Geology ch. 4 and 5 test 2

Define vesicle with respect to igneous rocks, of course.

Vesicular: Extrusive rock containing voids left by gas bubbles that escape as lava solidifies. SCORIA, PUMICE

Is basalt a higher or lower temperature magma compared to rhyolite

higher

Name the most common pyroclastic materials

volcanic bombs-large bombs of magma that harden in the air. the shape is caused by the magma spinning through the air as it cooled Lapilli-means "little stones" in Italian. they are pebblelike bits of magma that hardened before they hit the ground volcanic ash-forms when gases in stiff magma expand rapidly and the walls of the gas bubbles explode into tiny, glasslike silvers. volcanic blocks-the largest pieces of pyroclastic material, are pieces of solid rock erupted from a volcano

At what temperature do rhyolite/granite melt

600-900c

Glassy

An igneous rock gets this texture when the magma cools down so fast that there is absolutely no time for the formation of crystals

list the particles common in a pyroclastic rock

Ash: fragments of pulverized rock, minerals and volcanic glass, created during volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. Lapilli: term for tephra, which is material that falls out of the air during a volcanic eruption or during some meteorite impacts. (little stones) Bombs: molten rock (tephra) larger than 64 mm (2.5 inches) in diameter, formed when a volcano ejects viscous fragments of lava during an eruption.

Know how magmas evolve: assimilation, differentiation (crystal settling), magma mixing

Assimilation: Pulls in other elements Differentiation: Heavy crystals fall to the bottom changing the composition of magma Magma Mixing: 2 magma bodies mix together

Know the most common igneous rocks and their compositional equivalents: Granite is the plutonic equivalent of a rhyolite Gabbro is the plutonic equivalent of a: Diorite is the plutonic equivalent of a:

Basalt Andesite

Understand decompression melting and flux melting

Decompression melting: When two plates move apart, they create a space that can be filled by hot rock that rises buoyantly from below. As this hot rock rises, the pressure on it decreases, and the rock can melt. Can come from rift zones primarily, as well as hot spots. (most common type of melting) Flux melting: Occurs when water and other volatile components are added to a hot solid rock. Water carried down the subducting plate will start to melt the asthenosphere and rise creating stratovolcanoes and explosive eruptions.

What is a flood basalt and where can you find them geographically in the U.S.?

Fissure eruptions - aka Flood basalts, Columbia Plateau and Deccan Traps

Define the type of igneous rock making up the Sierra Nevada Mountains. What is the name of the plutonic structures making up the mountains.

Granitic rock makes the mountains. The plutonic structure is a batholith, a continuous body of granitic rock that is exposed at ground surface over an area of 100km^2

What do the terms ferromagnesian/non-ferromagnesian and felsic and mafic mean

Mafic (Basaltic): Igneous rocks with abundant magnesium and iron. At least 45% dark silicates and calcium-rich feldspar, Contain no quartz! Higher density than granitic rocks Felsic (Granitic): Light-colored silicates composed almost entirely of quartz and potassium feldspar Ferromagnesian/ non-ferromagnesian: ferromagnesian minerals have iron and magnesium (ferro=iron, magnesian refers to magnesium). Non-ferro's lack these elements.

Plutonic

Magma that crystallizes at depth forms plutonic or intrusive igneous rocks

How does silica content affect viscosity

More silica+ lower temperature= More Viscous

What type of magma is found on the ocean floor, on continents?

Ocean Floor: basaltic magma maybe mafic Continents: Felsic and andesitic magma

Differentiate between aa and pahoehoe basaltic lavas (appearance)

Pahoehoe- characterized by a smooth, billowy, or ropy surface. Pahoehoe flows tend to be relatively thin, from a few inches to a few feet thick Aa- rough, jagged, spinose, and generally clinkery surface. Aa lava flows tend to be relatively thick compared to pahoehoe

What defines a pyroclastic igneous rock

Pyroclastic (fragmental): Produced by the consolidation of garments that may include ash, once molten blobs, or large angular blocks that were ejected during an explosive volcanic eruption.

Where are the greatest concentrations of active volcanoes currently on Earth?

Ring of fire

Define what a porphyritic volcanic rock is and differentiate between groundmass and phenocrysts

Rocks that have larger grains (Phenocrysts) embedded in smaller grains called groundmass

How are igneous rocks classified? Based on

Texture and Composition

Porphyritic

The conditions change rapidly in course of magma cooling. For instance, magma starts cooling beneath the surface of the Earth, but is suddenly thrown out because of eruption. You can see both large and small crystals in these rocks ex:Porphyritic basalt, porphyritic granite, etc.

Aphanitic

The magma cools rapidly as it comes in contact with the atmosphere, thus giving very little time for the formation of crystals ex: Basalt, andesite, etc

Phaneritic

The magma is crystallized slowly below the Earth's surface owing to which large crystals―visible to the naked eye, are formed ex:Granite, diorite, etc

Volcanic

The solidification of lava or volcanic debris forms volcanic igneous rocks

Pegmatitic

This texture can be attributed to its formation process, wherein some minerals become very large in course of cooling of magma ex: Granite pegmatites, diorite pegmatites, etc

What is the most common volatile found in magma

Volcanic gases

Pyroclastic or Fragmental

When volcanic eruption blasts lava into the air, it results in its fragmentation. Rocks which are formed because of cooling of this fragmented magma sport the pyroclastic texture ex:Welded tuff, Breccia

Define peridotite and where it forms/exists in the earth

consisting mostly of the mineral's olivine and pyroxene. Peridotite is ultramafic, as the rock contains less than 45% silica It is high in magnesium. derived from the Earth's mantle, either as solid blocks and fragments, or as crystals accumulated from magmas that formed in the mantle.

Composite Volcano

layers of pyroclastic and lava flows (hence, composite), silica-rich lavas of andesitic or rhyolitic compositions, large, typical steep sided volcano many think of, Cascades (Mt. St. Helens) and the Andes

Shield volcanoes

many successive lava flows, low viscosity, basalt, most associated with hot spot volcanism. gentle, shield like appearance, Hawaiian Islands

Bowen's Reaction Series

sequential, predictable, dual-branched pattern in which minerals crystallize from cooling magma

Cinder Cones

steep sided, pyroclastic debris, cinders, some lava flows from base of cone, mainly basaltic, small, typically one eruptive event lasting from 1 month to a year, Paricutin (erupted for 9 years!)

Vesicular

texture is full of bubbles. It always indicates a volcanic rock, like this scoria ex: Scoria, Pumice

Define viscosity.

the measure of its resistance to gradual deformation by shear stress or tensile stress. For liquids, it corresponds to the informal concept of "thickness"

Texture

the visual and especially tactile quality of a surface

What factors makes a volcano's magma explosive?

thick high-viscosity magmas allow gas pressure to build up under the surface, which can result in violent explosions. Also happens near Flux melting

Define the different magma types (felsic, intermediate, etc) and define which is highest and lowest temperature.

• Basaltic (mafic) - silica poor • Andesitic - intermediate composition • Rhyolitic (felsic/granitic) - silica rich