1. Quantification of hydrothermal fluxes between seawater and ocean
crust Circulation of seawater through ridge flanks occurs at low temperatures
(<100°C), but because the fluid fluxes are so large the chemical
effects are comparable to or greater than the more spectacular high-temperature
axial systems that result in black smokers and sulfide deposits.
These flank systems may be the main sink for seawater Mg in the crust,
and the uptake of alkalis may balance the input from high temperature reactions
at the ridge axes.
In a recently submitted paper (Alt and Teagle, 1998) we show
that Carbon uptake in these flank systems exceeds outgassing at ridges,
and should be significant in the sedimentary carbon cycle and subduction
recycling. We have also documented evolution of temperature and fluid
composition in different portions of a well-documented ridge flank circulation
system (Alt et al., 1996a,b; Teagle et al., 1996), and I am continuing
this work at other seafloor sites. This work also has significance
for understanding recycling of altered ocean crust in subduction zones.
Other projects focusing on the 2 km Hole 504B upper crustal section
are dedicated to understanding the evolution of water-rock interaction
and controls on the isotopic compositions of hydrothermal fluids, and the
net composition of altered crust. (Alt et al., 1996a,b,c; Teagle et al.,
1995, 1997, 1998). We have extablised profiles for Li contents
and isotopic compositions (Chan et al., 1996 abstract), documenting a balance
between ridge crest and flank activity.
Data for alteration and vein abundances and distributions (Alt
et al., 1996a,b) are being combined with ICP-MS data for trace elements
in order to understand the mobility and distribution of these elements,
and to quantify their alteration budgets (Alt et al., 1997 abstract) In
collaboration with J. Erzinger, GeoForschungZentrum, Potsdam, FRG, and
W. Bach, Woods Hole Oceanographic Institution. Elements of particular
interest that exhibit significant mobility include Pb, U, Th, Cs, Tl, Rb,
and Ba. We also provide the first data for significant hydrothermal
mobility of Sb, Sn, Mo, and Cd.