The document discusses plate tectonics and the key concepts of plate tectonic theory. It describes how the lithosphere is broken into large plates that move over Earth's surface, driven by convection currents in the underlying mantle. It outlines the three main types of plate boundaries - divergent boundaries where new crust forms, transform boundaries where plates slide past each other, and convergent boundaries where plates collide and one slides under the other. It also discusses the evidence that supported the development of plate tectonic theory, such as seafloor spreading and magnetic reversals recorded in oceanic crust.
Study of plate tectonics of the earth, or plate movement, Jahangir Alam
a) Wegener’s Evidence (Continental Drift)
b) History of Plate Tectonics
c) Breakup and Appearence of Pangea
WHAT IS A PLATE?
Major continental and oceanic plates include:
Types of Earth’s Crust:
Plate tectonics (from the Late Latin tectonicus) is a scientific theory which describes the large scale motions of Earth's lithosphere.
THE DYNAMIC EARTH:
The earth is a dynamic planet, continuously changing both externally and internally. The earth’s surface is constantly being changed by endo-genetic processes resulting in volcanism and tectonism, and exogenetic processes such as erosion and deposition. These processes have been active throughout geological history. The processes that change the surface feature are normally very slow (erosion and deposition) except some catastrophic changes that occur instantaneously as in the case of volcanism or earthquakes. The interior of the earth is also in motion. Deeper inside the earth, the liquid core probably flows at a geologically rapid rate of a few tenths of mm/s. Several hypotheses attempted to explain the dynamism of the earth.
+ Horizontal movement hypothesis
+ Continental drift, displacement hypothesis
Development of the plate tectonic theory.
Plate tectonic theory arose out of the hypothesis of continental drift proposed by Alfred Wegener in 1912. He suggested that the present continents once formed a single land mass that drifted apart, thus releasing the continents from the Earth's core and likening them to "icebergs" of low density granite floating on a sea of denser basalt.
Seafloor Spreading
The first evidence that the lithospheric plates did move came with the discovery of variable magnetic field direction in rocks of differing ages.
Study of plate tectonics of the earth, or plate movement, Jahangir Alam
a) Wegener’s Evidence (Continental Drift)
b) History of Plate Tectonics
c) Breakup and Appearence of Pangea
WHAT IS A PLATE?
Major continental and oceanic plates include:
Types of Earth’s Crust:
Plate tectonics (from the Late Latin tectonicus) is a scientific theory which describes the large scale motions of Earth's lithosphere.
THE DYNAMIC EARTH:
The earth is a dynamic planet, continuously changing both externally and internally. The earth’s surface is constantly being changed by endo-genetic processes resulting in volcanism and tectonism, and exogenetic processes such as erosion and deposition. These processes have been active throughout geological history. The processes that change the surface feature are normally very slow (erosion and deposition) except some catastrophic changes that occur instantaneously as in the case of volcanism or earthquakes. The interior of the earth is also in motion. Deeper inside the earth, the liquid core probably flows at a geologically rapid rate of a few tenths of mm/s. Several hypotheses attempted to explain the dynamism of the earth.
+ Horizontal movement hypothesis
+ Continental drift, displacement hypothesis
Development of the plate tectonic theory.
Plate tectonic theory arose out of the hypothesis of continental drift proposed by Alfred Wegener in 1912. He suggested that the present continents once formed a single land mass that drifted apart, thus releasing the continents from the Earth's core and likening them to "icebergs" of low density granite floating on a sea of denser basalt.
Seafloor Spreading
The first evidence that the lithospheric plates did move came with the discovery of variable magnetic field direction in rocks of differing ages.
Download the lesson exemplar so you can follow this ppt. I have uploaded the lesson plan on this presentation too. Please search continental drift theory LP
if videos do not play, here are the links
https://www.youtube.com/watch?v=WaUk94AdXPA
https://www.youtube.com/watch?v=UwWWuttntio
This pdf covers theory of continental drift and plate tectonics.
Continental drift
Plate Tectonics
Mantle Convection
Convection currects
Types of Mantle convection
Drivers of the plate motion.
Bibliography_ Lutgens, Tarbuk and Tasa Publisher: Prentice Hall
Earth and Life Science
Earth Materials and Processes
Deformation of the Crust: Continental Drift Theory
Learning Competencies
The learners shall be able to explain how the continents drift (S11/12ESId-20), and cite evidence that support continental drift (S11/12ES-Id-21).
Specific Learning Outcomes
At the end of the lesson, the learners will be able to:
1. Discuss the history behind the Theory of Continental Drift;
2. Describe the Continental Drift Theory; and
3. Enumerate and explain the evidence used to support the idea of drifting continents.
Download the lesson exemplar so you can follow this ppt. I have uploaded the lesson plan on this presentation too. Please search continental drift theory LP
if videos do not play, here are the links
https://www.youtube.com/watch?v=WaUk94AdXPA
https://www.youtube.com/watch?v=UwWWuttntio
This pdf covers theory of continental drift and plate tectonics.
Continental drift
Plate Tectonics
Mantle Convection
Convection currects
Types of Mantle convection
Drivers of the plate motion.
Bibliography_ Lutgens, Tarbuk and Tasa Publisher: Prentice Hall
Earth and Life Science
Earth Materials and Processes
Deformation of the Crust: Continental Drift Theory
Learning Competencies
The learners shall be able to explain how the continents drift (S11/12ESId-20), and cite evidence that support continental drift (S11/12ES-Id-21).
Specific Learning Outcomes
At the end of the lesson, the learners will be able to:
1. Discuss the history behind the Theory of Continental Drift;
2. Describe the Continental Drift Theory; and
3. Enumerate and explain the evidence used to support the idea of drifting continents.
GOAL: To create a poster that explains the phenomena of blue sky using the concept of wavelength and frequency of visible light.
SITUATION: As the creative head in the science club of Macasandig National High School, you are tasked to create a poster showcasing the phenomena of blue sky on Science Club bulletin board.
PRODUCT: A creative poster explains the phenomena of blue sky. The poster should be in 1/8 illustration board.
faults generate earthquakes.
S8ES-IIa- 14
Objectives:
1. Describe what fault is and how these faults related to earthquakes.
2. Determine the extent of damage an earthquake can do in a particular location.
Article Reading
Earthquake wreaks havoc in the Philippines more than 1,000 people are killed when a 7.7-magnitude earthquake strikes Luzon Island in the Philippines on this day in 1990. The massive tremor wreaked havoc across a sizeable portion of Luzon, the country’s largest island, with Baguio City suffering the most devastating effects.
The epicenter of the quake, which struck at 4:26 p.m., was north of Manila in the Nueva Ecija province. Reports indicate that the shaking went on for nearly a full minute. Collapsing buildings were the main cause of damage and death. Getting out of a multi-story building was a good safety precaution that afternoon, although many people were injured and a few even died in stampedes of others doing the same thing.
At Christian College, a six-story building completely collapsed, trapping approximately 250 students and teachers inside. Heroic rescue efforts saved many, but some victims who did not die in the collapse were found dead later from dehydration because they were not pulled out in time.
All types of buildings, including several resort hotels in Baguio, known as the
Philippines’ Summer Capital, suffered tremendous damage. Most of the city’s 100,000
residents slept outdoors that evening and during the following week, afraid to return to
their homes amid the frequent aftershocks. For days, workers pulled bodies from the
demolished buildings in Baguio. The best estimate is that 1,000 bodies were eventually
recovered. At least another 1,000 people suffered serious injuries. Rescue efforts were
hampered severely because the three main roads into the city were blocked by landslides. Hundreds of motorists were stranded on the roads as well.
A fault is a fracture or zone of fractures between two blocks of
rock. Faults allow the blocks to move relative to each other.
This movement may occur rapidly, in the form of an earthquake - or may occur slowly, in the form of creep. Faults may range in length from a few millimeters to thousands of kilometers. Most faults produce repeated displacements over geologic time.
The ground in the area of fault tends to remain not moving
because of frictional force between the two opposing plates (boxes). As stronger forces (rubber band) shakes up the fault, the friction (tape) can no longer hold up the plates (box) thus resulting to a slip in the plates t
Plate Tectonic is a theory explaining the structure of the earth's crust and many associated phenomena as resulting from the interaction of rigid lithospheric plates which move slowly over the underlying mantle.
Oceanography is an interesting subject. Geological oceanography deals with a lot of unique aspects of the oceans including the ocean morphology and relief, continental margins, tectonic processes acting on the ocean bottoms, marine mineral resources, and the deep sea deposits. The subject also focuses on the never ending dynamic processes like ocean waters, ocean currents and their impacts with reference to space and time. Understanding the tectonic disposition and movement of crustal plates are an important part while studying the earth and atmospheric sciences, in general and oceanography, in particular. The continental margins and the deep ocean basins are the two major aspects to be understood in this subject. This lesson is on the characteristics of continental margins.
CSEC Geography- Internal Forces - Plate Tectonics and EarthquakesOral Johnson
This document looks at the Earth's internal forces. The main layers of the earth are described. The history surrounding plate tectonics is discussed. The different types of plate boundaries is also explained.
June 3, 2024 Anti-Semitism Letter Sent to MIT President Kornbluth and MIT Cor...Levi Shapiro
Letter from the Congress of the United States regarding Anti-Semitism sent June 3rd to MIT President Sally Kornbluth, MIT Corp Chair, Mark Gorenberg
Dear Dr. Kornbluth and Mr. Gorenberg,
The US House of Representatives is deeply concerned by ongoing and pervasive acts of antisemitic
harassment and intimidation at the Massachusetts Institute of Technology (MIT). Failing to act decisively to ensure a safe learning environment for all students would be a grave dereliction of your responsibilities as President of MIT and Chair of the MIT Corporation.
This Congress will not stand idly by and allow an environment hostile to Jewish students to persist. The House believes that your institution is in violation of Title VI of the Civil Rights Act, and the inability or
unwillingness to rectify this violation through action requires accountability.
Postsecondary education is a unique opportunity for students to learn and have their ideas and beliefs challenged. However, universities receiving hundreds of millions of federal funds annually have denied
students that opportunity and have been hijacked to become venues for the promotion of terrorism, antisemitic harassment and intimidation, unlawful encampments, and in some cases, assaults and riots.
The House of Representatives will not countenance the use of federal funds to indoctrinate students into hateful, antisemitic, anti-American supporters of terrorism. Investigations into campus antisemitism by the Committee on Education and the Workforce and the Committee on Ways and Means have been expanded into a Congress-wide probe across all relevant jurisdictions to address this national crisis. The undersigned Committees will conduct oversight into the use of federal funds at MIT and its learning environment under authorities granted to each Committee.
• The Committee on Education and the Workforce has been investigating your institution since December 7, 2023. The Committee has broad jurisdiction over postsecondary education, including its compliance with Title VI of the Civil Rights Act, campus safety concerns over disruptions to the learning environment, and the awarding of federal student aid under the Higher Education Act.
• The Committee on Oversight and Accountability is investigating the sources of funding and other support flowing to groups espousing pro-Hamas propaganda and engaged in antisemitic harassment and intimidation of students. The Committee on Oversight and Accountability is the principal oversight committee of the US House of Representatives and has broad authority to investigate “any matter” at “any time” under House Rule X.
• The Committee on Ways and Means has been investigating several universities since November 15, 2023, when the Committee held a hearing entitled From Ivory Towers to Dark Corners: Investigating the Nexus Between Antisemitism, Tax-Exempt Universities, and Terror Financing. The Committee followed the hearing with letters to those institutions on January 10, 202
Biological screening of herbal drugs: Introduction and Need for
Phyto-Pharmacological Screening, New Strategies for evaluating
Natural Products, In vitro evaluation techniques for Antioxidants, Antimicrobial and Anticancer drugs. In vivo evaluation techniques
for Anti-inflammatory, Antiulcer, Anticancer, Wound healing, Antidiabetic, Hepatoprotective, Cardio protective, Diuretics and
Antifertility, Toxicity studies as per OECD guidelines
Embracing GenAI - A Strategic ImperativePeter Windle
Artificial Intelligence (AI) technologies such as Generative AI, Image Generators and Large Language Models have had a dramatic impact on teaching, learning and assessment over the past 18 months. The most immediate threat AI posed was to Academic Integrity with Higher Education Institutes (HEIs) focusing their efforts on combating the use of GenAI in assessment. Guidelines were developed for staff and students, policies put in place too. Innovative educators have forged paths in the use of Generative AI for teaching, learning and assessments leading to pockets of transformation springing up across HEIs, often with little or no top-down guidance, support or direction.
This Gasta posits a strategic approach to integrating AI into HEIs to prepare staff, students and the curriculum for an evolving world and workplace. We will highlight the advantages of working with these technologies beyond the realm of teaching, learning and assessment by considering prompt engineering skills, industry impact, curriculum changes, and the need for staff upskilling. In contrast, not engaging strategically with Generative AI poses risks, including falling behind peers, missed opportunities and failing to ensure our graduates remain employable. The rapid evolution of AI technologies necessitates a proactive and strategic approach if we are to remain relevant.
Francesca Gottschalk - How can education support child empowerment.pptxEduSkills OECD
Francesca Gottschalk from the OECD’s Centre for Educational Research and Innovation presents at the Ask an Expert Webinar: How can education support child empowerment?
The French Revolution, which began in 1789, was a period of radical social and political upheaval in France. It marked the decline of absolute monarchies, the rise of secular and democratic republics, and the eventual rise of Napoleon Bonaparte. This revolutionary period is crucial in understanding the transition from feudalism to modernity in Europe.
For more information, visit-www.vavaclasses.com
Introduction to AI for Nonprofits with Tapp NetworkTechSoup
Dive into the world of AI! Experts Jon Hill and Tareq Monaur will guide you through AI's role in enhancing nonprofit websites and basic marketing strategies, making it easy to understand and apply.
Read| The latest issue of The Challenger is here! We are thrilled to announce that our school paper has qualified for the NATIONAL SCHOOLS PRESS CONFERENCE (NSPC) 2024. Thank you for your unwavering support and trust. Dive into the stories that made us stand out!
A Strategic Approach: GenAI in EducationPeter Windle
Artificial Intelligence (AI) technologies such as Generative AI, Image Generators and Large Language Models have had a dramatic impact on teaching, learning and assessment over the past 18 months. The most immediate threat AI posed was to Academic Integrity with Higher Education Institutes (HEIs) focusing their efforts on combating the use of GenAI in assessment. Guidelines were developed for staff and students, policies put in place too. Innovative educators have forged paths in the use of Generative AI for teaching, learning and assessments leading to pockets of transformation springing up across HEIs, often with little or no top-down guidance, support or direction.
This Gasta posits a strategic approach to integrating AI into HEIs to prepare staff, students and the curriculum for an evolving world and workplace. We will highlight the advantages of working with these technologies beyond the realm of teaching, learning and assessment by considering prompt engineering skills, industry impact, curriculum changes, and the need for staff upskilling. In contrast, not engaging strategically with Generative AI poses risks, including falling behind peers, missed opportunities and failing to ensure our graduates remain employable. The rapid evolution of AI technologies necessitates a proactive and strategic approach if we are to remain relevant.
WHAT IS A PLATE? MAJOR PLATES. Types of Earth’s Crust. Plate Boundary
1. PLATE TECTONICS
a) What Is A Plate?
b) Plate Boundary
c) Plate Tectonics Theory
d) Continental Drift
e) Sea Floor Spreading
f) Driving Forces of Plate Motion
g) Types of plate boundaries
h) Significance of Plate Tectonics
2. • The lithosphere is broken up into large segments what are called
tectonic plates. Tectonic plates consist of lithospheric mantle (upper
part of the upper mantle) overlain by either of two types of crustal
material: oceanic crust (in older texts called sima from silicon and
magnesium) and continental crust (sial from silicon and aluminium).
Average oceanic lithosphere is typically 100 km thick; its thickness is a
function of its age: as time passes, it conductively cools and becomes
thicker. Continental lithosphere is typically ~200 km thick, though this
also varies considerably between basins, mountain ranges, and stable
cratonic interiors of continents. The two types of crust also differ in
thickness, with continental crust being considerably thicker than
oceanic (35 km vs. 6 km).
• Major continental and oceanic plates include:
the Eurasian plate, Australian-Indian plate, Philippine plate, Pacific
plate, Juan de Fuca plate, Nazca plate, Cocos plate, North American
plate, Caribbean plate, South American plate, African plate, Arabian
plate, the Antarctic plate, and the Scotia plate. These plates consist of
WHAT IS A PLATE?
4. Types of Earth’s Crust
• Tectonic plates can include continental crust or oceanic crust, and
many plates contain both. For example, the African Plate includes the
continent and parts of the floor of the Atlantic and Indian Oceans. The
distinction between oceanic crust and continental crust is based on
their modes of formation. Oceanic crust is formed at sea-floor
spreading centers, and continental crust is formed through
arc volcanism and accretion of terranes through tectonic processes;
though some of these terranes may contain ophiolite sequences, which
are pieces of oceanic crust, these are considered part of the continent
when they exit the standard cycle of formation and spreading centers
and subduction beneath continents. Oceanic crust is also denser than
continental crust owing to their different compositions. Oceanic crust is
denser because it has less silicon and more heavier elements ("mafic")
than continental crust ("felsic"). As a result of this density stratification,
oceanic crust generally lies below sea level (for example most of the
Pacific Plate), while the continental crust buoyantly projects above sea
level (see isostasy for explanation of this principle).
6. Plate Boundary
• What is a plate boundary?
• The location where two plates meet is called a plate
boundary, and plate boundaries are commonly associated
with geological events such as earthquakes and the creation
of topographic features such as mountains, volcanoes,
mid-ocean ridges, and oceanic trenches. The majority of the
world's active volcanoes occur along plate boundaries, with
the Pacific Plate's Ring of Fire being most active and most
widely known.
• Tectonic plates can include continental crust or oceanic crust,
and many plates contain both. For example, the African Plate
includes the continent and parts of the floor of the Atlantic
and Indian Oceans. The distinction between oceanic crust and
continental crust is based on their modes of formation.
Oceanic crust is formed at sea-floor spreading centers, and
continental crust is formed through arc volcanism and
accretion of terranes through tectonic processes .
7. Key Principles
• The outer layers of the Earth are divided into lithosphere and
asthenosphere. This is based on differences in mechanical
properties and in the method for the transfer of heat.
Mechanically, the lithosphere is cooler and more rigid, while the
asthenosphere is hotter and flows more easily. In terms of heat
transfer, the lithosphere loses heat by conduction whereas the
asthenosphere also transfers heat by convection.
• The key principle of plate tectonics is that the lithosphere exists as
separate and distinct tectonic plates, which ride on the fluid-like (
visco-elastic solid) asthenosphere. Plate motions range up to a
typical 10–40 mm/a (Mid-Atlantic Ridge; about as fast as
fingernails grow), to about 160 mm/a (Nazca Plate; about as fast as
8. Plate Tectonics
• Plate tectonics (from the Late Latin
tectonicus) is a scientific theory which
describes the large scale motions of Earth's
lithosphere.
• The theory builds on the older concepts of
continental drift, developed during the first
decades of the 20th century by
Alfred Wegener, and seafloor spreading,
developed in the 1960s.
9. Development of the theory
• geosynclinal theory
• Plate tectonic theory arose out of the hypothesis of
continental drift proposed by Alfred Wegener in 1912. He
suggested that the present continents once formed a single
land mass that drifted apart, thus releasing the continents
from the Earth's core and likening them to "icebergs" of low
density granite floating on a sea of denser basalt.
•Seafloor Spreading
The first evidence that the lithospheric plates did move came
with the discovery of variable magnetic field direction in rocks
of differing ages.
10. Seafloor Spreading Theory
• A profound consequence of seafloor spreading is that
new crust was, and is now, being continually created
along the oceanic ridges. This idea found great favor with
some scientists, most notably S. Warren Carey, who
claimed that the shifting of the continents can be simply
explained by a large increase in size of the Earth since its
formation. However, this so-called "
Expanding Earth theory" hypothesis was unsatisfactory
because its supporters could offer no convincing
mechanism to produce a significant expansion of the
Earth. Certainly there is no evidence that the moon has
expanded in the past 3 billion years.
11. Explanation of magnetic striping and Sea
floor Spreading
•The discovery of magnetic striping and the stripes being
symmetrical around the crests of the mid-ocean ridges
suggested a relationship. In 1961, scientists began to
theorise that mid-ocean ridges mark structurally weak zones
where the ocean floor was being ripped in two lengthwise
along the ridge crest. New magma from deep within the
Earth rises easily through these weak zones and eventually
erupts along the crest of the ridges to create new
oceanic crust. This process, later called seafloor spreading,
operating over many millions of years continues to form
new ocean floor all across the 50,000 km-long system of
mid-ocean ridges.
13. Evidences of Seafloor Spreading
• at or near the crest of the ridge, the rocks are very
young, and they become progressively older away
from the ridge crest;
• the youngest rocks at the ridge crest always have
present-day (normal) polarity;
• stripes of rock parallel to the ridge crest alternated in
magnetic polarity (normal-reversed-normal, etc.),
suggesting that the Earth's magnetic field has reversed
many times
14. Driving Forces of Plate Motion
• Tectonic plates are able to move because the Earth's
lithosphere has a higher strength and lower density
than the underlying asthenosphere. Their movement
is driven by heat dissipation from the mantle. Lateral
density variations in the mantle result in convection,
which is transferred into tectonic plate motion
through some combination of drag, downward suction
at the subduction zones, and variations in topography
and density of the crust that result in differences in
gravitational forces.
16. Types of Plate Boundaries
• Three types of plate boundaries exist, characterized by the way the plates move
relative to each other. They are associated with different types of surface
phenomena. The different types of plate boundaries are:
• Transform boundaries occur where plates slide or, perhaps more accurately, grind
past each other along transform faults. The relative motion of the two plates is
either sinistral (left side toward the observer) or dextral (right side toward the
observer). The San Andreas Fault in California is an example of a transform
boundary exhibiting dextral motion.
• Divergent boundaries occur where two plates slide apart from each other. Mid-
ocean ridges (e.g., Mid-Atlantic Ridge) and active zones of rifting (such as Africa's
Great Rift Valley) are both examples of divergent boundaries.
• Convergent boundaries (or active margins) occur where two plates slide towards
each other commonly forming either a subduction zone (if one plate moves
underneath the other) or a continental collision (if the two plates contain
continental crust). Deep marine trenches are typically associated with subduction
zones. The subducting slab contains many hydrous minerals, which release their
water on heating; this water then causes the mantle to melt, producing volcanism.
Examples of this are the Andes mountain range in South America and the Japanese
17. Divergent Boundaries
• At divergent boundaries new crust is created as one or more
plates pull away from each other. Oceans are born and grow
wider where plates diverge or pull apart. As seen below, when
a diverging boundary occurs on land a 'rift', or separation will
arise and over time that mass of land will break apart into
distinct land masses and the surrounding water will fill the
space between them.
• Iceland is splitting along the Mid-Atlantic Ridge - a divergent
boundary between the North American and Eurasian Plates. As
North America moves westward and Eurasia eastward, new
crust is created on both sides of the diverging boundary.
20. Convergent Boundaries
• Crust is destroyed and recycled back into the interior of the Earth as one
plate dives under another. These are known as Subduction Zones -
mountains and volcanoes are often found where plates converge. There
are 3 types of convergent boundaries: Oceanic-Continental Convergence;
Oceanic-Oceanic Convergence; and Continental-Continental
Convergence.
• When an oceanic plate pushes into and subducts under a continental
plate, the overriding continental plate is lifted up and a mountain range
is created. Even though the oceanic plate as a whole sinks smoothly and
continuously into the subduction trench, the deepest part of the
subducting plate breaks into smaller pieces.
• These smaller pieces become locked in place for long periods of time
before moving suddenly generating large earthquakes. Such earthquakes
are often accompanied by uplift of the land by as much as a few meters.
22. Oceanic-Continental Convergence
• When a thin, dense oceanic plate collides with
a relatively light, thick continental plate, the
oceanic plate is forced under the continental
plate; this phenomenon is called subduction.
23. Subduction
• How can new crust be continuously added along the oceanic ridges without
increasing the size of the Earth?
• This question particularly intrigued Harry Hess, a Princeton University geologist
and a Naval Reserve Rear Admiral, and Robert S. Dietz, a scientist with the U.S.
Coast and Geodetic Survey who first coined the term seafloor spreading. Dietz
and Hess were among the small handful who really understood the broad
implications of sea floor spreading. If the Earth's crust was expanding along the
oceanic ridges, Hess reasoned, it must be shrinking elsewhere. He suggested
that new oceanic crust continuously spreads away from the ridges in a
conveyor belt-like motion. Many millions of years later, the oceanic crust
eventually descends into the oceanic trenches — very deep, narrow canyons
along the rim of the Pacific Ocean basin. Hess' ideas neatly explained why the
Earth does not get bigger with sea floor spreading, why there is so little
sediment accumulation on the ocean floor, and why oceanic rocks are much
younger than continental rocks.
25. Block diagram of an ocean-continent convergent boundary. Oceanic lithosphere moves from left to right and
is subducted beneath the overriding continental lithosphere. Magma is created by partial melting of the
asthenosphere.
28. Oceanic-Oceanic Convergence
• When two oceanic plates collide, one may be pushed under the
other and magma from the mantle rises, forming volcanoes in the
vicinity. When two oceanic plates converge one is usually
subducted under the other and in the process a deep oceanic
trench is formed. The Marianas Trench, for example, is a deep
trench created as the result of the Phillipine Plate subducting
under the Pacific Plate.
• Oceanic-oceanic plate convergence also results in the formation
of undersea volcanoes. Over millions of years, however, the
erupted lava and volcanic debris pile up on the ocean floor until a
submarine volcano rises above sea level to form an island
volcano. Such volcanoes are typically streched out in chains
called island arcs.
29. A volcanic island arc forms as a result of oceanic-oceanic plate convergence.
30. Continent-continent collision
Continent-continent convergence is preceded by the closing of an ocean basin while ocean-
continent convergence takes place. Figure at the right shows the position of India relative to
the Eurasian plate in time. The convergence of the two plates created the Himalaya.
31. Continental-Continental Convergence
• When two continents meet head-on, neither is subducted
because the continental rocks are relatively light and, like two
colliding icebergs, resist downward motion. Instead, the crust
tends to buckle and be pushed upward or sideways. As a result
of two continental plates collision, mountain ranges are created as
the colliding crust is compressed and pushed upwards. The collision
of India into Asia 50 million years ago caused the Eurasian Plate
to crumple up and override the Indian Plate. After the collision,
the slow continuous convergence of the two plates over
millions of years pushed up the Himalayas and the Tibetan
Plateau to their present heights. Most of this growth occurred
during the past 10 million years.
33. Continent-continent collision
Continent-continent convergence is preceded by the closing of an ocean basin while ocean-
continent convergence takes place. Figure at the right shows the position of India relative to
the Eurasian plate in time. The convergence of the two plates created the Himalaya.
34. Transform-Fault Boundaries
• Transform-Fault Boundaries are where two plates are sliding horizontally past one
another. These are also known as transform boundaries or more commonly as
faults.
• When two plates move sideways against each other (at a transform plate
boundary), there is a tremendous amount of friction which makes the movement
jerky. The plates slip, then stick as the friction and pressure build up to incredible
levels. When the pressure is released suddenly, and the plates suddenly jerk
apart, this cause an earthquake.
• Most transform faults are found on the ocean floor. They commonly offset active
spreading ridges, producing zig-zag plate margins, and are generally defined by
shallow earthquakes. A few, however, occur on land.
• The San Andreas fault zone in California is a transform fault that connects the East
Pacific Rise, a divergent boundary to the south, with the South Gorda -- Juan de
Fuca -- Explorer Ridge, another divergent boundary to the north. The San Andreas
is one of the few transform faults exposed on land.
The San Andreas fault zone, which is about 1,300 km long and in places tens of
kilometers wide, slices through two thirds of the length of California. Along it, the
Pacific Plate has been grinding horizontally past the North American Plate for 10
million years, at an average rate of about 5 cm/yr. Land on the west side of the
fault zone (on the Pacific Plate) is moving in a northwesterly direction relative to
the land on the east side of the fault zone (on the North American Plate).
37. Significance of Plate Tectonics
• The theory of plate tectonics (meaning "plate
structure") was developed in the 1960's. This
theory explains the movement of the Earth's
plates (which has since been documented
scientifically) and also explains the cause of
earthquakes, volcanoes, oceanic trenches,
mountain range formation, and many other
geologic phenomenon.