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