What might the seismic velocity signature of lithospheric alteration look like? Insights from geodynamic modelling

It is well established that interactions between hydrothermal fluids and heterogeneous lithospheric rocks provide the energy necessary to sustain microbial communities and macrofauna in the oceanic realm. These fluid-rock interactions drive the abiotic synthesis of reduced carbon compounds, such as methane, and the formation of hydrogen-rich fluids that are released at hydrothermal vents at slow and ultraslow spreading mid-ocean ridges. In these environments, solid carbon-bearing phases have also been identified in exhumed mantle rocks, and have formed in situ through fluid–magma–rock interaction processes within the lithosphere. These findings suggest that deep lithospheric processes may play a key role in the geological carbon cycle and in supporting biological activity at hydrothermal vents.

Insights into these processes have been provided by investigations of geological samples (e.g., vent fluids or drill cores) and through tomographic velocity models derived from wide-angle seismic data. Selected geological sampling combined with seismic tomography modeling provide the spatial coverage needed to investigate broader-scale processes. However, these seismic imaging techniques still challenge to distinguishing rock types and alteration assemblages at depth because the behavior of compressional and shear wave velocities of alteration is poorly constrained. How tectonic and hydrothermal processes interact over geological timescales, how the reaction products of local mineral equilibria are remobilized by tectonics, and the consecutive evolution of alteration assemblages remain poorly understood.

This presentation will examine the geodynamic aspects of lithospheric alteration during magma-poor, ultraslow seafloor spreading, and its potential seismic velocity signatures in detachment-dominated lithosphere. The implications of these results for oceanic detachment systems hosting hydrothermal vents will be discussed.