Nonconformity The third basic type of unconformity is a nonconformity. Here the break separates older metamorphic or intrusive igneous rocks from younger sedimentary strata(Figures 11.6 and 11.7). Just as angular unconformities and disconformities imply crustal movements, so too do nonconformi ties. Intrusive igneous masses and metamorphic rocks originate far below the surface. Thus, for a nonconformity to develop, there must be a period of uplift and the erosion of overlying rocks. Once exposed at the surface, the igneous or metamorphic rocks are subjected to weathering and erosion prior to subsi- dence and the renewal of sedimentation.