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Throughout the course of an organism’s life, the chemical signatures of environment, food consumption, and weather are recorded into their carbonate structures; these signatures can be directly linked to a time-resolved lifespan. Here we present trace element data from benthic foraminifera and tropical molluscs determined using an ESI NWR193UC excimer laser coupled with an Agilent 8900 triple quadrupole mass spectrometer in the MicroAnalytical Geochemistry and Isotope Characterization (MAGIC) Laboratory at the University of Maine. Benthic foraminifera are protists that live on the sea floor and produce calcite shells, progressively adding chambers. Changes in Mg/Ca in foraminifera are used as a proxy for ocean temperature. Laser ablation ICP-MS data for 18 trace elements were collected in individual growth chambers in foraminifera of the genus Uvigerina from the Bay of Plenty. Line scans were performed within thin (~10 µm) chamber walls using a spot size of 8 µm, beam energy density of 3 J/cm2, repetition rate of 12 Hz, and scan speeds of 2-3 µm/s. Concentrations were determined relative to the NIST610 glass. Ratios of Mg/Ca and other trace elements record the same range of values as those determined via bulk wet chemistry analysis of ~10 foraminifera for a given population, which suggests that LA-ICP-MS may be a viable alternative to wet chemistry. Trace element data were collected across shells of the warm-tropical mollusc species Chione subrugosa from the Ostra Base Camp area, Peru (78°37’22”W, 8°54’46”S). Previous studies of the area have suggested that a large climate transition occurred, transforming a warm water tropical bay into a desert surrounded by a coastal stand with cool waters. This area was occupied by humans at 6250-5450 radiocarbon years BP. This study examines Chione subrugosa, which were found in the living position at the fossilized Ostra Beach and are thought to have been the final living warm-tropical molluscs in the bay. Studies of modern molluscs have revealed that molluscs record massive climatic changes, such as El Niño, in their chemistry. Laser ablation provides a unique opportunity to examine chemical changes directly related to the changing coastal environment. Line scans transverse growth bands along the length of the shell, providing a high resolution record of daily variation in trace element chemistry over the lifespan of the mollusc. Eleven elements were analysed with a beam energy density of 2.4 J/cm2, repetition rate of 15 Hz, spot size of 5 x 25 µm, and a scan speed of 5 µm/s. Preliminary data suggest the preservation of yearly oscillations in trace elements, with high concentrations of La, Ce, U, and Pb during early shell growth. Continued study will examine catastrophic mollusc life events in an effort to link these with environmental climate changes over daily timescales. 

Titanite has the ability to incorporate significant amounts of common Pb, which leads to uncertainty when applying the U-Pb decay series for geochronology. The isobaric interference of 204Hg on 204Pb poses an additional complexity in applying common Pb corrections. Here we investigate the removal of 204Hg interferences during titanite U-Pb dating using reaction cell gas chemistry via triple quadrupole mass spectrometry. U-Pb dates were determined for the natural titanite reference materials MKED-1 and BLR1 using an ESI NWR193UC excimer laser coupled to an Agilent 8900 ‘triple quad’ mass spectrometer. The 8900 is equipped with an octopole collision/reaction cell, which enables online interference removal. Two experiments were run, one in which we collected data in NoGas mode, and one in which NH3 was used as a reaction cell gas in MS/MS mode, in order to assess the feasibility of determining U/Pb ratios with mass shifted isotopes. In all experiments, a signal smoothing device was placed inline just before the ICP-MS interface, downstream from the addition of the Ar nebulizer gas to the He carrier gas stream. For the NoGas experiment, titanite was ablated using a 25 µm spot, with a beam energy density of 3 J/cm2, and a pulse rate of 4 Hz. In NoGas mode, signal intensities for the isotopes 201Hg, 202Hg, 204Pb, 206Pb, 207Pb, 232Th, 235U, and 238U were counted. In MS/MS mode, titanite was ablated using a 40 µm spot, with a beam energy density of 5 J/cm2, and a pulse rate of 4 Hz. A larger spot size in this experiment was used to counteract the decrease in signal intensity due to use of the reaction cell. In MS/MS mode, NH3 was flowed through the reaction cell in order to enable a charge transfer reaction between NH3 and Hg+, effectively neutralizing Hg. The isotopes 201Hg, 202Hg, 204Pb, 206Pb, and 207Pb were measured on-mass, as the isotopes of Pb are not affected by the NH3 gas. Uranium and Th both exhibit partial reaction with NH3 gas; therefore, the isotopes 232Th, 235U, and 238U were measured mass-shifted up 15 mass units, at masses 247, 250, and 253 respectively. Ratios of 207Pb/235U, 206Pb/238U, and 207Pb/206Pb were determined using the UPbGeochron4 DRS in Iolite (v.3.71) with MKED-1 as the primary reference material. Dates were calculated using IsoplotR by applying the Stacey-Kramers correction for common Pb. All isotopes of Hg were effectively neutralized by the NH3 charge transfer reaction in MS/MS mode; zero counts were detected for Hg isotopes. Dates for the BLR-1 titanite were 1050.55 ± 2.72 (2σ, n=12) Ma in NoGas mode, and 1048 ± 1.88 (2σ, n=15) Ma in MS/MS mode. These dates are in excellent agreement with the TIMS 206Pb/238U date for the BLR-1 titanite of 1047.1 ± 0.4 Ma. This method has the potential to enable measurement of 204Pb without needing to correct for Hg interferences. 

The magnesium to calcium ratio (Mg/Ca) of benthic foraminiferal calcite serves as an important tool for reconstructing past deep water temperature. Application of this proxy relies upon accurate calibrations and an understanding of the factors that may influence the Mg/Ca ratios of foraminifer tests. Core-top calibrations are a method of assessing the temperature sensitivity of deep-dwelling benthic taxa which are difficult to raise in culture. This study contributes a new set of Mg/Ca core-top measurements for the infaunal species Uvigerina peregrina derived from a suite of sediment cores in the Southwest Pacific spanning water depths of 600 to 4400 m. Results agreed with previous calibrations for samples shallower than 2000 m, but unexpectedly high Mg/Ca values were found between the depths of 2400 and 3300 m, necessitating further investigation into potential non-temperature influences. Specimens of different morphotypes were analyzed separately, but variations between hispid and costate samples failed to account for the high-Mg anomaly observed. Lack of correlation between Mg/Ca and the contaminant indicators Mn/Ca, Al/Ca, Fe/Ca, and Ti/Ca suggests contaminant phases are not the source of excess Mg. Laser ablation ICP-MS analysis of chamber cross-sections revealed that the high-Mg signature is located within the interior of test walls, rather than contained in an external coating or contaminant phase. The high- Mg anomaly observed in mid-depth New Zealand waters is likely related to a secondary, non-temperature control on Mg incorporation. Samples with excess Mg are those most strongly influenced by carbon-rich (high dissolved inorganic carbon, high alkalinity) waters flowing south from the northern Pacific, suggesting that inorganic carbonate chemistry plays a role. 

Titanite and apatite can incorporate significant amounts of common Pb (204Pb) into their mineral structures, which leads to uncertainty when applying the U-Pb decay series for geochronology. The isobaric interference between 204Pb and 204Hg creates an additional complexity when calculating common lead corrections. Here we investigate the removal of 204Hg interferences during titanite U-Pb dating using reaction cell gas chemistry via triple quadrupole mass spectrometry compared with traditional methods that calculate U-Pb ages using a common lead correction. U-Pb dates for titanite natural reference materials MKED-1 and BLR-1 were determined using an ESI NWR193UC excimer laser coupled with an Agilent 8900 ‘triple quadrupole’ mass spectrometer. The 8900 is equipped with an octopole collision/reaction cell, which enables online interference removal. In order to compare traditional methods for U-Pb dating with interference removal methods, two experiments were run, one in which data was collected in NoGas mode, and one in which the 8900 was run in MS/MS mode, in order to assess the feasibility of determining U/Pb ratios with mass shifted isotopes. In MS/MS mode, NH3 was flowed through the reaction cell in order to enable a charge transfer reaction between NH3 and Hg+, effectively neutralizing Hg. During spot analyses in NoGas mode, masses 202Hg, 204Hg, 204Pb, 206Pb, 207Pb, 208Pb, 232Th, 235U, and 238U were monitored. For spot analyses in MS/MS mode, Th and U isotopes were measured on-mass at 232Th, 235U, 238U and mass-shifted to 247Th, 250U, and 253U. Pb isotopes were measured on-mass since Pb does not react with NH3. Ratios for 207Pb/235U, 206Pb/238U, and 207Pb/206Pb were calculated in Iolite (v.3.7.1) using the Geochron4 DRS using MKED-1 as the primary reference material and BLR-1 as a secondary reference material. Dates were calculated using IsoplotR. Weighted mean ages for titanite BLR-1 in MS/MS mode are 1043.8 ± 10.5 Ma (2σ, MSWD=1.08) for U isotopes measured on mass, and 1039.7 ± 8.3 Ma (2σ, MSWD=1.08) for mass-shifted U isotopes. These dates are both in agreement with the TIMS 206Pb/238U date for the BLR-1 titanite of 1047.1 ± 0.4 Ma. The use of NH3 for reaction cell chemistry has the potential to enable measurement of 204Pb without needing to correct for Hg interferences. 

Sulfide breakdown during subduction releases oxidizing fluids that transport chalcophile and siderophile elements (CSE) such as Ni ,Co, and As. These fluids are reincorporated into high-pressure rocks such as eclogites during exhumation and rehydration along the slab-mantle interface. Evidence for these rehydration reactions takes the form of large sulfide (pyrite, pyrrhotite, chalcopyrite) grains (up to 5 mm) associated with hydrous Fe3+-bearing minerals. Here we present results of trace element determination by LA-ICP-MS coupled with mass balance calculations for sulfide-silicate reactions in rehydrated eclogites from the Mariánské Lázně Complex and Moldanubian Zone, Bohemian Massif, Czech Republic. One key texture observed in these rocks is the breakdown of garnet + omphacite in the presence of fluid to produce hornblende + diopside + plagioclase + pyrite. This rehydration reaction involves the oxidation of Fe2+ in garnet to Fe3+ in hornblende. In order to oxidize the iron from the garnet, we propose that sulfate is brought into the rock by an infiltrating fluid, where it is reduced to form pyrite, consistent with the observed textures. Trace element analyses reveal the Co distribution within rehydrated eclogite: Co is measurable in garnet (~50 μg/g), omphacite (~26 μg/g), hornblende (~80 μg/g), and pyrite (~5000 μg/g). Mass balance calculations suggest that of the total amount of Co present in the rehydration products, only ~35 % can be supplied by the breakdown of garnet and omphacite, leaving ~65 % of the Co to be supplied by another source. Average concentrations of Ni are: in garnet (1–4 μg/g), omphacite (~57 μg/g), hornblende (~90 μg/g), and pyrite (~2500 μg/g). Mass balance calculations suggest that of the total amount of Ni present in the rehydration products, ~70 % comes from the breakdown of garnet + omphacite, with the other 30 % supplied external to this reaction. Arsenic is not present in the silicate minerals, but is in the 10s of μg/g range in pyrite, and must be supplied externally to the rock, likely from a fluid. We conclude that the fluids released from subducting slabs carry sulfate and CSEs, which infiltrate the slab-mantle interface and eventually make their way into the sub-arc mantle, where they can be incorporated into the arc magmatic system.