PRECAMBRIAN BASEMENT STRUCTURE AND LARAMIDE DEFORMATION REVEALED BY SEISMIC-REFLECTION PROFILING IN THE LARAMIE MOUNTAINS, WYOMING

The University of Wyoming conducted seismic reflection profiling in th e Laramie Mountains of Wyoming to investigate the nature of Precambria n crustal structure and Laramide deformation in the region. Here the i maging of layering in the Laramie Anorthosite complex confirms that la yered intrusions can be reflective and establishes an analog for inter preting events in other seismic reflection data sets where layered int rusions could be the cause of multicyclic events. Moreover, the presen ce of prominent primary layering in the Complex supports a conclusion that it formed in situ and not as the result of the emplacement of a d iapiric crystal mush. Imaging of Laramide thrusts in the Laramie Mount ains adds credence to the idea that brittle faults can be reflective i n some situations. Migrated apparent dips on these faults are 30-degre es westward. Basement-involved compressive structures, consisting of m onoclinal folding and a fault triple junction, demonstrate that compre ssion controlled the style of deformation during the Laramide orogen i n Wyoming. West dipping Precambrian structures imaged in these data ha ve a similar attitude to the Laramide structures, suggesting that Lara mide deformation was influenced by Precambrian features. These Precamb rian structures may be subthrust slices of exotic Proterozoic terranes .