We have seen that all eight continental major flood basalts are associated with tracks that exhibit a change in direction and/or rate of movement of the plate on which the impact has occurred. Dating techniques are being continually improved. The Atlas and similar programmes undergo continual revision. However, the specific reviewed program used here may be somewhat in error when compared with the latest radiometric dating. Moreover, the majority of the track changes, as inferred from the Atlas system occur immediately before the earliest dated extrusive rock. Consequently, we suggest that all (single) impacts precede the eruption of basaltic rocks. However, we note a later extrusion phase at about 90 Ma can be attributed to an impact-induced change in direction of movement for the Ontong-Java plateau.

Two questions immediately come to mind. (1) What mechanism can give rise to such relatively rapid changes in track? (2) Why is the largest oceanic plateau basalt so much larger than all the continental flood basalts? These two questions we shall address in the next two sections.

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