106. Distinct 238 U/ 235 U Ratios and REE Patterns in Plutonic And

Total Page:16

File Type:pdf, Size:1020Kb

106. Distinct 238 U/ 235 U Ratios and REE Patterns in Plutonic And Available online at www.sciencedirect.com ScienceDirect Geochimica et Cosmochimica Acta 213 (2017) 593–617 www.elsevier.com/locate/gca Distinct 238U/235U ratios and REE patterns in plutonic and volcanic angrites: Geochronologic implications and evidence for U isotope fractionation during magmatic processes Franc¸ois L.H. Tissot a,b,⇑, Nicolas Dauphas a, Timothy L. Grove b a Origins Laboratory, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, 5734 South Ellis Avenue, Chicago, IL, USA b Department of the Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA Received 28 December 2016; accepted in revised form 28 June 2017; Available online 8 July 2017 Abstract Angrites are differentiated meteorites that formed between 4 and 11 Myr after Solar System formation, when several short- lived nuclides (e.g., 26Al-26Mg, 53Mn-53Cr, 182Hf-182W) were still alive. As such, angrites are prime anchors to tie the relative chronology inferred from these short-lived radionuclides to the absolute Pb-Pb clock. The discovery of variable U isotopic composition (at the sub-permil level) calls for a revision of Pb-Pb ages calculated using an ‘‘assumed” constant 238U/235U ratio (i.e., Pb-Pb ages published before 2009–2010). In this paper, we report high-precision U isotope measurement for six angrite samples (NWA 4590, NWA 4801, NWA 6291, Angra dos Reis, D’Orbigny, and Sahara 99555) using multi- collector inductively coupled plasma mass-spectrometry and the IRMM-3636 U double-spike. The age corrections range from À0.17 to À1.20 Myr depending on the samples. After correction, concordance between the revised Pb-Pb and Hf-W and Mn- 53 55 Cr ages of plutonic and quenched angrites is good, and the initial ( Mn/ Mn)0 ratio in the Early Solar System (ESS) is recal- culated as being (7 ± 1) Â 10À6 at the formation of the Solar System (the error bar incorporates uncertainty in the absolute age of Calcium, Aluminum-rich inclusions – CAIs). An uncertainty remains as to whether the Al-Mg and Pb-Pb systems agree in large part due to uncertainties in the Pb-Pb age of CAIs. A systematic difference is found in the U isotopic compositions of quenched and plutonic angrites of +0.17‰. A difference is also found between the rare earth element (REE) patterns of these two angrite subgroups. The d238U values are consistent with fractionation during magmatic evolution of the angrite parent melt. Stable U isotope fractionation due to a change in the coordination environment of U during incorporation into pyroxene could be responsible for such a fractionation. In this con- text, Pb-Pb ages derived from pyroxenes fraction should be corrected using the U isotope composition measured in the same pyroxene fraction. Ó 2017 Elsevier Ltd. All rights reserved. Keywords: Angrites; U stable isotopes; Pb-Pb ages; Short-lived chronometers; U stable isotope fractionation 1. INTRODUCTION ⇑ Angrites are differentiated meteorites (achondrites) of Corresponding author at: Department of the Earth, Atmo- basaltic composition. They are of either volcanic (a.k.a. spheric and Planetary Sciences, Massachusetts Institute of Tech- quenched) or plutonic origin and display minimal post- nology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA. crystallization alteration, metamorphism, shock or impact E-mail address: [email protected] (F.L.H. Tissot). http://dx.doi.org/10.1016/j.gca.2017.06.045 0016-7037/Ó 2017 Elsevier Ltd. All rights reserved. 594 F.L.H. Tissot et al. / Geochimica et Cosmochimica Acta 213 (2017) 593–617 brecciation (e.g., Keil, 2012 and references therein). Their assumption of Pb-Pb dating. Because variation in the abso- old U-Pb (e.g., Amelin, 2008a, 2008b) and Pb-Pb ages lute 238U/235U ratio will impact absolute ages, both Pb and (e.g., Wasserburg et al., 1977; Lugmair and Galer, 1992; U isotopic compositions need to be measured to obtain pre- Baker et al., 2005; Connelly et al., 2008) make angrites cise and accurate Pb-Pb ages. The first goal of the present some of the earliest volcanic rocks known in the Solar Sys- paper is to provide high-precision U isotope data on a large tem, with crystallization ages for the oldest samples of 4 array of angrites in order to correct their Pb-Pb ages. These Myr after the formation of Calcium, Aluminum-rich inclu- U-isotope-corrected ages will be used to assess the degree of sions (CAIs, the oldest known solids in the Solar System). concordance between short-lived nuclides systems As such, these achondrites provide insights into early stages (26Al-26Mg, 53Mn-53Cr, 182Hf-182W) and the absolute Pb- of planetary melting and differentiation. They also play an Pb clock. important role as anchors for early solar system (ESS) The second aim of this study is concerned with identify- chronology. Indeed, the quenched angrite specimens have ing whether all angrites have a similar U isotopic composi- estimated cooling rate between 7 and 50 °C/h (Mikouchi tion, and, if not, what is(are) the process(es) responsible for et al., 2000, 2001), which means that it took 18–127 h this variability. Brennecka and Wadhwa (2012) measured a for them to cool from a liquidus temperature of 1190 °C series of angrite samples and suggested that all angrites had (Longhi, 1999) to below the closure temperature of a homogeneous U isotopic composition. They reached this 300 °C relevant to the decay systems discussed in this con- conclusion because they propagated the uncertainties on tribution (Pb: in clinopyroxene Cherniak, 1998, in plagio- the U isotopic composition of the two U double spikes that clase, Cherniak, 1995, in apatite, Cherniak et al., 1991; they used onto the final 238U/235U ratio of each sample. Cr: in olivine, Ito and Ganguly, 2006, in spinel, Posner However, the same double spike (IRMM-3636) was used et al., 2016; Mg: in olivine, Chakraborty, 1997, in plagio- for analysis of all bulk samples, while another spike (in- clase, Muller et al., 2013, in cpx, Van Orman et al., 2014; house ASU spike) was only used to measure a replicate of W: in olivine and model pyroxene, Cherniak and Van D’Orbigny and two mineral separate fractions (D’Orbigny Orman, 2014). Hence, most radiochronometric systems, pyroxenes, AdoR phosphates). Any error on the spike com- and in particular those commonly used in ESS chronology, position will shift the 238U/235U ratios of the samples by a closed simultaneously in quenched angrites (Dodson, 1973). constant value, so that difference in the U isotopic compo- Their mineralogy is also diverse, which makes them amen- sitions of samples corrected by the same double spike are able to dating with various chronometers. Because few sam- better known than one would be led to believe if uncertain- ples meet the requirements of non-disturbance, ties on the spike composition are propagated. When only synchronous isotope closure and phase diversity like the the isotope measurement error is considered, some variabil- quenched angrites, they have become important samples ity in the angrite 238U/235U ratio data set of Brennecka and to cross-calibrate short-lived dating techniques (e.g., Wadhwa (2012) is visible. It is presently unknown whether 26Al-26Mg, 53Mn-53Cr, 182Hf-182W) with absolute dating igneous processes can fractionate U isotopes but the U iso- techniques (i.e., U-Pb, Pb-Pb) (e.g., Nyquist et al., 2009; topic variability of 0.50‰ measured among igneous rocks Dauphas and Chaussidon, 2011; Kleine et al., 2012). As (see compilation in Fig. 6 of Tissot and Dauphas, 2015) the precision of isotope measurement improves, it is possi- raises the possibility that magmatic differentiation on the ble to test at finer levels the concordance of these angrite parent-body could have fractionated U isotopes. chronometers. For instance, and based on a 1.5 Myr dis- Here, we report high-precision U isotopic data for six crepancy between the Al-Mg and Pb-Pb ages of CAIs and angrite samples: NWA 4590, NWA 4801, NWA 6291, quenched angrites, Larsen et al. (2011) proposed that 26Al Angra dos Reis, D’Orbigny, and Sahara 99555. Using this was not uniformly distributed in the Solar System, thus data set and previously published measurements questioning one of the pillars of ESS chronology. To settle (Brennecka and Wadhwa, 2012; Connelly et al., 2012; the vigorous debate around this issue, improvement of the Goldmann et al., 2015), we question the homogeneity of absolute and relative ages of ESS anchors are therefore the U isotope composition of angrite specimens, and discuss critical. the possible processes by which different angrite samples can The most precise absolute ages of ESS objects are acquire different U isotopic compositions. After correcting obtained using the Pb-Pb dating method (Patterson et al., the Pb-Pb ages of angrites, we test their age concordance 1955; Patterson, 1956): a dual chronometer since 238U with short-lived chronometers and discuss the implications decays into 206Pb with a half-life of 4468.3 ± 4.8 Myr while for the distribution of short-lived radionuclides in the ESS. 235U decays into 207Pb with a half-life of 703.81 ± 0.96 Myr (Jaffey et al., 1971). In the late 1970s, to ensure that abso- 2. SAMPLES AND METHODS lute ages could be compared between laboratories, and based on the observed constancy of the 238U/235U ratio in All Teflon labware used in this study (i.e., PFA vials and natural samples, a ‘‘consensus” value of 238U/235U= beakers from Savillex) was pre-cleaned with boiling aqua 137.88 was adopted for use in geochronology (Steiger and regia (3:1 mixture of HCl:HNO3) three times, followed by Jager, 1977).
Recommended publications
  • Implications for the Solar Protoplanetary Disk from Short-Lived Radionuclides
    From Dust to Planetesimals: Implications for the Solar Protoplanetary Disk from Short-lived Radionuclides M. Wadhwa The Field Museum Y. Amelin Geological Survey of Canada A. M. Davis The University of Chicago G. W. Lugmair University of California at San Diego B. Meyer Clemson University M. Gounelle Muséum National d’Histoire Naturelle S. J. Desch Arizona State University ________________________________________________________________ Since the publication of the Protostars and Planets IV volume in 2000, there have been signifi- cant advances in our understanding of the potential sources and distributions of short-lived, now ex- tinct, radionuclides in the early Solar System. Based on recent data, there is definitive evidence for the presence of two new short-lived radionuclides (10Be and 36Cl) and a compelling case can be made for revising the estimates of the initial Solar System abundances of several others (e.g., 26Al, 60Fe and 182Hf). The presence of 10Be, which is produced only by spallation reactions, is either the result of irradiation within the solar nebula (a process that possibly also resulted in the production of some of the other short-lived radionuclides) or of trapping of Galactic Cosmic Rays in the protosolar mo- lecular cloud. On the other hand, the latest estimates for the initial Solar System abundance of 60Fe, which is produced only by stellar nucleosynthesis, indicate that this short-lived radionuclide (and possibly significant proportions of others with mean lives ≤10 My) was injected into the solar nebula from a nearby stellar source. As such, at least two distinct sources (e.g., irradiation and stellar nu- cleosynthesis) are required to account for the abundances of the short-lived radionuclides estimated to be present in the early Solar System.
    [Show full text]
  • A Perspective from Extinct Radionuclides on a Young Stellar Object: the Sun and Its Accretion Disk
    Annu. Rev. Earth Planet. Sci. 2011. 39: 351-386 doi:10.1146/annurev-earth-040610-133428 Copyright © 2011 by Annual Reviews. All rights reserved UNCORRECTED PREPRINT A PERSPECTIVE FROM EXTINCT RADIONUCLIDES ON A YOUNG STELLAR OBJECT: THE SUN AND ITS ACCRETION DISK Nicolas Dauphas,1 Marc Chaussidon2 1Origins Laboratory, Department of the Geophysical Sciences and Enrico Fermi Institute, Chicago, Illinois 60637; email: [email protected] 2Centre de Recherches Pétrographiques et Géochimiques (CRPG)-Nancy Université-CNRS, UPR 2300, 54501 Vandoeuvre-lès-Nancy, France ■ Abstract Meteorites, which are remnants of solar system formation, provide a direct glimpse into the dynamics and evolution of a young stellar object (YSO), namely our Sun. Much of our knowledge about the astrophysical context of the birth of the Sun, the chronology of planetary growth from micrometer-sized dust to terrestrial planets, and the activity of the young Sun comes from the study of extinct 26 radionuclides such as Al (t1/2 = 0.717 Myr). Here we review how the signatures of extinct radionuclides (short-lived isotopes that were present when the solar system formed and that have now decayed below detection level) in planetary materials influence the current paradigm of solar system formation. Particular attention is given to tying meteorite measurements to remote astronomical observations of YSOs and modeling efforts. Some extinct radionuclides were inherited from the long-term chemical evolution of the Galaxy, others were injected into the solar system by a nearby supernova, and some were produced by particle irradiation from the T-Tauri Sun. The chronology inferred from extinct radionuclides reveals that dust agglomeration to form centimeter-sized particles in the inner part of the disk was very rapid (<50 kyr), planetesimal formation started early and spanned several million years, planetary embryos (possibly like Mars) were formed in a few million years, and terrestrial planets (like Earth) completed their growths several tens of million years after the birth of the Sun.
    [Show full text]
  • Lecture 2: Radioactive Decay
    Geol. 655 Isotope Geochemistry Lecture 2 Spring 2005 RADIOACTIVE DECAY As we have seen, some combinations of protons and neutrons form nuclei that are only “metastable”. These ultimately transform to stable nuclei through the process called radioactive decay. Just as an atom can exist in any one of a number of excited states, so too can a nucleus have a set of discrete, quantized, excited nuclear states. The new nucleus produced by radioactive decay is often in one of these excited states. The behavior of nuclei in transforming to more stable states is somewhat similar to atomic transformation from excited to more stable states, but there are some important differences. First, energy level spacing is much greater; second, the time an unstable nucleus spends in an excited state can range from 10-14 sec to 1011 years, whereas atomic life times are usually about 10-8 sec; third, excited atoms emit photons, but excited nuclei may emit photons or particles of non-zero rest mass. Nuclear reactions must obey general physical laws, conservation of momentum, mass-energy, spin, etc. and conservation of nuclear particles. Nuclear decay takes place at a rate that follows the law of radioactive decay. There are two extremely interesting and important aspects of radioactive decay. First, the decay rate is dependent only on the energy state of the nuclide; it is independent of the history of the nucleus, and essentially independent of external influences such as temperature, pressure, etc. It is this property that makes radioactive decay so useful as a chronometer. Second, it is completely impossible to predict when a given nucleus will decay.
    [Show full text]
  • Isotope Geochemistry
    Isotope Geochemistry Chapter 5: Isotope Cosmochemistry Isotope Cosmochemistry 5.1 INTRODUCTION Meteorites are our primary source of in- formation about the early Solar System. Chemical, isotopic, and petrological fea- tures of meteorites reflect events that occurred in the first few tens of millions of years of Solar Sys- tem history. Obser- vations on meteor- ites, together with astronomical obser- vations on the birth of stars and the laws of physics, are the basis of our ideas on how the Solar Sys- tem, and the Earth, Figure 5.1. Photograph of the meteorite Allende, which fell in Mexico in 1969. formed. Circular/spherical features are chondrules. Irregular white patches are Meteorites can be CAI’s. divided into two broad groups: primitive meteorites and differentiated meteorites. The chondrites constitute the primitive group: most of their chemical, isotopic, and petrological features resulted from processes that occurred in the cloud of gas and dust that we refer to as the solar nebula. They are far more commonly observed to fall than differentiated meteorites*. All chondrites, however, have experienced at least some meta- morphism on “parent bodies”, the small planets (diameters ranging from a few km to a few hundred km) from which meteorites are derived by collisions. The differentiated meteorites, which include the achondrites, stony irons, and irons, were so extensively processed in parent bodies, by melting and brecciation, that information about nebular processes has largely been lost. On the other hand, the dif- ferentiated meteorites provide insights into the early stages of planet formation. We’ll provide only a brief overview here. More details of meteoritics (the study of meteorites) can be found in McSween and Huss (2010) and White (2013).
    [Show full text]
  • The I-Xe Chronometer and the Early Solar System
    Meteoritics & Planetary Science 41, Nr 1, 19–31 (2006) Abstract available online at http://meteoritics.org The I-Xe chronometer and the early solar system J. D. GILMOUR1*, O. V. PRAVDIVTSEVA2, A. BUSFIELD1, and C. M. HOHENBERG2 1School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Oxford Road, Manchester M13 9PL, UK 2McDonnell Center for the Space Sciences and Physics Department, Washington University, CB 1105, One Brookings Drive, Saint Louis, Missouri 63130, USA *Corresponding author. E-mail: [email protected] (Received 31 January 2005; revision accepted 05 August 2005) Abstract–We review the development of the I-Xe technique and how its data are interpreted, and specify the best current practices. Individual mineral phases or components can yield interpretable trends in initial 129I/127I ratio, whereas whole-rock I-Xe ages are often hard to interpret because of the diversity of host phases, many of which are secondary. Varying standardizations in early work require caution; only samples calibrated against Shallowater enstatite or Bjurbˆle can contribute reliably to the emerging I-Xe chronology of the early solar system. Although sparse, data for which I-Xe and Mn-Cr can be compared suggest that the two systems are concordant among ordinary chondrite samples. We derive a new age for the closure of the Shallowater enstatite standard of 4563.3 ± 0.4 Myr from the relationship between the I-Xe and Pb-Pb systems. This yields absolute I-Xe ages and allows data from this and other systems to be tested by attempting to construct a common chronology of events in the early solar system.
    [Show full text]
  • A Perspective from Extinct Radionuclides on a Young Stellar Object: the Sun and Its Accretion Disk
    EA39CH13-Dauphas ARI 30 March 2011 12:46 A Perspective from Extinct Radionuclides on a Young Stellar Object: The Sun and Its Accretion Disk Nicolas Dauphas1 and Marc Chaussidon2 1Origins Laboratory, Department of the Geophysical Sciences and Enrico Fermi Institute, Chicago, Illinois 60637; email: [email protected] 2Centre de Recherches Petrographiques´ et Geochimiques´ (CRPG)-Nancy Universite-CNRS,´ UPR 2300, 54501 Vandoeuvre-les-Nancy,` France Annu. Rev. Earth Planet. Sci. 2011. 39:351–86 Keywords The Annual Review of Earth and Planetary Sciences is radioactivity, meteorites, solar system, chronology, irradiation online at earth.annualreviews.org This article’s doi: Abstract 10.1146/annurev-earth-040610-133428 Meteorites, which are remnants of solar system formation, provide a direct Copyright c 2011 by Annual Reviews. glimpse into the dynamics and evolution of a young stellar object (YSO), All rights reserved namely our Sun. Much of our knowledge about the astrophysical context of 0084-6597/11/0530-0351$20.00 the birth of the Sun, the chronology of planetary growth from micrometer- sized dust to terrestrial planets, and the activity of the young Sun comes 26 = . from the study of extinct radionuclides such as Al (t1/2 0 717 Myr). Here by University of Chicago Libraries on 11/10/11. For personal use only. we review how the signatures of extinct radionuclides (short-lived isotopes that were present when the solar system formed and that have now decayed below detection level) in planetary materials influence the current paradigm Annu. Rev. Earth Planet. Sci. 2011.39:351-386. Downloaded from www.annualreviews.org of solar system formation.
    [Show full text]
  • Martian Xenon Components in Basaltic Shergottite Meteorites
    University of Tennessee, Knoxville TRACE: Tennessee Research and Creative Exchange Doctoral Dissertations Graduate School 12-2002 Martian Xenon Components in Basaltic Shergottite Meteorites Katherine Delene Ocker Stone University of Tennessee - Knoxville Follow this and additional works at: https://trace.tennessee.edu/utk_graddiss Part of the Geology Commons Recommended Citation Stone, Katherine Delene Ocker, "Martian Xenon Components in Basaltic Shergottite Meteorites. " PhD diss., University of Tennessee, 2002. https://trace.tennessee.edu/utk_graddiss/2200 This Dissertation is brought to you for free and open access by the Graduate School at TRACE: Tennessee Research and Creative Exchange. It has been accepted for inclusion in Doctoral Dissertations by an authorized administrator of TRACE: Tennessee Research and Creative Exchange. For more information, please contact [email protected]. To the Graduate Council: I am submitting herewith a dissertation written by Katherine Delene Ocker Stone entitled "Martian Xenon Components in Basaltic Shergottite Meteorites." I have examined the final electronic copy of this dissertation for form and content and recommend that it be accepted in partial fulfillment of the equirr ements for the degree of Doctor of Philosophy, with a major in Geology. Harry Y. McSween, Major Professor We have read this dissertation and recommend its acceptance: Jamie D. Gilmour, Norbert Thonnard, Larry A. Taylor, Claudia L. Mora Accepted for the Council: Carolyn R. Hodges Vice Provost and Dean of the Graduate School (Original signatures are on file with official studentecor r ds.) To the Graduate Council: I am submitting herewith a dissertation written by Katherine Delene Ocker Stone entitled “Martian Xenon Components in Basaltic Shergottite Meteorites.” I have examined the final electronic copy of this dissertation for form and content and recommend that it be accepted in partial fulfillment of the requirements for the degree of Doctor of Philosophy, with a major in Geology.
    [Show full text]
  • Isotopes of Iodine 1 Isotopes of Iodine
    Isotopes of iodine 1 Isotopes of iodine There are 37 known isotopes of iodine (I) from 108I to 144I, but only one, 127I, is stable. Iodine is thus a monoisotopic element. Its longest-lived radioactive isotope, 129I, has a half-life of 15.7 million years, which is far too short for it to exist as a primordial nuclide. Cosmogenic sources of 129I produce very tiny quantities of it that are too small to affect atomic weight measurements; iodine is thus also a mononuclidic element—one that is found in nature essentially as a single nuclide. Most 129I derived radioactivity on Earth is man-made: an unwanted long-lived byproduct of early nuclear tests and nuclear fission accidents. All other iodine radioisotopes have half-lives less than 60 days, and four of these are used as tracers and therapeutic agents in medicine. These are 123I, 124I, 125I, and 131I. Essentially all industrial production of radioactive iodine isotopes A Pheochromocytoma is seen as a involves these four useful radionuclides. dark sphere in the center of the body The isotope 135I has a half-life less than seven hours, which is too short to be (it is in the left adrenal gland). Image is by MIBG scintigraphy, with used in biology. Unavoidable in situ production of this isotope is important in radiation from radioiodine in the 135 nuclear reactor control, as it decays to Xe, the most powerful known neutron MIBG. Two images are seen of the absorber, and the nuclide responsible for the so-called iodine pit phenomenon. same patient from front and back.
    [Show full text]
  • This Article Appeared in a Journal Published by Elsevier. the Attached Copy Is Furnished to the Author for Internal Non-Commerci
    This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier’s archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright Author's personal copy ARTICLE IN PRESS Chemie der Erde 68 (2008) 339–351 www.elsevier.de/chemer INVITED REVIEW I–Xe dating: From adolescence to maturity C.M. HohenbergÃ, O.V. Pravdivtseva Department of Physics and McDonnell Center for Space Sciences, Washington University, CB1105, One Brookings Drive, St. Louis, MO 63130, USA Received 12 May 2008; accepted 24 June 2008 Abstract The I–Xe chronometer is based upon decay of now-extinct 129I where the ratio of accumulated daughter 129Xe to stable 127I reflects the iodine isotopic ratio at closure of the host mineral. Since none of the parent remains, I–Xe is by nature a relative chronometer but, when referenced by a standard mineral of known age, the I–Xe system becomes an absolute chronometer reflecting true closure times. Most iodine hosts are secondary minerals so the I–Xe system is unique in providing details of post-formational chronometry not readily available with other chronometers.
    [Show full text]
  • Extinct Radionuclides Were Defined As Short-Lived Nuclides That Were
    Abundance, distribution, and origin of 60Fe in the solar protoplanetary disk Haolan Tang,1* Nicolas Dauphas1 1Origins Laboratory, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, 5734 South Ellis Avenue, Chicago IL 60637. *To whom correspondence should be addressed. E-mail: [email protected] Tang H., Dauphas N. (2012) Abundance, distribution, and origin of 60Fe in the solar protoplanetary disk. Earth and Planetary Science Letters 359-360, 248-263. Abstract: Meteorites contain relict decay products of short-lived radionuclides that were present in the protoplanetary disk when asteroids and planets formed. Several 60 studies reported a high abundance of Fe (t1/2=2.62±0.04 Myr) in chondrites (60Fe/56Fe~610-7), suggesting that planetary materials incorporated fresh products of stellar nucleosynthesis ejected by one or several massive stars that exploded in the vicinity of the newborn Sun. We measured 58Fe/54Fe and 60Ni/58Ni isotope ratios in whole rocks and constituents of differentiated achondrites (ureilites, aubrites, HEDs, and angrites), unequilibrated ordinary chondrites Semarkona (LL3.0) and NWA 5717 (ungrouped petrologic type 3.05), metal-rich carbonaceous chondrite Gujba (CBa), and several other meteorites (CV, EL H, LL chondrites; IIIAB, IVA, IVB iron meteorites). We derive from these measurements a much lower initial 60Fe/56Fe ratio of (11.5±2.6)×10-9 and conclude that 60Fe was homogeneously distributed among planetary bodies. This low ratio is consistent with derivation of 60Fe from galactic background (60Fe/56Fe≈2.810-7 in the interstellar medium from -ray observations) and can be reconciled with high 26Al/27Al~5×10-5 in chondrites if solar material was contaminated through winds by outer layers of one or several massive stars (e.g., a Wolf-Rayet star) rich in 26Al and poor in 60Fe.
    [Show full text]
  • Radiometric Dating
    ARTICLE RADIOMETRIC DATING N. R. DAS* Since the discovery of natural radioactivity in uranium, in the last decade of the nineteenth century, the nuclear property of radioactive decay of radionuclides at immutable rates has been effectively utilized in dating of varieties of naturally occurring geological matrices and the organisms which constantly replenish their 14C supply through respiration when alive on earth. During the period, applications of radiometric dating techniques have been extensively diversified and have enabled the geologists to indicate the absolute time scales of geological formations and the evolution of the solar system, the earth, meteorites, lunar rocks, etc. and the archaeologists to record the facts of history of several important events like dinosaur era, Iceman, the Shroud in Turin and many other ancient artefacts. In the development of dating methods, varieties of naturally occurring radio-isotopic systems with favorable half-lives ranging from about 10 years to over 100 billion years have been used as radiometric clocks. Introduction development of the concept of systematic nuclear dating, the opinions of the scientists, the geologists and he phenomenon of nuclear decay has been archeologists in particular, regarding many geological and associated with the natural world since its formation biological events occurring on earth, have been changed some billions of years ago. After the discovery of T to a great extent. radioactivity in natural uranium by Henri Becquerel in 1896, the nuclear property of radioactive decay has been Several naturally occurring radionuclides such as fruitfully utilized in determining the ages and the history uranium-238, uranium-235, thorium-232, rubidium-87, of the solar system, earth, rocks and meteorites, natural potassium-40 and many others with long half-lives are waters, the living things on earth and several ancient effectively utilized in radiometric dating of geological artefacts1-7.
    [Show full text]
  • Irradiation Processes in the Early Solar System 323
    Chaussidon and Gounelle: Irradiation Processes in the Early Solar System 323 Irradiation Processes in the Early Solar System Marc Chaussidon Centre de Recherches Pétrographiques et Géochimiques Matthieu Gounelle Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse–Université Paris XI During recent years, a growing body of evidence, both astrophysical observations of young stellar objects and cosmochemical observations made on meteorites, has strengthened the case that a fraction of the dust and gas of the solar accretion disk has been irradiated by cosmic rays emitted by the young forming active Sun. We review this meteoritic evidence, specifically the most convincing data obtained on Ca-Al-rich inclusions (CAIs) of primitive chondrite me- teorites. Boron-isotopic variations in CAIs can be explained by decay products of short-lived 10 7 Be (T1/2 = 1.5 m.y.) while a combination of extinct Be (T1/2 = 53 d) and of spallogenic Li may explain 7Li/6Li variations. We then discuss irradiation models that attempt to account for the origin of short-lived radionuclides and evaluate the predictions of these models in light of experimental data. Several anomalies, such as 21Ne and 36Ar excesses, suggest an exposure of CAIs and of chondrules (or their precusors) to cosmic rays emitted by the young Sun. The possible effects of early solar irradiation processes on the mineralogy, chemistry, and light- element isotopic compositions (e.g., O, H, N) of early solar system solids are also considered and evaluated. 1. INTRODUCTION of interstellar graphite grains, which would be incorporated in the presolar nebula (Dwek, 1978a). It has long been recognized that, because light elements It is important to point out here that, historically, the (D, Li, Be, and B) could not be synthesized by thermonu- situation with short-lived 26Al is quite similar to that of Li- clear reactions taking place at temperatures higher than Be-B.
    [Show full text]