Geology: Igneous, Metamorphic, and Sedimentary Processes

A complete set of vocabulary flashcards covering metamorphic, igneous, and sedimentary geological processes, rock textures, and landforms based on the lecture notes.

Metamorphism

The process of solid-state change in a rock's original mineral crystals or clasts caused by specific heat and pressure conditions.

Metamorphic Grade

The relative degree of heat and pressure under which a metamorphic rock forms, ranging from low to high grades.

Protolith

The original, unmetamorphosed parent rock that undergoes metamorphism to form a new metamorphic rock.

Brittle-Ductile Transition

The boundary depth, typically near the lithosphere-asthenosphere boundary, where rock behavior transitions from breaking (brittle) to flowing in a solid state (ductile).

Contact Metamorphism

Metamorphism affecting a thin band of host rock around an igneous intrusion, driven primarily by high temperatures from the magma.

Regional Metamorphism

Widespread metamorphism occurring at convergent plate boundaries during continental plate collision and mountain building, characterized by moderate to ultra-high pressures and high temperatures.

Foliation

Planes within a rock produced by the parallel alignment or recrystallization of mineral grains under directed pressure.

Lineation

Linear features in a rock along which mineral grains are aligned, or the edges created by intersecting foliation and cleavage planes.

Isograd

A line drawn on a map connecting points of equal metamorphic grade where a specific index mineral first appears.

Metamorphic Facies

A categorization system for metamorphic rocks that groups specific mineral assemblages formed under distinct pressure and temperature conditions.

Barrovian Sequence

A progressive series of metamorphic zones mapped across a region (such as Scotland) indicating increasing metamorphic grade based on index minerals.

Metasomatism

The chemical alteration of a rock caused by hydrothermal fluids emanating from plutons, which transport ions and precipitate mineral veins.

Magma

Molten rock located beneath the surface of the Earth.

Lava

Molten rock that has breached and flows upon the surface of the Earth.

Phaneritic Texture

A coarse-grained igneous texture containing large crystals visible to the naked eye, produced by slow cooling within the Earth's interior.

Aphanitic Texture

A fine-grained igneous texture where individual crystals are too small to see without magnification, caused by rapid cooling at Earth's surface.

Porphyritic Texture

An igneous texture characterized by large crystals (phenocrysts) embedded in a finer-grained matrix (groundmass), formed by a two-stage cooling history.

Mafic

Igneous rock or magma rich in iron ($\text{Fe}$) and magnesium ($\text{Mg}$), typically dark-colored and crystallizing at higher temperatures.

Felsic

Igneous rock or magma rich in silica ($\text{SiO}_2$) and feldspar/sodium/potassium, typically light-colored and crystallizing at lower temperatures.

Bowen's Reaction Series

The predictable order in which silicate minerals crystallize from cooling magma between approximately $1200^\text{o}\text{C}$ and $600^\text{o}\text{C}$.

Obsidian

A dark volcanic glass formed by extremely rapid cooling of $\text{SiO}_2$-rich lava, lacking a crystal structure and displaying conchoidal fracture.

Viscosity

A fluid's internal resistance to flow; mafic lavas have low viscosity, while felsic magmas have high viscosity.

Pahoehoe and Aa

Two distinct surface textures of basaltic lava flows: Pahoehoe forms smooth, ropy surfaces, whereas Aa forms rough, jagged, clinkery surfaces.

Vesicles

Cavities or voids formed in extrusive igneous rocks when gas bubbles exsolve and become trapped in cooling molten rock.

Shield Volcano

A broad, gently sloped volcano covering a wide area, constructed from successive layers of low-viscosity, non-explosive basaltic lava flows.

Stratovolcano

A steep-sided, explosive volcano built of alternating layers of viscous lava and pyroclastic deposits (also called a composite volcano).

Pyroclastic Flow

A turbulent, hot, rapidly moving debris flow of gas, ash, and rock fragments formed by the collapse of an eruption column.

Lahar

A destructive mudflow composed of volcanic ash, rock debris, and water flowing rapidly down a volcano's slopes.

Nuées Ardentes

Superheated glowing avalanches of gas, lava, and ash that travel down volcanic slopes at speeds up to $500\text{ km/h}$.

Weathering

The physical disintegration, chemical dissolution, or biological breakdown of surface rock upon exposure to the atmosphere and hydrosphere.

Chemical Weathering

The breakdown of rocks through chemical reactions, such as dissolution or reaction with carbonic acid ($\text{H}_2\text{O} + \text{CO}_2 \rightleftharpoons \text{H}_2\text{CO}_3$).

Diagenesis

The low-temperature physical, chemical, and biological changes occurring after burial that compact, cement, and lithify sediments into sedimentary rock.

Conglomerate and Breccia

Coarse clastic sedimentary rocks; conglomerates contain rounded clasts from high-energy transport, whereas breccias contain angular clasts.

Graded Bedding

A sedimentary structure in which individual beds display a progressive upward decrease in grain size, typically formed by turbidity currents.

Evaporites

Chemical sedimentary rocks (such as gypsum and halite) formed by the precipitation of minerals during the evaporation of salty water.

Bioturbation

The disturbance and churning of sediment layers caused by the burrowing, foraging, and biological activity of living organisms.