Fully three-dimensional numerical models for along-axis variations in magmatic and tectonic processes at slow-spreading mid-ocean ridges

University Of Memphis, Memphis TN

Investigators

Abstract

The recent observations of oceanic core complexes (OCCs) are intriguing. OCCs are formed when faults keep slipping and eventually exhume lower crust and mantle rocks onto the seafloor. OCCs not only provide a glimpse into Earth's mantle by uncovering deep-seated rocks, but they commonly have hydrothermal vents associated with them which host large ecosystems. When first discovered, OCCs were assumed to form primarily near the ends of slow-spreading mid-ocean ridge segments where magma supply is low. However, they also have been found at locations far from spreading segment ends. Moreover, in some place the formation of OCCs alternates with normal seafloor spreading which produces short-lived faults. It is unclear what controls the alternating faulting styles. This project will produce a three-dimensional mechanical model to understand the controls on the formation of OCCs at mid-ocean ridges. The overarching goal is to understand the role of faulting in the formation and evolution of the ocean basins. The project will recruit undergraduate students to participate in the research with a priority on identifying participants from groups traditionally underrepresented in the sciences. Movies will be generated explaining the model and model results and will be used in graduate courses and adapted for use in K-12 schools. Diking frequencies and faulting styles are highly variable at slow-spreading mid-ocean ridges and correlated with each other to some degree. However, our understanding of the mechanism behind the correlation and other factors controlling faulting styles is still incomplete. The objectives of this project are to establish the mechanism that determines faulting styles in response to spatially and temporally varying diking frequencies at slow-spreading ridges and to quantify the sensitivity of the mechanism to fault-lubricating processes and magma extrusion and under-plating at spreading centers. The project proposes to develop a three-dimensional (3D) modeling approach by extending an existing two-dimensional (2D) method that has been successful in explaining the main morphological and structural features in across-axis sections of mid-ocean ridges in terms of diking frequencies. The fully 3D numerical models incorporate the along-axis mechanical loading arising from variability in diking and faulting. Furthermore, the modeling method will consider other important factors affecting faulting styles such as lubrication effects of frictionally weak minerals forming on fault surfaces. Four suites of numerical experiments will be conducted in the order of increasing complexity.