Imaging Subseafloor Hydrothermal Systems

Abstract:

Hydrothermal fluid circulation beneath the seafloor is an important ore-forming process, and results in the formation of volcanogenic massive sulfide (VMS) deposits. Existing understanding of the scale and geometry of sub-seafloor hydrothermal circulation from previous studies has been limited to numerical simulations and their manifestations on the seafloor. Here we use magnetic inverse modelling to generate a three-dimensional empirical model of a hydrothermal convection system. High-temperature fluid-rock reactions associated with fluid circulation destroy magnetic minerals in the Earth’s crust, thus allowing magnetic models to trace the fluid’s pathways through the seafloor.

An ongoing question regarding hydrothermal circulation is the source for the mobilized metals, with past suggestions that a contribution of metals directly from magma is required to complement metal leaching from the crust. This study quantifies the volume of rock contained within the convection cell’s reaction zone, and thus the amount of leachable metals directly from the crust. Through mass balance calculations, we quantify the possible source metal budgets of a seafloor hydrothermal system, which has significant implications for the generation of hydrothermal ore deposits on the modern and paleo-seafloor.

We present an application of this modelling at a hydrothermally active region of the East Manus Basin.