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Petrologagnea
Presentaciones Modificadas
de John Winter
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PETROLOG GNE
Prof. Teora: MSc. Julin A. Lpez I.
Prof. Prctica: Candidato a MSc. Julieta Pineda.
Primer Semestre 2012
Escuela de Geologa - UIS
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IgneousPetrology
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The Earths InteriorCrust:
Oceanic crustThin: 10 km
Relatively uniform stratigraphy
= ophiolite suite:
Sediments
pillow basalt
sheeted dikes
more massive gabbro
ultramafic (mantle)
Continental CrustThicker: 20-90 km average ~35 km
Highly variable composition
Average ~ granodiorite
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The Earths Interior
Mantle:Peridotite (ultramafic)
Upperto 410 km (olivine spinel)
Low Velocity Layer60-220 km
Transition Zoneas velocity increases ~ rapidly
660 spinel perovskite-type SiIV SiVI
Lower Mantlehas more gradualvelocity increase
Figure 1-2.Major subdivisions of the Earth.
Winter (2001) An Introduction to Igneousand Metamorphic Petrology. Prentice Hall.
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The Earths Interior
Core:Fe-Ni metallic alloy
Outer Coreis liquid No S-waves
Inner Coreis solid
Figure 1-2.Major subdivisions of the Earth.
Winter (2001) An Introduction to Igneousand Metamorphic Petrology. Prentice Hall.
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Figure 1-3.Variation in P and S wave velocities with depth. Compositionalsubdivisions of the Earth are on the left,rheologicalsubdivisions on the right. After Kearey and Vine (1990), Global Tectonics. Blackwell Scientific. Oxford.
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Figure 1-5. Relative atomic abundances of the seven most common elements that comprise 97% of the Earth's mass. AnIntroduction to Igneous and Metamorphic Petrology, by John Winter , Prentice Hall.
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The Pressure Gradient
P increases = gh
Nearly linear through
mantle ~ 30 MPa/km
1 GPa at base of ave crust
Core: incr. more rapidly
since alloy more dense
Figure 1-8.Pressure variation with depth. From Dziewonski andAnderson (1981). Phys. Earth Planet. Int., 25, 297-356. ElsevierScience.
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Heat Sources
in the Earth
1. Heat from the early accretion anddifferentiation of the Earth still slowly reaching surface
2. Heat released by the radioactivebreakdown of unstable nuclides
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Heat Transfer
1.Radiation
2.Conduction
3.Convection
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The Geothermal Gradient
Figure 1-11(new).Estimates of oceanic (bluecurves) and continental shield (red curves)geotherms to a depth of 300 km. The
thickness of mature (> 100Ma) oceaniclithosphere is hatched and that of continentalshield lithosphere is yellow. Data from Greenand Falloon ((1998), Green & Ringwood(1963), Jaupart and Mareschal (1999),McKenzie et al. (2005 and personalcommunication), Ringwood (1966), Rudnickand Nyblade (1999), Turcotte and Schubert
(2002).
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The
Geothermal
Gradient
Pattern of global heat flux variations compiled fromobservations at over 20,000 sites and modeled on a
spherical harmonic expansion to degree 12. From Pollack,Hurter and Johnson. (1993) Rev. Geophys. 31, 267-280.
Cross-section of the mantle based on a seismic tomography model. Arrowsrepresent plate motions and large-scale mantle flow and subduction zonesrepresented by dipping line segments. EPR =- East pacific Rise, MAR = Mid-Atlantic Ridge, CBR = Carlsberg Ridge. Plates: EA = Eurasian, IN = Indian, PA =
Pacific, NA = North American, SA = South American, AF = African, CO = Cocos.From Li and Romanowicz (1996). J. Geophys. Research, 101, 22,245-72.
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Figure 1-9.Estimated ranges ofoceanic and continental steady-state geotherms to a depth of100 km using upper and lower
limits based on heat flowsmeasured near the surface.After Sclater et al. (1980),Earth. Rev. Geophys. SpaceSci., 18, 269-311.
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Plate Tectonic - Igneous Genesis
1.Mid-ocean Ridges
2.Intracontinental Rifts
3. Island Arcs
4.Active ContinentalMargins
5.Back-arc Basins6.Ocean Island Basalts
7.Miscellaneous Intra-
Continental Activity kimberlites, carbonatites,
anorthosites...
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Fundamental Concepts in Igneous
Petrology (Chapter 1)
Ash-Rich Strombolian Activity, Stromboli Volcano, ItalyImage source: www.photovolcanica.com
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1. How do we know we are dealing
with igneous rocs k ?
A. Observational criteria (general)
i. Field Criteria
cross-cut thecountry rocksand truncatestructures
image source: Barb Dutrow,
2005
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1. How do we know we are dealingwith igneous rocs k ?
A. Observational criteria (general)
i. Field CriteriaContact effects: chilled marginsor contact metamorphic effects
(above) Salsbury Crags,Teschenite Sill
(Edinburgh)
(right) Huttonsstep contact Image source: Barb Dutrow and Darrell Henry (2002)
metamorphism of sandstone.
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1. How do we know we are dealingwith igneous rocs k ?
A. Observational criteria (general)
i. Field Criteria
Geological formsdirectly observedas igneous
events:
cinder cones,stratovolcanoes,flows, etc.
Ash-Rich Strombolian Activity, Stromboli Volcano,Italy
Image source: www.photovolcanica.com
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1. How do we know we are dealingwith igneous rocs k ?
A. Observational criteria (general)ii. Textural Criteria
Macroscopic/
microscopicdevelopment ofinterlocking texture.
first-crystallizing mineralsare most euhedral and laterminerals are less euhedral
Gabbro - Rustenberg layered suite,BushveldComplex:Image source:
http://web.uct.ac.za/depts/geolsci/dlr/bvthin.html
(paragenetic sequence)
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1. How do we know we are dealingwith igneous rocs k ?
A. Observational criteria (general)
ii. Textural Criteria glassy textures
Osidian from a flowImage source: Hamblin and Christiansen (2001)
Ash grain frompyroclasticeruption:e.g. Mt. St. Helens
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1. How do we know we are dealingwith igneous rocs k ?
A. Observational criteria (general)ii. Textural Criteria random orientation of
crystals
except where there is crystalsettling or magmatic flow
Granite (above) and Gabbro (right)Image source: Darrell Henry, 2007
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1. How do we know we are dealingwith igneous rocs k ?
A. Observational criteria (general)ii. Textural Criteriadevelopment of pyroclastic
deposits (explosive eruptive materials)
rapidly cooled/partly sedimentary
Rapidly- cooled fragments
of rock and ash extruded as
a hot volcanic ash deposit -welded tuff
Image source: Hamblin andChristiansen (2001)
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2. What does a igneous petrologist try
to assess:generaton i of mets l[how many ?]source of melting[where?]
material that is melted[what?]processes that modify melts duringcrystallization, etc.? [how changed?]
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3. How does a petrologist assess this?A. Experience at looking at rocks and
interpreting textures
Tokachi Volcano, Hokkaido, Japan (2006) Walter Maresch (Ruhr Univ.), BarbDutrow
(LSU) and Dan Dunkley (Univ. Tokyo). Image source: Darrell Henry
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3. How does a petrologist assess this?B. Experimental data to simulate the
conditions at depth
Piston cylinder apparatus and experimental assembly from Ruhr Univ.. Imagesource: BarbDutrow, 1987
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3. How does a petrologist assess this?
C. Theoretical models to extend experimental
data to other conditions i.e. thermodynamics
Theoretical melting models to relate decompression melting and the types ofmelts to rocks.
Image source: Ed Stolper (CalTech).
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3. How does a petrologist assess this?D. Knowledge of the interior of the Earth
direct samples of the mantle
Mantle xenolith in alkali basalt.Image source: Barb Dutrow, 2006
Seiad Ultramafic Complex, northernCalifornia.Image source: Darrell Henry , 1973
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3. How does a petrologist assess this?D. Knowledge of interior of the Earth
indirect samples - meteorites
Meteorites - arrested early
stages of development ofsolar nebula with nosubsequent alteration ordifferentiation
clues to the developmentof the planets
Meteor Crater, Arizona.The explosive impact of a meteorite.
Image source: Press and Siever, 2001
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3. How does a petrologist assess this?D. Knowledge of interior of the Earth
indirect samples - meteorites
Irons (Fe-Ni alloy) - planetarycores?
5% of falls[Iron meteorite MALTAHOHE, Namibia Image
source:http://www.meteoriteman.com/]
Stony-irons (Metal and silicate
minerals) - partial differentiation1% of falls
[Stony-iron meteorite palllasite, Dora, NewMexico.Image source: Smithsonian Institution]
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3. How does a petrologist assess this?D. Knowledge of interior of the Earth
indirect samples - meteorites
Stones (Achondrites)differentiatedalso SNC ground
8% of falls
Stones (Carbonaceous chondrite)primitive undifferentiated
86% of falls
[Chondrite Allende meteorite: Chihuahua,Mexico.Image source: http://www.meteoriteman.com/]
[Achondrite Martian meteorite, Nakhla, Egypt,
Image source: http://www.meteoriteman.com
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4. What do we think we know aboutEarths interior?
A. The Earth is layered
Earth has layeredstructure:
crust(oceanic andcontinental)
mantle
core(inner and outer)
image source: Press and Siever,2001
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4. What do we think we know about
Earthsinterior?A. The Earth is layered
Internal structure islargely established by
variations in P- and S-
seismic waves.
The Mohorovicic (Moho)discontinuity at interface
of crust and uppermantle is compositional
discontinuity.
image source: Winter
(2001)
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4. What do we think we know about
Earthsinterior?A. The Earth is layered
Low velocity zones in uppermantle is zone of 1-10%
melting
forms the asthenosphere
serves as interface oflithospheric plates andmesophere.
image source: Winter
(2001)
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4. What do we think we know about
Earthsinterior?A. The Earth is layered
Damping of S waves in theouter core signals presence
of liquid outer core.
Sharp increase in S- and P-wave velocities indicatesolid metallic inner core.
image source: Winter
(2001)
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4. What do we think we know about
Earths interior?
A. The Earth is layered
Continental crust Vs. ocean crust
Thicker: 25-60 km vs. 0-10 km
Older: some >4 Ga vs.
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4. What do we think we know aboutEarthsinterior?
A. The Earth is layeredWithin mantle there areadditional discontinuities thatmark polymorphic transitions ofolivine:
410 km olivine converts tospinel- type structures
660 km there is a transition to
a perovskite-type structure.
image source: Press and Siever
(2001)
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5. Hypothesis for origin of Earth?A. Early differentiation (first few 10s of
millions of years?)
image source: Press and Siever (2001)
Differentiation process
likely results fromheating due tocombinations of
gravitational collapseaccretion of
planetismalsSinking of iron to formcoreradioactive decay
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5. Hypothesis for origin of Earth?B. Resulting heterogeneous Earth composition
Differentiation
produced chemical
zonation in the Earth
Defines nature of rock
types that will develop.
image source: Press and Siever(2001)
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6. P-T-depth relation in the Earth?
Relationship between
depth and pressure
a function of weight of
the overlying column of
material.
image source: Winter (2001)
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5. P-T-depth relation in the Earth?
In systems that flow
(ductile), P is equal in all
directions i.e. lithostatic
P = gh= density
g = acceleration of
gravity
h = height of rockcolumn
Image source: Winter (2001)
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5. P-T-depth relation in the Earth?
with composition e.g.crust ~ 2.8 g/cm3and
Near surface, rocks
behave brittly
can accommodate small
amount of differential P
(a few kbars) beforefracturing.
mantle ~ 3.3 g/cm3.
density changes primarily
Image source: Winter (2001)
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5. P-depth-T relation in the Earth?Variation of T with
depth is geothermalgradient.
Related to factors
including cooling
initiated in the early
Earth and radioactivedecay.
Estimated ranges of oceanic and
continental steady-state geotherms to a
image source: Winter (2001)
depth of 100 km using upper and lowerlimits based on heat flows measured
near the surface.
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5. P-depth-T relation in the Earth?
Heat is transferred by:
radiation to space
(minor)
conduction (thermal
vibration)convection (densitydifferences
associated with T)
advection (transfer ofheat with rocks)
Image source: Winter (2001)
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7. Where are magmas from?where
it is hot enoughigneous genesis.
Plate tectonics1.Mid-ocean Ridges
2.Intracontinental Rifts
3. Island Arcs
4.Active Continental
Margins
5.Back-arc Basins
6.Ocean Island Basalts
7.Miscellaneous Intra-Continental Activity
kimberlites, carbonatites,
anorthosites...
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Classification of Igneous Rocks
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Classification of Igneous Rocks
Figure 2-1a. Method #1 for plotting a point with the components: 70% X, 20% Y, and 10% Z on
triangular diagrams. An Introduction to Igneous and Metamorphic Petrology, John Winter, Prentice Hall.
Classification of Igneous Rocks
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Classification of Igneous Rocks
Figure 2-1b. Method #2 for plotting a point with the components: 70% X, 20% Y, and 10% Z on triangular
diagrams. An Introduction to Igneous and Metamorphic Petrology, John Winter, Prentice Hall.
ClassificationThe rock must contain a total ofat least 10% of the minerals below.
(a)Quartzolite
Q
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Classification
of Igneous
Rocks
Figure 2-2. A classification of the phaneritic igneousrocks. a.Phaneritic rocks with more than 10% (quartz +feldspar + feldspathoids). After IUGS.
at least 10% of the minerals below.Renormalize to 100%
Quartz-richGranitoid
9090
6060
2020Alkali Fs.Quartz Syenite Quartz
SyeniteQuartz
MonzoniteQuartz
Monzodiorite
Syenite Monzonite Monzodiorite(Foid)-bearing
Syenite
5
10 35 65
(Foid)-bearingMonzonite
(Foid)-bearingMonzodiorite
90
Alkali Fs.
Syenite
(Foid)-bearingAlkali Fs. Syenite
10
(Foid)Monzosyenite
(Foid)Monzodiorite
Qtz. Diorite/Qtz. Gabbro
5
10
Diorite/Gabbro/Anorthosite
(Foid)-bearingDiorite/Gabbro
60
(Foid)olites
Quartzolite
Granite Grano-diorite
A P
F
60
Classification of Igneous Rocks
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Classification of Igneous Rocks
Figure 2-2. A classification of the phaneriticigneous rocks. b.Gabbroic rocks. c.Ultramaficrocks. After IUGS.
Plagioclase
OlivinePyroxene
Gabbro
Tro
ctoliteOlivine
gabbro
Plagioclase-bearing ultramafic rocks
90
(b)
Anorthosite
Olivine
ClinopyroxeneOrthopyroxene
Lherzolite
Websterite
Orthopyroxenite
Clinopyroxenite
Olivine Websterite
Peridotites
Pyroxenites
90
40
10
10
Dunite
(c)
Classification ofQ
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Classification of
Igneous Rocks
Figure 2-3. A classification and nomenclature
of volcanic rocks. After IUGS.
(foid)-bearing Trachyte
(foid)-bearing Latite
(foid)-bearingAndesite/Basalt
(Foid)ites
10
60 60
35 65
10
20 20
60 60
F
A P
Rhyolite Dacite
Trachyte Latite Andesite/Basalt
Phonolite Tephrite
Classification of Igneous Rocks
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Classification of Igneous Rocks
Figure 2-4. A chemical classification of volcanics based on total alkalis vs. silica. After Le Bas et al.
(1986) J. Petrol., 27, 745-750. Oxford University Press.
Classification of Igneous Rocks
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Classification of Igneous Rocks
Figure 2-5. Classification of the pyroclastic rocks. a.Based on type of material. After Pettijohn(1975) Sedimentary Rocks, Harper & Row, and Schmid (1981) Geology, 9, 40-43. b. Based on the