238
 U/
 235
 U Variations in Meteorites: Extant
 247
 Cm and Implications for Pb-Pb Dating

Brennecka, G. A.; Weyer, Stefan; Wadhwa, M.; Janney, P. E.; Zipfel, J.; Anbar, Ariel D.

doi:10.1126/science.1180871

Cited by 149 publications

(133 citation statements)

References 23 publications

Supporting

Mentioning

126

Contrasting

Order By: Relevance

“…Recent analytical advances leading to significantly greater precision along with renewed interest have led to several investigations of the U isotopic compositions of meteoritic materials in recent years. While refractory calcium-aluminum-rich inclusions (CAIs) in the carbonaceous chondrite Allende have been shown to have large variability in 238 U∕ 235 U ratios (3,5), the measured 238 U∕ 235 U ratios of bulk samples of several types of chondrites and achondrites are all within analytical uncertainty of one another, and have an average 238 U∕ 235 U ratio ≈ 137.78 (3-6, 20-22). There are many other meteorite types that have not yet been measured, but the current data suggest that while the 238 U∕ 235 U ratio of Solar System materials is resolvably distinct from the previously assumed value of 137.88, the extent of U isotopic variation among bulk meteorites is likely to be relatively small (i.e., smaller than the current level of precision of the U isotope measurements of AE1 − 2ε units).…”

Section: Discussionmentioning

confidence: 99%

“…The residue remaining from this acid leaching (designated as "Residue") was completely dissolved using a mix of concentrated HNO 3 , HF, and HCl. Hand-picked phosphates (5.4 mg) from ADOR were provided by G. J. Wasserburg (Caltech) and were dissolved directly in 3 M HNO 3 . Approximately 5% of each dissolved sample used in this study was reserved for trace element measurements.…”

Section: Methodsmentioning

confidence: 99%

“…Approximately 5% of each dissolved sample used in this study was reserved for trace element measurements. Uranium was separated from the remaining sample solutions for measurement of the 238 U∕ 235 U ratio, following previously published procedures (3,34).…”

Section: Methodsmentioning

confidence: 99%

See 2 more Smart Citations

Uranium isotope compositions of the basaltic angrite meteorites and the chronological implications for the early Solar System

Brennecka

Wadhwa

2012

Proc. Natl. Acad. Sci. U.S.A.

147

114

View full text Add to dashboard Cite

Events occurring within the first 10 million years of the Solar System's approximately 4.5 billion-year history, such as formation of the first solids, accretion, and differentiation of protoplanetary bodies, have determined the evolutionary course of our Solar System and the planetary bodies within it. The application of high-resolution chronometers based on short-lived radionuclides is critical to our understanding of the temporal sequence of these critical events. However, to map the relative ages from such chronometers onto the absolute time scale, they must be "anchored" to absolute ages of appropriate meteoritic materials using the high-precision lead-lead (Pb-Pb) chronometer. Previously reported Pb-Pb dates of the basaltic angrite meteorites, some of which have been used extensively as time anchors, assumed a constant 238 U∕ 235 U ratio (¼137.88). In this work, we report measurements of 238 U∕ 235 U ratios in several angrites that are distinct from the previously assumed value, resulting in corrections to the Pb-Pb ages of ≥1 million years. There is no resolvable variation in the 238 U∕ 235 U ratio among the angrite bulk samples or mineral separates, suggesting homogeneity in the U isotopic composition of the angrite parent body. Based on these measurements, we recalculated the Pb-Pb age for the commonly used anchor, the D'Orbigny angrite, to be 4563.37 AE 0.25 Ma. An adjustment to the Pb-Pb age of a time anchor (such as D'Orbigny) requires a corresponding correction to the "model ages" of all materials dated using that anchor and a shortlived chronometer. This, in turn, has consequences for accurately defining the absolute timeline of early Solar System events.anchor | geochronology T he time from the formation of the first solids in the Solar System to the accretion and differentiation of protoplanetary embryos is less than approximately 10 million years (Ma) (ref. 1 and references therein), and these events have determined the evolutionary course of our Solar System and the planetary bodies within it. Knowledge of the precise timing of events during this period is critical to a broader understanding of how star systems and planetary bodies form and evolve. As such, precise and accurate geochronology, allowing the resolution of events occurring within this critical approximately 10 Ma interval, is required to understand this earliest sequence of events in the Solar System. A very limited number of chronometers can provide the sub-Ma precision necessary to resolve early Solar System events. These include the long-lived lead-lead (Pb-Pb) chronometer, and the short-lived chronometers such as 26 Al-26 Mg (t 1∕2 approx. 0.72 Ma), 53 Mn-53 Cr (t 1∕2 approx. 3.7 Ma), and 182 Hf-182 W (t 1∕2 approx. 9 Ma). The Pb-Pb chronometer is based on two radioactive isotopes of uranium, utilizing the distinct decay schemes of 235 U → 207 Pb (t 1∕2 approx. 704 Ma) and 238 U → 206 Pb (t 1∕2 approx. 4.47 Ga) to calculate an absolute age of the sample. The short-lived or extinct radionuclide chronometers have parent isotopes ...

show abstract

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Uranium isotope compositions of the basaltic angrite meteorites and the chronological implications for the early Solar System

Brennecka

Wadhwa

2012

Proc. Natl. Acad. Sci. U.S.A.

147

114

View full text Add to dashboard Cite

show abstract

“…Browne, Amelin et al (2005) for Richardton, and Bouvier et al (2007) for Nadiabondi & Kernouvé. We note that Pb-Pb age values were slightly revised upwards (by 1 Ma) according to recent revisions of the uranium isotopic ratio (Brennecka et al 2010).…”

Section: Thermochronological Datamentioning

confidence: 73%

Thermal evolution and sintering of chondritic planetesimals

Gail

Henke

Trieloff

2015

A&A

View full text Add to dashboard Cite

Context. Reconstruction of the thermal history of individual meteorites which can be assigned to the same parent body allows us to derive general characteristics of the parent body, such as its size and formation time, which hold important clues on the planetary formation process. This requires us to construct a detailed model of the heating of such a body by short lived radioactives, in particular by 26 Al, and its cooling by heat conduction, which may then be compared to the reconstructed cooling histories of the meteorites. Aims. The heat conductivity of the material from which planetesimals are composed depends critically on the porosity of the chondritic material. This changes during the process of compaction (also called sintering) of the material at elevated temperatures and pressures. Therefore, compaction of an initially granular material is a key process determining the thermal history of the parent bodies of meteorites. The most realistic modelling of sintering of chondritic material is required. Methods. The modelling of the compaction process is improved by applying concepts originally developed for the modelling of hot isostatic pressing in metallurgical processes, and by collecting data available from geosciences for the materials of interest. It is extended to a binary mixture of granular components of very different diameters -matrix and chondrules -as observed in chondrites.Results. By comparison with some published data on sintering experiments it is shown that the algorithm to follow the decrease of porosity of granular material during progressive sintering allows a sufficiently accurate modelling of the compaction of silicate material. The dependence of the compaction process on the nature of the precursor material, either matrix-dominated or chondruledominated, is discussed. It is shown that the characteristic temperature at which sintering occurs is different for matrix or chondruledominated precursor material. We apply the new method for calculating compaction to the evolution of the parent body of the H chondrites and determine an improved optimised set of model parameters for this body.

show abstract

“…The most accurate determinations of absolute ages of the oldest SS objects currently are based on Pb-Pb ages, because of the precision in the half-lives of the progenitors 235 U and 238 U and the coupled age data of isotope pairs. The adopted most pristine solids for this purpose, chondrules and CAIs, were considered to have invariant SS abundance ratios of these two progenitors, which turned out to be an incorrect assumption (Brennecka et al, 2010). The first combined high-precision U and Pb isotopic data for a CAI, and U isotopic data for chondrules and whole rock fractions of the Allende meteorite (Amelin et al, 2010) show that the Allende meteorite bulk rock and chondrules data have distinctly lower ratios ( 238 U/ 235 U=137.747) than the CAI.…”

Section: Time Of Formation Of the Solar System (Ss)mentioning

confidence: 99%

Solar Wind and Solar System Matter After Mission Genesis

Marti¹,

Bochsler²

2012

Exploring the Solar Wind

View full text Add to dashboard Cite

²³⁸ U/ ²³⁵ U Variations in Meteorites: Extant ²⁴⁷ Cm and Implications for Pb-Pb Dating

Cited by 149 publications

References 23 publications

Uranium isotope compositions of the basaltic angrite meteorites and the chronological implications for the early Solar System

Uranium isotope compositions of the basaltic angrite meteorites and the chronological implications for the early Solar System

Thermal evolution and sintering of chondritic planetesimals

Solar Wind and Solar System Matter After Mission Genesis

Contact Info

Product

Resources

About

238 U/ 235 U Variations in Meteorites: Extant 247 Cm and Implications for Pb-Pb Dating

Cited by 149 publications

References 23 publications

Uranium isotope compositions of the basaltic angrite meteorites and the chronological implications for the early Solar System

Uranium isotope compositions of the basaltic angrite meteorites and the chronological implications for the early Solar System

Thermal evolution and sintering of chondritic planetesimals

Solar Wind and Solar System Matter After Mission Genesis

Contact Info

Product

Resources

About

²³⁸ U/ ²³⁵ U Variations in Meteorites: Extant ²⁴⁷ Cm and Implications for Pb-Pb Dating