Detachment tectonics at Mid-Atlantic Ridge 26°N

Abstract

Spreading processes associated with slow-spreading ridges are a complex interplay of volcanic accretion and tectonic dismemberment of the oceanic crust, resulting in an irregular seafloor morphology made up of blocks created by episodes of intense volcanic activity or tectonic deformation. These blocks undergo highly variable evolution, such as tilts or dissection by renewed tectonic extension, depending on their positions with respect to the spreading axis, core complexes, detachment or transform faults. Here, we use near-seafloor magnetic and bathymetric data and seismic profiles collected over the TAG Segment of the Mid-Atlantic Ridge to constrain the tectonic evolution of these blocks. Our study reveals that the presence and evolution of oceanic core complexes play a key role in triggering block movements. The deep subvertical detachment fault roots on the plate boundary, marked by a thermal anomaly and transient magma bodies. Thermal and magmatic variations control the structure and morphology of the seafloor above the subhorizontal detachment surface, occasionally leading to relocating the detachment.

Structural Control, Evolution, and Accumulation Rates of Massive Sulfides in the TAG Hydrothermal Field

“…Even though a tectonic overprinting of an older debris field cannot be ruled out, a tectonic origin for the chaotic zone seems likely, based on the high‐resolution topography. This agrees with the interpretation of high‐resolution magnetic data, acquired during our AUV surveys, that led Szitkar et al (2019) to highlight this location as a “transition zone” between crustal blocks of large differences in tilt.…”

“…The prominent corrugated surface that is visible in the northeast part of the AUV‐based high‐resolution map marks the presence of a detachment fault, indicating that a significant portion of the spreading in this area is accommodated by tectonic movement. This corrugated surface can be traced in seismic data for several kilometers, dipping at a shallow angle, toward the spreading axis in the west, where it seems to be bounded by another detachment fault (Szitkar et al, 2019). The relation between the corrugated detachment fault and the proposed major detachment structure at depth that is supposed to extend further to the east (Schouten et al, 2010; Smith et al, 2008; Zhao et al, 2012) cannot be determined based on our data sets alone.…”

“…However, it is unlikely that the corrugated surface visible in our AUV data is the upper exposed part of the detachment surface proposed by previous studies, as that surface is thought to be at a depth of 1 km beneath the TAG active mound, steepens toward the center of the axial valley, 2-3 km west of the active Mound (Canales et al, 2007;DeMartin et al, 2007), and dips at a much higher angle compared to the low-angle detachment fault associated with the corrugated surface. This implies that the corrugated surface is either superimposed over a larger detachment faults at depth or that the northern part of the hydrothermal field is structurally different from the southern part as suggested by Szitkar et al (2019). The TAG massif and especially its western part seems to be highly complex and might be formed by a sequence of detachment faults.…”

Detachment-parallel recharge explains high discharge fluxes at the TAG hydrothermal field

“…To explore the likely circulation pattern during phases of high temperature hydrothermal discharge, we use the three-dimensional hydrothermal flow model HydrothermalFoam 38 , which resolves porous convection of pure water under single-phase conditions. Based on the high-resolution AUV-bathymetry 32 , micro-earthquake locations 5 , and tomographic 36 plus seismic reflection 39 data, we implement the detachment surface as an inclined permeable plane dipping at 20 • . Here the assumption is that the detachment surface is a zone of enhanced permeability with respect to the adjacent foot-and hanging walls 40 .…”

Mid-Ocean Ridges and Their Geomorphological Features

“…Bathymetric corrugations (Figure 12) have lengths of several km, and are spaced laterally (along-axis) hundreds of m to a few km. Recent bathymetric surveys using deep-sea vehicles, together with in-situ observations, show that corrugations are observed down to outcrop scales, where fault surface striations also develop in the spreading direction (e.g., MacLeod et al, 2003;Parnell-Turner et al, 2018;Escartin et al, 2017;Szitkar et al, 2019). Their occurrence thus clearly disrupts the 'typical' ridge-parallel abyssal hill terrain, which is often present on the conjugate flank of the ridge, owing to the very asymmetric mode of oceanic accretion that takes place in the presence of detachments (Escartin et al, 2008;Reston & Ranero, 2011).…”