Accretion of interplanetary dust in polar ice

Measurements of helium isotopes in particles separated from polar ice demonstrate that extraterrestrial ³He dominates the ³He flux at the GISP2 (Greenland) and Vostok (Antarctica) ice core sites. Replicate measurements of late Holocene ice samples yield ³He fluxes of 0.62±0.27×10⁻¹² cm³ STP cm⁻² ka⁻¹ (GISP2) and 0.77 ± 0.25 × 10⁻¹² cm³ STP cm⁻² ka⁻¹ (Vostok), similar to results from marine sediments. These are the first detailed measurements of ³He in particles from ice core samples, and they demonstrate the utility of the ice core record for evaluating the temporal history of the extraterrestrial dust flux. Results from Vostok samples from 1096–1403 m depth (75–97 ka B.P.) are similar to the late Holocene data, with the exception of two highly anomalous results from 1307 m. The latter probably indicate the presence of rare, large or gas‐rich extraterrestrial particles

Flux and size fractionation of He-3 in interplanetary dust from Antarctic ice core samples

Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Earth and Planetary Science Letters 286 (2009): 565-569, doi:10.1016/j.epsl.2009.07.024.Accretion of extraterrestrial material to earth is of interest for a variety of reasons, including as a possible driver of long or short-term climate change, and as a record of solar system events preserved in the geological record. 3He is highly enriched in extraterrestrial material, and provides a useful tracer of its input into sedimentary archives. Previous work showed that polar ice could be a suitable archive for studying variations in extraterrestrial input. Additional measurements reported here confirm that the late Quaternary 3He flux derived from Antarctic ice samples is similar to 3He fluxes determined from marine sediments. The mean flux from nine replicate ~ 1 kg ice samples from the Vostok ice core site (112-115 m depth, age of ~ 3800 years) is 1.25 ± 0.37 x 10-12 cm3 STP cm-2 ka-1 (mean ± 2se). The large range for the 9 replicates is probably due to the small number of interplanetary dust particles (IDPs) present, and illustrates that large ice samples are required for precise constraints on temporal variations in the 3He flux. Size fraction experiments show that the majority of the 3He flux is delivered by particles in the 5-10 micron size range, consistent with the hypothesis that helium in IDPs is primarily solar helium implanted in particle surfaces.We thank the National Science Foundation (OPP-9909384 and OPP 99069663) and NASA (NAG5-9345) for financial support

The helium and carbon isotope characteristics of the Andean Convergent Margin

© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Barry, P. H., De Moor, J. M., Chiodi, A., Aguilera, F., Hudak, M. R., Bekaert, D. V., Turner, S. J., Curtice, J., Seltzer, A. M., Jessen, G. L., Osses, E., Blamey, J. M., Amenabar, M. J., Selci, M., Cascone, M., Bastianoni, A., Nakagawa, M., Filipovich, R., Bustos, E., Schrenk, M. O. , Buongiorno, J., Ramírez, C. J., Rogers, T. J., Lloyd, K. G. & Giovannelli, D. The helium and carbon isotope characteristics of the Andean Convergent Margin. Frontiers in Earth Science, 10, (2022): 897267, https://doi.org/10.3389/feart.2022.897267.Subduction zones represent the interface between Earth’s interior (crust and mantle) and exterior (atmosphere and oceans), where carbon and other volatile elements are actively cycled between Earth reservoirs by plate tectonics. Helium is a sensitive tracer of volatile sources and can be used to deconvolute mantle and crustal sources in arcs; however it is not thought to be recycled into the mantle by subduction processes. In contrast, carbon is readily recycled, mostly in the form of carbon-rich sediments, and can thus be used to understand volatile delivery via subduction. Further, carbon is chemically-reactive and isotope fractionation can be used to determine the main processes controlling volatile movements within arc systems. Here, we report helium isotope and abundance data for 42 deeply-sourced fluid and gas samples from the Central Volcanic Zone (CVZ) and Southern Volcanic Zone (SVZ) of the Andean Convergent Margin (ACM). Data are used to assess the influence of subduction parameters (e.g., crustal thickness, subduction inputs, and convergence rate) on the composition of volatiles in surface volcanic fluid and gas emissions. He isotopes from the CVZ backarc range from 0.1 to 2.6 RA (n = 23), with the highest values in the Puna and the lowest in the Sub-Andean foreland fold-and-thrust belt. Atmosphere-corrected He isotopes from the SVZ range from 0.7 to 5.0 RA (n = 19). Taken together, these data reveal a clear southeastward increase in 3He/4He, with the highest values (in the SVZ) falling below the nominal range associated with pure upper mantle helium (8 ± 1 RA), approaching the mean He isotope value for arc gases of (5.4 ± 1.9 RA). Notably, the lowest values are found in the CVZ, suggesting more significant crustal inputs (i.e., assimilation of 4He) to the helium budget. The crustal thickness in the CVZ (up to 70 km) is significantly larger than in the SVZ, where it is just ∼40 km. We suggest that crustal thickness exerts a primary control on the extent of fluid-crust interaction, as helium and other volatiles rise through the upper plate in the ACM. We also report carbon isotopes from (n = 11) sites in the CVZ, where δ13C varies between −15.3‰ and −1.2‰ [vs. Vienna Pee Dee Belemnite (VPDB)] and CO2/3He values that vary by over two orders of magnitude (6.9 × 108–1.7 × 1011). In the SVZ, carbon isotope ratios are also reported from (n = 13) sites and vary between −17.2‰ and −4.1‰. CO2/3He values vary by over four orders of magnitude (4.7 × 107–1.7 × 1012). Low δ13C and CO2/3He values are consistent with CO2 removal (e.g., calcite precipitation and gas dissolution) in shallow hydrothermal systems. Carbon isotope fractionation modeling suggests that calcite precipitation occurs at temperatures coincident with the upper temperature limit for life (122°C), suggesting that biology may play a role in C-He systematics of arc-related volcanic fluid and gas emissions.This work was principally supported by the NSF-FRES award 2121637 to PB, KL, and JM. Field work was also supported by award G-2016-7206 from the Alfred P. Sloan Foundation and the Deep Carbon Observatory to PB, KL, DG, and JM. Additional support came from The National Fund for Scientific and Technological Development of Chile (FONDECYT) Grant 11191138 (The National Research and Development Agency of Chile, ANID Chile), and COPAS COASTAL ANID FB210021 to GJ. DG was partially supported by funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program Grant Agreement No. 948972—COEVOLVE—ERC-2020-STG

Rapid helium isotopic variability in Mauna Kea shield lavas from the Hawaiian Scientific Drilling Project

Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 5 (2004): Q04G14, doi:10.1029/2002GC000439.This paper presents new magmatic helium isotopic compositions in a suite of lavas from phase II of the Hawaiian Scientific Drilling Project (HSDP2) core, which sampled Mauna Kea volcano to a maximum depth of 3098 m below sea level. Most of the measurements were performed by in vacuo crushing of olivine phenocrysts, but include submarine pillow glasses from the 2200 to 2500 meter depth interval, and orthopyroxene phenocrysts from an intrusive at 1880 m. The magmatic 3He/4He ratios range from 6 to 24.7 times atmospheric (Ra), which significantly extends the range of values for Mauna Kea volcano. The 3He/4He ratios are lowest (i.e., close to MORB values of ∼8 Ra) near the top of the Mauna Kea section and rise slowly, to 10–12 Ra, at 1000 m below sea level, consistent with results from the HSDP1 core. At depths greater than 1000 m in the core, primarily in the submarine lavas, there are brief periods when the 3He/4He ratios are higher than 14.5 Ra, always returning to a baseline value. Twelve such excursions were identified in the core; all but one are in the submarine section, and most (7) are in the deepest section, at depths of 1950 to 3070 m. The baseline 3He/4He value rises from 10–12 Ra near 1000 m depth to 12–14 Ra at 3000 m. The helium spikes are found only in lavas that are older than 380 Ka in age, based on an age model derived from Ar-Ar data (W. D. Sharp et al., manuscript in preparation, 2003). Excluding the excursions defined by single lava flows (3) and intrusive units (3), the average spike duration is approximately 15 (±9) Ka (n = 6). The high 3He/4He spikes are interpreted as pulses of magma from the center of the actively upwelling Hawaiian hot spot. The short duration of the high 3He/4He excursions suggests that Mauna Kea was never directly over high the 3He/4He component of the plume (during the HSDP2 eruptive period), presumed to be the plume center. Assuming that the Mauna Kea helium spikes result from melting of heterogeneities within the plume, their short duration implies that the length scales of heterogeneities in the solid upwelling mantle are between 60 m and 12 km (for upwelling rates of 2 to 40 cm/yr). The high 3He/4He are associated with high 208Pb/204Pb, and relatively low 143Nd/144Nd, Zr/Nb, and SiO2. The correlations with major elements, trace elements and isotopes demonstrate that helium is coupled to the other geochemical variations, and that the Mauna Kea isotopic variability is caused by heterogeneities within the upwelling plume.This work was supported by EAR/NSF through the Continental Dynamics and Instrumentation and Facilities programs

Mantle deformation and noble gases: Helium and neon in oceanic mylonites

a b s t r a c t a r t i c l e i n f o In an effort to constrain the behavior of noble gases during mantle deformation, we present new helium and neon data in mylonites from subaerial St. Peter and St. Paul Archipelago (Mid-Atlantic Ridge) and the submarine Southwest Indian Ridge. Coupled vacuum crushing and melting experiments show that most of the helium and neon within the mylonites is contained in the mineral matrices rather than fluid or melt inclusions: only 5 to 18% of the total helium is released by crushing. The mylonites and ultramylonites have much higher total helium concentrations than expected, based on their small grain size. The St. Paul's Rocks mylonites have helium contents equivalent to gas-rich MORB glasses, ranging from 6 × 10 − 6 to 3.8 × 10 − 5 cc STP He/g. The submarine mylonites and ultramylonites have helium contents between 5 × 10 − 8 and 4.4 × 10 −7 cc STP He/g, compared to 6.2 × 10 − 9 to 3.6 × 10 − 8 for the protogranular/porphyroclastic peridotites. Although the dataset is small, it suggests a relationship between metamorphic texture and noble gas abundance, and that mylonitization introduces mantle helium into mineral matrices. The mylonites are extremely fine grained, with an average grain size of~10 µm, so helium residence in grain boundaries is also plausible. St. Paul's Rocks have modal hornblende, extreme geochemical enrichments in incompatible elements, and high temperature alteration phases (e.g., talc) that are rare or absent in the other samples; mineralogy must also play an important role. The 3 He/ 4 He ratios in the peridotites are primarily mantle derived, based on comparison with MORB data, suggesting that peridotites reflect the source mantle isotopic compositions. Neon isotopes in St. Paul's Rocks are a mixture of air and normal mantle, and fall along the line defined by MORB glasses. The atmospheric neon signal is preferentially released by crushing in vacuum, suggesting it resides within weakly bound sites in cracks and grain boundaries. He/Ne ratios in St. Paul's Rocks vary widely (~20×) with deformation and mineralogy, with the highest He/Ne ratios (and helium concentration) found in the finest grained ultramylonite peridotite. The neon and helium isotopic data show that mantle gases are preserved in fine-grained mylonites at very high concentrations. The most likely mechanism is diffusive trapping within defects at pressure in the mantle. The relationship between texture and helium abundance in peridotites suggests that metamorphism is a potentially important control on noble gas distribution in the mantle and crust

Helium and neon isotopes in oceanic crust of ODP Hole 118-735B

In an attempt to determine the helium and neon isotopic composition of the lower oceanic crust, we report new noble gas measurements on 11 million year old gabbros from Ocean Drilling Program site 735B in the Indian Ocean. The nine whole rock samples analyzed came from 20 to 500 m depth below the seafloor. Helium contents vary from 3.3*10**-10 to 2.5*10**-7 ccSTP/g by crushing and from 5.4*10**-8 to 2.4*10**-7 ccSTP/g by melting. 3He/4He ratios vary between 2.2 and 8.6 Ra by crushing and between 2.9 and 8.2 by melting. The highest R/Ra ratios are similar to the mean mid-ocean ridge basalt (MORB) ratio of 8+/-1. The lower values are attributed to radiogenic helium from in situ alüha-particle production during uranium and thorium decay. Neon isotopic ratios are similar to atmospheric ratios, reflecting a significant seawater circulation in the upper 500 m of exposed crust at this site. MORB-like neon, with elevated 20Ne/22Ne and 21Ne/22Ne ratios, was found in some high temperature steps of heating experiments, but with very small anomalies compared to air. These first results from the lower oceanic crust indicate that subducted lower oceanic crust has an atmospheric 20Ne/22Ne ratio. Most of this neon must be removed during the subduction process, if the ocean crust is to be recirculated in the upper mantle, otherwise this atmospheric neon will overwhelm the upper mantle neon budget. Similarly, the high (U+Th)/3He ratio of these crustal gabbros will generate very radiogenic 4He/3He ratios on a 100 Ma time scale, so lower oceanic crust cannot be recycled into either MORB or oceanic island basalt without some form of processing