Geology Lecture Notes Review

Key Concepts of Metamorphic Rocks

• Parent Rock (Protolith): The original rock that transforms during metamorphism (e.g., limestone to marble).

• Metamorphism: Alteration of existing rocks via heat, pressure, and chemically active fluids, changing mineralogy and texture.

• Metamorphic Grade: Intensity of metamorphism, ranging from low-grade (slate) to high-grade (gneiss).

• Foliation: Alignment of mineral grains under pressure, creating a layered appearance (schist, gneiss).

• Non-Foliated Textures: Lack of alignment, seen in rocks like marble and quartzite, formed under uniform pressure.

• Contact Metamorphism: Heating of rocks by nearby magma, forming an aureole.

• Regional Metamorphism: Large-scale tectonic processes causing high pressure and temperature over broad areas.

• Hydrothermal Metamorphism: Alteration by hot, mineral-rich water, often at mid-ocean ridges.

• Subduction Zone Metamorphism: High-pressure, low-temperature conditions in subduction zones.

• Impact Metamorphism: High-pressure shock waves from meteorite impacts.

• Slate: Fine-grained, from shale, with excellent cleavage.

• Phyllite: Slightly coarser than slate, with a shiny appearance due to micas.

• Schist: Medium to coarse-grained, pronounced foliation, may contain garnet.

• Gneiss: High-grade, banded appearance due to mineral segregation.

• Marble: From limestone, used in sculpture and architecture.

Overview of Metamorphism

• Metamorphism is a solid-state process altering rock's minerals, structure, and texture without melting.

• Driven by heat, pressure, and hydrothermal fluids:

  • Heat: T increases atomic vibrations, leading to recrystallization.

  • Pressure: P compacts minerals and causes deformation.

  • Hydrothermal fluids: introduce/remove elements, facilitate new mineral growth.

• Metamorphic grade indicates intensity; higher grades mean larger grain sizes and index minerals.

• Foliation is a key texture from platy mineral alignment under differential stress.

  • Types: rock cleavage, schistosity, gneissic texture.

• Non-foliated textures occur in rocks lacking platy minerals, random crystal growth (marble, quartzite).

• Contact metamorphism: magma intrusion, creates non-foliated rocks like hornfels and marble.

• Hydrothermal metamorphism: hot, chemically active fluids alter rocks (mid-ocean ridges).

• Burial metamorphism: deep burial without tectonic deformation, low-grade metamorphism.

• Subduction zone metamorphism: high pressure, low temperature (oceanic crust pulled into mantle).

• Regional metamorphism: mountain-building, produces foliated rocks.

Fundamental Concepts of Plate Tectonics

• Plate Tectonics: Earth's lithosphere is divided into plates that float on the asthenosphere.

• Continental Drift Hypothesis: Alfred Wegener proposed continents were once joined and drifted apart.

• Divergent Boundaries: Plates move apart, causing seafloor spreading and oceanic ridges.

• Convergent Boundaries: Plates collide, leading to mountain building, subduction zones, and volcanoes.

• Transform Boundaries: Plates slide past each other, causing earthquakes (San Andreas Fault).

• Hot Spots: Volcanic activity from mantle plumes, independent of plate boundaries (Hawaiian Islands).

• Subduction Zones: One plate moves under another, forming deep ocean trenches and volcanic arcs.

• Seafloor Spreading: New oceanic crust forms at mid-ocean ridges.

• Paleomagnetism: Study of rock magnetism to understand plate movements.

• Curie Point: Temperature at which materials lose magnetic properties, relevant to understanding magnetic reversals.

• Earthquake: Sudden energy release in Earth's crust, often from fault movement.

• Hypocenter and Epicenter: Hypocenter is the earthquake origin; epicenter is the point above it on the surface.

• Seismic Waves: Energy waves from earthquakes (P-waves, S-waves, Love waves, Rayleigh waves).

• Magnitude and Intensity: magnitude measures energy released (Moment Magnitude Scale), while intensity measures the effects (Modified Mercalli Intensity Scale).

Seismology and Earth's Systems

• Tsunami: Ocean waves caused by underwater disturbances like earthquakes.

• Seismograph: Instrument recording ground motion during an earthquake.

• Elastic Rebound Theory: Energy stored in rocks released during earthquakes.

• Aftershocks and Foreshocks: Aftershocks follow a larger earthquake; foreshocks precede it.

• Fault Types: Normal, reverse, strike-slip faults linked to tectonic settings.

• Liquefaction: Saturated soil loses strength during an earthquake.

• Hydrosphere: All water on Earth, crucial for climate and ecosystems.

• Atmosphere: Gases surrounding Earth, essential for weather, climate, and protection from solar radiation.

• Biosphere: Global sum of all ecosystems, interacting with the environment.

• Geosphere: Solid part of Earth, interacting with the hydrosphere and atmosphere.

• Earth System Science: Interdisciplinary study of interactions between Earth's spheres.

• Rock Cycle: Continuous process of rock formation involving igneous, sedimentary, and metamorphic rocks.

Atomic Structure and Chemical Properties

• Atoms consist of protons, neutrons, and electrons.

  • Protons: positively charged, define the element (e.g., hydrogen has one proton, carbon has six)

  • Neutrons: neutral, stabilize the nucleus

  • Electrons: negatively charged, in orbitals, crucial for bonding

• Valence electrons are outermost electrons, determining bonding.

• Atoms with full valence shells (noble gases like helium and neon) are stable.

• Chemical compounds form when atoms bond in fixed ratios (e.g., quartz (SiO₂)).

• The periodic table organizes elements by atomic number, grouping similar properties.

• Elements in the same group have similar behaviors, predicting reactions.

• Examples: oxygen (O), silicon (Si), iron (Fe) are abundant in Earth's crust.

Origin of the Solar System and Earth

• Solar system formed from a solar nebula, a cloud of gas and dust from ancient supernovae.

• Gravity collapsed the nebula, forming a flat disk with the Sun at the center.

• Planets formed from clumping dust and gas.

  • Planetesimals: rocky/icy bodies that merged to form protoplanets.

  • Supernova: explosion dispersing heavy elements, forming planets.

  • Habitable Zone: region around a star where liquid water can exist.

  • Great Oxygenation Event: 2.4 billion years ago, increase in atmospheric oxygen from photosynthesis.

• Earth's Internal Structure:

  • Crust: thin, outermost layer

    • Continental: thicker, less dense

    • Oceanic: thinner, denser

  • Mantle: thick layer beneath the crust, solid rock that behaves plastically

  • Core: metallic center

    • Outer: Liquid

    • Inner: Solid

• Lithosphere: rigid outer shell (crust and upper mantle), broken into tectonic plates.

• Asthenosphere: partially molten layer allowing tectonic plates to move.

• Transition zone affects mantle material movement.

Mineralogy and Rock Formation

• Mineral: Naturally occurring, inorganic solid with a definite chemical composition and crystalline structure.

  • Requirements: naturally occurring, inorganic, solid, definite chemical formula, crystalline structure.

• Rock: Aggregate of one or more minerals (e.g., granite: quartz, feldspar, mica; limestone: calcite).

• Diagnostic Properties: Unique traits for identification (e.g., halite's salty taste, magnetite's magnetic properties).

• Ambiguous Properties: Traits varying among specimens (e.g., color in quartz).

• Luster: Light reflection from surface (metallic or nonmetallic).

• Mohs Hardness Scale: Ranks minerals from 1 (talc) to 10 (diamond), based on scratch resistance.

• Streak: Powder color when scratched on a streak plate (e.g., hematite's reddish streak).

• Crystal Habit: External shape influenced by internal structure (e.g., cubic (halite), hexagonal (quartz), sheet-like (micas)).

• Hardness measured from 1(talc) to 10(diamond)

• Cleavage vs. Fracture defines a mineral tendency to break along flat planes vs. irregular breakage.

• Tenacity describes a mineral's response to stress.

• Density and Specific Gravity defined as the measure of mass per unit volume compares a mineral's density to water. for instance quartz has specific gravity of ~2.7, while gold is ~19.3

Classification of Minerals

• Rock-forming Minerals: Two dozen minerals making up most of Earth's crust (quartz, feldspars, micas).

• Economic Minerals: Mined for practical use (hematite (iron ore), bauxite (aluminum ore), galena (lead)).

• Silicate Minerals: Largest group, with silicon-oxygen tetrahedron (SiO₄⁴⁻) (quartz, feldspars, micas).

• Nonsilicate Minerals: Lack silicate tetrahedra (carbonates (calcite), oxides (hematite), sulfides (pyrite)).

• Common Examples: Calcite (CaCO₃) bubbles with acid, dolomite (CaMg(CO₃)₂) reacts when powdered, halite (NaCl) forms through evaporation.

• Nonmetallic Mineral Resources: Essential for construction and agriculture (halite (salt), gypsum (drywall), clay (ceramics), phosphate (fertilizer)).

• Placer Deposits: Heavy minerals concentrated in streambeds (gold, diamonds).

• Secondary Enrichment: Weathering concentrates valuable metals near the surface.

• Disseminated Deposits: Ore minerals scattered throughout the rock (copper).

• Vein Deposits: Hydrothermal solutions fill cracks and precipitate minerals.

Igneous Rocks: Formation and Classification

• Definition: Igneous rocks form from cooling and solidification of molten rock (magma or lava).

• Intrusive vs. Extrusive: Intrusive (plutonic) form below the surface; extrusive (volcanic) form on the surface.

• Cooling History: Cooling rate influences crystal size and arrangement.

• Texture: Appearance based on crystal size and arrangement

  • Aphanitic (fine-grained)

  • Phaneritic (coarse-grained)

  • Vesicular (gas bubbles).

• Pyroclastic Texture: From volcanic fragments ejected during eruptions.

• Felsic Composition: High in silica (SiO₂), light color (granite, rhyolite).

• Intermediate Composition: Moderate silica, gray color (diorite, andesite).

• Mafic Composition: Low silica, high in iron and magnesium (gabbro, basalt).

• Ultramafic Composition: Very low silica, very high in iron and magnesium (peridotite).

• Common Igneous Rocks: Examples includes granite, rhyolite, basalt, and obsidian.

• Aphanitic fine-grained forms from rapid cool.

• Phaneritic coarse-grained forms from slow cool.

• Porphyritic contains two distinct crystal sizes.

• Vesicular contains gas bubbles, common in pumice.

Igneous Rocks and Their Structures

• Glassy Texture: No crystals, from rapid cooling (obsidian).

• Pegmatitic Texture: Extremely coarse-grained, from water-rich magmas that cool slowly.

• Igneous rocks form from magma/lava solidification, classified as intrusive/extrusive.

• Intrusive rocks crystallize slowly, larger crystals; extrusive cool quickly, smaller crystals.

• Examples: granite (intrusive), basalt (extrusive).

• Intrusion (Pluton): Igneous rock body formed from underground crystallized magma.

• Dikes and Sills: Dikes are vertical, sills are horizontal intrusions.

• Batholiths and Stocks: Batholiths are large, irregularly shaped intrusions; stocks are smaller.

• Lava Flows: Aa (rough surface), Pahoehoe (smooth, ropy surface) indicate viscosity and cooling rate.

• Volatiles: Gases (water vapor, CO₂) affect eruption styles.

• Pyroclastic Materials: Ejected fragments (ash, lapilli, blocks) vary in size and impact.

Sedimentary Rocks and Their Formation

• Sedimentary rocks form through deposition, compaction, and cementation.

• Deposition: Sediments settle out of water/air, influenced by environment.

• Compaction: Reduces pore space under pressure.

• Cementation: Minerals precipitate from water, binding sediment grains.

• Clastic Sedimentary Rocks: From fragments of other rocks, classified by particle size (shale, sandstone, conglomerate).

• Chemical Sedimentary Rocks: From precipitation of minerals (limestone, chert).

• Organic Sedimentary Rocks: From biological debris (coal, coquina).

• Fissility: Shale splits along flat layers.

• Sorting and Stratification: Sorting is uniformity of grain size; stratification is layering.

• Diagenesis: Post-deposition changes (compaction, cementation) leading to lithification.

Metamorphic rocks and Plate Tectonics

• Metamorphic rocks form from existing parent rocks subjected to heat, pressure, and chemically active fluids.

• Common parent rocks: shale (to slate), limestone (to marble), granite (to gneiss).

• Solid-state metamorphism occurs without melting.

• Metamorphic Grade: Intensity, with low-grade leading to slight changes and high-grade to complete recrystallization.

• Increasing grade increases grain size and forms index minerals.

• Recrystallization: Change in mineral size and shape without melting.

• Slate: Low-grade, from shale, splits into thin layers.

• Marble: From limestone, crystalline structure.

• Gneiss: High-grade, banded, from granite.

• The Theory of Plate Tectonics explains the movement of Earth's lithosphere.

• Alfred Wegener's Continental Drift Hypothesis proposed Pangaea.

• The lithosphere is approximately 100 km thick.

Plate Boundaries and Geological Features

• Divergent Plate Boundary: Plates move apart, creating new lithosphere (Mid-Atlantic Ridge).

• Convergent Plate Boundary: Plates collide, leading to subduction zones (Andes Mountains).

• Transform Plate Boundary: Plates slide past each other, causing earthquakes (San Andreas Fault).

• Seafloor Spreading: New crust forms at ridges, supporting continental drift.

• Rift Valley: Deep valley at divergent boundaries (East African Rift).

• Deep-Ocean Trench: Formed by subduction.

• Mantle Plume and Hot Spots: Volcanoes form as plates move over plumes (Hawaiian Islands).

• Paleomagnetism: Study of Earth's ancient magnetic field.

• Magnetic Reversal: Earth's magnetic field has flipped, symmetric patterns support seafloor spreading.

• Convection Currents: Heat transfer drives plate movement.

Discussion questions

How does the process of metamorphism transform parent rocks into metamorphic rocks, and what factors influence this transformation?
Discuss the significance of the Theory of Plate Tectonics in understanding Earth's geological processes.
What are the key differences between intrusive and extrusive igneous rocks, and how do their formation processes affect their characteristics?
Analyze the role of weathering and erosion in the rock cycle and their impact on sedimentary rock formation.
Evaluate the importance of mineral properties in identifying and classifying minerals within the field of mineralogy.
How do the concepts of uniformitarianism and catastrophism differ in explaining geological changes over time?

Earth Science is the study of Earth and its neighbors in space, encompassing geology, oceanography, meteorology, and astronomy.

Key Aspects of Earth Science

• Geology: Study of Earth’s solid materials and processes.

  • Physical Geology: Materials and surface processes (rock formation, erosion).

  • Historical Geology: Earth’s origin and development through time.

• Oceanography: Study of Earth’s oceans, their composition, movement, and life forms.

• Meteorology: Study of the atmosphere, weather, and climate.

• Astronomy: Study of the universe beyond Earth, understanding Earth's place in the solar system.

The Scientific Method

The scientific method is central to Earth Science.

• Observation: Recognizing a problem or pattern in nature.

• Hypothesis: A tentative explanation.

• Experimentation: Testing the hypothesis through data and observations.

• Theory: A well-tested, widely accepted explanation.

• Law or Principle: A theory with no known exceptions after extensive testing.

The Earth System

Earth is a complex, interconnected system of four major spheres:

• Geosphere: The solid Earth (rocks, mountains, volcanoes).

• Hydrosphere: All water on Earth (oceans, rivers, lakes).

• Atmosphere: Gases surrounding Earth (weather and climate).

• Biosphere: All life on Earth, interacting with the other spheres.

These spheres are interconnected; changes in one sphere affect others.

Earth’s Internal Structure

Earth has three major layers:

• Crust:

  • Continental: Thicker, less dense (granitic).

  • Oceanic: Thinner, denser (basaltic).

• Mantle: Composed of peridotite, includes the asthenosphere (plastic-like).

• Core:

  • Outer: Liquid iron-nickel (Earth’s magnetic field).

  • Inner: Solid iron-nickel due to immense pressure.

Layers are defined by composition and mechanical properties.

Plate Tectonics

Earth’s lithosphere is broken into tectonic plates that float on the asthenosphere and interact, causing geological phenomena.

Time Scales

Earth is approximately 4.6 billion years old. Geologists use:

• Relative Time: Sequence of events.

• Absolute Time: Radiometric dating for numerical age.

Tools and Techniques

• Remote Sensing: Satellites collect data.

• Seismographs: Detect earthquake waves.

• GPS: Measures plate motion and surface changes.

• Geologic Maps: Show rock types, ages, and geologic features.

Earth Science is the study of Earth and its neighbors in space, encompassing geology, oceanography, meteorology, and astronomy.

Earth Science is the study of Earth and its neighbors in space, encompassing geology, oceanography, meteorology, and astronomy.

Key Aspects of Earth Science

• Geology: Study of Earth’s solid materials and processes.

  • Physical Geology: Materials and surface processes (rock formation, erosion).

  • Historical Geology: Earth’s origin and development through time.

• Oceanography: Study of Earth’s oceans, their composition, movement, and life forms.

• Meteorology: Study of the atmosphere, weather, and climate.

• Astronomy: Study of the universe beyond Earth, understanding Earth's place in the solar system.

The Scientific Method

The scientific method is central to Earth Science.

• Observation: Recognizing a problem or pattern in nature.

• Hypothesis: A tentative explanation.

• Experimentation: Testing the hypothesis through data and observations.

• Theory: A well-tested, widely accepted explanation.

• Law or Principle: A theory with no known exceptions after extensive testing.

The Earth System

Earth is a complex, interconnected system of four major spheres:

• Geosphere: The solid Earth (rocks, mountains, volcanoes).

• Hydrosphere: All water on Earth (oceans, rivers, lakes).

• Atmosphere: Gases surrounding Earth (weather and climate).

• Biosphere: All life on Earth, interacting with the other spheres.

These spheres are interconnected; changes in one sphere affect others.

Earth’s Internal Structure

Earth has three major layers:

• Crust:

  • Continental: Thicker, less dense (granitic).

  • Oceanic: Thinner, denser (basaltic).

• Mantle: Composed of peridotite, includes the asthenosphere (plastic-like).

• Core:

  • Outer: Liquid iron-nickel (Earth’s magnetic field).

  • Inner: Solid iron-nickel due to immense pressure.

Layers are defined by composition and mechanical properties.

Plate Tectonics

Earth’s lithosphere is broken into tectonic plates that float on the asthenosphere and interact, causing geological phenomena.

Time Scales

Earth is approximately 4.6 billion years old. Geologists use:

• Relative Time: Sequence of events.

• Absolute Time: Radiometric dating for numerical age.

Tools and Techniques

• Remote Sensing: Satellites collect data.

• Seismographs: Detect earthquake waves.

• GPS: Measures plate motion and surface changes.

• Geologic Maps: Show rock types, ages, and geologic features.