Abstract: Peiying Wen
Mentor: Dr. Weil
This summer I will be assisting Professor Arlo Weil in a careful investigation of Laramide deformation of the Rocky Mountains in Wyoming. The ultimate goal of this project is to reconstruct a kinematic evolution and mechanics that will explain the origin of the complicated, multi-phase Laramide foreland deformation.
In July, we will collect oriented samples in the Wyoming foreland, and will concentrate on individual fold systems (Thermopolis anticline, Derby Dome, and Sheep Mountain areas). The samples come from Triassic red beds and Jurassic limestones that record primary remanent magnetization and interpretable AMS fabrics. We will use either a portable gas-powered drill and magnetic compass for collecting cores, or a hammer and chisel for collecting hand samples. Detailed structural data will also be collected, including orientations of beddings, lineations, minor folds, veins, and joint systems, as well as minor fault slip data.
When back from the field in August, we will run lab tests to systematically analyze the field samples on a range of scales; the key methods of such analysis are summarized as follows.
a) We will use anisotropy of low-field magnetic susceptibility (AMS) to acquire fabric information in each Triassic red bed site. AMS provides a sensitive technique for measuring preferred orientations of magnetic grains in such weakly deformed rocks, and can combine with typical structural analysis to develop improved kinematic models of Laramide deformation. In addition, x-ray diffraction of selected samples will be conducted to determine the mineral subfacbrics, and thus refine our AMS interpretations.
b) We will conduct paleomagnetic analysis of Triassic red beds over a range of scales. We will measure changes in paleomagnetic declination between individual sites to quantify absolute and relative magnitudes of vertical-axis rotations. Paleomagnetic studies reveal different spatial and temporal distributions of rotations, and test the kinematic models.