Geology Exam 2

Aphanitic means

Fine grained crystal texture and Rapid cooling

Basaltic lava flows may be erupted from

shield volcanos

basaltic lava flows are associated with

shield volcanos (low silica level)

Crystallization of mafic minerals from mafic magma makes magma

more silica rich

more high silica material minerals

more stable in weathering

A fine grained black rock came from

near the surface as an organic rock

Volcanic Precipitation

occurs when melts solidify or freeze

what kind of crystal habit do diamonds have

octahedral

Diamond and graphite are

polymorphs (of carbon): two minerals with the same composition, but with different chemical structures.

Geological settings of volcanism

-Mid-ocean ridges: spreading axes -Convergent boundaries: subduction zones -Continental rifts: incipient ocean basins -Oceanic hot spots Continental hot spots and flood basalts

What are the six major silicate rock forming minerals?

1. Olivine(least silica/highest temperature) 2. Pyroxene 3. Amphibole 4. Mica 5. Feldspar 6. Quartz (most silica/lowest temperature)

3 different types of melting in the magma chamber

1. Partial melting in the interior 2. fractional crystallization 3. assimilation

what are two important things to note about igneous rock

1. grain size 2. composition

Pillow lavas in basalts are evidence of

1. rapid cooling or lava on the ocean floor 2. volcanism along mid-ocean ridges

how do we classify sedimentary rocks

1.Grain Size (very from coarse to very fine gravel, sand, slir , clay) 2.Composition

Diamonds originate at

150 km in depth below the earths surface They are formed in old, deep, lithospheric cratonic roots

columnar jointing (basaltic lava flows)

A type of fracturing that yields a roughly hexagonal cross section. Pillow basalts; columnar joints form when a dike, sill, or lava flow cools.

graded bedding

Bedding in which the particle sizes become progressively heavier and coarser toward the bottom layers

Non-Classic Sedimentary Rock

Biochemical: cemented shells of organisms Organic: carbon-rich remains of once-living organisms Chemical: minerals that crystallize directly from water Made of biotic particles or chemical precipitates

physical weathering

Breaking down rocks through physical processes like freezing and thawing

Goldich Stability Series

Chart that describes the order/rate in which silicate minerals weather quartz on top olivine bottom

Phaneritic means

Coarse Grained crystal texture and Slow cooling

What is the term used to describe how rocks melt over a range of temperatures?

Composition

high viscosity

Cooler More SiO2 (Felsic) More volatiles

Deposition

Deposition is the process of moved particles being deposited

What is the term used to describe how different minerals crystallize at different temperatures?

Fractional Crystallization - bowen's reaction series indicates the succession of crystallization in cooling magmas

Andesitic Lava Flows

Higher SiO2 content makes andesitic lavas viscous. Unlike basalt, they do not flow rapidly. Instead, andesitic flows mound around the vent and flow slowly. The cooled external crust fractures into rubble, called blocky lava.

low viscosity

Hotter Less SiO2 (Mafic) Less volatiles

What is the difference between Intrusive and Extrusive:

Intrusive: Intrusive rocks are formed from magma that cools and solidifies within the crust of the planet. (realm is below ground.) Extrusive: Extrusive rocks are formed on the surface of the Earth from lava, which is magma that has emerged from underground (realm is above ground)

is the volcanic rock type that transports diamonds and mantle xenoliths to the surface. Diamonds are not precipitated from these rocks. (funnel shaped structures)

Kimberlites (Breccia)

What is the difference between magma and lava

Magma is intrusive and lava is extrusive

volcanic glass (obsidian)

Magma rapidly cooled to below its normal crystallization temperature becomes a supercooled liquid, and, with further rapid cooling, this becomes an amorphous solid.

What is magma?

Molten rock beneath the earth's surface It may contain solid crystals that float or sink

Ancient Mud Cracks

Mud cracks are present only in fine-grained rocks with enough clay content to cause shrinking

Mt. St. Helens

On May 18, 1980, 8:32 a.m., an earthquake triggered a massive landslide that sheared off the entire north side. This released pressure that resulted in a giant lateral blast that flattened 600 km2 of forest. Around 440 m of elevation was blasted away. The blast killed 61 people. Lahars plugged the Toutle River and closed the Columbia. Ash fell in North Dakota. Highways and rail lines were shut down. The blast destroyed several hundred million dollars worth of timber.

sedimentary rock

Particles, grains, clasts that were deposited in layers and cemented together made of other rocks

Rhyolitic Lava Flows

Rhyolite has the highest SiO2 and is the most viscous lava. Rhyolitic lava rarely flows. Rather, lava plugs the vent as a lava dome. Sometimes, rhyolitic lava domes are blown to smithereens during eruption.

chemical weathering

The process in which rock is broken down by changes in its chemical makeup

cross bedding

are created by ripple and dune migration. Sand moves up the gentle side and piles up at the crest. Then, it slips down the steep face. The slip face moves down-current and is buried by the next avalanche of sand. The slip faces are preserved as cross beds.

Depositional Environments

are locations where sediment accumulates. Different environments vary in energy regime, sediment transport, and depositional processes and chemical, physical, and biological characteristics, all of which conspire to create unique sedimentary rocks.

Stratigraphic Formations

are named for places where they are best exposed. Geologic maps display the distribution of formations.

intermediate melts

are so named because their composition lies partway between those of mafic and felsic melts.

Diamonds are not rare, but they are often smuggled in certain countries or the subject of civil wars. Diamond from these countries are technically called ___________ diamonds, or more informally, ___________ diamonds

blood diamonds/conflict diamonds

Limestone is made of

calcite skeletons of organisms, like those in a coral reef.

a course grained rock white and pink rock

came from deep in the earth

Andestic Lava Flow may be erupted from

cinder cone volcanos

Porphyritic means

coarse and fine crystal texture and slow then fast cooling

Breccia (classic sedimentary rock)

coarse sedimentary rock consisting of angular fragments; Angularity indicates the absence of rounding by transport, hence, deposited relatively close to clast source.

what is a rock

coherent, naturally occurring solid, consisting of aggregate minerals 3 major types (ignous, sedimentary, metamorphic)

mafic melts (igneous rock)

contain a relatively high proportion of magnesium oxide and iron oxide relative to silica.

Shallow flows

cool quickly

Crystal size tells us

cooling rate

Felsic

high silica magma, light colored

plume hot spots

cut through continental crust create large volumes of felsic magma. Three eruptions of Yellowstone deposited vast ignimbrite sheets across the western United States. The latest eruption created a caldera 72 km (45 miles) across. Magma beneath the caldera continues to fuel geysers.

As transport distance increases, grain size _______

decreases

A sea-level rise or transgression shifts

depositional beds landward.

A sea-level fall or regression shifts

environments toward the basin.

Viscosity characteristics

exceeds that of molasses, but not all molten rock has the same viscosity. The viscosity of molten rock depends primarily on its temperature, volatile content, and silica content. Hotter melt tends to be less viscous than cooler melt A melt containing more volatiles has lower viscosity than does a dry (volatile-free) melt. mafic melt is less viscous than felsic melt because relatively more silicon-oxygen tetrahedra occur in felsic melt.

Diamonds not found in the old cratons have been transported, often by glaciers, and are called

extra-terrestrial (carbonados)

Aphanitic

fine grained

diamonds are formed at

high temperatures and high pressures

Felsic melts (igneous rock)

have a relatively high proportion of silica relative to magnesium oxide and iron oxide.

ultramafic melts (igneous rock)

have an even higher proportion of magnesium oxide and iron oxide relative to silica.

What was Norm Bowen's major contribution to science?

his phase-equilibrium studies of silicate systems as they relate to the origin of igneous rocks

classic sedimentary rock

loose rock fragments (clasts) cemented together

mafic

low silica magma, dark colored

Geologic environments where decompression melting occurs:

mantle plumes, continental rifts, and divergent-plate boundaries.

decompression melting

melting involves the upward movement of Earth's mostly-solid mantle. This hot material rises to an area of lower pressure through the process of convection this melting occurs at mantle plumes, continental rifts, and divergent plate boundaries P decreases but T remains constant

Diamonds are NOT forever. They are

metastable (unstable, but so long-lived as to be stable for practical purposes)

sedimentary rocks are all formed by

physical or chemical weathering

fractional crystallization

process in which different minerals crystallize from magma at different temperatures, removing elements from magma with decreasing temperatures, the magma becomes more felsic

Weathering

process of natural forces breaking down rocks (in situ) into smaller pieces.

Erosion

process which the broken pieces are transported, or moved,

pyroclastic

relating to or consisting of fragments of rock erupted by a volcano "fragmental texture"

Viscosity

resistance to flow

Conglomerate

rounded rock clasts. Clasts are rounded as flowing water wears off corners and edges; deposited farther from the source than breccia.

Sediment deposition is strongly linked to

sea level

What feature of an igneous rock can give us an indication of cooling rate?

slow cooling allows large crystals to form, fast cooling yields small crystals.

Rhyolitic Lava Flow may be erupted from

stratovolcanoes

The carbon from diamonds likely originated from a deeply______oceanic slab in the Archean (>2.5 Ga ago

subducted

Assimilation

the process whereby solid or fluid foreign material is incorporated into magma.

Bowen's Reaction Series

the simplified pattern that illustrates the order in which minerals crystallize from cooling magma according to their chemical composition and melting point Rocks at the top are mafic rocks at the bottom are felsic olivene is is the first to melt and crytalize

basaltic (mafic) lava flow

very hot, low silica, and low viscosity

flux melting

volatiles help break chemical bonds, creating a melt Water, CO2, driven off the subducting slab into mantle above

Pillow basalts form

when the basalt flow is erupted into water on the ocean floor