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CEE 437 Rocks! Thomas Doe.

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Presentation on theme: "CEE 437 Rocks! Thomas Doe."— Presentation transcript:

1 CEE 437 Rocks! Thomas Doe

2 Outline Igneous Rocks Sedimentary Rocks Metamorphic Rocks
Rock Identification Lab

3 Rock Cycle Magma Igneous Rocks Metamorphic Rocks Sediments
Crystallization at depth or extrusion at surface Magma Melting Igneous Rocks Burial, metamorphism, recrystallization Metamorphic Rocks Weathering, Erosion Sediments Burial, metamorphism, recrystallization Sedimentary Rocks Lithification

4 Northwest Igneous and Metamorphic Rocks
Cascade Volcanoes (recent) Cascade Batholiths (Felsic, Cret-Miocene) Columbia River Basalts (miocene) Recent Basaltic Volcanism (Newberry Crater) Yellowstone Region Acidic Volcanics (Pleistocene to recent) Snake River Basalts (pliocene)

5 Geologic Settings for Igneous Rocks
Oceanic Hi Fe, Mg, Ca, low Si basalt, gabbro Continental Hi Si, Na, K granite, rhyolite, andesite

6 Igneous Origins Intrusive Extrusive
Batholithic or plutonic: phaneritic Dikes or sills that chill rapidly: aphanitic Extrusive deposition as melt (lava) pyroclastic tuff tephra pyroclastic flows

7 Identifying Igneous Rocks
Chemistry Acidic: Basic (more Si, less Si) Texture Aphanitic: crystals not visible Phaneritic: made of visible crystal components Porphyritic: Larger crustals in aphanitic or phaneritic ground mass

8 Igneous Rock Classification
Acidic, Felsic Basic, Mafic Ultramafic SERPENTINITE

9

10 Magma Generation on Continental Margins

11 Magma Generation in Convergent Continental Plate Margins

12 Extrusives Viscosity varies with Si and water content
Basalt — low viscosity Rhyolite — high viscosity Rhyolite flows relatively unusual as rhyolite does not flow well Explosive Tuffs, pyroclastics

13 Volcano Types Basaltic: low viscosity — Hawaii, Columbia Plateau
Andesitic/Rhyolitic

14 Structures of Basalt Flows
Lava Tubes Flow Stratigraphy collonade entablature flow top breccia/scoria

15 Hawaii Basalt Flows

16 Basalt Flow Structures

17 Eruptions of Acid-Rock Volcanoes

18 Rhyolite Dome

19 Caldera

20 Mt. St. Helen’s Blast Zone

21 Mt. Mazama Ash Distribution

22 Sedimentary Rocks Clastics, Siliciclastics, and Evaporites
Clastic rocks, depositional medium, and energy Diagenesis — chemical changes after deposition

23 Rock Cycle Magma Igneous Rocks Metamorphic Rocks Sediments
Crystallization at depth or extrusion at surface Magma Melting Igneous Rocks Burial, metamorphism, recrystallization Metamorphic Rocks Weathering, Erosion Sediments Burial, metamorphism, recrystallization Sedimentary Rocks Lithification

24 Sediment Sources

25 Clastic Sedimentary Rocks
Clastic — broken like iconoclast) Often referred to as Siliciclastics as having Si based rock forming minerals Based on grain size and to a lesser extent composition Grain size related to energy of depositional environment Relationship of medium velocity to maximum grain size)

26 Clastic Sedimentary Rocks
Clay, muds  shales, mudstones, claystones (difference based on fissility) Silts  siltstones Sands  sandstones Gravels  Conglomerates (Breccia if angular, breccia may also be a term for tectonically fragmented rock)

27 Weathering Cycle

28 Clastic Sediments

29 Clay Minerals Sheets of linked silica tetrahedra sandwiching octahedral layers of gibbsite composition, Al2(OH)6, or brucite Mg3(OH)6 Major Clay Groups kaolinite: single gibbsite layer montmorillonite:weak water bonding between layers, moderated by Ca, Na, or K (near-shore environments) illite: K bonds between layers (off-shore environments) bentonite: highly expansive, volcanic-derived, Na-rich montmorillonite

30 Clay Structure

31 Clay Structure Cont’d. Kaolinite Montmorillonite Illite

32 Lithification Cementation Crystallization Compaction Diagenesis
deposition of a material different from clasts Crystallization crystal growth on clasts to fill pore space Compaction Diagenesis Early post-depositional chemical transformation of sediments, e.g. calcite to dolomite

33 Carbonates Generally like siliciclastics — carbonate muds, sands, etc.
Often deposited in reefs Major portion of world oil deposits Properties depend strongly on post-depositional pore chemistry Cementation Dissolution

34 Carbonate Environments

35 Evaporites Rock salt (NaCl), Gypsum-Anhydrite (CaSO4), Sylvite (KCl)
Deposition in regions where evaporation exceeds recharge desert lakes restricted seas (Mediterranean) lagoons, back-reef areas Subject to flow and diapirism

36 Other Sedimentary Rocks
Chert: finely crystalline silica as replacement/diagenetic nodules as bedded material from silica-shelled biota Coal Derived from vegetation Banded Iron Formation Likely bacteria derived, mainly Pre-Cambrian

37 Sedimentary Rocks and Rock Properties
Properties for a given geologic description vary wildly based on cementation, porosity and other diagenetic factors. Properties can be strong anisotropic and heterogeneous based on bedding

38 Depositional Environments
Synchroneity of deposition of different rock types Sedimentary facies A rock unit is not everywhere the same age: Bright Angel Shale Related to energy of environment (example channels and banks in fluvial systems) Energy related to topography, climate, and tectonic activity

39 Sediment Sorting

40 Sedimentary Structure — Cross Bedding

41 Fluvial and Lacustrine Environments
Channelization Complex and close interrelationship of fine and course sediments Challenge for characterization due to high variability Special examples: glacial environments Lacustrine Deltaic deposits at margins, finer materials in lake beds

42 Deltaic Environments Variability based on proximity to source
Stratigraphy effected by progradation

43 Deltaic Development and Sedimentary Facies

44 Continental Slope Environments
Turbidites and turbidity currents Graded bedding poor sorting vertical zonation with fining upwards

45 Turbidites and Turbidity Currents

46 Metamorphic Classification
Original Material sandstone, limestone, shale, basalt) Metamorphic Grade (Temperature, Pressure) Source of Metamorphism (Regional, Contact)

47 Basic Metamorphic Types
Quartz Sandstone  Quartzite Limestone, Dolomite  Marble Shale  Slate — cleavage, no visible xl’s Phyllite — foliation, mica sheen but xl’s not visible Schist — clear foliation, visible mica Gneiss — like granite but with foliation/gneissosity Basalt  greenschist, amphibolite

48 Non-foliated Metamorphic Rocks
Sandstone —> Quartzite Limestone —> Marble Dolomite —> Dolomitic Marble

49 Foliated Metamorphic Rocks
Shale/Mudstone Slate Phyllite (Greek for leaves e.g. phyllo dough) Schist Gneiss

50 Origin of Foliation (gneissosity, schistosity)

51 Engineering Properties
Anisotropy of strength and elastic properties Preferred failure on foliation

52 Slate

53 Phyllite

54 Schist

55 Chlorite Schist

56 Gneiss

57 Banded Gneiss

58 Metamorphic Grade

59 Subduction-Zone Metamorphism

60 Metamorphism at Continental Collisions

61 Contact Metamorphism


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