geology Flashcards
Catastrophism
features of the Earth explained through a series of Biblical floods. Baron Cuvier & Abraham Gottlob Werner
Uniformitarianism
James Hutton proposed Deep Time and Earth features explained by every day observable processes operating gradually at the same rates over time. Charles Lyell, 1830’s “the present is the key to the past”
Actualism
Earth processes operating through Deep Time are responsible for observable features, but that rates and processes have changed over geologic time. global catastrophes have occurred
Crystalline structure
solids with elements arranged in a definite pattern
stability range
pressure, temperature, fluid composition, used to deduce the conditions under which the mineral in the rock formed
paleomagnetism
help to deduce location on planet where mineral cooled down
help to deduce where & how rocks were formed
numerous isotopic signatures
Formed from cooling of a silicate melt (magma/lava)
Composed of silicate minerals
Product of plate tectonics and hot spots
Records the melting and cooling history of the Earth
Igneous Crystalline texture
igneous rocks
Plutonic (Intrusive)
silicate melt (magma) cools slowly underground
Volcanic (Extrusive)
silicate melt (lava) cools rapidly at the Earth’s surface
Phaneritic Texture (coarse-grained)
minerals easily visible, >1mm in size - indicates slow cooling of the magma at depth within the earth
Aphanitic Texture (fine-grained)
too fine to see, <1mm - indicates rapid cooling of an igneous melt (lava) generally at/near earth surface
Pegmatitic texture
crystals very coarse, > than 1 cm for the most part - indicates slow cooling & crystal growth accelerated by large amounts of water in the magma
Aphanitic-Porphyritic texture
formed cooling to produce the large crystals (phenocrysts) then rapid cooling to produce the fine crystals (groundmass)
indicates initial slow cooling of the magma in the magma chamber to produce the large visible phenocrysts / eruption of the magma (liquid and the early formed crystals) to the surface where the liquid cools rapidly around the larger phenocrysts to become the aphanitic groundmass
Pyroclastic texture
fragments of volcanic rock, crystal fragments, and/or volcanic ash
formed by ash or air fall and ash flow eruptions
Ash or air fall eruptions
produce fragments that cool in the air and fall to the ground cold
Ash flow eruptions
produce hot incandescent ash that rushes down the flanks of a volcano to come to rest hot. fragments generally welded together into a dense, hard rock
Sedimentary Rocks
Formed by the compaction and/or cementation of sediment that was deposited at the Earth’s surface by water, wind, ice, or biological processes
Records the Surface History of the Earth
Mechanical weathering
breaks rock into pieces or fragments (clasts or detritus)
Chemical weathering
decomposes the unstable minerals by reacting with water and gas
Clastic Textures
Siliciclastic fragments (boulder to clay-size) are lithified by compaction and/or cementation, boulder to sand-size particles generally lithify by cementation to form sandstone or conglomerate
Silt and clay-size particles are lithified by mainly compaction and far less cementation; these form siltstone and shale (mudstone)
Chemical Precipitates (Sedimentary Crystalline Texture)
Interlocking, random oriented carbonate, sulfate, or halide minerals. produced when dissolved ions precipitate from saline waters to produce rock salt, gypsum rock or limestone.
Organic Precipitates (Bioclastic, Biochemical, and Crystalline Textures)
Fossil fragments in a matrix of crystalline calcite. Dissolved ions in seawater are precipitated by organisms in the form of shells that then accumulate on the seafloor. Commonly composed of calcareous or calcite shells.
metamorphic rocks
Formed by recrystallization of pre-existing rocks (protoliths) in the solid state; generally formed in the roots of mountain ranges at convergent plate boundaries
Comprise large portions of the continental basement and are found in the eroding old and young mountain ranges
Records the history and development of mountain ranges
Factors Influencing Metamorphism
Composition of the Original Protolith
Increasing Temperature & Pressure
Chemically Active Fluids
Foliated texture
interlocking minerals that are aligned in planes, dominated by platy or elongate minerals
Hydrologic Cycle
Movement of the Earth’s water & gas layer
Powered by solar radiation w/ minor geothermal energy
Sculpts the continental land surface & produces sediment for sedimentary rocks
Plate Tectonic Cycle
Motion of the Earth’s fragmented lithosphere over the plastic asthenosphere
Energy of cycle from escaping internal energy of Earth
Gravitational attractions - density contrasts between parts of the Earth
Divergent Plate Boundaries
2 plates spreading apart
Extensional or tensional stress
Hot rising mantle peridotite
Partial melting (p.m.)
Volcanism (extrusion) and plutonism (intrusion) of melts (magmas)
Thermal doming (isostatic response to heating)
Convergent Plate Boundaries
2 plates converging or colliding
Compressional stresses
Subduction of old, cold lithospheric oceanic plate & recycling
Accretion of sedimentary material and/or buoyant landmasses
Partial melting (p.m.)
Volcanism (extrusion) and plutonism (intrusion) of melts (magmas)
Transform Plate Boundaries
2 plates sliding horizontally passed each other
Horizontal shear stress
Boundary is marked by a major strike-slip fault system
No rising or sinking of material
No partial melting, volcanism or plutonism
Normal vs. Superplume Events
Production of Large Igneous Provinces (LIPs)
Superplume is short-lived mantle event
Hot Spot Cycle
Stationary to semi-stationary convecting mantle plumes that rise from deeper than the asthenosphere
Create a physiographic landform on the Earth - a linear volcanic chain or hot spot track
Linear hot spot tracks used to determine long-term absolute plate motions
Rock Cycle
recycling of earth’s materials driven by earth’s internal heat engine and hydrological cycle (water wind etc) - relationship to dynamic cycles of earth
Continental Basement
ancient eroded roots of mountain ranges, generally > 1.0 Ga; mainly igneous intrusions and metamorphic rocks, the exposed continental basement is known as the shield - precambrian
Stable Platform
thin veneer of young, undeformed, flat-lying sedimentary rocks within the continental interior, generally < 600 million years (Ma); makes up the Great Plains of North America
Orogenic Belts
elongated regions of deformation bordering continental cratons
Young in which subduction is still taking place, are characterized by frequent volcanic activity & earthquakes
Older typically deeply eroded to expose displaced and deformed strata. These are often highly metamorphosed and include vast bodies of intrusive igneous rock called batholiths
Relative Age Dating
Process of logically placing a related group of rocks into a progressive sequence of events
Principle of Horizontality
Most sedimentary rocks are deposited in approximately horizontal layers
conformable sequences or layers
when layers are deposited one on top of another without gaps or breaks in time
Principle of Superposition
Sedimentary rock layers are deposited one on top of another oldest rock layers are on the bottom unless they have undergone substantial deformation
Principle of Continuity
Sedimentary rock layers are often deposited over continuous areas of the basin of sedimentation. They may often be traced out over long distances (even between states).
Principle of Faunal Succession
Rock layers with several fossils can be used to determine concurrent time range when all fossils present would overlap in time
Principle of Cross Cutting Relationships
Intrusions, faults, buried erosional surfaces (unconformities)
Principle of Inclusion (Fragments)
Fragments (clasts) found in a rock or rock layers are older than the unit or layers they are included within
Xenoliths “foreign rocks” in igneous intrusions and/or lava flows
Disconformity
An erosional surface between parallel sedimentary layers
Nonconformity
Erosion surface between sedimentary rocks and igneous and/or metamorphic rocks
Angular Unconformity
Erosional surface between sedimentary layers that are tilted to each other
