Propagating Rift Hypothesis
(A) Regional compiled magnetic anomaly grid. (B) Satellite-derived free air gravity anomaly. Fine double line marks the current Reykjanes Ridge axis. Black lines show the reconstructed position of the current ridge axis rotated according to the Greenland–Eurasia finite rotation poles for anomalies 18, 20, 21, and 24 (labeled circles) of Smallwood and White (2002). The red and blue lines are flowlines calculated according to their stage poles to the present day for the Greenland and Eurasian plates respectively and trace the opening directions through time. Near anomaly 17 time (∼37 Ma) (adjacent to young side of labeled anomaly18) the direction of opening changed by about 30° and the plate boundary abruptly became segmented and offset as shown by offset magnetic lineations and the initiation of prominent fracture zone troughs. At this time the new ridge segments were spreading orthogonally to the new opening direction as shown by the parallel orientation of the fracture zone troughs and flow lines. Subsequently the plate boundary reconfigured diachronously from north to south (green line indicates the subsequent reconfiguration boundary from Hey et al., 2016). Offset segments merged back to their original linear configuration over the mantle as shown by the parallel geometry of the rotated axis (black lines) and the early-formed magnetic anomaly lineations, despite the current axis now being ∼30° oblique to the opening direction and the intervening stair-step fragmentation of the plate boundary.
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