GLY2010C Exam 2 Danny Goddard

Rock Classes

igneous, sedimentary, metamorphic

outcrop

a rock formation that is visible on the surface

igenous rock

Formed from melted lavas or magmas that crystalize and solidify after cooling

Magma

molten rock material under Earth's surface

Lava

Magma erupted at or near the surface

fast cooling magma

small crystals

slow cooling magma

large crystals

Lava flows

streams or mounds of cooled melt

pyroclastic debris

cooled fragments (volcanic ash, fragmented lava)

composition and cooling rate

how igneous rocks are organized

magma formation

- decrease in pressure
- increase in temperature
- addition of volatiles (increase in water)

solid

most of earth's interior is...

decompression melting

melting due to a drop in pressure that occurs as rock rises
(e.g., mantle plumes, beneath rift zones, beneath mid-ocean ridges)

flux melting

melting due to addition of volatiles (water, carbon dioxide)

Melt composition

Higher Si (felsic) to lower Si content that is Mg and Fe-rich (mafic/ ultramafic)

Mantle source

ultramafic and mafic magmas

crustal source

mafic, intermediate, and felsic magmas (mostly felsic)

Assimilation

partial melting of wall rock produces new magma that moves with magma below, this process causes wall rock and xenoliths to alter magma composition

magma mixing

The process whereby magmas of different composition mix together to yield a modified version of the parent magmas. (produces intermediate compositional magma and rocks e.g., diorite)

Bowen's Reaction Series

As a melt cools, minerals solidify in a specific order (series); Early mafic crystals cool first at high temperatures removing Fe, Mg, and Ca, leaving the melt to progressively become enriched in Si, Al, and Na

partial melting

typically only 2-30% of a rock will melt to produce magma yielding a silica-rich magma and creating mafic residue

Si rich minerals

melt first

Si-poor minerals

melt last

fractional crystallization

Changes in melt composition due to crystal formation and settling. Felsic magma can evolve from mafic magma as Fe, Mg, Ca are removed as early minerals and settle out, leaving the remaining melt to be enriched in Si, Al, Na, and K

Melt movement

Magma tends to rise upwards
Transfers mass from deep to shallow parts of earth

Density and boyancy

why magma rises upward

SiO

felsic magmas or melts are enriched in:

Fe and Mg

Mafic magmas or melts are enriched in:

Pitch Drop Experiment

longest running experiment since 1930; only 9 drops due to high viscosity

Viscosity

resistance to flow

higher viscosity

higher SiO2, slower flow, more explosive eruptions (e.g. lapilli)

lower viscosity

faster flow, higher temperature, higher volatiles, mellow eruptions (e.g. basalt)

dry magma

contain little to no volatiles

wet magma

up to 15% volatiles

volcanic rocks

extrusive igneous rocks formed by the eruption of molten rock at Earth's surface (i.e. basalt)

plutonic rocks

intrusive igneous rocks that crystallize below the earth's surface (i.e. granite)

Large Igneous Provinces

unusually large outpourings of magma; low viscosity melt that can flow hundreds of kilometers and accumulate in thick piles (e.g. Iceland)

intrusive igneous rock

there are more ______ igneous rocks on earth

Dikes and Sills (Tabular intrusions)

most common sheet like igneous intrusions

Dikes

cuts across pre-existing layers; forms in regions where the crust is stretched horizontally e.g., rifting and seafloor spreading

Sills

injected parallel to the rock layers; form near the earth's surface where magma is able to push the overlaying rock upward (which is why they are typically closer to the surface)

Laccolith

magma injected into a layer gets blocked and cannot spread laterally

Plutons

blob shaped intrusions (e.g. stone mountain)

Batholith

a group of plutons that covers a large area (e.g. Sierra Nevada range)

Crystalline Igneous Textures

aphanitic, phaneritic, porphyritic

Aphanitic

fine grained, rapid cooling, extrusive

Phaneritic

coarse-grained, crystals are large enough to be seen w/out a microscope, formed by slow cooling (intrusive)

Porphyritic

mixture of large and small crystals, indicates a two-stage cooling history

glassy texture

A texture formed when a rock cools so fast it doesn't have time to crystallize (e.g., obsidian)

Pegmatitic

Very large crystals (greater than 2cm) formed by extremely slow cooling

shape and cooling rate

Why are plutons more likely than dikes to show the effects of fractional crystallization?

mantle

what might be the origin of a rock composed almost entirely of olivine

various cooling rates (uneven melting)

what processes create the unequal sizes of crystals in igneous rocks?

True

Magma only forms in specific tectonic settings

Ultramafic

Which of the following melts would contain the least amount of silica?

silica rich magma

partial melting creates...

sedimentary rock

type of rock that can be formed two distinctly different ways

clastic sedimentary rock

Sedimentary rock that forms when fragments of preexisting rocks are compacted or cemented together. (ex: sandstone)

chemical sedimentary rock

Sedimentary rock that forms when minerals precipitate from a solution or settle from a suspension. Have a crystalline, interlocking structure (ex: halite, gypsum)

Biochemical sedimentary rock

chemical sedimentary rocks with a biological component (ex: chalk)

Erosion

The process by which wind, water, ice, or gravity transports sediment from one location to another

Weathering

The breaking down of rocks and other materials on the Earth's surface by physical or chemical means

Lithification

The process through which sediment turns into rock via compaction and cementation

Compaction

the process that presses sediments together by burial and squeezes out water

Cementation

precipitation or addition of new minerals cements sediment particles (ex: most common forms: silica and calcite)

siliclastic sediments

Made up of physically deposited particles such as grains of quartz and feldspar derived from weathered granite; these are laid down by running water wind and ice

chemical sediments

Sediments that form by the precipitation of minerals from water on earth's surface

biological sediments

form near their place of deposition, but they are the result of mineral precipitation by organisms

Quartz

one of the most stable/ slowest weathering rates

Halite

least stable, fastest weathering rates (next are calcite, and olivine)

weathering and climate

changes in levels of atmospheric carbon dioxide (CO2) lead to changes in the rate of weathering

erosion and transport

processes by which sediments are worn away and moved elsewhere by gravity, or by a moving transport agent- gravity, wind, water or ice

Burial

is the preservation of sediments with a sedimentary basin

Diagenesis

is the physical and chemical change that converts sediments to sedimentary rock

Wentworth Scale

particle size classification from boulders --> cobbles --> pebbles --> gravel --> sand --> silt --> clay

classifying clastic rocks

Size, composition, angularity & sphericity, sorting, cement

Sorting

the uniformity of grain size which gives clues to energy levels during transportation

clastic sedimentary rocks

breccia, conglomerate, sandstone, siltstone, shale

Biochemical sedimentary rocks

fossiliferous limestone, chert, chalk

organic sedimentary rock

made of organic carbon, the soft tissues of living things

organic sedimentary rocks

coal and oil shale

peat bog

early stage coal, very important for carbon cycling

chemical sedimentary rocks

evaporites (halite and gypsum), travertine (precipitated from groundwater in hot springs), precipitated chert

Basins

a low point on earth's surface, typically filled with water or sediment, sediment accumulates in these

sedimentary structures

features that developed during or shortly after the deposition of the sediments, provide strong evidence about condition at deposition

Stratigraphy

the study of rock layers and the sequence of events they reflect

conglomerate or breccia

this formation would most likely be found in a mountain stream environment

Varves

This formation would most likely be found in a lacustrine environment

well rounded sandstone

This formation would most likely be found in a coastal environment

chalks

this formation would most likely be found in deep marine environments

depositional environment

locations where sediment accumulates (ex: glacial, mountain stream, alluvial fan, desert, river, lake, coastal beaches)

metamorphic rock

rocks that are deformed/ formed when preexisting rock is exposed to intense heat and/ or pressure (NOT MELTED), characteristic deformations include foliations (layers) and folds

Metamoprhism

describes how heat, intense pressure, and/or chemical changes can make a new rock.

increased pressure

comes from burial (geobaric gradient) and tectonic plate movements (ex: subduction zones)

increased temperature

burial (geothermal gradient), cooling magma/ lava (nearby), heated fluids, tectonics

metamorphic facies

a set of metamorphic minerals that were formed under similar pressures and temperatures

Protolith

the original rock from which a metamorphic rock formed (parent rock)

texture and mineralogy

Protoliths undergo slow solid-state changes in:

Temperature, pressure, stresses, reactive water

metamorphic changes are due to variations in:

Foliation

Alignment of platy minerals. Forms repeating bands in metamorphic rocks (ex: creating light and dark bands)