|
Search | Add a publication |
| ID No : | 1048 Edit | Title: | The Chronology of Asteroid Accretion, Differentiation, and Secondary Mineralization |
| Summary / Review : | "We evaluate initial (Al-26/Al-27)(sub I), (Mn-53/Mn-55)(sub I), (Hf-182/Hf-180)(sub I), and Pb-207/Pb-206 ages for igneous differentiated meteorites and chondrules from ordinary chondrites for consistency with radioactive decay of the parent nuclides within a common, closed isotopic system, i.e., the early solar nebula. We find that the relative abundances of Al-26, Mn-53, and Hf-182, here denoted by I(Al)(sub CAI, I(Mn)(sub CAI) and I(Hf)(sub CAI), are consistent with decay from common initial values for the bulk solar system. I(Mn)(sub CAI) and I(Hf)(sub CAI) = 9.1+/-1.7 x 10(exp -6) and 1.06+/-0.09 x 10(exp -6) respectively, correspond to the canonical value of I(Al)(sub CAI) = 5.1 x 10(exp -5). I(Hf)(sub CAI) thus determined is consistent with I(Hf)(sub CAI) = 1.003+/-0.045 x 10(exp -6) directly determined in separate work. I(Mn)(sub CAI) is within error of the lowest value directly determined for CAI. We suggest that erratically higher values directly determined for CAI in carbonaceous chondrites reflect proton irradiation of unaccreted CAIs by the early Sun after other asteroids destined for melting by Al-26 decay had already accreted. The Mn-53 incorporated within such asteroids would have been shielded from further "local" spallogenic contributions. The relative abundances of the short-lived nuclides are less consistent with the Pb-207/Pb-206 ages of the corresponding materials with the best consistency being obtained between (Hf-182/Hf-180)(sub I) and Pb-207/Pb-206 ages of angrites. (Hf-182/Hf-180)(sub I) decreases with decreasing Pb-207/Pb-206 ages at the rate expected from the 8.90+/-0.09 Ma half-life of Hf-182. However, the model "CAI age" thus determined, T(sub CAI,Mn-W) = 4568.6+/-0.7 Ma, is older than the commonly accepted directly measured value T(sub CAI) = 4567.l+/-0.2 Ma. I(Al)(sub I), and (Mn-53/Mn-55)(sub I) are less consistent with Pb-207/Pb-206 ages, but determine T(sub CAI, Mn-Cr) = 4568.3+/-0.5 Ma relative to I(AI)(sub CAI)= 5.1 x 10(exp -5) and a Pb-207/Pb-206 age of 4558.6 Ma for the LEW86010 angrite. However. the (Mn-53/Mn-55)(sub I) and Pb-207/Pb-206 ages of "intermediate" age D'Orbigny-clan angrites and Asuka 881394 are inconsistent with radioactive decay from CAI values with a Mn-55 half-life of 3.7+/-0.4 Ma. in spite of consistency between (Mn-53/Mn-55)(sub I) and (Al-26/Al-27)(sub I). Nevertheless, it appears that the Mn-Cr method with I(Mn)(sub CAI) = 9.1+/-1.7 x 10(exp -6) can be used to date primary igneous events and also secondary mineralization on asteroid parent bodies. We summarize ages thus determined for igneous events on differentiated asteroids and for carbonate and fayalite formation on carbonaceous asteroids." (Author's abstract) |
| Author(s) : |
Nyquist, L. E.; Kleine, T.; Shih, C.-Y.; Reese, Y. D., [Johnson Space Center] |
| Publication Date: | 2008 |
| Category(s) : |
Exploration and resources / Asteroid / Geology and resources |
| Web URL : |
http://hdl.handle.net/2060/20080014318
If this link is broken, please Add Comment below. We try to keep author contact details, and a backup copy in our offline library. |
| PERMANENT code(s) : | L,U |
|
(Explanation of the last 3 rows above) |
In the row above, there are up to 4 possibilities: U = URL you can click on to get a copy instantly from another source on the internet, or request it from that source D = Downloadable from PERMANENT (such as because no other URL known...) L = LAN copy, PERMANENT has a digital copy but not downloadable from our website P = Paper copy in the PERMANENT office Typically, only 0 to 3 methods are available. |
| NTRS : | 20080014318 |
| Submitted by : | MEP |
| Comments: |
Please add your thoughtful Comments to this paper after reading it. All comments are reviewed and approved before being posted publicly below. If you wish to submit a private comment to the curator, instead of a public comment, just write "Private" at the start of your comment. Corrections and suggested additions to our records are appreciated. |
Add Comment |