Geophysical data from the northwestern portion of the Gander Zone of Newfoundland are used to test existing geological models and to propose amended ones for the upper crustal structure of the region. The eastern geophysical boundary of in situ Paleozoic oceanic crustal material associated with the Iapetus Ocean is interpreted to be the GRUB line. An enigmatic anomaly belt in the Gander Group east of the GRUB line is identified and modelled. Three hypotheses are advanced for its origin, none of which can be eliminated on simple geophysical grounds. This anomaly belt is interpreted to present obducted ophiolitic materials emplaced in the continental rise prism represented by the Gander Group sediments.