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Intrusives

Intrusives

How do oceans and differ? Chapter 4 The average ocean depth is 3000m.

If the ’s surface is 30% land and 70% ocean, why is IGNEOUS ROCKS there any land at all?

Why are there not just a few little islands?

How do oceans and continents How do oceans and continents differ? differ?

How do oceans and continents How do oceans and continents differ? differ?

Ocean is thin, dense, and young.

Continent crust is thick, light, and old.

1 Polymerization of Silica • Each Si atom is surrounded by 4 . • Polymerization is the degree to which the oxygens are shared with other Si atoms. • Polymerization is the number of Si-O-Si bonds per tetrahedron.

has none: isolated SiO4 groups

has 50% shared: SiO3 chains

has has 75% shared: Si4O10 sheets

and have 100% (Si,Al)O2 framework.

Polymerization of Silica Polymerization of Silica Pyroxene

Tetrahedron MgSiO3 Olivine (Mg2SiO4) Tetrahedron

Polymerization of Silica • Magma is the term for any molten Mica (Sheet) Quartz (Framework) material, whether below the surface or on top. • Volcanic rocks are erupted on the surface. – Volcanic rocks are fine-grained (<1 mm) • Intrusive igneous rocks crystallize from magma below the surface. – Intrusive igneous rocks are coarse- grained (> 1mm) – are very coarse-grained (> 1cm)

2 Igneous Rocks: Intrusive Igneous Rocks Learning Goals • Composition • What does ‘igneous’ mean? • • Composition • Geologic Setting • Mineralogy – – Mantle – – Oceanic Crust – – Continental Crust • Igneous Fractionation • Igneous Fractionation – How the chemistry evolves – How the chemistry evolves

Igneous Compositions Compositions

• Rock compositions are described • Igneous rocks vary in composition

in weight percents of oxides: (SiO2 content)

• SiO2, MgO, FeO, Al2O3, etc – ultramafic (~40 wt%) () • The principal variation in igneous – (45-55%) ( / ) – intermediate (55-65%) (/) rock compositions is silica (SiO2) content. – (65-75 wt %) (/) • The degree of polymerization of • The mantle is peridotite (ultramafic). silica increases with silica content. • The ocean crust is gabbro (mafic). (in both and melt). • The continents are granite (silicic)

Igneous Rock Names Igneous Rock Mineralogy and Compositions • Peridotite (Ultramafic) • Gabbro (Mafic) • Composition • Intrusive • Volcanic Name Rock Name Rock Name – Olivine ((Mg,Fe)2SiO4) – Feldspar – Pyroxene (CaAl2Si2O8) • Ultramafic • Peridotite • () ((Mg,Fe,Ca)SiO3) – Pyroxene •Mafic • Gabbro • Basalt – (Mg3Al2Si3O12) or ((Mg,Fe,Ca)SiO3) – (MgAl O ) • Intermediate • Diorite • Andesite 2 4 – Olivine • Silicic () • Granite • Rhyolite ((Mg,Fe)2SiO4)

3 Igneous Rock Mineralogy Igneous Rock Names and Compositions • Diorite (Intermediate) • Granite (Silicic) • Composition • Intrusive • Volcanic – Feldspar (CaAl2Si2O8) – Quartz (SiO2) Name – Feldspar (NaAlSi3O8) – Feldspar (NaAlSi3O8) Rock Name Rock Name

– Pyroxene ((Mg,Fe,Ca)SiO3) – Feldspar (KAlSi3O8) • Ultramafic • Peridotite • (Komatiite) – Mica – Mica () •Mafic • Gabbro • Basalt K(Mg,Fe,) (Si,Al) O (OH) (K(Mg,Fe,) (Si,Al) O (OH) 3 2 10 2 3 4 10 2 • Intermediate • Diorite • Andesite – Mica () • Silicic (felsic) • Granite • Rhyolite – (KAl2(Si,Al)4O10(OH)2

Geologic Settings: Mantle Geologic Settings Mid-ocean ridges Oceanic Islands Island arcs Continental • Compositions • Where? • Ultramafic • Mantle • Mafic • Oceanic • Intermediate • Zones • Silicic (felsic) • Continental Mass

There appear to be 13 major plates that cover the globe. Igneous Fractionation: Peridotite-basalt-granite • – Rocks have a melting interval of several hundred degrees C. – First melt is rich in silica, water and trace elements. • Fractional – First-formed crystals low in silica settle to the bottom.

4 Peridotite Peridotite Partial Melting

Peridotite Partial Melting First melt at 3- junctions

Garnet

Orthopyroxene Olivine

Clinopyroxene

Melt composition is different Melt is less dense from host

5 Melt flows when pockets touch Peridotite + Basalt Melt

Igneous Fractionation:

6 Layered Mafic Intrusion Granite Outcrop

Dikes: Intrusive forms Tabular discordant

• Pluton: Any large discordant intrusion at depth – : large > 100 km2 – : small < 100 km2 • Dike: Tabular non-conformable • : Tabular conformable

Dikes: Sills: Tabular discordant Tabular conformable

7 Sills: Tabular conformable

How do oceans and continents How do oceans and continents differ? differ? • Oceanic crust is: – Thin (~7 km), – Dense (~3.1g/cm3)

– Mafic (45-50% SiO2) – Young (< 200 my) • Continental Crust is: – Thick (>30 km), – Light (~2.7 g/cm3)

– Silicic (> 60% SiO2) – Old (> 1000 my)

How do oceans and continents Terms differ? • Polymerization • Silicic • Difference is result of partial • Magma • Peridotite melting and fractional • Pegmatitie • Gabbro crystallization. • Igneous • Diorite Fractionation • Granite – Mid ocean ridge makes basalt from • Partial melting • Pluton peridotite. • Fractional • Stock Crystallization – Partial melting at subduction zones • Batholith makes andesite from basalt. • Ultramafic • • Mafic • Sill • Intermediate

8 Assignment Clicker Question • What is the most likely •Grotzinger Chapter 5 geologic setting in which conglomerate was deposited? •Sedimentary Rocks – A. Continental alluvial fans – B. Continental deserts and beaches – C. Shallow-water marine – D. Deep-water marine – E. Reefs

Clicker Question Clicker Question • What is the most likely • What is the most likely geologic setting in which geologic setting in which was deposited? shale was deposited? – A. Continental alluvial fans – A. Continental alluvial fans – B. Continental deserts and beaches – B. Continental deserts and beaches – C. Shallow-water marine – C. Shallow-water marine – D. Deep-water marine – D. Deep-water marine – E. Reefs – E. Reefs (Tropical Shallow Marine)

Crust and Mantle Clicker Question 1 and Asthenosphere • The term for any molten silicate material on or below the Earth’s surface is:

– A. Granite – B. Basalt – C. Magma – D. – E.

9 Clicker Question 1 Clicker Question 2 • The term for any molten silicate • The most abundant element in material on or below the Earth’s the Earth is: surface is: – A. Hydrogen – A. Granite – B. – B. Basalt – C. –C. Magma – D. – D. Pegmatite – E. – E. Lava

Clicker Question 2 Clicker Question 3 • The most abundant element in • The composition of the mantle is the Earth is: said to be:

– A. Hydrogen – A. Ultramafic –B. Oxygen – B. Mafic – C. Magnesium – C. Intermediate – D. Silicon – D. Silicic – E. Iron – E. Sedimentary

Clicker Question 3 • The composition of the mantle is Clicker Question said to be: • Any small or large discordant intrusion at depth is known as a –A. Ultramafic – A. Pluton – B. Mafic – B. Batholith – C. Intermediate – C. Stock: – D. Silicic – D. Dike – E. Sedimentary – E. Sill

10 Clicker Question Clicker Question

• Any small or large discordant • A small conformable intrusion intrusion at depth is known as a between and parallel to – A. Pluton sedimentary layers is known as a – B. Batholith – A. Pluton – C. Stock: – B. Batholith – D. Dike – C. Stock: – E. Sill – D. Dike – E. Sill

Clicker Question Clicker Question

• A small conformable intrusion • A small discordant intrusion that between and parallel to cuts across sedimentary layers is sedimentary layers is known as a known as a – A. Pluton – A. Pluton – B. Batholith – B. Batholith – C. Stock: – C. Stock: – D. Dike – D. Dike –E. Sill – E. Sill

Clicker Question

• A small discordant intrusion that cuts across sedimentary layers is known as a – A. Pluton – B. Batholith – C. Stock: –D. Dike – E. Sill

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