roughly 200 million years ago (Figure6.24). Similar batholiths are likely forming beneath
the Andes and Cascades today.
Figure 6.24: The granite batholith of the Sierra Nevada Mountain range is well exposed here
at Mount Whitney, the highest mountain in the range at 14,505 feet (4,421 meters) and the
second highest mountain in North America. ( 1 )
When two oceanic plates converge, the older, denser plate will sink beneath the other plate
and plunge into the mantle. As the plate is pushed deeper into the mantle, it melts, which
forms magma. As the magma rises it forms volcanoes in a line known as anisland arc,
which is a line of volcanic islands (Figure6.25).
Figure 6.25: A convergent plate boundary subduction zone between two plates of oceanic
lithosphere. Melting of the subducting plate causes volcanic activity and earthquakes. ( 4 )
The Japanese, Indonesian, and Philippine islands are examples of island arc volcanoes. The