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| Boise State University Isotope Geology Laboratory (IGL) |
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| Department of Geosciences |
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The Boise State University Isotope Geology Laboratory (IGL) is a new NSF-funded facility for the analysis of radiogenic isotopes in Earth materials, with a focus on high-precision geochronology (U-Pb zircon) and tracer isotope geochemistry. These tools can be applied to a variety of problems in igneous and metamorphic petrology, structural geology and tectonics, paleobiological evolution and paleoclimate change in deep time.
The IGL infrastructure includes a 750 sq. ft. clean laboratory and mass spectrometry facility, along with supporting mineral separations laboratories in the Department of Geosciences at Boise State University. Details of the Laboratory's construction and facilities can be found on the IGL Infrastructure page. Visit the IGL Personnel page for profiles of our researchers.
The IGL is a node in the EARTHTIME Network for the Calibration of Earth History. In the spirit of teamwork and cooperation fostered by this initiative, please take a look at our developing LABSHARE archive of analytical procedures used in the IGL for isotope geochemistry and geochronology.
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| Boise State University |
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| Math/Geo 207 |
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| 1910 University Drive |
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| Boise, ID 83725 |
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| tel: (208) 426-4669 |
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| fax: (208) 426-4061 |
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Analytical Capabilities of the IGL Clean Lab & GV Instruments Isoprobe-T Mass Spectrometer
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U-Pb geochronology
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Among the most sensitive tests of the mass spectrometer’s ion counting system, as well as the cleanliness of the clean laboratory and chemical separation procedures, is the analysis of radiogenic Pb/U ratios in accessory minerals like zircon. Using an in-house 205Pb-233U-235U isotopic spike, we have analyzed a suite of zircon standards, including the TEMORA and R33 zircons. The total common Pb of these single zircon analyses (a maximum for our total procedural blank) ranged between 0.3 and 2.1 pg, and averaged 0.9 pg; such a low blank is state-of-the-art for established geochronology labs. We anticipate consistently lower blanks as our dissolution microcapsules (the demonstrated major source of contaminant Pb) are further cleaned; these low procedural blanks allow the analysis of single zircon grains as young as Pliocene-Miocene.
Purified Pb and U from single dissolved grains or grain fragments (e.g. plucked from grain mounts) are loaded together with a silica gel - phosphoric acid emitter solution on single Re filaments. Pb and U isotopic compositions are measured sequentially as Pb+ ions (emitted at approximately 1300-1400°C) or UO2+ ions (emitted at approximately 1550-1650°C). Pb isotope ratios are measured in either of two modes: for large samples, by a two sequence dynamic routine peak jumping 205Pb between Faraday and Daly detectors to establish a real-time gain; or for small samples by peak jumping all isotopes on the Daly detector. U isotope ratios are nearly always measured by static collection on three Faraday cups.
As shown below, our current standard results include: BSU TEMORA 206Pb/238U age = 417.7 ± 0.1 Ma, n=7 (for comparison, MIT value = 417.6 ± 0.1 Ma); BSU R33 206Pb/238U age = 419.7 ± 0.1 Ma, n=7 (MIT value = 419.7 ± 0.1 Ma). Thus our reproducibility and accuracy relative to the MIT laboratory are better than 0.05%. On the basis of this data we have applied for and recently received the EARTHTIME mixed 205Pb-233U-235U isotopic spike.
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U-series isotopes
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For larger samples, measurement of the 234U/238U ratio is accomplished by a two sequence dynamic analysis, peak-switching the 235U beam between Faraday cup and Daly detector to establish a real time gain, and fractionation correcting relative to the known 235U/238U ratio. Alternatively, for small samples, the same measurment is made by peak jumping all isotopes (including 238U) into the Daly detector due to its large dynamic range. Using the latter method and maintaining a 1 Mcps 238U beam, the external reproducibility of the 234U/238U ratio in an in-house secular equilibrium U standard is 0.00005484 ± 8 (0.15%; 1-sigma, n=18; accepted value=0.00005489). We are currently utilizing 234U/238U measurements in isotope hydrology studies, and plan to extend our U-series analyses to 230Th/238U and 234U/238U in carbonates in the near future. |
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Pb isotopes
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Lead isotope ratios are measured on single Re filaments with a silica gel - phosphoric acid emitter solution in static mode, maintaining a 3V 208Pb beam for 200 cycles. Over 100 analyses of the NBS-981 Pb standard yield a highly reproducible average fractionation factor of 0.111 ± 0. 013 %/amu for all isotope ratios measured on the Faraday cups. The reproducible fractionation of the 208Pb/204Pb and 208Pb/206Pb ratios are illustrated below; sample loads are carefully matched to the size of standard samples and are run at similar temperatures and filament currents to control fractionation. We are capable of measuring Pb isotopic compositions of a variety of rocks, minerals, and ores, as well as environmental and anthropogenic samples including waters, soils, paints and gasoline. |
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Sr isotopes
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Strontium isotope ratios are measured on single Re filaments with a tantalum oxide emitter solution in a three sequence dynamic routine utilizing five Faraday cups. By maintaining a 4V 88Sr beam for 150 cycles, an internal precision of 4 ppm (1-sigma) on the 87Sr/86Sr ratio is consistently achieved with an exponential law correction relative to 86Sr/88Sr = 0.1194. External reproducibility of the NBS-987 Sr standard since installation has been maintained at 0.710251 ± 4 (6 ppm, 1-sigma, n=61; literature value=0.710248). We are capable of measuring the Sr isotopic compositions of a variety of rocks, minerals, fossil material, waters and soils. |
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Nd isotopes
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| Neodymium isotope ratios are measured as metal ions in a Re triple filament assembly in a three sequence dynamic routine utilizing seven Faraday cups. By maintaining a 3V 144Nd beam for 150 cycles, an internal precision of 4 ppm (1-sigma) on the 143Nd/144Nd ratio is consistently achieved with an exponential law correction relative to 146Nd/144Nd = 0.7219. External reproducibility of the JNdi-1 Nd isotopic standard since installation has been maintained at 0.512104 ± 2 (4 ppm, 1-sigma, n=21; literature value=0.512110). We are capable of measuring the Nd isotopic compositions of a variety of rocks, minerals, fossil material, waters and soils. |
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last updated 09/01/07
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