Week 4-5 Flashcards
completely or partly molten rock, which on cooling solidifies to form an igneous rock composed of silicate minerals
Magma
It is the liquid component of magma composed of mobile ions of the common elements in the Earth’s crust
Melt
Gaseous components of magma
Volatiles
A process where cooling reverses the ecent of melting and ions pack more closely as temperature and rate of movement slows
Crystallization
The basic building block of silicate minerals
Silica Tetrahedron
Most abundant elements of igneous rocks
Silicon, Oxygen
Most abundant mineral group
Feldspars
Rocks between granitic and basaltic compostions are said to be
intermediate or andesitic
describe the overall appearance of rock based on size, shape, and arrangement of mineral grains
Texture
Rocks that consist of unordered ions that are frozen randomly in place are referred to as
glass
The various igneous textures result mainly from_________ whereas the minerology of an igneous rock is the consequence of _________
different cooling histories; the chemical makeup of its parent magma.
Large crystals in a porphrytic texture is called ______
Phenocrysts
The three components of magma
Liquid Component (Melt)
Solid Component
Gaseous Phase (Volatiles)
Common volatiles in magma
Water Vapor
Carbon Dioxide
Sulfur Dioxide
Common dark silicate minerals in the crust
Olivine, pyroxene, amphibple, biotite mica
Common light silicates
quartz, muscovite mica, feldspars
Factors that influence igneous texture
> cooling rate
silica content
amound of dissolved gases
Define polymerization
Union of two or more molecules of given structure to form a new compound with the same elemental proportions but with different properties and a higher molecular weight.
What are pegmatites
rocks composed of interlocking crystals all larger than a centimeter in diameter
What is pele’s hair
strands of volcanic glass from lava fountains
A pyroclastic rock can be classified a volcanic breccia if
pyroclastic fragments are greater than 2 mm
Define geothermal gradient
The increase in temperature as one goes down beneath the earth
Mineral assemblage of diorite
Sodic Plagiocalse, amphiboles, biotite
Ways for magma to generate
> increase of temp
decrease in pressure in constant heat
introduction of volatiles
Minerals under the discontinous series
olivine, pyroxene, amphibole, biotite, K-Feldspar, muscovite, quartz
Define Magmatic differentiation
Formation of one or more seconadary magmas from a single parent magma
Define magmatic assimilation
Incorporation of host rock by migrating magma
Assiilation v Magma mixing
> Assimilation involves disologing blocks of foreign host rock, melting it and then mixes with the intruding melt
Mixing of two chemically different magmas; younger buoyant magma overtakes and mix with the older existing magma.
If intrusive rocks form underground, why can geologists aquire such samples.
Observable intrusive rocks are observed at surfaces where uplifting and erosions stripped away overlying rocks
How does pegmatites form
> Form late in magma crystallization
unsually high percentage of volatiles in melt, encouraging enhanced ion migration
abnormally large crystals form
Granite has a variety of colors such as red and light gray. Why?
> reddish : k-felds dominant and dark pink
light gray: white to gray feldspars mized with small amounts of dark silicates
In a field, how would you distinguish grayish granite from diorite
> granite would have an absence of visible qtz in contrast to diorite
Explain decompression melting
> confining pressure increases rock melting temp
occurs in areas of mantle upwelling; lower pressure zones; divergent plate boundaries
removal of pressure lowers melting temp
decompression melting happeneds when confining pressure drops
How does volatiles induce melting?
> by causing rock to melt at lower temperatures; can be magnified by increased pressure
How is magma generated at subduction settings
> water is brought to the mantle via subducting lithosphere slabs
fluids migrate at the overlying mantle
addition of volatiels reduve melting temps of peridoite; generating melt
magma rises towards surface
in continental settings: ponding beneath crustal rocks; evolution from mafic to felsic magma
Explain and Illustrate Bowens Reaction Series
> an idealized sequence of mineral crystalization starting from basaltic magma under certain temperature regimes
The minerals biotite, sodic plagioclase, and amphibole belongs to the same temperature regime in the bowens rxn series. What does this imply?
> these minerals are found together in the same igneous rock particularly andesites or diorite
How is crystal settling relevant to magmatic differentiation?
> ferromagnesian minerals are dense and sinks below magma chamber
the resulting settling of minerals causes a difference in composition (mafic lower, felsic upper)
A melt produced via partial melting would be ____ compared to its parent magma. Why is that?
> richer in silica
partial melting causes felsic minerals to melt first while the mafic mineral stays in its solid form; mainly due to the difference in melting temperatures
the difference causes melt to be enriched in silica
Largest mineral group and most abundant in the crust
Silicates
Mineral with metal + oxygen combination
Oxides
The minerals iron chromiaum oxide, titanium dioxide, and hydrogen dioxide are known as
chromite , rutile, ice
minerals are are characterized with metallic luster, high density, and low hardness
a. Sulfides
These group of minerals are commonly found in evaporitic settings
Halides, Sulfates, Carbonates
The mineral the comprises the teeth and bones of living organisms
Apatite
O:Si of Cyclosilicates
[3:1]
O:Si of Nesosilicates
[4:1]
O:Si of Phyllosilicates
[2.5:1]
Most important parameters for mineral classification
> chemical composition
internal crystal structure
Classificaitons based on the Nickel-Strunz
Native Elements
Sulfides
Halides
Oxides
Nitrates
Carbonates
Borates
Sulfates
Phophates
Silicates
Organic compounds
Three types of closed rings found in cyclosilicates
> 3 tetrahedrons sharing an oxygen
6 tetrahedrons sharing an oxygen
4 tetrahedrons sharing an oxygen
Describe Inosilicates
> two oxygens atoms from each tetrahedrons bond to form open chains
Examples of tectosilicates
feldspars, quartz ,feldspathoids, zeolite group
essential mineral v accessory mineral
Essential: minerals forming the essential components of a rock
Accessory: minerals present in trivial amounds
Enumerate pyralspite
Pyrope, Almadine, Spessartine
Enumerate ugrandites
Uvarovite, grossularite, andradite
What is the Goldschmist Classification of elements
geochemical classification of elements groups the chemical elements according to their preferred host phases within the Earth
Types of chemical bonds
Ionic, Covalent, Metallic, Van der waals, Hydrogen
Minerals under K-feldspar series
Orthoclase, Microline, Sanidine
Minerals under plagioclase series
Albite, Bywotonite, Labradorite, Andesine, Oligoclase, Anorthoclase
How would you differentiate amphiboles from pyroxenes under PPL
Cleavage:
Px : 90 degrees
Amphi: 60 and 120 degrees
Can magmas be dominated by compositions other than silica (SiO2)
Yes. An example would be carbonatites which is rich in carbonate components.
How are trace elements dominant if they consitiute a small fraction of the magma compositions
They provide clues to the origin of igneous rocks.
Why is it that a magma with rich felsic composition is not expected to crystallize minerals such as olivines and pyroxenes.
> rich in silica, qtz, k-felds, sodic plag, are expected crystllizations
felsic magma depleted of Mg and FeO
How does SiO2 content relate to silicate structure and mineral strength
> more SiO2 = greater polymerization = greater mineral strength
Why does rising mantle plume pools at the moho discontinuity before rising further through the lithosphere
> rising mantle plume loses its density as when it reaches the moho
crystallization and differentiation of melt would increase its buoyancy and rise through lithosphere
Relate undercooling to the degree of crystalinity
> undercooling refers to magma cooling faster than it can crystallize
large undercooling results in high nucleation, low crystalinity
small undercooling results in lowe nucleation, high crystalinity
A thin section sample is found to be fine grained dominated by microlaths of plagioclases and volcanic glass. Phenocrysts of olivines, plagioclases, and pyroxenes generally have a feathery/skeletal texture and shows zoning. What would be its implications regarding its formation and its rock id.
> Mineral assemblage is characteristic to a mafic igneous rock
Dominance of volcanic glass and plag microliths indicate a aphanitic texure
Skeletal/feathery textures and zoning indicates rapid cooling rates
Rock may be Basalt
An outcrop far inland features pillow basalts overlain by intercalated limestones and sandstones. What would be its implication regarding its past environment.
> Sandstones usually form in terrestrial environment
Limestones form in shallow marine waters
Pillow basalts form when mafic magma extrudes and comes in contact with water
marine environment, mutiple episodes of transgression and regression
triple junction
a point at which three plates meet,
this triple juction is always stable
ridge-ridge-ridge
the approximation of the earth’s magnetic field
dipole field
difference between the Earth’s magnetic field and the best dipole field
non-dipole field
Inclination of the earth’s magnetic axis to the geographic axis
11.5 degrees
location of geomagnetic north
79 deg N, 71 deg W
the line along which the magnetic field is horizontal and has no vertical component
magnetic equator
constant stream of ionized particles emitted by the Sun
solar wind
produced where the solar wind is slowed by interaction with the Earth’s magnetic field.
bow shock
Two triple juctions that are always unstable
fault–fault–fault and fault–ridge–ridge junctions