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 Isotopes and Al-Mg Chronology of Wild 2 Particles: Origin of Crystalline Silicate in the Outer Solar System (NASA Laboratory Analysis of Returned Samples Program, 2020-2023): Major element chemistry and oxygen isotope ratios of coarse (≥2 μm) crystalline silicate particles from Wild 2 comet (Stardust Mission) provide important information on the origin of solid particles in outer Solar System. They show a significant similarity to those in chondrules and refractory inclusions from carbonaceous chondrites, though Wild 2 particles contain more FeO-rich and 16O-poor particles. There are two possible origins of 16O-poor particles; (1) from outer Solar System with enhancement of 16O-poor water ice precursors much more than those in asteroidal chondrule forming regions, or (2) particles originated from ordinary chondrite forming regions that were transported from inner disk to Kuiper Belt where comets formed. Furthermore, Al-rich minerals and glass are rare in Wild 2 particles, but existing data do not show resolvable excess of 26Mg from the decay of extinct nuclide 26Al (half-life 0.7 million years), suggesting that late formation (> 2-3 Ma) of these particles in the early Solar System.
In order to further understand the origin of cometary particles in the early Solar System, we conduct oxygen isotope and Mg isotope analyses of Wild 2 particles by using IMS 1280 secondary ion mass spectrometer (SIMS) at the University of Wisconsin-Madison. Collaborators Don Brownlee and Dave Joswiak, University of Washington, will extract particles from new aerogel tracks as a part of consortium study lead by Brownlee.
Task 1: In order to distinguish two possibilities, we plan to analyze oxygen isotope ratios of 20-25 Wild 2 particles with sizes >3 μm. Collaborators will provide us the polished sections of particles for SIMS analyses, which would be microtomed for the production of TEM sections. Brownlee and Joswiak will obtain mineralogy and major element analyses using the TEM sections. We plan to analyze maximum four SIMS spots per particle in order to improve analytical uncertainties of oxygen isotope ratios as good as 1 ‰, which may allow us to decipher if 16O-poor particles were originated from ordinary chondritic materials or not. We will also develop the analysis of 1 μm spots for identifying 16O-rich forsterite and enstatite among 1-2 μm in size, in order to estimate their abundance among Wild 2 particles.
Task 2: In order to constrain the timing of cometary silicate particle formation, we will perform Al-Mg isotope analyses using IMS 1280 SIMS. We will conduct test session to verify the analytical protocols in terms of precisions and accuracy. We will re-analyze plagioclase-bearing particle Pyxie with Collaborator Micheal Weisberg. If more particles with Al-rich phases larger than a few μm will be available from newly extracted particles, they will be analyzed. Modified multi-collector electron multiplier pulse counting system will be used for Mg isotope analyses that would reduce analytical errors compared to previous studies. If inferred initial 26Al/27Al ratios of Wild 2 particles are as low as those of chondrules in CR and CH chondrites, the results would further support late formation of solid particles in outer Solar System.
The proposed research is to obtain high precision isotope analyses of Wild 2 comet particles, which will maximize scientific return from the samples provided by Stardust Mission and advance our knowledge of the early evolution of outer Solar System. Therefore, it is relevant to the scope of the Laboratory Analysis of Returned Samples Program.
Al-Mg Chronology and Isotope Signatures of Chondrules: Unravelling the Diverse Forming Environments in the Protoplanetary Disk (NASA Emerging World Program, 2021-2023): Chondrules in primitive meteorites formed by transient heating in the proto-planetary disk and postdated the oldest refractory inclusions (Ca, Al-rich inclusions; CAIs) by 2-5 million years (Ma). They were likely formed by mechanism that involve growth of planetary system, such as proto-Jupiter, planetary embryos, impacts between planetesimals. Oxygen three-isotope systematics among chondrules have indicated a variety of precursor solids with distinct oxygen isotopes and different environments of their formation. Under the assumption of homogeneous distribution of 26Al (half-life of 0.7 Ma), studies on the Al-Mg chronology of chondrules suggest that chondrule formation ages are systematically different among chondrite groups; chondrules in ordinary chondrites (OC) formation in the inner disk at 1.8-2.2 Ma, which are systematically older than those in carbonaceous chondrites (CC), typically 2.2-2.7 Ma for CO, CM, CV, and Acfer 094 chondrites, and >3-4 Ma after CAIs for CR, CH, CB (CR-clan) chondrites.
Systematic investigation of formation ages at higher precisions (0.1-0.2 Ma) are required to fully resolve detail systematics against their chemistry and oxygen isotope signatures. Nucleosynthetic anomalies in 54Cr and 50Ti show two distinct systematic changes between carbonaceous chondrites (CC) and other meteorites (NC), which is known as isotope dichotomy and may help us to understand mixing of solids in the history of protoplanetary disk . However, investigations 54Cr and 50Ti anomaly among individual chondrules, especially those coordinated with oxygen isotopes and Al-Mg chronology are scarce.
Task -1: We propose to conduct high time-resolution (<0.1 Ma) Al-Mg chronology of 15-20 chondrules in pristine CV, CM, CO,
CR chondrites, which are combined with detailed petrology, oxygen three-isotopes. Least metamorphosed and aqueously altered carbonaceous chondrites are carefully selected. Silicate Mg# (= [MgO]/ [MgO+FeO] mole%) and mass independent fractionation of oxygen isotope ratios would indicate dust density of local disk and abundance of 16O-poor water ice in chondrule precursor solids. For selected chondrules in CV and CR, we will extract chondrules after SIMS analyses and obtain nucleosynthetic anomalies of 54Cr and 50Ti by using TIMS and ICPMS, respectively. Furthermore, we produce Na-rich plagioclase standards in order to improve accuracy of Al-Mg isochron ages to be better than 0.1 Ma.
Task -2: W we examine detail oxygen three isotope systematics of Al-rich chondrules (ARC) in CV and CO chondrites. Some ARCs show internally heterogeneous oxygen isotopes with extreme 16O-rich isotope signatures, close to those in CAIs. Examination
of oxygen isotope zoning in each ARC would help understanding the isotope exchange between 16O-rich chondrule melt with surrounding 16O-poor ambient gas. We will determine Al-Mg ages of ARCs to understand possible 26Al heterogeneity and formation time.
From the results, we will determine the total range of Al-Mg ages for each chondrite and evaluate any correlation between ages, chemical and isotope variabilities. We address following questions in order to better understand the mechanism of chondrule formation and the evolution of protoplanetary disk.
(1) Distribution of chondrule formation ages: Short time intervals (≤0.1 Ma) or continuous formation (>0.5 Ma), which may relate to different chondrule formation mechanisms.
(2) Younger ages for FeO-rich chondrules than FeO-poor chondrules in CC may imply increase of disk density and decrees of disk temperatures with time.
(3) Evidence for radial transport of chondrules, such as older chondrules in CCs show NC-like isotope signatures.
The proposed research is to explore the evolution of solids in the protoplanetary disk through the chemical and isotopic properties of extraterrestrial materials that represent primitive solids in the early Solar System. Therefore, it is relevant to the scope of the Emerging Worlds Program.
‣ 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)