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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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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


    • 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)


    http://www.ndsu.nodak.edu/instruct/ashworth/coursework/g410/evaporites/saltbeds.jpghttp://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


    Chemical sediments coal
    Chemical Sediments: Coalhttp://www.ndsu.nodak.edu/instruct/ashworth/coursework/g410/evaporites/saltbeds.jpg


    Sedimentary environment determines roundness sorting, mineral diversity

    6_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


    Graded bedding mineral diversity

    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


    • Sedimentary mineral diversityFacies

      • 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


    Some Facies in an oversimplified drawing mineral diversity

    Abyssal Ooze

    Stillwater muds

    Nearshore sands


    Strata bedding planes
    Strata- Bedding Planes mineral diversity



    Cross beds are ripples in cross section
    Cross Beds are mineral diversityripples 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.


    Cross bedding in Sand Dune deposits mineral diversity

    Navaho Sandstone

    Sandstone deposited

    in ancient sand dunes

    Frosted Grains, well sorted


    Mud Cracks: clay layer shrinks during drying, curls upward; cracks fill next flood. Useful for right-side up


    Terms for Marine (i.e. Ocean) Environments cracks fill next flood. Useful for right-side up

    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



    Dinosaur footprint in mudstone
    Dinosaur footprint in mudstone in sedimentary rock


    End of sedimentary rocks

    End of Sedimentary Rocks in sedimentary rock


    Part 2 in sedimentary rock

    Metamorphism and Metamorphic Rocks


    Metamorphism
    Metamorphism in sedimentary rock

    • … 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.


  • Minerals do not melt during metamorphism in sedimentary rock

    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? in sedimentary rock

    1. Heat

    • Most important agent

    • Heat drives recrystallization - creates new, stable minerals

    • Increasing Heat with Depth


    What causes metamorphism1
    What causes metamorphism? in sedimentary rock

    • 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 in sedimentary rock

    (Burial)

    (Convergent Margin)


    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 minerals to reorient perpendicular to the stress: “foliation”

    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 minerals to reorient perpendicular to the stress: “foliation”

    • 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 minerals to reorient perpendicular to the stress: “foliation”

    Produced mostly by local heat source


    2 hydrothermal metamorphism
    2. minerals to reorient perpendicular to the stress: “foliation”Hydrothermal Metamorphism

    • Due circulation of water near Magma

    • Important at mid-ocean ridge


    Hydrothermal metamorphism
    Hydrothermal Metamorphism minerals to reorient perpendicular to the stress: “foliation”


    Metamorphism in a Subduction Zone minerals to reorient perpendicular to the stress: “foliation”

    Shallow Lithosphere

    Near trench

    Deep Lithosphere


    Metamorphic grade and index minerals
    Metamorphic Grade and Index Minerals minerals to reorient perpendicular to the stress: “foliation”

    • Certain minerals, called index minerals, are good indicators of the metamorphic conditions in which they form


    Certain minerals, called minerals to reorient perpendicular to the stress: “foliation”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 minerals to reorient perpendicular to the stress: “foliation”

    Sillimanite

    Kyanite

    Polymorphs of Al2SiO5

    Andalusite


    7_21 minerals to reorient perpendicular to the stress: “foliation”

    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 minerals to reorient perpendicular to the stress: “foliation”

    • 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 minerals to reorient perpendicular to the stress: “foliation”

    • Nonfoliated rocks (cont.)

      • Marble

        • Coarse, crystalline

        • Parent rock usually limestone

        • Composed of calcite crystals

        • Fabric can be random or oriented


    Change in metamorphic grade with depth minerals to reorient perpendicular to the stress: “foliation”

    Metamorphism of a mudstone

    Increasing Directed Pressure and increasing Temps


    A mica garnet schist
    A mica garnet schist minerals to reorient perpendicular to the stress: “foliation”

    Definition: Schist

    Garnets are abrasives, long lasting bearings, and jewels


    Gneiss displays bands of light and dark minerals
    Gneiss displays bands of light and dark minerals minerals to reorient perpendicular to the stress: “foliation”


    Development of foliation due to directed pressure
    Development of foliation due to directed pressure minerals to reorient perpendicular to the stress: “foliation”

    Granodiorite

    Gneiss


    Migmatites when partial melting starts
    Migmatites- When Partial Melting Starts minerals to reorient perpendicular to the stress: “foliation”

    • 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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