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Yuji Sano - One of the best experts on this subject based on the ideXlab platform.
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Ion Microprobe u pb dating of zircon with a 15 micrometer spatial resolutIon using nanosims
Gondwana Research, 2008Co-Authors: Naoto Takahata, Yukiyasu Tsutsumi, Yuji SanoAbstract:Abstract We developed a 238U–206Pb⁎ and 207Pb⁎–206Pb⁎ zircon dating method using a Cameca NanoSIMS NS50 Ion Microprobe. A 7-to 9-nA O− primary beam was used to sputter a 15-μm crater, and secondary positive Ions were extracted for mass analysis using the Mattauch–Herzog geometry. The multicollector system was modified to detect 90Zr+, 204Pb+, 206Pb+, 238U16O+, and 238U16O2+ Ions simultaneously. A mass resolutIon of about 4000 at 10% peak height and with a flat peak top was attained, and the sensitivity of Pb was about 4 cps·nA− 1·ppm− 1. A multicrystal zircon standard (QGNG) from South Australia with a U–Pb age of 1842 Ma was used as a reference for Pb+/UO+–UO2+/UO+ calibratIon, and on the basis of the positive correlatIon between these ratios, we determined the sample 206Pb/238U ratios. 207Pb/206Pb ratios were measured by magnetic scanning in single-collector mode. The standard zircons 91500, from Canada, and SL13, from Sri Lanka, were analyzed against QGNG. Observed 238U–206Pb⁎ and 207Pb⁎–206Pb⁎ ages agreed well with published ages within experimental error. Then, 16 zircon grains in a metamorphic rock from Nagasaki, Japan, were analyzed. Observed ages were compatible with SHRIMP ages, suggesting that the NanoSIMS with a 15-μm probe diameter is suitable for Ion Microprobe U–Pb zircon dating.
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Ion Microprobe uranium-thorium-lead dating of Shergotty phosphates
Meteoritics & Planetary Science, 2000Co-Authors: Yuji Sano, Kentaro Terada, Setsuo Takeno, Lawrence A. Taylor, Harry Y. McsweenAbstract:— We report Ion Microprobe U-Th-Pb dating of Shergotty phosphates by means of the sensitive high-resolutIon Ion Microprobe (SHRIMP) recently installed at Hiroshima University, Japan. ten analyses of whitlockite (merrillite) and three analyses of apatite indicate a 238u/206pb isochron age of 225 ± 200 ma and a tera-wasserburg concordia-constrained linear three-dimensIonal isochron age of 217 ± 110 ma in the 238u/206pb-207pb/206pb204pb/206pb diagram. These ages agree well with the 232Th-208pb age of 189 ± 83 Ma, which suggests that primary crystallizatIon or a shock metamorphic event defined the formatIon age of the phosphate minerals. The average of the later two ages, 204 ± 68 Ma, is consistent with the previously published Rb-Sr age of 165 ± 11 Ma and U-Th-Pb age of ∼200 Ma. These show marginal agreement with the 40Ar-39Ar age of 254 ± 10 Ma but are significantly different from the Sm-Nd age of 360 ± 16 Ma. Taking into account the closure temperature of the U-Pb system in apatite, we suggest the time that Shergotty last experienced a temperature of ∼900 °C was 204 ± 68 Ma.
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Ion Microprobe U-PB DATING OF APATITE
Chemical Geology, 1999Co-Authors: Yuji Sano, Takayuki Oyama, Kentaro Terada, Hiroshi HidakaAbstract:Abstract To illustrate in situ Sensitive High ResolutIon Ion Microprobe (SHRIMP) analysis of apatites, Pb isotopes and Pb/U ratios of five apatite samples with different ages have been measured using SHRIMP II Ion Microprobe at Hiroshima University. The `PRAP' apatite from a carbonatite complex at Prairie Lake, Ontario with a 207 Pb ∗– 206 Pb ∗ age of 1156±45 Ma (2 σ) was used as the standard for 206 Pb + / 238 U + – 238 U 16 O + / 238 U + calibratIon. Apatites from the Poohbah Lake alkaline complex give 204 Pb / 206 Pb – 238 U / 206 Pb and 204 Pb / 206 Pb – 207 Pb / 206 Pb isochron ages of 2726±145 Ma (2 σ) and 2701±86 Ma (2 σ), in agreement with a conventIonal TIMS 207 Pb ∗– 206 Pb ∗ age of 2667±10 Ma (2 σ) and a K–Ar isochron age of 2706±46 Ma (2 σ). For the remaining three apatite samples the 204 Pb / 206 Pb – 238 U / 206 Pb and 204 Pb / 206 Pb – 207 Pb / 206 Pb isochron ages obtained by SHRIMP are consistent with radiometric and geological ages in the literature.
Joseph L Wooden - One of the best experts on this subject based on the ideXlab platform.
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Ion Microprobe measurement of strontium isotopes in calcium carbonate with applicatIon to salmon otoliths
Geochimica et Cosmochimica Acta, 2005Co-Authors: P K Weber, Charles R Bacon, I D Hutcheon, Lynn B Ingram, Joseph L WoodenAbstract:The Ion Microprobe has the capability to generate high resolutIon, high precisIon isotopic measurements, but analysis of the isotopic compositIon of strontium, as measured by the 87Sr/86Sr ratio, has been hindered by isobaric interferences. Here we report the first high precisIon measurements of 87Sr/86Sr by Ion Microprobe in calcium carbonate samples with moderate Sr concentratIons. We use the high mass resolving power (7000 to 9000 M.R.P.) of the SHRIMP-RG Ion Microprobe in combinatIon with its high transmissIon to reduce the number of interfering species while maintaining sufficiently high count rates for precise isotopic measurements. The isobaric interferences are characterized by peak modeling and repeated analyses of standards. We demonstrate that by sample-standard bracketing, 87Sr/86Sr ratios can be measured in inorganic and biogenic carbonates with Sr concentratIons between 400 and 1500 ppm with ∼2‰ external precisIon (2σ) for a single analysis, and subpermil external precisIon with repeated analyses. Explicit correctIon for isobaric interferences (peak-stripping) is found to be less accurate and precise than sample-standard bracketing. Spatial resolutIon is ∼25 μm laterally and 2 μm deep for a single analysis, consuming on the order of 2 ng of material. The method is tested on otoliths from salmon to demonstrate its accuracy and utility. In these growth-banded aragonitic structures, one-week temporal resolutIon can be achieved. The analytical method should be applicable to other calcium carbonate samples with similar Sr concentratIons.
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migratIon and rearing histories of chinook salmon oncorhynchus tshawytscha determined by Ion Microprobe sr isotope and sr ca transects of otoliths
Canadian Journal of Fisheries and Aquatic Sciences, 2004Co-Authors: Charles R Bacon, P K Weber, Kimberly Larsen, Reginald R Reisenbichler, John A Fitzpatrick, Joseph L WoodenAbstract:Strontium isotope and Sr/Ca ratios measured in situ by Ion Microprobe along radial transects of otoliths of juvenile chinook salmon (Oncorhynchus tshawytscha) vary between watersheds with contrasti...
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late pleistocene granodiorite beneath crater lake caldera oregon dated by Ion Microprobe
Geology, 2000Co-Authors: Charles R Bacon, Harold M Persing, Joseph L Wooden, Trevor IrelandAbstract:Variably melted granodiorite blocks ejected during the Holocene caldera-forming eruptIon of Mount Mazama were plucked from the walls of the climactic magma chamber at ∼5 km depth. Ion-Microprobe U-Pb dating of zircons from two unmelted granodiorite blocks with SHRIMP RG (sensitive high-resolutIon Ion Microprobe–reverse geometry) gives a nominal 238 U/ 206 Pb age of \(100^{{+}78}_{{-}80}\) ka, or \(174^{{+}89}_{{-}115}\) ka when adjusted for an initial 230 Th deficit. SHRIMP RG U-Th measurements on a subset of the zircons yield a 230 Th/ 238 U isochron age of 112 ± 24 ka, considered to be the best estimate of the time of solidificatIon of the pluton. These results suggest that the granodiorite is related to andesite and dacite of Mount Mazama and not to magmas of the climactic eruptIon. The unexposed granodiorite has an area of at least 28 km 2 . This young, shallow pluton was emplaced in virtually the same locatIon where a similarly large magma body accumulated and powered violent explosive eruptIons ∼7700 yr ago, resulting in collapse of Crater Lake caldera.
Charles R Bacon - One of the best experts on this subject based on the ideXlab platform.
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Ion Microprobe measurement of strontium isotopes in calcium carbonate with applicatIon to salmon otoliths
Geochimica et Cosmochimica Acta, 2005Co-Authors: P K Weber, Charles R Bacon, I D Hutcheon, Lynn B Ingram, Joseph L WoodenAbstract:The Ion Microprobe has the capability to generate high resolutIon, high precisIon isotopic measurements, but analysis of the isotopic compositIon of strontium, as measured by the 87Sr/86Sr ratio, has been hindered by isobaric interferences. Here we report the first high precisIon measurements of 87Sr/86Sr by Ion Microprobe in calcium carbonate samples with moderate Sr concentratIons. We use the high mass resolving power (7000 to 9000 M.R.P.) of the SHRIMP-RG Ion Microprobe in combinatIon with its high transmissIon to reduce the number of interfering species while maintaining sufficiently high count rates for precise isotopic measurements. The isobaric interferences are characterized by peak modeling and repeated analyses of standards. We demonstrate that by sample-standard bracketing, 87Sr/86Sr ratios can be measured in inorganic and biogenic carbonates with Sr concentratIons between 400 and 1500 ppm with ∼2‰ external precisIon (2σ) for a single analysis, and subpermil external precisIon with repeated analyses. Explicit correctIon for isobaric interferences (peak-stripping) is found to be less accurate and precise than sample-standard bracketing. Spatial resolutIon is ∼25 μm laterally and 2 μm deep for a single analysis, consuming on the order of 2 ng of material. The method is tested on otoliths from salmon to demonstrate its accuracy and utility. In these growth-banded aragonitic structures, one-week temporal resolutIon can be achieved. The analytical method should be applicable to other calcium carbonate samples with similar Sr concentratIons.
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migratIon and rearing histories of chinook salmon oncorhynchus tshawytscha determined by Ion Microprobe sr isotope and sr ca transects of otoliths
Canadian Journal of Fisheries and Aquatic Sciences, 2004Co-Authors: Charles R Bacon, P K Weber, Kimberly Larsen, Reginald R Reisenbichler, John A Fitzpatrick, Joseph L WoodenAbstract:Strontium isotope and Sr/Ca ratios measured in situ by Ion Microprobe along radial transects of otoliths of juvenile chinook salmon (Oncorhynchus tshawytscha) vary between watersheds with contrasti...
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late pleistocene granodiorite beneath crater lake caldera oregon dated by Ion Microprobe
Geology, 2000Co-Authors: Charles R Bacon, Harold M Persing, Joseph L Wooden, Trevor IrelandAbstract:Variably melted granodiorite blocks ejected during the Holocene caldera-forming eruptIon of Mount Mazama were plucked from the walls of the climactic magma chamber at ∼5 km depth. Ion-Microprobe U-Pb dating of zircons from two unmelted granodiorite blocks with SHRIMP RG (sensitive high-resolutIon Ion Microprobe–reverse geometry) gives a nominal 238 U/ 206 Pb age of \(100^{{+}78}_{{-}80}\) ka, or \(174^{{+}89}_{{-}115}\) ka when adjusted for an initial 230 Th deficit. SHRIMP RG U-Th measurements on a subset of the zircons yield a 230 Th/ 238 U isochron age of 112 ± 24 ka, considered to be the best estimate of the time of solidificatIon of the pluton. These results suggest that the granodiorite is related to andesite and dacite of Mount Mazama and not to magmas of the climactic eruptIon. The unexposed granodiorite has an area of at least 28 km 2 . This young, shallow pluton was emplaced in virtually the same locatIon where a similarly large magma body accumulated and powered violent explosive eruptIons ∼7700 yr ago, resulting in collapse of Crater Lake caldera.
J. N. Goswami - One of the best experts on this subject based on the ideXlab platform.
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DeterminatIon of rare earth and refractory trace element abundances in early solar system objects by Ion Microprobe
Journal of Earth System Science, 2003Co-Authors: S. Sahijpal, K. K. Marhas, J. N. GoswamiAbstract:Experimental and analytical procedures devised for measurement of rare earth element (REE) abundances using a secondary Ion mass spectrometer (Ion Microprobe) are described. This approach is more versatile than the conventIonal techniques such as neutron activatIon analysis and isotope dilutIon mass spectrometry by virtue of its high spatial resolutIon that allows determinatIon of REE abundances in small domains (10-20 micron) within individual mineral phases. The Ion Microprobe measurements are performed at a low mass-resolving power adopting the energy-filtering technique (Zinner and Crozaz 1986) for removal and suppressIon of unresolved complex molecular interferences in the REE masses of interest. Synthetic standards are used for determining various instrument specific parameters needed in the data deconvolutIon procedure adopted for obtaining REE abundances. Results obtained from analysis of standards show that our Ion Microprobe may be used for determining REE abundances down to ppm range with uncertainties of ∼ 10 to 15%. Abundances of rare earth and several other refractory trace elements in a set of early solar system objects isolated from two primitive carbonaceous chondrites were determined using the procedures devised by us. The results suggest that some of these objects could be high temperature nebular condensates, while others are products of melting and recrystallizatIon of precursor nebular solids in a high temperature environment.
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stabilizatIon of the aravalli craton of northwestern india at 2 5 ga an Ion Microprobe zircon study
Chemical Geology, 1996Co-Authors: M. Wiedenbeck, J. N. Goswami, A B RoyAbstract:Abstract In order to establish the stabilizatIon age of the Aravalli Craton of northwestern India, we have used an Ion Microprobe to measure 207 Pb 206 Pb ages of zircons from six samples collected from the southern Aravalli Mountains. Our analyses gave precise results for four granitoids whose minimum crystallizatIon ages ranged between 2562 ± 6 and 2440 ± 8 Ma (1 σ). A single sample of gneiss gave an age of 2502 ± 4 Ma, which is unexpectedly younger than an age of 3281 Ma which we previously obtained from another gneissic sample. We interpret the 2502 Ma age as the time of emplacement of the sample's igneous protolith, suggesting that the Mewar Gneiss contains multiple metamorphic components of differing ages. Based on our data, we conclude that the southern segment of the Aravalli Craton had broadly stabilized by ∼ 2.5 Ga. This stabilized landmass formed the basement on which the younger Aravalli Supergroup was unconformably deposited. This study represents the first applicatIon of a small geometry Ion Microprobe for routine geochronology.
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High precisIon 207Pb206Pb zircon geochronology using a small Ion Microprobe
Geochimica et Cosmochimica Acta, 1994Co-Authors: M. Wiedenbeck, J. N. GoswamiAbstract:Abstract A small geometry Ion Microprobe (Cameca ims 4f) has been successfully used for the routine measurement of 207 Pb 206 Pb ratios in individual zircons with a spatial resolutIon of $ -20 μm. In spite of the lower sensitivity of the small Ion Microprobe, resulting from operating at high mass resolutIon (M/ΔM > 4600) in order to resolve isobaric molecular interferences, we can discern Archean components whose ages differ by ⪰ 50 Ma. A single measurement requires 90 min of data acquisitIon; thus, a comprehensive study of a zircon populatIon can be accomplished in a few days. Three sets of Precambrian zircons, analyzed earlier by other techniques, yielded ages which are within ± 2 σ of their “true” values. As our first “unknown” we analyzed zircons from a sample of orthogneiss collected from the Aravalli Craton of northwestern India. For this sample, we obtained a minimum age of 3281 ± 3 Ma (1σ), which we believe closely approximates the time of crystallizatIon of the gneiss's igneous protolith.
William Compston - One of the best experts on this subject based on the ideXlab platform.
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crystal orientatIon effects during Ion Microprobe u pb analysis of baddeleyite
Chemical Geology, 2000Co-Authors: Michael T.d. Wingate, William CompstonAbstract:Abstract We show that 206 Pb/ 238 U ratios measured in baddeleyite by Ion Microprobe vary significantly (up to ±10% or more) and systematically with the relative orientatIon of the baddeleyite crystal structure and the primary Ion beam. Low dispersIon between multiple analyses of single crystals demonstrates that it is possible to measure undispersed 206 Pb/ 238 U ratios in multi-grain baddeleyite samples if all material is in a single orientatIon. Owing to the small size of most crystals and their ubiquitous polysynthetic {100} twinning, however, it is extremely difficult to arrange a reasonable number of crystals in identical orientatIons for analysis. These orientatIon effects constitute an intractable problem, and place unacceptable limits on the accuracy and precisIon that can be obtained for 206 Pb/ 238 U in baddeleyite by Ion Microprobe techniques. Comparisons with isotope dilutIon measurements indicate that any Pb isotope discriminatIon during analysis of baddeleyite by Ion Microprobe is negligible, and there is no evidence that Pb isotope ratios vary with crystal orientatIon. Although the precisIon of 207 Pb/ 206 Pb ages decreases for younger samples, rocks younger than 1 Ga can be dated precisely if the baddeleyite is enriched sufficiently in uranium and if enough analyses are performed. We speculate that orientatIon effects in baddeleyite might involve channelling of primary Ions into the crystal, emissIon of secondary Ions along preferred directIons, and/or differential IonisatIon of secondary species. No orientatIon-related differences in 206 Pb/ 238 U were detected during Ion Microprobe analysis of zircon or monazite.
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Crystal orientatIon effects during Ion Microprobe U–Pb analysis of baddeleyite
Chemical Geology, 2000Co-Authors: Michael T.d. Wingate, William CompstonAbstract:Abstract We show that 206 Pb/ 238 U ratios measured in baddeleyite by Ion Microprobe vary significantly (up to ±10% or more) and systematically with the relative orientatIon of the baddeleyite crystal structure and the primary Ion beam. Low dispersIon between multiple analyses of single crystals demonstrates that it is possible to measure undispersed 206 Pb/ 238 U ratios in multi-grain baddeleyite samples if all material is in a single orientatIon. Owing to the small size of most crystals and their ubiquitous polysynthetic {100} twinning, however, it is extremely difficult to arrange a reasonable number of crystals in identical orientatIons for analysis. These orientatIon effects constitute an intractable problem, and place unacceptable limits on the accuracy and precisIon that can be obtained for 206 Pb/ 238 U in baddeleyite by Ion Microprobe techniques. Comparisons with isotope dilutIon measurements indicate that any Pb isotope discriminatIon during analysis of baddeleyite by Ion Microprobe is negligible, and there is no evidence that Pb isotope ratios vary with crystal orientatIon. Although the precisIon of 207 Pb/ 206 Pb ages decreases for younger samples, rocks younger than 1 Ga can be dated precisely if the baddeleyite is enriched sufficiently in uranium and if enough analyses are performed. We speculate that orientatIon effects in baddeleyite might involve channelling of primary Ions into the crystal, emissIon of secondary Ions along preferred directIons, and/or differential IonisatIon of secondary species. No orientatIon-related differences in 206 Pb/ 238 U were detected during Ion Microprobe analysis of zircon or monazite.
