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

Abstract

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°N). The dipolar anomaly associated with the site is better reduced to the pole if the magnetization vector is tilted by 34°, an observation suggesting that the strongly faulted basalt surrounding the site has been rotated by ~53° 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.

High‐resolution magnetic signature of active hydrothermal systems in the back‐arc spreading region of the southern Mariana Trough

“…The narrow zones of low magnetization are centered on vent areas; moreover, low‐magnetization zones are confirmed in both HOV (~10 m altitude) and AUV (~100 m altitude) results, indicating the presence of low‐magnetization source at depths from near seafloor to hundreds of meters. The modeling study of the magnetization zone in the TAG hydrothermal site proposed a pipe‐like source body with a radius of 100 m [ Tivey et al ., ; Tivey and Dyment , ; Szitkar and Dyment , ]. The horizontal extent of this narrow pipe‐like body is comparable to our investigated sites and also to the stockwork zones found in volcanogenic massive sulfide deposits such as Cyprus ophiolite [e.g., Johnson et al ., ].…”

Near-seafloor magnetic signatures unveil serpentinization dynamics at ultramafic-hosted hydrothermal sites

“…The inclination may also reflect the domed structure of the OCC, with the VDVF located on the east-sloping, central axis of the domed structure. Buoyant fluids are known to be deflected by the geometry of the seafloor and migrate toward the center of bathymetric highs (e.g., Szitkar and Dyment, 2015). Alternatively, the decrease in temperature of the hydrothermal discharge and increase in age of the deposits toward the north, over a distance of 250 m, at the VDVF (Hodgkinson et al, 2015) suggest that the inclination in fluid flow has evolved from a near-vertical ascent to its now-inclined state, possibly as a result of closure of the permeability of the plumbing system by precipitation of hydrothermal precipitates over time.…”

Investigation of a marine magnetic polarity reversal boundary in cross section at the northern boundary of the Kane Megamullion, Mid‐Atlantic Ridge, 23°40′N

“…[] used reoriented core and formation microscanner well logs to show a 46° outward rotation of the gabbroic section drilled at Atlantis Massif. Conversely, Szitkar and Dyment [] suggest a 53° rotation in the hanging wall from magnetic anomalies at TAG. Estimates from the limited paleomagnetic data suggest that the KMM has only experienced approximately 15° of counterclockwise rotation [ Williams , ].…”