Geology Exam 2

convergent plate-boundary seismicity

shallow-focus earthquakes occur in both the subducting plate and the overriding plate. The bending that occurs during subduction stretches the downgoing plate and generates small normal faults in the plate. Large thrust faults develop along the contact between the downgoing and overriding plates. Most of the Earth's seismic energy is released at these plate boundaries.

S-waves

shear body waves - side-to-side waves; 2nd, slower, & go though solids;

planetesimals

small planetary objects that form through the action of gravity during the birth of a solar system.

meteorites

solid objects falling from space that land on a planet. Heavy bombardment in the early days of the solar system pulverized surfaces of the planets leaving huge craters and contributing to heating.

stratigraphic formation

'formations' within a stratigraphic column; recognizable intervals of a specific rock type or group of rock types deposited during a specific time interval, that can be traced over a fairly broad region

intraplate earthquakes

some earthquakes occur in the interiors of plates and are not associated with plate boundaries, active rifts, or collision zones. These type of earthquakes account for only about 5% of the earthquake energy released in a year, all of them have a shallow hypocenter. Thought to be caused by force being applied to the boundary of a plate causing the interior of the plate to break at weak, preexisting fault zones, some of which date back to the Precambrian. Alternatively, the activity may be due to forces resulting from shear between the lithosphere and asthenosphere.

lower mantle characteristics

specific gravity 3.8 to 5.5, depth of 660-2900 km

inner core characteristics

specific gravity of 11-14, depth of 5000-6000 km, consists of solid iron alloy

continental crust characteristics

specific gravity of 2.7, depth of 20-70 km

oceanic crust characteristics

specific gravity of 3.0, depth of 5-7 km

upper mantle characteristics

specific gravity of 3.3, depth of 100-200 km, composed entirely of peridotite

low-velocity zone (within the mantle) characteristics

specific gravity of 3.5, depth of 410 km, partial melting occurs here.

transition zone (within the mantle) characteristics

specific gravity of 3.7, depth of 410-660 km, area of mineral phase change

outer core characteristics

specific gravity of 5-9, depth of 3000-5000 km, consists of liquid iron alloy

galaxies

stars are not randomly scattered throughout the Universe; gravity pulls them together to form immense systems, or groups called...

stick-slip behavior

start and stop movement on a fault; between faulting events, stress builds up and in some cases the stress causes intact rocks to rupture and a new fault to form. Or in other cases, stress overcomes friction on an existing fault and the fault slips again.

eras

subdivision of an eon - from oldest to youngest they are Paleozoic, Mesozoic, Cenozoic.

L-waves

surface waves that cause the ground to ripple back and forth in a snake-like movement. Cause the rolling motion of the ground; have the largest amplitude and arrive over a long period of time.

R-waves

surface waves that cause the ground to ripple up and down

factors influencing seismic travel

the ability of a seismic wave to travel through a certain material and the velocity at which travels depend on the character of the material. Density (mass per unit volume), rigidity (how stiff or resistant to twisting a material is), and compressionability (how much a material's volume changes in response to squashing).

liquefaction

the abrupt loss of strength of a wet sediment (either sand or clay) in response to ground shaking. Can cause major damage during an earthquake, buildings whose foundations lie in liquified material may sink or even tip over.

relative age

the age of one feature with respect to another

wave front

the boundary between the rock through which a wave has passed and the rock through which it has not yet passed. Expands outward from the earthquake focus like a growing bubble.

seismic ray

the changing position of an imaginary point on a wave front as the front moves through rock. Perpendicular to wave fronts, so that each point on the wave front allows a slightly different ray.

exotic terranes

the compression created by a convergent boundary causes a mountain range to rise. During this time, offshore island volcanic arcs, oceanic plateaus, and small fragments of continental crust may drift into the convergent margin. These blocks are too buoyant to subduct, so they collide with the convergent margin and accrete, or attach, to the continent.Geologists refer to such blocks before they attach as ____ and after they have attached as accreted terranes.

isostasy

the condition that exists when the buoyancy force pushing lithosphere up equals the gravitational force pulling lithosphere down. In most places, isostatic equilibrium exists at the surface of the crust, so that the surface elevation of the crust reflects the level at which the lithosphere naturally floats.

light year

the distance that light travels in one Earth year, equals about 9.5 trillion km. Galaxies at the outer edge of the Universe lie over 13 billion light years away (78 trillion miles away). Light traveling to Earth from such locations began their journey 9 billion years ago before the Earth even existed.

Metamorphic aureole

the distinct belt of metamorphic rocks that forms around an igneous intrusion, also known as a contact aureole. Because this metamorphism takes place without application of differential stress, aureoles contain hornfels, a nonfoliated metamorphic rock.

fission tracks

the ejection of an atomic particle during the decay of a radioactive isotope damages the nearby crystal lattice, creating a line called a...; as time passes, more atoms undergo fission, so the number of fission ___ in the crystal increases.

the nature of fault systems

the faulting in a thrust-fault system shortens the crust; slip makes slices of the crust overlap like shingles. Faulting in normal-fault systems, on the other hand, stretches the crust. In such systems, elongate basins separate high blocks of rock. Individual basins may be bounded on each side by a normal fault dipping toward the basin. Typically, normal faults become shallower with depth and merge with a detachment fault.

fossil assemblage

the group of fossil species. Can occur only in a limited interval of strata, not above or below certain levels.

horst

the high block between two grabens.

fault trace (or fault line)

the intersection between a fault and the ground surface.

strain

the irreversible change in shape that deformation causes. There are different variations: if a layer of rock becomes longer, it has undergone 'stretching'. If the layer of rock becomes shorter, it has undergone 'shortening', and if a change in shape involves the movement of one part of a rock body past another so that the angles between features in the rock change, the result is 'shear strain'.

Eons

the largest subdivision of geologic time.

tectonic foliation

the layering created by the alignment of deformed and/or reoriented grains. Overall, deformation can produce inequant grains and can cause them to align parallel with one another, thereby generating metamorphic foliation in the rock.

Contact metamorphism

the local metamorphism caused by an igneous intrusion; develops adjacent to an intrusion. Occurs anywhere that the intrusion of plutons occurs. Plutons intrude into the crust at convergent plate boundaries, in rifts, and during mountain building that takes place when continents collide.

Thermal metamorphism

the local metamorphism caused by an igneous intrusion; develops in response to heat without a change in pressure and without differential stress.

Metamorphic texture

the nature of metamorphic rocks in which ways the grains in the rock have grown in place and interlock; slate, phyllite, schist, gneiss.

Protolith

the parent rock of metamorphism. Is subjected to heat, pressure, differential stress, and/or hydrothermal fluids. The mineral makeup of the parent will determine the degree to which each metamorphic agent will cause change.

refraction

the phenomenon of light bending when passing through a surface. As a rule, if waves enter a material through which they will travel more slowly, the rays representing the waves bend away from the interface. If the waves enter a material through which they will travel faster, the rays bend toward the interface.

reflection

the phenomenon of light bouncing off a surface. Since seismic energy travels in the form of waves, seismic waves reflect or refract when reaching the interface between two rock layers if the waves travel at different velocities in the two layers.

principle of fossil succession

the predictability of fossil distribution, which allows geologists to arrange fossil species in a progression from older at the bottom to younger at the top, has been found at countless locations around the world.

core-mantle boundary

the presence of a shadow zone means that deep in the Earth a major interface exists where seismic waves abruptly refract down (implying that the velocity of seismic waves suddenly decreases). This interface lies at a depth of about 2900 km. The density contrast across this boundary is greater than the density contrast between the crust and water.

Metasomatism

the process by which a rock's chemical composition changes because of a reaction with hydrothermal fluids. Dissolved ions carried away by hydrothermal fluids either react with rocks elsewhere, reach the Earth's surface and wash away, or precipitate to form veins.

uplift

the process by which the surface of the Earth moves vertically from a lower to a higher elevation. Mountain building produces substantial ___ of the Earth's surface.

Metamorphism

the process of forming metamorphic rock, new minerals may grow at the expense of old ones, and/or size, shape, and arrangement of grains in the rock may change; a solid-state process.

Metamorphic zones

the regions between two isograds (the line on a map along which an index mineral first appeared); zones are named after an index mineral that was not present in the previous, lower-grade zone.

Cambrian explosion

the remarkable diversification of life, indicated by the fossil record, that occurred at the beginning of the Cambrian Period.

Mylonite

the resulting rock from dynamic metamorphism; has a foliation that parallels the fault.

shear zones

the shear on some faults takes place under ductile conditions at depth in the crust. Where this happens, rock does not break up into breccia or gouge along the fault zone, but rather shears ductilely to form a band of fine-grained foliated rock called mylonite. The fine grain size of mylonite results not from brittle fracturing during shear, but rather from a type of metamorphic recrystallization that subdivides large grains into small ones. These ductile moving faults are called ____.

GEOLOGIC TIME

the span of time since Earth's formation.

stellar wind

the stream of atoms emitted from a star during its lifetime; particles that have been ejected from a star and are shooting through space

earthquakes at continental rifts

the stretching of continental crust at these rifts generates normal faults. Active rifts today include the East African Rift, the Basin and Range Province and the Rio Grande Rift. In all these places, shallow-focus earthquakes occur, similar in nature to the earthquakes at mid-ocean ridges.

COSMOLOGY

the study of the overall structure and evolution of the Universe.

closure temperature

the temperature below which isotopes are no longer free to move. This temperature level is typically significantly cooler than the melting temperature of a mineral. When we specify a radiometric date for a rock, we are defining the time at which a specific mineral in the rock cooled below its ___ temperature.

Metamorphic grade

the term used to indicate the intensity of metamorphism, the amount or degree of metamorphic change within a rock. Depends primarily on temperature, plays the dominant role in determining the extent of recrystallization/neocrystallization during metamorphism. Low to high grade: shale, slate, phyllite, schist, gneiss, migmatite.

travel time

the time it takes for a wave to travel from the focus to a seismograph station along a given ray is the ___ along that ray.

half-life

the time measured of how long it takes for half a group of isotopes to decay. We cannot predict which specific isotopes decay at which time, only that during a half-life, half the parent isotopes decay to form daughter isotopes. For a given reaction, the half life is a constant.

Universe

the workings of ourselves and all that surrounds us, our..

P-wave shadow zone

the zone 103° - 142° from the epicenter of an earthquake; explained by refraction of P-waves encountering the core-mantle boundary.

S-wave shadow zone

the zone ≥103° from the epicenter of an earthquake; suggests the outer core is a liquid, careful observations of P-wave refraction patterns indicate inner core is a solid. This means that S-waves cannot pass through the core at all.

nebular theory

theory that the sun and the planets condensed out of a spinning cloud of gas and dust.

Role of hydrothermal fluids

these fluids accelerate metamorphic reactions, for atoms involved in the reactions can migrate faster through a fluid than they can through a solid. Fluids provide water that can be absorbed during metamorphic reactions. And when passing through a rock, a fluid may pick up some dissolved ions and drop off others, thus changing the whole composition of a rock during metamorphism.

annual probability

this probability is the 1/earthquake recurrence interval

surface-wave magnitude

to apply Richter's concept to the description of distant earthquakes, seismologists developed a new scale based on measuring the amplitudes of certain R-waves, (Ms).

body-wave magnitude

to describe the size of deeper earthquakes, seismologists determined this type of measure, (mb), which is based on measurement of P-waves.

triangulation

to determine the map position of the epicenter, we use this method, by plotting the distance between the epicenter and three stations across the globe. The epicenter lies at the intersection of the three circles, for this is the only point at which the epicenter has the appropriate measured distance from all three stations.

displacement

to recognize a fault, there are generally offset distinctive beds, in such cases, the fault is the plane on which offset occurs. Geologists refer to this offset as the ____ on the fault. In some cases, faults juxtapose two different rock units so the fault is the surface of contact between the two units.

divergent plate-boundary seismicity

two kinds of faults develop in these regions: along spreading segments, newly formed crust at or near the mid-ocean ridge stretches and ruptures, generating normal faults, whereas along the transform faults that link spreading segments, strike-slip faulting occurs. Seismicity along mid-ocean ridges takes place at shallow depths (less than 10 km).

brittle deformation

type of deformation; a material breaks into two or more pieces, like a plate shattering on the floor. JOINTS and FAULTS are these types of structures. During this process, many chemical bonds within the rock break at once so that rocks can no longer hold together.

ductile deformation

type of deformation; a material changes shape without breaking, like a ball of dough squeezed beneath a book. FOLDS and FOLIATIONS are these types of structures. During this process, some chemical bonds do break but new ones quickly form, so that rocks do not separate into pieces as they change shape.

Shear stress

type of differential stress; one part of the material is moved sideways, relative to another.

Normal stress

type of differential stress; when material is pushed or pulled perpendicular to a surface. A push is called a compression (flattens) and a pull, tension (stretches).

Normal faults

type of dip-slip fault; the hanging-wall block moves down the slope of the fault relative to the footwall block. Accommodate lengthening, or extension, of the crust.

thrust/reverse faults

type of dip-slip fault; the hanging-wall block moves up the slope of the fault. Thrust faults differ from reverse only in terms of the fault-plane's slope: thrust have a slope of <35 degrees, whereas reverse faults have a slope of >35 degrees. Accommodate shortening of the crust with strong compressional forces.

strike-slip faults

type of fault; one block slides past another (therefore, parallel to the strike line). Form along transform fault boundaries.

oblique-slip faults

type of fault; sliding occurs diagonally on the fault plane.

dip-slip faults

type of fault; sliding occurs up or down the slope of the fault (therefore, up or down the dip). Types of these faults include: normal faults and thrust/reverse faults.

anticline

type of fold; a fold that has an archlike shape in which the limbs dip away from the hinge, involves sedimentary layers in the center and progressively younger layers away from the center; the stripes are symmetrically positioned around the hinge.

monocline

type of fold; a fold that has the shape of a carpet draped over a stairstep.

syncline

type of fold; a fold with a trough-like shape in which the limbs dip down toward the hinge. Involves sedimentary layers, the youngest layers crop out in the center and the oldest at the margins.

Hydrothermal metamorphism

type of metamorphism; hot magma rises beneath the axis of the mid-ocean ridges, so when cold seawater sinks through cracks down into the oceanic crust along ridges; it heats up and transforms into hydrothermal fluid. Metamorphoses ocean-floor basalt; produces chlorite, greenish hue.

terrestrial planets

type of planet that consists of a shell of rock surrounding a core of iron alloy; the inner planets (Mercury, Venus, Earth, Mars).

gas-giant planets

type of planet; the outer, Jovian planets (Jupiter, Saturn, Uranus, Neptune). Jupiter and Saturn have an elemental composition similar to the Sun's, predominantly hydrogen and helium. Uranus and Neptune, in contrast, consist predominantly of ice.

Beta emission

type of radioactive decay; an electron (beta particle) is given off from the nucleus. Mass number remains unchanged and the atomic number increases by 1.

Electron capture

type of radioactive decay; an electron is captured by the nucleus, the electron combines with a proton to form a neutron. Mass number remains unchanged and the atomic number decreases by 1.

Alpha emission

type of radioactive decay; emission of 2 protons and 2 neutrons (an alpha particle). The mass number of the element is reduced by 4 and the atomic number is lowered by 2.

compression

type of stress; develops when a rock is squeezed. Occurs during growth of a collisional mountain range, convergent plate boundaries.

shear stress

type of stress; develops when one side of a rock body moves sideways past the other side. Occurs at faults, transform plate boundaries.

tension

type of stress; occurs when a rock is pulled apart. Occurs during growth of a continental rift, divergent plate boundaries.

pressure

type of stress; refers to the special stress condition in which the same push acts on all sides of an object. A diver feels this when submerged.

nonconformity

type of unconformity; older metamorphic or intrusive igneous rocks in contact with younger sedimentary strata; type of unconformity at which sedimentary rocks overlie intrusive igneous rocks and/or metamorphic rocks. The igneous or metamorphic rocks must have cooled, been uplifted, and been exposed by erosion to form the substrate on which new sedimentary rocks were deposited. Here, you typically will find pebbles of the igneous or metamorphic in the lowest bed of the sedimentary sequence.

disconformity

type of unconformity; strata on either side are parallel; an unconformity parallel to the two sedimentary sequences it separates. Sediment deposited beneath a shallow sea, the deposited beds become exposed when sea level drops and during this time, no new sediment accumulates, and some of the preexisting sediment gets eroded away. Even though the beds above and below this type of unconformity are parallel, the contact between them represents an interruption in deposition.

angular unconformity

type of unconformity; tilted rocks are overlain by flat-lying rocks; rocks below an unconformity that were tilted or folded before the unconformity developed by faulting and then being uplifted and eroded. Cuts across the underlying layers; layers below have different orientation from the layers above.

stratigraphic column

used to summarize info about the sequence of strata at a location. Typically, these columns are drawn to scale, so that the relative thickness of layers portrayed on the column represent the thicknesses of layers in the outcrop.

compressional waves

waves in which particles of material move back and forth parallel to the direction in which the wave itself moves

shear waves

waves in which particles of material move back and forth perpendicular to the direction in which the wave itself moves

body waves

waves passing through the interior (body) of earth; a single earthquake produces many kinds of waves, distinguished from each other by where and how they move; (P-waves and S-waves) waves that pass through the interior of the planet. P-waves are compressional, similar to a spring, whereas S-waves are shear, resembling a moving rope.

seismogram

waves traced by the pen on a seismograph provide a record of the earthquake

surface waves

waves traveling along the surface of earth; a single earthquake produces many kinds of waves, distinguished from each other by where and how they move; (R-waves and L-waves) waves that propagate along the planet's surface.

sedimentation during orogeny

weathering and erosion in mountain belts generate vast quantities of sediment. This sediment tumbles down slopes and gets carried away by glaciers or streams that transport it to low areas where it accumulates in large fans or deltas. The weight of collisional mountain belts pushes down the surface of the lithosphere, thereby producing a deep sedimentary basin at the border of the range.

Differential stress

when a metamorphic material is squeezed or stretched unequally from different sides. Under these conditions, the push or pull in one direction differs in magnitude from the push or pull in another direciton.

Metamorphism due to pressure

when minerals are subjected to extreme pressure, denser minerals tend to form. Such transformations involve phase changes and/or neocrystallization. Rocks subjected to ultra-high pressure contain grains of coesite, a phase of SiO2 that is much denser than familiar quartz.

fold-thrust belt

when plate movements push the contingent tightly against the subduction zone, compression on the continent side of the volcanic arc generates a ____. In such belts, a thrust-fault system has developed above a nearly horizontal detachment fault, and folds form as strata are pushed up from the fault.

earthquakes at collision zones

zones where two continents collide after the oceanic lithosphere that once separated them has been completely subducted yield great mountain ranges such as the Alpine-Himalayan chain. The most common movements in these zones is on thrust faults, which formed when the crust was compressed, or squeezed.

Moment magnitude

(Mw), because the other measures of magnitude could not accurately define the sizes of very large earthquakes, seismologists developed this scale. To calculate, it is necessary to measure the amplitude of a number of different seismic waves, determine the area of the slipped portion of the fault that moved, determine how much slip occurred, and define physical characteristics of the rock that broke during faulting. Typically, the larger the area that slipped and amount of displacement, the greater the earthquake

big bang

(cosmology) the cosmic explosion that is hypothesized to have marked the origin of the universe. All matter and energy - everything that now constitutes the Universe - was initially packed into an infinitesimally small point. For reasons that no one fully understands, the point exploded about 13.7 billion years ago.

tsunamis

A giant wave caused by an earthquake on the ocean floor; water from the upthrust sea floor began moving outward from above the fault zone, a process that generates a series of giant waves traveling at speeds of about 800 km/hour (500mph).

seismic tomography

A method that uses the seismic waves from earthquakes recorded on thousands of seismographs all over the world to sweep Earth's interior in many different directions and construct a three-dimensional image of what's inside.

Wadati-Benioff zone

A sloping band of seismicity defined by intermediate and deep focus earthquakes that occur in the downgoing slab of a convergent plate boundary.

Migmatite

At very high temperatures, or if hydrothermal fluids enter the rock and lower its melting temperature, gneiss begins to partially melt, producing magma that is enriched in silica. In some cases, this melt does not move very far before freezing to form a light-colored igneous (felsic) rock. The resulting mixture of igneous and relict metamorphic rock is this type of rock.

protostar

Early form of a star; This stage lies between the collapsing of dust and gas and the beginning of nuclear fusion. The central ball of an accretion disk becomes hot enough to glow, due to kinetic energy and thermal energy.

expanding Universe theory

Edwin Hubble realized that the light from all distant galaxies, regardless of their direction from Earth, exhibits a red shift, all distant galaxies are moving rapidly away from us. No longer could we view the Universe as being fixed in dimension, with galaxies locked in position, Universe expansion was occurring.

orogeny

From the Greek word oros, meaning mountain, and genesis, meaning formation. It's a mountain-building event with a limited lifetime. The process begins, lasts for tens of millions of years, and then ceases. After this process ceases, erosion may eventually bevel the land surface almost back to sea level, sometimes in a little as 50 million years.

magnetostratigraphy

Geologists having determined when magnetic reversals took place, have constructed a reference column showing the succession of reversals through time. By comparing the pattern of the reversals in a sequence of strata with the bar code of the reference column, scientists can determine the age of the sequence.

stress

Geologists use this word instead of force when talking about the cause of deformation. Defined as: the action on a plane as the force applied per unit area of the plane. Written as an equation this becomes: _____ = force/area. During mountain building, the force of one plate interacting with another is distributed across the area of contact between the two plates, so the deformation resulting at any specific location actually depends on the ____ developed at that location, not on the total force involved in the plate interaction.

hogback

In some cases, the geometry of geologic structures affects the shape of mountains. If beds dip steeply, they form this narrow, more symmetrical ridge.

cuesta

In some cases, the geometry of geologic structures affects the shape of mountains. Mountain ridges formed by tilted layers of rock typically have an asymmetric shape, with a steep face on one side (where a cliff cuts across a layer) and a gentle slope on the other side (parallel to the layering, where the top layer becomes the surface of the hill); asymmetric.

Metamorphism to due pressure+temperature

In the Earth, pressure and temperature change together with increasing depth. At a depth of 8km, temperature in rock is about 200C and pressure is about 2.3 kbar. A depth of 20km yields temperature and pressure of 500C and 5.5 kbar respectively.

Precambrian

Interval of geologic time between Earth's formation about 4.57 Ga and the beginning of the Phanerozoic Eon 542 Ma

Principle of uniformitarianism

James Hutton's, the father of geology, principle theory, states that physical processes we observe today also operate in the past and were responsible for the formation of the geologic features we see in outcrops. The present is the key to the past.

mountain belts

Mountains do not occur in isolation, but rather as a part of linear ranges variously called _____, orogenic belts, or orogens. These develop because of subduction at convergent plate boundaries, rifting, continental collisions, and locally, because of motion on transform faults.

Dynamic metamorphism

Near the Earth's surface, the movement of faults sliding past each other breaks fracture rock into angular fragments, or crush into powder. But at greater depths rock is so warm that it behaves like soft plastic as shear along the fault takes place, during this process the minerals in the rock crystallize. It occurs as a consequence of shearing along, under metamorphic conditions, without requiring a change in temperature or pressure.

Paleozoic

Oldest era of the Phanerozoic Eon

seismic travel velocity

P-waves travel at 8 km per second in peridotite (ultramafic rock), but only 3.5 km per second in sandstone. Waves accelerate or slow down if they pass from one rock to another. P-waves in rock travel about 10 to 25 times faster than sound waves in air. Additionally, seismic waves travel faster in a solid than in a liquid. Only P-waves can travel through a liquid and are faster than S-waves in all materials.

velocity-versus-depth curve

S-waves: occur in the crust, mantle, and inner core, 7 or less km per second. P-waves: occur in the crust, mantle and core, 6-14 km per second.

seismic-risk (or seismic hazard assessment)

The earthquake damage that can be expected over the long term for a specified region, such as a county or state, usually measured in terms of average dollar loss per year.

Mesozoic

The middle of the three Phanerozoic eras; lasted from 245 Ma to 65 Ma

Cenozoic

The most recent era of the Phanerozoic Eon, lasting from 65 Ma up until present

seismic-reflection profile

To view rock structure beneath sea floor, strong low-frequency sounds are produced by explosions (depth charges) or air guns. These sound waves penetrate beneath the seafloor and reflect off the contacts between rock layers and fault zones just like sonar reflects off the bottom of the sea.

geocentric model

Universe structure theory in which the Earth sits motionless at the center of the Universe while the Sun and all planets follow perfectly circular orbits around it.

characteristics of deformation

When beds no longer have the same shape and position that they had when first formed, and the shape and orientation of grains has changed. Deformation includes one or more of the following: a change in location (translation), a change in orientation (rotation), or a change in shape (distortion),

Shock metamorphism

When large meteorites slam into the Earth, a vast amount of kinetic energy transforms into heat and a pulse of extreme compression (a shockwave) propagates the Earth. The heat may be sufficient to melt or even vaporize rock at the impact site, and the extreme compression of the shock waves causes the crystal structure of quartz grains in rocks below the impact site to suddenly undergo a phase change to a more compact mineral called coesite.

the Doppler effect

a change in the frequency of waves caused by a moving source, or a moving observer. 1.) Change in λ or frequency of a wave due to the source either approaching you or receding from you (works with sound and EMR) 2.) Blue Shift-towards you, Red Shift-away from you 3.) Used to detect motion, direction, and speed of stars

geologic column

a composite stratigraphic column; represents a specific interval of time. The largest subdivisions break Earth history into the Hadean, Archean, Proterozoic, and Phanerozoic Eons.

geologic history

a definition of the relative ages of events that took place in a certain region. Begin by noting the kinds of rocks and structures present, and then you look at the relationships between the igneous rocks and the sedimentary rocks. And lastly, you consider the fault and the land surface.

graben

a fault-bounded basin. The central block formed from a normal fault, these produce an elongated valley bounded by uplifted structures called horsts.

dome

a fold in the shape of an overturned bowl. The oldest layer occurs in the center.

basin

a fold shaped like a right-side up bowl. The youngest layer occurs in the center.

planet

a large, spherical solid object orbiting a star, and may itself travel with a moon or many moons.

Vein

a mineral filled crack that cuts across preexisting rock.

crustal root

a mountain range with a low-density _____ has less mass overall than a mountain range underlain by dense mantle, and so it exerts less pull on a plumb bob. These are important because without their buoyancy, mountain ranges would not be so high.

DEFORMATION

a process by which rocks change shape, tilt, or break in response to squeezing, stretching, or shearing. The process of forming a mountain not only uplifts the surface of the crust, but also causes rocks to undergo this process.

shield areas

a province of a craton; in these areas, we find intensively deformed metamorphic rocks - abundant examples of shear zones, flow folds, and tectonic foliation. These orogens are so old that erosion has worn away the original topography, in the process exposing deep crustal rocks at the Earth's surface.

the cratonic platform

a province of a craton; in this area, we can't see the Precambrian rocks and structures, except where they are exposed by deep erosion. Younger strata display less intense deformation. Includes two classes of structures: regional basins and domes, and local zones of folds and faults.

Blueschist

a relatively rare metamorphic rock that contains an unsual blue-colored amphibole called glaucophane. Occurs only in the accretionary prisms that form at subduction zones. Because of shear between the subducting plate and the overriding plate, foliation develops.

METAMORPHIC ROCK

a rock that forms from a preexisting rock, that undergoes mineralogical and textural changes in response to modification of its physical or chemical environment.

protoplanetary disk

a rotating circumstellar disk of dense gas surrounding a young newly formed star. It is thought that planets are eventually formed from the gas and dust within this formation.

supernova

a star that explodes and becomes extremely luminous in the process.

THE EARTHQUAKE HYPOCENTER

a sudden rupture of intact rock or the frictional slip of rock on a fault produces seismic waves. These waves move outward from the point of rupture in all directions at once.

unconformity

a surface, representing a period of non deposition and possibly erosion. The interval of time between deposition of the youngest rock below the uncomformity and deposition of the oldest rock above is called a hiatus. Essentially this type of structure occurs wherever the land surface does not receive and accumulate sediment.

numerical age

age of a feature given in years

correlation

age relationship between the strata at one locality and the strata of another. 'Lithographic' and 'method fossil' variations; nearby and broad relationships respectively.

displacement

amount of slip on the fault, by measuring the distance between two ends of a marker, such as distinctive sedimentary bed or igneous dike that's been offset by a fault, geologists can define this.

principle of baked or chilled contacts

an igneous intrusion metamorphoses surrounding rocks. The rock that has been 'baked' must be older than the intrusion. Similarly, since an intrusion injects into cooler rocks, the margin of the intrusion cools rapidly and its finer grained than the interior.

undeformed

an outcrop at which the beds have the same orientation that they had when first deposited. It contains no geologic structures other than a few joints.

Preferred mineral orientation

as a rock changes shape under elevated temperatures and pressures, the internal texture of the rock also changes, typically resulting in this type of development. In wet rocks low temperatures, pressure solution dissolves on the faces perpendicular to the direction of compression. At high temperatures, grains flatten in response to differential stress by means of plastic deformation. And grain growth (neocrystallization) may produce preferred orientation, because certain minerals grow faster in the direction in which a rock is stretching than in other directions.

Nebulae

as the Universe continued to expand and cool further, following the big bang, atoms and molecules slowed down and accumulated into these patchy clouds of gas.

open and tight folds

aspects of a fold; if the angle between the limbs is large, then the fold is an open fold, but if the angle between the limbs is small, then the fold is a tight fold.

nonplunging and plunging folds

aspects of a fold; if the hinge is horizontal, the fold is called a nonplunging fold, but if the hinge is tilted, the fold is called a plunging fold. Layers in a plunging fold have a U-shape on the ground surface.

transform plate-boundary seismicity

at this type of plate boundary, most faulting results in strike-slip motion. The majority of these faults in the world link segments of oceanic ridges, but a few, such as the Sand Andreas Fault and the Alpine Fault of New Zealand cut across continental lithosphere, these large ones on land can cause great disaster.

local magnitude

because of the Richter's scales limitations on distance, a number on the original Richter's scale is now called this, (ML)

deformation rate

behavior of rock dependence; a sudden change in shape causes brittle deformation, whereas a slow change in shape causes ductile deformation. For example, if you hit a marble bench with a hammer, it shatters, but if you leave it alone for a century, it gradually sags without breaking.

composition

behavior of rock dependence; some rock types are softer than others; for example, halite (rock salt) can deform ductilely under conditions in which granite behaves brittlely.

pressure

behavior of rock dependence; under great pressures deep in the Earth, rock behaves more ductilely than it does under low pressures near the surface. Pressure effectively prevents rock from separating into fragments.

temperature

behavior of rock dependence; warm rocks tend to deform ductilely, whereas cold rocks tend to deform brittlely. Like a candle, rocks will become malleable when subjected to heat.

low-velocity zone

between about 100 and 200 km deep in the mantle beneath oceanic lithosphere, seismic velocities are slower than in the overlying lithospheric mantle. Within this zone, the prevailing temperature and pressure conditions cause peridotite to melt partially, by up to 2%, the melt coats solid grains and fills voids between grains.

contact

boundary surface between two stratigraphic formations is a type of geologic...

differentiation

by this process, protoplanets and large planetesimals developed internal layering early in their history; due to increasing heat from two sources: the transformation of kinetic energy into thermal energy during collisions, and the decay of radioactive elements.

systematic joints

category of joint; long planar cracks that occur fairly regularly through a rock body.

non systematic joints

category of joint; short cracks that occur in a range of orientations and are randomly spaced.

deep-focus earthquake

classification of an earthquake based on the hypocenter depth; occur down to a depth of about 670 km. Only in subducting oceanic plates.

shallow-focus earthquake

classification of an earthquake based on the hypocenter depth; occur in the top 20 km of the earth. Cause the most damage, because the earthquake waves they produce do not lost much energy before vibrating the Earth's surface.

intermediate-focus earthquake

classification of an earthquake based on the hypocenter depth; take place between 20-300 km. Only in subducting oceanic plates.

axial plane

component of folds; an imaginary surface that encompasses the hinges of successive layers.

hinge

component of folds; refers to the portion of the fold where curvature is the greatest.

limbs

component of folds; the sides of the fold that show less curvature.

P-waves

compressional body waves - push/pull waves; 1st, fastest, & go through solids & liquids

growth rings

consequence of seasonal changes; develop in trees, travertine deposits, and shelly organisms

the brittle-ductile transition

considering that pressure and temperature both increase with depth in the Earth, geologists finds that in typical continental crust, rocks behave brittlely above about 10-15 km, whereas they behave ductilely below. Earthquakes in continental crust happen only above this depth because these earthquakes involve brittle breaking.

craton

consists of crust that has not been affected by orogeny for at least 1 billion years. Because of this, their crust has become quite cool, and therefore relatively strong and stable. Variations in the dip and thickness of these strata define regional basins, arches, and domes. Divided into two provinces: shields and the cratonic platform.

metamorphism during orogeny

contact metamorphic aureoles form adjacent to igneous intrusions in orogens. Regional metamorphism occurs during compression during mountain building produces faults on which one part of the crust thrusts over another. Rock of the footwall can end up at great depth and thus can be subjected to high temperature and pressure. Because deformation accompanies this process, the resulting metamorphic rocks contain tectonic foliation.

Mercalli intensity scale

defines the intensity of an earthquake by the amount of damage it causes; developed in 1902 by Italian scientist Giuseppe Mercalli. Denoted the measure of intensity with M followed by a Roman numeral - such MVII or MXI

fault scarp

displacement on a dip-slip or oblique-slip fault makes a small step on the ground surface; and because faults tend to break up rock, the fault may be preferentially eroded. If this happens, the fault trace (the line of intersection between the fault and the ground surface) will be marked by a linear valley.

Regional metamorphism

dynamothermal metamorphism affecting a large region. Metamorphism involving heat but also shearing and squashing. Produces the greatest quantity of metamorphic rock, associated with mountain building.

seismicity

earthquake activity, occurs for several reasons: formation of a new fault, slip on existing fault, sudden change in the arrangement of atoms in the minerals comprising rock, movement of magma in a volcano, explosion of volcano, giant landslide, meteorite impact, or underground nuclear-bomb tests.

seismic waves

earthquake energy traveling in the form of waves

seismic belts (or seismic zones)

earthquakes do not take place everywhere on the globe, by plotting the distribution of earthquake epicenters on a map, seismologists find that most, but not all, earthquakes occur in these narrow areas, most following plate boundaries.

EARTHQUAKE

episode of ground shaking. Most are a consequence of lithosphere plate movement; they punctuate each step in the growth of mountains, the drift of continents, and the opening and closing of ocean basins.

the distance from the hypocenter

factor in the nature and severity of earthquake shaking; earthquake energy decreases as waves pass through the Earth

the magnitude of the earthquake

factor in the nature and severity of earthquake shaking; larger-magnitude events release more energy.

the nature of the substrate at the location

factor in the nature and severity of earthquake shaking; the character and thickness of different materials beneath the ground surface. In places underlain by unconsolidated sediment or landfill, earthquake waves tend to be amplified and thus cause more ground motion

the frequency of earthquake waves

factor in the nature and severity of earthquake shaking; where frequency equals the number of oscillations that pass a point in a specified interval of time.

forming folds

folds develop in two principal ways. During formation of flexural folds, a stack of layers bends, and slip occurs between the layers. And flow folds form when the rock overall is so soft that it behaves like weak plastic; these folds develop simply because different parts of the rock body move at different rates.

Dynamothermal metamorphism

foliated rock metamorphism; as a consequence of developing mountain ranges, large slices of continental crust slip up and over portions of the crust, the resulting rock that was once near the Earth's surface along the margin of the continent ends up at depth beneath the mountain range. In this new environment, 3 changes occur: the protolith heats up due to the geothermal gradient and igneous activity, the protolith is subjected to greater pressure due to overburden, and the protolith undergoes squashing and shearing because of differential stress generated by plate interaction.

periods; epochs

from geologic eras, we can further divide each era into____and each of of these into_____

joints

geologic structures produced from deformation; cracks. Develop in response to tensional stress in brittle rock: a rock splits open because it has been pulled slightly apart. Some form when a rock cools and contracts, others when rock layers formerly at depth undergo a decrease in pressure as overlying rock erodes away, and thus change shape slightly.

faults

geologic structures produced from deformation; fractures along which one body of rock slides past another. A pulse of rapid deformation causes these to form.

foliation

geologic structures produced from deformation; layering resulting from the alignment of mineral grains or the development of compositional bands.

folds

geologic structures produced from deformation; the curving of rock layers, bends or wrinkles. Slow deformation yields these. May be defined by curving dikes, sills, or veins.

epeirogeny

geologists refer to the broad vertical movements that generate huge, but gentle, mid-continent domes and basins as ____.

sieche

ground motion from earthquakes can cause water in lakes, bays, reservoirs, and pools to slosh back and forth, in some cases thousands of kilometers from the epicenter. The water's rhythmic movement can build up waves almost 10 m high and can last for hours.

Metamorphism due to heating

heating causes atoms to vibrate, chemical bonds to detach and rearrange, as a consequence recrystallization and/or neocrystallization take place. These processes enable a metamorphic rock assemblage to grow in solid rock. Sources: contact metamorphism and increased depth. Temperatures between 200 and 850 deg C.

Shield

huge expanses of metamorphic rock crop out in older portions of a continent, where extensive areas of Precambrian rock crop out at the ground surface because overlying younger rock has eroded away.

isostatic compensation

if a geologic event happens that changes the density or thickness of the lithosphere, then the surface of the crust slowly rises or falls to reestablish isostatic equilibrium. For example, when glaciers grow during ice ages, their weight depresses the surface of the crust, and when they melt away after ice ages, the surface of the crust rises. Also the process of mountain uplift is commonly a manifestation of this process.

the principle of inclusions

if an igneous intrusion contains fragments of another rock, the fragments must be older than the intrusion. If a layer of sediment deposited on an igneous layer includes pebbles of the igneous rock, then the sedimentary layer must be younger. The fragments (xenoliths) in an igneous body and the pebbles in the sedimentary layer are inclusions, or pieces of one material incorporated in another. The rock containing the inclusion must be younger than the inclusion.

veins

if groundwater seeps through joints for a long period of time, minerals such as quartz or calcite can precipitate out of the groundwater and fill the joint. Such mineral-filled joints are called ____ and look like white stripes cutting across a body of rock.

principle of cross-cutting relations

if one geologic feature cuts across another, the feature that has been cut is older. For example, if an igneous dike cuts across a sequence of sedimentary beds, the beds must be older than the dike.

igneous activity during orogeny

in mountain belts formed along convergent plate boundaries, magma forms as a consequence of subduction. In rifts, stretching and thinning of lithosphere causes decompression melting of the underlying mantle. And during continental collision, melting may take place where deep portions of the crust undergo heating.

fault scarp

in places where an active normal or reverse fault intersects the ground, one side of the fault moves vertically with respect to the other side, creating a small step called a______.

fault creep

in some cases, movement on faults in the upper 15-20 km of the continental crust takes place slowly and steadily, without generating earthquakes. Seismologists speculate that this occurs in particularly weak rock, which can change shape without breaking or can slip smoothly without creating shock waves.

hanging-wall block

in the case of nonvertical faults (those that slope at an angle), this is the rock above the fault plane.

footwall block

in the case of nonvertical faults (those that slope at an angle), this is the rock below the fault plane.

accretion disk

in the young Universe, the gravitational pull of an initially denser region of nebula began to pull in surrounding gases and grew in mass and density. Because of rotation, the condensing portion of the nebula evolved into a spinning disk-shaped mass of gas...

arrival time

instant at which an earthquake wave appears at the seismograph station

range

interval in the sequence in which fossils occur. The sequence contains a definable succession of fossils that the range in which a particular species occurs overlaps with the range of other species, and that once a species vanishes, it does not reappear higher in the sequence.

moon

is an object locked in orbit around a planet; all but two of the planets have them.

rhythmic layering

layering that develops in sedimentary accumulations and glacier ice

seismograph

machine that can systematically record the ground motion from an earthquake happening anywhere on earth; , a measuring instrument for detecting and measuring the intensity and direction and duration of movements of the ground (as an earthquake)

Recrystallization

metamorphic formation process; changes the size/shape of the grains without changing the identity of the mineral constituting the grains.

Plastic deformation

metamorphic formation process; happens at elevated temperatures and pressures, conditions that permit some minerals to behave like soft plastic, that if they are stretched or squeezed, they become flattened or elongate without breaking.

Pressure solution

metamorphic formation process; happens when a rock is squeezed more strongly in one direction that in others at relatively low pressures and temperatures, in the presence of water. Mineral grains dissolve where their surfaces are pressed against other grains, producing ions that migrate through the water to precipitate elsewhere.

neocrystallization (or metamorphic reaction)

metamorphic formation process; results in the growth of new mineral crystals that differ from those of the protolith. During this process, one or more chemical reactions digest (reactants) minerals of the protolith to produce new minerals (products) of the metamorphic rock. For this process to take place, atoms must migrate, or diffuse, through solid crystals, a very slow process, and/or dissolve and reprecipitate at grain boundaries, with the aid of hydrothermal fluids sometimes.

Phase change

metamorphic formation process; transforms a grain of one mineral into a grain of another mineral with the same composition but a different crystal structure. At an atomic scale, phase change involves rearrangement of atoms.

Hydrothermal fluids

metamorphic reactions usually take place in the presence of these, because water occurs throughout the crust. Referred to as "hot water solutions", can include hot water, steam, and supercritical fluid. These fluids are chemically active, in that they are able to react chemically with rock; can dissolve certain minerals and enhance ion migration, thus they are present as solutions and not just water.

Phyllite

metamorphic texture; a fine-grained metamorphic rock with a foliation caused by the preferred orientation of very fine-grained white mica and chlorite. Forms by the metamorphism of slate at a temperature high enough to cause neocrystallization; metamorphic reactions produce a new assemblage of minerals out of clay.

Schist

metamorphic texture; a medium/coarse-grained metamorphic rock that possesses a type of foliation, defined by the preferred orientation of large mica.

Gneiss

metamorphic texture; compositionally layered metamorphic rock, typically composed of alternating dark-colored and light-colored layers or lenses that range in thickness.

Slate

metamorphic texture; the finest-grained foliated metamorphic rock, consists of slaty cleavage. Forms in response to differential stress, typically, cleavage planes form perpendicular to the direction of compression.

Burial metamorphism

metamorphism due only to the consequences of very deep burial; causes the organic molecules of oil to break up and for this reason, oil drillers stop drilling when the bottom of the hole reaches depths at which this metamorphism has begun.

induced seismicity

most earthquakes happen independent of human activity, but the timing of some earthquakes relative to human-caused events suggest that, in certain cases, people can influence seismicity. These are seismic events caused by actions of people, generally occurs in response to changes in groundwater pressure.

limitations of uplift

mountains much higher than Mt. Everest cannot exist on the Earth for two reasons. Erosion attacks mountains as soon as they rise, and in some cases it can tear mountains down as fast as uplift occurs. Also, rock does not infinite strength; as mountains rise, the weight of the overlying rock presses down on the rock that is now deeply buried at depth in the crust. The rock buried at depth is gradually growing warmer and softer because of heat rising from the Earth's interior, activating a process called orogenic collapse.

Metamorphic minerals

new minerals that only grow under metamorphic temperatures and pressures - metamorphism can produce a group of minerals called a metamorphic mineral assemblage.

Hornfels

nonfoliated metamorphic rock; a rock that undergoes metamorphism because of heating in the absence of differential stress. The crystals grow in random orientations, prevents foliation.

Quartzite

nonfoliated metamorphic rock; during metamorphism, preexisting quartz grains recrystallize, creating new, larger grains. Forms from quartz sandstone.

Amphibolite

nonfoliated metamorphic rock; metamorphism of mafic rocks (basalt and gabbro) can't produce quartz and muscovite when metamorphosed, for these rocks don't contain the right mix of chemicals to yield such minerals. They transform into this dark-colored rock containing hornblende and plagioclase.

Marble

nonfoliated metamorphic rock; the metamorphism of limestone, calcite composing the protolith recrystallizes; as a consequence original sedimentary features become hard to recognize, pore space disappears, and the distinction between grains and cement disappears.

earthquake magnitude scales

number that indicates its relative size, as determined by measuring the maximum amplitude of ground motion recorded by a seismograph at a given distance from the epicenter.

Richter scale

number used to compare against magnitude scale by measuring the amplitude of the largest deflection generated in response to seismic waves that have a period of one second; developed by Charles Richter 1935. The levels are logarithmic, thus a magnitude 8 is 10x greater than a magnitude 7, and 1000x greater than magnitude 5 earthquake.

detachment fault

numerous related faults are often found in groups called fault systems. Individual faults in a system may merge at depth with a nearly horizontal _____.

seismic-velocity discontinuities

occur at depths where pressure causes atoms in minerals to rearrange and pack together more tightly, thereby changing the rock's physical character. Corresponds to a phase change.

accretionary orogens

orogens that grow laterally by the attachment of exotic terranes; Once an exotic terrane accrete to a continent, a new subduction zone typically forms on the ocean side of the terrane, and a new volcanic arc develops on top of the terrane.

elastic-rebound theory

overall image of how earthquakes occur; After either faulting event, stress drops and the elastic strain stored in rock decreases - the rock rebounds so layers near the fault are no longer bent. Friction stops the movement and the fault locks, until stress builds up enough again to cause slip. (first explained by HF Reid)

hypocenter (focus)

place in the earth where rock ruptures and slips, or the place where an explosion occurs

travel time curve

plots the time since the earthquake began on the vertical axis and the distance to the epicenter on the horizontal axis. Used to determine the distance of an epicenter, start by measuring the time difference between P- and S-waves on the seismograph.

epicenter

point on the surface of the earth that lies directly above the hypocenter

geologic map

portrays the spatial distribution of rock units at the earths surface. Formed through correlated strata at many locations, allows you to trace individual formations of strata over fairly broad regions.

radioactive decay

process by which a radioactive atom undergoes fission or releases particles thereby transforming into a new element. All these reactions change the atomic number of the nucleus and thus form a different element.

Exhumation

process by which overlying rock is removed and deeper rock rises, these rocks are exposed as towering cliffs of gneiss and schist. The overall process by which deeply buried rocks end up back at the surface, occurs relatively quickly.

Metamorphic foliation

refers to the repetitions of planar surfaces or layers in a metamorphic rock. Can give a metamorphic rock a striped or streaked appearance in an outcrop, and/or give them the ability to split into thin sheets.

protoplanets

regions of condensed matter that serve as a starting point for the formation of a planet.

geologic time scale

scale that describes the intervals of geologic time. Dinosaurs appeared during the Triassic period, between 251 and 250 million years ago.

principle of original continuity

sediments generally accumulate in continuous sheets. If today you find a sedimentary layer cut by a canyon, then you can assume that the layer once spanned the canyon but was later eroded by the river that formed the canyon.

principle of original horizontality

sediments on Earth settle out of a fluid in a gravitational field. Typically, the surfaces on which sediments accumulate are fairly horizontal (such as a floodplain or the bed of a lake or sea), if sediments were deposited on a steep slope, they would slide down before being lithified into a layer. Therefore, when layers of sediment are originally deposited, they are fairly horizontal.

recurrence interval

seismologists base long-term earthquake predictions on two pieces of information: the identification of seismic zones and the ____ (the average time between successive events).

seismic gaps

seismologists mark these zones where a known active fault has not slipped for a long time as particularly dangerous.

principle of superposition

sequence of sedimentary rock layers, each layer must be younger than the one below, for a layer of sediment cannot accumulate unless there is already a substrate on which it can collect. Thus, the layer at the bottom of a sequence is the oldest, and the layer at the top is the youngest. (Nicolaus Steno)