A WORKFLOW FOR ANALYSIS OF MICROSCOPIC FRACTURES IN ROCK USING THIN SECTION MICROSCOPY

Recent advances in the study of subcritical fracturing in rock have revealed its potential importance as a means of mechanical weathering, with major implications for sediment production, soil development, and geochemical cycling. The focus of most research has been on macroscopic fractures in cobble-to-boulder sized clasts, but this leaves an incomplete picture of how fractures initiate and propagate in response to environmental stresses. Analysis of microscopic fractures in rock will be necessary to fully understand the evolution of subcritical fracture-driven rock weathering, but it is difficult and time consuming to analyze fractures in a large enough area of a sample to be reasonably confident that measured fracture properties are representative. To address this gap in the data, we are developing a protocol for reproducible microfracture mapping using thin section microscopy techniques that can be performed using equipment found in most Earth Science departments, and utilizing existing software tools for analysis of the products. Here, we present an initial microfracture dataset derived from a suite of rocks from Mullins Glacier, Antarctica alongside the workflow to generate a similar dataset. The McMurdo Dry Valleys (where Mullins Glacier is located) contain some of the oldest exposed surfaces on the planet, and along the length of the glacier rocks have exposure ages ranging from recent to ~2 Ma. We applied our workflow to produce fracture maps of thin section photomicrographs for a series of sandstone cobbles from a range of ages along the glacier and calculated fracture orientations, lengths, and densities over the time series. In addition to insights about mechanical weathering in a cold and dry end-member climate, we identify potential pitfalls and future directions for our method that could vastly accelerate research into environmental stress-driven rock fracturing and mechanical weathering.