火山活动与深部碳循环的关系

火山活动是导致地球深部碳向地表输送的重要途径之一,它促进了地球层圈物质交换与深部循环作用.目前,火山活动与深部碳循环关系的研究主要集中在: 1)火山喷发向大气圈中输送CO2气体的通量与总量; 2)火山气体的来源及其演变历史; 3)不同类型的火山喷发(例如,大火山岩省、洋中脊和俯冲带火山活动)对地球深部碳循环贡献的差异.文章通过对青藏高原北部阿什库勒火山群1951年阿什火山喷发物斑晶中原生岩浆包裹体和基质玻璃的实验室测定表明,阿什火山喷出的气体成分主要由H2O,CO2,S,Cl和F组成,利用"岩石学方法"计算的阿什火山喷发向大气圈输送的CO2气体总量为1.01×109kg.     

岩浆包裹体挥发组分的研究

对浙江省桐庐、寿昌中生代火山杂岩石英晶屑及斑晶中单个岩浆包裹体收缩气泡内的挥发组分,借助激光喇曼探针进行分析,定量给出的有CO_2、CH_4、H_2O、N_2、CO、H_2、H_2S、SO_2。 结合岩浆包裹体显微测温、测压和化学成分数据,计算了单个包裹体被捕获时的P_总、f_(O_2)、f_(CO_2)、f_(CH_4)、f_(H_2O)、f_(CO)和f_(H_2)等物理化学参数。并据此讨论了桐庐、寿昌中生代火山岩浆演化中的某些物理化学条体。 研究表明,此类研究已经成为现代岩浆岩石学,特别是现代火山岩石学研究中一个必不可少的新兴领域,它可以帮助我们重溯天然岩浆结晶演化的物理化学历史。     

火山喷发过程中岩浆脱气率和脱气量的估算方法及其意义

本文对前人使用的火山喷发过程中岩浆脱气率和脱气量的估算方法进行了评述,并介绍了如何利用岩石学方法估算火山喷发不同阶段岩浆脱气率和脱气量的具体步骤,同时以镜泊湖地区全新世火山为例说明利用该方法估算的具体过程。估算结果表明不同气体在火山喷发过程中的脱气率是不同的,不能用包裹体中挥发分相对含量的高低来判断火山喷发所释放到大气圈中的气体类型和质量。该方法对火山学的研究具有重要意义。     

云南腾冲新期火山岩矿物及其熔体包裹体研究

腾冲火山群位于我国云南省西部和缅甸的交界处,由黑空山、大空山、小空山、打鹰山、马鞍山等一系列火山组成,是我国著名的第四纪火山群,从喷发活动时间上可分为老期火山和新期火山.前人研究证实,打鹰山、马鞍山和黑空山为新期火山,它们在全新世都有过喷发活动.这些新期火山岩的主要斑晶矿物为辉石、橄榄石和长石,主要的斑晶矿物中都含有熔体包裹体,它们形态多样,分布不规则,且部分显示后期有变化.探针分析表明,新期火山岩矿物中熔体包裹体成分的变化范围大于其基质玻璃成分的变化范围,它们的化学成分分布范围涵盖了玄武粗安岩、粗面安山岩、粗面岩和流纹岩等岩石类型,与腾冲火山区晚更新世以来火山岩的成分分布范围基本一致.根据对新期火山岩斑晶和微晶矿物中熔体包裹体及基质玻璃成分的测试研究,其中挥发分Cl的含量在包裹体和基质中变化不大,但F、SO3在熔体包裹体中的含量高于基质,总体上腾冲新期火山喷发时岩浆的脱气率较低,喷发时并未向空中喷出大量气体,推测对当时的气候环境影响不大,但未来喷发的灾害效应不容忽视.     

西藏甲玛铜多金属矿床成因研究——来自流体包裹体的证据

甲玛铜多金属矿床位于西藏冈底斯斑岩铜矿带东段,是近年来勘探发现的超大型斑岩-矽卡岩型铜多金属矿床。通过冷热台显微观察与测温、扫描电镜、激光拉曼探针测试,对甲玛矿床各成矿阶段典型矿物的流体包裹体研究表明,成矿流体富含挥发分,临界相均一的流体来自岩浆超临界流体出溶,主成矿阶段具有沸腾包裹体组合特征,有机质包裹体荧光效应显著。显微测温结果显示,岩浆-热液阶段斑岩中石英斑晶的流体包裹体均一温度范围为250～540℃,含石盐子晶高盐度包裹体盐度范围为35～61(wt%)NaCl.eq,中等盐度的临界均一的气液包裹体盐度范围为3～29(wt%)NaCl.eq,岩浆期后热液阶段斑岩、角岩中石英脉的流体包裹体均一温度范围为210～410℃,盐度范围为33～41(wt%)NaCl.eq,与其不混溶共生的中低盐度气液两相流体包裹体盐度范围为5～25(wt%)NaCl.eq。矽卡岩阶段矿物均一温度范围为130～360℃,盐度范围为3～41(wt%)NaCl.eq,从岩浆热液过渡阶段到石英-硫化物阶段均一温度与盐度呈阶梯式降低趋势。斑岩体石英的流体包裹体中含有较多黄铜矿子矿物,岩浆结晶分异过程中已经具成矿元素的富集。激光拉曼探针测试结果显示,成矿早期至主成矿期矿物流体包裹体气相成分主要为CO2、CH4和N2,各阶段矿物流体包裹体气相成分具有继承性。成矿流体为高温度高盐度,富含CO2、CH4的流体。成矿流体主要源于岩浆,后期混有大气降水。当岩浆热液上升时因压力的突然释放造成高温含矿热流体发生减压沸腾,CO2和CH4等气体大量逃逸,导致成矿物质快速沉淀。矿床在成因上与岩浆-热液成矿作用密切相关。     

利用U—1000型激光拉曼探针测定流体包裹体气体成分的研究

本文利用U－1000型激光拉曼探针成功地测量出单个流体包裹体中H2S、CH4、CO2气体成分，并讨论了包裹体中这些气体的拉曼谱峰位移与包裹体内压的关系，分析了影响激光拉曼探针定量测定包裹体气相成分的取面积和拉曼定量因子因素。     

张家口中生代火山盆地火山喷发对古气候的影响

本文在详细地研究了张家口中生代火山盆地火山喷发物的基础上,利用岩石学及大气环境化学的基本原理,提出了一套系统估算火山喷出气体及气溶胶总量的程序与方法,并对张家口中生代火山喷出气体的种类、总量及气溶胶总量进行了估算;分析了火山硫化物气体转化为火山硫酸盐气溶胶的光化学过程及可能途径。在分别研究了本区火山喷发导致的“阳伞效应”与“温室效应”的基础上,探讨了该区火山喷发对地表温度的综合影响。初步结果表明：张家口中生代火山盆地火山喷发向当时大气圈中输送了约９．９６×１０１０ｋｇ的硫酸盐气溶胶,它们能导致当时北半球范围内太阳总幅射率降低０．８１％～３．６０％,最终造成地表温度下降约０．８１℃～３．６℃。     

中国休眠火山区岩浆来源气体地球化学特征

中国休眠火山区岩浆来源气体的最主要成分是CO2,含量占80％～99％;其它气体组分还有CH4、He、H2、N2、Ar、O2、H2S、SO2、CO等,其中CH4和He是CO2以外最值得重视的直接来自地幔岩浆体的气体组分。He的同位素组成（^3He／^4He比值）是休眠火山区最可靠的幔源物质的指示性参数;岩浆来源的CO2和CH4也具有特征的区别于浅源气体的稳定同位素组成（δ^13C值）。长白山火山区近期CO2和CH4的碳同位素分馏监测结果显示,2002年汪清7．2级深震虽然可能引发了深部岩浆的局部扰动,但是它可能并没有产生特别大量的、持续不断的上地幔岩浆物质流的上升迁移。这意味着,长白山天池火山区近期可能没有火山喷发活动的现实危险。     

岩浆包裹体研究在火山岩岩石学中的地位

岩浆包裹体研究已经成为现代火山岩岩石学的一项分支学科。研究方面涉及:重溯火山岩浆结晶演化的热历史,提供有关火山岩浆沿下降液相线的成分数据;查明火山岩浆结晶演化过程中化学成分(包括挥发组分)的变迁规律;查明各种岩浆事件的性质(分离结晶、不混溶、混合、混染),及其发生发展的物理化学条件;帮助探索解决某些疑难问题,如下地壳—上地幔的性质及玄武岩浆起源、细碧岩—角斑岩系的成因、测定蚀变火山岩建造的年龄等。此外,岩浆包裹体的实验岩石学研究,以及利用岩浆包裹体阐明火山建造的含矿性,研究火山沉积作用、地热作用等,对于火     

山东省平度市大庄子金矿流体包裹体研究

山东省平度市大庄子金矿含金硅化体及石英脉中流体包裹体发育程度一般,且粒度偏小,包裹体大小多为6～12μm,包裹体类型主要为气液二相包裹体、液相包裹体(LH2O LCO2),见少量三相包裹体(LH2O LCO2 GCO2).化学成分属K (Na )-SO4-2(Cl-)型,气相成分以H2O、CO2为主,含一定量CH4、CO、H2S等还原性气体.均一温度表明金矿的成矿温度为中温(200℃～260℃),成矿流体盐度低(1.05%～4.96%).成矿流体主要来源于岩浆水、变质水,并有大气降水的混合.     

Magma degassing during 7600 14C Kurile Lake caldera-forming eruption and its climatic impact

The main goal of this investigation is estimating volume of volatile emission, atmospheric and climatic impact of the Kurile Lake caldera-forming eruption, one of the Earth’s largest Holocene explosive eruptions. The volatile content of magma before the eruption was estimated by comparing H₂O, S, Cl and F contents in natural quenched glassy melt inclusions trapped by plagioclase phenocrysts. The volatile content of igneous rocks after eruption was estimated by comparing concentrations of degassed matrix glasses. As a result of KO-eruption not more than (3.7–4.2) × 10¹² kg of water, (4.3–4.9) × 10¹⁰ kg of chlorine, (8.6–9.8) × 10⁹ kg of fluorine and (2.6–2.9) × 10¹⁰ kg of sulphur were injected into the atmosphere. This eruption had to produce an important climatic impact.     

Volatile element zonation in Campanian Ignimbrite magmas (Phlegrean Fields, Italy): evidence from the study of glass inclusions and matrix glasses

The distribution of H₂O, F, Cl and S in the Campanian Ignimbrite (CI) magma chamber was investigated through study of primary glass inclusions and matrix glasses from pumices of the Plinian fall deposit. The eruption, fed by trachytic to phono-trachytic magmas, mainly produced a trachytic non-welded to partially welded tuff, underlain by a minor cogenetic fallout deposit. The entire chemical variability of the eruptive products is well represented in the pumices of the Plinian fall deposit, which we divide into a basal Lower Fall Unit (LFU) and an overlying Upper Fall Unit (UFU). Primary glass inclusions were only found in clinopyroxenes associated with the LFU pumice and contain a mean of 1.60ǂ.32 wt% H₂O (analysed by FTIR), 0.11ǂ.08 wt% F, 0.37ǂ.03 wt% Cl and 0.08ǂ.04 wt% SO₃ (EMP analysis); CO₂ concentrations were below the FTIR detection limit (10-20 ppm). The coexisting matrix glasses contain similar amounts of halogens and sulfur but less water (~0.60 wt%). Partially degassed matrix glasses from UFU pumices contain a mean of 0.30ǂ.02 H₂O, 0.28ǂ.10 F, 0.04ǂ.02 SO₃ and 0.80ǂ.04 wt% Cl. To reconstruct the total amount of volatiles dissolved in the most evolved trachytes we have used experimental solubility data and mass balance calculations concerning the amount of crystal fractionation required to produce the most evolved trachyte from the least evolved trachyte; these yield an estimated pre-eruptive magma volatile content (H₂O + Cl + F) of ~5.5 wt% for the most evolved magmas. On the basis of new determinations of Cl solubility limits in hydrous trachytic melts coexisting with an aqueous fluid phase + hydrosaline melt (brine), we suggest that the upper part of the magma chamber which fed the CI eruption was fluid(s) saturated and at a minimum depth of ~2 km. Variations in eruptive style (Plinian fallout, pyroclastic flows) do not appear to be related to significant variations in pre-eruptive volatile contents.     

熔体包裹体挥发分应用的研究进展

挥发分(例如H2O、CO2、F、Cl和S)是地幔的重要组成部分,虽然它们在地幔中的含量很低,但是在地幔熔融和熔体演化、地幔不均一、地幔流变学、地幔地震特性和电导率等研究方面具有重要作用。对矿物熔体包裹体和玻璃挥发分的研究已经成为当前的研究热点。其中,熔体包裹体研究凭借其独特的优势成为研究地幔和岩浆挥发分组成的重要手段。熔体包裹体直接捕获了矿物形成时岩浆中的成分,且由于寄主矿物的存在使得熔体包裹体能够保持独立演化而不受外界环境影响,因此能够较为完整地保存岩浆中的挥发分信息。同时,研究熔体包裹体中的挥发分是恢复岩浆喷发前挥发分含量最直接的途径。如果通过现代分析方法(如扫描电镜、电子探针和离子探针等)对熔体包裹体进行详细的岩相学观察以及对后期可能影响熔体包裹体原始挥发组分的作用(地壳混染、岩浆去气、扩散和水化作用)进行评估,并结合实验研究熔体包裹体被捕获后发生的变化而对数据进行矫正,那熔体包裹体对研究岩浆体系中的挥发分将大有可为。基于此,本文系统介绍了熔体包裹体挥发分研究的现状及主要研究内容,主要包括熔体包裹体挥发分的测试方法、挥发分在岩浆中的溶解度、判断挥发分数据可靠性和挥发分研究的经典应用等4个方面。     

Pre-eruptive melt composition and constraints on degassing of a water-rich pantellerite magma,Fantale volcano,Ethiopia

To determine the pre-eruptive composition of peralkaline magma at Frantale volcano, Ethiopia, we have studied glass inclusions in phenocrysts from a lateceupting, glassy pantelleritic lava flow. Matrix glass and crystal-free glass inclusions in quartz were analyzed for all major and most minor elements by electron microprobe and for H₂O and 15 lithophile trace elements by ion microprobe (SIMS). Compositions of inclusions may have been slightly modified by post-trapping quartz crystallization, the average concentrations of all constituents but silica may be artificially high by 10% relative. Glass inclusions contain extreme enrichments in H₂O (mean of 4.6 to 4.9 wt%) and several lithophile trace elements, which suggest that the lava erupted from a highly evolved, water-rich fraction of magma. The pre-eruptive concentration of water was much higher than that generally considered to occur in pantellerite magmas. Trends observed for lithophile elements in whole-rock samples from pre-,syn-and post-caldera eruptive units are mimicked in glass inclusions from the studied pantellerite lava; concentrations of Rb, Y, Zr, Nb, and Ce±Cl increase with progressive differentiation. With the exception of Cl and H₂O contents, the composition of matrix glass is similar to that of glass inclusions suggesting: that few constituents exsolved from magma or cooling glass; eruption and quench of the lava occurred rapidly; and the matrix glass is, largely, compositionally representative of melt. Higher average abundances of Cl and H₂O in glass inclusions suggest that these volatiles exsolved after melt entrapment; degassing could have occurred as either an equilibrium or disequilibrium process.     

Supra-Subduction Zone Environment and Economic Potential of the Nidar Ophiolite of Indus Suture Zone, Eastern Ladakh, the Himalaya

SUPRA-SUBDUCTION ZONE ENVIRONMENT AND ECONOMIC POTENTIAL OF THE NIDAR OPHIOLITE OF INDUS SUTURE ZONE, EASTERN LADAKH,THE HIMALAYA     

Volatiles in glasses from Mauna Loa Volcano,Hawai'i: implications for magma degassing and contamination,and growth of Hawaiian volcanoes

Glasses from Mauna Loa pillow basalts, recent subaerial vents, and inclusions in olivine were analyzed for S, Cl, F, and major elements by electron microprobe. Select submarine glasses were also analyzed for H₂O and CO₂ by infrared spectroscopy. The compositional variation of these tholeiitic glasses is dominantly controlled by crystal fractionation and they indicate quenching temperatures of 1,115-1,196 °C. Submarine rift zone glasses have higher volatile abundances (except F) than nearly all other submarine and subaerial glasses with the maximum concentrations increasing with water depth. The overwhelming dominance of degassed glasses on the submarine flanks of Mauna Loa implies that much of volcano's recent submarine growth involved subaerially erupted lava that reached great water depths (up to 3.1 km) via lava tubes. Anomalously high F and Cl in some submarine glasses and glass inclusions indicate contamination possibly by fumarolic deposits in ephemeral rift zone magma chambers. The relatively high CO₂ but variable H₂O/K₂O and S/K₂O in some submarine rift zone glasses indicates pre-eruptive mixing between degassed and undegassed magma within Mauna Loa's rift system. Volatile compositions for Mauna Loa magmas are similar to other active Hawaiian volcanoes in S and F, but are less Cl-rich than Ll'ihi glasses. However, Cl/K2O ratios are similar. Mauna Loa and Ll'ihi magmas have comparable, but lower H₂O than those from Kilauea. Thus, Kilauea's source may be more H₂O-rich. The dissimilar volatile distribution in glasses from active Hawaiian volcanoes is inconsistent with predictions for a simple, concentrically zoned plume model.     

S-rich apatite-hosted glass inclusions in xenoliths from La Palma: constraints on the volatile partitioning in evolved alkaline magmas

The composition of S-rich apatite, of volatile-rich glass inclusions in apatite, and of interstitial glasses in alkaline xenoliths from the 1949 basanite eruption in La Palma has been investigated to constrain the partitioning of volatiles between apatite and alkali-rich melts. The xenoliths are interpreted as cumulates from alkaline La Palma magmas. Apatite contains up to 0.89 wt% SO₃ (3560 ppm S), 0.31 wt% Cl, and 0.66 wt% Ce₂O₃. Sulfur is incorporated in apatite via several independent exchange reactions involving (P⁵⁺, Ca²⁺) vs. (S⁶⁺, Si⁴⁺, Na⁺, and Ce³⁺). The concentration of halogens in phonolitic to trachytic glasses ranges from 0.15 to 0.44 wt% for Cl and from <0.07 to 0.65 wt% for F. The sulfur concentration in the glasses ranges from 0.06 to 0.23 wt% SO₃ (sulfate-saturated systems). The chlorine partition coefficients (D_Cl^{apatite/glass}) range from 0.4 to 1.3 (average D_Cl^{apatite/glass} = 0.8), in good agreement with the results of experimental data in mafic and rhyolitic system with low Cl concentrations. With increasing F in glass inclusions D_F^{apatite/glass} decreases from 35 to 3. However, most of our data display a high partition coefficient (~30) close to D_F^{apatite/glass} determined experimentally in felsic rock. D_S^{apatite/glass} decreases from 9.1 to 2.9 with increasing SO₃ in glass inclusions. The combination of natural and experimental data reveals that the S partition coefficient tends toward a value of 2 for high S content in the glass (>0.2 wt% SO₃). D_S^{apatite/glass} is only slightly dependent on the melt composition and can be expressed as: SO_{3 apatite} (wt%) = 0.157 * ln SO_{3 glass} (wt%) + 0.9834. The phonolitic compositions of glass inclusions in amphibole and haüyne are very similar to evolved melts erupted on La Palma. The lower sulfur content and the higher Cl content in the phonolitic melt compared to basaltic magmas erupted in La Palma suggest that during magma evolution the crystallization of haüyne and pyrrhotite probably buffered the sulfur content of the melt, whereas the evolution of Cl concentration reflects an incompatible behavior. Trachytic compositions similar to those of the (water-rich) glass inclusions analyzed in apatite and clinopyroxene are not found as erupted products. These compositions are interpreted to be formed by the reaction between water-rich phonolitic melt and peridotite wall-rock.     

Melt inclusion constraints on volatile systematics and degassing history of the 2014–2015 Holuhraun eruption,Iceland

The mass of volatiles emitted during volcanic eruptions is often estimated by comparing the volatile contents of undegassed melt inclusions, trapped in crystals at an early stage of magmatic evolution, with that of the degassed matrix glass. Here we present detailed characterisation of magmatic volatiles (H₂O, CO₂, S, Fl and Cl) of crystal-hosted melt and fluid inclusions from the 2014–2015 Holuhraun eruption of the Bárðarbunga volcanic system, Iceland. Based on the ratios of magmatic volatiles to similarly incompatible trace elements, the undegassed primary volatile contents of the Holuhraun parental melt are estimated at 1500–1700 ppm CO₂, 0.13–0.16 wt% H₂O, 60–80 ppm Cl, 130–240 ppm F and 500–800 ppm S. High-density fluid inclusions indicate onset of crystallisation at pressures?≥?0.4 GPa (~?12 km depth) promoting deep degassing of CO₂. Prior to the onset of degassing, the melt CO₂ content may have reached 3000–4000 ppm, with the total magmatic CO₂ budget estimated at  23–55 Mt. SO₂ release commenced at 0.12 GPa (~?3.6 km depth), eventually leading to entrapment of SO₂ vapour in low-density fluid inclusions. We calculate the syn-eruptive volatile release as 22.2 Mt of magmatic H₂O, 5.9–7.7 Mt CO₂, and 11.3 Mt of SO₂ over the course of the eruption; F and Cl release were insignificant. Melt inclusion constraints on syn-eruptive volatile release are similar to estimates made during in situ field monitoring, with the exception of H₂O, where field measurements may be heavily biased by the incorporation of meteoric water.     

火山活动与辽西四合屯脊椎动物群死亡关系的初步研究

近年来在辽西北票四合屯发现了大量的早期岛类及“长毛”的小型兽脚类恐龙化石层,完美的化石形态表明本区发生过多次非正常生物集群死亡事件。化石层与火山凝灰岩层（或火山灰）密切共生在一起。本文选择了其中四个化石数量巨大的脊椎动物化石层,对其中凝灰岩（或火山灰）中的火山玻璃及五晶矿物内原生岩包裹体的挥发分成分进行了电子探针测定。研究结果表明,号世界相同成分的其它火山相比,本区火山喷出气体的含量较高;火山喷出的各种气体（HCl、HF、H2S、SO2、SO3和H2O蒸汽）的组成比例不同,对应着化层内脊椎动物化石组合也存在差异。作者认为,火山喷山的气体及火山灰（尘）的综合气体效应是造成本区生物集群死亡的重要原因。     

Glasses in the D'Orbigny angrite

The angrites are a small and heterogeneous group of achondritic meteorites with highly unusual chemical and mineralogical features. The abundant presence of glasses in D'Orbigny makes this rock a unique member of the angrite group. Glasses fill open spaces, form pockets, and occur as inclusions in olivines. Their physical settings exclude an incorporation from an external source. Major and trace element (rare earth elements [REE], Li, B, Be, transition elements, N and C) contents of these glasses and host olivines were measured combining laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), secondary-ion mass spectrometry (SIMS), Nuclear Reaction Analysis (NRA), and EMP techniques. Based on the major element composition, glasses filling voids could represent either a melt formed by melting an angritic rock or a melt from which angrites could have crystallized. Trace element contents of these glasses strongly indicate a direct link to the D'Orbigny bulk meteorite. They are incompatible with the formation of the glasses by partial melting of a chondritic source rock or by shock melting. The refractory elements (e.g., Al, Ti, Ca) have about 10 × CI abundances with CaO/TiO₂ and FeO/MnO ratios being approximately chondritic. Trace element abundances in the glasses appear to be governed by volatility and suggest that the refractory elements in the source had chondritic relative abundances. Although the glasses (and the whole rock) lack volatile elements such as Na and K, they are rich in some moderately volatile elements such as B, V, Mn, Fe (all with close to CI abundances), and Li (about 3-5 × CI). These elements likely were added to the glass in a sub-solidus metasomatic elemental exchange event. We have identified a novel mechanism for alteration of glass and rock compositions based on an exchange of Al and Sc for Fe and other moderately volatile elements in addition to the well-known metasomatic exchange reactions (e.g., Ca-Na and Mg-Fe).Because glass inclusions in olivine were partly shielded from the metasomatic events by the host crystal, their chemical composition is believed to be closer to the original composition than that of any other glasses. The relative trace element abundances in glasses of glass inclusions in olivine and glass pockets are also unfractionated and at the 10 to 20 × CI level. These glasses are chemically similar to the common void-filling glasses but show a much wider compositional variation. Inclusion glasses demonstrate that at least olivine grew with the help of a liquid. In analogy to olivines in carbonaceous chondrites, initial formation could also have been a vapor-liquid-solid condensation process. At that time, the glass had a purely refractory composition. This composition, however, was severely altered by the metasomatic addition of large amounts of FeO and other moderately volatile elements. The presence of volatile elements such as carbon and nitrogen in glasses of glass inclusions is another feature that appears to give these glasses a link with those hosted by olivines of carbonaceous chondrites. All these features point to an origin from a vapor with relative abundances of condensable elements similar to those in the solar nebula.