Ch. 2 Flashcards
what brought more evidence for COntinental drift
mapping the ocean floor (Marie Tharp)
Convergent Boundaries
lithospheric [plate moves toward each other
crust experiences compression- shortening and thickening of crust, crust recycled into mantle
Subduction and conitnental collision
Plate tectonics with NW native American myths
thunderbird and whale has terrible fight-
St Helens and Adams both belong to Rainer, fight and Helens blew her top and unheaded Rainer
Continetal collision is characterized by
tall broad mountains
little to no volcanoes
broad zones of freqeutn earthquakes (moderate to strong)
rate of spreading
width of stripes/ time duration
Evidence of continental drift analysis
coastlines of continents fit together like pieces- used contintal shelves
Observed matching rock formation, mountain, fossil, and glacial formations across oceans
(land-dwelling animals on different continents when not able to swim)
(evidence of glaciers in tropical parts and tropical animals in cold parts)
Transform boundary
plates slide horizontally, sideways, past each other in different directions (shearing motion)
faults at boundary called transform/stick slip fault
crust is not created or destroyed but transformed
Accretionary Wedge/Prism
scraped up/squish material from the subducted slab (highly deformed material)
where do majority of eathquakes and volcanoes fall
same location as the plate boundaries
Rock’s magnetism and Earth’s Magnetic field
when magma solidify, iron based inerals align themselves with earth;s current magnetic field
Continental rifts
continent breaking apart
crust thickening bc of extension, causing faults and crustal down-dropped blocks (rift valleys)
mantle meets up to crate, space below continents, mantle upwelling
as mantle upwells, ptrdsure descrease, metls form- bouyant and rises to top- volcanism
*** valleys within continents that have volcanoes and earthquakes **
slab pull
gravity pulls dense subducting slab in asthenosphere
OC-CC (oceanic to continental)
the denser one (OC) is subducted under CC
Failed contiental rifting
large scale rifting- multiple rift branches
some die out- no tectonic activity
Hotspots
area where magma breaks through OC or CC and creaes volcanic center, islands in ocean, and moutnain on land
NOT associated with plate boundaries
mantle plume is stable- but plarte moves causing bolcanic island- as plate mvoes, volcanic osurce cut off, forms new volcanic isalnd, sinks as gets colder
Divergent boundaries characteristics
crustal stretching/extension lead to normal faults and rift valleys (moderate earthwuakes occur)
volcanism common bc of decompression melting (formation of new crust)
movement of lithospheric plates
Slab pull
ridge push
mant;e convection (basal traction)
Rate of relative plate movement
measure position of GPS recievees over time
arrows show direction of motion, with highest rarte shwon by larger arrow
some arrow curve because plate rorating on spheres
Continental collision
2 continental lithospheric plates converging
no subduction- crust to buoyant
crust thickening, mountain building, high plateaus
Wadati-Benioff ZOnes
recognition of earthquake epicenters tracing shapes of oceanic plates that are sinking into the mantle
EQ epicenters starting at deep trenches on the ocean floor, concentrate along a descending plane angles beneath continents or island arcs
crust being pulled into mantles at the locations (convergent boundary)
What is primary cause of movement of lithosphere plates
slab pull
OC- OC
older (colder and denserO subducts under the uounger
trench- defines boundaryd
The wilson cycle
ongoing cyclical process of the origin and breakups of superconitinents
Continental Drift Analysis
1912, Alfred Weneger, all continentas connected but broke and drifted apart to present positions
Why was continental drift anaylsis rejected
not ahve the mechanism for continental movement
The Wilson Cycle
J. Tuzco Wilson porposed cyclical process of opening and closing of oceans leading to breaking apart and reassembly of continents
Subduction
Oceanic- Oceanic convergence and Oceanic-continental convergence
plates of different densities converge, the higher density plate is pushed beneath the more buoyant plate
What do subduction zones produce
largest earthquakes and tsunamis
where deepest earthquales occur, along subducting slab and megathrust
two types of rifts
narrow and broad
transform boundary characteristics
no volcanoes or mountains- mainly earthquakes
most associeated with MOR- help accomodate for different rates of sea floor spreading
zig zag pattern
ocean trench
deepest part, plate boundary at surface
OV subducts under CC, Causes CC to drag down and create deep crevice
oceanic fracture zone
plates along fractures still moving in same direction
Paleomagnetism
geologist study/measure the direction that magnetic minerals are oriented i nrocks and the strength of magnetism building a record of past magnetic polar changes- paleomagnetic record
broad rifts
create parallel ridges and valleys
graben- downfaulted stack
horst- upfaulted block
Seafloor Spreading
Harry Hess and ROvert Dietz- 1959-
propoed along Mid-Ocean Ridges-
Earth’s crust separates, new ocean crust is CREATED, newly formed ocean crust masss laterally, away from the ridge (divergent)
what happens in continental rift continues
continent will break apart and a new ocean floor will form- sea floor spreading developed
edges of two new continents called passive margins (no plate boundaries are there
Difference between magma with cc-oc and oc-oc
on cc-oc, its a mountain belt with volcano
on oc-oc, its a volcanic island arc (not island chain)
PLate tectonics and Japanese culture
Namazu- the earthquaker
catfish undergound that causes earthquakes when shaking
Japan has 1/10 of the world’s earthquakes
when was plate tectonic theory well established
1970s
total of 15 plates, named after conitnents
Divergent boundaries
tensional forces and/or upwelling of mantle
plates move away from each other
continental rifts and Mid-ocean ridges (MOR)
Earth’s magnetic field
generated by the outer core, iron is liquid and constantly moving (named dynamic effect)
Magnetic pattern of ocean floor
caused by earth’s magnetic field flipping back and forth reversing polarity
supports sea floor spreading
three types of plate motion
Divergent- move apart
Convergent - move towards each other
transform - move horizontally past each other
seafloor spreading rates
width of stripe/time duration
Magnetic stripes of the ocean floor
late 1950s, equipment to measure magnetic fields on ocean seafloor
the magnetic were alternating and mirrored each other on both sides
Ocean drilling program
began 1960s
ships drill in sea floor, collect rocks and sediment
brought up oceanic crust (ages at multiple locations)
youngest crust lives along the MOR
HARD PROOF of sea floor spreading
ophiolite
sequence of igneous rocks that represent a slice of oceanic crust
shows where ancient ocean floor was sceraped up ontio continental crust due to subduction
Mantle Convection
hotter material rises and cooler mterial sinks- drag force along base of plates
Continental converge in general
start with closing of ocean causign continents to join together
How is drilling giving the hard proof of Seafloor spreafing
shows the age at multiple locations- youngest at the MOR
sediments on sea floor shows increasing thickness with distance away from ridge
Cascadia earthquake
earthquake releases stress, falls down, water submerged again, ghost forect
fold and thrust belt
lots of faults, deformed rocks,
glacial strations
record direction of glacial flow
narrow rifts
East African rift system- narrow and long
Transform boundaries
continental transform fault occur along or within a continent as a single or sets of faults
how MOR form
rift valley in center (spreading center)
mantle upwelling form 2 plates splitting- decompression melting
abyssal plain- where mantle upwelling occurs
hot and thin so bouyant- edges result in higher elevation for the ridges
as crust moves away, become scolder and older oceanic crust, falls down, flattens out, flat deep abyssal plains
Mid ocean ridges
AKA spreading centers
oceanic plates move away from each other- widening of oceans
underwater ridges riaw 1 km above obyssal plain with rift valley in the center
Himalayan Moiuntains
sea closed up, India slammed into Eurasis, stopped volcanism, expansion of Mt: himalayan and tibetan plateau
Mapping of floor oceans
after WWII began mapping ocean floor using SONAR
Marie THarp and Bruce Heezen created first detailed map of the ocean floor and revealed the Mid-Atlantic ridge
volcanic arc and mountain belt
as plates subducted, magma is forming and rises to form the heart of the mountains and creates volcanoes
ridge push
gravity causes plates to slide away from topography of MOR, pushing plate outward
Plate Tectonics
theory that layer of earth (Lithosphere) is broken into several plates that move relative to one another
