origin&evolution of magmas
DESCRIPTION
origen y evolucion del magmaTRANSCRIPT
Textural Interpretations from Phase Textural Interpretations from Phase DiagramsDiagrams
Binary Systems with Binary Systems with Congruent MeltingCongruent Melting
Plagioclase forms before augite– Plagioclase forms before augite– DiabasicDiabasic tecture tectureThis forms on the right side of the eutectic
Binary Systems with Congruent MeltingBinary Systems with Congruent MeltingTextural Interpretations from Phase DiagramsTextural Interpretations from Phase Diagrams
Diabase dike
Left of the eutectic get a similar situation
Textural Interpretations from Phase Diagrams
Binary Systems with Congruent MeltingBinary Systems with Congruent Melting
Augite forms before plagioclase – Augite forms before plagioclase – OphiticOphitic tecture tectureThis forms on the left side of the eutectic
Gabbro of the Stillwater Complex, Montana
Binary Systems with Congruent MeltingBinary Systems with Congruent MeltingTextural Interpretations from Phase DiagramsTextural Interpretations from Phase Diagrams
Textural Interpretations from Phase DiagramsTextural Interpretations from Phase Diagrams
Binary Systems with Binary Systems with Incongruent MeltingIncongruent Melting
Olivine cores with pyroxene reaction rims
Textural Interpretations from Phase DiagramsTextural Interpretations from Phase Diagrams
Binary Systems with Binary Systems with Solid SolutionSolid Solution
CaCaNaNa
Textural Interpretations from Phase DiagramsTextural Interpretations from Phase Diagrams
Zoned plagioclaseZoned plagioclase
Diversification of MagmasDiversification of Magmas
Evolution of MagmasEvolution of MagmasWhy do we get so much variation in Why do we get so much variation in
igneous rocks?igneous rocks?
Evolution of MagmasEvolution of Magmas
Types of Magmas:Types of Magmas:• PrimitivePrimitive• PrimaryPrimary• ParentParent• DerivativeDerivative
Magmatic DifferentiationMagmatic Differentiation
Any process by which a magma is Any process by which a magma is able to diversify and produce a able to diversify and produce a magma or rock of different magma or rock of different compositioncomposition
Evolution of MagmasEvolution of Magmas
Evolution of MagmasEvolution of Magmas
Ways to produce variation:Ways to produce variation:• different source rocksdifferent source rocks• partial melt fractionationpartial melt fractionation
The Ab-Or-Qtz system with the ternary The Ab-Or-Qtz system with the ternary cotectic curves and eutectic minima from cotectic curves and eutectic minima from 0.1 to 3 GPa. Included is the locus of most 0.1 to 3 GPa. Included is the locus of most granite compositions from Figure 11-2 granite compositions from Figure 11-2 (shaded) and the plotted positions of the (shaded) and the plotted positions of the norms from the analyses in Table 18-2. norms from the analyses in Table 18-2. Note the effects of increasing pressure Note the effects of increasing pressure and the An, B, and F contents on the and the An, B, and F contents on the position of the thermal minima.position of the thermal minima. From From Winter (2001) An Introduction to Igneous Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prenticeand Metamorphic Petrology. Prentice Hall.Hall.
Evolution of MagmasEvolution of Magmas
Partial melt Partial melt fractionation:fractionation:
Melting begins at Melting begins at cotectic – more cotectic – more melting means melting means greater divergence greater divergence from cotectic melt.from cotectic melt.
Evolution of MagmasEvolution of Magmas
Ways to produce variation:Ways to produce variation:• different source rocksdifferent source rocks• partial melt fractionationpartial melt fractionation• fractional crystallizationfractional crystallization
Evolution of MagmasEvolution of MagmasBowen’s Reaction Bowen’s Reaction
Series:Series:
Evolution of MagmasEvolution of Magmas
Types of FX:Types of FX:• gravity settlinggravity settling• filter pressingfilter pressing• convective fractionation convective fractionation • congelation crystallizationcongelation crystallization• flow differentiationflow differentiation
Evolution of MagmasEvolution of Magmas
Ways to produce variation:Ways to produce variation:• different source rocksdifferent source rocks• partial melt fractionationpartial melt fractionation• fractional crystallizationfractional crystallization• assimilationassimilation• diffusion/volatile transferdiffusion/volatile transfer• magma mixingmagma mixing• post-solidification alterationpost-solidification alteration
Origin of MagmasOrigin of Magmas
ContinentalContinental
MORBsMORBsSubductionSubduction
Origin of MagmasOrigin of Magmas
Composition of the Mantle:Composition of the Mantle:• ocean crust 6-8km, continental crust ocean crust 6-8km, continental crust
30+ km30+ km• mantle: base of crust to 2900km mantle: base of crust to 2900km • crust+mantle to 70km: lithospherecrust+mantle to 70km: lithosphere• 70 – 145km: asthenosphere70 – 145km: asthenosphere
Origin of MagmasOrigin of Magmas
Composition of the Mantle:Composition of the Mantle:• peridotite: olivine + pyroxeneperidotite: olivine + pyroxene• eclogite: pyroxene + garneteclogite: pyroxene + garnet
• Low pressures (~30km): olivine, Al-poor pyroxene, Low pressures (~30km): olivine, Al-poor pyroxene, plagioclaseplagioclase
• Moderate pressures (30-70km: olivine, Al-rich pyroxene, Moderate pressures (30-70km: olivine, Al-rich pyroxene, spinel (MgAlspinel (MgAl22OO44))
• High pressures (>70km): olivine, Al-poor pyroxene, garnetHigh pressures (>70km): olivine, Al-poor pyroxene, garnet
Lherzolite: A type of peridotite with Olivine > Opx + Cpx
OlivineOlivine
ClinopyroxeneClinopyroxeneOrthopyroxeneOrthopyroxene
LherzoliteLherzoliteHa
rzbu
rgite
Wehrlite
Websterite
OrthopyroxeniteOrthopyroxenite
ClinopyroxeniteClinopyroxenite
Olivine Websterite
PeridotitesPeridotites
PyroxenitesPyroxenites
90
40
10
10
DuniteDunite
After IUGSAfter IUGS
Origin of MagmasOrigin of Magmas
Origin of MagmasOrigin of MagmasCan the mantle melt under normal heat flow?Can the mantle melt under normal heat flow?
Answer:Answer:
NO!NO!
How does the mantle melt??How does the mantle melt??1) Increase the temperature1) Increase the temperature
Melting by raising the temperature.Melting by raising the temperature.
Origin of MagmasOrigin of Magmas
SolidusSolidusSolidusSolidus
LiquidusLiquidus
May work for May work for Hot Spots,Hot Spots,Unlikely Unlikely
elsewhereelsewhere
2) Lower the pressure2) Lower the pressure– Adiabatic rise of mantle with no conductive heat lossAdiabatic rise of mantle with no conductive heat loss– Decompression melting could melt at least 30%Decompression melting could melt at least 30%
Melting by (adiabatic) pressure reduction. Melting begins when the adiabat crosses the solidus and traverses the shaded melting interval. Dashed lines represent approximate % melting.
Origin of MagmasOrigin of MagmasHow does the mantle melt??How does the mantle melt??
Probably Probably what what happens at happens at spreading spreading centerscenters
3) Add volatiles3) Add volatiles (especially H(especially H22O)O)
Dry peridotite solidus compared to several experiments on H2O-saturated peridotites.
Origin of MagmasOrigin of MagmasHow does the mantle melt??How does the mantle melt??
Probably what Probably what happens at happens at subduction subduction zoneszones
Origin of MagmasOrigin of Magmas
MORBs:MORBs:
Origin of MagmasOrigin of Magmas
MORBs:MORBs:
Primitive melt is olivine Primitive melt is olivine tholeiite; dunites, tholeiite; dunites, pyroxenites, anorthosites pyroxenites, anorthosites and alkaline basalts are and alkaline basalts are differentiatesdifferentiates
Oceanic Crust and Oceanic Crust and Upper Mantle Upper Mantle
StructureStructure
Typical OphioliteTypical Ophiolite
Lithology and thickness of a Lithology and thickness of a typical ophiolite sequence, based typical ophiolite sequence, based on the Samial Ophiolite in Oman. on the Samial Ophiolite in Oman. After Boudier and Nicolas (1985) After Boudier and Nicolas (1985) Earth Planet. Sci. Lett., 76, 84-92. Earth Planet. Sci. Lett., 76, 84-92.
Origin of MagmasOrigin of Magmas
Layer 1
A thin layer of pelagic sediment
Oceanic Crust and Upper Mantle StructureOceanic Crust and Upper Mantle Structure
Modified after Brown and Modified after Brown and Mussett (1993) Mussett (1993) The Inaccessible The Inaccessible Earth: An Integrated View of Earth: An Integrated View of Its Structure and Composition. Its Structure and Composition. Chapman & Hall. London.Chapman & Hall. London.
Origin of MagmasOrigin of Magmas
Layer 2 is basaltic
Subdivided into two sub-layers
Layer 2A & B = pillow basalts
Layer 2C = vertical sheeted dikes
Oceanic Crust and Upper Mantle StructureOceanic Crust and Upper Mantle Structure
Modified after Brown and Mussett (1993) The Inaccessible Earth: An Integrated View of Its Structure and Composition. Chapman & Hall. London.
Origin of MagmasOrigin of Magmas
Layer 3Layer 3 more complex and controversialmore complex and controversialBelieved to be mostly gabbros, crystallized from a shallowBelieved to be mostly gabbros, crystallized from a shallow axial magma chamberaxial magma chamber (feeds the dikes and basalts)(feeds the dikes and basalts)
Layer 3A = upper isotropic and lower, somewhat foliated (“transitional”) gabbros
Layer 3B is more layered, & may exhibit cumulate textures
Origin of MagmasOrigin of Magmas
Layer 4Layer 4 = ultramafic rocks = ultramafic rocks
Ophiolites: base of 3B grades into layered cumulate wehrlite & gabbro
Wehrlite intruded into layered gabbros
Below cumulate dunite with harzburgite xenoliths
Below this is a tectonite harzburgite and dunite (unmelted residuum of the original mantle)
Origin of MagmasOrigin of Magmas
Origin of MagmasOrigin of Magmas
Massive sulfide depositsMassive sulfide deposits
A more modern concept of the axial magma chamber beneath a fast-spreading ridge
After Perfit et After Perfit et al. (1994) al. (1994) Geology, 22, Geology, 22, 375-379.375-379.
Origin of MagmasOrigin of MagmasAny model for the origin of magmas at subduction Any model for the origin of magmas at subduction zones must account for:zones must account for:11. First stages of . First stages of volcanism volcanism tholeiitictholeiitic, then , then changes to changes to calcalkalinecalcalkaline
F
A M
Calc-alkaline
T
ho leiitic
Origin of MagmasOrigin of MagmasAny model for the origin of magmas at subduction Any model for the origin of magmas at subduction zones must account for:zones must account for:
2. Trend from 2. Trend from tholeiitictholeiitic volcanism nearest trench to volcanism nearest trench to calcalkalinecalcalkaline towards towards continentcontinent
tholeiitictholeiitic calcalkalinecalcalkaline
Origin of MagmasOrigin of MagmasA model for the origin of magmas at subduction A model for the origin of magmas at subduction zones.zones.
Ringwod (1974)
Early Phases1. Basalt 1. Basalt metamorphoses to metamorphoses to amphibolite; amphibolite; dunite alters to dunite alters to serpentiniteserpentinite
2. Amphibolites 2. Amphibolites dehydrate, H2O dehydrate, H2O triggers melting triggers melting of overlying of overlying mantle producing mantle producing tholeiitic tholeiitic magmas; magmas; dehydrated slab dehydrated slab becomes eclogitebecomes eclogite
Origin of MagmasOrigin of MagmasA model for the origin of magmas at subduction A model for the origin of magmas at subduction zones.zones.
Ringwod (1974)
Later Phases1. Dehydration of 1. Dehydration of serpentinite bodies; H2O serpentinite bodies; H2O causes partial melting of causes partial melting of eclogite to form eclogite to form rhyodacite-dacite rhyodacite-dacite magma magma
2. Magma reacts with 2. Magma reacts with overlying mantle –forms overlying mantle –forms less dense garnet less dense garnet pyroxenite; diapiric rise pyroxenite; diapiric rise initiates partial melting; initiates partial melting; fractionation produces fractionation produces calc-alkaline magmascalc-alkaline magmas
Origin of MagmasOrigin of Magmas
Continental Magmas:Continental Magmas:• alkaline rocksalkaline rocks• carbonatitescarbonatites• kimberlites kimberlites • anorthositesanorthosites• gabbroic layered intrusionsgabbroic layered intrusions• anorogenic granitesanorogenic granites
Schematic cross section of an asthenospheric mantle plume beneath a continental rift environment, and the genesis of nephelinite-carbonatites and kimberlite-carbonatites . Numbers correspond to Figure 19-13. After Wyllie (1989, Origin of carbonatites: Evidence from phase equilibrium studies. In K. Bell (ed.), Carbonatites: Genesis and Evolution. Unwin Hyman, London. pp. 500-545) and Wyllie et al., (1990, Lithos, 26, 3-19). Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.
Origin of MagmasOrigin of Magmas
Continental Alkaline Magmatism:Carbonatites
Model of an idealized kimberlite system, illustrating the hypabyssal dike-sill complex leading to a diatreme and tuff ring explosive crater. This model is not to scale, as the diatreme portion is expanded to illustrate it better. From Mitchell (1986) Kimberlites: Mineralogy, Geochemistry, and Petrology. Plenum. New York. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.
Continental Alkaline Magmatism:Kimberlites
Origin of MagmasOrigin of Magmas
a. Mantle-derived magma underplates the crust as it becomes density a. Mantle-derived magma underplates the crust as it becomes density equilibrated.equilibrated.
Origin of MagmasOrigin of MagmasA model for the origin of anorthositesA model for the origin of anorthosites
b. Crystallization of mafic phases (which sink), and partial melting of the Crystallization of mafic phases (which sink), and partial melting of the crust above the ponded magma. The melt becomes enriched in Al and crust above the ponded magma. The melt becomes enriched in Al and Fe/Mg.Fe/Mg.
Origin of MagmasOrigin of MagmasA model for the origin of anorthositesA model for the origin of anorthosites
c. Plagioclase forms when the melt is sufficiently enriched. Plagioclase c. Plagioclase forms when the melt is sufficiently enriched. Plagioclase rises to the top of the chamber whereas mafics sink.rises to the top of the chamber whereas mafics sink.
Origin of MagmasOrigin of MagmasA model for the origin of anorthositesA model for the origin of anorthosites
d. Plagioclase accumulations become less dense than the crust above d. Plagioclase accumulations become less dense than the crust above and rise as crystal mush plutons. and rise as crystal mush plutons.
Origin of MagmasOrigin of MagmasA model for the origin of anorthositesA model for the origin of anorthosites
e. Plagioclase plutons coalesce to form massif anorthosite, whereas e. Plagioclase plutons coalesce to form massif anorthosite, whereas granitoid crustal melts rise to shallow levels as well. Mafic cumulates granitoid crustal melts rise to shallow levels as well. Mafic cumulates remain at depth or detach and sink into the mantle.remain at depth or detach and sink into the mantle.
Origin of MagmasOrigin of Magmas