Includes bibliographical references (pages 13-15).
Sm-Nd survey of Precambrian granitic and metasedimentary rocks collected from several geophysically defined blocks in central Minnesota confirms the presence of some fundamental geologic boundaries previously mapped on the basis of structure. The Malmo discontinuity an Early Proterozoic structure separates the Archean Minnesota River Valley ter- ranes from an Early Proterozoic (Penokean magmatic) terrane and the McGrath Gneiss dome of east-central Minnesota North of this boundary, the Penokean fold-and-thrust belt can be divided into fault-bounded terranes that were assembled during the Penokean orogeny. Each terrane within the study area has distinct crust formation ages.
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