Intro to Geology - Midterm 2

geologic time

the span of time since the earths formation

relative age

The age of a rock compared to the ages of rock layers

numerical age

age of a feature given in years

absolute age

The age of a rock given as the number of years since the rock formed.

Principle of Uniformitarianism

Earth processes occurring today are similar to those that occurred in the past

Principle of Original Horizontality

layers of sediment are generally deposited in a horizontal position

Principle of Superposition

When artifacts are found in rock or earth that is layered, the deeper layers hold the older artifacts. Sediments need a layer of substate to accumulate on top of.

Principle of Lateral Continuity

Beds originate as continuous layers that extend in all directions until they eventually thin out or grade into a different sediment type

principle of cross-cutting relationships

younger features cut across older features

Unconformity

A break in the geologic record created when rock layers are eroded or when sediment is not deposited for a long period of time.

angular unconformity

tilted rocks are overlain by flat-lying rocks

Nonconformity

A type of unconformity in which layered sedimentary rocks lie on an erosion surface cut into igneous or metamorphic rocks

Disconformity

a type of unconformity in which the sedimentary layers above and below the unconformity are parallel

angular unconformity (diagram)

nonconformity (diagram)

Disconformity (diagram)

geologic contact

the boundary between two adjacent rock units

stratigraphic column

A diagram representing a series of rock layers

geologic map

A map showing the distribution of rock units and structures across a region.

geologic column

an arrangement of rock layers in which the oldest rocks are at the bottom

Eons

the largest division of geologic time

Precambrian

Name for the time in earths early history that accounts for ninety percent of earth's time, but only cellular organisms lived. (Hadean, Archean,Proterozoic, Phanerozoic)

era

a long and distinct period of history with a particular feature or characteristic.

period

further divided era of time

epoch

further divided period of time

isotopic dating

the use of naturally occurring radioactive elements to determine the ages of rocks

Geochronology

study of the ages of geologic events

Isotopes

Atoms of the same element that have different numbers of neutrons

radioactive decay

A spontaneous process in which unstable nuclei lose energy by emitting radiation

Parent Atom

the atom that undergoes radioactive decay in a nuclear reaction

Daughter Atom

the product atom from the radioactive decay of a parent atom

half-life

length of time required for half of the radioactive atoms in a sample to decay

closure temperature

the temperature below which isotopes are no longer free to move

metamorphic rock

A type of rock that forms from an existing rock that is changed by heat, pressure, or chemical reactions.

Protolith

the original rock from which a metamorphic rock formed

Metamorphism

the process in which one type of rock changes into metamorphic rock because of chemical processes or changes in temperature and pressure

metamorphic minerals

new minerals that grow in place within the solid rock only under metamorphic temperatures and pressures

Metamorphic textures

foliated and non-foliated

metamorphic foliation

A fabric defined by parallel surfaces or layers that develop in a rock as a result of metamorphism; schistocity and gneissic layering are examples.

differential stress

when stress is applied unequally in different directions

preferred orientation

The metamorphic texture that exists where platy grains lie parallel to one another and/or elongate grains align in the same direction.

Metasomatism

the process by which a rock's overall chemical composition changes during metamorphism because of reactions with hot water that bring in or remove elements

Foliation

An arrangement of minerals in flat or wavy parallel bands.

slate

A type of Metamorphic rock that was once shale rock formed by heat and pressure.

Phyllite

A fine-grained metamorphic rock with a foliation caused by the preferred orientation of very fine-grained mica.

Schist

Metamorphic, Foliated

Metaconglomerate

A metamorphic rock produced by metamorphism of a conglomerate; typically, it contains flattened pebbles and cobbles.

Gneiss

A metamorphic rock that has ribbon like layers. It was made from other rocks that have been squeezed and heated a long time in the Earth.

Migmatite

A rock formed when gneiss is heated high enough so that it begins to partially melt, creating layers, or lenses, of new igneous rock that mix with layers of the relict gneiss.

Hornfels

Rock that undergoes metamorphism simply because of a change in temperature, without being subjected to differential stress.

Quartzite

a metamorphic rock composed of quartz and transformed from a protolith of quartz sandstone

marble

metamorphic rock that was once limestone

metamorphic grade

the degree to which the parent rock changes during metamorphism

metamorphic facies

A set of metamorphic mineral assemblages indicative of metamorphism under a specific range of pressures and temperatures.

metamorphic zone

The region between two metamorphic isograds, typically named after an index mineral found within the region.

metamorphic aureole

The region around a pluton, stretching tens to hundreds of meters out, in which heat transferred into the country rock and metamorphosed the country rock.

thermal metamorphism

metamorphism caused by heat conducted into country rock from an igneous intrusion

contact metamorphism

A change in the texture, structure, or chemical composition of a rock due to contact with magma.

burial metamorphism

metamorphism due only to the consequences of very deep burial

dynamic metamorphism

metamorphism that occurs as a consequence of shearing alone, with no change in temperature or pressure

dynamothermal metamorphism

Metamorphism that involves heat, pressure, and shearing.

regional metamorphism

formation of metamorphic rock bodies that are hundreds of square kilometers in size

hydrothermal metamorphism

occurs when very hot water reacts with rock, altering its mineralogy and chemistry

shock metamorphism

the changes that can occur in a rock due to the passage of a shock wave, generally resulting from a meteorite impact

exhumation

The process (involving uplift and erosion) that returns deeply buried rocks to the surface.

shield

broad region of long lived, stable continental crust where sedimentary cover either was not deposited or has been eroded away so that precambrian basement rocks are exposed.

Mountain belts/orogens

a linear range of mountains

Mountain Building

Major geological event that occurs when continental plates of equal density converge, resulting in mountain chains.

Orogeny

a process in which a section of the earth's crust is folded and deformed by lateral compression to form a mountain range.

distortion

a change in the shape, size, or position of a place when it is shown on a map

ductile deformation

A type of solid-state flow that produces a change in the size and shape of a rock body without fracturing. Occurs at depths where temperatures and confining pressures are high.

Stress

A force that acts on rock to change its shape or volume

faults

Breaks in Earth's crust where rocks have slipped past each other.

strike-slip fault

a type of fault where rocks on either side move past each other sideways with little up or down motion

dip

angle of the planes slope

plunge

angle between a line and horizontal in the vertical plane that contains the line

bearing

compass heading of the line, meaning the angle between the projection of the line on the horizontal plane and the direction to true north

reverse fault

a type of fault where the hanging wall slides upward; caused by compression in the crust

thrust fault

a reverse fault in which the hanging wall slides over to the foot wall.

normal fault

A type of fault where the hanging wall slides downward; caused by tension in the crust

oblique-slip fault

A fault with both strike-slip and dip-slip components.

fault scarp

a small step on the ground surface where one side of a fault has moved vertically with respect to the other

slickensides

The polished surface of a fault caused by slip on the fault; lineated slickensides also have grooves that indicate the direction of fault movement.

Rock fold

occurs when one or a stack of originally flat and planar surfaces, such as sedimentary strata, are bent or curved as a result of permanent deformation

limbs

the two sides of a fold

hinge

refers to a line along which the curvature of the fold is greatest

axial surface

the imaginary surface that encompasses the hinges of successive layers of a fold

Anticline

an upward fold in rock formed by compression of Earth's crust

Syncline

A downward fold in rock formed by compression in Earth's crust

Monocline

a large steplike fold in otherwise horizontal sedimentary strata

nonplunging fold

has a horizontal hinge

plunging fold

A fold in which the hinge line (or axis) is not horizontal.

dome

a fold with the shape of an overturned bowl

basin

a natural depression in the surface of the land often with a lake at the bottom of it

Foliation

An arrangement of minerals in flat or wavy parallel bands.

suture

the boundary between blocks that have been separate before the collision

accretion

growth in size or increase in amount

Global Positioning System (GPS)

A system that determines the precise position of something on Earth through a series of satellites, tracking stations, and receivers.

Isostasy

The balancing of the downward force of the crust and the upward force of the mantle.

crustal root

low-density crustal rock that protrudes downward beneath a mountain range