@conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87157, title ="Establishing the liquid phase equilibrium of angrites to constrain their petrogenesis", author = "Tissot, F. L. H. and Collinet, M.", pages = "2937", month = "March", year = "2018", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180615-111233078", note = "© 2018 Lunar and Planetary Institute.", revision_no = "9", abstract = "Angrites are a series of differentiat-ed meteorites, extremely silica undersaturated and with unusally high Ca and Al contents [1]. They are thought to originate from a small planetesimal parent body of ~ 100-200 km in radius ([2-3]), can be either plutonic (i.e., cumulates) or volcanic (often referred to as quenched) in origin, and their old formation ages (4 to 11 Myr after CAIs) have made them prime anchors to tie the relative chronologies inferred from short-lived radionuclides (e.g., Al-Mg, Mn-Cr, Hf-W) to the absolute Pb-Pb clock [4]. They are also the most vola-tile element-depleted meteorites available, displaying a K-depletion of a factor of 110 relative to CIs.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87155, title ="I-Xe studies of aqueous alteration in the Allende CAI Curious Marie", author = "Pravdivtseva, O. and Meshik, A.", pages = "2959", month = "March", year = "2018", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180615-103711638", note = "© 2018 Lunar and Planetary Institute.\n\nSupported by NASA grants NNX13AD14G.", revision_no = "10", abstract = "The Allende fine-grained inclusion Curious Marie is a unique CAI. It is depleted in uranium but contains large ^(235)U excess [1], providing new evidence that ^(247)Cm was alive in the Early Solar System, as has been previously suggested [2], and leading to an updated (^(247)Cm/^(235)U)initial ratio of (1.1±0.3)×10^(-4).", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87154, title ="The REE isotopic compositions of the Earth", author = "Hu, J. Y. and Dauphas, N.", pages = "2968", month = "March", year = "2018", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180615-102635350", note = "© 2018 Lunar and Planetary Institute.", revision_no = "12", abstract = "Lanthanides are a group of 14 naturally occurring elements with atomic numbers ranging from 57 (La) to 74 (Lu), which are also known as rare earth elements (REE). REEs are ubiquitous in minerals and rocks. The chemical properties of REEs vary as smooth functions of their atomic numbers, a\nphenomenon known as the contraction of the lanthanides. This is the main control behind REE fractionation in minerals and rocks. The relative abundance of REEs is usually presented as the REE pattern by normalizing the concentrations in the sample to those in reference materials such as chondrites and shales.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87158, title ="^(238)U/^(235)U in marine carbonates as a tracer of Precambrian paleoredox conditions", author = "Chen, C. and Tissot, F. L. H.", pages = "2901", month = "March", year = "2018", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180615-111710023", note = "© 2018 Lunar and Planetary Institute.", revision_no = "9", abstract = "The timing and magnitude of the oxygenation of\nEarth’s ocean is still a matter of intense debate. Previous\nwork suggested that the uranium isotope variations\nrecorded in ancient marine sediments, such as shales\nand carbonates, could provide valuable insights into\npaleoredox conditions [e.g., 1-11]. In this work, we\nstudy U concentration and isotopic composition of a\nlarge number of Precambrian carbonates to place constraints\non long-term variations in oceanic redox conditions.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87164, title ="Defining the baseline of the REE stable isotope variations in solar system materials: Earth", author = "Hu, J. Y. and Tissot, F. L. H.", pages = "2602", month = "March", year = "2017", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180615-134047542", note = "© 2017 Lunar and Planetary Institute.", revision_no = "10", abstract = "Mass-dependent fractionations (MDFs) of stable isotopes record critical information regarding the origin and evolution of planetary materials [1]. Studies of MDF of refractory lithophile elements (RLEs) can provide insights into condensation/evaporation and planetary accretion\nprocesses in the early solar system. For example, the\nlighter calcium isotope composition observed in\ncarbonaceous meteorites compared to that of the bulk\nsilicate Earth, enstatite and ordinary chondrites [2, 3]\nmay be due to the contribution of refractory dust [4, 5],\nwhich has a light Ca isotope composition [6, 7]. In\ncontrast, titanium, another RLE with a similar\nchemical behavior in the early solar system, was found\nto have uniform isotope compositions among different\ngroups of meteorites including carbonaceous chondrites [8]. A potential explanation for the dichotomy of these two refractory elements could be connected to the higher 50% condensation temperature of Ti relative to Ca [9]. The isotopic results suggest that no Ti net loss took place from the CAI-forming region, while not all Ca condensed in the CAIs [7, 8]. Clearly, more proxies are needed to better understand the processes that occurred during the condensation of the solar nebula.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87189, title ="Strontium Stable Isotope Composition of Allende Fine-Grained Inclusions", author = "Charlier, B. L. A. and Tissot, F. L. H.", pages = "2352", month = "March", year = "2017", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180618-105540474", note = "© 2017 Lunar and Planetary Institute.", revision_no = "10", abstract = "Isotopic anomalies are departures from the laws of mass-dependent fractionation that cannot be explained by radioactive decay, cosmogenic effects, or exotic isotopic fractionation processes such as nuclear field shift or magnetic effects [1 and references therein]. These anomalies often have a nucleosynthetic origin and provide clues on the stellar origin and solar system processing of presolar dust. Anomalies are most often found in refractory elements of relatively low mass, so Sr is a prime target for study. The four stable isotopes of strontium are useful for discerning the various nucleosynthetic origins of early\nsolar system building blocks and the timing of\naccretion processes. Strontium-84 is the least abundant\n(0.56%) of these isotopes, but is particularly significant\nin being a p-process only nuclide that is produced in\ncore-collapse or type Ia supernovae [2,3]. The more\nabundant isotopes ^(86)Sr (9.86%), ^(87)Sr (7.00%) and ^(88)Sr (82.58%) are produced in s- and r-processes in\nasymptotic giant branch stars and other stellar types\n[4]. Additionally, ^(87)Sr is produced by ^(87)Rb decay in\nproportions that dominate over possible nucleosynthetic variations but provide timings of early solar system processes, most notably volatile element depletion [5-7]. Furthermore, variations in strontium isotopic ratios caused by high-temperature massdependent fractionation [8] are also important [9-12], as they provide insights into nebular and accretionary processes.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87163, title ="^(36)Cl-^(36)S in Allende CAIs: Implication for the origins of ^(36)Cl in the early solar system", author = "Tang, H. and Liu, M-C.", pages = "2618", month = "March", year = "2017", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180615-132505821", note = "© 2017 Lunar and Planetary Institute.", revision_no = "10", abstract = "Chlorine-36 (t_(1/2)=0.3 Myr) decays to either ^(36)Ar (98%, β-) or ^(36)S (1.9%, ε and β+). This radionuclide\ncan be produced by either charged particle irradiation\n[1,2] or stellar nucleosynthesis [3]. Evidence for the prior\nexistence of ^(36)Cl in the Early Solar System (ESS) comes\nfrom radiogenic excesses of ^(36)Ar [4,5] and/or ^(36)S [6-9] in secondary phases (e.g., sodalite and wadalite) of ESS materials such as Ca, Al-rich inclusions (CAIs) and chondrules. However, the inferred initial ^(36)Cl/^(35)Cl ratios vary over three orders of magnitude among different chondrite constituents (5×10^(-6)-9×10^(-3)) [6-9]. Interestingly, although the initial ^(36)Cl/^(35)Cl ratios inferred in previous studies vary widely, all secondary phases bearing evidence for live ^(36)Cl in the ESS measured so far lack resolvable ^(26)Mg excesses\ndue to the decay of ^(26)Al (t_(1/2) = 0.7 Myr), implying that ^(36)Cl and ^(26)Al may have been produced by different processes and/or incorporated into ESS solids at different times. Given that secondary phases may have formed late, the ^(36)S anomalies in secondary phases point to either a very high ^(36)Cl/^(35)Cl initial ratio (~10^(-2)) in the ESS, or a late irradiation scenario for the local production of ^(36)Cl (> 3 Myr after CAI formation) [9]. The elevated ESS ratio of ^(36)Cl/^(35)Cl ~10^(-2) inferred from [9] far exceeds the predictions from any\nmodel of stellar nucleosynthesis; therefore, a late irradiation scenario producing ^(36)Cl is currently the favored idea. In this framework, ^(36)Cl would be be produced in the nebular gas and then incorporated into the CAIs via aqueous alteration, which formed secondary phases.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87191, title ="Evidence for a Single Stellar Environment of R-Process Nucelosynthesis from Live ^(247)Cm in the Early Solar System", author = "Tissot, F. L. H. and Dauphas, N.", pages = "1605", month = "March", year = "2016", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180618-110835845", note = "© 2016 Lunar and Planetary Institute.", revision_no = "9", abstract = "The Early Solar System (ESS) abundance of short-lived radionuclides (SLR) can be interpreted in terms of a free-decay interval (Δ) or a mixing timescale (τ), which correspond to complete or partial isolation from fresh nucleosynthetic inputs of the molecular could core parental to the solar system. For r-nuclides, however, the abundances measured in ESS materials require less isolation for ^(107)Pd and ^(182)Hf (Δ~ 5 Myr) than for ^(129)I (Δ=100±7 Myr) and ^(244)Pu (Δ=158±85 Myr) [1]. To make sense of these observations, models have proposed the existence of up to three different r-processes producing, respectively, the light r-nuclides, the heavy r-nuclides and the actinides [1-4]. In this work [5], we determined the ESS abundance of another short-lived r-nuclide, the long sought after ^(247)Cm [e.g., 6-7], and show how this additional constraint is consistent with either three different r-processes, or, and more likely, a single stellar environment of r-process nucleosynthesis and a partial s-process origin for ^(107)Pd and ^(182)Hf.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87190, title ="^(238)U/^(235)U Ratio in Carbonates as a Global Paleoredox Proxy", author = "Chen, C. and Tissot, F. L. H.", pages = "1677", month = "March", year = "2016", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180618-110140466", note = "© 2016 Lunar and Planetary Institute.", revision_no = "9", abstract = "Uranium has two main oxidation states: 4+ and 6+.\nIn the modern ocean, U is present in its most oxidized,\nhighly soluble form, U^(6+) [1]. In the Archean, however,\nwhen the oxygen concentration in the atmosphere was\nlow, U was likely present in its reduced 4+ state, which\nhas low solubility. This contrast in solubility behavior\ndepending on the redox conditions makes U a very\nuseful proxy of the global oxygenation state of the\nEarth. Indeed, one of the most important indicators that\nthe pO_2 was low in the Archean is the survival of detrital\nuraninite [2], which is unstable under the modern\noxic conditions.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87187, title ="^(36)Cl-^(36)S Systematics in Curious Marie: A ^(26)Mg-Rich U-Depleted Fine-Grained CAI from Allende", author = "Tang, H. and Liu, M-C.", pages = "2539", month = "March", year = "2016", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180618-102607087", note = "© 2016 Lunar and Planetary Institute.", revision_no = "9", abstract = "Chlorine-36 (t_(1/2)=0.3 Myr) decays to either ^(36)Ar (98%, β-) or ^(36)S (1.9%, ε and β+). This radionuclide can be produced either by local irradiation of gas and/or dust of solar composition [1-2] or by stellar nucleosynthesis in AGB stars or Type II supernovae [3]. Evidence for the presence of 36Cl in the early Solar System (ESS) comes from radiogenic excesses of ^(36)Ar [4] and/or ^(36)S [5-9] in secondary phases (e.g., sodalite and wadalite) in ESS materials such as Calcium, Aluminum-rich inclusions (CAIs) and chondrules. Though the presence of ^(36)Cl in the ESS has been demonstrated, the inferred initial ^(36)Cl/^(35)Cl ratios vary a lot (from 1.0×10^(-7) to 2×10^(-5)) from one inclusion to another [5-9]. Interestingly, all secondary phases measured so far lack resolvable ^(26)Mg excesses that could be due to the decay of ^(26)Al (t_(1/2) = 0.7 Myr), implying that ^(36)Cl and ^(26)Al may not have been derived from the same source. Given that ^(26)Al could have come from a stellar source [10] and that secondary phases should have formed late, we are left with either a very high ^(36)Cl/^(35)Cl initial ratio (~ 10^(-2)) in the ESS, or a late (> 3 Myr after CAI formation) irradiation\nscenario for the production of ^(36)Cl [9]. ^(36)Cl/^(35)Cl ~10^(-2) far exceeds the predictions from any model (stellar\nnucleosynthesis or irradiation); therefore, a late irradiation scenario producing ^(36)Cl at the observed level is favored. In this framework, ^(36)Cl is produced in the early solar nebula and incorporated into CAIs via aqueous activities, which could also lead to the formation of sodalite.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87156, title ="Developments in PF-HPLC (pneumatic-fluoropolymer high performance liquid chromatography)", author = "Hu, J. Y. and Tissot, F. L. H.", pages = "2939", month = "March", year = "2015", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180615-105518983", note = "© 2015 Lunar and Planetary Institute.\n\n", revision_no = "10", abstract = "Return missions are providing unique opportunities\nto deepen our knowledge of the formation and\nevolution of the solar system. The six Apollo missions\nhave been critical in shaping our understanding of the\nEarth-Moon history [1], and the recent Genesis (solar\nwind; e.g., [2]), Stardust (cometary dust from Wild 2;\ne.g., [3,4]) and Hayabusa (dust from S-type asteroid\nfrom Itokawa; e.g., [5]) missions brought in a wealth\nof data.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87162, title ="Uranium isotope variations in group II refractory inclusions", author = "Tissot, F. L. H. and Dauphas, N.", pages = "2819", month = "March", year = "2015", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180615-132022061", note = "© 2015 Lunar and Planetary Institute.", revision_no = "9", abstract = "The ^(235)U/^(238)U ratio shows little variability in most\nterrestrial and meteoritic bodies (≤1 ‰) [1-3]. In contrast,\nlarge excesses of ^(235)U, up to 3.5 ‰, have been\nfound in a few Calcium-Aluminum rich inclusions\n(CAIs) and have been interpreted as evidence of live\n^(247)Cm (t_(1/2) = 15.6 My) in the early solar system (SS)\n[4]. Though this is a plausible explanation, it relies on\nfour points with high Nd/U ratio that define a “pseudochron”,\nso more work is needed to determine the cause\nof U isotope variations in CAIs. Here, we report some\npreliminary results on the identification, characterization\nand U isotopic analysis of 12 fine-grained, group\nII, CAIs from the Allende meteorite.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87186, title ="On the ^(238)U/^(235)U Paleoredox Proxy: A Word of Caution with Black Shales and the Need for Sequential Leaching of Carbonates", author = "Tissot, F. L. H. and Go, B. M.", pages = "2590", month = "March", year = "2014", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180618-101402583", note = "© 2014 Lunar and Planetary Institute.", revision_no = "11", abstract = "In the past several years, there has been a growing\ninterest in the emerging U stable isotope systematic as\nit could prove a useful tracer of the redox state of the\nglobal ocean through time. However, important questions\nremain to be addressed before the full potential of\nthis proxy can be exploited. In this abstract we show 1)\nhow detrital contamination can be dealt with to avoid\ndata misinterpretation, and 2) that bulk carbonates can\nrecord the δ^(238)U value of the seawater they form from.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87161, title ="Introducing Teflon-HPLC", author = "Tissot, F. L. H. and Ireland, T. J.", pages = "2867", month = "March", year = "2013", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180615-131518002", note = "© 2013 Lunar and Planetary Institute.", revision_no = "10", abstract = "With increasingly ambitious sample return missions and instrumentation of ever-increasing sensitivity and precision, column chromatography appears to be the neglected step-child of isotope geochemistry and little improvement has been brought to it in the past few decades. Traditional column chromatography (i.e., open-system, gravity driven) techniques\nsuffer from significant limitations pertaining to the overall length of column, resin size and diffusion effects, which can severely compromise separation efficiencies. Furthermore, some fine-scale separations still require complicated multi-step, highly time-consuming protocols (e.g. Ni-Mg, [1]). High-performance liquid chromatography (HPLC), while overcoming many of these limitations (e.g. a closed-system setup; the ability to pressurize the system, hence longer columns and better separation; a semi-automated set-up), is not immune to severe drawbacks. Mainly, 1) the liquid flow path often contains glass or metal parts which are easily corroded/dissolved by concentrated acids or organic solvents, leading to contamination of the samples, and 2) the electronic controls and housing are often spatially associated with the HPLC unit, drastically shortening the lifespan of the apparatus as the metallic parts rapidly corrode in these harsh chemical environments [e.g. 2].", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87206, title ="Controls on Iron Isotope Variations in Planetary Magmas", author = "Dauphas, N. and Roskosz, M.", pages = "1525", month = "March", year = "2012", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180618-152419999", note = "© 2012 Lunar and Planetary Institute.", revision_no = "12", abstract = "Of all documented planetary bodies\nsuch as Mars, Vesta, and the angrite parent-body\n(APB), Earth is the most oxidized [1]. Understanding\nhow and when Earth's mantle acquired its present redox\nconditions is a major standing question in planetary\nsciences. Previsous studies have suggested that\niron isotopes could be good tracers of redox conditions\nduring melting [2]. Terrestrial basalts, as well as more\nfelsic rocks, tend to have heavy iron isotopic composition\nrelative to chondrites and Earth’s mantle [2, 3 and\nreferences therein]. For example, the average MORB\nδ^(56)Fe value is ~+0.1 ‰ while chondrites have\nδ^(56)Fe~+0 ‰ (Fig. 1). In contrast, basalts from Mars\nand Vesta have Fe isotopic compositions identical to\nchondrites within uncertainty. Three interpretations\nhave been proposed to explain this feature: (1) during\nthe Moon-forming giant impact, some isotopically\nlight Fe was evaporated, leaving a residue enriched in\nheavy Fe isotopes [4]; (2) equilibriation between metal\nand high-pressure phases such as ferropericlase and\npost-perovskite created iron isotopic fractionation in\nEarth's mantle [5]; or (3) the isotopic composition\nmeasured in crustal rocks from Earth was produced by\nequilibrium or kinetic isotope fractionation between\nmantle peridotite and melt [2,6,7]. This poses several\ncritical questions. What aspect of the melting process\nproduces Fe isotopic fractionation? Why does melting\non Earth or the APB fractionate Fe isotopes while on\nMars and Vesta such fractionation is absent?", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87192, title ="Development of an Automated All-Teflon HPLC System for the Analysis of Precious Geological and Extraterrestrial Materials", author = "Ireland, T. J. and Dauphas, N.", pages = "2141", month = "March", year = "2012", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180618-111633329", note = "© 2012 Lunar and Planetary Institute.", revision_no = "8", abstract = "With the recent success of sample return missions such as Genesis (solar wind; e.g., [1-2]), Stardust (cometary dust particles; e.g., [3-5]) and Hayabusa (asteroid; e.g., [6-7]), as well as the recently announced OSIRIS-REx mission (estimated to collect more than 60 g of asteroidal material), it is clear that a new frontier of solar system research has been entered. Given the precious nature of these samples, it is also apparent that laboratory techniques need to be made as efficient as possible in order to maximize the information that we can gain from these unique and invaluable specimens. To determine the chemical and isotopic compositions of these samples, it is often necessary to separate and purify elements of cosmochemical interest from the host rocks. A widely used method for the chemical separation of elements, following sample digestion, is through column chromatography techniques.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87193, title ="^(238)U/^(235)U Ratios of Anagrams: Angrites and Granites", author = "Tissot, F. L. H. and Dauphas, N.", pages = "1981", month = "March", year = "2012", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180618-131630058", note = "© 2012 Lunar and Planetary Institute.", revision_no = "9", abstract = "Significant ^(238)U/^(235)U variations have been documented in meteoritic [e.g. 1-4] and terrestrial [5] samples, which can affect Pb-Pb ages. In most cases, the cause of these variations is not understood. Here, we report an extensive study of the U isotopic composition of planetary crustal rocks. Determination of ^(238)U/^(235)U ratio in angrites is critical to establish their age: an important anchor in early solar system chronology [6,7]. The extent to which the protolith of terrestrial granites affects their U isotopic composition is unknown. We report high-precision U isotope measurements of angrites and terrestrial granites to address these two outstanding questions in solar system chronology and crustal differentiation.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87212, title ="Development of High Precision ^(238)U/^(235)U Ratio Measurements for Cosmochemical Applications", author = "Tissot, F. and Dauphas, N.", pages = "1082", month = "March", year = "2011", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180619-085035219", note = "© 2011 Lunar and Planetary Institute.", revision_no = "11", abstract = "Observations of variations in the ^(238)U/^(235)U ratio at the 0.1‰ level in both terrestrial [1] and meteoritic samples [e.g. 2-5], challenged the assumption of a constant ^(238)U/^(235)U ratio throughout the solar system (SS). The light isotopic compositions measured in some CAIs could be due to the presence of live ^(247)Cm in the early SS as this short-lived radionuclide decays into ^(235)U with a half-life t_(1/2)=15.6Myr. The most immediate consequence of these variations is that the isotopic composition of uranium has to be measured in each CAI to get accurate Pb-Pb ages [5,6]. Given the scale of the variations, achieving high precision measurements is necessary to fully resolve\ncompositional differences between samples and to be\nable to use the potential of the U isotopic system in\nterrestrial and extraterrestrial samples.", }