It has been shown by laboratory studies that water has a drastic effect on the rheology of rocks, specifically influencing rock strength, strain rates, and recovery mechanisms. In this project, the a research team from Central Michigan University and the University of Missouri, Columbia, will use a natural laboratory approach to investigate the direct effects of variable fluid composition on naturally deformed quartzites and marbles. The team will examine the influence of variable water-carbon dioxide fluids on deformation and recrystallization of these rocks in the aureole surrounding the Eureka Valley-Joshua Flat-Beer Creek composite pluton in the White Mountains of California where a period of intense high temperature deformation was associated with pluton emplacement. The goal of the project is to determine how the rheology of the wall rocks, influenced by fluids, affected the emplacement and space-making processes of mid-crustal plutons, and from a broader perspective, to assess how fluids affect the deformation and the strength of the continental lithosphere. The constrained environment of the Eureka Valley-Joshua Flat-Beer Creek pluton aureole provides an opportunity to compliment the current understanding of rock deformation and recrystallization from laboratory experiments that must be done at much higher strain rates than are seen in nature. The study will integrate field, microstructural, petrologic and geochemical work to determine the influence of variable amount of water and fluid composition on deformation of quartzites and related marbles. The fieldwork will provide the context for the study and recognize areas of high and low strain. Electron backscatter diffraction, universal stage, and grain shape analyses will be used to determine the deformation and recovery mechanisms of the quartzites and marbles. Mineralogy and stable isotope ratios in the rocks will indicate the compositions of fluids that flowed through the individual lithologies, while analysis of fluid inclusions will directly show fluid compositions.
The rate of deformation of the Earth's lithosphere controls its topographic features. Laboratory experiments have shown that water in particular promotes the deformation and recrystallization of rocks at high temperatures and pressures experienced by the deep continental crust. Thus, while it is generally recognized that in the lower continental crust rocks are ductile, the temperature at which they become ductile is influenced by the composition of fluids that may exist in the rocks. In the upper crust, the deformation of rocks around magma plutons will also be influenced by fluid compositions. The application of laboratory experiments to deformation of the continental crust is sometimes difficult, however, because of the vastly different time scales at which deformation occurs in the laboratory and the crust and because laboratory experiments do not reproduce the complex deformation environments seen in nature. This project will evaluate the deformation and recrystallization of crustal lithologies in the natural laboratory of the metamorphic aureole of a pluton in the White Mountains of California. The rocks in the metamorphic aureole have experienced various degrees of deformation and recrystallization that appear to have been influenced by fluids with variable proportions of water and carbon dioxide. Field work and several sophisticated techniques will be used to determine the deformation and recrystallization mechanisms of rocks in the metamorphic aureole and the compositions of fluids that flowed through the rocks. This work will provide a better understanding of factors that influence rock deformation at rates that are controlled by tectonic forces and magma ascent through the crust.
