igneous rocks, minerals, and volcanos allan treiman lpi

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Igneous Rocks, Minerals, and Volcanos Allan Treiman LPI

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Page 1: Igneous Rocks, Minerals, and Volcanos Allan Treiman LPI

Igneous Rocks, Minerals, and Volcanos

Allan Treiman

LPI

Page 2: Igneous Rocks, Minerals, and Volcanos Allan Treiman LPI

Plan of Talk

Tyrrany of Three– Three types of volcanos– Three types of lavas

Volcanos in terms of Lava Properties and Environments

Lava Properties in terms of Atoms Igneous Rocks and Minerals

Page 3: Igneous Rocks, Minerals, and Volcanos Allan Treiman LPI

Three Types of Volcanos

Shield Composite /

Stratovolcano Cinder Cone

Page 4: Igneous Rocks, Minerals, and Volcanos Allan Treiman LPI

But So Many More …

Caldera Complex ‘Super-Volcano’

Lava Plateau Dome Single Flow Tuff Ring And …

Page 5: Igneous Rocks, Minerals, and Volcanos Allan Treiman LPI

What Controls the Shape of a Volcano?

Properties of lava– Viscosity of lava (runny or stiff) – Dissolved Gas - Explosive or Effusive– Solid grains in lava.

Volume of lava erupted Single or Multiple eruptions Environment around eruption

Page 6: Igneous Rocks, Minerals, and Volcanos Allan Treiman LPI

Lava Properties: Viscosity Different sorts of lavas are stiffer or runnier What is lava?

– Molten material in the Earth– Solidifies at surface conditions

Many sorts of ‘lava’– Most common is silicate - abundant SiO4

4-

– Molten sulfur, carbonate, iron oxide– Mud is not lava on Earth (but “mud volcanos”)– Water is not lava on Earth (but is elsewhere)

Page 7: Igneous Rocks, Minerals, and Volcanos Allan Treiman LPI

Silicate Lavas Large Range of Viscosity

– Basalt - as runny as motor oil – Andesite - stiffer than taffy– Rhyolite/Granite - like window glass

Depends on silica - SiO2 – Basalt: < 52% SiO2 in

chemical analysis– Andesite: 52 - 63% SiO2 – Dacite: 63 - 68 % SiO2 – Rhyolite: > 68 % SiO2

Andesite South Sister

SiO2 63.0 TiO2 1.15 Al2O3 16.24 Fe2O3 2.87 FeO 2.94 MnO 0.08 MgO 1.52 CaO 4.04 Na2O 4.86 K2O 2.00 P2O5 0.28 H2O 0.68 Sum 99.9

Page 8: Igneous Rocks, Minerals, and Volcanos Allan Treiman LPI

Why does silica matter?

Si - O bonds much stronger than others Silica tetrahedra, SiO4

4- polymerize

In lava, single silica tetrahedra flow easily, like little balls

In lava, large silicate polymers flow poorly, like noodles

Page 9: Igneous Rocks, Minerals, and Volcanos Allan Treiman LPI

Why does Water Matter? Force for explosive eruptions

– Water vapor bubbles out as magma nears surface

– No vapor, no explosion! Stiff water-rich magma makes

foam (pumice)& shards of glassy ash

Pumice + ash and water vapor can flow together as a ‘slurry’ = an ash flow

Page 10: Igneous Rocks, Minerals, and Volcanos Allan Treiman LPI

Ash flow = pyroclasticflow = ‘nuee ardent’

Page 11: Igneous Rocks, Minerals, and Volcanos Allan Treiman LPI

Caldera Complex “Super-Volcanos”

Valles Grandes, NM Caldera is 22 km across Rhyolite ash flows & domes Slope outside caldera ~2°

Yellowstone

Page 12: Igneous Rocks, Minerals, and Volcanos Allan Treiman LPI

An Invisible Caldera Complex “Super-

Volcano”:Harney Basin

A shallow basin, slightly east of our field trip path.

Multiple Ash Flows – Devine Canyon: 9 mybp– Prater Creek: 8.4 mybp – Rattlesnake: 6.4 mybp

Nearly invisible under later basalts, and erosion

Typical of later cenozoic geology of Basin & Range!

Page 13: Igneous Rocks, Minerals, and Volcanos Allan Treiman LPI

Crystals in Lava Solid crystals make lava more viscous What kinds of crystals?

– Olivine (Mg,Fe)2SiO4 - green, glassy

– Pyroxene (Ca,Mg,Fe)SiO3 - black/green, breaks on flat surfaces (cleavage)

– Feldspar - plagioclase (Ca, Na)(Al,Si)Si2O8 - clear-white-greenish, glassy, breaks on flat surfaces.

– Quartz - SiO2 - clear, glassy, curved fractures.

Page 14: Igneous Rocks, Minerals, and Volcanos Allan Treiman LPI

Single Eruption Paricutin Cinder Cone - 1.4

km3 lava Columbia River, Grande

Ronde - to 750 km long, 2000 km3 lava

Yellowstone - Lava Creek Tuff (like at Valles Caldera) - ~1000 km3 ash

How much is a cubic kilometer?

Page 15: Igneous Rocks, Minerals, and Volcanos Allan Treiman LPI

Many Eruptions Mauna Loa Shield -

~75,000 km3 lava Columbia River Basalts

~170,000 km3 lava Olympus Mons (Mars) -

~500,000 km3 volume Ontong-Java Plateau - ?

6,000,000 km3 lava

Page 16: Igneous Rocks, Minerals, and Volcanos Allan Treiman LPI

Environment of Eruption

Into Air– Typical

Into Water– Maar Explosion– Tuff Ring– Pillow Lava

Into Ice– Tuya Buttes

Page 17: Igneous Rocks, Minerals, and Volcanos Allan Treiman LPI

What Controls the Shape of a Volcano?

Properties of lava– Viscosity of lava (runny or stiff) – Dissolved Gas - Explosive or Effusive– Solid grains in lava.

Volume of lava erupted Single or Multiple eruptions Environment around eruption

Page 18: Igneous Rocks, Minerals, and Volcanos Allan Treiman LPI

Cinder Cone

Paricutin, Mexico– 1943 - 1952