Geology

Isotopes

Atoms of an element with different numbers of neutrons

Diapirs

Blobs of magma rising through country rock.

factors that affect weathering

availability of water, climate, temperature, slope

foliation

Penetrative planar rock texture of aligned minerals produced by differential stress

contact metamorphism

(also known as thermal metamorphism) occurs where high temperature is the dominant factor

greenschist facies

(contains chlorite, epidote, actinolite as index minerals, these minerals are green, hence the facies name) = lowest grade

granulite facies

(contains feldspar and pyroxene as index minerals) = highest grade

amphibolite facies

(contains hornblende, feldspar, and garnet as index minerals) = medium grade

Oil and Natural Gas

- originate from organic matter in marine sediment - subsurface "cooking" can change organic solids to oil and natural gas - can accumulate in porous overlying rocks

Types of Sedimentary Rocks

1. Chemical 2. Detrital 3. Organic

What are the factors that determine grain size during the solidification of igneous rocks?

1. Rate of cooling • glassy - volcanic glass without mineral crystals (Obsidian) -instantaneous cooling • fine-grained - most crystals < 1 mm - slower cooling • porphyritic - larger crystals (phenocrysts) in a matrix of much finer crystals or glass (ground mass) - like raisins in bread - represents two periods of solidification - slow cooling underground and then magma erupts and rapid cooling occurs 2. Viscosity • A rock that forms from a viscous lava is more likely to be obsidian or to be fine-grained because atoms in highly viscous lava cannot move as freely as those in more fluid lava

Sediment to Sedimentary Rock

1. Rounding 2. Sorting

What are the factors that influence lava viscosity?

1. Silica (SiO2) content of the lava 2. Temperature of the lava 3. Dissolved gases in magma, the greater the dissolved gas content, the more fluid the lava • Mafic lavas are low in SiO2 so they produce basalt and they are relatively low in silica and they flow easily • Silicic lavas are rich in SiO2 so they produce rhyolite and they are viscous and flow sluggishly • Lavas of intermediate composition (between basalt and rhyolite) form andesite

Arkose

> 25% feldspar and also contains quartz grains. Granite is a source for such sediment (mountainous area). It typically develops by rapid erosion of a granitic mountain range. It contains coarse, angular sand grains indicating short transportation distance

Felsic Rocks

>65% silica by weight, and contain light-colored minerals that are abundant in silica, aluminum, sodium and potassium -considered silica-rich

Quartz Sandstone

>90% quartz grains - resistant to weathering - most form in a beach environment or a dune environment

Rock

A naturally occurring aggregate of minerals or mineral-like substances.

Mineral

A naturally occurring, inorganic, crystalline solid that has a specific chemical composition.

Bedding

A sedimentary structure, series of visible layers within a rock

Pores

An arrangement with a great deal of open space between grains that forms as sediment grains are deposited

Pluton

An igneous body formed underground. Stocks- small plutons. Batholiths- large plutons.

Ions

Atoms or groups of atoms with unequal numbers of protons and electrons, thus having a nonzero charge

Lava Flows

Calm oozing of magma out of the ground

Vesicular texture

Cavities caused by the release of trapped gas bubbles

rock decomposition

Chemical weathering transforms rocks and minerals exposed to water and air into new chemical products

What is the texture of sedimentary rocks with grains bounded by cement?

Clastic texture

Mineral Properties

Color, Streak, Luster, Hardness, Crystal Form, Cleavage, Fracture, Specific Gravity, Magnetism, Chemical Reaction

lithostatic pressure

Confining pressure forces grains closer together in a rock and eliminates pore space

Glassy

Contains no crystals at all, and is formed by extremely rapid cooling

Baked Zones

Country rock immediately adjacent to intrusive rock

differential weathering

Different types of rock weather at different rates (e.g. shale weathers more easily than sandstone); hard rocks form cliffs. soft rocks form gentle slopes

Magma Evolution

Differentiation, partial melting, assimilation, magma mixing

Metallic Bonding

Electrons flow freely throughout metals; results in high electrical conductivity

Pyroclasts

Explosive eruptions can produce rapidly cooled rock fragments called pyroclasts. These are extrusive igneous rocks.

Pegmatitic

Extremely coarse-grained (most crystals >5 cm), formed when magma cools very slowly at depth

Igneous Rock Textures

Extrusive igneous rockscool quickly at or near Earth's surface and are typically fine-grained (smaller than 1mm). Intrusive igneous rocks cool slowly deep beneath Earth's surface and are typically coarse-grained (>1mm).

Shale

Fine-grained clastic sedimentary rock; fissile (splits into thin layers, so it is laminated) • silt and clay-sized grains • Clay commonly makes up about two-thirds of the sediment content • sediment deposited in lake bottoms, river deltas, floodplains, and on deep ocean floor

Other types of eruptions

Flood eruptions • very fluid (basalts) • extremely large in volume • create extensive lava plateaus • eruption times correspond with largest mass extinction events Submarine eruptions • nearly always basaltic • mid-ocean ridge eruptions • pillow basalts

Sandstone

Formed by the cementation of sand grains. Medium-grained, clastic sedimentary rock.

Principal of Superposition

In a series of horizontally bedded sedimentary rocks, the oldest beds are on the bottom and the rocks become younger toward the top

basement rocks

In the Great Plains, also a part of the craton metamorphic rocks are buried below younger sediments

Porphyritic

Includes two distinct crystal sizes, with the larger having formed first during slow cooling underground and the smaller crystals forming during more rapid cooling at the Earth's surface

Chill Zones

Intrusive rocks adjacent to contacts with country rocks

Covalent Bonding

Involves sharing of valence electrons among adjacent atoms

Ionic Bonding

Involves the transfer of valence electrons from one atom to another

Aa

Jagged, rubbly, blocky appearance volcanic structure

Clay Minerals

Kaolinite, Illite, Chlorite, Montmorillonite

Lava

Magma that has been extruded onto the Earth's surface (extrusive rock)

Intrusive Igneous Rocks

Magma that is not extruded onto the Earth's surface intrudes crustal rocks. They form when magma solidifies underground.

crayons

Metamorphic rocks common in the old, stable cores of continents

Bowen's Reaction Series

Minerals crystallize in a predictable order, over a large temperature range Discontinuous branch • ferromagnesian minerals crystallize in sequence with decreasing temperature • as one mineral becomes chemically unstable in the remaining magma, another begins to form Continuous branch • plagioclase feldspar chemical composition evolves from Carich to Na-rich with decreasing temperature

Magma

Molten rock created by melting of preexisting rock above a subduction zone

regional metamorphism

Most common type of metamorphism; Takes place at depth so high pressure is the dominant factor; results in rocks with foliated textures, so differential stress exists (dynamothermal metamorphism); prevalent in intensely deformed mountain ranges

Most Common Elements

O, Si, Al, Fe, Ca, Na, K, Mg

Decompression Melting

Occurs when hot mantle rock moves upward and pressure is reduced enough to lower the melting point to the temperature of the rising rock body because melting point of minerals generally increases with increasing pressure

Xenoliths

Pieces of country rock incorporated into an igneous body

Mud Cracks

Polygonal cracks formed in drying mud

Claystone

Predominantly clay-sized grains; non-fissile and does not contain any bedding (Pittsburgh Redbeds)

Sedimentary Rocks

Produced from weathering products of pre-existing rocks or accumulated biological matter

Geothermal Gradient

Rate at which temperature increases with increasing depth beneath the surface

colluvium

Residual soil that moves down slope through soil creep and slope wash

spheroidal weathering

Rock is rounded by weathering (edges weather and erode)

Chemical Rocks

Rocks that form by crystallization by precipitation from solution. They have a crystalline texture.

Pahoehoe

Ropy appearance volcanic structure

Graywacke

Sand grains surrounded by dark, fine-grained matrix, often clay-rich. Has 15% or more of its matrix comprised of fine-grained matrix. Believed to form from sediment-laden currents in deep ocean basins

Coal

Sedimentary rock forming from compaction of partially decayed plant material - organic material deposited in water with low oxygen content (i.e., stagnant)

Cross-bedding

Series of thin, inclined layers within a horizontal bed of rock

Deposition

Settling and coming to rest of transported material

Dike

Shallow, tabular intrusive structure that cuts across any layering in country rock (discordant - not parallel to any layering)

Sill

Shallow, tabular intrusive structure that parallels layering in country rock (concordant - parallel to layering)

Intermediate Rocks

Silica contents between those of mafic and felsic rocks

Basic building block of many common rocks

Silicon Tetrahedron

Mudstone

Silt- and clay-sized grains; massive/blocky with no bedding

Siltstone

Slightly coarser-grained than shale because it has a higher silt content; non-fissile but contains bedding planes

Ripple Marks

Small ridges formed on surface of sediment layer by moving wind or water (currents)

alluvium

Soil deposited by streams and rivers

dynamic metamorphism

Some metamorphic rocks form strictly by shearing during faulting

Factors controlling metamorphic rock characteristics:

Temperature and pressure during metamorphism, effects of tectonic forces, effects of fluids, such as water, parent rock composition, differential stress, compressive stress, fluids, time

Country Rock

The preexisting envelope of rocks into which an igneous magma is intruded

Compaction

The process where more sediment is deposited on top of previously grains (overburden), its weight packs deeper layers of sediment together decreasing the pore space, decreasing porosity

Extrusive Igneous Rocks

They form when magma solidifies at the Earth's surface (lava). Formed by pyroclasts and lava flows.

Fossils

Traces of plants or animals preserved in rock

Volcanic landforms

Vent - opening through which lava erupts (flank eruptions also occur) Crater - basin-like depression over the vent at the summit of the volcano Caldera - volcanic depression much larger than the original crater, having a diameter of at least 1 km

loess

Wind-transported soil

gneissic layering

a rock becomes ductile as it is being metamorphosed, and the new minerals segregate into light and dark layers

confining pressure

applied equally on all surfaces of a substance in all directions

compresive stress

causes flattening perpendicular to stress

A horizon

dark-colored, rich in organic matter and high in biological activity

effects of weathering

destroys rocks, produces soil, its products that dissolve in water are transported to oceans and help maintain salinity and provide nutrients for aquatic life

Rock Texture

foliated (layered) vs. non-foliated (non-layered)

methods of mechanical weathering

frost action, pressure-release fracturing, plant growth, burrowing animals, salt wedging, thermal cycling; pressure release, frost action most effective

Weathering

group of destructive processes that change physical and chemical character of rocks at or near Earth's surface

acid dissolution

hydrogen cations replace others in minerals

hematite

iron forms with oxygen to form iron oxide; can react with water to form the mineral limonite, which is an iron hydroxide

feldspars

most common minerals in crust; Weathers to an entirely new mineral (clay); Clay is a hydrous aluminum silicate with a sheet structure

soil

orms an essential interface between the solid Earth(geosphere), biosphere, hydrosphere, and atmosphere; known as regolith contains clay minerals, quartz, water, organic matter

C horizon

partially weathered bedrock

mechanical weathering

physical disintegration of rock

erosion

physical picking up of rock particles by water, ice, or wind

shock metamorphism

produced by rapid application of extreme pressure

metamorphism

refers to solid-state changes to rocks in Earth's interior

prograde metamorphism

results when a rock body becomes buried to increasingly greater depths. The minerals in a rock recrystallize into new minerals that are stable under the temperature and pressure conditions

hydrothermal

rocks precipitated from or altered by hot water

pressure release

s a significant type mechanical weathering in which reduction of pressure on a rock body causes it to expand and crack

transportation

the movement of eroded particles by water, ice, or wind

O horizon

uppermost layer; organic material (humus)

schistose

visible minerals that are platy or needle-shaped grow essentially parallel to a plane due to differential stress

formation of hydrothermal rocks

water passes through rocks and precipitates new minerals on walls of cracks and in pore spaces

residual soil

weathering of underlying rock - commonly retains structures of parent bedrock (e.g. bedding)

B horizon

zone of accumulation; clays and iron oxides leached down from above; formation of hardpan in wet climate

E horizon

zone of leaching; fine-grained components removed by percolating water

Mafic Rocks

~50% silica by weight, contain darkcolored minerals that are abundant in iron, magnesium and calcium - considered silica-poor

Cementation

• As underground water moves through remaining pores, cement can precipitate in the pore space and bind loose sediment grains together to form a solid rock • As cement continues to fill pores, the amount of pore space is reduced and loose sediment forms a hard, coherent rock by cementation

Shield Volcanoes

• Broad gently sloping (2° to 10°slopes) • composed of solidified lava flows - mostly basalt • Lava spreads over wide area due to low viscosity • e.g. Hawaiian Islands

Cinder Cones

• Constructed of pyroclastic fragments ejected from a central vent • Smaller than shield volcanoes • Steep slopes (commonly 30°) • The pyroclastic material is mafic • Life spans tend to be short because the loose cinders are easily eroded

Fragmental textures

• Dust (<1/8 mm) • ash (1/8 - 2 mm) • cinders (2 - 64 mm) • blocks and bombs (>64 mm)

Compositional classification

• Mafic rocks (gabbro-basalt) contain abundant dark-colored ferromagnesian minerals • Intermediate rocks (diorite-andesite) contain roughly equal amounts of dark- and light-colored minerals • Felsic rocks (granite-rhyolite) contain abundant light-colored minerals

Textural classification

• Plutonic rocks (gabbro-diorite-granite) are coarse-grained and cooled slowly at depth • Volcanic rocks (basalt-andesite-rhyolite) are typically finegrained and cooled rapidly at the Earth's surface

Rounding

• Rounding of particles occurs due to abrasion during transport (grinding of sharp edges and corners) • Rounding is pretty much limited to sand size particles and larger • The further a sediment is transported, the more round it typically becomes. • Rounding can also occur where sediment is worked and reworked by wave action (beach environment)

Types of Volcanoes

• Shield volcanoes • Cinder cones • Composite volcanoes

Sorting

• Sorting is the process by which sediment grains are selected and separated according to grain size by transport agents, especially running water • Sediment size decreases with increased transport distance • Well-sorted sediment is comprised of grains being all the same size • Poorly-sorted sediment has of a wide range of grain sizes (clay, silt, sand, gravel, boulders)

Organic Rocks

• accumulate from remains of organisms or plant material

Composite Volcanoes

• aka stratovolcanoes • moderately to steeply sloping • constructed of alternating layers of pyroclastic debris and solidified lava flows • composed primarily of intermediate composition volcanic rocks (i.e., andesite) • most common type of volcano at convergent plate boundaries

Sediment particle size

• boulder - >256 mm • cobble - 64 to 256 mm • pebble - 2 to 64 mm • sand - 1/16 to 2 mm • silt - 1/256 to 1/16 mm • clay - <1/256 mm

Breccia and Conglomerate

• coarse-grained clastic sedimentary rocks • breccia composed of coarse, angular rock fragments that are cemented together • Fragments are angular because they were not transported very far • conglomerate composed of rounded gravel that is cemented together • Not transported far but enough to round clasts (river or gravelly beach)

Chemical Rocks

• crystalline textures • form by precipitation of minerals from solution

What determines the violence of an eruption?

• dissolved gases in the magma • ease/difficulty of gases escaping to atmosphere which relates to the viscosity, which is a fluid's resistance to flow determines how readily gas can escape

Evaporites

• form from evaporating saline waters (lake, ocean) • common examples are rock gypsum, rock salt

Lithification

• general term for processes converting loose sediment into sedimentary rock • combination of compaction and cementation

Chert

• hard, compact, fine-grained, formed almost entirely of silica • can occur as layers or as lumpy nodules within other sedimentary rocks, especially limestones

Silicate Structures

• isolated tetrahedra (none shared) • chain silicates (2 shared) • double-chain silicates (alternating 2 and 3 shared) • sheet silicates (3 shared) • framework silicates (4 shared)

Detrital Rocks

• most common sedimentary rock type • form from cemented sediment grains that come from preexisting rocks

Graded Bedding

• progressive change in grain size from bottom to top of a bed • Indicates waning energy in the depositional environment

chemical weathering

•decomposition of rock from exposure to atmospheric gases (oxygen, water vapor and carbon dioxide) • new chemical compounds (minerals) form • rate increased by increased rock surface area