ERTH115- Quiz 1 Plate Tectonics

• Geology is briefly introduced.

Minerals

• Minerals are basic building blocks.
• Minerals are naturally occurring and inorganic.
• Minerals are crystalline with an orderly atomic structure.
• Minerals have a narrow chemical composition.
• Minerals have characteristic physical properties associated with individual minerals.

Common Elements

• The most common elements in the Earth's crust are Oxygen, Silicon, Aluminum, Iron, Calcium, Sodium, Potassium, Magnesium.
• An acronym can be used to remember these: O Si Al Fe Ca Na K Mg
• Oxygen is almost half the volume of elements in the Earth's crust.
• Silicon and oxygen are the two major elements in Earth’s crust.
• The abundance of elements in the Earth's Crust by volume %:
  • Oxygen is 46.6%
  • Silicon is 27.8%
  • Aluminum is 8.1%
  • Iron is 5%
  • Calcium is 3.6%
  • Sodium is 2.8%
  • Potassium is 2.6%
  • Magnesium is 2%
  • Other is 1.6%

Mineral Identification

• Minerals can come in many colors, for example quartz can be rose, clear, or smoky gray.
• Color is an elementary property but is generally unreliable.
• Streak is the color observed by scratching the mineral on a porcelain plate.
• Streak is basically the powdered residue of that mineral.
• The Mohs hardness scale is from 1 (softest) to 10 (hardest).
• The Mohs hardness scale was developed during mining and is easy to test.
• Cleavage is the characteristic way minerals split/geometry as it breaks.
• Fracture patterns are distinctive for many minerals that don't cleave.
• Minerals that don't cleave have no zones of weakness, therefore no cleavage.
• Luster is how a mineral reflects light.
  • Examples are metallic, non-metallic, oily, earthy, and dull.
• Common minerals:
  • Feldspar
  • Quartz
  • Muscovite
  • Hornblend

Mohs' Hardness Scale

• 1: Talc: Very soft; Common Example: Pencil lead (1-2)
• 2: Gypsum; Common Example: Fingernail (2 1/2)
• 3: Calcite; Common Example: Copper penny, Brass
• 4: Fluorite; Common Example: Iron
• 5: Apatite; Common Example: Tooth enamel, knife blade, Glass
• 6: Orthoclase (potassium feldspar); Common Example: Steel file (6 1/2)
• 7: Quartz
• 8: Topaz
• 9: Corundum; Common Example: Sapphire, ruby
• 10: Diamond: Hardest substance; Common Example: Synthetic diamond

Types of Rocks

• There are three major types of rocks: igneous, sedimentary, and metamorphic.
• Igneous rocks are crystallized from molten or partially-molten material, namely magma.
• Sedimentary rocks are lithified fragments of pre-existing rocks, or rocks are formed by chemical or biological action.
• Sedimentary rocks are broken down pieces of other rocks that have been lithified into new rocks; they can also form through chemical or biological action.
• Metamorphic rocks are altered by heat, fluids, or pressure in a solid state.
• Metamorphic rocks are formed from intense heat/pressure change, but not to the point of melting.
• Igneous rocks cool and crystallize from a melt.
• Intrusive igneous rocks: magma has not made it all the way to the surface but has moved away from the source and cooled over time.
  • Granite can be an example, as it tends to have large crystal and be silica-rich.
• Extruded igneous rocks magma has erupted on the surface of the earth, and cooled quicker due to its exposure to air.
  • Magma is thinner and runnier, so it is able to make it to the surface of the earth.
  • It may either have small crystals or micro-crystals
  • Basalt is an example, as it is micro-crystalline and poor in silica content.
• Sedimentary rocks have been lithified or transformed by increased pressure, or chemical processes that form cementation.
• Clastic sedimentary rocks: made of pieces or fragments of other rocks that, through burial, increased pressure, or cementation are lithified into solid rock.
• Clastic sedimentary rocks are Predominantly Silica Rich.
• Shale is if the grains are smaller than sand-sized particles. Sandstone is if equal to sand-sized particles.
• Conglomerate is large than sand-sized particles. Formation Process:
  • 1. Weathering
  • 2. Erosion
  • 3. Transport
  • 4. Deposition
  • 5. Lithification into rock
• Chemical sedimentary rocks include rocks that have been precipitated directly from a solution; these are generally precipitates also evaporites.
  • Chemical limestone, aka micrite and halite (aka rock-salt, where salts form as evaporites) are examplse.
• Biogenic sedimentary rocks form form biological activity.
  • Coal, which forms from lithified plant debris and fossiliferous limestone, are examples.
  • Fossiliferous limestone is MADe from calcium carbonate, which forms in marine basins, from calcium carbonate shells that settle at the sea floor, and then lithify into rock.
• Metamorphic rocks have been altered by increased temperature and increased pressure, such as tectonic forces, burial, and mountain building processes, but are not altered to to he point of melting.
• The solid state can change.
• One can start with parent rock material (a protolith) and after increased temperature and pressure, this will create a metamorphic rock.
  • For example: sedimentary shale with increased temperature and pressure forms slate, then as it continues to undergo increased temperature and pressure, forms schist, and then as it continuous the solid-state mineralization will form bands and we get Nice
    • Shale (not metamorphic) > Slate > Schist > Nice
  • Sandstone (has silica) > quartzite
  • Limestone (has calcium carbonate) > marble

Overall Rock Cycle:

• The rock cycle illustrates how rocks change between igneous sedimentary and metamorphic types through various processes like melting, erosion, transport, deposition, etc.
• The type of rock can change as well: _ Clastic Shale -> Schist _ Limstone -> Marble
• Intrusive = Gra
  • Extrusive = Basi

Igneous Rock Composition and Texture

• Different minerals settle out and crystallize out of magma in different orders; mafic ones with Mg crystallize first, leaving behind a melt with more felsic minerals.
• Silica content is determined by fractionation history of parent magma.
• Mafic minerals are rich in magnesium and iron; they crystallize first.
• Felsic minerals are richer in silica and crystallize after.
• Intrusive rocks are slow cooling (phaneritic).
• Extrusive rocks are Fast cooling (aphanetic) can have same composition but different textures.
• Glassy cools very fast; extrusive rocks have micro-crystalline. Texture.

Sedimentary Rocks

• Lithified sediments are turned to stone by pressure and/or cementation.
• Clastic sedimentary rocks contain clasts from preexisting rocks. "Clasts" are fragments.
• Chemical sedimentary rocks are chemically precipitated.
• Biogenic sedimentary rocks stem from biological activity.

Metamorphic Rocks

• Metamorphic rocks change in solid state from preexisting rocks by heat, pressure, and/or chemical processes.
• The process creates textures and new structures.
• Foliation is flattening and layering of minerals by non-uniform stresses.
• Re-crystallization occurs when heat or uniform stresses create larger, more perfect grains.

Common Metamorphic Rocks

• Foliated/Layered: _ Slate is formed from shale and mudstone. It splits into thin sheets. _ Schist originates from fine-grained rocks, silt-stone, shale, and/or tuff. It features mica minerals that often appear crinkled. _ Gneiss comes from coarse-grained rocks. It has aligned minerals making dark and light layers.
• Non-foliated/Re-crystallized: _ Marble springs from limestone. It features interlocking crystals. _ Quartzite is formed from sandstone. It features interlocking almost fused quartz grains.

Earth's Layers

• A solid inner core and a liquid outer core are present.
• The core is comprised mostly of metallic iron and nickel, so, the core is very dense.
• The mantle is magnesium-silicate, is the thickest layer, and convects in convection cycles and convection cells.
• The crust is thin; a "skin".
  • Oceanic crust of, has mostly basaltic rocks, and is dense and mafi.
  • Continental crust is, is mostly silica-rich igneous and sedimentary rocks ,and is less dense and felsic.
• Earth's crust to planet ratio:
  • Is the same as skin of apple to everything else inside. Meaning the crust is very thin compared to our planet.
• Hot chocolate analogy:
  • The continental crust is the marshmallows on top.
• From the asthenosphere down, everything is moving in convection cells and is in motion.

Tectonic plates

Tectonic plates: imagine chunks of hot chocolate or marshmallows breaking up.

• With plate boundaries, there is sea-floor spreading/ new material emerging. Plates move due to sea flooring spreading- can push or pull the tectonic plate.
• Pacific Plate- where Santa Barbara is, but is almost entirely oceanic
• Tectonic settings:
• Cascades, Mt Shasta: Continental-oceanic convergent boundary
• Himalayas: Continental-continental convergent plate
• Hotspots are not part of the normal convection cell or cycle; they are a point of heat that makes its way all the way up, creating volcanism at the surface.
  • Hawaii is an example.
• Continental crust:
  • will start to thin over time as the cell moves away.
  • can break into two pieces of continental crust > new oceanic crust > new ocean floor > "CONTINENTAL RIFT" AT A DIVERGENT PLATE BOUNDARY.
  • MID-OCEAN RIDGES are an example.
• If two pieces of continental crust collide:
  • Moving towards one another, as they push (same density) > mountain building in a "CONTINENTAL INTERACTION" AT A CONVERGENT PLATE BOUNDARY.
  • The Himalayas are an example.
• If continental crust moves towards oceanic crust:
  • The difference in density at a convergent plate boundary is that the more dense oceanic crust dives below > melt > becomes less dense, more buoyant > volcanism > OCEANIC-CONTINENTAL, PLATE SUBDUCTION RESULTING IN VOLCANISM.
  • CASCADE RANGE LIKE IN MT SHASTA OR MT ST HELENS IN WASHINGTON are examples
• OCEANIC/OCEANIC INTERACTION also exists-
  • As it comes to the surface, cools, and pushes apart continuously > new sea floor
• Plate boundaries will be either divergent or convergent, then, depending on either continental or oceanic.
  • Tension pulls plates apart and will eventually become two separate continents
    • Continental crust: east african rift valley
    • Oceanic crust: mid ocean ridge
      • seafloor spreading, plates move away from each other
• Volcanic erruptions are divergent boundaries
• Compression drives plates together.
  • Oceanic-Continental:
  • Subduction of oceanic crust under continental crust, major earthquakes, volcanic eruptions.
• Continental-Continental:
• Evident from structure of the himalayan mountain formations.

Plate Boundaries

• Convergence drives plates together.
• Oceanic-Continental Subduction or oceanic crust under continental crust create major earthquakes and/or volcanic eruptions. Continental-Continental interactions cause mountain-building.

Accretion

• Sometimes Subducting slab will carrying more continental rock on top of it. The Continental rock gets moved
• Add onto the sieze of continental rock
• plate boundaries.
  • Lots of earthquakes/shearing in Santa Barbara Shear forces cause plates to slide horizontally
• Long Linear faults:
  • San Andreas Fault in CA
  • Pacific moves to the NW, NA moves SE!
  • small sliver of crust being sheared in NA, including SB and SF.

Plate Motion Over Hot Spot

• Plate movement over a fixed hot spot creates long volcanic island chains.
• The end islands of the chain are older than their neighbors. -Example: Hawaii
• The current islands over the hot spot contains the most volcanic activity:
  • As a plate moves over a hot spot, whatever is currently over that hotspot is where the current volcanic activity will be, and as it moves, Hawaii will move off the hotspot, and the Loihi will start to grow in continental land mass.

Geologic Time

• Geologic Time studies dating and relationships of geological events
• Relative age determines sequences of events.
• Absolute age dating provides new dates.
• Law of Fossil succession: indicator fossils
• Radiometric dating
  • Radioactive element decay and release particles
• Stay the same or be a new element.
• Alpha decay : release Helium
• Beta Decay : release elctrons
• Half life is amount required to of atoms to decay
• Different compounds have different half lines and can be uses for different age ranges.

Reletive-Age Dating

• Structural relations of rocks: Law of Superposition: In unnderformed seimentary rocks

• The top layer is youngest

• Law of cross cutting reationships : fault is younger than the youngest rocks in its cut.

  • Principle of orginal horizontality : Material was orginally depostited horiznttally

• Discinuitnity: Beaks in geogicalquence : angular ,non compoformtity, discomforit

• Inculstions Oldent than rock found in

• INtutions Younver than rock formatution that intrure upon.