Assessing segment-scale compositional control over slow-spreading ridge morphology

University Of Nebraska-Lincoln, Lincoln NE

Investigators

Abstract

The formation of oceanic crust at mid-ocean ridges is a major component of plate tectonics, and plays a key role in long-term chemical cycles and energy budgets on Earth. The seafloor topography observed at mid-ocean ridges is generated through a combination of faulting and volcanic eruptions, but the underlying factors that control faulting and volcanism remain only partially understood. Variations in these two processes can result in dramatically different crustal and seafloor characteristics, particularly at mid-ocean ridges that spread apart at slow rates. This study uses the geochemistry of seafloor lavas erupted at the slow-spreading Mid-Atlantic Ridge to investigate and understand how underlying variations in Earth's mantle layer might influence the vigor of volcanic activity and therefore, the physical characteristics of the seafloor itself and the structure of the oceanic crust. The project supports the training of a PhD student, and public outreach materials describing the project will be distributed through the University of Nebraska State Museum. This project aims to investigate the causes of underlying variations in magma flux to slow-spreading ridge axes, which in turn drive crustal construction style and the presence, absence, or episodicity of long-lived detachment faults at the ridge axis. The project rationale is that constraints on crustal construction mechanisms will ultimately lead to a robust, comprehensive model that will accurately characterize global crustal growth at all spreading rates. The central hypothesis tested in the project states that slow-spreading ridge morphology is principally controlled at the segment scale by the compositional heterogeneity of the underlying mantle. The specific research goal for the proposed study is to identify and assess geochemical variations that fingerprint the contributions of partial melts derived from enriched, fertile mantle rocks at the ridge segment length scale. The project principally uses U-Th-Pa-Ra isotope disequilibria, which are particularly sensitive to mantle melt fertility. Disequilibria will be assessed through comparisons between second-order ridge segments that exhibit distinct morphologic types along the Kane-Atlantis supersegment of the northern Mid-Atlantic Ridge between 24-30N.