Warm Up 11/18Warm Up 11/18The broad, slightly dome-shaped volcanoes of Hawaii are ____.a. cinder cone volcanoes c. pyroclastic volcanoes

b. composite cone volcanoes d. shield volcanoesThe most violent volcanic eruptions are associated with what type of volcano?a. composite cones c. fissure eruptionsb. shield volcanoes d. cinder conesA magma’s viscosity is directly related to its ____.a. age c. silica contentb. depth d. color

Answers: 1) d. 2) a. 3) c.Answers: 1) d. 2) a. 3) c.

Intrusive Igneous ActivityIntrusive Igneous Activity

Chapter 10, Section 2Chapter 10, Section 2

PlutonsPlutons

Plutons –Plutons – structures that result from the structures that result from the cooling and hardening of magma at depthcooling and hardening of magma at depth

They can only be studied after uplift and They can only be studied after uplift and erosion have exposed them to the surfaceerosion have exposed them to the surface

Intrusive igneous bodies, or Intrusive igneous bodies, or plutonsplutons, are , are generally classified according to their generally classified according to their shape, size, and relationship to the shape, size, and relationship to the surrounding rock layerssurrounding rock layers

Sills and LaccolithsSills and Laccoliths

Sills and laccoliths are plutons that form when Sills and laccoliths are plutons that form when magma is intruded close to the surfacemagma is intruded close to the surface

Sill –Sill – forms when magma is injected along forms when magma is injected along sedimentary bedding surfaces, parallel to the sedimentary bedding surfaces, parallel to the bedding planesbedding planes

For a sill to form, the sedimentary rock must be For a sill to form, the sedimentary rock must be lifted to a height equal to the thickness of the silllifted to a height equal to the thickness of the sill

Laccoliths –Laccoliths – forms when magma intrudes into forms when magma intrudes into sedimentary bedding surfaces, collects as a sedimentary bedding surfaces, collects as a lens-shaped mass that pushes the overlying lens-shaped mass that pushes the overlying strata upwardsstrata upwards

SillsSills

LaccolithsLaccoliths

Concept CheckConcept Check

How are sills and laccoliths alike?How are sills and laccoliths alike?

They are both plutons formed by magma They are both plutons formed by magma intrusions close to the surfaceintrusions close to the surface

How are sills and laccoliths different?How are sills and laccoliths different?

They differ in shape and usually They differ in shape and usually compositioncomposition

Dikes and BatholithsDikes and Batholiths

Dikes –Dikes – plutons that form when magma is plutons that form when magma is injected into fractures, cutting across injected into fractures, cutting across preexisting rock layerspreexisting rock layersMany dikes form when magma from a Many dikes form when magma from a large magma chamber invades fractures in large magma chamber invades fractures in the surrounding rocksthe surrounding rocksBatholiths – Batholiths – the largest intrusive bodies, the largest intrusive bodies, must have a surface exposure greater must have a surface exposure greater than 100 square kilometersthan 100 square kilometersBatholiths may form the core of mountain Batholiths may form the core of mountain rangesranges

DikesDikes

BatholithsBatholiths

Basic Basic Igneous Igneous

StructuresStructures

Origin of MagmaOrigin of MagmaEarth’s crust and mantle are composed Earth’s crust and mantle are composed primarily of solid, not molten, rock, and the primarily of solid, not molten, rock, and the liquid iron in the outer core is too dense to liquid iron in the outer core is too dense to travel all the way to the surfacetravel all the way to the surfaceGeologists conclude that magma originates Geologists conclude that magma originates when essentially solid rock, located in the when essentially solid rock, located in the crust and upper mantle, partially meltscrust and upper mantle, partially meltsThe most obvious way to generate magma The most obvious way to generate magma from solid rock is to raise the temperature from solid rock is to raise the temperature above the level at which the rock begins to above the level at which the rock begins to meltmelt

The Role of HeatThe Role of HeatThe rate of change of temperature as you move The rate of change of temperature as you move down into the upper crust is ~20-30º per down into the upper crust is ~20-30º per kilometerkilometerGeothermal Gradient –Geothermal Gradient – the change in the change in temperature with depthtemperature with depthAt a depth of ~100 km, temperature ranges from At a depth of ~100 km, temperature ranges from 1400ºC and 1600ºC, almost the melting point of 1400ºC and 1600ºC, almost the melting point of rockrockSubduction zones add friction (another way to Subduction zones add friction (another way to produce heat) and water (which lowers the produce heat) and water (which lowers the melting temperature of rock) to give the added melting temperature of rock) to give the added heat needed to melt the crustal rocksheat needed to melt the crustal rocksHotter mantle rocks can rise and intrude into Hotter mantle rocks can rise and intrude into crustal rocks, melting themcrustal rocks, melting them

Geothermal GradientGeothermal Gradient

Concept CheckConcept Check

What is a geothermal gradient?What is a geothermal gradient?

The change in temperature with depthThe change in temperature with depth

Magma Formation at Subduction Magma Formation at Subduction ZonesZones

The Role of PressureThe Role of Pressure

Pressure also increases with depthPressure also increases with depth

Melting occurs at higher temperatures as you go Melting occurs at higher temperatures as you go deeper into Earth, because an increase in the deeper into Earth, because an increase in the confining pressure causes an increase in the confining pressure causes an increase in the rock’s melting temperaturerock’s melting temperature

Reducing that confining pressure lowers a rock’s Reducing that confining pressure lowers a rock’s melting temperaturemelting temperature

Decompression Melting –Decompression Melting – triggered when the triggered when the confining pressure drops enough to melt the confining pressure drops enough to melt the rockrock

Decompression MeltingDecompression Melting

AssignmentAssignment

Read Chapter 10Read Chapter 10

Do Chapter 10 AssessmentDo Chapter 10 Assessment– # 1 – 35 p. 303 – 304# 1 – 35 p. 303 – 304– # 1 – 7 p. 305# 1 – 7 p. 305