The crust and do not form a ridge at the surface.
Andesite is the most common rock type in composite cones.Īngular unconformity a type of unconformity in which stratified (layered) rocks beneath the unconformity are tilted or folded anticline a geologic fold that is convex upward.Īnticline ridge a ridge formed by an upward fold of rock layers. The Olympic Mountains in Washington State are considered a classic example of an accretionary complex.Īccretionary prism see accretionary complex.Īccretionary wedge see accretionary complex.Īlluvial fan a cone-shaped fan of sediment deposited by a stream where the stream leaves a steep slope and enters a relatively flat area.Īlluvium sediments deposited by a river or stream.Īlpine glacier a glacier on a mountain side or originating in mountains and confined to a valley.Īndesite volcanic rock that originates as a lava flow and has an intermediate composition. Evidence that a mass of rock is an accreted terrane includes: (1) it is bounded by faults (2) it contains a sequence of rocks that record a geologic history not shared by the "native" rocks of the continent (3) it contains fossils from exotic locales that do not match the fossils of the continent from the same geologic periods (4) it contains paleomagnetism that indicates it was not at the latitude of the corresponding part of the continent at the time the rocks of the terrane formed.Īccretionary complex a zone of accreted terranes shoved up along the leading edge of the upper plate at a subduction zone. active margin the edge of a continent along which plate convergence or transform plate motion is occurring.Īccreted terrane a body of rock that originated elsewhere, on a different tectonic plate, and was then transferred to the continent at a subduction zone or along a transform fault. Z A (back to top) absolute age the age of a geologic material measured quantitatively, in units of time,
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