A break that separates older metamorphic rocks form younger sedimentary rocks immediately above them is a type of unconformity called a nonconformity.
A nonconformity is a break that separate pre-existing (metamorphic rocks or igneous rocks) from overlying sedimentary rocks. Nonconformities usually show that a long period of erosion took place earlier before the sediments were deposited. Nonconformities can be seen in the Wind River gorge of Wyoming and at the base of the Grand Canyon succession.
