TREITEL RIDGE: A UNIQUE INSIDE CORNER HOGBACK ON THE WEST FLANK OF EXTINCT AEGIR RIFT, NORWAY BASIN - TECTONIC RESPONSE TO ABRUPT END OF NORTH AMERICA-GREENLAND MOTION?

Detailed shipborne mapping (sidescan sonar, swath bathymetry, seismic reflection, 3.5kHz profiling,gravity and magnetics) of the extinct Aegir spreading axis (ca.55-25Ma) in the Norway Basin revealed a highly unusual (in a MOR setting), narrow, 130km long, asymmetrical basement hogback (Treitel Ridge; TR) on the southern west flank of the extinct rift, close to its junction with the Iceland-Faeroe aseismic ridge and the putative paleo-Iceland hotspot center. The ridge seems to continue north another 130km in the form of a wider, more irregular basement rise, for a combined length of ca. 260km. The southern, narrow part of TR, approximately following or slightly younger than chron 18n (ca. 39 Ma), attains a basement relief of ca. 1000m in the south, its summit descending gradually (1.7:100) towards the NE. Although an east flank conjugate appears generally lacking along both northern and southern parts of TR, asymmetry of the southern portion (steeper slope facing towards the extinct rift valley) suggests volcanic formation and axially dipping normal faulting at or near the active plate boundary. Alternatively, southern TR may record a brief (0.1-1m.y.) inside-corner tectonic event (probably a flexurally compensated normal-faulted offset), in effect a “mega-abyssal hill”. We suggest TR was not an expression of change in Iceland hotspot activity, but rather the volcano-tectonic response of the Aegir accretion axis—at the time it became the eastern edge of the new Jan Mayen microplate—to extinction of the Mid-Labrador Sea spreading center. As proposed by A. Nunns (1983), the annexation of the Greenland plate by the North American plate forced a plate boundary reorganization east of Greenland—with northward propagation of the Mid-Atlantic Ridge rift along the Greenland margin to form the Jan Mayen microplate. Simultaneously, two ca. 107° trending transforms developed from the previously 146° trending Faeroes Fracture Zone. Because TR formation was clearly a brief event, spreading along the Mid-Labrador Sea ridge may have ceased abruptly as well.