IGPP is pleased to invite you to join its Fall 2023 Seminar Series presentation featuring Caltech's Jennifer M. Jackson. Dr. Jackson's talk, "The influence of iron on thermochemical heterogeneity, including water activity, in the deep mantle" will occur at 12pm November 14, 2023.
Time: 12:00 pm, Pacific Time
Location: Munk Conference Room and Zoom https://ucsd.zoom.us/j/93654851631?pwd=eHBzVkRxN3ZZZllxNHlmWXdRZjdEUT09 (password: igpp)
Abstract: The boundary layer separating the iron-dominant liquid outer core from the silicate-rich mantle is a region of great complexity, where extreme contrasts in material properties promote the persistence of multi-scale structural heterogeneities, as evidenced through seismic observations. The thermochemical variations at Earth’s mantle base play an important role in the evolutionary history of the Earth through regulation of heat flow that influences the dynamics of both the mantle and the core. Despite the significance of this region for Earth’s evolution, many open questions remain regarding its thermal state, as well as the characteristics, origins, and dynamic interactions of the observed heterogeneities, such as large thermochemical piles, regions of ultralow seismic velocities, and subducted former oceanic material. As individual observational studies of such features and experimental investigations into candidate compositions continue to develop, a synthesis of results from seismology, geodynamic modeling, and mineral physics provides quantitative and systematic avenues for revealing new insights into this complex region.
In this presentation, I will focus on the influence of iron on the thermochemical heterogeneity of Earth’s deep mantle and its relationship to near-surface processes. For example, the transport of volatile species, particularly hydrogen, plays a major role in dynamical processes spanning the deep Earth to the surface, such as magma mixing and recharge. Nevertheless, significant gaps in our understanding remain, including the depth extent of this transport, storage capacity, the role that iron plays in this process, and seismic detectability of such volatile-bearing hosts in the mantle. The discovery of hydrous inclusions in sublithospheric diamonds suggest metasomatism and locally hydrous conditions at the mantle transition zone base. It is here that oxyhydroxide phases in the (Al,Fe 3+ )OOH–MgSiO 2 (OH) 2 system can form within oceanic petrologies and are capable of retaining hydrogen in their crystal structures at lower-mantle PT conditions, where a spin crossover in ferric iron favors increased stability and hydrogen storage capacity. If dense hydrous phases can be transported to the vicinity of Earth’s core-mantle boundary, their phase stability will depend in part on the surrounding temperature.
The second half of the presentation will therefore focus on the temperature of Earth’s core-mantle boundary region. Our new developments pair independent in-situ techniques to study melting of iron-rich phases at high-pressures: x-ray diffraction, sensitive to the loss of long-range crystalline order due to melting, and time-domain Mössbauer spectroscopy, sensitive exclusively to the dynamics of solid-bound iron nuclei. Emphasizing different time and length scales of the involved spatiotemporal atomic arrangements, a recent application of this approach to iron-rich systems offers a comprehensive understanding of phase relations and melting, with implications for thermochemical heterogeneity and plume roots in the lowermost mantle.