Review slides for midterm2

Weathering

Weathering

Breakdown of rocks physically and chemically

Erosion

Particles carried away after weathering

Transportation

Particles move through

Streams

glaciers

wind

Sedimentation (Deposition)

Particles settle out or dissolved minerals precipitate

Burial

Layers of sediment accumulate and compact previous layers

Diagenesis

Physical and chemical processes that affect sedimentary materials after deposition and before metamorphism, between deposition and weathering

Lithification

Process whereby freshly deposited loose grains of sediment are converted into rock

Fragmentation Abrasion

One rock bumps against another rock

Wedging

A pre-existing crack is made larger by forcing it open with

water/ice

salt

plants

animal activity

Chemical weathering

Dissolution

Hydrolysis

Hydration/dehydration

Oxidation

Erosion: Moving water

Abrasion - scouring of stream bed by transported particles

Scouring and lifting - flowing water dislodges larger rocks

Dissolution - stream flows over soluble bedrock

Transport and sorting

Currents carry different particle sizes

particles sorted according to grain-size and density

Sand and gravel undergo extensive abrasion

Particle size - diameter decreases as material removed

Edges become more rounded

Sedimentary basins

Accumulate in the Earth’s crust

depressions filled with thick layers of sediment from weathering

Soil

Soil forms an essential interface between the solid Earth (geosphere), biosphere, hydrosphere, and atmosphere.

Regolith is the name for the loose, unconsolidated material that covers planetary surface.

Soil for the layer of weathered, unconsolidated material that contains organic matter and is capable of supporting plant growth.

A mature, fertile soil is the product of centuries of mechanical and chemical weathering of rock, combined with the addition and decay of plant and other organic matter.

Soil makeup

Complex mixture of minerals (<>45%), organic matter (<>5%), and 50% empty space filled with degrees of air and water

Mineral content dominated by clay and quartz, along with minor amounts of feldspar and rock fragments

Sedimentary structures

Characterized by bedding or stratification

range in thickness from < 1 cm to several meters

Differentiated by rock or mineral type and size

Sedimentary structures

Deposition within different sedimentary environments, all kinds of features in sediment formed at the time of deposition.

Bedding (stratification)

• Cross-bedding

• Ripples • Mud cracks

• Graded bedding

• Bioturbation structures

Graded bedding

Characterized by a change in grain size from bottom to top within a single bed

Form in submarine fan environment where sediment falls down a slope onto deeper sea floor

Burial

Clastic sediments become trapped following deposition in sedimentary basins

• New layers of sediment accumulate over older layers of sediment

• Older sediments subjected to:

• Increasing temperature

• Increasing pressure

• Chemical and biological reactions

Lithification

Converting sediment into sedimentary rock

Compaction

reduces the volume of a deposit by decreasing the amount of pore space as particles fit more closely together deposit settles under its own weight and the weight of any sediment deposited on top of it

Cementation

Takes place when minerals crystallize in pore spaces and effectively bind the particles to one another

Sedimentary Environments

Clastic sedimentary environments

Chemical and biological sedimentary environments

Carbonate environments Ca2+ (aq) + CO3 2- (aq) CaCO3(s)

• Siliceous environments: Silica (SiO2) forms in marine sedimentary environments by Chemical precipitation (Water reaches saturation with Si and O2), and Biomineralization (Diatoms precipitate amorphous silica→diatomite).

• Evaporite environments

Clastic sediments

The visible unconsolidated materials found on slopes, beneath glaciers, in stream valleys, on beaches, and in deserts are referred to as sediment, and the individual pieces that make it up are called clasts.

Broken and eroded pieces of rocks and minerals

• physical and chemical weathering of common silicate-bearing rocks

• range in size from boulders to sand, silt and clay

Chemical and Biogenic Sediments

Evaporation: Mineral precipitation due to seawater evaporation forms chemical sediments

• Dissolved ions accumulate in water due to chemical weathering

• Chemical and biological reactions precipitate minerals from these dissolved ions

Biomineralization

• Direct mechanism: organisms utilize dissolved ions or molecules to produce shells or skeletons

• Indirect mechanism: minerals precipitate due to environmental conditions created by organisms

Classification of sedimentary rocks

>85% of all sedimentary rocks are clastic

• Characterized by grain size • Chemical and biological sedimentary rocks account for ~14%

• Evaporites, cherts and other chemical and biological sedimentary rocks exist in minor amounts

• Characterized by chemical composition

Clastic sedimentary rock types

Distinguished by:

• grain size and shape

• grain type (mineralogy)

• texture of the grains, matrix and cements

Minerals

• Minerals that weather by dissolution (e.g., halite, gypsum, calcite) are the easiest to weather.

• Silicate minerals with lower silica to oxygen ratios (e.g., silicates made of isolated silica tetrahedra or single chains) are easier to weather than silicate minerals with higher ratios (e.g., those made of silica tetrahedra arranged sheets or frameworks).

• Minerals that are by-products of chemical weathering are some of the most resistant to further chemical weathering, although they may be more prone to physical weathering (e.g., clay minerals).

Types of sediment

Specific combinations of texture and composition for each type

• Determined by sediment’s history: transport energy and distance, weathering intensity, and composition of source rock.

Conglomerate - gravel

Sandstone - sand

Siltstone - silt

Shale - clay and silt

Chemical and Biogenic rocks

Siliceous sediments

• Lithify to form cherts (flint)

• Phosphorite sediments

• Lithified calcium phosphate

• Iron oxide sediments

• Indirecty precipitated by microorganisms

• Lithified after oxygen increased in oceans (i.e., ~3 Ga)

• Organic sediments

• Form from accumulation of wetland vegetation

• Burial and diagenesis converts peat to coal

Carbonate sediments and rocks

• Calcium carbonate [CaCO3 ] formed by direct or indirect precipitation by organisms

• Limestone forms by accumulation and lithification of CaCO3

• Dolomite [CaMg(CO3 )2 ] forms by chemical reaction between CaCO3 and dissolved magnesium.

Calcium carbonate [CaCO3 ]

• Calcite is the most abundant carbonate mineral.

• Aragonite is a polymorph of calcite, a mineral that has the same chemical composition as calcite, but has a slightly different crystal structure. Aragonite tends to convert to calcite over time.

• Dolomite is a mineral that most often forms as an alteration of calcite, as magnesium replaces much of the calcium in the crystal structure.

• The easiest way to distinguish calcite and dolomite is that dolomite will not readily react with dilute acid at room temperature.

• Hardness: 2.5 to 3.

Evaportites

• Chemically precipitated from evaporating sea water and (sometimes) lake water

• Seawater contains dissolved minerals, which are concentrated during evaporation to form:

Halite [NaCl]

Gypsum [CaSO4 •2H2O]

Metamorphism

• Earthquake

• Mountain building

• Metamorphic rock

• Shock metamorphism

Deformation

occurs when applied forces exceed the internal strength of rocks, physically changing their shapes. These forces are called stress, and the physical changes they create are called strain.

Original horizontality

The principle of original horizontality states that sediments accumulate in essentially horizontal layers under the influence of gravity. Subsequent deformation can cause folding or faulting of sedimentary strata

Rock responds to stress differently depending on the pressure and temperature (depth in Earth) and mineralogic composition of the rock.

• Elastic deformation: Fully reversible: rock returns to original shape

• Brittle deformation: Stress causes rock to fracture

• Ductile deformation: Irreversible: rock does not return to original shape

Faults

• Brittle deformation causes rocks to break, slip on both sides of a fracture

• Faulting occurs suddenly and produces earthquakes

Characterized by rock displacement Caused by different forces: Compression; Tension; Shear Type of fault classified by: Slip direction; Displacement (offset)

Folds

• Ductile deformation under directional pressure

• Develop slowly, common in metamorphic rocks

Joints

• Fractures without faulting

• Displacement of fracture opening greater than displacement by lateral movement along fracture plane

• Stress on rock from tectonic forces or thermal contraction

Faults

Characterized by rock displacement

Caused by different forces: Compression; Tension; Shear Type of fault classified by: Slip direction; Displacement (offset)

• When rock masses slip past each other parallel to the strike, the movement is known as strike-slip faulting. Movement parallel to the dip is called dip-slip faulting.

• Oblique-slip faults are defined by combinations of dip-slip and strikeslip displacement.

Elastic rebound theory

When rock experiences large amounts of shear stress and breaks with rapid, brittle deformation, energy is released in the form of seismic waves, commonly known as an earthquake.

• The point within the Earth where seismic waves first originate is called the focus (or hypocenter ) of the earthquake. This is the center of the earthquake, the point of initial breakage and movement on a fault. Rupture begins at the focus and then spreads rapidly along the fault plane. The point on the Earth’s surface directly above the focus is the epicenter .

Seismic Waves

• When a rock breaks, waves of energy are released and sent out through the Earth. These are seismic waves , the waves of energy produced by an earthquake. Two types of seismic waves are generated during earthquakes.

• Body waves are seismic waves that travel through the Earth’s interior, spreading outward from the focus in all directions.

• Surface waves are seismic waves that travel on Earth’s surface away from the epicenter, like water waves spreading out from a pebble thrown into a pond.

• The instrument used to measure seismic waves is a seismometer

Body waves

• A P wave is a compressional (or longitudinal) wave in which rock vibrates back and forth parallel to the direction of wave propagation. P wave is the fastest and first (or primary ) wave to arrive at a recording station following an earthquake. • An S wave ( secondary ) is a slower, transverse wave. The rock vibrates perpendicular to the direction of wave propagation, that is, crosswise to the direction the waves are moving.

• Both P waves and S waves pass easily through solid rock. A P wave can also pass through a fluid (gas or liquid), but an S wave cannot.

Surface waves

• Surface waves are the slowest waves set off by earthquakes. Surface waves cause more property damage than body waves because surface waves produce more ground movement and travel more slowly, taking longer to pass.

• Love waves are most like S waves that have no vertical displacement. The ground moves side to side in a horizontal plane that is perpendicular to the direction the wave is traveling or propagating.

• Rayleigh waves rolls along the ground with a more complex motion than Love waves. Rayleigh waves tend to be incredibly destructive to buildings because they produce more ground movement and take longer to pass.

Seismometer

Seismographs are instruments used to record the motion of the ground during an earthquake. A seismometer is the internal part of the seismograph

Moment Magnitude

The Moment Magnitude(MW) uses seismograms plus what physically occurs during an earthquake, known as the "seismic moment". The seismic moment defines how much force is needed to generate the recorded waves, determined from the strength of the rock, surface area of the rupture, and the amount of rock displacement along the fault

Types of earthquakes

• Tectonic Earthquakes

• Volcanism

• Impacts from meteoroids

• Artificial Induction

• Caused by human activities, including the injection of fluids into deep wells, the detonation of large underground nuclear explosions, the excavation of mines, and the filling of large reservoirs.

• Reservoir Induction

• More than 20 significant cases have been documented in which local seismicity has increased following the impounding of water behind high dams.

Types of Plate Boundaries

1. Divergent Boundaries a) Oceanic plate separation b) Continental plate separation

2. Convergent Boundaries a) Ocean-ocean convergence b) Ocean-continent convergence c) Continent-continent convergence

3. Transform-Fault Boundaries a) Mid-ocean ridge transform fault b) Continental transform fault

Divergent Boundaries

• Shallow earthquakes within ocean basins:

• Crests of mid-ocean ridges

• Offsets on transform faults

• Normal faults also responsible for earthquakes where continental crust undergoes extension

• East African Rift valley

• Basin and range province, USA

Largest Earthquakes occur at convergent plate boundaries

• Called megathrust earthquakes

• Overriding plate thrust upward relative to subducting plate

• Zone of seismicity along the plane of the subducting plate is called the Wadati-Benioff Zone

Transform boundary

• A strike-slip fault occurs where plates meet and slide against each other horizontally.

• Plates move past each other with earthquakes generating close to the surface. Earthquakes are shallow but powerful.

Earthquake hazards and risks

• Majority of fatalities due to collapse of buildings and other structures

• Earthquakes cause damage in several ways:

• Faulting and shaking – primary hazards

• Landslides

• Liquefaction

• Fires

• Tsunamis

Tsunamis

• Most tsunamis are caused by large earthquakes below or near the ocean floor • can also be caused by landslides, volcanic activity, certain types of weather and near earth objects (e.g., asteroids, comets).

• Not all earthquakes cause tsunamis. Megathrust earthquakes can cause tsunamis.

Folds

• Original planar structure bent into a curved structure

• Ductile deformation caused by compressional forces, horizontal or vertical

Anticline: it looks like an “A” or a dome (upward folding orientation of layers). The beds dip away from the axial trace, older going towards the axial trace. Syncline: it looks like a “U” (downward folding orientation of the rock layers). The beds dip towards the axial trace, younger going towards the axial trace.

Mountain building

Mountains may be created by volcanism, faulting, and folding

Divergent Boundaries

a) Continental plate separation

• Extension of boundaries; new lithosphere generated

• Rift valleys, mountains, volcanoes, and earthquakes

b) Oceanic plate separation

• Extension of boundaries; new lithosphere generated

• Submarine rift valleys, mountains and volcanoes, and earthquakes

• E.g. Mid-Atlantic Ridge

Mountain building along divergent margins

• When continents begin to split apart, normal faults form. This can lead to large blocks of crust that are tilted, raised, or lowered compared to adjacent blocks.

• Blocks that are elevated compared to adjacent blocks can form another type of mountain, called a fault -block mountain.

Fault-block mountains

crust is broken into large blocks and lifted above surrounding crust. • E.g. Grand Teton Mountains, WY

• Grabens = long, narrow valleys formed when large blocks of crust have dropped between normal faults

• E.g. Death Valley, CA • Horsts = forms when block of crust is thrust upward between two normal faults

• E.g. Basin and Range Province of Nevada

Convergent Boundaries

2a) Ocean-ocean convergence

• Oceanic trench, volcanic island arc, and deep earthquakes

2b) Ocean-continent convergence

• Volcanic mountain chain, folded mountains, and deep earthquakes

2c) Continent-continent convergence

• Crustal thickening, folded mountains, and earthquakes

Mountain Building Along Convergent Margins

• Mountain building along convergent margins is referred to as orogeny, and the mountains that are built are called orogens.

• Orogeny creates broad, linear regions of deformation known as orogenic belts

Ocean-continent collision

• In ocean-continent collision zones, folding and faulting of rocks combines with volcanism to build mountains. E.g. Sierra Nevada mountain.

• Mountains form from subduction zone volcanism, and from large sheets of rock that are thrust inland and folded. Materials accumulating on the leading edge of the continent in an accretionary wedge are eventually smashed onto the continent, adding to continental crust.

Continent-continent: Fold and Thrust Belts

• Large compressive stresses are generated in the crust at convergent margins when continental crust collides.

• Rocks located in the collision zone blocks are folded, faulted, and thrust faulted.

• Crustal thickening pushes peaks upward and builds deep roots, forming fold-and-thrust mountains.

• Fold-and-thrust belts form the highest and most structurally complex mountain belts

Rocks

naturally occurring solid aggregates of minerals, or in some cases, non-mineral solid matter. Rocks are grouped based on formation: Igneous, Sedimentary, Metamorphic.

Metamorphism meaning

Meta- Greek word, meaning Change.

Morph is from the Greek morphe meaning shape or form

ism- the action or result of…

Metamorphic Rock- forms when preexisting rock (parent rock), or protolith undergoes solid state change (recrystallization) in response to the modification of its environment

Metamorphism

• Driven by four principal factors:

• Temperature: Increases at a rate of 30°C per km depth

• Pressure: Increases at a rate of 0.23 kbar per km depth

• Fluid chemistry: Introduces dissolved minerals

• Time: Reactions involving silicate minerals are very slow

• Typically occurs between 200 and 800°C

• Diagenesis occurs at < 200°C

• Melting occurs at > 800°C

• These temperatures are typically encountered at depths of 10–30 km within the crust

The Role of pressure

• Pressure can also alter the chemical composition, mineralogy and texture of rocks

• Can control which minerals form and which are stable

• Minerals formed at higher pressure exhibit higher density

• Two basic kinds of pressure involved in metamorphism

• Confining pressure (lithostatic pressure)

• Directed pressure (differential stress)

Confining pressure

• Force is applied equally in all directions and increases with depth in the crust

• Recrystallized minerals become reoriented and tightly locked

Directed pressure

• Force applied in a particular direction

• Recrystallized minerals exhibit parallel alignment of textural and structural features

• Ductile rocks can be severely distorted

The role of heat

• Changes in composition, mineralogy and texture due to heat are associated with:

• Breaking of chemical bonds

• Changing of crystal structure

• Recrystallization and stability of minerals are temperature dependent

• Atoms combine differently at different temperatures

• Increasing temperature speeds up chemical reactions

• Geologists can use mineral composition of metamorphic rocks as a geothermometer

The rule of fluids

• Water and carbon dioxide present in varying amounts:

• Along grain boundaries

• In pore spaces

• Accelerate chemical reactions:

• Ions are transported rapidly from one place to another

• Different sources of fluids:

• Trapped in sedimentary rocks

• Released from magmas

• Breakdown of hydrated minerals

• Hydrothermal fluids can also transport heat and promote recrystallization

The role of time

• Most metamorphic reactions in tectonic processes occur very slowly, reach phase equilibrium.

• New material growth at a rate of approximately 1 mm per million years.

• Shock metamorphism likely not reaching phase equilibrium.

• Stable phase and metastable phase observed

Metamorphic textures

• Determined by properties of constituent minerals:

• Size

• Shape

• Arrangement

• Mineral

• Separated into three general classes:

• Foliated rocks

• Non-foliated (granoblastic) rocks

• Porphyroblasts

Foliated Texture

• Foliation is a term used that describes minerals lined up in planes. Certain minerals, e.g. mica, are mostly thin and planar by default.

• Other minerals linear like a pencil or a needle, referring as lineation. E.g. hornblende, tourmaline, or stretched quartz grains.

• Produced by directed stress related to regional metamorphism

Shock Metamorphism

• Hypervelocity impact event

• Localized metamorphism

• Shatter cones

• Planar deformation features,

• high-pressure polymorphs of quartz

• Impact melt