Detachment-parallel recharge explains high discharge fluxes at the TAG hydrothermal field-Insights from 3D numerical simulation

The Earth System appears increasingly interconnected and hydrothermal discharge at back smoker vent sites is not only visually appealing, it also sustains unique ecosystems, generates large polymetallic sulfide deposits, and modulates ocean biogeochemical cycles. At slow spreading ridges, fault zones seem to provide stable preferential fluid pathways resulting in the formation of the ocean’s largest sulfide deposits. The TAG hydrothermal mound at 26°N on the Mid-Atlantic Ridge (MAR) is a typical example located on the hanging wall of a detachment fault. It has formed through distinct phases of high-temperature fluid discharge lasting 10s to 100s of years throughout at least the last 50,000 years and is one of the largest sulfide accumulations on the MAR. Yet, the mechanisms that control the episodic behavior, keep the fluid pathways intact, and sustain the observed high heat fluxes of possibly up to 1800 MW remain poorly understood. Previous concepts involved long-distance channelized high-temperature fluid upflow along the detachment but that circulation mode is thermodynamically unfavorable and incompatible with TAG's high discharge fluxes. Here, based on the joint interpretation of hydrothermal flow observations and 3-D flow modeling, we show that the TAG system can be explained by episodic magmatic intrusions into the footwall of a highly permeable detachment surface. These intrusions drive episodes of hydrothermal activity with sub-vertical discharge and recharge along the detachment. This revised flow regime reconciles problematic aspects of previously inferred circulation patterns and allows to identify the prerequisites for generating substantive seafloor mineral systems.