Lecture-9-F10

Lecture-9-F10 - EAS 111 General Announcements 9/29/10 •...

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Unformatted text preview: EAS 111 General Announcements 9/29/10 • Today: Mineral systematics and melting of rock • This week, and the next couple of weeks: – Bring your textbooks to lab – it will help! – Keep up on your reading in Chapter 5 – see directed readings at the end of this PowerPoint and online on Blackboard – it will help! Earth and Atmospheric Sciences 111 Fall 2010 Earth Materials II - How Silicate Minerals Tell Amazing Stories about Melting - How to Melt a Rock -Where this Happens and Why Lecture 9 EAS 111: Earth Science News EAS 111: Earth Science News Minerals in Different Parts of Earth Continental crust Oceanic crust Upper Upper mantle mantle Core 04.10.a Three Types of Relative Plate Motions Move apart: Move divergent boundary divergent Move toward each other: Move convergent boundary con Move horizontally Move past one another: transform boundary transform 03.03.b1-3 Silicate Minerals Silicate Silicate tetrahedron tetrahedron Tetrahedra Tetrahedra bond together and with other elements elements 04.07.b Silica fun facts Silica 4 A Silicon (Si) and Oxygen (O) combine to form the Silicon basic silica tetrahedron, which is the fundamental building block of rock material All by itself, the silica is not electrically neutral [SiO4]-4 Needs to bond Needs with something with (metals, itself, etc.) The more silica The present in a mineral structure, the more silica will bond to itself the A Bowen’s Reaction Series 05.10.c1 Independent Tetrahedra 04.07.c Olivine Tetrahedra bond to Tetrahedra other elements, not other tetrahedra other 05.10.c1 Single Chains Tetrahedra bond Tetrahedra together to form single chains single Pyroxene 04.07.c 05.10.c1 Double Chains Tetrahedra bond Tetrahedra to form double chains chains 04.07.c Amphibole 05.10.c1 Sheet Silicates Mica 04.07.c 05.10.c1 Frameworks Tetrahedra bonded together Tetrahedra and with other elements in 3D framework in Quartz Feldspar 04.07.c 05.10.c1 Recap: Concentrating Silica Recap: 4 A A A A High temperature igneous environments tend to High favor silica-poor minerals favor Silica-rich minerals are tend to form in cooler Silica-rich igneous environments igneous Silica bound totally by itself (quartz) has a very Silica low melting point low In a mixed-mineral rock, quartz will be the first to In melt as the rock is heated melt Silica is concentrated by melting in tectonic Silica settings that maximize recycling older material settings CPS: Concentrating Silica CPS: 4 If a solid (i.e. frozen, not melted) crystalline If rock is brought to the point where it partially partially melts, why would this increase the silica increase content in the melt that is produced relative melt to the starting rock composition? to A. Because Because olivine melts first, releasing individual silica tetrahedra individual B. Because quartz melts first, putting lots of Because pure silica into the melt pure C. Because the whole rock melts evenly, Because increasing silica in the melt increasing Solid Melting Rocks Pressure tends Pressure to hold lattice together together Liquid Increasing temperate Increasing vibrates atoms and can break bonds can How could changing temperature How or pressure cause melting? or 05.05.a1-3 Observe Observe conditions where rocks are liquid and solid solid Line slopes Line because increased pressure acts to keep rocks solid solid 05.05.b1 How could changing How conditions cause a rock starting at point A to melt? starting How could changing How conditions cause a rock starting at point C to melt? starting Observe what happens when a rock at point A is heated, Observe with or without an increase in pressure with 05.05.c1 Observe what happens when a hot rock at point C is Observe uplifted so rapidly it does not have time to cool off uplifted 05.05.c2 Adding Adding water lowers melting temperature of rocks of 05.05.c3 Consider what happens to a rock at point E if a small Consider amount of water is added to hot, dry rocks? amount How could melting occur along a divergent boundary How (mid-ocean ridge)? (mid-ocean 05.06.a1 05.06.c2 Solid asthenosphere Solid rises to fill gap rises Decompression Decompression melting melting Igneous Rocks in Igneous Oceanic Crust Oceanic Sheeted dikes Sheeted of basalt of Pillow basalt Gabbro 05.06.b4 Mantle New, Important Terms! Mafic: A rock or melt with relatively LOW silica (~5055%) and HIGH concentrations of iron and magnesium – once crystallized will have high amounts of olivine, pyroxene, amphibole, etc. – the High Temperature end of Bowen’s Reaction Series Intermediate Felsic: A rock or melt with relatively HIGH silica (~6570%) and LOW concentrations of iron and magnesium – once crystallized will have high amounts of quartz, low-T feldspars, micas, etc. – the Low Temperature end of Bowen’s Reaction Series How could melting How occur in a continental rift? rift? 05.06.c Decompression Crustal Heating Melting in a Ocean-Ocean Convergent Boundary Melting (Subduction Zone) (Subduction Mostly mafic and Mostly intermediate rocks rocks 05.07.a Add water to Add hot mantle hot How Does Water Get Into a Subduction How Zone? Zone? Hot water circulates in ridge; added in Hot pores and in minerals pores 05.07.d1 Water in minerals released at depth 4 CPS: Melting Rocks CPS: So, how do you melt a rock? A. Heat it up to its melting point B. Decompress it at high temperature so it Decompress melts C. Add water to so the melting point goes C. Add down and it melts at the pressure and temperature where it was formerly solid temperature D. All of the above, depending on the details All of tectonic setting and rock types of How could melting occur along an ocean-continent How convergent boundary? convergent Mostly felsic and Mostly intermediate rocks intermediate Mafic magma Mafic melts crust melts Adding water Adding melts mantle melts 05.07.b1 Magmatism with Hot Spots Oceanic island Rising Rising mantle plume plume 05.08.a Crustal Crustal melting and caldera in continent Huge basalt flows on continents continents How could melting occur during a continental collision? Few volcanoes Felsic rocks Felsic (granite) (granite) Burial and heating Burial of crustal rocks of 05.07.c1 Melting during Melting subduction before collision (but shuts off) collision EAS 111: Assignments for 10/4/10 • Reading in Exploring Geology Chapter 5 : – Take a fresh look at 5.1, 5.2, 5.3 • Igneous rock textures and types and names - Take a fresh look at 5.6, 5.7, 5.8 - magmatism at plate boundaries - 5.9, 5.10, 5.11 ...
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