Download Ch 6 Powerpoint: Igneous Rocks Slide 1: n/a Slide 2: Igneous rocks

Ch 6 Powerpoint: Igneous Rocks
Slide 1: n/a
Slide 2: Igneous rocks form from _____________rock (magma) crystallizing below earth's surface or from
volcanic activity. They commonly form at plate ______________ and are commonly exposed in
_____________areas. Igneous _____________ form from crystallization of magma at depth (within the earth's
crust) or at the surface (from ____________eruptions)
There are two (2) basic types or forms of igneous rocks:
1. Plutonic rocks = intrusive igneous rocks = igneous rocks that form from cooling magma at depth
2. Extrusive igneous rocks = igneous rocks that form from volcanic activity (at or near surface)
*Plutonic rocks are usually _________-grained, *Extrusive rocks are usually ________-grained
Slide 3-4:
Slide 5: Igneous rock textures depend on cooling history
Intrusive textures:
1. Fine-grained texture (Aphanitic) -- due to _________ cooling (at or near surface)
2. Coarse-grained texture (Phaneritic) -- due to _________ cooling at depth
3. Porphyritic texture -- coarse __________ (phenocrysts) surrounded by fine-grained matrix (groundmass)
forms due to initial __________ cooling, then magma ___________ to (or close to) surface and the remaining
___________ cooling quickly
Extrusive textures:
4. Glassy texture -- due to very ___________ cooling -- magma cools so fast crystals don't have time to form.
Obsidian (volcanic glass) forms this way.
5. Vesicular texture -- full of rounded holes (vesicles) -- forms due to escape of _______ bubbles during cooling
of lava. Pumice is a _______________ rock with this vesicular texture.
6. Pyroclastic texture- chunks of ____________ material that fuse together
Slide 6-7: n/a
Slide 8:
Influences on rock melting temperature
Composition -- if rock contains a ____________of minerals it will melt at a lower temperature compared to rocks
that are mono-mineralic ( meaning _________ mineral)
Pressure -- ____________ pressure environments raise the melting _____________ of rocks
Water content -- rocks that contain some water melt at _________ temperatures than dry rocks
Magma composition
•
The composition of the magma determines the _______________ of the rock that forms
•
Igneous rock classification scheme shows that rocks vary in ________ content
•
Gabbros and basalts are low in silica, with bulk compositions less than about 60% silica
•
Granites and rhyolites are high in silica (bulk compositions with higher than 60% silica)
Slide 9 & 10:

Professor Norman L. Bowen summarized results of experiments done early in the 1900’s on crystallization
of granitic magmas. These ____________ showed that there is a sequence of minerals that crystallize as
the temperature of magma is lowered:
•
Bowen’s Reaction Series represents that ____________ that has implications for other types of rocks as
well, although it is only used to determine the crystallization sequence in a molten magma (intrusive igneous
rocks).
Slide 11:
•
Igneous intrusions are rock bodies that form from crystallization of magma at depth within earth's crust.
They are categorized based on their ____________ and overall size.
•
Discordant: cut across pre-existing __________ of rock layers
•
Dikes are small igneous ___________ that cut across rocks into which the magma intrudes. They are
commonly sheet-like, only a few meters wide, but possibly laterally ___________.
•
Stocks are fairly large (____________) igneous intrusions that cut across pre-existing rock layers. In
size, they are on the order of an individual ____________ peak.
•
Batholiths are huge igneous intrusions made of many____________. Their size is on the scale of an entire
mountain range (100’s of miles).
•
Concordant: follow pre-existing fabric of rock layers without ____________of layering.
•
Sills are also small ___________ intrusions. They are sheets of rock that, unlike dikes, are parallel to
pre-existing rocks. Think of magma invading sedimentary rocks by ____________ out between rock layers.
That magma would cool to form a sill.
•
Laccoliths are rather large, ____________-shaped intrusions that “puff up” in the center due to gases.
•
Lopoliths are also large, _____________ mushroom-shaped (spoon-shaped) intrusions that “sag down” in
the middle because of ___________