The significance of intrusive volatile release for the Earth´s atmosphere.

After the solidification of the magma ocean, outgassing from the interior is the prevailing volatile source of Earth´s atmosphere. Besides the well-studied extrusive degassing, this process also includes the often neglected intrusive volatile release. Although, intrusive magma production rates are assumed to be significantly higher compared to extrusive rates. This renders the investigation and quantification of possible volatile exsolution mechanisms from intrusive magma bodies crucial.

An emplaced magma body progressively crystallizes due to cooling. The precipitation of certain minerals fractionates the primitive mantle over time by incorporation of compatible elements and molecules into the crystal lattice. In contrast, incompatible elements and molecules, including volatiles like H₂O and CO₂ are precluded from the crystal lattice due to their unsuitable ion radius or charge. Thus, ongoing crystallization likely leads to an oversaturation of volatiles in the remaining melt and an enhanced exsolution.

In our study, we simulate the partitioning, solubility and release of H₂O and CO₂ from a magma body emplaced at different depths within the lithosphere. Additionally, we take the possibility of melt ascent and the formation of hydrous minerals into account. According to our simulations the release of H₂O and CO₂ from an intrusive magma body is possible to a depth of at least 100 km (~3 GPa, which is comparable to the average thickness of the Earth's lithosphere). However, the release strongly depends on the initial volatile budget, the formation of hydrous phases, the depth of the intrusion and the buoyancy of the melt. Considering all these factors, our model suggests that about 0 - 85 % H₂O and 100 % CO₂ can be released from mafic intrusions. This renders the incorporation of intrusive volatile release mandatory in order to determine the volatile fluxes and the composition of Earth's atmosphere.