Calcium and neodymium radiogenic isotopes of igneous rocks: Tracing crustal contributions in felsic magmas related to super-eruptions and continental rifting

Radioactive decay of 40K within the continental crust produces a unique Ca isotopic reservoir, with measurable radiogenic 40Ca excesses compared to Earth's mantle (εCa = 0). Thus, igneous rocks with values of εCa > 1 unambiguously indicate a significant old, crustal contribution to their source magma. At our current level of analytical precision, values of εCa < 0.5 are indistinguishable from mantle-like Ca isotope compositions. So, whereas 40Ca excesses clearly define crustal contributions, the source contributions of igneous rocks with mantle-like Ca isotopic composition are less certain. The calcium in these rocks could be derived from partial melting of: young crust, crust with mantle-like K/Ca compositions, or the mantle itself. Here we present Ca isotopic measurements of intermediate to felsic igneous rocks from the western United States, and two crustal xenoliths found within the Fish Canyon Tuff (FCT) of the southern Rocky Mountain volcanic field (SRMVF), USA. Their isotope geochemistry is used to explore their source compositions and to help distinguish new mantle-derived additions to the crust from reworked older crust. Irrespective of age or tectonic setting a majority of the intermediate to silicic igneous rocks studied exhibit mantle-like Ca isotope compositions. Mantle-like Ca isotopic data for leucogranites associated with the beginning of Rio Grande rifting in Colorado indicate that felsic melts were generated from newly formed lower crust related to earlier calc-alkaline magmatism. These data also indicate that the Nd isotopic signature in early rift magmas is controlled by the lithospheric mantle, even if the major mantle source reservoir is the asthenospheric mantle. The two crustal xenoliths found within the 28.2 Ma FCT yield εCa values of 3.6 and 7.0, respectively. The 40Ca excesses of these Precambrian source rocks are supported by K–Ca geochronology. However, like several other ignimbrites from the SRMVF and from Yellowstone, USA, the FCT (εCa ∼ 0.3) has a Ca isotope composition that is indistinguishable from the mantle. Nd isotopic analyses of the FCT imply that it was generated from 10–75% of an enriched component, and so the Ca isotopic data appear to restrict that component to newly formed lower crust, low K/Ca crust, or enriched mantle. Contrary to these findings, several large ignimbrites and one granitoid from the SRMVF show significant 40Ca excesses. These tuffs (Wall Mountain, Blue Mesa, and Grizzly Peak) and one granitoid (Mt. Princeton) are sourced from near, or within the Colorado Mineral Belt. Collectively, these data indicate that felsic, Precambrian crust likely contributed less than 50% of the material to the petrogenesis of many of the large ignimbrites that have erupted across the western United States. However, the crustal components that contributed to magmas in the Colorado Mineral Belt have 40Ca excesses; consistent with felsic, Precambrian crust

Isotopic Studies of Contaminant Transport at the Hanford Site,WA

Processes of fluid flow and chemical transport through thevadose zone can be characterized through the isotopic systematics ofnatural soils, minerals, pore fluids and groundwater. In thiscontribution, we first review our research using measured isotopicvariations, due both to natural and site related processes, of theelements H, O, N, Sr and U, to study the interconnection between vadosezone and groundwater contamination at the Hanford Site in south-centralWashington. We follow this brief review with a presentation of new datapertaining to vadose zone and groundwater contamination in the WMAT-TX-TY vicinity. Uranium (U) isotopic data for the C3832 core (WMA TX)indicates the involvement of processed natural U fuel, and links theobserved U contamination to the nearby single shelled tank TX-104. Thedata also precludes contamination from an early 1970 s TX-107 leak. Inthe case of the C4104 core (WMA T), the U isotopic data indicates amixture of processed natural and enriched U fuels consistent with themajor leak from T-106 in 1973. Uranium and Strontium isotopic data forthe cores also provides direct evidence for chemical interaction betweenhigh-pH waste fluid and sediment. Isotopic data for groundwater nitratecontamination in the vicinity of WMA-T strongly suggests high-level tankwaste (most likely from T-106) as the source of very high 99Tcconcentrations recently observed at the NE corner of WMAT

Identifying mantle carbonatite metasomatism through Os–Sr–Mg isotopes in Tibetan ultrapotassic rocks

Mantle-derived magmas at convergent plate boundaries provide unique insights into the nature of materials subducted to and recycled from depths. Here we present a study of Os–Sr–Mg isotopes on the Oligocene–Miocene ultrapotassic rocks aimed at better understanding sediment subduction and recycling beneath southern Tibet. New isotopic data confirm that ultrapotassic rocks in southern Tibet are of mantle origin, but underwent crustal contamination as evidenced by the variably high 187Os/188Os that obviously deviates from normal mantle reservoir. Still some samples with mantle-like 187Os/188Os exhibit δ26Mg significantly lower than mantle and crustal lithologies, suggesting that the isotopically light Mg may not result from crustal contamination but retain specific fingerprint of carbonate-related metasomatism in mantle sources. Mantle carbonatite metasomatism is manifested by the inverse δ26Mg–87Sr/86Sr correlations, as well as the depletion of high field strength elements relative to rare earth elements and the enrichment of CaO in ultrapotassic rocks. The positive co-variations between δ26Mg and Hf/Sm defined by those low-187Os/188Os ultrapotassic rocks provide evidence for the potential of recycled dolomites to modify mantle Mg isotopic composition. The correlated spatial variations of δ26Mg and Hf/Sm are interpreted to reflect carbonatitic metasomatism associated with the northward subduction of the Neo-Tethyan oceanic slab and its profound influence on postcollisional ultrapotassic magmatism

Factors Associated with Revision Surgery after Internal Fixation of Hip Fractures

Background: Femoral neck fractures are associated with high rates of revision surgery after management with internal fixation. Using data from the Fixation using Alternative Implants for the Treatment of Hip fractures (FAITH) trial evaluating methods of internal fixation in patients with femoral neck fractures, we investigated associations between baseline and surgical factors and the need for revision surgery to promote healing, relieve pain, treat infection or improve function over 24 months postsurgery. Additionally, we investigated factors associated with (1) hardware removal and (2) implant exchange from cancellous screws (CS) or sliding hip screw (SHS) to total hip arthroplasty, hemiarthroplasty, or another internal fixation device. Methods: We identified 15 potential factors a priori that may be associated with revision surgery, 7 with hardware removal, and 14 with implant exchange. We used multivariable Cox proportional hazards analyses in our investigation. Results: Factors associated with increased risk of revision surgery included: female sex, [hazard ratio (HR) 1.79, 95% confidence interval (CI) 1.25-2.50; P = 0.001], higher body mass index (fo

Evaluation of isotopic diagnostics for subsurface characterization and monitoring: Field experiments at the TAN and RWMC (SDA) Sites, INEEL. 1997 annual progress report

'This research is aimed at improving methods for characterizing underground contamination sites and for monitoring how they change with time. Particular emphasis is placed on identifying and quantifying the effects of intrinsic remediation and verifying the efficacy of engineered remediation activities. Isotopic measurements of elements such as C, O, H, He, Cl, and Sr, which are present in groundwater and soil gas, provide a quantitative measure of material balance. They can be used to identify the sites of origin of contaminants in groundwater, and to determine if contaminants are being destroyed as a result of natural processes or engineered processes. Isotope ratios also can be used to trace the migration of fluids that underground contaminants, such as steam and chemical reactions are occurring underground destruction of TCE usually produces carbon dissolution of calcite. are pumped down wells to destroy or confine grout, and they can be utilized to diagnose what and what materials are reacting. For example, dioxide, but carbon dioxide can also come from There are many isotopic ratios that can be measured in groundwater and vadose zone gas that could be valuable for characterizing remediation sites and monitoring remediation activities; The authors concentrate on a few that are particularly useful for the problems being addressed at the TAN (Test Area North) and RWMC (Radioactive Waste Management Complex) sites of the Idaho National Engineering Lab.. The isotopes the authors are using are {sup 13}C, {sup 14}C, {sup 3}He, {sup 87}Sr, {sup 37}Cl, and {sup 18}O.

He, Sr, Nd and U isotopic variations in post-shield lavas from the Big Island of Hawaii -- insight into magma production and the chemical structure of the Hawaiian plume

We present new isotopic and trace element data on post-shield alkalic lavas from the Hualalai, Mauna Kea, and Kohala. These small-volume eruptions, which presumably correspond to small-volume source regions in the mantle, serve as high resolution probes of geochemical heterogeneity to complement data available from shield-stage tholeiites that originate in the primary melting region. The post-shield isotopic ratios average over mantle volumes as much as 100 times smaller than those of the shield stage lavas. The post-shield volcanic vents are spread over an area of about 2500 km2 on the island of Hawaii. The locations extend about 35km on either side of the axis of the Hawaiian ridge and 60 to 110 km northwest of the centroid of the main melting anomaly (located between Kilauea and Loihi). Helium isotopic ratios were measured on olivine separates and, where present, pyroxene separates from the same samples. The Sr, Nd, and U-series isotopes were done on whole rock powders of the same samples. He isotopes range from 6-11 R/Ra, 87Sr/86Sr varies from 0.70345-0.70374, and epsilon-Nd from +5.3 to +7.4. The total range of Sr and Nd isotopic variations in these lavas is about twice that observed in the 2.84 km section of Mauna Kea drilled by HSDP, and similar to the range encompassed by Mauna Loa and Mauna Kea tholeiites excluding those erupted from ML since 30 Ka. For He the range is much smaller in the post-shield lavas than in the shield lavas. There is general SW NE asymmetry for all three isotope systems that could be viewed either as the Loa-Kea dichotomy or a reflection of the overall radial zoning of the plume. The amplitude of Sr and Nd heterogeneities is not markedly larger than in the shield sections of the volcanoes, which indicates that if there are larger amplitude variations in the plume, they are substantially smaller than the source regions of the post shield lavas. There is no evidence that the post-shield lavas are affected substantially by lithospheric interaction or that they are melted from isotopically anomalous material associated with pyroxene-rich domains

Isotopic Studies of Contaminant Transport at the Hanford Site, WA

Processes of fluid flow and chemical transport through the vadose zone can be characterized through the isotopic systematics of natural soils, minerals, pore fluids and groundwater. In this contribution, we first review our research using measured isotopic variations, due both to natural and site related processes, of the elements H, O, N, Sr and U, to study the interconnection between vadose zone and groundwater contamination at the Hanford Site in south-central Washington. We follow this brief review with a presentation of new data pertaining to vadose zone and groundwater contamination in the WMA T-TX-TY vicinity. Uranium (U) isotopic data for the C3832 core (WMA TX) indicates the involvement of processed natural U fuel, and links the observed U contamination to the nearby single shelled tank TX-104. The data also precludes contamination from an early 1970 s TX-107 leak. In the case of the C4104 core (WMA T), the U isotopic data indicates a mixture of processed natural and enriched U fuels consistent with the major leak from T-106 in 1973. Uranium and Strontium isotopic data for the cores also provides direct evidence for chemical interaction between high-pH waste fluid and sediment. Isotopic data for groundwater nitrate contamination in the vicinity of WMA-T strongly suggests high-level tank waste (most likely from T-106) as the source of very high 99Tc concentrations recently observed at the NE corner of WMAT