The 176Lu Decay Constant Controversy

Details The 176Lu Decay Constant Controversy The 176Lu Decay Constant Controversy

Dec 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.v52b1293s&link_type=abstract

American Geophysical Union, Fall Meeting 2002, abstract #V52B-1293

Mathematics

Logic

1020 Composition Of The Crust, 1025 Composition Of The Mantle, 1035 Geochronology, 3662 Meteorites, 8125 Evolution Of The Earth

Scientific paper

The Lu-Hf systematics of Earth\'{}s earliest zircons and rocks provide clues about the differentiation of the mantle into depleted and enriched reservoirs. However, initial ɛHf values and the interpretations derived from them hinge on the accuracy and precision of the 176Lu decay constant. At present, there is still a serious discrepancy between 1) 176Lu decay constants determined by physical counting methods and age comparisons of terrestrial samples, and 2) those determined by age comparisons of meteorite suites. The mean Lu decay constant determined by of the two most recent physical decay counting experiments [1, 2] together with 4 independent geological age comparisons [3] is 1.87 x 10-11yr-1. In contrast, decay constants determined by age comparisons in meteorites are systematically higher, with a mean value of ~1.95 x 10-11yr-1 (including eucrite data from [4, 5, 7, and this abstract] and chondrite data from [6]). The slope of a Lu-Hf isochron for four eucrites (Juvinas, Millbillillie, Pasamonte, and Moama) analyzed at M\x81nster by MC-ICPMS would suggest a decay constant of 1.97 x 10-11yr-1. Since the terrestrial age comparisons in [3] were made using the same methods and spike calibrations as for the Muenster eucrite isochron, the disagreement between the two sets of decay constants is apparently not an inter-laboratory artifact. Rather, a possible explanation for the disagreement may be that the meteorites do not conform to all of the assumptions required for an isochron (e.g., that all samples have the same age, all have the same initial Hf isotope composition). The Lu decay constant discrepancy must be resolved before any robust interpretations can be drawn from the initial ɛHf of Archean or Hadean samples with Lu/Hf ratios that differ significantly from the chondritic value (e.g., zircons). The existing Hf data viewed in light of a "high" decay constant would suggest substantial mantle depletion in the early Archean without much evidence for a complimentary enriched reservoir. On the other hand, the "low" decay constant would provide evidence for small volumes of enriched reservoirs, but no large-scale mantle depletion. [1] Dalmasso et al. 1992. Appl. Radiat. Isot. 43: 69-76. [2] Nir-El and Lavi 1998. Appl. Radiat. Isot. 49: 1653-1655. [3] E.E. Scherer et al. 2002. Science 293: 683-687. [4] Patchett and Tatsumoto 1980. Nature 288: 571-574. [5] Tatsumoto et al. 1981. Mem. Natl. Inst. Polar Res. (Tokyo), Special Issue 20: 237-249. [6] Bizzarro et al. 2002. Geochim Cosmochim. Acta 66: A79. [7] Blichert-Toft et al., 2002. Geochim Cosmochim. Acta 66: A82.

Affiliated with

Also associated with

No associations

Rating

The 176Lu Decay Constant Controversy does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with The 176Lu Decay Constant Controversy, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The 176Lu Decay Constant Controversy will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-1892481