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Controls on distribution, intensity, and extent of palagonitization in glaciovolcanic settings Leiter, Sophia


Palagonite, the first stable alteration product of basaltic glass, is an assemblage of altered glass and authigenic clays and zeolites commonly found in subaqueous volcanic environments. The process of palagonitization transforms volcaniclastic deposits physically, mineralogically, and chemically through the dissolution of basaltic glass and reprecipitation of gels and newly formed mineral phases. Despite its ubiquity in subaqueous volcanic environments, it is as yet poorly understood how palagonite propagates and what conditions drive its formation. We present mineralogical, physical, and chemical data for a set of 134 variably palagonitized cores collected from Cracked Mountain, a subglacial volcano crosscut by an abundant dike complex in the Mount Meager Volcanic Complex, British Columbia. The qualitative and quantitative mineralogy, density, porosity, permeability, uniaxial compressive strength, P-wave velocity, and whole rock geochemistry was studied with the aim of determining what factors control the intensity of palagonitization. Using this data set I investigate the extent to which palagonitization alters the physical, mineralogical, and chemical properties of volcanic deposits. I define three palagonitization environments, determined by their proximity to hot intrusive dikes and pillows. The first environment is defined by a lack of association to a hot intrusive body and allows two possible pathways of alteration determined by the fluid/rock ratio. In lower fluid/rock ratio systems, there is minor smectite growth but minimal changes in physical properties. Higher porosity and permeability areas within the low temperature environment are defined by widespread glass dissolution, which results in extensive, deep orange discoloration. As the degree of alteration increases, analcime forms and increases in abundance in the second and third environments which are defined by their increasing proximity to a hot, intrusive body. Alteration intensity is ultimately defined by the abundance of zeolites, which are representative of the relative duration of time at high temperature. Authigenic minerals cement the deposit, increasing the density and decreasing porosity and permeability. Similar patterns can be seen at other subaqueous volcanic edifices, including in Hawaii and at Surtsey, where mineralogical zones are defined by thermal regimes, and density increases as palagonitization intensity increases.

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