Exam 1 Flashcards
(115 cards)
1
Q
what makes earth habitable?
A
Heat, light, water, nutrients
HEAT
- External heat
- -solar radiation - internal heat
- -radioactive decay
- -accretionary heat from earth’s formation
- -produces changes in the earth’s features - slow movement of lithospheric plated
2
Q
Earth’s location
A
CONSTANTLY CHANGING, dynamic system - moving gas, liquid and solids that are INTERCONNECTED
habitable zone of our sun 0 earth’s location in this zone allows water to exist as a liquid on the surface - 4.6M miles closer or 34.3M miles farther away…wouldn’t work
–conservative and optimistic
earth’s place in solar system is unique
- -multi-phase liquid possible - not too hot/too cold
- -atmosphere allows nutrients to stay put - allowing life
earth’s location makes it ◦ Able to have an atmosphere and hydrosphere bc of its size and position from the sun - allows for water to exist as liquid, solid and gas
3
Q
the spheres
A
- Atmosphere
- Hydrosphere
- Biosphere
- Lithosphere
all driven by solar energy
4
Q
- Atmosphere
A
- -less than .01% of earth’s mass
- -in CONSTANT motion - heat differentials
- -78% nitrogen/ 21% oxygen
- -THIN shell of gas that surrounds the planet - fluid and in constant motion
- -other planets have atmospheres…but earth is unique bc it is 78% nitrogen and 21% oxygen
SOLAR HEAT is the driving force if atmospheric circulation (Greatest near equator)
◦ Heat causes water in oceans to evaporate - heat makes moist air less dense and it rises to form humid, air that is spotty clouds
5
Q
- Hydrosphere
A
composed of the total mass of water AT OR NEAR THE EARTHS SURFACE
–unique on earth bc water moves in an endless cycle from ocean to atmosphere,
over land surface then back to the sea again
—Water is in constant motion - evaporates from oceans and moves to atmosphere, precipitating as rain and snow, then returns to sea in rivers, glaciers, and groundwater
◦ As water moves it erodes and transports rock material and deposits it - helps modify earth’s landscape
6
Q
- Biosphere
A
- 6M known species
- -insects account for over 1/2
- -mammals only about 4000 species (.025%)
- -30M or more may exist
- -exists BECAUSE of the hydrosphere - small compared to other layers- Main factors that control life on planet are temp., pressure and chemistry of local environment
- Smallest, thin-est layer - but affects the composition of hydrosphere and present atmosphere
7
Q
- Lithosphere
A
Earth is called a “differentiated planet” bc it is separated into layers - why layers? Bc earth consists of internal layers of increasing density towards the center - internal layers produced as diff. materials rose or sank so least-dense materials went to surface
—GRAVITY IS MAJOR FORCE
◦ Compositional layers - crust, mantle, core
◦ Layers based on physical property - lithosphere, asthenosphere, mesosphere, outer core, inner core
(from outer to inner)
- Lithosphere (rigid)
- -solid and rigid, 10-300 km thick - crust and part of mantle - Asthenosphere (plastic)
- -T and P combine to partially melt rock - rocks lose strength and become soft and plastic
- -upper mantle
3 . Mesosphere (solid)
- -higher P offsets higher T
- -middle sphere - stronger rocks than above
- Outer Core (liquid)
- -flow creates magnetic field
- -liquid bc heat loss and rotation of the earth - also generates earth’s magnetic field - Inner core (solid)
- -dense, small and very hot
8
Q
surface features of the earth continents
A
shield platform
mountains
ocean ridge
trench
Continents have 3 major components: ancient shields, stable platforms, and belts of folded mountains - each reveals mobility of earth’s crust
9
Q
- shield
A
–large, flat areas of highly deformed crystalline rock - most more than 1B years old - “basement complex”
–where deformed ancient crystalline rocks are exposed
– ◦ also called basement complex - unchanging and very old
◦ Regional surface of low relief (relief = elevation diff. btwn low and high spots)
◦ Complex internal structure and complex arrangements of rock types
10
Q
- stable platform
A
areas where the basement complex is covered by layered sedimentary rocks (Kansas)
–sedimentary rocks are nearly horizontal and etched by treelike patterns
◦ In North America, stable platform lies btwn Appalachian mountains and the Rocky mountains - towards lake superior region and W Canada
• Sometimes refer to shield and stable platform together as a CRATON
11
Q
- Folded mountains
A
young, linear regions of deformed rocks
– ◦ Mountain belt means long, linear zone in earth’s crust where the rocks have been intensely deformed by horizontal stress during the slow collision btwn 2 lithospheric plates - usually intruded by molten rock
◦ Mountain belts are evidence that the earth’s lithosphere has been in motion
12
Q
- Sedimentary Basins
A
–relative low spots where sediment can accumulate]
Continents differentiated by region and geo diff. in size and shape and proportions of shields, stable platforms, and folded mountain belts
• North America. large shield (Canada - less than 300 m above sea level) - Appalachian and rocky mountains form mountain belt (Some still active)
• South America is similar - broad shield and stable platforms in Amazon basin - Andes mountains are part of Cordilleran folded mountain belt
13
Q
major features of oceans
1. ocean ridge
A
Major structural features of ocean floor are 1. oceanic ridges, 2. vast abyssal floor, 3. long, narrow and incredibly deep trenches, 4. seamounts, 5. continental margins
–Ocean floor holds the key to the evolution of earth’s crust - crust is mostly basalt, a dense volcanic rock - features somehow related to volcanic activity - rocks are fairly young
ocean ridge
–70000 km long
–broad ridge, highly fractures with a central Rift Valley
–most striking and important feature on ocean floor - Arctic basin to the center of Atlantic ocean, into Indian and across S Pacific
◦ Broad, fractured rise - a huge rift valley runs along the axis of the ridge
14
Q
major features of oceans
2. continental margins
A
continental margins
–continental shelf - submerged portions of continents
–part of the continent NOT ocean basin
–goes coast, then continental shelf (with water on continent), then slopes down to continental slope, continental rise then ocean
–Zone of transition btwn a continent and ocean basin
◦ Submerged part of a continent called CONTINENTAL SHELF (shallow sea around continents) - continental shelf is part of the continent, not ocean basin
◦ CONTINENTAL SLOPE - marks edge of continental rock mass
15
Q
major features of oceans
3. Abyssal floor
A
- –abyssal hills - small hills up to 900m (cover 80+% of ocean floor)
- -abyssal plains - smooth area adjacent to continents
- -seamounts - isolated peaks of submarine volcanoes. - some rise above sea and form islands - Hawaiian islands - provide insight to dynamics of inner earth
16
Q
ocean trenches
A
lowest areas on earth
- -adjacent to chains of volcanoes
- -Mariana Trench in Pacific ocean is deepest part of world’s oceans - show features of earth’s crust - adjacent to chains of volcanoes called island arcs (coastal mountain ranges of the continents)
17
Q
Earth is separated into layers according to density
A
◦ Internal layers classified by COMPOSITION: crust, mantle, and core
◦ Internal layers classified by PHYSICAL PROPERTIES: Asthenosphere, mesosphere, outer core, and inner core
◦ Material within each of these units is in motion - earth is changing, dynamic planet
18
Q
Geology
A
science of the earth - its origin, its history, its materials, its processes, and dynamics of how it changes
• Use to understand earth and our place in it - look at the place to make assumptions for future - learn how to avoid devastations and natural disasters - how to care for planet
19
Q
brief solar system
A
• All planets created at same time - orbit sun counter-clockwise
• Use DENSITY (mass per unit of volume) to examine dramatic differences in composition btwn planets (inner planets are more dense than the outer (which are made if ice and gas))
◦ Inner planets (Mercury, Venus, earth, Mars) - composed of rocky materials
◦ Outer planets - Jupiter, Saturn Uranus, Neptune - larger and made of gas and liquid - have no solid surface
◦ All planets imp.to study to understand earth - bc their composition/features show how planets evolve
20
Q
Earth (text)
A
formed 4.6B years ago
–if closer to sun, water would evaporate and further it would freeze - unique bc LIQUID WATER
–unique bc of its INTERNAL HEAT - comes from radioactivity - breakdown of potassium, uranium, and thorium is SOURCE of heat
– • Internal heat creates slow movements within earth - causes the lithosphere (outer layer) to split which creates continents and ocean basins - heat driven internal movement deforms earth’s outer layers and leads to earthquakes, mountain belts, and volcanoes
▪ Ex. Can be seen in East Africa - ripping apart - which separates the Arabian Peninsula from Africa and has formed the Red Sea as it fills with water
• Other planets are no longer hot inside to they have only slightly changed - larger planets have more internal heat and retain it longer than smaller planets
▪ Moon and mercury are so small that they were unable to generate and retain enough internal heat for activity - have stopped changing - they are like “fossils”
21
Q
Earth’s Internal structure based on chemical composition
A
- Crust - outermost compositional layer - crust of continents very diff. than crust of ocean basins
• Continental crust is thicker (75km) and composed of less-dense granite rock (billions years old) - the oceanic basin crust is composed of denser volcanic rock called basalt - Mantle - surrounds the core - 82% of earth’s vol. and 68% of its mass
• Composed of silicate rocks (Silicon and oxygen) - fragments of mantle have been brought to earth’s surface through volcanoes - more dense close to center - Core - 16% of earth’s vol., 32% of earth’s mass (bc so dense) - metallic iron
22
Q
Ecosphere
A
a model of planet earth
• A small glass globe, that contains 5 essential elements: energy, air, water, sand and living things (algae, seaweed. Shrimp, snails, microorganisms) - closed so only things that enter system are heat and light
◦ If one of 5 parts is missing, rest cannot survive - key to system is energy in the form of light - light generates photosynthesis
23
Q
ch. 2. Systems
A
- -Everything is interconnected on earth - systems show how they are related and operate - systems are groups of interacting devices that work together to accomplish a specific task
- -group of interdependent materials that interact with energy to form a unified whole. Most geologic systems are open; that is, they can exchange matter and energy across their boundaries
Open system
- -exchanges heat and matter with its surrounding
- -most geologic systems are open - river, rain water, snowmelt, rainfall to oceans
closed system
- -exchanged only heat
- -Earth is NEARLY close system
- -cooling lava flow (heat lost, but new matter not aded or lost)
Earth is a system - with many subsystems - it is nearly closed (mostly heat but small mass of meteorite/space dust input)
- -solar energy enters system
- -changes in one system component affect entire system
24
Q
Equilibrium in geologic systems
A
- -A system at its lowest possible energy level
- –Systems move toward equilibrium
- -Potential energy creates the need for flow in a system (Gravity/Landslide)
- -Progress towards equilibrium is not always constant
- That is how we can predict future changes
- Hot lava cools eventually - because it loses heat energy to reach equilibrium in environment
- Change is always in energy loss until reaches equilibrium
Why don’t geologic systems change more rapidly?
—Metastable – a system that needs a little energy boost to move towards equilibrium
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the hydrologic system
complex cycle by which water moves - movement driven by radiation from SUN
- -global scale - bc covers whole planet
- -6 components: evaporation, precipitation, runoff, infiltration, transpiration, condensation
• Movement of water from oceans to atmosphere is expressed in flow patterns of clouds - surfaces of other planets have remained unmodified for billions of years bc no hydrologic system
Lithosphere appears to be permanent, but it is also in constant motion (just slower) - entire lithosphere moves and continents split
26
Parts of Hydrologic system
| 1. Atmosphere - ocean system
--oceans store water
---water vapor moves in the atmosphere
--climate is controlled by ocean - atmosphere interactions
--Together with gases in atmosphere create the climate system
• Circulation driven by heat from sun - causes evaporation of huge quantities of water vapor into atmosphere and drives ocean currents
27
Parts of Hydrologic system
| 2. River systems
- --Surface drainage returns most rain water back to the ocean
- -Water flows rapidly ~0.0001% of Earth’s water
- -Most water precipitated onto land returns directly to oceans through surface drainage systems
- -River water provides the fluid medium that transports amounts of sand, silt and mud to the ocean - called deltas (Nile delta)
28
Parts of Hydrologic system
| 3. Glacial systems
Flow of water is very slow
Water can be “trapped” for 10,000 years
--Glaciers contain about 80% of fresh water, but less than 2% of Earth’s total water
--Precipitation falls as snow, sometimes stays frozen and does not immediately return to ocean - forms glaciers - greatly modify normal hydrologic system bc water does not immediately return to ocean
29
Parts of Hydrologic system
| 4. Groundwater systems
--Largest source of fresh liquid water
~20% of fresh water
--Moves slowly compared to rivers
--Water seeps into the ground and moves slowly through the pore spaces in soil and rocks
--As it moves, groundwater dissolves soluble rocks (limestone) and creates caverns/caves that enlarge or collapse to form surface depressions called sinkholes
30
Parts of Hydrologic system
| 5. Shoreline systems
Wave action modifies the interface between oceans-large lakes and the land
--all movements erode the coast and transport vast quantities of sediment
▪ Effects are seen in wave-cut cliffs, shoreline terraces, deltas, beaches, bars and lagoons
31
Parts of Hydrologic system
| 6. Eolian systems
- -Wind moves sediment in arid regions
- -Wind is a part of the hydrologic system
- --There are no completely dry spots on earth - Some water exists in even the most arid climates
- -Circulation of atmosphere forms Eolian system - wind transports loose sand and dust - moving fluid on planet's surface
32
Tectonics systems
Plate tectonics
- -explains the internal dynamics of earth
- -processes that form and deform the crust - developed in 1960s
EVIDENCE of plate tectonics
- -shape of continents
- -location of earthquakes/volcanoes
- -distribution of mountain belts, and fossils
DRIVING FORCES
- -Source of energy for plate movement is convection - earth's internal heat - hot mantle material rises to lithosphere's base, where it cools and eventually descends to become reheated and cont. the cycle
- -earth's internal heat and heat transfer by convection
- -slab pull or ridge push
33
plate margins
Lithosphere is divided into plates
- --Structural features, not land and ocean
- -Ridges, trenches and mountains
- --Not permanent (15 major ones today
34
Types of crust
- -diff. in composition, density and thickness
- -isostasy - gravitational adjustment of the crust
Continental
Oceanic
35
Divergent plate margins
When plates move apart, hot material from mantle wells up to fill void and create new lithosphere
- -Spreading of plates forms continental rifts, oceanic ridges, and new ocean basins
- -Most intense volcanism on earth occurs at divergent plate boundaries (but largely concealed below sea level)
- -Most divergent boundaries occur on seafloor, but continental rifts develop where divergent boundaries form on the continents - continental rift creates a new ocean basin
1. oceanic-oceanic crust
- -mid oceanic ridge with central rift valley
- -plates moving APART
- -hot material rises - lots of volcanoes
- -new ocean crust is formed
2. continental-continental crust
- -ex. East African Rift Valley
36
convergent plate margins
- -plates moving TOWARD one another
- -compressional forces
- -form igneous rocks
- -When plates converge, one slides beneath other and plunges into mantle
- -Forms folded mountain belts, volcanic arts, and deep-sea trenches
- -Where two plates converge, one tips down and slides beneath the other - called SUBDUCTION
- -Earthquakes and volcanoes line convergent plate margins - forms trenches in ocean
1. oceanic-oceanic - seafloor trench, volcanoes, Japan
2. oceanic-continental - subduction zone - volcanoes in a continental arc
- -cascade range - Oregon
- -South America
3. continental-continental
- -intensely folded/faulted mountain belts
- -metamorphic rocks dominate
- igneous rocks included
37
transform fault margins
Transform faults are large vertical fractures or faults in the crust
--Where plates slip horizontally past one another - transforms plate boundaries develop on long, straight faults - can cause shallow earthquakes
- -Movement is SIDE TO SIDE
- -May extend for long distances
- -In oceanic crust, deep valleys are formed
- -May extend onto continents
- -CALIFORNIA - San Andreas fault - Pacific plate is moving about 6 cm per year relative to N Am. Plate - causes stress btwn plates which causes earthquakes in California
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Intraplate tectonics
Little tectonic activity normally occurs
Mantle plumes may create hotspots
– Hawaiian Islands
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natural system
group of interdependent components that interact to form a unified whole - are under the influence of related forces
--Materials in a system change in an effort to reach and maintain equilibrium
* Earth's system of moving water, hydrologic system - as water moves, it erodes, transports, and deposits sediment, creating distinctive landforms and rock bodies
* Moving lithospheric plates - plate tectonic system - explains earth's major structural features - operates from earth's internal heat
40
Gravity and Isostacy
Gravity plays a fundamental role in Earth's dynamics - played vital role in formation of solar system, origin of planets, impact of meteorites
--also operates within earth's crust - causes "lighter" or less dense portions (continents) to stand higher than the rocks of heavier, denser ocean floor
Gravitational adjustment of earth's crust is ISOSTACY - earth's lithosphere responds to force of gravity as it tries to maintain a gravitational balance
--occurs bc crust is more buoyant than the denser mantle beneath it - each portion displaces mantle according to its thickness and density - denser material sinks deeper than less dense material
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8. Geologic Time
- -uniformitarianism vs. Catastrophism
UNIFORMITARIANISM
the interpretation of past events in earth's history is based on the principle that the laws of nature do not change with time
Uniformitarianism
- -Jamus Hutton (1726 - 1779)
- -challenged traditional theory of time that earth was 6000 years old
- -earth is old
- -earth's history has many chapters
- -earth in its current state (shape and arrangement of continents and oceans, mountains, atmosphere) is the result of NATURAL PROCESSES (modern chem., physical, bio laws) operating over VAST PERIODS OF TIME
RESULT: earth history is understandable and within the realm of human discovery
"the present is the key to the past"
ex. Shrimp burrows in modern, shallow marine in S Florida - Shrimp burrows in 75 M year old marine sedimentary rocks in central Utah
42
Geologic Time
--uniformitarianism vs. Catastrophism
CATASTROPHISM
Georges Cuvier French naturalist who studied fossils (1769 - 1832)
- -he concluded that fossil species was unique to a given sequence of rocks - theory was supported until Hutton challenged it
- -earth is young, maybe as young as 6000 years old
- -Earth's history consists of 2 chapters
1. Short period of upheaval during which earth's major features (oceans, continents, mountains, valleys) were formed through SUPERNATURAL FORCES
2. 6000 years of human existence during which the earth has been slowly decaying and modern laws of physics, chem are operating
RESULT - since creative supernatural forces are no longer in operation...we cannot unravel earth history by an appeal to modern earth processes
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Ordering Events (Relative dating)
Rocks are records of time!
--relative dating is determining the chronologic order of a sequence of events
1. Law of superposition
- -oldest rocks on the bottom
- -Assume layers were horizontal when deposited, and the rocks have not been overturned
2. original horizontality
- -in tilting...oldest rocks on bottom
3. Cross-cutting relations
- -if a fault cuts across - rocks inside fault are younger than rocks it cuts
4. Faunal Succession (William Smith)
- -groups of fossil animals and plants occur in the geologic record in a definite chronological order - a period of geologic time can be recognized by characteristic fossils
- -William smith - noticed several shales were alike but the fossils contained in rocks were not - correlated types of fossils with rock layers and was able to predict the location and properties of rocks beneath surface
- -trace character of fossils in younger rocks - oldest rocks contain only traces of soft-bodied organisms but younger rocks contain marine invertebrates with shells and simple marine life - amphibians appear in youngest rocks with reptiles, birds, mammals
5. Inclusions
- -ex. Granite inclusions in Basalt - the granite is older than the Basalt
- -a fragment of a rock incorporated or included in another is older than the host rock (the rock inside is older than the surrounding rock)
44
Geologic calendar
1. Eons
- -Azoic ("no life") (precambrian) - few or no fossils in rocks of this age - 4.6 B years - 85% OF EARTH HISTORY - time is represented by ancient metamorphic rocks with few fossils - evidence of volcanic activity
- -Phanerozoic ("visible life")(has Cenozoic, Mesozoic and Paleozoic inside it) - rocks with abundant fossils - many fossils
2. Eras
--Paleozoic "ancient life"
Diversification 540M years - invertebrate marine organisms
--Mesozoic "middle life"
mass extinction (90%) 225 M years - fossil reptiles - including dinosaurs are present
--Cenozoic "Recent life"
mass extinction (70%) 66 M years
3. Periods
- -inside Paleozoic - Permian, Pennsylvanian, Mississippian, Devonian, Silurian, Ordovician, Cambrian
- -inside Mesozoic - Cretaceous, Jurassic, Triassic
- -inside Cenozoic - Neogene and Paleogene
rocks tell about types of life at time, but nothing about the length of time represented
45
unconformities
- -Geologic time is continuous - but in sequence of rocks, unconformities (or major discontinuities) occur that interrupt rock-forming processes
- -boundaries btwn rock formations of markedly diff. ages
- -exist bc during some period of geologic time, the rock in that area was being eroded (or nothing was being deposited) rather than having new rock deposited on top
46
Scaling Events (absolute dating)
natural clocks
- -for absolute dating, geologists need some kind of "natural clock" that operates in a quantifiable fashion over time
1. process that operates at a fixed, constant rate
2. operations of that process produces an interpretable cumulative result
- -glacial ice layers, Varves in Green River formation in Wyoming, tree trunks
47
things that can go wrong with natural clocks
parent/daughter ratio changed
- -heat, pressure, circulating fluids (metamorphism)
- -loss of daughter product in gaseous form
rock too young
- -accurate measurement of extremely small quantities
- -weathered crystals
- -contamination
48
standards geologic column
- --established from studies of rock sequences in Euro. - now used worldwide - rocks were originally correlated from diff. parts of the world largely based on the fossils they contain - today radiometric dating is used to correlate major rock sequences
- -Numerical time designates a specific duration of time in units of hours, days or years - in geology, long period of numeric time are measured by radiometric dating
49
Rocks show earth's history
◦ Igneous rocks - records of thermal events…texture and composition show whether volcanic eruptions occurred or if the magma cooled beneath the surface
◦ Sedimentary rocks - record changing environments one earth's surface - the rise and fall of sea level, changes in climate, changes in life forms
◦ Layer of coal - record of lush vegetation growth (usually in a swamp)
◦ Limestone (composed of fossil shells) indicates deposition in a shallow sea
◦ Salt is precipitated from seawater or from saline lakes only in an arid climate…so a layer of salt carries specific climatic connotations
50
angular unconformity
--relationship btwn rock bodies - where the older strata dip at a different angle (usually steeper) than the younger strata
Four events involved to produce angular unconformity
1. An initial period of sedimentation during which older strata are deposited in a near-horizontal position
2. Subsequent period of deformation during which first sedimentary sequence is folded
3. Development of an erosional surface on the folded sequence of rock
4. Period of renewed sedimentation and development of a younger sequence of sedimentary rocks on top of old erosional surface
◦ Nonconformity - unconformity where the sedimentary rocks were deposited on the eroded surfaces of metamorphic or intrusive igneous rocks
◦ Disconformity - an unconformity in which beds above and below are parallel
• LOOK BACK AT ALL THESE PICTURES AND EXAMPLES BC MAKES NO SENSE HONESTLY
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radiometric dating
provides a method of directly measuring geologic time in terms of specific number of years - used in the past 50 years for numerical time scale for events of earth's history
numerical age - measured in hours, days and years - before 1900s, there was no method to measure long periods of geologic time
Henri Becquerel discovered natural radioactivity in 1896 and opened new vistas to fields of science - radioactivity is the spontaneous disintegration of an atomic nucleus with the emission of energy
1. Radioactive decay provided means to calculate ages for igneous rocks
2. Heat cont. produced by radioactive decay explained why earth was still hot billions of years after its formation (radiogenic heat produced by radioactive decay reactions)
Many atoms spontaneously change into other kinds of atoms through radioactive decay - if number of protons changes, the atom becomes a diff. element with its own set of physical and chemical properties
ATOM THAT DECAYS IS THE PARENT ISOTOPE AND PRODUCT IS DAUGHTER
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ch. 3 Minerals
| - -Basic chemistry
Atoms - smallest unit of element that retains its properties
- -molecules -small orderly group of atoms that possess specific properties
- -small nucleus -surrounded by cloud of electrons
- -nucleus contains protons and neutrons
mass = 1 atomic unit (au)
- -number of protons in nucleus determines the ATOMIC NUMBER
- -number of neutrons + protons = ATOMIC MASS
- -variable number of NEUTRONS in the nucleus = ISOTOPES
electrons - form clouds around nucleus - negative electrical charge - mass is not significant
--variations in # electrons produce IONS (positive and negative) - electrically charged...produced by gains/losses of electrons
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Atoms to molecules
bonding
- -atoms are stable when their outmost electron shell is filled to capacity with electrons (usually 8 electrons)
- -BUT MOST ELEMENTS HAVE AN INCOKMPETE OUTERMOST SHELL
- -electron structure like a novel gas - atoms lose, gain, or share electrons to achieve a noble gas structure
Compound - more than 1 element in its structure - opposites attract (neg. vs. positive charged)
- -types of bonds
1. metallic bonds
- -outer electrons are mobile, electrical conductivity
- -in a metal, each atom contributes 1+ outer electron that move freely through the ions - no specific electron is paired
2. covalent bonds
- -atoms share electrons to achieve noble gas structure
- -forms btwn elements that are near one another on periodic table - atoms attain electron arrangement of noble gas and share electrons - not ions bc no electrons are lost or gained (OX, Carbon, Hydrogen)
3. ionic bonds
- -formed btw ions of opposite charge
54
what is a mineral?
- -naturally occurring - substance of earth's natural systems - all of earth's dynamic processes involve the growth and destruction of minerals as matter changes from one state to another
- -inorganic, solid
- -with a specific chemical formula and a specific atomic structure
- -EXACT composition - expressed as a chemical formula - exact chemical formula is an orderly arrangement of atoms
- -ionic substitution may occur causing small variations in composition
states of matter - solid, liquid, gas
- -freezing at 0 C - 1 bar pressure
- -boiling point at 100 C - 1 bar pressure
- -triple point - .01 bar pressure and 0 C T
```
NOT MINERALS
oil
--organic, liquid
coal
--organic, no specific atomic structure
```
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Physical properties of minerals
| --crystal faces
1. Crystal faces, shape and form
- -growth in unrestricted env.
- -form reflects symmetry of internal structure
crystal face tell of internal structure - atoms arranged in long chain…crystal shaped like needle, atoms arranged in box….crystal like a cube
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Physical properties of minerals
| --density
common rock-formic minerals range from 2.6 - 3.4 grams/cm^3
--ratio of a weights substance to its volume - depends on types of atoms and how closely packed they are (more numerous and compact = higher density)
◦ At high PRESSURE - density increases bc atoms forced to be closer together
◦ At high TEMP. - density decreases bc atoms move apart
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Physical properties of minerals
| --cleavage
breakage along parallel planes of weakness
--due to internal structure - weaker bonds
--FRACTURE is uneven, NO natural planes of weakness
--If bonds are weak in a plane…cleavage occurs easily - diff. to have cleavage anywhere other than along cleavage plane
◦ Can occur in more than one direction, but number and direction of cleavage planes always same
◦ Some minerals have no weak planes and have no cleavage - usually break around curved surfaces (Diamonds lack cleavage)
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Physical properties of minerals
| --hardness
measure of resistance to abrasion
--strength of atomic bonds holding solid together
--MOHS hardness scale
(softest minerals down to 1 - harder closer to 10)
--arbitrary relative numbers assigned to 10 common minerals - scale is not linear
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Physical properties of minerals
| --color
most obvious property
- -not diagnostic for ID purposes
- -variations due to trace elements
- -minerals in hues with presence of inclusions and impurities
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Physical properties of minerals
| --streak
color of mineral in powder form
- -diagnostic property
- -hematite colors and streak
Tested by rubbing a mineral vigorously against surface of unglazed piece of white porcelain (soft minerals leave streak of fine powder…hard minerals have to be crushed)
61
Physical properties of minerals
| --luster
appearance of reflected light
- influenced by bonding
- -metallic luster - shines like metal
- -non-metallic - ranging form bright to dull - fluorescence - could be glassy, porcelain, resinous, earthy
Luster controlled by kinds of atoms and kinds of bonds that link atoms together
• Covalent bonds - usually produce brilliant, shiny minerals (like diamonds - called adamantine luster)
• Ionic bonding create vitreous luster (quartz)
• Metallic bonding - native metals (gold)
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Magnetism
characteristic of only a few minerals
| --acid (HCI) - calcite
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growth and destruction of minerals
Minerals grow and are broken down under specific conditions of temp., pressure, and chemical composition - minerals are a record of the changes that have occurred in Earth throughout history
crystallization - GROWTH
- -add ions to crystal face - follows internal structure - faces grow at different rates
- -Environment suitable for growth includes: 1. proper concentration of the kinds of atoms or ions required for a particular mineral, 2. proper temp. and pressure
- -When size increases, form and internal structure remain the same - new atoms added parallel to plane of atoms in basic structure
- -Usually happens in rock-forming minerals- like in molten lava flow…lots of crystals grow quickly and at same time so compete for space (Especially in igneous rocks…form by crystallization from molten rock material
mineral destruction
- -MELTING - remove atoms from crystal faces - solid to liquid - heat acuses melting inc. atomic vibrations enough to break bonds holding atoms in crystal structure
- -Or atoms can be pried loose and carried away by a solvent (water)
- -recrystallization - rearrangement of internal structure by changing P and T - metamorphism - occurs deepin inside crust and mantle at HIGH P and T - atoms do not move far but new bonds form and internal structure changes
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silicate minerals
most common minerals in earth
- -95% of volume in crust
- -75% of crusts mass made of silicon and oxygen
silicon-oxygen Tetrahedron
- -all silicate minerals are based on the silica tetrahedron
- -4 Oxygen atoms to one silicon atoms
within Silicate minerals
1. Felsic minerals - rich in silicon and aluminum
- -low densities and low crystallization T
- -Quartz, Feldspars, Mica - muscovite
2. Magic minerals rich in iron and magnesium
- -high Density and high crystallization T
- -olivine, pyroxenes and amphiboles, Mica- biotite
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Rock forming minerals
about 20 common minerals make up most rocks
--mostly composed of silicate minerals - silicate minerals dominate - Quartz, Fedspars, Mica, Amphiboles, Pyroxenes
rock? - a naturally occuring combinatio of one or more minerals
rock forming minerals rarely have deceloped crystal faces bc
- - 1. They grow by crystallization from melts (magma) or aqueous solutions (Seawater) and vigorously compete for space
2. They are abraded as they are transported as sediment
3. They are deformed under high temp. and pressure
4. Small (usually less that size of little fingernail), so physical properties are diff. to see without lens/microscope
5. Also variable composition bc of ionic substitution in crystal structure
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nonsilicate minerals
1. oxides - hematitie (iron)
2. halides - halite (salt)
3. sulfides - metallic ores (iron, copper, zinc, lead)
4. Carbonates - calcite (Cement), dolomoite (building stone)
5. Sulfates - gpsum - (Sheet rock)
6. Native elements - gold, silver, copper, sulfur, carbon
calcite, dolomite, gypsum, halite
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isotopes and Ions
ISOTOPES
--same # of protons (Ex. Iron = 26) but have diff. number neutrons --> so have properties of iron but diff. mass - isotopes are more unstable
IONS
- -usually elements of same # protons and electrons…if gains/loses electrons, element is no longer neutral and becomes a charged ION
- -Important bc the attraction btwn positive ions and negative ions is the bonding force that holds matter together
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States of matter
Diff. btwn solid, liquid, gas is the degree of ordering
1. Solid - usually arranged in rigid framework - crystal structure (clearly defined, regular, repeating, 3D pattern) - changes in structure occur with temperature/pressure changes
◦ There are AMORPHOUS solids with random arrangement (Glass)
2. Liquid - basic particles are in random motion, but packed closely together - held together by attraction, but slip and glide and collide
◦ When change from gas to liquid to solid -- density increases
◦ When heated - particle motion increases and atoms become separated - high speed
3. Gas - particles in rapid motion - travel in straight lines until changed by collision - pretty spaced out particles
• Changes btwn states occur through temperature and pressure changes - usually at high temp.
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Mineral structure - internal structure
consist of 1+ element - all specimens of a given mineral have same internal strucutre
- -Nicolaus Steno - discovered that sizes change but similar pairs of crystal faces always meet at same angle - LAW of constancy of interfacial angles
- -cleavage planes are planes of weakness in the crystal structure
Polymorphism - ability of specific chemical substance (carbon) to crystallize in more than one type of structure (use c-ray diffraction to study structures
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Composition of minerals
Minerals have definite chemical compositions - elements in specific proportions (allows to be written as chemical formula - ex. SiO2, CaCO)
Ionic substitution - a chemical change in the mineral w/o change in crystal structure - not very common - ability to substitute is based on size and electrical charge of ions (can if ionic radii differ by < 15%)
--Like changing brick wall - can be diff. composition (Glass, plastic) but same size and wall structure not affected --> however, composition changes - creates changes in hardness and color w/o changing internal structure
• All specimens of a given mineral have same physical and chemical properties (Ex. One piece of quartz is as hard and has same density as any other piece - no matter where, when, how formed)
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Mineral stability
Minerals are stable only over a fixed range of conditions
• Stable - if in equilibrium with its environment = little tendency for change - determined by pressure, temp., and composition
◦ Quartz is most common bc it is stable over range of temperatures and pressures found near earth's surface
◦ Changes in pressure or temperature can induce minerals to break down and form new species that are stable under new conditions
◦ Metamorphic processes are driven by tendency of minerals to react and change as environment changes
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Felsic silicate minerals (Feldspars, Quartz, Micas)
Feldspars
Felsic silicate minerals - make up major constiutents of continental crust - Rich in silicon and aluminum - low density and crystalize at low T in magmas
• Most abundant minerals in granite - granite is pink, porcelain mineral, rectangular form and milky-white mineral that is smaller but similarly shaped (that is the feldspars)
---Most abundant in earth's crust (50%)
• Good cleavage in 2 directions, porcelain luster, 6 hardness, 3D framework in crystal structure - silicate tetrahedrons
Ionic substitution creates potassium feldspar (pink in granite) and plagioclase feldspar which replaces sodium for calcium
---Causes the crust to have low density bc made of these
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Felsic silicate minerals (Feldspars, Quartz, Micas)
Quartz
Form glassy, irregularly shaped grains - usually grows in spaces btwn other minerals - result is that quartz usually lacks well-developed crystal faces
• When grow freely - form is elongated, 6 sides, and ends in a point
• In sandstones…quartz is rounded sand grains
• Abundant in 3 major rock types - has simple composition of SiO2 (silicon 2 oxygen) and is hard 7 - glassy luster - pure quartz are colorless - silicate tetrahedrons in tight framework
▪ All bonds are Si and O - includes no other elements so simple - makes it hard and tight bc bonds have same strength - hard and lacks cleavage
▪ Does not react with elements at or near earth's surface - hard mineral to alter or break down once formed
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Felsic silicate minerals (Feldspars, Quartz, Micas)
Micas
• Tiny black, shiny grains - potassium aluminum silicates - perfect cleavage in one direction - permits break into thin, elastic flakes
• Complex silicate with sheet structure
▪ Common in rocks: muscovite (white/colorless and in felsic minerals) and biotite (black, rich in iron and magnesium) - both contain water - abundant in granite and metamorphic rock
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Mafic silicate minerals (olivine, pyroxenes, amphioboles)
Olivine
Mafic silicate minerals - named bc contain magnesium and iron - dark green to black and HIGH densities
- -biotite is common in granite
- -common in earth's mantle and oceanic crust - crystallize at high T and have HIGHER Densities than Felsic
* Only mineral clearly visible in basalt (common mafic volcanic rock) - iron and magnesium substitute freely in crystal structure
* Olive green color (magnesium) and glassy luster
* Forms small crystals - high density forms at high temp.
* Deep in mantle, olivine not stable and recrystallizes to form denser mineral
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Mafic silicate minerals (olivine, pyroxenes, amphioboles)
Pyroxenes
* High temp. mineral - in crust and mantle - microscopic crystals - dark green to black - 2 directions of cleavage that intersect at right angles
* Internal structure - single chains of linked Si-O tetrahedrons
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Mafic silicate minerals (olivine, pyroxenes, amphioboles)
Amphiboles
* Similar to pyroxenes but contain hydroxyl ions - also differ in structure
* Double chains of silicon-O tetrahedrons - produce elongate crystals that cleave perfectly in 2 planes - green to black
* Common in igneous and metamorphic rocks
* Hornblende is most common variety - high density
* Asbestos - dangerous form of amphiboles - used to make fireproof fabrics, tiles, and insulation in buildings - miners working in mines become sick as small cleavage fragments become lodged in lungs - leads to lung disease
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Clay minerals
◦ Clays - silicate minerals
• Major part of soil - form at earth's surface where air and water react with silicate minerals to break them down into clay
• Sheet silicates but crystals are microscopic
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Nonsilicate minerals (Calcite, dolomite, halite, Gypsum)
Calcite
nonsilicate minerals - typically form at low T and pressures near earth's surface
* Composed of calcium carbonate - principal mineral in limestone
* Comes from seawater or remove from seawater by organisms as used to make their shells
* Dissolved by groundwater and re-precipitated as new crystals in caves
* Transparent or white…sometimes brown/grey - common at earth's surface - easy to identify - hardness 3 so can scratch with knife - perfect cleavage in 3 planes
* Major mineral in limestone and metamorphic rock marble
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Nonsilicate minerals (Calcite, dolomite, halite, Gypsum)
Dolomite
* Carbonate of calcium and magnesium - large crystals
* Widespread in sedimentary rocks - forms when calcite reacts with solutions of magnesium carbonate in seawater or groundwater
* Distinguished from calcite in powder form - it is denser than many silicate minerals
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Nonsilicate minerals (Calcite, dolomite, halite, Gypsum)
Halite
* (and gypsum - 2 most common minerals formed by evaporation of seawater or saline lake water
* Halite, common salt, is identified by taste
* Has one of simplest structures - sodium and chloride ions in cubical array
* Soluble and easily dissolves in water
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Nonsilicate minerals (Calcite, dolomite, halite, Gypsum)
Gypsum
* Composed of calcium sulfate and water - colorless with glassy or silky luster
* Soft mineral easily scratched with fingernail - cleaves perfectly in one plane to form thin, non-elastic plates
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Oxide minerals
◦ Lack silicon and includes other important iron oxides (magnetite (one of only minerals that is naturally magnetic) and hematite)
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Where do Igenous rocks come from?
Magma
- -partialy molten mix of solid, liquid gas
- -magma is LESS dense (and hotter) than solid rock so it rises
formation of magma
- -solid rock is at equilibrium with its surrounding
- -changes in the surroundings may turn solid rock to magma
- -decrease pressure - change composition - raise temp.
magma differentiation
- -partial melting - indiv. minerals melt at diff. T - magma is enriched in siO2 - less dense magma than source rock
- -fractional crystallization - Indiv. minerals precipitate at diff. T - magma enriched in siO2
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Magma vs. lava
magma is molten rock beneath the surface
- -magma solidifies to form INTRUSIVE igneous rocks (granite)
- -magma originates from melting of lower crust and upper mantle
lava is moten rock that has reached the surface
--lava solidifies to form EXTRUSIVE igneous rocks (Basalt)
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mafic magma/laca (Kilauea)
vs. silicic magma/lava
MAFIC
approx. 50% Silica
- -high T (1000 - 1200 C)
- -lots of Fe,Mg,Ca
- -minerals: olivine, pyroxene, CA Plagioclase
- -very hot too
SILICIC magma/lava
- -silica 65-77%
- -lower temp - less than 850C
- -lots of AL, NA, and K
- -minerals: feldspars, Quartz, Micas
- -prdices granite-rhyolite family
basalti magma produce gabbor-basalt family rocks
- -BASALTis most abundant type of extrusive rocks - erupts from fissures to produce thin lava flows
- -VERY HOT
- -masses of igneous rock formed by cooling of magma. beneath surfae called INTRUSIONSA or Plutons
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viscocity
contorlled by silica, and water content and Temp.
--as magma cools, silica tetrahedron form
tendency for material to resist flow - influenced by its siO2 content bc allows it to bond/link together to resist flow - temp. also affects
most igneous rocks form at converent plate margins
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Extrusive rocks "eruptions"
form of eruption. influenced by magma properties
- -composition: silica content and water
- -viscosity - volatile content, Temp.
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basaltic eruptions
--low silica HIGH T = low viscosity
produce:
--shield volcanoes
--lava flows - Pahoehoe
--flood basalts
--fissure eruptions
--spatter cones/cinder cones
--pillow lavas
--COLUMBIA RIVER flood basalts with several thick and thin layers - each layer represents a separate eruption
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volcanic ash - during Mount St. Helon's eruption in 1980, enough ash fell to cover a football field 150miles deep
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Inrusive rocks
intrusions form as magama solidifes beneath the surface
- -less dense magmas rise thruogh the crust
- -rising magmas slowly cool - viscocity and density increase
- -intrusions are classified by SIZE AND SHAPE
- -large intrusions: batholiths, stocks
- -small intrusions: dikes, sills, laccoliths
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occurrence of igneous rocks
found globally - formed in discrete geologic settings
| --convergent plate margins - divergent plate margins - mantle plumes/hot spots
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igneous textures
SIZE AND SHAPE of minerals in the rock
- -relates to COOLING HISTORY of the magma or lava - cooling time
- -slow cooling provides time for crystal growth (big crystals)
- -crystals grow until melt is completely solid
1. glassy
- -very rapid cooling - volcanic glass - no apparent crystals (Obsidian)
2. Aphanitic - find grained texture - few crystals visisble in hand - relatively rapid rate of cooling - bubbles may be formed by gases trapped in cooling lava (Basalt - gas bubbles called VESICLES, Rhyolite)
3. Phaneritic
- -coarse grained - slow rate of cooling - interlocking crystals (granite)
- -grains about the same size
- -magma from exploding volcano produces first 2...these are found after erosion has removed covering rock
4. Porphyritic texture
- -well formed crystals - fine grained matrix - initial stage of slow cooling (large) then later stage of rapid (fine grained matrix)
5. Pyroclastic
- -produced by explosive eruptions
- -matrix may be dominated by glassy fragments - also show distortion
- -forms when crystals, fragments of rock, and glass are blown out of a volcano as hot ash
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Classification of igneous rocks
texture
- -aphanitic
- -phanaratic
composition
- -silicic
- -intermediate
- -mafic
- -ultramafic
texture and composition give rock its name
--igneous rocks are record of thermal history of earth - best known acticity is volcanic eruptions
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Sedimentary rocks
Common at earth's surface - 75% of continents and nearly all ocean basins
- -major layers (formations) are easily reognized
- -smaller layers are bedsets, beds and laminations
- -change grain size, composition, color, or physical features related to deposition
contain evidence of their env. of formation - fossils, bedding, grain size
2 major categories: clastic (sandstone/shale) or chemical and biochemical (limestone/gypsum)
85-95% of mineral products in society come from sedimentary rocks
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Clastic sedimentary rocks
- -made of other rocks and mineral fragments
- -fragmens are broken, worn particles
- -carried to sites of deposition by water, wind, gravity or ice (streams, wind, glaxiers, and marine currents)
- -clastic rocks are sub-divided by grain size
grain size controlled by:
- -size of grains in source rocks
- -carrying capacity of transport proces
- -weathering and erosion that occurs during transportation
common clastic sedimentary rocks (in decreasing grain size order)
- -conglomerate
- -sandstone
- -mudrock or shale (siltstone, claystone)
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chemical or biochemical sedimentary rocks
formed by taking ions from solution to form a solid
- -chemical sediments - precipattes from water (inorganic NACL)
- -biochemical sediments - formed by growth or organisms (Reef)
limsetone, fossiliferous limestone, evaporates (gypsum)
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sedimentary structures
1. formations
- -larg scale stratification - contain numerous indiv. strata
- -consists of a ceratin # of rock strata that have a comparable lithology or similar properties (17000 in US)
- -formations grouped into sequences - groups of formations bounded by erosional surfaces (Represent missing time or change)
2. strata or beds
- -distinct layers having variations in texture, color or physical properties
- -stratification is most significant sedimentary structure
3. surface impressions
--indicate the top of a sedimentary bed
--preserve features indicating past environment (ripple marks, mud cracks)
-- ◦ Ripple marks - seen in streambeds, tidal flats - preserved in rocks and show info. Like depth of water, ancient current directions and trends of ancient shorelines
◦ Mud cracks - show that sedimentary env. Was occasionally exposed to the air during deposition - suggests that original sediment was deposited in shallow lakes or tidal flats -rain prints also preserved in some mudrocks
4. graded bedding
--progressive change in grain size upward through a bed - fining upward
--commonly formed by turbidies - subaquoes flows of "muddy" water - coarsest particles settle first
---Commonly produced on deep-ocean floor by turbidity currents - transport sediment from continental slope to adjacent deep ocean to form bodies of rock called turbidites
• Current generated by muddy water - denser than clear water and sinks beneath it to move rapidly down continental slope
Currents also commonly generated by earthquakes or submarine landslides - transport mud, sand and gravel downslope
5. fossil - indicate paleo-env.
- -detailed study may provide - depth of water, Temp. and salinity, relative age of rock
6. cross-bedding
- -layers are inclined - result of many bedforms passing throug the area - formed by movement of sand by waves or dunes
- -Sand grades moved by wind/water and form small ripples or large dunes (in mountain) - called sand waves
- --Direction of flow from ancient currents determined by measuring direction the strata are inclined - can determine historical current patterns
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sedimentary systems
sedimentary rocks form at earth's surface by the hydrologic system
- -result is new landforms and new bodies of sedimentary rock
- -Most of the energy that derives these systems comes form the sun - gravitational and chemical potential energy also transferred in various parts
work on the earth's surface
- -include:
1. weathering
- -of preexisting rock
- -nteraction btwn elements in atmosphere and rocks on earth - break down and decomposes preexisting rock and forms a layer of loose, decayed rock debris or soil - easily transported by water, wind, or glacial ice
2. transportation (Gravity, water, wind, glaciers)
--of material away from original site
--running water is most effective form - transported, sorted and separated according to grain size and composition
◦ Large particles accumulate in high energy env. - gravel, medium-sized grains are concentrated in sand - finer material settles out as mud
• So large particles carried by rapidly moving streams and small particles by slow streams
3. deposition - most significant factor
- -of eroded material in the sea or other env.
- -Each depositional system imprints specific characteristics on the rocks formed within in - small area creates a facies - a body of rock with distinct chemical, physical, and biological characteristics created by the env.
4. lithification
- -compaction and cementation
final sedimentary rock records the processes that produced it
plate tectonics plays a major role in
- -sediment deposition and geographic distribution
- -sediment source areas
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major sedimentary systems
1. dunes (eolian)
2. alluvial fan
3. playa lake
4. glacier
5. Flufial
6. beach
7. delta
8. tidal flat
9. barrier island
10. organic reef
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sedimentary rocks (Text book)
• Form from fragments derived from (mechanical breakdown and chemical decay) of other rocks and by precipitation from water - typically occur in layers, or strata, separated one from the other by bedding planes and composition differences
--most familiar type of rock to us
originla sediment composed of various substances
◦ Fragments of other rocks and minerals (gravel in river channel, sand on beach, or mud in ocean)
◦ Chemical precipitates (Salt in saline lake or gypsum in shallow sea)
◦ Organic materials formed by biochemical processes (Vegetation in a swamp, coral reefs, calcium carbonate precipitated in the ocean)
impt. be preserve a record of ancient landscapes, climate, mountain ranges - also erosion of the earth
occurs in distinct layers called STRATA (or formations) - layers are separated by BEDDING PLANES - marked by change in composition, grain size, or color
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clastic rocks - conglomerate
consolidated deposits of gravel with some sand and mud in btwn larger grains
- -gravel is smooth and well-rounded - stratified and includes beds and lenses of sandstone
- -high energy req. to transport so usually deposited in high energy env. where water flows rapidly - usually seen today at bases of mountain ranges, stream channels, and some beaches
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clastic rocks - sandstone
1. most familiar, but not most abundant - well exposed, recognized and resistant to weathering
• Can be composed of any material so any color - Quartz is most abundant so most common bc resistant to abrasion or chemical breakdown as particles are transported
• Particles in sand mostly cemented by calcite, quartz or iron oxide
• Composition of sandstone imp. - during long transportation, small rock fragments that readily decompose (olivine, feldspar, mica) break down to fine particles and left with only quartz
▪ Clean, well sorted sandstone is evidence of long transportation or several cycles of erosion and deposition
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clastic rocks - mudrocks
1. Fine-grained - most abundant sedimentary rocks - soft and weather rapidly to form slopes
• Usually deposited in river floodplains and deltas - or shallow-marine env.
• Further break down mudrocks
A. Siltstone - coarser than claystone - angular - flaky minerals like mica and clay
B. Sometimes contains thin layers (laminae) of shale - split easily along these layers to form sheets/flakes
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Biochemical and chemical sedimentary rocks (Text)
1. limestone
* Form when chemical processes remove ions dissolved in water to make solid particles
* Biochemical rocks - sediment formed during growth of organisms like algae, coral or swamp vegetation
* Inorganic chemical precipitates from lakes or shallow seas
LIMESTONE
1. most abundant chemically precipitated rock - composed of calcium carbonate - has variety of textures
• Most form in shallow continental shelves where water is warm and organic production is high
• 3 diff. types are
A. Skeletal limestone
▪ Compacted with shells and shell fragments from ocean floors - CHALK is ex. Bc skeletal fragments are remains of microscopic plants and animals
B. Oolitic limestone
▪ Form where small fragments of shells or tiny grains are coated with CaCO3 - as rolled along seafloor by waves and currents
C. Microcrystalline limestone
▪ Forms in quiet waters where CaCO3 is precipitated by algae as tiny, needlelike crystals that accumulate on seafloor in limy mud
▪ Dense, very fine-grained texture - indiv. Crystals can only be seen with heavy magnification
D. Inorganic limestone - precipitated from springs and from dripping water in caves to form beautiful layered rocks called travertine
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Biochemical and chemical sedimentary rocks (Text)
2. DOLOSTONE
◦ Carbonate rock composed of dolomite - similar to limestone in appearance but only reacts with acid when powdered - brown/yellow color or light gray
◦ Chemically precipitated from biochemical rocks
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Biochemical and chemical sedimentary rocks (Text)
3. CHERT
1. common - composed of microcrystalline quartz - hard, dense, breaks like glass - fibrous and granular texture - white or shades of gray, tan, red, green
• Recognized by color - flint (black) and jasper (red)
• Fractures into sharp edges - used for arrowheads, spear points and tools
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Biochemical and chemical sedimentary rocks (Text)
4. COAL
mp. Biochemical precipitate - forms by decomposition of organic material buried within sedimentary rocks
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Other sedimentary rocks
1. Rock salt - made of mineral halite - crystallized when evaporation concentrates sodium and chlorine ions
• Strong evaporation creates saline Lakes in closed desert basins (SLC)
2. Gypsum - originates from evaporation - collects in layers as calcium sulfate is precipitated form water
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what os env. for metamorphic rocks?
--Rocks that seem puzzling
--Conglomerate with flattened and fused cobbles
Granite with banding
--Rocks made of crystalline calcite but devoid of normal limestone textures and grains
Metamorphic rock is created when some bonds are broken btwn SOME of the ions in a mineral, allowing them to migrate to other sites in the rock and re-bond
---Any rock formed from preexisting rock by solid state recrystallization driven by changes in temp. and pressure and by chemical action of fluids
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metamorphism
• recrystallization change T, P , Or fluid composition - occurs entirely in the solid state - features of the original rock are masked or destroyed
◦ Textural changes occur during metamorphism - new minerals grow, replacing old minerals - env. Of formation influences crystal growth
◦ Plastic deformation
• Rocks at High T and P may be plastically deformed - deformation occurs at wide ranging scales - preferred growth of minerals results from applied stress during deformation
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origin of metamorphic rocks
begins when:
1. Temp. exceeds 200 degrees C
2. Pressure exceeds 2 kb (approx. 10,000 ft. deep)----when melting begins
Temp. effects
- --As T changes minerals become unstable
- --Below 200 C, reaction rates are slow
- --As T increases, reaction rates INCREASE
- --Rocks begin to melt at approx. 700 C
- --Sources of heat for metamorphism:
- --Contact metamorphism (igneous intrusions) - from cooling magma
- --Regional metamorphism (15-30 C increase per km) - metamorphism of deep mountain roots within the crust (close to mantle)
- --Craton across North America (map in power point)
- --Contact metamorphism - GRANITE
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origin of metamorphic rocks 2.
• LOW-GRADE METAMORPHISM - 200 to 350 C and relatively low pressures
• INTERMEDIATE-GRADE - 350 to 550 C and moderate to high pressures
• HIGH-GRADE - very high Temp. usually above 550 C and or very high pressures
Role of fluids
• Aids in the redistribution of elements
• Water and CO2 with dissolved ions - these fluids are at very high T and P
• Move along tiny fractures and btwn crystals
• Hydrothermal alteration creates ore deposits
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deformation
* Uniform stress - indicates that the stress or pressure is the same in all directions - NONFOLIATED
* Differential stress - implies that stress is greater in one direction - FOLIATED rocks
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Metamorphic rocks are classified by TEXTURE AND COMPOSITION
Texture is divided into foliated and non-foliated rocks
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1. Foliated rocks
Slate
- --Fine grained rock
- --Growth is perpendicular to stress
- --Cleavage does not = bedding planes
- --Originate from shales
PHYLLITE
- --Similar in composition to slate
- --Recrystallization has proceed further
- --Crystals are larger - lustrous surface
- --Also from shales
Schist
- --Strongly foliated rock
- --Medium to coarse grained
- --Dominated by platy minerals
- --Lots of accessory minerals
- --Numerous parent rock types
Gneiss
- --oarse grained granular rock
- --Foliation occurs as alternating bands of light and dark minerals
- --Quartz, feldspar, amphibole, biotite
- --Numerous parent rock types
- --May begin to partially melt
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non-foliated rocks
Marble
- --Interlocking, coarse grained calcite
- --Recrystallization of limestone or Dolostone
- --Marble
- --Dolomitic marble
- --Sedimentary features are destroyed
Quartzite
- --Metamorphism of quartz sandstone
- --sandstone is filled with silica cement
- --Entire rock is recryst
- --allized
