210Po-210Pb Dating of Very Young Submarine Basalts
The 210Po-210Pb dating technique provides ages of eruptions having occurred within
about 2 years of sample collection (Rubin et al., 1994). With this method one monitors the rate of change
of 210Po with time in a lava once it is sampled, to determine the date of eruption. Upon eruption,
210Po is degassed by the lava while its radioactive grandparent 210Pb is not significantly
volatilized. Following eruption, this Po isotope "grows back" toward radioactive equilibrium with
210Pb over a 138.4 day half-life. This phenomenon is illustrated in Figure 1.
We developed this dating method back in 1991 after divers in the manned submersible Alvin appeared on the scene soon after a submarine eruption at 9° 50'N on the East Pacific Rise (EPR), to determine when the eruption had occured. We have also applied this technique to lavas collected after suspected submarine eruptions at NW Rota-1 seamount, the Northeast Lau Spreading Center, Axial Seamount (project underway), the 2005-06 eruption at 9° 50'N and 2004 eruption 10° 45'N on the EPR, the Gorda Ridge, Boomerang Caldera (near South East Indian Ridge), and the Loihi Eruption in Aug 1996.
|Figure 1. Changes in 210Po in a single lava revealed by repeated measurements over time. Regression of the data to an ingrowth curve allows one to date the time since degassing (eruption).|
Our best-estimate of the timing of three example eruptions .
This figure is from an article in the NSF Ridge2000 program newsletter (Spring 2005, which is available in pdf-format)
For more info please see these papers, and the references therein:
KH Rubin, SA Soule, WW Chadwick, DJ Fornari, DS Clague, RW. Embley, ET Baker, MR Perfit, DW Caress, RP Dziak (2012) Volcanic Eruptions in the Deep Sea, Oceanography, 25(1), 142–157, http://dx.doi.org/10.5670/oceanog.2012.12.
ET Baker, WW Chadwick, JP Cowen, RP Dziak, KH Rubin, DJ Fornari (2012) Hydrothermal discharge during submarine eruptions: The importance of detection, response, and new technology, Oceanography, 25(1), 128–141, http://dx.doi.org/10.5670/oceanog.2012.11.
Rubin, K.H., Macdougall, J.D. and Perfit, M.R. (1994) 210Po-210Pb dating of recent volcanic eruptions on the sea floor, Nature, 368, 841-844.
Isotope Lab |
[ KenChron | Isotope Lab | SOEST]