PLATE TECTONICS andPLATE TECTONICS andCONTINENTAL DRIFT - Part 1CONTINENTAL DRIFT - Part 1

This has This has REVOLUTIONIZEDREVOLUTIONIZED the Earth Sciences the Earth Sciencesmuch the way Darwin and Natural Selection did tomuch the way Darwin and Natural Selection did to

biology in the 19th century.biology in the 19th century.

The earliest The earliest mapmakers noticed the mapmakers noticed the

apparent close fit of apparent close fit of continental margins.continental margins.

As map making improved, the possible fits of the As map making improved, the possible fits of the continents were noted by Francis Bacon (1561- continents were noted by Francis Bacon (1561- 1626), George Buffon (1707-1788), and 1626), George Buffon (1707-1788), and Alexander von Humboldt (1769-1859)! This isn't Alexander von Humboldt (1769-1859)! This isn't new!new!

BUT ….BUT ….With better, With better, modern modern mapping - the mapping - the fit got even fit got even better yet! - better yet! - about 96% about 96% perfect!perfect!

Alfred WegenerAlfred Wegenerproposed in 1912 that the proposed in 1912 that the continents were not only continents were not only moving, but actually plowing moving, but actually plowing through the sea floor.through the sea floor.

The leading physicists of his day, however, were The leading physicists of his day, however, were able to show that this was physically not possible. able to show that this was physically not possible. The proposed The proposed mechanismmechanism was thus discredited, was thus discredited, so the entire hypothesis was set aside (by most!) so the entire hypothesis was set aside (by most!) as yet more wishful thinking.as yet more wishful thinking.

Now, however, plate tectonics is accepted Now, however, plate tectonics is accepted by most of the scientific community as by most of the scientific community as beyond significant doubt.beyond significant doubt.

BASIC PREMISEBASIC PREMISE::The Earth's surface is comprised of 7 The Earth's surface is comprised of 7

major plates, and about 20 minor major plates, and about 20 minor plates, that behave as relatively brittle plates, that behave as relatively brittle slabs, called slabs, called LITHOSPHERELITHOSPHERE. They . They move over slow flow in an underlying move over slow flow in an underlying plastic layer, the plastic layer, the AESTHENOSPHEREAESTHENOSPHERE..

The The LITHOSPHERE LITHOSPHERE plates are ~100 km thick, but rigid plates are ~100 km thick, but rigid..The The AESTHENOSPHERE AESTHENOSPHERE is plastic (soft and deformable) and is plastic (soft and deformable) and

generally 200-400 km thick.generally 200-400 km thick.

SO, what's the SO, what's the EVIDENCE EVIDENCE ????????

1.1. Matching geology Matching geology across areas of across areas of apparent fit apparent fit

This even includes matching mountain belts!This even includes matching mountain belts!

Lystrosaurus, a primitive Triassic reptileLystrosaurus, a primitive Triassic reptile

Glossopteris, a primitive seed fern, ancestor of flowering plantsGlossopteris, a primitive seed fern, ancestor of flowering plantsspecimen from Africa specimen from Australia

2.2. Matching fossils distributed across areas of proposed fit. Matching fossils distributed across areas of proposed fit.

This is significant because …. This is significant because …. the the MODERNMODERN natural biotas are completely different! natural biotas are completely different!

<-------<------- Monkeys with Monkeys with prehensile tails are prehensile tails are found only in the found only in the New World…. while New World…. while the Great Apes ---> the Great Apes ---> are strictly in the Old are strictly in the Old World.World.

<--- <--- ForFor exampleexample, the plant , the plant family Cactaceae (the cacti) is family Cactaceae (the cacti) is also native also native onlyonly in the in the Western Hemisphere, while Western Hemisphere, while the shrubs and trees of the shrubs and trees of EucalyptusEucalyptus are found are found naturally only in Australianaturally only in Australia -->-->

3.3. Glacial geologic matching in ancient rocks - of glacial Glacial geologic matching in ancient rocks - of glacial patterns that make absolutely no sense unless the continents patterns that make absolutely no sense unless the continents WERE connected in the past.WERE connected in the past.

[ Oorlogskloof Nature Reserve,South Africa ]

4.4. Paleomagnetic signatures in rocks of the sea floor... Paleomagnetic signatures in rocks of the sea floor...

... supplemented by demonstrably supplemented by demonstrably greater sea-floor ages the farther greater sea-floor ages the farther one is from the center.one is from the center.

5.5. "Polar wandering" curves - those from North America "Polar wandering" curves - those from North America and Europe are very different. BUT there's only one northand Europe are very different. BUT there's only one north pole in the world!pole in the world!

This apparent discrepancy This apparent discrepancy ONLY makes sense if you ONLY makes sense if you allow the continents to allow the continents to move.move.

6.6. We now even have very We now even have very accurate GPS measurements accurate GPS measurements that show how fast the plates that show how fast the plates are actually moving - are actually moving - DIRECTLY!DIRECTLY!

This is driven by CONVECTION in the mantle, This is driven by CONVECTION in the mantle, produced by heat from the Earth's deep interior.produced by heat from the Earth's deep interior.

Soooo, how does this Soooo, how does this workwork??

If we look at the ocean floor, we see: If we look at the ocean floor, we see:

This mountain range is called theThis mountain range is called the Mid-Oceanic Rise and Ridge System (MORRS)Mid-Oceanic Rise and Ridge System (MORRS)

If we look closely at the MORRS, we see this topography: If we look closely at the MORRS, we see this topography:

The increased age of rocks from the center outwards The increased age of rocks from the center outwards implies the ridge in the center is pushing the implies the ridge in the center is pushing the continents apart as it grows.continents apart as it grows.

This is called a This is called a Zone of DivergenceZone of Divergence of lithospheric plates. of lithospheric plates.

BUTBUT, , if this is happening, either ...if this is happening, either ...

… … the Earth must be getting larger and the Earth must be getting larger and

larger,larger, OR …….OR …….

Something has to be destroyed somewhere else!Something has to be destroyed somewhere else!

This occurs in This occurs in Zones of Plate Zones of Plate ConConvergencevergence

Type I: oceanic lithosphere is Type I: oceanic lithosphere is subductedsubducted beneath a continental beneath a continental margin (an Andean-type subduction zone)margin (an Andean-type subduction zone)

"Subduction leads to orogeny.""Subduction leads to orogeny."

This process also generates a great deal of heat, which This process also generates a great deal of heat, which melts rocks, producing melts rocks, producing magmamagma. We'll come back to this.. We'll come back to this.

This subduction process creates earthquakes, This subduction process creates earthquakes, defining a plane called a defining a plane called a Benioff ZoneBenioff Zone..

This subduction is This subduction is evident in the evident in the increasing depth of increasing depth of earthquake origins earthquake origins (foci) inland - which (foci) inland - which is how this is how this hypothesis hypothesis originated in the first originated in the first place.place.

Earthquake Earthquake origins in origins in southern southern Alaska show Alaska show this pattern, this pattern, including one including one on last Friday, on last Friday, marked with marked with the brown star.the brown star.

THIS is the typical end product. These are the Andes, from the THIS is the typical end product. These are the Andes, from the south flank of Pichincha Volcano in Ecuador, at an elevation of south flank of Pichincha Volcano in Ecuador, at an elevation of about 4500 m (15,000 feet). about 4500 m (15,000 feet).

(The high peak at the left is Atacazo, another volcano.) (The high peak at the left is Atacazo, another volcano.)

Imbabura, Cotopaxi and Imbabura, Cotopaxi and Tungurahua are just three Tungurahua are just three of many volcanoes in of many volcanoes in Ecuador that have been Ecuador that have been produced by this process.produced by this process.

Imbabura Cotopaxi

Tungurahua

The same process is going on off the North American coastThe same process is going on off the North American coastin Oregon and Washington State:in Oregon and Washington State:

(Andesite, Dacite)

Mt. Rainier

Mt. Hood, Mt. Lassen, Mt. Shasta Mt. Hood, Mt. Lassen, Mt. Shasta and Mount St. Helens are all and Mount St. Helens are all products of the same process.products of the same process.

Mt. HoodMt. Shasta

Mt. Lassen

Mt. St. Helens,May 18, 1980

Type II: oceanic lithosphere is subducted beneath other Type II: oceanic lithosphere is subducted beneath other oceanic lithosphere - creating an oceanic lithosphere - creating an island arc systemisland arc system..

TYPICAL Island-arc systems include….TYPICAL Island-arc systems include….

The Aleutian The Aleutian Islands - Islands - with an with an earthquake earthquake from last from last Friday.Friday.

…………. or the . or the Philippines, where Philippines, where this earthquake this earthquake occurred this occurred this morning ...morning ...

... or Japan, where ... or Japan, where they also had one they also had one yesterday......yesterday......

... or Puerto rico, ... or Puerto rico, where THIS where THIS earthquake earthquake occurred the day occurred the day before yesterday.before yesterday.

((The purple lines The purple lines are the subduction are the subduction zones – note that zones – note that Puerto Rico lies Puerto Rico lies between TWO of between TWO of them!them!))

The Aleutian IslandsThe Aleutian IslandsThe Kuril IslandsThe Kuril Islands

The JapaneseThe Japanesearchipelagoarchipelago

TheThePhilippinesPhilippines

The The Lesser Lesser AntillesAntilles

So, So, island arc systemsisland arc systems include ... include ...

IndonesiaIndonesia

Fiji (and many other islands of the SW Pacific)Fiji (and many other islands of the SW Pacific)

The Aleutian IslandsThe Aleutian IslandsThe Kuril IslandsThe Kuril Islands

The JapaneseThe Japanesearchipelago archipelago

TheThePhilippinesPhilippines

The Lesser The Lesser AntillesAntilles

Subduction of oceanic lithosphere beneath continental Subduction of oceanic lithosphere beneath continental margins is taking place along .........margins is taking place along .........

NW North AmericaNW North AmericaCentral AmericaCentral America

The West The West Coast of Coast of South South AmericaAmerica

KamchatkaKamchatka

IndonesiaIndonesia

This is responsible for many of the major mountain This is responsible for many of the major mountain ranges in the modern world:ranges in the modern world:

The European AlpsThe European Alps

The AppalachiansThe AppalachiansThe UralsThe Urals

The Zagros Mtns. of IranThe Zagros Mtns. of Iran

The Brooks Range of N. AlaskaThe Brooks Range of N. Alaska

The HimalayaThe Himalaya

Type III. Continent-continent collisionsType III. Continent-continent collisions

The Verkhoyansk & Cherskiy Ranges of SiberiaThe Verkhoyansk & Cherskiy Ranges of Siberia

Case 1: the Alps of Europe Case 1: the Alps of Europe

Relative to Europe, Africa is moving northwards, at least in the Relative to Europe, Africa is moving northwards, at least in the northern part of the continent. This is slowly closing off the northern part of the continent. This is slowly closing off the Mediterranean Sea - the largest remnant of what used to be the Mediterranean Sea - the largest remnant of what used to be the Tethys Sea. (The Black, Caspian and Aral Seas are the other large Tethys Sea. (The Black, Caspian and Aral Seas are the other large pieces still in existence, all salt water.) pieces still in existence, all salt water.)

Case 2: The Zagros Mountains of IranCase 2: The Zagros Mountains of Iran

Case 3: The Grand-daddy of 'em all, the Himalaya!Case 3: The Grand-daddy of 'em all, the Himalaya!

By some estimates, the highest mountains on Earth in over 500,000,000 years!By some estimates, the highest mountains on Earth in over 500,000,000 years!

So, what's going on So, what's going on herehere??

A geologic map - even a A geologic map - even a simplesimple one (!) - gives one (!) - gives just a small hint of the complexity that just a small hint of the complexity that

dominates this region!dominates this region!

There are two opposing camps in the argument over the rise There are two opposing camps in the argument over the rise of the Himalaya. This is the scenario supported by some of the Himalaya. This is the scenario supported by some people:people:

That is, that the Indian subcontinent itself is being subducted That is, that the Indian subcontinent itself is being subducted beneath the southern margin of the Asian mainland block.beneath the southern margin of the Asian mainland block.

The The opposing view is that the subduction ceased when the opposing view is that the subduction ceased when the intervening oceanic crust disappeared, and that the intervening oceanic crust disappeared, and that the following is a more accurate cartoon image of what is taking following is a more accurate cartoon image of what is taking place:place:

The APPALACHIANS in this area owe their origin The APPALACHIANS in this area owe their origin to a two-part sequence:to a two-part sequence:

The Catskill Mountains of New York are part of The Catskill Mountains of New York are part of the sedimentary apron that was created to the west the sedimentary apron that was created to the west of the Acadian Mountains. of the Acadian Mountains.

The The NORUMBEGA NORUMBEGA FAULTFAULT marks the marks the boundary between the boundary between the North American block North American block and the sliver of and the sliver of Avalonia, which Avalonia, which extends southwards to extends southwards to at least at least Maryland andMaryland andVirginia. Virginia.

Farther south in the Appalachians, you can see the Farther south in the Appalachians, you can see the same kinds of folds as those being created today same kinds of folds as those being created today in the Zagros Mountains of Iran:in the Zagros Mountains of Iran:

Appalachian Mountains in centralPennsylvania -->