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Last update: August 15, 2014.
1

Plate Tectonics  

NSDL National Science Digital Library

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

Walls, Mrs.

2011-01-30

2

Plate Tectonics  

NSDL National Science Digital Library

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

2006-01-01

3

Plate Tectonics  

NSDL National Science Digital Library

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

Rohlfing, Mrs.

2011-02-03

4

Plate Tectonics  

NSDL National Science Digital Library

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

5

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

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 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

8

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

9

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

10

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

11

Tectonic Plates and Plate Boundaries  

NSDL National Science Digital Library

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

Foundation, Wgbh E.

2005-12-17

12

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

13

Earthquakes and plate tectonics.  

USGS Publications Warehouse

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

Spall, H.

1982-01-01

14

Caribbean plate tectonics  

NSDL National Science Digital Library

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

Sting; Commons, Wikimedia

15

Geology: Plate Tectonics  

NSDL National Science Digital Library

This site is the Plate Tectonics portion of the Geology site from the University of California, Berkeley, Museum of Paleontology. This exhibit has a section devoted to the explanation of the history of plate tectonics and a section that focuses on the mechanisms driving plate tectonics. The mechanisms section discusses convection, mid-oceanic ridges, geomagnetic anomalies, deep sea trenches, and island arcs. The site also contains links to numerous animations illustrating historical plate positions and movements.

16

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.

17

Earth's Decelerating Tectonic Plates  

Microsoft Academic Search

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

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

2008-01-01

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

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

20

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

21

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.

22

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.

2011-05-12

23

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

24

Plate tectonics, damage and inheritance  

NASA Astrophysics Data System (ADS)

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

Bercovici, David; Ricard, Yanick

2014-04-01

25

Internet Geography: Plate Tectonics  

NSDL National Science Digital Library

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

26

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.

27

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

28

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

29

Plate tectonics, damage and inheritance  

NASA Astrophysics Data System (ADS)

The initiation of plate tectonics on Earth is a critical event in our planet's history. The time lag between the first proto subduction about 4Ga, evident in geochemical analysis from ancient cratons, to global tectonics by 3-2.7Ga, suggests that plates and plate boundaries spread globally over a 1Gyr period. We hypothesize that when sufficient lithospheric damage, which promotes shear-localization and long-lived weak zones, combines with transient mantle flow and migrating proto-subduction, it leads to the accumulation of plate boundaries and eventually fully formed tectonic plates driven by subduction alone. We demonstrate this process with an idealized model of pressure-driven flow (wherein a low pressure zone is equivalent to downwelling suction or slab pull) in a lithosphere that self-weakens according to a mylonitic-type polycrystalline grain-damage mechanism (Bercovici and Ricard, Phys. Earth Planet. Int. v.202-203, pp27-55, 2012). In the simplest case, for Earth-like conditions, four successive orthogonal rotations of the driving pressure field yield relic damage zones that are inherited to form a nearly perfect plate, with passive spreading and strike-slip margins that persist and localize further, even as flow is only driven by subduction. For Venus' hotter surface conditions, accumulation and inheritance of damage is negligible; hence only subduction zones survive and plate tectonics does not spread, which is compatible with observations. After plates are developed, continued changes in driving forces combined with inherited damage and weak zones, promote increased tectonic complexity, such as oblique subduction, strike-slip boundaries that are subparallel to plate motion, and spalling of minor and micro plates.

Bercovici, D. A.; Ricard, Y. R.

2013-12-01

30

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

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

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

33

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

34

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.

35

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.

36

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

37

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.

38

Plate Tectonics and Volcanism  

NSDL National Science Digital Library

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

39

Episodic plate tectonics on Venus  

NASA Technical Reports Server (NTRS)

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

Turcotte, Donald

1992-01-01

40

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.

41

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

42

Global Topography and Tectonic Plates  

NSDL National Science Digital Library

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

Greene, David

43

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

44

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

45

Plate Tectonics: Lines of Evidence  

NSDL National Science Digital Library

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

National Science Teachers Association (NSTA)

2006-11-01

46

Initiation of plate tectonics, damage and inheritance  

NASA Astrophysics Data System (ADS)

The initiation of plate tectonics on Earth is a critical event in our planet's history. The time lag between the first proto subduction about 4Ga to global tectonics by 3Ga, suggests that plates and plate boundaries became widespread over a 1Gyr period. We hypothesize that during this period, transient mantle flow and migrating proto-subductions lead to lithospheric damage and eventually fully formed tectonic plates driven by subduction alone. We demonstrate this process using a grain evolution and damage mechanism (Bercovici and Ricard, 2012) with a composite rheology, which are compatible with field and laboratory observations of polycrystalline rocks coupled to an idealized model of pressure-driven lithospheric flow (wherein a low pressure zone is equivalent to the suction of convective downwellings). In the simplest case, for Earth-like conditions, a few successive rotations of the driving pressure field yield relic damage zones that are inherited to form a nearly perfect plate, with passive spreading and strike-slip margins that persist and localize further, even as flow is only driven by subduction. For Venus hotter surface conditions, accumulation and inheritance of damage is negligible; hence only subduction zones survive and plate tectonics does not spread, which corresponds to observations. After plates are developed, continued changes in driving forces, combined with inherited damage and weak zones, promote increased tectonic complexity, such as oblique subduction, strike-slip boundaries that are subparallel to plate motion, and spalling of minor plates.

Ricard, Yanick; Bercovici, David

2014-05-01

47

Tectonics of the Easter plate  

NASA Technical Reports Server (NTRS)

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

Engeln, J. F.; Stein, S.

1984-01-01

48

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

49

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

50

Tectonic Plates of China.  

National Technical Information Service (NTIS)

In this report we will give an overall description on the basic tectonic elements of China the subduction and collision fault zones and the available geophysical information. Then we will make a plausible tectonic subdivision from the point of view of sur...

N. C. Sun T. L. Teng

1977-01-01

51

Plate tectonics on Venus  

NASA Technical Reports Server (NTRS)

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

Anderson, D. L.

1981-01-01

52

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

NSDL National Science Digital Library

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

Egger, Anne

2003-03-18

53

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

54

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.

55

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

56

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

57

MACMA: a Virtual Lab for Plate Tectonics  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

58

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

59

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

60

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

61

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

62

Tectonic Plate Motion  

NSDL National Science Digital Library

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

63

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.

64

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

65

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

66

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

67

Plate Tectonics: A Framework for Understanding Our Living Planet.  

ERIC Educational Resources Information Center

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

Achache, Jose

1987-01-01

68

Plate Tectonic Cycle. K-6 Science Curriculum.  

ERIC Educational Resources Information Center

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

Blueford, J. R.; And Others

69

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

70

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

71

Continental tectonics in the aftermath of plate tectonics  

NASA Technical Reports Server (NTRS)

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

Molnar, Peter

1988-01-01

72

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

73

Subduction Drive of Plate Tectonics  

NASA Astrophysics Data System (ADS)

Don Anderson emphasizes that plate tectonics is self-organizing and is driven by subduction, which rights the density inversion generated as oceanic lithosphere forms by cooling of asthenosphere from the top. The following synthesis owes much to many discussions with him. Hinge rollback is the key to kinematics, and, like the rest of actual plate behavior, is incompatible with bottom-up convection drive. Subduction hinges (which are under, not in front of, thin leading parts of arcs and overriding plates) roll back into subducting plates. The Pacific shrinks because bounding hinges roll back into it. Colliding arcs, increasing arc curvatures, back-arc spreading, and advance of small arcs into large plates also require rollback. Forearcs of overriding plates commonly bear basins which preclude shortening of thin plate fronts throughout periods recorded by basin strata (100 Ma for Cretaceous and Paleogene California). This requires subequal rates of advance and rollback, and control of both by subduction. Convergence rate is equal to rates of rollback and advance in many systems but is greater in others. Plate-related circulation probably is closed above 650 km. Despite the popularity of concepts of plumes from, and subduction into, lower mantle, there is no convincing evidence for, and much evidence against, penetration of the 650 in either direction. That barrier not only has a crossing-inhibiting negative Clapeyron slope but also is a compositional boundary between fractionated (not "primitive"), sluggish lower mantle and fertile, mobile upper mantle. Slabs sink more steeply than they dip. Slabs older than about 60 Ma when their subduction began sink to, and lie down on and depress, the 650-km discontinuity, and are overpassed, whereas younger slabs become neutrally buoyant in mid-upper mantle, into which they are mixed as they too are overpassed. Broadside-sinking old slabs push all upper mantle, from base of oceanic lithosphere down to the 650, back under shrinking oceans, forcing rapid Pacific spreading. Slabs suck forward overriding arcs and continental lithosphere, plus most subjacent mantle above the transition zone. Changes in sizes of oceans result primarily from transfer of oceanic lithosphere, so backarcs and expanding oceans spread only slowly. Lithosphere parked in, or displaced from, the transition zone, or mixed into mid-upper mantle, is ultimately recycled, and regional variations in age of that submerged lithosphere may account for some regional contrasts in MORB. Plate motions make no kinematic sense in either the "hotspot" reference frame (HS; the notion of fixed plumes is easily disproved) or the no-net-rotation frame (NNR) In both, for example, many hinges roll forward, impossible with gravity drive. Subduction-drive predictions are fulfilled, and paleomagnetic data are satisfied (as they are not in HS and NNR), in the alternative framework of propulsionless Antarctica fixed relative to sluggish lower mantle. Passive ridges migrate away from Antarctica on all sides, and migration of these and other ridges permits tapping fresh asthenosphere. (HS and NNR tend to fix ridges). Ridge migration and spreading rates accord with subduction drive. All trenches roll back when allowance is made for back-arc spreading and intracontinental deformation. Africa rotates slowly toward subduction systems in the NE, instead of moving rapidly E as in HS and NNR. Stable NW Eurasia is nearly stationary, instead of also moving rapidly, and S and E Eurasian deformation relates to subduction and rollback. The Americas move Pacificward at almost the full spreading rates of passive ridges behind them. Lithosphere has a slow net westward drift. Reference: W.B. Hamilton, An alternative Earth, GSA Today, in press.

Hamilton, W. B.

2003-12-01

74

Google Earth Plate Tectonics File (.kmz)  

NSDL National Science Digital Library

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

Unavco

75

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

76

Investigating Students' Ideas About Plate Tectonics  

NSDL National Science Digital Library

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

Ford, Brent; Taylor, Melanie

2006-09-01

77

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

NASA Astrophysics Data System (ADS)

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

Grigne, C.; Combes, M.

2013-12-01

78

What on Earth is Plate Tectonics?  

NSDL National Science Digital Library

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

79

Tectonic Plates and Plate Boundaries (WMS)  

NSDL National Science Digital Library

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

Sokolowsky, Eric; Mitchell, Horace

2004-06-14

80

How mantle slabs drive plate tectonics.  

PubMed

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

Conrad, Clinton P; Lithgow-Bertelloni, Carolina

2002-10-01

81

Paleomagnetism: One Key to Plate Tectonics.  

National Technical Information Service (NTIS)

The article explains that glabal or plate tectonics combines the hypothesis of seafloor spreading and continental drift. It suggests that the earth's surface is made up of huge crustal plates which are moving relative to one another. The motion of one pla...

H. Spall

1973-01-01

82

Quantitative tests for plate tectonics on Venus  

Microsoft Academic Search

Quantitative comparisons are made between the characteristics of plate tectonics on the earth and those which are possible on Venus. Considerations of the factors influencing rise height and relating the decrease in rise height to plate velocity indicate that the rate of topographic dropoff from spreading centers should be about half that on earth due to greater rock-fluid density contrast

W. M. Kaula; R. J. Phillips

1981-01-01

83

Plate Tectonics: The Scientist Behind the Theory  

NSDL National Science Digital Library

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

Foundation, Wgbh E.

2005-12-17

84

Combining Estimates of Tectonic Plate Rotations  

Microsoft Academic Search

The relative motion between two diverging tectonic plates is a rotation of the sphere. Given measurements of points on the boundaries of the plates, the rotation can be estimated by minimizing a function which is asymptotically (as the concentration parameter of the data distribution goes to infinity) the sum of squared residuals of a linear regression. The linear approximation permits

Bessie H. Kirkwood; Ted Chang

1998-01-01

85

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

86

Tectonic Plates, Earthquakes, and Volcanoes  

NSDL National Science Digital Library

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

87

Plate Tectonics in the Late Paleozoic  

NASA Astrophysics Data System (ADS)

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

Domeier, Mat; Torsvik, Trond

2014-05-01

88

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

89

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 ...

90

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

91

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

92

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

93

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

94

Plate Tectonics and Continental Drift: Classroom Ideas.  

ERIC Educational Resources Information Center

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

Stout, Prentice K.

1983-01-01

95

Tour of Park Geology: Plate Tectonics  

NSDL National Science Digital Library

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

96

Global Cretaceous plate tectonics and paleogeography  

SciTech Connect

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

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

1985-01-01

97

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.

98

History and Evolution of Precambrian plate tectonics  

NASA Astrophysics Data System (ADS)

Plate tectonics is a global self-organising process driven by negative buoyancy at thermal boundary layers. Phanerozoic plate tectonics with its typical subduction and orogeny is relatively well understood and can be traced back in the geological records of the continents. Interpretations of geological, petrological and geochemical observations from Proterozoic and Archean orogenic belts however (e.g., Brown, 2006), suggest a different tectonic regime in the Precambrian. Due to higher radioactive heat production the Precambrian lithosphere shows lower internal strength and is strongly weakened by percolating melts. The fundamental difference between Precambrian and Phanerozoic tectonics is therefore the upper-mantle temperature, which determines the strength of the upper mantle (Brun, 2002) and the further tectonic history. 3D petrological-thermomechanical numerical modelling experiments of oceanic subduction at an active plate at different upper-mantle temperatures show these different subduction regimes. For upper-mantle temperatures < 175 K above the present day value a subduction style appears which is close to present day subduction but with more frequent slab break-off. At upper-mantle temperatures 175 - 250 K above present day values steep subduction continues but the plates are weakened enough to allow buckling and also lithospheric delamination and drip-offs. For upper-mantle temperatures > 250 K above the present day value no subduction occurs any more. The whole lithosphere is delaminating and due to strong volcanism and formation of a thicker crust subduction is inhibited. This stage of 200-250 K higher upper mantle temperature which corresponds roughly to the early Archean (Abbott, 1994) is marked by strong volcanism due to sublithospheric decompression melting which leads to an equal thickness for both oceanic and continental plates. As a consequence subduction is inhibited, but a compressional setup instead will lead to orogeny between a continental or felsic terrain and an oceanic or mafic terrain as well as internal crustal convection. Small-scale convection with plume shaped cold downwellings also in the upper mantle is of increased importance compared to the large-scale subduction cycle observed for present temperature conditions. It is also observed that lithospheric downwellings may initiate subduction by pulling at and breaking the plate. References: Abbott, D., Drury, R., Smith, W.H.F., 1994. Flat to steep transition in subduction style. Geology 22, 937-940. Brown, M., 2006. Duality of thermal regimes is the distinctive characteristic of plate tectonics since the neoarchean. Geology 34, 961-964. Brun, J.P., 2002. Deformation of the continental lithosphere: Insights from brittle-ductile models. Geological Society, London, Special Publications 200, 355-370.

Fischer, Ria; Gerya, Taras

2014-05-01

99

Strain weakening enables continental plate tectonics  

NASA Astrophysics Data System (ADS)

Much debate exists concerning the strength distribution of the continental lithosphere, how it controls lithosphere-scale strain localization and hence enables plate tectonics. No rheological model proposed to date is comprehensive enough to describe both the weakness of plate boundary and rigid-like behaviour of plate interiors. Here we show that the duality of strength of the lithosphere corresponds to different stages of microstructural evolution. Geological constraints on lithospheric strength and large strain numerical experiments reveal that the development of layers containing weak minerals and the onset of grain boundary sliding upon grain size reduction in olivine cause strain localisation and reduce strength in the crust and subcontinental mantle, respectively. The positive feedback between weakening and strain localization leads to the progressive development of weak plate boundaries while plate interiors remain strong.

Gueydan, F.; Prcigout, J.; Montesi, L. G.

2013-12-01

100

Reducing Plate Tectonic Misconceptions with Lecture Tutorials  

NASA Astrophysics Data System (ADS)

In order to address student difficulties with and common misconceptions about plate tectonics, we created five Lecture Tutorials suitable for introductory geoscience courses. Lecture Tutorials are 10-15 minute worksheets that students complete in class in small groups to make learning more student-centered. Students build their knowledge with questions that progressively become more difficult, requiring them think about their misconceptions. Our research indicates that the Lecture Tutorials successfully decrease student misconceptions. For example, few introductory students identify the mantle wedge as the location of melting at subduction zones. Instead, students frequently think melting occurs at the trench, in magma chambers within volcanoes, or where images commonly show the subducting slab disappearing. One of the Lecture Tutorials helps the students determine why melting occurs and therefore identify the correct locations of melting at convergent boundaries, divergent boundaries, and hotspots. This Lecture Tutorial includes a hypothetical debate with statements expressing the misconceptions and one expressing the correct scientific idea of where melting occurs. Students are asked to explain why they agree with one of the statements, so they must directly think about any misconceptions they may have. Additional difficulties addressed by the Lecture Tutorials include identification of the direction of plate movement at ocean ridges and the locations and formation of basic plate tectonic features, such as trenches, volcanoes, ocean ridges, and plate boundaries. After instruction, students completed questionnaires that probed their understanding of plate tectonics, and students who completed the Lecture Tutorials performed significantly better on relevant questions. For example, when asked to circle the locations on a diagram where melting occurred, students who completed the Lecture Tutorials correctly circled the mantle wedge more often than other students (33% vs. 8%). The percentage of students who drew incorrect arrows indicating converging plates at ocean ridges was smaller for students who completed the Lecture Tutorials (9%) than for those who did not (21%). Because the Lecture Tutorials frequently asked students to identify, explain, and draw basic features relevant to plate tectonics, we hypothesized that students who completed the Lecture Tutorials would correctly identify more of these features, and this is what we observed. Students who completed the Lecture Tutorials identified 6.3 features on average, compared to 2.8 for those students who did not complete the Lecture Tutorials. The Lecture Tutorial students correctly labeled 82% of the identified features, compared to 71% for other students. The plate tectonic Lecture Tutorials along with others on additional introductory geoscience topics are available as a workbook called Lecture Tutorials for Introductory Geoscience published by W. H. Freeman.

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

2009-12-01

101

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

102

Plate Tectonics: The Hawaiian Archipelago  

NSDL National Science Digital Library

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

103

Plate Tectonics: The Hawaiian Archipelago  

NSDL National Science Digital Library

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

2011-07-12

104

Plate Tectonic controls geomagnetic reversal frequency  

NASA Astrophysics Data System (ADS)

The discovery of the reversals of Earth's magnetic field and the description of plate tectonics are two of the main breakthroughs in geophysics in the 20th century. We claim that these two phenomena are correlated and that plate tectonics controls long-term changes in geomagnetic reversals frequency. More precisely, we show that geological periods characterized by an asymmetrical distribution of the continents with respect to the equator generate periods of high reversal frequency. We infer that the distribution and symmetry of mantle structures driving continental motions at the surface influence the equatorial symmetry of the flow within the core and thus changes the coupling between the dipolar and quadrupolar modes which controls the occurrence of reversals.

Petrelis, Francois; Besse, Jean; Valet, Jean-Pierre

2014-05-01

105

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.

106

Seismology: tectonic strain in plate interiors?  

PubMed

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

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

2005-12-15

107

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

108

Quantitative tests for plate tectonics on Venus  

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

109

Caribbean tectonics and relative plate motions  

NASA Technical Reports Server (NTRS)

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

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

1984-01-01

110

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

111

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

112

Plate tectonic history of the Arctic  

NASA Technical Reports Server (NTRS)

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

Burke, K.

1984-01-01

113

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

114

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

115

This Dynamic Earth: the Story of Plate Tectonics  

NSDL National Science Digital Library

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

2000-03-28

116

Learning Plate Tectonics Using a Pre-Analogy Step  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

117

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

118

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

PubMed

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

Korenaga, Jun

2012-07-01

119

Early plate tectonics versus single-plate tectonics on Mars: Evidence from magnetic field history and crust evolution  

Microsoft Academic Search

The consequences of an early epoch of plate tectonics on Mars followed by single-plate tectonics with stagnant lid mantle convection on both crust production and magnetic field generation have been studied with parameterized mantle convection models. Thermal history models with parameterized mantle convection, not being dynamo models, can provide necessary, but not sufficient, conditions for dynamo action. It is difficult

D. Breuer; T. Spohn

2003-01-01

120

Silurian to Early Carboniferous plate tectonic model of Central Europe  

NASA Astrophysics Data System (ADS)

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

Golonka, Jan; Barmuta, Jan; Barmuta, Maria

2014-05-01

121

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

122

Earthquakes Living Lab: The Theory of Plate Tectonics  

NSDL National Science Digital Library

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

Civil And Environmental Engineering Department

123

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

124

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

125

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

126

Dynamic interaction between tectonic plates, subducting slabs, and the mantle  

Microsoft Academic Search

Mantle convection models have been formulated to investi- gate the relation between plate kinematics and mantle dynamics. The cylin- drical geometry models incorporate mobile, faulted plate margins, a phase change at 670 km depth, non-Newtonian rheology, and tectonic plates. Models with a variety of parameters indicate that a relatively stationary trench is more likely to be associated with a subducted

Shijie Zhong; Michael Gurnis

1997-01-01

127

Fluid flow paths and upper plate tectonics at erosional margins  

Microsoft Academic Search

An understanding of fluid flow regime and tectonics of convergent margins dominated by subduction erosion processes lags behind that for accretionary margins. Recent seafloor mapping and seismic images along Middle America and North Chile indicate that tectonic processes that pervasively fracture the upper plate across the entire continental slope create a complex hydrological system characterizing erosional margins. The most spectacular

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

2003-01-01

128

On volcanism and thermal tectonics on one-plate planets  

Microsoft Academic Search

For planets with a single global lithospheric shell or 'plate', the thermal evolution of the interior affects the surface geologic history through volumetric expansion and the resultant thermal stress. Interior warming of such planets gives rise to extensional tectonics and a lithospheric stress system conductive to widespread volcanism. Interior cooling leads to compressional tectonics and lithospheric stresses that act to

S. C. Soloman

1978-01-01

129

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

130

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

131

Transition from Plate Tectonics to Stagnant Lid Convection on Venus 500 M.Y. Ago  

NASA Astrophysics Data System (ADS)

Cratering record suggests that resurfacing on Venus ended around 500 million years ago. Possible explanations of this event involve some change in global convective style of the interior of Venus. I assume that this was a transition from plate tectonics to stagnant lid convection and suggest that the cessation of plate tectonics is likely to be a relatively fast process caused by the drop of ratio of the stresses to the yield strength in the lithosphere. A drop of the rate of magma production and cessation of generation of the magnetic field on Venus are among consequences of this event.

Solomatov, V. S.

1996-03-01

132

On volcanism and thermal tectonics on one-plate planets  

NASA Technical Reports Server (NTRS)

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

Solomon, S. C.

1978-01-01

133

On the breakup of tectonic plates by polar wandering  

NASA Technical Reports Server (NTRS)

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

Liu, H.-S.

1974-01-01

134

Inferences of mantle viscosity from tectonic plate velocities  

Microsoft Academic Search

The present-day velocities of the earth's tectonic plates provide direct constraints on the absolute value of the mantle viscosity. This paper presents the results of a formal inversion of plate motion data and demonstrates its utility in constraining the depth variation of absolute viscosity.

A. M. Forte; A. M. Dziewonski; W. R. Peltier

1991-01-01

135

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

136

Inferences of mantle viscosity from tectonic plate velocities  

Microsoft Academic Search

The present-day velocities of the Earth's tectonic plates provide direct constraints on the absolute value of the mantle viscosity. We present the results of a formal inversion of plate motion data and demonstrate its utility in constraining the depth variation of absolute viscosity.

A. M. Forte; W. R. Peltier; A. M. Dziewonski

1991-01-01

137

Is plate tectonics a case of non-extensive thermodynamics?  

Microsoft Academic Search

Bird (2003) [5] proposed that the distribution of areas of the tectonic plates follows a power law and that this distribution fitted well with the concepts of a few major plates and a hierarchical self-similar organization of blocks at the boundary scale, a fractal plate distribution and a self-organized system. Here we apply the concepts of non-extensive statistical mechanics (NESM)

Filippos Vallianatos; Peter Sammonds

2010-01-01

138

Spherical shell models of mantle convection with tectonic plates  

Microsoft Academic Search

A simple three-dimensional spherical model of mantle convection, where plates are taken into account in the top boundary condition, allows to investigate the plate tectonicsmantle convection coupling in a self-consistent way. Avoiding the strong difficulties inherent in the numerical treatment of rheology, the plate condition appears efficient in reproducing the Earth-like features as subduction, mid-oceanic ridges and hotspots. Whereas the

Marc Monnereau; Sandrine Qur

2001-01-01

139

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

140

Caribbean tectonics and relative plate motions  

Microsoft Academic Search

During the last century, three different ways of interpreting the tectonic evolution of the Gulf of Mexico and the Caribbean have been proposed, taking into account the Bailey Willis School of a permanent pre-Jurassic deep sea basin, the Edward Suess School of a subsided continental terrain, and the Alfred Wegener School of continental separation. The present investigation is concerned with

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

1984-01-01

141

Tectonic plate motions derived from Lageos  

Microsoft Academic Search

Five years of laser data (1984-88) between the Lageos satellite and the ground station network based on precise monthly computations of the Lageos satellite are analyzed to recover tectonic motions affecting the stations. A global inversion over this period provides solutions for absolute velocities in latitude and longitude of a selected subset of 14 stations. Relative horizontal velocities are derived

R. Biancale; A. Cazenave; K. Dominh

1991-01-01

142

North Chilean forearc tectonics and cenozoic plate kinematics  

NASA Astrophysics Data System (ADS)

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

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

1993-04-01

143

Scaling of plate tectonic convection with pseudoplastic rheology  

NASA Astrophysics Data System (ADS)

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

Korenaga, Jun

2010-11-01

144

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

USGS Publications Warehouse

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

Hamilton, W.

1987-01-01

145

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.

146

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

147

Teaching about Plate Tectonics and Faulting Using Foam Models  

NSDL National Science Digital Library

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

Braile, Larry

148

Recent tectonic plate decelerations driven by mantle convection  

Microsoft Academic Search

We explore recent changes in tectonic plate velocities using a model of mantle flow that is based on a new high-resolution global tomography model derived from simultaneous inversions of global seismic, geodynamic and mineral physical data sets. This plate-coupled mantle convection model incorporates a viscosity structure that reconciles both glacial isostatic adjustment and global convection-related data sets. The convection model

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

2009-01-01

149

Plate Tectonism on Early Mars: Diverse Geological and Geophysical Evidence  

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

150

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

151

On the Breakup of Tectonic Plates by Polar Wandering.  

National Technical Information Service (NTIS)

The observed boundary system of the major tectonic plates on the surface of the earth lends fresh support to the hypothesis of polar wandering. A dynamic model of the outer shell of the earth under the influence of polar shift is developed. The analysis f...

H. Liu

1973-01-01

152

On the Breakup of Tectonic Plates by Polar Wandering  

Microsoft Academic Search

The observed boundary system of the major tectonic plates on the surface of the earth lends fresh sup- port to the hypothesis of polar wandering. In this paper a dynamic model of the outer shell of the earth under the influence of polar shift is developed. The analysis falls into tw o parts: (1) deriving equations for stresses caused by

Han-Shou Liu

1974-01-01

153

Numerical modelling of instantaneous plate tectonics  

NASA Technical Reports Server (NTRS)

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

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

1974-01-01

154

Inversion for the driving forces of plate tectonics  

NASA Technical Reports Server (NTRS)

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

Richardson, R. M.

1983-01-01

155

Generation of plate tectonics via grain-damage and pinning  

NASA Astrophysics Data System (ADS)

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

Bercovici, D.; Ricard, Y. R.

2012-12-01

156

Tectonic and Plate Tectonic Units at the North Gondwana Margin: Evidence from the Central European Variscides  

Microsoft Academic Search

In Middle Devonian time, the following plate-tectonic units can be recognized in the Variscides of Central Europe: ? Old Red Continent, consisting of Laurentia + Baltica + Avalonia, with a Silurian arc (resulting from the closure of the Rheic ocean) and stranded Armorican fragments accreted to its southern margin. ? Rhenohercynian narrow ocean ? Saxothuringian terrane or terrane(s) (basement

WOLFGANG FRANKE

157

Organization of the tectonic plates in the last 200 Myr  

NASA Astrophysics Data System (ADS)

The present tessellation of the Earth's surface into tectonic plates displays a remarkably regular plate size distribution, described by either one (Sornette and Pisarenko, 2003) or two (Bird, 2003) statistically distinct groups, characterised by large and small plate size. A unique distribution implies a hierarchical structure from the largest to the smallest plate. Alternatively, two distributions indicate distinct evolutionary laws for large and small plates, the first tied to mantle flow, the second determined by a hierarchical fragmentation process. We analyse detailed reconstructions of plate boundaries during the last 200 Myr and find that (i) large and small plates display distinct statistical distributions, (ii) the small plates display little organisational change since 60 Ma and (iii) the large plates oscillate between heterogeneous (200-170 Myr and 65-50 Ma) and homogeneous (120-100 Ma) plate tessellations on a timescale of about 100 Myr. Heterogeneous states are reached more rapidly, while the plate configuration decays into homogeneous states following a slower asymptotic curve, suggesting that heterogeneous configurations are excited states while homogeneous tessellations are equilibrium states. We explain this evolution by proposing a model that alternates between bottom- and top-driven Earth dynamics, physically described by fluid-dynamic analogies, the Rayleigh-Benard and Bnard-Marangoni convection, respectively. We discuss the implications for true polar wander (TPW), global kinematic reorganisations (50 and 100 Ma) and the Earth's magnetic field inversion frequency.

Morra, Gabriele; Seton, Maria; Quevedo, Leonardo; Mller, R. Dietmar

2013-07-01

158

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

159

Role of strain weakening on continental plate tectonics  

NASA Astrophysics Data System (ADS)

Much debate exists concerning the strength distribution of the continental lithosphere, how it controls lithosphere-scale strain localization and hence enables plate tectonics. No rheological model proposed to date is comprehensive enough to describe both the weakness of plate boundary and rigid-like behaviour of plate interiors. Here we show that the duality of strength of the lithosphere corresponds to different stages of microstructural evolution. Geological constraints on lithospheric strength and large strain numerical experiments reveal that the development of layers containing weak minerals and the onset of grain boundary sliding upon grain size reduction in olivine cause strain localisation and reduce strength in the crust and subcontinental mantle, respectively. The positive feedback between weakening and strain localization leads to the progressive development of weak plate boundaries while plate interiors remain strong.

Gueydan, Frdric; Precigout, Jacques; Montesi, Laurent

2014-05-01

160

Multi-Agent Simulations of Earth's Dynamics: Towards a Virtual Laboratory for Plate Tectonics  

NASA Astrophysics Data System (ADS)

MACMA (Multi-Agent Convective MAntle) is a new tool developed at Laboratoire Domaines Ocaniques (UMR CNRS 6538) and CERV-LabSTICC (Centre Europen de Ralit Virtuelle, UMR CNRS 6285) to simulate evolutive plates tectonics and mantle convection in a 2-D cylindrical geometry (Combes et al., 2012). In this approach, ridges, subduction zones, continents and convective cells are agents, whose behavior is controlled by analytical and phenomenological laws. These agents are autonomous entities which collect information from their environment and interact with each other. The dynamics of the system is mainly based on a force balance on each plate, that accounts for slab pull, ridge push, bending dissipation and viscous convective drag. Insulating continents are accounted for. Tectonic processes such as trench migration, plate suturing or continental breakup are controlled by explicit parameterizations. A heat balance is used to compute Earth's thermal evolution as a function of seafloor age distribution. We thereby obtain an evolutive system where the geometry and the number of tectonic plates are not imposed but emerge naturally from its dynamical history. Our approach has a very low computational cost and allows us to study the effect of a wide range of input parameters on the long-term thermal evolution of the Earth. MACMA can thus be seen as a 'plate tectonics virtual laboratory'. We can test not only the effect of input parameters, such as mantle initial temperature and viscosity, initial plate tectonics configuration, number and geometry of continents etc., but also study the effect of the analytical and empirical rules that we are using to describe the system. These rules can be changed at any time, and MACMA is an evolutive tool that can easily integrate new behavioral laws. Even poorly understood processes, that cannot be accounted for with differential equations, can be studied with this virtual laboratory. For Earth-like input parameters, MACMA yields plate velocities and heat flux that are in good agreement with observations. The long-term thermal evolution of the Earth obtained with our model shows a slow monotonous decrease of mantle mean temperature, with a cooling rate of around 50-100 K per billion years, which is in good agreement with petrological and geochemical constraints. Heat flux and plate velocities show a more irregular evolution, because tectonic events, such as a continental breakup, give rise to abrupt changes in Earth's surface dynamics and heat loss. Therefore MACMA is a powerful tool to study in a systematic way the effect of local events (subduction initiation, continental breakup, ridge vanishing) on plate reorganizations and global surface dynamics.

Grigne, C.; Combes, M.; Tisseau, C.; LeYaouanq, S.; Parenthoen, M.; Tisseau, J.

2012-12-01

161

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

162

Creep of phyllosilicates at the onset of plate tectonics  

SciTech Connect

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

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

2012-10-24

163

Beyond plate tectonics - Looking at plate deformation with space geodesy  

NASA Technical Reports Server (NTRS)

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

Jordan, Thomas H.; Minster, J. Bernard

1988-01-01

164

The magma ocean as an impediment to lunar plate tectonics  

NASA Technical Reports Server (NTRS)

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

Warren, Paul H.

1993-01-01

165

The magma ocean as an impediment to lunar plate tectonics  

NASA Astrophysics Data System (ADS)

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

Warren, P. H.

1993-03-01

166

Could plate tectonics on Venus be concealed by volcanic deposits  

NASA Technical Reports Server (NTRS)

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

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

1982-01-01

167

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

168

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

NASA Astrophysics Data System (ADS)

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

Luttrell, Karen Marie

169

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

170

One Effect of Plate Tectonics on the Hydrosphere  

NSDL National Science Digital Library

We have studied many ways that the movement of tectonic plates affects different systems on the Earth. Today, we are going to be talking about how that movement of plates affects the Earth's water, the hydrosphere. This is really an easy assignment. Make sure that you have both of your names on the top of your document. There are several different sites that you will be using. Please remember that you are only allowed to use the sites that are referenced in this website. Your ...

Woolley, Mr.

2007-11-27

171

Beyond plate tectonics - Looking at plate deformation with space geodesy  

Microsoft Academic Search

The requirements that must be met by space-geodetic systems in order to constrain the horizontal secular motions associated with the geological deformation of the earth's surface are explored. It is suggested that in order to improve existing plate-motion models, the tangential components of relative velocities on interplate baselines must be resolved to an accuracy of less than 3 mm\\/yr. Results

Thomas H. Jordan; J. Bernard Minster

1988-01-01

172

Plate tectonics and crustal deformation around the Japanese Islands  

NASA Technical Reports Server (NTRS)

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

Hashimoto, Manabu; Jackson, David D.

1993-01-01

173

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

174

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

175

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

NASA Astrophysics Data System (ADS)

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

Elkins-Tanton, L.; Tikoo, S.

2012-04-01

176

Gondwana Tales: an inquiry approach to plate tectonics  

NASA Astrophysics Data System (ADS)

Plate tectonics and its effects on the constitution of seas and continents are key models in science education. Fossil evidences are usually taught in demostrative key when Wegener's discoverings about Pangea are introduced. In order to introduce inquiry-based science education (IBSE) approaches to this topic, we propose "Gondwana Tales", an activity where students are asked to use fossil data to reconstruct the geologic history of an imaginary planet. Grouped in independent teams, each team is furnished with stratigraphic columns from several sites containing faunistic successions of real organisms existing in the past in Earth. Students are told to reconstruct a model of the evolution of the continents, by making calculations of relative ages of the fossils, and relating each fossil to a geologic era. The different teams have incomplete and complementary information. After a first step where they have to propose a partial model based on incomplete data, each team receives a "visitor scientist" from another team, this implying an informal scientific communication event. This process is performed several times, engaging a discussion in each team and getting a final consensus model created by the whole class. Correct answer is not given to the students, even at the end of the activity, to keep the activity under the parameters of real scientific experience, where there is not a "correct answer" to compare. Instead of this, and following the IBSE standards, a reflection on the process is proposed to students. The lack of complete information and the need to collaborate are part of classroom dynamics focused to the understanding of the process of creation of the scientific knowledge. This activity is part of the C3 Project on Creation of Scientific Knowledge that is being applied in the school.

Domnech Casal, Jordi

2014-05-01

177

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 mod- eling results that address for a hotter Earth the viability of subduction, one of

Jeroen van Hunen; Arie P. van den Berg

178

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

179

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

NASA Technical Reports Server (NTRS)

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

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

1973-01-01

180

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

ERIC Educational Resources Information Center

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

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

181

Subduction kinematics mirrors global plate tectonics, not local  

NASA Astrophysics Data System (ADS)

The long-standing quest for a correlation between intrinsic properties of subduction zones and subduction kinematics essentially yields disappointing results. A glance at subduction zones in the global plate tectonic framework reveals that subduction zones are not enough for a stochastic approach, which is what attempts of correlating local dynamic parameters of subduction zones implicitely do. The very existence of mountain belts, regarded as dynamometers, reveals that interplate forces are comparable in magnitude to the driving forces of subduction. In the Pacific system, from where most of the data arises, plate interactions are strong enough to force slabs down into the mantle at rates that dramatically departs from the natural subduction rates. Ultimately, it seems that the African superswell makes the Atlantic spread at the expense of the Pacific, regardless of the local dynamics of subduction zones. Now that we explored the many factors that influence isolated subduction systems, it is now time to consider subduction zones in the global framework of plate tectonics.

Husson, Laurent

2010-05-01

182

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

183

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

184

Observing tectonic plate motions and deformations from satellite laser ranging  

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

185

On the breakup of tectonic plates by polar wandering  

NASA Technical Reports Server (NTRS)

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

Liu, H. S.

1973-01-01

186

Episodic tectonic plate reorganizations driven by mantle convection  

Microsoft Academic Search

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) 14041420; P.A. Rona, E.S. Richardson, Earth Planet. Sci. Lett. 40 (1978) 111; D.C. Engebretson, A. Cox, R.G. Gordon, Geol. Soc. Am. Spec. Pap. 206 (1985); R.G. Gordon, D.M. Jurdy, J. Geophys. Res.

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

2002-01-01

187

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

188

Plate tectonics from VLBI and SLR global data  

NASA Technical Reports Server (NTRS)

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

Harrison, Christopher G. A.; Robaudo, Stefano

1992-01-01

189

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

190

Subduction and Plate Edge Tectonics in the Southern Caribbean  

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

191

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

192

Prototypical Concepts and Misconceptions of Plate Tectonic Boundaries  

NASA Astrophysics Data System (ADS)

Students of geology encounter many prototypical/exemplar concepts* that include representative, but not necessarily defining, features and characteristics. This study of students' prototypical representations of plate tectonic boundaries indicates that their representations are rich sources of information about their misconceptions about plate tectonics. After lectures in plate tectonics and mountain building, 353 students in a general education geology class were asked to draw a continent-continent convergent boundary. For this study, a correct answer is defined as having the major features in correct proportions as depicted in the plate boundary diagrams on the USGS web. Fifty-two percent of the drawings were either incorrect or incomplete such that they could not be interpreted. Only 48% were readily interpretable, and of these 22% drew the boundary correctly, showing a thickening of crust where two continents collide. Thirty-three percent drew the boundary showing concave slabs of continental crust as one might imagine two pieces of firm rubber pushed together on a rigid surface and 45% depicted mountains as one might imagine inverted ice cream cones on a rigid plank. Twenty-one senior class geology majors and graduate students were given the same assignment. Forty-eight percent rendered a correct drawing, whereas 38% drew the same ice cream cone on a plank type picture that 45% of the general education students drew. In a second class of 12 geology majors, only 1 student drew a cross section of a continent-ocean boundary similar to standard representation. Four of 12 drew mountains on the top of continental crust over a subduction zone but did not draw a compensating mass within the crust or lithosphere. Prototypical drawings provide more information about students' concepts than do most multiple-choice questions. For example, sixty-two percent of theses students who drew mountains similar to foam rubber pads pushed together on a desk or ice cream cones on a plank correctly answered a multiple-choice question that would appear to indicate a better understanding than the drawings reveal. Furthermore, 12 interviewed students made statements that could be interpreted to indicate that they understood the concept of mountain building at plate tectonic boundaries better than their drawings suggest. Incoherence of multiple-choice responses, verbal statements and drawings may be common in novice learners. If cognitive scientists are correct in their model of multiple types of mental representations for the same term, then the fact that novices may hold inconsistent representations is not surprising. The fact that students at various academic levels draw very similar prototypes that are incorrect is evidence that students have distinct and persistent prototype misconceptions. * Cognitive scientists define a prototypical/exemplar concept as a mental representation of the best examples or central tendencies of a term.

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

2003-12-01

193

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

194

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

195

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

196

Plate Tectonics: The Rocky History of an Idea  

NSDL National Science Digital Library

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

197

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

198

The Onset of Plate tectonics in a Compositionally Stratified mantle  

NASA Astrophysics Data System (ADS)

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

Hansen, U.; Dude, S.

2013-12-01

199

Self-consistent generation of tectonic plates in three-dimensional mantle convection  

Microsoft Academic Search

Despite the fundamental importance of plates in the Earth's mantle convection, plates have not generally been included in numerical convection models or analog laboratory experiments, mainly because the physical properties which lead to plate tectonic behavior are not well understood. Strongly temperature-dependent viscosity results in an immobile rigid lid, so that plates, where included at all in 3-D models, have

Paul J. Tackley

1998-01-01

200

Relationship of Seismic Events and Divergent Plate Motion In Iceland  

NASA Astrophysics Data System (ADS)

The hotspot-ridge interaction under Iceland creates complex tectonic structures of the earth surface. One element of the tectonic system is the transform zone in the south of the island, the so-called South Icelandic Seismic Zone (SISZ). To explain the dynamical importance of this tectonic element in relation to the whole system it is necessary to compare the impact of seismic events in the transform zone with the daily results of continuous geodetical measurements. Such results are avail- able for the two IGS permanent GPS stations in Reykjavk and Hfn since 1998. Instead of approaching the displacements of these IGS stations with linear regression we reduced the noise on processed GPS co-ordinates using an adapted KALMAN filter model. After this thorough statistical analysis it is possible to get daily station positions with an accuracy of a few millimetres. The so filtered displacement curves enable to inter- pret short-time changes of the movements. In addition, the statistical analysis of the loss of seismic energy in the SISZ in depen- dence of time shows a significant periodical distribution as well as a high correlation with short-time divergent plate motion of the whole island. This is essential to fully understand the complex tectonic system of Iceland.

Heinert, M.; Perlt, J.

201

Application of plate tectonics concepts in hydrocarbon exploration: Hokkaido Corner  

SciTech Connect

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

Sabitay, A.; Shirley, J.

1986-07-01

202

Dynamic Analysis of Modifications to Simple Plate Tectonic Theory  

NASA Astrophysics Data System (ADS)

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

Paczkowski, Karen

203

Geochemical and numerical approach to Neoarchean plate tectonics  

NASA Astrophysics Data System (ADS)

According to a shared view, the major part of the Earth's earliest granitic crust of TTG (tonalite-trondhjemite-granodiorite) composition was formed during a long period (4.0 Ga-2.7 Ga) of melting of basalts that constitute oceanic crust and plateaus. However, the site of melting is controversial and the opinions vary from the subducting slab to the lower part of thick basaltic crust. The former assumes that subduction initiated early in the Earth's history, whereas the latter requires an accumulation of thick basaltic piles. The long period of extraction of TTGs from basaltic crust (2.85-2.75 Ga in the Karelian Craton) was followed by an abrupt pulse of mantle magmatism (2.74-2.72 Ga in the same region) that formed granitoids known as sanukitoids. In the Karelian and Kola cratons of the Fennoscandian Shield, the crust-forming magmatism can be divided into three geochemical groups: (1) low-HREE (heavy rare earth elements) TTGs, (2) high-HREE TTGs, and (3) high Mg-Ba-Sr sanukitoids (Halla et al., 2009). The first two TTG groups differ mainly in their contrasting pressure-sensitive trace element contents, indicating a similar source but different conditions for melting. The enrichment of Mg in sanukitoids points to a mantle source, high Ba and Sr indicate source metasomatism, and a crustal isotope signature requires recycling of continental material into the mantle (Heilimo et al., in press). Their pressure-sensitive element concentrations point to variable conditions between the high- and low-pressure regimes of TTGs. We propose a possible tectonic scenario of an incipient hot subduction underneath a thick oceanic plateau/protocrust, which would enable simultaneous melting in deep and shallow sources. High-pressure melting in the lower eclogitic part of a thick basaltic pile could produce low-HREE TTGs, whereas low-pressure melting of shallow subducting slab (with possible interactions with the mantle wedge) would be capable of generating high-HREE TTGs. Numerical models predict that the weakness of and tensile stresses of the subducting plate could result in a slab break-off and (local) termination of the subduction process (van Hunen and van den Berg, 2008). Potential mantle upwelling from this effect, and the subsequent development of a new thermal state are likely to provide a situation in which partial melting and metasomatism of the enriched mantle wedge lead to the formation of sanukitoid magmas. References: Halla, J., van Hunen, J., Heilimo, E. & Hltta, P. 2009. Geochemical and numerical constraints on Neoarchean plate tectonics. Precambrian Research 174, 155-162. Heilimo, E., Halla, J. & Hltt, P. Discrimination and origin of the sanukitoid series: Geochemical constraints from the Neoarchean western Karelian Province (Finland), Lithos (in press). van Hunen, J., & van den Berg, A.P. 2008. Plate tectonics on the early Earth: limitations imposed by strength and buoyancy of subducted lithosphere. Lithos 103, 217-235.

Heilimo, Esa; Halla, Jaana; van Hunen, Jeroen; Hltt, Pentti

2010-05-01

204

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

205

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

206

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

NASA Astrophysics Data System (ADS)

We investigate the initiation of plate tectonics on Earth from scaling laws for plate tectonic style convection with grain-damage, and from numerical models of mantle convection immediately after magma ocean solidification. Using scaling laws for convection with grain-damage we constrain the likelihood of plate tectonics on the early Earth. Both mantle temperature and surface temperature play key roles in how plate speed and heat flow scale, and thus whether plate tectonics would be likely on the early Earth. Specifically either high mantle temperatures or high surface temperatures decrease plate speed because grain-growth (or healing) increases in lithospheric shear zones, causing viscosity to go up in these regions. When applied to the early Earth, we find that while higher mantle temperatures decrease plate speed, it is not enough to shut off plate tectonics; plate speed only decreases by a factor of 2 going from the present day to Hadean mantle temperatures. Surface temperature has a bigger influence as it more directly controls the temperature in lithospheric shear zones; at a Venusian surface temperature plate tectonics can be effectively shut off. Earth's surface temperature in the Hadean is unknown, however, given that Hadean zircons show evidence for liquid water, the surface temperature was lower than that of present day Venus. Even under hot greenhouse conditions plate speeds on the order of 1 cm/yr could exist in the Hadean. Therefore early Earth conditions were favorable for plate tectonics, even with a higher surface temperature, although Hadean plate tectonics would be sluggish (slower plate speed and thicker lithosphere) compared to the present day. We perform numerical convection experiments to constrain the timescales over which plate tectonics would initiate in the early Earth, starting from post-magma ocean conditions. Rapid solidification of the magma ocean leaves behind a solid mantle with a temperature profile following the solidus. There is also the possibility of chemical differentiation which would lead to an initially unstable compositional density profile in the newly solidified mantle. We thus perform numerical models with an initially unstable temperature profile (approximating the silicate solidus) both with and without an initially unstable compositional density profile. All models show an initial overturn beneath a stagnant lid, followed by stagnant lid convection and the eventual onset of plate tectonic style convection. The timescale for initiating plate tectonics depends on the Rayleigh number, parameters for healing and damage, and on the degree of chemical differentiation during magma ocean solidification. Similar to the results of the scaling analysis, higher surface temperature retards the initiation of plate tectonics, due to the effects of lithospheric healing. Compositional buoyancy significantly reduces the timescale for initiating plate tectonics due to the increased negative buoyancy of the lithosphere (i.e. including both thermal and chemical buoyancy). Thus chemical differentiation during magma ocean solidification provides a significant boost to initiating plate tectonics in the Hadean Earth.

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

2013-12-01

207

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

208

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

209

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

Microsoft Academic Search

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

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

2009-01-01

210

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

211

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

212

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

213

Vernal Point and Plate Tectonics: Indo-Australian  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

214

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

Microsoft Academic Search

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

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

1990-01-01

215

The Spherical Block Model: Dynamics of the Global System of Tectonic Plates and Seismicity  

Microsoft Academic Search

The spherical block model is used to study dynamics of the global system of tectonic plates and seismicity by means of numerical simulation. A brief description of the model is presented. Two block structures are considered: The first is characterized by specifying the largest plates as boundary blocks, whereas the second is the closed spherical structure without boundary blocks. Results

V. L. Rozenberg; P. O. Sobolev; A. A. Soloviev; L. A. Melnikova

2005-01-01

216

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

Microsoft Academic Search

Recent numerical studies of convection in the earth's mantle have included various features of plate tectonics. This paper describes three methods of modeling plates: through material properties, through force balance, and through a thin power-law sheet approximation. The results obtained are compared using each method on a series of simple calculations. From these results, scaling relations between the different parameterizations

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

1992-01-01

217

Sediment subduction - A probable key for seismicity and tectonics at active plate boundaries  

Microsoft Academic Search

A model involving extensive occurrence of sediment subduction and viscous interaction of lithospheric plates at convergent zones is applied to derive simple relations between extremal values of seismic and global tectonic parameters. The strength of mechanical coupling at the interface zone is defined as the maximum shear stress at the base of the over-thrusting plate. A test of these relations

Vladimir Kostoglodov

1988-01-01

218

Present-day tectonic plate motions and crustal deformations from the DORIS space system  

Microsoft Academic Search

Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) data acquired between January 1993 and December 1996 from the SPOT-2, SPOT-3, and TOPEX\\/Poseidon satellites have been analyzed to determine velocities for 45 sites on eight major tectonic plates. For 28 sites far from deformation zones, the velocity estimates agree with plate model predictions. Least squares computation of poles of rotation, which

Jean-Franois Crtaux; Laurent Soudarin; Anny Cazenave; Florence Bouill

1998-01-01

219

The Arctic Eurekan Orogen : A plate tectonic conundrum  

NASA Astrophysics Data System (ADS)

The Eurekan orogen is a fold and thrust belt that extends from West Spitsbergen across northernmost Greenland and into Ellesmere Island and the eastern Canadian Arctic Archipelago. The favored mechanisms for generating this orogenic belt are: 1. Counterclockwise rotation of Greenland; subduction and collision between Greenland and Ellesmere Island along Nares Straight and transpression between Greenland and Spritbergen along Fram Straight. 2. Wedge-like northward indentation of Greenland into Spitsbergen and Ellesmere island driven by seafloor spreading to the southeast and southwest, and accommodated along the dextral Spitsbergen transform to the northeast and the Wegener transform to the northwest. Both of these models have problems. The widely accepted rotation and collision model requires that Nares Straight is the final remnant of a former oceanic trough and that enough old, cold oceanic crust was present so as to initiate foundering of the oceanic lithosphere and negative buoyancy driven rotation and collision between Greenland (lower plate) and Ellesmere Island. However, evidence of an accretionary complex, clear collisional suture or a subduction-related volcanic edifice are lacking. The second, Greenland indentor, model lacks a viable source of potential energy. Contractional deformation of continental crust is usually associated with continental collision which is a process driven by the subduction of oceanic crust attached to or surrounding a continent (the potential energy of a sinking oceanic slab is converted into the kinetic energy of collision). Calling on "ridge push" to induce continental deformation and uplift is problematic because the ridge lacks the potential energy required to deform high standing continental crust. Further, the extensional stresses at ridges are significantly lower than the stresses required to break rocks in compression so it is hard to envision a scenario whereby ridge push could have much effect. Adding to the troubles of the above models are geological and geophysical observations from southern Nares Straight where a clear "linchpin" has been driven into the Smith Sound region. Here the geology of western Greenland can be clearly linked to Ellesmere Island on the west side of the sound. The Smith Sound Linchpin effectively requires that southeastern Ellesmere Island is attached to Greenland, thereby pushing any suture between Greenland and Ellesmere Island off to the west, into the interior of the Island. This linchpin is used as evidence to argue that the Wegener transform, commonly drawn through Smith Sound, does not exist. Our new work in the northern interior of Ellesmere Island is in part focused on developing a revised model to explain the presence of the Eurekan orogenic belt and its latest Cretaceous to Paleogene evolution. A key observation from our recent fieldwork is that many of the large E-W striking faults previously mapped as normal faults or thrust faults are in fact dextral strike slip or dextral oblique reverse faults. These findings suggest that the Eurekan Orogen may be a transpressional belt rather than a classical fold and thrust belt. Clarifying the internal kinematics of the belt may help resolve some of the large-scale plate tectonic questions

Guest, B.; Hill, M.; Beauchamp, B.

2011-12-01

220

Understanding LIP formation in relation to lithospheric thickness, plate boundaries and plumes from a global plate tectonic perspective  

NASA Astrophysics Data System (ADS)

Large igneous provinces (LIPs) have been defined as either forming in a range of tectonic settings, or predominantly in intraplate tectonic settings. Using plate tectonic reconstructions for the past 200 million years we investigate the relationships between LIP formation, the condition of the underlying lithosphere, and the type and proximity of the closest plume and plate boundaries. We assess >70 continental and oceanic LIPs and ~70 proposed hotspots in the framework of a global plate tectonic model which incorporates dynamically evolving plate boundaries. We investigate (1) the age of the lithosphere LIPs form on (ii) the most likely plume responsible for the formation of each LIP, (iii) differences between the surface expressions of 'deep' versus 'shallow' plumes, and (iv) relationships between active plate boundaries and triple junctions, and LIP formation. A key result of our analysis is that oceanic LIPs, other than seamount chains, form on young oceanic lithosphere (mean age of ~17 million years). We also find that the majority of these oceanic LIPs form within close proximity to hotspots that have previously been classified as originating from deep within the mantle on the basis of criteria such as seismic tomography, isotopic signature, buoyancy and associated seamount chains.

Whittaker, J. M.; Landgrebe, T. C.; Seton, M.; Williams, S.; Matthews, K. J.; Mller, R.

2012-12-01

221

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

222

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

223

Relationship Between Tectonic Plates and Thermal Mantle Plume Morphology.  

National Technical Information Service (NTIS)

Models incorporating plate-like behavior, i.e., near uniform surface velocity and deformation concentrated at plate boundaries, into a convective system, heated by a mix of internal and basal heating and allowing for temperature dependent viscosity, were ...

A. Lenardic W. M. Kaula

1993-01-01

224

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

225

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

NASA Astrophysics Data System (ADS)

In the Solar System, Earth is the only planet to be in a mobile-lid regime, whilst it is generally accepted that all the other terrestrial planets are currently in a stagnant-lid regime, showing little or no surface motion. A transitional regime between these two, showing episodic overturns of an unstable stagnant lid, is also possible and has been proposed for Venus (e.g. Armann and Tackley, JGR 2012). In recent years a number of studies have focused on the feasibility of plate tectonics on large (1-10 Earth masses) extra-solar terrestrial planets; so-called super-Earths, with some studies concluding that these bodies should be in a mobile-regime mode (Valencia et al., ApJ 2007; van Heck and Tackley, EPSL 2011), but others predicting that they should be in a stagnant-lid regime (O'Neill and Leonardic, GRL 2007; Stein et al., GRL 2011). Using plastic yielding to self-consistently generate plate tectonics on an Earth-like planet with strongly temperature-dependent viscosity is now well-established, but such models typically focus on purely thermal convection, whereas compositional variations in the lithosphere can alter the stress state and greatly influence the likelihood of plate tectonics. For example, Rolf and Tackley (GRL, 2011) showed that the addition of a continent can reduce the critical yield stress for mobile-lid behaviour by a factor of ~2, while Armann and Tackley (JGR, 2012) found that bursts of crustal production caused by partial melting my trigger lithospheric overturn events, suggesting that laterally-heterogeneous crustal production in earlier studies (e.g. papers by Nakagawa and Tackley) may also play an important role in facilitating plate tectonics. Complicating matters is the finding that the final state of the system (stagnant- or mobile-lid) can depend on initial condition (Tackley, G3 2000 - part 2); Weller and Lenardic (GRL, 2012) found that the parameter range in which two solutions are obtained increases with viscosity contrast, leading to Lenardic and Crowley (ApJ, 2012) proposing a bistability of the system, introducing bifurcation theory to predict the tectonic state of a planet. Here we thus test (i) whether melting-induced crustal production changes the critical yield stress needed to obtain mobile-lid behaviour as a function of governing parameters (particularly Rayleigh number and viscosity contrast (Moresi and Solomatov, GJI 1998) as well as internal heating rate), and (ii) whether, under these conditions, there is an initial-condition dependence (bimodality) to the state of the system Weller and Lenardic (GRL, 2012). We study these using StagYY (Tackley, PEPI 2008), which uses a finite-volume scheme for advection of temperature, a multigrid solver to obtain a velocity-pressure solution at each timestep, tracers to track composition, and a treatment of partial melting and crustal formation.

Loureno, Diogo; Tackley, Paul

2013-04-01

226

Tectonic plate generation and two-phase damage: Void growth versus grain size reduction  

Microsoft Academic Search

The generation of plate tectonics from mantle convection requires shear localization in order to yield narrow, weak plate boundaries separating broad strong plates. A plausible shear-localizing mechanism involves damage (e.g., distributed microcracking), one theoretical model of which involves two-phase mechanics. Two-phase damage theory employs a nonequilibrium relation between interfacial surface energy, pressure, and viscous deformation, thereby providing a description of

David Bercovici; Yanick Ricard

2005-01-01

227

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

228

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

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

229

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

NASA Astrophysics Data System (ADS)

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. At that time, older sedimentary basins, mostly ENE-WSW trending, were folded and inverted, including some basins along the Tethyan margin from Morocco to the Syrian Arc and the intraplate Benue-southern Chad basins and the Lugh-Mandera basin. In Oman, ophiolites were obducted. Following the Santonian tectonism, an extensive phase of rifting occurred in Central and North Africa and northern Arabia, spanning from Campanian to Maastrichtian or Paleocene times. Rejuvenation or acceleration of subsidence occurred in several basins located along the Tethyan margin, along the Atlantic and Indian Ocean margins, as well as within the intraplate domain. Rifting was sometimes accompanied by magmatic activity, especially in offshore northern Libya and along the Indian Ocean margin. Compressional deformations rejuvenated or developed by latest Maastrichtian times along the Tethyan margin and locally within the intraplate domain. One of the most remarkable attributes of the Santonian tectonic event, which we consider representative of the major trans-African stress field changes, is the rapidity with which the change was reflected stratigraphically across North and Central Africa, and its short duration. The cause of the Santonian compressional event is directly linked to the change in poles of rotation for the opening of the Atlantic at 83-85 Ma, the end of the Cretaceous Normal Magnetic Quiet Zone. This was also synchronous with the obduction of ophiolites along the northeast margin of Arabia (Oman), the onset of separation between India and Madagascar with formation of the Mascarene oceanic basin, and the development of the European Alpine Chain. We interpret these phenomena as causally related aspects of a global tectonic event. The Santonian compressional event, as well as the Campanian-Maastrichtian rifting event and the end Cretaceous compressional event, illustrate the critical connection between intraplate tectonic histories and processes occurring at sometimes very distant plate boundaries.

Guiraud, Ren; Bosworth, William

1997-12-01

230

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

231

New observations on mid-plate volcanism and the tectonic history of the Pacific plate, Tahiti to Easter microplate  

Microsoft Academic Search

We describe the geology and tectonics of a continuous swathe of seafloor between Tahiti and the western edge of the Easter microplate imaged by GLORIA and Sea Beam on two separate cruise transits in 1987 and 1988. The data reveal that mid-plate volcanism is common in this region, even on deep seafloor hundreds of kilometres from major lines of seamounts

R. C. Searle; J. Francheteau; B. Cornaglia

1995-01-01

232

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

NASA Astrophysics Data System (ADS)

Widespread Pacific Rim and Pacific plate tectonism both appear to be closely associated with a pronounced change in Pacific absolute plate motion (APM) that occurred about 43 Ma as revealed by the Hawaiian Emperor Bend. In the Western Pacific prior to the change, as the Pacific plate moved toward the north, Proto Izu -- Bonin -- Mariana (IBM) subduction was already occurring by 49 Ma, perhaps as early as 52 Ma near the northern end of the Proto IBM, evidenced by the emplacement of boninites in the forearc (Cosca et al., 1998). If the Philippine Basin -- Pacific plate circuit is traced though the Coral Sea basin after closing the Ayu and Sorel troughs, it is evident that the alignment of the Proto IBM (Kyushu -- Palau) subduction zone roughly paralleled the Pacific APM during the initiation of subduction. At ~ 43 Ma, Proto-IBM Trench subduction rapidly increased, possibly causing the major change in Pacific (and Australia) APM that produced the prominent bend in the Hawaiian-Emperor chain. This change also produced a the minor bend in the Louisville chain, as the Pacific plate began to move west-northwestward, as well as at least five more noticeable bends in other seamount chains across the Central Pacific. In the Northeastern Pacific, the expansive magmatic activity, which occurred during the early stage of Aleutian Arc growth between 55--50 Ma, began to wane between 45 and 40 Ma (Scholl et al., 1987). After the 43 Ma change in Pacific APM, the Aleutian subduction zone began to accommodate dextral slip at its western end, as well as continuing convergence at its eastern end. To the south, in the Eastern Pacific, Ridge propagation began about 43 Ma both north and south of the Murray FZ (extending southward to the Clarion FZ). Much farther to the south, changes are also apparent in the Pacific -- Antarctic spreading pattern at ~43 Ma. In the Central Pacific, following the 43 Ma change in Pacific plate motion, intraplate subduction began along the Manus -- North Solomon -- Vitiaz (Melanesian) Trench, which was aligned parallel to the post 43 Ma Pacific APM. Subduction was heralded by metamorphic events in the Solomon Islands' Florida Group and Eastern Belt Islands that occurred between ~44 and ~35 Ma (Neef and McDougal, 1976), after which the earliest Lemau Intrusives were emplaced between 38 and 32 Ma in New Ireland (Stewart and Sandy, 1988) near the western end of the Melanesian Arc. To the southwest, on the Australia Plate, the Louisiade Plateau also formed over the Lord Howe Hotspot about 43 Ma as a concomitant change in Australia APM also occurred.

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

2002-12-01

233

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

NASA Astrophysics Data System (ADS)

The discovery of extra-solar super-Earths has prompted interest in their possible mantle dynamics and evolution, and in whether their lithospheres are most likely to be undergoing active plate tectonics like on Earth, or be stagnant lids like on Mars and Venus. The origin of plate tectonics is poorly understood for Earth, likely involving a complex interplay of rheological, compositional, melting and thermal effects, which makes it challenging to make reliable predictions for other planets. Nevertheless, as a starting point it is common to parameterize the complex processes involved as a simple yield stress that is either constant or has a Byerlee's law dependence on pressure. Because the simplifying assumptions made in developing analytical scalings may not be valid over all parameter ranges, numerical simulations are needed; one numerical study on super-Earths finds that plate tectonics is less likely on a larger planet (O'Neill and Lenardic (2007)), in apparent contradiction of an analytical scaling study (Valencia et al. (2007)). To try and understand this we here present new calculations of yielding-induced plate tectonics as a function of planet size, focusing on the idealized end members of internal heating or basal heating as well as different strength profiles, and compared to analytical scalings. In the present study we model super-Earths as simple scaled up versions of Earth, i.e., assuming constant physical properties, keeping the ratio of core/mantle radii constant and applying the same temperature difference between top/bottom boundaries and the same internal heating rate. Effects that originate outside of the planet, such as tidal forces, meteor impacts and intense surface heating from a nearby star are not considered. We find that for internally-heated convection plate tectonics is equally likely for terrestrial planets of any size, whereas for basally-heated convection plate tectonics becomes more likely with increasing planet size. This is indicated both by analytical scalings and the presented numerical results, which agree with each other. When scalings are adjusted to account for increasing mean density with increasing planet size, plate tectonics becomes more likely with increasing planet size for all scenarios. The influence of the pressure variation of viscosity, thermal expansivity and conductivity may, however, act in the opposite sense and needs to be determined in future studies. At least in the simplest case, factors other than planet size, such as the presence of surface water, are likely most important for determining the presence or absence of plate tectonics.

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

2011-10-01

234

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

235

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

236

Subduction and Plate Edge Tectonics in the Southern Caribbean  

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

237

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

NASA Astrophysics Data System (ADS)

We investigate the initiation of plate tectonics on Earth from a compositional overturn immediately after magma ocean solidification, and the early maintenance of plate tectonics through thermo-chemical penetrative convection in the Archean mantle. Plate tectonics likely began early in Earth's history based on Archean arc and back-arc rock assemblages such as greenstone belts. Furthermore, the presence of zircons as early as 4.4 Ga indicates that at least some type of surface recycling was active on Earth soon after magma ocean solidification. However, how plate tectonics initiates is unknown. In the modern day Earth weak zones created through plate tectonic processes, such as oceanic fracture zones and dormant spreading ridges, provide nucleation points for new subduction zones, and hence the maintenance of plate tectonics. In the early Earth, prior to plate tectonics, this mechanism is absent. Therefore another process responsible for forming lithospheric weak zones is necessary. We hypothesize that compositional overturn in the mantle immediately following magma ocean solidification will drive lithospheric weakening through grain-damage, and that subsequent penetrative thermo-chemical mantle convection will sustain weak zones in the lithosphere and plate tectonic style mantle convection in the early Earth. We model an initially hot mantle cooling from the surface such that it undergoes convective instability. We use a damage-grainsize feedback mechanism (grain-damage) for lithospheric weak zone formation; this mechanism causes lithospheric weakening due to convective stresses, and allows for dormant weak zones. We also include an initially unstable compositional density profile to account for chemical differentiation during magma ocean solidification. Crystal settling at the bottom of the magma ocean, and compaction of melt out of this solid layer, isolates the solidifying mantle from the chemically evolving liquid. As a result, dense material solidifies last, at the surface, and the solid mantle is chemically unstable. The effect of compositional buoyancy is crucial; in its absence convection does not begin until a thick, rigid lid has formed, and thus stagnant lid convection results. Initiating plate tectonics from this state is extremely difficult. We therefore perform numerical calculations with initially unstable compositional profiles to map out the conditions that allow for weak zone formation and plate tectonic style convection in the early Earth. In calculations without damage, compositional overturn is followed immediately by penetrative convection, which eventually develops into full mantle convection as mixing eliminates the chemical heterogeneity. With strongly temperature dependent viscosity, the penetrative convection is suppressed and the lag time to full mantle convection is prolonged significantly. We propose that with grain-damage the initial overturn will form lithospheric weak zones; these weak zones will then allow for penetrative convection to occur, sustaining the damaged zones and surface mobility until full mantle convection develops. We present a suite of numerical calculations to assess the viability of this mechanism for initiating plate tectonics on the early Earth.

Foley, B. J.; Bercovici, D.

2012-12-01

238

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

239

Neogene Caribbean plate rotation and associated Central American tectonic evolution  

NASA Technical Reports Server (NTRS)

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

Wadge, G.; Burke, K.

1983-01-01

240

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

NASA Technical Reports Server (NTRS)

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

Frey, H.

1977-01-01

241

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

242

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

NSDL National Science Digital Library

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

243

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

ERIC Educational Resources Information Center

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

Cuff, Kevin

244

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

245

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

246

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

247

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

248

Tectonics of the Nazca-Antarctic plate boundary  

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

249

A diffuse plate boundary model for Indian Ocean tectonics  

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

250

Plate Tectonics and the Evolution of the Alpine System.  

National Technical Information Service (NTIS)

It is contended that the Late Triassic to present-day gross evolution of the Alpine system in the Mediterranean region has been the result of activity along an evolving network of accreting, transform, and subducting plate boundaries between the large sta...

J. F. Dewey J. Bonnin W. B. F. Ryan W. C. Pitman

1973-01-01

251

Plate Tectonics of the Red Sea and East Africa  

Microsoft Academic Search

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

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

1970-01-01

252

Seismicity and plate tectonics in south central Alaska  

NASA Technical Reports Server (NTRS)

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

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

1974-01-01

253

The rapid drift of the Indian tectonic plate  

Microsoft Academic Search

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

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

2007-01-01

254

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

PubMed

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

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

2010-08-27

255

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

256

Self-Consistent Generation of Tectonic Plates in Time Dependent Three-Dimensional Mantle Convection  

Microsoft Academic Search

Abstract. Presented here are the first three-dimensional simulations of mantle convection,to display self-consistently-generated plate tectonic-like behavior which,is continuous,in space and,time. Plate behavior,arises through,a reasonable material description of silicate deformation, with a simple yield stress being sufficient to give first-order plate-like behavior. Toroidal:poloidal ratios are within geologically-observed limits. The sensitivity of the system to yield strength and,the form,of strength envelope,is systematically

Paul J. Tackley

257

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

258

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

NASA Astrophysics Data System (ADS)

Two opposing visions of the Aegean backarc tectonics implicitly contain contrasting images of the rheological behaviour of the lihosphere, supported by different sets of observations. The propagation of the NAF and extension in the Corinth Rift suggest a strongly localising rheology whereas the formation of MCC in the Cyclades and the Rhodope suggests instead a more viscous behaviour. This paradox was the seminal question addressed by the ANR-EGEO programme (2007-2010) that leads to the following conclusions: (1) The exhumation of the Cycladic MCCs is accommodated by the N-dipping North Cycladic Detachment System (NCDS) that partly reworks the Vardar suture and at the base by a series of thrusts, including the basal contact of the Cycladic Blueschists (CBS) over the Cycladic Basement (CB). The activity of LANF is due to the reactivation of pre-existing discontinuities such as thrusts or earlier detachments and much less to the interaction with granitic plutons. (2) Exhumation in the Cyclades has proceeded in two stages: (a) Eocene syn-orogenic exhumation within the subduction lower/upperplate interface while the post-orogenic Rhodope MCC formed further north, (b) Oligo-Miocene post-orogenic extension in an MCC mode coeval with syn-orogenic exhumation in Crete and the Peloponnese. (3) Both stages were associated with slab retreat, as early as the Eocene with an acceleration at 30-35 Ma. (4) The localisation of the presently active steeply-dipping normal faults on the southern margin of the Corinth Rift may have been preceded by a partial reworking of thrusts and syn-orogenic detachments by shallow-dipping decollements. (5) The localisation of the NAF in the Marmara Sea region and the Northern Aegean Sea is now accurately dated between 5.3 and 5 Ma Ma using the erosion and deposition surfaces that mark the Messinian salinity Crisis and nannofossils ages. (6) The formation of MCCs in the Cyclades resulted in the draining of the low viscosity lower crust from the northern Aegean Sea and led to an easier coupling between upper mantle and upper crust, easing the localisation and propagation of the NAF. (7) A comparison between crustal and mantle finite strain suggests that mantle flow due to slab retreat controls the stretching of the crust. Our model involves progressive slab retreat and mantle flow below the overriding plate inducing the observed succession of tectonic episodes with a progressive localisation of extension due to several slab tearing events. There is no paradox in the tectonic history and rheological behaviour of the Aegean lithosphere but an evolution of the kinematic boundary conditions due to slab deformation at depth.

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

2010-12-01

259

Numerical modelling of tectonic plates subduction using X-FEM  

Microsoft Academic Search

The numerical modelling of plate subduction requires solving a coupled thermo-mechanical highly-nonlinear transient problem. The mechanical description of the phenomenon results in a multiphase quasi-static Stokes flow, where the inertia terms are neglected. The transient thermal problem is dominated by the advection term. Here, the representation and evolution of the different phases are described using level sets. The phase tracking

Sergio Zlotnik; Pedro Dez; Manel Fernndez; Jaume Vergs

2007-01-01

260

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

261

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

SciTech Connect

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

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

1989-01-01

262

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

Microsoft Academic Search

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

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

1990-01-01

263

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

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

264

The Cretaceous iron belt of northern Chile: role of oceanic plates, a superplume event, and a major shear zone  

Microsoft Academic Search

The Cretaceous constitutes a turning point in the tectonic, magmatic, and metallogenic history of Chile. The geological evidence indicates that a major change occurred in late Neocomian time when superplume emplacement (Mid-Pacific Superplume) and plate reorganization processes took place in the Pacific. The superplume event resulted in a major ridge-push force resulting in increased coupling between the subducting and overriding

Roberto Oyarzun; Jorge Oyarzn; Jean Jacques Mnard; Javier Lillo

2002-01-01

265

Organization of the tectonic plates in the last 200 Myr (Invited)  

NASA Astrophysics Data System (ADS)

The present tessellation of the Earth's surface into tectonic plates displays a remarkably regular plate size distribution, described by either one (Sornette and Pisarenko, 2003) or two (Bird, 2003) statistically distinct groups, characterised by large and small plate size. A unique distribution implies a hierarchical structure from the largest to the smallest plate. Alternatively, two distributions indicate distinct evolutionary laws for large and small plates, the first tied to mantle flow, the second determined by a hierarchical fragmentation process. We analyse detailed reconstructions of plate boundaries during the last 200 Myr and find that (i) large and small plates display distinct statistical distributions, (ii) the small plates display little organisational change since 60 Ma and (iii) the large plates oscillate between heterogeneous (200-170 Ma and 65-50 Ma) and homogeneous (120-100 Ma) plate tessellations on a timescale of about 100 Myr. Heterogeneous states are reached more rapidly, while the plate configuration decays into homogeneous states following a slower asymptotic curve, suggesting that heterogeneous configurations are excited states while homogeneous tessellations are equilibrium states. We explain this evolution by proposing a model that alternates between bottom- and top-driven Earth dynamics, physically described by fluid-dynamic analogies, the Rayleigh-Benard and Bnard-Marangoni convection, respectively. We discuss the implications for true polar wander (TPW), global kinematic reorganisations (50 and 100 Ma) and the Earth's magnetic field inversion frequency. Earth's present tessellation: grey scale proportional to the logarithm of plate size. Plot: logarithm of complementary 'cumulative plate count' (Y-axis) vs. the logarithm of the plate size (X-axis). Time evolution of the 'standard deviation' of the plate size every one million years.

Morra, G.; Seton, M.; Quevedo, L. E.; Mller, D.

2013-12-01

266

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

NASA Astrophysics Data System (ADS)

Several numerical studies have been published in the past years speculating about the existence of plate tectonics on large exoplanets. They focus on aspects like the mass of a planet, the interior heating rate and the occurrence of water in the mantle. Different trends in the propensity for plate tectonics have been observed in particular when varying the planetary mass: with increasing mass the surface mobilization is found to be either more, equally or less likely than on Earth. These studies and their implications are, however, difficult to compare as they assume different initial conditions and parameter sets, and either neglect the pressure effect on the viscosity or assume a rather small influence of the pressure on the rheology. Furthermore, the thermal evolution of the planets (i.e. cooling of core and decrease in radioactive heat sources with time) is typically neglected. In our study, we use a 2D finite volume code and apply a pseudo-plastic rheology. We investigate how a strong pressure-dependence of the viscosity influences not only the convective regime in the lower mantle, but also in the upper mantle and hence the likelihood to obtain plate tectonics. We examine how our results change when either assuming a wet or a dry rheology or when employing different initial conditions, focussing on the initial temperature in the lower mantle and at the core-mantle boundary. We find that the initial temperature conditions have a first-order influence on the likelihood of plate tectonics on large exoplanets. For standard literature values for initial temperatures of super-Earths, surface mobilization is less likely than on Earth, for warm initial temperature the result is vice versa. Simulations that neglect the time-dependence of internal heat sources on the other hand tend to lead to an increasing likelihood of plate tectonics with increasing mass. Finally, our investigations suggest that a wet rheology does not necessarily favor plate tectonics, but - depending on the reference viscosity - may rather lead to a stagnant-lid regime.

Noack, Lena; Breuer, Doris

2014-08-01

267

Plate Tectonics and Net Lithosphere Rotation over the past 150 My  

NASA Astrophysics Data System (ADS)

During the 20th century our description of the movement and deformation of the Earth's outer rigid layer evolved from the hypothesis of Continental Drift into Sea-Floor Spreading and to the theory of Plate Tectonics. Now a fourth shift is underway in which Plate Tectonics is being subsumed into a new Mantle Dynamics framework that requires plate motion reconstructions through time to include not only improved relative plate motions but also refined plate motions with respect to the mantle. By combining relative and absolute plate motion frames from the Indo-Atlantic and the Pacific realms we have developed an improved model of global digital palaeo-plate boundaries and plate motion to describe the distribution and history of plates since the Late Jurassic. From this history we computed net lithospheric rotation (NR) through time confirming the so-called westward drift, but only for the past 30 Myrs. The NR has significantly smaller magnitudes (0.13 deg./My, past 5 My) than for some other plate models; it averages to 0.11 0.03 deg./My for the past 50 My with a small but systematic increase toward the present. The westward drift, seen only for the past 30 My, is attributed to the increased dominance of a steadily growing and accelerating Pacific plate. NR shows peaks with time but only an Early Tertiary peak of 0.33 deg./My (when the Indian plate was undergoing the largest known acceleration/deceleration) can be interpreted with some confidence. NR fluctuates and gradually increases back in time, and by removing a linear time-trend in the data, averages to ~0.12 deg./Myr for the past 150 Myr. However, the oceanic area reconstructions rely on few constraints and many assumptions for older time intervals; about 60% of the lithosphere have been subducted since 150 Ma and plate motions are uncertain for this fraction. To realistically reconstruct the proto-Pacific through time, information about the oceanic crust consumed by subduction is needed. Subducted material is imaged by tomographic models and we envisage that the next generation of global plate reconstructions and plate boundaries will incorporate at least the first order estimate of the amount of subducted material based on tomography and iterative plate reconstructions.

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

2010-05-01

268

Global plate tectonics and the secular motion of the pole  

NASA Technical Reports Server (NTRS)

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

Soler, T.

1977-01-01

269

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

270

Changes in electrical resistivity track changes in tectonic plate coupling  

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

271

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

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

272

Cenozoic plate tectonic reconstructions and plate boundary processes in the Southwest Pacific  

Microsoft Academic Search

The Australia-Pacific-Antarctic plate circuit has long been a weak link in global plate reconstruction models for Cenozoic time. The time period spanning chron 20 to chron 7 (43-25 Ma) is particularly problematic for global plate models because seafloor spreading was occurring in two poorly constrained regions in the Southwest Pacific - the Macquarie Basin southwest of New Zealand, and the

William R. Keller

2005-01-01

273

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

274

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

275

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

USGS Publications Warehouse

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

Hanks, T. C.

1977-01-01

276

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

NASA Astrophysics Data System (ADS)

In support of a NASA-funded scientific application (SESDI; Semantically Enabled Science Data Integration Project; that needs to share volcano and climate data to investigate relationships between volcanism and global climate, we have generated a volcano and plate tectonic ontologies and leveraged and augmented the existing SWEET (Semantic Web for Earth and Environmental Terminology) ontoloy. Our goal is to create a package for integrating the relevant ontologies (meant to be shared and reused by a broad community of users) to provide access to the key volcanology, plate tectonic and atmospheric related databases. We present how we have put ontologies to work in this science application setting, and the methodologies employed to create the ontologies, map them to the underlying data and implement them for use by scientists. SESDI is an NASA/ESTO/ACCESS-funded project involving the High Altitude Observatory at the National Center for Atmospheric Research (NCAR), McGuinness Associates Consulting, NASA/JPL and Virginia Polytechnic University.

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

2007-12-01

277

Ordovician-Silurian tectonism in northern California:The Callahan event  

NASA Astrophysics Data System (ADS)

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

Cotkin, Spencer J.

1992-09-01

278

Duality of thermal regimes is the distinctive characteristic of plate tectonics since the Neoarchean  

NASA Astrophysics Data System (ADS)

Ultrahigh-temperature (UHT) granulite metamorphism is documented predominantly in the Neoarchean to Cambrian rock record, but UHT granulite metamorphism also may be inferred at depth in Cenozoic orogenic systems. The first occurrence of UHT granulite metamorphism in the record signifies a change in geodynamics that generated transient sites of very high heat flow. Many UHT granulite metamorphic belts may have developed in settings analogous to modern continental backarcs; on a warmer Earth, destruction of oceans floored by thinner lithosphere may have generated hotter backarcs than those associated with the modern Pacific ring of fire. Medium-temperature eclogite high- pressure (EHP) granulite metamorphism is documented in the Neoarchean rock record and at intervals throughout the Proterozoic and Paleozoic record. EHP granulite metamorphic belts are complementary to UHT granulite metamorphic belts in that they are generally inferred to record subduction-to-collision orogenesis. Blueschists become evident in the Neoproterozoic rock record, but lawsonite blueschist eclogite metamorphism (high pressure [HP]) and ultrahigh-pressure metamorphism (UHP) characterized by coesite or diamond are predominantly Phanerozoic phenomena. HP-UHP metamorphism registers the low thermal gradients and deep subduction of continental crust during the early stage of subduction-to-collision orogenesis. A duality of metamorphic beltsreflecting a duality of thermal regimesappears in the record only since the Neoarchean Era. A duality of thermal regimes is the hallmark of modern plate tectonics, and the duality of metamorphic belts is the characteristic imprint of plate tectonics in the rock record. The occurrence of both UHT and EHP granulite metamorphism since the Neoarchean marks the onset of a Proterozoic plate tectonics regime, which evolved during a Neoproterozoic transition to the modern plate tectonics regime, characterized by colder subduction as chronicled by HP-UHP metamorphism.

Brown, Michael

2006-11-01

279

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

Microsoft Academic Search

We suggest a method of fitting of a zero-range model of a tectonic plate under a boundary stress on the basis of comparison of the theoretical formulae for the corresponding eigenfunctions\\/eigenvalues with the results extraction under monitoring, in the remote zone, of non-random (regular) oscillations of the Earth with periods 0.2-6 h, on the background seismic process, in case of

L. Petrova; B. Pavlov

2008-01-01

280

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

Microsoft Academic Search

New plate-tectonic reconstructions of the Gondwana margin suggest that the location of Gondwana-derived terranes should not only be guided by the models, but should also consider the possible detrital input from some Asian blocks (Hunia), supposed to have been located along the Cambrian Gondwana margin, and accreted in the Silurian to the North-Chinese block. Consequently, the Gondwana margin has to

Jrgen F. von Raumer; Grard M. Stampfli

2008-01-01

281

Reidar Lvlie and Plate Tectonic consequences of sedimentary inclination shallowing  

NASA Astrophysics Data System (ADS)

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

Torsvik, Trond H.

2014-05-01

282

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.

283

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

284

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

285

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

USGS Publications Warehouse

Rubidium-strontium studies of Precambrian volcanic and plutonic rocks of the Arabian Shield document an early development of the Arabian craton between 900 and 680 m.y. (million years) ago. Geologic studies indicate an island-arc environment characterized by andesitic (dioritic) magmas, volcaniclastic sedimentation, rapid deposition, and contemporaneous deformation along north or northwest-trending axes. Magmatic trends show consistent variation in both composition and geographic location as a function of age. The oldest units belong to an assemblage of basaltic strata exposed in western Saudi Arabia that yield an age of 1165:!:110 m.y. The oldest andesitic strata studied yield an age of 912:!:76 m.y. The earliest plutonic units are diorite to trondhjemite batholiths that range from 800 to 9,00 m.y. in age and ,occur along the western and southern parts of Saudi Arabia. Younger plutonic units, 680 to 750 m.y. in age, range from quartz diorite to granodiodte and become more abundant in the central and northeastern parts of the Arabian Shield. Initial 'Sr/ 86 Sr ratios for both dioritic groups range from 0.7023 to 0.7030 and average 0.7027. The absence of sialic detritus in sedimentary units and the evidence for an island-arc environment suggest the early development of the Arabian craton at a convergent plate margin between plates of oceanic lithosphere. Active subduction apparently extended from at least 900 m.y. to about 680 m.y. Subsequent to this subduction-related magmatism and tectonism, called the Hijaz tectonic cycle, the Arabian craton was sutured to the late Precambrian African plate in a collisional event. This period of orogeny, represented in Arabia and eastern Africa by the Mozambiquian or Pan-African event, extended from some time before 650 m.y. to at least 540 m.y. and perhaps 520 m.y. B.P. Although the tectonic processes of subduction and continental collision during the 900+ to 500-m.y. period require similar directions of plate convergence, the differences in magmatic and tectonic. styles of Hijaz orogenesis from those of the Pan-African and the temporal break between them in much of the southern part of the Arabian Shield support division into at least two events. As defined by the ages of major plutonic units, the axis of magmatic and tectonic activity migrated eastward or northeastward during the Hijaz cycle, the predominantly dioritic plutonic rocks becoming younger and more siliceous to the east. Granodiorite to granite pl}.1tonism of the Pan-African event, however, shows no geographic bias, being distributed throughout the Arabian Shield. Although the Hijaz diorites and Pan-African granitic rocks exhibit strong contrasts in composition and age differences as great as 250 m.y. in the westernmost parts of the area, the two groups are less distinct compositionally and nearly the same age in the eastern part.

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

1980-01-01

286

Plate-Tectonic Circulation is Driven by Cooling From the Top and is Closed Within the Upper Mantle  

Microsoft Academic Search

Subduction drives plate tectonics and is due to cooling from the top: circulation is self-organized, and likely is closed above the discontinuity near 660 km. The contrary consensus that plate tectonics is driven by bottom heating and involves the entire mantle combines misunderstood kinematics with flawed concepts of through-the-mantle plumes and subduction. Plume conjecture came from the Emperor-Hawaii progression, the

W. B. Hamilton

2001-01-01

287

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

288

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

USGS Publications Warehouse

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

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

2006-01-01

289

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

NASA Astrophysics Data System (ADS)

The discovery of extra-solar super-Earths has prompted interest in their possible mantle dynamics and evolution, and in whether their lithospheres are most likely to be undergoing plate tectonics like on Earth, or be stagnant lids like on Mars and Venus. The origin of plate tectonics is poorly understood for the Earth, likely involving a complex interplay of rheological, compositional, melting and thermal effects, which makes it impossible to make reliable predictions for other planets. Nevertheless, as a starting point it is common to parameterize the complex processes involved as a simple yield stress that is either constant or has a linear "Byerlee's law" dependence on pressure (e.g., [Tackley, GCubed 2000ab] in 3D cartesian geometry; [van Heck and Tackley, GRL 2008] in 3D spherical geometry). For such a simple description, scaling with planet size is expected to depend on heating mode (internal versus basal) and lithospheric strength profile. Simple "back of the envelope" scaling laws (e.g., following Moresi and Solomatov, GJI 1998) ignoring the pressure- dependence of physical properties such as density and thermal expansivity, suggest that the threshold for plate tectonics (i.e., yield stress or friction coefficient) does not depend strongly on planet size, and plate tectonics is equally likely or more likely for larger planets. Scalings that take into account pressure-related changes in physical properties [Valencia et al., Astrophys. J., 2007] make a similar prediction for predominantly internally-heated convection. Because the simplifying assumptions made in developing analytical scalings may not be valid over all parameter ranges, numerical simulations are needed; the one numerical study on super-Earths to date (O'Neill and Lenardic, GRL 2007) finds that plate tectonics is less likely on a larger planet, in apparent contradiction of analytical results. To try and understand this we here present new calculations of yielding- induced plate tectonics as a function of planet size, focusing on the idealized endmembers of internal heating or basal heating as well as different strength profiles, and compare to analytical scalings. The temperature- dependence of viscosity is based on laboratory values, i.e., stronger than previously modelled. Preliminary results indicate some first order similarity to simple scalings although some differences exist. In Earth, physical properties such as density, thermal expansivity, thermal conductivity and viscosity change strongly with pressure so that their values change substantially between the surface and the CMB, and many modelling studies have shown that this has a strong effect on convection. On super-Earths this will be even more accentuated. Thus, in a second set of calculations, we include reasonable variations of physical properties with pressure for planets up to twice Earth radius, studying their effect on convection with rigid lids or plate tectonics.

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

2008-12-01

290

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

291

Mantle rheology and the scaling of bending dissipation in plate tectonics  

NASA Astrophysics Data System (ADS)

Plate tectonics on Earth involves the bending deformation of plates at subduction zones, and because plates are generally considered to be stiff owning to the rheology of mantle minerals, the role of energy dissipation by plate bending in the global energy balance has been frequently debated in the recent literature. Here we consider how bending dissipation should scale with slab parameters such as dip angle, plate age, the radius of curvature, and plate velocity by systematically exploring the parameter space with instantaneous Stokes flow calculations. We derive the scaling of bending dissipation for a range of mantle viscosity functions, including pseudoplastic rheology with olivine flow laws. Our results indicate that, as we move away from the isoviscous case, the scaling gradually deviates from what has commonly been assumed in previous studies, most notably for the radius exponent, which exhibits more than threefold reduction and even a sign reversal in some cases. These modifications in scaling exponents originate in the complication of the deformation field caused by viscosity variations within the bending plate. Approximating the lithospheric rheology by a single effective viscosity in the dynamical models of subduction has been a common practice, but we suggest that such approximation may limit the geological relevance of modeling studies, in particular when estimating the significance of bending dissipation.

Rose, I. R.; Korenaga, J.

2011-06-01

292

Plate tectonic modelling: virtual reality with GMAP 1 GMAP Standard is available as a freeware on http:\\/\\/www.ngu.no\\/geophysics 1  

Microsoft Academic Search

Palaeogeographic reconstructions have been an integral part of global tectonic research since the advent of the plate tectonic paradigm, and GMAP is a state of the art computer program which performs all processing and plotting tasks associated with the generation of palaeogeographic reconstructions and plate tectonic modelling. GMAP is menu-driven and easy to use; the user is never far removed

Trond Helge Torsvik; Mark Andrew Smethurst

1999-01-01

293

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

NASA Technical Reports Server (NTRS)

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

Lenardic, A.; Kaula, W. M.

1994-01-01

294

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

NASA Astrophysics Data System (ADS)

Complexity in the tectonic model for Pacific-North America transform motion in the offshore southern California region is demonstrated by earthquakes near San Clemente Island and Fortymile Bank. Observed focal mechanisms show movements opposite to those predicted by the plate tectonic theory for right-slip on NW- trending transform faults and observed in other parts of the California Continental Borderland. Also, there is evidence suggesting that moderate earthquakes in the Inner Borderland have greater magnitudes based on long-period seismic waves than the nominal Richter local magnitudes reported in earthquake catalogs. With better data showing the geologic structure of the area now available, we can try to derive a more complete understanding of this complex tectonic behavior and resulting consequences for local tsunamigenesis. The "backwards" earthquakes suggest the occurrence of plate boundary deformation and/or microplate tectonics with the western side of a block containing Fortymile Bank moving instantaneously faster to the northwest than the adjacent block to the west. Such motions may be consistent with clockwise rotation of blocks in the continental borderland due to the regional dextral shear couple as proposed by Crouch (1978) and Luyendyk and others (1980) based upon paleomagnetic and other geologic data. Alternatively, as initially observed for the 1986 Offshore Oceanside earthquake (MS=5.8) by Hauksson and Jones (1988), the anomalous focal mechanism may be due to an inaccurate model of crustal seismic velocity structure for the offshore region. Use of a refined velocity model may show these anomalous earthquakes to have oblique-reverse mechanisms like the 1986 mainshock. Furthermore, more recent seismicity, located with greater accuracy due to expansion of the Southern California Seismograph Network (SCSN), has apparent NE alignments suggestive of significant active secondary fault structure located off the major NW-trending right-slip faults. Such faulting was also inferred to be significant during the clockwise vertical-axis block rotations of the western Transverse Ranges. Interaction between faults within conjugate systems may enhance vertical movements including subsidence at basins where blocks diverge and uplift where blocks converge, thereby producing local tsunamis during large earthquakes. It was not until recently that local earthquake sources were identified offshore Southern California as potentially damaging tsunami sources. Erroneous magnitude estimate of offshore earthquakes can have serious implications for tsunamigenesis and tsunami warning. A half magnitude error can make the difference between a non-tsunamigenic and a tsunamigenic event especially when a marginal event is considered. Better magnitude estimates using long-period seismographs may be necessary for more accurate identification of potentially tsunamigenic local earthquakes.

Legg, M. R.; Barberopoulou, A.

2007-12-01

295

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

USGS Publications Warehouse

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

Bohannon, R. G.; Parsons, T.

1995-01-01

296

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

NASA Astrophysics Data System (ADS)

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

Choblet, G.; Amit, H.

2013-12-01

297

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

298

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

SciTech Connect

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

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

2011-07-20

299

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

300

Tertiary plate tectonics and high-pressure metamorphism in New Caledonia  

USGS Publications Warehouse

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

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

1973-01-01

301

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

Microsoft Academic Search

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

Nance

1993-01-01

302

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

NASA Astrophysics Data System (ADS)

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

Husson, Laurent; Yamato, Philippe; Bezos, Antoine

2014-05-01

303

Earth Exploration Toolbook: Writing to Support the Theory of Plate Tectonics  

NSDL National Science Digital Library

How does one write about plate tectonics? It's an important question for those studying the earth sciences. This resource from the Earth Exploration Toolbook was created by Sabina F. Thomas and William A. Prothero and is designed to help students use a range of images of earthquakes, volcanoes, and seafloor ages to craft just such a paper. On this site, visitors can take advantage of teaching notes, step-by-step instructions, and a range of tools. Instructors will find this material quite useful and it's important to note that students are encouraged to use these resources for improving their own skills of scientific inquiry and synthesis.

304

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

305

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

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

306

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

307

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

308

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

NASA Astrophysics Data System (ADS)

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

David-Ameline, Jacques

2014-05-01

309

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

310

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

USGS Publications Warehouse

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 7060 Ma. In contrast, exhumation of the island arc sequence exposed on Bonaire occurred at 8580 Ma and 5545 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 5545 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 Oligoceneearly Miocene dextral transtension within the Bonaire Block drove subsidence and burial of crystalline basement rocks of the Leeward Antilles to ?1 km. Late Miocenerecent 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

2010-01-01

311

Geodynamic modeling of passive margin systems from tectonic reconstructions with deforming plate boundaries  

NASA Astrophysics Data System (ADS)

The effect of mantle flow on surface topography has been the subject of considerable interest over the last few years. A common approach to the problem is to link plate tectonic reconstructions and global geodynamic models. An important limitation of this approach is that traditional plate tectonic reconstructions do not take the deformation of the lithosphere into account. We introduce quantitative models of surface plate kinematics that include areas of deforming continental crust. We present a series of global reconstructions including deforming plates in key areas, derived using tools developed within the open source plate modeling software GPlates. In traditional plate reconstructions, the continents are represented as rigid blocks that overlap in full-fit reconstructions. Models that use topological polygons avoid continental overlaps, but plate velocities are still derived on the basis of Euler poles for rigid blocks. To resolve these issues, we use a methodology that requires at minimum two inputs; (1) the relative motions of the rigid blocks within continents; (2) a definition of the regions in which continental crust deformed between these blocks. We use geological and geophysical data to interpret the landward limit of significant extension and crustal thinning along conjugate passive margins. These boundaries are used to construct polygons along both margins that define the extent of the stretched continental crust on either side of the rift. We derive individual motion histories for each point on the conjugate continent/ocean boundaries (COBs). Joined together, these COB points form the topological boundaries of deforming domains in which each vertex moves independently. The deforming domains represented by topological meshes extend forward in time as the major rigid plates drift apart. In our tectonic reconstruction with deforming plates, the timing and the intensity of continental extension is imposed by the progressive, diachronous breakup and initiation of seafloor spreading for each major margin system. The velocity field derived from the plate reconstructions is used as a time-dependent surface boundary condition in mantle convection models that include compositionally distinct crust and continental lithosphere embedded within the thermal lithosphere. In deforming areas, the velocity field is obtained by linearly interpolating velocities from adjacent non-deforming areas within GPlates. We computed forward global mantle flow models using 3D-spherical finite-element code CitcomS to simultaneously quantify the relative contributions of lithospheric stretching, thermal subsidence, and deep mantle flow to the subsidence of passive margins. Applied to the South Atlantic, the method reproduces the first-order asymmetry of the margins. In particular, the large subsidence of the Argentinian margin is due to the dynamic topography induced by ongoing subduction along the narrow southern portion of South America. This result illustrates the importance of dynamic topography to the total subsidence at passive margins.

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

2012-04-01

312

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

NASA Astrophysics Data System (ADS)

We present a revised regional plate tectonic model for the Indian Ocean from the Late Jurassic to present, which assimilates both marine geophysical data constraining the seafloor spreading history as well as a variety of geological observations from the Eurasian collision zone. This model includes relative motion between Greater India, Sri Lanka, West Australia, East Antarctica, East Madagascar, the Seychelles and Argoland, a continental sliver which began migrating towards Eurasia in the Late Jurassic, forming the northern margins of Greater India and western Australia. Recently collected data offshore northwest Australia suggest that the majority of Greater India reached only halfway along the West Australian margin in an Early Mesozoic reconstruction, bounded by the Wallaby-Zenith Fracture Zone. The revised geometries and relative motion histories redefine the timing and nature of collisional events, as well as the history of back-arc basins and intra-oceanic arcs, such as the Kohistan-Ladakh intra-oceanic arc in northwest India and Pakistan. Abundant ophiolites have been identified throughout the Yarlung-Tsangpo Suture Zone, between the Indian-Himalaya and Tibet, several have boninitic compositions and almost all date to either the Mid Jurassic or late Early Cretaceous. Further evidence suggests that an intra-oceanic arc collided with Greater India before colliding with Eurasia. Our model features a transform boundary running north of East Africa, which initiated an oceanic arc following short-lived compression between the western and central Mesotethys in the Late Jurassic, coinciding with the initial motion of Argoland. The arc developed through extension and ophiolite generation until at least the mid-Cretaceous and consumed a narrow thinned sliver of West Argoland between ~120-65 Ma. The arc remained active in the same position until its eventual collision with Greater India ~55 Ma. The eastern portion of the intra-oceanic arc accreted to eastern Eurasia (near Burma) causing anticlockwise rotation/retreat of the margin until collision between the main portion of Greater India and central Eurasian margin took place ~36 Ma. This relatively young collision between India and Eurasia is supported by subduction-related magmatism, which continued into the Late Eocene. The Upper Eocene Pengqu Formation also suggests that marine conditions prevailed south of the suture zone until that time, while the Upper Oligocene to Lower Miocene Gangrinboche conglomerates mark the initial mixing and deposition of both Eurasian and Indian-sourced sediments.

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

2012-12-01

313

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

314

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

315

Reconstruction of multiple tectonic events in continental margins by integrated tectonostratigraphic and geochronological analysis: the Mesozoic to Paleogene Caribbean-South American interaction in northeastern Colombia  

NASA Astrophysics Data System (ADS)

Although the older record and successive tectonic scenarios experienced by a continental margin is commonly fragmentary, integrated field, petrological and geochronological analysis can reconstruct the long term tectonic evolution of continental margins and characterized major controls on the orogenic style. We present new geochronological constraints from igneous and low to very low grade metasedimentary rocks from the Caribbean continental margin of northeastern Colombia (Guajira region) in order to reconstruct the different tectonic events recorded by the margin before, during and following the arc-continent collision with the front of the Caribbean plate. Zircon U-Pb LA-ICP-MS geochronology results from leucogranites associated with garnet amphibolites, tonalites and volcanic rocks that made the continental basement of northeastern Colombia reveals and Early to Middle Mesozoic tectonic activity with peaks at ca. 220-230 Ma and 170-180 Ma. This magmatic record is related to a collisional belt link to the final agglutination of Pangea and was followed by an overimposed far field back-arc setting associated to the subduction of the Pacific (Farrallon) plate under the Pangea supercontinent. Muscovite and biotite Ar-Ar geochronology from basement rocks and low grade Mesozoic metasediments also reveals the existence of Middle Jurassic to Early Cretaceous thermal events link to the final opening of the proto-Caribbean ocean. The South American continental margin was subsequently affected by an arc-continent collisional event with the front of the Caribbean plate. This event is recorded by the growth of a Banda-type collisional melange that mixed South American continental margin sediments with mafic and ultramafic blocks of intra-oceanic arc origin, the formation of a coherent metasedimentary belt also made of South American margin sediments, and the mylonitization of the continental basement. Ar-Ar temporal constraints on the low grade metasedimentary rocks and detrital apatite fission track ages from younger sedimentary sequences suggest a Late Campanian age for this deformational event. Continuous convergence and the formation of a new subduction zone in the South American margin were responsible for the remobilization of inland extensional structures and the associated growth of an Early Paleocene mylonitic belt. During the Eocene the installation of a short duration magmatic arc and a widespread cooling event record the final installation of an oblique subduction setting. We argue that the pre-collisional tectonic evolution of the South American continental margin have prepare a warm continental margin with significant weakness zone that determined an arc-continent collisional style characterized by frontal accretion of the South American plate over the intra-oceanic Caribbean domain, and in which the younger compressional and thermal events are link to the remobilization of older structures.

Cardona, Agustin; Montes, Camilo; Bayona, German; Valencia, Victor; Ramirez, Diego; Zapata, Sebastian; Lara, Mario; Lopez-Martinez, Margarita; Thomson, Stuart; Weber, Marion

2013-04-01

316

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

317

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

NASA Astrophysics Data System (ADS)

The Philippine Mobile Belt, a seismically active, rapidly deforming plate boundary zone situated along the convergent Philippine Sea/Eurasian plate boundary, is examined using geodetic and seismological data. Oblique convergence between the Philippine Sea Plate and the Eurasian plate is accommodated by nearly orthogonal subduction along the Philippine Trench and the Manila Trench, as well as by strike-slip faulting along the Philippine Fault system. We develop a model of active plate boundary deformation in this region, using elastic block models constrained by known fault geometries, published GPS observations and focal mechanism solutions. We then present an estimate of block rotations, fault coupling, and intra-block deformation, based on the best-fit model that minimizes the misfit between observed and predicted geodetic vectors and earthquake slip vectors. Slip rates along the Philippine fault vary from ~22 - 36 mm/yr in the Central Visayas and about 10 to 40 mm/yr in Luzon, trending almost parallel to the fault trace. In northern Luzon, Philippine Fault splays accommodate transpressional strain. The Central Visayas block experiences convergence with the Sundaland block along the Negros Trench and the Mindoro-Palawan collision zone. On the eastern side of Central Visayas, sinistral strike-slip faulting occurs along the NNW-SSE-trending Philippine Fault. Mindanao Island in southern Philippines is dominated by east-verging subduction along the Cotabato Trench, and strain partitioning (strike- slip faulting with west-verging subduction) in eastern Mindanao along the southern Philippine Fault and Philippine Trench, respectively. Oblique active sinistral strike slip faults in Central and Eastern Mindanao that were hypothesized to be responsible for basin formation are obvious boundaries for tectonic blocks. Located south of Mindanao Island we define an adjoining oceanic block defined by the N-S trending complex dual subduction zone of Sangihe and Halmahera, primarily delineated by seismicity, bathymetric profiles and E-W thrust mechanisms. In our preferred model, the Philippine Mobile Belt can be represented by at least 12 independently moving rigid tectonic blocks, separated by active faults and subduction zones.

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

2007-12-01

318

The cause of loss of lithospheric rigidity in areas far from plate tectonic activity  

NASA Astrophysics Data System (ADS)

Significant losses of lithospheric strength are generally considered to be almost entirely associated with abnormal heating or steep lithospheric bending and/or stretching near to active plate boundaries. Several areas-the western Greater Caucasus, the North Crimean basin, the Carpathian foredeep, the Peri-Caspian basin and the Trans-Caspian areas-are shown to have steep basement slopes, usually comprising a difference in height of several kilometres over lateral distances of only 20-30km, corresponding to very low, ~3-5km, effective elastic thicknesses of the lithosphere. Each of these areas is shown to have undergone rapid steepening of the basement slope, usually within 1-2Myr but in up to 10Myr in some areas. At such times, these localities were far from active plate boundaries and in positions where bending forces could not have been transmitted to them from far-distant plate activities. Surface and/or subsurface loading can similarly be excluded as mechanisms for such steepening, and there is no apparent outflow of crustal materials into adjacent regions. It is suggested that such rapid subsidence far from plate tectonic activity is caused by rapid increases in the local density of the lithosphere. This could occur as a result of, for example, a gabbro-eclogite transformation in the lower crust, catalysed by the infiltration of volatiles from the asthenosphere. The resultant contraction of the mafic rocks would be non-uniform in space and produce high deviatory stresses, reducing the viscosity in the lower crust to ~1023Pas. This would result in the rapid subsidence of the top of this layer, accompanied by steep ductile bending of the overlying upper crust. Such steep downwarping of the basement would be accompanied by a similar steepening of the underlying weakened mantle. The formation of such steep slopes thus indicates a weakening of the entire lithospheric layer, most probably due to the infiltration of volatiles from the asthenosphere, and unrelated to coeval plate tectonic activity.

Artyushkov, Eugene V.; Mrner, Nils-Axel; Tarling, Donald H.

2000-12-01

319

On the Dynamics of Plate Tectonics: Multiple Solutions, the Influence of Water, and Thermal Evolution  

NASA Astrophysics Data System (ADS)

An analytic boundary layer model for thermal convection with a finite-strength plate and depth-dependent viscosity is developed. The model includes a specific energy balance for the lithosphere and accounts for coupling between the plate and underlying mantle. Multiple solutions are possible with three solution branches representing three distinct modes of thermal convection. One branch corresponds to the classic boundary layer solution for active lid plate tectonics while two new branches represent solutions for sluggish lid convection. The model is compared to numerical simulations with highly temperature dependent viscosity and is able to predict both the type of convection (active, sluggish, or stagnant lid) as well as the presence of single and multiple solution regimes. The existence of multiple solutions suggests that the mode of planetary convection may be history dependent. The dependence of mantle viscosity on temperature and water concentration is found to introduce a strong dynamic feedback with plate tectonics. A dimensionless parameter is defined to quantitatively evaluate the relative strength of this feedback and demonstrates that water and heat transport may be equally important in controlling present-day plate-mantle dynamics for the Earth. A simple parameterized evolution model illustrates the feedback and agrees well with our analytic results. This suggests that a simple relationship may exist between the rate of change of water concentration and the rate of change of temperature in the mantle. This study concludes by investigating the possibility of a magnetic field dynamo in early solar system planetesimals. The thermal evolution of planetesimals is modeled by considering melting, core formation, and the onset of mantle convection and then employing thermal boundary layer theory for stagnant lid convection (if possible) to determine the cooling rate of the body. We assess the presence, strength and duration of a dynamo for a range of planetesimal sizes and other parameters. We find that a minimum radius of O(500) km is required for a thermally driven dynamo of duration O(10) My. The dependence of the results on model parameters is made explicit through the derivation of an analytic solution.

Crowley, John W.

320

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

2010-06-22

321

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

322

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

NASA Astrophysics Data System (ADS)

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 expansion and the Rayleigh number making the deep mantle a sluggish system with gigantic features, consistent with tomography,and isolating it from the upper mantle and plate tectonics (except by conduction and gravity).Large scale chemical stratification is therefore likely. Plate tectonics, with adjectives such as rigid, homogeneous, isothermal, fixed, subsolidus, reservoir, steady-state etc. dropped, is a much more powerful concept than generally believed. Cracks, rifts, dikes, incipient plate boundaries, melting anomalies and variations in melt volume and chemistry are natural parts of the general theory of plate tectonics. The long-sought alternative theory to deep mantle plumes may just be a less restricted view of plate tectonics. It appears to be the adjectives, assumptions and other baggage that are the problem. Many of the geochemical paradoxes associated with deep plumes and primordial views of the mantle can be traced to the reservoir concept where deep seismic boundaries are assumed to delineate reservoirs. The mantle is heterogeneous, as it should be from plate tectonic considerations (recycling, inefficient melt and gas extraction, history ).This suggests that sampling theory and dispersed components may explain the diversity of basalts. The central limit theorem (CLT) predicts that large scale averagers, such as ridges, should have less variance and less extreme values than xenoliths,inclusions,seamounts or OIB, as observed. Homogeneity is achieved by partial melting, averaging and magma chamber processes, not by large scale convection. This idea is tested with Os and He isotopes, which are as different from each other and from the standard isotopes as possible. The conclusion is that both MORB and OIB are products of a heterogeneous upper mantle, sampled in different ways (volume of mantle averaged, degree of melting, magma chamber processes). The CLT plus mass balance calculations obviate the need for an undegassed reservoir or lower mantle components . High 3He/4He components can be ubiquitous in the shallow mantle but only expressed in OIB, off-axis seamounts and other volcanic systems sampling small mantle volumes, or at the onset of volcanism.

Anderson, D. L.; Meibom, A.

2002-12-01

323

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

NASA Astrophysics Data System (ADS)

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

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

1985-03-01

324

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

USGS Publications Warehouse

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

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

2007-01-01

325

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

NASA Astrophysics Data System (ADS)

Within the Solar System, Earth is the only planet to be in a mobile-lid regime, whilst it is generally accepted that all the other terrestrial planets are currently in a stagnant-lid regime, showing little or no surface motion. A transitional regime between these two, showing episodic overturns of an unstable stagnant lid, is also possible and has been proposed for Venus (Armann and Tackley, JGR 2012). Using plastic yielding to self-consistently generate plate tectonics on an Earth-like planet with strongly temperature-dependent viscosity is now well-established, but such models typically focus on purely thermal convection, whereas compositional variations in the lithosphere can alter the stress state and greatly influence the likelihood of plate tectonics. For example, Rolf and Tackley (GRL, 2011) showed that the addition of a continent can reduce the critical yield stress for mobile-lid behaviour by a factor of around 2. Moreover, it has been shown that the final state of the system (stagnant- or mobile-lid) can depend on the initial condition (Tackley, G3 2000 - part 2); Weller and Lenardic (GRL, 2012) found that the parameter range in which two solutions are obtained increases with viscosity contrast. We can also say that partial melting has a major role in the long-term evolution of rocky planets: (1) partial melting causes differentiation in both major elements (like Fe and Si) and trace elements, which are generally incompatible (Hofmann, Nature 1997). Trace elements may contain heat-producing isotopes, which contribute to the heat loss from the interior; (2) melting and volcanism are an important heat loss mechanism at early times that act as a strong thermostat, buffering mantle temperatures and preventing it from getting too hot (Xie and Tackley, JGR 2004b; Armann and Tackley, JGR 2012); (3) mantle melting dehydrates and hardens the shallow part of the mantle (Hirth and Kohlstedt, EPSL 1996) and introduces viscosity and compositional stratifications in the shallow mantle due to viscosity variations with the loss of hydrogen upon melting (Faul and Jackson, JGR 2007; Korenaga and Karato, JGR 2008). In this work we present a set of 2D spherical annulus simulations (Hernlund and Tackley, PEPI 2008) using StagYY (Tackley, PEPI 2008), which uses a finite-volume scheme for advection of temperature, a multigrid solver to obtain a velocity-pressure solution at each timestep, tracers to track composition, and a treatment of partial melting and crustal formation. We address the question whether melting-induced crustal production changes the critical yield stress needed to obtain mobile-lid behaviour as a function of governing parameters. Our results show that melting and crustal production strongly influence plate tectonics on terrestrial planets, by making plate tectonics both easier and harder; i.e., for the same yield stress and reference viscosity the use or not of a treatment for melting and crustal production may result in a change from a stagnant-lid regime into an episodic-lid regime or a change from mobile-lid regime to an episodic-lid regime. Several factors can play a role on these, namely lateral heterogeneities and differences in the lid thickness induced by melting and crustal production, the maximum depth of melting, etc.

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

2013-12-01

326

Satellite elevation magnetic and gravity models of major South American plate tectonic features  

NASA Technical Reports Server (NTRS)

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

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

1984-01-01

327

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.

328

The Cretaceous iron belt of northern Chile: role of oceanic plates, a superplume event, and a major shear zone  

NASA Astrophysics Data System (ADS)

The Cretaceous constitutes a turning point in the tectonic, magmatic, and metallogenic history of Chile. The geological evidence indicates that a major change occurred in late Neocomian time when superplume emplacement (Mid-Pacific Superplume) and plate reorganization processes took place in the Pacific. The superplume event resulted in a major ridge-push force resulting in increased coupling between the subducting and overriding plates. This completely changed the tectonic setting of Chile ending the Early Cretaceous extensional period (aborted rifting in the back-arc basin), and increasing stress at a crustal scale. As a consequence, overpressurized dioritic magmas were pushed up mainly along the best possible structural path in northern Chile, i.e., the Atacama Fault Zone, eventually forming a +500-km-long belt of Kiruna-type iron deposits with reserves of ~2,000 Mt (60% Fe), a unique case in Chile's geological history.

Oyarzun, Roberto; Oyarzn, Jorge; Mnard, Jean Jacques; Lillo, Javier

2003-08-01

329

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

330

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

NASA Astrophysics Data System (ADS)

From the British Isles to Poland, Europe experienced contractional deformation in Late Cretaceous and Paleogene time. The closest contemporaneous plate margins were the incipient Mid-Atlantic rift in the west and northwest, and the Mediterranean system of subduction zones in the south. Each of these plate margins was located more than 1000 km away from the site of deformation. This tectonic event thus represents an outstanding example of large-scale intraplate shortening and may serve as a template for comparison with modern examples. Its effects are seen in a ca. 500 km wide strip that stretches in NW-SE-direction along the Tornquist Line, a regional fault zone separating thick lithosphere of the Baltic Shield from much thinner lithosphere to the southwest. Most faults and folds also trend NW-SE, but some are linked by large N-S-striking transfer zones. In the southeast, the shortening structures are truncated by the Neogene Carpathian thrust front; their original extent is unknown. In the west, the fault zones fan out into more northerly trends in the Central North Sea and more easterly trends in the Channel area before dying out on the shelf. Late Cretaceous (ca. 90-70 Ma) shortening dominates from Poland to the North Sea, while the main shortening event in Southern Britain is of Paleogene age. Many Late Cretaceous to Paleogene structures have been conditioned by Permian or Triassic through Early Cretaceous extensional faulting, whereas some large basement uplifts and reverse faults have no demonstrable inheritance from earlier extension. The thick, mobile Zechstein salt has modified extensional and contractional structures, but both extend beyond its depositional borders. Even where thick evaporates underlie the Mesozoic sedimentary cover, the basement is typically involved in the deformation, except for localized thin-skinned imbricate thrusting and salt-cored anticlines. Different structural styles do not appear to correlate with the magnitude of shortening which is similar for transects across the inverted Lower Saxony Basin and areas of predominant basement thrusting. Bulk contraction of the entire deformed belt is unlikely to exceed a few tens of kilometers, corresponding to <<10% of horizontal shortening. Shortening rate estimates are around 1 mm/yr both for well-constrained local structures and for order-of-magnitude estimates of the entire belt, suggesting that a limited number of faults were active at any given time. Space geodetic data indicate similar modern shortening rates across Central Europe on a decade scale, but there is no geologic evidence for focused deformation comparable to the Mesozoic event. Fold orientations, fault slip data and stylolite teeth indicate relatively uniform, SSW-NNE-directed shortening. This direction is consistent with the convergence direction of Africa, Iberia and Eurasia that was established between ca. 120 Ma and 85 Ma in the course of global plate motion reorganization. The European short-lived pulse of intraplate deformation was apparently caused by a switch to near-orthogonal convergence across former transform boundaries, whereas modern examples of intraplate shortening seem to be bound to coeval orogens.

Kley, Jonas; Jhne, Fabian; Malz, Alexander

2014-05-01

331

NEPTUNE: real-time, long-term ocean and Earth studies at the scale of a tectonic plate  

Microsoft Academic Search

The NEPTUNE project will establish a linked array of undersea observatories on the Juan de Fuca tectonic plate. The NEPTUNE infrastructure, consisting of fiber-optic\\/power cable and junction boxes, will provide significant amounts of power and an Internet communications link to sensors and sensor networks on, above, and below the seafloor. This observatory will provide a new kind of research platform

John Delaney; G. R. Heath; Alan Chave; Harold Kirkham; Bruce Howe; William Wilcock; Patricia Beauchamp; Andrew Maffei

2001-01-01

332

Real-Time, Long-Term Ocean and Earth Studies at the Scale of a Tectonic Plate  

Microsoft Academic Search

The NEPTUNE project will establish a linked array of undersea observatories on the Juan de Fuca tectonic plate. The NEPTUNE infrastructure, consisting of fiber-optic\\/power cable and junction boxes, will provide significant amounts of power and an Internet communications link to sensors and sensor networks on, above, and below the seafloor. This observatory will provide a new kind of research platform

John Delaney; Alan Chave; G. Ross Heath; Bruce Howe; Patricia Beauchamp; William Wilcock; Andrew Maffei

333

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

334

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

NASA Astrophysics Data System (ADS)

An existing geodetic flow velocity model, obtained by using an internal free network adjustment technique, is used to derive estimates for various strain rates parameters in NE Japan. The greatest shortening rates of the principal strains, trending E-W, are located in regions where much steady, internal, frame-invariant plastic flow deformation is observed to be taking place. The internal geodetic adjustment technique yielded the internal deformation in the Tohoku arc; most of the intraplate deformations, including the much folding deformations observed in the inner zone, are produced from within. An interseismic transient elastic loading at a strongly coupled/locked Japan trench would not be needed. The observed ongoing extensive ductile folding deformation in the inner zone of Tohoku may mean that the geodetic strain rates, causing shortening at 2-3 cm/yr, probably reflect the more correct level of the deformation, which is steady/permanent, in NE Japan as compared with seismic/faulting data, which indicate 0.5 cm/yr shortening. The calculated principal strain rates are used to make an interpretation for the origin of the deviatoric principal stresses within the greater regional plate tectonic framework. The tectonic stress state in NE Japan, as part of the Okhotsk plate, could mostly be influenced by the Okhotsk plate, which is extruding southward to lessen the significant accumulated contractional deformation in NE Asia in the Verkhoyansk-Cherskii mountains. The principal strain rates are N-S extensional essentially everywhere in NE Japan, as a result of the southerly extrusion, except in its southernmost leading edge, in the Uetsu/Fossa Magna province, where the Japan Alps rampart rises in front of the extrusion. Here an E-W compressional stress state prevails. A second E-W contractional zone is found in north-central Tohoku, extending from the Sanriku province in the outer zone to the inner zone in the Japan Sea side, being more prevalent in the latter zone. The calculated rotation rates from the geodetic flow model are clockwise (CW) in both of the E-W contractional regions. NE Japan, extruding southward, faces buttresses in (1) the Oga-Ojika Line (OOL), and/or a crustal weakness zone between the northern and the southern halves of Tohoku approx. at 38.5N latitude, and, especially, (2) the Japanese Alps rampart; these obstacles cause the northern and southernmost Tohoku to veer to its right and rotate CW, thereby setting up the E-W-trending compressional deformation in their respective inner zones. Between the OOL (or the 38.5N boundary) and the Kanto Tectonic Line (KTL), the sense of the differential rotations is counterclockwise (CCW), towards the ocean to the SE. The northern Tohoku (north of the OOL) and the southernmost Tohoku (south of the KTL) cannot rotate CCW towards the ocean because of the Izu block's collision in the south and the relatively strong coupling along the subduction interface beneath the Japan trench in the north off-Sanriku. The relatively stronger long-term coupling between the northern Tohoku and the Pacific plate at the Sanriku coast, with respect to that in off-Fukushima, is due to a flatter subduction of the Pacific slab there, increasing the plates' interface contact area; the flattening of the subduction dip angle was caused by CCW rotation and shifting of the northern Tohoku along the dextral Honjo-Matsushima Line, roughly corresponding to the OOL, towards the Pacific and overriding of the subduction zone during the formation of the Japan Sea.

Altis, Sungat

2001-09-01

335

Missing plate tectonics in Venus caused by rheological contrast at Moho  

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

336

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

NASA Astrophysics Data System (ADS)

Within the Solar System, Earth is the only planet to be in a mobile-lid regime, whilst it is generally accepted that all the other terrestrial planets are currently in a stagnant-lid regime, showing little or no surface motion. A transitional regime between these two, showing episodic overturns of an unstable stagnant lid, is also possible and has been proposed for Venus (Armann and Tackley, JGR 2012). Using plastic yielding to self-consistently generate plate tectonics on an Earth-like planet with strongly temperature-dependent viscosity is now well-established, but such models typically focus on purely thermal convection, whereas compositional variations in the lithosphere can alter the stress state and greatly influence the likelihood of plate tectonics. For example, Rolf and Tackley (GRL, 2011) showed that the addition of a continent can reduce the critical yield stress for mobile-lid behaviour by a factor of around 2. Moreover, it has been shown that the final tectonic state of the system can depend on the initial condition (Tackley, G3 2000 - part 2); Weller and Lenardic (GRL, 2012) found that the parameter range in which two solutions are obtained increases with viscosity contrast. We can also say that partial melting has a major role in the long-term evolution of rocky planets: (1) partial melting causes differentiation in both major elements and trace elements, which are generally incompatible (Hofmann, Nature 1997). Trace elements may contain heat-producing isotopes, which contribute to the heat loss from the interior; (2) melting and volcanism are an important heat loss mechanism at early times that act as a strong thermostat, buffering mantle temperatures and preventing it from getting too hot (Xie and Tackley, JGR 2004b); (3) mantle melting dehydrates and hardens the shallow part of the mantle (Hirth and Kohlstedt, EPSL 1996) and introduces viscosity and compositional stratifications in the shallow mantle due to viscosity variations with the loss of hydrogen upon melting (Faul and Jackson, JGR 2007; Korenaga and Karato, JGR 2008). We present a set of 2D spherical annulus simulations (Hernlund and Tackley, PEPI 2008) using StagYY (Tackley, PEPI 2008), which uses a finite-volume scheme for advection of temperature, a multigrid solver to obtain a velocity-pressure solution at each timestep, tracers to track composition, and a treatment of partial melting and crustal formation. We address the question whether melting-induced crustal production changes the critical yield stress needed to obtain mobile-lid behaviour as a function of governing parameters. Our results show that melting and crustal production strongly influence plate tectonics on terrestrial planets. For the same parameters the use of a treatment for melting and crustal production facilitates breaking the stagnant-lid, replacing it with episodic-lid; however, a smoothly evolving mobile lid can also be replaced by episode-lid. Several factors can play a role on these, namely lateral heterogeneities, differences in the lid thickness and internal planetary temperatures induced by melting and crustal production.

Loureno, Diogo L.; Tackley, Paul J.

2014-05-01

337

The Mesozoic and Cenozoic Motion of Greenland and its Importance for Understanding Arctic Plate Tectonics  

NASA Astrophysics Data System (ADS)

Although today Greenland is part of the North American Plate, through much of the Mesozoic and Cenozoic, the Greenlandic lithosphere behaved largely as an independent plate. Details regarding its precise motion relative to both North America and Europe are complicated by the fact that our understanding of Arctic plate boundaries remains rudimentary, especially with regard to the Amerasian Basin. The various poles of rotation that have been proposed for Greenland generally imply significant northward motion of Greenland, with significant implications for possible deformation patterns in the Arctic basins surrounding Greenland. In this contribution, we review the possible motion of Greenland relative to the surrounding plates and examine the constraints available for determining these motions. A key problem is that only the North Atlantic and Eurasian basins show well-defined magnetic spreading anomalies. Thus, while the motion of Greenland relative to the European plate is reasonably well constrained back to the Paleocene, the motion of Greenland relative to North America is highly uncertain. Anomalies in the Labrador Sea can be identified, but their interpretation is more uncertain and anomalies in the Baffin Bay cannot be convincingly identified. Structural trends identified in gravity anomaly data thus remain ambiguous in terms of identifying directions of motion. Nevertheless, pronounced shortening between Greenland and Ellesmere Island during the Eurekan orogeny is clear as is shortening along Northern Greenland as evidenced by an exposed and young fold and thrust belt near Kap Washington. Thus, some component of northward motion and/or counterclockwise rotation of Greenland relative to North America is clearly indicated during the Cenozoic. A key data gap exists in the area north of Greenland in the Lincoln Sea where the Lomonosov Ridge connects to Greenland and Arctic Canada. Understanding the deformation history of this area is clearly critical for constraining the motion of Greenland. The importance of the tectonic history is also important for Arctic Ocean paleoceanography. Potential gateway configurations between Baffin Bay and the Arctic Ocean during the Neogene will clearly be affected by vertical movements of northern Greenland in response to its motion relative to the surrounding plates.

Hopper, J. R.; Marcussen, C.; Funck, T.; Gregersen, U.; Knutz, P. C.

2010-12-01

338

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

339

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

340

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

PubMed Central

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

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

2007-01-01

341

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

PubMed

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

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

2007-09-01

342

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

NASA Technical Reports Server (NTRS)

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

Baltuck, M.; Dixon, T. H.

1984-01-01

343

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

SciTech Connect

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

Holcombe, T.L.

1985-01-01

344

Plate tectonic controls on atmospheric CO2 levels since the Triassic  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

345

Plate tectonic controls on atmospheric CO2 levels since the Triassic.  

PubMed

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

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

2014-03-25

346

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

347

Thrust tectonics in the North Patagonian Massif (Argentina): Implications for a Patagonia plate  

NASA Astrophysics Data System (ADS)

In the northeastern segment of the North Patagonian Massif (southern Argentina), S to SW directed thrusting affected a Late Proterozoic to Cambrian phyllite succession and the Silurian to Lower Devonian Sierra Grande formation. Thrust tectonics was partly combined with the formation of mylonites and followed by the intrusion of the Navarrete granodiorite. Mylonites of the Tardugno granitoids are attributed to a ductile shear horizon in the subsurface. As second stage of deformation after cessation of thrusting, NW-SE compression led to the formation of widely distributed fold structures around NE-SW trending axes as well as SE directed reverse faults. It was followed by the late kinematic intrusion of a porphyric granite as final pulse of the Navarrete Intrusive Complex. Local folding around N-S to NW-SE trending axes represents the final stage of the compressive deformational history. Thrust tectonics plus subsequent stages of deformation can be assigned to the Late Paleozoic time interval, probably the Permian. They are seen in conjunction with the formation of granite mylonites within the North Patagonian Massif, the Cerro de los Viejos granite mylonite of the La Pampa Province, and the compressive structures in the Sierras Australes fold-and-thrust belt north of the boundary between Patagonia and Gondwana South America. Also, the lack of Early Paleozoic (Famatinian) deformation in this part of the North Patagonian Massif and the inferred boundary of the Early Paleozoic Cuyania (Precordillera) Terrane north of Patagonia support the interpretation that extra-Andean Patagonia collided with Gondwana South America during the Gondwanide orogeny. It is possible that Patagonia was part of a plate and that the long Gondwanide fold belt represented its collision zone.

von Gosen, W.

2003-02-01

348

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

NASA Technical Reports Server (NTRS)

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

Toksoz, M. Nafi; Reilinger, Robert

1992-01-01

349

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

350

Tectonics of the Philippine Sea Plate as Seen From GPS Observations  

NASA Astrophysics Data System (ADS)

We analyzed the Global Positioning System (GPS) data in and around the Philippine Sea plate (PHS) to provide a velocity field for discussing tectonics of the plate and the mechanism of subduction process around PHS. In the present study, first, we revised the previously determined Euler vector of PHS relative to stable Eurasia using newly obtained data. Eastern part of Europe was assumed to be in a rigid block according to Nocquet et al. (2001) and we estimated the seven parameters of Helmert Transformation of this block relative to ITRF97. Then these parameters were used to estimate the Euler vector of PHS relative to stable Eurasia. For this purpose, we re-analyzed GPS data of up until 2001 at Chichi-jima, Okino-Tori Shima, Minami-Daito, Palau, Aogashima and Hachijo islands in ITRF97 reference together with surrounding IGS sites. Results suggest that the Euler vector of PHS relative to _gstable Eurasia_h is to be (61.4N, 163.7E, 1.003deg/my). Contrary to our previous estimate, the result suggests that Palau may be considered as in the rigid part of PHS. In contrast, the northern Izu islands are suggested to be affected by local volcanic disturbances. Then, we studied tectonic motions of Mariana arc and Palau-Yap arc. The Mariana Islands have been repeatedly observed since 1992. Kotake (2000) analyzed data at Anatahan, Guguan, Pagan and Agrigan as well as Saipan and Guam sites and showed that the velocities are much slower than what we expect from rigid motion of PHS. Residual velocities at these islands clearly show eastward motion of the Mariana Islands, suggesting that the Mariana Islands are subject to the spreading of the Mariana Trough. The rotation pole of the Mariana block was re-estimated as (20.6N, 145.2E) and angular velocity to be 4.17deg/ma, according to the re-estimated PHS motion. The position of the rotation pole is a few degrees south to the geographical hinge point of the Mariana arc and west Mariana ridge at about 24N. Estimated eastward velocities at these islands are consistent with those estimated from magnetic anomaly observations. Small arc parallel extension of about 1cm/yr between Agrigan and Guam suggest that the formation of the arc is not simple fan-shape expansion, as was indicated by Karig et al. (1978). Convergence at Yap trench has also been studied using GPS. Motions of Uliti and Fais suggest slight convergence at Yap trench with about 1cm/yr, but have some northward component relative to the trench.

Kato, T.; Kotake, Y.

2002-12-01

351

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

NASA Astrophysics Data System (ADS)

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

Hamilton, Warren B.

2011-04-01

352

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

NASA Astrophysics Data System (ADS)

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

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

2008-11-01

353

Global Love wave phase velocity variation and its significance to plate tectonics  

NASA Astrophysics Data System (ADS)

Global Love wave phase velocity variation was constructed for periods between 80 and 200 s by using approximately 9000 paths from 971 earthquakes (with M ? 5.5). The data set was from GDSN and GEOSCOPE networks between 1980 and 1987. We examined both the spherical harmonic expansion method and the block parameterization method. With a simple, constant damping parameter approach, synthetic tests showed that more accurate results were obtained by the block parameterization method than by the spherical harmonic expansion method. We adopted the block inversion method with a (nearly) equal area block (5 5 near the equator) discretization. The general pattern of the resulting maps were consistent with previous global and local studies. With a discretization of 5 by 5, the maps were detailed enough to test some plate tectonic models. For the Pacific, Atlantic and Indian Oceans, surface-wave velocities increased smoothly to plate ages older than 100 Ma. Simple forward modeling showed that seismic phase velocity variation with a continuous thickening of lithosphere up to about 150 Ma fits the present observation, disagreeing with the model deduced from the heat flow and ocean depth data, which change variations at about 60-80 Ma. The seismic phase velocity variations in different oceans showed systematic differences at younger ages, and convergence beyond 100 Ma. The difference at younger ages implies a failure of scaling derived from a simple thermal boundary layer model for oceanic plates. Age-seismic phase velocity relationships on each side of ridges were also examined and asymmetric velocity variations were found, which suggests differences in thermal states from one side of the ridge to the other. In order to further examine the thermal state of the lithosphere, average age-phase velocity relations were established for each ocean, and subtracted from phase velocity variation maps. The results indicated broad, low-velocity regions in the south Pacific (super-swell region), the south and west Indian Ocean, and high-velocity regions east of the East Pacific Rise and in the north to northeast Indian Ocean. The results reflect the asymmetry of phase velocity variation about ridges. There is some correlation between hot-spot locations and low-velocity anomalies, but additional, large-scale thermal anomalies exist under old oceanic plate.

Zhang, Yu-Shen; Tanimoto, Toshiro

1991-04-01

354

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

PubMed

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

Li, Jun; Fu, Cuizhang; Lei, Guangchun

2011-01-01

355

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  

Microsoft Academic Search

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

M. Murakami

2003-01-01

356

Dating upper plate normal fault slip events in Late Pleistocene and Holocene sediments of northern Chile  

NASA Astrophysics Data System (ADS)

In order to understand how subduction earthquakes along the Nazca-South America plate boundary affect upper plate faults in the coastal forearc of northern Chile, we are developing the first detailed paleoseismological study to characterize the Late Quaternary activity of the Mejillones and Salar del Carmen faults, located around 40 km north and 15 km east of Antofagasta, respectively. There is currently a lack of basic palaeo-seismological data on these and other upper plate faults, such as long term slip rates, amount of slip per event, palaeo-earthquake magnitude and recurrence intervals. This lack of knowledge impedes understanding of how large subduction earthquakes, occurring at depths of around 50 km in this region, relate to upper plate seismicity and deformation. We have used OSL dating of fault-related sediments, and cosmogenic-ray nuclide dating of terrace surfaces, to constrain slips rates over the last 45 ka. Several trenches were excavated across both faults in order to expose and log the most recent fault-related sediments. In the hanging wall of these normal faults, vertically stacked colluvial wedges and hillslope deposits are the product of discrete slip events and post-slip fault scarp degradation. Multiple trenches along each fault permit the spatial variability in slip amount and fault-related sedimentation to be investigated. Long-term slip rates have been measured using cosmogenic-ray nuclide exposure dating of the alluvial terraces offset by the Mejillones Fault. OSL dating of the fault-related sediments in the trenches has been used to compare the ages of individual slip events on both faults, and the age of events recorded along the trace of each fault. The application of both cosmogenic-ray nuclide and OSL methods in this type of setting (hyper-arid with low erosion rates, yet tectonically active) is non-trivial, due to cosmogenic inheritance accumulated in cobbles on the terrace surfaces, low sensitivity of the quartz for OSL dating, and the potential for partial bleaching in both quartz and feldspar. However, we have established that slip events occur about the same time (within uncertainty) on both faults, but that fault slip rate and the estimated earthquake magnitudes are greater on the Mejillones Fault than the Salar del Carmen Fault. Since 13 ka, there have been 3 - 4 slip events on both faults and the recurrence interval of the largest predicted palaeo-earthquake (Mw ~7) on the Mejillones Fault is about 4.8 ka.

Robinson, R. A.; Binnie, S.; Gonzalez, G.; Corts, J.

2011-12-01

357

Large Igneous Provinces and supercontinents: Toward completing the plate tectonic revolution  

NASA Astrophysics Data System (ADS)

Regional groupings of a majority, or all, of Earth's crustal blocks have occurred several times in Earth history, but only the most recent supercontinent Paleozoic Pangea/Gondwana, is well characterized. Prior Precambrian supercontinents are postulated: Rodinia (ca. 1 to 0.7 Ga), Nuna/Columbia (ca. 1.8 to 1.3 Ga) and Kenorland/supercratons (ca. > 2.7 to 2.0 Ga), but the configuration of each is poorly known. A new methodology using Large Igneous Provinces (LIPs) offers an opportunity for fast-tracking progress toward robust Precambrian reconstructions. Comparison of the LIP barcode' record between crustal blocks allows identification of which blocks were likely to have been nearest neighbors in past supercontinents. Restoration of the primary geometry (radiating or linear) of regional dyke swarms (the plumbing system of LIPs) offers another reconstruction criterion. A consortium of companies is providing funding for dating of essentially all major regional dyke swarms and sill provinces to complete the barcoding of all major crustal blocks, and 13 of the papers in this special issue provides examples of this progress. Seven additional papers provide overviews of important LIPs. Together these 20 papers illustrate the potential for rapid progress using the LIP record for Precambrian supercontinent reconstructions toward completing the plate tectonic revolution which began nearly five decades ago.

Ernst, Richard E.; Bleeker, Wouter; Sderlund, Ulf; Kerr, Andrew C.

2013-08-01

358

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

359

Cenozoic tectonic history of the North America-Caribbean plate boundary zone in western Cuba  

NASA Astrophysics Data System (ADS)

Structural studies of well-dated Jurassic to lower Miocene rocks in western Cuba constrain the sequence of structural events affecting this oblique collisional zone between the late Cretaceous island arc and the Jurassic-Cretaceous North America passive margin in the southeastern Gulf of Mexico and Straits of Florida. Results of detailed mapping and collection of fault slip data at 34 sites define a regionally consistent, five phase tectonic model for the period from the late Paleocene to the post-early Miocene. During the late Paleocene to the early Eocene, the Cuban island arc collided with the North American passive margin (Bahamas Platform). Northwest-ward overthrusting during the collision defines tectonic phase I. A NNE-SSW compression concurrent with early Eocene left-lateral strike-slip faulting along the Pinar fault zone defines phase II. This result is consistent with structural mapping showing sinistral shear within the 065 striking Pinar fault zone. An ENE-WSW to E-W compression defining phase III overprinted phase II faults in the lower Eocene and older rocks. Post-early Miocene normal faulting characterizes phase IV. Inversion of fault slip data indicates two contemporaneous directions of tension of 120 and 170. Strike-slip faults that overprint phase IV normal faults yield a 120 compression (phase V). The direction of compression associated with the arc/continent collision rotates clockwise from NW-SE in the late Paleocene/early Eocene (phase I), to NNE-SSW (phase II) and to ENE-WSW by the middle Eocene (phase III). The rotation in the compression direction occurred because the arc turned toward an oceanic area in the present-day area of central and eastern Cuba. Progressive collision led to complete subduction of the remnant oceanic crust by middle to late Eocene time.

Gordon, Mark B.; Mann, Paul; CCeres, DMaso; Flores, Ral

1997-05-01

360

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

361

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

NASA Astrophysics Data System (ADS)

The discovery of extra-solar "super-Earth" planets with sizes up to twice that of Earth has prompted interest in their possible lithosphere and mantle dynamics and evolution. Simple scalings [1,2] suggest that super-Earths are more likely than an equivalent Earth-sized planet to be undergoing plate tectonics. Generally, viscosity and thermal conductivity increase with pressure while thermal expansivity decreases, resulting in lower convective vigor in the deep mantle, which, if extralopated to the largest super-Earths might, according to conventional thinking, result a very low effective Rayleigh number in their deep mantles and possibly no convection there. Here we evaluate this. (i) As the mantle of a super-Earth is made mostly of post-perovskite we here extend the density functional theory (DFT) calculations of post-perovskite activation enthalpy of [3] to a pressure of 1 TPa. The activation volume for diffusion creep becomes very low at very high pressure, but nevertheless for the largest super-Earths the viscosity along an adiabat may approach 10^30 Pa s in the deep mantle, which would be too high for convection. (ii) We use these DFT-calculated values in numerical simulations of mantle convection and lithosphere dynamics of planets with up to ten Earth masses. The models assume a compressible mantle including depth-dependence of material properties and plastic yielding induced plate-like lithospheric behavior, solved using StagYY [4]. Results confirm the likelihood of plate tectonics and show a novel self-regulation of deep mantle temperature. The deep mantle is not adiabatic; instead internal heating raises the temperature until the viscosity is low enough to facilitate convective loss of the radiogenic heat, which results in a super-adiabatic temperature profile and a viscosity increase with depth of no more than ~3 orders of magnitude, regardless of what is calculated for an adiabat. It has recently been argued [5] that at very high pressures, deformation by intersticial diffusion may become more effective than by vacancy diffusion, possibly causing in a decrease of viscosity with pressure along an adiabat. This would allow ~adiabatic temperatures in the deepest mantle. (iii) In the context of planetary evolution: If, as is likely, a super-Earth was extremely hot/molten after its formation, it is thus likely that even after billions of years its deep interior is still extremely hot and possibly substantially molten with a "super basal magma ocean" - a larger version of the proposal of [6] that would affect outgassing history, although this depends on presently unknown melt-solid density contrast and solidus. [1] Valencia, D., R. J. O'Connell and D. D. Sasselov (2007) Astro. J. 670, L45-L48. [2] van Heck, H. and P. J. Tackley (2011) Earth Planet. Sci. Lett., submitted. [3] Ammann, M.W., Brodholt, J.P., Wookey, J., Dobson, D.P. (2010) Nature 465, 462-465. [4] Tackley P. J. (2008) PEPI 171, 7-18. [5] Karato, S. (2011) Icarus, 212, 14-23. [6] Labrosse, S., Hernlund, J.W., Coltice, N. (2007) Nature 450, 866-869.

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

2011-12-01

362

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

363

The Start of Plate Tectonics in the Eoarchean: A Tribute to Gilbert N Hanson, Pioneer in Archean Geochemistry  

NASA Astrophysics Data System (ADS)

The use of isotopic and trace element geochemistry and igneous petrology to understand the petrogenesis of Archean rocks was pioneered by Gilbert Hanson and Joseph Arth at SUNY Stony Brook in the 1970's. Extension of these approaches allows the onset of plate tectonics on Earth shortly after the end of the Hadean to be specified. Nb/Th and Th/U ratios of mafic-ultramafic rocks from the depleted upper mantle begin to change from 7 to 18.2 and 4.7 to 2.9 (respectively) at 3.6 Ga. This signals the appearance of subduction-altered slabs in general mantle circulation from subduction initiated at 3.8 Ga. Juvenile crustal rocks begin to show derivation from progressively depleted mantle with typical igneous ?Nd:?Hf = 1:2 after 3.6 Ga. Cratons with stable mantle keels that have subduction imprints begin to appear at 3.5 Ga. These changes all suggest that extraction of continental crust by plate tectonic processes was progressively depleting the mantle from 3.6 Ga onwards. Neoarchean subduction appears largely analogous to present subduction except in being able to produce large cratons with thick mantle keels. The earliest Eoarchean juvenile rocks and Hadean zircons have compositions that reflect the integrated effects of separation of an early enriched reservoir and fractionation of perovskite from the Mars-size impact-derived magma ocean, rather than separation of voluminous continental crust or oceanic plate tectonics. Hadean zircons most likely were derived from a continent-absent, mafic to ultramafic protocrust that was multiply remelted between 4.4 and 4.0 Ga under wet conditions to produce evolved felsic rocks. If the protocrust was produced by global mantle overturn at ca 4.4 Ga, then the transition to plate tectonics resulted from radioactive decay-driven mantle heating. Otherwise, such protocrust would have been the typical product of mantle convection and the transition to plate tectonics resulted from cooling to the extent that large lithospheric plates stabilized.

Shirey, S. B.; Kamber, B. S.; Whitehouse, M. J.; Mueller, P. A.; Basu, A. R.

2007-05-01

364

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

365

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

366

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

367

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

SciTech Connect

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

Stanley, D.J.

1983-03-01

368

Carbon Cycle in the Archean Plate Tectonics: Hydrothermal Carbonation, Metamorphic Decarbonation and Storage in the Mantle  

NASA Astrophysics Data System (ADS)

Geological studies in the Archean greenstone belt have shown that hydrothermal alteration at mid-oceanic ridge (MOR) had caused extensive carbonation in the oceanic crust. Hence, the MOR hydrothermal carbonation and subsequent subduction-zone metamorphism had an important role in the Archean carbon cycle. The aim of this study is phase-petrological characterization of carbonation-decarbonation processes in the Archean ocean floor and subduction zone, and incorporate these processes to the Archean carbon cycle model. Basic parameters for bulk rock-composition and physicochemical conditions of the hydrothermal process are taken from those of greenstones in the 3.5Ga North Pole area, Pilbara Craton, Australia. In the North Pole area, carbonate-bearing mineral assemblage is restricted within upper 1 km from the bottom of bedded chert which represents ancient ocean floor. The mean modal abundance of carbonate mineral reaches to roughly 30 vol. percent in the carbonated-zone. A pressure condition of the hydrothermal carbonation at the MOR is estimated to be about 30 MPa, and the temperature of the hydrothermal fluid was 350 degC. Amount of the carbonate depends on XCO2 of the source hydrothermal fluid and rock/fluid ratio, at constant P-T condition. The amount of the carbonate changes intermittently as a function of XCO2, because the stability of carbonate is constrained by discontinuous reactions. Stability of carbonate minerals in the oceanic crust and hanging wall peridotite in the subduction zone is estimated including transfer of fluid from the oceanic crust to the wedge mantle. During the subduction-zone metamorphism along the Archean subduction-zone geotherm, the carbonated oceanic crust releases H2O-CO2 fluids with various XCO2 to the wedge mantle, and the fluid reacts with hanging-wall peridotite to form carbonates again. Although the oceanic crust could not keep CO2 as carbonate in the Archean high-T subduction, the carbonate was still stable in the peridotite. The peridotite could store about 6 wt percent of CO2. Assuming that the hanging-wall peridotite was dragged down to deep mantle with the subducting plate, the subduction flux of CO2 into the deep mantle is estimated to be 1E12 kg/y. A flux-reservoir model calculation showed that the Archean plate tectonic sub-system worked as a CO2 remover from the Archean atmosphere. This process compensated increasing solar luminosity and kept the ocean planet Earth.

Omori, S.; Kitajima, K.

2005-12-01

369

Tectonics and Relative Plate Motions Around the Andaman Sea and Sumatra  

NASA Astrophysics Data System (ADS)

There are several R-F-R models of the active back-arc opening system in the Andaman Sea proposed by authors, e.g., Curray et al. (1978), Eguchi et al. (1979), Eguchi (1991), Mantovani et al. (2001) and Nielsen et al. (2004). Most of the previous authors, except Eguchi et al. (1978) and Eguchi (1991), documented NW-SE or NNW-SSE striking relative plate motion at the Central Andaman Rift. Recent multi-beam bathymetry study by GEODYSSEA Project group confirmed the detailed configuration of the ENE-WSW striking Central Andaman Rift and adjacent transcurrent faults. All of data from the marine survey and recent shallow earthquakes as well as their strike-slip type focal mechanisms along the N-S striking fault segment at 95.2E from 11N to 12.5N support the approximate N-S opening at the adjacent Central Andaman Rift. The magnetic anomaly survey data of Curray et al. (1978) suggest that, in the case of N-S opening, the rate becomes 4.0 cm/y, although Curray et al. (1978) proposed the total rate of 3.7 cm/y in the case of NNW-SSE opening. We then studied the realistic geometry of plate boundaries from Sumatra through the Andaman sea including the Central Andaman Rift to Myanmar, using recent seismological data and GPS studies. As is important, the Sundaland is not part of the Eurasia plate as revealed by recent GPS surveys. Furthermore, based on data of GPS velocity vectors w.r.t. Eurasia plate (e.g., Pradirodirdjo et al., 1997; Michel et. al., 2001), we can recognize some differential motion within the NW-SE striking fore-arc block, which is bounded by the Sumatra transcurrent fault and Java trench. The GPS data indicate 'differential motion' in both the trench-parallel and trench-normal directions within the NW-SE striking fore-arc block. We must resolve whether such kind differential movement within the fore-arc block is steady or not, to investigate the detailed spatio-temporal nature of dynamic coupling at the subduction zones with intermittent activity of larger interplate seismic events. We have constrained 'plate motion polygons' at selected points by modifying the result of Eguchi (1991). For example, by assuming the NUVEL 1 model and introducing the shear faulting with the averaged rate of 2.6 cm/y along the Sumatra fault system, we obtained the ENE-WSW plate convergence with the rate of 1.2 cm/y at 12N and the convergence of 3.0 +- 0.3 cm/y at 5N, between the Indo-Australia plate and the fore-arc block at the western Java trench subduction zone. We, however, cannot constrain the instantaneous rotation vectors of the relative plate motions, mainly because of limited observation data.

Eguchi, T.; Murakoshi, T.

2005-12-01

370

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

NASA Astrophysics Data System (ADS)

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 magnetization. Declination anomalies, after tectonic corrections, are interpreted as rigid body rotations about a vertical axis of sample sites relative to the Pacific plate. All palaeomagnetic data from Marlborough cluster into three main groups. A 60-100 clockwise rotation affected Palaeocene to Middle Miocene sedimentary sequences across Marlborough between 18 Ma and 8 Ma, coeval with a phase of low-angle thrusting. The absence of this rotation in a Late Cretaceous dyke swarm defines the present western limit of the early rotating zone. A regional 20 clockwise rotation occurred in the last 4 Ma during the development of the Marlborough Fault System in a zone of dextral transpression, although locally clockwise rotations ? 40 may have occurred near some of the major dextral strike-slip faults. However, a negligible rotation is observed in the same period in the region to the southeast of the major Kekerengu dextral strike-slip fault, which appears to have acted as a hinge zone, accommodating relative rotation by dextral strike-slip on an arcuate fault, bending, and internal deformation. The observed tectonic rotations record the overall clockwise rotation of the trend of the southern end of the Hikurangi margin from W to NW in the Early Miocene to NE today, determined independently from the long-term relative plate motion data for the Pacific and Australian plates.

Vickery, Sara; Lamb, Simon

1995-11-01

371

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

NASA Technical Reports Server (NTRS)

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

Toksoz, M. Nafi

1988-01-01

372

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

NASA Technical Reports Server (NTRS)

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

Toksoz, M. Nafi

1987-01-01

373

Tilt effects of Sudeten mountain blocks produced by motions of tectonic plates -  

NASA Astrophysics Data System (ADS)

Since 1974 we observed repeatedly effects of large changes of the horizontal pendulums azimuths of equilibrium. The epoch of changes appeared irregularly in different phases of each year and lasted several dozen days. Magnitude of changes corresponds to hundred miliarcseconds of plumb line variations. Several months after event of strong changes the azimuth of pendulums comes back to old position but in significantly longer time. The construction in 2002 of long water-tube tiltmeter and installation of the system of monitoring temperature, pressure and humidity in surrounding of instruments opened new possibilities of investigation of the anomalous plumb line variations. Due to high resolution and possibility of reduction of instrumental drift, the measurements of plumb line variations carried out with help of new instrument are much more reliable than the pendulums measurements. The measurements obtained during five years with help of long water-tube tiltmeter confirmed existence of strong non-tidal signals. We observed effects of magnitude and time of duration close to magnitude and time of duration of effects registered earlier by horizontal pendulums. Sudeten Mountain area is divided into small blocks. Ksiaz laboratory is located on such block which is at the border of Sudetian area limited from the North-East direction by Sudetian margin fault. Ksiaz block is built with very hard and mechanically resistant rocks consisting of Devonian conglomerates of gneisses not saturated with water. Horizontal sizes of this block amount ten kilometers while it's height exceed twenty or more kilometers. We propose the following model of the block tilting. Narrow pillar is affected by moment of horizontal forces originated by tectonic stresses and simultaneously by friction forces at the bedrock of the block (between the bottom of the block and upper mantle). Coupling of forces causes rotation of the block registered by tiltmeters as plumb line variations. For such model we can expect horizontal surface displacements of the block with the magnitude of ten millimeters.

Kaczorowski, M.

2009-04-01

374

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

NASA Astrophysics Data System (ADS)

Mantle convection and plate tectonics are one system, because oceanic plates are cold upper thermal boundary layers of the convection cells. As a corollary, Phanerozoic-style of plate tectonics or more likely a different version of it (i.e. a larger number of slowly moving plates, or similar number of faster plates) is expected to have operated in the hotter, vigorously convecting early Earth. Despite the recent advances in understanding the origin of Archean greenstone-granitoid terranes, the question regarding the operation of plate tectonics in the early Earth remains still controversial. Numerical model outputs for the Archean Earth range from predominantly shallow to flat subduction between 4.0 and 2.5 Ga and well-established steep subduction since 2.5 Ga [Abbott, D., Drury, R., Smith, W.H.F., 1994. Flat to steep transition in subduction style. Geology 22, 937-940], to no plate tectonics but rather foundering of 1000 km sectors of basaltic crust, then "resurfaced" by upper asthenospheric mantle basaltic melts that generate the observed duality of basalts and tonalities [van Thienen, P., van den Berg, A.P., Vlaar, N.J., 2004a. Production and recycling of oceanic crust in the early earth. Tectonophysics 386, 41-65; van Thienen, P., Van den Berg, A.P., Vlaar, N.J., 2004b. On the formation of continental silicic melts in thermochemical mantle convection models: implications for early Earth. Tectonophysics 394, 111-124]. These model outputs can be tested against the geological record. Greenstone belt volcanics are composites of komatiite-basalt plateau sequences erupted from deep mantle plumes and bimodal basalt-dacite sequences having the geochemical signatures of convergent margins; i.e. horizontally imbricated plateau and island arc crust. Greenstone belts from 3.8 to 2.5 Ga include volcanic types reported from Cenozoic convergent margins including: boninites; arc picrites; and the association of adakites-Mg andesites- and Nb-enriched basalts. Archean cratons were intruded by voluminous norites from the Neoarchean through Proterozoic; norites are accounted for by melting of subduction metasomatized Archean continental lithospheric mantle (CLM). Deep CLM defines Archean cratons; it extends to 350 km, includes the diamond facies, and xenoliths signify a composition of the buoyant, refractory, residue of plume melting, a natural consequence of imbricated plateau-arc crust. Voluminous tonalites of Archean greenstone-granitoid terranes show a secular trend of increasing Mg#, Cr, Ni consistent with slab melts hybridizing with thicker mantle wedge as subduction angle steepens. Strike-slip faults of 1000 km scale; diachronous accretion of distinct tectonostratigraphic terranes; and broad Cordilleran-type orogens featuring multiple sutures, and oceanward migration of arcs, in the Archean Superior and Yilgarn cratons, are in common with the Altaid and Phanerozoic Cordilleran orogens. There is increasing geological evidence of the supercontinent cycle operating back to 2.7 Ga: Kenorland or Ur 2.7-2.4 Ga; Columbia 1.6-1.4 Ga; Rodinia 1100-750 Ma; and Pangea 230 Ma. High-resolution seismic reflection profiling of Archean terranes reveals a prevalence of low angle structures, and evidence for paleo-subduction zones. Collectively, the geological-geochemical-seismic records endorse the operation of plate tectonics since the early Archean.

Kerrich, Robert; Polat, Ali

2006-03-01

375

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

NASA Astrophysics Data System (ADS)

DIRTY SUBPOLAR GLACIERS: Deeply etched internal structures of debris-covered glaciers or rock glaciers occur widely on Mars at middle latitudes. Differentially sublimated folds, crevasses, medial moraines and flow lines are expressed now as a variety of pits, troughs, hummocks, and ridges; they reveal much about the extent of sublimation and the history of flow and accumulation that originally gave rise to these structures. In many regards, they appear like usual terrestrial debris-covered glaciers (including rock glaciers). These sublimated remnant structures are not uniformly distributed on the planet; they exhibit a definite relationship to latitude. The more deeply etched icy flows occur generally in the latitude belt from 30 to 40 degrees (north and south), where possibly very little ice remains near the surface. Between 40 and 55 degrees, most of these partly sublimated flows appear to be still icy. Poleward of that, many of them show very little evidence of any sublimational loss of ice, and instead appear as thick mantling blankets sometimes having subtle flow lines. Inferences for the distribution of ground ice and the role of sublimation are similar to those inferred from the distribution and morphology of small polygons; these results are also consistent with theoretical models of the distribution of ground ice and with Mars Odyssey neutron spectroscopy of the distribution of hydrogen in the upper meter of Mars. A peculiar aspect of dirty glaciers on Mars is their current lack of an evident zone of atmospherically driven accumulation; instead, accumulation of some dirty glaciers appears to be due to load-driven expression of ice originating probably in massive crustal layers; for others, atmospheric accumulation may occur at other times during the obliquity cycle of Mars. SOUTH POLAR ICE SHEET: Previously I have reported on evidence for flowing, faulting, folding south polar ice, with the evidence for the more ductile types of deformation concentrated within the area of perennial CO2 ice. This part of the polar cap exhibits strong evidence for convergent flow tending to close the quasi-spiral structured troughs, as predicted by finite-element modelers. A rich phenomenology accompanies this closure. In some cases, good evidence exists for one icy sheet overriding another. Elastic plate flexural responses, with attendant small-scale tectonism, is quite common, as is evidence for ductile deformation. Analogs drawn from Earth's lithosphere provide compelling explanations for some of these features. Smooth, topographically enclosed flat areas in the south polar deposits may be the surface expressions of subglacial lakes or refrozen lakes.

Kargel, J. S.

2003-12-01

376

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

377

Archean plate tectonics geodynamics: example from the Belomorian province, Fennoscandian Shield  

NASA Astrophysics Data System (ADS)

A fragment of the Archean collisional Belomorian orogen has been identified as the Belomorian province (BP) of the Fennoscandian Shield (Slabunov, 2008; Holtta et al., 2014). The province consists dominantly of Archean rocks, Early Paleoproterozoic rocks being less abundant. Rock of BP exhumed from middle crustal depths in Paleoproterozoic time (1.94-1.8 Ga). Seismic (CDP) profiling data (Sharov et al., 2010) show that the internal structure of BP reflects nappe tectonics: in Archean time, a collage of numerous slides was formed, and in Paleoproterozoic time the BP was thrusted on the Karelian craton and, in turn, was thrusted by rocks of the Kola province. The BP consists dominantly of Meso- and Neoarchean rock association (Slabunov et al. 2006). Neoarchean granitoids predominate, but eclogite-bearing metam?lange (Volodichev et al., 2004; Mints et al., 2010; Shchipansky et al., 2012), island-arc volcanics, front-arc basin sediments, ophiolite-type oceanic plateau-type rocks, collisional S-granites, kyanite-facies metamorphic rocks, molassa-type rocks, subalkaline granitoids and leucogabbro have been revealed among supracrustal rock associations. Rocks of the Belomorian province were subjected to multiple metamorphism in Archean and Paleoproterozoic time at moderately high to high pressures and were considerably deformed. High-grade supracrustal complexes make up not more than 20 % of the BP, but as they probably host ore and are crucial for the understanding of the formation and evolution of the structure, they are given close attention. Five generations of greenstone complexes of different ages: 2.88-2.82 Ga, 2.8-2.78 Ga, ca. 2.75 Ga , ca. 2.72 Ga and not later than 2.66 Ga, and two paragneiss complex in which sediments were formed 2.89-2.82 and 2.78 Ga ago, are distinguished. The main stages of crustal evolution in the BP: ca 2.88-2.82 Ga - the first subduction-accretion event marked by the following complexes: island-arc volcanics of the Keret GB; metagraywacke (front-arc basin sediments) of the Chupa paragneiss belt; Salma eclogites; 2.81?2.78 Ga - the second subduction-accretion event marked by the following complexes: island-arc volcanics, supra-subduction ophiolite (Iringora), graywackes, granulites (Notozero) and 4) eclogites (Kuru-Vaara); 2.75 Ga - the third subduction event marked by island-arc volcanics (Chelozero); 2.73-2.72 Ga - the fourth subduction-accretion event marked by : island-arc volcanics (Mil'kevich et al., 2007), granulites and Gridino eclogites; ca 2.7-2.66 Ga - collisional event marked by: collisional S-granites, kyanite-facies metamorphic rocks, molassa-type rocks, subalkaline granitoids and leucogabbro. The crustal evolution of the BP in the period 2.88-2.66 Ga is similar to the evolution of Phanerozoic collision orogens. This is a contribution to RFBR Project 13-05-91162.

Slabunov, Alexander

2014-05-01

378

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

379

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

380

Subduction Zone Geometry and Pre-seismic Tectonic Constraints From the Andaman Micro- plate Region.  

NASA Astrophysics Data System (ADS)

The 2004 Sumatra-Andaman mega-thrust rupture broke along the narrow fore-arc sliver boundary of the Indo- Burmese collision. Earlier events of 1679 (M~7.5), 1941 (M 7.7), 1881 (M~7.9) and 2002 (Mw 7.3) generated spatially restricted ruptures along this margin. Spatio-temporal analysis of the pre-seismic earthquakes showed dense seismicity in the back-arc region but negligible activity towards the trench. The hypocentral distribution highlights the shallow subduction at the northern segment, which becomes steeper and deeper to the south. The pre-earthquake stress distribution, inferred from the P and T-axes of earthquake faulting mechanisms, represents the compressional fore-arc and extensional back-arc stress regimes. Shallow NNE-SSW under- thrusting and NNW-SSE opening up of the marginal sea basin stresses were observed and this trend changes to NE-SW to N-S at intermediate depths. We collected three epochs of campaign mode GPS data along the arc from May 2002 to September 2004. These observations show nearly pure convergence along the Andaman trench prior to the earthquake. During this period the GPS sites moved westward relative to India at ~5.5 mm/yr, consistent with the earlier results. Along arc GPS velocity vectors suggest that the Andaman trench is part of a purely slip partitioned boundary, with the strike- slip component of the India-Sunda relative plate motion being taken up on the transform fault in the Andaman Sea or on the West Andaman Fault, and the convergent component on the Andaman trench. Although near normal convergence was observed, it sampled only a fraction of a possible full Andaman microplate convergence velocity, because elastic deformation from the locked shallow megathrust caused displacements toward the overriding plate, that is, away from India. Based on the Indian plate velocity and Andaman spreading rates, this component amounts to ~85% of the pre-seismic convergence. These geodetic velocities represent the present day geologic deformation rates and have been used to build an empirical relation for replenishment time required for megathrust occurrence. For Indo/Andaman convergence rates obtained from this study, renewal rates of ~630-1100 years are observed. Assuming the convergence represents the lower limit of the deformation happening there, which may actually vary over the entire seismic cycle, a value of ~1000 years may be appropriate for a 2004 type megathrust earthquake recurrence along the Andaman - Nicobar margin.

Earnest, A.; Freymueller, J. T.; Rajendran, K.; C. P, R.

2007-12-01

381

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

NASA Technical Reports Server (NTRS)

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

Demets, Charles; Stein, Seth

1990-01-01

382

Self-Consistent Generation of Tectonic Plates in Time Dependent, Three-Dimensional Mantle Convection Simulations. Part 1: PseudoPlastic Yielding  

Microsoft Academic Search

Presented here are the first three-dimensional simulations of mantle convection to display self-consistently-generated plate tectonic-like behavior which is continuous in space and time. Plate behavior arises through a reasonable material description of silicate deformation, with a simple yield stress being sufficient to give first-order plate-like behavior. Toroidal:poloidal ratios are within geologically-observed limits. The sensitivity of the system to yield strength

Paul J. Tackley

383

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

Microsoft Academic Search

SUMMARY 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

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

2001-01-01

384

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

SciTech Connect

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

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

1995-02-01

385

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

NASA Technical Reports Server (NTRS)

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

Bercovici, David

1995-01-01

386

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