The contact between older rocks and younger sedimentary rocks in which at least some erosion has removed some of the older rocks before deposition of the younger. A mineral-filled fracture or fault in a rock. A product of chemical precipitation from a watery solution, in contrast to a dike crystallized from magma , although gradations exist. A thin, widespread layer of sediment covering an older surface. A small bubble formed in volcanic rock during solidification.
Volcanoes produce volcanic rock.
The arc forms where the downgoing descending plate becomes hot enough to release water and gases that rise into the overlying mantle and cause it to melt. Arc rocks are mostly volcanic rocks from the volcanoes and sedimentary rocks made up of eroded debris from the volcanoes. Melted rock in the deeper plumbing of the arc which may crystallizes at depth to become an arc root plutons . . W wash A normally dry stream bed that ocassionally fills with water. Both processes occur in place.