Layer-Parallel-Shortening Strain: a Key to the Sevier-Laramide Deformational Sequence in the Tendoy Range, Southwestern Montana

Identifier

6067

Author

Christopher Dale Loyacano

Date

2017

Document Type

Thesis

Degree Name

Master of Science

Major

Earth Sciences

Concentration

Geology

Committee Chair

Mervin J Bartholomew

Committee Member

Daniel Larsen

Committee Member

Youngsang Kwon

Abstract

Layer-parallel-shortening (LPS) strain records the first strain experienced by rocks during tectonic events. LPS indicators preserved in vertical to overturned fold limbs along the leading edge of the fold-thrust belt in southwestern Montana are used to determine which deformation came first there: Sevier or Laramide. LPS-strain was analyzed for 22 samples collected in the Dixon Mountain area from different beds containing ooids, Pentacrinus, or brachiopods within a 580-meter stratigraphic interval. Field orientations of strain ellipses were then adjusted for: 1) trend and plunge of fold axes; 2) rotation of thrust sheets relative to the trend of the Sevier-emplaced, overturned Deadwood Gulch syncline; and 3) bedding dip. Retrodeformed orientations of 15 samples show an average shortening direction of ~227o, consistent with Sevier shortening (~213o); 4 samples show a shortening direction of ~268o; and 3 samples show a shortening direction of ~171o, perhaps indicating Sevier shortening across a lateral ramp.

Comments

Data is provided by the student.

Library Comment

Dissertation or thesis originally submitted to the local University of Memphis Electronic Theses & dissertation (ETD) Repository.

Recommended Citation

Loyacano, Christopher Dale, "Layer-Parallel-Shortening Strain: a Key to the Sevier-Laramide Deformational Sequence in the Tendoy Range, Southwestern Montana" (2017). Electronic Theses and Dissertations. 1752.
https://digitalcommons.memphis.edu/etd/1752