Summer Science Research at Bryn Mawr

'Weil, Dr. Arlo' Archive

Examining Deformation Evolution in the Wyoming Laramide Foreland

Posted August 4, 2011

Abstract: Amelia Zhi Yi Mentor: Laramide foreland deformation in Wyoming represents a classic tectonic province, yet there are outstanding questions about the kinematic and mechanical processes responsible for the mountain systems seen today. The archetype Laramide orogen, which spans over 1,200km from Central Montana to New Mexico, was formed during the Late Cretaceous to early […]

Kinematics of Laramide Deformation

Posted July 26, 2011

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 […]

Examining Deformation Evolution in the Wyoming Laramide Foreland

Posted July 13, 2011

Abstract: Amelia Lee Mentor: Arlo Weil Laramide foreland deformation in Wyoming represents a classic tectonic province, yet there are outstanding questions about the kinematic and mechanical processes responsible for the mountain systems seen today. The archetype Laramide orogen, which spans over 1,200km from Central Montana to New Mexico, was formed during the Late Cretaceous to […]

Kinematics of Laramide Deformation

Posted July 10, 2011

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, […]

Investigating the Laramide Deformation of the Rocky Mountains

Posted June 29, 2010

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.

Paleomagnetic and Structural Investigation of the Wyoming Salient: Insights into the Curvature of Mountain Belts

Posted May 28, 2010

Curved mountain belts are common throughout the world, but the controlling factors and mechanisms in their formation are not well understood and likely vary from location to location. The Wyoming Salient (term for curved orogen that is convex towards the mountain belts interior) in the Sevier Mountains of the Western United States is an example of a classic curved mountain belt on which much research has been done, making it an ideal location to explore questions about the kinematics and mechanics of curved orogens. The first order question for any curved mountain belt is whether curvature was attained at the beginning of mountain belt formation (primary arc), formed after mountain-building was complete (orocline), or curved progressively as the belt developed (progressive orocline). If the rocks making up the mountain belt rotated about a vertical axis (suggesting curvature occurred after or during initial formation of the orogen), this will be revealed in the orientations of magnetic minerals in rocks within the arc. Paleomagnetism, the study of the Earth’s ancient magnetic field as it is recorded in the rock record, is an ideal tool to quantify these rotations.

Analysis of Deformation History Using Anisotropy of Magnetic Susceptibility in the Brevard Zone, North Carolina

Posted May 28, 2010

The Brevard Shear Zone is a prominent tectonic feature in the Appalachian Mountains . A shear zone is an area that has undergone intense deformation due to motion along a fault deep in the Earth’s crust. As the rocks in the zone accommodate stress they deform in a ductile fashion such that they do not break or lose cohesion. Consequently, the deformation history of the area is recorded by changes in the internal shape and orientation of the initial rock fabric.

Anisotropy of Magnetic Susceptibility (AMS) can be used in shear zones to determine the intensity and orientation of deformation, which is often difficult to assess. AMS is based on the fact that all minerals are susceptible to acquiring a magnetization, and because each mineral has a unique crystallographic shape, a mineral’s magnetic susceptibility varies with orientation. AMS measurements record the variability of susceptibility with orientation, which can be strongly affected by deformation. Every rock forms with an initial magnetic susceptibility fabric that is the result of the original rock-forming environment. Different geologic processes can subsequently alter a rock’s primary fabric, producing a finite strain geometry that can be analyzed and interpreted using AMS.

An Investigation of the Wyoming Salient: The What, When, Where, and Why of Mountain Belt Curvature

Posted May 28, 2010

The mechanics behind the formation of mountain belts is a central aspect of structural geology. As most mountain belts display some curvature in their plan view, the development of curved mountain belts is of particular interest. Curved mountain belts are classified into three different groups based on their kinematic history, or the means and timing by which they acquire their curvature. Primary Arcs are curved during the initial phase of formation, Oroclines are belts that acquire their curvature during a secondary deformational phase, and Progressive Oroclines are mountain belts that acquire their curvature synchronous with deformation. Thus, answering the question of when curvature in a mountain belt occurred is essential to understanding their formation. This summer’s project will focus on the Wyoming Salient, a highly curved portion of the Rocky Mountains between Jackson Hole , Wyoming and Salt Lake City , Utah .

David Wicks in 2009

Posted May 12, 2010

The kinematic evolution of curved mountain belts can be examined by combining several different types of paleomagnetic analyses with detailed structural studies of finite strain. The combination of these methods provides a data set varied enough to produce quantifiable data that can be compared to general patterns of curvature in mountain belts. While many mountain belts have been assessed in this method, not much analysis has done on what occurs simultaneously farther into the foreland of the continent. We are now examining the expression of orogenies(mountain building events) in locations further away from the source of deformation, as well as seeing if the same analytical methods can still be used to create a rigorous model for the dynamics of the creation of a mountain chain.

Explaining the Kinematics of the Kootenay Arc: a Paleomagnetic Analysis

Posted May 11, 2010

Many mountain (orogenic) belts are curved like a bow in map view (e.g., the Appalachians, Himalayas, Alps, etc.). These orogenic belts can fall under one of three kinematic (history of deformation and motion) classifications: the belt was initially curved and experienced no rotation (primary arc); the belt was originally linear and experienced rotation (orocline); the belt acquired it’s rotation as it was being formed, or was initially bent and experienced further rotation (progressive arc). To date, the only robust and quantitative method of determining vertical-axis rotations is paleomagnetism (the study of the Earth’s ancient magnetic field as it is recorded in the rock record). When combined with structural and geologic data, paleomagnetic data is an extremely useful tool for constraining the kinematics of a curved orogen. Our study concerns the curvature of the Kootenay Arc in British Columbia, Canada. The Kootenay Arc, situated in the Canadian Rockies, is thought to be one of a number of terranes that have collided with what was once the western margin of North America. Previous papers have described this arc as both an orocline and as a primary arc. There has, however, been no paleomagnetic study of this region. Ferromagnetic minerals present in most rocks align themselves with the Earth’s magnetic field, and as a result record the rock’s paleo-latitude as well as the rock’s orientation with respect to the Earth’s spin-axis at the time of magnetization acquisition. If the ChRM (Characteristic Remanant Magnetizion) of a rock is acquired prior to the deformation that generates the orogenic belt, then kinematic classification of the belt should be relatively straight forward. The ChRM of a primary arc would show no rotations, the ChRM of an orocline would show a one-to-one correlation between rotations and map-view curvature, and the ChRM of a progressive arc would show a correlation between structural trend and magnetization that is less than one-to-one (orocline), but greater than zero (primary arc). Professor Arlo Weil, Alexi Ernstoff, and I plan to obtain samples from the Kootenay Arc that can be used for paleomagnetic analysis. The eventual goal of this project is to use paleomagnetism to help explain the kinematics of the Kootenay Arc, and thus broaden our understanding of orogenic evolution in general and the evolution of the Rocky Mountains in specific.

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