Chapter 27, Problem 8TE

Provide an explanation for why granite frequently forms at oceanic-continental convergent boundaries but infrequently at oceanic-oceanic convergent boundaries.

To determine

The reason for frequent formation of granite at oceanic-continental convergent boundaries but infrequently at oceanic-oceanic convergent boundaries

Answer to Problem 8TE

The reason for frequent formation of granite at oceanic-continental convergent boundaries but infrequently at oceanic-oceanic convergent boundaries is the presence of high content of silica in oceanic-continental convergent boundaries.

Explanation of Solution

With oceanic-oceanic convergence, magma is created. But the rising through the thicker continental crusts takes longer and this changes the composition of the magma. It becomes even more enriched in silica than with oceanic-oceanic convergence.

As the magma rises through the overlying continental plate, varying amounts of continental crust begin to melt and mixed into magma. With the higher silica content, the magma develops a more granitic composition.

Conclusion:

Therefore, the reason for frequent formation of granite at oceanic-continental convergent boundaries but infrequently at oceanic-oceanic convergent boundaries is the presence of high content of silica in oceanic-continental convergent boundaries.