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Decarbonation of Stagnant Slab in the Mantle Transition Zone
Author(s) -
Zhang Yanfei,
Wang Chao,
Jin Zhenmin
Publication year - 2020
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1029/2020jb019533
Subject(s) - geology , solidus , mantle (geology) , mantle wedge , slab , transition zone , geochemistry , basalt , oceanic crust , carbonate , lithosphere , geophysics , subduction , seismology , materials science , tectonics , alloy , metallurgy , composite material
Phase relations of carbonated basalts have been investigated at 13–20 GPa and 1200–1600°C, to model the decarbonation process of stagnant slab in the mantle transition zone (MTZ). Two synthetic mixes with CO 2 contents of 2.5 wt% (PC‐a) and 5.0 wt% (PC‐b) were used as the starting materials. The estimated solidus was ~1350°C at the top of the MTZ (~13–15 GPa), which declined to ~1250°C for pressures of above ~15–16 GPa for both mixes. The average slab geotherms are lower than the obtained solidus, creating a carbonate‐bearing stagnant slab, followed by decarbonation of stagnant slab with increased residence time. Dehydration of stagnant oceanic lithosphere could induce decarbonation of the upper oceanic crust for temperatures below the solidus of carbonated basalts. The resulting carbonate melt is highly reactive with the ambient mantle, producing a carbonated domain in the MTZ or at the top of the 410‐km seismic discontinuity. A portion of carbonate melt could ascend to shallow depth because of low density and low viscosity and bring oceanic crust signatures into the source of some volcanoes after complex interactions with the surrounding mantle. On the example of Eastern Asia, decarbonation of stagnant slab is inferred to be a possible prerequisite for the formation of the big mantle wedge and triggered the intraplate volcanoes of Eastern Asia.