Igneous Petrology Flashcards
is molten rock material generated by partial melting of Earth’s mantle and crust
Magma
magma that rises and erupts onto the surface of Earth
Lava
is the liquid portion, is composed mainly of mobile ions of the eight most common elements in the crust.
Melt
the gaseous components of magma, are materials that will vaporize (form a gas) at surface pressures
Volatiles
called when magma loses its mobility before reaching the surface it eventually crystallizes
Intrusive
Plutonic
called when igneous rocks form by solidification of lava and volcanic debris on Earth’s surface, producing rocks with small crystals and/or non-crystalline particles of various sizes.
Extrusive
Volcanic
refers to the partial melting of a source rock
Anatexis
The type of magma produced by partial melting and subsequent processes depends upon factors such as:
The composition, temperature and depth of the source rock.
The percent partial melting of the source rock.
The source rock’s previous melting history. - Diversification processes that change the composition of the magma after it leaves the source region.
Ways of Generating Magma from solid rock
Increase in Temperature
Heat Transfer
Decrease in Pressure
Flux Melting
also known as adiabatic melting , results from a decrease in pressure.
occurs where hot, solid mantle rock ascends in zones of convective upwelling, thereby moving into regions of lower pressure
Decompression Melting
Crystallization along the walls of the magma chamber in which crystals preferentially form and adhere to the edges results in marginal accretion.
Marginal Accretion
Inward Crystallization
includes fractionation processes that occur when crystals develop with significantly different densities than the surrounding magma.
Gravitational Separation
occurs when higher density, ferromagnesian crystals settle to the base of a magma chamber relative to the lower density liquid magma
Crystal Settling
can occur if early formed crystals, such as plagioclase, are less dense than the magma
Crystal Flotation
occurs whereby liquids and crystals are segregated due to factors such as velocity, density or temperature.
Convective Flow Segregation
process whereby a magma chamber containing a mix of crystals and liquids is compressed, squeezing out the more mobile liquid into a new chamber and leaving behind a crystal residue in the original chamber.
Filter Pressing
involves the preferential diffusion of select ions within the magma in response to compositional, thermal or density gradients as well as water content.
Differential Diffusion
also called liquid – liquid fractionation , occurs when magma separates into two or more distinct immiscible liquid phases
Liquid Immiscibility
occurs when two or more dissimilar magmas coexist, displaying contact relations but retaining their distinctive individual magma characteristics.
Magma Mingling
implies thorough mixing so that the individual magma components are no longer recognizable.
Magma Mixing
record a progressive decrease in iron and magnesium with increasing SiO2 and alkali concentrations
Calc-alkaline Magma
with increasing fractionation, experience iron enrichment at low to moderate SiO2 concentrations
Tholeiitic Magma
are highly enriched in Na2O and/or K2O and are less common than either calc-alkaline or tholeiitic magmas or rocks
Alkaline Magma
are characterized by the voluminous occurrence of silicic and basic rocks with few intermediate rocks
Bimodal Magma Suites
are defined as plutons of more or less irregular shape with surface exposures ≥ 100 km2
Batholiths
are plutons with surface exposures ≤ 100 km2
Stocks
is a tabular, concordant pluton that parallels country rock.
Sill
is a blister-like concordant pluton characterized by a flat floor and domed roof
Laccolith
are dish-shaped to funnel-shaped concordant plutons that resemble a champagne glass in cross-section view.
Lopolith
tabular intrusions that cross-cut country rock layers.
Dikes
cylindrical plutonic dikes exposed at the surface by subsequent erosion. They represent ancient conduit pipes that funneled magma upward to a volcano that has long since been removed by erosion.
Neck
Volcanic Neck
carrot-shaped, cylindrical pipes that can extend to depths of 200 km. It develop via explosive intrusions that originate deep within the mantle. The explosiveness is due to the high volatile content which propels magma and xenolith fragments upward towards the surface.
Diatreme
Major distinctions in rock type are based on two criteria
Magma Chemical Composition
Environment of Magma Emplacement
Gas Content of
Mafic
Intermediate
Felsic
1-2%
3-4%
4-6%
Igneous rocks are classified according to (a) and (b).
(a) is determined by magma chemistry.
(b) refers to the size, shape, arrangement and degree of crystallinity of a rock’s constituent
Composition
Texture
The most straightforward approach to determining the mineralogy involves visually identifying the minerals and determining their percentages by volume
Modal or Mode Composition
systems are commonly used in aphanitic or glassy volcanic rocks, in which a rock’s modal mineral composition can not be determined
Normative Mineralogy
Weight percentage of Silica of;
Ultrabasic
Basic
Intermediate
Acidic
<45%
45-52%
52-66%
>66%
Percent of Dark Colored Minerals
Ultramafic
Mafic
Intermediate
Felsic
> 90%
70-90%
40-70%
<40%
General description of rock color based on mineral composition
Dark greenish rocks rich in olivine; may also contain pyroxene and amphibole
Ultramafic
General description of rock color based on mineral composition
Light colored or red rocks rich in potassium feldspar, quartz, biotite or muscovite
Felsic
General description of rock color based on mineral composition
Dark colored rocks containing pyroxene, amphibole, olivine, biotite
Mafic
What rock is it?
Ultramafic and Aphanitic
Komatiite
General description of rock color based on mineral composition
grayish to salt and pepper colored rocks rich in plagioclase, amphibole, biotite, quartz
Intermediate
a very dark-colored rock, depleted in SiO2 and commonly enriched in the minerals pyroxene, olivine, amphibole and plagioclase.
Peridotite
dark-colored, SiO2-poor rocks rich in plagioclase, pyroxene and olivine
Basalt
Gabbro
are gray-colored to salt and pepper-colored rocks rich in hornblende, pyroxene and plagioclase. Contain more than half to almost two-thirds SiO2.
Andesite and Diorite
are light-colored rocks, containing approximately two-thirds SiO2, rich in plagioclase, alkali feldspar and quartz and also containing small amounts of hornblende and biotite.
Dacite
Granodiorite
are light-colored rocks containing more than two-thirds SiO2 and rich in quartz, alkali feldspar with small percentages of plagioclase and biotite
Rhyolite
Granite
Magma composition of Scoria
Basaltic
contain complete crystal faces that are not impinged upon by other crystalss, developed under circumstances such as slow cooling of magma.
Euhedral
Idiomorphic
partially complete crystal form
Subhedral
Magma composition of Pumice
Felsic
lack any observable crystal faces, they have had to take the shapes of whatever open spaces were available between the already crystallized minerals
Anhedral
Xenomorphic
there is a mix of euhedral, subhedral and anhedral grains.
Hypidiomorphic-Granular Texture
wholly crystalline texture
Holocrystalline
wholly glassy textures
Holohyaline
partially crystalline/partially glass texture
Hypocrystalline
very fine-grained as a result of rapid cooling at the surface. -implies high crystal nucleation rates
Aphanitic texture
-grains are too small to be resolved optically but are visible with an electron microscope and can be identified by XRD.
Crypocrystalline
can be discerned with a petrographic microscope ; ________rocks in which elongate rectangular grains of feldspars are dominant have felty texture
Microcrystalline
(A) or coarse-grained mineral sizes that has crystal diameters ranging from 1to 30mm.
(B) 1mm to 3mm
(C) 3mm to 10mm
(D) 10mm to 30mm
Phaneritic
Fine grained
Medium grained
Coarse grained
(A) texture consist of two distinctly different size crystals. large crystals and finer grained material
(B) large crystals in the rock is called
(C) finer grained material in the is called
Porphyritic
Phenocrysts
Groundmass
characterized by large crystals averaging more than30 mm in diameter
Pegmatitic
This texture is in contrast with Pegmatitic texture, this texture refers to extremely fine grained minerals
Aplitic Texture
a porphyritic rock that contains scattered phenocrysts in a glassy matrix.
Vitrophyre
Important alteration product of divitrification
Palagonite
texture that is a product of devitrification; _______ are spherical to ellipsoidal clusters of radiating fibrous alkali feldspars and a polymorph of SiO2
Spherulitic Texture
develops by hydration of obsidian on fracture surfaces that are exposed to moisture in the atmosphere or to meteoric water (groundwater).
Perlitic texture
Texture in which minerals filled the cavities
Amygdaloidal Texture
Texture in which gas cavities filled with primary minerals
Miarolitic Texture
rocks formed at intermediate depth not clearly distinct from those of volcanic and plutonic rocks. They can have fabric similar to that of plutonic and volcanic rocks.
Hypabyssal Rocks
Temperature at which a rock will first start to melt
or
temperature in which the phase is 100% solid
Solidus
The main factor that determines the texture of an igneous rock is the ___________
Other factors are
a
b
c
Cooling Rate
Diffusion Rate
Rate of Nucleation
Crystal growth rate
the rate at which enough of the chemical constituents of a crystal can come together in one place without dissolving
Rate of Nucleation
the rate at which atoms or molecules can migrate through magma.
Diffusion rate
a measure of the increase in crystal radius over time
Crystal Growth Rate
Temperature at which a rock will be fully molten.
or
temperature in which crystallization starts
Liquidus
is an amorphous solid. Possess a disordered form, lacking an ordered crystalline structure
Glass or Vitric
occurs when melts of any composition come into contact with liquid water or air.
Quenching
formed by partial crystallization of magma that contains scattered phenocrysts in a glassy matrix.
Vitrophyre
produced by fragmenting processes that creates broken pieces of volcanic rock and/or mineral grains
Volcaniclastic
Pyroclastic
texture contains spherical to ellipsoidal void spaces.
- develop due to exsolution and entrapment of gas bubbles in lava as it cools and solidifies.
Vesicular texture
8 most abundant elements in the earth’s crust by weight percent
O-47% Si-28% Al-8% Fe-5% Ca-3.5% Na-3% K-2.5% Mg-2%
Shand Classification base %DCM
DCM- dark colored minerals
<30% Leucocratic
30-60% Mesocratic
60-90% Melanocratic
>90% Hypermelanic
Is it saturated, oversaturated or undersaturated?
- Qtz + feldspars and/or Mg orthopyroxene
- Forsterite, Nepheline, Leucite and other feldspathoids + feldspar and/or orthopyroxene minerals
- felds and/or Mg orthopyroxene only
Oversaturated
Undersaturated
Saturated
Ellis Classification of % DCM
<10% Holofelsic 10-40% Felsic 40-70% Mafelsic 70-90% Mafic >90% Ultramafic
Aluminum abundance
1) Al2O3 > CaO + Na2O + K2O
2) Al2O3 < Na2O + K2O
3) Al2O3 = Na2O + K2O
4) Na2O + K2O < Al2O3 < CaO + Na2O + K2O
- Peraluminous
- Peralkaline
- Subaluminous
- Metaluminous
are suites of rocks that form in response to similar geological conditions.
Petrotectonic Association
Oceanic lithospheres’s four distinct layers;
This Layer contains well - stratified marine pelagic sediments and sedimentary rocks that accumulate on the ocean floor.
Layer 1 - Sediment
Oceanic lithospheres’s four distinct layers;
This layer contains mantle peridotite is marked by high temperature, solid state strain fabric (metamorphosed) and represents the lowest layer of the oceanic lithosphere.
Layer 4 - Peridotite
Oceanic lithospheres’s four distinct layers;
This layer can be subdivided into two basaltic rock layers.
a) __________
b) __________
Layer 2
a) Pillow basalt
b) Basalt dikes
Mid-ocean ridge basalts can be subdivided:
a)
b)
N-MORB
E-MORB
Mid-ocean ridge basalts
represent 20-30% partial melting of a well-mixed, depleted mantle source
N-MORB
Mid-ocean ridge basalts
- have higher incompatible elements
- represent smaller degrees (10-15%) of partial melting of residual mantle rock so that the incompatible elements are more highly concentrated
E-MORB
Chemically diverse igneous assemblages erupt in the convergent margins widely distributed in a) b) c) d)
Pacific Ocean
Eastern Indian Ocean
Carribean
Scotia Sea
Oceanic lithospheres’s four distinct layers:
This layer contains massive gabbro in the upper section, layered gabbro in a middle section, and increasing amounts of layered peridotite towards the bottom of the section, marking the base of ocean crust.
Layer 3
Plutonic rocks at convergent margins (7)
Diorite Granodiorite Quartz Diorite Granite Gabbro Tonalite Trondhjemite
Convergent Plate Boundaries
Variables in which can diversify magma composition.
5
1) Composition and thickness of overlying plate
2) Composition of rock experiencing anatexis
3) Flux Melting
4) Diversification Processes
a) Fractionation
b) Assimilation
c) Magma Mixing
d) Metamorphic Reactions
5) Dip angle of the subduction zone
is the signature volcanic rock suite of convergent margins and constitutes one of the most voluminous rock assemblages on Earth, second only to MORB.
BADR
Basalt, Andesite, Dacite, Rhyolite
contain 45 – 52% SiO2 and can be subdivided into a number of different varieties based upon major and minor element concentrations
Basalt
Basalts common in convergent margins
Aphanitic & Aphanitic-Porphyritic varieties of Tholeiites
Calc-alkaline Basalts
Basalt with higher concentrations of Al2O3, typically in concentrations greater than 16 wt %.
Arc tholeiites
Basalt with higher alkali concentrations and not displaying iron enrichment typical of tholeiitic fractionation trends.
Calc-alkaline Basalts
Rock with 52 – 63% SiO2.
Andesite
Andesite with
1) > 52 – 57% SiO2
2) > 57 – 63% SiO2
1) Basaltic Andesite
2) Silicic Andesite
Rock with 63 – 68% SiO 2, that extends to 77%
Dacite
Rock with 66 – 69% SiO 2, although the lower TAS limit begins at 57% SiO 2
Trachyandesite also called as
Latite
Shoshonite
Rock with >69% SiO2
Rhyolite
Rock with 68 – 73% SiO2 - are associated with explosive silicic eruptions producing fragmental, glassy and aphanitic to aphantic – porphyritic textures
Rhyodacite
develop on the overlying ocean lithosphere plate, above the subduction zone.
are underlain by intermediate to mafic plutonic suites dominated by diorite, quartz diorite, granodiorite, tonalite and even gabbro.
Island Arc
High magnesium intermediate volcanic rocks that contain a SiO2 - saturated (52 – 68% SiO 2) groundmass
named from ______ of ________
Boninite
Bonin Island
Western Pacific Ocean
This rock is silica-saturated ( >56% SiO 2 ) rocks with high Sr/Y and La/Yb ratios and low HFS (such as Nb and Ta) concentrations
This rock is named from ____ Islands of the ____
Adakites
Adak Island
Aleutian Island Chain
How does backarc extension occur?
“Trench pull” forces move the volcanic arc towards the subduction zone resulting in the seaward movement of the trench and volcanic arc.
are dark-colored, potassium - rich trachyandesites, commonly containing olivine and augite phenocrysts with a groundmass of labradorite plagioclase, alkali feldspar, olivine, augite and leucite.
Shoshonite
Also called as Plagiogranite
Trondhjemite
are fault - bounded, deformed rock sequences that mark the site of present or former convergent margins
Alpine Orogenic Complexes
Zone in which the lower continental lithosphere does not subduct to great depths but essentially breaks off and underplates the overlying continental lithosphere plate producing a doubly thick lithosphere.
Continent-Continent Collision Zone
is an intensely sheared, heterogeneous rock assemblage embbedded within a highly deformed mud matrix.
Tectonic Melange
Magma body that consist of concentrically layered (zoned) plutons formed in convergent margin settings
Alaskan type intrusion
Refers to magma generation and igneous rock suites generated within lithospheric plates
can be initiated by
Hotspot
Continental Rifts
Overthickened Continental Lithosphere
Intraplate Magmatism
are volcanic landforms that rise upward above sea level
Ocean island
are volcanically produced peaks below sea level
Seamount
are broad flat-topped areas that result from massive outpourings of lava flowing laterally from source vents
Oceanic Plateau
3 largest flood basalt events
Permo–Triassic Siberian traps
Triassic–Early Jurassic Central Atlantic Magmatic Province
Cretaceous–Tertiary Deccan traps
Consist predominantly of tholeiitic basalt flows tens to a few hundreds of meters thick with minor trachyandesites, nephelinites, picrites, volcanic agglomerates and tuffs
- recognized as one of the greatest known outpourings of lava when the ___________ basalt province was discovered
- analogous to burying half of the contiguous United States in lava
Siberian Flood Basalts
Formed during the early Jurassic
-rocks consist of tholeiitic to andesitic basalts, with rare alkaline and silicic rocks.
CAMP
Central Atlantic Magmatic Province
dominated by tholeiitic basalts with minor amounts of alkalic basalts
- famous for the beds of fossils that have been found between layers of lava
Deccan Trap
What is the driving force behind the lithospheric extension that leads to the development of continental rifts?
Upwelling of hot plumes
Partial melting at great depths
Subduction of ocean spreading ridges
3 of the largest layered intrusions on Earth
Bushveld Complex in South Africa
Skaergaard Intrusion in Greenland
Stillwater Complex in Montana
world’s largest layered igneous intrusion
Bushveld Complex
Bushveld Complex consists of four main zones
Upper Zone
-Gabbro & Norite
Main Zone
-Gabbro & Anorthosite
Critical Zone
-Anorthosite, Norite, Pyroxenite
Basal Zone
-Orthopxn, Harzburgite, Dunite, PeridotiteIntraplate volcanics and Shallow intrusives
Komatiites Kimberlites Carbonatites Lamprophyres Lamproites Anorogenic (A-type) granites
are ultrabasic volcanic rocks found almost exclusively in Archean ( > 2.5 Ga) greenstone belts
- High in magnesium ( > 18% MgO), olivine - rich volcanic rocks, depleted in titanium and LREE.
Komatiite
Texture that commonly occurs in the upper parts of komatiite flows or in the chilled margins of sills and dikes where rapid quenching produced skeletal, acicular crystals
Spinifex texture
are brecciated, magnesium - rich, ultrabasic rocks that rapidly rise to Earth ’s surface via cylindrical diatremes from deep within the mantle
Kimberlite
are shallow intrusive to volcanic rocks that contain > 20% CO 3 minerals such as natrolite, trona, sodic calcite, magnesite and ankerite as well as other minerals such as barite and fluorite.
Carbonatite
are magnesium rich, volatile - rich, porphyritic rocks containing mafic phenocrysts such as biotite, phlogopite, amphibole, clinopyroxene and melilite.
Lamprophyre
are potassium - rich, peralkaline rocks containing minerals such as leucite, sanidine, phlogopite, richterite, diopside and olivine
Lamproite
are silicic plutonic rocks that are not associated with convergent margin tectonism
A-type granite
Anorogenic Granite
texture refers to sodium plagioclase overgrowths on pre existing orthoclase crystals
Rapakivi
A naturally occurring landform produced where lava erupts onto Earth’s surface.
Volcano
Types of Lava
Aa
Pahoehoe
Types of Volcano
according to morphology
Shield
Stratovolcano
Cinder Cone
Produced by the accumulation of fluid basaltic lavas and exhibit the shape of a broad , slightly domed structured that resembles a warrior’s shield
- Gently sloping, 15° or less
Shield
Also called scoria cones, built from layers of volcanic cinders (ash, glassy fragments) that often start as small fissures that rapidly grow
- Steeply sloping, 30° to 40°
Cinder Cone
Also called ______ volcanoes, built from interlayered tephra and lava flows, generally products of gas-rich andesitic magma
- Gradually sloping
- Most dangerous and eruptive
Stratovolocano
Composite Volcano
Types of Volcano
according to activity
Active
Potentially Active
Inactive
Had at least one eruption during the past 10,000 years. - Locally, a volcano is active if it had a recorded eruption for the past 600 years, and has datable material since 10,000 years ago
Active Volcano
Has not had an eruption for at least 10,000 years, and is not expected to erupt again in a comparable time scale of the future
Inactive Volcano
Geomorphologically young volcano that is currently not erupting, but is supposed to erupt again
Potentially Active Volcano
A systematic classification of volcanic eruptions based on observations during an eruption
Tephra volume (m3) Column height Eruption type Description Duration
VEI
Volcanic Explosivity Index
Calmest eruption type with steady lava fountaining and the production of thin lava flows
Hawaiian
Occur as a series of discrete, canon-like explosions that are short-lived, lasting for only minutes to a few hours, often with high-velocity ejections of bombs and blocks – a process of “throat clearing”
Vulcanian
Large, explosive eruptions involving high-viscosity magmas of andesitic to rhyolitic composition.
These eruptive columns produce widespread dispersals of tephra which cover large areas with an even thickness of pumice and ash
Plinian
The eruption of heated water and steam without magma
Often associated with hot springs, geysers, and fumaroles or solfataras
Phreatic
Also called Surtseyan, produced by the interaction of magma with groundwater or surface water
Much more explosive – as the water is heated, it flashes to steam and expands explosively
Phreatomagmatic
A volcanic landform that resulted from the collapse of the summit of a volcano following an explosive silica-rich eruption
Caldera
Dome-shaped mass produced from squeezed-out thick lava from volcanic vents
Lava Dome
Low relief volcanic craters that form by shallow explosive phreatomagmatic eruptions
Maar
Broken rock particles with varying sizes produced from volcanic eruptions
Pyroclasts
rock consisting of unreworked solid material of various sizes ejected from a volcanic vent
Pyroclastic Rock
or tephra, are volcanic materials with varying sizes produced by volcanic eruptions
Pyroclastic Material
solid or liquid ejecta with sizes greater than 64mm
Block and Bomb
rock fragments with grain sizes ranging from 264mm formed from droplets of lava
Lapilli
tephra that is usually glass having grain sizes lesser than 2mm
Ash
a fractured surface texture formed when bombs cool
Breadcrust texture
Pyroclastic fragments that fall to the ground due to gravity. Identified by having a good sorting of angular juvenile clasts.
Pyroclastic Fall
Moves at speeds up to 300m/s and can reach over to a 1000°C.
Can generate Nuee Ardentes , or “glowing cloud”
Developed with poorly sorted beds with rounded clasts that can produce block - and ash flows.
Pyroclastic Flow
Have low concentrations of particles mixed with gases that travels at high velocity and horizontally from the eruption site
Usually associated with phreatic and phreatomagmatic eruptions
Identified by having a “pinch and swelling” beds with moderate sorting of moderately rounded clasts
Pyroclastic Surge
It is a very fluid mudflow that occurs when volcanic debris becomes saturated with water and rapidly moves down steep volcanic slopes, generally following gullies and stream valleys
Lahar
these are derived directly from magma involved in the volcanic activity
Juvenile or Cognate Clasts
these are rock inclusions from the vent walls or brought from the surface by lava or pyroclastic walls
Accidental Clasts
It is the explosive ejection and aerial dispersal of pyroclasts of rock and magma from a volcanic vent
Pyroclastic process
a result of breaking up the cooler and rigid exterior of the lava as it continuously moves that can include block-sized autoclasts
Autoclastic process
It is brought by the weathering and disentigration of volcanic rocks
Epiclastic process
It is group of clasts with interstitial fluid that interact and move together
Massive Flow Transport
called whenclasts behaving independently in moving interstitial fluids
Traction
called when fully suspended clasts in interstitial fluid
Suspension
