The Mid-Atlantic Ridge near 45 °N. V. Fission track and ferro-manganese chronology

Abstract

Specimens from 42 dredge stations taken over a 120 × 220 km area across the axis of the Mid-Atlantic Ridge were dated by a combination of fission track and ferro-manganese deposition rate methods, and results were compared with previous K–Ar determinations.The chronological data is in close agreement with the hypotheses of ocean floor spreading: ages increase outwardly in a systematic way from the axis of the Ridge, and although there is a scarcity of data on the eastern Crest Mountains, a chronological axis of symmetry may exist coincident with the axis of the Ridge. The spreading rates calculated fall into two distinct groups: a faster rate on the Crest Mountains (average 3 cm/yr); and a slower rate on the High Fractured Plateau (average 1 cm/yr). The transition point between the two spreading rates coincides with the morphological boundaries between the Crest Mountains and the High Fractured Plateaus; this line of demarcation has also significant structural and sedimentary implications.