using geochemistry as a tool for correlating proximal andesitic tephra: case studies from mt rainier...
TRANSCRIPT
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Using geochemistry as a ta:n
1* 2 SMITH3
ng, Honancouve
3 Department of Geology, University of Auckland, Auckland, New Zealand4
or systematic temporal trends in geochemistry within either eruptive record. This complexity in tephra
uniquely identified, they can be important marker beds usefulto temporal correlation as well as age dating of Quaternaryvolcaniclastic and sedimentary deposits with which they are
JOURNAL OF QUATERNARY SCIENCE (2007) 22(4) 395410Copyright 2006 John Wiley & Sons, Ltd.Published online 13 December 2006 in Wiley InterScience(www.interscience.wiley.com) DOI: 10.1002/jqs.1065
SAR, China. E-mail: [email protected]/grant sponsor: Research Grants Council of the Hong Kong SpecialAdministrative Region, China; contract/grant number: HKU 255/95p.geochemistry limits the application of geochemical approaches to tephrostratigraphic studies,beyond a general characterisation useful to provenance assignation. Petrological and geochemicaldata suggest that the products of andesite systems are inherently variable and thereforeintractable to discrimination by simple geochemical methods alone. Copyright# 2006 John Wiley& Sons, Ltd.
KEYWORDS: Mount Ruapehu; Mount Rainier; andesite; tephra; geochemical correlation
Introduction
The principal tool used to decipher the stratigraphic sucessionin volcanic environments is the identification of temporallydefined tephra horizons which allow correlation of depositsover a range of sedimentary environments. In large-scale silicicsystems, the wide dispersal and relatively large volume of
tephra has provided an extremely useful framework forunderstanding eruptive histories. A similar approach tounderstanding andesite volcanoes is hampered by the smallervolume, more localised dispersion and, critically, the morecomplex nature of andesitic tephra. In this paper we evaluatethe problems associated with deciphering the volcanologicalhistory of andesite systems using data from two well known andwell studied volcanoes, Mt Rainier in the Pacific northwest ofUSA and Mt Ruapehu in the central North Island of NewZealand. Andesitic tephra comprise much of the proximaleruptive record of these and other stratovolcanoes, and mayalso be preserved in a range of sedimentary environments in themedial and distal regions of the surrounding ring plain. Where
* Correspondence to: S. L. Donoghue, Department of Earth Sciences, 3F JamesLee Science Building, The University of Hong Kong, Pokfulam Road, Hong Kong,tephra are potentially valuable stratigraphic marker beds useful to the temporal correlation and agedating of Quaternary volcanic, volcaniclastic and epiclastic sedimentary deposits with which they areinterbedded. At Mt Ruapehu (New Zealand) and Mt Rainier (USA), much of the detail of the recentvolcanic record remains unresolved because of the difficulty in identifying proximal tephra. This studyinvestigates the value of geochemical methods in discriminating andesitic tephra. Our datasetcomprises petrological and geochemical analyses of tephra that span the late Quaternary eruptiverecord of each volcano. Our data illustrate that andesitic tephra are remarkably heterogeneous incomposition. Tephra compositions fluctuate widely over short time intervals, and there are no simple(USA) and Mt Ruapehu (New Zealand). J. Quaternary Sci., Vol. 22 pp. 395410. ISSN 02678179.
Received 2 September 2005; Revised 2 July 2006; Accepted 17 July 2006
ABSTRACT: Volcanic hazards assessments at andesite stratovolcanoes rely on the assessment offrequency and magnitude of past events. The identification and correlation of proximal and distalandesitic tephra, which record the explosive eruptive history, are integral to such assessments. TheseDonoghue, S. L., Vallance, J., Smith, I. E. M. and Stewart, R. B. 2006. Using geochInstitute of Natural Resources, Massey University, Palmerston North, New Zealand
emistry as a tool for correlating proximal andesitic tephra: case studies from Mt RainierSUSAN L. DONOGHUE, JAMES VALLANCE, IAN E. M.1 Department of Earth Sciences, The University of Hong Ko2 US Geological Survey, Cascades Volcano Observatory, Vproximal andesitic tephrfrom Mt Rainier (USA) a(New Zealand)Contract/grant sponsor: The Croucher Foundation (Hong Kong).ool for correlatingcase studiesd Mt Ruapehu
and ROBERT B. STEWART4
g Kong, SAR, Chinar, WA, USAinterbedded.
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At mounts Ruapehu and Rainier, the numerous proximalandesitic tephra offer particular value in establishing astratigraphy and chronology of late Quaternary lahar depositsand young edifice lavas with which they intercalate (e.g.Mullineaux, 1974; Vallance and Donoghue, 1999; Waightet al., 1999; Donoghue and Neall, 2001). The proximaltephrostratigraphy at both volcanoes is, however, complex, andmuch of the detail of the recent volcanic record at thesevolcanoes is unresolved. The ability to identify and correlate themultitude of proximal andesitic tephra is critical to establishinga detailed and integrated late Quaternary volcanic history atthese volcanoes that can be used in hazards assessments. Tephrapreserved distally, within sedimentary environments severalhundred kilometres from source (Sarna-Wojcicki et al., 1983;Lowe, 1998a; Sandiford et al., 2001, Shane, 2005), are alsoimportant to our understanding of the eruptive history of thesevolcanoes as they record part of the proximal explosive volcanicrecord that may be missing because of local erosion andreworking of surficial deposits.
The establishment of a regional andesite tephrostratigraphy,wherein distal andesite tephras could be used as regionalstratigraphic marker beds in Quaternary palaeoenvironmentalstudies (e.g. Eden and Froggatt, 1996), also depends upontephra being demonstrably distinguished at source. Andesitictephra are more numerous than silic tephra within the
istry) to do this. We use the late Quaternary pyroclastic records
canoes of Tongariro Volcanic Centre (TgVC) which is located atthe southwestern end of the Taupo Volcanic Zone, NorthIsland, New Zealand. Mt Rainier is an andesitedacitestratovolcano in the Cascade volcanic arc, and is located inWashington State, USA (Lescinsky and Sisson, 1998).
The late Quaternary (ca. 22 500 14C yr BP to present)explosive eruptive history at Ruapehu Volcano is recorded inthree tephra formations (Bullot Formation, Taurewa Formationand Tufa Trig Formation; Table 1) (Donoghue et al., 1995,1999). The Bullot and Taurewa formations comprise numerousPlinian, coarse, pumiceous tephra recording tephra-fall andpyroclastic-flow events, whereas the much younger Tufa TrigFormation comprises a sequence of predominantly fine ash-grade vitric tephra erupted during the late Holocene (ca. 185014C yr BP) (Donoghue et al., 1997). Although several proximallapilli-grade tephra have distinctive lithologies (Donoghueet al., 1995; Donoghue and Neall, 1996), much of the tephrarecord is unresolved to member level.
The Holocene (ca. 10 000 14C yr BP to present) explosiveeruptive history at Mt Rainier is recorded in a sequence of 11coarse, pumiceous andesitic tephra (Mullineaux, 1974) and atleast 20 predominantly ash-grade vitric and lithic tephra(Pringle, 1994; Vallance and Donoghue, 1999). The mostcomplete tephra record is preserved in high alpine meadowswithin Mt Rainier National Park (MRNP). Mt Rainier-derived
ationwn in
e (199laye
396 JOURNAL OF QUATERNARY SCIENCEof Mt Rainier and Mt Ruapehu, two exemplar andesitestratovolcanoes with detailed records of eruptive history andsimilar patterns of behaviour.
The late Quaternary tephrostratigraphy ofRuapehu and Rainier
Mt Ruapehu and Mt Rainier are young Pacific-rim stratovolca-noes. Mt Ruapehu is the largest of several andesite stratovol-
Table 1 Summary stratigraphy of proximal late Quaternary tephra formtephra formations erupted from other North Island volcanic centres (shobasis of pyroclast type and morphology
Formation Members
Tufa Trig Formation Tf19Tf1Taupo Tephra (Tp)
Bullot Formation (upper) Ng-2Ng-1
Taurewa FormationBullot Formation (upper) BL18BL17
Waiohau Tephra (Wh) Shawcroft LapilliBL16
Bullot Formation (upper) BL15BL8Rerewhakaaitu Tephra (Rk)
Bullot Formation (middle) BL7BL4Okareka Tephra (Ok)
Bullot Formation (lower) BL3BL1Kawakawa Tephra (Kk)
a Conventional radiocarbon ages in yr BP; data from Froggatt and Lowb Estimated age based on stratigraphic position relative to dated tephraQuaternary sedimentary record and potentially could providefor more detailed chronostratigraphic subdivision withinQuaternary sedimentary sequences (Shane, 2005).
This study thus specifically addresses the problem ofdiscriminating proximal andesitic tephra, and the potentialuse of geochemical methods (glass and whole-rock geochem-Copyright 2006 John Wiley & Sons, Ltd.tephra are also identified in sediment cores extracted from near-source lakes and wetlands. The more voluminous Rainier lapillitephra layers are identified within MRNP on the basis oftheir stratigraphic position in relation to distal silicic tephramarker beds, sets P, Y, W and O (Table 2), macroscopic fieldcharacteristics, specifically colour, grain-size and composition(proportions of scoria, lithics and pumice) and petrography(phenocryst assemblages) (Mullineaux, 1974).
At both volcanoes it has, however, proved particularlydifficult to identify and correlate the numerous fine ash-gradevitric and lithic tephra, and at Ruapehu, the numerous lapillitephra erupted in close succession that constitute much of theproximal tephra record. A few such tephra have diagnosticcharacteristics, such as distinctive lithic assemblages orpresence of basal strombolian pumice beds, but most are notdistinguished and are therefore not mapped. Some lapillitephra are distinctive because they contain macroscopically
s erupted from Mt Ruapehu, New Zealand, and interbedded distal silicicitalics). Tephra are classified as lapilli tephra and black ashes on the
Approximateage (14C yr BP)
Pyroclast type
ca. 1850b to present black ashesca. 1850a
ca. 10 100b lapilli tephra
ca. 11 850a
lapilli tephraca. 14 700a
lapilli tephraca. 18 000a
lapilli tephraca. 22 590a
0).rs; data from Donoghue et al. (1995, 1999).J. Quaternary Sci., Vol. 22(4) 395410 (2007)DOI: 10.1002/jqs
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om Mers ar
Layer Bunnamed unnamedLayer H
CORRELATING PROXIMAL ANDESITE TEPHRA 397unnamed unnamed4
Layer Funnamed unnamedLayer SLayer NLayer Dunnamed unnamedLayer LTable 2 Summary stratigraphy of proximal Holocene tephra erupted frCascade Range volcanoes (shown in italics). Rainier-derived tephra layblack ashes on the basis of pyroclast type and morphology
Tephra layer/set Members
Tephra Set X XmLayer Xunnamed unnamed1
Tephra Set W1100 Year ashLayer Cunnamed unnamed2
Tephra Set P Set Pupperunnamed unnamed3
Tephra Set P Set Pmiddleunnamed unnamed
Tephra Set Y Yncolour-banded or colour-streaked pumice lapilli, or because insections along the dispersal axis they are consistently thecoarsest deposits.
Individual tephra need to be identified in order to determinepast eruption frequency and magnitude, and to support the use ofproximal tephra as local stratigraphic marker beds useful toestablishing integrated volcanic histories at these centres.
Tephra identification and provenance
The historic emphasis on using silicic tephra as regionalchronostratigraphic marker beds (for example, see Mullineaux,1974; Pilcher and Hall, 1992; Beget et al., 1997; Hildreth andFierstein, 1997; Lowe et al., 1999) has seen development of arange of fingerprinting methods to facilitate their identificationand correlation (e.g. Westgate and Gorton, 1981; Froggatt,1983; Perkins et al., 1994; Westgate et al., 1998). Most silicictephra are identified on the basis of their ferromagnesianmineral assemblage (mineral types and abundances) and themajor-element geochemistry of glass shards determined bygrain-discrete electron microprobe (EMP) analysis (Westgateand Gorton, 1981; Froggatt, 1983; Turney et al., 2004), inconjunction with field characteristics and relative stratigraphicposition within depositional sequences. Occasionally more
unnamed unnamed5
Layer Aunnamed unnamed6
Tephra O (Mazama Ash)Layer R
a Conventional radiocarbon ages in yr BP.b Estimated age based on stratigraphic position relative to dated tephra layec Average aged based on several radiocarbon dates. Data from Mullineaux (1 Includes L12, R0930 and L13; 2 includes R064, R065, L9, R024, R08 and R0R01020 (see Fig. 3(d)).
Copyright 2006 John Wiley & Sons, Ltd.t Rainier, USA, and interbedded distal silicic tephra erupted from othere analogous to formations. Tephra are classified as lapilli tephra and
Approximate age (14C yr BP) Pyroclast type
ca. 450 lapilli tephraca. 100 to 130a lapilli tephra
black ashesca. 450a
ca. 1100 black ashca. 2200a lapilli tephra
black ashesca. 2700 to 2500a
black ashesca. 3000 to 2460a
black ashesca. 3400a
ca. 4500a lapilli tephrablack ashes
ca. 4700a lapilli tephrablack ashes
ca. 5000c lapilli tephrablack ashes
ca. 5200a lithic tephraca. 5500a lapilli tephraca. 6000a lapilli tephra
black ashesca. 6400a lapilli tephracomplex approaches are employed to distinguish same sourcetephra. Successful approaches include analysis of the majorelement compositions of phenocryst phases, particularly FeTioxides, by EMP analysis (e.g. Smith and Leeman, 1982; Sarna-Wojcicki et al., 1983; Bussacca et al., 1992; Beget et al., 1997;Shane, 1998; Smith et al., 2002), and trace-element geochem-istry of glass separates by bulk-rock methods, typically X-rayfluorescence spectrometry (XRF) (Sarna-Wojcicki et al., 1983),as well as solution inductively coupled plasma mass spec-trometry (ICPMS) and laser ablation inductively coupledplasma mass spectrometry (LA-ICPMS) (Perkins et al., 1994;Westgate et al., 1998). Multivariate statistical analysis, such asdiscriminant function analysis (DFA), of glass major elementoxide data (e.g. Stokes et al., 1992; Shane and Froggatt, 1994;Beget et al., 1997; Cronin et al., 1997; Charman and Grattan,1999) can also help identify and determine provenance of distalsilicic tephra. Grain-discrete methods of analysis (EMP on glassshards and single crystals, and XRF and solution ICPMS on largeindividual clasts) are preferred to bulk sample methods (XRFand ICPMS/LA-ICPMS of separates) because they can detectcontamination effects, for example from aeolian reworkedtephra and accessory lithics, and are capable of detectinginhomogeneities in samples (Froggatt, 1992).
Readily applicable methods for identifying proximal anddistal andesitic tephra similarly need to be developed to allowandesitic tephra to be used as stratigraphic marker beds. The
black ashesca. 6500a lapilli tephra
black ashesca. 6600c
ca. >8750b lapilli tephra
rs.1974, 1996), Clynne et al. (2004) and this study.31; 3 includes L7; 4 includes R09; 5 includes R032 and R034; 6 includes
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blages are not diagnostic and, further, that the geochemistry ofphenocryst phases within pumice lapilli and glass shards is not
l.,ic
tephra based on compositions of FeTi oxides used inconjunction with DFA methods. At Rainier, phenocrysts
Palmer, 1990) on fused glass disks using a Philips PW 1400s,d
minor element (Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K, P and S) isbetter than 1% (1s) of the reported value. Trace elements
398 JOURNAL OF QUATERNARY SCIENCEassemblages are diagnostic for a few lapilli units (Mullineaux,1974). Other approaches have yet to be investigated.
In New Zealand tephrostratigraphic studies (see, forexample, Lowe, 1988b; Sandiford et al., 2001; Shane, 2005),assignation of provenance for distal andesitic tephra is based onlimited published data for proximal eruptives from Ruapehu(and other volcanoes of TgVC) and Egmont Volcanic Centre(EgVC), the other principal North Island andesitic volcaniccentre. A general observation is that glass compositions ofTgVC tephra show lower SiO2 and alkali (K2O and Na2O)contents than tephra erupted from EgVC (Lowe, 1988b; Shane,2005). In the USA, provenance of distal tephras preserved inloess on the Columbia Plateau similarly is based on limited datafor proximal Rainier tephra (Bussacca et al., 1992).
There is little published geochemical data on andesitictephras erupted from mounts Ruapehu and Rainier. Mostpublished data pertains to the cone-building lava flowsequences (Gamble et al., 1999; Waight et al., 1999; Stockstillet al., 2003). In this study, our focus is on use of glass andwhole-rock geochemistry to distinguish andesitic tephra. Glassis the most ubiquitous material in the tephra succession. Itscomposition represents liquid present in the system at the timeof its eruption, and is readily determined by EMP analysis. It is,therefore, potentially the most useful phase to tephrafingerprinting studies. Whole-rock compositions representthe bulk composition of the magma undergoing eruption andare useful to interpreting causes of compositional variations inandesites. Their compositions are readily measured by XRFmethods.
Samples and analytical methods
Tephra collected for study represent principal tephra formationsand members at Mt Ruapehu and Mt Rainier (Mullineaux, 1974;Donoghue et al., 1995), (Tables 1 and 2). Tephra were sampledwherever possible from type and reference sections alongdispersal axes on the Mt Ruapehu ring plain and within MRNP.All member notations are informal. We use the term vitric todescribe hypocrystalline pyroclasts and lithic to describedense crystalline holocrystalline pyroclasts and accessory rockfragments.
Data assembled for purposes of defining source character-istics and discriminating eruptives includes the petrology oftephra components, the major-element geochemistry ofgroundmass glasses of shards and pumice clasts, and whole-a particularly sensitive fingerprint. Other authors (Cronin et a1996) reported limited success in discriminating andesitpetrological complexity of andesitic pyroclasts has deterreddetailed examination of these, and relatively few studies havesought to assess the efficacy of geochemical fingerprintingmethods to discriminating them (Kohn and Neall, 1973;Froggatt and Rodgers, 1990; Bussacca et al., 1992; Croninet al., 1996; Clynne et al., 2004; Shane, 2005).
Donoghue and Neall (1996) suggested that geochemicalfingerprinting techniques, specifically analysis of the ground-mass glass geochemistries of pumice lapilli and shards, areneeded to aid identification of proximal andesitic tephra and tosupport correlation of distal tephra and provenance assigna-tion. These authors concluded that for the vast majority ofproximal Ruapehu tephra, ferromagnesian mineral assem-Copyright 2006 John Wiley & Sons, Ltd.were determined by XRF (Norrish and Chappell, 1977) usingpressed powder pellets. Precision varies from 210% withdetection limits generally about 1 ppm (Price et al., 1992).
Results
Tephra petrology
Lapilli tephra layers (hereafter referred to as lapilli tephra) arevolumetrically dominant (>0.2 km3) in the eruptive records atmounts Ruapehu and Rainier. These include tephra belongingto the older Ruapehu Bullot and Taurewa formations(Donoghue et al., 1999) and the Rainier tephra Layers (Tables1 and 2). They represent the products of more explosive Plinianand sub-Plinian eruptions and comprise typically coarse-grained pumice, scoria and lithic lapilli in varying proportions.Lithic lapilli are angular to subrounded, typically porphyriticandesite.
Fine ash-grade vitric and lithic tephra record more frequent,but smaller volume (
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CORRELATING PROXIMAL ANDESITE TEPHRA 399Mount Adams (Cascade Range) (Hildreth and Fierstein, 1997).The vitric shards have distinctive groundmass texturescharacterised by relatively few phenocrysts of feldspar andpyroxene, but abundant acicular feldspar microlites togetherwith microphenocryst feldspar laths and pyroxene (Fig. 1).
Plagioclase, orthopyroxene and clinopyroxene are thepredominant phenocryst minerals in Ruapehu and Rainier-derived tephra. The two-pyroxene assemblage, dominated byorthopyroxene is characteristic of all tephra erupted from thesecentres. Olivine and hornblende occur in the lapilli tephra butrarely as a dominant mineral phase. FeTi oxides are rare asphenocrysts, occurring more often as inclusions withinphenocryst phases (Mullineaux, 1974; Donoghue et al.,1995; Venezky and Rutherford, 1997; this study).
Orthopyroxene phenocrysts are generally normally zoned,with core and rim compositions ranging betweenhypersthene and bronzite and melt inclusions are a
Figure 1 Scanning electron micrographs of vitric pyroclasts (glass shards) in Formation member Tf6 (Table 1) showing equant blocky morphology (see H(sample no. R03000) showing an equivalent morphology. (c) Backscattereddensity of plagioclase and pyroxene microlites; field of view 150mm across. ((b); field of view 180mm across. Glass, and plagioclase microlites and phenocare black
Copyright 2006 John Wiley & Sons, Ltd.ubiquitous feature. Orthopyroxene also occurs as micro-phenocrysts (commonly skeletal in habit) in all tephra, and asacicular microlites in black ashes. Clinopyroxene pheno-crysts are generally normally zoned but may show markedvariations in core FeO and MgO contents such that core andrim compositions collectively fall within the augitesaliteand endiopsidediopside compositional fields. In Ruapehulapilli tephra, olivine occurs as colourless euhedral tosubhedral, equant to tabular phenocrysts, and also aseuhedral crystals with skeletal habit, where compositionsrange between Fo8471. In earlier studies (Mullineaux, 1974),olivine was identified in trace to minor amounts in nearly allRainier lapilli tephra, but it has not been identified insubsequent studies (Venezky and Rutherford, 1997; thisstudy). In Ruapehu lapilli tephra, calcic amphibole(hornblende) occurs as subhedral, acicular micropheno-crysts. In Rainier tephra it occurs as phenocrysts. Broken
black ash tephra from Ruapehu and Rainier. (a) Pyroclast from Tufa Trigeiken et al., 1983). (b) Pyroclast from an unnamed Rainier black ashelectron image showing the groundmass texture in (a); note the high
d) Backscattered electron image showing similar groundmass texture inrysts are grey. Pyroxene microlites and phenocrysts are white. Vesicles
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hornblende crystals (with glassy selvedges) are present intrace amounts in the crystal fractions of a few Rainier blackashes and may be accidental.
Tephra geochemistry
The compositions of Ruapehu and Rainier tephra are reportedin terms of major-element groundmass glass compositions(Figs 2 and 3; Appendix 1) and major-element and trace-element whole-rock (pumice clast) compositions (Figs 2, 4 and5; Appendix 2). Temporal variations in composition (reflectingchanging magma compositions) are shown in Fig. 6.
Matrix glass compositions of Ruapehu and Rainier tephra arepredominantly dacite, but range from basaltic andesite torhyolite, with Rainier compositions trending to trachyandesite(Fig. 2). The Rainier black ashes record some of the moresilicic compositions. Whole-rock (magma) compositions rangefrom basaltic andesite to dacite (Fig. 2). Ruapehu lapilli tephraare predominantly basaltic andesite, whilst at Rainier they arepredominantly andesite. Clast compositions are notably moremafic than the respective groundmass glass compositions.
All major oxides, except CaO, show linear trends withrespect to SiO2 in both glass major-element variation diagramsand whole-rock Harker diagrams (Figs 3 and 4). K2O and TiO2show the strongest correlation to SiO2 content. For sometephra, K2O contents lie off the trend suggesting some loss of
7 wt% CaO within individual tephra deposits. This variability isreflected in the high standard deviations for major-oxideelements (Appendix 1).
Most lapilli tephra are of mixed composition, with silicicand mafic end member groundmass glass compositions, forexample Bullot Formation members BL13 and BL18 (Fig. 3(a))and Layers C and D (Fig 3(b)). This compositional diversitywithin tephra is also evident in the whole-rock (pumice clast)compositions (Figs 4 and 5).
Glass compositions in the black ashes vary more widelythan for the lapilli tephra, particularly those from Rainier(Figs 3(c) and (d). The wide range in shard compositionspossibly indicates, in part, mixed glass populations due to post-depositional contamination with local andesitic ash. Thepetrography of analysed shards shows that this variability isdue to mixing with other andesitic shards and is not due toinclusion of reworked shards from interbedded silicic tephra.Many of the Rainier black ashes probably fell onto heavy snowpack within the high alpine meadows and then mixed togetheras they melted into place.
Samples arranged in stratigraphic order show no evidenttemporal trends in tephra composition at either volcano (Fig. 6).Compositions switch back and forth, from more to less siliciccompositions, on timescales of hundreds to thousands of years.
Discussion
Figure 2 Total alkalisilica diagram (after Le Bas et al., 1986) showing wholand Rainier (b) based on>60 XRF analyses of pumice clasts and 950 single po
er Cta). Ciangle(R)
400 JOURNAL OF QUATERNARY SCIENCEet al. (1999) and included in (b) is EMP and whole-rock XRF data for Laybasis before plotting (see Appendices 1 and 2 for representative mean dagrey circles groundmass glass compositions of lapilli tephra; open trbasalt (B), basaltic andesite (BA), andesite (A), dacite (D) and rhyoliteK2O due to post-depositional weathering of glasses.Ruapehu and Rainier tephra plot separately but show parallel
trends with respect to most major oxides, particularly MgO,TiO2 and K2O (Fig. 4). Rainier tephra show noticeably higherTiO2 and Al2O3 contents, and lower K2O contents relative toSiO2 contents, and are more silicic in composition.
The data presented in Figs 3 to 5 show that tephra eruptedfrom Ruapehu and Rainier are remarkably heterogeneous incomposition. Matrix glass compositions can vary by up to8 wt% SiO2, 4 wt% alkalis (Na2OK2O), 5 wt% FeO, andCopyright 2006 John Wiley & Sons, Ltd.e-rock and groundmass glass compositions for tephra from Ruapehu (a)int EMP analyses of glasses. Included in (a) is EMP data from Donoghuefrom Venezky and Rutherford (1997). All data normalised to a loss-freerosseswhole-rock compositions of pumice clasts from lapilli tephra;s glass shard compositions of black ashes. Compositional fields areTephra identification
A consequence of the compositional heterogeneity weobserved is that the compositions of many individual tephralayers represent, to a large extent, the compositional range ofmost other eruptives from the same source centre. In terms ofidentifying tephra, and resolving eruptive histories, thisheterogeneity presents particular difficulties. The identificationof proximal and distal tephra requires that tephra areJ. Quaternary Sci., Vol. 22(4) 395410 (2007)DOI: 10.1002/jqs
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CORRELATING PROXIMAL ANDESITE TEPHRA 401compositionally distinctive, or where compositions are similar,that they can be distinguished on the basis of relativestratigraphic position and age. Where tephra occur in closesuccession as at Ruapehu (i.e. Bullot Formation lapilli tephraand Tufa Trig Formation black ashes), distinguishing one fromanother is not possible.
Glass geochemical analyses show broad compositionaldifferences between lapilli tephra and also black ashes(Fig. 3), but in all cases are not diagnostic of individualeruptives.
Within the lapilli tephra, the geochemical analyses whenused in conjunction with stratigraphic position, do enableseveral of the Rainier lapilli tephra (Layer R, Layer D, Layer Fand Layer H) to be distinguished, (Table 2, Fig. 3(b)). None ofthe Ruapehu lapilli tephra can be distinguished on this basis,however.
Within the Ruapehu black ashes, represented by the TufaTrig Formation (Table 1), compositional fields for individualtephra are poorly defined (Fig. 3(c)). Regression values (r2)
Figure 3 Alkali-silica variation diagrams showing the compositions of glasseshow heterogeneous glass compositions. Glass compositions in the black ashtrend suggest some loss of alkalis due to post-depositional weathering of glassefor representative mean data). For both Ruapehu and Rainier tephra, the prolegend shows tephra in stratigraphic order from oldest (top) to youngest (seetephra; note the clearly mixed glass compositions in Bullot Formation memberFormation is from Donoghue et al. (1999). (b) Groundmass glass compositionEMP glass data for Layer C is from Venezky and Rutherford (1997). (c) Glassindividual tephra are poorly defined; regression values (r2) for tephra are alyoungest member (Tf19) shows the least compositional variability (r2 0.46discernible compositional trends within the Rainier black ashes; L7, L9,overlapping, compositional fields; regression values (r2) calculated for these
Copyright 2006 John Wiley & Sons, Ltd.calculated for these tephra are all
- 402 JOURNAL OF QUATERNARY SCIENCE1100 14C yr BP ash) have reasonably well-defined, but partlyoverlapping, compositional fields (Fig. 3(d); Table 2).Regression values (r2) calculated for these tephra are
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CORRELATING PROXIMAL ANDESITE TEPHRA 403records are geochemically distinct. However, the single mostlimiting factor to tephra identification is the lack of consistenttemporal trends in composition within the eruptive records.Although glass compositions show clear linear trends in SiO2vs. alkali contents, the progression to more silicic compositions
Figure 5 Trace-element geochemistry (XRF data) of Ruapehu and Rainierdifferent, and in many cases, multiple magmas. Molar magnesium numberinclude whole-rock data for Taurewa Formation from Donoghue et al. (1995representative data
Figure 6 Chemical stratigraphy of Ruapehu and Rainier tephra sequences.glass data; molar magnesium number of glasses plotted against age. Open circtrianglesRuapehu black ashes; open trianglesRainier black ashes. Plo(1997). (c) XRF whole-rock data; plot of SiO2 against age date. (d) plot of mtephra; grey circlesRainier lapilli tephra; plots includes XRF data for Layer Cbasis before plotting; see Appendices 1 and 2 for representative data. Molar mset at 0.2). Note the range in composition of individual tephra and the lack oreflecting magma recharge processes
Copyright 2006 John Wiley & Sons, Ltd.is, in most cases, not temporally consistent (Fig. 3). Thisinconsistency is also demonstrated in Fig. 6, where thecompositions of lapilli tephra and black ashes are shownaccording to their stratigraphic position. Whole-rock data(Figs 4, 5, and 6(c) and (d) produce similar results. Magma
tephra. The different Rb/Sr ratios indicate derivation of tephra from (Mol.MgO/MgO FeO100 with Fe2O3/FeO ratio set at 0.2). Plots) and Layer C from Venezky and Rutherford (1997); see Appendix 2 for
(a) EMP glass data; SiO2 content of glasses plotted against age. (b) EMPlesRuapehu lapilli tephra; grey circlesRainier lapilli tephra; greyt includes mean glass data for Layer C from Venezky and Rutherfordolar magnesium number against age. Open circlesRuapehu lapillifrom Venezky and Rutherford (1997). All data normalised to a loss-free
agnesium number (Mol.MgO/MgO FeO100 with Fe2O3/FeO ratiof systematic temporal variation in SiO2 and molar magnesium number,
J. Quaternary Sci., Vol. 22(4) 395410 (2007)DOI: 10.1002/jqs
-
compositions at these volcanoes are shown to be constantlychanging, on short timescales, and there are no systematictemporal trends in composition.
These findings are significant because clear temporal trendsin composition would facilitate geochemical correlation ofunknown proximal and distal tephra to specific stratigraphicintervals, thereby constraining member identification, if notactually allowing identification. This approach would requiregeochemically fingerprinting a limited number of proximaltephra only that span the eruptive record. Our results suggestquite the opposite, however, and demonstrate that withinproximal sequences of closely spaced lapilli and ash layers, thevast majority of tephra units would need to be geochemicallyfingerprinted in order to be able to constrain correlation. This isclearly an impracticable approach.
We therefore conclude that geochemical analyses of glassand whole-rock samples are largely ineffective as a routine toolfor identifying proximal andesitic tephra. The consequences ofthis ineffectiveness are that we cannot resolve critical parts ofthe proximal eruptive record at these volcanic centres insufficient detail (particularly the recent record, which wouldhelp us establish a more constrained chronology for laharevents). We also cannot reliably correlate distal andesitictephra to known eruptives at source and therefore cannot usethese to help elucidate the detailed eruptive histories at thesecentres, or to establish regional andesitic tephrostratigraphicframeworks.
tephra erupted from other TgVC centre volcanoes andtherefore defines an andesitic TgVC field. TgVC eruptivesare unequivocally distinguished from andesitic tephraerupted from the neighbouring EgVC based on the totalalkali (Na2OK2O) and SiO2 contents of their glasses.TgVC and Egmont compositions trend differently withEgmont glasses showing higher alkali contents relative toSiO2 contents. This trend supports earlier observations (e.g.Eden and Froggatt, 1996; Lowe, 1998a; Sandiford et al.,2001; Shane, 2005) and assignation of provenance fordistal andesitic tephra found in the Waikato and Aucklandregions.
At both Ruapehu and Rainier, the more evolved glasses arecompositionally similar in terms of total alkali and SiO2contents to the glasses of distal silicic tephra erupted fromcentral North Island volcanoes and Cascade Range volcanoes(Figs 7(a) and (b)). They can, however, be distinguished on thebasis of TiO2 and Al2O3 contents, for example, which arenotably higher in the Ruapehu and Rainier tephra, and also onthe basis of morphology and groundmass textures of glassshards.
In distal andesitic tephra, the compositions of glass shards arelikely to be of variable composition, and could easily rangefrom andesitic to rhyolitic compositions within individual units.This is important to note because in studies of distal silicictephra, such variability in glass compositions is commonlyattributed to post-depositional mixing and contamination asrelatively few silicic tephra display this compositional com-plexity (Blake et al., 1992; Shane, 2005).
the problem of understanding petrogenetic processes atandesitic stratovolcanoes (e.g. Waight et al., 1999; Gamble
ing gsenta
TgVCdata
a fielh tephGlass(B), b
404 JOURNAL OF QUATERNARY SCIENCEFigure 7 Total alkali silica diagram (after Le Bas et al., 1986) comparerupted from neighbouring volcanic centres (see Appendix 1 for repreComparison of Ruapehu tephra (crosses) with tephra erupted from othercentral North Island rhyolitic volcanic centres (grey circles). Included areFroggatt (1996) for distal andesites assigned a TgVc or EgVK source. Datand EgVC andesitic tephra. (b) Comparison of Rainier tephra (crosses) witcircles). The andesite Mount St. Helens compositions are from Layer Xm.other Cascade Range volcanic centres. Compositional fields are basaltTephra provenance
Glass compositional fields for proximal Ruapehu andRainier tephra are shown in Fig. 7. These fields are basedon >900 single point glass analyses. Also shown are theglass compositional fields for eruptives from neighbouringvolcanic centres. The Ruapehu field (Fig. 7(a)) encompassesCopyright 2006 John Wiley & Sons, Ltd.lass compositions in Ruapehu and Rainier tephra with those of tephrative data). All data normalised to a loss-free basis before plotting. (a)volcanoes (grey diamonds), Egmont Volcanic Centre [EgVC] (stars), andfrom Shane (2005), Sandiford et al. (2001), Lowe (1988b), and Eden and
ds show that glass compositions can be used to provenance distal TgVCra erupted from Crater Lake (white triangles) and Mount St. Helens (greycompositions do not distinguish Rainier tephra from those erupted fromasaltic andesite (BA), andesite (A), dacite (D) and rhyolite (R)Significance to andesite petrogenesis
Detailed sampling of cone-forming lavas has been applied toJ. Quaternary Sci., Vol. 22(4) 395410 (2007)DOI: 10.1002/jqs
-
et al., 1999; Dungan et al., 2001; Price et al., 2005). However,it is often difficult to develop a detailed temporal frameworkfrom sequences of laterally discontinuous lava flows on steepandesite cones. Proximal pyroclastic deposits, because of theirtemporal detail, are therefore an important complementary toolin understanding eruptive processes at volcanoes. Tephrapetrography and geochemistry define temporal change in the
of the pyroclastic record could be expected to reveal similartrends.
Conclusions
tephra variation. Such variability appears inherent in andesites,reflecting the complex processes underlying eruptions at these
eyy-
tephra discrimination at andesite volcanoes by simple
tives.
earchChina
(Project no: HKU 255/95p) and The Croucher Foundation (Hong Kong).
CORRELATING PROXIMAL ANDESITE TEPHRA 405magmatic systems that produced them, and provide usefulinsights into the evolution of volcanic systems over relativelyshort timescales.
The presently accepted paradigm for andesite volcanoes isthat erupting magmas are generated through interaction ofmantle-derived magmas with lower crustal melts and restites.The processes that act to modify magmas in the crust are crustalassimilation and fractionation (AFC) and recharge (Gambleet al., 1999; Dungan et al., 2001; Price et al., 2005). Andesitemagmas are thus complex mixtures of fractionated mantle melt,crustal melt, restitic crystals, lithic crustal fragments andphenocrysts.
Temporal variations in the petrography and geochemistry ofRuapehu and Rainier tephra indicate the complexity ofprocesses (recharge and AFC processes) underlying theireruption.
Magma recharge events, involving the mixing of freshmagma with stagnant melts in dykes and sills, are clearlyassociated with eruptions of the more voluminous lapillitephra. Relatively rapid ascent of mixed or mingled melts isindicated by disequilibrium groundmass textures and mineralassemblages (sieve-textured, zoned, and resorbed phenocrysts;low microlite densities; skeletal microphenocrysts of olivineand hornblende) and mixed glass compositions (Donoghueet al., 1995, 1999; Venezky and Rutherford, 1997; Cashmanand Blundy, 2000).
The petrography of the black ashes suggests that they arelargely the products of eruptions of shallow, stagnant batchmelts (Cashman and Blundy, 2000). Temporal changes incompositions suggest complex processes, possibly invol-ving periodic eruptions from a single fractionating melt(where compositions become more silicic), eruption ofmixed magmas (indicating varying degrees of interactionbetween melt pockets), and recharge events (indicated byabrupt reversals to more mafic compositions). The compo-sitional variation in glass chemistry within tephra mayreflect differences in the degrees of crystallinity of melts(Cashman and Blundy, 2000) and mixing. The compositionof Tufa Trig Formation member Tf19, representing the199596 eruptions at Ruapehu, is notably less silicic thanmany earlier eruptives (Fig. 6). Recent studies (Gambleet al., 1999; Nakagawa et al., 1999) have demonstrated thatcompositional variations in the 19451996 Ruapehueruptives (tephra and lavas) can be explained by tappingof pockets of stagnant magma in the upper crusttogether with some involvement of a deep-seated rechargemagma.
From the pyroclastic record we show that these processesoperated on relatively short timescales of just hundreds to tensof hundreds of years. Geochemical variations, explained byAFC and recharge processes, have been shown to occur oneven shorter timescales (over 50 years) within the Ruapehueffusive record (Gamble et al., 1999). A more detailed samplingCopyright 2006 John Wiley & Sons, Ltd.We thank Mr Gary Ahlstrand and Ms Barbara Somora (Mount RainierNational Park) for logistics support during fieldwork at Mount Rainier,Professor Richard Price and Dr Tod Waight for assisting with XRFanalysis, Dr Rick Hoblitt for providing us with samples of Mount St.Helens tephra, Professor Paul Robinson (Dalhousie University) for usefuldiscussion, Mr Doug Hopcroft for the SEM micrographs, and Ms LilyChiu for assistance with preparation of thin-sections. Dr David Lowe isthanked for his thorough and thoughtful review of the manuscript.
Appendix 1
Electron microprobe analyses of groundmass glasses inproximal Ruapehu and Rainier derived lapilli tephra andblack ashes, and distal and proximal tephras erupted fromneighbouring volcanic centres. All data normalised to a loss-free basis. Mean and 1s (in parentheses) based on n analyses.Tephra in each group are listed in stratigraphic order fromoldest (top) to youngest (bottom) (see Tables 1 and 2).
Appendix 2
Representative whole-rock analyses of Ruapehu and Rainierderived lapilli tephra. Rainier tephra layers are identified bysingle capital letters; all other labels refer to Ruapehu tephra(see Tables 1 and 2). Tephra are listed in stratigraphic orderfrom oldest (left) to youngest (right). The full data set can beobtained from the authors on request.Acknowledgements This work has been supported by the ResGrants Council of the Hong Kong Special Administrative Region,geochemical methods, and limits our ability to further resolvethe eruptive histories at these volcanoes for hazard assessmentpurposes.
These observations are significant in terms of guiding futuretephrostratigraphic studies wherein andesitic tephras arerecognised, and possible development of alternativeapproaches to geochemical fingerprinting of andesitic erup-volcanoes and in particular the short timescales on which thoperate. This variability renders intractable detailed tephra-bWe conclude that our ability to discriminate proximal tephra islimited by the complexities of the magmatic systems thatproduce them. At Ruapehu and Rainier, compositionalvariation within tephras is marked, and there is significantcompositional overlap between individual eruptives such thatintra-tephra variation is of a similar order of magnitiude to inter-J. Quaternary Sci., Vol. 22(4) 395410 (2007)DOI: 10.1002/jqs
-
Appen
dix
1El
ectr
on
mic
ropro
be
anal
yses
ofg
roundm
ass
glas
ses
inpro
xim
alR
uap
ehu
and
Rai
nie
rder
ived
lap
illi
tephra
and
bla
ckas
hes
,an
ddis
tala
nd
pro
xim
alte
phra
ser
upte
dfr
om
nei
ghbouri
ng
volc
anic
centr
es.A
lldat
anorm
alis
edto
alo
ss-f
ree
bas
is.
Mea
nan
d1s
(in
par
enth
eses
)bas
edon
nan
alys
es.
Tep
hra
inea
chgr
oup
are
list
edin
stra
tigr
aphic
ord
erfr
om
old
est
(top)
toyo
unge
st(b
ott
om
)(s
eeTab
les
1an
d2).
Tep
hra
SiO
2A
l 2O
3TiO
2Fe
2O
3Fe
OM
nO
MgO
CaO
Na 2
OK
2O
Cl
Wat
ern
Ruap
ehu
lap
illi
tephra
B
L360.0
2(1
.41)
17.0
2(1
.33)
0.9
1(0
.19)
1.0
8(0
.24)
5.3
8(1
.21)
0.1
8(0
.11)
3.7
7(1
.20)
6.2
4(0
.83)
3.2
3(0
.88)
2.0
4(0
.30)
0.1
4(0
.08)
0.2
8(0
.68)
10
BL4
66.9
4(1
.26)
15.2
2(0
.05)
0.9
8(0
.08)
0.7
6(0
.07)
3.8
0(0
.33)
0.2
1(0
.10)
1.3
5(0
.08)
4.1
0(0
.34)
3.5
6(0
.52)
2.8
5(0
.14)
0.2
3(0
.05)
2.6
3(1
.51)
4B
L566.6
1(1
.59)
15.5
3(0
.38)
0.9
1(0
.10)
0.8
6(0
.11)
4.2
8(0
.54)
0.1
5(0
.06)
1.5
9(0
.38)
3.9
6(0
.62)
3.0
8(0
.34)
2.8
0(0
.38)
0.2
4(0
.05)
1.2
8(1
.26)
10
BL6
61.5
9(1
.06)
16.9
4(1
.43)
1.0
3(0
.11)
1.0
2(0
.13)
5.1
2(0
.65)
0.2
3(0
.10)
2.3
2(0
.48)
5.7
7(0
.64)
3.4
8(0
.32)
2.3
0(0
.34)
0.2
1(0
.03)
1.7
3(0
.74)
10
BL1
162.0
7(0
.30)
16.2
8(0
.23)
0.9
6(0
.06)
1.0
4(0
.05)
5.1
9(0
.27)
0.1
9(0
.09)
2.3
9(0
.17)
6.0
6(0
.25)
3.5
1(0
.21)
2.1
7(0
.15)
0.1
4(0
.05)
2.4
4(1
.07)
9B
L13
69.4
8(7
.32)
14.2
4(1
.31)
0.7
2(0
.46)
0.7
2(0
.54)
3.5
8(2
.72)
0.1
4(0
.10)
1.3
2(1
.28)
2.9
2(2
.31)
2.8
0(0
.26)
3.8
8(1
.37)
0.2
2(0
.09)
3.0
6(1
.57)
21
BL1
561.7
0(0
.79)
16.5
2(0
.67)
1.0
6(0
.09)
1.1
1(0
.09)
5.5
6(0
.47)
0.2
1(0
.08)
2.4
9(0
.39)
5.3
9(0
.62)
3.4
4(0
.24)
2.3
0(0
.21)
0.2
1(0
.06)
1.3
7(0
.91)
17
BL1
773.3
3(0
.68)
13.8
9(0
.27)
0.5
2(0
.07)
0.4
4(0
.04)
2.1
8(0
.21)
0.1
1(0
.06)
0.4
7(0
.03)
1.9
0(0
.10)
3.1
6(0
.48)
3.7
5(0
.37)
0.2
5(0
.03)
1.2
7(1
.82)
11
BL1
866.1
7(3
.82)
15.5
0(1
.17)
0.9
2(0
.29)
0.8
990.2
6)
4.4
4(1
.31)
0.0
5(0
.10)
1.6
2(0
.70)
4.3
1(1
.16)
3.0
9(0
.36)
3.0
3(0
.66)
nd
2.9
9(0
.54)
10
Rai
nie
rl
apil
lite
phra
La
yer
R73.0
9(1
.45)
13.6
6(0
.47)
0.7
0(0
.25)
0.5
3(0
.08)
2.6
7(0
.42)
0.1
1(0
.07)
0.5
5(0
.14)
1.4
7(0
.51)
4.0
4(0
.25)
3.0
0(1
.15)
0.1
7(0
.10)
1.6
5(1
.46)
11
Laye
rA
62.5
0(0
.50)
16.5
8(0
.28)
1.3
5(0
.10)
0.9
4(0
.07)
4.7
1(0
.35)
0.1
6(0
.12)
2.3
8(0
.14)
5.0
2(0
.23)
3.8
6(0
.17)
2.3
0(0
.13)
0.1
9(0
.05)
1.4
4(1
.98)
13
Laye
rL
70.1
6(0
.57)
14.6
4(0
.36)
0.9
0(0
.07)
0.5
9(0
.03)
2.9
7(0
.15)
0.1
3(0
.05)
0.8
7(0
.07)
2.5
8(0
.20)
3.6
8(0
.18)
3.2
9(0
.16)
0.1
8(0
.02)
1.3
8(1
.09)
11
Laye
rD
66.0
9(3
.23)
15.8
7(1
.71)
1.1
8(0
.13)
0.7
6(0
.12)
3.7
9(0
.61)
0.1
6(0
.07)
1.5
5(0
.59)
4.0
5(1
.25)
3.7
0(0
.41)
2.6
4(0
.58)
1.1
6(0
.84)
1.8
3(2
.15)
25
Laye
rN
67.0
9(2
.17)
15.2
5(1
.98)
1.2
4(0
.23)
0.8
5(0
.15)
4.2
6(0
.75)
0.2
3(0
.13)
1.2
1(0
.44)
3.4
4(1
.13)
3.2
7(0
.76)
3.0
2(0
.73)
0.1
4(0
.12)
0.9
6(1
.07)
26
Laye
rF
72.3
3(0
.34)
14.0
8(0
.18)
0.7
4(0
.05)
0.5
2(0
.02)
2.5
8(0
.12)
0.1
4(0
.03)
0.5
9(0
.09)
1.9
3(0
.11)
3.5
2(0
.14)
3.4
7(0
.13)
0.1
0(0
.02)
3.1
2(0
.55)
9La
yer
H59.2
7(1
.41)
15.3
0(0
.38)
1.7
0(0
.10)
1.2
5(0
.07)
6.2
7(0
.35)
0.2
0(0
.07)
3.9
4(0
.62)
6.8
0(0
.65)
3.4
3(0
.22)
1.7
5(0
.25)
0.0
9(0
.04)
0.3
3(0
.63)
20
Ruap
ehu
bla
ckas
hes
Tf2
60.2
5(0
.37)
16.1
0(0
.21)
0.9
8(0
.07)
1.1
2(0
.07)
5.5
9(0
.37)
0.3
0(0
.19)
3.5
2(0
.19)
6.9
0(0
.14)
3.3
3(0
.22)
1.8
2(0
.13)
0.0
9(0
.05)
0.6
7(0
.63)
10
Tf4
67.2
4(0
.90)
14.3
8(0
.53)
1.1
6(0
.08)
0.9
5(0
.12)
4.7
7(0
.60)
0.1
9(0
.11)
1.4
4(0
.60)
3.7
0(0
.47)
2.7
7(0
.44)
3.2
9(0
.51)
0.1
2(0
.05)
0.7
8(0
.74)
27
Tf5
65.7
8(0
.62)
14.3
6(0
.45)
1.2
7(0
.14)
1.1
1(0
.06)
5.5
7(0
.31)
0.1
7(0
.08)
1.5
2(0
.31)
4.1
9(0
.42)
3.0
8(0
.36)
2.8
0(0
.35)
0.1
4(0
.06)
0.2
9(0
.53)
16
Tf6
64.3
0(0
.97)
14.6
6(0
.50)
1.2
2(0
.07)
1.2
0(0
.06)
6.0
1(0
.29)
0.2
1(0
.13)
1.7
7(0
.29)
4.3
6(0
.36)
3.1
3(0
.49)
2.9
8(0
.48)
0.1
6(0
.11)
0.7
6(0
.58)
16
Tf7
64.5
0(1
.40)
15.0
4(0
.77)
1.2
2(0
.19)
1.0
9(0
.06)
5.4
6(0
.29)
0.1
9(0
.06)
1.8
4(0
.64)
4.3
9(0
.67)
3.2
7(0
.36)
2.8
8(0
.52)
0.1
1(0
.04)
0.4
1(0
.56)
19
Tf9
66.0
5(1
.27)
14.6
2(0
.76)
1.1
5(0
.13)
1.0
4(0
.10)
5.2
0(0
.48)
0.2
5(0
.16)
1.4
9(0
.53)
3.8
5(0
.64)
3.1
7(0
.58)
3.0
4(0
.57)
0.1
6(0
.12)
0.8
4(0
.68)
20
Tf1
065.6
2(1
.08)
14.7
2(0
.77)
1.0
690.1
6)
1.0
4(0
.08)
5.2
2(0
.40)
0.1
7(0
.05)
1.7
7(0
.57)
3.8
5(0
.62)
3.7
4(0
.39)
2.7
2(0
.38)
0.1
0(0
.06)
1.0
3(0
.83)
12
Tf1
464.0
6(0
.79)
15.1
8(0
.41)
1.0
3(0
.22)
1.1
3(0
.10)
5.6
7(0
.52)
0.1
7(0
.05)
2.0
2(0
.32)
4.0
8(0
.48)
3.9
4(0
.39)
2.6
0(0
.78)
0.1
1(0
.03)
1.1
4(1
.00)
11
Tf1
962.3
7(1
.11)
15.7
3(1
.07)
1.0
1(0
.12)
1.0
6(0
.10)
5.3
1(0
.50)
0.2
3(0
.10)
2.4
2(0
.69)
5.6
9(0
.79)
3.7
3(0
.28)
2.3
4(0
.29)
0.1
2(0
.04)
2.3
5(1
.16)
17
Rai
nie
rb
lack
ashes
R
01020
70.2
5(3
.62)
14.6
6(1
.54)
0.9
9(0
.42)
0.5
6(0
.22)
2.8
1(1
.08)
0.1
4(0
.09)
0.6
2(0
.52)
2.1
0(1
.13)
4.2
8(0
.38)
3.5
1(0
.93)
0.0
9(0
.06)
0.8
6(1
.48)
15
R032
64.7
7(5
.21)
15.5
9(1
.48)
1.3
9(0
.50)
0.8
7(0
.34)
4.3
3(1
.70)
0.1
6(0
.11)
1.4
3(0
.97)
3.9
6(1
.95)
4.2
5(0
.78)
3.0
9(1
.49)
0.1
4(0
.05)
1.7
7(1
.01)
30
R034
65.3
3(3
.94)
15.9
3(2
.18)
1.2
4(0
.35)
0.7
0(0
.26)
3.5
0(1
.31)
0.1
3(0
.09)
1.1
9(0
.83)
4.1
5(1
.59)
4.8
9(0
.77)
2.8
3(0
.76)
0.1
1(0
.05)
1.8
3(1
.06)
20
R09
64.4
6(5
.94)
15.3
5(1
.82)
1.2
9(0
.43)
0.9
1(0
.32)
4.5
5(1
.60)
0.1
5(0
.10)
2.0
6(1
.85)
4.5
0(2
.35)
4.1
7(0
.83)
2.4
4(1
.16)
0.1
2(0
.05)
1.1
5(1
.09)
27
L775.6
8(2
.09)
12.8
0(0
.86)
0.7
8(0
.25)
0.4
1(0
.14)
2.0
5(0
.72)
0.1
1(0
.06)
0.2
5(0
.16)
1.2
3(0
.85)
2.5
7(0
.50)
4.0
1(0
.58)
0.1
0(0
.05)
0.7
4(0
.59)
18
R031
70.4
9(4
.01)
14.2
0(2
.32)
0.8
1(0
.23)
0.5
1(0
.29)
2.5
4(1
.43)
0.1
6(0
.09)
1.1
5(1
.60)
2.5
1(1
.46)
4.3
5(0
.68)
3.2
1(0
.84)
0.0
9(0
.03)
2.9
6(0
.81)
22
R08
65.0
0(4
.98)
14.9
9(1
.76)
1.4
9(0
.66)
0.8
8(0
.38)
4.3
8(1
.91)
0.1
9(0
.08)
1.9
9(1
.97)
4.0
1(1
.75)
3.9
5(0
.81)
2.9
6(0
.96)
0.1
6(0
.07)
0.9
1(1
.48)
28
R024
70.4
2(3
.57)
15.1
7(2
.94)
0.7
5(0
.23)
0.4
3(0
.24)
2.1
7(1
.20)
0.1
5(0
.12)
0.5
5(0
.80)
2.9
5(1
.56)
3.9
7(0
.70)
3.2
8(0
.97)
0.1
5(0
.11)
1.7
9(1
.16)
22
L974.8
0(2
.16)
12.4
3(0
.45)
0.9
8(0
.15)
0.5
4(0
.16)
2.7
2(0
.82)
0.1
8(0
.07)
0.3
7(0
.24)
1.3
7(0
.69)
2.5
2(0
.22)
3.9
8(0
.59)
0.1
1(0
.03)
0.3
2(0
.55)
10
R065
71.6
4(3
.04)
14.4
6(2
.46)
0.6
8(0
.21)
0.4
1(0
.20)
2.0
5(0
.99)
0.0
9(0
.07)
0.4
4(0
.60)
2.4
1(1
.29)
4.5
2(0
.98)
3.1
1(1
.04)
0.1
8(0
.49)
2.3
3(1
.33)
26
R064
72.6
7(3
.09)
13.2
3(0
.88)
1.0
1(0
.39)
0.5
4(0
.25)
2.7
2(1
.27)
0.1
1(0
.06)
0.4
8(0
.35)
1.8
2(1
.01)
3.7
6(0
.27)
3.5
6(0
.62)
0.0
9(0
.04)
0.5
1(0
.55)
12
L12
74.8
4(1
.10)
12.4
4(0
.31)
0.9
6(0
.12)
0.5
6(0
.09)
2.8
1(0
.44)
0.1
1(0
.07)
0.3
5(0
.12)
1.5
0(0
.29)
2.9
2(0
.27)
3.4
0(0
.27)
0.1
1(0
.04)
0.7
3(0
.61)
20
R0930
71.1
1(6
.18)
13.7
8(1
.65)
1.0
0(0
.63)
0.6
8(0
.37)
3.3
9(1
.84)
0.1
1(0
.07)
0.8
4(0
.62)
2.0
9(1
.59)
3.2
3(0
.77)
3.6
8(1
.04)
0.1
0(0
.04)
1.9
0(0
.87)
9L1
364.8
8(5
.99)
16.2
4(2
.67)
1.1
9(0
.60)
0.7
9(0
.38)
3.9
7(1
.92)
0.1
9(0
.11)
1.5
9(1
.45)
4.0
6(1
.69)
4.8
5(0
.93)
2.1
3(0
.57)
0.1
2(0
.06)
3.3
2(1
.59)
33 )
Copyright 2006 John Wiley & Sons, Ltd. J. Quaternary Sci., Vol. 22(4) 395410 (2DOI: 10.1002
406 JOURNAL OF QUATERNARY SCIENCE(Continues007)/jqs
-
Table.(C
ontinued)
Tep
hra
SiO
2A
l 2O
3TiO
2Fe
2O
3Fe
OM
nO
MgO
CaO
Na 2
OK
2O
Cl
Wat
ern
1100
yras
h76.3
0(2
.06)
12.6
6(1
.18)
0.8
1(0
.29)
0.3
8(0
.12)
1.9
2(0
.59)
0.1
2(0
.07)
0.2
8(0
.22)
1.1
7(0
.75)
2.4
7(0
.60)
3.8
0(0
.63)
0.0
8(0
.06)
0.9
1(0
.98)
32
Dis
tal
centr
alN
ort
hIs
land
rhyo
liti
cte
phra
Kk
78.7
8(0
.38)
12.1
7(0
.11)
0.1
4(0
.06)
0.1
8(0
.02)
0.9
1(0
.11)
nd
0.1
2(0
.03)
1.0
5(0
.07)
3.3
6(0
.21)
3.1
1(0
.18)
0.1
8(0
.09)
3.5
1(0
.66)
21
Ok
78.2
3(0
.27)
12.1
4(0
.09)
0.1
1(0
.05)
0.1
6(0
.01)
0.7
9(0
.07)
nd
0.1
1(0
.04)
0.8
5(0
.08)
3.6
9(0
.17)
3.7
6(0
.45)
0.1
4(0
.03)
2.2
1(1
.28)
23
Rk
77.8
1(0
.40)
12.5
5(0
.35)
0.1
2(0
.06)
0.1
6(0
.04)
0.8
0(0
.20)
nd
0.1
1(0
.08)
0.8
3(0
.33)
3.6
6(0
.16)
3.8
3(0
.56)
0.1
4(0
.03)
2.1
5(0
.99)
17
Wh
78.6
7(0
.45)
12.1
0(0
.15)
0.1
3(0
.06)
0.1
4(0
.02)
0.7
1(0
.11)
nd
0.1
2(0
.03)
0.8
8(0
.08)
3.7
4(0
.34)
3.3
6(0
.16)
0.1
4(0
.03)
2.0
9(1
.47)
21
Oth
erTgV
Cte
phra
Unnam
ed68.7
5(1
.30)
15.3
6(1
.19)
0.8
9(0
.12)
0.6
3(0
.06)
3.1
6(0
.32)
0.1
3(0
.07)
0.9
1(0
.29)
3.1
7(0
.72)
3.3
4(0
.31)
3.4
2(0
.40)
0.2
590.0
6)
2.3
1(1
.32)
10
Pah
oka
Tep
hra
63.8
7(1
.59)
17.2
7(1
.09)
0.5
8(0
.12)
0.8
2(0
.19)
4.0
8(0
.95)
0.2
6(0
.08)
1.8
3(0
.83)
5.3
8(0
.77)
3.7
6(0
.21)
1.9
4(0
.35)
0.2
1(0
.06)
3.1
0(1
.96)
16
Dis
tal
Mount
St.
Hel
ens
tephra
Set
Y75.2
3(0
.48)
14.8
5(0
.20)
0.2
1(0
.05)
0.2
2(0
.02)
1.0
9(0
.10)
0.0
9(0
.06)
0.4
2(0
.06)
1.8
2(0
.09)
3.9
3(0
.24)
1.9
7(0
.31)
0.1
6(0
.04)
3.0
5(1
.19)
11
Set
Pm
iddle
75.7
6(1
.03)
13.7
0(0
.83)
0.4
1(0
.19)
0.2
8(0
.05)
1.3
9(0
.27)
0.1
2(0
.10)
0.3
3(0
.10)
1.4
2(0
.55)
3.6
6(0
.78)
2.8
1(0
.75)
0.1
3(0
.07)
1.4
7(1
.49)
16
Set
Pupper
74.6
9(0
.55)
14.2
8(0
.31)
0.4
0(0
.05)
0.2
9(0
.02)
1.4
4(0
.10)
0.1
2(0
.09)
0.4
7(0
.08)
1.9
0(0
.15)
3.8
7(0
.16)
2.4
0(0
.09)
0.1
5(0
.06)
2.6
1(1
.03)
12
Set
W75.0
4(0
.67)
14.5
4(0
.20)
0.2
2(0
.05)
0.3
0(0
.04)
1.5
2(0
.21)
0.0
8(0
.04)
0.3
3(0
.04)
1.7
1(0
.15)
3.7
7(0
.42)
2.3
5(0
.11)
0.1
5(0
.09)
2.9
1(0
.67)
10
Pro
xim
alM
ount
St.
Hel
ens
tephra
Xm
61.7
1(1
.02)
16.7
1(0
.26)
1.4
3(0
.12)
1.0
2(0
.06)
5.1
1(0
.32)
0.1
8(0
.08)
2.3
4(0
.18)
4.9
8(0
.45)
4.5
1(0
.22)
1.8
6(0
.13)
0.1
4(0
.04)
0.2
5(0
.64)
13
Dis
tal
Cra
ter
Lake
tephra
Tep
hra
O73.4
6(0
.24)
14.8
2(0
.20)
0.4
9(0
.06)
0.3
2(0
.03)
1.5
9(0
.13)
0.1
1(0
.08)
0.4
9(0
.03)
1.5
7(0
.06)
4.1
8(0
.23)
2.7
5(0
.09)
0.2
3(0
.04)
1.0
3(1
.37)
10
Appen
dix
2R
epre
senta
tive
whole
-rock
anal
yses
ofR
uap
ehu
and
Rai
nie
rder
ived
lap
illi
tephra
.R
ainie
rte
phra
laye
rsar
eid
enti
fied
by
singl
eca
pit
alle
tter
s;al
loth
erla
bel
sre
fer
toR
uap
ehu
tephra
(see
Tab
les
1an
d2).
Tep
hra
are
list
edin
stra
tigr
aphic
ord
erfr
om
old
est
(lef
t)to
younge
st(r
ight)
.The
full
dat
aset
can
be
obta
ined
from
the
auth
ors
on
reques
t.
Ruap
ehu
lap
illi
tephra
R
ainie
rl
apil
lite
phra
BL2
BL3
BL4
BL5
BL6
BL7
BL8
BL1
1B
L13
BL1
4B
L15
BL1
6Sh
awcr
oft
Lapil
liB
L17
BL1
8N
g-1
Ng-
2R
AL
DF
HB
C
SiO
260.0
752.3
757.4
254.3
554.7
154.3
49.6
255.4
451.3
453.1
553.3
151.8
857.6
53.1
757.3
952.8
850.8
149.8
63.7
860.2
556.2
861
58.6
52.2
58.6
Al 2
O3
16.6
917.3
416.4
117.7
117.8
718.3
619.7
718.2
20.1
418.0
718.8
319.8
317.5
19.7
917.9
119.3
119.8
121.2
916.3
517.0
119.1
217.4
17.3
718.1
17.3
TiO
20.8
60.7
70.7
40.8
0.7
50.8
10.8
30.7
90.9
20.9
0.8
70.9
20.7
0.8
20.7
70.8
20.8
51.4
80.6
60.9
40.9
90.8
60.9
71.4
31.0
4Fe
2O
31.8
43.7
71.9
82.1
23.0
72.9
44.5
43.3
83.8
44.0
27.0
73.6
2.5
3.4
43.6
28.5
80.5
11.3
3.0
15.5
5.8
67.9
26.2
5Fe
O3.9
33.7
75.1
5.5
97.6
54.7
58.2
54.6
23.9
4.4
84.2
94.4
14.3
74.5
84.4
54.2
53.3
33.9
32.9
20
MnO
0.1
10.1
30.1
50.1
50.1
10.1
50.1
10.1
40.1
40.1
50.1
50.1
40.1
20.1
40.1
40.1
50.1
40.0
90.0
70.1
10.0
90.0
90.1
0.1
20.1
MgO
2.8
5.8
44.7
64.9
34.2
94.7
23.6
94.2
3.6
54.1
84.1
43.9
3.6
43.7
13.9
4.2
4.1
3.1
2.5
43.5
33.1
62.8
3.7
15.4
34.1
CaO
5.6
56.4
57.3
37.3
86.5
67.2
56.1
97.0
27.0
96.9
7.0
56.9
16.8
17.0
67.1
7.4
6.8
25.7
54.8
26.0
16.9
15.3
27.0
68.0
76.1
1N
a 2O
3.4
91.9
92.7
82.3
92.6
62.5
62.1
72.7
52.3
92.5
22.4
62.3
63.0
42.6
33.1
32.6
12.4
83.2
54.1
24.1
3.9
24
3.8
53.3
13.9
8K
2O
1.7
70.7
61.4
11.0
51.2
70.9
90.8
81.1
30.6
91.0
80.9
60.7
91.4
40.8
81.3
20.7
50.7
30.8
92.1
11.6
21.1
31.7
21.4
51.0
51.5
8P
2O
50.1
70.1
20.1
40.1
20.1
20.1
20.1
0.1
30.1
20.1
80.1
30.1
40.1
20.1
30.1
50.1
40.1
60.3
0.1
50.2
50.3
20.1
60.1
70.3
0.2
SO3
00.0
20
0.0
1nd
0nd
0.0
30
0.0
10
0.0
1nd
00.0
10.0
10.0
3nd
0.0
20
0.0
4nd
0.3
nd
nd
CO
20.5
0.8
0.3
20.4
nd
0.5
nd
0.4
0.7
80.5
50.4
70.6
8nd
0.5
0.3
80.9
51.9
6nd
0.5
50.5
1.0
9nd
nd
nd
nd
H2O
1.5
32.8
20.8
41.9
nd
1.8
1nd
1.8
52.7
11.8
52.2
42.6
3nd
1.8
50.7
1.7
21.8
4nd
0.9
90.6
31.1
8nd
nd
nd
nd
H2O
1.0
52.7
50.7
21.0
1nd
1.0
7nd
0.7
21.4
31.6
41.7
21.4
7nd
1.2
30.5
91.7
22.5
3nd
0.3
20.1
90.3
2nd
nd
nd
nd
(Continues
)
Copyright 2006 John Wiley & Sons, Ltd.
CORRELATING PROXIMAL ANDESITE TEPHRA 407J. Quaternary Sci., Vol. 22(4) 395410 (2007)DOI: 10.1002/jqs
-
Table.(C
ontinued)
Ruap
ehu
lap
illi
tephra
R
ainie
rl
apilli
tephra
BL2
BL3
BL4
BL5
BL6
BL7
BL8
BL1
1B
L13
BL1
4B
L15
BL1
6Sh
awcr
oft
Lapil
liB
L17
BL1
8N
g-1
Ng-
2R
AL
DF
HB
C
LOI
3.5
88.0
41.0
40
4.9
80.9
11.2
70.3
5Tota
l100.4
699.7
100.1
99.9
199.5
7100.4
699.6
5100.3
699.8
499.0
4100.4
6100.0
999.0
899.8
8100.5
7100.5
5100.1
399.5
1100.3
2100.3
7100.4
899.7
699.4
499.2
99.6
1R
b68
32
56
43
nd
39
nd
46
29
41
38
31
54
33
52
29
29
23
61
43
25
48
40
21
37
Sr250
237
220
227
nd
231
nd
232
279
233
293
329
255
258
233
219
219
498
406
485
745
438
489
514
495
Pb
13
11
10
10
nd
11
nd
910
12
10
11
36
910
89
19
10
98
27
727
38
Th
76
66
nd
5nd
54
75
64
65
56
410
69
25
22
U0
22
3nd
2nd
21
40
30
44
34
03
21
21
33
Mo
10
10
nd
0nd
10
00
0nd
10
10
nd
21
1nd
nd
nd
nd
Zr
141
111
118
111
nd
109
nd
108
102
127
110
125
119
112
118
100
119
206
189
181
227
158
158
143
164
Nb
54
54
nd
4nd
44
55
54
45
45
17
12
13
910
11
15
10
Y22
23
20
23
nd
20
nd
20
22
20
22
23
22
22
21
17
16
15
16
15
17
19
16
18
18
Ga
17
17
17
18
nd
19
nd
19
20
20
19
20
17
21
18
20
20
22
14
21
17
18
22
19
19
Ni
17
107
26
31
nd
33
nd
25
817
16
17
50
27
16
11
14
23
20
34
14
32
12
145
73
Cu
42
78
52
57
nd
50
nd
50
32
37
36
35
36
34
40
35
33
17
10
41
18
27
31
27
38
Zn
64
62
67
77
nd
78
nd
81
82
61
76
80
71
155
69
67
58
206
47
64
69
59
58
60
99
Sc18
25
20
25
nd
23
nd
24
27
24
26
26
23
23
22
25
24
20
313
11
11
17
24
12
Ce
25
22
22
22
nd
18
nd
13
15
23
24
19
33
13
23
17
10
34
53
32
52
36
39
26
29
Cr
134
361
157
103
nd
94
nd
120
42
55
85
53
50
35
88
38
39
32
63
95
632
149
145
73
La14
14
14
11
nd
12
nd
13
13
14
13
13
15
814
912
17
19
20
23
20
14
23
29
Ba
490
388
384
419
nd
363
nd
367
436
306
432
411
331
824
342
238
215
282
659
479
409
445
334
264
420
V180
162
215
211
nd
230
nd
223
204
265
211
207
160
236
219
261
276
171
48
108
127
101
122
201
124
Nd
24
19
25
23
nd
17
nd
18
21
19
20
18
54
13
20
16
17
23
17
29
20
48
40
21
37
Appen
dix
2(C
onti
nued
)
Copyright 2006 John Wiley & Sons, Ltd. J. Quaternary Sci., Vol. 22(4) 395410 (2DOI: 10.1002
408 JOURNAL OF QUATERNARY SCIENCE007)/jqs
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and ignimbrite stratigraphy in new Zealand using electronmicroprobe analysis of glass shards. Quaternary Research 19:
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