喜马拉雅东段错那洞钨-锡-铍矿床中铍的赋存状态及成因机制初探

近年来喜马拉雅淡色花岗岩带被认为是稀有金属成矿的有利地区,并已在该区伟晶岩中发现诸多稀有金属矿物。错那洞矿床是该带内发现最早并具有较大规模的钨锡铍（W-Sn-Be）矿床,Be矿化包括伟晶岩型和矽卡岩型,但目前铍元素的赋存状态还没有被清晰地查明。伟晶岩型矿化主要为伟晶岩中晶型较好的绿柱石晶体;而矽卡岩型铍矿化表现形式则复杂多样。Be元素除了赋存于绿柱石、硅铍石、羟硅铍石等含铍矿物中,还可以广泛分布于矽卡岩矿物中。其中,符山石（Be含量：43×10^-6~887×10^-6）和方柱石（Be含量：1333×10^-6~4643×10^-6）是铍元素赋存的主要载体。矽卡岩型矿化与淡色花岗岩有关,岩浆高分异演化使熔体中Be、Sn、W及挥发分逐步富集,在伟晶岩中饱和绿柱石;之后Be元素在F的络合下随出溶流体进入碳酸盐岩,发生水岩相互作用,萤石的析出引起Be-F络合物失稳,导致Be元素的沉淀。含铍矿物种类及成因机制的研究将有助于指导喜马拉雅地区同类型矿化的评价。     

黄土和红粘土中宇宙成因核素定年的潜力: 10 Be浓度与化学成分的关系*

宇宙成因核素¹⁰ Be(半衰期1.5Ma)不但是古环境变化的示踪剂,而且具有确定地质年龄的能力。80个全岩样品的¹⁰ Be和化学分析数据表明,黄土高原约6Ma以来的红粘土和黄土序列中年龄校正的¹⁰ Be浓度与沉积物粒度和风化程度的化学指标具有显著的关系。根据这种关系建立的¹⁰ Be浓度与化学指标的经验回归线性模型,可以估计红粘土和黄土形成时的¹⁰ Be浓度,确定红粘土和黄土形成的¹⁰ Be放射性年龄。     

60 Myr records of major elements and Pb–Nd isotopes from hydrogenous ferromanganese crusts: reconstruction of seawater paleochemistry

We compare the time series of major element geochemical and Pb- and Nd-isotopic composition obtained for seven hydrogenous ferromanganese crusts from the Atlantic, Indian, and Pacific Oceans which cover the last 60 Myr.Average crust growth rates and age–depth relationships were determined directly for the last about 10 Myr using ¹⁰Be/⁹Be profiles. In the absence of other information these were extrapolated to the base of the crusts assuming constant growth rates and constant initial ¹⁰Be/⁹Be ratios due to the lack of additional information. Co contents have also been used previously to estimate growth rates in Co-rich Pacific and Atlantic seamount crusts (Puteanus and Halbach, 1988). A comparison of ¹⁰Be/⁹Be- and Co-based dating of three Co-rich crusts supports the validity of this approach and confirms the earlier chronologies derived from extrapolated ¹⁰Be/⁹Be-based growth rates back to 60 Ma. Our data show that the flux of Co into Co-poor crusts has been considerably lower. The relationship between growth rate and Co content for the Co-poor crusts developed from these data is in good agreement with a previous study of a wider range of marine deposits (Manheim, 1986). The results suggest that the Co content provides detailed information on the growth history of ferromanganese crusts, particularly prior to 10–12 Ma where the ¹⁰Be-based method is not applicable.The distributions of Pb and Nd isotopes in the deep oceans over the last 60 Myr are expected to be controlled by two main factors: (a) variations of oceanic mixing patterns and flow paths of water masses with distinct isotopic signatures related to major paleogeographic changes and (b) variability of supply rates or provenance of detrital material delivered to the ocean, linked to climate change (glaciations) or major tectonic uplift. The major element profiles of crusts in this study show neither systematic features which are common to crusts with similar isotope records nor do they generally show coherent relationships to the isotope records within a single crust. Consequently, any interpretation of time series of major element concentrations of a single crust in terms of paleoceanographic variations must be considered with caution. This is because local processes appear to have dominated over more basin-wide paleoceanographic effects. In this study Co is the only element which shows a relationship to Pb and Nd isotopes in Pacific crusts. A possible link to changes of Pacific deep water properties associated with an enhanced northward advection of Antarctic bottom water from about 14 Ma is consistent with the Pb but not with the Nd isotopic results. The self-consistent profiles of the Pb and Nd isotopes suggest that postdepositional diagenetic processes in hydrogenous crusts, including phosphatization events, have been insignificant for particle reactive elements such as Pb, Be, and Nd. Isotope time series of Pb and Nd show no systematic relationships with major element contents of the crusts, which supports their use as tracers of paleo-seawater isotopic composition.     

Meteoric Be in soil profiles - A global meta-analysis

In order to assess current understanding of meteoric ¹⁰Be dynamics and distribution in terrestrial soils, we assembled a database of all published meteoric ¹⁰Be soil depth profiles, including 104 profiles from 27 studies in globally diverse locations, collectively containing 679 individual measurements. This allows for the systematic comparison of meteoric ¹⁰Be concentration to other soil characteristics and the comparison of profile depth distributions between geologic settings. Percent clay, ⁹Be, and dithionite-citrate extracted Al positively correlate to meteoric ¹⁰Be in more than half of the soils where they were measured, but the lack of significant correlation in other soils suggests that no one soil factor controls meteoric ¹⁰Be distribution with depth. Dithionite-citrate extracted Fe and cation exchange capacity are only weakly correlated to meteoric ¹⁰Be. Percent organic carbon and pH are not significantly related to meteoric ¹⁰Be concentration when all data are complied.The compilation shows that meteoric ¹⁰Be concentration is seldom uniform with depth in a soil profile. In young or rapidly eroding soils, maximum meteoric ¹⁰Be concentrations are typically found in the uppermost 20 cm. In older, more slowly eroding soils, the highest meteoric ¹⁰Be concentrations are found at depth, usually between 50 and 200 cm. We find that the highest measured meteoric ¹⁰Be concentration in a soil profile is an important metric, as both the value and the depth of the maximum meteoric ¹⁰Be concentration correlate with the total measured meteoric ¹⁰Be inventory of the soil profile.In order to refine the use of meteoric ¹⁰Be as an estimator of soil erosion rate, we compare near-surface meteoric ¹⁰Be concentrations to total meteoric ¹⁰Be soil inventories. These trends are used to calibrate models of meteoric ¹⁰Be loss by soil erosion. Erosion rates calculated using this method vary based on the assumed depth and timing of erosional events and on the reference data selected.     

Constraining Holocene 10Be production rates in Greenland

The absence of a production rate calibration experiment on Greenland has limited the ability to link ¹⁰Be exposure dating chronologies of ice‐margin change to independent records of rapid climate change. We use radiocarbon age control on Holocene glacial features near Jakobshavn Isbræ, western Greenland, to investigate ¹⁰Be production rates. The radiocarbon chronology is inconsistent with the ¹⁰Be age calculations based on the current globally averaged ¹⁰Be production rate calibration data set, but is consistent with the ¹⁰Be production rate calibration data set from north‐eastern North America, which includes a calibration site nearby on north‐eastern Baffin Island. Based on the best‐dated feature available from the Jakobshavn Isbræ forefield, we derive a ¹⁰Be production rate value of 3.98 ± 0.24 atoms g a^?1, using the ‘St’ scaling scheme, which overlaps with recently published reference ¹⁰Be production rates. We suggest that these ¹⁰Be production rate data, or the very similar data from north‐eastern North America, are used on Greenland. Copyright © 2011 John Wiley & Sons, Ltd.     

Marine biogeochemistries of Be and Al: A study based on cosmogenic10Be, Be and Al in marine calcite, aragonite, and opal

The geochemical behaviors of Be and Al in ocean waters have been successfully studied in recent years using natural, cosmogenic, radioactive¹⁰Be and²⁶Al as tracers. The present day dissolved concentrations and distribution of the stable and radioactive isotopes of Be and Al in ocean waters have revealed their short residence times and appreciable effects of exchange fluxes at the coastal and ocean-sediment interfaces. It follows that concentrations of these particle-active elements must have varied in the past with temporal changes in climate, biological productivity and aeolian flux of continental detritus to the oceans. We therefore investigated the feasibility of extending the measurements of Be and Al isotope concentrations in marine systems to the 10³–10⁶ y BP time scale. We report here the discovery of significant amounts of intrinsic Be and Al in marine foraminiferal calcite and coral aragonite, and of Al in opal (radiolarians) and aragonite (coral), which makes it possible to determine¹⁰Be/Be and²⁶Al/Al in oceans in the past. We also report measured¹⁰Be/⁹Be in foraminiferal calcite in Pacific Ocean cores, which reveal that the concentrations and ratios of the stable and cosmogenic isotopes of Be and Al have varied significantly in the past 30 ky. The implications of these results are discussed.     

The dissolved Beryllium isotope composition of the Arctic Ocean

We present the first comprehensive set of dissolved ¹⁰Be and ⁹Be concentrations in surface waters and vertical profiles of all major sub-basins of the Arctic Ocean, which are complemented by data from the major Arctic rivers Mackenzie, Lena, Yenisey and Ob. The results show that ¹⁰Be and ⁹Be concentrations in waters below 150 m depth are low and only vary within a factor of 2 throughout the Arctic Basin (350-750 atoms/g and 9-15 pmol/kg, respectively). In marked contrast, Be isotope compositions in the upper 150 m are highly variable and show systematic variations. Cosmogenic ¹⁰Be concentrations range from 150 to 1000 atoms/g and concentrations of terrigenous ⁹Be range from 7 to 65 pmol/kg, resulting in ¹⁰Be/⁹Be ratios (atom/atom) between 0.5 and 14 × 10⁻⁸. Inflowing Atlantic water masses in the Eurasian Basin are characterized by a ¹⁰Be/⁹Be signature of 7 × 10⁻⁸. The inflow of Pacific water masses across the Bering Strait is characterized by lower ratios of 2-3 × 10⁻⁸, which can be traced into the central Arctic Ocean, possibly as far as the Fram Strait. A comparison of the high dissolved surface ¹⁰Be and ⁹Be concentrations (corresponding to low ¹⁰Be/⁹Be signatures of ∼2 × 10⁻⁸) in the Eurasian Basin with hydrographic parameters and river data documents efficient and rapid transport of Be with Siberian river waters across the Siberian Arctic shelves into the central Arctic Basin, although significant loss and exchange of Be on the shelves occurs. In contrast, fresh surface waters from the Canada Basin also show high cosmogenic ¹⁰Be contents, but are not enriched in terrigenous ⁹Be (resulting in high ¹⁰Be/⁹Be signatures of up to 14 × 10⁻⁸). This is explained by a combination of efficient scavenging of Be in the Mackenzie River estuary and the shelves and additional supply of cosmogenic ¹⁰Be via atmospheric fallout and melting of old sea ice. The residence time of Be in the deep Arctic Ocean estimated from our data is 800 years and thus similar to the average Be residence time in the global ocean.     

河流阶地样品中石英纯化和宇宙核素~(10)Be和~(26)Al分离方法研究

经历反复埋藏暴露演化过程的河流阶地样品,难以用常规方法将原生宇宙核素10Be、26Al有效分离。本文在前人实验方法基础上,使用人工挑选、磁选仪分选及酸洗方法,分离样品中碳酸盐、含铁矿物及大气生成的10Be,进一步优化了石英提纯实验流程。结果表明:长度为9 cm、内径为1 cm的阴离子交换树脂装置匹配4 mol/L氢氟酸淋滤液,可将B、Mg、Ca、Cr、Fe、Mn、Ni、Ti和Be、Al有效分离,Be、Al回收率分别可达95.7%、85.7%。阳离子交换树脂能有效分离Be、Al,两元素回收率均达到85%。获得10Be/9Be和26Al/27Al流程空白分别为2.19×10-15和1.63×10-15。优化后的实验方法显著提高了河流阶地样品中原生宇宙核素10Be、26Al的纯化效率,且10Be/9Be和26Al/27Al流程空白数值与国内外实验室具有可比性。采用本方法获得了成都平原冲积物10Be、26Al暴露年龄分别是76.36±9.51 ka和69.44±14.13 ka,为评价龙门山前缘隐伏断裂构造特征和活动性提供了年代学依据。     

深海沉积物10Be记录研究

DSDP519钻孔¹⁰Be测定结果表明，在B／M，M／G两地磁极性倒转期间，¹⁰Be产生率均约增加20％。DSDP519孔δ¹⁰Be曲线与DSDP502孔δ¹⁸O曲线具有明显的正相关关系。CT85－5钻孔¹⁰Be曲线在34000±3000aB．P存在明显的峰，峰值比正常值高出2．5倍，⁹Be，Zn变化曲线中均未观察到此峰，与Vostok冰芯¹⁰Be峰在时间上属于同期。这进一步说明了此时期内¹⁰Be浓度增加是全球性的，只能归因于¹⁰Be产生率的增加。Raisbeck峰讯号可以成为某些储存库精确时标。     

Fractionation of Th, Pa, and Be induced by particle size and composition within an opal-rich sediment of the Atlantic Southern Ocean

This study centers on the question: How sensitive are ²³¹Pa/²³⁰Th and ¹⁰Be/²³⁰Th to sediment composition and redistribution? The natural radionuclides ²³¹Pa, ²³⁰Th and ¹⁰Be recorded in deep sea sediments are tracers for water mass advection and particle fluxes. We investigate the influence of oceanic particle composition on the element adsorption in order to improve our understanding of sedimentary isotope records. We present new data on particle size specific ²³¹Pa and ¹⁰Be concentrations. An additional separation step, based on settling velocities, led to the isolation of a very opal-rich phase. We find that opal-rich particles contain the highest ²³¹Pa and ¹⁰Be concentrations, and higher ²³¹Pa/²³⁰Th and ¹⁰Be/²³⁰Th isotope ratios than opal-poor particles. The fractionation relative to ²³⁰Th induced by the adsorption to opal-rich particles is more pronounced for ²³¹Pa than for ¹⁰Be. We conclude that bulk ²³¹Pa/²³⁰Th in Southern Ocean sediments is most suitable as a proxy for past opal fluxes. The comparison between two neighboring cores with rapid and slow accumulation rates reveals that these isotope ratios are not influenced significantly by the intensity of sediment focusing at these two study sites. However, a simulation shows that particle sorting by selective removal of sediment (winnowing) could change the isotope ratios. Consequently, ²³¹Pa/²³⁰Th should not be used as paleocirculation proxy in cases where a strong loss of opal-rich material due to bottom currents occurred.     

南黄海、东海陆架及冲绳海槽北部 沉积物的10 Be和9 Be记录*

文章讨论了南黄海泥质区、东海陆架及冲绳海槽北部表层沉积物和柱状岩芯中¹⁰ Be及⁹ Be含量的水平和垂直分布,并与重金属Pb的分布进行了比较。表层沉积物中的¹⁰ Be,⁹ Be和Pb三者表现出完全不同的分布特征。¹⁰ Be的分布主要受黑潮及其支流黄海暖流所支配; ⁹ Be的分布受黄河陆源物质输入的影响,主要集中在南黄海泥质区; Pb则主要分布在长江口和琉球群岛附近,反映了人类活动的影响。冲绳海槽北部末次冰期和全新世时¹⁰ Be的沉积通量变化在整体上反映了¹⁰ Be大气生产率的变化,即地球磁场屏蔽效应的影响。03孔全新世时¹⁰ Be的沉积通量 (1.12×10⁹atoms/cm²ka)基本上等于¹⁰ Be的现代大气平均生产率,而在末次冰期时平均为4.06×10⁹atoms/cm²ka, 高于¹⁰ Be 的现代大气平均生产率3倍以上。在冲绳海槽由于黑潮的缘故,¹⁰ Be对气候的变化响应要比极地冰芯的¹⁰ Be变化响应灵敏的多,对气候变化信号起了放大的作用。冰期时冲绳海槽北部¹⁰ Be的沉积通量远远高于太平洋大洋海区,充分反映了黑潮的传送带作用和边缘海的聚焦沉积作用,并表明末次冰期时在千年尺度上黑潮仍流经冲绳海槽,且强度并未减弱。 ¹⁰ Be的通量在新仙女木时降到整个岩芯所跨时期的最低点,甚至低于¹⁰ Be的现代大气平均生产率,因此推测在新仙女木事件时,黑潮的变动特别大,有可能改向或断流。     

26Al-10Be systematics in deep-sea sediments

We report the development of a NaOH-leaching technique to extract the authigenic Al and Be in marine sediments, which should allow the sedimentary signals of cosmogenic ²⁶Al and ¹⁰Be to be more effectively studied as geochemical/geophysical tracers. The technique has been applied to the study of ²⁶Al and ¹⁰Be in opal-rich sediments from the North Pacific. The ²⁶Al/²⁷Al and ¹⁰Be/⁹Be ratios of ~3 × 10⁻¹⁴ and 1 × 10⁻⁷ leached from the sediments are higher than those in the total sediments by factors of 3–10 and 2–3, respectively. The authigenic ¹⁰Be/⁹Be ratios are similar to those in deep waters at the study site, pointing to the potential usefulness of the ratios in paleoceanographic studies. The fractions of total Be and Al in the sediment studied that are of authigenic origin average about 40 and 17%, respectively. Estimated ²⁶AL/²⁷A1 ratios in detrital sediments are ≤ 10⁻¹⁵, low enough to indicate that the source of ²⁶Al in the ocean mainly comes from atmospheric production. In the study area, the deposition flux of ²⁶Al is comparable to its atmospheric supply. However, the deposition flux of ¹⁰Be is about threefold higher than the atmospheric input, signifying lateral transport of ¹⁰Be from the open ocean to this area of relatively high particle flux. The ²⁶Al/¹⁰Be ratio, being insensitive to the oceanic influx of lithogenic particles, may serve as a valuable proxy for paleoproductivity. Both the authigenic and total-sediment ²⁶Al/²⁷Al and ¹⁰Be/ ⁹Be ratios decreased significantly at ~6 ka, which could reflect an enhanced input of windblown lithogenic particles to the North Pacific. While the enhanced dust input did not significantly alter the deep-water ⁹Be concentration, it contributed to the observed increase of authigenic ⁹Be flux to the sediment.     

Meltwater discharge during the Holocene from the Wilkes subglacial basin revealed by beryllium isotope analysis of marine sediments

Understanding Antarctic Ice Sheet dynamics related to global climate change is of scientific and societal interest as the future behaviour of the ice sheet under the currently changing climate is unknown. We present beryllium‐10 (¹⁰Be) analysis of a high‐resolution marine sediment core from the Adélie Basin near the eastern Wilkes Land margin, which is susceptible to marine ice sheet instability due to the low‐lying nature and down‐sloping trough of the Wilkes Subglacial Basin. Combined with a newly constructed age model using compound specific radiocarbon dates, the data reveal three events associated with high meteoric ¹⁰Be at ca. ~10 ka, ca. ~6.5 ka and from ca. ~4 ka. We interpret these high meteoric ¹⁰Be events to be derived from the deposition of ¹⁰Be released from the ice sheet during meltwater discharge. In particular, the shift to higher meteoric ¹⁰Be concentration at~4 ka may correspond to changes in climate patterns at this time. Copyright © 2019 John Wiley & Sons, Ltd.     

晚更新世黄土堆积物中的10Be记录

给出西峰黄土剖面0.15Ma以来¹⁰Be浓度、CaCO₃含量、粒度分布和有机质含量曲线。通过与深海沉积物δ¹⁸O曲线拟合,建立了西峰黄土剖面¹⁰Be时标,并与洛川黄土剖面¹⁰Be记录进行了对比研究。进一步计算了黄土堆积速率及¹⁰Be沉降量。     

Beryllium-10 contents of core samples from the St. Severin meteorite

Eleven samples taken from along the 35-cm core AIII of the LL-chondrite St. Severin have ¹⁰Be contents ranging from 20 to 28 dpm/kg and averaging 24.5 ± 0.9 dpm/kg. The ¹⁰Be contents increase with depth in the outermost 8 cm while at depths greater than 8 cm the ¹⁰Be contents change little. Calculations based on cross sections for proton-induced reactions that make ¹⁰Be disagree seriously with the measured values. Relatively large cross sections were constructed for neutron-induced reactions below 1 GeV. They give calculated ¹⁰Be production rates that agree with the measured values to within 10%. Cosmogenic ¹⁰Be in stony meteorites is better described as a medium-energy product than as a high-energy one.     

Volcanic and solar activity, and atmospheric circulation influences on cosmogenic Be fallout at Vostok and Concordia (Antarctica) over the last 60 years

The cosmogenic nuclide beryllium-10 (¹⁰Be), recovered from ice cores, is often used to study solar activity on long timescales. However, the ¹⁰Be signal is also influenced by factors other than the Sun. To identify and quantify various contributions to the ¹⁰Be signal, two Antarctic snow records from the Vostok and Concordia sites spanning the last 60 years were studied at a sub-annual resolution. Three factors that contribute to the ¹⁰Be signal were identified. First, a significant period of approximately 11 yr that can be associated with the modulation of ¹⁰Be production by solar activity was detected in both records. The solar imprint constitutes 20-35% of the variance within the total signal. The 11-yr ¹⁰Be snow component was attenuated by a factor of ∼0.5 and was delayed by ∼1.4 yr compared to the ¹⁰Be production expected within the polar atmosphere. The result could be interpreted as the composite response of a stratospheric ¹⁰Be reservoir with an 11-yr modulation that was attenuated and delayed (with respect to ¹⁰Be polar production) and to a tropospheric ¹⁰Be reservoir with an 11-yr modulation that was not attenuated or delayed. Then, peaks in ¹⁰Be concentrations that were ∼66% and ∼35% higher than the average concentration were observed during the stratospheric volcanic eruptions of Agung (in 1963) and Pinatubo (in 1991), respectively. In light of these new results, published ¹⁰Be ice core records could be reinterpreted because spikes in ¹⁰Be concentration appear at the time of several stratospheric events. The data indicate that stratospheric volcanic eruptions can impact ¹⁰Be transport and deposition as a result of the roles played by the sedimentation of sulfate aerosols and the formation and rapid settling of polar stratospheric clouds (PSC). Also, an interannual variability of ∼4 yr was determined in both ¹⁰Be records, corresponding to ∼26% of the variance within the signal at Vostok. As with species of marine origin (sodium), this 4-yr variability is interpreted as a tropospheric modulation. The 4-yr variability could be associated with atmospheric circulation associated with the coupled Southern Ocean ocean-atmosphere system. The results presented here, from sites within the high Antarctic plateau, open new possibilities for ice core dating over the last few centuries and for the reconstruction of past solar activity in relation to climate.     

Sediment incorporation in island-arc magmas: Inferences from 10Be

The radioisotope ¹⁰Be has been used as a tracer to evaluate subduction and recycling of sediments in island arcs. As a cosmogenic isotope strongly enriched in oceanic sediments, it is especially suitable for monitoring sediment subduction.We report here ¹⁰Be results for 106 arc volcanic rocks and 33 basalts from mid-ocean ridges, oceanic islands, continental rifts, and continental flood basalt provinces. The 33 basalts from non-arc environments all contain < 1 × 10⁶ atom/gram (g⁻¹) and form a reference or “control group” against which the arc data may be compared. Lavas from the Sunda, Mariana and Halmahera arcs, each with 12 samples, are indistinguishable from the control group. Nine samples from Japan range from 0.1 × 10⁶ to 13.5 × 10⁶ g⁻¹ of ¹⁰Be. Lavas from the Aleutians and Central America (excluding Costa Rica) consistently have ¹⁰Be contents greater than those of the control group, extending to 15.3 × 10⁶ g⁻¹ for the Aleutians and 24 × 10⁶ g⁻¹ for Central America. Both the Japan and Central American arcs show a geographic variation in ¹⁰Be abundances; the Aleutian arc does not.Conceptually, four models may be used to explain the incorporation of ¹⁰Be in island arcs. Model 1 is the limiting case calculation presented in Brownet al. (1982). Physically, it corresponds to an assumption that all ¹⁰Be in the uppermost sediment layers is carried to depth, the ¹⁰Be is mechanically decoupled from the sediment pile and is added to the arc magma source region. This model results in the highest calculated ¹⁰Be contents in arc lavas. In the more physically reasonable Model 2, the ¹⁰Be-rich upper sediments are assumed to mix with the deeper, ¹⁰Be-poor, sediments and the sediments are subsequently incorporated into the source region. Model 3 assumes ¹⁰Be to be incorporated from sedimentary layers encountered during magma ascent. In Model 4 only sediments contained within grabens in the downgoing slab may be subducted. As yet insufficient data exist to permit conclusive evaluation of these models, but correlations between ¹⁰Be contents in arc volcanic rocks and recent sedimentation rates and sediment thickness, measured outboard of the trench, suggest that Model 2 may be the most important mechanism for ¹⁰Be incorporation in many island arcs.     

Beryllium-10 in Australasian tektites: Constraints on the location of the source crater

By using accelerator mass spectrometry we have measured the ¹⁰Be concentrations of 86 Australasian tektites. Corrected to the time of tektite production ∼0.8 My ago, the ¹⁰Be concentrations (10⁶ atom/g) range from 59 for a layered tektite from Huai Sai, Thailand, to 280 for an australite from New South Wales, Australia. The average value is 143 ± 50. When tektites are sorted by country, their average measured ¹⁰Be concentrations increase slowly with increasing distance from Southeast Asia, the probable location of the tektite producing event, from 59 ± 9 for 6 layered tektites from Laos to 136 ± 20 for 20 splash-form tektites from Australia. The lowest ¹⁰Be concentrations for tektites fall on or within a contour centered off the shore of Vietnam, south of the Gulf of Tonkin (107°E; 17°N), but also encompassing two other locations in the area of northeastern Thailand previously proposed for the site of a single tektite-producing impact. The ¹⁰Be concentrations of layered tektites show only a weak anticorrelation (R ∼ −0.3) with the numbers of relict crystalline inclusions.Loosely consolidated, fine-grained terrestrial sediments or recently consolidated sedimentary rocks are the most likely precursor materials. Dilution of sediments with other kinds of rock raises problems in mixing and is not supported by petrographic data. Sedimentary columns that have the right range of ¹⁰Be concentrations occur off the coasts of places where sedimentation rates are high relative to those in the deep sea. A single impact into such a region, 15 to 300 m thick, could have propelled near-surface, high-¹⁰Be material farthest—to Australia—while keeping the deeper-lying, low-¹⁰Be layers closer to home. We do not rule out, however, other proposed mechanisms for tektite formation.     

New data for Late Pleistocene Pinedale alpine glaciation from southwestern Colorado

New cosmogenic surface-exposure ages of moraine-crest boulders from southwestern Colorado are compared with published surface-exposure ages of boulders from moraine complexes in north-central Colorado and in west-central (Fremont Lake basin) Wyoming. ¹⁰Be data sets from the three areas were scaled to a single ¹⁰Be production rate of 5.4 at/g/yr at sea level and high latitude (SLHL), which represents the average ¹⁰Be production rate for two high-altitude, mid-latitude sites in the western United States (US) and Austria. Multiple nuclide ages on single boulders indicate that this ¹⁰Be production rate yields ages comparable to those calculated with a commonly used ³⁶Cl production scheme. The average age and age range of moraine-crest boulders on terminal moraines at the southwestern Colorado and Wyoming sites are similar, indicating a retreat from their positions ∼16.8 ³⁶Cl ka (Cosmogenic ages in this paper are labeled ¹⁰Be or ³⁶Cl ka or just ka when both ¹⁰Be or ³⁶Cl ages are being discussed; radiocarbon ages are labeled ¹⁴C ka, calibrated radiocarbon are labeled cal ka, and calendar ages are labeled calendar ka. Errors (±1σ) associated with ages are shown in tables. Radiocarbon ages were calibrated using the data of Hughen et al. (Science 303 (2004) 202). This suggests a near-synchronous retreat of Pinedale glaciers across a 470-km latitudinal range in the Middle and Southern Rocky Mountains. Hypothetical corrections for snow shielding and rock-surface erosion shifts the time of retreat to between 17.2 and 17.5 ¹⁰Be ka at Pinedale, Wyoming, and between 16.3 and 17.3 ³⁶Cl ka at Hogback Mountain, Colorado.