GEOL 1100 Vachula Exam 2 (Slides)
Metamorphic Facies
A facies is a specific set of features that are tied together in an interpretive group. Facies can be based on mineralogy, biologic factors, fossils, rock types, etc
Index fossils
A fossil which is characteristic of a particular span of geologic time or environment and can be used to identify and date the containing rocks. Key Features: - Limited vertical range - (often coupled with rapid evolution) - Wide geographic distribution
The geologic time scale
Boundaries were placed where important changes occur (such as extinction events), and subsequent numeric age dates have been determined later for those boundaries.
Hadean Eon
Characterized by Earth's initial formation—from the accretion of dust and gases and the frequent collisions of larger planetesimals
Archean Eon: Cratons stabilized
Craton: the old, stable part of a continent - Composed of ancient crystalline basement rock (although it can be covered by younger sedimentary rocks) - Shield: the basement rock crops out at the surface - Platform: any coverage of sedimentary rocks - Thick "roots", extending over 150km deep into the Earth
Stress (Metamorphic Process)
Creates squeezing and stretching from unequal directions (Plastic deformation and foliation; linations)
Regional metamorphism: Dynamothermal
Deep burial, thick crust, high temperatures and high pressures. - Common in mountain building tectonic regions (continent-continent)
Archean Eon: Continental Crust
Exact method during the Archean is unknown - Today continental crust is formed by tectonic activity - When a crust melts, lighter material floats up and is expelled through volcanism - This solidifies on the Earth's surface as our continental crust - Early protocontinents accumulated lighter felsic materials as developing plate -tectonic processes brought lighter material from the mantle to the surface.
Archean Eon:
First life Chemical signatures- 4.1 Ga zircon crystals have carbon signatures suggesting life - Life prefers to use lighter isotopes, so will try to usecarbon-12 over carbon-13 - Zircons will contain a higher than expected amount of carbon-13 in the presence of life Microfilaments- Shapes are similar to what we see created by life at modern hydrothermal vents
Pressure (Metamorphic Process)
Forces compaction and alters crystal structure (Phase change and Plastic deformation)
Absolute Dating
Gives specific ages to events
Temperature (Metamorphic Process)
Heat causes atoms to vibrate, snapping bonds (Recrystallization and Neocrystallization)
Hydrothermal metamorphism
Heated water moves through fractures and pores and dissolve/transport minerals. Metasomatism (adding and/or subtracting to the minerals) occurs. Minerals then recrystallize in more stabilize conditions Intex minerals: Chlorite and serpentine
Differentiation: Stratification of Earth Layers
Heavy metals (iron, nickel) sink to the center forming the core. Lighter elements (Oxygen, aluminum, silicon) concentrate on the outer part forming the mantle and core
Lineation
If the minerals are longer than wide, they will develop lineation. Lineation has all the minerals in one direction, but doesn't need to be on a single plane like foliation
Differential Stress (Metamorphic)
In many cases, rock may experience an additional, unequal stress due to tectonic forces. There are three basic kinds. Causes rock to develop layered texture called foliation
Steno
Interest in stratigraphy (the study of rock layers) lead the several key principles we still use today
Absolute Age
Isotopic dating - Radioactive decay (half-life) - Stable isotope ratios Paleomagnetic dating
Relative Dating Principles (All together)
Law of superposition- Oldest on the bottom! Principle of original horizontality- Tilting and folding come after stacking! Principle of lateral continuity- Separate units does always not mean separate rocks Principle of cross-cutting relationships- Igneous intrusions, faults, animal burrows Unconformities- Disconformity, Nonconformity, Angular unconformity Principle of included fragments- Xenoliths (xenocrysts) Principle of faunal succession- Correlation of beds via fossils; index fossils
Which minerals to use
Limited by the number of half-lives - Carbon cannot date things older than 60,000 years - Rubidium decay is slow so isn't accurate at precise decades Limited by the minerals/source material - What can be found and where - Reheating can destroy the daughter isotopes - what does this mean about the rocks/minerals that can be used? Contamination might occur What about sedimentary rocks?
Subduction Zone metamorphism
Low temperature, high pressures (Contact) - Blueschists and eclogites
The Cambrian: Alabama's Piedmont Region
Marine algae contributed massive amounts of mineral sediments composed primarily of calcium carbonate (CaCO). Alabama Marble Deposit = 32 miles long, up to a mile and a half wide, and over 600 feet deep
Atom's Mass
Mass= Protons + Neutrons
The Paleozoic, "Age of Spineless, not Heartless"542 - 251 mya
- "Complex" marine life - Cambrian explosion - Plants - First life on land - Most of the coal we used today formed - Formation of Pangea (supercontinent)
The Cretaceous: K - T Extinction
- A massive asteroid hit the earth, causing waves of destruction - Caused a massive global cooling event by blocking out the sun and CO2 released - Around 75% of species went extinct - onland
The Silurian
- Appalachian Mountains forming - Vascular plants - Fungal expansion - Arthropods started taking over land - Jawed and bony fish - First record of charcoal in the fossil record
The Silurian: Iron Ore deposits
- Attracted both Native American artisans and European settlers - Allowed for the massive iron and steel industry in Birmingham - Erosion from the formation of the young Appalachian Mountains flowed into the shallow seas and created these iron rich beds
The Cretaceous
- Breakup of Gondwana - Arrival of flowers - Mesozoic Marine Revolution effects are widespread - Birds and mammals as we know them today appear - Massive diversification of insects
The Carboniferous
- Coal- Tetrapods on land - age of amphibians - Ended in the formation of the supercontinent Pangea (the final event in the formation of Appalachian uplift - Amniote egg
Regional metamorphism: Burial
- Deep enough for recrystallization and neocrystallization, but no foliation or lineation- Quartzite and other low grade metamorphic rocks
The Permian
- Diversification of amniotes as the sauropsida (reptiles and birds) and synapsids (everything else) - Dominated by the supercontinent Pangea - Largest mass extinction event in known history ended the Permian - First modern trees ● The Great Dying- Cause remains unknown. The scientific consensus is the Siberian Traps (flood basalts), which released sulfur dioxide and carbon dioxide, elevating global temperatures and acidifying the oceans
Foliation
- Foliation forms when stress squeezes the flat or elongated minerals within a rock, so they became aligned - Non-foliated metamorphic rocks lack a planar (oriented) fabric
In the Archean Eon
- Formation of the continental crusts - Plate tectonics stabilized (?) - Liquid water - First life - Lots of celestial body impacts - Beginning of the rock record
The Paleogene
- Grasslands - Radiation of mammals on land - Return of mammals into the oceans - Birds get big - Extreme temperature shifts from hot to cold
The Quaternary
- Homo sapien appears - Extinction of many large mammals - Glaciers retreat - Formation of the Great Lakes
Relative Age Stenos***
- Inclusions - Fossil Correlation - Steno's principles - Superposition - Horizontality - Lateral continuity - Cross-cutting relationships
The Cenozoic, "Age of Mammals"
- Modern geological landscape evolves - The creation of California via the subduction of the Farallon plate - Creation of the Rockies and other major mountain ranges in the west - Mammals get big and dominant on land - Humans came around
The Triassic
- Pangea starts to break up - Rise of the Dinosaurs and other sauropsids - First flying vertebrates and reptiles returned to the seas - Mammals evolve - Ended in yet another extinction! - Rise of major
Proterozoic Eon (2.5 Ga - 541 Mya)
- Plate tectonics in full effect - Great Oxidation Event - Multicellular life
Pressure VS Stress (Metamorphic)
- Pressure is when all stresses on the body are equal - Directed Stress is one or more directions of stress are not equal
The Devonian
- Radiation of life on land - Tetrapod morphs (ancestors of all four -limbed animals) evolve - South China left Gondwana - Acadian orogeny increases the lift and formation of the Appalachian Mountains - Second of our 5 major mass extinction events - Age of fishes
Modes of Metamorphism
- Recrystallization - Neocrystallization - Phase change - Pressure solution - Plastic deformation
The Cambrian
- The Cambrian Explosion - Shallow oceans - Break up of the supercontinent Pannotia
Pore fluid
- liquids or gases found in the spaces (pores) between grains of sediment, sedimentary rocks, and other geologic materials (Metamorphism) - Driven out of the rock as pressure and temperature increases, forming veins. Can also lower melting point causing pockets of magma
Metamorphism
- process by which pre-existing rocks (igneous, sedimentary, or older metamorphic rocks) undergo physical and chemical changes due to heat, pressure, and/or chemically active fluids, without melting - This process alters the rock's mineral composition, texture, and structure while remaining in the solid state.
The Jurassic
-Continued breakup of Pangea - The beginning of the Atlantic Ocean - Dominance of the dinosaurs - Tectonic activity in western N.America, the beginnings of the rockies - Feathers are found in the fossil record - Mesozoic Marine Revolution takes off
The Cretaceous: The Black Belt Region of Alabama
-Defined by both cultural and physicalgeography - The region is underlain by a thin layer of rich, black soil developed atop the chalk of the Selma Group - Plankton left behind exoskeletons rich in calcium carbonate—the accumulation of which resulted in the Black Belt's chalk subsoil - During the twentieth century, Alabama's Black Belt became a hotbed of activity for the civil rights movement in the South.
The Neogene
-Grasslands spread and drive mammal evolution - Kelp forests evolve - Beginnings of hominoid evolution - Animals evolve to become very similar to what is seen today
The Ordovician
-Greater diversity of vertebrates and invertebrates - critically reef building organisms (e.g., crinoids) - Land plants - Rise of the Appalachian Mountains - First Mass Extinction
How was the timescale created?
Relative Age: - Steno's principles - Superposition - Horizontality - Lateral continuity - Cross-cutting relationships - Inclusions - Fossil Correlation Absolute Age: - Isotopic dating - Radioactive decay (half-life) - Stable isotope ratios - Paleomagnetic dating
Atomic Number
The number of protons in an atom
Disconformity
Two layered rocks that may seem conformable, but an erosional surface exist between them
(Steno) principle of superposition:
Unless deformed, overturned, or otherwise disturbed, newer rocks will always lie atop older rocks
Cenozoic Era
age of mammals "recent life"
Mesozoic Era
age of reptiles "middle life"
Paleozoic Era
age of trilobites "ancient life"
Hadean, Archean, and Proterozoic
are together referred to as the Precambrian, meaning "before Cambrian period." "Precambrian" is an informal term that encompasses 88% of geologic history
Recrystallization
change in the shape and size of mineral grains
Plastic deformation
change of mineral shape without breaking
Phanerozoic Eon
evidence of life
Isotopes
have the same number of protons but different numbers of neutrons. Consequently, different mass
Pressure solution
minerals dissolve at high pressure in water then flow to a place of lower pressure (stress) and recrystallize into something else or the same mineral (but a little different)
Neocrystallization
new mineral growth from the destruction of old minerals
Contact metamorphism
occurs adjacent to igneous intrusions and results from high temperatures associated with the igneous intrusion
Regional metamorphism
occurs over large areas and generally does not show any relationship to igneous bodies. • Result from collisions between tectonic plates
Metasomatism
occurs when a large volume of fluid flows into or out of a rock. It is a process that changes the rock composition by removal or addition of chemical elements.
Protolith (or Parent rock)
pre-existing rock before metamorphism
(Steno) Cross-cutting relationships
the geologic feature which cuts another is the younger of the two features - Faults - Intrusions - Streams - Impact crater - Animal burrows
Half Life
the time period that is characterized by the time it takes for half of the substance to decay
Phanerozoic Eon
time of "visible life" on Earth Although life originated in the Archean not until the Phanerozoic did a rapid expansion and evolution of forms occur and fill the various ecological niches available
Phase change
transformation of one mineral into another by changing the crystal structure
Angular Unconformity
two rock layers that have different angles of deposition relative to horizontal
index mineral
used in geology to determine the degree of metamorphism a rock has experienced
Shock metamorphism
very high pressures and temperatures caused by meteorite impact
Nonconformity
where sedimentary strata are deposited on crystalline (igneous or metamorphic) rocks
Evolution
• Evolution = cross-generational changes in characteristics of biological populations • Developed by Charles Darwin • Natural selection and genetic drift are the mechanisms for evolution
Geochronologic Units
• From the largest geochronologic units to• smaller units: •Eons > Eras > Periods > Epochs
Sadler Effect
• Global sediment rates • Longer time spans incorporate more "missing time"
Proterozoic Eon
During the Proterozoic, the atmosphere and oceans changed significantly. Proterozoic rocks contain many definite traces of primitive life-forms
Hadean: surficial water
Earth's water isotopically matches meteorite water better than comet water. But, Earth processes could have changed the water's isotopic signature over the last 4 Ga Possibly mixed sources contributed to the origin of Earth's water.
Fluids (Metamorphic Process)
Allows for minerals to move from high stress and reform in low stress (Pressure solution and rock veins)
Stable v Unstable
An atom is unstable (radioactive) if the nucleus has an excess of internal energy
Unconformity
Any time the contact between two layers is suspected to not be continuous - Metamorphism - Intrusion - Erosion
When does metamorphism start
At a depth of 5 km, the temperature is about 150oC, which is the line between sedimentary diagenesis (creation of sediment to sedimentary rock) and metamorphism (5 and lower is metamorphism)
Relative Dating
Puts Earth history events in order (older to younger) without specific ages
Lithostatic stress (Metamorphic)
Rock beneath the Earth's surface experiences equal pressure exerted on it from all directions because of the weight of the overlying rock
Metamorphic Processes
Temperature, Pressure, Fluid, and Stress
Proterozoic Eon:
The Great Oxidation Event- Cyanobacteria altered atmospheric oxygen concentrations - (early atmosphere only had 0.001% of today's oxygen atmospheric level)
Archean Eon
Time of the "archaic" rocks on Earth. When life first formed on Earth. The Archean Eon began about 4 billion years ago
hornfels
rock produced in contact metamorphism is often a fine-grained rock that shows no foliation
principle of faunal succession
states fossils succeed each other vertically in a specific, reliable order that can be identified over wide horizontal distances. Key Features: - Limited vertical range- (often coupled with rapid evolution) - Wide geographic distribution
principle of included fragments
states that clasts in a rock are older than the rock itself
(Steno) principle of original horizontality
states that layers of sediment are originally deposited horizontally under the action of gravity.
(Steno) principle of lateral continuity
suggests all rock layers initially extend laterally in all directions.
Archean Eon: Cratons stabilized
● Hot rock upwells from the deep Earth ● This material collides with existing lithosphere (surface rock) and melts it. Lighter minerals preferentially go into the melt phase, while the surrounding rock becomes more enriched with heavier minerals ● The melt cools and forms new, light lithosphere ● Horizontal shortening of the new lithosphere transforms it into a thick craton.