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Lecture 6-7 Sedimentary and Metamorphic Rocks. Part 1 Sedimentary Rocks. Kyanite, Sillimanite, and Andalucite. What is a sedimentary rock?. Sedimentary rocks result from mechanical and chemical weathering Comprise ~ 5% of Earth’s upper crust About 75% of rocks at surface

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slide1
Lecture 6-7Sedimentary and Metamorphic Rocks

Part 1

Sedimentary Rocks

Kyanite, Sillimanite, and Andalucite

what is a sedimentary rock
What is a sedimentary rock?
  • Sedimentary rocks result from mechanical and chemical weathering
  • Comprise ~ 5% of Earth’s upper crust
  • About 75% of rocks at surface
  • Contain evidence of past environments
      • Record how sediment is transported
      • Often contain fossils
what is the economic importance of sedimentary rocks
What is the economic importance of sedimentary rocks?
  • They are important for economic reasons because they contain
      • Coal
      • Petroleum and natural gas
      • Iron, aluminum, uranium and manganese
      • Geologists use them to read Earth’s history
cementation
Cementation
  • Precipitation of chemicals dissolved in water binds grains of a sediment together.
  • After the cements solidify, compaction drives out the excess water.
  • Important part of Lithification
  • Remember where cements come from?
types of sedimentary rocks
Types of sedimentary rocks
  • Chemical rocks – sediment from ions that were once in solution
  • Detrital rocks –sediment transported as solid particles
detrital sedimentary rocks
Detrital sedimentary rocks
  • Constituents of detrital rocks can include
      • Clay minerals
      • Quartz
      • Feldspars
      • Micas
  • Particle size is used to distinguish among the various types of detrital rocks
detrital sedimentary rocks1
Detrital sedimentary rocks
  • Mudrocks: less than .063 mm
    • 1. Mud: small particles easily kept in suspension
    • Settles in quiet water
    • Includes Shale: mud-sized particles <.004 mm deposited in thin bedding layers called laminae

Most common sedimentary rock

2. Larger mudrock grains called silts

silt-sized particles .004-.063 mm

Gritty grains can be felt

detrital sedimentary rocks2
Detrital sedimentary rocks
  • Sandstone
    • Made of sand-sized particles larger than .063 mm and less than 2mm
    • Forms in a variety of environments
    • Sorting, angularity and composition of grains can be used to interpret the rock’s history
    • Quartz is the predominant mineral (due to its durable nature)
detrital sedimentary rocks3
Detrital sedimentary rocks
  • Conglomerate and breccia
    • Both composed of particles > 2mm in diameter
    • Conglomerateconsists largely of rounded clasts. Rounded pebbles in high velocity areas
    • Breccia is composed of large angular particles Breccia is made of shattered rock that accumulates at the base of a cliff
energy
Energy
  • Coarse sediments are deposited in high energy (fast water) environments such as under breaking waves at the beach, or in the beds of fast streams.
  • Fine sediments are deposited in low energy environments, e.g. the slow water of deep lagoons, the abyssal plain, etc.
chemical sedimentary rocks
Chemical sedimentary rocks
  • Precipitated material once in solution
  • Precipitation of material occurs two ways:
      • Inorganic processes: the minerals precipitate out of water
      • Organic processes: animals and plants precipitate the minerals to use as shells or skeletons

http://www.ucmp.berkeley.edu/collections/micro.html

slide12
Common chemical sedimentary rocks
      • Limestone
        • Most abundant chemical rock
        • Made of the mineral calcite CaCO3
        • Marine biochemical limestones form as coral reefs,coquina (broken shells), and chalk (microscopic organisms)
        • Inorganic limestones include travertine(caves) and oolitic limestone (Bahamas)
slide13
http://www.ndsu.nodak.edu/instruct/ashworth/coursework/g410/evaporites/saltbeds.jpg
  • Common chemical sedimentary rocks
      • Evaporites
        • Evaporation triggers deposition of chemical precipitates
        • Examples include rock salt and rock gypsum
slide15
Sedimentary environment determines roundness sorting, mineral diversity6_5

Character of detrital sediments depends on time, distance, and energy. For example, in streams:

Particles are large and

irregular, and consist of

a variety of lithologies,

including the least

resistant.

Particles are mid-sized

and of intermediate

sphericity, and include

resistant and nonresistant

lithologies.

Particles are small and

nearly spherical, and

consist mainly of the

most resistant lithologies,

such as quartz.

HIGHLANDS

LOWLANDS

NEAR-COASTAL

slide16
Graded bedding

Floods change the local conditions

6_6

Fine-grained sediment

On floodplain

Older sediment

1

Pre-flood

Bounders on bottom, sands and muds suspended

Flood water

Erosion of uppermost

fine-grained sediment

2

Flood stage

Waning flow

Fine-grained above

Coarse-grained

below

Bedding plane

3

Post-flood

slide17
Sedimentary Facies
      • Different sediments accumulate next to each other at same time
      • Each unit (called a facies) possesses a distinctive characteristics reflecting the conditions in a particular environment
      • The merging of adjacent facies tends to be a gradual transition
slide18
Some Facies in an oversimplified drawing

Abyssal Ooze

Stillwater muds

Nearshore sands

cross beds are ripples in cross section
Cross Beds areripples in cross section
  • Irregularities lead to ripples, dunes, sand bars.
  • In cross section these look like lines at an angle to the horizontal – “cross beds”
  • Ripples can indicate direction of air or water flow if asymmetrical, a tidal environment if symmetrical. Size and shape indicate fluid velocity.
slide22
Cross bedding in Sand Dune deposits

Navaho Sandstone

Sandstone deposited

in ancient sand dunes

Frosted Grains, well sorted

slide23
Mud Cracks: clay layer shrinks during drying, curls upward; cracks fill next flood. Useful for right-side up
slide24
Terms for Marine (i.e. Ocean) Environments

and some characteristic sediment facies

6_27

Continental

slope

Muds

Continental

shelf

Sands

Shallow

marine

Abyssal

Plain

Turbidite Graded Beds

Ooze

Deep marine

Define Graded Beds

Submarine

volcanoes

slide28
Part 2

Metamorphism and Metamorphic Rocks

metamorphism
Metamorphism
  • … is the transformation of rock by high temperatures (heat) and pressure
  • Metamorphic rocks are produced by transformation of:
      • Sedimentary and Igneous rocks, and by the further alteration of other metamorphic rocks
  • These are the source of many important minerals

– Talc (lubricant, insulators, refractories), Corundum, Garnet (abrasives), Kyanite (ceramics), Micas (insulators), Chrysotile (“asbestos” for fireproofing), etc., etc.

slide30
Minerals do not melt during metamorphism

Sedimentary

rock

0km

Metamorphic

rock

Igneous

Sediment

rock

10 km

~200ºC

Sedimentary

rock

Metamorphismoccurs between about 10 and 50 km of depth

Metamorphism

Increasing depth

and temperature

50km

Melting

~800ºC

what causes metamorphism
What causes metamorphism?

1. Heat

  • Most important agent
  • Heat drives recrystallization - creates new, stable minerals
  • Increasing Heat with Depth
what causes metamorphism1
What causes metamorphism?
  • 2. Pressure (stress)
      • Increases with depth
      • Pressure can be applied equally in all directions or differentially
      • All Directions = “Confining Pressure”
      • Differential = “Directed Pressure”
origin of pressure in metamorphism
Origin of pressure in metamorphism

(Burial)

(Convergent Margin)

slide34
Directed Pressure causes rocks to become folded, and minerals to reorient perpendicular to the stress: “foliation”

Source:Kenneth Murray/Photo Researchers Inc.

main factors affecting metamorphism
Main factors affecting metamorphism

3. Parent rock

  • Metamorphic rocks usually have the same chemical composition as the rock they were formed from.
  • Different minerals, but made of the same atoms.
  • Exception: water carries in new atoms and removes others. Important at MOR and in subduction zones.
metamorphic settings
Metamorphic Settings
  • Three types of metamorphic settings:
      • Contact metamorphism – due heat from adjacent rocks
      • Hydrothermal metamorphism – chemical alterations from hot, ion-rich water
      • Regional metamorphism -- Occurs in the cores of mountain belts and subduction zones (Converging Margins) . Makes great volumes of metamorphic rock. Includes:
        • Burial Metamorphism – e.g. Burial of sediments deeper than 10 km – non-foliated
        • Dynamothermal Metamorphism – Directed pressure in Plate Tectonic Processes - foliated
contact metamorphism
Contact metamorphism

Produced mostly by local heat source

2 hydrothermal metamorphism
2.Hydrothermal Metamorphism
  • Due circulation of water near Magma
  • Important at mid-ocean ridge
slide40
Metamorphism in a Subduction Zone

Shallow Lithosphere

Near trench

Deep Lithosphere

metamorphic grade and index minerals
Metamorphic Grade and Index Minerals
  • Certain minerals, called index minerals, are good indicators of the metamorphic conditions in which they form
slide42
Certain minerals, called index minerals, are good indicators of the metamorphic conditions in which they form

Notice Quartz and Feldspars are useless

Note Quartz and Feldspar are not index minerals: Why?

Some index minerals give us temperature info

some useful as thermometers and pressure gauges
Some Useful as Thermometers and Pressure Gauges

Sillimanite

Kyanite

Polymorphs of Al2SiO5

Andalusite

slide44
7_21

CANADA

New England

Dynamothermal

Metamorphism

Mapped by index minerals

MAINE

Augusta

CANADA

U.S.A.

Montpelier

NEW

HAMPSHIRE

VERMONT

Concord

ATLANTIC

OCEAN

Boston

Albany

MASSACHUSETTS

NEW YORK

R.I.

Hartford

Providence

Binghamton

CONNECTICUT

Unmetamorphosed

y

e

Chlorite/muscovite zone

Low

grade

l

a

l

PENNSYLVANIA

v

Biotite zone

Scranton

Long

Island

Garnet zone

Medium

grade

t

f

Staurolite zone

i

r

NEW

Newark

High grade

Sillimanite zone

JERSEY

Increasing pressure and temperature

LOW GRADE

DIAGENESIS

HIGH GRADE

MELTING

INTERMEDIATE GRADE

Chlorite and muscovite

Biotite

Garnet

Staurolite

Sillimanite

common metamorphic rocks
Common metamorphic rocks
  • 1. Nonfoliated rocks
      • Quartzite
        • Formed from a parent rock of quartz-rich sandstone
        • Quartz grains are fused together
        • Forms in intermediate T, P conditions
common metamorphic rocks1
Common metamorphic rocks
  • Nonfoliated rocks (cont.)
      • Marble
        • Coarse, crystalline
        • Parent rock usually limestone
        • Composed of calcite crystals
        • Fabric can be random or oriented
slide47
Change in metamorphic grade with depth

Metamorphism of a mudstone

Increasing Directed Pressure and increasing Temps

a mica garnet schist
A mica garnet schist

Definition: Schist

Garnets are abrasives, long lasting bearings, and jewels

migmatites when partial melting starts
Migmatites- When Partial Melting Starts
  • Heat the rock, when the minerals with the lowest melting points (Quartz, Feldspar) at that pressure melt, then recrystallize. We get separate regions of Metamorphic (dark, mafic) and Igneous (light, felsic) rock

Part igneous, part metamorphic

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