Oxygen isotope characteristics of chondrules from the Yamato‐82094 ungrouped carbonaceous chondrite: Further evidence for common O‐isotope environments sampled among carbonaceous chondrites

High‐precision secondary ion mass spectrometry (SIMS) was employed to investigate oxygen three isotopes of phenocrysts in 35 chondrules from the Yamato (Y) 82094 ungrouped 3.2 carbonaceous chondrite. Twenty‐one of 21 chondrules have multiple homogeneous pyroxene data (?¹⁷O 3SD analytical uncertainty: 0.7‰); 17 of 17 chondrules have multiple homogeneous pyroxene and plagioclase data. Twenty‐one of 25 chondrules have one or more olivine data matching coexisting pyroxene data. Such homogeneous phenocrysts (1) are interpreted to have crystallized from the final chondrule melt, defining host O‐isotope ratios; and (2) suggest efficient O‐isotope exchange between ambient gas and chondrule melt during formation. Host values plot within 0.7‰ of the primitive chondrule mineral (PCM) line. Seventeen chondrules have relict olivine and/or spinel, with some δ¹⁷O and δ¹⁸O values approaching ?40‰, similar to CAI or AOA‐like precursors. Regarding host chondrule data, 22 of 34 have Mg#s of 98.8–99.5 and ?¹⁷O of ?3.9‰ to ?6.1‰, consistent with most Acfer 094, CO, CR, and CV chondrite chondrules, and suggesting a common reduced O‐isotope reservoir devoid of ¹⁶O‐poor H₂O. Six Y‐82094 chondrules have ?¹⁷O near ?2.5‰, with Mg#s of 64–97, consistent with lower Mg# chondrules from Acfer 094, CO, CR, and CV chondrites; their signatures suggest precursors consisting of those forming Mg# ~99, ?¹⁷O: ?5‰ ± 1‰ chondrules plus ¹⁶O‐poor H₂O, at high dust enrichments. Three type II chondrules plot slightly above the PCM line, near the terrestrial fractionation line (?¹⁷O: ~+0.1‰). Their O‐isotopes and olivine chemistry are like LL3 type II chondrules, suggesting they sampled ordinary chondrite‐like chondrule precursors. Finally, three Mg# >99 chondrules have ?¹⁷O of ?6.7‰ to ?8.1‰, potentially due to ¹⁶O‐rich refractory precursor components. The predominance of Mg# ~99, ?¹⁷O: ?5‰ ± 1‰ chondrules and a high chondrule‐to‐matrix ratio suggests bulk Y‐82094 characteristics are closely related to anhydrous dust sampled by most carbonaceous chondrite chondrules.     

Comparison of the acid-base responses to CO2 and acidification in Japanese flounder (Paralichthys olivaceus)

To investigate whether the biological toxicity of aquatic hypercapnia is due to the direct effects of CO2 or to the effects of acidification of seawater by CO2, the Japanese flounder (Paralichthys olivaceus) was subjected to seawater equilibrated with a gas mixture of air containing 5% CO2 (pH 6.18) or seawater acidified to the same pH with 1 N H2SO4. All the fish died within 72 h in the CO2 exposure group, whereas no mortality occurred in the acid group. Acid-base parameters as well as plasma ion concentrations were severely perturbed in the CO2 exposure group, whereas they were minimally affected in the acid group. These results clearly demonstrate that the mortality in the CO2 group is a direct result of the elevated levels of dissolved CO2 and not to the effects of the reduced water pH.     

An alkaline spring system within the Del Puerto Ophiolite (California,USA): A Mars analog site

Mars appears to have experienced little compositional differentiation of primitive lithosphere, and thus much of the surface of Mars is covered by mafic lavas. On Earth, mafic and ultramafic rocks present in ophiolites, oceanic crust and upper mantle that have been obducted onto land, are therefore good analogs for Mars. The characteristic mineralogy, aqueous geochemistry, and microbial communities of cold-water alkaline springs associated with these mafic and ultramafic rocks represent a particularly compelling analog for potential life-bearing systems. Serpentinization, the reaction of water with mafic minerals such as olivine and pyroxene, yields fluids with unusual chemistry (Mg–OH and Ca–OH waters with pH values up to ～12), as well as heat and hydrogen gas that can sustain subsurface, chemosynthetic ecosystems. The recent observation of seeps from pole-facing crater and canyon walls in the higher Martian latitudes supports the hypothesis that even present conditions might allow for a rock-hosted chemosynthetic biosphere in near-surface regions of the Martian crust. The generation of methane within a zone of active serpentinization, through either abiogenic or biogenic processes, could account for the presence of methane detected in the Martian atmosphere. For all of these reasons, studies of terrestrial alkaline springs associated with mafic and ultramafic rocks are particularly timely. This study focuses on the alkaline Adobe Springs, emanating from mafic and ultramafic rocks of the California Coast Range, where a community of novel bacteria is associated with the precipitation of Mg–Ca carbonate cements. The carbonates may serve as a biosignature that could be used in the search for evidence of life on Mars.     

The geochemical and petrological characteristics of prenatal caldera volcano: a case of the newly formed small dacitic caldera,Hijiori, Northeast Japan

Evaluating the magma depth and its physical properties is critical to conduct a better geophysical assessment of magma chambers of caldera volcanoes that may potentially cause future volcanic hazards. To understand pre-eruptive conditions of a magma chamber before its first appearance at the surface, this paper describes the case of Hijiori caldera volcano in northeastern Japan, which emerged approximately 12,000 years ago at a place where no volcano ever existed. We estimated the depth, density, bulk modulus, vesicularity, crystal content, and bulk H\(_2\)O content of the magma chamber using petrographic interpretations, bulk and microchemical compositions, and thermodynamic calculations. The chemical mass balance calculations and thermodynamic modeling of the erupted magmas indicate that the upper portion of the Hijiori magmatic plumbing system was located at depths between 2 and 4 km, and had the following characteristics: (1) pre-eruptive temperature: about 780 \(^{\circ }\)C; (2) bulk magma composition: 66 ± 1.5 wt% SiO\(_{2}\); (3) bulk magmatic H\(_2\)O: approximately 2.5 wt%, and variable characteristics that depend on depth; (4) crystal content: \(\le\)57 vol%; (5) bulk modulus of magma: 0.1–0.8 GPa; (6) magma density: 1.8–2.3 g/cm³; and (7) amount of excess magmatic H\(_2\)O: 11–32 vol% or 48–81 mol%. The range of melt water contents found in quartz-hosted melt inclusions (2–9 wt%) suggests the range of depth phenocrysts growth to be wide (2\(\sim\)13 km). Our data suggest the presence of a vertically elongated magma chamber whose top is nearly solidified but highly vesiculated; this chamber has probably grown and re-mobilized by repeated injections of a small amount of hot dacitic magma originated from the depth.     

Effects of CO2 on benthic biota: An in situ benthic chamber experiment in Storfjorden (Norway)

Carbon capture and storage (CCS) methods, either sub-seabed or in ocean depths, introduces risk of CO₂ leakage and subsequent interaction with the ecosystem. It is therefore important to obtain information on possible effects of CO₂. In situ CO₂ exposure experiments were carried out twice for 10 days during 2005 using a Benthic Chamber system at 400 m depth in Storfjorden, Norway. pCO₂ in the water above the sediment in the chambers was controlled at approximately 500, 5000 and 20,000 μatm, respectively. This article describes the experiment and the results from measured the biological responses within the chamber sediments. The results show effects of elevated CO₂ concentrations on biological processes such as increased nanobenthos density. Methane production and sulphate reduction was enhanced in the approximately 5000 μatm chamber.     

The origin of high δ<Superscript>18</Superscript>O zircons: marbles,megacrysts, and metamorphism

The oxygen isotope ratios (δ¹⁸O) of most igneous zircons range from 5 to 8‰, with 99% of published values from 1345 rocks below 10‰. Metamorphic zircons from quartzite, metapelite, metabasite, and eclogite record δ¹⁸O values from 5 to 17‰, with 99% below 15‰. However, zircons with anomalously high δ¹⁸O, up to 23‰, have been reported in detrital suites; source rocks for these unusual zircons have not been identified. We report data for zircons from Sri Lanka and Myanmar that constrain a metamorphic petrogenesis for anomalously high δ¹⁸O in zircon. A suite of 28 large detrital zircon megacrysts from Mogok (Myanmar) analyzed by laser fluorination yields δ¹⁸O from 9.4 to 25.5‰. The U–Pb standard, CZ3, a large detrital zircon megacryst from Sri Lanka, yields δ¹⁸O = 15.4 ± 0.1‰ (2 SE) by ion microprobe. A euhedral unzoned zircon in a thin section of Sri Lanka granulite facies calcite marble yields δ¹⁸O = 19.4‰ by ion microprobe and confirms a metamorphic petrogenesis of zircon in marble. Small oxygen isotope fractionations between zircon and most minerals require a high δ¹⁸O source for the high δ¹⁸O zircons. Predicted equilibrium values of Δ¹⁸O(calcite-zircon) = 2–3‰ from 800 to 600°C show that metamorphic zircon crystallizing in a high δ¹⁸O marble will have high δ¹⁸O. The high δ¹⁸O zircons (>15‰) from both Sri Lanka and Mogok overlap the values of primary marine carbonates, and marbles are known detrital gemstone sources in both localities. The high δ¹⁸O zircons are thus metamorphic; the 15–25‰ zircon values are consistent with a marble origin in a rock-dominated system (i.e., low fluid_(external)/rock); the lower δ¹⁸O zircon values (9–15‰) are consistent with an origin in an external fluid-dominated system, such as skarn derived from marble, although many non-metasomatized marbles also fall in this range of δ¹⁸O. High δ¹⁸O (>15‰) and the absence of zoning can thus be used as a tracer to identify a marble source for high δ¹⁸O detrital zircons; this recognition can aid provenance studies in complex metamorphic terranes where age determinations alone may not allow discrimination of coeval source rocks. Metamorphic zircon megacrysts have not been reported previously and appear to be associated with high-grade marble. Identification of high δ¹⁸O zircons can also aid geochronology studies that seek to date high-grade metamorphic events due to the ability to distinguish metamorphic from detrital zircons in marble.     

26Al‐26Mg isotope systematics of the first solids in the early solar system

High‐precision bulk aluminum‐magnesium isotope measurements of calcium‐aluminum‐rich inclusions (CAIs) from CV carbonaceous chondrites in several laboratories define a bulk ²⁶Al‐²⁶Mg isochron with an inferred initial ²⁶Al/²⁷Al ratio of approximately 5.25 × 10^?5, named the canonical ratio. Nonigneous CV CAIs yield well‐defined internal ²⁶Al‐²⁶Mg isochrons consistent with the canonical value. These observations indicate that the canonical ²⁶Al/²⁷Al ratio records initial Al/Mg fractionation by evaporation and condensation in the CV CAI‐forming region. The internal isochrons of igneous CV CAIs show a range of inferred initial ²⁶Al/²⁷Al ratios, (4.2–5.2) × 10^?5, indicating that CAI melting continued for at least 0.2 Ma after formation of their precursors. A similar range of initial ²⁶Al/²⁷Al ratios is also obtained from the internal isochrons of many CAIs (igneous and nonigneous) in other groups of carbonaceous chondrites. Some CAIs and refractory grains (corundum and hibonite) from unmetamorphosed or weakly metamorphosed chondrites, including CVs, are significantly depleted in ²⁶Al. At least some of these refractory objects may have formed prior to injection of ²⁶Al into the protosolar molecular cloud and its subsequent homogenization in the protoplanetary disk. Bulk aluminum and magnesium‐isotope measurements of various types of chondrites plot along the bulk CV CAI isochron, suggesting homogeneous distribution of ²⁶Al and magnesium isotopes in the protoplanetary disk after an epoch of CAI formation. The inferred initial ²⁶Al/²⁷Al ratios of chondrules indicate that most chondrules formed 1–3 Ma after CAIs with the canonical ²⁶Al/²⁷Al ratio.     

Assessment of a monumental masonry bell-tower after 2016 Central Italy seismic sequence by long-term SHM

The response of the San Pietro monumental bell-tower located in Perugia, Italy, to the 2016 Central Italy seismic sequence is investigated, taking advantage of the availability of field data recorded by a vibration-based SHM system installed in December 2014 to detect earthquake-induced damages. The tower is located about 85 km in the NW direction from the epicenter of the first major shock of the sequence, the Accumoli Mw6.0 earthquake of August 24th, resulting in a small local PGA of about 30 cm/s², whereby near-field PGA was measured as 915.97 cm/s² (E–W component) and 445.59 cm/s² (N–S component). Similar PGA values also characterized the two other major shocks of the sequence (Ussita Mw5.9 and Norcia Mw6.5 earthquakes of October 26th and 30th, respectively). Despite the relatively low intensity of such earthquakes in Perugia, the analysis of long-term monitoring data clearly highlights that small permanent changes in the structural behavior of the bell-tower have occurred after the earthquakes, with decreases in all identified natural frequencies. Such natural frequency decays are fully consistent with what predicted by non-linear finite element simulations and, in particular, with the development of microcracks at the base of the columns of the belfry. Microcracks in these regions, and in the rest of tower, are however hardly distinguishable from pre-existing ones and from the physiological cracking of a masonry structure, what validates the effectiveness of the SHM system in detecting earthquake-induced damage at a stage where this is not yet detectable by visual inspections.     

Ti-in-zircon thermometry: applications and limitations

The titanium concentrations of 484 zircons with U-Pb ages of ∼1 Ma to 4.4 Ga were measured by ion microprobe. Samples come from 45 different igneous rocks (365 zircons), as well as zircon megacrysts (84) from kimberlite, Early Archean detrital zircons (32), and zircon reference materials (3). Samples were chosen to represent a large range of igneous rock compositions. Most of the zircons contain less than 20 ppm Ti. Apparent temperatures for zircon crystallization were calculated using the Ti-in-zircon thermometer (Watson et al. 2006, Contrib Mineral Petrol 151:413–433) without making corrections for reduced oxide activities (e.g., TiO₂ or SiO₂), or variable pressure. Average apparent Ti-in-zircon temperatures range from 500° to 850°C, and are lower than either zircon saturation temperatures (for granitic rocks) or predicted crystallization temperatures of evolved melts (∼15% melt residue for mafic rocks). Temperatures average: 653 ± 124°C (2 standard deviations, 60 zircons) for felsic to intermediate igneous rocks, 758 ± 111°C (261 zircons) for mafic rocks, and 758 ± 98°C (84 zircons) for mantle megacrysts from kimberlite. Individually, the effects of reduced or , variable pressure, deviations from Henry’s Law, and subsolidus Ti exchange are insufficient to explain the seemingly low temperatures for zircon crystallization in igneous rocks. MELTs calculations show that mafic magmas can evolve to hydrous melts with significantly lower crystallization temperature for the last 10–15% melt residue than that of the main rock. While some magmatic zircons surely form in such late hydrous melts, low apparent temperatures are found in zircons that are included within phenocrysts or glass showing that those zircons are not from evolved residue melts. Intracrystalline variability in Ti concentration, in excess of analytical precision, is observed for nearly all zircons that were analyzed more than once. However, there is no systematic change in Ti content from core to rim, or correlation with zoning, age, U content, Th/U ratio, or concordance in U-Pb age. Thus, it is likely that other variables, in addition to temperature and , are important in controlling the Ti content of zircon. The Ti contents of igneous zircons from different rock types worldwide overlap significantly. However, on a more restricted regional scale, apparent Ti-in-zircon temperatures correlate with whole-rock SiO₂ and HfO₂ for plutonic rocks of the Sierra Nevada batholith, averaging 750°C at 50 wt.% SiO₂ and 600°C at 75 wt.%. Among felsic plutons in the Sierra, peraluminous granites average 610 ± 88°C, while metaluminous rocks average 694 ± 94°C. Detrital zircons from the Jack Hills, Western Australia with ages from 4.4 to 4.0 Ga have apparent temperatures of 717 ± 108°C, which are intermediate between values for felsic rocks and those for mafic rocks. Although some mafic zircons have higher Ti content, values for Early Archean detrital zircons from a proposed granitic provenance are similar to zircons from many mafic rocks, including anorthosites from the Adirondack Mts (709 ± 76°C). Furthermore, the Jack Hills zircon apparent Ti-temperatures are significantly higher than measured values for peraluminous granites (610 ± 88°C). Thus the Ti concentration in detrital zircons and apparent Ti-in-zircon temperatures are not sufficient to independently identify parent melt composition. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Origin and Evolution of Silicic Magmatism at Yellowstone Based on Ion Microprobe Analysis of Isotopically Zoned Zircons

The origin of large-volume Yellowstone ignimbrites and smaller-volumeintra-caldera lavas requires shallow remelting of enormous volumesof variably ¹⁸O-depleted volcanic and sub-volcanic rocks alteredby hydrothermal activity. Zircons provide probes of these processesas they preserve older ages and inherited ¹⁸O values. This studypresents a high-resolution, oxygen isotope examination of volcanismat Yellowstone using ion microprobe analysis with an averageprecision of ± 0·2 and a 10 µm spot size.We report 357 analyses of cores and rims of zircons, and isotopeprofiles of 142 single zircons in 11 units that represent majorYellowstone ignimbrites, and post-caldera lavas. Many zirconsfrom these samples were previously dated in the same spots bysensitive high-resolution ion microprobe (SHRIMP), and all zirconswere analyzed for oxygen isotope ratios in bulk as a functionof grain size by laser fluorination. We additionally reportoxygen isotope analyses of quartz crystals in three units. Theresults of this work provide the following new observations.(1) Most zircons from post-caldera low-¹⁸O lavas are zoned,with higher ¹⁸O values and highly variable U–Pb ages inthe cores that suggest inheritance from pre-caldera rocks exposedon the surface. (2) Many of the higher-¹⁸O zircon cores in theselavas have U–Pb zircon crystallization ages that postdatecaldera formation, but pre-date the eruption age by 10–20kyr, and represent inheritance of unexposed post-caldera sub-volcanicunits that have ¹⁸O similar to the Lava Creek Tuff. (3) Youngand voluminous 0·25–0·1 Ma intra-calderalavas, which represent the latest volcanic activity at Yellowstone,contain zircons with both high-¹⁸O and low-¹⁸O cores surroundedby an intermediate-¹⁸O rim. This implies inheritance of a varietyof rocks from high-¹⁸O pre-caldera and low-¹⁸O post-calderaunits, followed by residence in a common intermediate-¹⁸O meltprior to eruption. (4) Major ignimbrites of Huckleberry Ridge,and to a lesser extent the Lava Creek and Mesa Falls Tuffs,contain zoned zircons with lower-¹⁸O zircon cores, suggestingthat melting and zircon inheritance from the low-¹⁸O hydrothermallyaltered carapace was an important process during formation ofthese large magma bodies prior to caldera collapse. (5) The¹⁸O zoning in the majority of zircon core–rim interfacesis step-like rather than smoothly inflected, suggesting thatprocesses of solution–reprecipitation were more importantthan intra-crystalline oxygen diffusion. Concave-downward zirconcrystal size distributions support dissolution of the smallercrystals and growth of rims on larger crystals. This study suggeststhat silicic magmatism at Yellowstone proceeded via rapid, shallow-levelremelting of earlier erupted and hydrothermally altered Yellowstonesource rocks and that pulses of basaltic magma provided theheat for melting. Each post-caldera Yellowstone lava representsan independent homogenized magma batch that was generated rapidlyby remelting of source rocks of various ages and ¹⁸O values.The commonly held model of a single, large-volume, super-solidus,mushy-state magma chamber that is periodically reactivated andproduces rhyolitic offspring is not supported by our data. Rather,the source rocks for the Yellowstone volcanism were cooled belowthe solidus, hydrothermally altered by heated meteoric watersthat caused low ¹⁸O values, and then remelted in distinct pocketsby intrusion of basic magmas. Each packet of new melt inheritedzircons that retained older age and ¹⁸O values. This interpretationmay have significance for interpreting seismic data for crustallow-velocity zones in which magma mush and solidified areasexperiencing hydrothermal circulation occur side by side. Newbasalt intrusions into this solidifying batholith are requiredto form the youngest volcanic rocks that erupted as independentrhyolitic magmas. We also suggest that the Lava Creek Tuff magmawas already an uneruptable mush by the time of the first post-calderaeruption after 0·1 Myr of the climactic caldera-formingeruption. KEY WORDS: Yellowstone; oxygen isotopes; geochronology; isotope zoning; zircon; U–Pb dating; caldera; rhyolite; ion microprobe