Final (prior to second midterm) Flashcards
TOPIC QUESTION What are some volcanic hazards?
- Intrusive igneous activity
- Granitic and andesitic melts are higher in silica and therefore more viscous than basaltic magmas - Gas content -
Magmas contain dissolved gases (violations - water vapour, CO2, SO2, H2S) as magma rises pressures decreases - gases come out of solution to form bubbles
TOPIC QUESTION What are the three types of caldera formed by volcanic eruptions?
- Crater lake type - collapse of the summit of a large stratovolcano
- Hawaiian type - caused by the collapse of the top of a shield volcano by subterranean damage
- Yellowstone type - caused by collapse of a large area by discharge or pyroclastic material
TOPIC QUESTION Hot lava that is low in viscosity will result in what type of eruption style?
Effusive
TOPIC QUESTION A low viscosity basaltic lava flow would form what type of volcano?
Shield volcano
TOPIC QUESTION What are the characteristics of a stratovolcano or composite cone?
- are made of alternating layers of lava and ash (other volcanos just made of lava)
- eruptions from these volcanos may be pyroclastic flow rather than lava
- flow can roll down sides very fast with temperatures over 400C
TOPIC QUESTION How do gases effect eruption style?
- gases create explosions if they cannot easily escape from viscous magma
- they can be released without explosion from less viscous magma in an effusive style
TOPIC QUESTION What is the effect of the temperature of the lava on the eruption style?
- the higher the lava temperature the lower the viscosity of the lava, high temperature lava will be less viscous and have an effusive eruption style
- low temperature lava is less viscous and more likely to have an explosive eruption style as they do not flow easily
TOPIC QUESTION What are the characteristics of a cinder cone volcanos?
- Made of unconsolidated material (rejected pyroclastic material)
- have a large crater
- Steep sided 30-40 degree angle < 300m high
- Single, short lived
eruptive event (days or years) - Fields (Arizona) or parasitic cones (on the flanks of a larger volcano)
TOPIC QUESTION What are the characteristics of a stratovolcano (composite cone)?
- Dangerous/ violent
- Periodic eruptions
- conical shape/steep summit
- eruption of gas rich and esitic lava or rhylotic pyroclastic - lava is viscous in nature
- Some fluid basaltic video
TOPIC QUESTION How is a caldera formed?
- By collapse of the summit of a large stratovolcano (crater lake type caldera)
- By collapse of the top of a shield volcano by subterranean drainage of magma (Hawaiian type caldera)
- By collapse of a larger area caused by huge discharge of pyroclastic material (Yellowstone type caldera)
TOPIC QUESTION Describe the composition of a shield volcano
Shield volcanos are broad dome shaped structures with gently sloping sides
They are composed of accumulated basaltic lava flows that is low viscosity and runny
They have large circular depressions (caldera) at the summit
They have frequent but gentle eruptions
i.e. Olympus Mons on Mars
What is the theory of plate tectonics?
Describes the large scale motion of the lithosphere
- theory is that the Earth’s outer shell (lithosphere) is divided into several plates that glide over the mantle
Combination of two earlier ideas continental drift and sea floor spreading
Explain how the modern theory of plate tectonics arose
- Came from Alfred Wegener’s hypothesis of Continental Drift (1915)
- Which came from Edward Seuss idea of the supercontinent (1831-1914)
TOPIC QUESTION What is the evidence to support modern plate tectonics theory
- Fits of continents
- similarity between coastlines
- tried to fit shorelines but instead need to look at the seaward edge of the continental shelf - Fossils
- fossils of mesosaurus found only in black shale from the Permian (~250ma) in eastern south America and Southern Africa
- if it could swim far enough to cross the ocean the fossil would be widespread and it is not and it only lived in freshwater - Rock types and structure match
- rock types and mountain belts found in separate continents match in age, rock type and fossil - Ancient Climates -
paleoclimatic support for the idea of mobile continents
- possible coral reefs in Alberta
- glacial sediments in Southern Africa, South America, India and Australia
- tropical ice sheets rejected because fossils of the same age from other locations indicate warm climates
Interpretation of largest pre-existing data set can help test theory
- ocean drilling programs
- mantle hot spots
- paleomagnetism
- earthquake depths
- age of crust
TOPIC QUESTION What are the issues with Wegener’s theory?
- compelling evidence but idea was not accepted until 1960
- Wegener was unable to find a mechanism by which continents could move
- gravitational forces of the moon and sun refuted because forces that string would stop the earth’s rotation
- icebreaker continents were refuted because no evidence suggesting the ocean floor was weak enough
TOPIC QUESTION Describe the three types of plate boundaries?
- Divergent boundaries
- two plates move apart and creates new lithosphere (constructive margins) - Convergent boundaries
- plates move together and lithosphere is destroyed (destructive margins) - Transform fault boundaries
- lithosphere is neither created or destroyed
TOPIC QUESTION Describe divergent plate margins
- ocean ridges spread between 2-15cm per year average 5cm
- elevated - new oceanic crust is hotter and larger volume
- ocean lithosphere away from the ridge cools and contracts increasing its density
- accumulates sediment
- site of submarine volcanoes and earthquake activity
- ridge ~2-3km above ocean floor pillow basalt in ocean floor
- continental rifting - divergent plate boundaries can develop within continents
- cause landmass splits like break up of Pangaea
TOPIC QUESTION Describe the three types of convergent plate convergences?
- Oceanic - continental
- example - western margin of the USA which is the subduction of the Juan de Fuca plate
- associated with volcanic arc because water is squeezed from subducted plates, which lowers the melting temperature of surrounding rock
- magma is less dense and rises - Oceanic-oceanic
- When an oceanic plate meets another one cosmic plate the thicker more dense plate subducts
- example Aleutian Islands, Japan, The Antilles, most of the west pacific
- typically, simple structures made of numerous volcanic cones undressing by oceanic crust (<20km thick) - Continental - continental
- also called collision boundaries
- examples Himalayas, alps, Appalschians, Urals
TOPIC QUESTION Describe and explain the characteristics of transform plate boundaries
- plates slide horizontally past one another with destroying or creating new lithosphere (conservative)
- most occur in ocean basins (offsets along mud-Atlantic range) a few occur in continental crust (e.g. San Andreas fault)
- transform fault running length of California’s coast located at the boundary between the Pacific and North American plates
TOPIC QUESTION Diagram and explain the plate tectonic cycle
No answer will need to look up diagram and explanation
- Mantle convection
- Ridge push
- slab pull
TOPIC QUESTION Define weathering
The various mechanical and chemical processes that cause exposed rock to decompose
The physical breakdown (disintegration is mechanical) and chemical alteration (decomposition) of rick at or near the earth’s surface
TOPIC QUESTION Define and provide examples of mechanical weathering
Rocks broken down into smaller pieces by physical forces but the mineral composition remains unchanged
- e.g. frost wedging, pressure release (granite), wind sculpting (Bolivia), clam boring
- mechanical weathering adds to the effectiveness of chemical weathering because it increases the surface area of the rock exposed to chemical attack
TOPIC QUESTION Define and provide examples of chemical weathering
Alternation of internal structures by removing or adding elements which leads to solid particles and ions in solution
- weak acids like carbonic acid (H2CO3) in rain and groundwater react with minerals to destroy their crystalline structure as can oxygen (oxidation) in the atmosphere
- dissolution - rock is dissolved usually by an weak acid like carbonic acid making limestone caves, rarely rocks are dissolvable in water (halite is water soluble)
- hydrolysis - chemical reaction with water, silicates decompose primarily through hydrolysis, hydrogen atom attacks and replace K+ in Feldspar structures
- clay minerals are end products of weathering and are very stable under surface conditions
- shale the most abundant sedimentary rock is made mostly of clay
- quartz is highly resistant to chemical weathering
TOPIC QUESTION What are the three types of chemical weathering
- Hydrolysis
- Dissolution
- Oxidation
TOPIC QUESTION Describe the chemical weathering process of oxidation
Oxidation can only occur after Fe (iron) is freed from the silicate structure by hydrolysis
- rust color that appears in some rocks from removal of an electron from iron 4 Fe + 3O2-> 2Fe2O3
- presence of water speeds up the oxidation reaction
TOPIC QUESTION What factors control weathering?
- Rock type
- mineralogy
- sensitivity of ions in crystal to chemical weathering
- strength - interlocking crystals (igneous, metamorphic) or cemented (sedimentary)
- structure and loading history
- thermal expansion rates - Climate
- temperature
- moisture
- availability
- vegetation
- soil/ground water chemistry - Diagenesis
- Lithification
TOPIC QUESTION What is the definition of diagenesis?
Collective term that includes all chemical, physical, and biological changes that take place after sediment is deposited and during and after lithification
What are the two main process of lithification
- Compaction
- packing sediment grains through burial, reduces volume by 40% and desiccation (loss of water from pore spaces resulted by from compaction/evaporation) - Cementation
- minerals precipitate from sediment pore fluids to bind grains together most common cements are calcite (CaCO3) and quartz (SiO2)
TOPIC QUESTION What are the classes of sedimentary rocks
- Detrital
- solid particles from weathered rocks
- sandstone, shale, claystone - Chemical
- soluble materials (chemical weathering) are re-precipitated either in an inorganic or biochemical process (limestone) - Organic (coal) - carbon rich remains of organisms
TOPIC QUESTION What does the shape of sedimentary rocks indicate?
Degree of weathering or time involved in transportation of sediments by current of air or water
- more rounded means greater degree of abrasion and therefore transportation Substantial weathering and long transportation lead to gradual destruction of weaker or less stable minerals.
- quartz is durable but Feldspar and ferromagnesian silicates are not
TOPIC QUESTION: What are the different by particle sizes in sedimentary rocks?
- Boulder size (>;256mm)
- Cobble size (64-245mm)
- Pebble size (4-64mm)
- Granule (2-4mm)
- Sand size (0.06-2mm)e.g. sandstone
- Fine grained or slit particles (0.06- 0.004mm)e.g. shale/siltstone
- clay size particles (<0.004)e.g. clay stone
TOPIC QUESTION explain sorting and particle shape
Sorting refers to the range of particle sizes present in the rock
- can be very poorly sorted (wide range of size of particles) to very well sorted (rocks of particles are all very nearly the same size)
- Shape described in terms of angularity which is the degree to which edges and corners can be are rounded and sphericity (how close the shape is to a sphere)
- shape can be angular, subrounded or well rounded and high sphericity or low sphericity - e.g. conglomerate has rounded particles while breccia has angular particles
TOPIC QUESTION Describe the characteristics of chemical sedimentary rocks
- soluble materials produced by chemical weathering
- precipitation results in chemical sediments which can then undergo a physical or biochemical process to form sedimentary rocks e.g. salt left behind as water evaporates (DeadSea) or gypsum and sylvite
TOPIC QUESTION What is the definition of erosion
Process by which soil and rock particles are worn away
TOPIC QUESTION What is transport
Process of moving rock particles by gravity or a transporting agent
- wind, water or ice
TOPIC QUESTION Explain how different sedimentary rocks form
- Detrital sedimentary rocks are from weathered rocks
- Chemical sedimentary rocks are soluble materials from chemical weathering that are re-precipitated; also biochemical process such as water dwelling animals extract dissolved minerals to form shells
- organic sedimentary rocks are carbon rock remains from organisms
TOPIC QUESTION define lithification
Is the process in which unconsolidated sediments are converted to sedimentary rock 2 processes
- compacting
- Cementation
TOPIC QUESTION identify different continental, marine and transitional sedimentary environments, their depositional energies and size of sediment deposited
Continental environments 1. Alluvial fan 2. Fluvial river 3. Lacustrine (freshwater lake) 4. Deserts 5. glacial 6. Swamp (Paludal) 7. Evaporitic lake (inland sea)Transitional environments 8. Deltas 9. Beaches and barrier islands 10.Lagoons 11. Tidal flats Marine environments 12. Coral reef 13. Continental shelf 14. Continental slope and rise 15. Abyssal plain High energy - waves and currents have larger grain size, well to poor sorted dependent on transportation and rounded grains examples - fluvial (stream), alluvial fan, beach, desert, glacial deposits, delta, reef Low energy - small grain sizes, generally well sorted, quiet waters allow clays and silts to settle Examples - lakes, abyssal plain, lagoon, swamp
TOPIC QUESTION identify and Describe several sedimentary structures and correlate them to possible depositions environments
- Stratas and beds are the most common and characteristic feature of sedimentary rocks
- variations in texture, composition and thickness reflect the different conditions under which each layer is formed
- ripple marks (high energy, beach)
- helminthopsis- graded bedding (delta)
- mud cracks
- trace fossils (lakes)
- cross bedding (sand dunes, river deltas and steam channels)
TOPIC QUESTION Describe transport and deposition of sediments
- soluble products of chemical weathering become dissolved in groundwater and streams
- chemical and mechanical weathering decompose and disintegrate rock
- gravity moves solid particles down slope
- rivers, glaciers and wind transport sediment
- deposition of solid particles produces glacial ridges, dunes, flood plains, deltas, and ultimately reaches the ocean floor
- as sediment is buried it is compacted and cemented into solid rock
- when material dissolves in water precipitates it is the source of such features as reefs and deposits rich in shells
TOPIC QUESTION name the major sedimentary rock forms
1 detrital
- conglomerate, breccia, sandstone, siltstone, shale
2. Chemical and organic - crystalline limestone, travertine, coquina, fossikerous limestone, chalk, chert, flint, rock gypsum, rock salt, bituminous coal
Define metamorphism
Transformation of one rock type into another rock type
The parent rock (prolith) turns into metamorphic rock In this process the mineralogy, texture and sometimes chemical composition of prolith is changed Low grade changes are slight changes while high growth are changes are substantial changes
TOPIC QUESTION - What are mineral polymorhps and how can they be used to differentiate dentists between high and low grade metamorphism
Minerals with the same chemical composition but different structure Respond similarly to changing temperature and pressure conditions Therefore can be used to differentiate between high and low grade metamorphism dependent on type of polymorphism present
E.g andalusite low temp low pressure indicate low grade metamorphism while siliminate is made high temp and high pressure indicate high grade metamorphism
TOPIC QUESTION What are the four agents of metamorphism
- Heat
- Confining Pressure
- Directional stress
- Chemically active fluids
TOPIC QUESTION Explain the impact of heat on metamorphism
- provides energy for chemical reactions to recrystallize existing minerals
- the newly formed mineral grains tend to be larger than the original grains
- mineralogy may or may not change
- source is geothermal gradient or rising magma
Geothermal heat- temperature increases as move downward from upper crust - different minerals are stable at different depths (different temperatures)
- clay unstable at ~8km (200C)
- quartz and feldspar alter at higher temperatures
Rising magma- cools by releasing heat to surrounding rock - bakes host rock
TOPIC QUESTION Explain the impact of pressure on metamorphism
Pressure increases with depth
Confining pressure is equal in all directions
- pressure increases with depth
- causes pore spaces to close
- can cause atoms in minerals to pack more closely
- can cause phase change
- does not fold or fracture rock
Differential pressure stress is greater in one direction then another
- compressional strength results in shortening in direction of greatest pressure
- occurs at convergent boundaries
- crust is shortened and thickened
- rocks are ductile in high temperature, high pressure
- minerals can be flattened when subjected to differential stress
- deform by flowing and folding
TOPIC QUESTION Explain the impact of chemically active fluids on metamorphism
- hot fluids (water and CO2) surround mineral grains and act as catalysts for ion migration
- speeds up recrystallization
- hot fluids transport matter long distances
- ion exchange between solution and hot rock
TOPIC QUESTION name and describe common non-foliated metamorphic rocks
- Marble
- medium to coarse grained
- relatively soft 3 on Mohs scale
- interlocking calcite or dolomite grains
- prolith (parent rock) limestone or dolostone - Quartzite
- moderate to high grade
- medium to coarse grained
- very hard
- massive
- fused quartz grains
- prolith (parent rock) quartz or sandstone - Hornifels
- baked by intruding magma body
- fine grained
- variable composition
- grey to black in color
- exceedingly tough and durable
- prolith (parent rock) often shale but can have any composition
TOPIC QUESTION What is the difference between foliated and non-foliated textures
Foliated
- any planar (nearly flat) arrangement of mineral grains/structural features within a rock
Non -foliated
- metamorphic rocks with interlocking crystals
TOPIC QUESTION name and describe common foliated rocks and order then by metamorphic grade
- slate (low grade)
- prolith (parent rock) shale, mudstone or siltstone
- very fined grains bed, has mica, chlorite, with some quartz and feldspar
- breaks in flat slabs called slaty cleave
- preexisting sedimentary bedding may still be apparent
- smooth dull surface
- can be black, green or red - phyllite (intermediate grade)
- no evidence of prolith remains
- prolith (parent rock) shale, mudstone or siltstone
- continued from slate
- mineral crystals especially micas are visible
- pronounced wavy foliation breaks along wavy surface
- shinier then slate, glossy sheen - schist (medium to high grade metamorphic rock)
- further continuation from phyllite
- parent rock or prolith - shale, slate or mudstone
- minerals are medium to coarse grained
- platy minerals dominant
- scaly foliation
- can have biotite and muscovite mica, quartz, K and Na feldspar, garnet and siliminate
- very shiny metallic appearance
- schistose foliation - gneiss (high grade metaphoric rock)
- further continuation from phyllite and schist
- prolith or parent rock - slate, granite or volcanic rocks
- minerals are medium to coarse grained
- granular and elongated minerals dominate
- quartz, K and Na feldspar, biotite and muscovite mica, amphibole, garnet and silimanite
- very distinct segregation into wide bands (gneissic foliation)
- often resembles granite apart from banding
- much of Canadian Shield
TOPIC QUESTION What are temperature, pressure and geologic environment for contact or thermal metamorphism
By contact with magma
- rock is intruded by magma
- high temperature 600-1000c but low pressure less than 2 kilobars
- close to surface
- types of metamorphic rocks produced are non- foliated type depends on prolith
- many different metamorphic rocks can be produced at the same time
TOPIC QUESTION What are temperature, pressure and geologic environment for hydrothermal metamorphism
Hot fluids (geysers, hot springs)circulate through cracks in a rock causing chemical alternation by enhancing recrystallization
- can be low to high temp 0-400C
- low pressure
- close to surface
- produce non-foliated metamorphic rock
TOPIC QUESTION What are temperature, pressure and geologic environment for burial metamorphism
Huge amounts of sediment or volcanic material accumulated in a basin
- deeper in the ground ~8km
- low temp around 200C and low to medium pressure
- form non-foliated metamorphic rock
TOPIC QUESTION What are temperature, pressure and geologic environment for subduction metamorphism
Rock and sediment carries to great depths (oceanic plate)
- low temperature
- high pressure
- deep
- differential stress can produce foliation
TOPIC QUESTION What are temperature, pressure and geologic environment for regional metamorphism
Common, widespread type of metamorphism.
Typically associated with mountain building where large portions of the crust are intensely deformed by collusion of two crystal blocks
- variable temp and pressure but highest of both core regions
- foliated rocks
- folding and faulting also common
TOPIC QUESTION define metamorphic facies and identify temperature, pressure and the tectonic environment where each is created
Metamorphic facies means metamorphic rocks formed in a very similar metamorphic environment Metamorphic rocks that contains the same set of minerals belong to the same metamorphic facies Subduction zone (ocean-continent) Eclogites facies - high temp - extremely high pressure - very deep Blueschists facies - low temperature - high pressure Hornfels facies - low to high temp - low pressure - from contact and hydrothermal metamorphism Subduction zone (continent-continent) - dominated by regional metamorphism Zeolite facies -low temp - low pressure -burial metamorphism Greenschist facies - med temp - med pressure Amphiobiotite facies - medium temp - med to high pressure Granulite facies - high temp - high pressure Passive margin dominated by burial metamorphism and therefore zeolite facies Divergent boundary dominated by hydrothermal metamorphism
TOPIC QUESTION Explain how index minerals are used to differentiate between high and low grade metamorphism
Index minerals are used to establish the metamorphic grade of a rock
- index minerals form over a specific pressure and temperature range and therefore are good indicators of the environment in which they are formed
E.g cholrite forms at low temp and pressure indicate rocks with chlorite are low grade while siliminate forms at high temp and pressure indicate high grade
What is a galaxy?
A massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component called dark matter
Explain the big bang
- massive blast 13.7 Ga forms all the universe’s known matter and energy
- even space and time
- Immediately after, universe expanded within comprehensible speed from pebble-size origin to astronomical scope
- Expansion has continued, but much more slowly, over ensuing billions of years.
Explain the term universe
- equals all of time and space and its contents.
- Includes planets, stars, galaxies, the contents of intergalactic space, the smallest subatomic particles, and all matter and energy.
What is the Nebular Theory?
Earth and other planets formed at the same time from the same primordial material as the Sun
- collapse of a giant molecular cloud ~5 billion years ago
Gravity pulls the gas and dust together (starts to rotate)
- first material to condense is chondrules
- Forms a solar nebula (dust cloud)
- as the nebulae cooled more rock, icy, metallic material condensed and impact collisions caused accretion (growth)
- two broad category of planets formed the inner terrestial planets and the outer gas planets
- which is a function of distance and temperature from the sun ((division is known as the frost line) - Composition: is Hydrogen (H) and helium (He) with small amounts of heavier elements (C, O,Si, Fe etc.)
There is conservation of angular momentum; the nebula spins faster as it collapses which causes inward pull of gravity balanced by outward rotational movement of nebula changing from cloud to flat disk and a protostar forms as the cloud continues to flatten
What are chondrules?
The first molten particles to condense out of the nebula
What is a planet?
celestial body orbiting a star, massive enough to be rounded by its own gravity but is not massive enough to cause thermonuclear fusion and has cleared its neighboring region of planetesimals
What is a moon?
a celestial body that orbits a planet or smaller body, and is non-artificial
What are the Jovian planets in our solar system?
Jupiter, Saturn, Uranus and Neptune
What are the terrestrial planets in our solar system?
Earth, Venus, Mars and Mercury
How do scientist belief the Earth’s moon was formed?
Giant Impact Hypothesis: the moon formed by collision of a Mars-sized body ~4.5 Ga when the Earth was semi-molten
Where are most comets found?
Kuiper Belt hosts short-period comets (+ asteroids and dwarf planets)
[=> orbital period around the Sun <200 yrs]
- Oort Cloud - edge of the solar system hosts long-period comets
What is a dwarf planet?
celestial body orbiting the Sun that is massive enough to be rounded by its own gravity but has not cleared its neighboring region of planetesimals and is not a satellite
What is planetary differentiation?
process of separating different constituents of a planetary body as a consequence of their physical and/or chemical behavior which results in compositionally distinct layers
Chemically the earth’s crust in the continental region is composed of _________
felsic (granite_
- rich in feldspar and silica (quartz)
- some facts
- average thickness 35-40 km
- density 2.7g/cm3
Chemically the earth’s crust in the oceanic region is composed of ________
mafic (basalt)
- rich in magnesium and iron
- some facts
- average thickness 7 km
- density 3.g /cm3
The mantle of the earth is composed of _______
ultramafic
The boundary between the crust and mantle is called the Moho
The core of the earth is composed of _______
FeNi (IronNickel) metal with small amounts of oxygen and sulfur
- density 11 g/cm3
The earth’s core is divided based on _______ properties
physical- inner core is solid- outer core is liquid
Explain the difference between the lithosphere and the asthenosphere
The lithosphere is composed of the crust and upper mantle, average thickness is 100km. It is cool and has a rigid outer layer. The asthenosphere is beneath the lithosphere it is softer and hotter and its rock behaves plastically (can deform slowly)
- contains the lower part of the upper mantle and the transition zone between the mantle between the upper and lower mantle
Do the lithosphere and asthenosphere move dependently or independently of each other?
independently
The earth’s interior can be layered by physical properties which include
Whether the layer is liquid or solid, strong or weak.
The earth’s interior can be layered by chemical properties which include
The chemical composition of the layer
What is a seismic wave?
Waves of force that travel through the earth
- they result from an abrupt release of stored energy and occur naturally
What are body waves?
Seismic waves that move through the interior of the earth they can be primary or secondary
What are surface waves?
Seismic waves that travel near the Earth’s surface
What are the three types of rocks found on earth?
Igneous - molten rock that cools and becomes solid
Sedimentary - form by sedimentation of material at the earth’s surface or within bodies of water
Metamorphic - transformation of an existing rock as a result of changing temperature and pressure conditions
What is geologic time in terms of relative dating?
determines the sequential order of prehistoric events but not exactly when they occur
What is geologic time in terms of absolute time?
Gives an exact age using radiometric dating (natural occurrence of radioactive elements in nature)
Explain the rock cycle
Weathering of rocks on the surface –> erosion and transport –> deposition of sediment –> burial and compaction –> SEDIMENTARY ROCK–> deformation and metamorphism –> METAMORPHIC ROCK –> melting –> crystallization of magma –> IGNEOUS ROCK –> weathering of rocks at the surface
What are the key principles for relative dating?
- Principle of Superposition
- Principle of original horizontality
- Principle of lateral continuity
- Principle of cross-cutting relationships
- Fossils
What is the law of superposition?
In an undeformed sequence of sedimentary rocks, the youngest rocks are on the top and the oldest rocks are at the bottom”
What is the law of original horizontality?
- Sediment layers deposited in a horizontal position
- Flat rocks retain their original horizontality
- Folded or inclined rocks were moved after deposition
What is the principle of lateral continuity?
- sediment layers spread out until they reach an obstacle that keeps them from spreading further
- Allows relating rock layers over distances (correlation)
What is principle of crosscutting relationships?
- Rock fragments enclosed within another (xenoliths); the inclusion must be older
- Igneous rock cutting across sedimentary layering
Why are fossils are important for geologic dating?
- Fossils document the evolution of life throughtime
- Remains or traces of prehistoric life (paleontology)
- What is preserved are the hard parts
What are index fossils?
Geographically wide spread fossils that existed for a geologically short period of time (~100,000 years or less)
What are trace fossils?
- Ophiomorpha are a geographically wide-spread trace fossil
- Appeared ~400 Ma and are still forming today
- Provide information about animal feeding behaviour and environment (soft sediment)
What are the three common mechanisms of radioactive decay that are used in determining absolute geologic time?
- Alpha Emission = parent nucleus emits an alpha particle which is 2 protons and 2 neutrons
- Beta Emission = Parent nucleus emits a beta particle which is an electron that was part of a neutron
- Electron capture: proton captures an electron to become a neutron
Why is radiometric dating important in geology?
- Radiometric dating is important because radioactivity is a“clock” for numerical ages because the rate of decay for a given isotope is constant and can be measured
- Half life = the time required for exactly one half of the nuclei in the parent
isotope to decay
What are the subdivisions of geologic timescale?
Eons > Eras >Periods > Epochs Eons • Hadean (4.57 – 4.0Ga) • Archean (4.0 – 2.5Ga) • Proterozoic (2.5 Ga– 542 Ma) • Phanerozoic (542Ma to present)
What is uniformitarianism?
Uniformitarianism, in geology, the doctrine suggesting that Earth’s geologic processes acted in the same manner and with essentially the same intensity in the past as they do in the present and that such uniformity is sufficient to account for all geologic change. This principle is fundamental to geologic thinking and underlies the whole development of the science of geology. BUT geologic processes have not always had the same relative importance nor have they operated at the same rate.
Explain how minerals are classified
- you must use multiple properties to definitively identify minerals
- follow the flow charts in your lab manual
- use diagnostic properties to your advantage (i.e those properties that help differentiate similar minerals or similar appearance)
Define the characteristics used to describe minerals
Optical properties
- luster (how a mineral surface) reflects light
- ability to transmit light
- color-streak (the color of a powdered mineral made by scratching it on a porcelain plate)
Crystal shape or habit (the external shape of the mineral)
Mineral strength
- hardness (scratchability of a mineral
- how easy one mineral scratches another)
- tenacity (resistance to breaking or deformation)
- cleavage (tendency for a mineral to break along planes of atomic weakness)
- fracture (how a mineral breaks when it does not yield cleavage)
Density and specific gravity
Other mineral properties
- taste
- striations
- odor
- acid reaction
-magnetism
- fluorescence
- double refraction
Explain the four types of atomic bonds relevant to minerals
- stated as an outcome for topic 4 but nothing in notes for that week
Identify whether a mineral is a silicate or non-silicate
- stated as an outcome for topic 4 but nothing in notes for that week
Identify silicate mineral structures
- stated as an outcome for topic 4 but nothing in notes for that week
Differentiate between magma and lava
Magma is composed of Molten rock and is stored in the Earth’s crust. Lava is magma that reaches the surface through a volcano vent.
Explain how igneous rocks are classified
Igneous rocks can be:
1. Intrusive - cooling within the earth, because it cools very fast minerals are small
2. Extrusive - cooling at the earth’s surface or very close to it, because it cools over a long period of time minerals grow larger
Note: color is very important in identifying different minerals in that rock as it formed in a rock by using
Bowen’s reaction scale - different minerals form at different temperatures
Calcium rich minerals form at high temperatures and sodium rich rocks form with less temperature
Differentiate between magma and lava
Magma is composed of partial or completely molten rock and is stored in the Earth’s crust. Lava is magma that reaches the surface through a volcano vent.
Describe the different types of intrusive igneous structures
Tabular intrusive structures
Dikes - a tabular igneous body that cuts across sedimentary structures or other linear features (discordant)
Sills - are formed from magmas that entered the country rock parallel to the bedding layer and are horizontal tabular igneous intrusions, concordant with the country rock
Both dikes and sills are shallow features
Massive Intrusive structures
Plutons- are discordant intrusive rock formed at great depths - are large, course grained and irregular in shape
-Batholith - a pluton that is larger than 100km2 is the largest of the intrusive bodies
Are almost always felsic and intermediate rock types
- Stocks - a pluton that is less than 100km2
Explain the difference between mafic and felsic igneous rocks
Mafic is composed of minerals rich in Magnesium and Iron, has a higher melting point, it is higher density 3.0g/cm3 and is found primarily in oceanic crust
Felsic - is composed of minerals rich in Feldspar and silica, it has a lower melting point than Mafic, lower density 2.7mg:cm3 and is found predominantly in the continental crust
