Eos, Transactions American Geophysical Union

Cores drilled into active smokers on Juan de Fuca Ridge



The October 1991 Chronology expedition to the Endeavour Segment of the Juan de Fuca Ridge sought to exploit shipboard and land-based radioisotope analyses based on detailed geological observations and comprehensive sampling to determine the absolute ages of an actively venting ridge-axis hydrothermal field. Samples collected from a 1988 expedition indicated that some of the hydrothermal deposits in this area are unusually rich in barium (Ba) and radium (Ra) and thus extraordinarily amenable to radioisotopic techniques [Stakes and Moore, 1991]. An in situ gamma detector was developed to permit mapping of the distribution of radioactive components in the hydrothermal deposits and selection of subsamples that could easily be dated. To obtain samples that represent progressive mineral growth for the entire age of a chimney, we developed the HSTR drill (Figure 1), a diamond-bit drill to be operated by the submersible ALVIN.