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Plate Tectonic Theory

When a continent (plate x) rides up against a subduction zone (plate y) it over rides the igneous arc causing magma to rise into the continental crust. Some magma reaches the surface, forming a volcano and often forming a mountain peak. Some magma cools within the crust, forming plutons of igneous rock.

An Igneous arc forms the core of a mountain. Along either side of this core is a metamorphic belt consisting of crustal rocks that have been metamorphosed by heat from the core and intruded activity.

Toward the continental interior the metamorphic belt changes to a fold-and-thrust belt, typically overturned away from the core of the mountain. The preexisting sedimentary rocks, in the fold-and thrust, belt are largely unchanged by metamorphism and are folded less severely than the rock closer to the core.

On the seaside of the subduction zone, rocks are also deformed by folds and thrust faults causing an accretionary wedge formed by material scraped up by the descending oceanic plate (plate y).

See Rock Classification below for list of gems and minerals found in various layers.

—SUSAN VARNEY




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