MORE VISCOUS high-SiO 2 (Quartz) cold LESS VISCOUS low-SiO 2 - - PowerPoint PPT Presentation

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more viscous high sio 2 quartz cold less viscous low sio
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MORE VISCOUS high-SiO 2 (Quartz) cold LESS VISCOUS low-SiO 2 - - PowerPoint PPT Presentation

Feb 28, 2023 494 likes •604 views

HIGHER TEMPERATURE SiO 2 MAKES LAVA DECREASES VISCOSITY MORE VISCOUS MORE VISCOUS high-SiO 2 (Quartz) cold LESS VISCOUS low-SiO 2 (Olivine) hot Image: S. Marshak Earth, Portrait of a Planet SiO 2 = silica SIO15-15:

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SLIDE 1

SIO15-15: Volcanoes: The Basics

LESS VISCOUS low-SiO2 (Olivine) hot

Image: S. Marshak “Earth, Portrait of a Planet”

MORE VISCOUS high-SiO2 (Quartz) cold

SiO2 MAKES LAVA MORE VISCOUS HIGHER TEMPERATURE DECREASES VISCOSITY

SiO2 = silica

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SLIDE 2

SIO15-15: Volcanoes: The Basics

crustal thickness composition (SiO2 content) SiO2: silica CONTINENTAL CRUST HAS MORE SiO2 THAN OCEANIC CRUST

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SLIDE 3

SIO15-15: Volcanoes: The Basics

OCEANIC CRUST

  • thin
  • dense, dark rock

Image: S. Marshak “Earth, Portrait of a Planet”

CONTINENTAL CRUST

  • thick
  • less dense, light rock
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SLIDE 4

SIO15-15: Volcanoes: The Basics

silicic (or felsic or rhyolitic) 65-70% intermediate (or andesitic) 55-65% mafic 40- 55%; rich in Mg, Fe

Volcanic/Plutonic Rock Rhyolite/Granite Andesite/Diorite Basalt/Gabbro

S i O

2

40% 70% density 2.5 g/cm3 3.4 g/cm3

dark color light color

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SLIDE 5

SIO15-15: Volcanoes: The Basics

Granite: plutonic (coarse grained) silicic (light-colored) Basalt: volcanic (fine-grained) mafic (dark-colored)

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SLIDE 6

SIO15-15: Volcanoes: The Basics

  • rock consists of many minerals
  • melting T of SiO2-rich minerals

(e.g. Quartz) 650oC

  • melting T of SiO2-poor minerals

(e.g. Olivine) 1100oC Melting T depends on composition: Granite 650ºC, Gabbro 1100ºC

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SLIDE 7

SIO15-15: Volcanoes: The Basics

  • molten rock

+ dissolved grains + dissolved volatiles up to 15% (50% H2O, 20% CO2, SO2, H2S, others)

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SLIDE 8

SIO15-15: Volcanoes: The Basics

LAVA

  • surface
  • volcanic
  • extrusive

Image: S. Marshak “Earth, Portrait of a Planet”

MAGMA

  • underground
  • plutonic
  • intrusive
  • ven T:

260oC/500oF melting T or freezing point: 650 - 1100oC Quartz: 650ºC Olivine: 1100ºC yoF = xoC*9/5+32 1200 - 2000oF

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SLIDE 9

SIO15-15: Volcanoes: The Basics

  • melting solid rock: Quartz earliest to melt
  • solidifying hot melt: Quartz latest to crystallize
  • > lava has more SIO2 than mantle rock left behind