Quartz
Silicate mineral (SiO2) that is highly resistant to weathering. Quartz is found in lightcoloured igneous rocks, as well as many sedimentary and metamorphic rocks. There are
many colour variations, depending on what elements are substituted into the structure, eg.
amethyst is a form of quartz.
Feldspar
Type of silicate rock containing silicon, oxygen, and aluminum, as well as potassium,
sodium, calcium. Feldspars are the most abundant group of rock-forming minerals found
in the crust of the Earth. They are common constituents of igneous and metamorphic
rocks. There are two main groups of feldspars, K-feldspar and Plagioclase feldspar (Na,
Ca).
2 photos
Granite
A coarse grained igneous rock containing the minerals mica, quartz and feldspar. Granite
forms from the solidification of magma deep below the Earth's surface. The magma cools
very slowly, allowing big crystals to be formed.
(http://www.ga.gov.au/education/minerals/glossary.html, sept. 27)
Arkose
Type of red sandstone containing quartz and large amounts of feldspar.
Gneiss
Coarse-grained metamorphic rock with banding of light and dark minerals.
gneiss.jpg, met17.jpg in VITAL
Slab pull
As a crustal plate moves further from an oceanic ridge, it cools and becomes increasingly
dense. This causes it to sink beneath the continental crust in a subduction zone. The
weight from this sinking, cooling plate causes a major pulling action, which causes the
rest of the plate to be pulled downwards as well.
Ridge push
Gravitational force that causes a plate to move away from the crest of an ocean ridge, and
into a subduction zone. It works together with Slab Pull, but is much less significant.
Hot-spots
Geographic location where a plume of magma has risen from the mantle, and penetrated
through a plate to reach the crust and sometimes the surface of the Earth. These might
result from areas of anomalously high heat generated by radioactivity, or by the upward
motion of mantle material in a plume. Examples exist beneath the Hawaiian islands, and
Yellowstone National Park.
Radiogenic
Produced by radioactivity.
Mantle plumes
Hot upwellings of material which rise from the mantle, deep below the surface of the
Earth. This creates geological hotspots at the surface. Examples include areas such as
Iceland and Hawaii. At this point, this is a still a theory that is being tested.
Radiometric dating
Determining the age of materials based on the decay rates (see Half-life) of naturally
occurring isotopes, and the abundance at which they occur in the present.
Half-life
Asthenosphere
The fluid layer of the mantle just beneath the rocky upper mantle and crust (lithosphere).
Rift
Valley created where two plates are moving apart. Can be on land (eg. The Great Valley
Rift of East Africa), or in the ocean (eg. The centre of the Mid-Atlantic Ridge).
Strato-volcano
Steep-sided, symmetrical volcanoes that often produce viscous andesitic or rhyolitic
magmas. This volcanic cone is internally layered because of alternating lava and
pyroclastic eruptions. Mount Fuji is an example of a strato-volcano.
http://gojapan.about.com/od/japanpicture1/l/blnat_tanofuji7.htm
www.usgs.gov
Shield volcanoes
These are the largest types of volcanoes, but they are very gently arching structures with
low slopes. Eruptions are relatively frequent, but non-explosive, and produce low silica
content, fluid magmas. eg. Mauna Loa
J.D. Griggs, www.usgs.gov
Mauna Loa
www.usgs.gov
Subduction zone
Convergence of two plates, where the more dense plate is forced beneath the less dense
one. (eg. oceanic plate is forced underneath a continental plate). The surface expression
of subduction zones are oceanic trenches, such as the Marianas trench.
Island arcs
Group of volcanic islands along a subduction zone.
http://www.landsat.org/landsat_gallery
Aleutian islands from space
http://barbados.america-atlas.com/pictures/lesser-antilles.jpg
Lesser Antilles - island arc
Tethys sea
Ocean separating India from Asia prior to India colliding with Asia approximately 50
million years ago. photo
Plutonic igneous rocks
Intrusive igneous rocks, formed by the slow solidification of magma deep below the
surface and characterized by large crystals. Named after Pluto, the Roman god of the
underworld.
Supercontinent
Massive landmass that was made of all the modern-day continents. Pangaea was an
example of a supercontinent.
www.usgs.gov
Convection
A process of heat transfer where hot material at depth rises upward due to its lower
density while cooler material above sinks because of its higher density. (Abbott, glossary)
movie:
http://www.solarviews.com/eng/edu/convect.htm
also see lava lamp movies!