Igneous Petrology Flashcards
The science concerned with rocks, including their mode of occurrence, composition, classification, origin, and their relations to geological processes and history.
Petrology
A branch of petrology that deals with the history and origin of the rock; interpretations of the origin of rocks
Petrogenesis
places emphasis on the purely descriptive part of rock science from textural, mineralogical, and chemical points of view.
Petrography
Study of description and classification of rocks. It is considered an observational science because it looks at the physical features such as color, mineralogy, texture, etc.
Petrography
the branch of geology dealing with the origin, occurrence,
structure, and history of rocks.
Petrology
Rocks that directly solidify from molten or partially molten material, i.e. magma.
Igneous Rocks
two basic types of igneous rocks
intrusive igneous rocks and extrusive igneous rocks
what is the difference between intrusive igneous rocks and extrusive igneous rocks?
intrusive igneous rocks are formed beneath the surface of the Earth
extrusive igneous rocks are formed at the surface of the earth.
another term for extrusive igneous rocks
Volcanic rocks
another term for intrusive igneous rocks
Plutonic Rocks
three general types of magma based on their chemical composition
Basaltic magma
Andesitic magma
Rhyolitic magma
Magma that has 45-55% SiO2, high in Fe, Mg, Ca; low in K, Na; and has temperature range of 1000-1200°C
Basaltic Magma
Magma that has: 55-65% SiO2, intermediate in Fe, Mg, Ca, K, and Na; has a temperature range of 800-1000°C
Andesitic Magma
Magma that has 65-75% SiO2, low in Fe, Mg, Ca; high in K, Na; and has a temperature range of 650-800°C.
Rhyolitic Magma
Low viscosity, low gas content, high-temperature magma
Basaltic Magma
intermediate viscosity, intermediate gas content, intermediate temperature magma
Andesitic Magma
High viscosity, High gas content, Low-temperature magma
Rhyolitic Magma
Magma is generated for? and with what process?
Mantle; through Partial Melting
Heat sources on the Earth
- Heat from the early accretion and differentiation of the Earth;
- Heat released by the radioactive breakdown of unstable nuclides
similar to the melting of dry minerals, melting temperatures increase with increasing pressure, except there is a range of temperature over which there exists a partial melt, Partial melting can range from 0 to 100%
Melting of dry rocks
similar to the melting of wet minerals, melting temperatures initially decrease with increasing pressure, except there is a range of temperatures over which there exists a partial melt
Melting of rocks containing water or carbon dioxide
What are the ways to generate magma on (solid part of) the earth?
increase/ raise the geothermal gradient
lower the melting temperature of rocks.
3 mechanisms of Magmatic Differentiation.
Fractional Crystallization
Magma mixing
Magmatic assimilation
Likely to be the most important in controlling magmatic differentiation.
Crystal fractionation
Magma is close to its original composition and has therefore in theory not undergone crystal fractionation.
primitive magma
Magma in which crystal fractionation has taken place such the magma composition is different from the starting composition.
Evolved Magma
where two magmas with different compositions happen to come in contact with one another and mix together and have a composition somewhere between that of the original two magma compositions.
Magmatic Mixing
magma reacts with the “country rock” which is adjacent to the magma chamber.
Assimilation
incompletely melted chunks of country rock. these materials contaminate the magma by incorporating materials originally present in the country rock.
Inclusions
The reaction between the magma and the wall rock/ host rock
Magmatic assimilation
Minerals in Bowen’s reaction series: Discontinuous series (in order from high to low temp, and increasing SiO2 Liquids)
Olivine, Pyroxene, Hornblende (amphibole), Biotite
Minerals in Bowen’s reaction series: continuous series (in order from high to low temp, and increasing SiO2 Liquids)
Ca-rich to Na-rich Plagioclase (ABLAOA)
Refers to any process that cause magma composition to change.
Magmatic Differentiation
the proposed processes of Magmatic Differentiation
- Distinct melting events from distinct sources
- Various degrees of partial melting from the same source
- Crystal Fractionation / Fractional Crystallization
- Mixing of 2 or more magma (Magma mixing)
- Assimilation/ Contamination of magma by crustal rocks
- Liquid Immiscibility
Each magma might represent melting at a different
source rock at different times during the heating event
Distinct melting events from distinct
sources
In multicomponent rock systems, each component has its own melting range temperature.
Various degrees of partial melting from
the same source
the liquid composition changes as a result of removing crystals from the liquid as they form creating a magma with a different composition from the parent magma
Crystal Fractionation / Fractional Crystallization
2 mechanism of fractional crystallization
Crystal settling/ floating crystals
Inward crystallization
Forming from magma will have different densities; Higher-density crystal sinks and lower-density crystal floats.
Crystal settling/ Floating Crystals
The magma body is hot and the country rock that surrounds it is expected to be cooler, heat will move outward, away from the magma; the walls of the magma body will be coolest, crystallization is expected to take place in the cooler portion; magma expected to
crystallize from walls inward
Inward crystallization
Two or more magma with different compositions come in contact with one another beneath the surface and mix to produce magma with a composition intermediate between the end member (the two magma).
Magma Mixing
factors that can inhibit (hinder) mixing.
Temperature contrast
Density contrast
Viscosity contrast
The mechanism that makes magma mixing possible
Stirring e.g. Convection
(where hotter magma rising through the cooler magma)
Evidence(s) of Mixing
Mingling of Magmas
Disequilibrium mineral assemblages
Reverse Zoning
Glass Inclusions
Chemical Evidences
“marble cake” appearance, dark-colored mafic rock intermingled with lighter-colored rhyolitic rock (banding)
Mingling of magma
basaltic magma containing Mg-rich olivine mixed
with rhyolite magma containing quartz
Disequilibrium mineral assemblages
minerals placed in an environment different than the one in which it originally formed, will react, instead of dissolving completely, solid solution minerals start precipitating new composition that is stable – zoned crystals
Reverse Zoning in Minerals
Crystal grows trapping liquid inside; glass should represent the composition of magma that precipitated the crystal.
Glass inclusions
oxide-oxide variation diagrams
Chemical evidence
A state in which two liquids with different compositions coexist in equilibrium with each other.
Liquid Immiscibility
___________ do not mix and form an emulsion of droplets or network of one liquid within the other
Immiscible
