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/ Calculus, math / CAL 105 / What is the meaning of tensile fractures in rock deformation?

# What is the meaning of tensile fractures in rock deformation? Description

##### Description: Week 7 notes, going into the origin of the Earth
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## What is the meaning of tensile fractures in rock deformation?

Rock Deformation :

- Rock Fractures

- tensile fractures open out

- shear fractures slip along the fracture surface

- natural faults are a type of shear fracture

Structures in zones of continental rifting

Normal fault: the top side slips down relative to the bottom side

- A normal fault occurs when the crust is extended

- Hanging wall has moved down relative to the footwall

## What is the meaning of shear fractures in rock deformation?

-

Graben structure:

- A valley which is defined by two normal faults (horsts), inclined in opposite directions.

Structures in zones of plate convergence :

- Tibet, area of shortening and thickening of continental crust

- 3

Reverse fault: the top side slips up, relative to the bottom side  If you want to learn more check out What is the rate of change of temperature with height called?

## What is the meaning of tectonic associations of faults?

A thrust is a low-angle reverse fault

- Glarus Thrust, Central Alps

Transform zones

- Strike-slip faults, slip horizontally parallel to fault surface

- San Andreas fault

- Right-slip fault, when crossing the fault, have to go down to your right to find the  fault

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Rock Deformation II cont’d

Retaining and releasing bends

- A bend to the right on a right-slip fault is a releasing bend, this may produce a basin - A bend to the left on a right-slip fault is a restraining bend, this may produce uplift and  mountains  If you want to learn more check out How is culture transmitted through enculturation?

( example : Salton sea pull-apart basin along San Andreas Fault)

- San Andreas fault unique because of its “Big Bend”

- Restraining bends cause overlap of the crust, creating mountains

Tectonic associations of faults: Summary:

- Normal faults are most common in right zones

- Thrust faults are common in zones of plate convergence

- Strike-slip faults are dominant in transform zones  Don't forget about the age old question of What is equality of opportunity in sociology?

Fault Rocks:

- Faults contain zones a few mm to a km wide of fault rock

- Fault rocks are produced by mechanical and chemical breakdown of the rocks on either  side of the fault

- Fault breccia: produced by mechanical fragmentation dominant Don't forget about the age old question of What does positive strain mean?

- Fault gouge: chemical alteration to clay - Mylonite : Ductile deformation

Folds:

- Bedded strata may be tilted and folded by forces associated with plate motion  • Attitude of bedding – strike and dip

Strike and dip

- The strike is the orientation of the horizontal line in the plane of bedding - The dip is the inclination of the bedding from the horizontal - The direction of dip is perpendicular to the strike and must be specific  Don't forget about the age old question of What is the meaning of ethnocentrism in anthropology?

- An anticline is afold that closes upwards

- The oldest rocks are in the core of the fold - A syncline is a fold that closes downwards

- The youngest rocks are in the core of the fold

Structures and maps :

- A geological map is a direct representation of the geology seen on the Earth’s surfaceWe also discuss several other topics like What is the meaning of conditional proofs?

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Origin of the Earth and the Solar System:

Stages in the formation of the solar system:

1. Formation of solar nebula and protostar

2. Accretion of planetesimals

3. Formation of planets

- Processes started 4560 million years ago, and took a few tens of millions of years to  complete.

Eagle Nebula :

- Cloud of gas and dust like these are the birthplace of stars

- very big and dilute

- Would not be able to distinguish space from a vacuum

- Visible through telescope

- “Black yama”

- Suppression of gas and dust creates Eagle Nebula, starts to contract under its own  gravity and start a new star or several

- gravitational collapse is first step of creating a star

1. Collapsing cloud

- a diffuse, roughly spherical, slowly rotating nebula begins to contract   - As contact, start to spin, “concentration of angular momentum” (like a figure  skater)

- gas clouds contracting hundreds to thousands of times

- centrifugal force, shorthand way of expressing when something rotates, in order  to keep it together have to pull in ( flying away from the force)

2. Formation of solar nebula

- Stars and planetary systems form by collapse of interstellar clouds under  gravity

- Clouds collapse into a disk

- central part of disk collapses to form a protostar

- hot, fairly high density ball of gas in the middle

3. Accretion of planetesimals

- planetesimals- little, proto planets

- grands of rock dust, minerals and ices accreted to form km-sized bodies   - gas getting more concentrated as result of collapse of the cloud   - first, form dirty snow. Bits of dust and ice stick to each other   - dirty snow flakes turn into dirty snowballs, they grow bigger until  becoming big enough to regard as celestial object

- Planetesimal.

4. Formation of planets

- start of nuclear fusion in proto-star generates solar wind- strips gas from inner  solar system

- planetesimals accrete to form terrestrial planets in the inner solar system   - gas giants grow around larger planetesimals in outer solar system   - * know about inner planets- Venus, Earth, Mercury, Mars   * outer planets - Jupiter, Saturn, Uranus, Neptune, Pluto   - asteroid belt between jupiter and inner planets

- Jupiter’s gravity stops asteroid belt substances from becoming planets   - collisions of planetesimals form creations of planets

- larger objects pull in more and more material, gas, and planetesimals   -while planets were developing, sun developed from a proto-star.   - nuclear fusion produces massive amounts of energy   - gas in outer part of the solar system was able to form the gas giants   ^one big problem with this theory of creation of planets   - most gas giant planets found around other stars are very close to  their parent stars

Terrestrial (rocky) planets

- Mercury, Venus, Earth- Moon System

- Venus

- Earth-Moon system

- Mars

- Several of the moons of Jupiter and Saturn and some of the asteroids are comparable in  size composition and structure to the terrestrial planets

Venus :

- Sister planet , remarkably similar in size and composition to Earth

- Very weak magnetic field

- No plate tectonics

- Curious why different from Earth in this way

- Extensive volcanic activity ( but no plate tectonic so mostly mantle plume, more vigorous  convection in the mantle)

- Cryptic tectonic structures

- “arachnoid” because looks like spider webb

- Very thick, hot atmosphere

- No oceans ( completely dry)

Landforms on Venus

- Tesserae

- Corona

- Do not know how these things were formed

Mars :

- About half the diameter of Earth

- No magnetic field- solid core?

- No plate tectonics

- Active volcanic and tectonic activity during first billion years

- Mantle plumes probably most common volcanic process on the planets - Very thin, cold atmosphere

- No surface water, but there may have been in the past

- Some features look like once frozen glaciers

- Alluvial channels on Mars look like once stream channels

- Valle Marineris : 5 km deep , largest feature on mars, many times deeper than the Grand  Canyon

-

Saturn :

- Titan is Saturn’s biggest moon

- Saturn’s rings massive compared to its rings, but Titan could be responsible for  movement of the rings

- Titan

- Larger than the planet Mercury

- Rocky core, water mantle, thick ice crust

- Nitrogen atmosphere

- Lakes of methane, rains methane, snows methane

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The Early Earth:

Origin of the Earth-Moon system

- Earth’s moon unique in that it is a significant fraction of the size of the Earth - Composition of the Moon is very similar to the Earth’s mantle

- Theories for the origin of the Moon

- Capture

- Moon was formed as separate, mini planet and captured by the orbit of  the Earth

- Fission

- Moon formed out of part of the Earth and thrust into space

- Formation together w/ the Earth in the same orbit

- Formed together as separate objects in the same orbit from the start

- Interplanetary collision

- Formed out of interplanetary catastrophe

^ most of these not possible or improbable.

- Capture : not possible unless two objects touch each other   - Fissure: no way Earth could spin so rapidly to throw the moon off.   - Formation W/ Earth: possible, but then why is the moon so much larger   comparison to the Earth compared to other planets and their moons.

- Interplanetary Collision: Most likely

- Mars sized body impacted Earth

- giant impact propelled shower of debris into space   - Earth reformed as largely as molten body and moon   aggregated from debris

- impact sped up Earth’s rotation and tilted Earth’s orbital  plane 23 degrees.

- Moon pushed further and further away by time and forces

- Moon/ Earth 1:81 Titan/Jupiter 1:20,000 (<-- Size)

- Composition of the moon very similar of composition of Earth’s mantle - Moon does not have core, ball of rock, close relationship to the Earth - Moon always presents the same face to the Earth, always seen the same side of  the moon ( before Apollo, had never seen backside of the moon)

The First Crust:

- After formation of the moon, the Earth’s mantle may have been largely molten - An early crust may have formed on magma ocean, made of anorthosite: not now  preserved (composed almost entirely of plagioclase)

- Early anorthosite crust on the moon still there: 4.5 billion years old - Earth’s early crust was continuously destroyed and recycled by mantle  convection and asteroid impacts

- Earth’s moon a clue to the nature of the early Earth:

- The lunar highlands are made of anorthosite

- Lunar mare are floored by basalt

- Lunar surface is dominated by impacts

- Euler crater: probably formed as result of relatively small object. When  impacting body hits surface of a planet, hits and evaporates, instantly  creating crater

- Central Peak, after hugs mass of hot material is ejected leaves  central peak.

- Mare Orientalis: a multi-ring impact basin ( on other side of the moon)

- Result of bringing sizable object in and hits the moon, produces

700 km crater. Rings are effects of progressive collapse into lunar

hole ( a few hundred kilometers deep)

- Mare are themselves impact basins

- Lunar “seas” were formed as giant impact structures before 3.9 Ga (gigayears),   later filled by flood basalt. Similar impacts must have occurred on Earth.   - Because Earth so close to moon during all   this violent collision, impact events.

- Many early impactors may have been comets, which supplied Earth with water   and organic compound; may be formed Earth’s oceans and atmosphere

The Early Earth:

- Heavy Bombardment by asteroids and comets during first few hundred million years - Rapid convective overturn of mantle continuously recycled the primitive crust - Early was 20% less bright than at present ( meaning ice age)

- Early atmosphere rich in N2, C02, Possibly CH4

- Early oceans hot, acidic

- No life, and hence no oxygen

- Oxygen almost 100% due to photosynthesis

- Remember Eons and Sequence by which they occur

- 4560-3900 Ma: Origin of Earth to first preserved crustal rocks

- Heavy bombardment by asteroids and comets during first few hundred million years - Rapid convective overturn of mantle

- Early sun 20% less bright

- Atmosphere rich in N2, C02, CH4

- Early oceans hot, acidic

- No Oxygen

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