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Project Updates
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Konter's group has been working on multiple projects over the last few years, including both sample analysis of natural samples, and method development. Here is a link to published work via Google Scholar. In April 2022, we started the installation of a new Nu TIMS, funded by NSF-MRI (and a cost-match by the University and SOEST). This instrument will enable us to measure at significantly higher precision, while reducing required sample sizes. The instrument has 16 faraday collectors (using amplifiers with software-switchable resistors between 10^11, and either 10^12 or 10^13 Ohm), 2 daly collectors, and 3 SEM ion counters. Nu TIMS page  In January-February 2022, we ran a research cruise in the Pacific Ocean, between Hawaii, Wake Islands, Marcus Island (Minami Torishima), and Guam. Despite a delay and a cut in ship time, we (Konter (UH), Jackson (UCSB), and Koppers (OSU) and their students) sampled over 40 West Pacific Seamounts, to investigate the potential Cretaceous-aged path of the Rurutu- Arago and Samoa hotspots. This NSF-funded project also includes 40Ar/39Ar age and Sr-Nd-Pb-Hf isotope analyses to track the hotspots. Work on the Samoa hotspot has continued with multiple projects, including an examination of stable Fe isotopes, which revealed some of the most fractionated Fe isotopes among hotspot volcanoes . Based on a comparison with elemental abundances, source compositions based on radiogenic isotopes, and magmatic modeling, we propose that Samoan mantle lithology (pyroxenites, known to have fractionated Fe), or metasomatism of the source likely caused the observed values.  A separate focus of our research group has been on the use of Laser Induced Breakdown Spectroscopy (LIBS), which can be used for fast chemical characterization of samples, with minimal to no sample preparation. This was applied to dredge samples during our  Tuvalu cruise, where it helped distinguish different sample groups for further study. More recently, we have modified our LIBS system to include a high resolution spectrometer, which was used to study the glass from Kilauea 2018 erupted spatter (Beucler's MSc project). One of our main foci has been the work on the Rurutu (Arago, young Rurutu, Atiu trend) hotspot. This hotspot has the rare radiogenic Pb isotope compositions of the "HIMU" mantle compositions (blue dots, light blue fields below), that help in tracing this hotspot across the Pacific Plate.  Based on a cruise in 2013, we have now shown using a combination of radiogenic isotopes and Ar-ages that this hotspot continues from the Cook-Austral Islands through the Samoan area, making a Hawaiian-Emperor style bend at ~50 million years, in the southern Tuvalu Islands, before   turning north through Tuvalu and the Gilbert Ridge, into the West Pacific. This Rurutu hotspot remains at a constant distance with respect to the Louisville hotspot, while the distance to the Hawaiian hotspot track changes, prior to ~50 million years ago. This implies that the Hawaiian hotspot likely moved with respect to other hotspots like Louisville and Rurutu.  ANALYTICAL CAPABILITIES OF THE NU PLASMAKonter has also been working on technique setup and development both in a Class 100 Clean lab environment, and on the Nu Plasma HR. For radiogenic isotope measurements, samples from 1 digestion are first passed through Eichrom's Sr resin (shrink teflon columns) which allows for Sr and Pb separation. Pb is then cleaned up through Pb chemistry (HBr-HCl on AG1 resin; shrink teflon columns), while Sr is purified with another pass through Eichrom's Sr-resin. REEs are separated from the Sr-resin wash on Eichrom's LN-Spec (Savillex 15ml columns), and Hf with a primary column (Savillex 30 ml), followed by Eichrom's TODGA resin (shrink teflon columns). Sr-Pb-Nd-Hf has been tested and produces the same results as the previous technique (technique and results in Konter and Storm, 2014). Below follows the analytical capabilities of the HR Nu Plasma, as measured at UTEP before, and UHM subsequently. NU PLASMA STANDARD RESULTS For Pb isotopes, the NBS 981 Pb standard average 206Pb/204Pb = 16.9435+/-0.0039, 207Pb/204Pb = 15.5003+/-0.0038, and 208Pb/204Pb = 36.7260+/-0.0102. Errors given as 2 standard deviations (not standard errors) of 74 runs. The current procedure uses Tl (NBS 997) doping. For Nd isotopes, the JNdi-1 standard is used on a daily basis, but the more commonly used La Jolla standard averages 143Nd/144Nd = 0.511839 +/- 0.0000095 (N = 12). In one experiment, the La Jolla standard and the JNdi-1 standard were run alternating during two different analytical sessions. When corrected to the accepted value for La Jolla of 143Nd/144Nd = 0.511859, our JNdi-1 standard averages 0.512116 +/- 0.0000098. We also tested static versus dynamic run performance. A triple dynamic program collecting 3 x 20 ratios generates smaller variations within analytical sessions. For static analysis, daily session errors (2 standard deviations) range from 6e-6 to 9e-6, while dynamic runs show 2e-6 to 7e-6. Over several analytical sessions this results in an error of 9.8e-6 for the static routine, while the dynamic routine has 2 sigma of 6.7e-6, mainly this high due to 1 day with a higher daily variation. For Sr isotopes, the NBS 987 Sr standard is used on a dialy basis. We have found that an internal correction for Kr interference on 86Sr yields more precise data than an on-peak-zeroes subtraction. The UTEP Sr routine is a double dynamic program that uses 84Kr for the Kr correction on 86Kr, after deconvolving the 84Sr intensity. In addition, the common (85/87)Rb interference correction is employed. As a result, a daily external precision of 1.1e-5 is achieved (n about 7). Day to day shifts in the average make the long-term precision closer to 3e-5 (while each day stays within 1.1e-5): The 987 standard averages 0.71030 +/- 0.00003 for multi-session average. This method is in revision as a paper at Chemical Geology. For Hf isotopes, an Alfa Aesar Hf ICP standard (14374) is used on a daily basis, but the commonly used JMC 475 standard averaged 176Hf/177Hf = 0.282154 +/- 0.000004 (N = 8). In an experiment running both JMC 475 and Alfa 14374 in one day, the JMC 475 value reported was obtained, while the Alfa 14374 standard averaged 0.282219 +/- 0.000007 (N = 10). Our static routine incorporates a correction for 176Lu (through 175) and 176Yb (through 173), as well as Ta and W for interference on 180Hf. We are working on a dynamic routine to improve our overall Hf precision and reproducibility. |