ESCI 1001 Midterm (Lecture 3)

What is a Magnetic anomaly?

The difference between the expected strength of Earth's main dipole at a certain location and the actual measured strength of the magnetic field at that location.

What are seamount chains?

Chains of underwater mountains.

What does a negative magnetic anomaly indicate?

Field strength weaker than expected

What happens to the plates in convergent boundaries?

Lithospheric plates move toward one another.

What is Pangea?

The supercontinent of Earth before splitting apart. Supercontinent that existed from 300-200 Mya.

What is Continental Drift?

Large-scale horizontal movements of continents relative from one another and to the ocean basins during one or more episodes of geologic time.

What is Continental Fit?

Theory in which continents seem to 'fit', like a jigsaw puzzle.

What is Subduction?

The sideways and downward movement of the edge of a plate of the Earth's crust into the mantle beneath another plate (seafloor spreading).

What are Mid-ocean ridges?

Underwater mountain ranges, such as the Mid-Atlantic Ridge.

What are Deep-ocean trenches?

Deep depressions in the ocean floor, such as the Mariana Trench.

What is Sediment?

A layer of sediment on the ocean floor.

When you think of ocean, you think of what?

Basalt

What is an example of a Magnetic reversal?

When the North Pole transforms into a South Pole and the South Pole becomes a North Pole.

What is a Continental shelf?

A ~150 km thick, granitic crust that is ~35-40 km thick, light, and more buoyant.

What is an Oceanic shelf?

A ~7-100 km thick, basaltic crust that is more dense and less buoyant.

What is a Passive margin?

Margins far from a plate boundary.

What is an Active margin?

Margins near a plate boundary.

What happens in a Divergent plate boundary?

Tectonic plates move apart.

What happens in a Convergent plate boundary?

Tectonic plates move together, involving subduction.

What happens in a Transform plate boundary?

Tectonic plates slide past each other or sideways

What is Pillow basalt?

Magma quenched at the sea floor.

What is an Accretionary prism?

A mass of sedimentary material scraped off a region of oceanic crust during subduction and piled up at the edge of the overriding plate.

What is a Continental transform?

A fault that chops continental crust, such as the San Andreas Fault.

What is the new idea regarding plate tectonics?

Ridge push; elevated mid-ocean ridges push the lithosphere away.

What is the old idea regarding plate tectonics?

Plates are dragged atop a convecting mantle.

What is Yellowstone?

Yellowstone is a supervolcano.

What is the relationship between Pangea and continental drift?

Continental drift is hypothesized to be the break-up of the supercontinent Pangea.

Where are glaciations located?

Permian glacial tills found on 4 continents, including Africa and India near the equator.

Was the whole Earth cooler during the Permian glaciations?

No, because Permian tropical plant fossils have been recovered.

What are fossils?

Identical fossils found on widely separated landmasses.

What aspects of geology match across the Atlantic?

Geological phenomena, rock types, rock ages, mountain belts (Appalachians, Caledonides, Atlas).

What is paleoclimate?

By placing Pangea over the Permian South Pole, Wegener correctly predicted the location of tropical coals, reefs, deserts, and evaporites.

What happened to Wegener's hypothesis of continental drift?

Wegener died in 1930, but it was revived in the 1950s by Harry Hess and Robert Dietz.

What is the theory of plate tectonics?

The idea that there are 20 plates that slowly move relative to each other.

What observations confirm the theory of plate tectonics?

Observations of plate boundaries, earthquakes, and volcanic activity.

What does the term 'tekton' mean?

Greek for 'builder', referring to the movement of Earth's plates.

What is paleomagnetism?

Earth's magnetic field preserved in rocks, indicating the location of magnetic poles.

How are iron minerals in rocks related to paleomagnetism?

They align to the magnetic field when cooling from a melt, preserving information about Earth's magnetic field.

What does the consistency of paleomagnetism in rocks of the same age on different continents indicate?

That the continents were fixed in place during that time.

What is the apparent polar-wander path?

The path followed by the magnetic poles as they wander.

What is bathymetry?

Study of the depth of the ocean floor

What is bathymetric profiling?

The process of creating a profile of the ocean floor's depth.

What are abyssal plains?

Flat areas of the ocean floor at depths of 4-5 km.

What are submarine mountain ranges?

Underwater mountain ranges at depths of 2-2.5 km.

What are deep-ocean trenches?

Narrow, elongated troughs in the ocean floor at depths of 8-12 km.

What are border volcanic arcs?

Volcanic arcs formed at the boundaries of tectonic plates.

What are isolated submarine mountains?

Individual underwater mountains not part of a chain.

What are Guyots?

Flat-topped underwater mountains.

Seamount chains occur in chains, but unlike volcanic arc islands, only island (at the end of the chain) remains...?

Only the island at the end of the chain remains capable of erupting.

How does the thickness of sediment on the ocean floor change?

The sediment layer thickens away from mid-ocean ridges.

Why is the sediment layer on the ocean floor not thick enough to have accumulated throughout Earth's history?

Possibly because the ocean floor is younger.

Where is geothermal heat flow highest?

Geothermal heat flow is highest at mid-ocean ridges.

Where do oceanic earthquakes occur?

Oceanic earthquakes occur along belts that coincide with trenches, ridges, and fracture zones.

What is the theory of sea-floor spreading?

The theory that new ocean floor is produced at mid-ocean ridges and spreads apart, causing the ocean floor to move.

What provides a mechanism for continental drift?

The theory of sea-floor spreading.

What provides a mechanism for keeping the globe spherical?

Subduction.

What are the two lines of evidence supporting sea-floor spreading?

Magnetic anomaly and submarine sediment thickness.

What does a magnometer measure?

The strength of the Earth's magnetic field.

What are the two parts of the measured magnetic field?

The magnetic field produced by the main dipole and the magnetic field produced by the magnetism of near-surface rock.

What is the magnetic anomaly formula?

Expected strength - measured strength

What is a magnetic anomaly?

Deviation in magnetic field strength from expected value

What does a positive magnetic anomaly indicate?

Field strength stronger than expected

What are magnetic reversals?

Sudden changes in Earth's magnetic field polarity

How can magnetic reversals be observed?

Through layered lava flows

What can magnetic anomalies explain?

Reversals in polarity

What does a positive magnetic anomaly indicate in terms of polarity?

Normal polarity

What does a negative magnetic anomaly indicate in terms of polarity?

Reversed polarity

How are magnetic anomalies distributed across a mid-ocean ridge?

Symmetrically

What does plate tectonic theory explain? In other words, what is the formula?

Wegener (continental drift) + Hess (sea-floor spreading)

Plate tectonic theory explains the unifying mechanism for:

Igneous, sedimentary and metamorphic rocks, the distribution of earthquakes and volcanoes, origin of continents and ocean basins, distribution of fossil plants and animals, genesis and destruction of mountain chains and continental drift

What is the lithosphere?

The crust and upper mantle

What is the asthenosphere?

Plastic flowing layer below the lithosphere

What are the two types of asthenosphere?

Continental and oceanic

What are the characteristics of continental asthenosphere?

Granitic crust, 35-40 km thick, light and buoyant

What are the characteristics of oceanic asthenosphere?

Basaltic crust, more dense and less buoyant

How many tectonic plates are there?

Approximately 20

What is the average rate of plate motion?

1-15 cm/yr

Where are plate boundaries located?

Located and identified by concentrations of earthquake epicenters

What are plate interiors almost always?

Earthquake free.

What are the two types of continental margins?

Active and passive.

What happens to the continental crust in passive margins?

It thins seaward and transitions to oceanic crust.

What are the three types of active margins?

Divergent, convergent, and transform.

What happens to the lithosphere in divergent active margins?

It thickens away from the ridge axis.

What is the process of plate consumption in convergent active margins?

Subduction.

What is another name for a convergent margin?

Subduction zone.

What happens in transform active margins?

Tectonic plates slide sideways.

What is special about plate material in transform active margins?

It is neither created nor destroyed.

What causes plates to move apart in divergent boundaries?

Sea-floor spreading.

What fills the gap created by plates moving apart in divergent boundaries?

Magma.

What happens to the magma in divergent boundaries?

It cools and adds material to each plate.

What are mid-ocean ridges?

Linear mountain ranges in the Earth's ocean basins.

Underwater mountain ranges formed by tectonic plate divergence.

What is an example of a mid-ocean ridge?

The Mid-Atlantic Ridge.

What opens up due to sea-floor spreading in mid-ocean ridges?

The axial rift valley.

What forms when rising asthenosphere melts in mid-ocean ridges?

Mafic magma.

What does pooled magma solidify into in mid-ocean ridges?

Oceanic crustal rock.

What is formed when magma quenches at the sea floor in mid-ocean ridges?

Pillow basalt.

What are 'black smokers'?

An example of hydrothermal vents producing a mineral that looks black. These are formed through hot magma chambers underneath the surface, heating up water creating hot spots.

What happens when water enters fractured rock in mid-ocean ridges?

It is heated by magma.

What happens when hot water reaches the sea in mid-ocean ridges?

Minerals precipitate.

What happens to the ocean crust in mid-ocean ridges?

It spreads away from the ridge axis.