To investigate channelization during migration of a reactive melt, we performed a series of Darcy-type experiments in which an alkali basalt infiltrated partially molten harzburgites and lherzolites at a confining pressure of 300 MPa, temperatures of 1200°C and 1250°C, and pore pressure gradients of ~2 to 60 MPa/mm. We compare our results to those from previously published experiments performed on wehrlites. In all experiments, irrespective of the exact mineralogy, a planar reaction layer composed of olivine + melt developed in which all of the pyroxene was consumed. Under specific conditions controlled primarily by the melt flow velocity, finger-like channels composed of olivine + melt also developed. In wehrlites, these reaction infiltration instabilities formed at 1200°C and 1250°C at pressure gradients >25 and >5 MPa/mm, respectively. In harzburgites, channelization occurred only at 1250°C at a pressure gradient of 35 MPa/mm. In lherzolites, a planar melt-filled vein developed at 1250°C; no finger-like channels formed under a pressure gradient of ~25 MPa/mm. Both the finger-like channels and the planar vein led to very efficient extraction of melt from the reservoir. Channelization established large compositional variations over short distances in the crystalized phases as well as in the local melt and greatly enhanced the abundance of the reaction product, olivine, similar to dunite channels in the Earth. The range of chemical-mechanical responses displayed by this array of compositions provides a set of targets for reactive transport and mechanical modeling studies.
Bibliographical noteFunding Information:
We thank Anette von der Handt for priceless help with EMPA measurements and numerous discussions, Brian Bagley for acquiring μCT data and help with visualization and analysis, and Chris Frethem for assistance with SEM imaging. Alejandra Quintanilla‐Terminel, Amanda Dillman, Marc Hirschmann, Oliver Jagoutz, and Timothy Grove are gratefully acknowledged for discussions, and Neel Chatterjee for EMPA assistance. Yan Liang and Clint Conrad are thanked for providing the alkali basalt used in this study. Nick Dygert and Richard Katz are thanked for detailed reviews. The Hitachi SU8320 SEM was provided by NSF MRI DMR‐1229263. Parts of this work were carried out in the Characterization Facility, University of Minnesota, a member of the NSF‐funded Materials Research Facilities Network ( www.mrfn.org ) via the MRSEC program. The funding by the National Science Foundation Grant OCE‐1459717 and the funding through MIT's Charles E. Reed Faculty Initiatives Fund are gratefully acknowledged.
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- experimental geophysics
- melt channelization
- melt migration
- melt-rock reactions