OEAS 520 Midterm (The Solid Earth)

weeks 1-4 material (Kevin as lecturer)

Chondrites

Primitive "space sedimentary rocks" that represent the original solid building blocks of the solar system.

Differentiated Meteorites:

Fragments from "mini planets" that have undergone melting and separation into layers (core/mantle).

Differentiation:

The process by which Earth developed a dense iron-rich core and a lighter silicate mantle early in its history.

Mantle:

The largest layer of the Earth (>99% of silicate Earth); it is ultramafic, solid, but behaves as a plastic that convects over time.

Lithosphere:

The brittle, rigid outer layer of the Earth, consisting of the crust and the uppermost mantle.

Asthenosphere:

The plastic, ductile layer of the mantle beneath the lithosphere that allows for convection and plate movement.

Mesosphere:

The solid lower mantle located between the asthenosphere and the core.

Seismic Tomography:

A technique used to map Earth’s internal structure by measuring the speed of seismic waves.

Multibeam Sonar:

A ship-mounted tool that uses overlapping sonar paths to create a high-resolution 3D swath of the seafloor.

Satellite Altimetry:

A method of inferring ocean depth by measuring the distance between a satellite and the ocean surface relative to the geoid.

Refraction (Seismic):

A method used to resolve gross crustal velocities; it requires large velocity changes and long offset distances.

Reflection (Seismic):

A method used for detailed, shallow imaging of the subsurface; it requires a change in seismic impedance.

Impedance:

The product of a medium's density and its seismic velocity; changes in impedance cause seismic waves to reflect.

Bathymetry:

The measurement of depth of water in oceans, seas, or lakes (underwater topography).

Backscatter:

The intensity of a reflected sonar signal, used to determine the roughness and composition of the seafloor.

Divergent Boundary:

Where plates move apart, such as Mid-Ocean Ridges or continental rifts.

Convergent Boundary:

Where plates move together, resulting in subduction zones or mountain building.

Transform Boundary:

Where plates slide past each other horizontally (e.g., transform faults and fracture zones).

Mantle Plume:

A rising column of hot mantle material rooted below the asthenosphere, often creating stationary "hotspots."

Age-Progressive Volcanism:

A track of volcanoes formed as a tectonic plate moves over a stationary mantle plume (e.g., Hawaii).

Wilson Cycle:

The cyclical process of ocean basin birth (rifting), growth (spreading), and death (subduction/collision).

Pangea:

The most recent supercontinent that existed approximately 280 million years ago.

Continental Drift:

The precursor hypothesis to plate tectonics suggesting that continents move across Earth's surface.

Continental Shelf:

The submerged edge of a continent; large in passive margins and thin/narrow in active margins.

Continental Rise:

The lower slope region composed primarily of turbidite deposits with graded bedding.

Abyssal Plain:

Large, flat areas of the deep ocean floor formed as oceanic crust cools, thickens, and sinks.

Abyssal Hill Fabric:

Small ridges on the seafloor created by faulting at Mid-Ocean Ridges; their size is representative of the spreading rate.

Fracture Zone:

An inactive, fossil trace of a transform fault that extends beyond the active ridge segments.

Accretionary Wedge:

A pile of sediment scrapped off a subducting plate and accumulated onto the overriding plate.

Trenches:

Extremely deep regions of the seafloor where one tectonic plate subducts beneath another.

Decompression Melting:

Melting of the mantle that occurs when it rises toward the surface and pressure decreases (occurs at MORs).

Fast Spreading Center:

Characterized by thinner crust, high volcanic activity, and small abyssal hill fabric (e.g., East Pacific Rise).

Slow Spreading Center:

Characterized by thicker crust, more pronounced faulting/hills, and exposure of gabbro/peridotite (e.g., Mid-Atlantic Ridge).

Ophiolite:

A section of oceanic crust and upper mantle that has been uplifted and exposed on land (e.g., Oman Ophiolite).

Pillow Basalt:

Rounded volcanic structures formed when magma erupts underwater and cools rapidly.

Sheeted Dikes:

A layer of the oceanic crust consisting of vertical, parallel igneous intrusions.

Gabbro:

Coarse-grained, mafic intrusive rock that makes up the lower portion of the oceanic crust.

Serpentinization:

A chemical reaction between seawater and mantle rocks (peridotite) that alters the mineralogy and creates heat.

Volatile Flux Melting:

Melting triggered by the introduction of water (volatiles) from a subducting slab into the overlying mantle wedge.

Wadati-Benioff Zone:

A planar zone of seismicity corresponding with the down-going slab in a subduction zone.

Interseismic Period:

The phase where a subduction zone is "locked," building up elastic stress.

Coseismic Period:

The rapid release of built-up stress during an earthquake.

Fore-arc Basin:

The region between a subduction trench and the associated volcanic arc.

Back-arc Basin:

A basin that forms behind a volcanic arc due to extensional forces.

Ferromanganese (FeMn) Nodules:

Round aggregates of iron and manganese found on top of sediments in abyssal plains.

FeMn Crusts:

Mineral-rich coatings that form on hard substrates, primarily on the sides of seamounts.

Hydrothermal Vent:

A fissure on the seafloor where geothermally heated water discharges.

Black Smoker:

A high-temperature (>350°C) hydrothermal vent rich in sulfides.

White Smoker:

A cooler hydrothermal vent (30–350°C) characterized by barium sulfate and silica.

Carbonate Chimneys:

Low-temperature vents (30–75°C) associated with serpentinized rocks rather than volcanic heat (e.g., Lost City).

Ultramafic

• Rocks with very low silica content (less than 45%) and very high levels of iron and magnesium.

• They are usually dark green to black and very dense.

• Common Example: Peridotite (the primary rock of Earth's mantle).

• the mantle is ultramafic and makes up >99% of the silicate Earth.

Mafic

• Rocks with low silica content (45–52%) and high iron and magnesium. The name comes from Magnesium and Ferrum (iron).

• Dark-colored and dense.

• Common Examples: Basalt (oceanic crust) and Gabbro (lower oceanic crust).

• Oceanic lithosphere is primarily mafic

Felsic

• Rocks with high silica content (usually >63%) and high levels of aluminum, potassium, and sodium. The name comes from Feldspar and Silica.

• Light-colored (pinks, whites, light greys) and less dense than mafic rocks.

• Common Example: Granite (typical of continental crust).

• Felsic rocks stay "buoyant" on the mantle, which is why continental crust sits higher than oceanic crust.

Earth’s density gradient (high→low)

• Ultramafic (Mantle) = Most Dense

• Mafic (Oceanic Crust) = Middle Density

• Felsic (Continental Crust) = Least Dense