More igneous rocks

Classification of igneous rocks.. Naming Igneous RocksIgneous rocks are classified by their: Texture Mineral Composition depends on: chemical makeup of parent magma depends on: how fa

1 Geology in the news presentation by Michael

Zara.

2 Classification of igneous rocks.

3 Nature and classification of igneous plutons.

4 Origins of magma and relationship to plate

tectonic setting.

In Lecture Today:

Naming Igneous Rocks

Igneous rocks are classified by their:

Texture

Mineral Composition

depends on: chemical makeup of parent magma depends on: how fast/slow magma cools

which is in

turn,

determined

by proximity to

Grain size in igneous rocks

is determined by cooling rate

Fig 6.14cd

Stephen Marshak

Fig 6.12

W W Norton

Fig 6.19

Stephen Marshak

Naming Igneous Rocks

Basic magma types:

Mafic

Felsic

High in Si Lighter, less dense

High in Mg, Fe Dark, dense

ma gnesium + fe rrum

fel dspar + si lica (quartz)

Naming igneous rocks

Fig 6.17a

Figure 6.17 Text, page 155

Naming igneous rocks

Fig 6.17a

Figure 6.17 Text, page 155

Naming igneous rocks

Fig 6.17a

W W Norton Mineral proportions

after Hamblin and Howard.

Naming Igneous Rocks:

Upper mantle plutonic

igneous rocks,

“peridotite” or “dunite”

Ultramafic: ~ 40% Silica (less than gabbro/basalt, with more Fe and Mg).

Naming Igneous Rocks:

Glassy Volcanic Rocks

Minerals with the highest melting temperatures come

out first, followed by minerals with successively lower melting temperatures

The sequence of silicate mineral crystallization in magmas was first studied by

University of Chicago geologist, N.L Bowen, in the

1920’s

Bowen’s Reaction Series

Magmas don’t crystallize all at once!

Basaltic lavas are very fluid and travel far from the vent to

produce volcanoes with low profiles.

Fig 6.20a

W W Norton

Columbia River

basalts

Basalt eruptions on land produce flows

that travel great distances.

Fig 6.21a

W W Norton

Basaltic lavas erupted under water produce “pillows”

Fig 6.21b

Stephen Marshak

Fig 6.21c

© Peter Kresan

Fig 6.02

W W Norton

Products

of volcanic eruptions includes morethan just lava

Explosive Volcanic

Eruptions

Pyroclastic Volcanic Rocks

Violently explosove volcanic

eruptions produce:

Rock fragments

(all sizes) Finely-fragmented ash

Molten bombs

These accumulate

to form:

Fig 6.08a

W W Norton

Naming Igneous Rocks

Pyroclastic volcanic rocks:

Composed of rock fragments ejected during eruptions Types include:

“Tuff”: Composed of ash, finely fragmented

volcanic rock Welded tuffs form when ash is

so hot, it deforms plastically.

Scoria: Red or black, frothy lava, denser than

pumice.

Volcanic Breccia: Coarse, angular rock

Volcanic ash:

Lithifies to form a

volcanic tuff

Pumice: Formed by the quenching ofgas-charged lava.Obsidian: Volcanic glass

Formed by quenching of lava