Near-seafloor magnetics reveal tectonic rotation and deep structure at the TAG (Trans-Atlantic Geotraverse) hydrothermal site (Mid-Atlantic Ridge, 26 degrees N)

摘要

We take advantage of geological constraints from Ocean Drilling Program drill holes and high-resolution bathymetry to revisit the near-seafloor magnetic anomaly at the Trans-Atlantic Geotraverse hydrothermal site (Mid-Atlantic Ridge, 26 degrees N). The dipolar anomaly associated with the site is better reduced to the pole if the magnetization vector is tilted by 34 degrees, an observation suggesting that the strongly faulted basalt surrounding the site has been rotated by similar to 53 degrees along an axis parallel to the Mid-Atlantic Ridge as a probable consequence of the detachment tectonics inferred in this area. The faults and the deeper detachment focus and guide the hot ascending hydrothermal fluid. Magnetic modeling shows that the nonmagnetic stockwork zone is a significant contributor to the observed negative anomaly, the rest being accounted for by a deeper source probably related to thermal demagnetization of an ascending hydrothermal pipe beneath the active part of the site.