the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Origin of Changbaishan volcano inferred from simulation of the Cenozoic Pacific plate subduction using geodynamic models with data assimilation
Abstract. The Changbaishan volcano has been considered a giant active intraplate volcano with hidden potentially disastrous eruptive risks, so its origin has attracted widespread attention from all over the world. However, this issue has not been adequately settled down due to its complexity. So far, three primary conceptual mechanisms have been proposed based on seismic tomography and geochemistry. All three mechanisms have been considered to be correlated with the subduction of the Pacific plate. Therefore, we use the best-fit thermochemical geodynamic model with data assimilation, which was determined by tracking the seismically inferred structure of the subducted Pacific slab beneath the Changbaishan volcanic province (CVP), to assess the their relative significance. The findings suggest that the super-hydrous melts in the mantle atop the Pacific slab, resulting from the slab dehydration in the mantle transition zone (MTZ), may primarily contribute to the volcanism of the Changbaishan volcano. Meanwhile, the other two mechanisms, the upward escape of the entrained oceanic asthenospheric material as well as the piling up and thickening of the subducted Pacific slab, may play secondary roles.
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EC1: 'Comment on egusphere-2024-3219', Juliane Dannberg, 11 Nov 2024
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Dear authors,
I had a look through your manuscript before sending it out for review, and I already wanted to bring up a few points that would need improvement before I can consider the manuscript for publication.
Specifically,
(1) There are several statements in the text that contradict the current view in the field, without justification being given. If this study makes assumptions deviating from the classical view, there needs to be strong evidence supporting that.
(2) The current state of knowledge is not represented well by the references given in the manuscript, and key references are missing. I found this to be the case throughout the text, including general concepts such as geodynamic modelling of volcanoes and dehydration of slabs, data assimilation, viscosity laws, and the subduction history of the Pacific plate.
(3) There are several statements in the text that are confusing, or where key information is missing. This makes it very difficult to follow both the arguments for the proposed hypothesis and the setup and execution of the modeling study. This information is needed to judge if the proposed model is appropriate to address the question the manuscript poses.
Examples include:“Therefore, some researchers suggested that the subducting Pacific plate entrains enormously its underlying asthenospheric material into the MTZ”
If the slab is stagnating in the MTZ, the asthenosphere can not be below.“utilizing a four-dimensional mantle convection model”
What is a four-dimensional mantle convection model?
(In addition, this paragraph also does not accurately represent the literature; many geodynamic models do suggest a mantle plume as the cause for Yellowstone volcanism.)“The amount of water dehydrated from the subducting plates at deep mantle is the primary factor influencing the magma volume and eruptive intensity of the Changbaishan volcano.”
There is no reference for this. How do we know this?“The thermochemical mantle convection is governed by the equations for the conservation of mass, momentum, and energy”
Is the model compressible or incompressible? Does it include adiabatic heating/shear heating? This information is key, for example to understand if the CMB temperature of 2500 degrees C includes an adiabatic gradient or not (if the former, it seems too low).The description of the oceanic plate composition is confusing: It sounds like it contains oceanic crust and a buoyant layer, but the buoyant layer is also described as crust.
Equation (1): The gas constant seems to be missing here. Furthermore, activation energies of 17 to 42 kJ/mol seem more than an order of magnitude too low for the mantle.
“Considering that the Pacific plate started to subduct between 25 and 20 Ma”
I think the whole tectonic setting requires additional justification. All the plate reconstructions I have seen show the Pacific Plate starting to subduct much earlier (with the exact time depending on the part of the plate boundary and the plate reconstruction). In addition, I would have thought the subduction of the Philippine Plate would play an important role as well.I am confused by Figure 2:
Why is the whole CMB covered by material that is ~1000 K colder than the surrounding mantle? Why is there no hot material? In addition, the colorscale is not perceptually uniform and therefore makes it hard to judge temperature anomalies. Furthermore, the slab deforms a lot, so I would recommend to show the viscosity so that the reader can understand why this happens.What water content in the mantle is implied by a 25% wt fraction in the melt? Is the amount of water consistent with the amount of water that could dehydrate from the slab in the MTZ?
There is no discussion of model uncertainties or limitations.
Best regards,
Juliane DannbergCitation: https://doi.org/10.5194/egusphere-2024-3219-EC1
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