Midterm 2 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
<p>TOPIC QUESTION: What are the different by particle sizes in sedimentary rocks?</p>
<p>1. Boulder size (>;256mm)
2. Cobble size (64-245mm)
3. Pebble size (4-64mm)
4. Granule (2-4mm)
5. Sand size (0.06-2mm)e.g. sandstone
6. Fine grained or slit particles (0.06- 0.004mm)e.g. shale/siltstone
7. clay size particles (<0.004)e.g. clay stone </p>
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 for five 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 (patent rick) 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
