Fluent Essays

Check attach Find an event that occurred this week that moves you. You must be able to relate it to the current chapter in some way – creativity is welcome. For instance, let’s say you read about the war in Afghanistan and parts of Pakistan. After reading the article, you check a world map and find that some remote parts of Pakistan are near the Himalayan Mountain Range. You will discover in Chapter 3 that the Himalayas were formed by a convergence of two continental plates, the Indian plate and the Eurasian plate, which causes a convergence zone that resulted in mountain uplift. And, voila!, the Himalayans are formed. Remember, geology is all about connections. The physical environment always sets the context for human events, and, often, they have a more direct influence than you may initially imagine. For example, you’re not worried about a tsunami if you live in North Dakota, but you are much more aware of the Pleistocene glaciations than you would be if you lived in Arizona. You may use an article from the following sources: Reuters National Public Radio Another news outlet if you include a paragraph telling me why you chose it. Turn in: A document that includes the entire story (copy and pasted from the original site). The citation (where you got it and when). The link. A map of the location of the event that was not included in the article. Paragraph of what you think about the news (good, bad, indifferent – just tell me why). Paragraph explaining at least one geologic connection that relates to this week’s chapter. Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics  The hypothesis that continents are mobile.  Proposed by German meteorologist Alfred Wegener.  The Origins of Oceans and Continents published in 1915.  Wegener hypothesized a former supercontinent, Pangaea.  Idea was founded on strong evidence. “Fit” of continents. Location of glaciations. Fossil organisms. Rock type and structural similarities. Paleoclimates preserved in rocks. Continental Drift Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Continental Drift  Wegener’s idea was debated and ridiculed.  Most scientists didn’t believe him.  Lack of a mechanism for drift a major criticism.  Wegener died in 1930 at the age of 40.  Lacking an advocate, the drift hypothesis faded.  His idea was revived in the 1950s. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Continental Drift  Wegener was right!  Sea-floor spreading.  Subduction.  Plate Tectonics.  Why did scientists dismiss Wegener’s model? Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Continental “Fit”  Wegener noted that continents seem to fit together.  He argued that the fit could not be coincidental.  Present shorelines make a rough fit.  The continental shelf edges make a better fit. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Glacial Evidence  Permian glacial till is found on four continents.  The tills in Africa and India are now near the equator.  A cooler earth? No. Permian tropical plants are known. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Paleoclimatic Evidence  Placing Pangaea over the Permian South Pole…  He correctly predicted…  Tropical coals.  Tropical reefs.  Subtropical deserts.  Subtropical evaporites. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Fossil Evidence  Identical fossils found on widely separated landmasses.  Mesosaurus – A freshwater reptile.  Glossopteris – A subpolar plant with heavy seeds. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Fossil Evidence  Identical fossils found on widely separated land.  Lystrosaurus – A non-swimming, land-dwelling reptile.  Cynognathus – A non-swimming, land-dwelling mammal- like reptile.  These organisms could not have crossed an ocean. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics  Geologic phenomenan match across the Atlantic.  Geologic structures.  Rock types.  Rock ages. Matching Geology Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics  Geologic phenomenan match across the Atlantic.  Mountain belts. The Appalachians. The Caledonides. Matching Geology Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Criticisms of Drift  Why wasn’t the continental drift hypothesis accepted?  There were no mechanisms for moving continents.  When Wegener died, the debate did too.  The drift hypothesis needed new and different evidence.  This was provided by paleomagnetism. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics The Earth’s Magnetic Field  Earth’s magnetic field acts like a giant bar magnet.  It’s N and S ends are tilted ~11° from the axis of rotation.  Measured everywhere on Earth, it extends out into space.  Some iron minerals in rocks align to the magnetic field.  This permits some rocks to preserve magnetic information.  Preserved magnetism can be read from these rocks. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Magnetic Poles  The “bar magnet” intersects Earth’s surface.  Magnetic North Pole; magnetic south pole.  Differs from geographic north pole (rotational axis).  The magnetic poles move constantly, but stay in the vicinity of the N and S geographic poles. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics  Above 350-550°C.  Thermal energy of atoms high.  Magnetic dipoles randomly oriented.  No magnetic signature.  Below 350-550°C.  Thermal energy slows atoms.  Dipoles align with Earth’s field.  Material permanently magnetized.  Fe-minerals can lock in the Earth’s magnetic signal at the time formed.  Can be used to determine lat / long. Magnetic Overprinting Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Paleomagnetism  Rock magnetism can be measured in the laboratory.  Study of fossil magnetism is called paleomagnetism.  Ancient rocks reveal latitudes / longitudes unlike today. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Polar Wander  Paleomagnetism from ancient lavas didn’t align with the present magnetic field.  This lack of alignment indicates past magnetic polar wandering. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Polar Wander  Each continent had a separate polar-wander path.  Either the location of the magnetic pole is not fixed, or…  The lava flows themselves have moved.  These curves align when continents are assembled. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Apparent Polar Wander  Polar wander is now known to be an artifact.  Not the signature of a wandering pole on a fixed continent.  The signature of a fixed pole on a wandering continent.  Apparent polar wander is strong evidence for drift. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics  Sonar was used to map the ocean bathymetry.  Oceanographers were surprised to discover that…  The deepest parts of the ocean occur near land.  A mountain range runs through every ocean basin.  Submarine volcanoes form lines across ocean floors. The Ocean Floor Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics The Ocean Floor  Modern views of the ocean floor reveal…  Mid-ocean ridges.  Trenches.  Fracture zones. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics New Observations: Oceanic Crust  By 1950, we had learned much about oceanic crust.  Oceanic crust is covered by sediment. It is…  Thickest near the continents.  Thinnest (or absent) at the mid-ocean ridge.  Oceanic crust is mafic (basalt and gabbro).  No granitic rocks.  No metamorphic rocks.  High heat flow characterizes the mid-ocean ridge. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics New Observations: Oceanic Crust  Belts of concentrated subsea earthquakes were found.  The earthquakes were surprising. They were limited to…  Parts of oceanic fracture zones.  Mid-ocean ridge axes.  Deep ocean trenches. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Sea-Floor Spreading  In 1960, Harry Hess published his “Essay in Geopoetry.”  He called his theory “sea-floor spreading”.  Upwelling mantle erupts at the mid-ocean ridges.  New crust moves away from ridges, gathering sediment.  At trenches, the sea-floor dives back into the mantle.  Provided a potential mechanism for continental drift. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Sea-Floor Spreading  Drilling in the late 1960s recovered crust samples.  Ages increase away from the mid-ocean ridge.  Ages are “mirror images” across the mid-ocean ridge.  Strong supporting evidence for sea-floor spreading. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Plate Tectonics  The paradigm of “How the Earth Works.”  Earth’s outer shell is broken into rigid plates that move.  Moving plates change the face of planet Earth.  A case study of a Scientific Revolution.  A powerful idea based on multiple lines of evidence.  Allows scientists to predict events and rebuild the past. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Plate Tectonics  Tectonic theory evolved in the 1960s.  Previous research provided a strong foundation.  Wegener (1915) – Evidence supporting continental drift  Hess / Dietz (1960) – The sea-floor spreading hypothesis.  By 1968, evidence for tectonics was overwhelming.  This evidence changed the view of most geologists.  Even reluctant scientists were eventually won over. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Plate Tectonics  Plate Tectonic theory is powerful.  It provides a unified mechanism explaining:  Igneous, sedimentary and metamorphic rocks.  The distribution of earthquakes and volcanoes.  The origin of continents and ocean basins.  The distribution of fossil plants and animals.  The genesis and destruction of mountain chains.  Continental drift. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Lithosphere  Tectonic plates are fragments of lithosphere.  Lithosphere is made of both crust and the upper mantle.  The lithosphere is in motion over the asthenosphere.  Lithosphere bends elastically when loaded.  Asthenosphere flows plastically when loaded. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Two Types of Lithosphere  Continental ~ 150 km thick.  Granitic crust. 35-40 km thick. Lighter (less dense) . More buoyant – Floats higher.  Oceanic ~ 7 to 100 km thick.  Basaltic crust. 7-10 km thick. Heavier (more dense). Less buoyant – Sinks lower. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Plate Boundaries  Lithosphere is fragmented into ~ 20 tectonic plates.  Plates move continuously at a rate of 1 to 15 cm/yr.  Slow on a human time scale; extremely rapid geologically.  Plates interact along their boundaries. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics  Locations on Earth where tectonic plates meet.  Identified by concentrations of earthquakes.  Associated with many other dynamic phenomena.  Plate interiors are almost earthquake free. Plate Boundaries Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Continental Margins  Where land meets the ocean.  Margins near plate boundaries are “active.”  Margins far from a plate boundaries are “passive.”  Passive margin continental crust thins seaward.  Transitions into oceanic crust.  Traps eroded sediment.  Develops into the continental shelf. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Plate Boundaries: Three Types  Divergent – Tectonic plates move apart.  Lithosphere thickens away from the ridge axis. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Plate Boundaries: Three Types  Convergent – Tectonic plates move together.  The process of plate consumption is called subduction. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Plate Boundaries: Three Types  Transform – Tectonic plates slide sideways.  Plate material is neither created, nor destroyed. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Divergent Boundaries  Sea-floor spreading causes plates to move apart.  Magma wells up to fill the gap.  Magma cools, adding material to each plate. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Divergent Boundaries  Sea-floor spreading progression.  Early stage Rifting has progressed to Mid-Ocean Ridge formation. Before substantial widening of the ocean. Forms a long, thin ocean basin with young oceanic crust.  Example: The Red Sea Note: This diagram only depicts the crust, not the entire lithosphere. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Divergent Boundaries  Sea-floor spreading progression.  Mid-stage Ocean begins to widen. New seafloor is added at the Mid-Ocean Ridge. Continents move farther apart.  Example: Greenland and the North Atlantic. Note: This diagram only depicts the crust, not the entire lithosphere. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Divergent Boundaries  Sea-floor spreading progression.  Late Stage Mature, wide ocean basin. Linear increase in age with distance from central ridge. Edge of ocean basin - oldest; ridge proximal - youngest.  Example: The Atlantic Ocean Note: This diagram only depicts the crust, not the entire lithosphere. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Mid-Ocean Ridges  Linear mountain ranges in Earth’s ocean basins.  Example: The Mid-Atlantic Ridge  Snakes N-S through the entire Atlantic Ocean.  Elevated ridge (1500 km wide) 2 km above abyssal plains.  Axial rift valley. 500 m deep. 10 km wide. Symmetric. Site of eruptions. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Mid-Ocean Ridges  Sea-floor spreading opens the axial rift valley.  Rising asthenosphere melts, forming mafic magma.  Pooled magma solidifies into oceanic crustal rock.  Pillow basalt – Magma quenched at the sea floor.  Dikes – Preserved magma conduits.  Gabbro – Deeper magma. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Mid-Ocean Ridges  “Black smokers” are found at some MORs.  Water entering fractured rock is heated by magma.  Hot water dissolves minerals and cycles back out of rock.  When water reaches the sea, minerals precipitate quickly. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Ocean Crustal Age  Oceanic crust spreads away from the ridge axis.  New crust is closer to the ridge; older crust farther away.  Oldest oceanic crust is found at the far edge of the basin. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics  The hot asthenosphere is at the base of the MOR.  Aging ocean crust moves away from this heat source…  Cooling, increasing in density and slowly sinking.  Accumulating an increasing thickness of sediment. Oceanic Lithosphere Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Convergent Boundaries  Lithospheric plates move toward one another.  One plate dives back into the mantle (subduction).  The subducting plate is always oceanic lithosphere.  Subduction recycles oceanic lithosphere.  Subduction is balanced by sea-floor spreading.  Earth maintains a constant circumference. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Subduction  Old oceanic lithosphere is more dense than mantle.  A flat-lying oceanic plate doesn’t subduct easily.  Once bent downward, however, the leading edge sinks like an anchor rope. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Convergent Boundaries  The subducting plate descends at an average of 45  Plate descent is revealed by Wadati-Benioff earthquakes. Mark frictional contact and mineral transformations. Earthquakes deepen away from trench.  Quakes cease below 660 km. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Fate of Subducted Plates?  Plate descent may continue past the earthquake limit.  The lower mantle may be a “plate graveyard.” Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Subduction Features  Subduction is associated with unique features.  Accretionary prisms.  Volcanic arcs. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics  Accretionary Prism – A deformed sediment wedge.  Sediments are scraped off of subducting plates.  This thrusts them onto the overriding plate.  Contorted prism sediments can be pushed above sea-level. Olympic Peninsula. Taiwan. Convergent Boundaries Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Convergent Boundaries  Volcanic Arc – A chain of volcanoes on overriding plate.  The descending plate partially melts at ~ 150 km depth.  Magmas burn through overriding plate.  Volcanic arcs are curved because the Earth is a sphere.  Arc type depends upon the overriding plate.  Continental crust – Continental Arc.  Oceanic – Island Arc. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Transform Boundaries  Lithosphere slides past; not created or destroyed.  Many transforms offset spreading ridge segments.  Some transforms cut through continental crust.  Characterized by…  Earthquakes.  Absence of volcanism. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Oceanic Transforms  The Mid-Ocean Ridge axis is offset by transform faults.  A geometric necessity for a line spreading on a sphere.  Transforms bear strong evidence of sea-floor spreading. Abundant earthquakes common when offsets are opposed. Earthquakes vanish when offsets are concurrent. Figure 2.23a Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Transform Boundaries  Continental transforms – Chop continental crust.  Example: The San Andreas Fault. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Triple Junctions  Places where three plate boundaries coincide.  Multiple boundary combinations occur.  Triple junctions migrate and change across time. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics  Volcanic plumes independent of tectonic plates.  Most are located far from plate boundaries.  Comprised of mafic magmas from the lower mantle.  Tattoo overriding plates with volcanoes. Hot Spots Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 2: The Way the Earth Works: Plate TectonicsChapter 2: The Way the Earth Works: Plate Tectonics Hot Spots  Hot spot perforates overriding plate.  Volcano builds above sea …