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

Abstract

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.