Special Lamont75 Earth Science Colloquium, where eminent alumni and former staff showcase their research and reflect on what makes LDEO special presents:
Milankovitch writ large? Models of sea-level control on fault pacing at fast-spreading mid-ocean ridges
with Dr. Richard Katz, Professor of Geodynamics, University of Oxford.
Abstract
Mid-ocean ridges are flanked by a progression of fault-bounded abyssal hills that represent the most common topographic pattern on Earth. The wavelength spectrum of measured abyssal-hill topography contains the fingerprint of orbital cycles including the eccentricity and obliquity of Earth's orbit around the sun [1]. How would such cycles come to be imprinted on abyssal hills? We develop a theory that is driven by the record of variations in sea-level over the past 2 million years. These variations are climatically controlled, and hence are characterised by the orbital-cycle frequencies. The rate of sea-level change drives variations in melting rate and hence mid-ocean ridge crustal thickness [e.g., 2]. When the oceanic plate moves away from the topographic high of the mid-ocean ridge, it flattens out due to the force of gravity [3]. This unbending creates stresses in the plate that induce faulting. We show that tiny variations in crustal thickness can control the spacing of faults, and hence can transfer the sea-level frequencies into the spacing of abyssal hills.
This prediction arises from a novel theory for abyssal-hill formation. The theory assumes Euler–Bernoulli bending of a thin, elastic–viscoplastic plate. In the absence of plate thickness variations, it produces spaced plastic kinks representing tectonic faults. Even at very low amplitude of perturbations, these kinks/faults undergo nonlinear phase-locking with the crustal/elastic thickness. This suggests that if unbending is an appropriate model of tectonic stress generation at fast-spreading mid-ocean ridges, the signature of sea-level variation will be readily imparted on abyssal-hill topography. Using temporally aligned bathymetric data from the Juan de Fuca ridge, we show that rapid changes in sea level are associated with large-throw normal faults, consistent with the theory.
Host: Dr. Marc Spiegelman, Arthur D. Storke Memorial Professor, Department of Earth and Environmental Sciences (DEES), Columbia Univsersity.
The Earth Science Colloquium Series The Earth Science Colloquium Series, sponsored by Lamont-Doherty Earth Observatory and Columbia University Department of Earth and Environmental Sciences (DEES), provides a lively forum for discussing a wide variety of topics within the Earth sciences and related fields. Colloquia are attended by the full range of scientific and technical staff at LDEO. Colloquium attendance is required of all pre-orals DEES graduate students. The Colloquium Series supports the Lamont Seminar Diversity Initiative.
