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Towards consistent chronology in the early Solar System: high resolution 53Mn-53Cr chronometry for chondrules.

Description: New high-precision {sup 53}Mn-{sup 53}Cr data obtained for chondrules extracted from a primitive ordinary chondrite, Chainpur (LL3.4), define an initial {sup 53}Mn/{sup 55}Mn ratio of (5.1 {+-} 1.6) x 10{sup -6}. As a result of this downward revision from an earlier higher value of (9.4 {+-} 1.7) x 10{sup -6} for the same meteorite (Nyquist et al. 2001), together with an assessment of recent literature, we show that a consistent chronology with other chronometers such as the {sup 26}Al-{sup 26}Mg and {sup 207}Pb-{sup 206}Pb systems emerges in the early Solar System.
Date: May 2, 2007
Creator: Yin, Q; Jacobsen, B; Moynier, F & Hutcheon, I D
Partner: UNT Libraries Government Documents Department

Renewed Search for FUN (Fractionated and Unidentified Nuclear Effects) in Primitive Chondrites

Description: Ca-Al-rich inclusions (CAIs) found in primitive chondrites record processes and conditions of the earliest solar system as they are the oldest known solid objects formed in the solar system [1,2]. CAIs with fractionation and unidentified nuclear anomalies (FUN CAIs; [3]) are very rare and thusfar found exclusively in CV carbonaceous chondrites (e.g., Allende and Vigarano)[4]. FUN CAIs are characterized by large nucleosynthetic anomalies in several elements (Ca, Ti, Si, Sr, Ba, Nd, and Sm), large mass-dependant isotope fractionation (Mg, Si, and O), and very little initial {sup 26}Al [4,5 and reference therein]. Formation of FUN CAIs by thermal processing of presolar dust aggregates prior to the injection of {sup 26}Al into the protoplanetary disk has been proposed. More recently [5] proposed that FUN CAIs formed from a protosolar molecular cloud after injection of {sup 26}Al but before {sup 26}Al and {sup 27}Al were completely homogenized. Therefore discovering more FUN CAIs to perform U-Pb and other short-lived chronometric dating will provide key constraints on the age of the solar system, the isotopic composition of the protosolar molecular cloud, the earliest stages of the thermal processing in the solar system and the timing of {sup 26}Al and other short-lived radionuclide injection into the nascent solar system. Most known FUN CAIs were discovered and studied > 30 yr ago, and their isotope ratios determined using thermal ionization mass spectrometry (TIMS). Most of these FUN CAIs were almost or entirely consumed during their respective analyses. [5] recently identified a new FUN CAI (NWA 779 KS-1) based on O and Mg isotope ratios determined by SIMS and MCICPMS, respectively. We have initiated a systematic search for FUN CAIs in primitive chondrites, taking advantage of the large mass-dependant Mg isotope effects known for FUN inclusions with little or no inferred {sup 26}Al. Our strategy is to ...
Date: April 7, 2011
Creator: Tollstrup, D L; Wimpenny, J B; Yin, Q -; Ebel, D S; Jacobsen, B & Hutcheon, I D
Partner: UNT Libraries Government Documents Department

A novel method to develop an otolith microchemistry model to determine striped bass habitat use in the San Francisco Estuary

Description: Otolith Sr/Ca has become a popular tool for hind casting habitat utilization and migration histories of euryhaline fish. It can readily identify habitat shifts of diadromous fish in most systems. Inferring movements of fish within estuarine habitat, however, requires a model of that accounts of the local water chemistry and the response of individual species to that water chemistry, which is poorly understood. Modeling is further complicated by the fact that high marine Sr and Ca concentrations results in a rapid, nonlinear increase in water Sr/Ca and {sup 87}Sr/{sup 86}Sr between fresh and marine waters. Here we demonstrate a novel method for developing a salinity-otolith Sr/Ca model for the purpose of reconstructing striped bass (Morone saxatilis) habitat use in the San Francisco Bay estuary. We used correlated Sr/Ca and {sup 87}Sr/{sup 86}Sr ratios measurements from adult otoliths from striped bass that experienced a range of salinities to infer striped bass otolith Sr/Ca response to changes in salinity and water Sr/Ca ratio. Otolith {sup 87}Sr/{sup 86}Sr can be assumed to accurately record water {sup 87}Sr/{sup 86}Sr because there is no biological fractionation of Sr isotopes. Water {sup 87}Sr/{sup 86}Sr can in turn be used to estimate water salinity based on the mixing of fresh and marine water with known {sup 87}Sr/{sup 86}Sr ratios. The relationship between adjacent analyses on otoliths of Sr/Ca and {sup 87}Sr/{sup 86}Sr by LA-ICP-MS and MC-ICP-MS (r{sup 2} = 0.65, n = 66) is used to predict water salinity from a measured Sr/Ca ratio. The nature of this non-linear model lends itself well to identifying residence in the Delta and to a lesser extent Suisun Bay, but does not do well locating residence within the more saline bays west of Carquinez Strait. An increase in the number of analyses would improve model confidence, but ultimately the precision ...
Date: June 14, 2006
Creator: Phillis, C C; Ostrach, D J; Gras, M; Yin, Q; Ingram, B L; Zinkl, J G et al.
Partner: UNT Libraries Government Documents Department

Discovery, Mineral Paragenesis and Origin of Wadalite in Meteorites

Description: The mineral wadalite (ideal and simplified formula: Ca{sub 6}Al{sub 5}Si{sub 2}O{sub 16}Cl{sub 3}) has been discovered for the first time in a meteorite, specifically in the coarse-grained, igneous Type B calcium-aluminum-rich inclusions (CAIs) from the CV carbonaceous chondrite Allende. We report the results of electron microprobe, scanning electron microscopy and transmission electron microscopy analyses of wadalite-bearing assemblages in the Allende CAIs and propose that wadalite formed by metamorphic reaction between akermanitic melilite and anorthite, likely mediated by chlorine-bearing fluids. Petrographic relationships support the likelihood of multistage alterations by fluids of different chemistries interspersed or coinciding with thermal metamorphic episodes on the Allende parent asteroid. Fluid involvement in metamorphism of Allende CAIs implies that these objects experienced open-system alteration after accretion into the CV chondrite parent asteroid which may have resulted in disturbances of their oxygen- and magnesium-isotope systematics.
Date: July 9, 2009
Creator: Ishii, H A; Krot, A N; Bradley, J P; Keil, K; Nagashima, K; Teslich, N et al.
Partner: UNT Libraries Government Documents Department

Formation of short-lived radionuclides in the protoplanetary disk during late-stage irradiation of a volatile-rich reservoir

Description: The origin of short-lived (t{sub 1/2} < 5 Myr) and now extinct radionuclides ({sup 10}Be, {sup 26}Al, {sup 36}Cl, {sup 41}Ca, {sup 53}Mn, {sup 60}Fe; hereafter SLRs) is fundamental to understanding the formation of the early solar system. Two distinct classes of models have been proposed to explain the origin of SLRs: (1) injection from a nearby stellar source (e.g., supernova, asymptotic giant branch star or Wolf-Rayet star) and (2) solar energetic particle irradiation of dust and gas near the proto-Sun. Recent studies have demonstrated that {sup 36}Cl was extant in the early solar system. However, its presence, initial abundance and the noticeable decoupling from {sup 26}Al raise serious questions about the origin of SLRs. Here we report {sup 36}Cl-{sup 36}S and {sup 26}Al-{sup 26}Mg systematics for wadalite and grossular, secondary minerals in a calcium-aluminum-rich inclusion (CAI) from the CV chondrite Allende that allow us to reassess the origin of SLRs. The inferred abundance of {sup 36}Cl in wadalite, corresponding to a {sup 36}Cl/{sup 35}Cl ratio of (1.81 {+-} 0.13) x 10{sup -5}, is the highest {sup 36}Cl abundance reported in any early solar system material. The high level of {sup 36}Cl in wadalite and the absence of {sup 26}Al ({sup 26}Al/{sup 27}Al {le} 3.9 x 10{sup -6}) in co-existing grossular indicates that (1) {sup 36}Cl formed by late-stage solar energetic particle irradiation and (2) the production of {sup 36}Cl, recorded by secondary minerals, is unrelated to the origin of {sup 26}Al and other SLRs ({sup 10}Be, {sup 53}Mn) recorded by primary minerals of CAIs and chondrules. We conclude that 36Cl was produced by solar energetic particle irradiation of a volatile-rich reservoir in an optically thin protoplanetary disk adjacent to the accretion region of the CV chondrite parent asteroid.
Date: November 30, 2010
Creator: Jacobsen, B; Matzel, J; Hutcheon, I D; Krot, A N; Yin, Q -; Nagashima, K et al.
Partner: UNT Libraries Government Documents Department