Ch 01 Intro-Conceptos Basicos

8/12/2019 Ch 01 Intro-Conceptos Basicos

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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 ?


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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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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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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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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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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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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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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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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Low velocity zones in uppermantle is zone of 1-10%

melting

forms the asthenosphere

serves as interface oflithospheric plates andmesophere.


(2001)


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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.


(2001)


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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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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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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



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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)



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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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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.



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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



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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



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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.



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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

Ch 01 Intro-Conceptos Basicos

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