Test 3

Impact metamorphism

"strike metamorphism" occurs when meteorites strike Earth's surface rocks called impsctiles Ultra high T & P

Saltation particle movement

(intermittent hopping) "Bedload" wind or water larger materials

Subduction zone metamorphism

-High pressure, low temperature -restricted to narrow belts (smaller than regional) -forms at temps below average geothermal gradient, but very high pressure -Accretionary prisms at subduction zones is only site (Blueschist facies)

Metamorphism

-Metamorphism occurs when a protolith undergoes a solid state (not magma) change in response to a modification of environment -TEMPERATURE, PRESSURE, COMPOSITION OF FLUID

Carbonate depositional sites

-Warm temperatures to supersaturate water with CaCO3 -abundance of calcareous- shelled organisms -Water must be very shallow & away from sediment source -Epicontinental Seas -Reefs grow at platform margins -Deep sea carbonates formed by settling of carbonate shells

Blueschist facies

-low temp, high pressure facies -correspond to subduction zone metamorphism experienced by a subducting slab (sinking crust remains cool, well down into mantle) and very deep lower crust and mantle conditions often contains blue amphibole, glaucophane

halite (halide mineral)

-most abundant in marine deposits -Mechanically unstable: deforms by flowing when deeply buried. -forms salt dome structures. -extremely restricted basin shows halite

Siliciclastic sedimentary rocks

-most abundant sedimentary rocks. -formed from detritus left over from weathering of igneous and metamorphic & older sedimentary rocks. -pyroclastic materials if close to active volcano -rock composition depends on source region, weathering, and separation of grains/minerals during transport. -most derived from continents (terrestrial siliciclastic sediment)

Chert

-rock name for cryptocrystalline quartz -occurs in bedded deposits and as nodules in sedimentary sequences -precipitates in water, mostly marine -silica sources include some plankton (diatoms/radiolaria) and sponge spicules

sequence of evaporite formation

1. Calcite - begins when seawater 1st starts to evaporate 2. Gypsum- begins when ~75% water removed 3. Halite- begins when ~90% water removed 4. Various Mg/K salts- ~95% removed

sedimentary weathering rates influenced by:

1. Chemical composition and bonding of mineral material (Quartz=high stability, Olivine=low) 2. Structural integrity of mineral; fractures, cleavage (increases particles) 3. Sizes & Impurities of crystals 4. Chemical character of environment (water availability[no soil without water], temperature[polar regions- low weathering]) 5. Areas with high topographic relief promote weathering and transport of sediment. (convergent and divergent plate boundaries)

Sandstones

1/4 of all sedimentary rocks Quartz 2/3 of detrital grains(durable), Feldspars 15% detrital grains, Lithic fragments 15-20%, mica flakes small% Accessory minerals <1% (magnetite)

Mudrocks

2/3 of all sedimentary rocks siltstone, claystone, shales source of organic materials from which oil and gas form. (contain 95% of all organic matter in sed rocks) low permeability, good cap rocks for oil reservoirs and confined aquifers. Silt (mostly quartz-angular bc never at stream bottom) and clay sized mineral may be finely layered (laminated, fall like sheets of paper)

Quartz arenites

<5% feldspar/lithic fragments mature sandstone long periods of abrasion (rounded) small amount resistant accessory minerals. porosity ranges.

Wackes

>15% mud matrix immature (poorly sorted, angular-subangular submarine fan, slope, and abyssal deposits tribitity currents- graded bedding convergent boundary, volcanic dark color; cement absent

Feldspathic arenites (arkose)

>25% feldspar immature (angular), short transport. fluvial/alluvial settings rapid deposit.

Lithic arenites

>25% lithic clasts (but <15% mud matrix) submature; some transport (subangular-rounded) occur at base of uplift where rock fragments plentiful; cold and arid environments, floodplains

role of CO2

CO2 gas dissolved in water is KEY to deposition less CO2 in water, more CaCO3 deposits how to get less CO2 in water: Increase temperature Agitate water (more area to lose gas dissolved in water) Increase salinity (through evaporation) (CO2=less soluble) Enhance organic activity (Plants absorb CO2 during day) Expose groundwater saturated with CaCO3 to atmosphere

Aragonite Group of sedimentary rocks

CO3 complex with large divalent cations (Br, Sr, Pb, Ca) orthorhombic structure. Members: Aragonite(CaCO3) Witherite(BaCO3 Strontianite(SrCO3) Cerussite(PbCO3) polymorph of calcite group

Calcite group of sedimentary rocks

CaCO3 rhombohedral cleavage MEMBERS: calcite(CaCO3), magnesite(MgCO3), siderite(FeCO3), rhodochrosite(MnCO3), smithsonite(ZnCO3) interchange easily, small ion radius

Carbonate matrix

Calcium carbonate mud that binds allochems together

Types of cements

Carbonate cement- calcite Quartz cement- arenites Clay cement- wackes Hematite cement- iron oxide in sandstone

Greenstone

Chlorite gives green color Mafic protolith, such as basalt

Hydrocarbons

Coal- from buried plant material before it oxidizes Oil- burial of animal and plant remains Natural gas- same as oil but higher temperatures

Formation of mudrocks

Compaction is most notable change because porosity loss. (loss bc increasing depth of burial for muds)

Barrovian sequence

Developed sequence of index minerals

Schistocity

Geological foliation with medium to large grained flakes in a preferred sheetlike orientation

Gneissic banding

Gneiss appears to be striped in bands

Heat as agent in metamorphism

Heat between diagenesis and melting, recrystallization results in new, stable minerals. hotter = faster

Agents of metamorphism

Heat, prograde changes (heating), retrograde changes (cooling), confining pressure, differential stress, hydrothermal fluids.

Dolomite group of sedimentary rocks

Hexagonal Main minerals: Dolomite CaMg(CO3)2 Ankerite CaFe(CO3)2 dolomite often occurs with calcite

A sedimentary deposit containing angular sand grains in a clayey matrix would be described as

Immature

Carbonate minerals

Limestones, Dolostones tectonic setting- Limestone=low latitudes (warm, clear waters)

Turbidites are associated with which type of depositional environment?

Marine

Phosphorites

Marine sedimentary rocks composed mostly of apatite with >20% P2O5 Apatite, Collophane, Chert

Gneiss

Medium to coarse grained high-grade metamorphism exhibits gneissic banding (color segregation)

Micrite

Microcrystalline carbonate 1 to 5 microns in size (dull in hand sample) precipitates in low energy environments may recrystallize within few million years to microspar (spar)

Spar

Microspar Micrite that recrystallizes

Which of the following sedimentary structures only occurs in fine-grained sediment?

Mudcracks

Siltstone

Mudrock; commonly layered with fluvial sandstone lithified, non-fissile mudrock smaller than sand particles

Dynamic metamorphism

Occurs at depth and high temperatures along fault zones Pre-existing minerals deform by ductile flow result of shearing (Mylonite) Mylonite- large grains in protolith recrystallize to fine grained

protolith

Parent rock

Cementation

Pore fluids may become saturated in minerals they are in contact with. fluids rise through compacting sediment and precipitate, forming a cement binding detrital grains. stable precipitates may replace less stable minerals porosity decreases.

Organically produced limestone/carbonate sediment

Precambrian- explosion of life Carbonate sediment- forms from hard parts of variety of organisms that are broken by wave/current action or by other organisms on them. gravels to sands to muds

Biogenic and Chemical sedimentary rocks

Precipitate out of water- chem Skeletons of corals- bio

Claystone

Shale- most abundant sedimentary rock, recognized by fissility (split into thin sheets) doesn't grit on teeth

Slate

Slate is a hard mudstone that has undergone metamorphosis, and has well-developed cleavage

In stratified glacial meltwater deposits, you might assume that a layer with larger grain size was deposited during

Summer

Regional metamorphism

Widespread metamorphic zones, producing greatest quantity of metamorphic rock Associated with mountain building/convergence (folding) temperature very high, associated with depth/igneous activity higher pressure due to overburden weight, plus compression and shearing foliation develops

Mylonite

a fine-grained metamorphic rock, typically banded, resulting from the grinding or crushing of other rocks.

isograd

a plane of constant metamorphic grade in the field; it separates metamorphic zones of different metamorphic index minerals points along have same meta grade

Migmatites

a rock composed of two intermingled but distinguishable components, typically a granitic rock within a metamorphic host rock.

Continental depositional environment

always above sea level on land or in fresh water; alluvial fans, fluvial (streams), glacial, desert (eolian), and lacustrine (lake)

Marine depositional environment

always below sea level; includes continental shelf, continental slope, and deep marine. Turbidility currents

Compaction

as fluids are expelled from pores, porosity decreases. particles may rotate bc stress. at deposition particles=scattered, during diagenesis particles=aligned parallel

Burial metamorphism

associated with very thick sedimentary strata increasing T & P with additional burial/subsidence typically low grade little to no internal deformation of rocks

Sedimentary structures

bedding (layering)- most common cross bedding graded bedding ripple marks mudcracks tracks/trails burrows

Bedload vs. Suspended load

bedload=faster suspended load= slower effective sorting by grain size results. both contribute to alluvial deposits.

metamorphic index minerals

can approximate grade Chlorite (lowest) Biotite Garnet Staurolite Kyanite Silimanite (highest)

Metasomatism

change in rock's composition by reactions with hydrothermal fluids

Changes to beddings in sandstone (5)

change in: composition size shape orientation packing

Retrogarde

changes that take place during cooling

Prograde

changes that take place during heating

Hydrothermal metamorphism

chemical alteration caused when hot, ion rich fluids circulate through fissures and cracks Most widespread along axis of the mid-ocean ridge system, altering ocean-floor basalt (divergent boundaries)

Sedimentary rock compositions

chemical composition- wide range caused by weathering clastic reflect source rock undergoing erosion (angular or rounded) strongly reflect biochemical environment of deposition

weathering of sedimentary rocks

chemical weathering= decomposition of minerals with formation of new minerals (change composition) removal of some material in solution (oxidation, hydration, hydrolysis, carbonation) Physical= size reduction and increases in surface area without chemical alteration they work together, physical triggers chemical

Limestones

chemically reactive rocks with good premeability Reserviors for groundwater cement industry agriculture source of lime building stone statues

Limestone Peloids/Pellets

coarse-silt to fine-sand sized carbonate grains that often lack internal structure Origin of most thought to be fecal pellets from burrowing organisms

Graded beds have ________ particles at the bottom.

coarser

Graded bedding

coarser grains at bottom, finer at top. forms as sediment heavy currents slow down characteristic of turbidites

Marble

composed mostly of calcite (sometimes dolomite) protolith of limestone or dolostone usually granoblastic foliation may be present

Types of siliciclastic sedimentary rocks

conglomerates, sandstones, mudrocks (shales)

Serpentinites

consists mostly of serpintine

Mudcracks depositional environment

continental

calcite

continental deposits carbonates & Borates (borax)

limestone diagenesis

determined by pore water chemistry and rate of water movement (need slow water) most carbonates experience early cementation later dagenesis consists of mechanical(siliclastic sediments), chemical compaction (developes stylolites) and Burial cementation (pressure solution major source for cements)

Products of physical weathering of sedimentary rocks

detritus: loose material and grains resistant minerals more abundant (quartz) can later form rocks if cemented together ex. conglomerate, sandstone, siltstone, shale.

Metamorphic environments based on

different types based on temperature & pressure

Limestone fossils

easiest observed are inequant, biologically determined shapes often broken and hard to see

Carbonate deposition

equation for equilibrium: CaCO3 + CO2 + H2O <-----> Ca+2 + 2H+ + 2CO3+2

evaporites

evaporation concentrates these dissolved ions in restricted marine basins or lakes, with eventual precipitation or evaporite minerals (~3% of sed. rocks) -minerals precipitate from waters in a predictable sequence, marine most common, lake more common to see. Permian- greatest time of abundance

Shale

fine grained, hard, laminated mudrock, consisting of clay minerals, and quartz and feldspar silt. Shale is lithified and fissile

Phyllite

fine-grained Gradational between slate & schist Glossy reflective sheen due to platey mineral grains wavy surfaces

siliciclastic sedimentary rocks

form from detritus: fragments of other rocks- loosely bounded mudrocks sandstones

Limestone allochems

fossils, ooids, peloids/pellets, limeclasts

Limestone Limeclasts

fragments of earlier formed limestones or partially lithified carbonate sediment may have been torn from seafloor by storm and moved

Hornsfels

generic name for fine-grained, granoblastic, contact metamorphic rocks that are typically: hard, dense, baked appearance, gray to brown to black & smooth to touch depends on where magma intruds- changes composition

some sedimentary structures that help determine "up direction" in rocks that have been overturned

graded beds, cross beds, mudcracks, symmetrical ripples, burrows, tracks

As sediment matures what happens

grain size reduce by abrasion(sands), breakage, solution, chemical weathering = more rounded

Detrital textures

grains can be spherical, rod shaped, disc shaped coarser= rounder, finer=more angular

Conglomerates

gravel sized particles high energy environments (fast flowing rivers) Clast supported- larger amount of larger particles Matrix supported- larger amounts of smaller particles Angular=breccia

Metamorphic Facies

group of metamorphic mineral assemblages that develop under a specified range of temperature and pressure conditions a more complete indication of metamorphic intensity address different protolith compositions

high energy= __________ textural maturity

high (mature)

Turbulent flow

high energy, irregular flow path, air (desert) & water (early river stages) always flows turbulently

Honsfels facies

high temp, low pressure contact metamorphism most common is upper crust where the country rocks are relatively "cold" compared to intruding magma

Detrital grain size

imp. feature in conglomerate and sandstone most rocks have single size; reflects conditions at deposition

Confining pressure in metamorphic rocks

increases with depth applies force equally in all directions may cause recrystallization to more compact crystalline form

Transitional depositional environment

influenced by marine and continental processes; deltas, beaches, and lagoons.

Cross bedding

internal stratification at an angle to main stratification of deposit Most common in sands and silts cross bedding dip downstream

Stylolites

irregular surface or seam in rock developed when chemical compaction where carbonate is removed by pressure solution

Turbidity currents

lakes and ocean basins. rapidly moving suspension of particles. dislodged sediment is taken by current and travels as far downslope as it can go. triggered by slumping or earthquakes graded bedding is characteristic

Porphyroblasts

larger recrystallized grain occurring in a finer groundmass

Detritus

loose material and grains

low energy= __________ textural maturity

low (immature)

Zeolite facies

low temp/low pressure burial metamorphism hydrothermal metamorphism of volcanic rocks

Laminar flow

lower energy, predictable, similar to thin sheets sliding over eachother, flow of glacial ice always laminar

Carbonate compensation depth

lowest depth at which carbonate will precipitate

Slate (metamorphic)

lowest grade metamorphism of shale/mudstone can't identify grains green/dark colored Growth of very fine-grained chlorite and micas results in slaty cleavage

Hydrothermal fluids in metamorphic rocks

mainly water enhances migration of ions aid in recrystallization of existing minerals

Collophane

massive cryptocrystalline variety of apatite found in phosphorites major source of phosphate used in fertilizer

Granoblast textures

may form during recrystallization crystals of roughly the same size:quartzite and marble exhibit polygonal grain boundaries

Schist

medium to coarse grained Conspicuous platy mineral grains exhibits irregular planar foliation of visible mica flakes called schistosity Composition indicated by using mineral names (biotite)

Amphibolites

medium to coarse grained dark colored hornblende and plagioclase metamorhism of mafic rock- gabbro

Contact metamorphism

metamorphism due to contact with or proximity to an igneous intrusion magma invades host rock temperature rises (high T, low P) zone of alteration forms produces massive rock (ex. hornsfeld)

Metaquartzite

metamorphism of quartz arenite and cherts recrystallization with interlocking crystals of quartz rich in water fractures across grain boundaries hard- very stable

Soapstones

mixture of serpentine and talc both typically form by hydrothermal alteration of ultramafic igneous rocks

mudstone

mixture of silt- and clay-sized particles

gypsum (sulfate mineral)

most abundant in marine deposits only common in arid climates soft so easy to identify in outcrop

chemical and biogenic rocks

most commonly carbonates(limestones and dolomites)

sediment transport

most moved by fluids responding to stress (wind water & ice) depends on viscosity and velocity Laminar flow= lower energy turbulent flow=high energy (air & water) Particle movement by fluid flow- rolling, saltation(intermittent hopping), suspension by turbulent eddy currents (clay and silt sized particles) (mixed throughout water)

common/abundant sedimentary rocks

mudrocks (siltstones and claystones) (65%) sandstones (25%) limestones & dolomites chert

Products of chemical weathering of sedimentary rocks

newly formed minerals can stay at site of weathering ex. clays formed by weathering of feldspars dissolved materials transported in solution can later precipitate to form chemical sedimentary rocks ex. carbonates (limestone), evaporites (gypsum)

Rolling particle movement

on stream bed "bedload" largest materials

Skarns

originate from contact metamorphism of limestone show evidence of having exchanged constituents with intruding magma (metasomatism) calcium rich- wollostone diopside, plagioclase may form ore deposits

Apatite

phosphate mineral hardness of 5 mined for phosphorite occurs in shallow marine settings

Depositional environments

physical, chemical, biological and geographic conditions under which sediments are deposited. yield distinctive rocks characteristic of various environments Marine, Continental, and Transitional

Mudcracks

polygonal pattern of cracks produced when mud dries suspended load deposited in floodplains fine grained and clay rich form 3 fractures at 120 degree angles

Metamorphic rocks

pressure, heat, and

Pressure solution

process by which dissolution of minerals occurs at grain-grain contacts under high stress in an aqueous solution. The dissolved components can be either removed from the rock or deposited in a low stress area of the rock

Dolomitization

process by which limestone is altered into dolomite Diagenetic replacement solutions dissolve CaCO3 and precipitate dolomite Mg substitutes Ca

Ripple marks

produced as wind or water moves across sand finer particles=faster; coarser particles= slower alluvial, beach, stream bottoms, deserts go in direction of flow wavy appearance symmetrical= back & forth (beaches) asymmetrical= one flow direction (alluvial)

Trace fossils

provide us with indirect evidence of life in the past tracks, trails, or burrows determining "up direction"

metamorphic zone

region between isogrades represent different metamorphic intensities (temperature and pressure)

Greenschist facies

regional meta in continental collision zones most common facies corresponds approx. to the Barrovian chlorite, biotite & garnet zones. epidote, chlorite, actinolite (green amphibole)

Amphibolite facies

regional metamorphism corresponds approximately to the Barrovian upper garnet through silimanite facies

Granulite facies

regional metamorphism highest grade metamorphism experienced by continental rocks Hydrous minerals absent common in Precambrain rocks may form migmatites at upper end

Eclogite facies

relatively rare, dense rocks may represent crust-mantle boundary

how do sedimentary rocks form

sediments are transported, deposited, and lithified. -preexsiting rocks weathered -directly by organisms -as a direct chemical precipitate

debris flows

sediments loaded down with water (boulders to clays) travel downslope at various speeds. called mudflow if particles travel quickly in mud matrix. common around volcanoes and alluvial fans.

types of mudrocks

siltstone, claystone, mudstone, slate, and shale

Chemically produced sediment

some weathering products may be removed in solution, and these ions may end up in the ocean, a lake, or a rift basin.

Metamorphic Grade

somewhat informal way to indicate intensity of metamorphism Yield different mineral assemblages Metamorphic index minerals can approximate grade Increasing grade= grain size coarsens, stable at higher temp and pressure (slate, phylilite, schist, gniess)

Slaty cleavage

splitting into thin sheets along foliation Found in the rocks slate and phyllite

Limestone Ooids

subrounded sand-sized particles fromed by precipitation of calcite or aragonate in concentric layers around a nucleus grain as it washes back and forth in shallow marine waters. looks like bullseye when cut in half more rounded than sandstone aragonite over time converts to calcite pisoliths are >2mm

Diagenesis

the physical and chemical and biological changes sediment is subject to after initial deposition (excluding weathering or metamorphism bs it hasn't effected it yet) main processes= Compaction & Cementation (lithification) lost porosity, gained strength.

Foliation

the process of being split into thin sheets or laminae

Limestone depositional environment

transitional

deposits of turbidity currents

turbidites

Suspension particle movement

turbulent eddy currents, suspended load clay and silt sized particles, mixed throughout water, doesn't settle. smallest materials

Limestone textures described by:

types of grains (allochems) forming framework of rock carbonate mud matrix- fine grained presence or absence of coarsely crystalline calcite cement texture and structures

differential stress in metamorphic rocks

unequal in different directions can result in preferred orientation of mineral grains (ex. convergent plate boundaries)

Till

unsorted material deposited from glacial ice.

Sedimentary deposits with ________ grains would likely make better reservoirs for petroleum, natural gas, or groundwater because they tend to have a higher porosity and permeability

well-sorted

Carbonate rocks

~10% of total sedimentary rocks biological activity in marine waters more limestone than dolomite.