Module 3: Plate Tectonics (copy)

Lithospheric Plates

Lithospheric Plates

rigid, outermost layer of the earth’s lithosphere that are fragmented and fit together like a jigsaw puzzle

Plate Boundaries

edges of the lithospheric plates

3 Plate Boundaries

1. convergent

2. transform

3. divergent

Tectonics

refers to the structure and deformation of the Earth’s crust, and the processes that lead to the creation, movement, and interaction of the Earth’s lithospheric plates

• overall deformations from interactions/movements

Geological Phenomena

any natural events or processes that occur on or within the earth’s crust resulted from the interaction of the plate boundaries

Major Classifications of Earth Layers based on Mechanical Properties

1. Lithosphere

2. Asthenosphere

3. Mesosphere

4. Outer core

5. Inner Core

Lithosphere

crust and uppermost mantle; outermost layer

Consistency of the Lithosphere

rigid; brittle

Asthenosphere

upper-mantle

Consistency of the Asthenosphere

relatively weak; molten (composed of liquid, solid, and some gas → can flow)

Continental Drift Hypothesis

proposed by alfred wegener, who stated that the earth once existed as a whole chunk of a continent (pangaea) and a whole chunk of ocean (panthalassa)

Pangaea

“all land”; the super continent proposed by wegener

period that the Pangaea continent existed

existed 250 million years ago; during Permian period

period that the Pangaea started separating

after Triassic period (~200 million years ago)

2 major supercontinents of the Pangaea

1. Laurasia (northern pole of the earth)

2. Gondwanaland (southern pole of the earth)

Current continents that consisted the Laurasia continent

(NEA):

• North America

• Europe

• Asia

Current continents that consisted the Gondwanaland continent

• South America,

• Africa,

• Australia,

• Antarctica

Panthalassa

“all sea”; the large body of water that surrounded the Pangaea

Tethys Sea

a smaller sea formed during the triassic period when the pangaea broke into two

4 evidences for the continental drift theory

1. continental jigsaw puzzle fit

2. fossil match across continents

3. rock type and geological features

4. paleoclimatic evidence

Proof for the Continental Jigsaw Puzzle Fit

Africa and South America fits if Atlantic Ocean is closed;

• if you connect the continents, they form a puzzle where their boundaries match

Continental Shelf

the edge of a continent that lies under the ocean

Reason why the continental shelf is used as the boundary for reference in proving the jigsaw puzzle fit theory

edges above the ocean are easily eroded due to exposure to the surface

Proof for the theory on fossil match across continents

Fossils of animals and plants that could not have travelled through the oceans: Mesosaurus, Glossopteris, and Lystrosaurus

Where the Lystrosaurus was seen

africa, india, antarctica

Where the Glossopteris was seen

South Amrica, Africa, India, Antarctica, Australia

Where the Cynognathus & Mesosaurus were seen

South America & Africa

Reason why the Glossopteris was used in the fossil theory

glossopteris is very big, so it is questionable how it could have travelled

Reason why the Lystrosaurus was used in the fossil theory

it is a terrestrial animal, thus could not cross nor swim water

Reason why the Mesosaurus was used in the fossil theory

it is a marine animal, unsure how it could survive the varying temperature gradient conditions as it swam across the oceans, since salinity conditions across continents are different

Proof for the rock type and geologic feature thoery

Appalachian-Caledonian Mountains

• appalachian → north america

• caledonian mountains → north eastern europe

Proof for Paleoclimate/Ancient Climate theorem

1. Coal Seams in North Hemisphere with tropical trees

2. Glacial till and striations in Southern Africa, South America, Australia, and India

the driving mechanism of alfred wegener on continent movement

Tides, and the gravitational attraction between sun, moon, and earth

debunk of tides as a driving mechanism for continent movement

however, for tidal forces this strong and to cause movement in plate boundaries or continental plates, such equivalent force could also affect overall rotation of earth

Seafloor Spreading

proposed by harry hess, in which it centers on the formation of oceanic crust in a mid-oceanic ridge

Mid Oceanic Ridge

large scale earth feature formed at divergent plate boundaries

Mechanism/purpose of a mid-oceanic ridge

• plates move away from the mid-oceanic ridge because of volcanic/mantle activity

• new materials from the mantle comes out of this ridge, causing the creation of new oceanic crust along the ridge

Relationship of thickness of sediments and its distance from the mid-oceanic ridge

Thickness of sediments increase as it moves further away from the ridge due to accumulation;

moves faster as it is farther away from ridge

3 Additional Evidences for Plate Motion

1. Paleomagnetism and Polar Wandering

2. Hot Spot Volcanism

3. Seismicity and Plate Boundaries

Curie Point

temperature at which a mineral’s magnetic properties change (e.g. magnetite 585ºC)

Paleomagnetism

the record of the magnetic quality of a mineral wherein they “point” toward the position of the magnetic poles at the time of their formation;

Why does paleomagnetism happen

usually when after a mineral melts (reaching curie point), they cool down and become magnetic, and their magnetism freezes once they solidify

Polar Wandering

migration of magnetic poles

How is polar wandering related to moving continents?

if the magnetic poles remain stationary, their apparent movement is produced by continental drift

connection of magnetic pole to geographic poles according to polar wandering

the positions of magnetic poles (averaged over thousands of years) correspond closely to the positions of the geographic poles

proof of polar wandering and its connection to continental drift

of north america and europe are moved back to pre-drift positions, their wandering paths coincide (but separated by the atlantic ocean)

magnetic reversal

phenomenon wherein the earth’s magnetic field periodically reverses polarity, wherein the north magnetic pole becomes the south magnetic pole, and vise versa

normal polarity

when rocks exhibit the same magnetism as the present magnetic field

reverse polarity

when rocks exhibit the opposite magnetism

connection of magnetic reversals to seafloor spreading

alternating, equal mirror strips of high and low intensity magnetism mapped out that arose from underlying crustal rocks in the mid-oceanic ridge

hot spot volcanism

localized; long-lasting hot regions below the lithosphere that originated from the core mantle boundary, wherein magma plumes move upward and cause pacific plates around the plumes to move

where are hot spot volcanisms formed

magma plumes beneath the lithospheric plates

implication on age of volcano relative to distance from mantle plume

as a volcano/island moves further away from plumes, it implies it is older in age and more dense

example on proof of hot spot volcanims

islands of hawaii, where the hawaii island is more active given that it is under a hot spot volcanism, and niihau and kauai (which are further from the plume) are dormant (no magnetic materials created beneath island)

Seismicity and Plate Boundaries

areas of shallow earthquakes: regions of rifting

Wadati-benioff zone

anar zone of seismicity corresponding with the down-going slab in a subduction zone

areas if sub-ducting plate relative to the wadati-benioff zone

on top (along conversion boundaries): seismicity is concentrated

below: weak and negligible seismicity

relationship of seismicity and plate boundaries

plate boundaries are the edges of lithospheric plates and where plates interact, and it is where seismic activity (earthquakes) are seen

debunk of seafloor spreading

“If new materials are create along mid oceanic ridge, that means that new crust created along MOR, does it mean that the earth is expanding?”

Plate Tectonics Theory

unifying theory of geology; states that the lithosphere is composed of segments (tectonic plates) and that plates are in constant motion relative to one another

3 classifications of plate boundaries

1. major plate boundaries

2. minor plates

3. micro plates

7 major plate boundaries

1. North American

2. South American

3. Pacific

4. Eurasian

5. Australian

6. Indian

7. Antarctic

another name for convergent boundary

destructive boundary

convergent boundary

where two plates move together forming either arcs or mountain systems, forms subduction zones when oceanic lithosphere is involved

tectonic featured formed from two oceanic plates converging

island arcs

how are island arcs formed

when the older, denser, and colder oceanic plate sub-ducts beneath the younger, less dense oceanic plate

example of a tectonic feature of two oceanic crusts converge

mt. pinatubo

tectonic feature created from an oceanic and continental crust converging

continental volcanic arc

how are continental volcanic arcs formed

when the dense oceanic crust sub-ducts under the continental crust

example of tectonic feature from continental and oceanic converge

andes mountains

tectonic feature created when two continental plates converge

mountain ranges

how are mountain ranges formed

continental crusts crumple upwards; do not subduct

example of tectonic feature when continental plates converge

mt. everest

another name for divergent boundaries

constructive boundary

divergent boundary

where two plates move apart, leading to the formation of new oceanic crusts as seafloor

tectonic feature formed when oceanic crusts diverge

mid-oceanic ridge

example of mid-ocean ridge

mid-atlantic ridge that cuts iceland into 2 parts

tectonic feature formed when continental crusts diverge

rift vally

example of a rift valley

east african rift zone

example of where a triple junction is formed

african plate, arabian plate, indian plate moving away from each other

triple junction

when there are three continental plates diverging away from each other

phenomenon that takes place when divergent plates do not progress to form rift valleys

in tensional forces when plates move away from each other, the others just form a depression or basin, and overtime may discharge of water where it creates lakes (i.e. lake victoria)

another name for transform boundaries

conservative boundaries

transform boundaries

where two plates grind past each other; connects oceanic ridge systems into a continuous network

tectonic feature formed from transform boundaries

strike-slip faults

direction of strike slip faults relative to divergent plate boundaries

forms perpendicular lines with respect to the boundary

example of a strike slip dextral fault

san andreas fault

types of strike slip faults

1. dextral

2. sinistral

dextral faults

right lateral strike-slip faults

sinistral faults

left lateral strike-slip faults

mantle convection

movement of mantle in mantle plumes and active hotspot volcanisms, wherein warmer materials tend to rise up, cooler material tend to sink

processes involved in mantle convection

ridge push & slab pull

ridge push

process in which mantle plumes are extruded to the surface causing rifting (divergent plate boundary)

slab pull

process in which density and gravity differences further strengthens the subduction process (convergent plate boundary)

Type of tectonic feature of the Philippines

island arc system

How the philippines was created

created from the convergent boundaries of 2 oceanic plates (south china sea and philippine sea plate) that are moving toward each other

trenches of the philippines that subduct in the east direction (but are west geographically)

manila trench and sulu negros trench

trenches of the philippines that subduct in the west direction (but are east geographically)

east luzon trough & philippine trench

result of the net forces created by subduction zones (in the PMB area)

philippine fault zone

type of strike slip of the philippine fault zone

left-lateral strike slip