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magma

(Encyclopedia) magma măg´mə: see lava.

petrology

(Encyclopedia) petrology, branch of geology specifically concerned with the origin, composition, structure, and properties of rocks, primarily igneous and metamorphic, and secondarily sedimentary. It…

Kikai Caldera

(Encyclopedia) Kikai Caldera, massive caldera, c.12 mi (19 km) in diameter, Ryukyu Islands, Kagoshima Prefecture, Japan. Located c.30 mi (48 km) from the southern tip of the densely populated major…

subduction zone

(Encyclopedia) subduction zone, large-scaled narrow region in the earth's crust where, according to plate tectonics, masses of the spreading oceanic lithosphere bend downward into the earth…

lava

(Encyclopedia) lava lä´və, molten rock that erupts on the earth's surface, either on land or under the ocean, by a volcano or through a fissure. It solidifies into igneous rock that is also…

granite

(Encyclopedia) granite, coarse-grained igneous rock of even texture and light color, composed chiefly of quartz and feldspars. It usually contains small quantities of mica or hornblende, and minor…

basalt

(Encyclopedia) basalt bəsôlt´, băs´ôlt, fine-grained rock of volcanic origin, dark gray, dark green, brown, reddish, or black in color. Basalt is an igneous rock, i.e., one that has congealed from a…

seafloor spreading

(Encyclopedia) seafloor spreading, theory of lithospheric evolution that holds that the ocean floors are spreading outward from vast underwater ridges. First proposed in the early 1960s by the…

paleomagnetism

(Encyclopedia) paleomagnetism, study of the intensity and orientation of the earth's magnetic field as preserved in the magnetic orientation of certain minerals found in rocks formed throughout…

hydrothermal vent

(Encyclopedia) hydrothermal vent, crack along a rift or ridge in the deep ocean floor that spews out water heated to high temperatures by the magma under the earth's crust. Some vents are in…