Thermal effects of variable material properties and metamorphic reactions in a three-component subducting slab
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We explore the effects of variable material properties, phase
transformations, and metamorphic devolatilization reactions on the
thermal structure of a subducting slab using thermodynamic phase
equilibrium calculations combined with a thermal evolution model. The
subducting slab is divided into three layers consisting of oceanic
sediments, altered oceanic crust, and partially serpentinized or
anhydrous harzburgite. Solid-fluid equilibria and material properties
are computed for each layer individually to illustrate distinct thermal
consequences when chemical and mechanical homogenization within the slab
is limited. Two extreme scenarios are considered for a newly forming
fluid phase: complete retention in the rock pore space or instantaneous
fluid escape due to porosity collapse. Internal heat generation or
consumption due to variable heat capacity, compressional work, and
energetics of progressive metamorphic and devolatilization reactions
contribute to the thermal evolution of the slab in addition to the
dominating heat flux from the surrounding mantle. They can be considered
as a perturbation on the temperature profile obtained in dynamic or
kinematic subduction models. Our calculations indicate that subducting
sediments and oceanic crust warm by 40 and 70°C, respectively,
before the effect of wedge convection and heating is encountered at 1.7
GPa. Retention of fluid in the slab pore space plays a negligible role
in oceanic crust and serpentinized peridotites. By contrast, the large
volatile budget of oceanic sediments causes early fluid saturation and
fluid-retaining sediments cool by up to 150°C compared to their
fluid-free counterparts.
Originalsprog | Engelsk |
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Tidsskrift | Journal of Geophysical Research: Solid Earth |
Vol/bind | 120 |
Udgave nummer | 10 |
Sider (fra-til) | 6823-6845 |
Antal sider | 23 |
ISSN | 2169-9313 |
DOI | |
Status | Udgivet - 2015 |
ID: 167095952