USING MAGNETICS TO APPROXIMATE THE RELATIVE AGE OF MAFIC SILLS WITHIN DAGGER MOUNTAIN IN BIG BEND NATIONAL PARK, TX

The main goal of this project was to obtain additional magnetic surveys of mafic sills located at Dagger Mountain in Big Bend National Park, TX in order to better determine the shape of the sills in relation to the surrounding bedrock. By understanding the shape of the sills, we will be able to interpret the relative age of the intrusions. According to Cullen et al, (2013), it was believed that the intrusions were tertiary aged and had been folded with the Cretaceous sedimentary layers during the Laramide Orogeny (~70-50 MA) since the orientations of the sills appeared to resembled the orientation of bedrock at map scale. However, a study conducted by Mata and Lehto (2014) used magnetic surveys of one sill in Dagger Mountain to conclude that the mafic stills were in fact not folded with the surrounding bedrock and instead appeared to be flat lying and intruded through the folded bedrock. Since the sills did not appear to have been folded with the Cretaceous age sedimentary bedrock, Mata and Lehto (2014) concluded that the sills were emplace post Laramide (~50-70 MA). Our study aimed to collected additional magnetic data over other sills in the Dagger Mountain area to compare to the previously collected data. In addition, there were several lines of magnetic data collected for the previous study that had not been modeled and as such we have included that data in our study.

We collected data in the Fall of 2016 with the assistance of the geophysics course at Angelo State University. The new data and data from the previous study will be modeled and we expect to find similar results to the Mata and Lehto (2014) study; namely that the sills are flat-lying and intrude through the folded sedimentary rocks at the site and are thus post-Laramide.