Kinematics of Laramide Deformation

Posted July 26th, 2011 at 5:11 pm.

Abstract: Mary Schultz

Mentor: Arlo Weil

This summer I will work with Professor Arlo Weil on a collaborative study of the Wyoming foreland, specifically investigating the kinematics of Laramide deformation in the context of the larger tectonic evolution of the North American Cordillera.

Throughout the month of July, we will be in the field collecting oriented samples from the Wyoming foreland, concentrating on several individual structural domains: the southwestern Big Horn Mountains, the Ferris Mountains, and the Seminal Mountains. Sampling will be concentrated in the Triassic Chugwater Group, with emphasis on clastic red mudstones, siltstones and sandstones, and shallow marine limestones.  At each locality, the orientation of bedding, deformation lineations, minor folds, veins, joint systems, as well as minor fault slip data will be measured. Strain will be estimated from calcite twin analysis of Jurassic sparry limestone or reduction spots in Triassic red beds and eight to twelve oriented cores will be drilled for Anisotropy of low-field magnetization (AMS) and paleomagnetic analysis in red beds. A gas-powered drill and magnetic compass will be used for collecting cores, with a hammer and chisel used for collecting hand samples.

When we return in August, the collected core samples will be prepped, trimmed, and measured using the following methods: 1) AMS will be used to acquire tectonic shortening directions for all Triassic red bed sites. AMS provides a fast and reliable technique for measuring preferred orientations of grains in weakly deformed rocks and is especially useful when analyzed in conjunction with associated structural data (e.g., veins, fractures and fault slip data), 2) Paleomagnetic analysis will be used to measure changes in paleomagnetic declination between individual sites in order to quantify the absolute and relative magnitudes of vertical-axis rotations. All of these data will then be combined to construct working models to test different spatial ad temporal distributions of rotations, and possible kinematic explanations for Laramide deformation.

Filed under: 2011,Schultz, Mary,Weil, Dr. Arlo by Michelle Han

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