Cordilleran front range structural features in northwest Montana interpreted from vintage seismic 2 reflection data

摘要

Industry seismic reflection data were collected in 1983 in the Rocky Mountain Cordillera front ranges of northwest Montana. These seismic profiles represent 160 km of deep reflection data that cross the eastern Purcell anticlinorium, Rocky Mountain Trench (RMT), Rocky Mountain Basal Detachment (RMBD), and Lewis thrust. We have reprocessed these data using modern processing techniques including refraction statics, pre-stack time migration (PSTM), and pre- and post-stack depth migration. The RMT contains Tertiary fill to 1 km depth and the RMT fault system has a minimum of 3-4 km of normal displacement. The RMT and Flathead fault systems are interpreted to be structurally linked and may represent a synthetic, en echelon extensional fault system. The RMBD is present in every profile with a depth of 8 km in the east and 13 km in the west, dipping 3-10° west. Evidence for the autochthonous Mesoproterozoic Belt supracrustal and basal Cambrian rocks is present in all of the five profiles beneath the RMBD and extends east of the RMT. The Lewis thrust is identified and the sole position of the thrust into the RMBD is interpreted to be east of the RMT.