Towards consistent chronology in the early Solar System: high resolution 53Mn-53Cr chronometry for chondrules. Page: 4 of 13
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be rigorously tested by cross calibrating the different chronometers through acquisition of
high precision isotope data in a suite of early Solar System materials suitable for this purpose.
Classically, short-lived chronometers such as the 53Mn-53Cr system (tl/2= 3.7Ma) are an-
chored to the absolute Pb-Pb age of 4557.8+0.5Ma (Lugmair & Galer 1992) for angrites LEW
86010 (LEW) and Angra dos Reis (ADOR) with the 53Mn/55Mn ratio of (1.25+0.07)x10-6
(Lugmair & Shukolyukov 1998). A growing number of new high precision data suggests that
short-lived relative chronometers such as the 26A1-26Mg system (tl/2= 0.73 Ma) are broadly
consistent with the high precision long-lived 201Pb-206Pb chronometer (Sanders & Taylor
2005). It has been recognized for sometime however, that there are some inconsistencies in
the 53Mn-53Cr chronometry (c.f. McKeegan & Davis (2003)). For example, when using
the angrite age anchor (Lugmair & Shukolyukov 1998) based on the 53Mn/55Mn ratios, the
chondrules of ordinary chondrites (Nyquist et al. 2001) are older than that of Ca-Al-rich
inclusions (CAIs) (Amelin et al. 2002), the oldest known solid objects of our Solar System.
This is opposite to what one would conclude based on 26A1-26Mg and U-Pb chronometers,
where most chondrules appear to be ~2 Ma younger than the CAIs (c.f. Kita et al. (2005)
for a recent review). Such results could be interpreted prematurely as an argument against
a chronological interpretation for short-lived radioactivity in the early Solar System and
instead as favoring arguments for production of 53Mn within the solar nebula and/or het-
erogeneous distribution of 53Mn and 26A1 within the early solar system. The importance
of this problem prompted us to revisit this issue using MC-ICP-MS to obtain high preci-
sion 53Mn-53Cr data in a suite of chondrules from a primitive ordinary chondrite, Chainpur
2. Samples and analytical methods
Six individual chondrules extracted from a primitive ordinary chondrite, Chainpur
(LL3.4), weighing between 20-30 mg were dissolved in a mixture of HF and HNO3 in pressur-
ized vessels. Subsequently, dissolution in aqua regia (concentrated HCl and HNO3 mixture
in 3:1 ratio) ensures complete digestion of fluoride complexes and Cr-rich refractory phases,
such as spinel. The chemical purification used for our study is adapted and refined from
procedures in Birck & Allegre (1984), Lugmair & Shukolyukov (1998), Nyquist et al. (2001)
and Glavin et al. (2004). First, Cr was separated from the major elements with iN HCl by
elution through cationic-exchange resin. This step was repeated twice to completely elimi-
nate traces of major elements. Cr was further purified from other elements, in particular Ti
and V, on a cation exchange resin with HNO3/HF/HCl. The total yield was > 90%. The
samples were analyzed by high-resolultion multi-collector inductively-coupled plasma mass
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Yin, Q; Jacobsen, B; Moynier, F & Hutcheon, I D. Towards consistent chronology in the early Solar System: high resolution 53Mn-53Cr chronometry for chondrules., article, May 2, 2007; Livermore, California. (digital.library.unt.edu/ark:/67531/metadc896272/m1/4/: accessed September 21, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.