igneous rock unit test

How is magma formed?

formed by partial melting that occurs at various levels within earths crust and upper mantle

igneous rocks

forms as molten rock cools and solidifies

whats another name for pyroclastic texture?

fragmental

what are pyroclastic textures made out of?

fragments ejected during a volcanic eruption; fine volcanic ash, molten blobs, or large angular blocks form the walls of a vent during an eruption

how do we know information about earths crust and mantle? what do we know?

from the study of earthquake waves, earths crust and mantle are composed primarily of solid, non molten rock

when does vesicular texture form?

gasses dissolved in the magma are able to come out of solution, forming bubbles inside it

what do the feldspar grains in granite look like?

generally white, gray, or salmon pink in color, blocky or rectangular in shape

how can we know information about the rock by the texture?

geologists can make inferences about a rocks origin based on careful observations of grain size and other characteristics of the rock

what is a pluton?

magma chamber

are intermediate volcanos dangerous, why or why not?

more dangerous, high amount of dissolved gasses, very explosive

are felsic volcanos dangerous, why or why not

most dangerous, high amount of dissolved gasses, VER EXPLOSIVE

what does granite make up?

most of the continental crust

what does welded tuff contain?

mostly of tiny glass shards, may contain walnut-size pieces of pumice and other rock fragments

are all eruptions violent? if no, what are they?

no, quiet outpouring of fluid lava

does water crystallize with the bulk of the magma body? what percentage of the melt does what phase?

no. they make up a high percentage of the melt during the final phase of cooling and solidification

what are the mafic minerals?

potassium feldspar, muscovite, quartz

how does depth affect pressure, why?

pressure increases with depth. steady increase in confining pressure exerted by the weight of overlaying rocks

what happens when gasses come out of the magma?

pressure is reduced to to its rising

what do dark/ferromagnesian silicates contain?

rich in iron and/or magnesium and comparatively low in silica

what does quenched mean?

when lava cools instantly

when are sills formed?

when magma exploits weaknesses between sedimentary beds or other rock structure

when are tabular intrusive bodies produced?

when magma is forcibly injected into a fracture or zone of weakness, such as a bedding surface

when are dikes formed?

when magma is forcibly injected into fractures and cut across bedding surfaces and other structures in the host rock

what is partial melting?

when melting isnt complete

when is glassy texture achieved?

when molten rock is ejected into the atmosphere and quenched to a solid when unordered atoms are "frozen in place" before they are able to unite in orderly crystalline structure

how is lava formed?

when molten rock reaches earths surface

what is cryptocrystalline, frothy or glassy texture?

when quenched rocks have no crystals at all

how does decompression melting form andesitic magma?

when rising basaltic magmas assimilate crystal rocks that are rich in silica

how are vein deposits produced?

when some of the fluids move along openings such as fractures or bedding planes, where they cool and precipitate metals

what is welded tuff?

when the ash particles remained hot enough to fuse

when does melting occur?

when the atoms are vibrating rapidly enough to overcome the force of their chemical bonds

why does crystal settling happen?

when the earlier formed minerals are denser than the melt, and sink toward the bottom of the magma chamber

how does partial melting form granitic magma?

when the heat from the hot basaltic magma partially melts the overlying crystal rocks, which are silica rich and have a much lower melting point

how does fractional crystallization form andesitic magma?

when the iron rich components (that crystallized first) are separated from the liquid by crystal settling, the remaining melt has an andesitic composition

when does the environment change enough for porphyritic texture to form?

when the large crystals move to a different environment

how do the tetrahedrons join together?

when the magma continues to lose heat to its surroundings

how are the gasses able to come out of vesicular rocks?

when the magma is near or a the earth surface because the pressure is reduced in these areas

how do vesicular rocks form?

when the magma reaches the surface as lava and cools, the rock solidifies around the gas bubbles and traps them inside, perserving them as holes filled with gas

what is a dissemination deposit?

when the ores are distributed as minute masses throughout the entire rock mass, rather than being concentrated in narrow veins and dikes

how does the parent magma produce a rock that is more felsic than the parent magma?

when the remaining melt solidifies, if it migrates into fractures in the surrounding rock

how is aphanitic texture formed?

when the rock is extrusively and the cooling is fast

how do pegmatites form?

when they crystallize in a fluid rich environment

what happens at subduction zones

where oceanic lithosphere descends into the mantle

what 3 factors influence the texture?

- the rate that the magma rock cools - the amount of silica in the magma - the amount of dissolved gasses in the magma

what is the composition of granite?

10-20% quarts, roughly 50% feldspar, less than 10% of: minor amounts of dark silicates, particular biotite and amphibole, and sometimes muscovite standing out

What happens when magma bodies cut across existing structures?

The magma is injected between the between the sedimentary layers such as sedimentary strata

what is a sill?

a horizontal intrusion

what is a stock?

a large (but smaller than batholith) pluton

what is a laccolith?

a lense shaped intrusion

what makes up magma?

a liquid component, a solid component, and a gaseous component

what is a rock with porphyritic texture called?

a porphyry

how does magmatic differentiation form andesitic magma?

a rising mantle derived basaltic magma undergoes magmatic differentiation as it slowly makes its way through the continental crust

define magma and its use?

a rock that is completely or partly molten, and when cooled it solidifies to form igneous rocks mainly composed of silicate minerals

what is crystal settling?

a separation of various components during the magma crystallization process.

what is a dike?

a vertical intrusion

when can intrusions from below earths surface be studied?

after uplifting and erosion have exposed them

how are igneous rocks formed?

all of the melt is transformed into a solid mass of interlocking silicate minerals aka from the cooling and solidification of magma or lava

what are the intermediate minerals?

amphibole, biotite, albite

how do many of the most productive deposits occur? and what are they?

as hydrothermal vein deposits. gold, silver, copper, and mercury

how are hydrothermal veins usually deposited?

as sulfides of various metals

how are diamonds formed?

at depths nearly 200 km, the confining pressure is great enough to generate this high pressure form of carbon

in oceanic settings, what type of magmas erupt more often?

basaltic magmas

why does the palisades sill form an imposing cliff?

because it is resistant to erosion

what does massive mean?

blob

what does phaneritic mean?

coarse grained

describe granite

coarse grained, commonly exhibits porphyritic texture with elongated feldspar crystals a few centimeters in length

what does phaneritic mean?

coarse or very coarse

what classifies igneous rocks?

composition and texture

what does magmatic differentiation do ?

concentrates some metals, producing major deposits

are sills discordant or concordant?

concordant

what happens in crystallization?

cooling reverses the events of melting and the melt crystallizes

what are the solid portions of magma made up of?

crystals of silicate minerals

describe obsidian

dark colored glassy rock, felsic, unordered atoms, generally black or reddish brown in color,

describe the characteristics of mafic

dark in color, high density

are dikes discordant or concordant?

discordant bodies

what are volatiles?

dissolved gasses

where are greatest quantities of magma produced?

divergent plate boundaries

what is produced when lava explosively ejected?

dramatic eruptions of steam and volcanic ash

when do the metallic atoms accumulate near the top of the magma chamber?

during the cooling process

where does most magma come from?

earths uppermost mantle

why is lava emitted as fountains?

escaping gasses propel it from a magma chamber

where do vesicular rocks form?

extrusive

where is the term 'felsic' derived from?

feldspar and silica

what is the composition of a rock with the lowest melting point?

felsic

what is the composition of the melted part of a partial melt?

felsic

what is yielded when there is partial melting of intermediate rocks?

felsic

what does aphanitic mean?

fine grained

describe rhyolite

fine grained, essentially light colored silicates, buff pink or light gray, frequently contains glass fragments, rapidly cooled extrusively, low frequent and small rhyolite deposits

what does aphanitic mean?

fine or glassy crystals

describe the outer core

fluid, iron rich, very dense, deep in earth

describe pumice

glassy volcanic, vesicular texture, gray, frothy mass, resembles fine shards of intertwined glass, float in water.

what are some of the most important accumulations of metals, how are they produced?

gold, silver, copper, mercury, lead, platinum, and nickel. by igneous processes

what is the most present mineral in the lower portion of the palisade sills, why?

great thickness, slow rate of solidification, it sank first

what do light/nonferromagnesian silicates contain?

greater amounts of silica, potassium, sodium, and calcium

how are felsic rocks classified?

high in silica, less iron/magnesium

characteristics of felsic lava and volcano?

high viscosity, steep slope

what are vesicles?

holes filled with gas, nearly spherical openings

whats an example of decompression melting?

hot mantle rock ascends as part of slow moving convective flow at mid ocean ridges

what is hydrothermal?

hot, atom rich fluid solutions

where do the majority of hydrothermal deposits originate?

hot, metal rich fluids that are remnants of late stage magmatic processes

where do the majority of hydrothermal veins originate?

hot, metal rich fluids that are remnants of late stage magmatic processes

what does discordant mean?

if they cut across existing structures

what does concordant mean?

if they inject parallel to features such as sedimentary strata

what is a laccolith and how was it formed?

igneous intrusion that was forcibly injected between sedimentary strata so as to arch the beds above while leaving those below relatively flat

what does extrusive igneous rocks mean?

igneous rocks that formed from lava near the surface of the earth or in the atmosphere/water

what is an intrusive igneous rock?

igneous rocks that formed from magma inside the earth

define porphyritic texture?

igneous rocks that has large crystals embedded in a matrix of smaller crystals

where are the best known and most important ore deposits formed?

in hydrothermal sollutions

what does crystallization in a fluid rich environment result in?

in the formation of large or very large crystals

how are pyroclastic rocks formed and what makes them up?

individual particles or fragments rather than interlocking crystals

what is yielded when there is partial melting of mafic rocks?

intermediate

characteristics of intermediate lava and volcano?

intermediate viscosity, not very thin or very thick, intermediate slope

describe diorite

intrusive, coarse, gray, little or no visible quartz crystals, higher percentage of dark silicate mineral; primarily plagioclase feldspar and amphibole, light colored; feldspar, salt pepper appearance

describe gabbro

intrusive, dark green to black, primarily composed of pyroxene and calcium rich plagioclase feldspar, uncommon in continental crust, makes up a significant percent of oceanic crust

how does the composition of the melt change throughout crystalllization?

it becomes more and more felsic (richer and richer in silica) because the iron and magnesium gets used in the rocks that form first

what does magma mixing do to the composition of the magma?

it changes it

what does the incorporation of a foreign material to a magma body do?

it changes the composition

what does assimilation do?

it changes the overall composition of the rising magma body

what does magma rising do to the preexisting crustal rock?

it forcefully displaces them

what is the composition of the partial melted magma in comparison to the parent rock?

it is nearer the felsic end of the compositional spectrum than the parent rock

how does decrease of pressure affect the melting point?

it lowers the melting point

what is magma mixing?

it occurs during the ascent of 2 chemically distinct magma bodies as the more buoyant mass overtakes the more slowly rising body. once they are joined, convective flow stirs the 2 magmas, generating a single mass that is intermediate

how does water in the subduction affect the melting of magmas?

it promotes partial melting of the mantle rocks that lie above.

why is texture important?

it reveals a great deal about the environment and cooling histories in which the rock formed

what is porphritic texture and how is it formed?

larger crystals are embedded in a fine grained groundmass

what is the name of a felsic volcano?

lava dome, sleep slope

what is a bedding plane?

layers of sedimentary rock

are mafic volcanos dangerous, why or why not?

least dangerous, low amount of dissolved gasses- low explosivity

describe the characteristics of felsic

light in color, low density

characteristics of mafic lava and volcano?

low viscosity so its thin and runny, gentle slope

what is the composition of a rock with the highest melting point?

mafic

what is the composition of the solid part of a partial melt?

mafic

how does composition affect density and buoyancy?

mafic magma tends to be less dense that the surrounding rock, causing the magma to be more buoyant and rise to the surface

what is yielded when there is partial melting of ultramafic rocks?

mafic magmas

describe andesite

medium gray, fine grained rock, volcanic and continental margins origin, porphyritic texture

what is the liquid portion of magma called and what is it composed of?

melt, mainly composed of silicon and oxygen with lesser amounts of aluminum, potassium, calcium, sodium, iron and magnesium

which minerals are often found together in the same igneous rocks?

minerals that form at the same general temperature

what are the felsic minerals?

olivine, pyroxene, anorite

how do diamonds go from being deep beneath earth to near the surface?

once crystallized, the diamonds are carried upward through pipe shaped conduits that increase in diameter toward the surface.

what is one of the larges, most studied sills in the us?

palisades sill

what is responsible for the volcanic activity in and around yellowstone national park?

partial melting that forms granitic magma

describe batholiths

plutonic body having a surface exposure greater than 100 square km

what are divergent plate boundaries associated with?

seafloor spreading

what is the name of a mafic volcano?

shield volcano

what is an example of a continuous granitic structure?

sierra nevada batholith

what is the environmental impact of disseminated deposits?

significant, including problems related to waste disposal

as basaltic magma solidifies, what is the composition of the minerals crystallizing first?

silica poor ferromagnesian minerals crystallize first

what are igneous rocks mainly composed of?

silicate minerals

why is obsidian dark but felsic?

small amounts of metallic atoms in an otherwise relatively clear, glassy substance

what do the quartz grains in granite look like?

somewhat rounded in shape, glassy, clear to gray in color

where is the most productive kimberlite pipe?

south africa

what is the name of a intermediate volcano?

stratovolcano/composite volcano

where are lesser quantities of magma produced?

subduction zones

what does volcanic mean?

synonym for extrusive igneous rocks

what is plutonic?

synonym for intrusive igneous rock

what does tabular mean?

table

what shape do plutons have?

tabular shape

what triggers melting of the mantle? what else is an effect?

tectonic processes, through various means reducing the mantle rocks melting point

why does fast cooling lead to many, small crystals?

the atoms quickly lose their mobiliy and readily combine to form crystals

what does the mineral composition depend on?

the chemical makeup of its parent magma

what happens during the crystallization process of magmA?

the composition of the remaining liquid portion continually changes

what happens to the pressure and volatiles as the melt rises toward the surface?

the confining pressure is reduced the volatiles begin to separate from the melt

what is the matrix/groundmass?

the fine grained groundmass in porphyritic texture

What is magmatic differentiation?

the formation of a magma body having a mineralogy or chemical composition that is different than the parent magma

what happens to the level of gasses as the pressure goes down?

the gasses escape

what caused the demand for metallic natural resources to increase exponentially?

the growth of the middle class in countries such as china, india, and brazil

what happens to the volatiles when magma is deep below the surface?

the immense confining pressure keeps these volatiles dissolved in the melt.

what is geothermal gradient?

the increase of temperature with depth increase in Earths crust

what is phenocrysts?

the larger crystals in porphyritic texture

what is a batholith?

the largest intrusive igneous body

what happens after magma is formed

the magma body buoyantly rises toward the surface because it is less dense than the surrounding rocks

how does the rock for assimilation form?

the magma pushing upward can cause the overlying rock to fracture into numerous pieces. the force of the injected magma is often sufficient to dislodge and incorporate blocks of the surrounding host rock

what is assimilation?

the melting of the dislodged surrounding host rock

how does partial melting occur?

the minerals with the lowest melting point melt first. if melting continues, minerals with a higher melting point melt

how does the amount of volatiles depend on the felcicity?

the more felsic, the more volatiles

how is a secondary melt generated?

the overlying crystal rocks have lower melting points than basaltic magmas, the hot basaltic magma may heat them sufficiently to generate a secondary melt

what is a kimberlite?

the pipe that contains nearly all diamond crystals that are disseminated throughout an ultramafic rock

what is a host rock or country rock?

the preexisting crustal rock

what is the dominant factor that influences the texture?

the rate of cooling

why does slower cooling lead to fewer, larger crystals?

the slow cooling permits ions to migrate freely until they eventually join one of the existing crystals

how does the speed of cooling affect the size of the crystals?

the slower the magma cools, the larger the crystals will become the faster the magma cools, the smaller the crystals will become

how is a pluton or intrusion formed?

the structures that result from the emplacement of magma into preexisting rocks.

how are diamonds commonly used?

they are economically important and used extensively as abrasives

what happens happens when magma is buried deeply?

they begin to crystallize, the remaining volatiles collect as hot, water rich, fluids that migrate through openings in the surrounding rocks

how are rocks classified as mafic?

they contain at least 45% dark silicates

what happens if the crystal continues to be in contact with the magma? what can happen?

they continue to react chemically, the outside layer can change into a different mineral.

why are rocks with similar mineral constituents given different names?

they exhibit different textures

how do volatiles affect the type of erruption?

they make the eruption more explosive

what happens to the crystal rocks during continental collision?

they may melt

what does the mobility of hydrothermal veins do before they are eventually deposited?

they migrate great distances through the surrounding rock before they are eventually deposited

why do intrusive magmas cool slower?

they remain insulated from lower surface temps by the surrounding rock, therefore cool very slowly over a period of like 10,000 to millions of years

commonly, what happens to the earliest formed mineral?

they seperate from the melt, stopping them from evolving

what happens to the heavy minerals that crystallize early in a large basaltic magma body?

they tend to settle to the lower portion of the magma chamber

what happens to the atoms as the temperature rises?

they vibrate more rapidly

what does pyroclastic texture resemble?

those exhibited by sedimentary rocks

when exposed what appearance do dikes have? how do they get exposed?

through erosion, they tend to have wall like appearance

how are pyroclastic rocks formed?

tiny, ash size fragments that were later cemented together

how is the term texture used?

to describe the overall appearance of a rock based on the size, shape, and arrangement of its mineral grains

what is the most common pyroclasic rock?

tuff

what are pegmatites?

unusually large crystals

describe basalt

very dark green to black, fine grained rock, primarily of pyroxene and calcium rich plag feld, lesser amounts of olivine and amphibole, most common extrusive igneous rock, makes up volcanic islands, makes up the upper layers of the continental crust

what is the gaseous portion of magma called and what is it composed of?

volatiles, materials that vaporize at surface pressures

how does water affect melting point?

water lowers melting point

what are the most common volatiles found in magma?

water vapor, carbon dioxide, sulfur dioxide

how do the silicon oxygen tetrahedrons form?

when a magma body cools, the silicon and oxygen atoms link together

what is vesicular texture?

when an igneous rock contains gas pockets

how/when does porphyritic texture develop?

when conditions during the cooling of the magma change relatively quickly. earlier textures formed slow and remained as large crystals and sudden cooling causes the remainder of the melt to become fine grained matrix

when is magma formed (with melt)?

when crystal rocks are heated sufficiently to melt

how does most granitic magma form?

when hot basaltic magma ponds below continental crust

when does columnar jointing occur?

when igneous rocks cool and develop shrinkage fractures that produce elongated, pillar like columns that often have 6 sides

how is phaneritic texture formed?

when large masses of magma slowly crystalize intrusively

what is decompression melting?

wherever hot, solid mantle rock ascends, moving to lower pressure

can a single volcano extrude lavas that change in composition over time?

yes

can granitic magmas be formed by magmatic differentiation of andesitic magmas?

yes

does decompression melting trigger partial melting?

yes

can granitic magmas become rich in rare elements?

yes, even heavy metals

can magmas change over time? can a igneous rock have a range of compositions?

yes, yes