Hydrothermal Circulation Beneath and Within Active Vent Deposits: A Preliminary Model of the Effect of Chemical Reaction on Fluid Flow


DOEI Project Funded: 2002

Proposed Research

Seafloor hydrothermal vent sites are the locus of significant exchanges of heat and mass from the deep Earth to the ocean. The mineral deposits that exist at these sites range in size from 10 to 150 meters and form as a result of complex and poorly understood interactions among hydrothermal fluid, seawater, solid substrates, and biological organisms. In addition, these deposits and the ocean crust directly beneath harbor important chemosynthetically based biological communities. In this project, we will model fluid flow at hydrothermal vents with the goal of understanding the interaction between source fluids and the feedback between mineral precipitation and fluid flow at these sites.

Final Report

What were the primary questions you were trying to address with this research?
Seafloor hydrothermal vents are the locus of heat and mass exchange between the solid earth and the overlying ocean. The goal of this study is to develop a model to map out thermal and chemical regimes, including fluxes, within active vent sites. The modeling results can provide important information on ore deposit formation, and possible habitats for microorganism and macrofauna.

What have you discovered or learned that you didn't know before you started this work?
We used a modified 2-D finite element code SUTRA to simulate density-dependent fluid flow and energy transport at the TAG hydrothermal mound. Our simulation results indicate that heterogeneous permeability structure is required for vent fluid to flow out from the main conduit into the surrounding mound. We also demonstrated that fractures within the mound can serve as fast conduits for flows, and these fast conduits may play an important role in the mixing of the high temperature vent fluid and cold oxygenated seawater.

What is the significance of your findings for others working in this field of inquiry and for the broader scientific community?
It has been recognized that in order to adequately map out the range of environments in which microbes may reside, we must have a better understanding of how high temperature reduced vent fluids and cold, oxygenated seawater interact within the outflow portions of vent sites. Our work will elucidate the factors that control the distributions of related focused and diffused flow, the precipitation of important mineral deposits, and the likely thermal and chemical environments present within and at the seafloor vent sites.

What is the significance of this research for society?
Seafloor vent deposits are analogs of a type of economic deposit (volcanic-associated massive sulfide). Our research will elucidate the factors that control the distribution of economic metals (i.e., Ag, Au, Cd, Sb, Se, Co) within these types of massive sulfide deposits.

What were the most unusual or unexpected results and opportunities in this investigation?
This project provided the opportunity for 3 researchers (Wen-lu Zhu , Ann Mulligan and Meg Tivey, who is a DOEI fellow from 2001-2004) with very different background to apply their combined expertise to model a complex system. Our most surprising result was that we could simulate the existing thermal regime within the TAG mound simply by assuming that there exists a constriction within the vent conduit.

What were the greatest challenges and difficulties?
The numerical model is complex and requires tight controls on computational progress. This results in simulations that require a significant amount of time to run. This difficulty will ultimately limit either the size of the vent system or the geologic complexities that can be represented in the model.

When and where was this investigation conducted?
This research presents a new analysis of existing data, and took advantage of M.K. Tivey’s expertise in seafloor vent deposits, Wen-lu Zhu’s expertise in fluid transport properties, and Ann Mulligan’s expertise in hydrogeology and groundwater modeling.

Is this research part of a larger project or program?
The numerical modeling is done on PCs.

What are your next steps?
This study led to a new NSF proposal “Numerical modeling to elucidate factors controlling distributions of focused and diffused flow at mid-ocean ridges” (PIs: Ann Mulligan, Meg Tivey, and Wenlu Zhu, submitted 8/15/2004).

We have developed a modified version of the 2-D finite element code SUTRA to simulate the flow filed at the TAG mound. Our immediate next step is to refine our model by incorporating feedback mechanisms to best reproduce the field observations. We will apply this model to other vents sites such as East Pacific Rise (EPR) hydrothermal field and Endeavour Hydrothermal field.

Please provide some biographical information, such as place of birth, degrees earned, significant awards or honors, research interests, reasons why you became a scientist or why you are interested in this line of research, and any personal interests, hobbies, or details that you are willing to share. You can find a few good examples here:

Wen-lu Zhu is an associate scientist in the G&G department. She received the Mineral and Rock Physics Best Student Award (1997) for her Ph. D. thesis work at SUNY Stony Brook. Her research interest is to understand fluid transport processes in the Earth’s crust and mantle, and their geological implications. Ann Mulligan is an assistant scientist in the Marine Policy Center. Her research interests are in groundwater-seawater interactions and modeling fluid flow in porous media.