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.