Journal Article

Detachment‐Fault Structure Beneath the TAG Hydrothermal Field, Mid‐Atlantic Ridge, Revealed From Dense Wide‐Angle Seismic Data

Murton, B. J., Minshull, T. A., Lai, Szu‐Ying, Bayrakci, G.

2025

Overview

The Trans‐Atlantic Geotraverse (TAG) field on the Mid‐Atlantic Ridge is one of the largest currently active seafloor hydrothermal fields known. An underlying detachment is inferred to maintain TAG's long‐lived hydrothermal discharge, but the detachment lacks a widespread corrugated surface. We used dense wide‐angle seismic data to define TAG's detachment structure at a finer scale than has previously been possible. We generated two P‐wave velocity profiles of the shallow section of the detachment using first‐arrival travel‐time tomography, preconditioned by downward continuation. Our results reveal a low‐angle detachment, dipping at ∼15° (±5°) at 5 km east of the ridge axis, and evidence for uplifted lower‐crustal gabbro in the footwall. Increasing footwall velocities southward suggest a more intense exhumation of deep‐seated rocks, showing the detachment's geometry changes along the ridge axis. We conclude the detachment is a complex 3‐D structure, and a young system without a dome‐shaped footwall can exhumes deep‐seated crustal rocks. Plain Language Summary Hydrothermal vents, where seawater is superheated by magma and discharges mineral‐rich fluids through the seafloor, help regulate global ocean chemistry and are a potential resource for base metals. The Trans‐Atlantic Geotraverse (TAG) field on the Mid‐Atlantic Ridge is one of the largest known deep‐sea hydrothermal systems. A long‐lived extensional fault, called an oceanic detachment, is believed to localize hydrothermal circulation and venting off the ridge axis. However, current knowledge is still limited on the 3‐D geometry of the underlying detachment and how it influences high‐temperature hydrothermal activity. We present active‐source seismic data to characterize the detachment's subseafloor structure and properties at TAG, where no widespread seafloor outcrop of the fault surface is observed. Our results reveal lower crustal rocks are uplifted by the detachment, with possibly more intense fault deformation to the south of the TAG field. We suggest that the TAG detachment is a young system and expresses variable geometry along strike, with a series of concurrent faults to the north merging into one main fault dominating the south. This observation indicates detachments are complex 3‐D structures and even a young detachment lacking a clear exposed fault surface, can accommodate significant tectonic displacement and uplift of deep‐seated lithologies. Key Points P‐wave velocity model from dense seismic refraction data reveal the detailed structure of the detachment at the TAG hydrothermal field The TAG hydrothermal field is underlain by a detachment fault with a complex 3‐D geometry Young detachments, such as under TAG, could exhume lower‐crustal gabbro despite limited corrugations and a lack of a dome‐shaped footwall

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Deformation / Discharge / Fault lines / Fluids / Footwalls / Gabbro / Geometry / Hydrothermal activity / Hydrothermal fields / Hydrothermal flow / hydrothermal system / Hydrothermal systems / Hydrothermal vents / Lava / Magma / Metals / Mid‐Atlantic ridge / Ocean floor / Oceanic crust / oceanic detachment / Outcrops / Potential resources / Rock / Rocks / Seawater / Seismic data / Seismic velocities / Seismological data / Tectonics / Tomography / Travel time / traveltime tomography / Velocity distribution / Velocity profiles / Wave velocity / wide‐angle seismic data