They cause the melting point of the upper mantle (that is wedged between the two plates) to drop and magma is formed.
(They; cause; the melting point of the upper mantle) Context(They cause,List([0, 10))):(that; is wedged; between the two plates; to drop and magma is formed)
They cause,List([0, 10))
They that
cause is wedged
the melting point of the upper mantle
between the two plates to drop and magma is formed