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Global Observations of Melt-induced Low Velocity Zones Surrounding the Mantle Transition Zone

Description: 

The mantle transition zone (MTZ) is an important part of global volatile circulation because its primary minerals, wadsleyite and ringwoodite, have an affinity for H, and therefore water, compared to the rest of the mantle. Mineral phase changes from olivine to wadsleyite and from ringwoodite to bridgmanite define MTZ at ~ 410 and ~660 km depth, respectively. Deeply subducting slabs can transport water to the MTZ, a process which buffers the Earth’s oceans and atmosphere. In the presence of flowing material or a local instability, hydrous MTZ rock can be displaced and generate dehydration-induced partial melting. These partial melts are seismically detectable as seismic low velocity zones (LVZs). The presence or absence of these signals can be used to infer MTZ water content and mantle flow. Here, I apply global seismic imaging, primarily SS and PP precursors, to search for LVZs that may be induced by water. These waveforms are ideal for a global study because they image the mid-point between an earthquake and a seismic station; they do not require a seismic station to be located directly above the imaging target. However, detection of LVZs is complicated by signal-processing artifacts such as side-lobes. In this work, I first define the nature of all signal-processing artifacts prior to any interpretation. My data set has SS and PP precursors recorded on over 9,000 permanent and temporary seismic stations. Preliminary results indicate that there are detectable reductions in seismic velocity between ~300-400 km depths.

Session: Earth’s Structure from the Crust to the Core - IV

Type: Oral

Date: 4/16/2025

Presentation Time: 05:00 PM (local time)

Presenting Author: William

Student Presenter: No

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