New aeromagnetic data, K‐Ar age determinations of dredged marine igneous rocks, as well as other geophysical evidence have shed light on the chronology, nature and evolution of the northern Iceland Plateau. Correspondence between seismic refraction profiles taken on the Jan Mayen Ridge and westward through Jan Mayen Island, suppressed aeromagnetic anomalies, earthquake surface wave studies, and ages of dredged igneous rocks suggest these strata may form an extended region of thickened crust, possibly of Caledonian age, extending westward toward the Kolbeinsey Ridge and northwest to the south wall of the Jan Mayen Fracture Zone.

Age determinations for rock samples collected by Fridtjof Nansen during his trans‐Arctic expedition from 1893‐1896 have yielded additional information on the tectonic chronology of the Arctic Basin. The data suggest pulses of volcanic activity in the Frans Josef Land Archipelago with approximate averages of 120 ma and 135 ma. These ages are consistent with postulated opening dates for the western Arctic and thus suggest that initial volcanism affected the entire Arctic margin.

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