EAS 2600: Volcanoes, Metamorphic Rocks, Geologic Dating, and Earth History

Comprehensive vocabulary flashcards covering volcanology, metamorphic petrology, stratigraphic and radiometric dating, and historical geology.

Volcano

An opening or vent on the Earth's surface through which lava, tephra (small rocks), and steam erupt; typically distributed along plate boundaries (mid-ocean ridges and subduction zones) and hot spots.

Hunga Tonga–Hunga Haʻapai (2022)

A major volcanic eruption recognized as the largest eruption of the $21\text{st}$ century.

Decompression Melting

A magma-generation process where upward movement of Earth's mantle causes confining pressure to decrease, thereby lowering the melting temperature of the rock without requiring additional heat; common at divergent boundaries and hot spots.

Volatiles (Magma Formation)

Chemical substances such as water ($\text{H}_2\text{O}$) that lower the melting temperature of mantle rocks, primarily driving melting in subduction zones.

Mafic Magma

Magma characterized by low silica content ($\text{around } 50\text{\%}$), low volatile/gas content ($\text{around } 0.5\text{\%}$), high eruption temperatures ($1100\text{--}1200\text{ }^{\circ}\text{C}$), and low viscosity, producing effusive lava flows.

Felsic Magma

Silica-rich magma ($\text{around } 70\text{\%} \text{ silica}$) with higher volatile/water content ($\text{around } 5.0\text{\%}$), lower eruption temperatures ($750\text{--}900\text{ }^{\circ}\text{C}$), and high viscosity, making it highly explosive and prone to forming lava domes and pyroclastic deposits.

Shield Volcano

A broad volcano with a rounded, low-profile dome formed by successive flows of fluid basaltic lava during effusive eruptions (e.g., Hawaiian volcanoes).

Stratovolcano (Composite Volcano)

A tall, steep-sided volcanic cone built by alternating layers of extrusive lava flows and pyroclastic deposits, characterized by explosive eruptions (e.g., Mount St. Helens).

Cinder Cone

A small ($<300\,\text{m}$), steep-sided conical pile of loose volcanic debris (lapilli and bombs), typically constructed during a single short-lived eruptive phase (e.g., SP Crater in Arizona).

Lahar

A dangerous volcanic debris flow or mudflow composed of volcanic debris mixed with water rushing down the slopes of a volcano.

Pyroclastic Flow

A high-speed, lethal avalanche of superheated gas, ash, and volcanic rock fragments flowing rapidly down volcanic flanks.

Tephra

All fragmented rock material ejected into the air during a volcanic eruption, classified by size into ash ($<2\,\text{mm}$), lapilli ($2\text{--}64\,\text{mm}$), and volcanic blocks or bombs ($>64\,\text{mm}$).

Volcanic Explosivity Index (VEI)

A relative scale ranging from $0$ (nonexplosive, Hawaiian) to $8$ (megacolossal, Ultra-Plinian) used to measure and compare the explosiveness of eruptions based on magma composition, temperature, and gas volume.

Phreatic Eruption

An explosive volcanic eruption produced when groundwater or hydrothermal fluids interact with hot magma, vaporizing water and pulverizing surrounding host rocks into ash without expelling new juvenile magma.

Plinian Eruption

A huge, highly explosive eruption characterized by catastrophic ejection of gas, ash, and pyroclastic debris extending high into the stratosphere.

Metamorphic Rock

Rock produced when pre-existing parent rock undergoes solid-state recrystallization and transformation under elevated heat, pressure, or hot chemically active hydrothermal fluids without melting.

Protolith

The original parent rock (sedimentary, igneous, or older metamorphic) that is transformed into a metamorphic rock.

Recrystallization

A solid-state metamorphic process in which the shape and size of existing mineral grains change while the mineral identity remains unaltered.

Phase Change (Metamorphism)

The transformation of one mineral species into another with identical chemical composition but an altered crystal lattice structure (polymorphs) due to changing pressure and temperature.

Neocrystallization

The growth of entirely new metamorphic minerals through solid-state chemical reactions among unstable minerals of the protolith.

Pressure Solution

A metamorphic alteration process driven by differential stress in the presence of pore fluid, where mineral grains dissolve at contacts under highest stress and precipitate in lower-stress zones.

Plastic Deformation

A mechanism by which rock minerals under elevated heat and confining pressure squeeze, stretch, or shear into new shapes without fracturing.

Foliation

A parallel planar fabric or banding in metamorphic rocks formed by the alignment of platy or elongated mineral grains under directed compression or shearing.

Nonfoliated Texture

The texture of metamorphic rocks that lack layered mineral alignment or compositional banding, typically containing equi-dimensional minerals (e.g., marble, quartzite, hornfels).

Contact Metamorphism

Thermal metamorphism occurring adjacent to an intruded igneous body, characterized by high temperatures and low pressures ("baking" of the host country rock).

Metamorphic Grade Progression of Shale

The systematic transformation sequence of a shale protolith with increasing heat and pressure: $\text{Shale} \rightarrow \text{Slate} \rightarrow \text{Phyllite} \rightarrow \text{Schist} \rightarrow \text{Gneiss}$.

Relative Age

The age of a geologic feature, rock layer, or event determined by its sequential order relative to other features using logical stratigraphic principles.

Absolute (Radiometric) Age

The quantitative age of a geologic material or event measured in precise units of numerical time using parent-to-daughter radioactive isotope ratios in a closed system.

Half-Life

The time required for exactly one-half ($50\text{\%}$) of the unstable parent radioactive atoms in a closed system to decay into stable daughter isotopes.

Carbon-14 Dating

A radiometric dating method based on the decay of radioactive Carbon-14, which has a half-life of $5730\,\text{years}$, used to date young organic materials and recent geologic events.

Law of Superposition

A fundamental stratigraphic principle stating that in an undeformed sequence of sedimentary strata, the oldest rock layer lies at the bottom and the youngest at the top.

Principle of Original Horizontality

The rule stating that sedimentary layers and extrusive volcanic rocks are initially deposited in horizontal or near-horizontal layers; tilted or folded layers must have undergone post-depositional deformation.

Principle of Inclusions

A relative dating principle stating that rock fragments contained within an adjacent host rock must be older than the host rock that encloses them.

Principle of Cross-Cutting Relationships

A stratigraphic principle establishing that any geologic structure or feature (such as an igneous intrusion or fault) cutting across another rock body must be younger than the body it cuts.

Baked Contacts

Metamorphic heat aureoles where an igneous intrusion thermal-bakes the surrounding host rock, proving that the baked rock is older than the intrusion.

Unconformity

A buried structural surface representing a gap in the geologic record caused by a prolonged period of non-deposition or erosion.

Disconformity

An unconformity where older, horizontal sedimentary strata are separated from younger, overlying horizontal strata by an erosional boundary.

Angular Unconformity

An unconformity where younger, flat-lying sedimentary beds overlie tilted, folded, or deformed older rock strata with contrasting dip angles.

Nonconformity

An unconformity where younger sedimentary rocks directly overlie eroded, older igneous plutonic or metamorphic basement rocks.

Geologic Time Scale

The hierarchical calendar of Earth's history subdivided sequentially into Eons, Eras, Periods, Epochs, and Ages based on major changes in the fossil record and planetary systems.

Period (Geology)

The basic chronological unit of geologic time during which a single continuous rock system or rock type forms.

Precambrian

The interval spanning the earliest $88\text{\%}$ of Earth history ($4.6\,\text{Ga}$ to $542\,\text{Ma}$), encompassing the Hadean, Archean, and Proterozoic eons, during which roughly $80\text{\%}$ of modern continental crust formed.

Hadean Eon

The earliest geologic eon ($\sim 4.6\,\text{Ga}$ to $\sim 4.0\,\text{Ga}$), characterized by accretion remnants, a molten surface, atmospheric ammonia, methane, and $\text{CO}_2$, and the formation of the Moon.

Archean Eon

An early eon marked by significant continental crust development, oxygen-poor atmospheres, and widespread deposition of banded iron formations (BIFs) through chemical reaction with dissolved marine iron.

Stromatolites

Laminated sedimentary structures created by cyanobacterial mats that trapped and bound sediments, providing direct evidence of early photosynthetic organisms.

Great Oxidation Event (GOE)

A transformative planetary transition occurring at approximately $2.45\,\text{Ga}$ in the Proterozoic Eon when cyanobacterial oxygen production outpaced surface oxygen sinks, leading to rising atmospheric oxygen and terrestrial red beds.

Snowball Earth Hypothesis

A model proposing that global glaciation during the Proterozoic Eon was triggered by intense chemical weathering of the Rodinia supercontinent coupled with ice-albedo positive feedback, terminated by volcanic $\text{CO}_2$ greenhouse accumulation.

Sevier Orogeny

A western North American mountain-building event ($120\text{--}50\,\text{Ma}$) characterized by thin-skinned compressive folding and thrust faulting.

Laramide Orogeny

A western North American tectonic event ($80\text{--}40\,\text{Ma}$) driven by shallow flat-slab subduction that produced thick-skinned basement deformation and deep-seated uplifts farther eastward from the plate boundary.

Paleozoic Era

The 'Early Life' era ($540\text{--}251\,\text{Ma}$) featuring the Cambrian explosion of organisms with hard mineralized parts, extensive coal-forming swamps, and ending with Earth's largest mass extinction.

Mesozoic Era

The 'Middle Life' era characterized by a warm global climate, lack of major glaciations, diversification of reptiles (dinosaurs), the Western Interior Seaway, and ending with the K–P extinction event.

Cenozoic Era

The 'New Life' era ($66\,\text{Ma}$ to present), known as the 'Age of Mammals,' marked by continental glaciations, modern tectonic configurations, rapid mammal radiation, and late Pleistocene megafaunal extinctions.