- Arc
- See volcanic arc.
- Asthenosphere
- The weak layer in the earth’s mantle that sits below the lithosphere. It deforms plastically when stressed and is the layer in the earth on which the lithospheric plates ride.
- Absolute age
- Age as measured in a specific quantity such as years, millions of years (Ma), or billions of years (Ba) before present.
- Basalt
- A fine-grained (volcanic) igneous
rock composed of olivine, pyroxene, and plagioclase. See also gabbro.
- Batholith
- An exposed, irregular mass of igneous rock greater than 100 kms2 in total area and composed of individual plutons.
- Continental crust
- A large mass of lower density material, consisting of granitic igneous and/or sedimentary
rocks, that sits on top of the earth’s mantle. Continental crust varies from about 70 to 30 kms in thickness.
- Dike
- A planar or tabular mass of igneous rock that formed by the injection of melt into a preexisting fracture that cuts across older rock structures.
- Emplacement age
- The time at which an igneous body solidifies in the Earth’s crust.
- Gabbro
- A coarse-grained (plutonic) igneous rock composed of various amounts of olivine, pyroxene, and plagioclase. See also basalt.
- Gneiss
- A metamorphic rock with elongate clusters of dark minerals.
- Grus
- Deeply weathered, disintegrated igneous rock.
- Igneous
- A category of rock formed by the crystallization of molten material. See also magma.
- Lithosphere
- The outer, rigid shell of the earth that consists of continental and oceanic
crust as well as approximately 80-100 kms of underlying mantle.
- Lithospheric plate
- A segment of the earth’s lithosphere that is overlain by either oceanic crust or continental crust. Same as tectonic plate. See oceanic
crust, continental
crust.
- Magma
- Molten rock material consisting of melt and any contained solids.
- Mantle
- That portion of the earth that lies between the crust and the earth’s outer core.
- Melt
- The molten portion of a magma.
- Metamorphic
- A category of rock formed deep within the earth from pre-existing rock material as the result of high temperatures and pressures, or by reaction with chemically active fluids.
- Metasedimentary
- Metamorphosed sedimentary rocks.
- Oceanic crust
- A large mass of medium density material, consisting of basaltic igneous and/or sedimentary rocks, that sits on top of the earth’s mantle. Oceanic crust typically underlies ocean basins and varies from about 5 to 10 kms in thickness.
- Paleomagnetism
- The study of fossil magnetic fields as recorded in iron-bearing minerals.
- Paleolatitude
- The initial latitude of a rock mass prior to its movement via plate tectonic.
- Pluton
- An intrusion of igneous material that solidified at depth. See also batholith.
- Rift zone
- See spreading center.
- Schist
- A metamorphic rock characterized by an abundance of platy minerals such as mica or chlorite.
- Sedimentary
- A category of rock formed by the accumulation and lithification of weathered rock debris.
- Spreading center
- A linear zone in the earth’s crust whose opposite sides are moving away from one another.
- Spreading rate
- The speed at which two sides of a spreading center are moving apart.
Generally given in inches or centimeters/year.
- Strike-slip fault
- A vertical fault in the earth’s crust whose sides are moving in opposite directions.
- Subduction
- The process whereby one tectonic plate is forced beneath another.
- Volcanic arc
- An arcuate band of volcanic rocks formed at approximately the same time from a single subduction event.
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