Program > Browse abstracts by speaker > Kasumov Bakhtiyar

Smectites are 2:1 phyllosilicate minerals, which are characterized by their capacity to incorporate a variable, up to large, amount of water, in the interlayer space. In a number of large-scale fault zones, such as plate boundary faults (e.g., the subduction fault that hosted the Mw9.1 earthquake in 2011 in Japan), the fault core is dominated by smectite. Although the hydration/dehydration reactions have been much studied for ambient pressure conditions, little is known about their properties at depth, particularly in settings where these reactions may influence fault mechanics and earthquake generation. In this study, we investigate this dehydration process for four cation-purified smectite samples (Ca, Mg, Na, and K) from Texas (STX) and Wyoming (SWy2) deposits. Wide angle X-ray scattering (WAXS) experiments were conducted using an internally heated pressure vessel, in the temperature range of 150–400°C and pressure range of 100–1400 bar. Under these conditions, the smectite evolves from a tri-layer (3W) to a di-layer (2W) interlayer water configuration. Our analyses indicate that dehydration transition temperatures systematically increase with pressure across all samples, regardless of the cation or source material. Notably, Ca-purified Wyoming smectite exhibits a lower transition temperature than Na-purified samples. Furthermore, comparisons between Texas and Wyoming deposits indicate that while Ca-purified smectite is similar between both types of smectite, Na-purified smectite from Wyoming exhibits a transition temperature 20–35°C higher than the sample from Texas. This research bridges a gap in our knowledge of smectite dehydration under geologically relevant conditions and it is a first step toward developing more predictive models of the mechanical behaviour of fault zones.