Chapter 2 Flashcards
What are the four sub-cycles of the geologic cycle?
- Tectonic cycle
- Rock cycle
- Hydrologic cycle
- Biogeochemical cycle
What is the tectonic cycle?
Large scale geologic processes that deform the Earth’s crust producing landforms such as ocean basins, continents, and mountains
What are the lithosphere and crust?
The outer layers of the Earth, which as stronger and more rigid, that reach to about 100 km
What is the lithosphere broken into?
Lithospheric plates that move relative to one another, in a process collectively known as plate tectonics
What is the athenosphere?
A hot and plasticky flowing layer of relatively low strength rock about 250 km deep that is thought to be continuous
What is a subduction zone?
An area on a convergent plate boundary where the expanding plate is pushed beneath another plate
What are the inner layers of the Earth, from outside in?
Asthenosphere, mantle, outer core, inner core
What are divergent boundaries?
Where new lithosphere is being produced, which pushes the plates away from the ridge
What is are examples of a divergent boundary?
Mid-ocean ridges and continental rift valleys
What are convergent plate boundaries?
When plates are colliding
Which type of plates are typically subducted at convergent plate boundaries?
Oceanic plates that have higher density will be subducted under continental plates
What is a continental collision boundary, and what is an example of this?
When two colliding plates are composed of continental rocks, instead of one subducting, both plates instead crumple to form mountains. An example is the Himalayas
What are the three convergent plate boundary subtypes?
Continental-continental, continental-oceanic, oceanic-oceanic
What occur at C-C boundaries?
Major young mountain belts and shallow, frequent earthquakes
What occur at C-O boundaries?
Major volcanic mountain belts, subduction zones and deep oceanic trenches, and earthquakes
What occur at O-O boundaries?
Subduction zones where older, denser plate sinks below the younger, less dense ocean plate; deep oceanic trenches, volcanic island arcs, and wide earthquake zones
What is a transform boundary and provide an example?
Occurs when the offset segments of two plates slide past one another. San Andreas Fault
What is the likely mechanism that causes plate tectonics?
Earth’s interior convection
What is the rate of plate movement?
About a few centimeters per year, though the rates of movement changes over time
What is Wilson’s cycle?
A cycle that describes the continuous creation, movement, and destruction of the Earth’s crust
What are hot spots?
Places on Earth where volcanoes have magma source from deep mantle or possible core-mantle boundary
What are two examples of hotspots?
Hawaii and Yellowstone National Park
Why is knowledge of plate tectonics useful in environmental geology?
- Typically indicates where zones of resources are located
- Earthquake zones and volcanic activity
- Landscape and climate impacts
- Foundation for urban development and hazard mitigation
What is a rock?
An aggregate of one or more minerals
What is the rock cycle?
The largest geologic sub-cycle, by which rocks are formed from magma, eroded, deposited, lithified, and metamorphized.
What is the hydrologic cycle?
A solar driven process by which water is evaporated, transpired, precipitated, and involved in runoff or subsurface flow processes
What percentage of water is non-ocean surface water?
~0.3%
What percentage of water is oceanic?
97%
What is the biogeochemical cycle?
The transfer or cycling of an element through the atmosphere, lithosphere, hydrosphere, and biosphere
What are 5 reasons rocks and minerals are important?
- Fundamental building blocks of Earth
- Used in various modern economic developments
- Indicators of Earth’s history
- Mineral and rock knowledge necessary for resource management
- Important factors in the environment and for human health
What is a mineral?
A substance made of an element or chemical compound that has a definitive chemical composition, a crystalline structure, that is generally inorganic and solid and formed by natural geologic processes
What is a crystalline structure?
Orderly, regular repeating internal atomic arrangement
What are 5 diagnostic properties for minerals?
Color and streak, luster, cleavage, crystal form, and hardness
What are some special properties of minerals?
Smell, taste, feel, reaction to acid, and magnetism
How many minerals are there?
Over 4000
How many minerals roughly are common on or near Earth’s surface?
A few dozen
What are silicates?
Contain Si-O tetrahedron as a fundamental building unit
What is the most abundant mineral group in the Earth’s crust and at what percentage does it appear there?
Silicates and about 75% by weight
What is an example of a silicate?
Quartz
How does quartz fracture?
Conchoidally
Where is quartz most common?
River and moist beach sands, as it is resistance to most other forms of natural breakdown
What are feldspars? What is the alternate name for them?
Silicates composed of Si, O2, aluminum, and some K, Na, Ca; aluminosilicates
What color are feldspars generally?
White, pink, and gray
What industries are silicates important in?
Ceramics and glass industries
What do silicates generally weather chemically into?
Clays
What are ferromagnesian minerals?
Silicate minerals formed from Si, O2, Fe, and Mg
What colors are ferromagnesian minerals?
Generally dark colors
What are two examples of ferromagnesian minerals?
Biotite and pyroxene
What do ferromagnesian minerals generally weather into?
Rust, clays, and soluble salts
Are ferromagnesian minerals resistant to weathering?
No, very susceptible to weathering and erosion
What are carbonates?
Minerals consisting of the carbonate ion CO3 (2-)
What are two examples of carbonates?
Calcite and dolomite
What is calcite a major constituent of?
Limestone and marble
What are oxides?
Minerals containing oxygen atoms bonded to an atom of another element
What are two examples of oxides?
Hematite (FE2O3) and Bauxite (AL203)
What are sulfides?
Minerals containing sulfur atoms bonded to one or more metallic elements
What are two examples of a sulfide?
Pyrite (FeS2) and Galena (PbS)
What environmental effect are sulfides commonly associated with?
Acid rain
What are native elements?
Minerals made of a single element
What is a rock?
An aggregated solid composed of minerals
What are the three classifications of rocks?
Igneous, sedimentary, metamorphic
How are igneous rocks formed?
Cooled and crystallized/solidified from magma
What are intrusive rocks and provide an example?
Igneous rocks formed beneath the Earth’s surface that are coarse grained and where individual minerals can be seen due to slow cooling and crystallization; granite
What are extrusive rocks and provide an example?
Igneous rocks formed at or near the Earth surface; basaltic rocks
What is pyroclastic debris?
A form of extrusive igneous rocks form when magma is ejected from a volcano
What are the three types of pyroclastic debris?
- Volcanic ash (4mm or less in size)
- Tuff
- Breccia or conglomerate
What is tuff?
Compacted, cemented, or welded ash and is generally a very soft rock
What are the three types of igneous rock regarding composition?
- Felsic/granitic
- Intermediate/andesitic
- Mafic/basaltic
What is felsic igneous rock composed of and where is it typically found
Typically silica rich; continental crust
Where is intermediate/andesitic igneous rock typically found?
Convergent boundaries around Pacific rim
What is mafic/basaltic rock composed of and where is it typically found?
Silica poor; oceanic crust
What are an intrusive and extrusive example of a felsic igneous rock?
Granite and rhyolite
What are an intrusive and extrusive example of an intermediate igneous rock?
Diorite and andesite
What are an intrusive and extrusive example of an mafic igneous rock?
Gabbro and basalt
What are sedimentary rocks?
Rocks formed at surface environment conditions due to weathering
What percentage of rock at the Earth’s surface is sedimentary rock?
75%
What is the law of original horizontality?
Sediment layers are initially deposited in a horizontal position due to gravity
What are the two types of sedimentary rocks?
- Detrital
- Chemically-deposited
What are detrital formed sedimentary rocks?
Form when sediments are transported, deposited, and then lithified via natural cementation, compression, etc.
What are chemically-deposited sedimentary rocks?
Formed via precipitation from chemical solutions and/or accumulated chemical or biological matter
Which type of sedimentary rock contains fossils?
Detrital sedimentary rocks
How are detrital sedimentary rocks classified?
Based on particle size
What is the most abundant clastic rocks?
Shale, which has the finest texture
What size constitutes gravel sediments and what do rock does gravel form?
Greater than 2 mm; conglomerate
What is a conglomerate called if it has angular particles?
Breccia
What size constitutes sand sediments and what do rock does sand form?
1/16 - 2mm; sandstones
What are the three important types of sandstone?
- Quartzose sandstone
- Arkosic sandstone
- Graywacke
What is quartzose sandstone?
Consists mainly of quartz
What is arkosic sandstone?
Also know as arkose, and is over 20% feldspars
What is graywacke?
Poorly sorted sandstone which contains rock fragments with a clay matrix
What size constitutes silt sediments and what do rock does silt form?
1/256 - 1/16 mm; siltstones/mudstones
What size constitutes clay sediments and what do rock does clay form?
Less than 1/256 mm; shale or claystone
What is the biggest difference between shales, claystones, and siltstones, besides particle size?
Shales have laminations and fissility, clays have laminations, and mudstone lacks laminations; claystones are also exclusively made of clays
What are the two types of shales?
Compacted vs cemented
What are compacted shales?
Shales held together primarily by molecular attraction of fine clay particles
What are issues with compacted shales?
Possibly can be very weak and have a high risk of sliding or slaking
What is the benefit of cemented shales?
Very stable and strong, which makes it more suitable for engineering applications
What percentage of sedimentary rock is composed of coarse grained rock?
25%
Why are calcium carbonate conglomerates and sandstones possibly unstable?
Tend to dissolve in weak acids
What is the strongest cementing material?
Silica cementing materials
How are chemical sedimentary rocks classified?
Composition and texture
What are three examples of chemical sedimentary rocks?
Halite (NaCl), Gypsum, Limestone (CACO3)
What is the most abundant chemical sedimentary rock?
Limestone
What are common textures for chemical sedimentary rocks?
Crystalline, microcrystalline, skeletal, oolitic, massive
What does cross-bedding indicate?
Movement of ancient currents
What is the law of superposition?
Within a sequence of layers of sedimentary rock, the oldest layer is at the base
What are metamorphic rocks?
Rocks formed when pre-existing rocks under solid state are subject to conditions that result in changes to mineralogy and rock textures
What conditions lead to rocks being metamorphosized?
Temperature, pressure, and chemically active fluids
What is foliation?
Preferred mineral alignment of platy mineral particles
What are the texture classifications for foliated metamorphic rocks?
Slate, phyllite, schist, and gneiss
Is slate suitable for foundation materials?
Yes
Is schist suitable for foundation materials?
No
Is gneiss suitable for engineering purposes?
No
What does non-foliation mean with regards to metamorphic rocks?
Mineral particles are randomly arranged and interlocked
How are non-foliated metamorphic rocks classified?
By composition
What are two examples of non-foliated metamorphic rocks?
Quartzite and marble
What is quartzite?
Metamorphosed sandstone suitable for many engineering purposes
What is marble?
Metamorphic rock composed of mineral calcite
What is the law of crosscutting relationships?
Rocks are younger than any other rock that it cuts
What are the three types of stress rocks are subjected to?
Compression, tensile, and shear
What are the two types of deformation caused by stress?
Brittle and ductile
What does brittle deformation result in?
Fractures, joints, and faults
What can be caused by brittle deformation?
Landslides, earthquakes. and infrastructure failures
What does ductile deformation result in?
Folds
What is an anticline?
An ductile deformation that results in an uplifting of rock along an arc
What is a syncline?
An ductile deformation that results in a dropping of rock along an arc
What is an uncomformity?
A geologic contact, or boundary, that represents a break in the continuous rock record
What is noncomformity?
A nonconformity is a geological feature that occurs when sedimentary rock is deposited on top of eroded igneous or metamorphic rock, creating a gap in the geologic record
What is an angular unconformity?
younger sedimentary rocks are located upon an erosion surface, below which older sedimentary rocks are tilted or folded
What is a disconformity?
the junction between two parallel series of stratified rocks, representing a considerable period of erosion of the much older underlying rocks before the more recent ones were deposited.
