Using Magnetics to Approximate the Relative Age of Mafic Sills Within Dagger Mountain in Big Bend National Park,Tx

Understanding the geometry of the mafic sills within Dagger Mountain using magnetometry

The goal of our project was to analyze the geometry of the mafic sills within Dagger Mountain, found in Big Bend National Park, TX. Understanding the geometry of the sills within Dagger Mountain is vital to obtaining the relative age of the sills. According to Cullen et al(2013), the mafic sills are believed to be Tertiary age(~70-50 MA) because at map scale the shape of the mafic sills appear to be folded along with folded local Cretaceous bedrock (~145.5-65.5). This folding is correlated with the Laramide orogeny (mountain building event). However, according to a magnetometry survey conducted by Mario & Lehto (2014), the shape of the mafic sills do not appear to be folded with the surrounding bedrock. In actuality the survey shows the mafic sills to be lying flat. This would mean that the sills would have had to have been intruded after the folding caused by the Laramide orogeny. This project expands upon Mario & Lehto’s research to gain a further understand of the sills by modeling the sills in 3D. We utilized the IGMAS+ geophysics program to analyze the data that was collected by Mario Mata in 2014 and created a 3D model of the anomaly. Within this project we will test two different models. One model will show the mafic sills folded with the beds, while the other model will focus on altering the shape to fit the calculated magnetic field. By fitting the shape of the sill to the measured data we can determine the actual geometry of the mafic sills, and thus, be able to tell if the mafic sills are pre or post laramide. This project collected data in Fall of 2016 with the assistance of students in the ASU geophysics course. In addition, we used data collected by Mario & Lehto (2014) on the same map area. We expect to find similar results to Mario & Lehto (2014). This project was sponsored by the Angelo State University research experience with the mentorship of Dr. Heather Lehto. The field work was made possible by the assistance of the Fall 2016 geophysics course and alumni Mario Mata.