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Rocks: Sedimentary Igneous Metamorphic Keepers of Earth’s History 1.

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Presentation on theme: "Rocks: Sedimentary Igneous Metamorphic Keepers of Earth’s History 1."— Presentation transcript:

1 Rocks: Sedimentary Igneous Metamorphic Keepers of Earth’s History 1

2 Granite What’s in your rock?: Hornblende Orthoclase Quartz
aggregates of minerals Biological material Fossil fragments Plant material 3

3 Understanding rocks is the basic foundation of
knowledge for earth scientists and materials that make up the earth. Every rock “speaks” to the observer and gives clues about where and how it was formed. Rocks are divided into 3 major groups: Igneous formed from solidifying hot molten rock (magma) Sedimentary formed on the surface of the earth from weathering processes Metamorphic pre-existing rocks are subjected to various pressure and temperature relationships 4

4 All rocks are identified based on their texture and composition.
How does an earth scientist distinguish between the three rock types (Ig, Seed, and Met)? Texture: the appearance of the rock size, shape, and arrangement of mineral grains. Composition (mineral assemblages) types and relative proportions of minerals making up a rock composition, mineral make-up, chemistry--all indicators of a rock’s composition All rocks are identified based on their texture and composition. 5

5 6 The Rock Cycle The Sedimentary Cycle

6 where the earth’s internal forces meet
The Rock Cycle: where the earth’s internal forces meet the earth’s external forces (at the earth’s surface) 7 Earth’s internal forces Earth’s external forces the hydrosphere (HC) atmosphere erosion (wind, water, ice) biosphere activities moving continents (PT) earthquakes elevation of mountains volcanic eruptions Produce a continuous cycle of rising mountains only to be weathered down and uplifted repeatedly. As a result, igneous sedimentary, and metamorphic rocks are created.

7 I Earth Science, especially the rock cycle !!!!!!!!!!!!! 8
Discuss with a friend: Briefly identify each rock group and its geologic environment. 2. Draw the rock cycle, and explain how the rock cycle works to your neighbor. 3. Why is the rock cycle a “cycle”??? I will get an A on my exams and quizzes.

8 Geology – Chapter 3 – Igneous Rocks

9 Magma Extrusive - igneous rocks – above the earth’s surface
the parent material for igneous rocks (if not all rock groups) typical temperature 1,200oC (2,200oF) forms about 250 km or 150 miles below the earth’s surface Extrusive - igneous rocks – above the earth’s surface volcanic rocks lava flows Example – Hawaiian Volcanoes Intrusive - igneous rocks – below the earth’s surface plutonic rocks large granite mountains Example – Sierra Nevada Mountain Range 10 Grain size determines if the ig rock is extrusive or intrusive. Magma determines the rock’s composition.

10 surface (fine-grained) surface (coarse-grained)
When observing “frozen magma” (an igneous rock), how does a geologist know if the rock is an Extrusive or Intrusive igneous rock? checking the crystal size - Does the rock contain visible crystals, or are crystals non-existent? Igneous Rock Textures Factors that affect crystal size in an igneous rock: The rate at which magma cools slow cooling – visible minerals rapid cooling – non-visible minerals visible minerals slow cooling magma intrusive ig rock non-visible minerals rapid cooling magma extrusive ig rock Cooled above the surface (fine-grained) Cooled below the surface (coarse-grained) 11

11 Composition of Igneous Rocks 14
How much silica (SiO2) is in your igneous rock? Felsic compositions (feldspar + silica) light-colored igneous rocks common minerals: feldspar and quartz 70% SiO2 Intermediate compositions: mixture of felsic and mafic minerals about 60% silica (SiO2) Mafic compositions (magnesium + iron) dark-colored igneous rocks common minerals: olivine and pyroxene 50% SiO2 ultramafic: composed entirely of olivine and pyroxene and less than 50% silica (SiO2)

12 How are igneous rocks classified? Using their TEXTURE and COMPOSITION
Igneous rocks are classified based on TEXTURE and COMPOSITION. COMPOSITION Felsic (light color) 70% silica Intermediate color 60% silica Mafic (dark color) 50% silica phaneritic COARSE Granite Diorite Gabbro TEXTURE aphanitic FINE Rhyolite Andesite Basalt Igneous rocks have the same chemistry but different textural characteristics due to the type of geologic environment (cools quickly or slowly).

13 I Earth Science, especially igneous rocks.
What is the difference between extrusive and intrusive igneous rocks? 2. How can one tell the difference between an extrusive and intrusive rock texture? 3. The composition of a mafic ig rock is…. The composition of a felsic ig rock is …. 4. A fine-grained, light-colored ig rock is called a …………………. I will get an A on my exams and quizzes. 17

14 Sedimentary Rocks 18

15 How is a sedimentary rock formed??? 19
Why is the earth’s surface 75% sedimentary rocks? erosion Pre-existing Rock sediment water, wind, ice breaks down pre-existing rock Rivers Deposited transported Lakes lithified compacted cemented Sedimentary Rock

16 Erosional processes – later (Chapter 4)
21 Erosional processes – later (Chapter 4) Sediments are separated into 3 broad categories: Clastic sediments: inorganic grains or mineral fragments ranging in size from boulders to clay particles (flour size) Chemical sediment: formed by the precipitation of minerals dissolved in lakes, rivers, or seawater environments Biogenic (bioclastic) sediment: sediment composed of animal and plant remains or material precipitated by biological processes To be a sedimentary rock, it must be lithified.

17 Lithification: processes by which sediment is
transformed into sedimentary rock Sediment can be lithified in three common processes: Compaction: Overlying weight of the sediment “squeezes” and compresses pore spaces, which pushes particles together. A. loose, unconsolidated sediment with abundant pore space B. compacted, compressed sediment with reduced pore space A B Cementation: Pore water is expelled from voids, and rising water carries iron, calcium carbonate, and silica which precipitates as geological glue (cement) holding the grains together. Grains are cemented together by three types of cements: iron cement calcium carbonate cement silica cement 22

18 Grain boundaries convert compositions, “cementing”
Lithification processes Recrystallization: Overlying pressure causes less stable minerals to convert to more stable minerals, producing new substances that cement pre-existing grains. Grain boundaries convert to more stable mineral compositions, “cementing” grains together. Overlying pressure 23

19 Clastic Sediment: conglomerate sandstone siltstone shale 24 lithified
gravel sediment ranging from pea-sized to larger conglomerate lithified sand-sized particles (fine to coarse sandpaper) sandstone lithified finer particles – size of table salt siltstone finest sedimentary particles (flour-size) lithified shale 24

20 Chemical Sediments and Sedimentary Rocks
Chemical Sediment: sediment formed by the precipitation of minerals dissolved in a lake, river, or seawater All surface water and groundwater contain dissolved ions (chemicals), creating a venue for precipitation of chemical sediment. Precipitation of chemical rocks takes place in two ways: Plants and animals alter the chemical balance of the water body (lake, ocean). Increasing amounts of calcium carbonate cause precipitation of limestone. evaporation of chemically saturated water bodies 26

21 Evaporation of chemically saturated water creates
a chemical sedimentary rock (evaporite). Na+ Na+ Cl- a lake containing sodium (Na+) and chlorine (Cl-)--free ions Cl- Cl- Na+ Na+ Cl- Evaporation Lake water is evaporated, concentrating sodium and chloride ions (saturation). Sodium and chlorine combine to form halite (table salt). NaCl 27

22 The Great Salt Lake, Utah
(evaporite halite) 28 As lake becomes saturated, density of water increases. Utah

23 Chemical – sedimentary rocks that have been
precipitated or are the result of evaporation Gypsum – evaporite CaSO4 Halite – evaporite NaCl Limestone-- precipitated calcium carbonate 29

24 Biogenic Sediments and Biogenic Rocks:
Biogenic sediment is composed of organic remains of plants and animals (bioclastic rocks). shell, bones, teeth, plant fragments, wood, roots 30 Common Biogenic Rocks: Limestone most abundant biogenic sedimentary rock composed of calcium carbonate CaCO3(calcite, dolostone, aragonite) lithified shells, skeletal material Chert composed of silica SiO2 precipitated silica shells (made by sea animals) that protect microscopic sea animals – Animals die, and silica shells sink, creating layers of chert beds on the ocean floor. “When the animal dies, it loses the chert off its back.”

25 Common Biogenic Rocks 31 Peat to Coal Peat Anthracite coal
accumulated remains of terrestrial plants with time and pressure ---- peat continued pressure and lithification coal lithification Peat Increasing pressure metamorphism Anthracite coal Bituminous coal

26 Biogenic (bio-clastic) rocks –
result from animal and plant secretions -- The term “clastic” indicates that these rocks contain fossils or parts of plants, shells, compacted plant material Animal parts Cemented shell fragments Fossil Limestone Microscopic fossils Coquina 32 Chalk

27 What do sedimentary rocks tell the earth scientist?
These rock “layers” were deposited one layer at a time and lithified. The banded appearance is known as bedding or groups of layers called strata. The boundary between each stratum is called a bedding surface. Bedding surface bedding strata By observing the sedimentary rock type (clastic, chemical, biogenic) and depositional patterns, an earth scientist can decipher the geologic history – like reading pages in a book. 33

28 Sedimentary Rock Classification Summary Tree
Sedimentary Rocks are divided into 3-classification categories: Clastic sediments Chemical sediments Bio-clastic (chemical) sediments formed by precipitation composed of “animal parts” composed of inorganic grains from plants and animals evaporation processes Classification based on Observed fossils, animal parts, Plant/animal secretions classification based on distribution of grain sizes Classification based on lack of grains and chemical composition Fossil-limestone Conglomerate Gypsum (CaSO4) Sandstone Coquina Decreasing grain size Siltstone Halite (NaCl) Chalk Shale Limestone (CaCO3)

29 I sedimentary rock classification. 36 Discuss with a friend:
Describe at least 2 characteristics of each sedimentary rock classification (clastic, biogenic, chemical). Give a rock example for each classification. I will get an A on my exams and quizzes.

30 Metamorphic Rocks 37

31 What is “metamorphism?”
meta (change) morphism (form) transformation of pre-existing rock to a metamorphic rock through pressure and temperature relationships All changes take place through solid state transformation. 38

32 takes place around 150oC (Temperature)
Types of Metamorphism takes place around 150oC (Temperature) typically at depths of 5 km below the earth’s surface (Pressure) At this temperature and pressure, new minerals are formed – changed from one mineral to another. 39

33 I metamorphic rocks. Discuss with a friend:
How do you define metamorphism? – Be specific. What two major factors are necessary for pre-existing rocks to become metamorphosed? 3. Where does metamorphism typically take place within the earth? I will get an A on my exams and quizzes. 40

34 2 Common types of metamorphism
contact metamorphism regional metamorphism 44

35 What is contact metamorphism?
magma “contacts” solid rock – heat is transferred into overlying rocks through conduction – changing the pre-existing rock it intruded high heat/low pressure localized metamorphism “fast-acting,” like touching a hot frying pan 45

36 Country rock (surrounding) is baked from conduction.

37 What is regional metamorphism?
Pre-existing rock is subjected to intense stresses and strains (deformation) usually from the forces of mountain building. high heat/high pressure very widespread geographically like experiencing a slow sunburn 47

38 Mountain building widespread belts 48

39 I the different ways to create Metamorphism. Discuss with a friend:
Describe the conditions necessary for each type of metamorphism: contact metamorphism regional metamorphism I will get an A on my exams and quizzes. 49

40 Metamorphic heat sources:
contact with hot magma – heat penetrates overlying rocks (conduction) geothermal gradient – heat increases with depth – rocks are hotter when buried 50

41 51 Geothermal Gradient Steep gradient Temperature increases
as depth increases. Large thermal gradient is at the surface. Gradient decreases after 1000 km depth. Steep gradient 1000 2000 3000 4000 51

42 Pressure – increases with depth,
Pressure associated with metamorphism 52 Pressure – increases with depth, various types of pressure rearrange minerals – minerals compact or elongate Confining pressure Differential pressure

43 How does one know how much metamorphism has taken place in a rock?
53 How does one know how much metamorphism has taken place in a rock? reflected in the rock’s texture Metamorphosed – mineral grains are in a preferred direction -- FOLIATION Not Metamorphosed

44 I to metamorphose. 54 Discuss with a friend:
Describe two heat sources associated with metamorphism. Define the differences between confining and differential pressures. 3. Draw a diagram that shows mineral orientation due to confining and differential type pressures. I will get an A on my exams and quizzes.

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