A synthesis of geological and geochemical investigations of the TAG hydrothermal field; insights into fluid-flow and mixing processes in a hydrothermal system

Author(s): Humphris, Susan E.; Tivey, Margaret K.
Author Affiliation(s): Primary:
Woods Hole Oceanographic Institution, Department of Geology and Geophysics, Woods Hole, MA, United States
Other:
University of California at Davis, United States
University of Houston, United States
Université de Montpellier II, France
Volume Title: Ophiolites and oceanic crust; new insights from field studies and the Ocean Drilling Program
Volume Author(s): Dilek, Yildirim, editor; Moores, Eldridge M.; Elthon, Don; Nicolas, Adolphe
Source: Special Paper - Geological Society of America, Vol.349, p.213-235; Penrose conference on Ophiolites and oceanic crust; new insights from field studies and the Ocean Drilling Program, Marshall, CA, Sept. 13-17, 1998, edited by Yildirim Dilek, Eldridge M. Moores, Don Elthon and Adolphe Nicolas. Publisher: Geological Society of America (GSA), Boulder, CO, United States. ISSN: 0072-1077. ISBN: 0-8137-2349-3 CODEN: GSAPAZ
Note: In English. 103 refs.; illus., incl. 6 tables, sketch map
Summary: The TAG (Trans-Atlantic Geotraverse) hydrothermal field (26°08'N on the Mid-Atlantic Ridge) is one of the largest and best-studied sites of high-temperature hydrothermal activity and mineralization that has been found to date on the seafloor. The assemblage of active and relict deposits, with ages ranging from 0 to 140 ka, attests to a long, complex and episodic history of hydrothermal activity that appears to be controlled dominantly by large-scale faulting associated with the formation of the eastern wall of the median valley. The alternation between periods of activity and quiescence may reflect either episodic magmatism and the replenishment of the heat source or the occurrence of faulting events that reactivate fluid-flow pathways. The construction of large circular mounds, rather than the elongate deposits commonly seen in ophiolites, requires focusing of fluids along discrete pipe-like up-flow zones. Geochemical and isotopic studies of the TAG active mound and underlying shallow up-flow zone provide strong evidence that variable amounts of entrainment of seawater play a key role in the generation of distinct fluid chemistries and the minerals that form the precipitates, the alteration of the basalts, and the growth and structural evolution of the entire deposit. We present a model for the formation and growth of the TAG active mound in which the current activity is dominated by seawater entrainment and precipitation of anhydrite due to the vigorous and focused nature of the current black smoker activity. We suggest that the pervasive, high-temperature alteration of the basement in the shallow up-flow zone likely occurs during either waxing or waning of activity, when subsurface fluid-flow rates are substantially lower and seawater entrainment is not as prevalent.
Year of Publication: 2000
Research Program: ODP Ocean Drilling Program
Key Words: 18 Geophysics, Solid-Earth; Atlantic Ocean; Black smokers; Crust; Hydrothermal vents; Leg 158; Magmatism; Massive deposits; Massive sulfide deposits; Mid-Atlantic Ridge; Mid-ocean ridges; Mineralization; North Atlantic; ODP Site 957; Ocean Drilling Program; Ocean floors; Oceanic crust; Ophiolite complexes; Plate tectonics; Sea-floor spreading; Spreading centers; Sulfides; TAG hydrothermal field; Volcanic features
Coordinates: N260600 N261000 W0444600 W0444800
Record ID: 2002010614
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