Geo final
Ultramafic igneous rocks occur in the Green mountains.
a) What part of the oceanic lithosphere were they once part of? b) These rocks have been altered by hot water to produce what new minerals? c) What are rocks composed of these new minerals used for?
What processes take place at a "Hot Spot?"
-A hot spot = a volcanic region thought to be fed through a column from underlying mantle to the lithosphere that is anomalously hot compared with the surrounding mantle (mantle plume). Occurs in the center of a plate rather than along a boundary. -The rock in the plume is solid, but soft enough to flow, thus rises buoyantly because it is less dense than the cooler surrounding rock. When the rock reaches the lithosphere, it melts partially, producing magma -The position of the heat source causing a hot spot volcano is fixed relative to the moving plate. This is why there is often an active volcano at the front of a chain of dead volcanoes
What are the hazards associated with volcanic ash?
-Ash is hard, abrasive, mildly corrosive, conducts electricity when wet, and does not dissolve in water. Ash is spread over broad areas by wind. -Contains carbon dioxide, sulfates (sulfur dioxide), hydrochloric & hydrofluoric acid -Impairs driving visibility
37) What is the difference between volcanic ash, bombs, and tuff?
-Ash: loosely used to refer to all explosive eruption products, including particles larger than 2mm; formed during explosive volcanic eruptions when dissolved gases in magma expand & escape violently into the atmosphere -Bombs: a mass of molten rock (tephra) larger than 64 mm (2.5 inches) in diameter, formed when a volcano ejects viscous fragments of lava during an eruption; cool into solid fragments before they reach the ground -Tuff: a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is compacted into a solid rock in a process called consolidation.
What landforms define the edges of tectonic plates?
-Divergent Plate boundaries- mid-ocean ridges (new seafloor formation takes place at the axis of the ridge, in an elongate valley), architecture of a mid ocean ridge includes zone of partial melting, crystal mush, pillow basalt, fault/fault scarps, dikes, gabbro faults, cliffs, scarps occur parallel to the ridge axis -Convergent Plate Boundaries- subduction zones, deep-ocean trenches, accretionary prisms (wedge shaped masses, much like snow in front of a plow, sediment is squashed and contorted), volcanic arc develops behind the accretionary prism -Wadati-Benioff Zones- Earthquake bands (belt outlines the edges of subducting plates); fracturing and slipping occurs along plate boundaries -Collisional mountain belts (ex: the Himalayas) -Transform Plate Boundaries- fracture zones perpendicular to mid-ocean ridges (consist of active transform fault and inactive fracture zone)
What kinds of faults occur along the mid-ocean ridges?
-Divergent plate boundary, mainly -Transform boundaries = perpendicular
Why aren't there any oceanic rocks much older than 180 million years?
-Old ocean crust is subducted down ocean trenches into the mantle; crust going down trenches in the western Pacific has traveled farthest and is the oldest -Sea floor spreading- basaltic magma rose upward beneath mid-ocean ridges, which solidified into oceanic crust basalt. This constant formation of new rock meant that the oceanic crust must also be disappearing somewhere, or the earth would be growing. This is where deep-ocean trenches come in. The ocean floor sinks into the mantle (subducts), which is a cause of earthquakes. These processes combined explain continental drift
What is the difference between "Ridge Push" and "Slab Pull
-Ridge push force uses gravity to push the newly formed elevated lithosphere away from the mid-ocean ridge axis toward the lower abyssal plain in divergent plate boundaries, causing it to move away -Slab pull relates to the gravitational pull of a cold, dense subducting oceanic lithosphere at a convergent plate boundary. It is a gravitational force similar to what makes rocks sink in water.
What happens to the sediments that have accumulated on the ocean floor at convergent plate boundaries?
-Sediments such as clay, sand and plankton get scraped up and incorporated into the wedge-shaped mass known as the accretionary prism. -The oceanic lithosphere sinks into the asthenosphere (a consumes l). Downgoing plates generate large earthquakes up to 660 km beneath the surface, but sometimes continue to sink further without generating earthquakes
What are some of the processes that cause mountains to form at convergent plate boundaries?
-Subduction- compressional stresses cause crustal shortening and uplift in the overriding plate. This may produce a fold-thrust belt, causing thrust slices to push up and over their neighbors, and rocks within become bend and fold. If subduction happens over a long period of time, crustal blocks too buoyant to subduct back into the mantle collide with the overriding plate and suture (attach) to the edge (exotic terrane when offshore, accreted terrane once it is attached). -Continental collision- when the oceanic lithosphere completely subducts and the continents themselves collide, causing the formation of large mountain ranges (eg Himalayas, Alps). Intense compression generates fold-thrust belts on the orogen margin. One continent overrides the edge of the other, causing high-grade metamorphism as well as passive-flow folds and tectonic foliation- crustal thickening -Strong compressive forces are usually located at the boundaries of these plates producing mountain belts. -Oceanic sediment and other rocks are deformed at convergent plate boundaries (form into accretionary prism) -The Green Mountains were once an accretionary prism
Why do the youngest rocks in the oceans occur at the mid-ocean ridges and the oldest at farthest from the ridges?
-The ridge continually creates new layers of rock as magma comes to the ocean floor and cools with ocean water contact so the older layers are pushed aside as they cool getting farther and farther away from the ridge. -These ridges are good examples of divergent plate boundaries and are roughly symmetrical
What defines the bottom of a tectonic plate?
-This is where the lithosphere, which is rigid, changes to the asthenosphere, which is plastic and can flow. This difference is due to temperature -Where seismic waves abruptly slow down at the boundary of the lithosphere and asthenosphere. Velocity of the waves at this point is approximately 8km/sec. -Continental lithosphere is much thicker than oceanic, averaging at thicknesses of 150km and 100km respectively
How do columnar joints form?
A structure that forms in rocks (most commonly in basalt) that consists of columns (mostly commonly hexagonal in shape) that are separated by joints or fractures in the rock that formed when the rock contracted, most often during cooling
Ho do vesicular volcanic rocks form?
As magma rises to the surface the pressure on it decreases. When this happens gasses dissolved in the magma are able to come out of solution, forming gas bubbles (the cavities) inside it. When the magma finally reaches the surface as lava and cools, the rock solidifies around the gas bubbles and traps them inside, preserving them as holes filled with gas called vesicles.
How are the hypocenters of faults used to define the geometry of plates at convergent plate boundaries?
Because earthquakes occur along fault boundaries, hypocenters outline the boundaries of the plate
What are the differences between dikes and sills?
Dikes are vertical, sills are horizontal
Where (in what plate tectonic environments) does decompression melting occur?
Divergent plate boundaries
How does "decompression melting" occur?
Earth's mantle moves upward to an area of lower pressure; the reduction in overlying pressure enables the rock to melt, leading to magma formation
How does volcanic glass form?
High viscosity + sudden cooling + loss of volatiles Chemical composition close to granite (quartz + alkali feldspar)
What are lahars and why are they potentially hazardous?
Lahars are a type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris, and water Potentially hazardous b/c they usually travel much faster than their turbulent counterparts; can float boulders, cars, buildings, and bridges
What is the difference between magma and lava?
Lava = above ground, magma = below
What is the magnitude of an earthquake and how is it determined?
Magnitude is a measure of the amount of energy released during an earthquake. It can be expressed using several magnitude scales (ex: the Richter scale)
How do volcanic aerosols affect climate?
Most of the particles spewed from volcanoes cool the planet by shading incoming solar radiation. The cooling effect can last for months to years depending on the characteristics of the eruption
Do earthquakes occur along all parts of fracture zones?
No only the transform boundary of the fraction zone (active transform fault)
Are all parts of fracture zones plate boundaries?
No some have no movement at all (inactive fracture zone)
What kinds of faults occur where continental rifting has taken place?
Normal faults
Why can't continental lithosphere be subducted at convergent plate boundaries?
Oceanic lithosphere is denser than the asthenosphere. Continental crust cannot be subducted because it is too buoyant, it contains low density rocks that act as life preservers. This means continental crust can be significantly older than oceanic crust, sometimes more than 3.8 billion years old.
In which context do the majority of earthquakes occur?
Plate boundaries
55) What is the difference between a pluton, a stock, and a batholith?
Pluton is the intrusion within an igneous rock. The difference between the two is mainly the size. Stocks are smaller than 100 km square batholiths are larger than 100 km square
What are the different waves produced during an earthquake?
Seismic waves, p waves, s waves
What sequence of processes occur when a continent undergoes rifting to produce a new ocean?
Stretching horizontally and thinning vertically of continental lithosphere occurs which produces a new divergent plate boundary. Near the surface of the continent the crust is cold and brittle, so stretching causes rock to break and faults to develop. Rock slips down the fault surfaces, which forms a low area which is gradually buried by sediment. Deeper in the crust, rock is warmer and softer, so it is stretched instead of broken. As continental lithosphere thins, hot asthenosphere rises and starts to form volcanoes. If this rifting last long enough, it can cause the continental plate to break in two, forming a new mid-ocean ridge creating a new ocean. If the rifting doesn't continue for long enough, it leaves a scar on the land with belt faults, volcanic rocks, and a thick layer of sediment.
How do pillow basalts form?
Sub-marine environment
How can you locate the epicenter of an earthquake?
The difference in arrival time between the two types of seismic wave can be used to calculate the distance of the earthquake's epicenter from the seismometer, as the further away an earthquake is, the greater the lag time between the detection of the S waves relative to the P waves.
What is the difference between and earthquake "hypocenter" (also called the "focus") and an earthquake "epicenter?"
The hypocenter/focus is where the point within the Earth where the first movement occurs (commonly the place on the fault where the slip took place) and the epicenter is the point directly above the focus on the earth's surface.
Fracture zones are prominent landforms on the ocean floor. What type of plate boundary exists along fracture zones?
Transform faults fracture zones perpendicular to mid-ocean ridges (consist of active transform fault and inactive fracture zone)
Where, with respect to the geometry of convergent plate boundaries, do volcanoes form?
Volcanoes form behind the accretionary prisms, in arcs. The magma that feeds such volcanos forms just above the surface of the downgoing plate at a depth of about 150 km. If the subduction is between a continental and oceanic plate, the volcanic arc forms on the continent. If the subduction is with two oceanic plates, they form a volcanic island arc. A back arc basin forms where subduction begins offshore, which traps oceanic lithosphere behind the arc, or stretching causes a small spreading ridge.
What processes (sequence of events) lead to an earthquake occurring?
When rocks are first put under stress they bend and then break. The sudden release of energy when rocks break allows rocks to slide past one another along faults that produces an earthquake shaking the ground.
What is asbestos?
a heat-resistant fibrous silicate mineral that can be woven into fabrics, and is used in fire-resistant and insulating materials such as brake linings