Clay Neomineralization and the Timing, Thermal Conditions and Geofluid History of Upper Crustal Deformation Zones

Abstract

The various occurrences of clay neomineralization often coincide with zones of crustal deformation, making this family of minerals uniquely suited to record and retain the temperature, timing, and chemical conditions of upper crustal deformation. This dissertation comprises a suite of studies that employ various aspects of clay mineralogy, crystallography and clay chemistry to answer major questions in regional structural geology. These studies are diverse in their geography, timing and structural/tectonic setting, while 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 is the refinement of this method, both improving its accuracy by using state-of-the-art, Rietveld-type quantitative X-ray powder diffraction techniques, as well as broadening its application 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 geochronometers, geothermometers, and stable isotopic recorders. It outlines how the 3-dimensional arrangement of mineral populations and the properties of clays can be useful in understanding the structural history and mechanical behavior of deformed rock. Chapter II presents a new illite polytype analysis technique that represents significant advances on prior approaches, which is further utilized in subsequent chapters. Chapter III constrains the timing, temperatures, and mineralizing fluid characteristics of clays present in principal slip zone gouges from the Alpine Fault Zone (New Zealand), and concludes that both illitic and chloritic material in the fault zone are recent, surface-localized alteration. Chapter IV is an experimental study of 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 along the trace of the modern North Anatolian Fault Zone, and indicates that the modern fault exploits pre-existing, weak clay material. Additionally, it shows that surface fluids infiltrated to depths >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) coincides with the timing of maximum burial, and, therefore, hottest basinal temperatures, and that the fluid was surface-derived at spatial scales small enough to preserve a rain shadow effect from the nearby Appalachian orogen. This study challenges reigning views on tectonically-mobilized, older fluid flow for associated geologic processes. Chapter VII offers concluding remarks that highlight the main themes of this dissertation. Three appendices are included, presenting data tables and preliminary results of ongoing research efforts on pseudotachylytes from gneiss-dome bounding faults (Papua New Guinea), a fault dating campaign in the Istanbul Zone of northwest Turkey, and isotopic work on clay minerals recovered from principal slip zones in the San Andreas Fault Observatory at Depth borehole. The overarching themes of the dissertation are the fingerprinting and timing of surface-derived (meteoric) signals in authigenic clay phases that formed at shallow to mid-crustal depths in major fault zones. This requires significant down-dip fluid flow. Emphasis is placed on how pre-existing, deep-seated weaknesses in the crust control deformation styles and facilitate fluid flow and mineralization, and on insights into the nature of deformation-related fluid flow and clay authigenesis.