Thermal Stress Models for Hydrothermal Circulation, and Relation to Microseismicity Near 9°50'N Along the East Pacific Rise

Author

Karen Godfrey, Southern Illinois University CarbondaleFollow

Date of Award

8-1-2011

Degree Name

Master of Science

Department

Geology

First Advisor

Conder, James

Abstract

Hydrothermal circulation at mid-ocean ridges plays an important role in the interaction between oceanic lithosphere and the overlying ocean. Changes in fluid flux within hydrothermal systems may directly impact ocean circulation, temperature, and chemistry, and hence the lives of biological organisms in hydrothermal vent environments. The permeability structure within a hydrothermal environment is an important control on fluid flow throughout the system. Common suggestions for mechanisms that might increase permeability within the system include thermal cracking due to contraction of the hot rock from interaction with cold seawater, fluid pressure of the water moving through the rock, tectonics, or tidal forces. Additional factors such as mineral precipitation can decrease permeability in the system, further complicating the permeability structure. Though there are many factors to consider within a hydrothermal system, few quantitative studies of these cracking mechanisms exist. This study examines the role of thermal cracking near hydrothermal vents via a numerical model created in Matlab. Flow was modeled using the Laplace equation, and the heat transfer equation was used to determine temperature differences in the rock, which lead to thermal cracking. The numerical results were compared with microearthquakes observed by Tolstoy et al. (2008) near a hydrothermal vent field along the East Pacific Rise. The model suggests that thermal cracking does occur, and this cracking occurs within the area of microearthquakes observed. Though thermal cracking is important for increasing permeability within the system, there are no obvious spatial or temporal trends within the earthquake data that support a direct relation between the modeled thermal cracking and observed earthquakes. It is likely that the observed earthquakes are due to a combination of cracking mechanisms, such as cracking due to fluid pressure, tectonics, or tides, in addition to the modeled thermal stresses.