Essentials of Geology: Chapter 3

magma assimilation

A magma chamber may incorporate the rocks that make up the wall of the magma chamber by rocks falling into the magma chamber and melting, or when heat from the magma chamber melts the wall of the chamber.

25 °C

Average value of the temperature gradient

magmatic differentiation

Bowen's experiments account for the great diversity of igneous rocks. It has been shown that, at one or more stages during the crystallization of magma, a separation of various components can occur. What do you call this process of separation?

Peridotite

Dense, dark igneous rock that makes up the mantle.

dike swarms

Dikes and sills can occur as solitary bodies, but dikes in particular tend to form in roughly parallel groups called ___________.

rate of cooling

Dominant factor of a rock's texture

Felsic

Geologists also refer to granitic rocks as being _________ , a term derived from feldspar and silica (quartz).

700°C

Granitic magma, which has a high silica content, is quite viscous ("thick") and may erupt at temperatures as low as _____ °C.

Pele's hair and Pele's tears

Hawaiian volcanoes sometimes generate lava fountains, which spray basaltic lava tens of meters into the air. Such activity can produce strands and tiny blobs of volcanic glass called________________ and ________________ respectively, after the Hawaiian goddess of volcanoes.

1. Increase in Temperature 2. Decompression Melting 3. Addition/Introduction of Volatiles

Magma can be generated in the upper mantle in three ways:

Uppermost mantle/Asthenosphere

Most magma originates in what layer of the geosphere?

Kirava, Sweden

Place in Europe where a pegmatite deposit that is composed of over 60% magnetite

Magmatic Segregation serves to concentrate selected metals producing major deposits of chromite (ore of chromium), magnetite, and platinum. Heavy minerals that crystallize early tend to settle to the lower portion of the magma chamber.

Primary magmatic process in ore deposition at Stillwater Complex in Montana and Bushveld Complex in South Africa.

Glass

Rocks that consist of unordered ions that are "frozen" randomly in place are referred to as ________.

andesitic composition

Rocks with a composition between granitic and basaltic rocks. Contain at least 25 percent dark silicate minerals, mainly amphibole, pyroxene, and biotite mica with the other dominant mineral being plagioclase feldspar.

volatiles

The gaseous components of magma, called ____________ , are materials that will vaporize (form a gas) at surface pressures. The most common volatiles found in magma are water vapor (H 2 O), carbon dioxide (CO 2 ), and sulfur dioxide (SO 2 )

Norman Levi Bowen FRS was a Canadian geologist. Bowen "revolutionized experimental petrology and our understanding of mineral crystallization".

The guy who pioneered the investigation into the crystallization of magma in the early 20th century?

Melt

The liquid portion of magma, called ________ , is composed mainly of mobile ions of the eight most common elements found in Earth's crust—silicon and oxygen, along with lesser amounts of aluminum, potassium, calcium, sodium, iron, and magnesium

magma mixing

The process whereby magmas of different composition mix together to yield a modified version of the parent magmas.

intrusions or plutons

The structures that result from the emplacement of magma into preexisting rocks are called __________________.

Silcon and Oxygen

Two elements that are the main constituent of Igneous rocks

Dikes and Sills

Two kinds of tabular intrusive bodies:

1. Radioactive Minerals and Rare Earths 2. Semi-Precious Gems: tourmali, topaz, beryl

Valuable Minerals and Elements typically found in Granitic Pegmatites

basaltic composition

a compositional group of igneous rocks indication that the rock contains substantial dark silicate minerals and calcium rich plagioclase feldspar

Dikes (can extend for many kilometers they are assumed to be the product of very fluid, and therefore, mobile magmas.)

are discordant bodies that cut across bedding surfaces or other structures in the host rock.

1100 and 1250 °C / 1000 °C

basaltic magmas are low in silica and are generally more fluid. Basaltic magmas also erupt at higher tem- peratures than granitic magmas—usually at temperatures between__________________ °C and are completely solid when cooled to ______ °C.

Pegmatites Pegmatites form late in the crystallization of a magma, when water and other volatiles, such as carbon dioxide, chlorine, and fluorine, make up an unusually high percentage of the melt. Because ion migration is enhanced in these fluid-rich environments, the crystals that form are abnormally large. Thus, the large crystals in pegmatites are not the result of inordinately long cooling histories; rather, they are the consequence of a fluid-rich environment that enhances crystallization.

composed of interlocking crystals all larger than a centimeter in diameter

discordant

cut across existing structures

Mafic

describes magma or igneous rock that is rich in magnesium and iron and that is generally dark in color

tabular or massive

describing a feature such as an igneous pluton that has two dimensions that are much longer than the third (table-like)

columnar joints

form as igneous rocks cool and develop shrinkage fractures that produce elongated, pillar-like columns.

Sills Further, because sills generally form in near-surface environments and may be only a few meters thick, the emplaced magma often cools quickly enough to generate a fine-grained texture

horizontal intrusions of solidified magma that was forced between rock layers

concordant

if they form parallel to features such as sedimentary strata.

Laccolith A 19th century study by G. K. Gilbert of the U.S. Geological Survey in the Henry Mountains of Utah produced the first clear evidence that igneous intrusions can lift the sedimentary strata they penetrate.

igneous rock forcibly injected between sedimentary strata, so as to arch the beds above, while leaving those below relatively flat.

Granite (Has quartz crystals, which are roughly spheri- cal in shape, are often glassy and clear to light gray in color. By contrast, feldspar crystals are generally white to gray or salmon pink in color and exhibit a rectan- gular rather than spherical shape. Other minor constituents of granite include mus- covite and some dark silicates, particularly biotite and amphibole. Although the dark components generally make up less than 10 percent of most granites, dark minerals appear to be more prominent than their percentage would indicate. When potassium feldspar is dominant and dark pink in color, granite appears reddish (see Figure 3.11). This variety of granite is popular for monuments and as a building stone. However, the feldspar grains are more often white to gray, so when they are mixed with lesser amounts of dark silicates, granite appears light gray in color.)

is a coarse-grained rock composed of about 25 percent quartz and roughly 65 percent feldspar, mostly potassium-and sodium-rich varieties.

tuff

is composed mainly of tiny, ash-size fragments that were later cemented together

Welded Tuff

is composed of fine fragments of glass that remained hot enough during their flight to fuse together upon impact.

Texture

is used to describe the overall appearance of a rock based on the size, shape, and arrangement of its mineral grains

Batholith

largest intrusive igneous bodies. plutonic body that has a surface exposure greater than 100 square kilometers

Magma mixing

may occur during the ascent of two chemically distinct magma bodies as the more buoyant mass overtakes the more slowly moving mass.

Decompression Melting

occurs where hot, solid mantle rock ascends in zones of convective upwelling, thereby moving into regions of lower pressure. This process is responsible for generating magma along divergent plate boundaries (oceanic ridges) where plates are rifting apart

Stocks Many stocks appear to be portions of much larger intrusive bodies that would be called batholiths if they were fully exposed.

plutonic body that has a surface exposure less than 100 square kilometers

Ultramafic

relating to or denoting igneous rocks composed chiefly of mafic minerals.

pyroclastic texture

result of the consolidation of rock fragments that were ejected during a violent volcanic eruption.

magmatic segregation

separation of heavy minerals that crystallize early or enrichment of rare elements in the residual melt

magmatic differentiation

the formation of one or more secondary magmas from a single parent magma

partial melting

the process by which different minerals in rock melt at different temperatures

Bowen's Reaction Series

the simplified pattern that illustrates the order in which minerals crystallize from cooling magma according to their chemical composition and melting point