geology midterm 2

aftershocks

numerous small earthquakes, usually follow a major earthquake

xeno in greek means

foreign

igneous rocks

form from cooling and solidification of magma

metamorphic rocks

formed by changing pre existing igneous rocks, sedimentary rocks, or other metamorphic rocks driven by forces of heat and pressure

sedimentary rocks

formed from weathering of preexisting rocks sediments lithify into sedimentary rocks

pluonic/intrusive igenous rocks

magma that crystallizes at depths underground

glassy texture

rapid cooling, ions freeze before forming a structure

Ultramafic composition

rare, mostly comp. of olivine and pyroxene, ferromagensium minerals

andesitic/intermediate composition

25% or more dark silicates from volcanic island arcs ex. andesite (extrusive), diorite (intrusive)

lava composition

90% is basaltic <10% is andesitic 1% is rhyolitic

syncline

A downward fold in rock formed by compression in Earth's crust youngest layers in the middle

Viscosity

A liquid's resistance to flowing controls type of volcanic eruption

xenolith

Suspended blocks of country rocks found in plutons

monocline

a large steplike fold in otherwise horizontal sedimentary strata upward displacement

cleavage

a mineral's ability to split easily along flat surfaces # of cleavage planes, angle and shape

mineral

a naturally occurring, inorganic solid that has a crystal structure and a definite chemical composition

axial plane

center of an anticline or syncline

rock

a solid mass of minerals

fracture

absence of cleavage where a mineral is broken

largest wave recorded was

an s wave on the wood anderson scale wood anderson scale records p and s waves but cannot pick up surface waves

anticline

an upward fold in rock formed by compression of Earth's crust oldest layers in the middle

tuff

ash fragments cemented together

plunging anticline/syncline

axis of fold penetrates the ground

mafic examples

basalt (extrusive) gabbro (intrusive)

shield volcano

basaltic

mineralogy is influenced by

chemical composition of parent magma

Phaneritic texture

coarse grained, large crystals, slow cooling

pegmatitic texture

coarse grained; formed in late stages of crystallization; large crystals (over 1 cm)

properties for mineral identification

color, streak, cleavage, hardness, density, taste, feel, magnetism, luster, refraction, effervescence etc

liquidus

conditions at which rock completely melts

solidus

conditions at which rock starts to melt

pyroclastic (fragmental) texture

consolidation of rock fragments ejected during eruptions

pluton

cooled, emplaces magma into preexisting rock

texture is influenced by

cooling history of a rock

crystallization

cooling of magma leads to arrangement of ions into orderly patterns

mafic (basaltic) composition

dark silicates, calcium rich feldspar MA(gnesium) F(e/iron)IC higher density than felsic/granitic rocks forms oceanic crust

ductile deformation in anticlines and synclines

domes-upward circular features (oldest rock in center) basins- downward circular features (youngest rock in center)

magnitude

estimate of amount of energy released at source of earthquake

aphanitic texture

fine grained, small crystals, rapid cooling

rock sliippage originates at the

focus/hypocenter

examples of felsic rock

granite (intrusive) rhyolite (extrusive) obsidian pumice

types of eruptions

high viscosity causes explosive eruptions low viscosity causes slow, Hawaiian style eruptions

welded tuff

hot ash that fused together, contains pieces of pumice and other rock

partial melting

incomplete melting of rocks produces most magmas melt is enriched with ions

time intervals between p and s waves...

increase as distance from epicenter increases we use this time lag to find the epicenter using data from at least three stations

intensity is easier to use because

it requires no equipment but it can vary due to type of ground material the earthquake affected (ex mud shakes more than granite) historical reports can determine intensity based on human accounts

causes of earthquakes

landslides, meteorites, and eruptions cause weak quakes stress builds from plate movement and overcomes frictional resistance along faults, causing faults to slip and rock to break

Porphyritic texture

large crystals (phenocrystals) embedded in a matrix of smaller crystals

batholith

largest intrusive body

possible bonus

last San Fransisco quake was in 1906, fault wasnt exactly located 1989 last significant quake south of san fran but still affected it

Aa lava

lava that hardens into rough, jagged rocks with a crumbly texture

stratovolcano

layered rhyolitic/andesitic

Felsic (Granitic) Composition

light colored, contains quartz or potassium feldspar major component of continental crust FEL(dspar) (sil)IC(on)

EC

lodestone is a natural magnet calcite has double refraction carbonates effervesce

intensity

measure of degree of earthquake shaking based on damage

richter scale

measures amplitude of largest seismic wave logarithmic scale, accounts for decrease in wave amplitude over distance

magma is composed of

melt (liquid) solids (minerals) and crystallized silicates volatiles: dissolved gasses that vaporize at surface pressure (water vapor, silicon dioxide and carbon dioxide)

deecompression melting

melting occurs at higher temp with increasing depth higher pressures require higher temps to melt rocks addition of water lowers melting temp

overturned anticline/syncline

one limb is tilted beyond the vertical

speed of waves

p waves are faster than s waves any wave travels faster through denser,colder material waves speed up deeper in the earth and then come up and out

volcanic breccia

particles larger than ash

the epicenter

point on ground surface above focus

vesicular texture

rock has voids/holes due to gas bubbles in lava usually extrusive igneous rocks

elastic rebound

rocks snap back into their original position ductile deformation --> brittle deformation

the subducting plate doesnt melt

sediment from ocean floor melts water is squeezed out of oceanic lithospehre, density decreases and it rises up seeps into mantle, creating wedge where water seeps in, lowers MP, and melts

stored energy is released as

seismic waves that radiate in all directions from focus/hypocenter

habit

shape/aggregate of a crystal

Si-O tetrahedron

silicon and oxygen link together first to form Si-O tetrahedron (silicates)

cooling rate and crystals

slower cooling rate= fewer, larger crystals faster cooling rate= many smaller crystals

foreshocks

small earthquakes that come before a major earthquakes only determined foreshocks after mainshock

Pahoehoe lava

smooth surfaced, resembles a twisted braided rope

volcanic/extrusive igneous rocks

solidification of lava/volcanic debris at the surface

earthquakes

sudden ground shaking caused by sudden rapid movement of a sliding fault rocks slide in fractures in crust (faults) faults that dont creep and cause high magnitude earthquakes are the only parts in earths crust that arent moving

viscosity is affected by

temp: hotter magma less viscous composition silica: higher SiO2 content is more viscous dissolved gasses: dissolved water reduces viscosity

using seismology to find the epicenter does not take... into account

the depth of the focus beneath the ground

geotherm

the temperature as a function of depth

moment magnitude

total energy released during an earthquake uses average amount of slip on the fault, area of fault, and strength of faulted rock to determine earthquake strength

partial melting formations

ultramafic rock produces mafic magma mafic rock produces intermediate magma intermediate rock produces felsic magma

Mercalli Intensity Scale

uses california buildings as a standard to measure shaking based on property destruction, so its subjective