The deformation and compaction of partial molten zones |
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| Authors: | Neil M Ribe |
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| Institution: | Department of Geology and Geophysics, Yale University, PO Box 6666, New Haven, CT06511, USA |
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| Abstract: | Summary. The segregation of melt from a partially molten source region requires a corresponding deformation of the unmelted residue ('matrix'). The role of matrix deformation during melt segregation is examined using simple one-dimensional models, for which the deformation consists only of bulk compression or 'compaction'. In model I, a volume fraction φ0 of ascending mantle material undergoes pressure-release melting at a depth z = 0 (localized melting). Compaction of the matrix occurs in a boundary layer whose thickness (reduced compaction length δR) is proportional to the square root of the matrix viscosity. In the Earth's mantle, δR～ 10–100 m, indicating that compaction cannot be important over large distances. Model II examines the case in which melting occurs over a depth range of order h (distributed melting). In the limit h ?δR, the solution is the same as for the case of localized melting, except in a 'melting layer' of thickness ～ h near z = 0. In the more realistic limit h ?δR, compaction makes a negligible contribution to the balance of forces associated with melt segregation. This result is also valid for the more general case of two-dimensional flow. Compaction is therefore likely to be of negligible importance in the Earth's mantle, with the consequence that melt segregation can be accurately described by Darcy's law. |
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