Article,
The Grimsey hydrothermal field offshore North Iceland: crustal structure, faulting, and related gas venting
Earth and Planetary Science Letters, 193 (3-4): 409--421 (Dec 15, 2001)
DOI: 10.1016/S0012-821X(01)00519-2
Abstract
The results of a combined geophysical and geochemical research program
are presented that focused on Grimsey hydrothermal field (GHF) which
is located at 66:35:30N, 17:39:30W east of the island of Grimsey
in the Tjörnes Fracture Zone. The vent field is situated at the
sourthernmost tip of a submarine ridge which is connected to the
offshore part of the Theistareykir Fissure Swarm. Reflection seismic
recordings were interpreted in conjunction with earthquake catalogue
data to detect active fault structures and potential heat sources
in the subsurface. An inter-linked fracture network forming a downwards
converging system of faults connected to a deep-reaching normal fault
is assumed to provide the preferential pathways for gases (3He, CO2,
CH4 etc.) migrating from a possible deep-seated gas source (lower
crust/upper mantle) to the surface.The location of hydrothermal vents
was detected by concentration measurements of dissolved methane in
the water column, which coincide with polarity reversals in the seismic
seafloor reflection. Both the molecular composition of the gas and
the isotopic composition of methane at GHF indicate a predominating
abiogenic source (Fischer-Tropsch reactions at 250-500C) mixed with
thermogenic hydrocarbons. New seismic data from the GHF were compared
with gas geochemical data which indicate that the thermogenic hydrocarbons
are related to (up to 60 m thick) sediments deposited in a basin
located east of the ridge.
