Mountain Belt Geology

Posted May 10th, 2010 at 12:00 pm.

Anna Mazzariello

Mentor: Arlo Weil

One of the long standing debates in geology is how mountain belts (e.g., Appalachians, Alps) become curved in their map view. My summer research project is focused on understanding, quantifying and classifying the actual rotations involved in curvature formation in two belts – the Wyoming Salient (a “salient” is a geometric term meaning that there is a curvature towards the foreland) in the western U.S. and the Cantbrian Mountains in northern Spain. Ultimately this work will lead to a better understanding of the evolution of curved mountain belts in general. Paleomagnetism, the study of the earth’s ancient magnetic field as recorded in the rock record, will be used to quantify the rotations, document fold and deformation evolution, and construct an internally consistent deformation history for the two belts.

It should be noted that just because a mountain belt is curved, does not necessarily require that the belt experienced significant rotation during its formation. In fact many belts have a primary curvature related to the ancient geometry of the landscape prior to mountain belt evolution. Consequently, the first step in understanding the evolution of a belt is classifying the relationship between a belts curvature and its total experienced rotation. The term orocline refers to a mountain belt configuration where first a linear mountain belt is created through convergence, and then it is bent into a horseshoe shape—like bending a long eraser between your thumb and index finger. A primary arc describes when curvature is acquired during an initial deformation event without significant secondary rotation. Lastly, a progressive arc acquires its curvature progressively throughout the belt’s deformation history.

The two mountain belts that we are researching and classifying this summer are the Wyoming Salient and the Cantabrian Arc. The Wyoming Salient (a portion of the Rocky Mountains between Salt Lake City, Utah and Jackson, Wyoming) is argued to me created through a deformation gradient where deformation is greatest at the tips of the salient and less in the midsection, causing the entire salient to bend. This gradient is an example of “work hardening”, where the pile-up of strain at the salient tips causes the geology to lock itself in place. On the other hand, the Cantabrian Arc is related to the convergence between Gondwana (an ancient landmass that encompassed all of the southern hemisphere continents) and Laurussia (an ancient continent that comprised North America and northern Europe). The curvature in the Cantabian Arc was acquired in two phases: 1) the early phase was an east-west shortening event that produced a north-south linear belt, and 2) a final phase in which north-south shortening caused arc tightening.

With increasing research and understanding, hopefully an accurate, three-dimensional kinematic model of mountain belt curvature can be created for both the Wyoming Salient and the Cantabiran Arc, and ultimately these models will enlighten our understanding of mountain belt curvature in general.

Filed under: 2006,Mazzariello, Anna,Weil, Dr. Arlo by Ann Dixon

Comments are closed.