Data System (ADS)

    Garcia, A. F.; Stokes, M.

    2003-12-01

    Transverse drainage is often assumed to form as a result of either antecedence or superposition. Drainage-basin geomorphology in the Diablo Range of central California suggests that Pancho Rico Creek established transverse drainage as result of headward erosion, and drainage diversion caused by a landslide. Stream piracy may have also played a significant role. Mesoscale stream catchments within the Diablo Range of central California are elongate parallel to the NW trending San Andreas Fault zone (SAFZ). Principal streams draining these catchments ultimately flow to the west and form transverse drainages across the western ridges of the Diablo Range. Examples include the San Lorenzo River (SLR), which flows into the Salinas Valley at King City, and Pancho Rico Creek (PRC), which flows into the Salinas Valley at San Ardo. Incision patterns, fluvial stratigraphy, wind gaps, and beheaded, SW-flowing piedmont streams suggest that southeastward expansion of the SLR catchment occurred via headward erosion parallel to the SAFZ. Expansion occurred at the expense of SW-flowing piedmont streams, which were separated from the upland parts of their catchment by headward expansion of the SLR catchment. Preliminary results suggest that the upper PRC catchment was captured by the SLR after Qf2 time, but before Qt3 time. PRC recaptured its upper catchment when a Quaternary landslide (Qls) diverted both PRC and the SLR, an event that probably occurred after Qt3 time. Upper PRC drainage basin morphology also suggests recent stream capture. Thus, since Qls time, PRC has been a southeastward expanding transverse drainage.

  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 after one revolution of Mecca-Spiral. Position of Mecca as a geodynamic pole (as well as contribution of lands and waters) satisfies golden ratio with respect to North/South-Pole and Hawaii-Meridian. Mecca with minimum magnetic inclination is a nucleus of global sigmoid (GS). Scorpion-like GS which bended around geomagnetic axis is mature form of primordial Mecca-spiral. Himalaya in the head-center, Rocky/Ands in the tail-bends and Pacific spread between inverse rotations of head-tail. East and West part of GS represent D and T arm respectively. Extended D-arms after one revolution meet each other around Iceland and make constructive interferences therefore highest gravity anomaly formed in the north Atlantic but T-arms after one revolution meet each other in the Indian Ocean and make destructive interferences so lowest gravity anomaly occurred. Earth's face partitionized via tectonic domains each domain has local east and local west and all of them related fractaly to GS. Also we could dissolve earth face via basic topological shape such as sigmoid, Mobius, cup-like, scorpion-like , etc. all of them originated from cycloids.

  12. 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.

  13. Take a Tectonic Vacation

    NSDL National Science Digital Library

    2012-06-26

    This multi-part activity from the National Parks Service blends the science of plate tectonics with the culture and history of places with dramatic geologic landscapes. Learners design an imaginary year-long trip to several tectonically active locations worldwide, investigating the significant human and rock stories of their destinations. This web page has links to educator instructions and learner handouts, including worksheets for trip planning and masters for "Tectonic Passports" and colorful passport stamps and decals. Educators can also download masters for trip journals, which learners assemble and then use to document their observations of the geology and communities they "visit" (via research). After their 'trip,' learners can also create a print, audio, or video advertisement for their favorite tectonic destination.

  14. Tectonic evolution and paleogeography of Europe

    SciTech Connect

    Yilmaz, P.O.; Norton, I.O.; Chuchla, R.J. (Exxon Production Research Company, Houston, TX (United States)); Leary, D.A. (Exxon Exploration Company, Houston, TX (United States))

    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.

  15. 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.

  16. 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.

  17. Reconciling strong slab pull and weak plate bending: The plate motion constraint on the strength of mantle slabs

    E-print Network

    Demouchy, Sylvie

    Keywords: subduction zones plate bending mantle slabs plate tectonics mantle convection rheology Although subducting slabs undergo a bending deformation that resists tectonic plate motions, the magnitude. This gentle bending may ultimately permit plate tectonics on Earth. © 2008 Elsevier B.V. All rights reserved

  18. 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

    Convection in the interiors of planetesimals (asteroids), planets, and satellites is driving the thermal and chemical evolution of these bodies including the generation of possible magnetic fields. The wide size range induces a wide of range of time scales from hundreds of thousands of years for small planetesimals to a few tens of Gigayears for massive super-Earths. Evolution calculations are often based on energy (and entropy) balances parameterizing the transport properties of the interior in suitable ways. These thereby allow incorporating (in parameterized forms) interesting physical processes that depend in one way or another on the transport properties of the interior. The interior will usually be chemically layered in mantles and cores and include ice layers if icy satellites are considered. In addition to magnetic field generation calculated via energy balances of the core and using semi-empirical dynamo strength relations, processes that can be considered include sintering and compaction for small bodies and mantle (or ice) melting, differentiation and even continental growth for full-scaled terrestrial planets. The rheology of the interior is considered temperature and pressure dependent and the concentration of volatiles can be important. For super-Earths, probably the most critical consideration is how the mantle rheology would vary with pressure and thus with depth. It is possible that the increasing pressure will frustrate deep mantle convection thereby reducing the vigor of mantle convection. Possibly, the generation of a magnetic field in a putative iron-rich core will be impossible, if super-Earths at all have earth-like cores. On a much smaller scale, the decay of short-lived radioactives suffices to heat and melt planetesimals, the melting being helped by the low thermal conductivity of the initially porous body. This allows planets to form from pre-differentiated planetesimals thus helping to differentiate and form cores rapidly. On active 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

  19. Plate Tectonics: Lake Mead, Nevada

    NSDL National Science Digital Library

    Earth's surface has changed in countless ways during the 4.6 billion years since it formed, and it continues to change today. This video segment looks at some of the geologic processes that have shaped the landscape near Lake Mead, Nevada, and shows how tensional movement in the vicinity of Lake Mead has begun pulling the North American continent apart. The segment is two minutes thirteen seconds in length.

  20. Plate tectonics of the Mediterranean

    SciTech Connect

    Le Pichon, X.

    1988-08-01

    The present Mediterranean basins are small oceanic crust basins, surrounded by thinned continental margins. They were initially formed through extensional processes within the framework of a broadly collisional regime between Africa and Eurasia. The Eastern Mediterranean was most probably formed during the Cretaceous for the most part. This area is rapidly subducted below the Hellenic arc at least since the middle Miocene and most probably since the Oligocene, and active extension has fragmented the Aegean continent since the middle Miocene. The Western Mediterranean basins were formed during the Neogene and are not yet affected by subduction. The formation of the Western Mediterranean basins presents analogies with the still-active formations of the Aegean basins. Both sets of basins resulted from extension behind a retreating subduction zone. On the other hand, the Eastern Mediterranean basin was generated by rifting between Africa and the Apulian landmass. In all cases, this complex process of successive creations and destructions of extensional basins correspond to dynamic adjustments by continuous redistribution of the oceanic space within the collisional zone.