Thrust belt curvature: Structural and paleomagnetic analyses in the Catalunyan Pyrenees and Sevier orogen
AdvisorChase, Clement G.
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PublisherThe University of Arizona.
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AbstractThe question of how curved geologic structures form, from arcuate faults to curvilinear orogenic belts, is one that transcends scale as well as rock properties. Many scale-independent lines of evidence suggest that material within fold-thrust belts is transported in three dimensions. Paleomagnetic analysis is the primary method for determining distribution and magnitude of vertical-axis rotations in arcuate regions. Thus paleomagnetic information is essential to deciphering the three-dimensional kinematic evolution of a curved orogen. In addition, most studies of foreland fold-and-thrust belts focus on geometries and timing relationships, but do not identify the deformations internal to the thrust-bounded rock packages. The Southern Pyrenean and Sevier orogenic systems both provide an outstanding opportunity to investigate thrust-belt curvature by integrating paleomagnetic and structural studies. This dissertation addresses the interplay between three-dimensional motions and the structures they cause. In the Pyrenees, the Oliana anticline is a foreland structure related to the South Central Salient, a major curve in the thrust belt. Paleomagnetic data from the Oliana anticline document counter clockwise rotations about a vertical axis. The average rotation is R ± Δ R = -19.6° ± 10.5°. Based on the stratigraphic horizons that record the rotation, as well as the structural evolution of the Oliana anticline, the age of rotation is ≥ 35 Ma. This rotation is attributed to continued motion along the Serres Marginals thrust, causing rotation along the blind thrusts that underlie the Oliana anticline. Mode I fracture data from this region highlights the progressive development of joints in growing structures. Measurements were taken from four regions around the anticline, and from four sequential synorogenic conglomerates. A consistent NW-SW orientation for the development of joints was determined by performing sequential restorations of the Oliana anticline and incrementally analyzing joint orientations. Reanalysis of previously published data from the Wyoming salient of the western United States demonstrates the relationship between irregular fault traces and the three-dimensional motions that caused them to form. Interaction between rotation, strain and net translation is a global phenomenon and suggests that geologic shortening estimates can be improved by incorporating the effects of tectonic rotations.
Degree ProgramGraduate College