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Last update: November 12, 2013.
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

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

3

Plate Tectonics  

NSDL National Science Digital Library

In this activity students use data from underwater earthquakes to outline the location of plate boundaries. Data from the Northeast Pacific, eastern Equatorial Pacific, and North Atlantic are examined in more detail. Background information on plate tectonics is provided.

2002-01-01

4

Plate Tectonics  

NSDL National Science Digital Library

This site contains 25 questions on the topic of plate tectonics, which covers the development of the theory, crustal movements, geologic features associated with tectonics, and plate boundaries (convergent, divergent, transform). This is part of the Principles of Earth Science course at the University of South Dakota. Users submit their answers and are provided immediate verification.

Heaton, Timothy

5

Plate Tectonics: Plate Interactions  

NSDL National Science Digital Library

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

National Science Teachers Association (NSTA)

2006-11-01

6

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.

7

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

8

Plate Tectonics  

NSDL National Science Digital Library

Plate tectonic activity is being observed presently on a historic timescale, especially in the form of volcanic eruptions and earthquakes, but, as with many large-scale Earth science phenomena, it is hard to ...

9

Petrology and plate tectonics  

Microsoft Academic Search

Petrology played an important role in the formulation of plate tectonics and early plate tectonic interpretations of the geologic past. In the last few years widespread interest in plate tectonics and progress in plate tectonic interpretations have begun to give petrology various feedback effects.In the period 19711974 there were two symposiums intended particularly to connect petrology with plate tectonics [Wyllie,

Akiho Miyashiro

1975-01-01

10

Intermittent Plate Tectonics  

Microsoft Academic Search

Intermittent Plate Tectonics A basic premise of Earth Science is that plate tectonics has been continuously operating since it began early in Earth's history. Yet, plate-tectonic theory itself, specifically the collisional phase of the Wilson Cycle, constitutes a process that is capable of stopping all plate motion. The plausibility of a plate-tectonic hiatus is most easily illustrated by considering the

P. G. Silver; M. D. Behn

2006-01-01

11

Plate Tectonics: Plates  

NSDL National Science Digital Library

This Science Object is the second of five Science Objects in the Plate Tectonics SciPack. It provides a conceptual understanding of what plates are and how they move, contributing to a constantly changing surface. The Earth's continents and ocean basins are made up of plates consisting of the crust and the upper part of the mantle. One plate can consist of both continental and oceanic crust. These plates move very slowly (an inch or so per year) on the hot, deformable layer of the mantle beneath them. The outward transfer of Earth's internal heat drives convection circulation in the mantle. This convection, together with gravitational pull on the plates themselves, causes the plates to move. Learning Outcomes:� 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.

National Science Teachers Association (NSTA)

2006-11-01

12

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

13

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

14

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

15

Plate Tectonic Theory  

NSDL National Science Digital Library

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

Louie, John

16

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

17

Earthquakes and Plate Tectonics  

NSDL National Science Digital Library

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

18

Plate Tectonics: 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.

19

Plate Tectonics with GIS  

Microsoft Academic Search

The concept of Plate Tectonics involves piecing together a wide variety of evidence to build a picture. This includes the location of earthquakes, volcanoes, mountains, fossils, and other paleoclimate data. The theory of Plate Tectonics is driven by information that is attached to a location. Even further, the theory is driven by looking and analyzing all these pieces of information

Nate Ruder

2006-01-01

20

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

21

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

22

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

23

Paleomagnetism and Plate Tectonics.  

National Technical Information Service (NTIS)

Paleomagnetism and plate tectonics are combined in a new procedure for producing paleogeographic reconstructions of the evolution of present day world geography from proto-continents. For each geologic epoch, the continents are first subjected to rotation...

J. Francheteau

1970-01-01

24

Seismology and Plate Tectonics  

Microsoft Academic Search

This introduction to seismological theory and the principles of plate tectonics also develops a practical approach to the interpretation of seismograms for physicists and mathematicians as well as geologists.

David Gubbins

1990-01-01

25

Tectonic Plate Movement.  

ERIC Educational Resources Information Center

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

Landalf, Helen

1998-01-01

26

Plate Tectonics: An Introduction  

NSDL National Science Digital Library

In the early 1900s, most geologists thought that Earth's appearance, including the arrangement of the continents, had changed little since its formation. This video segment describes the impact the theory of plate tectonics has had on our understanding of Earth's geological history, and provides a brief overview of what is currently known about the Earth's tectonic plates and their motions. The segment is two minutes twenty-one seconds in length. A background essay and list of discussion questions are also provided.

27

Earth's Decelerating Tectonic Plates  

SciTech Connect

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

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

2008-08-22

28

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

29

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.

30

Plate Tectonics: Consequences of Plate Interactions  

NSDL National Science Digital Library

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

National Science Teachers Association (NSTA)

2006-11-01

31

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.

32

Tectonic Plates and Plate Boundaries  

NSDL National Science Digital Library

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

2011-05-09

33

Tectonic Plates and Plate Boundaries  

NSDL National Science Digital Library

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

34

Plate Tectonics Learning Module  

NSDL National Science Digital Library

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

Haberlin, Rita

35

The Plate Tectonics Project  

ERIC Educational Resources Information Center

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

Hein, Annamae J.

2011-01-01

36

Plate Tectonics: A Continuous Process  

NSDL National Science Digital Library

This page provides an introduction to plate tectonics for secondary students. Topics include plate motions, the layers of the Earth and oceanic versus continental plates. A set of links provides access to material on the processes of plate tectonics occuring at plate boundaries, zones of movement and instability.

37

Tectonic Plates, Earthquakes, and Volcanoes  

NSDL National Science Digital Library

According to theory of plate tectonics, Earth is an active planet -- its surface is composed of many individual plates that move and interact, constantly changing and reshaping Earth's outer layer. Volcanoes and earthquakes both result from the movement of tectonic plates. This interactive feature shows the relationship between earthquakes and volcanoes and the boundaries of tectonic plates. By clicking on a map, viewers can superimpose the locations of plate boundaries, volcanoes and earthquakes.

2011-05-12

38

The Biggest Plates on Earth: Plate Tectonics  

NSDL National Science Digital Library

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

39

Plate Tectonics: The Mechanism  

NSDL National Science Digital Library

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

40

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

Microsoft Academic Search

Plates makes up earth's surface, and tectonic activity is generally concentrated on plate boundary zones. In restrict meaning, plate tectonics of the earth is regarded as mixture of plate boundary zone tectonics and extensive intraplate tectonics. For example, the Asian continent never behaves as rigid plate that was deformed extensively when the Indian continent collided with it. I infer that

M. Ishikawa

2004-01-01

41

Martian plate tectonics  

NASA Astrophysics Data System (ADS)

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

Sleep, N. H.

1994-03-01

42

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

43

Plate Tectonics: Further Evidence  

NSDL National Science Digital Library

Early evidence showing striking similarities between regions on opposite sides of vast oceans suggested that in Earth's distant past what are now separate continents may once have been connected. However, this evidence said nothing about how the continents could have moved to their present positions. This video shows how seafloor spreading creates new oceanic crust and how the crust is destroyed by subduction into Earth's mantle, providing the mechanism and forces that propel tectonic plates across Earth's surface. The segment is two minutes nine seconds in length.

44

Plate Tectonics: Further Evidence  

NSDL National Science Digital Library

Early evidence showing striking similarities between regions on opposite sides of vast oceans suggested that in Earth's distant past what are now separate continents may once have been connected. However, this evidence said nothing about how the continents could have moved to their present positions. This video shows how seafloor spreading creates new oceanic crust and how the crust is destroyed by subduction into Earth's mantle, providing the mechanism and forces that propel tectonic plates across Earth's surface. The segment is two minutes nine seconds in length.

2011-10-14

45

Plate Tectonics: Lake Mead, Nevada  

NSDL National Science Digital Library

Using animations to illustrate the theory of plate tectonics, this video segment adapted from Discovering Women takes you to Lake Mead, Nevada, to see visual evidence of how plate movement has been stretching the North American continent.

Foundation, Wgbh E.

2005-10-21

46

Plate Tectonics in the Caribbean  

Microsoft Academic Search

Freeland and Dietz1 have presented a speculative geological history of the Caribbean using plate tectonic theory, and simultaneously Dickinson2 suggested that two types of plate convergence may be distinguished by examining sedimentary and tectonic evidence. Geological data from the Caribbean support much of the proposed geological history but differ in significant details. On the other hand, the Caribbean seems to

Peter H. Mattson

1972-01-01

47

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

48

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

49

Tectonic stress in the plates  

Microsoft Academic Search

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

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

1979-01-01

50

Tectonic stress in the plates  

Microsoft Academic Search

The state of stress in the lithosphere provides strong constraints on the forces acting on the plates. The directions of principal stresses in the plates as indicated by midplate earthquake mechanisms, in situ stress measurements, and stress-sensitive geological features are used to test plate tectonic driving force models. Force models include buoyancy forces at ridges, subduction zones, and continental convergence

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

1979-01-01

51

Plate tectonics conserves angular momentum  

NASA Astrophysics Data System (ADS)

A new combined understanding of plate tectonics, Earth internal structure, and the role of impulse in deformation of the Earth's crust is presented. Plate accelerations and decelerations have been revealed by iterative filtering of the quaternion history for the Euler poles that define absolute plate motion history for the past 68 million years, and provide an unprecedented precision for plate angular rotation variations with time at 2-million year intervals. Stage poles represent the angular rotation of a plate's motion between adjacent Euler poles, and from which the maximum velocity vector for a plate can be determined. The consistent maximum velocity variations, in turn, yield consistent estimates of plate accelerations and decelerations. The fact that the Pacific plate was shown to accelerate and decelerate, implied that conservation of plate tectonic angular momentum must be globally conserved, and that is confirmed by the results shown here (total angular momentum ~1.4 E+27 kgm2s-1). Accordingly, if a plate decelerates, other plates must increase their angular momentums to compensate. In addition, the azimuth of the maximum velocity vectors yields clues as to why the "bend" in the Emperor-Hawaiian seamount trend occurred near 46 Myr. This report summarizes processing results for 12 of the 14 major tectonic plates of the Earth (except for the Juan de Fuca and Philippine plates). Plate accelerations support the contention that plate tectonics is a product of torques that most likely are sustained by the sinking of positive density anomalies due to phase changes in subducted gabbroic lithosphere at depth in the upper lower mantle (above 1200 km depth). The tectonic plates are pulled along by the sinking of these positive mass anomalies, rather than moving at near constant velocity on the crests of convection cells driven by rising heat. These results imply that spreading centers are primarily passive reactive features, and fracture zones (and wedge-shaped sites of seafloor spreading) are adjustment zones that accommodate strains in the lithosphere. Further, the interlocked pattern of the Australian and Pacific plates the past 42 Million years (with their absolute plate motions near 90 to each other) is taken as strong evidence that large thermally driven "roller" convection cells previously inferred as the driving mechanism in earlier interpretations of continental drift and plate tectonics, have not been active in the Earth's mantle the past 42 Million years, if ever. This report also presents estimates of the changes in location and magnitude of the Earth's axis of total plate tectonic angular momentum for the past 62 million years.

Bowin, C.

2009-03-01

52

Tectonic Plate Movement in Alaska  

NSDL National Science Digital Library

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

Foundation, Wgbh E.

2009-02-27

53

IRIS: Animations of Plate Tectonics  

NSDL National Science Digital Library

This is a collection of animations on dynamic earth processes: plate tectonics, earthquakes, volcanoes, and seismic waves. Users can explore the interaction of Earth's tectonic plates, view models of P and S wave propagation, study how seismographs work, monitor earthquakes and volcanoes, and get instructions for modeling earthquakes in the classroom. This resource is part of IRIS, the Incorporated Research Institutions for Seismology, a consortium of international laboratories and data collection centers.

2011-03-18

54

The Number of Tectonic Plates  

NASA Astrophysics Data System (ADS)

The number of tectonic plates on Earth described in the literature has expanded greatly since the early days of plate tectonics, when only a dozen or so plates were considered in global models of present day plate motions. Recently, with new techniques of more accurate earthquake epicenter locations, modern ways of measuring ocean bathymetry using swath mapping, the use of space based geodetic techniques &c, there has been a huge growth in the number of plates thought to exist. Bird (2003) proposed 52 plates, many of which were delineated on the basis of earthquake locations. Because of the pattern of areas of these plates, he suggested that there should be more small plates than he could identify. In this paper, I gather together publications that have proposed additional plates and discuss the new area arrangement which has been produced by the addition of these 23 new plates to Bird's catalogue. In addition I have measured the areas of the very small plates along the San Andreas fault identified by Bird and Rosenstock (1984) and added these 17 plates to the list as well as five plates proposed by Meade and Hager (2005). Sorting the plates by size allows us to investigate how size varies as a function of order. There are several changes of slope in the log-log plots of plate number (largest to smallest) against plate linear dimension. One set of relatively small plates shows a negative slope of -2.5, the same slope that has been found by modelling studies of two-dimensional structures such as rifted margins as well as three dimensional fragmentation models. Plates were characterized by what types of boundary they had. On looking at boundary type as a function of plate order, there seems to be no obvious pattern apart from what has been caused by non-uniform study of Earth's plate tectonic boundaries.

Harrison, C. G.

2011-12-01

55

Earthquakes, Volcanoes, and Plate Tectonics  

NSDL National Science Digital Library

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

56

Plate Tectonics: A Paradigm under Threat.  

ERIC Educational Resources Information Center

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

Pratt, David

2000-01-01

57

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.

58

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.

Oberrecht, Kenn

2007-03-28

59

Accelerated plate tectonics.  

PubMed

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

Anderson, D L

1975-03-21

60

Learning Assessment #1 - Plate Tectonics  

NSDL National Science Digital Library

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

Speta, Michelle; Reid, Leslie

61

Plate tectonics conserves angular momentum  

NASA Astrophysics Data System (ADS)

A new combined understanding of plate tectonics, Earth internal structure, and the role of impulse in deformation of the Earth's crust is presented. Plate accelerations and decelerations have been revealed by iterative filtering of the quaternion history for the Euler poles that define absolute plate motion history for the past 68 million years, and provide an unprecedented precision for plate angular rotation variations with time at 2-million year intervals. Stage poles represent the angular rotation of a plate's motion between adjacent Euler poles, and from which the maximum velocity vector for a plate can be determined. The consistent maximum velocity variations, in turn, yield consistent estimates of plate accelerations and decelerations. The fact that the Pacific plate was shown to accelerate and decelerate, implied that conservation of plate tectonic angular momentum must be globally conserved, and that is confirmed by the results shown here (total angular momentum ~1.4+27 kg m2 s-1). Accordingly, if a plate decelerates, other plates must increase their angular momentums to compensate. In addition, the azimuth of the maximum velocity vectors yields clues as to why the "bend" in the Emperor-Hawaiian seamount trend occurred near 46 Myr. This report summarizes processing results for 12 of the 14 major tectonic plates of the Earth (except for the Juan de Fuca and Philippine plates). Plate accelerations support the contention that plate tectonics is a product of torques that most likely are sustained by the sinking of positive density anomalies revealed by geoid anomalies of the degree 4-10 packet of the Earth's spherical harmonic coefficients. These linear positive geoid anomalies underlie plate subduction zones and are presumed due to phase changes in subducted gabbroic lithosphere at depth in the upper lower mantle (above 1200 km depth). The tectonic plates are pulled along by the sinking of these positive mass anomalies, rather than moving at near constant velocity on the crests of convection cells driven by rising heat. The magnitude of these sinking mass anomalies is inferred also to be sufficient to overcome basal plate and transform fault frictions. These results imply that spreading centers are primarily passive reactive features, and fracture zones (and wedge-shaped sites of seafloor spreading) are adjustment zones that accommodate strains in the lithosphere. Further, the interlocked pattern of the Australian and Pacific plates the past 42 Million years (with their absolute plate motions near 90 to each other) is taken as strong evidence that large thermally driven "roller" convection cells previously inferred as the driving mechanism in earlier interpretations of continental drift and plate tectonics, have not been active in the Earth's mantle the past 42 Million years, if ever. This report also presents estimates of the changes in location and magnitude of the Earth's axis of total plate tectonic angular momentum for the past 62 million years.

Bowin, C.

2010-03-01

62

Plate tectonics hiati as the cause of global glaciations: 1. Early Proterozoic events and the rise of oxygen  

NASA Astrophysics Data System (ADS)

Plate tectonics is the main way in which the Earth's internal heat is brought to the surface and lost, so it seems that global tectonics should not stop and start. Consequently the long-standing fact that, globally, no orogenic granitoid or greenstone U-Pb ages have been found in the 2.45--2.22 Ga interval has been attributed to defective sampling. Here I argue that this interval was indeed a prolonged hiatus in plate tectonics, being the first of two. The other, but differently caused, was in the late Proterozoic and is the topic of Part 2. The feature common to both hiati, and relevant to global glaciation, is that mid-ocean ridges (MORs) die and subside, potentially lowering sea-level by several kilometres, causing loss of atmospheric CO2 by weathering and an increase in planetary albedo. For the origin of the first hiatus we must first go back to formation of the core. The current iron-percolation model is invalidated by the fact that its corollary, the arrival of a water and siderophile-rich "late veneer" at the end of percolation, would be required to arrive some 60 Ma after the Moon, which never had a late veneer, was already in Earth orbit. The available alternative [1] would have given the early Earth a wet and low-viscosity convecting mantle able to dispose of the early heat with high efficiency; so that by 2.8 Ga MORs began to deepen, exposing cratons to massive weathering which lowered atmospheric CO2. The well-documented late Archaean acceleration of crustal addition to cratons, or, more precisely, of TTG-granitoid intrusion of greenstone belts, is also, paradoxically, evidence of waning mantle heat. Such wide-belt intrusion, grouped into quasi-coeval 'events', are examples of post-subduction magmatism (PSM), marking interruption of flat-slab subduction under a greenstone belt when a microcraton arrived [2]. On each occasion the TTG, derived from the subducted and reheated oceanic crust, advected subducting-plate heat to the surface that would otherwise have been returned to the mantle heat budget. This worsened the heat-budget problem, finally precipitating a collapse of mantle convection and the ensuing Huronian global glaciations at 2.35 Ga. The unparalleled deposition of banded iron-formation (BIF) during the early part of this hiatus supports this picture. Throughout the Archaean, Fe2+ had accumulated in the deep ocean, stabilized by acidic input from MORs, despite the efforts of oxygenic life (OL) in shallow water. Removal of this input enabled OL to "win its battle", the BIF was deposited and the ocean largely oxygenated. ?13C rose as OL really flowered at 2.22 Ga, when MORs resumed, patchily at first, and sea-level rose and flooded planated cratons. [1] Osmaston, M.F. (Goldschmidt 2002) GCA 66 (15A) A571.

Osmaston, M. F.

2003-04-01

63

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

64

Plate tectonics and mountain building  

Microsoft Academic Search

\\u000a One of the greatest strengths of the modern plate tectonics theory is its ability to explain the origin of virtually all of\\u000a the present and most ancient mountain belts on Earth. In other words, mountain building (orogeny) stands in strong causal\\u000a interrelation with the global plate drift pattern. The motor of orogeny is subduction. To enable subduction, a basin floored

Wolfgang Frisch; Martin Meschede; Ronald Blakey

65

Metamorphic Rocks and Plate Tectonics  

NSDL National Science Digital Library

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

Smoothstone; Company, Houghton M.

66

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

67

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

68

Comment on ``Intermittent Plate Tectonics?''  

Microsoft Academic Search

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.

Jun Korenaga

2008-01-01

69

From point defects to plate tectonic faults  

Microsoft Academic Search

Understanding and explaining emergent constitutive laws in the multi-scale evolution from point defects, dislocations and two-dimensional defects to plate tectonic scales is an arduous challenge in condensed matter physics. The Earth appears to be the only planet known to have developed stable plate tectonics as a means to get rid of its heat. The emergence of plate tectonics out of

K. Regenauer-Lieb; B. Hobbs; D. A. Yuen; A. Ord; Y. Zhang; H. B. Mulhaus; G. Morra

2006-01-01

70

Indian Ocean violates conventional plate tectonic theory  

Microsoft Academic Search

A new study of magnetic profiles and other plate tectonic data in the Indian Ocean predicts that India and Australia, previously thought to move in unison as part of the same rigid plate, are approaching each other at about 12 mm\\/year. According to conventional plate tectonic theory, plates are internally rigid with earthquakes concentrated at plate boundaries and occurring only

Richard G. Gordon

1991-01-01

71

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.

72

Manganese ore deposits and plate tectonics  

Microsoft Academic Search

IT is now generally accepted that the oceanic crust and overlying pelagic sediments are enriched in several metals, including copper and manganese1-3. The theory of plate tectonics has demonstrated that the oceanic lithosphere is likely to be remobilised or emplaced along convergent continental margins through magmatic or tectonic activity. The plate tectonic model has been used to explain the metallogenesis

Michael Thonis; ROGER G. BURNS

1975-01-01

73

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

74

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

75

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

76

Geodetic contribution helped validate plate tectonics  

Microsoft Academic Search

Direct measurements of contemporary plate motion rates by geodesists are generally acknowledged as having been essential for confirming plate tectonic theory. For example, in Oreskes [2001], Tanya Atwater attests that ``The real test of plate motions, however, required that we measure the ongoing motions of the plate interiors, far from any plate boundary complications. Global-scale measurements of relative positions on

Bill Carter

2003-01-01

77

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 ...

78

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

79

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

80

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

81

Self-Organized Criticality in Plate Tectonics  

Microsoft Academic Search

\\u000a A review of scaling laws observed in earthquake processes (short time scale) and in plate tectonics (large time scale) is\\u000a given. Laboratory experiments which model the mechanical deformations and ruptures of large continental plates are presented\\u000a and analyzed. Comparison with a field theory suggests that plate tectonics maybe one of the best natural realization of self-organized\\u000a criticality, viewed front the

Didier Sornette

82

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

83

Why do i not accept plate tectonics?  

Microsoft Academic Search

The `new global tectonics' or theory of `plate tectonics' has its background in the observations made on the oceanic areas. It claims to extend the same principles to the continents as well. At first glance this attitude seems to be sound because the oceans occupy two thirds of the surface of the earth. But comparing the known age of the

V. V. Beloussov

1979-01-01

84

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

85

Representations of Rotations and Tectonic Plate Motions.  

National Technical Information Service (NTIS)

The thesis discusses alternative representations of rotations and tectonic plate motions. The representation of a rotation by a quaternion has theoretical as well as computational advantages over the conventional matrix representation. It can be shown tha...

A. J. M. Verheijen

1990-01-01

86

Plate Tectonics, The Cause of Earthquakes  

NSDL National Science Digital Library

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

Louie, John

87

Global Dynamic Numerical Simulations of Plate Tectonic Reorganizations  

Microsoft Academic Search

We use a new numerical approach for global geodynamics to investigate the origin of present global plate motion and to identify the causes of the last two global tectonic reorganizations occurred about 50 and 100 million years ago (Ma) [1]. While the 50 Ma event is the most well-known global plate-mantle event, expressed by the bend in the Hawaiian-Emperor volcanic

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

2010-01-01

88

Plate Tectonic Eraplacement Upper Mantle Peridotires along  

Microsoft Academic Search

Recently developed ideas of global tectonics have provided a new framework within which to consider the origin of alpine-type peridotites. In plate theory, compressional zones associated with island arcs are considered to represent plate boundaries where oceanic lithosphere is subducted. The subduction zones are characterized by lithospheric underthrusting, andesitic volcanoes, and deep seismic activity that generally dips under the continental

89

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

90

Plate Tectonics is Enhanced by Continents  

Microsoft Academic Search

Plate tectonics can be obtained self-consistently in numerical models of mantle convection by using a strongly temperature-dependent viscosity, which stiffens the cold upper thermal boundary layer into a rigid lid, combined with plastic behavior above a given yield stress, which allows the lid to break into plates (e.g. Moresi and Solomatov, 1998; Tackley 2000). The plate-like regime obtained in such

C. Grigne; P. J. Tackley

2005-01-01

91

Plate tectonics of the Scotia Sea  

NASA Astrophysics Data System (ADS)

The opening of the Scotia Sea ended a period of direct terrestrial connection between Antarctica and South America that had started with the amalgamation of Gondwana, and inaugurated the more recent period during which high latitude oceanic circulation between the Pacific and Atlantic oceans increased. The consequences of these changes have been suggested to include the end of terrestrial biogeographic communication across the region in Paleogene times, and the subsequent onset of southern polar isolation, bottom water formation, and Antarctic glaciation by early Neogene times. These events, responding to the configuration of land and sea, would ultimately have been governed by the configuration of continental crustal units around the margins of the Scotia Sea, which in turn responded primarily to plate motions and the associated plate boundary processes. This presentation will put forward a model for the region's tectonic development that is derived largely from marine and satellite-derived geophysical data within it, and surrounding it. In this model, the Scotia Sea develops by extension of existing continental crust and accretion of new oceanic crust around the margins of a core of Jurassic-Cretaceous oceanic crust that formed and was abandoned within the region as a result of large-scale rotation of the South American plate around the northern end of the Antarctic Peninsula in Cretaceous times. The later extension and accretion happened in response to the westwards (since ~50 Ma) and eastwards (since ~17 Ma) motions of southernmost South America and the subduction-related ancestral South Sandwich Trench away from its western and eastern edges. Whilst these events are broadly consistent with what is known about disruption of the biogeographic 'Scotia Portal' in the region, they imply that the onset of Pacific to Atlantic oceanographic connectivity pre-dated, and thus cannot have directly influenced, the onset of Antarctic glaciation.

Eagles, Graeme

2013-04-01

92

A Hypothesis Explaining The Dynamics Of Plate Tectonics  

Microsoft Academic Search

Since the introduction of the plate tectonics theory, one of the unsolved fundamental problems has been the understanding of how and when plate tectonics began, as well as initial dynamics of plate tectonics although several mechanisms have been suggested (i.e. the hypothesis that asthenospheric convections drive plates, which is not supported by modern geodynamic theories). The kinematics behind the subduction

H. Cetin; F. Ozkirim

2007-01-01

93

A Hypothesis Explaining the Dynamics of Plate Tectonics  

Microsoft Academic Search

Since the introduction of the plate tectonics theory, one of the unsolved fundamental problems has been the understanding of how and when plate tectonics began, as well as the initial dynamics of plate tectonics although several mechanisms have been suggested (i.e. the hypothesis that asthenospheric convections drive plates, which is not supported by modern geodynamic theories). The kinematics behind the

H. Cetin; F. Ozkirim

2008-01-01

94

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

95

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

96

LOWLID FORMATION AND PLATE TECTONICS ON EXOPLANETS  

NASA Astrophysics Data System (ADS)

The last years of astronomical observation have opened the doors to a universe filled with extrasolar planets. Detection techniques still only offer the possibility to detect mainly Super-Earths above five Earth masses. But detection techniques do steadily improve and are offering the possibility to detect even smaller planets. The observations show that planets seem to exist in many possible sizes just as the planets and moons of our own solar system do. It is only a natural question to ask if planetary mass has an influence on some key habitability factors such as on plate tectonics, allowing us to test which exoplanets might be more likely habitable than others, and allowing us to understand if plate tectonics on Earth is a stable or a critical, instable process that could easily be perturbed. Here we present results derived from 1D parameterized thermal evolution and 2D/3D computer models, showing how planetary mass influences the propensity of plate tectonics for planets with masses ranging from 0.1 to 10 Earth masses. Lately [2, 3] studied the effect of planetary mass on the ability to break plates and hence initiate plate tectonics - but both derived results contradictory to the other. We think that one of the reasons why both studies [2, 3] are not acceptable in their current form is partly due to an oversimplification. Both treated viscosity only temperature-dependent but neglected the effect pressure has on enlarging the viscosity in the deep mantle. More massive planets have therefore a stronger pressure-viscosity-coupling making convection at high pressures sluggish or even impossible. For planets larger than two Earth masses we observe that a conductive lid (termed low-lid) forms above the core-mantle boundary and thus reduces the effective convective part of the mantle when including a pressure-dependent term into the viscosity laws as shown in [1]. Moreover [2, 3] use time independent steady state models neglecting the fact that plate tectonics is a dynamic process changing with time. By combining 1D thermal time evolution models and 2D/3D steady state models we are able to conclude that planetary mass does influence the propensity of plate tectonics on planets. The pressure dependence changes the scaling laws for parameterized models and influences the scaling of stresses associated with breaking of plates and thus the initiation of plate tectonics. The results indicate that for planets with masses larger than Earth lithospheric plates are either becoming thicker or remain similar in thickness and yield stresses to break the plates increase - making it harder to assume that plate tectonics is more likely on Super-Earths. Moreover, convective stresses decrease more than yield stresses do for planets smaller than Earth, leading to the fact that planets with masses close to one Earth mass seem to have better chances to exhibit plate tectonics than larger or smaller planets with similar composition and structure. References [1] Noack, L. Stamenkovic, V., and Breuer, D. (2009) ESLAB 09, P1.04. [2] Valencia, D., OConnell, R.J., and Sasselov, D.D. (2007) Astroph. J., 670, 45-48. [3] ONeill, C. and Lenardic, A. (2007) GRL, 34, L19204

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

2009-12-01

97

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

98

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 ...

99

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

100

Dynamic Earth: The Story of Plate Tectonics.  

National Technical Information Service (NTIS)

In the early 1960s, the emergence of the theory of plate tectonics started a revolution in the earth sciences. Since then, scientists have verified and refined this theory, and now have a much better understanding of how our planet has been shaped by plat...

P. Lindeberg

2001-01-01

101

Plate tectonics on the terrestrial planets  

Microsoft Academic Search

Plate tectonics is largely controlled by the buoyancy distribution in oceanic lithosphere, which correlates well with the lithospheric age. Buoyancy also depends on compositional layering resulting from pressure release partial melting under mid-ocean ridges, and this process is sensitive to pressure and temperature conditions which vary strongly between the terrestrial planets and also during the secular cooling histories of the

P van Thienen; N. J Vlaar; A. P van den Berg

2004-01-01

102

Continental volcanism, xenoliths, and lithospheric plate tectonics  

Microsoft Academic Search

A comparison of data on the evolution of Cenozoic volcanism in the Baikal rift zone and Mongolia and of Pliocene-Quaternary volcanism in the Minor Caucasus indicates that the data do not support the theory of plate tectonics. It is shown that the evolution of these regions as well as the evolution of the deep-magma composition and that of the deep

Iu. S. Genshaft; A. Ia. Saltykovskii

1989-01-01

103

Acceptance of plate tectonic theory by geologists  

Microsoft Academic Search

How do scientific theories come to be accepted? What roles do age, education, type of employment, area of specialization, and familiarity with relevant literature play in the acceptance of theories? The present study was designed to provide preliminary answers to these questions with respect to the theory of plate tectonics and to give direction to a more extensive study of

Matthew H. Nitecki; J. L. Lemke; Howard W. Pullman; Markes E. Johnson

1978-01-01

104

Paleomagnetism, continental drift, and plate tectonics  

Microsoft Academic Search

The title of this chapter might induce the reader to expect rather more than what actually is being offered; this review restricts itself to those aspects of paleomagnetism that are related to continental drift, polar wandering, and plate tectonics, and vice versa. A sensu lato interpretation would not only lead to a lengthy recitation; it would also in fact be

Rob Van der Voo

1975-01-01

105

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

106

Dangerous Earth: A Plate Tectonic Story  

NSDL National Science Digital Library

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

107

Plate Tectonics: The Splitting Apart of Pangea  

NSDL National Science Digital Library

After a teacher led discussion (some background provided), students will break into groups and recreate global maps at four different points in earth's history. By completing this exploration activity, the learner will: recognize that continents of the western hemisphere "fit" together, create a model that demonstrates the similarity of the continents, identify the major tectonic plates, and calculate the rate of divergence for the mid-Atlantic ridge. Several key words are linked to images that can further enhance understanding.

108

Mars plate tectonics (1) :An Earth prospective  

NASA Astrophysics Data System (ADS)

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

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

2001-12-01

109

Plate tectonics on the terrestrial planets  

Microsoft Academic Search

Abstract Plate tectonics is largely controlled by the buoyancy distribution in oceanic lithosphere, which correlates well with the lithospheric age. Buoyancy,also depends,on compositional,layering resulting from pressure release partial melting under mid-ocean ridges, and this process is sensitive to pressure and temperature conditions which vary strongly between the terrestrial planets and also during the secular cooling histories of the planets. In

P. Van Thienen; N. j. Vlaar; A. p. Van Den Berg

110

High-Technology Investigations Of Rift Propogation And Plate Tectonics  

Microsoft Academic Search

Plate tectonics as originally formulated was so successful in revolutionizing geology that only very few modifications have been necessary. One of these modifications is the suggestion that spreading centers sometimes increase their length by propagation, progressively rifting apart preexisting lithospheric plates and reorganizing the Earth's plate boundary geometry. This small change to plate tectonic theory, known as the propagating rift

R. Hey

1983-01-01

111

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

112

What on Earth is Plate Tectonics?  

NSDL National Science Digital Library

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

2007-02-26

113

Plate Tectonics and Terrestrial Carbon Isotope Records  

NASA Astrophysics Data System (ADS)

In 2001, we reported a negative excursion in early-Aptian atmospheric ?13CO2 (? = -3.6 to -6.5), based on ?13C analyses of organic matter and land-plant isolates from coarsely-sampled Colombian estuarine and near-shore sediments. Here we present similar results for an Aptian section of the Arundel Clay (Potomac Group, central Maryland), which is well-known for its exceptional preservation of terrestrial plant materials. Sampling across 13 meters of sediment at ~10-cm intervals revealed a clear shift in the ?13C of terrestrial organic matter (n=153) and land-plant isolates (n=33) of ? = -2.3 and -2.9 , respectively. The shift was observed within palynological Zone I, which is temporally well-correlated with our previous work. Using an empirical relationship between ?13Cplant and ?13Catm, we calculated ??13Catm = -2.1 to -2.6 during the early Aptian from the Arundel Clay shift. Given the probable composition of the early Cretaceous atmosphere, mass balance calculations favor a methane hydrate release as the cause of this excursion. In consideration of a mechanism for methane release, we calculated changes in global subduction indicated by the well-established and rapid 2-fold increase in seafloor production that was unique within the early Aptian compared to the last 144 million years. We show that increased frictional interaction between overriding and subducting plates caused uplift and compression sufficient to continuously destabilize a portion of the probable methane hydrate reservoir, thus creating a perturbation in the C-isotope record of the Aptian atmosphere, as reflected in the ?13C of terrestrial photosynthesizers. The Aptian methane release is a new example of mechanistic coupling between major tectonic events and the global biosphere.

Jahren, H.; Conrad, C.; Arens, N.

2005-12-01

114

Plate Tectonics, Sea-Floor Spreading, and Continental Drift.  

National Technical Information Service (NTIS)

Over the past decade a geologic revolution has transpired. It can be summarized in the expression, 'the new global tectonics,' or more succinctly as plate tectonics. This, in turn, involves sea-floor spreading, descending lithospheric slabs, transform fau...

R. S. Dietz

1972-01-01

115

Voyage Through Time: Plate Tectonics Flipbook  

NSDL National Science Digital Library

This activity will enable students to view the breakup of the super-continent Pangaea over the past 190 million years and chart the subsequent movement of land masses, and to better understand plate tectonics. Students are provided with copies of map sheets with frames which are reconstructed maps of the land masses that existed on Earth at a specific time. Beginning with frame 20 and working backwards students identify the land masses listed in an available table. By assigning different land masses to different groups, the students will be able to share their results when the flipbooks are completed and several different continental movements and tectonic interactions will be illustrated on the different flipbooks. All required maps and tables are provided at this site.

Braile, Larry; Braile, Sheryl

116

This Dynamic Earth: The Story of Plate Tectonics  

NSDL National Science Digital Library

The US Geological Survey provides an online version of the book, This Dynamic Earth: The Story of Plate Tectonics. Topics discussed in the text are Historical perspective, Developing the theory, Understanding plate motions, "Hotspots":Mantle thermal plumes, and Plate tectonics and people, among others. Each section provides summaries and images of the discussed topic.

117

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.

118

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

119

Mars crustal magnetism, plate tectonics, and more  

NASA Astrophysics Data System (ADS)

Mars has no global magnetic field of internal origin, but must have had one in the past when the crust acquired intense magnetization, presumably by cooling in the presence of an Earth-like magnetic field (thermoremanent magnetization or TRM). The Mars crust is at least an order of magnitude more intensely magnetized than that of the Earth. The apparent lack of magnetization associated with major impact basins suggests that the crust acquired magnetic remanence early in its history, about 4 billion years ago. A new map of the magnetic field of Mars, compiled at 400 km mapping altitude by Mars Global Surveyor, is presented here. The spatial resolution and sensitivity of this global map is unprecedented, inviting geologic interpretation heretofor reserved for aeromagnetic and ship surveys on Earth. These data provide new insight into the origin and evolution of the Mars crust. The apparent lack of magnetization associated with volcanic provinces may indicate that the magnetic layer resides within a few km of the surface, requiring magnetization intensity of order few 100 A/m, almost unthinkable. Two parallel great faults are identified in Terra Meridiani by offset magnetic field contours. They appear similar to transform faults that occur in oceanic crust on Earth, and describe the relative motion of two ancient Mars plates on the surface of a sphere. The magnetic imprint in Meridiani is consistent with that observed above a mid-ocean ridge on Earth. It is a relic of an era of plate tectonics on Mars, an era of crustal spreading, rifting, plate motions, and widespread volcanism following the demise of the dynamo. We present this new data in the context of the early development of plate tectonics on Earth, as advanced by the Vine-Matthews hypothesis and the work of W. Jason Morgan and others. Finally, we discuss the next logical steps in Mars exploration: magnetic surveys on global and regional scales.

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

120

Plate tectonics: Magma for 50,000 years  

NASA Astrophysics Data System (ADS)

Intrusions of magma into the crust help accommodate the divergence between tectonic plates. A magnetotelluric survey of the crust and mantle beneath Afar, Ethiopia, has identified enough magma to accommodate plate separation there for about 50,000 years.

Buck, W. Roger

2013-10-01

121

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

122

Plate tectonics, surface mineralogy, and the early evolution of life  

Microsoft Academic Search

In addition to the accepted roles of plate tectonics in regulating planetary habitability through the composition of the atmosphere and temperature, and creating continents to enhance land-based evolution and biodiversity, it has a hitherto unexplored role in influencing surface mineralogy with possible implications for early evolution. Plate tectonics creates continents through the accretion of buoyant granitic crust. Erosion of the

J. Parnell

2004-01-01

123

Inevitability of Plate Tectonics on Super-Earths  

Microsoft Academic Search

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 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

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

2007-01-01

124

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

Microsoft Academic Search

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

J. Marvin Herndon

2005-01-01

125

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

2012-01-18

126

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

NASA Astrophysics Data System (ADS)

Our understanding of lithospheric evolution and global plate motions throughout the Earth's history is based largely upon detailed knowledge of plate boundary structures, inferences about tectonic regimes, ocean isochrons and palaeomagnetic data. Most currently available plate models are either regionally restricted or do not consider palaeogeographies in their construction. Here, we present an integrated methodology in which derived hypotheses have been further refined using global and regional palaeogeographic, palaeotopological and palaeobathymetric maps. Iteration between our self-consistent and structurally constrained global plate model and palaeogeographic interpretations which are built on these reconstructions, allows for greater testing and refinement of results. Our initial structural and tectonic interpretations are based largely on analysis of our extensive global database of gravity and magnetic potential field data, and are further constrained by seismic, SRTM and Landsat data. This has been used as the basis for detailed interpretations that have allowed us to compile a new global map and database of structures, crustal types, plate boundaries and basin definitions. Our structural database is used in the identification of major tectonic terranes and their relative motions, from which we have developed our global plate model. It is subject to an ongoing process of regional evaluation and revisions in an effort to incorporate and reflect new tectonic and geologic interpretations. A major element of this programme is the extension of our existing plate model (GETECH Global Plate Model V1) back to the Neoproterozic. Our plate model forms the critical framework upon which palaeogeographic and palaeotopographic reconstructions have been made for every time stage in the Cretaceous and Cenozoic. Generating palaeogeographies involves integration of a variety of data, such as regional geology, palaeoclimate analyses, lithology, sea-level estimates, thermo-mechanical events and regional tectonics. These data are interpreted to constrain depositional systems and tectonophysiographic terranes. Palaeotopography and palaeobathymetry are derived from these tectonophysiographic terranes and depositional systems, and are further constrained using geological relationships, thermochronometric data, palaeoaltimetry indicators and modern analogues. Throughout this process, our plate model is iteratively tested against our palaeogeographies and their environmental consequences. Both the plate model and the palaeogeographies are refined until we have obtained a consistent and scientifically robust result. In this presentation we show an example from Southeast Asia, where the plate model complexity and wide variation in hypotheses has huge implications for the palaeogeographic interpretation, which can then be tested using geological observations from well and seismic data. For example, the Khorat Plateau Basin, Northeastern Thailand, comprises a succession of fluvial clastics during the Cretaceous, which include the evaporites of the Maha Sarakham Formation. These have been variously interpreted as indicative of saline lake or marine incursion depositional environments. We show how the feasibility of these different hypotheses is dependent on the regional palaeogeography (whether a marine link is possible), which in turn depends on the underlying plate model. We show two models with widely different environmental consequences. A more robust model that takes into account all these consequences, as well as data, can be defined by iterating through the consequences of the plate model and geological observations.

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

2012-04-01

127

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

128

Plate tectonics and hotspots: the third dimension.  

PubMed

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

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

1992-06-19

129

Plate Tectonic Models for Orogeny at Continental Margins  

Microsoft Academic Search

IN the theory of plate tectonics convergent plate junctures are the loci of orogeny1, marked surficially by arc-trench systems2, and the margin of one plate is consumed in a trench subduction zone. The overriding or consuming plate margin is characterized by a magmatic belt supporting both arc volcanism and batholithic intrusion at crustal levels. For rock assemblages formed within active

William R. Dickinson

1971-01-01

130

This Dynamic Earth: the Story of Plate Tectonics  

NSDL National Science Digital Library

This booklet gives a brief introduction to the concept of plate tectonics and complements the visual and written information in the map entitled This Dynamic Planet, which was published in 1994 by the U.S. Geological Survey (USGS) and the Smithsonian Institution. The booklet highlights some of the people and discoveries that advanced the development of the theory and traces its progress since its proposal. Although the general idea of plate tectonics is now widely accepted, many aspects still continue to confound and challenge scientists. Chapter headings include; Historical perspective, Developing the theory, Understanding plate motions, Hotspots : Mantle thermal plumes, Some unanswered questions, and Plate tectonics and people.

2000-01-01

131

Constraints on the Character of Plate Tectonics From the Study of Diffuse Plate Boundaries  

Microsoft Academic Search

While the main global expression of tectonics at Earth's surface is that of plate tectonics, i.e., narrow boundaries between rigid plates, a significant fraction of the lithosphere (perhaps 15% of both ocean basins and continents) is undergoing diffuse deformation. The existence of these zones of deformation (often termed ``diffuse plate boundaries'') raises the question of why the majority of deformation

R. G. Gordon; S. Zatman

2001-01-01

132

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

133

Driving forces of plate tectonics and the importance of inertia  

NSDL National Science Digital Library

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

Forsyth, Donald

134

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

135

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

136

Mantle plume heads and the initiation of plate tectonic reorganizations  

Microsoft Academic Search

We present results of numerical simulations which examine the plausibility of a reorganization of plate motions brought about by the interaction of a hot, low-viscosity plume head with the underside of a tectonic plate. A numerical model of highly viscous fluid flow driven by thermal buoyancy is employed to examine the interaction of mantle plumes with surface plates in a

James Todd Ratcliff; David Bercovici; Gerald Schubert; Loren W. Kroenke

1998-01-01

137

The Relation Between Mantle Dynamics and Plate Tectonics: A Primer  

Microsoft Academic Search

We present an overview of the relation between mantle dynam- ics and plate tectonics, adopting the perspective that the plates are the surface manifestation, i.e., the top thermal boundary layer, of mantle convection. We review how simple convection pertains to plate formation, regarding the aspect ratio of convection cells; the forces that drive convection; and how internal heating and temperature-dependent

David Bercovici; Yanick Ricard; Mark A. Richards

2000-01-01

138

The generation of plate tectonics on a planet  

Microsoft Academic Search

A major question in Earth and planetary science is why does Earth exhibit plate tectonics and the other terrestrial planets do not? The difference in tectonic behavior between Earth and Venus is even more striking given their similarity in size, composition, and average density. While our general knowledge of material behavior suggests that all the terrestrial planets, Earth included, should

William Landuyt III

2009-01-01

139

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

140

Martian Rifting in the Absence of Plate Tectonics?  

NASA Astrophysics Data System (ADS)

We investigate the stresses necessary to induce rifting in the Thaumasia Highlands. We show that forces connected to plate tectonics need not be invoked to explain the observed lithosphere-scale faulting and present an alternative scenario.

Grott, M.; Hauber, E.; Kronberg, P.

2007-07-01

141

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

Microsoft Academic Search

Textbooks frequently extol plate tectonics theory without questioning what\\u000amight be wrong with the theory or without discussing a competitive theory. How\\u000acan students be taught to challenge popular ideas when they are only presented\\u000aa one-sided view? In just a few pages, I describe more than a century of\\u000ageodynamic ideas. I review what is wrong with plate tectonics

J. Marvin Herndon

2005-01-01

142

An Introduction to the ABCs of Plate Tectonics  

NSDL National Science Digital Library

This introduction to plate tectonics covers plates and boundaries, subduction zones, colliding continents, plumes, and earthquakes. There is also more advanced material on buoyancy, floating continents, and rates of isostasy; sedimentation, continental growth, rifts and creation of continental margins, passive and active margins, and island arcs and back-arc basins; continental collision, folding of sedimentary layers, and collision of cratons; and the mechanism of plate tectonics including convective mantles, convection models, distribution of plumes, plume driven convection, plate rifting models, and triple junctions.

Blanchard, Donald

143

Computational methods for calculating geometric parameters of tectonic plates  

Microsoft Academic Search

Present day and ancient plate tectonic configurations can be modelled in terms of non-overlapping polygonal regions, separated by plate boundaries, on the unit sphere. The computational methods described in this article allow an evaluation of the area and the inertial tensor components of a polygonal region on the unit sphere, as well as an estimation of the associated errors. These

Antonio Schettino

1999-01-01

144

The conditions for plate tectonics: what went wrong everywhere else  

Microsoft Academic Search

A necessary precursor for the onset of plate tectonics on a terrestrial planet is that the intrinsic system stresses, generally associated with buoyancy anomalies, are great enough to overcome the resistance of the lithosphere to deformation. On Earth, these stresses are generally associated with the subduction of oceanic lithosphere - leading to the notion that the plates drive themselves. On

M. Jellinek; C. O'Neill; A. Lenardic

2005-01-01

145

Plate tectonics and the Gulf of California region  

Microsoft Academic Search

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

N. Schmidt

1990-01-01

146

Some remarks on geodetic methods useful for plate tectonic research  

Microsoft Academic Search

Geometric and dynamic geodetic observations are discussed with respect to their ability to monitor plate tectonic processes. Various evaluation models are summarized, and their possible application to geodynamics is discussed. The present day capabilities of available geodetic data do not fulfill the requirements for describing the global plate dynamics, but existing and forthcoming techniques should provide improved data for this

H. Drewes

1984-01-01

147

Modelling continental deformation within global plate tectonic reconstructions  

Microsoft Academic Search

A limitation of regional and global plate tectonic models is the way continental deformation is represented. Continental blocks are typically represented as rigid polygons - overlaps or gaps between adjacent continental blocks represent extension or compression respectively. Full-fit reconstructions of major ocean basins result in large overlaps between the conjugate continental plates, on the basis that the continental margins are

S. Williams; J. Whittaker; C. Heine; P. Mller

2010-01-01

148

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

Microsoft Academic Search

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

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

1996-01-01

149

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

150

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

151

A new compilation of plate tectonics in the Indian Ocean  

NASA Astrophysics Data System (ADS)

A new compilation of plate tectonics in the Indian Ocean is presented. It is based on a synthesis of all magnetic anomaly interpretations and on the identifications of fracture zone in the most recent satellite gravity data. We detail the development of the Indian Ocean by 12 phases. The analysis solves all the problems of gaps and overlaps between the continents that border the Indian Ocean (at a scale of about 50-100 km) and matches well the magnetic anomalies and identified fracture zones. The initial opening of the Indian Ocean started some 180 Ma ago with the breakup between Africa and Madagascar-India-Antarctica, in a northwest-southeast direction and at 160 Ma it turned to a north-south direction. This single ridge geometry continued until 140 Ma, at which time India, Antarctica and Australia all broke from each other. This new plate configuration, with two triple junctions, lasted until 120 Ma, when spreading between Africa and Madagascar stopped. At 96 Ma, a major reorganization of plate movements occurred: spreading stopped between Antarctica and Australia while spreading direction between Antarctica and India rotated by more than 40 and right lateral shear motion began between India and Madagascar. At 84 Ma, spreading started in the Mascarene Basin in a northeast-southwest direction and continued until 63 Ma. From 77 Ma to 54 Ma, spreading between Africa and Antarctica at the Southwest Indian Ridge was oblique by more than 40. At 63 Ma, spreading stopped in the Mascarene Basin and started along the Carlsberg and Central Indian ridges. This event can be interpreted as a ridge jump. The last large reorganization of plate motions in the Indian Ocean occurred at 44 Ma. At that time, spreading directions between Australia and Antarctica restarted, spreading direction between Antarctica and Africa, Madagascar and India and India and Antarctica, all rotated.

Munschy, M.; Bernard, A.; Rotstein, Y.; Ravaut, P.

2003-04-01

152

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

153

Plate Tectonics on Earth-like Planets: Implications for Habitability  

NASA Astrophysics Data System (ADS)

Plate tectonics has been suggested to be essential for life (see e.g. [1]) due to the replenishment of nutrients and its role in the stabilization of the atmosphere temperature through the carbon-silicate cycle. Whether plate tectonics can prevail on a planet should depend on several factors, e.g. planetary mass, age of the planet, water content (at the surface and in the interior), surface temperature, mantle rheology, density variations in the mantle due to partial melting, and life itself by promoting erosion processes and perhaps even the production of continental rock [2]. In the present study, we have investigated how planetary mass, internal heating, surface temperature and water content in the mantle would factor for the probability of plate tectonics to occur on a planet. We allow the viscosity to be a function of pressure [3], an effect mostly neglected in previous discussions of plate tectonics on exoplanets [4, 5]. With the pressure-dependence of viscosity allowed for, the lower mantle may become too viscous in massive planets for convection to occur. When varying the planetary mass between 0.1 and 10 Earth masses, we find a maximum for the likelihood of plate tectonics to occur for planetary masses around a few Earth masses. For these masses the convective stresses acting at the base of the lithosphere are strongest and may become larger than the lithosphere yield strength. The optimum planetary mass varies slightly depending on the parameter values used (e.g. wet or dry rheology; initial mantle temperature). However, the peak in likelihood of plate tectonics remains roughly in the range of one to five Earth masses for reasonable parameter choices. Internal heating has a similar effect on the occurrence of plate tectonics as the planetary mass, i.e. there is a peak in the probability of plate tectonics depending on the internal heating rate. This result suggests that a planet may evolve as a consequence of radioactive decay into and out of the plate tectonics regime. References [1] Parnell, J. (2004): Plate tectonics, surface mineralogy, and the early evolution of life. Int. J. Astrobio. 3(2): 131-137. [2] Rosing, M.T.; D.K. Bird, N.H. Sleep, W. Glassley, and F. Albar (2006): The rise of continents - An essay on the geologic consequences of photosynthesis. Palaeogeography, Palaeoclimatology, Palaeoecology 232 (2006) 99-11. [3] Stamenkovic, V.; D. Breuer and T. Spohn (2011): Thermal and transport properties of mantle rock at high pressure: Applications to super-Earths. Submitted to Icarus. [4] Valencia, D., R.J. O'Connell and D.D. Sasselov (2007): Inevitability of plate tectonics on super-Earths. Astrophys. J. Let. 670(1): 45-48. [5] O'Neill, C. and A. Lenardic (2007). Geological consequences of super-sized Earths. GRL 34: 1-41.

Noack, L.; Breuer, D.

2011-12-01

154

Comments on Active Plate Tectonic Hypotheses  

Microsoft Academic Search

Hypotheses of plate motion in which the plate plays an active role in the convection process are suspect because they require the relatively thin lithosphere to transmit horizontal stresses over long distances and because there seems to be no force to produce the return flow. To judge the seriousness of the first objection, we consider a model in which an

George Z. Forristall

1972-01-01

155

Hierarchical self-organization of tectonic plates  

NASA Astrophysics Data System (ADS)

It is well known that the earth surface is divided in plates of different size and it has been already proposed by (Bird, 2003) and (Sornette and Pisarenko, 2003) that their distribution follows a fractal law. It is however controversial the origin of the size of the largest ones, whether their dimension is caused by coupling with mantle convection or due to a fragmentation process as well. We investigate the time evolution of the distribution of plate size in the last 140Ma employing the most up-to-date available reconstructions of plate boundary. We find that (1) the distribution of the largest plates and of the smallest plates are always decoupled in the last 45Myrs and therefore they respond to different physical mechanisms; (2) the distribution of the smallest plates is relatively constant in the last 45Myrs and corresponds to a fragmentation law, confirming what envisaged by Bird; (3) a power law type distribution of the largest plates in the last 140Myrs has been detected for the first time, involving no more then 7-8 plates but being always a robust verifiable feature; (4) the fluctuations of the power law exponent for the largest plates oscillate in a timeframe of tens of millions of years, reaching a maximum of almost one about 60-50Ma, and a minimum of almost zero 110-100Ma: this last tessellation corresponds to a perfect Benard convection; (5) the growth, mostly in the period 100-80Ma, is much faster then the following relaxation and seems to indicate a pulsation, probably due to a radical change in the dynamics of the Earth deep interiors.

Morra, Gabriele; Mueller, Dietmar; Seton, Maria

2010-05-01

156

The secular variantion of longitudes and plate tectonic motion  

Microsoft Academic Search

SummaryAccording to the plate tectonic theory of Le Pichon [1968] we summarized the absolute values of the angular rate of rotation\\u000a of the Eurasia and America plates determined by astronomical latitude observations. The authors then tried to use the data\\u000a of longitude observation so far available to emphasize the existence of similar crust movements. The analysis of longitude\\u000a data has

E. Proverbio; V. Quesada

1974-01-01

157

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.

158

Alfred Wegener, from research in Greenland to plate tectonics  

Microsoft Academic Search

The life of the most famous German Polar researcher is described. The investigations during his four journeys to Greenland are considered in detail. Through his hypothesis concerning the drift of the continents derived from localizations in the Polar region and the collection of numerous arguments of various geoscientific aspects Alfred Wegener has stimulated the modern, mobilistic conception of plate tectonics.

G. Stblein

1983-01-01

159

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

160

Plate tectonic reconstruction of the Carpathian-Pannonian region  

Microsoft Academic Search

Plate tectonics of the Carpathian area is controlled by microcontinents between the European and African margins and the relative movements of these margins. Beside the generally accepted Apulian (Austroalpine, West Carpathian, Dinaric) microcontinents two others: the Bihor-Getic (Tisza) and Drina-Ivanjica are introduced. The first was attached to the European margin, the second to the Apulian microcontinent. During Permian a major

L. Csontos; A. Vrs

2003-01-01

161

Plate tectonics, surface mineralogy, and the early evolution of life  

NASA Astrophysics Data System (ADS)

In addition to the accepted roles of plate tectonics in regulating planetary habitability through the composition of the atmosphere and temperature, and creating continents to enhance land-based evolution and biodiversity, it has a hitherto unexplored role in influencing surface mineralogy with possible implications for early evolution. Plate tectonics creates continents through the accretion of buoyant granitic crust. Erosion of the granites yields specific minerals including quartz, radioactive (uranium-, thorium-bearing) phases and phosphates, which could play a role in early evolution. Radioactive grains could help to concentrate carbon and increase its complexity through irradiation-induced polymerization at the prebiotic stage, and possibly influence mutation rates once life was established. Weathering of phosphate minerals was an important source of phosphorus for the biochemistry that is essential to life. Quartz-rich sands provide a translucent refuge for early photosynthesizers below the harmful effects of ultra-violet irradiation at the surface. Uranium is also important to the development of nuclear power in an advanced civilization. The mineralogy that engenders these processes is distinct from that to be expected on a planet without plate tectonics, where volcanogenic sediments would predominate, and further emphasizes the importance of plate tectonics to the evolution of life.

Parnell, J.

2004-04-01

162

Scaling of plate tectonic convection with pseudoplastic rheology  

Microsoft Academic Search

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.

Jun Korenaga

2010-01-01

163

Scaling of Convection and Plate Tectonics in Super-Earths  

Microsoft Academic Search

The discovery of three Super-Earths around different stars, possible only in the last year, prompts us to study the characteristics of our planet within a general context. The Earth, being the most massive terrestrial object in the solar system is the only planet that exhibits plate tectonics. We think this might not be a coincidence and explore the role that

D. C. Valencia; R. J. O'Connell; D. D. Sasselov

2006-01-01

164

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

165

The ERESE Project: Modeling Inquiry-Based Plate Tectonic Lessons  

Microsoft Academic Search

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

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

2004-01-01

166

Generation of Plate Tectonics via Grain-Damage  

Microsoft Academic Search

The physics of shear localization in the lithosphere is an essential ingredient for understanding how and whether plate tectonics is generated from mantle convection on terrestrial planets. Grainsize reduction and subsequent softening is a leading candidate for lithospheric localization. Such a mechanism is appealing because it can work over most lithospheric depths, has memory effects that permit dormant weak zones

D. Bercovici; Y. R. Ricard

2010-01-01

167

A Model for Plate Tectonic Evolution of Mantle Layers  

Microsoft Academic Search

In plate tectonic theory, lithosphere that descends into the mantle has a largely derivative composition, because it is produced as a refractory residue by partial melting, and cannot be resorbed readily by the parent mantle. We suggest that lithosphere sinks through the asthenosphere, or outer mantle, and accumulates progressively beneath to form an accretionary mesosphere, or inner mantle. According to

W. R. Dickinson; W. C. Luth

1971-01-01

168

A citation study of significant papers in plate tectonics  

Microsoft Academic Search

A consideration of the use made of selected papers in physical oceanography, magnetic stratigraphy, and earthquake distribution traces the development of the ideas necessary to the theory of plate tectonics, the presently accepted theory to explain geologic processes. The citation analysis undertaken of some thirty significant papers supports a previously proposed revolution m earth science thinking in the early 1970s.

A. P. W. Hodder; C. Balog

1984-01-01

169

Applicability of Plate Tectonics to Pre-Mesozoic Time  

Microsoft Academic Search

Plate tectonic theory has provided a synthesis to account for the geological development of the Earth's crust during the past 10% of its history. Doubts are now being expressed, however, about the applicability of this theory to the origin of some zones of deformed Precambrian rocks.

J. C. Briden

1973-01-01

170

Continental Rifting and the Implications For Plate Tectonic Reconstructions  

Microsoft Academic Search

Previous plate tectonic reconstructions have tried to recreate the pre-rifiing (Pangea) configuration of the continents by matching contours or lineaments that are thought to represent the continental boundaries. Such reconstructions have the inherent assumptions that no extension occurs within the continent during rifting, that the continental boundaries are isochrons, and that the continents rift without distortion. This paper proposes a

Gregory E. Vink

1982-01-01

171

The Onset of Plate Tectonics on Super-Earths Using a Damage Rheology  

Microsoft Academic Search

Numerical simulations of mantle convection with a damage - grainsize feedback are used to develop scaling laws to predict conditions at which super-Earths would have plate tectonics. Plate tectonics on a terrestrial planet requires some form of lithospheric weakening, which is typically thought of in terms of yielding or failure. However, all mechanisms for achieving plate tectonic style convection rely

B. J. Foley; D. Bercovici; W. Landuyt

2010-01-01

172

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.

173

Visual Abilities and Misconceptions About Plate Tectonics  

Microsoft Academic Search

Diagrams, drawings, and pictures are prototypical representations of concepts. Students' drawings of their concepts of convergent plate boundaries provided an efficient means of discovering some widely held misconceptions. Over 600 general education students' drawings of continent -continent convergent boundaries reveal two common misconceptions. Approximately one-third drew a continent-continent convergent boundary with concave slabs of continental crust as one might imagine

Duncan F. Sibley

174

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

175

The conditions for plate tectonics: what went wrong everywhere else  

NASA Astrophysics Data System (ADS)

A necessary precursor for the onset of plate tectonics on a terrestrial planet is that the intrinsic system stresses, generally associated with buoyancy anomalies, are great enough to overcome the resistance of the lithosphere to deformation. On Earth, these stresses are generally associated with the subduction of oceanic lithosphere - leading to the notion that the plates drive themselves. On planets without existing plate tectonics, the most significant buoyancy anomalies are associated with the formation and sinking of cold downwelling 'thermals'. The question we address is under what conditions are stresses associated these cold thermals sufficient to initiate failure of the lithosphere? Lithospheric strength is a function of its friction coefficient and elastic thickness (or, equivalently, the depth to the brittle-ductile transition). Both and plate's yield strength, and convective stresses, depend critically on the size and thermal evolution of a planet. We use numerical simulations and scaling theory to identify conditions under which mantle convection generates lithospheric failure, for parameters appropriate to the terrestrial planets. While the Moon and Mercury are predicted to have always been in a stagnant lid regime, Earth is, predictably, in a 'failed-lid' regime. Venus and Io currently fall on the transition between the two regimes. This is consistent with an episodic-style of convection on Venus, and suggests a tectonic component of deformation on Io. Mars is in a stagnant lid regime now, and probably was for most its history; however, early Martian plate tectonics is plausible if the lithosphere was weakened by the presence of surface water during the first 500Myr of its history.

Jellinek, M.; O'Neill, C.; Lenardic, A.

2005-12-01

176

Creep of phyllosilicates at the onset of plate tectonics  

NASA Astrophysics Data System (ADS)

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 lizarditethe low temperature serpentine varietyusing 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 10-4 and 10-6 s-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 Moortle, Bertrand; Hilairet, Nadge; Wang, Yanbin

2012-09-01

177

Could Plate Tectonics Have Operated on Early Mars?  

NASA Astrophysics Data System (ADS)

We consider the likelihood of plate tectonics operating on early Mars and Earth. Crust produced by mid-ocean ridge spreading at the same potential temperature is ~ 3 times thicker on Mars than on Earth; the density contrast between crust and mantle is probably similar on the two planets. Assuming that the radiogenic heat flux is balanced by plate tectonic heat loss, the maximum mechanical boundary layer (MBL) thickness on Mars is twice as great, and plate velocities ~ 4 times slower, for similar size plates. For both planets, subduction is favoured at potential temperatures less than 1500-1600o C, where crustal thicknesses are low. The maximum MBL thickness on the present-day Earth is limited to about 100 km by the dropoff of the thermal boundary layer. The viscosity of this layer is about 1019 Pa s, probably because of the presence of melt. For a similar layer on Mars, the maximum MBL thickness would be ~ 150 km, reducing the potential temperature at which subduction could have occurred to less than ~ 1400o C. Plate velocities are probably limited by viscous drag on the descending slab, which depends on the density contrast, slab length, MBL thickness and mantle viscosity. For a slab length of 300 km, the ancient terrestrial mantle viscosity needs to be < ~ 1020 Pa s to allow the drag-limited plate velocity to remove all the heat. On early Mars, the limiting viscosity is a factor of 4 larger. Whether plate tectonics could have operated on early Mars therefore depends mainly on the viscosity structure of the mantle, which will be strongly affected by the presence or absence of water. If early Mars possessed a low viscosity zone similar to the present-day Earth's, subduction is unlikely to have occurred. In the absence of such a zone, subduction was probably easier to sustain on Mars than on Earth.

Nimmo, F.; Stevenson, D. J.

2000-10-01

178

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

179

Generation of Plate Tectonics From Spherical, Viscoplastic Convection Models  

Microsoft Academic Search

The formation of plate tectonics from mantle convection is a major, unresolved problem in geophysics. Visco- plastic models have shown success and initial spherical results were discussed by van Heck & Tackley [submitted] for a restricted parameter space. Here, we present visco-plastic, mainly internally heated, 3-D spherical convection results with temperature-dependent viscosity, and strive to explore the Rayleigh number (Ra)---yield

B. J. Foley; T. W. Becker

2008-01-01

180

Developing the plate tectonics from oceanic subduction to continental collision  

Microsoft Academic Search

The studies of continental deep subduction and ultrahigh-pressure metamorphism have not only promoted the development of solid\\u000a earth science in China, but also provided an excellent opportunity to advance the plate tectonics theory. In view of the nature\\u000a of subducted crust, two types of subduction and collision have been respectively recognized in nature. On one hand, the crustal\\u000a subduction occurs

YongFei Zheng; Kai Ye; LiFei Zhang

2009-01-01

181

Tectonics of one-plate planets  

SciTech Connect

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

Janes, D.M.

1990-01-01

182

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

Microsoft Academic Search

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

Edgardo Can-Tapia; George P. L Walker

2004-01-01

183

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

Microsoft Academic Search

Although Mars is currently not tectonically active, it may have experienced plate tectonics early in its history. The southern hemisphere of Mars possesses a thick crust which probably renders the lithosphere positively buoyant. We present numerical and scaling arguments which show that if the area of positively buoyant lithosphere grows beyond a critical fraction, plate tectonics will stop. Heat transfer

A. Lenardic; F. Nimmo; L. Moresi; M. Collier

2004-01-01

184

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

Microsoft Academic Search

The tectonic style and viability of modern plate tectonics in the early Earth is still debated. Field observations and theoretical arguments both in favor and against the uniformitarian view of plate tectonics back until the Archean continue to accumulate. Here, we present the first numerical modeling results that address for a hotter Earth the viability of subduction, one of the

Jeroen van Hunen; Arie P. van den Berg

2008-01-01

185

Creep of phyllosilicates at the onset of plate tectonics  

NASA Astrophysics Data System (ADS)

Plate tectonics occur only after the onset of subduction at the Earth's surface. Subduction initiates if a material with low yield strength is present in the otherwise stiff cold lithosphere at the thermal boundary layer with hydrosphere. 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). Previous deformation experiments on serpentine minerals for pressure up to 4 GPa suggested plastic behavior and flow strength of antigorite an order of magnitude lower than dry lithospheric rocks. However, extrapolations from laboratory strain rates (10-4-10-6 s-1) to tectonic strain rate (as low as 10-15 s-1) have large uncertainties because they are based on empirical rheological laws and the structural differences in serpentine variety may influence the deformation mechanisms and rheological behavior. We carried out high-pressure deformation experiments with in-situ stress and strain measurements on polycrystalline Elba Island lizardite - the low temperature variety of serpentine - using a Deformation-DIA apparatus coupled with monochromatic synchrotron light source (APS), at the GeoSoilEnviroCARS, Argonne National Laboratory. Fourteen deformation cycles were performed on four specimens at pressures (P) and temperatures (T) ranging from 1 to 8 GPa and 150 to 400 C, with strain rates (dot?) between 10-4 and 10-6 s-1. Thin sections were extracted parallel to the compression direction using Focused Ion Beam. TEM observations of 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.The alignment of the basal (001) planes normal to the compression axis leads to high stresses corresponding to the elastic response of crystals whose orientation precludes glide on (001). Crystals where basal planes are oblique to the compression, allowing glide on (001) show yield stress in the range 50-200 MPa with no systematic dependence with strain rate, grain size, pressure or temperature within experimental uncertainties. 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, and aseismic sliding on the plate interface below the seismogenic zone. 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, E.; Reynard, B.; Caracas, R.; Van De Moortle, B.; Hilairet, N.; Wang, Y.

2012-04-01

186

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

187

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

Microsoft Academic Search

The recent article by Jean-Claude Mareschal (``Plate Tectonics: Scientific Revolution or Scientific Program?'' in Eos, May 19, 1987, p. 529) adds to the interesting literature on the evolution of the theory of plate tectonics. It is curious that an aspect of the general theory that seems to be little considered and mentioned by Mareschal or others who write about the

Bruce R. Doe

1987-01-01

188

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

189

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

190

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

191

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

Microsoft Academic Search

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

Matthew L. Schuchardt

2010-01-01

192

The effect of continents on the initiation and configuration of plate tectonics  

Microsoft Academic Search

Numerical models of mantle convection can exhibit plate tectonics when a strongly temperature-dependent viscosity is used, which stiffens the cold upper thermal boundary layer into a rigid lid, combined with plastic behavior above a given yield stress, which allows the rigid lid to break into plates (e.g. Moresi and Solomatov, 1998; Tackley, 2000). The geometry of tectonic plates thus obtained

C. Grigne; P. J. Tackley

2006-01-01

193

Aligned buoyant highs, across-trench deformation, clustered volcanoes, and deep earthquakes are not aligned with plate-tectonic theory  

Microsoft Academic Search

Bathymetry shows the regional interaction of aseismic, buoyant highs in northern Pacific subduction zones. Seamounts, ridges, and fractures on the seaward side of the trench are associated with events that do not support the accepted plate-tectonics paradigm, including an altered slab dip angle (Benioff zone) and the clustered volcanoes and earthquakes within the convergent margin. Most of the examples in

N. Christian Smoot

1997-01-01

194

Episodic tectonic plate reorganizations driven by mantle convection  

NASA Astrophysics Data System (ADS)

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

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

2002-10-01

195

A model for plate tectonic evolution of mantle layers.  

PubMed

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

Dickinson, W R; Luth, W C

1971-10-22

196

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

ERIC Educational Resources Information Center

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

Chamberlain, Valerie Elaine

1989-01-01

197

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

198

Yin and yang of continental crust creation and destruction by plate tectonic processes  

Microsoft Academic Search

Earth's continental crust today is both created and destroyed by plate tectonic processes, a balance that is encapsulated by the traditional Chinese concept of yinyang, whereby dualities act in concert as well as in opposition. Yinyang conceptualizations of crustal growth and destruction are mostly related to plate tectonics; both occur mostly at subduction zones, by arc magmatic creation and by

Robert J. Stern; David W. Scholl

2010-01-01

199

Plate tectonics and the detection of land-based biosignatures on Mars and extrasolar planets  

Microsoft Academic Search

On Earth, surface detritus has a quartz-rich mineralogy as a consequence of plate tectonics. Rocky planets without plate tectonics, like Mars, have surface detritus derived from volcanic rocks. There is a marked contrast in the transmission of photosynthetically active radiation (PAR) through the upper few millimetres of the two sediment types. Quartz-rich sediment allows PAR to penetrate below the level

John Parnell

2005-01-01

200

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

Microsoft Academic Search

The discovery of extra-solar super-Earths has prompted interest in their possible mantle dynamics and evolution, and in whether their lithospheres are most likely to be undergoing active plate tectonics like on Earth, or be stagnant lids like on Mars and Venus. The origin of plate tectonics is poorly understood for Earth, likely involving a complex interplay of rheological, compositional, melting

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

2011-01-01

201

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

Microsoft Academic Search

The discovery of extra-solar super-Earths has prompted interest in their possible mantle dynamics and evolution, and in whether their lithospheres are most likely to be undergoing plate tectonics like on Earth, or be stagnant lids like on Mars and Venus. The origin of plate tectonics is poorly understood for the Earth, likely involving a complex interplay of rheological, compositional, melting

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

2008-01-01

202

Numerical Modeling Of Plate Tectonics Initiation And Its Style In The Early Earth  

Microsoft Academic Search

Plate tectonics is an outstanding example of a self organizing complex system, driven by the negative buoyancy of the thermal boundary layer resulting in subduction. Although the signature of plate tectonics is recognized with some confidence in the Phanerozoic geologic record of the continents, its action becomes less certain further back in time. The best way to improve our understanding

E. Sizova; T. Gerya

2008-01-01

203

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

Microsoft Academic Search

Plate tectonics on Earth is driven by the subduction and stirring of dense oceanic lithosphere into the underlying mantle. For such a regime to exist on any planet, stresses associated with mantle convection must exceed the strength of the lithosphere. This condition is sufficiently restrictive that plate tectonics currently operates only on Earth, and mantle convection in most terrestrial planets

C. O'Neill; A. M. Jellinek; A. Lenardic

2007-01-01

204

Mantle Convection and Plate Tectonics: Toward an Integrated Physical and Chemical Theory  

Microsoft Academic Search

Plate tectonics and convection of the solid, rocky mantle are responsible for transporting heat out of Earth. However, the physics of plate tectonics is poorly understood; other planets do not exhibit it. Recent seismic evidence for convection and mixing throughout the mantle seems at odds with the chemical composition of erupted magmas requiring the presence of several chemically distinct reservoirs

Paul J. Tackley

2000-01-01

205

Plate Tectonics: A Plastic as Opposed to a Rigid Body Model  

Microsoft Academic Search

The concept that the lithosphere behaves as a perfectly rigid body during plate tectonism is challenged as a fundamental rule in the theory of new global tectonics. Experimental studies in rock mechanics indicate that confining pressure, temperature, solutions, the size of masses, and strain rate produce plates of little fundamental strength which can be subjected to plastic deformation by conventional

Paul J. Roper

1974-01-01

206

Plate tectonics, energy and mineral resources: Basic research leading to payoff  

Microsoft Academic Search

We like to believe that basic research ultimately pays off in practical benefits. Yet when the theory of plate tectonics was developed during the 1960's, the prognosis for its impact on mineral prospects was generally negative. The conceptual changes of plate tectonics from old to young ocean basins and from deterministic to indeterministic geotectonic cycles were initially considered to be

Peter A. Rona

1977-01-01

207

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

208

Scaling of Convection and Plate Tectonics in Super-Earths  

NASA Astrophysics Data System (ADS)

The discovery of three Super-Earths around different stars, possible only in the last year, prompts us to study the characteristics of our planet within a general context. The Earth, being the most massive terrestrial object in the solar system is the only planet that exhibits plate tectonics. We think this might not be a coincidence and explore the role that mass plays in determining the mode of convection. We use the scaling of convective vigor with Rayleigh number commonly used in parameterized convection. We study how the parameters controlling convection: Rayleigh number (Ra), boundary layer thickness (?), internal temperature (T_i) and convective velocities (u) scale with mass. This is possible from the scaling of heat flux, mantle density, size and gravity with mass which we reported in Valencia, et. al 2006. The extrapolation to massive rocky planets is done from our knowledge of the Earth. Even though uncertainties arise from extrapolation and assumptions are needed we consider this simple scaling to be a first adequate step. As the mass of a planet increases, Ra increases, yielding a decrease in ? and an increase in u, while T_i increases very slightly. This is true for an isoviscous case and is more accentuated in a temperature dependent viscosity scenario. In a planet with vigorous convection (high u), a thin lithosphere (low ?) is easier to subduct and hence, initiate plate tectonics. The lithosphere also has to be dense enough (cold and thick) to have the bouyancy necessary for subduction. We calculate that a convective cycle for an isoviscous planet is ? ~ M^{-0.3} considering whole mantle convection. Meaning that if these planets have continents, the timescale for continental rearrangement is shorter (about half the Earth's for a 5 earth-mass planet). Additionally, we explore the negative feedback cycle between convection and temperature dependent viscosity and estimate a timescale for this effect.

Valencia, D. C.; O'Connell, R. J.; Sasselov, D. D.

2006-12-01

209

The Dynamics of Plate Tectonics and Mantle Flow: From Local to Global Scales  

Microsoft Academic Search

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

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

2010-01-01

210

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

211

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

NASA Astrophysics Data System (ADS)

Continents slowly drift at the top of the mantle, undergoing episodic events like collision, aggregation or splitting. Continental drift and oceanic plate tectonics are surface expressions of mantle convection and closely linked to the thermal state of the mantle. In the present study we will present a number of 3D spherical numerical simulations of mantle convection with self-consistently generated plates and compositionally and rheologically-distinct continents floating at the top of the mantle. We will focus on the question of how continental drift, oceanic plate tectonics and the thermal state of the Earth's mantle are linked, by using different continent configurations ranging from one supercontinent to six small continents. With a supercontinent present we find a strong time-dependence of the oceanic surface heat flow and suboceanic mantle temperature, driven by the generation of new plate boundaries. Very large oceanic plates correlate with periods of hot suboceanic mantle, while the mantle below smaller oceanic plates tends to be colder. Temperature fluctuations of subcontinental mantle are significantly smaller than in oceanic regions and caused by a time-variable efficiency of thermal insulation of the continental convection cell. With multiple continents present the temperature below individual continents is generally lower than below a supercontinent and is more time-dependent, with fluctuations as large as 15% that may be caused by continental assembly and dispersal. The periods of hot subcontinental mantle correlate with strong clustering of the continents and periods of cold subcontinental mantle, at which it can even be colder than suboceanic mantle, with a more dispersed continent configuration. Our findings with multiple continents imply that periods of partial melting and strong magmatic activity inside the continents, which may contribute to continental rifting and pronounced growth of continental crust, might be episodic processes related to the supercontinent cycle [Rolf et al., submitted]. In a further step we will investigate the effects of the mantle Rayleigh number, heating mode (internal versus basal heating), yield strength of the lithosphere and a depth-dependent viscosity structure of the mantle. Reference: Rolf, T., Coltice, N. and Tackley, P.J., Linking continental drift, plate tectonics and the thermal state of the Earth's mantle, submitted to Earth Planet Science Letters

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

2012-04-01

212

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

PubMed

Plate tectonics and convection of the solid, rocky mantle are responsible for transporting heat out of Earth. However, the physics of plate tectonics is poorly understood; other planets do not exhibit it. Recent seismic evidence for convection and mixing throughout the mantle seems at odds with the chemical composition of erupted magmas requiring the presence of several chemically distinct reservoirs within the mantle. There has been rapid progress on these two problems, with the emergence of the first self-consistent models of plate tectonics and mantle convection, along with new geochemical models that may be consistent with seismic and dynamical constraints on mantle structure. PMID:10856206

Tackley

2000-06-16

213

Conditions for Plate Tectonics on Super-Earths: Inferences From Convection Models With Damage  

NASA Astrophysics Data System (ADS)

Numerical simulations of mantle convection with a damage-grainsize feedback are used to develop scaling laws for predicting conditions at which super-Earths would have plate tectonics. In particular, the numerical simulations are used to determine how large a viscosity ratio between pristine lithosphere and mantle (?l/?m) can be offset by damage to allow mobile (plate-like) convection. Regime diagrams of ?l/?m versus the damage number (D) show that the transition from stagnant lid to mobile convection occurs for higher ?l/?m as D increases; a similar trend occurs for increasing Rayleigh number. We hypothesize a new criterion for the onset of plate tectonics on terrestrial planets: that damage must reduce the viscosity of shear zones in the lithosphere to a critical value equivalent to the underlying mantle viscosity; 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. We scale our 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 conditions are found to be 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.

Foley, B. J.; Bercovici, D.

2012-04-01

214

The conditions for plate tectonics on super-Earths: Inferences from convection models with damage  

NASA Astrophysics Data System (ADS)

Numerical simulations of mantle convection with a damage-grainsize feedback are used to develop scaling laws for predicting conditions at which super-Earths would have plate tectonics. In particular, the numerical simulations are used to determine how large a viscosity ratio between pristine lithosphere and mantle (?l/?m) can be offset by damage to allow mobile (plate-like) convection. Regime diagrams of ?l/?m versus the damage number (D) show that the transition from stagnant lid to mobile convection occurs for higher ?l/?m as D increases; a similar trend occurs for increasing Rayleigh number. We hypothesize a new criterion for the onset of plate tectonics on terrestrial planets: that damage must reduce the viscosity of shear zones in the lithosphere to a critical value equivalent to the underlying mantle viscosity; 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. We scale our 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 conditions are found to be 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.

Foley, Bradford J.; Bercovici, David; Landuyt, William

2012-05-01

215

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

216

Thin-Skinned Plate-Tectonic Model for Collision-Type Orogenesis.  

National Technical Information Service (NTIS)

The plate-tectonic theory postulates the presence of three elements in a mountain-belt: (1) overriding plate, (2) suture, and (3) underthrusting plate. A thin-skinned model for collision type of mountain ranges suggests that both the overriding and undert...

K. J. Hsue

1980-01-01

217

A hot-plate tectonic model for Proterozoic crustal evolution in Australia  

Microsoft Academic Search

Proterozoic terranes in Australia record complex tectonic histories in the interval 2000-1100 Ma, that have previously been interpreted using simple intracratonic or plate-tectonic models. However these models cannot fully account for: (1) repeated tectonic reactivation (both orogenesis and rifting); (2) large aspect-ratio orogenic belts; (3) mainly high temperature-low pressure metamorphism; (4) rifting and sag giving thick sedimentary basins; (5) the

S. McLaren; R. Powell

2003-01-01

218

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

Microsoft Academic Search

Apatite fission track analysis was performed on 56 samples from central Spain to unravel the far field effects of the Alpine plate tectonic history of Iberia. The modelled thermal histories reveal complex cooling in the Cenozoic, indicative of intermittent denudation. Accelerated cooling events occurred across the Spanish Central System (SCS) from the Middle Eocene to Recent. These accelerated cooling events

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

2002-01-01

219

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

220

Hadean Crustal Processes and the Transition to Phanerozoic-style Plate Tectonics  

Microsoft Academic Search

Tectonic processes on the early Earth were controlled largely by heat transfer from the deep Earth to the surface. Thermal modeling shows that convective heat transfer driven by heating from below results in hot material rising in columns, which is thought to be the dominant mode of Hadean heat transfer. In contrast, Phanerozoic-style plate tectonics probably requires liquid water to

K. Andreasen; J. W. Shervais

2006-01-01

221

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

Microsoft Academic Search

Although Mars is currently not tectonically active, it may have experienced plate tectonics early in its history. The southern hemisphere of Mars possesses a thick crust which probably renders the lithosphere positively buoyant. In this paper we present numerical and scaling arguments which show that if the area of positively buoyant lithosphere grows beyond a critical fraction (?50% for Mars),

A. Lenardic; F. Nimmo; L. Moresi

2004-01-01

222

Transitions in Tectonic Mode Based on Calculations of Self-Consistent Plate Tectonics in a 3D Spherical Shell  

Microsoft Academic Search

In the past decade, several studies have documented the effectiveness of plastic yielding in causing a basic approximation of plate tectonic behavior in mantle convection models with strongly temperature dependent viscosity, strong enough to form a rigid lid in the absence of yielding. The vast majority of such research to date has been in either two-dimensional, or three-dimensional cartesian geometry.

H. van Heck; P. Tackley

2008-01-01

223

Transitions in Tectonic Mode based on calculations of self-consistent plate tectonics in a 3D spherical shell  

Microsoft Academic Search

In the past decade, several studies have documented the effectiveness of plastic yielding in causing a basic approximation of plate tectonic behavior in mantle convection models with strongly temperature dependent viscosity, strong enough to form a rigid lid in the absence of yielding. The vast majority of such research to date has been in either two-dimensional, or three-dimensional cartesian geometry.

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

2009-01-01

224

Transitions in tectonic mode based on calculations of self-consistent plate tectonics in a 3D spherical shell  

Microsoft Academic Search

In the past decade, several studies have documented the effectiveness of plastic yielding in causing a basic approximation of plate tectonic behavior in mantle convection models with strongly temperature dependent viscosity, strong enough to form a rigid lid in the absence of yielding. The vast majority of such research to date has been in either two-dimensional, or three-dimensional cartesian geometry.

Hein van Heck; Paul Tackley

2010-01-01

225

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

226

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

ERIC Educational Resources Information Center

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

King, Chris

2000-01-01

227

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

228

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

Microsoft Academic Search

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

Robert Reilinger; Simon McClusky

2011-01-01

229

Plume And Plate Tectonics Mechanisms: Mutual Influence, Interference, Interaction And Intertwining  

Microsoft Academic Search

The plate tectonics mechanism is commonly described as a near-horizontal mantle convection-driven movement and deformation of lithospheric plates giving birth to middle-oceanic ridges and orogens, forming new parts of thin oceanic crust in oceans and accreting new portions of thickened crust to continents. On the contrary, plume tectonics is thought to be a result of an action of quicker near-vertical

V. Puchkov

2003-01-01

230

Mantle convection models featuring plate tectonic behavior: An overview of methods and progress  

Microsoft Academic Search

Arguably, the presence of plate-tectonic-type surface motion for periods that endure over hundreds of millions of years is the primary feature a mantle convection model must possess in order to be considered Earth-like. From the early days of mantle dynamics modeling, research has been dedicated to understanding how mantle convection produces the first order observations of plate tectonics as well

Julian P. Lowman

2011-01-01

231

The effect of weak sediments and a free surface on self-consistent plate tectonics  

Microsoft Academic Search

Previous dynamic models of global mantle convection indicated that a visco-plastic rheology is successful in generating plate tectonics-like behaviour self-consistently (Moresi & Solomatov, GJI 1998; Tackley, GCubed 2000a,b). Yet these models fail to create Earth-like plate tectonics: so far in all models subduction is two-sided and more or less symmetric, whereas terrestrial subduction is one-sided and characterized by a distinctive

F. I. Lw; P. J. Tackley; T. V. Gerya

2009-01-01

232

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

233

Reconstructing plate motion paths where plate tectonics doesn't strictly apply  

NASA Astrophysics Data System (ADS)

The classical approach to reconstructing plate motion invokes the assumption that plates are rigid and therefore that their motions can be described as Eulerian rotations on a spherical Earth. This essentially two-dimensional, map view of plate motion is generally valid for large-scale systems, but is not practicable for small-scale tectonic systems in which plates, or significant parts thereof, deform on time scales approaching the duration of their motion. Such "unplate-like" (non-rigid) behaviour is common in systems with a weak lithosphere, for example, in Mediterranean-type settings where (micro-)plates undergo distributed deformation several tens to hundreds of km away from their boundaries. The motion vector of such anomalous plates can be quantified by combining and comparing information from two independent sources: (1) Balanced cross sections that are arrayed across deformed zones (orogens, basins) and provide estimates of crustal shortening and/or extension. Plate motion is then derived by retrodeforming the balanced sections in a stepwise fashion from external to internal parts of mountain belts, then applying these estimates as successive retrotranslations of points on stable parts of the upper plate with respect to a chosen reference frame on the lower plate. This approach is contingent on using structural markers with tight age constraints, for example, depth-sensitive metamorphic mineral parageneses and syn-orogenic sediments with known paleogeographic provenance; (2) Geophysical images of 3D subcrustal structure, especially of the MOHO and the lithospheric mantle in the vicinity of the deformed zones. In the latter case, travel-time seismic tomography of velocity anomalies can be used to identify subducted lithospheric slabs that extend downwards from the zones of crustal shortening to the mantle transitional zone and beyond. Synthesizing information from these two sources yields plate motion paths whose validity can be tested by the degree of consistency between crustal shortening estimates and the amount of subducted lithosphere imaged at depth. This approach has several limitations: (1) shortening values in mountain belts are usually minimum estimates due to the erosion of deformational fronts and out-of-sequence thrusting that obscure or even eliminate zones of shortening. Also, subduction may occur without accretion of material to the upper plate; (2) sedimentary ages are often loosely bracketed and only high-retentivity isotopic systems yield ages near the age of mineral formation in metamorphic rocks; (3) images of seismic velocity anomalies are highly model-dependent and the anomalies themselves may have been partly lost to thermal erosion, especially in areas that have experienced heating, for example, beneath extensional basins. Thus, only a few orogens studied so far (e.g., the circum-Mediterreanean belts) have the density of geological and geophysical data needed to constrain the translation of a sufficient number of reference points to obtain a reliable plate-motion vector. Nevertheless, this approach complements established methods for determining plate motion (plate-circuits using paleomagnetic information, ocean-floor magnetic lineaments) and provides a viable alternative where such paleomagnetic information is sparse or lacking.

Handy, M. R.; Ustaszewski, K.

2012-04-01

234

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

Microsoft Academic Search

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

Tobias Rolf; Jrg Schmalzl; Claudia Stein

2010-01-01

235

Numerical Models of Plate Tectonics and Mantle Convection in Three Dimensions  

Microsoft Academic Search

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

Carl Walter Gable

1989-01-01

236

Plate-tectonic Regulation of Faunal Diversity and Sea Level: a Model  

Microsoft Academic Search

A GROWING body of evidence and theory supports the idea that processes of plate tectonics have been operating for the past 3 109 years1. The hypothesis of ocean-driven plates implies that certain mountain systems represent the remains of former large ocean basins. An important corollary of this notion is that the history of continental assembly and fragmentation can be

J. W. Valentine; E. M. Moores

1970-01-01

237

Speculations on the Mesozoic Plate Tectonic Evolution of Eastern China  

NASA Astrophysics Data System (ADS)

Several orogenic belts transecting eastern China are the sites of former convergent plate margins, although there have been varying views on the collisional framework of individual continental blocks, styles of convergence at these zones, and the timing of respective collisions. A tectonic study of eastern China, Mongolia and the southern Soviet Far East indicates the collision of the South China Block with a combined North China-Northeast China Fold Zone Block in the Late Triassic-Early Jurassic, their collective suturing to Eurasia in the Late Jurassic-Early Cretaceous, followed by the Sikhote Alin-Japan Block in the Mid to Late Cretaceous. The evidence is as follows: (1) A linear belt of Late Triassic-Early Cretaceous granites and granodiorites trends east from the Qinlingshan through the Dabieshan to the Huaiyang massif. Ophiolites, flysch, subduction zone mlange, a paired metamorphic belt indicating north dipping subduction and marine strata of Carboniferous to Late Triassic age from the Qinlingshan define the suture between the North and South China Blocks, (2) A sinuous belt of ultramafics, blueschists, silicic to intermediate magmatism and west and north vergent folds and thrusts trend from the west margin of the Ordos Basin through central Inner Mongolia and along the east Great Khingan Range to the Amur River. Coupled with a Mid Jurassic-Early Creataceous unconformity a suturing of eastern Chinese blocks to Eurasia along this zone is suggested, (3) A fold and thrust belt with ultramafics, flysch, blueschists and subduction zone mlange along the Ussuri River in northeast China indicates the suturing of the Sikhote Alin-Japan Block to Eurasia along a west dipping subduction zone in the Mid to Late Cretaceous. Similarly, a tectonic study of southern China and Southeast Asia has revealed a complex regional mosaic of suture-bounded terrains which nucleated about the eastern, western and southern margins of the Yangtze Craton during the Late Triassic and Early Jurassic. The evidence is as follows: (4) A north-south trending belt of ophiolites, blueschists, calc-alkaline volcanics and subduction zone mlange, including granites, granodiorites and strongly deformed marine strata all of Late Triassic age exposed in the Longmenshan of Sichuan merge with the Kekexilishan ophiolite zone into the Ailaoshan-Tengtiaohe ophiolite and blueschist belt in central Yunnan along which the Songban-Ganzi Complex and the Shan-Thai-Malaya Block join the Craton, and (5) A southeastern prolongation of the Ailaoshan-Tengtiaohe belt bifurcates into the southeast trending Konvoi zone of northern Vietnam and the north-south trending Pak Lay-Luang Prabang zone of Laos and eastern Thailand. Zones of ophiolite, calc-alkaline volcanics and strong Late Triassic deformation, they separate the Indosinia and Shan-Thai-Malaya Blocks from the Craton respectively. These findings differ significantly from previous interpretations of a Late Paleozoic consolidation of South-Eastern Asia as well as disputing the existence of a true Pangea.

Klimetz, Michael P.

1983-04-01

238

Collisional tectonics between the Eurasian and Philippine Sea plates from tomography evidences in Southeast China  

NASA Astrophysics Data System (ADS)

The upper mantle structure of Southeast China is important for us to understand the deformation and mantle dynamics process associated with the interaction between the Eurasian plate and Philippine Sea (PHS) slab. We determined a detailed three-dimensional P-wave velocity (Vp) structure of the crust and upper mantle down to 400 km depth beneath Southeast China by applying teleseismic tomography to 6869 high-quality P-wave arrival times. The data were collected very carefully from the original seismograms of 635 teleseismic events recorded by 65 broadband stations deployed in Southeast China. Our images show that the high-Vp PHS slab subducts toward the north along the Ryukyu trench at the latitude of about 24N and extends down to 350 km depth and even more. High-Vp anomalies are imaged in the upper mantle under central and southern Taiwan, which represent the subducted Eurasian plate. Break-off Eurasian plate at a big angle subducting eastward is revealed under central Taiwan at depths from the upper mantle to 400 km. While continuous Eurasian plate under South Taiwan is mainly imaged from the Moho down to 400 km depth, a torn mantle window within the Eurasian continent beneath central and northern Taiwan created by the northward motion of the Philippine Sea plate is the upwelling path of the asthenosphere. The tomographic images also show the low-Vp anomalies spread widely under the coastal areas of Mainland China and Taiwan Strait. The structure of the crust and upper mantle suggests that the mountain building process in the central part of Taiwan is mainly attributed to the subductioncollision tectonics at the boundary between the Eurasian continental lithosphere and the subducting oceanic lithosphere of the PHS slab.

Zheng, Hong-Wei; Gao, Rui; Li, Ting-Dong; Li, Qiu-Sheng; He, Ri-Zheng

2013-10-01

239

Initiation of plate tectonics from post-magma ocean chemical overturn  

NASA Astrophysics Data System (ADS)

We investigate the initiation of plate tectonics on Earth from thermo-chemical mantle convection after magma ocean solidification. Plate tectonics likely began early in Earth's history, based on Archean arc and back-arc rock assemblages such as greenstone belts. Furthermore, the presence of zircons as early as 4.4 Ga indicates that plate tectonics, or at least some type of surface recycling, was active on Earth soon after magma ocean solidification. However, initiating plate tectonic style surface recycling is extremely difficult. In the modern day Earth weak zones created through plate tectonic processes, such as oceanic fracture zones and dormant spreading ridges, provide nucleation points for new subduction zones, and hence the maintenance of plate tectonics. In the early Earth, prior to plate tectonics, this mechanism is absent. Therefore another process responsible for forming the lithospheric weak zones that are requisite for the initiation of plate tectonics is necessary. We hypothesize that thermo-chemical convection in the mantle immediately following magma ocean solidification will create damaged weak zones before the proto-lithosphere cools and becomes to stiff to sink back into the mantle (i.e. before a stagnant lid forms). We model an initially hot mantle, cooling from the surface such that it undergoes convective instability. We use a damage-grainsize feedback mechanism (referred to as grain-damage) for lithospheric weak zone formation; this mechanism causes lithospheric weakening due to convective stresses, similar to the psuedoplastic yield stress rheology, and allows for dormant weak zones, which psuedoplasticity does not. We also include an initially unstable compositional density profile created by chemical differentiation during magma ocean solidification. Crystal settling at the bottom of the magma ocean, and compaction of melt out of this solid layer, isolates the solidifying mantle from the chemically evolving liquid. As a result, dense material solidifies last, at the surface, and the solid mantle is chemically unstable. This chemical instability is crucial because without any chemical effects, convective instability naturally does not occur until the surface becomes cold and dense. Therefore the lithosphere becomes too stiff to subduct before convective stresses can form lithospheric weak zones through grain-damage, and a stagnant lid forms. We thus perform calculations with various compositional density gradients and amounts of damage to map out the conditions that allow weak zones to form, and assess the viability of this mechanism for initiating plate tectonics on the early Earth.

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

2011-12-01

240

Dynamic role of tectonic mlange during interseismic process of plate boundary mega earthquakes  

NASA Astrophysics Data System (ADS)

Tectonic mlange has a key role in subduction zones because its thick pile forms the plate boundary itself; therefore, the plate boundary process is nearly identical to the mlange-forming process. We examined three tectonic mlanges in the Shimanto Belt in southwest Japan to decipher their progressive deformation process with subduction, especially within the seismogenic zone. Here we report detailed observation of sandstone blocks and the strain history of the shale matrix of a sediment-dominated tectonic mlange. The necessity of tectonic mlange accompanying fossil seismogenic dcollement is unveiled. Several deformation processes continue by turn until the depth of the down-dip limit of the seismogenic zone is reached. The results support the space-time partition of deformation in terms of seismic behavior and suggest a possible candidate for a geological consequence of recently observed slow earthquakes.

Kitamura, Yujin; Kimura, Gaku

2012-09-01

241

A Simple Class Exercise on Plate Tectonic Motion.  

ERIC Educational Resources Information Center

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

Bates, Denis E. B.

1990-01-01

242

Statistical tests of recent plate tectonic units by using geodetic data  

Microsoft Academic Search

The statistical testing models of the plate tectonic units and the hypothesis of their rigidity is presented by using the\\u000a dense geodetic data, and to a certain extent the established statistic value can be regarded as a quantitative index to compare\\u000a the rigidity degrees of different blocks. The several conclusions about the global megaplates and the regional tectonics of\\u000a China

Zhi-Ping Lu; Xian-Bing Wu; Chao Zhang

1997-01-01

243

Frontiers in Computational Geophysics: Simulations of Mantle Circulation, Plate Tectonics and Seismic Wave Propagation  

Microsoft Academic Search

Recent progress in geophysical modelling of global plate tectonic, mantle convection and seismic wave propagation problems\\u000a is reviewed, while paying particular attention to novel adjoint methods for the efficient inversion of seismic and tectonic\\u000a data. Observed is that the continuing growth in high performance and cluster computing promises the crossing of long standing\\u000a barriers in the simulation of first-order geophysical

J. Oeser; H.-P. Bunge; M. Mohr; H. Igel

244

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

245

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

246

Mantle convection models featuring plate tectonic behavior: An overview of methods and progress  

NASA Astrophysics Data System (ADS)

Arguably, the presence of plate-tectonic-type surface motion for periods that endure over hundreds of millions of years is the primary feature a mantle convection model must possess in order to be considered Earth-like. From the early days of mantle dynamics modeling, research has been dedicated to understanding how mantle convection produces the first order observations of plate tectonics as well as how the plates and deep mantle interact. Fledgling studies of the effect of plates on the mantle recognized the ability of imposed plate-scale surface motion to influence global temperatures and heat flux and organize convective planform. Later studies featuring model plates with dynamically determined velocities discovered that the interaction between convection and the plates could result in cyclic plate motion patterns and other time-dependent behavior that was not manifested in systems in which dynamic plates were absent. Focussing on different aspects of system realism (with respect to terrestrial mantle convection) has spawned multiple approaches for modeling convection with dynamic integrated plates. In broadest terms, the two main approaches can be categorized as rheological modeling methods and methods utilizing evolving surface boundary conditions. Over the past dozen years, studies focussing on the former approach have steadily made progress in modeling the self-generation of plate tectonics from convection dynamics. Continual advances have been encouraging, and a consensus is beginning to form regarding the necessary requirements for obtaining the primary elements of plate-like surface motion. However, despite significant progress, the generation of plates over long periods has not yet been modeled with Earth-like convective vigor. In contrast, models utilizing dynamically determined boundary conditions to achieve plate-like surface motion have relatively little difficulty with emulating terrestrial convective vigor or simulations of billions of years. Instead, their weakness is more fundamental; they can only provide insight into the reciprocating dynamics of the mantle and plates once the existence of the plates is assumed and they cannot model any aspects of the dynamics responsible for the origin of the plates. This paper briefly reviews the evolution of mantle convection models featuring plates and examines the progress that has been made in our understanding of the feedback between the mantle and plate tectonics through the use of both rheological and boundary condition modeling methods. Common findings, recent advances and unbridged problems are identified and discussed.

Lowman, Julian P.

2011-09-01

247

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

248

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

SciTech Connect

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

Boudjema, A.; Tremolieres, P.

1988-01-01

249

Plate tectonic origin for the Cape Fold Belt?  

Microsoft Academic Search

SEVERAL theories based on geological findings have been proposed for the origin of the Cape Fold Belt1-3. An understanding of the tectonic conditions leading to the folding is not only of academic importance, but may be valuable in assessing the possibilities of finding oil in the southern Karroo.

J. H. de Beer; J. S. V. van Zijl

1974-01-01

250

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

251

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

Microsoft Academic Search

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

H. van Heck; P. Tackley

2007-01-01

252

Numerical Modeling Of Plate Tectonics Initiation And Its Style In The Early Earth  

NASA Astrophysics Data System (ADS)

Plate tectonics is an outstanding example of a self organizing complex system, driven by the negative buoyancy of the thermal boundary layer resulting in subduction. Although the signature of plate tectonics is recognized with some confidence in the Phanerozoic geologic record of the continents, its action becomes less certain further back in time. The best way to improve our understanding of the early Earth is to combine our knowledge from petrological data and facilities of numerical modeling. Based on 2D petrological-thermomechanical numerical model of oceanic-continental subduction (using the I2VIS code (Gerya and Yuen, 2003)) we determined sharp first order transition from modern style of subduction to transitional "pre-subduction" tectonic regime at upper mantle temperature rising by around 160C above the present one. This condition roughly corresponds to upper bound for Neoarchean (about 3Ga) mantle temperature (Davies, 1993; Komiya et al., 1999). In the "pre-subduction" tectonic regime plates are strongly internally deformable by intense percolation of melts continuously generated from underlying partially molten mantle. Their convergence results in shallow underthrusting of continental crust by oceanic plate. Oceanic plate goes quite far (to 200 km) under continental crust moving away and folding continental lithospheric mantle. In some experiments after the underthrusting oceanic plate starts to sink into the mantle forming at first stages two-sided subduction. In contrast to present time in the hotter "pre-subduction" regime there is no formation of backarc basin and new spreading center (the same was assumed by de Wit, 1998 for Archean time). Relatively shallow and hot tectonic style dominates. Oceanic plates weakened by sub- lithospheric melts are subjected to buckling and shallow undethrusting (rather then subduction) associated by local melting. This triggers formation of characteristic metamorphic and magmatic rocks found in Archean (such as, ultra-high-temperature and eclogite-high-pressure granulites, adakites and granitoids). Further increase in the mantle temperature (by around 250C above present) causes transition from "pre- subduction regime" to "horizontal-tectonics" regime. At this stage horizontal movements of small deformable plate fragments are predominant and even shallow underthrusts do not form under imposed convergence. Our experiments also show that apart of mantle temperature another crucial parameter controlling the tectonic regime is degree of lithospheric weakening induced by upward movement of extracted sub- lithospheric melts. At the high Archean mantle temperatures when melts are always present in the upper mantle lithospheric weakening by melts should be low to preserve coherency of the plates and to allow stable subduction. Neither increasing radiogenic heat production nor lithospheric weakening by slab derived fluids has notable effects for the identified transitions in the early Earth.

Sizova, E.; Gerya, T.

2008-12-01

253

Mountain belt growth inferred from histories of past plate convergence: A new tectonic inverse problem  

NASA Astrophysics Data System (ADS)

Past plate motions display a range of variability, including speedups and slowdowns that cannot easily be attributed to changes in mantle related driving forces. One key controlling factor for these variations is the surface topography at convergent margins, as previous modeling shows that the topographic load of large mountain belts consumes a significant amount of the driving forces available for plate tectonics by increasing frictional forces between downgoing and overriding plates. Here we use this insight to pose a new tectonic inverse problem and to infer the growth of mountain belts from a record of past plate convergence. We introduce the automatic differentiation method, which is a technique to produce derivative code free of truncation error by source transformation of the forward model. We apply the method to a publicly available global tectonic thin-shell model and generate a simple derivative code to relate Nazca/South America plate convergence to gross topography of the Andes mountain belt. We test the code in a search algorithm to infer an optimal paleotopography of the Andes 3.2 m.y. ago from the well-known history of Nazca/South America plate convergence. Our modeling results are in excellent agreement with published estimates of Andean paleotopography and support the notion of strong feedback between mountain belt growth and plate convergence.

Iaffaldano, Giampiero; Bunge, Hans-Peter; Bcker, Martin

2007-08-01

254

Three-Dimensional Variations in Tectonic Stress Along a Complex Plate Boundary: Australia-Pacific Plate Interaction in Central New Zealand  

NASA Astrophysics Data System (ADS)

In recent years, a number of regional seismological studies have determined the present-day principal tectonic stress directions at points along the Australia-Pacific plate boundary in central New Zealand. To date, however, there has not been a broader-scale study of tectonic stress that capitalises on high-quality seismological data recorded by the GeoNet monitoring system. In this study, we have computed tectonic stress parameters throughout central New Zealand (latitudes 38-43S) using a data set of almost 3500 earthquake focal mechanisms recorded by GeoNet between January 2004 and February 2011. Each earthquake has been relocated using the nationwide 3D seismic velocity model of Eberhart-Phillips et al. (2010, SRL) and the NonLinLoc algorithm of Lomax et al. (2000, Advances in Seismic Event Location). The estimated uncertainties in each hypocenter are propagated into the focal mechanism calculations, and thereby into the stress parameter estimates using Bayesian algorithms (Arnold & Townend, 2007, GJI; Walsh et al., 2009, GJI). In most regional or broader-scale studies of tectonic stress it is common to compute the azimuth of maximum horizontal compressive stress, SHmax. Here we describe a method of representing the stresses acting on dipping structures, notably the Hikurangi subduction thrust beneath the North Island, and on arbitrarily oriented cross-sections.

Townend, J.; Sherburn, S.; Arnold, R.

2011-12-01

255

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

256

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

257

Seismicity and tectonics of the subducted cocos plate  

Microsoft Academic Search

We have examined teleseismic earthquake locations reported by the International Seismological Centre (ISC) for the Middle America region and selectedd 220 as the most reliable. These hypocenters and other data are used to delineate the deep structure of the subducted Cocos Plate. The results indicate that the subducted plate consists of three major segments: Segment I extends from the Panama

George VanNess Burbach; Cliff Frohlich; Wayne D. Pennington; Tosimatu Matumoto

1984-01-01

258

Seismicity and Tectonics of the Subducted Cocos Plate  

Microsoft Academic Search

We have examined teleseismic earthquake locations reported by the International Seismological Centre (ISC) for the Middle America region and selected 220 as the most reliable. These hypocenters and other data are used to delineate the deep structure of the subducted Cocos Plate. The results indicate that the subducted plate consists of three major segments: Segment I extends from the Panama

George VanNess Burbach; Cliff Frohlich; Wayne D. Pennington; Tosimatu Matumoto

1984-01-01

259

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

260

Depth Distribution in Ocean Basins and Plate Tectonics  

Microsoft Academic Search

IN this article I shall show that relationships between the movement of lithospheric plates1-3 and the depths of the sea floor are leading towards a quantitative theory of the distribution of oceanic depths, and that some predictions can be made. Several principal lithospheric plates have now been recognized; their relative motion over the mantle is described by a rotation of

Peter A. Rona

1971-01-01

261

3-D Simulation of Tectonic Evolution in Mariana with a Coupled Model of Plate Subduction and Back-Arc Spreading  

Microsoft Academic Search

We obtained the expressions for internal deformation fields due to a moment tensor in an elastic-viscoelastic layered holf-space. This unified formulation of internal deformation fields for shear faulting and crack opening enabled us to deal with the problem of tectonic deformation at a composite type of plate boundary zones. The tectonic deformation can be ascribed to mechanical interaction at plate

A. Hashima; M. Matsu'Ura

2006-01-01

262

Discussions on the sedimentary-tectonic event and tectonic setting of the North Tarim Basin in Cryogenian-Cambrian  

NASA Astrophysics Data System (ADS)

Across the Tarim Basin, limited surface outcrops of Cryogenian to Cambrian sedimentary succession are completely exposed in the vicinity of Aksu area(Northwest Tarim), Kuruktag(Northeast Tarim)and Southwest Tarim, thus provides a unique, well preserved and accessible means by which to study the early development of the north Tarim Basin. Based on the field geological investigation in the northwestern and northeastern of Tarim Basin, with the referencing of paleomagnetism mapping and previous research, basin evolution process in Cryogenian-Cambrian is discussed according to sedimentary-tectonic event and other evidences. The major lithological types of Cryogenian-Cambrian system in Northeast Tarim are: tillite, clastic rocks(rich in organic matter) and carbonate ,with interbeds of volcanic rocks while in Northwest Tarim, the calstic rocks and carbonate are the common rock type, with tillite and volcanic interbeds in a small amount. The north margin of Tarim Block, which was a part of Rodinia supercontinent, neighboring the northwestern margin of Australia, was deeply rifted in Cryogenian-Ediacaran and developed into two rifts in the northwestern and northeastern margin, while formed a thick layer of the rift-passive margin deposits and the layer in the northwestern rift was not completely developed as the northeastern. The deepest rift-passive magin sediment which can be observed is Cryogenian-Middle Ordovician strata, and the period can be divided into Cryogenian faulted period (supercontinent rifting stage) and Ediacaran-Middle Ordovician subsidence period (plate drifting stage).

Zhou, X. B.; Li, J. H.; Li, W. S.

2012-04-01

263

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

Microsoft Academic Search

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

Masaki Yoshida; M. Santosh

2011-01-01

264

A New Tectonic Plate Model Based on ITRF2005: Implications on the Global Kinematics  

Microsoft Academic Search

Tectonic plate models have been routinely computed in the last years using space-geodetic solutions of the motions of discrete points on the Earth's surface. Such models have been referenced with respect to different realizations of the ITRS (International Terrestrial Reference System). In particular, several models were produced based on the different ITRF solutions. This is the case of DEOSVel (Fernandes

R. M. Fernandes; M. S. Bos; B. A. Ambrosius

2007-01-01

265

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

266

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

267

Platonic Plate Tectonics: On the Regularity of the Distribution of 'Triple Points' on the Earth's Surface.  

National Technical Information Service (NTIS)

The geometry of the division of the earth's surface by the major tectonic plates is remarkably regular and symmetric, and several models based on the platonic solids have been proposed to describe this pattern. Under such a model, the triple points, those...

A. J. Arnold A. F. Siegel

1981-01-01

268

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

269

Deep Water Cycle: its Role in Earth's Thermal Evolution and Plate Tectonics  

Microsoft Academic Search

Earth is unique among the terrestrial planets in our solar system because it has plate tectonics and abundant surface water. It has long been suggested that these two salient features are intimately related. New constraints on water concentrations in the Earth's interior and on mechanisms for mantle degassing and regassing have improved our knowledge of Earth's deep water cycle; however,

T. W. Becker; J. W. Crowley; M. Grault; T. Hink; A. J. Schaeffer; P. H. Barry; J. Frost; J. Girard; M. Nunez-Valdez; M. Hirschmann; S. Hier-Majumder; R. J. O'Connell

2010-01-01

270

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

ERIC Educational Resources Information Center

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

Glenn, William Harold

1992-01-01

271

Plate tectonics and convection in the Earth's mantle: toward a numerical simulation  

Microsoft Academic Search

Numerical models of mantle convection are starting to reproduce many of the essential features of continental drift and plate tectonics. The authors show how such methods can integrate a wide variety of geophysical and geological observations. The goal is to combine the Stokes and energy equations with a realistic rheology, thereby letting us understand the complex dynamic coupling that occurs

LOUIS MORESI; MICHAEL GURNIS; Shijie Zhong

2000-01-01

272

A Model of Convergent Plate Margins Based on the Recent Tectonics of Shikoku, Japan  

Microsoft Academic Search

Displacements generated by a (viscoelastic finite element) plate tectonic model are compared with and found to be compatible with geodetic survey data taken on the island of Shikoku, Japan. The model indicates that prior to the 1946 Nankaid0 earthquake, large vertical displacements occurred along the continental slope, increasing in magnitude toward and approaching a maximum of 7 m at the

Richard Edward Bischke

1974-01-01

273

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

274

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

275

From point defects to plate tectonic faults K. REGENAUER-LIEB*y, B. HOBBSz, D. A. YUEN}, A. ORDz, Y. ZHANGz, H. B. MULHAUS and G. MORRA  

Microsoft Academic Search

Understanding and explaining emergent constitutive laws in the multi-scale evolution from point defects, dislocations and two-dimensional defects to plate tectonic scales is an arduous challenge in condensed matter physics. The Earth appears to be the only planet known to have developed stable plate tectonics as a means to get rid of its heat. The emergence of plate tectonics out of

276

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

277

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

NASA Astrophysics Data System (ADS)

A fluid above the critical Rayleigh number is far from equilibrium and spontaneously organizes itself into patterns involving the collective motion of large numbers of molecules which are resisted by the viscosity of the fluid. No external template is involved in forming the pattern. In 1928 Pearson showed that Bnard's experiments were driven by variations in surface tension at the top of the fluid and the surface motions drove convection in the fluid. In this case, the surface organized itself AND the underlying fluid. Both internal buoyancy driven flow and flow driven by surface forces can be far-from-equilibrium self-organized open systems that receive energy and matter from the environment. In the Earth, the cold thermal boundary layer at the surface drives plate tectonics and introduces temperature, shear and pressure gradients into the mantle that drive mantle convection. The mantle provides energy and material but may not provide the template. Plate tectonics is therefore a candidate for a far-from-equilibrium dissipative self-organizing system. Alternatively, one could view mantle convection as the self-organized system and the plates as simply the surface manifestation. Lithospheric architecture also imposes lateral temperature gradients onto the mantle which can drive and organize flow. Far-from-equilibrium self-organization requires; an open system, interacting parts, nonlinearities or feedbacks, an outside steady source of energy or matter, multiple possible states and a source of dissipation. In uniform fluids viscosity is the source of dissipation. Sources of dissipation in the plate system include bending, breaking, folding, shearing, tearing, collision and basal drag. These can change rapidly, in contrast to plate driving forces, and introduce the sort of fluctuations that can reorganize far-from-equilibrium systems. Global plate reorganizations can alternatively be thought of as convective overturns of the mantle, or thermal weakening of plates or the asthenosphere by hot upwellings. The study of soft matter, bubble rafts, foam, fragile systems, force bridges and jamming may give insights into the physics of plate tectonics. For example, plates might be defined as "force bridges" that carry lateral compression, but dissolve and reform if the stress system changes. In the plate tectonic problem it is not clear what, if anything, is being minimized. Is it dissipation, or toroidal energy or something else? This session should stimulate new ways of thinking about plates, plate boundaries and lithospheric rheology.

Anderson, D. L.

2001-12-01

278

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

279

Seismicity and tectonics of the subducted Cocos Plate  

NASA Astrophysics Data System (ADS)

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

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

1984-09-01

280

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

281

Feedback between mountain belt growth and plate convergence revealed by forward and inverse tectonic models  

NASA Astrophysics Data System (ADS)

While it is generally assumed that global plate motions are driven by the pattern of convection in the Earth's mantle, the details of that linkage remain obscure. Bouyancy forces associated with subduction of cool, dense lithosphere at zones of plate convergence are thought to provide significant driving force, but the relative magnitudes of other driving and resisting forces are less clear. The ability to consider past as well as present plate motions provides significant additional constraints, because changes in plate motion are necessarily driven by changes in one or more driving or resisting forces, which may be inferred from independent data. Here we first exploit the capabilities of forward tectonic models of the Andean region to infer plate motion changes as far back as Miocene time. By accurately predicting observed convergence rates between Nazca and South America plates over the last 10 Myrs, we demonstrate for the first time that the topographic load of the Andes increases frictional forces between downgoing and overriding plates and thus consumes a significant amount of the driving force available for plate tectonics. This result suggests a strong feedback between mountain belt growth and plate convergence. We then test this notion by performing a numerical inversion of the same model. We use the Automatic Differentiation approach to generate a derivative code that relates convergence of the Nazca/South America plates to gross topography of the Andes mountain belt. We test the derivative code in a simple search algorithm to infer an optimal paleotopography of the Andes at 3.2 m.y. from the well-known history of Nazca/South America plate convergence. Our modeling result is in good agreement with independent published estimates of Andean paleotopography.

Iaffaldano, G.; Bunge, H.; Dixon, T. H.; Buecker, M.

2006-12-01

282

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

283

Subduction hinge migration: The backwards component of plate tectonics  

Microsoft Academic Search

There are approximately 50 distinct segments of subduction zones in the world, of which 40% have oceanic lithosphere subducting under oceanic lithosphere. All of these ocean-ocean systems are currently experiencing hinge-rollback, with the exception of 2 (Mariana and Kermadec). In hinge-rollback, the surface trace of the suduction zone (trench) is moving in the opposite direction as the plate is moving

D. Stegman; J. Freeman; W. Schellart; L. Moresi; D. May

2005-01-01

284

The Curious Decoupling of Magmatism and Plate Tectonics During the Cenozoic in Western North America: Insight From the NAVDAT Database  

NASA Astrophysics Data System (ADS)

Since the widespread acceptance of plate tectonics, magmatism in the western U.S. has been explained by subduction along the west coast of North America and destruction of the subduction system by development of the San Andreas transform fault system. However, re-analysis of space-time patterns of magmatism in western North America calls many of these inferred patterns of magmatism into question. Animation of space-time patterns found in the developing NAVDAT dataset (which currently hosts about 10,000 Cenozoic age and/or geochemical analyses; navdat.geongrid.org), demonstrates that: (1) subduction-type (e.g., intermediate) volcanism is poorly linked to the subduction system; (2) there is little evidence that slab windows controlled magmatism; (3) magmatism was clearly migratory, but not in ways that can be explained by plate-tectonic processes; and (4) magmatism was migratory at length scales ranging from 1000s of km (continental) to 10s of km (county). Several space-time patterns are evident in the NAVDAT animations, including: (1) a sweep from Montana into Nevada from 50 to about 20 Ma; (2) a clockwise sweep around the Colorado Plateau from New Mexico to southern Nevada, from about 30 to 15 Ma; (3) a burst of magmatism at about 16 Ma in northern Nevada, followed by outward sweeps to Yellowstone, central Oregon, and the Sierra Nevada; (4) a burst of magmatism in the Sierra Nevada at 3.5 Ma; and (5) several local migrations, including from Phoenix north onto the Colorado Plateau and from the San Francisco Bay area north to the Geysers geothermal field. Some of these patterns have been tied to specific events (e.g., impingement of the Yellowstone plume and Pliocene delamination), but the others are difficult to relate to plate-tectonic events. They may be caused by local tectonic events (propagating rifts?), minor convective rolls in the asthenosphere, lithospheric delamination, or delamination of a flat Laramide slab. Whatever their origin, database animation provides a powerful tool for examining these space-time patterns.

Glazner, A. F.; Walker, J. D.; Farmer, G. L.; Bowers, T. D.

2004-12-01

285

The role of liquid water in maintaining plate tectonics and the regulation of surface temperature  

NASA Astrophysics Data System (ADS)

Water plays an important role in mantle convection. In the ductile creep regime, the viscosity of wet rocks is weaker than the viscosity of dry rocks by several orders of magnitude. In the brittle regime, the most substantial effect is probably serpentinization which can reduce the friction coefficient by a factor of 2 or more. The difference between the strength of a wet lithosphere and that of a dry lithosphere seems to be big enough to control the very existence of plate tectonics. Because of dehydration due to partial melting the oceanic lithosphere is expected to be essentially dry above some critical depth, around 60-80 km. This would make the lithosphere strong enough to prevent plate motion. Percolation of water from the surface can be the main mechanism supplying water to the upper parts of the lithosphere. This implies that liquid water can be crucial for maintaining plate tectonics. On the other hand, the surface temperature is above the freezing point because of the greenhouse gases such as carbon dioxide. A simple model shows that if the blackbody temperature of the Earth is slightly below the freezing point of water, the feedback between plate tectonics, volcanism, and water and carbon cycles can result in an equilibrium state in which the surface temperature is established within the stability field of liquid water.

Solomatov, V. S.

2001-12-01

286

Feedback Between Mountain Belt Growth and Plate Convergence Revealed by Forward and Inverse Tectonic Models  

NASA Astrophysics Data System (ADS)

While it is generally assumed that global plate motions are driven by the pattern of convection in the Earth's mantle, the details of that linkage remain obscure. Bouyancy forces associated with subduction of cool, dense lithosphere at convergent zones are thought to provide significant driving force, but the relative magnitudes of other driving and resisting forces are less clear. The ability to consider past as well as present plate motions provides significant additional constraints, because changes in plate motion must be necessarily driven by changes in one or more driving or resisting forces, which may be inferred from independent data. Here we first exploit the capabilities of forward global tectonic models focused on the Andean region to infer plate motion changes as far back as Miocene time. By accurately predicting observed convergence rates between Nazca and South America plates over the past 10 Myrs, we demonstrate that the topographic load of the Andes increases resistive forces between downgoing and overriding plates and thus consumes a significant amount of the driving force available for plate tectonics. This result suggests a strong feedback between mountain belt growth and plate convergence. We then test this notion by performing a numerical inversion of the same model. We use the Automatic Differentiation approach to generate a derivative code that relates convergence of the Nazca/South America plates to gross topography of the Andes mountain belt. We test the derivative code in a simple search algorithm to infer an optimal paleotopography of the Andes at 3.2 Myrs from the well-known history of Nazca/South America plate convergence. Our modeling result is in good agreement with independent published estimates of Andean paleotopography.

Iaffaldano, G.; Buecker, M.

2009-05-01

287

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

288

Introduction to the Special Issue on Correlations Between Plate Motions and Cordilleran Tectonics  

NASA Astrophysics Data System (ADS)

This special issue contains papers that grew out of the American Geophysical Union Symposium "Models for motion of North America and plates of the Pacific basin, and the tectonic history of the western Cordilleraa search for correlations." This symposium was held in San Francisco on December 13 and 14, 1982. Forty-two papers were presented on such diverse topics as plate motion and microplate accretion histories, paleomagnetism of Cordilleran terranes and their displacement histories, the volcanic and plutonic history of the western Cordillera, and the timing of important geological episodes of regional extent (onset of extensional tectonics, onset and termination of episodes of strike slip faulting, etc.). Mechanisms of deformation within the Cordilleran continental margin were also discussed. The reader is referred to Eos Trans. AGU (vol. 63, no. 45, 1982) for the full set of abstracts.

Beck, Myrl E., Jr.

1984-04-01

289

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

Microsoft Academic Search

Five types of sedimentary basins in Kazakhstan have been recognized by using plate tectonics to reinterpret geological and geophysical data: (1) intracontinental, central pre-Caspian, above rift, south pre-Caspian; (2) passive margin, east pre-Caspian; (3) back-arc, Turgan and Sir-Daria; (4) intra-arc, north Kisil-Koum, interior, Tengis and Chu-Sarisiu; and (5) marginal, north Usturt. Paleozoic history of these basins was connected with the

Zholtayev

1994-01-01

290

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

Microsoft Academic Search

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

STAVROS T. TASSOS; DAVID J. FORD

2005-01-01

291

Mantle Convection Modeling with Viscoelastic\\/Brittle Lithosphere: Numerical Methodology and Plate Tectonic Modeling  

Microsoft Academic Search

--The earth's tectonic plates are strong, viscoelastic shells which make up the outermost part of a thermally convecting, predominantly viscous layer. Brittle failure of the lithosphere occurs when stresses are high. In order to build a realistic simulation of the planet's evolution, the complete viscoelastic\\/brittle convection system needs to be considered. A particle-in-cell finite element method is demonstrated which can

LOUIS MORESI; FREDERIC DUFOUR; H.-B. Mhlhaus

2002-01-01

292

Mantle Convection Modeling with Viscoelastic\\/Brittle Lithosphere: Numerical Methodology and Plate Tectonic Modeling  

Microsoft Academic Search

\\u000a The earths tectonic plates are strong, viscoelastic shells which make up the outermost part of a thermally convecting, predominantly\\u000a viscous layer. Brittle failure of the lithosphere occurs when stresses are high. In order to build a realistic simulation\\u000a of the planets evolution, the complete viscoelastic\\/brittle convection system needs to be considered. A particle-in-cell\\u000a finite element method is demonstrated which can

Louis Moresi; Frdric Dufour; Hans-Bernd Mhlhaus

293

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

294

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

295

Focussing of stress by continents in 3D spherical mantle convection with self-consistent plate tectonics  

Microsoft Academic Search

3D simulations with self-consistent plate tectonics and deformable continentsIncrease of critical yield strength due to presence of continentsRegime of mantle convection depends on size and thickness of the continent

T. Rolf; P. J. Tackley

2011-01-01

296

Determination of the tectonic plate motion by satellite laser ranging in 1999-2003  

NASA Astrophysics Data System (ADS)

The paper presents results of the tectonic plates motion determination from satellite laser ranging in the period 1999-2003 The SLR station velocities were calculated from station geocentric coordinates determined from one month orbital arcs of Lageos-1 and Lageos-2 satellites for the first day of each arc The mean orbital RMS-of-fit for 5 years was equal to 15 mm The station velocities were determined for 29 stations and points in 1999-2003 it means for all SLR stations with data time span longer than 20 months The accuracy of station velocities determination varied from 0 4 mm year to 3 mm year dependent on quality of data and data span The difference of station velocities between ITRF2000 and the presented results were in the range 0-5 mm year Only for four stations Riyad Maidanak-2 Beijng and Arequipa after earthquake in 2001 the differences were statistically significant For the most stations is a good agreement with the NUVEL1A model of tectonic plates motion The significant differences were detected for stations Arequipa Concepcion Shanghai and Simosato The results differs from the model NUVEL1A in the station velocities and azimuths for South America tectonic plate and Japan

Schillak, S.; Wnuk, E.

297

Relationship between tectonic evolution of North China craton and Pacific plate subduction slab evolution since ~47 Ma  

NASA Astrophysics Data System (ADS)

The Pacific plate movement happened some obviously changes at ~47 Ma. If we only consider the Pacific plate subduction just since this time, we can find that the subduction slab can reach eastern North China after ~20My (at ~27 Ma), and the slab may be destructed completely when it reach this position (An et al., 2009, G-cubed, doi:10.1029/2009GC002562). In the 20-My-movement processes, the evolution of the cold slab can be divided into several stages with the slab is heated and destructed. In different evolution stages, the slab also can result in different effects on the overlying asthenosphere and lithosphere. The slab evolution showed some temporal consistence with the tectonic activities in the eastern North China, and also with the Japan Sea opening; Furthermore, the possible effects acted on the overlying lithosphere by the slab in different stages can interpret the tectonic events happened in eastern North China since the early Paleogene (An et al., 2011, Earth Science Frontiers, 18(3)(in Chinese with English abstract), http://www.earthsciencefrontiers.net.cn/CN/abstract/abstract4277.shtml). For example, regional lithosphere seems to be thickening, Tangshan-Xingtai faults became active but the activities of the Taihangshan Piedmont faults decreased.

An, M.

2011-12-01

298

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

299

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.

300

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

NASA Astrophysics Data System (ADS)

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

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

2001-12-01

301

Mars Crustal Magnetism: Plate Tectonics and Flood Basalts  

NASA Astrophysics Data System (ADS)

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

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

2006-12-01

302

The General Theory of Plate Tectonics; No Role for Lower Mantle Components, Thermals or Other ad hoc Adjustments  

Microsoft Academic Search

Plate tectonics introduces chemical,thermal,viscosity,melting and density inhomogeneities into the mantle and stress inhomogeneity into the plates.Idealized models often assume uniform mantle, rigid homogeneous plates,non-passive mantle, and ad hoc explanations for island chains, melting anomalies and continental breakup. Plates, however, drive and break themselves and organize the underlying mantle, in common with other cooled-from-above systems.Pressure, often ignored in simulations, suppresses thermal

D. L. Anderson; A. Meibom

2002-01-01

303

Present-day kinematics of Eastern African Rift tectonic plates using continuous and episodic GPS data  

NASA Astrophysics Data System (ADS)

This paper focuses on the tectonic setup of the East African Rift, a complex system that extends from the Afar region where the triple junction between Somalia, Nubia and Arabia plates is located to the South West Indian Ridge where the Nubia and Antarctica meets with a third tectonic unit - possibly the so-called Lwandle block which is considered by several authors as an independent unit of the Somalia plate. We present a consistent velocity field derived from continuous and episodic GPS observations. The analyzed data were obtained from several permanent stations distributed all over the African continent and surrounding regions and significantly extended with episodic data acquired in the framework of the KINEMA (KINEmatics of Margins of Africa) and other projects. Some of the available episodic observations had a significant low quality due to short observation periods and/or lack of proper re-centring during the different occupations since many of the observations were not acquired for scientific purposes. However, they have been evaluated and they are considerably contributing to densify our velocity field. The network of permanent stations also includes some stations recently installed in the framework of KINEMA. Most of them still have short data spans to properly access his linear motion. Nevertheless, they already provide valuable indications about the present-day kinematics of the blocks where they are located. The estimated angular velocities are computed with respect to ITRF2005. On the near-field, two regions are discussed in more detail: the interactions between the Nubia and the tectonic blocks of Rovuma and Lwandle in the Mozambican region (where the episodic observations are located), and the kinematics of Victoria plate in the Kenyan region. With respect to the triplet Nubia-Rovuma-Lwandle, the small number of data points associated with to the low magnitude of the relative angular velocity between these different blocks has prevented to quantify their relative motion. In this case, we are using mainly campaign observations, acquired since 1995, to reduce such uncertainties. The plate boundaries of the Victoria plate with respect to Nubia and Somalia plates are clearly defined by the two arms of the East African Rift. We attempt to quantify between this tectonic unit and the Rovuma block by differencing their estimated angular velocities with respect to ITRF2005.

Fernandes, R. M.; Ferreira, J. P.; Quembo, J. L.; Combrinck, L.; Kamamia, C. M.; Al-Aydrus, A.; Boodhoo, Y.

2009-12-01

304

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

305

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

306

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

NASA Astrophysics Data System (ADS)

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 gsim400 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

2011-07-01

307

Tectonics  

NASA Astrophysics Data System (ADS)

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

308

Development of the Plate Tectonics and Seismology markup languages with XML  

NASA Astrophysics Data System (ADS)

The Extensible Markup Language (XML) and its specifications such as the XSD Schema, allow geologists to design discipline-specific vocabularies such as Seismology Markup Language (SeismML) or Plate Tectonics Markup Language (TectML). These languages make it possible to store and interchange structured geological information over the Web. Development of a geological markup language requires mapping geological concepts, such as "Earthquake" or "Plate" into a UML object model, applying a modeling and design environment. We have selected four inter-related geological concepts: earthquake, fault, plate, and orogeny, and developed four XML Schema Definitions (XSD), that define the relationships, cardinalities, hierarchies, and semantics of these concepts. In such a geological concept model, the UML object "Earthquake" is related to one or more "Wave" objects, each arriving to a seismic station at a specific "DateTime", and relating to a specific "Epicenter" object that lies at a unique "Location". The "Earthquake" object occurs along a "Segment" of a "Fault" object, which is related to a specific "Plate" object. The "Fault" has its own associations with such things as "Bend", "Step", and "Segment", and could be of any kind (e.g., "Thrust", "Transform'). The "Plate" is related to many other objects such as "MOR", "Subduction", and "Forearc", and is associated with an "Orogeny" object that relates to "Deformation" and "Strain" and several other objects. These UML objects were mapped into XML Metadata Interchange (XMI) formats, which were then converted into four XSD Schemas. The schemas were used to create and validate the XML instance documents, and to create a relational database hosting the plate tectonics and seismological data in the Microsoft Access format. The SeismML and TectML allow seismologists and structural geologists, among others, to submit and retrieve structured geological data on the Internet. A seismologist, for example, can submit peer-reviewed and reliable data about a specific earthquake to a Java Server Page on our web site hosting the XML application. Other geologists can readily retrieve the submitted data, saved in files or special tables of the designed database, through a search engine designed with J2EE (JSP, servlet, Java Bean) and XML specifications such as XPath, XPointer, and XSLT. When extended to include all the important concepts of seismology and plate tectonics, the two markup languages will make global interchange of geological data a reality.

Babaie, H.; Babaei, A.

2003-04-01

309

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

310

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

311

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

NASA Astrophysics Data System (ADS)

Variations in the rates of seafloor generation and recycling have potentially far-reaching consequences for sea level, ocean chemistry and climate. A parameterized framework to describe such variations could guide the study of non-uniformitarian plate tectonic activity, but there is little agreement on the appropriate mechanical description of the surface boundary layer. A strong constraint on the statistics of oceanic convection systems comes from the preserved seafloor age distribution, and additional inferences are possible when paleo-seafloor is modeled based on plate motion reconstructions. Based on previously reconstructed seafloor ages, we recently inferred that oceanic heat flow was larger by ~15% at 60~Ma than today. This signal is mainly caused by the smaller plates that existed previously in the Pacific basin with relatively larger ridge-proximal area of young seafloor. The associated decrease in heat flow is larger than any plausible decrease due to cooling, and therefore hint at cyclic behavior in plate tectonics. We also consider area-per-age statistics for the present-day and back to 140~Ma from new paleo-age reconstructions. Using a simplified seafloor age evolution model we explore which physical parameterizations for the average behavior of the oceanic lithosphere are compatible with broad trends in the data. In particular, we show that a subduction probability based on lithospheric buoyancy ("sqrt(age)") leads to results that are comparable to, or better than, that of the probability distribution that is required to obtain the "triangular" age distribution with age-independent destruction of ocean floor. The current, near triangular distribution of ages and the relative lull in heat flow are likely only snapshots of a transient state during the Wilson cycle. Current seafloor ages still contain hints of a ?sssim 60~Myr period, cyclic variation of seafloor production, and using paleo-ages for 140~Ma, we find a ~ 400~Myr best-fitting variation that is broadly consistent with geologically based reconstructions of production rate variations. From the new reconstructions, a consistent decrease of total oceanic heat flow by ~ -0.25%/Myr over the last 140~Ma is inferred. Our study provides some of the required input for an improved understanding of the non-uniformitarian evolution of plate tectonics and the interplay between continental cycles and the self-organization of the oceanic plates.

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

2008-12-01

312

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

NASA Astrophysics Data System (ADS)

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

Stanley, Daniel Jean

1982-03-01

313

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

314

This Dynamic Planet: World Map of Volcanoes, Earthquakes, Impact Craters, and Plate Tectonics  

NSDL National Science Digital Library

Published by the US Geological Survey (USGS), this Adobe Acrobat (.pdf) document contains text and figures depicting volcanoes, earthquakes, impact craters, and plate tectonics located around the world, as well as a 44 inch wide world map. The text explains the geological reasoning for the distribution of volcanoes and earthquakes (shown in the figures) and the formation of impact craters, and describes the preparation of the complex This Dynamic Planet world map. A hardcopy version of the map may be ordered from the USGS. Selected references contain additional editor's notes throughout the document.

315

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

PubMed

The Archean Kolar Schist Belt, south India, is a suture zone where two gneiss terranes and at least two amphibolite terranes with distinct histories were accrted. Amphibolites from the eastern and western sides of the schist belt have distinct incompatible element and isotopic characteristics sugesting that their volcanic protoliths were derived from dint mantle sources. The amphibolite and gneiss terranes were juxtaposed by horizontal compression and shearing between 2530 and 2420 million years ago (Ma) along a zone marked by the Kolar Schist Belt. This history of accretion of discrete crustal terranes resembles those of Phanerozoic convergent margins and thus suggests that plate tectonics operated on Earth by 2500 Ma. PMID:17808265

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

1989-03-10

316

This Dynamic Planet: World Map of Volcanoes, Earthquakes, Impact Craters, and Plate Tectonics  

NSDL National Science Digital Library

This map shows Earth's tectonic features, volcanoes, earthquakes, and impact craters. Smaller inset maps are included to depict the North and South Poles. The back of the map provides additional information, highlighting examples of fundamental processes; and providing text, timelines, references, and other resources to enhance understanding. The main and polar maps feature online interactive versions. Users can use the zoom and pan functions to make their own regional maps, and choose from a selection of data layers including volcanoes, plate motion symbols, earthquakes, plate boundary types, and others. Data for any volcano, earthquake, or impact symbol can be found by using the 'Identify' tool. This map is the companion to the United States Geological Survey's (USGS) publication 'This Dynamic Earth'. Downloadable, printable versions of the entire map and selected smaller portions are available, and a hardcopy version is available for purchase.

2010-09-21

317

The effect of plate movements in the northern region of South America on tectonics and sedimentation in the Eastern Llanos Basin  

SciTech Connect

The geological configuration of the Eastern Llanos pericratonic mega-basin has been directly affected by the overall tectonic regime experienced in the Northern part of South America. Interaction between the Pacific (Cocos), South American and Caribbean Plates generated a regional compressional dextral rotational force expressed as a regional North-South striking structural trend in the southern part of the basin and an east-west striking trend in portion nearest the Caribbean Plate Boundary. Nearly 90% of the strike-slip faults in this northern area show right lateral displacement. The majority of the structures in the East Llanos basin are related to the Late Miocene uplift of the Eastern Andes. Nevertheless we can subdivide the structures into two major groups: pre-Miocene and post-Miocene. By being able to recognize pre-Miocene Cretaceous age structures, much altered by later movements, we can envision remigration of hydrocarbons out of early traps into those created more recently. Plate tectonic events in the north of South America have produced a general regional structure strike directional through time. Sedimentary-tectonic relationships depend upon regional phenomena which, if interpreted correctly, help to sub-divide the mega-basin into genetically related parts. By understanding the mechanism that creates large scale structural features, the geologist is thus provided with an important tool that can aid him in exploring the Eastern Llanos basin.

Pena, L.E. (Empresa Colombiana de Petroleos, Santafe de Bogota (Colombia))

1993-02-01

318

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

319

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

320

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

321

GIS Plate Tectonic Reconstruction of the Gulf of California-Salton Trough Oblique Rift  

NASA Astrophysics Data System (ADS)

We present GIS-based plate tectonic reconstruction maps for the Gulf of California-Salton Trough oblique rift. The maps track plate boundary deformation in 2 and 1 Myr slices (6-2 Ma and 2 Ma-present) using a custom ArcGIS add-in tool to close extensional basins and restore slip on dextral faults. The tool takes a set of polygons depicting present day locations of tectonic blocks and sequentially restores displacement of their centroids along a vector specific to that time slice. Tectonic blocks are defined by faults, geology, seismic data, and bathymetry/topography. Spreading center and fault-slip rates were acquired from geologic data, cross-Gulf tie points, GPS studies, and aeromagnetic data. A recent GPS study indicated that ~92% of modern-day Pacific-North America (PAC-NAM) plate motion is localized between the Baja California microplate and North America. Relative plate motion azimuth varies from ~302 in the southern Gulf to ~314 in the Salton Trough. Baja-North America GPS rates agree remarkably with ~6 Ma geologic offsets across the Gulf and are used during reconstruction steps back to 6 Ma. In the southern Gulf, unpublished GPS data indicate that modern plate motion is partitioned between the plate boundary, Gulf-margin system, and borderland faults west of Baja California. The Alarcon and Guaymas spreading centers initiated at 2.4 Ma and 6 Ma (Lizarralde et al., 2007), respectively, while the Farallon, Pescadero, and Carmen spreading centers began between ~2-1 Ma (Lonsdale, 1989). Therefore, the 2, 4, and 6 Ma reconstruction steps include a long transtensional fault zone along much of the southern Gulf, connecting the Guaymas spreading center with either the Alarcon spreading center or East Pacific Rise. In the northern Gulf, transtensional strain initiated in coastal Sonora by ~7 Ma and migrated westward as the Gulf opened. At ~6 Ma strain migrated west into marine pull-apart basins that now lie within the eastern Gulf. Seismic reflection studies suggest that these eastern basins were abandoned ~3.3-2.0 Ma as strain migrated west, forming new transtensional basins that host the modern-day plate boundary. Cross-rift geologic tie points include a fusulinid-bearing clast conglomerate, the Poway conglomerate, and 12.5 Ma & 6.1-6.4 Ma correlative tuffs. Since ~6.1 Ma, the magnitude of extension across the northern Gulf requires that ~90% of PAC-NAM relative plate motion has been located in marine pull-apart basins, while ~10% has been accommodated by faults west of Baja California. In the Salton Trough, roughly 90% of the relative plate motion became localized at 7-8 Ma, prior to regional marine incursion at 6.3-6.5 Ma. Plio-Pleistocene strain was accommodated linked dextral slip on the San Andreas fault and oblique extension on the West Salton detachment fault. Initiation of new strike slip faults at ~1.1-1.3 Ma resulted in westerly expansion and widening of the dextral deformation zone. Modern strain is accommodated by a network of transtensional pull-aparts and transpressional fold-thrust belts.

Skinner, L. A.; Bennett, S. E.; Umhoefer, P. J.; Oskin, M. E.; Dorsey, R. J.; Nava, R. A.

2011-12-01

322

Rheology of the mantle and tectonics of the oceanic lithospheric plates  

NASA Astrophysics Data System (ADS)

The modern concepts of the rheology of viscous mantle and brittle lithosphere, as well as the results of the numerical experiments on the processes in a heated layer with a viscosity dependent on pressure, temperature, and shear stress, are reviewed. These dependences are inferred from the laboratory studies of olivine and measurements of postglacial rebound (glacial isostatic adjustment) and geoid anomalies. The numerical solution of classical conservation equations for mass, heat, and momentum shows that thermal convection with a highly viscous rigid lithosphere develops in the layer with the parameters of the mantle with the considered rheology under a temperature difference of 3500 K, without any special additional conditions due to the self-organization of the material. If the viscosity parameters of the lithosphere correspond to dry olivine, the lithosphere remains monolithic (unbroken). At a lower strength (probably due to the effects of water), the lithosphere splits into a set of separate rigid plates divided by the ridges and subduction zones. The plates submerge into the mantle, and their material is involved in the convective circulation. The results of the numerical experiment may serve as direct empirical evidence to validate the basic concepts of the theory of plate tectonics; these experiments also reveal some new features of the mantle convection. The probable structure of the flows in the upper and lower mantle (including the asthenosphere), which shows the primary role of the lithospheric plates, is demonstrated for the first time.

Trubitsyn, V. P.

2012-06-01

323

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

NASA Astrophysics Data System (ADS)

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

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

2012-07-01

324

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

Microsoft Academic Search

A new view of plate tectonics coupled to mantle dynamics is emerging from recent paleomagnetic reconstructions of tectonic plate histories obtained in the hotspot and no-net-rotation reference frames. A number of fundamental differences relative to past plate reconstructions have been discerned. Firstly, in previous models the difference between present-day plate motions in the global hotspot and no-net-rotation reference frames consisted

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

2007-01-01

325

Shape of the subducted Rivera and Cocos plates in southern Mexico: Seismic and tectonic implications  

NASA Astrophysics Data System (ADS)

The geometry of the subducted Rivera and Cocos plates beneath the North American plate in southern Mexico was determined based on the accurately located hypocenters of local and teleseismic earthquakes. The hypocenters of the teleseisms were relocated, and the focal depths of 21 events were constrained using a body wave inversion scheme. The suduction in southern Mexico may be approximated as a subhorizontal slab bounded at the edges by the steep subduction geometry of the Cocos plate beneath the Caribbean plate to the east and of the Rivera plate beneath North America to the west. The dip of the interplate contact geometry is constant to a depth of 30 km, and lateral changes in the dip of the subducted plate are only observed once it is decoupled from the overriding plate. On the basis of the seismicity, the focal mechanisms, and the geometry of the downgoing slab, southern Mexico may be segmented into four regions: (1) the Jalisco region to the west, where the Rivera plate subducts at a steep angle that resembles the geometry of the Cocos plate beneath the Caribbean plate in Central America; (2) the Michoacan region, where the dip angle of the Cocos plate decreases gradually toward the southeast, (3) the Guerrero-Oaxaca region, bounded approximately by the onshore projection of the Orozco and O'Gorman fracture zones, where the subducted slab is almost subhorizontal and underplates the upper continental plate for about 250 km, and (4) the southern Oaxaca and Chiapas region, in southeastern Mexico, where the dip of the subduction gradually increases to a steeper subduction in Central America. These drastic changes in dip do not appear to take place on tear faults, suggesting that smooth contortions accommodate these changes in geometry. The inferred 80 and 100 km depth contours of the subducted slab lie beneath the southern front of the Trans-Mexican Volcanic Belt, suggesting it is directly related to the subduction. Thus the observed nonparallelism with the Middle American Trench is apparently due to the changing geometry of the Rivera and Cocos plates beneath the North American plate in southern Mexico, and not to zones of weakness in the crust of the North American plate as some authors have suggested.

Pardo, Mario; SuRez, Gerardo

1995-07-01

326

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

NASA Astrophysics Data System (ADS)

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

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

2009-02-01

327

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

PubMed

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

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

2010-06-07

328

The boundary between the Indian and Asian tectonic plates below Tibet  

PubMed Central

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

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

2010-01-01

329

Cocos plate structure along the Middle America subduction zone off Oaxaca and Guerrero, Mexico: Influence of subducting plate morphology on tectonics and seismicity  

Microsoft Academic Search

Two new bathymetric and magnetic surveys are presented from which the history and recent tectonics of the Cocos plate off the Middle America subduction zone are determined. The East O'Gorman fracture zone, a previously proposed outer rise feature, is not present along the Oaxaca trench outer rise near the trench axis. Several parallel ridges of seamounts are entering the subduction

Nancy Marie Kanjorski

2003-01-01

330

Tectonic implications of a remagnetization event in the Newark basin  

Microsoft Academic Search

The Newark basin red beds contain a secondary magnetization (the B component) acquired during the Middle Jurassic after the 5-20 basin-wide northwesterly dip was imparted to the strata of the basin and after most, if not all, of the limb rotation in the Jacksonwald syncline. The B component magnetization was most likely related to the same hydrothermal event which evidently

William K. Witte; Dennis V. Kent

1991-01-01

331

Evolution and timing of tectonic events in the Arabia-Eurasia convergence zone as inferred from igneous geochemistry from the EarthChem database  

NASA Astrophysics Data System (ADS)

The timing of tectonic events in the Anatolia-Iranian region can be inferred from analysis of igneous rocks. Magmatic activities in the region are generally associated with the convergence of the African-Arabian and Eurasian plates and the subduction of the Neotethys Ocean. Ancillary processes such as subduction of continental crust, delamination of upper plate lithosphere or lower crust, or asthenospheric decompression accompanying post-collisional relaxation also contribute to the composition of igneous rocks. Here we use geochemical data gathered from the EarthChem database to assess broad chemical implications of Cenozoic tectonic activities of the convergence region. We search for geochemical signal of the timing of first contact of the subducting Arabian and overriding Eurasian continental crust. Of particular interest is how igneous rock compositions vary during the transition from pre- to post-contact of the continental crusts. Also, is there a geographic variation along the convergence zone during this tectonic transition? We generate maps and geochemical plots for four different epochs and two different regions since Cenozoic time: Iran and Anatolia in the Eocene, Oligocene, Miocene and Plio-Quaternary. This board, region-scaled analysis of major and trace element patterns suggests the following tectonic events: Subduction-related medium K calc-alkaline igneous rocks reflect Eocene subduction of the Neo-Tethys oceanic lithosphere. Oligocene igneous rocks are characterized by K2O-SiO2 trends scattering to higher silica and alkaline content, which may reflect subduction of stretched continental margin lithosphere and sediments. A bimodal pattern of potash-silica trends during Miocene time may mark the transition from subduction-related to intra-plate magmatism, perhaps signaling contact between the continental crust of Arabia-Africa with Eurasia. Pliocene and younger igneous rocks show an intra-plate and ocean island basalt trend, as the region's activities transition to orogenic magmatism. Warren K Lieu and Robert J Stern The University of Texas at Dallas

Lieu, W. K.; Stern, R. J.

2011-12-01

332

Models of mantle convection incorporating plate tectonics: The Australian region since the Cretaceous  

NASA Astrophysics Data System (ADS)

We propose that the anomalous Cretaceous vertical motion of Australia and distinctive geochemistry and geophysics of the Australian-Antarctic Discordance (AAD) were caused by a subducted slab which migrated beneath the continent during the Cretaceous, stalled within the mantle transition zone, and is presently being drawn up by the Southeast Indian Ridge. During the Early Cretaceous the eastern interior of the Australian continent rapidly subsided, but must have later uplifted on a regional scale. Beneath the AAD the mantle is cooler than normal, as indicated by a variety of observations. Seismic tomography shows an oblong, slab-like structure orientated N-S in the transition zone and lower mantle, consistent with an old subducted slab. Using a three-dimensional model of mantle convection with imposed plate tectonics, we show that both of these well documented features are related. The models start with slabs dipping toward the restored eastern Australian margin. As Australia moves east in a hot spot reference frame from 130-90 Ma, a broad dynamic topography depression of decreasing amplitude migrates west across the continent causing the continent to subside and then uplift. Most of the slab descends into the deeper mantle, but the models show part of the cooler mantle becomes trapped within the transition zone. Prom 40 Ma to the present, wisps of this cool mantle are drawn up by the northwardly migrating ridge between Australia and Antarctica. This causes a circular dynamic topography depression and thinner crust to develop at the present position of the AAD. The AAD is unique within the ocean basins because it is the only place where a modern ridge has migrated over the position of long term Mesozoic subduction. Our study demonstrates the predictive power of mantle convection models when they incorporate plate tectonics.

Gurnis, Michael; Moresi, Louis; Dietmar Mller, R.

333

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

NASA Astrophysics Data System (ADS)

The southeastern Korean Peninsula has experienced multiple crustal deformations according to changes of global tectonic setting during the Cenozoic. Characteristics of the crustal deformations in relation to major Cenozoic tectonic events are summarized as follows. (1) Collision of Indian and Eurasian continents and abrupt change of movement direction of the Pacific plate (50 ~ 43 Ma): The collision of Indian and Eurasian continents caused the eastward extrusion of East Asia block as a trench-rollback, and then the movement direction of the Pacific plate was abruptly changed from NNW to WNW. As a result, the strong suction-force along the plate boundary produced a tensional stress field trending EW or WNW-ESE in southeastern Korea, which resultantly induced the passive intrusion of NS or NNE trending mafic dike swarm pervasively. (2) Opening of the East Sea (25 ~ 16 Ma): The NS or NNW-SSE trending opening of the East Sea generated a dextral shear stress regime trending NNW-SSE along the eastern coast line of the Korean Peninsula. As a result, pull-apart basins were developed in right bending and overstepping parts along major dextral strike slip faults trending NNW-SSE in southeastern Korea. The basins can be divided into two types on the basis of geometry and kinematics: Parallelogram-shaped basin (rhombochasm) and wedged-shaped basin (sphenochasm), respectively. At that time, the basins and adjacent basement blocks experienced clockwise rotation and northwestward tilting, and the eastward propagating rifting also occurred. At about 17 Ma, the Yeonil Tectonic Line, which is the westernmost border fault of the Miocene crustal deformation in southeastern Korea, began to move as a major dextral strike slip fault. (3) Clockwise rotation of southeastern Japan Island (16~15 Ma): The collision of the Izu-Bonin Arc and southeastern Japan Island, as a result of northward movement of the Philippine sea-plate, induced the clockwise rotation of southeastern Japan Islands. The event caused a NW-SE compression in the Korea Strait as a tectonic inversion, which resultantly terminated the basin extension and caused locally counterclockwise rotation of blocks in southeastern Korea. At that time, the folding of the San'in folded zone commenced. The folding in the Tsushima Island was almost completely accomplished at about 15 Ma and then an extensive intrusion of felsic magma occurred in the southern part of the island which led the island to be tilted about 20 into northeast. Simultaneously, the Tsushima-Goto fault was reactivated as major sinistral strike-slip faults owing to the accumulated NNW-trending compressional stress. The adjacent blocks to the fault were rotated horizontally about 28 counterclockwise due to the sinistral movement, and resultantly the western part of the San'in folded zone was dragged counterclockwise. (4) E-W compression in the East Asia (after about 5 Ma): Decreasing subduction angle of the Pacific plate and eastward movement of the Amurian plate have constructed the-top-to-west thrusts and become a major cause for earthquakes in southeastern Korea.

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

2010-12-01

334

Assessment of the cooling capacity of plate tectonics and flood volcanism in the evolution of Earth, Mars and Venus  

Microsoft Academic Search

Geophysical arguments against plate tectonics in a hotter Earth, based on buoyancy considerations, require an alternative means of cooling the planet from its original hot state to the present situation. Such an alternative could be extensive flood volcanism in a more stagnant-lid like setting. Starting from the notion that all heat output of the Earth is through its surface, we

P. van Thienen; N. J. Vlaar; A. P. van den Berg

2005-01-01

335

Deep-Sea Drilling for Landlubber Geologists --- The Southwest Pacific, an Accordion Plate Tectonics Analog for the Cordilleran Geosyncline  

Microsoft Academic Search

The Deep Sea Drilling Project offers the geologist who is not trained in marine geology an unparalleled opportunity to study deep-sea sediments and volcanic rocks in their environment of formation and an opportunity to evaluate concepts of plate tectonics theory. Results of deep-sea drilling in the southwest Pacific are useful in interpreting the early history of the Cordilleran geosyncline as

Michael Churkin Jr.

1974-01-01

336

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

Microsoft Academic Search

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

J. Nedoma

1986-01-01

337

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

338

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

339

Interaction of weak faults and non-newtonian rheology produces plate tectonics in a 3D model of mantle flow  

NASA Astrophysics Data System (ADS)

ACCORDING to the theory of plate tectonics, relatively rigid plates are bounded by large faults; plate motion has negligible internal strain1,2,with significant toroidal component to the velocity3. By contrast, models of mantle flow with viscous rheology in an intact medium predict little toroidal component and substantial internal strain in surface motion4. It has been suggested5 that the observed characteristics of plate motion are related to faulted plate margins, which are observed to be weak6. Here we confirm this suggestion, using three-dimensional models of mantle flow that incorporate faults and the forces exerted on plates by subducting slabs ("slab pull') and mid-ocean ridges ('ridge push'). Our models show that plate-like motion results from the interaction between weak faults and a strain-weakening power-law rheology. Weak transform faults tend to guide plate motion. This guiding effect and the decoupling that occurs at thrust faults may result in oblique subduction. Convergent margins are associated with realistic trench and fore-bulge topography. By simultaneously predicting surface kinematics, topography and gravity, the models achieve a useful degree of tectonic realism.

Zhong, Shijie; Gurnis, Michael

1996-09-01

340

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

2007-08-24

341

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

342

Strainmeter observations of the 2010 slow slip event in Cascadia: A critical look at noise, artifacts, and tectonic signals  

NASA Astrophysics Data System (ADS)

Periodic slow-slip events along the Cascadia subduction zone represent the transient release of accumulated strain along the plate interface. The location of these events helps to map the lower edge of the seismogenic zone and constrain the seismic hazard. The primary observations of these slow-slip events have come from a large array of GPS stations in the Pacific Northwest. However, newly installed borehole strainmeters provide greater temporal resolution and greater precision than GPS. Incorporating strainmeter data into current slip inversion models, which have previously depended upon GPS data, will help to further constrain models of the slip distribution at depth. Understanding the capabilities and limitations of strainmeter data, especially in regards to the quantification of noise sources and identification of non-tectonic artifacts, is necessary for the data to be used in formal inversions. The method of power density spectra is used to analyze noise as a function of frequency for several strainmeters in the PBO network. Preliminary work shows that the noise spectra obey a random walk model where the amplitude is proportional to f-2. The noise levels of these strainmeters are compared to each other and to closely located GPS stations in order to evaluate their ability to detect tectonic signals. We particularly focus our analysis of the time series for the August 2010 slow slip event in Washington State. Our initial analysis of the data suggests that the event originated under Puget Sound and propagated both to the north and south. A clear signal of approximately 0.10 microstrain can be seen in several strainmeters in the Olympic Peninsula area of the PBO network, including stations B003, B004, B005, B006, B007, B014 and B018. The temporal signal of the transient strain correlates with the timing and location of tremor activity associated with the slow-slip event. By calculating strain from the GPS displacement measurements, the magnitude and quality of the strainmeters signals are compared to the corresponding GPS signals for the event. This comparison can potentially offer a useful calibration check to compare with current tidal calibration models. A slip inversion model combining GPS and strainmeter data is performed using the Kalman-filter-based Extended Network Inversion Filter. Coupling the sensitivity of strainmeter data with the spatial resolution of the current GPS network provides better constraints on slow-slip events. The incorporation of strainmeter data into current GPS inversion models reveals strainmeters to be a valuable monitoring tool for slow-slip events.

Krogstad, R.; Schmidt, D. A.

2010-12-01

343

The Triple Junction of the North America, Cocos, and Caribbean Plates: Seismicity and tectonics  

NASA Astrophysics Data System (ADS)

The triple junction of the North America, Cocos, and Caribbean plates is ambiguously defined, mainly because the North America-Caribbean plate boundary does not clearly continue beyond its known surface trace (the Motagua fault zone) in western Guatemala to intersect the Middle America trench. Well-located regional shallow earthquakes (h?70 km) show that there is no intermediate or large-magnitude seismic activity associated with a presumed extension of the North America-Caribbean plate boundary to the west, beyond its well-defined surface trace. There is, however, a clear zone of shallow seismic activity from the western section of the fault system through southern Mexico. Fault plane solutions for these events indicate a left-lateral strike-slip displacement, which is in good agreement with surface faulting. We suggest that these strike-slip faults, together with the Salina Cruz fault in the isthmus of Tehuantepec, mark the boundaries of a broad zone of deformation in southern Mexico and northern central America which takes up the interactions of the three plates. In this sense, no single point constitutes the triple junction. The geologic record suggests that the Motagua fault zone developed because the westernmost portion of the Caribbean plate became locked against North America.

GuzmN-Speziale, Marco; Pennington, Wayne D.; Matumoto, Tosimatu

1989-10-01

344

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

NASA Astrophysics Data System (ADS)

It is now widely accepted that the continents or land masses are constantly, slowly moving, or drifting over the asthenosphere as the sea floors spread in response to the mantle convection. These continents were joined together at one time, some 250 million years ago, in a single giant landmass called Pangaea. Alfred Wegener, who proposed originally the hypothesis of continental drift, succeeded in reconstructing the Pangaea in early 20th century, by gathering evidences such as land features, fossils, and climate change. The shape of Pangaea shown by Wegener is a huge landmass which is in rounded shape close to an oval. The Pangaea of Wegener was found to be in good agreement with the supercontinent which was reconstructed by modern scientists in late 1960s based on concrete and sophisticated sciences such as the plate tectonics. There are a couple of shapes describing the Pangaea by now, other than the Wegener's, that are recognized by the geological community. In spite of profound geological data and development of related-area sciences, uncertainties still remains on the precise shape of Pangaea before the stage of breaking up and drifting apart. In this study, the Pangaea is reconstructed taking the recent progresses of plate tectonics into full consideration with the use of an elaborate Geographical Information System (GIS) mapping technique. For a better visualization of the shape of the supercontinent the equidistant map projection is incorporated to display the Pangaea, where the central point of Pangaea is placed on the center of the map. The Pangaea reconstructed in this way appears in an almost circular shape, which has never been seen in previous studies (Fig. 1). The radius of the circle which circumscribes the Pangaea is about 9 000 km, giving the total area slightly above that of continents and lands of present day, because some of the continental margins were considered as a part of continents. This result suggests us that the Pangaea might have existed in an exact circular shape until it started to break into parts. Comparing the Pangaea to the present geography reveals that the Pangaea's geometric center falls on somewhere in Sinai Peninsula. One of notable features of the Pangaea reconstructed in this study is that there are two inland seas in circular shape: One is small and corresponds to Tethis sea, and the other corresponding to present Arctic ocean is several times larger than Tethis. From the geological viewpoint, these inland seas seem to be the oceanic crusts located inside the continental crusts, and it is likely that they were connected to the Panthalassa by sea. The main result of the present study that the Pangaea appears to be a circle may give us much more important implication than just being in a beautiful geometric configuration. Figure 1 Pangaea on a equidistant projection map, reconstructed with the use of GIS technique incorporating recent progresses in plate tectonics.

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

2012-04-01

345

Seismic Structure, Crustal Architecture and Tectonic Evolution of the Anatolian-African Plate Boundary and the Cenozoic Orogenic Belts  

NASA Astrophysics Data System (ADS)

The modern Anatolian-African plate boundary is represented by a north-dipping subduction zone that is part of a broad domain of regional convergence between Eurasia and Afro-Arabia since the latest Mesozoic. A series of collisions between Gondwana-derived ribbon continents and trench-rollback systems in the Tethyan realm produced nearly E-W-trending, subparallel mountain belts with high elevation and thick orogenic crust in this region. Ophiolite emplacement, terrane stacking, high-P and Barrovian metamorphism, and crustal thickening occurred during the accretion of these microcontinents into the upper plates of Tethyan subduction rollback systems during the late Cretaceous-early Eocene. Continued convergence and oceanic lithospheric subduction within the Tethyan realm were punctuated by slab breakoff events following the microcontinental accretion episodes. Slab breakoff resulted in asthenospheric upwelling and partial melting, which facilitated post-collisional magmatism along and across the suture zones. Resumed subduction and slab rollback-induced upper plate extension triggered a tectonic collapse of the thermally weakened orogenic crust in Anatolia in the late Oligocene-Miocene. This extensional phase resulted in exhumation of high-P rocks and medium- to lower-crustal material leading to the formation of metamorphic core complexes in the hinterland of the young collision zones. The geochemical character of the attendant magmatism has progressed from initial shoshonitic and high-K calc-alkaline to calc-alkaline and alkaline affinities through time, as more asthenosphere-derived melts found their way to the surface with insignificant degrees of crustal contamination. The occurrence of discrete high-velocity bodies in the mantle beneath Anatolia, as deduced from lithospheric seismic velocity data, supports our Tethyan slab breakoff interpretations. Pn velocity and Sn attenuation tomography models indicate that the uppermost mantle is anomalously hot and thin, consistent with the existence of a shallow asthenosphere beneath the collapsing Anatolian orogenic belts and widespread volcanism in this region. The sharp, north-pointing cusp (Isparta Angle) between the Hellenic and Cyprus trenches along the modern Anatolian-African plate boundary corresponds to a subduction-transform edge propagator (STEP) fault, which is an artifact of a slab tear within the downgoing African lithosphere.

Dilek, Y.; Sandvol, E.

2009-04-01

346

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

NASA Astrophysics Data System (ADS)

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

zalaybey, Serdar; Savage, Martha K.

1995-09-01

347

Bang! You're Alive!: Plate Tectonics and the History of Life (title provided or enhanced by cataloger)  

NSDL National Science Digital Library

This lesson focuses on the origin and structure of the Earth and will help students to describe and explain the theory of plate tectonics and the big bang theory for the origin of the universe. Students will be able to identify the approximate age of the Earth and the point in Earth's history at which living organisms first appeared, according to current geological evidence. Students will also be able to explain at least two ways in which understanding the theory of plate tectonics and the history of life on Earth are of direct benefit to humans. All of the lessons emphasize hands-on activities using online data resources, and each inquiry-based activity includes focus questions, learning objectives, teaching time, background information, evaluations and extensions, as well as resources and student handouts.

348

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

349

Some remarks on the models for plate tectonics on terrestrial planets: From a point of view of mantle rheology  

NASA Astrophysics Data System (ADS)

Plate tectonic mode of convection is unique in that it helps maintain habitable conditions on planetary surface through global volatile circulation. Motivated by the discovery of super-Earths, a number of models have been proposed to understand under which conditions plate tectonics style of convection might occur. However, previous studies on this topic have two major limitations in the way in which the rheological complexities of planetary materials are incorporated in the model. A common approach is to compare driving force by convection with the resistance force caused by the strength of the lithosphere. When the force (stress) caused by convection exceeds the resistance force determined by the strength of the lithosphere, then plate tectonics is considered to operate (otherwise stagnant-lid mode of convection occurs). In the previous formulation, this question was examined using two parameters related to the rheological properties, "average" viscosity and the viscosity contrast between the deep (average) mantle and the lithosphere. There are two major issues in this approach. First, the pressure dependence of viscosity was ignored in most cases. This is not justifiable, because of a large pressure range expected in super-Earths (to ~1 TPa or more) where viscosity could change more than 100 orders of magnitude if one uses a conventional model. Second, the resistance against lithosphere deformation has not been properly formulated: (a) The "strength" of the lithosphere is affected by shear localization, but the existing theoretical formulation of shear localization or weakening lacks the key aspects of micro-structural heterogeneity. (b) The lithosphere thickness versus planet size relationship assumed in the previous models did not consider some key elements such as the influence of planetary size on the dehydration depth. Possible implications of new experimental results or theoretical considerations on the conditions of plate tectonics will be discussed.

Karato, Shun-ichiro

2013-04-01

350

Large tectonic rotations since the Early Miocene in a convergent plate-boundary zone, South Island, New Zealand  

Microsoft Academic Search

A palaeomagnetic study in part of the New Zealand plate-boundary zone provides new constraints on the temporal and spatial distribution of Neogene and Quaternary tectonic rotations. Thermal demagnetization of samples from Cretaceous basaltic dykes, Palaeocene-Oligocene micritic limestone, and Miocene and Pliocene siltstones in the Marlborough region, South Island, have defined stable, high-temperature magnetic components, which are interpreted as the primary

Sara Vickery; Simon Lamb

1995-01-01

351

3-D Simulation of Tectonic Loading at Convergent Plate Boundary Zones: Internal Stress Fields in Northeast Japan  

Microsoft Academic Search

The evidence of east-west compression in northeast Japan has been reported by many investigators on the basis of geodetic,\\u000a geologic and geomorphic data, but its origin still remains far from understood. In the present study we have proposed a mechanical\\u000a model of tectonic loading at convergent plate boundary zones, and demonstrated its validity through the numerical simulation\\u000a of internal stress

Chihiro Hashimoto; Mitsuhiro Matsu'ura

2006-01-01

352

Assessment of the cooling capacity of plate tectonics and flood volcanism in the evolution of Earth, Mars and Venus  

NASA Astrophysics Data System (ADS)

Geophysical arguments against plate tectonics in a hotter Earth, based on buoyancy considerations, require an alternative means of cooling the planet from its original hot state to the present situation. Such an alternative could be extensive flood volcanism in a more stagnant-lid like setting. Starting from the notion that all heat output of the Earth is through its surface, we have constructed two parametric models to evaluate the cooling characteristics of these two mechanisms: plate tectonics and basalt extrusion/flood volcanism. Our model results show that for a steadily (exponentially) cooling Earth, plate tectonics is capable of removing all the required heat at a rate of operation comparable to or even lower than its current rate of operation, contrary to earlier speculations. The extrusion mechanism may have been an important cooling agent in the early Earth, but requires global eruption rates two orders of magnitude greater than those of known Phanerozoic flood basalt provinces. This may not be a problem, since geological observations indicate that flood volcanism was both stronger and more ubiquitous in the early Earth. Because of its smaller size, Mars is capable of cooling conductively through its lithosphere at significant rates, and as a result may have cooled without an additional cooling mechanism. Venus, on the other hand, has required the operation of an additional cooling agent for probably every cooling phase of its possibly episodic history, with rates of activity comparable to those of the Earth.

van Thienen, P.; Vlaar, N. J.; van den Berg, A. P.

2005-06-01

353

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

354

A Lower Paleozoic Plate Tectonic Model for the North Qilian Mountains, NW China  

NASA Astrophysics Data System (ADS)

The north Qilian mountains are a strongly-lineated Caledonian fold belt. Their mountain ranges, major rivers, fold axes, fault lines, and the spatial distribution of major rock types are all more or less parallel to one another and trend in NWW-SEE direction. The Caledonian plate tectonic structures have still been well preserved despite modifications by the Indosinian and Himalayan crustal disturbances. The north Qilian mountains may be considered as a plate suture zone which sutured the Alashan craton and the central-south Qilian craton in the lower Paleozoic time. This suture zone consists of an active continental margin, a passive continental margin, and an intervening oceanic domain. The southern margin of the Alashan craton was an active continental margin in the lower Paleozoic time, on which continental margin arcs, forearc basin, forearc ridge, and accretionary prism were very well developed. The northern margin of the central-south Qilian craton was chiefly a passive continental margin, but might be active locally in the lower Paleozoic time. The intervening oceanic domain consists of oceanic island arcs, oceanic islands, oceanic ridges, major oceanic floor, and backarc basin ocean floor. A Paleo-Qilian ocean with well-developed oceanic islands and oceanic ridges is presumed to have existed during the late Proterozoic-early Cambrian period. It started to contract in the mid-Cambrian and a Mariana type subduction occurred to have formed an oceanic island arc and a backarc basin. The Andean type subduction followed in the late-Cambrian through the Silurian periods, during which the paleo-Qilian oceanic lithosphere obliquely subducted northward beneath the southern margin of the Alashan craton, converting it from passive to active, and produced continental margin arc, forearc basin, forearc ridge, and accretionary prism, accompanied by the abundant granitoid intrusions. During the same period of time, the northern margin of the central-south Qilian craton had remained largely as a passive continental margin, but the paleo-Qilian oceanic lithosphere might have also subducted southward locally probably in the middle section of the north Qilian mountains. The cessation of the northerly oblique subduction in the late Silurian-Devonian period resulted an arc-continent collision and formed a backarc basin in the eastern section, and also left behind a segment of mid-oceanic ridge, an oceanic island arc, the enclosed remnant ocean, and a backarc basin on the surface of the earth in the western section. In summary, the lower Paleozoic plate tectonic structures of the north Qilian mountains are characterized by the orderly-arranged, well preserved mid-oceanic ridges, oceanic island arcs, accretionary prism, continental margin arcs, and backarc basins, and by the occurrence of Mariana-type and Andean-type subductions, dipolar subduction, and continental reworking and reactivation.

Yang, H.; Tseng, C.; Zuo, G.; Wu, H.; Xu, Z.; Yang, J.

2003-12-01

355

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

Microsoft Academic Search

The formation of the Virgin Islands Basin in the north eastern part of the Caribbean is controlled by the plate boundary between the Puerto Rico-Virgin Islands Micro Plate and the stable part of the Caribbean Plate. The Puerto Rico-Virgin Islands Micro Plate is one of three micro plates located in a complex plate boundary zone in the north eastern part

S. Raussen; H. Lykke-Andersen

2009-01-01

356

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

357

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

NASA Astrophysics Data System (ADS)

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

Condit, C. D.

2002-12-01

358

Heat Flow Scaling of Convection with Damage Theory and the Onset of Plate Tectonics  

NASA Astrophysics Data System (ADS)

Damage theory, which uses the observation that mineral grains tend to shrink under deformation, making the material weaker, and grow in the absence of applied stress, making the material stronger, has been proposed as a possible mechanism for shear localization in the Earth. A theoretical description of this rheology for continuum models has been developed, and it has been shown capable of producing a plate-like style of convection in 2-D convection models with a low (4-6 order of magnitude) viscosity contrast due to temperature dependence. This rheology utilizes a temperature and grain-size dependent viscosity, where grain-size in turn depends on deformational work and temperature. This results from assuming that in a statistical distribution of grain sizes, dislocation creep dominates in the larger grains, decreasing their size through dynamic recrystallization, while smaller grains deform in a diffusion creep regime. The bulk viscosity of the material is then controled by its weakest component, the small grains deforming by grain-size sensitive diffusion creep. Grains grow faster at higher temperatures, tending to increase viscosity in competition with the effect from thermally activated creep processes. This competition can therefore cause convection on the Earth to undergo changes in convective style due to its thermal evolution. A simple thermal evolution model assuming that the Nusselt number (Nu) scales as the Rayleigh number (Ra) to the 1/3 shows that two convection states, a stagnant surface and mobile surface, exist depending on material properties and thermal conditions. However, a heat flow scaling law for our more complicated viscosity model is dependent on more non-dimensional parameters than Ra, and perhaps completely different from the classical law for isoviscous convection. An investigation of the heat flow scaling law through 2-D numerical convection experiments is presented, as well as an extension of the regime diagram to higher viscosity contrasts. These results have important implications for possible shifts in tectonic regimes due to the Earths thermal evolution.

Foley, B. J.; Bercovici, D.

2009-12-01

359

Dynamics of subduction and plate motion in laboratory experiments: Insights into the ``plate tectonics'' behavior of the Earth  

Microsoft Academic Search

Three-dimensional laboratory experiments have been designed to investigate the way slab-bearing plates move during subduction inside the mantle. In our experiments a viscous plate of silicone (lithosphere) subducts under its negative buoyancy in a viscous layer of pure honey (mantle). Varying thickness, width, viscosity, and density of the plate and mantle, three characteristic modes of subduction are observed: a retreating

Nicolas Bellahsen; Claudio Faccenna; Francesca Funiciello

2005-01-01

360

Maximum horizontal stress orientations in the Cooper Basin, Australia: implications for plate-scale tectonics and local stress sources  

NASA Astrophysics Data System (ADS)

Borehole breakouts and drilling-induced tensile fractures (DITFs) were interpreted in 61 wells in the Cooper Basin indicating an average maximum horizontal stress orientation of 101N. A total of 890 borehole breakouts and 608 DITFs were interpreted in the Cooper Basin. The approximately east-west maximum horizontal stress orientation is consistent over much of the basin, except in the Patchawarra Trough where maximum horizontal stress rotates to a northwest-southeast orientation. This rotation in maximum horizontal stress orientation is consistent with in situ stress data to the northwest of the Cooper Basin. The stress field in the Cooper Basin appears to mark the apex of a major horseshoe-shaped rotation in maximum horizontal stress direction across central eastern Australia. Finite element modelling of the in situ stress field of the Indo-Australian Plate (IAP) using a range of plate-scale tectonic forces is able to match the regional maximum horizontal stress orientation over most of Australia reasonably well, including the mean east-west maximum horizontal stress orientation in the Cooper Basin. However, plate boundary-scale modelling does not adequately match the horseshoe-shaped stress rotation across central eastern Australia. The average east-west maximum horizontal stress orientation in the Cooper Basin indicates that stresses from tensional forces acting along the Tonga-Kermadec subduction zone are not transmitted into the interior of the Australian plate. The majority of the tensional forces associated with the Tonga-Kermadec subduction zone are most likely accommodated along the numerous spreading centres within the Lau-Havre backarc basin. A number of more localized stress anomalies have also been identified. These cannot be explained by plate-scale tectonic forces and are possibly a result of geological structure and/or density contrasts locally perturbing the stress field.

Reynolds, Scott D.; Mildren, Scott D.; Hillis, Richard R.; Meyer, Jeremy J.; Flottmann, Thomas

2005-01-01

361

Subcontinental mantle evidence for the onset of plate tectonics at 3 Ga in relation to Earth's thermal evolution  

NASA Astrophysics Data System (ADS)

Recent insights regarding the temporal distribution of components in the subcontinental lithospheric mantle (SCLM), coupled with tectonic aspects of the crust, provide a window into the thermal evolution of the Earth. Mantle evolution, crustal growth, and geochemical cycles of heat-producing elements may be linked to profound geodynamic changes. Substantial differences exist globally between >3.2 Ga versus <3.0 Ga old crust and SCLM. This age has been proposed as a boundary between different geodynamic regimes, marking the onset of plate tectonics and decline of pre-plate tectonic styles [1,2]. Geochemical studies of silicate and sulfide inclusions in cratonic macrodiamonds have been used to characterize the SCLM through time. Diamonds formed at >3.2 Ga contain exclusively peridotitic (harzburgitic) silicate and sulfide inclusions whereas diamonds formed at <3.0 Ga contain inclusions that are predominantly eclogitic and to a lesser extent lherzolitic. Similarly, >3.0 Ga old kimberlite-borne eclogite xenoliths are largely absent in the SCLM rock record, whereas they are common thereafter [1]. The lack of early eclogite implies an absence of steep slab subduction. Archean crust also records major differences across the 3.0-3.2 Ga interval. Prior to 3.2 Ga, crust grew by vertical accretion over upwelling mantle in long-lived plateaux floored by extremely depleted residual harzburgitic SCLM or via slab melting and crustal imbrication over shallow subduction zones, whereas lateral accretion, allochthonous greenstone belt growth and calcalkaline magmatic products of mantle wedge melting emerge only after 3.2 Ga [2]. A step-wise shift in tectonic style is evident from rapid mantle convection, small plates, shallow subduction, and localized recycling at >3.2 Ga, followed by large plates, steep subduction, and full upper mantle recycling at <3.0 Ga. These changes occur around the time (3 Ga) when the convecting mantle temperature reaches a maximum as heat-producing elements start to partition into the growing continental crust and diminish in the convecting mantle [3]. [1] Shirey and Richardson (2011) Science 333, 434-436. [2] Van Kranendonk (2011) Science 333, 413-414. [3] Labrosse and Jaupart (2007) EPSL 260, 465-481.

Richardson, S. H.; Shirey, S. B.

2011-12-01

362

Discovering Plate Boundaries, A Data-Rich Inquiry-Based Classroom Exercise for Teaching Plate Tectonic Boundary Processes  

Microsoft Academic Search

Discovering Plate Boundaries is a classroom exercise based on 4 world maps containing earthquake, volcano, topography, and seafloor age data. A novel aspect of the exercise is the jigsaw manner in which student groups access the maps and use them to discover, classify, and describe plate boundary types. The exercise is based only on observation and description, which makes it

D. S. Sawyer

2005-01-01

363

Diffuse Oceanic Plate Boundaries, Thin Viscous Sheets of Oceanic Lithosphere, and Late Miocene Changes in Plate Motion and Tectonic Regime  

Microsoft Academic Search

Diffuse plate boundaries are often viewed as a characteristic only of continental lithosphere and as a consequence of its rheology, while narrow boundaries and plate rigidity are viewed as characteristic of oceanic lithosphere. Here we review some of the evidence that shows that deformation in the ocean basins is in many places just as diffuse as deformation in the continents.

R. G. Gordon; J. Royer

2005-01-01

364

UPb evidence of ?1.7 Ga crustal tectonism during the Nimrod Orogeny in the Transantarctic Mountains, Antarctica: implications for Proterozoic plate reconstructions  

Microsoft Academic Search

The Pacific margin of East Antarctica records a long tectonic history of crustal growth and breakup, culminating in the early Paleozoic Ross Orogeny associated with Gondwanaland amalgamation. Periods of older tectonism have been proposed (e.g. Precambrian Nimrod and Beardmore Orogenies), but the veracity of these events is difficult to document because of poor petrologic preservation, geochronologic uncertainty due to isotopic

John W. Goodge; C. Mark Fanning; Vickie C. Bennett

2001-01-01

365

Thermochronology and Tectonics of the Leeward Antilles: evolution of the Southern Caribbean Plate Boundary Zone and accretion of the Bonaire Block  

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 zircon 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

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

2010-01-01

366

Evidence for a Major Late Precambrian Tectonic Event (RIFTING?) in the Eastern Midcontinent Region, United States  

NASA Astrophysics Data System (ADS)

Recently acquired gravity and aeromagnetic data delineate a large linear gravity anomaly which extends through eastern Kentucky and Tennessee and coincides with a zone of complex, high-amplitude magnetic anomalies. Basement lithologies in the area can be interpreted as a bimodal volcanic suite which is locally peralkaline in nature. These volcanics appear to be metamorphosed where they lie east of the Grenville front, suggesting they predate the Grenville metamorphic event. The available gravity, aeromagnetic, seismic refraction, and petrologic data, along with regional correlations, suggest that the best tectonic interpretation of these data is that a Keweenawan rift zone extended through the area. This rift can be roughly outlined by the gravity high, which is locally offset, suggesting the presence of transform faults. The boundaries of this rift have been locally reactivated and, in fact, a recent earthquake was located along its western boundary in northern Kentucky.

Keller, G. R.; Bland, A. E.; Greenberg, J. K.

1982-04-01

367

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

368

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)

1995-02-01

369

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

Microsoft Academic Search

The Kanto region of Japan is in a highly complex tectonic setting with four plates interacting with each other: beneath Kanto, situated on the Eurasian and North American plates, the Philippine sea plate subducts and the Pacific plate further descends beneath the North American and Philippine sea plates, forming the unique trench-trench-trench triple junction on the earth. In addition, the

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

2010-01-01

370

Slab width control on current global plate and trench velocities, and on Cenozoic western North America tectonics  

NASA Astrophysics Data System (ADS)

Subduction of tectonic plates into the Earth's mantle is accommodated by subducting plate motion and trench migration. How these two modes contribute to the subduction velocity and what controls their partitioning remain unsolved. Here we present a global compilation for 17 active subduction zones and three-dimensional numerical models of progressive free subduction showing that slab width (W) provides a first-order control on subduction partitioning, subducting plate velocity and trench velocity. In nature, subducting plate velocity increases progressively from -1 to 3 cm/yr for W = 300-600 km to 5-7 cm/yr for W = 7000 km, while the models show an increase from 2.5-3 cm/yr to 6 cm/yr. Furthermore, trench velocity decreases from 1-7 cm/yr for W = 300-600 km to -1 to 1 cm/yr for W = 7000 km in nature, whilst the models show an decrease from 6-7 cm/yr to ~1.5 cm/yr. The subduction zone data, numerical models and a scaling formulation for sinking of slabs in the upper mantle show that subducting plate velocity scales with ~Wexp(2/3), while trench velocity scales with ~1/W. Correlation coefficients for the numerical models with respect to the scaling formulation are in the range 0.95-0.99 for subducting plate velocity, trench velocity and subduction partitioning, while those for the natural data are in the range 0.70-0.72. It is thus found that slab width provides a first-order control plate velocity, trench velocity and subduction partitioning. Comparison of slab age and subduction kinematics for natural subduction zones gives significantly lower correlation coefficients (0.29-0.38), indicating that slab age provides a second-order control on trench velocity and subducting plate velocity. Our findings provide an explanation for the Cenozoic progressive decrease in subducting plate velocity and subduction partitioning of the Farallon plate, which we interpret as resulting from the progressive decrease in trench-parallel width of the Farallon slab during the Cenozoic from ~14000 km to only 1400 km at present. This decrease in slab width also explains the change from Sevier-Laramide orogenesis to Basin and Range extension in North America in the Eocene to Miocene. Shortening took place during wide-slab subduction and overriding-plate-driven trench retreat (push-back), whilst extension took place during intermediate to narrow-slab subduction and slab-driven trench retreat (pull-back).

Stegman, D. R.; Schellart, W. P.; Farrington, R. J.; Freeman, J. C.; Moresi, L. N.

2010-12-01

371

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

372

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

373

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

Microsoft Academic Search

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

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

1981-01-01

374

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

Microsoft Academic Search

Following several huge oil and gas discoveries during the mid-1980s in the Northern Venezuela overthrust belt more detailed geological and geophysical studies have increased their perception of structural control on sedimentary basin development. Significant improvements in seismic data quality and seismic lines positioned close to outcrops of the frontal thrust give evidence of Miocene to Pleistocene thin-skinned tectonics as the

J. Fuentes; S. Oum; R. Lander

1990-01-01

375

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

376

Tectonics of the Hjort region of the Macquarie Ridge Complex, southernmost Australian-Pacific plate boundary, southwest Pacific Ocean  

NASA Astrophysics Data System (ADS)

The Hjort Ridge, Trench, and Plateau comprise the southernmost portion of the Macquarie Ridge Complex (MRC), the Australian-Pacific plate boundary south of New Zealand. The MRC is an ideal location to study deformation and structural development at an obliquely convergent plate boundary involving oceanic lithosphere. This dissertation documents structures and processes in the Hjort region associated with incipient subduction, an outstanding problem in plate tectonics. I investigated the evolution of the plate boundary from 33 Ma to the present day, concentrating on the active and recent structural development. Interpretations are based on analyses of recently collected geophysical data in the Hjort region, including swath bathymetry, reflectivity, seismic reflection, gravity, magnetics, and seismicity. The Australian plate is actively underthrusting the Pacific plate along the Hjort Trench, but self-sustaining subduction does not appear to have commenced. Transpression along the length of the plate boundary has been accommodated by lithospheric flexure, strike slip faulting, and geographically limited underthrusting. A consistent relationship exists between the convergence angle and the amount of dynamically supported topography; up to 50 km of convergence has been accommodated by flexure forming ridges and troughs. A continuous, strike slip fault accommodates oblique convergence along the length of the boundary. Where angles of convergence are highest (>20), underthrusting is observed in addition. Gravity modeling and seismicity suggest 50 km of underthrusting in the southern Hjort Trench, but only define an eastwardly dipping Australian slab to about 20 km depth. Lithosphere underthrust in the southern trench is translated subparallel to the N-trending boundary, limiting the eastward extent of underthrust slab. Reconstructions of the plate boundary since 33.3 Ma show that the Antarctic-Australian-Pacific triple junction migrated southward with respect to the Australian plate resulting in the present day curved plate boundary. Migration resulted in lengthening of the dextral transform fault connecting the Macquarie Ridge and Southeast Indian Ridge spreading centers and shortening of the easternmost ridge-segment of latter spreading center. The MRC in the Hjort region changed from a dextral transform into an obliquely convergent zone of incipient subduction.

Meckel, Timothy Ashworth

377

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

NASA Astrophysics Data System (ADS)

The dynamic coupling between plate motion and mantle convection is investigated in a suite of Cartesian models by systematically varying aspect ratios and plate geometries. The aim of the study presented here is to determine to what extent plates affect mantle flow patterns, temperature and surface heat flux. To this end, we compare numerical convection models with free-slip boundary conditions to models that incorporate between one and six plates, where the geometries of the plates remain fixed while the plate velocities evolve dynamically with the flow. We also vary the widths of the plates and the computational domain in order to determine what constraint these parameters place on the mean temperature, heat flux and plate velocity of mantle convection models. We have investigated the influence of plates for three whole-mantle convection cases that differ in their heating modes (internally heated and basally heated) and rheologies (isoviscous and depth-dependent viscosity). We present a systematic investigation of over 30 models that exhibit increasingly complex behaviour in order to understand highly time-dependent systems using the insight gained from simpler models. In models with aspect ratios from 0.5 to 12 we find that for the same heating mode, variations in temperature can be as much as 40 per cent when comparing calculations with unit-width plates to models incorporating plates with widths equal to five times the model depth. Mean surface heat flux may decrease by 60 per cent over the same range of plate widths. We also find that internally heated mantle convection models incorporating plates exhibit novel behaviour that, we believe, has not been described previously in mantle convection studies. Specifically, in internally heated models, plate motion is characterized by episodic reversals in direction driven by changes in the mantle circulation from clockwise to counterclockwise and vice versa. These flow reversals occur in internally heated convection and are caused by a build-up of heat in the interiors of wide convection cells close to mantle downwellings. We find that flow reversals occur rapidly and are present in both single-plate and multiple-plate models that include internal heating. This behaviour offers a possible explanation for why the Pacific plate suddenly changed its direction some 43Ma.

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

2001-09-01

378

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

379

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

380

Intraplate Earthquakes, Lithospheric Stresses and the Driving Mechanism of Plate Tectonics.  

National Technical Information Service (NTIS)

An attempt is made to determine the type of faulting and to infer the state of stress within lithospheric plates on a worldwide scale from analyses of focal mechanisms of about eighty earthquakes, most of which are located well away from plate boundaries.

L. R. Sykes M. L. Sbar

1973-01-01

381

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

Microsoft Academic Search

The Pacific plate moved northwest rela- tive to North America since 42 Ma. The rapid half rate of Pacific-Farallon spread- ing allowed the ridge to approach the con- tinent at about 29 Ma. Extinct spreading ridges that occur offshore along 65% of the margin (Lonsdale, 1991) document that fragments of the subducted Farallon slab became captured by the Pacific plate

Tom Parsons

382

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

Microsoft Academic Search

Several studies have highlighted the role of a low viscosity asthenosphere in promoting plate-like behavior in mantle convection models. It has also been argued that the asthenosphere is fed by mantle plumes (Phipps- Morgan et al. 1993; Deffeyes 1972) and that the existence of the specific plume types required for this depends on plate subduction (Lenardic and Kaula 1995; Jellinek

A. Lenardic; T. Hoink

2008-01-01

383

Discovering Plate Boundaries, A Data-Rich Inquiry-Based Classroom Exercise for Teaching Plate Tectonic Boundary Processes  

NASA Astrophysics Data System (ADS)

Discovering Plate Boundaries is a classroom exercise based on 4 world maps containing earthquake, volcano, topography, and seafloor age data. A novel aspect of the exercise is the jigsaw manner in which student groups access the maps and use them to discover, classify, and describe plate boundary types. The exercise is based only on observation and description, which makes it useful at a wide variety of levels. We have used it successfully with middle school, high school, and college major and non-major earth science classes, as well as with pre-service and in-service teachers. The exercise takes three to four 50 minute class periods to complete and involves the students making presentations to one another in small groups and to the whole class. The students come away from the exercise with knowledge of the key features of each type of plate boundary and a sense of why each looks the way it does. While the materials are accessible on the web (http://terra.rice.edu/plateboundary/ and through http://www.dlese.org ), the actual exercise is not based on student access to the Web and is not dependent on classroom technology equipment.

Sawyer, D. S.

2005-12-01

384

Geological evidence for the geographical pattern of mantle return flow and the driving mechanism of plate tectonics  

SciTech Connect

Tectonic features at the earth's surface can be used to test models for mantle return flow and to determine the geographic pattern of this flow. A model with shallow return and deep continental roots places the strongest constraints on the geographical pattern of return flow and predicts recognizable surface manifestations. Because of the progressive shrinkage of the Pacific (averaging 0.5 km/sup 2//yr over the last 180 m.y.) this model predicts upper mantle outflow through the three gaps in the chain of continents rimming the Pacific (Carribbean, Drake Passage, Australian-Antartic gap). In this model, upper mantle return flow streams originating at the western Pacific trenches and at the Java Trench meet south of Australia, filling in behind this rapidly northward-moving continent and provding an explanation for the negative bathymetric and gravity anomalies of the 'Australian-Antarctic-Discordance'. The long-continued tectonic movements toward the east that characterize the Caribbean and the eastenmost Scotia Sea may be produced by viscous coupling to the predicted Pacific outflow through the gaps, and the Caribbean floor slopes in the predicted direction. If mantle outflow does not pass through the gaps in the Pacific perimeter, it must pass beneath three seismic zones (Central America, Lesser Antiles, Scotia Sea); none of these seismic zones shows foci below 200 km. Mantle material flowing through the Caribbean and Drake Passage gaps would supply the Mid-Atlantic Ridge, while the Java Trench supplies the Indian Ocean ridges, so that deep-mantle upwellings need not be centered under spreading ridges and therefore are not required to move laterally to follow ridge migrations. The analysis up to this point suggests that upper mantle return flow is a response to the motion of the continents. The second part of the paper suggest driving mechanism for the plate tectonic process which may explain why the continents move.

Alvarez, W.

1982-08-10

385

Possible effects of lateral viscosity variations induced by plate-tectonic mechanism on geoid inferred from numerical models of mantle convection  

Microsoft Academic Search

In a traditional analytical method, the convective features of Earths mantle have been inferred from surface signatures obtained by the geodynamic model only with depth-dependent viscosity structure. The moving and subducting plates, however, bring lateral viscosity variations in the mantle. To clarify the effects of lateral viscosity variations caused by the plate-tectonic mechanism, I have first studied systematically instantaneous dynamic

Masaki Yoshida

2004-01-01

386

Strainmeter observations of the 2010 slow slip event in Cascadia: A critical look at noise, artifacts, and tectonic signals  

Microsoft Academic Search

Periodic slow-slip events along the Cascadia subduction zone represent the transient release of accumulated strain along the plate interface. The location of these events helps to map the lower edge of the seismogenic zone and constrain the seismic hazard. The primary observations of these slow-slip events have come from a large array of GPS stations in the Pacific Northwest. However,

R. Krogstad; D. A. Schmidt

2010-01-01

387

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

PubMed

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

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

2013-05-22

388

The importance of mineral physics and a free surface in large-scale numerical models of mantle convection and plate tectonics  

Microsoft Academic Search

Here, our recent progress in understanding the large-scale dynamics of the mantle convection - plate tectonics system is summarised, with particular focus on the influence of realistic mineral physics and a free surface. High pressure and temperature experiments and calculations of the properties of mantle minerals show that many different mineral phases exist as a function of pressure, temperature and

Paul Tackley; Takashi Nakagawa; Fabio Crameri; James Connolly; Frdric Deschamps; Boris Kaus; Taras Gerya

2010-01-01

389

The effect of plate movements in the northern region of South America on tectonics and sedimentation in the Eastern Llanos Basin  

Microsoft Academic Search

The geological configuration of the Eastern Llanos pericratonic mega-basin has been directly affected by the overall tectonic regime experienced in the Northern part of South America. Interaction between the Pacific (Cocos), South American and Caribbean Plates generated a regional compressional dextral rotational force expressed as a regional North-South striking structural trend in the southern part of the basin and an

1993-01-01

390

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

ERIC Educational Resources Information Center

Grade five students' (n=58) conceptual understanding of plate tectonics was measured by analysis of student-generated summaries and diagrams, and by posttest assessment of both the spatial/static and causal/dynamic aspects of the domain. The diagram group outperformed the summary and text-only groups on the posttest measures. Discusses the effects

Gobert, Janice D.; Clement, John J.

1999-01-01

391

Archean and Early Proterozoic Events Along the Snowbird Tectonic Zone in Northern Saskatchewan, Canada  

Microsoft Academic Search

The Snowbird tectonic zone is a major boundary structure in the Canadian shield, separating rocks of the Rae and Hearne lithostructural domains. Field investigations along portions of the Snowbird tectonic zone exposed in Northern Saskatchewan have revealed a major granulite facies mylonite belt that records deformation and metamorphism at several intervals in the Archean and early Proterozoic. Early assemblages are

Christopher F. Kopf

2002-01-01

392

Fostering Inquiry and Scientific Investigation in Students by Using GPS Data to Explore Plate Tectonics and Volcanic Deformation  

NASA Astrophysics Data System (ADS)

The Education and Outreach program at UNAVCO has developed free instructional materials using authentic high-precision GPS data for secondary education and undergraduate students in Earth science courses. Using inquiry-based, data-rich activities, students investigate crustal deformation and plate motion using GPS data and learn how these measurements are important to scientific discovery and understanding natural hazards and the current state of prediction. Because this deformation is expressed on Earth's surface over familiar time scales and on easily visualized orders of magnitude, GPS data represent an effective method for illustrating the geomorphic effects of plate tectonics and, in essence, allow students to 'see' plates move and volcanoes deform. The activities foster student skills to critically assess different forms of data, to visualize abstract concepts, and to evaluate multiple lines of evidence to analyze scientific problems. The activities are scaffolded to begin with basic concepts about GPS data and analyzing simple plate motion and move towards data analyses for more complex motion and crustal deformation. As part of assessment, students can apply new knowledge to explore other geographic regions independently. Learning activities currently include exploring motion along the San Andreas Fault, monitoring volcano deformation and ground movement at the Yellowstone Caldera, and analyzing ground motion along the subduction zone in the Cascadia region. To support educators and their students in their investigations, UNAVCO has developed the Data for Educators portal; http://www.unavco.org/edu_outreach/data.html. This portal provides a Google-map displaying the locations of GPS stations, web links to numerical GPS data that illustrate specific Earth processes, and educational activities that incorporate this data. The GPS data is freely available in a format compatible with standard spreadsheet and graphing programs as well as visualization and analysis tools such as the Integrated Data Viewer (IDV). After becoming familiar with the data available through the Data for Educators portal, students are more prepared to use the full UNAVCO data archive to conduct their own independent investigations.

Olds, S. E.; Eriksson, S.

2007-12-01

393

Age progressive volcanism in the Comores Archipelago, western Indian Ocean and implications for Somali plate tectonics  

NASA Astrophysics Data System (ADS)

The Comores Islands together with the Tertiary volcanic province of northern Madagascar form a sublinear trend of alkali olivine basalt shield volcanoes across the northern entrance of the Mozambique Channel. Potassium-argon dating of shield-building lavas confirms an eastward increase in age of volcanism along the chain, consistent with a hotspot origin for the lineament. The velocity of the Somali plate over the mantle magma source is 50 mm/yr. We use the distribution of ages along the Comores-Madagascar chain in conjunction with existing age data for the Reunion-Mascarene Plateau hotspot track to model the absolute motion of the Somali plate for the last 10 m.y. We calculate the relative motion across the East African Rift by subtracting the Somali plate absolute motion from African plate absolute motion during this period. The model predicts 320 km of total separation across the East African Rift during the past 10 m.y. which is greater than has been estimated from surface geological evidence The geometry of older portions of the Comores and Reunion trends indicates that there was no significant relative motion between the African and Somali plates prior to about 10 m.y. ago.

Emerick, C. M.; Duncan, R. A.

1982-10-01

394

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

395

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

396

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

397

What Controls Space-Time Patterns of Magmatism in Western North America: Plate Tectonics, Delamination, or Convection?  

NASA Astrophysics Data System (ADS)

Mesozoic and Cenozoic magmatism in western North America is commonly explained by shallowing and steepening of subduction along the west coast of North America, and progressive destruction of the subduction system by development of the San Andreas transform fault system. This hypothesis makes several specific predictions about space-time patterns of magmatism, including eastward and westward sweeps, development of slab-window magmatism, and progressive northward extinction of an ancestral Cascade arc. However, analysis of space-time patterns using the NAVDAT database indicates that these predicted patterns are curiously obscure in the magmatic record, although other unexplained patterns are strong. Animation of about 29,000 Cenozoic U.S. points from NAVDAT (www.navdat.org) demonstrates that: (1) calc- alkaline, intermediate volcanism is poorly linked to the subduction system; (2) there is little evidence for slab- window magmatism; (3) there was no ancestral Cascade arc south of Oregon until ca. 10 Ma; (4) magmatism shifted from primarily silicic to dominantly basaltic throughout the Miocene; and (5) magmatism was clearly migratory in several directions in ways that cannot be explained by plate-tectonic processes, at length scales ranging from 1000s to 10s of km. Space-time patterns that cannot be readily linked to plate-tectonic control include: (1) a silicic sweep from Montana into Nevada from 50 to 20 Ma; (2) a clockwise sweep around the Colorado Plateau from New Mexico to southern Nevada from about 30 to 15 Ma; (3) a burst of magmatism at about 16 Ma in northern Nevada, followed by outward sweeps to Yellowstone, Oregon, and the Sierra Nevada; (4) progressive encroachment of basaltic magmatism onto the Colorado Plateau, and (5) several local migrations, including from Phoenix north onto the Colorado Plateau and from the San Francisco Bay area north to the Geysers geothermal field. These migrations typically occurred at 20-50 mm/yr. Possible origins include convective upwelling related to extension, local, migrating delamination of the North American lithosphere or subducted Farallon plate, edge-driven convection at lithospheric discontinuities, and forced convection as the subducted Mendocino fracture zone scraped under North America.

Glazner, A. F.

2007-05-01

398

Cocos plate structure along the Middle America subduction zone off Oaxaca and Guerrero, Mexico: Influence of subducting plate morphology on tectonics and seismicity  

NASA Astrophysics Data System (ADS)

Two new bathymetric and magnetic surveys are presented from which the history and recent tectonics of the Cocos plate off the Middle America subduction zone are determined. The East O'Gorman fracture zone, a previously proposed outer rise feature, is not present along the Oaxaca trench outer rise near the trench axis. Several parallel ridges of seamounts are entering the subduction zone 15--20 from orthogonal to the trench axis. These ridges lie roughly parallel to the spreading direction and were created as off-axis volcanism. The southern Mexico trench outer rise exhibits reactivation of the inherited abyssal-hill and trench-parallel faults to accommodate extension from plate flexure. Plate boundary forces also produce a new unusual family of normal faults parallel to and flanking the seamounts. An anomalous increase in outer rise earthquakes accompany these faults indicating they are seismically active. Trench-parallel extension related to the geometry of the trench axis bend and increasing plate convergence angle may contribute to their genesis. Unusual outer-rise faulting off of the Japan trench (Kobayashi et al., 1998) which is coincident with a trench axis bend is used to argue that specific conditions at subduction zones may activate inherited fracture-zone-parallel weakness. This controls fault orientation at the Japan and Mexico outer rises. Seafloor morphology and seismicity evidence leads to a "slivered" ocean-crust model that is broken along the seamount-parallel faults at the subduction zone. This accounts for the consistent rupture geometry (40--100 km fault failure) and the uniformity in the character of the thrust waveforms. Limited magnitudes of shallow thrust earthquakes appear to be a consequence of the subducted slivering crust. A review of regions whose structures and forces are similar to those present in the subducting Cocos plate off Oaxaca indicates that crustal slivering is not unique. Forces other than a trench axis bend must be present to furnish the entirely unique seamount-parallel outer-rise faulting. Either/both convergence direction and spreading-parallel inherited weakness orientation may determine outer-rise fault strike. Methods for resolving ambiguous data are proposed.

Kanjorski, Nancy Marie

399

Plate Tectonics ; The General Theory The Complex Earth is Simpler Than You Think  

Microsoft Academic Search

The standard model of mantle dynamics and chemistry involves complex interactions between rigid plates and hot plumes, and exchanges between the upper and lower mantles. This model requires many assumptions and produces many paradoxes. The problems and complexities can be traced to a series of unnecessary and unfruitful assumptions. A simpler and more general hypothesis is described that is based

Don L. Anderson

400

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

401

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

402

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

403

Tectonic evolution of the AntarcticPhoenix plate system since 15 Ma  

Microsoft Academic Search

Joint inversion of magnetic isochron and fracture zone data from the extinct AntarcticPhoenix spreading system in SW Drake Passage yields seven new finite reconstruction poles. The inversion results are very well constrained for such a short length of plate boundary. Although this is partly because the finite poles are located close to the reconstructed region, the optimum use of fracture

Graeme Eagles

2004-01-01

404

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

NASA Astrophysics Data System (ADS)

Sea-floor age-depth and age-trench-depth relations suggest that the oceanic lithosphere continues to thicken and subside with age beyond 80 Ma. If so, slab-pull (FS) and ridge-push (FR) forces can be calculated from the age of the sea floor at trenches (t), and if the shear stress acting on the base of the plate increases with absolute velocity (?a), the approximate force balance equation isFD1 Dva2=Svat32+Rt where D, S and R are constants related to drag, slab pull and ridge push, respectively. The relation between velocity and age is FD2 va2=S?vat12+R? We have tested this model by linear regression using rate and age data for 15 trenches: FD3 va(mm/a)2=(9.20.32)vat12+(26250) The strength of this correlation (r = 0.98) is strong evidence in favor of the validity of this simple model. These results suggest that ridge push is just sufficient to overcome drag at the base of the plate, and does not contribute significantly to the motions of oceanic plates, though the value of R? is consistent with the motions of plates not attached to subducted slabs.

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

1983-04-01

405

Combining floating continents and a free surface in a 3D spherical mantle convection model with self-consistent plate tectonics  

NASA Astrophysics Data System (ADS)

The dynamics of the Earth's lithosphere and mantle are strongly influenced by its upper mechanical boundary condition. For instance, our previous work has shown that a necessity for the evolution of Earth-like, single-sided subduction is a free surface, which allows for vertical movement of the two converging plates, i.e. the development of surface topography [Crameri et al (2012), in press]. Single-sided subduction has an important effect on the evolution of self-consistent plate tectonics, e.g. by shaping subduction trenches. However, due to the usage of a homogeneous, i.e. purely oceanic, lithosphere these models tend to favour the rigid lid mode of plate tectonics for a realistic strength of the lithosphere, which is in contradiction to the present-day Earth. In contrast, our previous work with a pre-existing heterogeneous structure of the lithosphere has shown that the presence of continents floating at the top of the mantle may play an important role in the evolution of plate tectonics. Convective stresses may be focussed at the rheological boundary between continent and ocean, which facilitates the formation of plate boundaries and makes the Earth-like, mobile lid mode of plate tectonics easier to observe [Rolf & Tackley (2011)]. However, in these models subduction is single-sided when one oceanic and one continental plate converge, but double-sided in the case of two converging oceanic plates. Taking the previous findings as a motivation, we now combine both ingredients: the free surface and the heterogeneous lithosphere, in one self-consistent model. We approximate the free surface by using a "sticky air" layer [Schmeling et al, 2008; Crameri et al., submitted] and the continents by strong Archaean cratons, which can resist recycling on long timescales [Rolf & Tackley (2011)]. Such a model might produce single-sided subduction that is continuously evolving supported by the presence of continents. Performing global-scale self-consistent mantle convection and using constraints from geological observations and laboratory experiments will further allow for constraining the conditions - in particular the rheological and properties of oceanic and continental lithosphere - that allow for Earth-like evolution of plate tectonics.

Rolf, T.; Crameri, F.; Tackley, P. J.

2012-04-01

406

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 NubiaEurasia 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 NubiaEurasia 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 NubiaEurasia 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 (38.5N39.5N) is intermediate between the EurasiaNorth America rate measured at 39.5N and the NubiaNorth America rate measured at 38.5N, consistent with the joint conclusions that the NubiaEurasia 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

407

Exhumation and Coupling at the Plate Interface: Large Tectonic Slices V. Melange Formation? Key Contexts and Possible Controlling Parameters  

NASA Astrophysics Data System (ADS)

Fragments of subducted oceanic lithosphere returned along the plate interface convey crucial information regarding the thermal and rheological conditions of convergent plate boundaries. Geological evidence indicate that, unlike subduction, exhumation is non-steady (Agard et al., Earth Sci. Rev. 2009). We herein focus on deep processes along the plate interface (40-80 km depth), for which there is no counterflow (unlike in accretionary prisms) and no other known mechanisms to return eclogites than interplate friction or buoyancy. These eclogites are of two major types: large scale (>km) slices with coherent PT estimates (W. Alps) versus isolated fragments (frequently m-hm) in a serpentinite- or sedimentary-rich matrix showing contrasting equilibration depths (with hints of punctuated exhumation and even reburial; Franciscan, Cuba, Sistan; e.g., Garcia-Casco et al., Geol. Acta 2006). This latter type tends to show warmer equilibration paths, whereas the larger tectonic slices from the former type remain systematically cold. Serpentinites are crucial for both in permitting decoupling and acting as a buoy, and fluid budget is important too in enhancing floatability and allowing large slices to survive (Angiboust and Agard, Lithos 2010). Numerical models implementing free migration of fluids in the subduction zone also show that the plate interface is strongly localized in the absence of fluids: mechanical decoupling efficiently occurs along the sediment veneer and/or at the top of the highly hydrothermalized crust. Whenever fluids are released in greater amounts (depending on initial fluid content and/or thermal structure), deformation becomes much more distributed and affects both the mantle wedge and the top of the downgoing lithosphere (crust and hydrated mantle top), thereby increasing mechanical coupling between the two plates. Based on natural data and numerical modelling we herein propose that rheological contrast chiefly controls mechanical decoupling. On a steady-state basis the subduction interface is apparently efficiently decoupled. In this context, we hypothetize that the liberation of fluid through pulses (or a somewhat increased amount of fluids) is required to locally modify mechanical coupling and induce the slicing of large pieces of oceanic material along the subduction interface (type 1). By contrast, an extreme hydration of the subduction interface and mantle wedge will result in the formation of serpentinite melanges and extensive material mixing (e.g., cold plumes, mafic pods and localized melting; type 2). This latter situation may be promoted by young/fast/wet subduction, such as subduction initiation and/or subduction of young lithosphere or subduction of a particularly hydrated lithosphere section (e.g., at the ridge and/or prior to entering the trench), whereas cold, slow subduction (type 1) will result in irregular hydration and localized coupling able to detach large slices.

Agard, P.; Angiboust, S.; Guillot, S.; Garcia-Casco, A.

2011-12-01

408

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

Microsoft Academic Search

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 parentdaughter isotopic variations

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

2004-01-01

409

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

Microsoft Academic Search

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

Didier Sornette; Anne Sornette; Philippe Davy

1990-01-01

410

Hotspot trails in the South Atlantic controlled by plume and plate tectonic processes  

NASA Astrophysics Data System (ADS)

The origin of hotspot trails is controversial. Explanations range from deep mantle plumes rising from the core-mantle boundary (CMB) to shallow plate cracking. However, these mechanisms cannot explain uniquely the scattered hotspot trails distributed across a 2,000-km-wide swell in the sea floor of the southeast Atlantic Ocean. This swell projects down to one of the two largest and deepest distinct regions at the CMB, the Africa Low Shear Wave Velocity Province. Here we use 40Ar/39Ar isotopic analyses to date lava samples erupted at several hotspot trails across the Atlantic swell. We combine the eruption ages with an analysis of the structure and age of the sea floor, and find that the trails formed synchronously, in a pattern consistent with movement of the African Plate over plumes rising from the edge of the Africa Low Shear Wave Velocity Province. However, we also find that the seamounts initially formed only at the edge of the swell, where the oceanic crust was spreading apart. Later, about 44 million years ago, the hotspot trails began to cross the swell, but only in locations where the lithosphere was sufficiently young and thin that magma could reach the surface. We conclude that the distribution of hotspot trails in the southeast Atlantic Ocean is controlled by the interplay between deep-sourced mantle plumes and the motion and structure of the African Plate.

O'Connor, John M.; Jokat, Wilfried; Le Roex, Anton P.; Class, Cornelia; Wijbrans, Jan R.; Keling, Stefanie; Kuiper, Klaudia F.; Nebel, Oliver

2012-10-01

411

23.4 Ellipsoidal Features on Earth that fit Impact Origins Better than Plate Tectonic Origins  

NASA Astrophysics Data System (ADS)

Earth has 16 large lakes, seas, ocean features, and depressions that are ellipsoidal with their major axis ~23.4 degrees. The tilt of the Earth cannot relate to tectonic processes. Impact origins fit the geology better than tectonic origins.

Burgener, J. A.

2013-09-01

412

Triassic post collision igneous activity and granulite facies metamorphic event in the Yangpyeong area, South Korea and its meaning to the tectonics of Northeast Asia  

NASA Astrophysics Data System (ADS)

The Korean peninsula is tectonically positioned in the eastern margin of the Asia continent and the Gyeonggi massif is situated in the center part of Korean peninsula. Triassic (231 Ma) eclogite was first found in the Hongseong area, the southwestern part of the Gyeonggi Massif, which suggested that the Hongseong area is the extension of Triassic collision belt between the North and South China blocks, in China. The 257-226 post-collisional mangerite was also found in the Odesan area, the eastern part of Gyeonggi massif. Based on these new findings, it was proposed that the line connecting Hongseong and Odesan areas is the collision belt between the North and South China blocks. It was also reported that 247 Ma ultrahigh temperature metamorphism occurred together with the intrusion of mangerite in the Odesan area indicating that regional metamorphism occurred together with the post-collision igneous activity. The Yangpyeong area locates in the middle part of the Hongseong-Odesan collision belt. The area mainly consists of Precambrian migmatitic gneiss which was intruded by Triassic igneous complex. The igneous complex mainly consists of gabbro and porpyritic syeno-diorite and SHRIMP age dating indicates that they intruded at 227 4 Ma. They are shoshonitic and high-K series and have high Ba, Sr contents. They show LREE enriched pattern and Nb, Ta, P, Ti depletion in the chondrite- and primitive-mantle-normalized trace element patterns, respectively. In the tectonic discrimination diagrams, gabbros are plotted in the within plate tectonic field and porpyritic syeno-diorites are plotted in the Post-collision field. These geochemical characters indicate that they formed in the within plate after continental collision. Two metamorphic ages (1861 6 Ma, and 235 6 Ma) are obtained from the migmatitic gneiss. The peak metamorphic conditions of the first Precambrian metamorphism are 750-780C and 8-10 kbar indicating intermediate-P/T metamorphism. On the other hand, the second Triassic metamorphism is low-P/T type granulite facies metamorphism with peak metamorphic condition of 775C and 5.4 kbar. These Triassic post-collisional igneous activity and low-P/T type granulite facies metamorphic event are expected to be caused by heat supplied from asthenosphere through the opening formed by oceanic slab break-off from the continental slab after collision. Triassic post collisional igneous activities are also widespread in area to the north of the Hongseong-Odesan belt in Korean Peninsula and these igneous activities may be correlated to the Triassic post collisional igneous activities along the southern margin of the North China block in China.

Lee, S.; Oh, C.

2009-12-01

413

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

ERIC Educational Resources Information Center

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

Clary, Renee; Wandersee, James

2011-01-01

414

A Magmatic System as an Indicator of Tectonic Stresses around Plate Boundary; Crustal Deformation in and around Izu-Oshima Japan Derived from Continuous GPS Measurments  

NASA Astrophysics Data System (ADS)

The area around Izu peninsula Japan is situated in a boundary region between the Philippine Sea plate and a continental plate. There are a number of things that bring a complexity to the tectonic setting of the region; the proximity to a triple junction of a continental and two oceanic plates and a volcanic front running through being accompanied by a line of volcanic islands and several major volcanoes on land. There still remain a number of questions yet to be solved. The crustal deformation data set provided by continuous GPS measurements is one of the key pieces of information to understand the ongoing complex tectonic processes in the region. Among the results, an interesting and even intriguing finding from GPS is that a large horizontal strain is not seen in and around the northern part of Izu peninsula which is thought to be the plate boundary. A high rate of shear strain accumulation is found between the peninsula and Izu-Oshima, which is a volcanic island located in further south of the plate. Even in the historical period several earthquakes as large as M7.0 and a number of eruptions of the volcano were recorded. A simple estimation of the accumulated strain suggests that there is an enough energy to produce at least M6 earthquake in the area. As a first step to understand the tectonic situation we are interested in the temporal and spatial change of strain field in the region. We find an interesting interaction between the magmatic system of the volcano and surrounding tectonic situation. We detected an inflation of the island suggesting a swell of a magma chamber located at about 5 km depth beneath the caldera. The trend of the inflation changed when Miyakejima, which is another island volcano about 70 km to the south of Izuoshima, erupted in 2000. The eruption was associated with a huge dike intrusion which deformed the crust within a distance of about 200 km. Another interesting finding is the episodicity of the inflation which is correlated with the occurrence of earthquake swarm. The focal mechanism of the swarms is accordant with the surrounding tectonic situation. Those suggest a multi-layered interaction between the magmatic system and the tectonic stresses around it. In the presentation we will discuss the details of the relationship between crustal deformation and seismicity in Izu-Oshima volcano revealed by multidisciplinary geophysical monitoring.

Murakami, M.

2003-12-01

415

Pan-African tectonic evolution and glacial events registered in Neoproterozoic to Cambrian cratonic and foreland basins of West Africa  

NASA Astrophysics Data System (ADS)

This paper attempts to describe the Neoproterozoic Cambrian lithostratigraphic successions occurring on the West African craton and in the surrounding Pan-African fold belts, with special reference to glacial or glacially influenced deposits. It provides a brief synthesis of these terrains in order to propose inter-regional correlations, and to place the glacial events already described in the literature within the tectonic framework of this part of the world. Correlations are based on facies associations and isotopic databases, and supported by the occurrence of glacial deposits when these are ascribed to continental-scale glaciation. As expected, there is a diachronism of the main tectonic events around the craton when the mobile belts display a roughly similar overall facies trend reflecting the successive stages of the Pan-African orogenic cycle from rifting to collision. Contrary to most of the Neoproterozoic glacial strata elsewhere, which consist generally of marine diamictites preserved in marginal basins, West Africa displays the cratonic counterpart (tillites and associated terrestrial facies) deposited on exposed land surface by continental ice sheets. Lithostratigraphic correlations and a combination of relative dates on sedimentary rocks and on tectonic markers show that a major West African glaciation occurred between 630 and 610 Ma and can be correlated with the Marinoan ice age. This major climatic event is contemporaneous with the final stages of the Pan-African orogenic cycle. Under favourable climatic conditions (mid to high latitudes), the presence of surging reliefs at the rim of a wide cratonic platform may account for the development of the West African Marinoan ice sheet. The diachronism around the craton of collision-surrection events may also account for the occurrence of unrelated local mountain-type glaciation that could be mistaken with the craton-scale glaciation.

Deynoux, Max; Affaton, Pascal; Trompette, Roland; Villeneuve, Michel

2006-12-01

416

Fabric development as the key for forming ductile shear zones and enabling plate tectonics  

NASA Astrophysics Data System (ADS)

Lithospheric deformation on Earth is localized under both brittle and ductile deformation conditions. As high-temperature ductile rheologies are fundamentally strain-rate hardening, the formation of localized ductile shear zones must involve a structural or rheological change or a change in deformation conditions such as an increase in temperature. In this contribution, I develop a localization potential that quantifies the weakening associated with these changes. The localization potential corresponds to the increase in strain rate resulting from that change under constant stress conditions. I provide analytical expressions for the localization potential associated with a temperature increase, grain size reduction, an increase in water fugacity, melt content, or the abundance of a weak mineral phase. I show that these processes cannot localize deformation from a mantle convection scale (103 km) to a ductile shear zone scale (1 km). To achieve this, is it necessary to invoke a structural transition whereby the weak phase in a rock forms interconnected layers. This process is efficient only if one phase is much weaker than the others or if the weakest phase has a highly non-linear rheology. Micas, melt, and fine-grained aggregates - unless dry rheologies are used - have the necessary characteristics. As none of these phases is expected to be present in the dry lithosphere of Venus, this concept can explain why Venus, unlike the Earth, does not display a global network of plate boundaries. The diffuse plate boundary in the Central Indian Ocean may be as yet non-localized because serpentinization has not reached the ductile levels of the lithosphere.

Montsi, Laurent G. J.

2013-05-01

417

Global tectonics and space geodesy  

Microsoft Academic Search

Much of the success of plate tectonics can be attributed to the near rigidity of tectonic plates and the availability of data that describe the rates and directions of motion across narrow plate boundaries of about 1 to 60 kilometers. Nonetheless, many plate boundaries in both continental and oceanic lithosphere are not narrow but are hundreds to thousands of kilometers

Richard G. Gordon; Seth Stein

1992-01-01

418

Lateral rheological lithospheric heterogeneities in the tectonic evolution of intra-plate deformation  

NASA Astrophysics Data System (ADS)

Lithospheric-scale analogue models were used to investigate the deformation pattern and topography development characterizing mountain building in intra-plate settings as a function of the presence of lateral rheological heterogeneities. The presented series of models is the first part of a broader project that aims at the understanding of the interference pattern of short and long wavelength deformation as a function of the location and reactivation of pre-existing heterogeneities within the lithosphere (crust versus mantle) upon shortening and its bearing on dynamically supported topography. Three layers (brittle crust/ductile crust/weak ductile mantle) models characterized by the presence of a "disturbance zone" (DZ) were deformed at a constant velocity under normal gravity conditions. DZ is striking perpendicular to the compression direction and located either in the ductile mantle or in both ductile crust and mantle. Lithospheric thickness, width of the DZ and relative lateral strength contrasts have been the main investigated parameters. Experimental results show that in the absence of a DZ the deformation history of a relatively weak lithosphere is characterized by early occurrence of pop-up and pop-down structures in the central part of the model. There deformation remains localized, in correspondence of a broad synform developed in the ductile part of the lithosphere. The presence of a DZ located in the ductile mantle and characterized by a small strength contrast with respect to the surrounding lithospheric blocks localizes the deformation at its boundaries. Deformation starts close to the DZ inner boundary and propagates forward (away from the moving wall), leaving an undeformed region underlined by a relatively flat Moho above the DZ. Distribution of pop-up and pop-down structures in the brittle crust appears to correlate with the position of synforms in the ductile lithosphere. Reducing the thickness of the lithosphere the strain becomes wider distributed in the upper crust where fore- and back-thrusts are closely spaced although an undeformed region above the DZ located in the ductile mantle remains present. The width of the DZ determines the wavelength of upper crustal deformation and the timing of its forward propagation. When a wider DZ is present strain concentrates at the inner boundary and structures at its outer boundary appear later in the deformation history. When the upper boundary of the DZ is located at the brittle-ductile transition a broader undeformed region is present in the central part of the model. Upper crustal structures are not directly aligned with the DZ boundaries. The results of this series of models contrast with the deformation pattern observed in previously conducted models characterized by stronger strength contrast between converging plates and an intervening weak zone. In this case the weak zone was deformed into a broad slightly asymmetric antiformal structure with prominent Moho uplift, flanked by a doubly vergent fold and thrust belt. Our modelling results provide valuable insight in favourable rheological conditions for the transfer of strain in intra-plate settings and are applicable to natural laboratories.

Calignano, E.; Sokoutis, D.; Willingshofer, E.; Burg, J. P.

2012-04-01

419

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

PubMed

We investigated the phylogenetic relationships of Pseudophoxinus (Cyprinidae: Leuciscinae) species from central Anatolia, Turkey to test the hypothesis of geographic speciation driven by early Pliocene orogenic events. We analyzed 1141 aligned base pairs of the complete cytochrome b mitochondrial gene. Phylogenetic relationships reconstructed by maximum likelihood, Bayesian likelihood, and maximum parsimony methods are identical, and generally well supported. Species and clades are restricted to geologically well-defined units, and are deeply divergent from each other. The basal diversification of central Anatolian Pseudophoxinus is estimated to have occurred approximately 15 million years ago. Our results are in agreement with a previous study of the Anatolian fish genus Aphanius that also shows a diversification pattern driven by the Pliocene orogenic events. The distribution of clades of Aphanius and Pseudophoxinus overlap, and areas of distribution comprise the same geological units. The geological history of Anatolia is likely to have had a major impact on the diversification history of many taxa occupying central Anatolia; many of these taxa are likely to be still unrecognized as distinct. PMID:15186815

Hrbek, Tomas; Stlting, Kai N; Bardakci, Fevzi; Kk, Fahrettin; Wildekamp, Rudolf H; Meyer, Axel

2004-07-01

420

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

Microsoft Academic Search

The response of lithospheric plate boundaries to rapid changes in plate motions provide constraints used to determine the manner in which transitions in plate motions and plate boundary configurations can occur. In the case of the Australia - Pacific plate boundary in the Macquarie Ridge region south of New Zealand a substantial change in plate motions has occurred since the

G. P. Hayes; K. P. Furlong

2007-01-01

421

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

NASA Astrophysics Data System (ADS)

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

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

2004-12-01

422

Subduction of aseismic ridges beneath the Caribbean Plate: Implications for the tectonics and seismic potential of the northeastern Caribbean  

NASA Astrophysics Data System (ADS)

Normal seafloor entering the Puerto Rico and northern Lesser Antillean trenches in the northeastern Caribbean is interrupted by a series of aseismic ridges on the North and South American plates. These topographic features lie close to the expected trend of fracture zones created about 80-110 m.y. ago when this seafloor was formed at the Mid-Atlantic Ridge. The northernmost of the ridges that interact with the Lesser Antillean subduction zone, the Barracuda Ridge, intersects the arc in a region of high seismic activity. Some of this seismicity including a large shock in 1974, occurs within the overthrust plate and may be related to the deformation of the Caribbean plate as it overrides the ridge. A large bathymetric high, the Main Ridge, is oriented obliquely to the Puerto Rico trench and intersects the subduction zone north of the Virgin Islands in another cluster of seismic activity along the inner wall of the trench. Data from a seismic network in the northeastern Caribbean indicate that this intersection is also characterized by both interpolate and intraplate seismic activity. Magnetic anomalies, bathymetric trends, and the pattern of deformed sediments on the inner wall of the trench strongly suggest that the Main and Barracuda ridges are parts of a formerly continuous aseismic ridge, a segment of which has recently been overridden by the Caribbean plate. Reconstruction of mid-Miocene to Recent plate motions also suggest that at least two aseismic ridges, and possibly fragments of the Bahama Platform, have interacted with the subduction zone in the northeastern Caribbean. The introduction of these narrow segments of anomalous seafloor into the subduction zone has segmented the arc into elements about 200 km long. These ridges may act as tectonic barriers or asperities during the rupture processes involved in large earthquakes. They also leave a geologic imprint on segments of the arc with which they have interacted. A 50-km landward jump of the locus of island arc volcanism occurred in Late Miocene time along the northern half of the Lesser Antilles. We postulate that the subduction of a segment of seafloor of anomolously thick crust, being more buoyant than adjacent seafloor, resulted in a marked shoaling in the dip of the descending slab and, therefore, a shift of the locus of volcanism. In the region near western Puerto Rico and eastern Hispanolia, Plio-Pleistocene interaction with a similar feature, in this case a part of the Bahama Platform, about 3-4 m.y. ago led to a jump in the locus of subduction as evidenced by a gap in the downgoing seismic zone. That segment of the Bahama Platform interferred with the subduction process and was subsequently sutured onto the Caribbean plate when the boundary jumped about 60 km to the northeast. The maximum size of historic shallow earthquakes along the Lesser Antillean arc varies from about 7.0-7.5 in the center of the arc where the dip of the shallow part of the plate boundary is steep to 8.0-8.5 along the northern part of the arc where the dip is shallow. The interaction of anomalous seafloor, as along the northern Lesser Antilles, can lead to the development of a wider than normal zone of interplate contact and hence to earthquakes that are larger than those associated with more typical seafloor entering subduction zones. Major seismic gaps and regions of high seismic potential currently exist along the northern Lesser Antilles and to the north of Puerto Rico. Both gaps are bounded by anomalous features on the downgoing plate. The intersection of these features with the plate boundary created large asperities that may be good places to search for precursors to future large earthquakes. A great shock in 1787 may have ruptured an existing seismic gap north of Puerto Rico between 65 and 67W. Thus that gap can be expected to eventually rupture again in a great shock and not to accommodate