Congratulations to Austin Boles who successfully defended his dissertation on March 9, 2017.
Advisor: Ben van der Pluijm
Abstract:The various habitats wherein clay neomineralization occurs often coincide with zones of brittle deformation, making this family of minerals uniquely suited to record and retain in memory the temperature, timing, and chemical conditions of upper crustal deformation. This dissertation comprises a suite of studies that each employ various aspects of clay mineralogy, crystallography, and chemistry to solve problems of a structural nature. These studies are diverse in their geography, timing, and structural/tectonic setting, but are united in their utilization of applied clay science. A key methodological tool used in these investigations is the illite polytype analysis method; an important contribution of this work is the refinement of this method, both increasing its accuracy by using state-of-the-art, Rietveld-type quantitative X-ray powder diffraction techniques, as well as broadening its scope to include H isotopic analysis.
Chapter I serves to preface the dissertation and includes an introduction to practical aspects of clay mineralogy that distinguish them as useful geochronometers, geothermometers, and stable isotopic recorders. It outlines how the 3-dimensional arrangement of mineral populations and the frictional properties of clays can be useful in understanding the structural history and mechanical behavior of deformed rock. Chapter II is an in-depth treatment of illite polytype analysis techniques that presents advances on the method that are utilized in later chapters. Chapter III constrains the timing, temperatures, and mineralizing fluid characteristics of clays present in principle slip zone gouges from the Alpine Fault Zone (New Zealand), and concludes that both illitic and chloritic material in the fault zone must be recent, surface-localized alteration. Chapter IV is an experimental investigation of the temperature-dependent hydration behavior of natural smectite from the borehole of the Japan Trench Fast Drilling Project, which provides physical limits for estimates of coseismic heating during the 2011 Tohoku earthquake of <200ºC. Chapter V constrains illite mineralization timing in fault gouges from the trace of the modern North Anatolian Fault Zone, and indicates that the fault exploited pre-existing, weak clay material during initiation. Additionally, it shows that meteoric fluids circulate to depths of >5 km in the upper crust. Chapter VI is a study of diagenetic illite in mudstones of the Appalachian Plateau. The study presents evidence that mineralization timing (Early-Mid Triassic) coincided with the timing of maximum burial, and therefore hottest basinal temperatures, and that the fluid source was surface-derived from spatial scales small enough to record a rain shadow effect from the nearby Appalachian orogen. This study challenges reigning views on tectonically-mobilized fluid flow. Chapter VII includes concluding remarks that highlight the themes of this dissertation. Three appendices are also included, and they present data tables and preliminary results of ongoing research efforts on pseudotachylytes from gneiss-dome bounding faults (Papua New Guinea), a brittle fault dating campaign in the Istanbul Zone of northwest Turkey, and isotopic work on clay minerals recovered from principle slip zones of the San Andreas Fault Observatory at Depth borehole.
Themes include the fingerprinting of surface-derived (meteoric) signals in authigenic clay phases present at mid-crustal depths in major fault zones, indicating significant down-dip fluid flow; an emphasis on how pre-existing, deep-seated weaknesses in the crust control neotectonic deformation styles and facilitate fluid flow and mineralization; and comments on the nature of deformation-related fluid flow and synkinematic clay authigenesis.