iv. modern plate tectonic theory a. major plates and plate margins names and types of major plates...
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IV. Modern Plate Tectonic Theory
A. Major plates and plate margins Names and types of major plates Symbols for plate margins
B. Divergent (constructive) margins
C. Convergent margins
D. Transform or Strike Slip margins
E. Volcanic Hotspots
F. What drives it all?
Image from USGS plate tectonics web site
IV. Modern Plate Tectonic Theory
A. Major plates and plate margins Names and types of major plates
A. Major plates and plate margins Symbols for plate margins
IV. Modern Plate Tectonic Theory
Convergent marginTeeth on upper plate side
Divergent margin
Transform margin
Major tectonic plates, plate boundaries, plate motion vectors
Arrow are plate vectors, numbers are rates of plate motion in centimeters per year
IV. Modern Plate Tectonic TheoryA. Major plates and plate margin
IV. Modern Plate Tectonic TheoryA. Major plates and plate margin
A slightly different representation from This Dynamic Earth USGS poster
Shading (red) shows diffuse zones of crustal deformation, most of these are associated with (adjacent to ) plate boundaries and are areas of high earthquake activity
Red dots are locations of “hot spot” volcanism, many of these are within plates
IV. Modern Plate TectonicsA. Major plates and plate margins
B. Divergent (constructive) margins mid-ocean ridges (=spreading centers) Continental rift zones (incipient divergent margins)
Divergent plate margins are also referred to a constructive plate margins; this is because igneous activity at these plate margins generates new lithospheric plates including new oceanic crust
B. Divergent (constructive) margins• mid-ocean ridges (=spreading centers)
IV. Modern Plate Tectonic Theory
B. Divergent (constructive) margins• mid-ocean ridges (=spreading centers)
elevated ridge but with an axial rift (faulted) valley along the ridge axis
active magmatism including sea floor volcanism
IV. Modern Plate Tectonic Theory
Water depth or depth below sea-level
highest rate of heat loss (surface heat flow) on Earth
magmatism generates new oceanic crust and lithospheric plates
Mid Atlantic Ridge is a slow spreading ridge
East Pacific Rise is a fast spreading ridge
B. Divergent (constructive) margins• mid-ocean ridges (=spreading centers)
IV. Modern Plate Tectonic Theory
highest rate of heat loss (surface heat flow) on Earth
magmatism generates new oceanic crust and lithospheric plates
East Pacific Rise is a fast spreading ridge
Another look at an axial rift valley
B. Divergent (constructive) margins• mid-ocean ridges (=spreading centers)
IV. Modern Plate Tectonic Theory
Major Tectonic Plates & Plate Boundaries• Divergent (constructive) margins
• Continental rift zones (incipient divergent margins)• Magmatism and volcanic activity accompanies continental rifting (ex. East
Africa Rift)• Such rifting can lead to development of a new plate margin and ultimately a new
ocean basin (ex. Red Sea)
Major Tectonic Plates & Plate Boundaries
Image from USGS plate tectonics web site
• Divergent (constructive) margins• Continental rift zones (incipient
divergent margins)• East African Rift Zone• Red Sea is a new ocean basin
Active volcanoes
IV. Modern Plate Tectonic Theory
A. Major plates and plate margins
B. Divergent (constructive) margins
C. Convergent margins (two main types) Subduction zones (two sub-types)
○ Ocean-ocean○ Ocean-continent
Continent-Continent collision zones
D. Transform or Strike Slip margins
E. What drives it all?
• Convergent margins• Subduction zones
• ocean-ocean• ocean-continent
IV. Modern Plate Tectonic Theory
Ocean-continentOcean-ocean
Deep-sea trench is site where oceanic lithosphere starts to descend into mantle
• Convergent margins• Subduction zones are sites where an oceanic tectonic plate descends into
the mantle• Overriding plate may also be an oceanic tectonic plate (ocean-ocean) or
may be a continental tectonic plate (ocean-continent)• Chain of volcanoes are found on the overriding plate
• Island arcs (ocean-ocean)• Continental volcanic arcs (ocean-continent)
IV. Modern Plate Tectonic Theory
Ocean-continentOcean-ocean
Convergent marginsSubduction zones are sites of deepest earthquakes on earth (to 700 km)Array of earthquakes marks the subducting lithosphere = Benioff ZoneEarthquake array starts at trench (shallow) and gets progressively deeper beneath the over
riding plate
IV. Modern Plate Tectonic Theory
Japan
Convergent marginsSubduction zones are sites of deepest earthquakes on earth (to 700 km)Array of earthquakes marks the subducting lithosphere = Benioff ZoneEarthquake array starts at trench (shallow) and gets progressively deeper beneath the over
riding plate
IV. Modern Plate Tectonic Theory
Benioff Zone = earthquakes within the cold subducting lithospheric plate
IV. Modern Plate Tectonic Theory
A. Major plates and plate margins
B. Divergent (constructive) margins
C. Convergent margins (two main types) Subduction zones (two sub-types)
○ Ocean-ocean○ Ocean-continent
Continent-Continent collision zones
D. Transform or Strike Slip margins
E. What drives it all?
Image from USGS plate tectonics web site
• Convergent margins• Continent-Continent collision zones
• Himalayas (India & Tibet)• Zargos (Middle East)• Alps (Southern Europe)
IV. Modern Plate Tectonic Theory
• Convergent margins• Continent-Continent collision zones
IV. Modern Plate Tectonic Theory
Clay block model
Rigid indenter
Escape tectonics
• Convergent margins• Continent-Continent collision zones
IV. Modern Plate Tectonic Theory
Escape tectonics
A. Major plates and plate margins
B. Divergent (constructive) margins
C. Convergent margins
D. Transform or Strike Slip plate margins At mid-ocean ridges San Andreas fault zone
IV. Modern Plate Tectonic Theory
Image from USGS plate tectonics web site
Transform or Strike Slip Plate Margins
IV. Modern Plate Tectonic Theory
San Andreas fault zone
At mid-ocean ridges
A. Major plates and plate margins
B. Divergent (constructive) margins
C. Convergent margins
D. Transform or Strike Slip margins
E. Volcanic Hotspots
IV. Modern Plate Tectonic Theory
E. Volcanic Hotspots
IV. Modern Plate Tectonic Theory
A volcanic hotspot is mantle plume that is stationary with respect to overriding tectonic plate.
Examples include:
Hawaii (oceanic hotspot)
Yellowstone (continental hotspot)
E. Volcanic Hotspots
IV. Modern Plate Tectonic Theory
A hotspot is mantle plume that is stationary with respect to overriding tectonic plate.
E. Volcanic Hotspots
IV. Modern Plate Tectonic Theory
A hotspot is mantle plume that is stationary with respect to overriding tectonic plate.
Emperor-Hawaii Seamount Chain
Hotspot (mantle plume stationary with respect to overriding tectonic plate)
E. Volcanic Hotspots
IV. Modern Plate Tectonic Theory
A hotspot is mantle plume that is stationary with respect to overriding tectonic plate.
Pacific plate has moved over the Hawaii hotspot for over 60 million years (Ma) leaving a hotspot track of now extinct volcanoes, all similar to Hawaii
The Hawaii-Emperor Volcanic Chain
E. Volcanic Hotspots
IV. Modern Plate Tectonic Theory
A hotspot is mantle plume that is stationary with respect to overriding tectonic plate.
Yellowstone-Snake River Plain
Hot Spot (mantle plume stationary with respect to overriding tectonic plate)
A. Major plates and plate margins
B. Divergent (constructive) margins
C. Convergent margins
D. Transform or Strike Slip margins
E. Volcanic Hot Spots
F. What drives it all?1. Earth’s internal heat engine
2. Density “currents” in plastic mantle
IV. Modern Plate Tectonic Theory
F. What drives it all?1. Earth’s internal (endogenic) heat engine
Geothermal gradients (evidence of hot interior)
○ Temperature increases with depth in solid earth, most obvious surface expressions of geothermal gradients Volcanic eruptions, geysers and hot springs,
fumaroles Radioactive heat production and residual heat of
planet formation
IV. Modern Plate Tectonic Theory
Hot springs
Volcanoes
Heat production with time
Heat produced by impact during planet formation
Radioactive heat production declining with time
Only during earth’s formation
Rocks are poor heat conductors
Earth is still cooling
F. What drives it all?
2. Density “currents” in plastic mantle Ridge push (rising mantle) Slab pull (sinking plate)
Mid-ocean spreading ridges have the highest surface heat flow on earth Subduction zone
trenches have the lowest surface heat flow on earth
IV. Modern Plate Tectonic Theory
Slab pullNew (young) oceanic lithospheric plates are hot, but they cool over 10’s of millions of years as they move away from the oceanic spreading ridge.
As the oceanic plates cool they become more dense, eventually becoming dense enough to sink into the mantle.
Age of the CrustShield areas on the continents are Precambrian in age (0.54 – 4.2 billion years)Remainder of continental crust is Phanerozoic in age (Recent to 542 million years)Oceanic crust is Mesozoic and Cenozoic in age (170 million years [Jurassic] to Recent)
Age of the CrustOceanic crust is generated by igneous activity at mid-ocean ridges and eventually is recycled back into the mantle at subduction zone (due to its higher density)
Age of the CrustIgneous activity above subduction zones (island arcs and continental volcanic arcs) generates lower density continental crustThis lower density crust is too buoyant to be subducted The inability to subduct explains why much of the continental crust is so old (billions of years)