Lecture 3a Igneous Rocks

Lecture 3a Igneous Rocks - Igneous Rocks: Igneous : Latin...

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Unformatted text preview: Igneous Rocks: Igneous : Latin ignis = fire; form from cooling of melted rock. Extrusive (volcanic): Produced when magma gets to the surface. At that point called lava, crystallizes rapidly into volcanic rocks. Intrusive (plutonic) : produced when magma cools to solid before it has reached the surface. magma crystallizes slowly at depth; we can ` t see this happening. have to wait for uplift and erosion to expose deep rocks. Intrusive Extrusive Plate Tectonic Settings Where Igneous Rocks Form Melted rock =magma = melt + crystals + gasses. Consists of: Liquid made of elements found in silicate minerals. Gasses: H 2 O CO 2 S Crystals: either old that didn ` t melt; Or new that grew from melt. Temperature Control of Rock Melting At constant pressure: Rocks are solid at low temperatures Rocks are liquid at very high temperatures As temperature increases, rocks do not melt uniformly That is, some minerals melt at lower temperatures than others This is called l partial melting z Pressure Temperature 0 % melt 10 % melt 50 % melt 100 % melt Liquid Solid Pressure Control of Rock Melting As pressure decreases, rocks can begin to melt without a change in temperature This process is called l decompression melting z Decompression melting is responsible for mid- ocean ridge magmatism Pressure Temperature 0 % melt 10 % melt 50 % melt 100 % melt Liquid Solid Fluid Control of Rock Melting At constant pressure and temperature, addition of Fuids, such as water, lowers the melting temperature Therefore, if Fuid is added, rocks can begin to melt without a change in temperature or pressure This process is called l Fuid- induced melting z luid-induced melting is responsible for subduction-zone magmatism 0 % melt 10 % melt 50 % melt 100 % melt Pressure Temperature Liquid Solid Little fluid Fluid Control of Rock Melting At constant pressure and temperature, addition of Fuids, such as water, lowers the melting temperature Therefore, if Fuid is added, rocks can begin to melt without a change in temperature or pressure...
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This note was uploaded on 04/02/2012 for the course GEOL 105 taught by Professor Platt,davis during the Spring '08 term at USC.

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Lecture 3a Igneous Rocks - Igneous Rocks: Igneous : Latin...

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