Geology Test #3 For Dr. Deibert

Front 1

METAMORPHIC ROCK

Back 1

a rock formed by metamorphism

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METAMORPHISM

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the transformation of a rock into a distinct new rock by high temperature
and/or high pressure, without melting the rock

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Original rock before metamorphism is called

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Parent Rock

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Increase in temperature comes from

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burial and proximity to magma

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Pressure increase comes from burial and tectonic forces
deep depths - __________ shallow depths - ___________

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high pressure
low pressure

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2 major controls on type of rocks formed during metamorphism

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1) COMPOSITION OF PARENT ROCK TYPE
2) TEMPERATURE AND PRESSURE CONDITIONS

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Usually no new minerals are added to the parent rocks except_____

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water

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Different mineral can form from the same elements at

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different pressures and temperatures

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Growth of minerals during metamorphism is very

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slow

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If the forces are stronger or weaker in different directions, a body is subjected to

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differential stress

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causes platy minerals in metamorphic rocks to align in a parallel fashion

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Differential Stress

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Differential stress causes a texture called

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foliation

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foliation is:

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parallel alignment of minerals

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2 types of metamorphism

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1) CONTACT METAMORPHISM
2) REGIONAL METAMORPHISM

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CONTACT METAMORPHISM

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metamorphism occurring from the heating of rocks near an igneous intrusion

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list some characteristics of CONTACT METAMORPHISM

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- small area of metamorphism 1 - 50 m wide

- usually no differential stress - no foliation in rocks

- produce high temperature - low pressure conditions

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REGIONAL METAMORPHISM

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caused by relatively high temperatures and pressures produced by the regional burial of rocks

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list some characteristics of regional metamorphism

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- produces a wide variety of metamorphic conditions

- temperature can vary depending on the geothermal gradient

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Metamorphic rocks are classified into two categories
________ and ________

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NONFOLIATED and FOLIATED

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MIGMATITE

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a mixed igneous and metamorphic rock, formed from the partial melting of a gneiss

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PROGRESSIVE METAMORPHISM

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how rocks are changed by regional metamorphism during
progressive burial

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LOW GRADE ----------> HIGH GRADE
(progressive metamorphism)

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SLATE PHYLLITE SCHIST GNEISS

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IN AREAS OF RISING MAGMA

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GEOTHERMAL GRADIENT IS HIGHER THAN NORMAL

- PRODUCES HIGH TEMP - LOW PRESSURE CONDITIONS

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IN SUBDUCTION ZONES

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- GEOTHERMAL GRADIENT IS LOWER THAN NORMAL

- PRODUCES LOW TEMP - HIGH PRESSURE CONDITIONS

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HYDROTHERMAL ROCKS

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are formed from the precipitation of minerals from hot water solutions

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hydrothermal rocks

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- commonly form above bodies of magma (mid-ocean ridges, magmatic arcs, mantle plumes)

- cold water from the surface migrates near magma body through cracks

- water heats up , dissolves ions, ions and hot water move upward

- as water rises it cools and pressure is reduced, minerals come out of solution (precipitate)

- form veins of: mostly quartz, less commonly calcite
also minor amounts of zinc, lead, silver, gold, + other metals

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UNIFORMITARIANISM

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geologic processes operating at present are the same processes that have operated in the past

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Two ways of determining age

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1) RELATIVE AGE
2) ABSOLUTE AGE

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what is RELATIVE AGE?

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age of rock or event relative to some other rock or event

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what is ABSOLUTE AGE?

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age given in units of time (years, months, days etc.)

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3 principles used in determining relative age

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1) ORIGINAL HORIZONTALITY
2) SUPERPOSITION
3) CROSS-CUTTING RELATIONSHIPS

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UNCONFORMITY

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a surface (contact) that represents a break in the geologic record, with the rock unit above the surface being considerably younger than the rock below the surface

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3 types of unconformities

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A) DISCONFORMITY
B) ANGULAR UNCONFORMITY
C) NONCONFORMITY

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what is DISCONFORMITY?

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produced by deposition of layers after a period of erosion or non-deposition

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what is ANGULAR UNCONFORMITY?

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produced when horizontal layers are tilted or folded then eroded and horizontal rocks are deposited over erosion surface

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what is NONCONFORMITY?

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an unconformity that separates a body of igneous rocks below from horizontal sedimentary rocks above.

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CORRELATION

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means of determining relative age relationships (rocks and events) in separate areas

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3 types of correlation

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1) Physical continuity
2) Similarity of rock types
3) Fossils

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what is Physical continuity correlation?

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ability to trace rock units to different areas

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what is Similarity of rock types correlation?

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correlations based on the same rock type and/or vertical sequence of rock layers

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what is Fossils correlation?

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correlation based on similar fossils in rock units

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FAUNAL SUCCESSION

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fossil species succeed one another in a definite and recognizable order.

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INDEX FOSSIL

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A fossil that lived for a very short time

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FOSSIL ASSEMBLAGE

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a group of several different fossils found in a rock.
very useful for determining age

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STANDARD GEOLOGIC TIME SCALE

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a worldwide relative time scale based on fossils

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Time scale divided in ERAS

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Cenozoic - recent life
Mesozoic - middle life
Paleozoic - ancient life
Precambrian - before life

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For determining the absolute age of a rock, scientists use typically use

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RADIOMETRIC DATING

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DAUGHTER PRODUCT

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isotope produced by radioactive decay

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The rate of decay of a large number of atoms of a radioactive isotope
is

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CONSTANT

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Rate of decay is given in terms of

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HALF-LIFE

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HALF-LIFE

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is the time it takes for a given amount of radioactive isotope to be reduced by one-half
half-lives can be a short as a fraction of second or billions of years long

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MASS WASTING

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movement in which bedrock, rock debris, or soil moves downslope
because of gravity

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LANDSLIDE

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a general term for the slow to very rapid descent of rock or soil

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Mass wasting is classified based on:

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1) Rate of movement
2) Type of material
3) Type of movement

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what are the type of materials?

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a) debris- unconsolidated rock or soil of any size
b) consolidated material - referred to as rock or bedrock

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what are the different types of movement?

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FLOW - material moves like liquid

SLIDE - material moves as a coherent block along one or more well
defined planes

FALL - material free-falls or bounces down a cliff

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what are the different types of SLIDEs?

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aa) Translational Slide- moves parallel to slope

bb) Rotational Slide - moves a along a curved surface,
top moves down, base moves out

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TRIGGERING MECHANISMS - are commonly:

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1) earthquakes

2) weight added to upper part of slope

3) undercutting of bottom of slope

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common types of mass wasting

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1) CREEP
2) DEBRIS FLOWS
3) FALLS
4) SLIDES

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3 types of debris flow

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A) EARTHFLOW
B) MUDFLOW
C) AVALANCHES

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list 2 types of falls

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ROCKFALLS and DEBRIS FALLS
TALUS

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what is a TALUS?

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an apron of fallen rock fragments at the base of a cliff

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what is a STREAM?

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a body of running water that is confined to a channel and moves downhill

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Erosion and deposition in streams is controlled by _____ and ___

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VELOCITY
DISCHARGE

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what is VELOCITY?

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speed of the water, distance per unit time

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what is DISCHARGE?

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volume of water per unit time

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3 controls on velocity

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1) GRADIENT
2) CHANNEL SHAPE
3) CHANNEL ROUGHNESS

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Streams erode rock and sediment three ways:

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1) HYDRAULIC ACTION
2) ABRASION
3) SOLUTION

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what is HYDRAULIC ACTION?

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ability of flowing water to pick-up and transport sediment

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TRANSPORTATION OF SEDIMENT IN STREAMS can be divided into 3 types

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1) BED LOAD
2) SUSPENDED LOAD
3) DISSOLVED LOAD

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Sediment transported in streams is deposited when stream _____ and _____ are decreased

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velocity
discharge

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STREAM DEPOSITION types:

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BAR
BRAIDED STREAMS
MEANDERING STREAMS
FLOOD PLAIN
NATURAL LEVEES
DELTA
ALLUVIAL FAN

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types of VALLEY DEVELOPMENT

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1) DOWNCUTTING
2) WIDENING

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SLOT CANYON

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pure downcutting

produces very narrow valleys

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WIDENING - is produce by:

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a) MASS WASTING
b) LATERAL EROSION