Title: Application of field and lab x-ray methods to understand fluid-rock interactions

Name: Anna Paulding
Mentor: Dr. Kelly Bradbury

A dramatic increase in seismicity has occurred in the midcontinent region since 2009 (Rubinstein and Mahani, 2015), causing public concern for the stability of infrastructure and buildings. Several studies have directly linked this seismicity to the reactivation of buried fault systems near the Paleozoic sedimentary bedrock-Precambrian crystalline basement contact as a result of high volumes of injection of wastewater produced by the oil and gas industry (Ellsworth, 2013; Keranen et al., 2013).
The reactivation of fault zones due to fluid injection is not only influenced by injection rates but also by the ability of fluids to migrate along or across the contact, which is controlled by the rock properties and geologic setting. To better understand the rock property variations that may occur along the nonconformity interface, we use an outcrop analog site of an exhumed fault near Gunnison, Colorado. My undergraduate research focuses on using a portable handheld X-Ray Fluorescence Unit (pXRF) as a tool to measure compositional variations in outcrop. To directly compare data, a calibration using 16 USGS Concentration Standards as well as 12 analog samples will be used to create a calibration optimized for this specific suite of rocks which informs the accuracy of in-situ field data measurements against laboratory measurements of powdered samples, influencing how future pXRF measurements can be analyzed. Micro-scale variations of major and trace element concentrations reflect alteration and related fluid-rock interactions and may serve as a proxy for fluid migration along or across faulted sections of a nonconformity interface. I propose that calibrated pXRF data and whole rock XRF data is a useful tool for understanding the nature and degree of rock alteration in fault zones and across analog sites nonconformity interface. These data can aid in a more broad understanding of how pXRF data can be used in the field to characterize the nonconformity interface and fault zones.