GENERAL GEOLOGY (GLOBAL TECTONICS) Flashcards
What is the basic tenet of Plate Tectonic Theory?
The lithosphere is broken along major fault systems into larger slabs called as plates which move relative to one another. The presence of a breakable strong lithosphere allowed the formation of the plates while the fact that they overlie a plastic astenosphere accounts for their movement.
What marks the ends of plate boundaries?
Triple Junctions (where three plates meet)
What are the minor plates?
Caribbean, Cocoz, JuandeFuca,Philppines,Arabian, Nazca and Scotia
What are the seven major lithospheric plates which account for 94% of the Earth’s Surface Area?
NAm, S Am, Pacific, African, Eurasian, Australian-Indian and Antarctic
What are the major plate boundary which is defined by the relative movment of plates
Divergent, Convergent, Transform plate boundaries
What are the hybrid plate bboundaries
Divergent Transform and Convergent Transform
Occurs where two plates are moving apart relative to the boundary resulting in upwelling of hot material from the mantle to create new sea floor?
Divergent Plate bOundaries
Another term for divergent plate boundaries relative to creation of new seafloor
Spreading Centers
Characteristics of DPB?
Horizontal Extension and vertical thinning of the lithosphere
What marks extension in continental and oceanic lithosphere respectively?
Continental Rifts and
Oceanic Ridge system
how do continental rift systems form?
1) They form though progressive stretching and thinning of continental lithosphere.
2) Stretching occurs throgh brittle normal faulting at the surface and ductile flow below warmer level.
3) Once the lithosphere is thinned, uplift will happen due to rising of hot plastic astenophere 4) which will lead to rifting along normal fault which produce continental rift valleys
Name 3 rift valley and their locations
East African Rift,
Rio Grande Rift,
Dead Sea Rift
Surface evidence of an active upflow of mantle material in East African Rift?
Volcanism in Mt. Kilimanjaro and MT Kenya
the process in which prolonged extension and thinning of continental lithosphere produces two separate continents
Continental Rifting
What happens when continents rift?
When continents rift a ridge will remain as the remnant which will initiate sea floor spreading and eventually forms of new and growing ocean basin. as SFS continues, oceanic basin will continue to widen when sediments covers continental margins
MOst recent example of Continental Rifting
Arabian peninsula rifting from Africa which created the Red Sea Basin 5Ma ago
Age and ocean basin formed when india rifted from africa?
115Ma NW Indian Ocean basin
Age and ocean basin formed when NAm rifted frm Africa?
180 Ma N Antlanic Ocean Basin
What happens to the divergent boundary once the continents completely rifted?
It is now situated along spreading ridges in the oceanic crust where it is produced and grows through SFS
Elevated areas of the seafloor characterized by high heat flow and volcanism
Oceanic RIdges
This is a deep canyonlike structure formed along crests of some ridge segments
Rift Valley
This is the largest/longest mountain range of the Earth which convers roughly 20% of the Surface?
Oceanic Ridge System
Segments of the Oceanic Ridge system?
east Pacific Rise, MidAtlantic Ridge, Mid indian rige, SW and SE indian ridge, Galapagos Ridge (N of Nazca), Chile Ride (S of Nzaca)
The average dimensions of oceanic Ridge system?
L:>65,000km W: 1,500 km H: 3km above surroundin sea floor
Average slope of ORS?
0.4 deg
Which have gentler and steeper slopes in the ORS of Earth?
Warmer, faster east pacific ridge system is gentler colder and slower mid atlanic ridge is steeper
Movement rate or east pacific ridge system?
6-18cm/yr (Heff) 15cm (tarbuck)
Movement rate of midatlantic ridge?
2-4cm/yr (Heff), 2cm/yr (tarbuck)
What marks the central or axial portion of ORS which marks the divergen plate boundary in oceanic lithosphere?
Rift valley
Explain the theory of seafloor spreading
oceanic crust and lithosphere forms along the axis of ridge systems or in rift valleys and tends to spread away from it in both directions which causes the ocean to grow through time
who discovered Theory of Seafloor Spreading?
harry Hess
Explain how an ophiolite is formed?
A gabbroic melt which crystallizes well below the chamber forms the plutonic grabbroic unit, when some of those melts intrudes near vertical faractures above the chamber it forms the basalti-gabbroic sheeted dikes. Meanwhile as magma intrudes to the surface, it forms the pillow basalt unit due to the quenchin of sea water. Layer 1 represents the seds that are deposited on top of the basltc unit. Meanwhile below the magma chamber is a representative of the mantle consisting of ultramafic rocks which is formed by differentiaton near the base of the gabbroic magma bodies
Explain underplating?
Thickening of lithosphere from below which occurs as the solid, unmelted portion of the asthneosphere spreads laterally and cools through a critical temp below which it become strong enough to fracture. Underplating preceeds subduction
When will subduction happen?
When density of oceanic lithosphere exceeds that of the underlying asthenosphere
What does seafloor spreading theory imply with the age of OC?
As OC moves away from the ridge axis, it becomes older
General relationship between age and thickness of OC?
The older, the cooler the thicker
This is the process by which the leading edge of a denser lithospheric plate is forced downard into the underlying asthenosphere
Subduction
What do you call the downgoing plate?
Subducted plate or downgoing slab
What do you call the less dense plate?
Overriding plate
in which setting will a subduction have relatively low angle?
In young subduction zone near spreading centers
At what depths woul partial melting of subducting slab occur?
100km
What is the product of oceanic-continental convergence?
Continental Volcanic Arc
what is the product of oceanic-oceanic convergence?
Volcanic Island Arc
Where is Mt. Pelee located? which erupted in 1902 killing 28K
Martinique
What is the composition of the subducting slab that have ave thickness of 100km
oceanic lithosphere
What is the role of subduction in recycling of plates?
It is the major process by which oceanic lithosphere is destroyed and recycle into astenhosphere at rates similar to that of MOR production
What is the surface expression of subduction zones?
Trench-arc Systems
What are trenches?
These are deep, elongated troughs in the ocean floors marked by water depths that can approach 11km
How are trenches formed?
When the subducting plate forces the overriding slab to bend downwars thus forming a narrowlong trough along the boundary
What is the Wadati-Benioff Zone?
It is an inclines seismic zone which is the source of some of the notable eqartquake produced by the stress-reaction of the cool interior of the subducting slab as the asthenosphere resists its downward movement
To whom was this zone named after?
Kiyoo Wadati and Hugo Benioff
examples of equakes produced in inclined seismic zones?
CHile (1909), Alaska (1964), and Sumatra (2004)
A tsunami event in 2004 caused by subduction zone beneath sumatra?
Banda Aceh tsunami
What is the ultimate fate of subducting slab?
Either it flatten out as they reach 660 km above the transition zone or they may reach the D’’ layer and eventually melt to contribute in the formation of mantle plumes
This image is a 3D variation in seismic wave velocity w/in the mantle and was used to understand the d’’
Seismic Tomography
There are the two processes in which the continental crust is generated
Underplating and intrusion
Aside from volcanic magmatic arcs what are the other possible product of subduction zones especially when magma just intrude the crust?
Batholith Belts
in which parts of a magmatic arc are the huge volumes of detrital sed rocks produced by erosion deposited?
Forearc and Backarc basins
When does continental collision occur?
When almost the entire oceanic curst have already been consume and subduction cease because continental lithosphere s too bouyant to be subducted, as convergence continues, the margins of both continenta plates are compressed and shortened horizontally and thickened veritically
What are the possible products of continental collision?
Uplift of a mountain belt or extensive elevated plateau which marks the closing of an ancient oceanic basin
These are long mountain belts formed along convergent plate boundaries?
Orogenic Belts
How does foreland basins formed?
When thickening continues adjacent continental lithosphere bend downwards thus producing basin shaped landform
Type of metamporphism usually associated with orogeny?
Regional met
Tibetan Name of Mt. Everest?
Chomolungma
To where will you associate a limestone found near the summit of Mr.Everest
Oceanic floor of Tethys Sea which were thrusted to an elevation of 9km when Indian-Eurasian collision happened
This river flows approx east west along the trough which represent the foreland basin of the himalayas
Ganges River in Northern India
Characterized by horizontal motion, along fault systems, which is parallel to the plate boundary segment that separates two plates
Transform Plate Boundaries
Who first envisioned transform faults to explain the seismic activity along facture zone in the ocean floor?
J.T. Wilson (1965)
These are curvilinear zones of intensely faulted, fractures ocanic crust generally oriented nearly perpendicular to the ridge axis
Fracture Zones
These are exterior portions of fracture zones outside ridge segments which represent oceanic crust that was faulted and fractured when it was between ridge segments, then carried beyond adjecnt ridge segment by additional sea floor spreading
Healed tranforms or transform scars
What cause strike slip faulting in fracture zones?
If sea floor continues to spread in two offset ridge segment, then the movement along the farcture zone in between the two sgments is characterized by opposing spreading direction this producing shear stress
This is the transform fault which bounds Juan de Fuca in the south
Mendocino Fault
Best known continental transform plate boundary?
San Andreas Fault in California
What bounds San Andres Faullt?
Separates N Am from Pacific Plate connecting spreading ridges ni gulf of California with Juan de Fuca plate
Example of transform fault in New Zealand?
Alpine Fault System
Example of continental transform fault in Eurasia?
Anatolia Faults system
Can plate move through divergence or convergence alone?
no, they need horizontal fault movement via transform plate boundaries
These are long-lived areas in the mantle where anomalously large volumes of magmas are generated which occurs beneath both continenral and oceanic lithosphere
Hotspots
An example of hotspot along divergent plate boundaries
Iceland
Direction of sea floor spreading relative to Hawaii volcanic chain?
WNW
Direction of plate motion relative to volcanism in yellowstone caldera?
SW
These are hypothesized to be the subsurface source of Hotspots which originated from ULVZ of D’’ layer at the base of mantle and may represent dregs of subducte slabs warmed sufficiently by contact with the outer core and became buoyant enough to rise
Mantle plume
These were hypothesized to be significat players in extinction events, the initiation of continental riftnig, and in super cintinent cycle
Superplumes
What balances differences in displacement between plates?
Transfom faults
What type of convergence created the Cordilleran mountain chains of Andes and NAm?
Subduction
What mountain range was produced by the closing of a proto atlantic ocean?
Appalachian-Variscan Mountain chain
What is Wilson Cycle?
The cyclic opening and closing of oceans
What is accretionary tectonics?
suspect and exotic terranes of less than continental proportions are moved by plate motion to collition with each other or with continents
Differentiate exotic and suspect terrane
Suspect terrane is a rock mass in which orignal position is questionable with respect to adjacent terrane or continent which it is present attached while exotic terrane bears no resemblance o the mass to which it is attached
Year when theory of plate tectonics was developed?
1968
Book which first discussed the continental drift theory and when was it published?
The Origin of Continents and Oceans, 1915
A german meteorlogist and physcisit who formulated the continental dirft hypothesis
Alfred Wegener
A single supercontinent consisiting of all Earth’s landmasses in the continentral drift hypothesis?
Pangaea
Whats the literal meaning of the greek Pangaea?
All lands
He was the first person to discover glossopteris and glaciation evidence in rock sequence which led him to conclude a giant land mass of the southern conitents
Edward Suess
An american who first believed continental drift in which he said that mountain ranges are result of lateral movements of continents and that gigantic tidal forces are the main mechanism of this movement. He aksi suggested the Mid Atlantic Ridge
Frank Taylor
Evidences of Continental Drift
1) Continental Fit/Jigsaw Fit; 2) Fossil Matching accross seas
He was the one to proved that continental shelves of SAm and Africa at depth of abt 900 meters (3000ft) fit together in 1960
Sir Edward Bullard
A small aquatic freshwater reptile found in SAm and SW Africa
Mesosaurus
In which start sequence are mesosaurus limited?
Permian Black Shales
These are tongue-shaped leaves and seeds that were too large to be carried by wind and also known as Seed Fern
Glossopteris
Continents which have glossopteris
Africa, Australia,Antarctica, S.Am and India
Land reptiles which have fossils in Africa, India, and Antarctica?
Lystrosaurus
Land reptiles which have fossils in South America and Africa
Cynognathus
Mountain belts which were one of the evidences of similarity in rock types
Appalachians (NE,USA Newfoundland) and British isles, Western africa and caledonian in Scandinavia
The age of glaciation found in glacial evidences in southern continents?
L Paleozoic
What was the downside of the continental drift?
Wegener was not able to identify a credible mechanism and porposed that gravitional forces from the moon and the sun which produce tides accounts for the gradual movement of continents
When and where did Wegener die?
1930s at Eismitte, Greenland in his fourth expedition to the Ice sheets
a South African geologist who named Laurasia as the northern landmass of Pangaea and came up with the idea that Gondwana moved south pole due to glacial evidence and northern continent moved along the equator due to coal evidence.
Alexander du Toit
What would happen to NAm?
Bajan Peninsula will collide with the Aleutian Islands
What would happen to Africa?
Will collide Northward with Eurasia, closing of Miditerranean sea (last remnant of tethys sea)
What would happen with Australia?
Australia will continue to move towards the equator along with PNG and SEA
What will happen to S am and N am?
will continue to separate since Atlantic ocean and Indian ocean will continue to grow
When will the next supercontinent arise?
250 million years in the future Pangaea Proxima
What are the evidences of plate tectonics?
1) Ocean Drilling (Sea Floor Spreading) ;
2) Mantle Plumes and Hot Spots;
3) Paleomagnetism
This is the year (range) that the deep sea drilling project operated?
1968-1983
The drilling ship capable of working under water in thousands of meter used to map the ocean floor
Glomar challenger
This new international effort for exploration of the seafloor to recover a complete section of the ocean crust from top to bottom which uses multiple vessels
JOIDES Resolution, Integrated Ocean Driling Project (IODP)
A vessel 770ft long which means “planet earth” in Japanese; part of the IODP
Chikyu
Location on Earth’s Surface where there is anomalous heat which forms usually volcanous
Hotspots
Staionary column of magma originating deep wion mantle which is slowly moving to the surface
Mantle Plume
Trail of extinct and progressively older volcanoes resulting from the movement of plates over stationary mantle plumes within the mantle
Aseismic Ridge
One of the most studied linera chains of volcanic structures in the pacific ocean
Hawaiian Island-Emperor Seamount Chain
When did Hawaii rose from the ocean floor?
0.7 Ma (Pleisto)
Oldest volcano in the Hawaiian volcanic chain
Kauai (3.8-5.6)
The temp at which Fe-bearing minerals gain magnetization. If heated above this temp, minerals will lose their remanent magnetization
Curie Temp
Curie temperature value
585 deg C or 1085 deg F
When does fe-rich minerals align themselves to the magnetic field?
during cooling
These are the magnetic alignment preserved in rocks which formed thousand or million years ago and contain a record of the directions of the magnetic poles at the time of their formation
Paleomagnetism or Fossil magnetism
This pertains to the apparent movement of the magnetic pole based on paleomagnetic readings of lava flows which turned out to be caused by movements of plates
Aparrent Polar Wandering
Differentiate Normal and reverse polarity relative to magnetic revesal phenomenon
Normal Polarity follow the present magnetic field
This is the time scale established by dating lava flows and measuring their magnetic polarity
Magnetic Time Scale
Major Division of Magnetic Time Scale?
Chrons
equivalent of 1 chron?
1Ma
Equivalent of subchron
<200,000 years
Instruments used to do magnetic surveys of the ocean
Magnetometer
IN terms of magnetic revesarl, which features of the sea floor implies reverse polarity?
Low-intenstity stripes
How do geologists examine the direction of plate motion
1) Relative Motion by Sed dating divided by the distance from the spreading ridges; 2) Magnetic Anomaly 3) Satellite laser ranging techniques
This is a type of heat transfer that involves the actual movement of substance
Convection
Heat source of mantle convection
Decay or Radioactive Elements and remnant heat
A major dirving force of plate motion wherein cold slabs of denser oceanic lithosphere are sinking that is pulled down into the mantle by gravity
Slab Pull
A gravity driven mehcanism resulting from the elevated position of the oceanic ridge which causes slabs of lithosphere to slide down the flanks of the ridge
Ridge Push
This happens when flow in the asthenosphere is moving at a velocity that exceeds that of the plate
Mantle Drag
This is a major mechanism for transporting heat away from the earth’s interior to the surface and eventually radiated into space
Convection Flow
This model suggest that the ultimate burial ground for subducting slabs is the core-mantle boundary and this downward flow is balance by buoyantly rising mantle plumes that transport hot material to the surface
Whole Mantle Convection / Plume Model
Differentate the two types of plumes proposed in Whole Mantle Convection
Narrow tube like plumes that extend to from the core-mantle boundary which are associated to hotspot volcanism, and Large Megaplumes or Giant upwellings are those that are associated beneath pacific basin and southern africa
What drives heat for Whole Mantle Convection?
Heat from the Core
This model suggest that the earth has two largely disconected convective layers: A dynamic upper layer drived by descending slabs of cold oceanic lithosphere and a sluggish lower layer that carries heat upward w/p appreciably mixing with the above layer
Layer Cake Model
The division of Layer Cake Model
660km - 1000km
