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1

Plate Tectonics  

NSDL National Science Digital Library

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 ...

Walls, Mrs.

2011-01-30

2

Plate Tectonics  

NSDL National Science Digital Library

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.

2006-01-01

3

Plate Tectonics  

NSDL National Science Digital Library

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 ...

Rohlfing, Mrs.

2011-02-03

4

Plate Tectonics  

NSDL National Science Digital Library

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.

Smoothstone; Company, Houghton M.

5

Plate Tectonics  

NSDL National Science Digital Library

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.

National Science Teachers Association (NSTA)

2007-03-21

6

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.

2002-09-01

7

Plate TectonicsPlate Tectonics Plate TectonicsPlate Tectonics  

E-print Network

ridge systems #12;Concentration of earthquakes #12;Mid-ocean ridge systems #12;Deep Sea Drilling Project, transform boundaries ­ travel 1 to 11 cm/yr relative to one another #12;14 tectonic plates today #12;Mid-ocean

Siebel, Wolfgang

8

Plate Tectonics as Expressed in Geological Landforms and Events  

NSDL National Science Digital Library

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.

Ryan, Jeff

9

Mapping Plate Tectonic Boundaries  

NSDL National Science Digital Library

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.

Kerwin, Michael

10

External Resource: Plate Tectonics  

NSDL National Science Digital Library

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.

1900-01-01

11

Plate Tectonics Animation  

NSDL National Science Digital Library

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.

2002-01-01

12

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.

13

An 8--10 Ma tectonic event on the Cocos Plate offshore Costa Rica: Result of Cocos Ridge collision?  

E-print Network

An 8--10 Ma tectonic event on the Cocos Plate offshore Costa Rica: Result of Cocos Ridge collision 2004. [1] Upper oceanic crust within the Cocos Plate offshore northwestern Costa Rica is dominated Costa Rica: Result of Cocos Ridge collision?, Geophys. Res. Lett., 31, L18601, doi:10.1029/2004GL020272

Fisher, Andrew

14

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.

15

Plate Tectonics Prof. Thomas Herring  

E-print Network

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

Herring, Thomas

16

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

17

Earthquakes and Plate Tectonics  

NSDL National Science Digital Library

This activity, from the Real World Learning Objects Resource Library, allows students to use first-hand data analysis to "determine if there is any pattern to earthquake events and speculate on the causes of earthquakes." Intended to be an introductory activity for a unit of study on earthquakes, this 60-minute activity is complete with learning goals, step-by-step classroom procedures, materials, assessment activities, and resources for further information. The "Content Materials" section contains directions for students and graphics to help students understand earthquakes and plate tectonics. This is an excellent resource for geology and earth science instructors that is ready to use for the classroom.

2007-10-04

18

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

SciTech Connect

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.

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

1993-04-01

19

Plate Tectonic Primer  

NSDL National Science Digital Library

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.

Fichter, Lynn

20

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.

21

Intro to Plate Tectonic Theory  

NSDL National Science Digital Library

This website from PBS provides information about the plate tectonics, the theory that the Earth's outer layer is made up of plates, which have moved throughout time. The four types of plate boundaries are described and illustrated with animations. The first page of plate tectonics also provides a plate tectonics activity and information about related people and discoveries.

2008-05-28

22

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.

23

Beyond Plate Tectonics: Plate Dynamics  

E-print Network

Plate tectonics dogma has resulted in a variety of theories that frequently violate first principles. In this article it is suggested that ridges are in compression, not tension from convection cells, triple junctions cause hot spots (not vice versa), mantle plumes do not cause hot spot tracks, chord push creates pressures well in excess of lithostatic load, the arch effect demonstrates that rifts form both in compression and tension, surging (i.e. the sudden and rapid motion of the plates) occurs episodically, the presence of a basal shear zone a few meters thick during surging, the preferred initiation of subduction zones at the ridge, revision of the Wilson Cycle, the conformance of old school geologists and plate tectonicians, earth-based non bolide impact mass extinctions, the loss of the earths magnetic field and its subsequent reappearance, additional application of the least work (or maximum

Richard Moody

24

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.

2007-04-15

25

Lesson 3. Plate Tectonics Overview  

E-print Network

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

Chen, Po

26

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.

27

Episodic plate tectonics on Venus  

NASA Technical Reports Server (NTRS)

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.

Turcotte, Donald

1992-01-01

28

Plate Tectonics: Earthquake Epicenter  

NSDL National Science Digital Library

This lesson provides an overview of destructive earthquakes and their connection to tectonic movements of the Earth's crust. It includes a discussion of some especially destructive historic earthquakes, and a brief introduction to contintental drift and the theory of plate tectonics. There is also discussion of basic seismology (types of waves) and measures of the magnitude of an earthquake (the Richter Scale). The lesson inlcudes an activity in which students use an online simulator to locate the epicenter of an earthquake using readings from three different seismograph stations. After they have completed the simulation, they attempt to locate the epicenter of a real earthquake using data from the United States Geological Survey (USGS) earthquake website.

Pratte, John

29

Dynamics of Tectonic Plates  

E-print Network

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.

Pechersky, E; Sadowski, G; Yambartsev, A

2014-01-01

30

Intermittent plate tectonics?  

PubMed

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

Silver, Paul G; Behn, Mark D

2008-01-01

31

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

E-print Network

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

Cerveny, Vlastislav

32

The science behind Plate Tectonics  

NSDL National Science Digital Library

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.

Weber, John

33

Plate Tectonics: Lines of Evidence  

NSDL National Science Digital Library

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.

National Science Teachers Association (NSTA)

2006-11-01

34

Tectonics of the Easter plate  

NASA Technical Reports Server (NTRS)

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.

Engeln, J. F.; Stein, S.

1984-01-01

35

The Nature of Tectonic Plates  

NSDL National Science Digital Library

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.

Rhinehart, Ken

36

Plate tectonics on Venus  

NASA Technical Reports Server (NTRS)

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.

Anderson, D. L.

1981-01-01

37

Plate Tectonics II: Plates, plate boundaries, and driving forces  

NSDL National Science Digital Library

The distribution of earthquakes and volcanoes around the world confirmed the theory of plate tectonics first proposed by Wegener. These phenomena also help categorize plate boundaries into three different types: convergent, divergent, and transform.

Egger, Anne

2003-03-18

38

The Theory of Plate Tectonics  

NSDL National Science Digital Library

This is a brief overview of the Theory of Plate Tectonics. According to the theory, the Earth's surface layer, or lithosphere, consists of seven large and 18 smaller plates that move and interact in various ways. Along their boundaries, they converge, diverge, and slip past one another, creating the Earth's seismic and volcanic activities. These plates lie atop a layer of partly molten rock called the asthenosphere. The plates can carry both continents and oceans, or exclusively one or the other. The site also explains interaction at the plate boundaries, which causes earthquakes, volcanoes and other forms of mountain building.

39

Introduction to Plate Tectonics  

NSDL National Science Digital Library

In this lab students interpret bathymetric, topography, sea floor ages, and earthquake distributions to reinforce concepts about the different types of plate boundaries. Each student must interpret several sets of data to determine the location and type of plate boundary. To develop a set of basic analytical skills, the students draw several diagrams and graphs to reinforce the data presented in figures. Students are also asked to think critically about plate rates and what happens to the crust at the different plate boundaries. This activity uses online and/or real-time data and has minimal/no quantitative component.

Cochran, Elizabeth

40

Plate Tectonics Jigsaw  

NSDL National Science Digital Library

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.

Egger, Anne

41

Petroleum occurrences and plate tectonics  

SciTech Connect

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.

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

1983-01-01

42

Comment on "Intermittent plate tectonics?".  

PubMed

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

Korenaga, Jun

2008-06-01

43

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.

44

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.

45

OBSERVATIONS RELATED TO PLATE TECTONICS  

E-print Network

It is useful to assess the global data sets that are most relevant to plate tectonics. Below are a series of global maps that help to confirm various aspects of plate tectonic theory. Plate boundaries are classified as ridges, transform faults, or subduction zones based on basic observations of topography (Figure 1) and seismicity (Figure 2). Remarkably, nearly all seafloor spreading ridges lie at a depth of 2500-3000 m below sea level which is the level of isostasy for hot thin lithosphere. Depths gradually increase away from the ridges because of cooling and thermal contraction so old ocean basins are commonly 4500- 5000 m deep. Fracture zones and aseismic ridges also show up on these maps. Global seismicity (magnitude> 5.1 Figure 2) highlights the plate boundaries and reveals their tectonic style. Shallow normal-faulting earthquakes (< 30 km deep) are common along slow-spreading ridges but largely absent along faster-spreading ridges where the plates are too thin and weak to retain sufficient elastic energy to generate large earthquakes. Transform faults are characterized by relatively shallow (< 30 km) strike-slip earthquakes and they are common along both fast- and slow-spreading ridges. The deeper earthquakes (green and blue dots in Figure 2) occur only in subduction zones where sheets of seismicity (i.e., Benioff zones) are critical evidence that relatively cold lithosphere is

David T. S

46

6, 793830, 2014 Plate tectonic raster  

E-print Network

by a reverse projection onto rotated5 tectonic plates on the surface of the globe. This decouples the rendering data attached to tectonic plates and reconstructed through geological time. This capability forms to tectonic plates on the surface of the globe and reconstructing them to past geological configurations using

Müller, Dietmar

47

First Draft 1 April 2003 Plate Tectonics ;  

E-print Network

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

Anderson, Don L.

48

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

E-print Network

Author's personal copy Plate tectonic reconstructions with continuously closing plates$ Michael are downwellings controlled by the history of subduction, that these mantle down- wellings push hot mantle

Bower, Dan J.

49

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

E-print Network

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

Sheldon, Nathan D.

50

Musical Plates: A Study of Plate Tectonics  

NSDL National Science Digital Library

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.

2007-01-01

51

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

52

Planetary science: Plate tectonics on ice  

NASA Astrophysics Data System (ADS)

Jupiter's icy moon Europa is criss-crossed by extensional features. A tectonic reconstruction suggests that Europa's extension is balanced by subduction -- if so, Earth may not be the only planetary body with a plate tectonic system.

Selvans, Michelle M.

2014-10-01

53

Continental tectonics in the aftermath of plate tectonics  

Microsoft Academic Search

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

Peter Molnar

1988-01-01

54

How Mantle Slabs Drive Plate Tectonics  

Microsoft Academic Search

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

Clinton P. Conrad; Carolina Lithgow-Bertelloni

2002-01-01

55

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 ...

56

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

57

Plate Tectonics, the Cause of Earthquakes  

NSDL National Science Digital Library

This site from the University of Nevada at Reno provides a large number of images that illustrate plate tectonics and the resulting volcanoes and earthquakes. Diagrams and maps, along with numerous satellite images, show the effect of plate tectonics on Earth's surface. Links provide further information.

2009-04-14

58

Plate Tectonic Cycle. K-6 Science Curriculum.  

ERIC Educational Resources Information Center

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

Blueford, J. R.; And Others

59

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

NASA Astrophysics Data System (ADS)

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

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

2010-01-01

60

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

Microsoft Academic Search

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

G. M Stampfli; G. D. Borel

2002-01-01

61

Mantle dynamics with induced plate tectonics  

Microsoft Academic Search

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

Yanick Ricard; Christophe Vigny

1989-01-01

62

Continental tectonics in the aftermath of plate tectonics  

NASA Technical Reports Server (NTRS)

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.

Molnar, Peter

1988-01-01

63

Igneous Rock Compositions and Plate Tectonics  

NSDL National Science Digital Library

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.

Glazner, Allen

64

Hierarchical self-organization of tectonic plates  

E-print Network

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.

Morra, Gabriele; Mller, R Dietmar

2010-01-01

65

Google Earth Plate Tectonics File (.kmz)  

NSDL National Science Digital Library

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.

Unavco

66

Plate Tectonics-Discover Our Earth  

NSDL National Science Digital Library

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.

Institute for the Study of the Continents (INSTOC); University, Cornell

67

Investigating Plate Tectonics with Google Earth  

NSDL National Science Digital Library

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.

Pratt-Sitaula, Beth

68

What on Earth is Plate Tectonics?  

NSDL National Science Digital Library

This web site was put together by the U.S.G.S. (United States Geological Survey) and the N.P.S. (National Park Service) and provides an overview of plate tectonics. It begins by explaining about the Earth's core, mantle, and crust. It then discusses the crustal plates and the types of plate boundaries (convergent, divergent and transform). The lesson ends with paleogeographic reconstructions of plate distributions from the past 650 million years.

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

E-print Network

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

van Thienen, Peter

70

Tectonic events in Greenland  

NASA Astrophysics Data System (ADS)

In Greenland a station separation of around 400km mean that many earthquakes are only detected on one or two stations. The development of the seismic monitoring have gone from having only three seismic stations in Greenland up to the late 1990'ies, till today where there are 18 permanent stations. All stations are equipped with broadband sensors and all of the permanent stations transmit data in real time. The recent major improvement of the seismic monitoring is performed by the Greenland ice sheet monitoring network (GLISN, http://glisn.info). The primary goal of GLISN is to provide broadband seismic data for the detection of glacial earthquakes. GLISN is now fully implemented with Iridium real time data transfer is in operation at five stations. In the Ammassalik region in Southeast Greenland, where small earthquakes often are felt, data from a temporary additional station has been utilized for a study covering 9 months in 2008/9. In this period 62 local earthquakes have been analyzed and re-located. Some of the events had formerly been located from distant stations by using a universal earth model. The result of this localization was a scattered distribution of the events in the region. The locations have now been improved by using a local earth model along with phase readings from two local stations not previously included; ANG in Tasiilaq and ISOG in Isortoq. From relocating the events two zones with a higher degree of seismicity than in the rest of the region are observed. The first zone is located by felsic intrusions. The second zone is at the boundary between the Archaean Craton and the Ammasalik region where reworked Archaean gneisses are dominating the geology. During the analysis it was observed that the additional information from the local stations are of great importance for the result. Active broad band stations in Greenland

Dahl-Jensen, T.; Voss, P.; Larsen, T.; Pinna, L.

2012-12-01

71

Plate Tectonics: Moving Middle School Science  

NSDL National Science Digital Library

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.

Barber, Carolee; Ridgway, Judith

2004-11-01

72

Spreading continents kick-started plate tectonics  

NASA Astrophysics Data System (ADS)

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.

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

2014-09-01

73

Spreading continents kick-started plate tectonics.  

PubMed

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

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

2014-09-18

74

Tectonic Plate Movements and Hotspots  

NSDL National Science Digital Library

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.

Rhinehart, Ken

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Plate Tectonics Education Website and CD  

NSDL National Science Digital Library

'Learning With Data' is a complete learning package aimed at supporting science process teaching and learning through the exploration of Earth Data. All of the data, tools, activities, background learning materials, homework assignments, and inquiry activities needed to implement data-rich investigations into the theory of Plate Tectonics are described on the website and provided in an accompanying CD-ROM, available for purchase. Students may select and plot earthquakes, recent quakes from USGS, elevation profiles, sea floor age profiles, volcano locations, island ages, and heat flow data, then assemble and annotate the plots to use in writing activities or lab reports. The content contains animated presentations of plate tectonics theory, interior of the Earth, and volcanoes and their role in plate tectonics.

76

Plate Tectonics in the Late Paleozoic  

NASA Astrophysics Data System (ADS)

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

Domeier, Mat; Torsvik, Trond

2014-05-01

77

Plate Tectonics: Recycling the Seafloor  

NSDL National Science Digital Library

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.

Lawrence, Lisa A.

2012-12-27

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The generation of plate tectonics from mantle convection David Bercovici  

E-print Network

Frontiers The generation of plate tectonics from mantle convection David Bercovici � 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

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Compare Data for Plate Tectonics  

NSDL National Science Digital Library

Andrew Goodwillie, Chris Condit, Pat Kennelly, Warren Tomkiewicz, Mark Leckie, Ed Nuhfer, Mark Abolins, Lensyl Urbano, Jose Hurtado, Ned Gardiner, Gareth Fanning, Elli Goeke, and Glenn Richard Topic: plate ...

80

Tracking Tectonic Plates Using Two Independent Methods  

NSDL National Science Digital Library

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.

Goodell, Laurel

81

Plate tectonics and hotspots - The third dimension  

Microsoft Academic Search

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

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

1992-01-01

82

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.

83

Global Cretaceous plate tectonics and paleogeography  

SciTech Connect

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

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

1985-01-01

84

FUNDAMENTALS OF PLATE TECTONICS Fall Semester 2012-13  

E-print Network

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

Polly, David

85

Lab 4: Plate Tectonics Locating Geologic Hazards Introduction  

E-print Network

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

Chen, Po

86

Assessment of the cooling capacity of plate tectonics and  

E-print Network

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

van Thienen, Peter

87

Afrotheria: Plate tectonics meets genomics S. Blair Hedges*  

E-print Network

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

Hedges, Blair

88

Strain weakening enables continental plate tectonics  

NASA Astrophysics Data System (ADS)

Much debate exists concerning the strength distribution of the continental lithosphere, how it controls lithosphere-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. Here we show that the duality of strength of the lithosphere corresponds to different stages of microstructural evolution. Geological constraints on lithospheric strength and large strain numerical experiments reveal that the development of layers containing weak minerals and the onset of grain boundary sliding upon grain size reduction in olivine cause strain localisation and reduce strength in the crust and subcontinental mantle, respectively. The positive feedback between weakening and strain localization leads to the progressive development of weak plate boundaries while plate interiors remain strong.

Gueydan, Frdric; Prcigout, Jacques; Montsi, Laurent G. J.

2014-09-01

89

Reducing Plate Tectonic Misconceptions with Lecture Tutorials  

NASA Astrophysics Data System (ADS)

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 research indicates that the Lecture Tutorials successfully decrease student misconceptions. For example, few introductory students identify the mantle wedge as the location of melting at subduction zones. Instead, students frequently think melting occurs at the trench, in magma chambers within volcanoes, or where images commonly show the subducting slab disappearing. One of the Lecture Tutorials helps the students determine why melting occurs and therefore identify the correct locations of melting at convergent boundaries, divergent boundaries, and hotspots. This Lecture Tutorial includes a hypothetical debate with statements expressing the misconceptions and one expressing the correct scientific idea of where melting occurs. Students are asked to explain why they agree with one of the statements, so they must directly think about any misconceptions they may have. Additional difficulties addressed by the Lecture Tutorials include identification of the direction of plate movement at ocean ridges and the locations and formation of basic plate tectonic features, such as trenches, volcanoes, ocean ridges, and plate boundaries. After instruction, students completed questionnaires that probed their understanding of plate tectonics, and students who completed the Lecture Tutorials performed significantly better on relevant questions. For example, when asked to circle the locations on a diagram where melting occurred, students who completed the Lecture Tutorials correctly circled the mantle wedge more often than other students (33% vs. 8%). The percentage of students who drew incorrect arrows indicating converging plates at ocean ridges was smaller for students who completed the Lecture Tutorials (9%) than for those who did not (21%). Because the Lecture Tutorials frequently asked students to identify, explain, and draw basic features relevant to plate tectonics, we hypothesized that students who completed the Lecture Tutorials would correctly identify more of these features, and this is what we observed. Students who completed the Lecture Tutorials identified 6.3 features on average, compared to 2.8 for those students who did not complete the Lecture Tutorials. The Lecture Tutorial students correctly labeled 82% of the identified features, compared to 71% for other students. The plate tectonic Lecture Tutorials along with others on additional introductory geoscience topics are available as a workbook called Lecture Tutorials for Introductory Geoscience published by W. H. Freeman.

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

2009-12-01

90

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

Microsoft Academic Search

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

Erwin Scheibner

1973-01-01

91

IRIS: Videos on Plate Tectonics and Earthquakes  

NSDL National Science Digital Library

This is a collection of short informational videos on dynamic Earth processes, developed to teach how earthquakes happen and why they are studied. The videos explore tectonic plate motion, elastic rebound, fault models, types of boundaries, locating earthquake epicenters, seismic wave paths, and more. This resource is part of IRIS, the Incorporated Research Institutions for Seismology, a consortium of international laboratories and data collection centers.

2011-03-18

92

Whole Earth Structure and Plate Tectonics  

E-print Network

/29/2010 Age of Ocean Floor http://www.ngdc.noaa.gov/ #12;© EarthStructure (2nd ed) 1311/29/2010 Oceanic vsWhole 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

93

Generation and Initiation of Plate Tectonics on Terrestrail Planets  

NASA Astrophysics Data System (ADS)

The question of why plate tectonics occurs on Earth, but not on the other planets of our solar system, is one of the most fundamental issues in geophysics and planetary science. I study this problem using numerical simulations of mantle convection with a damage-grainsize feedback (grain-damage) to constrain the conditions necessary for plate tectonics to occur on a terrestrial planet, and how plate tectonics initiates. In Chapter 2, I use numerical simulations to determine how large a viscosity ratio, between pristine lithosphere and mantle, damage can offset to allow mobile (plate-like) convection. I then use the numerical results to formulate a new scaling law to describe the boundary between stagnant lid and plate-like regimes of mantle convection. I hypothesize that damage must reduce the viscosity of shear zones in the lithosphere to a critical value, equivalent to the underlying mantle viscosity, in order for plate tectonics to occur, and demonstrate that a scaling law based on this hypothesis reproduces the numerical results. For the Earth, damage is efficient in the lithosphere and provides a viable mechanism for the operation of plate tectonics. I apply my theory to super-Earths and map out the transition between plate-like and stagnant lid convection with a "planetary plate-tectonic phase" diagram in planet size-surface temperature space. Both size and surface temperature are important, with plate tectonics being favored for larger, cooler planets. This gives a natural explanation for Earth, Venus, and Mars, and implies that plate tectonics on exoplanets should correlate with size, incident solar radiation, and atmospheric composition. In Chapters 3 and 4 I focus on the initiation of plate tectonics. In Chapter 3, I develop detailed scaling laws describing plate speed and heat flow for mantle convection with grain-damage across a wide parameter range, with the intention of applying these scaling laws to the early Earth in Chapter 4. Convection with grain-damage scales differently than Newtonian convection; whereas the Nusselt number, Nu, typically scales with the Rayleigh number, Ra, to the 1/3 power, for grain-damage this exponent is larger because increasing Ra also enhances damage. In addition, Nu and plate velocity are also functions of the damage to healing ratio, (D/H); increasing D/H increases Nu (or plate speed) because more damage leads to more vigorous convection. In Chapter 4, I demonstrate that subduction can be sustained on the early Earth, that the style of subduction at this time was different than modern day plate tectonics, and that such subduction (or proto-subduction) can initiate rapidly after magma ocean solidification. The scaling laws from Chapter 3 show that, though either higher interior mantle temperatures or higher surface temperatures lead to slower plates, proto-subduction, with plate speeds of at least 1.5 cm/yr, can still be maintained in the Hadean, even if the primordial atmosphere was CO2 rich. Furthermore, when the interior mantle temperature is high (e.g. above ? 2000 K), the mode of subduction switches to a "sluggish subduction" style, where downwellings are more drip-like than slab-like and plate boundaries are more diffuse. Numerical models of post-magma ocean mantle convection, and a scaling analysis based on the results of these models, demonstrate that proto-plate tectonics likely initiates within 100 Myrs of magma ocean solidification. Combined with the conclusion that proto-subduction could be maintained on the early Earth, my results are consistent with evidence for Hadean subduction from zircon data, and indicate that the subduction inferred from zircons may have been distinct from modern day plate tectonics. After the initiation of proto-subduction, which occurs as a rapid overturn of the whole lithosphere, mobile lid convection takes place as non-plate tectonic "sluggish subduction" As both the mantle interior and climate cool, modern style plate tectonics develops. The rapid, initial subduction event may help hasten the onset of

Foley, Bradford J.

94

Writing and Visualization for Teaching Plate Tectonics  

NASA Astrophysics Data System (ADS)

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

Thomas, S. F.

2004-12-01

95

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

E-print Network

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

Müller, Dietmar

96

Quantitative tests for plate tectonics on Venus  

NASA Technical Reports Server (NTRS)

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.

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

1981-01-01

97

Caribbean tectonics and relative plate motions  

NASA Technical Reports Server (NTRS)

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.

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

1984-01-01

98

Dynamic Plate Boundaries and Restored Synthetic Isochrons: The Indispensable Tools To Constrain Plate Tectonic Models  

NASA Astrophysics Data System (ADS)

We developed a plate tectonics 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 have been constructed through time by adding/removing oceanic material symbolized by syntethic isochrones, to ma- jor continents and terranes. These oceanic isochrons have been constructed through time in order to define the location of the spreading ridges and to restore subducted ocean basins. To simplify the process we worked with a symmetrical sea floor spread- ing for the main oceans (Paleo- and NeoTethys). Driving forces like slab pull and slab buoyancy were used to constrain the evolution of paleo-oceanic domains. This ap- proach offers a good control on the sea floor spreading and plate kinematics. This new method represents a distinct departure from classical continental drift reconstructions, which are not constrained due to the lack of plate boundaries. This model allows a more comprehensive analysis of the development of the Tethyan realm in space and time. In particular, the relationship between the Variscan and the Cimmerian cycles in the Mediterranean-Alpine realm is clearly illustrated by numerous maps. For the Alpine cycle, the relationship between the Alpides senso stricto and the Tethysides is also explicable in terms of plate tectonic development of the Alpine Tethys-Atlantic domain versus the NeoTethys domain.

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

99

Inevitability of Plate Tectonics on Super-Earths  

E-print Network

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.

Valencia, Diana; Sasselov, Dimitar D

2007-01-01

100

Inevitability of Plate Tectonics on Super-Earths  

E-print Network

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.

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

2007-10-03

101

Inevitability of Plate Tectonics on Super-Earths  

E-print Network

The recent discovery of super-Earths (masses ? 10 M?) has initiated a discussion about conditions for habitable worlds. Among these is the mode of convection, which influences a planets 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. Subject headings: planetary systems planets and satellites Earth 1 corresponding author 2

Diana Valencia; Richard J. Oconnell; Dimitar D. Sasselov

102

Tectonic development of the Maya plate  

SciTech Connect

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.

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

1985-01-01

103

Plate tectonic history of the Arctic  

NASA Technical Reports Server (NTRS)

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.

Burke, K.

1984-01-01

104

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

SciTech Connect

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.

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

1995-12-31

105

Catastrophic Plate Tectonics: A Global Flood Model of Earth History  

Microsoft Academic Search

In 1859 Antonio Snider proposed that rapid, horizontal divergence of crustal plates occurred during Noah's Flood. Modern plate tectonics theory is now conflated with assumptions of uniformity of rate and ideas of continental \\

Steven A. Austin; John R. Baumgardner; D. Russell Humphreys; Andrew A. Snelling; Larry Vardiman; Kurt P. Wise

106

The spots and stains of plate tectonics  

NASA Astrophysics Data System (ADS)

This paper describes a synthesis characterized by broad scope, substantial support, and some speculation. The framework for the synthesis is the speculative concept that the process of convergence and collision of large landmasses disrupts the fluid regime of the collision zone and adjoining areas. The disturbed fluids leave a record of their disruption and transport in great spots and stains. Some of these spots and stains persist in the modern geologic record where they are known as mineral deposits, mineral occurrences, oil fields, gas fields, tar sands, diagenesis, authigenesis, metamorphism, dolomitization, fluid inclusions, and paleoremagnetization. Various observed characteristics of these phenomena provide supporting evidence of such diversity and consistency that the concept seems firmly rooted in observation. Nevertheless, many opportunities for further testing remain. If the synthesis is more or less correct, then a major link between plate tectonics, or global-scale geodynamics, and a wide variety of terrestrial geological observations of lesser scale is in hand.

Oliver, Jack

1992-01-01

107

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

PubMed

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

Korenaga, Jun

2012-07-01

108

Plate tectonics and petroleum potential of the Laptev Sea region  

SciTech Connect

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

Savostin, L.; Drachev, S.; Baturin, D. (LARGE International, Moscow (USSR))

1991-08-01

109

This Dynamic Earth: The Story of Plate Tectonics  

NSDL National Science Digital Library

This site offers the online version of a book published by the United States Geological Survey (USGS). It is intended to provide a brief introduction to the concept of plate tectonics, highlighting some of the people and discoveries that advanced the development of the theory. It is the companion volume to the map, 'This Dynamic Planet', which shows the locations of major volcanic belts, fault systems, and other tectonic features. Topics include a history of the theory; scientific developments that spurred its development; the mechanics of plate motions; and the relationship of hotspots to plate tectonic theory. There is also an overview of unanswered questions regarding plate tectonics and a discussion of impacts of tectonic activity (earthquakes and volcanoes) on human populations. A downloadable, printable version (PDF) of the book is available, and hardcopies can be purchased.

110

Silurian to Early Carboniferous plate tectonic model of Central Europe  

NASA Astrophysics Data System (ADS)

The presented plate tectonic model focuses on Silurian to Early Carboniferous evolution of Central Europe with special attention given to the Sudetes region (north and north-east part of the Bohemian Massif). During our studies, we tested alternative models focused on the position of the Armorican terranes, known as the Armorican Terrane Assembly (ATA) (e.g.: Matte, 2001) and tried to refine the existing reconstructions, which describe Armorica as an individual continent during the Late Silurian and Devonian (e.g. Lewandowski, 2003, Winchester, 2002). Our plate tectonic model depict that these small blocks were scattered along the northern margin of Gondwana, where they formed the "Armorican Spour" as suggested by Kroner and Romer (2013). The seaways were present between blocks. Because of the north dipping subduction zone along the southern margin of the Laurussia continent the back-arc basin and island arc were formed. The narrowing of the Rheic ocean led to the complicated collision of Gondwana and Laurussia. Three main stages of this event can be distinguished: (1) collision of the Armorican Spour with the Laurussian island arc, (2) back-arc basin closure, (3) final Gondwana and Laurussian collision. Those stages correlate well with Variscan Subduction Zone System proposed by Kroner and Romer (2013). Interactive modeling performed in GPlates, shows that the presented model is valid from kinematic and geometrical point of view. Kroner U., Romer R., L., 2013, Two plates - many subduction zones: the Variscan orogeny reconsidered. Gondwana Research, 24: 298-329. Lewandowski M., 2003, Assembly of Pangea: Combined paleomagnetic and paleoclimatic approach, Advances in Geophysics, 46: 199-236 Matte P., 2001, The Variscan collage and orogeny (480 290 Ma) and the tectonic definition of the Armorica microplate: a review. Terra Nova, 13: 122C128. Winchester J., A., The Pace TMR Network Team, 2002, Palaeozoic amalgamation of Central Europe: new results from recent geological and geophysical investigations, Tectonophysics, 360: 5-21

Golonka, Jan; Barmuta, Jan; Barmuta, Maria

2014-05-01

111

Earthquakes Living Lab: The Theory of Plate Tectonics  

NSDL National Science Digital Library

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.

Civil And Environmental Engineering Department

112

Plate tectonics and the Gulf of California region  

SciTech Connect

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.

Schmidt, N.

1990-11-01

113

The Uncertainties of Finite Rotations in Plate Tectonics  

Microsoft Academic Search

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

S. J. Hellinger

1981-01-01

114

Seismic gaps and plate tectonics: Seismic potential for major boundaries  

Microsoft Academic Search

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

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

1979-01-01

115

Recent tectonic plate decelerations driven by mantle convection  

NASA Astrophysics Data System (ADS)

We explore recent changes in tectonic plate velocities using a model of mantle flow that is based on a new high-resolution global tomography model derived from simultaneous inversions of global seismic, geodynamic and mineral physical data sets. This plate-coupled mantle convection model incorporates a viscosity structure that reconciles both glacial isostatic adjustment and global convection-related data sets. The convection model successfully reproduces present-day plate velocities and global surface gravity and topography constraints. We predict time-dependent changes in mantle buoyancy that give rise to present-day decelerations of several major plates, in particular the fast-moving Pacific and Nazca plates. We verify the plausibility of these predicted plate decelerations using space geodetic and oceanic magnetic anomaly constraints on tectonic plate motions. These plate kinematic constraints are employed to determine a new global map of present-day plate decelerations that agree well with the mantle flow predictions.

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

2009-12-01

116

Earth Exploration Toolbook Chapter: Evidence for Plate Tectonics  

NSDL National Science Digital Library

DATA: Sea Floor Age, Volcano and Earthquake Distributions. TOOL: My World GIS. SUMMARY: Identify relationships among sea-floor age, earthquakes, and volcanoes to understand how they support the theory of plate tectonics.

Smith, David; Kao, Franklin; Holzer, Missy

117

On volcanism and thermal tectonics on one-plate planets  

NASA Technical Reports Server (NTRS)

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.

Solomon, S. C.

1978-01-01

118

Geological and plate tectonic setting of the Longitudinal Valley  

E-print Network

of the Luzon arc. (b)Regional Tectonic of Taiwan. The South China Sea crust subducts beneath the Philippine Sea 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

Winfree, Erik

119

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

E-print Network

GEOPHYSICAL JOURNAL INTERNATIONAL, 133, 379�389, 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

120

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

E-print Network

The influence of tectonic plates on mantle convection patterns, temperature and heat flow Julian P by the geometry of tectonic plates. In comparison with a small plate, less heat per unit area must be lost through

Gable, Carl W.

121

Optimal Planet Properties For Plate Tectonics Through Time And Space  

NASA Astrophysics Data System (ADS)

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

Stamenkovic, Vlada; Seager, Sara

2014-11-01

122

The generation of plate tectonics from mantle convection  

Microsoft Academic Search

In the last decade, significant progress has been made toward understanding how plate tectonics is generated from mantle dynamics. A primary goal of plate-generation studies has been the development of models that allow the top cold thermal boundary layer of mantle convection, i.e. the lithosphere, to develop broad and strong plate-like segments separated by narrow, weak and rapidly deforming boundaries;

David Bercovici

2003-01-01

123

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

E-print Network

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

Smith-Konter, Bridget

124

Archean magmatism and deformation were not products of plate tectonics  

Microsoft Academic Search

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

Warren B. Hamilton

1998-01-01

125

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

NASA Astrophysics Data System (ADS)

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 evolution of paleo-oceanic domains. This approach offers good control of sea-floor spreading and plate kinematics. This new method represents a distinct departure from classical continental drift reconstructions, which are not constrained, due to the lack of plate boundaries. This model allows a more comprehensive analysis of the development of the Tethyan realm in space and time. In particular, the relationship between the Variscan and the Cimmerian cycles in the Mediterranean-Alpine realm is clearly illustrated by numerous maps. For the Alpine cycle, the relationship between the Alpides senso stricto and the Tethysides is also explicable in terms of plate tectonic development of the Alpine Tethys-Atlantic domain versus the NeoTethys domain.

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

2002-02-01

126

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

E-print Network

Organization of the tectonic plates in the last 200 Myr Gabriele Morra a,n , Maria Seton b a c t The present tessellation of the Earth's surface into tectonic plates displays a remarkably in the past to explore the dynamics governing this timescale. The Pacific plate is the largest tectonic plate

Müller, Dietmar

127

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

E-print Network

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

Sandiford, Mike

128

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

E-print Network

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

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

129

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

E-print Network

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

Torsvik, Trond Helge

130

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

E-print Network

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

Anderson, Don L.

131

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.

132

Teaching about Plate Tectonics and Faulting Using Foam Models  

NSDL National Science Digital Library

This demonstration of plate tectonic principles, plate boundary interactions, and the geometry and relative motions of faulting of geologic layers uses 3-D foam models. The models aid in visualization and understanding of plate motions and faulting because they are three-dimensional, concrete rather than abstract descriptions or diagrams, can be manipulated by the instructor and the students, and can show the motions of the plates and faults through time in addition to the three-dimensional configuration of the plates or layers. The models illustrate relatively simple motions and geologic structures, including faulting and plate boundaries, compressional motion and resulting reverse (also called thrust) faults, horizontal slip or strike-slip fault motion, slip or strike-slip fault motion, transform or strike-slip plate boundaries, and elastic rebound.

Braile, Larry

133

Repeating tectonic tremors on a middle-aged oceanic plate: Kyushu, Japan & North Island, New Zealand  

NASA Astrophysics Data System (ADS)

Tectonic tremors and low-frequency earthquakes (LFEs) are observed in many subduction zones, where typically young and warm oceanic plate is subducting. Here we report the discovery of tectonic tremor in Kyushu, Japan and the North Island of New Zealand, where a middle-aged oceanic plate (>50Ma) is subducting. Generally, old oceanic plate is considered incapable of supplying water near the Moho discontinuity of the overriding plate, where tectonic tremor occurs in warm subduction zones, This is probably because dehydration reaction is delayed by the low temperature of old subducting plate, but the limit of the age or temperature for tremor generation has not been clear yet. Thus the discovery of tremor in middle-aged subduction zones helps to constrain the condition for tremor generation. We apply the envelope correlation method of Ide et al. (2010) to continuous records of Hi-net NIED for Kyushu and Geo-Net for the North Island. In both data sets, we find characteristic waveforms of tectonic tremors, which are dominant in frequency range at 2-8 Hz, with detectable S-wave arrivals and obscure P-waves, and successive for a long time. However, waveforms have very small amplitude, which makes low signal to noise ratio and has prevented detection. In Kyushu, we identify eight tremor episodes repeated almost every eight month, from April 2004 to September 2009. S-P times measured by cross-correlating envelopes between vertical and horizontal components indicate that these tremors occurred at 35-45 km depth, which might be a little shallower than the plate interface, since a receiver function study estimated the local depth of the plate interface as about 50 km (Abe et al., 2011). The distribution of tectonic tremors is limited in a small area, unlike wide and dense tremor activities in the Nankai subduction zone next to Kyushu. Beneath the North Island, Kim et al., (2011) discovered tectonic tremor near the northern end of the island and Fry et al. (2011) detected tectonic tremors triggered by surface wave from 2010 Chile Mw8.8 Earthquake near the center of the island. Tectonic tremors discovered in the present study are close to that reported by Fry et al. (2011), but they are not accompanied with triggering events. These tectonic tremors are located near the bottom edge of slow slip events (Wallace and Beavan, 2006), suggesting close relations.

Yabe, S.; Ide, S.

2011-12-01

134

Multi Phase Flows and Computational Aspects of Plate Tectonics  

E-print Network

A Lagrangian Particle Finite Element scheme is presented which is suited to problems in which material composition and history must be tracked through very large deformations associated with creeping fluid flow. The method is applied to large-scale geodynamic modeling in which some parts of the system are actively convecting which others remain nearly stagnant. Introduction Geology records the slow movements of the continents with respect to one another; the theory of plate tectonics describes the manner in which this happens. Plate tectonics is regarded as the surface manifestation of solid-state convection in underlying rocky mantle which is responsible for releasing the Earths inner heat. In the past it has proved to be very difficult to reproduce plate-like behaviour selfconsistently at the surface of a convection experiment. The intimate connection between plate boundaries and earthquakes suggests that this is because such experiments lack a description of the brittle nature of ...

Louis Moresi; Hans-Bernd Mhlhaus

135

Catastrophic Plate Tectonics: The Physics Behind the Genesis Flood  

Microsoft Academic Search

The wealth of new data, mostly from the ocean bottom, that precipitated the acceptance of plate tectonics during the 1960s simultaneously also opened the door for the first time in more than 200 years to a technically credible defense of the Genesis Flood. From the mid-1700s through the days of Hutton, Lyell, and Darwin to the 1960s, it overwhelmed the

John R. Baumgardner

136

Plate Tectonism on Early Mars: Diverse Geological and Geophysical Evidence  

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

137

INTRODUCTION Unlike Earth, Venus apparently lacks plate tectonics. Thus  

E-print Network

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

Jurdy, Donna M.

138

Catastrophic plate tectonics: A global Flood model of earth history  

E-print Network

In 1859 Antonio Snider proposed that rapid, horizontal divergence of crustal plates occurred during Noahs Flood. Modern plate tectonics theory is now conflated with assumptions of uniformity of rate and ideas of continental drift. Catastrophic plate tectonics theories, such as Snider proposed more than a century ago, appear capable of explaining a wide variety of dataincluding biblical and geologic data which the slow tectonics theories are incapable of explaining. We would like to propose a catastrophic plate tectonics theory as a framework for Earth history. Geophysically, we begin with a pre-Flood earth differentiated into core, mantle, and crust, with the crust horizontally differentiated into sialic craton and mafic ocean floor. The Flood was initiated as slabs of oceanic floor broke loose and subducted along thousands of kilometers of pre-Flood continental margins. Deformation of the mantle by these slabs raised the temperature and lowered the viscosity of the mantle in the vicinity of the slabs. A resulting thermal runaway of the slabs through the mantle led to meters-per-second mantle convection. Cool oceanic crust which descended to the core/mantle boundary induced rapid reversals of the earths magnetic field. Large plumes originating near the core/mantle boundary expressed themselves at the surface as fissure eruptions and flood basalts. Flow

Steven A. Austin; John R. Baumgardner; D. Russell Humphreys; Andrew A. Snelling; Larry Vardiman Phd; Kurt P. Wise

1994-01-01

139

Intraplate Stress as an Indicator of Plate Tectonic Driving Forces  

Microsoft Academic Search

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

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

1976-01-01

140

Numerical modelling of instantaneous plate tectonics  

NASA Technical Reports Server (NTRS)

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.

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

1974-01-01

141

Inversion for the driving forces of plate tectonics  

NASA Technical Reports Server (NTRS)

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.

Richardson, R. M.

1983-01-01

142

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

E-print Network

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

143

A New Test of Plate Tectonics.  

ERIC Educational Resources Information Center

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)

Shea, James Herbert

1989-01-01

144

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.

145

Integrating Seismological and Tectonic Studies to Constrain Lithospheric Evolution at Complex Plate Boundaries.  

E-print Network

??The relative motion of tectonic plates across their boundaries generates deformation in the surrounding lithosphere. How this deformation is expressed reflects both present-day plate configurations (more)

Hayes, Gavin

2007-01-01

146

Scaling of plate-tectonic convection with pseudoplastic rheology  

E-print Network

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...

Korenaga, Jun

2010-01-01

147

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

E-print Network

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

Pedersen, Tom

148

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

E-print Network

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

Long, Bernard

149

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

E-print Network

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

Tackley, Paul J.

150

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

151

Conditions for the onset of plate tectonics on terrestrial planets and moons  

E-print Network

Conditions for the onset of plate tectonics on terrestrial planets and moons C. O'Neill a,, A online 26 May 2007 Abstract Plate tectonics on Earth is driven by the subduction and stirring of dense restrictive that plate tectonics currently operates only on Earth, and mantle convection in most terrestrial

Jellinek, Mark

152

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

E-print Network

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

Tackley, Paul J.

153

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

E-print Network

Linking continental drift, plate tectonics and the thermal state of the Earth's mantle T. Rolf a, as well as oceanic plate tectonics, are surface expressions of mantle convection and closely linked between continental drift, oceanic plate tectonics and the thermal state of the Earth's mantle, by using

Tackley, Paul J.

154

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

E-print Network

. 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

Tackley, Paul J.

155

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

E-print Network

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's deceleration supplies energy to plate tectonics comparable to the computed budget dissipated by the deformation

Doglioni, Carlo

156

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 mechanics 1. Introduction The unique occurrence of plate tectonics on Earth amongst all terrestrial planets

157

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

158

Catastrophic Plate Tectonics: The Physics behind the Genesis Flood  

E-print Network

The wealth of new data, mostly from the ocean bottom, that precipitated the acceptance of plate tectonics during the 1960s simultaneously also opened the door for the first time in more than 200 years to a technically credible defense of the Genesis Flood. From the mid-1700s through the days of Hutton, Lyell, and Darwin to the 1960s, it overwhelmed the human mind to imagine a mechanism that could possibly deliver, in a single brief event, the magnitude and complexity of geological change evident in the continental rock record above the point where fossils first appear. However, with the new awareness that the earths interior could participate in the process and that the stiff layer of rock some 50 miles thick beneath the oceans could be recycled into the earth, the stage was set for a breakthrough in regard to the mechanism for the Flood cataclysm. The crucial final piece of the puzzle has come from laboratory experiments that have carefully measured the way in which silicate minerals deform under conditions of high temperature and high stress. These experiments reveal silicate material can weaken dramatically, by factors of a billion or more, at mantle temperatures and for stress conditions that can exist in the mantles of planets the size of the earth. The scenario in which all the earths ocean lithosphere is rapidly recycled into the mantle via a runaway process, enabled by this stress-weakening behavior, is

John R. Baumgardner

2003-01-01

159

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

SciTech Connect

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.

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

1996-01-01

160

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

SciTech Connect

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.

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

1996-12-31

161

Beyond plate tectonics - Looking at plate deformation with space geodesy  

NASA Technical Reports Server (NTRS)

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.

Jordan, Thomas H.; Minster, J. Bernard

1988-01-01

162

Creep of phyllosilicates at the onset of plate tectonics  

SciTech Connect

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.

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

2012-10-24

163

The magma ocean as an impediment to lunar plate tectonics  

NASA Technical Reports Server (NTRS)

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.

Warren, Paul H.

1993-01-01

164

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

E-print Network

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.

Herndon, J M

2005-01-01

165

Could plate tectonics on Venus be concealed by volcanic deposits  

NASA Technical Reports Server (NTRS)

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.

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

1982-01-01

166

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

Microsoft Academic Search

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.

Ren Guiraud; William Bosworth

1997-01-01

167

Plate tectonics and crustal deformation around the Japanese Islands  

NASA Technical Reports Server (NTRS)

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.

Hashimoto, Manabu; Jackson, David D.

1993-01-01

168

Multi-Agent Modelling of Earths Dynamics: Towards a Virtual Laboratory of Plate Tectonics  

E-print Network

MACMA (Multi-Agent Convective MAntle) is a new tool developed to simulate plate tectonics and mantle convection in a 2-D cylindrical geometry (Combes et al., 2012). Evolutive plate tectonics We obtain an evolutive system where the geometry and the number of plates are not imposed but emerge naturally from the dynamics of plate tectonics. Fig. 4: Three configurations of plate tectonics obtained with the initial system shown in Fig. 1, showing the evolutive number of plates and continents. Short-term thermal and dynamical evolution

Ccile Grign; Manuel Combes; Chantal Tisseau; Sbastien Le Yaouanq; Marc Parenthon; Jacques Tisseau

169

Plate tectonic history of the Arctic  

SciTech Connect

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.

Burke, K.

1985-02-01

170

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

NASA Astrophysics Data System (ADS)

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

Noack, L.; Breuer, D.

2012-04-01

171

Your Mission: (1) Investigate the relationship between tectonic plates, earthquakes, volcanoes, and other geophysical data through a computer mapping  

E-print Network

Your Mission: (1) Investigate the relationship between tectonic plates, earthquakes, volcanoes tectonic plates move. Your Supplies: (1) Earth's Tectonic Plates map handout (2) Protractor Your Task: In this lab we are going to explore the nature of Earth's tectonic plates by using a new web-based mapping

Smith-Konter, Bridget

172

Tectonic mlange as fault rock of subduction plate boundary  

NASA Astrophysics Data System (ADS)

An assemblage of quantitative data sets is examined to evaluate tectonic mlange as a plate boundary fault rocks in subduction zone. The research object is the latest Cretaceous Mugi mlange in the Shimanto Belt, southwest Japan. Systematic age younging from pelagic to terrigenous through hemipelagic sediments is well-documented even though original stratigraphy is disrupted. Systematic shear fabric consistent with ancient plate convergence is reconstructed. The mlange was formed at temperatures of ~ 130-200 C by cataclastic comminution of sandstone layers accompanied by tensile cracking, and plastic deformation and the dehydration of clayey shale matrix, with subsequent peeling off and underplating of the oceanic basement. The temperature setting for the Mugi mlange indicates around the up-dip limit of the seismogenic zone, therefore includes various fault rocks suggestive of earthquake fault; pseudotachylyte, fluidized ultracataclasite with heating evidence, amorphous silica and so on. These suggest that fluid induced lubrication was dominated. Localized cataclastic shear, which is a candidate of small earthquake or very low frequency earthquake, is also recognized especially in sandstone blocks dominated portion in mlange. These observations are consistent with the mlange being a fault rock along the plate boundary that records various types of earthquakes in a subduction zone. The quantitative examination of the Mugi mlange suggests several criteria to define the tectonic mlange of the plate boundary fault in subduction zone from other mlanges in orogenic belt.

Kimura, Gaku; Yamaguchi, Asuka; Hojo, Megumi; Kitamura, Yujin; Kameda, Jun; Ujiie, Kohtaro; Hamada, Yohei; Hamahashi, Mari; Hina, Shoko

2012-09-01

173

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

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

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

2001-01-01

174

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

Microsoft Academic Search

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

James Andrew Conder

2001-01-01

175

Plate Tectonic Evolution of Eastern Australian Marginal Ocean M. Sdrolias1  

E-print Network

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

Müller, Dietmar

176

The ERESE Project: Modeling Inquiry-Based Plate Tectonic Lessons  

NASA Astrophysics Data System (ADS)

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

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

2004-12-01

177

Booting Up Plate Tectonics: Feedbacks Between Mantle Viscosity, The Wavelength of Mantle Convection, and the Mode of Planetary Tectonics  

NASA Astrophysics Data System (ADS)

Previous studies have demonstrated that a low viscosity region in the upper mantle (i.e., the asthenosphere) can: 1) generate long wavelength mantle flow; and 2) favor a plate tectonic like mode of mantle convection. We show that wavelength and tectonics can feedback into the system and increase the degree of viscosity variation from the upper to the lower mantle. Plate subduction generates a non-adiabatic temperature gradient which, together with temperature-dependent viscosity, leads to a relatively low viscosity region in the upper mantle and a higher viscosity lower mantle. The degree of depth-variable viscosity increases with the wavelength of convection and decreases as plate margins become stronger, dropping to near zero as the system transitions from a plate tectonic to a single plate mode of convection. The plate strength needed to initiate that tectonic transition increases for long wavelength cells. The coupled feedbacks suggest a model in which the asthenosphere can not be defined solely in terms of material properties but must also be defined in terms of an active process, plate tectonics, which both maintains it and is maintained by it. The bootstrap aspect of the model is its circular causality between plates and the asthenosphere, neither being more fundamental than the other and the existence of each depending on the other. As the system is booting up, it is at its lowest state of tectonic resilience and a nascent mode of plate tectonics can become unstable in response to relatively small perturbations (e.g., changes in surface conditions driven by climate, changes in lithospheric strength associated with volatile cycling). As the feedbacks go to work and the system fully boots up, a plate tectonic mode of behavior stabilizes and the system becomes more resilient to changing conditions.

Lenardic, A.; Hoeink, T.; Richards, M. A.

2013-12-01

178

Geoid Data and Implications for Plate Tectonic Dynamics  

NASA Astrophysics Data System (ADS)

It has long been recognized that the motion of the mechanically rigid lithospheric plates of the earth are the surface expression of large-scale convection in the mantle. It is also accepted that the stresses driving plate motion are an amalgam of the basal tractions associated with this convection and long-wavelength density variations within the plates themselves. Parsing the relative contribution from these two sources to the geodynamics of the lithosphere continues to be an important topic of plate dynamics research. Because geoid anomalies are directly related to the local dipole moment of the density-depth distribution, they provide an ideal method for evaluating density variations within the lithosphere and the associated tectonic stresses. The main challenge with this approach is isolating the lithospheric geoid contribution from the full geoid (which is dominated by sources from deeper in the earth, namely the lower mantle). We address this issue by using a high-pass spherical harmonic filtering of the EGM2008-WGS84 geoid (which is complete to spherical harmonic degree and order 2159), with a cosine taper between orders 9 to 13 and 78 to 82 to produce a 'lithospheric' geoid. In the present study we focus on tectonic implications of the lithospheric geoid in three different areas: 1) passive continental margins where we have evaluated over 150 margin-transects spaced roughly every three degrees. The global average geoid anomaly associated with the transition from old oceanic lithosphere to the continent was found to 6-9 meters and appears to be insensitive to a range of geoid filtering degrees and orders; 2) The geoid highs associated with the mid-ocean ridges and the cooling oceanic lithospheric, where we have examined a number of geoid profiles across ridges and find that previous estimates of a geoid anomaly of 10-15 meters associated with ridges to be valid; and 3) continental regions which are characterized by both elevated geoid anomalies (e.g., the Western U.S.) and geoid lows (e.g., the Congo Basin in Africa). All three of these geoid studies have implications for our understanding of the dynamics of plate tectonics. The 10-15 m geoid highs associated globally with ridges are consistent with a net force of ~3x1012 N/m due to 'ridge push.' Converting gradients in the oceanic 'lithospheric' geoid produce net torques on the plates consistent with this magnitude of 'ridge push.' The 6-9 meter geoid step up across passive continental margins is important for two reasons. First, it is consistent with a reduction of the ridge force acting on the continents, as evidenced by increased strike slip and normal deformation on the continents compared to oceanic lithosphere. Second, the very fact that such a small geoid step can affect tectonic style is evidence that even relatively small forces, like the ridge force compared to the negative buoyancy of subducted lithosphere, can be important in plate dynamics. Furthermore, the predicted intraplate stresses computed using a finite-element analysis of a lithospheric shell under traction from the gravitational potential energy forces associated with the lithospheric geoid provide a remarkably good fit between the predicted and observed intraplate stress field at long wavelengths (~1000km) and indicates that tectonic forces associated with the lithospheric density moment play an important role in global geodynamics.

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

2013-12-01

179

Tectonic database and plate tectonic model of the former USSR territory  

SciTech Connect

A digital geographic database for the former USSR was compiled using published geologic and geodynamic maps and the unpublished suture map of Lev Zonenshain (1991). The database includes more than 900 tectonic features: strike-slip faults, sutures, thrusts, fossil and active rifts, fossil and active subduction zones, boundaries of the major and minor Precambrian blocks, ophiolites, and various volcanic complexes. The attributes of each structural unit include type of structure, name, age, tectonic setting and geographical coordinates. Paleozoic and Early Mesozoic reconstructions of the former USSR and adjacent regions were constructed using this tectonic database together with paleomagnetic data and the motions of continent over fixed hot spots. Global apparent polar wander paths in European and Siberian coordinates were calculated back to Cambrian time, using the paleomagnetic pole summaries of Van der Voo (1992) and Khramov (1992) and the global plate tectonic model of the Paleomap Project (Scotese and Becker, 1992). Trajectories of intraplate volcanics in South Siberia, Mongolia, Scandinavia and data on the White Mountain plutons and Karoo flood basalts were also taken into account. Using new data, the authors recalculated the stage and finite poles for the rotation of the Siberia and Europe with respect to the hot spot reference frame for the time interval 160 to 450 Ma.

Bocharova, N.Yu.; Scotese, C.R.; Pristavakina, E.I.; Zonenshain, L.P. (Univ. of Texas, Arlington, TX (United States). Center for Russian Geology and Tectonics)

1993-02-01

180

Observing tectonic plate motions and deformations from satellite laser ranging  

NASA Technical Reports Server (NTRS)

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.

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

1985-01-01

181

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

E-print Network

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

Ahmad, Sajjad

182

Plate tectonics from VLBI and SLR global data  

NASA Technical Reports Server (NTRS)

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.

Harrison, Christopher G. A.; Robaudo, Stefano

1992-01-01

183

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

E-print Network

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 with earthquakes, volcanoes, and plate tectonics in the region. Part 1: Analyze real time-series data of two GPS

Polly, David

184

Paleomap PC: Plate tectonic reconstructions on IBM compatible computers  

SciTech Connect

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

Walsh, D.B.; Scotese, C.R. (Univ. of Texas, Arlington, TX (United States). Dept. Geology)

1993-02-01

185

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

E-print Network

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

186

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

E-print Network

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

Paris-Sud XI, Université de

187

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

188

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

189

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

E-print Network

by regional unconformities. The arrival of the Sulawesi ophiolite, which collided with west Sulawesi in the late Oligocene, was the earliest event in collision between Sulawesi and the Birds Head microcontinent. Continental crust was thrust beneath Sulawesi in the early Miocene, and the Tukang Besi and Sula platforms

Royal Holloway, University of London

190

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

NASA Astrophysics Data System (ADS)

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

Hall, Robert

2002-04-01

191

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

E-print Network

: 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

Becker, Thorsten W.

192

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

PubMed

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

Hampe, Arndt; Petit, Rmy J

2007-12-01

193

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

NASA Astrophysics Data System (ADS)

Plates are driven by buoyancy forces distributed in the mantle, within cooling oceanic plates (ridge push) and within subducted slabs. Although the case is often made that subducted slabs provide the principle driving force on plate motion, consensus has not been achieved. This is at least partially due to the great difficulty in realistically capturing the role of slabs in observationally-constrained models as slabs act to drive and resist plate motions through their high effective viscosity. Slab buoyancy acts directly on the edge of the plate (slab pull), while inducing mantle flow that tends to drag both subducting and overriding plates toward the trench. While plates bend during subduction they undergo a form of 'plastic failure' (as evident through faulting, seismicity and reduction of flexural parameters at the outer trench wall). The birth of a new subduction zone, subduction initiation, provides important insight into plate motions and subduction dynamics. About half of all subduction zones initiated over the Cenozoic and the geophysical and geological observations of them provide first order constraints on the mechanics of how these margins evolved from their preexisting tectonic state to self-sustaining subduction. We have examples of subduction initiation at different phases of the initiation process (e.g. early versus late) as well as how margins have responded to different tectonic forcings. The consequences of subduction initiation are variable: intense trench roll back and extensive boninitic volcanism followed initiation of the Izu-Bonin-Mariana arc while both were absent during Aleutian arc initiation. Such differences may be related to the character of the preexisting plates, the size of and forces on the plates, and how the lithosphere was initially bending during initiation. I will address issues associated with the forces driving plate tectonics and initiating new subduction zones from two perspectives. A common thread is the origin and evolution of intense back arc spreading and rapid roll back associated with some ocean-ocean subduction zones. I will look at the dynamics driving global plate motions and the time-dependence of trench rollback regionally. Capitalizing on advances in adaptive mesh refinement algorithms on parallel computers with individual plate margins resolved down to a scale of 1 kilometer, observationally constrained, high-resolution models of global mantle flow now capture the role of slabs and show how plate tectonics is regulated by the rheology of slabs. Back-arc extension and slab rollback are emergent consequences of slab descent in the upper mantle. I will then describe regional, time-dependent models, address the causes and consequences of subduction initiation, and show that most back arc extension follows subduction initiation. Returning to the global models, inverse models using the full adjoint of the variable viscosity, Stokes equation are now possible and allow an even greater link between present-day geophysical observations and the dynamics from local to global scales.

Gurnis, Michael

2013-04-01

194

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.

195

The Cariris Velhos tectonic event in Northeast Brazil  

NASA Astrophysics Data System (ADS)

The Borborema Province in northeastern South America is a typical Brasiliano-Pan-African branching system of Neoproterozoic orogens that forms part of the Western Gondwana assembly. The province is positioned between the So Luis-West Africa craton to the north and the So Francisco (Congo-Kasai) craton to the south. For this province the main characteristics are (a) its subdivision into five major tectonic domains, bounded mostly by long shear zones, as follows: Mdio Corea, Cear Central, Rio Grande do Norte, Transversal, and Southern; (b) the alternation of supracrustal belts with reworked basement inliers (Archean nuclei + Paleoproterozoic belts); and (c) the diversity of granitic plutonism, from Neoproterozoic to Early Cambrian ages, that affect supracrustal rocks as well as basement inliers. Recently, orogenic rock assemblages of early Tonian (1000-920 Ma) orogenic evolution have been recognized, which are restricted to the Transversal and Southern domains of the Province. Within the Transversal Zone, the Alto Paje terrane locally includes some remnants of oceanic crust along with island arc and continental arc rock assemblages, but the dominant supracrustal rocks are mature and immature pelitic metasedimentary and metavolcaniclastic rocks. Contiguous and parallel to the Alto Paje terrane, the Riacho Gravat subterrane consists mainly of low-grade metamorphic successions of metarhythmites, some of which are clearly turbiditic in origin, metaconglomerates, and sporadic marbles, along with interbedded metarhyolitic and metadacitic volcanic or metavolcaniclastic rocks. Both terrane and subterrane are cut by syn-contractional intrusive sheets of dominantly peraluminous high-K calc-alkaline, granititic to granodioritic metaplutonic rocks. The geochemical patterns of both supracrustal and intrusive rocks show similarities with associations of mature continental arc volcano-sedimentary sequences, but some subordinate intra-plate characteristics are also found. In both the Alto Paje and Riacho Gravat terranes, TIMS and SHRIMP U-Pb isotopic data from zircons from both metavolcanic and metaplutonic rocks yield ages between 1.0 and 0.92 Ga, which define the time span for an event of orogenic character, the Cariris Velhos event. Less extensive occurrences of rocks of Cariris Velhos age are recognized mainly in the southernmost domains of the Province, as for example in the Poo Redondo-Maranc terrane, where arc-affinity migmatite-granitic and meta-volcano-sedimentary rocks show U-Pb ages (SHRIMP data) around 0.98-0.97 Ga. For all these domains, Sm-Nd data exhibit TDM model ages between 1.9 and 1.1 Ga with corresponding slightly negative to slightly positive ?Nd( t) values. These domains, along with the Borborema Province as a whole, were significantly affected by tectonic and magmatic events of the Brasiliano Cycle (0.7-0.5 Ga), so that it is possible that there are some other early Tonian rock assemblages which were completely masked and hidden by these later Brasiliano events. Cariris Velhos processes are younger than the majority of orogenic systems at the end of Mesoproterozoic Era and beginning of Neoproterozoic throughout the world, e.g. Irumide belt, Kibaride belt and Namaqua-Natal belt, and considerably younger than those of the youngest orogenic process (Ottawan) in the Grenvillian System. Therefore, they were probably not associated with the proposed assembly of Rodinia. We suggest, instead, that Cariris Velhos magmatism and tectonism could have been related to a continental margin magmatic arc, with possible back-arc associations, and that this margin may have been a short-lived (<100 m.y.) leading edge of the newly assembled Rodinia supercontinent.

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

196

Application of plate tectonics concepts in hydrocarbon exploration: Hokkaido Corner  

SciTech Connect

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

Sabitay, A.; Shirley, J.

1986-07-01

197

Dynamic Analysis of Modifications to Simple Plate Tectonic Theory  

NASA Astrophysics Data System (ADS)

A number of geological and geophysical observations suggest significant departures from simple, first-order plate tectonic theory. In this thesis we address the dynamic implications of some of these observations and propose generalized theories to explain their dynamics and conditions of formation. In Chapter 2, we develop a generalized theory and analytic model to predict the conditions under which large-volume removal of continental lithosphere can occur through the formation of drip instabilities. Using damage physics relevant for Earth, we find a large portion of the lithosphere may be mobilized and entrained into growing drip instabilities. For a critical amount of damage, the growth is accelerated sufficiently that large-volume drip instabilities may form within geologically feasible time frames. Our model suggests large-volume lithospheric drip instabilities may arise independently of tectonic settings through damage-assisted mobilization and entrainment of the highly viscous lithosphere. In Chapter 3, we develop a mechanical model independent of volcanism and thermal weakening to explain the initial formation and length scale of rifting and extension near convergent plate boundaries. We conduct a linear stability analysis of a simple viscous necking model, which includes the lithosphere's negative buoyancy, non-Newtonian rheology, and freely moving top surface, to determine which properties of the lithosphere govern the location of rifting. We find that the negative buoyancy of the lithosphere promotes the formation of rifting structures when simple Newtonian viscosities are present. However, localized weakening, introduced through a power law exponent, is required to generate realistic rifting length scales. Our model suggests that the initial location of rifting in the overriding plate at subduction zones is primarily due to the mechanical extension induced by rollback of the subducting slab. In Chapter 4, we propose a theory to explain the seismic anisotropy directions observed in the subslab mantle of subduction zones globally. We develop a three-dimensional model using COMSOL Multiphysics to investigate how interactions among the background mantle flow, trench migration, and the geometry of the slab determine the flow direction in the subslab mantle. We find that flow directions are determined primarily by the amount of coupling between the slab and the mantle, and the interaction between the net background flow (including trench migration) and the slab geometry. We present three-dimensional finite strain calculations, which demonstrate that the maximum stretching directions are aligned with the model subslab flow directions, allowing us to compare our flow directions directly to seismic anisotropy splitting directions of subduction zones globally. Our model successfully predicts the flow directions (parallel or perpendicular) suggested by a global dataset of fast splitting directions using only the net background mantle flow, and slab dip and depth.

Paczkowski, Karen

198

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

NASA Astrophysics Data System (ADS)

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 sharply defined tectonic boundaries are overprinted boundaries from volcanism during passage of Cocos Plate over the Galapagos hot spot. The subducted segment boundaries correspond with distinct changes in upper plate tectonic structure and features of the subducted slab. Newly identified seafloor-spreading anomalies show oceanic lithosphere formed during initial breakup of the Farallon Plate at 22.7 Ma and opening of the Cocos-Nazca spreading center. A revised regional compilation of magnetic anomalies allows refinement of plate tectonic models for the early history of the Cocos-Nazca spreading center. At 19.5 Ma a major ridge jump reshaped its geometry, and after 14.5 Ma multiple southward ridge jumps led to a highly asymmetric accretion of lithosphere. A suspected cause of ridge jumps is an interaction of the Cocos-Nazca spreading center with the Galapagos hot spot.

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

2001-09-01

199

Your Mission: Investigate the relationship between tectonic plates, earthquakes, volcanoes, and other geophysical data through a computer mapping  

E-print Network

Your Mission: Investigate the relationship between tectonic plates, earthquakes, volcanoes, and other geophysical data through a computer mapping program. Your Supplies: (1) Earth's Tectonic Plates (2) map handouts Your Task: In this lab we are going to explore the nature of Earth's tectonic plates

Smith-Konter, Bridget

200

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

E-print Network

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

Sandwell, David T.

201

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

E-print Network

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

Boyer, Edmond

202

Physics of the Earth and Planetary Interiors 150 (2005) 287315 Assessment of the cooling capacity of plate tectonics and flood  

E-print Network

of plate tectonics and flood volcanism in the evolution of Earth, Mars and Venus P. van Thienen, N.J. Vlaar 29 November 2004 Abstract Geophysical arguments against plate tectonics in a hotter Earth, based) cooling Earth, plate tectonics is capable of removing all the required heat at a rate of operation

van Thienen, Peter

203

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 139�151 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

204

Young Tectonic Events in Martian Chaotic Terrain  

NASA Astrophysics Data System (ADS)

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 Universitt 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.

Martel, L. M. V.

2012-03-01

205

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

PubMed

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

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

2004-09-16

206

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

E-print Network

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

Demouchy, Sylvie

207

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

E-print Network

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 reconstruction. Plate boundaries shifted rapidly in the Cenozoic. During convergence of the major plates

Royal Holloway, University of London

208

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

E-print Network

1 Strain weakening enables continental plate tectonics Frédéric GUEYDAN (1), Jacques PR?CIGOUT (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

Paris-Sud XI, Université de

209

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

NSDL National Science Digital Library

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.

Guertin, Laura

210

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

E-print Network

Plate tectonic modelling: virtual reality with GMAPp Trond Helge Torsvika, b, *, Mark Andrew, is a useful tool to understand local and regional geologic relationships as well as the fundamental driving tectonic driving forces are (1) divergent boundaries where new crust is generated and subsequently cooled

Torsvik, Trond Helge

211

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

Microsoft Academic Search

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

J. Golonka

2004-01-01

212

Global aspects of volcanism: the perspectives of ''plate tectonics'' and ''volcanic systems''  

NASA Astrophysics Data System (ADS)

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 point-like distribution of volcanic centers that does not fit the predictions. Also, it is observed that many volcanoes share common characteristics despite being located in different tectonic settings, while other volcanoes sharing the same tectonic setting display very different behavior. For instance, so far, there is no congruent explanation offered by plate tectonics about why in similar tectonic conditions volcanism is sometimes polygenetic and elsewhere monogenetic. On the other hand, volcanic activity on a global scale tends to define a series of rules that are independent of the tectonic setting, and therefore should reflect general processes that are not controlled directly by the plate tectonic engine. We show that, by concentrating on the relationship among processes (from the moment of magma generation to the moment of eruption) and by incorporating all of these processes as components of a single system, a coherent picture of volcanism on a global scale emerges and allows us to interpret better many otherwise puzzling aspects of volcanism such as those mentioned above, hence providing a general framework that fills the conceptual gap left between plate tectonics and most (if not all) of the characteristics of volcanic activity at a global scale.

Can-Tapia, Edgardo; Walker, George P. L.

2004-06-01

213

Vernal Point and Plate Tectonics: Indo-Australian  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

214

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

Microsoft Academic Search

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

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

215

PNG ON THE MOVE- GPS MONITORING OF PLATE TECTONICS AND EARTHQUAKES  

E-print Network

PNG is one of the most tectonically active countries in the world. Major earthquakes and volcanic eruptions resulting from this tectonic activity pose significant threats to PNG's population and fragile infrastructure. Modern surveying techniques such as GPS can measure movement of tectonic plates to within a centimetre anywhere in PNG. These measurements have provided a much better understanding of PNG's tectonic setting and also have the potential to significantly improve the accuracy of PNGs geodetic datum. This paper highlights contributions made by The Australian National University, the National Mapping Bureau, RVO and UniTech's Department of Surveying and Land Studies showing some startling results from these surveys.

Richard Stanaway

216

Global pattern of earthquakes and seismic energy distributions: Insights for the mechanisms of plate tectonics  

E-print Network

.F., Global pattern of earthquakes and seismic energy distri- butions: Insights for the mechanisms of plate energy distributions: insights for the mechanisms of plate tectonics P. Vargaa , F. Krummb , F. Riguzzic?? ? ??? ? ?? Global pattern of earthquakes and seismic energy distributions: Insights

Stuttgart, Universität

217

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

Microsoft Academic Search

Northwestern Europe is tectonically more active, in terms of seismicity, vertical motions and volcanism, than would be expected from its location far from any plate boundaries. In the context of the Netherlands Earth System Dynamics Initiative, we investigated the implications of two recent modeling efforts, of Eurasian plate forces and European mantle structure, for our understanding of the dynamics of

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

2000-01-01

218

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

NASA Astrophysics Data System (ADS)

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.

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

2014-05-01

219

The driving force of plate tectonics evaluated in spherical coordinates  

E-print Network

, 2557, 2567, 1974. Stauder, W. , Mechanism and spatial distribution of Chilean earthquakes with relation to subduction of the oceanic plate, J. Geophys. Res. , 78, 5033-5061, 1973. Stsuder, W. , Subduction of the Hazes plate under Peru as evidenced..., 2557, 2567, 1974. Stauder, W. , Mechanism and spatial distribution of Chilean earthquakes with relation to subduction of the oceanic plate, J. Geophys. Res. , 78, 5033-5061, 1973. Stsuder, W. , Subduction of the Hazes plate under Peru as evidenced...

Donahue, John Michael

2012-06-07

220

Focal Mechanisms and Plate Tectonics of the Southwest Pacific  

Microsoft Academic Search

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

Tracy Johnson; Peter Molnar

1972-01-01

221

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

E-print Network

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...

Foley, Bradford J; Elkins-Tanton, Linda T

2014-01-01

222

Sediment deformation and plate tectonics in the Gulf of Oman  

Microsoft Academic Search

The continental margin off the Makran coast of Iran and Pakistan is an excellent example of active deformation of sediments at a compressive plate boundary. Seismic reflection profiles across the margin suggest that relatively flat-lying sediments from the Oman abyssal plain are being scraped off the Arabian plate and accreted onto the Eurasian plate in a series of tightly folded

R. S. White; K. Klitgord

1976-01-01

223

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

Microsoft Academic Search

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

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

2010-01-01

224

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

NASA Astrophysics Data System (ADS)

Plate tectonic reconstructions are a useful tool in the modern exploration industry. A variety of interpretative applications and data sets require robust plate models; specific examples include the rotation of well data to their past locations, analysis of palaeogeographic environments and predictions of properties such as heat flux through time. As plate tectonic reconstructions become more widely used they become more ambitious, pushing further back in time and including older stratigraphic units, often with increasingly complex tectonic histories. Geological data becomes increasingly sparse for these older units, leading to more subjective choices when creating plate models. In our global plate tectonic model we collate data from numerous sources, including geological structure mapping, interpretation and analysis of potential field data and depth to basement maps, palaeomagnetism and geological relationships from published literature. The plate model is strongly interlinked with on-going global studies at Getech, such as palaeoenvironment mapping, palaeotopography and palaeoclimate; direct feedback from these studies is used to refine and test tectonic solutions both within a regional and global framework. Our global plate model is currently undergoing major improvements extending it back to the start of the Permian (300 Ma). This includes updates to oceanic structures and ocean-continent boundaries to better constrain the internal boundaries and fit of the Pangaea supercontinent. The update also includes Permian-Triassic modelling of South East Asia and China, improvements in Kazakhstan, Central Asia and the North American Cordillera and a re-evaluation of our existing Arctic tectonics. These regions also contain feedback from Jurassic palaeoenvironment mapping to improve the current tectonic reconstructions. We present the multi-disciplinary approach to plate modelling with particular focus on North America and the Arctic. Numerous and often conflicting hypotheses exist for the formation of the North American Cordillera; including the accretion of a series of allochthonous and parautochthonous terranes to ancestral North America in a prolonged orogeny, the formation of a ribbon continent in the Panthalassa Ocean which eventually accreted to North America or the accretion of two superterranes migrating northwards from significantly south of their present day position. To some degree, Russian Arctic tectonics mirrors the North American counterpart, with the Arctic Alaska and Chukotka terranes thought to be of similar or contiguous origin. The Verkhoyansk fold and thrust belt is formed during the collision of a micro-continent with the Siberian Craton and a series of arcs and back arcs accrete on the Pacific side of the craton. We demonstrate the construction of the plate model using the techniques described above to assess the validity of hypotheses and the origin of exotic Arctic terranes.

Webb, Peter; Masterton, Sheona; Eue, Dorothea

2013-04-01

225

Central Indian Ocean Plate Tectonics Between Chrons 34 to 20 (83 to 42 Ma) Revisited  

NASA Astrophysics Data System (ADS)

The Indian Ocean is the result of East Gondwanaland fragmentation and dispersal since Jurassic. Its complex plate tectonic history is the result of several major events such as the Kerguelen and Reunion hotspot inception and the Indo-Eurasian collision. Indian and French scientists have collected a large amount of marine geophysical data in the conjugate basins of the northern and southern Indian Ocean, respectively. Using these data and under the auspices of an Indo-French collaborative project, we revisited the Central Indian (CIB), Crozet (CZB) and Madagascar (MDB) basins to understand their evolution. We created a common database consisting of magnetic data from 148 cruises belonging to the Indian and French scientists along with the so-called international data archived at NGDC. From these magnetic profiles, (1) we identified the anomalies using the inter-profile correlation and forward modelling as well as a detailed analysis of the characteristic shape of the anomalies (including the tiny wiggles); (2) we precisely located the magnetic isochrons using the analytic signal technique; and (3) we validated these isochrons by plate reconstructions. We present the updated magnetic isochrons and the associated fracture zones (depicted from the free air gravity anomaly derived from satellite altimetry) in the Central Indian, Crozet and Madagascar basins between chron 34ny (83 Ma) and chron 20ny (42.5 Ma). The 1399 magnetic anomaly crossings (846, 287 and 266 picks from CIB, CZB, and MDB respectively) enabled us to estimate improved finite rotation parameters for Indian-Antarctic and Indian-African plate boundaries and provide better constrained plate reconstruction models of the study area for closer time intervals ( ~2 Ma).

Yatheesh, V.; Dyment, J.; Bhattacharya, G.; Jensen, J.; Ramprasad, T.; Royer, J.; Kamesh Raju, K.; Patriat, P.; Chaubey, A.; Choi, Y.; Srinivas, K.

2008-12-01

226

Identifying Plate Tectonic Boundaries for a Virtual Ocean Basin  

NSDL National Science Digital Library

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.

Reynolds, Stephen

227

A diffuse plate boundary model for Indian Ocean tectonics  

Microsoft Academic Search

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

D. A. Wiens; Charles DeMets; R. G. Gordon; Seth Stein; Don Argus; Joseph F. Engeln; Paul Lundgren; Dan Quible; Carol Stein; Stuart Weinstein; Dale F. Woods

1985-01-01

228

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

SciTech Connect

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.

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

1994-07-01

229

Mesozoic plate tectonic reconstruction of the Carpathian region  

Microsoft Academic Search

Palaeomagnetic, palaeobiogeographic and structural comparisons of different parts of the AlpineCarpathian 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 JurassicCretaceousPalaeogene history. Palaeomagnetic and tectonic data suggest that the Carpathians are built up by two

Lszl Csontos; Attila Vrs

2004-01-01

230

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

NASA Astrophysics Data System (ADS)

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.

Foley, B. J.; Bercovici, D.

2012-12-01

231

Neogene Caribbean plate rotation and associated Central American tectonic evolution  

NASA Technical Reports Server (NTRS)

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.

Wadge, G.; Burke, K.

1983-01-01

232

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

NASA Technical Reports Server (NTRS)

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.

Frey, H.

1977-01-01

233

Absence of plate tectonics in Venus is supported from deformation experiments and numerical simulation  

NASA Astrophysics Data System (ADS)

Plate tectonics is one of the most important mechanism for material and heat circulation in Earth (Turcotte et al., 1999), however it does not exist on Venus for unknown reasons. The strength of planetary materials is a key control on plate tectonics because temperature, pressure, stress, and chemical composition produce strong rheological layering (Kohlstedt et al., 1995). We conducted two-phase deformation experiments to consider the reason of absence of plate tectonics on Venus in terms of rheological structure. Our deformation experiments show that mantle olivine is much stronger than crustal plagioclase under conditions corresponding to Venusian Moho (i.e. Venus has a large strength contrast between the crust and mantle at the Moho.). Consequently, this strength contrast may cause the mechanical decoupling between crust and mantle convection in Venus. One-dimensional simulations using our experimental results show that strength contrast at the Moho prevent the motion of Venusian crust. This is an important factor to explain the absence of plate tectonics on Venus. Also, we conduct the two-dimensional simulation comprising the weak zone and our experimental data to verify the effect of the strength contrast on subduction. In our presentation, we will report these specific results of deformation experiments and numerical simulations.

Azuma, S.; Katayama, I.; Nakakuki, T.

2013-12-01

234

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

Microsoft Academic Search

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

F. Nimmo; D. J. Stevenson

2000-01-01

235

Plate Tectonics and Sea-Floor Spreading: Maps and Graphics, etc.  

NSDL National Science Digital Library

This page offers access to maps and graphics of earthquakes, active volcanoes and plate tectonics for the world, the Cascade Range , Juan de Fuca Ridge, Gorda Ridge and Axial Seamount in North America, South America, and Western Canada. The Ring of Fire is noted in some maps, and others offer data for the years 1994-1999.

236

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

237

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

Microsoft Academic Search

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

Richard Hey

1977-01-01

238

Developing packages and integrating ontologies for Volcanoes, Plate Tectonics and Atmospheric Science Data Integration  

Microsoft Academic Search

In support of a NASA-funded scientific application (SESDI; Semantically Enabled Science Data Integration Project; that needs to share volcano and climate data to investigate relationships between volcanism and global climate, we have generated a volcano and plate tectonic ontologies and leveraged and augmented the existing SWEET (Semantic Web for Earth and Environmental Terminology) ontoloy. Our goal is to create a

K. Sinha; R. Raskin; D. McGuinness; P. Fox

2007-01-01

239

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

E-print Network

that a combination of temperature- dependent viscosity and viscoplastic yielding is sufficient to give rudimentary plate tectonic-like behavior in three-dimensional models of mantle convection. Here the calculations an asthenosphere by reducing the viscosity by a factor of 10 where material reaches a solidus (1) dramatically

Tackley, Paul J.

240

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

Microsoft Academic Search

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 \\

L. W. Braile; S. J. Braile

2002-01-01

241

Tectonics of the Nazca-Antarctic plate boundary  

NASA Technical Reports Server (NTRS)

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.

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

1987-01-01

242

A diffuse plate boundary model for Indian Ocean tectonics  

NASA Technical Reports Server (NTRS)

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.

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

1985-01-01

243

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

NASA Technical Reports Server (NTRS)

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.

Bischke, R. E.

1974-01-01

244

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

PubMed

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

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

2010-08-27

245

Seismicity and plate tectonics in south central Alaska  

NASA Technical Reports Server (NTRS)

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.

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

1974-01-01

246

Plate Tectonics of the Red Sea and East Africa  

Microsoft Academic Search

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.

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

1970-01-01

247

Nubia-Arabia-Eurasia Plate Motions and the Dynamics of Mediterranean and Middle East Tectonics  

NASA Astrophysics Data System (ADS)

We use geodetic and plate tectonic observations to constrain the tectonic evolution of the Nubia-Arabia-Eurasia plate system. Two phases of slowing of Nubia-Eurasia convergence, each of which resulted in an ~ 50% decrease in the rate of convergence, coincided with the initiation of Nubia-Arabia continental rifting along the Red Sea and Somalia-Arabia rifting along the Gulf of Aden at 24 4 Ma, and the initiation of oceanic rifting along the full extent of the Gulf of Aden at 11 2 Ma. In addition, both the northern and southern Red Sea (Nubia-Arabia plate boundary) underwent changes in the configuration of extension at 11 2 Ma, including the transfer of extension from the Suez Rift to the Gulf of Aqaba/Dead Sea fault system in the north, and from the central Red Sea basin (Bab al Mandab) to the Afar volcanic zone in the south. While Nubia-Eurasia convergence slowed, the rate of Arabia - Eurasia convergence remained constant within the resolution of our observations, and is indistinguishable from the present-day GPS rate. The timing of the initial slowing of Nubia-Eurasia convergence (24 4 Ma) corresponds to the initiation of extensional tectonics in the Mediterranean Basin, and the second phase of slowing to changes in the character of Mediterranean extension reported at ~ 11 Ma. These observations are consistent with the hypothesis that changes in Nubia-Eurasia convergence, and associated Nubia-Arabia divergence, are the fundamental cause of both Mediterranean and Middle East post-Late Oligocene tectonics. We speculate about the implications of these kinematic relationships for the dynamics of Nubia-Arabia-Eurasia plate interactions, and favor the interpretation that slowing of Nubia-Eurasia convergence, and the resulting tectonic changes in the Mediterranean Basin and Middle East, resulted from a decrease in slab pull from the AR subducted lithosphere across the Nubia-Arabia, evolving plate boundary.

Reilinger, R. E.; Mcclusky, S.

2011-12-01

248

Nubia-Arabia-Eurasia plate motions and the dynamics of Mediterranean and Middle East tectonics  

NASA Astrophysics Data System (ADS)

We use geodetic and plate tectonic observations to constrain the tectonic evolution of the Nubia-Arabia-Eurasia plate system. Two phases of slowing of Nubia-Eurasia convergence, each of which resulted in an 50 per cent decrease in the rate of convergence, coincided with the initiation of Nubia-Arabia continental rifting along the Red Sea and Somalia-Arabia rifting along the Gulf of Aden at 24 4 Ma, and the initiation of oceanic rifting along the full extent of the Gulf of Aden at 11 2 Ma. In addition, both the northern and southern Red Sea (Nubia-Arabia plate boundary) underwent changes in the configuration of extension at 11 2 Ma, including the transfer of extension from the Suez Rift to the Gulf of Aqaba/Dead Sea fault system in the north, and from the central Red Sea Basin (Bab al Mandab) to the Afar volcanic zone in the south. While Nubia-Eurasia convergence slowed, the rate of Arabia-Eurasia convergence remained constant within the resolution of our observations, and is indistinguishable from the present-day global positioning system rate. The timing of the initial slowing of Nubia-Eurasia convergence (24 4 Ma) corresponds to the initiation of extensional tectonics in the Mediterranean Basin, and the second phase of slowing to changes in the character of Mediterranean extension reported at 11 Ma. These observations are consistent with the hypothesis that changes in Nubia-Eurasia convergence, and associated Nubia-Arabia divergence, are the fundamental cause of both Mediterranean and Middle East post-Late Oligocene tectonics. We speculate about the implications of these kinematic relationships for the dynamics of Nubia-Arabia-Eurasia plate interactions, and favour the interpretation that slowing of Nubia-Eurasia convergence, and the resulting tectonic changes in the Mediterranean Basin and Middle East, resulted from a decrease in slab pull from the Arabia-subducted lithosphere across the Nubia-Arabia, evolving plate boundary.

Reilinger, Robert; McClusky, Simon

2011-09-01

249

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

SciTech Connect

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

Yangshen, S.; Huafu, L.; Dong, J. [Nanjing Univ. (China)] [and others

1994-11-01

250

The Rapid Drift of the Indian Tectonic Plate  

NASA Astrophysics Data System (ADS)

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 was caused by heating of the lithosphere from below by a large plume whose relicts are the Marion, Kerguelen and Reunion plumes. Plate reconstructions based on paleomagnetic data suggest that the Indian plate attained a very high speed (18-20 cm/yr during late Cretaceous) subsequent to its breakup from the Gondwanaland and slowed down to ~5 cm/yr since the continental collision with Asia during the last ~50 Ma. The Australian and African plates moved comparatively lesser distances and at much lesser speed of 2-4 cm/yr. Antarctica remained almost stationary. This super mobility makes India unique compared to the other fragments of Gondwanaland. We propose that when the parts of Gondwanaland were separated by the plume, the penetration of their lithospheric roots into the asthenosphere played an important role in determining their speed. We estimated the thickness of the lithospheric plates of the different parts of Gondwanaland around the Indian Ocean using the S-receiver function technique. We found that the part of Gondwanaland with clearly the thinnest lithosphere has travelled with the highest speed - India. The lithospheric root in South Africa, Australia and Antarctica is between 180 and 300 km deep. The Indian lithosphere is in contrast only about 100 km thick. Our interpretation is that the plume that partitioned Gondwanaland has also melted the lower half of the Indian lithosphere thus permitting faster motion due to the ridge push or slab pull.

Kumar, P.; Yuan, X.; Kumar, R.; Kind, R.; Li, X.; Chadha, R.

2007-12-01

251

The rapid drift of the Indian tectonic plate.  

PubMed

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 Runion 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

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

2007-10-18

252

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

E-print Network

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

Tackley, Paul J.

253

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

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

Stern, Robert J.

254

A new plate tectonic concept for the eastern-most Mediterranean  

NASA Astrophysics Data System (ADS)

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.

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

2012-04-01

255

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

SciTech Connect

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.

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

1993-09-01

256

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

NASA Technical Reports Server (NTRS)

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.

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

1988-01-01

257

Plate tectonics on rocky exoplanets: Influence of initial conditions and mantle rheology  

NASA Astrophysics Data System (ADS)

Several numerical studies have been published in the past years speculating about the existence of plate tectonics on large exoplanets. They focus on aspects like the mass of a planet, the interior heating rate and the occurrence of water in the mantle. 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, equally or less 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 use a 2D finite volume code and apply a pseudo-plastic rheology. We investigate how a strong pressure-dependence of the viscosity influences not only the convective regime in the lower mantle, but also in the upper mantle and hence the likelihood to obtain plate tectonics. We examine how our results change when either assuming a wet or a dry rheology or when employing 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. For standard literature values for initial temperatures of super-Earths, surface mobilization is less likely than on Earth, for warm initial temperature the result is vice versa. Simulations that neglect the time-dependence of internal heat sources on the other hand tend to lead to an increasing likelihood of plate tectonics with increasing mass. Finally, our investigations suggest that a wet rheology does not necessarily favor plate tectonics, but - depending on the reference viscosity - may rather lead to a stagnant-lid regime.

Noack, Lena; Breuer, Doris

2014-08-01

258

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

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

Tackley, Paul J.

259

Global plate tectonics and the secular motion of the pole  

NASA Technical Reports Server (NTRS)

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.

Soler, T.

1977-01-01

260

Petroleum formation by Fischer-Tropsch synthesis in plate tectonics  

SciTech Connect

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.

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

1989-08-01

261

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

NASA Technical Reports Server (NTRS)

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.

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

1981-01-01

262

Thermal Evolution of the Earth from a Plate Tectonics Point of View  

NASA Astrophysics Data System (ADS)

Earth's thermal history is classically studied using scaling laws that link the surface heat loss to the temperature and viscosity of the convecting mantle. When such a parameterization is used in the global heat budget of the Earth to integrate the mantle temperature backwards in time, a runaway increase of temperature is obtained, leading to the so-called "thermal catastrophe". We propose a new approach that does not rely on convective scaling laws but instead considers the dynamics of plate tectonics, including temperature-dependent surface processes. We use a multi-agent system to simulate time-dependent plate tectonics in a 2D cylindrical geometry with evolutive plate boundaries. Plate velocities are computed using local force balance and explicit parameterizations for plate boundary processes such as trench migration, subduction initiation, continental breakup and plate suturing. The number of plates is not imposed but emerges naturally. At a given time step, heat flux is integrated from the seafloor age distribution and a global heat budget is used to compute the evolution of mantle temperature. This approach has a very low computational cost and allows us to study the effect of a wide range of input parameters on the long-term thermal evolution of the system. For Earth-like parameters, an average cooling rate of 60-70K per billion years is obtained, which is consistent with petrological and rheological constraints. Two time scales arise in the evolution of the heat flux: a linear long-term decrease and high-amplitude short-term fluctuations due to tectonic rearrangements. We show that the viscosity of the mantle is not a key parameter in the thermal evolution of the system and that no thermal catastrophe occurs when considering tectonic processes. The cooling rate of the Earth depends mainly on its ability to replace old insulating seafloor by young thin oceanic lithosphere. Therefore, the main controlling factors are parameters such as the resistance of continental lithosphere to breakup or the critical age for subduction initiation. We infer that simple convective considerations alone cannot account for the complex nature of mantle heat loss and that tectonic processes dictate the thermal evolution of the Earth.

Grigne, C.; Combes, M.; Le Yaouanq, S.; Husson, L.; Conrad, C. P.; Tisseau, C.

2011-12-01

263

High-resolution global upper mantle structure and plate tectonics  

Microsoft Academic Search

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

Yu-Shen Zhang; Toshiro Tanimoto

1993-01-01

264

A window of opportunity for plate tectonics in evolution of Earth-like planets?  

NASA Astrophysics Data System (ADS)

A rocky planet may exhibit stagnant lid behaviour under hot internal conditions due to a decrease in internal viscosity, associated with high internal temperatures, which results in lower induced lithospheric stress. These conditions may be relevant to a planet's early evolution. At the other extreme, cold, sluggish planets, approaching the end of their evolutionary cycle, may also exhibit stagnant behaviour, due to low mantle velocities, and the development of a thick, strong lithospheric lid. This leads to the possibility of a 'window' for plate tectonic behaviour in the evolution of rocky planets; where initial hot planets may exhibit stagnant lid behaviour, evolving into tectonically active planets, before, eventually, entering into a slow decline of tectonism and eventually entering a cold, senescent stagnant mode more typical of Mars today. Here we explore models of viscoplastic mantle convection, with varying internal heating and bottom temperature conditions, and demonstrate a stress maximum exists for middle-aged planets. We present an implementation of evolving internal heat production and basal temperatures through time, and show the viability of a 'window' for plate tectonic behaviour in the evolution of Earth-like planets.

O'Neill, C.

2011-12-01

265

Global change at the Paleocene-Eocene boundary: climatic and evolutionary consequences of tectonic events  

Microsoft Academic Search

Rea, D. K., Zachos, J. C., Owen, R. M. and Gingerich, P. D., 1990. Global change at the Paleocene-Eocene boundary: climatic and evolutionary consequences of tectonic events. Palaeogeogr., Palaeoclimatol., Palaeoecol., 79: 117-128. Events of the Paleocene-Eocene boundary provide the clearest example to date of how a tectonic event may have global climatic consequences. Recent advances permit well-constrained stratigraphic determination of

David K. Rea; James C. Zachos; Robert M. Owen; Philip D. Gingerich

1990-01-01

266

Plate Tectonics and Sea-Floor Spreading, Subduction Zones, "Hot Spots", and the "Ring of Fire"  

NSDL National Science Digital Library

This site is part of the United States Geological Survey, Cascade Volcano Observatory web site. It provides general information about the theory of plate tectonics. It correlates specific landform types and physical processes with the types of plate boundaries where they occur. The explanation of each boundary type includes real world examples and links to United States Geological Survey web pages about each example. The links between volcanism, earthquakes, and plate boundaries is also discussed. There is a section of the site that explores the types of volcanism that occur at spreading ridges, subduction zones, and hot spots (intraplate volcanism). Links are also provided to information on specific areas. These areas include: Cascade Range Volcanoes, Gorda Ridge, Juan de Fuca Plate, Juan de Fuca Ridge, North Cascades, Olympic Mountains, and the Yellowstone Caldera.

267

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

PubMed

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

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

2013-06-27

268

Reidar Lvlie and Plate Tectonic consequences of sedimentary inclination shallowing  

NASA Astrophysics Data System (ADS)

Reidar Lvlie was my mentor and supervisor in the early 1980s and he thought me all about laboratory experiments and palaeomagnetic methods, but also various aspects of science philosophy. My first fieldworks were together with him and I enjoyed memorable trips to the Bear Island, Spitsbergen and Scotland. Acquisition of magnetism in sediments was always a favourite topic of Reidar and in the early 1980s he was particularly interested in sedimentary inclination shallowing. From one of our fieldtrips to Spitsbergen we sampled unconsolidated flood-plain deposits of hematite-bearing Devonian red sand/siltstone from Dicksonfjorden. These were used for redeposition experiments in a coil system that could simulate different latitudes (field inclinations) and in 1994 we published a paper entitled"Magnetic remanence and fabric properties of laboratory-deposited hematite-bearing red sandstone" that demonstrated the tangent relationship between inclinations of detrital remanent magnetization and the ambient magnetic field. Inclination (I) error in sediments is latitude dependent, antisymmetric and the bias closely mimics errors produced by octupole fields of the same sign as the dipole field. Inclination shallowing is commonly predicted from tan (Observed Inclination) = f * tan (Field Inclination) where f is the degree of inclination error. In our study we calculated a f value of 0.4 and this laboratory value (and many others) is significant lower than those estimated from the E/I or the magnetic fabric methods developed in the past decade (f typically around 0.6). There is now little doubt that inclination shallowing in detrital sediments is a serious problem that affects plate reconstructions and apparent polar wander paths. As an example, a f value of 0.6 amounts to a latitude error of 1600 km at around 50 degrees N or S (comparable to the effects of octupole contributions as high as 22%) and this have led to erroneous Pangea reconstructions.

Torsvik, Trond H.

2014-05-01

269

Complex Faulting in the Pacific-North America Transform Offshore Southern California And Implications on Plate Boundary Tectonics and Tsunamigenesis  

Microsoft Academic Search

Complexity in the tectonic model for Pacific-North America transform motion in the offshore southern California region is demonstrated by earthquakes near San Clemente Island and Fortymile Bank. Observed focal mechanisms show movements opposite to those predicted by the plate tectonic theory for right-slip on NW- trending transform faults and observed in other parts of the California Continental Borderland. Also, there

M. R. Legg; A. Barberopoulou

2007-01-01

270

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

Microsoft Academic Search

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

Robert Hall

2002-01-01

271

Active Tectonics in the Outer Himalaya: Dating a Landslide Event in the Kumaun Sector  

Microsoft Academic Search

Of the entire Himalayan terrain, the Outer Himalaya is believed to show excellent signatures of active tectonics. The Main Boundary Thrust (MBT) that separates the Outer and Lesser Himalayas has a recorded history of tectonic activities in the recent past. The present study incorporates an additional example of a major landslide event, the Amiyan landslide, associated with the MBT that

Rameshwar Bali; A. R. Bhattacharya; T. N. Singh

2009-01-01

272

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

Microsoft Academic Search

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

Martin Meschede; Wolfgang Frisch

1998-01-01

273

The birth of the Rheic Ocean Early Palaeozoic subsidence patterns and subsequent tectonic plate scenarios  

NASA Astrophysics Data System (ADS)

New plate-tectonic reconstructions of the Gondwana margin suggest that the location of Gondwana-derived terranes should not only be guided by the models, but should also consider the possible detrital input from some Asian blocks (Hunia), supposed to have been located along the Cambrian Gondwana margin, and accreted in the Silurian to the North-Chinese block. Consequently, the Gondwana margin has to be subdivided into a more western domain, where the future Avalonian blocks will be separated from Gondwana by the opening Rheic Ocean, whereas in its eastern continuation, hosting the future basement areas of Central Europe, different periods of crustal extension should be distinguished. Instead of applying a rather cylindrical model, it is supposed that crustal extension follows a much more complex pattern, where local back-arcs or intra-continental rifts are involved. Guided by the age data of magmatic rocks and the pattern of subsidence curves, the following extensional events can be distinguished: During the early to middle Cambrian, a back-arc setting guided the evolution at the Gondwana margin. Contemporaneous intra-continental rift basins developed at other places related to a general post-Pan-African extensional phase affecting Africa Upper Cambrian formation of oceanic crust is manifested in the Chamrousse area, and may have lateral cryptic relics preserved in other places. This is regarded as the oceanisation of some marginal basins in a context of back-arc rifting. These basins were closed in a mid-Ordovician tectonic phase, related to the subduction of buoyant material (mid-ocean ridge?) Since the Early Ordovician, a new phase of extension is observed, accompanied by a large-scale volcanic activity, erosion of the rift shoulders generated detritus (Armorican Quartzite) and the rift basins collected detrital zircons from a wide hinterland. This phase heralded the opening of Palaeotethys, but it failed due to the Silurian collision (Eo-Variscan phase) of an intra-oceanic arc with the Gondwana margin. During this time period, at the eastern wing of the Gondwana margin begins the drift of the future Hunia microcontinents, through the opening of an eastern prolongation of the already existing Rheic Ocean. The passive margin of the remaining Gondwana was composed of the Galatian superterranes, constituents of the future Variscan basement areas. Remaining under the influence of crustal extension, they will start their drift to Laurussia since the earliest Devonian during the opening of the Palaeotethys Ocean.

von Raumer, Jrgen F.; Stampfli, Grard M.

2008-12-01

274

The role of image design in communicating the plate tectonic model  

NASA Astrophysics Data System (ADS)

As the unifying concept of the geosciences, the plate tectonic model is arguably the most important concept for students to understand about the Earth. The scale of plate tectonic processes is far beyond the everyday scale of human lives. Maps and schematic images within textbooks, on-line, or on television are the only access that most lay people, students, and even geologists will ever have to these inherently intangible processes. This means that images play a critical role in communicating aspects of plate tectonics and in developing conceptual models of these earth-scale processes to both experts and novices. In this study, non-science majors to geoscience faculty answered questions about a simplified version of a well-known schematic cross-section that illustrates various plate tectonic processes. Findings from questionnaires and interviews, including eye-tracking data, reveal the differences in how experts and novices visually inspect and interpret the cross-section. Findings include: Experts will focus on the relevant aspects of the image and may completely filter and dismiss aspects of the image they deem irrelevant. However, those same, irrelevant aspects can pose significant distractions to novices, and may mislead novices either by creating new misconceptions or supporting prior misconceptions. Two examples of commonly seen and possibly distracting aspects in cross sections of the plate tectonic model are a red, orange, or yellow asthenosphere under a gray lithosphere, and subducting slabs that terminate in the asthenosphere. The color scheme supports a misconception held by some of a hot, liquid mantle. Subducting slabs that either terminate abruptly or fade away are frequently interpreted to be melting at the tip. These findings support research that has clearly indicated that experts attend to relevant aspects of visual stimuli whereas novices do not. Images designed for experts may simply be too confusing for novices to focus on the salient and scientifically relevant aspects. One implication is that comprehension can be improved by designing images so as to draw the attention of novices to the relevant aspects of the image (de Koning et al., 2009; Jarodzka et al., 2009); and as a corollary, not to draw undue attention to irrelevant aspects, especially when irrelevant aspects can lead to supporting or creating misconceptions.

Clark, S. K.

2009-12-01

275

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

SciTech Connect

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.

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

276

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

SciTech Connect

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.

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

1993-03-01

277

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

NASA Astrophysics Data System (ADS)

There are two dominating hypotheses about composition of the primordial Earths 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 Earths 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 its accretion completion, which moved inside the planet as a result of acceleration of the bodys rotation around axis due to momentum conservation law as a result of material compaction and its radius shortening.

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

2009-12-01

278

A Simple Linear Age Progression for the Ninetyeast Ridge, Indian Ocean: New Constraints on Indian Plate Tectonics and Hotspot Dynamics  

Microsoft Academic Search

New Ar\\/Ar age constraints on basalt from DSDP and ODP drill sites and new (2007) dredge sites confirm that the Ninetyeast Ridge (NER) is a 5000 km long hotspot track in the Indian Ocean created as the Indian Plate moved rapidly northward from c. 80 to 40 Ma at the fastest known rate of any tectonic plate with significant continental

M. S. Pringle; F. A. Frey; E. E. Mervine

2008-01-01

279

Ultra-slow spreading ridges: a response to the interplay between mantle convection and plate tectonics  

NASA Astrophysics Data System (ADS)

Ultra-slow spreading ridges such as the South West Indian ridge or the Arctic ridge system are oddities amongst oceanic ridges. Conversely to faster oceanic ridges, petrographic and seafloor studies have shown that they are characterized by low melt supply and present low crustal thicknesses and heat flow; these features are interpreted as an evidence for a cooler sublithospheric mantle. In cartoonish sketches of plate tectonics, ridges open above upwellings, subduction zones occur over downwellings, and plates are riding over the mantle convection cells. In this study, we designed a simple yet dynamically consistent thermal convection model to test the impact of far-field forces on spreading ridges and show that this pattern is disrupted by plate tectonics. In particular, continental collisions modulate the spreading rates because resisting forces build up at plate boundaries. As a consequence, this modifies the surface boundary conditions and therefore the underlying mantle flow. We show that the ideal convection cell pattern quickly breaks down when plate motion is impeded by continental collisions in the far field. Not only the decreasing spreading rates are diagnostic, but in the same time, (i) the heat flow is decreasing at the ridge, (ii) the thermal structure of the cooling lithosphere no longer matches the cooling half-space model, and (iii) the mantle temperature beneath the ridge drops by more than 100 degrees. We compare our model predictions to available observables and show that this simple mechanism explains the atypical thermo-mechanical evolution of the South West Indian ridge and Arctic ridge system. Last, the recent S wave seismic tomography model of Debayle and Ricard (2012) reveals that only away from those two ridges does lithospheric thickening departs from the half-space cooling model, in accord with our model predictions.

Husson, Laurent; Yamato, Philippe; Bezos, Antoine

2014-05-01

280

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

and interactions of large, rigid, interlocking fragments of lithosphere called tectonic plates. Plates form plates on the surface of the Earth, and many minor ones. The present-day configuration of tectonic plates of tectonic plates at an instant in the history of the Earth. The visualization of reconstruc- tions

Torsvik, Trond Helge

281

Earth and Planetary Science Letters 157 (1998) 9-22 Self-consistent generation of tectonic plates in three-dimensional  

E-print Network

Elsevier Science B.V. All rights reserved. Ke~uorcls: plate tectonics: plates: mantle; convection: modelsEPSL Earth and Planetary Science Letters 157 (1998) 9-22 Self-consistent generation of tectonic plates in three-dimensional mantle convection Paul J. Tackley * Department of Earth and Space Scirrm

Tackley, Paul J.

282

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

E-print Network

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

Paris-Sud XI, Université de

283

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

NASA Astrophysics Data System (ADS)

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.

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

1989-03-01

284

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

NASA Technical Reports Server (NTRS)

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.

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

1989-01-01

285

The Wacky Wonderful World of Cordilleran Tectonics Event Timing Description  

E-print Network

Fault system; sealing off of southern entrance to Great Valley of California as sliver of crust along California Coast Middle Miocene - Holocene As North American Plate overran the divergent boundary of the Farallon and Pacific plates, change in sense of motion from subduction to transform; birth of San Andreas

Holtz Jr., Thomas R.

286

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

E-print Network

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.

Petrova, L

2008-01-01

287

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

E-print Network

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.

L. Petrova; B. Pavlov

2008-01-18

288

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

NASA Astrophysics Data System (ADS)

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 17S 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.

Conder, James Andrew

289

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

NASA Astrophysics Data System (ADS)

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

Bartlett, M. G.

2006-12-01

290

Some remarks on the models of plate tectonics on terrestrial planets: From the view-point of mineral physics  

NASA Astrophysics Data System (ADS)

Some mineral physics-related issues are reviewed that are closely related to the operation of plate tectonics on terrestrial planets with different mass. Plate tectonic style of convection would occur when the surface layer has only modest strength relative to the stress generated by mantle convection so that it can deform and subduct into the mantle. Both the stress on the lithosphere generated by mantle convection and the resistance of the lithosphere for subduction depend on the relevant materials properties. A review is presented on the scaling relationships between relevant physical properties and planet mass and on the strength of the lithosphere. It is shown that if physically plausible scaling is made both for the relevant materials properties and the macroscopic energy balance, a large Earth-like planet may not necessarily have plate tectonics. In addition to the internal processes, the surface conditions such as the surface temperature may also play an important role via its effects on the thickness of thermal or chemical lithosphere, making it difficult for plate tectonics to operate on small planets. Therefore, in this model, plate tectonics would operate on planets with modest size like Earth, but the validity of this conclusion hinges on the characterization of (i) the influence of pressure-dependent properties on the vigor of convection and of (ii) the resistance for subduction. In particular, the processes determining the resistance for subduction have an important influence on the operation of plate tectonics. Key issues are highlighted that require further studies including the influence of depth-dependent properties on convection and the formulation of the resistance of the lithosphere for subduction.

Karato, Shun-ichiro

2014-09-01

291

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

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

292

The Azores-Gibraltar plate boundary: Focal mechanisms, depths of earthquakes, and their tectonic implications  

Microsoft Academic Search

We have analyzed the focal mechanisms and depths of 10 moderately sized earthquakes along the Azores-Gibraltar plate boundary by a variety of methods including formal inversion of the waveform and amplitude of teleseismic P and SH waves, first motion readings, and the identification of depth phases. Our data, together with a compilation of results reported for very large events from

Nina L. Grimison; Wang-Ping Chen

1986-01-01

293

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

SciTech Connect

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.

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

1988-08-01

294

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

NASA Astrophysics Data System (ADS)

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.

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

2013-12-01

295

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

E-print Network

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.

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

2014-01-01

296

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

NASA Astrophysics Data System (ADS)

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.

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

2014-08-01

297

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

NASA Astrophysics Data System (ADS)

The area investigated lies between latitude 2640' and 2715' south and longitude 6930' and 6830' west in the Andean Range. A combination of K-Ar dating, petrology, geochemistry and geophysical data has led to the recognition of an important change in the tectonic control of volcanic activity during the early Pliocene. Five volcanic cycles are recognized and grouped into two units according to tectonic control. The first unit comprises the following cycles; (a) La Coipa-Maricunga 23.0-15.7 Ma; (b) Pastillito 13.9-12.9 Ma; and (c) Wheelwright 8.84-6.14 Ma; representing a progression of active belts, striking N5E, towards the east. The second group is represented by Penas Biancas 4.90-2.64 Ma and Ojos del Salado 1.84-Recent (active) having a N65E strike, extending over a distance of some 250 km in the high Andes. The volcanic rocks of both groups belong to the calc-alkali series ranging from andesitic basalt to andesite, dacite and rhyolite, though with significant variations in total alkali content. Changes in the orientation of the volcanic belt may be related to changes in the spreading rate of the Nazca Plate or to changes in the angle of subduction on either side of latitude 27S i.e. along the latitude of the Easter Hot Line.

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

1985-03-01

298

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

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

Jean-Yves Royer; Ted Chang

1991-01-01

299

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

NASA Astrophysics Data System (ADS)

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.

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

2004-12-01

300

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

301

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

E-print Network

Rifting beneath Antarctica's ice sheet: A plate tectonic approach Supervisors: Graeme Eagles (RHUL Pacific can be used to determine by how much, and when, eastern and western Antarctica moved apart from Antarctica-West Antarctica motion. One specific advantage will come from using a modelling tool

Royal Holloway, University of London

302

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

NASA Astrophysics Data System (ADS)

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 for the tectonic escape: the Chaochou fault system, which separates the Eo-Miocene slate belt of the Central Range and an extensive composite of alluvium plains. Structural data show that the Chaochou fault cut across the strike of the slaty cleavage within the Central Range, suggesting that the fault developed at later stages during the Pio-Pleistocene plate convergence. Morphologic features along the Chaochou fault suggest presence of several active fault strands and changeable mountain front characteristics. The northern and middle portions of the fault show evidence of compression and uplifting based on alluvial fans and river terraces. In contrast, the southern portion of the fault shows significant embayments at river mouths, which may suggest slower rate of uplifting or even subsidence in the southern segment. GPS data from this area indicate extensional deformation with some left lateral movement component in the southern portion. Data from seismicity indicate complex deformation at present along the length of the fault. Locations of three swarms of seismicity suggest current fault activities are underneath the Central Range. Unexpectedly, just below the Chaochou fault shows little seismicity, suggesting the fault may be locked and the deformation is largely taking place in the Central Range at the moment. These observations indicate diverse patterns of deformation along the Chaochou fault, the eastern boundary fault for the tectonic escape in the SW Taiwan. The patterns of deformation imply that the process of tectonic escape may involve compression and relaxation through various faulting mechanisms during the process. In addition, extension may be common at the outer portion of the escaped block where widened space contributes to such tectonic adjustment.

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

2002-12-01

303

Missing plate tectonics in Venus caused by rheological contrast at Moho  

NASA Astrophysics Data System (ADS)

Venus has been regarded as a twin planet to the Earth, because of density, mass, size and distance from the Sun (Taylor and McLennan, 2008). However, the Magellan mission revealed that plate tectonics is unlikely to work on the Venus (Turcotte et al., 1999). The plate tectonics is one of the most important mechanism of heat transport and material circulation of the Earth, consequently, its absence might cause the different tectonic evolution between Earth and Venus. Rheological structure is a key to inferring mantle structure and convection style of planet interiors because the rock rheology controls strength and viscosity. In previous study, the behavior of Venusian lithosphere has been inferred from the power-law type flow law of dry diabase (Mackwell et al., 1998). They indicated that lower crust can be weaker than upper mantle, which might result decoupling at the crust-mantle boundary (Moho depth) and mantle convection without crustal entrainment. However, the power-law creep may not be applicable to infer the rheological structure at Moho depths, because the dislocation-glide control creep (Peierls mechanism) is known to become dominant at relatively low temperatures in materials with a relatively strong chemical bonding such as silicates (Tsenn and Carter 1987). In this study, we conduct two-phase deformation experiments to directly investigate rheological contrast between plagioclase (crust) and olivine (mantle) using solid-medium deformation apparatus and discuss the difference between these planets in terms of rheological behaviors. Moreover, we conduct numerical simulation utilizing the results of deformation experiments to investigate the effect of the strength contrast between the crust and the mantle to the motion of planetary surface. In this study, we perform experiments to directly investigate the relative strength between plagioclase and olivine without any extrapolating of flow law; the crustal materials consist predominantly of plagioclase that largely control deformation of the crust, whereas deformation of the upper mantle is largely controlled by olivine. These samples are together sandwiched between alumina pistons in a simple shear geometry and we used the hot-pressed samples and perform deformation experiments using solid-medium deformation apparatus. The experimental conditions are ranging 1-2 GPa and 400-1000oC, corresponding conditions approximately to Moho of the Venus at dry and wet conditions. Under wet environments, olivine is weaker than plagioclase at temperature less than 400oC, whereas plagioclase becomes weaker at temperature higher than 600oC. In contrast, under dry conditions, olivine is still weaker than plagioclase at temperature as high as 600oC. Based on microstructures and mechanical data, we found that the deformation mechanism is dominated by Peierls mechanism (dislocation-glide) in each sample under experimental condition. The investigated strength contrast between plagioclase and olivine are applied for the Venus's Moho in numerical simulation, in which the strength contrast at Moho plays a key role on the activation of plate tectonics. In presentation, we will report additional results of deformation experiments, and hope to propose the rheological structure of Venus based on the experimental and numerical results.

Azuma, S.; Katayama, I.; Nakakuki, T.

2012-12-01

304

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

NASA Astrophysics Data System (ADS)

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.

Loureno, Diogo L.; Tackley, Paul J.

2014-05-01

305

The influence of plate tectonics on the mixing properties of the Earth's mantle  

NASA Astrophysics Data System (ADS)

During the last decade an improved understanding of the physical processes in the Earth's interior has led to the acceptance of an integrated system coupling mantle convection and plate tectonics. Higher computer power and new modelling techniques are now allowing the numerical calculation of this system in a self-consistent manner [1]. While former studies concentrated on the evolution of plate-like features [2] and the dependence on rheological parameters, the present study has a more geochemical motivation. It focusses on the influence of a plate-like surface on the mixing of chemical heterogeneities in the mantle to get a deeper understanding of the observed heterogeneous structure of the mantle and the existence of chemical distinct reservoirs. The mixing properties of isoviscous 3D time-dependent convection has already been investigated [3]. One basic finding is the existence of two different mixing time scales. Mixing inside one convective cell is rather effective and causes homogenization on the order of several 100 Ma. Mixing between different convective cells occurs on a much longer timescale, such that heterogeneities in the mantle can survive for several Ga. The main purpose of the present investigation is a comparison between findings from isoviscous convective flows and from a flow with a viscoplastic rheology that show plate-like behaviour on the surface. We use an approach of tracer dispersal for investigation, where tracers are infinite and passive (i.e. they are not affecting the flow), and confirm the results from isoviscous flows for more complex rheologies. In both cases mixing is influenced by the initial position of a heterogeneity in the flow and is still incomplete after about a dozen tracer overturns, which may corresponds to several Ga. Qualitative differences between the mixing properties of the two described flow types can hardly be observed with the used setup. References [1] Trompert, R., Hansen, U. (1998): Mantle convection simulations with rheologies that generate plate-like behaviour, Nature, 395, 686-689 [2] Stein, C., Schmalzl, J., Hansen, U. (2004): The effect of rheological parameters on plate behaviour in a self-consistent model of mantle convection, Phys. Earth Plan. Int., 142, 225-255 [3] Schmalzl, J., Hansen, U., Houseman, G. (1996): Mixing in vigorous, time dependent three-dimensional convection and application to Earth's Mantle, Jour. Geophys. Res., 110, B10, 21847-21858

Rolf, Tobias; Schmalzl, Jrg; Stein, Claudia

2010-05-01

306

On the competing roles of fault reactivation and brittle failure in generating plate tectonics from mantle convection  

NASA Astrophysics Data System (ADS)

Fault reactivation plays a fundamental role in the generation of plate tectonics from mantle convection. Converging and transform plate margins are mechanically weak due to both preexisting faults and preserved shear zones within the crust and lithosphere, on the one hand, and continuous brittle failure of lithosphere, on the other hand. Transform margins are the site for nucleating new converging margins. Lithospheric earthquakes demonstrate that oceanic lithosphere within a trench can deform as fast as the upper mantle. Models demonstrate that faulted converging plate margins contribute to producing plate tectonic-like motion. Preexisting faults and a power law plastic rheology dynamically interact and together give rise to plate-like motion. Faults have an important influence over outer rise and trench topography and by comparing models with observations, interplate stress is about 10-30 MPa. Subduction can initiate on preexisting faults when interplate coupling is as high as 10-30 MPa if the oceanic plate already has slabs attached to it as was the case for the Pacific plate when the Marianas nucleated. Modeled plates only change velocity slowly in response to the initiation of new subduction zones; the initiation of subduction in the Western Pacific at ? 45 Ma was likely the result of a change in Pacific plate motion as opposed to causing the change in the direction of plate motion. The locations of the greatest amount of present day brittle failure within oceanic lithosphere are not located at arbitrary positions on oceanic plates, rather brittle failure occurs in close proximity t o long lived zones of preexisting weakness. Old weak structures are reused by the convecting system because it takes less energy t o reactivate a preexisting structure than it does t o create an entirely new plate margin from pristine, intact lithosphere.

Gurnis, Michael; Zhong, Shijie; Toth, John

307

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

SciTech Connect

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.

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

1996-12-31

308

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

PubMed

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

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

2007-09-01

309

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

NASA Astrophysics Data System (ADS)

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 that superdownwelling along multiple subduction zones might provide an effective mechanism to pull together dispersed continental fragments into a closely packed assembly. The recycled subducted material that accumulates at the mantle transition zone and sinks down into the core-mantle boundary (CMB) provides the potential fuel for the generation of plumes and superplumes which ultimately fragment the supercontinent. Geological evidence related to the disruption of two major supercontinents (Columbia and Gondwana) attest to the involvement of plumes. The re-assembly of dispersed continental fragments after the breakup of a supercontinent occurs through complex processes involving 'introversion', 'extroversion' or a combination of both, with the closure of the intervening ocean occurring through Pacific-type or Atlantic-type processes. The timescales of the assembly and dispersion of supercontinents have varied through the Earth history, and appear to be closely linked with the processes and duration of superplume genesis. The widely held view that the volume of continental crust has increased over time has been challenged in recent works and current models propose that plate tectonics creates and destroys Earth's continental crust with more crust being destroyed than created. The creation-destruction balance changes over a supercontinent cycle, with a higher crustal growth through magmatic influx during supercontinent break-up as compared to the tectonic erosion and sediment-trapped subduction in convergent margins associated with supercontinent assembly which erodes the continental crust. Ongoing subduction erosion also occurs at the leading edges of dispersing plates, which also contributes to crustal destruction, although this is only a temporary process. The previous numerical studies of mantle convection suggested that there is a significant feedback between mantle convection and continental drift. The process of assembly of supercontinents induces a temperature increase beneath the supercontinent due to the thermal insulating effect. Such thermal insulation leads to a planetary-scale reorganization of mantle flow and results in longest-wavelength thermal heterogeneity in the mantle, i.e., degree-one convection in three-dimensional spherical geometry. The formation of degree-one convection seems to be integral to the emergence of periodic supercontinent cycles. The rifting and breakup of supercontinental assemblies may be caused by either tensional stress due to the thermal insulating effect, or large-scale partial melting resulting from the flow reorganization and consequent temperature increase beneath the supercontinent. Supercontinent breakup has also been correlated with the temperature increase due to upwelling plumes originating from the deeper lower mantle or CMB as a return flow of plate subduction occurring at supercontinental margins. The active mantle plumes from the CMB may disrupt the regularity of supercontinent cycles. Two end-member scenarios can be envisaged for the mantle convection cycle. One is that mantle convection with dispersing continental blocks has a short-wavelength structure, or close to degree-two structure as the present Earth, and when a supercontinent forms, mantle convection evolves into degree-one structure. Another is that mantle convection with dispersing continental blocks has a degree-one structure, and when a supercontinent forms, mantle convection evolves into degree-two structure. In the case of the former model, it would take longer time to form a supercontinent, because continental blocks would be trapped by different downwellings thus inhibiting collis

Yoshida, Masaki; Santosh, M.

2011-03-01

310

Plate tectonic controls on atmospheric CO2 levels since the Triassic  

NASA Astrophysics Data System (ADS)

Climate trends on time-scales of 10's to 100's 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 mid-ocean ridges. So far, such degassing estimates were based on reconstructions of ocean floor production for the last 150 Million years (Myr) and indirectly, through sea level inversion before 150 Myr. 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 Myr) until Present, the total paleo-subduction 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 Myr suggests average global subduction rates have been constant, ~6 cm/year: 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.

van der Meer, Douwe; Zeebe, Richard; van Hinsbergen, Douwe; Sluijs, Appy; Spakman, Wim; Torsvik, Trond

2014-05-01

311

Plate tectonic controls on atmospheric CO2 levels since the Triassic.  

PubMed

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

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

2014-03-25

312

Plate tectonic controls on atmospheric CO2 levels since the Triassic  

PubMed Central

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 (250200 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

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

2014-01-01

313

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)

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.

Toksoz, M. Nafi; Reilinger, Robert

1992-01-01

314

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

NASA Astrophysics Data System (ADS)

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.

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

2012-12-01

315

Grenville tectonic events and evolution of the Yenisei Ridge at the western margin of the Siberian Craton  

NASA Astrophysics Data System (ADS)

Geological, petrologic, geochemical, and isotopic geochronological evidence for Grenville events at the western margin of the Siberian Craton are considered. These events were related to assembly of the Rodinia supercontinent. Multiple manifestations of riftogenic and within-plate magmatism at the final stage of orogenic evolution gave rise to breakdown of Rodinia and the formation of the Paleoasian ocean. The results allowed us to develop a new concept on the Precambrian geological evolution of the Yenisei Ridge and the processes that created its tectonic structure. The chronological sequence of events in the history of the Transangarian Yenisei Ridge is based on geological evidence and isotopic dating of Precambrian complexes variable in geodynamic nature. Four tectonic stages dated at 1.4-1.1, 1.1-0.9, 0.90-0.85, and 0.8-0.6 Ga were controlled by collision and extension recognized from large regional linear crustal structural elements. The evolution of the Transangarian Yenisei Ridge, which lasted for 650 Ma, corresponds in duration to supercontinental cycles that begin from rifting and breakdown of the predated supercontinent and was completed by orogeny and the formation of a new supercontinent. The regional geodynamic history correlates with the synchronous sequence and similar style of tectonothermal events at the periphery of the large Precambrian Laurentia and Baltica cratons. This is evidenced by paleocontinental reconstructions, which confirm close spatiotemporal links of Siberia with cratons in the northern Atlantic 1400-600 Ma ago and indicate incorporation of the Siberian Craton into the ancient Nuna and Rodinia supercontinents.

Likhanov, I. I.; Nozhkin, A. D.; Reverdatto, V. V.; Kozlov, P. S.

2014-09-01

316

On the Generation of Supercontinent Cycles from Mantle Convection with Self-Consistent Plate Tectonics and Mobile Continents  

NASA Astrophysics Data System (ADS)

Kenorland, Columbia, Rodinia, Pangaea : there is some evidence in the geologic record that continental blocks have been assembled into a large landmass during some periods of Earth's history. These periods were interrupted by continental break-up events and subsequent dispersal of the fragments. The alternation between assembled and dispersed continent configurations is often called the supercontinent cycle. Plate reconstruction techniques allow for looking back into Earth's tectonic history, but only for the last 200 Ma is the necessary data well accessible, such that only the existence of the last supercontinent, Pangaea, is well documented. Especially for the first supercontinents only poor evidence exist: one of them is the correlation of peaks in the production rate of continental crust that can be detected by analyzing the osmium decay system [1] and the suggested assembly times of some of the older supercontinents. These are derived from the argument that almost all cratons that stabilized at a certain time were located next to each other in Pangaea, which is very unlikely if they have not formed in a single continental block [2]. Supercontinents are thought to generate a large-scale thermal anomaly by insulation beneath them, which enhances melting processes and with that the growth of continental crust. However, although some progress has been made, the details of the dynamic origin of the supercontinent cycle are still not well understood. What causes continental fragments to assemble into a single unit? What causes the breakup of the supercontinent? On which timescales do these processes occur? Here we use fully dynamic models of mantle convection that feature self-consistently generated plate-like behavior and buoyant, rheologically distinct continents that drift over the surface, eventually colliding or splitting. In contrast to our previous models [3] the continents in this study consist of a rheologically strong interior surrounded by a weaker exterior. The former represents the Archaean cratons on Earth, which hardly deform and are thought be tectonically stable since > 2.5 Ga. The weak material represents the mobile belts from the Proterozoic or Phanerozoic. In the present study we investigate in 2D and 3D numerical models how the properties of the mobile belts as well as those of the convective flow (mode of heating, yield strength of the lithosphere) control the existence of a supercontinent cycle and its periodicity. In order to generate a supercontinent cycle a harmonic degree-1 convection pattern is needed to assemble the continental fragments, which is disturbed by the onset of higher degree structures when a supercontinent splits. References [1] D. G. Pearson, S. W. Parman, G. M. Nowell (2007), A link between large scale mantle melting and continent growth seen in osmium isotopes, Nature, 449, 202-205. [2] J. J. W. Rogers, M. Santosh (2003), Supercontinents in Earth History, Gondwana Res., 6, 357-368. [3] T. Rolf, N. Coltice, P. J. Tackley (2012), Linking continental drift, plate tectonics and the thermal state of the Earth's mantle, Earth Planet. Sci. Lett., doi: 10.1016/j.epsl.2012.07.011

Rolf, T.; Tackley, P. J.; Coltice, N.

2012-12-01

317

Plate tectonics began in Neoproterozoic time, and plumes from deep mantle have never operated  

NASA Astrophysics Data System (ADS)

Archean, Paleoproterozoic, and Mesoproterozoic rocks, assemblages, and structures differ greatly both from each other and from modern ones, and lack evidence for subduction and seafloor spreading such as is widespread in Phanerozoic terrains. Most specialists nevertheless apply non-actualistic plate-tectonic explanations to the ancient terrains and do not consider alternatives. This report evaluates popular concepts with multidisciplinary information, and proposes options. The key is fractionation by ca. 4.45 Ga of the hot young Earth into core, severely depleted mantle, and thick mafic protocrust, followed by still-continuing re-enrichment of upper mantle from the top. This is opposite to the popular assumption that silicate Earth is still slowly and unidirectionally fractionating. The protocrust contained most material from which all subsequent crust was derived, either directly, or indirectly after downward recycling. Tonalite, trondhjemite, and granodiorite (TTG), dominant components of Archean crust, were derived mostly by partial melting of protocrust. Dense restitic protocrust delaminated and sank into hot, weak dunite mantle, which, displaced upward, enabled further partial melting of protocrust. Sinkers enriched the upper mantle, in part maintaining coherence as distinct dense rocks, and in part yielding melts that metasomatized depleted-mantle dunite to more pyroxenic and garnetiferous rocks. Not until ca. 3.6 Ga was TTG crust cool enough to allow mafic and ultramafic lavas, from both protocrust and re-enriched mantle, to erupt to the surface, and then to sag as synclinal keels between rising diapiric batholiths; simultaneously upper crust deformed ductily, then brittly, above slowly flowing hot lower TTG crust. Paleoproterozoic and Mesoproterozoic orogens appear to be largely ensialic, developed from very thick basin-filling sedimentary and volcanic rocks on thinned Archean or Paleoproterozoic crust and remaining mafic protocrust, above moderately re-enriched mantle. Subduction, and perhaps the continent/ocean lithospheric dichotomy, began ca. 850 Ma - although fully modern plate-tectonic processes began only in Ordovician time - and continued to enrich the cooling mantle in excess of partial melts that contributed to new crust. "Plumes" from deep mantle do not operate in the modern Earth and did not operate in Precambrian time.

Hamilton, Warren B.

2011-04-01

318

Recent plate tectonics of the Arctic Basin and of northeastern Asia  

NASA Astrophysics Data System (ADS)

The recent tectonics of the Arctic Basin and northeastern Asia are considered as a result of interaction between three lithospheric plates: North-America, Eurasia and Spitsbergen. Seismic zones (coinciding in the Norway-Greenland basin with the Kolbeinsey, Mohns and Knipovich ridges, and in the Arctic Ocean with the Gakkel Ridge) clearly mark the boundaries between them. In southernmost Svalbard (Spitsbergen), the secondary seismic belt deviates from the major seismic zone. This belt continues into the seismic zone of the Franz Josef Land and then merges into the seismic zone of the Gakkel Ridge at 70-90E. The smaller Spitsbergen plate is located between the major seismic zone and its secondary branch. Within northeastern Asia, earthquake epicenters with magnitude over 4.5 are concentrated within a 300-km wide belt crossing the Eurasian continent over a distance of 3000 km from the Lena estuary to the Komandorskye Islands. A single seismic belt crosses the northern sections of the Verkhoyansky Ridge and runs along the Chersky Ridge to the Kolymo-Okhotsk Divide. To compute the poles of relative rotation of the Eurasian, North-American and Spitsbergen plates we use 23 new determinations of focal-mechanism solutions for earthquakes, and 38 azimuths of slip vectors obtained by matching of symmetric mountain pairs on both sides of the Knipovich and Gakkel ridges; we also use 14 azimuths of strike-slip faults within the Chersky Ridge determined by satellite images. The following parameters of plate displacement were obtained: Eurasia/North America: 62.2N, 140.2E (from the Knipovich Ridge section south of the triple junction); 61.9N, 143.1E (from fault strikes in the Chersky Ridge); 60.42N, 141.56C (from the Knipovich section and from fault strikes in the Chersky Ridge); 59.48N, 140.83E, ? = 1.89 10 -7 deg/year (from the Knipovich section, from fault strikes in the Chersky Ridge and from the Gakkel Ridge section east of the triple junction). The rate was calculated by fitting the 2' magnetic lineations within the Gakkel Ridge). North-America/Spitsbergen: 70.96N, 121.18E, ? = -2.7 10 -7 deg/year from the Knipovich Ridge section north of the triple junction, from earthquakes in the Spitsbergen fracture zone and from the Gakkel Ridge section west of the triple junction). Eurasia/Spitsbergen: 70.7N, 25.49E, ? = -0.99 10 -7 deg/year (from closure of vector triangles).

Savostin, L. A.; Karasik, A. M.

1981-04-01

319

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

SciTech Connect

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.

Holcombe, T.L.

1985-01-01

320

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

SciTech Connect

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

Husseini, M.I. (Aramco, Dhahran (Saudi Arabia))

1991-01-01

321

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

E-print Network

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...

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

2012-01-01

322

Discovering Plate Boundaries  

NSDL National Science Digital Library

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

Henning, Alison

323

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

E-print Network

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...

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

2012-01-01

324

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 generated at plate edges and within plates? What do earthquakes tell us about the internal structure of the earth? Can earthquake activity be understood well enough to predict future occurrences related to it

325

On December 26, 2004 the world saw yet again how strains built up over hundreds of years by slow and almost imperceptible motions of tectonic plates are released with devastating effect. A  

E-print Network

and almost imperceptible motions of tectonic plates are released with devastating effect. A giant earthquake the Tibetan plateau. The plate collision continues today as the In- dian plate moves northward, forcing pieces The Earth Scientist Fig. 1a. Approximate plate tectonic bounda- ries in the region of the Sumatra earthquake

Stein, Seth

326

Tectonics changes in NW South American Plate and their effect on the movement pattern of the Bocon Fault System during the Mrida Andes evolution  

NASA Astrophysics Data System (ADS)

The NE-SW trending Mrida-Andes fold-and-thrust belt, in the southern boundary of the Maracaibo Block, formed by a collisional event in Late Miocene at the boundary of the Maracaibo Block and Guyana Shield in the northwestern South American plate. The 500 km long, NE-SW striking right-lateral strike-slip Bocon Fault System lies in the Mrida-Andes area. Mylonitic fault rocks along the Bocon Fault System developed during pre-Late Miocene-Early Pliocene. Microscopic and mesoscopic structures such as mica fish, asymmetrical porphyroclasts, S-C shear bands, and asymmetrical ductile folds in Bocon Fault mylonite indicate a sinistral movement along the fault. The movement is probably related to pre-collision extensional tectonics that began in the Late Triassic-Jurassic interval, and continued until the Late Cretaceous or Middle Eocene. Following the collision of the Panam Arc and the South American plate in the Late Miocene, and the change from extensional to contractional tectonic regime, the Bocon was reactivated as a dextral fault system.

Javadi, Hamid Reza; Foroutan, Mohammad; Ashtiani, Marzieh Esterabi; Urbina, Jose Angel; Saidi, Abdollah; Faridi, Mohammad

2011-07-01

327

From subduction to collision: constraining the early history of the Taiwan Mountain Belt by plate tectonic reconstructions  

NASA Astrophysics Data System (ADS)

Understanding formation of the Taiwan orogen is important, because it is an active case-example to test geodynamic theories of mountain building processes, such as the critical wedge model, or of subduction zone reversal. Nevertheless, large uncertainties exist regarding the pre-collisional architecture of the orogen, timing of collision, as well as peak metamorphic conditions of the Cenozoic orogeny. The goal of this contribution is to re-evaluate existing models in the light of recent geophysical datasets, and constrain the evolution towards the present day plate tectonic configuration with a comprehensive reconstruction of plate movements since the Late Cretaceous. To this end, we present a revised analysis of the plate tectonic framework of Southeast Asia since the Late Cretaceous, a time when subduction polarity was still opposite to what is observed at present (westward subduction of the Pacific Plate, as opposed to eastward subduction of Eurasia at present). This is independent of the subduction zone reversal thought to occur at present in the northern part of the Taiwan orogen. We place our reconstructions within a global plate tectonic frame, and discuss (1) the consequences of subduction zone reversal for the evolving passive margin, (2) the influence of opening on the (proto-) South China Sea on the pre-collisional architecture. This yields a new model for the collisional history of Taiwan, which reconciles the pre-collisional architecture with the metamorphic conditions of the Cenozoic orogeny, and makes predictions about timing of peak-pressures, as well as the timing of collision and present subduction zone reversal.

von Hagke, Christoph; Philippon, Mlody; Avouac, Jean-Philippe

2014-05-01

328

Biogeographical Consequences of Cenozoic Tectonic Events within East Asian Margins: A Case Study of Hynobius Biogeography  

PubMed Central

Few studies have explored the role of Cenozoic tectonic evolution in shaping patterns and processes of extant animal distributions within East Asian margins. We select Hynobius salamanders (Amphibia: Hynobiidae) as a model to examine biogeographical consequences of Cenozoic tectonic events within East Asian margins. First, we use GenBank molecular data to reconstruct phylogenetic interrelationships of Hynobius by Bayesian and maximum likelihood analyses. Second, we estimate the divergence time using the Bayesian relaxed clock approach and infer dispersal/vicariance histories under the dispersalextinctioncladogenesis model. Finally, we test whether evolutionary history and biogeographical processes of Hynobius should coincide with the predictions of two major hypotheses (the vicariance/out of southwestern Japan hypothesis). The resulting phylogeny confirmed Hynobius as a monophyletic group, which could be divided into nine major clades associated with six geographical areas. Our results show that: (1) the most recent common ancestor of Hynobius was distributed in southwestern Japan and Hokkaido Island, (2) a sister taxon relationship between Hynobius retardatus and all remaining species was the results of a vicariance event between Hokkaido Island and southwestern Japan in the Middle Eocene, (3) ancestral Hynobius in southwestern Japan dispersed into the Taiwan Island, central China, Korean Peninsula and northeastern China as well as northeastern Honshu during the Late EoceneLate Miocene. Our findings suggest that Cenozoic tectonic evolution plays an important role in shaping disjunctive distributions of extant Hynobius within East Asian margins. PMID:21738684

Li, Jun; Fu, Cuizhang; Lei, Guangchun

2011-01-01

329

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

SciTech Connect

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

Stanley, D.J.

1983-03-01

330

The Jan Mayen Microcontinent: Computers animations of the plate tectonic history  

NASA Astrophysics Data System (ADS)

Local reinterpretation of magnetic seafloor anomalies in the NE Atlantic (e.g. Gaina et al., EPSL, 2002), and the Arctic (Oakey et al, GSC-Open File, 1999) has led to a revised Tertiary plate model for the region. Our model suggests complete separation between the North American and Eurasian plates was established first in the Oligocene, when a southward propagating Arctic spreading system linked with a northward propagating Atlantic spreading system. The Arctic system consisted of the Nansen, Mohns, and Aegir Ridges, with a series of left-lateral offsets, around the Greenland craton. The Atlantic system consisted of the Reykjanes and Kolbeinsey Ridges and stepped right around Greenland for the same reason. The final configuration became one of opposed and overlapping propagating spreading systems, where both the Aegir and the Kolbeinsey spreading ridges were active, a concept discussed by Vogt (1986). This configuration resembles that seen for microcracks, mode 1 fractures, normal faults, rifts, and minor offsets along spreading axes (e.g. Macdonald and Sempere, JGR, 1984). The interaction of the spreading ridge system with the Iceland Hotspot, likely influenced the timing and style of rifting and break-up (e.g. Mueller et al., Geology, 2001). As a result of the overlapping tips of the Arctic and Atlantic spreading axes, the Jan Mayen microcontinent gradually became separated from East Greenland and rotated c. 50 counter clockwise in the process. Our reconstructions indicate that this separation and rotation started approximately at Chron 22 (49 Ma) and ended approximately at Chron 12 (30 Ma) when the Aegir Ridge became extinct. During its rotation, the Jan Mayen microcontinent formed a bridge between NW Europe (the Faroes area) and southern East Greenland for quite some time. Clearly, the presence of the Jan Mayen continental sliver must have influenced oceanic circulation patterns between the NE Atlantic and Norwegian-Greenland Sea. We present a series of computer graphic animations, using magnetic, gravity and bathymetric data, to illustrate this complex tectonic history and its implications.

Roest, W. R.; Lundin, E. R.; Torsvik, T. H.; Olesen, O.

2002-12-01

331

TOPSIDE TECTONICS Don L. Anderson  

E-print Network

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

Anderson, Don L.

332

Snack Tectonics  

NSDL National Science Digital Library

This activity uses food to demonstrate plate tectonic motions. Students construct a model using different snacks, which represent various parts of the Earth. For example, frosting represents the asthenosphere, fruit rollups are the Earth's plates, and graham crackers are meant to be the Earth's crust. Students learn how tectonic plates (lithosphere) ride atop the slow flowing asthenosphere layer, and how they interact at their boundaries.

Johnson, Roberta

333

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)

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

Toksoz, M. Nafi

1987-01-01

334

New paradigm for the early Earth: did plate tectonics as we know it not operate until the end of the Archean?  

Microsoft Academic Search

Here, I question the apparent absence of oceanic crust from the Archean and whether plate tectonics as we know it, involving ridges, deep oceans, subduction and continent-sized plates, operated during the Archean. The suggestion is advanced that the early seas were formed after the initiation of continental crust at >4 Ga; that this crust was globe enveloping; and that the

G. J. H. McCall

2010-01-01

335

Fabrics of Precambrian Mantle Lithosphere - an Evidence for Early Plate Tectonics?  

NASA Astrophysics Data System (ADS)

We model anisotropic structure in one of the oldest continental region on the planet - the Fennoscandian Shield. In general, large-scale seismic anisotropy reflects a rock texture, created by orientation of crystals of olivine (LPO) in a stress field, acting during formation of the mantle or its later deformations. We show results of our study of anisotropy from teleseismic data recorded during several passive experiments (Varmland'91, TOR-96/97, SVEKALAPKO-98/99) as well as from permanent observatories in Fennoscandia. Joint inversion of independent data (shear-wave splitting and P-residual spheres) allows us to invert for orientation of elastic tensor, symmetry and thickness of the anisotropic medium (Kozlovskaya et al., 2006). Geographical variations of anisotropic parameters of teleseismic body waves and their distinct dependence on direction of wave propagation through the upper mantle allow us to model several mantle lithosphere domains with different fabrics both in the Proterozoic and in the Archean parts. The domains can be separated by a steep narrow zone, e.g. the Protogine Zone between the Sveconorwegian and Svecofennian lithospheres in the Proterozoic part of the shield (Plomerova et al., 2001). A similarly steep boundary was found by different methods (Arlit et al., 1999; Plomerova et al., 2002; Cotte et al., 2002; Plomerova and Babuska, 2004) between the Shield and the Phanerozoic Europe. On the other hand, intercalating wedges of the Proterozic and Archean lithospheres of different fabrics are seen by seismic anisotropy in south-central Finland (Plomerova et al., 2006; Vecsey et al , 2006).The model meets with recently studied mantle xenolith ages (Peltonen and Brugmann, 2006), surface wave tomography (Bruneton et al., 2004, Pedersen et al., 2006) and location of the upper mantle reflectors (Yliniemi et al., 2004). Moreover, several domains were revealed within the Archean mantle lithosphere itself. We interpret the anisotropic domains as fragments of mantle lithosphere retaining an old fossil olivine fabric which was created before these micro-continents assembled (Babuska and Plomerova, 2006). The mantle lithosphere composed of blocks with differently oriented fabrics supports an idea that lithospheric roots have been formed during and an early form of plate tectonics, i.e., by an subduction-related processes, i.e., thrust stacking of oceanic (proto-cratonic) lithospheres and accretion of magmatic arcs, since Archean (Benn et al., 2006).

Plomerova, J.; Babuska, V.; Kozlovskaya, E.; Vecsey, L.

2006-12-01

336

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

. 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

Tullos, Desiree

337

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

NASA Technical Reports Server (NTRS)

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?

Demets, Charles; Stein, Seth

1990-01-01

338

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

NASA Astrophysics Data System (ADS)

Several different mechanisms have been proposed to account for the 50 Ma plate-mantle event, including India-Eurasia collision, the time dependence of the Reunion plume-push force, the subduction of the Izanagi-Pacific mid-ocean ridge, and transient ridge capture of the Hawaiian plume. We use a recent digital global seafloor tectonic fabric map derived from vertical gravity gradients together with magnetic anomaly identifications to analyse the geometry and timing of Late Cretaceous-Early Cenozoic fracture zone (FZ) bends. Two sets of closely spaced FZ bends in the North Atlantic, Weddell Sea and at the Southwest Indian Ridge between Antarctica and Africa produce an S-shape in the seafloor fabric. The older spreading ridge reorganisation initiated close to 70 Ma, and was completed around 55 Ma. The younger FZ bends are sharper, were initiated approximately 55-49 Ma and completed around 40-42 Ma, after which time spreading returned to its pre-S-bend azimuth. Additionally there is a distinct increase in seafloor roughness at the mid-Atlantic ridge at about 70 Ma reflecting a decrease in spreading rate. Seafloor fabric indicators of plate motion change produced at around 70 Ma coincide with emplacement of the Reunion plume and are restricted to parts of the Atlantic-Indian realm. The Pacific domain appears unaffected by the mechanism that drove plate motion changes in the Atlantic and Indian Oceans at this time. Yet, from ~55-40 Ma Pacific FZ bends and other oceanic and plate margin events are widespread. Along with formation of the younger part of the Atlantic-Indian S-bends, FZ bends and changes in FZ morphology in the northeast Pacific signify a reorientation of the Pacific-Farallon spreading ridge, a northward propagation of the Pacific-Antarctic ridge, increases in spreading rates at the Australia-Pacific ridge and a change in the direction of plate motion, with spreading terminating in the Tasman Sea. And initiation of Izu-Bonin-Mariana subduction. This clustering of observations in the Pacific suggests that the driving mechanism of the Eocene reorganisation is situated in this region. For the plume-push forces associated with the arrival of the Reunion plume head at 67 Ma to have driven Eocene plate motion changes, we would expect to see tectonic events in the Pacific beginning at round this time to coincide with initial plume emplacement. Additionally, for the emplacement and waning of the Reunion plume to have driven all the changes we see from ~70-40 Ma it might be expected that sharp FZ bends would form at 70 Ma in the Atlantic-Indian realm and would be succeeded by gradual FZ bends, but we observe the opposite. We favour subduction of the Pacific-Izanagi ridge as the driver of Eocene plate motion changes, and consider the Reunion plume to have perhaps only had a strong influence on plate motions at around the time of its initial eruption and only in parts of the Atlantic-Indian realm. Slab pull is a major driver of plate tectonics and therefore intersection of a young buoyant sub-parallel ridge at the northwest Pacific subduction zone is expected to significantly affect motion of the Pacific and neighbouring plates, and have a more subdued effect on distal regions.

Mller, R. D.; Matthews, K. J.

2011-12-01

339

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

SciTech Connect

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.

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

1995-02-01

340

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

NASA Technical Reports Server (NTRS)

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.

Bercovici, David

1995-01-01

341

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

NASA Astrophysics Data System (ADS)

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

Bird, P.; Kagan, Y. Y.

2003-12-01

342

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)

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).

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

2013-04-01

343

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

Microsoft Academic Search

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

Tanya Atwater; Joann Stock

1998-01-01

344

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

Microsoft Academic Search

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

Charles Demets; Seth Stein

1990-01-01

345

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

NASA Technical Reports Server (NTRS)

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.

Solomon, S. C.

1980-01-01

346

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

Microsoft Academic Search

During the late Precambrian, the terranes of the Arabian and adjoining plates were fused along the northeastern flank of the African plate in Gondwanaland. This phase, which ended approximately 640 to 620 Ma, was followed by continental failure (620 to 580 Ma) and intracontinental extension (600 to approximately 550 Ma). During the Infracambrian extensional phase, a triple junction may have

Husseini

1989-01-01

347

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

SciTech Connect

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

Nance, M.A. (Univ. of California, Davis, CA (United States). Geology Dept.)

1993-04-01

348

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

E-print Network

of the plate material or yield strength profile. In the casematerial by selecting the shape of the lithospheres yield strengthmaterial has an elastic-plastic rheology and it has been stressed to its yield strength,

Luttrell, Karen Marie

2010-01-01

349

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

E-print Network

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.

Garai, Jozsef

2007-01-01

350

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

E-print Network

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.

Jozsef Garai

2007-09-10

351

On plate tectonics and the geologic evolution of southwestern North America  

NASA Astrophysics Data System (ADS)

Very rapid subduction of the Farallon plate under southwestern North America between 60 and 40 Ma was accompanied by a relatively low volume of magmatism throughout the southwestern United States and northern Mexico. Between 40 and 20 Ma, when subduction slowed significantly and in one area may have even stopped, magmatism became widespread and voluminous from Nevada and Utah to central Mexico. This correlation of rapid subduction with a relatively low volume of magmatism can be explained by the observation that subduction-related andesitic arc volcanism, often formed in a Laramide-style compressional regime, is relatively low volume compared to continental volcanism. The shallow roots of arc volcanic systems are clearly exposed in the porphyry copper deposits found in currently active arcs and common throughout southwestern North America between 60 and 50 Ma. By 43 Ma, worldwide plate motions changed, the Pacific plate began moving away from North America, and subduction of the Farallon plate slowed. By around 36 Ma, the easternmost part of the East Pacific Rise, which was located between the Pioneer and Murray fracture zones, approached the trench and the young, hot, buoyant lithosphere appears to have clogged part of the subduction zone. Uplift on land became widespread. Voluminous continental magmatism formed the Sierra Madre Occidental (SMO) of Mexico, one of the largest batholiths in the world, as well as volcanic centers now exposed in the San Juan Mountains of Colorado and the Rio Grande Rift of New Mexico. Vectors of motion of the Pacific plate relative to the North American plate determined by Stock and Molnar (1988) are consistent with formation of a transtensional environment along the plate boundary sufficient to create a 100- to 200-km-wide void just landward of the old volcanic arc. While the SMO batholith was forming within this void, the Monterey and Arguello microplates just offshore to the west were broken off from the Farallon plate and rotated so that the East Pacific Rise in this immediate area became nearly perpendicular to the trench and perpendicular to the vector of motion of the Pacific plate relative to North America. Formation of the SMO batholith was followed between 24 and 20 Ma by a major increase in the rate of subduction of the Guadalupe plate, a fragment of the former Farallon plate, and by increasing mylonitization, extension, and uplift in the metamorphic core complexes that extend northwestward through southern Arizona from the northern end of the SMO batholith. The plate margin underwent another major change between 12.5 and 10 Ma when subduction again stopped, strike slip faulting became dominant along the coast, the Basin and Range Province opened, and numerous tectonostratigraphic terranes in southern California underwent large rotations. By 3 Ma a large, new terrane had been severed from North America immediately west of the SMO batholith as the Gulf of California opened. These observations can be explained by a model for the weakening and ultimate falling apart of the uppermost part of the subducted oceanic plate in the 20-30 m.y. after the end of rapid subduction. As the plate falls apart, not only is compressional stress relieved, but significant backslip along the old subduction zone is also possible, perhaps bringing blueschists rapidly upward from 20- to 30-km depths.

Ward, Peter L.

1991-07-01

352

Plates on the Move  

NSDL National Science Digital Library

This fun Web article is part of OLogy, where kids can collect virtual trading cards and create projects with them. Here, they learn about the Earth's outer shell and its constant movement. It begins with an overview that explains tectonic plates. There is an animation that shows recent earthquakes and their relationship to plate boundaries. Students can click to explore 12 individual volcanoes, mountains, hotspots, and earthquakes. For each of the geological formations or events, they will see a map that shows how the plates are moving, an animation about plate interaction, stats, and a story about that particular formation or event.

353

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

on California and its San Andreas Fault. A team led by Southern California Earthquake Center (SCEC) director by Geoffrey Ely, University of Southern California. Jaguar OverviewEarthquake Simulation Rocks SouthernCalifornia takes earthquakes very seriously. The state straddles two major tectonic plates

354

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

NASA Astrophysics Data System (ADS)

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.

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

2014-03-01

355

Episodic vs. Continuous Accretion in the Franciscan Accretionary Prism and Direct Plate Motion Controls vs. More Local Tectonic Controls on Prism Evolution  

NASA Astrophysics Data System (ADS)

Subduction at the Franciscan trench began ?170-165 Ma and continues today off Oregon-Washington. Plate motion reconstructions, high-P metamorphic rocks, and the arc magmatic record suggest that convergence and thus subduction were continuous throughout this period, although data for 170 to 120 Ma are less definitive. About 25% of modern subduction zones are actively building an accretionary prism, whereas 75% are nonaccretionary, in which subduction erosion is gradually removing the prism and/or forearc basement. These contrasting behaviors in modern subduction zones suggest that the Franciscan probably fluctuated between accretionary and nonaccretionary modes at various times and places during its 170 million year lifespan. Accumulating geochronologic data are beginning to clarify certain accretionary vs. nonaccretionary intervals. (1) The oldest Franciscan rocks are high-P mafic blocks probably metamorphosed in a subophiolitic sole during initiation of subduction. They yield garnet Lu-Hf and hornblende Ar/Ar ages from ?169 to 147 Ma. Their combined volume is extremely small and much of the Franciscan was probably in an essentially nonaccretionary mode during this period. (2) The South Fork Mountain Schist forms the structural top of the preserved wedge in northern California and thus was apparently the first genuinely large sedimentary body to accrete. This occurred at ?123 Ma (Ar/Ar ages), suggesting major accretion was delayed a full ?45 million years after the initiation of subduction. The underlying Valentine Spring Fm. accreted soon thereafter. This shift into an accretionary mode was nearly synchronous with the end of the Early Cretaceous magmatic lull and the beginning of the prolonged Cretaceous intensification of magmatism in the Sierra Nevada arc. (3) The Yolla Bolly terrane has generally been assigned a latest Jurassic to earliest Cretaceous age. Detrital zircon data confirm that some latest Jurassic sandstones are present, but they may be blocks in olistotromes and the bulk of the terrane may be mid-Cretaceous trench sediments. (4) New data from the Central mlange belt are pending. (5) Detrital zircon ages suggest much of the voluminous Coastal belt was deposited in a short, rapid surge in the Middle Eocene, coincident with major extension, core complex development, volcanism, and erosion in sediment source areas in Idaho-Montana. Rapid Tyee Fm deposition in coastal Oregon occurred at virtually the same time from the same sources. (6) Exposed post-Eocene Franciscan rocks are rare. It is tempting to ascribe subduction zone tectonic events directly to changes in relative motions between the subducting and overriding lithospheric plates. However, in modern subduction zones, varying sediment supply to the trench appears to be a more important control on accretionary prism evolution and this seems to be the case in the Franciscan as well. Franciscan accretion was apparently influenced primarily by complex continental interior tectonics controlling sediment supply from the North American Cordillera (which may in part reflect plate motion changes), rather than directly by changes in the motions of tectonic plates.

Dumitru, T. A.; Ernst, W. G.; Wakabayashi, J.

2011-12-01

356

On Plate Tectonics and the Geologic Evolution of Southwestern North America  

Microsoft Academic Search

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 southwestem United States and north- em 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

Peter L. Ward

1991-01-01

357

On plate tectonics and the geologic evolution of southwestern North America  

Microsoft Academic Search

Very rapid subduction of the Farallon plate under southwestern North America between 60 and 40 K 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

Peter L. Ward

1991-01-01

358

A plate tectonic mechanism for methane hydrate release along subduction zones  

E-print Network

June 2005 Editor: E. Boyle Abstract Negative carbon isotope excursions from a new record of terrestrial), as evidenced by a new high-res- olution terrestrial d13 C (carbon stable isotope) record. We suggest that plate during the uplift and found it to be within 20% of the amount of carbon implied by the isotopic records

Conrad, Clint

359

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

NASA Technical Reports Server (NTRS)

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.

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

1995-01-01

360

Global pattern of earthquakes and seismic energy distributions: Insights for the mechanisms of plate tectonics  

E-print Network

Global pattern of earthquakes and seismic energy distributions: Insights for the mechanisms mechanism able to release elastic energy at great depths and the distributions of N and E (Abe and Kanamori October 2011 Keywords: Global seismicity Declustered catalogue Earthquake energy distribution Plate

Doglioni, Carlo

361

Quantifying the net slab pull force as a driving mechanism for plate tectonics  

Microsoft Academic Search

It has remained unclear how much of the negative buoyancy force of the slab (FB) is used to pull the trailing plate at the surface into the mantle. Here I present three-dimensional laboratory experiments to quantify the net slab pull force (FNSP) with respect to FB during subduction. Results show that FNSP increases with increasing slab length and dip up

W. P. Schellart

2004-01-01

362

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

Microsoft Academic Search

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

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

1987-01-01

363

Subduction of the Pacific Plate Beneath the Kamchatka: Volcanism and Tectonic Earthquakes  

Microsoft Academic Search

The results of studying subduction process of the Pacific plate beneath the Kamchatka and related processes are described. The focal mechanism solutions estimated from Centroid Moment Tensor (CMT) catalog and sequence of the largest earthquakes occurred in Kamchatka were used to asses velocity of subducted slab. The boundary of contact for subducted slab is determined at a depth of 30-70

E. I. Gordeev

2008-01-01

364

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

E-print Network

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...

van Summeren, Joost; Gaidos, Eric

2011-01-01

365

GPS and tectonic evidence for a diffuse plate boundary at the Azores Triple Junction  

NASA Astrophysics Data System (ADS)

We use GPS, bathymetric/structural, and seismic data to define the pattern of present deformation along the northern half of the Azores plateau, where the Nubia-Eurasia plate boundary terminates at the axis of the Mid-Atlantic Ridge (MAR). New and existing campaign GPS velocities from the Azores islands reveal extension oblique to a series of en chelon volcanic ridges occupied by Terceira, S. Jorge, Pico, and Faial islands. In a frame of reference defined by 69 continuous GPS stations on the Eurasia plate, Terceira Island moves 21 mm/yr away from Eurasia, consistent with the island's location within the Terceira Rift and plate boundary structure. The volcanic ridges south of the Terceira Rift move toward WSW at progressively faster rates, reaching a maximum of 3.50.5 mm/yr (2-?) for the Pico/Faial volcanic ridge. The hypothesis that the Terceira Rift accommodates all Nubia-Eurasia plate motion is rejected at high confidence level based on the motions of sites on S. Jorge Island just west of Terceira Rift. All of the islands move relative to the Nubia plate, with Pico Island exhibiting the slowest motion, only 10.5 mm/yr (2-?). Detailed bathymetry from the interior of the hypothesized Azores microplate reveals faults that crosscut young MAR seafloor fabric. These observations and the GPS evidence for distributed deformation described above argue against the existence of a rigid or semi-rigid Azores microplate, and instead suggest that Nubia-Eurasia plate motion is accommodated by extension across a 140-km-wide zone east of the MAR axis, most likely bounded to the north by the northern shoulder of the Terceira Rift. The MAR spreading rate along the western end of the Azores deformation zone (38.5N-39.5N) is intermediate between the Eurasia-North America rate measured at 39.5N and the Nubia-North America rate measured at 38.5N, consistent with the joint conclusions that the Nubia-Eurasia boundary is broad where it intersects the MAR, and the Azores Triple Junction is diffuse rather than discrete.

Marques, F. O.; Catalo, J. C.; DeMets, C.; Costa, A. C. G.; Hildenbrand, A.

2013-11-01

366

Earth: Plates on the Move  

NSDL National Science Digital Library

In this activity, students explore how the movement of tectonic plates forms mountains, volcanoes, oceans, and earthquakes. It first describes the plates and the various types of interaction at plate boundaries. An interactive map of the world shows the relationship between plate boundaries and earthquakes, allowing the student to click on selected place to explore a volcano, mountain, hotspot or earthquake. They then zoom in the see how the plates are moving, play an animation about the plate interaction, and read a story about the event. In addition, a set of links lead to more detailed information.

367

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

368

Tree Tectonics  

NASA Astrophysics Data System (ADS)

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).

Vogt, Peter R.

2004-09-01

369

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

E-print Network

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 years

California at Berkeley, University of

370

Collision tectonics  

SciTech Connect

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.

Coward, M.P.; Ries, A.C.

1985-01-01

371

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

NASA Astrophysics Data System (ADS)

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 Palaeotethys suture in Thailand are revised, the Tertiary Mae Yuam fault is seen as the emplacement of the suture. East of the suture we identify an Indochina derived terrane for which we keep the name Shan-Thai, formerly used to identify the Cimmerian block present in Southeast Asia, now called Sibumasu. This nomenclatural choice was made on the basis of the geographic location of the terrane (Eastern Shan States in Burma and Central Thailand) and in order not to introduce new confusing terminology. The closure of the Eastern Palaeotethys is related to a southward subduction of the ocean, that triggered the Eastern Neotethys to open as a back-arc, due to the presence of Late Carboniferous-Early Permian arc magmatism in Mergui (Burma) and in the Lhasa block (South Tibet), and to the absence of arc magmatism of the same age East of the suture. In order to explain the presence of Carboniferous-Early Permian and Permo-Triassic volcanic arcs in Cambodia, Upper Triassic magmatism in Eastern Vietnam and Lower Permian-Middle Permian arc volcanites in Western Sumatra, we introduce the Orang Laut terranes concept. These terranes were detached from Indochina and South China during back-arc opening of the Poko-Song Ma system, due to the westward subduction of the Palaeopacific. This also explains the location of the Cathaysian West Sumatra block to the West of the Cimmerian Sibumasu block.

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

2008-04-01

372

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

SciTech Connect

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.

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

1993-04-01

373

From rock fracture to plate tectonics. Evidence of non extensive statistical mechanics in Earth physics, A review  

NASA Astrophysics Data System (ADS)

The non-extensive statistical mechanics pioneered by the Tsallis group offers a consistent theoretical framework, based on a generalization of entropy, to analyze the behavior of systems with fractal or multi-fractal distribution of their elements. Such systems where long-range interactions or intermittency are important, lead to power law behavior. The question of whether earth systems are described by non-extensive statistical physics, even at the phenomenological level (i.e., without specifying any underlying model), represents a challenge. This is the problem we review here. Our aim is not to present a precise model, but rather to emphasize in simple arguments of physical plausibility. Examples supporting the non-additive behavior of earth system, from rocks fracture (e.g., acoustic emissions) to geodynamic (e.g., plate tectonics, global seismicity) scale are presented. Acknowledgments. This work was partly supported by the THALES Program of the Ministry of Education of Greece and the European Union in the framework of the project entitled "Integrated understanding of Seismicity, using innovative Methodologies of Fracture mechanics along with Earthquake and non extensive statistical physics - Application to the geodynamic system of the Hellenic Arc. SEISMO FEAR HELLARC".

Vallianatos, F.

2012-04-01

374

Subduction of the Pacific Plate Beneath the Kamchatka: Volcanism and Tectonic Earthquakes  

NASA Astrophysics Data System (ADS)

The results of studying subduction process of the Pacific plate beneath the Kamchatka and related processes are described. The focal mechanism solutions estimated from Centroid Moment Tensor (CMT) catalog and sequence of the largest earthquakes occurred in Kamchatka were used to asses velocity of subducted slab. The boundary of contact for subducted slab is determined at a depth of 30-70 km, and is considered as a plane at azimuth 217 and with a dip angle of 25. The rate of subduction estimated from CMT mechanisms yields V=0.9 cm/yr for southern zone (south of Shipunsky Cape), and V=1.4 cm/yr for central zone (from Shipunsky Cape to Kronotsky Cape). The largest coupled consistent earthquakes recorded from 1737 were used for analysis. The results show, that for the southern area V=6.6 - 7.1 cm yr (two couples), and for the central part V=6.6 cm yr. The estimated value of velocity for the creep part of subducted slab is about 5 to 15 per cent of the bulk velocity. The Pacific plate subducts at a rate of 8 cm yr. Series of GPS observations conducted from 1997 up to 2007 were used to estimate the rate at which Kamchatka is deformed under the effect of the subducted slab (along-slab direction). The average values of rate and velocity variations versus the average rate were estimated response to permanent GPS station PETR. It was shown that the motion at BKI (Bering) regardless KlU (Klyuchi) is uneven: variations of velocity reach up to 30 per cent (at average running window of 1 year). There are about 28 active volcanoes in Kamchatka that provide intensive volcanic activity in this region. The volcanoes produce about 16-17% of magmatic rocks erupted by all volcanoes in the Earth. Over the past 5 years, eruptions of Sheveluch, Klyuchevskoy, Bezymianny, Karymsky, and Mutnovsky volcanoes have occurred. Although many of these volcanoes are in sparsely populated areas, they lie adjacent to the heavily North Pacific air routes between North America, Europe and Asia. The Institute of Volcanology and Seismology (IVS) of the Russian Academy of Sciences (RAS) and Kamchatka Branch of Geophysical Survey (KB GS) of RAS monitor and study Kamchatka's hazardous volcanoes, to forecast and record eruptive activity, and implement public safety measures. To meet its mission, the IVS and KB GS maintains a volcano monitoring network to detect signs of volcanic unrest; conducts basic geological, geophysical, and geochemical investigations of Kamchakan volcanoes; and provides accurate and timely warnings of imminent activity to local, state and federal agencies.

Gordeev, E. I.

2008-12-01

375

Thick shell tectonics on one-plate planets - Applications to Mars  

NASA Technical Reports Server (NTRS)

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.

Banerdt, W. B.; Saunders, R. S.; Phillips, R. J.; Sleep, N. H.

1982-01-01

376

A review of the isotopic and trace element evidence for mantle and crustal processes in the Hadean and Archean: Implications for the onset of plate tectonic subduction  

Microsoft Academic Search

Considerable geochemical evidence supports initiation of plate tectonics on Earth shortly after the end of the Hadean. Nb\\/Th and Th\\/U of mafi c-ultramafi c rocks from the depleted upper mantle began to change from 7 to 18.2 and 4.2 to 2.6 (respectively) at 3.6 Ga. This signals the appearance of subduction-altered slabs in general mantle circulation from subduction initiated by

Steven B. Shirey; Balz S. Kamber; Martin J. Whitehouse; Paul A. Mueller; Asish R. Basu

2008-01-01

377

Tectonics, Climate, and Landscape -1 EAS 4803/8803KF  

E-print Network

plate tectonics and climate that act to sculpt Earth's surface. Students will develop the skills and anthropogenic topics, including: plate tectonics, structural geology, earthquake occurrence, hydrology

Black, Robert X.

378

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

NASA Astrophysics Data System (ADS)

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 compilation of magnetic anomalies and fracture zone traces from the Southeast, Southwest, Central Indian and the Carlsberg ridges. Additional reconstructions at chrons 23 (55 Ma) and 26 (61 Ma) are used to estimate the overall motion between India and Australia. Relative motions between the Indian and Australian plates are estimated using the plate circuit India ? Africa ? Australia. A new statistical approach, based on spherical regression analyses, is used to assess the uncertainty of the "best-fitting" finite rotations from the uncertainties in the data. The uncertainty in a rotation is described by a covariance matrix directly related to the geometry of the reconstructed plate boundary, to the distribution and estimated errors of the data points along it. Our parameterization of the rotations allows for simple combination of the rotation uncertainties along a plate circuit path. Results for chron 5 are remarkably consistent with present-day kinematics in the Indian Ocean, except that the Arabian and Indian plates are found to be separate plates. Comparisons of the motions between the Indian and African plates across the Carlsberg Ridge with that between the Australian and African plates across the Central Indian Ridge evidence a significant counterclockwise rotation of the Australian plate relative to the Indian plate about a pole located in the Central Indian Basin. The determinations are consistent for chrons 26, 13, 6 and 5. Determination at chron 23 is different but questionable due to the small number of available data. We propose two alternative solutions that both predict convergence within the Wharton and Central Indian basins and extension in the vicinity of the Chagos-Laccadive Ridge. The first solution assumes that all the deformation in the equatorial Indian Ocean started 7 Ma ago as found by Ocean Drilling Program Leg 116. Hence all the determinations at different times represent the total motion between India and Australia. The averaged India/Australia Euler vector (chrons 5, 6, 13, and 26: 11.1S, 78.0, ?=3.54) lies within the Central Indian Basin and yields a N-S contraction of 4652 km at 85, and 8063 km at 90. However, the difference of the India/Australia Euler vectors at chrons 5 and 6 suggests that the India/Australia convergence started between 10 and 21 Ma, following the continent-continent collision of India with Asia in the Early Miocene. The second averaged solution (chrons 6, 13, and 26: 5.2S, 74.3E, ?=5.93) predicts a total N-S contraction of 12373 km at 85E, and 17891 km at 90E. Both models are compatible with the deformation pattern observed in the equatorial Indian Ocean.

Royer, Jean-Yves; Chang, Ted

1991-07-01

379

The role that plate tectonics, inferred stress changes and stratigraphic unconformities have on the evolution of the West and Central African Rift System and the Atlantic continental margins  

NASA Astrophysics Data System (ADS)

The Muglad rift basin of Sudan, is a good example of polyphase rifting, with at least three major phases of basin development. Each phase has resulted in the generation of source rock, reservoir and seal geology with structural traps often closely linked to basement highs. In this paper we investigate on a regional scale the tectonic processes that have contributed to rift basin development. On a regional scale, the evolution of the Africa-wide Mesozoic rift system is intimately linked to relative movements of African sub-plates and to global plate tectonic processes and plate interactions. Changes in plate interactions are observed in the oceanic crust as azimuth changes of fracture zone geometries and by inference have caused significant modifications to both the orientation and magnitude of the motions of the African sub-plates. Such plate motion processes have controlled the polyphase development of the West and Central African Rift System. On the basinal scale, changes of sub-plate motions have resulted in changes in the stress field which have had a clear impact on the deformation and fault geometries of rift basins and on the resulting stratigraphy. The construction of the first unified stratigraphic chart for the West and Central African Rift System shows a close correlation in the timing of the major unconformities with the timing of changes in relative plate motion as observed in the changes of the azimuthal geometry of the oceanic fracture zones in the Central Atlantic. Since similarly timed unconformities exist along the continental margins of Africa and South America, we propose that the causative mechanism is change in relative plate motion which leads to an increase or decrease in the tension on the plate and thus controls the strength or effective elastic thickness, Te, of the crust/plate beneath the margins. This results in a focused change in isostatic response of the margin during short-period changes in relative plate motion; i.e. more tension will mean that loads are not compensated locally resulting in local uplift of the margin.

Fairhead, J. D.; Green, C. M.; Masterton, S. M.; Guiraud, R.

2013-05-01

380

The Core as the Third Pivotal End Member of the Earth's Plate Tectonic Cycle: A New Theory  

NASA Astrophysics Data System (ADS)

Existing data and use of a hypothetical model, post-Stishovite-Magnesiowustite-Iron, indicate that the Earth's core could be the the convertor end member of the Earth's Plate Tectonic Cycle (EPTC): a new theory. This third pivitol end member, the core, is the place where the cycle begins and ends, to begin again. The first pivotal end member of the EPTC, for a three end member system, is the global MORB end member where new oceanic crust and lithosphere are created. Sea-floor spreading connects it to the second end member, the subduction end member, where oceanic crust and lithosphere disappear to become cold lithospheric-crust complexes descending through the mantle toward the Earth's core. When complexes break into it they are slowed, turned and endothermally ingested. Partial melting frees lower mantle phases and iron while forming metallic liquid and a densified immiscible silicate liquid, of which 17 vol.% reduces the bulk density of a convecting outer core by 10 %. Freed crystalline phases form micro-phases of micrometer to millimeter in size that more or less fill mega-bodies of <83 vol.% metallic liquid and <17 vol.% immiscible silicate liquid, both of centimeters to kilometers in size. Excess core energy starting each cycle comes mainly from irreversible exothermal reactions at numerous unstable phase contacts by stable phases within and between mega-bodies to yield stable products of lower Gibbs free energy, only to make new contacts and react...and react again. Other sources of exothermal energy come from radioactive silicate liquid and friction at stable phase contacts during mega-body convection. Heat accumulated from these energy sources tends to expand the outer core as univariant boundary reactions of the core and the lower mantle reverse, with +5.0 cm3g-1comming from the inner core boundary reaction alone. The outer core's pervasive expansion against the passively resisting strength of the mantle results in explosive ejection of silicate liquid along a line of weakness or at a point of weakness of the CMB when it fails, as it must. Superheated actions of this liquid with lower mantle phases result in hybrid, hot and solid domains that ascent as hot basic plumes in a cooler and denser ultrabasic mantle. Decompression melting of the plume above 290 km contributes new basalt crust at mid-oceanic ridges, the MORB end member, from a line source of the CMB. New crust for oceanic islands basalts arrives there, after similar processes yield plumes from point sources of the CMB. Both of these basalt types are thought to be linked with silicate liquid ejected fron the Earth's outer core as expressed by the ubiquitous and unexplained C-component of Pb isotope ratios of Atlantic-, Indian- and Pacific mid-oceanic basalts, major segments of the MORB end member of the EPTC, and by its corresponding FOZO isotope component of oceanic island basalts. Oceanic crust and lithosphere disappear at the subduction end member before it is a twenty-third the age of the Earth, and leads to its ingestion and eventual energization in the Earth's outer core, the convertor, and third end member of the EPTC, to drive ensuing cycles. It seems unavoidable that egress features for silicate liquid on the CMB could serve as a template for the EPTC in a bottom-up dynamic, except for the actions of the subduction end member of the EPTC. There is no shortage of silicate liquid in the outer core as 17 vol.% is almost twice the volume of the entire crust of the Earth. Finally, it seems possible that some of the unexplained heat flux of the Earth, over and above the radioactivity of the mantle, may be attributed to this new paradigm that drives the Earth's Plate Tectonic Cycle.

Carman, J. H.

2005-05-01

381

Evolution of U-Pb and Sm-Nd systems in numerical models of mantle convection and plate tectonics  

NASA Astrophysics Data System (ADS)

The development of U-Th-Pb and Sm-Nd isotopic signatures in a convecting mantle is studied using a numerical convection model with melting-induced differentiation and tracking of major and trace elements. The models include secular cooling and the decay of heat-producing elements, a rudimentary "self-consistent" treatment of plate tectonics, and both olivine system and garnet-pyroxene system phase transitions. The system self-consistently evolves regions with a high ?(=U/Pb) (HIMU)-like Pb signature and regions with low 143Nd/144Nd. However, the isotopic "age" determined from the slope in (207Pb/204Pb)-(206Pb/204Pb) space is much larger than observed. Several hypotheses are examined to explain this discrepancy. Sampling length scale has a minimal effect on age. The extent of crustal settling above the core-mantle boundary makes some difference but not enough. More frequent remelting is a possible explanation but requires the rate of crustal production to have been much higher in the past. Not introducing HIMU into the mantle prior to 2.0-2.5 Gyr before present, because of a change in the surface oxidization environment or subduction zone processes, can account for the difference, but its effect on other isotope systems needs to be evaluated. Improved treatment of the stretching of heterogeneities, which reduces them to length scales at which they cease to be identifiable magma sources, greatly reduces the Pb-Pb age. The mantle develops substantial chemical stratification from a homogeneous start, including stratification around 660 km caused by the two-component phase transitions. A deep layer of subducted crust may provide storage for some of the "missing" heat-producing elements. Magmatic heat transport is important in the first 2 Gyr of model time.

Xie, Shunxing; Tackley, Paul J.

2004-11-01

382

Tectonic evolution of the Pacific margin of Antarctica 2. Structure of Late Cretaceous-early Tertiary plate boundaries in the Bellingshausen Sea from seismic reflection and gravity data  

NASA Astrophysics Data System (ADS)

Interpretations of multichannel seismic (MCS) reflection and potential field data suggest that some prominent gravity anomalies in the Bellingshausen Sea are associated with plate boundaries that were active during the Late Cretaceous and early Tertiary. Between 83 and 93W, a belt of negative anomalies extends along the West Antarctic continental slope, which we term the continental slope gravity anomaly (CSGA). MCS profiles show that the CSGA coincides with an acoustically opaque structural high imaged beneath the lower slope. We interpret this structure as the upper part of an accretionary prism which formed during southward subduction of the Phoenix and Charcot plates, before Chatham Rise separated from West Antarctica. MCS profiles crossing the same margin to the northeast show no evidence of an extensive buried accretionary prism, but instead reveal an abrupt northeastward steepening of the continental slope near 78W. We attribute this change in tectonic style, at least in part, to subduction erosion resulting from subduction of rough oceanic basement which formed at the Antarctic-Phoenix ridge after an abrupt decrease in spreading rate at chron 23r (52 Ma). Near 95W, the Bellingshausen gravity anomaly (BGA) consists of a prominent low-high gravity couple which crosses the West Antarctic continental shelf, slope, and rise. The BGA corresponds to a buried asymmetric basement trough, where Cretaceous oceanic basement dips beneath more elevated basement to the east. The trough probably formed after subduction of Charcot plate ocean floor stalled at the nearby Antarctic Peninsula margin, near the end of the Cretaceous Normal Superchron. Ocean floor to the east of the BGA became attached to the Antarctic Peninsula, and the BGA trough subsequently accommodated a small amount of convergent motion between the Antarctic Peninsula and the ocean floor to the west (initially part of the Marie Byrd Land plate and later part of the Bellingshausen plate). Tectonism probably ceased at the BGA at chron 27 (61 Ma), as a result of a general plate reorganization in the South Pacific.

Cunningham, Alex P.; Larter, Robert D.; Barker, Peter F.; Gohl, Karsten; Nitsche, Frank O.

2002-12-01

383

Geology: Plate Tectonics  

NSDL National Science Digital Library

This site is based on work by researcher Christopher Scotese of the University of Texas, Arlington. It is from the University of California, Berkeley, and it provides black-and-white animations based on Scotese's paleogeographic maps; these animations are organized by time period and offer the viewer insights into the shifting of the continents through different time periods. Both sites provide a fascinating geologic historical perspective and will be of great interest to researchers and educators, alike.

384

Epeirogeny and plate tectonics  

NASA Technical Reports Server (NTRS)

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.

Menard, H. W.

1975-01-01

385

Plate tectonics summary paper  

NSDL National Science Digital Library

The assignment is to summarize papers that students have been individually reading about their study areas which were assigned in the beginning of the course semester. From this assignment students can be familiarize with the linux system and know how to execute scripts to make plots.

Kim, Younghee

386

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

NASA Astrophysics Data System (ADS)

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.

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

2011-12-01

387

Plate Puzzle Page 1 of 20 Plate Puzzle 1  

E-print Network

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

Benitez-Nelson, Claudia

388

Last Friday, Oct. 3 Group exercise on Mars' Tectonics  

E-print Network

and the web (hints indicated) to argue in favor of ONE of these two. 1) Mars had plate tectonics. 2) Mars did not have plate tectonics. TURN IN: 3 distinct bullets that define your argument. Each bullet can have AT MOST three sentences. Hypothesis: Mars had plate tectonics (google: Mars, plate tectonics; Mars early

Jellinek, Mark

389

In-phase dynamics of the exhalation sequence in Popocatpetl volcano and slow-slip events in Cocos-North American plate boundary  

NASA Astrophysics Data System (ADS)

It has long been considered that the Trans-Mexican Volcanic Belt (TMVB) is related to subduction along the Middle America trench. Within this view, it is expected that the tectonic dynamics of the Cocos plate can be reflected, to some extent, in the Popocatpetl's volcanic activity This work uses detrended fluctuation analysis, a method borrowed from statistical mechanics, to quantify the fractality and autocorrelations in the exhalation sequence of the Popocatepetl. It is found that the autocorrelations exhibit cyclic, non-periodic, dynamics with dominant periods of the order of 0.85 to 1.25 years. Interestingly, it is shown that the occurrence of slow-slip events in Southern (Guerrero and Oaxaca) Mexico coincides with peaks of the autocorrelation cycle of the exhalation sequence. The result suggests the use of the volcano exhalation sequence as a proxy of aseismic events in the Cocos-North American plate boundary. That is, by monitoring the autocorrelation dynamics of the exhalation sequence in the Popocatepetl, one could be able to suspect the occurrence of a slow-slip event in Southern Mexico.

Alvarez-Ramirez, Jose; Sosa, Eliceo; Hernandez-Martinez, Eliseo

2011-02-01

390

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

391

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

NASA Astrophysics Data System (ADS)

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?

M P, R.; Rajendran, K.

2013-12-01

392

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

NASA Astrophysics Data System (ADS)

The thermal consequences of flow transients generated by deformation induced leakage at fault zones intersecting confined aquifers have been examined using a simple analytical model. The recharge of the aquifer is assumed to take place by vertical infiltration through the confining layers. The energy equation relevant in this case has been derived by evaluating enthalpy fluxes associated with lateral and vertical components of fluid flows as well as that due to volume changes in the permeable layer, generated by deformation induced alterations in the hydraulic head. Results of numerical simulations indicate that thermal transients arise during the stress build-up period when the infiltrating fluids mix with those in the aquifer, but relatively rapid return to equilibrium conditions occur as soon as the leakage is cut-off. The model is thus capable of reproducing the characteristic features of thermal precursors found in observational records. According to model results, the growth of thermal perturbation as well as the time for attaining steady-state conditions is proportional to the recharge rate. The magnitude of the perturbation is related to the thermal gradients in the confining layers but permeability contrast between the confining layer and the aquifer also plays a significant role. The model results also indicate that precursory signals are likely to be significant only in areas close to the fault plane where tectonic leakage has a direct influence on the hydraulic head of the aquifer. If the fault plane is sensitive to deformation the tectonic leakage rate may undergo substantial changes in response to changing stress patterns and this in turn may easily lead to abrupt and substantial changes in the local thermal regime. Some of the transient thermal anomalies observed in records of temperatures in boreholes in tectonically active areas have characteristics similar to those predicted by the 'deformation induced leakage' model. Examples are presented illustrating model fits to thermal transients, identified as precursors to seismic events, in Firjusa (Turkmenistan), Didiweli (Georgia) and Izu peninsula (Japan). The possibility of obtaining complementary information on processes responsible for fluid flow during pre-seismic periods is pointed out. It appears that the occurrence of thermal anomalies associated with small-scale tectonic deformation may not be uncommon. Its detection depends on availability of suitable boreholes and of the facilities for monitoring of temperatures using high precision sensors over periods comparable to local recurrence periods of earthquakes.

Hamza, Valiya M.

2001-11-01

393

Tectonics Geospatial Investigations  

NSDL National Science Digital Library

Tectonics is a series of geospatial investigations designed to augment existing middle school Earth science curriculum. Students use Web GIS to investigate important tectonics concepts. The investigations include scientific practices, crosscutting concepts, and core ideas from the National Research Council (2012) Framework for K-12 Science Education. Students will explore six questions: 1. What geologic hazards exist near me? Which plate boundary is closest to me? 2. How do we recognize plate boundaries? 3. How does thermal energy move around the Earth? 4. What happens when plates diverge? 5. What happens when plates move sideways past each other? 6. What happens when plates collide?

394

Evolution of the Theory of the Earth: A Contextualized Approach for Teaching the History of the Theory of Plate Tectonics to Ninth Grade Students  

NASA Astrophysics Data System (ADS)

Current high school Earth Science curricula and textbooks organize scientific content into isolated units of knowledge. Within this structure, content is taught, but in the absence of the context of fundamental understandings or the process of how the science was actually done to reach the conclusions. These are two key facets of scientific literacy. I have developed curriculum from a historical perspective that addresses two particular units of study in Earth Science (geologic time and plate tectonics). The curriculum traces the evolution of the theory of plate tectonics. It includes contextualized experiences for students such as telling stories, utilizing original historical texts, narratives, and essential questions, to name a few. All of the strategies are utilized with the goal of building understanding around a small set of common themes. Exploring the historical models in this way allows students to analyze the models, while looking for limitations and misconceptions. This methodology is used to encourage students to develop more scientifically accurate understandings about the way in which the world and the process of scientific discovery work. Observations of high student engagement during the utilization of this contextualized approach has demonstrated that a positive effect on student understanding is promising.

Dolphin, Glenn

2009-04-01

395

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)

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.

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

2013-12-01

396

Late mesozoic-quaternary plate tectonics and the Geysers-Clear Lake geothermal anomaly, Northern Coast Ranges, California (Abstract)  

Microsoft Academic Search

The development of structures related to the Geysers-Clear Lake geothermal anomaly can be explained in terms of relative motions of the North American and Pacific plates. Hypothetically, plate convergence during Late Jurassic to mid-Tertiary time produced a west-stepping subduction zone that thrust successively younger plates of sediments and volcanic rocks of the Franciscan assemblage eastward beneath oceanic crust and depositionally

1977-01-01

397

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

NASA Technical Reports Server (NTRS)

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.

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

1989-01-01

398

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

NASA Astrophysics Data System (ADS)

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.

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

2009-04-01

399

Misconceptions and Conceptual Changes Concerning Continental Drift and Plate Tectonics among Portuguese Students Aged 16-17.  

ERIC Educational Resources Information Center

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)

Marques, Luis; Thompson, David

1997-01-01

400

Late Tertiary paleogeographic and tectonic evolution of the Mediterranean area  

SciTech Connect

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.

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

1988-08-01

401

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

402

Tectonics, Earthquakes, Volcanoes  

NSDL National Science Digital Library

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.

Holmgren, Camille

403

Widespread remagnetizations associated with sedimentary greigite (Fe3S4): Implications for Neogene tectonic rotations within the Australia-Pacific plate boundary zone, New Zealand  

NASA Astrophysics Data System (ADS)

Greigite (Fe3S4) can grow at any time during diagenesis when dissolved iron and sulfide are available in sedimentary pore waters. Greigite can produce syn-depositional paleomagnetic signals that are useful for paleomagnetic studies, but it can also produce late remagnetizations that make paleomagnetic interpretations much more complicated. Determining the timing of remanence acquisition is therefore a key aspect of paleomagnetic studies of the spatially and stratigraphically widespread sedimentary sequences in which greigite is the dominant remanence carrier. We demonstrate from paleomagnetic results, which are constrained rigorously by field tests, that late diagenetic greigite growth has remagnetized up to 65% of sampled localities on the Hikurangi margin, East Coast, New Zealand. This means that the magnetizations that record large, clockwise vertical axis tectonic rotations (50-80) of the Hikurangi margin are often considerably younger than the age of the host sediments, with remagnetizations clustered at 5-8 Ma. The remagnetizations require much greater rotation rates (8-14/Ma) than were inferred before the remagnetizations were recognized and that are also much greater than the present geodetically observed rate (3-4/Ma). This requires a change in tectonic regime, with slower rotation rates since development of the North Island shear belt at 1-2 Ma. Our results are consistent with long- and short-term deformation on the Hikurangi margin being driven by realignment of the subducting Pacific plate, with collision of the Hikurangi Plateau in the late Miocene potentially being key to both initiation of tectonic rotations and widespread remagnetization of Neogene sediments. The remagnetizations are inferred to have been caused by migration of gas hydrates through the sediments in association with collision of the Hikurangi Plateau.

Rowan, C.; Roberts, A. P.

2011-12-01

404

The Distribution and Composition Characteristics of Siliceous Rocks from Qinzhou Bay-Hangzhou Bay Joint Belt, South China: Constraint on the Tectonic Evolution of Plates in South China  

PubMed Central

The Qinzhou Bay-Hangzhou Bay joint belt is a significant tectonic zone between the Yangtze and Cathaysian plates, where plentiful hydrothermal siliceous rocks are generated. Here, the authors studied the distribution of the siliceous rocks in the whole tectonic zone, which indicated that the tensional setting was facilitating the development of siliceous rocks of hydrothermal genesis. According to the geochemical characteristics, the Neopalaeozoic siliceous rocks in the north segment of the Qinzhou Bay-Hangzhou Bay joint belt denoted its limited width. In comparison, the Neopalaeozoic Qinzhou Bay-Hangzhou Bay joint belt was diverse for its ocean basin in the different segments and possibly had subduction only in the south segment. The ocean basin of the north and middle segments was limited in its width without subduction and possibly existed as a rift trough that was unable to resist the terrigenous input. In the north segment of the Qinzhou Bay-Hangzhou Bay joint belt, the strata of hydrothermal siliceous rocks in Dongxiang copper-polymetallic ore deposit exhibited alternative cycles with the marine volcanic rocks, volcanic tuff, and metal sulphide. These sedimentary systems were formed in different circumstances, whose alternative cycles indicated the release of internal energy in several cycles gradually from strong to weak. PMID:24302882

Li, Hongzhong; Zhai, Mingguo; Zhang, Lianchang; Zhou, Yongzhang; Yang, Zhijun; He, Junguo; Liang, Jin; Zhou, Liuyu

2013-01-01

405

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

SciTech Connect

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).

Aleman, A.M. (Amoco Production Company, Houston, TX (United States))

1993-02-01

406

Microseismicity and tectonics of Sinai  

NASA Astrophysics Data System (ADS)

Five microearthquake seismographs were used at 11 sites in northern Sinai in the period February 1987 to February 1988 to study the microseismicity of the area around the Maghara coal mine for mine-development studies. A total of 270 events were recorded on 850 records. The magnitude, epicenter and depth of each event were calculated using suitable software for an Egyptian Geological Survey and Mining Authority's (EGSMA) XT computer. The interpretation of the seismic activity in the area is given in view of plate tectonics, the Sinai subplate boundary follows the Gulf of Aqaba and the Dead Sea. The plate and subplate boundaries are presently active, and there seems to be a diffuse zone of deformation between "NW Africa" and "Nubia" affecting the Cairo-Suez district.

El Hakim, B. A.; Dessoky, M. M.; El Sayed, A. A.; Basta, N. Z.; Mohamed, B. S.; Salem, E. M.

407

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)

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).

Toksoz, M. Nafi; Reilinger, Robert E.

1990-01-01

408

Tectonic evolution in the Archaean and Proterozoic  

NASA Astrophysics Data System (ADS)

Evidence for continental motion since at least 3.3 Ga and at minimum average velocities comparable to those of today leaves little doubt that Precambrian tectonic styles are essentially comparable to those of the Phanerozoic plate-tectonic regime and were governed by deformation along and within continental plates. The detailed mechanisms for these motions, however, remain a matter of considerable dispute. For the earliest Archaean, from > 4.2 Ga to perhaps 3.9 Ga, plate tectonics appear unlikely because of thin and "soft" lithosphere: high heat flow probably favoured global hotspot activity with crustal growth of Iceland type through vertical magmatic accretion. The tectonic environment for the generation of about 3.9-2.5 Ga granite-gneiss-greenstone terrains with voluminous production of tonalite-trondhjemite-granodiorite magmas is still uncertain, and both plate margin and intraplate scenarios are possible. Deformation styles in greenstones and adjacent high-grade orthogneisses with intercalated shallow-water supracrustal assemblages suggest extensive horizontal shortening and crustal interstacking. This probably resulted from collisional and/or rotational motion and produced significant intracrustal melting as early as 3.9 Ga. By the end of the Archaean, and locally much earlier, crustal thicknesses reached 35-50 km or more, and the extraordinary high global crust-production rate between about 2.8 and 2.5 Ga may be ascribed to both subduction-related lateral accretion and to extensive magmatic underplating, which finally led to large, stable cratons. The apparent worldwide gap in major tectonic and magmatic activity during the early Proterozoic between about 2.5 and 2.2 Ga is an artifact due to lack of precise age data; both intracontinental as well as arc-type magmatic rocks were produced, though only locally. The voluminuous and worldwide crust-formation event at about 2.1-1.8 Ga provides the first evidence of modern-style plate tectonics, many magmatic rocks, such as in the Canadian Trans-Hudson orogen and in the Svecofennian of southwest Finland, have arc-type geochemical signatures, and both obducted ophiolites and blueschist assemblages have recently been discovered. In addition, the Proterozoic is characterized by long, linear mobile belts whose origin and evolution are still under debate. Many of these belts have tectonic features comparable to Phanerozoic collisional orogens, but in Australia and parts of southern Africa some Proterozoic belts appear to have formed through crustal stretching without lithospheric separation, and subsequent shortening leading to orogenic deformation may have been due to delamination and crustal subduction. Towards the end of the Proterozoic, evidence for modern-style plate tectonics becomes abundant through the recognition of island arc accretion, ophiolite obduction, foreland thrust and fold belts and exotic terranes. One of the best documented example for this tectonic environment is the Arabian-Nubian shield. Although it is doubtful whether modern plate tectonic settings can serve as analogues for all Precambrian tectonic styles, it is clear that global crustal evolution since the early Archaean was governed by the motion of plates which repeatedly came together to form supercontinents and then dispersed again. We shall not understand the detailed mechanism of Precambrian crustal tectonics before we learn how to interpret recent large-scale crustal deformation and its causes.

Krner, Alfred

1991-03-01

409

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)

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.

Toksoz, M. Nafi

1987-01-01

410

Understanding seismic heterogeneities in the lower mantle beneath the Americas from seismic tomography and plate tectonic history  

Microsoft Academic Search

We combine results from seismic tomography and plate motion history to investigate slabs of subducted lithosphere in the lower mantle beneath the Americas. Using broadband waveform cross correlation, we measured 37,000 differential P and S traveltimes, 2000 PcP-P and ScS-S times along a wide corridor from Alaska to South America. We invert the data simultaneously to obtain P and S

Yong Ren; Elonore Stutzmann; Robert D. van der Hilst; Jean Besse

2007-01-01

411

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

NASA Technical Reports Server (NTRS)

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.

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

1987-01-01

412

Geochemical and Nd?Sr isotopic composition of deep-sea turbidites: Crustal evolution and plate tectonic associations  

NASA Astrophysics Data System (ADS)

Petrographic, geochemical, and isotopic data for turbidites from a variety of tectonic settings exhibit considerable variability that is related to tectonic association. Passive margin turbidites (Trailing Edge, Continental Collision) display high framework quartz (Q) content in sands, evolved major element compositions (high Si/Al, K/Na), incompatible element enrichments (high Th/Sc, La/Sc, La/Yb), negative Eu-anomalies and variable Th/U ratios. They have low 143Nd /144Nd and high 87Sr /86Sr ( ?Nd = -26 to -10; 87Sr /86Sr = 0.709 to 0.734 ), indicating a dominance of old upper crustal sources. Active margin settings (Fore Arc, Continental Arc, Back Arc, Strike Slip) commonly exhibit quite different compositions. Th/Sc varies from <0.01 to 1.8, and ?Nd varies from -13.8 to +8.3. Eu-anomalies range from no anomaly ( Eu/Eu ? = 1.0 ) to Eu-depletions typical of post-Archean shales ( Eu/Eu ? = 0.65 ). Active margin data are explained by mixtures of young arc-derived material, with variable composition and old upper crustal sources. Major element data indicate that passive margin turbidites have experienced more severe weathering histories than those from active settings. Most trace elements are enriched in muds relative to associated sands because of dilution effects from quartz and calcite and concentration of trace elements in clays. Exceptions include Zr, Hf (heavy mineral influence) and Tl (enriched in feldspar) which display enrichments in sands. Active margin sands commonly exhibit higher Eu/Eu ? than associated muds, resulting from concentration of plagioclase during sorting. Some associated sands and muds, especially from active settings, have systematic differences in Th/Sc ratios and Nd-isotopic composition, indicating that various provenance components may separate into different grain-size fractions during sedimentary sorting processes. Trace element abundances of modern turbidites, from both active and passive settings, differ from Archean turbidites in several important ways. Modern turbidites have less uniformity, for example, in Th/Sc ratios. On average, modern turbidites have greater depletions in Eu (lower Eu/Eu ?) than do Archean turbidites, suggesting that the processes of intracrustal differentiation (involving plagioclase fractionation) are of greater importance for crustal evolution at modern continental margins than they were during the Archean. Modern turbidites do not display HREE depletion, a feature commonly seen in Archean data. HREE depletion ( Gd N/Yb N > 2.0 ) in Archean sediments results from incorporation of felsic igneous rocks that were in equilibrium (or their sources were in equilibrium) with garnet sometime in their history. Absence of HREE depletion at modern continental margins suggests that processes of crust formation (or mantle source compositions) may have differed. Differences in trace element abundances for Archean and modern turbidites add support to suggestions that upper continental crust compositions and major processes responsible for continental crust differentiation differed during the Archean. Neodymium model ages, thought to approximate average provenance age, are highly variable ( TDMND = 0-2.6 Ga) in modern turbidites, in contrast with studies that indicate Nd-model ages of lithified Phanerozoic sediment are fairly constant at about 1.5-2.0 Ga. This variability indicates that continental margin sediments incorporate new mantle-derived components, as well as continental crust of widely varying age, during recycling. The apparent dearth of ancient sediments with Nd-model age similar to stratigraphic age supports the suggestion that preservation potential of sediments is related to tectonic setting. Many samples from active settings have isotopic compositions similar to or only slightly evolved from mantle-derived igneous rocks. Subduction of active margin turbidites should be considered in models of crust-mantle recycling. For short-term recycling, such as that postulated for island arc petrogenesis, arc-derived turbidites cannot be easily recognized a

McLennan, S. M.; Taylor, S. R.; McCulloch, M. T.; Maynard, J. B.

1990-07-01

413

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

SciTech Connect

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.

Lewis, S.E.; Berg, R.B. (eds.)

1988-07-01

414

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)

Between 1978 and 1983, Petrleos 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 Subdireccin de Exploracin (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.

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

415

Plate kinematics in the western Pacific derived from geodetic observations  

E-print Network

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

Tregoning, Paul

416

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)

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 an