Comprehensive Physical Geology: Weathering, Sedimentary, Metamorphic, Geologic Time, Deformation, Earthquakes, and Earth Interior

Comprehensive practice flashcards matching vocabulary terms and rigorous scientific definitions across physical weathering, soil profiles, sedimentary facies and structures, metamorphic textures and facies, relative and absolute geologic dating principles, structural deformation, earthquake mechanics, and deep Earth interior geophysics.

Physical Weathering

The mechanical process of breaking rock into smaller fragments without altering its chemical or mineralogical composition.

Chemical Weathering

The breakdown of rock through chemical alteration and decomposition, transforming existing minerals into new minerals and dissolved ions.

Frost Wedging

A mechanical weathering process in which water percolates into fractures within rock, expands upon freezing, and drives the cracks wider.

Unloading (Sheeting)

A physical weathering process occurring when deep confining pressure is removed through uplift and erosion, causing igneous rock masses to expand and fracture into outward-flaking, onion-like sheets.

Dissolution

A chemical weathering process in which polar water molecules pull mineral ions apart and hold them in solution, such as the dissolution of halite or the dissolving of limestone by carbonic acid.

Oxidation

A chemical weathering reaction in which oxygen reacts with iron-bearing minerals, transforming soluble ferrous iron ($\text{Fe}^{2+}$) into insoluble ferric iron ($\text{Fe}^{3+}$) and precipitating iron oxides.

Hydrolysis

A chemical weathering reaction wherein mineral cations are replaced by hydrogen ions ($\text{H}^+$) from water, converting silicate minerals like feldspar into clay minerals.

Spheroidal Weathering

A weathering phenomenon combining physical jointing and chemical decomposition where joints, edges, and corners are decomposed faster than planar rock faces, producing rounded, spherical boulders.

Differential Weathering

The process whereby different rocks and minerals decompose and erode at unequal rates due to contrasts in mineral solubility, rock structure, and degree of fracturing.

Talus

An accumulation of coarse, angular rock fragments fallen from a cliff face that forms a steep, debris-covered slope at the base.

Ideal Soil Composition

A balanced, four-part volumetric mixture of weathered earth materials consisting of approximately $45\%$ mineral matter, $5\%$ organic matter (humus), $25\%$ air, and $25\%$ water.

Zone of Leaching

The upper portion of a soil profile (including the A and E horizons) where percolating rainwater dissolves minerals and carries downward mobile ions and fine clays.

Zone of Accumulation

The subsoil horizon (B horizon) where clays, iron oxides, and dissolved ions transported downward by percolating water precipitate and collect.

Detrital (Clastic) Sediments

Solid mineral and rock fragments produced by the mechanical disintegration and physical weathering of pre-existing rocks, which are subsequently transported and deposited.

Siliciclastic Sediments

Detrital sediment particles consisting predominantly of silicate minerals, such as quartz and feldspar grains, derived from weathered crustal rocks.

Bioclastic Sediments

Sediment composed of physical fragments, shells, and skeletal parts generated by organisms.

Competence

The measure of the maximum particle size that a transport medium (such as water, wind, or glacial ice) is capable of transporting.

Sorting

The degree of similarity in grain size within a sedimentary deposit, reflecting the energy fluctuations and consistency of the transporting medium.

Cross-bedding

A sedimentary structure composed of thin beds deposited at an angle inclined to the main horizontal bedding surface, formed by the deposition on the slip faces of migrating dunes or ripples.

Graded Bed

A sedimentary layer characterized by a systematic vertical change in grain size from coarse particles at the base to fine particles at the top.

Turbidite

A graded sedimentary deposit formed by a submarine turbidity current that flows downslope along continental margins into deep-sea fans.

Mudcracks

Polygonal fracture structures that form when saturated, fine-grained mud or clay shrinks and cracks upon drying as water evaporates in an enclosed subaerial environment.

Oolite

A sedimentary structure composed of small, spherical, sand-sized grains (ooids) formed by chemical precipitation of concentric calcium carbonate layers in warm, agitated shallow marine waters.

Sedimentary Facies

A distinct assemblage of sedimentary rocks that possess specific physical, chemical, and biological attributes reflecting their deposition in a particular environment.

Marine Transgression

A geological event during which relative sea level rises, causing the shoreline and coastal depositional environments to advance inland across the continental surface.

Diagenesis

All chemical, physical, and biological changes that occur to sediment after deposition and prior to metamorphism, primarily compaction and cementation that drive lithification.

Quartz Arenite

A highly mature detrital sandstone composed almost entirely of well-rounded, sand-sized quartz grains.

Arkose

A detrital sandstone containing an appreciable quantity of feldspar (typically $\ge 25\%$) alongside quartz, reflecting limited chemical weathering and transport.

Protolith

The original, unmetamorphosed parent rock (whether sedimentary, igneous, or older metamorphic) from which a metamorphic rock is derived.

Metasomatism

Metamorphic alteration driven by the circulation of active, hot hydrothermal fluids along rock fractures that exchanges ions and modifies bulk chemical composition.

Foliation

A planar arrangement of mineral grains or structural features within a metamorphic rock, caused by directed pressure and differential stress.

Slaty Cleavage

A low-grade metamorphic foliation where clay and mica minerals align perpendicularly to compressional stress, allowing the rock to split smoothly into thin, planar sheets.

Gneissic Banding

A high-grade metamorphic texture characterized by segregated alternating compositional bands of light-colored felsic minerals (quartz and feldspar) and dark-colored mafic minerals.

Granoblastic Texture

A non-foliated metamorphic rock texture composed of roughly equigranular, interlocking crystals (such as calcite in marble or quartz in quartzite) lacking preferred directional orientation.

Porphyroblastic Texture

A metamorphic texture characterized by unusually large crystals (porphyroblasts, such as garnet or staurolite) that grew within a much finer-grained mineral groundmass.

Contact Metamorphism

Local metamorphism driven primarily by high thermal energy and fluids emanating from an adjacent intruding magma body under low confining pressures.

Metamorphic Aureole

A concentrically zoned halo of altered rock surrounding an igneous intrusion, displaying a progressive decrease in metamorphic grade outward from the heat source.

Mylonite

A foliated, fine-grained metamorphic rock generated deep along active fault zones where rocks undergo ductile flow, high shear strain, and dynamic recrystallization.

Regional Metamorphism

Widespread metamorphism associated with large-scale plate collisions and mountain building, characterized by high directed pressures and elevated temperatures affecting extensive crustal belts.

Metamorphic Facies

A distinct group of metamorphic mineral assemblages that consistently crystallize together within specific temperature and pressure regimes, serving as indicators of tectonic environment.

Prograde Metamorphism

The progressive recrystallization and mineral transformation of a rock as it encounters steadily increasing temperature and pressure conditions.

Retrograde Metamorphism

Metamorphic reactions that take place when deep, high-grade rocks are returned toward the surface, experiencing declining temperature and pressure.

Deep Time

The immense concept of geologic time, extending across billions of years, which far exceeds the limits of human generational experience and recorded history.

Principle of Superposition

The relative dating principle stating that in an undeformed sequence of sedimentary rocks, the oldest rock layer is on the bottom and the youngest is on the top.

Principle of Original Horizontality

The relative dating principle stating that layers of sediment are originally deposited in nearly flat, horizontal beds under the influence of gravity.

Principle of Original Lateral Continuity

The relative dating principle stating that sedimentary beds extend laterally in all directions until they gradually thin out, grade into another sediment type, or terminate at the margin of the depositional basin.

Principle of Cross-Cutting Relationships

The relative dating principle stating that a geologic feature (such as an igneous intrusion or a fault) that cuts across another rock unit is younger than the rock unit being cut.

Principle of Inclusions

The relative dating principle stating that fragments of rock contained within another rock mass are older than the rock mass that encloses them.

Principle of Biotic Succession

The principle formulated by William Smith stating that fossil organisms follow one another through time in a definite, recognizable chronological sequence, meaning any geologic period can be identified by its fossil content.

Stratigraphic Correlation

The process of establishing age equivalence and matching rock strata or formations across separated geographic localities using physical lithology or index fossils.

Unconformity

A surface within a rock sequence representing a substantial gap in the geologic record, caused by an extended interval of nondeposition, weathering, or erosion.

Angular Unconformity

A boundary where younger, flat-lying sedimentary beds overlie the eroded, dipping edges of older tilted or folded rock strata.

Nonconformity

An unconformity where younger sedimentary strata are deposited atop an eroded surface of older crystalline igneous or metamorphic rocks.

Disconformity

A break in the sedimentary record where the strata above and below the erosional surface remain parallel to each other.

Radioactive Half-Life

The duration of time ($t_{1/2} = \frac{\log_e(2)}{\lambda}$) required for half of the original parent atoms in a radioactive sample to decay into stable daughter isotopes.

Isochron Dating

A radiometric dating method analyzing multiple mineral or cogenetic rock samples to test closed-system assumptions and accurately establish absolute crystallization age.

Stress

The force applied per unit area across a body of rock, classified into compressional, tensional, or shear stress.

Strain

The resulting change in shape, size, or orientation of a rock body that occurs in response to applied stress.

Elastic Deformation

A nonpermanent deformation where a rock strains under stress but returns to its original dimensions when the stress is removed.

Ductile Deformation

A permanent strain mechanism where rock undergoes bending, stretching, or plastic flow at depth without fracturing.

Brittle Fracture

Mechanical deformation occurring at shallow depths and low temperatures where applied stress exceeds the elastic limit, causing the rock to crack or break.

Strike and Dip

A coordinate system describing the spatial orientation of a tilted planar rock layer, where strike is the compass bearing of a horizontal line on the plane and dip is the angle of maximum downward inclination.

Joint

A planar fracture in a rock mass along which there has been no perceptible displacement or movement.

Fault

A planar fracture in rock along which measurable relative displacement and slip of adjacent rock blocks has occurred.

Normal Fault

A dip-slip fault caused by tensional stress where the hanging wall block moves downward relative to the footwall block.

Reverse Fault

A dip-slip fault caused by compressional stress where the hanging wall block moves upward relative to the footwall block.

Thrust Fault

A reverse fault with a low angle of inclination (dip less than $45^\circ$), typically accommodating significant crustal shortening.

Strike-Slip Fault

A fault governed by shear stress along which opposing blocks slide horizontally past each other parallel to the trend of the fault trace.

Anticline

An upfolded arch of rock strata in which the limbs dip away from the axial plane and the oldest rock layers are exposed in the core.

Syncline

A downfolded trough of layered rock in which the limbs dip inward toward the axial plane and the youngest strata occupy the center.

Monocline

A large, step-like flexure or one-limbed fold in otherwise horizontal sedimentary rock strata, frequently draped over an underlying basement fault.

Structural Basin

A circular or elliptical downwarped fold where rock strata dip inward toward a central low point, leaving the youngest layers at the center.

Elastic Rebound Theory

The mechanism explaining earthquake generation wherein tectonic stress gradually strains rock elastically until frictional resistance fails, abruptly releasing stored energy as seismic waves.

Hypocenter (Focus)

The exact underground location along a fault plane where strain energy is first released and earthquake rupture originates.

Epicenter

The point on Earth's geographic surface located vertically directly above the hypocenter (focus) of an earthquake.

Seismograph

An instrument consisting of a supported mass and recording device that detects, amplifies, and graphs ground vibrations produced by passing seismic waves.

P-Wave (Primary Wave)

A compressional body wave that alternates pushing and pulling the medium parallel to the direction of wave travel, transmitting through solids, liquids, and gases at the highest velocities.

S-Wave (Secondary Wave)

A shear body wave that vibrates rock particles perpendicularly to the direction of propagation, traveling slower than P-waves and capable of passing only through solid materials.

Love Wave

A seismic surface wave that causes horizontal, side-to-side shearing motion of the ground perpendicular to the wave's path of travel, responsible for severe damage to building foundations.

Rayleigh Wave

A surface wave that creates an elliptical, rolling retrograde ground motion in a vertical plane parallel to the direction of wave advance.

Modified Mercalli Intensity Scale

A subjective scale ranging from I to XII that assesses earthquake shaking based on human sensations and observed physical damage to structures.

Richter Magnitude Scale

An objective, open-ended logarithmic scale that quantifies earthquake size based on the maximum ground wave amplitude recorded on a standard Wood-Anderson seismograph, corrected for distance.

Moment Magnitude ($M_w$)

A modern, objective measure of earthquake size determined from the surface area of the fault rupture, the average amount of fault slip, and the shear modulus of the rock.

Wadati-Benioff Zone

A narrow, dipping planar zone of earthquake foci extending into the mantle beneath an active subduction margin, tracing the trajectory of the descending oceanic plate.

Soil Liquefaction

The temporary transformation of loosely packed, water-saturated sandy sediments into a fluid-like slurry during prolonged seismic shaking, resulting in ground subsidence and sand volcanoes.

Tsunami

A rapidly traveling series of destructive oceanic sea waves generated by the sudden vertical displacement of the seafloor during an earthquake, volcanic collapse, or submarine landslide.

Mohorovičić Discontinuity (Moho)

The compositional boundary separating Earth's crust from the underlying ultramafic mantle, marked by an abrupt increase in seismic P-wave velocity from approximately $6\,\text{km/s}$ to $8\,\text{km/s}$.

S-Wave Shadow Zone

The geographic zone between $105^\circ$ and $180^\circ$ from an earthquake epicenter where direct shear waves are completely blocked, confirming that Earth's outer core is a liquid.

P-Wave Shadow Zone

A band extending between $105^\circ$ and $140^\circ$ from an earthquake epicenter where direct compressional waves are absent due to downward refraction at the core-mantle boundary.

Geodynamo

The process by which thermal convection and planetary rotation produce electrically charged spiral flow within the liquid iron-nickel outer core, generating Earth's magnetic field.

Diamond Anvil Cell

A laboratory apparatus that squeezes microscopic samples between the polished facets of two opposing diamond gems to simulate extreme planetary interior pressures.

Geoid

The theoretical equipotential surface of Earth's gravity field that matches mean sea level in the open ocean and varies according to uneven internal mass distribution.