Conditions of melt ascent leading to the igneous composition of the Martian surface
Abstract
Rising melt within the Martian lithosphere likely becomes trapped beneath a relatively deep layer known as the permeability barrier (Schools and Montési, 2018), a feature that forms when the pore spaces of the lithospheric matrix through which melt travels become clogged, impeding further percolation. The depth of the permeability barrier has changed over time, and the composition of melt that stalls at the barrier is expected to have changed over time as well. Melt composition may be inferred from the mineralogy of the extrusive igneous rocks of the Martian surface, which can be interrogated using remote sensing data. However, it is important to determine to what extent the composition of melt may have changed as it rises from the permeability barrier to the surface. In this regard, we calculated the chemical and mineralogical evolution of melt during ascent through the Martian lithosphere using the MELTS thermodynamic calculator. We varied mantle temperature, lithosphere thickness, mode of crystal extraction, and the location of a permeability barrier. Mineralogical compositions were compared between models and Martian surface spectroscopy data taken by spacecraft. MELTS calculations suggest that under ambient mantle temperatures, melt is rich in Si and poor in Fe, while the reverse case was found under hotter plume temperatures. Accordingly, TES and GRS data shows depletion in Si around Tharsis and Elysium, locations interpreted as being produced by a mantle plume. Data on Fe abundance is less conclusive, with depletion in Tharsis but not Elysium. Lithosphere thickness was also found to deplete Si and increase Fe content. Parameters of this type were input into our models whose results closely resemble actual surface composition. We found that isothermal models of melt rising from the barrier to the surface matched most closely to surface composition data. More refined surface composition data and further modeling work, such as an investigation of crustal assimilation, may further constrain the thermal history and structure of the Martian crust and lithosphere.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.V51B0115H
- Keywords:
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- 8120 Dynamics of lithosphere and mantle: general;
- TECTONOPHYSICSDE: 8147 Planetary interiors;
- TECTONOPHYSICSDE: 8411 Thermodynamics;
- VOLCANOLOGYDE: 8412 Reactions and phase equilibria;
- VOLCANOLOGY