Document Type

Thesis

Date of Degree Completion

Spring 2019

Degree Name

Master of Science (MS)

Department

Geological Sciences

Committee Chair

Dr. Audrey Huerta

Second Committee Member

Dr. Paul Winberry

Third Committee Member

Dr. Walter Szeliga

Abstract

Continental rifting is a fundamental earth process that displays a wide variety of styles ranging from narrow to wide, symmetric and asymmetric, magmatic and amagmatic. The key conditions and processes that control the evolution of rifts remain enigmatic. Previous research suggests that the initial thermal structure may have a first order control on the evolving styles of these systems. This project examines the impact of the initial thermal structure on the spatial and temporal evolution of continental rifts using finite element thermo-mechanical modeling.

The initial thermal structure is a product of crustal heat production rates and heat conducted from the asthenosphere (lithospheric thickness); therefore, we explore the impact of varying crustal heat production rates from 0.75 to 2.25 µw/m3, and lithospheric thicknesses of 100 to 200 km. The model captures continental lithospheric crust and mantle with an orogenic welt of over-thickened crust. The modeled strength, strain field, and thermal structure evolve in response to initial conditions using an iterative time-stepping algorithm. The model results display distinct styles of continental rifting.

Simulations with initially cold temperatures at the base of the orogenic crustal welt result in narrow rifts. Simulations with initially cooler temperatures at the base of the crustal welt result in symmetric rift geometries, while simulations with initially higher basal crust temperatures deform asymmetrically. Simulations with more asthenospheric contribution to basal crust temperatures evolve as wider rifts, whereas simulations with more crustal contribution evolve as less wide rifts.

Thus, our results show that the initial thermal structure has a first-order control on the symmetry of rifting, on wide versus narrow extension styles, and the width of the rift zone. Models compare favorably to real rift systems such as the Red Sea Rift and the West Antarctic Rift System, verifying the application of the models.

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