Melt segregation and depletion during ascent of buoyant diapirs in subduction zones

Date
2020-01-31Author
Zhang, Nan
Concept link
Behn, Mark D.
Concept link
Parmentier, E. Marc
Concept link
Kincaid, Christopher
Concept link
Metadata
Show full item recordCitable URI
https://hdl.handle.net/1912/25871As published
https://doi.org/10.1029/2019JB018203DOI
10.1029/2019JB018203Abstract
Cold, low‐density diapirs arising from hydrated mantle and/or subducted sediments on the top of subducting slabs have been invoked to transport key chemical signatures to the source region of arc magmas. However, to date there have been few quantitative models to constrain melting in such diapirs. Here we use a two‐phase Darcy‐Stokes‐energy model to investigate thermal evolution, melting, and depletion in a buoyant sediment diapir ascending through the mantle wedge. Using a simplified 2‐D circular geometry, we investigate diapir evolution in three scenarios with increasing complexity. In the first two scenarios we consider instantaneous heating of a diapir by thermal diffusion with and without the effect of the latent heat of melting. Then, these simplified calculations are compared to numerical simulations that include melting, melt segregation, and the influence of depletion on the sediment solidus along pressure‐temperature‐time (P ‐T ‐t ) paths appropriate for ascent through the mantle wedge. The high boundary temperature induces a rim of high porosity, into which new melts are focused and then migrate upward. The rim thus acts like an annulus melt channel, while the effect of depletion buffers additional melt production. Solid matrix flow combined with recrystallization of melt pooled near the top of the diapir can result in large gradients in depletion across the diapir. These large depletion gradients can either be preserved if the diapir leaks melt during ascent, or rehomogenized in a sealed diapir. Overall our numerical simulations predict less melt production than the simplified thermal diffusion calculations. Specifically, we show that diapirs whose ascent paths favor melting beneath the volcanic arc will undergo no more than ~40–50% total melting.
Description
Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Solid Earth 125(2), (2020): e2019JB018203, doi:10.1029/2019JB018203.
Collections
Suggested Citation
Zhang, N., Behn, M. D., Parmentier, E. M., & Kincaid, C. (2020). Melt segregation and depletion during ascent of buoyant diapirs in subduction zones. Journal of Geophysical Research-Solid Earth, 125(2), e2019JB018203.Related items
Showing items related by title, author, creator and subject.
-
Timescales for the growth of sediment diapirs in subduction zones
Miller, Nathaniel C.; Behn, Mark D. (John Wiley & Sons, 2012-07-10)In this study, we calculate timescales for the growth of gravitational instabilities forming in the sediment layer on the downgoing slab at subduction zones. Subducted metasediments are buoyant with respect to the overlying ... -
Arc magmas sourced from melange diapirs in subduction zones
Marschall, Horst R.; Schumacher, John C. (2012-10-11)At subduction zones, crustal material is recycled back into the mantle. A certain proportion, however, is returned to the overriding plate via magmatism. The magmas show a characteristic range of compositions that have ... -
Diapirs as the source of the sediment signature in arc lavas
Behn, Mark D.; Kelemen, Peter B.; Hirth, Greg; Hacker, Bradley R.; Massonne, Hans-Joachim (2011-05-31)Many arc lavas show evidence for the involvement of subducted sediment in the melting process. There is debate whether this “sediment melt” signature forms at relatively low temperature near the fluid-saturated solidus or ...