UA geology exam 2 (Igneous and volcanos)

glassy texture

- Very rapid cooling of lava - Resulting rock called obsidian

dike geology

- tabular, discordant pluton

pegmatitic texture

-Exceptionally coarse grained (> 1 cm) -Form in late stages of crystallization of magmas

pyroclastic texture

-Fragmental appearance produced by violent volcanic eruptions

Batholith

-Largest intrusive body - Surface exposure > 100+ km2 (smaller bodies termed stocks) - Cores of mountains

The explosivity of a volcano is determined by _________.

1) Composition (% silica) 3) Temperature 3) Dissolved gases (volatiles)

what are the three components of magma

1) Liquid portion = melt 2) Solids, if present, silicate minerals 3) Volatiles = dissolved gases in melt, e.g. water vapor (H2O), carbon dioxide (CO2)

Evolution of magma

1. magmatic differentiation 2. assimilation 3. magma mixing

Igneous rocks that cool fast tend to exhibit ________ texture.

A. Aphanitic - not visible crystals

______ igneous rocks cool relatively slow exhibiting ________ texture

A. Intrusive; Phaneritic

lava tubes

Active lava tube, lava flows faster in insulated tube 50 km/hr

Higher silica (SiO2 ) content in magma can be associated with:

B. Increased viscosity

Bowen's Reaction Series

Both branches in operation as magma cools One mineral changes to another over specific temp. At biotite & Na-rich plag. point, remaining magma depleted in Fe, Mg, Ca, & Na remaining magma enriched in K, Al, & Si

Which two felsic rock types have the same composition but formed differently (i.e. intrusive / extrusive)?

C. Andesite/ diorite

What is an igneous rock?

Form as molten rock cools and solidifies Magma

Assimilation

Incorporation of surrounding rock bodies into magma

columnar joints

Lava contracts as cools, open up fractures Form polygonal (6- sided) fractures Polygonal fractures extend downward into flow

Laccolith

Lens shaped mass (not large as batholith) - Arches overlying strata upward

magma mixing

Mixing of 2 chemically distinct magmas

Aphanitic

Rapid cooling- mineral nuclei form quicker than rate of growth-- results in fine grained rock extrusive

magmatic differentiation

Separation of melt from earlier formed crystals (solid)

What is the most common type of rock forming mineral group?

Silicates (i.e. Quartz, Augite)

Most of the rocks making up the Earth's crust are composed dominantly of what elements?

Silicon and Oxygen

Phaneritic

Slow cooling- rate of growth exceeds rate of nuclei formation—results in coarse-grained rock intrusive

Stock (geology)

a smaller, remnant of a batholith

phaneritic texture

coarse grained Slow cooling -Large, visible crystals

Mafic Composition

dark in color (even more iron and magnesium) - Ferromagnesian silicates & Ca-rich feldspar - Silica poor (45-52%) - magnesium and ferrum, for iron - Comprise ocean floor & volcanic islands

What is lava?

extrusive rocks or volcanic rocks

slow rate of cooling

fewer but larger crystals

aphanitic texture

fine grained Rapid rate of cooling -Microscopic crystals

low viscosity

flows easily (water)

high viscosity

flows slowly (honey)

very fast rate of cooling

forms glass

factors generating magma from solid rock

heat pressure volatiles

felsic magmas

high silica content and highly viscous (i.e. honey)

What is magma?

intrusive rocks or plutonic rocks

Felsic Composition

light in color - No ferromagnesian silicates , feldspar and silica - Silica rich (SiO2 ) (>65%) - Major constituent of continental crust

mafic magma

lower silica content & more fluid-like behavior (less viscous) (i.e. water)

fast rate of cooling

many small crystals

intermediate composition

medium in color (silica rich & iron poor) - No ferromagnesian silicates , feldspar and silica - Silica rich (SiO2 ) (>65%) - Major constituent of continental crust

viscocity

resistance to flow

What is texture?

size, shape, and arrangement of minerals in a rock.

sill

tabular, concordant pluton (e.g., Palisades Sill in New York)

what is the most important factor in crystal size

the rate of cooling

Ultramafic composition

very dark in color most iron/magnesium) - Rare, high in Mg and Fe - Entirely ferromagnesian silicates - <45% silica

Pahoehoe lava

(ropey texture) Low viscosity

aalava

(rough, blocky texture) Higher viscosity

dissolved gasses

- Gases expand near Earth's surface due to decreasing pressure - Explosivity of eruption related to how easily gases escape!! **More Silica = gases don't escape as easily!! Pressure buildup! Boom!

porphyritic texture

- Indicates 2 stages of cooling -Large crystals (phenocrysts) embedded in matrix of smaller crystals (groundmass)