Geology

Nonfoliated metamorphic rocks

1 mineral forming equidimensional crystals high temperature, low pressure metamorphism

Confining pressure

Applied equally in all directions-> dense rock

load casts

Bottom of stratum sinks into lower layer Due to differential compaction Indicates which way is "up," rocks can tilt over time, which way time went

origins of igneous rocks

Bowen's Reaction Series (fractional crystallization) melted a basalt and slowly cooled it; found it didn't cool and crystallize all at once; certain things crystallized and melted at different temperatures First to crystallize out at high temp- basaltic, low silica minerals- less complex silicate structures Last to crystallize out at cooler temp- high silica minerals Fractional (partial) melting Decompression melting

2 most important mineral groups

CO3 and SiO4 (carbonates and silicates) most important by abundance in rocks

volcanic eruptions and climate

Carbon dioxide and sulfur dioxide from eruptions can effect global climate CO2 causes greenhouse effect Sulfur dioxide can cool climate Dust thrown into atmosphere by violent eruption can cool climate (violent eruption= high viscosity)

channels

Caused by stream meandering across floodplain Fluvial- deposited by a river Big thing in middle equals channel deposit, little ones outside are deposits on overbanks due to flooding

turbidities

Caused by turbidity flows in marine or lake settings Muddy current at bottom due to shaken delta

classification of igneous rocks

Classification based on composition and texture Composition: Three types-basaltic, andesitic, and rhyolitic (silica increasing) Basaltic, Andesitic, Rhyolitic

Classification of Sedimentary Rocks

Classification based on grain size and composition Classification tells us something about environment of deposition- different from igneous; (was it deposited deep in ocean? In a swamp?) Classification also tells us something about source (provenance) of sediment; what was eroded to form this sedimentary rock? Two basic types of sedimentary rocks Clastic: made of chunks of something that was broken Chemical: sedimentary rocks that deposited chemically, usually from precipitation of water

Clastic Sedimentary Rocks

Composed of fragments (clasts) of eroded rocks Classification - texture (grain size) Texture: environment of deposition, distance transported from provenance area to deposition area Clastic rocks (in order of decreasing grain size): Conglomerate Sandstone Siltstone Shale

mud cracks

Dessication on mudflats, in what environment was it formed? All mudcracks are formed in subaerial environment, had to be dried out by air, could have been under shallow water at one point

Hornblende (an amphibole)

Elongated structure recrystallizes w preferred orientation

Pressure/stress

Exerted on buried rocks by load above

Differential stresses

Forces during mountain building unequal in diff directions

Hydrothermal solutions

Form new minerals during metamorphic process in rocks adjacent to magma

Igneous Rocks

Formed by volcanic processes Impact on atmosphere, biosphere, climate Sulfates reflect solar energy & mitigate climate change Give information about geosphere processes Definition of igneous rocks: Rock cooled from a magma Formed of intergrown crystals

ripple marks

Formed in shallow water due to currents; if you see ripple marks in a rock, you know it was formed in shallow water Indicates direction of currents

Most effective agent of metamorphism

Heat bc it provides energy to drive reactions

Agents of metamorphism

Heat pressure and chemically active fluids

Magma

High temperature, molten rock material with a range of compositions but silica always present Composition: Elemental composition reflects common crustal elements (Si, O, Fe, Al, Mg, Ca, Na) in order of most to least common; cations: magnesium, calcium, sodium Gasses-mainly CO2 and H2O SiO2 content important to classification and volcanic eruptive style Viscosity depends on silica content, more silica- more explosive; less silica- fluid magma More interlocked silicate tetrahedras, more silica- more viscous Temperature: 1000˚C to 1200˚C

Most common chemically active fluid

Hot water w ions, enhances metamorphic process; ex seawater circulated through hot basaltic rocks transforming the existing iron rich minerals into metamorphic minerals such as serpentine and talc

Metamorphic rocks can form from

Igneous, sedimentary, or other metamorphic rocks

In a given igneous rock, the major light colored minerals will be

K-feldspar, plagioclase, quartz, and/or muscovite

Low grade metamorphism

Makes rocks more dense

aluminum silicates

Many of the chain, sheet and framework silicates, including feldspars, micas and clays, are aluminum silicates. Since the aluminum ion and the silicon ion are nearly the same size, aluminum can occupy the center of a tetrahedron. In aluminum silicates, some of the tetrahedra have silicon in the center, others have aluminum.

New orientation after metamorphism= foliation

Perpendicular to direction of stress

Classification of Sed Rocks: Mineralogy is also important

Presence of quartz, clay, feldspars etc indicates the degree of chemical weathering and distance transported from the source (provenance) area Chemical weatherinig- chemical changes in minerals at the surface; more clay- more chemical weathering; result of hot humid weather; not in desert or cold areas Feldspars and mafics (pyroxenes and amphiboles) are easily weathered chemically Clay is the product of that weathering Graywacke is an "immature" sandstone with quartz, feldspars, and clay; these are chemically weathered easily

Agents that increase with depth in earth

Pressure and temperature

Sand dunes are typically dominated by quartz grains and very little other mineral matter. Why does this selection occur?

Quartz is extremely resistant to all forms of chemical weathering.

Degree of metamorphism

Reflected in rocks texture and or mineral composition

Sedimentary Structures

Sed. Structures: indicate depositional processes in environment of desposition In ocean, accumulation of sediment takes longer than in lake Examples of Sedimentary Structure: Cross-bedding- not in all sed rock Ripples in streams or sand dunes; formed from moving fluid (water or air) in one direction, usually bigger means wind caused them Indicates direction of fluid flow Also used to tell geologists which way is "up" Larger cross beds; cross beds- cross sections of ripples indicate eolian deposition Eolian- deposited from air/wind; like in desert environmont

Mica

Sheet structure, recrystallizes w preferred orientation

More extreme pressure/temp

Some minerals recrystallize to form larger crystals ex clay to mica

carbonates calcite, dolomite

The carbonates minerals are formed at the Earth's surface through chemical or biochemical activity. Many marine organisms make their skeletal parts from calcite. This material accumulates to form the sedimentary rock limestone. The rock-forming carbonates are calcite and dolomite. Carbonates "fiz" when hydrochloric acid is placed on them. The acid reacts with the mineral releasing carbon dioxide gas. completely dissolved by water

mafic and felsic

The chemical composition of silicates is related to their structure. As more oxygen is shared, fewer metallic ions are needed to balance the charge on the crystal. Thus the relative amounts of oxygen, silicon and aluminum in the mineral increase, as the amount of iron, magnesium and calcium decrease. Silicate minerals rich in iron, magnesium or calcium are called mafic. Silicate minerals rich in silicon, aluminum and potassium, and relatively poor in iron, magnesium and calcium are called felsic. Mafic and felsic can be used as absolute or relative terms for silicate composition

silicates Olivine, Pyroxene, Amphibole, Mica, Clay Minerals, Feldspar, Quartz

The silicates are the most abundant mineral group. The most abundant mineral group; the crust and mantle of the Earth, about 80% of the volume of the planet are predominantly made of silicates. The complex anion of silicates is a tetrahedron of four oxygen atoms surrounding one silicon atom, connected with strong covalent bonds. In silicate minerals, the tetrahedra are packed together, so that the entire mineral crystal can be thought of as a pile of tightly packed oxygen atoms with silicon atoms between some of the oxygens, and other metallic atoms occupying other spaces between the oxygens. Because silicon atoms can share oxygen atoms, there are a variety of ways to build silicate structures. This gives rise to a set of basic groups of silicate minerals

The Hawaiian Islands contain active volcanoes and are known for nutrient-rich soils and lush vegetation. What is the most powerful explanation for this?

Volcanic rocks contain minerals susceptible to hydrolysis. There is abundant rainfall. Volcanic rocks contain minerals rich in iron, so they are susceptible to oxidation. Minerals in the volcanic rocks produce clay minerals as weathering by-products.

jointing

aids physical weathering result from brittle fracture of a rock body or layer as the result of tensile stresses. These tensile stresses either were induced or imposed from outside, e.g. by the stretching of layers; the rise of pore fluid pressure as the result of either external compression or fluid injection; or the result of internal stresses induced by the shrinkage caused by the cooling or desiccation of a rock body or layer whose outside boundaries remained fixed.[1

cross bedding

almost vertical, slanted towards opposite direction of wind

chemical weathering

alters the internal structure of rock materials

K-feldspar & plagioclase

are blocky, not translucent, and show flat cleavage surfaces. They occur in shades of opaque pink, white, gray, or dark gray. Early-formed feldspars tend to be rectangular; late formed feldspars fill in gaps between other minerals and thus are irregular in shape.

hornblende and augite

are often confused. Most reliable is cleavage: hornblende forms ~120°/60° cleavages whereas augite forms ~90° cleavages. In addition, hornblende tends to form very black and shiny cleavages, whereas augite forms duller black and not-very-reflective cleavages. Finally, hornblende tends to form long rectangular crystals whereas augite forms blocky crystals.

zeolite facies

associated with low grade, regional metamorphism; low temp, low pressure

Decompression Melting

asthenosphere rises, pressure is reduced and decompression melting starts, new oceanic lithosphere is formed

foliation

banding in metamorphic rocks that results from the reorientation of minerals

The major dark colored minerals in a typical igneous rock will be

biotite, hornblende, augite, and/or olivine

Mechanical Weathering

breaks down preexisting rocks into smaller pieces through biological processes, unloading, frost wedging, and thermal expansion

dissolution

certain minerals such as calcium chloride react to water, natural acidity of rain speeds up the rate of dissolution in minerals like calcite

Granite

coarse grained intrusive, high silica

Diorite

coarse grained intrusive, medium silica

Gabbro

coarse grained intrusive, silica poor; same comp as basalt but cools more slowly

mica schist

coarse grained micaceous minerals metamorphic; foliated

Gneiss

color-banding, non-micaceous minerals metamorphic; foliated coarse-grained texture, minimal amounts of mica, and contains minerals that are segregated into bands granite that has undergone metamorphism & now exhibits foliation

ferromagnesium silicates

contain iron and magnesium. iron and magnesium make dense. Since these two metal ions are nearly identical in size, they easily substitute for one another in the crystal structure. Ferromagnesian silicates are usually dark in color. Olivine, pyroxene, amphibole and biotite mica are ferromagnesian silicates.

shale

dark color, imprints of ferns, deposited in swamp

grain size

dictates where grains settle in water

3 common types of chemical weathering

dissolution, hydrolysis, oxidation

framework silicates

each silicon shares all four of its oxygen with adjacent silicon resulting in a three dimensional framework of strong covalent bonds. The simplest framework silicates is quartz which contains only silicon and oxygen. The feldspars are framework aluminum silicates. Since aluminum occupies the middle of some of the tetrahedra, other metals, namely K, Na and Ca are needed to balance the charge of the crystal.

chain silicates

each silicon shares either two, or three oxygen atoms with adjacent silicon atoms. Thus each tetrahedron is not distinct, and they are linked together in strong, covalently bonded chains. The chains are then held together by ionic bonds. Pyroxenes are a single-chain silicates. Amphiboles (including hornblende) are double-chain silicates.

sheet silicates

each silicon shares three oxygens with adjacent silicon atoms resulting in strong, covalently bonded sheets. The sheets are then held together with ionic bonds. Micas are sheet silicates. Micas split apart along planes of ionic bonding with K atoms. Biotite mica contains Fe and Mg giving it a dark color, while muscovite contains only K. Clay minerals are sheet silicates, but the crystals are too small to see with the naked eye. Micas and clays are also aluminum silicates

isosilicates

each tetrahedron is independent. They are bonded together ionically by metal ions, often iron and magnesium, between the tetrahedra. Olivine, one of the rock-forming silicates, is an isosilicate. Olivine is a good example of the variability in the chemical composition of minerals. Olivine is an ferromagnesian silicate. In olivine, the ratio of iron to magnesium can vary from 0 to 1. In otherwords, some olivines might contain no iron, only magnesium. Other olivines might contain no magnesium, only iron, while most olivines contain a mixture of iron and magnesium

phyllite

fine to med grained silky shiny luster metamorphic; foliated; a bit higher grade than slate

hydrolysis

frees iron from silicate structure making oxidation possible

quartz

grains tend to be translucent gray, rounded to irregular blobs. The lack of a cleavage means their exposed surfaces are rounded and bumpy.

unloading

great reduction in pressure caused by overlying rock being eroded

Metamorphism involves the transformation of pre-existing rocks by

heat and pressure

folding

heat and pressure in one direction

hornfels facies

high temp, low pressure

muscovite

is easiest because of its silvery or clear color and perfect flaky cleavage. use a needle or knife to see if you can flake the mineral into thin sheets.

biotite

is easy because it forms perfect shiny black cleavages and can be peeled into flakes. It can be confused with hornblene, but hornblende does not flake.

calcite

is soluble in water and dissolves, especially if the water is slightly acidic.

when a rock is buried in earth

it experiences the high pressure and temperature; ex regional metamorphism

sheeting

large areas of igneous rock like granite are exposed by erosion and slabs break off like layers of an onion

conglomerate

large pebbles and smaller chunks, not well sorted; has not traveled far; some rounded some not, some transport but not much, most likely not found in ocean (too angular, ocean contains more fine grained, uniform sediment); not river because of angularity, not transported much, near source, perhaps mountain stream

Basaltic

least silica; not viscous, not explode, just flow magma; fine grained extrusive Olivine-isolated tetrahedra, pyroxene-single chain, feldspar- 3D (no free quartz)

Sandstone

light sandy color, fine grain, deposited in beach

shallow burial

low pressure low temp

blueschist

low temp high pressure, formed by shallow subduction

subduction zone metamorphism

low temperature, high pressure; happens when one cold (seafloor)plate sinks below another plate and takes a very long time to heat up

Andesitic

medium silica, fine grained, extrusive Intermediate between rhyolite and basalt=dark Plagioclases, some pyroxenes, and some free quartz

Partial (fractional) melting

melted rock in volcanoes tend to be andesitic; water gets into rock on way down and lowers melting temperature, leads to partial melting- all of rock doesn't all melt at once, more silica rich minerals at lower temperatures; opposite of Bowen's reaction series

slate

metamorphic fine grained; splits into slabs, slaty cleavage; foliated

quartzite

metamorphic rock that lacks foliation and is composed primarily of interlocking sand-sized grains that will scratch glass; parent rock: quartzite sandstone

marble

metamorphic rock that lacks foliation and reacts to hydrochloric acid; parent rock limestone; interlocking calcite grains

hydrothermal metamorphism

moderate temperature low pressure

clay minerals

most abundant product of chemical weathering of feldspars

Rhyolitic

most silica, most viscous, fine grained extrusive Free quartz, plagioclase 3d silicate, and biotite; light rock mostly

anthracite coal

no reaction to hcl, no scratch, parent rock: bituminous coal, black, shiny conchoidal fractures

Plagioglase

often shows striations whereas K-feldspar does not. If a rock has two feldspars, carefully search for striations to learn which is which. In very dark rocks it is tough to distinguish the boundaries of one black mineral from another. In these rocks, plagioclase crystals frequently create long, thin rectangular crystals that, upon close inspection, show striations on their shiny cleavages

How will foliation in continental metamorphic rocks formed during subduction be oriented

perpendicular to the direction of plate movement

silicates most common mineral group

primarily decomposed by hydrolysis

common nonfoliated metamorphics

quartzite, marble, anthracite coal, stretched pebble conglomerate

Contact metamorphism

rocks near surface subjected to intense heat when intruded by magma, baked by magma

classification of magma

same as classification of igneous rocks Main parameter is silica content: Lowest silica content (50%) basaltic magma (lowest gas content compared to other igneous rocks) Intermediate silica content (60%) andesitic magma Highest silica content (70%) rhyolitic magma (highest gas content) Viscosity How easily the magma flows controlled by silica content, low silica, low viscosity, flows easily High silica, high viscosity, doesn't easily flow Temperature High temperature magmas are less viscous Lower temperature magmas are more viscous

increasing in grade of metamorphism

slate, phyllite, schist, gneiss

Do metamorphic rocks look like the preexisting rock from which they form

sometimes; if not highly metamorphosed

quartz

very resistant to chemical weathering; when granite is decomposed, feldspar is released

frost wedging

water fills crack, water freezes and expands, pushing rocks apart and lifting out In temperate and polar regions, the accumulation of talus slopes at the base of steep, rocky cliffs is most often attributed to; gravity brings talus to final resting place

Sedimentary Rocks

~ 5% of Earth's crust Continuous record of Earth history Where biosphere, hydrosphere, atmosphere, and geosphere all interact Formed by weathering, transport, and either deposition of detrital particles or precipitation chemically A lot of flat lined layers- characteristic of seds