-German Meteorologist

-First proposed continental drift Hypothesis in 1915

-Published: The Origin of Continents and Oceans

Continental Drift Hypothesis:

-Supercontinent called Pangaea began breaking apart about 200 million years ago

-The break-up of Pangaea and subsequent movement of the individual continents to their present positions formed the basis for Wegener's continental drift theory

EVIDENCE:

-fit of continents (continental shelves, not coastline)

-fossil evidence

-rock type and structural similarities

-Paleoclimatic evidence

Objections:

-inability to provide a mechanism capable of moving continents across the globe

-Wegener suggested that continens broke through the ocean crust, much like ice breakers cut through ice

-this was correct in principle, but contained incorrect details

-Earth's magnetic pole (where lines of forceare vertical) is 11 degrees from the geographic pole... in N Canada

-Magnetic declination is the angle b/w true north and magnetic north, measured in a horizontal plane

-initial impetus for the renewed interest in continental drift came from rock paleomagnetism

-Magnetized minerals in rocks show the direction to Earth's magnetic poles and provide a means of determining their latitude of origin

What happens to rocks when they cool beneath the Curie point (about 580 deg C)?

 -Magnetic minerals in them are magnetized in the direction of the earth's magnetic field

-the study of this preserved magnetism is paleomagnetism

-these magnetic minerals are fossil magnets which point toward the magnetic poles that existed at that time

-the inclination is the angle between horizontal and the earth's field

-At the north magnetic pole, inclination =90 degrees and the magnetic equator 0 degrees and at Los Angeles about 55 degrees

-in other words the inclination tells you how far away the magnetic pole is and therefore tells you the latitude of the rock at the time it cooled

-For example, paleomagnetism shows that the European coal seams were formed when the continent was closer to the equator

-A rock that cooled in the past can give the position of the apparent pole for that time

-Why, in many cases, was the real pole not in that position? (pole positions from 300 my rocks in western north america show the pole to be in the western Pacific ocean)

-Evidently the continents have rotated and translated after the rocks were magnetized

Polar Wandering:

The apparent movement of the magnetic poles illustrated in magnetized rocks indicates that the continents have moved

-Shows that Europe was much closer to the equator when coal-producing swamps existed

-Polar wandering curves for North America and Europe have similar paths, but are separated by about 24deg of longitude

-Differences b/w the paths can be reconciled if the continents are placed next to one another

-During the 50s and 60s, technological strides permitted extensive mapping of the ocean floor

-Seafloor spreading hypothesis was proposed by Harry Hess in the early 1960s

GEOMAGNETIC REVERSALS

-Earth's magnetic field periodically reverses polarity - the north magnetic pole become the south magnetic pole, and vice versa

-Dates when the polarity of Earth's magnetism changed were determined from lava flows

normal polarity: positive pole of the compass pointing north (as it is today)

reverse polarity: compass points south towards south magnetic pole (positive is south)

-present normal polarity began about 700k years ago

-the average length of time for magnetic reversals to take place is about 500k years.

-these reversals are recorded in the ocean crust

-in 1963 Fred Vine and D. Matthews tied the discovery or magnetic stripes in the ocean crust near ridges to Hess's concept of seafloor spreading

-the stripes of positive and negative magnetization parallel the mid-ocean ridges and continue all the way to the borders of the ocean

-the oldest oceanic crust is Jurassic in Age (shown by paleomagnetism or radioactive dating)

**the ocean floor is a magnetic tape recorder!

-more encompassing theory than continental drift

-the composite of a variety of ideas that explain the observed motion of Earth's lithosphere through the mechanisms of subduction and seafloor spreading

-associated with Earth's strong, rigid outer layer

-known as the lithosphere

-consists of uppermost mantle and overlying crust

-overlies a weaker region in the mantle called the asthenosphere

-there are twelve major lithospheric plates

-plates are in motion and continually changing in shape and size

-largest plate is the Pacific Plate

-several pltes include an entire continent plus a large area of seafloor

-Plates move relative to each other at a very slow but continuous rate

-average about 5cm per year

-cooler, denser slabs of oceanic lithosphere descend into the mantle

-plate movement may be caused by convection

-convection currents ar circular currents or morement within a liquid due to different denities of the hotter and cooler parts

-in the earth's deep mantle and outer core, he magma that is closer to the extremely hot inner core rises because it's less dense and then pushes the cooler magma that is further from the intense heat down

-when cooler magma is pushed down, it is heated more and rises

-the somewhat less hot magma is more ense and so sinks

-this motion is convection currents and is what causes the plates to move that are riding on the surface of all of this

-each plate is bounded by a combination of three types of boundaries

-new plate boundaries can be created in response to changes in the forces acting on these rigid slabs

divergent plate boundaries

-also called constructive margins

-plates move away from each other; spreading centers

transform fault boundaries

-also called conservative margins

-plates slide by each other horizontally

convergent boudnaries

-also called destructive margins

-plates move towards each other; subduction zones

-plate collisions can cause earthquakes along faults

-all major interactions among individual plates occur along their boundaries

Divergent plate boundaries

-most are located along the crests of oceanic ridges and can be thought of as constructive plate margins

-oceanic ridges and seafloor spreading

-oceanic ridges are formed along well-developed divergent plate boundaries

-evidence suggsts that divergent boundaries form above temperature instabilitis near the boundary b/w core and mantle

-just above the core hot blobs of mantle begin to move slowly upward, eventually forming conveyor belt-like convection currents within the semi-fluid asthenosphere

-convection currents diverge where they reach the surface

-the diverging currents exert a weak tension or pull on the plate above it

-tension and high heat weakens the floating plate and it begins to break apart

-the two sides move away in opposite directions ~ creating divergent plate boundary

-this continuous process builds a chain of volcanoes and rift valleys called a mid-ocean ridge or spreading ridge

Divergent plate boundaries have the following characteristics:

1)marked by mid-ocean ridges

2)plate motion is away from boundary

3)lithosphere is created

4)regions of high flow from the crust and mantle due to volcanism

5)exhibit seafloor spreading

6)shallow - focus earthquakes

**topographic differences are controlled by spreading rates

-at slow spreading rates (1-5cm/yr) a prominent rift valley develops along the ridge crest that is wide and deep

-at intermediate spreading rates (5-9), rift valleys that develop are shallow with subdued topography

-when rates are greater than 9, no median rift valley develops and these areas are usually narow and extensively faulted

-continental rifts split landmasses into two or more smaller segments

-examples include the East African rift valleys and the Rhine Valley in Northern Europe

-produced by extensional forces acting on the lithospheric plates

-not all rift valleys develop into full-fledged spreading centres

-older portions of oceanic plates are returned to the mantle in these destructive plate margins

-surface expression of the descending plate is an ocean trench

-called subduction zones

-average angle at which oceanic lithosphere descends into the mantle is 45 degrees

-convergent plates can cause deep-sea trenches and continental-scale mountain ranges

-heavy, but thin oceanic crust tends to be forced under continental crust

-deep trenches form at these subduction zones

-volcanoes and earthquakes are common in subduction zones (ie. ring of fire)

Oceanic Crust
-Ocean basins
-Mafic rocks ~ SIMA (silica, magnesium)
-Thinner than continental crust >10km
-More dense ~ mean density of 3.3g/cm3

Continental Crust
-Earth’s surface
-Sialic rocks ~ SIAL (silica, alumina)
-Thicker than oceanic crust 30 -70km
-Less dense than oceanic crust – 2.7g/cm3

-although all have the same basic characteristics, they are highly variable features

TYPES

oceanic-continental convergence

-denser oceanic slab sinks into the asthenosphere

-lighter continental plate "floats"

-sediments, oceanic crust scraped off and plastered against the edge of the overriding continental block:  accretionary wedge

-partial melting of mantle rock ude to water and other volatils generate magmas having a basaltic or occasionally andesitic composition

continental volcanic arc: mountains produced in part by volcanic activity associated with subduction of oceanic lithosphere

oceanic-oceanic convergence

-when two oceanic slabs converge, one descends beneath the other

-initiates volcanic activity

-volcanoes form on ocean floor rather than on a cntinent

-if volcanoes energe as islands, a volcanic island arc is formed

-island arcs located 200-300km from the trench axis (Aleutian Trench, Mariana Trench)

-most of them are in the West Pacific

-only 2 found in atlandic (lesser Antilles and Sandwich)

continental-continental convergence

-continued subduction can bring two continents together

-result is a collision b/w two continental blocks ~ buckling, deformation, fracturing of continental crust - shortening and thickening

-process produces mountains (Himalayas, Alps, Urals, Appalachians)

-There are more than 500 active volcanoes (erupted at least once in recorded history)

-50 of these in US

-most actvie are part of the Ring of Fire

-major earthquakes also occur along these belts, indicating that volcanism and seismic activity are often closely related

Island-Arc Volcanics: Aleutian Islands

-In a typical "island-arc" environment, volcanoes lie along the crest of an arcuate, crustal ridge bounded on its convex side by a deep oceanic trench
-The granitic layer of the continental crust extends beneath the ridge to the vicinity of the trench
-Basaltic magmas, generated in the mantle beneath the ridge, rise along fractures through the granitic layer
-These magmas commonly will be modified or changed in composition during passage through the granitic layer and erupt on the surface to form volcanoes built largely of non-basaltic rocks

Oceanic Volcanics: Japan

-In a typical "oceanic" environment, volcanoes are aligned along the crest of a broad ridge that marks an active fracture system in the oceanic crust
-Basaltic magmas, generated in the upper mantle beneath the ridge, rise along fractures through the basaltic layer
-Because the granitic crustal layer is absent, the magmas are not appreciably modified or changed in composition and they erupt on the surface to form basaltic volcanoes.

Continental Volcanics: Cascade Range

-In the typical "continental" environment, volcanoes are located in unstable, mountainous belts that have thick roots of granite or granite-like rock
-Magmas generated near the base of the mountain root, rise slowly or intermittently along fractures in the crust
-During passage through the granite layer, magmas are commonly modified or changed in composition and erupt on the surface to form volcanoes constructed of non-basaltic rocks.

-Plates slide past one another and no new lithosphere is created or destroyed

-because the edges of the plates are rough, they can catch and allow stress to build

-earthquakes may then occur when stress is suddenly released

transform faults- most join two segments of a mid-ocean ridge as parts of prominent linear breaks in teh oceanic crust known as fracture zones

-a few (ie. San Andreas Fault) cut thorugh continental crust

-transform faults are locations of recurring earthquake activity and faulting

-the earthquakes are usually shallow because they occur within and b/w plates that are not involved in subduction

-volcanic activity is normally not present because the typical magma sources of an upwelling convection current or a melting subduction plate are not present

Plate Tectonics and Earthquakes

-Plate tectonics model accounts for the global idstribution of earthquakes

-absence of deep-focus earthquakes along the oceanic ridge is consistent with plate tectonics theory

-deep-focus earthquakes are closely associated with subduction zones

-the pattern of earthquakes along a trench provides a method for tracking the plate's descent

-some of the most convincing evidence confirming seafloor spreading has come from drilling directly into ocean-floor sediment

-age of deepest sediments

-thickness of ocean-floor sediments verifies seafloor spreading

Hot Spots

-caused by rising plumes of mantle material

-volcanoes can form over mantle plumes (Hawaiian Island chain)

-most mantle plumes are long-lived struture and at least some originate at great depth, perhaps at the mantle-core boundary

-plates move over hotspots (ie. Hawaii)

-this is currently possible with pace-age technology to directly measure relative motion b/w plates

-Two methods used are Very Long Baseline Interferometry and Global Positioning System

-Calculations show that Hawaii is moving NW and approaching Japan at 8.3 cm/year

-No one mechanism accounts for all major facets of plate tectonics

-several mechanisms generate forces that contribute to plate motion (slab-pull, ridge-push)

-Any model describing mantle convection must explain why basalts erupt along the oceanic ridge

-MODELS: layering at 660 km, whole-mantle convection, keep-layer model

Geologic Time (intro)

-the scientific concept that the Earth is very old began developing in the 18th Century

-Geologists distinguish b/w relative age and numerical age

-geologists of the 19th built geologic time scale from the time/space relationships of rocks exposed at the surface or from drill holes

Stratigraphic Record

-strata: layer of rock or soil with internally consistent characteristics that distinguishes it from contiguous layers

-geologists study rock strate and categorize them

-formation - made up of a numner of layers or stratum (The Burgess Shale formation)

-a stratigraphic column is made up of a number of formations

law of superposition (in an undeformed sequence of sedimentary rocks, the oldest rocks are on the bottom)

the principle of uniformitarianism

the physical processes we observe today also operated in the past

principle of original Horizontality

-layers of sediment are generally deposited in a horizontal position

-rock layers that are flat have not been disturbed

Principle of Original Continuity

-sediments generally accuulate in continuous sheets

Principle of Cross-Cutting Relationships

Principle of Inclusions

Principle of baked or chilled contacts

-contact metamorphism

-baked margins are visible in outcrops

Other things used:

-tree rings

-cores of glacial ice from Antarctica and Greenland

-Unlithified sediments on the seafloor

-matchine ofrocks of similar ages in different regions is known as correlation

-correlation often relies upon fossils

-William Smith (late 1700s and early 1800s) noted that sedimentary strata in widely separated areas could be identified and correlated by fossil content

Principle of Fossil Succession:

-fossil organisms succeed one another in a definite and determinable order that documents the evolution of life; therefore any time period can be recognized by its fossil content

-this principle follows primarily from the principle of superposition

-fossils that occur in rocks at the bottom of a sequence are older than fossils in rocks at the top of the sequence

-correlation often relies upon fossils

-in addition, groups of fossils in one rock succeed one another through time in a regular and predictable order

index fossils

-represent best fossils for correlation; they are widespread geographically and are limited to a short time space

-index fossils or guide fossils are very important in narrowing the time period over which sediments were deposited

-An index fossil is a fossilized member of a species of plant or animal tht has the following characteristics:

-the species existed for a rather short period of time

-the fossil has distinct characteristics that make it relatively easy to recognize

-the species lived over a wide geographic area

-an unconformity is a break in teh rock record produced by erosion and/or non-deposition of rock unites

-the interval of time b/w deposition of the youngest rock below an unconformity and deposition of the oldest rock above is called a hiatus

-when there is no break the rocks are considered conformable

-unconformities are breaks in the rock record; a gap produced by erosion and/or non-deposition ~ uplift and erosion followed by a subsidence and renewed sedimentation

TYPES:

angular unconformity - lower beds that have been folded or tilted and eroded away are overlain by flat-lying rocks

disconformity - erosional surface b/w tw parallel sedimentary beds

non-conformity - when sedimentary rocks are in contact with intrusive igneous or metamorphic rocks

contacts- boundary surface b/w 2 formations

-ie. the Grand Canyon - the succession of rocks in the Grand Canyon is divided into formations based on:

-cahnges in rock type

-changes in fossil assemblage

-Spontaneous changes (decay) in the structure of atomic nuclei

TYPES
-alpha particle emission

-emission of 2 protons and 2 neutrons (an alpha particle)

-mass number is reduced by 4 and the atomic number is lowered by 2

beta particle emission

-an electron (beta particle) is ejected from the nucleus

-mass number remains unchanged and the atomic number increases by 1 (remember a neutron is a combination of a proton and an electron)

Electron Capture

-an electron is captured by the nucleus

-the electron combines with a proton to form a neutron

-mass number remains unchanged and the atomic number decreases by 1

parent - an unstable radioactive isotope

daughter - the isotopes that result from the decay of a parent

half-life - the time required for one-half of the radioactive nuclei in the sample to decay

-The percentage of radioactive atoms that decay during one half-life is always the same (50%)

-however, the actual number of atoms that decay continally decreases

-comparing the ratio of parent to daughter yields the age

Useful radioactive isotopes:

-rubidium-87

-thorium-232

-two isotopes of uranium (235 and 238)

-potassium-40 (1.3 b.y. half life)

SOURCES OF ERROR

-a closed system is required

-if temperature is too high, daughter products may be lost

-to avoid potential problems, only fresh unweathered rock samples should be used

CARBON-14

-half-life only 5730 years

-used to date very recent events

-is produced in the upper atmosphere

-usedful tool for anthropologists, archaeologists, and geologists who study recent events

-certain rocks have been dated at more than 3billion years

-the history of the earth is broken up into a hierarchical set of divisions for describing geologic time

-and increasingly smaller units of time, the gereally accepted divisions are eon, era, period, epoch, age

-this is kind of like a calendar of Earth history

-eon is the greatest expanse of time

EONS

-phanerozoic (visible life)

-the most recent eon, began just over 540 million years ago; rocks and deposits of this eon contain abundant fossils ~ document major evolutionary trends

-majority of macroscopic organisms, algal, fungal, plant and animal lived

**other eons were proterozoic, archean, and Hadean (the oldest)

PRECAMBRIAN TIME

-nearly 4 billion years prior to cambrian period

-not divided into smaller time units because the events of precambrian history are not known in great enough detail

-also, first abundant fossil evidence does not appear until the beginning of the cambrian

-precarmbrian represents about 88% of Earth's history

-simple life forms existed - algae, bacteria, fungi and worms predominated - no preservation due to lack of hard parts

-Meager Precambrian fossil record

-Precambrian rocks are very old and have been subjected to a great many changes

ERAS

-subdivision of an eon

-eras of phanerozoic are cenozoic, mesozoic, and paleozoic

-eras are divided into periods

-periods are subdivided into epochs

PERIODS

Paleozoic: Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian

Mesozoic: Triassic, Jurassic, Cretaceous

Cenozoic: Paleogene, Neogene, Quaternary

-Cenozoic is divided into 7 epochs

-holocene is the current, and is reserved for the last 11k years

*Carboniferous = Pennsylvanian + Mississippian

DIFFICULTIES

-not all rocks can be dated by radiometric methods

-grains comprising detrital sedimentary rocks are not the same age as the rock in which they formed

-the age of a particular mineral in a metamorphic rock may not necessarily represent the time when the rock formed

-datable materials (ie. volcanic ash beds and igneous intrusions) are often used to bracket various episodes in Earth history and arrive at ages

-dates change as brackets become narrower and methods refined

Within the Earth rocks are continualy being subjected to forces that bend, twist and fracture them

-when rocks bend, twist or fracture, they deform

-the forces that cause deformation of rock are referred to as stresses (Force/unit area)

deformation- a general term that refers to all changes in the original form and/or size of a rock body

-most crustal deformation occurs along plate margins

-plate motions and interactions along plate boundaries generate tectonic forces that cause rock to deform

force: that tends to put stationary objects in motion or changes the motions of moving objects

stress: forces that deform rocks

-the amount of force applied to a given area

-the magnitude of stress is a function of amount of force and amount of area

-stress may be uniform or differential

compression - occurs when rock masses are pushed together like that which occurs when plates collide

-rocks tend to shorten laterally and thicken vertically when exposed to compressional stress

-subduction zones

tension - pulls the crust apart

-occurs along diverging plate boundaries

-tension extends the crust causing it to thin and lengthen (rifting)

shear stress: when plates slide past one another inopposite directions along transform plate boundaries, a shearing stress is created

-cuts the crust into parallel blocks displacing them horizontally relative to one another

-San Andreas Fault where the Pacific Plate is moving past the North American Plate

strain- changes in the shape or size of a rock body caused by stress

-this is a measure of how rocks deform

-the reaction of rock material to an imposed stress depends on the temperature and pressure conditions

-as stress is imposed on rock it starts to deform up to its yield point

-before it gets to the yield point, the rock will undergo elastic deformation

-like a rubber band, if the stress is released before reaching the yield point, the rock material will return to its original shape

brittle failure: under low temperature and pressure conditions, once the rock reaches its yield point it will break

-rocks near the surface (low T and P) behave like a brittle solid and fracture once strength is exceeded

-brittle failure may occur if stress is imposed suddenly

elastic deformation: the rock returns to nearly is original size and shape when stress is removed

-once the elastic limit of a rock is surpassed, it either flows (ductile deformation) or fractures (brittle deformation)

1. Temperature and Confining Pressure

-low temperature and pressure = behave like a brittle solid and fracture (break) once their strength is exceeded

-at depths - high temperature and confining pressure ~ rocks exhibit ductile behavior ... type of solid-state flow

2. Rock Type

-crystalline rocks - britle fracture

-Sedimentary rocks - zones of weakness such as foliation - ductile flow

-weak rocks - rock salt, gypsum, and shale

-ineermediate strength - limestone, schist, marble

3.Time

-geologists have not been able to duplicate how ocks respond to stress over geologic time

-bookshelves over time tend to sag under extended stress

-remember there is a continuum that ranges from pure brittle fracture at one end to ductile flow at the other.

Strike (trend) - the compass direction of the line produced by the intersection of an inclined rock layer or fault with a horizontal plane

-generally expressed on an angle relative to north

Dip (inclination)

-the angle of inclination of the surface of a horizontal plane

-includes both an inclination and a direction toward which the rock is inclined

-during crustal deformation rocks are often bent into a series of wave-like undulations called folds

-most folds result from compressional stresses which shorten and thicken the crust

Parts

limbs -refers to the two sides of a fold

axis -a line drawn down the points of maximum curvature of each layer

axial plane - an imaginary suface that divides a fold symmetrically

anticline - upfolded or arched rock layers

syncline- downfolds or trought of rock layers

-anticlines and synclines, depending on orientation, can be symmetrical, asymmetrical, recumbant (overturned), or plunging

monocline- large, step-like folds in otherwise horizontal sedimentary strata

dome - upward displacement of rocks

-circular or slightly elongated structure

-oldest rocks in centre, younger rocks on the flanks

basin - circular or slightly elongated structure

-downwarped displacement of rocks

-youngest rocks are found near the centre, oldest on the flanks

chevron folds

-angular fold - called a chevron where the hinge is very abrupt and the limbs are straight

-developed in carboniferous sandstones and shales, saundersfoot, Pembrokeshire

-thei is the Lady's Cave fold - a famous structure

-Faults are fractures in rocks along which appreciable displacement has taken place
-Sudden movements along faults are the cause of most earthquakes
-Along faults, rock is often pulverized into gouge or polished as slickenslides
-Faults are classified by their relative movement which can be horizontal, vertical, or oblique

TYPES

dip-slip

-movement is mainly parallel to the dip of the fault surface

-may produce long, low clifs called fault scarps

-parts of a dip-slip fault include the hanging wall (rock surface above the fault) and the footwall (rock surface below the fault)

Normal Faults

-is a type of dip-slip fault

-hanging wall block moves down relative to the footwall block

-accomodate lengthening or extension of the crust

-most are small with displacements of a metre or so

-larger scale normal faults are associatedwith structures called fault-block mountains

-normal faulting is prevalent at spreading centres where plate divergence occurs

-graben: central block bounded by normal faults drops as plate separates

horst: - grabens bound by relatively uplifted structures

reverse and thrust faults

-another type of dip-slip faults

-hanging wall block moves up relative to the footwall block

-reverse faults have dips greater than 45 degrees and thrust faults have dips less than 45

-accommodate shortening of the crust

-strong compressional forces

-common in mountain belts like the alps and rockies; isolated remnant of a thrust sheet is called a klippe

Strike-Slip Fault

-dominant displacement is horizontal and parallel to the strike of the fault

-can be right lateral (as you face the fault, the block on the opposite side of the fault moves to the right) or left lateral (as you face the fault, the block on the opposite side of the fault moves to the left)

-a transform fault is a large strike-slip fault that cuts through the lithosphere

-accommodates motion b/w two large crustal plates

oblique-slip fault - movement along the strike and simultaneously up or down the dip

-results shear in combination with either compression or tension

-among the most common rock structre

-technically, a joint is a fracture with no movement

-most occur in roughly parallel groups

-significance of joints: chemical weathering tends to be concentrated along joints

-a joint is a generally planar fracture formed in a rock as a result of extensional stress

-joints form in solid, hard rock when a rock is stretched past its elasticity

-at this point the rock fractures: in a plane perpendicular to the extensional stress, in a plane parallel with the minimum compressive stress... which is usually vertical

-joints are typically formed due to: erosion of the overlying strata exposed at the surface ~ removal of overlying rock results in extensional stresses and the fracturing of underlying rock

-cooling of hot rock masses, particularly lava, which form cooling joints, the underlying structure of columnar jointing

-chemical weathering tends to be concentrated along joints

-many important mineral deposits are emplaced along join systems (veins)

-highly jointed rocks often represent a risk to construction projects

-depth was originally measured by lowering weighted lines overboard

-echo sounder (also referred to as sonar) was invented in the 20s, and is primary instrument for measuring depth .... reflects sound from ocean floor

multibean sonar employs an array of sound sources and listening devices

-obtains a profile of a narrow strip of seafloor

Passive Continental Margins

-found along most coastal areas that surround the Atlantic ocean

-not associated with plate boundaries

-experience little volcanism and few earthquakes

continental shelf- flooded extension of the continent

-varies greatly in width

-gently sloping

-contains important mineral deposits

-some areas are mantled by extensive glacial deposits

Continental Slope

-marks the seaward edge of the continental shelf

-relatively steep structure

-boundary b/w continental crust and oceanic crust

Continental Rise

-found in regions where trenches are absent

-continental slope merges into a more gradual incline - the continental rise

-thick accumulation of sedimetn

-at the base of the continental slope turbidity currents deposit sediment that forms deep-sea fans

ACTIVE Continental Margins

-continental slope descends abruptly into a deep=ocean trench

-located primarily around the Pacific Ocean

-Accumulations of deformed sediment and scraps of ocean crust form acretionary wedges

Submarine Canyons

-deep, steep-sided valleys cut into the continental slope

-some are extensions of river valleys

-most appear to have been eroded by turbidity currents

Turbidity Currents

-downslope movements of dense, sediment-laden water

-deposits are called turbidites

-turbidites are layered and exhibit graded bedding (decrease in sediment grain size from bottom to top)

Deep Ocean Trenches

-long, relatively narrow features

-deepest parts of ocean

-most are located in the Pacific

-sites where moving lithospheric plates plunge into the mantle

-associated with volcanic activity

Abyssal Plains

-likely the most level places on earth

-sites of thick accumulations of sediment

-found in all oceans

Seamounts

-isolated volcanic peaks

-many form near oceanic ridges

-may emerge as an island

-may sink and form flat-topped seamounts called guyots

Coral Reefs

-constructed primarily from skeletal remains and secretions of corals and certain algae

-confined alrgely to the warm, clear waters of the Pacific and Indian Oceans

Atolls

-Coral islands- a continuous ring of coral reef surrounding a central lagoon

-form on the flanks of a sinking volcanic island (hypothesis proposed by Darwin)

-ocean floor is mantled with sediment

-sources are turbidity currents and sediment that slowly settles to the bottom from above

-the thickness varies.... thickest in trenches... accumulations may exceed 9 km

-thickness is much greater in Atlantic Ocean than Pacific

-mud is the most common sediment on the deep-ocean floor

TYPES

terrigenous Sediments

-material weathered from continental rocks

-virtually every part of the ocean receives some

-fine particles remain suspended for a long time

-oxidation often produces red and brown coloured sediments

biogenous Sediments

-shells and skeletons of marine animals and plants

-most common are calcareous oozes produced from microscopic organisms that inhabit warm surface waters

-siliceous oozes composed of opaline skeletons of diatoms and radiolarians

Hydrogenous Sediments

-minerals that crystallize directly from seawater

-important deposits with economic potential include manganese nodules and sulfide deposits

-interconnected ridge system is the longest topographic feature on earth's surface

-over 70Mm in length

-20% of earth's surface

-winds through all major oceans

-along the axis of some segments are deep down faulted structures called rift valleys

-consist of layer upon layer of basaltic rocks that have been faulted and uplifted

-mid-atlantic ridge has been studied more thoroughly than any other ridge system

characterized by:

-an elevated position

-extensive faulting

-numerous volcanic structures that have developed on newly formed crust

-seafloor spreading occurs along relatively narrow zones, called rift ones, located at the crests of ocean ridges

-as plates move apart, magma wells up into the newly created fractures and generates new slivers of oceanic lithosphere

-new lithosphere moves from the ridge crest in a coneyor-belt fashion

-newly created crust at the ridge is elevated because it is hot and thererfore occupies more volume than the cooler rocks of the deep-ocean basin

Structure of the Oceanic Crust

Three distinct layers:

upper layer- consisting of pillow lavas

middle layer - numerous interconnected dykes called sheet dykes

lower layer - gabbro, in a sequence of rocks called an ophiolite complex

-magma that creates new ocean floor originates from partially melted peridotite in the asthenosphere

seismology - uses the travel times and amplitudes of seismic waves to study variations in seismic wave velocity and density

gravity studies measure variations in density

magnetic studies give insight into the core's magnetic field together with results from laboratory studies of rock proterties and other data these yield our models of the earth's composition, temperature, and internal processes

-study of earthquake waves ~ accurately measuring the time required for P and S waves to travelfrom an earthquake to a seismograph station ~ travel times

-depends on properties of the materials encountered - density and elasticity

-seismic waves pass through Earth carrying information to the surface about the materials through which they were transmitted

-as seismic waves travel through rocks their amplitude and direction changes

-seismic waves are reflected and transmitted (refracted)

-both the angles and size (amplitude) of waves change, depending on the velocity and density change

Velocity of seismic waves is a function of density and elasticity of the material

-crystalline rock transmits seismic waves more rapidly than unconsolidated mud

Speed of seismic waves increases with depth

-pressure increasses and squeezes the rock into a more compact elastic material

P (compressional) wavs propagate through liquids and solids

-when these materials compress, they behave elastically and return to their original shape as a wave passes

Shear (S) waves cannot propagate through liquids

-liquids have no shear strength

In all materials, P aves travel faster than S waves

-seismic waves pass from one material to another, the path of the wave is refracted

-depending on the nature of teh layers through which they pass, seismic waves speed up or slow down, and may be refracted or reflected

Layers Defined by Physical Proerties

-with increasing depth, Earth's interior is characterized by gradual increases in temperature, pressure, and density

-seismic waves ~ discontinuities detected worldwide

-earth must be composed of distinct shells' have varying compositions and/or mechanical properties

-depending on the temperature and depth, a particular Earth material may behave like a brittle solid, deform in a plastic-like manner, or melt and become liquid

-main layers of Earth's interior are based on physical properties

Lithosphere

-earth's outermost layer

-consists of the crust and uppermost mantle

-relatively cool, rigid shell

-averages about 100km in thickness, but may be 250 km or more thick beneath the older portions of the continents

Asthenosphere

-beneath the lithosphere, in the upper mantle to a depth of about 600km

-small amount of melting in the upper portion mechanically detaches the lithosphere from the layer below allowing the lithosphere to move independently of the asthenosphere

Mesosphere/Lower Mantle

-rigid layer b/w the depths of 660km and 2900km

-rocks are very hot and capable of very gradual flow

Outer Core

-composed mostly of an iron-nickel alloy

-liquid layer

-2270 km thick

-convective flow within outer core generates Earth's magnetic field

Inner Core

-composed mostly of an iron-nickel alloy

-sphere with a radius of 3486km

-material is stronger tan the outer core

-behaves like a solid

Layers Defined By Composition

-Crust: oceanic is silica and magnesium, while continental is silica and aluminum)

-Mantle: solid rocky silica-rich shell

-Core: Iron rich sphere

The MOHO

-(Mohorovicic discontinuity)

-discovered in 1909 by Andriaja Mohorovicic

-separates crustal materials from underlying mantle

-identified by a change in the velocity of P waves

The Core-Mantle Boundary

-discovered in 1914 by Beno Gutenberg

-based on the observation that P waves die out at 105 degrees from the earthquake and reappear at about 140 degrees - this 35 degree wide belt is named the P-wave shadow zone

-characterized by bending (refracting) of the Pwaves

-the fact that S waves do not travel through the core provides evidence for the existence of a liquid layer beneath rocky mantle

Discovery of Inner Core

-predicted by Inge Lehmann in 1936

-P waves passing through the inner core show increased velocity suggesting that the inner core is solid

The Crust

-very thin and brittle

-varies in thickneww >70 km under some mountainous regions; oceanic crust is 3-15 km

-accounts for 1% of earth's volume

continental crust: average density is 2.7 g/cm3 and composition comparable to the felsic igneous rock granodiorite

oceanic crust: density around 3g/cm3 and composed mainly of basalt

The Mantle

-contains 84% of Earth's volume

-solid rocky layer

-upper portion has the composition of the ultramafic rock peridotite

-two parts: asthenosphere (upper) and mesosphere (lower mantle)

The Core

-largr than the planet Mars

-Earth's dense central sphere ~15%

-outer: liquid layer about 2270km thick

-inner: solid inner sphere with a radius of 1216km

-temp at center is 6700C

-travel times of waves can be used to measure the depth of the inner core

-average density is 11g/cm3

-earth's center is around 14 times H2O

-mostly iron, with 5-10% nickel

Origin of the Core

-more accepted explanation is that the core formed early in Earth's history from a relatively homogeneous body

-blobs of heavy iron-rich materials sank toward the centre as Earth's internal temperature increased

-As earth began to cool, iron in the core began to crystallize and the inner core began to form

-the requirements for the core to produce Earth's magnetic field are met in that it is made of material that conducts electricity and it is mobile

-inner core rotates faster than the Earth's surface and the axis of rotation is offset about 10 degres from the Earth's poles

Earth's temperature gradually increases with an increase in depth at a rate known as the geothermal gradient

-varies considerably from place to place

-averages b/w about 20C and 30C per km in the crust (rate of increase is much less in the mantle and core)

Major processes that have contributed to Earth's internal heat

-heat emitted by radioactive decay of isotopes of uranium, thorium, and potassium

-heat released as iron crystallized to form the solid inner core

-heat released by colliding particles during the formation of Earth

Heat Flow In the Crust

-process called conduction

-rates of heat flow in crust vary

Mantle Convection

-there is not a large change in temperature withdepth in the matnle

-Mantle must have an effective method of transmitting heat from the core outward

Isostasy: Why the Earth isn't Smooth

-concept of floating crust in gravitational balance is calledisostasy

-state of gravitational equilibrium achieved by floatation of buoyant lithosphere on more dense asthenosphere

-envision series of wooden blocks floating in water (thin blocks float low, thick stand high)

mountain: landform with an obvious peak rising significantly above surrounding area

-mountains are not distributed randomly

-mountains occur in linear patterns from small ranges to regionally extensive belts

-deformed belts or orogens are products of crustal interaction and fit into plate tectonic scheme

Long (continental length), relatively narrow, earth's crust have been subjected to immense horizontal compressive stress:

-the formation of folds, faults and other deformational structures

-the emplacement of intrusive igneous bodies

-metamorphism

-uplift of the deformed rock mass to form mountain belts

-orogenesis occurs mainly at convergent boundaries

Rift Valleys

-significant relief on margins as blocks near axis slide downward along normal faults

-East African rift is an example

-Volcanism often accompanies crustal stretching, forming high relieflike Mount Kilimanjaro in Tanzania

Passive Margins

-precursors to convergent margins

When a rift valley evolves into an oceanic spreading centre the margins become passive continental margins

-little tectonic activity, although some crustal movement associated with loading of marine sediment

-a thick wedge of sediments accumulate on these passive margins, which may become deformed later as tectonic settings change

-sedimentation at passive margins reflects the progressive increase in water depth

-miogeoclinal deposits: near shore deposits are coarser - sand grading to silt and clay ~ further out on the continental shelf in clear shallow water - carbonate reefs form (tropical regions)

-eugeoclinal deposits: on the deeper continental slope and rise, mostly fine-grained clastic sediments accumulate ~ forming shales and greywackes.

Simple Subduction = Andean-type Mountain Building

-mountain muilding along continental margins

-involves the convergence of an oceanic plate and a plate whose leading edge contains continental crust

Stages of Development - Active Continental Margins

-subduction zone forms

-deformation process begins

-convergence of the continental block and the subducting oceanic plate leads to deformation and metamorphism of the continental margin

-continental volcanic arc develops

-accretionary wedge may form (chaotic accumulation of sedimentary rocks and metamorphic rocks with occasional scraps of ocean crust)

Composd of roughly two parallel zones

Volcanic Arc

-develops on the ocntinental block

-consists of large intrusive bodies intermixed with high-temperature metamorphic rocks

Accretionary Wedge

-seaward segment

-consists of folded, faulted, and metamorphosed sediments and volcanic debris

Sierra Nevada and Coast Ranges

-one of the best examples of an active Andean-type orogenic belt

-subduction of the pacific Basin under the wester edge of the North American plate

-Sierra Nevada batholith is a remnant of a portion of the continental volcanic arc

-where two ocean plates converge and one is subducted beneath the other

-volcanic island arcs result from the steady subduction of oceanic lithosphere

-most are found in teh Pacific

-continued development can result in the formation of mountainous topography consisting of igneous and metamorphic rocks

Small-Scale Collisions: Accreted Terrances

-small crustal fragments (microcontinents, island arcs, oceanic plateaus) collide and merge with continental margins

-responsible form any of the mountainous regions rimming the Pacific

-Accreted crustal blocks are called terranes

-uplift of the North American Cordillera is a classic example of mountain building associated with terrane accretion

-Terranes were sattered across eastern Pacific and since breakup of Pangaea (200 MYA) NA has been migrating westward adding on these fragments

Large Scale Collisions: When two continents collide

-two lithospheric plates, both carrying continental crust

-the Himalayan Mountains are a youthful mountain range formed from the collision of India with the Eurasian plate about 45mya

Complex Histories

-the appalachian Mountains formed about 250-300 mya resulting from the collision of North America, Europe, and Africa

-orogenesis here is complex including divergence, initial convergence, accretion of teranes, and continental collision

-studies of old complex mountains like Appalachians has led to an idealized global tectonic cycle

-Named the Wilson Cycle after J. Tuzo Wilson (Canadian geophysicist)

-Cycle includes:

1)accumulation of sediment wedge on passive margin

2)plate motion changes and basin closes and continents converge

3)subduction of oceanic slab leads to Andean-type volcanic arc

4)Continental blocks eventually collide

5)Finally, change in plate boundary ends growth of mountains

Mountains in Convergent Margin Settins:

Obduction, Ophiolites, and Isostatic Adjustment

Convergene and the Obduction of Oceanic Crust

-Sometimes subduction of oceanic crust is not 100% efficient

-pieces of oceanic plate may break off and become thrust onto continents; called obduction

-result is an ophiolite complex as in teh Franciscan Formation of California and the Bay of Islands Ophiolite in Newfoundland

Ophiolites

-distinctive assemblages of mafic, ultramafic, and felsic igneous rocks that are commonly thought to represent oceanic crust and mantle that has been accreted to a continental margin

-the accretion of ophiolite and island arc terrances has been the primary mechanism of continental growth since the Proterozoic

Isostatic Adjustment after Active Convergence

-erosion lowers the summits of mountains

-crust rises by isostatic adjustment in reponse to reduced load

-process continues until mountain block reaches "normal" thickness

-then mountains will be eroded to near sea level

-accounts for lower elevation and exposed roots of the Appalachian Mountains

-stresses imposed on crust at transform margins are more localized than at convergent margins

-lateral movement along the fault ~ local areas of intense compression ~ deformation

-San Andreas fault system does have mountains associated however (the Transverse Ranges just north of LA)

Crustal thickness suggests that the elevation differene where the Great Plains meet the Rockies must somehow be the result of hot mantle upwelling

-hot mantle may have provided teh buoyancy to raise the southern Rockies, as well as teh Colorado Plateau and tha Basin and Range topography of the American West

Upwelling associated with the Basin and Range province started about 50 million years ago and remains active today

-not all geologists studying teh region agree with the model

-another hypothesis suggests that the addition of terranes to NA produced the observed uplift in the American West

Possible mechanism for crustal subsidence

-downwarping - simply result of extra loading to crust such as occurred during last ice age

-some downwarped areas may be linked to flow dynamics of the mantle

Downwarping of Continental Margins and Interiors may be linked to subduction of oceanic lithosphere

-a subducting, detached lithospheric plate creates a downward flow in its wake that tugs on the base of the overriding continent

-more observational data is needed to test the hypothesis

Foreland and Intracratonic Basins

-Foreland Basins are elongate trough-like depressions preduced by loading along teh edge of a continent (ie. Western Canada Foreland Basin inland of the rocky mountains)

-Intracratonic Basins are circular, bowl-shaped depressions in continent interior possible related to independent mantle process (ie. Williston Basin of Canadian Prairies)

-Cordillera is the largest of all the world's orogens

-extend along the full length of western N/S America

-Formed mainly during the later half of the mesozoic era and the early part of the Cenozoic Era

-Contains a wide variety of igneous and sedimentary rocks

-range from Proterozoic to early Tertiary, as well as post-orogenic volcanic and sedimentary rocks

Within the Cordillera, the Appalachian and the Inutian orogens, the rocks can be divided into Eugeosynclinal and Miogeosynclinal deposits

Platform deposits

-in all cases the rocks grade from platform deposits beside and on top of buried Canadian Shield, to miogeosynclinal and eugeosynclinal rocks that flank the NA continent

-in Canada and Alaska the boundary b/w eugeosynclinal and miogeosynclinal rocks is marked by a large fault-controlled valley called the Tintina Trench in the Yukon and Alaska and the Rocky Mountain Trench in BC

Eugeosynclinal Rocks (late Precambrian to early Mesozoic) are of two differing origins:

1) "in situ" deposits - rocks deposited a few hundred km west of the miogeosyncline (sedimentary deposits that are deep-water deposits, and volcanic-arc to subduction zone to back-arc volcanic)

2)Accreted terranes 0 regions containing rocks that were deposited in some distant places, and which have been transported as large blocks (islands) to their present position by plate tectonics

Miogeosynclinal Rocks

-late precambrian to early Tertiary

-rests on the subsurface extension of teh Canadian Shield

-Include sand and shale of deltaic origin; sand shale and liestone of shallow marine origin and some volcanic rocks

-paleozoic rocks are mainly shallow marine limestones and shales

-mesozoic rocks are similar to platform deposits except for a nearly complete lack of terrestrial deposits

-cenozoic rocks are mostly terrestrial

Volcanic Rocks

-still active volcanoes

-fields of lava from extinct volcanoes (combined lava fields ofthe Columbia Plateau and the Snake River Plains)

Platform Rocks

-Range in age from early Paleozoic (~543mya) to Quarternary (~1.8mya)
-Lie in angular unconformity on rarely exposed rocks of the Precambrian Shield
-Paleozoic rocks mainly limestone and shale
-Mesozoic rocks mainly shale and sandstone and coal beds
-Early Tertiary deposits mostly river and lake sands, silts and clay beds; some coal
-Late Tertiary to Quarternary time mostly erosional with glacial deposits coating much of northern NA

Antler Orogeny

-affected an area in western US; weak-moderate deformation intensity; middle to late Paleozoic

-production of westerly dipping thrust faults

-uplift

Columbian Orogeny

-late triassic to leate cretaceous

-affected mainly the eugeosynclinal part of the Cordilleran geosyncline

-Pacific Plate moved north, the crust was subducted below the NA Plate

-the plate closed in on the 1st Terrane, this land mass was too buoyant to be forced downward and so it was added onto the edge of the continent

-much of BC joined NA then

-along with this collision came intense forces compressing the already existing land mass

-this brought on the first orogeny, known as teh Columbia (it formed the Columbia Mountains made up of the Caribous, Selkirks, Purcells and the Monashees)

-Columbia Orogeny occurred about 175 mya

-thrust faulting, which was instrumental in the formation of the Rockies

-the shock wave began piling up the western ranges, and then the main ranges, around 120mya

Laramide Orogeny

-late cretaceous to early Tertiary

-affected mainly the miogeosynclinal and platform deposits of the Cordilleran geosyncline

-despite teh separate names, orogenesis was a continuous process

-the 2nd Terrane collided around 85 mya setting off a whole new series of shock waves and beginning the Laramide Orogeny

-the force begind this second collision provided enough energy to form the front ranges and the foothills

-eventually the forced died out as it approached Cgy and so the prairies were left undisturbed

Cordilleran Orogeny Produced 3 main effects:

1)major intrusion

-coast range batholith, which forms most of the Coast Mountains running the full N-S length of the west coast of BC

-idaho batholith and Sierra Nevada batholith

2)Thrust Faulting and Folding

3)Uplift, which, along with erosion resulting in the Cordilleran Mountain Belt

Thrust Faulting and Folding

-Foothills belt is bounded by the Brazeau Thrust and the McConnell Thrust
-The front ranges are bounded by the McConnell thrust and the Pipestone Pass-Simpson Pass Thrust complex
-The Main Ranges by the Pipestone Pass-Simpson Pass Thrust complex and the Chatter Creek Thrust (marks the eastern side of the Rocky Mountain Trench)

Uplift and Erosion

-The modern landscape develop through differential erosion
-Rocks lay in parallel bands of soft and hard layers
-Hard layers become the ridges; soft layers become the valleys – valleys deepened faster than the ridges
-Today's landscape is glacially carved ~ over the last 1.8m years, the last just over 18,000y

It is the vibration of the Earth produced by the rapid release of energy

-energy released radiates in all directions from its source, the focus

-energy is in the form of waves

-sensitive instruments around the world record the event

-the point on the earth's surface above the focus is called the  epicentre

Earthquakes and Faults

-movements that produce earthquakes are usually associated with large fractures in Earth's crust called faults

-most of the motion along faults can be explained by plate tectonics theory

-on faults rocks begin to slip; slip doesn't go on forever due to friction

-stick-slip behavior - move in sudden increments

-the moment a fault slips the rock around the fault feels a sudden push or pull

-movement sends a sudden pulse of energy ~"shock"

-vibration generated by the sudden slip on the fault radiates through the surrounding rock and creates the shaking - earthquake

-bigger the amount of slip = greater the vibrations =larger the earthquake

Elastic Rebound

-machanism for earthquakes was first explained by H.F. Reid

-rocks on both sides of an existing fault are deformed by tectonic forces

-rocks bend and store elastic energy

-Frictional resistance holding the rocks together is overcome

-earthquakes most often occur along existing faults whenever the frictional forces on the fault surfaces are overcome

Foreshocks and Aftershocks

-adjustments that follow a major earthquake often generate smaller earthquakes called aftershocks

-amall earthquakes, called foreshocks, often precede a major earthquake by days or, in some cases by as much as several years

-most earthquaks occur in seismic belts of zones

-majority lie along plte boundaries

-intraplate earthquakes do occur but relatively infrequent

The initial break that creates a fault, along with these sudden, intense shifts along already formed faults, are the main sources of earthquakes

-most earthquakes occur around plate boundaries, because this is where the strain from the plate movements is felt most intensely, creating fault zones, groups of interconnected faults

-in a fault ozne, the release of kinetic energy at one fault may increase the stress -- the potential energy --- in a nearby fault, leading to other earthquakes

-this is one of the reasons that several earthquakes may occur in an area in a short period of time

Different kinds of earthquakes occur at different types of plate boundaries

-shallow-focus earthquakes ~normal faults~ diverent plate boundaires and rifts

-intermediate and deep-focus earthquakes ~ thrust and reverse faults ~ convergent plate boundaries - Wadati-Benioff zone

-shallow-focus strike slip earthquakes ~ transform boundaries (shear)

-San Andreas is the most studies fault system in the world

-displacement occurs along discrete segments 100 to 200 km long

-some portions exhibit slow, gradual displacement known as fault creep

-other segments regularly slip, producing small earthquakes

Displacements along the San Andreas Fault

-still other segments store elastic energy for hundreds of years before rupturing in great earthquakes

-process described as stick-slip motion

-great earthquakes should occur about every 50 to 200 years along these sections

-the study of earthquake waves, which dates back almost 2000 years to Chinese

-seismographs record the movement of earth in relation to a stationary mass on a rotating drum or magnetic tape

-more than one type of seismograph is needed to record both vertical and horizontal ground motion

-records obtained are called seismographs

surface waves: travel along outer part of earth and are the slowest

-complex motion; up and down; side to side

-cause greatest destruction

-waves exhibit greatest amplitude and slowest velocity

-waves have the greatest periods (time interval b/w crests) - long waves L waves

-2 types: Love (L) waves and Raleigh waves

Body Waves

-travel through earth's interior

-primary waves(P): push-pull (compress and expand) motion, changing the volume of the intervening material

-travel through solids, liquids, and gases

-generally, in any solid material, P waves travel about 1.7 times faster than S waves

-secondary (S) waves: "shake" motion at right angles to their direction of travel

-travel only through solids

-though slower, slightly greater amplitude than P waves

-epicentre is located using the difference in velocities of P and S waves

-three station recordings are needed to locate an epicentre

-each station determines the time interval b/w the arrival of the first P wave and the first S wave at their location

-a travel-time graph is used to determine each station's distance to the epicentre

-a circle with a radius equal to the distance to the epicentre is drawn around each station

-the point where all three circles intersect is the earthquake epicentre

-this method is called triangulation

Earthquake Belts

-about 95% of the energy released by earthquakes originates in a few relatively narrow zones that wind around the globe

-major earthquake zones include the circum-pacific belt, mediterranean sea region to the Himalayan complex, and the oceanic ridge system

Earthquake Depth

-earthquakes originate at depths raning from 5-700km

-earthquake foci arbitrarily classified as shallow (surface to 70 km) intermediate (b/w 70 and 300), and deep (300+)

-shallow focus occur along the oceanic ridge system - divergent plate margins

-almost all deep-focus earthquakes occur in the circum-Pacific belt, particularly in regions situated landward of deep-ocean trenches - subduction plate margins

Intensity Scales

Modified Mercalli Intensity Scale

-developed using California buildings as its standard - describes damage to structures

-Ranges from I (felt by only a few) to XII (total destruction)

-intensity depends on distance to epicentre, building materials and design, type of ground rock material

-though destruction may not be a true measure of severity

Richter Scale

-concept introduced by Charles Richter in 1935

-based on the ampitude of the largest seismic wave recorded on the seismogram

-accounts for the decrease in wave amplitude with increased distance

-largest magnitude ever recorded on a Wood-Anderson seismograph was 8.9

-magnitudes of less than 2.0 are not felt by humans

-each unit of Richter magnitude increase corresponds to a tenfold increase in wave amplitude and a 32-fold increase in energy

Other Magnitude Scales

-several "Richter-like" magnitude scales have been developed

moment magnitude was developed becasue non of the "Richter-like" magnitude scales adequately estimates the size of very large earthquakes

-derived from the amount of displacement that occurs along a fault

ground shaking

-regions within 20 to 50 km of the epicentre will experience about the same intensity of ground shaking

-however, destruction varies considerable mainly due to the nature of the ground on which the structures are built

liquefaction of the ground

-unconsolidated materials saturated with water turn into a mobile fluid

seiches

-the rhythmic sloshing of water in lakes, reservoirs, and enclosed basins

-waves can weaken reservoir walls and cause destruction

Tsunamis

-Destructive waves that are often inappropriately called “tidal waves”
-Result from vertical displacement along a fault located on the ocean floor or a large undersea landslide triggered by an earthquake
---About 95% of tsunamis are caused by earthquakes under ocean floors or near the shore
-Tsunami of Dec. 26 2004 – 9.0 magnitude earthquake ~ 160km off the western coast of Indonesia’s Sumatra Island

-in the open ocean, height is usually les than 1 metre

-in shallower coastal waters the water piles up to heights that occasionally exceed 30m

-landslide may also cause considerable damage

Short-Range

-Goal is to provide a warning of the location and magnitude of a large earthquake within a narrow time frame
-Research has concentrated on monitoring possible precursors – phenomena that precede a forthcoming earthquake such as measuring uplift, subsidence, and strain in the rocks

-Currently, no reliable method exists for making short-range earthquake predictions

Long Range

-Give the probability of a certain magnitude earthquake occurring on a time scale of 30 to 100 years, or more
-Based on the premise that earthquakes are repetitive or cyclical
---Using historical records or paleoseismology to show quiet zones or seismic gaps
-Are important because they provide information used to
---Develop the Uniform Building Code
---Assist in land-use planning

-Ore deposits are naturally occurring geological bodies that may be worked for one or more metals

-the metals may be present as native elements, or, more commonly, as oxides, sulfides, sulfates, silicates, or other compounds

-the term ore is often used loosely to include such nonmetallix mineralys as fluorite and gypsum

-minerals of little or no value which occur with ore minerals are called gangue

-some gangue minerals may not be worthless in that they are used as by-products; for instance, limestone for fertilizer or flux, pyrite for making sulfuric acid, and rock for road material

Seven mineral deposit types have contributed over 90% of the value of non-ferrous metalliferous mineral production in Canada

-based on average 1996 to 2005 inflation-adjusted metal prices, to the end of 2005 the most productive mineral deposit sypes have been:

1)magmatic Ni-Cu deposits (>372bil), mainly from Proterozoic rocks in the Sudbury and Thompson areas

2)volcanogenic massive sulphide (VMS) deposits (192bil), mainly from Archean greenstone belts of Quebec and Ontario, the Proterozoic volcanic belts of Manitoba, and Paleozoic volcanic rocks of New Brunswick

3)Iode gold deposits (132bil), mainly from quart-carbonate veins of Archean greenstone belts of Quebec and Ontario

Collectively,

4)porphyry

5)sedimentary exhalative (SEDEX)

6)Mississippi Valley

7)uranium deposit types

-have all contributed about 140bil and diamonds, a relatively new but growing mineral commodity for canada, has contributed 8 billion

ore - refers to useful metallic minerals that can be mined at a profit and, in common usage, to some nonmetallic minerals such as fluorite and sulphur

-to be considered of value, an element must be concentrated above the level of is average crustal abundance

-most nonmetallic minerals are generally not called ores, but rather they are called industrial minerals

-some of the most important accumulations of metals are associated with magma that forms igneous rocks

-certain metals are enriched in certain magmas and further concentrated during cooling of th magma

gravitational settling - heavy minerals that crystallize early settle and concentrate on the bottom of the magma chamber

immiscibility - separation and non-mixing of liquid phases of a magma

-nickel deposits of Sudbury and Voisey's Bay have similar origins, but different triggering mechanisms

Pegmatites - melt remaining in last stages of cooling is rich in volatiles and rare elements

-such a melt is very fluid and invades cracks and results in large crystals

Hydrothermal Deposits Associated With Igneous Activity

-among the best known and important ore deposits, generated from hot-water solutions

-majority originate from hot, metal-rich fluids that are remnants of late-stage magmatic processes

-move along fractures, cool, and precipitate the metallic ions to produce vein deposits

-can occur as disseminated deposits, which are distributed throughout the rock body, rather than concentrated in veins; called porphyry deposits (low grade;large volume)

-most of the world's copper, molybdenum and smaller quantities of other metals such as gold and silver

-Volcanogenic Massive Sulphide (VMS) deposits are pod-shaped bodies composed entirely of interlocking sulphide minerals

-heated seawater, rich in dissolved metals gushing from seafloor as black smokers today, may have produced VMS deposits in ancient rocks

Sediment-Associated Hydrothermal Deposits

-Sedimentary Exhalative (SEDEX) Deposits

-this layers of massive sulphide interbedded with sedimentary rocks

-Sedimentary-Hosted Stratiform Deposits

-copper-bearing brines moving through coarse-grained sedimentary rock are forced upward through oxygen-poor sulphide-rich mud, which promotes precipitation of minerals

mississippi valley-type deposits

-metal-bearing brines migrate toward basin edge and react with limestone

Banded Iron Formations

-Reducing conditions for much of the early Precambrian resulted in large quantities of ferrous iron in solution
-At some point, photosynthesizing bacteria (cyanobacteria) generated sufficient oxygen to precipitate insoluble iron oxide minerals

-Form very important source of iron-ore on many continents including the Lake Superior region

Placer Deposits - formed when heavy metals are mechanically concentrated by currents (examples include gold, platinum, diamonds)

Metamorphic

-many of the most important metamorphic ore deposits are produced by contact metamorphism ~ skarn

-sphalerite (zinc), galena (lead), and chalcopyrite (copper)

Weathering

-secondary enrichment- concentrating metals into economically valuable concentrations

-Bauxite - principal ore of aluminum

-forms in rainy tropical climates from chemical weathering and the removal of undesirable elements by leaching

-other deposits, such as many copper and silver deposits, result when weathering concentrates metals that are deposited through a low-grade primary ore

-Two Common Groups

Aggregate and Stone

-natural aggregate (crushed stone, sand, and gravel; latter two associated with glacial outwash deposits throughout Canada)

Industrial Minerals

-Diamonds

-most diamonds are found in unique ultramafic igneous rocks called kimberlites

-magma generated by partial melting of asthenosphere below 150 km and then rises quickly to the surface, picking up diamonds from solid lithospheric mantle

Other Industrial Minerals

-clays

-carbonate minerals

-evaporite salts (potash)

-phsophate

-sulphur

PETROLEUM

-origin lies in the alteration by heat of organic-matter concentrated in source rocks (black oranic shale)

-organic matter is transformed into a solid waxy material called keroen

-at higher termperatures the C-C bonds break in a process called cracking, eventually producing oil and then gas with progressively increasing temperatures

-oil forms in what geologists call the "oil window"

-50C to 100C

-below the temp oil remians trapped in the form of kerogen

-above the max the oil is converted to natural gas by thermal cracking

3 Requirements for Oil:

1)a source rock rich in organic material buried deep enough for subterranean heat to cook it into oil

2)a porous and permeable reservoir rock for it to accumulate in

3)a cap rock (seal) or other mechanism that prevents it from escaping to surface

-typically reservoirs will become organized in layers of water-oil-gas

*a geologic environment that allos for economically significant amounts of oil and gas to accumulate underground is termed a petroleum trap (common oil and natural gs traps include anticlinal traps, fault traps, and stratigraphic traps)

common oil traps: anticline, fault, salt dome, stratigraphic

Western Canada petroleum, esp in AB, is found in Devonian reefs and Mesozoic sandstone units

-formed mostly from plant material

-along with oild and natural gas, coal is commonly called a fossil fuel

-the major fuel used in power plants to generate electricity

-problems with coal use include enironmental damage from mining and air pollution

-most wester Canada coal is Cretaceous-Tertiary, but coal of Nove Scotia is Pennsylvanian (upper carbonierous)

Heavy Oil Sands

-Mixtures of sediment, water, and bitumen (a viscous black tar-like material)
-Several substantial deposits around the world, including huge reserves in Alberta
-Obtaining oil from tar sands is costly, but will play a major role as global conventional petroleum supplies decrease

Oil Shale

-Contains enormous amounts of untapped oil
-Currently, because of world markets and with current technologies, not yet economic to extract

Methane Hydrates

-Solid substance with methane surrounded by water molecule cages
-Found in permafrost and continental shelves
-Currently uneconomic and many environmental concerns

Coal Bed Methane

-Heating of coaly organic matter liberates methane
-Occur trapped in the pore spaces of coal seams and associated detrital sediments
-Currently uneconomic
---Difficult to extract by conventional means
---Methane can be released by pumping large quantities of water
-Surface & Groundwater contamination & depletion concerns
---Escape of methane in the atmosphere

-generates 14% of Canada's electricity

Uranium occurrences:

-residual fluids of felsic magmas ~ veins of uraninite

-fluid interaction of soluble uranium in oxidizing environments and insoluble in reducing environments rich deposits of N Sask's Athabasca Basin (accounts for Canada's entire uranium production)

-dissolved near the earth's surface by oxygenated ground water - Arizona, New Mexico, Utah

-Placers n precambrian rocks~ uranium ores of Elliot Lake, Ontario

Organic Based Sources

-Landfill Methane – produced by microbial decomposition of organic matter ~ significant contributor of greenhouse gases
---¼ of all landfill methane is collected in Canada
---About 70% used in energy production
-Biomass Energy ~ primary source of energy in 3rd world countries in the form of wood & dung
---Ethanol ~ anaerobic fermentation

Hydroelectric Power

-Can is a world leader in hydroelectricity

-62% of Canada's electricity is hydro-generated

CENOZOIC

-glacial hills

-porcupine hills

MESOZOIC

cretaceous

-St Mary River Formation

-Bearpaw Formation

-Belly River Formation

-Cardium Formation

-Trachyte Volcaniclastics

-Blairmore Formation

-Cadomin Formation (overlain disconformably on)

-Kootenay Formation (oldest Cretaceous)

PALEOZOIC

-Livingstone Group

CP1

-marine shale (late cretaceous) - bearpaw

-glacial deposits

CP2

-brocket

-procupine hills

-till deposits (Glacial)

CP3

-close to lundbreck

-Belly river formation (sandstone anticline)

-east and west dipping

CP4

-lundbreck, core of anticline

-Belly River Formation

-St Mary Formation (above)

-monocline (tertiary)

CP5

-near Bellevue

-Blairmore formation (maroon)

-Kootenay group (bitunimous coal)

-fault separates

CP 6

-Frank Slide

-carbonate rocks - Paleozoic (Mount Rundle Formation) aka. (Livingstone Formation)

CP 7

-Cadomin Conglomerate

-Blairmore formation

(crowsnest mountain)

CP 8

-cardium formation

-Alberta group

-iron nodules, marine conglomerates

CP 9

-Lewis thrust

-Mid-Cambrian ss from Gordon Formation

-Belly River group on opposite side

-major fault exists her

CP 10

-Volcanics - ash ridge

-Trachyte (rock)

-90 milion y.o.

-klippe

-older rock thrust up on top (thrust fault)

(top) Livingstone Formation

Banff Formation

Loewis thrust fault

(tree line)

Magmatic Deposits

-gravitational crystallization

-immiscibility

-pagmitite deposits (felsic- last stages,  large crystals)

Hydrothermal Deposits /w igneous activity

-vein deposits

-porphyry deposits (disseminated- low ore grade but large volume)

VMS - occur in all provinces but AB and PEI (pre cambrian)

Sediment Associated Hydrotherma Deposits

-SEDEX - smoke stacks

-failed rift systems

-sediment hosted stratified deposit (sheet-like/lens)

-mississippi deposits

Sedimentary Deposits

-banded iron deposits (pre cambrian-cambrian) (don't occur now due to atmspheric oxygen) (banded with chert)

-placer deposits (running water)

Deposits Associated with Metamorphism

-skarn

Deposits Associated with Weathering

-bauxite (canada must import)

-enriched deposits (pyrite)