Collaborative Research: An Experimental Investigation of Reactive Melt channelization in Partially Molten Rocks

Lead PI: Dr. Ben Holtzman

Unit Affiliation: Seismology, Geology and Tectonophysics, Lamont-Doherty Earth Observatory (LDEO)

August 2015 - July 2019
Project Type: Research

DESCRIPTION: Melting occurs beneath the plate tectonic boundary zones as well as volcanic hotspots, such as Hawaii and Iceland. The physical and chemical interactions between the migrating melt and the surrounding rock determine how planets evolve over time. However, the means by which melt formed deep in the Earth migrates upward to the surface to either erupt or cool slowly in a crustal magma chamber are not well understood. Geologists want to know how bulk planetary composition evolves to produce crustal rocks that have fundamentally different mineralogy than the underlying mantle rock. Such information underpins knowledge about the extent of chemical exchange between the Earth's interior and surface. This study will feature an early career scientist working with established experts to implement new laboratory techniques that, for the first, should produce results that can be related to the inaccessible natural system. As the experimental procedures are honed, new undergraduate lab exercises will be developed. They will employ glass beads and salt and introduce students to techniques that make is possible to investigate complex processes where there are feedbacks between the physics and chemistry of the system. Melt extraction affects much of the chemical exchange between mantle, crust and the atmosphere. Geochemical, geophysical and geological evidence suggests that, at some stage of melt extraction, melt must segregate into high permeability channels. These channels must be isolated enough to preserve chemical disequilibrium and permeable enough to allow fast melt extraction in order to preserve radiogenic disequilibrium. In nature, melt segregation is inferred to occur due to an interplay between reaction and deformation. Experimental investigations provide key insights into the processes occurring during melt migration and motivate further theoretical developments. A recently developed experimental methodology has reproduced the reaction infiltration instability. Since the gradient in pore pressure can be controlled in these experiments, it is possible to independently control melt velocity and melt-solid reactivity. Thus, the evolution of permeability with time can be explored as the reaction modifies the rock microstructure, the increase in melt flux due to channelization can be quantified, and melt migration regimes can be documented as a function of physical and chemical driving forces. A first set of experiments will be conducted on dual composition samples of olivine with clinopyroxene, and with orthopyroxene at high temperature and pressure. A second set will combine olivine with both pyroxenes in a single sample. This study will also develop new methods for analyzing the resulting microstructures and test/refine parameters that allow for scaling of laboratory data to natural environments.