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

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

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

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

Extrusive Igneous Rocks Include: rocks formed from the cooling of lavas rocks 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 © 1999. George Mitrevski Last Days of Pompeii-Karl Briullov--Copyright © 1999. George Mitrevski. Auburn University

Mt St Helens crater 08-7-80, 60 mph, 800 deg F-pyroclastic flow- USGS

Composition and Classification of Igneous Rocks Chemistry: e.g. % SiO2 Mineralogy: e.g. Felsic (Feldspar and Silica) Intermediate Mafic (Magnesium and Ferric) Ultramafic

Why Figure 5.4 I 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 Felsic Igneous Rocks: -Igneous rocks rich in minerals high in silica. They include: Granite Rhyolite

Intermediate Igneous Rocks: -Igneous rocks in between in composition between felsic and mafic igneous rocks. They include: Granodiorite Dacite Diorite Andesite

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? *External pressure *and Water content *Internal composition (including internal water content)

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

When rocks melt (or partially melt). How do magmas form? When rocks melt (or partially melt). Why do rocks melt? 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

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???

Fractional Crystallization!

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????

What do we know about the shape of magmatic bodies. Are they sheets 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.

www.jemmoore.com/flying/ 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.

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

IGNEOUS ROCKS-rocks from liquid melts END of CHAPTER 5 IGNEOUS ROCKS-rocks from liquid melts