Noriko KitaSenior Scientist Director, WiscSIMS Laboratory
The University of Wisconsin SIMS lab (WiscSIMS) was installed in 2005 and became a National Facility for Stable Isotope Geochemistry in 2008 with support from NSF, Division of Earth Sciences, Instrumentation and Facilities Program. The WiscSIMS lab houses a CAMECA IMS-1280. The IMS-1280 is a large radius multi-collector ion microprobe incorporating many improvements over earlier instruments, several of which are designed to enhance precision and accuracy of isotope ratio analysis.
Primitive meteorites recorded the early evolution of the solar system. We use SIMS to obtain high precision isotope analyses of pristine meteorite samples, such as Ca, Al-rich inclusions and chondrules in order to address the timing of their formation and the condition of proto-planetary disk in which they formed. We are also interested in precious particles collected from asteroidsand comets by space missions, such as NASA Stardust Mission.
NASA Funded Research Projects
Oxygen and magnesium isotope studies of Wild 2 particles and their origins in the early solar system (NASA Laboratory Analysis of Returned Samples Program, 2016-2019): We propose to obtain high precision oxygen and magnesium isotope analyses of particles recovered from the comet 81P/Wild 2 (Stardust Mission) using a secondary ion mass spectrometer IMS 1280 at University of Wisconsin (WiscSIMS) in order to understand the origin of the particles in the early solar system. A relationship between oxygen isotope ratios and Mg# =molar MgO/(MgO+Fe)% of olivine and pyroxene is indicative to their formation environments and isotope reservoirs and provide a clue to the location where they formed in the protoplanstary disk. Magnesium isotopes provide chronology of particles through the decay of 26Al to daughter 26Mg (half life of 0.7 million years) and/or evidence of high temperature processes between solid and gas (evaporation and condensation) as stable isotope fractionation. Detailed isotope studies combined with mineralogy and chemistry will be a key to understand how these high temperature particles formed and were transported to comet forming regions. We plan to analyze relatively larger (≥ a few μm) crystalline silicates using ~2μm SIMS spot size. Particles are selected according to the mineralogy and major element chemistry that are obtained from the microtome TEM sections by Collaborators Brownlee and Joswiak (U. Washington) and Zolensky (NASA JSC). We focus on high Mg# olivine and pyroxene, which are known to be either chondrule-like objects or condensates of the early solar system, such as LIME (low-iron, manganese-enriched) olivine. Magnesium isotope analyses will be performed all particles that show 16O-rich isotope signatures and those containing Al-rich phases larger than 3μm in size. We propose to acquire new oxygen primary ion source of the IMS 1280 (RF Plasma source) that will provide higher primary beam intensity for small spot sizes at least 10 times or even higher than that of current ion source. The higher primary beam intensity will improve secondary ion intensities, which results in improvements in analytical precisions. Results obtained from the proposed studies will maximize scientific return from the samples provided by Stardust Mission and advance our knowledge of the early evolution of Solar System, which could not be obtained solely from studies of primitive meteorites. Analytical techniques established in the proposed research will benefit the analysis of meteorites, interplanetary dust particles, and samples from future planetary return missions.
High Resolution Al-Mg Chronology of Chondrules and Implication to the Evolution of Protoplanetary Disk (NASA Emerging World Program, 2017-2020): Chondrules in primitive meteorites are considered to record chemical properties and isotope reservoirs of dust particles existed in the proto-planetary disk. By using the short-lived nuclide chronometer 26Al-26Mg (half life: 0.7 million years, Ma), formation time of most chondrule are estimated at 2-3 Ma after the formation of refractory inclusions. However, detailed systematics among Al-Mg ages chondrules in comparison to their chemical and isotope properties are not well-resolved mainly due to the limitation of analytical uncertainties in inferred ages (typically 0.2-0.5 Ma). The goal of the study is to obtain 0.1 Ma precisions and accuracy for inferred Al-Mg ages in order to address several questions that would help us to constrain disk evolution and chondrule formation models (1) total range of chondrule formation ages in a single chondrite group, (2) time difference between FeO-rich and FeO-poor chondrules in a single chondrite group, (3) test partial melting of porphyritic chondrules from magnesium isotope ratios of olivine and pyroxene. Chondrules are selected from multiple primitive chondrites that we have already studied in the past and are known to have minimal effects of secondary processes in the parent bodies. Selected chondrules were examined by using electron microscopies (scanning electron microscope, electron microprobe analyzer) and laser Raman spectrometry and analyzed for Al-Mg chronology by using IMS 1280 at WiscSIMS. Additional oxygen isotope analyses would be also performed for those that were not analyzed previously. We will develop method of high time resolution Al-Mg chronology with upgraded high brightness primary oxygen ion source. We will also study O-isotope ratios of crystalline silicate in Giant Cluster IDP, which are considered to be cometary origin. The results from IDPs will be compared to those of Wild 2 particles. The proposed research is to study chemical and isotopic properties of early solar system materials and would enhance our understanding of protoplanetary disk evolution. Therefore, it is relevant to the scope of the Emerging Worlds Program.
Selected Recent Papers:
Oxygen isotope systematics of chondrules in the Murchison CM2 chondrite and implications for the CO-CM relationship. Geochimica et Cosmochimica Acta 228, 220-242. 10.1016/j.gca.2018.02.040(2018)
Formation of chondrules in a moderately high dust enriched disk: Evidence from oxygen isotopes of chondrules from the Kaba CV3 chondrite. Geochimica et Cosmochimica Acta 224, 116-131. 10.1016/j.gca.2017.12.013(2018)
‣ Kohei Fukuda
‣ Daisuke Nakashima (Tohoku University, Japan)
‣ Takayuki Ushikubo (JAMSTEC Kochi, Japan)
‣ Rudraswami Gowda (National Institute of Oceanography, India)
‣ Travis Tenner (Los Alamos National Laboratory)