Chapter 5 : Rocks from molten liquids Rocks from molten liquids Including adaptions from Dupre and Copeland (2004)

Concepts you should know for the exam Texture – grain size of intrusive (e.g., granite) and extrusive rocks (e.g., basalt) Relative cooling rates of intrusive and extrusive igneous rocks Rocks from lavas vs. pyroclastic rocks Mafic, intermediate and felsic rocks Know table! (Temperature, Silica, Na, K, Fe, Mg, Ca content) Melting point as a function of pressure, water content and composition Partial melting of magma-generating rocks Fractional crystallization Shapes of magmatic bodies – sills, dykes, batholiths Hot spots and volcanoes (mafic composition) Volcanoes at convergent margins ( mafic to felsic composition) Volcanoes at divergent margins (mafic composition) Lavas, welded tuff, vesicular basalt, volcanic bombs, pyroclastic flows, volcanic cloud Relation between the shape of volcano, chemistry, viscosity of lavas (shield volcano, cinder cone volcano,composite volcano) Dangerous pyroclastic flows cause almost 30% fatalities natural disasters vs. tsunamis (~20%)

Lecture Outline 1. Where do magmas form? 2.How do igneous rocks differ from one another? 3. How do magmas form? 4. Magmatic differentiation 5. Forms of magmatic intrusion 6. Igneous activity and plate tectonics

Lecture Outline 1. Where do magmas form? 2.How do igneous rocks differ from one another? 3. How do magmas form? 4. Magmatic differentiation 5. Forms of magmatic intrusion 6. Igneous activity and plate tectonics

Divergent Plate Boundary Usually start within continents— grows to become ocean basin

How do igneous rocks differ 2. How do igneous rocks differ from one another? Texture – size of crystals Coarse-grained rocks Fine-grained rocks Mixed texture rocks

How do igneous rocks differ 1. How do igneous rocks differ from one another? Texture is related to rate of cooling. Intrusive igneous rocks Extrusive igneous rocks

Andesite - granite near the surface Hand sample-Santiago de Chile Microscope slide

Giant’s Causeway, Ireland

Genetic Classification of Igneous Rocks IntrusiveIntrusive: crystallized from slowly cooling magma intruded within the Earth’s crust; e.g. granite, gabbro

Genetic Classification of Igneous Rocks ExtrusiveExtrusive: crystallized from rapidly cooling magma extruded on the surface of the Earth as lava or erupted as pyroclastic material.

Extrusive Igneous Rocks Include: lavasrocks formed from the cooling of lavas pyroclasticrocks formed by the cooling of pyroclastic material, i.e. fragmented pieces of magma and material erupted into the air

Last Days of Pompeii-Karl Briullov-- Copyright © George Mitrevski. Auburn UniversityGeorge Mitrevski

Mt St Helens crater , 60 mph, 800 deg F- pyroclastic flow- USGS

Composition and Classification of Igneous Rocks Chemistry: e.g. % SiO 2 Mineralogy: e.g. –Felsic (Feldspar and Silica) –Intermediate –Mafic (Magnesium and Ferric) –Ultramafic

Two basic compositional groups: Felsic igneous rocks Mafic igneous rocks

Why last figure is so important The color and mineral distribution indicate an increasing density and melting temperature. Darker igneous rocks generally weigh more and are formed at higher temperatures and pressures. This reflects the density- stratification of the whole Earth!

Felsic Igneous Rocks: - Igneous rocks rich in minerals high in silica. They include: GraniteRhyolite

Intermediate Igneous Rocks: - Igneous rocks in between in composition between felsic and mafic igneous rocks. They include: DioriteAndesite

Mafic Igneous rocks -very low silica content, and consist primarily of mafic minerals. The most common ultramafic rock is: Peridotite

What controls the melting temperatures of minerals? pressure *External pressure composition *Internal composition (including internal water content)

Factors Affecting Melting of Minerals (and Rocks) PressurePressure: Increased Pressures raises melting points Water Content (internal to the mineral)Water Content (internal to the mineral): Increased Water Content lowers melting points CompositionComposition: Felsic minerals melt at lower temperatures than mafic minerals

Which rocks are hardest to melt? 1.Granite countertop 2.Hawaiian beach sands? 3.marble

At which plate boundary does water-aided melting help generate magma? 1.Divergent? 2.Transform 3.Convergent?

Lecture Outline 1. Where do magmas form? 2.How do igneous rocks differ from one another? 3. How do magmas form? 4. Magmatic differentiation 5. Forms of magmatic intrusion 6. Igneous activity and plate tectonics

4. How do magmas form? When rocks melt (or partially melt). Why do rocks melt? melting point When the temperature exceeds the melting point of the rock or some minerals within the rock.

Partial Melting --Occurs when some of the minerals forming a rock melt at lower temperatures than other minerals within the same rock

different minerals melt at different pressures mineral types over time as a magma body cools ??? If different minerals melt at different pressures that means that different minerals become solid at different temperatures too. What does this imply about the mineral types over time as a magma body cools ???

Fractional Crystallization!

Lecture Outline 1. Where do magmas form? 2.How do igneous rocks differ from one another? 3. How do magmas form? 4. Magmatic differentiation 5. Forms of magmatic intrusion 6. Igneous activity and plate tectonics

different minerals melt at different pressures internal composition of a magma body as it cools ??? If different minerals melt at different pressures that means that different minerals become solid at different temperatures too. What does this imply about the internal composition of a magma body as it cools ???

What is Magmatic Differentiation ? If, during fractional crystallization, the remaining magma were to erupt it would be (a) more felsic or (b) more mafic than the original magma????

Lecture Outline 1. Where do magmas form? 2.How do igneous rocks differ from one another? 3. How do magmas form? 4. Magmatic differentiation 5. Forms of magmatic intrusion 6. Igneous activity and plate tectonics

shape What do we know about the shape of magmatic bodies? Are they sheets? Blobs? Spheres?

“Magmatic Pipes -101” Dykes are near-vertical Sills are horizontal and squeeze in between other layers of rock Plutons are deep (km) bodies of solidified magma. An example of a plutonic rock is granite or gabbro.

shiprock.html Shiprock, NM. It's hard to tell, mainly because I was flying at about 12,000ft when I took this picture, but this massive piece of rock sticks up over 2,000ft from the surrounding plain, and is as big as a small city. It is on Navajo land, and is a significant spiritual site for the Navajo. The hard, volcanic spines radiating out from the main spire are really amazing. From this high up, you couldn't even see an eighteen-wheeler on the ground next to Shiprock, it would be just a speck.

Shiprock, NM shiprock.html “Shiprock, NM. It's hard to tell, mainly because I was flying at about 12,000ft when I took this picture, but this massive piece of rock sticks up over 2,000ft from the surrounding plain, and is as big as a small city. It is on Navajo land, and is a significant spiritual site for the Navajo. The hard, volcanic spines radiating out from the main spire are really amazing. From this high up, you couldn't even see an eighteen-wheeler on the ground next to Shiprock, it would be just a speck.”

6. Igneous activity and plate tectonics Magmatic geosystems: Island arc plate subduction Plate divergence Hot-spot volcanism Continental plate subduction

Geomagmatic systems of Earth

ISLAND ARC PLATE SUBDUCTION Mafic to intermediate intrusives (plutonism) Mafic to intermediate extrusives (volcanism) Island arc volcano Subduction zone Oceanic lithosphere Oceanic lithosphere Island arc plate subduction

PLATE DIVERGENCE Basaltic extrusives Basaltic intrusives Mid-ocean ridge Partial melting Of upper mantle Partial melting Of upper mantle Rising magma Plate divergent boundary

HOT-SPOT VOLCANISM Basaltic extrusives Basaltic intrusives Hot-spot volcano Mantle plume (hot spot) Mantle plume (hot spot) Mantle Hot-spot volcanism

CONTINENTAL PLATE SUBDUCTION Mafic to felsic intrusives Mafic to felsic extrusives Subduction zone Continental margin volcano Oceanic lithosphere Continental mantle lithosphere Continental mantle lithosphere Continental crust Oceanic crust Oceanic crust Continental plate subduction

Summary of Volcanoes Subduction volcanoes in continental crustal and oceanic crust at convergent plate margins Hot spot volcanoes (anywhere) decompression volcanoes at divergent plate margins

END of CHAPTER 5 IGNEOUS ROCKS-rocks from liquid melts