Chapter 6 Tectonic Settings Continued Chapter 5 Tectonic Settings
Volcanic Processes and Eruption Styles 1. Plate Tectonics and Ridge Mechanics
Magma Composition and Volatiles: Magma is a mixture of molten rock (melt), suspended solids (crystals or country rock), and volatiles such as Ridge Axis: The formally known center line of a mid-ocean ridge that serves as the "spreading center" where magma rises to form new crust.
$H_{2}O$, $CO_{2}$, and $SO_{2}$. At depth, high confining pressure keeps these volatiles dissolved. As magma rises and pressure decreases, Ridge Push: A critical driver of plate movement where gravity causes newly formed oceanic crust to slide atop the asthenosphere, moving away
volatiles exsolve to form bubbles; the expansion of these bubbles is the primary driver of explosive eruptions. from the ridge axis.
Eruption Style Determinants: Composition alone does not predict eruption style. While low-silica mafic magmas are usually effusive and high- Slab Pull: The primary driver of subduction where the weight of a dense, sinking oceanic plate pulls the rest of the plate down with it.
silica felsic magmas are usually explosive, exceptions exist. Mafic magma can be explosive if it interacts with external water (phreatomagmatic Lithospheric Thickening: The lithosphere thickens as it moves away from the ridge because it loses heat to the ocean, causing the underlying
eruptions), and felsic magma can be effusive if it contains little gas or if the gas escapes gradually during a slow ascent. asthenosphere to cool, solidify, and transform into rigid lithospheric mantle.
Sector Collapse: This refers to the structural failure of a volcanic edifice. It can trigger an explosive eruption by rapidly reducing the confining Absolute vs. Relative Motion: Relative motion describes plates moving compared to each other (e.g., North American vs. Eurasian plates). Absolute
pressure (the weight of overlying rock) on the magma chamber, causing dissolved gases to expand violently. motion describes plate movement relative to a fixed point in the deep mantle, such as a mantle plume.
Lava Textures: Basaltic (mafic) flows often form 'A'a lava, which is rough and vesicular because gas escapes easily. Intermediate to felsic flows Ridge Jump: A process where a spreading center reorganizes by linking a mid-ocean ridge to new fissure swarms, causing the former ridge segment
are often "blocky," featuring smooth, angular blocks with fewer vesicles because they have less gas and higher viscosity.Stratovolcanoes and to become inactive.
Deposits: Stratovolcanoes consist of alternating layers of lava flows and pyroclastic deposits, reflecting changing gas content and eruption 2. Physics and Chemistry of Magma
styles over time. Ignimbrites are formed from hot pyroclastic flows that weld together. Tephra layers are best preserved in quiet environments Magma Composition: Composed of "melt" (liquid rock), dissolved gases, water vapor, silicon, oxygen, and metallic cations. Crystalline Solid (Crystal):
like lakes or marine basins rather than on land where they are easily eroded. Characterized by a repeating pattern where atoms are fixed and do not move or change neighbors. Liquid Melt: Lacks a repeating structure; atoms
Lahars: These are volcanic mudflows (water mixed with ash and debris) triggered by rainfall, snowmelt, or lake drainage. appear randomly and chemical bonds are dynamic, allowing atoms to shift and change neighbors. Glassy Solid (Glass): A non-crystalline solid formed
Earthquake Mechanics and Megathrust Events when magma cools instantaneously, freezing atoms in their random liquid positions before crystals can grow. Chemical differentiation: The process
Elastic Rebound: The lithosphere is rigid but can bend elastically under stress like a rubber band. Earthquakes store energy through this elastic where distinct layers or compositions form within a body due to the physical segregation of materials based on density or affinity. For instance, both
deformation. When the stress overcomes friction at a locked plate boundary, the lithosphere rebounds to its original shape, releasing energy as an fractional crystallization and partial melting results in chemical differentiation. Nucleation: The start of crystallization, where a few atoms form a bond
earthquake. to create a "nuclear seed". Cooling Rates: Slow cooling starts from fewer nucleation seeds, allowing crystals time to grow large (coarse-grained). Fast
Megathrust Earthquakes: These occur at subduction zones where friction between the subducting and overriding plates locks the boundary. They cooling creates many simultaneous nucleation seeds that have little ime to grow, resulting in many tiny crystals (fine-grained).
involve massive fault areas and release enormous energy. They generate tsunamis through sudden seafloor displacement.
3. Igneous Rock Types and Textures
Vertical Movement: During a single megathrust event, different regions can experience simultaneous uplift and subsidence over minutes.
Basalt vs. Gabbro: Both have the same chemical composition, but basalt is fine-grained due to rapid cooling at the surface, while gabbro is coarse-
Tsunamis: Tsunami heights increase near distant shorelines because wave speed decreases in shallow water, causing the waves to compress and
grained due to slow cooling in underground magma chambers.
grow taller (shoaling).
Pillow Lava: Formed when magma hits cold water, creating a hard outer crust while the warm interior continues to push forward until the pressure
Tectonic Settings and Regional Geography breaks the crust into spherical shapes. The crust is glassy because cooling is instantaneous.
Continental Margins: Components include the continental shelf, slope, and rise. The slope is typically steeper than the shelf. Sheeted Dikes: Formed at mid-ocean ridges as magma travels through vertical fissures; as seafloor spreads, new dikes are injected into the center,
Plate Boundary Types: Plate boundaries control faulting styles: subduction zones produce thrust/megathrust faults, while transform boundaries creating parallel vertical sheets.
(like the San Andreas Fault) produce strike-slip faults where plates slide horizontally. Columnar Basalt: Formed as thick lava flows contract while cooling; they fracture into vertical hexagonal columns because hexagons are the most
Specific Regions: efficient shape to relieve tensile stress with the shortest boundary length.
Cascadia: Small plates (Juan de Fuca, Explorer, Gorda) subduct under the North American Plate, creating megathrust risk for regions like Magmatic Differentiation: In a magma chamber, dense mafic minerals (rich in iron and magnesium) crystallize early and sink to the bottom, while
Vancouver. the remaining melt becomes enriched in silica.
Chile: The 1960 magnitude 9.5 earthquake was a megathrust event caused by subduction.
Aleutian Arc: Formed by ocean-ocean and ocean-continent subduction. 4. Case Study: Iceland and the Laki Eruption
San Francisco: Located on a transform boundary (San Andreas Fault) involving strike-slip faulting. Iceland's Elevation and Thickness: Iceland's crust is 30-40 km thick (vs. the 7 km average) because a mantle plume provides excess magma. It stays
Asia/Himalayas: The India-Eurasia collision involves a "rigid indenter" (India) colliding with Eurasia. This causes continental crust to thicken and above sea level because the plume's heat keeps the mantle thermally buoyant and less dense than normal lithosphere. Laki Eruption (1783):
shorten into mountains (orogeny) because it is too buoyant to subduct. Released massive quantities of Sulfur Dioxide $(SO_2)$. Anti-Greenhouse Effect: $SO_2$ reacts with moisture to form sulfuric acid aerosols that
reflect sunlight, cooling the Earth's surface and causing crop failures.
Structural Geology and Crustal Deformation Atmospheric Circulation: The "volcanic fog" reached Europe via the polar front; air rose over Iceland and sank over Continental Europe.
Folding vs. Faulting: Folding is a ductile form of deformation favored at depth due to high temperatures and high confining pressure. Faulting is Socio-Political Result: The resulting famine in France was a key trigger for the French Revolution in 1789
brittle deformation. This does not contradict the "rigid" nature of the crust because the behavior changes based on the environment (depth and
heat). 5. Subduction Zones and Volcanism
Obduction and Ophiolites: Obduction is the process where oceanic lithosphere is thrust onto a continent. Ophiolites are the preserved sequences Subduction Density: When two oceanic plates collide, the older, colder, denser plate subducts. Oceanic crust always subducts under continental
of these oceanic rocks (sediments, basalts, dikes, gabbros, peridotite) found on land. crust because continental crust is less dense. Slab Rollback: Occurs with old, very dense plates that subduct at a steep angle.Shallow Under-
Indentation and Escape Tectonics: A rigid indenter (like the Indian Plate) forces surrounding crustal blocks to move laterally. This "escape thrusting: Occurs with young, buoyant plates that slide at a shallow angle beneath the overriding plate. Accretionary Wedge: A deformed mass of
tectonics" spreads seismic hazards far from the actual plate boundary, primarily through strike-slip faulting. marine sediment and rock scraped off the subducting plate by the overriding plate. Flux Melting: Magma is created when the subducting slab
releases water (stored in minerals) into the mantle wedge, lowering the melting point of the peridotite. Phreatomagmatic Eruptions: Highly
Urban Risk and Liquefaction explosive eruptions caused by magma interacting with ice/water; the water flashes to steam, expanding violently and shattering magma into
Liquefaction Mechanism: During strong shaking, water-saturated, unconsolidated sediments cause soil grains to lose frictional contact and behave glassy volcanic ash. Viscosity and Explosivity: High silica content makes magma viscous ("thick/sticky"), trapping gas bubbles. As pressure
like a fluid. decreases during ascent, these trapped gases expand rapidly, causing violent explosions or sector collapses (landslide-triggered blasts).
Susceptibility: Areas built on loose sediments or reclaimed land with shallow groundwater (like Vancouver’s Fraser Delta or parts of San Francisco) Pyroclastic Flow and Ignimbrite: Fast-moving clouds of ash and gas. They are "unsorted" because they move too fast for grains to settle by size,
have higher seismic risk because buildings can sink or collapse during liquefaction. 19. How does continental collision lead to mountain building depositing a chaotic mixture of all sizes simultaneously. The resulting deposit is called an ignimbrite. Stratovolcanoes: Built from alternating layers
rather than continued subduction? Answer: Continental crust is buoyant and resists subduction, so convergence causes of thick lava flows and pyroclastic debris.
crustal shortening, thickening, folding, and uplift. The remediation and management of a landfill site like Beare Hill involve three critical layers designed to contain and repurpose waste byproducts.
The Andes Mountains are formed by subduction of the Nazca Plate beneath the South American Plate. Continuous subduction generates magma The first layer is a soil cap consisting of clay or silt with a thickness between 1.2m and 1.8m, which serves to prevent water infiltration and
through mantle melting and causes crustal shortening and uplift along the continental margin, building both a volcanic arc and an orogenic belt. significantly reduce the formation of leachate. Beneath the surface, the second layer is a leachate collection system that uses a pumping
mechanism, likely operating via a cone of depression, to remove contaminated water and prevent it from spreading into the environment. The third
30. How was Mount Logan formed? Answer: Mount Logan formed through crustal shortening and uplift of continental margin sediments during
layer involves a methane capture system where gas wells collect methane produced by decomposing waste so it can be converted into electricity
tectonic compression
rather than being released into the atmosphere. These integrated systems effectively transform hazardous industrial areas into safe public spaces
31. Which tectonic plates are involved in megathrust earthquakes in Japan, and why is Japan home to megathrust earthquakes? Answer: like parks
Megathrust earthquakes in Japan result from subduction of the Pacific Plate beneath the Philippine Plate, and further interaction with the
CHAPTER (9) Law of Superposition (2. Law of Original Horizontality Sedimentary layers are originally deposited in flat, horizontal sheets. If you
Eurasian Plate. Locked
see layers that are tilted (like features 4 and 5) or folded, it means some tectonic force moved them after they were formed. 3. Law of Cross-
The Himalayan–Alpine orogen formed during closure of the Tethys Ocean, a now-dying ocean basin consumed by subduction prior to continental Cutting RelationshipsIf a feature (like an igneous intrusion or a fault) cuts through another body of rock, the feature doing the cutting is younger
collision. than the rock it cuts. In your image, 4. Law of Lateral Continuity Layers of sediment initially extend laterally in all directions. If a valley or river
Calculating sediment timeline (9) carves a gap (like the dip in the cente of your image), we can assume the layers on either side were once connected. 5. Law of Inclusions If a rock
Which Eon do Sediment 1 and 6 belong to? The half life of U-235 → Pb-207 is 0.7 billion years. a. The age of pluton 2: Initial U = 80 ppm. Remaining contains fragments (inclusions) of another rock, the fragments must be older than the rock containing them. 6.Law of intrusion The fundamental
U = 20 ppm 80 → 40 → 20 Two half-lives elapsed. 2×0.7=1.4 billion years Pb check: Initial Pb = 20 ppm U lost = 60 ppm Final Pb = 20 + 60 = 80 principle is that an igneous intrusion is always younger than the rock it cuts through. For magma to flow into a crack or space, that space (and the
ppmb. The age of pluton 3: U went from 80 ppm → 40 ppm, which is one half-life. Age = 1×0.7 = 0.7 billion years. Pb check: U lost = 40 ppm, Pb rock surrounding it) must have already existed.
increases from 20 to 40 ppm: 20 + 40 = 60 ppm (matches). c. Sediment 1 and 6 is in between Pluton 2 and 3 in age, and thus between 0.7 and Extra Notes (9)
1.4 billion years old. Therefore, they were formed during Proterozoic. A radioactive isotope has a half-life of 1 billion years. If only 25% of the original parent sotope remains, how old is the rock? a. Answer: 25%
remaining means two half-lives have passed. Age = 2 × 1 billion years = 2 billion years.
(7) Plate tectonics Paradigm, and earth Materials Chapter 8 Earth Materials Continued and Geological Time
1. Continental Drift and Wegener’s Evidence
Permanentism: The view that continents and ocean basins are fixed in place. Continental Drift: Proposed by Alfred Wegener in the 1910s, suggesting 1. Mineral Properties & Identification
continents were once a single landmass called Pangaea. Streak and Color: Mineral color arises from light interacting with crystal structure. Some wavelengths are absorbed or reflected based on crystal
Fossil Evidence: Matching fossil bands of organisms (~250 million years old) found on separate continents. defects and internal structure. Powdered streak color may differ from the hand-sample because powdered minerals allow more refracted light to be
Paleoclimate Evidence: 300+ million-year-old glacial deposits found in currently separate continents, and the alignment of salt (dry), coal (tropical), and observed, revealing the intrinsic color. Lustre: This is how a mineral reflects light. Metallic minerals reflect light primarily at the surface (shiny). Non-
glacial (polar) deposits. metallic minerals (like vitreous/glass-like) transmit some light into the interior before it returns to the observer. Crystal Symmetry (Quartz vs. Feldspar):
Objections to Drift: Critics argued land bridges once connected continents, ancient climates were simply different, vertical subsidence created ocean Crystal shape reflects internal atomic arrangement. Quartz is a framework silicate of pure silicon and oxygen, forming highly symmetrical hexagonal
basins, or Earth's contraction caused mountain folding. prisms. Feldspar contains aluminum and cations (potassium, sodium, calcium) that distort the symmetry, resulting in blocky, less symmetrical crystals.
Cleavage: The tendency to break along planes of structural weakness. Mica has one perfect cleavage plane because of weak bonding (often potassium)
2. Paleomagnetism and Polar Wander
between strong TOT (tetrahedral-octahedral-tetrahedral) sheets. Hardness & Mohs Scale: Hardness measures resistance to scratching. The Mohs scale
Earth’s Magnetic Field: Acts like a dipole magnet where magnetic north roughly aligns with geographic north.
Inclination Angle: The angle between the magnetic field and the horizontal surface. It is $0^{\circ}$ at the equator, $+90^{\circ}$ at the North Pole, and $-90^{\circ}$ at the
(1-10) is relative and non-linear. For example, Diamond (10) is exponentially harder than Corundum (9). Hardness depends on bond strength; Talc is soft
South Pole. due to weak interlayer bonds, while Diamond is hard due to strong carbon bonds and no weak planes. DIamond can sratch steel file Diamond,
Magnetic Record: When lava cools (igneous rocks), magnetic minerals lock in the field direction and generally do not change unless reheated. corundum, topaz, quartz can scratch a steel file. Orthoclase,apatite, fluorite, calcite, gypsum and talc get scratched by a steel file.
Apparent Polar Wander Path (APWP): A path showing the perceived change in the pole's position over time. Older rocks show poles far from today, while younger ones are
closer.
2. The Rock Cycle & Igneous Rocks
Rejecting Permanentism: Because different continents produced different APWPs, the poles couldn't have moved differently for each; therefore, the continents themselves The Rock Cycle: This describes how igneous, sedimentary, and metamorphic rocks interconvert. Igneous Formation: Formed from crystallized
must have moved. magma via partial melting (only some minerals melt) or fractional crystallization (early minerals crystallize and separate, changing the melt
4. Hotspots and Island Formation composition). Intrusive vs. Extrusive: Intrusive rocks (e.g., Granite, Diorite, Gabbro) cool slowly underground, forming coarse grains. Extrusive
Hotspots (Mantle Plumes): Stationary plumes with a large head (flood basalts) and narrow tail (volcano chains). rocks (e.g., Rhyolite, Andesite, Basalt) cool quickly at the surface, forming fine grains. Composition and Color: Mafic rocks are dark (Basalt,
Volcano Chains: Form as a plate moves over a plume (e.g., Hawaii); the oldest volcanoes are farthest from the active hotspot. Gabbro). Felsic rocks are light (Rhyolite, Granite). Intermediate rocks (Andesite, Diorite) fall in between. Granite often appears pink due to
Seamount: An underwater volcanic mountain. potassium feldspar. Most rocks are polymineralic, and thus has a mixture of colors.
Guyot: A flat-topped seamount.
3. Sedimentary Processes & Lithification
Atoll: A ring-shaped coral reef formed in stages: volcanic island forms $\rightarrow$ coral grows $\rightarrow$ volcano subsides $\rightarrow$ coral
Formation Steps: The four stages are Weathering, Transport, Deposition, and Lithification. Weathering: Mechanical weathering breaks rock
grows upward $\rightarrow$ volcano sinks completely, leaving only the coral ring.
physically (freeze-thaw, root growth, abrasion, rockfall). Chemical weathering involves the dissolution of ions in water. Lithification: This converts
3. Seafloor Spreading and Plate Tectonics sediment into rock via Compaction (weight reduces pore space) and Cementation. Cementing ions come from external sources or pressure
Seafloor Topography: SONAR mapping revealed Mid-Ocean Ridges (MOR), deep ocean trenches, and broad continental shelves. Continental shelves fit dissolution where highly stressed grain boundaries dissolve into water. Transport and Sorting: Transport occurs via fluvial (river), aeolian (wind),
together better than coastlines. glacial, or gravity-driven means. Grain size indicates energy: large grains (gravel) require high energy; fine grains (clay) deposit in low energy.
Seafloor Spreading: Proposed in the 1960s; new oceanic crust forms at MOR, spreads symmetrically, and old crust is destroyed at subduction zones Glacial vs. Beach Sorting: Glaciers transport unsorted material. Beaches are often well-sorted and rounded because oscillatory wave motion re-
(trenches).
works sediment, removing fines and rounding clasts. Why are glacial deposits poorly sorted? a. Because glaciers push mixed grain sizes without
Magnetic Stripes: Symmetrical patterns of alternating magnetic polarity on both sides of MOR confirmed spreading. The youngest rocks are at the ridge,
selective sorting.Rock Types & Structures
4. Sedimentary
and rocks get older as you move away.
Geomagnetic Polarity Chron: A period of constant magnetic polarity, averaging 0.5 million years. Categories: Clastic (fragments of pre-existing rocks), Chemical (precipitated ions), and Biochemical (biological material like limestone). Grain Size
Transform Faults: Necessary because curved ridges cannot spread symmetrically; these strike-slip boundaries offset ridge segments to resolve Ranking: Largest to smallest: Pebble, Sand, Silt, Clay. Gravel forms Conglomerate (rounded) or Breccia (angular). Sand forms sandstone; silt/clay
geometric inconsistencies. form shale or mudstone. Evaporites: Form when water evaporates, leaving minerals like halite (rock salt) or gypsum. Sedimentary Structures: A
bedform is the surface structure (e.g., a dune) before lithification. Cross-bedding forms as dunes migrate; sediment erodes on the gentle "stoss"
5. Silicate Mineral Structures
side and deposits on the steep "lee" side. Environmental Indicators: Asymmetrical ripples indicate unidirectional flow (rivers). Symmetrical
Basic Unit: The silicate tetrahedron ($SiO_4$).
Polymerization: The sharing of oxygen atoms (Si-O-Si bridges) between tetrahedra. Non-bridging bonds are those that do not link tetrahedra. ripples indicate oscillatory flow (waves). Mud cracks indicate drying conditions. Flame structures occur when dense sand sinks into soft, wet
Silicate Types and Si:O Ratios: mud.
5. Case Studies: Fans & Basins
Isolated Tetrahedra: 1:4 (e.g., Olivine). Alluvial Fans: Form on land where steep mountain streams hit flat areas. Energy drops suddenly, depositing coarse material first and finer grains
Single Chain: 1:3 (e.g., Pyroxene). further away. Submarine Fans: Form underwater as sediment moves from the continental shelf to the deep basin. Both fan types reflect a change
Double Chain: 4:11 (e.g., Amphibole). in slope, a decrease in energy, and progressive sorting. Basins: Accommodation space is the vertical space available for sediment. Base level of
Sheet: 2:5 (e.g., Mica/Biotite/Muscovite). erosion is the lowest level erosion can reach (sea or lake level).
Framework: 1:2 (e.g., Feldspar, Quartz).
6. Stratigraphy & Geological Time
6. Structural Mechanics and Cleavage Law of Superposition: In undeformed layers, the oldest is at the bottom and the youngest is at the top. Law of Original Horizontality: Sedimentary
I-Beam Structure: Found in pyroxenes and amphiboles where two opposing tetrahedral chains sandwich cations. layers are deposited horizontally; tilting or folding (anticlines/synclines) happens after deposition. Law of Cross-Cutting Relationships: Igneous
T-O-T Layers: In micas, two silicate sheets sandwich a cation layer, with weak bonding between these T-O-T units. intrusions are younger than the rocks they cut through. They may leave a "contact metamorphosed zone" (evidence of heat). Unconformities: A
Cleavage (Weak Planes): disconformity is an erosional gap between parallel layers representing missing time. Index Fossils: Best fossils are those that lived for a short time,
Pyroxene: 2 weak planes at $\sim90^{\circ}$. evolved rapidly, and were widespread. Fossil assemblages (groups of fossils) help narrow down the age of a rock layer more precisely.
Amphibole: 2 weak planes at $\sim60^{\circ}$ and $120^{\circ}$.
Mica: 1 perfect weak plane between T-O-T layers. Chapter 7
OH Groups (Hydrous Minerals): Located in the center of I-beams in amphiboles and between silicate sheets in the T-O-T structure of micas.
10. Case Study: Submarine Fan
. Phase Relations: Melting and Crystallization
A submarine fan forms in deep marine environments when sediments from the continental shelf move downslope into deeper water. Soft mud may
Partial Melting: At fixed pressure, more polymerized minerals often melt earlier (lower temperature) because Si-O-Si bridges are easily disrupted.
already be accumulating in the deep basin. When coarser sediment is transported downslope and deposited on top of softer material, gravitational
Exception: Quartz melts at a high temperature.
instability can occur, producing structures such as flame structures. Like alluvial fans, submarine fans spread outward from a point source and show
Fractional Crystallization: At fixed pressure, less polymerized minerals (like olivine) crystallize first because isolated tetrahedra momentarily exist in the
changes in grain size as energy decreases during transport. The key similarity between the two systems is that both reflect: A change in slope, a
liquid and are easier to assemble pressure Effects: Higher pressure favors denser, less polymerized structures (isolated tetrahedra and single chains
decrease in energy, and progressive sorting of sediment. The difference lies in setting: Alluvial fans form on land; Submarine fans form underwater in
survive better). Exception: Quartz is a dense framework and can survive high pressure.
deep marine environments.
8. Magma and Viscosity
Viscosity: Higher silica content ($SiO_2$) leads to a more polymerized melt structure and higher viscosity. 11. Basin Formation and Accommodation Space
Melt Structure: Felsic magmas are more viscous because dynamic Si-O bonds allow "momentary" polymerized structures to exist even in liquid form. Sediments accumulate in basins. The vertical space available for sediment accumulation is called accommodation space. Base level of erosion is the
Silica wt%: Measures the $SiO_2$-equivalent portion of a mineral's composition. lowest level to which erosion can occur, often represented by lake or sea level. Once river erosion reaches base level, downward erosion stops.
Accommodation space changes through: Subsidence, Water-level changes, and Sediment infill. As long as accommodation space exists, sediments
9. Mineral Classification
accumulate in relatively horizontal layers.
Silicate vs. Non-Silicate: Silicates contain the $SiO_4$ building block. Non-silicate examples include Calcite and Dolomite (carbonates) and Halite
(evaporite). 12. Stratigraphy: Reading the Rock Record
Metallic Lustre: Caused by the presence of free electrons in the mineral structure. Ore: A metallic mineral of economic value. Stratigraphy reconstructs relative geological time using layered rocks. Law of Superposition: In undeformed strata, oldest layers lie at the bottom,
Note on "Hard" Practice Questions: youngest at the top. Disconformity: Represents a gap in deposition due to erosion. It appears as parallel layers but indicates missing time. Index
Question 32: Use molecular weights ($Mg=24, Si=28, O=32$) to calculate $Mg_2SiO_4$ mass. $SiO_2$ mass is $28 + (32 \times 2) = 60$. Total mass is $(24 Fossils: Ideal index fossils: Lived for short time intervals, evolved rapidly, and were widespread. Assemblages of multiple fossils narrow age ranges
\times 2) + 28 + (32 \times 4) = 48 + 28 + 128 = 204$. Silica $wt\% \approx (60/204) \times 100 \approx 29\%$ (Mafic). more precisely. Law of Cross-Cutting Relationships: Igneous intrusions are younger than the rocks they cut. Intrusions may cause contact
Question 46: Eclogite forms under very high pressure, so it will be dominated by dense, less polymerized silicates like isolated tetrahedra (garnet) or metamorphism along boundaries. Law of Original Horizontality: Sedimentary layers are deposited horizontally. If tilted, deformation occurred after
single chains (pyroxene). deposition. Folding can produce anticlines (arch-shaped) and synclines (trough-shaped). Complex folding can complicate age interpretation. The
axis of the fold is called the hinge line, and the plane that contains the hinge line and divides the fold into two limbs is called the axial plane.
Volcanic Processes and Eruption Styles 1. Plate Tectonics and Ridge Mechanics
Magma Composition and Volatiles: Magma is a mixture of molten rock (melt), suspended solids (crystals or country rock), and volatiles such as Ridge Axis: The formally known center line of a mid-ocean ridge that serves as the "spreading center" where magma rises to form new crust.
$H_{2}O$, $CO_{2}$, and $SO_{2}$. At depth, high confining pressure keeps these volatiles dissolved. As magma rises and pressure decreases, Ridge Push: A critical driver of plate movement where gravity causes newly formed oceanic crust to slide atop the asthenosphere, moving away
volatiles exsolve to form bubbles; the expansion of these bubbles is the primary driver of explosive eruptions. from the ridge axis.
Eruption Style Determinants: Composition alone does not predict eruption style. While low-silica mafic magmas are usually effusive and high- Slab Pull: The primary driver of subduction where the weight of a dense, sinking oceanic plate pulls the rest of the plate down with it.
silica felsic magmas are usually explosive, exceptions exist. Mafic magma can be explosive if it interacts with external water (phreatomagmatic Lithospheric Thickening: The lithosphere thickens as it moves away from the ridge because it loses heat to the ocean, causing the underlying
eruptions), and felsic magma can be effusive if it contains little gas or if the gas escapes gradually during a slow ascent. asthenosphere to cool, solidify, and transform into rigid lithospheric mantle.
Sector Collapse: This refers to the structural failure of a volcanic edifice. It can trigger an explosive eruption by rapidly reducing the confining Absolute vs. Relative Motion: Relative motion describes plates moving compared to each other (e.g., North American vs. Eurasian plates). Absolute
pressure (the weight of overlying rock) on the magma chamber, causing dissolved gases to expand violently. motion describes plate movement relative to a fixed point in the deep mantle, such as a mantle plume.
Lava Textures: Basaltic (mafic) flows often form 'A'a lava, which is rough and vesicular because gas escapes easily. Intermediate to felsic flows Ridge Jump: A process where a spreading center reorganizes by linking a mid-ocean ridge to new fissure swarms, causing the former ridge segment
are often "blocky," featuring smooth, angular blocks with fewer vesicles because they have less gas and higher viscosity.Stratovolcanoes and to become inactive.
Deposits: Stratovolcanoes consist of alternating layers of lava flows and pyroclastic deposits, reflecting changing gas content and eruption 2. Physics and Chemistry of Magma
styles over time. Ignimbrites are formed from hot pyroclastic flows that weld together. Tephra layers are best preserved in quiet environments Magma Composition: Composed of "melt" (liquid rock), dissolved gases, water vapor, silicon, oxygen, and metallic cations. Crystalline Solid (Crystal):
like lakes or marine basins rather than on land where they are easily eroded. Characterized by a repeating pattern where atoms are fixed and do not move or change neighbors. Liquid Melt: Lacks a repeating structure; atoms
Lahars: These are volcanic mudflows (water mixed with ash and debris) triggered by rainfall, snowmelt, or lake drainage. appear randomly and chemical bonds are dynamic, allowing atoms to shift and change neighbors. Glassy Solid (Glass): A non-crystalline solid formed
Earthquake Mechanics and Megathrust Events when magma cools instantaneously, freezing atoms in their random liquid positions before crystals can grow. Chemical differentiation: The process
Elastic Rebound: The lithosphere is rigid but can bend elastically under stress like a rubber band. Earthquakes store energy through this elastic where distinct layers or compositions form within a body due to the physical segregation of materials based on density or affinity. For instance, both
deformation. When the stress overcomes friction at a locked plate boundary, the lithosphere rebounds to its original shape, releasing energy as an fractional crystallization and partial melting results in chemical differentiation. Nucleation: The start of crystallization, where a few atoms form a bond
earthquake. to create a "nuclear seed". Cooling Rates: Slow cooling starts from fewer nucleation seeds, allowing crystals time to grow large (coarse-grained). Fast
Megathrust Earthquakes: These occur at subduction zones where friction between the subducting and overriding plates locks the boundary. They cooling creates many simultaneous nucleation seeds that have little ime to grow, resulting in many tiny crystals (fine-grained).
involve massive fault areas and release enormous energy. They generate tsunamis through sudden seafloor displacement.
3. Igneous Rock Types and Textures
Vertical Movement: During a single megathrust event, different regions can experience simultaneous uplift and subsidence over minutes.
Basalt vs. Gabbro: Both have the same chemical composition, but basalt is fine-grained due to rapid cooling at the surface, while gabbro is coarse-
Tsunamis: Tsunami heights increase near distant shorelines because wave speed decreases in shallow water, causing the waves to compress and
grained due to slow cooling in underground magma chambers.
grow taller (shoaling).
Pillow Lava: Formed when magma hits cold water, creating a hard outer crust while the warm interior continues to push forward until the pressure
Tectonic Settings and Regional Geography breaks the crust into spherical shapes. The crust is glassy because cooling is instantaneous.
Continental Margins: Components include the continental shelf, slope, and rise. The slope is typically steeper than the shelf. Sheeted Dikes: Formed at mid-ocean ridges as magma travels through vertical fissures; as seafloor spreads, new dikes are injected into the center,
Plate Boundary Types: Plate boundaries control faulting styles: subduction zones produce thrust/megathrust faults, while transform boundaries creating parallel vertical sheets.
(like the San Andreas Fault) produce strike-slip faults where plates slide horizontally. Columnar Basalt: Formed as thick lava flows contract while cooling; they fracture into vertical hexagonal columns because hexagons are the most
Specific Regions: efficient shape to relieve tensile stress with the shortest boundary length.
Cascadia: Small plates (Juan de Fuca, Explorer, Gorda) subduct under the North American Plate, creating megathrust risk for regions like Magmatic Differentiation: In a magma chamber, dense mafic minerals (rich in iron and magnesium) crystallize early and sink to the bottom, while
Vancouver. the remaining melt becomes enriched in silica.
Chile: The 1960 magnitude 9.5 earthquake was a megathrust event caused by subduction.
Aleutian Arc: Formed by ocean-ocean and ocean-continent subduction. 4. Case Study: Iceland and the Laki Eruption
San Francisco: Located on a transform boundary (San Andreas Fault) involving strike-slip faulting. Iceland's Elevation and Thickness: Iceland's crust is 30-40 km thick (vs. the 7 km average) because a mantle plume provides excess magma. It stays
Asia/Himalayas: The India-Eurasia collision involves a "rigid indenter" (India) colliding with Eurasia. This causes continental crust to thicken and above sea level because the plume's heat keeps the mantle thermally buoyant and less dense than normal lithosphere. Laki Eruption (1783):
shorten into mountains (orogeny) because it is too buoyant to subduct. Released massive quantities of Sulfur Dioxide $(SO_2)$. Anti-Greenhouse Effect: $SO_2$ reacts with moisture to form sulfuric acid aerosols that
reflect sunlight, cooling the Earth's surface and causing crop failures.
Structural Geology and Crustal Deformation Atmospheric Circulation: The "volcanic fog" reached Europe via the polar front; air rose over Iceland and sank over Continental Europe.
Folding vs. Faulting: Folding is a ductile form of deformation favored at depth due to high temperatures and high confining pressure. Faulting is Socio-Political Result: The resulting famine in France was a key trigger for the French Revolution in 1789
brittle deformation. This does not contradict the "rigid" nature of the crust because the behavior changes based on the environment (depth and
heat). 5. Subduction Zones and Volcanism
Obduction and Ophiolites: Obduction is the process where oceanic lithosphere is thrust onto a continent. Ophiolites are the preserved sequences Subduction Density: When two oceanic plates collide, the older, colder, denser plate subducts. Oceanic crust always subducts under continental
of these oceanic rocks (sediments, basalts, dikes, gabbros, peridotite) found on land. crust because continental crust is less dense. Slab Rollback: Occurs with old, very dense plates that subduct at a steep angle.Shallow Under-
Indentation and Escape Tectonics: A rigid indenter (like the Indian Plate) forces surrounding crustal blocks to move laterally. This "escape thrusting: Occurs with young, buoyant plates that slide at a shallow angle beneath the overriding plate. Accretionary Wedge: A deformed mass of
tectonics" spreads seismic hazards far from the actual plate boundary, primarily through strike-slip faulting. marine sediment and rock scraped off the subducting plate by the overriding plate. Flux Melting: Magma is created when the subducting slab
releases water (stored in minerals) into the mantle wedge, lowering the melting point of the peridotite. Phreatomagmatic Eruptions: Highly
Urban Risk and Liquefaction explosive eruptions caused by magma interacting with ice/water; the water flashes to steam, expanding violently and shattering magma into
Liquefaction Mechanism: During strong shaking, water-saturated, unconsolidated sediments cause soil grains to lose frictional contact and behave glassy volcanic ash. Viscosity and Explosivity: High silica content makes magma viscous ("thick/sticky"), trapping gas bubbles. As pressure
like a fluid. decreases during ascent, these trapped gases expand rapidly, causing violent explosions or sector collapses (landslide-triggered blasts).
Susceptibility: Areas built on loose sediments or reclaimed land with shallow groundwater (like Vancouver’s Fraser Delta or parts of San Francisco) Pyroclastic Flow and Ignimbrite: Fast-moving clouds of ash and gas. They are "unsorted" because they move too fast for grains to settle by size,
have higher seismic risk because buildings can sink or collapse during liquefaction. 19. How does continental collision lead to mountain building depositing a chaotic mixture of all sizes simultaneously. The resulting deposit is called an ignimbrite. Stratovolcanoes: Built from alternating layers
rather than continued subduction? Answer: Continental crust is buoyant and resists subduction, so convergence causes of thick lava flows and pyroclastic debris.
crustal shortening, thickening, folding, and uplift. The remediation and management of a landfill site like Beare Hill involve three critical layers designed to contain and repurpose waste byproducts.
The Andes Mountains are formed by subduction of the Nazca Plate beneath the South American Plate. Continuous subduction generates magma The first layer is a soil cap consisting of clay or silt with a thickness between 1.2m and 1.8m, which serves to prevent water infiltration and
through mantle melting and causes crustal shortening and uplift along the continental margin, building both a volcanic arc and an orogenic belt. significantly reduce the formation of leachate. Beneath the surface, the second layer is a leachate collection system that uses a pumping
mechanism, likely operating via a cone of depression, to remove contaminated water and prevent it from spreading into the environment. The third
30. How was Mount Logan formed? Answer: Mount Logan formed through crustal shortening and uplift of continental margin sediments during
layer involves a methane capture system where gas wells collect methane produced by decomposing waste so it can be converted into electricity
tectonic compression
rather than being released into the atmosphere. These integrated systems effectively transform hazardous industrial areas into safe public spaces
31. Which tectonic plates are involved in megathrust earthquakes in Japan, and why is Japan home to megathrust earthquakes? Answer: like parks
Megathrust earthquakes in Japan result from subduction of the Pacific Plate beneath the Philippine Plate, and further interaction with the
CHAPTER (9) Law of Superposition (2. Law of Original Horizontality Sedimentary layers are originally deposited in flat, horizontal sheets. If you
Eurasian Plate. Locked
see layers that are tilted (like features 4 and 5) or folded, it means some tectonic force moved them after they were formed. 3. Law of Cross-
The Himalayan–Alpine orogen formed during closure of the Tethys Ocean, a now-dying ocean basin consumed by subduction prior to continental Cutting RelationshipsIf a feature (like an igneous intrusion or a fault) cuts through another body of rock, the feature doing the cutting is younger
collision. than the rock it cuts. In your image, 4. Law of Lateral Continuity Layers of sediment initially extend laterally in all directions. If a valley or river
Calculating sediment timeline (9) carves a gap (like the dip in the cente of your image), we can assume the layers on either side were once connected. 5. Law of Inclusions If a rock
Which Eon do Sediment 1 and 6 belong to? The half life of U-235 → Pb-207 is 0.7 billion years. a. The age of pluton 2: Initial U = 80 ppm. Remaining contains fragments (inclusions) of another rock, the fragments must be older than the rock containing them. 6.Law of intrusion The fundamental
U = 20 ppm 80 → 40 → 20 Two half-lives elapsed. 2×0.7=1.4 billion years Pb check: Initial Pb = 20 ppm U lost = 60 ppm Final Pb = 20 + 60 = 80 principle is that an igneous intrusion is always younger than the rock it cuts through. For magma to flow into a crack or space, that space (and the
ppmb. The age of pluton 3: U went from 80 ppm → 40 ppm, which is one half-life. Age = 1×0.7 = 0.7 billion years. Pb check: U lost = 40 ppm, Pb rock surrounding it) must have already existed.
increases from 20 to 40 ppm: 20 + 40 = 60 ppm (matches). c. Sediment 1 and 6 is in between Pluton 2 and 3 in age, and thus between 0.7 and Extra Notes (9)
1.4 billion years old. Therefore, they were formed during Proterozoic. A radioactive isotope has a half-life of 1 billion years. If only 25% of the original parent sotope remains, how old is the rock? a. Answer: 25%
remaining means two half-lives have passed. Age = 2 × 1 billion years = 2 billion years.
(7) Plate tectonics Paradigm, and earth Materials Chapter 8 Earth Materials Continued and Geological Time
1. Continental Drift and Wegener’s Evidence
Permanentism: The view that continents and ocean basins are fixed in place. Continental Drift: Proposed by Alfred Wegener in the 1910s, suggesting 1. Mineral Properties & Identification
continents were once a single landmass called Pangaea. Streak and Color: Mineral color arises from light interacting with crystal structure. Some wavelengths are absorbed or reflected based on crystal
Fossil Evidence: Matching fossil bands of organisms (~250 million years old) found on separate continents. defects and internal structure. Powdered streak color may differ from the hand-sample because powdered minerals allow more refracted light to be
Paleoclimate Evidence: 300+ million-year-old glacial deposits found in currently separate continents, and the alignment of salt (dry), coal (tropical), and observed, revealing the intrinsic color. Lustre: This is how a mineral reflects light. Metallic minerals reflect light primarily at the surface (shiny). Non-
glacial (polar) deposits. metallic minerals (like vitreous/glass-like) transmit some light into the interior before it returns to the observer. Crystal Symmetry (Quartz vs. Feldspar):
Objections to Drift: Critics argued land bridges once connected continents, ancient climates were simply different, vertical subsidence created ocean Crystal shape reflects internal atomic arrangement. Quartz is a framework silicate of pure silicon and oxygen, forming highly symmetrical hexagonal
basins, or Earth's contraction caused mountain folding. prisms. Feldspar contains aluminum and cations (potassium, sodium, calcium) that distort the symmetry, resulting in blocky, less symmetrical crystals.
Cleavage: The tendency to break along planes of structural weakness. Mica has one perfect cleavage plane because of weak bonding (often potassium)
2. Paleomagnetism and Polar Wander
between strong TOT (tetrahedral-octahedral-tetrahedral) sheets. Hardness & Mohs Scale: Hardness measures resistance to scratching. The Mohs scale
Earth’s Magnetic Field: Acts like a dipole magnet where magnetic north roughly aligns with geographic north.
Inclination Angle: The angle between the magnetic field and the horizontal surface. It is $0^{\circ}$ at the equator, $+90^{\circ}$ at the North Pole, and $-90^{\circ}$ at the
(1-10) is relative and non-linear. For example, Diamond (10) is exponentially harder than Corundum (9). Hardness depends on bond strength; Talc is soft
South Pole. due to weak interlayer bonds, while Diamond is hard due to strong carbon bonds and no weak planes. DIamond can sratch steel file Diamond,
Magnetic Record: When lava cools (igneous rocks), magnetic minerals lock in the field direction and generally do not change unless reheated. corundum, topaz, quartz can scratch a steel file. Orthoclase,apatite, fluorite, calcite, gypsum and talc get scratched by a steel file.
Apparent Polar Wander Path (APWP): A path showing the perceived change in the pole's position over time. Older rocks show poles far from today, while younger ones are
closer.
2. The Rock Cycle & Igneous Rocks
Rejecting Permanentism: Because different continents produced different APWPs, the poles couldn't have moved differently for each; therefore, the continents themselves The Rock Cycle: This describes how igneous, sedimentary, and metamorphic rocks interconvert. Igneous Formation: Formed from crystallized
must have moved. magma via partial melting (only some minerals melt) or fractional crystallization (early minerals crystallize and separate, changing the melt
4. Hotspots and Island Formation composition). Intrusive vs. Extrusive: Intrusive rocks (e.g., Granite, Diorite, Gabbro) cool slowly underground, forming coarse grains. Extrusive
Hotspots (Mantle Plumes): Stationary plumes with a large head (flood basalts) and narrow tail (volcano chains). rocks (e.g., Rhyolite, Andesite, Basalt) cool quickly at the surface, forming fine grains. Composition and Color: Mafic rocks are dark (Basalt,
Volcano Chains: Form as a plate moves over a plume (e.g., Hawaii); the oldest volcanoes are farthest from the active hotspot. Gabbro). Felsic rocks are light (Rhyolite, Granite). Intermediate rocks (Andesite, Diorite) fall in between. Granite often appears pink due to
Seamount: An underwater volcanic mountain. potassium feldspar. Most rocks are polymineralic, and thus has a mixture of colors.
Guyot: A flat-topped seamount.
3. Sedimentary Processes & Lithification
Atoll: A ring-shaped coral reef formed in stages: volcanic island forms $\rightarrow$ coral grows $\rightarrow$ volcano subsides $\rightarrow$ coral
Formation Steps: The four stages are Weathering, Transport, Deposition, and Lithification. Weathering: Mechanical weathering breaks rock
grows upward $\rightarrow$ volcano sinks completely, leaving only the coral ring.
physically (freeze-thaw, root growth, abrasion, rockfall). Chemical weathering involves the dissolution of ions in water. Lithification: This converts
3. Seafloor Spreading and Plate Tectonics sediment into rock via Compaction (weight reduces pore space) and Cementation. Cementing ions come from external sources or pressure
Seafloor Topography: SONAR mapping revealed Mid-Ocean Ridges (MOR), deep ocean trenches, and broad continental shelves. Continental shelves fit dissolution where highly stressed grain boundaries dissolve into water. Transport and Sorting: Transport occurs via fluvial (river), aeolian (wind),
together better than coastlines. glacial, or gravity-driven means. Grain size indicates energy: large grains (gravel) require high energy; fine grains (clay) deposit in low energy.
Seafloor Spreading: Proposed in the 1960s; new oceanic crust forms at MOR, spreads symmetrically, and old crust is destroyed at subduction zones Glacial vs. Beach Sorting: Glaciers transport unsorted material. Beaches are often well-sorted and rounded because oscillatory wave motion re-
(trenches).
works sediment, removing fines and rounding clasts. Why are glacial deposits poorly sorted? a. Because glaciers push mixed grain sizes without
Magnetic Stripes: Symmetrical patterns of alternating magnetic polarity on both sides of MOR confirmed spreading. The youngest rocks are at the ridge,
selective sorting.Rock Types & Structures
4. Sedimentary
and rocks get older as you move away.
Geomagnetic Polarity Chron: A period of constant magnetic polarity, averaging 0.5 million years. Categories: Clastic (fragments of pre-existing rocks), Chemical (precipitated ions), and Biochemical (biological material like limestone). Grain Size
Transform Faults: Necessary because curved ridges cannot spread symmetrically; these strike-slip boundaries offset ridge segments to resolve Ranking: Largest to smallest: Pebble, Sand, Silt, Clay. Gravel forms Conglomerate (rounded) or Breccia (angular). Sand forms sandstone; silt/clay
geometric inconsistencies. form shale or mudstone. Evaporites: Form when water evaporates, leaving minerals like halite (rock salt) or gypsum. Sedimentary Structures: A
bedform is the surface structure (e.g., a dune) before lithification. Cross-bedding forms as dunes migrate; sediment erodes on the gentle "stoss"
5. Silicate Mineral Structures
side and deposits on the steep "lee" side. Environmental Indicators: Asymmetrical ripples indicate unidirectional flow (rivers). Symmetrical
Basic Unit: The silicate tetrahedron ($SiO_4$).
Polymerization: The sharing of oxygen atoms (Si-O-Si bridges) between tetrahedra. Non-bridging bonds are those that do not link tetrahedra. ripples indicate oscillatory flow (waves). Mud cracks indicate drying conditions. Flame structures occur when dense sand sinks into soft, wet
Silicate Types and Si:O Ratios: mud.
5. Case Studies: Fans & Basins
Isolated Tetrahedra: 1:4 (e.g., Olivine). Alluvial Fans: Form on land where steep mountain streams hit flat areas. Energy drops suddenly, depositing coarse material first and finer grains
Single Chain: 1:3 (e.g., Pyroxene). further away. Submarine Fans: Form underwater as sediment moves from the continental shelf to the deep basin. Both fan types reflect a change
Double Chain: 4:11 (e.g., Amphibole). in slope, a decrease in energy, and progressive sorting. Basins: Accommodation space is the vertical space available for sediment. Base level of
Sheet: 2:5 (e.g., Mica/Biotite/Muscovite). erosion is the lowest level erosion can reach (sea or lake level).
Framework: 1:2 (e.g., Feldspar, Quartz).
6. Stratigraphy & Geological Time
6. Structural Mechanics and Cleavage Law of Superposition: In undeformed layers, the oldest is at the bottom and the youngest is at the top. Law of Original Horizontality: Sedimentary
I-Beam Structure: Found in pyroxenes and amphiboles where two opposing tetrahedral chains sandwich cations. layers are deposited horizontally; tilting or folding (anticlines/synclines) happens after deposition. Law of Cross-Cutting Relationships: Igneous
T-O-T Layers: In micas, two silicate sheets sandwich a cation layer, with weak bonding between these T-O-T units. intrusions are younger than the rocks they cut through. They may leave a "contact metamorphosed zone" (evidence of heat). Unconformities: A
Cleavage (Weak Planes): disconformity is an erosional gap between parallel layers representing missing time. Index Fossils: Best fossils are those that lived for a short time,
Pyroxene: 2 weak planes at $\sim90^{\circ}$. evolved rapidly, and were widespread. Fossil assemblages (groups of fossils) help narrow down the age of a rock layer more precisely.
Amphibole: 2 weak planes at $\sim60^{\circ}$ and $120^{\circ}$.
Mica: 1 perfect weak plane between T-O-T layers. Chapter 7
OH Groups (Hydrous Minerals): Located in the center of I-beams in amphiboles and between silicate sheets in the T-O-T structure of micas.
10. Case Study: Submarine Fan
. Phase Relations: Melting and Crystallization
A submarine fan forms in deep marine environments when sediments from the continental shelf move downslope into deeper water. Soft mud may
Partial Melting: At fixed pressure, more polymerized minerals often melt earlier (lower temperature) because Si-O-Si bridges are easily disrupted.
already be accumulating in the deep basin. When coarser sediment is transported downslope and deposited on top of softer material, gravitational
Exception: Quartz melts at a high temperature.
instability can occur, producing structures such as flame structures. Like alluvial fans, submarine fans spread outward from a point source and show
Fractional Crystallization: At fixed pressure, less polymerized minerals (like olivine) crystallize first because isolated tetrahedra momentarily exist in the
changes in grain size as energy decreases during transport. The key similarity between the two systems is that both reflect: A change in slope, a
liquid and are easier to assemble pressure Effects: Higher pressure favors denser, less polymerized structures (isolated tetrahedra and single chains
decrease in energy, and progressive sorting of sediment. The difference lies in setting: Alluvial fans form on land; Submarine fans form underwater in
survive better). Exception: Quartz is a dense framework and can survive high pressure.
deep marine environments.
8. Magma and Viscosity
Viscosity: Higher silica content ($SiO_2$) leads to a more polymerized melt structure and higher viscosity. 11. Basin Formation and Accommodation Space
Melt Structure: Felsic magmas are more viscous because dynamic Si-O bonds allow "momentary" polymerized structures to exist even in liquid form. Sediments accumulate in basins. The vertical space available for sediment accumulation is called accommodation space. Base level of erosion is the
Silica wt%: Measures the $SiO_2$-equivalent portion of a mineral's composition. lowest level to which erosion can occur, often represented by lake or sea level. Once river erosion reaches base level, downward erosion stops.
Accommodation space changes through: Subsidence, Water-level changes, and Sediment infill. As long as accommodation space exists, sediments
9. Mineral Classification
accumulate in relatively horizontal layers.
Silicate vs. Non-Silicate: Silicates contain the $SiO_4$ building block. Non-silicate examples include Calcite and Dolomite (carbonates) and Halite
(evaporite). 12. Stratigraphy: Reading the Rock Record
Metallic Lustre: Caused by the presence of free electrons in the mineral structure. Ore: A metallic mineral of economic value. Stratigraphy reconstructs relative geological time using layered rocks. Law of Superposition: In undeformed strata, oldest layers lie at the bottom,
Note on "Hard" Practice Questions: youngest at the top. Disconformity: Represents a gap in deposition due to erosion. It appears as parallel layers but indicates missing time. Index
Question 32: Use molecular weights ($Mg=24, Si=28, O=32$) to calculate $Mg_2SiO_4$ mass. $SiO_2$ mass is $28 + (32 \times 2) = 60$. Total mass is $(24 Fossils: Ideal index fossils: Lived for short time intervals, evolved rapidly, and were widespread. Assemblages of multiple fossils narrow age ranges
\times 2) + 28 + (32 \times 4) = 48 + 28 + 128 = 204$. Silica $wt\% \approx (60/204) \times 100 \approx 29\%$ (Mafic). more precisely. Law of Cross-Cutting Relationships: Igneous intrusions are younger than the rocks they cut. Intrusions may cause contact
Question 46: Eclogite forms under very high pressure, so it will be dominated by dense, less polymerized silicates like isolated tetrahedra (garnet) or metamorphism along boundaries. Law of Original Horizontality: Sedimentary layers are deposited horizontally. If tilted, deformation occurred after
single chains (pyroxene). deposition. Folding can produce anticlines (arch-shaped) and synclines (trough-shaped). Complex folding can complicate age interpretation. The
axis of the fold is called the hinge line, and the plane that contains the hinge line and divides the fold into two limbs is called the axial plane.
