玄武岩斑晶的熔体包裹体岩石学研究和实验测试

1、第85期ODMEmail：chlzh_电 话enry Clifton SorbyThe first to document microscopic melt inclusions in crystals in 1858（Norman et al.2002）能够捕获比全岩更可观的多样性熔体，为研究岩浆过程提供高分辨率证据(Kamenetsky V.S. et.al., 2002)保存最原始保存最原始岩浆信息岩浆信息What are melt inclusions & how do they form?熔体包裹体(又称岩浆包裹体) 是指岩浆岩形成过程中，各种岩浆岩矿物在其

2、结晶生长过程中所捕获的微量天然岩浆珠滴，随着主矿物冷却，它们或淬火凝结成玻璃，或进一步结晶析出硅酸盐子矿物、金属相和流体相（夏林圻，2002）。(1) 降压和丧失挥发组分，升高了岩浆的过饱和程度，引 起晶体突然迅速生长，产生骸晶状边缘；(2) 早期晶体被部分熔蚀，在晶面上产生一些凹陷或熔蚀港湾(3) 温度降低，也可以使岩浆成为过饱和，从而导致结晶成核作用发生，晶芽呈骸晶状和树枝状快速生长；(4) 固体物质被粘着于生长中晶体的晶面上，可以导致微量岩浆熔体与固体物质一道被捕获，形成一种“固体包裹体+ 熔体包裹体”的混合式包裹体，这种包裹体中，熔体包裹体通常位于固体包裹体向着主矿物晶体外侧的那一面上

3、，该特点可帮助我们区别固体包裹体和子矿物；(5) 晶体的定向优先生长也可以导致熔体包裹体被捕获（夏林圻，2002，及其中参看文献）知微而见著？100 mmExperimental and natural polyhedral olivine with melt inclusions (slow cooling)Keanakakoi Ash, Kilauea, HawaiiFaure & Schiano (2005)Experimental & natural skeletal (hopper morphology) olivine with melt inclusions (faster co

4、oling)Paricutin, Mexico500 mmKeanakakoi AshFaure & Schiano (2005)100 m mmJorullo volcano, MexicoFaure & Schiano (2005)Experiments in CMAS system.Effect of Growth Rate on Trapped Melt Compositions Rapid growth morphologies have inclusions that are moderately to strongly enriched in Al2O3. This is cau

5、sed by boundary layer enrichment due to slow diffusion of Al2O3 relative to CaO.Differences between Experimental & Natural Melt Inclusions Most natural melt inclusions show no evidence of anomalous enrichment in slowly diffusing elements, even in small inclusions and rapid growth forms like skeletal

6、 or hopper crystals. Volatile components have faster diffusivities than Al2O3 and thus should not generally be affected by boundary layer enrichment effects. Data from Johnson et al. (2008)Post-Entrapment Modification of Melt InclusionsDiffusive loss of H2 or molecular H2OCrystalMeltinclusionInclusi

7、on entrapmentCoolingShrinkage vaporbubbleCrystallization alongmelt crystal interfaceFe Diffusive loss of H-species Should be limited to 1 wt% H2O by redox equilibria & melt FeO if loss occurs by H2 diffusion (Danyushevsky, 2001). Leaves distinct textural features magnetite dust from oxidation. Possi

8、ble rapid diffusion of molecular H2O (Almeev et al., 2008).V 收缩泡/ V 包裹体 0.5 % ,该收缩泡内几乎不含挥发份,近于真空参考文献：(Tait 1992; Schiano and Bourdon 1999).(Sobolev 1996; Newman et al. 2000; Saal et al. 2002).Solubilities with 2 Volatile Components Present H2O and CO2 contribute the largest partial pressures, so peo

9、ple often focus on these when comparing pressure & volatile solubilitySolid lines show solubility atdifferent constant total pressuresDashed lines show the vaporcomposition in equilibrium withmelts of different H2O & CO2From Dixon & Stolper (1995)熔体与矿物再平衡熔体与矿物再平衡1200在接近均一温度停留时间长时（b-c），斜长石的橄榄石微晶重结晶成单

10、个晶体给定主矿物成分下均一温度的过热现象（Sobolev and Danyushevsky, 1994）EMP和SIMS要求玻璃质熔体包裹体或对异质包裹体淬火均一化！nLA-ICP-MS作为最新发展起来的原位微区测试技术，具有高灵敏度、快速测定多种元素等特点，广泛用于微量元素测试和富U矿物定年。nTaylor（1997）首次应用于熔体包裹体测试,展示了不受包裹体矿物相控制、不需要均一化等优点；nLA-ICP-MS测试结果与EMP、SIMS相媲美（Pettke T. et. Al.,2004）二、单个熔体包裹体LA-ICPMS测试技术中国地质大学（武汉）地质过程与矿产资源国家重点实验室mixih

11、ostiincliC1CxCx)-(1)/( ,)(100C1isamjrmjrmjNjjjsamiisamcpsCllcpslcpsl是利用USGS标准物质（BCR-2G、BHVO-2G、BIR-1G）作为多外标回归分析计算获得，分子中的“100”代表全部金属氧化物总和为100%。 l)1/()()(100C11iinclxlcpscpsxlcpscpslNjjjhostihostNjjjmiximixi要获得 只要知道主矿物占混合物的质量因子x，即可计算得到包裹体中的元素含量。cpxMg#186. 0109. 0Kdmelt/CpxMgFe)1 (03. 030. 0Kdmelt/OlMg

12、Fe)1 (037. 027. 0Kdmelt/CpxMgFe主要为二辉橄榄岩，并有少量方辉橄榄岩，多为原变粒结构、镶嵌粒状结构及残碎斑结构，含黑色的辉石脉流体包裹体中碳酸盐矿物的成因捕获 or 反应菱镁矿只在斜方辉石中发育, 白云石(或富Mg 碳酸钙)只在单斜辉石中发育(熔体包裹体与寄主矿物的反应？)n乔山橄榄岩中，两中辉石中两种碳酸盐矿物都有捕获！地幔碳酸盐质熔体的成因n(1) 含碳酸盐橄榄岩的部分熔融（Frezzotti M L, et al. 2002）（伴随富Al, Na质玻璃的发育） n(2) 地幔中富硅碳酸盐熔体的不混溶作用（Schiano P, et al. 1994; Fre

13、zzotti M L, et al. 1994 ） （硅酸盐、碳酸盐共生）n(3) 硅酸盐-碳酸盐熔体/流体与橄榄岩之间 的交代作用（Schrauder M, et al. 2002）（富硅碳酸盐熔体/流体具富碱特征）与碳酸盐熔体和斜方辉石同时相关的主要反应n2Mg2SiO4( 橄榄石)+CaMgSi2O6( 单斜辉石)+2CO2=4Mg2Si2O6(斜方辉石)+CaMg(CO3)2(碳酸盐)n2Mg2SiO4( 橄榄石)+2CO2 =Mg2Si2O6 ( 斜方辉石)+2MgCO3(碳酸盐)早期富CO2 流体包裹体沿斜方辉石生长环带发育的现象说明CO2 参与了与斜方辉石生长有关的反应. 在这些

14、反应中由于斜方辉石和碳酸盐都在反应的一侧, 所以碳酸盐是斜方辉石生长过程中捕获的根据i2含量，熔体玻璃成分可以分为低硅（ ）和高硅（ ）两类，但它们普遍富碱（2a2 ）、Al2O3（变化于 ，少数 ）n涠洲岛低硅熔体分布于解体的橄榄石矿物中，它们将橄榄石分隔成不同的块体，熔体围绕块体隙间分布（图、），直接提供了低硅熔体是由富硅熔体与橄榄石发生交代作用生成的证据。这可以用富熔体贫熔体反应解释，其结果是消耗橄榄石生成斜方辉石（，）。MORB ：Ol（Fo90-87）；Cpx（Mg#89-87）； Pl（An86-80）； Sp（Cr#38-47）从早期结晶的矿物中获得相对原始的熔体组成OlOpxC

15、px亏损熔体是和二辉橄榄岩亏损熔体是和二辉橄榄岩/方辉橄榄岩残余平衡的方辉橄榄岩残余平衡的原始地幔熔体原始地幔熔体离子探针，两个点，不扣除重结晶影响亏损并分异亏损并分异REE、Zr、Tioceanic-crust gabbroic rocks enriched in cumulus plagioclase?谢谢 谢！谢！QuickTime and a decompressorare needed to see this picture. Ni-NiOH2O-CO2 fluidMoore et al, 2008Figure 4Rhyolite500 MPa200 MPaDaciteXH2O(fl

16、uid)0.45P 400 MPaT = 1200CVolatile Abundances in Basaltic Magmas & Their Degassing Paths Tracked by Melt InclusionsNicole MtrichLaboratoire Pierre SueCNRS-CEA, FrancePaul WallaceDept. of Geological SciencesUniversity of Oregon, USAVolcan Colima, MexicoPhoto by Emily JohnsonReview of Experimentally M

17、easured Solubilities for Volatiles Volatiles occur as dissolved species in silicate melts & also in a separate vapor phase if a melt is vapor saturated. In laboratory experiments, melts can be saturated with a nearly pure vapor phase (e.g., H2O saturated). In natural systems, however, multiple volat

18、ile components are always present (H2O, CO2, S, Cl, F, plus noble gases, volatile metals, alkalies, etc.). When the sum of the partial pressures of all dissolved volatiles in a silicate melt equals the confining pressure, the melt becomes saturated with a multicomponent (C-O-H-S-Cl-F-noble gases, et

19、c.) vapor phase. Referring to natural magmas as being H2O saturated or CO2 saturated is, strictly speaking, incorrect because the vapor phase always contains other volatiles.Some key things to remember:Solubilities with 2 Volatile Components Present H2O and CO2 contribute the largest partial pressur

20、es, so people often focus on these when comparing pressure & volatile solubilitySolid lines show solubility atdifferent constant total pressuresDashed lines show the vaporcomposition in equilibrium withmelts of different H2O & CO2From Dixon & Stolper (1995)Estimating Vapor-Saturation Pressures for M

21、elt InclusionsEtna 3900 BP eruption Melt inclusions (12-14wt% MgO) in olivine Fo91 (Kamenetsky et al., Geology 2007)Etna 2001,2002Ca,Mg-bearing carbonatesArc basalts (Wallace 2005)CO2 diffuses into a shrinkage bubble during cooling CO2 loss demonstrated in heating experiments on olivine (Fo88) from

22、a Mauna Loa picrite. Melt inclusions re-homogenized at 1400C for 10 min. As much as 80% of the initial CO2 can be transferred to a shrinkage bubble over a cooling interval of 100C.Carbonate crystals lining bubble wallsTotal vapor pressure (PH2O+PCO2) for an inclusion can be calculated assuming: Vapo

23、r saturation how do we know melts were vapor saturated? Large variations in ratios of bubble volume to inclusion volume Presence of dense CO2 liquid in bubbles Homogenization not possible in heating experiments No post-entrapment loss of CO2 or H2O to bubbles, no leakage, no H2O diffusive loss. CO2

24、lost to bubbles lowers vapor saturation pressure. Cervantes et al., (2002)Chlorine Solubility in Basaltic Melts In this simplified experimental system, basaltic melts are either saturated with H2O-Cl vapor or molten NaCl with dissolved H2O (hydrosaline melt) Natural basaltic melts typically have 200

25、MPa - Melt interaction with CO2-rich gas CO2-rich gas fluxing depletes melt in H2O and thereby causes olivine crystallizationJorullo (Mexico) monogenic basaltic cinder coneCentral part of the subduction-related Trans-Mexican Volcanic Belt Phase diagram for early Jorullo melt composition (10.5 wt.% M

26、gO) constructed using MELTS (Ghiorso & Sack,1995; Asimow & Ghiorso,1998) and pMELTS (Ghiorso et al., 2002). Crystallization recorded by melt inclusions mainly driven by H2O loss during magma ascent- At 400-200 MPa: Water loss likely due to gas fluxing olivine crystallization- At low pressure: CO2-de

27、pleted melts lose H2O by its direct exsolution in the vapor phaseJorullo (Mexico) monogenic basaltic cinder coneH2O loss and crystallizationJohnson et al., 2008 , EPSL 269Melt inclusion studies provide evidence for crystallization driven by H2O loss (+ cooling) at many volcanoes.Message can be diffi

28、cult to decipher because of additional processes such as: - Mixing involving degassed and undegassed magmas (Popocatpetl & Colima; Atlas et al., 2006) - Mingling (e.g. Fuego, Roggensack 2001) - Assimilation (Paricutin, Lurh 2001; Jorullo, Mexico, Johnson et al., 2008) A case of efficient control of

29、H2O degassing on magma crystallization is Stromboli - an open conduit volcanoe with low magma production rate and high degassing excess - where magmas share same chemical composition but have contrasting textures, crystal abundances (10-50%) and viscosities (Mtrich et al., 2001, Landi et al., 2004;

30、Bertagnini et al., 2003, 2008)H2O loss and crystallization Sulfur and halogen degassing140 MPa140 MPa 80% S is lost between 140 and 10 MPa, whereas Cl starts degassing at low pressure (Ptot20-10MPa) and F at Ptot submarine sulfide-saturated basalts (Dixon et al., 1991)Iraz: Benjamin et al. 2007, JVG

31、R,168, 68-92Arenal: Wade et al. 2006, JVGR,157, 94-120 Etna: Spilliaert et al., 2006, EPSL, 248, 772-786Sulfide saturationEruption styles and degassing budgetInformation from melt inclusionsWhat are the recent improvements?Stromboli - 2006Basalt: LK: Laki 1783-84 eruption; K: Kilauea, annual average

32、; ML Mauna Loa; PC Pacaya 1972 eruption; St: Stromboli annual averageVolatile budget for basaltic fissure eruptions Predicted relationship between SO2 emissions and eruptive magma volume assuming that SO2 released during eruption is provided by the sulfur dissolved in silicate melt Compared to sulfu

33、r emissions measured by independent methods as ulraviolet correlation spectrometer (COSPEC), atmospheric turbidity and Total Ozone Mapping Spectrometer (TOMS)Uncertainties in SO2 emission data are generally considered to be about 30% for the TOMS data and 2050% for COSPEC. Pre-requisite: no differen

34、tial transfer of gas DS = CS(M.I.) CS(res) Wallace 2005, JVGR CS(M.I.): S content in primitive melt (melt inclusion)CS(res.) : Residual S content in bulk lava or in matrix glass corrected for crystallizationPetrologic estimates of the sulfur output 1,3 Thordarson &Self: (1993) Bull Vocanol 93 and (1

35、996) JVGR 74; 2 Thordarson et al., (2001), JVGR, 108Eldgj 2Laki 1Melt inclusionsp-tephra*s-tephralava M.I. and W.R. have comparable composition 95% of initial sulfur releasedSulfur partly exsolved in gas phase during magma ascent at shallow depth prior to eruption 75% escaped at vents, lofted by the

36、 eruptive column (strong fire fountaining) to 5-15 km altitudes at the beginning of each eruptive phase and 25% during the lava flowing*p-tephra : quenched melts indicative of magma degassing during during ascent Approach used for assessing the impact of large flood basalts on the atmosphere (Self e

37、t al; 2008 Science)Volatile budget for basaltic fissure eruptions Petrologic estimates commonly used for assessing the degassing budget of other volatiles in particular Cl and F The 94 days long flank eruption that occurred in 2002 at Mt Etna: Modelling of the pressure related behavior of sulfur at

38、Etna (2002 eruption) 80% sulfur released in the gas phase during magma ascent (between 140 and 10 MPa) in agreement with conclusions drawn by Self, Thordarson and co-authorsSO2 flux: 6.9 108 kg (Petrologic estimates, Spilliaert et al. 2006) / 8.6 108 kg (COSPEC, Caltabiano et al. 2006)Comparable S/C

39、l molar ratio (5) in vapor phase derived from melt inclusion data and measured in gas emissions no differential degassing of S (or Cl) Arenal (COSPEC 0.41 Mt of SO2 released since 1968 )Better agreement with COSPEC when considering the S content (2000 ppm) of olivine-hosted melt inclusions represent

40、ative of the undegassed basaltic andesitic magma rather than partly degassed melt trapped in Plag & CpxPetrologic estimates even COSPEC a part of sulfur could be lost?Sulfur partly exsolved in gas phase during magma ascent at shallow depth without differential transfer of sulfur Consistency between

41、petrologic estimates of SO2 budget and independent estimates (COSPEC or others)(Wade et al., 2007)Volatile budget for basaltic fissure eruptionsDifferential transfer of gas bubbles Excessive degassing- Izu-Oshima in Japan (Kazahaya et al 1994) - Villarica in Chile (Witter et al., 2004), - Popocatepe

42、tl in Mexico (Delgado-Granados et al., 2001; Witter et al., 2005) - Etna & Stromboli in Italy (Allard., 1997; Burton et al., 2007) - Masaya in Nicaragua (Delmelle et al., 1999, Stix, 2007). Stromboli Magma supply rate is assessed to be 0.001 km3 y-1, 154 higher than the magma extrusion rateAssuming

43、0.22 wt% S dissolved in magma as derived from M.I. 10% of magma is extruded given that quiescent degassing contributes to 95% total SO2 degassing (Allard et al., 2008) Excessive degassing at persistently active basaltic volcanoes such as:e.g. Jaupart et Vergniolle, 1988, Vergniolle, 1996; Philips an

44、d Wood 1998 Differential transfer of gas bubbles MI data used for assessing the mass (volume) of unerupted magma when combined with gas flux measurements Qm = SO2 /2D DSQm : Mass flux of magma2DS = SO2 degassed from the magmaSO2 = SO2 flux measured by COSPEC or other techniquesUnresolved questions a

45、nd directions for future studiesBenbow (Ambrym, Vanuatu) Most suitable melt inclusions for volatile studies quenched pyroclastites Efforts dedicated in the last 15 years basic data for assessing:- the SO2 output from syn-eruptive degassing of basaltic magmas ascending in closed system conditions, with no differential gas transfer (gas loss) prior to eruption- the vo