Tag: Mark Reed

Strain In Butte, Montana

Presenter(s): Owen Smith − Geology

Faculty Mentor(s): Ray Weldon, Mark Reed

Poster 3

Research Area: Geology

From the uplift of the Rocky Mountains to the basin and range extension, Butte Montana has undergone dramatic tectonic deformation. This deformation does not just make for an interesting landscape but also affects the shape of mineral grains in the rock. The shape of grains can show us the amount of tectonic compression or extension the region has experienced, however the grains only record the amount of strain since it formed. Using quartz veins and the quartz grains that compose them, I measured the minor/major axis lengths of the grains. This shows us how the grain has been stretched or compressed relative to the veins orientation. The main method used for this analysis is the Fry method and it allows us to see the amount of compression or extension has occurred along the quartz veins. The results show us that if veins have not be cross cut then the grains are compressed along the vein orientation and extension occurs perpendicular to the vein orientation. When a vein does get crosscut, then the grains show less extension perpendicular to the vein and less compression along the vein orientation. This tells us that on the vein level, when a vein crosscuts another vein, there is strain accumulated parallel to the crosscutting veins orientation. This research will help complete the picture of the total amount of strain built up in the Butte, Montana region.

Palepiezometry Analysis of Recrystallized Quartz from Pre-Main Stage Veins in the Porphyry Copper Deposit in Butte, Montana

Presenter(s): Molly Pickerel

Faculty Mentor(s): Mark Reed & James Watkins

Poster 21

 Session: Sciences

Recrystallized quartz grains from pre-main stage veins in the porphyry copper deposit in Butte, Montana show microscopic evidence of different temperature and pressure conditions seen through the presence of all three recrystallization regime patterns that imply a range of conditions. In this study new methods are applied to analyze recrystallized quartz veins to generate strain rate conditions not previously constrained for these veins. Thin sections of these recrystallized quartz grains are densely populated with a range of different sized fluid and mineral inclusions. The presence of these inclusions prevents the standard application of the analysis function in ImageJ to accurately measure the area of the grains and create a grain boundary map. In order to overcome this obstacle in the study Fourier transforms were created of the images and a bandpass filter applied to eliminate the frequencies of those inclusions so that the inverse Fourier Transform images did not include them. More image processing was needed to skeletonize and fill left over holes in the images before ImageJ analysis. The grain diameters collected are inputted into paleopiezometry equations from Fazio and Ortlano et al. (2018) with temperature estimates from Fouriner et al. (1999). These determined strain rates can provide insights into the conditions of the porphyry system in early stages.