CONTINENTAL GROWTH AND TECTONIC HISTORY OF SOUTHERN LAURENTIA AS INDICATED BY BASEMENT DATA AND PHANEROIC STRUCTURES

Much of central North America is mantled by unconsolidated sediments masking bedrock features. However, the scattered bedrock outcrops and the thousands of deep drill holes have provided data to construct the structural features and sedimentation history present in the Phanerozoic rocks. These structures, in large part, are rejuvenated trends that provide clues to the patterns of crustal weakness present in the Precambrian basement. Sixteen positive structures have been defined or redefined that reflect basement features. These basement trends, in turn, define the locations of suture zones created by the accumulation of terranes that accomplished the southward growth of Laurentia during the period from 1.8 to 1.6 billion years. Geophysical data and the available rock samples from the subsurface of the Nebraska area provide the distribution of rock type and some radiometric ages to further describe these terranes. It is suggested that these data allow definition of a series of seven accreted terranes and their boundary suture zones that comprise much of the Central Plains orogen within the Transcontinental Proterozoic province. These terranes consist mainly of orthogneisses and metasedimentary gneiss and schist. Isolated quartzite bodies are interpreted as multicycle clastics deposited in forearc basins. Many of the granitic bodies represent the inboard magmatic arcs with ages indicating the age of each of the associated accreted terranes. It is these suture zones, created during each of the accretions, that have been rejuvenated to control the sedimentation patterns and the structural trends during the Phanerozoic.