ANIMATED PALINSPASTIC MAP OF THE MESOPROTEROZOIC BELT-PURCELL BASIN, WESTERN LAURENTIA

Phanerozoic thrust faults and folds significantly deformed and displaced the Mesoproterozoic Belt-Purcell basin of the northwestern United States and adjacent Canada. Stepwise palinspastic restoration of the thrust plates leads to an animated portrayal of the emplacement of the basin into the Cordilleran fold-thrust belt. The individual animation frames are sequentially restored maps that are balanced in that they conserve the line-lengths of thrust traces and other geologic lines, such as the zero isopach for the Belt-Purcell basin. They thus provide incremental tests of the palinspastic restoration.

The restoration implies an overall clockwise thrust rotation of the Belt-Purcell basin, with major sinistral shear along the transverse Lewis and Clark line. However, in the animation, individual thrust plates do not rotate significantly relative to the Laurentian craton. The overall rotation results from lateral transfer among en echelon thrusts that obliquely intersect the restored basin. The rotations of the individual thrust plates implied by the animation are consistent with those suggested by paleomagnetic data from the Belt-Purcell Supergroup (Elston et al., 2000).

The palinspastic restoration provides a base for analysis of depositional facies and isopachs of the Belt-Purcell Supergroup. It supports interpretations that the Belt-Purcell basin was truncated at the west Laurentian rift margin, that much of the sediment was delivered to the basin through a point source to the southwest, and that the source region was separated from Laurentia by rifting and continental drift.